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GDB User Manual - C programming language ressources

1. 321 B 1 Requirements for Building GDB 00 00 ee eee 321 B 2 Invoking the GDB configure Script 0004 321 B 3 Compiling GDB in Another Directory 0006 323 B 4 Specifying Names for Hosts and Targets 323 H3 configure 1 puOne a ies ipae drap eadera sq aug aa edo 324 Appendix C Maintenance Commands 327 Appendix D GDB Remote Serial Protocol 333 Di OVervIEW eiue Ee eT Ld e ec ede ea eae 333 D2 Packets c asmenea a a a oaa a da A OEE Eg o 334 D 3 Stop Reply Packets lsssseesseeeesee eh 341 D 4 General Query Packets llsuueessleseeseleeeeeel 342 D 5 Register Packet Format 0 00 cee cece eee 351 D 6 Tracepoint Packets 000 0 cece 351 Dif Interrupts ics see dad emere tbe t out bade eee aiia eR e a 354 DS Examples eese Ren eee RE UR d no ede 354 D 9 File I O Remote Protocol Extension 00000 354 D91 File I D Overview coeccbebcecbdxekexbeeer es i eed 354 13 9 2 Protocol Basis sssr reet oe erat oa e een 355 D 9 3 The F Request Packet sssessessee else 356 D 9 4 The F Reply Packet ssssseseesssee eh 356 D 9 5 The Ctrl C Message s esses ne 356 DAG Console lO 2 so vaskeko axe dan C krass io Mb Rada 357 D 9 7 List of Supported Calls 0 0 00 eee ee eee eee 357 Dl ida eed eh Cee eee eee ee oo 357 di P 359 POAC PEEL 359 WIC T rp 359 ISCO Ke
2. 0 000 00 1 Contributors t GDR osu ute eee nena bak aca PO BR TR RR Rc 3 1 A Sample GDB S68S1OB sco ur nw os T 2 Getting In and Out of GDB 11 2 1 Inyoking GDBa s veteri eee wide to ext ba bets 11 2 1 1 Choosing Files 0 00 cece eet eee eens 12 2 1 2 Choosing Modes 00 c eee e ea ee eens 13 2 1 3 What GDB Does During Startup 000 15 2 0 Quittng GDB visincdpcteraie tiene oe Slee RD Re due OA E e eho 16 2 3 Shell Commands 00 ccc cece eect eee enn 16 2 4 Logging Outputs 35 2244 eae eee Wek n PO aad cete Pd 16 3 GDB Cominandes usan erodes reg vx RES 19 3 1 Command Syntax sares eee cette tenes 19 3 2 Command Completion 00 cece eee teen eens 19 3 3 Getting Helpis icis cerne enu tede ig eee neo 21 4 Running Programs Under GDB 25 4 1 Compiling for Debugging sssssee esse 25 4 2 Starting your Program 3 624 ne LESE P Poe ERR Tn el 26 4 3 Your Program s Arguments ssseseeseeee esee 27 4 4 Your Program s Environment 0 00 e eee eese 28 4 5 Your Program s Working Directory 0000 eee eee 29 4 6 Your Program s Input and Output 0 00 000 cee eae 29 4 7 Debugging an Already running Process uueeuuusuu 30 4 8 Killing the Child Process 000 eee eee eens 31 4 9 Debugging Programs with Multiple Threads 31 4 10 Debugging Programs wit
3. 81 remote monitor prompt 00 197 remote packets enabling and disabling 176 Debugging with GDB remote programs interrupting 172 remote protocol debugging 214 remote protocol binary data 333 remote protocol field separator 333 remote query requests oer m efe re eyes 342 remote serial debugging summary 180 remote serial debugging overview 177 remote serial protocol 000 00 333 remote serial stub 0 sees eee 178 remote serial stub list 000005 178 remote serial stub initialization 178 remote serial stub main routine 178 remote stub example 000 177 remote stub support routines 179 remote target eurn RR dee nese 168 remote target limit break and watchpoints 175 remote Liieout i err I eria RED 175 remotetimeout sees 199 remove actions from a tracepoint 107 rename file i o system call 360 IREMESAS PX 178 repeated array elements 00 84 repeating command sequences 19 repeating commands 000 19 reporting bugs in GDB 0 291 reprint the last value 0000 75 reset SDI connection M32R 194 response time MIPS debugging 203 testate a
4. c To allow GDB to recognize foo c as a single symbol enclose it in single quotes for example p foo c x looks up the value of x in the scope of the file foo c Set case sensitive on Set case sensitive off Set case sensitive auto Normally when GDB looks up symbols it matches their names with case sensi tivity determined by the current source language Occasionally you may wish to control that The command set case sensitive lets you do that by specify ing on for case sensitive matches or off for case insensitive ones If you specify auto case sensitivity is reset to the default suitable for the source language The default is case sensitive matches for all languages except for Fortran for which the default is case insensitive matches show case sensitive This command shows the current setting of case sensitivity for symbols lookups info address symbol Describe where the data for symbol is stored For a register variable this says which register it is kept in For a non register local variable this prints the stack frame offset at which the variable is always stored Note the contrast with print amp symbol which does not work at all for a regis ter variable and for a stack local variable prints the exact address of the current instantiation of the variable info symbol addr Print the name of a symbol which is stored at the address addr If no symbol is stored exactly at addr GDB prints
5. gdb tdump Data collected at tracepoint 2 trace frame 1 do Oxc4aa0085 995491707 di 0x18 24 d2 0x80 128 d3 0x33 51 d4 0x7 1aea3d 119204413 d5 0x22 34 d6 OxeO 224 d 0x380035 3670069 a0 0x19e24a 1696330 al 0x3000668 50333288 a2 0x100 256 a3 0x322000 3284992 a4 0x3000698 50333336 ab Oxiad3cc 1758156 fp Ox30bf3c Ox30bf3c sp Ox30bf34 Ox30bf34 ps 0x0 0 pc Ox20b2c8 Ox20b2c8 fpcontrol 0x0 0 fpstatus 0x0 0 fpiaddr 0x0 0 p 0Ox20e5b4 gdb test pi void 0x11 p2 void 0x22 p3 void 0x33 p4 void 0x44 p5 void 0x55 p6 void 0x66 gdb_long_test 17 021 gdb 112 Debugging with GDB 10 2 3 save tracepoints filename This command saves all current tracepoint definitions together with their actions and pass counts into a file filename suitable for use in a later debugging session To read the saved tracepoint definitions use the source command see Section 20 3 Command Files page 219 10 3 Convenience Variables for Tracepoints int trace frame The current trace snapshot a k a frame number or 1 if no snapshot is se lected int tracepoint The tracepoint for the current trace snapshot int trace line The line number for the current trace snapshot char trace file The source file for the current trace snapshot char trace func The name of the function containing tracepoint Note trace file is not suitable for
6. 00 32 thread identifier GDB on HP UX 32 thread identifier system 00 31 thread identifier system on HP UX 32 thread info Solaris 000000 33 thread information remote request 344 thread number 222 abe lr IRR es 32 thread properties GNU Hurd 189 thread suspend count GNU Hurd 189 thread threadno ceci bees 33 threads and watchpoints lusus 45 threads of execution 000 eee eee 31 threads automatic switching 38 threads continuing ser eit ea 58 threads stopped 0 cece eee eee eee 58 tild expand M soe se rt RR 312 time of command execution 330 timeout for commands 000 331 Appendix H Index timeout for serial communications 175 timeout MIPS protocol 196 tlo d M32B ou re eERRAPUPROREE LES 194 CI CO i red D E Fab AER ade badass 105 trace experiment status of 108 braceback 22 eg pedet red 62 iracepoint actions eem deed E 107 tracepoint data display 0 IU tracepoint deletion eeeeeeesuus 106 tracepoint number seseeleeeeeees 106 tracepoint packets 0 eee eee 351 tracepoint pass count sees eese 106 tracepoint variables 0 eens 112 TLACEPOMUS s 25 sae ds pelea te e
7. Delete any section Entitled Endorsements Such a section may not be included in the Modified Version Do not retitle any existing section to be Entitled Endorsements or to conflict in title with any Invariant Section Preserve any Warranty Disclaimers If the Modified Version includes new front matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document you may at your option designate some or all of these sections as invariant To do this add their titles to the list of Invariant Sections in the Modified Version s license notice These titles must be distinct from any other section titles Appendix H GNU Free Documentation License 397 You may add a section Entitled Endorsements provided it contains nothing but endorsements of your Modified Version by various parties for example statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard You may add a passage of up to five words as a Front Cover Text and a passage of up to 25 words as a Back Cover Text to the end of the list of Cover Texts in the Modified Version Only one passage of Front Cover Text and one of Back Cover Text may be added by or through arrangements made by any one entity If the Document already includes a cover text for the same cover previously added by you or by arrangement made by the same entity you are acting on behal
8. Add a binding to refresh the line which is unbound NC xr redraw current line Edit variable on current line M C v C a C k C y M C e C a C y endif use a visible bell if one is available set bell style visible don t strip characters to 7 bits when reading set input meta on allow iso latini characters to be inserted rather than converted to prefix meta sequences set convert meta off display characters with the eighth bit set directly rather than as meta prefixed characters set output meta on if there are more than 150 possible completions for a word ask the user if he wants to see all of them set completion query items 150 Chapter 27 Command Line Editing 307 For FTP if Ftp C xg get M C xt put M M yank last arg endif 27 4 Bindable Readline Commands This section describes Readline commands that may be bound to key sequences Command names without an accompanying key sequence are unbound by default In the following descriptions point refers to the current cursor position and mark refers to a cursor position saved by the set mark command The text between the point and mark is referred to as the region 27 4 1 Commands For Moving beginning of line C a Move to the start of the current line end of line C e Move to the end of the line forward char C f Move forward a character backward char C b Move back a character forward wo
9. The first two options are always 0 cancel and 1 all Typing 1 sets a breakpoint at each definition of function and typing O aborts the break command without setting any new breakpoints For example the following session excerpt shows an attempt to set a breakpoint at the overloaded symbol String after We choose three particular definitions of that function name gdb b String after 0 cancel 1 all 2 file String cc line number 867 3 file String cc line number 860 4 file String cc line number 875 5 file String cc line number 853 6 file String cc line number 846 7 file String cc line number 735 gt 246 Breakpoint 1 at Oxb26c file String cc line 867 Breakpoint 2 at Oxb344 file String cc line 875 Breakpoint 3 at Oxafcc file String cc line 846 Multiple breakpoints were set Use the delete command to delete unwanted breakpoints gdb 5 1 9 Cannot insert breakpoints Under some operating systems breakpoints cannot be used in a program if any other process is running that program In this situation attempting to run or continue a program with a breakpoint causes GDB to print an error message Cannot insert breakpoints The same program may be running in another process When this happens you have three ways to proceed Remove or disable the breakpoints then continue 2 Suspend GDB and copy the file containing your program to a new name Resume GDB and use the exe
10. gdb We can use the show charset command to see what character sets GDB is currently using to interpret and display characters and strings gdb show charset The current host and target character set is IS0 8859 1 gdb For the sake of printing this manual let s use ASCII as our initial character set gdb set charset ASCII gdb show charset The current host and target character set is ASCII gdb Let s assume that ASCII is indeed the correct character set for our host system in other words let s assume that if GDB prints characters using the ASCII character set our terminal will display them properly Since our current target character set is also ASCH the contents of ascii hello print legibly gdb print ascii hello 1 0x401698 Hello world Wn gdb print ascii_hello 0 2 72 l gdb GDB uses the target character set for character and string literals you use in expressions 98 Debugging with GDB gdb print 3 43 e gdb The ASCII character set uses the number 43 to encode the character GDB relies on the user to tell it which character set the target program uses If we print ibm1047 hello while our target character set is still ASCH we get jibberish gdb print ibmi047 hello 4 0x4016a8 N310N205N223N223N226k0N 246N 226N231N223N204Z 7 gdb print ibmi047 hello 0 5 200 310 gdb If we invoke the set target charset followed by TAB TAB GDB tel
11. Using a convenience variable for the first time creates it but its value is void until you assign a new value You can alter the value with another assignment at any time Convenience variables have no fixed types You can assign a convenience variable any type of value including structures and arrays even if that variable already has a value of a different type The convenience variable when used as an expression has the type of its current value show convenience Print a list of convenience variables used so far and their values Abbreviated show conv init if undefined variable expression Set a convenience variable if it has not already been set This is useful for user defined commands that keep some state It is similar in concept to using local static variables with initializers in C except that convenience variables are global It can also be used to allow users to override default values used in a command script If the variable is already defined then the expression is not evaluated so any side effects do not occur One of the ways to use a convenience variable is as a counter to be incremented or a pointer to be advanced For example to print a field from successive elements of an array of structures set i 0 print bar i gt contents Repeat that command by typing RET Some convenience variables are created automatically by GDB and given values likely to be useful _ The variable _ is automatical
12. below refers to any such manual or work Any member of the public is a licensee and is addressed as you You accept the license if you copy modify or distribute the work in a way requiring permission under copyright law A Modified Version of the Document means any work containing the Document or a portion of it either copied verbatim or with modifications and or translated into another language A Secondary Section is a named appendix or a front matter section of the Document that deals exclusively with the relationship of the publishers or authors of the Document to the Document s overall subject or to related matters and contains nothing that could fall directly within that overall subject Thus if the Document is in part a textbook of mathematics a Secondary Section may not explain any mathematics The relationship could be a matter of historical connection with the subject or with related matters or of legal commercial philosophical ethical or political position regarding them The Invariant Sections are certain Secondary Sections whose titles are designated as being those of Invariant Sections in the notice that says that the Document is released 394 Debugging with GDB under this License If a section does not fit the above definition of Secondary then it is not allowed to be designated as Invariant The Document may contain zero Invariant Sections If the Document does not identify any Invariant Section
13. gdb_loc in gdbtk Example N A The symbol type Command Synopsis symbol type variable Show type of variable GDB Command The corresponding GDB command is ptype gdbtk has gdb_obj_variable Example N A 24 18 GDB MI File Commands This section describes the GDB MI commands to specify executable file names and to read in and obtain symbol table information The file exec and symbols Command Synopsis file exec and symbols file Specify the executable file to be debugged This file is the one from which the symbol table is also read If no file is specified the command clears the executable and symbol information If breakpoints are set when using this command with no arguments GDB will produce error messages Otherwise no output is produced except a completion notification GDB Command The corresponding GDB command is file Example gdb file exec and symbols kwikemart marge ezannoni TRUNK mbx hello mbx done gdb The file exec file Command Synopsis file exec file file Specify the executable file to be debugged Unlike file exec and symbols the symbol table is not read from this file If used without argument GDB clears the information about the executable file No output is produced except a completion notification Chapter 24 The GDB MI Interface 277 GDB Command The corresponding GDB command is exec file Example gdb file exec file kwikemart mar
14. nione Iw eua pet erg 196 set monitor prompt MIPS remote 197 set monitor warnings MIPS remote 197 Set new CcOnSO le eo save gue aes s 185 Bet new EIOUD icsrag us pape E d Rees 185 set opaque type resolution 146 Set osabi o edu devas PUER addons 210 set output radix i e rp e 210 set overload resolution 128 414 Set pagination 4 2 2 4 geek pe RARE da 209 set print iiec nrin Eae dees dd eget 82 Set processOP oss i doc tee hee cae aed tees 167 set procts fyle 2 222122 re lA Res 182 Set procfs tra6e ulnas eo eei P 182 Bet prompti diee dee E cede steer 207 Set radix sh gsc rt e eke cus do Rcg pus 210 set rdiheartbeat sei e t rr hn 194 set rdiromnatz6rOo4 x es nae RR ODER PPS 193 Set remote llb Rer e Hue PERPE NES TERRA 174 set remote system call allowed 363 set remote mips64 transfers 32bit regs 204 set remotecache 2 6 cb ear hh hn 98 set Temoteflow ose e tori Eeti 175 set retransmit timeout sss 196 set rstack high address 203 set sdstimeout cere p nnn 199 set server address esee essen 194 set she lkl uos rre bb end OP Es naa 186 set sSignal thread s easier de re imiss 188 set signals Hurd command 188 set sigs Hurd command 188 set Sigthr ad 2522220302 sag d iR ee RES 188 set solib absolute prefix 1
15. width 4 alignment 1 col_name disp colhdr Disp width 3 alignment 1 col_name enabled colhdr Enb width 10 alignment 1 col_name addr colhdr Address width 40 alignment 2 col_name what colhdr What body bkpt number 1 type breakpoint disp keep enabled y addr 0x00010734 func callee4 file devo gdb testsuite gdb mi basics c fullname home foo devo gdb testsuite gdb mi basics c line 8 times 1 gdb 24 10 GDB MI Program Context The exec arguments Command Synopsis exec arguments args Set the inferior program arguments to be used in the next exec run GDB Command The corresponding GDB command is set args Example Don t have one around The exec show arguments Command Synopsis exec show arguments Print the arguments of the program GDB Command The corresponding GDB command is show args Example N A The environment cd Command 248 Debugging with GDB Synopsis environment cd pathdir Set GDB s working directory GDB Command The corresponding GDB command is cd Example gdb environment cd kwikemart marge ezannoni flathead dev devo gdb done gdb The environment directory Command Synopsis environment directory r pathdir Add directories pathdir to beginning of search path for source files If the r option is used the search path is reset to the default
16. 22 5 e o ye eR REIR 291 debugging C programs 126 debugging information directory global 161 debugging information in separate files 161 debugging multiple processes 34 debugging multithreaded programs on HP UX s E Ao ate PAD REN BR aps rre te LEE 32 debugging optimized code 25 debugging stub example 177 debugging target 00008 167 debugging the Cygwin DLL 185 default system root 0000 00s 161 define inci pep pe hdd er Eaux 217 defining macros interactively 101 definition showing a macro s 101 d letesiccedri sipor ninn eee oes re he dae 47 delete breakpoints sese 47 delete checkpoint checkpoint id 36 delete display e i e re ebrei 82 delete fork fork id osa ns 35 delete mem we o egadohbnepePOEe d EERE beds 93 delete tracepoint 2s 0 v e gb 106 405 delete char U d dieimo hr tete 309 delete char or list sss ALT delete horizontal space 310 deleting breakpoints watchpoints catchpoints 46 deliver a signal to a program 151 demangling C names 0 86 deprecated commands 0000005 327 derived type of an object printing 87 descriptor tables display lusus 183 detach greoi te
17. Example s formatted for readability Some of the described commands have not been implemented yet and these are labeled N A not available 24 9 GDB MI Breakpoint Commands This section documents GDB MI commands for manipulating breakpoints The break after Command Synopsis break after number count The breakpoint number number is not in effect until it has been hit count times To see how this is reflected in the output of the break list command see the description of the break list command below 240 Debugging with GDB GDB Command The corresponding GDB command is ignore Example gdb break insert main done bkpt number 1 addr 0x000100d0 file hello c fullname home foo hello c line 5 times 0 gdb break after 1 3 done gdb break list done BreakpointTable nr_rows 1 nr_cols 6 hdr width 3 alignment 1 col_name number colhdr Num width 14 alignment 1 col_name type colhdr Type width 4 alignment 1 col_name disp colhdr Disp width 3 alignment 1 col_name enabled colhdr Enb width 10 alignment 1 col_name addr colhdr Address width 40 alignment 2 col_name what colhdr What body bkpt number 1 type breakpoint disp keep enabled y addr 0x000100d0 func main file hello c fullname home foo hello c line 5 times 0 ignore 3 gdb The break condition Command Synopsis break
18. When you use return GDB discards the selected stack frame and all frames within it You can think of this as making the discarded frame return prematurely If you wish to specify a value to be returned give that value as the argument to return This pops the selected stack frame see Section 6 3 Selecting a Frame page 64 and any other frames inside of it leaving its caller as the innermost remaining frame That frame becomes selected The specified value is stored in the registers used for returning values of functions The return command does not resume execution it leaves the program stopped in the state that would exist if the function had just returned In contrast the finish command see Section 5 2 Continuing and Stepping page 52 resumes execution until the selected stack frame returns naturally 152 Debugging with GDB 14 5 Calling Program Functions print expr Evaluate the expression expr and display the resulting value expr may include calls to functions in the program being debugged call expr Evaluate the expression expr without displaying void returned values You can use this variant of the print command if you want to execute a function from your program that does not return anything a k a a void function but without cluttering the output with void returned values that GDB will otherwise print If the result is not void it is printed and saved in the value history It is possible for the function you
19. break list done BreakpointTable nr_rows 1 nr_cols 6 hdr width 3 alignment 1 col_name number colhdr Num width 14 alignment 1 col_name type colhdr Type width 4 alignment 1 col_name disp colhdr Disp width 3 alignment 1 col_name enabled colhdr Enb width 10 alignment 1 col_name addr colhdr Address width 40 alignment 2 col_name what colhdr What body bkpt number 2 type breakpoint disp keep enabled y addr 0x000100d0 func main file hello c fullname home foo hello c line 5 times 0 gdb The break info Command Synopsis break info breakpoint Get information about a single breakpoint GDB Command The corresponding GDB command is info break breakpoint Example N A The break insert Command Synopsis break insert t h r c condition i ignore count p thread line addr If specified line can be one of e function e filename linenum e filename function e address Chapter 24 The GDB MI Interface 243 The possible optional parameters of this command are Insert a temporary breakpoint p Insert a hardware breakpoint c condition Make the breakpoint conditional on condition i ignore count Initialize the ignore count r Insert a regular breakpoint in all the functions whose names match the given regular expression Other flags are not appli
20. gdb 6 7 50_20071011 include GNU include files gdb 6 7 50_20071011 libiberty source for the liberty free software library lig you have a more recent version of GDB than 6 7 50 20071011 look at the README file in the sources we may have improved the installation procedures since publishing this manual 322 Debugging with GDB gdb 6 7 50_20071011 opcodes source for the library of opcode tables and disassemblers gdb 6 7 50_20071011 readline source for the GNU command line interface gdb 6 7 50 20071011 glob source for the GNU filename pattern matching subroutine gdb 6 7 50_20071011 mmalloc source for the GNU memory mapped malloc package The simplest way to configure and build GDB is to run configure from the gdb version number source directory which in this example is the gdb 6 7 50_20071011 directory First switch to the gdb version number source directory if you are not already in it then run configure Pass the identifier for the platform on which GDB will run as an argument For example cd gdb 6 7 50_20071011 configure host make where host is an identifier such as sun4 or decstation that identifies the platform where GDB will run You can often leave off host configure tries to guess the correct value by examining your system Running configure host and then running make builds the bfd readline mmalloc and lib
21. gdbtk has the gdb get line and gdb get file commands Example N A The symbol info symbol Command Synopsis symbol info symbol addr Describe what symbol is at location addr GDB Command The corresponding GDB command is info symbol Example N A The symbol list functions Command Synopsis symbol list functions List the functions in the executable GDB Command info functions in GDB gdb_listfunc and gdb search in gdbtk Chapter 24 The GDB MI Interface 275 Example N A The symbol list lines Command Synopsis symbol list lines filename Print the list of lines that contain code and their associated program addresses for the given source filename The entries are sorted in ascending PC order GDB Command There is no corresponding GDB command Example gdb symbol list lines basics c done lines pc 0x08048554 line 7 pc 0x0804855a line 8 gdb The symbol list types Command Synopsis symbol list types List all the type names GDB Command The corresponding commands are info types in GDB gdb_search in gdbtk Example N A The symbol list variables Command Synopsis symbol list variables List all the global and static variable names GDB Command info variables in GDB gdb_search in gdbtk Example N A The symbol locate Command Synopsis symbol locate 276 Debugging with GDB GDB Command
22. qGetTLSAddr is not supported by the stub qL startflag threadcount nextthread Obtain thread information from RTOS Where startflag one hex digit is one to indicate the first query and zero to indicate a subsequent query threadcount two hex digits is the maximum number of threads the response packet can contain and nextthread eight hex digits for subsequent queries startflag is zero is returned in the response as argthread Don t use this packet use the qfThreadInfo query instead see above Reply qM count done argthread thread Where count two hex digits is the number of threads being returned done one hex digit is zero to indicate more threads and one indicates no further threads argthreadid eight hex dig its is nextthread from the request packet thread is a sequence of thread IDs from the target threadid eight hex digits See remote c parse_threadlist_response qOffsets Get section offsets that the target used when relocating the downloaded image Reply Text xxx Data yyy Bss zzz Relocate the Text section by xxx from its original address Relocate the Data section by yyy from its original address If the object file format provides segment information e g ELF PT_LOAD program headers GDB will relocate entire segments by the supplied offsets Note while a Bss offset may be included in the response GDB ignores this and instead applies the Data offset t
23. watchpoint Normal explicitly set watchpoint longjmp Internal breakpoint used to handle correctly stepping through longjmp calls longjmp resume Internal breakpoint at the target of a longjmp until Temporary internal breakpoint used by the GDB until command finish Temporary internal breakpoint used by the GDB finish command shlib events Shared library events maint check symtabs Check the consistency of psymtabs and symtabs maint cplus first_component name Print the first C class namespace component of name maint cplus namespace Print the list of possible C namespaces maint demangle name Demangle a C or Objective C mangled name maint deprecate command replacement maint undeprecate command Deprecate or undeprecate the named command Deprecated commands cause GDB to issue a warning when you use them The optional argument replacement says which newer command should be used in favor of the deprecated one if it is given GDB will mention the replacement as part of the warning 328 Debugging with GDB maint dump me Cause a fatal signal in the debugger and force it to dump its core This is supported only on systems which support aborting a program with the SIGQUIT signal maint internal error message text maint internal warning message text Cause GDB to call the internal function internal error or internal warning and hence behave as though an internal error or internal warning has been detected
24. 004 227 d packet c i sivciibia gates aches eed ons 337 Q packet cens der RR Rex ad ede eee 337 QC packet esit eere REPRE RI Da on 342 QCRG packets eres oo eta hebr DEREES 343 qfThreadInfo packet 0000 343 qGetTLSAddr packet 0005 343 QNX Neutrino 2s oii cade tre Eh eee es 190 q0ffsets packet 0 0008 344 aP packet isos erected ate TERRE 344 412 QPassSignals packet 005 345 gRend packet si sess cres sse RRRER Hp 345 qsThreadInfo packet 0000 343 qSupported packet 0000 008 345 qSymbol packet 2er os chee ta encesek oe 348 qThreadExtralInfo packet 348 query annotation s penea e eerie 288 quit expression ener Reus 16 quit annotation occ esd gs snime kiai Rare as 288 quoted insert C q or C v 309 quotes in commands seeeeee eese 20 quoting Ada internal identifiers 140 quoting names isccesag ur eR Rd ee 143 tgXter packet ei eedder rh e ped DEEE 349 e Y PUN 2 po kata payed e hi S APE oo Behe GAGs 26 r SingleKey TUI key 0 004 227 E packet 22a eie et emot ede n 337 R packet lt 2 atten civ biet ped been avide 33T False excepilons Lll sbre 4 bd habeas dees 46 range checking c oedoeke DIR pP ERE TER Ios 122 ranges of breakpoints 37 EDLC AK fois
25. 10 Debugging with GDB Success The new quotes now work just as well as the default ones The problem seems to have been just the two typos defining the wrong lengths We allow m4 exit by giving it an EOF as input Ctrl d Program exited normally The message Program exited normally is from GDB it indicates m4 has finished execut ing We can end our GDB session with the GDB quit command gdb quit Chapter 2 Getting In and Out of GDB 11 2 Getting In and Out of GDB This chapter discusses how to start GDB and how to get out of it The essentials are e type gdb to start GDB e type quit or Ctrl d to exit 2 1 Invoking GDB Invoke GDB by running the program gdb Once started GDB reads commands from the terminal until you tell it to exit You can also run gdb with a variety of arguments and options to specify more of your debugging environment at the outset The command line options described here are designed to cover a variety of situations in some environments some of these options may effectively be unavailable The most usual way to start GDB is with one argument specifying an executable program gdb program You can also start with both an executable program and a core file specified Edb program core You can instead specify a process ID as a second argument if you want to debug a running process Edb program 1234 would attach GDB to process 1234 unless you also have a file named 1234 GDB do
26. 17 2 1 Monitor Commands for gdbserver During a GDB session using gdbserver you can use the monitor command to send special requests to gdbserver Here are the available commands they are only of interest when debugging GDB or gdbserver monitor help List the available monitor commands monitor set debug O monitor set debug 1 Disable or enable general debugging messages monitor set remote debug O monitor set remote debug 1 Disable or enable specific debugging messages associated with the remote pro tocol see Appendix D Remote Protocol page 333 17 3 Remote Configuration This section documents the configuration options available when debugging remote pro grams For the options related to the File I O extensions of the remote protocol see system page 362 Chapter 17 Debugging Remote Programs 175 Set remoteaddresssize bits Set the maximum size of address in a memory packet to the specified number of bits GDB will mask off the address bits above that number when it passes addresses to the remote target The default value is the number of bits in the target s address show remoteaddresssize Show the current value of remote address size in bits Set remotebaud n Set the baud rate for the remote serial I O to n baud The value is used to set the speed of the serial port used for debugging remote targets show remotebaud Show the current speed of the remote connection set remotebreak If set to on GDB s
27. 18 1 5 Features for Debugging MS Windows PE Executables 185 18 1 5 1 Support for DLLs without Debugging Symbols 186 18 1 5 2 DLL Name Prefixes ssssssessseee sere 186 18 1 5 8 Working with Minimal Symbols 187 18 1 6 Commands Specific to GNU Hurd Systems 188 18 17 QNX Neutrinos d eee tela RR PORT REIR 190 18 2 Embedded Operating Systems 00 000 eee leise 190 18 2 1 Using GDB with VxWorks sseeeseeeee mrama 190 18 2 1 Connecting to VxWorks ssseseseesesss 191 18 2 1 2 VxWorks Download 00 00 e eee eee 191 18 2 1 8 Running Tasks lesser 192 18 3 Embedded Processors 0 000 ce cece ce ee eee a 192 T8 9 L ARM Led toco e eaa aud ee tetas pia baute 192 18 3 2 Renesas M32R D and M32R SDI 194 18 3 9 MOS auia iet ebeer Sb e HD Td ERU PAUSA DE dus 195 18 3 4 MIPS Embedded rn 195 18 3 5 OpenRISC 1000 0 eee ee eee eee 197 18 3 6 PowerP 324 eideatng 4p d nd bei Rel tud ad aed 199 18 3 7 HP PA Embedded saps trahas aiai ee dew heeded sous 199 18 3 8 Tsqware Sparclet 0 seii eee eee 199 18 3 8 1 Setting File to Debug 004 200 18 3 8 2 Connecting to Sparclet 0 0 00 200 18 3 8 3 Sparclet Download 0 000 c eee eee 200 18 3 8 4 Running and Debugging 201 18 3 9 Fujitsu Sparclite 0 eke eee 201 183 10 Zilog 8000 eert
28. AY packets veles iy vet X bbosd ied i 334 ADDECVIEHON sssini crees isa P RBS aA 19 abort C aceite etch ected eae hide enone 312 accept line Newline or Return 307 acknowledgment for GDB remote 333 ACTIONS v occu needa pie LUCERE ote RS cus 107 active targets coepere prre bog EN dehors d 167 RBIs screen eter ammo 1a aaepe due tac tus 137 Ada exception catching 00 45 Ada mode general 0 000 I37 Ada deviations from 0000000 139 Ada omissions from isssssslslessls 138 Ada problems sste sririrsandt inon idi asaan 140 adbg find memory in frame 376 add new commands for external monitor 172 add shared symbol files 157 add symbol file 2 uot ers 156 add symbol file from memory 157 address of asymbol 00 143 address size for remote targets 175 ADP Angel Debugger Protocol logging 193 advange location ie sere it E EISE 55 aggregates Ada eee e eee eee ee eee 138 AIX threads eap eee Cete eee t 213 alignment of remote memory accesses 336 Alpha stack 2 2 21 3 3 wee bep ERE AER E 203 AMD 29K register stack 00004 203 annotating ewm REPRE RP E ud 287 annotations for errors warnings and interrupts TET 288 annotations for invalidation messages 289 annotations for prompts 004 288 annotations f
29. Many times we have heard a GNU user eagerly describe a manual that he is writing his intended contribution to the community only to learn that he had ruined everything by signing a publication contract to make it non free Free documentation like free software is a matter of freedom not price The problem with the non free manual is not that publishers charge a price for printed copies that in itself is fine The Free Software Foundation sells printed copies of manuals too The problem is the restrictions on the use of the manual Free manuals are available in source code form and give you permission to copy and modify Non free manuals do not allow this The criteria of freedom for a free manual are roughly the same as for free software Redistribution including the normal kinds of commercial redistribution must be permitted so that the manual can accompany every copy of the program both on line and on paper Permission for modification of the technical content is crucial too When people mod ify the software adding or changing features if they are conscientious they will change the manual too so they can provide accurate and clear documentation for the modified program A manual that leaves you no choice but to write a new manual to document a changed version of the program is not really available to our community Some kinds of limits on the way modification is handled are acceptable For example requirements to preserve t
30. This option is useful in conjunction with batch or batch silent when GDB is being used as a remote program loader or simulator interface nowindows nw No windows If GDB comes with a graphical user interface GUI built in then this option tells GDB to only use the command line interface If no GUI is available this option has no effect windows W If GDB includes a GUI then this option requires it to be used if possible cd directory Run GDB using directory as its working directory instead of the current direc tory fullname f GNU Emacs sets this option when it runs GDB as a subprocess It tells GDB to output the full file name and line number in a standard recognizable fashion each time a stack frame is displayed which includes each time your program stops This recognizable format looks like two 032 characters followed by the file name line number and character position separated by colons and a newline The Emacs to GDB interface program uses the two 032 characters as a signal to display the source code for the frame epoch The Epoch Emacs GDB interface sets this option when it runs GDB as a subpro cess It tells GDB to modify its print routines so as to allow Epoch to display values of expressions in a separate window annotate level This option sets the annotation level inside GDB Its effect is identical to using set annotate level see Chapter 25 Annotations page 28
31. add gnu debuglink foo debug foo unsigned long gnu_debuglink_crc32 unsigned long crc unsigned char buf size_t len static const unsigned long crc32_table 256 0x00000000 Ox706af48f OxeOdbe91e Ox90bfid91 Oxiadad47d 0Ox646ba8c0 Oxfa0f3d63 0xa2677172 Ox35b5a8fa Ox45dfb5cT75 Oxc8d75180 Oxb8bda5Of Ox2f6f7c87 0x01db7106 Ox9fbfe4a5 0xe10e9818 Ox6b6b51f4 Ox1b01a57b Ox8bbeb8ea Oxfbd44c65 Ox4adfab41 Ox346ed9fc Oxaa0a4cbf 0xc90c2086 Ox5edef90e Ox2eb40d81 Ox03b6e20c 0x73dc1683 Oxe40ecf0b 0x8708a3d2 0x77073096 0xe963a535 0x97d2d988 Ox1db71064 Ox6ddde4eb Oxfd62f97a 0x8d080df5 Ox3c03e4d1 0x42b2986c Oxdcd60dcf Oxbfd06116 0x2802b89e 0x58684c11 0x98d220bc 0xe8b8d433 Ox7f6a0dbb Ox1c6c6162 0x8208f4c1 Oxfcb9887c Ox4db26158 0x3dd895d7 Oxad678846 OxddOd7cc9 0x5768b525 0x29d9c998 Oxb7bd5c3b 0x74b1d29a 0xe3630b12 0x9309ff9d 0x1e01f268 Oxee0e612c 0x9e6495a3 0x09b64c2b Ox6ab020f2 Oxf4d4b551 Ox8a65c9ec Ox3b6e20c8 Ox4b04d447 Oxdbbbc9d6 Oxabd13d59 Ox21b4f4b5 Ox5f058808 Oxci611dab Oxefd5102a 0x7807c9a2 0x086d3d2d 0x856530d8 Oxf50 c457 Ox62ddiddf Ox3ab551ce Oxa4di1c46d Oxda60b8d0 0x5005713c Ox206f85b3 Oxb0d09822 OxcOba6cad Oxead54739 0x94643b84 0x0a00ae27 0x6906c2fe 0x990951ba OxOedb8832 Ox7eb17cbd Oxf3b97148 0x83d385c7 Ox14015c4f 0x4c69105e Oxd20d85fd Oxacbcf940 0x26d930ac
32. but select the first tracepoint frame after the currently se lected frame whose PC is addr addr is a hexadecimal number QTFrame tdp t Like QTFrame n but select the first tracepoint frame after the currently se lected frame that is a hit of tracepoint t t is a hexadecimal number QTFrame range start end Like QTFrame n but select the first tracepoint frame after the currently se lected frame whose PC is between start inclusive and end exclusive start and end are hexadecimal numbers QTFrame outside start end QTStart QTStop QTinit Like QTFrame range start end but select the first frame outside the given range of addresses Begin the tracepoint experiment Begin collecting data from tracepoint hits in the trace frame buffer End the tracepoint experiment Stop collecting trace frames Clear the table of tracepoints and empty the trace frame buffer QTro starti endi1 start2 end2 qTStatus Establish the given ranges of memory as transparent The stub will answer requests for these ranges from memory s current contents if they were not collected as part of the tracepoint hit GDB uses this to mark read only regions of memory like those containing pro gram code Since these areas never change they should still have the same contents they did when the tracepoint was hit so there s no reason for the stub to refuse to
33. display If you do not specify thread threadno when you set a breakpoint the break point applies to all threads of your program You can use the thread qualifier on conditional breakpoints as well in this case place thread threadno before the breakpoint condition like this gdb break frik c 13 thread 28 if bartab gt lim 58 Debugging with GDB Whenever your program stops under GDB for any reason all threads of execution stop not just the current thread This allows you to examine the overall state of the program including switching between threads without worrying that things may change underfoot There is an unfortunate side effect If one thread stops for a breakpoint or for some other reason and another thread is blocked in a system call then the system call may return prematurely This is a consequence of the interaction between multiple threads and the signals that GDB uses to implement breakpoints and other events that stop execution To handle this problem your program should check the return value of each system call and react appropriately This is good programming style anyways For example do not write code like this sleep 10 The call to sleep will return early if a different thread stops at a breakpoint or for some other reason Instead write this int unslept 10 while unslept gt 0 unslept sleep unslept A system call is allowed to return early so the system is still conforming
34. for an error Indicating an unrecognized query Write register n with value r The register number n is in hexadecimal and r contains two hex digits for each byte in the register target byte order Reply OK for success E NN for an error q name params Q name params General query q and set Q These packets are described fully in Sec tion D 4 General Query Packets page 342 T Reset the entire system Don t use this packet use the R packet instead R XX Restart the program being debugged XX while needed is ignored This packet is only available in extended mode The R packet has no reply s addr Single step addr is the address at which to resume If addr is omitted resume at same address Reply See Section D 3 Stop Reply Packets page 341 for the reply specifica tions S sig addr Step with signal This is analogous to the C packet but requests a single step rather than a normal resumption of execution Reply See Section D 3 Stop Reply Packets page 341 for the reply specifica tions t addr PP MM Search backwards starting at address addr for a match with pattern PP and mask MM PP and MM are 4 bytes addr must be at least 3 digits 338 Debugging with GDB T XX Find out if the thread XX is alive Reply OK thread is still alive E NN thread is dead ty Packets starting with v are i
35. for example a download pro gram These are often supplied by the hardware manufacturer but you may have to write your own from hardware documentation The next step is to arrange for your program to use a serial port to communicate with the machine where GDB is running the host machine In general terms the scheme looks like this On the host GDB already understands how to use this protocol when everything else is set up you can simply use the target remote command see Chapter 16 Specifying a Debugging Target page 167 On the target you must link with your program a few special purpose subroutines that imple ment the GDB remote serial protocol The file containing these subroutines is called a debugging stub 178 Debugging with GDB On certain remote targets you can use an auxiliary program gdbserver instead of linking a stub into your program See Section 17 2 Using the gdbserver Program page 173 for details The debugging stub is specific to the architecture of the remote machine for example use sparc stub c to debug programs on SPARC boards These working remote stubs are distributed with GDB 1386 stub c For Intel 386 and compatible architectures m68k stub c For Motorola 680x0 architectures sh stub c For Renesas SH architectures sparc stub c For SPARC architectures sparcl stub c For Fujitsu SPARCLITE architectures The README file in the GDB distribution may list o
36. gt Q c string log stream output amp c string nl CR CR LF token any sequence of digits Notes e All output sequences end in a single line containing a period e The token is from the corresponding request If an execution command is interrupted by the exec interrupt command the token associated with the stopped message is the one of the original execution command not the one of the interrupt command e status async output contains on going status information about the progress of a slow operation It can be discarded All status output is prefixed by e exec async output contains asynchronous state change on the target stopped started disappeared All async output is prefixed by e notify async output contains supplementary information that the client should handle e g a new breakpoint information All notify output is prefixed by e console stream output is output that should be displayed as is in the console It is the textual response to a CLI command All the console output is prefixed by e target stream output is the output produced by the target program All the target output is prefixed by e log stream output is output text coming from GDB s internals for instance messages that should be displayed as part of an error log All the log output is prefixed by amp e New GDB MI commands should only output lists containing values See S
37. lt DOCTYPE target SYSTEM gdb target dtd gt lt target version 1 0 gt architecture feature lt target gt The description is generally insensitive to whitespace and line breaks under the usual common sense rules The XML version declaration and document type declaration can generally be omitted GDB does not require them but specifying them may be useful for XML validation tools The version attribute for lt target gt may also be omitted but we recommend including it if future versions of GDB use an incompatible revision of gdb target dtd they will detect and report the version mismatch F 2 1 Inclusion It can sometimes be valuable to split a target description up into several different annexes either for organizational purposes or to share files between different possible target descrip tions You can divide a description into multiple files by replacing any element of the target description with an inclusion directive of the form lt xi include href document When GDB encounters an element of this form it will retrieve the named XML document and replace the inclusion directive with the contents of that document If the current description was read using qXfer then so will be the included document document will be interpreted as the name of an annex If the current description was read from a file GDB will look for document as a file in the same directory where it found the original descripti
38. meta bit set print sevenbit strings off Print full eight bit characters T his allows the use of more international char acter sets and is the default show print sevenbit strings Show whether or not GDB is printing only seven bit characters set print union on Tell GDB to print unions which are contained in structures and other unions This is the default setting set print union off Tell GDB not to print unions which are contained in structures and other unions GDB will print instead 86 Debugging with GDB Show print union Ask GDB whether or not it will print unions which are contained in structures and other unions For example given the declarations typedef enum Tree Bug Species typedef enum Big tree Acorn Seedling Tree forms typedef enum Caterpillar Cocoon Butterfly Bug forms struct thing Species it union Tree_forms tree Bug_forms bug form Y struct thing foo Tree Acorn with set print union on in effect p foo would print 1 it Tree form tree Acorn bug Cocoon and with set print union off in effect it would print 1 it Tree form set print union affects programs written in C like languages and in Pascal These settings are of interest when debugging C programs set print demangle set print demangle on Print C names in their source form rather than in the encoded mangled form passed to the assembler and linker for
39. overload debugging info set debug remote Turns on or off display of reports on all packets sent back and forth across the serial line to the remote machine The info is printed on the GDB standard output stream The default is off show debug remote Displays the state of display of remote packets set debug serial Turns on or off display of GDB serial debugging info The default is off Show debug serial Displays the current state of displaying GDB serial debugging info set debug solib frv Turns on or off debugging messages for FR V shared library code show debug solib frv Display the current state of FR V shared library code debugging messages set debug target Turns on or off display of GDB target debugging info This info includes what is going on at the target level of GDB as it happens The default is 0 Set it to 1 to track events and to 2 to also track the value of large memory transfers Changes to this flag do not take effect until the next time you connect to a target or use the run command show debug target Displays the current state of displaying GDB target debugging info set debugvarobj Turns on or off display of GDB variable object debugging info The default is off show debugvarobj Displays the current state of displaying GDB variable object debugging info Chapter 19 Controlling GDB 215 set debug xml Turns on or off debugging messages for built in XML parsers show debug xml Displays the
40. watch rwatch awatch The packet indicates a watchpoint hit and r is the data address in hex library The packet indicates that the loaded libraries have changed GDB should use qXfer libraries read to fetch a new list of loaded libraries r is ignored W AA The process exited and AA is the exit status This is only applicable to certain targets X AA The process terminated with signal AA 342 Debugging with GDB O XX XX is hex encoding of AsCII data to be written as the program s console output This can happen at any time while the program is running and the debugger should continue to wait for W T etc F call id parameter call id is the identifier which says which host system call should be called This is just the name of the function Translation into the correct system call is only applicable as it s defined in GDB See Section D 9 File I O Remote Protocol Extension page 354 for a list of implemented system calls parameter is a list of parameters as defined for this very system call The target replies with this packet when it expects GDB to call a host system call on behalf of the target GDB replies with an appropriate F packet and keeps up waiting for the next reply packet from the target The latest C c S or s action is expected to be continued See Section D 9 File I O Remote Protocol Extension
41. 3 addr 0x000107a4 func foo file recursive2 c fullname home foo bar recursive2 c line 14 gdb The stack list locals Command Synopsis stack list locals print values Display the local variable names for the selected frame If print values is 0 or no values print only the names of the variables if it is 1 or all values print also their values and if it is 2 or simple values print the name type and value for simple data types and the name and type for arrays structures and unions In this last case a frontend can immediately display the value of simple data types and create variable objects for other data types when the user wishes to explore their values in more detail GDB Command info locals in GDB gdb get locals in gdbtk Example gdb stack list locals 0 done locals name A name B name C gdb stack list locals all values done locals name A value 2 1 name B value 2 name C value 1 2 3 stack list locals simple values done locals name A type int value 1 name B type int value 2 name C type int 3 gdb Chapter 24 The GDB MI Interface 261 The stack select frame Command Synopsis stack select frame framenum Change the selected frame Select a different frame framenum on the stack GDB Command The corresponding GDB commands are frame up down select frame up s
42. 6d by eens a evii 299 eight bit characters in strings 85 elaboration phase seeesseeeeess 27 GlS6 px redline eee Pee eee P pns 220 Emacs iit ss il od Meare PLURI PEDIR 231 emacs editing mode C e 313 empty response for unsupported packets 334 enable ek dr ReR Peas Oo nes oF PEE 47 enable display sro peii sale tices g u b pc de 82 enable Menso cerpi ok RETE E RE 93 enable tracepoint 2 21 sae ETE ERA 106 enable keypad i2 ple A EERIERMPEEURR 299 enable disable a breakpoint 4T end breakpoint commands 50 end if else while commands 220 end user defined commands 217 end kbd macro C x J sesssssss 312 end of history M gt cee eee eee 308 end of line C 6 access rr Epp 307 entering numbers 002200 210 environment of your program 28 errno values in file i o protocol 365 error annotation cessie Gils use Epp 288 error on valid input 0 000 eee 291 error begin annotation 289 event debugging info 0 213 event designators sleeeeeeeeeeee 315 event handling osise peed ya e ed dae es 45 examine process image esses ees 181 examining data ccerewRiP e pr REP ETE 75 EXAMINING MEMOLY os o5o5 erdia expe rub bem E 79 exception handlers eese esee 45 ex
43. An extreme example if you define a variable but never use it GDB never sees that variable because the compiler optimizes it out of existence Some things do not work as well with g 0 as with just g particularly on machines with instruction scheduling If in doubt recompile with g alone and if this fixes the problem please report it to us as a bug including a test case See Section 8 2 Variables page 76 for more information about debugging optimized code 3 Older versions of the GNU C compiler permitted a variant option gg for debugging information GDB no longer supports this format if your GNU C compiler has this option do not use it GDB knows about preprocessor macros and can show you their expansion see Chapter 9 Macros page 101 Most compilers do not include information about preprocessor macros in the debugging information if you specify the g flag alone because this information is rather large Version 3 1 and later of GCC the GNU C compiler provides macro information if you specify the options gdwarf 2 and g3 the former option requests debugging information in the Dwarf 2 format and the latter requests extra information In the future we hope to find more compact ways to represent macro information so that it can be included with g alone 26 Debugging with GDB 4 2 Starting your Program run r Use the run command to start your program under GDB
44. EROFS The file is on a read only filesystem Appendix D GDB Remote Serial Protocol 361 ENOSPC The device containing the file has no room for the new directory entry EINTR The call was interrupted by the user unlink Synopsis int unlink const char pathname Request X Funlink pathnameptr len Return value On success zero is returned On error 1 is returned Errors EACCES No access to the file or the path of the file EPERM The system does not allow unlinking of directories EBUSY The file pathname cannot be unlinked because it s being used by another process EFAULT pathnameptr is an invalid pointer value ENAMETOOLONG pathname was too long ENOENT A directory component in pathname does not exist ENOTDIR A component of the path is not a directory EROFS The file is on a read only filesystem EINTR The call was interrupted by the user stat fstat Synopsis int stat const char pathname struct stat buf int fstat int fd struct stat buf Request X Fstat pathnameptr len bufptr Ffstat fd bufptr Return value On success zero is returned On error 1 is returned Errors EBADF fd is not a valid open file ENOENT A directory component in pathname does not exist or the path is an empty string ENOTDIR A component of the path is not a directory EFAULT pathnameptr is an invalid pointer value EACCES No access to the file or the path of the file 362 Debugging with GDB ENAMETOOLONG pathname
45. GDB also provides a pseudo language called minimal It does not represent a real programming language but provides a set of capabilities close to what the C or assembly languages provide This should allow most simple operations to be performed while debugging an application that uses a language currently not supported by GDB If the language is set to auto GDB will automatically select this language if the current frame corresponds to an unsupported language 142 Debugging with GDB Chapter 13 Examining the Symbol Table 143 13 Examining the Symbol Table The commands described in this chapter allow you to inquire about the symbols names of variables functions and types defined in your program This information is inherent in the text of your program and does not change as your program executes GDB finds it in your program s symbol table in the file indicated when you started GDB see Section 2 1 1 Choosing Files page 12 or by one of the file management commands see Section 15 1 Commands to Specify Files page 155 Occasionally you may need to refer to symbols that contain unusual characters which GDB ordinarily treats as word delimiters The most frequent case is in referring to static variables in other source files see Section 8 2 Program Variables page 76 File names are recorded in object files as debugging symbols but GDB would ordinarily parse a typical file name like foo c as the three words foo
46. Kill all characters on the current line no matter where point is By default this is unbound kill word M d Kill from point to the end of the current word or if between words to the end of the next word Word boundaries are the same as forward word backward kill word M DEL Kill the word behind point Word boundaries are the same as backward word unix word rubout C w Kill the word behind point using white space as a word boundary The killed text is saved on the kill ring unix filename rubout Kill the word behind point using white space and the slash character as the word boundaries The killed text is saved on the kill ring delete horizontal space Delete all spaces and tabs around point By default this is unbound kill region Kill the text in the current region By default this command is unbound copy region as kill Copy the text in the region to the kill buffer so it can be yanked right away By default this command is unbound copy backward word Copy the word before point to the kill buffer The word boundaries are the same as backward word By default this command is unbound copy forward word Copy the word following point to the kill buffer The word boundaries are the same as forward word By default this command is unbound yank C y Yank the top of the kill ring into the buffer at point Chapter 27 Command Line Editing 311 yank pop M y Rotate the kill ring and yank
47. Scroll the active window one line down Scroll the active window one column left Scroll the active window one column right C L Refresh the screen Because the arrow keys scroll the active window in the TUI mode they are not available for their normal use by readline unless the command window has the focus When another window is active you must use other readline key bindings such as C p C n C b and C f to control the command window 22 3 TUI Single Key Mode The TUI also provides a SingleKey mode which binds several frequently used GDB com mands to single keys Type C x s to switch into this mode where the following key bindings are used continue d down f finish n next q exit the SingleKey mode r run S step u up v info locals Ww where Other keys temporarily switch to the GDB command prompt The key that was pressed is inserted in the editing buffer so that it is possible to type most GDB commands without interaction with the TUI SingleKey mode Once the command is entered the TUI SingleKey mode is restored The only way to permanently leave this mode is by typing q or C x s 22 4 TUI specific Commands The TUI has specific commands to control the text windows These commands are always available even when GDB is not in the TUI mode When GDB is in the standard mode most of these commands will automatically switch to the TUI mode info win List and give the size of all displayed windows layout next Di
48. T 312 doc ment ida ei MS ee eee 217 documentation 1 2 21 ectetur pp ura 319 don t repeat command 0005 217 dont repeat ccs shite ee cede tei aeree 217 DOS serial data link remote debugging 184 DOS serial port status lisse sees 185 OWE CD 64 DOWD skr E E EDEVPRBRIA EN do E aU poe 227 down silently i siccdtnwiaeand iene idee iuda 65 downcase word M 1 cee eee 309 download server address M32R 194 download to Sparclet 0 000 esus 200 download to VxWorks 0 0000 2 00 191 DEM 222 mtRbRERenAU RERO ele araertye en ANS 183 406 dump iauic e prer yeEER NEG aa a niee 94 dump all data collected at tracepoint pr dump core from inferior 95 dump data to a file ooo dms 94 dumup functions Q ica dawn Rd e 313 duup macros sinici kerero dakit ei Red Dres 313 duup variables RR ERR UE 313 dump restore files 0 00 00 005 94 DWARF 2 compilation units cache 330 DWARF 2 CFI and CRIS 202 dynamic linking seters 2t rcm reb 156 E e edit eter e PL ENTE EE iari i 68 EBCDIC character set 0 97 OCHO 4 cosa da REY RH Wee Eee Ee aa Reese 220 editis ge oe bOE d erae phates bade ae 68 editing iaces vomer tune ee CHEER RIS TES 207 editing command lines 295 editing source files 2 00000 68 editing mod i
49. The exact contents and layout vary depending on the floating point chip Currently info float is supported on the ARM and x86 machines 92 Debugging with GDB 8 12 Vector Unit Depending on the configuration GDB may be able to give you more information about the status of the vector unit info vector Display information about the vector unit The exact contents and layout vary depending on the hardware 8 13 Operating System Auxiliary Information GDB provides interfaces to useful OS facilities that can help you debug your program When GDB runs on a Posix system such as GNU or Unix machines it interfaces with the inferior via the ptrace system call The operating system creates a special sata structure called struct user for this interface You can use the command info udot to display the contents of this data structure info udot Display the contents of the struct user maintained by the OS kernel for the program being debugged GDB displays the contents of struct user as a list of hex numbers similar to the examine command Some operating systems supply an auxiliary vector to programs at startup This is akin to the arguments and environment that you specify for a program but contains a system dependent variety of binary values that tell system libraries important details about the hardware operating system and process Each value s purpose is identified by an inte ger tag the meanings are well known but system spe
50. aschar where 272 Debugging with GDB address An expression specifying the address of the first memory word to be read Complex expressions containing embedded white space should be quoted using the C convention word format The format to be used to print the memory words The notation is the same as for GDB s print command see Section 8 4 Output Formats page 78 word size The size of each memory word in bytes nr rows The number of rows in the output table nr cols The number of columns in the output table aschar If present indicates that each row should include an ascu dump The value of aschar is used as a padding character when a byte is not a member of the printable ASCII character set printable ASCII characters are those whose code is between 32 and 126 inclusively byte offset An offset to add to the address before fetching memory This command displays memory contents as a table of nr rows by nr cols words each word being word size bytes In total nr rows nr cols word size bytes are read returned as total bytes Should less than the requested number of bytes be returned by the target the missing words are identified using N A The number of bytes read from the target is returned in nr bytes and the starting address used to read memory in addr The address of the next previous row or page is available in next row and prev row
51. comprising the printable string containing the extra information about the thread s attributes Note that the qThreadExtraInfo packet s name is separated from the com mand by a not a contrary to the naming conventions above Please don t use this packet as a model for new packets See Section D 6 Tracepoint Packets page 351 qXfer object read annex offset length Read uninterpreted bytes from the target s special data area identified by the keyword object Request length bytes starting at offset bytes into the data The content and encoding of annex is specific to object it can supply additional details about what data to access Here are the specific requests of this form defined so far All qXfer object read requests use the same reply formats listed below qXfer auxv read offset length Access the target s auxiliary vector See Section 8 13 OS Informa tion page 92 Note annex must be empty This packet is not probed by default the remote stub must re quest it by supplying an appropriate qSupported response see qSupported page 345 qXfer features read annex offset length Access the target description See Appendix F Target Descrip tions page 381 The annex specifies which XML document to ac cess The main description is always loaded from the target xm1 annex This packet is not probed by default the remote stub must re quest it b
52. e you can determine the address at which every section was loaded and provide these to the add symbol file command Some embedded operating systems like Sun Chorus and VxWorks can load relocatable files into an already running program such systems typically make the requirements above easy to meet However it s important to recognize that many native systems use complex link procedures linkonce section factoring and C constructor table assembly for example that make the requirements difficult to meet In general one cannot assume that using add symbol file to read a relocatable object file s symbolic information will have the same effect as linking the relocatable object file into the program in the normal way add symbol file does not repeat if you press after using it add symbol file from memory address Load symbols from the given address in a dynamically loaded object file whose image is mapped directly into the inferior s memory For example the Linux kernel maps a syscall DSO into each process s address space this DSO provides kernel specific code for some system calls The argument can be any expres sion whose evaluation yields the address of the file s shared object file header For this command to work you must have used symbol file or exec file commands in advance add shared symbol files library file assf library file The add shared symbol files command can currently be used only in the Cygwin build of GDB on MS Win
53. in this way behave just like other arrays in terms of subscripting and are coerced to pointers when used in expressions Artificial arrays most often appear in expressions via the value history see Section 8 8 Value History page 88 after printing one out Another way to create an artificial array is to use a cast This re interprets a value as if it were an array The value need not be in memory gdb p x short 2 0x12345678 1 0x1234 0x5678 As a convenience if you leave the array length out as in type value GDB calcu lates the size to fill the value as sizeof value sizeof type gdb p x short 0x12345678 2 0x1234 0x5678 Sometimes the artificial array mechanism is not quite enough in moderately complex data structures the elements of interest may not actually be adjacent for example if you are interested in the values of pointers in an array One useful work around in this situation is to use a convenience variable see Section 8 9 Convenience Variables page 88 as a counter in an expression that prints the first interesting value and then repeat that expression via RET For instance suppose you have an array dtab of pointers to structures and you are interested in the values of a field fv in each structure Here is an example of what you might type set i 0 p dtab it gt fv 8 4 Output Formats By default GDB prints a value according to its data type Sometimes this i
54. lt ELEMENT memory property gt lt memory Specifies a memory region and its type or device gt lt ATTLIST memory type CDATA REQUIRED start CDATA REQUIRED length CDATA REQUIRED device CDATA IMPLIED gt lt property Generic attribute tag gt lt ELEMENT property PCDATA property gt lt ATTLIST property name CDATA REQUIRED gt Appendix E The GDB Agent Expression Mechanism 369 Appendix E The GDB Agent Expression Mechanism In some applications it is not feasible for the debugger to interrupt the program s execution long enough for the developer to learn anything helpful about its behavior If the program s correctness depends on its real time behavior delays introduced by a debugger might cause the program to fail even when the code itself is correct It is useful to be able to observe the program s behavior without interrupting it Using GDB s trace and collect commands the user can specify locations in the pro gram and arbitrary expressions to evaluate when those locations are reached Later using the tfind command she can examine the values those expressions had when the program hit the trace points The expressions may also denote objects in memory structures or arrays for example whose values GDB should record while visiting a particular tra cepoint the user may inspect those objects as if they were in memory at that moment However because GDB records these values without inte
55. reason function finished frame addr 0x000107b0 func foo args name a value 1 name b value 9 file recursive2 c fullname home foo bar recursive2 c line 14 gdb result var 1 return value 0 gdb The exec interrupt Command Synopsis exec interrupt Interrupts the background execution of the target Note how the token associated with the stop message is the one for the execution command that has been interrupted The token for the interrupt itself only appears in the done output If the user is trying to interrupt a non running program an error message will be printed GDB Command The corresponding GDB command is interrupt Example gdb 111 exec continue 111 running gdb 222 exec interrupt 222 done gdb 111 stopped signal name SIGINT signal meaning Interrupt frame addr 0x00010140 func foo args file try c fullname home foo bar try c line 13 gdb gdb exec interrupt error msg mi cmd exec interrupt Inferior not executing gdb Chapter 24 The GDB MI Interface 253 The exec next Command Synopsis exec next Resumes execution of the inferior program stopping when the beginning of the next source line is reached GDB Command The corresponding GDB command is next Example exec next running gdb stopped reason end stepping range line 8 file hello c gdb The exec next instruction Command Synopsis
56. resides and then to reference the file by its name without any path For instance a program prog o may reside in vxpath vw demo rdb in VxWorks and in hostpath vw demo rdb on the host To load this program type this on VxWorks cd vxpath vw demo rdb Then in GDB type vxgdb cd hostpath vw demo rdb vxgdb load prog o GDB displays a response similar to this Reading symbol data from wherever vw demo rdb prog o done You can also use the load command to reload an object module after editing and recom piling the corresponding source file Note that this makes GDB delete all currently defined breakpoints auto displays and convenience variables and to clear the value history This is necessary in order to preserve the integrity of debugger s data structures that reference the target system s symbol table 18 2 1 3 Running Tasks You can also attach to an existing task using the attach command as follows vxgdb attach task where task is the VxWorks hexadecimal task ID The task can be running or suspended when you attach to it Running tasks are suspended at the time of attachment 18 3 Embedded Processors This section goes into details specific to particular embedded configurations Whenever a specific embedded processor has a simulator GDB allows to send an arbitrary command to the simulator sim command Send an arbitrary command string to the simulator Consult the documentation for the
57. s esee 112 scheduler locking mode 2 58 SCODE S e edades tree Re erue oU EP TRI P RE PUE 136 scripting commands 000000 219 Sdireset apie ipobyeRRR EARS PUE meee ee ad 194 Sdistatusas o SE Ore ewe es eee Eds 194 NDS protocol user LR me deed ed 199 sds command oce 199 tae Rev PES VEDI dens vk m ees 69 searching source files 69 SeCLIOn nhlgilboe de eer pIeuvaeer DOPO CE 157 section offsets remote request 344 segment descriptor tables 183 select trace snapshot e ee eee 109 Select frale 2 cas ieee e Key up cen eee 62 selected frame 2234 62 2008 he waviness tineis 61 selecting frame silently 62 self insert a b A 1 309 send command to remote monitor 172 send command to simulator 192 send PMON command 45 197 send rights GNU Hurd 189 separate debugging information files 161 sequence id for GDB remote 333 serial connections debugging 214 serial line target remote eral serial protocol GDB remote 4 333 server prefix i le es etn n ee qb da ius 288 server command prefix seseeess 208 SOG raya tert EEE iet cub US Rida Es d 22 set ABI fot MIPS isse eR EXER 203 set annotate ene ae nuns melee d 287 set architecture ise a sr rre ne 1
58. system to another but in general the threads of a single program are akin to multiple processes except that they share one address space that is they can all examine and modify the same variables On the other hand each thread has its own registers and execution stack and perhaps private memory GDB provides these facilities for debugging multi thread programs e automatic notification of new threads e thread threadno a command to switch among threads e info threads a command to inquire about existing threads e thread apply threadno all args a command to apply a command to a list of threads e thread specific breakpoints Warning These facilities are not yet available on every GDB configuration where the operating system supports threads If your GDB does not support threads these commands have no effect For example a system without thread support shows no output from info threads and always rejects the thread command like this gdb info threads gdb thread 1 Thread ID 1 not known Use the info threads command to see the IDs of currently known threads The GDB thread debugging facility allows you to observe all threads while your program runs but whenever GDB takes control one thread in particular is always the focus of debugging This thread is called the current thread Debugging commands show program information from the perspective of the current thread Whenever GDB detects a new t
59. variables with the shell and they are inherited by all the other programs you run When debugging it can be useful to try running your program with a modified environment without having to start GDB over again path directory Add directory to the front of the PATH environment variable the search path for executables that will be passed to your program The value of PATH used by GDB does not change You may specify several directory names separated by whitespace or by a system dependent separator character on Unix on MS DOS and MS Windows If directory is already in the path it is moved to the front so it is searched sooner You can use the string cwd to refer to whatever is the current working direc tory at the time GDB searches the path If you use instead it refers to the directory where you executed the path command GDB replaces in the di rectory argument with the current path before adding directory to the search path show paths Display the list of search paths for executables the PATH environment variable show environment varname Print the value of environment variable varname to be given to your program when it starts If you do not supply varname print the names and values of all environment variables to be given to your program You can abbreviate environment as env set environment varname value Set environment variable varname to value The value changes for your pro
60. 0x56b3c423 Oxc60cd9b2 Oxb6662d3d Ox71b18589 Ox0f00f934 0x91646c97 0xf262004e Ox65b0d9c6 Ox15da2d49 Oxa3bc0074 Oxd3d6f4fb 0x44042d73 0x270241aa 0xb966d409 Oxc7d7a8b4 Oxedb88320 Ox9dd277af Ox0d6d6a3e 0x7d079eb1 Oxf 762575d 0x076dc419 Ox79dcb8a4 Oxe7b82d07 Ox84be41de 0x136c9856 0x63066cd9 Oxd56041e4 OxabOab56b 0x32d86ce3 Ox51de003a Oxcfba9599 Oxb10be924 0x76dc4190 Ox06b6b51f 0x9609a88e Oxe6635c01 Ox6c0695ed Ox12b7e950 Ox8cd37cf3 Oxd4bb30e2 0x4369e96a 0x33031de5 Oxbe0b1010 Oxce61e49f Ox59b33d17 Ox9abfb3b6 Ox04db2615 Ox7a6abaa8 Oxf00f9344 0x806567cb 164 Debugging with GDB 0x196c3671 Ox6e6b06e7 Oxfed41b76 Ox89d32be0 Oxi10da7ab5a Ox67dd4acc Oxf9b9df6f Ox8ebeeff9 Ox17b7be43 Ox60b08ed5 Oxd6d6a3e8 0xaidi1937e 0x38d8c2c4 Ox4fdff252 Oxdibb67f1 Oxa6bc5767 Ox3fb506dd 0x48b2364b Oxd80d2bda OxafOaib4c 0x36034af6 0x41047a60 Oxdf60efc3 Oxa867df55 0x316e8eef 0x4669be79 Oxcb61b38c Oxbc66831a Ox256fd2a0 0x5268e236 Oxcc0c7795 Oxbb0b4703 0x220216b9 0x5505262f Oxcbba3bbe Oxb2bd0b28 Ox2bb45a92 Ox5cb36a04 Oxc2d7ffa7 Oxb5d0cf31 Ox2cd99e8b Ox5bdeaeld Ox9b64c2b0 Oxec63f226 0x756aa39c 0x026d930a 0x9c0906a9 Oxeb0e363f 0x72076785 0x05005713 Ox95bf4a82 Oxe2b87a14 OxTbbi2bae OxOcb61b38 0x92d28e9b Oxe5d5be0d Ox7cdcefb7 OxObdbdf21 Ox86d3d2d4 Oxfid4e242 Ox68ddb3f8 Oxi1fda836e Ox81bei6cd Oxf6b9265b Ox6fb077e1 0x18b74777 Ox880
61. 295 27 2 2 Readline Movement Commands sss 296 27 2 3 Readline Killing Commands sseeeleeseess 296 27 2 4 Readline Arguments 00 eee cece eee e eee 297 27 2 5 Searching for Commands in the History 297 27 8 Readline Init File eee ee eee 298 27 3 1 Readline Init File Syntax 0 0 0 e cece eee 298 27 8 2 Conditional Init Constructs ssse esses essen 303 27 8 8 Sample Init File 0 eee ee 304 27 4 Bindable Readline Commands 0 000e eee eee 307 27 4 1 Commands For Moving 0 0 0 eee eens 307 27 4 Commands For Manipulating The History 307 27 4 5 Commands For Changing Text 0 309 25 44 Killing And Yanking ic oto E eee 310 27 4 5 Specifying Numeric Arguments 00000 311 27 4 6 Letting Readline Type For You 04 311 27 4 7 Keyboard Macros 0 000 cece cece cece ak a 311 27 4 8 Some Miscellaneous Commands suuuss 312 97 5 Readlime vi Mode E EEpERPUEPCPP ea eee eens 313 Debugging with GDB viii 28 Using History Interactively 315 28 1 History ExpanslOB zn ero eth Rey eph Rr das 315 28 1 1 Event Designators seeeeeeeee nnn 315 28 1 2 Word Designators sssssseeeese esee 315 28 1 3 Modifiers 00 0 cece cence rn 316 Appendix A Formatting Documentation 319 Appendix B Installing GDB
62. 341 to GDB as a result of successfully stopping the program Interrupts received while the program is stopped will be discarded D 8 Examples Example sequence of a target being re started Notice how the restart does not get any direct output ROO lt target restarts gt lt T001 1234123412341234 gt Example sequence of a target being stepped by a single instruction gt G1445 lt S gt S lt time passes lt T001 1234123412341234 gt D 9 File I O Remote Protocol Extension D 9 1 File I O Overview The File I O remote protocol extension short File I O allows the target to use the host s file system and console I O to perform various system calls System calls on the target system are translated into a remote protocol packet to the host system which then performs Appendix D GDB Remote Serial Protocol 355 the needed actions and returns a response packet to the target system This simulates file system operations even on targets that lack file systems The protocol is defined to be independent of both the host and target systems It uses its own internal representation of datatypes and values Both GDB and the target s GDB stub are responsible for translating the system dependent value representations into the internal protocol representations when data is transmitted The communication is synchronous A system call is possible only when GDB is waiting for a response fr
63. 367 GDB groups flash memory programming operations together and sends a vFlashDone request after each group the stub is allowed to delay erase operation until the vFlashDone packet is received Reply OK for success E NN for an error Appendix D GDB Remote Serial Protocol 339 vFlashWrite addr XX Direct the stub to write data to flash address addr The data is passed in binary form using the same encoding as for the X packet see Binary Data page 333 The memory ranges specified by vFlashWrite packets preceding a vFlashDone packet must not overlap and must appear in order of increasing addresses although vFlashErase packets for higher addresses may already have been received the ordering is guaranteed only between vFlashWrite packets If a packet writes to an address that was neither erased by a preceding vFlashErase packet nor by some other target specific method the results are unpredictable Reply OK for success E memtype for vFlashWrite addressing non flash memory E NN for an error vFlashDone Indicate to the stub that flash programming operation is finished The stub is permitted to delay or batch the effects of a group of vFlashErase and vFlashWrite packets until a vFlashDone packet is received The contents of the affected regions of flash memory are unpredictable until the vFlashDone request is complet
64. 375 EA Varying Target Capabilities 0 02 aineissa hi 376 E 5 Tracing on Symmetri presigi pia giia c cece eee ee eens 376 E6 Rationale nsec Re Gepebee thr te neha 378 Appendix F Target Descriptions 381 F 1 Retrieving Descriptions 0 eee eee eee ee 381 F 2 Target Description Format 0 eee eee eee 382 B2 THOIUSIOB quce enced deeia ro m nese ng cee dtes up E ae qund 382 E 2 2 Architecture iios de te Rode bebe EE RE oe et 382 B 2 9 HOAGULCS uu zer pedes dto aca dun dede big nation hte pU wes 383 FA TYPOS reris ane bide aoe ate neers ie DEC es don 383 2 9 Registers ia eee acre Deum sa eto et gate ewe danas 383 F 3 Predefined Target Types 0 000 e eee eee eee eens 384 F 4 Standard Target Features 00000 cece esses 385 FA ARM Features sesiis soani head each geag ena ee hee 385 F 4 2 MIPS Features 0 cece cece cece es 385 F 4 8 M68K Features 0 cece ccc nnn 386 Appendix G GNU GENERAL PUBLIC LICENSE lt i4ad5 00604 bd eweendcebesee das 387 Preamble i cbe te hn eee igen ghee GOD ud ede Ba dk dk hho 387 TERMS AND CONDITIONS FOR COPYING DISTRIBUTION AND MODIFICATION 388 How to Apply These Terms to Your New Programs 392 ix x Debugging with GDB Appendix H GNU Free Documentation License ee ee E E E ee ee ee 393 H 1 ADDENDUM How to use this License for your documents 399 Summary of GDB The purpose
65. 530 530 if lquote def_lquote The display that shows the subroutine where m4 is now suspended and its arguments is called a stack frame display It shows a summary of the stack We can use the backtrace command which can also be spelled bt to see where we are in the stack as a whole the backtrace command displays a stack frame for each active subroutine gdb bt 0 set quotes 1q 0x34c78 lt QUOTE gt rq 0x34c88 lt UNQUOTE gt at input c 530 1 0x6344 in m4_changequote argc 3 argv 0x33c70 at builtin c 882 2 0x8174 in expand macro sym 0x33320 at macro c 242 3 Ox7a88 in expand token obs 0x0 t 209696 td Oxf7fffa30 at macro c 71 4 Ox79dc in expand input at macro c 40 5 0x2930 in main argc 0 argv Oxf7fffb20 at m4 c 195 We step through a few more lines to see what happens The first two times we can use s the next two times we use n to avoid falling into the xstrdup subroutine gdb s Ox3b5c 532 if rquote def rquote gdb s Ox3b80 535 lquote lq nil lq 0 def lquote xstrdup 1q gdb n 536 rquote rq nil rq N0 def_rquote xstrdup rg gdb n 538 len lquote strlen rquote Chapter 1 A Sample GDB Session 9 The last line displayed looks a little odd we can examine the variables 1quote and rquote to see if they are in fact the new left and right quotes we specified We use the command p print to see their values gdb p l
66. A call to exec This is currently only available for HP UX fork A call to fork This is currently only available for HP UX vfork A call to vfork This is currently only available for HP UX load load libname The dynamic loading of any shared library or the loading of the library libname This is currently only available for HP UX 46 Debugging with GDB unload unload libname The unloading of any dynamically loaded shared library or the unloading of the library libname This is currently only available for HP UX tcatch event Set a catchpoint that is enabled only for one stop The catchpoint is automat ically deleted after the first time the event is caught Use the info break command to list the current catchpoints There are currently some limitations to C exception handling catch throw and catch catch in GDB e If you call a function interactively GDB normally returns control to you when the function has finished executing If the call raises an exception however the call may bypass the mechanism that returns control to you and cause your program either to abort or to simply continue running until it hits a breakpoint catches a signal that GDB is listening for or exits This is the case even if you set a catchpoint for the exception catchpoints on exceptions are disabled within interactive calls e You cannot raise an exception interactively e You cannot install an exception handler interactively Sometimes catc
67. Acknowledgements and any sections Entitled Dedications You must delete all sections Entitled Endorsements 6 COLLECTIONS OF DOCUMENTS You may make a collection consisting of the Document and other documents released under this License and replace the individual copies of this License in the various documents with a single copy that is included in the collection provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects You may extract a single document from such a collection and distribute it individu ally under this License provided you insert a copy of this License into the extracted document and follow this License in all other respects regarding verbatim copying of that document 7 AGGREGATION WITH INDEPENDENT WORKS A compilation of the Document or its derivatives with other separate and independent documents or works in or on a volume of a storage or distribution medium is called 398 10 Debugging with GDB an aggregate if the copyright resulting from the compilation is not used to limit the legal rights of the compilation s users beyond what the individual works permit When the Document is included in an aggregate this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document If the Cover Text requirement of section 3 is applicable to these copies of the Document then if the Docum
68. GDB Text User Interface 225 2244 TUL Overview acc ee epCREe eared PEOR eons deg ad de 225 22 2 TUL Key Bindings eg dod eed res ead pid bedded ox 226 22 3 TUI Single Key Mode 0 ccc ccc ccc eee 227 22 4 TUl specific Commands 0 00 eee kepies onines 227 22 5 TUI Configuration Variables lisse eese cece eee 229 23 Using GDB under GNU Emacs 231 24 The GDB MI Interface 233 Function and Purpose ssseesssseeeesee e 233 Notation and Terminology lsssssssseee esses 233 24 3 GDB MI Command SydildX iui ros ar Ek ene ERRORES ys 233 24 3 1 GDB MI Input Synbdxaenesesases edd Fes o ERR Sora an cn 233 24 32 QGDB MI Output Syntax esisi necare dene beso Pers 234 24 4 GDB MI Compatibility with CLI 14 4 ec aC rene 236 24 5 GDB MI Development and Front Ends ss 236 24 6 dDB MI Output Records iic sesso ere y 236 24 6 1 GDB MI Result Records 2 2 deseo bester era o p ens 236 24 6 2 GDB MI Stream Records 24 0 2 ereesnd gis ERI Rake ds 237 24 6 3 GDB MI Out of band Records 00s eee 237 24 7 Simple Examples of GDB MI Interaction 238 24 8 GDB MI Command Description Format 239 vii 24 9 GDB MI Breakpoint Commands eeeeeeesesee 239 94 10 GDB MI Program Context 22 nda odes die CREE d rbd n 247 24 11 GbB MI Thread Commands 2 22 ubdud tero RERO Red 249 24 12 GDB MI Pr
69. If frame does not record any memory at address set size to the distance from address to the start of the saved region with the lowest address higher than address If there is no memory saved from any higher address set size to zero Return NOT FOUND TARGET RESPONSE These two possibilities allow the caller to either retrieve the data or walk the address space to the next saved area This function allows the GDB agent to map the regions of memory saved in a particular frame and retrieve their contents efficiently This function also provides a clean interface between the GDB agent and the Symmetrix tracing structures making it easier to adapt the GDB agent to future versions of the Appendix E The GDB Agent Expression Mechanism 377 Symmetrix system and vice versa This function searches all data saved in frame whether the data is there at the request of a bytecode expression or because it falls in one of the format s memory ranges or because it was saved from the top of the stack EMC can arbitrarily change and enhance the tracing mechanism but as long as this function works properly all collected memory is visible to GDB The function itself is straightforward to implement A single pass over the trace frame s stack area memory ranges and expression blocks can yield the address of the buffer if the requested address was saved and also note the address of the next higher range of memory to be returned when the search
70. In addition to reporting the internal problem these functions give the user the opportunity to either quit GDB or create a core file of the current GDB session These commands take an optional parameter message text that is used as the text of the error or warning message Here s an example of using internal error gdb maint internal error testing 1 2 maint c 121 internal error testing 1 2 A problem internal to GDB has been detected Further debugging may prove unreliable Quit this debugging session y or n n Create a core file y or n n gdb maint packet text If GDB is talking to an inferior via the serial protocol then this command sends the string text to the inferior and displays the response packet GDB supplies the initial character the terminating character and the checksum maint print architecture file Print the entire architecture configuration The optional argument file names the file where the output goes maint print dummy frames Prints the contents of GDB s internal dummy frame stack gdb b add gdb print add 2 3 Breakpoint 2 add a 2 b 3 at 58 return a b The program being debugged stopped while in a function called from GDB gdb maint print dummy frames Oxia57c80 pc 0x01014068 fp 0x0200bddc sp 0x0200bdd6 top 0x0200bdd4 id stack 0x200bddc code 0x101405c call_lo 0x01014000 call_hi 0x01014001 gdb Takes an optional file parameter main
71. Normally GDB knows the size of the screen from the terminal driver software For example on Unix GDB uses the termcap data base together with the value of the TERM environment variable and the stty rows and stty cols settings If this is not correct you can override it with the set height and set width commands set height lpp show height set width cpl show width These set commands specify a screen height of Ipp lines and a screen width of cpl characters The associated show commands display the current settings If you specify a height of zero lines GDB does not pause during output no matter how long the output is This is useful if output is to a file or to an editor buffer Likewise you can specify set width 0 to prevent GDB from wrapping its out put set pagination on set pagination off Turn the output pagination on or off the default is on Turning pagination off is the alternative to set height 0 show pagination Show the current pagination mode 210 Debugging with GDB 19 5 Numbers You can always enter numbers in octal decimal or hexadecimal in GDB by the usual conventions octal numbers begin with 0 decimal numbers end with and hexadecimal numbers begin with Ox Numbers that neither begin with 0 or Ox nor end with a are by default entered in base 10 likewise the default display for numbers when no particular format is specified is base 10 You can change the
72. When triggered it can capture low level data like PC LSEA LDATA SDATA READSPR WRITESPR INSTR htrace commands hwatch conditional Set hardware watchpoint on combination of Load Store Effective Address es or Data For example hwatch LEA my var amp amp LDATA lt 50 SEA my var amp amp SDATA gt 50 hwatch LEA my_var amp amp LDATA lt 50 SEA my var amp amp SDATA gt 50 htrace info Display information about current HW trace configuration htrace trigger conditional Set starting criteria for HW trace htrace qualifier conditional Set acquisition qualifier for HW trace htrace stop conditional Set HW trace stopping criteria htrace record data Selects the data to be recorded when qualifier is met and HW trace was trig gered htrace enable htrace disable Enables disables the HW trace Chapter 18 Configuration Specific Information 199 htrace rewind filename Clears currently recorded trace data If filename is specified new trace file is made and any newly collected data will be written there htrace print start 1en Prints trace buffer using current record configuration htrace mode continuous Set continuous trace mode htrace mode suspend Set suspend trace mode 18 3 6 PowerPC target dink32 dev DINK32 ROM monitor target ppcbug dev target ppcbugi dev PPCBUG ROM monitor for PowerPC target sds dev SDS monitor running o
73. You must first specify the program name except on VxWorks with an argument to GDB see Chap ter 2 Getting In and Out of GDB page 11 or by using the file or exec file command see Section 15 1 Commands to Specify Files page 155 If you are running your program in an execution environment that supports processes run creates an inferior process and makes that process run your program In environments without processes run jumps to the start of your program The execution of a program is affected by certain information it receives from its superior GDB provides ways to specify this information which you must do before starting your program You can change it after starting your program but such changes only affect your program the next time you start it This information may be divided into four categories The arguments Specify the arguments to give your program as the arguments of the run com mand If a shell is available on your target the shell is used to pass the argu ments so that you may use normal conventions such as wildcard expansion or variable substitution in describing the arguments In Unix systems you can control which shell is used with the SHELL environment variable See Section 4 3 Your Program s Arguments page 27 The environment Your program normally inherits its environment from GDB but you can use the GDB commands set environment and unset environment to change parts of the environment that af
74. _exitcode convenience variable 90 bpnum convenience variable 38 cdir convenience variable 71 cwd convenience variable 71 SUDBUl esee REC ches apie tees 106 trace file 2d2 zWy vedere 112 trace frame dae gue kr awarded inna 112 trace f n x65 cae 929 deed b ERI aer dcn 112 trace line ize v e uere e PIE 112 tracepoint 2259 je P we eR MEE 112 ccannobabt dry E pP dames ws 14 zz m 14 ccbpatch i pocas diri ibd RE Gus and ded ean 13 Sbatch Sirlent esseeri hex rd Rue eR RR 13 LC E CCP DE 14 Lll pp 14 sccommadd csee 2 ndr Subs di odio dese d ars 12 zd rse ca Aae naaa Sale e aei A 12 S di rectory oiis aishe ERES TERA pe ERS Eiai 12 sSepOCli ids nique eiua E EE RU ERI Rp 14 eSeyal command rsen ne eb ERE NE 12 o RH 12 sef llname 5nleed C v wear REA 14 cjnterpreter ieevi eek mei DEOR 15 S NOWIMNGOWS 2givervui sugiere PRGUE 14 rcov DP 13 ml MP 12 mma P 13 SCEGAdDB OW 22344 59 eae d denda EROR Ad de Brawls 13 r turn child result 5 s ds 13 ud EEEE EE ES N TS EUR 12 PDOSRl6nt 2252354 u ER Ag po e BERTA Ga e c d 13 SSSCACTSULCS i eek einsi eian EROR ARR ao 15 401 xus L 15 SEU o oue utes EE Baran shea oan Meas Bai a fend Dira T5 SSUKSPSI B E E Red E EEEE 15 WAJndOWS areco Pineda aad aper Godan de 14 lt With SyShoot veu b ove PR er ERI 161 CWETEG e E ue ae dapibu
75. a mapped overlay its mapped address is its address in the instruction memory An overlay not present or only partially present in instruction memory is called unmapped its load address is its address in the larger memory The mapped address is also called the virtual memory address or VMA the load address is also called the load memory address or LMA Unfortunately overlays are not a completely transparent way to adapt a program to limited instruction memory They introduce a new set of global constraints you must keep in mind as you design your program e Before calling or returning to a function in an overlay your program must make sure that overlay is actually mapped Otherwise the call or return will transfer control to the right address but in the wrong overlay and your program will probably crash e If the process of mapping an overlay is expensive on your system you will need to choose your overlays carefully to minimize their effect on your program s performance e The executable file you load onto your system must contain each overlay s instruc tions appearing at the overlay s load address not its mapped address However each overlay s instructions must be relocated and its symbols defined as if the overlay were at its mapped address You can use GNU linker scripts to specify different load and relocation addresses for pieces of your program see section Overlay Description in Using Id the GNU linker e The procedu
76. after point moving point past that word as well If the insertion point is at the end of the line this transposes the last two words on the line upcase word M u Uppercase the current or following word With a negative argument upper case the previous word but do not move the cursor downcase word M 1 Lowercase the current or following word With a negative argument lowercase the previous word but do not move the cursor capitalize word M c Capitalize the current or following word With a negative argument capitalize the previous word but do not move the cursor overwrite mode Toggle overwrite mode With an explicit positive numeric argument switches to overwrite mode With an explicit non positive numeric argument switches to insert mode This command affects only emacs mode vi mode does overwrite differently Each call to readline starts in insert mode 310 Debugging with GDB In overwrite mode characters bound to self insert replace the text at point rather than pushing the text to the right Characters bound to backward delete char replace the character before point with a space By default this command is unbound 27 4 4 Killing And Yanking kill line C k Kill the text from point to the end of the line backward kill line C x Rubout Kill backward to the beginning of the line unix line discard C u Kill backward from the cursor to the beginning of the current line kill whole line
77. all shared libraries Symbols from shared libraries that were loaded by explicit user requests are not discarded Sometimes you may wish that GDB stops and gives you control when any of shared library events happen Use the set stop on solib events command for this set stop on solib events This command controls whether GDB should give you control when the dynamic linker notifies it about some shared library event The most common event of interest is loading or unloading of a new shared library show stop on solib events Show whether GDB stops and gives you control when shared library events happen Shared libraries are also supported in many cross or remote debugging configurations A copy of the targets libraries need to be present on the host system they need to be the same as the target libraries although the copies on the target can be stripped as long as the copies on the host are not For remote debugging you need to tell GDB where the target libraries are so that it can load the correct copies otherwise it may try to load the host s libraries GDB has two variables to specify the search directories for target libraries set sysroot path Use path as the system root for the program being debugged Any absolute shared library paths will be prefixed with path many runtime loaders store the absolute paths to the shared library in the target program s memory If you use set sysroot to find shared libraries they need to be laid ou
78. and exits 174 Debugging with GDB You can debug processes by name instead of process ID if your target has the pidof utility target gdbserver comm attach pidof program In case more than one copy of program is running or program has multiple threads most versions of pidof support the s option to only return the first process ID On the host machine first make sure you have the necessary symbol files Load symbols for your application using the file command before you connect Use set sysroot to locate target libraries unless your GDB was compiled with the correct sysroot using with system root The symbol file and target libraries must exactly match the executable and libraries on the target with one exception the files on the host system should not be stripped even if the files on the target system are Mismatched or missing files will lead to confusing results during debugging On GNU Linux targets mismatched or missing files may also prevent gdbserver from debugging multi threaded programs Connect to your target see Section 17 1 Connecting to a Remote Target page 171 For TCP connections you must start up gdbserver prior to using the target remote command Otherwise you may get an error whose text de pends on the host system but which usually looks something like Connection refused You don t need to use the load command in GDB when using gdbserver since the program is already on the target
79. and variables in an overlay whether or not the overlay is mapped This allows most GDB com mands like break and disassemble to work normally even on unmapped code However GDB s breakpoint support has some limitations e You can set breakpoints in functions in unmapped overlays as long as GDB can write to the overlay at its load address e GDB can not set hardware or simulator based breakpoints in unmapped overlays How ever if you set a breakpoint at the end of your overlay manager and tell GDB which overlays are now mapped if you are using manual overlay management GDB will re set its breakpoints properly 11 3 Automatic Overlay Debugging GDB can automatically track which overlays are mapped and which are not given some simple co operation from the overlay manager in the inferior If you enable automatic overlay debugging with the overlay auto command see Section 11 2 Overlay Commands page 114 GDB looks in the inferior s memory for certain variables describing the current state of the overlays Here are the variables your overlay manager must define to support GDB s automatic overlay debugging ovly table This variable must be an array of the following structures struct 1 The overlay s mapped address unsigned long vma The size of the overlay in bytes unsigned long size The overlay s load address unsigned long lma Non zero if the overlay is currently mapped zero otherwis
80. and the debugger reports a change in value at the exact instruction where the change occurs If GDB cannot set a hardware watchpoint it sets a software watchpoint which executes more slowly and reports the change in value at the next statement not the instruction after the change occurs You can force GDB to use only software watchpoints with the set can use hw watchpoints 0 command With this variable set to zero GDB will never try to use hardware watchpoints even if the underlying system supports them Note that hardware assisted watchpoints that were set before setting can use hw watchpoints to zero will still use the hardware mechanism of watching expression values set can use hw watchpoints Set whether or not to use hardware watchpoints 44 Debugging with GDB show can use hw watchpoints Show the current mode of using hardware watchpoints For remote targets you can restrict the number of hardware watchpoints GDB will use see set remote hardware breakpoint limit page 175 When you issue the watch command GDB reports Hardware watchpoint num expr if it was able to set a hardware watchpoint Currently the awatch and rwatch commands can only set hardware watchpoints be cause accesses to data that don t change the value of the watched expression cannot be detected without examining every instruction as it is being executed and GDB does not do that currently If GDB finds that it is unable to set a hardware breakpoin
81. are An exception is made for pointers to buffers for which the length isn t transmitted as part of the function call namely strings Strings are transmitted as a pointer length pair both as hex values e g 1aaf 12 which is a pointer to data of length 18 bytes at position Oxlaaf The length is defined as the full string length in bytes including the trailing null byte For example the string hello world at address 0x123456 is transmitted as 123456 d Memory Transfer Structured data which is transferred using a memory read or write for example a struct stat is expected to be in a protocol specific format with all scalar multibyte datatypes being big endian Translation to this representation needs to be done both by the target before the F packet is sent and by GDB before it transfers memory to the target Transferred pointers to structured data should point to the already coerced data at any time 364 Debugging with GDB struct stat The buffer of type struct stat used by the target and GDB is defined as follows struct stat unsigned int st dev device unsigned int st ino inode mode t st mode protection unsigned int st nlink number of hard links unsigned int st uid user ID of owner unsigned int st gid group ID of owner unsigned int st rdev device type if inode device unsigned long st size total size in bytes unsigned long st blksize blocksize for filesy
82. are installed for both TUI mode and the GDB standard mode C x C a C x a C x A C x 1 C x 2 C x o C x S Enter or leave the TUI mode When leaving the TUI mode the curses window management stops and GDB operates using its standard mode writing on the terminal directly When reentering the TUI mode control is given back to the curses windows The screen is then refreshed Use a TUI layout with only one window The layout will either be source or assembly When the TUI mode is not active it will switch to the TUI mode Think of this key binding as the Emacs C x 1 binding Use a TUI layout with at least two windows When the current layout already has two windows the next layout with two windows is used When a new layout is chosen one window will always be common to the previous layout and the new one Think of it as the Emacs C x 2 binding Change the active window The TUI associates several key bindings like scrolling and arrow keys with the active window This command gives the focus to the next TUI window Think of it as the Emacs C x o binding Switch in and out of the TUI SingleKey mode that binds single keys to GDB commands see Section 22 3 TUI Single Key Mode page 227 The following key bindings only work in the TUI mode Scroll the active window one page up Scroll the active window one page down Chapter 22 GDB Text User Interface 227 Up Scroll the active window one line up
83. args It prints out all matches found For example apropos reload results in set symbol reloading Set dynamic symbol table reloading multiple times in one run Show symbol reloading Show dynamic symbol table reloading multiple times in one run complete args The complete args command lists all the possible completions for the begin ning of a command Use args to specify the beginning of the command you want completed For example complete i results in if ignore info inspect This is intended for use by GNU Emacs In addition to help you can use the GDB commands info and show to inquire about the state of your program or the state of GDB itself Each command supports many topics of inquiry this manual introduces each of them in the appropriate context The listings under info and under show in the Index point to all the sub commands See Index page 401 info This command abbreviated i is for describing the state of your program For example you can list the arguments given to your program with info args list the registers currently in use with info registers or list the breakpoints you have set with info breakpoints You can get a complete list of the info sub commands with help info set You can assign the result of an expression to an environment variable with set For example you can set the GDB prompt to a sign with set prompt show In contrast to info show is for describing the state of GDB it
84. avoid unexpected substitution results a rule is applied only if the from part of the directory name ends at a directory separator For instance a rule substituting usr source into mnt cross will be applied to usr source foo 1 0 but not to usr sourceware foo 2 0 And because the substitution is applied only at the beginning of the directory name this rule will not be applied to root usr source baz c either In many cases you can achieve the same result using the directory command However set substitute path can be more efficient in the case where the sources are organized in a complex tree with multiple subdirectories With the directory command you need to add each subdirectory of your project If you moved the entire tree while preserving its internal organization then set substitute path allows you to direct the debugger to all the sources with one single command set substitute path is also more than just a shortcut command The source path is only used if the file at the original location no longer exists On the other hand set substitute path modifies the debugger behavior to look at the rewritten location instead Chapter 7 Examining Source Files 71 So if for any reason a source file that is not relevant to your executable is located at the original location a substitution rule is the only method available to point GDB at the new location directory dirname dir dirname directory Add d
85. be either yes or no The default is yes which is appropriate for most registers except for some system control registers this is not related to the target s ABI type The type of the register type may be a predefined type a type defined in the current feature or one of the special types int and float int is an integer type of the correct size for bitsize and float is a floating point type in the architecture s normal floating point format of the correct size for bitsize The default is int group The register group to which this register belongs group must be either general float or vector If no group is specified GDB will not display the register in info registers F 3 Predefined Target Types Type definitions in the self description can build up composite types from basic building blocks but can not define fundamental types Instead standard identifiers are provided by GDB for the fundamental types The currently supported types are int8 int16 int32 int64 Signed integer types holding the specified number of bits uint8 uinti6 uint32 uint64 Unsigned integer types holding the specified number of bits code ptr data ptr Pointers to unspecified code and data The program counter and any dedicated return address register may be marked as code pointers printing a code pointer converts it into a symbolic address The stack pointer and any dedicated address registers may be marked as data pointers ieee single Si
86. be individually enabled or disabled by passing breakpoint number location number as argument to the enable and disable commands It s quite common to have a breakpoint inside a shared library The shared library may be loaded and unloaded explicitly and possibly repeatedly as the program is executed To support this use case GDB updates breakpoint locations whenever any shared library is loaded or unloaded Typically you would set a breakpoint in a shared library at the beginning of your debugging session when the library is not loaded and when the symbols from the library are not available When you try to set breakpoint GDB will ask you if you want to set a so called pending breakpoint breakpoint whose address is not yet resolved After the program is run whenever a new shared library is loaded GDB reevaluates all the breakpoints When a newly loaded shared library contains the symbol or line referred to by some pending breakpoint that breakpoint is resolved and becomes an ordinary breakpoint 42 Debugging with GDB When a library is unloaded all breakpoints that refer to its symbols or source lines become pending again This logic works for breakpoints with multiple locations too For example if you have a breakpoint in a C template function and a newly loaded shared library has an instan tiation of that template a new location is added to the list of locations for the breakpoint Except for having unresolved address pend
87. beginning with are comments d d First include any systemwide bindings and variable assignments from etc Inputrc include etc Inputrc d Set various bindings for emacs mode set editing mode emacs if mode emacs Meta Control h backward kill word Text after the function name is ignored Arrow keys in keypad mode M OD backward char M OC forward char M OA previous history M OB next history Arrow keys in ANSI mode NM D backward char NM C forward char NM A previous history M B next history Arrow keys in 8 bit keypad mode NM NC OD backward char M C O0C forward char M C OA previous history NM NC OB next history Arrow keys in 8 bit ANSI mode M C D backward char HUN i NM NC C forward char 306 Debugging with GDB M C A previous history M C B next history C q quoted insert endif An old style binding This happens to be the default TAB complete Macros that are convenient for shell interaction if Bash edit the path C xp PATH PATH e C e C a ef C prepare to type a quoted word insert open and close double quotes and move to just after the open quote BNC e BENIN OS M insert a backslash testing backslash escapes in sequences and macros NOR E PN Quote the current or previous word NC xq eb ef
88. behavior of this packet in the presence of such a target is not defined Reply OK success e not supported E NN for an error z1 addr length Z1 addr length Insert Z1 or remove z1 a hardware breakpoint at address addr of size length A hardware breakpoint is implemented using a mechanism that is not dependant on being able to modify the target s memory Implementation note A hardware breakpoint is not affected by code movement Reply OK success e not supported E NN for an error z2 addr length Z2 addr length Insert Z2 or remove z2 a write watchpoint Reply OK success not supported E NN for an error 23 addr length 23 addr length Insert Z3 or remove z3 a read watchpoint Reply OK success e not supported E NN for an error Z4 addr length Z4 addr length Insert Z4 or remove z4 an access watchpoint Reply Appendix D GDB Remote Serial Protocol 341 OK success EJ not supported E NN for an error D 3 Stop Reply Packets The C c S s and packets can receive any of the below as a reply In the case of the c S and s packets that reply is only returned when the target halts In the below the exact meaning of signal number is defined by the header includ
89. character names are recognized while pro cessing this key binding syntax DEL ESC ESCAPE LFD NEW LINE RET RETURN RUBOUT SPACE SPC and TAB keyseq function name or macro keyseq differs from keyname above in that strings denoting an en tire key sequence can be specified by placing the key sequence in double quotes Some GNU Emacs style key escapes can be used as in the following example but the special character names are not recognized C u universal argument C x C r re read init file Ne 11 Function Key 1 In the above example C u is again bound to the function universal argument just as it was in the first example C x C r is bound to the function re read init file and ESC D 0 0 is bound to insert the text Function Key 1 The following GNU Emacs style escape sequences are available when specifying key sequences c M e V control prefix meta prefix an escape character backslash 5 a double quotation mark a single quote or apostrophe In addition to the GNU Emacs style escape sequences a second set of backslash escapes is available a b d f n XE Nt v alert bell backspace delete form feed newline carriage return horizontal tab vertical tab Chapter 27 Command Line Editing 303 nnn xHH the eight bit character whose value is the octal value nnn one to three digits the eight bit character whose value is t
90. command file are generally executed sequentially unless the order of execution is changed by one of the flow control commands described below The commands are not printed as they are executed An error in any command terminates execution of the command file and control is returned to the console GDB searches for filename in the current directory and then on the search path specified with the directory command If v for verbose mode is given then GDB displays each command as it is executed The option must be given before filename and is interpreted as part of the filename anywhere else Commands that would ask for confirmation if used interactively proceed without asking when used in a command file Many GDB commands that normally print messages to say what they are doing omit the messages when called from command files 220 Debugging with GDB GDB also accepts command input from standard input In this mode normal output goes to standard output and error output goes to standard error Errors in a command file supplied on standard input do not terminate execution of the command file execution continues with the next command gdb lt cmds gt log 2 gt amp 1 The syntax above will vary depending on the shell used This example will execute commands from the file cmds All output and errors would be directed to log Since commands stored on command files tend to be more general than commands typed interactively
91. condition number expr Breakpoint number will stop the program only if the condition in expr is true The con dition becomes part of the break list output see the description of the break list command below GDB Command The corresponding GDB command is condition Example gdb break condition 1 1 done gdb break list done BreakpointTable nr_rows 1 nr_cols 6 hdr width 3 alignment 1 col_name number colhdr Num width 14 alignment 1 col_name type colhdr Type width 4 alignment 1 col_name disp colhdr Disp width 3 alignment 1 col_name enabled colhdr Enb width 10 alignment 1 col_name addr colhdr Address width 40 alignment 2 col_name what colhdr What body bkpt number 1 type breakpoint disp keep enabled y addr 0x000100d0 func main file hello c fullname home foo hello c line 5 cond 1 times 0 ignore 3 gdb Chapter 24 The GDB MI Interface 241 The break delete Command Synopsis break delete breakpoint Delete the breakpoint s whose number s are specified in the argument list This is obviously reflected in the breakpoint list GDB Command The corresponding GDB command is delete Example gdb break delete 1 done gdb break list done BreakpointTable nr_rows 0 nr_cols 6 hdr width 3 alignment 1 col_name number colhdr Num width 14 ali
92. confirmation requests If you need to debug user defined commands or sourced files you may find it useful to enable command tracing In this mode each command will be printed as it is executed pre fixed with one or more symbols the quantity denoting the call depth of each command set trace commands on Enable command tracing set trace commands off Disable command tracing show trace commands Display the current state of command tracing Chapter 19 Controlling GDB 213 19 8 Optional Messages about Internal Happenings GDB has commands that enable optional debugging messages from various GDB subsystems normally these commands are of interest to GDB maintainers or when reporting a bug This section documents those commands set exec done display Turns on or off the notification of asynchronous commands completion When on GDB will print a message when an asynchronous command finishes its exe cution The default is off show exec done display Displays the current setting of asynchronous command completion notification set debug arch Turns on or off display of gdbarch debugging info The default is off show debug arch Displays the current state of displaying gdbarch debugging info set debug aix thread Display debugging messages about inner workings of the AIX thread module Show debug aix thread Show the current state of AIX thread debugging info display set debug event Turns on or off display of GDB e
93. count other times it is the sign of the argument that is significant If you pass a negative argument to a command which normally acts in a forward direction that command will act in a backward direction For example to kill text back to the start of the line you might type M C k The general way to pass numeric arguments to a command is to type meta digits before the command If the first digit typed is a minus sign then the sign of the argument will be negative Once you have typed one meta digit to get the argument started you can type the remainder of the digits and then the command For example to give the C d command an argument of 10 you could type M 1 0 C d which will delete the next ten characters on the input line 27 2 5 Searching for Commands in the History Readline provides commands for searching through the command history for lines containing a specified string There are two search modes incremental and non incremental Incremental searches begin before the user has finished typing the search string As each character of the search string is typed Readline displays the next entry from the history matching the string typed so far An incremental search requires only as many characters as needed to find the desired history entry To search backward in the history for a particular string type C r Typing C s searches forward through the history The characters present in the value of the isearch
94. current state of XML debugging messages 216 Debugging with GDB Chapter 20 Canned Sequences of Commands 217 20 Canned Sequences of Commands Aside from breakpoint commands see Section 5 1 7 Breakpoint Command Lists page 49 GDB provides two ways to store sequences of commands for execution as a unit user defined commands and command files 20 1 User defined Commands A user defined command is a sequence of GDB commands to which you assign a new name as a command This is done with the define command User commands may accept up to 10 arguments separated by whitespace Arguments are accessed within the user command via arg0 arg9 A trivial example define adder print argO argi arg2 end To execute the command use adder 1 2 3 This defines the command adder which prints the sum of its three arguments Note the arguments are text substitutions so they may reference variables use complex expressions or even perform inferior functions calls In addition argc may be used to find out how many arguments have been passed This expands to a number in the range 0 10 define adder if argc print argO argi end if argc print argO argi arg2 end end define commandname Define a command named commandname If there is already a command by that name you are asked to confirm that you want to redefine it The definition of the command is made up of other GDB command lines which are given follow
95. das seer g cute 335 B packet siecle Bo ay hs aged See dees the 335 backtrace o uo ume Rei ehaeaaeieew fas 62 backtrace beyond main function 63 backtrace limit 2 oer bre t ees oma 64 backward char C b cece eee ee eee 307 backward delete char Rubout 309 backward kill line C x Rubout 310 backward kill word M DEL 310 backward word M b 000 307 baud rate for remote targets 175 bcache statistics verior pere err wt 329 beginning of history M lt 308 beginning of line C a 307 bell style i i2niniskeele feni ot Ree rens 298 bind tty special charS 5 ES 299 bits in remote address 2 0 175 bookmark ves oiiaii Raus 35 Dr ak s snessiedgccdobe ale E E Odie wera wis REGES 38 break thread threadno 57 break in overloaded functions 128 break on fork xet s reprenis ree innpeniiias 45 break on load unload of shared library 45 BREAK signal instead of Ctrl C 175 break and Objective C 00 129 breakpoint address adjusted 52 breakpoint annotation 3e n 290 breakpoint commands 00 000 49 breakpoint commands for GDB MI 239 breakpoint conditions lisse lesse 48 breakpoint numbers seeeee esses 3T breakpoint on events seseee e
96. data checksum lt The host GDB sends commands and the target the debugging stub incorporated in your program sends a response In the case of step and continue commands the response is only sent when the operation has completed the target has again stopped packet data consists of a sequence of characters with the exception of and see X packet for additional exceptions to 6 3 Fields within the packet should be separated using or Except where otherwise noted all numbers are represented in HEX with leading zeros suppressed Implementors should note that prior to GDB 5 0 the character could not appear as the third character in a packet as it would potentially conflict with the sequence id Binary data in most packets is encoded either as two hexadecimal digits per byte of binary data This allowed the traditional remote protocol to work over connections which were only seven bit clean Some packets designed more recently assume an eight bit clean connection and use a more efficient encoding to send and receive binary data The binary data representation uses 7d ASCII as an escape character Any escaped byte is transmitted as the escape character followed by the original character XORed with 0x20 For example the byte Ox7d would be transmitted as the two bytes Ox7d 0x5d The bytes 0x23 AScII 0x24 Ascii and Ox7d Ascii must always be e
97. data struc ture the overlay manager maintains in the inferior to see which overlays are mapped For details see Section 11 3 Automatic Overlay Debugging page 116 overlay load target overlay load Re read the overlay table from the inferior Normally GDB re reads the table GDB automatically each time the inferior stops so this command should only be necessary if you have changed the overlay mapping yourself using GDB This command is only useful when using automatic overlay debugging overlay list overlays overlay list Display a list of the overlays currently mapped along with their mapped ad dresses load addresses and sizes Normally when GDB prints a code address it includes the name of the function the address falls in gdb print main 3 int Oxi1a0 main When overlay debugging is enabled GDB recognizes code in unmapped overlays and prints the names of unmapped functions with asterisks around them For example if foo is a function in an unmapped overlay GDB prints it this way gdb overlay list No sections are mapped gdb print foo 116 Debugging with GDB 5 int int 0x100000 lt foo gt When foo s overlay is mapped GDB prints the function s name normally gdb overlay list Section ov foo text loaded at 0x100000 0x100034 mapped at 0x1016 Oxi04a gdb print foo 6 int int Ox1016 foo When overlay debugging is enabled GDB can find the correct address for functions
98. debuggee will be started with a shell 18 1 5 1 Support for DLLs without Debugging Symbols Very often on windows some of the DLLs that your program relies on do not include sym bolic debugging information for example kerne132 d11 When GDB doesn t recognize any debugging symbols in a DLL it relies on the minimal amount of symbolic information contained in the DLL s export table This section describes working with such symbols known internally to GDB as minimal symbols Note that before the debugged program has started execution no DLLs will have been loaded The easiest way around this problem is simply to start the program either by setting a breakpoint or letting the program run once to completion It is also possible to force GDB to load a particular DLL before starting the executable see the shared library information in Section 15 1 Files page 155 or the dll symbols command in Section 18 1 5 Cygwin Native page 185 Currently explicitly loading symbols from a DLL with no debugging information will cause the symbol names to be duplicated in GDB s lookup table which may adversely affect symbol lookup performance 18 1 5 2 DLL Name Prefixes In keeping with the naming conventions used by the Microsoft debugging tools DLL export symbols are made available with a prefix based on the DLL name for instance Chapter 18 Configuration Specific Information 187 KERNEL32 CreateFileA The plain name is also entered int
99. define macro arglist replacement list This command is not yet implemented Introduce a definition for a preproces sor macro named macro invocations of which are replaced by the tokens given in replacement list The first form of this command defines an object like macro which takes no arguments the second form defines a function like macro which takes the arguments given in arglist 102 Debugging with GDB A definition introduced by this command is in scope in every expression eval uated in GDB until it is removed with the macro undef command described below The definition overrides all definitions for macro present in the program being debugged as well as any previous user supplied definition macro undef macro This command is not yet implemented Remove any user supplied definition for the macro named macro This command only affects definitions provided with the macro define command described above it cannot remove definitions present in the program being debugged macro list This command is not yet implemented List all the macros defined using the macro define command Here is a transcript showing the above commands in action First we show our source files cat sample c include lt stdio h gt include sample h define M 42 define ADD x M x main define N 28 printf Hello world n undef N printf We re so creative n define N 1729 printf Goodbye world
100. digits and optionally followed by an exponent An exponent is of the form e nnn where nnn is another sequence of digits The is optional 126 Debugging with GDB for positive exponents A floating point constant may also end with a letter f or F specifying that the constant should be treated as being of the float as opposed to the default double type or with a letter 1 or L which specifies a long double constant e Enumerated constants consist of enumerated identifiers or their integral equivalents e Character constants are a single character surrounded by single quotes or a number the ordinal value of the corresponding character usually its ASCII value Within quotes the single character may be represented by a letter or by escape sequences which are of the form nnn where nnn is the octal representation of the character s ordinal value or of the form x where x is a predefined special character for example n for newline e String constants are a sequence of character constants surrounded by double quotes Any valid character constant as described above may appear Double quotes within the string must be preceded by a backslash so for instance a b c is a string of five characters e Pointer constants are an integral value You can also write pointers to constants using the C operator amp e Array constants are comma separ
101. eee 89 Show COPYING iore EO eee eer bebe Pure ances 28 Show Cp bi jleseeenebiohuepiperees rbv 211 show cygwin exceptions esses 185 Show debug sone h es epE Ebr ace dud 213 show debug mipsS selo gd mers 204 show debug monitor ssessss 169 show debug nto debug 190 show debug file directory 162 show detach on follow 00 34 Show directoris 4 oe ates ee eee nd 71 show disassembly flavor 73 show download path ieee eee 194 show diting is ecw c ce kem bare eee dd 207 show environment i r eredi we 28 show exceptions Hurd command 188 show exec done display ss 213 show follow fork mode ls press 34 show gn target 2 2 0 ceed ages da d yd 168 show hash for remote monitors 169 show height erskk pre Y RA EET bd 209 show history oue eR RESTER 208 show host charset sees esee 96 show inferior tty 2 dr ab aus oa 8 30 show input radix s rs Rr br Rs 210 show language 3 cco ais er dae tegen dace 121 Appendix H Index show last commands 00000 show listSiz ibs ceases i eei bb RE EE Y show logging lssssseens eden rye hd rb show max user call depth Show mem inaccessible by default show MEPS abi ne vumeRe Ilse RIS eR en RE show mips mask address show nipSf
102. either nothing has happened or the full action has been completed D 9 6 Console I O By default and if not explicitly closed by the target system the file descriptors 0 1 and 2 are connected to the GDB console Output on the GDB console is handled as any other file output operation write 1 or write 2 Console input is handled by GDB so that after the target read request from file descriptor 0 all following typing is buffered until either one of the following conditions is met e The user types Ctrl c The behaviour is as explained above and the read system call is treated as finished e The user presses RET This is treated as end of input with a trailing newline e The user types Ctrl d This is treated as end of input No trailing character neither newline nor Ctr1 D is appended to the input If the user has typed more characters than fit in the buffer given to the read call the trailing characters are buffered in GDB until either another read 0 is requested by the target or debugging is stopped at the user s request D 9 7 List of Supported Calls open Synopsis int open const char pathname int flags int open const char pathname int flags mode t mode Request Fopen pathptr len flags mode flags is the bitwise OR of the following values O_CREAT Ifthe file does not exist it will be created The host rules apply as far as file ownership and time stamps are concerned 0 EXCL When used w
103. exec async output records stopped reason reason reason can be one of the following breakpoint hit A breakpoint was reached watchpoint trigger A watchpoint was triggered read watchpoint trigger A read watchpoint was triggered access watchpoint trigger An access watchpoint was triggered function finished An exec finish or similar CLI command was accomplished 238 Debugging with GDB location reached An exec until or similar CLI command was accomplished watchpoint scope A watchpoint has gone out of scope end stepping range An exec next exec next instruction exec step exec step instruction or sim ilar CLI command was accomplished exited signalled The inferior exited because of a signal exited The inferior exited exited normally The inferior exited normally signal received A signal was received by the inferior 24 7 Simple Examples of GDB MI Interaction This subsection presents several simple examples of interaction using the GDB MI interface In these examples gt means that the following line is passed to GDB MI as input while means the output received from GDB MI Note the line breaks shown in the examples are here only for readability they don t appear in the real output Setting a Breakpoint Setting a breakpoint generates synchronous output which contains detailed information of the breakpoint gt break insert main lt done bkpt number 1 type bre
104. exec next instruction Executes one machine instruction If the instruction is a function call continues until the function returns If the program stops at an instruction in the middle of a source line the address will be printed as well GDB Command The corresponding GDB command is nexti Example gdb exec next instruction running gdb stopped reason end stepping range addr 0x000100d4 line 5 file hello c gdb The exec return Command Synopsis exec return Makes current function return immediately Doesn t execute the inferior Displays the new current frame GDB Command The corresponding GDB command is return Example gdb 254 Debugging with GDB 200 break insert callee4 200 done bkpt number 1 addr 0x00010734 file devo gdb testsuite gdb mi basics c line 8 gdb 000 exec run 000 running gdb 000 stopped reason breakpoint hit bkptno 1 frame func callee4 args file devo gdb testsuite gdb mi basics c fullname home foo bar devo gdb testsuite gdb mi basics c line 8 gdb 205 break delete 205 done gdb 111 exec return 111 done frame level 0 func callee3 args name strarg value 0x11940 A string argument file devo gdb testsuite gdb mi basics c fullname home foo bar devo gdb testsuite gdb mi basics c line 18 gdb The exec run Command Synopsis exec run Starts execution of
105. exec show arguments lesse 247 xSexec SbLepoo daa cmt ceed ote os E o Sets 255 5exec sStep instr ctaioh jae occ REIS 255 SeXec Until u zeeee e 94d EE que i 256 Efolbsiduuguieduug4 Pests pIppuee ed pins 14 file exec and symbols 276 fil exe c file6 2s olus decis red 276 file list exec sections 277 file list exec source file 277 file list exec source files 21T file list shared libraries 278 file List symbol fil68 2 2 2 ux 278 sfile Symbol file 22 6 RR 278 zBdb exit 22e dd aset didus om s 283 Rdb S6t i242 boe e Fed Po iR EUR REOR LE 283 402 SEdb ShOW assa nni ep NOE Daai E wade 284 sgdb versSion eissii Medd bp Pe das 284 inferior tty set i c cou m p iaaii 285 inferior tty ShOW i 2 cee eet piede 285 sinterpreter exeC oiioo BRL va edd ia 285 LU EEEE E EE EE E TE 14 SIist features coner inara Cae E ieu 284 a a E ant 2 hate deduc EEE E 13 PNW Gaede 14 SPutid E E EER et ee beret beer 12 E nv 13 I M 13 pr nnS 12 Stack info depth i2 ni e Rd pend 257 Stack info frame c ep ete acs 256 stack list arguments 257 Stack list f rames 266d ncaedades er ees 259 5etack list loc8lS 2 c ese inate 260 stack select frame sess 261 ssymbol info addr ss m me 273 symbolInfo file isin oe edits Reps 273 sy
106. execution is stopped at line 206 yet when we use until we get to line 195 Chapter 5 Stopping and Continuing 55 gdb f 0 main argc 4 argv Oxf7fffae8 at m4 c 206 206 expand inputO gdb until 195 for argc gt 0 NEXTARG This happened because for execution efficiency the compiler had generated code for the loop closure test at the end rather than the start of the loop even though the test in a C for loop is written before the body of the loop The until command appeared to step back to the beginning of the loop when it advanced to this expression however it has not really gone to an earlier statement not in terms of the actual machine code until with no argument works by means of single instruction stepping and hence is slower than until with an argument until location u location Continue running your program until either the specified location is reached or the current stack frame returns location is any of the forms of argument acceptable to break see Section 5 1 1 Setting Breakpoints page 38 This form of the command uses breakpoints and hence is quicker than until without an argument The specified location is actually reached only if it is in the current frame This implies that until can be used to skip over recursive function invocations For instance in the code below if the current location is line 96 issuing until 99 will execute the program up to line 99 in the same invocation of fa
107. experiment an arbitrary number of tracepoints can be set Like a breakpoint see Section 5 1 1 Set Breaks page 38 a tracepoint has a number assigned to it by GDB Like with breakpoints tracepoint numbers are successive integers starting from one Many of the commands associated with tracepoints take the tracepoint number as their argument to identify which tracepoint to work on For each tracepoint you can specify in advance some arbitrary set of data that you want the target to collect in the trace buffer when it hits that tracepoint The collected data can include registers local variables or global data Later you can use GDB commands to examine the values these data had at the time the tracepoint was hit This section describes commands to set tracepoints and associated conditions and ac tions 10 1 1 Create and Delete Tracepoints trace The trace command is very similar to the break command Its argument can be a source line a function name or an address in the target program See Section 5 1 1 Set Breaks page 38 The trace command defines a tracepoint which is a point in the target program where the debugger will briefly stop collect some data and then allow the program to continue Setting a tracepoint or changing its commands doesn t take effect until the next tstart command thus you cannot change the tracepoint attributes once a trace experiment is running Here are some examples of using the trace command 1
108. find memory in frame f char Oxf000 amp buffer amp size This would set size to zero and return NOT FOUND TARGET RESPONSE This shows how the function tells the caller that no further memory ranges have been saved As another example here is a function which will print out the addresses of all memory saved in the trace frame frame on the Symmetrix INLINES console void print frame addresses FRAME DEF frame 1 char addr char buffer unsigned long size addr 0 378 for Debugging with GDB 53 Either find out how much memory we have here or discover where the next saved region is if adbg find memory in frame frame addr amp buffer amp size OK TARGET RESPONSE printp saved x to x n addr addr size if size 0 break addr size Note that there is not necessarily any connection between the order in which the data is saved in the trace frame and the order in which adbg_find_memory_in_frame will return those memory ranges The code above will always print the saved memory regions in order of increasing address while the underlying frame structure might store the data in a random order This section should cover the rest of the Symmetrix functions the stub relies upon too E 6 Rationale Some of the design decisions apparent above are arguable What about stack overflow underflow GDB should be able to query the target to discover its stack s
109. frame In particular whenever you ask GDB for the value of a variable in your program the value is found in the selected frame There are special GDB commands to select whichever frame you are interested in See Section 6 3 Selecting a Frame page 64 When your program stops GDB automatically selects the currently executing frame and describes it briefly similar to the frame command see Section 6 4 Information about a Frame page 65 6 1 Stack Frames The call stack is divided up into contiguous pieces called stack frames or frames for short each frame is the data associated with one call to one function The frame contains the arguments given to the function the function s local variables and the address at which the function is executing When your program is started the stack has only one frame that of the function main This is called the initial frame or the outermost frame Each time a function is called a new frame is made Each time a function returns the frame for that function invocation is eliminated If a function is recursive there can be many frames for the same function The frame for the function in which execution is actually occurring is called the innermost frame This is the most recently created of all the stack frames that still exist Inside your program stack frames are identified by their addresses A stack frame consists of many bytes each of which has its own address each kind of computer has a con
110. from a file whose name ends with mod sets the working language to Modula 2 See Section 12 1 3 Having GDB Infer the Source Language page 120 for further details 12 4 5 6 Deviations from Standard Modula 2 A few changes have been made to make Modula 2 programs easier to debug This is done primarily via loosening its type strictness e Unlike in standard Modula 2 pointer constants can be formed by integers This allows you to modify pointer variables during debugging In standard Modula 2 the actual address contained in a pointer variable is hidden from you it can only be modified through direct assignment to another pointer variable or expression that returned a pointer e C escape sequences can be used in strings and characters to represent non printable characters GDB prints out strings with these escape sequences embedded Single non printable characters are printed using the CHR nnn format e The assignment operator returns the value of its right hand argument e All built in procedures both modify and return their argument 12 4 5 7 Modula 2 Type and Range Checks Warning in this release GDB does not yet perform type or range checking GDB considers two Modula 2 variables type equivalent if e They are of types that have been declared equivalent via a TYPE t1 t2 statement e They have been declared on the same line Note This is true of the GNU Modula 2 compiler but it may not be true of other compiler
111. from addr using the natural target endianness Push the fetched value as an unsigned integer Note that addr may not be aligned in any particular way the refn bytecodes should operate correctly for any address If attempting to access memory at addr would cause a processor exception of some sort terminate with an error 374 Debugging with GDB ref float Oxlb addr gt d ref double Oxlc addr d ref long double Oxld addr gt d 1_to_d Oxle a gt d d to l 0xlf d a Not implemented yet dup 0x28 a gt a a Push another copy of the stack s top element swap 0x2b ab ba Exchange the top two items on the stack pop 0x29 a gt Discard the top value on the stack if goto 0x20 offset a Pop an integer off the stack if it is non zero branch to the given offset in the bytecode string Otherwise continue to the next instruction in the bytecode stream In other words if a is non zero set the pc register to start offset Thus an offset of zero denotes the beginning of the expression The offset is stored as a sixteen bit unsigned value stored immediately fol lowing the if goto bytecode It is always stored most significant byte first regardless of the target s normal endianness The offset is not guaranteed to fall at any particular alignment within the bytecode stream thus on machines where fetching a 16 bit on an unaligned address raises an exception you should fetch the o
112. goto and if_goto instructions Neither of these registers is directly visible to the bytecode language itself but they are useful for defining the meanings of the bytecode operations There are no instructions to perform side effects on the running program or call the pro gram s functions we assume that these expressions are only used for unobtrusive debugging not for patching the running code Most bytecode instructions do not distinguish between the various sizes of values and operate on full width values the upper bits of the values are simply ignored since they do not usually make a difference to the value computed The exceptions to this rule are memory reference instructions ref n There are distinct instructions to fetch different word sizes from memory Once on the stack however the values are treated as full size integers They may need to be sign extended the ext instruction exists for this purpose the sign extension instruction ext n These clearly need to know which portion of their operand is to be extended to occupy the full length of the word If the interpreter is unable to evaluate an expression completely for some reason a mem ory location is inaccessible or a divisor is zero for example we say that interpretation terminates with an error This means that the problem is reported back to the inter preter s caller in some helpful way In general code using agent expressions should assume that they
113. group inside the parentheses may repeat one or more times e string means a literal string 24 3 GDB MI Command Syntax 24 3 1 GDB MI Input Syntax command gt cli command mi command cli command gt token cli command nl where cli command is any existing GDB CLI com mand mi command token operation option parameter nl token any sequence of digits option parameter parameter parameter gt non blank sequence c string operation any of the operations described in this chapter non blank sequence anything provided it doesn t contain special characters such as nl and of course 234 Debugging with GDB c string gt U seven bit iso c string content nl CR CR LF Notes e The CLI commands are still handled by the MI interpreter their output is described below e The token when present is passed back when the command finishes e Some MI commands accept optional arguments as part of the parameter list Each option is identified by a leading dash and may be followed by an optional argument parameter Options occur first in the parameter list and can be delimited from normal parameters using this is useful when some parameters begin with a dash Pragmatics e We want easy access to the existing CLI syntax for debugging e We want it to be easy to spot a MI operation 24 3 2 GDB MI Output S
114. i examples 12 26 net ELDER DE deg tinii 366 file i o overview 000 0 cess eee eee 354 File I O remote protocol extension 354 file i o reply packet 0 cess eee eee 356 file i o request packet 0000 200s 356 find downloadable SREC files M32R 194 find trace snapshot 00e eee 109 PINUS 34 bees oF eae Had ade EY DE ees 54 flinching ese b sleds ols n eec BEI dons 212 float promotion ssssese esee 211 floating point rx irer rr RRPREPEYU Ded 91 floating point registers 004 90 floating point MIPS remote 196 flush i1 cache 124 520 4 quae cd a8 CS EU s 180 flushfegS ecese einste HR PU Rd d ead Ide 329 FOCUS ac o De Rua Cep Oak SERERE FPE 228 focus of debugging s eves to th rorem 31 LOO paix ueber een A Rp ee tat ee mae 165 fork fork id 4 reru Sekt ditur mole 34 fork debugging programs which call 38 format options iiec rr ER da ea eres ep een 82 formatted output ee serere oak piecewise ee os 78 Fortran eee 1 Fortran Defaults 2 ua nm 130 Fortran operators and expressions 130 Fortran specific support in GDB 130 forward backward delete char 309 forward char C sereis pae ER d eee 307 forward search dac ete dg e e ee es 69 Appendix H Index forward search history C s 308 forward word M f 2 222 dr reme IS 307 FR V shared library d
115. i i irse tects eee be AES 199 target output in GDB MI 00 235 target pmon port v et wee es 195 target ppcbug ii gs ince ke bau ce ye P neds 199 target ppcbugi 242 226 ees emus si mes e hd ed 199 target r3900 cocca ti Led e Rb yd eter Pas 195 target Tdi nile 244 de Edu OPER ERR EE iri 192 target rdp cs su bee eed pde Yu e RR ER dan 192 target remote oa e EIER gern s Lr target Sd8 i 4 eec WE Re bkn cx Red ed 199 target sim with Z8000 201 target sparClit 65 354 es e ehe oid 201 target stack description 329 target vXWOIKS 22 006 teas 190 target w89k oisia Ala eps EE ee cba es 199 task attributes GNU Hurd 188 task exception port GNU Hurd 189 task suspend count eee eee eee 189 CDESC AG vice Mea Read ERR A eed ot Peewee eee 39 TCP port target remote 171 taupe Reet eee ane ee aa eae ee eee E TI terminal x 223 reuera ean pb eins 29 Text User Interface 00020000 225 AAG easton Grasatve snus Wane war med tie a bd EE 109 thbreak ase bp PR Halas PP eae IE 39 this inside C member functions 126 thread apply rm siea bonega x Rd 33 thread attributes info remote request 348 thread breakpoints 00 eee e eee 57 thread breakpoints and system calls 58 thread default settings GNU Hurd 190 thread identifier GDB
116. id id a comma separated list of thread ids id lower case letter L denotes end of list In response to each query the target will reply with a list of one or more thread ids in big endian unsigned hex separated by commas GDB will respond to each reply with a request for more thread ids using the qs form of the query until the target responds with 1 lower case el for last qGetTLSAddr thread id offset lm Fetch the address associated with thread local storage specified by thread id offset and Im thread id is the big endian hex encoded thread id associated with the thread for which to fetch the TLS address offset is the big endian hex encoded offset associated with the thread local variable This offset is obtained from the debug information associated with the variable Im is the big endian hex encoded OS ABI specific encoding of the the load module associated with the thread local storage For example a GNU Linux system will pass the link map address of the shared object associated with the thread local storage under consideration Other operating environments may choose to represent the load module differently so the precise meaning of this parameter will vary Reply XX Los Hex encoded big endian bytes representing the address of the thread local storage requested 344 Debugging with GDB E nn An error occurred nn are hex digits EJ An empty reply indicates that
117. in GDB Your bug reports play an essential role in making GDB reliable Reporting a bug may help you by bringing a solution to your problem or it may not But in any case the principal function of a bug report is to help the entire community by making the next version of GDB work better Bug reports are your contribution to the maintenance of GDB In order for bug report to serve its purpose you must include the information that enables us to fix the bug 26 1 Have You Found a Bug If you are not sure whether you have found a bug here are some guidelines e If the debugger gets a fatal signal for any input whatever that is a GDB bug Reliable debuggers never crash e If GDB produces an error message for valid input that is a bug Note that if you re cross debugging the problem may also be somewhere in the connection to the target e If GDB does not produce an error message for invalid input that is a bug However you should note that your idea of invalid input might be our idea of an extension or support for traditional practice e If you are an experienced user of debugging tools your suggestions for improvement of GDB are welcome in any case 26 2 How to Report Bugs A number of companies and individuals offer support for GNU products If you obtained GDB from a support organization we recommend you contact that organization first You can find contact information for many support companies and indi
118. in Section 20 3 Command Files page 219 When user defined commands are executed the commands of the definition are not printed An error in any command stops execution of the user defined command If used interactively commands that would ask for confirmation proceed without asking when used inside a user defined command Many GDB commands that normally print mes sages to say what they are doing omit the messages when used in a user defined command 20 2 User defined Command Hooks You may define hooks which are a special kind of user defined command Whenever you run the command foo if the user defined command hook foo exists it is executed with no arguments before that command A hook may also be defined which is run after the command you executed Whenever you run the command foo if the user defined command hookpost foo exists it is executed with no arguments after that command Post execution hooks may exist simultaneously with pre execution hooks for the same command It is valid for a hook to call the command which it hooks If this occurs the hook is not re executed thereby avoiding infinite recursion In addition a pseudo command stop exists Defining hook stop makes the asso ciated commands execute every time execution stops in your program before breakpoint commands are run displays are printed or the stack frame is printed For example to ignore SIGALRM signals while s
119. internal fork number assigned by GDB as shown in the first field of the info forks display Chapter 4 Running Programs Under GDB 35 To quit debugging one of the forked processes you can either detach from it by using the detach fork command allowing it to run independently or delete and kill it using the delete fork command detach fork fork id Detach from the process identified by GDB fork number fork id and remove it from the fork list The process will be allowed to run independently delete fork fork id Kill the process identified by GDB fork number fork id and remove it from the fork list If you ask to debug a child process and a vfork is followed by an exec GDB executes the new target up to the first breakpoint in the new target If you have a breakpoint set on main in your original program the breakpoint will also be set on the child process s main When a child process is spawned by vfork you cannot debug the child or parent until an exec call completes If you issue a run command to GDB after an exec call executes the new target restarts To restart the parent process use the file command with the parent executable name as its argument You can use the catch command to make GDB stop whenever a fork vfork or exec call is made See Section 5 1 3 Setting Catchpoints page 45 4 11 Setting a Bookmark to Return to Later On certain operating systems GDB is able to save a snapshot of a program s state ca
120. is resumed The step mode optimizes for single stepping It stops other threads from seizing the prompt by preempting the current thread while you are stepping Other threads will only rarely or never get a chance to run when you step They are more likely to run when you next over a function call and they are completely free to run when you use commands like continue Chapter 5 Stopping and Continuing 59 until or finish However unless another thread hits a breakpoint during its timeslice they will never steal the GDB prompt away from the thread that you are debugging show scheduler locking Display the current scheduler locking mode 60 Debugging with GDB Chapter 6 Examining the Stack 61 6 Examining the Stack When your program has stopped the first thing you need to know is where it stopped and how it got there Each time your program performs a function call information about the call is generated That information includes the location of the call in your program the arguments of the call and the local variables of the function being called The information is saved in a block of data called a stack frame The stack frames are allocated in a region of memory called the call stack When your program stops the GDB commands for examining the stack allow you to see all of this information One of the stack frames is selected by GDB and many GDB commands refer implicitly to the selected
121. libraries 160 unmap an overlay 00 eee eee eee 115 unmapped overlays eee eee ee eee 113 unset environment sees eese 28 unset substitute path esses ra unset tdesc filename 381 unsupported languages esses 141 ntdl ites esce Xie avia oor Pha er n 54 unwind stack in called functions 152 417 D TC p 226 up silently eiemB E dei RE d 65 upcase word M u 0 eee eee 309 Update d sweet E ueber eig ens 228 upload M32EU soos ee pan HER e med td 194 use only software watchpoints 43 use dbt break oenhe6 eed cde ees 195 use debug dma eoe nme ep Ies 194 use 3b Dfeak ulu je eU aie I eget 195 usSe mon Code isis so pee T RA AA eR 195 user defined command 000045 217 user defined macroS 0 eee e eee eee 101 user defined variables 000 0000 ee 88 V v SingleKey TUI key sseeeeeeens 227 Vale history Rs space sang Emp RE s 88 value optimized out in backtrace 63 variable name conflict 000005 76 variable object debugging info 214 variable objects in GDB MI 261 variable values wrong 0 0222 0005 76 variables readline 02 eee eee 298 variables setting ice pe RE eRRE EY e 149 vCont packetg ieemeenkR ecu eeme pev 338 vCon
122. may attempt to divide by zero fetch arbitrary memory locations and misbehave in other ways Even complicated C expressions compile to a few bytecode instructions for example the expression x y z would typically produce code like the following assuming that x and y live in registers and z is a global variable holding a 32 bit int reg 1 reg 2 const32 address of z ref32 ext 32 mul add Appendix E The GDB Agent Expression Mechanism 371 end In detail these mean reg 1 Push the value of register 1 presumably holding x onto the stack reg 2 Push the value of register 2 holding y const32 address of z Push the address of z onto the stack ref32 Fetch a 32 bit word from the address at the top of the stack replace the address on the stack with the value Thus we replace the address of z with z s value ext 32 Sign extend the value on the top of the stack from 32 bits to full length This is necessary because z is a signed integer mul Pop the top two numbers on the stack multiply them and push their product Now the top of the stack contains the value of the expression y z add Pop the top two numbers add them and push the sum Now the top of the stack contains the value of x y z end Stop executing the value left on the stack top is the value to be recorded E 2 Bytecode Descriptions Each bytecode description has the following form add 0x02 a b a b Pop the top two stack items a and b a
123. n cat sample h define Q lt Now we compile the program using the GNU C compiler GCC We pass the gdwarf 2 and g3 flags to ensure the compiler includes information about preprocessor macros in the debugging information gcc gdwarf 2 g3 sample c o sample Now we start GDB on our sample program gdb nw sample GNU gdb 2002 05 06 cvs Copyright 2002 Free Software Foundation Inc GDB is free software gdb We can expand macros and examine their definitions even when the program is not running GDB uses the current listing position to decide which macro definitions are in Scope gdb list main 3 4 define M 42 Chapter 9 C Preprocessor Macros 5 define ADD x M x 6 T main 8 1 9 define N 28 10 printf Hello world n 11 undef N 12 printf We re so creative n gdb info macro ADD Defined at home jimb gdb macros play sample c 5 define ADD x M x gdb info macro Q Defined at home jimb gdb macros play sample h 1 included at home jimb gdb macros play sample c 2 define Q lt gdb macro expand ADD 1 expands to 42 1 gdb macro expand once ADD 1 expands to once M 1 gdb 103 In the example above note that macro expand once expands only the macro invocation explicit in the original text the invocation of ADD but does not expand the invocation of the macro M which was introduced by ADD Once the program is runn
124. newlines no nn The value is not entered in the value history either See Section 8 1 Expressions page 75 for more information on expressions output fmt expression Print the value of expression in format fmt You can use the same formats as for print See Section 8 4 Output Formats page 78 for more information printf template expressions Print the values of one or more expressions under the control of the string template To print several values make expressions be a comma separated list of individual expressions which may be either numbers or pointers Their values are printed as specified by template exactly as a C program would do by executing the code below printf template expressions As in C printf ordinary characters in template are printed verbatim while conversion specification introduced by the character cause subsequent ex pressions to be evaluated their values converted and formatted according to type and style information encoded in the conversion specifications and then printed For example you can print two values in hex like this printf foo bar foo Ox x Ox 4xMn foo bar foo printf supports all the standard C conversion specifications including the flags and modifiers between the character and the conversion letter with the following exceptions e The argument ordering modifiers such as 2 are not supported e The modifier is not supported for s
125. no charge to all third parties under the terms of this License c If the modified program normally reads commands interactively when run you must cause it when started running for such interactive use in the most ordinary way to print or display an announcement including an appropriate copyright notice and a notice that there is no warranty or else saying that you provide a warranty and that users may redistribute the program under these conditions and telling the user how to view a copy of this License Exception if the Program itself is interactive but does not normally print such an announcement your work based on the Program is not required to print an announcement These requirements apply to the modified work as a whole If identifiable sections of that work are not derived from the Program and can be reasonably considered independent and separate works in themselves then this License and its terms do not apply to those sections when you distribute them as separate works But when you distribute the same sections as part of a whole which is a work based on the Program the distribution of the whole must be on the terms of this License whose permissions for other licensees extend to the entire whole and thus to each and every part regardless of who wrote it Appendix G GNU GENERAL PUBLIC LICENSE 389 Thus it is not the intent of this section to claim rights or contest your rights to work written entirely by you rather the
126. not available unless the program is running This means that you cannot examine the contents of a variable or disassemble a function within a DLL without a running program Variables are generally treated as pointers and dereferenced automatically For this reason it is often necessary to prefix a variable name with the address of operator amp and provide explicit type information in the command Here s an example of the type of problem gdb print cygwini argv 1 268572168 gdb x cygwini __argv 0x10021610 230y And two possible solutions gdb print char cygwin1 __argv 0 2 0x22fd98 cygdrive c mydirectory myprogram gdb x 2x amp cygwin1 __argv 0x610cOaa8 lt cygwini __argv gt 0x10021608 0x00000000 gdb x x 0x10021608 0x10021608 0x0022fd98 gdb x s 0x0022fd98 0x22fd98 cygdrive c mydirectory myprogram 188 Debugging with GDB Setting a break point within a DLL is possible even before the program starts execu tion However under these circumstances GDB can t examine the initial instructions of the function in order to skip the function s frame set up code You can work around this by using amp to set the breakpoint at a raw memory address gdb break amp python22 Py0S_Readline Breakpoint 1 at OxieO4effO0 The author of these extensions is not entirely convinced that setting a break point within a shared DLL like kernel32 d11 is completely safe
127. number of a symbol in the symbolic form of an address Another situation where it is helpful to show symbol filenames and line numbers is when disassembling code GDB shows you the line number and source file that corresponds to each instruction Also you may wish to see the symbolic form only if the address being printed is reason ably close to the closest earlier symbol set print max symbolic offset max offset Tell GDB to only display the symbolic form of an address if the offset between the closest earlier symbol and the address is less than max offset The default is 0 which tells GDB to always print the symbolic form of an address if any symbol precedes it show print max symbolic offset Ask how large the maximum offset is that GDB prints in a symbolic address 84 Debugging with GDB If you have a pointer and you are not sure where it points try set print symbol filename on Then you can determine the name and source file location of the variable where it points using p a pointer This interprets the address in symbolic form For example here GDB shows that a variable ptt points at another variable t defined in hi2 c gdb set print symbol filename on gdb p a ptt 4 Oxe008 t in hi2 c gt Warning For pointers that point to a local variable p a does not show the symbol name and filename of the referent even with the appropriate set print options turned on Other settings control how differe
128. oen o etri d pet tete trad alanis eater ace a 360 IODBIUO 2224 cecal tei e ios Rega ov ents e ei Rog Rb teli n RR a pc 360 unlinle emekdER ia PERRA eek pea Popp Ad e ERR dip 361 CUCMPADUD UMP ETEIEEESS DITE 361 gettimeofday 0c cece cence tne hh 362 ISA LU y esos sese PERS Mang din gang as eee See eae 362 SVSUCM 441a wht hed dad rend ol c RR pa baa o aly 362 D 9 8 Protocol specific Representation of Datatypes 363 Integral Datatypes 0 00 eee cette ee 363 Pointer Values 000 tenini E eee cence hh 363 Memory Transter asd ed bad eren ERI eddie aad ie a 363 Struct SUNG eser LR dae ago ENT pie Seed e plod EUR n edes 364 struct timeval niei per ase ig hu EY Wug ve deep duds 364 D 9 9 Constants 523 240b de dO Re 4 ERU abe Deda 365 Open Flagge areia aaa na eee enean ar o dn Ra D Pe n 365 mode t Values rant hun eR A AR RR Rd 365 Errno Values caeca ced alee ek E REX d dS 365 seek Flags 2 EE e e LE RR RHET Ries 366 IEE E ERR ER ETATS TEE A E 366 D 9 10 File I O Examples er tre ker eb 366 D 10 Library List Format sssseeeeeee nee 366 D 11 Memory Map Format eseeeeeeee eee eens 367 Appendix E The GDB Agent Expression NieChANISMIG 22 2223 4392229324242 90255929 2 2x 369 E 1 General Bytecode Design 0000 ce cece ee eee ee 369 E 2 Bytecode Descriptions 0 0 cece eee eee eens 371 E 3 Using Agent Expressions 00 0000 c eee esee
129. of a debugger such as GDB is to allow you to see what is going on inside another program while it executes or what another program was doing at the moment it crashed GDB can do four main kinds of things plus other things in support of these to help you catch bugs in the act e Start your program specifying anything that might affect its behavior e Make your program stop on specified conditions e Examine what has happened when your program has stopped e Change things in your program so you can experiment with correcting the effects of one bug and go on to learn about another You can use GDB to debug programs written in C and C For more information see Section 12 4 Supported Languages page 123 For more information see Section 12 4 1 C and C page 123 Support for Modula 2 is partial For information on Modula 2 see Section 12 4 5 Modula 2 page 131 Debugging Pascal programs which use sets subranges file variables or nested functions does not currently work GDB does not support entering expressions printing values or similar features using Pascal syntax GDB can be used to debug programs written in Fortran although it may be necessary to refer to some variables with a trailing underscore GDB can be used to debug programs written in Objective C using either the Ap ple NeXT or the GNU Objective C runtime Free Software GDB is free software protected by the GNU General Public License GPL The GP
130. of the Free Software Foundation s software and to any other program whose authors commit to using it Some other Free Software Foundation software is covered by the GNU Library General Public License instead You can apply it to your programs too When we speak of free software we are referring to freedom not price Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software and charge for this service if you wish that you receive source code or can get it if you want it that you can change the software or use pieces of it in new free programs and that you know you can do these things To protect your rights we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights These restrictions translate to certain responsibilities for you if you distribute copies of the software or if you modify it For example if you distribute copies of such a program whether gratis or for a fee you must give the recipients all the rights that you have You must make sure that they too receive or can get the source code And you must show them these terms so they know their rights We protect your rights with two steps 1 copyright the software and 2 offer you this license which gives you legal permission to copy distribute and or modify the software Also for each author s protection and ours we want to make certain that everyone under
131. of x has changed Show values Print the last ten values in the value history with their item numbers This is like p 9 repeated ten times except that show values does not change the history show values n Print ten history values centered on history item number n show values Print ten history values just after the values last printed If no more values are available show values produces no display Pressing to repeat show values n has exactly the same effect as show values 8 9 Convenience Variables GDB provides convenience variables that you can use within GDB to hold on to a value and refer to it later These variables exist entirely within GDB they are not part of your Chapter 8 Examining Data 89 program and setting a convenience variable has no direct effect on further execution of your program That is why you can use them freely Convenience variables are prefixed with Any name preceded by can be used for a convenience variable unless it is one of the predefined machine specific register names see Section 8 10 Registers page 90 Value history references in contrast are numbers preceded by See Section 8 8 Value History page 88 You can save a value in a convenience variable with an assignment expression just as you would set a variable in your program For example set foo object ptr would save in foo the value contained in the object pointed to by object ptr
132. often useful in silent breakpoints See Section 20 4 Commands for Controlled Output page 220 For example here is how you could use breakpoint commands to print the value of x at entry to foo whenever x is positive break foo if x gt 0 commands silent printf x is d n x cont end One application for breakpoint commands is to compensate for one bug so you can test for another Put a breakpoint just after the erroneous line of code give it a condition to detect the case in which something erroneous has been done and give it commands to assign correct values to any variables that need them End with the continue command so that your program does not stop and start with the silent command so that no output is produced Here is an example break 403 commands silent set x yt 4 cont end Chapter 5 Stopping and Continuing 51 5 1 8 Breakpoint Menus Some programming languages notably C and Objective C permit a single function name to be defined several times for application in different contexts This is called overloading When a function name is overloaded break function is not enough to tell GDB where you want a breakpoint If you realize this is a problem you can use something like break function types to specify which particular version of the function you want Otherwise GDB offers you a menu of numbered choices for different possible breakpoints and waits for your selection with the prompt gt
133. one pointed to by the specified entry in the Page Directory These commands are useful when your program uses DMA Direct Memory Access which needs physical addresses to program the DMA controller These commands are supported only with some DPMI servers info dos address pte addr This command displays the Page Table entry for a specified linear address The argument addr is a linear address which should already have the appropriate segment s base address added to it because this command accepts addresses which may belong to any segment For example here s how to display the Page Table entry for the page where a variable i is stored gdb info dos address pte djgpp base address char amp i Page Table entry for address Ox11a00d30 Base 0x02698000 Dirty Acc Not Cached Write Back Usr Read Write 0xd30 This says that i is stored at offset Oxd30 from the page whose physical base address is 0x02698000 and shows all the attributes of that page Note that you must cast the addresses of variables to a char since otherwise the value of djgpp base address the base address of all variables and func tions in a DJGPP program will be added using the rules of C pointer arithmetics if i is declared an int GDB will add 4 times the value of djgpp base address to the address of i Here s another example it displays the Page Table entry for the transfer buffer gdb info dos address pte unsigned amp go32 info bloc
134. one with its item number but without showing the values This includes dis abled expressions which are marked as such It also includes expressions which would not be displayed right now because they refer to automatic variables not currently available If a display expression refers to local variables then it does not make sense outside the lexical context for which it was set up Such an expression is disabled when execution enters a context where one of its variables is not defined For example if you give the command display last_char while inside a function with an argument last_char GDB displays this argument while your program continues to stop inside that function When it stops elsewhere where there is no variable last_char the display is disabled automatically The next time your program stops where last_char is meaningful you can enable the display expression once again 8 7 Print Settings GDB provides the following ways to control how arrays structures and symbols are printed These settings are useful for debugging programs in any language set print address set print address on GDB prints memory addresses showing the location of stack traces structure values pointer values breakpoints and so forth even when it also displays the Chapter 8 Examining Data 83 contents of those addresses The default is on For example this is what a stack frame display looks like with set print address on gdb f 0 set qu
135. or count add the expression expr to the auto display list but arrange to display it each time in the specified format fmt See Section 8 4 Output Formats page 78 82 Debugging with GDB display fmt addr For fmt i or s or including a unit size or a number of units add the expres sion addr as a memory address to be examined each time your program stops Examining means in effect doing x fmt addr See Section 8 5 Examining Memory page 79 For example display i pc can be helpful to see the machine instruction about to be executed each time execution stops pc is a common name for the program counter see Section 8 10 Registers page 90 undisplay dnums delete display dnums Remove item numbers dnums from the list of expressions to display undisplay does not repeat if you press after using it Otherwise you would just get the error No display number disable display dnums Disable the display of item numbers dnums A disabled display item is not printed automatically but is not forgotten It may be enabled again later enable display dnums Enable display of item numbers dnums It becomes effective once again in auto display of its expression until you specify otherwise display Display the current values of the expressions on the list just as is done when your program stops info display Print the list of expressions previously set up to display automatically each
136. overlay s machine code from the large memory into the space set aside for it in the instruction memory and then jump to its entry point there Data Instruction Larger Address Space Address Space Address Space 4 4 4 l l pem Fanes been lt overlay 1 program main overlay 1 load address variables program es 4 and heap a a a E lt overlay 2 load address overlay 2 tl mapped 4 99 2 address d overlay lt area lt overlay 3 load address overlay 3 l 4 4 l 4 A code overlay The diagram see A code overlay page 113 shows a system with separate data and instruction address spaces To map an overlay the program copies its code from the larger address space to the instruction address space Since the overlays shown here all use the same mapped address only one may be mapped at a time For a system with a single address space for data and instructions the diagram would be similar except that the program variables and heap would share an address space with the main program and the overlay area 114 Debugging with GDB An overlay loaded into instruction memory and ready for use is called
137. packet contains all information needed to allow GDB to call the appropriate host system call e A unique identifier for the requested system call e All parameters to the system call Pointers are given as addresses in the target memory address space Pointers to strings are given as pointer length pair Numerical values are given as they are Numerical control flags are given in a protocol specific representation At this point GDB has to perform the following actions e Ifthe parameters include pointer values to data needed as input to a system call GDB requests this data from the target with a standard m packet request This additional communication has to be expected by the target implementation and is handled as any other m packet e GDB translates all value from protocol representation to host representation as needed Datatypes are coerced into the host types e GDB calls the system call e It then coerces datatypes back to protocol representation 356 Debugging with GDB e If the system call is expected to return data in buffer space specified by pointer pa rameters to the call the data is transmitted to the target using a M or X packet This packet has to be expected by the target implementation and is handled as any other M or X packet Eventually GDB replies with another F packet which contains all necessary information for the target to continue This at least contains e Return value e errno if has been cha
138. process related information including the user ID and group ID how many threads are there in the process its virtual memory usage the signals that are pending blocked and ignored its TTY its consumption of system and user time its stack size its nice value etc For more information see the proc man page type man 5 proc from your shell prompt info proc all Show all the information about the process described under all of the above info proc subcommands set procfs trace This command enables and disables tracing of procfs API calls show procfs trace Show the current state of procfs API call tracing set procfs file file Tell GDB to write procfs API trace to the named file GDB appends the trace info to the previous contents of the file The default is to display the trace on the standard output show procfs file Show the file to which procfs API trace is written proc trace entry proc trace exit proc untrace entry proc untrace exit These commands enable and disable tracing of entries into and exits from the syscall interface info pidlist For QNX Neutrino only this command displays the list of all the processes and all the threads within each process Chapter 18 Configuration Specific Information 183 info meminfo For QNX Neutrino only this command displays the list of all mapinfos 18 1 4 Features for Debugging DJGPP Programs DJGPP is a port of the GNU development tools to MS DOS and MS Wi
139. qXfer libraries read packet see qXfer li brary list read page 349 instead The remote stub queries the targets operating system and reports which libraries are loaded The qXfer libraries read packet returns an XML document which lists loaded li braries and their offsets Each library has an associated name and one or more segment base addresses which report where the library was loaded in memory The segment bases are start addresses not relocation offsets they do not depend on the library s link time base addresses A simple memory map with one loaded library relocated by a single offset looks like this lt library list gt lt library name lib libc so 6 gt lt segment address 0x10000000 gt lt library gt lt library list gt The format of a library list is described by this DTD lt library list Root element with versioning gt lt ELEMENT library list library gt lt ATTLIST library list version CDATA FIXED 1 0 gt lt ELEMENT library segment gt lt ATTLIST library name CDATA REQUIRED gt lt ELEMENT segment EMPTY gt lt ATTLIST segment address CDATA REQUIRED gt D 11 Memory Map Format To be able to write into flash memory GDB needs to obtain a memory map from the target This section describes the format of the memory map The memory map is obtained using the qXfer memory map read see qXfer memory map read page 350 packet and is an XML document that lists
140. relaxation on the code after I generate it which seems like a big waste of time I can imagine a reasonable expression being longer than 256 bytes I can t imagine one being longer than 64k Thus we need 16 bit offsets This kind of reasoning is so bogus but relaxation is pathetic The other approach would be to generate code right to left Then I d always know my offset size That might be fun Where is the function call bytecode When we add side effects we should add this Why does the reg bytecode take a 16 bit register number Intel s A 64 architecture has 128 general purpose registers and 128 floating point registers and I m sure it has some random control registers Why do we need trace and trace quick Because GDB needs to record all the memory contents and registers an expres sion touches If the user wants to evaluate an expression x y z the agent must record the values of x and x y as well as the value of x gt y gt z Don t the trace bytecodes make the interpreter less general They do mean that the interpreter contains special purpose code but that doesn t mean the interpreter can only be used for that purpose If an expression doesn t use the trace bytecodes they don t get in its way Why doesn t trace quick consume its arguments the way everything else does In general you do want your operators to consume their arguments it s con sistent and generally reduces the amount of stack rearrangement ne
141. returning as its value the value of its right hand operand This allows for example complex conditional breaks break f condition 1 report i k 1 A k gt 100 Rather than use catenation and symbolic character names to introduce special charac ters into strings one may instead use a special bracket notation which is also used to 140 Debugging with GDB print strings A sequence of characters of the form XX within a string or character literal denotes the single character whose numeric encoding is XX in hexadecimal The sequence of characters also denotes a single quotation mark in strings For example One line Oa Next line Oa contains an ASCII newline character Ada Characters Latin 1 LF after each period The subtype used as a prefix for the attributes Pos Min and Max is optional and is ignored in any case For example it is valid to write print max x y When printing arrays GDB uses positional notation when the array has a lower bound of 1 and uses a modified named notation otherwise For example a one dimensional array of three integers with a lower bound of 3 might print as 3 gt 10 17 1 That is in contrast to valid Ada only the first component has a gt clause You may abbreviate attributes in expressions with any unique multi character subse quence of their names an exact match gets preference For example you may use a len a gth or a 1h in place of
142. search path If directories pathdir are supplied in addition to the r option the search path is first reset and then addition occurs as normal Multiple directories may be specified separated by blanks Specifying multiple directories in a single command results in the directories added to the beginning of the search path in the same order they were presented in the command If blanks are needed as part of a directory name double quotes should be used around the name In the command output the path will show up separated by the system directory separator character The directory separator character must not be used in any directory name If no directories are specified the current search path is displayed GDB Command The corresponding GDB command is dir Example gdb environment directory kwikemart marge ezannoni flathead dev devo gdb done source path kwikemart marge ezannoni flathead dev devo gdb cdir cwd gdb environment directory done source path kwikemart marge ezannoni flathead dev devo gdb cdir cwd gdb environment directory r home jjohnstn src gdb usr src done source path home jjohnstn src gdb usr src cdir cwd gdb environment directory r done source path cdir cwd gdb The environment path Command Synopsis environment path r pathdir Chapter 24 The GDB MI Interface 249 Add directories pathdir to beginning of search path for object files If the
143. set any number of breakpoints at the same place in your program There is nothing silly or meaningless about this When the breakpoints are conditional this is even useful see Section 5 1 6 Break Conditions page 48 It is possible that a breakpoint corresponds to several locations in your program Ex amples of this situation are e For a C constructor the GCC compiler generates several instances of the function body used in different cases e For a C template function a given line in the function can correspond to any number of instantiations e For an inlined function a given source line can correspond to several places where that function is inlined In all those cases GDB will insert a breakpoint at all the relevant locations A breakpoint with multiple locations is displayed in the breakpoint table using several rows one header row followed by one row for each breakpoint location The header row has lt MULTIPLE gt in the address column The rows for individual locations contain the actual addresses for locations and say what functions those locations are in The number column for a location has number in the format breakpoint number location number For example Num Type Disp Enb Address What 1 breakpoint keep y lt MULTIPLE gt stop only if i 1 breakpoint already hit 1 time y 0x080486a2 in void foo lt int gt at t cc 8 1 1 1 2 y 0x080486ca in void foo lt double gt at t cc 8 Each location can
144. source file Search proceeds forward from the last examined trace snapshot If no argument n is given it means find the next line other than the one currently being examined thus saying tfind line repeatedly can appear to have the same effect as stepping from line to line in a live debugging session The default arguments for the tfind commands are specifically designed to make it easy to scan through the trace buffer For instance tfind with no argument selects the next trace snapshot and tfind with no argument selects the previous trace snapshot So by giving one tfind command and then simply hitting repeatedly you can examine all the trace snapshots in order Or by saying tfind and then hitting repeatedly you can examine the snapshots in reverse order The tfind line command with no argument selects the snapshot for the next source line executed The tfind pc command with no argument selects the next snapshot with the same program counter PC as the current frame The tfind tracepoint command with no argument selects the next trace snapshot collected by the same tracepoint as the current one In addition to letting you scan through the trace buffer manually these commands make it easy to construct GDB scripts that scan through the trace buffer and print out whatever collected data you are interested in Thus if we want to examine the PC FP and SP registers from each trace frame in the buffer we can say this gdb tfind start g
145. stored Negative Defined on integral and floating point types Same precedence as Logical negation Defined on integral types Same precedence as Bitwise complement operator Defined on integral types Same precedence as Structure member and pointer to structure member For convenience GDB regards the two as equivalent choosing whether to dereference a pointer based on the stored type information Defined on struct and union data Dereferences of pointers to members Array indexing a i is defined as a i Same precedence as gt Function parameter list Same precedence as gt C scope resolution operator Defined on struct union and class types Doubled colons also represent the GDB scope operator see Section 8 1 Expres sions page 75 Same precedence as above If an operator is redefined in the user code GDB usually attempts to invoke the redefined version instead of using the operator s predefined meaning 12 4 1 2 C and C Constants GDB allows you to express the constants of C and C in the following ways e Integer constants are a sequence of digits Octal constants are specified by a leading i e zero and hexadecimal constants by a leading Ox or OX Constants may also end with a letter 1 specifying that the constant should be treated as a long value e Floating point constants are a sequence of digits followed by a decimal point followed by a sequence of
146. subprocess of Emacs with input and output through a newly created Emacs buffer Running GDB under Emacs can be just like running GDB normally except for two things e All terminal input and output goes through an Emacs buffer called the GUD buffer This applies both to GDB commands and their output and to the input and output done by the program you are debugging This is useful because it means that you can copy the text of previous commands and input them again you can even use parts of the output in this way All the facilities of Emacs Shell mode are available for interacting with your program In particular you can send signals the usual way for example C c C c for an inter rupt C c C z for a stop e GDB displays source code through Emacs Each time GDB displays a stack frame Emacs automatically finds the source file for that frame and puts an arrow gt at the left margin of the current line Emacs uses a separate buffer for source display and splits the screen to show both your GDB session and the source Explicit GDB list or search commands still produce output as usual but you probably have no reason to use them from Emacs We call this text command mode Emacs 22 1 and later also uses a graphical mode enabled by default which provides further buffers that can control the execution and de scribe the state of your program See section GDB Graphical Interface in The GNU Emacs Manual If y
147. target sim simulates either the Z8002 the unsegmented variant of the Z8000 architecture or the Z8001 the segmented variant The simulator recognizes which architecture is appropriate by inspecting the object code target sim args Debug programs on a simulated CPU If the simulator supports setup options specify them via args After specifying this target you can debug programs for the simulated CPU in the same style as programs for your host computer use the file command to load a new program image the run command to run your program and so on As well as making available all the usual machine registers see Section 8 10 Registers page 90 the Z8000 simulator provides three additional items of information as specially named registers cycles Counts clock ticks in the simulator insts Counts instructions run in the simulator time Execution time in 60ths of a second You can refer to these values in GDB expressions with the usual conventions for example b fputc if cycles gt 5000 sets a conditional breakpoint that suspends only after at least 5000 simulated clock ticks 18 3 11 Atmel AVR When configured for debugging the Atmel AVR GDB supports the following AVR specific commands 202 Debugging with GDB info io registers This command displays information about the AVR I O registers For each register GDB prints its number and value 18 3 12 CRIS When configured for debugging CRIS GDB provides the followin
148. terminators variable are used to terminate an incremental search If that variable has not been assigned a value the and C J characters will terminate an incremental search C g will abort an incremental search and restore the original line When the search is terminated the history entry containing the search string becomes the current line To find other matching entries in the history list type C r or C s as appropriate This will search backward or forward in the history for the next entry matching the search string typed so far Any other key sequence bound to a Readline command will terminate the 298 Debugging with GDB search and execute that command For instance a will terminate the search and accept the line thereby executing the command from the history list A movement command will terminate the search make the last line found the current line and begin editing Readline remembers the last incremental search string If two C rs are typed without any intervening characters defining a new search string any remembered search string is used Non incremental searches read the entire search string before starting to search for matching history lines The search string may be typed by the user or be part of the contents of the current line 27 3 Readline Init File Although the Readline library comes with a set of Emacs like keybindings installed by default it is possible to use a different set of keybindings Any user can cust
149. textbook or other functional and useful document free in the sense of freedom to assure everyone the effective freedom to copy and redistribute it with or without modifying it either commercially or non commercially Secondarily this License preserves for the author and publisher a way to get credit for their work while not being considered responsible for modifications made by others This License is a kind of copyleft which means that derivative works of the document must themselves be free in the same sense It complements the GNU General Public License which is a copyleft license designed for free software We have designed this License in order to use it for manuals for free software because free software needs free documentation a free program should come with manuals providing the same freedoms that the software does But this License is not limited to software manuals it can be used for any textual work regardless of subject matter or whether it is published as a printed book We recommend this License principally for works whose purpose is instruction or reference APPLICABILITY AND DEFINITIONS This License applies to any manual or other work in any medium that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License Such a notice grants a world wide royalty free license unlimited in duration to use that work under the conditions stated herein The Document
150. tfind n which finds trace snapshot number n counting from zero If no argument n is given the next snapshot is selected Here are the various forms of using the tfind command tfind start Find the first snapshot in the buffer This is a synonym for tfind 0 since 0 is the number of the first snapshot tfind none Stop debugging trace snapshots resume live debugging tfind end Same as tfind none tfind No argument means find the next trace snapshot tfind Find the previous trace snapshot before the current one This permits retracing earlier steps tfind tracepoint num Find the next snapshot associated with tracepoint num Search proceeds for ward from the last examined trace snapshot If no argument num is given it means find the next snapshot collected for the same tracepoint as the current snapshot tfind pc addr Find the next snapshot associated with the value addr of the program counter Search proceeds forward from the last examined trace snapshot If no argument 110 Debugging with GDB addr is given it means find the next snapshot with the same value of PC as the current snapshot tfind outside addri addr2 Find the next snapshot whose PC is outside the given range of addresses tfind range addri addr2 Find the next snapshot whose PC is between addr1 and addr2 tfind line file n Find the next snapshot associated with the source line n If the optional argu ment file is given refer to line n in that
151. the Symbol Table page 143 Set print demangle show print demangle set print asm demangle Show print asm demangle Control whether C symbols display in their source form both when displaying code as C source and when displaying disassemblies See Section 8 7 Print Settings page 82 Set print object show print object Choose whether to print derived actual or declared types of objects See Section 8 7 Print Settings page 82 Set print vtbl Show print vtbl Control the format for printing virtual function tables See Section 8 7 Print Settings page 82 The vtbl commands do not work on programs compiled with the HP ANSI C compiler aCC set overload resolution on Enable overload resolution for C expression evaluation The default is on For overloaded functions GDB evaluates the arguments and searches for a function whose signature matches the argument types using the standard C conver sion rules see Section 12 4 1 3 C Expressions page 126 for details If it cannot find a match it emits a message Chapter 12 Using GDB with Different Languages 129 set overload resolution off Disable overload resolution for C expression evaluation For overloaded func tions that are not class member functions GDB chooses the first function of the specified name that it finds in the symbol table whether or not its argu ments are of the correct type For overloaded functions that are class member functions GDB
152. the Unix host and on the VxWorks target The program gdb is installed and executed on the Unix host It may be installed with the name vxgdb to distinguish it from a GDB for debugging programs on the host itself VxWorks timeout args All VxWorks based targets now support the option vxworks timeout This option is set by the user and args represents the number of seconds GDB waits for responses to rpc s You might use this if your VxWorks target is a slow software simulator or is on the far side of a thin network line The following information on connecting to VxWorks was current when this manual was produced newer releases of VxWorks may use revised procedures To use GDB with VxWorks you must rebuild your VxWorks kernel to include the remote debugging interface routines in the VxWorks library rdb a To do this define INCLUDE RDB in the VxWorks configuration file configA11 h and rebuild your VxWorks kernel The resulting kernel contains rdb a and spawns the source debugging task tRdbTask when VxWorks is booted For more information on configuring and remaking VxWorks see the manufacturer s manual Once you have included rdb a in your VxWorks system image and set your Unix execution search path to find GDB you are ready to run GDB From your Unix host run gdb or vxgdb depending on your installation GDB comes up showing the prompt vxgdb 18 2 1 1 Connecting to VxWorks The GDB command target lets
153. the documentation for those compilers e The command arguments you gave the compiler to compile your example and observe the bug For example did you use 0 To guarantee you will not omit something important list them all A copy of the Makefile or the output from make is sufficient If we were to try to guess the arguments we would probably guess wrong and then we might not encounter the bug e A complete input script and all necessary source files that will reproduce the bug e A description of what behavior you observe that you believe is incorrect For example t gets a fatal signal Of course if the bug is that GDB gets a fatal signal then we will certainly notice it But if the bug is incorrect output we might not notice unless it is glaringly wrong You might as well not give us a chance to make a mistake Even if the problem you experience is a fatal signal you should still say so explicitly Suppose something strange is going on such as your copy of GDB is out of synch or you have encountered a bug in the C library on your system This has happened Your copy might crash and ours would not If you told us to expect a crash then when ours fails to crash we would know that the bug was not happening for us If you had not told us to expect a crash then we would not be able to draw any conclusion from our observations To collect all this information you can use a session recording program such as script w
154. the expression cond each time the breakpoint is reached and stop only if the value is nonzero that is if cond evaluates as true stands for one of the possible arguments described above or no argument specifying where to break See Section 5 1 6 Break Conditions page 48 for more information on breakpoint conditions tbreak args Set a breakpoint enabled only for one stop args are the same as for the break command and the breakpoint is set in the same way but the breakpoint is automatically deleted after the first time your program stops there See Sec tion 5 1 5 Disabling Breakpoints page 47 hbreak args Set a hardware assisted breakpoint args are the same as for the break com mand and the breakpoint is set in the same way but the breakpoint requires hardware support and some target hardware may not have this support The main purpose of this is EPROM ROM code debugging so you can set a break point at an instruction without changing the instruction This can be used with the new trap generation provided by SPARClite DSU and most x86 based targets These targets will generate traps when a program accesses some data or instruction address that is assigned to the debug registers However the hardware breakpoint registers can take a limited number of breakpoints For example on the DSU only two data breakpoints can be set at a time and GDB will reject this command if more than two are used Delete or disable unused har
155. the feature containing ARM core registers is named org gnu gdb arm core The names of registers are not case sensitive for the purpose of recognizing standard features but GDB will only display registers using the capitalization used in the description F 4 1 ARM Features The org gnu gdb arm core feature is required for ARM targets It should contain regis ters rO through r13 sp lr pce and cpsr The org gnu gdb arm fpa feature is optional If present it should contain registers fO through 7 and fps The org gnu gdb xscale iwmmxt feature is optional If present it should contain at least registers wRO through wR15 and wCGRO through wCGR3 The wCID wCon wCSSF and wCASF registers are optional F 4 2 MIPS Features The org gnu gdb mips cpu feature is required for MIPS targets It should contain reg isters rO through r31 lo hi and pc They may be 32 bit or 64 bit depending on the target The org gnu gdb mips cpO feature is also required It should contain at least the status badvaddr and cause registers They may be 32 bit or 64 bit depending on the target The org gnu gdb mips fpu feature is currently required though it may be optional in a future version of GDB It should contain registers fO through 31 fcsr and fir The
156. the inferior from the beginning The inferior executes until either a breakpoint is encountered or the program exits In the latter case the output will include an exit code if the program has exited exceptionally GDB Command The corresponding GDB command is run Examples gdb break insert main done bkpt number 1 addr 0x0001072c file recursive2 c line 4 gdb exec run running gdb stopped reason breakpoint hit bkptno 1 frame func main args file recursive2 c fullname home foo bar recursive2 c line 4 gdb Program exited normally gdb exec run running gdb x 55 stopped reason exited normally gdb Chapter 24 The GDB MI Interface 255 Program exited exceptionally gdb exec run running gdb x 55 stopped reason exited exit code 01 gdb Another way the program can terminate is if it receives a signal such as SIGINT In this case GDB MI displays this gdb stopped reason exited signalled signal name SIGINT signal meaning Interrupt The exec step Command Synopsis exec step Resumes execution of the inferior program stopping when the beginning of the next source line is reached if the next source line is not a function call If it is stop at the first instruction of the called function GDB Command The corresponding GDB command is step Example Stepping into a function exec step runnin
157. the nearest symbol and an offset from it gdb info symbol 0x54320 initialize vx 396 in section text This is the opposite of the info address command You can use it to find out the name of a variable or a function given its address whatis arg Print the data type of arg which can be either an expression or a data type With no argument print the data type of the last value in the value history 144 Debugging with GDB If arg is an expression it is not actually evaluated and any side effecting oper ations such as assignments or function calls inside it do not take place If arg is a type name it may be the name of a type or typedef or for C code it may have the form class class name struct struct tag union union tag or enum enum tag See Section 8 1 Expressions page 75 ptype arg info types info types info scope ptype accepts the same arguments as whatis but prints a detailed description of the type instead of just the name of the type See Section 8 1 Expressions page 75 For example for this variable declaration struct complex double real double imag v the two commands give this output gdb whatis v type struct complex gdb ptype v type struct complex 1 double real double imag As with whatis using ptype without an argument refers to the type of the last value in the value history Sometimes programs use opaque data types or incomplete speci
158. the standard forms Some features are flags A stub which supports a flag feature should respond with a form response Other features require values and the stub should respond with an form response Appendix D GDB Remote Serial Protocol 34T Each feature has a default value which GDB will use if qSupported is not available or if the feature is not mentioned in the qSupported response The default values are fixed a stub is free to omit any feature responses that match the defaults Not all features can be probed but for those which can the probing mechanism is useful in some cases a stub s internal architecture may not allow the protocol layer to know some information about the underlying target in advance This is especially common in stubs which may be configured for multiple targets These are the currently defined stub features and their properties Feature Name Value Required Default Probe Allowed PacketSize Yes d No qXfer auxv read No xd Yes qXfer features read No Yes qXfer libraries read No Yes qXfer memory map read No isi Yes qXfer spu read No Yes qXfer spu write No idi Yes QPassSignals No d Yes These are the currently defined stub features in more detail PacketSize bytes The remote stub can accept packets up to at least bytes in length GDB will send packets up to this size for bulk transfers and will never send larger packet
159. to be evenhanded have been unfairly omitted from this list we would like to add your names So that they may not regard their many labors as thankless we particularly thank those who shepherded GDB through major releases Andrew Cagney releases 6 3 6 2 6 1 6 0 5 3 5 2 5 1 and 5 0 Jim Blandy release 4 18 Jason Molenda release 4 17 Stan Shebs release 4 14 Fred Fish releases 4 16 4 15 4 13 4 12 4 11 4 10 and 4 9 Stu Grossman and John Gilmore releases 4 8 4 7 4 6 4 5 and 4 4 John Gilmore releases 4 3 4 2 4 1 4 0 and 3 9 Jim Kingdon releases 3 5 3 4 and 3 3 and Randy Smith releases 3 2 3 1 and 3 0 Richard Stallman assisted at various times by Peter TerMaat Chris Hanson and Richard Mlynarik handled releases through 2 8 Michael Tiemann is the author of most of the GNU C support in GDB with significant additional contributions from Per Bothner and Daniel Berlin James Clark wrote the GNU C demangler Early work on C was by Peter TerMaat who also did much general update work leading to release 3 0 GDB uses the BFD subroutine library to examine multiple object file formats BFD was a joint project of David V Henkel Wallace Rich Pixley Steve Chamberlain and John Gilmore David Johnson wrote the original COFF support Pace Willison did the original support for encapsulated COFF Brent Benson of Harris Computer Systems contributed DWARF 2 support Adam de Boor and Bradley Davis con
160. to look up any more symbols qSymbol sym_name The target requests the value of symbol sym_name hex encoded GDB may provide the value by using the qSymbol sym_value sym_name message described below qSymbol sym_value sym_name Set the value of sym_name to sym value sym name hex encoded is the name of a symbol whose value the target has previously requested sym value hex is the value for symbol sym name If GDB cannot supply a value for sym name then this field will be empty Reply OK The target does not need to look up any more symbols qSymbol sym_name The target requests the value of a new symbol sym_name hex encoded GDB will continue to supply the values of symbols if available until the target ceases to request them QTDP QTFrame See Section D 6 Tracepoint Packets page 351 qThreadExtralInfo id Obtain a printable string description of a thread s attributes from the target OS id is a thread id in big endian hex This string may contain anything that the target OS thinks is interesting for GDB to tell the user about the thread The string is displayed in GDB s info threads display Some examples of possible thread extra info strings are Runnable or Blocked on Mutex Reply Appendix D GDB Remote Serial Protocol 349 QTStart QTStop QTinit QTro qTStatus XX Where XX is a hex encoding of ASCII data
161. treats it as an address 372 Debugging with GDB We do not fully describe the floating point operations here although this design can be extended in a clean way to handle floating point values they are not of immediate interest to the customer so we avoid describing them to save time float 0x01 Prefix for floating point bytecodes Not implemented yet add 0x02 a b a b Pop two integers from the stack and push their sum as an integer sub 0x03 a b a b Pop two integers from the stack subtract the top value from the next to top value and push the difference mul 0x04 a b a b Pop two integers from the stack multiply them and push the product on the stack Note that when one multiplies two n bit numbers yielding another n bit number it is irrelevant whether the numbers are signed or not the results are the same div signed 0x05 a b gt a b Pop two signed integers from the stack divide the next to top value by the top value and push the quotient If the divisor is zero terminate with an error div unsigned 0x06 a b a b Pop two unsigned integers from the stack divide the next to top value by the top value and push the quotient If the divisor is zero terminate with an error rem signed 0x07 a b a modulo b Pop two signed integers from the stack divide the next to top value by the top value and push the remainder If the divisor is zero terminate with an error rem unsign
162. type name or types that have been declared equivalent through typedef Range checking if turned on is done on mathematical operations Array indices are not checked since they are often used to index a pointer that is not itself an array 12 4 1 6 GDB and C The set print union and show print union commands apply to the union type When set to on any union that is inside a struct or class is also printed Otherwise it appears as ils 128 Debugging with GDB The 6 operator aids in the debugging of dynamic arrays formed with pointers and a memory allocation function See Section 8 1 Expressions page 75 12 4 1 7 GDB Features for C Some GDB commands are particularly useful with C and some are designed specifically for use with C Here is a summary breakpoint menus When you want a breakpoint in a function whose name is overloaded GDB breakpoint menus help you specify which function definition you want See Section 5 1 8 Breakpoint Menus page 51 rbreak regex Setting breakpoints using regular expressions is helpful for setting breakpoints on overloaded functions that are not members of any special classes See Sec tion 5 1 1 Setting Breakpoints page 38 catch throw catch catch Debug C exception handling using these commands See Section 5 1 3 Set ting Catchpoints page 45 ptype typename Print inheritance relationships as well as other information for type typename See Chapter 13 Examining
163. type safe linkage The default is on show print demangle Show whether C names are printed in mangled or demangled form set print asm demangle Set print asm demangle on Print C names in their source form rather than their mangled form even in assembler code printouts such as instruction disassemblies The default is off Show print asm demangle Show whether C names in assembly listings are printed in mangled or de mangled form set demangle style style Choose among several encoding schemes used by different compilers to represent C names The choices for style are currently auto Allow GDB to choose a decoding style by inspecting your program gnu Decode based on the GNU C compiler g encoding algorithm This is the default hp Decode based on the HP ANSI C aCC encoding algorithm Chapter 8 Examining Data 87 lucid Decode based on the Lucid C compiler 1cc encoding algorithm arm Decode using the algorithm in the C Annotated Reference Man ual Warning this setting alone is not sufficient to allow debugging cfront generated executables GDB would require further enhance ment to permit that If you omit style you will see a list of possible formats show demangle style Display the encoding style currently in use for decoding C symbols set print object set print object on When displaying a pointer to an object identify the actual derived type of the object rather than the declared ty
164. upper case equivalent otherwise it returns its argument Returns the character whose ordinal value is i Decrements the value in the variable v by one Returns the new value Decrements the value in the variable v by i Returns the new value Removes the element m from the set s Returns the new set Returns the floating point equivalent of the integer i Returns the index of the last member of a Increments the value in the variable v by one Returns the new value Increments the value in the variable v by i Returns the new value Adds the element m to the set s if it is not already there Returns the new set Returns the maximum value of the type t Returns the minimum value of the type t Returns boolean TRUE if i is an odd number Returns the ordinal value of its argument For example the ordinal value of a character is its ASCII value on machines supporting the ASCII character set x must be of an ordered type which include integral character and enumerated types Returns the size of its argument x can be a variable or a type Returns the integral part of r Returns the member of the type t whose ordinal value is i Warning Sets and their operations are not yet supported so GDB treats the use of procedures INCL and EXCL as an error 12 4 5 3 Constants GDB allows you to express the constants of Modula 2 in the following ways e Integer constants are simply a sequence of digits When used in an expressio
165. use in printf use output instead Here s a simple example of using these convenience variables for stepping through all the trace snapshots and printing some of their data gdb tfind start gdb while trace frame 1 gt output trace file gt printf line d tracepoint 7 d n trace line tracepoint gt tfind gt end Chapter 11 Debugging Programs That Use Overlays 113 11 Debugging Programs That Use Overlays If your program is too large to fit completely in your target system s memory you can some times use overlays to work around this problem GDB provides some support for debugging programs that use overlays 11 1 How Overlays Work Suppose you have a computer whose instruction address space is only 64 kilobytes long but which has much more memory which can be accessed by other means special instructions segment registers or memory management hardware for example Suppose further that you want to adapt a program which is larger than 64 kilobytes to run on this system One solution is to identify modules of your program which are relatively independent and need not call each other directly call these modules overlays Separate the overlays from the main program and place their machine code in the larger memory Place your main program in instruction memory but leave at least enough space there to hold the largest overlay as well Now to call a function located in an overlay you must first copy that
166. use it just as expressions in your program do Since one scope may be defined in another you can use repeatedly if necessary for example in an expression like scope1 scope2 name GDB also allows resolving name scope by reference to source files in both C and C debugging see Section 8 2 Program Variables page 76 In addition when used with HP s C compiler GDB supports calling virtual functions correctly printing out virtual bases of objects calling functions in a base subobject casting objects and invoking user defined operators 12 4 1 4 C and C Defaults If you allow GDB to set type and range checking automatically they both default to off whenever the working language changes to C or C This happens regardless of whether you or GDB selects the working language If you allow GDB to set the language automatically it recognizes source files whose names end with c C or cc etc and when GDB enters code compiled from one of these files it sets the working language to C or C See Section 12 1 3 Having GDB Infer the Source Language page 120 for further details 12 4 1 5 C and C Type and Range Checks By default when GDB parses C or C expressions type checking is not used However if you turn type checking on GDB considers two variables type equivalent if e The two variables are structured and have the same structure union or enumerated tag e The two variables have the same
167. use the quit command abbreviated q or type an end of file character usually Ctrl d If you do not supply expression GDB will terminate normally otherwise it will terminate using the result of expression as the error code An interrupt often Ctrl c does not exit from GDB but rather terminates the action of any GDB command that is in progress and returns to GDB command level It is safe to type the interrupt character at any time because GDB does not allow it to take effect until a time when it is safe If you have been using GDB to control an attached process or device you can release it with the detach command see Section 4 7 Debugging an Already running Process page 30 2 3 Shell Commands If you need to execute occasional shell commands during your debugging session there is no need to leave or suspend GDB you can just use the she11 command Shell command string Invoke a standard shell to execute command string If it exists the environment variable SHELL determines which shell to run Otherwise GDB uses the default shell bin sh on Unix systems COMMAND COM on MS DOS etc The utility make is often needed in development environments You do not have to use the shell command for this purpose in GDB make make args Execute the make program with the specified arguments This is equivalent to shell make make args 2 4 Logging Output You may want to save the output of GDB commands to a file There a
168. variables or nested functions does not currently work GDB does not support entering expressions printing values or similar features using Pascal syntax The Pascal specific command set print pascal static members controls whether static members of Pascal objects are displayed See Section 8 7 Print Settings page 82 12 4 5 Modula 2 The extensions made to GDB to support Modula 2 only support output from the GNU Modula 2 compiler which is currently being developed Other Modula 2 compilers are not currently supported and attempting to debug executables produced by them is most likely to give an error as GDB reads in the executable s symbol table 12 4 5 1 Operators Operators must be defined on values of specific types For instance is defined on numbers but not on structures Operators are often defined on groups of types For the purposes of Modula 2 the following definitions hold e Integral types consist of INTEGER CARDINAL and their subranges e Character types consist of CHAR and its subranges e Floating point types consist of REAL e Pointer types consist of anything declared as POINTER TO type e Scalar types consist of all of the above e Set types consist of SET and BITSET types e Boolean types consist of BOOLEAN The following operators are supported and appear in order of increasing precedence Function argument or array index separator Assignment The value of var value is value lt gt Le
169. was too long EINTR The call was interrupted by the user gettimeofday Synopsis int gettimeofday struct timeval tv void tz Request Fgettimeofday tvptr tzptr Return value On success 0 is returned 1 otherwise Errors EINVAL tz is a non NULL pointer EFAULT tvptr and or tzptr is an invalid pointer value isatty Synopsis int isatty int fd Request Fisatty fd Return value Returns 1 if fd refers to the GDB console 0 otherwise Errors EINTR The call was interrupted by the user Note that the isatty call is treated as a special case it returns 1 to the target if the file descriptor is attached to the GDB console 0 otherwise Implementing through system calls would require implementing ioctl and would be more complex than needed system Synopsis int system const char command Request Fsystem commandptr len Return value If len is zero the return value indicates whether a shell is available A zero return value indicates a shell is not available For non zero len the value re turned is 1 on error and the return status of the command otherwise Only the exit status of the command is returned which is extracted from the host s system return value by calling WEXITSTATUS retval In case bin sh could not be executed 127 is returned Errors EINTR The call was interrupted by the user Appendix D GDB Remote Serial Protocol 363 GDB takes over the full task of calling t
170. watchpoint maint space Control whether to display memory usage for each command If set to a nonzero value GDB will display how much memory each command took following the command s own output This can also be requested by invoking GDB with the statistics command line switch see Section 2 1 2 Mode Options page 13 maint time Control whether to display the execution time for each command If set to a nonzero value GDB will display how much time it took to execute each com mand following the command s own output This can also be requested by invoking GDB with the statistics command line switch see Section 2 1 2 Mode Options page 13 maint translate address section addr Find the symbol stored at the location specified by the address addr and an optional section name section If found GDB prints the name of the closest Appendix C Maintenance Commands 331 symbol and an offset from the symbol s location to the specified address This is similar to the info address command see Chapter 13 Symbols page 143 except that this command also allows to find symbols in other sections The following command is useful for non interactive invocations of GDB such as in the test suite set watchdog nsec Set the maximum number of seconds GDB will wait for the target operation to finish If this time expires GDB reports and error and the command is aborted show watchdog Show the current setting of the ta
171. will be loaded auto matically when the inferior begins execution you attach to an independently started inferior or when the dynamic linker informs GDB that a new library has been loaded If mode is off symbols must be loaded manually using the sharedlibrary command The default value is on If your program uses lots of shared libraries with debug info that takes large amounts of memory you can decrease the GDB memory footprint by prevent ing it from automatically loading the symbols from shared libraries To that 160 Debugging with GDB end type set auto solib add off before running the inferior then load each library whose debug symbols you do need with sharedlibrary regexp where regexp is a regular expression that matches the libraries whose symbols you want to be loaded show auto solib add Display the current autoloading mode To explicitly load shared library symbols use the sharedlibrary command info share info sharedlibrary Print the names of the shared libraries which are currently loaded Sharedlibrary regex share regex Load shared object library symbols for files matching a Unix regular expression As with files loaded automatically it only loads shared libraries required by your program for a core file or after typing run If regex is omitted all shared libraries required by your program are loaded nosharedlibrary Unload all shared object library symbols This discards all symbols that have been loaded from
172. write data into object remote request 350 write file i o system call sssseu 359 writing into corefiles 000 152 writing into executables 152 WOME values reri eRxE Ia asda a 76 X x examine memory ssseeseeessse 79 x command default address 72 packet sn 50h oa ness ee MO pb rbd 339 x examine and info line 72 x86 hardware debug registers 330 PIMclide ic oues to EM MPH RR edn 382 XML parser debugging 215 Y Debugging with GDB yank Oe ob Ptr ec ee gp d 310 yank last arg M or M _ 308 yank nth arg M C y i cles e ees 308 yank pop M y ssssssssles ee 311 yankiDng CONG soos Dwee ree ERR RO PPP PE 296 Z z packet ree RUE RHET RES 339 Z packets codec LRetERRI E AERIS 339 z0 paeket csncercteBerBerteeneRet pP ERO e oe 339 ZO packet ccceeddci pices se end I neebre be E dae 339 21 PaCkel s cime d posee mox RR d 340 Z1 packet zsteneicceiceau eda w RES 340 22 packet X 340 22 packet cue die aceiat esee peter 340 Z3 Daekel cese Eres tert pe d eet ed mud 340 23 paeket eise Dp toc ERROR Sid oleae wilh oa 340 ZA packet insit Dieta ane doses digi DEED Rude 340 24 packet creme opener ce y IRE RE 340 LQ OOO MR 201 Appendix H Index 419 The body of this manual is set in cmrl0 at 10 95pt with headings in cmb10 at 10 9
173. 06 Debugging with GDB gdb trace foo c 121 a source file and line number gdb trace 2 2 lines forward gdb trace my_function first source line of function gdb trace my_function EXACT start address of function gdb trace 0x2117c4 an address You can abbreviate trace as tr The convenience variable tpnum records the tracepoint number of the most recently set tracepoint delete tracepoint num Permanently delete one or more tracepoints With no argument the default is to delete all tracepoints Examples gdb delete trace 1 23 remove three tracepoints gdb delete trace remove all tracepoints You can abbreviate this command as del tr 10 1 2 Enable and Disable Tracepoints disable tracepoint num Disable tracepoint num or all tracepoints if no argument num is given A disabled tracepoint will have no effect during the next trace experiment but it is not forgotten You can re enable a disabled tracepoint using the enable tracepoint command enable tracepoint num Enable tracepoint num or all tracepoints The enabled tracepoints will become effective the next time a trace experiment is run 10 1 3 Tracepoint Passcounts passcount n num Set the passcount of a tracepoint The passcount is a way to automatically stop a trace experiment If a tracepoint s passcount is n then the trace exper iment will be automatically stopped on the n th time that tracepoint is hit If the tracepo
174. 18 1 6 Commands Specific to GNU Hurd Systems This subsection describes GDB commands specific to the GNU Hurd native debugging set signals set sigs This command toggles the state of inferior signal interception by GDB Mach exceptions such as breakpoint traps are not affected by this command sigs is a shorthand alias for signals show signals show sigs Show the current state of intercepting inferior s signals set signal thread set sigthread This command tells GDB which thread is the libc signal thread That thread is run when a signal is delivered to a running process set sigthread is the shorthand alias of set signal thread show signal thread show sigthread These two commands show which thread will run when the inferior is delivered a signal set stopped This commands tells GDB that the inferior process is stopped as with the SIGSTOP signal The stopped process can be continued by delivering a signal to it show stopped This command shows whether GDB thinks the debuggee is stopped set exceptions Use this command to turn off trapping of exceptions in the inferior When exception trapping is off neither breakpoints nor single stepping will work To restore the default set exception trapping on show exceptions Show the current state of trapping exceptions in the inferior set task pause This command toggles task suspension when GDB has control Setting it to on takes effect immediately and the task is suspended w
175. 2 and 3 above provided that you release the Modified Version under precisely this License with the Modified Version filling the role of the Document thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it In addition you must do these things in the Modified Version A Use in the Title Page and on the covers if any a title distinct from that of the Document and from those of previous versions which should if there were any be listed in the History section of the Document You may use the same title as a previous version if the original publisher of that version gives permission 396 N O Debugging with GDB List on the Title Page as authors one or more persons or entities responsible for authorship of the modifications in the Modified Version together with at least five of the principal authors of the Document all of its principal authors if it has fewer than five unless they release you from this requirement State on the Title page the name of the publisher of the Modified Version as the publisher Preserve all the copyright notices of the Document Add an appropriate copyright notice for your modifications adjacent to the other copyright notices Include immediately after the copyright notices a license notice giving the public permission to use the Modified Version under the terms of this License in the form shown in the Addendum below Preserve in that lic
176. 24 GDB MI page 233 25 1 What is an Annotation Annotations start with a newline character two control z characters and the name of the annotation If there is no additional information associated with this annotation the name of the annotation is followed immediately by a newline If there is additional information the name of the annotation is followed by a space the additional information and a newline The additional information cannot contain newline characters Any output not beginning with a newline and two control z characters denotes literal output from GDB Currently there is no need for GDB to output a newline followed by two control z characters but if there was such a need the annotations could be extended with an escape annotation which means those three characters as output 6 The annotation level which is specified using the annotate command line option see Section 2 1 2 Mode Options page 13 controls how much information GDB prints together with its prompt values of expressions source lines and other types of output Level 0 is for no annotations level 1 is for use when GDB is run as a subprocess of GNU Emacs level 3 is the maximum annotation suitable for programs that control GDB and level 2 annotations have been made obsolete see section Limitations of the Annotation Interface in GDB s Obsolete Annotations set annotate level The GDB command set annotate sets the lev
177. 5pt and examples in cmtt10 at 10 95pt cmti10 at 10 95pt cmb10 at 10 95pt and cmsl10 at 10 95pt are used for emphasis 420 Debugging with GDB
178. 60 set solib search p th isis eus 161 Set step mod6 coli mede Rip breed 54 set stop on solib events 160 set stopped Hurd command 188 set struct convention 202 set s bstit te path 2 2 1 e Ree es 71 set symbol reloading 146 set syn garbage limit MIPS remote 196 Set SySroot tied ocka vit none pe ped qe deed 160 set target charset 0 4 Suet ews PRA ess 96 set task Hurd commands 188 set tdesc filename 005 381 set thread Hurd command 189 set timeout denis EE alo reto e 196 set trace commands lees lesse 212 set tracepomt pocis prci ic d is eed RR RESO 105 set trust readonly sections 159 set tui active border mode 229 set tuiborder kind ons os 229 set tui border mode soo et n 229 set unwindonsignal sees lens 152 set variable eve ewm orem 149 set vVerbOBG seine ieee dee i Pi E 212 set watchdog kl ek eene ee ed Red 331 set width imer RR aD Y FPES 209 Set WHITE desde pe e e rd PP vh es 152 set mark C 0 oso ru hue ae 312 Set debug traps s cog ina anD 178 setting variables i 2p beerrpkR v b dade 149 setting watchpoints 00 43 DH perane ieda EaR Ea S HE ap RES PS 178 shestub kd ep ERE et HE REPAS 178 FS 1 TE 160 shared libraries 2 5 nent tdos 159 Debuggin
179. 65 info frame show the source language 121 INFO functions 220 26 REDE ure RS 145 info handle isvrse sioe NO upan FEES 56 info io registers AVR 202 info lin6 vore Re sare E HERES erect 72 info line and Objective C 129 info localS 2i e Re Eire aed 66 INFO macro vr uec eme ep br d ERU E e ee 101 info m i ess re na aiaa nina Ur ed er PNEU ea 93 info meminfo disse ase end aed pinsiad 183 info orik SDE e d o e IDEO he ERR 197 info pidliste 4 osirddunsreshiadecs sie ees 182 infOo DEOGin iie aoea Stale antares a 181 info program sopire p EnA EEEE DRAR heeds 37 info reglSt rS ecepto hasa riaria U iinit 90 info isCOpe e nce Eb a ee hate A e 144 info Selectors cse ep eer nr eh ew 146 info Serialcosveowegu pe ee ira e dert de 185 info BObololekeesq0eREP A E pennis Eie 22 info Slate eve rers PaE eraa EA 160 info shared library ee cots eens eter aretes 160 info Signals i ced chases eee rtk PRG derert 56 info SOlrCO ii hse aed ob pas ne eeed pres 145 info source show the source language 121 info SOWNrCOS lille ee eH EP A Y rey 145 info Spi oder ee bee boat anes de dE RI 205 info SUaCk dep D deg Edad poe 62 info symbOl 4 be bent egere 143 info Lt rget diessgedoac ee bond dui akan si 158 info terminal vae dy ek dese ded 29 info threads one HER RU RR a hes 32 Debugging with GDB info threads HP UX sisse 32 info CPs ss dened d
180. 67 Set AL Pm 27 Set arlm ssi exue asd eR EYE RE RRSRRRELUOS 192 set auto solib add ioo ee ets 159 Set backtraCce sso exse s Ra repii hg 63 set board address e rens 194 set breakpoint auto hw 42 set breakpoint pending 42 set breakpoints in many functions 39 set breakpoints on all functions 40 set can use hw watchpoints 43 set case sensitive 00008 143 Set Charset g cedes ee ey eee Er Rad 96 set check Tange i esd sd eae sehen e eh es 123 set check type ioo uk wheel 122 set coerce float to double 211 set comibase ii e agen R RR RA 184 set comlirq 2 ee ESAE REERR bees 184 413 Set com2base seco heec P GER RUE 184 set com2irq i ec n oradi n REPE Seed 184 set com3base ececc m ere RODPRS ERR 184 Set COMB ING o ensoceps aint Gece tbe 184 Set com4base ci iol Dek ede Eds 184 Set COMA i eee aa pee 184 Set complaints 22l14 desea dax ee 212 Set Conf I Merire ensien sewed eae ER RILUIUE 212 get Ccp aDbl s ill descr PREXG ar peter Eats 211 set cygwin exceptions sees 185 set debug c EE ep re Pe ara er d eee 213 set debug hppa oc 9 Rees eee rev Eg 204 set debug mipS s usus ur ree 204 set debug monitor eeesele 169 set debug nto debug 4 190 set debug file directory 162 set debugevents icici else ga b neri
181. 7 The annota tion level controls how much information GDB prints together with its prompt values of expressions source lines and other types of output Level 0 is the normal level 1 is for use when GDB is run as a subprocess of GNU Emacs level 3is the maximum annotation suitable for programs that control GDB and level 2 has been deprecated The annotation mechanism has largely been superseded by GDB MI see Chap ter 24 GDB MI page 233 args Change interpretation of command line so that arguments following the exe cutable file are passed as command line arguments to the inferior This option stops option processing baud bps b bps Set the line speed baud rate or bits per second of any serial interface used by GDB for remote debugging l timeout Set the timeout in seconds of any communication used by GDB for remote debugging Chapter 2 Getting In and Out of GDB 15 tty device t device Run using device for your program s standard input and output tui Activate the Text User Interface when starting The Text User Interface man ages several text windows on the terminal showing source assembly regis ters and GDB command outputs see Chapter 22 GDB Text User Interface page 225 Alternatively the Text User Interface can be enabled by invoking the program gdbtui Do not use this option if you run GDB from Emacs see Chapter 23 Using GDB under GNU Emacs page 231 interpreter interp Use the inter
182. 7 language Some Fortran compilers GNU Fortran 77 and Fortran 95 compilers among them append an underscore to the names of variables and functions When you debug programs com piled by those compilers you will need to refer to variables and functions with a trailing underscore 12 4 3 1 Fortran Operators and Expressions Operators must be defined on values of specific types For instance is defined on numbers but not on characters or other non arithmetic types Operators are often defined on groups of types X The exponentiation operator It raises the first operand to the power of the second one The range operator Normally used in the form of array low high to represent a section of array 12 4 3 2 Fortran Defaults Fortran symbols are usually case insensitive so GDB by default uses case insensitive matches for Fortran symbols You can change that with the set case insensitive command see Chapter 13 Symbols page 143 for the details 12 4 3 3 Special Fortran Commands GDB has some commands to support Fortran specific features such as displaying common blocks Chapter 12 Using GDB with Different Languages 131 info common common name This command prints the values contained in the Fortran COMMON block whose name is common name With no argument the names of all COMMON blocks visible at the current program location are printed 12 4 4 Pascal Debugging Pascal programs which use sets subranges file
183. 8 length 4 Symbol linebuffer is in static storage at address 0x150a18 length 4 Symbol linelength is in static storage at address 0x150aic length 4 Symbol p is a local variable in register esi length 4 Symbol pi is a local variable in register ebx length 4 Symbol nline is a local variable in register edx length 4 Symbol repeat is a local variable at frame offset 8 length 4 This command is especially useful for determining what data to collect during a trace experiment see Section 10 1 4 Tracepoint Actions page 107 info source Show information about the current source file that is the source file for the function containing the current point of execution e the name of the source file and the directory containing it e the directory it was compiled in e its length in lines e which programming language it is written in e whether the executable includes debugging information for that file and if so what format the information is in e g STABS Dwarf 2 etc and e whether the debugging information includes information about preproces sor macros info sources Print the names of all source files in your program for which there is debugging information organized into two lists files whose symbols have already been read and files whose symbols will be read when needed info functions Print the names and data types of all defined functions info functions regexp Print the names and data types of all def
184. 85ae6 Oxff0f6a70 Ox66063bca Ox11010b5c Ox8f659eff Oxf862ae69 Ox616bffd3 Oxi66ccf45 Oxa00ae278 Oxd70dd2ee 0x4e048354 0x3903b3c2 0xa7672661 Oxd06016f7 0x4969474d Ox3e6e77db Oxaedi6a4a Oxd9d65adc Ox40dfO0b66 Ox37d83bf0 Oxa9bcae53 Oxdebb9ec5 Ox47b2cf7f Ox30b5ffe9 Oxbdbdf21c Oxcabac28a 0x53b39330 Ox24b4a3a6 Oxbad03605 Oxcdd70693 0x54de5729 0x23d967bf Oxb3667a2e Oxc4614ab8 0x5d681b02 0x2a6f2b94 Oxb40bbe37 Oxc30c8eal Ox5a05df1b Ox2d02ef8d 3 unsigned char end crc crc amp Oxffffffff for end buf len buf lt end buf crc crc32 table crc buf amp Oxff crc gt gt 8 return crc amp Oxffffffff F This computation does not apply to the build ID method 15 3 Errors Reading Symbol Files While reading a symbol file GDB occasionally encounters problems such as symbol types it does not recognize or known bugs in compiler output By default GDB does not notify you of such problems since they are relatively common and primarily of interest to peo ple debugging compilers If you are interested in seeing information about ill constructed symbol tables you can either ask GDB to print only one message about each such type of problem no matter how many times the problem occurs or you can ask GDB to print more messages to see how many times the problems occur with the set complaints command see Section 19 7 Optional Warnings and Messages page 211 The messages currently p
185. 9 convert meta sic se rae ene pd er rre d s 299 copy backward word ssssssss 310 copy forward word sssuue 310 copy region as kill sess 310 core dump fil amp reels Rem 155 core dump file target 04 168 COre fil cise ach age pe pma ne eae bie 156 crash Of debugger 2 rere Rr erg 291 CRC of memory block remote request 343 Sid EHI 202 CRIS mode leni be RIFex e eb Ed 202 CRIS VeESIOLR cis pessan sede ra Rees esee 202 ctrl c message in file i o protocol 356 Ctrl o operate and get next 19 current directory nn cue eR PEE eR ens 71 current stack frame 0 e ee eee 62 current thread s 2222 ne ended seekers 31 current thread remote request 342 CWQ sisse Go RE AER SR eral e Te Da ee RAS 71 Cygwin DLL debugging 185 Cygwin specific commands 185 D d delete iLcicebiee tesir ren erona eY 47 d SingleKey TUI key 00 0044 227 d packet e 22a ener canes eno e Pad des 335 Di packet 2 vods oblati qed beoe ii aede 335 data breakpoints ons eri pee oodles 34 data manipulation in GDB MI 266 dead names GNU Hurd 00 189 debug formats and Ct 00 00 126 debug link sections 004 162 debug remote protocol 0 214 debug Chaos 2 4 ne eee ime 194 debugger crash
186. B has control Setting it to on takes effect immediately and the current thread is suspended whenever GDB gets control Setting it to off will take effect the next time the inferior is continued Normally this command has no effect since when GDB has control the whole task is suspended However if you used set task pause off see above this command comes in handy to suspend only the current thread Show thread pause This command shows the state of current thread suspension set thread run This command sets whether the current thread is allowed to run show thread run Show whether the current thread is allowed to run Set thread detach suspend count This command sets the suspend count GDB will leave on a thread when de taching This number is relative to the suspend count found by GDB when it 190 Debugging with GDB notices the thread use set thread takeover suspend count to force it to an absolute value Show thread detach suspend count Show the suspend count GDB will leave on the thread when detaching Set thread exception port Set thread excp Set the thread exception port to which to forward exceptions This overrides the port set by set task exception port see above set thread excp is the shorthand alias set thread takeover suspend count Normally GDB s thread suspend counts are relative to the value GDB finds when it notices each thread This command changes the suspend counts to be absolute instead set threa
187. B reads the first argument that does not have an associated option flag as equivalent to the se option followed by that argument and the second argument that does not have an associated option flag if any as equivalent to the c p option followed by that argument If the second argument begins with a decimal digit GDB will first attempt to attach to it as a process and if that fails attempt to open it as a corefile If you have a corefile whose name begins with a digit you can prevent GDB from treating it as a pid by prefixing it with e g 12345 If GDB has not been configured to included core file support such as for most embedded targets then it will complain about a second argument and ignore it Many options have both long and short forms both are shown in the following list GDB also recognizes the long forms if you truncate them so long as enough of the option is present to be unambiguous If you prefer you can flag option arguments with rather than though we illustrate the more usual convention symbols file s file Read symbol table from file file exec file e file Use file file as the executable file to execute when appropriate and for examining pure data in conjunction with a core dump se file Read symbol table from file file and use it as the executable file core file c file Use file file as a core dump to examine c number pid number p number C
188. By default this variable is set to off input meta If set to on Readline will enable eight bit input it will not clear the eighth bit in the characters it reads regardless of what the terminal claims it can support The default value is off The name meta flag is a synonym for this variable isearch terminators The string of characters that should terminate an incremental search without subsequently executing the character as a command see Section 27 2 5 Searching page 297 If this variable has not been given a value the characters and C J will terminate an incremental search keymap Sets Readline s idea of the current keymap for key binding com mands Acceptable keymap names are emacs emacs standard emacs meta emacs ctlx vi vi move vi command and vi insert vi is equivalent to vi command emacs is equivalent to emacs standard The default value is emacs The value of the editing mode variable also affects the default keymap mark directories If set to on completed directory names have a slash appended The default is on mark modified lines This variable when set to on causes Readline to display an as terisk at the start of history lines which have been modified This variable is off by default mark symlinked directories If set to on completed names which are symbolic links to di rectories have a slash appended subject to the value of mark director
189. DB command is until Example exec until recursive2 c 6 running gdb x 55 stopped reason location reached frame func main args file recursive2 c fullname home foo bar recursive2 c line 6 gdb 24 13 GDB MI Stack Manipulation Commands The stack info frame Command Synopsis stack info frame Get info on the selected frame Chapter 24 The GDB MI Interface 257 GDB Command The corresponding GDB command is info frame or frame without arguments Example gdb stack info frame done frame level 1 addr 0x0001076c func callee3 file devo gdb testsuite gdb mi basics c fullname home foo bar devo gdb testsuite gdb mi basics c line 17 gdb The stack info depth Command Synopsis stack info depth max depth Return the depth of the stack If the integer argument max depth is specified do not count beyond max depth frames GDB Command There s no equivalent GDB command Example For a stack with frame levels 0 through 11 gdb stack info depth done depth 12 gdb stack info depth 4 done depth 4 gdb stack info depth 12 done depth 12 gdb stack info depth 11 done depth 11 gdb stack info depth 13 done depth 12 gdb The stack list arguments Command Synopsis stack list arguments show values low frame high frame Display a list of the arguments for the frames between low frame and high frame i
190. DB command names may always be truncated if that abbreviation is unambiguous Other possible command abbreviations are listed in the documentation for individual com mands In some cases even ambiguous abbreviations are allowed for example s is specially defined as equivalent to step even though there are other commands whose names start with s You can test abbreviations by using them as arguments to the help command A blank line as input to GDB typing just RET means to repeat the previous command Certain commands for example run will not repeat this way these are commands whose unintentional repetition might cause trouble and which you are unlikely to want to repeat User defined commands can disable this feature see Section 20 1 Define page 217 The list and x commands when you repeat them with RET construct new arguments rather than repeating exactly as typed This permits easy scanning of source or memory GDB can also use in another way to partition lengthy output in a way similar to the common utility more see Section 19 4 Screen Size page 209 Since it is easy to press one too many in this situation GDB disables command repetition after any command that generates this sort of display Any text from a to the end of the line is a comment it does nothing This is useful mainly in command files see Section 20 3 Command Files page 219 The Ctrl o binding is useful for repeating a complex sequence of commands Thi
191. Debugging with GDB The GNU Source Level Debugger Ninth Edition for GDB version 6 7 50 20071011 Richard Stallman Roland Pesch Stan Shebs et al Send bugs and comments on GDB to bug gdb gnu org Debugging with GDB TEXinfo 2004 02 19 09 Copyright 1988 1989 1990 1991 1992 1993 1994 1995 1996 1998 1999 2000 2001 2002 2003 2004 2006 Free Software Foundation Inc Published by the Free Software Foundation 51 Franklin Street Fifth Floor Boston MA 02110 1301 USA ISBN 1 882114 77 9 Permission is granted to copy distribute and or modify this document under the terms of the GNU Free Documentation License Version 1 1 or any later version published by the Free Software Foundation with the Invariant Sections being Free Software and Free Software Needs Free Documentation with the Front Cover Texts being A GNU Manual and with the Back Cover Texts as in a below a The FSF s Back Cover Text is You are free to copy and modify this GNU Man ual Buying copies from GNU Press supports the FSF in developing GNU and promoting software freedom This edition of the GDB manual is dedicated to the memory of Fred Fish Fred was a long standing contributor to GDB and to Free software in general We will miss him Table of Contents Summary Of GOB 26355 hd55 4 Reds sesebeeesdines 1 Free Sottwar 2 icc2 420400008 cag ead TAE end d d Padded he cata ded ds 1 Free Software Needs Free Documentation
192. EXTENT PERMITTED BY APPLI CABLE LAW EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPY RIGHT HOLDERS AND OR OTHER PARTIES PROVIDE THE PROGRAM AS IS WITHOUT WARRANTY OF ANY KIND EITHER EXPRESSED OR IMPLIED INCLUDING BUT NOT LIMITED TO THE IMPLIED WARRANTIES OF MER CHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU SHOULD THE PROGRAM PROVE DEFECTIVE YOU ASSUME THE COST OF ALL NECESSARY SERVICING REPAIR OR CORRECTION IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER OR ANY OTHER PARTY WHO MAY MODIFY AND OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE BE LIABLE TO YOU FOR DAMAGES INCLUDING ANY GENERAL SPECIAL INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES END OF TERMS AND CONDITIONS 392 Debugging with GDB How to Apply These Terms to Your New Programs If you develop a new program and you want it to be of the greatest possible use to the public the best way to achieve this is to make it free software which everyone can redistribute and change under these terms To do so attach the followin
193. FC DMA status Shows all pending commands in the MFC DMA queue For each entry opcode tag class IDs effective and local store addresses and transfer size are shown info spu proxydma Display MFC Proxy DMA status Shows all pending commands in the MFC Proxy DMA queue For each entry opcode tag class IDs effective and local store addresses and transfer size are shown 206 Debugging with GDB Chapter 19 Controlling GDB 207 19 Controlling GDB You can alter the way GDB interacts with you by using the set command For commands controlling how GDB displays data see Section 8 7 Print Settings page 82 Other settings are described here 19 1 Prompt GDB indicates its readiness to read a command by printing a string called the prompt This string is normally gdb You can change the prompt string with the set prompt command For instance when debugging GDB with GDB it is useful to change the prompt in one of the GDB sessions so that you can always tell which one you are talking to Note set prompt does not add a space for you after the prompt you set This allows you to set a prompt which ends in a space or a prompt that does not set prompt newprompt Directs GDB to use newprompt as its prompt string henceforth show prompt Prints a line of the form Gdb s prompt is your prompt 19 2 Command Editing GDB reads its input commands via the Readline interface This GNU library provides consis tent behavior for pro
194. GCC in Using the GNU Compiler Collection GCC 12 4 1 1 C and C Operators Operators must be defined on values of specific types For instance is defined on numbers but not on structures Operators are often defined on groups of types For the purposes of C and C the following definitions hold e Integral types include int with any of its storage class specifiers char enum and for C bool e Floating point types include float double and long double if supported by the target platform e Pointer types include all types defined as type e Scalar types include all of the above The following operators are supported They are listed here in order of increasing prece dence The comma or sequencing operator Expressions in a comma separated list are evaluated from left to right with the result of the entire expression being the last expression evaluated Assignment The value of an assignment expression is the value assigned De fined on scalar types op Used in an expression of the form a op b and translated to a a op b op and have the same precedence op is any one of the operators amp lt lt gt gt 73 5 The ternary operator a b c can be thought of as if a then b else c a should be of an integral type Logical oR Defined on integral types amp amp Logical AND Defined on integral types Bitwise OR Defined on integral types Bitwise exclusive OR Defi
195. GDB configure also has several other options not listed here See Info file configure info node What Configure Does for a full explanation of configure configure help prefix dir exec prefix dir srcdir dirname norecursion rm target target host You may introduce options with a single rather than if you prefer but you may abbreviate option names if you use help Display a quick summary of how to invoke configure prefix dir Configure the source to install programs and files under directory dir exec prefix dir Configure the source to install programs under directory dir Appendix B Installing GDB 325 srcdir dirname Warning using this option requires GNU make or another make that imple ments the VPATH feature Use this option to make configurations in directories separate from the GDB source directories Among other things you can use this to build or main tain several configurations simultaneously in separate directories configure writes configuration specific files in the current directory but arranges for them to use the source in the directory dirname configure creates directories un der the working directory in parallel to the source directories below dirname norecursion Configure only the directory level where configure is executed do not prop agate configuration to subdirectori
196. IPS target syscall DSO bes pena erbe rd end SySIDfO e ad escent bu eue eR be deserun system calls and thread breakpoints system root alternate 000 system file i o system call 0 T w packet iai uere pucr ebur ae ipu ue T Packets 2 2 iti eren wee once eee ie elev T packet reply iie oahu esas tretia eee ee tab insert M TAB cccceee eens Target aneia ee le ehdctuete a top a al end dorsi stus target architecture 2 eee eee target array asc eda peara aa hace obeys target byte order 000 05 target character set s eese target db g ida widened ae aed target ddb pore i sb eh target debugging info 0 target descriptions 08 target descriptions ARM features target descriptions inclusion target descriptions M68K features target descriptions MIPS features 155 157 Debugging with GDB target descriptions predefined types 384 target descriptions standard features 385 target descriptions XML format 382 target dink32 lioc d een 199 target jb8g lic eco up n EED EEs 197 target lsi port luisse d eene 195 target mS 2r eee vies Mawes epa p aa needs 194 target m32rsdi iioosslddacaldigase ea 194 target mips port x ugeet terse ER 195 target opbOn
197. ISO C90 compiler GDB is written in ISO C90 It should be buildable with any working C90 compiler e g GCC Tools Packages Optional for Building GDB Expat GDB can use the Expat XML parsing library This library may be included with your operating system distribution if it is not you can get the latest version from http expat sourceforge net The configure script will search for this library in several standard locations if it is installed in an unusual path you can use the with libexpat prefix option to specify its location Expat is used for remote protocol memory maps see Section D 11 Memory Map Format page 367 and for target descriptions see Appendix F Target Descriptions page 381 B 2 Invoking the GDB configure Script GDB comes with a configure script that automates the process of preparing GDB for installation you can then use make to build the gdb program The GDB distribution includes all the source code you need for GDB in a single directory whose name is usually composed by appending the version number to gdb For example the GDB version 6 7 50 20071011 distribution is in the gdb 6 7 50_20071011 directory That directory contains gdb 6 7 50 20071011 configure and supporting files script for configuring GDB and all its supporting libraries gdb 6 7 50_20071011 gdb the source specific to GDB itself gdb 6 7 50_20071011 bfd source for the Binary File Descriptor library
198. L gives you the freedom to copy or adapt a licensed program but every person getting a copy also gets with it the freedom to modify that copy which means that they must get access to the source code and the freedom to distribute further copies Typical software companies use copyrights to limit your freedoms the Free Software Foundation uses the GPL to preserve these freedoms Fundamentally the General Public License is a license which says that you have these freedoms and that you cannot take these freedoms away from anyone else Free Software Needs Free Documentation The biggest deficiency in the free software community today is not in the software it is the lack of good free documentation that we can include with the free software Many of our most important programs do not come with free reference manuals and free introductory texts Documentation is an essential part of any software package when an important free software package does not come with a free manual and a free tutorial that is a major gap We have many such gaps today 2 Debugging with GDB Consider Perl for instance The tutorial manuals that people normally use are non free How did this come about Because the authors of those manuals published them with restrictive terms no copying no modification source files not available which exclude them from the free software world That wasn t the first time this sort of thing happened and it was far from the last
199. MAX 4294967295 LONG MIN 9223372036854775808 LONG MAX 9223372036854775807 ULONG MAX 18446744073709551615 D 9 10 File I O Examples Example sequence of a write call file descriptor 3 buffer is at target address 0x1234 6 bytes should be written Fwrite 3 1234 6 request memory read from target m1234 6 XXXXXX return 6 bytes written F6 Example sequence of a read call file descriptor 3 buffer is at target address 0x1234 6 bytes should be read Fread 3 1234 6 request memory write to target X1234 6 XXXXXX return 6 bytes read F6 Example sequence of a read call call fails on the host due to invalid file descriptor EBADF Fread 3 1234 6 F 1 9 Example sequence of a read call user presses Ctrl c before syscall on host is called Fread 3 1234 6 F 1 4 C TO2 Example sequence of a read call user presses Ctrl c after syscall on host is called lt Fread 3 1234 6 X1234 6 XXXXXX lt T02 D 10 Library List Format On some platforms a dynamic loader e g 1d so runs in the same process as your appli cation to manage libraries In this case GDB can use the loader s symbol table and normal memory operations to maintain a list of shared libraries On other platforms the operating system manages loaded libraries GDB can not retrieve the list of currently loaded libraries Appendix D GDB Remote Serial Protocol 367 through memory operations so it uses the
200. NG gt A breakpoint with several locations will have lt MULTIPLE gt in this field see below for details What Where the breakpoint is in the source for your program as a file and line number For a pending breakpoint the original string passed to the breakpoint command will be listed as it cannot be resolved until the appropriate shared library is loaded in the future If a breakpoint is conditional info break shows the condition on the line fol lowing the affected breakpoint breakpoint commands if any are listed after that A pending breakpoint is allowed to have a condition specified for it The condition is not parsed for validity until a shared library is loaded that allows the pending breakpoint to resolve to a valid location Chapter 5 Stopping and Continuing 41 info break with a breakpoint number n as argument lists only that break point The convenience variable _ and the default examining address for the x command are set to the address of the last breakpoint listed see Section 8 5 Examining Memory page 79 info break displays a count of the number of times the breakpoint has been hit This is especially useful in conjunction with the ignore command You can ignore a large number of breakpoint hits look at the breakpoint info to see how many times the breakpoint was hit and then run again ignoring one less than that number This will get you quickly to the last hit of that breakpoint GDB allows you to
201. Occasionally you may wish to produce a core file of the program you are debugging in order to preserve a snapshot of its state GDB has a special command for that generate core file file gcore file Produce a core dump of the inferior process The optional argument file specifies the file name where to put the core dump If not specified the file name defaults to core pid where pid is the inferior process ID Note that this command is implemented only for some systems as of this writing GNU Linux FreeBSD Solaris Unixware and 390 8 17 Character Sets If the program you are debugging uses a different character set to represent characters and strings than the one GDB uses itself GDB can automatically translate between the character 96 Debugging with GDB sets for you The character set GDB uses we call the host character set the one the inferior program uses we call the target character set For example if you are running GDB on a GNU Linux system which uses the ISO Latin 1 character set but you are using GDB s remote protocol see Chapter 17 Remote Debug ging page 171 to debug a program running on an IBM mainframe which uses the EBCDIC character set then the host character set is Latin 1 and the target character set is EBCDIC If you give GDB the command set target charset EBCDIC US then GDB translates be tween EBCDIC and Latin 1 as you print character or string values or use character and string literals
202. Printing Source LINES eeds sires tad cece eee eee lesen 67 G2 Editing Source Files id gue e idee e ERU EET 68 1 2 1 Choosing your Editor siose esiisasid pie aniei i a 69 1 9 Searching Source Elles us ie a maha ai ed 69 7 4 Specifying Source Directories 00 00 cece iile eelsesn 69 7 5 Source and Machine Code 0 00 c cece eee tenes 72 Examining Data o y 9n 75 8 l EXpressiOnS 4 crescon ut REDE ERR eke ta edenda 75 8 2 Program Variables iu suas epe npe a gebe Ra de 16 8 3 Artificial ATTIV Sepse ei singani ia pia dio aain hh 77 8 4 Output Formats osei tie Ped tee bae eee 78 8 5 Examining Memory estes Renee oe kee o poer dose 79 8 6 Automatic Display 000 eee tee ee 81 8 7 Print Settings uc hs deed xe Ran dew ea ead eae dds 82 8 8 Value History tec ad dad eben dd kee EUR RR nt ea E eit 88 8 9 Convenience Variables 000 cece eee cent es 88 8 10 Registers i icexever mikes reri gourex ke ER Meee gee Shae Hebe 90 8 11 Floating Point Hardware 00 0 esses 91 8 12 Mector UTI Ludo dee ste tret ertt eto ne dog eres 92 8 13 Operating System Auxiliary Information 92 8 14 Memory Region Attributes sselsese essere 92 S A Attributes aesa ecce oe orbe EE eee aden gees 93 8 14 1 1 Memory Access Mode ssluseseiiesesse 93 8 14 1 2 Memory Access Size 0 ee eee eee eee 94 8 14 1 3 Data Cache 22242 c cece re ate bres 94 8 14 2 Memory Access Chec
203. The GDB Agent Expression Mechanism 379 all four asymmetrical comparison operators For example x lt y is x gt y which is y lt x Why do you have 1og not Why do you have ext Why do you have zero ext These are all easily synthesized from other instructions but I expect them to be used frequently and they re simple so I include them to keep bytecode strings short log not is equivalent to const8 0 equal it s used in half the relational oper ators ext n is equivalent to const8 s n lsh const8 s n rsh signed where s is the size of the stack elements it follows refm and reg bytecodes when the value should be signed See the next bulleted item zero ext n is equivalent to constm mask log and it s used whenever we push the value of a register because we can t assume the upper bits of the register aren t garbage Why not have sign extending variants of the ref operators Because that would double the number of ref operators and we need the ext bytecode anyway for accessing bitfields Why not have constant address variants of the ref operators Because that would double the number of ref operators again and const32 address ref32 is only one byte longer Why do the refn operators have to support unaligned fetches GDB will generate bytecode that fetches multi byte values at unaligned ad dresses whenever the executable s debugging information tells it to Further more GDB does not know the value the po
204. Tracepoint Passcounts page 106 or if the trace buffer becomes full tstatus This command displays the status of the current trace data collection Here is an example of the commands we described so far Chapter 10 Tracepoints 109 gdb trace gdb c test gdb actions Enter actions for tracepoint 1 one per line gt collect regs locals args gt while stepping 11 gt collect regs gt end gt end gdb tstart time passes gdb tstop 10 2 Using the Collected Data After the tracepoint experiment ends you use GDB commands for examining the trace data The basic idea is that each tracepoint collects a trace snapshot every time it is hit and another snapshot every time it single steps All these snapshots are consecutively numbered from zero and go into a buffer and you can examine them later The way you examine them is to focus on a specific trace snapshot When the remote stub is focused on a trace snapshot it will respond to all GDB requests for memory and registers by reading from the buffer which belongs to that snapshot rather than from real memory or registers of the program being debugged This means that all GDB commands print info registers backtrace etc will behave as if we were currently debugging the program state as it was when the tracepoint occurred Any requests for data that are not in the buffer will fail 10 2 1 tfindn The basic command for selecting a trace snapshot from the buffer is
205. Ts es caida sunseaugus POLT Rx digs eb dca dae RS 183 TE sc HR 220 INOPS is pcan siu E UR ER es aed ad PLES 49 ignore count of breakpoint 49 INCLUDE RDB reacer eisiaa sn ERE a 191 incomplete type 222 hr RE RR 144 408 indentation in structure display 85 inferior debugging info 0 213 inferior functions calling 152 inferior 6by oe cassa epPRTEP PRESE ES 30 infinite recursion in user defined commands 218 INE Osta cd faa 22 info addKESS ise se bead eerti ikeen ER EE dln ee 143 info all r gisterS i 993 aol 90 info args wedded bp esi eere tex ra E Rit onda 66 IFO AUX s 26 ids ded e RE Irem ter E ROT RE 92 info breakpoints 2 i dur ee per RD 40 info catchiclolcics6eseestre e e eee aie eee 66 info checkpoints ace deed br dene 35 info classes eest ieies eR Y Eee PIE En 145 info colon ed er 9e Pad e ee Pres 131 info cODylng I 22cm odes ebd 23 info dcache essc Ree Lite E Pent ws 99 info display nin hIe REPERI eden 82 info QVM 5 5 43e a de Ru ble easet 185 ANE OO Sis uw riens ep aee umi dudum d bun ales 183 info extensiOHs8 2 x 6reneeh hale arais 121 info f info frame isseeeee e RR EERAS 65 info fi1l6S 6 wm e te beg 158 info float osse eo oda eoe pea pe r iaoei RR 91 info for known object files 0 329 info Forks aooo et Des exon e a s 34 INFO fral g c bhi bod RP nr aoe Re
206. UR RR Rot 219 Source annotation da d RR RENT 290 source file and line of a symbol 83 source line and its code address T2 source path 24 iroerresro dace deswec RES D set 69 SDpalGo essente ted TEn EETA der EATE RES 178 Sparc Stub 6 sos tat WP E ie Salad I ns 178 sparcl stu b 6 s ls DeesteecehrvpbaesbeRirdu 178 SDafclels sumen od Tobi ot diee das 199 DParchite 2 24 apu ntred ie tetas headsets 178 Special Fortran commands suus 130 SPP eects redd E RR E Ea TRIP RUREPUREPI 197 PU 5 cys cise enii aunts ape sled aan eae gaan 204 SSE registers x86 iri crierii ci ehi pen eee 91 stack frame sisse pna tri RAREN ERRES 61 stack on Alpha n piii eiim ae dad paueiuebo 203 stack on MIPS ccr REESE d 203 stack pointer register 90 stacking bLargels 5 o er o9 ie gniiis 167 standard registers 00 90 SUAEU S oL ev eese tre antenna OU Ra tee Wis ade ees 27 start a new trace experiment 108 start kbd macro C x Q sss 311 SCAT GUNG Pm 26 starting annotation 289 startup code and backtrace 63 stat file i o system call ususe 361 static members of C objects 8T static members of Pascal objects 87 status of trace data collection 108 status output in GDB MI 000 235 Stepessiederiv Reg ua pie ne aN iaaa ded 53 Stepil e
207. You can also print the contents of variables declared using these type This section gives a number of simple source code examples together with sample GDB sessions The first example contains the following section of code VAR s SET OF CHAR r 20 40 and you can request GDB to interrogate the type and value of r and s gdb print s PA iat n zy gdb ptype s SET OF CHAR gdb print r 21 gdb ptype r 20 40 Likewise if your source code declares s as VAR s SET A Z then you may query the type of s by gdb ptype s type SET A Z7 Note that at present you cannot interactively manipulate set expressions using the debugger The following example shows how you might declare an array in Modula 2 and how you can interact with GDB to print its type and contents VAR S ARRAY 10 10 OF CHAR gdb ptype s ARRAY 10 10 OF CHAR Note that the array handling is not yet complete and although the type is printed correctly expression handling still assumes that all arrays have a lower bound of zero and not 10 as in the example above Unbounded arrays are also not yet recognized in GDB Here are some more type related Modula 2 examples Chapter 12 Using GDB with Different Languages 135 TYPE colour blue red yellow green t blue yellow VAR src 5 BEGIN S blue The GDB interaction shows how you can query the data type and value of a variable gdb print s 1 blue
208. a length Since Ada is case insensitive the debugger normally maps identifiers you type to lower case The GNAT compiler uses upper case characters for some of its internal identifiers which are normally of no interest to users For the rare occasions when you actually have to look at them enclose them in angle brackets to avoid the lower case mapping For example gdb print JMPBUF SAVE 0 Printing an object of class wide type or dereferencing an access to class wide value will display all the components of the object s specific type as indicated by its run time tag Likewise component selection on such a value will operate on the specific type of the object 12 4 6 4 Stopping at the Very Beginning It is sometimes necessary to debug the program during elaboration and before reaching the main procedure As defined in the Ada Reference Manual the elaboration code is invoked from a procedure called adainit To run your program up to the beginning of elaboration simply use the following two commands tbreak adainit and run 12 4 6 5 Known Peculiarities of Ada Mode Besides the omissions listed previously see Section 12 4 6 2 Omissions from Ada page 138 we know of several problems with and limitations of Ada mode in GDB some of which will be fixed with planned future releases of the debugger and the GNU Ada compiler Currently the debugger has insufficient information to determine whether certain point ers represent poin
209. a aren ek hoa 201 18 3 11 Atmel AVE i uie erem et eb rere 201 18 9 12 ORIS t4024o208ab he cahdbdan tian Ha kaeeeacnd tace 202 18 3 13 Renesas Super H 0 gaitada eee eee 202 18 4 Architectures 0 ccc cece aE a a a 202 18 4 1 x86 Architecture specific Issues 0 0000 202 182 2 A2OK Lotus bata h ORE ER edd dere bole n 203 vi Debugging with GDB 18 4 3 Alpha cet MERECE 203 DS AAS MIE S oS ck ecto th tad fed ipo Sur usibus tid 203 ISAS HPPA 225 uci p Ede aed an EUER ata das 204 18 4 6 Cell Broadband Engine SPU architecture 204 19 Controlling GDB 2222 on e oe s 207 19 1 Prompte peraan ote eee ee Ree os dee eae oe dae 207 19 2 Command Editing 0 00 cee 207 19 3 Command History 0 0 c eee eee eee eee eee 207 IQA Sereen SIZE eb bes oS GE eee pd the eh es n 209 19 5 UNUM BOTS scusa e o td rie i aus he bound a ca ala ud 210 19 6 Configuring the Current ABI 00 0000s eee 210 19 7 Optional Warnings and Messages 0000 eee eee 211 19 8 Optional Messages about Internal Happenings 213 20 Canned Sequences of Commands 217 20 1 User defined Commands 0000 eee cece eee eee 217 20 2 User defined Command Hooks 000 eens 218 20 8 Command Files 0 0 0 0 ccc ccc cect s 219 20 4 Commands for Controlled Output 0000065 220 21 Command Interpreters 223 22
210. a program accesses some data or instruc tion address that is assigned to the debug registers For the data addresses DSU facilitates the watch command However the hardware breakpoint registers can only take two data watchpoints and both watchpoints must be the same kind For example you can set two watchpoints with watch commands two with rwatch commands or two with awatch com mands but you cannot set one watchpoint with one command and the other with a different command GDB will reject the command if you try to mix watchpoints Delete or disable unused watchpoint commands before setting new ones If you call a function interactively using print or call any watchpoints you have set will be inactive until GDB reaches another kind of breakpoint or the call completes GDB automatically deletes watchpoints that watch local automatic variables or expres sions that involve such variables when they go out of scope that is when the execution leaves the block in which these variables were defined In particular when the program being debugged terminates all local variables go out of scope and so only watchpoints Chapter 5 Stopping and Continuing 45 that watch global variables remain set If you rerun the program you will need to set all such watchpoints again One way of doing that would be to set a code breakpoint at the entry to the main function and when it breaks set all the watchpoints In multi threaded programs watchpoints wi
211. aaa 168 help user defined uc os ewes ui 218 heuristic fence post Alpha MIPS 203 history events i0edoasden iee aai RE TOES 315 history expansion 000000 315 history expansion turn on off 208 history file to iscvscsssvesw turer t iaei heu 208 history n mbet essi prr hpne EE Ene EmN 88 history of values printed by GDB 88 l story 8126 29 0x mre tw hence ERE PED Gee edes 208 history s bstit tion 2 2 ee M eb ERR Yu 208 history preserve point sess 300 history search backward 308 history search forward 308 HISTSIZE environment variable 208 NOOK dm 218 hooKDpOSt i vhi Reeder aE QUSE 218 hooks for commands 0000 000 218 hooks post command osses iesi sriirerisiosas 218 hooks pre command 00 00e sees 218 horizontal scroll mode 300 host character seti 24a ce hebben ER edu 95 how many arguments user defined commands rr 217 HPPA Support 2 s DERRRRR Re RES 204 librae ver eek bees er EE ede 198 lwatch 2 br RR Ea RS PR E ae 198 I i nfo onou i e EE DEREN Bw d d 22 3 packets deest teats dees etc Rn 336 E packet x i ek repe thu er dr ic enn 336 PORE MT 29 I O registers Atmel AVR 0 202 1980 iuo sro ECL Reda Er P ees 178 1386 stub c lee iled prag elem peg adele 178 IBM1047 character set 2 0000 97 WY
212. able being set to off A great deal of run time behavior is changeable with the following variables bell style Controls what happens when Readline wants to ring the termi nal bell If set to none Readline never rings the bell If set to Chapter 27 Command Line Editing 299 visible Readline uses a visible bell if one is available If set to audible the default Readline attempts to ring the terminal s bell bind tty special chars If set to on Readline attempts to bind the control characters treated specially by the kernel s terminal driver to their Readline equivalents comment begin The string to insert at the beginning of the line when the insert comment command is executed The default value is st completion ignore case If set to on Readline performs filename matching and completion in a case insensitive fashion The default value is off completion query items The number of possible completions that determines when the user is asked whether the list of possibilities should be displayed If the number of possible completions is greater than this value Readline will ask the user whether or not he wishes to view them otherwise they are simply listed This variable must be set to an integer value greater than or equal to 0 A negative value means Readline should never ask The default limit is 100 convert meta If set to on Readline will convert characters with the eigh
213. about how the fields of a struct or a class are declared use the ptype exp command rather than print See Chapter 13 Examining the Symbol Table page 143 8 1 Expressions print and many other GDB commands accept an expression and compute its value Any kind of constant variable or operator defined by the programming language you are using is valid in an expression in GDB This includes conditional expressions function calls casts and string constants It also includes preprocessor macros if you compiled your program to include this information see Section 4 1 Compilation page 25 GDB supports array constants in expressions input by the user The syntax is element element For example you can use the command print 1 2 3 to build up an array in memory that is malloced in the target program Because C is so widespread most of the expressions shown in examples in this manual are in C See Chapter 12 Using GDB with Different Languages page 119 for information on how to use expressions in other languages In this section we discuss operators that you can use in GDB expressions regardless of your programming language Casts are supported in all languages not just in C because it is so useful to cast a number into a pointer in order to examine a structure at that address in memory GDB supports these operators in addition to those common to programming languages Q is a binary operator for treating parts of mem
214. acters Chapter 22 GDB Text User Interface 229 22 5 TUI Configuration Variables Several configuration variables control the appearance of TUI windows set tui border kind kind Select the border appearance for the source assembly and register windows The possible values are the following space ascii acs Use a space character to draw the border Use ASCII characters and to draw the border Use the Alternate Character Set to draw the border The border is drawn using character line graphics if the terminal supports them set tui border mode mode set tui active border mode mode Select the display attributes for the borders of the inactive windows or the active window The mode can be one of the following normal standout reverse half M M a se normal attributes to display the border se standout mode se reverse video mode se half bright mode half standout bold U U se half bright and standout mode se extra bright or bold mode bold standout U se extra bright or bold and standout mode 230 Debugging with GDB Chapter 23 Using GDB under GNU Emacs 231 23 Using GDB under GNU Emacs A special interface allows you to use GNU Emacs to view and edit the source files for the program you are debugging with GDB To use this interface use the command M x gdb in Emacs Give the executable file you want to debug as an argument This command starts GDB as a
215. ad been deleted but remembers the information on the breakpoint so that you can enable it again later You disable and enable breakpoints watchpoints and catchpoints with the enable and disable commands optionally specifying one or more breakpoint numbers as arguments Use info break or info watch to print a list of breakpoints watchpoints and catchpoints if you do not know which numbers to use A breakpoint watchpoint or catchpoint can have any of four different states of enable ment e Enabled The breakpoint stops your program A breakpoint set with the break com mand starts out in this state e Disabled The breakpoint has no effect on your program e Enabled once The breakpoint stops your program but then becomes disabled e Enabled for deletion The breakpoint stops your program but immediately after it does so it is deleted permanently A breakpoint set with the tbreak command starts out in this state You can use the following commands to enable or disable breakpoints watchpoints and catchpoints disable breakpoints range Disable the specified breakpoints or all breakpoints if none are listed A disabled breakpoint has no effect but is not forgotten All options such as ignore counts conditions and commands are remembered in case the breakpoint is enabled again later You may abbreviate disable as dis 48 Debugging with GDB enable breakpoints range Enable the specified breakpoints or all defined
216. addresses a stack pointer and a program counter On the 29k architecture it needs three addresses a register stack pointer a program counter and a memory stack pointer upn Move n frames up the stack For positive numbers n this advances toward the outermost frame to higher frame numbers to frames that have existed longer n defaults to one down n Move n frames down the stack For positive numbers n this advances toward the innermost frame to lower frame numbers to frames that were created more recently n defaults to one You may abbreviate down as do Chapter 6 Examining the Stack 65 All of these commands end by printing two lines of output describing the frame The first line shows the frame number the function name the arguments and the source file and line number of execution in that frame The second line shows the text of that source line For example gdb up 1 0x22f0 in main argc 1 argv Oxf7fffbf4 env Oxf7fffbfc at env c 10 10 read input file argv il After such a printout the list command with no arguments prints ten lines centered on the point of execution in the frame You can also edit the program at the point of execution with your favorite editing program by typing edit See Section 7 1 Printing Source Lines page 67 for details up silently n down silently n These two commands are variants of up and down respectively they differ in that they do their work silently without causing di
217. after executing the command If you exit GDB while you have an attached process you detach that process If you use the run command you kill that process By default GDB asks for confirmation if you try to do either of these things you can control whether or not you need to confirm by using the set confirm command see Section 19 7 Optional Warnings and Messages page 211 Chapter 4 Running Programs Under GDB 31 4 8 Killing the Child Process kill Kill the child process in which your program is running under GDB This command is useful if you wish to debug a core dump instead of a running process GDB ignores any core dump file while your program is running On some operating systems a program cannot be executed outside GDB while you have breakpoints set on it inside GDB You can use the kill command in this situation to permit running your program outside the debugger The kill command is also useful if you wish to recompile and relink your program since on many systems it is impossible to modify an executable file while it is running in a process In this case when you next type run GDB notices that the file has changed and reads the symbol table again while trying to preserve your current breakpoint settings 4 9 Debugging Programs with Multiple Threads In some operating systems such as HP UX and Solaris a single program may have more than one thread of execution The precise semantics of threads differ from one operating
218. akpoint disp keep enabled y addr 0x08048564 func main file myprog c fullname home nickrob myprog c line 68 times 0 lt gdb Program Execution Program execution generates asynchronous records and MI gives the reason that execution stopped gt exec run lt running lt gdb lt stopped reason breakpoint hit bkptno 1 thread id 0 frame addr 0x08048564 func main args name argce value 1 name argv value 0xbfc4d4d4 file myprog c fullname home nickrob myprog c line 68 lt gdb gt exec continue running gdb lt stopped reason exited normally lt gdb Chapter 24 The GDB MI Interface 239 Quitting GDB Quitting GDB just prints the result class exit gdb lt gdb exit lt exit A Bad Command Here s what happens if you pass a non existent command rubbish lt error msg Undefined MI command rubbish gdb 24 8 GDB MI Command Description Format The remaining sections describe blocks of commands Each block of commands is laid out in a fashion similar to this section Motivation The motivation for this collection of commands Introduction A brief introduction to this collection of commands as a whole Commands For each command in the block the following is described Synopsis command args Result GDB Command The corresponding GDB CLI command s if any Example
219. akpoint or watchpoints A limit of 1 the default is treated as unlimited The GDB remote protocol autodetects the packets supported by your debugging stub If you need to override the autodetection you can use these commands to enable or disable individual packets Each packet can be set to on the remote target supports this packet off the remote target does not support this packet or auto detect remote target support for this packet They all default to auto For more information about each packet see Appendix D Remote Protocol page 333 During normal use you should not have to use any of these commands If you do that may be a bug in your remote debugging stub or a bug in GDB You may want to report the problem to the GDB developers For each packet name the command to enable or disable the packet is set remote name packet The available settings are Command Name fetch register set register binary download read aux vector symbol lookup verbose resume software breakpoint hardware breakpoint write watchpoint read watchpoint access watchpoint target features library info Remote Packet P P X qXfer auxv read qSymbol vCont Z0 Zi Z2 Z3 Z4 qXfer features read qXfer libraries read Related Features info registers set load set info auxv Detecting multiple threads Stepping or resum ing multiple threads break hbreak watch rwatch awatch set archit
220. al can be the number of a signal or its name with or without the SIG at the beginning a list of signal numbers of the form low high or the word all meaning all the known signals Optional arguments keywords described below say what change to make The keywords allowed by the handle command can be abbreviated Their full names are nostop GDB should not stop your program when this signal happens It may still print a message telling you that the signal has come in Chapter 5 Stopping and Continuing 57 stop GDB should stop your program when this signal happens This implies the print keyword as well print GDB should print a message when this signal happens noprint GDB should not mention the occurrence of the signal at all This implies the nostop keyword as well pass noignore GDB should allow your program to see this signal your program can handle the signal or else it may terminate if the signal is fatal and not handled pass and noignore are synonyms nopass ignore GDB should not allow your program to see this signal nopass and ignore are synonyms When a signal stops your program the signal is not visible to the program until you continue Your program sees the signal then if pass is in effect for the signal in question at that time In other words after GDB reports a signal you can use the handle command with pass or nopass to control whether your program sees that signal when you continue T
221. ant to set a breakpoint on a subroutine whose name begins with make_ but when you type b make_ TAB GDB just sounds the bell Typing again displays all the function names in your program that begin with those characters for example gdb b make_ GDB sounds bell press again to see make_a_section_from_file make_environ make_abs_section make_function_type make_blockvector make_pointer_type make_cleanup make_reference_type make_command make_symbol_completion_list gdb b make_ After displaying the available possibilities GDB copies your partial input b make_ in the example so you can finish the command If you just want to see the list of alternatives in the first place you can press M rather than pressing twice M means 7 You can type this either by holding down a key designated as the shift on your keyboard if there is one while typing or as followed by Sometimes the string you need while logically a word may contain parentheses or other characters that GDB normally excludes from its notion of a word To permit word completion to work in this situation you may enclose words in single quote marks in GDB commands The most likely situation where you might need this is in typing the name of a C function This is because C allows function overloading multiple definitions of the same function distinguished by argument type For example when you want to set a breakpoint you may need to dist
222. append binary value filename expr Append the contents of memory from start_addr to end_addr or the value of expr to the file filename in raw binary form GDB can only append data to files in raw binary form restore filename binary bias start end Restore the contents of file filename into memory The restore command can automatically recognize any known BFD file format except for raw binary To restore a raw binary file you must specify the optional keyword binary after the filename If bias is non zero its value will be added to the addresses contained in the file Binary files always start at address zero so they will be restored at address bias Other bfd files have a built in location they will be restored at offset bias from that location If start and or end are non zero then only data between file offset start and file offset end will be restored These offsets are relative to the addresses in the file before the bias argument is applied 8 16 How to Produce a Core File from Your Program A core file or core dump is a file that records the memory image of a running process and its process status register values etc Its primary use is post mortem debugging of a program that crashed while it ran outside a debugger program that crashes automatically produces a core file unless this feature is disabled by the user See Section 15 1 Files page 155 for information on invoking GDB in the post mortem debugging mode
223. arameters that specify how much memory to display and how addr is an expression giving the address where you want to start displaying memory If you use defaults for nfu you need not type the slash Several commands set convenient defaults for addr 80 Debugging with GDB n the repeat count The repeat count is a decimal integer the default is 1 It specifies how much memory counting by units u to display f the display format The display format is one of the formats used by print x d u o t a c f s and in addition i for machine instructions The default is x hexadecimal initially The default changes each time you use either x or print u the unit size The unit size is any of b Bytes h Halfwords two bytes W Words four bytes This is the initial default g Giant words eight bytes Each time you specify a unit size with x that size becomes the default unit the next time you use x For the s and i formats the unit size is ignored and is normally not written addr starting display address addr is the address where you want GDB to begin displaying memory The expression need not have a pointer value though it may it is always inter preted as an integer address of a byte of memory See Section 8 1 Expressions page 75 for more information on expressions The default for addr is usu ally just after the last a
224. are included If you use maint print symbols GDB includes all the symbols for which it has already collected full details that is filename reflects symbols for only those files whose symbols GDB has read You can use the command info sources to find out which files these are If you use maint print psymbols instead the dump shows information about symbols that GDB only knows partially that is symbols defined in files that GDB has skimmed but not yet read completely Finally maint print msymbols dumps just the minimal symbol information required for each object file from which GDB has read some symbols See Section 15 1 Commands to Specify Files page 155 for a discussion of how GDB reads symbols in the description of symbol file maint info symtabs regexp maint info psymtabs regexp List the struct symtab or struct partial_symtab structures whose names match regexp If regexp is not given list them all The output includes expres sions which you can copy into a GDB debugging this one to examine a particular structure in more detail For example gdb maint info psymtabs dwarf2read objfile home gnu build gdb gdb struct objfile 0x82e69d0 psymtab home gnu src gdb dwarf2read c struct partial symtab 0x8474b10 readin no fullname null text addresses 0x814d3c8 0x8158074 globals struct partial symbol 0x8507a08 Q0 9 statics struct partial symbol Ox40e95b78 2882 dependenci
225. arguments for your program The usual syntax is target gdbserver comm program args comm is either a device name to use a serial line or a TCP hostname and portnumber For example to debug Emacs with the argument foo txt and communicate with GDB over the serial port dev com1 target gdbserver dev comi emacs foo txt Edbserver waits passively for the host GDB to communicate with it To use a TCP connection instead of a serial line target gdbserver host 2345 emacs foo txt The only difference from the previous example is the first argument specifying that you are communicating with the host GDB via TCP The host 2345 argument means that gdbserver is to expect a TCP connection from machine host to local TCP port 2345 Currently the host part is ignored You can choose any number you want for the port number as long as it does not conflict with any TCP ports already in use on the target system for example 23 is reserved for telnet You must use the same port number with the host GDB target remote command On some targets gdbserver can also attach to running programs This is accomplished via the attach argument The syntax is target gdbserver comm attach pid pid is the process ID of a currently running process It isn t necessary to point gdbserver at a binary for the running process lig you choose a port number that conflicts with another service gdbserver prints an error message
226. ascal 23e iid Een oe aa ep B y ed deed ruedas 131 12 4 5 Modilas2 4 creto duet E br Re PI Reid 151 12 4 5 Operators sesssseeeses nnn 131 12 4 5 2 Built in Functions and Procedures 132 12 4 5 3 Constants sc cues eet obs heads hdd ee eee 133 12 4 5 4 Modula 2 Types 0 cee eee eee 134 12 4 5 5 Modula 2 Defaults 00 0 00 e eee eee 136 12 4 5 6 Deviations from Standard Modula 2 136 12 4 5 7 Modula 2 Type and Range Checks 136 12 4 5 8 The Scope Operators and 136 12 4 5 9 GDB and Modula 2 0 resam eee eee 137 12 4 0 CAO os edic eH kde GR HAA Raa eg 137 12 4 6 4 Introduction 0 eee eee 137 12 4 6 2 Omissions from Ada 0 000 cece sinira 138 12 4 6 3 Additions to Ada sise esasa iadan ee 139 12 4 6 4 Stopping at the Very Beginning 140 12 4 6 5 Known Peculiarities of Ada Mode 140 12 5 Unsupported Languages 0 000 cece nh 141 13 Examining the Symbol Table 143 14 Altering Execution 222 rw we 149 14 1 Assignment to Variables iiiilliiiee esses 149 14 2 Continuing at a Different Address 004 150 14 8 Giving your Program a Signal 0 0 00 eee eee eee 151 14 4 Returning from a Function 000 soiree eee ee 151 14 5 Calling Program Functions 000000 eee eee eee 152 14 6 Patchi
227. associated with a filename extension See Section 12 2 Displaying the Language page 120 This is most commonly a problem when you use a program such as cfront or 2c that generates C but is written in another language In that case make the program use line directives in its C output that way GDB will know the correct language of the source code of the original program and will display that source code not the generated C code 12 1 1 List of Filename Extensions and Languages If a source file name ends in one of the following extensions then GDB infers that its language is the one indicated 6 ada ads adb 6 3 a Ada source file xe C source file Cpp CXX Lott C source file 120 Debugging with GDB m Objective C source file EN SE Fortran source file mod Modula 2 source file Ca oO Assembler source file This actually behaves almost like C but GDB does not skip over function prologues when stepping In addition you may set the language associated with a filename extension See Sec tion 12 2 Displaying the Language page 120 12 1 2 Setting the Working Language If you allow GDB to set the language automatically expressions are interpreted the same way in your debugging session and your program If you wish you may set the language manually To do this issue the command set language lang where lang is the name of a language such as c or modula 2 For a l
228. at debugger startup Chapter 24 The GDB MI Interface 285 The command returns a list of strings with each string naming an available feature Each returned string is just a name it does not have any internal structure The list of possible feature names is given below Example output gdb list features done result featurei feature2 The current list of features is frozen varobjs indicates presence of the var set frozen command as well as possible presense of the frozen field in the output of varobj create The interpreter exec Command Synopsis interpreter exec interpreter command Execute the specified command in the given interpreter GDB Command The corresponding GDB command is interpreter exec Example gdb interpreter exec console break main amp During symbol reading couldn t parse type debugger out of date n amp During symbol reading bad structure type format Wn Breakpoint 1 at Ox8074fc6 file src gdb main c line 743 n done gdb The inferior tty set Command Synopsis inferior tty set dev pts 1 Set terminal for future runs of the program being debugged GDB Command The corresponding GDB command is set inferior tty dev pts 1 Example gdb inferior tty set dev pts 1 done gdb The inferior tty show Command Synopsis inferior tty show Show terminal for future runs of program being debugged 286 Debugging with GDB GDB Co
229. at triggers either on a read from or on a write to the memory location With the r option the watchpoint created is a read watchpoint i e it will trigger only when the memory location is accessed for reading Without either of the options the watchpoint created is a regular watchpoint i e it will trigger when the memory location is accessed for writing See Section 5 1 2 Setting Watchpoints page 43 Note that break list will report a single list of watchpoints and breakpoints inserted GDB Command The corresponding GDB commands are watch awatch and rwatch Example Setting a watchpoint on a variable in the main function gdb break watch x done wpt number 2 exp x gdb exec continue running gdb stopped reason watchpoint trigger wpt number 2 exp x value old 268439212 new 55 frame func main args file recursive2 c fullname home foo bar recursive2 c line 5 gdb Setting a watchpoint on a variable local to a function GDB will stop the program execution twice first for the variable changing value then for the watchpoint going out of scope gdb break watch C done wpt number 5 exp C gdb exec continue running gdb stopped reason watchpoint trigger wpt number 5 exp C value old 276895068 new 3 frame func callee4 args file devo gdb testsuite gdb mi basics c 246 Debugging
230. ated lists surrounded by braces and for ex ample 1 2 3 is a three element array of integers 1 2 3 4 5 6 isa three by two array and amp hi amp there amp fred is a three element array of pointers 12 4 1 3 C Expressions GDB expression handling can interpret most C expressions Warning GDB can only debug C code if you use the proper compiler and the proper debug format Currently GDB works best when debugging C code that is compiled with Gcc 2 95 3 or with GCC 3 1 or newer using the options gdwarf 2 or gstabs DWARF 2 is preferred over stabs Most configurations of GCC emit either DWARF 2 or stabs as their default debug format so you usually don t need to specify a debug format explicitly Other compilers and or debug formats are likely to work badly or not at all when using GDB to debug C code 1 Member function calls are allowed you can use expressions like count aml Get riginal x y 2 While a member function is active in the selected stack frame your expressions have the same namespace available as the member function that is GDB allows implicit references to the class instance pointer this following the same rules as C 3 You can call overloaded functions GDB resolves the function call to the right definition with some restrictions GDB does not perform overload resolution involving user defined type conversions calls to constructor
231. ath the cursor Printing characters Insert the character into the line at the cursor C _ or C x C u Undo the last editing command You can undo all the way back to an empty line Depending on your configuration the key be set to delete the character to the left of the cursor and the key set to delete the character underneath the cursor like C d rather than the character to the left of the cursor 27 2 2 Readline Movement Commands The above table describes the most basic keystrokes that you need in order to do editing of the input line For your convenience many other commands have been added in addition to C b C f C d and DEL Here are some commands for moving more rapidly about the line C a Move to the start of the line C e Move to the end of the line M f Move forward a word where a word is composed of letters and digits M b Move backward a word C 1 Clear the screen reprinting the current line at the top Notice how C f moves forward a character while M f moves forward a word It is a loose convention that control keystrokes operate on characters while meta keystrokes operate on words 27 2 3 Readline Killing Commands Killing text means to delete the text from the line but to save it away for later use usually by yanking re inserting it back into the line Cut and paste are more recent jargon for kill and yank If the description for a command says that it kills text then yo
232. ations which GDB was in the middle of may end abruptly For example if a value history begin annotation is followed by a error one cannot expect to receive the matching value history end One cannot expect not to receive it either however an error annotation does not necessarily mean that GDB is immediately returning all the way to the top level A quit or error annotation may be preceded by Z Zerror begin Any output between that and the quit or error annotation is the error message Warning messages are not yet annotated 25 5 Invalidation Notices The following annotations say that certain pieces of state may have changed Z Zframes invalid The frames for example output from the backtrace command may have changed Z Zbreakpoints invalid The breakpoints may have changed For example the user just added or deleted a breakpoint 25 6 Running the Program When the program starts executing due to a GDB command such as step or continue Z Zstarting is output When the program stops Z Zstopped is output Before the stopped annotation a variety of annotations describe how the program stopped Z Zexited exit status The program exited and exit status is the exit status zero for successful exit otherwise nonzero Z Zsignalled The program exited with a signal After the Z Zsignalled the annotation continues intro text Z Zsignal name name Z Zsignal name end middle text Z Zsignal string string Z Zsig
233. b M x If the metafied character x is lowercase run the command that is bound to the corresponding uppercase character prefix meta ESC Metafy the next character typed This is for keyboards without a meta key Typing ESO f is equivalent to typing M f undo C or C x C u Incremental undo separately remembered for each line revert line M r Undo all changes made to this line This is like executing the undo command enough times to get back to the beginning tilde expand M Perform tilde expansion on the current word set mark C 0 Set the mark to the point If a numeric argument is supplied the mark is set to that position exchange point and mark C x C x Swap the point with the mark The current cursor position is set to the saved position and the old cursor position is saved as the mark character search C A character is read and point is moved to the next occurrence of that character A negative count searches for previous occurrences character search backward M C A character is read and point is moved to the previous occurrence of that character A negative count searches for subsequent occurrences insert comment M Without a numeric argument the value of the comment begin variable is in serted at the beginning of the current line If a numeric argument is supplied Chapter 27 Command Line Editing 313 this command acts as a toggle if the characters at the beginning of the line
234. ble by default onloff If on is specified make GDB treat memory not explicitly described by the mem ory ranges as non existent and refuse accesses to such memory The checks are only performed if there s at least one memory range defined If off is specified make GDB treat the memory not explicitly described by the memory ranges as RAM The default value is off show mem inaccessible by default Show the current handling of accesses to unknown memory 8 15 Copy Between Memory and a File You can use the commands dump append and restore to copy data between target memory and a file The dump and append commands write data to a file and the restore command reads data from a file back into the inferior s memory Files may be in binary Motorola S record Intel hex or Tektronix Hex format however GDB can only append to binary files dump format memory filename start addr end addr dump format value filename expr Dump the contents of memory from start addr to end_addr or the value of expr to filename in the given format The format parameter may be any one of binary Raw binary form ihex Intel hex format Chapter 8 Examining Data 95 srec Motorola S record format tekhex Tektronix Hex format GDB uses the same definitions of these formats as the GNU binary utilities like objdump and objcopy If format is omitted GDB dumps the data in raw binary form append binary memory filename start addr end addr
235. ble with the REAL 2 3 For the expressions you use in GDB commands you can tell the GDB type checker to skip checking to treat any mismatches as errors and abandon the expression or to only issue warnings when type mismatches occur but evaluate the expression anyway When you choose the last of these GDB evaluates expressions like the second example above but also issues a warning Even if you turn type checking off there may be other reasons related to type that prevent GDB from evaluating an expression For instance GDB does not know how to add an int and a struct foo These particular type errors have nothing to do with the language in use and usually arise from expressions such as the one described above which make little sense to evaluate anyway Each language defines to what degree it is strict about type For instance both Modula 2 and C require the arguments to arithmetical operators to be numbers In C enumerated types and pointers can be represented as numbers so that they are valid arguments to mathematical operators See Section 12 4 Supported Languages page 123 for further details on specific languages GDB provides some additional commands for controlling the type checker Set check type auto Set type checking on or off based on the current working language See Sec tion 12 4 Supported Languages page 123 for the default settings for each language set check type on Set check type off Set type checking
236. body it is included Execution branches to the beginning of the while loop where it evaluates the controlling expression end Terminate the block of commands that are the body of if else or while flow control commands 20 4 Commands for Controlled Output During the execution of a command file or a user defined command normal GDB output is suppressed the only output that appears is what is explicitly printed by the commands in the definition This section describes three commands useful for generating exactly the output you want echo text Print text Nonprinting characters can be included in text using C escape se quences such as n to print a newline No newline is printed unless you specify Chapter 20 Canned Sequences of Commands 221 one In addition to the standard C escape sequences a backslash followed by a space stands for a space This is useful for displaying a string with spaces at the beginning or the end since leading and trailing spaces are otherwise trimmed from all arguments To print and foo use the command echo and foo A backslash at the end of text can be used as in C to continue the command onto subsequent lines For example echo This is some text n which is continued n onto several lines n produces the same output as echo This is some text n echo which is continued n echo onto several lines n output expression Print the value of expression and nothing but that value no
237. breakpoints They become effective once again in stopping your program enable breakpoints once range Enable the specified breakpoints temporarily GDB disables any of these break points immediately after stopping your program enable breakpoints delete range Enable the specified breakpoints to work once then die GDB deletes any of these breakpoints as soon as your program stops there Breakpoints set by the tbreak command start out in this state Except for a breakpoint set with tbreak see Section 5 1 1 Setting Breakpoints page 38 breakpoints that you set are initially enabled subsequently they become disabled or enabled only when you use one of the commands above The command until can set and delete a breakpoint of its own but it does not change the state of your other breakpoints see Section 5 2 Continuing and Stepping page 52 5 1 6 Break Conditions The simplest sort of breakpoint breaks every time your program reaches a specified place You can also specify a condition for a breakpoint A condition is just a Boolean expression in your programming language see Section 8 1 Expressions page 75 A breakpoint with a condition evaluates the expression each time your program reaches it and your program stops only if the condition is true This is the converse of using assertions for program validation in that situation you want to stop when the assertion is violated that is when the condition is false I
238. built and is likely before the user entry point main or equivalent is called Set backtrace past entry off Backtraces will stop when they encounter the internal entry point of an appli cation This is the default Show backtrace past entry Display the current internal entry point backtrace policy set backtrace limit n set backtrace limit O Limit the backtrace to n levels A value of zero means unlimited show backtrace limit Display the current limit on backtrace levels 6 3 Selecting a Frame Most commands for examining the stack and other data in your program work on whichever stack frame is selected at the moment Here are the commands for selecting a stack frame all of them finish by printing a brief description of the stack frame just selected frame n fn Select frame number n Recall that frame zero is the innermost currently executing frame frame one is the frame that called the innermost one and so on The highest numbered frame is the one for main frame addr f addr Select the frame at address addr This is useful mainly if the chaining of stack frames has been damaged by a bug making it impossible for GDB to assign numbers properly to all frames In addition this can be useful when your program has multiple stacks and switches between them On the SPARC architecture frame needs two addresses to select an arbitrary frame a frame pointer and a stack pointer On the MIPS and Alpha architecture it needs two
239. by adjusting a breakpoint s address to the first in the bundle It is not uncommon for optimized code to have bundles which contain instructions from different source statements thus it may happen that a breakpoint s address will be adjusted from one source statement to another Since this adjustment may significantly alter GDB s breakpoint related behavior from what the user expects a warning is printed when the breakpoint is first set and also when the breakpoint is hit A warning like the one below is printed when setting a breakpoint that s been subject to address adjustment warning Breakpoint address adjusted from 0x00010414 to 0x00010410 Such warnings are printed both for user settable and GDB s internal breakpoints If you see one of these warnings you should verify that a breakpoint set at the adjusted address will have the desired affect If not the breakpoint in question may be removed and other breakpoints may be set which will have the desired behavior E g it may be sufficient to place the breakpoint at a later instruction A conditional breakpoint may also be useful in some cases to prevent the breakpoint from triggering too often GDB will also issue a warning when stopping at one of these adjusted breakpoints warning Breakpoint 1 address previously adjusted from 0x00010414 to 0x00010410 When this warning is encountered it may be too late to take remedial action except in cases where the breakpoint is hit earli
240. c file command to specify that GDB should run your program under that name Then start your program again 3 Relink your program so that the text segment is nonsharable using the linker option N The operating system limitation may not apply to nonsharable executables A similar message can be printed if you request too many active hardware assisted breakpoints and watchpoints Stopped cannot insert breakpoints You may have requested too many hardware breakpoints and watchpoints 52 Debugging with GDB This message is printed when you attempt to resume the program since only then GDB knows exactly how many hardware breakpoints and watchpoints it needs to insert When this message is printed you need to disable or remove some of the hardware assisted breakpoints and watchpoints and then continue 5 1 10 Breakpoint address adjusted Some processor architectures place constraints on the addresses at which breakpoints may be placed For architectures thus constrained GDB will attempt to adjust the breakpoint s address to comply with the constraints dictated by the architecture One example of such an architecture is the Fujitsu FR V The FR V is a VLIW archi tecture in which a number of RISC like instructions may be bundled together for parallel execution The FR V architecture constrains the location of a breakpoint instruction within such a bundle to the instruction with the lowest address GDB honors this constraint
241. c operations on the native VAX floating point formats are not supported It is not possible to slice a packed array 4 6 3 Additions to Ada it does for other languages GDB makes certain generic extensions to Ada see Section 8 1 Expressions page 75 If the expression E is a variable residing in memory typically a local variable or array element and N is a positive integer then E N displays the values of E and the N 1 adjacent variables following it in memory as an array In Ada this operator is generally not necessary since its prime use is in displaying parts of an array and slicing will usually do this in Ada However there are occasional uses when debugging programs in which certain debugging information has been optimized away B var means the variable named var that appears in function or file B When B is a file name you must typically surround it in single quotes The expression type addr means the variable of type type that appears at address addr A name starting with is a convenience variable see Section 8 9 Convenience Vars page 88 or a machine register see Section 8 10 Registers page 90 In addition GDB provides a few other shortcuts and outright additions specific to Ada The assignment statement is allowed as an expression returning its right hand operand as its value Thus you may enter set x y 3 print A tmp y 1 The semicolon is allowed as an operator
242. cable to regular expressions Result The result is in the form done bkpt number number type type disp del keep enabled y n addr hex func funcname file filename fullname full filename line lineno thread threadno times times where number is the GDB number for this breakpoint funcname is the name of the function where the breakpoint was inserted filename is the name of the source file which contains this function lineno is the source line number within that file and times the number of times that the breakpoint has been hit always 0 for break insert but may be greater for break info or break list which use the same output Note this format is open to change GDB Command The corresponding GDB commands are break tbreak hbreak thbreak and rbreak p g Example gdb break insert main done bkpt number 1 addr 0x0001072c file recursive2 c fullname home foo recursive2 c line 4 times 0 gdb break insert t foo done bkpt number 2 addr 0x00010774 file recursive2 c fullname home foo recursive2 c line 11 times 0 gdb break list done BreakpointTable nr_rows 2 nr_cols 6 hdr width 3 alignment 1 col_name number colhdr Num width 14 alignment 1 col_name type colhdr Type width 4 alignment 1 col_name disp colhdr Disp width 3 alignment 1 col_name enabled colhdr Enb
243. call via the print or call command to generate a signal e g if there s a bug in the function or if you passed it incorrect arguments What happens in that case is controlled by the set unwindonsignal command set unwindonsignal Set unwinding of the stack if a signal is received while in a function that GDB called in the program being debugged If set to on GDB unwinds the stack it created for the call and restores the context to what it was before the call If set to off the default GDB stops in the frame where the signal was received show unwindonsignal Show the current setting of stack unwinding in the functions called by GDB Sometimes a function you wish to call is actually a weak alias for another function In such case GDB might not pick up the type information including the types of the function arguments which causes GDB to call the inferior function incorrectly As a result the called function will function erroneously and may even crash A solution to that is to use the name of the aliased function instead 14 6 Patching Programs By default GDB opens the file containing your program s executable code or the corefile read only This prevents accidental alterations to machine code but it also prevents you from intentionally patching your program s binary If you d like to be able to patch the binary you can specify that explicitly with the set write command For example you might want to turn on internal debugging f
244. ccess a GNAT extension Address e The names in Characters Latin_1 are not available and concatenation is not imple mented Thus escape characters in strings are not currently available e Equality tests and on arrays test for bitwise equality of representations They will generally work correctly for strings and arrays whose elements have integer or enumeration types They may not work correctly for arrays whose element types have user defined equality for arrays of real values in particular IEEE conformant floating point because of negative zeroes and NaNs and for arrays whose elements contain unused bits with indeterminate values e The other component by component array operations and or xor not and relational tests other than equality are not implemented e There is limited support for array and record aggregates They are permitted only on the right sides of assignments as in these examples 1 2 3 4 5 6 set An Array 1 others gt 0 set An Array 0 4 gt 1 1 3 gt 2 5 gt 6 set A_2D_Array 1 2 3 4 5 6 7 8 9 set A_Record 1 Peter True set A_Record Name gt Peter Id gt 1 Alive gt True set An_Array Changing a discriminant s value by assigning an aggregate has an undefined effect if that discriminant is used within the record However you can first modify discriminants by directly assigning to them which normally would not be allowe
245. ced by a debugger might cause the program to change its behavior drastically or perhaps fail even when the code itself is correct It is useful to be able to observe the program s behavior without interrupting it Using GDB s trace and collect commands you can specify locations in the program called tracepoints and arbitrary expressions to evaluate when those tracepoints are reached Later using the tfind command you can examine the values those expressions had when the program hit the tracepoints The expressions may also denote objects in memory structures or arrays for example whose values GDB should record while visiting a partic ular tracepoint you may inspect those objects as if they were in memory at that moment However because GDB records these values without interacting with you it can do so quickly and unobtrusively hopefully not disturbing the program s behavior The tracepoint facility is currently available only for remote targets See Chapter 16 Targets page 167 In addition your remote target must know how to collect trace data This functionality is implemented in the remote stub however none of the stubs distributed with GDB support tracepoints as of this writing The format of the remote packets used to implement tracepoints are described in Section D 6 Tracepoint Packets page 351 This chapter describes the tracepoint commands and features 10 1 Commands to Set Tracepoints Before running such a trace
246. ceive copies directly or indirectly through you then the only way you could satisfy both it and this License would be to refrain entirely from distribution of the Program If any portion of this section is held invalid or unenforceable under any particular circumstance the balance of the section is intended to apply and the section as a whole is intended to apply in other circumstances It is not the purpose of this section to induce you to infringe any patents or other property right claims or to contest validity of any such claims this section has the sole purpose of protecting the integrity of the free software distribution system which is implemented by public license practices Many people have made generous contri butions to the wide range of software distributed through that system in reliance on consistent application of that system it is up to the author donor to decide if he or she is willing to distribute software through any other system and a licensee cannot impose that choice This section is intended to make thoroughly clear what is believed to be a consequence of the rest of this License If the distribution and or use of the Program is restricted in certain countries either by patents or by copyrighted interfaces the original copyright holder who places the Program under this License may add an explicit geographical distribution limitation excluding those countries so that distribution is permitted only in or among countrie
247. ception handlers how to list 66 exceptionHandler sere e 179 exchange point and mark C x C x 312 exec fil6 oss Ray aude PROP 155 executable file nnan ccc cece cece eee 155 Debugging with GDB executable file target 005 168 execute commands from a file 219 execute remote command remote request 345 exited annotation ggg etae ees 289 exiting GDB i scents ee antitana ai OnE genes 16 expand macro once 0 eee eee eee eee 101 expand tilde 2 e ee ree p eed 299 expanding preprocessor macros 101 expression debugging info 213 expressiOnS Leseieicrintebenego bed RR d 75 expressions in Ada eeeeeeee 137 expressions in C or CHo esersierrsrcs eread 123 expressions 1n O sue o diene i SER 126 expressions in Modula 2 suse 131 extend GDB for remote targets 172 F f frame ilsse ete Pam ey nae E EE 64 f SingleKey TUI key 0 004 227 E packet oes she weg che rrr REP banaue 335 F reply packet ret t4 ahh2 td sone eme RIDERS 356 F request packet ico te Rete 356 fatal Signal iSo RITEERR RP E OCRTIY eo md 291 fatalssignals eri te EY ER Pew E 56 FDL GNU Free Documentation License 393 features of the remote protocol 345 fg resume foreground execution 53 fil 4lsendb weBq beau are RS GR arte dae 155 file
248. cessary However trace quick is a kludge to save space it only exists so we needn t write dup const8 SIZE trace before every memory reference Therefore it s okay for it not to consume its arguments it s meant for a specific context in which we know exactly what it should do with the stack If we re going to have a kludge it should be an effective kludge Why does trace16 exist That opcode was added by the customer that contracted Cygnus for the data tracing work I personally think it is unnecessary objects that large will be quite rare so it is okay to use dup const16 size trace in those cases Whatever we decide to do with trace16 we should at least leave opcode 0x30 reserved to remain compatible with the customer who added it Appendix F Target Descriptions 381 Appendix F Target Descriptions Warning target descriptions are still under active development and the contents and format may change between GDB releases The format is expected to stabilize in the future One of the challenges of using GDB to debug embedded systems is that there are so many minor variants of each processor architecture in use It is common practice for vendors to start with a standard processor core ARM PowerPC or MIPS for example and then make changes to adapt it to a particular market niche Some architectures have hundreds of variants available from dozens of vendors This leads to a number of problems e With so many different custo
249. cific Depending on the configuration and operating system facilities GDB may be able to show you this information For re mote targets this functionality may further depend on the remote stub s support of the qXfer auxv read packet see qXfer auxiliary vector read page 349 info auxv Display the auxiliary vector of the inferior which can be either a live process or a core dump file GDB prints each tag value numerically and also shows names and text descriptions for recognized tags Some values in the vector are numbers some bit masks and some pointers to strings or other data GDB displays each value in the most appropriate form for a recognized tag and in hexadecimal for an unrecognized tag 8 14 Memory Region Attributes Memory region attributes allow you to describe special handling required by regions of your target s memory GDB uses attributes to determine whether to allow certain types of memory accesses whether to use specific width accesses and whether to cache target memory By default the description of memory regions is fetched from the target if the current target supports this but the user can override the fetched regions Defined memory regions can be individually enabled and disabled When a memory region is disabled GDB uses the default attributes when accessing memory in that region Similarly if no memory regions have been defined GDB uses the default attributes when accessing all memory When a memory r
250. command allows you to move from one stack frame to an other without printing the frame This is the silent version of frame 6 2 Backtraces A backtrace is a summary of how your program got where it is It shows one line per frame for many frames starting with the currently executing frame frame zero followed by its caller frame one and on up the stack backtrace bt Print a backtrace of the entire stack one line per frame for all frames in the stack You can stop the backtrace at any time by typing the system interrupt charac ter normally Ctrl c backtrace n bt n Similar but print only the innermost n frames backtrace n bt n Similar but print only the outermost n frames backtrace full bt full bt fulln bt full n Print the values of the local variables also n specifies the number of frames to print as described above The names where and info stack abbreviated info s are additional aliases for backtrace In a multi threaded program GDB by default shows the backtrace only for the current thread To display the backtrace for several or all of the threads use the command thread apply see Section 4 9 Threads page 31 For example if you type thread apply all backtrace GDB will display the backtrace for all the threads this is handy when you debug a core dump of a multi threaded program Each line in the backtrace shows the frame number and the function name The program counter value is also shown
251. commands accept a range of breakpoints on which to operate A breakpoint range is either a single breakpoint number like 5 or two such numbers in increasing order separated by a hyphen like 5 7 When a breakpoint range is given to a command all breakpoints in that range are operated on 5 1 1 Setting Breakpoints Breakpoints are set with the break command abbreviated b The debugger convenience variable bpnum records the number of the breakpoint you ve set most recently see Sec tion 8 9 Convenience Variables page 88 for a discussion of what you can do with conve nience variables You have several ways to say where the breakpoint should go break function Set a breakpoint at entry to function function When using source languages that permit overloading of symbols such as C function may refer to more than one possible place to break See Section 5 1 8 Breakpoint Menus page 51 for a discussion of that situation break offset break offset Set a breakpoint some number of lines forward or back from the position at which execution stopped in the currently selected stack frame See Section 6 1 Frames page 61 for a description of stack frames break linenum Set a breakpoint at line linenum in the current source file The current source file is the last file whose source text was printed The breakpoint will stop your program just before it executes any of the code on that line break filename line
252. convention Show the current setting of the convention to return structs from functions Chapter 18 Configuration Specific Information 203 18 4 2 A29K Set rstack high address address On AMD 29000 family processors registers are saved in a separate register stack There is no way for GDB to determine the extent of this stack Normally GDB just assumes that the stack is large enough This may result in GDB referencing memory locations that do not exist If necessary you can get around this problem by specifying the ending address of the register stack with the set rstack high address command The argument should be an address which you probably want to precede with Ox to specify in hexadecimal show rstack high address Display the current limit of the register stack on AMD 29000 family processors 18 4 3 Alpha See the following section 18 4 4 MIPS Alpha and MIPS based computers use an unusual stack frame which sometimes requires GDB to search backward in the object code to find the beginning of a function To improve response time especially for embedded applications where GDB may be restricted to a slow serial line for this search you may want to limit the size of this search using one of these commands set heuristic fence post limit Restrict GDB to examining at most limit bytes in its search for the beginning of a function A value of 0 the default means there is no limit However except for 0 the larger
253. could involve values of one or more variables combined by operators such as a b This is sometimes called data breakpoints You must use a different command to set watchpoints see Section 5 1 2 Setting Watchpoints page 43 but aside from that you can manage a watchpoint like any other breakpoint you enable disable and delete both breakpoints and watchpoints using the same commands You can arrange to have values from your program displayed automatically whenever GDB stops at a breakpoint See Section 8 6 Automatic Display page 81 A catchpoint is another special breakpoint that stops your program when a certain kind of event occurs such as the throwing of a C exception or the loading of a library As with watchpoints you use a different command to set a catchpoint see Section 5 1 3 Setting Catchpoints page 45 but aside from that you can manage a catchpoint like any other breakpoint To stop when your program receives a signal use the handle command see Section 5 3 Signals page 56 GDB assigns a number to each breakpoint watchpoint or catchpoint when you create it these numbers are successive integers starting with one In many of the commands for controlling various features of breakpoints you use the breakpoint number to say which breakpoint you want to change Each breakpoint may be enabled or disabled if disabled it has no effect on your program until you enable it again 38 Debugging with GDB Some GDB
254. cremental reverse search history M p Search backward starting at the current line and moving up through the his tory as necessary using a non incremental search for a string supplied by the user non incremental forward search history M n Search forward starting at the current line and moving down through the the history as necessary using a non incremental search for a string supplied by the user history search forward Search forward through the history for the string of characters between the start of the current line and the point This is a non incremental search By default this command is unbound history search backward Search backward through the history for the string of characters between the start of the current line and the point This is a non incremental search By default this command is unbound yank nth arg M C y Insert the first argument to the previous command usually the second word on the previous line at point With an argument n insert the nth word from the previous command the words in the previous command begin with word 0 A negative argument inserts the nth word from the end of the previous command Once the argument n is computed the argument is extracted as if the n history expansion had been specified yank last arg M or M Insert last argument to the previous command the last word of the previous history entry With an argument behave exactly like yank nth arg S
255. cribes details specific to particular native configurations 18 1 1 HP UX On HP UX systems if you refer to a function or variable name that begins with a dollar sign GDB searches for a user or system name first before it searches for a convenience variable 18 1 2 BSD libkvm Interface BSD derived systems FreeBSD NetBSD OpenBSD have a kernel memory interface that provides a uniform interface for accessing kernel virtual memory images including live systems and crash dumps GDB uses this interface to allow you to debug live kernels and kernel crash dumps on many native BSD configurations This is implemented as a special kvm debugging target For debugging a live system load the currently running kernel into GDB and connect to the kvm target gdb target kvm For debugging crash dumps provide the file name of the crash dump as an argument gdb target kvm var crash bsd 0 Once connected to the kvm target the following commands are available kvm pcb Set current context from the Process Control Block PCB address kvm proc Set current context from proc address This command isn t available on modern FreeBSD systems 18 1 3 SVR4 Process Information Many versions of SVR4 and compatible systems provide a facility called proc that can be used to examine the image of a running process using file system subroutines If GDB is configured for an operating system with this facility the command info proc is available to report info
256. ction packets for a given tracepoint at most one can have an S before its first action If such a packet is sent it and the following packets define while stepping actions Any prior packets define ordinary actions that is those taken when the tracepoint is first hit If no action packet has an S then all the packets in the series specify ordinary tracepoint actions The action portion of the packet is a series of actions concatenated with out separators Each action has one of the following forms R mask Collect the registers whose bits are set in mask mask is a hexadec imal number whose i th bit is set if register number i should be collected The least significant bit is numbered zero Note that mask may be any number of digits long it may not fit in a 32 bit word M basereg offset len Collect len bytes of memory starting at the address in register num ber basereg plus offset If basereg is 1 then the range has a fixed address offset is the address of the lowest byte to collect The basereg offset and len parameters are all unsigned hexadecimal values the 1 value for basereg is a special case X len expr Evaluate expr whose length is len and collect memory as it directs expr is an agent expression as described in Appendix E Agent Expressions page 369 Each byte of the expression is encoded as a two digit hex number in the packet Jen is the number of bytes in the
257. ctor registers which can be treated as arrays of scalar elements These types are written as lt vector gt elements specifying the array element type type and the number of elements count vector id id type type count count If a register s value is usefully viewed in multiple ways define it with a union type con taining the useful representations The lt union gt element contains one or more lt field gt elements each of which has a name and a type union id id gt lt field name name type type lt union gt F 2 5 Registers Each register is represented as an element with this form lt reg name name bitsize size regnum num Save restore save restore type type Eroup group The components are as follows name The register s name it must be unique within the target description bitsize The register s size in bits regnum The register s number If omitted a register s number is one greater than that of the previous register either in the current feature or in a preceeding feature the first register in the target description defaults to zero This register 384 Debugging with GDB number is used to read or write the register e g it is used in the remote p and P packets and registers appear in the g and G packets in order of increasing register number save restore Whether the register should be preserved across inferior function calls this must
258. ctorial i e after the inner invocations have returned 94 int factorial int value 95 96 if value gt 1 97 value factorial value 1 98 99 return value 100 advance location stepi stepi arg si Continue running the program up to the given location An argument is re quired which should be of the same form as arguments for the break command Execution will also stop upon exit from the current stack frame This command is similar to until but advance will not skip over recursive function calls and the target location doesn t have to be in the same frame as the current one Execute one machine instruction then stop and return to the debugger It is often useful to do display i pc when stepping by machine instructions This makes GDB automatically display the next instruction to be executed each time your program stops See Section 8 6 Automatic Display page 81 An argument is a repeat count as in step 56 Debugging with GDB nexti nexti arg ni Execute one machine instruction but if it is a function call proceed until the function returns An argument is a repeat count as in next 5 3 Signals A signal is an asynchronous event that can happen in a program The operating system defines the possible kinds of signals and gives each kind a name and a number For example in Unix SIGINT is the signal a program gets when you type an interrupt character often Ctrl c SIGSEGV is t
259. ctories you want in the source path You can add all the directories in one command 7 5 Source and Machine Code You can use the command info line to map source lines to program addresses and vice versa and the command disassemble to display a range of addresses as machine instruc tions When run under GNU Emacs mode the info line command causes the arrow to point to the line specified Also info line prints addresses in symbolic form as well as hex info line linespec Print the starting and ending addresses of the compiled code for source line linespec You can specify source lines in any of the ways understood by the list command see Section 7 1 Printing Source Lines page 67 For example we can use info line to discover the location of the object code for the first line of function m4_changequote gdb info line m4_changequote Line 895 of builtin c starts at pc Ox634c and ends at 0x6350 We can also inquire using addr as the form for linespec what source line covers a par ticular address gdb info line 0x63ff Line 926 of builtin c starts at pc 0x63e4 and ends at 0x6404 After info line the default address for the x command is changed to the starting address of the line so that x i is sufficient to begin examining the machine code see Section 8 5 Examining Memory page 79 Also this address is saved as the value of the convenience variable _ see Section 8 9 Convenience Variables page 88 disa
260. cular source file are being read The set verbose command can turn these pauses into messages if desired See Section 19 7 Optional Warnings and Messages page 211 We have not implemented the two stage strategy for COFF yet When the symbol table is stored in COFF format symbol file reads the symbol table data in full right away Note that stabs in COFF still does the two stage strategy since the debug info is actually in stabs format symbol file filename readnow file filename readnow You can override the GDB two stage strategy for reading symbol tables by us ing the readnow option with any of the commands that load symbol table information if you want to be sure GDB has the entire symbol table available core file filename core Specify the whereabouts of a core dump file to be used as the contents of memory Traditionally core files contain only some parts of the address space of the process that generated them GDB can access the executable file itself for other parts core file with no argument specifies that no core file is to be used Note that the core file is ignored when your program is actually running under GDB So if you have been running your program and you wish to debug a core file instead you must kill the subprocess in which the program is running To do this use the kill command see Section 4 8 Killing the Child Process page 31 add symbol file filename address add symbo
261. d e A patch for the bug A patch for the bug does help us if it is a good one But do not omit the necessary information such as the test case on the assumption that a patch is all we need We might see problems with your patch and decide to fix the problem another way or we might not understand it at all Sometimes with a program as complicated as GDB it is very hard to construct an example that will make the program follow a certain path through the code If you do not send us the example we will not be able to construct one so we will not be able to verify that the bug is fixed And if we cannot understand what bug you are trying to fix or why your patch should be an improvement we will not install it A test case will help us to understand e A guess about what the bug is or what it depends on Such guesses are usually wrong Even we cannot guess right about such things without first using the debugger to find the facts 294 Debugging with GDB Chapter 27 Command Line Editing 295 27 Command Line Editing This chapter describes the basic features of the GNU command line editing interface 27 1 Introduction to Line Editing The following paragraphs describe the notation used to represent keystrokes The text C k is read as Control K and describes the character produced when the amp key is pressed while the Control key is depressed The text M k is read as Meta K and describes the character produced when the M
262. d default show thread default Each of the above set thread commands has a set thread default counter part e g set thread default pause set thread default exception port etc The thread default variety of commands sets the default thread prop erties for all threads you can then change the properties of individual threads with the non default commands 18 1 7 QNX Neutrino GDB provides the following commands specific to the QNX Neutrino target set debug nto debug When set to on enables debugging messages specific to the QNX Neutrino support show debug nto debug Show the current state of QNX Neutrino messages 18 2 Embedded Operating Systems This section describes configurations involving the debugging of embedded operating sys tems that are available for several different architectures GDB includes the ability to debug programs running on various real time operating sys tems 18 2 1 Using GDB with VxWorks target vxworks machinename A VxWorks system attached via TCP IP The argument machinename is the target system s machine name or IP address On VxWorks load links filename dynamically on the current target system as well as adding its symbols in GDB GDB enables developers to spawn and debug tasks running on networked VxWorks targets from a Unix host Already running tasks spawned from the VxWorks shell can also be Chapter 18 Configuration Specific Information 191 debugged GDB uses code that runs on both
263. d in Ada and then performing an aggregate assignment For example given a variable A_Rec declared to have a type such as type Rec Len Small_Integer 0 is record Id Integer Vals IntArray 1 Len end record you can assign a value with a different size of Vals with two assignments set A_Rec Len 4 set A_Rec Id gt 42 Vals gt 1 2 3 4 Chapter 12 Using GDB with Different Languages 139 12 As As this example also illustrates GDB is very loose about the usual rules concerning aggregates You may leave out some of the components of an array or record aggre gate such as the Len component in the assignment to A_Rec above they will retain their original values upon assignment You may freely use dynamic values as indices in component associations You may even use overlapping or redundant component asso ciations although which component values are assigned in such cases is not defined Calls to dispatching subprograms are not implemented The overloading algorithm is much more limited i e less selective than that of real Ada It makes only limited use of the context in which a subexpression appears to resolve its meaning and it is much looser in its rules for allowing type matches As a result some function calls will be ambiguous and the user will be asked to choose the proper resolution The new operator is not implemented Entry calls are not implemented Aside from printing arithmeti
264. db while trace_frame 1 gt printf Frame 4d PC 408X SP 08X FP 408X n trace_frame pc sp fp gt tfind gt end Frame 0 PC 0020DC64 SP OO30BF3C FP 0030BF44 Frame 1 PC 0020DC6C SP OO30BF38 FP 0030BF44 Frame 2 PC 0020DC70 SP 0030BF34 FP 0030BF44 Frame 3 PC 0020DC74 SP OO30BF30 FP 0030BF44 Frame 4 PC 0020DC78 SP OO30BF2C FP 0030BF44 Frame 5 PC 0020DC7C SP 0030BF28 FP 0030BF44 Frame 6 PC 0020DC80 SP 0030BF24 FP 0030BF44 Frame 7 PC 0020DC84 SP 0030BF20 FP 0030BF44 Frame 8 PC 0020DC88 SP OO30BF1C FP 0030BF44 Frame 9 PC O0020DC8E SP 0030BF18 FP 0030BF44 Frame 10 PC 00203F6C SP OO30BE3C FP 0030BF14 Or if we want to examine the variable X at each source line in the buffer gdb tfind start gdb while trace_frame 1 Chapter 10 Tracepoints 111 gt printf Frame 4d X d n trace frame X gt tfind line gt end Frame 0 X 1 Frame 7 X Frame 13 X 255 10 2 2 tdump This command takes no arguments It prints all the data collected at the current trace snapshot gdb trace 444 gdb actions Enter actions for tracepoint 2 one per line gt collect regs locals args gdb long test gt end gdb tstart gdb tfind line 444 0 gdb test pi Oxii p2 0x22 p3 0x33 p4 0x44 p5 0x55 p6 0x66 at gdb test c 444 444 printp As arguments Ox X Ox 4X OxAX OxA4X Ox 4X OxAXWNn
265. ddr 0x000013a4 data addr 0x000013a8 data addr 0x000013ac data addr 0x000013b0 data addr 0x000013b4 data addr 0x000013b8 data addr 0x000013bc data gdb 0x10 Ox11 0x12 Ox13 ascii xxxx 0x14 0x15 0x16 0x17 ascii xxxx Ox18 0x19 0xla 0x1b ascii xxxx Oxic Oxid Oxie Ox1f ascii xxxx 0x20 0x21 0x22 Ox23 asciis 0x24 0x25 0x26 Ox27 ascii 7Z amp 0x28 0x29 0x2a 0x2b ascii Ox2c 0x2d 0x2e 0x2f ascii 24 16 GDB MI Tracepoint Commands The tracepoint commands are not yet implemented 24 17 GDB MI Symbol Query Commands The symbol info address Command Synopsis symbol info address symbol Describe where symbol is stored GDB Command The corresponding GDB command is info address Example N A The symbol info file Command Synopsis symbol info file Show the file for the symbol GDB Command There s no equivalent GDB command gdbtk has gdb find file Example N A 214 Debugging with GDB The symbol info function Command Synopsis symbol info function Show which function the symbol lives in GDB Command gdb_get_function in gdbtk Example N A The symbol info line Command Synopsis symbol info line Show the core addresses of the code for a source line GDB Command The corresponding GDB command is info line
266. ddress examined but several other commands also set the default address info breakpoints to the address of the last breakpoint listed info line to the starting address of a line and print if you use it to display a value from memory For example x 3uh 0x54320 is a request to display three halfwords h of memory formatted as unsigned decimal integers u starting at address 0x54320 x 4xw sp prints the four words w of memory above the stack pointer here sp see Section 8 10 Registers page 90 in hexadecimal x Since the letters indicating unit sizes are all distinct from the letters specifying output formats you do not have to remember whether unit size or format comes first either order works The output specifications 4xw and 4wx mean exactly the same thing However the count n must come first wx4 does not work Even though the unit size u is ignored for the formats s and i you might still want to use a count n for example 3i specifies that you want to see three machine instructions including any operands For convenience especially when used with the display command the i format also prints branch delay slot instructions if any beyond the count specified which immediately follow the last instruction that is within the count The command disassemble gives an alternative way of inspecting machine instructions see Section 7 5 Source and Mach
267. de attributes set whether GDB may make read or write accesses to a memory region While these attributes prevent GDB from performing invalid memory accesses they do nothing to prevent the target system I O DMA etc from accessing memory ro Memory is read only wo Memory is write only rw Memory is read write This is the default 94 Debugging with GDB 8 14 1 2 Memory Access Size The access size attribute tells GDB to use specific sized accesses in the memory region Often memory mapped device registers require specific sized accesses If no access size attribute is specified GDB may use accesses of any size 8 Use 8 bit memory accesses 16 Use 16 bit memory accesses 32 Use 32 bit memory accesses 64 Use 64 bit memory accesses 8 14 1 3 Data Cache The data cache attributes set whether GDB will cache target memory While this generally improves performance by reducing debug protocol overhead it can lead to incorrect results because GDB does not know about volatile variables or memory mapped device registers cache Enable GDB to cache target memory nocache Disable GDB from caching target memory This is the default 8 14 2 Memory Access Checking GDB can be instructed to refuse accesses to memory that is not explicitly described This can be useful if accessing such regions has undesired effects for a specific target or to provide better error checking The following commands control this behaviour set mem inaccessi
268. default base for both input and output with the commands described below set input radix base Set the default base for numeric input Supported choices for base are decimal 8 10 or 16 base must itself be specified either unambiguously or using the current input radix for example any of set input radix 012 set input radix 10 set input radix Oxa sets the input base to decimal On the other hand set input radix 10 leaves the input radix unchanged no matter what it was since 10 being without any leading or trailing signs of its base is interpreted in the current radix Thus if the current radix is 16 10 is interpreted in hex i e as 16 decimal which doesn t change the radix set output radix base Set the default base for numeric display Supported choices for base are decimal 8 10 or 16 base must itself be specified either unambiguously or using the current input radix show input radix Display the current default base for numeric input Show output radix Display the current default base for numeric display set radix base show radix These commands set and show the default base for both input and output of numbers set radix sets the radix of input and output to the same base without an argument it resets the radix back to its default value of 10 19 6 Configuring the Current ABI GDB can determine the ABI Application Binary Interface of your application automati cally However sometimes y
269. dentified by a multi letter name up to the first or or the end of the packet yCont action tid Resume the inferior specifying different actions for each thread If an action is specified with no tid then it is applied to any threads that don t have a spe cific action specified if no default action is specified then other threads should remain stopped Specifying multiple default actions is an error specifying no actions is also an error Thread IDs are specified in hexadecimal Currently supported actions are e Continue C sig Continue with signal sig sig should be two hex digits tg Step S sig Step with signal sig sig should be two hex digits The optional addr argument normally associated with these packets is not sup ported in vCont Reply See Section D 3 Stop Reply Packets page 341 for the reply specifica tions vCont Request a list of actions supported by the vCont packet Reply vCont action The vCont packet is supported Each action is a supported com mand in the vCont packet 6 The vCont packet is not supported vFlashErase addr length Direct the stub to erase length bytes of flash starting at addr The region may enclose any number of flash blocks but its start and end must fall on block boundaries as indicated by the flash block size appearing in the memory map see Section D 11 Memory Map Format page
270. details The hypothetical commands show w and show c should show the appropriate parts of the General Public License Of course the commands you use may be called something other than show w and show c they could even be mouse clicks or menu items whatever suits your program You should also get your employer if you work as a programmer or your school if any to sign a copyright disclaimer for the program if necessary Here is a sample alter the names Yoyodyne Inc hereby disclaims all copyright interest in the program Gnomovision which makes passes at compilers written by James Hacker signature of Ty Coon 1 April 1989 Ty Coon President of Vice This General Public License does not permit incorporating your program into proprietary programs If your program is a subroutine library you may consider it more useful to permit linking proprietary applications with the library If this is what you want to do use the GNU Library General Public License instead of this License Appendix H GNU Free Documentation License 393 Appendix H GNU Free Documentation License Version 1 2 November 2002 Copyright c 2000 2001 2002 Free Software Foundation Inc 51 Franklin Street Fifth Floor Boston MA 02110 1301 USA Everyone is permitted to copy and distribute verbatim copies of this license document but changing it is not allowed 0 PREAMBLE The purpose of this License is to make a manual
271. discarded for example with the file or symbol file commands When the symbol table changes the value history is discarded since the values may contain pointers back to the types defined in the symbol table The values printed are given history numbers by which you can refer to them These are successive integers starting with one print shows you the history number assigned to a value by printing num before the value here num is the history number To refer to any previous value use followed by the value s history number The way print labels its output is designed to remind you of this Just refers to the most recent value in the history and refers to the value before that n refers to the nth value from the end 2 is the value just prior to 1 is equivalent to and 0 is equivalent to For example suppose you have just printed a pointer to a structure and want to see the contents of the structure It suffices to type p If you have a chain of structures where the component next points to the next one you can print the contents of the next one with this p next You can print successive links in the chain by repeating this command which you can do by just typing RET Note that the history records values not expressions If the value of x is 4 and you type these commands print x set x 5 then the value recorded in the value history by the print command remains 4 even though the value
272. displaying the hash mark set debug monitor Enable or disable display of communications messages between GDB and the remote monitor show debug monitor Show the current status of displaying communications between GDB and the remote monitor load filename Depending on what remote debugging facilities are configured into GDB the load command may be available Where it exists it is meant to make filename an executable available for debugging on the remote system by downloading or dynamic linking for example load also records the filename symbol table in GDB like the add symbol file command If your GDB does not have a 1oad command attempting to execute it gets the error message You can t do that when your target is The file is loaded at whatever address is specified in the executable For some object file formats you can specify the load address when you link the program for other formats like a out the object file format specifies a fixed address 170 Debugging with GDB Depending on the remote side capabilities GDB may be able to load programs into flash memory load does not repeat if you press again after using it 16 3 Choosing Target Byte Order Some types of processors such as the MIPS PowerPC and Renesas SH offer the ability to run either big endian or little endian byte orders Usually the executable or symbol will include a bit to designate the endian ness and you will not need to worry about which t
273. do not match the value of comment begin the value is inserted otherwise the characters in comment begin are deleted from the beginning of the line In either case the line is accepted as if a newline had been typed dump functions Print all of the functions and their key bindings to the Readline output stream If a numeric argument is supplied the output is formatted in such a way that it can be made part of an inputrc file This command is unbound by default dump variables Print all of the settable variables and their values to the Readline output stream If a numeric argument is supplied the output is formatted in such a way that it can be made part of an inputrc file This command is unbound by default dump macros Print all of the Readline key sequences bound to macros and the strings they output If a numeric argument is supplied the output is formatted in such a way that it can be made part of an inputrc file This command is unbound by default emacs editing mode C e When in vi command mode this causes a switch to emacs editing mode vi editing mode M C j When in emacs editing mode this causes a switch to vi editing mode 27 5 Readline vi Mode While the Readline library does not have a full set of vi editing functions it does contain enough to allow simple editing of the line The Readline vi mode behaves as specified in the POSIX 1003 2 standard In order to switch interactively between emacs and vi editin
274. dows OS where it is an alias for the d11 symbols command see Section 18 1 5 Cygwin Native page 185 GDB auto matically looks for shared libraries however if GDB does not find yours you can invoke add shared symbol files It takes one argument the shared library s file name assf is a shorthand alias for add shared symbol files 158 Debugging with GDB Section section addr The section command changes the base address of the named section of the exec file to addr This can be used if the exec file does not contain section addresses such as in the a out format or when the addresses specified in the file itself are wrong Each section must be changed separately The info files command described below lists all the sections and their addresses info files info target info files and info target are synonymous both print the current target see Chapter 16 Specifying a Debugging Target page 167 including the names of the executable and core dump files currently in use by GDB and the files from which symbols were loaded The command help target lists all possible targets rather than current ones maint info sections Another command that can give you extra information about program sections is maint info sections In addition to the section information displayed by info files this command displays the flags and file offset of each section in the executable and core dump files In addition maint info sections provides the followi
275. dware breakpoints before setting new ones see Section 5 1 5 Dis abling Breakpoints page 47 See Section 5 1 6 Break Conditions page 48 For remote targets you can restrict the number of hardware breakpoints GDB will use see set remote hardware breakpoint limit page 175 thbreak args Set a hardware assisted breakpoint enabled only for one stop args are the same as for the hbreak command and the breakpoint is set in the same way However like the tbreak command the breakpoint is automatically deleted after the first time your program stops there Also like the hbreak command the breakpoint requires hardware support and some target hardware may not have this support See Section 5 1 5 Disabling Breakpoints page 47 See also Section 5 1 6 Break Conditions page 48 rbreak regex Set breakpoints on all functions matching the regular expression regex This command sets an unconditional breakpoint on all matches printing a list of all breakpoints it set Once these breakpoints are set they are treated just like the breakpoints set with the break command You can delete them disable them or make them conditional the same way as any other breakpoint 40 Debugging with GDB The syntax of the regular expression is the standard one used with tools like grep Note that this is different from the syntax used by shells so for instance foo matches all functions that include an fo followed by zero or more os There is an impl
276. e unsigned long mapped _novlys This variable must be a four byte signed integer holding the total number of elements in _ovly_table To decide whether a particular overlay is mapped or not GDB looks for an entry in _ovly_table whose vma and 1ma members equal the VMA and LMA of the overlay s section Chapter 11 Debugging Programs That Use Overlays 117 in the executable file When GDB finds a matching entry it consults the entry s mapped member to determine whether the overlay is currently mapped In addition your overlay manager may define a function called ovly debug event If this function is defined GDB will silently set a breakpoint there If the overlay manager then calls this function whenever it has changed the overlay table this will enable GDB to accurately keep track of which overlays are in program memory and update any breakpoints that may be set in overlays This will allow breakpoints to work even if the overlays are kept in ROM or other non writable memory while they are not being executed 11 4 Overlay Sample Program When linking a program which uses overlays you must place the overlays at their load addresses while relocating them to run at their mapped addresses To do this you must write a linker script see section Overlay Description in Using ld the GNU linker Un fortunately since linker scripts are specific to a particular host system target architecture and target memory layout this
277. e Also the step command only enters a function if there is line number infor mation for the function Otherwise it acts like the next command This avoids problems when using cc gl on MIPS machines Previously step entered sub routines if there was any debugging information about the routine step count Continue running as in step but do so count times If a breakpoint is reached or a signal not related to stepping occurs before count steps stepping stops right away 54 Debugging with GDB next count Continue to the next source line in the current innermost stack frame This is similar to step but function calls that appear within the line of code are executed without stopping Execution stops when control reaches a different line of code at the original stack level that was executing when you gave the next command This command is abbreviated n An argument count is a repeat count as for step The next command only stops at the first instruction of a source line This prevents multiple stops that could otherwise occur in switch statements for loops etc set step mode set step mode on The set step mode on command causes the step command to stop at the first instruction of a function which contains no debug line information rather than stepping over it This is useful in cases where you may be interested in inspecting the machine instructions of a function which has no symbolic info and do not want GDB to automat
278. e gdb The target disconnect Command Synopsis target disconnect Disconnect from the remote target There s no output and the target is generally not resumed 280 Debugging with GDB GDB Command The corresponding GDB command is disconnect Example gdb target disconnect done gdb The target download Command Synopsis target download Loads the executable onto the remote target It prints out an update message every half second which includes the fields section The name of the section section sent The size of what has been sent so far for that section section size The size of the section total sent The total size of what was sent so far the current and the previous sections total size The size of the overall executable to download Each message is sent as status record see Section 24 3 2 GDB MI Output Syntax page 234 In addition it prints the name and size of the sections as they are downloaded These messages include the following fields section The name of the section section size The size of the section total size The size of the overall executable to download At the end a summary is printed GDB Command The corresponding GDB command is load Example Note each status message appears on a single line Here the messages have been broken down so that they can fit onto a page gdb targ
279. e home foo bar devo gdb testsuite gdb mi basics c line 27 frame level 4 addr 0x000107e0 func main file devo gdb testsuite gdb mi basics c fullname home foo bar devo gdb testsuite gdb mi basics c line 32 gdb stack list arguments 0 done stack args frame level 0 args frame level 1 args name strarg frame level 2 args name intarg name strarg frame level 3 args name intarg name strarg name fltarg frame level 4 args gdb stack list arguments 1 done stack args frame level 0 args frame level 1 args name strarg value 0x11940 A string argument frame level 2 args name intarg value 2 name strarg value 0x11940 A string argument frame level 3 args name intarg value 2 name strarg value 0x11940 A string argument name fltarg value 3 5 frame level 4 args gdb stack list arguments 0 2 2 done stack args frame level 2 args name intarg name strarg gdb Chapter 24 The GDB MI Interface 259 stack list arguments 1 2 2 done stack args frame level 2 args name intarg value 2 name strarg value 0x11940 A string argument gdb The stack list frames Command Synopsis stack list frames low frame high frame List the frames currently on the stack For each frame it displays the followi
280. e The string is generally not valid expression in the current language and cannot be evaluated For example if a is an array and variable object A was created for a then we ll get this output gdb var info expression A 1 done lang C exp 1 Here the values of lang can be C C Java Note that the output of the var list children command also includes those expres sions so the var info expression command is of limited use The var info path expression Command Synopsis var info path expression name Returns an expression that can be evaluated in the current context and will yield the same value that a variable object has Compare this with the var info expression command which result can be used only for UI presentation Typical use of the var info path expression command is creating a watchpoint from a variable object For example suppose C is a C class derived from class Base and that the Base class has a member called m size Assume a variable c is has the type of C and a variable object C was created for variable c Then we ll get this output gdb var info path expression C Base public m size done path expr Base c m size Chapter 24 The GDB MI Interface 265 The var show attributes Command Synopsis var show attributes name List attributes of the specified variable object name status attr attr where attr is editable noneditable TBD The var evaluate ex
281. e spaces in some of the templates for clarity these are not part of the packet s syntax No GDB packet uses spaces to separate its components Here are the currently defined query and set packets 6 qc Return the current thread id Reply 1 The qP and qL packets predate these conventions and have arguments without any terminator for the packet name we suspect they are in widespread use in places that are difficult to upgrade The qC packet has no arguments but some existing stubs e g RedBoot are known to not check for the end of the packet Appendix D GDB Remote Serial Protocol 343 QC pid Where pid is an unsigned hexadecimal process id anything else Any other reply implies the old pid qCRC addr length Compute the CRC checksum of a block of memory Reply E NN An error such as memory fault C crc32 The specified memory region s checksum is crc32 qfThreadInfo qsThreadInfo Obtain a list of all active thread ids from the target OS Since there may be too many active threads to fit into one reply packet this query works iteratively it may require more than one query reply sequence to obtain the entire list of threads The first query of the sequence will be the qfThreadInfo query subsequent queries in the sequence will be the qsThreadInfo query NOTE This packet replaces the qL query see below Reply m id A single thread id m
282. e 75 For example print x 4 stores the value 4 into the variable x and then prints the value of the assignment expression which is 4 See Chapter 12 Using GDB with Different Languages page 119 for more information on operators in supported languages If you are not interested in seeing the value of the assignment use the set command instead of the print command set is really the same as print except that the expression s value is not printed and is not put in the value history see Section 8 8 Value History page 88 The expression is evaluated only for its effects If the beginning of the argument string of the set command appears identical to a set subcommand use the set variable command instead of just set This command is identical to set except for its lack of subcommands For example if your program has a variable width you get an error if you try to set a new value with just set width 13 because GDB has the command set width gdb whatis width type double gdb p width 4 13 gdb set width 47 Invalid syntax in expression The invalid expression of course is 47 In order to actually set the program s variable width use gdb set var width 47 Because the set command has many subcommands that can conflict with the names of program variables it is a good idea to use the set variable command instead of just set For example if your program has a variable g you run into problems if you tr
283. e M32R monitor Set download path path Set the default path for finding downloadable SREC files show download path Show the default path for downloadable SREC files set board address addr Set the IP address for the M32R EVA target board show board address Show the current IP address of the target board Set server address addr Set the IP address for the download server which is the GDB s host machine Show server address Display the IP address of the download server upload file Upload the specified SREC file via the monitor s Ethernet upload capability If no file argument is given the current executable file is uploaded tload file Test the upload command The following commands are available for M32R SDI sdireset This command resets the SDI connection sdistatus This command shows the SDI connection status debug_chaos Instructs the remote that M32R Chaos debugging is to be used use_debug_dma Instructs the remote to use the DEBUG_DMA method of accessing memory Chapter 18 Configuration Specific Information 195 use mon code Instructs the remote to use the MON CODE method of accessing memory use ib break Instructs the remote to set breakpoints by IB break use dbt break Instructs the remote to set breakpoints by DBT 18 3 3 M68k The Motorola m68k configuration includes ColdFire support and a target command for the following ROM monitor target dbug dev dBUG ROM monitor for Motorola Co
284. e RREA 78 output syntax of GDB MI 04 234 Appendix H Index Output meta derisine eaaa Rb savas Ron Bog eas Overlay iness bruni nbles a pd RR d Overlay ALCO cuo eer erbe E a N overlay example program lesse Overlay Seane da tpe x eed celere n overlays setting breakpoints in overload choice annotation overloaded functions calling overloaded functions overload resolution Overloading Miss sede XR Bless qum ra overloading in Ct 00008 overwrite mode eee eee eee eee P NP packet ears derat sne aii a e qu RU daha s SP packet 22 bie mede t mp E et oth packet size remote protocol packets reporting on stdout packets tracepoint lesse eeeees page tables display MS DOS page completions i sc e nrbes partial symbol dump 05 partial symbol tables listing GDB s internal Pascal se doen odes ied parete Eee es Pascal objects static members display Pascal support in GDB limitations pass signals to inferior remote request passcount ieislie kei Boor aes eee ee patching binaries 0 patching object files 00000 path nei suse utt exta tot dob dut det d pause current task GNU Hurd pause current thread GNU Hurd pauses in output uere Rh pending b
285. e a board connected to dev ttya on the machine running GDB you could say Chapter 16 Specifying a Debugging Target 169 target remote dev ttya target remote supports the load command This is only useful if you have some other way of getting the stub to the target system and you can put it somewhere in memory where it won t get clobbered by the download target sim Builtin CPU simulator GDB includes simulators for most architectures In general target sim load run works however you cannot assume that a specific memory map device drivers or even basic I O is available although some simulators do provide these For info about any processor specific simulator details see the appropriate section in Section 18 3 Embedded Processors page 192 Some configurations may include these targets as well target nrom dev NetROM ROM emulator This target only supports downloading Different targets are available on different configurations of GDB your configuration may have more or fewer targets Many remote targets require you to download the executable s code once you ve success fully established a connection You may wish to control various aspects of this process set hash This command controls whether a hash mark is displayed while downloading a file to the remote monitor If on a hash mark is displayed after each S record is successfully downloaded to the monitor show hash Show the current status of
286. e gdb signals h in the GDB source code As in the description of request packets we include spaces in the reply templates for clarity these are not part of the reply packet s syntax No GDB stop reply packet uses spaces to separate its components S AA The program received signal number AA a two digit hexadecimal number This is equivalent to a T response with no n r pairs T AA ni ri n2 r2 The program received signal number AA a two digit hexadecimal number This is equivalent to an S response except that the n r pairs can carry values of important registers and other information directly in the stop reply packet reducing round trip latency Single step and breakpoint traps are reported this way Each n r pair is interpreted as follows e If nisa hexadecimal number it is a register number and the corresponding r gives that register s value r is a series of bytes in target byte order with each byte given by a two digit hex number e If nis thread then r is the thread process ID in hex e If n is a recognized stop reason it describes a more specific event that stopped the target The currently defined stop reasons are listed below aa should be 05 the trap signal At most one stop reason should be present e Otherwise GDB should ignore this n r pair and go on to the next this allows us to extend the protocol in the future The currently defined stop reasons are
287. e language can be used by a main program written in a different source language Using set language auto in this case frees you from having to set the working language manually 12 2 Displaying the Language The following commands help you find out which language is the working language and also what language source files were written in Chapter 12 Using GDB with Different Languages 121 show language Display the current working language This is the language you can use with commands such as print to build and compute expressions that may involve variables in your program info frame Display the source language for this frame This language becomes the working language if you use an identifier from this frame See Section 6 4 Information about a Frame page 65 to identify the other information listed here info source Display the source language of this source file See Chapter 13 Examining the Symbol Table page 143 to identify the other information listed here In unusual circumstances you may have source files with extensions not in the standard list You can then set the extension associated with a language explicitly set extension language ext language Tell GDB that source files with extension ext are to be assumed as written in the source language language info extensions List all the filename extensions and the associated languages 12 3 Type and Range Checking Warning In this release the GDB commands f
288. e packet s overall syntax followed by an explanation of the packet s meaning We include spaces in some of the templates for clarity these are not part of the packet s syntax No GDB packet uses spaces to separate its components For example a template like foo bar baz describes a packet beginning with the three ASCII bytes foo followed by a bar followed directly by a baz GDB does not transmit a space character between the foo and the bar or between the bar and the baz Note that all packet forms beginning with an upper or lower case letter other than those described here are reserved for future use Here are the packet descriptions Un Enable extended mode In extended mode the remote server is made persistent The R packet is used to restart the program being debugged Reply OK The remote target both supports and has enabled extended mode Up Indicate the reason the target halted The reply is the same as for step and continue Reply See Section D 3 Stop Reply Packets page 341 for the reply specifica tions A arglen argnum arg M Initialized argv array passed into program arglen specifies the number of bytes in the hex encoded byte stream arg See gdbserver for more details Reply Appendix D GDB Remote Serial Protocol 335 b baud OK The arguments were set E NN An error occurred Don t use this packet its behavior is not well defined Change t
289. e preferred form of the work for making modifi cations to it For an executable work complete source code means all the source code for all modules it contains plus any associated interface definition files plus the scripts used to control compilation and installation of the executable However as a spe cial exception the source code distributed need not include anything that is normally distributed in either source or binary form with the major components compiler kernel and so on of the operating system on which the executable runs unless that component itself accompanies the executable If distribution of executable or object code is made by offering access to copy from a designated place then offering equivalent access to copy the source code from the same place counts as distribution of the source code even though third parties are not compelled to copy the source along with the object code 4 You may not copy modify sublicense or distribute the Program except as expressly provided under this License Any attempt otherwise to copy modify sublicense or distribute the Program is void and will automatically terminate your rights under this License However parties who have received copies or rights from you under this License will not have their licenses terminated so long as such parties remain in full compliance 5 You are not required to accept this License since you have not signed it However nothing else grants you
290. e signal nostop noprint pass Reply OK The request succeeded E nn An error occurred nn are hex digits e An empty reply indicates that QPassSignals is not supported by the stub Use of this packet is controlled by the set remote pass signals command see Section 17 3 Remote Configuration page 174 This packet is not probed by default the remote stub must request it by supplying an appropriate qSupported response see qSupported page 345 qRcmd command command hex encoded is passed to the local interpreter for execution Invalid commands should be reported using the output string Before the final result packet the target may also respond with a number of intermediate Ooutput console output packets Implementors should note that providing access to a stubs s interpreter may have security implications Reply OK A command response with no output OUTPUT A command response with the hex encoded output string OUT PUT E NN Indicate a badly formed request e An empty reply indicates that qRcmd is not recognized Note that the qRcmd packet s name is separated from the command by a not a contrary to the naming conventions above Please don t use this packet as a model for new packets qSupported gdbfeature gdbfeature Tell the remote stub about features supported by GDB and query the stub for features it supports Th
291. e the file command to get both symbol table and program to run from the same file symbol file with no argument clears out GDB information on your program s symbol table The symbol file command causes GDB to forget the contents of some break points and auto display expressions This is because they may contain pointers 156 Debugging with GDB to the internal data recording symbols and data types which are part of the old symbol table data being discarded inside GDB symbol file does not repeat if you press again after executing it once When GDB is configured for a particular environment it understands debugging information in whatever format is the standard generated for that environment you may use either a GNU compiler or other compilers that adhere to the local conventions Best results are usually obtained from GNU compilers for example using GCC you can generate debugging information for optimized code For most kinds of object files with the exception of old SVR3 systems using COFF the symbol file command does not normally read the symbol table in full right away Instead it scans the symbol table quickly to find which source files and which symbols are present The details are read later one source file at a time as they are needed The purpose of this two stage reading strategy is to make GDB start up faster For the most part it is invisible except for occasional pauses while the symbol table details for a parti
292. e total number of files open on the system has been reached EINTR The call was interrupted by the user Appendix D GDB Remote Serial Protocol 359 close Synopsis int close int fd Request Fclose fd Return value close returns zero on success or 1 if an error occurred Errors EBADF fd isn t a valid open file descriptor EINTR The call was interrupted by the user read Synopsis int read int fd void buf unsigned int count Request Fread fd bufptr count Return value On success the number of bytes read is returned Zero indicates end of file If count is zero read returns zero as well On error 1 is returned Errors EBADF fd is not a valid file descriptor or is not open for reading EFAULT bufptr is an invalid pointer value EINTR The call was interrupted by the user write Synopsis int write int fd const void buf unsigned int count Request Fwrite fd bufptr count Return value On success the number of bytes written are returned Zero indicates nothing was written On error 1 is returned Errors EBADF fd is not a valid file descriptor or is not open for writing EFAULT bufptr is an invalid pointer value EFBIG An attempt was made to write a file that exceeds the host specific maximum file size allowed ENOSPC No space on device to write the data EINTR The call was interrupted by the user 360 lseek Synopsis Request Debugging with GDB long lseek in
293. e which happens to fetch from the location where that name is stored in memory perhaps if the name were different the contents of that location would fool the debugger into doing the right thing despite the bug Play it safe and give a specific complete example That is the easiest thing for you to do and the most helpful Keep in mind that the purpose of a bug report is to enable us to fix the bug It may be that the bug has been reported previously but neither you nor we can know that unless your bug report is complete and self contained Sometimes people give a few sketchy facts and ask Does this ring a bell Those bug reports are useless and we urge everyone to refuse to respond to them except to chide the sender to report bugs properly To enable us to fix the bug you should include all these things e The version of GDB GDB announces it if you start with no arguments you can also print it at any time using show version Without this we will not know whether there is any point in looking for the bug in the current version of GDB e The type of machine you are using and the operating system name and version number e What compiler and its version was used to compile GDB e g gcc 2 8 1 e What compiler and its version was used to compile the program you are debugging e g gcc 2 8 1 or HP92453 01 A 10 32 03 HP C Compiler For GCC you can say gcc version to get this information for other compilers see
294. e working directory 0 29 character Sels 2 44 dsescag spew ea cea RR beg 95 character search C 1 suus 312 Debugging with GDB character search backward M C 312 GHALSC tics soe PEE 95 checkpoint Rieti Ge eee ph 35 checkpoints and process id 00 36 checks Yanges uocis pri e dee emo 122 checks types sisse ee A pinera nN 121 checksum for GDB remote 4 333 choosing target byte order 0 170 CLG AM cot Re vau a eae Cb aum ER ote bad e AT clear and Objective C 00 0 129 clear screen C 1 0 cee eee eee 307 clearing breakpoints watchpoints catchpoints 46 close file i o system call use 359 closest symbol and offset for an address 143 code address and its source line 72 collect tracepoints 0000 107 collected data discarded 00 04 108 colon doubled as scope operator 136 colon colon context for variables functions 76 command editing essersi RE ters 295 command files iie RR a es bane HER 219 command history bata RR Een 207 command hooks inu ERU 218 command interpreters s esses esses 223 command line editing 207 command scripts debugging 212 command tracing Rr RR 212 COMMANGS Luce tere ERHERE MesdPst ee dau eb e 50 commands annotation sees iti
295. eat if you press a second time after executing the command To use attach your program must be running in an environment which supports pro cesses for example attach does not work for programs on bare board targets that lack an operating system You must also have permission to send the process a signal When you use attach the debugger finds the program running in the process first by looking in the current working directory then if the program is not found by using the source file search path see Section 7 4 Specifying Source Directories page 69 You can also use the file command to load the program See Section 15 1 Commands to Specify Files page 155 The first thing GDB does after arranging to debug the specified process is to stop it You can examine and modify an attached process with all the GDB commands that are ordinarily available when you start processes with run You can insert breakpoints you can step and continue you can modify storage If you would rather the process continue running you may use the continue command after attaching GDB to the process detach When you have finished debugging the attached process you can use the detach command to release it from GDB control Detaching the process continues its execution After the detach command that process and GDB become com pletely independent once more and you are ready to attach another process or start one with run detach does not repeat if you press again
296. ebugging 214 frame debugging info 213 fr menumbet 2rd terieri Hs APR Bae 61 frame POINTER os ook Gass ns re ert rar E RENDES 61 frame pointer register 00 90 frame command 2 49r ee deb Ere 62 frame definition i 22 sre mme RR rine 61 frame selecting ssec rr pr rta 64 frameless execution seleeees esee 61 frames invalid annotation 289 free memory information MS DOS 183 fstat file i o system call Lus 361 WIGS US oe hr Pio eee ER iR URN Rear eka 178 full symbol tables listing GDB s internal 147 function call arguments optimized out 63 function entry exit wrong values of variables 76 functions without line info and stepping 54 G g packet arepas tate eG b pope k EEEN 335 G packets mearra errari oer RUE E Pn 336 tt GNU C compiler iios 123 garbled pointers ee e rRR RP 183 GOC and CHEF eeceromad obese REA E er REY 126 ECOLGG iets theca red gu neers nde EE ER INE 95 GDB bugs reporting iecore REX Rn 291 GDB reference Card iv sees ec eb ves 319 GDB startup crit eee a eder ep reb E ERE 15 GDB version number ese sees 23 Aa DLP NER RN ch canes REOR ERE RE 16 GDB MI development ess esses 236 GDB MI breakpoint commands 239 GDB MI compatibility with CLI 236 GDB MI data manipulation 266 GDB MI input s
297. ecaad adag RR EA EP es 172 monitor commands for gdbserver 174 Mototrola 680x0 2 ie ta e e a SOR 178 MS Windows debugging 00 185 MS DOS system info 183 MS DOS specific commands 183 multiple processes 0 eee eee ee eee 33 multiple targets sore dereri iire nn 167 multiple threads 2 2 2 oor bee care 31 multiple threads backtrace 62 Debugging with GDB N D Dert eerie sry erare E aes everett 53 n SingleKey TUI key 00000005 227 names of symbols esses siup rerien etiaai 143 namespace in C 2 eee ee ee eee eee 126 native Cygwin debugging 185 native DJGPP debugging 0 183 negative breakpoint numbers 42 NetROM ROM emulator target 169 New systag message eissllsage eds pee neces 31 New systag message on HP UX 32 NOX Gi tha hives ed a Pe pet math eat lek ion eae 53 next history C n ercsi i o rone 308 iexti i s one du e RE e TERR OR oh i S 56 Di bexti cs sede ek IAN ATE EEEIEE 56 non incremental forward search history M n E T E E gh eee DR paret mid eu 308 non incremental reverse search history M p eoori ee eee eee te gam 308 non member C functions set breakpoint in 40 noninvasive task options suus 189 hosharedlai brary ico es hehe cesses cece 160 notation readline 0 eee e
298. eceiving characters on the serial port may also trigger a trap again in that situation Chapter 17 Debugging Remote Programs 179 you don t need to call breakpoint from your own program simply running target remote from the host GDB session gets control Call breakpoint if none of these is true or if you simply want to make certain your program stops at a predetermined point for the start of your debugging session 17 4 2 What You Must Do for the Stub The debugging stubs that come with GDB are set up for a particular chip architecture but they have no information about the rest of your debugging target machine First of all you need to tell the stub how to communicate with the serial port int getDebugChar Write this subroutine to read a single character from the serial port It may be identical to getchar for your target system a different name is used to allow you to distinguish the two if you wish void putDebugChar int Write this subroutine to write a single character to the serial port It may be identical to putchar for your target system a different name is used to allow you to distinguish the two if you wish If you want GDB to be able to stop your program while it is running you need to use an interrupt driven serial driver and arrange for it to stop when it receives a C 003 the control C character That is the character which GDB uses to tell the remote system to stop Getting the debuggin
299. ection 24 6 2 GDB MI Stream Records page 237 for more details about the various output records 236 Debugging with GDB 24 4 GDB MI Compatibility with CLI For the developers convenience CLI commands can be entered directly but there may be some unexpected behaviour For example commands that query the user will behave as if the user replied yes breakpoint command lists are not executed and some CLI commands such as if when and define prompt for further input with gt which is not valid MI output This feature may be removed at some stage in the future and it is recommended that front ends use the interpreter exec command see interpreter exec page 285 24 5 GDB MI Development and Front Ends The application which takes the MI output and presents the state of the program being debugged to the user is called a front end Although GDB Mtr is still incomplete it is currently being used by a variety of front ends to GDB This makes it difficult to introduce new functionality without breaking existing usage l his section tries to minimize the problems by describing how the protocol might change Some changes in MI need not break a carefully designed front end and for these the MI version will remain unchanged The following is a list of changes that may occur within one level so front ends should parse MI output in a way that can handle them e New MI commands may be added e New fields may be added to the output of a
300. ecture info sharedlibrary Chapter 17 Debugging Remote Programs memory map read spu object write spu object get thread local storage address supported packets pass signals qXfer memory map read qXfer spu read qXfer spu write qGetTLSAddr qSupported QPassSignals 17 4 Implementing a Remote Stub info mem info spu info spu Displaying __thread variables Remote com munications parameters handle signal irf The stub files provided with GDB implement the target side of the communication protocol and the GDB side is implemented in the GDB source file remote c Normally you can simply allow these subroutines to communicate and ignore the details If you re implementing your own stub file you can still ignore the details start with one of the existing stub files sparc stub c is the best organized and therefore the easiest to read To debug a program running on another machine the debugging target machine you must first arrange for all the usual prerequisites for the program to run by itself For example for a C program you need 1 A startup routine to set up the C runtime environment these usually have a name like crtO The startup routine may be supplied by your hardware supplier or you may have to write your own 2 A C subroutine library to support your program s subroutine calls notably managing input and output 3 A way of getting your program to the other machine
301. ed X addr length XX Write data to memory where the data is transmitted in binary addr is address length is number of bytes XX is binary data see Binary Data page 333 Reply OK for success E NN for an error z type addr length Z type addr length Insert Z or remove z a type breakpoint or watchpoint starting at address address and covering the next length bytes Each breakpoint and watchpoint packet type is documented separately Implementation notes A remote target shall return an empty string for an un recognized breakpoint or watchpoint packet type A remote target shall support either both or neither of a given Ztype and aztype packet pair To avoid potential problems with duplicate packets the operations should be imple mented in an idempotent way 20 addr length Z0 addr length Insert Z0 or remove z0 a memory breakpoint at address addr of size length 340 Debugging with GDB A memory breakpoint is implemented by replacing the instruction at addr with a software breakpoint or trap instruction The length is used by targets that indicates the size of the breakpoint in bytes that should be inserted e g the ARM and MIPS can insert either a 2 or 4 byte breakpoint Implementation note It is possible for a target to copy or move code that con tains memory breakpoints e g when implementing overlays The
302. ed 0x08 a b a modulo b Pop two unsigned integers from the stack divide the next to top value by the top value and push the remainder If the divisor is zero terminate with an error lsh 0x09 a b a b Pop two integers from the stack let a be the next to top value and b be the top value Shift a left by b bits and push the result rsh signed 0x0a a b signed a b Pop two integers from the stack let a be the next to top value and b be the top value Shift a right by b bits inserting copies of the top bit at the high end and push the result rsh unsigned 0x0b a b a gt gt b Pop two integers from the stack let a be the next to top value and b be the top value Shift a right by b bits inserting zero bits at the high end and push the result log not 0x0e a gt Ja Pop an integer from the stack if it is zero push the value one otherwise push the value zero Appendix E The GDB Agent Expression Mechanism 373 bit and 0x0f a b a amp b Pop two integers from the stack and push their bitwise and bit or 0x10 a b gt alb Pop two integers from the stack and push their bitwise or bit xor 0x11 ab a b Pop two integers from the stack and push their bitwise exclusive or bit not 0x12 a a Pop an integer from the stack and push its bitwise complement equal 0x13 a b a b Pop two integers from the stack if they are equal push the value one otherwise push the value z
303. ed The commands to specify a file are set tdesc filename path Read the target description from path unset tdesc filename Do not read the XML target description from a file GDB will use the description supplied by the current target Show tdesc filename Show the filename to read for a target description if any 382 Debugging with GDB F 2 Target Description Format A target description annex is an XML document which complies with the Document Type Definition provided in the GDB sources in gdb features gdb target dtd This means you can use generally available tools like xmllint to check that your feature descriptions are well formed and valid However to help people unfamiliar with XML write descriptions for their targets we also describe the grammar here Target descriptions can identify the architecture of the remote target and for some architectures provide information about custom register sets GDB can use this information to autoconfigure for your target or to warn you if you connect to an unsupported target Here is a simple target description target version 1 0 gt lt architecture gt i386 x86 64 lt architecture gt lt target gt This minimal description only says that the target uses the x86 64 architecture A target description has the following overall form with marking optional elements and marking repeatable elements The elements are explained further below lt xml version 1 0 gt
304. ed The possible values of this options are the same as for var list children see var list children page 263 It is recommended to use the 266 Debugging with GDB all values option to reduce the number of MI commands needed on each program stop Example gdb var assign vari 3 done value 3 gdb var update all values vari done changelist name vari value 3 in_scope true type_changed false gdb The field in scope may take three values true The variable object s current value is valid false The variable object does not currently hold a valid value but it may hold one in the future if its associated expression comes back into scope invalid The variable object no longer holds a valid value This can occur when the executable file being debugged has changed either through recompilation or by using the GDB file command The front end should normally choose to delete these variable objects In the future new values may be added to this list so the front should be prepared for this possibility See Section 24 5 GDB MI Development and Front Ends page 236 The var set frozen Command Synopsis var set frozen name flag Set the frozenness flag on the variable object name The flag parameter should be either 4 to make the variable frozen or 0 to make it unfrozen If a variable object is frozen then neither itself nor any of its children are implicitly updated by var update o
305. ed in target byte order The two nibbles within a register byte are transferred most significant least significant MIPS32 All registers are transferred as thirty two bit quantities in the order 32 general purpose sr lo hi bad cause pc 32 floating point registers fsr fir fp MIPS64 All registers are transferred as sixty four bit quantities including thirty two bit registers such as sr The ordering is the same as MIPS32 D 6 Tracepoint Packets Here we describe the packets GDB uses to implement tracepoints see Chapter 10 Trace points page 105 QTDP n addr ena step pass Create a new tracepoint number n at addr If ena is E then the tracepoint is enabled if it is D then the tracepoint is disabled step is the tracepoint s step count and pass is its pass count If the trailing is present further QTDP packets will follow to specify this tracepoint s actions Replies OK The packet was understood and carried out 352 Debugging with GDB 6 The packet was not recognized QTDP n addr S action Define actions to be taken when a tracepoint is hit n and addr must be the same as in the initial QTDP packet for this tracepoint This packet may only be sent immediately after another QTDP packet that ended with a If the trailing is present further QTDP packets will follow specifying more actions for this tracepoint In the series of a
306. ee 295 notational conventions for GDB MI 233 notify output in GDB MI 00 235 NULL elements in arrayS 0 85 number of array elements to print 84 number representation s lesse 210 numbers for breakpoints 000 3T O object files relocatable reading symbols from suai du anchsee baut ean bok a cle ng datu tima 157 Objective O iis ciate ER ROEPERPL ERR 129 Objective C classes and selectors 145 Objective C print objects 130 observer debugging info 00 214 octal escapes in stringS 000 85 online documentation sees esee 21 opaque data types ee cece eee eee 146 open flags in file i o protocol 365 open file i o system call ssseesse 357 OpenRISG 1000 sis cee iinei 197 OpenRISC 1000 htrace 0 198 optimized code debugging 25 optimized code wrong values of variables 76 optional debugging messages 213 optional warnings s eese 211 orlk boards Le bem steno ees 197 OFIKSIN naor i e rere peo I PS ora red ais 197 OS ABL gemere br Ie ree er Reds 210 OS informatio sessen p 2265082 eee cee ee pedis 92 out of band records in GDB MI 237 outermost frame i cc002 edepeca ence emere 61 OULPUE 434k eve e eee dae Behe es 221 output formals x cierto ena es ee
307. ee aaa Ee 105 trailing underscore in Fortran symbols 130 translating between character sets 95 transpose chars C t 004 309 transpose words M t sssss 309 tSUaTU I4 pa ie pre trac d Re ENS 108 tSUtatuS i esc a d PO RU RR REAPER RR 108 SCOP dics darned Beate bola tod dea a odds nde 108 by Asentue cud euam diced ane Sate aie Eaten Acts 29 TOL aeai Sea de de OREL nib di 225 TUL commands 3 eee RR RR LELP SEIS 227 TUI configuration variables 229 TUL key bindings 2 es 226 CULTES idesi anie ia naa E anh ate EAE E 228 TUI single key mode 44 227 type casting memory 6 0 ee eee 76 type chain of a data type 329 type checking 0 ese e eee ee ene 121 type conversions in C 000004 126 U u SingleKey TUI key isses 227 D until eissdeneeseerebeemdRebbefucdede 54 UDP port target remote sess 172 ndisplay orerar 9 Y nb vE Ebr Ea DERES 82 undo C _ or C x C u oo eee 312 unions in structures printing 85 universal argument ss sss 311 unix filename rubout 310 unix line discard C u ss 310 unix word rubout C w s esses 310 unknown address locating 79 unlink file i o system call 361 unlinked object files 0 00 155 unload symbols from shared
308. ees tees agen stad eens 108 info tracepointS 2 9 y n d pem ees 108 info types cc hades chad ale goad teense andl ak 144 info WOE se ian oco Fore aeo bid eae 92 info variables ru er hx dua 145 info V CtOE ss ebbe ERCYORGRUETR AER HEURE eon 92 info WED peada a wie kg Fg ad RURSUS ES 185 info warranty cisicsuetietwrtedtbeer neers 23 info watchpoints n sss 43 info wifi lig iw 9e pee b OE E ae Pees 227 information about tracepoints 108 inheritance oii doesent ende pada e er sees 128 init fille 125 srk scores bee RAL waa dares adds 15 init fle names scopre RR Ri ae eine tanta bees 16 init if ndefined s sates Pa e ra us 89 initial frames 22i babiwe ees oe eben eS 61 initialization file readline 298 innermost frame 00 eee eee eee 61 input syntax for GDB MI 200 233 input mota uei yer ERORE Gere dires 300 insert comment M amp s ss 312 insert completions M 311 INBPOCt nn 75 installation 2 122 op DERE S rers i ts 321 instructions assembly 00 000 T2 integral datatypes in file i o protocol 363 Intel feb eke el dicts Weteccterkbdbewe ge 178 Intel disassembly flavor 004 T3 interaction readline 05 295 internal commands 22 ocurre 327 internal GDB breakpoints 0 42 interprete r exec ilol2sssce e rese ERES 223 in
309. effect for all user written packages making it unnecessary to fully qualify most names with their packages regardless of context Where this causes ambiguity GDB asks the user s intent The debugger will start in Ada mode if it detects an Ada main program As for other languages it will enter Ada mode when stopped in a program that was translated from an Ada source file 6 While in Ada mode you may use for comments This is useful mostly for docu menting command files The standard GDB comment still works at the beginning of a line in Ada mode but not in the middle to allow based literals The debugger supports limited overloading Given a subprogram call in which the func tion symbol has multiple definitions it will use the number of actual parameters and some 138 Debugging with GDB information about their types to attempt to narrow the set of definitions It also makes very limited use of context preferring procedures to functions in the context of the call command and functions to procedures elsewhere 12 4 6 2 Omissions from Ada Here are the notable omissions from the subset e Only a subset of the attributes are supported First Last and Length on array objects not on types and subtypes Min and Max Pos and Val Tag Range on array objects not subtypes but only as the right operand of the membership in operator Access Unchecked Access and Unrestricted A
310. egion is defined it is given a number to identify it to enable disable or remove a memory region you specify that number Chapter 8 Examining Data 93 mem lower upper attributes Define memory region bounded by lower and upper with attributes attributes and add it to the list of regions monitored by GDB Note that upper 0 is a special case it is treated as the target s maximum memory address Oxffff on 16 bit targets Oxffffffff on 32 bit targets etc mem auto Discard any user changes to the memory regions and use target supplied regions if available or no regions if the target does not support delete mem nums Remove memory regions nums from the list of regions monitored by GDB disable mem nums Disable monitoring of memory regions nums A disabled memory region is not forgotten It may be enabled again later enable mem nums Enable monitoring of memory regions nums info mem Print a table of all defined memory regions with the following columns for each region Memory Region Number Enabled or Disabled Enabled memory regions are marked with y Disabled memory regions are marked with n Lo Address The address defining the inclusive lower bound of the memory re gion Hi Address The address defining the exclusive upper bound of the memory region Attributes The list of attributes set for this memory region 8 14 1 Attributes 8 14 1 1 Memory Access Mode The access mo
311. el of annotations to the specified level show annotate Show the current annotation level This chapter describes level 3 annotations A simple example of starting up GDB with annotations is gdb annotate 3 GNU gdb 6 0 Copyright 2003 Free Software Foundation Inc GDB is free software covered by the GNU General Public License and you are welcome to change it and or distribute copies of it under certain conditions Type show copying to see the conditions There is absolutely no warranty for GDB Type show warranty for details This GDB was configured as i386 pc linux gnu Z Zpre prompt gdb Z Zprompt quit 288 Debugging with GDB Z Zpost prompt Here quit is input to GDB the rest is output from GDB The three lines beginning Z Z where Z denotes a control z character are annotations the rest is output from GDB 25 2 The Server Prefix If you prefix a command with server then it will not affect the command history nor will it affect GDB s notion of which command to repeat if is pressed on a line by itself This means that commands can be run behind a user s back by a front end in a transparent manner The server prefix does not affect the recording of values into the value history to print a value without recording it into the value history use the output command instead of the print command 25 3 Annotation for GDB Input When GDB prompts for input it annotates th
312. emote Show SYSLOG pi synced cohesive Rhee eed show target charset sccis esee eere show task Hurd commands show tdesc filename 2 4 show thread Hurd command show timeout Re rep show unwindonsignal enres id Show SO gegen e bp RP eis SHOW valud recer arcera uae b be REIR show verbOS6 n dace n gere be RE 415 Show version sd o po e Fate e RR s 23 show WarTanbyie 2502 9 cde ecc s xe ped a RER 23 show widthD 6 asta dmm er e Ron ws 209 SHOW Write cire e ep EXC Ge RR Rees 153 show all if ambiguous 301 show all if unmodified 301 Si Stepi nee eR ETE PIE AAT 55 SJgnalilsi22202 4 0058 RI UTI AU deuda 151 signal annotation lessen ee ees 290 signal name annotation 289 signal name end annotation 289 signal string annotation 289 signal string end annotation 289 signalled annotation 289 Siena soe vec PE eee TE ee Reda 56 SIGQUIT signal dump core of GDB 328 Silent 2g ds eria eed aon ener es 50 SIM MT 201 sim a commarnd zleiiececu eem Pedes 192 simulator Z8000 2 4 hr Rem mre 201 size of remote memory accesses 336 Size Of SCREENS reniei eean aai uu RN repe 209 snapshot of a process 00 eee e ee eee 35 software watchpoints 0ee eee 43 SOUC Steco pL RR ER Pee A
313. en cycle step See step with signal packet page 337 See cycle step packet page 336 Kill request FIXME There is no description of how to operate when a specific thread context has been selected i e does k kill only that thread m addr length Read length bytes of memory starting at address addr Note that addr may not be aligned to any particular boundary The stub need not use any particular size or alignment when gathering data from memory for the response even if addr is word aligned and length is a multiple of the word size the stub is free to use byte accesses or not For this reason this packet may not be suitable for accessing memory mapped I O devices Reply XX Memory contents each byte is transmitted as a two digit hexadec imal number The reply may contain fewer bytes than requested if the server was able to read only part of the region of memory E NN NN is errno Appendix D GDB Remote Serial Protocol 337 M addr length XX Write length bytes of memory starting at address addr XX is the data each byte is transmitted as a two digit hexadecimal number Reply OK for success E NN for an error this includes the case where only part of the data was written Read the value of register n n is in hex See read registers packet page 335 for a description of how the returned register value is encoded Reply XX eee the register s value E NN
314. ends a BREAK signal to the remote when you type Ctrl c to interrupt the program running on the remote If set to off GDB sends the Ctrl C character instead The default is off since most remote systems expect to see Ctrl C as the interrupt signal show remotebreak Show whether GDB sends BREAK or Ctrl C to interrupt the remote program Set remoteflow on set remoteflow off Enable or disable hardware flow control RTS CTS on the serial port used to communicate to the remote target show remoteflow Show the current setting of hardware flow control set remotelogbase base Set the base a k a radix of logging serial protocol communications to base Supported values of base are ascii octal and hex The default is ascii show remotelogbase Show the current setting of the radix for logging remote serial protocol set remotelogfile file Record remote serial communications on the named file The default is not to record at all show remotelogfile Show the current setting of the file name on which to record the serial commu nications set remotetimeout num Set the timeout limit to wait for the remote target to respond to num seconds The default is 2 seconds Show remotetimeout Show the current number of seconds to wait for the remote target responses 176 Debugging with GDB set remote hardware watchpoint limit limit Set remote hardware breakpoint limit limit Restrict GDB to using limit remote hardware bre
315. ense notice the full lists of Invariant Sections and required Cover Texts given in the Document s license notice Include an unaltered copy of this License Preserve the section Entitled History Preserve its Title and add to it an item stating at least the title year new authors and publisher of the Modified Version as given on the Title Page If there is no section Entitled History in the Docu ment create one stating the title year authors and publisher of the Document as given on its Title Page then add an item describing the Modified Version as stated in the previous sentence Preserve the network location if any given in the Document for public access to a Transparent copy of the Document and likewise the network locations given in the Document for previous versions it was based on These may be placed in the History section You may omit a network location for a work that was published at least four years before the Document itself or if the original publisher of the version it refers to gives permission For any section Entitled Acknowledgements or Dedications Preserve the Title of the section and preserve in the section all the substance and tone of each of the contributor acknowledgements and or dedications given therein Preserve all the Invariant Sections of the Document unaltered in their text and in their titles Section numbers or the equivalent are not considered part of the section titles
316. ent Languages 119 12 1 Switching Between Source Languages 00 119 12 1 1 List of Filename Extensions and Languages 119 12 1 2 Setting the Working Language 120 12 1 3 Having GDB Infer the Source Language 120 12 2 Displaying the Language 0 0 essen 120 12 3 Type and Range Checking 0 0 0 cece eee eee 121 12 3 1 An Overview of Type Checking 2 121 12 3 2 An Overview of Range Checking 122 12 4 Supported Languages sssssessseeeess ee 123 RAT Cand C il deo eo eta a a e Lee egg 123 12 4 1 1 C and C Operators 0 000 ee 124 12 4 1 2 C and C Constants 0 0000 cece ee eee 125 12 4 1 38 C Expressions edass ga a a cece eee eee 126 12 4 1 4 Cand C Defaults 0 0 eee eee ee 127 12 4 1 5 C and C Type and Range Checks 127 12 4 1 0 GDB and C rid aiia aa ba o tee PR ER ends 127 12 4 1 7 GDB Features for C iiisslsiisssllsseese 128 12 4 2 Objective C ciscus eR PLE CRETM pde 129 12 4 2 1 Method Names in Commands 129 12 4 2 2 The Print Command With Objective C 130 12 4 3 BOrtr nz sex ER e RERO Rab etx EE 130 12 4 3 1 Fortran Operators and Expressions 130 12 4 3 2 Fortran Defaults sees 130 iv Debugging with GDB 12 4 3 8 Special Fortran Commands 130 IAA P
317. ent is less than one half of the entire aggregate the Document s Cover Texts may be placed on covers that bracket the Document within the aggregate or the electronic equivalent of covers if the Document is in electronic form Otherwise they must appear on printed covers that bracket the whole aggregate TRANSLATION Iranslation is considered a kind of modification so you may distribute translations of the Document under the terms of section 4 Replacing Invariant Sections with translations requires special permission from their copyright holders but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections You may include a translation of this License and all the license notices in the Document and any Warranty Disclaimers provided that you also include the original English version of this License and the original versions of those notices and disclaimers In case of a disagreement between the translation and the original version of this License or a notice or disclaimer the original version will prevail If a section in the Document is Entitled Acknowledgements Dedications or His tory the requirement section 4 to Preserve its Title section 1 will typically require changing the actual title TERMINATION You may not copy modify sublicense or distribute the Document except as expressly provided for under this License Any other attempt to copy m
318. ent stack frame GDB uses the macros in scope at that frame s source code line Otherwise GDB uses the macros in scope at the current listing location see Section 7 1 List page 67 At the moment GDB does not support the token splicing operator the stringification operator or variable arity macros Whenever GDB evaluates an expression it always expands any macro invocations present in the expression GDB also provides the following commands for working with macros explicitly macro expand expression macro exp expression Show the results of expanding all preprocessor macro invocations in expression Since GDB simply expands macros but does not parse the result expression need not be a valid expression it can be any string of tokens macro expand once expression macro exp expression This command is not yet implemented Show the results of expanding those preprocessor macro invocations that appear explicitly in expression Macro invocations appearing in that expansion are left unchanged This command allows you to see the effect of a particular macro more clearly without being confused by further expansions Since GDB simply expands macros but does not parse the result expression need not be a valid expression it can be any string of tokens info macro macro Show the definition of the macro named macro and describe the source location where that definition was established macro define macro replacement list macro
319. ents the problem by considering the symbol to have the name foo which may cause other problems if many symbols end up with this name unknown symbol type Oxnn The symbol information contains new data types that GDB does not yet know how to read Oxnn is the symbol type of the uncomprehended information in hexadecimal GDB circumvents the error by ignoring this symbol information This usually allows you to debug your program though certain symbols are not accessible If you encounter such a problem and feel like debugging it you can debug gdb with itself breakpoint on complain then go up to the function read dbx symtab and examine bufp to see the symbol stub type has NULL name GDB could not find the full definition for a struct or class const volatile indicator missing ok if using g v1 x got The symbol information for a C member function is missing some information that recent versions of the compiler should have output for it info mismatch between compiler and debugger GDB could not parse a type specification output by the compiler 166 Debugging with GDB Chapter 16 Specifying a Debugging Target 167 16 Specifying a Debugging Target A target is the execution environment occupied by your program Often GDB runs in the same host environment as your program in that case the de bugging target is specified as a side effect when you use the file or core commands When you need more flexibility for example runn
320. er or more frequently than expected 5 2 Continuing and Stepping Continuing means resuming program execution until your program completes normally In contrast stepping means executing just one more step of your program where step may mean either one line of source code or one machine instruction depending on what particular command you use Either when continuing or when stepping your program may stop even sooner due to a breakpoint or a signal If it stops due to a signal you may want to use handle or use signal 0 to resume execution See Section 5 3 Signals page 56 Chapter 5 Stopping and Continuing 53 continue ignore count c ignore count fg ignore count Resume program execution at the address where your program last stopped any breakpoints set at that address are bypassed The optional argument ignore count allows you to specify a further number of times to ignore a break point at this location its effect is like that of ignore see Section 5 1 6 Break Conditions page 48 The argument ignore count is meaningful only when your program stopped due to a breakpoint At other times the argument to continue is ignored The synonyms c and fg for foreground as the debugged program is deemed to be the foreground program are provided purely for convenience and have exactly the same behavior as continue To resume execution at a different place you can use return see Section 14 4 Returning from a F
321. erminal interface which uses the curses library to show the source file the assembly output the program registers and GDB commands in separate text windows The TUI mode is supported only on platforms where a suitable version of the curses library is available The TUI mode is enabled by default when you invoke GDB as either gdbtui or gdb tui You can also switch in and out of TUI mode while GDB runs by using various TUI commands and key bindings such as C x C a See Section 22 2 TUI Key Bindings page 226 22 1 TUI Overview In TUI mode GDB can display several text windows command This window is the GDB command window with the GDB prompt and the GDB output The GDB input is still managed using readline source The source window shows the source file of the program The current line and active breakpoints are displayed in this window assembly The assembly window shows the disassembly output of the program register This window shows the processor registers Registers are highlighted when their values change The source and assembly windows show the current program position by highlighting the current line and marking it with a gt marker Breakpoints are indicated with two markers The first marker indicates the breakpoint type B Breakpoint which was hit at least once b Breakpoint which was never hit H Hardware breakpoint which was hit at least once h Hardware breakpoint which was never hit The seco
322. ermine the appropriate address of a function or variable depending on whether the overlay is mapped or not GDB s overlay commands all start with the word overlay you can abbreviate this as ov or ovly The commands are Chapter 11 Debugging Programs That Use Overlays 115 overlay off Disable GDB s overlay support When overlay support is disabled GDB assumes that all functions and variables are always present at their mapped addresses By default GDB s overlay support is disabled overlay manual Enable manual overlay debugging In this mode GDB relies on you to tell it which overlays are mapped and which are not using the overlay map overlay and overlay unmap overlay commands described below overlay map overlay overlay overlay map overlay Tell GDB that overlay is now mapped overlay must be the name of the object file section containing the overlay When an overlay is mapped GDB assumes it can find the overlay s functions and variables at their mapped addresses GDB assumes that any other overlays whose mapped ranges overlap that of overlay are now unmapped overlay unmap overlay overlay overlay unmap overlay Tell GDB that overlay is no longer mapped overlay must be the name of the object file section containing the overlay When an overlay is unmapped GDB assumes it can find the overlay s functions and variables at their load addresses overlay auto Enable automatic overlay debugging In this mode GDB consults a
323. ernal GDB variable GDB Command The corresponding GDB command is set 283 284 Debugging with GDB Example The gdb gdb set f00 3 done gdb gdb show Command Synopsis gdb show Show the current value of a GDB variable GDB Command The corresponding GDB command is show Example The gdb gdb show annotate done value 0 gdb gdb version Command Synopsis gdb version Show version information for GDB Used mostly in testing GDB Command The GDB equivalent is show version GDB by default shows this information when you start an interactive session Example The gdb gdb version 7GNU gdb 5 2 1 Copyright 2000 Free Software Foundation Inc GDB is free software covered by the GNU General Public License and you are welcome to change it and or distribute copies of it under 7 certain conditions Type show copying to see the conditions There is absolutely no warranty for GDB Type show warranty for 7 details This GDB was configured as host sparc sun solaris2 5 1 target ppc eabi done gdb list features Command Returns a list of particular features of the MI protocol that this version of gdb implements A feature can be a command or a new field in an output of some command or even an important bugfix While a frontend can sometimes detect presence of a feature at runtime it is easier to perform detection
324. ero less signed 0x14 a b a b Pop two signed integers from the stack if the next to top value is less than the top value push the value one otherwise push the value zero less unsigned 0x15 a b a b Pop two unsigned integers from the stack if the next to top value is less than the top value push the value one otherwise push the value zero ext 0x16 n a a sign extended from n bits Pop an unsigned value from the stack treating it as an n bit twos complement value extend it to full length This means that all bits to the left of bit n 1 where the least significant bit is bit 0 are set to the value of bit n 1 Note that n may be larger than or equal to the width of the stack elements of the bytecode engine in this case the bytecode should have no effect The number of source bits to preserve n is encoded as a single byte unsigned integer following the ext bytecode zero ext 0x2a n a a zero extended from n bits Pop an unsigned value from the stack zero all but the bottom n bits This means that all bits to the left of bit n 1 where the least significant bit is bit 0 are set to the value of bit n 1 The number of source bits to preserve n is encoded as a single byte unsigned integer following the zero ext bytecode ref8 0x17 addr a ref16 0x18 addr gt a ref32 0x19 addr gt a ref64 Oxla addr gt a Pop an address addr from the stack For bytecode refn fetch an n bit value
325. error F RC EE CF XX A reply from GDB to an F packet sent by the target This is part of the File I O protocol extension See Section D 9 File I O Remote Protocol Extension page 354 for the specification Read general registers Reply KK a Each byte of register data is described by two hex digits The bytes with the register are transmitted in target byte order The size of 336 G XX Het Debugging with GDB each register and their position within the g packet are determined by the GDB internal gdbarch functions DEPRECATED_REGISTER_RAW_ SIZE and gdbarch_register_name The specification of several standard g packets is specified below E NN for an error Write general registers See read registers packet page 335 for a description of the XX data Reply OK for success E NN for an error Set thread for subsequent operations m M g G et al c depends on the operation to be performed it should be c for step and continue operations g for other operations The thread designator t may be 1 meaning all the threads a thread number or 0 which means pick any thread Reply OK for success E NN for an error i addr nnn 0e Step the remote target by a single clock cycle If nnn is present cycle step nnn cycles If addr is present cycle step starting at that address Signal th
326. es target target host Configure GDB for cross debugging programs running on the specified target Without this option GDB is configured to debug programs that run on the same machine host as GDB itself There is no convenient way to generate a list of all available targets Configure GDB to run on the specified host There is no convenient way to generate a list of all available hosts There are many other options available as well but they are generally needed for special purposes only 326 Debugging with GDB Appendix C Maintenance Commands 327 Appendix C Maintenance Commands In addition to commands intended for GDB users GDB includes a number of commands intended for GDB developers that are not documented elsewhere in this manual These commands are provided here for reference For commands that turn on debugging mes sages see Section 19 8 Debugging Output page 213 maint agent expression Translate the given expression into remote agent bytecodes This command is useful for debugging the Agent Expression mechanism see Appendix E Agent Expressions page 369 maint info breakpoints Using the same format as info breakpoints display both the breakpoints you ve set explicitly and those GDB is using for internal purposes Internal breakpoints are shown with negative breakpoint numbers The type column identifies what kind of breakpoint is shown breakpoint Normal explicitly set breakpoint
327. es Typically these two classes of target are complementary since core files contain only a program s read write memory variables and so on plus machine status while executable files contain only the program text and initialized data When you type run your executable file becomes an active process target as well When a process target is active all GDB commands requesting memory addresses refer to that target addresses in an active core file or executable file target are obscured while the process target is active Use the core file and exec file commands to select a new core file or executable target see Section 15 1 Commands to Specify Files page 155 To specify as a target a process that is already running use the attach command see Section 4 7 Debugging an Already running Process page 30 168 Debugging with GDB 16 2 Commands for Managing Targets target type parameters Connects the GDB host environment to a target machine or process A target is typically a protocol for talking to debugging facilities You use the argument type to specify the type or protocol of the target machine Further parameters are interpreted by the target protocol but typically include things like device names or host names to connect with process numbers and baud rates The target command does not repeat if you press again after executing the command help target Displays the names of all targets available To display targets current
328. es none gdb maint info symtabs gdb We see that there is one partial symbol table whose filename contains the string dwarf 2read belonging to the gdb executable and we see that GDB has not read in any symtabs yet at all If we set a breakpoint on a function that will cause GDB to read the symtab for the compilation unit containing that function gdb break dwarf2_psymtab_to_symtab Breakpoint 1 at 0x814e5da file home gnu src gdb dwarf2read c line 1574 gdb maint info symtabs objfile home gnu build gdb gdb struct objfile 0x82e69d0 symtab home gnu src gdb dwarf2read c struct symtab 0x86c1f38 dirname null fullname null blockvector struct blockvector Ox86cibdO primary debugformat DWARF 2 gdb 148 Debugging with GDB Chapter 14 Altering Execution 149 14 Altering Execution Once you think you have found an error in your program you might want to find out for certain whether correcting the apparent error would lead to correct results in the rest of the run You can find the answer by experiment using the GDB features for altering execution of the program For example you can store new values into variables or memory locations give your pro gram a signal restart it at a different address or even return prematurely from a function 14 1 Assignment to Variables To alter the value of a variable evaluate an assignment expression See Section 8 1 Ex pressions pag
329. es there are several ways of writing them but the effect is always to specify some source line Here is a complete description of the possible arguments for list list linespec Print lines centered around the line specified by linespec list first last Print lines from first to last Both arguments are linespecs 68 Debugging with GDB list last Print lines ending with last list first Print lines starting with first list Print lines just after the lines last printed list Print lines just before the lines last printed list As described in the preceding table Here are the ways of specifying a single source line all the kinds of linespec number Specifies line number of the current source file When a list command has two linespecs this refers to the same source file as the first linespec offset Specifies the line offset lines after the last line printed When used as the second linespec in a list command that has two this specifies the line offset lines down from the first linespec offset Specifies the line offset lines before the last line printed filename number Specifies line number in the source file filename function Specifies the line that begins the body of the function function For example in C this is the line with the open brace filename function Specifies the line of the open brace that begins the body of the function function in the file filename You only need the file name with a fu
330. es RR edd eerte 82 print structures in indented form 85 print object if os gor sero bed eben e 130 print don t print memory addresses 82 printf ps gx ee eR ROGER ees 221 printing byte arrays eese 19 printing dabas mre rni read Ede ae 75 printing StriNgS enini RR IREEURRRO DRE 19 proc trace entry 22s2 593 pires 182 proc trace exit i e bg Pde anes 182 proc untrace entry gosse in nn 182 proc untrace exit i idem ERRORES Ee 182 process detailed status information 182 process Dm 181 process info via pro score 181 process list QNX Neutrino 182 process status register iles se ue 90 processes multiple 0 2 2 eeeeee 33 procfs API calls 4 2 Losses euderpoins 182 profiling GDB 51i ie ete 330 program counter register 000 90 program entry point senate ERR 63 DIOnID emeccnureexee haee d e p eene Debs 207 prompt ANNOTATION 3 eed 2 029 Eee 288 prompt for continue annotation 288 protocol basics file i o ee eee eee 355 protocol GDB remote serial 333 protocol specific representation of datatypes in file i o protocol 0 0 000 363 ptrace system call i cre serra 92 PUY Peles rm 144 putDebugChar sos dne eee ede ee 179 PWG oc bts es chit bed elie eg ener Staaten d 29 Q q quit csissecepceERR DP EE E PES 16 q SingleKey TUI key
331. es are selected To pop entire frames off the stack regardless of machine architecture use return see Section 14 4 Returning from a Function page 151 Chapter 8 Examining Data 91 GDB always considers the contents of an ordinary register as an integer when the register is examined in this way Some machines have special registers which can hold nothing but floating point these registers are considered to have floating point values There is no way to refer to the contents of an ordinary register as floating point value although you can print it as a floating point value with print f regname Some registers have distinct raw and virtual data formats This means that the data format in which the register contents are saved by the operating system is not the same one that your program normally sees For example the registers of the 68881 floating point coprocessor are always saved in extended raw format but all C programs expect to work with double virtual format In such cases GDB normally works with the virtual format only the format that makes sense for your program but the info registers command prints the data in both formats Some machines have special registers whose contents can be interpreted in several differ ent ways For example modern x86 based machines have SSE and MMX registers that can hold several values packed together in several different formats GDB refers to such registers in struct n
332. es as the original file but they need not contain any data much like a bss section in an ordinary executable The GNU binary utilities Binutils package includes the objcopy utility that can pro duce the separated executable debugging information file pairs using the following com mands Chapter 15 GDB Files objcopy only keep debug foo foo debug strip g foo These commands remove the debugging information from the executable file foo and place it in the file foo debug You can use the first second or both methods to link the two files e The debug link method needs the following additional command to also leave behind a debug link in foo Ulrich Drepper s elfutils package starting with version 0 53 contains a version of the strip command such that the command strip foo f foo debug has the same functionality as the two objcopy commands and the 1n s command above together e Build ID gets embedded into the main executable using 1d build id or the GCC counterpart gcc W1 build id Build ID support plus compatibility fixes for debug files separation are present in GNU binary utilities Binutils package since version 2 18 Since there are many different ways to compute CRC s for the debug link different polynomials reversals byte ordering etc the simplest way to describe the CRC used in gnu debuglink sections is to give the complete code for a function that computes it objcopy
333. es check for a core file first Taking advantage of the second command line argument requires a fairly complete op erating system when you use GDB as a remote debugger attached to a bare board there may not be any notion of process and there is often no way to get a core dump GDB will warn you if it is unable to attach or to read core dumps You can optionally have gdb pass any arguments after the executable file to the inferior using args This option stops option processing Edb args gcc 02 c foo c This will cause gdb to debug gcc and to set gcc s command line arguments see Sec tion 4 3 Arguments page 27 to 02 c foo c You can run gdb without printing the front material which describes GDB s non warranty by specifying silent gdb silent You can further control how GDB starts up by using command line options GDB itself can remind you of the options available Type gdb help to display all available options and briefly describe their use gdb h is a shorter equiva lent All options and command line arguments you give are processed in sequential order The order makes a difference when the x option is used 12 Debugging with GDB 2 1 1 Choosing Files When GDB starts it reads any arguments other than options as specifying an executable file and core file or process ID This is the same as if the arguments were specified by the se and c or p options respectively GD
334. es providing command line editing and command history Andrew Beers of SUNY Buffalo wrote the language switching code the Modula 2 sup port and contributed the Languages chapter of this manual Fred Fish wrote most of the support for Unix System Vr4 He also enhanced the command completion support to cover C overloaded symbols Hitachi America now Renesas America Ltd sponsored the support for H8 300 H8 500 and Super H processors NEC sponsored the support for the v850 Vr4xxx and Vr5xxx processors Mitsubishi now Renesas sponsored the support for D10V D30V and M32R D proces sors Toshiba sponsored the support for the TX39 Mips processor Matsushita sponsored the support for the MN10200 and MN10300 processors Fujitsu sponsored the support for SPARClite and FR30 processors Kung Hsu Jeff Law and Rick Sladkey added support for hardware watchpoints Michael Snyder added support for tracepoints Stu Grossman wrote gdbserver Jim Kingdon Peter Schauer Ian Taylor and Stu Grossman made nearly innumerable bug fixes and cleanups throughout GDB The following people at the Hewlett Packard Company contributed support for the PA RISC 2 0 architecture HP UX 10 20 10 30 and 11 0 narrow mode HP s implementation of kernel threads HP s aC compiler and the Text User Interface nee Terminal User Interface Ben Krepp Richard Title John Bishop Susan Macchia Kathy Mann Satish Pai India Paul Steve Rehrauer and E
335. ese 3T breakpoint on memory address 3T breakpoint on variable modification 37 breakpoint ranges i oec ere eee pees 3T breakpoint subroutine remote 178 breakpointing Ada elaboration code 140 breakpoints eet tog taewieee soa ROI EAS 37 breakpoints and threads 04 ov breakpoints in functions matching a regexp 39 breakpoints in overlays 00 116 breakpoints invalid annotation 289 bt backtrace 12 d d dp e E dee Db phre 62 bug crilerla eseeto Re pese RE ERR 291 404 DUG TEPOTIS o sexe ewe hu RU Pr ERE 291 b gs I GDB ig ngs ag af etse tue path aig dais 291 build ID sections 4 rr rr niti ero 162 build ID and separate debugging files 161 building GDB requirements for 321 built in simulator target 00 169 C continue ls mee tee near ROME ME 53 c SingleKey TUI key sseseseses 227 C and CET LobllilBassneeefeeeteke ee dd eee bed 123 C and C checks loteiss e RR REIR 127 C and C constants esl esee eese 125 C and C defaults 2200520 coc tn 127 C and C operators 2 eee eee eee 124 BG packeb oss ovem doodete audere tede aaee cd 335 GC packets dp ea nea edad PROP NE En 335 e pn 123 G Compile S eus 3h Rr pai ai i EVO EIEN 126 C exception handling 128 C overload debugging info 214 C sc
336. esponding GDB command is info shared Example N A The file list symbol files Command Synopsis file list symbol files List symbol files GDB Command The corresponding GDB command is info file part of it Example N A The file symbol file Command Synopsis file symbol file file Read symbol table info from the specified file argument When used without arguments clears GDB s symbol table info No output is produced except for a completion notification GDB Command The corresponding GDB command is symbol file Example gdb file symbol file kwikemart marge ezannoni TRUNK mbx hello mbx done gdb Chapter 24 The GDB MI Interface 279 24 19 GpB MI Target Manipulation Commands The target attach Command Synopsis target attach pid file Attach to a process pid or a file file outside of GDB GDB Command The corresponding GDB command is attach Example N A The target compare sections Command Synopsis target compare sections section Compare data of section section on target to the exec file Without the argument all sections are compared GDB Command The GDB equivalent is compare sections Example N A The target detach Command Synopsis target detach Detach from the remote target which normally resumes its execution There s no output GDB Command The corresponding GDB command is detach Example gdb target detach don
337. et a SIGTRAP signal which unless it catches the signal will cause it to terminate However if you want to debug the child process there is a workaround which isn t too painful Put a call to sleep in the code which the child process executes after the fork It may be useful to sleep only if a certain environment variable is set or a certain file exists so that the delay need not occur when you don t want to run GDB on the child While the child is sleeping use the ps program to get its process ID Then tell GDB a new invocation of GDB if you are also debugging the parent process to attach to the child process see Section 4 7 Attach page 30 From that point on you can debug the child process just like any other process which you attached to 34 Debugging with GDB On some systems GDB provides support for debugging programs that create additional processes using the fork or vfork functions Currently the only platforms with this feature are HP UX 11 x and later only and GNU Linux kernel version 2 5 60 and later By default when a program forks GDB will continue to debug the parent process and the child process will run unimpeded If you want to follow the child process instead of the parent process use the command set follow fork mode set follow fork mode mode Set the debugger response to a program call of fork or vfork A call to fork or vfork creates a new process The mode argument can be parent The original process
338. et download download section text section size 6668 total size 9880 Chapter 24 The GDB MI Interface download section text section sent 512 section size 6668 total sent 512 total size 9880 download section text section sent 1024 section size 6668 total sent 1024 total size 9880 download section text section sent 1536 section size 6668 total sent 1536 total size 9880 download section text section sent 2048 section size 6668 total sent 2048 total size 9880 download section text section sent 2560 section size 6668 total sent 2560 total size 9880 download section text section sent 3072 section size 6668 total sent 3072 total size 9880 download section text section sent 3584 section size 6668 total sent 3584 total size 9880 download section text section sent 4096 section size 6668 total sent 4096 total size 9880 download section text section sent 4608 section size 6668 total sent 4608 total size 9880 download section text section sent 5120 section size 6668 total sent 5120 total size 9880 download section text section sent 5632 section size 6668 total sent 5632 total size 9880 download section text section sent 6144 section size 6668 total sent 6144 total size 9880 download section text section sent 6656 section size 6668 total sent 6656 tota
339. eta key if you have one is depressed and the k key is pressed The Meta key is labeled on many keyboards On keyboards with two keys labeled usually to either side of the space bar the on the left side is generally set to work as a Meta key The key on the right may also be configured to work as a Meta key or may be configured as some other modifier such as a Compose key for typing accented characters If you do not have a Meta or key or another key working as a Meta key the identical keystroke can be generated by typing first and then typing E Either process is known as metafying the key The text M C k is read as Meta Control k and describes the character produced by metafying C k In addition several keys have their own names Specifically DEL ESC LFD GPO RET and all stand for themselves when seen in this text or in an init file see Section 27 3 Readline Init File page 298 If your keyboard lacks a key typing will produce the desired character The key may be labeled or on some keyboards 27 2 Readline Interaction Often during an interactive session you type in a long line of text only to notice that the first word on the line is misspelled The Readline library gives you a set of commands for manipulating the text as you type it in allowing you to just fix your typo and not forcing you to retype the majority of the line Using these editing commands you move the cursor to the place that
340. expression and thus one half the number of hex digits in the packet Any number of actions may be packed together in a single QTDP packet as long as the packet does not exceed the maximum packet length 400 bytes for many stubs There may be only one R action per tracepoint and it must precede any M or X actions Any registers referred to by M and X actions must be collected by a preceding R action The while stepping actions are treated as if they were attached to a separate tracepoint as far as these restrictions are concerned Replies OK The packet was understood and carried out 6 The packet was not recognized Appendix D GDB Remote Serial Protocol 353 QTFrame n Select the n th tracepoint frame from the buffer and use the register and mem ory contents recorded there to answer subsequent request packets from GDB A successful reply from the stub indicates that the stub has found the requested frame The response is a series of parts concatenated without separators describing the frame we selected Each part has one of the following forms Ff The selected frame is number n in the trace frame buffer f is a hexadecimal number If f is 1 then there was no frame matching the criteria in the request packet Tt The selected trace frame records a hit of tracepoint number t t is a hexadecimal number QTFrame pc addr Like QTFrame n
341. f args name format value 0x8048e9c WV A sAc 4d h c n name arg value 0x2 file vprintf c line 31 gdb 24 12 GDB MI Program Execution These are the asynchronous commands which generate the out of band record stopped Currently GDB only really executes asynchronously with remote targets and this interaction is mimicked in other cases The exec continue Command Synopsis y D conte Resumes the execution of the inferior program until a breakpoint is encountered or until the inferior exits GDB Command The corresponding GDB corresponding is continue Example ec continue running gdb Hello world stopped reason breakpoint hit bkptno 2 frame func foo args file hello c fullname home foo bar hello c line 13 gdb The exec finish Command Synopsis exec finish Resumes the execution of the inferior program until the current function is exited Dis plays the results returned by the function 252 Debugging with GDB GDB Command The corresponding GDB command is finish Example Function returning void exec finish running gdb Ohello from foo stopped reason function finished frame func main args file hello c fullname home foo bar hello c line 7 gdb Function returning other than void The name of the internal GDB variable storing the result is printed together with the value itself exec finish running gdb stopped
342. f number 26 value Oxfffffffb number 27 value Oxffffffff number 28 value Oxf7bfffff number 29 value Ox0 number 30 value Oxfe010000 number 31 value 0x0 number 32 value 0x0 number 33 value 0x0 number 34 value 0x0 number 35 value 0x0 number 36 value 0x0 number 37 value 0x0 number 38 value 0x0 number 39 value 0x0 number 40 value 0x0 number 41 value 0x0 number 42 value 0x0 number 43 value 0x0 number 44 value 0x0 number 45 value 0x0 number 46 value 0x0 number 47 value 0x0 number 48 value 0x0 number 49 value 0x0 number 50 value 0x0 number 51 value 0x0 number 52 value 0x0 number 53 value 0x0 number 54 value 0x0 number 55 value 0x0 number 56 value 0x0 number 57 value 0x0 number 58 value 0x0 number 59 value 0x0 number 60 value 0x0 number 61 value 0x0 number 62 value 0x0 number 63 value 0x0 number 64 value 0xfe00a300 number 65 value 0x29002 number 66 value 0x202f04b5 number 67 value 0xfe0043b0 number 68 value 0xfe00b3e4 number 69 value 0x20002b03 gdb The data read memory Command Synop amp i amp read nenory o byte offset address word format word size nr rows nr cols
343. f a parent variable or by var update Only var update of the variable itself will update its value and values of its children After a variable object is unfrozen it is implicitly updated by all subsequent var update operations Unfreezing a variable does not update it only subsequent var update does Example gdb var set frozen V 1 done gdb 24 15 GDB MI Data Manipulation This section describes the GDB MI commands that manipulate data examine memory and registers evaluate expressions etc The data disassemble Command Chapter 24 The GDB MI Interface 267 Synopsis data disassemble s start addr e end addr f filename 1 linenum n lines mode Where start addr is the beginning address or pc end addr is the end address filename is the name of the file to disassemble linenum is the line number to disassemble around lines is the number of disassembly lines to be produced If it is 1 the whole function will be disassembled in case no end addr is specified If end addr is specified as a non zero value and lines is lower than the number of disassembly lines between start addr and end addr only lines lines are displayed if lines is higher than the number of lines between start addr and end addr only the lines up to end addr are displayed mode is either 0 meaning only disassembly or 1 meaning mixed source and disas sembly Result The out
344. f of you may not add another but you may replace the old one on explicit permission from the previous publisher that added the old one The author s and publisher s of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version 5 COMBINING DOCUMENTS You may combine the Document with other documents released under this License under the terms defined in section 4 above for modified versions provided that you include in the combination all of the Invariant Sections of all of the original documents unmodified and list them all as Invariant Sections of your combined work in its license notice and that you preserve all their Warranty Disclaimers The combined work need only contain one copy of this License and multiple identical Invariant Sections may be replaced with a single copy If there are multiple Invariant Sections with the same name but different contents make the title of each such section unique by adding at the end of it in parentheses the name of the original author or publisher of that section if known or else a unique number Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work In the combination you must combine any sections Entitled History in the vari ous original documents forming one section Entitled History likewise combine any sections Entitled
345. fails As an example suppose the trace frame f has saved sixteen bytes from address 0x8000 in a buffer at 0x1000 and thirty two bytes from address 0xc000 in a buffer at 0x1010 Here are some sample calls and the effect each would have adbg_find_memory_in_frame f char 0x8000 amp buffer amp size This would set buffer to 0x1000 set size to sixteen and return OK_TARGET_ RESPONSE since f saves sixteen bytes from 0x8000 at 0x1000 adbg_find_memory_in_frame f char 0x8004 amp buffer amp size This would set buffer to 0x1004 set size to twelve and return OK_TARGET_ RESPONSE since f saves the twelve bytes from 0x8004 starting four bytes into the buffer at 0x1000 This shows that request addresses may fall in the middle of saved areas the function should return the address and size of the remainder of the buffer adbg_find_memory_in_frame f char 0x8100 amp buffer amp size This would set size to 0x3 00 and return NOT FOUND TARGET RESPONSE since there is no memory saved in f from the address 0x8100 and the next memory available is at 0x8100 Ox3f00 or Oxc000 This shows that request addresses may fall outside of all saved memory ranges the function should indicate the next saved area if any adbg find memory in frame f char 0x7000 amp buffer amp size This would set size to 0x1000 and return NOT FOUND TARGET RESPONSE since the next saved memory is at 0x7000 0x1000 or 0x8000 adbg
346. fect your program See Section 4 4 Your Program s Environment page 28 The working directory Your program inherits its working directory from GDB You can set the GDB working directory with the cd command in GDB See Section 4 5 Your Pro gram s Working Directory page 29 The standard input and output Your program normally uses the same device for standard input and standard output as GDB is using You can redirect input and output in the run command line or you can use the tty command to set a different device for your program See Section 4 6 Your Program s Input and Output page 29 Warning While input and output redirection work you cannot use pipes to pass the output of the program you are debugging to another program if you attempt this GDB is likely to wind up debugging the wrong program When you issue the run command your program begins to execute immediately See Chapter 5 Stopping and Continuing page 37 for discussion of how to arrange for your program to stop Once your program has stopped you may call functions in your program using the print or call commands See Chapter 8 Examining Data page 75 Chapter 4 Running Programs Under GDB 27 If the modification time of your symbol file has changed since the last time GDB read its symbols GDB discards its symbol table and reads it again When it does this GDB tries to retain your current breakpoints start The name of the main procedure can vary from la
347. ffset one byte at a time goto 0x21 offset Branch unconditionally to offset in other words set the pc register to start offset The offset is stored in the same way as for the if goto bytecode const8 0x22 n n consti6 0x23 n n const32 0x24 n gt n const64 0x25 n gt n Push the integer constant n on the stack without sign extension To produce a small negative value push a small twos complement value and then sign extend it using the ext bytecode The constant n is stored in the appropriate number of bytes following the constb bytecode The constant n is always stored most significant byte first regardless of the target s normal endianness T he constant is not guaranteed to fall at any particular alignment within the bytecode stream thus on machines where fetching a 16 bit on an unaligned address raises an exception you should fetch n one byte at a time reg 0x26 n a Push the value of register number n without sign extension The registers are numbered following GDB s conventions Appendix E The GDB Agent Expression Mechanism 375 The register number n is encoded as a 16 bit unsigned integer immediately fol lowing the reg bytecode It is always stored most significant byte first regard less of the target s normal endianness The register number is not guaranteed to fall at any particular alignment within the bytecode stream thus on machines where fetching a 16 bit on an una
348. fications of complex data structure If the debug information included in the program does not allow GDB to display a full declaration of the data type it will say lt incomplete type gt For example given these declarations struct foo struct foo fooptr but no definition for struct foo itself GDB will say gdb ptype foo 1 lt incomplete type gt Incomplete type is C terminology for data types that are not completely specified regexp Print a brief description of all types whose names match the regular expression regexp or all types in your program if you supply no argument Each complete typename is matched as though it were a complete line thus i type value gives information on all types in your program whose names include the string value but i type value gives information only on types whose complete name is value This command differs from ptype in two ways first like whatis it does not print a detailed description second it lists all source files where a type is defined location List all the variables local to a particular scope This command accepts a location argument a function name a source line or an address preceded by Chapter 13 Examining the Symbol Table 145 a and prints all the variables local to the scope defined by that location For example gdb info scope command line handler Scope for command line handler Symbol rl is an argument at stack frame offset
349. for example the goto instruction is followed by a destination for the jump The bytecode interpreter is a stack based machine most instructions pop their operands off the stack perform some operation and push the result back on the stack for the next instruction to consume Each element of the stack may contain either a integer or a floating point value these values are as many bits wide as the largest integer that can be directly manipulated in the source language Stack elements carry no record of their type bytecode could push a value as an integer then pop it as a floating point value However GDB will not generate code which does this In C one might define the type of a stack element as follows union agent val LONGEST 1 DOUBLEST d 370 Debugging with GDB where LONGEST and DOUBLEST are typedef names for the largest integer and floating point types on the machine By the time the bytecode interpreter reaches the end of the expression the value of the expression should be the only value left on the stack For tracing applications trace bytecodes in the expression will have recorded the necessary data and the value on the stack may be discarded For other applications like conditional breakpoints the value may be useful Separate from the stack the interpreter has two registers pc The address of the next bytecode to execute start The address of the start of the bytecode expression necessary for interpreting the
350. g gdb stopped reason end stepping range frame func foo args name a value 10 name b value 0 file recursive2 c fullname home foo bar recursive2 c line 11 gdb Regular stepping exec step running gdb stopped reason end stepping range line 14 file recursive2 c gdb The exec step instruction Command Synopsis exec step instruction Resumes the inferior which executes one machine instruction The output once GDB has stopped will vary depending on whether we have stopped in the middle of a source line or not In the former case the address at which the program stopped will be printed as well 256 Debugging with GDB GDB Command The corresponding GDB command is stepi Example exec step instruction running gdb stopped reason end stepping range frame func foo args file try c fullname home foo bar try c line 10 gdb exec step instruction running gdb stopped reason end stepping range frame addr 0x000100f4 func foo args file try c fullname home foo bar try c line 10 gdb The exec until Command Synopsis location Executes the inferior until the location specified in the argument is reached If there is no argument the inferior executes until a source line greater than the current one is reached The reason for stopping in this case will be location reached GDB Command The corresponding G
351. g CRIS specific commands set cris version ver Set the current CRIS version to ver either 10 or 32 The CRIS version affects register names and sizes This command is useful in case autodetection of the CRIS version fails show cris version Show the current CRIS version set cris dwarf2 cfi Set the usage of DWARF 2 CFI for CRIS debugging The default is on Change to off when using gcc cris whose version is below R59 show cris dwarf2 cfi Show the current state of using DWARF 2 CFI set cris mode mode Set the current CRIS mode to mode It should only be changed when debugging in guru mode in which case it should be set to guru the default is normal show cris mode Show the current CRIS mode 18 3 13 Renesas Super H For the Renesas Super H processor GDB provides these commands regs Show the values of all Super H registers 18 4 Architectures This section describes characteristics of architectures that affect all uses of GDB with the architecture both native and cross 18 4 1 x86 Architecture specific Issues set struct convention mode Set the convention used by the inferior to return structs and unions from functions to mode Possible values of mode are pcc reg and default the default default or pcc means that structs are returned on the stack while reg means that a struct or a union whose size is 1 2 4 or 8 bytes will be returned in a register show struct
352. g modes use the command M C j bound to emacs editing mode when in vi mode and to vi editing mode in emacs mode The Readline default is emacs mode When you enter a line in vi mode you are already placed in insertion mode as if you had typed an i Pressing switches you into command mode where you can edit the text of the line with the standard vi movement keys move to previous history lines with k and subsequent lines with j and so forth 314 Debugging with GDB Chapter 28 Using History Interactively 315 28 Using History Interactively This chapter describes how to use the GNU History Library interactively from a user s standpoint It should be considered a user s guide For information on using the GNU History Library in other programs see the GNU Readline Library Manual 28 1 History Expansion The History library provides a history expansion feature that is similar to the history expansion provided by csh This section describes the syntax used to manipulate the history information History expansions introduce words from the history list into the input stream making it easy to repeat commands insert the arguments to a previous command into the current input line or fix errors in previous commands quickly History expansion takes place in two parts The first is to determine which line from the history list should be used during substitution The second is to select portions of that line for inc
353. g notices to the program It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty and each file should have at least the copyright line and a pointer to where the full notice is found one line to give the program s name and a brief idea of what it does Copyright C year name of author This program is free software you can redistribute it and or modify it under the terms of the GNU General Public License as published by the Free Software Foundation either version 2 of the License or at your option any later version This program is distributed in the hope that it will be useful but WITHOUT ANY WARRANTY without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE See the GNU General Public License for more details You should have received a copy of the GNU General Public License along with this program if not write to the Free Software Foundation Inc 51 Franklin Street Fifth Floor Boston MA 02110 1301 USA Also add information on how to contact you by electronic and paper mail If the program is interactive make it output a short notice like this when it starts in an interactive mode Gnomovision version 69 Copyright C year name of author Gnomovision comes with ABSOLUTELY NO WARRANTY for details type show w This is free software and you are welcome to redistribute it under certain conditions type show c for
354. g target to return the proper status to GDB probably requires changes to the standard stub one quick and dirty way is to just execute a breakpoint instruction the dirty part is that GDB reports a SIGTRAP instead of a SIGINT Other routines you need to supply are void exceptionHandler int exception number void exception address Write this function to install exception address in the exception handling ta bles You need to do this because the stub does not have any way of knowing what the exception handling tables on your target system are like for example the processor s table might be in ROM containing entries which point to a table in RAM exception number is the exception number which should be changed its meaning is architecture dependent for example different numbers might represent divide by zero misaligned access etc When this exception occurs control should be transferred directly to exception address and the processor state stack registers and so on should be just as it is when a processor excep tion occurs So if you want to use a jump instruction to reach exception address it should be a simple jump not a jump to subroutine For the 386 exception address should be installed as an interrupt gate so that interrupts are masked while the handler runs The gate should be at privilege level 0 the most privileged level The SPARC and 68k stubs are able to mask interrupts themselves without help from excepti
355. g the i or interpreter startup options Defined interpreters include console The traditional console or command line interpreter This is the most often used interpreter with GDB With no interpreter specified at runtime GDB will use this interpreter mi The newest GDB MI interface currently mi2 Used primarily by programs wishing to use GDB as a backend for a debugger GUI or an IDE For more information see Chapter 24 The GDB MI Interface page 233 mi2 The current GDB MI interface mit The GDB MI interface included in GDB 5 1 5 2 and 5 3 The interpreter being used by GDB may not be dynamically switched at runtime Al though possible this could lead to a very precarious situation Consider an IDE using GDB MI If a user enters the command interpreter set console in a console view GDB would switch to using the console interpreter rendering the IDE inoperable Although you may only choose a single interpreter at startup you may execute com mands in any interpreter from the current interpreter using the appropriate command If you are running the console interpreter simply use the interpreter exec command interpreter exec mi data list register names GDB MI has a similar command although it is only available in versions of GDB which support GDB MI version 2 or greater 224 Debugging with GDB Chapter 22 GDB Text User Interface 225 22 GDB Text User Interface The GDB Text User Interface TUI is a t
356. g with GDB shared library events remote reply 341 sharedlibrary i ic ccc e dda eeiciag hraa iies 160 SHEL 6 6 pc cob e scm ERREUR eee a team needs RF 16 Shelli scape 2 22e pur RR RIABPREE PETS 16 ja Shad Looe 22 show all user variables 89 show annotate c ge ea e Re eer R 287 show architecture o sc d e t 167 SHOW APES erc ord eH EE Re ae Ire ae wens 27 SHOW AEfnesniecnrebvIQ X eka eee eee Re dae 192 show auto solib add eee rege 160 Show backtrace c b gb reLevrE E RETENE 63 show board address lees sss 194 show breakpoint auto hw 42 show breakpoint pending 42 show can use hw watchpoints 44 show case sensitive uses essen 143 SHOW chartSet oso e py Ra ma ee RE AN 96 show ch ck rang i ceed e RE hh 123 show check typ6e senkIam RR RE RP 122 Show coerce float to double 211 show comibase c a eb e E Y 185 show comliYrq i us lnscn elc calender 185 show com2base oi eke eae de EE RU DARE 185 show com21rq elu pes RE SLE QU ate 185 show com3base c coo RR ee ae 185 show com3irQ ineememe ee REG we PRSE 185 show comAbase oes cee teed area 185 show comdirQ oec v eR ETE eee Pase 185 show conmnands recae Ee Lene DUE 209 show conplaint8 jv pa iet 212 Show confirm ecca ks erben DD Dp dn 212 show convenience 00 cece eee ee
357. gdb ptype t type blue yellow In this example a Modula 2 array is declared and its contents displayed Observe that the contents are written in the same way as their C counterparts VAR s ARRAY 1 5 OF CARDINAL BEGIN s 1 1 gdb print s 1 1 0 0 0 0 gdb ptype s type ARRAY 1 5 OF CARDINAL The Modula 2 language interface to GDB also understands pointer types as shown in this example VAR s POINTER TO ARRAY 1 5 OF CARDINAL BEGIN NEW s s 1 1 and you can request that GDB describes the type of s gdb ptype s type POINTER TO ARRAY 1 5 OF CARDINAL GDB handles compound types as we can see in this example Here we combine array types record types pointer types and subrange types TYPE foo RECORD f1 CARDINAL f2 CHAR f3 myarray END myarray ARRAY myrange OF CARDINAL myrange 2 2 VAR s POINTER TO ARRAY myrange OF foo and you can ask GDB to describe the type of s as shown below gdb ptype s type POINTER TO ARRAY 2 2 OF foo RECORD f1 CARDINAL f2 CHAR f3 ARRAY 2 2 OF CARDINAL END 136 Debugging with GDB 12 4 5 5 Modula 2 Defaults If type and range checking are set automatically by GDB they both default to on whenever the working language changes to Modula 2 T his happens regardless of whether you or GDB selected the working language If you allow GDB to set the language automatically then entering code compiled
358. ge ezannoni TRUNK mbx hello mbx done gdb The file list exec sections Command Synopsis file list exec sections List the sections of the current executable file GDB Command The GDB command info file shows among the rest the same information as this com mand gdbtk has a corresponding command gdb 1oad info Example N A The file list exec source file Command Synopsis file list exec source file List the line number the current source file and the absolute path to the current source file for the current executable GDB Command The GDB equivalent is info source Example gdb 123 file list exec source file 123 done line 1 file foo c fullname home bar foo c gdb The file list exec source files Command Synopsis file list exec source files List the source files for the current executable It will always output the filename but only when GDB can find the absolute file name of a source file will it output the fullname GDB Command The GDB equivalent is info sources gdbtk has an analogous command gdb_listfiles 278 Debugging with GDB Example gdb file list exec source files done files file foo c fullname home foo c file home bar c fullname home bar c file gdb_could_not_find_fullpath c gdb The file list shared libraries Command Synopsis file list shared libraries List the shared libraries in the program GDB Command The corr
359. gion attributes 92 memory Lracmg i e sitdeRpesrteen prd 3T memory transfer in file i o protocol 363 memory used by commands 330 memory used for symbol tables 159 memory alignment and size of remote accesses Debs de dd hoe anamer I EP uda Guage ne Mate 336 memory viewing as typed object 76 pensete idranti edades Ea adeps 180 menu complete 0c eee ee eee 311 met flaga ioise mede Xe Der eH EE eirca 300 f liDUberPpreLer i 222 see 0B RR PREGGR be 223 mil mterpreter i 2 2e et Re E 223 Mid interpreter zi dies eh aed crees 223 minimal language eee eens 141 Minimal symbols and DLLs 186 MIPS addresses masking 204 MIPS boardss c05 520c00 eeadiee ee ed eeheae ness 195 MIPS remote floating point 196 MIPS stack 2224 12225 202aae Oo ew ed hea 203 MMX registers x86 0 00000 2 eee ee 91 mode t values in file i o protocol 365 Modilaz2 2o kRR PEG nU EPI diede 1 Modula 2 built ins 0 000 000 132 Modula 2 checks weve ccnseeedacege REED 136 Modula 2 constants 000 riei ee eee 133 Modula 2 defaults 00 0 eee ee 136 Modula 2 operators 00 eee eee eee 131 Modula 2 types 4 is censet rx ERRRRI tes 134 Modula 2 deviations from 136 Modula 2 GDB support lesse 131 MOTTE OM 5518s e
360. gnment 1 col_name type colhdr Type width 4 alignment 1 col_name disp colhdr Disp width 3 alignment 1 col_name enabled colhdr Enb width 10 alignment 1 col_name addr colhdr Address width 40 alignment 2 col_name what colhdr What body gdb The break disable Command Synopsis break disable breakpoint Disable the named breakpoint s The field enabled in the break list is now set to n for the named breakpoint s GDB Command The corresponding GDB command is disable Example gdb break disable 2 done gdb break list done BreakpointTable nr_rows 1 nr_cols 6 hdr width 3 alignment 1 col_name number colhdr Num width 14 alignment 1 col_name type colhdr Type width 4 alignment 1 col_name disp colhdr Disp width 3 alignment 1 col_name enabled colhdr Enb width 10 alignment 1 col_name addr colhdr Address width 40 alignment 2 col_name what colhdr What body bkpt number 2 type breakpoint disp keep enabled n addr 0x000100d0 func main file hello c fullname home foo hello c line 5 times 0 gdb 242 Debugging with GDB The break enable Command Synopsis break enable breakpoint Enable previously disabled breakpoint s GDB Command The corresponding GDB command is enable Example gdb break enable 2 done gdb
361. gram only not for GDB itself value may be any string the values of environment variables are just strings and any interpretation is supplied by your program itself The value parameter is optional if it is eliminated the variable is set to a null value For example this command set env USER foo tells the debugged program when subsequently run that its user is named foo The spaces around are used for clarity here they are not actually required unset environment varname Remove variable varname from the environment to be passed to your program This is different from set env varname unset environment removes the variable from the environment rather than assigning it an empty value Warning On Unix systems GDB runs your program using the shell indicated by your SHELL environment variable if it exists or bin sh if not If your SHELL variable names a Chapter 4 Running Programs Under GDB 29 shell that runs an initialization file such as cshrc for C shell or bashrc for BASH any variables you set in that file affect your program You may wish to move setting of environment variables to files that are only run when you sign on such as login or profile 4 5 Your Program s Working Directory Each time you start your program with run it inherits its working directory from the current working directory of GDB The GDB working directory is initially whatever it inheri
362. grams which provide a command line interface to the user Advantages are GNU Emacs style or vistyle inline editing of commands csh like history substitution and a storage and recall of command history across debugging sessions You may control the behavior of command line editing in GDB with the command set set editing set editing on Enable command line editing enabled by default set editing off Disable command line editing show editing Show whether command line editing is enabled See Chapter 27 Command Line Editing page 295 for more details about the Readline interface Users unfamiliar with GNU Emacs or vi are encouraged to read that chapter 19 3 Command History GDB can keep track of the commands you type during your debugging sessions so that you can be certain of precisely what happened Use these commands to manage the GDB command history facility GDB uses the GNU History library a part of the Readline package to provide the history facility See Chapter 28 Using History Interactively page 315 for the detailed description of the History library 208 Debugging with GDB To issue a command to GDB without affecting certain aspects of the state which is seen by users prefix it with server see Section 25 2 Server Prefix page 288 This means that this command will not affect the command history nor will it affect GDB s notion of which command to repeat if is pressed on a line by itself The server
363. h Multiple Processes 33 4 11 Setting a Bookmark to Return to Later 35 4 11 1 A Non obvious Benefit of Using Checkpoints 36 5 Stopping and Continuing 37 5 1 Breakpoints Watchpoints and Catchpoints 3T 5 1 1 Setting Breakpoints 0c cece eee eee 38 5 1 2 Setting WatchpointSsa scars startigi inia eee eee 43 5 1 3 Setting Catchpoints 0 00 c cece eee eee ee 45 5 1 4 Deleting Breakpoints 0 000 essere 46 Debugging with GDB 5 1 5 Disabling Breakpoints sesseeeeeesee ee eee ee 4T 5 1 6 Break Conditions uuessseeeeeeeeee E 48 5 1 7 Breakpoint Command Lists 00 00 ee eee eee 49 5 1 8 Breakpoint Menus 00 cece eee 51 5 1 9 Cannot insert breakpoints 0000 0 cee e ee eee 51 5 1 10 Breakpoint address adjusted 0 0000 0000 52 5 2 Continuing and Stepping 0 0 e eee eee eee eee 52 5 39 Bighals ose ners eek eee fee eee qe Ra CupU ERE RU Pee S 56 5 4 Stopping and Starting Multi thread Programs 57 Examining the Stack 61 6 1 Stack Pram 8 con et Re dads ebEREP HP E RE 61 0 2 Ba ckUraceS uu debere iim Mada dened ERES weed 62 6 3 Selecting a Bram au ese e oet oed c eR Ten gn 64 6 4 Information About a Frame isessseeseles eee ee eee 65 Examining Source Files 67 T 1
364. h a single match from the list of possible completions Repeated execution of menu complete steps through the list of possible completions inserting each match in turn At the end of the list of completions the bell is rung subject to the setting of bell style and the original text is restored An argument of n moves n positions forward in the list of matches a negative argument may be used to move backward through the list This command is intended to be bound to TAB but is unbound by default delete char or list Deletes the character under the cursor if not at the beginning or end of the line like delete char If at the end of the line behaves identically to possible completions This command is unbound by default 27 4 7 Keyboard Macros start kbd macro C x Begin saving the characters typed into the current keyboard macro 312 Debugging with GDB end kbd macro C x Stop saving the characters typed into the current keyboard macro and save the definition call last kbd macro C x e Re execute the last keyboard macro defined by making the characters in the macro appear as if typed at the keyboard 27 4 8 Some Miscellaneous Commands re read init file C x C r Read in the contents of the inputrc file and incorporate any bindings or variable assignments found there abort C g Abort the current editing command and ring the terminal s bell subject to the setting of bell style do uppercase version M a M
365. h is not the best way to debug exception handling if you need to know exactly where an exception is raised it is better to stop before the exception handler is called since that way you can see the stack before any unwinding takes place If you set a breakpoint in an exception handler instead it may not be easy to find out where the exception was raised To stop just before an exception handler is called you need some knowledge of the implementation In the case of GNU C exceptions are raised by calling a library function named raise exception which has the following ANSI C interface addr is where the exception identifier is stored id is the exception identifier void raise exception void addr void id To make the debugger catch all exceptions before any stack unwinding takes place set a breakpoint on raise exception see Section 5 1 Breakpoints Watchpoints and Excep tions page 37 With a conditional breakpoint see Section 5 1 6 Break Conditions page 48 that de pends on the value of id you can stop your program when a specific exception is raised You can use multiple conditional breakpoints to stop your program when any of a number of exceptions are raised 5 1 4 Deleting Breakpoints It is often necessary to eliminate a breakpoint watchpoint or catchpoint once it has done its job and you no longer want your program to stop there This is called deleting the breakpoint A breakpoint that has been dele
366. has no effect on the meaning of this License VERBATIM COPYING You may copy and distribute the Document in any medium either commercially or noncommercially provided that this License the copyright notices and the license notice saying this License applies to the Document are reproduced in all copies and Appendix H GNU Free Documentation License 395 that you add no other conditions whatsoever to those of this License You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute However you may accept compensation in exchange for copies If you distribute a large enough number of copies you must also follow the conditions in section 3 You may also lend copies under the same conditions stated above and you may publicly display copies 3 COPYING IN QUANTITY If you publish printed copies or copies in media that commonly have printed covers of the Document numbering more than 100 and the Document s license notice requires Cover Texts you must enclose the copies in covers that carry clearly and legibly all these Cover Texts Front Cover Texts on the front cover and Back Cover Texts on the back cover Both covers must also clearly and legibly identify you as the publisher of these copies The front cover must present the full title with all words of the title equally prominent and visible You may add other material on the covers in addition Copying with changes
367. he default is set to nostop noprint pass for non erroneous signals such as SIGALRM SIGWINCH and SIGCHLD and to stop print pass for the erroneous signals You can also use the signal command to prevent your program from seeing a signal or cause it to see a signal it normally would not see or to give it any signal at any time For example if your program stopped due to some sort of memory reference error you might store correct values into the erroneous variables and continue hoping to see more execution but your program would probably terminate immediately as a result of the fatal signal once it saw the signal To prevent this you can continue with signal 0 See Section 14 3 Giving your Program a Signal page 151 5 4 Stopping and Starting Multi thread Programs When your program has multiple threads see Section 4 9 Debugging Programs with Mul tiple Threads page 31 you can choose whether to set breakpoints on all threads or on a particular thread break linespec thread threadno break linespec thread threadno if linespec specifies source lines there are several ways of writing them but the effect is always to specify some source line Use the qualifier thread threadno with a breakpoint command to specify that you only want GDB to stop the program when a particular thread reaches this breakpoint threadno is one of the numeric thread identifiers assigned by GDB shown in the first column of the info threads
368. he first prompt comes up very quickly We now tell GDB to use a narrower display width than usual so that examples fit in this manual gdb set width 70 We need to see how the m4 built in changequote works Having looked at the source we know the relevant subroutine is m4 changequote so we set a breakpoint there with the GDB break command gdb break m4_changequote Breakpoint 1 at Ox62f4 file builtin c line 879 Using the run command we start m4 running under GDB control as long as control does not reach the m4_changequote subroutine the program runs as usual 8 Debugging with GDB gdb run Starting program work Editorial gdb gnu m4 m4 define foo 0000 foo 0000 To trigger the breakpoint we call changequote GDB suspends execution of m4 displaying information about the context where it stops changequote lt QUOTE gt lt UNQUOTE gt Breakpoint 1 m4_changequote argc 3 argv 0x33c70 at builtin c 879 879 if bad argc TOKEN DATA TEXT argv 0 argc 1 3 Now we use the command n next to advance execution to the next line of the current function gdb n 882 set quotes argc gt 2 TOKEN_DATA_TEXT argv 1 amp nil set quotes looks like a promising subroutine We can go into it by using the command s step instead of next step goes to the next line to be executed in any subroutine so it steps into set quotes gdb s set quotes 1q 0x34c78 lt QUOTE gt rq 0x34c88 lt UNQUOTE gt at input c
369. he hexadecimal value HH one or two hex digits When entering the text of a macro single or double quotes must be used to indicate a macro definition Unquoted text is assumed to be a function name In the macro body the backslash escapes described above are expanded Backslash will quote any other character in the macro text including and For example the following binding will make C x insert a single into the line C x n NN 27 3 2 Conditional Init Constructs Readline implements a facility similar in spirit to the conditional compilation features of the C preprocessor which allows key bindings and variable settings to be performed as the result of tests There are four parser directives used if endif else The if construct allows bindings to be made based on the editing mode the terminal being used or the application using Readline The text of the test extends to the end of the line no characters are required to isolate it mode term The mode form of the if directive is used to test whether Readline is in emacs or vi mode This may be used in conjunction with the set keymap command for instance to set bindings in the emacs standard and emacs ctlx keymaps only if Readline is starting out in emacs mode The term form may be used to include terminal specific key bind ings perhaps to bind the key sequences output by the terminal s function keys The word on t
370. he necessary host calls to perform the system call The return value of system on the host is simplified before it s returned to the target Any termination signal information from the child process is discarded and the return value consists entirely of the exit status of the called command Due to security concerns the system call is by default refused by GDB The user has to allow this call explicitly with the set remote system call allowed 1 command Set remote system call allowed Control whether to allow the system calls in the File I O protocol for the remote target The default is zero disabled show remote system call allowed Show whether the system calls are allowed in the File I O protocol D 9 8 Protocol specific Representation of Datatypes Integral Datatypes The integral datatypes used in the system calls are int unsigned int long unsigned long mode t and time t int unsigned int mode t and time t are implemented as 32 bit values in this protocol long and unsigned long are implemented as 64 bit types See Limits page 366 for corresponding MIN and MAX values similar to those in limits h to allow range checking on host and target time t datatypes are defined as seconds since the Epoch All integral datatypes transferred as part of a memory read or write of a structured datatype e g a struct stat have to be given in big endian byte order Pointer Values Pointers to target data are transmitted as they
371. he original author s copyright notice the distribution terms or the list of authors are ok It is also no problem to require modified versions to include notice that they were modified Even entire sections that may not be deleted or changed are acceptable as long as they deal with nontechnical topics like this one These kinds of restrictions are acceptable because they don t obstruct the community s normal use of the manual However it must be possible to modify all the technical content of the manual and then distribute the result in all the usual media through all the usual channels Otherwise the restrictions obstruct the use of the manual it is not free and we need another manual to replace it Please spread the word about this issue Our community continues to lose manuals to proprietary publishing If we spread the word that free software needs free reference manuals and free tutorials perhaps the next person who wants to contribute by writing documentation will realize before it is too late that only free manuals contribute to the free software community If you are writing documentation please insist on publishing it under the GNU Free Documentation License or another free documentation license Remember that this deci sion requires your approval you don t have to let the publisher decide Some commercial publishers will use a free license if you insist but they will not propose the option it is up to you to raise the
372. he right side of the is tested against both the full name of the terminal and the portion of the terminal name before the first This allows sun to match both sun and sun cnd for instance application The application construct is used to include application specific set tings Each program using the Readline library sets the application name and you can test for a particular value This could be used to bind key sequences to functions useful for a specific program For instance the following command adds a key sequence that quotes the current or previous word in Bash if Bash Quote the current or previous word NC xq eb ef endif This command as seen in the previous example terminates an if command Commands in this branch of the if directive are executed if the test fails 304 Debugging with GDB include This directive takes a single filename as an argument and reads commands and bindings from that file For example the following directive reads from etc inputre include etc inputrc 27 3 3 Sample Init File Here is an example of an inputrc file This illustrates key binding variable assignment and conditional syntax Chapter 27 Command Line Editing 305 This file controls the behaviour of line input editing for programs that use the GNU Readline library Existing programs include FTP Bash and GDB d You can re read the inputrc file with C x C r Lines
373. he serial line speed to baud JTC When does the transport layer state change When it s received or after the ACK is transmitted In either case there are problems if the command or the acknowledgment packet is dropped Stan If people really wanted to add something like this and get it working for the first time they ought to modify ser unix c to send some kind of out of band message to a specially setup stub and have the switch happen in between packets so that from remote protocol s point of view nothing actually happened B addr mode Set mode is S or clear mode is C a breakpoint at addr Don t use this packet Use the Z and z packets instead see insert breakpoint or watchpoint packet page 339 c addr Continue addr is address to resume If addr is omitted resume at current address Reply See Section D 3 Stop Reply Packets page 341 for the reply specifica tions C sig addr Continue with signal sig hex signal number If addr is omitted resume at same address Reply See Section D 3 Stop Reply Packets page 341 for the reply specifica tions a Toggle debug flag Don t use this packet instead define a general set packet see Section D 4 General Query Packets page 342 D Detach GDB from the remote system Sent to the remote target before GDB disconnects via the detach command Reply 0K for success E NN for an
374. he signal a program gets from referencing a place in memory far away from all the areas in use SIGALRM occurs when the alarm clock timer goes off which happens only if your program has requested an alarm Some signals including SIGALRM are a normal part of the functioning of your program Others such as SIGSEGV indicate errors these signals are fatal they kill your program immediately if the program has not specified in advance some other way to handle the signal SIGINT does not indicate an error in your program but it is normally fatal so it can carry out the purpose of the interrupt to kill the program GDB has the ability to detect any occurrence of a signal in your program You can tell GDB in advance what to do for each kind of signal Normally GDB is set up to let the non erroneous signals like SIGALRM be silently passed to your program so as not to interfere with their role in the program s functioning but to stop your program immediately whenever an error signal happens You can change these settings with the handle command info signals info handle Print a table of all the kinds of signals and how GDB has been told to handle each one You can use this to see the signal numbers of all the defined types of signals info signals sig Similar but print information only about the specified signal number info handle is an alias for info signals handle signal keywords Change the way GDB handles signal signal sign
375. hen more than one substitution rule have been defined the rules are evaluated one by one in the order where they have been defined The first one matching if any is selected to perform the substitution For instance if we had entered the following commands gdb set substitute path usr src include mnt include gdb set substitute path usr src mnt src GDB would then rewrite usr src include defs h into mnt include defs by using the first rule However it would use the second rule to rewrite usr src lib foo c into mnt src lib foo c unset substitute path path If a path is specified search the current list of substitution rules for a rule that would rewrite that path Delete that rule if found A warning is emitted by the debugger if no rule could be found If no path is specified then all substitution rules are deleted h 72 Debugging with GDB show substitute path path If a path is specified then print the source path substitution rule which would rewrite that path if any If no path is specified then print all existing source path substitution rules If your source path is cluttered with directories that are no longer of interest GDB may sometimes cause confusion by finding the wrong versions of source You can correct the situation as follows 1 Use directory with no argument to reset the source path to its default value 2 Use directory with suitable arguments to reinstall the dire
376. henever GDB gets control Setting it to off will take effect the next time the inferior is continued If this option is set to off you can use set thread default pause on or set thread pause on see below to pause individual threads Chapter 18 Configuration Specific Information 189 show task pause Show the current state of task suspension Set task detach suspend count This command sets the suspend count the task will be left with when GDB detaches from it show task detach suspend count Show the suspend count the task will be left with when detaching set task exception port set task excp This command sets the task exception port to which GDB will forward excep tions The argument should be the value of the send rights of the task set task excp is a shorthand alias Set noninvasive This command switches GDB to a mode that is the least invasive as far as interfering with the inferior is concerned This is the same as using set task pause set exceptions and set signals to values opposite to the defaults info send rights info receive rights info port rights info port sets info dead names info ports info psets These commands display information about respectively send rights receive rights port rights port sets and dead names of a task There are also shorthand aliases info ports for info port rights and info psets for info port sets Set thread pause This command toggles current thread suspension when GD
377. hich is available on many Unix systems Just run your GDB session inside script and then include the typescript file with your bug report Chapter 26 Reporting Bugs in GDB 293 Another way to record a GDB session is to run GDB inside Emacs and then save the entire buffer to a file e If you wish to suggest changes to the GDB source send us context diffs If you even discuss something in the GDB source refer to it by context not by line number The line numbers in our development sources will not match those in your sources Your line numbers would convey no useful information to us Here are some things that are not necessary e A description of the envelope of the bug Often people who encounter a bug spend a lot of time investigating which changes to the input file will make the bug go away and which changes will not affect it This is often time consuming and not very useful because the way we will find the bug is by running a single example under the debugger with breakpoints not by pure deduction from a series of examples We recommend that you save your time for something else Of course if you can find a simpler example to report instead of the original one that is a convenience for us Errors in the output will be easier to spot running under the debugger will take less time and so on However simplification is not vital if you do not want to do this report the bug anyway and send us the entire test case you use
378. hread in your program it displays the target system s iden tification for the thread with a message in the form New systag systag is a thread iden tifier whose form varies depending on the particular system For example on GNU Linux you might see 32 Debugging with GDB New Thread 46912507313328 LWP 25582 when GDB notices a new thread In contrast on an SGI system the systag is simply something like process 368 with no further qualifier For debugging purposes GDB associates its own thread number always a single integer with each thread in your program info threads Display a summary of all threads currently in your program GDB displays for each thread in this order 1 the thread number assigned by GDB 2 the target system s thread identifier systag 3 the current stack frame summary for that thread An asterisk to the left of the GDB thread number indicates the current thread For example gdb info threads 3 process 35 thread 27 0x34e5 in sigpause 2 process 35 thread 23 0x34e5 in sigpause 1 process 35 thread 13 main argc 1 argv OxT7ffffff8 at threadtest c 68 On HP UX systems For debugging purposes GDB associates its own thread number a small integer assigned in thread creation order with each thread in your program Whenever GDB detects a new thread in your program it displays both GDB s thread number and the target system s identification for the thread with a mes
379. i breeds 263 var set frozen coo uod br eR eden 266 var show attributes oiee ui RR 265 var show format M Reb 263 Debugging with GDB yar pdate scje itis deasude oh eased ds 265 Lr 14 EX quA Ded Reeds LAS alts ecd FEE REI TN ae 12 Modula 2 scope operator 0 136 puild id directory eR nrbs 161 debug subdirectories scende e 161 go o0 Neu 16 gnu debuglink sections sess 162 note gnu build id sections 162 o files reading symbols from 157 nM 181 context for variables functions 76 tin M dula 2 4 22e tite BERE Seth glee es 136 lt architecture 2e weeds is aad aerate eee 382 KIGAG UTED iuste vu d E pice ae opt e perds 383 XFOg niei sep que E i ecg ieee ED a 383 SUDIOB2 24223 p pL PET p UR UD EAD Rr 383 LVE TOTS Celo Rime EM RGRqd aee ls D EG Sek 383 xiiclude inserirtenserbee reRU Y Y eee VE 382 P e packets css uA bEGpMET RR HE MEE 334 referencing memory as an array TT Connected rne bp eese fel tds 237 LONG s osoby Erden deers iid D mei beats 236 GXEO sip o RP REI RI restet 237 eXYtlgcoeeenpe 4 o Yn ev EE Bae sede ae oe 237 TEULDEIDEB 5acerdopeek Hp Robe ance RU INE anes 236 _NSPrintForDebugger and printing Objective C ODOC ecce ber E meee anes 130 6 No symbol foo in current context 77 Appendix H Index
380. i vec e n mer pbi deme gees 55 416 stepping into functions with no line info stop a running trace experiment stop on C exceptions 000 00 stop reply packets 0 eee ee ee stop a pseudo command stopped threads usse soran elniena sed ass stopping annotatiOn ii rsosaga s e eds stream records in GDB M1 205 struct return convention lesse struct stat in file i o protocol struct timeval in file i o protocol struct user contents 62 52 64 cogere struct union returned in registers stub example remote debugging stupid Questions sc cs remm S per H ocagi neepa ia ERI Em Ib supported packets remote query switching threads 04 switching threads automatically symbol decoding style C Luuuuuu sytnbol dump sr re rehhhcRRERR RR RREPRESE symbol from address 00202000 symbol lookup remote request Symbol Dames uu credo CrRePEOEPREE YRUE RIS symbol overloading 0 symbol table dn vb geese E REED te eee symbol tables listing GDB s internal symbol source file and line symbol fil 23 sh ck mE terres symbols reading from relocatable object files symbols reading immediately synchronize with remote M
381. iberty libraries then gdb itself The configured source files and the binaries are left in the corresponding source directories configure is a Bourne shell bin sh script if your system does not recognize this automatically when you run a different shell you may need to run sh on it explicitly sh configure host If you run configure from a directory that contains source directories for multiple libraries or programs such as the gdb 6 7 50_20071011 source directory for version 6 7 50 20071011 configure creates configuration files for every directory level underneath unless you tell it not to with the norecursion option You should run the configure script from the top directory in the source tree the gdb version number directory If you run configure from one of the subdirectories you will configure only that subdirectory That is usually not what you want In particular if you run the first configure from the gdb subdirectory of the gdb version number directory you will omit the configuration of bfd readline and other sibling directories of the gdb subdirectory This leads to build errors about missing include files such as pfd bfd h You can install gdb anywhere it has no hardwired paths However you should make sure that the shell on your path named by the SHELL environment variable is publicly readable Remember that GDB u
382. ically skip over this function set step mode off Causes the step command to step over any functions which contains no debug information This is the default show step mode finish until u Show whether GDB will stop in or step over functions without source line debug information Continue running until just after function in the selected stack frame returns Print the returned value if any Contrast this with the return command see Section 14 4 Returning from a Function page 151 Continue running until a source line past the current line in the current stack frame is reached This command is used to avoid single stepping through a loop more than once It is like the next command except that when until encoun ters a jump it automatically continues execution until the program counter is greater than the address of the jump This means that when you reach the end of a loop after single stepping though it until makes your program continue execution until it exits the loop In con trast a next command at the end of a loop simply steps back to the beginning of the loop which forces you to step through the next iteration until always stops your program if it attempts to exit the current stack frame until may produce somewhat counterintuitive results if the order of machine code does not match the order of the source lines For example in the following excerpt from a debugging session the f frame command shows that
383. icit leading and trailing the regular expression you supply so to match only functions that begin with foo use foo When debugging C programs rbreak is useful for setting breakpoints on overloaded functions that are not members of any special classes The rbreak command can be used to set breakpoints in all the functions in a program like this gdb rbreak info breakpoints n info break n info watchpoints n Print a table of all breakpoints watchpoints and catchpoints set and not deleted Optional argument n means print information only about the spec ified breakpoint or watchpoint or catchpoint For each breakpoint following columns are printed Breakpoint Numbers Type Breakpoint watchpoint or catchpoint Disposition Whether the breakpoint is marked to be disabled or deleted when hit Enabled or Disabled Enabled breakpoints are marked with y n marks breakpoints that are not enabled An optional p suffix marks pending break points breakpoints for which address is either not yet resolved pending load of a shared library or for which address was in a shared library that was since unloaded Such breakpoint won t fire until a shared library that has the symbol or line referred by breakpoint is loaded See below for details Address Where the breakpoint is in your program as a memory address For a pending breakpoint whose address is not yet known this field will contain lt PENDI
384. ide by 8 5 inches high You will need to specify this form of printing as an option to your DVI output program All the documentation for GDB comes as part of the machine readable distribution The documentation is written in Texinfo format which is a documentation system that uses a single source file to produce both on line information and a printed manual You can use one of the Info formatting commands to create the on line version of the documentation and TEX or texi2roff to typeset the printed version GDB includes an already formatted copy of the on line Info version of this manual in the gdb subdirectory The main Info file is gdb 6 7 50_20071011 gdb gdb info and it refers to subordinate files matching gdb info in the same directory If necessary you can print out these files or read them with any editor but they are easier to read using the info subsystem in GNU Emacs or the standalone info program available as part of the GNU Texinfo distribution If you want to format these Info files yourself you need one of the Info formatting programs such as texinfo format buffer or makeinfo If you have makeinfo installed and are in the top level GDB source directory gdb 6 7 50_20071011 in the case of version 6 7 50 20071011 you can make the Info file by typing cd gdb make gdb info If you want to typeset and print copies of this manual you need TEX a program to print its DVI output files and texinfo
385. ies The default is off match hidden files This variable when set to on causes Readline to match files whose names begin with a hidden files when performing filename completion unless the leading is supplied by the user in the filename to be completed This variable is on by default Chapter 27 Command Line Editing 301 output meta If set to on Readline will display characters with the eighth bit set directly rather than as a meta prefixed escape sequence The default is off page completions If set to on Readline uses an internal more like pager to display a screenful of possible completions at a time This variable is on by default print completions horizontally If set to on Readline will display completions with matches sorted horizontally in alphabetical order rather than down the screen The default is off show all if ambiguous This alters the default behavior of the completion functions If set to on words which have more than one possible completion cause the matches to be listed immediately instead of ringing the bell The default value is off show all if unmodified This alters the default behavior of the completion functions in a fashion similar to show all if ambiguous If set to on words which have more than one possible completion without any possible par tial completion the possible completions don t share a comm
386. ile with a particular name is seen again Set symbol reloading off Do not replace symbol definitions when encountering object files of the same name more than once This is the default state if you are not running on a system that permits automatic relinking of modules you should leave symbol reloading off since otherwise GDB may discard symbols when linking large programs that may contain several modules from different directories or libraries with the same name show symbol reloading Show the current on or off setting set opaque type resolution on Tell GDB to resolve opaque types An opaque type is a type declared as a pointer to a struct class or union for example struct MyType that is used in one source file although the full declaration of struct MyType is in another source file The default is on A change in the setting of this subcommand will not take effect until the next time symbols for a file are loaded Set opaque type resolution off Tell GDB not to resolve opaque types In this case the type is printed as follows lt no data fields show opaque type resolution Show whether opaque types are resolved or not maint print symbols filename maint print psymbols filename maint print msymbols filename Write a dump of debugging symbol data into the file filename These commands are used to debug the GDB symbol reading code Only symbols with debugging Chapter 13 Examining the Symbol Table 147 data
387. ilent and down silent Example gdb stack select frame 2 done gdb 24 14 GDB MI Variable Objects Introduction to Variable Objects Variable objects are object oriented MI interface for examining and changing values of expressions Unlike some other MI interfaces that work with expressions variable objects are specifically designed for simple and efficient presentation in the frontend A variable object is identified by string name When a variable object is created the frontend specifies the expression for that variable object The expression can be a simple variable or it can be an arbitrary complex expression and can even involve CPU registers After creating a variable object the frontend can invoke other variable object operations for example to obtain or change the value of a variable object or to change display format Variable objects have hierarchical tree structure Any variable object that corresponds to a composite type such as structure in C has a number of child variable objects for example corresponding to each element of a structure A child variable object can itself have children recursively Recursion ends when we reach leaf variable objects which always have built in types Child variable objects are created only by explicit request so if a frontend is not interested in the children of a particular variable object no child will be created For a leaf variable object it is possible to obtain
388. in expressions GDB has no way to automatically recognize which character set the inferior program uses you must tell it using the set target charset command described below Here are the commands for controlling GDB s character set support set target charset charset Set the current target character set to charset We list the character set names GDB recognizes below but if you type set target charset followed by TAB TAB GDB will list the target character sets it supports set host charset charset Set the current host character set to charset By default GDB uses a host character set appropriate to the system it is running on you can override that default using the set host charset command GDB can only use certain character sets as its host character set We list the character set names GDB recognizes below and indicate which can be host character sets but if you type set target charset followed by TAB TAB GDB will list the host character sets it supports set charset charset Set the current host and target character sets to charset As above if you type set charset followed by TAB TAB GDB will list the name of the character sets that can be used for both host and target show charset Show the names of the current host and target charsets show host charset Show the name of the current host charset show target charset Show the name of the current target charset GDB currently includes support for the foll
389. ine Code page 72 All the defaults for the arguments to x are designed to make it easy to continue scanning memory with minimal specifications each time you use x For example after you have Chapter 8 Examining Data 81 inspected three machine instructions with x 3i addr you can inspect the next seven with just x 7 If you use to repeat the x command the repeat count n is used again the other arguments default as for successive uses of x The addresses and contents printed by the x command are not saved in the value history because there is often too much of them and they would get in the way Instead GDB makes these values available for subsequent use in expressions as values of the convenience variables _ and __ After an x command the last address examined is available for use in expressions in the convenience variable _ The contents of that address as examined are available in the convenience variable __ If the x command has a repeat count the address and contents saved are from the last memory unit printed this is not the same as the last address printed if several units were printed on the last line of output When you are debugging a program running on a remote target machine see Chapter 17 Remote Debugging page 171 you may wish to verify the program s image in the remote machine s memory against the executable file you downloaded to the target The compare sections command is provided for such situat
390. ined functions whose names contain a match for regular expression regexp Thus info fun step finds all functions whose names include step info fun step finds those whose names start with step If a function name contains characters that conflict with the regular expression language e g operator they may be quoted with a backslash info variables Print the names and data types of all variables that are declared outside of functions i e excluding local variables info variables regexp Print the names and data types of all variables except for local variables whose names contain a match for regular expression regexp 146 Debugging with GDB info classes info classes regexp Display all Objective C classes in your program or with the regexp argument all those matching a particular regular expression info selectors info selectors regexp Display all Objective C selectors in your program or with the regexp argu ment all those matching a particular regular expression Some systems allow individual object files that make up your program to be replaced without stopping and restarting your program For example in Vx Works you can simply recompile a defective object file and keep on running If you are running on one of these systems you can allow GDB to reload the symbols for automatically relinked modules set symbol reloading on Replace symbol definitions for the corresponding source file when an object f
391. ing GDB uses the macro definitions in force at the source line of the current stack frame gdb break main Breakpoint 1 at 0x8048370 file sample c line 10 gdb run Starting program home jimb gdb macros play sample Breakpoint 1 main at sample c 10 10 printf Hello world n gdb At line 10 the definition of the macro N at line 9 is in force gdb info macro N Defined at home jimb gdb macros play sample c 9 define N 28 gdb macro expand N Q M expands to 28 lt 42 gdb print N Q M 1 1 gdb As we step over directives that remove N s definition and then give it a new definition GDB finds the definition or lack thereof in force at each point gdb next Hello world 12 printf We re so creative n gdb info macro N The symbol N has no definition as a C C preprocessor macro at home jimb gdb macros play sample c 12 gdb next We re so creative 14 printf Goodbye world n gdb info macro N Defined at home jimb gdb macros play sample c 13 104 define N 1729 gdb macro expand N Q M expands to 1729 42 gdb print N Q M 2 0 gdb Debugging with GDB Chapter 10 Tracepoints 105 10 Tracepoints In some applications it is not feasible for the debugger to interrupt the program s execution long enough for the developer to learn anything helpful about its behavior If the program s correctness depends on its real time behavior delays introdu
392. ing GDB on a physically separate host or controlling a standalone system over a serial port or a realtime system over a TCP IP connection you can use the target command to specify one of the target types configured for GDB see Section 16 2 Commands for Managing Targets page 168 It is possible to build GDB for several different target architectures When GDB is built like that you can choose one of the available architectures with the set architecture command set architecture arch This command sets the current target architecture to arch The value of arch can be auto in addition to one of the supported architectures show architecture Show the current target architecture set processor processor These are alias commands for respectively set architecture and show architecture 16 1 Active Targets There are three classes of targets processes core files and executable files GDB can work concurrently on up to three active targets one in each class This allows you to for example start a process and inspect its activity without abandoning your work on a core file For example if you execute gdb a out then the executable file a out is the only active target If you designate a core file as well presumably from a prior run that crashed and coredumped then GDB has two active targets and uses them in tandem looking first in the corefile target then in the executable file to satisfy requests for memory address
393. ing breakpoints do not differ from regular breakpoints You can set conditions or commands enable and disable them and perform other breakpoint operations GDB provides some additional commands for controlling what happens when the break command cannot resolve breakpoint address specification to an address Set breakpoint pending auto This is the default behavior When GDB cannot find the breakpoint location it queries you whether a pending breakpoint should be created Set breakpoint pending on This indicates that an unrecognized breakpoint location should automatically result in a pending breakpoint being created Set breakpoint pending off This indicates that pending breakpoints are not to be created Any unrecog nized breakpoint location results in an error This setting does not affect any pending breakpoints previously created Show breakpoint pending Show the current behavior setting for creating pending breakpoints The settings above only affect the break command and its variants Once breakpoint is set it will be automatically updated as shared libraries are loaded and unloaded For some targets GDB can automatically decide if hardware or software breakpoints should be used depending on whether the breakpoint address is read only or read write This applies to breakpoints set with the break command as well as to internal breakpoints set by commands like next and finish For breakpoints set with hbreak GDB will alway
394. ing the define command The end of these commands is marked by a line containing end document commandname Document the user defined command commandname so that it can be ac cessed by help The command commandname must already be defined This command reads lines of documentation just as define reads the lines of the command definition ending with end After the document command is fin ished help on command commandname displays the documentation you have written You may use the document command again to change the documentation of a command Redefining the command with define does not change the docu mentation 218 Debugging with GDB dont repeat Used inside a user defined command this tells GDB that this command should not be repeated when the user hits see Section 3 1 Command Syntax page 19 help user defined List all user defined commands with the first line of the documentation if any for each Show user Show user commandname Display the GDB commands used to define commandname but not its documen tation If no commandname is given display the definitions for all user defined commands show max user call depth set max user call depth The value of max user call depth controls how many recursion levels are allowed in user defined commands before GDB suspects an infinite recursion and aborts the command In addition to the above commands user defined commands frequently use control flow commands described
395. ingle stepping but treat them normally during normal execution you could define define hook stop handle SIGALRM nopass end Chapter 20 Canned Sequences of Commands 219 define hook run handle SIGALRM pass end define hook continue handle SIGALRM pass end As a further example to hook at the beginning and end of the echo command and to add extra text to the beginning and end of the message you could define define hook echo echo end define hookpost echo echo gt gt gt n end gdb echo Hello World Hello World gt gt gt gdb You can define a hook for any single word command in GDB but not for command aliases you should define a hook for the basic command name e g backtrace rather than bt If an error occurs during the execution of your hook execution of GDB commands stops and GDB issues a prompt before the command that you actually typed had a chance to run If you try to define a hook which does not match any known command you get a warning from the define command 20 3 Command Files A command file for GDB is a text file made of lines that are GDB commands Comments lines starting with may also be included An empty line in a command file does nothing it does not mean to repeat the last command as it would from the terminal You can request the execution of a command file with the source command source v filename Execute the command file filename The lines in
396. ings are identified as arrays of char values without specified signedness Arrays of either signed char or unsigned char get printed as arrays of 1 byte sized integers fsigned char or funsigned char GCC options have no effect as GDB defines literal string type char as char without a sign For program code char varO A signed char vari A You get during debugging gdb print varO 1 au gdb print vari 2 65 A 0 N0O 8 3 Artificial Arrays It is often useful to print out several successive objects of the same type in memory a section of an array or an array of dynamically determined size for which only a pointer exists in the program You can do this by referring to a contiguous span of memory as an artificial array using the binary operator The left operand of should be the first element of the desired array and be an individual object The right operand should be the desired length of the array The result is an array value whose elements are all of the type of the left argument The first element is actually the left argument the second element comes from bytes of 78 Debugging with GDB memory immediately following those that hold the first element and so on Here is an example If a program says int array int malloc len sizeof int you can print the contents of array with p array len The left operand of must reside in memory Array values made with
397. inguish whether you mean the version of name that takes an int parameter name int or the version that takes a float parameter name float To use the word completion facilities in this situation type a single quote at the beginning of the function name This alerts GDB that it may need to consider more information than usual when you press or M to request word completion gdb b bubble M bubble double double bubble int int gdb b bubble In some cases GDB can tell that completing a name requires using quotes When this happens GDB inserts the quote for you while completing as much as it can if you do not type the quote in the first place gdb b bub GDB alters your input line to the following and rings a bell gdb b bubble Chapter 3 GDB Commands 21 In general GDB can tell that a quote is needed and inserts it if you have not yet started typing the argument list when you ask for completion on an overloaded symbol For more information about overloaded functions see Section 12 4 1 3 C Expressions page 126 You can use the command set overload resolution off to disable overload resolution see Section 12 4 1 7 GDB Features for C page 128 3 3 Getting Help You can always ask GDB itself for information on its commands using the command help help h You can use help abbreviated h with no arguments to display a short list of named classes of commands gdb help List of classes of co
398. int number num is not specified the passcount command sets the passcount of the most recently defined tracepoint If no passcount is given the trace experiment will run until stopped explicitly by the user Examples gdb passcount 5 2 Stop on the 5th execution of tracepoint 2 gdb passcount 12 Stop on the 12th execution of the most recently defined tracepoint gdb trace foo gdb pass 3 gdb trace bar Chapter 10 Tracepoints 107 gdb pass 2 gdb trace baz gdb pass1 Stop tracing when foo has been executed 3 times OR when bar has been executed 2 times OR when baz has been executed 1 time 10 1 4 Tracepoint Action Lists actions num This command will prompt for a list of actions to be taken when the tracepoint is hit If the tracepoint number num is not specified this command sets the actions for the one that was most recently defined so that you can define a tracepoint and then say actions without bothering about its number You specify the actions themselves on the following lines one action at a time and terminate the actions list with a line containing just end So far the only defined actions are collect and while stepping To remove all actions from a tracepoint type actions num and follow it im mediately with end gdb collect data collect some data gdb while stepping 5 single step 5 times collect data gdb end signals the end of actions In
399. intent is to exercise the right to control the distribution of derivative or collective works based on the Program In addition mere aggregation of another work not based on the Program with the Program or with a work based on the Program on a volume of a storage or distribution medium does not bring the other work under the scope of this License 3 You may copy and distribute the Program or a work based on it under Section 2 in object code or executable form under the terms of Sections 1 and 2 above provided that you also do one of the following a Accompany it with the complete corresponding machine readable source code which must be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange or b Accompany it with a written offer valid for at least three years to give any third party for a charge no more than your cost of physically performing source distri bution a complete machine readable copy of the corresponding source code to be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange or c Accompany it with the information you received as to the offer to distribute cor responding source code This alternative is allowed only for noncommercial dis tribution and only if you received the program in object code or executable form with such an offer in accord with Subsection b above The source code for a work means th
400. inter will have when GDB generates the bytecode so it cannot determine whether a particular fetch will be aligned or not In particular structure bitfields may be several bytes long but follow no align ment rules members of packed structures are not necessarily aligned either In general there are many cases where unaligned references occur in correct C code either at the programmer s explicit request or at the compiler s discretion Thus it is simpler to make the GDB agent bytecodes work correctly in all circumstances than to make GDB guess in each case whether the compiler did the usual thing Why are there no side effecting operators Because our current client doesn t want them That s a cheap answer I think the real answer is that I m afraid of implementing function calls We should re visit this issue after the present contract is delivered Why aren t the goto ops PC relative The interpreter has the base address around anyway for PC bounds checking and it seemed simpler 380 Debugging with GDB Why is there only one offset size for the goto ops Offsets are currently sixteen bits I m not happy with this situation either Suppose we have multiple branch ops with different offset sizes As I generate code left to right all my jumps are forward jumps there are no loops in ex pressions so I never know the target when I emit the jump opcode Thus I have to either always assume the largest offset size or do jump
401. ion is the only way to impose a further condition on a catchpoint Chapter 5 Stopping and Continuing 49 condition bnum expression Specify expression as the break condition for breakpoint watchpoint or catch point number bnum After you set a condition breakpoint bnum stops your program only if the value of expression is true nonzero in C When you use condition GDB checks expression immediately for syntactic correctness and to determine whether symbols in it have referents in the context of your breakpoint If expression uses symbols not referenced in the context of the breakpoint GDB prints an error message No symbol foo in current context GDB does not actually evaluate expression at the time the condition command or a command that sets a breakpoint with a condition like break if is given however See Section 8 1 Expressions page 75 condition bnum Remove the condition from breakpoint number bnum It becomes an ordinary unconditional breakpoint A special case of a breakpoint condition is to stop only when the breakpoint has been reached a certain number of times This is so useful that there is a special way to do it using the ignore count of the breakpoint Every breakpoint has an ignore count which is an integer Most of the time the ignore count is zero and therefore has no effect But if your program reaches a breakpoint whose ignore count is positive then instead of stopping it just decrements the igno
402. ions compare sections section name Compare the data of a loadable section section name in the executable file of the program being debugged with the same section in the remote machine s memory and report any mismatches With no arguments compares all loadable sections This command s availability depends on the target s support for the qCRC remote request 8 6 Automatic Display If you find that you want to print the value of an expression frequently to see how it changes you might want to add it to the automatic display list so that GDB prints its value each time your program stops Each expression added to the list is given a number to identify it to remove an expression from the list you specify that number The automatic display looks like this 2 foo 38 3 bar 5 struct hack 0x3804 This display shows item numbers expressions and their current values As with displays you request manually using x or print you can specify the output format you prefer in fact display decides whether to use print or x depending your format specification it uses x if you specify either the i or s format or a unit size otherwise it uses print display expr Add the expression expr to the list of expressions to display each time your program stops See Section 8 1 Expressions page 75 display does not repeat if you press again after using it display fmt expr For fmt specifying only a display format and not a size
403. irectory dirname to the front of the source path Several directory names may be given to this command separated by on MS DOS and MS Windows where usually appears as part of absolute file names or white space You may specify a directory that is already in the source path this moves it forward so GDB searches it sooner You can use the string cdir to refer to the compilation directory if one is recorded and cwd to refer to the current working directory cwd is not the same as the former tracks the current working directory as it changes during your GDB session while the latter is immediately expanded to the current directory at the time you add an entry to the source path Reset the source path to its default value cdir cwd on Unix systems This requires confirmation show directories Print the source path show which directories it contains set substitute path from to Define a source path substitution rule and add it at the end of the current list of existing substitution rules If a rule with the same from was already defined then the old rule is also deleted For example if the file foo bar baz c was moved to mnt cross baz c then the command gdb set substitute path usr src mnt cross will tell GDB to replace usr src with mnt cross which will allow GDB to find the file baz c even though it was moved In the case w
404. irectory is different from your home directory Thus you can have more than one init file one generic in your home directory and another specific to the program you are debugging in the directory where you invoke GDB 5 Reads command files specified by the x option See Section 20 3 Command Files page 219 for more details about GDB command files 1 On DOS Windows systems the home directory is the one pointed to by the HOME environment variable 16 Debugging with GDB 6 Reads the command history recorded in the history file See Section 19 3 Command History page 207 for more details about the command history and the files where GDB records it Init files use the same syntax as command files see Section 20 3 Command Files page 219 and are processed by GDB in the same way The init file in your home directory can set options such as set complaints that affect subsequent processing of command line options and operands Init files are not executed if you use the nx option see Section 2 1 2 Choosing Modes page 13 The GDB init files are normally called gdbinit The DJGPP port of GDB uses the name gdb ini due to the limitations of file names imposed by DOS filesystems The Windows ports of GDB use the standard name but if they find a gdb ini file they warn you about that and suggest to rename the file to the standard name 2 2 Quitting GDB quit expression q To exit GDB
405. is target list current targets Describe the current target GDB Command The corresponding information is printed by info file among other things Example N A The target list parameters Command Synopsis target list parameters GDB Command No equivalent Example N A The target select Command Synopsis target select type parameters Connect GDB to the remote target This command takes two args type The type of target for instance async remote etc parameters Device names host names and the like See Section 16 2 Commands for Man aging Targets page 168 for more details The output is a connection notification followed by the address at which the target program is in the following form Chapter 24 The GDB MI Interface connected addr address func function name args arg list GDB Command The corresponding GDB command is target Example gdb target select async dev ttya connected addr 0xfe00a300 func args gdb 24 20 Miscellaneous GDB MI Commands The gdb exit Command Synopsis gdb exit Exit GDB immediately GDB Command Approximately corresponds to quit Example gdb gdb exit exit The exec abort Command Synopsis exec abort Kill the inferior running program GDB Command The corresponding GDB command is kill Example N A The gdb set Command Synopsis gdb set Set an int
406. is debugged after a fork The child process runs unimpeded This is the default child The new process is debugged after a fork The parent process runs unimpeded show follow fork mode Display the current debugger response to a fork or vfork call On Linux if you want to debug both the parent and child processes use the command set detach on fork set detach on fork mode Tells gdb whether to detach one of the processes after a fork or retain debugger control over them both on The child process or parent process depending on the value of follow fork mode will be detached and allowed to run indepen dently This is the default off Both processes will be held under the control of GDB One process child or parent depending on the value of follow fork mode is debugged as usual while the other is held suspended show detach on follow Show whether detach on follow mode is on off If you choose to set detach on follow mode off then GDB will retain control of all forked processes including nested forks You can list the forked processes under the control of GDB by using the info forks command and switch from one fork to another by using the fork command info forks Print a list of all forked processes under the control of GDB The listing will include a fork id a process id and the current position program counter of the process fork fork id Make fork number fork id the current process The argument fork id is the
407. is fact so it is possible to know when to send output when the output from a given command is over etc Different kinds of input each have a different input type Each input type has three annotations a pre annotation which denotes the beginning of any prompt which is being output a plain annotation which denotes the end of the prompt and then a post anno tation which denotes the end of any echo which may or may not be associated with the input For example the prompt input type features the following annotations Z Zpre prompt Z Zprompt Z Zpost prompt The input types are prompt When GDB is prompting for a command the main GDB prompt commands When GDB prompts for a set of commands like in the commands command The annotations are repeated for each command which is input overload choice When GDB wants the user to select between various overloaded functions query When GDB wants the user to confirm a potentially dangerous operation prompt for continue When GDB is asking the user to press return to continue Note Don t expect this to work well instead use set height O to disable prompting This is because the counting of lines is buggy in the presence of annotations 25 4 Errors Z Zquit This annotation occurs right before GDB responds to an interrupt Chapter 25 GDB Annotations 289 Z Zerror This annotation occurs right before GDB responds to an error Quit and error annotations indicate that any annot
408. is may also happen when the compiler does significant optimizations To be sure of always seeing accurate values turn off all optimization when compiling Another possible effect of compiler optimizations is to optimize unused variables out of existence or assign variables to registers as opposed to memory addresses Depending on the support for such cases offered by the debug info format used by the compiler GDB might not be able to display values for such local variables If that happens GDB will print a message like this No symbol foo in current context To solve such problems either recompile without optimizations or use a different debug info format if the compiler supports several such formats For example GCC the GNU C C compiler usually supports the gstabs option gstabs produces debug info in a format that is superior to formats such as COFF You may be able to use DWARF 2 gdwarf 2 which is also an effective form for debug info See section Options for Debugging Your Program or GCC in Using the GNU Compiler Collection GCC See Section 12 4 1 C and C page 123 for more information about debug info formats that are best suited to C programs If you ask to print an object whose contents are unknown to GDB e g because its data type is not completely specified by the debug information GDB will say lt incomplete type gt See Chapter 13 Symbols page 143 for more about this Str
409. is packet allows GDB and the remote stub to take advan tage of each others features qSupported also consolidates multiple feature probes at startup to improve GDB performance a single larger packet per forms better than multiple smaller probe packets on high latency links Some features may enable behavior which must not be on by default e g because it would confuse older clients or stubs Other features may describe packets which could be automatically probed for but are not These features must be 346 Debugging with GDB reported before GDB will use them This default unsupported behavior is not appropriate for all packets but it helps to keep the initial connection time under control with new versions of GDB which support increasing numbers of packets Reply stubfeature stubfeature The stub supports or does not support each returned stubfeature depending on the form of each stubfeature see below for the pos sible forms An empty reply indicates that qSupported is not recognized or that no features needed to be reported to GDB The allowed forms for each feature either a gdbfeature in the qSupported packet or a stubfeature in the response are name value The remote protocol feature name is supported and associated with the specified value The format of value depends on the fea ture but it must not include a semicolon name The remote protocol feature name is suppo
410. isplay entries from the descriptor tables Without an argument all entries from the specified table are displayed An argument which should be an integer expression means display a single entry whose index is given by the argument For example here s a convenient way to display information about the debugged program s data segment gdb info dos ldt ds 0x13f base 0x11970000 limit 0x0009ffff 32 Bit Data Read Write Exp up This comes in handy when you want to see whether a pointer is outside the data segment s limit i e garbled info dos pde info dos pte These two commands display entries from respectively the Page Directory and the Page Tables Page Directories and Page Tables are data structures which control how virtual memory addresses are mapped into physical addresses A Page Table includes an entry for every page of memory that is mapped into the 184 Debugging with GDB program s address space there may be several Page Tables each one holding up to 4096 entries A Page Directory has up to 4096 entries one each for every Page Table that is currently in use Without an argument info dos pde displays the entire Page Directory and info dos pte displays all the entries in all of the Page Tables An argument an integer expression given to the info dos pde command means display only that entry from the Page Directory table An argument given to the info dos pte command means display entries from a single Page Table the
411. ission is granted to copy distribute and or modify this document under the terms of the GNU Free Documentation License Version 1 2 or any later version published by the Free Software Foundation with no Invariant Sections no Front Cover Texts and no Back Cover Texts A copy of the license is included in the section entitled GNU Free Documentation License If you have Invariant Sections Front Cover Texts and Back Cover Texts replace the with Texts line with this with the Invariant Sections being list their titles with the Front Cover Texts being list and with the Back Cover Texts being list If you have Invariant Sections without Cover Texts or some other combination of the three merge those two alternatives to suit the situation If your document contains nontrivial examples of program code we recommend releasing these examples in parallel under your choice of free software license such as the GNU General Public License to permit their use in free software 400 Debugging with GDB Appendix H Index Index it acommnenb cus ceste Uie ees 19 iin Modula 2 2 cere RR Renan 137 oscslsen age Atia dRRFPTCRR UC Pewee Gee Ez 88 laldlccddg e eere ne ebd pua b eive eu 88 _ and info breakpoints 4 40 and info line uc tah eee ais 72 _ __ and value history 81 _ convenience variable 00 89 __ convenience variable 004 89
412. issue and say firmly that this is what you want If the publisher you are dealing with refuses please try other publishers If you re not sure whether a proposed license is free write to licensingOgnu org You can encourage commercial publishers to sell more free copylefted manuals and tutorials by buying them and particularly by buying copies from the publishers that paid for their writing or for major improvements Meanwhile try to avoid buying non free documentation at all Check the distribution terms of a manual before you buy it and insist that whoever seeks your business must respect your freedom Check the history of the book and try to reward the publishers that have paid or pay the authors to work on it The Free Software Foundation maintains a list of free documentation published by other publishers at http www fsf org doc other free books html Contributors to GDB Richard Stallman was the original author of GDB and of many other GNU programs Many others have contributed to its development This section attempts to credit major contrib utors One of the virtues of free software is that everyone is free to contribute to it with regret we cannot actually acknowledge everyone here The file ChangeLog in the GDB distribution approximates a blow by blow account Changes much prior to version 2 0 are lost in the mists of time Plea Additions to this section are particularly welcome If you or your friends or enemies
413. ist of the supported languages type set language Setting the language manually prevents GDB from updating the working language au tomatically This can lead to confusion if you try to debug a program when the working language is not the same as the source language when an expression is acceptable to both languages but means different things For instance if the current source file were written in C and GDB was parsing Modula 2 a command such as printa bte might not have the effect you intended In C this means to add b and c and place the result in a The result printed would be the value of a In Modula 2 this means to compare a to the result of b c yielding a BOOLEAN value 12 1 3 Having GDB Infer the Source Language To have GDB set the working language automatically use set language local or set language auto GDB then infers the working language That is when your program stops in a frame usually by encountering a breakpoint GDB sets the working language to the language recorded for the function in that frame If the language for a frame is unknown that is if the function or block corresponding to the frame was defined in a source file that does not have a recognized extension the current working language is not changed and GDB issues a warning This may not seem necessary for most programs which are written entirely in one source language However program modules and libraries written in one sourc
414. ith 0 CREAT if the file already exists it is an error and open fails O TRUNC Ifthe file already exists and the open mode allows writing O_RDWR or O_WRONLY is given it will be truncated to zero length 358 0 APPEND 0 RDONLY 0 WRONLY O_RDWR Debugging with GDB The file is opened in append mode The file is opened for reading only The file is opened for writing only The file is opened for reading and writing Other bits are silently ignored mode is the bitwise OR of the following values S_IRUSR S_IWUSR S_IRGRP S_IWGRP S_IROTH S_IWOTH User has read permission User has write permission Group has read permission Group has write permission Others have read permission Others have write permission Other bits are silently ignored Return value open returns the new file descriptor or 1 if an error occurred Errors EEXIST pathname already exists and O_CREAT and 0 EXCL were used EISDIR pathname refers to a directory EACCES The requested access is not allowed ENAMETOOLONG pathname was too long ENOENT A directory component in pathname does not exist ENODEV pathname refers to a device pipe named pipe or socket EROFS pathname refers to a file on a read only filesystem and write access was requested EFAULT pathname is an invalid pointer value ENOSPC No space on device to create the file EMFILE The process already has the maximum number of files open ENFILE The limit on th
415. its for other registers set this option to on show remote mips64 transfers 32bit regs Show the current setting of compatibility with older MIPS 64 targets set debug mips This command turns on and off debugging messages for the MIPS specific target code in GDB show debug mips Show the current setting of MIPS debugging messages 18 4 5 HPPA When GDB is debugging the HP PA architecture it provides the following special commands set debug hppa This command determines whether HPPA architecture specific debugging mes sages are to be displayed show debug hppa Show whether HPPA debugging messages are displayed maint print unwind address This command displays the contents of the unwind table entry at the given address 18 4 6 Cell Broadband Engine SPU architecture When GDB is debugging the Cell Broadband Engine SPU architecture it provides the following special commands Chapter 18 Configuration Specific Information 205 info spu event Display SPU event facility status Shows current event mask and pending event status info spu signal Display SPU signal notification facility status Shows pending signal control word and signal notification mode of both signal notification channels info spu mailbox Display SPU mailbox facility status Shows all pending entries in order of pro cessing in each of the SPU Write Outbound SPU Write Outbound Interrupt and SPU Read Inbound mailboxes info spu dma Display M
416. its value as a string or set the value from a string String value can be also obtained for a non leaf variable object but it s generally a string that only indicates the type of the object and does not list its contents Assignment to a non leaf variable object is not allowed A frontend does not need to read the values of all variable objects each time the program stops Instead MI provides an update command that lists all variable objects whose values has changed since the last update operation This considerably reduces the amount of data that must be transferred to the frontend As noted above children variable objects are created on demand and only leaf variable objects have a real value As result gdb will read target memory only for leaf variables that frontend has created The automatic update is not always desirable For example a frontend might want to keep a value of some expression for future reference and never update it For another example fetching memory is relatively slow for embedded targets so a frontend might want 262 Debugging with GDB to disable automatic update for the variables that are either not visible on the screen or closed This is possible using so called frozen variable objects Such variable objects are never implicitly updated The following is the complete set of GDB MI operations defined to access this function ality Operation Description var create create a variable object va
417. ize Given that information GDB can determine at translation time whether a given expression will overflow the stack But this spec isn t about what kinds of error checking GDB ought to do Why are you doing everything in LONGEST Speed isn t important but agent code size is using LONGEST brings in a bunch of support code to do things like division etc So this is a serious concern First note that you don t need different bytecodes for different operand sizes You can generate code without knowing how big the stack elements actually are on the target If the target only supports 32 bit ints and you don t send any 64 bit bytecodes everything just works The observation here is that the MIPS and the Alpha have only fixed size registers and you can still get C s semantics even though most instructions only operate on full sized words You just need to make sure everything is properly sign extended at the right times So there is no need for 32 and 64 bit variants of the bytecodes Just implement everything using the largest size you support GDB should certainly check to see what sizes the target supports so the user can get an error earlier rather than later But this information is not necessary for correctness Why don t you have gt or lt operators I want to keep the interpreter small and we don t need them We can combine the less opcodes with log not and swap the order of the operands yielding Appendix E
418. k 3 Page Table entry for address 0x29110 Base 0x00029000 Dirty Acc Not Cached Write Back Usr Read Write 0x110 The 3 offset is because the transfer buffer s address is the 3rd member of the 032 info block structure The output clearly shows that this DPMI server maps the addresses in conventional memory 1 1 i e the physical 0x00029000 0x110 and linear 0x29110 addresses are identical This command is supported only with some DPMI servers In addition to native debugging the DJGPP port supports remote debugging via a serial data link The following commands are specific to remote serial debugging in the DJGPP port of GDB set comibase addr This command sets the base I O port address of the COM1 serial port set comiirq irq This command sets the Interrupt Request IRQ line to use for the COM1 serial port Chapter 18 Configuration Specific Information 185 There are similar commands set com2base set com3irq etc for setting the port address and the IRQ lines for the other 3 COM ports The related commands show comibase show comlirq etc display the cur rent settings of the base address and the IRQ lines used by the COM ports info serial This command prints the status of the 4 DOS serial ports For each port it prints whether it s active or not its I O base address and IRQ number whether it uses a 16550 style FIFO its baudrate and the counts of various errors encou
419. k frames follow The values of arguments that were not saved in their stack frames are shown as lt value optimized out gt If you need to display the values of such optimized out arguments either deduce that from other variables whose values depend on the one you are interested in or recompile without optimizations Most programs have a standard user entry point a place where system libraries and startup code transition into user code For C this is main When GDB finds the entry function in a backtrace it will terminate the backtrace to avoid tracing into highly system specific and generally uninteresting code If you need to examine the startup code or limit the number of levels in a backtrace you can change this behavior set backtrace past main set backtrace past main on Backtraces will continue past the user entry point set backtrace past main off Backtraces will stop when they encounter the user entry point This is the default show backtrace past main Display the current user entry point backtrace policy Note that embedded programs the so called free standing environment are not required to have a main function as the entry point They could even have multiple entry points 64 Debugging with GDB Set backtrace past entry Set backtrace past entry on Backtraces will continue past the internal entry point of an application This entry point is encoded by the linker when the application is
420. king 0 000000 eee eee ee eee 94 8 15 Copy Between Memory and a File 2 00 005 94 8 16 How to Produce a Core File from Your Program 95 8 17 Character Setsc Coburg do dre e EROR Proba Rl 95 8 18 Caching Data of Remote Targets 0 0 000 cease 98 9 C Preprocessor Macros LL 101 I0 Tracepoints see R e EE Ure 99s 105 10 1 Commands to Set Tracepoints 0 0 0000 sessiles 105 10 1 1 Create and Delete Tracepoints 004 105 10 1 2 Enable and Disable Tracepoints 4 106 10 1 3 Tracepoint Passcounts 0 0 0 c eee cece eee 106 10 1 4 Tracepoint Action Lists ls sies else 107 10 1 5 Listing Tracepoints esseeri esigia iania iii enia ee eee ee 108 10 1 6 Starting and Stopping Trace Experiments 108 10 2 Using the Collected Data 0 00 ete 109 I0 2 1 tfind incer erre tA etta cxt dre eg ig 109 10 2 2 tdumpuliilnigiipuewee ER ade Ren abe eee 111 10 2 3 save tracepoints filename 0 112 10 8 Convenience Variables for Tracepoints 4 112 11 Debugging Programs That Use Overlays TTT TPC Ce Te ee TT eee ee eC eee 113 I1 How Overlays Work inei e eer hea a 113 11 2 Overlay Commands 0000 cece eect eet ees 114 11 3 Automatic Overlay Debugging lesse esses 116 11 4 Overlay Sample Program ssueeessseee esee TIT 12 Using GDB with Differ
421. l file filename address readnow add symbol file filename ssection address The add symbol file command reads additional symbol table information from the file filename You would use this command when filename has been dynamically loaded by some other means into the program that is running Chapter 15 GDB Files 157 address should be the memory address at which the file has been loaded GDB cannot figure this out for itself You can additionally specify an arbitrary number of ssection address pairs to give an explicit section name and base address for that section You can specify any address as an expression The symbol table of the file filename is added to the symbol table originally read with the symbol file command You can use the add symbol file command any number of times the new symbol data thus read keeps adding to the old To discard all old symbol data instead use the symbol file command without any arguments Although filename is typically a shared library file an executable file or some other object file which has been fully relocated for loading into a process you can also load symbolic information from relocatable o files as long as e the file s symbolic information refers only to linker symbols defined in that file not to symbols defined by other object files e every section the file s symbolic information refers to has actually been loaded into the inferior as it appears in the file and
422. l of commands are enough to get started using the debugger This chapter illustrates those commands In this sample session we emphasize user input like this input to make it easier to pick out from the surrounding output One of the preliminary versions of GNU m4 a generic macro processor exhibits the following bug sometimes when we change its quote strings from the default the commands used to capture one macro definition within another stop working In the following short m4 session we define a macro foo which expands to 0000 we then use the m4 built in defn to define bar as the same thing However when we change the open quote string to lt QUOTE gt and the close quote string to lt UNQUOTE gt the same procedure fails to define a new synonym baz cd gnu m4 m4 define foo 0000 foo 0000 define bar defn foo bar 0000 changequote lt QUOTE gt lt UNQUOTE gt define baz defn lt QUOTE gt foo lt UNQUOTE gt baz Ctrl d m4 End of input 0 fatal error EOF in string Let us use GDB to try to see what is going on gdb m4 GDB is free software and you are welcome to distribute copies of it under certain conditions type show copying to see the conditions There is absolutely no warranty for GDB type show warranty for details GDB 6 7 50_20071011 Copyright 1999 Free Software Foundation Inc gdb GDB reads only enough symbol data to know where to find the rest when needed as a result t
423. l size 9880 download section init section size 28 total size 9880 download section fini section size 28 total size 9880 download section data section size 3156 total size 9880 download section data section sent 512 section size 3156 total sent 7236 total size 9880 download section data section sent 1024 section size 3156 total sent 7748 total size 9880 download section data section sent 1536 section size 3156 total sent 8260 total size 9880 download section data section sent 2048 section size 3156 total sent 8772 total size 9880 download section data section sent 2560 section size 3156 total sent 9284 total size 9880 download section data section sent 3072 section size 3156 total sent 9796 total size 9880 done address 0x10004 load size 9880 transfer rate 6586 write rate 429 gdb The target exec status Command Synopsis target exec status 281 Provide information on the state of the target whether it is running or not for instance GDB Command There s no equivalent GDB command Example N A 282 Debugging with GDB The target list available targets Command Synopsis target list available targets List the possible targets to connect to GDB Command The corresponding GDB command is help target Example N A The target list current targets Command Synops
424. laced with the octal escape nnn for characters outside the 7 bit ASCII range Without this format GDB displays char unsigned char and signed char data as character constants Single byte members of vectors are displayed as integer data Regard the bits of the value as a floating point number and print using typical floating point syntax Regard as a string if possible With this format pointers to single byte data are displayed as null terminated strings and arrays of single byte data are displayed as fixed length strings Other values are displayed in their natural types Without this format GDB displays pointers to and arrays of char unsigned char and signed char as strings Single byte members of a vector are displayed as an integer array For example to print the program counter in hex see Section 8 10 Registers page 90 type p x p c Note that no space is required before the slash this is because command names in GDB cannot contain a slash To reprint the last value in the value history with a different format you can use the print command with just a format and no expression For example p x reprints the last value in hex 8 5 Examining Memory You can use the command x for examine to examine memory in any of several formats independently of your program s data types x nfu addr x addr x n f and to format it Use the x command to examine memory u are all optional p
425. lags or even to make emergency repairs set write on set write off If you specify set write on GDB opens executable and core files for both reading and writing if you specify set write off the default GDB opens them read only If you have already loaded a file you must load it again using the exec file or core file command after changing set write for your new setting to take effect Chapter 14 Altering Execution 153 show write Display whether executable files and core files are opened for writing as well as reading 154 Debugging with GDB Chapter 15 GDB Files 155 15 GDB Files GDB needs to know the file name of the program to be debugged both in order to read its symbol table and in order to start your program To debug a core dump of a previous run you must also tell GDB the name of the core dump file 15 1 Commands to Specify Files You may want to specify executable and core dump file names The usual way to do this is at start up time using the arguments to GDB s start up commands see Chapter 2 Getting In and Out of GDB page 11 Occasionally it is necessary to change to a different file during a GDB session Or you may run GDB and forget to specify a file you want to use Or you are debugging a remote target via gdbserver see Section 17 2 Using the gdbserver Program page 173 In these situations the GDB commands to specify new files are useful file filename Use filename as the p
426. ldFire 18 3 4 MIPS Embedded GDB can use the MIPS remote debugging protocol to talk to a MIPS board attached to a serial line This is available when you configure GDB with target mips idt ecoff Use these GDB commands to specify the connection to your target board target mips port To run a program on the board start up gdb with the name of your program as the argument To connect to the board use the command target mips port where port is the name of the serial port connected to the board If the program has not already been downloaded to the board you may use the 1oad command to download it You can then use all the usual GDB commands For example this sequence connects to the target board through a serial port and loads and runs a program called prog through the debugger host gdb prog GDB is free software and gdb target mips dev ttyb gdb load prog gdb run target mips hostname portnumber On some GDB host configurations you can specify a TCP connection for in stance to a serial line managed by a terminal concentrator instead of a serial port using the syntax hostname portnumber target pmon port PMON ROM monitor target ddb port NEC s DDB variant of PMON for Vr4300 target lsi port LSI variant of PMON target r3900 dev Densan DVE R3900 ROM monitor for Toshiba R3900 Mips 196 Debugging with GDB target array dev Array Tech LSI33K RAID controller board GDB also sup
427. lena Zannoni Kim Haase provided HP specific information in this manual DJ Delorie ported GDB to MS DOS for the DJGPP project Robert Hoehne made significant contributions to the DJGPP port Cygnus Solutions has sponsored GDB maintenance and much of its development since 1991 Cygnus engineers who have worked on GDB fulltime include Mark Alexander Jim Blandy Per Bothner Kevin Buettner Edith Epstein Chris Faylor Fred Fish Martin Hunt Jim Ingham John Gilmore Stu Grossman Kung Hsu Jim Kingdon John Metzler Fernando Nasser Geoffrey Noer Dawn Perchik Rich Pixley Zdenek Radouch Keith Seitz Stan Shebs David Taylor and Elena Zannoni In addition Dave Brolley Ian Carmichael Steve Chamberlain Nick Clifton J T Conklin Stan Cox DJ Delorie Ulrich Drepper Frank Figler Doug Evans Sean Fagan David Henkel Wallace Richard Henderson Jeff Holcomb Jeff Law Jim Lemke Tom Lord Bob Manson Michael Meissner Jason Merrill Catherine Moore Drew Moseley Ken Raeburn Gavin Romig Koch Rob Savoye Jamie Smith Mike Stump Ian Taylor Angela Thomas Michael Tiemann Tom Tromey Ron Unrau Jim Wilson and David Zuhn have made contributions both large and small Andrew Cagney Fernando Nasser and Elena Zannoni while working for Cygnus Solu tions implemented the original GDB MI interface Jim Blandy added support for preprocessor macros while working for Red Hat Andrew Cagney designed GDB s architecture vector Many people incl
428. libiberty a in the directory gdb sun4 libiberty and GDB itself in gdb sun4 gdb Make sure that your path to the configure script has just one instance of gdb in it If your path to configure looks like gdb 6 7 50_20071011 gdb configure you are configuring only one subdirectory of GDB not the whole package This leads to build errors about missing include files such as bfd bfd h One popular reason to build several GDB configurations in separate directories is to con figure GDB for cross compiling where GDB runs on one machine the host while debugging programs that run on another machine the target You specify a cross debugging target by giving the target target option to configure When you run make to build a program or library you must run it in a configured directory whatever directory you were in when you called configure or one of its sub directories The Makefile that configure generates in each source directory also runs recursively If you type make in a source directory such as gdb 6 7 50_20071011 or in a separate configured directory configured with srcdir dirname gdb 6 7 50 20071011 you will build all the required libraries and then build GDB When you have multiple hosts or targets configured in separate directories you can run make on them in parallel for example if they are NFS mounted on each of the hosts they will not i
429. ligned address raises an exception you should fetch the register number one byte at a time trace 0x0c addr size gt Record the contents of the size bytes at addr in a trace buffer for later retrieval by GDB trace quick O0x0d size addr addr Record the contents of the size bytes at addr in a trace buffer for later retrieval by GDB size is a single byte unsigned integer following the trace opcode This bytecode is equivalent to the sequence dup const8 size trace but we provide it anyway to save space in bytecode strings trace16 0x30 size addr gt addr Identical to trace_quick except that size is a 16 bit big endian unsigned integer not a single byte This should probably have been named trace quick16 for consistency end 0x27 Stop executing bytecode the result should be the top element of the stack If the purpose of the expression was to compute an lvalue or a range of memory then the next to top of the stack is the lvalue s address and the top of the stack is the lvalue s size in bytes E 3 Using Agent Expressions Here is a sketch of a full non stop debugging cycle showing how agent expressions fit into the process e The user selects trace points in the program s code at which GDB should collect data e The user specifies expressions to evaluate at each trace point These expressions may denote objects in memory in which case those objects contents are recorded as the program runs or comp
430. limited to the covers as long as they preserve the title of the Document and satisfy these conditions can be treated as verbatim copying in other respects If the required texts for either cover are too voluminous to fit legibly you should put the first ones listed as many as fit reasonably on the actual cover and continue the rest onto adjacent pages If you publish or distribute Opaque copies of the Document numbering more than 100 you must either include a machine readable Transparent copy along with each Opaque copy or state in or with each Opaque copy a computer network location from which the general network using public has access to download using public standard network protocols a complete Transparent copy of the Document free of added material If you use the latter option you must take reasonably prudent steps when you begin distribution of Opaque copies in quantity to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy directly or through your agents or retailers of that edition to the public It is requested but not required that you contact the authors of the Document well before redistributing any large number of copies to give them a chance to provide you with an updated version of the Document 4 MODIFICATIONS You may copy and distribute a Modified Version of the Document under the conditions of sections
431. ll detect changes to the watched expression from every thread Warning In multi threaded programs software watchpoints have only limited usefulness If GDB creates a software watchpoint it can only watch the value of an expression in a single thread If you are confident that the expression can only change due to the current thread s activity and if you are also confident that no other thread can become current then you can use software watch points as usual However GDB may not notice when a non current thread s activity changes the expression Hardware watchpoints in contrast watch an expression in all threads See set remote hardware watchpoint limit page 175 5 1 3 Setting Catchpoints You can use catchpoints to cause the debugger to stop for certain kinds of program events such as C exceptions or the loading of a shared library Use the catch command to set a catchpoint catch event Stop when event occurs event can be any of the following throw The throwing of a C exception catch The catching of a C exception exception An Ada exception being raised If an exception name is specified at the end of the command eg catch exception Program_Error the debugger will stop only when this specific exception is raised Otherwise the debugger stops execution when any Ada exception is raised exception unhandled An exception that was raised but is not handled by the program assert A failed Ada assertion exec
432. lled a checkpoint and come back to it later Returning to a checkpoint effectively undoes everything that has happened in the pro gram since the checkpoint was saved This includes changes in memory registers and even within some limits system state Effectively it is like going back in time to the moment when the checkpoint was saved Thus if you re stepping thru a program and you think you re getting close to the point where things go wrong you can save a checkpoint Then if you accidentally go too far and miss the critical statement instead of having to restart your program from the beginning you can just go back to the checkpoint and start again from there This can be especially useful if it takes a lot of time or steps to reach the point where you think the bug occurs To use the checkpoint restart method of debugging checkpoint Save a snapshot of the debugged program s current execution state The checkpoint command takes no arguments but each checkpoint is assigned a small integer id similar to a breakpoint id info checkpoints List the checkpoints that have been saved in the current debugging session For each checkpoint the following information will be listed 1 Currently only GNU Linux 36 Debugging with GDB Checkpoint ID Process ID Code Address Source line or label restart checkpoint id Restore the program state that was saved as checkpoint number checkpoint id All program variables registe
433. looks up the named file in the directory of the executable file then in a subdirectory of that directory named debug and finally under the global debug directory in a subdirectory whose name is identical to the leading directories of the executable s absolute file name 162 Debugging with GDB e For the build ID method GDB looks in the build id subdirectory of the global debug directory for a file named nn nnnnnnnn debug where nn are the first 2 hex characters of the build ID bit string and nnnnnnnn are the rest of the bit string Real build ID strings are 32 or more hex characters not 10 So for example suppose you ask GDB to debug usr bin 1s which has a debug link that specifies the file 1s debug and a build ID whose value in hex is abcdef1234 If the global debug directory is usr lib debug then GDB will look for the following debug information files in the indicated order usr lib debug build id ab cdef1234 debug usr bin 1s debug usr bin debug 1s debug usr lib debug usr bin 1s debug You can set the global debugging info directory s name and view the name GDB is currently using set debug file directory directory Set the directory which GDB searches for separate debugging information files to directory show debug file directory Show the directory GDB searches for separate debugging information files A debug link is a special section of the execu
434. ls like the GDB next command Then update the display window to show the current file and location C c C i Execute one instruction like the GDB stepi command update display window accordingly C c C f Execute until exit from the selected stack frame like the GDB finish command C c C r Continue execution of your program like the GDB continue command C c Go up the number of frames indicated by the numeric argument see section Numeric Arguments in The GNU Emacs Manual like the GDB up command C c gt Go down the number of frames indicated by the numeric argument like the GDB down command In any source file the Emacs command C x gud break tells GDB to set a break point on the source line point is on In text command mode if you type M x speedbar Emacs displays a separate frame which shows a backtrace when the GUD buffer is current Move point to any frame in the stack and type to make it become the current frame and display the associated source in the source buffer Alternatively click Mouse 2 to make the selected frame become the current one In graphical mode the speedbar displays watch expressions If you accidentally delete the source display buffer an easy way to get it back is to type the command f in the GDB buffer to request a frame display when you run under Emacs this recreates the source buffer if necessary to show you the context of the current frame The source files displayed in Emacs are in ordi
435. ls us the character sets it supports gdb set target charset ASCII EBCDIC US IBM1047 IS0 8859 1 gdb set target charset We can select IBM1047 as our target character set and examine the program s strings again Now the ASCII string is wrong but GDB translates the contents of ibm1047 hello from the target character set IBM1047 to the host character set ASCII and they display correctly gdb set target charset IBM1047 gdb show charset The current host character set is ASCII The current target character set is IBM1047 gdb print ascii hello 6 0x401698 110 145 7 054 040 1677 162 144 041 012 gdb print ascii_hello 0 7 72 110 gdb print ibmi047 hello 8 0x4016a8 Hello world n gdb print ibmi047 hello 0 9 200 H gdb As above GDB uses the target character set for character and string literals you use in expressions gdb print 10 78 v gdb The IBM1047 character set uses the number 78 to encode the character 8 18 Caching Data of Remote Targets GDB can cache data exchanged between the debugger and a remote target see Chapter 17 Remote Debugging page 171 Such caching generally improves performance because it reduces the overhead of the remote protocol by bundling memory reads and writes into large chunks Unfortunately GDB does not currently know anything about volatile registers and thus data caching will produce incorrect results when vola
436. lusion into the current one The line selected from the history is called the event and the portions of that line that are acted upon are called words Various modifiers are available to manipulate the selected words The line is broken into words in the same fashion that Bash does so that several words surrounded by quotes are considered one word History expansions are introduced by the appearance of the history expansion character which is by default 28 1 1 Event Designators An event designator is a reference to a command line entry in the history list Start a history substitution except when followed by a space tab the end of the line or n Refer to command line n n Refer to the command n lines back n Refer to the previous command This is a synonym for 1 Istring Refer to the most recent command starting with string I string Refer to the most recent command containing string The trailing may be omitted if the string is followed immediately by a newline stringi string2 Quick Substitution Repeat the last command replacing string with string2 Equivalent to s string1 string2 n The entire command line typed so far 28 1 2 Word Designators Word designators are used to select desired words from the event A separates the event specification from the word designator It may be omitted if the word designator begins with a or Word
437. ly selected use either info target or info files see Section 15 1 Commands to Specify Files page 155 help target name Describe a particular target including any parameters necessary to select it set gnutarget args GDB uses its own library BFD to read your files GDB knows whether it is reading an executable a core or a o file however you can specify the file format with the set gnutarget command Unlike most target commands with gnutarget the target refers to a program not a machine Warning lo specify a file format with set gnutarget you must know the actual BFD name See Section 15 1 Commands to Specify Files page 155 show gnutarget Use the show gnutarget command to display what file format gnutarget is set to read If you have not set gnutarget GDB will determine the file format for each file automatically and show gnutarget displays The current BDF target is auto Here are some common targets available or not depending on the GDB configuration target exec program An executable file target exec program is the same as exec file pro gram target core filename A core dump file target core filename is the same as core file file name target remote medium A remote system connected to GDB via a serial line or network connection This command tells GDB to use its own remote protocol over medium for debugging See Chapter 17 Remote Debugging page 171 For example if you hav
438. ly set by the x command to the last address examined see Section 8 5 Examining Memory page 79 Other commands which provide a default address for x to examine also set _ to that address these commands include info line and info breakpoint The type of _ is void except when set by the x command in which case it is a pointer to the type of __ __ The variable __ is automatically set by the x command to the value found in the last address examined Its type is chosen to match the format in which the data was printed 90 Debugging with GDB exitcode The variable _exitcode is automatically set to the exit code when the program being debugged terminates On HP UX systems if you refer to a function or variable name that begins with a dollar sign GDB searches for a user or system name first before it searches for a convenience variable 8 10 Registers You can refer to machine register contents in expressions as variables with names starting with The names of registers are different for each machine use info registers to see the names used on your machine info registers Print the names and values of all registers except floating point and vector registers in the selected stack frame info all registers Print the names and values of all registers including floating point and vector registers in the selected stack frame info registers regname Print the relativized value of each specified register reg
439. machine you will need an unstripped copy of your program since GDB needs symbol and debugging information Start up GDB as usual using the name of the local copy of your program as the first argument GDB can communicate with the target over a serial line or over an IP network using TCP or UDP In each case GDB uses the same protocol for debugging your program only the medium carrying the debugging packets varies The target remote command establishes a connection to the target Its arguments indicate which medium to use target remote serial device Use serial device to communicate with the target For example to use a serial line connected to the device named dev ttyb target remote dev ttyb If you re using a serial line you may want to give GDB the baud option or use the set remotebaud command see Section 17 3 Remote Configuration page 174 before the target command target remote host port target remote tcp host port Debug using a TCP connection to port on host The host may be either a host name or a numeric IP address port must be a decimal number The host could be the target machine itself if it is directly connected to the net or it might be a terminal server which in turn has a serial line to the target For example to connect to port 2828 on a terminal server named manyfarms target remote manyfarms 2828 If your remote target is actually running on the same machine as your debugger session e g a sim
440. mand allows sending an arbitrary command string to the monitor The monitor must be in debug mode for this to work 18 3 5 OpenRISC 1000 See OR1k Architecture document www opencores org for more information about plat form and commands target jtag jtag host port Connects to remote J TAG server JTAG remote server can be either an orlksim or JTAG server connected via parallel port to the board Example target jtag jtag localhost 9999 oriksim command If connected to oriksim OpenRISC 1000 Architectural Simulator proprietary commands can be executed info orik spr Displays spr groups info orik spr group info orik spr groupno Displays register names in selected group info orlk spr group register info or1k spr register info or1k spr groupno registerno info orik spr registerno Shows information about specified spr register 198 Debugging with GDB spr group register value spr register value spr groupno registerno value spr registerno value Writes value to specified spr register Some implementations of OpenRISC 1000 Architecture also have hardware trace It is very similar to GDB trace except it does not interfere with normal program execution and is thus much faster Hardware breakpoints watchpoint triggers can be set using LEA LDATA Load effective address data SEA SDATA Store effective address data AEA SADATA Access effective address 8EA or LEA or data 5SSDATA SLDATA FETCH Fetch data
441. manual cannot provide portable sample code demonstrating GDB s overlay support However the GDB source distribution does contain an overlaid program with linker scripts for a few systems as part of its test suite The program consists of the following files from gdb testsuite gdb base overlays c The main program file ovlymgr c A simple overlay manager used by overlays c foo c bar c baz c grbx c Overlay modules loaded and used by overlays c d10v 1d m32r 1d Linker scripts for linking the test program on the d10v elf and m32r elf targets You can build the test program using the d10v elf GCC cross compiler like this diO0v elf gcc g c overlays c diO0v elf gcc g c ovlymgr c diOv elf gcc g c foo c diO0v elf gcc g c bar c diO0v elf gcc g c baz c diO0v elf gcc g c grbx c diOv elf gcc g overlays o ovlymgr o foo o bar o baz o grbx o W1 Td10v 1d o overlays 9 G 9 9 9 HSA The build process is identical for any other architecture except that you must substitute the appropriate compiler and linker script for the target system for diOv elf gcc and d10v 1d 118 Debugging with GDB Chapter 12 Using GDB with Different Languages 119 12 Using GDB with Different Languages Although programming languages generally have common aspects they are rarely expressed in the same manner For instance in ANSI C dereferencing a pointer p i
442. mat remote protocol 366 limit hardware breakpoints and watchpoints 175 limit on number of printed array elements 84 limits in file i o protocol sss 366 Iinespee aue E eg ret RED rede 67 Linux lightweight processes 214 hr 67 list active threads remote request 343 list of supported file i o calls 357 list output in GDB MI 2 0000 235 list and Objective C 129 list how many lines to display 67 listing GDB s internal symbol tables 147 listing machine instructions issus 72 listing mapped overlays 115 load address overlay s 00000 113 Load filename lea oae pER ee anes 169 load shared library 5 5 debe R RR ets 160 load symbols from memory 157 local vari blese sien Een ERREUR I 144 locate address osse eb tene 79 lock scheduller iorri rrin ee ri ad nee 58 log output in GDB MI isses 235 logging file name 22d eer te P logging GDB output sees 16 loop break 4 bee PED PR PP RUPES 220 loop continue 4c fece Rees 220 Iseek flags in file i o protocol 366 Iseek file i o system call 04 360 409 M n packet 29 ue eaquep RP e 336 M packet 245232 diae bebra e na epe 337 M32 EVA target board address 194 M32R Chaos debugging 0000 194 MOSO ernie
443. mat Command Synopsis var show format name Returns the format used to display the value of the object name format gt format spec The var info num children Command Synopsis var info num children name Returns the number of children of a variable object name numchild n The var list children Command Synopsis var list children print values name Return a list of the children of the specified variable object and create variable objects for them if they do not already exist With a single argument or if print values has a 264 Debugging with GDB value for of 0 or no values print only the names of the variables if print values is 1 or all values also print their values and if it is 2 or simple values print the name and value for simple data types and just the name for arrays structures and unions Example gdb var list children n done numchild n children name name numchild n type type repeats N times gdb var list children all values n done numchild n children name name numchild n value value type type repeats N times The var info type Command Synopsis var info type name Returns the type of the specified variable name The type is returned as a string in the same format as it is output by the GDB CLI type typename The var info expression Command Synopsis var info expression name Returns a string that is suitable for presenting this variable object in user interfac
444. mbol info function 274 sSymbol info lin6 2 5 9103248394 9303 274 symbol info symbol 006 274 symbol list functions 274 Symbol list lin s gs gcse 92 4 o Rep 275 ssymbol list typ6e8S RR REIS 275 symbol list variables 00 00 e 275 SYMbOIFLOCATG ec cn kr Rer EPIS 275 nSymbOl type o x ev 3 ade bebe debe 276 b su cra dene tb ga eeu C pp eS EE BC Eds 15 Ltarget attach i ag 4 PRac bere ga ed 279 target compare sections 279 barget detach iir PE de eee ped 279 target discomn Ct c sci berisping iuis 279 target download 2 0 04 iss deris 280 target exec Status vs eg nca ee 281 target list available targets 282 target list current targets 282 target list parameters 282 starget select ied p d ud 282 sthread 3nfO oec snaRec lv EE p p RETE IAS 249 thread list all threads s 250 sthread l3st idS 3 c ee e 250 sthread sel ct ic onec pre ead 250 cCyar asSlgh l2gxesrprllsudoseeesrae ts edd ui 265 nVAr CPOatec esee peche pee ee XE 262 esvar delete 2 1 2m eee RIP EE LAS 263 var evaluate expression 265 Var info expression i 226 6 ede ded 264 var info num children 2 2 2 9 ce ede 263 var info path expression 264 Syar infO type i i iege c PEE id etA de 264 yar list childrem 2 9 6 RB d inns 263 var set form t 2 4
445. me home foo bar recursive2 c line 14 frame level 5 addr 0x000107a4 func foo file recursive2 c fullname home foo bar recursive2 c line 14 frame level 6 addr 0x000107a4 func foo file recursive2 c fullname home foo bar recursive2 c line 14 frame level 7 addr 0x000107a4 func foo file recursive2 c fullname home foo bar recursive2 c line 14 frame level 8 addr 0x000107a4 func foo file recursive2 c fullname home foo bar recursive2 c line 14 260 frame level 9 addr 0x000107a4 func foo Debugging with GDB file recursive2 c fullname home foo bar recursive2 c line 14 frame level 10 addr 0x000107a4 func foo file recursive2 c fullname home foo bar recursive2 c line 14 frame level 11 addr 0x00010738 func main file recursive2 c fullname home foo bar recursive2 c line 4 gdb Show frames between low frame and high frame gdb stack list frames 3 5 done stack frame level 3 addr 0x000107a4 func foo file recursive2 c fullname home foo bar recursive2 c line 14 frame level 4 addr 0x000107a4 func foo file recursive2 c fullname home foo bar recursive2 c line 14 frame level 5 addr 0x000107a4 func foo file recursive2 c fullname home foo bar recursive2 c line 14 gdb Show a single frame gdb stack list frames 3 3 done stack frame level
446. memory regions The top level structure of the document is shown below lt xml version 1 0 7 gt lt DOCTYPE memory map PUBLIC IDN gnu org DTD GDB Memory Map V1 0 EN http sourceware org gdb gdb memory map dtd gt lt memory map gt region lt memory map gt Each region can be either e A region of RAM starting at addr and extending for length bytes from there lt memory type ram start addr length length gt e A region of read only memory lt memory type rom start addr length length gt e A region of flash memory with erasure blocks blocksize bytes in length memory type flash start addr length length gt lt property name blocksize gt blocksize lt property gt lt memory gt Regions must not overlap GDB assumes that areas of memory not covered by the memory map are RAM and uses the ordinary M and X packets to write to addresses in such ranges 368 Debugging with GDB The formal DTD for memory map format is given below l 22443 b4cl3gc a go e QUE TOO QU C Cpep qaa v EE gt lt l Memory Map AML DTD 2 2 ca ciridaaaa tas oR a deeds gt lt le File Mmemory mapidtd 2b Sistecar redatto ieos gt elc do S E tret Se Cute so ante nay ay ay E ead DE utar iuit lt memory map dtd gt lt memory map Root element with versioning gt lt ELEMENT memory map memory property gt lt ATTLIST memory map version CDATA FIXED 1 0 0 gt
447. mized processors it is difficult for the GDB maintainers to keep up with the changes e Since individual variants may have short lifetimes or limited audiences it may not be worthwhile to carry information about every variant in the GDB source tree e When GDB does support the architecture of the embedded system at hand the task of finding the correct architecture name to give the set architecture command can be error prone To address these problems the GDB remote protocol allows a target system to not only identify itself to GDB but to actually describe its own features This lets GDB support processor variants it has never seen before to the extent that the descriptions are accurate and that GDB understands them GDB must be compiled with Expat support to support XML target descriptions See Expat page 321 F 1 Retrieving Descriptions Target descriptions can be read from the target automatically or specified by the user manually The default behavior is to read the description from the target GDB retrieves it via the remote protocol using qXfer requests see Section D 4 General Query Packets page 342 The annex in the qXfer packet will be target xml The contents of the target xml annex are an XML document of the form described in Section F 2 Target Description Format page 382 Alternatively you can specify a file to read for the target description If a file is set the target will not be queri
448. mmand The corresponding GDB command is show inferior tty Example gdb inferior tty set dev pts 1 done gdb inferior tty show done inferior tty terminal dev pts 1 gdb The enable timings Command Synopsis enable timings yes no Toggle the printing of the wallclock user and system times for an MI command as a field in its output This command is to help frontend developers optimize the performance of their code No argument is equivalent to yes GDB Command No equivalent Example gdb enable timings done gdb break insert main done bkpt number 1 type breakpoint disp keep enabled y addr 0x080484ed func main file myprog c fullname home nickrob myprog c line 73 times 0 time wallclock 0 05185 user 0 00800 system 0 00000 gdb enable timings no done gdb exec run running gdb stopped reason breakpoint hit bkptno 1 thread id 0 frame addr 0x080484ed func main args name arge value 1 name argv value 0xbfb60364 file myprog c fullname home nickrob myprog c line 73 gdb Chapter 25 GDB Annotations 287 25 GDB Annotations This chapter describes annotations in GDB Annotations were designed to interface GDB to graphical user interfaces or other similar programs which want to interact with GDB at a relatively high level The annotation mechanism has largely been superseded by GDB MI see Chapter
449. mmands aliases Aliases of other commands breakpoints Making program stop at certain points data Examining data files Specifying and examining files internals Maintenance commands obscure Obscure features running Running the program stack Examining the stack Status Status inquiries support Support facilities tracepoints Tracing of program execution without stopping the program user defined User defined commands Type help followed by a class name for a list of commands in that class Type help followed by command name for full documentation Command name abbreviations are allowed if unambiguous gdb help class Using one of the general help classes as an argument you can get a list of the individual commands in that class For example here is the help display for the class status gdb help status Status inquiries List of commands info Generic command for showing things about the program being debugged Show Generic command for showing things about the debugger Type help followed by command name for full documentation Command name abbreviations are allowed if unambiguous gdb 22 Debugging with GDB help command With a command name as help argument GDB displays a short paragraph on how to use that command apropos args The apropos command searches through all of the GDB commands and their documentation for the regular expression specified in
450. mple gdb break list done BreakpointTable nr_rows 2 nr_cols 6 hdr width 3 alignment 1 col_name number colhdr Num width 14 alignment 1 col_name type colhdr Type width 4 alignment 1 col_name disp colhdr Disp width 3 alignment 1 col_name enabled colhdr Enb width 10 alignment 1 col_name addr colhdr Address width 40 alignment 2 col_name what colhdr What body bkpt number 1 type breakpoint disp keep enabled y addr 0x000100d0 func main file hello c line 5 times 0 bkpt number 2 type breakpoint disp keep enabled y addr 0x00010114 func foo file hello c fullname home foo hello c line 13 times 0 gdb Here s an example of the result when there are no breakpoints gdb break list done BreakpointTable nr_rows 0 nr_cols 6 Chapter 24 The GDB MI Interface 245 hdr width 3 alignment 1 col name number colhdr Num width 14 alignment 1 col_name type colhdr Type width 4 alignment 1 col_name disp colhdr Disp width 3 alignment 1 col_name enabled colhdr Enb width 10 alignment 1 col_name addr colhdr Address width 40 alignment 2 col_name what colhdr What body gdb The break watch Command Synopsis break watch a r Create a watchpoint With the a option it will create an access watchpoint i e a watchpoint th
451. n a con stant is interpreted to be type compatible with the rest of the expression Hexadecimal integers are specified by a trailing H and octal integers by a trailing B e Floating point constants appear as a sequence of digits followed by a decimal point and another sequence of digits An optional exponent can then be specified in the form E nnn where nnn is the desired exponent All of the digits of the floating point constant must be valid decimal base 10 digits 134 Debugging with GDB e Character constants consist of a single character enclosed by a pair of like quotes either single or double They may also be expressed by their ordinal value their ASCII value usually followed by a C e String constants consist of a sequence of characters enclosed by a pair of like quotes either single or double Escape sequences in the style of C are also allowed See Section 12 4 1 2 C and C Constants page 125 for a brief explanation of escape sequences e Enumerated constants consist of an enumerated identifier e Boolean constants consist of the identifiers TRUE and FALSE e Pointer constants consist of integral values only e Set constants are not yet supported 12 4 5 4 Modula 2 Types Currently GDB can print the following data types in Modula 2 syntax array types record types set types pointer types procedure types enumerated types subrange types and base types
452. n C if you want to test an assertion expressed by the condition assert you should set the condition I assert on the appropriate breakpoint Conditions are also accepted for watchpoints you may not need them since a watchpoint is inspecting the value of an expression anyhow but it might be simpler say to just set a watchpoint on a variable name and specify a condition that tests whether the new value is an interesting one Break conditions can have side effects and may even call functions in your program This can be useful for example to activate functions that log program progress or to use your own print functions to format special data structures The effects are completely predictable unless there is another enabled breakpoint at the same address In that case GDB might see the other breakpoint first and stop your program without checking the condition of this one Note that breakpoint commands are usually more convenient and flexible than break conditions for the purpose of performing side effects when a breakpoint is reached see Section 5 1 7 Breakpoint Command Lists page 49 Break conditions can be specified when a breakpoint is set by using if in the arguments to the break command See Section 5 1 1 Setting Breakpoints page 38 They can also be changed at any time with the condition command You can also use the if keyword with the watch command The catch command does not recognize the if keyword condit
453. n a PowerPC board such as Motorola s ADS The following commands specific to the SDS protocol are supported byGDB set sdstimeout nsec Set the timeout for SDS protocol reads to be nsec seconds The default is 2 seconds show sdstimeout Show the current value of the SDS timeout sds command Send the specified command string to the SDS monitor 18 3 7 HP PA Embedded target op50n dev OP50N monitor running on an OKI HPPA board target w89k dev WS89K monitor running on a Winbond HPPA board 18 3 8 Tsqware Sparclet GDB enables developers to debug tasks running on Sparclet targets from a Unix host GDB uses code that runs on both the Unix host and on the Sparclet target The program gdb is installed and executed on the Unix host remotetimeout args GDB supports the option remotetimeout This option is set by the user and args represents the number of seconds GDB waits for responses 200 Debugging with GDB 6 When compiling for debugging include the options g to get debug information and Ttext to relocate the program to where you wish to load it on the target You may also want to add the options n or N in order to reduce the size of the sections Example sparclet aout gcc prog c Ttext 0x12010000 g o prog N You can use objdump to verify that the addresses are what you intended sparclet aout objdump headers syms prog Once you have set your Unix execution search path to find GDB y
454. n one such variable or function with the same name in different source files If that happens referring to that name has unpredictable effects If you wish you can specify a static variable in a particular function or file using the colon colon notation file variable function variable Here file or function is the name of the context for the static variable In the case of file names you can use quotes to make sure GDB parses the file name as a single word for example to print a global value of x defined in 2 c gdb p f2 c x This use of is very rarely in conflict with the very similar use of the same notation in C GDB also supports use of the C scope resolution operator in GDB expressions Warning Occasionally a local variable may appear to have the wrong value at certain points in a function just after entry to a new scope and just before exit Chapter 8 Examining Data 77 You may see this problem when you are stepping by machine instructions This is because on most machines it takes more than one instruction to set up a stack frame including local variable definitions if you are stepping by machine instructions variables may appear to have the wrong values until the stack frame is completely built On exit it usually also takes more than one machine instruction to destroy a stack frame after you begin stepping through that group of instructions local variable definitions may be gone Th
455. nabled The following commands are available when an ARM target is debugged using the RDI interface rdilogfile file Set the filename for the ADP Angel Debugger Protocol packet log With an argument sets the log file to the specified file With no argument show the current log file name The default log file is rdi log rdilogenable arg Control logging of ADP packets With an argument of 1 or yes enables logging with an argument 0 or no disables it With no arguments displays the current setting When logging is enabled ADP packets exchanged between GDB and the RDI target device are logged to a file Set rdiromatzero Tell GDB whether the target has ROM at address 0 If on vector catching is disabled so that zero address can be used If off the default vector catching is enabled For this command to take effect it needs to be invoked prior to the target rdi command 194 Debugging with GDB show rdiromatzero Show the current setting of ROM at zero address set rdiheartbeat Enable or disable RDI heartbeat packets It is not recommended to turn on this option since it confuses ARM and EPI JTAG interface as well as the Angel monitor Show rdiheartbeat Show the setting of RDI heartbeat packets 18 3 2 Renesas M32R D and M32R SDI target m32r dev Renesas M32R D ROM monitor target m32rsdi dev Renesas M32R SDI server connected via parallel port to the board The following GDB commands are specific to th
456. nal string end end text 290 Debugging with GDB where name is the name of the signal such as SIGILL or SIGSEGV and string is the explanation of the signal such as Illegal Instruction or Segmentation fault intro text middle text and end text are for the user s benefit and have no particular format Z Zsignal The syntax of this annotation is just like signalled but GDB is just saying that the program received the signal not that it was terminated with it Z Zbreakpoint number The program hit breakpoint number number Z Zwatchpoint number The program hit watchpoint number number 25 7 Displaying Source The following annotation is used instead of displaying source code Z Zsource filename line character middle addr where filename is an absolute file name indicating which source file line is the line number within that file where 1 is the first line in the file character is the character position within the file where 0 is the first character in the file for most debug formats this will necessarily point to the beginning of a line middle is middle if addr is in the middle of the line or beg if addr is at the beginning of the line and addr is the address in the target program associated with the source which is being displayed addr is in the form Ox followed by one or more lowercase hex digits note that this does not depend on the language Chapter 26 Reporting Bugs in GDB 291 26 Reporting Bugs
457. name As discussed in detail below register values are normally relative to the selected stack frame regname may be any register name valid on the machine you are using with or without the initial GDB has four standard register names that are available in expressions on most machines whenever they do not conflict with an architecture s canonical mnemonics for registers The register names pc and sp are used for the program counter register and the stack pointer fp is used for a register that contains a pointer to the current stack frame and ps is used for a register that contains the processor status For example you could print the program counter in hex with p x pc or print the instruction to be executed next with x i pc or add four to the stack pointer with set sp 4 Whenever possible these four standard register names are available on your machine even though the machine has different canonical mnemonics so long as there is no conflict The info registers command shows the canonical names For example on the SPARC info registers displays the processor status register as psr but you can also refer to it as ps and on x86 based machines ps is an alias for the EFLAGS register Thisisa way of removing one word from the stack on machines where stacks grow downward in memory most machines nowadays This assumes that the innermost stack frame is selected setting sp is not allowed when other stack fram
458. nary Emacs buffers which are visiting the source files in the usual way You can edit the files with these buffers if you wish but keep in mind that GDB communicates with Emacs in terms of line numbers If you add or delete lines from the text the line numbers that GDB knows cease to correspond properly with the code A more detailed description of Emacs interaction with GDB is given in the Emacs manual see section Debuggers in The GNU Emacs Manual Chapter 24 The GDB MI Interface 233 24 The GpB MI Interface Function and Purpose GDB MI is a line based machine oriented text interface to GDB and is activated by specifying using the interpreter command line option see Section 2 1 2 Mode Options page 13 It is specifically intended to support the development of systems which use the debugger as just one small component of a larger system This chapter is a specification of the GDB MI interface It is written in the form of a reference manual Note that GDB MI is still under construction so some of the features described below are incomplete and subject to change see Section 24 5 GDB MI Development and Front Ends page 236 Notation and Terminology This chapter uses the following notation e separates two alternatives e something indicates that something is optional it may or may not be given e group means that group inside the parentheses may repeat zero or more times e group means that
459. nce debugging information can be very large sometimes larger than the executable code itself some systems distribute debugging information for their executables in separate files which users can install only when they need to debug a problem GDB supports two ways of specifying the separate debug info file e The executable contains a debug link that specifies the name of the separate debug info file The separate debug file s name is usually executable debug where exe cutable is the name of the corresponding executable file without leading directories e g ls debug for usr bin 1s In addition the debug link specifies a CRC32 checksum for the debug file which GDB uses to validate that the executable and the debug file came from the same build e The executable contains a build ID a unique bit string that is also present in the corresponding debug info file This is supported only on some operating systems notably those which use the ELF format for binary files and the GNU Binutils For more details about this feature see the description of the build id command line option in section Command Line Options in The GNU Linker The debug info file s name is not specified explicitly by the build ID but can be computed from the build ID see below Depending on the way the debug info file is specified GDB uses two different methods of looking for the debug file e For the debug link method GDB
460. nclu sive If low frame and high frame are not provided list the arguments for the whole call stack If the two arguments are equal show the single frame at the corresponding level It is an error if low frame is larger than the actual number of frames On the other hand high frame may be larger than the actual number of frames in which case only existing frames will be returned 258 Debugging with GDB The show values argument must have a value of 0 or 1 A value of 0 means that only the names of the arguments are listed a value of 1 means that both names and values of the arguments are printed GDB Command GDB does not have an equivalent command gdbtk has a gdb get args command which partially overlaps with the functionality of stack list arguments Example stack list frames done stack frame level 0 addr 0x00010734 func callee4 file devo gdb testsuite gdb mi basics c fullname home foo bar devo gdb testsuite gdb mi basics c line 8 frame level 1 addr 0x0001076c func callee3 file devo gdb testsuite gdb mi basics c fullname home foo bar devo gdb testsuite gdb mi basics c line 17 frame level 2 addr 0x0001078c func callee2 file devo gdb testsuite gdb mi basics c fullname home foo bar devo gdb testsuite gdb mi basics c line 22 frame level 3 addr 0x000107b4 func calleei file devo gdb testsuite gdb mi basics c fullnam
461. nction name to avoid ambiguity when there are identically named functions in different source files address Specifies the line containing the program address address address may be any expression 7 2 Editing Source Files To edit the lines in a source file use the edit command The editing program of your choice is invoked with the current line set to the active line in the program Alternatively there are several ways to specify what part of the file you want to print if you want to see other parts of the program Here are the forms of the edit command most commonly used edit Edit the current source file at the active line number in the program edit number Edit the current source file with number as the active line number edit function Edit the file containing function at the beginning of its definition edit filename number Specifies line number in the source file filename Chapter 7 Examining Source Files 69 edit filename function Specifies the line that begins the body of the function function in the file file name You only need the file name with a function name to avoid ambiguity when there are identically named functions in different source files edit address Specifies the line containing the program address address address may be any expression 7 2 1 Choosing your Editor You can customize GDB to use any editor you want By default it is bin ex but you can change this by setting the environme
462. nd F The integral datatypes conform to the definitions given in the appropriate section see Integral Datatypes page 363 for details so this structure is of size 8 bytes Appendix D GDB Remote Serial Protocol D 9 9 Constants The following values are used for the constants inside of the protocol GDB and target are responsible for translating these values before and after the call as needed Open Flags All values are given in hexadecimal representation O_RDONLY O_WRONLY O_RDWR O_APPEND O_CREAT O_TRUNC O_EXCL mode_t Values All values are given in octal representation S_IFREG S_IFDIR S_IRUSR S_IWUSR S_IXUSR S_IRGRP S_IWGRP S_IXGRP S_IROTH S_IWOTH S_IXOTH Errno Values All values are given in decimal representation EPERM ENOENT EINTR EBADF EACCES EFAULT EBUSY EEXIST ENODEV ENOTDIR EISDIR EINVAL ENFILE EMFILE EFBIG ENOSPC ESPIPE EROFS ENAMETOOLONG EUNKNOWN 0 0 0 0 Ox2 Ox4 0x8 010 04 ORNE 13 14 16 Tf 19 20 21 22 23 24 27 28 29 30 91 99 x0 x1 x2 x8 00 00 00 0000 0000 0400 0200 0100 040 020 010 04 02 01 99 365 EUNKNOWN is used as a fallback error value if a host system returns any error value not in the list of supported error numbers 366 Debugging with GDB Lseek Flags SEEK SET 0 SEEK CUR 1 SEEK END 2 Limits All values are given in decimal representation INT MIN 2147483648 INT MAX 2147483647 UINT
463. nd abbreviated 1 By default ten lines are printed There are several ways to specify what part of the file you want to print Here are the forms of the list command most commonly used list linenum Print lines centered around line number linenum in the current source file list function Print lines centered around the beginning of function function list Print more lines If the last lines printed were printed with a list command this prints lines following the last lines printed however if the last line printed was a solitary line printed as part of displaying a stack frame see Chapter 6 Examining the Stack page 61 this prints lines centered around that line list Print lines just before the lines last printed By default GDB prints ten source lines with any of these forms of the list command You can change this using set listsize set listsize count Make the list command display count source lines unless the list argument explicitly specifies some other number show listsize Display the number of lines that list prints Repeating a list command with discards the argument so it is equivalent to typing just list This is more useful than listing the same lines again An exception is made for an argument of that argument is preserved in repetition so that each repetition moves up in the source file In general the list command expects you to supply zero one or two linespecs Linespecs specify source lin
464. nd begin debugging it again and you can change the course of events so as to debug a different execution path this time Finally there is one bit of internal program state that will be different when you return to a checkpoint the program s process id Each checkpoint will have a unique process id or pid and each will be different from the program s original pid If your program has saved a local copy of its process id this could potentially pose a problem 4 11 1 A Non obvious Benefit of Using Checkpoints On some systems such as GNU Linux address space randomization is performed on new processes for security reasons This makes it difficult or impossible to set a breakpoint or watchpoint on an absolute address if you have to restart the program since the absolute location of a symbol will change from one execution to the next A checkpoint however is an identical copy of a process Therefore if you create a checkpoint at eg the start of main and simply return to that checkpoint instead of restarting the process you can avoid the effects of address randomization and your symbols will all stay in the same place Chapter 5 Stopping and Continuing 37 5 Stopping and Continuing The principal purposes of using a debugger are so that you can stop your program before it terminates or so that if your program runs into trouble you can investigate and find out why Inside GDB your program may stop for any of several reason
465. nd marker indicates whether the breakpoint is enabled or not Breakpoint is enabled Breakpoint is disabled The source assembly and register windows are updated when the current thread changes when the frame changes or when the program counter changes These windows are not all visible at the same time The command window is always visible The others can be arranged in several layouts e source only e assembly only e source and assembly e source and registers or e assembly and registers 226 Debugging with GDB A status line above the command window shows the following information target process function line pc Indicates the current GDB target see Chapter 16 Specifying a Debugging Target page 167 Gives the current process or thread number When no process is being de bugged this field is set to No process Gives the current function name for the selected frame The name is demangled if demangling is turned on see Section 8 7 Print Settings page 82 When there is no symbol corresponding to the current program counter the string is displayed Indicates the current line number for the selected frame When the current line number is not known the string is displayed Indicates the current program counter address 22 2 TUI Key Bindings The TUI installs several key bindings in the readline keymaps see Chapter 27 Command Line Editing page 295 The following key bindings
466. ndows DJGPP programs are 32 bit protected mode programs that use the DPMI DOS Protected Mode Interface API to run on top of real mode DOS systems and their emulations GDB supports native debugging of DJGPP programs and defines a few commands specific to the DJGPP port This subsection describes those commands info dos This is a prefix of DJGPP specific commands which print information about the target system and important OS structures info dos sysinfo This command displays assorted information about the underlying platform the CPU type and features the OS version and flavor the DPMI version and the available conventional and DPMI memory info dos gdt info dos ldt info dos idt These 3 commands display entries from respectively Global Local and Inter rupt Descriptor Tables GDT LDT and IDT The descriptor tables are data structures which store a descriptor for each segment that is currently in use The segment s selector is an index into a descriptor table the table entry for that index holds the descriptor s base address and limit and its attributes and access rights A typical DJGPP program uses 3 segments a code segment a data segment used for both data and the stack and a DOS segment which allows access to DOS BIOS data structures and absolute addresses in conventional memory However the DPMI host will usually define additional segments in order to support the DPMI environment These commands allow to d
467. ned on integral types amp Bitwise AND Defined on integral types Equality and inequality Defined on scalar types The value of these expressions is 0 for false and non zero for true Less than greater than less than or equal greater than or equal Defined on scalar types The value of these expressions is 0 for false and non zero for true Chapter 12 Using GDB with Different Languages 125 Sih SK C Q left shift and right shift Defined on integral types The GDB artificial array operator see Section 8 1 Expressions page 75 Addition and subtraction Defined on integral types floating point types and pointer types Multiplication division and modulus Multiplication and division are defined on integral and floating point types Modulus is defined on integral types Increment and decrement When appearing before a variable the operation is performed before the variable is used in an expression when appearing after it the variable s value is used before the operation takes place Pointer dereferencing Defined on pointer types Same precedence as Address operator Defined on variables Same precedence as For debugging C GDB implements a use of amp beyond what is allowed in the C language itself you can use amp amp ref or if you prefer simply amp amp ref to examine the address where a C reference variable declared with amp ref is
468. needs correction and delete or insert the text of the corrections Then when you are satisfied with the line you simply press RET You do not have to be at the end of the line to press RET the entire line is accepted regardless of the location of the cursor within the line 27 2 1 Readline Bare Essentials In order to enter characters into the line simply type them The typed character appears where the cursor was and then the cursor moves one space to the right If you mistype a character you can use your erase character to back up and delete the mistyped character Sometimes you may mistype a character and not notice the error until you have typed several other characters In that case you can type C b to move the cursor to the left and then correct your mistake Afterwards you can move the cursor to the right with C f When you add text in the middle of a line you will notice that characters to the right of the cursor are pushed over to make room for the text that you have inserted Likewise 296 Debugging with GDB when you delete text behind the cursor characters to the right of the cursor are pulled back to fill in the blank space created by the removal of the text A list of the bare essentials for editing the text of an input line follows C b Move back one character C f Move forward one character DEL Or Backspace Delete the character to the left of the cursor C d Delete the character underne
469. next page and prev page GDB Command The corresponding GDB command is x gdbtk has gdb_get_mem memory read command Example Read six bytes of memory starting at bytes 6 but then offset by 6 bytes Format as three rows of two columns One byte per word Display each word in hex gdb 9 data read memory o 6 bytest6 x 132 9 done addr 0x00001390 nr bytes 6 total bytes 6 next row 0x00001396 prev row 0x0000138e next page 0x00001396 prev page 0x0000138a memory addr 0x00001390 data 0x00 0x01 addr 0x00001392 data 0x02 0x03 addr 0x00001394 data 0x04 0x05 gdb Read two bytes of memory starting at address shorts 64 and display as a single word formatted in decimal gdb 5 data read memory shorts 64 d 21 1 5 done addr 0x00001510 nr bytes 2 total bytes 2 next row 0x00001512 prev row 0x0000150e Chapter 24 The GDB MI Interface 273 next page 0x00001512 prev page 0x0000150e memory addr 0x00001510 data gdb 128 Read thirty two bytes of memory starting at bytes 16 and format as eight rows of four columns Include a string encoding with x used as the non printable character gdb 4 data read memory bytes 16 x 1 8 4 x 4 done addr 0x000013a0 nr bytes 32 total bytes 32 next row 0x000013c0 prev row 0x0000139c next page 0x000013c0 prev page 0x00001380 memory addr 0x000013a0 data a
470. ng Programs 0 000 c cece eee eens 152 15 GDS Puletwscostatnce chee ese cee the eae 155 15 1 Commands to Specify Files 0 00 cece ee eee eee 155 15 2 Debugging Information in Separate Files 161 15 3 Errors Reading Symbol Files 0 000 0000 164 16 Specifying a Debugging Target 167 16 1 Active Targets eee erectae Renten Det oe BY 167 16 2 Commands for Managing Targets 00 00 ee eee 168 16 3 Choosing Target Byte Order lluusssseess eee eee 170 17 Debugging Remote Programs 171 17 1 Connecting to a Remote Target lesse eese 171 17 2 Using the gdbserver Program 0 cece eee eee ee 173 17 2 1 Monitor Commands for gdbserver 174 17 3 Remote Configuration 0 000 c cece eee tenes 174 17 4 Implementing a Remote Stub 00 000 20 eee 177 17 4 4 What the Stub Can Do for You 05 178 17 4 2 What You Must Do for the Stub 179 17 4 8 Putting it All Together 02 e eee eee eee 180 18 Configuration Specific Information 181 19 1 NAVE gc ors ee ee ed Ae eens tope ee ee ee os eee eee a 181 181 HPUX 5 S unm RaeE due RR bien x adeo hog dE 181 18 1 2 BSD libkvm Interface 0 0 cee eere 181 18 1 3 SVRA Process Information esses esee 181 18 1 4 Features for Debugging DJGPP Programs 183
471. ng command options which may be arbitrarily combined ALLOBJ Display sections for all loaded object files including shared li braries sections Display info only for named sections section flags Display info only for sections for which section flags are true The section flags that GDB currently knows about are ALLOC Section will have space allocated in the process when loaded Set for all sections except those containing de bug information LOAD Section will be loaded from the file into the child pro cess memory Set for pre initialized code and data clear for bss sections RELOC Section needs to be relocated before loading READONLY Section cannot be modified by the child process CODE Section contains executable code only DATA Section contains data only no executable code ROM Section will reside in ROM CONSTRUCTOR Section contains data for constructor destructor lists HAS CONTENTS Section is not empty Chapter 15 GDB Files 159 NEVER LOAD An instruction to the linker to not output the section COFF SHARED LIBRARY A notification to the linker that the section contains COFF shared library information IS COMMON Section contains common symbols set trust readonly sections on Tell GDB that readonly sections in your object file really are read only i e that their contents will not change In that case GDB can fetch values from these sections out of the object file rather than from the target
472. ng info level The frame number 0 being the topmost frame i e the innermost function addr The pc value for that frame func Function name file File name of the source file where the function lives line Line number corresponding to the pc If invoked without arguments this command prints a backtrace for the whole stack If given two integer arguments it shows the frames whose levels are between the two arguments inclusive If the two arguments are equal it shows the single frame at the corresponding level It is an error if low frame is larger than the actual number of frames On the other hand high frame may be larger than the actual number of frames in which case only existing frames will be returned GDB Command The corresponding GDB commands are backtrace and where Example Full stack backtrace gdb stack list frames done stack frame level 0 addr 0x0001076c func foo file recursive2 c fullname home foo bar recursive2 c line 11 frame level 1 addr 0x000107a4 func foo file recursive2 c fullname home foo bar recursive2 c line 14 frame level 2 addr 0x000107a4 func foo file recursive2 c fullname home foo bar recursive2 c line 14 frame level 3 addr 0x000107a4 func foo file recursive2 c fullname home foo bar recursive2 c line 14 frame level 4 addr 0x000107a4 func foo file recursive2 c fullna
473. ng old versions of GDB and it should contain a version number It should contain at least the following information e whether floating point is supported e whether long long is supported e maximum acceptable size of bytecode stack e maximum acceptable length of bytecode expressions e which registers are actually available for collection e whether the target supports disabled tracepoints E 5 Tracing on Symmetrix This section documents the API used by the GDB agent to collect data on Symmetrix systems Cygnus originally implemented these tracing features to help EMC Corporation debug their Symmetrix high availability disk drives The Symmetrix application code already includes substantial tracing facilities the GDB agent for the Symmetrix system uses those facilities for its own data collection via the API described here DTC RESPONSE adbg find memory in frame FRAME DEF frame Function char address char buffer unsigned int size Search the trace frame frame for memory saved from address If the memory is available provide the address of the buffer holding it otherwise provide the address of the next saved area e Ifthe memory at address was saved in frame set buffer to point to the buffer in which that memory was saved set size to the number of bytes from address that are saved at buffer and return OK TARGET RESPONSE Clearly in this case the function will always set size to a value greater than zero e
474. ng the program via the disassemble or x i commands Currently this command is only defined for the Intel x86 family You can set instruction set to either intel or att The default is att the AT amp T flavor used by default by Unix assemblers for x86 based targets show disassembly flavor Show the current setting of the disassembly flavor 74 Debugging with GDB Chapter 8 Examining Data 15 8 Examining Data The usual way to examine data in your program is with the print command abbreviated p or its synonym inspect It evaluates and prints the value of an expression of the language your program is written in see Chapter 12 Using GDB with Different Languages page 119 print expr print f expr expr is an expression in the source language By default the value of expr is printed in a format appropriate to its data type you can choose a different for mat by specifying f where f is a letter specifying the format see Section 8 4 Output Formats page 78 print print f If you omit expr GDB displays the last value again from the value history see Section 8 8 Value History page 88 This allows you to conveniently inspect the same value in an alternative format A more low level way of examining data is with the x command It examines data in memory at a specified address and prints it in a specified format See Section 8 5 Examining Memory page 79 If you are interested in information about types or
475. nged by the system call e Ctrl C flag After having done the needed type and value coercion the target continues the latest continue or step action D 9 3 The F Request Packet The F request packet has the following format Fcall id parameter call id is the identifier to indicate the host system call to be called This is just the name of the function parameter are the parameters to the system call Parameters are hexadeci mal integer values either the actual values in case of scalar datatypes pointers to target buffer space in case of compound datatypes and unspecified memory areas or pointer length pairs in case of string parameters These are appended to the call id as a comma delimited list All values are transmitted in ASCII string representation pointer length pairs separated by a slash D 9 4 The F Reply Packet The F reply packet has the following format Fretcode errno Ctrl C flag call specific attachment retcode is the return code of the system call as hexadecimal value errno is the errno set by the call in protocol specific representation This parameter can be omitted if the call was successful Ctrl C flag is only sent if the user requested a break In this case errno must be sent as well even if the call was successful The Ctrl C flag itself consists of the character C F0 0 C or if the call was interrupted before the host call has been performed F 1 4 C assuming 4 is the pro
476. ngle precision IEEE floating point ieee double Double precision IEEE floating point arm fpa ext The 12 byte extended precision format used by ARM FPA registers Appendix F Target Descriptions 385 F 4 Standard Target Features A target description must contain either no registers or all the target s registers If the description contains no registers then GDB will assume a default register layout selected based on the architecture If the description contains any registers the default layout will not be used the standard registers must be described in the target description in such a way that GDB can recognize them This is accomplished by giving specific names to feature elements which contain standard registers GDB will look for features with those names and verify that they contain the expected registers if any known feature is missing required registers or if any required feature is missing GDB will reject the target description You can add additional registers to any of the standard features GDB will display them just as if they were added to an unrecognized feature This section lists the known features and their expected contents Sample XML docu ments for these features are included in the GDB source tree in the directory gdb features Names recognized by GDB should include the name of the company or organization which selected the name and the overall architecture to which the feature applies so e g
477. nguage to language With C or C the main procedure name is always main but other languages such as Ada do not require a specific name for their main procedure The debugger provides a convenient way to start the execution of the program and to stop at the beginning of the main procedure depending on the language used The start command does the equivalent of setting a temporary breakpoint at the beginning of the main procedure and then invoking the run command Some programs contain an elaboration phase where some startup code is exe cuted before the main procedure is called This depends on the languages used to write your program In C for instance constructors for static and global objects are executed before main is called It is therefore possible that the debugger stops before reaching the main procedure However the temporary breakpoint will remain to halt execution Specify the arguments to give to your program as arguments to the start command These arguments will be given verbatim to the underlying run command Note that the same arguments will be reused if no argument is provided during subsequent calls to start or run It is sometimes necessary to debug the program during elaboration In these cases using the start command would stop the execution of your program too late as the program would have already completed the elaboration phase Under these circumstances insert breakpoints in y
478. nit references such as those produced by the GCC option feliminate dwarf2 dups the DWARF 2 reader needs to frequently refer to previously read compilation units This setting controls how long a compilation unit will remain in the cache if it is not referenced A higher limit means that cached compilation units will be stored in memory longer and more total memory will be used Setting it to zero disables caching which will slow down GDB startup but reduce memory consumption maint set profile maint show profile Control profiling of GDB Profiling will be disabled until you use the maint set profile command to enable it When you enable profiling the system will begin collecting timing and execution count data when you disable profiling or exit GDB the results will be written to a log file Remember that if you use profiling GDB will overwrite the profiling log file often called gmon out If you have a record of important profiling data in a gmon out file be sure to move it to a safe location Configuring with enable profiling arranges for GDB to be compiled with the pg compiler option maint show debug regs Control whether to show variables that mirror the x86 hardware debug registers Use ON to enable OFF to disable If enabled the debug registers values are shown when GDB inserts or removes a hardware breakpoint or watchpoint and when the inferior triggers a hardware assisted breakpoint or
479. nt kinds of objects are printed Set print array Set print array on Pretty print arrays This format is more convenient to read but uses more space The default is off Set print array off Return to compressed format for arrays show print array Show whether compressed or pretty format is selected for displaying arrays Set print array indexes Set print array indexes on Print the index of each element when displaying arrays May be more convenient to locate a given element in the array or quickly find the index of a given element in that printed array The default is off Set print array indexes off Stop printing element indexes when displaying arrays Show print array indexes Show whether the index of each element is printed when displaying arrays Set print elements number of elements Set a limit on how many elements of an array GDB will print If GDB is printing a large array it stops printing after it has printed the number of elements set by the set print elements command This limit also applies to the display of strings When GDB starts this limit is set to 200 Setting number of elements to zero means that the printing is unlimited Show print elements Display the number of elements of a large array that GDB will print If the number is 0 then the printing is unlimited Set print repeats Set the threshold for suppressing display of repeated array elements When the number of consecutive identical elements of an arra
480. nt print raw registers 328 maint print reggroups lessen 329 maint print register groups 328 Maint print registers sss sissss 328 naint print Statistics d des 329 naint print Symbols 2 i xcigm un 146 maint print target stack 329 MAING print type 5e esi gum et etek 329 maint print unwind HPPA 204 maint set dwarf2 max cache age 330 meint set profile i deseo 4 2 eee 330 maint show dwarf2 max cache age 330 naint show profile oe escheat aden e kb 330 maint show debug regs 000 330 MAING Spd6Oo o i Adele teach dls care lane 330 naint CIM yo sha tren teens aa Se a 330 maint translate address 330 paint undepfeCate ilocec le e RES 327 maintenance commands 327 410 CI rm 16 manual overlay debugging 115 nap an oyerlay eroro r enti PENI E N RA 115 mapinfo list QNX Neutrino 183 mapped address luuuseeuusesss 113 mapped overlays lessen 113 mark modified lines sss 300 mark symlinked directories 300 natch hidden fil88S eee te wRR 300 maximum value for offset of closest symbol 83 MOM iate suede n heh Eee ERU ER ea biie amd 93 member functions ssleeseeeeeeeess 126 memory address space mappings 182 memory map format e ree 367 memory re
481. nt variable EDITOR before using GDB For example to configure GDB to use the vi editor you could use these commands with the sh shell EDITOR usr bin vi export EDITOR gdb or in the csh shell setenv EDITOR usr bin vi gdb 7 3 Searching Source Files There are two commands for searching through the current source file for a regular expres sion forward search regexp search regexp The command forward search regexp checks each line starting with the one following the last line listed for a match for regexp It lists the line that is found You can use the synonym search regexp or abbreviate the command name as fo reverse search regexp The command reverse search regexp checks each line starting with the one before the last line listed and going backward for a match for regexp It lists the line that is found You can abbreviate this command as rev 7 4 Specifying Source Directories Executable programs sometimes do not record the directories of the source files from which they were compiled just the names Even when they do the directories could be moved between the compilation and your debugging session GDB has a list of directories to search for source files this is called the source path Each time GDB wants a source file it tries all the directories in the list in the order they are present in the list until it finds a file with the desired name For example suppose an executable reference
482. ntered so far 18 1 5 Features for Debugging MS Windows PE Executables GDB supports native debugging of MS Windows programs including DLLs with and without symbolic debugging information There are various additional Cygwin specific commands described in this section Working with DLLs that have no debugging symbols is described in Section 18 1 5 1 Non debug DLL Symbols page 186 info w32 This is a prefix of MS Windows specific commands which print information about the target system and important OS structures info w32 selector This command displays information returned by the Win32 API GetThreadSelectorEntry function It takes an optional argument that is evaluated to a long value to give the information about this given selector Without argument this command displays information about the six segment registers info dll This is a Cygwin specific alias of info shared dll symbols This command loads symbols from a dll similarly to add sym command but without the need to specify a base address Set cygwin exceptions mode If mode is on GDB will break on exceptions that happen inside the Cygwin DLL If mode is off GDB will delay recognition of exceptions and may ignore some exceptions which seem to be caused by internal Cygwin DLL bookkeeping This option is meant primarily for debugging the Cygwin DLL itself the default value is off to avoid annoying GDB users with false SIGSEGV signals show cygwin exceptions Displa
483. nterfere with each other B 4 Specifying Names for Hosts and Targets The specifications used for hosts and targets in the configure script are based on a three part naming scheme but some short predefined aliases are also supported The full naming scheme encodes three pieces of information in the following pattern 324 Debugging with GDB architecture vendor os For example you can use the alias sun4 as a host argument or as the value for target in a target target option The equivalent full name is sparc sun sunos4 The configure script accompanying GDB does not provide any query facility to list all supported host and target names or aliases configure calls the Bourne shell script config sub to map abbreviations to full names you can read the script if you wish or you can use it to test your guesses on abbreviations for example 4 sh config sub i386 linux i1386 pc linux gnu 4 sh config sub alpha linux alpha unknown linux gnu 4 sh config sub hp9k700 hppai i hp hpux 4 sh config sub sun4 Sparc sun sunos4 1 1 4 sh config sub sun3 m68k sun sunos4 1 1 4 sh config sub i986v Invalid configuration i986v machine i986v not recognized config sub is also distributed in the GDB source directory gdb 6 7 50_20071011 for version 6 7 50 20071011 B 5 configure Options Here is a summary of the configure options and arguments that are most often useful for building
484. nts of all the registers must be returned Allowed formats for fmt are x Hexadecimal o Octal t Binary d Decimal P Raw N Natural GDB Command The corresponding GDB commands are info reg info all reg and in gdbtk gdb fetch registers Chapter 24 The GDB MI Interface 271 Example For a PPC MBX board note line breaks are for readability only they don t appear in the actual output gdb data list register values r 64 65 done register values number 64 value Oxfe00a300 number 65 value 0x00029002 gdb data list register values x done register values number 0 value 0xfe0043c8 number 1 value 0x3ff 88 number 2 value 0xfffffffe number 3 value 0x0 number 4 value 0xa number 5 value Ox3fff68 number 6 value Ox3fff58 number 7 value 0xfe011e98 number 8 value 0x2 number 9 value 0xfa202820 number 10 value 0xfa202808 number 11 value 0xi number 12 value 0x0 number 13 value 0x4544 number 14 value 0xffdfffff number 15 value 0xfffffffF number 16 value 0xfffffeff number 17 value Oxefffffed number 18 value Oxfffffffe number 19 value Oxffffffff number 20 value Oxffffffff number 21 value Oxffffffff number 22 value Oxfffffff7 number 23 value Oxffffffff number 24 value Oxffffffff number 25 value Oxfffffff
485. num Set a breakpoint at line linenum in source file filename break filename function Set a breakpoint at entry to function function found in file filename Specifying a file name as well as a function name is superfluous except when multiple files contain similarly named functions break address Set a breakpoint at address address You can use this to set breakpoints in parts of your program which do not have debugging information or source files break When called without any arguments break sets a breakpoint at the next in struction to be executed in the selected stack frame see Chapter 6 Examining the Stack page 61 In any selected frame but the innermost this makes your program stop as soon as control returns to that frame This is similar to the effect of a finish command in the frame inside the selected frame except that finish does not leave an active breakpoint If you use break without an ar gument in the innermost frame GDB stops the next time it reaches the current location this may be useful inside loops Chapter 5 Stopping and Continuing 39 GDB normally ignores breakpoints when it resumes execution until at least one instruction has been executed If it did not do this you would be unable to pro ceed past a breakpoint without first disabling the breakpoint This rule applies whether or not the breakpoint already existed when your program stopped break if cond Set a breakpoint with condition cond evaluate
486. ny MI command e The range of values for fields with specified values e g in scope see var update page 266 may be extended If the changes are likely to break front ends the MI version level will be increased by one This will allow the front end to parse the output according to the MI version Apart from mi0 new versions of GDB will not support old versions of MI and it will be the responsibility of the front end to work with the new one The best way to avoid unexpected changes in MI that might break your front end is to make your project known to GDB developers and follow development on gdb sourceware org and gdb patches sourceware org There is also the mailing list dmi discuss lists freestandards org hosted by the Free Standards Group which has the aim of creating a more general MI protocol called Debugger Machine Interface DMI that will become a standard for all debuggers not just GDB 24 6 GDB MI Output Records 24 6 1 GDB MI Result Records In addition to a number of out of band notifications the response to a GDB MI command includes one of the following result indications done results The synchronous operation was successful results are the return values running The asynchronous operation was successfully started The target is running Chapter 24 The GDB MI Interface 231 connected GDB has connected to a remote target error c string The operation failed The c string contains
487. ny implementations of C mathematical overflow causes the result to wrap around to lower values for example if m is the largest integer value and s is the smallest then mti s This too is specific to individual languages and in some cases specific to individual compilers or machines See Section 12 4 Supported Languages page 123 for further details on specific languages GDB provides some additional commands for controlling the range checker set check range auto Set range checking on or off based on the current working language See Sec tion 12 4 Supported Languages page 123 for the default settings for each language set check range on Set check range off Set range checking on or off overriding the default setting for the current work ing language A warning is issued if the setting does not match the language default If a range error occurs and range checking is on then a message is printed and evaluation of the expression is aborted set check range warn Output messages when the GDB range checker detects a range error but at tempt to evaluate the expression anyway Evaluating the expression may still be impossible for other reasons such as accessing memory that the process does not own a typical example from many Unix systems Show range Show the current setting of the range checker and whether or not it is being set automatically by GDB 12 4 Supported Languages GDB supports C C Objective C F
488. o use However you may still find it useful to adjust GDB s idea of processor endian ness manually set endian big Instruct GDB to assume the target is big endian Set endian little Instruct GDB to assume the target is little endian set endian auto Instruct GDB to use the byte order associated with the executable show endian Display GDB s current idea of the target byte order Note that these commands merely adjust interpretation of symbolic data on the host and that they have absolutely no effect on the target system Chapter 17 Debugging Remote Programs 171 17 Debugging Remote Programs If you are trying to debug a program running on a machine that cannot run GDB in the usual way it is often useful to use remote debugging For example you might use remote debugging on an operating system kernel or on a small system which does not have a general purpose operating system powerful enough to run a full featured debugger Some configurations of GDB have special serial or TCP IP interfaces to make this work with particular debugging targets In addition GDB comes with a generic serial protocol specific to GDB but not specific to any particular target system which you can use if you write the remote stubs the code that runs on the remote system to communicate with GDB Other remote targets may be available in your configuration of GDB use help target to list them 17 1 Connecting to a Remote Target On the GDB host
489. o the Bss section TextSeg xxx DataSeg yyy Relocate the first segment of the object file which conventionally contains program code to a starting address of xxx If DataSeg is specified relocate the second segment which conventionally con tains modifiable data to a starting address of yyy GDB will report an error if the object file does not contain segment information or does not contain at least as many segments as mentioned in the reply Extra segments are kept at fixed offsets relative to the last relocated segment qP mode threadid Returns information on threadid Where mode is a hex encoded 32 bit mode threadid is a hex encoded 64 bit thread ID Don t use this packet use the qThreadExtraInfo query instead see below Reply see remote c remote unpack thread info response Appendix D GDB Remote Serial Protocol 345 QPassSignals signal signal Each listed signal should be passed directly to the inferior process Signals are numbered identically to continue packets and stop replies see Section D 3 Stop Reply Packets page 341 Each signal list item should be strictly greater than the previous item These signals do not need to stop the inferior or be reported to GDB All other signals should be reported to GDB Multiple QPassSignals packets do not combine any earlier QPassSignals list is completely replaced by the new list This packet improves performance when using handl
490. o the symbol table so CreateFileA is often sufficient In some cases there will be name clashes within a program particularly if the executable itself includes full debugging symbols necessitating the use of the fully qualified name when referring to the contents of the DLL Use single quotes around the name to avoid the exclamation mark being interpreted as a language operator Note that the internal name of the DLL may be all upper case even though the file name of the DLL is lower case or vice versa Since symbols within GDB are case sensitive this may cause some confusion If in doubt try the info functions and info variables commands or even maint print msymbols see Chapter 13 Symbols page 143 Here s an example gdb info function CreateFileA All functions matching regular expression CreateFileA Non debugging symbols Ox77e885f4 CreateFileA Ox77e885f4 KERNEL32 CreateFileA gdb info function All functions matching regular expression Non debugging symbols 0x6100114c cygwinl assert 0x61004034 cygwini dll crtOQ00 0x61004240 cygwini dll crtO per process etes 18 1 5 3 Working with Minimal Symbols Symbols extracted from a DLL s export table do not contain very much type information All that GDB can do is guess whether a symbol refers to a function or variable depending on the linker section that contains the symbol Also note that the actual contents of the memory contained in a DLL are
491. odify sublicense or distribute the Document is void and will automatically terminate your rights under this License However parties who have received copies or rights from you under this License will not have their licenses terminated so long as such parties remain in full compliance FUTURE REVISIONS OF THIS LICENSE The Free Software Foundation may publish new revised versions of the GNU Free Documentation License from time to time Such new versions will be similar in spirit to the present version but may differ in detail to address new problems or concerns See http www gnu org copyleft Each version of the License is given a distinguishing version number If the Document specifies that a particular numbered version of this License or any later version applies to it you have the option of following the terms and conditions either of that specified version or of any later version that has been published not as a draft by the Free Software Foundation If the Document does not specify a version number of this License you may choose any version ever published not as a draft by the Free Software Foundation Appendix H GNU Free Documentation License 399 H 1 ADDENDUM How to use this License for your documents To use this License in a document you have written include a copy of the License in the document and put the following copyright and license notices just after the title page Copyright C year your name Perm
492. of register names for the current target If no arguments are given it shows a list of the names of all the registers If integer numbers are given as arguments it will print a list of the names of the registers corresponding to the arguments To ensure consistency between a register name and its number the output list may include empty register names GDB Command GDB does not have a command which corresponds to data list register names In gdbtk there is a corresponding command gdb_regnames Example For the PPC MBX board gdb data list register names done register names rO ri r2 r3 r4 p5 p6 pT z8 r9 r10 r11 r12 r13 r14 r15 r16 r17 r18 r19 220 r21 r22 r23 r24 r25 r26 427 r28 r29 730 231 E0 MET E2 MES EA fb fon EPI fat PON f10 f11 f12 f13 f14 f15 f16 f17 f18 19 20 f 21 f22 f23 f24 T9b 26 f27 28 f29 30 31 pe pg opm Irt etn rer gdb data list register names 1 2 3 done register names ri r2 r3 gdb The data list register values Command Synopsis data list register values fmt regno Display the registers contents fmt is the format according to which the registers contents are to be returned followed by an optional list of numbers specifying the registers to display A missing list of numbers indicates that the conte
493. of your own choosing with the following commands jump linespec Resume execution at line linespec Execution stops again immediately if there is a breakpoint there See Section 7 1 Printing Source Lines page 67 for a description of the different forms of linespec It is common practice to use the tbreak command in conjunction with jump See Section 5 1 1 Setting Breakpoints page 38 The jump command does not change the current stack frame or the stack pointer or the contents of any memory location or any register other than the program counter If line linespec is in a different function from the one cur rently executing the results may be bizarre if the two functions expect different patterns of arguments or of local variables For this reason the jump command requests confirmation if the specified line is not in the function currently exe cuting However even bizarre results are predictable if you are well acquainted with the machine language code of your program jump address Resume execution at the instruction at address address Chapter 14 Altering Execution 151 On many systems you can get much the same effect as the jump command by storing a new value into the register pc The difference is that this does not start your program running it only changes the address of where it will run when you continue For example set pc 0x485 makes the next continue command or stepping command execute at address 0x485 rather
494. ogram Execution ee eee eee ee eeee 251 24 13 GDB MI Stack Manipulation Commands 256 24 14 GDB MI Variable Objects sesees ese cue tenes peace dees 261 24 15 GDB MI Data Manipulation Li ccce ree hx nh enn 266 24 16 GDB MI Tracepoint Commands eee eee eee 273 24 17 GDB MI Symbol Query Commands 273 24 18 GDB MI File Commands 0 eee eee eee eeeee 276 24 19 GDB MI Target Manipulation Commands 279 24 20 Miscellaneous GDB MI Commands 00 000 283 25 GDB Annotations sv 56 Eso Rr RES 287 25 1 What is an Annotation 0 0 cece eee eee eee 287 25 2 The Server Prefix 0 0 c eee e eee cee es 288 25 8 Annotation for GDB Input 0 e eee eee eee 288 29 BOS sed si st ee RUE a a eque tcutts wed dees asus LEE E 288 25 5 Invalidation Notices 0 e cece cece eee eee eee 289 25 6 Running the Program 2 2222 che detrei rap PRI dads 289 25 Displaying SOWICQ se atte dens eee eee ee eA RR oa 290 26 Reporting Bugs in GDB 291 26 1 Have You Found a Bug 0 eee eee eee 291 26 2 How to Report Bugs cece eee teenies 291 27 Command Line Editing 295 27 1 Introduction to Line Editing 0 0 ee eee 295 27 2 Readline Interaction lllusesseeeeeelse eee 295 27 2 1 Readline Bare Essentials llis eeeeeeleeeeel
495. old 276895068 new 3 frame func callee4 args file devo gdb testsuite gdb mi basics c fullname home foo bar devo gdb testsuite gdb mi basics c line 13 gdb break list done BreakpointTable nr_rows 2 nr_cols 6 hdr width 3 alignment 1 col_name number colhdr Num width 14 alignment 1 col_name type colhdr Type width 4 alignment 1 col_name disp colhdr Disp width 3 alignment 1 col_name enabled colhdr Enb width 10 alignment 1 col_name addr colhdr Address width 40 alignment 2 col_name what colhdr What body bkpt number 1 type breakpoint disp keep enabled y addr 0x00010734 func 2 callee4 file devo gdb testsuite gdb mi basics c fullname home foo devo gdb testsuite gdb mi basics c line 8 times 1 bkpt number 2 type watchpoint disp keep enabled y addr what C times 5 gdb exec continue Chapter 24 The GDB MI Interface 247 running done reason watchpoint scope wpnum 2 frame func callee3 args name strarg value 0x11940 A string argument file devo gdb testsuite gdb mi basics c fullname home foo bar devo gdb testsuite gdb mi basics c line 18 gdb break list done BreakpointTable nr_rows 1 nr_cols 6 hdr width 3 alignment 1 col_name number colhdr Num width 14 alignment 1 col_name type colhdr Type
496. om the C c S or s packets While GDB handles the request for a system call the target is stopped to allow deterministic access to the target s memory Therefore File I O is not interruptible by target signals On the other hand it is possible to interrupt File I O by a user interrupt Ctrl C within GDB The target s request to perform a host system call does not finish the latest C c S or s action That means after finishing the system call the target returns to continuing the previous activity continue step No additional continue or step request from GDB is required gdb continue lt target requests system call X target is stopped GDB executes system call GDB returns result target continues GDB returns to wait for the target lt target hits breakpoint and sends a Txx packet The protocol only supports I O on the console and to regular files on the host file system Character or block special devices pipes named pipes sockets or any other communication method on the host system are not supported by this protocol D 9 2 Protocol Basics The File I O protocol uses the F packet as the request as well as reply packet Since a File I O system call can only occur when GDB is waiting for a response from the continuing or stepping target the File I O request is a reply that GDB has to expect as a result of a previous C c S or s packet This F
497. omize programs that use Readline by putting commands in an inputrc file conventionally in his home directory The name of this file is taken from the value of the environment variable INPUTRC If that variable is unset the default is inputre When a program which uses the Readline library starts up the init file is read and the key bindings are set In addition the C x C r command re reads this init file thus incorporating any changes that you might have made to it 27 3 1 Readline Init File Syntax There are only a few basic constructs allowed in the Readline init file Blank lines are ignored Lines beginning with a are comments Lines beginning with a indicate conditional constructs see Section 27 3 2 Conditional Init Constructs page 303 Other lines denote variable settings and key bindings Variable Settings You can modify the run time behavior of Readline by altering the values of variables in Readline using the set command within the init file The syntax is simple set variable value Here for example is how to change from the default Emacs like key binding to use vi line editing commands set editing mode vi Variable names and values where appropriate are recognized without regard to case Unrecognized variable names are ignored Boolean variables those that can be set to on or off are set to on if the value is null or empty on case insensitive or 1 Any other value results in the vari
498. ommands from initialization files if not inhibited with n Exit with nonzero status if an error occurs in executing the GDB commands in the command files Batch mode may be useful for running GDB as a filter for example to download and run a program on another computer in order to make this more useful the message Program exited normally which is ordinarily issued whenever a program running under GDB control terminates is not issued when running in batch mode batch silent Run in batch mode exactly like batch but totally silently All GDB output to stdout is prevented stderr is unaffected This is much quieter than silent and would be useless for an interactive session This is particularly useful when using targets that give Loading section mes sages for example Note that targets that give their output via GDB as opposed to writing directly to stdout will also be made silent return child result The return code from GDB will be the return code from the child process the process being debugged with the following exceptions e GDB exits abnormally E g due to an incorrect argument or an internal error In this case the exit code is the same as it would have been without return child result e The user quits with an explicit value E g quit 1 e The child process never runs or is not allowed to terminate in which case the exit code will be 1 14 Debugging with GDB
499. on F 2 2 Architecture An lt architecture gt element has this form lt architecture gt arch lt architecture gt arch is an architecture name from the same selection accepted by set architecture see Chapter 16 Specifying a Debugging Target page 167 Appendix F Target Descriptions 383 F 2 3 Features Each lt feature gt describes some logical portion of the target system Features are currently used to describe available CPU registers and the types of their contents A lt feature gt element has this form feature name name gt type reg eae lt feature gt Each feature s name should be unique within the description The name of a feature does not matter unless GDB has some special knowledge of the contents of that feature if it does the feature should have its standard name See Section F 4 Standard Target Features page 385 F 2 4 Types Any register s value is a collection of bits which GDB must interpret The default interpreta tion is a two s complement integer but other types can be requested by name in the register description Some predefined types are provided by GDB see Section F 3 Predefined Target Types page 384 and the description can define additional composite types Each type element must have an id attribute which gives a unique within the con taining lt feature gt name to the type Types must be defined before they are used Some targets offer ve
500. on prefix cause the matches to be listed immediately instead of ring ing the bell The default value is off visible stats If set to on a character denoting a file s type is appended to the filename when listing possible completions The default is off Key Bindings The syntax for controlling key bindings in the init file is simple First you need to find the name of the command that you want to change The following sections contain tables of the command name the default keybinding if any and a short description of what the command does Once you know the name of the command simply place on a line in the init file the name of the key you wish to bind the command to a colon and then the name of the command The name of the key can be expressed in different ways depending on what you find most comfortable In addition to command names readline allows keys to be bound to a string that is inserted when the key is pressed a macro keyname function name or macro keyname is the name of a key spelled out in English For example Control u universal argument Meta Rubout backward kill word Control o output 302 Debugging with GDB In the above example C u is bound to the function universal argument M DEL is bound to the function backward kill word and C o is bound to run the macro expressed on the right hand side that is to insert the text gt output into the line A number of symbolic
501. on on command you may sometimes need to follow when it is used as logical not in an expression with a space or a tab to prevent it from being expanded The readline history facilities do not attempt substitution on the strings and even when history expansion is enabled The commands to control history expansion are set history expansion on set history expansion Enable history expansion History expansion is off by default set history expansion off Disable history expansion Chapter 19 Controlling GDB 209 show history Show history filename show history save Show history size Show history expansion These commands display the state of the GDB history parameters show history by itself displays all four states show commands Display the last ten commands in the command history show commands n Print ten commands centered on command number n show commands Print ten commands just after the commands last printed 19 4 Screen Size Certain commands to GDB may produce large amounts of information output to the screen To help you read all of it GDB pauses and asks you for input at the end of each page of output Type when you want to continue the output or q to discard the remaining output Also the screen width setting determines when to wrap lines of output Depending on what is being printed GDB tries to break the line at a readable place rather than simply letting it overflow onto the following line
502. on or off overriding the default setting for the current working language Issue a warning if the setting does not match the language default If any type mismatches occur in evaluating an expression while type checking is on GDB prints a message and aborts evaluation of the expression Set check type warn Cause the type checker to issue warnings but to always attempt to evaluate the expression Evaluating the expression may still be impossible for other reasons For example GDB cannot add numbers and structures Show type Show the current setting of the type checker and whether or not GDB is setting it automatically 12 3 2 An Overview of Range Checking In some languages such as Modula 2 it is an error to exceed the bounds of a type this is enforced with run time checks Such range checking is meant to ensure program correctness by making sure computations do not overflow or indices on an array element access do not exceed the bounds of the array For expressions you use in GDB commands you can tell GDB to treat range errors in one of three ways ignore them always treat them as errors and abandon the expression or issue warnings but evaluate the expression anyway Chapter 12 Using GDB with Different Languages 123 A range error can result from numerical overflow from exceeding an array index bound or when you type a constant that is not a member of any type Some languages however do not treat overflows as an error In ma
503. onHandler 180 Debugging with GDB void flush i cache On SPARC and SPARCLITE only write this subroutine to flush the instruction cache if any on your target machine If there is no instruction cache this subroutine may be a no op On target machines that have instruction caches GDB requires this function to make certain that the state of your program is stable You must also make sure this library routine is available void memset void int int This is the standard library function memset that sets an area of memory to a known value If you have one of the free versions of libc a memset can be found there otherwise you must either obtain it from your hardware manufacturer or write your own If you do not use the GNU C compiler you may need other standard library subroutines as well this varies from one stub to another but in general the stubs are likely to use any of the common library subroutines which GCC generates as inline code 17 4 3 Putting it All Together In summary when your program is ready to debug you must follow these steps 1 Make sure you have defined the supporting low level routines see Section 17 4 2 What You Must Do for the Stub page 179 getDebugChar putDebugChar flush_i_cache memset exceptionHandler 2 Insert these lines near the top of your program set debug traps breakpoint 3 For the 680x0 stub only you need to provide a variable called exceptionHook Nor mally yo
504. onnect to process ID number as with the attach command If there is no such process GDB will attempt to open a core file named number command file x file Execute GDB commands from file file See Section 20 3 Command files page 219 eval command command ex command Execute a single GDB command This option may be used multiple times to call multiple commands It may also be interleaved with command as required gdb ex target sim ex load x setbreakpoints ex run a out directory directory d directory Add directory to the path to search for source and script files Chapter 2 Getting In and Out of GDB 13 r readnow Read each symbol file s entire symbol table immediately rather than the default which is to read it incrementally as it is needed This makes startup slower but makes future operations faster 2 1 2 Choosing Modes You can run GDB in various alternative modes for example in batch mode or quiet mode nx n Do not execute commands found in any initialization files Normally GDB exe cutes the commands in these files after all the command options and arguments have been processed See Section 20 3 Command Files page 219 quiet silent q Quiet Do not print the introductory and copyright messages These mes sages are also suppressed in batch mode batch Run in batch mode Exit with status O after processing all the command files specified with x and all c
505. ope resolution 2 0ee eee 76 C symbol decoding style 86 Ct symbol displays i222 ER n E RES 128 Oi ences ones betas ae ees 227 CAR D E E uta ha bd antag ec RE RR 226 CHR 2s llo ber dana br eh P RET 226 O S E er au Ia Cheeta eee T dd EQ ERE 226 Ox Rita 2 esti dana neste anes aoe de 226 CHR CHa iocos a pede nese Mod E E EE 226 CHR Osi dae igh qub pee qu es PPP PI pu ERR dde 226 C X Baweswauegecx ret b rePbbUbRe E dd Ep E 226 caching data of remote targets 98 Cal hones cad ine dE Ree pa P a abite e werte 152 call dummy stack unwinding 152 call overloaded functions 04 126 call STACK assay ces tee ose ERE bre Ed 61 call stack traces seda edere pus 62 call last kbd macro C x e 312 calling functlonS u Cosas pro t CORE ra 152 calling inake isses rese tpe REERESD RR 16 capitalize word M c ssssss 309 case sensitivity in symbol names 143 case insensitive symbol names 143 casts in expressions lees esee eee 75 casts to view memory 00 e eee eee 76 orig PCI TETTE 45 catch Ada exceptions ssssesssssss 45 catch exceptions list active handlers 66 catchpoLlnlts is user cre Reste ch ree pr 3T catchpoints setting ssseeeee eese 45 GSO EEEE NE E ET E EE E EE 29 COLT E EE E EET E EUR ERR eds 71 Cell Broadband Engine 204 chang
506. or running programs 289 annotations for source display 290 Append seanci oprie eec docete e erra rei Reuha 95 append data to a file 006 94 apply command to several threads 33 Aprpo Bierin ERRD anes E oe hese tesa tee eS 22 architecture debugging info 213 argument count in user defined commands 217 arguments to your program 27 arguments to user defined commands 217 ARM 32 bit mode sees 193 ARM RDI 23 Ree PETER 192 array aggregates Ada ssssseeeess 138 AITAYSo e Lien PS eerie e EN beata erede 77 arrays in Expressions 20sec eae erre 75 artificial array 2 Eb pee peore ELE ewe 77 ASCII character set 2 ee esse eee eee 96 assembly instructions o acorar nozir nire iiis 12 e E E E E E EA E EAEE EEEE 157 assignment lese eati aar kao eae 149 async output in GDB MI 04 235 403 AT amp T disassembly flavor 0000 73 attach oe lere wr Rbicdbee E PERRE nia Ai 30 attach to a program by name 173 automatic display een ns 81 automatic hardware breakpoints 42 automatic overlay debugging 116 automatic thread selection 33 auxiliary vector esee per ade hpER REM Re 92 Drm 201 awatch iillsiiei ratet eer erenn IRE CPPIMSYSS 43 B b break ex erthsrxpRG3ep IDA ese Rene 38 ib packet zuo tete ise Ea uten
507. or type and range checking are included but they do not yet have any effect This section documents the intended facilities Some languages are designed to guard you against making seemingly common errors through a series of compile and run time checks These include checking the type of arguments to functions and operators and making sure mathematical overflows are caught at run time Checks such as these help to ensure a program s correctness once it has been compiled by eliminating type mismatches and providing active checks for range errors when your program is running GDB can check for conditions like the above if you wish Although GDB does not check the statements in your program it can check expressions entered directly into GDB for evaluation via the print command for example As with the working language GDB can also decide whether or not to check automatically based on your program s source language See Section 12 4 Supported Languages page 123 for the default settings of supported languages 12 3 1 An Overview of Type Checking Some languages such as Modula 2 are strongly typed meaning that the arguments to operators and functions have to be of the correct type otherwise an error occurs These checks prevent type mismatch errors from ever causing any run time problems For example 1 2 gt 3 but error 1 2 3 122 Debugging with GDB The second example fails because the CARDINAL 1 is not type compati
508. ore than one for some architectures that you specify in the frame command See Section 6 3 Selecting a Frame page 64 info args Print the arguments of the selected frame each on a separate line info locals Print the local variables of the selected frame each on a separate line These are all variables declared either static or automatic accessible at the point of execution of the selected frame info catch Print a list of all the exception handlers that are active in the current stack frame at the current point of execution To see other exception handlers visit the associated frame using the up down or frame commands then type info catch See Section 5 1 3 Setting Catchpoints page 45 Chapter 7 Examining Source Files 67 7 Examining Source Files GDB can print parts of your program s source since the debugging information recorded in the program tells GDB what source files were used to build it When your program stops GDB spontaneously prints the line where it stopped Likewise when you select a stack frame see Section 6 3 Selecting a Frame page 64 GDB prints the line where execution in that frame has stopped You can print other portions of source files by explicit command If you use GDB through its GNU Emacs interface you may prefer to use Emacs facilities to view source see Chapter 23 Using GDB under GNU Emacs page 231 7 1 Printing Source Lines To print lines from a source file use the list comma
509. ortran Java Pascal assembly Modula 2 and Ada Some GDB features may be used in expressions regardless of the language you use the GDB and operators and the type addr construct see Section 8 1 Expressions page 75 can be used with the constructs of any supported language The following sections detail to what degree each source language is supported by GDB These sections are not meant to be language tutorials or references but serve only as a reference guide to what the GDB expression parser accepts and what input and output formats should look like for different languages There are many good books written on each of these languages please look to these for a language reference or tutorial 12 4 1 C and C Since C and C are so closely related many features of GDB apply to both languages Whenever this is the case we discuss those languages together 124 Debugging with GDB The C debugging facilities are jointly implemented by the C compiler and GDB Therefore to debug your C code effectively you must compile your C programs with a supported C compiler such as GNU g or the HP ANSI C compiler aCC For best results when using GNU C use the DWARF 2 debugging format if it doesn t work on your system try the stabs debugging format You can select those formats explicitly with the g command line options gdwarf 2 and gstabs See section Options for Debugging Your Program or
510. ory as arrays See Section 8 3 Artificial Arrays page 77 for more information 16 Debugging with GDB allows you to specify a variable in terms of the file or function where it is defined See Section 8 2 Program Variables page 76 type addr Refers to an object of type type stored at address addr in memory addr may be any expression whose value is an integer or pointer but parentheses are required around binary operators just as in a cast This construct is allowed regardless of what kind of data is normally supposed to reside at addr 8 2 Program Variables The most common kind of expression to use is the name of a variable in your program Variables in expressions are understood in the selected stack frame see Section 6 3 Selecting a Frame page 64 they must be either e global or file static or e visible according to the scope rules of the programming language from the point of execution in that frame This means that in the function foo a int a bar a int b test O bar b you can examine and use the variable a whenever your program is executing within the function foo but you can only use or examine the variable b while your program is executing inside the block where b is declared There is an exception you can refer to a variable or function whose scope is a single source file even if the current execution point is not in this file But it is possible to have more tha
511. otation gdb print xmmi 1 f v4 float 0 3 43859137e 038 1 54142831e 044 1 821688e 044 v2 double 9 92129282474342e 303 2 7585945287983262e 313 v16_int8 000 000 000 000 3706 001 v 000 000 000 r 000 000 v8 inti6 0 0 14072 315 11 0 13 O v4_int32 0 20657912 11 13 v2_int64 88725056443645952 55834574859 uint128 0x0000000d0000000b013b36 800000000 To set values of such registers you need to tell GDB which view of the register you wish to change as if you were assigning value to a struct member gdb set xmmi uinti28 0x000000000000000000000000FFFFFFFF Normally register values are relative to the selected stack frame see Section 6 3 Select ing a Frame page 64 This means that you get the value that the register would contain if all stack frames farther in were exited and their saved registers restored In order to see the true contents of hardware registers you must select the innermost frame with frame 0 However GDB must deduce where registers are saved from the machine code generated by your compiler If some registers are not saved or if GDB is unable to locate the saved registers the selected stack frame makes no difference 8 11 Floating Point Hardware Depending on the configuration GDB may be able to give you more information about the status of the floating point hardware info float Display hardware dependent information about the floating point unit
512. otes 1q 0x34c78 lt lt rq 0x34c88 gt gt at input c 530 530 if 1quote def_lquote set print address off Do not print addresses when displaying their contents For example this is the same stack frame displayed with set print address off gdb set print addr off gdb f 0 set quotes lq lt lt rq gt gt at input c 530 530 if lquote def_lquote You can use set print address off to eliminate all machine dependent dis plays from the GDB interface For example with print address off you should get the same text for backtraces on all machines whether or not they involve pointer arguments show print address Show whether or not addresses are to be printed When GDB prints a symbolic address it normally prints the closest earlier symbol plus an offset If that symbol does not uniquely identify the address for example it is a name whose scope is a single source file you may need to clarify One way to do this is with info line for example info line 0x4537 Alternately you can set GDB to print the source file and line number when it prints a symbolic address set print symbol filename on Tell GDB to print the source file name and line number of a symbol in the symbolic form of an address set print symbol filename off Do not print source file name and line number of a symbol This is the default show print symbol filename Show whether or not GDB will print the source file name and line
513. ou are ready to run GDB From your Unix host run gdb or sparclet aout gdb depending on your installation GDB comes up showing the prompt gdbslet 18 3 8 1 Setting File to Debug The GDB command file lets you choose with program to debug gdbslet file prog GDB then attempts to read the symbol table of prog GDB locates the file by searching the directories listed in the command search path If the file was compiled with debug information option g source files will be searched as well GDB locates the source files by searching the directories listed in the directory search path see Section 4 4 Your Program s Environment page 28 If it fails to find a file it displays a message such as prog No such file or directory When this happens add the appropriate directories to the search paths with the GDB commands path and dir and execute the target command again 18 3 8 2 Connecting to Sparclet The GDB command target lets you connect to a Sparclet target To connect to a target on serial port ttya type gdbslet target sparclet dev ttya Remote target sparclet connected to dev ttya main at prog c 3 GDB displays messages like these Connected to ttya 18 3 8 3 Sparclet Download Once connected to the Sparclet target you can use the GDB 1oad command to download the file from the host to the target T he file name and load offset should be given as arguments to the 1oad command Since the file fo
514. ou may start GDB with its arguments if any in an environment of your choice If you are doing native debugging you may redirect your program s input and output debug an already running process or kill a child process 4 1 Compiling for Debugging In order to debug a program effectively you need to generate debugging information when you compile it This debugging information is stored in the object file it describes the data type of each variable or function and the correspondence between source line numbers and addresses in the executable code To request debugging information specify the g option when you run the compiler g Programs that are to be shipped to your customers are compiled with optimizations using the 0 compiler option However many compilers are unable to handle the g and Q options together Using those compilers you cannot generate optimized executables containing debugging information GCC the GNU C C compiler supports g with or without 0 making it possible to debug optimized code We recommend that you always use g whenever you compile a program You may think your program is correct but there is no sense in pushing your luck When you debug a program compiled with g 0 remember that the optimizer is rearranging your code the debugger shows you what is really there Do not be too surprised when the execution path does not exactly match your source file
515. ou need to override its conclusions Use these commands to manage GDB s view of the current ABI One GDB configuration can debug binaries for multiple operating system targets either via remote debugging or native emulation GDB will autodetect the OS ABI Operating System ABI in use but you can override its conclusion using the set osabi command One example where this is useful is in debugging of binaries which use an alternate C library e g UCLIBC for GNU Linux which does not have the same identifying marks that the standard C library for your platform provides Chapter 19 Controlling GDB 211 show osabi Show the OS ABI currently in use set osabi With no argument show the list of registered available OS ABI s set osabi abi Set the current OS ABI to abi Generally the way that an argument of type float is passed to a function depends on whether the function is prototyped For a prototyped i e ANSI ISO style function float arguments are passed unchanged according to the architecture s convention for float For unprototyped i e K amp R style functions float arguments are first promoted to type double and then passed Unfortunately some forms of debug information do not reliably indicate whether a func tion is prototyped If GDB calls a function that is not marked as prototyped it consults set coerce float to double Set coerce float to double Set coerce float to double on Arguments of type float will be promoted
516. ou specify an absolute file name when prompted for the M x gdb argument then Emacs sets your current working directory to where your program resides If you only specify the file name then Emacs sets your current working directory to to the directory associated with the previous buffer In this case GDB may find your program by searching your environment s PATH variable but on some operating systems it might not find the source So although the GDB input and output session proceeds normally the auxiliary buffer does not display the current source and line of execution The initial working directory of GDB is printed on the top line of the GUD buffer and this serves as a default for the commands that specify files for GDB to operate on See Section 15 1 Commands to Specify Files page 155 By default M x gdb calls the program called gdb If you need to call GDB by a different name for example if you keep several configurations around with different names you can customize the Emacs variable gud gdb command name to run the one you want In the GUD buffer you can use these special Emacs commands in addition to the standard Shell mode commands C h m Describe the features of Emacs GUD Mode 232 Debugging with GDB C c C s Execute to another source line like the GDB step command also update the display window to show the current file and location C c C n Execute to next source line in this function skipping all function cal
517. our elaboration code before running your program 4 3 Your Program s Arguments The arguments to your program can be specified by the arguments of the run command They are passed to a shell which expands wildcard characters and performs redirection of I O and thence to your program Your SHELL environment variable if it exists specifies what shell GDB uses If you do not define SHELL GDB uses the default shell bin sh on Unix On non Unix systems the program is usually invoked directly by GDB which emulates I O redirection via the appropriate system calls and the wildcard characters are expanded by the startup code of the program not by the shell run with no arguments uses the same arguments used by the previous run or those set by the set args command set args Specify the arguments to be used the next time your program is run If set args has no arguments run executes your program with no arguments Once you have run your program with arguments using set args before the next run is the only way to run it again without arguments show args Show the arguments to give your program when it is started 28 Debugging with GDB 4 4 Your Program s Environment The environment consists of a set of environment variables and their values Environment variables conventionally record such things as your user name your home directory your terminal type and your search path for programs to run Usually you set up environment
518. owing character sets ASCII Seven bit U S ASCII GDB can use this as its host character set IS0 8859 1 The ISO Latin 1 character set This extends ASCII with accented characters needed for French German and Spanish GDB can use this as its host character set Chapter 8 Examining Data 97 EBCDIC US IBM1047 Variants of the EBCDIC character set used on some of IBM s mainframe op erating systems GNU Linux on the 390 uses U S ASCII GDB cannot use these as its host character set Note that these are all single byte character sets More work inside GDB is needed to support multi byte or variable width character encodings like the UTF 8 and UCS 2 encodings of Unicode Here is an example of GDB s character set support in action Assume that the following source code has been placed in the file charset test c include lt stdio h gt char ascii hello 72 101 108 108 111 44 32 119 111 114 108 100 33 10 0 char ibmi047 hello 200 133 147 147 150 107 64 166 150 153 147 132 90 37 0 main 1 printf Hello world Nn In this program ascii hello and ibm1047_hello are arrays containing the string Hello world followed by a newline encoded in the ASCII and IBM1047 character sets We compile the program and invoke the debugger on it gcc g charset test c o charset test gdb nw charset test GNU gdb 2001 12 19 cvs Copyright 2001 Free Software Foundation Inc
519. page 354 for more details D 4 General Query Packets Packets starting with q are general query packets packets starting with Q are general set packets General query and set packets are a semi unified form for retrieving and sending information to and from the stub The initial letter of a query or set packet is followed by a name indicating what sort of thing the packet applies to For example GDB may use a qSymbol packet to exchange symbol definitions with the stub These packet names follow some conventions e The name must not contain commas colons or semicolons e Most GDB query and set packets have a leading upper case letter e The names of custom vendor packets should use a company prefix in lower case fol lowed by a period For example packets designed at the Acme Corporation might begin with qacme foo for querying foos or Qacme bar for setting bars The name of a query or set packet should be separated from any parameters by a the parameters themselves should be separated by or Stubs must be careful to match the full packet name and check for a separator or the end of the packet in case two packet names share a common prefix New packets should not begin with qC qP or qL Like the descriptions of the other packets each description here has a template showing the packet s overall syntax followed by an explanation of the packet s meaning We includ
520. pe using the virtual function table set print object off Display only the declared type of objects without reference to the virtual func tion table This is the default setting show print object Show whether actual or declared object types are displayed set print static members set print static members on Print static members when displaying a C object The default is on set print static members off Do not print static members when displaying a C object show print static members Show whether C static members are printed or not set print pascal static members Set print pascal static members on Print static members when displaying a Pascal object The default is on Set print pascal static members off Do not print static members when displaying a Pascal object Show print pascal static members Show whether Pascal static members are printed or not Set print vtbl Set print vtbl on Pretty print C virtual function tables The default is off The vtbl com mands do not work on programs compiled with the HP ANSI C compiler aCC Set print vtbl off Do not pretty print C virtual function tables show print vtbl Show whether C virtual function tables are pretty printed or not 88 Debugging with GDB 8 8 Value History Values printed by the print command are saved in the GDB value history This allows you to refer to them in other expressions Values are kept until the symbol table is re read or
521. pecify a list of commands for breakpoint number bnum The commands them selves appear on the following lines Type a line containing just end to terminate the commands To remove all commands from a breakpoint type commands and follow it im mediately with end that is give no commands With no bnum argument commands refers to the last breakpoint watchpoint or catchpoint set not to the breakpoint most recently encountered Pressing as a means of repeating the last GDB command is disabled within a command list You can use breakpoint commands to start your program up again Simply use the continue command or step or any other command that resumes execution Any other commands in the command list after a command that resumes execution are ignored This is because any time you resume execution even with a simple next or step you may encounter another breakpoint which could have its own command list leading to ambiguities about which list to execute If the first command you specify in a command list is silent the usual message about stopping at a breakpoint is not printed This may be desirable for breakpoints that are to print a specific message and then continue If none of the remaining commands print anything you see no sign that the breakpoint was reached silent is meaningful only at the beginning of a breakpoint command list The commands echo output and printf allow you to print precisely controlled output and are
522. pecifying precision or width e The flag for separation of digits into groups according to LC NUMERIC is not supported e The type modifiers hh j t and z are not supported e The conversion letter n as in n is not supported 222 Debugging with GDB e The conversion letters a and A are not supported Note that the 11 type modifier is supported only if the underlying C imple mentation used to build GDB supports the long long int type and the L type modifier is supported only if long double type is available As in C printf supports simple backslash escape sequences such as n t AN S N Na and f that consist of backslash followed by a single character Octal and hexadecimal escape sequences are not supported Chapter 21 Command Interpreters 223 21 Command Interpreters GDB supports multiple command interpreters and some command infrastructure to allow users or user interface writers to switch between interpreters or run commands in other interpreters GDB currently supports two command interpreters the console interpreter sometimes called the command line interpreter or CLI and the machine interface interpreter or GDB MI This manual describes both of these interfaces in great detail By default GDB will start with the console interpreter However the user may choose to start GDB with another interpreter by specifyin
523. permission to modify or distribute the Program or its derivative works These actions are prohibited by law if you do not accept this License Therefore by modifying or distributing the Program or any work based on the Program you indicate your acceptance of this License to do so and all its terms and conditions for copying distributing or modifying the Program or works based on it 390 6 10 Debugging with GDB Each time you redistribute the Program or any work based on the Program the recipient automatically receives a license from the original licensor to copy distribute or modify the Program subject to these terms and conditions You may not impose any further restrictions on the recipients exercise of the rights granted herein You are not responsible for enforcing compliance by third parties to this License If as a consequence of a court judgment or allegation of patent infringement or for any other reason not limited to patent issues conditions are imposed on you whether by court order agreement or otherwise that contradict the conditions of this License they do not excuse you from the conditions of this License If you cannot distribute so as to satisfy simultaneously your obligations under this License and any other pertinent obligations then as a consequence you may not distribute the Program at all For example if a patent license would not permit royalty free redistribution of the Program by all those who re
524. plicate name is found The frame under which the expression should be evaluated can be specified by frame addr A indicates that the current frame should be used expression is any expression valid on the current language set must not begin with a or one of the following e xaddr where addr is the address of a memory cell e addr addr a memory address range TBD e regname a CPU register name Chapter 24 The GDB MI Interface 263 Result This operation returns the name number of children and the type of the object created Type is returned as a string as the ones generated by the GDB CLI name name numchild N type type The var delete Command Synopsis var delete c name Deletes a previously created variable object and all of its children With the c option just deletes the children Returns an error if the object name is not found The var set format Command Synopsis var set format name format spec Sets the output format for the value of the object name to be format spec The syntax for the format spec is as follows format spec gt binary decimal hexadecimal octal natural The natural format is the default format choosen automatically based on the variable type like decimal for an int hex for pointers etc For a variable with children the format is set only on the variable itself and the children are not affected The var show for
525. ports these special commands for MIPS targets Set mipsfpu double Set mipsfpu single Set mipsfpu none Set mipsfpu auto show mipsfpu If your target board does not support the MIPS floating point coprocessor you should use the command set mipsfpu none if you need this you may wish to put the command in your GDB init file This tells GDB how to find the return value of functions which return floating point values It also allows GDB to avoid saving the floating point registers when calling functions on the board If you are using a floating point coprocessor with only single precision floating point support as on the RA650 processor use the command set mipsfpu single The default double precision floating point coprocessor may be selected using set mipsfpu double In previous versions the only choices were double precision or no floating point so set mipsfpu on will select double precision and set mipsfpu off will se lect no floating point As usual you can inquire about the mipsfpu variable with show mipsfpu set timeout seconds set retransmit timeout seconds show timeout show retransmit timeout You can control the timeout used while waiting for a packet in the MIPS remote protocol with the set timeout seconds command The default is 5 seconds Similarly you can control the timeout used while waiting for an acknowledge ment of a packet with the set retransmit timeout seconds command The defa
526. prefix does not affect the recording of values into the value history to print a value without recording it into the value history use the output command instead of the print command Here is the description of GDB commands related to command history Set history filename fname Set the name of the GDB command history file to fname This is the file where GDB reads an initial command history list and where it writes the command history from this session when it exits You can access this list through history expansion or through the history command editing characters listed below This file defaults to the value of the environment variable GDBHISTFILE or to gdb_history gdb history on MS DOS if this variable is not set Set history save Set history save on Record command history in a file whose name may be specified with the set history filename command By default this option is disabled Set history save off Stop recording command history in a file Set history size size Set the number of commands which GDB keeps in its history list This defaults to the value of the environment variable HISTSIZE or to 256 if this variable is not set History expansion assigns special meaning to the character See Section 28 1 1 Event Designators page 315 for more details Since is also the logical not operator in C history expansion is off by default If you decide to enable history expansion with the set history expansi
527. pression Command Synopsis var evaluate expression name Evaluates the expression that is represented by the specified variable object and returns its value as a string The format of the string can be changed using the var set format command value value Note that one must invoke var list children for a variable before the value of a child variable can be evaluated The var assign Command Synopsis var assign name expression Assigns the value of expression to the variable object specified by name The object must be editable If the variable s value is altered by the assign the variable will show up in any subsequent var update list Example gdb var assign vari 3 done value 3 gdb var update done changelist name vari in_scope true type_changed false gdb The var update Command Synopsis var update print values name Reevaluate the expressions corresponding to the variable object name and all its direct and indirect children and return the list of variable objects whose values have changed name must be a root variable object Here changed means that the result of var evaluate expression before and after the var update is different If is used as the variable object names all existing variable objects are updated except for frozen ones see var set frozen page 266 The option print values determines whether both names and values or just names are print
528. preter interp for interface with the controlling program or device This option is meant to be set by programs which communicate with GDB using it as a back end See Chapter 21 Command Interpreters page 223 interpreter mi or interpreter mi2 causes GDB to use the GDB MI interface see Chapter 24 The GDB MI Interface page 233 included since GDB version 6 0 The previous GDB MI interface included in GDB version 5 3 and selected with interpreter mi1 is deprecated Earlier GDB MI interfaces are no longer supported write Open the executable and core files for both reading and writing This is equiv alent to the set write on command inside GDB see Section 14 6 Patching page 152 statistics This option causes GDB to print statistics about time and memory usage after it completes each command and returns to the prompt version This option causes GDB to print its version number and no warranty blurb and exit 2 1 3 What GDB Does During Startup Here s the description of what GDB does during session startup 1 Sets up the command interpreter as specified by the command line see Section 2 1 2 Mode Options page 13 2 Reads the init file if any in your home directory and executes all the commands in that file 3 Processes command line options and operands 4 Reads and executes the commands from init file if any in the current working direc tory This is only done if the current d
529. program For some targets notably embedded ones this can be a significant enhancement to debugging performance The default is off Set trust readonly sections off Tell GDB not to trust readonly sections This means that the contents of the section might change while the program is running and must therefore be fetched from the target when needed show trust readonly sections Show the current setting of trusting readonly sections All file specifying commands allow both absolute and relative file names as arguments GDB always converts the file name to an absolute file name and remembers it that way GDB supports GNU Linux MS Windows HP UX SunOS SVr4 Irix and IBM RS 6000 AIX shared libraries GDB automatically loads symbol definitions from shared libraries when you use the run command or when you examine a core file Before you issue the run command GDB does not understand references to a function in a shared library however unless you are debugging a core file On HP UX if the program loads a library explicitly GDB automatically loads the symbols at the time of the shl_load call There are times however when you may wish to not automatically load symbol defini tions from shared libraries such as when they are particularly large or there are many of them To control the automatic loading of shared library symbols use the commands set auto solib add mode If mode is on symbols from all shared object libraries
530. provide their contents Ask the stub if there is a trace experiment running right now Replies TO There is no trace experiment running TL There is a trace experiment running 354 Debugging with GDB D 7 Interrupts When a program on the remote target is running GDB may attempt to interrupt it by sending a Ctrl C or a BREAK control of which is specified via GDB s remotebreak setting see set remotebreak page 175 The precise meaning of BREAK is defined by the transport mechanism and may in fact be undefined GDB does not currently define a BREAK mechanism for any of the network interfaces Ctrl C on the other hand is defined and implemented for all transport mechanisms It is represented by sending the single byte 0x03 without any of the usual packet overhead described in the Overview section see Section D 1 Overview page 333 When a 0x03 byte is transmitted as part of a packet it is considered to be packet data and does not represent an interrupt E g an X packet see X packet page 339 used for binary downloads may include an unescaped 0x03 as part of its packet Stubs are not required to recognize these interrupt mechanisms and the precise meaning associated with receipt of the interrupt is implementation defined If the stub is successful at interrupting the running program it is expected that it will send one of the Stop Reply Packets see Section D 3 Stop Reply Packets page
531. pu is e E ipi ireti eee ie show monitor prompt MIPS remote show monitor warnings MIPS remote show new console ea ug rr ha show new group cei ceed ehe y era eene Show opaque type resolution show OSADL iei erede Em ood e a Re show output radix eR RIEGR RR DEI show overload resolution show pagination 2 4 2 t rara rg show pathS x hic ps Rise E SHOW print paw ode antaa EDE EFE show proCeSSOFE cies Gc i Ri ODER Rs Show procfS flle 2 5 e BRI RR show PROCES trace ou gc s ERI was Show prompt dece tae neema raare show radix li os hes pbi A A Er ah aes show rdiheartbeat za see aen show rdiromatzero vois e a ee rase show remote ooiieeedc rert EY roc ee rr a show remote system call allowed show remote mips64 transfers 32bit regs show retransmit timeout show rstack_high_address show SdStimeout 2 2 2 2 zur n vu eg show server addreSS ecc eR RET show shell 4 c p GRE he cdc eee show signal thread osea oi show signals Hurd command show sigs Hurd command Show sigthr ad isece ccc case e y nase nes show solib search path eius show stop on solib events show stopped Hurd command show struct convention sess show substitute path IP show symbol reloading show syn garbage limit MIPS r
532. put and call In gdbtk only there s a corresponding gdb_eval command Example In the following example the numbers that precede the commands are the tokens described in Section 24 3 GDB M1 Command Syntax page 233 Notice how GDB MI returns the same tokens in its output 211 data evaluate expression A 211 done value 1 gdb 311 data evaluate expression amp A 311 done value Oxefffeb7c gdb 411 data evaluate expression A 3 411 done value 4 gdb 511 data evaluate expression A 3 5b11 done value 4 gdb The data list changed registers Command Synopsis data list changed registers Display a list of the registers that have changed GDB Command GDB doesn t have a direct analog for this command gdbtk has the corresponding command gdb changed register list Example On a PPC MBX board gdb exec continue running gdb stopped reason breakpoint hit bkptno 1 frame func main args file try c fullname home foo bar try c line 5 gdb data list changed registers done changed registers 0 jw mow wan 3 p me y ngu gu qo iq 5 Ub CU 3 14 ib Z 16 y wu 18 19 A 90 5 an 122 5 93 s 24 25 5 26 beu s 98 5 30 31 64 5 65 5 66 5 67 69 gdb The data list register names Command 270 Debugging with GDB Synopsis data list register names regno Show a list
533. put for each instruction is composed of four fields e Address e Func name e Offset e Instruction Note that whatever included in the instruction field is not manipulated directly by GDB MI i e it is not possible to adjust its format GDB Command There s no direct mapping from this command to the CLI Example Disassemble from the current value of pc to pc 20 gdb data disassemble s pc e pc 20 0 done asm_insns address 0x000107c0 func name main offset 4 inst mov 2 4o0 j address 0x000107c4 func name main offset 8 inst sethi hi 0x11800 o2 268 Debugging with GDB address 0x000107c8 func name main offset 12 inst or 402 0x140 o1 t Ox11940 lt _lib_version 8 gt address 0x000107cc func name main offset 16 inst sethi hi 0x11800 74o2 address 0x000107d0 func name main offset 20 inst or 402 0x168 04 t 0x11968 lt _lib_version 48 gt gdb Disassemble the whole main function Line 32 is part of main data disassemble f basics c 1 32 0 done asm insns address 0x000107bc func name main offset 0 inst save Asp 112 sp address 0x000107c0 func name main offset 4 inst mov 2 o0 address 0x000107c4 func name main offset 8 inst sethi hi 0x11800 o2 besad address 0x0001081ic func name main offset 96 inst ret address 0x00010820 func name main offset 100 ins
534. qSupported response see qSupported page 345 Reply m data Data data see Binary Data page 333 has been read from the target There may be more data at a higher address although it is permitted to return m even for the last valid block of data as long as at least one byte of data was read data may have fewer bytes than the length in the request l data Data data see Binary Data page 333 has been read from the target There is no more data to be read data may have fewer bytes than the length in the request T The offset in the request is at the end of the data There is no more data to be read E00 The request was malformed or annex was invalid E nn The offset was invalid or there was an error encountered reading the data nn is a hex encoded errno value An empty reply indicates the object string was not recognized by the stub or that the object does not support reading qXfer object write annex offset data Write uninterpreted bytes into the target s special data area identified by the keyword object starting at offset bytes into the data data is the binary encoded data see Binary Data page 333 to be written The content and encoding of annex is specific to object it can supply additional details about what data to access Here are the specific requests of this form defined so far All qXfer object write requests use the same reply forma
535. quote 1 Ox35d40 lt QUOTE gt gdb p rquote 2 Ox35d50 lt UNQUOTE gt lquote and rquote are indeed the new left and right quotes To look at some context we can display ten lines of source surrounding the current line with the 1 list command gdb 1 533 xfree rquote 534 535 lquote lq nil 1q 0 def_lquote xstrdup 19 536 rquote rq nil rq N0 def_rquote xstrdup rq 537 538 len_lquote strlen rquote 539 len_rquote strlen lquote 540 h 541 542 void Let us step past the two lines that set len_lquote and len rquote and then examine the values of those variables gdb n 539 len rquote strlen lquote gdb n 540 gdb p len lquote 3 9 gdb p len rquote 4 7 That certainly looks wrong assuming len lquote and len rquote are meant to be the lengths of lquote and rquote respectively We can set them to better values using the p command since it can print the value of any expression and that expression can include subroutine calls and assignments gdb p len_lquote strlen Iquote 5 7 gdb p len_rquote strlen rquote 6 9 Is that enough to fix the problem of using the new quotes with the m4 built in defn We can allow m4 to continue executing with the c continue command and then try the example that caused trouble initially gdb c Continuing define baz defn lt QUOTE gt foo lt UNQUOTE gt baz 0000
536. r option is used the search path is reset to the original search path that existed at gdb start up If directories pathdir are supplied in addition to the r option the search path is first reset and then addition occurs as normal Multiple directories may be specified separated by blanks Specifying multiple directories in a single command results in the directories added to the beginning of the search path in the same order they were presented in the command If blanks are needed as part of a directory name double quotes should be used around the name In the command output the path will show up separated by the system directory separator character The directory separator character must not be used in any directory name If no directories are specified the current path is displayed GDB Command The corresponding GDB command is path Example gdb environment path done path usr bin gdb environment path kwikemart marge ezannoni flathead dev ppc eabi gdb bin done path kwikemart marge ezannoni flathead dev ppc eabi gdb bin usr bin gdb environment path r usr local bin done path usr local bin usr bin gdb The environment pwd Command Synopsis environment pwd Show the current working directory GDB Command The corresponding GDB command is pwd Example gdb environment pwd done cwd kwikemart marge ezannoni flathead dev devo gdb gdb 24 11 GDB MI Thread Commands The
537. r delete delete the variable object and or its children var set format set the display format of this variable var show format show the display format of this variable var info num children tells how many children this object has var list children return a list of the object s children var info type show the type of this variable object var info expression print parent relative expression that this variable ob ject represents var info path expression print full expression that this variable object represents var show attributes is this variable editable does it exist here var evaluate expression get the value of this variable var assign set the value of this variable var update update the variable and its children var set frozen set frozeness attribute In the next subsection we describe each operation in detail and suggest how it can be used Description And Use of Operations on Variable Objects The var create Command Synopsis var create name frame addr expression This operation creates a variable object which allows the monitoring of a variable the result of an expression a memory cell or a CPU register The name parameter is the string by which the object can be referenced It must be unique If is specified the varobj system will generate a string varNNNNNN automatically It will be unique provided that one does not specify name on that format The command fails if a du
538. r ir eter rere teh e ere 178 puisisi quid m 178 machine instructions 00 T2 macro define 9 9 gb vad iat EN 101 macro definition showing 101 MaAcrouexpl sooo y lle c RIED PRERE PPS 101 m cro expand ci2sipee err ade YS 101 macro expansion showing the results of PIEPLOCESSOR ucet aineen kos daare Fx 101 acro LIUStcces hack ethetenedecwe ern PRSE 102 macro undef cete crs kab akiw eai iai 102 macros example of debugging with 102 macros user defined 000 000 101 mailine sls ie ea etal Rb meer 236 maint agent 4e Ere ter de rrr 327 Maint check symtabS er eivs 327 maint cplus first_component 327 maint cplus namespace sees 327 Maint demangl wiser sia de eee ee ees 327 paint deprecate enigi tide 9 2 be ete 327 MAINT GUMpPHMeE 6204 settee ee eee es 327 maint info breakpoints ss 327 meint info psymtabS ewes esac es RR 147 naint INFO Sections 2e rzricc sm enel 158 maint info sol threads ois 33 maint info symtabs 0 05 147 meint internal error 2 me ES 328 maint internal warning 328 naint packet meg dees weeded 328 maint print architecture 328 maint print cooked registers 328 maint print dummy frames 328 Maint print objfiles 000 329 maint print psymbols 2 22 c ens 146 mai
539. racting with the user it can do so quickly and unobtrusively hopefully not disturbing the program s behavior When GDB is debugging a remote target the GDB agent code running on the target computes the values of the expressions itself To avoid having a full symbolic expression evaluator on the agent GDB translates expressions in the source language into a simpler bytecode language and then sends the bytecode to the agent the agent then executes the bytecode and records the values for GDB to retrieve later The bytecode language is simple there are forty odd opcodes the bulk of which are the usual vocabulary of C operands addition subtraction shifts and so on and various sizes of literals and memory reference operations The bytecode interpreter operates strictly on machine level values various sizes of integers and floating point numbers and requires no information about types or symbols thus the interpreter s internal data structures are simple and each bytecode requires only a few native machine instructions to implement it The interpreter is small and strict limits on the memory and time required to evaluate an expression are easy to determine making it suitable for use by the debugging agent in real time applications E 1 General Bytecode Design The agent represents bytecode expressions as an array of bytes Each instruction is one byte long thus the term bytecode Some instructions are followed by operand bytes
540. railing suffix of the form suffix leaving the basename e Remove all but the trailing suffix p Print the new command but do not execute it s old new Substitute new for the first occurrence of old in the event line Any delimiter may be used in place of The delimiter may be quoted in old and new with a single backslash If amp appears in new it is replaced by old A single backslash will quote the amp The final delimiter is optional if it is the last character on the input line Chapter 28 Using History Interactively 317 amp Repeat the previous substitution g a Cause changes to be applied over the entire event line Used in conjunction with s as in gs old new or with amp G Apply the following s modifier once to each word in the event 318 Debugging with GDB Appendix A Formatting Documentation 319 Appendix A Formatting Documentation The GDB 4 release includes an already formatted reference card ready for printing with PostScript or Ghostscript in the gdb subdirectory of the main source directory If you can use PostScript or Ghostscript with your printer you can print the reference card im mediately with refcard ps The release also includes the source for the reference card You can format it using TEX by typing make refcard dvi The GDB reference card is designed to print in landscape mode on US letter size paper that is on a sheet 11 inches w
541. rd M f Move forward to the end of the next word Words are composed of letters and digits backward word M b Move back to the start of the current or previous word Words are composed of letters and digits clear screen C 1 Clear the screen and redraw the current line leaving the current line at the top of the screen redraw current line Refresh the current line By default this is unbound 27 4 2 Commands For Manipulating The History accept line Newline or Return Accept the line regardless of where the cursor is If this line is non empty it may be added to the history list for future recall with add history O If this line is a modified history line the history line is restored to its original state previous history C p Move back through the history list fetching the previous command 308 Debugging with GDB next history C n Move forward through the history list fetching the next command beginning of history M Move to the first line in the history end of history M gt Move to the end of the input history i e the line currently being entered reverse search history C r Search backward starting at the current line and moving up through the his tory as necessary This is an incremental search forward search history C s Search forward starting at the current line and moving down through the the history as necessary This is an incremental search non in
542. re argument list Defined on PROCEDURE objects Same precedence as GDB and Modula 2 scope operators Warning Set expressions and their operations are not yet supported so GDB treats the use of the operator IN or the use of operators lt gt lt and gt on sets as an error 12 4 5 2 Built in Functions and Procedures Modula 2 also makes available several built in procedures and functions In describing these the following metavariables are used a C i represents an ARRAY variable represents a CHAR constant or variable represents a variable or constant of integral type represents an identifier that belongs to a set Generally used in the same func tion with the metavariable s The type of s should be SET OF mtype where mtype is the type of m represents a variable or constant of integral or floating point type represents a variable or constant of floating point type represents a type represents a variable represents a variable or constant of one of many types See the explanation of the function for details Chapter 12 Using GDB with Different Languages 133 All Modula 2 built in procedures also return a result described below ABS n CAP c CHR i DEC v DEC v i EXCL m s FLOAT i HIGH a INC v INC v i INCL m s MAX t MIN t ODD i ORD x SIZE x TRUNC r VAL t i Returns the absolute value of n If c is a lower case letter it returns its
543. re count by one and continues As a result if the ignore count value is n the breakpoint does not stop the next n times your program reaches it ignore bnum count Set the ignore count of breakpoint number bnum to count The next count times the breakpoint is reached your program s execution does not stop other than to decrement the ignore count GDB takes no action To make the breakpoint stop the next time it is reached specify a count of zero When you use continue to resume execution of your program from a break point you can specify an ignore count directly as an argument to continue rather than using ignore See Section 5 2 Continuing and Stepping page 52 If a breakpoint has a positive ignore count and a condition the condition is not checked Once the ignore count reaches zero GDB resumes checking the condition You could achieve the effect of the ignore count with a condition such as foo lt 0 using a debugger convenience variable that is decremented each time See Section 8 9 Convenience Variables page 88 Ignore counts apply to breakpoints watchpoints and catchpoints 5 1 7 Breakpoint Command Lists You can give any breakpoint or watchpoint or catchpoint a series of commands to execute when your program stops due to that breakpoint For example you might want to print the values of certain expressions or enable other breakpoints 50 Debugging with GDB commands bnum comnand list end S
544. re for loading executable files onto your system must be able to load their contents into the larger address space as well as the instruction and data spaces The overlay system described above is rather simple and could be improved in many ways e If your system has suitable bank switch registers or memory management hardware you could use those facilities to make an overlay s load area contents simply appear at their mapped address in instruction space This would probably be faster than copying the overlay to its mapped area in the usual way e If your overlays are small enough you could set aside more than one overlay area and have more than one overlay mapped at a time e You can use overlays to manage data as well as instructions In general data overlays are even less transparent to your design than code overlays whereas code overlays only require care when you call or return to functions data overlays require care every time you access the data Also if you change the contents of a data overlay you must copy its contents back out to its load address before you can copy a different data overlay into the same mapped area 11 2 Overlay Commands To use GDB s overlay support each overlay in your program must correspond to a separate section of the executable file The section s virtual memory address and load memory address must be the overlay s mapped and load addresses Identifying overlays with sections allows GDB to det
545. re several commands to control GDB s logging Chapter 2 Getting In and Out of GDB 17 set logging on Enable logging set logging off Disable logging set logging file file Change the name of the current logfile The default logfile is gdb txt set logging overwrite on off By default GDB will append to the logfile Set overwrite if you want set logging on to overwrite the logfile instead set logging redirect on off By default GDB output will go to both the terminal and the logfile Set redirect if you want output to go only to the log file show logging Show the current values of the logging settings 18 Debugging with GDB Chapter 3 GDB Commands 19 3 GDB Commands You can abbreviate a GDB command to the first few letters of the command name if that abbreviation is unambiguous and you can repeat certain GDB commands by typing just RET You can also use the key to get GDB to fill out the rest of a word in a command or to show you the alternatives available if there is more than one possibility 3 1 Command Syntax A GDB command is a single line of input There is no limit on how long it can be It starts with a command name which is followed by arguments whose meaning depends on the command name For example the command step accepts an argument which is the number of times to step as in step 5 You can also use the step command with no arguments Some commands do not allow any arguments G
546. reakpoints 00 PUP iis peered eee tere ee ee mee per ue dd physical address from linear address pipe target remote to 00 0 Pipes maa c uePqedae en ve eta equip phon MIPS remote sated ir irais po print object ci dee res pointer values in file i o protocol pointer finding referent port rights GNU Hurd 22 rei ikore rris port sets GNU H rd 4 possible completions M post commands annotation post overload choice annotation post prompt annotation post prompt for continue annotation post query annotation ss pre commands annotation pre overload choice annotation pre prompt annotation pre prompt for continue annotation pre query annotation sss 411 prefix for shared library file names 160 prefix meta ESQ lsssssessssssssse 312 premature return from system calls 58 preprocessor macro expansion showing the results OL cantur rua que m N ei aee aaa 101 pretty print arrays es 224i Ra regat 84 pretty print C virtual function tables 87 previous history C p 000 307 primnt eese ee rn athe tee ales PARES 75 print an Objective C object description 130 print array indexes 005 84 print setUngs ced
547. ress assuming an int occupies 4 bytes e Anarbitrarily complex expression such as a b c d The expression can use any op erators valid in the program s native language see Chapter 12 Languages page 119 Depending on your system watchpoints may be implemented in software or hardware GDB does software watchpointing by single stepping your program and testing the variable s value each time which is hundreds of times slower than normal execution But this may still be worth it to catch errors where you have no clue what part of your program is the culprit On some systems such as HP UX GNU Linux and most other x86 based targets GDB includes support for hardware watchpoints which do not slow down the running of your program watch expr Set a watchpoint for an expression GDB will break when the expression expr is written into by the program and its value changes The simplest and the most popular use of this command is to watch the value of a single variable gdb watch foo rwatch expr Set a watchpoint that will break when the value of expr is read by the program awatch expr Set a watchpoint that will break when expr is either read from or written into by the program info watchpoints This command prints a list of watchpoints breakpoints and catchpoints it is the same as info break see Section 5 1 1 Set Breaks page 38 GDB sets a hardware watchpoint if possible Hardware watchpoints execute very quickly
548. rget wait timeout 332 Debugging with GDB Appendix D GDB Remote Serial Protocol 333 Appendix D GDB Remote Serial Protocol D 1 Overview There may be occasions when you need to know something about the protocol for example if there is only one serial port to your target machine you might want your program to do something special if it recognizes a packet meant for GDB In the examples below gt and lt are used to indicate transmitted and received data respectively All GDB commands and responses other than acknowledgments are sent as a packet A packet is introduced with the character the actual packet data and the terminating character followed by a two digit checksum packet data checksum The two digit checksum is computed as the modulo 256 sum of all characters between the leading and the trailing an eight bit unsigned checksum Implementors should note that prior to GDB 5 0 the protocol specification also included an optional two digit sequence id sequence id packet data checksum That sequence id was appended to the acknowledgment GDB has never output sequence ids Stubs that handle packets added since GDB 5 0 must not accept sequence id When either the host or the target machine receives a packet the first response expected is an acknowledgment either to indicate the package was received correctly or to request retransmission gt packet
549. rinted and their meanings include inner block not inside outer block in symbol The symbol information shows where symbol scopes begin and end such as at the start of a function or a block of statements This error indicates that an inner scope block is not fully contained in its outer scope blocks GDB circumvents the problem by treating the inner block as if it had the same scope as the outer block In the error message symbol may be shown as don t know if the outer block is not a function Chapter 15 GDB Files 165 block at address out of order The symbol information for symbol scope blocks should occur in order of in creasing addresses This error indicates that it does not do so GDB does not circumvent this problem and has trouble locating symbols in the source file whose symbols it is reading You can often determine what source file is affected by specifying set verbose on See Section 19 7 Optional Warnings and Messages page 211 bad block start address patched The symbol information for a symbol scope block has a start address smaller than the address of the preceding source line This is known to occur in the SunOS 4 1 1 and earlier C compiler GDB circumvents the problem by treating the symbol scope block as starting on the previous source line bad string table offset in symbol n Symbol number n contains a pointer into the string table which is larger than the size of the string table GDB circumv
550. rmat is aout the program must be loaded to the starting address You can use objdump to find out what this value is The load offset is an offset which is added to the VMA virtual memory address of each of the file s sections For instance if the program prog was linked to text address 0x1201000 with data at 0x12010160 and bss at 0x12010170 in GDB type gdbslet load prog 0x12010000 Loading section text size OxdbO vma 0x12010000 If the code is loaded at a different address then what the program was linked to you may need to use the section and add symbol file commands to tell GDB where to map the symbol table Chapter 18 Configuration Specific Information 201 18 3 8 4 Running and Debugging You can now begin debugging the task using GDB s execution control commands b step run etc See the GDB manual for the list of commands gdbslet b main Breakpoint 1 at 0x12010000 file prog c line 3 gdbslet run Starting program prog Breakpoint 1 main argc 1 argv Oxeffff21c at prog c 3 3 char symarg 0 gdbslet step 4 char execarg hello gdbslet 18 3 9 Fujitsu Sparclite target sparclite dev Fujitsu sparclite boards used only for the purpose of loading You must use an additional command to debug the program For example target remote dev using GDB standard remote protocol 18 3 10 Zilog Z8000 When configured for debugging Zilog Z8000 targets GDB includes a Z8000 simulator For the Z8000 family
551. rmation about the process running your program or about any process running on your system info proc works only on SVR4 systems that include the procfs code This includes as of this writing GNU Linux OSF 1 Digital Unix Solaris Irix and Unixware but not HP UX for example info proc info proc process id Summarize available information about any running process If a process ID is specified by process id display information about that process otherwise 182 Debugging with GDB display information about the program being debugged The summary includes the debugged process ID the command line used to invoke it its current working directory and its executable file s absolute file name On some systems process id can be of the form pid tid which specifies a certain thread ID within a process If the optional pid part is missing it means a thread from the process being debugged the leading still needs to be present or else GDB will interpret the number as a process ID rather than a thread ID info proc mappings Report the memory address space ranges accessible in the program with in formation on whether the process has read write or execute access rights to each range On GNU Linux systems each memory range includes the object file which is mapped to that range instead of the memory access rights to that range info proc stat info proc status These subcommands are specific to GNU Linux systems They show the
552. rogram to be debugged It is read for its symbols and for the contents of pure memory It is also the program executed when you use the run command If you do not specify a directory and the file is not found in the GDB working directory GDB uses the environment variable PATH as a list of directories to search just as the shell does when looking for a program to run You can change the value of this variable for both GDB and your program using the path command You can load unlinked object o files into GDB using the file command You will not be able to run an object file but you can disassemble functions and inspect variables Also if the underlying BFD functionality supports it you could use gdb write to patch object files using this technique Note that GDB can neither interpret nor modify relocations in this case so branches and some initialized variables will appear to go to the wrong place But this feature is still handy from time to time file file with no argument makes GDB discard any information it has on both executable file and the symbol table exec file filename Specify that the program to be run but not the symbol table is found in file name GDB searches the environment variable PATH if necessary to locate your program Omitting filename means to discard information on the executable file symbol file filename Read symbol table information from file filename PATH is searched when nec essary Us
553. rograms 173 17 2 Using the gdbserver Program Edbserver is a control program for Unix like systems which allows you to connect your program with a remote GDB via target remote but without linking in the usual debugging stub gdbserver is not a complete replacement for the debugging stubs because it requires essentially the same operating system facilities that GDB itself does In fact a system that can run gdbserver to connect to a remote GDB could also run GDB locally gdbserver is sometimes useful nevertheless because it is a much smaller program than GDB itself It is also easier to port than all of GDB so you may be able to get started more quickly on a new system by using gdbserver Finally if you develop code for real time systems you may find that the tradeoffs involved in real time operation make it more convenient to do as much development work as possible on another system for example by cross compiling You can use gdbserver to make a similar choice for debugging GDB and gdbserver communicate via either a serial line or a TCP connection using the standard GDB remote serial protocol On the target machine you need to have a copy of the program you want to debug gdbserver does not need your program s symbol table so you can strip the program if necessary to save space GDB on the host system does all the symbol handling To use the server you must tell it how to communicate with GDB the name of your program and the
554. roprietary formats that can be read and edited only by proprietary word processors SGML or XML for which the DTD and or processing tools are not generally available and the machine generated HTML PostScript or PDF produced by some word processors for output purposes only The Title Page means for a printed book the title page itself plus such following pages as are needed to hold legibly the material this License requires to appear in the title page For works in formats which do not have any title page as such Title Page means the text near the most prominent appearance of the work s title preceding the beginning of the body of the text A section Entitled XYZ means a named subunit of the Document whose title either is precisely XYZ or contains XYZ in parentheses following text that translates XYZ in another language Here XYZ stands for a specific section name mentioned below such as Acknowledgements Dedications Endorsements or History To Preserve the Title of such a section when you modify the Document means that it remains a section Entitled XYZ according to this definition The Document may include Warranty Disclaimers next to the notice which states that this License applies to the Document These Warranty Disclaimers are considered to be included by reference in this License but only as regards disclaiming warranties any other implication that these Warranty Disclaimers may have is void and
555. rs stack frames etc will be returned to the values that they had when the checkpoint was saved In essence gdb will wind back the clock to the point in time when the checkpoint was saved Note that breakpoints GDB variables command history etc are not affected by restoring a checkpoint In general a checkpoint only restores things that reside in the program being debugged not in the debugger delete checkpoint checkpoint id Delete the previously saved checkpoint identified by checkpoint id Returning to a previously saved checkpoint will restore the user state of the program being debugged plus a significant subset of the system OS state including file pointers It won t un write data from a file but it will rewind the file pointer to the previous location so that the previously written data can be overwritten For files opened in read mode the pointer will also be restored so that the previously read data can be read again Of course characters that have been sent to a printer or other external device cannot be snatched back and characters received from eg a serial device can be removed from internal program buffers but they cannot be pushed back into the serial pipeline ready to be received again Similarly the actual contents of files that have been changed cannot be restored at this time However within those constraints you actually can rewind your program to a previ ously saved point in time a
556. rted and does not need an associated value name The remote protocol feature name is not supported name The remote protocol feature name may be supported and GDB should auto detect support in some other way when it is needed This form will not be used for gdbfeature notifications but may be used for stubfeature responses Whenever the stub receives a qSupported request the supplied set of GDB features should override any previous request This allows GDB to put the stub in a known state even if the stub had previously been communicating with a different version of GDB No values of gdbfeature for the packet sent by GDB are defined yet Stubs should ignore any unknown values for gdbfeature Any GDB which sends a qSupported packet supports receiving packets of unlimited length earlier ver sions of GDB may reject overly long responses Values for gdbfeature may be defined in the future to let the stub take advantage of new features in GDB e g incompatible improvements in the remote protocol support for unlimited length responses would be a gdbfeature example if it were not implied by the qSupported query The stub s reply should be independent of the gdbfeature entries sent by GDB first GDB describes all the features it supports and then the stub replies with all the features it supports Similarly GDB will silently ignore unrecognized stub feature responses as long as each response uses one of
557. s As long as type checking is enabled any attempt to combine variables whose types are not equivalent is an error Range checking is done on all mathematical operations assignment array index bounds and all built in functions and procedures 12 4 5 8 The Scope Operators and There are a few subtle differences between the Modula 2 scope operator and the GDB scope operator The two have similar syntax module id Scope id where scope is the name of a module or a procedure module the name of a module and id is any declared identifier within your program except another module Using the operator makes GDB search the scope specified by scope for the identifier id If it is not found in the specified scope then GDB searches all scopes enclosing the one specified by scope Chapter 12 Using GDB with Different Languages 137 Using the operator makes GDB search the current scope for the identifier specified by id that was imported from the definition module specified by module With this operator it is an error if the identifier id was not imported from definition module module or if id is not an identifier in module 12 4 5 9 GDB and Modula 2 Some GDB commands have little use when debugging Modula 2 programs Five subcom mands of set print and show print apply specifically to C and C vtbl demangle asm demangle object and union The first four apply to C and the last to the C
558. s This is a limit on the data characters in the packet including the frame and checksum There is no trailing NUL byte in a remote protocol packet if the stub stores packets in a NUL terminated format it should allow an extra byte in its buffer for the NUL If this stub feature is not supported GDB guesses based on the size of the g packet response qXfer auxv read The remote stub understands the qXfer auxv read packet see qXfer auxiliary vector read page 349 qXfer features read The remote stub understands the qXfer features read packet see qXfer target description read page 349 qXfer libraries read The remote stub understands the qXfer libraries read packet see qXfer library list read page 349 348 Debugging with GDB qXfer memory map read The remote stub understands the qXfer memory map read packet see qXfer memory map read page 350 qXfer spu read The remote stub understands the qXfer spu read packet see qXfer spu read page 350 qXfer spu write The remote stub understands the qXfer spu write packet see qXfer spu write page 350 QPassSignals The remote stub understands the QPassSignals packet see QPassSignals page 345 qSymbol Notify the target that GDB is prepared to serve symbol lookup requests Accept requests from the target for the values of symbols Reply OK The target does not need
559. s command accepts the current line like RET and then fetches the next line relative to the current line from the history for editing 3 2 Command Completion GDB can fill in the rest of a word in a command for you if there is only one possibility it can also show you what the valid possibilities are for the next word in a command at any time This works for GDB commands GDB subcommands and the names of symbols in your program Press the key whenever you want GDB to fill out the rest of a word If there is only one possibility GDB fills in the word and waits for you to finish the command or press to enter it For example if you type gdb info bre GDB fills in the rest of the word breakpoints since that is the only info subcommand beginning with bre 20 Debugging with GDB gdb info breakpoints You can either press at this point to run the info breakpoints command or backspace and enter something else if breakpoints does not look like the command you expected If you were sure you wanted info breakpoints in the first place you might as well just type immediately after info bre to exploit command abbreviations rather than command completion If there is more than one possibility for the next word when you press TAB GDB sounds a bell You can either supply more characters and try again or just press a second time GDB displays all the possible completions for that word For example you might w
560. s not thus excluded In such case this License incorporates the limitation as if written in the body of this License The Free Software Foundation may publish revised and or new versions of the General Public License from time to time Such new versions will be similar in spirit to the present version but may differ in detail to address new problems or concerns Each version is given a distinguishing version number If the Program specifies a version number of this License which applies to it and any later version you have the option of following the terms and conditions either of that version or of any later version published by the Free Software Foundation If the Program does not specify a version number of this License you may choose any version ever published by the Free Software Foundation If you wish to incorporate parts of the Program into other free programs whose distri bution conditions are different write to the author to ask for permission For software Appendix G GNU GENERAL PUBLIC LICENSE 391 11 12 which is copyrighted by the Free Software Foundation write to the Free Software Foun dation we sometimes make exceptions for this Our decision will be guided by the two goals of preserving the free status of all derivatives of our free software and of promoting the sharing and reuse of software generally NO WARRANTY BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE THERE IS NO WARRANTY FOR THE PROGRAM TO THE
561. s or instantiations of templates that do not exist in the program It also cannot handle ellipsis argument lists or default arguments It does perform integral conversions and promotions floating point promotions arith metic conversions pointer conversions conversions of class objects to base classes and standard conversions such as those of functions or arrays to pointers it requires an exact match on the number of function arguments Chapter 12 Using GDB with Different Languages 127 Overload resolution is always performed unless you have specified set overload resolution off See Section 12 4 1 7 GDB Features for C page 128 You must specify set overload resolution off in order to use an explicit function signature to call an overloaded function as in p foo char int x 13 The GDB command completion facility can simplify this see Section 3 2 Command Completion page 19 4 GDB understands variables declared as C references you can use them in expressions just as you do in C source they are automatically dereferenced In the parameter list shown when GDB displays a frame the values of reference variables are not displayed unlike other variables this avoids clutter since references are often used for large structures The address of a reference variable is always shown unless you have specified set print address off 5 GDB supports the C name resolution operator your expressions can
562. s such as a signal a break point or reaching a new line after a GDB command such as step You may then examine and change variables set new breakpoints or remove old ones and then continue execu tion Usually the messages shown by GDB provide ample explanation of the status of your program but you can also explicitly request this information at any time info program Display information about the status of your program whether it is running or not what process it is and why it stopped 5 1 Breakpoints Watchpoints and Catchpoints A breakpoint makes your program stop whenever a certain point in the program is reached For each breakpoint you can add conditions to control in finer detail whether your program stops You can set breakpoints with the break command and its variants see Section 5 1 1 Setting Breakpoints page 38 to specify the place where your program should stop by line number function name or exact address in the program On some systems you can set breakpoints in shared libraries before the executable is run There is a minor limitation on HP UX systems you must wait until the executable is run in order to set breakpoints in shared library routines that are not called directly by the program for example routines that are arguments in a pthread create call A watchpoint is a special breakpoint that stops your program when the value of an expression changes The expression may be a value of a variable or it
563. s use hardware breakpoints You can control this automatic behaviour with the following commands Set breakpoint auto hw on This is the default behavior When GDB sets a breakpoint it will try to use the target memory map to decide if software or hardware breakpoint must be used Set breakpoint auto hw off This indicates GDB should not automatically select breakpoint type If the target provides a memory map GDB will warn when trying to set software breakpoint at a read only address GDB itself sometimes sets breakpoints in your program for special purposes such as proper handling of longjmp in C programs These internal breakpoints are assigned negative numbers starting with 1 info breakpoints does not display them You can see these breakpoints with the GDB maintenance command maint info breakpoints see maint info breakpoints page 327 Chapter 5 Stopping and Continuing 43 5 1 2 Setting Watchpoints You can use a watchpoint to stop execution whenever the value of an expression changes without having to predict a particular place where this may happen This is sometimes called a data breakpoint The expression may be as simple as the value of a single variable or as complex as many variables combined by operators Examples include e A reference to the value of a single variable e An address cast to an appropriate data type For example int 0x12345678 will watch a 4 byte region at the specified add
564. s accomplished by p but in Modula 2 it is accomplished by p Values can also be represented and displayed differently Hex numbers in C appear as Ox1ae while in Modula 2 they appear as 1AEH Language specific information is built into GDB for some languages allowing you to express operations like the above in your program s native language and allowing GDB to output values in a manner consistent with the syntax of your program s native language The language you use to build expressions is called the working language 12 1 Switching Between Source Languages There are two ways to control the working language either have GDB set it automatically or select it manually yourself You can use the set language command for either purpose On startup GDB defaults to setting the language automatically The working language is used to determine how expressions you type are interpreted how values are printed etc In addition to the working language every source file that GDB knows about has its own working language For some object file formats the compiler might indicate which language a particular source file is in However most of the time GDB infers the language from the name of the file The language of a source file controls whether C names are demangled this way backtrace can show each frame appropriately for its own language There is no way to set the language of a source file from within GDB but you can set the language
565. s are numbered from the beginning of the line with the 316 Debugging with GDB first word being denoted by 0 zero Words are inserted into the current line separated by single spaces For example n designates the preceding command When you type this the preceding com mand is repeated in toto I designates the last argument of the preceding command This may be shortened to fi 2 designates the second argument of the most recent command starting with the letters fi Here are the word designators O zero The Oth word For many applications this is the command word n The nth word The first argument that is word 1 The last argument hh The word matched by the most recent string search x y A range of words y abbreviates 0 y All of the words except the Oth This is a synonym for 1 It is not an error to use if there is just one word in the event the empty string is returned in that case x Abbreviates x x Abbreviates x like x but omits the last word If a word designator is supplied without an event specification the previous command is used as the event 28 1 3 Modifiers After the optional word designator you can add a sequence of one or more of the following modifiers each preceded by a h Remove a trailing pathname component leaving only the head t Remove all leading pathname components leaving the tail r Remove a t
566. s ea dia D dus 15 Ql crm 14 cbr ak aft rbiclnioLeRIRAPGS ge We Sredcess 239 break condition 2 scss ess e rens 240 break delete ssesles esses 241 break disable 0 cece cece eee 241 break enabl w 2 ii scaneke soe tees dene DDR 242 sbreak info 525se44 os tes ed ss 242 Sbreak inSert 2J eec dances ange dee ales 242 sbreak sIdSt 2c29 4k Rina ldem ied 244 sbreak watch i2i22 3h bv exa da uds 245 l rr 12 LC E RI T c P Mee teint fee 12 data disassemble 0 e eee eee 266 data evaluate expression 268 data list changed registers 269 data list register names 269 data list register values 270 data read memory cc cr pi E 271 Lo E EE A beac Se es dd EE 12 enable timings ce b ed c de ved REG eaa 286 environment cd llle 247 environment directory sss 248 environment path beets eee eee 248 ENVITONMeNt pwWd vetoed e lp ewes 249 xoc 6 tee tre E eta Sailnet Ws dae eee ae ena 12 6X6C abOrt visas 3iddd e es MiG UP RUP 283 xec argum nts iclsisnexcieduua be e nes 247 exec continue eee ees 2 51 sexec finrsSh 2222221922 22 d 40d 29i exec interr pt aio ec oes n Rn RES 252 X C ReXUt ob dd ace thew eed dd es rns Fd 253 exec next instruction 253 X C FOL rH i ies dd lee das ordeo bdo dea rna 253 ceXGC EUB i6eqa ede We Ead oboe 254
567. s integers push their sum as an integer In this example add is the name of the bytecode and 0x02 is the one byte value used to encode the bytecode in hexadecimal The phrase a b a b shows the stack before and after the bytecode executes Beforehand the stack must contain at least two values a and b since the top of the stack is to the right b is on the top of the stack and a is underneath it After execution the bytecode will have popped a and b from the stack and replaced them with a single value a b There may be other values on the stack below those shown but the bytecode affects only those shown Here is another example const8 0x22 n n Push the 8 bit integer constant n on the stack without sign extension In this example the bytecode const8 takes an operand n directly from the bytecode stream the operand follows the const8 bytecode itself We write any such operands imme diately after the name of the bytecode before the colon and describe the exact encoding of the operand in the bytecode stream in the body of the bytecode description For the const8 bytecode there are no stack items given before the this simply means that the bytecode consumes no values from the stack If a bytecode consumes no values or produces no values the list on either side of the may be empty If a value is written as a b or n then the bytecode treats it as an integer If a value is written is addr then the bytecode
568. s not what you want For example you might want to print a number in hex or a pointer in decimal Or you might want to view data in memory at a certain address as a character string or as an instruction To do these things specify an output format when you print a value The simplest use of output formats is to say how to print a value already computed This is done by starting the arguments of the print command with a slash and a format letter The format letters supported are x Regard the bits of the value as an integer and print the integer in hexadecimal d Print as integer in signed decimal u Print as integer in unsigned decimal o Print as integer in octal t Print as integer in binary The letter t stands for two 1 4 cannot be used because these format letters are also used with the x command where b stands for byte see Section 8 5 Examining Memory page 79 Chapter 8 Examining Data 79 Print as an address both absolute in hexadecimal and as an offset from the nearest preceding symbol You can use this format used to discover where in what function an unknown address is located gdb p a 0x54320 3 0x54320 lt _initialize_vx 396 gt The command info symbol 0x54320 yields similar results See Chapter 13 Symbols page 143 Regard as an integer and print it as a character constant This prints both the numerical value and its character representation The character representation is rep
569. s source path includes only cdir and cwd in that order To add other directories use the directory command The search path is used to find both program source files and GDB script files read using the command option and source command In addition to the source path GDB provides a set of commands that manage a list of source path substitution rules A substitution rule specifies how to rewrite source directories stored in the program s debug information in case the sources were moved to a different directory between compilation and debugging A rule is made of two strings the first specifying what needs to be rewritten in the path and the second specifying how it should be rewritten In set substitute path page 71 we name these two parts from and to respectively GDB does a simple string replacement of from with to at the start of the directory part of the source file name and uses that result instead of the original file name to look up the sources Using the previous example suppose the foo 1 0 tree has been moved from usr src to mnt cross then you can tell GDB to replace usr src in all source path names with unt cross The first lookup will then be mnt cross foo 1 0 lib foo c in place of the original location of usr src foo 1 0 1lib foo c To define a source path substitu tion rule use the set substitute path command see set substitute path page 71 To
570. s the file usr src foo 1 0 lib foo c and our source path is mnt cross The file is first looked up literally if this fails The only restriction is that your editor say ex recognizes the following command line syntax ex tnumber file The optional numeric value number specifies the number of the line in the file where to start editing 70 Debugging with GDB mnt cross usr src foo 1 0 lib foo c is tried if this fails mnt cross foo c is opened if this fails an error message is printed GDB does not look up the parts of the source file name such as mnt cross src foo 1 0 lib foo c Likewise the subdirectories of the source path are not searched if the source path is mnt cross and the binary refers to foo c GDB would not find it under mnt cross usr src foo 1 0 1ib Plain file names relative file names with leading directories file names containing dots etc are all treated as described above for instance if the source path is mnt cross and the source file is recorded as lib foo c GDB would first try lib foo c then mnt cross lib foo c and after that mnt cross foo c Note that the executable search path is not used to locate the source files Whenever you reset or rearrange the source path GDB clears out any information it has cached about where source files are found and where each line is in the file When you start GDB it
571. s then there are none The Cover Texts are certain short passages of text that are listed as Front Cover Texts or Back Cover Texts in the notice that says that the Document is released under this License A Front Cover Text may be at most 5 words and a Back Cover Text may be at most 25 words A Transparent copy of the Document means a machine readable copy represented in a format whose specification is available to the general public that is suitable for revising the document straightforwardly with generic text editors or for images com posed of pixels generic paint programs or for drawings some widely available drawing editor and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters A copy made in an otherwise Iransparent file format whose markup or absence of markup has been arranged to thwart or discourage subsequent modification by readers is not Transparent An image format is not Transparent if used for any substantial amount of text A copy that is not Transparent is called Opaque Examples of suitable formats for Transparent copies include plain ASCII without markup Texinfo input format La TEX input format SGML or XML using a publicly available DTD and standard conforming simple HTML PostScript or PDF designed for human modification Examples of transparent image formats include PNG XCF and JPG Opaque formats include p
572. sage in the form New systag systag is a thread identifier whose form varies depending on the particular system For example on HP UX you see New thread 2 system thread 26594 when GDB notices a new thread info threads Display a summary of all threads currently in your program GDB displays for each thread in this order 1l the thread number assigned by GDB 2 the target system s thread identifier systag 3 the current stack frame summary for that thread An asterisk to the left of the GDB thread number indicates the current thread For example gdb info threads 3 system thread 26607 worker wptr 0x7b09c318 Q at quicksort c 137 2 system thread 26606 0x7b0030d8 in __ksleep O from usr lib libc 2 1 system thread 27905 0x7b003498 in brk O Chapter 4 Running Programs Under GDB 33 from usr lib libc 2 On Solaris you can display more information about user threads with a Solaris specific command maint info sol threads Display info on Solaris user threads thread threadno Make thread number threadno the current thread The command argument threadno is the internal GDB thread number as shown in the first field of the info threads display GDB responds by displaying the system identifier of the thread you selected and its current stack frame summary gdb thread 2 Switching to process 35 thread 23 0x34e5 in sigpause As with the New message the form of the
573. scaped Responses sent by the stub must also escape 0x2a ASCII so that it is not interpreted as the start of a run length encoded sequence described next 334 Debugging with GDB Response data can be run length encoded to save space A means that the next character is an ASCII encoding giving a repeat count which stands for that many repetitions of the character preceding the The encoding is n 29 yielding a printable character where n gt 3 which is where rle starts to win The printable characters and or with a numeric value greater than 126 should not be used So Ox means the same as 0000 The error response returned for some packets includes a two character error number That number is not well defined For any command not supported by the stub an empty response 00 should be returned That way it is possible to extend the protocol A newer GDB can tell if a packet is supported based on that response 6 A stub is required to support the g G m M c and s commands All other commands are optional D 2 Packets The following table provides a complete list of all currently defined commands and their cor responding response data See Section D 9 File I O Remote Protocol Extension page 354 for details about the File I O extension of the remote protocol Each packet s description has a template showing th
574. searches for a function whose signature exactly matches the argument types show overload resolution Show the current setting of overload resolution Overloaded symbol names You can specify a particular definition of an overloaded symbol using the same notation that is used to declare such symbols in C type symbol types rather than just symbol You can also use the GDB command line word com pletion facilities to list the available choices or to finish the type list for you See Section 3 2 Command Completion page 19 for details on how to do this 12 4 2 Objective C This section provides information about some commands and command options that are useful for debugging Objective C code See also Chapter 13 Symbols page 143 and Chapter 13 Symbols page 143 for a few more commands specific to Objective C support 12 4 2 1 Method Names in Commands The following commands have been extended to accept Objective C method names as line specifications e clear e break e info line e jump e list A fully qualified Objective C method name is specified as Class methodName where the minus sign is used to indicate an instance method and a plus sign not shown is used to indicate a class method The class name Class and method name methodName are enclosed in brackets similar to the way messages are specified in Objective C source code For example to set a breakpoint at the create instance method of class Fruit in the program curren
575. self You can change most of the things you can show by using the related command set for example you can control what number system is used for displays with set radix or simply inquire which is currently in use with show radix To display all the settable parameters and their current values you can use show with no arguments you may also use info set Both commands produce the same display Here are three miscellaneous show subcommands all of which are exceptional in lacking corresponding set commands Chapter 3 GDB Commands 23 show version Show what version of GDB is running You should include this information in GDB bug reports If multiple versions of GDB are in use at your site you may need to determine which version of GDB you are running as GDB evolves new commands are introduced and old ones may wither away Also many system vendors ship variant versions of GDB and there are variant versions of GDB in GNU Linux distributions as well The version number is the same as the one announced when you start GDB show copying info copying Display information about permission for copying GDB show warranty info warranty Display the GNU NO WARRANTY statement or a warranty if your version of GDB comes with one 24 Debugging with GDB Chapter 4 Running Programs Under GDB 25 4 Running Programs Under GDB When you run a program under GDB you must first generate debugging information when you compile it Y
576. ses the shell to start your program some systems refuse to let GDB debug child processes whose programs are not readable Appendix B Installing GDB 323 B 3 Compiling GDB in Another Directory If you want to run GDB versions for several host or target machines you need a different gdb compiled for each combination of host and target configure is designed to make this easy by allowing you to generate each configuration in a separate subdirectory rather than in the source directory If your make program handles the VPATH feature GNU make does running make in each of these directories builds the gdb program specified there To build gdb in a separate directory run configure with the srcdir option to specify where to find the source You also need to specify a path to find configure itself from your working directory If the path to configure would be the same as the argument to srcdir you can leave out the srcdir option it is assumed For example with version 6 7 50 20071011 you can build GDB in a separate directory for a Sun 4 like this cd gdb 6 7 50 20071011 mkdir gdb sun4 cd gdb sun4 gdb 6 7 50 20071011 configure sun4 make When configure builds a configuration using a remote source directory it creates a tree for the binaries with the same structure and using the same names as the tree under the source directory In the example you d find the Sun 4 library
577. specific simulator in use for information about acceptable commands 18 3 1 ARM target rdi dev ARM Angel monitor via RDI library interface to ADP protocol You may use this target to communicate with both boards running the Angel monitor or with the EmbeddedICE J TAG debug device target rdp dev ARM Demon monitor GDB provides the following ARM specific commands set arm disassembler This commands selects from a list of disassembly styles The std style is the standard style show arm disassembler Show the current disassembly style Chapter 18 Configuration Specific Information 193 set arm apcs32 This command toggles ARM operation mode between 32 bit and 26 bit Show arm apcs32 Display the current usage of the ARM 32 bit mode Set arm fpu fputype This command sets the ARM floating point unit FPU type The argument fputype can be one of these auto Determine the FPU type by querying the OS ABI softfpa Software FPU with mixed endian doubles on little endian ARM processors fpa GCC compiled FPA co processor softvfp Software FPU with pure endian doubles vfp VFP co processor show arm fpu Show the current type of the FPU set arm abi This command forces GDB to use the specified ABI Show arm abi Show the currently used ABI set debug arm Toggle whether to display ARM specific debugging messages from the ARM target support subsystem show debug arm Show whether ARM specific debugging messages are e
578. splay of the new frame They are intended primarily for use in GDB command scripts where the output might be unnecessary and distracting 6 4 Information About a Frame There are several other commands to print information about the selected stack frame frame f When used without any argument this command does not change which frame is selected but prints a brief description of the currently selected stack frame It can be abbreviated f With an argument this command is used to select a stack frame See Section 6 3 Selecting a Frame page 64 info frame info f This command prints a verbose description of the selected stack frame includ ing e the address of the frame e the address of the next frame down called by this frame e the address of the next frame up caller of this frame e thelanguage in which the source code corresponding to this frame is written e the address of the frame s arguments e the address of the frame s local variables e the program counter saved in it the address of execution in the caller frame e which registers were saved in the frame The verbose description is useful when something has gone wrong that has made the stack format fail to fit the usual conventions 66 Debugging with GDB info frame addr info f addr Print a verbose description of the frame at address addr without selecting that frame The selected frame remains unchanged by this command This requires the same kind of address m
579. splay the next layout layout prev Display the previous layout 228 Debugging with GDB layout src Display the source window only layout asm Display the assembly window only layout split Display the source and assembly window layout regs Display the register window together with the source or assembly window focus next Make the next window active for scrolling focus prev Make the previous window active for scrolling focus src Make the source window active for scrolling focus asm Make the assembly window active for scrolling focus regs Make the register window active for scrolling focus cmd Make the command window active for scrolling refresh Refresh the screen This is similar to typing C L tui reg float Show the floating point registers in the register window tui reg general Show the general registers in the register window tui reg next Show the next register group The list of register groups as well as their order is target specific The predefined register groups are the following general float system vector all save restore tui reg system Show the system registers in the register window update Update the source window and the current execution point winheight name count winheight name count Change the height of the window name by count lines Positive counts increase the height while negative counts decrease it tabset nchars Set the width of tab stops to be nchars char
580. ss than greater than on integral floating point or enumerated types lt gt Less than or equal to greater than or equal to on integral floating point and enumerated types or set inclusion on set types Same precedence as lt lt gt Equality and two ways of expressing inequality valid on scalar types Same precedence as lt In GDB scripts only lt gt is available for inequality since conflicts with the script comment character IN Set membership Defined on set types and the types of their members Same precedence as lt OR Boolean disjunction Defined on boolean types 132 DIV MOD NOT OQ Debugging with GDB Boolean conjunction Defined on boolean types The GDB artificial array operator see Section 8 1 Expressions page 75 Addition and subtraction on integral and floating point types or union and difference on set types Multiplication on integral and floating point types or set intersection on set types Division on floating point types or symmetric set difference on set types Same precedence as Integer division and remainder Defined on integral types Same precedence as Negative Defined on INTEGER and REAL data Pointer dereferencing Defined on pointer types Boolean negation Defined on boolean types Same precedence as RECORD field selector Defined on RECORD data Same precedence as Array indexing Defined on ARRAY data Same precedence as Procedu
581. ssemble This specialized command dumps a range of memory as machine instructions The default memory range is the function surrounding the program counter of the selected frame A single argument to this command is a program counter value GDB dumps the function surrounding this value Two arguments specify a range of addresses first inclusive second exclusive to dump The following example shows the disassembly of a range of addresses of HP PA RISC 2 0 code gdb disas 0x32c4 0x32e4 Dump of assembler code from Ox32c4 to 0x32e4 Ox32c4 lt main 204 gt addil O dp Chapter 7 Examining Source Files 73 0x32c8 Ox32cc 0x32d0 0x32d4 0x32d8 Ox32dc 0x32e0 End of lt main 208 gt ldw 0x22c sr0 r1 r26 lt maint212 gt ldil 0x3000 r31 lt maint 216 gt ble Ox3f8 sr4 r31 lt main 220 gt ldo O r31 rp lt maint 224 gt addil 0x800 dp lt main 228 gt ldo 0x588 r1 r26 lt maint 232 gt ldil 0x3000 r31 assembler dump Some architectures have more than one commonly used set of instruction mnemonics or other syntax For programs that were dynamically linked and use shared libraries instructions that call functions or branch to locations in the shared libraries might show a seemingly bogus location it s actually a location of the relocation table On some architectures GDB might be able to resolve these to actual function names Set disassembly flavor instruction set Select the instruction set to use when disassembli
582. stands that there is no warranty for this free software If the software is modified by someone else and passed on we want its recipients to know that what they have is not the original so that any problems introduced by others will not reflect on the original authors reputations Finally any free program is threatened constantly by software patents We wish to avoid the danger that redistributors of a free program will individually obtain patent licenses in effect making the program proprietary To prevent this we have made it clear that any patent must be licensed for everyone s free use or not licensed at all The precise terms and conditions for copying distribution and modification follow 388 Debugging with GDB TERMS AND CONDITIONS FOR COPYING DISTRIBUTION AND MODIFICATION 0 This License applies to any program or other work which contains a notice placed by the copyright holder saying it may be distributed under the terms of this General Public License The Program below refers to any such program or work and a work based on the Program means either the Program or any derivative work under copyright law that is to say a work containing the Program or a portion of it either verbatim or with modifications and or translated into another language Hereinafter translation is included without limitation in the term modification Each licensee is addressed as you Activities other than copying distrib
583. stem I 0 unsigned long st blocks number of blocks allocated time t st atime time of last access time t st mtime time of last modification time t st ctime time of last change Js The integral datatypes conform to the definitions given in the appropriate section see Integral Datatypes page 363 for details so this structure is of size 64 bytes The values of several fields have a restricted meaning and or range of values st dev A value of 0 represents a file 1 the console st ino No valid meaning for the target Transmitted unchanged st mode Valid mode bits are described in Section D 9 9 Constants page 365 Any other bits have currently no meaning for the target st uid st gid st rdev No valid meaning for the target Transmitted unchanged st atime st mtime st ctime These values have a host and file system dependent accuracy Especially on Windows hosts the file system may not support exact timing values The target gets a struct stat of the above representation and is responsible for coercing it to the target representation before continuing Note that due to size differences between the host target and protocol representations of struct stat members these members could eventually get truncated on the target struct timeval The buffer of type struct timeval used by the File I O protocol is defined as follows struct timeval time t tv sec second long tv usec microseco
584. symbols the number of types defined by the objfile the number of as yet unexpanded psym tables the number of line tables and string tables and the amount of memory used by the various tables The bcache statistics include the counts sizes and counts of duplicates of all and unique objects max average and median entry size total memory used and its overhead and savings and various measures of the hash table size and chain lengths maint print target stack A target is an interface between the debugger and a particular kind of file or process Targets can be stacked in strata so that more than one target can potentially respond to a request In particular memory accesses will walk down the stack of targets until they find a target that is interested in handling that particular address This command prints a short description of each layer that was pushed on the target stack starting from the top layer down to the bottom one maint print type expr Print the type chain for a type specified by expr The argument can be either a type name or a symbol If it is a symbol the type of that symbol is described 330 Debugging with GDB The type chain produced by this command is a recursive definition of the data type as stored in GDB s data structures including its flags and contained types maint set dwarf2 max cache age maint show dwarf2 max cache age Control the DWARF 2 compilation unit cache In object files with inter compilation u
585. t packet dcos eee reme 338 Vector unit ier cox c URP RR eePERCUPE EYE 92 vector auxiliary o erierw err rere 92 verbose operation cece eee eese 211 verify remote memory image 81 vFlashDone packet 0 0 esee 339 vFlashErase packet 00 000 338 vFlashWrite packet 000 339 vi editing mode M C j 00 313 virtual functions C display 87 Visible stats i ere m rey erinin iiti 301 VIEBL display xir rrr mehr ht 8T VX WOES isennd treeni paien ERR Rs 190 vxworks timeout i so sees tr b rh 191 W w SingleKey TUI key 000 0005 227 Wart GH oreet eed EE UV v E Glands 43 watchdog timer rrio LR terenie OE vx 331 watchpoint annotation ioi ees 290 NWatchpolnntscssetereenbteteneePP eed ib prud oT watchpoints and threads lusus 45 weak alias functions sees eeeseess 152 WhatisS ere don shh Re E ee Heat dee gemens 143 WHOLE sas seca Bodine Pale eae acd nied pels iub 62 where to look for shared libraries 160 Wlilleila seneshedeebeentemaubieeE al emper en e NR 220 while stepping tracepoints 108 wild pointer interpreting 84 winheight hob era RE e I Rees 228 word completion mtm mee 19 418 working directory eese eses 71 working directory of your program 29 working language eee eR RE rer RR RS 119
586. t restore gdb Disassemble 3 instructions from the start of main gdb data disassemble f basics c 1 32 n 3 0 done asm insns address 0x000107bc func name main offset 0 inst save Asp 112 sp address 0x000107c0 func name main offset 4 inst mov 2 4o0 j address 0x000107c4 func name main offset 8 inst sethi hi 0x11800 02 gdb Disassemble 3 instructions from the start of main in mixed mode gdb data disassemble f basics c 1 32 n 3 1 done asm insns src and asm line line 31 file kwikemart marge ezannoni flathead dev devo gdb testsuite gdb mi basics c line asm insn address 0x000107bc func name main offset 0 inst save Asp 112 sp src_and_asm_line line 32 file kwikemart marge ezannoni flathead dev devo gdb testsuite gdb mi basics c line asm insn address 0x000107c0 func name main offset 4 inst mov 2 4o0 j address 0x000107c4 func name main offset 8 inst sethi hi 0x11800 02 gdb The data evaluate expression Command Synopsis data evaluate expression expr Chapter 24 The GDB MI Interface 269 Evaluate expr as an expression The expression could contain an inferior function call The function call will execute synchronously If the expression contains spaces it must be enclosed in double quotes GDB Command The corresponding GDB commands are print out
587. t 186 Set debugexcepti nS o ossa dese inn 186 set debugexe 3 0 uses das pese endo hen 186 Set debugmeMmory iis abe RE 186 set demangle style sesosus knees 86 set deta ch On fOrk us Sees ween Re 34 set disassembly flavor 73 set download path dci dh ie ERR 194 set editing posi RR ea E RERUM dus 207 Set endins ee ide hk Bade oue emis ee 170 setenvironment 2 9 blt nieces eet ee 28 set exceptions Hurd command 188 set exec done display ssess 213 set extension language sss 121 Set follow fork mode fe ecce bags 34 set gnutarget sis cde ieee ene du needs 168 set hash for remote monitors 169 Set hedight sl2mi l6 rgedOoceise pi ed ud 209 set history expansiTO0mD 26 epe RR 208 set history filename 208 set history SBV6 o m erp Rs 208 set history Si26 5 de b bees 208 set host charset e gu RR eee 96 set inferior controlling terminal 30 set inferjor tty eR SII RR PD 30 set jnput r dix insures gin eek eua DI 210 s t language dlsns esp e ii 120 Set 318tSIZO 212 09 Api hog Uibdegicubi edu uM 67 set logging 44 sateen bie eh ag HE ETIY E SA 17 set max user call depth 218 set mem inaccessible by default 94 get mips abi po wcccicianeeetatadiese tegedaas 203 set mips mask address niri otier 204 Set mipSfpu
588. t and output is with the tty command This command accepts a file name as argument and causes this file to be the default for future run commands It also resets the controlling terminal for the child process for future run commands For example tty dev ttyb directs that processes started with subsequent run commands default to do input and output on the terminal dev ttyb and have that as their controlling terminal An explicit redirection in run overrides the tty command s effect on the input output device but not its effect on the controlling terminal 30 Debugging with GDB When you use the tty command or redirect input in the run command only the input for your program is affected The input for GDB still comes from your terminal tty is an alias for set inferior tty You can use the show inferior tty command to tell GDB to display the name of the terminal that will be used for future runs of your program set inferior tty dev ttyb Set the tty for the program being debugged to dev ttyb Show inferior tty Show the current tty for the program being debugged 4 7 Debugging an Already running Process attach process id This command attaches to a running process one that was started outside GDB info files shows your active targets The command takes as argument a process ID The usual way to find out the process id of a Unix process is with the ps utility or with the jobs 1 shell command attach does not rep
589. t fd long offset int flag Flseek fd offset flag flag is one of SEEK_SET The offset is set to offset bytes SEEK CUR The offset is set to its current location plus offset bytes SEEK END The offset is set to the size of the file plus offset bytes Return value Errors rename Synopsis Request On success the resulting unsigned offset in bytes from the beginning of the file is returned Otherwise a value of 1 is returned EBADF fd is not a valid open file descriptor ESPIPE fd is associated with the GDB console EINVAL flag is not a proper value EINTR The call was interrupted by the user int rename const char oldpath const char newpath Frename oldpathptr len newpathptr len Return value Errors On success zero is returned On error 1 is returned EISDIR newpath is an existing directory but oldpath is not a directory EEXIST newpath is a non empty directory EBUSY oldpath or newpath is a directory that is in use by some process EINVAL An attempt was made to make a directory a subdirectory of itself ENOTDIR A component used as a directory in oldpath or new path is not a directory Or oldpath is a directory and newpath exists but is not a directory EFAULT oldpathptr or newpathptr are invalid pointer values EACCES No access to the file or the path of the file ENAMETOOLONG oldpath or newpath was too long ENOENT A directory component in oldpath or newpath does not exist
590. t in the same way that they are on the target with e g a lib and usr lib hierarchy under path Chapter 15 GDB Files 161 The set solib absolute prefix command is an alias for set sysroot You can set the default system root by using the configure time with sysroot option If the system root is inside GDB s configured binary prefix set with prefix or exec prefix then the default system root will be updated automatically if the installed GDB is moved to a new location show sysroot Display the current shared library prefix set solib search path path If this variable is set path is a colon separated list of directories to search for shared libraries solib search path is used after sysroot fails to locate the library or if the path to the library is relative instead of absolute If you want to use solib search path instead of sysroot be sure to set sysroot to a nonexistent directory to prevent GDB from finding your host s libraries sysroot is preferred setting it to a nonexistent directory may interfere with automatic loading of shared library symbols show solib search path Display the current shared library search path 15 2 Debugging Information in Separate Files GDB allows you to put a program s debugging information in a file separate from the exe cutable itself in a way that allows GDB to find and load the debugging information automat ically Si
591. t print registers file maint print raw registers file maint print cooked registers file maint print register groups file Print GDB s internal register data structures Appendix C Maintenance Commands 329 The command maint print raw registers includes the contents of the raw register cache the command maint print cooked registers includes the cooked value of all registers and the command maint print register groups includes the groups that each register is a member of See section Registers in GDB Internals These commands take an optional parameter a file name to which to write the information maint print reggroups file Print GDB s internal register group data structures The optional argument file tells to what file to write the information The register groups info looks like this gdb maint print reggroups Group Type general user float user all user vector user system user save internal restore internal flushregs This command forces GDB to flush its internal register cache maint print objfiles Print a dump of all known object files For each object file this command prints its name address in memory and all of its psymtabs and symtabs maint print statistics This command prints for each object file in the program various data about that object file followed by the byte cache bcache statistics for the object file The objfile data includes the number of minimal partial full and stabs
592. t with the awatch or rwatch command it will print a message like this Expression cannot be implemented with read access watchpoint Sometimes GDB cannot set a hardware watchpoint because the data type of the watched expression is wider than what a hardware watchpoint on the target machine can handle For example some systems can only watch regions that are up to 4 bytes wide on such sys tems you cannot set hardware watchpoints for an expression that yields a double precision floating point number which is typically 8 bytes wide As a work around it might be pos sible to break the large region into a series of smaller ones and watch them with separate watchpoints If you set too many hardware watchpoints GDB might be unable to insert all of them when you resume the execution of your program Since the precise number of active watch points is unknown until such time as the program is about to be resumed GDB might not be able to warn you about this when you set the watchpoints and the warning will be printed only when the program is resumed Hardware watchpoint num Could not insert watchpoint If this happens delete or disable some of the watchpoints Watching complex expressions that reference many variables can also exhaust the re sources available for hardware assisted watchpoints That s because GDB needs to watch every variable in the expression with separately allocated resources The SPARClite DSU will generate traps when
593. table file named gnu_debuglink The section must contain e A filename with any leading directory components removed followed by a zero byte e zero to three bytes of padding as needed to reach the next four byte boundary within the section and e a four byte CRC checksum stored in the same endianness used for the executable file itself The checksum is computed on the debugging information file s full contents by the function given below passing zero as the crc argument Any executable file format can carry a debug link as long as it can contain a section named gnu_debuglink with the contents described above The build ID is a special section in the executable file and in other ELF binary files that GDB may consider This section is often named note gnu build id but that name is not mandatory It contains unique identification for the built files the ID remains the same across multiple builds of the same build tree The default algorithm SHA1 produces 160 bits 40 hexadecimal characters of the content for the build ID string The same section with an identical value is present in the original built binary with symbols in its stripped variant and in the separate debugging information file The debugging information file itself should be an ordinary executable containing a full set of linker symbols sections and debugging information The sections of the debugging information file should have the same names addresses and siz
594. tas ood Galea bw Wu er E 30 detach remote 2 02 e500 le et rice eas es 172 detach fork fork id 5 eere ves 35 detach from task GNU Hurd 189 detach from thread GNU Hurd 189 digit argument M 0 M 1 M 311 dif ipee bed ea ce eer eh ac Pc e Ra 70 direct memory access DMA on MS DOS 184 directories for source files 00 69 directory ucc uae e LiT p RR EEG Y 70 directory compilation 000005 vail directory GUTTENE m eere RE yall di disable proinne neien na a Aii pE Aaa 47 disable RR Ras ER a a don Ces 47 disable display i iocus sss haeo 82 disable mem n o eek RR ROC SUR 93 disable trace point 2 25 sa eee pe 106 disable completion i 2 2e rie ees 299 disdssemble 22 2 em ER rer ERR E T2 disconnect 624 RE cece HIP re He 172 display edu roti i bes E En he deg eds 81 display command history lusus 209 display derived types 004 87 display disabled out of scope 82 display GDB copyright 23 display of expressions s lesse eese 81 display remote monitor communications 169 display remote packets 000005 214 DJGPP debugging eese 183 dli symbolS i e tela ewe geee ohare ed 185 DLLs with no debugging symbols 186 do down 22 so gece saarg idorani E IOn 64 do uppercase version M a M b M x
595. te program if you type the interrupt character often Ctr1 c GDB attempts to stop the program This may or may not succeed depending in part on the hardware and the serial drivers the remote system uses If you type the interrupt character once again GDB displays this prompt Interrupted while waiting for the program Give up and stop debugging it y or n If you type y GDB abandons the remote debugging session If you decide you want to try again later you can use target remote again to connect once more If you type n GDB goes back to waiting detach When you have finished debugging the remote program you can use the detach command to release it from GDB control Detaching from the target normally resumes its execution but the results will depend on your particular remote stub After the detach command GDB is free to connect to another target disconnect The disconnect command behaves like detach except that the target is gener ally not resumed It will wait for GDB this instance or another one to connect and continue debugging After the disconnect command GDB is again free to connect to another target monitor cmd This command allows you to send arbitrary commands directly to the remote monitor Since GDB doesn t care about the commands it sends like this this command is the way to extend GDB you can add new commands that only the external monitor will understand and implement Chapter 17 Debugging Remote P
596. ted Ee EE E E EEE 39 RDI heartbeat irem Eme 194 rdilogenabl 2 22 poo eR asias 193 rdilogfile ese o na Ra ipi pE pikasi 193 re read init file C x C r 312 read special object remote request 349 read file i o system call unsurunun 359 read only sections 000 tatan pi 159 reading symbols from relocatable object files 157 reading symbols immediately 156 readline os as Per bert ERE ERR doles 207 readnOW eene dd e OCDE deb EE a 156 receive rights GNU Hurd 189 recent tracepoint number sess 106 record aggregates Ada sssssssssse 138 record serial communications on file 175 recording a session script 292 Tedirecilon 22 urba AR d ERR RERO 29 redraw current line 307 reference Gard ias re PRE GIL EREE a 319 reference declarations 0 0000 127 refresliii cies d VR RU Rh ee Fdo nor Ree 228 register stack AMD29K 203 TeEISLefS verc ret ebbe br n FERRE ERE E 90 regs Superi sels gr e RYE VERSA 202 regular expression sseeeeeeeeee eese 39 reloading symbols 000222000 146 reloading the overlay table 115 relocatable object files reading symbols from 157 remote connection without stubs 173 remote debugging 0222000 171 remote memory comparison
597. ted from its parent process typically the shell but you can specify a new working directory in GDB with the cd command The GDB working directory also serves as a default for the commands that specify files for GDB to operate on See Section 15 1 Commands to Specify Files page 155 cd directory Set the GDB working directory to directory pwd Print the GDB working directory It is generally impossible to find the current working directory of the process being debugged since a program can change its directory during its run If you work on a system where GDB is configured with the proc support you can use the info proc command see Section 18 1 3 SVR4 Process Information page 181 to find out the current working directory of the debuggee 4 6 Your Program s Input and Output By default the program you run under GDB does input and output to the same terminal that GDB uses GDB switches the terminal to its own terminal modes to interact with you but it records the terminal modes your program was using and switches back to them when you continue running your program info terminal Displays information recorded by GDB about the terminal modes your program is using You can redirect your program s input and or output using shell redirection with the run command For example run gt outfile starts your program diverting its output to the file outfile Another way to specify where your program should do inpu
598. ted no longer exists it is forgotten With the clear command you can delete breakpoints according to where they are in your program With the delete command you can delete individual breakpoints watchpoints or catchpoints by specifying their breakpoint numbers Chapter 5 Stopping and Continuing 4T It is not necessary to delete a breakpoint to proceed past it GDB automatically ignores breakpoints on the first instruction to be executed when you continue execution without changing the execution address clear Delete any breakpoints at the next instruction to be executed in the selected stack frame see Section 6 3 Selecting a Frame page 64 When the innermost frame is selected this is a good way to delete a breakpoint where your program just stopped clear function clear filename function Delete any breakpoints set at entry to the named function clear linenum clear filename linenum Delete any breakpoints set at or within the code of the specified linenum of the specified filename delete breakpoints range Delete the breakpoints watchpoints or catchpoints of the breakpoint ranges specified as arguments If no argument is specified delete all breakpoints GDB asks confirmation unless you have set confirm off You can abbreviate this command as d 5 1 5 Disabling Breakpoints Rather than deleting a breakpoint watchpoint or catchpoint you might prefer to disable it This makes the breakpoint inoperative as if it h
599. terrupii v DR eb Re PEIPER bee ER 16 interrupt remote programs 175 interrupting remote programs 172 interrupting remote targets 179 interrupts remote protocol 354 invalid input 263600202 reep ipee gwen tears 291 invoke another interpreter 223 isatty file i o system call sess 362 isearch terminators ss sess 300 ISO 8859 1 character set 0 0000 96 ISO Latin 1 character set ssssssse 96 J Appendix H Index K IE packet erronis ER EE Ra dede 336 kernel crash dump isst Imre 181 kernel memory image seseseeesse 181 KGYMAP ie ici bead bas ddd rerata i Se RR REG AR 300 killoiisose ieu le rese RU ede tau REGE 2s 31 Kill FINS cs hide s BSR NS rU RES EIER 296 kill line O k 0 o eehnt patel ESPES EE 310 kill region 232025 vkeodei meee ee PRA eni 310 kill whole line 0 00s eee 310 kill word M d neni Ere RroREDRREAREE 310 kiling text ione rer Rete ere sede IS 296 E Vilis see dade DOE A E E ERES 181 E1386 cosas ud EAS UPEAEXI Bat RD dE 67 languages eei RC PRELMOPRERLETRERE TS 119 last tracepoint number 000 05 106 latest breakpoint 2 ioc 38 layout enotek Dna de das pue si Rp 227 DD ETE 183 leaving GDB reveren eRUEPRI RU e niad 16 LeftilobeerBREP CU ER REBEL 227 WIS K Vitis iecore ie deh ane Be eae pee ke 181 library list for
600. ters to objects or the objects themselves Thus the user may have to tack an extra all after an expression to get it printed properly Static constants that the compiler chooses not to materialize as objects in storage are invisible to the debugger Named parameter associations in function argument lists are ignored the argument lists are treated as positional Chapter 12 Using GDB with Different Languages 141 Many useful library packages are currently invisible to the debugger Fixed point arithmetic conversions input and output is carried out using floating point arithmetic and may give results that only approximate those on the host machine The type of the Address attribute may not be System Address The GNAT compiler never generates the prefix Standard for any of the standard symbols defined by the Ada language GDB knows about this it will strip the prefix from names when you use it and will never look for a name you have so qualified among local symbols nor match against symbols in other packages or subprograms If you have defined entities anywhere in your program other than parameters and local variables whose simple names match names in Standard GNAT s lack of qualification here can cause confusion When this happens you can usually resolve the confusion by qualifying the problematic names with package Standard explicitly 12 5 Unsupported Languages In addition to the other fully supported programming languages
601. tex the Texinfo definitions file TEX is a typesetting program it does not print files directly but produces output files called Dv files To print a typeset document you need a program to print DVI files If your system has TEX installed chances are it has such a program The precise command to use depends on your system lpr d is common another for PostScript devices is dvips The DVI print command may require a file name without any extension or a dvi extension TEX also requires a macro definitions file called texinfo tex This file tells TEX how to typeset a document written in Texinfo format On its own TEX cannot either read or typeset a Texinfo file texinfo tex is distributed with GDB and is located in the gdb version number texinfo directory If you have TEX and a DVI printer program installed you can typeset and print this manual First switch to the gdb subdirectory of the main source directory for example to gdb 6 7 50_20071011 gdb and type L In gdb 6 7 50_20071011 gdb refcard ps of the version 6 7 50 20071011 release 320 Debugging with GDB make gdb dvi Then give gdb dvi to your DVI printing program Appendix B Installing GDB 321 Appendix B Installing GDB B 1 Requirements for Building GDB Building GDB requires various tools and packages to be available Other packages will be used only if they are found Tools Packages Necessary for Building GDB
602. text after Switching to depends on your system s conventions for identifying threads thread apply threadno a11 command The thread apply command allows you to apply the named command to one or more threads Specify the numbers of the threads that you want affected with the command argument threadno It can be a single thread number one of the numbers shown in the first field of the info threads display or it could be a range of thread numbers as in 2 4 To apply a command to all threads type thread apply all command Whenever GDB stops your program due to a breakpoint or a signal it automatically selects the thread where that breakpoint or signal happened GDB alerts you to the context switch with a message of the form Switching to systag to identify the thread See Section 5 4 Stopping and Starting Multi thread Programs page 57 for more infor mation about how GDB behaves when you stop and start programs with multiple threads See Section 5 1 2 Setting Watchpoints page 43 for information about watchpoints in programs with multiple threads 4 10 Debugging Programs with Multiple Processes On most systems GDB has no special support for debugging programs which create addi tional processes using the fork function When a program forks GDB will continue to debug the parent process and the child process will run unimpeded If you have set a breakpoint in any code which the child then executes the child will g
603. th bit set to an ASCII key sequence by stripping the eighth bit and prefixing an character converting them to a meta prefixed key sequence The default value is on disable completion If set to On Readline will inhibit word completion Completion characters will be inserted into the line as if they had been mapped to self insert The default is off editing mode The editing mode variable controls which default set of key bind ings is used By default Readline starts up in Emacs editing mode where the keystrokes are most similar to Emacs This variable can be set to either emacs or vi enable keypad When set to on Readline will try to enable the application keypad when it is called Some systems need this to enable the arrow keys The default is off expand tilde If set to on tilde expansion is performed when Readline attempts word completion The default is off 300 Debugging with GDB history preserve point If set to on the history code attempts to place point at the same location on each history line retrieved with previous history or next history The default is off horizontal scroll mode This variable can be set to either on or off Setting it to on means that the text of the lines being edited will scroll horizontally on a single screen line when they are longer than the width of the screen instead of wrapping onto a new screen line
604. than at the address where your program stopped See Section 5 2 Continuing and Stepping page 52 The most common occasion to use the jump command is to back up perhaps with more breakpoints set over a portion of a program that has already executed in order to examine its execution in more detail 14 3 Giving your Program a Signal signal signal Resume execution where your program stopped but immediately give it the signal signal signal can be the name or the number of a signal For example on many systems signal 2 and signal SIGINT are both ways of sending an interrupt signal Alternatively if signal is zero continue execution without giving a signal This is useful when your program stopped on account of a signal and would ordinary see the signal when resumed with the continue command signal 0 causes it to resume without a signal signal does not repeat when you press a second time after executing the command Invoking the signal command is not the same as invoking the ki11 utility from the shell Sending a signal with kill causes GDB to decide what to do with the signal depending on the signal handling tables see Section 5 3 Signals page 56 The signal command passes the signal directly to your program 14 4 Returning from a Function return return expression You can cancel execution of a function call with the return command If you give an expression argument its value is used as the function s return value
605. that the symbol table for a source file is being read see symbol file in Section 15 1 Commands to Specify Files page 155 212 Debugging with GDB Set verbose on Enables GDB output of certain informational messages set verbose off Disables GDB output of certain informational messages show verbose Displays whether set verbose is on or off By default if GDB encounters bugs in the symbol table of an object file it is silent but if you are debugging a compiler you may find this information useful see Section 15 3 Errors Reading Symbol Files page 164 set complaints limit Permits GDB to output limit complaints about each type of unusual symbols before becoming silent about the problem Set limit to zero to suppress all com plaints set it to a large number to prevent complaints from being suppressed show complaints Displays how many symbol complaints GDB is permitted to produce By default GDB is cautious and asks what sometimes seems to be a lot of stupid questions to confirm certain commands For example if you try to run a program which is already running gdb run The program being debugged has been started already Start it from the beginning y or n If you are willing to unflinchingly face the consequences of your own commands you can disable this feature set confirm off Disables confirmation requests set confirm on Enables confirmation requests the default show confirm Displays state of
606. the corresponding error message exit GDB has terminated 24 6 2 GDB MI Stream Records GDB internally maintains a number of output streams the console the target and the log The output intended for each of these streams is funneled through the GDB MI interface using stream records Each stream record begins with a unique prefix character which identifies its stream see Section 24 3 2 GDB MI Output Syntax page 234 In addition to the prefix each stream record contains a string output This is either raw text with an implicit new line or a quoted C string which does not contain an implicit newline string output The console output stream contains text that should be displayed in the CLI console window It contains the textual responses to CLI commands Q string output The target output stream contains any textual output from the running target This is only present when GDB s event loop is truly asynchronous which is currently only the case for remote targets amp string output The log stream contains debugging messages being produced by GDB s internals 24 6 3 GDB MI Out of band Records Out of band records are used to notify the GDB MI client of additional changes that have oc curred Those changes can either be a consequence of GDB MI e g a breakpoint modified or a result of target activity e g target stopped The following is a preliminary list of possible out of band records In particular the
607. the following example the action list begins with collect commands in dicating the things to be collected when the tracepoint is hit Then in order to single step and collect additional data following the tracepoint a while stepping command is used followed by the list of things to be collected while stepping The while stepping command is terminated by its own separate end command Lastly the action list is terminated by an end command gdb trace foo gdb actions Enter actions for tracepoint 1 one per line gt collect bar baz gt collect regs gt while stepping 12 gt collect fp sp gt end end collect expri expr2 Collect values of the given expressions when the tracepoint is hit This com mand accepts a comma separated list of any valid expressions In addition to global static or local variables the following special arguments are supported regs collect all registers args collect all function arguments locals collect all local variables You can give several consecutive collect commands each one with a single argument or one collect command with several arguments separated by com mas the effect is the same 108 Debugging with GDB The command info scope see Chapter 13 Symbols page 143 is particularly useful for figuring out what data to collect while stepping n Perform n single step traces after the tracepoint collecting new data at each step The while stepping command is followed b
608. the limit the more bytes heuristic fence post must search and therefore the longer it takes to run You should only need to use this command when debugging a stripped executable show heuristic fence post Display the current limit These commands are available only when GDB is configured for debugging programs on Alpha or MIPS processors Several MIPS specific commands are available when debugging MIPS programs set mips abi arg Tell GDB which MIPS ABI is used by the inferior Possible values of arg are auto The default ABI associated with the current binary this is the default 932 064 n32 n64 eabi32 204 Debugging with GDB eabi64 auto show mips abi Show the MIPS ABI used by GDB to debug the inferior set mipsfpu show mipsfpu See Section 18 3 4 MIPS Embedded page 195 set mips mask address arg This command determines whether the most significant 32 bits of 64 bit MIPS addresses are masked off The argument arg can be on off or auto The latter is the default setting which lets GDB determine the correct value show mips mask address Show whether the upper 32 bits of MIPS addresses are masked off or not set remote mips64 transfers 32bit regs This command controls compatibility with 64 bit MIPS targets that transfer data in 32 bit quantities If you have an old MIPS 64 target that transfers 32 bits for some registers like SR and FSR and 64 b
609. the new top You can only do this if the prior command is yank or yank pop 27 4 5 Specifying Numeric Arguments digit argument M 0 M 1 M Add this digit to the argument already accumulating or start a new argument M starts a negative argument universal argument This is another way to specify an argument If this command is followed by one or more digits optionally with a leading minus sign those digits define the ar gument If the command is followed by digits executing universal argument again ends the numeric argument but is otherwise ignored As a special case if this command is immediately followed by a character that is neither a digit or minus sign the argument count for the next command is multiplied by four The argument count is initially one so executing this function the first time makes the argument count four a second time makes the argument count six teen and so on By default this is not bound to a key 27 4 6 Letting Readline Type For You complete TAB Attempt to perform completion on the text before point The actual completion performed is application specific The default is filename completion possible completions M List the possible completions of the text before point insert completions M Insert all completions of the text before point that would have been generated by possible completions menu complete Similar to complete but replaces the word to be completed wit
610. ther recently added stubs 17 4 1 What the Stub Can Do for You The debugging stub for your architecture supplies these three subroutines set_debug_traps This routine arranges for handle_exception to run when your program stops You must call this subroutine explicitly near the beginning of your program handle_exception This is the central workhorse but your program never calls it explicitly the setup code arranges for handle_exception to run when a trap is triggered handle_exception takes control when your program stops during execution for example on a breakpoint and mediates communications with GDB on the host machine This is where the communications protocol is implemented handle_exception acts as the GDB representative on the target machine It begins by sending summary information on the state of your program then con tinues to execute retrieving and transmitting any information GDB needs until you execute a GDB command that makes your program resume at that point handle_exception returns control to your own code on the target machine breakpoint Use this auxiliary subroutine to make your program contain a breakpoint De pending on the particular situation this may be the only way for GDB to get control For instance if your target machine has some sort of interrupt button you won t need to call this pressing the interrupt button transfers control to handle exception in effect to GDB On some machines simply r
611. they frequently need to deal with complicated situations such as different or unexpected values of variables and symbols changes in how the program being debugged is built etc GDB provides a set of flow control commands to deal with these complexities Using these commands you can write complex scripts that loop over data structures execute commands conditionally etc if else This command allows to include in your script conditionally executed com mands The if command takes a single argument which is an expression to evaluate It is followed by a series of commands that are executed only if the expression is true its value is nonzero There can then optionally be an else line followed by a series of commands that are only executed if the expression was false The end of the list is marked by a line containing end while This command allows to write loops Its syntax is similar to if the command takes a single argument which is an expression to evaluate and must be fol lowed by the commands to execute one per line terminated by an end These commands are called the body of the loop The commands in the body of while are executed repeatedly as long as the expression evaluates to true loop break This command exits the while loop in whose body it is included Execution of the script continues after that whiles end line loop continue This command skips the execution of the rest of the body of commands in the while loop in whose
612. thread info Command Synopsis thread info GDB Command No equivalent 250 Debugging with GDB Example N A The thread list all threads Command Synopsis thread list all threads GDB Command The equivalent GDB command is info threads Example N A The thread list ids Command Synopsis thread list ids Produces a list of the currently known GDB thread ids At the end of the list it also prints the total number of such threads GDB Command Part of info threads supplies the same information Example No threads present besides the main process gdb thread list ids done thread ids number of threads 0 gdb Several threads gdb thread list ids done thread ids thread id 3 thread id 2 thread id 1 number of threads 3 gdb The thread select Command Synopsis thread select threadnum Make threadnum the current thread It prints the number of the new current thread and the topmost frame for that thread GDB Command The corresponding GDB command is thread Chapter 24 The GDB MI Interface 251 Example exec next running gdb stopped reason end stepping range thread id 2 line 187 file devo gdb testsuite gdb threads linux dp c gdb thread list ids done thread ids thread id 3 thread id 2 thread id 1 number of threads 3 gdb thread select 3 done new thread id 3 frame level 0 func vprint
613. ti 288 commands for C9 ilolsseec erre Leeds 128 comitete pridd i 9 46 xp eov rare pe 19 comment begin 6 2 42 Ree eere 299 COMMON blocks Fortran 00 5 131 common targ t irrite p neresti dyna onim 168 compare seCtjohnsS ll ede nardi Rene 81 compatibility GDB MI and CLI 236 compilation directory 004 yall compiling on Sparclet 0 5 200 complete eR Eg BR Bee GG ee ee 22 complete TAB sec82e2oatsdereccedeas ees 311 Completion 05 vacet soak deeds ae gee 19 completion of quoted strings 20 completion query items 299 Foto 0 0 b 0g alk 0 een aan E X kate ee ed 49 conditional breakpoints 00 48 configuring GDB 2419 wec eRre ree bee ER 321 CONMTMALION 122ecebiIeerebeBeseema et pee es 212 console i o as part of file i o Lus 357 console interpreter ieccriireiierissri ias 223 console output in GDB MI sssseeeeee 235 constants in file i o protocol 365 eoi arie i ot DI rca gg pr RE ER E OY TE HH EO 53 CONMMUING sege cocus heec repere EG E bids 52 continuing threads 00000 58 control C and remote debugging 179 controlling terminal 05 29 convenience variables sss esee 88 convenience variables for tracepoints 112 Appendix H Index convenience variables initializing 8
614. tier napana beta aid sha dees Hades 35 restart checkpoint id lio Re de ee dn 36 f68tOX6 e 9 uer ee eae PEU ad ns 95 restore data from a file 0 94 result records in GDB MI 0 005 236 resuming execution 2 ar eene 52 RET repeat last command 19 retransmit timeout MIPS protocol 196 fet rn ad ev v ee ae lie beset bleed 151 returning from a function 151 revers search ev ei aprenia HP 69 reverse search history C r 308 revert line M r ace eceket ese gar RETE 312 rewind program state 22000 35 Right prc aspe pU UR nag PEE PEE 227 ROM at zero address RDI 193 Pino cp wer dq p RETE DR ERE ROI Hee aoe ERE 26 run to main procedure 0 27 run until specified location 54 TUNDIDE ceni ewe ERTER tebe ered eileen 26 running and debugging Sparclet programs 201 running VxWorks tasks 192 running on Sparclet 222 mum rends 200 IfWatCh hus des wisi apie Rp UU GU IRURE RO EROR 43 Appendix H Index un s SingleKey TUI key sseeeesessss 227 S SEP PREX c eaten ag nde 53 S paketoin eee Peto tub ede eden 337 S packet suc neve aaee MC ROME STRE EUR 337 save command history 04 208 save GDB output to a file 16 save tracepoints for future sessions 112 save tracepoints
615. tile registers are in use set remotecache on set remotecache off Set caching state for remote targets When ON use data caching By default this option is OFF Chapter 8 Examining Data 99 show remotecache Show the current state of data caching for remote targets info dcache Print the information about the data cache performance The information displayed includes the dcache width and depth and for each cache line how many times it was referenced and its data and state dirty bad ok etc This command is useful for debugging the data cache operation 100 Debugging with GDB Chapter 9 C Preprocessor Macros 101 9 C Preprocessor Macros Some languages such as C and C provide a way to define and invoke preprocessor macros which expand into strings of tokens GDB can evaluate expressions containing macro invocations show the result of macro expansion and show a macro s definition including where it was defined You may need to compile your program specially to provide GDB with information about preprocessor macros Most compilers do not include macros in their debugging information even when you compile with the g flag See Section 4 1 Compilation page 25 A program may define a macro at one point remove that definition later and then provide a different definition after that Thus at different points in the program a macro may have different definitions or have no definition at all If there is a curr
616. tly being debugged enter break Fruit create To list ten program lines around the initialize class method enter list NSText initialize In the current version of GDB the plus or minus sign is required In future versions of GDB the plus or minus sign will be optional but you can use it to narrow the search It is also possible to specify just a method name 130 Debugging with GDB break create You must specify the complete method name including any colons If your program s source files contain more than one create method you ll be presented with a numbered list of classes that implement that method Indicate your choice by number or type 0 to exit if none apply As another example to clear a breakpoint established at the makeKeyAndOrderFront method of the NSWindow class enter clear NSWindow makeKeyAndOrderFront 12 4 2 2 The Print Command With Objective C The print command has also been extended to accept methods For example print object hash will tell GDB to send the hash message to object and print the result Also an additional command has been added print object or po for short which is meant to print the description of an object However this command may only work with certain Objective C libraries that have a particular hook function _NSPrintForDebugger defined 12 4 3 Fortran GDB can be used to debug programs written in Fortran but it currently supports only the features of Fortran 7
617. to double when passed to an un prototyped function This is the default setting Set coerce float to double off Arguments of type float will be passed directly to unprototyped functions show coerce float to double Show the current setting of promoting float to double GDB needs to know the ABI used for your program s C objects The correct C ABI depends on which C compiler was used to build your application GDB only fully supports programs with a single C ABI if your program contains code using multiple C ABI s or if GDB can not identify your program s ABI correctly you can tell GDB which ABI to use Currently supported ABI s include gnu v2 for g versions before 3 0 gnu v3 for g versions 3 0 and later and hpaCC for the HP ANSI C compiler Other C compilers may use the gnu v2 or gnu v3 ABI s as well The default setting is auto show cp abi Show the C ABI currently in use set cp abi With no argument show the list of supported C ABI s set cp abi abi set cp abi auto Set the current C ABI to abi or return to automatic detection 19 7 Optional Warnings and Messages By default GDB is silent about its inner workings If you are running on a slow machine you may want to use the set verbose command This makes GDB tell you when it does a lengthy internal operation so you will not think it has crashed Currently the messages controlled by set verbose are those which announce
618. to its specifica tion But GDB does cause your multi threaded program to behave differently than it would without GDB Also GDB uses internal breakpoints in the thread library to monitor certain events such as thread creation and thread destruction When such an event happens a system call in another thread may return prematurely even though your program does not appear to stop Conversely whenever you restart the program all threads start executing This is true even when single stepping with commands like step or next In particular GDB cannot single step all threads in lockstep Since thread scheduling is up to your debugging target s operating system not controlled by GDB other threads may execute more than one statement while the current thread completes a single step Moreover in general other threads stop in the middle of a statement rather than at a clean statement boundary when the program stops You might even find your program stopped in another thread after continuing or even single stepping This happens whenever some other thread runs into a breakpoint a signal or an exception before the first thread completes whatever you requested On some OSes you can lock the OS scheduler and thus allow only a single thread to run set scheduler locking mode Set the scheduler locking mode If it is off then there is no locking and any thread may run at any time If on then only the current thread may run when the inferior
619. tocol specific representation of EINTR D 9 5 The Ctrl C Message If the Ctrl C flag is set in the GDB reply packet see Section D 9 4 The F Reply Packet page 356 the target should behave as if it had gotten a break message The meaning for the target is system call interrupted by SIGINT Consequentially the target should actually stop as with a break message and return to GDB with a TO2 packet Appendix D GDB Remote Serial Protocol 307 It s important for the target to know in which state the system call was interrupted There are two possible cases e The system call hasn t been performed on the host yet e The system call on the host has been finished These two states can be distinguished by the target by the value of the returned errno If it s the protocol representation of EINTR the system call hasn t been performed This is equivalent to the EINTR handling on POSIX systems In any other case the target may presume that the system call has been finished successfully or not and should behave as if the break message arrived right after the system call GDB must behave reliably If the system call has not been called yet GDB may send the F reply immediately setting EINTR as errno in the packet If the system call on the host has been finished before the user requests a break the full action must be finished by GDB This requires sending M or X packets as necessary The F packet may only be sent when
620. tributed the ISI Optimum V support Per Bothner Noboyuki Hikichi and Alessandro Forin contributed MIPS support Jean Daniel Fekete contributed Sun 386i support Chris Hanson improved the HP9000 support Noboyuki Hikichi and Tomoyuki Hasei contributed Sony News OS 3 support David Johnson con tributed Encore Umax support Jyrki Kuoppala contributed Altos 3068 support Jeff Law contributed HP PA and SOM support Keith Packard contributed NS32K support 4 Debugging with GDB Doug Rabson contributed Acorn Risc Machine support Bob Rusk contributed Harris Nighthawk CX UX support Chris Smith contributed Convex support and Fortran de bugging Jonathan Stone contributed Pyramid support Michael Tiemann contributed SPARC support Tim Tucker contributed support for the Gould NP1 and Gould Powern ode Pace Willison contributed Intel 386 support Jay Vosburgh contributed Symmetry support Marko Mlinar contributed OpenRISC 1000 support Andreas Schwab contributed M68K GNU Linux support Rich Schaefer and Peter Schauer helped with support of SunOS shared libraries Jay Fenlason and Roland McGrath ensured that GDB and GAS agree about several machine instruction sets Patrick Duval Ted Goldstein Vikram Koka and Glenn Engel helped develop remote debugging Intel Corporation Wind River Systems AMD and ARM contributed remote debugging modules for the 1960 VxWorks A29K UDI and RDI targets respectively Brian Fox is the author of the readline librari
621. ts listed below qXfer spu write annex offset data Write data to an spufs file on the target system The annex spec ifies which file to write it must be of the form id name where Appendix D GDB Remote Serial Protocol 351 id specifies an SPU context ID in the target process and name identifes the spufs file in that context to be accessed This packet is not probed by default the remote stub must re quest it by supplying an appropriate qSupported response see qSupported page 345 Reply nn nn hex encoded is the number of bytes written This may be fewer bytes than supplied in the request E00 The request was malformed or annex was invalid E nn The offset was invalid or there was an error encountered writing the data nn is a hex encoded errno value An empty reply indicates the object string was not recognized by the stub or that the object does not support writing qXfer object operation Requests of this form may be added in the future When a stub does not recognize the object keyword or its support for object does not recognize the operation keyword the stub must respond with an empty packet D 5 Register Packet Format The following g G packets have previously been defined In the below some thirty two bit registers are transferred as sixty four bits Those registers should be zero sign extended which to fill the space allocated Register bytes are transferr
622. u can be sure that you can get the text back in a different or the same place later When you use a kill command the text is saved in a kill ring Any number of consecutive kills save all of the killed text together so that when you yank it back you get it all The kill ring is not line specific the text that you killed on a previously typed line is available to be yanked back later when you are typing another line Here is the list of commands for killing text Chapter 27 Command Line Editing 297 C k Kill the text from the current cursor position to the end of the line M d Kill from the cursor to the end of the current word or if between words to the end of the next word Word boundaries are the same as those used by M f M DEL Kill from the cursor the start of the current word or if between words to the start of the previous word Word boundaries are the same as those used by M b C w Kill from the cursor to the previous whitespace This is different than M DEL because the word boundaries differ Here is how to yank the text back into the line Yanking means to copy the most recently killed text from the kill buffer C y Yank the most recently killed text back into the buffer at the cursor M y Rotate the kill ring and yank the new top You can only do this if the prior command is C y or M y 27 2 4 Readline Arguments You can pass numeric arguments to Readline commands Sometimes the argument acts as a repeat
623. u just use void exceptionHook 0 but if before calling set_debug_traps you set it to point to a function in your program that function is called when GDB continues after stopping on a trap for example bus error The function indicated by exceptionHook is called with one parameter an int which is the exception number 4 Compile and link together your program the GDB debugging stub for your target architecture and the supporting subroutines 5 Make sure you have a serial connection between your target machine and the GDB host and identify the serial port on the host 6 Download your program to your target machine or get it there by whatever means the manufacturer provides and start it 7 Start GDB on the host and connect to the target see Section 17 1 Connecting to a Remote Target page 171 Chapter 18 Configuration Specific Information 181 18 Configuration Specific Information While nearly all GDB commands are available for all native and cross versions of the de bugger there are some exceptions This chapter describes things that are only available in certain configurations There are three major categories of configurations native configurations where the host and target are the same embedded operating system configurations which are usually the same for several different processor architectures and bare embedded processors which are quite different from each other 18 1 Native This section des
624. ucces sive calls to yank last arg move back through the history list inserting the last argument of each line in turn The history expansion facilities are used to extract the last argument as if the history expansion had been specified Chapter 27 Command Line Editing 309 27 4 3 Commands For Changing Text delete char C d Delete the character at point If point is at the beginning of the line there are no characters in the line and the last character typed was not bound to delete char then return EOF backward delete char Rubout Delete the character behind the cursor A numeric argument means to kill the characters instead of deleting them forward backward delete char Delete the character under the cursor unless the cursor is at the end of the line in which case the character behind the cursor is deleted By default this is not bound to a key quoted insert C q or C v Add the next character typed to the line verbatim This is how to insert key sequences like C q for example tab insert M Insert a tab character self insert a b A 1 Insert yourself transpose chars C t Drag the character before the cursor forward over the character at the cursor moving the cursor forward as well If the insertion point is at the end of the line then this transposes the last two characters of the line Negative arguments have no effect transpose words M t Drag the word before point past the word
625. uding Andrew Cagney Stephane Carrez Randolph Chung Nick Duffek Richard Henderson Mark Ket tenis Grace Sainsbury Kei Sakamoto Yoshinori Sato Michael Snyder Andreas Schwab Jason Thorpe Corinna Vinschen Ulrich Weigand and Elena Zannoni helped with the migration of old architectures to this new framework Andrew Cagney completely re designed and re implemented GDB s unwinder framework this consisting of a fresh new design featuring frame IDs independent frame sniffers and the sentinel frame Mark Kettenis implemented the DWARF 2 unwinder Jeff Johnston the libunwind unwinder and Andrew Cagney the dummy sentinel tramp and trad unwinders The architecture specific changes each involving a complete rewrite of the architecture s frame code were carried out by Jim Blandy Joel Brobecker Kevin Buettner Andrew Cagney Stephane Carrez Randolph Chung Orjan Friberg Richard Henderson Daniel Jacobowitz Jeff Johnston Mark Kettenis Theodore A Roth Kei Sakamoto Yoshinori Sato Michael Snyder Corinna Vinschen and Ulrich Weigand Christian Zankel Ross Morley Bob Wilson and Maxim Grigoriev from Tensilica Inc contributed support for Xtensa processors Others who have worked on the Xtensa port of GDB in the past include Steve Tjiang John Newlin and Scott Foehner Debugging with GDB Chapter 1 A Sample GDB Session 7 1 A Sample GDB Session You can use this manual at your leisure to read all about GDB However a handfu
626. ulator for your target running on the same host you can omit the hostname For example to connect to port 1234 on your local machine target remote 1234 Note that the colon is still required here 172 Debugging with GDB target remote udp host port Debug using UDP packets to port on host For example to connect to UDP port 2828 on a terminal server named manyfarms target remote udp manyfarms 2828 When using a UDP connection for remote debugging you should keep in mind that the U stands for Unreliable UDP can silently drop packets on busy or unreliable networks which will cause havoc with your debugging session target remote command Run command in the background and communicate with it using a pipe The command is a shell command to be parsed and expanded by the system s com mand shell bin sh it should expect remote protocol packets on its standard input and send replies on its standard output You could use this to run a stand alone simulator that speaks the remote debugging protocol to make net connections using programs like ssh or for other similar tricks If command closes its standard output perhaps by exiting GDB will try to send it a SIGTERM signal If the program has already exited this will have no effect Once the connection has been established you can use all the usual commands to examine and change data and to step and continue the remote program Whenever GDB is waiting for the remo
627. ult is 3 seconds You can inspect both values with show timeout and show retransmit timeout These commands are only available when GDB is con figured for target mips idt ecoff The timeout set by set timeout does not apply when GDB is waiting for your program to stop In that case GDB waits forever because it has no way of knowing how long the program is going to run before stopping set syn garbage limit num Limit the maximum number of characters GDB should ignore when it tries to synchronize with the remote target The default is 10 characters Setting the limit to 1 means there s no limit show syn garbage limit Show the current limit on the number of characters to ignore when trying to synchronize with the remote system Chapter 18 Configuration Specific Information 197 set monitor prompt prompt Tell GDB to expect the specified prompt string from the remote monitor The default depends on the target pmon target PMON ddb target NECO10 lsi target PMON gt show monitor prompt Show the current strings GDB expects as the prompt from the remote monitor set monitor warnings Enable or disable monitor warnings about hardware breakpoints This has effect only for the 1si target When on GDB will display warning messages whose codes are returned by the 1si PMON monitor for breakpoint commands show monitor warnings Show the current setting of printing monitor warnings pmon command This com
628. unction page 151 to go back to the calling function or jump see Section 14 2 Continuing at a Different Address page 150 to go to an arbitrary location in your program A typical technique for using stepping is to set a breakpoint see Section 5 1 Breakpoints Watchpoints and Catchpoints page 37 at the beginning of the function or the section of your program where a problem is believed to lie run your program until it stops at that breakpoint and then step through the suspect area examining the variables that are interesting until you see the problem happen step Continue running your program until control reaches a different source line then stop it and return control to GDB This command is abbreviated s Warning If you use the step command while control is within a function that was compiled without debugging information ex ecution proceeds until control reaches a function that does have debugging information Likewise it will not step into a function which is compiled without debugging information To step through functions without debugging information use the stepi command described below The step command only stops at the first instruction of a source line This pre vents the multiple stops that could otherwise occur in switch statements for loops etc step continues to stop if a function that has debugging information is called within the line In other words step steps inside any functions called within the lin
629. union type which has no direct analogue in Modula 2 The operator see Section 8 1 Expressions page 75 while available with any lan guage is not useful with Modula 2 Its intent is to aid the debugging of dynamic arrays which cannot be created in Modula 2 as they can in C or C However because an address can be specified by an integral constant the construct type adrexp is still useful In GDB scripts the Modula 2 inequality operator is interpreted as the beginning of a comment Use lt gt instead 12 4 6 Ada The extensions made to GDB for Ada only support output from the GNU Ada GNAT compiler Other Ada compilers are not currently supported and attempting to debug executables produced by them is most likely to be difficult 12 4 6 1 Introduction The Ada mode of GDB supports a fairly large subset of Ada expression syntax with some extensions The philosophy behind the design of this subset is e That GDB should provide basic literals and access to operations for arithmetic deref erencing field selection indexing and subprogram calls leaving more sophisticated computations to subprograms written into the program which therefore may be called from GDB e That type safety and strict adherence to Ada language restrictions are not particularly important to the GDB user e That brevity is important to the GDB user Thus for brevity the debugger acts as if there were implicit with and use clauses in
630. unless you use set print address off The backtrace also shows the source file name and line number as well as the arguments to the function The program counter value is omitted if it is at the beginning of the code for that line number Chapter 6 Examining the Stack 63 Here is an example of a backtrace It was made with the command bt 3 so it shows the innermost three frames 0 m4 traceon obs 0x24eb0 argc 1 argv 0x2b8c8 at builtin c 993 1 0x6e38 in expand macro sym 0x2b600 at macro c 242 2 0x6840 in expand token obs 0x0 t 177664 td Oxf7fffb08 at macro c 71 More stack frames follow The display for frame zero does not begin with a program counter value indicating that your program has stopped at the beginning of the code for line 993 of builtin c If your program was compiled with optimizations some compilers will optimize away arguments passed to functions if those arguments are never used after the call Such opti mizations generate code that passes arguments through registers but doesn t store those arguments in the stack frame GDB has no way of displaying such arguments in stack frames other than the innermost one Here s what such a backtrace might look like 0 m4 traceon obs 0x24eb0 argc 1 argv 0x2b8c8 at builtin c 993 1 0x6e38 in expand macro sym lt value optimized out at macro c 242 2 0x6840 in expand token obs 0x0 t lt value optimized out td Oxf7fffb08 at macro c 71 More stac
631. uted values in which case the values themselves are recorded e GDB transmits the tracepoints and their associated expressions to the GDB agent running on the debugging target e The agent arranges to be notified when a trace point is hit Note that on some systems the target operating system is completely responsible for collecting the data see Section E 5 Tracing on Symmetrix page 376 e When execution on the target reaches a trace point the agent evaluates the expressions associated with that trace point and records the resulting values and memory ranges e Later when the user selects a given trace event and inspects the objects and expression values recorded GDB talks to the agent to retrieve recorded data as necessary to meet the user s requests If the user asks to see an object whose contents have not been recorded GDB reports an error 376 Debugging with GDB E 4 Varying Target Capabilities Some targets don t support floating point and some would rather not have to deal with long long operations Also different targets will have different stack sizes and different bytecode buffer lengths Thus GDB needs a way to ask the target about itself We haven t worked out the details yet but in general GDB should be able to send the target a packet asking it to describe itself The reply should be a packet whose length is explicit so we can add new information to the packet in future revisions of the agent without confusi
632. ution and modification are not covered by this License they are outside its scope The act of running the Program is not restricted and the output from the Program is covered only if its contents constitute a work based on the Program independent of having been made by running the Program Whether that is true depends on what the Program does 1 You may copy and distribute verbatim copies of the Program s source code as you receive it in any medium provided that you conspicuously and appropriately publish on each copy an appropriate copyright notice and disclaimer of warranty keep intact all the notices that refer to this License and to the absence of any warranty and give any other recipients of the Program a copy of this License along with the Program You may charge a fee for the physical act of transferring a copy and you may at your option offer warranty protection in exchange for a fee 2 You may modify your copy or copies of the Program or any portion of it thus forming a work based on the Program and copy and distribute such modifications or work under the terms of Section 1 above provided that you also meet all of these conditions a You must cause the modified files to carry prominent notices stating that you changed the files and the date of any change b You must cause any work that you distribute or publish that in whole or in part contains or is derived from the Program or any part thereof to be licensed as a whole at
633. vent debugging info The default is off show debug event Displays the current state of displaying GDB event debugging info set debug expression Turns on or off display of debugging info about GDB expression parsing The default is off show debug expression Displays the current state of displaying debugging info about GDB expression parsing set debug frame Turns on or off display of GDB frame debugging info The default is off show debug frame Displays the current state of displaying GDB frame debugging info set debug infrun Turns on or off display of GDB debugging info for running the inferior The default is off infrun c contains GDB s runtime state machine used for im plementing operations such as single stepping the inferior show debug infrun Displays the current state of GDB inferior debugging 214 Debugging with GDB set debug lin lwp Turns on or off debugging messages from the Linux LWP debug support Show debug lin lwp Show the current state of Linux LWP debugging messages set debug observer Turns on or off display of GDB observer debugging This includes info such as the notification of observable events show debug observer Displays the current state of observer debugging Set debug overload Turns on or off display of GDB C overload debugging info This includes info such as ranking of functions etc The default is off Show debug overload Displays the current state of displaying GDB C
634. vention for choosing one byte whose address serves as the address of the frame Usually this address is kept in a register called the frame pointer register see Section 8 10 Registers page 90 while execution is going on in that frame GDB assigns numbers to all existing stack frames starting with zero for the innermost frame one for the frame that called it and so on upward These numbers do not really exist in your program they are assigned by GDB to give you a way of designating stack frames in GDB commands Some compilers provide a way to compile functions so that they operate without stack frames For example the GCC option fomit frame pointer generates functions without a frame This is occasionally done with heavily used li brary functions to save the frame setup time GDB has limited facilities for dealing with these function invocations If the innermost function invocation has no stack frame GDB 62 Debugging with GDB nevertheless regards it as though it had a separate frame which is numbered zero as usual allowing correct tracing of the function call chain However GDB has no provision for frameless functions elsewhere in the stack frame args The frame command allows you to move from one stack frame to another and to print the stack frame you select args may be either the address of the frame or the stack frame number Without an argument frame prints the current stack frame select frame The select frame
635. viduals in the file etc SERVICE in the GNU Emacs distribution In any event we also recommend that you submit bug reports for GDB The preferred method is to submit them directly using GDB s Bugs web page Alternatively the e mail gateway can be used Do not send bug reports to info gdb or to help gdb or to any newsgroups Most users of GDB do not want to receive bug reports Those that do have arranged to receive bug gdb The mailing list bug gdb has a newsgroup gnu gdb bug which serves as a repeater The mailing list and the newsgroup carry exactly the same messages Often people think of posting bug reports to the newsgroup instead of mailing them This appears to work but it has one problem which can be crucial a newsgroup posting often lacks a mail path back to the sender Thus if we need to ask for more information we may be unable to reach you For this reason it is better to send bug reports to the mailing list The fundamental principle of reporting bugs usefully is this report all the facts If you are not sure whether to state a fact or leave it out state it Often people omit facts because they think they know what causes the problem and assume that some details do not matter Thus you might assume that the name of the 292 Debugging with GDB variable you use in an example does not matter Well probably it does not but one cannot be sure Perhaps the bug is a stray memory referenc
636. width 10 alignment 1 col_name addr colhdr Address width 40 alignment 2 col_name what colhdr What body bkpt number 1 type breakpoint disp keep enabled y addr 0x0001072c func main file recursive2 c fullname home foo recursive2 c line 4 times 0 bkpt number 2 type breakpoint disp del enabled y addr 0x00010774 func foo file recursive2 c 244 Debugging with GDB fullname home foo recursive2 c line 11 times 0 gdb break insert r foo int foo int int done bkpt number 3 addr 0x00010774 file recursive2 c fullname home foo recursive2 c line 11 times 0 gdb The break list Command Synopsis break list Displays the list of inserted breakpoints showing the following fields Number number of the breakpoint Type type of the breakpoint breakpoint or watchpoint Disposition should the breakpoint be deleted or disabled when it is hit keep or nokeep Enabled is the breakpoint enabled or no y or n Address memory location at which the breakpoint is set What logical location of the breakpoint expressed by function name file name line number Times number of times the breakpoint has been hit If there are no breakpoints or watchpoints the BreakpointTable body field is an empty list GDB Command The corresponding GDB command is info break Exa
637. with GDB fullname home foo bar devo gdb testsuite gdb mi basics c line 13 gdb exec continue running gdb stopped reason watchpoint scope wpnum 5 frame func callee3 args name strarg value 0x11940 A string argument file devo gdb testsuite gdb mi basics c fullname home foo bar devo gdb testsuite gdb mi basics c line 18 gdb Listing breakpoints and watchpoints at different points in the program execution Note that once the watchpoint goes out of scope it is deleted gdb break watch C done wpt number 2 exp C gdb break list done BreakpointTable nr_rows 2 nr_cols 6 hdr width 3 alignment 1 col_name number colhdr Num width 14 alignment 1 col_name type colhdr Type width 4 alignment 1 col_name disp colhdr Disp width 3 alignment 1 col_name enabled colhdr Enb width 10 alignment 1 col_name addr colhdr Address width 40 alignment 2 col_name what colhdr What body bkpt number 1 type breakpoint disp keep enabled y addr 0x00010734 func callee4 file devo gdb testsuite gdb mi basics c fullname home foo devo gdb testsuite gdb mi basics c line 8 times 1 bkpt inumber 2 type watchpoint disp keep enabled y addr what C times 0 gdb exec continue running gdb stopped reason watchpoint trigger wpt number 2 exp C value
638. y exceeds the threshold GDB prints the string lt repeats n times gt where n is the number of identical repetitions instead of displaying the identical elements themselves Setting the Chapter 8 Examining Data 85 threshold to zero will cause all elements to be individually printed The default threshold is 10 Show print repeats Display the current threshold for printing repeated identical elements Set print null stop Cause GDB to stop printing the characters of an array when the first NULL is encountered This is useful when large arrays actually contain only short strings The default is off show print null stop Show whether GDB stops printing an array on the first NULL character Set print pretty on Cause GDB to print structures in an indented format with one member per line like this 1 1 next 0x0 flags sweet 1 sour 1 meat 0x54 Pork set print pretty off Cause GDB to print structures in a compact format like this 1 next 0x0 flags sweet 1 sour 1 meat 0x54 Pork This is the default format show print pretty Show which format GDB is using to print structures set print sevenbit strings on Print using only seven bit characters if this option is set GDB displays any eight bit characters in strings or character values using the notation nnn This setting is best if you are working in English ASCII and you use the high order bit of characters as a marker or
639. y may be 32 bit or 64 bit depending on the target The org gnu gdb mips linux feature is optional It should contain a single register restart which is used by the Linux kernel to control restartable syscalls 386 Debugging with GDB F 4 3 M68K Features org gnu gdb m68k core org gnu gdb coldfire core org gnu gdb fido core One of those features must be always present The feature that is present determines which flavor of m86k is used The feature that is present should contain registers dO through d7 a0 through a5 fp sp ps and pc org gnu gdb coldfire fp This feature is optional If present it should contain registers fp0 through fp7 fpcontrol fpstatus and fpiaddr Appendix G GNU GENERAL PUBLIC LICENSE 387 Appendix G GNU GENERAL PUBLIC LICENSE Version 2 June 1991 Copyright 1989 1991 Free Software Foundation Inc 51 Franklin Street Fifth Floor Boston MA 02110 1301 USA Everyone is permitted to copy and distribute verbatim copies of this license document but changing it is not allowed Preamble The licenses for most software are designed to take away your freedom to share and change it By contrast the GNU General Public License is intended to guarantee your freedom to share and change free software to make sure the software is free for all its users This General Public License applies to most
640. y supplying an appropriate qSupported response see qSupported page 345 qXfer libraries read annex offset length Access the targets list of loaded libraries See Section D 10 Library List Format page 366 The annex part of the generic qXfer packet must be empty see qXfer read page 349 Targets which maintain a list of libraries in the program s memory do not need to implement this packet it is designed for platforms where the operating system manages the list of loaded libraries This packet is not probed by default the remote stub must re quest it by supplying an appropriate qSupported response see qSupported page 345 350 Debugging with GDB qXfer memory map read offset length Access the target s memory map See Section D 11 Memory Map Format page 367 The annex part of the generic qXfer packet must be empty see qXfer read page 349 This packet is not probed by default the remote stub must re quest it by supplying an appropriate qSupported response see qSupported page 345 qXfer spu read annex offset length Read contents of an spufs file on the target system The annex specifies which file to read it must be of the form id name where id specifies an SPU context ID in the target process and name identifes the spufs file in that context to be accessed This packet is not probed by default the remote stub must re quest it by supplying an appropriate
641. y the list of what to collect while stepping followed by its own end command gt while stepping 12 gt collect regs myglobal gt end gt You may abbreviate while stepping as ws or stepping 10 1 5 Listing Tracepoints info tracepoints num Display information about the tracepoint num If you don t specify a tracepoint number displays information about all the tracepoints defined so far For each tracepoint the following information is shown its number whether it is enabled or disabled its address its passcount as given by the passcount n command its step count as given by the while stepping n command where in the source files is the tracepoint set its action list as given by the actions command gdb info trace Num Enb Address PassC StepC What I y 0x002117c4 O 0 lt gdb_asm gt 2 y 0x0020dc64 O 0 in g_test at g_test c 1375 3 y 0x0020b1f4 0 0 in get_data at f00 c 41 gdb This command can be abbreviated info tp 10 1 6 Starting and Stopping Trace Experiments tstart This command takes no arguments It starts the trace experiment and begins collecting data This has the side effect of discarding all the data collected in the trace buffer during the previous trace experiment tstop This command takes no arguments It ends the trace experiment and stops collecting data Note a trace experiment and data collection may stop automatically if any tracepoint s passcount is reached see Section 10 1 3
642. y to set a new value with just set g 4 because GDB has the command set gnutarget abbreviated set g 150 Debugging with GDB gdb whatis g type double gdb p g 1 1 gdb set g 4 gdb p g 2 1 gdb r The program being debugged has been started already Start it from the beginning y or n y Starting program home smith cc_progs a out home smith cc_progs a out can t open to read symbols Invalid bfd target gdb show g The current BFD target is 4 The program variable g did not change and you silently set the gnutarget to an invalid value In order to set the variable g use gdb set var g 4 GDB allows more implicit conversions in assignments than C you can freely store an integer value into a pointer variable or vice versa and you can convert any structure to any other structure that is the same length or shorter To store values into arbitrary places in memory use the construct to generate a value of specified type at a specified address see Section 8 1 Expressions page 75 For example int 0x83040 refers to memory location 0x83040 as an integer which implies a certain size and representation in memory and set int 0x83040 4 stores the value 4 into that memory location 14 2 Continuing at a Different Address Ordinarily when you continue your program you do so at the place where it stopped with the continue command You can instead continue at an address
643. yntax sisse 233 GDB MI its purpose sseeee eee eee 233 GDB MI out of band records 237 GDB MI output syntax nne 234 GDB MI result records 000 236 GDB MI simple examples 0 238 GDB MI stream records 204 237 gdbarch debugging info 0 213 GDBHISTFILE environment variable 208 EgdbServer oadsses khe reds de 1E WG een 173 GDI ul dis ts eed sh ebanien aE dad genas 183 generate cor e fi le iia tinea weds ed xen 95 get thread local storage address remote request gid Sa UDr 343 getDebugChar iis ssid sear enea neis Ona add 179 gettimeofday file i o system call 362 global debugging information directory 161 GNU CFF be oi Taruni teens 2d eed daa cba 123 GNU EMACS erro rorida hbase eaday TREE as 231 GNU Hurd debugging 188 GNU Linux LWP debug messages 214 407 gnu debuglink crc32 s 163 H h help 2 eer Recibe PETRA idiki 21 H packet 559 epe Rep dade taney 336 WANG C555 ies olLrees eR ree arredi pari nos 56 handle exception cire e e ioi rest 178 handling signals tere 6b eco stead Gast 56 hardware breakpoints 0000000 39 hardware watchpoints 000005 43 hash mark while downloading 169 hbr ak l osscbR sees ood ert deed Y are RE eed 39 help Pose leeds Yum Eb egit 21 help target scriti 9 per ate
644. yntax The output from GDB MI consists of zero or more out of band records followed optionally by a single result record This result record is for the most recent command The sequence of output records is terminated by gdb If an input command was prefixed with a token then the corresponding output for that command will also be prefixed by that same token output gt out of band record result record gdb n1 result record token result class result nl out of band record gt async record stream record async record gt exec async output status async output notify async output exec async output gt token async output status async output token async output notify async output gt token async output async output async class result nl result class done running connected error exit Chapter 24 The GDB MI Interface 235 async class gt stopped others where others will be added depending on the needs this is still in development result gt variable value variable string value gt const tuple list const c string tuple is rn nyu result n result yu list KR L n value Wn value a result ow result j stream record gt console stream output target stream output log stream output console stream output gt uo c string target stream output
645. you connect to a VxWorks target on the network To connect to a target whose host name is tt type vxgdb target vxworks tt GDB displays messages like these Attaching remote machine across net Connected to tt GDB then attempts to read the symbol tables of any object modules loaded into the VxWorks target since it was last booted GDB locates these files by searching the directories listed in the command search path see Section 4 4 Your Program s Environment page 28 if it fails to find an object file it displays a message such as prog o No such file or directory When this happens add the appropriate directory to the search path with the GDB command path and execute the target command again 18 2 1 2 VxWorks Download If you have connected to the VxWorks target and you want to debug an object that has not yet been loaded you can use the GDB 1oad command to download a file from Unix to VxWorks incrementally The object file given as an argument to the load command is actually opened twice first by the VxWorks target in order to download the code then by GDB in order to read the symbol table This can lead to problems if the current working directories on the two systems differ If both systems have NFS mounted the same filesystems you can avoid these problems by using absolute paths Otherwise it is 192 Debugging with GDB simplest to set the working directory on both systems to the directory in which the object file
646. ys whether GDB will break on exceptions that happen inside the Cygwin DLL itself Set new console mode If mode is on the debuggee will be started in a new console on next start If mode is offi the debuggee will be started in the same console as the debugger show new console Displays whether a new console is used when the debuggee is started 186 Debugging with GDB set new group mode This boolean value controls whether the debuggee should start a new group or stay in the same group as the debugger This affects the way the Windows OS handles Ctr1 C show new group Displays current value of new group boolean set debugevents This boolean value adds debug output concerning kernel events related to the debuggee seen by the debugger This includes events that signal thread and process creation and exit DLL loading and unloading console interrupts and debugging messages produced by the Windows OutputDebugString API call set debugexec This boolean value adds debug output concerning execute events such as re sume thread seen by the debugger set debugexceptions This boolean value adds debug output concerning exceptions in the debuggee seen by the debugger set debugmemory This boolean value adds debug output concerning debuggee memory reads and writes by the debugger set shell This boolean values specifies whether the debuggee is called via a shell or di rectly default value is on show shell Displays if the

GDB User Manual - C programming language ressources

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