GDB QUICK REFERENCE GDB Version 4 Breakpoints and Watchpoints Execution Control break [file:]line set breakpoint at line number [in file] continue [count] continue running; if count specified, ignore Essential Commands b [file:]line eg: break main.c:37 c [count] this breakpoint next count times gdb program [core] debug program [using coredump core] break [file:]func set breakpoint at func [in file] step [count] execute until another line reached; repeat b [file:]function set breakpoint at function [in file] break +offset set break at offset lines from current stop s [count] count times if specified break -offset run [arglist] start your program [with arglist] break *addr set breakpoint at address addr stepi [count] step by machine instructions rather than bt backtrace: display program stack break set breakpoint at next instruction si [count] source lines p expr display the value of an expression break . . . if expr break conditionally on nonzero expr c continue running your program next [count] execute next line, including any function n next line, stepping over function calls cond n [expr] new conditional expression on breakpoint n [count] calls s next line, stepping into function calls n; make unconditional if no expr tbreak . . . temporary break; disable when reached nexti [count] next machine instruction rather than rbreak regex break on all functions matching regex ni [count] source line Starting GDB watch expr set a watchpoint for expression expr gdb start GDB, with no debugging files catch event break at event, which may be catch, until [location] run until next instruction (or location) gdb program begin debugging program throw, exec, fork, vfork, load, or finish run until selected stack frame returns gdb program core debug coredump core produced by unload. return [expr] pop selected stack frame without program info break show defined breakpoints executing [setting return value] gdb --help describe command line options info watch show defined watchpoints signal num resume execution with signal s (none if 0) jump line resume execution at specified line number Stopping GDB clear delete breakpoints at next instruction jump *address or address quit exit GDB; also q or EOF (eg C-d) clear [file:]fun delete breakpoints at entry to fun() set var=expr evaluate expr without displaying it; use for altering program variables INTERRUPT (eg C-c) terminate current command, or clear [file:]line delete breakpoints on source line send to running process delete [n] delete breakpoints [or breakpoint n] Display Getting Help disable [n] disable breakpoints [or breakpoint n] print [/f ] [expr] show value of expr [or last value $] help list classes of commands p /f expr according to format f: enable [n] enable breakpoints [or breakpoint n] [ ] [ ] help class one-line descriptions for commands in x hexadecimal class enable once [n] enable breakpoints [or breakpoint n]; d signed decimal help command describe command disable again when reached u unsigned decimal enable del [n] enable breakpoints [or breakpoint n]; o octal Executing your Program delete when reached t binary ignore n count ignore breakpoint n, count times a address, absolute and relative run arglist start your program with arglist c character run start your program with current argument f floating point list commands n execute GDB command-list every time run . . . outf start your program with input, output [silent] breakpoint n is reached. [silent call [/f ] expr like print but does not display void command-list redirected suppresses default display] x [/Nuf ] expr examine memory at address expr; optional kill kill running program end end of command-list format spec follows slash N count of how many units to display tty dev use dev as stdin and stdout for next run Program Stack u unit size; one of set args arglist specify arglist for next run b individual bytes set args specify empty argument list backtrace [n] print trace of all frames in stack; or of n h halfwords (two bytes) show args display argument list bt [n] frames—innermost if n>0, outermost if w words (four bytes) n<0 g giant words (eight bytes) show env show all environment variables frame [n] select frame number n or frame at address f printing format. Any print format, or show env var show value of environment variable var n; if no n, display current frame s null-terminated string set env var string set environment variable var up n select frame n frames up i machine instructions unset env var remove var from environment down n select frame n frames down disassem [addr] display memory as machine instructions info frame [addr] describe selected frame, or frame at addr Shell Commands info args arguments of selected frame info locals local variables of selected frame Automatic Display cd dir change working directory to dir pwd Print working directory info reg [rn]. . . register values [for regs rn] in selected display [/f ] expr show value of expr each time program make . . . call “make” info all-reg [rn] frame; all-reg includes floating point stops [according to format f ] shell cmd execute arbitrary shell command string display display all enabled expressions on list undisplay n remove number(s) n from list of automatically displayed expressions [ ] surround optional arguments . . . show one or more arguments disable disp n disable display for expression(s) number n enable disp n enable display for expression(s) number n c 1998 Free Software Foundation, Inc. Permissions on back info display numbered list of display expressions Expressions Controlling GDB Source Files expr an expression in C, C++, or Modula-2 set param value set one of GDB’s internal parameters dir names add directory names to front of source (including function calls), or: show param display current setting of parameter path addr@len an array of len elements beginning at Parameters understood by set and show: dir clear source path addr complaint limit number of messages on unusual symbols show dir show current source path file::nm a variable or function nm defined in file confirm on/off enable or disable cautionary queries list show next ten lines of source {type}addr read memory at addr as specified type editing on/off control readline command-line editing list - show previous ten lines $ most recent displayed value height lpp number of lines before pause in display list lines display source surrounding lines, specified $n nth displayed value language lang Language for GDB expressions (auto, c or as: $$ displayed value previous to $ modula-2) file: num line number in named file $$n nth displayed value back from $ listsize n number of lines shown by list [ ] [ ] $ last address examined with x prompt str use str as GDB prompt [file:]function beginning of function [in named file] $ value at address $ radix base octal, decimal, or hex number +off off lines after last printed $var convenience variable; assign any value representation -off off lines previous to last printed verbose on/off control messages when loading symbols *address line containing address show values [n] show last 10 values [or surrounding $n] width cpl number of characters before line folded list f,l from line f to line l show conv display all convenience variables write on/off Allow or forbid patching binary, core files info line num show starting, ending addresses of (when reopened with exec or core) compiled code for source line num history . . . groups with the following options: info source show name of current source file Symbol Table h . . . info sources list all source files in use info address s show where symbol s is stored h exp off/on disable/enable readline history expansion forw regex search following source lines for regex info func [regex] show names, types of defined functions h file filename file for recording GDB command history rev regex search preceding source lines for regex (all, or matching regex) h size size number of commands kept in history list h save off/on control use of external file for command info var [regex] show names, types of global variables (all, history GDB under GNU Emacs or matching regex) M-x gdb run GDB under Emacs print . . . groups with the following options: whatis [expr] show data type of expr [or $] without C-h m describe GDB mode p . . . ptype expr evaluating; ptype gives more detail M-s step one line (step) [ ] p address on/off print memory addresses in stacks, values ptype type describe type, struct, union, or enum M-n next line (next) p array off/on compact or attractive format for arrays M-i step one instruction (stepi) p demangl on/off source (demangled) or internal form for C-c C-f finish current stack frame (finish) GDB Scripts C++ symbols M-c continue (cont) source script read, execute GDB commands from file p asm-dem on/off demangle C++ symbols in machine- M-u up arg frames (up) script instruction output M-d down arg frames (down) p elements limit number of array elements to display C-x & copy number from point, insert at end define cmd create new GDB command cmd; execute p object on/off print C++ derived types for objects C-x SPC (in source file) set break at point command-list script defined by command-list p pretty off/on struct display: compact or indented end end of command-list p union on/off display of union members document cmd create online documentation for new GDB GDB License help-text command cmd p vtbl off/on display of C++ virtual function tables show copying Display GNU General Public License end end of help-text show commands show last 10 commands show warranty There is NO WARRANTY for GDB. show commands n show 10 commands around number n Display full no-warranty statement. Signals show commands + show next 10 commands handle signal act specify GDB actions for signal: print announce signal Working Files noprint be silent for signal file [file] use file for both symbols and executable; stop halt execution on signal Copyright c 1991, ’92, ’93, ’98 Free Software Foundation, Inc. with no arg, discard both nostop do not halt execution Roland H. Pesch pass allow your program to handle signal core [file] read file as coredump; or discard The author assumes no responsibility for any errors on this card. nopass do not allow your program to see signal exec [file] use file as executable only; or discard info signals show table of signals, GDB action for each This card may be freely distributed under the terms of the GNU symbol [file] use symbol table from file; or discard General Public License. load file dynamically link file and add its symbols Please contribute to development of this card by annotating it. Debugging Targets add-sym file addr read additional symbols from file, Improvements can be sent to [email protected]. target type param connect to target machine, process, or file dynamically loaded at addr help target display available targets info files display working files and targets in use GDB itself is free software; you are welcome to distribute copies of attach param connect to another process path dirs add dirs to front of path searched for it under the terms of the GNU General Public License. There is detach release target from GDB control executable and symbol files absolutely no warranty for GDB. show path display executable and symbol file path info share list names of shared libraries currently loaded