Appendix: Quick Reference

• Starting GDB
  • gdb <program>: debug the program <program>
  • gdb <program> <core>: debug the program <program> with core file <core>
  • gdb -p <pid>: debug the running program with PID <pid>
  • ulimit -S -c unlimited: allow the system to produce core files of unlimited size [shell command, not gdb]
  • ulimit -S -c 0: limit core file sizes to 0 bytes (ie, disable core dumps) [shell command, not gdb]
• Running a Program
  • run: run the program without command-line arguments
  • run <arg1> [<arg2>...]: run the program with command-line arguments
• Setting Breakpoints
  • break <function>: set a breakpoint at the first instruction of <function>
  • break *<function> + <offset>: set a breakpoint at the instruction <offset> bytes from the start of function <function>
  • break <line>: set a breakpoint at line <line>
  • break <file>:<line>: set a breakpoint at line <line> in source file <file>
• Controlling Execution
  • next: execute one source code statement in the current function
  • next <num>: run next <num> times
  • step: execute one source code statement, descending into other functions if appropriate
  • step <num>: run step <num> times
  • stepi: execute one instruction
  • stepi <num>: run stepi <num> times
  • continue: run until a breakpoint is encountered or the program terminates
• Examining the Code
  • disassemble: display the assembly code for the current function
  • disassemble <function>: display the assembly code for the function <function>
  • disassemble/r: like disassemble, but includes the raw bytes of each instruction
  • disassemble/s: like disassemble, but groups instructions with corresponding lines of source code, which are also displayed
  • disassemble/rs: combines /r and /s options
• Viewing the Backtrace
  • where, bt, backtrace: displays the program’s stack frames, starting with the function containing the instruction pointer
• Changing the Current Function View
  • up: change the active stack frame to the current frame’s caller
  • down: change the active stack frame to the current frame’s callee
• Inspecting Frame Information
  • info frame: display stack frame information for the active stack frame
  • info frame <num>: display stack frame information for the frame <num>, which is numbered the same as in the backtrace
• Local Variables
  • info locals: display the current function’s local variables, with values
  • info args: display the current function’s arguments, with values
  • print <expression>: print the value of <expression>
  • set variable <var> = <val>: set the variable <var> to <val>
• Registers
  • info registers: display all registers and their values
  • info registers <reg1> [<reg2> ...]: display the specified registers and their values
  • print $<reg>: print the value of register <reg>
  • set $<reg> = <val>: set the value of register <reg> to <val>
• Examining Memory
  • x <addr-expression>: examine the memory specified by <addr-expression>
  • x/<fmt> <addr-expression>: examine the memory specified by <addr-expression> with the format string <fmt>
• Format Strings
  • <N>: repeat count of <N> items, where each item is determined by the format and size letters
  • format letter
    • t: binary
    • o: octal
    • d: decimal
    • u: unsigned decimal
    • x: hexadecimal
    • z: 0-padded hexadecimal
    • f: floating-point
    • a: address
    • i: instruction
    • c: character
    • s: string
  • size letter
    • b: bytes
    • h: half-word (2 bytes)
    • w: word (4 bytes)
    • g: giant (8 bytes)