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gdb Cheatsheet

Open gdb

  • Start gdb with binary: gdb <binary>
  • Start gdb with binary and args: gdb --args <binary> <args>
  • Attach gdb to process: gdb -p <pid>
  • Open coredump: gdb <binary> <coredump of binary>

Handling Execution

  • Start execution: run

  • Start execution and break at start: start

  • Breakpoint at address: break *<addr>

  • Breakpoint at function: break <fun-name>

  • Breakpoint at functions matching regex: rbreak <prefix-name>.*

  • Breakpoint at source line: break <file>:<line-number>

  • List breakpoints: info breakpoints

  • Delete breakpoint: delete <breakpoint-no>

  • Run until next breakpoint: continue

  • Run until return of function: finish

  • Run program until condition is false: watch <condition>

  • Run program until address is read: rwatch *<addr>

  • Run program until address is written: watch *<addr>

  • Run program until address is read or written: awatch *<addr>

  • Step to next source-code instruction: step

  • Step to next assembly instruction: stepi or si

  • Step-over (source-line): next

  • Step-over (instruction): nexti

Altering Execution

  • Set register to a certain value: set <reg>=<value>, e.g., set $rax=1337

Concurrent Execution

  • List threads: info threads
  • Follow thread: thread <no>
  • Configure fork behavior: set follow-fork-mode <child|parent>

Memory

  • Print variable content: print <var-name>
  • Print memory: x/<num-bytes><unit><format> <addr>
    • <unit>:
      • b: Byte
      • h: Half-word (2 bytes)
      • w: Word (4 bytes)
      • g: Giant (8 bytes)
    • <format>:
      • s: C-string
      • c: character
      • i: instruction
      • d: decimal
      • x: hexa-decimal
      • b: binary
    • e.g. x/gx $rdi
  • Dump memory to a file: dump binary memory <out-filename> <memory-addr-start> <memory-addr-end>
    • note that the end address is exclusive
  • Show memory pages (gef-specific): vmmap

Gather Information

  • Show disassembly: disassemble
  • Show disassembly for function/address: disassemble <fun-name/addr>
  • Show functions: info functions
  • Show source-code: list <filename>:<fun-name/line-number>

Miscellaneous

  • Handling signals: handle <signal> <options>
    • <options>:
      • (no)print: (Don't) print a message upon catching signal
      • (no)stop: (Don't) stop the program upon catching signal
      • (no)pass: (Don't) pass the signal to debuggee upon catching signal
    • e.g. handle SIGSEGV nostop noprint pass (useful for debugging Java programs)

gef-specific

  • Heap-base: p $_heap()
  • Libc-base: p $_base("libc")
  • Binary-base: p $_base()
  • Show Address and surroundings telescope <addr>

gdb config (vanilla gdb)

Just add the following to ~/.gdbinit:

set disassembly intel
set print asm-demangle on
layout asm
layout regs
winheight REGS -2
winheight CMD -5
winheight ASM +5
focus cmd

some nice gdb helpers

The following tools really make your life in gdb easier and enhance the features gdb provides: