Wiki/gdb.md

GDB

• Compile code for GDB: -ggdb3

• Run code: gdb ./<compiledFile>

• Go to TUI: tui enable

• Start running: start

• Take one Step: step or s

• Go to end of function: finish

• Create Breakpoint: break <lineNr>

  • Go on with start
  • Go no breakpoint: c

• Inspect variable: print <ariable>

• Refresh window when "broken": ctrl + L

• Print: p

Debug Assembly

• Load file

• Enable assembly: layout asm

• Start at first instruction: starti

• Step through using stepi (si) and nexti (ni)

• Show top 10 elements of the stack: x/10x $sp

TUI

• Change window: CTRL + x o

• Previous/Next Command: CTRL + P/CTRL + N

• Change size: winheight <window> <+/-> <size>

  • When leaving out <+/-> it is set to absolute size

• Execute command n times: python [gdb.execute('<YOUR_COMMAND>') for x in range(n)]

• Disassemble function: disassemble <function>

Breakpoint

• At function + offset: b *FUNC+OFFSET
• At Address: b *ADDR

Stripped Binaries

Entry Point

• Sometimes this works: b __libc_start_main
  • Only works when dynamic libraries (libc) were loaded (which is only after start of program)
  • When hitting this breakpoint, GDB tells us the location of main, which is the first argument to __libc_start_main
• (gdb) info file tells the entry point address

x x/s x/10xw 32 bit x/10xX 64 bit

vmmap gives overwie of virtual memory