Debugging a program from assembly ( thanks to this tutorial! )

• compile such that it will correlate with the assembler
  • gcc -S foo.c
  • gcc -Wa,--gstabs, foo.s
    • it also seems acceptable to simply do gcc -g foo.s

• run it
  • gdb ./a.out
  • b main (easy way to find start of program)
  • r (run till breakpoint)
  • info registers (shows all registers)
  • p/x $eax (shows register eax in hex)
  • p/t $-16 (shows the number 16 in binary)
  • display/i $pc print instruction as you go

Misc

• Tell gdb to save its history
  • set history save on
  • It is convenient to put this in .gdbinit in the directory you are working in

• specify arguments for program at launch time
  • use the --args command... gdb --args ./mpg123 -C -a /dev/dsp1 /share/music/Trance/*

• set breakpoint: break <line # or function name&gt
  • info break - list breakpoints

• clear breakpoints: clear <line #, filename:line#, function>
  • delete all breakpoints: delete
  • delete breakpoint #2: delete 2
  • disable all breakpoints: disable

• memory dump:
  • dump 40 values starting at 10 bytes before the value pointed to by esp: x/40 ($esp - 10)

• memory write:
  • set {int}0x7fbffff71c = 4 sticks 4 at the shown memory location

• step, jump over function calls: n
• step, enter function calls: s
• start a run from the beginning: run
• continue till next breakpoint: c
• continue till return to guy that called you finish
• call stack (backtrace): bt

• print: p <variable>
  • print in hex: p/x <variable>
    • ...or x &<variable>
  • show a value at each prompt: display <value>
  • stop showing values at each prompt: undisplay
  • print sse registers in hex: p/x $xmm0

• • x/2d $rsp - print two 4-byte words starting at address in $rsp in decimal
  • x/g  $rsp - print one 8-byte word starting at address in $rsp.
  • x/gd $rsp - print one 8-byte word starting at address in $rsp in decimal
  • x/20b sum - print first 20 opcode bytes of function sum
  • x/10i sum - print first 10 instructions of function sum

• show all registers
  • info registers

• program list: l with...
  • line number - list centered around this line
  • function name - list from start of function

• tell gdb to catch a signal, but also let the debugged program catch it
  • handle SIGINT pass

-- MattWalsh - 03 Aug 2004