notes

Debugging using gdb

Before debugging

  1. Complile your programm with debug information

     gcc -g<0,1,2,3> # 3 shows all debug info

  2. Turn off optimization level

     gcc -o<0,1,2,3> # 0 means without optimization

  3. To show to the compilator that we will use gdb to debug use. Within linux platform it’s the same as gcc -g3

     gcc -ggdb

Running debuger

  1. Run your executable

     gdb ./executable

  2. If we have core dumb (memory image before process crash) and want to restore this moment in memory.

     gdb ./executable -c core

    • to record core dumb we need to run the following command before our executable file

        ulimit -c unlimited

  3. If we want to attach to working process

     gdb -p pid

Getting information

  1. help
  2. info - show info about current state
    • args
    • breakpoints
    • watchpoints
    • registers
    • threads
    • signals
  3. where - shows stack

Execution

  1. r/run
  2. r/run args
  3. c/continue
  4. c/continue breaks-number-to-ignore - continue ignore break
  5. finish - continue to the end of function
  6. kill
  7. q/quit

Line execution

  1. step (into a function)
  2. next (next line of code)
  3. until line-number
  4. stepi/nexti step for assembler instruction

Break and watch

  1. break function/line

  2. break +/- relative-position

     break +3
  3. break filename:line
  4. break filename:function
  5. break ... if condition
  6. break line thread tid
  7. enable/disable
  8. watch condition

Stack Inspection

  1. bt/backstrace - show stack frames
  2. f/frame [number] - change to frame to [number]
  3. up/down number - go up and down inside stack
  4. info frame - go into stack frame

Variable and sources

  1. list +n -n - show source code
  2. set listsize num - set source code size
  3. p/print[format] variable print using format (x, o, d, f, c)