7

How to debug python script in C level using GDB. Give me a simple example for this.My primary goal is to get the trace of libc function called from my python script.

ankit jain
  • 350
  • 2
  • 12
  • 1
    Please say you're using `ctypes` or trying to do a low-level hack... And that you've got the debug version of Python. – wizzwizz4 Jul 26 '18 at 11:43
  • Yes, I am using python-devel version. Also I want to do a low-level hack – ankit jain Jul 26 '18 at 11:48
  • Oh, good. You get an up vote then. Any particular reason you've picked Python 2 for your hack? – wizzwizz4 Jul 26 '18 at 11:50
  • I need to go for both python 2 and 3.. starting from python 2 for now – ankit jain Jul 26 '18 at 11:57
  • You can follow instructions on https://wiki.python.org/moin/DebuggingWithGdb to debug python script. To get the trace of libc function you can set a breakpoint on it with `b `. – ks1322 Jul 27 '18 at 14:35

2 Answers2

4

See the thing is for binary(.so) files, you surely cannot apply breakpoint to a particular line, but surely you can apply breakpoint to a function. Say using 

(gdb) b func_name

you can easily apply breakpoint to a function and thereby obtain the backtrace whenever the breakpoint is found. First run your python sc

  1. Start gdb:

    gdb -ex r --args python demo.py

  2. Apply breakpoint:

    (gdb) b func_name

  3. Run:

    (gdb) run

This should work for your case.

laike9m
  • 18,344
  • 20
  • 107
  • 140
sumit_suthar
  • 412
  • 3
  • 15
  • So where would this look for function "func_name". I need to know this. This would play a crucial role in my case. – ankit jain Jul 27 '18 at 11:44
1

You can always Python using gdb and set breakpoints as you like

gdb -ex r --args python script.py args

If you want to look what happens in Python while running Python script I suggest to use mixed mode

gdb -ex r --args python -m pdb script.py

This way, you can break in pdb, then press Ctrl-C and end up inside gdb. Then, bt will give you stack trace inside Python.

Oo.oO
  • 12,464
  • 3
  • 23
  • 45
  • So where to add breakpoints in such a case? say for a c file abc.c, I add "b abc.c:10"... but for the python file, I cannot add the breakpoint directly to python as far as my understanding goes. The c files used here would be the binary(.so) files... how to add breakpoint to them now? – ankit jain Jul 27 '18 at 11:04
  • You also need: python-debuginfo package – Oo.oO Jul 27 '18 at 11:56