How to debug python script in C level using GDB. Give me a simple example for this

Question

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.

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
– wizzwizz4, Commented Jul 26, 2018 at 11:43
Yes, I am using python-devel version. Also I want to do a low-level hack — ankit jain
– ankit jain, Commented Jul 26, 2018 at 11:48
Oh, good. You get an up vote then. Any particular reason you've picked Python 2 for your hack? — wizzwizz4
– wizzwizz4, Commented Jul 26, 2018 at 11:50
I need to go for both python 2 and 3.. starting from python 2 for now — ankit jain
– ankit jain, Commented Jul 26, 2018 at 11:57
You can follow instructions on 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 <libc function name>. — ks1322
– ks1322, Commented Jul 27, 2018 at 14:35

laike9m · Accepted Answer · 2020-04-26 22:57:34Z

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

Start gdb:
```
gdb -ex r --args python demo.py
```
Apply breakpoint:
```
(gdb) b func_name
```
Run:
```
(gdb) run
```

This should work for your case.

edited Apr 26, 2020 at 22:57

laike9m

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answered Jul 27, 2018 at 11:28

sumit_suthar

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1 Comment

ankit jain Over a year ago

So where would this look for function "func_name". I need to know this. This would play a crucial role in my case.

Oo.oO · Accepted Answer · 2018-07-27 11:57:51Z

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.

edited Jul 27, 2018 at 11:57

answered Jul 27, 2018 at 8:07

Oo.oO

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2 Comments

ankit jain Over a year ago

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?

Oo.oO Over a year ago

You also need: python-debuginfo package

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