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Debugging Python with gdb

·2 mins

Here’s a quick reference for getting set up to debug Python with gdb, aimed at Debian and Ubuntu users.

Although I’d love to make this a full-fledged write up, it’s going to have to be a note to my future self for now.

It assumes you have virtualenvwrapper installed.

  1. Get all of the things we need for Python debugging:

    sudo apt-get install python2.7-dbg python2.7-dev gdb
  2. Make sure we use Python with debugging symbols:

    mkvirtualenv -p python2.7-dbg $PROJECT-dbg
  3. Install dependencies with their debugging symbols:

    pip install --no-binary :all: --global-option build --global-option debug -e .
  4. Make Python GDB extensions available in virtualenv:

    ln -s /usr/lib/debug/usr/bin/ ~/.virtualenvs/$PROJECT-dbg/bin`

Once that’s set up, a handy thing is to run tests in gdb over and over again until they segfault:

gdb -ex r --args python ~/.virtualenvs/$PROJECT-dbg/bin/trial -u testcase

You might see errors about C files that can’t be found. Pay them no mind. If you had the libc6 source code in the right location, they would go away, and you’d learn very little about your Python program.

Core #

I have literally no idea how Ubuntu handles core dumps by default. Here’s what I ended up doing:

$ ulimit -c unlimited

Then, as root:

$ echo "core" > c/proc/sys/kernel/core_pattern

This means core will be dumped in the current working directory.

Note: if you are using trial, the coredump will be in _trial_temp/core.

Note: for it to be any use at all, you have to have a coredump from a debugging build of Python.