Support and document debugging with gdbgui

[arialwhite]

I figured out how to debug libopenage with gdbgui. It is a browser-based frontend to gdb built with Python and JavaScript.

gdbgui: https://github.com/cs01/gdbgui

This PR:

• Add a .gdbinit (gdb commands) to debug openage and break at main.cpp
• Document how to debug openage and how to do this with gdbgui

[TheJJ]

Hi! Thanks for your additions.
I wouldn't add the .gdbinit file. I would instead write a code block in the debugging documentation that this could be done. If ever, we should put that file to etc/gdbinit, but it will outdate there once the linenumbers change.
The best place is a "recommendation" in the debug.md.

We create a run executable which is a compiled version of run.py, which also embeds the interpreter. This allows to easily run gdb -ex 'set breakpoint pending on' -ex 'b openage::run_game' -ex run --args run game (which could be the recommended command line in the debug.md file or a -x command file).

-> I think it's better do not commit the .gdbinit file

Do you have other suggestions?

[arialwhite]

Thanks for the review I agree with you and will do some changes.

I have also tried to use python3-dbg instead of python3 to be able to do this:
https://wiki.python.org/moin/DebuggingWithGdb

But this looks not very useful, and I am currently blocked by the '_imaging' module of python3-pil.

I tried also on a dummy Cython project:
http://cython.readthedocs.io/en/latest/src/userguide/debugging.html

I would be nice to debug Cython code, but it looks to be a difficult task on a real project

[TheJJ]

Thanks :)
I fear you need to do a quick rebase to solve the conflict in copying.md.

[TheJJ]

In my setup I can debug cython and python code. My setup is mainly this (I wrote large parts of the article): https://wiki.gentoo.org/wiki/Debugging

So I have (relevant for openage):

sys-libs/glibc installsources debugsyms
dev-libs/libuv debugsyms installsources
media-libs/libsdl2 installsources debugsyms
media-libs/libepoxy installsources debugsyms
dev-lang/python installsources debugsyms
media-libs/opusfile installsources debugsyms

Most importantly, python is built with debug infos and source files are provided.
Python also installs gdb helper functions like py-bt and the like, or py-print, which you can use to examine stacktraces with python-vm calls (as described in the DebuggingWithGdb wiki page)

I've never used cython --gdb so far, but it seems like this would be rather easy to add to the buildsystem.

My debugging setup uses gdb and voltron and I just launch the run program, set a breakpoint or use our BREAKPOINT macro, that's it.

[arialwhite]

Thanks for your reply, I rebased my branch.

I was not aware of voltron it looks to be a great tool.