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Debugging a Mixed Python and C Language Stack

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Re: Debugging a Mixed Python and C Language Stack

#11
post #2

GDB can decode Python stack traces as Python code, as long as you have have python-gdb.py from the Python source distribution in the same place as your Python executable.

Wow, that's pretty amazing. I wonder how it's implemented, and if there are any tutorials on implementing something similar, for programming language designers/creators.

I think it uses gdb's frame filter API: https://sourceware.org/gdb/onlinedocs/gdb/Writing-a-Frame-Fi...

Re: Debugging a Mixed Python and C Language Stack

#12
post #2

GDB can decode Python stack traces as Python code, as long as you have have python-gdb.py from the Python source distribution in the same place as your Python executable.

From https://github.com/jupyterlab/debugger/issues/284 en ENH: Mixed Python/C debugging (GDB,) #284

> "Users can do [mixed mode] debugging with GDB (and/or other debuggers) and log the session in a notebook; in particular in order to teach.

> Your question is specifically about IDEs with support for mixed-mode debugging (with gdb), so I went looking for an answer:

> https://wiki.python.org/moin/DebuggingWithGdb (which is not responsive and almost unreadable on a mobile device) links to https://fedoraproject.org/wiki/Features/EasierPythonDebuggin... , which mentions the py-list, py-up and py-down, py-bt, py-print, and py-locals GDB commands that are also described in * https://devguide.python.org/gdb/ *

> https://wiki.python.org/moin/PythonDebuggingTools Ctrl-F "gdb" mentions: DDD, pyclewn (vim), trepan3k (which is gdb-like and supports breaking at c-line and also handles bytecode disassembly)

> Apparently, GHIDRA does not have a debugger but there is a plugin for following along with gdb in ghidra called https://github.com/Comsecuris/gdbghidra [...] https://github.com/Comsecuris/gdbghidra/blob/master/data/gdb... (zero dependencies)

> https://reverseengineering.stackexchange.com/questions/1392/... lists a number of GUIs for GDB; including voltronnn:

>> There's Voltron, which is an extensible Python debugger UI that supports LLDB, GDB, VDB, and WinDbg/CDB (via PyKD) and runs on macOS, Linux and Windows. For the first three it supports x86, x86_64, and arm with even arm64 support for lldb while adding even powerpc support for gdb. https://github.com/snare/voltron

> "The GDB Python API" https://developers.redhat.com/blog/2017/11/10/gdb-python-api... describes the GDB Python API.

> https://pythonextensionpatterns.readthedocs.io/en/latest/deb... may be helpful [for writing-a-c-function-to-call-any-python-unit-test]

> The GDB Python API docs: https://sourceware.org/gdb/onlinedocs/gdb/Python-API.html

> The devguide gdb page may be the place to list IDEs with support for mixed-mode debugging of Python and C/C++/Cython specifically with gdb?

These days, we have CFFI and Apache Arrow for C+Python etc.

Re: Debugging a Mixed Python and C Language Stack

#13

That reminds me of the time I debugged some code (also neural network) that was in both Java and C++ and I was able to attach both gdb and jdb to the same process but had to disable the segfault trap on gdb because the jvm segfaults all the time in normal operation.

Which reminds me that with IntelliJ you can get a really nice combo for debugging Java/C/C++ code: https://youtu.be/8Cjeq4l5COU

Re: Debugging a Mixed Python and C Language Stack

#14
post #7

Earlier quoted context omitted.

Wow, that's pretty amazing. I wonder how it's implemented, and if there are any tutorials on implementing something similar, for programming language designers/creators.

Theres also Py Spy, a profiling tool that can generate flame charts containing a mix of python and C (or C++) calls. https://github.com/benfred/py-spy It's worked really well for my needs

py-spy also makes it very easy to scrape from existing processes, which is invaluable if you are e.g. ever trying to diagnose a deadlock

Re: Debugging a Mixed Python and C Language Stack

#15
post #2

GDB can decode Python stack traces as Python code, as long as you have have python-gdb.py from the Python source distribution in the same place as your Python executable.

What I would love is also to be able to set python breakpoints from gdb. And integration with rr, so I could reverse-continue to said breakpoints. And ponies.

Re: Debugging a Mixed Python and C Language Stack

#16
post #2

GDB can decode Python stack traces as Python code, as long as you have have python-gdb.py from the Python source distribution in the same place as your Python executable.

GDB does so much cool. It just sucks that it's missing a high quality front-end. I know there are a bunch out there, but they all seem pretty janky and get confused a lot; I just want a really serious group of people (some Red Hat people for example) to make a high quality native debugging app which properly speaks the GDB protocol and handles all the edge cases.

(And no, I don't want it integrated into an IDE.)

Re: Debugging a Mixed Python and C Language Stack

#17

That reminds me of the time I debugged some code (also neural network) that was in both Java and C++ and I was able to attach both gdb and jdb to the same process but had to disable the segfault trap on gdb because the jvm segfaults all the time in normal operation.

As a C++ developer, I'm struggling to understand how and why segfaults would ever be part of normal operation. In my mental model, the presence of a segfault means that a program has gone so far off the expected path that no guarantees can be made about its state whatsoever, so the only safe thing to do is to let the program crash. Is there a reason why the JVM regularly segfaults?

Re: Debugging a Mixed Python and C Language Stack

#18
It's unfortunate that no one thinks about the debugging experience with anything they build today. It's always a "strap yourself in" experience like in the post.

I dream of an IDE that is one-click, full-stack, local debug.

I dropped some ideas here: https://news.ycombinator.com/item?id=35650253

Re: Debugging a Mixed Python and C Language Stack

#19
post #2

GDB can decode Python stack traces as Python code, as long as you have have python-gdb.py from the Python source distribution in the same place as your Python executable.

From https://github.com/jupyterlab/debugger/issues/284 en ENH: Mixed Python/C debugging (GDB,) #284 > "Users can do [mixed mode] debugging with GDB (and/or other debuggers) and log the session in a notebook; in particular in order to teach. > Your question is specifically about IDEs with support for mixed-mode debugging (with gdb), so I went looking for an answer: > https://wiki.python.org/moin/DebuggingWithGdb (whic…

https://wiki.python.org/moin/DebuggingWithGdb lists the GDB debugging symbol packages for various distros

FWIU Fedora GDB now optionally automatically installs debug syms; from attempting to debug TuxMath SDL with GDB before just installing the Flatpak.

https://developers.redhat.com/articles/2021/09/08/debugging-... (2021) describes more recent efforts to improve Python debugging with c extensions

Re: Debugging a Mixed Python and C Language Stack

#20

That reminds me of the time I debugged some code (also neural network) that was in both Java and C++ and I was able to attach both gdb and jdb to the same process but had to disable the segfault trap on gdb because the jvm segfaults all the time in normal operation.

As a C++ developer, I'm struggling to understand how and why segfaults would ever be part of normal operation. In my mental model, the presence of a segfault means that a program has gone so far off the expected path that no guarantees can be made about its state whatsoever, so the only safe thing to do is to let the program crash. Is there a reason why the JVM regularly segfaults?

A pretty good investigation into this matter - "segfaults in Java (redux)":

https://www.lukeshu.com/blog/java-segfault-redux.html

Read the prior article for some context, too ..

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