[issue9263] Try to print repr() when an C-level assert fails (in the garbage collector, beyond?)

[STINNER Victor]

STINNER Victor <vstinner at redhat.com> added the comment:

I pushed the change and even more, so I consider that the issue can now be closed... 8 years later! Thank you very much Dave Malcolm for this nice idea, and for its implementation. Thanks Bohuslav "Slavek" Kabrda for the rebase in 2013, and thanks to my colleagues who rebased the patch frequently since 2013 in the Fedora package!

Maybe some people (like me?) want to use _PyObject_ASSERT() in more places, but I consider that we don't need to leave this issue open just for that.


I took the 00170-gc-assertions.patch rebased on Python 3.7.1 by my colleagues for the Fedora package, and I rebased it on master. I modified more functions in object.c and typeobject.c to use _PyObject_ASSERT(). I tried to not replace all assert(), but only when it's revelant.

I added code to detect if the object memory has been freed to avoid derefering 0xdbdbdbdbdbdbdbdb pointers which is very likely to cause a segmantation fault. It should reduce the risk of crash when dumping the faulty object.


Dave Malcolm:
> - Only tested on gcc-4.4.3 so far; the __STRING(expr) and __PRETTY_FUNCTION__ look non-portable.

I used Py_STRINGIFY() and __func__ in the final patch. __func__ is part of the C99 standard which is now required since Python 3.6: see PEP 7.


Dave Malcolm:
> - no test case; I thought about using ctypes to extract PyObject_IncRef from the implementation, but this is likely to lead to brittle test cases.  Alternatively, is xxmodule to be used for this kind of thing?

I reworked the unit test to not use ctypes, but write the crashing code in C instead.


Antoine Pitrou:
> How about turning these asserts into Py_FatalError()s and then enabling Victor's faulthandler extension?

Done.

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resolution:  -> fixed
stage: patch review -> resolved
status: open -> closed

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue9263>
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