GH-127970: find the runtime library when dladdr is available

[FFY00]

• Issue: Inconsistent platform support for taking the loaded libpython path into account in getpath #127970

[FFY00]

If this gets backported, GH-127974 should too, to ensure we don't end up with mismatched prefixes from different installations.

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @FFY00 for commit 5230b61 🤖

If you want to schedule another build, you need to add the 🔨 test-with-buildbots label again.

[FFY00]

@edelsohn, @ayappanec, I was unable to find much concrete information regarding the dladdr availability on AIX? I see some references to it not being available, like boostorg/stacktrace#89, but the 2022 documentation, the oldest available on the IBM website, mention it being available. Do you know which AIX version added dladdr, so that I can it that to our documentation? Thanks!

[ayappanec]

AIX don't have dladdr. The IBM documentation is about z/TPF operating system ( and not AIX).

[FFY00]

Ah, gotcha! Thanks!

[FFY00]

I tested this on macOS in framework and non-framework builds, and seems to work fine. I'll give it a couple more days for other to have time to review.

[ned-deily]

My apologies for the delay in testing.

The PR as it stands appears to break installed macOS frameworks builds, the standard configuration used by many downstream distributors including python.org installers. To reproduce without doing a system-wide install:

cd cpython
./configure --enable-framework=$HOME/test_127970/Library/Frameworks
make -j4 && make install
cd
$HOME/test_127970/bin/python3.14

Resulting in:

Exception ignored in running getpath:
Traceback (most recent call last):
File "<frozen getpath>", line 313, in <module>
TypeError: argument 1 must be str, not None
Fatal Python error: error evaluating path
Python runtime state: core initialized
Current thread 0x00000001f5598240 (most recent call first):
<no Python frame>

[FFY00]

Thank you for the feedback, I'll have a look!

[FFY00]

Okay, this was a bit tricky to debug, but it seems like the path variable was somehow being optimized out and messing things up. Simply changing from -O3 to -Og causes the issue to go away, for eg. That's why I didn't catch the issue previously, I tested with --with-pydebug. To solve the issue I just went away with the variable, and instead return directly from Dl_info.

Could you confirm that it fixes the issue on your side?

[ned-deily]

Could you confirm that it fixes the issue on your side?

Yes, thanks, that does solve the build problem.

[ned-deily]

With the build fix, I did builds and tests on current macOS versions of all three install variants - default (non-shared), shared, and framework - and noted no regressions. I also did a framework build and test on an older (macos 10.11) system with no apparent regression. Unfortunately, I didn't have available an applicable test of embedding Python on macOS. And I did not do any testing on other (non-macOS) platforms including iOS nor did I do any additional testing of venv's outside of the standard test suite. I didn't note any obvious red flags in the getpath.c changes but I'm not an expert in the details of interpreter startup across the various platforms. As such, I'm +0 on making this change; if we want to do it, we should do it soon, that is, early in the release cycle to get exposure.

[FFY00]

Thanks for the feedback, I am gonna go ahead and sync the branch with main to solve the generated files CI failure, and merge afterwards. If we notice any issues, we can come back and re-consider, reverting if necessary.