GitHub Action MSan job: test_os.test_posix.test_fexecve() fails

[vstinner]

test_os.test_posix fails in the MSan job:

FAIL: test_fexecve (test.test_os.test_posix.PosixTester.test_fexecve)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/runner/work/cpython/cpython/Lib/test/test_os/test_posix.py", line 219, in test_fexecve
    support.wait_process(pid, exitcode=0)
    ~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
  File "/home/runner/work/cpython/cpython/Lib/test/support/__init__.py", line 2491, in wait_process
    raise AssertionError(f"process {pid} exited with code {exitcode2}, "
                         f"but exit code {exitcode} is expected")
AssertionError: process 21288 exited with code 1, but exit code 0 is expected

MSan logs:

==> /home/runner/work/cpython/cpython/san_log.13546 <==
==13546==WARNING: MemorySanitizer failed to allocate 0x4000000000000021 bytes

==> /home/runner/work/cpython/cpython/san_log.21288 <==
execve failed, errno 2

Does MSan change excve() behavior?

So far, I failed to reproduce the issue on Fedora 44 with clang version 22.1.8:

$ cat Modules/Setup.local
*disabled*
_bz2 _ctypes _curses _curses_panel _dbm _decimal _gdbm _hashlib
_lzma _sqlite3 _ssl _tkinter _uuid _zstd readline zlib

$ ./configure OPT="-O2 -g" --with-memory-sanitizer --with-assertions CC=clang LD=clang
$ make
$ ./python -m test -v test_os.test_posix 

The GHA CI uses CC.version: [clang] Ubuntu clang version 21.1.8 (6ubuntu1) on Ubuntu 26.04.1 LTS (Resolute Raccoon).

cc @StanFromIreland

Linked PRs

• gh-158868: Make GitHub Action MSan job optional for now #158865