gh-148286: Run test_capi and test_faulthandler on GHA UBSan

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• Issue: Various UB warnings found by UBSan #148286

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These 2 tests have been skipped by commit ade914b (PR gh-148168).

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I cannot reproduce test_capi or test_faulthandler failure locally. I built Python with ./configure --with-pydebug --with-undefined-behavior-sanitizer CC=clang LD=clang:

$ UBSAN_OPTIONS='halt_on_error=1' ./python -m test -j0 test_capi test_faulthandler ...
0:00:16 load avg: 0.69 mem: 61.4 MiB [1/2] test_faulthandler passed
0:00:23 load avg: 0.90 mem: 34.7 MiB [2/2] test_capi passed
...
All 2 tests OK.
...

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Ah, the "Sanitizers / UBSan" CI failed:

• 1 test failed: test_capi
• The "Display logs" step contains many errors related to faulthandler

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I rebuilt Python with CC=clang ./configure --config-cache --with-undefined-behavior-sanitizer --with-strict-overflow --with-pydebug && make clean && make.

Aha. This time I'm able to reproduce the error:

$ UBSAN_OPTIONS="halt_on_error=1" ./python -m test -v test_capi -m test_fromwidechar
test_fromwidechar (test.test_capi.test_unicode.CAPITest.test_fromwidechar)
Test PyUnicode_FromWideChar() ...
Objects/unicodeobject.c:1942:38: runtime error: addition of unsigned offset to 0x0000017b51d8 overflowed to 0x0000017b51d4
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior Objects/unicodeobject.c:1942:38 

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test_capi pass with this change:

diff --git a/Lib/test/test_capi/test_unicode.py b/Lib/test/test_capi/test_unicode.py
index 5dee25756fe..16ee04ba22b 100644
--- a/Lib/test/test_capi/test_unicode.py+++ b/Lib/test/test_capi/test_unicode.py@@ -842,9 +842,9 @@ def test_fromwidechar(self):
if SIZEOF_WCHAR_T == 2:
self.assertEqual(fromwidechar('a\U0001f600'.encode(encoding), 2), 'a\ud83d')
- self.assertRaises(MemoryError, fromwidechar, b'', PY_SSIZE_T_MAX)+ #self.assertRaises(MemoryError, fromwidechar, b'', PY_SSIZE_T_MAX)
self.assertRaises(SystemError, fromwidechar, b'\0'*SIZEOF_WCHAR_T, -2)
- self.assertRaises(SystemError, fromwidechar, b'\0'*SIZEOF_WCHAR_T, PY_SSIZE_T_MIN)+ #self.assertRaises(SystemError, fromwidechar, b'\0'*SIZEOF_WCHAR_T, PY_SSIZE_T_MIN)
self.assertEqual(fromwidechar(NULL, 0), '')
self.assertRaises(SystemError, fromwidechar, NULL, 1)
self.assertRaises(SystemError, fromwidechar, NULL, PY_SSIZE_T_MAX)

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I created #151278 to fix test_faulthandler. Once test_faulthandler will be fixed, I will create an issue to fix test_capi.

I close this PR since it's wrong. We cannot just reenable the tests since they fail.