Python binaries built on Fedora 43 segfaulting in test_frame_pointer_unwind test

[ferdnyc]

Even after #145499 I'm seeing test_frame_pointer_unwind segfaults on Fedora 43 x86_64 after building Python using system GCC 15.2.1 (wrapped with automatic ccache), configured with --enable-shared but without --fno-omit-frame-pointer. Exact commands used:

mkdir _build
cd _build
../configure --prefix=$(pwd)/dist --enable-shared
make -j8
make test -j8

Output for failing test:

0:00:54 load avg: 5.11 [ 81/501/1] test_frame_pointer_unwind worker non-zero exit code (Exit code -11 (SIGSEGV))
test_manual_unwind_respects_frame_pointers (test.test_frame_pointer_unwind.FramePointerUnwindTests.test_manual_unwind_respects_frame_pointers) ... Fatal Python error: Segmentation fault

Current thread 0x00007f52c3cfdbc0 [python] (most recent call first):
  File "/home/ferd/devel/cpython/Lib/test/test_frame_pointer_unwind.py", line 161 in setUp
  File "/home/ferd/devel/cpython/Lib/unittest/case.py", line 610 in _callSetUp
  File "/home/ferd/devel/cpython/Lib/unittest/case.py", line 663 in run
  File "/home/ferd/devel/cpython/Lib/unittest/case.py", line 723 in __call__
  File "/home/ferd/devel/cpython/Lib/unittest/suite.py", line 122 in run
  File "/home/ferd/devel/cpython/Lib/unittest/suite.py", line 84 in __call__
  File "/home/ferd/devel/cpython/Lib/unittest/suite.py", line 122 in run
  File "/home/ferd/devel/cpython/Lib/unittest/suite.py", line 84 in __call__
  File "/home/ferd/devel/cpython/Lib/unittest/runner.py", line 257 in run
  File "/home/ferd/devel/cpython/Lib/test/libregrtest/single.py", line 84 in _run_suite
  File "/home/ferd/devel/cpython/Lib/test/libregrtest/single.py", line 42 in run_unittest
  File "/home/ferd/devel/cpython/Lib/test/libregrtest/single.py", line 162 in test_func
  File "/home/ferd/devel/cpython/Lib/test/libregrtest/single.py", line 118 in regrtest_runner
  File "/home/ferd/devel/cpython/Lib/test/libregrtest/single.py", line 165 in _load_run_test
  File "/home/ferd/devel/cpython/Lib/test/libregrtest/single.py", line 210 in _runtest_env_changed_exc
  File "/home/ferd/devel/cpython/Lib/test/libregrtest/single.py", line 319 in _runtest
  File "/home/ferd/devel/cpython/Lib/test/libregrtest/single.py", line 348 in run_single_test
  File "/home/ferd/devel/cpython/Lib/test/libregrtest/worker.py", line 99 in worker_process
  File "/home/ferd/devel/cpython/Lib/test/libregrtest/worker.py", line 134 in main
  File "/home/ferd/devel/cpython/Lib/test/libregrtest/worker.py", line 138 in <module>
  File "<frozen runpy>", line 87 in _run_code
  File "<frozen runpy>", line 196 in _run_module_as_main

Current thread's C stack trace (most recent call first):
  Binary file "/home/ferd/devel/cpython/_build/libpython3.15.so.1.0", at _Py_DumpStack+0x2e [0x7f52c38810fe]
  Binary file "/home/ferd/devel/cpython/_build/libpython3.15.so.1.0", at +0x29d5cc [0x7f52c389d5cc]
  Binary file "/lib64/libc.so.6", at +0x1a290 [0x7f52c32e3290]
  Binary file "/home/ferd/devel/cpython/_build/build/lib.linux-x86_64-3.15/_testinternalcapi.cpython-315-x86_64-linux-gnu.so", at +0x4b02 [0x7f52b41d1b02]
  Binary file "/home/ferd/devel/cpython/_build/libpython3.15.so.1.0", at PyObject_Vectorcall+0x56 [0x7f52c36675f6]
  Binary file "/home/ferd/devel/cpython/_build/libpython3.15.so.1.0", at _Py_VectorCallInstrumentation_StackRefSteal+0x76 [0x7f52c37d87b6]
  Binary file "/home/ferd/devel/cpython/_build/libpython3.15.so.1.0", at _PyEval_EvalFrameDefault+0x4cae [0x7f52c37e2e8e]
  Binary file "/home/ferd/devel/cpython/_build/libpython3.15.so.1.0", at +0x1ec544 [0x7f52c37ec544]
  Binary file "/home/ferd/devel/cpython/_build/libpython3.15.so.1.0", at +0x6aec8 [0x7f52c366aec8]
  Binary file "/home/ferd/devel/cpython/_build/libpython3.15.so.1.0", at _PyEval_EvalFrameDefault+0x63f4 [0x7f52c37e45d4]
  Binary file "/home/ferd/devel/cpython/_build/libpython3.15.so.1.0", at +0x1ec544 [0x7f52c37ec544]
  Binary file "/home/ferd/devel/cpython/_build/libpython3.15.so.1.0", at +0x68e23 [0x7f52c3668e23]
  Binary file "/home/ferd/devel/cpython/_build/libpython3.15.so.1.0", at +0x69025 [0x7f52c3669025]
  Binary file "/home/ferd/devel/cpython/_build/libpython3.15.so.1.0", at +0x11e649 [0x7f52c371e649]
  Binary file "/home/ferd/devel/cpython/_build/libpython3.15.so.1.0", at _PyObject_MakeTpCall+0xbc [0x7f52c366739c]
  Binary file "/home/ferd/devel/cpython/_build/libpython3.15.so.1.0", at _Py_VectorCall_StackRefSteal+0x5f [0x7f52c37d866f]
  Binary file "/home/ferd/devel/cpython/_build/libpython3.15.so.1.0", at _PyEval_EvalFrameDefault+0x58bf [0x7f52c37e3a9f]
  Binary file "/home/ferd/devel/cpython/_build/libpython3.15.so.1.0", at +0x1ec544 [0x7f52c37ec544]
  Binary file "/home/ferd/devel/cpython/_build/libpython3.15.so.1.0", at +0x6aec8 [0x7f52c366aec8]
  Binary file "/home/ferd/devel/cpython/_build/libpython3.15.so.1.0", at _PyEval_EvalFrameDefault+0x6768 [0x7f52c37e4948]
  Binary file "/home/ferd/devel/cpython/_build/libpython3.15.so.1.0", at +0x1ec544 [0x7f52c37ec544]
  Binary file "/home/ferd/devel/cpython/_build/libpython3.15.so.1.0", at +0x68e23 [0x7f52c3668e23]
  Binary file "/home/ferd/devel/cpython/_build/libpython3.15.so.1.0", at +0x69025 [0x7f52c3669025]
  Binary file "/home/ferd/devel/cpython/_build/libpython3.15.so.1.0", at +0x11e649 [0x7f52c371e649]
  Binary file "/home/ferd/devel/cpython/_build/libpython3.15.so.1.0", at _PyObject_MakeTpCall+0xbc [0x7f52c366739c]
  Binary file "/home/ferd/devel/cpython/_build/libpython3.15.so.1.0", at _Py_VectorCallInstrumentation_StackRefSteal+0x76 [0x7f52c37d87b6]
  Binary file "/home/ferd/devel/cpython/_build/libpython3.15.so.1.0", at _PyEval_EvalFrameDefault+0x4cae [0x7f52c37e2e8e]
  Binary file "/home/ferd/devel/cpython/_build/libpython3.15.so.1.0", at +0x1ec544 [0x7f52c37ec544]
  Binary file "/home/ferd/devel/cpython/_build/libpython3.15.so.1.0", at +0x6aec8 [0x7f52c366aec8]
  Binary file "/home/ferd/devel/cpython/_build/libpython3.15.so.1.0", at _PyEval_EvalFrameDefault+0x63f4 [0x7f52c37e45d4]
  Binary file "/home/ferd/devel/cpython/_build/libpython3.15.so.1.0", at +0x1ec544 [0x7f52c37ec544]
  Binary file "/home/ferd/devel/cpython/_build/libpython3.15.so.1.0", at +0x68e23 [0x7f52c3668e23]
  <truncated rest of calls>

Extension modules: _testinternalcapi (total: 1)

Originally posted by @ferdnyc in #144741

I posted a bunch more info in followup comments on #144741, but I have no idea if any of its is useful or even coherent, so I'll refrain from burdening this report with it. It's there if anyone is interested.

[akanil18]

Hi @ferdnyc, I'd like to investigate this issue and work on a fix. I'll start looking into the test_frame_pointer_unwind segfaults. Feel free to assign this to me!

[vstinner]

_testinternalcapi.manual_frame_pointer_unwind() is a new function (added to Python 3.15). Its test_frame_pointer_unwind is also fresh and needs fine tuning.

For example, if Python is built with gcc -O0 (on Fedora 43), the test fails with:

AssertionError: 102 not less than or equal to 1 : unexpected Python frames counted on x86_64 with env {'PYTHON_JIT': '0'}

The test expects that the function fails to unwind whereas it just works well with gcc -O0.

Using gcc -O2, the test does crash. manual_unwind_from_fp() is called with frame_pointer=0x7fffffffbdb0 which is invalid: in manual_unwind_from_fp(), frame_pointer[1] fails with Cannot access memory at address 0x8000000000000008 in gdb.

Using gcc -O2 -fno-omit-frame-pointer, it just works fine, the test pass successfully.

Unwinding is really complex on an optimized program. Using -fno-omit-frame-pointer, it works reliably.

Maybe for now, we can skip the test on x86-64 Linux if -fno-omit-frame-pointer option is missing, to avoid crashes.

cc @diegorusso

[vstinner]

I also tested clang (21.1.8) on Fedora 43 x86-64:

• clang -O0: test fails with AssertionError: 102 not less than or equal to 1 : unexpected Python frames counted on x86_64 with env {'PYTHON_JIT': '0'}
• clang -O2: test pass successfully (this one is surprising!)
• clang -O2 -fno-omit-frame-pointer: test pass successfully