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SIGSEGV in test_isinstance and test_json with --enable-experimental-jit=yes and --with-lto=full #142543
Description
Bug report
Bug description:
I encountered segmentation faults (SIGSEGV, Exit code -11) while running the test suite on the main branch (3.15). The crashes occur during recursion tests in test_isinstance and test_json.
Build Environment:
- Compiler: Clang 21
- Flags:
-march=native - Configuration:
CC=clang-21 CXX=clang++-21 CFLAGS='-march=native' ./configure --enable-optimizations --enable-experimental-jit=yes --with-lto=full && make -j8
Reproduction:
./python -X dev -m test -j8 -uallCrash 1: test_isinstance
Test: test_isinstance.py -> test_infinite_cycle_in_bases
Fatal Python error: Segmentation fault
Current thread 0x00007bac0e60f780 [python] (most recent call first):
File "/home/shamil/oss/cpython/main/Lib/test/test_isinstance.py", line 338 in __bases__
...
File "/home/shamil/oss/cpython/main/Lib/test/test_isinstance.py", line 340 in test_infinite_cycle_in_bases
...
Current thread's C stack trace (most recent call first):
Binary file "/home/shamil/oss/cpython/main/python", at _Py_DumpStack+0x29
...
Binary file "/home/shamil/oss/cpython/main/python", at _PyEval_EvalFrameDefault+0x1aa1a
Binary file "/home/shamil/oss/cpython/main/python", at _PyFunction_Vectorcall+0xb83
Binary file "/home/shamil/oss/cpython/main/python", at PyObject_CallOneArg+0x54
...
<repeated calls>
Crash 2: test_json
Test: test_json/test_recursion.py -> test_endless_recursion
Fatal Python error: Segmentation fault
Current thread 0x00007e1fc251b780 [python] (most recent call first):
File "/home/shamil/oss/cpython/main/Lib/test/test_json/test_recursion.py", line 109 in default
File "/home/shamil/oss/cpython/main/Lib/json/encoder.py", line 263 in iterencode
...
Current thread's C stack trace (most recent call first):
Binary file "/home/shamil/oss/cpython/main/python", at _Py_DumpStack+0x29
...
Binary file "/home/shamil/oss/cpython/main/build/lib.linux-x86_64-3.15/_json.cpython-315-x86_64-linux-gnu.so", at +0x6afb
Binary file "/home/shamil/oss/cpython/main/build/lib.linux-x86_64-3.15/_json.cpython-315-x86_64-linux-gnu.so", at +0x6a7c
<repeated calls>
Full tests log - tests.log
CPython versions tested on:
CPython main branch
Operating systems tested on:
Linux
Activity
Fidget-Spinner commentedon Dec 10, 2025
Did you manage to narrow down where the SEGV is pointing to?
Recursion shouldn't even trigger JIT compilation, only loops at the moment.
ashm-dev commentedon Dec 10, 2025
I'm still trying to understand
ashm-dev commentedon Dec 13, 2025
In this case, I don’t understand what’s causing the issue, since the segfaults do not reproduce in debug mode and/or with ASan enabled.
Fidget-Spinner commentedon Dec 13, 2025
Does it reproduce with the tail call interpreter option with:
If it doesn't, then it's likely the C stack taking up too much space again on JIT builds.
Fidget-Spinner commentedon Dec 13, 2025
Also can you provide the full stack trace please instead of a partial one? That will give much more info.
ashm-dev commentedon Dec 16, 2025
CC=clang-21 CXX=clang++-21 CFLAGS='-march=native' ./configure --enable-optimizations --enable-experimental-jit=yes --with-lto=full
test_isinstance
test_json
CC=clang-21 CXX=clang++-21 CFLAGS='-march=native' ./configure --enable-optimizations --with-tail-call-interp --enable-experimental-jit=yes --with-lto=full
test_isinstanse
test_json
Fidget-Spinner commentedon Dec 16, 2025
Ok so that pretty much confirms this is a stack overflow issue. Thank you.
Fidget-Spinner commentedon Dec 16, 2025
I think this is similar to #137731
gh-142543: Mark tracer functions as Py_NO_INLINE (GH-142846)
Fidget-Spinner commentedon Dec 17, 2025
@ashm-dev thanks for the bug report. Can you please try main now again? I checked on my machine that it should've fixed your issues.
ashm-dev commentedon Dec 17, 2025
Yes, it's all right now.