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[3.13] gh-140815: Fix faulthandler for invalid/freed frame (#140921) - #140985
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) faulthandler now detects if a frame or a code object is invalid or freed. Add helper functions: * _PyCode_SafeAddr2Line() * _PyFrame_SafeGetCode() * _PyFrame_SafeGetLasti() _PyMem_IsPtrFreed() now detects pointers in [-0xff, 0xff] range as freed. (cherry picked from commit a84181c)
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November 4, 2025 11:16
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Summary: This diff adds a patch to the `third-party/python/3.12` Meta-internal fork. It backports the trampoline-frame part of the upstream gh-140815 fix to fix a crash in `faulthandler`'s traceback dump. Upstream fixed this in main, 3.14 and 3.13, but not in 3.12, which only takes security fixes. Upstream: - 3.13 backport: python/cpython#140985 - 3.14 backport: python/cpython#140981 (shipped in 3.14.1, already in `third-party/python/3.14`) - main: python/cpython#140921 - issue: python/cpython#140815 The hunks were checked against the 3.14 backport in `third-party/python/3.14/pristine/Python/traceback.c` rather than the 3.13 PR diff. **Problem** A `__del__` that runs while a frame called from C (e.g. by `map()`) is being popped sees two `FRAME_OWNED_BY_CSTACK` shim frames in a row, because a frame is unlinked before it is cleared (GH-99729). `dump_traceback()` skips only one shim and passes the second to `dump_frame()`: - Debug builds fail `assert(frame->owner != FRAME_OWNED_BY_CSTACK)`. - Release builds call `PyUnstable_InterpreterFrame_GetLine()` on the shim. Meta's `_PyFrame_EnsureFrameFullyInitialized()` then reads the shim's `f_funcobj`, which release builds leave uninitialized, and crashes with SIGSEGV. This killed rank 90 of f1134899418. The stuck-job detector's stack-dump signal arrived while a finalizer was in this state, and the dump died right after printing `File "<shim>"`. **Fix** Same as upstream: `dump_frame()` ignores trampoline frames, and the one-shim skip in the `dump_traceback()` loop is removed along with its assert. Adapted to 3.12: - the owner is still `FRAME_OWNED_BY_CSTACK` (3.14 renamed it `FRAME_OWNED_BY_INTERPRETER`); - `dump_frame()` stays `void`, so the early return is `return;` instead of `return 0;`. As upstream, shims now count toward `MAX_FRAME_DEPTH`. The rest of gh-140815 (`_PyFrame_SafeGetCode()`, `_PyFrame_SafeGetLasti()`, `_PyCode_SafeAddr2Line()`, `<freed frame>` / `<invalid frame>`) is not backported. Its frame validation needed a CinderX JIT-frame adaptation in 3.14 (`third-party/python/3.14/patches/21-jit-frame-safe-get-code`) and would need a separate one for 3.12. Upstream added no test for this, so `test_dump_traceback_consecutive_shims` is Meta-local. Reviewed By: itamaro Differential Revision: D121622997 fbshipit-source-id: 7315ccecef7e3432116334db435a0c62a201b332
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faulthandler now detects if a frame or a code object is invalid or freed.
Add helper functions:
_PyMem_IsPtrFreed() now detects pointers in [-0xff, 0xff] range as freed.
(cherry picked from commit a84181c)
faulthandler.dump_traceback_later#140815