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[3.14] gh-137185: Fix _Py_DumpStack() async signal safety (gh-137187) #137206

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[3.14] gh-137185: Fix _Py_DumpStack() async signal safety (gh-137187) #137206

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1 change: 1 addition & 0 deletions Include/internal/pycore_traceback.h
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Original file line number Diff line number Diff line change
Expand Up @@ -100,6 +100,7 @@ extern int _Py_WriteIndentedMargin(int, const char*, PyObject *);
extern int _Py_WriteIndent(int, PyObject *);

// Export for the faulthandler module
PyAPI_FUNC(void) _Py_InitDumpStack(void);
PyAPI_FUNC(void) _Py_DumpStack(int fd);

#ifdef __cplusplus
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2025-07-28-20-48-32.gh-issue-137185.fgI7-B.rst
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@@ -0,0 +1,2 @@
Fix a potential async-signal-safety issue in :mod:`faulthandler` when
printing C stack traces.
5 changes: 5 additions & 0 deletions Modules/faulthandler.c
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Expand Up @@ -525,6 +525,11 @@ faulthandler_enable(void)
}
#endif

// gh-137185: Initialize C stack trace dumping outside of the signal
// handler. Specifically, we call backtrace() to ensure that libgcc is
// dynamically loaded outside of the signal handler.
_Py_InitDumpStack();

for (size_t i=0; i < faulthandler_nsignals; i++) {
fault_handler_t *handler;
int err;
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10 changes: 10 additions & 0 deletions Python/traceback.c
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Expand Up @@ -1327,3 +1327,13 @@ _Py_DumpStack(int fd)
PUTS(fd, " <cannot get C stack on this system>\n");
}
#endif

void
_Py_InitDumpStack(void)
{
#ifdef CAN_C_BACKTRACE
// gh-137185: Call backtrace() once to force libgcc to be loaded early.
void *callstack[1];
(void)backtrace(callstack, 1);
#endif
}
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