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gh-139653: If platform API doesn't give the current stack, use generic fallback #139667

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gh-139653: If platform API doesn't give the current stack, use generic fallback #139667

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gh-139653: If platform API doesn't give the current stack, use generi…
encukou Oct 6, 2025
abdafaf
Define Py_C_STACK_SIZE on Windows
encukou Oct 6, 2025
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31 changes: 21 additions & 10 deletions Python/ceval.c
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Original file line number Diff line number Diff line change
Expand Up @@ -369,7 +369,8 @@ _Py_EnterRecursiveCallUnchecked(PyThreadState *tstate)
#if defined(__s390x__)
# define Py_C_STACK_SIZE 320000
#elif defined(_WIN32)
// Don't define Py_C_STACK_SIZE, ask the O/S
// Normally unused; we ask the O/S
# define Py_C_STACK_SIZE 4000000
#elif defined(__ANDROID__)
# define Py_C_STACK_SIZE 1200000
#elif defined(__sparc__)
Expand Down Expand Up @@ -442,6 +443,7 @@ int pthread_attr_destroy(pthread_attr_t *a)
void
_Py_InitializeRecursionLimits(PyThreadState *tstate)
{
uintptr_t here_addr = _Py_get_machine_stack_pointer();
_PyThreadStateImpl *_tstate = (_PyThreadStateImpl *)tstate;
#ifdef WIN32
ULONG_PTR low, high;
Expand All @@ -458,8 +460,8 @@ _Py_InitializeRecursionLimits(PyThreadState *tstate)
_tstate->c_stack_top = (uintptr_t)stack_addr;
_tstate->c_stack_hard_limit = _tstate->c_stack_top - stack_size;
_tstate->c_stack_soft_limit = _tstate->c_stack_hard_limit + _PyOS_STACK_MARGIN_BYTES;
#else
uintptr_t here_addr = _Py_get_machine_stack_pointer();
#else // other platform
_tstate->c_stack_top = 0;
/// XXX musl supports HAVE_PTHRED_GETATTR_NP, but the resulting stack size
/// (on alpine at least) is much smaller than expected and imposes undue limits
/// compared to the old stack size estimation. (We assume musl is not glibc.)
Expand All @@ -477,22 +479,31 @@ _Py_InitializeRecursionLimits(PyThreadState *tstate)
if (err == 0) {
uintptr_t base = ((uintptr_t)stack_addr) + guard_size;
_tstate->c_stack_top = base + stack_size;
#ifdef _Py_THREAD_SANITIZER
# ifdef _Py_THREAD_SANITIZER
// Thread sanitizer crashes if we use a bit more than half the stack.
_tstate->c_stack_soft_limit = base + (stack_size / 2);
#else
# else
_tstate->c_stack_soft_limit = base + _PyOS_STACK_MARGIN_BYTES * 2;
#endif
# endif
_tstate->c_stack_hard_limit = base + _PyOS_STACK_MARGIN_BYTES;
assert(_tstate->c_stack_soft_limit < here_addr);
assert(here_addr < _tstate->c_stack_top);
}
# endif // musl
#endif // platform-specific code

/* Check that we currently are inside the discovered stack.
* gh-139653: Boost's make_fcontext (and presumably other stack-switching
* mechanisms) may be incompatible with platform API.
*/
if (_tstate->c_stack_top
&& _tstate->c_stack_soft_limit < here_addr
&& here_addr < _tstate->c_stack_top
) {
return;
}
# endif
// Generic fallback
_tstate->c_stack_top = _Py_SIZE_ROUND_UP(here_addr, 4096);
_tstate->c_stack_soft_limit = _tstate->c_stack_top - Py_C_STACK_SIZE;
_tstate->c_stack_hard_limit = _tstate->c_stack_top - (Py_C_STACK_SIZE + _PyOS_STACK_MARGIN_BYTES);
#endif
}

/* The function _Py_EnterRecursiveCallTstate() only calls _Py_CheckRecursiveCall()
Expand Down
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