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gh-159879: Do not limit the C stack below what the interpreter assumes - #159883
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…assumes Where a thread's stack size cannot be queried, the interpreter assumes Py_C_STACK_SIZE, and a smaller thread overflows instead of raising RecursionError. run_with_limited_c_stack() now raises such a size to C_STACK_SIZE. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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Where
hardware_stack_limits()cannot query the running thread's stack (AIX, NetBSD, non-glibc Linux), the interpreter assumesPy_C_STACK_SIZE. A test thread created with less than that overflows before the recursion guard notices, so the test crashes instead of gettingRecursionError.test_lazy_importasks for 256 KiB and does exactly that on Alpine.run_with_limited_c_stack()now probes once whether the real size is visible — two threads of different sizes report the same headroom only when the fixed estimate is in use — and raises a too-small size toC_STACK_SIZEwhen it is not.Verified both ways: on Alpine the probe returns False, the clamp applies and
test_lazy_importpasses with an unpatchedceval.c; on glibc it returns True, nothing is clamped, and the tests using the helper are unaffected.Independent of #159882, which fixes the detection itself.
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