Recursive _testcapi.pyobject_vectorcall() aborts with fatal stack overflow instead of raising RecursionError in a small-stack thread

Reproducer

import _testcapi, threading

threading.stack_size(1 << 20)  # 1 MiB

def c_recurse(n):
    if n:
        _testcapi.pyobject_vectorcall(c_recurse, (n - 1,), ())

t = threading.Thread(target=lambda: c_recurse(13))
t.start()
t.join()

Actual result

The process aborts with:

Fatal Python error: _Py_CheckRecursiveCall: Unrecoverable stack overflow (used 1017 kB)

Expected result

RecursionError should be raised instead of aborting the process.

Notes

Lib/test/test_call.py::TestRecursion.test_super_deep expects RecursionError for deep recursion through _testcapi.pyobject_vectorcall().

Environment

CPython main
Linux x86_64
glibc

I don't think this is a bug? If you set a small stack size, any program including Python will overflow.

Each Python entry takes roughly 2kB. This doesn't count the other frames entering the Python part. So that doesn't leave Python with any space.

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Recursive _testcapi.pyobject_vectorcall() aborts with fatal stack overflow instead of raising RecursionError in a small-stack thread #148443

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Recursive _testcapi.pyobject_vectorcall() aborts with fatal stack overflow instead of raising RecursionError in a small-stack thread #148443

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Fidget-Spinner commented on Apr 12, 2026

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