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Building a ctypes.CField with wrong byte_size aborts #132470
Description
Crash report
What happened?
The following code will cause an abort due to byte_size not matching the size of ctypes.c_byte, failing an assertion that byte_size == info->size.
import ctypes
ctypes.CField(name="a", type=ctypes.c_byte, byte_size=2, byte_offset=2, index=1, _internal_use=True)Abort message:
python: ./Modules/_ctypes/cfield.c:102: PyCField_new_impl: Assertion `byte_size == info->size' failed.
Aborted (core dumped)
CPython versions tested on:
CPython main branch
Operating systems tested on:
Linux
Output from running 'python -VV' on the command line:
Python 3.14.0a6+ (heads/main:be2d2181e62, Mar 31 2025, 07:30:17) [GCC 11.4.0]
Activity
picnixz commentedon Apr 13, 2025
Fieldwasn't meant to be used publicly for now but, since it's a real crash and if we're to expose this interface in the future, we would be happy to have this check.Fix: Prevent crash in ctypes.CField when byte_size does not match typ…
Add regression test for invalid byte_size in ctypes.CField
Add regression test for invalid byte_size in ctypes.CField
Add regression test for invalid byte_size in ctypes.CField
gh-132470: Prevent crash in ctypes.CField when `byte_size` is incorre…
encukou commentedon Apr 28, 2025
To set expectations: the
CFieldinitializer is indeed not public. If you use_internal_use=True, you are on your own -- don't blame CPython if it crashes.With that said, thank you for testing this internal API! And thank you for the fix -- when
CFieldbecomes public, there'll be one less thing to do.