_ctypes fails to extend the return value per libffi contract

Bug report

Bug description:

The current implementation is relying on restype->size to write the data into a buffer, however, per libffi contract

integral types narrower than the system register size are widened

Which is not happening here. This has caused a failure on s390x when using libclang. cindex.py calls into libclang through ctypes, which builds the callback closures using libffi. With a c_int return, ctypes writes only the low 32 bits and skips the extension that both the ABI and libffi's closure contract require.

We have also opened a PR to fix this temporarily under llvm: https://github.com/llvm/llvm-project/pull/221024

CPython versions tested on:

3.11

Operating systems tested on:

Linux

Linked PRs

• gh-157045

Commencez dans Modules/_ctypes/callbacks.c, au niveau de la gestion liée de la valeur de retour, et lisez le contrat de closure de libffi référencé. Reproduisez ou examinez le comportement du callback c_int sur s390x, puis vérifiez que les valeurs de retour intégrales étroites suivent l’extension ABI requise au lieu de seulement copier restype->size octets. Consultez le PR CPython lié pour voir le travail déjà en cours.