_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

Comece em Modules/_ctypes/callbacks.c, no tratamento vinculado do valor de retorno, e leia o contrato de closure do libffi referenciado. Reproduza ou inspecione o comportamento do callback c_int em s390x e, em seguida, verifique se os valores de retorno integrais estreitos seguem a extensão ABI necessária, em vez de apenas copiar restype->size bytes. Verifique o PR vinculado do CPython para consultar o trabalho já em andamento.