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_ctypes fails to extend the return value per libffi contract #156933
Description
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: llvm/llvm-project#221024
CPython versions tested on:
3.11
Operating systems tested on:
Linux
Linked PRs
- gh-156933: Widen narrow integer results in ctypes callbacks #157045
- [3.15] gh-156933: Widen narrow integer results in
ctypescallbacks (GH-157045) #158295 - [3.14] gh-156933: Widen narrow integer results in
ctypescallbacks (GH-157045) #158296 - [3.13] gh-156933: Widen narrow integer results in
ctypescallbacks (GH-157045) #158297
Activity
ZeroIntensity commentedon Sep 5, 2026
Would you like to submit a PR?
miladfarca commentedon Sep 25, 2026
There is already a PR submitted which seems to pass the single test case I have shared there.
gh-156933: Widen narrow integer results in `ctypes` callbacks (GH-157045
[3.13] gh-156933: Widen narrow integer results in `ctypes` callbacks (G…
[3.14] gh-156933: Widen narrow integer results in `ctypes` callbacks (G…
ZeroIntensity commentedon Sep 27, 2026
3.15 backport will be merged separately. Thanks @miladfarca and @lazerg for the fix!
[3.15] gh-156933: Widen narrow integer results in `ctypes` callbacks (G…