In file included from /builds/cryptomilk/pam_wrapper/src/python/pypamtest.c:21:
In file included from /usr/include/python3.8/Python.h:147:
In file included from /usr/include/python3.8/abstract.h:837:
/usr/include/python3.8/cpython/abstract.h:91:11: error: cast from 'char *' to 'vectorcallfunc *' (aka 'struct _object *(**)(struct _object *, struct _object *const *, unsigned long, struct _object *)') increases required alignment from 1 to 8 [-Werror,-Wcast-align]
    ptr = (vectorcallfunc*)(((char *)callable) + offset);
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.


The correct way to do it would be:

union {
   char *data;
   vectorcallfunc *ptr;
} vc;

vc.data = (char *)callable + offset;
return *vc.ptr;

Hi! I cannot reproduce the error. Could you provide the way to reproduce?

thanks

clang -Werror -Wcast-align ...

rpm -q clang9
clang9-9.0.1-8.1.x86_64

Does that help? Found in CI of

https://gitlab.com/cwrap/pam_wrapper

I forgot, for detecting alignment issues or strict aliasing and this also falls under strict aliasing, you need to turn on optimizations.

clang -O2 -Werror -Wcast-align ...

New changeset 056c08211b402b4dbc1530a9de9d00ad5309909f by Petr Viktorin in branch 'master':
bpo-40052: Fix alignment issue in PyVectorcall_Function() (GH-23999)
https://github.com/python/cpython/commit/056c08211b402b4dbc1530a9de9d00ad5309909f

New changeset 6e72ab909de58e89b5a7cd6899587e203cf129a3 by Miss Islington (bot) in branch '3.9':
[3.9] bpo-40052: Fix alignment issue in PyVectorcall_Function() (GH-23999) (GH-24005)
https://github.com/python/cpython/commit/6e72ab909de58e89b5a7cd6899587e203cf129a3

New changeset 187f76def8a5bd0af7ab512575cad30cfe624b05 by Petr Viktorin in branch '3.8':
[3.8] bpo-40052: Fix alignment issue in PyVectorcall_Function() (GH-23999) (GH-24120)
https://github.com/python/cpython/commit/187f76def8a5bd0af7ab512575cad30cfe624b05