[issue15119] ctypes mixed-types bitfield layout nonsensical; doesn't match compiler.

[Mark Dickinson]

Mark Dickinson <dickinsm at gmail.com> added the comment:

There are two separate issues here.  The first is that the layout that ctypes chooses for a struct of bitfields fails basic sanity checks, like having each bitfield actually fit in the corresponding type.  As a result, the C-level bitshifting code used to get bitfields ends up invoking undefined behaviour.

A secondary problem is that the ctypes layout doesn't match what the compiler does, at least for the system supplied gcc (4.2) on OS X 10.6.

The attached patch fixes the first issue, but not the second.

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keywords: +patch
title: Bug in ctypes bitfield layout? -> ctypes mixed-types bitfield layout nonsensical; doesn't match compiler.
Added file: http://bugs.python.org/file26072/ctypes_mixed_bitfields.patch

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