Re: emacs-26 9e59de9: Use GCALIGNED properly for GCC

[Philipp Stephani <p.stephani2@gmail.com>]

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Stefan Monnier <monnier@iro.umontreal.ca> schrieb am Fr., 10. Nov. 2017 um
19:03 Uhr:

> >>> union gcaligned_foo { struct foo s; int64_t gcaligned; };
> >> Are int64_t necessarily aligned on multiples of 8 on 32bit platforms?
> > No, unfortunately.
>
> That was my impression as well.
>
> > That does not work either, alas, as C11 says 'alignas (8)' is an error
> when
> > the natural alignment of the object is less than 8. This is one of the
> > problems that we have encountered in earlier attempts to fix this bug.
> 'char
> > alignas (8)' avoids this problem.
>
> I don't follow: the natural alignment for `char` is definitely less than
> 8, so if "'alignas (8)' is an error when the natural alignment of the
> object is less than 8", how can "char alignas (8)" avoid the problem?
>
>
It's the other way round: alignas(8) is an error when the natural alignment
of the object is *greater* than 8.

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