>>> 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?