Re: Can we drop upstream Linux x32 support?

From: Rich Felker
Date: Thu Dec 13 2018 - 11:28:39 EST

On Thu, Dec 13, 2018 at 05:04:59PM +0100, Florian Weimer wrote:
> * Rich Felker:
> >> If the compiler can handle the zeroing, that would be great, though not
> >> sure how (some __attribute__((zero)) which generates a type constructor
> >> for such structure; it kind of departs from what the C language offers).
> >
> > The compiler fundamentally can't. At the very least it would require
> > effective type tracking, which requires shadow memory and is even more
> > controversial than -fstrict-aliasing (because in a sense it's a
> > stronger version thereof).
> It's possible to do it with the right types. See _Bool on 32-bit Darwin
> PowerPC for an example, which is four bytes instead of the usual one.
> Similarly, we could have integer types with trap representations.
> Whether it is a good idea is a different matter, but the amount of
> compiler magic required is actually limited.

If you do this you just have LP64 with value range restricted to
32-bit. This does not accomplish anything useful since it uses just as
much memory as normal LP64 but you don't get anything beneficial out
of it.