* Rich Felker: > 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. You have to a type different from long int for the relevant struct fields. This type would have zero padding. Florian
