Re: Can we drop upstream Linux x32 support?

Florian Weimer
2018-12-14T11:42:43Z

* 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