Re: [RFC PATCH for 4.18] rseq: use __u64 for rseq_cs fields, validate user inputs

[Linus Torvalds]

On Mon, Jul 2, 2018 at 4:17 PM Mathieu Desnoyers
<mathieu.desnoyers@xxxxxxxxxxxx> wrote:
>
> Are there any kind of guarantees that a __u64 update on a 32-bit architecture
> won't be torn into something daft like byte-per-byte stores when performed
> from C code ?

Guarantees? No. Not that there are any guarantees that the same won't
happen for a plain 32-bit value either.

Will compilers generate that kind of code? I guess some crazy compiler
could simply be really bad at handling 64-bit values, and just happen
to handle 32-bit values better. So in that sense a 64-bit entity is
certainly a bit riskier. But that would be a really bad compiler, I
have to say.

                Linus