On Fri, Apr 16, 2021 at 10:58 PM Willy Tarreau <w@xxxxxx> wrote:
>
> No, two:
> - ok in %rax (seems like it's "!ok" technically speaking since it
> returns 1 on !ok and 0 on ok)
> - foo_or_err in %rdx
Yes, but that is the implementation -- conceptually you only have one
or the other, and Rust won't allow you to use the wrong one.
> However then I'm bothered because Miguel's example showed that regardless
> of OK, EINVAL was always returned in foo_or_err, so maybe it's just
> because his example was not well chosen but it wasn't very visible from
> the source:
That is the optimizer being fancy since the error can be put
unconditionally in `rdx`.
If you compile:
pub fn it_is_ok() -> KernelResult<Bar> {
Ok(Bar)
}
you will see it just clears `rax`.
Cheers,
Miguel
