On Fri, Apr 16, 2021 at 03:34:50PM -0500, Connor Kuehl wrote:
> On 4/16/21 3:22 PM, Willy Tarreau wrote:
> > So it simply does the equivalent of:
> >
> > #define EINVAL -1234
> >
> > struct result {
> > int status;
> > int error;
> > };
>
> Result and Option types are more like a union with a tag that
> describes which variant it is.
>
> struct foo_result {
> /* if ok, then access foo_or_err.successful_foo
> * else, access foo_or_err.error
> */
> bool ok;
> union {
> struct foo successful_foo;
> int error;
> } foo_or_err;
> };
OK.
> > [..]
> >
> > So it simply returns a pair of values instead of a single one, which
>
> It will only return 1 value.
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
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:
bar:
push rbx
mov ebx, 1
call qword ptr [rip + black_box@GOTPCREL]
test al, al
jne .LBB2_2
call qword ptr [rip + kill_foo@GOTPCREL]
xor ebx, ebx
.LBB2_2:
mov eax, ebx
mov edx, -1234
pop rbx
ret
Willy
