> On Apr 17, 2025, at 10:55 AM, Miguel Ojeda <miguel.ojeda.sandonis@xxxxxxxxx> wrote:
>
> On Thu, Apr 17, 2025 at 6:31 PM Prasad Singamsetty
> <prasad.singamsetty@xxxxxxxxxx> wrote:
>>
>> When CONFIG_FAIL_MAKE_REQUEST is not enabled, gcc may optimize out
>> calls to should_fail_bio() because the content of should_fail_bio()
>> is empty returning always 'false'. The gcc compiler then detects
>
> `should_fail_request` is the one that returns `false`, no? i.e.
> `should_fail_bio` is the one that gets optimized due to that to return
> `0`.
>
That is correct. I will update the commit message text.
>> This issue is seen with gcc compiler version 14. Previous versions
>> of gcc compiler (checked 9, 11, 12, 13) don't have this optimization.
>
> I wonder if whatever changed could be making other things fail.
>
> Anyway, given what Jens said, this may not be needed to begin with.
>
> But if it is, then as far as I recall, we try to avoid that kind of
> "don't optimize" attribute (the one you used for Clang). So it would
> be nice to find other ways to do it.
Thanks for the clarification.
>
> For instance, if what you need is to keep the actual calls to
> `should_fail_bio` (not `should_fail_request`), then adding a side
> effect like the GCC manual suggests in the `noinline` attribute seems
> also to work from a quick test:
>
> Even if a function is declared with the noinline attribute, there
> are optimizations other than inlining that can cause calls to be
> optimized away if it does not have side effects, although the function
> call is live. To keep such calls from being optimized away, put asm
> (""); in the called function, to serve as a special side effect.
Thanks for the clarifications. The asm(“”) option also works and we will
use that option to fix the issue as that is a preferred method.
>
> And if you also need to keep the function name emitted as-is, then
> `__used` is also needed in GCC, but that would make sense to add
> anyway if these functions were expected to be there. Given what Jens
> said, I imagine that is why they aren't annotated like that already.
Currently GCC is keeping the function even though the call is optimized out.
I will update the patch to use asm(“”) option and resend it for review.
Thanks,
—Prasad
>
> I hope that helps.
>
> Cheers,
> Miguel
