Re: [PATCH] ACPICA: fix -Wfallthrough

[Miguel Ojeda]

On Fri, Nov 13, 2020 at 1:09 AM Nick Desaulniers
<ndesaulniers@xxxxxxxxxx> wrote:
>
> Thank you for the explicit diagnostics observed.  Something fishy is
> going on though, https://godbolt.org/z/Gbxbxa is how I expect MSVC to
> handle include/linux/compiler_attributes.h.
>
> The C preprocessor should make it such that MSVC never sees
> `__attribute__` or `__fallthrough__`; that it does begs the question.
> That would seem to imply that `#if __has_attribute(__fallthrough__)`
> somehow evaluates to true on MSVC, but my godbolt link shows it does
> not.
>
> Could the upstream ACPICA project be #define'ing something that could
> be altering this? (Or not #define'ing something?)
>
> Worst case, we could do as Joe Perches suggested and disable
> -Wfallthrough for drivers/acpi/acpica/.

I agree, something is fishy. MSVC has several flags for conformance
and extensions support, including two full C preprocessors in newer
versions; which means we might be missing something, but I don't see
how the code in compiler_attributes.h could be confusing MSVC even in
older non-conforming versions.

Cheers,
Miguel