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Date: Fri, 13 Nov 2020 09:14:01 +0100 From: Miguel Ojeda <miguel.ojeda.sandonis@...il.com> To: Nick Desaulniers <ndesaulniers@...gle.com> Cc: "Moore, Robert" <robert.moore@...el.com>, "Kaneda, Erik" <erik.kaneda@...el.com>, "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>, "Gustavo A . R . Silva" <gustavoars@...nel.org>, "clang-built-linux@...glegroups.com" <clang-built-linux@...glegroups.com>, Len Brown <lenb@...nel.org>, "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>, "devel@...ica.org" <devel@...ica.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] ACPICA: fix -Wfallthrough On Fri, Nov 13, 2020 at 1:09 AM Nick Desaulniers <ndesaulniers@...gle.com> 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
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