I can do it this way: In the global header actypes.h: #ifndef ACPI_FALLTHROUGH #define ACPI_FALLTHROUGH #endif In the gcc-specific header (acgcc.h): #define ACPI_FALLTHROUGH __attribute__((__fallthrough__)) This would not be #defined in the MSVC-specific header (acmsvc.h) -- thus using the default (null) in actypes.h (The per-environment headers are always included first). (We do all macros in upper case, prefixed with "ACPI_") If you can update your patch to use ACPI_FALLTHROUGH, I can do the rest (above). Thanks, Bob -----Original Message----- From: Joe Perches <joe@xxxxxxxxxxx> Sent: Friday, November 13, 2020 8:30 AM To: Miguel Ojeda <miguel.ojeda.sandonis@xxxxxxxxx>; Nick Desaulniers <ndesaulniers@xxxxxxxxxx> Cc: Moore, Robert <robert.moore@xxxxxxxxx>; Kaneda, Erik <erik.kaneda@xxxxxxxxx>; Wysocki, Rafael J <rafael.j.wysocki@xxxxxxxxx>; Gustavo A . R . Silva <gustavoars@xxxxxxxxxx>; clang-built-linux@xxxxxxxxxxxxxxxx; Len Brown <lenb@xxxxxxxxxx>; linux-acpi@xxxxxxxxxxxxxxx; devel@xxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx Subject: Re: [PATCH] ACPICA: fix -Wfallthrough On Fri, 2020-11-13 at 09:14 +0100, Miguel Ojeda wrote: > 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. I believe this has nothing to do with linux and only to do with compiling acpica for other environments like Windows. From: https://acpica.org/ The ACPI Component Architecture (ACPICA) project provides an operating system (OS)-independent reference implementation of the Advanced Configuration and Power Interface Specification (ACPI). It can be easily adapted to execute under any host OS.
