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Message-ID: <61039da395c8a28444e2f3958d29deda4c0d49b3.camel@perches.com>
Subject: Re: [PATCH] ACPICA: fix -Wfallthrough
From:   Joe Perches <joe@perches.com>
To:     Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
        Nick Desaulniers <ndesaulniers@google.com>
Cc:     "Moore, Robert" <robert.moore@intel.com>,
        "Kaneda, Erik" <erik.kaneda@intel.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@intel.com>,
        "Gustavo A . R . Silva" <gustavoars@kernel.org>,
        "clang-built-linux@googlegroups.com" 
        <clang-built-linux@googlegroups.com>, Len Brown <lenb@kernel.org>,
        "linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>,
        "devel@acpica.org" <devel@acpica.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Date:   Fri, 13 Nov 2020 08:29:52 -0800
In-Reply-To: <CANiq72k13K_zA5aH5hameoe4TSf2o5cA294bA4UEZG0M6S3DXQ@mail.gmail.com>
References: <20201111021131.822867-1-ndesaulniers@google.com>
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On Fri, 2020-11-13 at 09:14 +0100, Miguel Ojeda wrote:
> On Fri, Nov 13, 2020 at 1:09 AM Nick Desaulniers
> <ndesaulniers@google.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.

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.