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From: Nick Desaulniers <ndesaulniers@google.com>
Date: Mon, 22 Oct 2018 10:17:44 -0700
Message-ID: <CAKwvOdn1TOzZYg_i0zB0rU+K3jaQQ8XmWnLXz01NCG9V+8PxHw@mail.gmail.com>
Subject: Re: [PATCH 1/2] Compiler Attributes: add support for __fallthrough
 (gcc >= 7.1)
To: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Cc: Kees Cook <keescook@chromium.org>, gustavo@embeddedor.com,
        "Theodore Ts'o" <tytso@mit.edu>,
        Greg KH <gregkh@linuxfoundation.org>,
        LKML <linux-kernel@vger.kernel.org>, dan.carpenter@oracle.com,
        adilger.kernel@dilger.ca,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        Michal Marek <michal.lkml@markovi.net>, rostedt@goodmis.org,
        mchehab+samsung@kernel.org, olof@lxom.net,
        Konstantin Ryabitsev <konstantin@linuxfoundation.org>,
        "David S. Miller" <davem@davemloft.net>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>,
        Paul Lawrence <paullawrence@google.com>,
        sandipan@linux.vnet.ibm.com,
        Andrey Konovalov <andreyknvl@google.com>,
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        Will Deacon <will.deacon@arm.com>,
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        paul.burton@mips.com, David Rientjes <rientjes@google.com>,
        Willy Tarreau <w@1wt.eu>, msebor@gmail.com, sparse@chrisli.org,
        Jonathan Corbet <corbet@lwn.net>,
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Sender: linux-ext4-owner@vger.kernel.org

On Mon, Oct 22, 2018 at 2:43 AM Miguel Ojeda
<miguel.ojeda.sandonis@gmail.com> wrote:
>
> On Mon, Oct 22, 2018 at 11:41 AM Miguel Ojeda
> <miguel.ojeda.sandonis@gmail.com> wrote:
> >
> >   * clang does *not* support the attribute in C.
>
> ...nor the warning at all, by the way (which is why this is OK).
>
> Cheers,
> Miguel

Oh? We're going through and annotating all of Android's C++ source
right now with it.
https://clang.llvm.org/docs/DiagnosticsReference.html#wimplicit-fallthrough

Though it looks like the attribute syntax I like from GCC is not yet
supported in Clang.
https://bugs.llvm.org/show_bug.cgi?id=37135
https://github.com/ClangBuiltLinux/linux/issues/235
I'll take a look at adding support.

So Kees sent me this embarrassing example:
https://godbolt.org/z/gV_c9_
(try changing the language from C++ to C; it works)!  That's embarrassing!
https://bugs.llvm.org/show_bug.cgi?id=39382
https://github.com/ClangBuiltLinux/linux/issues/236
Will get these both fixed up.
-- 
Thanks,
~Nick Desaulniers