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From:   Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Date:   Mon, 22 Oct 2018 15:39:47 +0200
Message-ID: <CANiq72k_uBxjzguG8YBmSaV5XUYoOsuHk+UHFdgCarr4--uGDA@mail.gmail.com>
Subject: Re: [PATCH 1/2] Compiler Attributes: add support for __fallthrough
 (gcc >= 7.1)
To:     Kees Cook <keescook@chromium.org>
Cc:     "Gustavo A. R. Silva" <gustavo@embeddedor.com>,
        "Ted Ts'o" <tytso@mit.edu>, Greg KH <gregkh@linuxfoundation.org>,
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On Mon, Oct 22, 2018 at 1:24 PM Miguel Ojeda
<miguel.ojeda.sandonis@gmail.com> wrote:
>
> On Mon, Oct 22, 2018 at 12:53 PM Kees Cook <keescook@chromium.org> wrote:
> >
> > On Mon, Oct 22, 2018 at 2:41 AM, Miguel Ojeda
> > <miguel.ojeda.sandonis@gmail.com> wrote:
> >
> > >   * clang does *not* support the attribute in C.
> >
> > Well that's not good. :)
>
> I will see with clang if they plan to add it.
>

So I have looked in the clang sources and I have seen that clang is
already preparing for C2x: since clang >= 6 we can actually enable the
C++-like attributes with "-fdouble-square-bracket-attributes" in C
mode, which in turn makes the warning work in C mode and can be
suppressed with [[fallthrough]]. This would give us the warning also
in clang, which would be a win vs. the comments. Nick?

However, I don't see a way to enable [[fallthrough]] in C mode for gcc
>= 7.1 -- from a quick look, the C parser does not know about [[]]
attributes, so I don't think we can use [[fallthrough]] for both
compilers (yet).

Cheers,
Miguel