MIME-Version: 1.0
References: <20181021171414.22674-1-miguel.ojeda.sandonis@gmail.com>
 <20181021171414.22674-2-miguel.ojeda.sandonis@gmail.com> <20181021222712.GI1617@thunk.org>
 <CANiq72mXV6WTyHXNZJDTfFOpPrXD0zD6cB30bGOuKO44AvRiog@mail.gmail.com>
 <CAGXu5jKb-0H+smRAW6ngQKDZ-PbTThhMwhmu34iB8vjTa-4H8Q@mail.gmail.com>
 <CANiq72n4+HDXPqr7xySSGx49g8vEcXaxO7a-By9cSg7YSxOS_A@mail.gmail.com>
 <CAGXu5jLzfuEnWpJFL1Caq94nKbPps-QTaYGpge2CfZWj1Zzf9g@mail.gmail.com> <CANiq72kpCoVwCzMUVYB_km+9xr41gBZLo_K203e_t4_QZ9-r1Q@mail.gmail.com>
In-Reply-To: <CANiq72kpCoVwCzMUVYB_km+9xr41gBZLo_K203e_t4_QZ9-r1Q@mail.gmail.com>
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>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Dan <dan.carpenter@oracle.com>,
        Andreas Dilger <adilger.kernel@dilger.ca>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        Michal Marek <michal.lkml@markovi.net>,
        Steven Rostedt <rostedt@goodmis.org>,
        Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
        Olof Johansson <olof@lxom.net>,
        Konstantin Ryabitsev <konstantin@linuxfoundation.org>,
        David 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 Das <sandipan@linux.vnet.ibm.com>,
        Andrey Konovalov <andreyknvl@google.com>,
        David Woodhouse <dwmw2@infradead.org>,
        Will Deacon <will.deacon@arm.com>,
        Philippe Ombredanne <pombredanne@nexb.com>,
        Paul Burton <paul.burton@mips.com>,
        David Rientjes <rientjes@google.com>, Willy Tarreau <w@1wt.eu>,
        Martin Sebor <msebor@gmail.com>,
        Christopher Li <sparse@chrisli.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Joe Perches <joe@perches.com>, Arnd Bergmann <arnd@arndb.de>,
        Dominique Martinet <asmadeus@codewreck.org>,
        Stefan Agner <stefan@agner.ch>,
        Luc Van Oostenryck <luc.vanoostenryck@gmail.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Linux Doc Mailing List <linux-doc@vger.kernel.org>,
        Ext4 Developers List <linux-ext4@vger.kernel.org>,
        linux-sparse@vger.kernel.org, linux-kbuild@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Sender: linux-ext4-owner@vger.kernel.org

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