linux-kernel - Re: [PATCH 1/2] Compiler Attributes: add support for _

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Message-ID: <CANiq72k_uBxjzguG8YBmSaV5XUYoOsuHk+UHFdgCarr4--uGDA@mail.gmail.com>
Date:   Mon, 22 Oct 2018 15:39:47 +0200
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        "Ted Ts'o" <tytso@....edu>, Greg KH <gregkh@...uxfoundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Dan <dan.carpenter@...cle.com>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Olof Johansson <olof@...m.net>,
        Konstantin Ryabitsev <konstantin@...uxfoundation.org>,
        David Miller <davem@...emloft.net>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Paul Lawrence <paullawrence@...gle.com>,
        Sandipan Das <sandipan@...ux.vnet.ibm.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Will Deacon <will.deacon@....com>,
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        Christopher Li <sparse@...isli.org>,
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        Dominique Martinet <asmadeus@...ewreck.org>,
        Stefan Agner <stefan@...er.ch>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
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        Andrew Morton <akpm@...ux-foundation.org>,
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        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
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        linux-sparse@...r.kernel.org, linux-kbuild@...r.kernel.org
Subject: Re: [PATCH 1/2] Compiler Attributes: add support for __fallthrough
 (gcc >= 7.1)

On Mon, Oct 22, 2018 at 1:24 PM Miguel Ojeda
<miguel.ojeda.sandonis@...il.com> wrote:
>
> On Mon, Oct 22, 2018 at 12:53 PM Kees Cook <keescook@...omium.org> wrote:
> >
> > On Mon, Oct 22, 2018 at 2:41 AM, Miguel Ojeda
> > <miguel.ojeda.sandonis@...il.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