linux-ext4 - Re: [PATCH 1/2] Compiler Attributes: add support for _

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Date:   Mon, 22 Oct 2018 22:59:16 +0200
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Kees Cook <keescook@...omium.org>,
        "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>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Paul Burton <paul.burton@...s.com>,
        David Rientjes <rientjes@...gle.com>, Willy Tarreau <w@....eu>,
        Martin Sebor <msebor@...il.com>,
        Christopher Li <sparse@...isli.org>,
        Jonathan Corbet <corbet@....net>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Joe Perches <joe@...ches.com>, Arnd Bergmann <arnd@...db.de>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Stefan Agner <stefan@...er.ch>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        Ext4 Developers List <linux-ext4@...r.kernel.org>,
        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 7:17 PM Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
>
> On Mon, Oct 22, 2018 at 2:43 AM Miguel Ojeda
> <miguel.ojeda.sandonis@...il.com> wrote:
> >
> > On Mon, Oct 22, 2018 at 11:41 AM Miguel Ojeda
> > <miguel.ojeda.sandonis@...il.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
>

Sure, but I am talking about the C mode only. Please read the previous
messages in the thread :-)

> Though it looks like the attribute syntax I like from GCC is not yet
> supported in Clang.

Indeed, that is what I explained in the last message.

> 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!

Yup, that is what I have been testing yesterday -- see the linked
thread in the commit message for the summary of the results.

> https://bugs.llvm.org/show_bug.cgi?id=39382
> https://github.com/ClangBuiltLinux/linux/issues/236
> Will get these both fixed up.

Cheers,
Miguel