linux-kernel - Re: [PATCH 2/2] kbuild: clang: Disable the 'duplicate-decl-specifier' warning

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Date:   Wed, 24 May 2017 10:21:04 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     Doug Anderson <dianders@...omium.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <mmarek@...e.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Grant Grundler <grundler@...omium.org>,
        Greg Hackmann <ghackmann@...gle.com>,
        Michael Davidson <md@...gle.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH 2/2] kbuild: clang: Disable the 'duplicate-decl-specifier' warning

On Wed, May 24, 2017 at 2:04 AM, Matthias Kaehlcke <mka@...omium.org> wrote:
> El Wed, May 17, 2017 at 11:45:29AM -0700 Matthias Kaehlcke ha dit:
>> El Wed, May 17, 2017 at 09:35:57AM +0200 Arnd Bergmann ha dit:
>> > On Tue, May 16, 2017 at 11:41 PM, Doug Anderson <dianders@...omium.org> wrote:
> It seems the duplicate-decl-specifier warning targets specifically C89:
>
> "The same type qualifier shall not appear more than once in the same
> specifier list or qualifier list, either directly or via one or more
> typedefs."
>
> C89 (6.5.3)
>
> gcc also raises a warning when '-pedantic' is specified and
> -std=gnu89/c89 (or unspecified), but not with -std=gnu99/c99.
>
> This bug might help to shed more light on this:
> https://bugs.llvm.org/show_bug.cgi?id=32985

I also notice that neither compiler differentiates between a)

typedef const int cint;
const cint i;

and b)
const int i;
const typeof(a) j;

I would have expected a warning for a) but not b), but both 'clang --std=gnu89'
and 'gcc --pedantic --std=gnu89' warn about both of b as well, and don't warn
for newer standards.

       Arnd