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

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Message-ID: <CAK7LNASXC1T_OkXD-T5XSKAHSNWrxAQCHPfk4dgnyq7MJBCSnQ@mail.gmail.com>
Date:   Wed, 21 Jun 2017 18:11:51 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Matthias Kaehlcke <mka@...omium.org>,
        Doug Anderson <dianders@...omium.org>,
        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

Hi.


2017-05-24 17:21 GMT+09:00 Arnd Bergmann <arnd@...db.de>:
> 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




I think we agreed to apply 1/2.

How about 2/2?

I think we mostly discussed preferable behavior of -Wduplicate-decl-specifier,
but we did not come up with an idea to solve the problem for
already shipped clang versions.
(BTW, we have not defined the minimal supported version of clang yet.)


-- 
Best Regards
Masahiro Yamada