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

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Date:   Wed, 21 Jun 2017 12:11:55 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
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

On Wed, Jun 21, 2017 at 11:11 AM, Masahiro Yamada
<yamada.masahiro@...ionext.com> wrote:
> 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.)

I see that container_of() has been modified in linux-next and no longer adds
the 'const' keyword, do we actually still need the patch?

        Arnd