From: Masahiro Yamada <yamada.masahiro@socionext.com>
To: Matthias Kaehlcke <mka@chromium.org>
Cc: Michal Marek <mmarek@suse.com>,
Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Grant Grundler <grundler@chromium.org>,
Greg Hackmann <ghackmann@google.com>,
Michael Davidson <md@google.com>
Subject: Re: [PATCH 2/2] kbuild: clang: Disable the 'duplicate-decl-specifier' warning
Date: Mon, 8 May 2017 17:29:14 +0900 [thread overview]
Message-ID: <CAK7LNARykfPkKg8GR6a-kThRXt7Nuog6xe53esRHS-V_wcGGmg@mail.gmail.com> (raw)
In-Reply-To: <20170504195034.GZ128305@google.com>
Hi Matthias,
2017-05-05 4:50 GMT+09:00 Matthias Kaehlcke <mka@chromium.org>:
> Hi Masahiro,
>
> El Sun, Apr 30, 2017 at 11:01:11PM +0900 Masahiro Yamada ha dit:
>
>> 2017-04-22 6:39 GMT+09:00 Matthias Kaehlcke <mka@chromium.org>:
>> > clang generates plenty of these warnings in different parts of the code.
>> > They are mostly caused by container_of() and other macros which declare
>> > a "const <type> *" variable for their internal use which triggers a
>> > "duplicate 'const' specifier" warning if the <type> is already const
>> > qualified.
>> >
>> > Wording-mostly-from: Michael Davidson <md@google.com>
>> > Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
>>
>>
>>
>> I think container_of() can be more simple,
>> dropping the 'const'.
>>
>> The following patch worked for me.
>>
>>
>> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
>> index 4c26dc3..d53672b 100644
>> --- a/include/linux/kernel.h
>> +++ b/include/linux/kernel.h
>> @@ -846,11 +846,9 @@ static inline void ftrace_dump(enum
>> ftrace_dump_mode oops_dump_mode) { }
>> * @ptr: the pointer to the member.
>> * @type: the type of the container struct this is embedded in.
>> * @member: the name of the member within the struct.
>> - *
>> */
>> #define container_of(ptr, type, member) ({ \
>> - const typeof( ((type *)0)->member ) *__mptr = (ptr); \
>> - (type *)( (char *)__mptr - offsetof(type,member) );})
>> + (type *)((void *)(ptr) - offsetof(type, member));})
>>
>> /* Rebuild everything on CONFIG_FTRACE_MCOUNT_RECORD */
>> #ifdef CONFIG_FTRACE_MCOUNT_RECORD
>
> Thanks, this eliminates indeed a huge amount of these warnings.
I noticed this solution will drop precious type checking
from container_of(). So, my workaround is not nice.
> The other big source of warnings is MODULE_DEVICE_TABLE which declares
> a const alias of a type that in most cases is already const. One possible
> solution would be to remove the 'additional' const qualifier, which
> might leave some tables non-const. Another option could be some
> hackery to suppress the warning just for the macro. Not sure if any of
> this would be acceptable.
Me neither.
>> For also this one,
>> I'd like to try to fix the code rather than hiding warnings.
>
> I totally agree with the general approach. My clang kernel builds
> started with plenty of warnings disabled. I fixed the code for most of
> them until I was left with these two extremely noisy ones, for which I
> didn't see a clear path.
If we do not come up with a good solution,
I will pick up this patch.
--
Best Regards
Masahiro Yamada
next prev parent reply other threads:[~2017-05-08 8:29 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-21 21:39 [PATCH 0/2] kbuild: clang: Disable spurious warnings Matthias Kaehlcke
2017-04-21 21:39 ` [PATCH 1/2] kbuild: clang: Disable 'address-of-packed-member' warning Matthias Kaehlcke
2017-04-30 13:59 ` Masahiro Yamada
2017-05-02 1:23 ` Matthias Kaehlcke
2017-05-06 16:52 ` Masahiro Yamada
2017-05-08 23:18 ` Matthias Kaehlcke
2017-05-16 6:31 ` Masahiro Yamada
2017-05-16 21:32 ` Doug Anderson
2017-06-22 1:19 ` Masahiro Yamada
2017-04-21 21:39 ` [PATCH 2/2] kbuild: clang: Disable the 'duplicate-decl-specifier' warning Matthias Kaehlcke
2017-04-30 14:01 ` Masahiro Yamada
2017-05-04 19:50 ` Matthias Kaehlcke
2017-05-08 8:29 ` Masahiro Yamada [this message]
2017-05-16 21:41 ` Doug Anderson
2017-05-17 7:35 ` Arnd Bergmann
2017-05-17 18:45 ` Matthias Kaehlcke
2017-05-24 0:04 ` Matthias Kaehlcke
2017-05-24 8:21 ` Arnd Bergmann
2017-06-21 9:11 ` Masahiro Yamada
2017-06-21 10:11 ` Arnd Bergmann
2017-06-21 16:58 ` Matthias Kaehlcke
2017-06-21 17:59 ` Arnd Bergmann
2017-06-21 21:19 ` Matthias Kaehlcke
2017-07-31 16:35 ` Matthias Kaehlcke
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