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From:   Masahiro Yamada <yamada.masahiro@socionext.com>
Date:   Thu, 18 Jan 2018 12:33:12 +0900
Message-ID: <CAK7LNARW2MhicQ7YPrRrJjfxburMXNyF69H1O2mgt6SFWEHexA@mail.gmail.com>
Subject: Re: [PATCH] Kbuild: suppress packed-not-aligned warning for default
 setting only
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     Xiongfeng Wang <wangxiongfeng2@huawei.com>,
        Michal Marek <michal.lkml@markovi.net>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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Hi Arnd,

2018-01-18 4:40 GMT+09:00 Arnd Bergmann <arnd@arndb.de>:
> On Wed, Jan 17, 2018 at 5:12 PM, Masahiro Yamada
> <yamada.masahiro@socionext.com> wrote:
>> 2018-01-11 18:22 GMT+09:00 Xiongfeng Wang <wangxiongfeng2@huawei.com>:
>>> From: Xiongfeng Wang <xiongfeng.wang@linaro.org>
>>>
>>> gcc-8 reports many -Wpacked-not-aligned warnings. The below are some
>>> examples.
>>>
>>> ./include/linux/ceph/msgr.h:67:1: warning: alignment 1 of 'struct
>>> ceph_entity_addr' is less than 8 [-Wpacked-not-aligned]
>>>  } __attribute__ ((packed));
>>>
>>> ./include/linux/ceph/msgr.h:67:1: warning: alignment 1 of 'struct
>>> ceph_entity_addr' is less than 8 [-Wpacked-not-aligned]
>>>  } __attribute__ ((packed));
>>>
>>> ./include/linux/ceph/msgr.h:67:1: warning: alignment 1 of 'struct
>>> ceph_entity_addr' is less than 8 [-Wpacked-not-aligned]
>>>  } __attribute__ ((packed));
>>>
>>> This patch suppress this kind of warnings for default setting.
>>>
>>> Signed-off-by: Xiongfeng Wang <xiongfeng.wang@linaro.org>
>>> ---
>>>  scripts/Makefile.extrawarn | 3 +++
>>>  1 file changed, 3 insertions(+)
>>>
>>> diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
>>> index c6ebf42..8d53570 100644
>>> --- a/scripts/Makefile.extrawarn
>>> +++ b/scripts/Makefile.extrawarn
>>> @@ -11,6 +11,8 @@
>>>  # are not supported by all versions of the compiler
>>>  # ==========================================================================
>>>
>>> +KBUILD_CFLAGS += $(call cc-disable-warning, packed-not-aligned)
>>> +
>>
>> I moved this to else case of  KBUILD_ENABLE_EXTRA_GCC_CHECKS
>>
>> Please let me know if you see a problem.
>
> It means we get the warning for any argument to W=, not just W=1, but
> that's probably fine.

Oops, you are right.

I retrace it.

> I'd like to one day clean up the clang warnings
> and those that we disable unconditionally in the top-level Makefile
> so that each warning gets enabled at a specific level.

Yup.

As a loosely related item,
I see some confusion for DTC extra warning checks.
I have sent a patch.


> For the time
> being, I'm happy with the packed-not-aligned disabled by default.
>
>        Arnd


Anyway, I picked the original patch.
You may move it to the top-level Makefile when you work on it.


-- 
Best Regards
Masahiro Yamada