linux-kernel - Re: [PATCH] Kbuild: use cc-disable-warning consistently for maybe-uninitialized

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Date:   Thu, 16 Mar 2017 15:23:58 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Michal Marek <mmarek@...e.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Fengguang Wu <fengguang.wu@...el.com>, kbuild-all@...org,
        stable@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Kbuild: use cc-disable-warning consistently for maybe-uninitialized

On Tue, Mar 14, 2017 at 9:52 PM, Arnd Bergmann <arnd@...db.de> wrote:
> On Tue, Mar 14, 2017 at 5:17 PM, Masahiro Yamada
> <yamada.masahiro@...ionext.com> wrote:
>> Hi Arnd,
>>
>> 2017-01-14 0:40 GMT+09:00 Arnd Bergmann <arnd@...db.de>:
>>> In commit a76bcf557ef4 ("Kbuild: enable -Wmaybe-uninitialized warning
>>> for "make W=1""), I reverted another change that happened to fix a problem
>>> with old compilers, and now we get this report again with old compilers
>>> (prior to gcc-4.8) and GCOV enabled:
>>>
>>>    cc1: warnings being treated as errors
>>>    drivers/gpu/drm/i915/intel_ringbuffer.c: In function 'intel_ring_setup_status_page':
>>>    drivers/gpu/drm/i915/intel_ringbuffer.c:438: error: 'mmio.reg' may be used uninitialized in this function
>>>    At top level:
>>>>> cc1: error: unrecognized command line option "-Wno-maybe-uninitialized"
>>>
>>> The problem is that we turn off the warning conditionally in a number
>>> of places as we should, but one of them does it unconditionally.
>>> Instead, change it to call cc-disable-warning as we do elsewhere.
>>>
>>> The original patch that caused it was merged into linux-4.7, then
>>> 4.8 removed the change and 4.9 brought it back, so we probably want
>>> a backport to 4.9 once this is merged.
>>>
>>> Cc: stable@...r.kernel.org
>>> Fixes: a76bcf557ef4 ("Kbuild: enable -Wmaybe-uninitialized warning for "make W=1"")
>>> Fixes: e72e2dfe7c16 ("gcov: disable -Wmaybe-uninitialized warning")
>>> Reported-by: kbuild test robot <fengguang.wu@...el.com>
>>> Signed-off-by: Arnd Bergmann <arnd@...db.de>
>>
>>
>> Applied to linux-kbuild/fixes.

Hmm, after I've carried this patch for months, I now found that it
caused a build
time regression. I'm sending a fix for that too, please either apply the fix
on top, or fold it into the first patch.

     Arnd