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

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Date:   Fri, 17 Mar 2017 02:38:57 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Arnd Bergmann <arnd@...db.de>
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

Hi Arnd,

2017-03-16 23:23 GMT+09:00 Arnd Bergmann <arnd@...db.de>:
> 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.
>

It is good that I had forgot to push my branch.
I will squash the two.

I'd like to combine the two git-log.

The git-log of the squashed one will be like follows.
If you want to edit it more, please let me know. Thanks!


---------------------------------------->8-------------------------------------

build: use cc-disable-warning consistently for maybe-uninitialized

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.

Use a ':=' assignment instead of '=' to force the cc-disable-warning
call to only be evaluated once instead of every time.

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>
Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>

---------------------------------------->8-------------------------------------




-- 
Best Regards
Masahiro Yamada