linux-kernel - Re: [kbuild-all] Re: arch/powerpc/kernel/signal_32.c:297:2: warning: Value stored to 'msr' is never read [clang-analyzer-deadcode.DeadStores]

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Date:   Wed, 25 Aug 2021 16:48:23 +0800
From:   Rong Chen <rong.a.chen@...el.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        kernel test robot <lkp@...el.com>
Cc:     clang-built-linux@...glegroups.com, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org, Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [kbuild-all] Re: arch/powerpc/kernel/signal_32.c:297:2: warning:
 Value stored to 'msr' is never read [clang-analyzer-deadcode.DeadStores]



On 8/24/21 3:29 PM, Christophe Leroy wrote:
>
>
> Le 24/08/2021 à 08:59, Chen, Rong A a écrit :
>>
>>
>> On 8/23/2021 10:35 PM, Christophe Leroy wrote:
>>>
>>>
>>> Le 23/08/2021 à 12:59, kernel test robot a écrit :
>>>> tree: 
>>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 
>>>> master
>>>> head:   e22ce8eb631bdc47a4a4ea7ecf4e4ba499db4f93
>>>> commit: ef75e73182949a94bde169a774de1b62ae21fbbc powerpc/signal32: 
>>>> Transform save_user_regs() and save_tm_user_regs() in 'unsafe' version
>>>> date:   9 months ago
>>>> config: powerpc-randconfig-c003-20210821 (attached as .config)
>>>> compiler: clang version 14.0.0 
>>>> (https://github.com/llvm/llvm-project 
>>>> d9c5613e856cf2addfbf892fc4c1ce9ef9feceaa)
>>>> reproduce (this is a W=1 build):
>>>>          wget 
>>>> https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross 
>>>> -O ~/bin/make.cross
>>>>          chmod +x ~/bin/make.cross
>>>>          # install powerpc cross compiling tool for clang build
>>>>          # apt-get install binutils-powerpc-linux-gnu
>>>>          # 
>>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ef75e73182949a94bde169a774de1b62ae21fbbc 
>>>>
>>>>          git remote add linus 
>>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
>>>>          git fetch --no-tags linus master
>>>>          git checkout ef75e73182949a94bde169a774de1b62ae21fbbc
>>>>          # save the attached .config to linux build tree
>>>>          COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross 
>>>> ARCH=powerpc clang-analyzer
>>>>
>>>> If you fix the issue, kindly add following tag as appropriate
>>>> Reported-by: kernel test robot <lkp@...el.com>
>>>>
>>>>
>>>> clang-analyzer warnings: (new ones prefixed by >>)
>>>>             ^
>>>>>> arch/powerpc/kernel/signal_32.c:297:2: warning: Value stored to 
>>>>>> 'msr' is never read [clang-analyzer-deadcode.DeadStores]
>>>>             msr &= ~MSR_VSX;
>>>>             ^      ~~~~~~~~
>>>>     arch/powerpc/kernel/signal_32.c:297:2: note: Value stored to 
>>>> 'msr' is never read
>>>>             msr &= ~MSR_VSX;
>>>>             ^      ~~~~~~~~
>>>
>>>
>>> This is wrong.
>>>
>>> msr is used at line 326:
>>>
>>> ef75e73182949a arch/powerpc/kernel/signal_32.c Christophe Leroy 
>>> 2020-08-18  326 unsafe_put_user(msr, &frame->mc_gregs[PT_MSR], failed);
>>
>> Hi Christophe,
>>
>> The usage is under CONFIG_VSX, the test config 
>> (powerpc-randconfig-c003-20210821) didn't enable it which triggered 
>> this warning.
>
>
> No no, the 'unsafe_put_user(msr, &frame->mc_gregs[PT_MSR], failed) ' 
> at line 326 is not under CONFIG_VSX as far as I can see.
>
>
> Christophe

Hi Christophe,

It's my fault, I didn't see it correctly, and I have no idea why 
clang-analyzer reported it as a issue,
we'll double check such warning next time.

Best Regards,
Rong Chen