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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Message-ID: <7955eec5-c1d7-e0d7-280a-138d96b2daa9@intel.com>
Date:   Tue, 24 Aug 2021 14:59:24 +0800
From:   "Chen, Rong A" <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 8/23/2021 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.

Best Regards,
Rong Chen

> 
> 
> 
> 
> 
>>     arch/powerpc/kernel/signal_32.c:765:16: warning: Value stored to 
>> 'msr' during its initialization is never read 
>> [clang-analyzer-deadcode.DeadStores]
>>             unsigned long msr = regs->msr;
>>                           ^~~   ~~~~~~~~~
>>     arch/powerpc/kernel/signal_32.c:765:16: note: Value stored to 
>> 'msr' during its initialization is never read
>>             unsigned long msr = regs->msr;
>>                           ^~~   ~~~~~~~~~
>>     arch/powerpc/kernel/signal_32.c:869:16: warning: Value stored to 
>> 'msr' during its initialization is never read 
>> [clang-analyzer-deadcode.DeadStores]
>>             unsigned long msr = regs->msr;
>>                           ^~~   ~~~~~~~~~
>>     arch/powerpc/kernel/signal_32.c:869:16: note: Value stored to 
>> 'msr' during its initialization is never read
>>             unsigned long msr = regs->msr;
>>                           ^~~   ~~~~~~~~~
>>
>> vim +/msr +297 arch/powerpc/kernel/signal_32.c
>>
>> 968c4fccd1bb8b arch/powerpc/kernel/signal_32.c Christophe Leroy 
>> 2020-08-18  262
>> ef75e73182949a arch/powerpc/kernel/signal_32.c Christophe Leroy 
>> 2020-08-18  263  static int save_user_regs_unsafe(struct pt_regs 
>> *regs, struct mcontext __user *frame,
>> 8d33001dd650b8 arch/powerpc/kernel/signal_32.c Christophe Leroy 
>> 2020-08-18  264                   struct mcontext __user *tm_frame, 
>> int ctx_has_vsx_region)
>> ^1da177e4c3f41 arch/ppc64/kernel/signal32.c    Linus Torvalds   
>> 2005-04-16  265  {
>> 9e7511861c4f8d arch/powerpc/kernel/signal_32.c Michael Neuling  
>> 2008-06-25  266      unsigned long msr = regs->msr;
>> 9e7511861c4f8d arch/powerpc/kernel/signal_32.c Michael Neuling  
>> 2008-06-25  267
>> c6e6771b87d4e3 arch/powerpc/kernel/signal_32.c Michael Neuling  
>> 2008-06-25  268      /* save general registers */
>> ef75e73182949a arch/powerpc/kernel/signal_32.c Christophe Leroy 
>> 2020-08-18  269      unsafe_save_general_regs(regs, frame, failed);
>> ^1da177e4c3f41 arch/ppc64/kernel/signal32.c    Linus Torvalds   
>> 2005-04-16  270
>> ^1da177e4c3f41 arch/ppc64/kernel/signal32.c    Linus Torvalds   
>> 2005-04-16  271  #ifdef CONFIG_ALTIVEC
>> ^1da177e4c3f41 arch/ppc64/kernel/signal32.c    Linus Torvalds   
>> 2005-04-16  272      /* save altivec registers */
>> ^1da177e4c3f41 arch/ppc64/kernel/signal32.c    Linus Torvalds   
>> 2005-04-16  273      if (current->thread.used_vr) {
>> ef75e73182949a arch/powerpc/kernel/signal_32.c Christophe Leroy 
>> 2020-08-18  274          unsafe_copy_to_user(&frame->mc_vregs, 
>> &current->thread.vr_state,
>> ef75e73182949a arch/powerpc/kernel/signal_32.c Christophe Leroy 
>> 2020-08-18  275                      ELF_NVRREG * sizeof(vector128), 
>> failed);
>> ^1da177e4c3f41 arch/ppc64/kernel/signal32.c    Linus Torvalds   
>> 2005-04-16  276          /* set MSR_VEC in the saved MSR value to 
>> indicate that
>> ^1da177e4c3f41 arch/ppc64/kernel/signal32.c    Linus Torvalds   
>> 2005-04-16  277             frame->mc_vregs contains valid data */
>> 9e7511861c4f8d arch/powerpc/kernel/signal_32.c Michael Neuling  
>> 2008-06-25  278          msr |= MSR_VEC;
>> ^1da177e4c3f41 arch/ppc64/kernel/signal32.c    Linus Torvalds   
>> 2005-04-16  279      }
>> ^1da177e4c3f41 arch/ppc64/kernel/signal32.c    Linus Torvalds   
>> 2005-04-16  280      /* else assert((regs->msr & MSR_VEC) == 0) */
>> ^1da177e4c3f41 arch/ppc64/kernel/signal32.c    Linus Torvalds   
>> 2005-04-16  281
>> ^1da177e4c3f41 arch/ppc64/kernel/signal32.c    Linus Torvalds   
>> 2005-04-16  282      /* We always copy to/from vrsave, it's 0 if we 
>> don't have or don't
>> ^1da177e4c3f41 arch/ppc64/kernel/signal32.c    Linus Torvalds   
>> 2005-04-16  283       * use altivec. Since VSCR only contains 32 bits 
>> saved in the least
>> ^1da177e4c3f41 arch/ppc64/kernel/signal32.c    Linus Torvalds   
>> 2005-04-16  284       * significant bits of a vector, we "cheat" and 
>> stuff VRSAVE in the
>> ^1da177e4c3f41 arch/ppc64/kernel/signal32.c    Linus Torvalds   
>> 2005-04-16  285       * most significant bits of that same vector. --BenH
>> 408a7e08b2112f arch/powerpc/kernel/signal_32.c Paul Mackerras   
>> 2013-08-05  286       * Note that the current VRSAVE value is in the 
>> SPR at this point.
>> ^1da177e4c3f41 arch/ppc64/kernel/signal32.c    Linus Torvalds   
>> 2005-04-16  287       */
>> ef75e73182949a arch/powerpc/kernel/signal_32.c Christophe Leroy 
>> 2020-08-18  288      unsafe_put_user(current->thread.vrsave, (u32 
>> __user *)&frame->mc_vregs[32],
>> ef75e73182949a arch/powerpc/kernel/signal_32.c Christophe Leroy 
>> 2020-08-18  289              failed);
>> ^1da177e4c3f41 arch/ppc64/kernel/signal32.c    Linus Torvalds   
>> 2005-04-16  290  #endif /* CONFIG_ALTIVEC */
>> ef75e73182949a arch/powerpc/kernel/signal_32.c Christophe Leroy 
>> 2020-08-18  291      unsafe_copy_fpr_to_user(&frame->mc_fregs, 
>> current, failed);
>> ec67ad82814bee arch/powerpc/kernel/signal_32.c Michael Neuling  
>> 2013-11-25  292
>> ec67ad82814bee arch/powerpc/kernel/signal_32.c Michael Neuling  
>> 2013-11-25  293      /*
>> ec67ad82814bee arch/powerpc/kernel/signal_32.c Michael Neuling  
>> 2013-11-25  294       * Clear the MSR VSX bit to indicate there is no 
>> valid state attached
>> ec67ad82814bee arch/powerpc/kernel/signal_32.c Michael Neuling  
>> 2013-11-25  295       * to this context, except in the specific case 
>> below where we set it.
>> ec67ad82814bee arch/powerpc/kernel/signal_32.c Michael Neuling  
>> 2013-11-25  296       */
>> ec67ad82814bee arch/powerpc/kernel/signal_32.c Michael Neuling  
>> 2013-11-25 @297      msr &= ~MSR_VSX;
>> 6a274c08f2f4df arch/powerpc/kernel/signal_32.c Michael Neuling  
>> 2008-07-02  298  #ifdef CONFIG_VSX
>> ce48b2100785e5 arch/powerpc/kernel/signal_32.c Michael Neuling  
>> 2008-06-25  299      /*
>> ce48b2100785e5 arch/powerpc/kernel/signal_32.c Michael Neuling  
>> 2008-06-25  300       * Copy VSR 0-31 upper half from thread_struct to 
>> local
>> ce48b2100785e5 arch/powerpc/kernel/signal_32.c Michael Neuling  
>> 2008-06-25  301       * buffer, then write that to userspace.  Also 
>> set MSR_VSX in
>> ce48b2100785e5 arch/powerpc/kernel/signal_32.c Michael Neuling  
>> 2008-06-25  302       * the saved MSR value to indicate that 
>> frame->mc_vregs
>> ce48b2100785e5 arch/powerpc/kernel/signal_32.c Michael Neuling  
>> 2008-06-25  303       * contains valid data
>> ce48b2100785e5 arch/powerpc/kernel/signal_32.c Michael Neuling  
>> 2008-06-25  304       */
>> 16c29d180becc5 arch/powerpc/kernel/signal_32.c Michael Neuling  
>> 2008-10-23  305      if (current->thread.used_vsr && 
>> ctx_has_vsx_region) {
>> ef75e73182949a arch/powerpc/kernel/signal_32.c Christophe Leroy 
>> 2020-08-18  306          unsafe_copy_vsx_to_user(&frame->mc_vsregs, 
>> current, failed);
>> ce48b2100785e5 arch/powerpc/kernel/signal_32.c Michael Neuling  
>> 2008-06-25  307          msr |= MSR_VSX;
>> ec67ad82814bee arch/powerpc/kernel/signal_32.c Michael Neuling  
>> 2013-11-25  308      }
>> c6e6771b87d4e3 arch/powerpc/kernel/signal_32.c Michael Neuling  
>> 2008-06-25  309  #endif /* CONFIG_VSX */
>> 81e7009ea46c95 arch/powerpc/kernel/signal_32.c Stephen Rothwell 
>> 2005-10-18  310  #ifdef CONFIG_SPE
>> 81e7009ea46c95 arch/powerpc/kernel/signal_32.c Stephen Rothwell 
>> 2005-10-18  311      /* save spe registers */
>> 81e7009ea46c95 arch/powerpc/kernel/signal_32.c Stephen Rothwell 
>> 2005-10-18  312      if (current->thread.used_spe) {
>> ef75e73182949a arch/powerpc/kernel/signal_32.c Christophe Leroy 
>> 2020-08-18  313          unsafe_copy_to_user(&frame->mc_vregs, 
>> current->thread.evr,
>> ef75e73182949a arch/powerpc/kernel/signal_32.c Christophe Leroy 
>> 2020-08-18  314                      ELF_NEVRREG * sizeof(u32), failed);
>> 81e7009ea46c95 arch/powerpc/kernel/signal_32.c Stephen Rothwell 
>> 2005-10-18  315          /* set MSR_SPE in the saved MSR value to 
>> indicate that
>> 81e7009ea46c95 arch/powerpc/kernel/signal_32.c Stephen Rothwell 
>> 2005-10-18  316             frame->mc_vregs contains valid data */
>> 9e7511861c4f8d arch/powerpc/kernel/signal_32.c Michael Neuling  
>> 2008-06-25  317          msr |= MSR_SPE;
>> 81e7009ea46c95 arch/powerpc/kernel/signal_32.c Stephen Rothwell 
>> 2005-10-18  318      }
>> 81e7009ea46c95 arch/powerpc/kernel/signal_32.c Stephen Rothwell 
>> 2005-10-18  319      /* else assert((regs->msr & MSR_SPE) == 0) */
>> 81e7009ea46c95 arch/powerpc/kernel/signal_32.c Stephen Rothwell 
>> 2005-10-18  320
>> 81e7009ea46c95 arch/powerpc/kernel/signal_32.c Stephen Rothwell 
>> 2005-10-18  321      /* We always copy to/from spefscr */
>> ef75e73182949a arch/powerpc/kernel/signal_32.c Christophe Leroy 
>> 2020-08-18  322      unsafe_put_user(current->thread.spefscr,
>> ef75e73182949a arch/powerpc/kernel/signal_32.c Christophe Leroy 
>> 2020-08-18  323              (u32 __user *)&frame->mc_vregs + 
>> ELF_NEVRREG, failed);
>> 81e7009ea46c95 arch/powerpc/kernel/signal_32.c Stephen Rothwell 
>> 2005-10-18  324  #endif /* CONFIG_SPE */
>> 81e7009ea46c95 arch/powerpc/kernel/signal_32.c Stephen Rothwell 
>> 2005-10-18  325
>> ef75e73182949a arch/powerpc/kernel/signal_32.c Christophe Leroy 
>> 2020-08-18  326      unsafe_put_user(msr, &frame->mc_gregs[PT_MSR], 
>> failed);
>> ef75e73182949a arch/powerpc/kernel/signal_32.c Christophe Leroy 
>> 2020-08-18  327
>> 1d25f11fdbcc53 arch/powerpc/kernel/signal_32.c Michael Neuling  
>> 2013-06-09  328      /* We need to write 0 the MSR top 32 bits in the 
>> tm frame so that we
>> 1d25f11fdbcc53 arch/powerpc/kernel/signal_32.c Michael Neuling  
>> 2013-06-09  329       * can check it on the restore to see if TM is 
>> active
>> 1d25f11fdbcc53 arch/powerpc/kernel/signal_32.c Michael Neuling  
>> 2013-06-09  330       */
>> ef75e73182949a arch/powerpc/kernel/signal_32.c Christophe Leroy 
>> 2020-08-18  331      if (tm_frame)
>> ef75e73182949a arch/powerpc/kernel/signal_32.c Christophe Leroy 
>> 2020-08-18  332          unsafe_put_user(0, 
>> &tm_frame->mc_gregs[PT_MSR], failed);
>> 1d25f11fdbcc53 arch/powerpc/kernel/signal_32.c Michael Neuling  
>> 2013-06-09  333
>> ^1da177e4c3f41 arch/ppc64/kernel/signal32.c    Linus Torvalds   
>> 2005-04-16  334      return 0;
>> ef75e73182949a arch/powerpc/kernel/signal_32.c Christophe Leroy 
>> 2020-08-18  335
>> ef75e73182949a arch/powerpc/kernel/signal_32.c Christophe Leroy 
>> 2020-08-18  336  failed:
>> ef75e73182949a arch/powerpc/kernel/signal_32.c Christophe Leroy 
>> 2020-08-18  337      return 1;
>> ^1da177e4c3f41 arch/ppc64/kernel/signal32.c    Linus Torvalds   
>> 2005-04-16  338  }
>> ^1da177e4c3f41 arch/ppc64/kernel/signal32.c    Linus Torvalds   
>> 2005-04-16  339
>>
>> :::::: The code at line 297 was first introduced by commit
>> :::::: ec67ad82814bee92251fd963bf01c7a173856555 powerpc/signals: 
>> Improved mark VSX not saved with small contexts fix
>>
>> :::::: TO: Michael Neuling <mikey@...ling.org>
>> :::::: CC: Benjamin Herrenschmidt <benh@...nel.crashing.org>
>>
>> ---
>> 0-DAY CI Kernel Test Service, Intel Corporation
>> https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
>>
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