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

From: Chen, Rong A
Date: Tue Aug 24 2021 - 02:59:36 EST

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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@xxxxxxxxx>

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@xxxxxxxxxxx>
:::::: CC: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>

---
0-DAY CI Kernel Test Service, Intel Corporation
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