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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,
>> ¤t->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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