arch/alpha/include/asm/xchg.h:234:32: sparse: sparse: cast truncates bits from constant value (5f0ecafe becomes fe)

arch/alpha/include/asm/xchg.h:234:32: sparse: sparse: cast truncates bits from constant value (5f0ecafe becomes fe)

[kernel test robot]

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tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   23ee3e4e5bd27bdbc0f1785eef7209ce872794c7
commit: 47e4937a4a7ca4184fd282791dfee76c6799966a erofs: move erofs out of staging
date:   11 months ago
config: alpha-randconfig-s031-20200725 (attached as .config)
compiler: alpha-linux-gcc (GCC) 9.3.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # apt-get install sparse
        # sparse version: v0.6.2-93-g4c6cbe55-dirty
        git checkout 47e4937a4a7ca4184fd282791dfee76c6799966a
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' ARCH=alpha 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>


sparse warnings: (new ones prefixed by >>)

   fs/erofs/zdata.c: note: in included file (through arch/alpha/include/asm/cmpxchg.h, arch/alpha/include/asm/atomic.h, include/linux/atomic.h, ...):
>> arch/alpha/include/asm/xchg.h:234:32: sparse: sparse: cast truncates bits from constant value (5f0ecafe becomes fe)
>> arch/alpha/include/asm/xchg.h:236:32: sparse: sparse: cast truncates bits from constant value (5f0ecafe becomes cafe)
>> arch/alpha/include/asm/xchg.h:234:32: sparse: sparse: cast truncates bits from constant value (5f0ecafe becomes fe)
>> arch/alpha/include/asm/xchg.h:234:32: sparse: sparse: cast truncates bits from constant value (5f0edead becomes ad)
>> arch/alpha/include/asm/xchg.h:236:32: sparse: sparse: cast truncates bits from constant value (5f0ecafe becomes cafe)
>> arch/alpha/include/asm/xchg.h:236:32: sparse: sparse: cast truncates bits from constant value (5f0edead becomes dead)

vim +234 arch/alpha/include/asm/xchg.h

a6209d6d71f2ab Ivan Kokshaysky 2009-03-31  227  
a6209d6d71f2ab Ivan Kokshaysky 2009-03-31  228  static __always_inline unsigned long
a6209d6d71f2ab Ivan Kokshaysky 2009-03-31  229  ____cmpxchg(, volatile void *ptr, unsigned long old, unsigned long new,
a6209d6d71f2ab Ivan Kokshaysky 2009-03-31  230  	      int size)
a6209d6d71f2ab Ivan Kokshaysky 2009-03-31  231  {
a6209d6d71f2ab Ivan Kokshaysky 2009-03-31  232  	switch (size) {
a6209d6d71f2ab Ivan Kokshaysky 2009-03-31  233  		case 1:
a6209d6d71f2ab Ivan Kokshaysky 2009-03-31 @234  			return ____cmpxchg(_u8, ptr, old, new);
a6209d6d71f2ab Ivan Kokshaysky 2009-03-31  235  		case 2:
a6209d6d71f2ab Ivan Kokshaysky 2009-03-31 @236  			return ____cmpxchg(_u16, ptr, old, new);
a6209d6d71f2ab Ivan Kokshaysky 2009-03-31  237  		case 4:
a6209d6d71f2ab Ivan Kokshaysky 2009-03-31  238  			return ____cmpxchg(_u32, ptr, old, new);
a6209d6d71f2ab Ivan Kokshaysky 2009-03-31  239  		case 8:
a6209d6d71f2ab Ivan Kokshaysky 2009-03-31  240  			return ____cmpxchg(_u64, ptr, old, new);
a6209d6d71f2ab Ivan Kokshaysky 2009-03-31  241  	}
a6209d6d71f2ab Ivan Kokshaysky 2009-03-31  242  	__cmpxchg_called_with_bad_pointer();
a6209d6d71f2ab Ivan Kokshaysky 2009-03-31  243  	return old;
a6209d6d71f2ab Ivan Kokshaysky 2009-03-31  244  }
a6209d6d71f2ab Ivan Kokshaysky 2009-03-31  245  

:::::: The code at line 234 was first introduced by commit
:::::: a6209d6d71f2ab8c63cc1587ef65490d83022baf alpha: xchg/cmpxchg cleanup and fixes

:::::: TO: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
:::::: CC: Linus Torvalds <torvalds@linux-foundation.org>

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

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Re: arch/alpha/include/asm/xchg.h:234:32: sparse: sparse: cast truncates bits from constant value (5f0ecafe becomes fe)

[Gao Xiang]

Hi,

On Sat, Jul 25, 2020 at 03:15:39PM +0800, kernel test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   23ee3e4e5bd27bdbc0f1785eef7209ce872794c7
> commit: 47e4937a4a7ca4184fd282791dfee76c6799966a erofs: move erofs out of staging
> date:   11 months ago
> config: alpha-randconfig-s031-20200725 (attached as .config)
> compiler: alpha-linux-gcc (GCC) 9.3.0
> reproduce:
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # apt-get install sparse
>         # sparse version: v0.6.2-93-g4c6cbe55-dirty
>         git checkout 47e4937a4a7ca4184fd282791dfee76c6799966a
>         # save the attached .config to linux build tree
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' ARCH=alpha 
> 
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@intel.com>
> 
> 
> sparse warnings: (new ones prefixed by >>)
> 
>    fs/erofs/zdata.c: note: in included file (through arch/alpha/include/asm/cmpxchg.h, arch/alpha/include/asm/atomic.h, include/linux/atomic.h, ...):
> >> arch/alpha/include/asm/xchg.h:234:32: sparse: sparse: cast truncates bits from constant value (5f0ecafe becomes fe)
> >> arch/alpha/include/asm/xchg.h:236:32: sparse: sparse: cast truncates bits from constant value (5f0ecafe becomes cafe)
> >> arch/alpha/include/asm/xchg.h:234:32: sparse: sparse: cast truncates bits from constant value (5f0ecafe becomes fe)
> >> arch/alpha/include/asm/xchg.h:234:32: sparse: sparse: cast truncates bits from constant value (5f0edead becomes ad)
> >> arch/alpha/include/asm/xchg.h:236:32: sparse: sparse: cast truncates bits from constant value (5f0ecafe becomes cafe)
> >> arch/alpha/include/asm/xchg.h:236:32: sparse: sparse: cast truncates bits from constant value (5f0edead becomes dead)

I'm not sure what's wrong here? What should I proceed with it
(it seems relating with Alpha architecture? since I didn't notice the sparse warning in x86 and arm)

Z_EROFS_PCLUSTER_TAIL is a pointer with magic value to indicate
the end of opening decompressing chain, whose function is likewise
the function of POISON_POINTER_DELTA and CONFIG_ILLEGAL_POINTER_VALUE.

Thanks,
Gao Xiang