Re: [kbuild-all] Re: arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffffe0f510cc becomes cc)

[Rong Chen <rong.a.chen@intel.com>]

On 8/12/20 11:09 AM, Gao Xiang wrote:
> Hi,
>
> On Wed, Aug 12, 2020 at 09:49:38AM +0800, kernel test robot wrote:
>> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
>> head:   fb893de323e2d39f7a1f6df425703a2edbdf56ea
>> commit: 47e4937a4a7ca4184fd282791dfee76c6799966a erofs: move erofs out of staging
>> date:   12 months ago
>> config: sparc64-randconfig-s032-20200812 (attached as .config)
>> compiler: sparc64-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: v0.6.2-168-g9554805c-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=sparc64
>>
>> 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/utils.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>>>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffffe0f510cc becomes cc)
>> --
>>     fs/erofs/zdata.c: note: in included file (through arch/sparc/include/asm/cmpxchg.h, arch/sparc/include/asm/atomic_64.h, arch/sparc/include/asm/atomic.h, ...):
>>>> arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (ffffffffe0f510cc becomes cc)
>>     arch/sparc/include/asm/cmpxchg_64.h:161:50: sparse: sparse: cast truncates bits from constant value (5f0ecafe becomes fe)
>>     arch/sparc/include/asm/cmpxchg_64.h:161:50: sparse: sparse: cast truncates bits from constant value (5f0ecafe becomes fe)
>>     arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast truncates bits from constant value (5f0edead becomes ad)
>>
>> vim +161 arch/sparc/include/asm/cmpxchg_64.h
>>
>> d550bbd40c0e10 David Howells 2012-03-28  155
>> d550bbd40c0e10 David Howells 2012-03-28  156  static inline unsigned long
>> d550bbd40c0e10 David Howells 2012-03-28  157  __cmpxchg(volatile void *ptr, unsigned long old, unsigned long new, int size)
>> d550bbd40c0e10 David Howells 2012-03-28  158  {
>> d550bbd40c0e10 David Howells 2012-03-28  159  	switch (size) {
>> a12ee2349312d7 Babu Moger    2017-05-24  160  		case 1:
>> a12ee2349312d7 Babu Moger    2017-05-24 @161  			return __cmpxchg_u8(ptr, old, new);
>> d550bbd40c0e10 David Howells 2012-03-28  162  		case 4:
>> d550bbd40c0e10 David Howells 2012-03-28  163  			return __cmpxchg_u32(ptr, old, new);
>> d550bbd40c0e10 David Howells 2012-03-28  164  		case 8:
>> d550bbd40c0e10 David Howells 2012-03-28  165  			return __cmpxchg_u64(ptr, old, new);
>> d550bbd40c0e10 David Howells 2012-03-28  166  	}
>> d550bbd40c0e10 David Howells 2012-03-28  167  	__cmpxchg_called_with_bad_pointer();
>> d550bbd40c0e10 David Howells 2012-03-28  168  	return old;
>> d550bbd40c0e10 David Howells 2012-03-28  169  }
>> d550bbd40c0e10 David Howells 2012-03-28  170
> Again, I have no idea how to deal with that in my current
> gatekeeping code.
>
> I got these reports, but I cannot help to resolve that.
> Even I don't know if that's another sparse issue (since I
> only got such reports on sparc and alpha arch, but no x86
> or arm64.)
>
> https://lore.kernel.org/r/202007251532.y5A10ZoO%25lkp@intel.com
> https://lore.kernel.org/r/202007272132.1AgbBO3U%25lkp@intel.com
> https://lore.kernel.org/r/202008100408.Wc6WGrac%25lkp@intel.com
> https://lore.kernel.org/r/202008120933.YrVhHyoA%25lkp@intel.com
>
> If no one can help that, could you please silence such reports.
> It really makes me confusing.


Hi Gao Xiang,

Sorry for the inconvenience, we'll silence the reports on this commit.

Best Regards,
Rong Chen

>
> Thanks,
> Gao Xiang
>
>> :::::: The code at line 161 was first introduced by commit
>> :::::: a12ee2349312d7112b9b7c6ac2e70c5ec2ca334e arch/sparc: Introduce cmpxchg_u8 SPARC
>>
>> :::::: TO: Babu Moger <babu.moger@oracle.com>
>> :::::: CC: David S. Miller <davem@davemloft.net>
>>
>> ---
>> 0-DAY CI Kernel Test Service, Intel Corporation
>> https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
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