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

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Date:   Wed, 12 Aug 2020 11:09:56 +0800
From:   Gao Xiang <hsiangkao@...hat.com>
To:     kernel test robot <lkp@...el.com>
Cc:     Gao Xiang <hsiangkao@....com>, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: arch/sparc/include/asm/cmpxchg_64.h:161:55: sparse: sparse: cast
 truncates bits from constant value (ffffffffe0f510cc becomes cc)

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@...el.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.

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@...cle.com>
> :::::: CC: David S. Miller <davem@...emloft.net>
> 
> ---
> 0-DAY CI Kernel Test Service, Intel Corporation
> https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org