Re: arch/alpha/include/asm/xchg.h:234:32: sparse: sparse: cast truncates bits from constant value (ffffffffe0f510cc becomes cc)

[Gao Xiang]

Hi,

On 2023/2/10 11:52, kernel test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   38c1e0c65865426676123cc9a127526fa02bcac6
> commit: 2f44013e39984c127c6efedf70e6b5f4e9dcf315 erofs: fix pcluster use-after-free on UP platforms
> date:   5 months ago
> config: alpha-randconfig-s042-20230210 (https://download.01.org/0day-ci/archive/20230210/202302101104.mgetTzwR-lkp@xxxxxxxxx/config)
> compiler: alpha-linux-gcc (GCC) 12.1.0
> 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: v0.6.4-39-gce1a6720-dirty
>          # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=2f44013e39984c127c6efedf70e6b5f4e9dcf315
>          git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
>          git fetch --no-tags linus master
>          git checkout 2f44013e39984c127c6efedf70e6b5f4e9dcf315
>          # save the config file
>          mkdir build_dir && cp config build_dir/.config
>          COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=alpha olddefconfig
>          COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=alpha SHELL=/bin/bash fs/erofs/
>
> If you fix the issue, kindly add following tag where applicable
> | Reported-by: kernel test robot <lkp@xxxxxxxxx>
> | Link: https://lore.kernel.org/oe-kbuild-all/202302101104.mgetTzwR-lkp@xxxxxxxxx/
>
> sparse warnings: (new ones prefixed by >>)
>     fs/erofs/utils.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 (ffffffffe0f510cc becomes cc)
> > > arch/alpha/include/asm/xchg.h:236:32: sparse: sparse: cast truncates bits from constant value (ffffffffe0f510cc becomes 10cc)
> --
>     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 (ffffffffe0f510cc becomes cc)
> > > arch/alpha/include/asm/xchg.h:236:32: sparse: sparse: cast truncates bits from constant value (ffffffffe0f510cc becomes 10cc)
>     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)

As I reported in
https://lore.kernel.org/r/b8dfa8cd-f3f9-d10c-fbd0-eac8067ee39c@xxxxxxxxx

I'm not sure how we could do something for these reports in EROFS.

Thanks,
Gao Xiang

> 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@xxxxxxxxxxxxxxxxxxxx>
> :::::: CC: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>