linux-kernel - include/asm-generic/cmpxchg-local.h:29:33: sparse: sparse: cast truncates bits from constant value (5f0ecafe becomes fe)

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Date:   Sun, 26 Feb 2023 08:41:48 +0800
From:   kernel test robot <lkp@...el.com>
To:     Matt Evans <mev@...osinc.com>
Cc:     oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>
Subject: include/asm-generic/cmpxchg-local.h:29:33: sparse: sparse: cast
 truncates bits from constant value (5f0ecafe becomes fe)

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   1ec35eadc3b448c91a6b763371a7073444e95f9d
commit: 6246541522845a443b7ae4a8f0e16facc5a91198 locking/atomic: cmpxchg: Make __generic_cmpxchg_local compare against zero-extended 'old' value
date:   3 weeks ago
config: nios2-randconfig-s053-20230226 (https://download.01.org/0day-ci/archive/20230226/202302260820.OtjXVnT4-lkp@intel.com/config)
compiler: nios2-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=6246541522845a443b7ae4a8f0e16facc5a91198
        git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
        git fetch --no-tags linus master
        git checkout 6246541522845a443b7ae4a8f0e16facc5a91198
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=nios2 olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=nios2 SHELL=/bin/bash fs/erofs/

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@...el.com>
| Link: https://lore.kernel.org/oe-kbuild-all/202302260820.OtjXVnT4-lkp@intel.com/

sparse warnings: (new ones prefixed by >>)
   fs/erofs/zdata.c: note: in included file (through include/asm-generic/cmpxchg.h, arch/nios2/include/generated/asm/cmpxchg.h, include/asm-generic/atomic.h, ...):
   include/asm-generic/cmpxchg-local.h:30:42: sparse: sparse: cast truncates bits from constant value (e0f510cc becomes cc)
   include/asm-generic/cmpxchg-local.h:34:44: sparse: sparse: cast truncates bits from constant value (e0f510cc becomes 10cc)
>> include/asm-generic/cmpxchg-local.h:29:33: sparse: sparse: cast truncates bits from constant value (5f0ecafe becomes fe)
>> include/asm-generic/cmpxchg-local.h:33:34: sparse: sparse: cast truncates bits from constant value (5f0ecafe becomes cafe)
>> include/asm-generic/cmpxchg-local.h:29:33: sparse: sparse: cast truncates bits from constant value (5f0ecafe becomes fe)
   include/asm-generic/cmpxchg-local.h:30:42: sparse: sparse: cast truncates bits from constant value (5f0edead becomes ad)
>> include/asm-generic/cmpxchg-local.h:33:34: sparse: sparse: cast truncates bits from constant value (5f0ecafe becomes cafe)
   include/asm-generic/cmpxchg-local.h:34:44: sparse: sparse: cast truncates bits from constant value (5f0edead becomes dead)

vim +29 include/asm-generic/cmpxchg-local.h

     7	
     8	extern unsigned long wrong_size_cmpxchg(volatile void *ptr)
     9		__noreturn;
    10	
    11	/*
    12	 * Generic version of __cmpxchg_local (disables interrupts). Takes an unsigned
    13	 * long parameter, supporting various types of architectures.
    14	 */
    15	static inline unsigned long __generic_cmpxchg_local(volatile void *ptr,
    16			unsigned long old, unsigned long new, int size)
    17	{
    18		unsigned long flags, prev;
    19	
    20		/*
    21		 * Sanity checking, compile-time.
    22		 */
    23		if (size == 8 && sizeof(unsigned long) != 8)
    24			wrong_size_cmpxchg(ptr);
    25	
    26		raw_local_irq_save(flags);
    27		switch (size) {
    28		case 1: prev = *(u8 *)ptr;
  > 29			if (prev == (u8)old)
    30				*(u8 *)ptr = (u8)new;
    31			break;
    32		case 2: prev = *(u16 *)ptr;
  > 33			if (prev == (u16)old)
    34				*(u16 *)ptr = (u16)new;
    35			break;
    36		case 4: prev = *(u32 *)ptr;
    37			if (prev == (u32)old)
    38				*(u32 *)ptr = (u32)new;
    39			break;
    40		case 8: prev = *(u64 *)ptr;
    41			if (prev == old)
    42				*(u64 *)ptr = (u64)new;
    43			break;
    44		default:
    45			wrong_size_cmpxchg(ptr);
    46		}
    47		raw_local_irq_restore(flags);
    48		return prev;
    49	}
    50	

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