include/linux/bitops.h:52:11: warning: array subscript 0 is outside array bounds of 'long unsigned int[0]'

[kernel test robot]

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   dd72f9c7e512da377074d47d990564959b772643
commit: b90ebfc018b087ba1e4981b298b58733236ff296 net/mlx5: Allocate command stats with xarray
date:   3 months ago
config: parisc-randconfig-r006-20230313 (https://download.01.org/0day-ci/archive/20231019/202310191307.RwgNqy0s-lkp@xxxxxxxxx/config)
compiler: hppa-linux-gcc (GCC) 13.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231019/202310191307.RwgNqy0s-lkp@xxxxxxxxx/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@xxxxxxxxx>
| Closes: https://lore.kernel.org/oe-kbuild-all/202310191307.RwgNqy0s-lkp@xxxxxxxxx/

All warnings (new ones prefixed by >>):

   In file included from include/linux/kernel.h:22,
                    from arch/parisc/include/asm/bug.h:5,
                    from include/linux/bug.h:5,
                    from include/linux/thread_info.h:13,
                    from include/asm-generic/preempt.h:5,
                    from ./arch/parisc/include/generated/asm/preempt.h:1,
                    from include/linux/preempt.h:79,
                    from include/linux/spinlock.h:56,
                    from include/linux/wait.h:9,
                    from include/linux/wait_bit.h:8,
                    from include/linux/fs.h:6,
                    from include/linux/highmem.h:5,
                    from drivers/net/ethernet/mellanox/mlx5/core/main.c:33:
   drivers/net/ethernet/mellanox/mlx5/core/main.c: In function 'mlx5_vf_get_core_dev':
>> include/linux/bitops.h:52:11: warning: array subscript 0 is outside array bounds of 'long unsigned int[0]' [-Warray-bounds=]
      52 |           __builtin_constant_p(*(const unsigned long *)(addr))) ?       \
         |           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/bitops.h:61:41: note: in expansion of macro 'bitop'
      61 | #define test_bit(nr, addr)              bitop(_test_bit, nr, addr)
         |                                         ^~~~~
   drivers/net/ethernet/mellanox/mlx5/core/main.c:2256:14: note: in expansion of macro 'test_bit'
    2256 |         if (!test_bit(MLX5_INTERFACE_STATE_UP, &mdev->intf_state)) {
         |              ^~~~~~~~
   cc1: note: source object is likely at address zero
   In file included from include/linux/bitops.h:34:
   In function 'generic_test_bit',
       inlined from 'mlx5_vf_get_core_dev' at drivers/net/ethernet/mellanox/mlx5/core/main.c:2256:7:
>> include/asm-generic/bitops/generic-non-atomic.h:128:27: warning: array subscript 0 is outside array bounds of 'long unsigned int[0]' [-Warray-bounds=]
     128 |         return 1UL & (addr[BIT_WORD(nr)] >> (nr & (BITS_PER_LONG-1)));
         |                       ~~~~^~~~~~~~~~~~~~
   In function 'mlx5_vf_get_core_dev':
   cc1: note: source object is likely at address zero


vim +52 include/linux/bitops.h

0e862838f29014 Alexander Lobakin 2022-06-24  35  
b03fc1173c0c2b Alexander Lobakin 2022-06-24  36  /*
b03fc1173c0c2b Alexander Lobakin 2022-06-24  37   * Many architecture-specific non-atomic bitops contain inline asm code and due
b03fc1173c0c2b Alexander Lobakin 2022-06-24  38   * to that the compiler can't optimize them to compile-time expressions or
b03fc1173c0c2b Alexander Lobakin 2022-06-24  39   * constants. In contrary, generic_*() helpers are defined in pure C and
b03fc1173c0c2b Alexander Lobakin 2022-06-24  40   * compilers optimize them just well.
b03fc1173c0c2b Alexander Lobakin 2022-06-24  41   * Therefore, to make `unsigned long foo = 0; __set_bit(BAR, &foo)` effectively
b03fc1173c0c2b Alexander Lobakin 2022-06-24  42   * equal to `unsigned long foo = BIT(BAR)`, pick the generic C alternative when
b03fc1173c0c2b Alexander Lobakin 2022-06-24  43   * the arguments can be resolved at compile time. That expression itself is a
b03fc1173c0c2b Alexander Lobakin 2022-06-24  44   * constant and doesn't bring any functional changes to the rest of cases.
b03fc1173c0c2b Alexander Lobakin 2022-06-24  45   * The casts to `uintptr_t` are needed to mitigate `-Waddress` warnings when
b03fc1173c0c2b Alexander Lobakin 2022-06-24  46   * passing a bitmap from .bss or .data (-> `!!addr` is always true).
b03fc1173c0c2b Alexander Lobakin 2022-06-24  47   */
e69eb9c460f128 Alexander Lobakin 2022-06-24  48  #define bitop(op, nr, addr)						\
b03fc1173c0c2b Alexander Lobakin 2022-06-24  49  	((__builtin_constant_p(nr) &&					\
b03fc1173c0c2b Alexander Lobakin 2022-06-24  50  	  __builtin_constant_p((uintptr_t)(addr) != (uintptr_t)NULL) &&	\
b03fc1173c0c2b Alexander Lobakin 2022-06-24  51  	  (uintptr_t)(addr) != (uintptr_t)NULL &&			\
b03fc1173c0c2b Alexander Lobakin 2022-06-24 @52  	  __builtin_constant_p(*(const unsigned long *)(addr))) ?	\
b03fc1173c0c2b Alexander Lobakin 2022-06-24  53  	 const##op(nr, addr) : op(nr, addr))
e69eb9c460f128 Alexander Lobakin 2022-06-24  54  

:::::: The code at line 52 was first introduced by commit
:::::: b03fc1173c0c2bb8fad61902a862985cecdc4b1b bitops: let optimize out non-atomic bitops on compile-time constants

:::::: TO: Alexander Lobakin <alexandr.lobakin@xxxxxxxxx>
:::::: CC: Yury Norov <yury.norov@xxxxxxxxx>

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