include/vdso/unaligned.h:23:9: warning: '__builtin_memcpy' reading 4 bytes from a region of size 0

[kernel test robot]

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   bfe62a454542cfad3379f6ef5680b125f41e20f4
commit: a339671db64b12bb02492557d2b0658811286277 vdso: Switch get/put_unaligned() from packed struct to memcpy()
date:   3 months ago
config: mips-randconfig-r111-20260406 (https://download.01.org/0day-ci/archive/20260407/202604070917.ZVd6Ugz4-lkp@xxxxxxxxx/config)
compiler: mips-linux-gcc (GCC) 13.4.0
sparse: v0.6.5-rc1
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260407/202604070917.ZVd6Ugz4-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
| Fixes: a339671db64b ("vdso: Switch get/put_unaligned() from packed struct to memcpy()")
| Reported-by: kernel test robot <lkp@xxxxxxxxx>
| Closes: https://lore.kernel.org/oe-kbuild-all/202604070917.ZVd6Ugz4-lkp@xxxxxxxxx/

All warnings (new ones prefixed by >>):

   In file included from include/linux/byteorder/little_endian.h:5,
                    from arch/mips/include/uapi/asm/byteorder.h:15,
                    from arch/mips/include/asm/bitops.h:21,
                    from include/linux/bitops.h:67,
                    from include/linux/kernel.h:23,
                    from arch/mips/boot/compressed/decompress.c:14:
   In function 'get_unaligned_le32',
       inlined from 'decompress_kernel' at arch/mips/boot/compressed/decompress.c:113:16:
>> include/vdso/unaligned.h:23:9: warning: '__builtin_memcpy' reading 4 bytes from a region of size 0 [-Wstringop-overread]
      23 |         __builtin_memcpy(&__get_unaligned_val, (void *)(ptr),           \
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      24 |                          sizeof(__get_unaligned_val));                  \
         |                          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/uapi/linux/byteorder/little_endian.h:35:51: note: in definition of macro '__le32_to_cpu'
      35 | #define __le32_to_cpu(x) ((__force __u32)(__le32)(x))
         |                                                   ^
   include/linux/unaligned.h:23:28: note: in expansion of macro '__get_unaligned_t'
      23 |         return le32_to_cpu(__get_unaligned_t(__le32, p));
         |                            ^~~~~~~~~~~~~~~~~
   In file included from arch/mips/boot/compressed/decompress.c:22:
   arch/mips/boot/compressed/decompress.h: In function 'decompress_kernel':
   arch/mips/boot/compressed/decompress.h:6:39: note: at offset -4 into source object '__image_end' of size [0, 2147483647]
       6 | extern unsigned char __image_begin[], __image_end[];
         |                                       ^~~~~~~~~~~


vim +/__builtin_memcpy +23 include/vdso/unaligned.h

     6	
     7	/**
     8	 * __get_unaligned_t - read an unaligned value from memory.
     9	 * @type:	the type to load from the pointer.
    10	 * @ptr:	the pointer to load from.
    11	 *
    12	 * Use memcpy to affect an unaligned type sized load avoiding undefined behavior
    13	 * from approaches like type punning that require -fno-strict-aliasing in order
    14	 * to be correct. As type may be const, use __unqual_scalar_typeof to map to a
    15	 * non-const type - you can't memcpy into a const type. The
    16	 * __get_unaligned_ctrl_type gives __unqual_scalar_typeof its required
    17	 * expression rather than type, a pointer is used to avoid warnings about mixing
    18	 * the use of 0 and NULL. The void* cast silences ubsan warnings.
    19	 */
    20	#define __get_unaligned_t(type, ptr) ({					\
    21		type *__get_unaligned_ctrl_type __always_unused = NULL;		\
    22		__unqual_scalar_typeof(*__get_unaligned_ctrl_type) __get_unaligned_val; \
  > 23		__builtin_memcpy(&__get_unaligned_val, (void *)(ptr),		\
    24				 sizeof(__get_unaligned_val));			\
    25		__get_unaligned_val;						\
    26	})
    27	

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