linux-kernel - [tip:timers/vdso 12/15] include/vdso/unaligned.h:23:9: warning: '__builtin_memcpy' reading 4 bytes from a region of size 1

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Message-ID: <202509051042.7KOze0fZ-lkp@intel.com>
Date: Fri, 5 Sep 2025 10:43:00 +0800
From: kernel test robot <lkp@...el.com>
To: Ian Rogers <irogers@...gle.com>
Cc: oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org,
	x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: [tip:timers/vdso 12/15] include/vdso/unaligned.h:23:9: warning:
 '__builtin_memcpy' reading 4 bytes from a region of size 1

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git timers/vdso
head:   e994a4197086cd5df809277b3b96c88f75e1e860
commit: 34a1cbf21227f1327ead30dcf2a52aac79bf4f15 [12/15] vdso: Switch get/put_unaligned() from packed struct to memcpy()
config: parisc-allnoconfig (https://download.01.org/0day-ci/archive/20250905/202509051042.7KOze0fZ-lkp@intel.com/config)
compiler: hppa-linux-gcc (GCC) 15.1.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250905/202509051042.7KOze0fZ-lkp@intel.com/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@...el.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202509051042.7KOze0fZ-lkp@intel.com/

All warnings (new ones prefixed by >>):

   In file included from include/linux/swab.h:5,
                    from include/uapi/linux/byteorder/big_endian.h:14,
                    from include/linux/byteorder/big_endian.h:5,
                    from arch/parisc/include/uapi/asm/byteorder.h:5,
                    from arch/parisc/include/asm/bitops.h:11,
                    from include/linux/bitops.h:67,
                    from include/linux/kernel.h:23,
                    from arch/parisc/include/asm/bug.h:5,
                    from include/linux/bug.h:5,
                    from include/linux/thread_info.h:13,
                    from include/linux/sched.h:14,
                    from include/linux/uaccess.h:9,
                    from arch/parisc/boot/compressed/misc.c:7:
   In function 'get_unaligned_le32',
       inlined from 'decompress_kernel' at arch/parisc/boot/compressed/misc.c:312:16:
>> include/vdso/unaligned.h:23:9: warning: '__builtin_memcpy' reading 4 bytes from a region of size 1 [-Wstringop-overread]
      23 |         __builtin_memcpy(&__get_unaligned_val, (void *)(ptr),           \
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      24 |                          sizeof(__get_unaligned_val));                  \
         |                          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/uapi/linux/swab.h:120:19: note: in definition of macro '__swab32'
     120 |         __fswab32(x))
         |                   ^
   include/linux/byteorder/generic.h:89:21: note: in expansion of macro '__le32_to_cpu'
      89 | #define le32_to_cpu __le32_to_cpu
         |                     ^~~~~~~~~~~~~
   include/linux/unaligned.h:23:28: note: in expansion of macro '__get_unaligned_t'
      23 |         return le32_to_cpu(__get_unaligned_t(__le32, p));
         |                            ^~~~~~~~~~~~~~~~~
   arch/parisc/boot/compressed/misc.c: In function 'decompress_kernel':
   arch/parisc/boot/compressed/misc.c:29:13: note: source object 'output_len' of size 1
      29 | extern char output_len;
         |             ^~~~~~~~~~


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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https://github.com/intel/lkp-tests/wiki