Re: [PATCH v2 1/3] vdso: Switch get/put unaligned from packed struct to memcpy

[kernel test robot <lkp@intel.com>]

Hi Ian,

kernel test robot noticed the following build warnings:

[auto build test WARNING on linus/master]
[also build test WARNING on v6.16-rc2 next-20250618]
[cannot apply to tip/timers/vdso acme/perf/core]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Ian-Rogers/vdso-Switch-get-put-unaligned-from-packed-struct-to-memcpy/20250618-045610
base:   linus/master
patch link:    https://lore.kernel.org/r/20250617205320.1580946-2-irogers%40google.com
patch subject: [PATCH v2 1/3] vdso: Switch get/put unaligned from packed struct to memcpy
config: parisc-allnoconfig (https://download.01.org/0day-ci/archive/20250618/202506182044.OhyWGCSm-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/20250618/202506182044.OhyWGCSm-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@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202506182044.OhyWGCSm-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:30:9: warning: '__builtin_memcpy' reading 4 bytes from a region of size 1 [-Wstringop-overread]
      30 |         __builtin_memcpy(&__get_unaligned_val, (void *)(ptr),           \
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      31 |                          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 +30 include/vdso/unaligned.h

     4	
     5	#define ____get_unaligned_type(type) type: (type)0
     6	/**
     7	 * __get_unaligned_t - read an unaligned value from memory.
     8	 * @ptr:	the pointer to load from.
     9	 * @type:	the type to load from the pointer.
    10	 *
    11	 * Use memcpy to affect an unaligned type sized load avoiding undefined behavior
    12	 * from approaches like type punning that require -fno-strict-aliasing in order
    13	 * to be correct. As type may be const, use _Generic to map to a non-const type
    14	 * - you can't memcpy into a const type. The void* cast silences ubsan warnings.
    15	 */
    16	#define __get_unaligned_t(type, ptr) ({					\
    17		type __get_unaligned_map_ctrl = 0;				\
    18		typeof(_Generic(__get_unaligned_map_ctrl,			\
    19			____get_unaligned_type(short int),			\
    20			____get_unaligned_type(unsigned short int),		\
    21			____get_unaligned_type(int),				\
    22			____get_unaligned_type(unsigned int),			\
    23			____get_unaligned_type(long),				\
    24			____get_unaligned_type(unsigned long),			\
    25			____get_unaligned_type(long long),			\
    26			____get_unaligned_type(unsigned long long),		\
    27			default: (type)0					\
    28			)) __get_unaligned_val;					\
    29		(void)__get_unaligned_map_ctrl;					\
  > 30		__builtin_memcpy(&__get_unaligned_val, (void *)(ptr),		\
    31				 sizeof(__get_unaligned_val));			\
    32		__get_unaligned_val;						\
    33	})
    34	

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