[linux-next:master 12407/12657] include/linux/fortify-string.h:27:30: warning: '__builtin_strncpy' output may be truncated copying between 5 and 9 bytes from a string of length 9

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
head:   d01f2f7e35573049673b71e18be7abfe3f80323f
commit: 7adafccdc8693db2cd0a2eae9a21619347b55ca1 [12407/12657] string.h: move fortified functions definitions in a dedicated header.
config: i386-randconfig-r031-20210225 (attached as .config)
compiler: gcc-9 (Debian 9.3.0-15) 9.3.0
reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=7adafccdc8693db2cd0a2eae9a21619347b55ca1
        git remote add linux-next https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
        git fetch --no-tags linux-next master
        git checkout 7adafccdc8693db2cd0a2eae9a21619347b55ca1
        # save the attached .config to linux build tree
        make W=1 ARCH=i386 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <redacted>

All warnings (new ones prefixed by >>):

   In file included from include/linux/string.h:269,
                    from include/linux/uuid.h:12,
                    from fs/xfs/xfs_linux.h:10,
                    from fs/xfs/xfs.h:22,
                    from fs/xfs/xfs_xattr.c:7:
   In function 'strncpy',
       inlined from '__xfs_xattr_put_listent' at fs/xfs/xfs_xattr.c:119:2,
       inlined from 'xfs_xattr_put_listent' at fs/xfs/xfs_xattr.c:181:2:

quoted

include/linux/fortify-string.h:27:30: warning: '__builtin_strncpy' output may be truncated copying between 5 and 9 bytes from a string of length 9 [-Wstringop-truncation]

      27 | #define __underlying_strncpy __builtin_strncpy
         |                              ^
   include/linux/fortify-string.h:38:9: note: in expansion of macro '__underlying_strncpy'
      38 |  return __underlying_strncpy(p, q, size);
         |         ^~~~~~~~~~~~~~~~~~~~


vim +/__builtin_strncpy +27 include/linux/fortify-string.h

     4	
     5	
     6	#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
     7	extern void *__underlying_memchr(const void *p, int c, __kernel_size_t size) __RENAME(memchr);
     8	extern int __underlying_memcmp(const void *p, const void *q, __kernel_size_t size) __RENAME(memcmp);
     9	extern void *__underlying_memcpy(void *p, const void *q, __kernel_size_t size) __RENAME(memcpy);
    10	extern void *__underlying_memmove(void *p, const void *q, __kernel_size_t size) __RENAME(memmove);
    11	extern void *__underlying_memset(void *p, int c, __kernel_size_t size) __RENAME(memset);
    12	extern char *__underlying_strcat(char *p, const char *q) __RENAME(strcat);
    13	extern char *__underlying_strcpy(char *p, const char *q) __RENAME(strcpy);
    14	extern __kernel_size_t __underlying_strlen(const char *p) __RENAME(strlen);
    15	extern char *__underlying_strncat(char *p, const char *q, __kernel_size_t count) __RENAME(strncat);
    16	extern char *__underlying_strncpy(char *p, const char *q, __kernel_size_t size) __RENAME(strncpy);
    17	#else
    18	#define __underlying_memchr	__builtin_memchr
    19	#define __underlying_memcmp	__builtin_memcmp
    20	#define __underlying_memcpy	__builtin_memcpy
    21	#define __underlying_memmove	__builtin_memmove
    22	#define __underlying_memset	__builtin_memset
    23	#define __underlying_strcat	__builtin_strcat
    24	#define __underlying_strcpy	__builtin_strcpy
    25	#define __underlying_strlen	__builtin_strlen
    26	#define __underlying_strncat	__builtin_strncat
  > 27	#define __underlying_strncpy	__builtin_strncpy
    28	#endif
    29	

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