tree:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86/core
head:   d31c3c683ee668ba5d87c0730610442fd672525f
commit: d31c3c683ee668ba5d87c0730610442fd672525f [1/1] x86/csum: Rewrite/optimize csum_partial()
config: um-x86_64_defconfig (attached as .config)
compiler: gcc-9 (Debian 9.3.0-22) 9.3.0
reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?id=d31c3c683ee668ba5d87c0730610442fd672525f
        git remote add tip https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git
        git fetch --no-tags tip x86/core
        git checkout d31c3c683ee668ba5d87c0730610442fd672525f
        # save the attached .config to linux build tree
        make W=1 ARCH=um SUBARCH=x86_64

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

   arch/x86/um/../lib/csum-partial_64.c: In function 'csum_partial':
>> arch/x86/um/../lib/csum-partial_64.c:98:12: error: implicit declaration of function 'load_unaligned_zeropad' [-Werror=implicit-function-declaration]
      98 |   trail = (load_unaligned_zeropad(buff) << shift) >> shift;
         |            ^~~~~~~~~~~~~~~~~~~~~~
   cc1: some warnings being treated as errors


vim +/load_unaligned_zeropad +98 arch/x86/um/../lib/csum-partial_64.c

    23	
    24	/*
    25	 * Do a checksum on an arbitrary memory area.
    26	 * Returns a 32bit checksum.
    27	 *
    28	 * This isn't as time critical as it used to be because many NICs
    29	 * do hardware checksumming these days.
    30	 *
    31	 * Still, with CHECKSUM_COMPLETE this is called to compute
    32	 * checksums on IPv6 headers (40 bytes) and other small parts.
    33	 * it's best to have buff aligned on a 64-bit boundary
    34	 */
    35	__wsum csum_partial(const void *buff, int len, __wsum sum)
    36	{
    37		u64 temp64 = (__force u64)sum;
    38		unsigned odd, result;
    39	
    40		odd = 1 & (unsigned long) buff;
    41		if (unlikely(odd)) {
    42			if (unlikely(len == 0))
    43				return sum;
    44			temp64 += (*(unsigned char *)buff << 8);
    45			len--;
    46			buff++;
    47		}
    48	
    49		while (unlikely(len >= 64)) {
    50			asm("addq 0*8(%[src]),%[res]\n\t"
    51			    "adcq 1*8(%[src]),%[res]\n\t"
    52			    "adcq 2*8(%[src]),%[res]\n\t"
    53			    "adcq 3*8(%[src]),%[res]\n\t"
    54			    "adcq 4*8(%[src]),%[res]\n\t"
    55			    "adcq 5*8(%[src]),%[res]\n\t"
    56			    "adcq 6*8(%[src]),%[res]\n\t"
    57			    "adcq 7*8(%[src]),%[res]\n\t"
    58			    "adcq $0,%[res]"
    59			    : [res] "+r" (temp64)
    60			    : [src] "r" (buff)
    61			    : "memory");
    62			buff += 64;
    63			len -= 64;
    64		}
    65	
    66		if (len & 32) {
    67			asm("addq 0*8(%[src]),%[res]\n\t"
    68			    "adcq 1*8(%[src]),%[res]\n\t"
    69			    "adcq 2*8(%[src]),%[res]\n\t"
    70			    "adcq 3*8(%[src]),%[res]\n\t"
    71			    "adcq $0,%[res]"
    72				: [res] "+r" (temp64)
    73				: [src] "r" (buff)
    74				: "memory");
    75			buff += 32;
    76		}
    77		if (len & 16) {
    78			asm("addq 0*8(%[src]),%[res]\n\t"
    79			    "adcq 1*8(%[src]),%[res]\n\t"
    80			    "adcq $0,%[res]"
    81				: [res] "+r" (temp64)
    82				: [src] "r" (buff)
    83				: "memory");
    84			buff += 16;
    85		}
    86		if (len & 8) {
    87			asm("addq 0*8(%[src]),%[res]\n\t"
    88			    "adcq $0,%[res]"
    89				: [res] "+r" (temp64)
    90				: [src] "r" (buff)
    91				: "memory");
    92			buff += 8;
    93		}
    94		if (len & 7) {
    95			unsigned int shift = (8 - (len & 7)) * 8;
    96			unsigned long trail;
    97	
  > 98			trail = (load_unaligned_zeropad(buff) << shift) >> shift;
    99	
   100			asm("addq %[trail],%[res]\n\t"
   101			    "adcq $0,%[res]"
   102				: [res] "+r" (temp64)
   103				: [trail] "r" (trail));
   104		}
   105		result = add32_with_carry(temp64 >> 32, temp64 & 0xffffffff);
   106		if (unlikely(odd)) { 
   107			result = from32to16(result);
   108			result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
   109		}
   110		return (__force __wsum)result;
   111	}
   112	EXPORT_SYMBOL(csum_partial);
   113	

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