linux-kernel - Re: [PATCH] arm64/lib: add accelerated do

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Date:   Fri, 28 Dec 2018 22:46:50 +0800
From:   kbuild test robot <lkp@...el.com>
To:     huhai <huhai@...inos.cn>
Cc:     kbuild-all@...org, will.deacon@....com, catalin.marinas@....com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        liuyun01@...inos.cn, huhai <huhai@...inos.cn>
Subject: Re: [PATCH] arm64/lib: add accelerated do_csum for arm64

Hi huhai,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on arm64/for-next/core]
[also build test WARNING on v4.20 next-20181224]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/huhai/arm64-lib-add-accelerated-do_csum-for-arm64/20181228-155335
base:   https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-next/core
config: arm64-allmodconfig (attached as .config)
compiler: aarch64-linux-gnu-gcc (Debian 7.2.0-11) 7.2.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        GCC_VERSION=7.2.0 make.cross ARCH=arm64 

Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
http://gcc.gnu.org/wiki/Better_Uninitialized_Warnings

All warnings (new ones prefixed by >>):

   arch/arm64/lib/checksum.c: In function 'do_csum':
>> arch/arm64/lib/checksum.c:85:5: warning: 'tmp1' may be used uninitialized in this function [-Wmaybe-uninitialized]
        __asm__ __volatile__(
        ^~~~~~~

vim +/tmp1 +85 arch/arm64/lib/checksum.c

    41	
    42	/*
    43	 * Do a 64-bit checksum on an arbitrary memory area.
    44	 * Returns a 16bit checksum.
    45	 */
    46	unsigned int do_csum(const unsigned char *buff, unsigned len)
    47	{
    48		unsigned odd, count;
    49		unsigned long result = 0;
    50	
    51		if (unlikely(len == 0))
    52			return result;
    53		odd = 1 & (unsigned long) buff;
    54		if (odd) {
    55			result = *buff << 8;
    56			len--;
    57			buff++;
    58		}
    59		count = len >> 1;		/* nr of 16-bit words.. */
    60		if (count) {
    61			if (2 & (unsigned long) buff) {
    62				result += *(unsigned short *)buff;
    63				count--;
    64				len -= 2;
    65				buff += 2;
    66			}
    67			count >>= 1;		/* nr of 32-bit words.. */
    68			if (count) {
    69				unsigned long zero;
    70				unsigned long tmp1;
    71				unsigned count64;
    72	
    73				if (4 & (unsigned long) buff) {
    74					result += *(unsigned int *) buff;
    75					count--;
    76					len -= 4;
    77					buff += 4;
    78				}
    79				count >>= 1;	/* nr of 64-bit words.. */
    80	
    81				/* main loop using 64byte blocks */
    82				zero = 0;
    83				count64 = count >> 3;
    84				while (count64) {
  > 85					__asm__ __volatile__(

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