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Date: Fri, 26 May 2023 20:22:30 +0800
From: kernel test robot <lkp@...el.com>
To: Noah Goldstein <goldstein.w.n@...il.com>
Cc: llvm@...ts.linux.dev, oe-kbuild-all@...ts.linux.dev,
linux-kernel@...r.kernel.org, x86@...nel.org,
Dave Hansen <dave.hansen@...ux.intel.com>
Subject: [tip:x86/misc 1/1] arch/x86/lib/csum-partial_64.c:74:20: warning:
variable 'result' is uninitialized when used here
tree: https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86/misc
head: 688eb8191b475db5acfd48634600b04fd3dda9ad
commit: 688eb8191b475db5acfd48634600b04fd3dda9ad [1/1] x86/csum: Improve performance of `csum_partial`
config: x86_64-randconfig-x073-20230525 (https://download.01.org/0day-ci/archive/20230526/202305262039.3HUYjWJk-lkp@intel.com/config)
compiler: clang version 14.0.6 (https://github.com/llvm/llvm-project f28c006a5895fc0e329fe15fead81e37457cb1d1)
reproduce (this is a W=1 build):
mkdir -p ~/bin
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?id=688eb8191b475db5acfd48634600b04fd3dda9ad
git remote add tip https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git
git fetch --no-tags tip x86/misc
git checkout 688eb8191b475db5acfd48634600b04fd3dda9ad
# save the config file
mkdir build_dir && cp config build_dir/.config
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang ~/bin/make.cross W=1 O=build_dir ARCH=x86_64 olddefconfig
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang ~/bin/make.cross W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash
If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@...el.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202305262039.3HUYjWJk-lkp@intel.com/
All warnings (new ones prefixed by >>):
>> arch/x86/lib/csum-partial_64.c:74:20: warning: variable 'result' is uninitialized when used here [-Wuninitialized]
return csum_tail(result, temp64, odd);
^~~~~~
arch/x86/lib/csum-partial_64.c:48:22: note: initialize the variable 'result' to silence this warning
unsigned odd, result;
^
= 0
1 warning generated.
vim +/result +74 arch/x86/lib/csum-partial_64.c
33
34 /*
35 * Do a checksum on an arbitrary memory area.
36 * Returns a 32bit checksum.
37 *
38 * This isn't as time critical as it used to be because many NICs
39 * do hardware checksumming these days.
40 *
41 * Still, with CHECKSUM_COMPLETE this is called to compute
42 * checksums on IPv6 headers (40 bytes) and other small parts.
43 * it's best to have buff aligned on a 64-bit boundary
44 */
45 __wsum csum_partial(const void *buff, int len, __wsum sum)
46 {
47 u64 temp64 = (__force u64)sum;
48 unsigned odd, result;
49
50 odd = 1 & (unsigned long) buff;
51 if (unlikely(odd)) {
52 if (unlikely(len == 0))
53 return sum;
54 temp64 = ror32((__force u32)sum, 8);
55 temp64 += (*(unsigned char *)buff << 8);
56 len--;
57 buff++;
58 }
59
60 /*
61 * len == 40 is the hot case due to IPv6 headers, but annotating it likely()
62 * has noticeable negative affect on codegen for all other cases with
63 * minimal performance benefit here.
64 */
65 if (len == 40) {
66 asm("addq 0*8(%[src]),%[res]\n\t"
67 "adcq 1*8(%[src]),%[res]\n\t"
68 "adcq 2*8(%[src]),%[res]\n\t"
69 "adcq 3*8(%[src]),%[res]\n\t"
70 "adcq 4*8(%[src]),%[res]\n\t"
71 "adcq $0,%[res]"
72 : [res] "+r"(temp64)
73 : [src] "r"(buff), "m"(*(const char(*)[40])buff));
> 74 return csum_tail(result, temp64, odd);
75 }
76 if (unlikely(len >= 64)) {
77 /*
78 * Extra accumulators for better ILP in the loop.
79 */
80 u64 tmp_accum, tmp_carries;
81
82 asm("xorl %k[tmp_accum],%k[tmp_accum]\n\t"
83 "xorl %k[tmp_carries],%k[tmp_carries]\n\t"
84 "subl $64, %[len]\n\t"
85 "1:\n\t"
86 "addq 0*8(%[src]),%[res]\n\t"
87 "adcq 1*8(%[src]),%[res]\n\t"
88 "adcq 2*8(%[src]),%[res]\n\t"
89 "adcq 3*8(%[src]),%[res]\n\t"
90 "adcl $0,%k[tmp_carries]\n\t"
91 "addq 4*8(%[src]),%[tmp_accum]\n\t"
92 "adcq 5*8(%[src]),%[tmp_accum]\n\t"
93 "adcq 6*8(%[src]),%[tmp_accum]\n\t"
94 "adcq 7*8(%[src]),%[tmp_accum]\n\t"
95 "adcl $0,%k[tmp_carries]\n\t"
96 "addq $64, %[src]\n\t"
97 "subl $64, %[len]\n\t"
98 "jge 1b\n\t"
99 "addq %[tmp_accum],%[res]\n\t"
100 "adcq %[tmp_carries],%[res]\n\t"
101 "adcq $0,%[res]"
102 : [tmp_accum] "=&r"(tmp_accum),
103 [tmp_carries] "=&r"(tmp_carries), [res] "+r"(temp64),
104 [len] "+r"(len), [src] "+r"(buff)
105 : "m"(*(const char *)buff));
106 }
107
108 if (len & 32) {
109 asm("addq 0*8(%[src]),%[res]\n\t"
110 "adcq 1*8(%[src]),%[res]\n\t"
111 "adcq 2*8(%[src]),%[res]\n\t"
112 "adcq 3*8(%[src]),%[res]\n\t"
113 "adcq $0,%[res]"
114 : [res] "+r"(temp64)
115 : [src] "r"(buff), "m"(*(const char(*)[32])buff));
116 buff += 32;
117 }
118 if (len & 16) {
119 asm("addq 0*8(%[src]),%[res]\n\t"
120 "adcq 1*8(%[src]),%[res]\n\t"
121 "adcq $0,%[res]"
122 : [res] "+r"(temp64)
123 : [src] "r"(buff), "m"(*(const char(*)[16])buff));
124 buff += 16;
125 }
126 if (len & 8) {
127 asm("addq 0*8(%[src]),%[res]\n\t"
128 "adcq $0,%[res]"
129 : [res] "+r"(temp64)
130 : [src] "r"(buff), "m"(*(const char(*)[8])buff));
131 buff += 8;
132 }
133 if (len & 7) {
134 unsigned int shift = (-len << 3) & 63;
135 unsigned long trail;
136
137 trail = (load_unaligned_zeropad(buff) << shift) >> shift;
138
139 asm("addq %[trail],%[res]\n\t"
140 "adcq $0,%[res]"
141 : [res] "+r"(temp64)
142 : [trail] "r"(trail));
143 }
144 return csum_tail(result, temp64, odd);
145 }
146 EXPORT_SYMBOL(csum_partial);
147
--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
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