linux-kernel - arch/mips/ralink/mt7621.c:123:22: warning: '__builtin_memcmp' reading between 1 and 4 bytes from a region of size 0

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Date:   Wed, 19 Jan 2022 15:20:31 +0800
From:   kernel test robot <lkp@...el.com>
To:     Chuanhong Guo <gch981213@...il.com>
Cc:     kbuild-all@...ts.01.org, linux-kernel@...r.kernel.org,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Ilya Lipnitskiy <ilya.lipnitskiy@...il.com>
Subject: arch/mips/ralink/mt7621.c:123:22: warning: '__builtin_memcmp'
 reading between 1 and 4 bytes from a region of size 0

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   99613159ad749543621da8238acf1a122880144e
commit: 139c949f7f0ac0dd1c0da132675be80e6d76c65d MIPS: ralink: mt7621: add memory detection support
date:   10 months ago
config: mips-randconfig-r036-20220119 (https://download.01.org/0day-ci/archive/20220119/202201191557.OISJHNMi-lkp@intel.com/config)
compiler: mipsel-linux-gcc (GCC) 11.2.0
reproduce (this is a W=1 build):
        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/torvalds/linux.git/commit/?id=139c949f7f0ac0dd1c0da132675be80e6d76c65d
        git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
        git fetch --no-tags linus master
        git checkout 139c949f7f0ac0dd1c0da132675be80e6d76c65d
        # save the config file to linux build tree
        mkdir build_dir
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 make.cross O=build_dir ARCH=mips SHELL=/bin/bash arch/mips/ralink/

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

All warnings (new ones prefixed by >>):

   In file included from include/linux/kernel.h:10,
                    from arch/mips/ralink/mt7621.c:8:
   arch/mips/ralink/mt7621.c: In function 'mt7621_memory_detect':
>> arch/mips/ralink/mt7621.c:123:22: warning: '__builtin_memcmp' reading between 1 and 4 bytes from a region of size 0 [-Wstringop-overread]
     123 |                 if (!__builtin_memcmp(dm, dm + size, sizeof(detect_magic)))
         |                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/compiler.h:58:52: note: in definition of macro '__trace_if_var'
      58 | #define __trace_if_var(cond) (__builtin_constant_p(cond) ? (cond) : __trace_if_value(cond))
         |                                                    ^~~~
   arch/mips/ralink/mt7621.c:123:17: note: in expansion of macro 'if'
     123 |                 if (!__builtin_memcmp(dm, dm + size, sizeof(detect_magic)))
         |                 ^~
   arch/mips/ralink/mt7621.c:54:14: note: at offset 33554432 into source object 'detect_magic' of size 4
      54 | static void *detect_magic __initdata = detect_memory_region;
         |              ^~~~~~~~~~~~
   In file included from include/linux/kernel.h:10,
                    from arch/mips/ralink/mt7621.c:8:
   arch/mips/ralink/mt7621.c:129:13: warning: '__builtin_memcmp' reading between 1 and 4 bytes from a region of size 0 [-Wstringop-overread]
     129 |             __builtin_memcmp(dm, dm + size, sizeof(detect_magic))) {
         |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/compiler.h:69:10: note: in definition of macro '__trace_if_value'
      69 |         (cond) ?                                        \
         |          ^~~~
   include/linux/compiler.h:56:28: note: in expansion of macro '__trace_if_var'
      56 | #define if(cond, ...) if ( __trace_if_var( !!(cond , ## __VA_ARGS__) ) )
         |                            ^~~~~~~~~~~~~~
   arch/mips/ralink/mt7621.c:127:9: note: in expansion of macro 'if'
     127 |         if ((size == 256 * SZ_1M) &&
         |         ^~
   arch/mips/ralink/mt7621.c:54:14: note: at offset 268435456 into source object 'detect_magic' of size 4
      54 | static void *detect_magic __initdata = detect_memory_region;
         |              ^~~~~~~~~~~~
   {standard input}: Assembler messages:
   {standard input}:127: Error: found '(', expected: ')'
   {standard input}:127: Error: found '(', expected: ')'
   {standard input}:127: Error: non-constant expression in ".if" statement
   {standard input}:127: Error: junk at end of line, first unrecognized character is `('
   {standard input}:154: Error: found '(', expected: ')'
   {standard input}:154: Error: found '(', expected: ')'
   {standard input}:154: Error: non-constant expression in ".if" statement
   {standard input}:154: Error: junk at end of line, first unrecognized character is `('


vim +/__builtin_memcmp +123 arch/mips/ralink/mt7621.c

   116	
   117	static void __init mt7621_memory_detect(void)
   118	{
   119		void *dm = &detect_magic;
   120		phys_addr_t size;
   121	
   122		for (size = 32 * SZ_1M; size < 256 * SZ_1M; size <<= 1) {
 > 123			if (!__builtin_memcmp(dm, dm + size, sizeof(detect_magic)))
   124				break;
   125		}
   126	
   127		if ((size == 256 * SZ_1M) &&
   128		    (CPHYSADDR(dm + size) < MT7621_LOWMEM_MAX_SIZE) &&
   129		    __builtin_memcmp(dm, dm + size, sizeof(detect_magic))) {
   130			memblock_add(MT7621_LOWMEM_BASE, MT7621_LOWMEM_MAX_SIZE);
   131			memblock_add(MT7621_HIGHMEM_BASE, MT7621_HIGHMEM_SIZE);
   132		} else {
   133			memblock_add(MT7621_LOWMEM_BASE, size);
   134		}
   135	}
   136	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org