[palmer:riscv-no_attributes-v2 33/34] lib/test_string.c:237 strncmp_selftest() warn: unsigned 'res' is never less than zero.

[kernel test robot <lkp@intel.com>]

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/palmer/linux.git riscv-no_attributes-v2
head:   858affb61bd0d79d702fe73d9316fd32693aacc4
commit: 51e24314e0a1f193799351c06af8727ab92fd4d2 [33/34] lib/test_string.c: Add strncmp() tests
config: m68k-randconfig-m031-20230226 (https://download.01.org/0day-ci/archive/20230227/202302270931.S9Ju89sL-lkp@intel.com/config)
compiler: m68k-linux-gcc (GCC) 12.1.0

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@intel.com>
| Link: https://lore.kernel.org/oe-kbuild-all/202302270931.S9Ju89sL-lkp@intel.com/

New smatch warnings:
lib/test_string.c:237 strncmp_selftest() warn: unsigned 'res' is never less than zero.
lib/test_string.c:237 strncmp_selftest() warn: always true condition '(s->retval >= 0) => (0-u32max >= 0)'

Old smatch warnings:
lib/test_string.c:14 memset16_selftest() warn: returning -1 instead of -ENOMEM is sloppy
lib/test_string.c:50 memset32_selftest() warn: returning -1 instead of -ENOMEM is sloppy
lib/test_string.c:86 memset64_selftest() warn: returning -1 instead of -ENOMEM is sloppy

vim +/res +237 lib/test_string.c

   209	
   210	static __init int strncmp_selftest(void)
   211	{
   212		static const struct strncmp_test {
   213			const char *str_a;
   214			const char *str_b;
   215			unsigned long count;
   216			unsigned long max_off;
   217			size_t retval;
   218		} tests[] __initconst = {
   219			{ "/dev/vda", "/dev/",    5, 4, 0 },
   220			{ "/dev/vda", "/dev/vdb", 5, 4, 0 },
   221		};
   222		size_t i;
   223	
   224		for (i = 0; i < ARRAY_SIZE(tests); ++i) {
   225			const struct strncmp_test *s = tests + i;
   226			size_t off;
   227	
   228			for (off = 0; off <= s->max_off; ++off) {
   229				size_t res = strncmp(s->str_a + off,
   230						     s->str_b + off,
   231						     s->count - off);
   232	
   233				if (res == 0 && s->retval != 0)
   234					return 0x1000 + 0x100*off + 0x10*i + 0x0;
   235				if (res > 0 && s->retval <= 0)
   236					return 0x1000 + 0x100*off + 0x10*i + 0x1;
 > 237				if (res < 0 && s->retval >= 0)
   238					return 0x1000 + 0x100*off + 0x10*i + 0x2;
   239			}
   240		}
   241		return 0;
   242	}
   243	

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