selftests/bpf: Fix a tautological-constant-out-of-range-compare compiler warning

When using clang to build selftests with LLVM=1 in make commandline,
I hit the following compiler warning:

  benchs/bench_bloom_filter_map.c:84:46: warning: result of comparison of constant 256
    with expression of type '__u8' (aka 'unsigned char') is always false
    [-Wtautological-constant-out-of-range-compare]
                if (args.value_size < 2 || args.value_size > 256) {
                                           ~~~~~~~~~~~~~~~ ^ ~~~

The reason is arg.vaue_size has type __u8, so comparison "args.value_size > 256"
is always false.

This patch fixed the issue by doing proper comparison before assigning the
value to args.value_size. The patch also fixed the same issue in two
other places.
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211112204838.3579953-1-yhs@fb.com

tools/testing/selftests/bpf/benchs/bench_bloom_filter_map.c

@@ -63,29 +63,34 @@ static const struct argp_option opts[] = {
 
 static error_t parse_arg(int key, char *arg, struct argp_state *state)
 {
+	long ret;
+
 	switch (key) {
 	case ARG_NR_ENTRIES:
-		args.nr_entries = strtol(arg, NULL, 10);
-		if (args.nr_entries == 0) {
+		ret = strtol(arg, NULL, 10);
+		if (ret < 1 || ret > UINT_MAX) {
 			fprintf(stderr, "Invalid nr_entries count.");
 			argp_usage(state);
 		}
+		args.nr_entries = ret;
 		break;
 	case ARG_NR_HASH_FUNCS:
-		args.nr_hash_funcs = strtol(arg, NULL, 10);
-		if (args.nr_hash_funcs == 0 || args.nr_hash_funcs > 15) {
+		ret = strtol(arg, NULL, 10);
+		if (ret < 1 || ret > 15) {
 			fprintf(stderr,
 				"The bloom filter must use 1 to 15 hash functions.");
 			argp_usage(state);
 		}
+		args.nr_hash_funcs = ret;
 		break;
 	case ARG_VALUE_SIZE:
-		args.value_size = strtol(arg, NULL, 10);
-		if (args.value_size < 2 || args.value_size > 256) {
+		ret = strtol(arg, NULL, 10);
+		if (ret < 2 || ret > 256) {
 			fprintf(stderr,
 				"Invalid value size. Must be between 2 and 256 bytes");
 			argp_usage(state);
 		}
+		args.value_size = ret;
 		break;
 	default:
 		return ARGP_ERR_UNKNOWN;