perf diff: Constify strchr() return variables

commit f6f41ae upstream.

Newer glibc versions return const char for strchr() when the 's' arg is
const, change the return variable to const to match that.

Also we don't need to turn that ',' into a '\0', as strtol() will stop
in the first invalid char. No need to touch read only memory.

First noticed with fedora 44.

Reviewed-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20251211221756.96294-3-acme@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: acmel

tools/perf/builtin-diff.c

@@ -178,10 +178,9 @@ static struct header_column {
 	}
 };
 
-static int setup_compute_opt_wdiff(char *opt)
+static int setup_compute_opt_wdiff(const char *opt)
 {
-	char *w1_str = opt;
-	char *w2_str;
+	const char *w1_str = opt, *w2_str;
 
 	int ret = -EINVAL;
 
@@ -192,8 +191,7 @@ static int setup_compute_opt_wdiff(char *opt)
 	if (!w2_str)
 		goto out;
 
-	*w2_str++ = 0x0;
-	if (!*w2_str)
+	if (!*++w2_str)
 		goto out;
 
 	compute_wdiff_w1 = strtol(w1_str, NULL, 10);
@@ -214,7 +212,7 @@ static int setup_compute_opt_wdiff(char *opt)
 	return ret;
 }
 
-static int setup_compute_opt(char *opt)
+static int setup_compute_opt(const char *opt)
 {
 	if (compute == COMPUTE_WEIGHTED_DIFF)
 		return setup_compute_opt_wdiff(opt);
@@ -234,7 +232,7 @@ static int setup_compute(const struct option *opt, const char *str,
 	char *cstr = (char *) str;
 	char buf[50];
 	unsigned i;
-	char *option;
+	const char *option;
 
 	if (!str) {
 		*cp = COMPUTE_DELTA;