perf pmu: Suppress potential format-truncation warning

BugLink: https://bugs.launchpad.net/bugs/1811647

commit 11a64a05 upstream.

Depending on which functions are inlined in util/pmu.c, the snprintf()
calls in perf_pmu__parse_{scale,unit,per_pkg,snapshot}() might trigger a
warning:

  util/pmu.c: In function 'pmu_aliases':
  util/pmu.c:178:31: error: '%s' directive output may be truncated writing up to 255 bytes into a region of size between 0 and 4095 [-Werror=format-truncation=]
    snprintf(path, PATH_MAX, "%s/%s.unit", dir, name);
                               ^~

I found this when trying to build perf from Linux 3.16 with gcc 8.
However I can reproduce the problem in mainline if I force
__perf_pmu__new_alias() to be inlined.

Suppress this by using scnprintf() as has been done elsewhere in perf.
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/20181111184524.fux4taownc6ndbx6@decadent.org.ukSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

tools/perf/util/pmu.c

@@ -100,7 +100,7 @@ static int perf_pmu__parse_scale(struct perf_pmu_alias *alias, char *dir, char *
 	char path[PATH_MAX];
 	const char *lc;
 
-	snprintf(path, PATH_MAX, "%s/%s.scale", dir, name);
+	scnprintf(path, PATH_MAX, "%s/%s.scale", dir, name);
 
 	fd = open(path, O_RDONLY);
 	if (fd == -1)
@@ -147,7 +147,7 @@ static int perf_pmu__parse_unit(struct perf_pmu_alias *alias, char *dir, char *n
 	ssize_t sret;
 	int fd;
 
-	snprintf(path, PATH_MAX, "%s/%s.unit", dir, name);
+	scnprintf(path, PATH_MAX, "%s/%s.unit", dir, name);
 
 	fd = open(path, O_RDONLY);
 	if (fd == -1)
@@ -177,7 +177,7 @@ perf_pmu__parse_per_pkg(struct perf_pmu_alias *alias, char *dir, char *name)
 	char path[PATH_MAX];
 	int fd;
 
-	snprintf(path, PATH_MAX, "%s/%s.per-pkg", dir, name);
+	scnprintf(path, PATH_MAX, "%s/%s.per-pkg", dir, name);
 
 	fd = open(path, O_RDONLY);
 	if (fd == -1)
@@ -195,7 +195,7 @@ static int perf_pmu__parse_snapshot(struct perf_pmu_alias *alias,
 	char path[PATH_MAX];
 	int fd;
 
-	snprintf(path, PATH_MAX, "%s/%s.snapshot", dir, name);
+	scnprintf(path, PATH_MAX, "%s/%s.snapshot", dir, name);
 
 	fd = open(path, O_RDONLY);
 	if (fd == -1)