[PATCH] Check jvmti_agent snprintf return value to avoid build failures with GCC-8.1.1

[William Cohen <wcohen@redhat.com>]

Newer versions of GCC perform static analysis to determine whether
string truncation is possible with functions such as snprintf and
provide a warning if truncation could occur.  The make for
jvmti_agent.c uses the compiler option that treats any compiler
warnings as compiler errors.  For GCC-8.1.1 in Fedora 28 this causes
the build to fail.  The return value of the snprint is now checked to
ensure snprintf produced a NULL-terminated string.  If the string for
the path is invalid, the code does attempt to use the string.

Signed-off-by: William Cohen <wcohen@redhat.com>
---
 tools/perf/jvmti/jvmti_agent.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/tools/perf/jvmti/jvmti_agent.c b/tools/perf/jvmti/jvmti_agent.c
index 0c6d1002b524..30f14eafe4b3 100644
--- a/tools/perf/jvmti/jvmti_agent.c
+++ b/tools/perf/jvmti/jvmti_agent.c
@@ -227,7 +227,7 @@ void *jvmti_open(void)
 {
 	char dump_path[PATH_MAX];
 	struct jitheader header;
-	int fd;
+	int retlen, fd;
 	FILE *fp;
 
 	init_arch_timestamp();
@@ -249,7 +249,10 @@ void *jvmti_open(void)
 	/*
 	 * jitdump file name
 	 */
-	snprintf(dump_path, PATH_MAX, "%s/jit-%i.dump", jit_path, getpid());
+	retlen = snprintf(dump_path, PATH_MAX, "%s/jit-%i.dump",
+			  jit_path, getpid());
+	if (retlen <= 0 || ((int) sizeof(dump_path)) <= retlen)
+		return NULL;
 
 	fd = open(dump_path, O_CREAT|O_TRUNC|O_RDWR, 0666);
 	if (fd == -1)
-- 
2.17.1