tools lib traceevent: Fix strerror_r() use in pevent_strerror

glibc-2.16 starts to mark the function with attribute warn_unused_result
so that it can cause a build warning.

Since GNU version of strerror_r() can return a pointer to a string
without setting @buf, check the return value and copy/truncate it to our
buffer if needed.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/1345618831-9148-5-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/lib/traceevent/event-parse.c b/tools/lib/traceevent/event-parse.c
index 1373e4c..f978c59 100644
--- a/tools/lib/traceevent/event-parse.c
+++ b/tools/lib/traceevent/event-parse.c
@@ -4809,7 +4809,12 @@
 	const char *msg;
 
 	if (errnum >= 0) {
-		strerror_r(errnum, buf, buflen);
+		msg = strerror_r(errnum, buf, buflen);
+		if (msg != buf) {
+			size_t len = strlen(msg);
+			char *c = mempcpy(buf, msg, min(buflen-1, len));
+			*c = '\0';
+		}
 		return 0;
 	}