perf stat: Report unsupported events properly

Commit 1971f59 (perf stat: Use read_counter in read_counter_aggr )
broke the perf stat output for unsupported counters.

 $ perf stat -v -a -C 0 -e CCI_400/config=24/ sleep 1
 Warning:
 CCI_400/config=24/ event is not supported by the kernel.

  Performance counter stats for 'system wide':

                  0      CCI_400/config=24/

        1.080265400 seconds time elapsed

Where it used to be :

$ perf stat -v -a -C 0 -e CCI_400/config=24/ sleep 1
 Warning:
 CCI_400/config=24/ event is not supported by the kernel.

  Performance counter stats for 'system wide':

    <not supported>      CCI_400/config=24/

        1.083840675 seconds time elapsed

This patch fixes the issues by checking if the counter is supported,
before reading and logging the counter value.

Signed-off-by: Suzuki K. Poulose <suzuki.poulose@arm.com>
Acked-by: David Ahern <dsahern@gmail.com>
Tested-by: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/1423852858-8455-1-git-send-email-suzuki.poulose@arm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-stat.c

@@ -510,6 +510,9 @@ static int read_counter(struct perf_evsel *counter)
 	int ncpus = perf_evsel__nr_cpus(counter);
 	int cpu, thread;
 
+	if (!counter->supported)
+		return -ENOENT;
+
 	if (counter->system_wide)
 		nthreads = 1;
 
@@ -1285,7 +1288,7 @@ static void print_counter_aggr(struct perf_evsel *counter, char *prefix)
 	if (prefix)
 		fprintf(output, "%s", prefix);
 
-	if (scaled == -1) {
+	if (scaled == -1 || !counter->supported) {
 		fprintf(output, "%*s%s",
 			csv_output ? 0 : 18,
 			counter->supported ? CNTR_NOT_COUNTED : CNTR_NOT_SUPPORTED,