perf stat-shadow: In prepare_metric fix guard on reading NULL perf_stat_evsel

The aggr value is setup to always be non-null creating a redundant
guard for reading from it. Switch to using the perf_stat_evsel (ps)
and narrow the scope of aggr so that it is known valid when used.

Fixes: 3d65f64 ("perf stat-shadow: Read tool events directly")
Reported-by: Andres Freund <andres@anarazel.de>
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Dapeng Mi <dapeng1.mi@linux.intel.com>
Cc: Dr. David Alan Gilbert <linux@treblig.org>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Falcon <thomas.falcon@intel.com>
Cc: Thomas Richter <tmricht@linux.ibm.com>
Cc: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Author: captain5050

tools/perf/util/stat-shadow.c

@@ -57,7 +57,6 @@ static int prepare_metric(struct perf_stat_config *config,
 		bool is_tool_time =
 			tool_pmu__is_time_event(config, metric_events[i], &tool_aggr_idx);
 		struct perf_stat_evsel *ps = metric_events[i]->stats;
-		struct perf_stat_aggr *aggr;
 		char *n;
 		double val;
 
@@ -82,8 +81,7 @@ static int prepare_metric(struct perf_stat_config *config,
 			}
 		}
 		/* Time events are always on CPU0, the first aggregation index. */
-		aggr = &ps->aggr[is_tool_time ? tool_aggr_idx : aggr_idx];
-		if (!aggr || !metric_events[i]->supported || aggr->counts.run == 0) {
+		if (!ps || !metric_events[i]->supported) {
 			/*
 			 * Not supported events will have a count of 0, which
 			 * can be confusing in a metric. Explicitly set the
@@ -93,11 +91,21 @@ static int prepare_metric(struct perf_stat_config *config,
 			val = NAN;
 			source_count = 0;
 		} else {
-			val = aggr->counts.val;
-			if (is_tool_time)
-				val *= 1e-9; /* Convert time event nanoseconds to seconds. */
-			if (!source_count)
-				source_count = evsel__source_count(metric_events[i]);
+			struct perf_stat_aggr *aggr =
+				&ps->aggr[is_tool_time ? tool_aggr_idx : aggr_idx];
+
+			if (aggr->counts.run == 0) {
+				val = NAN;
+				source_count = 0;
+			} else {
+				val = aggr->counts.val;
+				if (is_tool_time) {
+					/* Convert time event nanoseconds to seconds. */
+					val *= 1e-9;
+				}
+				if (!source_count)
+					source_count = evsel__source_count(metric_events[i]);
+			}
 		}
 		n = strdup(evsel__metric_id(metric_events[i]));
 		if (!n)