perf script: Fix allocation of evsel->priv related to per-event dump files

When printing output we may want to generate per event files, where the
--per-event-dump option should be used, creating perf.data.EVENT.dump
files instead of printing to stdout.

The callback thar processes event thus expects that evsel->priv->fp
should point to either the per-event FILE descriptor or to stdout.

The a3af66f5 ("perf script: Fix crash because of missing
evsel->priv") changeset fixed a case where evsel->priv wasn't setup,
thus set to NULL, causing a segfault when trying to access
evsel->priv->fp.

But it did it for the non --per-event-dump case by allocating a 'struct
perf_evsel_script' just to set its ->fp to stdout.

Since evsel->priv is only freed when --per-event-dump is used, we ended
up with a memory leak, detected using ASAN.

Fix it by using the same method as perf_script__setup_per_event_dump(),
and reuse that static 'struct perf_evsel_script'.

Also check if evsel_script__new() failed.

Fixes: a3af66f5 ("perf script: Fix crash because of missing evsel->priv")
Reported-by: Ian Rogers <irogers@google.com>
Tested-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Link: https://lore.kernel.org/lkml/ZH+F0wGAWV14zvMP@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-script.c

@@ -2410,6 +2410,9 @@ static int process_sample_event(struct perf_tool *tool,
 	return ret;
 }
 
+// Used when scr->per_event_dump is not set
+static struct evsel_script es_stdout;
+
 static int process_attr(struct perf_tool *tool, union perf_event *event,
 			struct evlist **pevlist)
 {
@@ -2418,7 +2421,6 @@ static int process_attr(struct perf_tool *tool, union perf_event *event,
 	struct evsel *evsel, *pos;
 	u64 sample_type;
 	int err;
-	static struct evsel_script *es;
 
 	err = perf_event__process_attr(tool, event, pevlist);
 	if (err)
@@ -2428,14 +2430,13 @@ static int process_attr(struct perf_tool *tool, union perf_event *event,
 	evsel = evlist__last(*pevlist);
 
 	if (!evsel->priv) {
-		if (scr->per_event_dump) {
+		if (scr->per_event_dump) { 
 			evsel->priv = evsel_script__new(evsel, scr->session->data);
-		} else {
-			es = zalloc(sizeof(*es));
-			if (!es)
+			if (!evsel->priv)
 				return -ENOMEM;
-			es->fp = stdout;
-			evsel->priv = es;
+		} else { // Replicate what is done in perf_script__setup_per_event_dump()
+			es_stdout.fp = stdout;
+			evsel->priv = &es_stdout;
 		}
 	}
 
@@ -2741,7 +2742,6 @@ static int perf_script__fopen_per_event_dump(struct perf_script *script)
 static int perf_script__setup_per_event_dump(struct perf_script *script)
 {
 	struct evsel *evsel;
-	static struct evsel_script es_stdout;
 
 	if (script->per_event_dump)
 		return perf_script__fopen_per_event_dump(script);