perf trace: Use zfree() to reduce chances of use after free

Do defensive programming by using zfree() to initialize freed pointers
to NULL, so that eventual use after free result in a NULL pointer deref
instead of more subtle behaviour.
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-trace.c

@@ -2288,7 +2288,7 @@ static void syscall__exit(struct syscall *sc)
 	if (!sc)
 		return;
 
-	free(sc->arg_fmt);
+	zfree(&sc->arg_fmt);
 }
 
 static int trace__sys_enter(struct trace *trace, struct evsel *evsel,
@@ -3124,7 +3124,7 @@ static void evlist__free_syscall_tp_fields(struct evlist *evlist)
 		if (!et || !evsel->tp_format || strcmp(evsel->tp_format->system, "syscalls"))
 			continue;
 
-		free(et->fmt);
+		zfree(&et->fmt);
 		free(et);
 	}
 }
@@ -4670,11 +4670,11 @@ static void trace__exit(struct trace *trace)
 	int i;
 
 	strlist__delete(trace->ev_qualifier);
-	free(trace->ev_qualifier_ids.entries);
+	zfree(&trace->ev_qualifier_ids.entries);
 	if (trace->syscalls.table) {
 		for (i = 0; i <= trace->sctbl->syscalls.max_id; i++)
 			syscall__exit(&trace->syscalls.table[i]);
-		free(trace->syscalls.table);
+		zfree(&trace->syscalls.table);
 	}
 	syscalltbl__delete(trace->sctbl);
 	zfree(&trace->perfconfig_events);