perf thread-stack: Allocate an array of thread stacks

In preparation for fixing thread stack processing for the idle task,
allocate an array of thread stacks.
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/20181221120620.9659-7-adrian.hunter@intel.com
[ No need to check for NULL when calling zfree(), noticed by Jiri Olsa ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/thread-stack.c

@@ -114,20 +114,25 @@ static int thread_stack__init(struct thread_stack *ts, struct thread *thread,
 static struct thread_stack *thread_stack__new(struct thread *thread,
 					      struct call_return_processor *crp)
 {
-	struct thread_stack *ts;
-
-	ts = zalloc(sizeof(struct thread_stack));
-	if (!ts)
-		return NULL;
-
-	ts->arr_sz = 1;
-
-	if (thread_stack__init(ts, thread, crp)) {
-		free(ts);
-		return NULL;
+	struct thread_stack *ts = thread->ts, *new_ts;
+	unsigned int old_sz = ts ? ts->arr_sz : 0;
+	unsigned int new_sz = 1;
+
+	if (!ts || new_sz > old_sz) {
+		new_ts = calloc(new_sz, sizeof(*ts));
+		if (!new_ts)
+			return NULL;
+		if (ts)
+			memcpy(new_ts, ts, old_sz * sizeof(*ts));
+		new_ts->arr_sz = new_sz;
+		zfree(&thread->ts);
+		thread->ts = new_ts;
+		ts = new_ts;
 	}
 
-	thread->ts = ts;
+	if (!ts->stack &&
+	    thread_stack__init(ts, thread, crp))
+		return NULL;
 
 	return ts;
 }