diff --git a/tools/perf/builtin-diff.c b/tools/perf/builtin-diff.c
index 4f19513..d29d350 100644
--- a/tools/perf/builtin-diff.c
+++ b/tools/perf/builtin-diff.c
@@ -24,6 +24,11 @@
 static bool  force;
 static bool show_displacement;
 
+struct perf_diff {
+	struct perf_tool tool;
+	struct perf_session *session;
+};
+
 static int hists__add_entry(struct hists *self,
 			    struct addr_location *al, u64 period)
 {
@@ -32,12 +37,14 @@
 	return -ENOMEM;
 }
 
-static int diff__process_sample_event(struct perf_tool *tool __used,
+static int diff__process_sample_event(struct perf_tool *tool,
 				      union perf_event *event,
 				      struct perf_sample *sample,
 				      struct perf_evsel *evsel __used,
 				      struct machine *machine)
 {
+	struct perf_diff *_diff = container_of(tool, struct perf_diff, tool);
+	struct perf_session *session = _diff->session;
 	struct addr_location al;
 
 	if (perf_event__preprocess_sample(event, machine, &al, sample, NULL) < 0) {
@@ -49,24 +56,26 @@
 	if (al.filtered || al.sym == NULL)
 		return 0;
 
-	if (hists__add_entry(&evsel->hists, &al, sample->period)) {
+	if (hists__add_entry(&session->hists, &al, sample->period)) {
 		pr_warning("problem incrementing symbol period, skipping event\n");
 		return -1;
 	}
 
-	evsel->hists.stats.total_period += sample->period;
+	session->hists.stats.total_period += sample->period;
 	return 0;
 }
 
-static struct perf_tool perf_diff = {
-	.sample	= diff__process_sample_event,
-	.mmap	= perf_event__process_mmap,
-	.comm	= perf_event__process_comm,
-	.exit	= perf_event__process_task,
-	.fork	= perf_event__process_task,
-	.lost	= perf_event__process_lost,
-	.ordered_samples = true,
-	.ordering_requires_timestamps = true,
+static struct perf_diff diff = {
+	.tool = {
+		.sample	= diff__process_sample_event,
+		.mmap	= perf_event__process_mmap,
+		.comm	= perf_event__process_comm,
+		.exit	= perf_event__process_task,
+		.fork	= perf_event__process_task,
+		.lost	= perf_event__process_lost,
+		.ordered_samples = true,
+		.ordering_requires_timestamps = true,
+	},
 };
 
 static void perf_session__insert_hist_entry_by_name(struct rb_root *root,
@@ -107,12 +116,6 @@
 	self->entries = tmp;
 }
 
-static void hists__set_positions(struct hists *self)
-{
-	hists__output_resort(self);
-	hists__resort_entries(self);
-}
-
 static struct hist_entry *hists__find_entry(struct hists *self,
 					    struct hist_entry *he)
 {
@@ -146,30 +149,37 @@
 static int __cmd_diff(void)
 {
 	int ret, i;
+#define older (session[0])
+#define newer (session[1])
 	struct perf_session *session[2];
 
-	session[0] = perf_session__new(input_old, O_RDONLY, force, false, &perf_diff);
-	session[1] = perf_session__new(input_new, O_RDONLY, force, false, &perf_diff);
+	older = perf_session__new(input_old, O_RDONLY, force, false,
+				  &diff.tool);
+	newer = perf_session__new(input_new, O_RDONLY, force, false,
+				  &diff.tool);
 	if (session[0] == NULL || session[1] == NULL)
 		return -ENOMEM;
 
 	for (i = 0; i < 2; ++i) {
-		ret = perf_session__process_events(session[i], &perf_diff);
+		diff.session = session[i];
+		ret = perf_session__process_events(session[i], &diff.tool);
 		if (ret)
 			goto out_delete;
+		hists__output_resort(&session[i]->hists);
 	}
 
-	hists__output_resort(&session[1]->hists);
 	if (show_displacement)
-		hists__set_positions(&session[0]->hists);
+		hists__resort_entries(&older->hists);
 
-	hists__match(&session[0]->hists, &session[1]->hists);
-	hists__fprintf(&session[1]->hists, &session[0]->hists,
+	hists__match(&older->hists, &newer->hists);
+	hists__fprintf(&newer->hists, &older->hists,
 		       show_displacement, true, 0, 0, stdout);
 out_delete:
 	for (i = 0; i < 2; ++i)
 		perf_session__delete(session[i]);
 	return ret;
+#undef older
+#undef newer
 }
 
 static const char * const diff_usage[] = {