[PATCH] perf: fix uninitialized variable in thread__set_comm()

[Stephane Eranian]

In thread__set_comm(), a command string could be freed and then
reused to point to a new command. Yet, the length was never reset
nor recomputed. This could lead to bogus column formatting.

This patch below fixes the problem by having thread__set_comm()
immediately compute the string length in thread->comm_len. It
gets rid of thread__comm_len() which is not needed anymore.
It was doing the lazy eval of strlen() which could cause the
issue.

Signed-off-by: Stephane Eranian <eranian@xxxxxxxxxx>
---

diff --git a/tools/perf/util/hist.c b/tools/perf/util/hist.c
index 677e1da..b883821 100644
--- a/tools/perf/util/hist.c
+++ b/tools/perf/util/hist.c
@@ -61,7 +61,7 @@ static void hists__calc_col_len(struct hists *self, struct hist_entry *h)
 					   unresolved_col_width);
 	}
 
-	len = thread__comm_len(h->thread);
+	len = h->thread->comm_len;
 	if (hists__new_col_len(self, HISTC_COMM, len))
 		hists__set_col_len(self, HISTC_THREAD, len + 6);
 
@@ -731,7 +731,7 @@ static size_t hist_entry__fprintf_callchain(struct hist_entry *self,
 		struct sort_entry *se = list_first_entry(&hist_entry__sort_list,
 							 typeof(*se), list);
 		left_margin = hists__col_len(hists, se->se_width_idx);
-		left_margin -= thread__comm_len(self->thread);
+		left_margin -= self->thread->comm_len;
 	}
 
 	return hist_entry_callchain__fprintf(fp, self, session_total,
diff --git a/tools/perf/util/thread.c b/tools/perf/util/thread.c
index d5d3b22..3ce2a80 100644
--- a/tools/perf/util/thread.c
+++ b/tools/perf/util/thread.c
@@ -35,26 +35,18 @@ int thread__set_comm(struct thread *self, const char *comm)
 
 	if (self->comm)
 		free(self->comm);
+
 	self->comm = strdup(comm);
+
 	err = self->comm == NULL ? -ENOMEM : 0;
 	if (!err) {
 		self->comm_set = true;
+		self->comm_len = strlen(self->comm);
 		map_groups__flush(&self->mg);
 	}
 	return err;
 }
 
-int thread__comm_len(struct thread *self)
-{
-	if (!self->comm_len) {
-		if (!self->comm)
-			return 0;
-		self->comm_len = strlen(self->comm);
-	}
-
-	return self->comm_len;
-}
-
 static size_t thread__fprintf(struct thread *self, FILE *fp)
 {
 	return fprintf(fp, "Thread %d %s\n", self->pid, self->comm) +
diff --git a/tools/perf/util/thread.h b/tools/perf/util/thread.h
index e5f2401..701ea09 100644
--- a/tools/perf/util/thread.h
+++ b/tools/perf/util/thread.h
@@ -23,7 +23,6 @@ struct perf_session;
 void thread__delete(struct thread *self);
 
 int thread__set_comm(struct thread *self, const char *comm);
-int thread__comm_len(struct thread *self);
 struct thread *perf_session__findnew(struct perf_session *self, pid_t pid);
 void thread__insert_map(struct thread *self, struct map *map);
 int thread__fork(struct thread *self, struct thread *parent);
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