[PATCH 2/3] dump_to_file: check for backtrace_symbols errors

[Eric Wong <e@80x24.org>]

We can also limit the scope of its return value since the
pointers inside the return value do not get freed.
---
 mwrap_core.h | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/mwrap_core.h b/mwrap_core.h
index 291a078..f3b25b7 100644
--- a/mwrap_core.h
+++ b/mwrap_core.h
@@ -624,16 +624,20 @@ static void *dump_to_file(struct dump_arg *a)
 		goto out_unlock;
 	cds_lfht_for_each_entry(t, &iter, l, hnode) {
 		const void *p = l->k;
-		char **s = 0;
 		if (l->total <= a->min) continue;
 
 		if (loc_is_addr(l)) {
-			s = backtrace_symbols(p, 1);
-			p = s[0];
+			char **s = backtrace_symbols(p, 1);
+			if (s) {
+				p = s[0];
+				free(s);
+			} else {
+				fprintf(stderr, "backtrace_symbols: %s\n",
+					strerror(errno));
+			}
 		}
 		fprintf(a->fp, "%16zu %12zu %s\n",
 			l->total, l->allocations, (const char *)p);
-		if (s) free(s);
 	}
 out_unlock:
 	rcu_read_unlock();