perf annotate: Fix up usage of the build id cache

It was assuming that the cache was always available and also wasn't
checking if the file found in the build id cache was just a kallsyms
file, that is not supported by objdump for disassembly.
Reported-by: Ingo Molnar <mingo@elte.hu>
Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Cc: Tom Zanussi <tzanussi@gmail.com>
LKML-Reference: <new-submission>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/hist.c

@@ -990,6 +990,7 @@ int hist_entry__annotate(struct hist_entry *self, struct list_head *head)
 	struct map *map = self->ms.map;
 	struct dso *dso = map->dso;
 	char *filename = dso__build_id_filename(dso, NULL, 0);
+	bool free_filename = true;
 	char command[PATH_MAX * 2];
 	FILE *file;
 	int err = 0;
@@ -1001,11 +1002,19 @@ int hist_entry__annotate(struct hist_entry *self, struct list_head *head)
 			       sym->name);
 			return -ENOMEM;
 		}
+		goto fallback;
+	} else if (readlink(filename, command, sizeof(command)) < 0 ||
+		   strstr(command, "[kernel.kallsyms]") ||
+		   access(filename, R_OK)) {
+		free(filename);
+fallback:
 		/*
-		 * If we don't have build-ids, well, lets hope that this
+		 * If we don't have build-ids or the build-id file isn't in the
+		 * cache, or is just a kallsyms file, well, lets hope that this
 		 * DSO is the same as when 'perf record' ran.
 		 */
 		filename = dso->long_name;
+		free_filename = false;
 	}
 
 	if (dso->origin == DSO__ORIG_KERNEL) {
@@ -1045,7 +1054,7 @@ int hist_entry__annotate(struct hist_entry *self, struct list_head *head)
 
 	pclose(file);
 out_free_filename:
-	if (dso->has_build_id)
+	if (free_filename)
 		free(filename);
 	return err;
 }