perf evlist: Check that there is a thread_map when preparing a workload

The perf_evlist__prepare_workload expects a thread map to be in place
so that it can store the pid of the workload being started, so check it
and tell the developer about it instead of segfaulting.

Cc: Adrian Hunter <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Don Zickus <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: Jean Pihet <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Mike Galbraith <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Stephane Eranian <[email protected]>
Link: http://lkml.kernel.org/n/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

tools/perf/util/evlist.c

@@ -1276,8 +1276,14 @@ int perf_evlist__prepare_workload(struct perf_evlist *evlist, struct target *tar
 		sigaction(SIGUSR1, &act, NULL);
 	}
 
-	if (target__none(target))
+	if (target__none(target)) {
+		if (evlist->threads == NULL) {
+			fprintf(stderr, "FATAL: evlist->threads need to be set at this point (%s:%d).\n",
+				__func__, __LINE__);
+			goto out_close_pipes;
+		}
 		evlist->threads->map[0] = evlist->workload.pid;
+	}
 
 	close(child_ready_pipe[1]);
 	close(go_pipe[0]);