perf script: perf script tests fails with segfault

pert script tests fails with segmentation fault as below:

92: perf script tests:
--- start ---
test child forked, pid 103769
DB test
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.012 MB /tmp/perf-test-script.7rbftEpOzX/perf.data (9 samples) ]
/usr/libexec/perf-core/tests/shell/script.sh: line 35:
103780 Segmentation fault (core dumped)
perf script -i "${perfdatafile}" -s "${db_test}"
--- Cleaning up ---
---- end(-1) ----
92: perf script tests : FAILED!

Backtrace pointed to :
#0 0x0000000010247dd0 in maps.machine ()
#1 0x00000000101d178c in db_export.sample ()
#2 0x00000000103412c8 in python_process_event ()
#3 0x000000001004eb28 in process_sample_event ()
#4 0x000000001024fcd0 in machines.deliver_event ()
#5 0x000000001025005c in perf_session.deliver_event ()
#6 0x00000000102568b0 in __ordered_events__flush.part.0 ()
#7 0x0000000010251618 in perf_session.process_events ()
#8 0x0000000010053620 in cmd_script ()
#9 0x00000000100b5a28 in run_builtin ()
#10 0x00000000100b5f94 in handle_internal_command ()
#11 0x0000000010011114 in main ()

Further investigation reveals that this occurs in the `perf script tests`,
because it uses `db_test.py` script. This script sets `perf_db_export_mode = True`.

With `perf_db_export_mode` enabled, if a sample originates from a hypervisor,
perf doesn't set maps for "[H]" sample in the code. Consequently, `al->maps` remains NULL
when `maps__machine(al->maps)` is called from `db_export__sample`.

As al->maps can be NULL in case of Hypervisor samples , use thread->maps
because even for Hypervisor sample, machine should exist.
If we don't have machine for some reason, return -1 to avoid segmentation fault.

Reported-by: Disha Goel <[e-mail]>
Signed-off-by: Aditya Bodkhe <[e-mail]>
Reviewed-by: Adrian Hunter <[e-mail]>
Tested-by: Disha Goel <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Suggested-by: Adrian Hunter <[e-mail]>
Signed-off-by: Namhyung Kim <[e-mail]>

tools/perf/util/db-export.c

···
 	if (al->map) {
 		struct dso *dso = map__dso(al->map);
 
-		err = db_export__dso(dbe, dso, maps__machine(al->maps));
+		err = db_export__dso(dbe, dso, maps__machine(thread__maps(al->thread)));
 		if (err)
 			return err;
 		*dso_db_id = dso__db_id(dso);
···
 		al.map = map__get(node->ms.map);
 		al.maps = maps__get(thread__maps(thread));
 		al.addr = node->ip;
+		al.thread = thread__get(thread);
 
 		if (al.map && !al.sym)
 			al.sym = dso__find_symbol(map__dso(al.map), al.addr);
···
 	};
 	struct thread *main_thread;
 	struct comm *comm = NULL;
-	struct machine *machine;
+	struct machine *machine = NULL;
 	int err;
+
+	if (thread__maps(thread))
+		machine = maps__machine(thread__maps(thread));
+	if (!machine)
+		return -1;
 
 	err = db_export__evsel(dbe, evsel);
 	if (err)
 		return err;
 
-	machine = maps__machine(al->maps);
 	err = db_export__machine(dbe, machine);
 	if (err)
 		return err;

tools/perf/util/scripting-engines/trace-event-python.c

···
 
 	tuple_set_d64(t, 0, es->db_id);
 	tuple_set_d64(t, 1, es->evsel->db_id);
-	tuple_set_d64(t, 2, maps__machine(es->al->maps)->db_id);
+	tuple_set_d64(t, 2, maps__machine(thread__maps(es->al->thread))->db_id);
 	tuple_set_d64(t, 3, thread__db_id(es->al->thread));
 	tuple_set_d64(t, 4, es->comm_db_id);
 	tuple_set_d64(t, 5, es->dso_db_id);