[PATCH] perf script: perf script tests fails with segfault

[Aditya Bodkhe <adityab1@linux.ibm.com>]

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perf script: pert script tests fails with segmentation fault as below:

1. Run perf test -vvv 'perf script tests'

	 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`.

To prevent this NULL pointer dereference, add a check for `al->maps == NULL`
before calling `maps__machine()`. If `al->maps` is NULL, return `-1` to avoid
the segmentation fault.

Reported-by: Disha Goel <Disha.Goel@ibm.com>
Signed-off-by: Aditya Bodkhe <aditya.b1@linux.ibm.com>
---
 tools/perf/util/db-export.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tools/perf/util/db-export.c b/tools/perf/util/db-export.c
index 50f916374d87..f355878a8c82 100644
--- a/tools/perf/util/db-export.c
+++ b/tools/perf/util/db-export.c
@@ -365,6 +365,11 @@ int db_export__sample(struct db_export *dbe, union perf_event *event,
        if (err)
                return err;

+       if (!al->maps) {
+          err = -1;
+          goto out_put;
+       }
+
        machine = maps__machine(al->maps);
        err = db_export__machine(dbe, machine);
        if (err)
-- 
2.43.0