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

[Adrian Hunter <adrian.hunter@intel.com>]

On 21/03/25 08:04, Namhyung Kim wrote:
> CC-ing Adrian,

Thanks!

> 
> On Thu, Mar 20, 2025 at 02:45:51PM +0530, Aditya Bodkhe wrote:
>> 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;
>> +       }
> 
> Maybe better to check it before db_export__evsel().  Also it seems it
> should not goto out_put as it doesn't get the main_thread yet.

There has to be a machine to have found a thread.  I'd suggest
getting the machine from the thread, like this:

diff --git a/tools/perf/util/db-export.c b/tools/perf/util/db-export.c
index 50f916374d87..7ea6fd474c4c 100644
--- a/tools/perf/util/db-export.c
+++ b/tools/perf/util/db-export.c
@@ -181,7 +181,7 @@ static int db_ids_from_al(struct db_export *dbe, struct addr_location *al,
 	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);
@@ -358,14 +358,18 @@ int db_export__sample(struct db_export *dbe, union perf_event *event,
 	};
 	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;
diff --git a/tools/perf/util/scripting-engines/trace-event-python.c b/tools/perf/util/scripting-engines/trace-event-python.c
index 520729e78965..00f2c6c5114d 100644
--- a/tools/perf/util/scripting-engines/trace-event-python.c
+++ b/tools/perf/util/scripting-engines/trace-event-python.c
@@ -1306,7 +1306,7 @@ static void python_export_sample_table(struct db_export *dbe,
 
 	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);