Re: [PATCH v2] perf script: perf script tests fails with segfault

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

On 21/04/25 12:25, Aditya Bodkhe wrote:
> perf script: pert script tests fails with segmentation fault as below:
> 
>  92: perf script tests:
> --- start ---

Using --- here and below messes up the commit message
e.g. when applied with git am
Needs to be prefixed by at least 1 space

> 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 ---

Ditto

> ---- end(-1) ----

Ditto

> 	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 <disgoel@linux.ibm.com>
> Signed-off-by: Aditya Bodkhe <aditya.b1@linux.ibm.com>
> Suggested-by: Adrian Hunter <adrian.hunter@intel.com>

With --- fixes:

Reviewed-by: Adrian Hunter <adrian.hunter@intel.com>

> ---
> Changelog:
> v1 -> v2:
> The below patch contains changes suggested by Adrian Hunter<adrian.hunter@intel.com> to handle the segmentation fault ,
> as well as initialisation of al.thread
> 
>  tools/perf/util/db-export.c                           | 11 ++++++++---
>  .../perf/util/scripting-engines/trace-event-python.c  |  2 +-
>  2 files changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/perf/util/db-export.c b/tools/perf/util/db-export.c
> index 50f916374d87..8f52e8cefcf3 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);
> @@ -256,6 +256,7 @@ static struct call_path *call_path_from_sample(struct db_export *dbe,
>  		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);
> @@ -358,14 +359,18 @@ 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);
> --
> 2.43.0
>