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| author | Yafang Shao <laoar.shao@gmail.com> | 2023-02-12 15:13:03 +0000 |
|---|---|---|
| committer | Steven Rostedt (Google) <rostedt@goodmis.org> | 2023-02-12 10:23:39 -0500 |
| commit | b6c7abd1c28a63ad633433d037ee15a1bc3023ba (patch) | |
| tree | 6dc4c11b959cd099c2579ed358b1406be19e9669 /include/trace | |
| parent | 3e46d910d8acf94e5360126593b68bf4fee4c4a1 (diff) | |
| download | lwn-b6c7abd1c28a63ad633433d037ee15a1bc3023ba.tar.gz lwn-b6c7abd1c28a63ad633433d037ee15a1bc3023ba.zip | |
tracing: Fix TASK_COMM_LEN in trace event format file
After commit 3087c61ed2c4 ("tools/testing/selftests/bpf: replace open-coded 16 with TASK_COMM_LEN"),
the content of the format file under
/sys/kernel/tracing/events/task/task_newtask was changed from
field:char comm[16]; offset:12; size:16; signed:0;
to
field:char comm[TASK_COMM_LEN]; offset:12; size:16; signed:0;
John reported that this change breaks older versions of perfetto.
Then Mathieu pointed out that this behavioral change was caused by the
use of __stringify(_len), which happens to work on macros, but not on enum
labels. And he also gave the suggestion on how to fix it:
:One possible solution to make this more robust would be to extend
:struct trace_event_fields with one more field that indicates the length
:of an array as an actual integer, without storing it in its stringified
:form in the type, and do the formatting in f_show where it belongs.
The result as follows after this change,
$ cat /sys/kernel/tracing/events/task/task_newtask/format
field:char comm[16]; offset:12; size:16; signed:0;
Link: https://lore.kernel.org/lkml/Y+QaZtz55LIirsUO@google.com/
Link: https://lore.kernel.org/linux-trace-kernel/20230210155921.4610-1-laoar.shao@gmail.com/
Link: https://lore.kernel.org/linux-trace-kernel/20230212151303.12353-1-laoar.shao@gmail.com
Cc: stable@vger.kernel.org
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Kajetan Puchalski <kajetan.puchalski@arm.com>
CC: Qais Yousef <qyousef@layalina.io>
Fixes: 3087c61ed2c4 ("tools/testing/selftests/bpf: replace open-coded 16 with TASK_COMM_LEN")
Reported-by: John Stultz <jstultz@google.com>
Debugged-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Diffstat (limited to 'include/trace')
| -rw-r--r-- | include/trace/stages/stage4_event_fields.h | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/include/trace/stages/stage4_event_fields.h b/include/trace/stages/stage4_event_fields.h index affd541fd25e..b6f679ae21aa 100644 --- a/include/trace/stages/stage4_event_fields.h +++ b/include/trace/stages/stage4_event_fields.h @@ -26,7 +26,8 @@ #define __array(_type, _item, _len) { \ .type = #_type"["__stringify(_len)"]", .name = #_item, \ .size = sizeof(_type[_len]), .align = ALIGN_STRUCTFIELD(_type), \ - .is_signed = is_signed_type(_type), .filter_type = FILTER_OTHER }, + .is_signed = is_signed_type(_type), .filter_type = FILTER_OTHER,\ + .len = _len }, #undef __dynamic_array #define __dynamic_array(_type, _item, _len) { \ |