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linux/include/trace
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Yafang Shao b6c7abd1c2 tracing: Fix TASK_COMM_LEN in trace event format file 
After commit 3087c61ed2 ("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: 3087c61ed2 ("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>
History 2023-02-12 10:23:39 -05:00
..
events rxrpc: Move client call connection to the I/O thread 2023-01-06 09:43:33 +00:00
misc NFSD: add CB_RECALL_ANY tracepoints 2022-12-10 11:01:12 -05:00
stages tracing: Fix TASK_COMM_LEN in trace event format file 2023-02-12 10:23:39 -05:00
bpf_probe.h tracing: Add __cpumask to denote a trace event field that is a cpumask_t 2022-11-23 19:08:30 -05:00
define_custom_trace.h tracing: Add TRACE_CUSTOM_EVENT() macro 2022-03-11 11:49:24 -05:00
define_trace.h tracepoint: Optimize using static_call() 2020-09-01 09:58:06 +02:00
perf.h tracing: Add __cpumask to denote a trace event field that is a cpumask_t 2022-11-23 19:08:30 -05:00
syscall.h tracepoints: Migrate to use SYSCALL_WORK flag 2020-11-16 21:53:15 +01:00
trace_custom_events.h tracing: Rename the staging files for trace_events 2022-04-02 08:40:04 -04:00
trace_events.h tracing: Rename the staging files for trace_events 2022-04-02 08:40:04 -04:00