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Yafang Shao
b6c7abd1c2
After commit3087c61ed2("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/[email protected]/ Link: https://lore.kernel.org/linux-trace-kernel/[email protected]/ Link: https://lore.kernel.org/linux-trace-kernel/[email protected] Cc: [email protected] Cc: Alexei Starovoitov <[email protected]> Cc: Kajetan Puchalski <[email protected]> CC: Qais Yousef <[email protected]> Fixes:3087c61ed2("tools/testing/selftests/bpf: replace open-coded 16 with TASK_COMM_LEN") Reported-by: John Stultz <[email protected]> Debugged-by: Mathieu Desnoyers <[email protected]> Suggested-by: Mathieu Desnoyers <[email protected]> Suggested-by: Steven Rostedt <[email protected]> Signed-off-by: Yafang Shao <[email protected]> Signed-off-by: Steven Rostedt (Google) <[email protected]>