Re: perf list dumps core using 5.13.0.rc2

[Ian Rogers <irogers@google.com>]

On Wed, May 19, 2021 at 7:57 AM Thomas Richter <tmricht@linux.ibm.com> wrote:
>
> Using kernel 5.13.0.rc2 command perf list dumps core on my x86
> virtual machine:
>
> [root@f34 perf]# ./perf list
> Segmentation fault (core dumped)
> ^C
> [root@f34 perf]#
>
> The root case this this change in file ../include/uapi/linux/perf_event.h:
> enum perf_sw_ids {
>         PERF_COUNT_SW_CPU_CLOCK                 = 0,
>         ...
>  --->   PERF_COUNT_SW_CGROUP_SWITCHES           = 11,
>
>         PERF_COUNT_SW_MAX,                      /* non-ABI */
> };
>
> This change increases PERF_COUNT_SW_MAX to 12. However this
> change is not reflected in file util/parse-events.c where data structure
>
> struct event_symbol event_symbols_sw[PERF_COUNT_SW_MAX] = {
>         ....
> }
>
> is defined and it misses the symbol name and alias for this new software
> event. So when command 'perf list' is called, the call chain sequence
> is
>   cmd_list()
>     print_events()
>       print_symbol_events(event_glob, PERF_TYPE_SOFTWARE,
>                           event_symbols_sw, PERF_COUNT_SW_MAX, name_only);
>
> where PERF_COUNT_SW_MAX is 12 and  structure event_symbols_sw[] contains
> only 11 elements. This ends up with the last element of the array being
> all zeroes and the line:
>
>     if (!name_only && strlen(syms->alias))
>
> dumps core because syms->alias is a NULL pointer.
>
> Is this dummy event PERF_COUNT_SW_CGROUP_SWITCHES simply missing in the
> event_symbols_sw[] array or is there more to it (which I am missing).
>
> Thanks.
>
> PS: I can sent a patch if needed....

I believe Namhyung's pending change will fix this:
https://lore.kernel.org/lkml/20210210083327.22726-3-namhyung@kernel.org/

Thanks,
Ian

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> Thomas Richter, Dept 3303, IBM s390 Linux Development, Boeblingen, Germany
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