Re: [PATCH] perf: Ignore format attributes with an unknown perf_event_attr field

[Rob Herring <robh@kernel.org>]

On Thu, Sep 1, 2022 at 2:22 PM Arnaldo Carvalho de Melo
<arnaldo.melo@gmail.com> wrote:
>
>
>
> On September 1, 2022 3:47:10 PM GMT-03:00, Rob Herring <robh@kernel.org> wrote:
> >If the kernel exposes a new perf_event_attr field in a format attr, perf
> >will return an error stating the specified PMU can't be found. For
> >example, a format attr with 'config3:0-63' causes an error if config3 is
> >unknown to perf. This causes a compatibility issue between a newer
> >kernel and an older perf tool.
> >
> >The addition here makes any attr string up to the ':' ignored, but
> >still checks the 'bits' portion.
>
> So, can you please show what is the behavior of the tool, with an actual command line and it's output, before and after your patch?

Before this patch with a kernel adding 'config3' I get:

# perf record -e arm_spe// -- true
event syntax error: 'arm_spe//'
                     \___ Cannot find PMU `arm_spe'. Missing kernel support?
Run 'perf list' for a list of valid events

 Usage: perf record [<options>] [<command>]
    or: perf record [<options>] -- <command> [<options>]

    -e, --event <event>   event selector. use 'perf list' to list
available events

After this patch, I get:

# perf record -e arm_spe// -- true
[ perf record: Woken up 2 times to write data ]
[ perf record: Captured and wrote 0.091 MB perf.data ]

Rob