Messages in this thread | | | From | Rob Herring <> | Date | Fri, 2 Sep 2022 10:25:36 -0500 | Subject | Re: [PATCH] perf: Ignore format attributes with an unknown perf_event_attr field |
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On Fri, Sep 2, 2022 at 1:53 AM Namhyung Kim <namhyung@kernel.org> wrote: > > Hello, > > On Thu, Sep 1, 2022 at 11:55 AM 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. > > > > Signed-off-by: Rob Herring <robh@kernel.org> > > --- > > This is the YACC mud I threw and seems to stick. Maybe there's a better > > way to handle this. It doesn't seem like there's a way to do wildcards > > (i.e. config.*) in YACC. > > > > This is needed for this series[1]. Unfortunately the best we do to avoid > > the issue is applying this to stable. I think there's some time before > > v8.7 h/w is deployed, too. > > Maybe you could change the format_term rule to take an identifier instead > of PP_CONFIG* directly and pass it to perf_pmu__new_format(). Then > it could check the string and create an appropriate PERF_PMU_FORMAT_VALUE_* > or ignore it according to the PERF_ATTR_SIZE_VER*.
That only moves parsing of configN from YACC to strcmp in C. In doing so, we'd be left with just the 'error' token case which seems a bit odd (if there's another way to do it, I don't know. yacc is not my thing). Is that really better? Unless there is some way to retrieve the PERF_ATTR_SIZE_VER* from the kernel at runtime?
Rob
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