linux-kernel - Re: [PATCH 02/26] perf: Introduce mmap3 version of mmap event

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Date:   Mon, 14 Sep 2020 21:38:41 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Ingo Molnar <mingo@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Michael Petlan <mpetlan@...hat.com>,
        Song Liu <songliubraving@...com>,
        "Frank Ch. Eigler" <fche@...hat.com>,
        Ian Rogers <irogers@...gle.com>,
        Stephane Eranian <eranian@...gle.com>,
        Alexey Budankov <alexey.budankov@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCH 02/26] perf: Introduce mmap3 version of mmap event

On Mon, Sep 14, 2020 at 02:38:27PM +0900, Namhyung Kim wrote:

SNIP

> > diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> > index 077e7ee69e3d..facfc3c673ed 100644
> > --- a/include/uapi/linux/perf_event.h
> > +++ b/include/uapi/linux/perf_event.h
> > @@ -384,7 +384,8 @@ struct perf_event_attr {
> >                                 aux_output     :  1, /* generate AUX records instead of events */
> >                                 cgroup         :  1, /* include cgroup events */
> >                                 text_poke      :  1, /* include text poke events */
> > -                               __reserved_1   : 30;
> > +                               mmap3          :  1, /* include bpf events */
> 
> ???
> 
> > +                               __reserved_1   : 29;
> >
> >         union {
> >                 __u32           wakeup_events;    /* wakeup every n events */
> > @@ -1060,6 +1061,30 @@ enum perf_event_type {
> >          */
> >         PERF_RECORD_TEXT_POKE                   = 20,
> >
> > +       /*
> > +        * The MMAP3 records are an augmented version of MMAP2, they add
> > +        * build id value to identify the exact binary behind map
> > +        *
> > +        * struct {
> > +        *      struct perf_event_header        header;
> > +        *
> > +        *      u32                             pid, tid;
> > +        *      u64                             addr;
> > +        *      u64                             len;
> > +        *      u64                             pgoff;
> > +        *      u32                             maj;
> > +        *      u32                             min;
> > +        *      u64                             ino;
> > +        *      u64                             ino_generation;
> > +        *      u32                             prot, flags;
> > +        *      u32                             reserved;
> > +        *      u8                              buildid[20];
> > +        *      char                            filename[];
> > +        *      struct sample_id                sample_id;
> > +        * };
> > +        */
> > +       PERF_RECORD_MMAP3                       = 21,
> > +
> >         PERF_RECORD_MAX,                        /* non-ABI */
> >  };
> >
> [SNIP]
> > @@ -8098,6 +8116,9 @@ static void perf_event_mmap_event(struct perf_mmap_event *mmap_event)
> >         mmap_event->prot = prot;
> >         mmap_event->flags = flags;
> >
> > +       if (atomic_read(&nr_mmap3_events))
> > +               build_id_parse(vma, mmap_event->buildid);
> 
> What about if it failed?  We should zero out the build-id..

it is initialized to zero in perf_event_mmap

        mmap_event = (struct perf_mmap_event){
                .vma    = vma,
	...

I'll double check build_id_parse won't leave anything half
baked there, but I dont think so

thanks,
jirka