linux-kernel - Re: [PATCH] perf report: Provide libtraceevent with a kernel symbol resolver

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Date:   Thu, 18 Jan 2018 22:22:30 +0800
From:   Wang YanQing <udknight@...il.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     acme@...nel.org, peterz@...radead.org, mingo@...hat.com,
        alexander.shishkin@...ux.intel.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf report: Provide libtraceevent with a kernel symbol
 resolver

On Thu, Jan 18, 2018 at 10:43:18AM +0100, Jiri Olsa wrote:
> On Wed, Jan 17, 2018 at 12:48:12AM +0800, Wang YanQing wrote:
> > On Mon, Jan 15, 2018 at 11:06:11AM +0100, Jiri Olsa wrote:
> > > On Mon, Jan 15, 2018 at 12:47:32PM +0800, Wang YanQing wrote:
> > > > So that beautifiers wanting to resolve kernel function addresses to
> > > > names can do its work, and when we use "perf report" for output of
> > > > "perf kmem record", we will get kernel symbol output.
> > > > 
> > > > Signed-off-by: Wang YanQing <udknight@...il.com>
> > > > ---
> > > >  tools/perf/builtin-report.c | 9 +++++++++
> > > >  1 file changed, 9 insertions(+)
> > > > 
> > > > diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
> > > > index dd4df9a..7b65100 100644
> > > > --- a/tools/perf/builtin-report.c
> > > > +++ b/tools/perf/builtin-report.c
> > > > @@ -1317,6 +1317,15 @@ int cmd_report(int argc, const char **argv)
> > > >  		report.range_num = 1;
> > > >  	}
> > > >  
> > > > +	if (session->tevent.pevent &&
> > > > +	    pevent_set_function_resolver(session->tevent.pevent,
> > > > +					 machine__resolve_kernel_addr,
> > > > +					 &session->machines.host) < 0) {
> > > > +		pr_err("%s: failed to set libtraceevent function resolver\n",
> > > > +		       __func__);
> > > > +		return -1;
> > > > +	}
> > > 
> > > why not calling the wrapper trace_event__register_resolver?
> > The reason is the same as builtin-script doesn't use trace_event__register_resolver,
> > because we only use report and script to analyze offline perf.data, and there could
> > be no tracepoints in perf.data.
> 
> hum, I missed this functionality.. so we need this even if there
> are no tracepoints in the perf.data?

In "perf report", when there are tracepoints in perf.data, session->tevent.pevent
will be initialized in trace-event-read.c:trace_report, then "if (session->tevent.pevent"
will become true, and we should calling pevent_set_function_resolver.

But if we calling trace_event__register_resolver, then it will initialize tevent.pevent
no matter whether there are tracepoints in perf.data.

Thanks.
> 
> The only related interface function I could found is pevent_find_function
> and it seems to be called only from within traceevent library.
> 
> thanks,
> jirka