linux-kernel - Re: [RFC PATCH 6/6] perf cs-etm: Add warnings for missing DSOs

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Message-ID: <YQlDefz+g45dqFsP@kernel.org>
Date:   Tue, 3 Aug 2021 10:24:09 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     James Clark <james.clark@....com>, mathieu.poirier@...aro.org,
        coresight@...ts.linaro.org, linux-perf-users@...r.kernel.org,
        suzuki.poulose@....com, mike.leach@...aro.org,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        John Garry <john.garry@...wei.com>,
        Will Deacon <will@...nel.org>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH 6/6] perf cs-etm: Add warnings for missing DSOs

Em Mon, Aug 02, 2021 at 11:41:45PM +0800, Leo Yan escreveu:
> On Thu, Jul 29, 2021 at 04:58:05PM +0100, James Clark wrote:
> > Currently decode will silently fail if no binary data is available for
> > the decode. This is made worse if only partial data is available because
> > the decode will appear to work, but any trace from that missing DSO will
> > silently not be generated.
> > 
> > Add a UI popup once if there is any data missing, and then warn in the
> > bottom left for each individual DSO that's missing.
> > 
> > Signed-off-by: James Clark <james.clark@....com>
> > ---
> >  tools/perf/util/cs-etm.c | 10 +++++++++-
> >  1 file changed, 9 insertions(+), 1 deletion(-)
> > 
> > diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> > index 32ad92d3e454..e6851260d059 100644
> > --- a/tools/perf/util/cs-etm.c
> > +++ b/tools/perf/util/cs-etm.c
> > @@ -746,8 +746,16 @@ static u32 cs_etm__mem_access(struct cs_etm_queue *etmq, u8 trace_chan_id,
> >  
> >  	len = dso__data_read_offset(al.map->dso, machine, offset, buffer, size);
> >  
> > -	if (len <= 0)
> > +	if (len <= 0) {
> > +		ui__warning_once("CS ETM Trace: Missing DSO. Use 'perf archive' to export data from the traced system.\n");
> > +		if (!al.map->dso->auxtrace_warned) {
> > +			pr_err("CS ETM Trace: Debug data not found for address %#"PRIx64" in %s\n",
> > +				    address,
> > +				    al.map->dso->long_name ? al.map->dso->long_name : "Unknown");
> > +			al.map->dso->auxtrace_warned = true;
> > +		}
> 
> This is very useful.
> 
> Just one comment: in particularly if the perf fails to find the kernel
> symbols, the user needs to enable config "CONFIG_PROC_KCORE=y" or
> specify option "-k /path/to/vmlinux".  In this case, using 'perf
> archive' is not helpful.  So I think the UI warning can be imporved
> like:
> 
>         ui__warning_once("CS ETM Trace: Missing DSO. Use 'perf archive' to export data from the traced system.\n"
>                          " Enable CONFIG_PROC_KCORE or use option '-k /path/to/vmlinux' for kernel symbols\n");

one can also use debuginfod-client, which, as time passes, probably will
be the main way of finding DSOs now that we have build-ids in
PERF_RECORD_MMAP2 and debuginfod servers such as:

export DEBUGINFOD_URLS=https://debuginfod.fedoraproject.org/

https://fedoraproject.org/wiki/Debuginfod
 
> With this improvement, the patch looks good to me:
> 
> Reviewed-by: Leo Yan <leo.yan@...aro.org>

Does this apply to the other 5 patches in this series?

- Arnaldo
 
> >  		return 0;
> > +	}
> >  
> >  	return len;
> >  }
> > -- 
> > 2.28.0
> > 

-- 

- Arnaldo