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Date:   Fri, 12 Feb 2021 18:07:34 -0300
From:   Arnaldo Carvalho de Melo <acme@kernel.org>
To:     Nicholas Fraser <nfraser@codeweavers.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Ian Rogers <irogers@google.com>,
        "Frank Ch. Eigler" <fche@redhat.com>,
        Song Liu <songliubraving@fb.com>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Kim Phillips <kim.phillips@amd.com>,
        Tommi Rantala <tommi.t.rantala@nokia.com>,
        Remi Bernon <rbernon@codeweavers.com>,
        linux-kernel@vger.kernel.org,
        Ulrich Czekalla <uczekalla@codeweavers.com>,
        Huw Davies <huw@codeweavers.com>
Subject: Re: [PATCH 3/4] perf archive: Fix filtering of empty build-ids
Message-ID: <20210212210734.GK1398414@kernel.org>
References: <7708cca1-b8f6-c394-75f1-5f9681d625d0@codeweavers.com>
 <20210212122901.GB1398414@kernel.org>
 <8f50e586-ae58-ef4e-a594-e2248203a2a7@codeweavers.com>
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Em Fri, Feb 12, 2021 at 01:49:36PM -0500, Nicholas Fraser escreveu:
> The current version of "perf buildid-list" prints missing build-ids as
> blank even when loading perf.data files generated from older versions of
> perf. I've tested with a few older versions.
> 
> Since perf-archive is an external script that calls back into perf, it
> could in theory find a different older version that still returns zeroes.
> We could make it look for a matching perf, e.g. "$(dirname "$0")/perf".
> Unfortunately that won't work in general because at least on my system
> perf-archive is installed to a different path than perf.

It shouldn't try to find a "matching perf" as the userspace perf is not
in lockstep with the kernel perf subsystem :-)

If a current 'perf archive' is called on some perf.data file, it should
know that a zero-filled or a blank filled build-id means the same and
act accordingly.

- Arnaldo
  
> Nick
> 
> 
> On 2021-02-12 7:29 a.m., Arnaldo Carvalho de Melo wrote:
> > Em Wed, Feb 10, 2021 at 02:17:49PM -0500, Nicholas Fraser escreveu:
> >> A non-existent build-id used to be treated as all-zero SHA-1 hash.
> >> Build-ids are now variable width. A non-existent build-id is an empty
> >> string and "perf buildid-list" pads this with spaces.
> >>
> >> This fixes "perf-archive" to skip missing build-ids by skipping lines
> >> that start with a padding space rather than with zeroes.
> >>
> >> Signed-off-by: Nicholas Fraser <nfraser@codeweavers.com>
> >> ---
> >>  tools/perf/perf-archive.sh | 3 +--
> >>  1 file changed, 1 insertion(+), 2 deletions(-)
> >>
> >> diff --git a/tools/perf/perf-archive.sh b/tools/perf/perf-archive.sh
> >> index 0cfb3e2cefef..133f0eddbcc4 100644
> >> --- a/tools/perf/perf-archive.sh
> >> +++ b/tools/perf/perf-archive.sh
> >> @@ -20,9 +20,8 @@ else
> >>  fi
> >>  
> >>  BUILDIDS=$(mktemp /tmp/perf-archive-buildids.XXXXXX)
> >> -NOBUILDID=0000000000000000000000000000000000000000
> >>  
> >> -perf buildid-list -i $PERF_DATA --with-hits | grep -v "^$NOBUILDID " > $BUILDIDS
> >> +perf buildid-list -i $PERF_DATA --with-hits | grep -v "^ " > $BUILDIDS
> >>  if [ ! -s $BUILDIDS ] ; then
> >>  	echo "perf archive: no build-ids found"
> >>  	rm $BUILDIDS || true
> > 
> > What should we do when using older files? We have to support both cases.
> > 
> > - Arnaldo
> > 

-- 

- Arnaldo