linux-kernel - Re: [PATCH 2/7] perf trace: Correctly handle arrays

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Date:	Sat, 15 May 2010 05:20:34 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Ian Munsie <imunsie@....ibm.com>, linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Tom Zanussi <tzanussi@...il.com>
Subject: Re: [PATCH 2/7] perf trace: Correctly handle arrays

On Thu, May 13, 2010 at 12:29:05PM -0400, Steven Rostedt wrote:
> On Thu, 2010-05-13 at 16:03 +1000, Ian Munsie wrote:
> > From: Ian Munsie <imunsie@....ibm.com>
> > 
> > Previously, perf was assuming that an array from an ftrace event was an
> > array of longs, which will not always be the case. Additionally,
> > long_size is not even being initialised, so it would fail to read the
> > data and would erroneously report that the array was filled with zeroes.
> > 
> > This patch adds two extra entries into the field structure - arraylen
> > and elementsize, so that the code can easily look them up instead of
> > assuming that the elements are long_size. The element size is currently
> > derived by the size of the entire array and the number of elements
> > within the array.
> > 
> > This problem can be demonstrated with:
> > perf record -e raw_syscalls:sys_enter -a sleep 0.1
> > perf trace
> > 
> 
> I'm added this to trace-cmd too.
> 
> > Without this patch, output similar to the following is produced:
> >  perf-4355  [004]  1871.504685: sys_enter: NR 319 (0, 0, 0, 0, 0, 0)
> >  perf-4355  [004]  1871.504723: sys_enter: NR 3 (0, 0, 0, 0, 0, 0)
> >  perf-4355  [004]  1871.504733: sys_enter: NR 204 (0, 0, 0, 0, 0, 0)
> > 
> > After applying this patch, the output looks like:
> >  perf-4355  [004]  1871.504685: sys_enter: NR 319 (10247ac0, ffffffff, 5, ffffffff, 0, 107a80d8)
> >  perf-4355  [004]  1871.504723: sys_enter: NR 3 (a, ffb6fcf0, 20, ffffffff, 0, 10112c20)
> >  perf-4355  [004]  1871.504733: sys_enter: NR 204 (a, 4, 800, 6, 0, 10112c20)
> > 
> > Signed-off-by: Ian Munsie <imunsie@....ibm.com>
> > ---
> >  tools/perf/util/trace-event-parse.c |   11 ++++++++++-
> >  tools/perf/util/trace-event.h       |    2 ++
> >  2 files changed, 12 insertions(+), 1 deletions(-)
> > 
> > diff --git a/tools/perf/util/trace-event-parse.c b/tools/perf/util/trace-event-parse.c
> > index 8f470f6..f360f75 100644
> > --- a/tools/perf/util/trace-event-parse.c
> > +++ b/tools/perf/util/trace-event-parse.c
> > @@ -852,6 +852,9 @@ static int event_read_fields(struct event *event, struct format_field **fields)
> >  			field->flags |= FIELD_IS_ARRAY;
> >  
> >  			type = read_token(&token);
> > +			if (test_type(type, EVENT_ITEM))
> > +				goto fail;
> 
> Note this will incorrectly fail on:
> 
> 	field:__data_loc char[] name;
> 
> -- Steve



Nice patch, but indeed this part needs to be fixed.

Thanks.

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