Re: [PATCH] perf report: Support caller callchain order when using DWARF unwinder.

[Milian Wolff <milian.wolff@kdab.com>]

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On Montag, 5. Oktober 2015 13:08:36 CEST Jiri Olsa wrote:
> On Sun, Oct 04, 2015 at 05:38:17PM -0300, Arnaldo Carvalho de Melo wrote:
> > Em Sun, Oct 04, 2015 at 05:16:37PM +0200, Milian Wolff escreveu:
> > > We cannot reverse the order of the libunwind stepper. To workaround
> > > this, we store the IPs in a temporary stack buffer and then walk
> > > this buffer in reverse order when callchain_param.order is set to
> > > ORDER_CALLER.
> > > 
> > > Signed-off-by: Milian Wolff <milian.wolff@kdab.com>
> > 
> > Jiri,
> > 
> > 	Can you please take a look at this?
> > 
> > - Arnaldo
> > 
> > > Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
> > > ---
> > > 
> > >  tools/perf/util/unwind-libunwind.c | 21 +++++++++++++++++----
> > >  1 file changed, 17 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/tools/perf/util/unwind-libunwind.c
> > > b/tools/perf/util/unwind-libunwind.c index 4c00507..bf631f1 100644
> > > --- a/tools/perf/util/unwind-libunwind.c
> > > +++ b/tools/perf/util/unwind-libunwind.c
> > > @@ -621,11 +621,24 @@ static int get_entries(struct unwind_info *ui,
> > > unwind_entry_cb_t cb,> > 
> > >  	if (ret)
> > >  	
> > >  		display_error(ret);
> > > 
> > > -	while (!ret && (unw_step(&c) > 0) && max_stack--) {
> > > -		unw_word_t ip;
> > > +	if (callchain_param.order == ORDER_CALLEE) {
> > > +		while (!ret && (unw_step(&c) > 0) && max_stack--) {
> > > +			unw_word_t ip;
> > > 
> > > -		unw_get_reg(&c, UNW_REG_IP, &ip);
> > > -		ret = ip ? entry(ip, ui->thread, cb, arg) : 0;
> > > +			unw_get_reg(&c, UNW_REG_IP, &ip);
> > > +			ret = ip ? entry(ip, ui->thread, cb, arg) : 0;
> > > +		}
> > > +	} else {
> > > +		unw_word_t ips[max_stack];
> > > +		int i = 0;
> > > +
> > > +		while ((unw_step(&c) > 0) && i < max_stack) {
> > > +			unw_get_reg(&c, UNW_REG_IP, &ips[i]);
> > > +			++i;
> > > +		}
> > > +		max_stack = i;
> > > +		for (i = max_stack - 1; i >= 0; --i)
> > > +			entry(ips[i], ui->thread, cb, arg);
> 
> there's no check for return value of entry callback
> 
> also I wonder would it be better to store into ips[] within
> the single loop all the time, and iterate throught it after
> forward/backward based on the callchain_param.order
> 
> please check attached patch, totaly untested, probably leaking some index
> ;-)
> 
> any chance this could be done also for util/unwind-libdw.c ?

That patch looks much better than mine. I'll try it out later next week and 
will also have a look at util/unwind-libdw.c. Question: How can I test the 
behavior of the latter? Do I need to uninstall libunwind, or can I change the 
unwinder at runtime somehow (env var?).

Also, are there unit tests for this behavior somewhere?
-- 
Milian Wolff | milian.wolff@kdab.com | Software Engineer
KDAB (Deutschland) GmbH&Co KG, a KDAB Group company
Tel: +49-30-521325470
KDAB - The Qt Experts

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