linux-kernel - Re: [PATCH 21/57] perf c2c report: Add offset dimension key

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Date:   Wed, 5 Oct 2016 14:11:22 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Jiri Olsa <jolsa@...nel.org>, lkml <linux-kernel@...r.kernel.org>,
        Don Zickus <dzickus@...hat.com>, Joe Mario <jmario@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Namhyung Kim <namhyung@...nel.org>,
        David Ahern <dsahern@...il.com>,
        Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH 21/57] perf c2c report: Add offset dimension key

On Wed, Oct 05, 2016 at 07:57:07AM -0300, Arnaldo Carvalho de Melo wrote:
> Em Thu, Sep 22, 2016 at 05:36:49PM +0200, Jiri Olsa escreveu:
> > Adding cacheline offset dimension key support.
> > It displays cacheline offset as hex number.
> > 
> > Link: http://lkml.kernel.org/n/tip-m0424ye98lqveg5nopto8qww@git.kernel.org
> > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> > ---
> >  tools/perf/builtin-c2c.c | 35 +++++++++++++++++++++++++++++++++++
> >  1 file changed, 35 insertions(+)
> > 
> > diff --git a/tools/perf/builtin-c2c.c b/tools/perf/builtin-c2c.c
> > index 335c0fd30757..7c52481ec36b 100644
> > --- a/tools/perf/builtin-c2c.c
> > +++ b/tools/perf/builtin-c2c.c
> > @@ -300,6 +300,32 @@ static int dcacheline_entry(struct perf_hpp_fmt *fmt, struct perf_hpp *hpp,
> >  	return snprintf(hpp->buf, hpp->size, "%*s", width, hex_str(addr));
> >  }
> >  
> > +static int offset_entry(struct perf_hpp_fmt *fmt, struct perf_hpp *hpp,
> > +			struct hist_entry *he)
> > +{
> > +	uint64_t addr = 0;
> > +	int width = c2c_width(fmt, hpp, he->hists);
> > +
> > +	if (he->mem_info)
> > +		addr = cl_offset(he->mem_info->daddr.al_addr);
> > +
> > +	return snprintf(hpp->buf, hpp->size, "%*s", width, hex_str(addr));
> 
> Please don't use snprintf when you actually use the return from this
> function, see this part of its man page:
> 
> "If the output was trun‐ cated due to this limit, then the return value
> is the number of characters (excluding the terminating null byte) which
> would have been written  to the  final  string  if enough space had been
> available.  Thus, a return value of size or more means that the output
> was truncated.  (See also below under NOTES.)"
> 
> That is why we're using scnprintf where we need to use its return value.
> 
> I'm checking how you use the return value and changing all to scnprintf
> instead, ok?

ok, always forget this one ;-)

thanks,
jirka