linux-kernel - Re: buggy perf callgraph output

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Date:	Thu, 23 Dec 2010 14:08:20 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Nick Piggin <npiggin@...nel.dk>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: buggy perf callgraph output


* Frederic Weisbecker <fweisbec@...il.com> wrote:

> On Fri, Dec 17, 2010 at 04:32:58PM +1100, Nick Piggin wrote:
> > That would be great, thanks! It's a really awesome tool, I appreciate
> > your effort on it.
> 
> Thanks :)
> 
> So the below patch should fix the issue. Tell me if you encounter it
> again, or anything else.
> 
> diff --git a/tools/perf/util/hist.c b/tools/perf/util/hist.c
> index d503670..c749ba6 100644
> --- a/tools/perf/util/hist.c
> +++ b/tools/perf/util/hist.c
> @@ -356,7 +356,7 @@ static size_t ipchain__fprintf_graph_line(FILE *fp, int depth, int depth_mask,
>  
>  static size_t ipchain__fprintf_graph(FILE *fp, struct callchain_list *chain,
>  				     int depth, int depth_mask, int period,
> -				     u64 total_samples, int hits,
> +				     u64 total_samples, u64 hits,
>  				     int left_margin)

Hmm ... nice fix but why didnt GCC warn about the loss of half of the 'cumul' bits 
in this call:

                        ret += ipchain__fprintf_graph(fp, chain, depth,
                                                      new_depth_mask, i++,
                                                      new_total,
                                                      cumul,
                                                      left_margin);

We really, really want GCC to warn about this - it's such a common mistake. What 
disabled that warning? Very weird.

Thanks,

	Ingo
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