linux-kernel - Re: [PATCH] perf hist browser: change print format from lu to llu to fit u64 type

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Date:	Tue, 25 Nov 2014 15:51:30 -0800
From:	Matt Mullins <mmullins@...x.us>
To:	Tom Huynh <tom.huynh@...escale.com>
Cc:	mingo@...hat.com, acme@...nel.org, namhyung@...nel.org,
	jolsa@...nel.org, a.p.zijlstra@...llo.nl, paulus@...ba.org,
	kim.phillips@...escale.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf hist browser: change print format from lu to llu
 to fit u64 type

On Tue, Nov 18, 2014 at 05:00:27PM -0600, Tom Huynh wrote:
> nr_events in tools/perf/ui/browsers/hists.c is of type u64, thus it should
> be printed as %llu instead of %lu. The print format %lu causes perf report
> to show 0 event count when running with 32-bit userspace without 
> redirection. This patch fixes that problem.
> 
> Signed-off-by: Tom Huynh <tom.huynh@...escale.com>
> ---
>  tools/perf/ui/browsers/hists.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/perf/ui/browsers/hists.c b/tools/perf/ui/browsers/hists.c
> index cfb976b..49b2471 100644
> --- a/tools/perf/ui/browsers/hists.c
> +++ b/tools/perf/ui/browsers/hists.c
> @@ -1254,7 +1254,7 @@ static int hists__browser_title(struct hists *hists,
>  
>  	nr_samples = convert_unit(nr_samples, &unit);
>  	printed = scnprintf(bf, size,
> -			   "Samples: %lu%c of event '%s', Event count (approx.): %lu",
> +			   "Samples: %lu%c of event '%s', Event count (approx.): %llu",
>  			   nr_samples, unit, ev_name, nr_events);

If I enable __attribute__((format(printf, ...))) on scnprintf, on a 64-bit
build this gives me:

ui/browsers/hists.c: In function ‘hists__browser_title’:
ui/browsers/hists.c:1258:7: error: format ‘%llu’ expects argument of type ‘long long unsigned int’, but argument 7 has type ‘u64’ [-Werror=format=]
       nr_samples, unit, ev_name, nr_events);
       ^

I would usually suggest using the PRIu64 macro which should(TM) evaluate to the
right string constant for the platform, but that appears to be a C99 thing.
I'm not sure if that's kosher in tools/perf, but it does seem to build for me
(on Fedora 20).
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