linux-kernel - Re: perf tools: interface for improved PEBS ABI can accept wrong parameter

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Message-ID: <20111018181943.GC21666@elte.hu>
Date:	Tue, 18 Oct 2011 20:19:43 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	"Xu, Anhua" <anhua.xu@...el.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: perf tools: interface for improved PEBS ABI can accept wrong
 parameter


Added more Cc:s of maintainers.

thanks,

	Ingo

* Xu, Anhua <anhua.xu@...el.com> wrote:

> For the commit: ab60834 perf, x86: Improve the PEBS ABI
> The precise_ip is restricted to 2 bits. The values larger than 3 are truncated less or equal to 3.
> This can effectively restricted value passing to syscall. But the user space interface can accept other wrong values which are larger than 3 and lowest 2 bits are 0 can meet the requirement.
> 
> # Here is an example, Monitor "All branches" events on Sandybridge platform( Please refer to SDM 3B Table 30-21 to check Sandybridge specific events )
> 
> perf top -e r04c4:p  # precise_ip = 1 , Correct
> perf top -e r04c4:pp  # precise_ip =2, Correct
> perf top -e r04c4:ppp  # not supported, Correct
> perf top -e r04c4:pppppp  # should not be supported, but after truncation , the number of 'p' treated as 2 which is accepted
> 
> 
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index c816075..07d3cf9 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -216,6 +216,7 @@ struct perf_event_attr {
>  				 *
>  				 *  See also PERF_RECORD_MISC_EXACT_IP
>  				 */
> +#define SAMPLE_IP_MAX	3 
>  				precise_ip     :  2, /* skid constraint       */
>  				mmap_data      :  1, /* non-exec mmap data    */
>  				sample_id_all  :  1, /* sample_type all events */
> diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
> index 928918b..a2068cc 100644
> --- a/tools/perf/util/parse-events.c
> +++ b/tools/perf/util/parse-events.c
> @@ -775,7 +775,10 @@ parse_event_modifier(const char **strp, struct perf_event_attr *attr)
>  	attr->exclude_user   = eu;
>  	attr->exclude_kernel = ek;
>  	attr->exclude_hv     = eh;
> -	attr->precise_ip     = precise;
> +	if ( precise < SAMPLE_IP_MAX )
> +		attr->precise_ip = precise;
> +	else
> +		return -1;
>  
>  	return 0;
>  }
> --
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-- 
Thanks,

	Ingo
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