linux-kernel - Re: [BUG] perf_event: sampling buffer format cannot handle multi-event sampling

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 19 Apr 2011 21:22:15 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>, mingo@...e.hu,
	Paul Mackerras <paulus@...ba.org>,
	Robert Richter <robert.richter@....com>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [BUG] perf_event: sampling buffer format cannot handle
 multi-event sampling

On Tue, 2011-04-19 at 19:10 +0000, Stephane Eranian wrote:
> Hi,
> 
> I was looking at the sampling buffer format and I think there is an
> issue in case
> one samples on more than one event at a time and each event as a different
> sample_type value (i.e., what it wants to record in each sample).
> 
> The sample_type is exported per-event by the API. In order to decode a sample
> (PERF_RECORD_SAMPLE) one has to know which event caused it. To identify
> the event, one has to include PERF_SAMPLE_ID in the sample_type. Each such
> id uniquely identifies an event. Assuming the tool keeps a mapping of event to
> ID, we can then reconstruct. This is what perf does.
> 
> The problem is that to extract the event ID, one has to already parse the sample
> itself. That means, you need sample_type to extract the event ID.
> 
> Thus, we have a catch 22 situation.
> 
> Looking at the perf tool, it sort of works today simply because the
> same sample_type
> is applied to all events.
> 
> To solve this, we could either:
>    - add the event ID to the header for PERF_RECORD_SAMPLE
>    - enforce event ID is systematically saved at the beginning on
> PERF_RECORD_SAMPLE
> 
> None of those options is transparent, I am afraid, unless we introduce
> new record types.

Or simply don't mix different sample_types in the same buffer?
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/