linux-kernel - Re: [PATCH] i386 add Intel PEBS and BTS cpufeature bits and detection

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:	Fri, 17 Nov 2006 05:29:02 +0100
From:	Andi Kleen <ak@...e.de>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	eranian@....hp.com, linux-kernel@...r.kernel.org, akpm@...l.org
Subject: Re: [PATCH] i386 add Intel PEBS and BTS cpufeature bits and detection

On Friday 17 November 2006 02:34, Jeremy Fitzhardinge wrote:
> Stephane Eranian wrote:
> > Here is a small patch that adds two cpufeature bits to represent
> > Intel's Precise-Event-Based Sampling (PEBS) and Branch Trace Store
> > (BTS) features. Those features can be found on Intel P4 and Core 2 
> > processors among others and can be used by perfmon.
> >   
> 
> I've been thinking it would be useful for kernel debugging if kernel
> oops messages could use the branch history to show the last few jumps on
> processors which support it.  It would help a lot with the "oh, an oops
> with eip==esp==0" type crashes, which are otherwise pretty unhelpful.

I have had private patches for that myself, using the MSRs on AMD
and Intel.

The problem is that you have to insert hooks early into the exception
handlers to read the branch history MSRs, and that gets fairly ugly
and a little slow and we can't really enable it by default.

But using BTS with a long in memory buffer would be fine. It would
just be slower so it couldn't be enabled by default. But as a debugging
feature it would be nice.

-Andi
-
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/