linux-kernel - Re: [RFC] Unify KVM kernel-space and user-space code into a single project

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Message-ID: <878w9if4l5.fsf@basil.nowhere.org>
Date:	Wed, 24 Mar 2010 10:31:50 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Avi Kivity <avi@...hat.com>
Cc:	Joerg Roedel <joro@...tes.org>,
	Anthony Liguori <anthony@...emonkey.ws>,
	Ingo Molnar <mingo@...e.hu>,
	Pekka Enberg <penberg@...helsinki.fi>,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Sheng Yang <sheng@...ux.intel.com>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Jes Sorensen <Jes.Sorensen@...hat.com>,
	Gleb Natapov <gleb@...hat.com>,
	Zachary Amsden <zamsden@...hat.com>, ziteng.huang@...el.com,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Fr?d?ric Weisbecker <fweisbec@...il.com>,
	Gregory Haskins <ghaskins@...ell.com>
Subject: Re: [RFC] Unify KVM kernel-space and user-space code into a single project

Avi Kivity <avi@...hat.com> writes:

> On 03/24/2010 09:38 AM, Andi Kleen wrote:
>>> If you're profiling a single guest it makes more sense to do this from
>>> inside the guest - you can profile userspace as well as the kernel.
>>>      
>> I'm interested in debugging the guest without guest cooperation.
>>
>> In many cases qemu's new gdb stub works for that, but in some cases
>> I would prefer instruction/branch traces over standard gdb style
>> debugging.
>>    
>
> Isn't gdb supposed to be able to use branch traces? 

AFAIK not. The ptrace interface is only used by idb I believe.
I might be wrong on that.

Not sure if there is even a remote protocol command for 
branch traces either.

There's a concept of "tracepoints" in the protocol, but it 
doesn't quite match at.

> It makes sense to
> expose them via the gdb stub then.  Not to say an external tool
> doesn't make sense.

Ok that would work for me too. As long as I can set start/stop
triggers and pipe the log somewhere it's fine for me.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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