linux-kernel - RE: [patch] x86, ptrace: support pebs in ds.c and disableptraceand ds support

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Date:	Thu, 27 Mar 2008 10:16:10 -0000
From:	"Metzger, Markus T" <markus.t.metzger@...el.com>
To:	"Ingo Molnar" <mingo@...e.hu>, <roland@...hat.com>
Cc:	<ak@...e.de>, <hpa@...or.com>, <linux-kernel@...r.kernel.org>,
	<tglx@...utronix.de>, <markus.t.metzger@...il.com>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	<akpm@...ux-foundation.org>, <mtk.manpages@...il.com>,
	<eranian@...glemail.com>,
	"Villacis, Juan" <juan.villacis@...el.com>
Subject: RE: [patch] x86, ptrace: support pebs in ds.c and disableptraceand ds support

>-----Original Message-----
>From: Ingo Molnar [mailto:mingo@...e.hu] 
>Sent: Donnerstag, 27. März 2008 10:58
>To: Metzger, Markus T

Ingo,

Thanks for your comments.

>> The patch is not adding new features. It is merely 
>re-establishing the 
>> state before the patch mysteriously disappeared from x86#testing.
>
>well, Roland is the de-facto ptrace maintainer and he has NAK-ed the 
>current approach of extending ptrace, so i removed the patch. Is there 
>anything particularly wrong about doing this based on utrace? The API 
>will hit upstream in 2.6.26 or 2.6.27.

There is nothing wrong with a utrace interface.

It's just that if I want to enable existing debuggers, I need to offer ptrace, as well - at least until utrace is widely used. The intel debugger, for example, will not speak utrace for the next version; but it would support execution tracing, if it were available.

Regarding the patch, it merely restructures the existing (and still present) implementation and adds support for PEBS so Stephane can use this as the low-level interface.

It does not invent any new ptrace commands (although it changes bits in an existing ptrace command).

The patch further allows the ptrace and ds parts to be completely disabled - including all changes to context switching or task destruction (requested by Roland).

I think it is a definite improvement over what we have today.

regards,
markus.
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