linux-kernel - Re: [patch 1/2] x86, ptrace: support pebs in ds.c

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Date:	Tue, 26 Feb 2008 09:51:54 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Roland McGrath <roland@...hat.com>
Cc:	Markus Metzger <markus.t.metzger@...el.com>, ak@...e.de,
	hpa@...or.com, linux-kernel@...r.kernel.org, tglx@...utronix.de,
	markus.t.metzger@...il.com, suresh.b.siddha@...el.com,
	akpm@...ux-foundation.org, mtk.manpages@...il.com,
	eranian@...glemail.com
Subject: Re: [patch 1/2] x86, ptrace: support pebs in ds.c


* Roland McGrath <roland@...hat.com> wrote:

> Sorry I haven't replied in this thread sooner.
> 
> I would like to see all the BTS and DS work wait until after 2.6.25. 
> We have a lot of x86 churn in 2.6.25 already, and I think we'd do 
> better without adding this wrinkle at the same time.
> 
> The low-level implementation pieces should gel a bit more in -mm or 
> whereever.  They should both get more testing and also get more 
> concrete use from the perfmon2 integration effort to iron out their 
> internal interface kinks.
> 
> For the user-level interface, we should not be hasty with cooking up 
> hairy ptrace extensions.  Personally, I'd prefer that we never add a 
> ptrace-based interface for this (ptrace must die).  I think it will 
> fit much better either merged into the interfaces that come from 
> perfmon2 integration, or into what replaces ptrace when that comes. 
> There is not yet any different userland interface framework in the 
> tree to base it on, so ptrace extensions may be better than nothing if 
> they are well-gelled in 2.6.26 and nothing else is close to ready. But 
> I also don't know of anyone desperate and about to burst from lack of 
> BTS functionality.

i'd you'd like to have something like the patch below to happen?

what API should BTS/DS functionality use towards user-space if not 
ptrace? Should it be utrace?

	Ingo

--------------------->
Subject: x86: disable BTS ptrace extensions for now
From: Ingo Molnar <mingo@...e.hu>
Date: Tue Feb 26 09:40:27 CET 2008

based on general objections from Roland McGrath:

    http://lkml.org/lkml/2008/2/21/323

we'll let the BTS functionality cook some more and enable
it in v2.6.26.

(X86_BTS is not defined at the moment)

Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 arch/x86/kernel/ptrace.c |    5 +++++
 1 file changed, 5 insertions(+)

Index: linux-x86.q/arch/x86/kernel/ptrace.c
===================================================================
--- linux-x86.q.orig/arch/x86/kernel/ptrace.c
+++ linux-x86.q/arch/x86/kernel/ptrace.c
@@ -961,6 +961,10 @@ long arch_ptrace(struct task_struct *chi
 		break;
 #endif
 
+	/*
+	 * These bits need more cooking - not enabled yet:
+	 */
+#ifdef X86_BTS
 	case PTRACE_BTS_CONFIG:
 		ret = ptrace_bts_config
 			(child, data, (struct ptrace_bts_config __user *)addr);
@@ -988,6 +992,7 @@ long arch_ptrace(struct task_struct *chi
 		ret = ptrace_bts_drain
 			(child, data, (struct bts_struct __user *) addr);
 		break;
+#endif
 
 	default:
 		ret = ptrace_request(child, request, addr, data);
--
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