linux-kernel - Re: [PATCH] Linux Kernel Markers 0.5 for Linux 2.6.17 (with probe management)

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Message-ID: <45141759.8060600@opersys.com>
Date:	Fri, 22 Sep 2006 13:03:21 -0400
From:	Karim Yaghmour <karim@...rsys.com>
To:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
CC:	Ingo Molnar <mingo@...e.hu>, Martin Bligh <mbligh@...gle.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	prasanna@...ibm.com, Andrew Morton <akpm@...l.org>,
	Paul Mundt <lethal@...ux-sh.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Jes Sorensen <jes@....com>, Tom Zanussi <zanussi@...ibm.com>,
	Richard J Moore <richardj_moore@...ibm.com>,
	Michel Dagenais <michel.dagenais@...ymtl.ca>,
	Christoph Hellwig <hch@...radead.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	William Cohen <wcohen@...hat.com>, ltt-dev@...fik.org,
	systemtap@...rces.redhat.com, Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH] Linux Kernel Markers 0.5 for Linux 2.6.17 (with probe
 management)


Mathieu Desnoyers wrote:
> First of all, I think that specific architecture-specific optimisations can and
> should be integrated in a more generic portable framework.

No disagreement there. If Ingo would care to comment, I think it might
be an acceptable compromise to have x86 fully use kprobes/djprobes
immediately, and the other archs could walk there at their rate.
Practically, some stuff in include/asm-i386/markers.h and
include/asm-x86_64/markers.h would contain the binary modifiable stuff
and include/asm-generic/markers.h could contain a platform-independent
fallback.

> Hrm, your comment makes me think of an interesting idea :
> 
> .align
> jump_address:
>   near jump to end
> setup_stack_address:
>   setup stack
>   call empty function
> end:
> 
> So, instead of putting nops in the target area, we fill it with a useful
> function call. Near jump being 2 bytes, it might be much easier to modify.
> If necessary, making sure the instruction is aligned would help to change it
> atomically. If we mark the jump address, the setup stack address and the end
> tag address with symbols, we can easily calculate (portably) the offset of the
> near jump to activate either the setup_stack_address or end tags.

That's another possibility. It seems more C friendly than the simple
short-jump+3bytes.

Ingo?

Karim
-- 
President  / Opersys Inc.
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