linux-kernel - Re: [PATCH] Linux Kernel Markers 0.8 for 2.6.17 (with near jump for i386)

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Date:	Sat, 23 Sep 2006 15:57:32 -0400
From:	Karim Yaghmour <karim@...rsys.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC:	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>,
	Ingo Molnar <mingo@...e.hu>, 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>,
	Jeremy Fitzhardinge <jeremy@...p.org>
Subject: Re: [PATCH] Linux Kernel Markers 0.8 for 2.6.17 (with near jump for
 i386)

Mathieu Desnoyers wrote:
> --- a/arch/i386/Kconfig
> +++ b/arch/i386/Kconfig
> @@ -1082,6 +1082,8 @@ config KPROBES
>  	  for kernel debugging, non-intrusive instrumentation and testing.
>  	  If in doubt, say "N".
>  
> +source "kernel/Kconfig.marker"
> +
>  source "ltt/Kconfig"

diffing against an LTT tree ...

> --- /dev/null
> +++ b/include/asm-alpha/marker.h
...
> --- /dev/null
> +++ b/include/asm-arm/marker.h
...
> --- /dev/null
> +++ b/include/asm-arm26/marker.h
...
...

Not sure about the need for asm-foo/marker.h if the file contains no
code at all. If there's going to be one marker.h per arch, it might
as well have a purpose. So instead of:

> --- /dev/null
> +++ b/include/asm-i386/marker.h
...
> +#define ARCH_HAS_MARK_NEAR_JUMP

and

> --- /dev/null
> +++ b/include/linux/marker.h
...
> +#ifndef ARCH_HAS_MARK_NEAR_JUMP
...

Why not just have asm-foo/marker.h either implement the optimization
or point to an asm-generic/marker.h which contains the non-optimized
code. No #ifndefs needed.

> --- /dev/null
> +++ b/kernel/Kconfig.marker
...
> +config MARK_SYMBOL
...
> +config MARK_JUMP_CALL
...
> +config MARK_JUMP
...

My understanding of Ingo's input is that he'd rather not have this
multiple options. Either the markers are active or they aren't.
So ...
MARK_ACTIVE ... speaks for itself, enables both the markers and
the set/disable infrastructure. Markers are enabled in their
optimized per-architecture implementation.

MARK_FORCE_DIRECT_CALL ... forces all markers to be non-optimized
(good for embedded systems where the image is in rom/flash and
can therefore not have runtime binary modifications.) Maybe this
should depend on CONFIG_EMBEDDED.

Karim
-- 
President  / Opersys Inc.
Embedded Linux Training and Expertise
www.opersys.com  /  1.866.677.4546
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