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

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Date:	Mon, 25 Sep 2006 13:45:25 -0400
From:	"Frank Ch. Eigler" <fche@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	"Frank Ch. Eigler" <fche@...hat.com>,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	Martin Bligh <mbligh@...gle.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	prasanna@...ibm.com, Andrew Morton <akpm@...l.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	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)

Hi -

On Thu, Sep 21, 2006 at 08:50:29PM +0200, Ingo Molnar wrote:

> [...]  let me qualify that: parameters must be prepared there too -
> but no actual function call inserted. (at most a NOP
> inserted). [...]  Does a simple asm() that takes read-only
> parameters but only adds a NOP achieve this result?

You mean something like this?

#define MARK(n,v1,v2,v3) asm ("__mark_" #n ": nop" ::  \
                              "X" (v1), "X" (v2), "X" (v3))

I haven't been able to get gcc to emit any better debuginfo for
parameters pseudo-passed like this. 

(I've tested such a marker inserted into an inner loop of dhrystone.
It was compiled with "-ggdb -O3".  Neither gdb nor systemtap could
resolve the same values/symbols being passed as MARK() arguments,
though at least the breakpoint address was nicely marked.)

- FChE

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