linux-kernel - Re: tracepoint maintainance models

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Message-ID: <20061006130156.GA3566@redhat.com>
Date:	Fri, 6 Oct 2006 09:01:56 -0400
From:	"Frank Ch. Eigler" <fche@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Vara Prasad <prasadav@...ibm.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"Frank Ch. Eigler" <fche@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Paul Mundt <lethal@...ux-sh.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Jes Sorensen <jes@....com>, Andrew Morton <akpm@...l.org>,
	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>,
	"Martin J. Bligh" <mbligh@...igh.org>,
	systemtap <systemtap@...rceware.org>
Subject: Re: tracepoint maintainance models

Hi -

On Fri, Oct 06, 2006 at 01:33:11AM -0400, Steven Rostedt wrote:
> Coming into this really late, and I'm still behind in reading this and
> related threads, but I want to throw this idea out, and it's getting
> late.
> [...]
> #define MARK(label, var)			\
> 	asm ("debug_" #label ":\n"		\
> 	     ".section .data\n"			\
> 	     #label "_" #var ": xor %0,%0\n"	\
> 	     ".previous" : : "r"(var))
> [...]
> $ gcc -O2 -o mark mark.c
> $ ./mark
> func y is in reg B at 0x80483ce
> [...]

Clever.

> Now the question is, isn't MARK() in this code a non intrusive marker?

Not quite.  The assembly code forces gcc to materialize the data that
it might already have inlined, and to borrow a register for the
duration.  It's still a neat idea though.

- FChE
-
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