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Date: Fri, 6 Oct 2006 09:01:56 -0400
From: "Frank Ch. Eigler" <fche@redhat.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Vara Prasad <prasadav@us.ibm.com>, Alan Cox <alan@lxorguk.ukuu.org.uk>,
       "Frank Ch. Eigler" <fche@redhat.com>, Ingo Molnar <mingo@elte.hu>,
       Paul Mundt <lethal@linux-sh.org>,
       Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
       linux-kernel <linux-kernel@vger.kernel.org>, Jes Sorensen <jes@sgi.com>,
       Andrew Morton <akpm@osdl.org>, Tom Zanussi <zanussi@us.ibm.com>,
       Richard J Moore <richardj_moore@uk.ibm.com>,
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       Christoph Hellwig <hch@infradead.org>,
       Greg Kroah-Hartman <gregkh@suse.de>,
       Thomas Gleixner <tglx@linutronix.de>, William Cohen <wcohen@redhat.com>,
       "Martin J. Bligh" <mbligh@mbligh.org>,
       systemtap <systemtap@sourceware.org>
Subject: Re: tracepoint maintainance models
Message-ID: <20061006130156.GA3566@redhat.com>
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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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