linux-kernel - Re: tracepoint maintainance models

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Date:	Mon, 18 Sep 2006 20:49:40 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Vara Prasad <prasadav@...ibm.com>
Cc:	"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

Ar Llu, 2006-09-18 am 12:10 -0700, ysgrifennodd Vara Prasad:
> I am not sure i quiet understand your line number part of the proposal. 
> Does this proposal assume we have access to source code while generating 
> dynamic probes?

Its one route - or we dump it into an ELF section in the binary.

> This still doesn't solve the problem of compiler optimizing such that a 
> variable i would like to read in my probe not being available at the 
> probe point.

Then what we really need by the sound of it is enough gcc smarts to do
something of the form

	.section "debugbits"
	
	.asciiz 'hook_sched'
	.dword l1	# Address to probe
	.word 1		# Argument count
	.dword gcc_magic_whatregister("next"); [ reg num or memory ]
	.dword gcc_magic_whataddress("next"); [ address if exists]


Can gcc do any of that for us today ?

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