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

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Date:	Thu, 21 Sep 2006 20:50:29 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	"Frank Ch. Eigler" <fche@...hat.com>
Cc:	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)


* Frank Ch. Eigler <fche@...hat.com> wrote:

> > +#define MARK_SYM(name) \
> > +		here: asm volatile \
> > +			(MARK_KPROBE_PREFIX#name " = %0" : : "m" (*&&here)); \
> 
> Regarding MARK_SYM, if I read Ingo's message correctly, this is the 
> only type of marker he believes is necessary, since it would put a 
> place for kprobes to put a breakpoint.  FWIW, this still appears to be 
> applicable only if the int3 overheads are tolerable, and if parameter 
> data extraction is unnecessary or sufficiently robust "by accident".

let me qualify that: parameters must be prepared there too - but no 
actual function call inserted. (at most a NOP inserted). The register 
filling doesnt even have to be function-calling-convention compliant - 
that makes the symbolic probe almost zero-impact to register 
allocation/scheduling, the only thing it should ensure is that the 
parameters that are annotated to be available in register, stack or 
memory _somewhere_. (i.e. not hidden or destroyed at that point by gcc) 
Does a simple asm() that takes read-only parameters but only adds a NOP 
achieve this result?

	Ingo
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