linux-kernel - Re: [PATCH] Linux Kernel Markers 0.11 for 2.6.17

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Message-ID: <20060925160115.GE25296@redhat.com>
Date:	Mon, 25 Sep 2006 12:01:15 -0400
From:	"Frank Ch. Eigler" <fche@...hat.com>
To:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
Cc:	Martin Bligh <mbligh@...gle.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	prasanna@...ibm.com, Andrew Morton <akpm@...l.org>,
	Ingo Molnar <mingo@...e.hu>,
	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>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Karim Yaghmour <karim@...rsys.com>,
	Pavel Machek <pavel@...e.cz>, Joe Perches <joe@...ches.com>,
	"Randy.Dunlap" <rdunlap@...otime.net>,
	"Jose R. Santos" <jrs@...ibm.com>
Subject: Re: [PATCH] Linux Kernel Markers 0.11 for 2.6.17

Hi -

> [...]
> - It _does not_ change the compiler optimisations.

Like any similar mechanism, it does force the compiler to change its
code generation, so one can't claim this too strongly.

> [...]  Comments are welcome,

I'm still uneasy about the use of varargs.  The current code now uses
the formatting string as metadata to be matched (strcmp) between
producer and consumer.  A general tool that would use them would have
to start parsing general printf directives.  I believe they are not
quite general enough either e.g. to describe a raw binary blob.

I realize they serve a useful purpose in abbreviating what otherwise
one might have to do (like that multiplicity of STAP_MARK_* type/arity
permutations).  But maybe there is a better way.

Also, while regparm(0) may provide some comfort on x86, is there good
reason to believe that the same trick works (and will continue to
work) on non-x86 platforms to invoke a non-varargs callee with a
varargs caller?

- FChE

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