linux-kernel - Re: [PATCH 05/22 -v7] add notrace annotations to vsyscall.

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Date:	Wed, 30 Jan 2008 08:15:06 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Hellwig <hch@...radead.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Gregory Haskins <ghaskins@...ell.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tim Bird <tim.bird@...sony.com>,
	Sam Ravnborg <sam@...nborg.org>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	John Stultz <johnstul@...ibm.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 05/22 -v7] add notrace annotations to vsyscall.


On Wed, 30 Jan 2008, Peter Zijlstra wrote:

>
> On Tue, 2008-01-29 at 22:15 -0500, Steven Rostedt wrote:
> > plain text document attachment
> > (mcount-add-x86-vdso-notrace-annotations.patch)
> > Add the notrace annotations to some of the vsyscall functions.
>
> Would the VDSO stuff crash a kernel without these annotations and
> CONFIG_MCOUNT=y ?
>
> If so, I think it would be best of you placed these annotations before
> adding the core code, this would improve bisectability.

The thing is that MCOUNT needs something to select it, it's not a visible
option:

config MCOUNT
        bool
        select FRAME_POINTER

Nothing selects MCOUNT before the annotations are in, which really makes
the mcount code a nop until the tracer code comes in. A bisect (as long as
make oldconfig is done) should not be harmed by this patch ordering.
Note: the mcount patch introduces the annotation of notrace, which means
switching the order as it is will break it.

-- Steve

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