linux-kernel - Re: [PATCH] tracing: Cleanup the convoluted softirq tracepoints

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Message-ID: <1287538590.16971.548.camel@gandalf.stny.rr.com>
Date:	Tue, 19 Oct 2010 21:36:30 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Jason Baron <jbaron@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Koki Sanagi <sanagi.koki@...fujitsu.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	nhorman@...driver.com, scott.a.mcmillan@...el.com,
	laijs@...fujitsu.com, "H. Peter Anvin" <hpa@...or.com>,
	LKML <linux-kernel@...r.kernel.org>, eric.dumazet@...il.com,
	kaneshige.kenji@...fujitsu.com, David Miller <davem@...emloft.net>,
	izumi.taku@...fujitsu.com, kosaki.motohiro@...fujitsu.com,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	"Luck, Tony" <tony.luck@...el.com>
Subject: Re: [PATCH] tracing: Cleanup the convoluted softirq tracepoints

On Wed, 2010-10-20 at 00:17 +0200, Thomas Gleixner wrote:
> On Tue, 19 Oct 2010, Thomas Gleixner wrote:
> > On Tue, 19 Oct 2010, Jason Baron wrote:
> > > > Now even worse, when you NOP out the jmpq then your tracepoint is
> > > > still not enabled. Brilliant !
> > > > 
> > > 
> > > The 'jmpq' in the enabled case is patched with a jmpq to the body of the
> > > tracepoint itself.
> > 
> > Brilliant.
> 
> IOW, We now jump around the jump which jumps around the disabled code.
> 


Do you happen to have CONFIG_CC_OPTIMIZE_FOR_SIZE set? If so, then this
is a known issue. We even originally had jump label enabled _only_ if
CC_OPTIMIZE_FOR_SIZE was not set, but hpa NAK'd it.

http://lkml.org/lkml/2010/9/22/482

http://lkml.org/lkml/2010/9/20/488

http://lkml.org/lkml/2010/9/24/259

-- Steve


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