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Subject: Re: [PATCH] tracing: Cleanup the convoluted softirq tracepoints
From: Steven Rostedt <rostedt@goodmis.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Jason Baron <jbaron@redhat.com>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Koki Sanagi <sanagi.koki@jp.fujitsu.com>,
        Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@elte.hu>,
        Frederic Weisbecker <fweisbec@gmail.com>, nhorman@tuxdriver.com,
        scott.a.mcmillan@intel.com, laijs@cn.fujitsu.com,
        "H. Peter Anvin" <hpa@zytor.com>, LKML <linux-kernel@vger.kernel.org>,
        eric.dumazet@gmail.com, kaneshige.kenji@jp.fujitsu.com,
        David Miller <davem@davemloft.net>, izumi.taku@jp.fujitsu.com,
        kosaki.motohiro@jp.fujitsu.com,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        "Luck, Tony" <tony.luck@intel.com>
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Date: Tue, 19 Oct 2010 21:36:30 -0400
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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