linux-kernel - Re: [PATCH v7 5/7] arm64: ftrace: Add dynamic ftrace support

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Date:	Wed, 16 Apr 2014 14:48:15 +0100
From:	Will Deacon <will.deacon@....com>
To:	AKASHI Takahiro <takahiro.akashi@...aro.org>
Cc:	"rostedt@...dmis.org" <rostedt@...dmis.org>,
	"fweisbec@...il.com" <fweisbec@...il.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"tim.bird@...ymobile.com" <tim.bird@...ymobile.com>,
	"gkulkarni@...iumnetworks.com" <gkulkarni@...iumnetworks.com>,
	"dsaxena@...aro.org" <dsaxena@...aro.org>,
	"arndb@...db.de" <arndb@...db.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7 5/7] arm64: ftrace: Add dynamic ftrace support

On Sat, Mar 15, 2014 at 05:45:51AM +0000, AKASHI Takahiro wrote:
> This patch allows "dynamic ftrace" if CONFIG_DYNAMIC_FTRACE is enabled.
> Here we can turn on and off tracing dynamically per-function base.
> 
> On arm64, this is done by patching single branch instruction to _mcount()
> inserted by gcc -pg option. The branch is replaced to NOP initially at
> kernel start up, and later on, NOP to branch to ftrace_caller() when
> enabled or branch to NOP when disabled.
> Please note that ftrace_caller() is a counterpart of _mcount() in case of
> 'static' ftrace.
> 
> More details on architecture specific requirements are described in
> Documentation/trace/ftrace-design.txt.
> 
> Signed-off-by: AKASHI Takahiro <takahiro.akashi@...aro.org>

  Acked-by: Will Deacon <will.deacon@....com>

Will
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