linux-kernel - Re: [PATCH v2 1/2] arm64: implement FTRACE_WITH

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Message-ID: <20160708115710.5c657b5f@gandalf.local.home>
Date:	Fri, 8 Jul 2016 11:57:10 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Josh Poimboeuf <jpoimboe@...hat.com>
Cc:	Petr Mladek <pmladek@...e.com>, Torsten Duwe <duwe@....de>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>, takahiro.akashi@...aro.org,
	Jungseok Lee <jungseoklee85@...il.com>,
	Arnd Bergmann <arnd@...db.de>,
	Li Bin <huawei.libin@...wei.com>,
	Ingo Molnar <mingo@...hat.com>,
	Christopher Li <sparse@...isli.org>,
	Jiri Kosina <jikos@...nel.org>, andrew.wafaa@....com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	live-patching@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-sparse@...r.kernel.org
Subject: Re: [PATCH v2 1/2] arm64: implement FTRACE_WITH_REGS

On Fri, 8 Jul 2016 10:48:24 -0500
Josh Poimboeuf <jpoimboe@...hat.com> wrote:


> My understanding is that other arches don't need this check because they
> use -mfentry, so they have to modify the "call fentry" instruction to a
> nop on startup.
> 
> Here, with -fprolog-pad, it's already a nop, so no change is needed.
> 

That's what I was thinking. But as I stated in another email (probably
in the air when you wrote this), the call to ftrace_modify_code() may be
completely circumvented by ftrace_make_nop() if the addr is MCOUNT_ADDR.

-- Steve