linux-kernel - Re: [RFC PATCH 3/4] ftrace: Do not test frame pointers if -mfentry is used

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Message-ID: <50232772.4070102@hitachi.com>
Date:	Thu, 09 Aug 2012 11:58:58 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>, yrl.pp-manager.tt@...achi.com
Subject: Re: [RFC PATCH 3/4] ftrace: Do not test frame pointers if -mfentry
 is used

(2012/08/08 21:49), Steven Rostedt wrote:
> On Wed, 2012-08-08 at 13:34 +0900, Masami Hiramatsu wrote:
>>  
>>> -#ifdef CONFIG_HAVE_FUNCTION_GRAPH_FP_TEST
>>> +#if defined(CONFIG_HAVE_FUNCTION_GRAPH_FP_TEST) && !defined(CC_USING_FENTRY)
>>
>> I think CONFIG_HAVE_FENTRY would better unselect
>> CONFIG_HAVE_FUNCTION_GRAPH_FP_TEST in arch/x86/Kconfig explicitly.
> 
> No, CONFIG_HAVE_FENTRY just means fentry is supported, it does not mean
> that it is being used. It only gets used if CC_USING_FENTRY is set,
> which is set by the Makefile at time of compile.
> 
> If CONFIG_HAVE_FENTRY is defined, a test is done to see if the gcc
> compiling the kernel supports -mfentry. If it does, then it defines the
> CC_USING_FENTRY macro, if not, the macro is not defined and the old way
> is performed.
> 
> If the old way is performed, even if CONFIG_HAVE_FENTRY is defined, then
> we still need the above test. We can not have CONFIG_HAVE_FENTRY
> unselect CONFIG_HAVE_FUNCTION_GRAPH_FP_TEST.

Ah, I see. OK, I don't see any other issue.

Thank you,

-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com


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