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Date: Wed, 08 Aug 2012 08:49:08 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
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>
Subject: Re: [RFC PATCH 3/4] ftrace: Do not test frame pointers if -mfentry
is used
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.
-- Steve
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