linux-kernel - Re: [PATCH 6/6] ARM: ftrace: enable function graph tracer

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Date:	Tue, 9 Nov 2010 19:16:45 +0530
From:	Rabin Vincent <rabin@....in>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Tim Bird <tim.bird@...sony.com>
Subject: Re: [PATCH 6/6] ARM: ftrace: enable function graph tracer

On Mon, Nov 08, 2010 at 10:42:57AM +0000, Catalin Marinas wrote:
> 2010/11/8 Uwe Kleine-König <u.kleine-koenig@...gutronix.de>:
> > On Sat, Nov 06, 2010 at 07:06:28PM +0000, Catalin Marinas wrote:
> >> On Saturday, November 6, 2010, Rabin Vincent <rabin@....in> wrote:
> >> > --- a/kernel/trace/Kconfig
> >> > +++ b/kernel/trace/Kconfig
> >> > @@ -141,6 +141,7 @@ config FUNCTION_TRACER
> >> >
> >> >  config FUNCTION_GRAPH_TRACER
> >> >         bool "Kernel Function Graph Tracer"
> >> > +       select FRAME_POINTER if ARM_UNWIND
> >>
> >> Would it be better to modify FRAME_POINTER definition in the ARM
> >> Kconfig so that it is enabled automatically when FUNCTION_GRAPH_TRACER
> >> is enabled?
> > I don't like that suggestion much because it hides the dependency.
> > Moreover a "default y if FUNCTION_GRAPH_TRACER" doesn't work if a
> > precondition for FRAME_POINTER isn't true.  Rabin's approach at least
> > generates a warning.
> 
> If a precondition for FRAME_POINTER isn't true, we should not force it
> via 'select'. We try to get rid of such warnings in the kernel.
> 
> However, on ARM the FRAME_POINTER depends on !THUMB2_KERNEL but for
> Thumb-2 kernels HAVE_FUNCTION_GRAPH_TRACER is also disabled, so there
> isn't a dependency issue here. It's more like a personal preference to
> keep the changes within the arch/arm tree.

OK, new patch below.

>From ce3856933234b0976068be8bdc46340dcf31ef6f Mon Sep 17 00:00:00 2001
From: Rabin Vincent <rabin@....in>
Date: Sat, 6 Nov 2010 23:03:53 +0530
Subject: [PATCHv2] ARM: ftrace: enable function graph tracer

Add the options to enable the function graph tracer on ARM.  Function
graph tracer support requires frame pointers, so exclude Thumb-2 and
also make sure FRAME_POINTER gets enabled when FUNCTION_GRAPH_TRACER is
used, since FUNCTION_TRACER doesn't "select FRAME_POINTER" when
ARM_UNWIND is used.  Therefore, with GCC 4.4.0+, you get plain function
tracing without frame pointers, but you'll need them if you want
function graph tracing.

Signed-off-by: Rabin Vincent <rabin@....in>
---
 arch/arm/Kconfig       |    1 +
 arch/arm/Kconfig.debug |    2 +-
 2 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index a19a526..c5e96ff 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -14,6 +14,7 @@ config ARM
 	select HAVE_FUNCTION_TRACER if (!XIP_KERNEL)
 	select HAVE_FTRACE_MCOUNT_RECORD if (!XIP_KERNEL)
 	select HAVE_DYNAMIC_FTRACE if (!XIP_KERNEL)
+	select HAVE_FUNCTION_GRAPH_TRACER if (!THUMB2_KERNEL)
 	select HAVE_GENERIC_DMA_COHERENT
 	select HAVE_KERNEL_GZIP
 	select HAVE_KERNEL_LZO
diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug
index 2fd0b99..eac62085 100644
--- a/arch/arm/Kconfig.debug
+++ b/arch/arm/Kconfig.debug
@@ -23,7 +23,7 @@ config STRICT_DEVMEM
 config FRAME_POINTER
 	bool
 	depends on !THUMB2_KERNEL
-	default y if !ARM_UNWIND
+	default y if !ARM_UNWIND || FUNCTION_GRAPH_TRACER
 	help
 	  If you say N here, the resulting kernel will be slightly smaller and
 	  faster. However, if neither FRAME_POINTER nor ARM_UNWIND are enabled,
-- 
1.7.2.3

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