linux-kernel - Re: [RFC][ PATCH -tip v2 3/7] Kbuild: disable gcc crossjumping

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Date:	Sat, 27 Jun 2009 16:13:04 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Masami Hiramatsu <mhiramat@...hat.com>
cc:	Ingo Molnar <mingo@...e.hu>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	lkml <linux-kernel@...r.kernel.org>,
	systemtap <systemtap@...rces.redhat.com>,
	DLE <dle-develop@...ts.sourceforge.net>,
	Jim Keniston <jkenisto@...ibm.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Christoph Hellwig <hch@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Anders Kaseorg <andersk@...lice.com>,
	Tim Abbott <tabbott@...lice.com>, sam@...nborg.org
Subject: Re: [RFC][ PATCH -tip v2 3/7] Kbuild: disable gcc crossjumping


A change like this requires an ACK from Sam Ravnborg.

-- Steve



On Mon, 22 Jun 2009, Masami Hiramatsu wrote:

> Add CONFIG_DISABLE_CROSSJUMP option which disables gcc's cross-function
> jumping. This option is required by the kprobes jump optimization.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@...hat.com>
> Cc: Ananth N Mavinakayanahalli <ananth@...ibm.com>
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Jim Keniston <jkenisto@...ibm.com>
> Cc: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
> Cc: Christoph Hellwig <hch@...radead.org>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Cc: H. Peter Anvin <hpa@...or.com>
> Cc: Anders Kaseorg <andersk@...lice.com>
> Cc: Tim Abbott <tabbott@...lice.com>
> ---
> 
>  Makefile          |    4 ++++
>  lib/Kconfig.debug |    7 +++++++
>  2 files changed, 11 insertions(+), 0 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index 2903e13..f73b139 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -524,6 +524,10 @@ else
>  KBUILD_CFLAGS	+= -O2
>  endif
>  
> +ifdef CONFIG_DISABLE_CROSSJUMP
> +KBUILD_CFLAGS	+= -fno-crossjumping
> +endif
> +
>  include $(srctree)/arch/$(SRCARCH)/Makefile
>  
>  ifneq ($(CONFIG_FRAME_WARN),0)
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 8da7467..f88e6b8 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -673,6 +673,13 @@ config FRAME_POINTER
>  	  larger and slower, but it gives very useful debugging information
>  	  in case of kernel bugs. (precise oopses/stacktraces/warnings)
>  
> +config DISABLE_CROSSJUMP
> +	bool "Disable cross-function jump optimization"
> +	help
> +	  This build option disables cross-function jump optimization
> +	  (crossjumping) of gcc. Disabling crossjumping might increase
> +	  kernel binary size a little.
> +
>  config BOOT_PRINTK_DELAY
>  	bool "Delay each boot printk message by N milliseconds"
>  	depends on DEBUG_KERNEL && PRINTK && GENERIC_CALIBRATE_DELAY
> 
> 
> -- 
> Masami Hiramatsu
> 
> Software Engineer
> Hitachi Computer Products (America), Inc.
> Software Solutions Division
> 
> e-mail: mhiramat@...hat.com
> 
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