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SubjectRe: [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@redhat.com>
> Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
> Cc: Ingo Molnar <mingo@elte.hu>
> Cc: Jim Keniston <jkenisto@us.ibm.com>
> Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
> Cc: Christoph Hellwig <hch@infradead.org>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: H. Peter Anvin <hpa@zytor.com>
> Cc: Anders Kaseorg <andersk@ksplice.com>
> Cc: Tim Abbott <tabbott@ksplice.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@redhat.com
>


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