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

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Date:	Mon, 22 Jun 2009 17:23:13 -0400
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	lkml <linux-kernel@...r.kernel.org>
Cc:	systemtap <systemtap@...rces.redhat.com>,
	DLE <dle-develop@...ts.sourceforge.net>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Jim Keniston <jkenisto@...ibm.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Christoph Hellwig <hch@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Anders Kaseorg <andersk@...lice.com>,
	Tim Abbott <tabbott@...lice.com>
Subject: [RFC][ PATCH -tip v2 3/7] Kbuild: disable gcc crossjumping

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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