[patch 5/5] -fstack-protector feature: Enable the compiler flagsin CFLAGS

[Arjan van de Ven]

Subject: [patch 5/5] Add the -fstack-protector option to the CFLAGS
From: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>

Add a feature check that checks that the gcc compiler has stack-protector
support and has the bugfix for PR28281 to make this work in kernel mode.
The easiest solution I could find was to have a shell script in scripts/
to do the detection; if needed we can make this fancier in the future 
without making the makefile too complex.

Signed-off-by: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
CC: Andi Kleen <ak@xxxxxxx>
CC: Sam Ravnborg <sam@xxxxxxxxxxxx>

---
 arch/x86_64/Makefile                      |    3 +++
 scripts/gcc-x86_64-has-stack-protector.sh |    8 ++++++++
 2 files changed, 11 insertions(+)

Index: linux-2.6.18-rc4-stackprot/arch/x86_64/Makefile
===================================================================
--- linux-2.6.18-rc4-stackprot.orig/arch/x86_64/Makefile
+++ linux-2.6.18-rc4-stackprot/arch/x86_64/Makefile
@@ -55,6 +55,9 @@ cflags-y += $(call cc-option,-funit-at-a
 # prevent gcc from generating any FP code by mistake
 cflags-y += $(call cc-option,-mno-sse -mno-mmx -mno-sse2 -mno-3dnow,)
 
+cflags-$(CONFIG_CC_STACKPROTECTOR) += $(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-x86_64-has-stack-protector.sh $(CC) -fstack-protector )
+cflags-$(CONFIG_CC_STACKPROTECTOR_ALL) += $(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-x86_64-has-stack-protector.sh $(CC) -fstack-protector-all )
+
 CFLAGS += $(cflags-y)
 CFLAGS_KERNEL += $(cflags-kernel-y)
 AFLAGS += -m64
Index: linux-2.6.18-rc4-stackprot/scripts/gcc-x86_64-has-stack-protector.sh
===================================================================
--- /dev/null
+++ linux-2.6.18-rc4-stackprot/scripts/gcc-x86_64-has-stack-protector.sh
@@ -0,0 +1,6 @@
+#!/bin/sh
+
+echo "int foo(void) { char X[200]; return 3; }" | $1 -S -xc -c -O0 -mcmodel=kernel -fstack-protector - -o - | grep -q "%gs"
+if [ "$?" -eq "0" ] ; then
+	echo $2
+fi

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