[PATCH] kbuild: add -fno-pie to KBUILD_CFLAGS

[Sven Joachim]

If GCC is configured with --enable-default-pie, the build fails early
because this default is incompatible with -mcmodel=kernel.

kernel/bounds.c:1:0: error: code model kernel does not support PIC mode

Avoid that by adding -fno-pie to KBUILD_CFLAGS, if supported by the
compiler.  This flag is also needed in the x86_64 stack-protector test
script which otherwise errors out.

Cannot use CONFIG_CC_STACKPROTECTOR_STRONG: -fstack-protector-strong available but compiler is broken

See https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=841420 and
https://bugs.launchpad.net/ubuntu/+source/gcc-defaults/+bug/1574982.

Signed-off-by: Sven Joachim <svenjoac@xxxxxx>
---
 Makefile                                  | 1 +
 scripts/gcc-x86_64-has-stack-protector.sh | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index 93beca4..81ef816 100644
--- a/Makefile
+++ b/Makefile
@@ -619,6 +619,7 @@ ARCH_AFLAGS :=
 ARCH_CFLAGS :=
 include arch/$(SRCARCH)/Makefile
 
+KBUILD_CFLAGS	+= $(call cc-option,-fno-pie,)
 KBUILD_CFLAGS	+= $(call cc-option,-fno-delete-null-pointer-checks,)
 KBUILD_CFLAGS	+= $(call cc-disable-warning,maybe-uninitialized,)
 KBUILD_CFLAGS	+= $(call cc-disable-warning,frame-address,)
diff --git a/scripts/gcc-x86_64-has-stack-protector.sh b/scripts/gcc-x86_64-has-stack-protector.sh
index 973e8c1..274cba1 100755
--- a/scripts/gcc-x86_64-has-stack-protector.sh
+++ b/scripts/gcc-x86_64-has-stack-protector.sh
@@ -1,6 +1,6 @@
 #!/bin/sh
 
-echo "int foo(void) { char X[200]; return 3; }" | $* -S -x c -c -O0 -mcmodel=kernel -fstack-protector - -o - 2> /dev/null | grep -q "%gs"
+echo "int foo(void) { char X[200]; return 3; }" | $* -S -x c -c -O0 -mcmodel=kernel -fno-pie -fstack-protector - -o - 2> /dev/null | grep -q "%gs"
 if [ "$?" -eq "0" ] ; then
 	echo y
 else
-- 
2.10.1


--=-=-=--