[PATCH] x86: Detect CFI support in the assembler at runtime

... instead of using a CONFIG option. The config option still controls
if the resulting executable actually has unwind information.

This is useful to prevent compilation errors when users select
CONFIG_STACK_UNWIND on old binutils and also allows to use
CFI in the future for non kernel debugging applications.

Cc: jbeulich@novell.com
Cc: sam@ravnborg.org

Signed-off-by: Andi Kleen <ak@suse.de>

1 files changed, 3 insertions, 0 deletions

diff --git a/arch/x86_64/Makefile b/arch/x86_64/Makefile
index 431bb4bc36cd..d6472ddf5f6e 100644
--- a/arch/x86_64/Makefile
+++ b/arch/x86_64/Makefile
@@ -54,6 +54,9 @@ endif
 cflags-y += $(call cc-option,-funit-at-a-time)
 # prevent gcc from generating any FP code by mistake
 cflags-y += $(call cc-option,-mno-sse -mno-mmx -mno-sse2 -mno-3dnow,)
+# do binutils support CFI?
+cflags-y += $(call as-instr,.cfi_startproc\n.cfi_endproc,-DCONFIG_AS_CFI=1,)
+AFLAGS += $(call as-instr,.cfi_startproc\n.cfi_endproc,-DCONFIG_AS_CFI=1,)
 
 CFLAGS += $(cflags-y)
 CFLAGS_KERNEL += $(cflags-kernel-y)