commit 6123a6becd80a9bb146ff9562095a9e54429fe01
author David Woodhouse <dwmw@amazon.co.uk> Mon Feb 19 10:50:57 2018 +0000
committer Greg Kroah-Hartman <gregkh@linuxfoundation.org> Sun Mar 18 11:18:52 2018 +0100
tree ce839caf34d2ad7756b406ee522ff0f35c2f661f
parent a27ede1bedcb21b8514f9bd9fcfc37773b816701

x86/retpoline: Support retpoline builds with Clang

commit 87358710c1fb4f1bf96bbe2349975ff9953fc9b2 upstream.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: arjan.van.de.ven@intel.com
Cc: bp@alien8.de
Cc: dave.hansen@intel.com
Cc: jmattson@google.com
Cc: karahmed@amazon.de
Cc: kvm@vger.kernel.org
Cc: pbonzini@redhat.com
Cc: rkrcmar@redhat.com
Link: http://lkml.kernel.org/r/1519037457-7643-5-git-send-email-dwmw@amazon.co.uk
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/x86/Makefile

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index cd22cb8..b609961 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -184,7 +184,10 @@
 
 # Avoid indirect branches in kernel to deal with Spectre
 ifdef CONFIG_RETPOLINE
-    RETPOLINE_CFLAGS += $(call cc-option,-mindirect-branch=thunk-extern -mindirect-branch-register)
+    RETPOLINE_CFLAGS_GCC := -mindirect-branch=thunk-extern -mindirect-branch-register
+    RETPOLINE_CFLAGS_CLANG := -mretpoline-external-thunk
+
+    RETPOLINE_CFLAGS += $(call cc-option,$(RETPOLINE_CFLAGS_GCC),$(call cc-option,$(RETPOLINE_CFLAGS_CLANG)))
     ifneq ($(RETPOLINE_CFLAGS),)
         KBUILD_CFLAGS += $(RETPOLINE_CFLAGS) -DRETPOLINE
     endif