x86/retpoline: Add initial retpoline support

[uclinux-h8/linux.git] / arch / x86 / Makefile

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index a20eacd..974c618 100644 (file)
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -235,6 +235,16 @@ KBUILD_CFLAGS += -Wno-sign-compare
 #
 KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
 
+# Avoid indirect branches in kernel to deal with Spectre
+ifdef CONFIG_RETPOLINE
+    RETPOLINE_CFLAGS += $(call cc-option,-mindirect-branch=thunk-extern -mindirect-branch-register)
+    ifneq ($(RETPOLINE_CFLAGS),)
+        KBUILD_CFLAGS += $(RETPOLINE_CFLAGS) -DRETPOLINE
+    else
+        $(warning CONFIG_RETPOLINE=y, but not supported by the compiler. Toolchain update recommended.)
+    endif
+endif
+
 archscripts: scripts_basic
        $(Q)$(MAKE) $(build)=arch/x86/tools relocs