From: Thomas Gleixner <tglx@linutronix.de>

In preparation for mitigating the Intel SKL RSB underflow issue in
software, add a new configuration symbol which allows to build the
required call thunk infrastructure conditionally.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 arch/x86/Kconfig |    7 +++++++
 1 file changed, 7 insertions(+)

--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2432,6 +2432,13 @@ config CC_HAS_SLS
 config CC_HAS_RETURN_THUNK
 	def_bool $(cc-option,-mfunction-return=thunk-extern)
 
+config HAVE_CALL_THUNKS
+	def_bool y
+	depends on RETHUNK && OBJTOOL
+
+config CALL_THUNKS
+	def_bool n
+
 menuconfig SPECULATION_MITIGATIONS
 	bool "Mitigations for speculative execution vulnerabilities"
 	default y