--- 4.9.9-gentoo/build/include/linux/compiler.h	2016-12-11 20:17:54.000000000 +0100
+++ 4.9.11-gentoo/build/include/linux/compiler.h	2017-02-19 16:48:37.245713902 +0100
@@ -299,6 +299,7 @@
  * with an explicit memory barrier or atomic instruction that provides the
  * required ordering.
  */
+#ifndef __cplusplus
 
 #define __READ_ONCE(x, check)						\
 ({									\
@@ -309,6 +310,17 @@
 		__read_once_size_nocheck(&(x), __u.__c, sizeof(x));	\
 	__u.__val;							\
 })
+#else
+#define __READ_ONCE(x, check)						\
+({									\
+	union { typeof(x) __val; char __c[1]={0}; } __u;		\
+	if (check)							\
+		__read_once_size(&(x), __u.__c, sizeof(x));		\
+	else								\
+		__read_once_size_nocheck(&(x), __u.__c, sizeof(x));	\
+	__u.__val;							\
+})
+#endif
 #define READ_ONCE(x) __READ_ONCE(x, 1)
 
 /*