-#define likely(x) __builtin_expect((x),1)
-#define unlikely(x) __builtin_expect((x),0)
+#define WARN_UNUSED_RESULT __attribute__((__warn_unused_result__))
+#define SENTINEL(N) __attribute__((sentinel(N)))
+#else
+#define NO_RETURN
+#define OVS_UNUSED
+#define PRINTF_FORMAT(FMT, ARG1)
+#define STRFTIME_FORMAT(FMT)
+#define MALLOC_LIKE
+#define ALWAYS_INLINE
+#define WARN_UNUSED_RESULT
+#define SENTINEL(N)
+#endif
+
+/* ISO C says that a C implementation may choose any integer type for an enum
+ * that is sufficient to hold all of its values. Common ABIs (such as the
+ * System V ABI used on i386 GNU/Linux) always use a full-sized "int", even
+ * when a smaller type would suffice.
+ *
+ * In GNU C, "enum __attribute__((packed)) name { ... }" defines 'name' as an
+ * enum compatible with a type that is no bigger than necessary. This is the
+ * intended use of OVS_PACKED_ENUM.
+ *
+ * OVS_PACKED_ENUM is intended for use only as a space optimization, since it
+ * only works with GCC. That means that it must not be used in wire protocols
+ * or otherwise exposed outside of a single process. */
+#if __GNUC__ && !__CHECKER__
+#define OVS_PACKED_ENUM __attribute__((__packed__))
+#else
+#define OVS_PACKED_ENUM
+#endif