atomic: add stub atomic_load_consume_ptr

sys/sys/_cscan_atomic.h

@@ -236,6 +236,11 @@ void	kcsan_atomic_thread_fence_seq_cst(void);
 	__retptr;								\
 })
 #define	atomic_load_acq_ptr		kcsan_atomic_load_acq_ptr
+#define	atomic_load_consume_ptr(x)	({					\
+	__typeof(*x) __retptr;							\
+	__retptr = (void *)kcsan_atomic_load_acq_ptr((volatile uintptr_t *)(x));\
+	__retptr;								\
+})
 #define	atomic_readandclear_ptr		kcsan_atomic_readandclear_ptr
 #define	atomic_set_ptr			kcsan_atomic_set_ptr
 #define	atomic_set_acq_ptr		kcsan_atomic_set_acq_ptr

sys/sys/atomic_common.h

@@ -70,4 +70,12 @@
     (*(volatile uint64_t *)(p) = (uint64_t)(v))
 #endif
 
+/*
+ * Currently all architectures provide acquire and release fences on their own,
+ * but they don't provide consume. Kludge below allows relevant code to stop
+ * openly resorting to the stronger acquire fence, to be sorted out.
+ */
+#define	atomic_load_consume_ptr(p)	\
+    ((__typeof(*p)) atomic_load_acq_ptr((uintptr_t *)p))
+
 #endif