Index: head/sys/arm64/include/proc.h
===================================================================
--- head/sys/arm64/include/proc.h
+++ head/sys/arm64/include/proc.h
@@ -54,4 +54,18 @@
 	int narg;
 };
 
+#ifdef _KERNEL
+
+#include <machine/pcb.h>
+
+#define	GET_STACK_USAGE(total, used) do {				\
+	struct thread *td = curthread;					\
+	(total) = td->td_kstack_pages * PAGE_SIZE - sizeof(struct pcb);	\
+	(used) = (char *)td->td_kstack +				\
+	    td->td_kstack_pages * PAGE_SIZE -				\
+	    (char *)&td;						\
+} while (0)
+
+#endif
+
 #endif /* !_MACHINE_PROC_H_ */