Implement GET_STACK_USAGE.

Discussed with:	mav

Approved by:	re (kib)
MFC after:	1 week

sys/sparc64/include/proc.h

@@ -55,6 +55,17 @@ struct mdproc {
 
 #ifdef _KERNEL
 
+#include <machine/pcb.h>
+
+/* Get the current kernel thread stack usage. */
+#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)
+
 struct syscall_args {
 	u_int code;
 	struct sysent *callp;