#define	KSTACK_MAGIC	0xdeadbeaf

/* XXX should be per process basis? */
static int	kstackleftmin = KSTACK_SIZE;
static int	kstackleftthres = KSTACK_SIZE / 8;

void
kstack_setup_magic(const struct lwp *l)
{
	uint32_t *ip;
	uint32_t const *end;

	KASSERT(l != NULL);
	KASSERT(l != &lwp0);

	/*
	 * fill all the stack with magic number
	 * so that later modification on it can be detected.
	 */
	ip = (uint32_t *)KSTACK_LOWEST_ADDR(l);
	end = (uint32_t *)((char *)KSTACK_LOWEST_ADDR(l) + KSTACK_SIZE);
	for (; ip < end; ip++) {
		*ip = KSTACK_MAGIC;
	}
}

/*
 * kthread_fpu_enter()
 *
 *	Allow the current lwp, which must be a kthread, to use the FPU.
 *	Return a cookie that must be passed to kthread_fpu_exit when
 *	done.  Must be used only in thread context.  Recursive -- you
 *	can call kthread_fpu_enter several times in a row as long as
 *	you pass the cookies in reverse order to kthread_fpu_exit.
 */
int
kthread_fpu_enter(void)
{
	struct lwp *l = curlwp;
	int s;

	KASSERTMSG(!cpu_intr_p(),
	    "%s is not allowed in interrupt context", __func__);
	KASSERTMSG(!cpu_softintr_p(),
	    "%s is not allowed in interrupt context", __func__);

	/*
	 * Remember whether this thread already had FPU access, and
	 * mark this thread as having FPU access.
	 */
	lwp_lock(l);
	KASSERTMSG(l->l_flag & LW_SYSTEM,
	    "%s is allowed only in kthreads", __func__);
	s = l->l_flag & LW_SYSTEM_FPU;
	l->l_flag |= LW_SYSTEM_FPU;
	lwp_unlock(l);

	/* Take MD steps to enable the FPU if necessary.  */
	if (s == 0)
		kthread_fpu_enter_md();

	return s;
}