Index: sys/amd64/amd64/support.S
===================================================================
--- sys/amd64/amd64/support.S
+++ sys/amd64/amd64/support.S
@@ -915,27 +915,22 @@
 .macro COPYINSTR smap
 	PUSH_FRAME_POINTER
 	movq	%rdx,%r8			/* %r8 = maxlen */
-	movq	%rcx,%r9			/* %r9 = *len */
-	xchgq	%rdi,%rsi			/* %rdi = from, %rsi = to */
-	movq	PCPU(CURPCB),%rcx
-	movq	$cpystrflt,PCB_ONFAULT(%rcx)
+	movq	PCPU(CURPCB),%r9
+	movq	$cpystrflt,PCB_ONFAULT(%r9)
 
 	movq	$VM_MAXUSER_ADDRESS,%rax
 
 	/* make sure 'from' is within bounds */
-	subq	%rsi,%rax
+	subq	%rdi,%rax
 	jbe	cpystrflt
 
 	SMAP_DISABLE \smap
 
 	/* restrict maxlen to <= VM_MAXUSER_ADDRESS-from */
 	cmpq	%rdx,%rax
-	jae	1f
-	movq	%rax,%rdx
-	movq	%rax,%r8
+	jb	8f
 1:
 	incq	%rdx
-
 2:
 	decq	%rdx
 .if \smap == 0
@@ -944,9 +939,11 @@
 	jz	copyinstr_toolong_smap
 .endif
 
-	lodsb
-	stosb
-	orb	%al,%al
+	mov	(%rdi),%al
+	mov	%al,(%rsi)
+	incq	%rsi
+	incq	%rdi
+	test	%al,%al
 	jnz	2b
 
 	SMAP_ENABLE \smap
@@ -956,30 +953,42 @@
 	xorl	%eax,%eax
 
 	/* set *lencopied and return %eax */
-	movq	PCPU(CURPCB),%rcx
-	movq	$0,PCB_ONFAULT(%rcx)
+	movq	%rax,PCB_ONFAULT(%r9)
 
-	testq	%r9,%r9
+	testq	%rcx,%rcx
 	jz	3f
 	subq	%rdx,%r8
-	movq	%r8,(%r9)
+	movq	%r8,(%rcx)
 3:
 	POP_FRAME_POINTER
 	ret
+	ALIGN_TEXT
+8:
+	movq	%rax,%rdx
+	movq	%rax,%r8
+	jmp 1b
+
 .endm
 
+ENTRY(copyinstr_nosmap)
+	COPYINSTR smap=0
+END(copyinstr_nosmap)
+
+ENTRY(copyinstr_smap)
+	COPYINSTR smap=1
+END(copyinstr_smap)
+
 cpystrflt:
 	/* Fault entry clears PSL.AC */
 	movl	$EFAULT,%eax
 cpystrflt_x:
 	/* set *lencopied and return %eax */
-	movq	PCPU(CURPCB),%rcx
-	movq	$0,PCB_ONFAULT(%rcx)
+	movq	$0,PCB_ONFAULT(%r9)
 
-	testq	%r9,%r9
+	testq	%rcx,%rcx
 	jz	1f
 	subq	%rdx,%r8
-	movq	%r8,(%r9)
+	movq	%r8,(%rcx)
 1:
 	POP_FRAME_POINTER
 	ret
@@ -994,14 +1003,6 @@
 	movl	$ENAMETOOLONG,%eax
 	jmp	cpystrflt_x
 
-ENTRY(copyinstr_nosmap)
-	COPYINSTR smap=0
-END(copyinstr_nosmap)
-
-ENTRY(copyinstr_smap)
-	COPYINSTR smap=1
-END(copyinstr_smap)
-
 /*
  * copystr(from, to, maxlen, int *lencopied)
  *         %rdi, %rsi, %rdx, %rcx