Index: lib/libc/amd64/string/bcopy.S
===================================================================
--- lib/libc/amd64/string/bcopy.S
+++ lib/libc/amd64/string/bcopy.S
@@ -66,6 +66,9 @@
 	movsq
 	movq	%rdx,%rcx
 	andq	$7,%rcx		/* any bytes left? */
+	jne	2f
+	ret
+2:
 	rep
 	movsb
 	ret