diff -r d4a0706d6747 unmodified_drivers/linux-2.6/mkbuildtree
--- a/unmodified_drivers/linux-2.6/mkbuildtree	Tue May 15 15:14:02 2007 +0100
+++ b/unmodified_drivers/linux-2.6/mkbuildtree	Fri May 18 07:48:18 2007 -0400
@@ -10,8 +10,17 @@ fi
 
 C=$PWD
 
-XEN=$C/../../xen
-XL=$C/../../linux-2.6-xen-sparse
+if [ -n "$XEN" -a -d "$XEN" ]; then
+	XEN=$(cd $XEN && pwd)
+else
+	XEN=$C/../../xen
+fi
+
+if [ -n "$XL" -a -d "$XL" ]; then
+	XL=$(cd $XL && pwd)
+else
+	XL=$C/../../linux-2.6-xen-sparse
+fi
 
 for d in $(find ${XL}/drivers/xen/ -maxdepth 1 -type d | sed -e 1d); do
     if ! echo $d | egrep -q back; then