diff --git a/.rootkeys b/.rootkeys
index 7fd3ddd868..9f2d05bfcc 100644
--- a/.rootkeys
+++ b/.rootkeys
@@ -313,8 +313,8 @@
 413cb3b5F56TvQWAmO5TsuzhtzLFPQ netbsd-2.0-xen-sparse/sys/arch/xen/xen/xenkbc.c
 413cb3b53nyOv1OIeDSsCXhBFDXvJA netbsd-2.0-xen-sparse/sys/nfs/files.nfs
 413aa1d0oNP8HXLvfPuMe6cSroUfSA patches/linux-2.6.9/agpgart.patch
-40e1b09db5mN69Ijj0X_Eol-S7dXiw tools/Make.defs
 3f776bd1Hy9rn69ntXBhPReUFw9IEA tools/Makefile
+40e1b09db5mN69Ijj0X_Eol-S7dXiw tools/Rules.mk
 4124b307nRyK3dhn1hAsvrY76NuV3g tools/check/Makefile
 4124b307vHLUWbfpemVefmaWDcdfag tools/check/README
 4124b307jt7T3CHysgl9LijNHSe1tA tools/check/check_brctl
diff --git a/Makefile b/Makefile
index 33bac70d43..094acb7fe4 100644
--- a/Makefile
+++ b/Makefile
@@ -21,6 +21,12 @@ XKERNELS := $(foreach kernel, $(KERNELS), $(patsubst buildconfigs/mk.%,%,$(wildc
 
 export DESTDIR
 
+# Export target architecture overrides to Xen and Linux sub-trees.
+ifneq ($(ARCH),)
+export TARGET_SUBARCH := $(ARCH)
+export SUBARCH        := $(subst x86_32,i386,$(ARCH))
+endif
+
 include buildconfigs/Rules.mk
 
 .PHONY:	all dist install xen tools kernels docs world clean mkpatches mrproper
@@ -36,8 +42,8 @@ install: xen checked-tools kernels docs
 
 # Only check for install req'mts on 'make install', not on 'make dist'.
 checked-tools:
-	$(MAKE) -C tools/check install
-	$(MAKE) -C tools install
+	$(MAKE) ARCH=$(ARCH) -C tools/check install
+	$(MAKE) ARCH=$(ARCH) -C tools install
 
 # build and install everything into local dist directory
 dist: xen tools kernels docs
@@ -51,7 +57,7 @@ xen:
 	$(MAKE) -C xen install
 
 tools:
-	$(MAKE) -C tools install
+	$(MAKE) ARCH=$(ARCH) -C tools install
 
 kernels:
 	for i in $(XKERNELS) ; do $(MAKE) $$i-build || exit 1; done
@@ -86,7 +92,7 @@ world:
 # clean doesn't do a kclean
 clean: 
 	$(MAKE) -C xen clean
-	$(MAKE) -C tools clean
+	$(MAKE) ARCH=$(ARCH) -C tools clean
 	$(MAKE) -C docs clean
 
 # clean, but blow away kernel build tree plus tar balls
diff --git a/tools/Make.defs b/tools/Rules.mk
similarity index 54%
rename from tools/Make.defs
rename to tools/Rules.mk
index 132e4347cc..2876c7eb61 100644
--- a/tools/Make.defs
+++ b/tools/Rules.mk
@@ -1,4 +1,15 @@
 #  -*- mode: Makefile; -*-
+
 XEN_XC             = $(XEN_ROOT)/tools/python/xen/lowlevel/xc
 XEN_LIBXC          = $(XEN_ROOT)/tools/libxc
 XEN_LIBXUTIL       = $(XEN_ROOT)/tools/libxutil
+
+ifeq ($(ARCH),x86_32)
+CFLAGS  += -m32 -march=i686
+LDFLAGS += -m elf_i386
+endif
+
+ifeq ($(ARCH),x86_64)
+CFLAGS  += -m64
+LDFLAGS += -m elf_x86_64
+endif
diff --git a/tools/libxc/Makefile b/tools/libxc/Makefile
index bbbbe897af..ef41c2ed40 100644
--- a/tools/libxc/Makefile
+++ b/tools/libxc/Makefile
@@ -10,7 +10,7 @@ SONAME   = libxc.so.$(MAJOR)
 CC       = gcc
 
 XEN_ROOT = ../..
-include $(XEN_ROOT)/tools/Make.defs
+include $(XEN_ROOT)/tools/Rules.mk
 
 vpath %c       $(XEN_LIBXUTIL)
 INCLUDES += -I $(XEN_LIBXUTIL)
diff --git a/tools/libxutil/Makefile b/tools/libxutil/Makefile
index 63cb4fe0d1..1fb2da295d 100644
--- a/tools/libxutil/Makefile
+++ b/tools/libxutil/Makefile
@@ -4,7 +4,7 @@ INSTALL_DATA	= $(INSTALL) -m0644
 INSTALL_PROG	= $(INSTALL) -m0755
 INSTALL_DIR	= $(INSTALL) -d -m0755
 
-include $(XEN_ROOT)/tools/Make.defs
+include $(XEN_ROOT)/tools/Rules.mk
 
 CC = gcc
 
diff --git a/tools/misc/Makefile b/tools/misc/Makefile
index 84166c72fc..b339e300db 100644
--- a/tools/misc/Makefile
+++ b/tools/misc/Makefile
@@ -3,10 +3,10 @@ INSTALL_PROG	= $(INSTALL) -m0755
 INSTALL_DIR	= $(INSTALL) -d -m0755
 
 XEN_ROOT=../..
-include $(XEN_ROOT)/tools/Make.defs
+include $(XEN_ROOT)/tools/Rules.mk
 
-CC         = gcc
-CFLAGS     = -Wall -Werror -O3 
+CC        = gcc
+CFLAGS   += -Wall -Werror -O3 
 
 INCLUDES += -I $(XEN_XC)
 INCLUDES += -I $(XEN_LIBXC)
@@ -27,7 +27,8 @@ install: all
 	$(INSTALL_DIR) $(DESTDIR)/usr/sbin
 	$(INSTALL_PROG) $(INSTALL_BIN) $(DESTDIR)/usr/bin
 	$(INSTALL_PROG) $(INSTALL_SBIN) $(DESTDIR)/usr/sbin
-	$(MAKE) -C miniterm install
+#       No sense in installing miniterm on the Xen box.
+#	$(MAKE) -C miniterm install
 
 clean:
 	$(RM) *.o $(TARGETS) *~
diff --git a/tools/python/Makefile b/tools/python/Makefile
index 18bfeb1f7d..7d152e12ae 100644
--- a/tools/python/Makefile
+++ b/tools/python/Makefile
@@ -1,9 +1,12 @@
 
+XEN_ROOT = ../..
+include $(XEN_ROOT)/tools/Rules.mk
+
 all:
-	python setup.py build
+	CFLAGS="$(CFLAGS)" python setup.py build
 
 install: all
-	python setup.py install --home="$(DESTDIR)/usr"
+	CFLAGS="$(CFLAGS)" python setup.py install --home="$(DESTDIR)/usr"
 
 clean:
 	rm -rf build *.pyc *.pyo *.o *.a *~
diff --git a/tools/vnet/vnetd/Makefile b/tools/vnet/vnetd/Makefile
index a507666b5d..3783fa3833 100644
--- a/tools/vnet/vnetd/Makefile
+++ b/tools/vnet/vnetd/Makefile
@@ -21,7 +21,7 @@ all: vnetd
 #----------------------------------------------------------------------------
 
 XEN_ROOT  = ../../..
-include $(XEN_ROOT)/tools/Make.defs
+include $(XEN_ROOT)/tools/Rules.mk
 
 VNETD_INSTALL_DIR = /usr/sbin
 
diff --git a/tools/x2d2/Makefile b/tools/x2d2/Makefile
index fbe408107f..43f6964cae 100644
--- a/tools/x2d2/Makefile
+++ b/tools/x2d2/Makefile
@@ -1,8 +1,8 @@
 XEN_ROOT=../..
-include $(XEN_ROOT)/tools/Make.defs
+include $(XEN_ROOT)/tools/Rules.mk
 
 CC       = gcc
-CFLAGS   = -Wall -Werror -O3 -fno-strict-aliasing
+CFLAGS  += -Wall -Werror -O3 -fno-strict-aliasing
 
 CFLAGS  += -I $(XEN_XC)
 CFLAGS  += -I $(XEN_LIBXC)
diff --git a/tools/xentrace/Makefile b/tools/xentrace/Makefile
index 9133271b66..5fe6a9d61d 100644
--- a/tools/xentrace/Makefile
+++ b/tools/xentrace/Makefile
@@ -4,10 +4,10 @@ INSTALL_DIR	= $(INSTALL) -d -m0755
 INSTALL_DATA	= $(INSTALL) -m0644
 
 XEN_ROOT=../..
-include $(XEN_ROOT)/tools/Make.defs
+include $(XEN_ROOT)/tools/Rules.mk
 
 CC       = gcc
-CFLAGS   = -Wall -Werror -O3
+CFLAGS  += -Wall -Werror -O3
 
 CFLAGS  += -I $(XEN_XC)
 CFLAGS  += -I $(XEN_LIBXC)
diff --git a/tools/xfrd/Makefile b/tools/xfrd/Makefile
index 1b07ffa498..e986755140 100644
--- a/tools/xfrd/Makefile
+++ b/tools/xfrd/Makefile
@@ -9,7 +9,7 @@ INSTALL_PROG	= $(INSTALL) -m0755
 INSTALL_DIR	= $(INSTALL) -d -m0755
 
 XEN_ROOT  = ../..
-include $(XEN_ROOT)/tools/Make.defs
+include $(XEN_ROOT)/tools/Rules.mk
 
 XFRD_INSTALL_DIR = /usr/sbin