diff --git a/core/base_rules.mk b/core/base_rules.mk
index 04a9d67..0c49478 100644
--- a/core/base_rules.mk
+++ b/core/base_rules.mk
@@ -190,7 +190,7 @@
 LOCAL_SDK_VERSION:=$(strip $(LOCAL_SDK_VERSION))
 ifdef LOCAL_SDK_VERSION
 ifneq ($(LOCAL_SDK_VERSION),current)
-aidl_preprocess_import := -p$(TOPDIR)prebuilt/sdk/$(LOCAL_SDK_VERSION)/framework.aidl
+aidl_preprocess_import := -p$(HISTORICAL_SDK_VERSIONS_ROOT)/$(LOCAL_SDK_VERSION)/framework.aidl
 endif # !current
 endif # LOCAL_SDK_VERSION
 $(aidl_java_sources): PRIVATE_AIDL_FLAGS := -b $(aidl_preprocess_import) -I$(LOCAL_PATH) -I$(LOCAL_PATH)/src $(addprefix -I,$(LOCAL_AIDL_INCLUDES))
diff --git a/core/config.mk b/core/config.mk
index 82090fa..0877ebd 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -315,22 +315,26 @@
 # For use with the LOCAL_SDK_VERSION variable for include $(BUILD_PACKAGE)
 # ###############################################################
 
-# The files that we can convert into android.jars are are in config/api/*.xml
-# The 'current' version is whatever this source tree is.  Once the apicheck
-# tool can generate the stubs from the xml files, we'll use that to be
-# able to build back-versions.  In the meantime, 'current' is the only
-# one supported.
+HISTORICAL_SDK_VERSIONS_ROOT := $(TOPDIR)prebuilt/sdk
+
+# Historical SDK version N is stored in $(HISTORICAL_SDK_VERSIONS_ROOT)/N.
+# The 'current' version is whatever this source tree is.
 #
 # sgrax     is the opposite of xargs.  It takes the list of args and puts them
 #           on each line for sort to process.
 # sort -g   is a numeric sort, so 1 2 3 10 instead of 1 10 2 3.
-TARGET_AVAILABLE_SDK_VERSIONS := current \
-        $(shell function sgrax() { \
-                while [ -n "$$1" ] ; do echo $$1 ; shift ; done \
-            } ; \
-            ( sgrax $(patsubst $(SRC_API_DIR)/%.xml,%, \
-                $(filter-out $(SRC_API_DIR)/current.xml, \
-                $(shell find $(SRC_API_DIR) -name "*.xml"))) | sort -g ) )
 
+# Numerically sort a list of numbers
+# $(1): the list of numbers to be sorted
+define numerically_sort
+$(shell function sgrax() { \
+    while [ -n "$$1" ] ; do echo $$1 ; shift ; done \
+    } ; \
+    ( sgrax $(1) | sort -g ) )
+endef
+
+TARGET_AVAILABLE_SDK_VERSIONS := current $(call numerically_sort,\
+    $(patsubst $(HISTORICAL_SDK_VERSIONS_ROOT)/%/android.jar,%, \
+    $(wildcard $(HISTORICAL_SDK_VERSIONS_ROOT)/*/android.jar)))
 
 INTERNAL_PLATFORM_API_FILE := $(TARGET_OUT_COMMON_INTERMEDIATES)/PACKAGING/public_api.xml
diff --git a/core/package.mk b/core/package.mk
index d5de77b..e7be05f 100644
--- a/core/package.mk
+++ b/core/package.mk
@@ -244,17 +244,24 @@
 # Most packages should link against the resources defined by framework-res.
 # Even if they don't have their own resources, they may use framework
 # resources.
+ifneq ($(filter-out current,$(LOCAL_SDK_VERSION)),)
+# for released sdk versions, the platform resources were built into android.jar.
+framework_res_package_export := \
+	$(HISTORICAL_SDK_VERSIONS_ROOT)/$(LOCAL_SDK_VERSION)/android.jar
+framework_res_package_export_deps := $(framework_res_package_export)
+else # LOCAL_SDK_VERSION
 framework_res_package_export := \
 	$(call intermediates-dir-for,APPS,framework-res,,COMMON)/package-export.apk
-$(LOCAL_INTERMEDIATE_TARGETS): \
-	PRIVATE_AAPT_INCLUDES := $(framework_res_package_export)
 # We can't depend directly on the export.apk file; it won't get its
 # PRIVATE_ vars set up correctly if we do.  Instead, depend on the
 # corresponding R.stamp file, which lists the export.apk as a dependency.
 framework_res_package_export_deps := \
 	$(dir $(framework_res_package_export))src/R.stamp
+endif # LOCAL_SDK_VERSION
 $(R_file_stamp): $(framework_res_package_export_deps)
-endif
+$(LOCAL_INTERMEDIATE_TARGETS): \
+	PRIVATE_AAPT_INCLUDES := $(framework_res_package_export)
+endif # LOCAL_NO_STANDARD_LIBRARIES
 
 ifneq ($(full_classes_jar),)
 $(LOCAL_BUILT_MODULE): PRIVATE_DEX_FILE := $(built_dex)
diff --git a/core/tasks/apicheck.mk b/core/tasks/apicheck.mk
index 044e4af..740668c 100644
--- a/core/tasks/apicheck.mk
+++ b/core/tasks/apicheck.mk
@@ -41,13 +41,18 @@
 # Run the checkapi rules by default.
 droidcore: checkapi
 
+last_released_sdk_version := $(lastword $(call numerically_sort,\
+    $(patsubst $(SRC_API_DIR)/%.xml,%, \
+    $(filter-out $(SRC_API_DIR)/current.xml, \
+    $(wildcard $(SRC_API_DIR)/*.xml)))))
+
 # INTERNAL_PLATFORM_API_FILE is the one build by droiddoc.
 
 # Check that the API we're building hasn't broken the last-released
 # SDK version.
 $(eval $(call check-api, \
 	checkapi-last, \
-	$(SRC_API_DIR)/$(lastword $(TARGET_AVAILABLE_SDK_VERSIONS)).xml, \
+	$(SRC_API_DIR)/$(last_released_sdk_version).xml, \
 	$(INTERNAL_PLATFORM_API_FILE), \
 	-hide 2 -hide 3 -hide 4 -hide 5 -hide 6 -hide 24 -hide 25 \
 	-error 7 -error 8 -error 9 -error 10 -error 11 -error 12 -error 13 -error 14 -error 15 \
diff --git a/tools/Android.mk b/tools/Android.mk
new file mode 100644
index 0000000..aea2785
--- /dev/null
+++ b/tools/Android.mk
@@ -0,0 +1,23 @@
+#
+# Copyright (C) 2010 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+LOCAL_PATH := $(my-dir)
+
+ifeq ($(strip $(is_unbundled_app_build)),true)
+include $(LOCAL_PATH)/signapk/Android.mk
+else
+include $(call first-makefiles-under,$(LOCAL_PATH))
+endif