diff --git a/core/main.mk b/core/main.mk
index 3c64d9555..8a5b407d3 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -466,8 +466,12 @@ subdir_makefiles := \
 	$(shell build/tools/findleaves.py --prune=out --prune=.repo --prune=.git $(subdirs) Android.mk)
 
 include $(subdir_makefiles)
+
 endif # ONE_SHOT_MAKEFILE
 
+# Now with all Android.mks loaded we can do post cleaning steps.
+include $(BUILD_SYSTEM)/post_clean.mk
+
 ifeq ($(stash_product_vars),true)
   $(call assert-product-vars, __STASHED)
 endif
diff --git a/core/package.mk b/core/package.mk
index 195b346d3..c68903137 100644
--- a/core/package.mk
+++ b/core/package.mk
@@ -94,12 +94,14 @@ endif
 ifeq (,$(LOCAL_RESOURCE_DIR))
   LOCAL_RESOURCE_DIR := $(LOCAL_PATH)/res
 endif
-LOCAL_RESOURCE_DIR := \
-  $(wildcard $(foreach dir, $(PRODUCT_PACKAGE_OVERLAYS), \
-    $(addprefix $(dir)/, $(LOCAL_RESOURCE_DIR)))) \
-  $(wildcard $(foreach dir, $(DEVICE_PACKAGE_OVERLAYS), \
-    $(addprefix $(dir)/, $(LOCAL_RESOURCE_DIR)))) \
-  $(LOCAL_RESOURCE_DIR)
+
+package_resource_overlays := $(strip \
+    $(wildcard $(foreach dir, $(PRODUCT_PACKAGE_OVERLAYS), \
+      $(addprefix $(dir)/, $(LOCAL_RESOURCE_DIR)))) \
+    $(wildcard $(foreach dir, $(DEVICE_PACKAGE_OVERLAYS), \
+      $(addprefix $(dir)/, $(LOCAL_RESOURCE_DIR)))))
+
+LOCAL_RESOURCE_DIR := $(package_resource_overlays) $(LOCAL_RESOURCE_DIR)
 
 all_assets := $(call find-subdir-assets,$(LOCAL_ASSET_DIR))
 all_assets := $(addprefix $(LOCAL_ASSET_DIR)/,$(patsubst assets/%,%,$(all_assets)))
@@ -399,6 +401,9 @@ endif
 # Save information about this package
 PACKAGES.$(LOCAL_PACKAGE_NAME).OVERRIDES := $(strip $(LOCAL_OVERRIDES_PACKAGES))
 PACKAGES.$(LOCAL_PACKAGE_NAME).RESOURCE_FILES := $(all_resources)
+ifdef package_resource_overlays
+PACKAGES.$(LOCAL_PACKAGE_NAME).RESOURCE_OVERLAYS := $(package_resource_overlays)
+endif
 
 PACKAGES := $(PACKAGES) $(LOCAL_PACKAGE_NAME)
 
diff --git a/core/post_clean.mk b/core/post_clean.mk
new file mode 100644
index 000000000..213c43c0e
--- /dev/null
+++ b/core/post_clean.mk
@@ -0,0 +1,53 @@
+# Copyright (C) 2012 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.
+
+# Clean steps that need global knowledge of individual modules.
+# This file must be included after all Android.mks have been loaded.
+
+# Checks the current build configurations against the previous build,
+# clean artifacts in TARGET_COMMON_OUT_ROOT if necessary.
+# If a package's resource overlay has been changed, its R class needs to be
+# regenerated.
+previous_package_overlay_config := $(TARGET_OUT_COMMON_INTERMEDIATES)/APPS/previous_overlays.txt
+current_package_overlay_config := $(TARGET_OUT_COMMON_INTERMEDIATES)/APPS/current_overlays.txt
+current_all_packages_config := $(dir $(current_package_overlay_config))current_packages.txt
+
+$(shell rm -rf $(current_package_overlay_config) \
+    && mkdir -p $(dir $(current_package_overlay_config)) \
+    && touch $(current_package_overlay_config))
+$(shell echo '$(PACKAGES)' > $(current_all_packages_config))
+$(foreach p, $(PACKAGES), $(if $(PACKAGES.$(p).RESOURCE_OVERLAYS), \
+  $(shell echo '$(p)' '$(PACKAGES.$(p).RESOURCE_OVERLAYS)' >> $(current_package_overlay_config))))
+
+ifneq (,$(wildcard $(previous_package_overlay_config)))
+packages_overlay_changed := $(shell build/tools/diff_package_overlays.py \
+    $(current_all_packages_config) $(current_package_overlay_config) \
+    $(previous_package_overlay_config))
+ifneq (,$(packages_overlay_changed))
+overlay_cleanup_cmd := $(strip rm -rf $(foreach p, $(packages_overlay_changed),\
+    $(TARGET_OUT_COMMON_INTERMEDIATES)/APPS/$(p)_intermediates))
+$(info *** Overlay change detected, clean shared intermediate files...)
+$(info *** $(overlay_cleanup_cmd))
+$(shell $(overlay_cleanup_cmd))
+overlay_cleanup_cmd :=
+endif
+packages_overlay_changed :=
+endif
+
+# Now current becomes previous.
+$(shell mv -f $(current_package_overlay_config) $(previous_package_overlay_config))
+
+previous_package_overlay_config :=
+current_package_overlay_config :=
+current_all_packages_config :=
diff --git a/tools/diff_package_overlays.py b/tools/diff_package_overlays.py
new file mode 100755
index 000000000..0e2c773d1
--- /dev/null
+++ b/tools/diff_package_overlays.py
@@ -0,0 +1,91 @@
+#!/usr/bin/env python
+#
+# Copyright (C) 2012 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.
+
+"""
+Prints to stdout the package names that have overlay changes between
+current_overlays.txt and previous_overlays.txt.
+
+Usage: diff_package_overlays.py <current_packages.txt> <current_overlays.txt> <previous_overlays.txt>
+current_packages.txt contains all package names separated by space in the current build.
+This script modfies current_packages.txt if necessary: if there is a package in
+previous_overlays.txt but absent from current_packages.txt, we copy that line
+from previous_overlays.txt over to current_packages.txt. Usually that means we
+just don't care that package in the current build (for example we are switching
+from a full build to a partial build with mm/mmm), and we should carry on the
+previous overlay config so current_overlays.txt always reflects the current
+status of the entire tree.
+
+Format of current_overlays.txt and previous_overlays.txt:
+  <package_name> <resource_overlay> [resource_overlay ...]
+  <package_name> <resource_overlay> [resource_overlay ...]
+  ...
+"""
+
+import sys
+
+def main(argv):
+  if len(argv) != 4:
+    print >> sys.stderr, __doc__
+    sys.exit(1)
+
+  f = open(argv[1])
+  all_packages = set(f.read().split())
+  f.close()
+
+  def load_overlay_config(filename):
+    f = open(filename)
+    result = {}
+    for line in f:
+      line = line.strip()
+      if not line or line.startswith("#"):
+        continue
+      words = line.split()
+      result[words[0]] = " ".join(words[1:])
+    f.close()
+    return result
+
+  current_overlays = load_overlay_config(argv[2])
+  previous_overlays = load_overlay_config(argv[3])
+
+  result = []
+  carryon = []
+  for p in current_overlays:
+    if p not in previous_overlays:
+      result.append(p)
+    elif current_overlays[p] != previous_overlays[p]:
+      result.append(p)
+  for p in previous_overlays:
+    if p not in current_overlays:
+      if p in all_packages:
+        # overlay changed
+        result.append(p)
+      else:
+        # we don't build p in the current build.
+        carryon.append(p)
+
+  # Add carryon to the current overlay config file.
+  if carryon:
+    f = open(argv[2], "a")
+    for p in carryon:
+      f.write(p + " " + previous_overlays[p] + "\n")
+    f.close()
+
+  # Print out the package names that have overlay change.
+  for r in result:
+    print r
+
+if __name__ == "__main__":
+  main(sys.argv)