diff --git a/core/cleanbuild.mk b/core/cleanbuild.mk
new file mode 100644
index 0000000..b2e04a7
--- /dev/null
+++ b/core/cleanbuild.mk
@@ -0,0 +1,86 @@
+# Copyright (C) 2007 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.
+#
+
+INTERNAL_CLEAN_STEPS :=
+
+# Builds up a list of clean steps.  Creates a unique
+# id for each step by taking INTERNAL_CLEAN_BUILD_VERSION
+# and appending an increasing number of '@' characters.
+#
+# $(1): shell command to run
+define _add-clean-step
+  $(if $(strip $(INTERNAL_CLEAN_BUILD_VERSION)),, \
+      $(error INTERNAL_CLEAN_BUILD_VERSION not set))
+  $(eval _acs_id := $(strip $(lastword $(INTERNAL_CLEAN_STEPS))))
+  $(if $(_acs_id),,$(eval _acs_id := $(INTERNAL_CLEAN_BUILD_VERSION)))
+  $(eval _acs_id := $(_acs_id)@)
+  $(eval INTERNAL_CLEAN_STEPS += $(_acs_id))
+  $(eval INTERNAL_CLEAN_STEP.$(_acs_id) := $(1))
+  $(eval _acs_id :=)
+endef
+define add-clean-step
+$(if $(call _add-clean-step,$(1)),)
+endef
+
+# Defines INTERNAL_CLEAN_BUILD_VERSION and the individual clean steps.
+# cleanspec.mk is outside of the core directory so that more people
+# can have permission to touch it.
+include build/cleanspec.mk
+INTERNAL_CLEAN_BUILD_VERSION := $(strip $(INTERNAL_CLEAN_BUILD_VERSION))
+
+# If the clean_steps.mk file is missing (usually after a clean build)
+# then we won't do anything.
+CURRENT_CLEAN_BUILD_VERSION := $(INTERNAL_CLEAN_BUILD_VERSION)
+CURRENT_CLEAN_STEPS := $(INTERNAL_CLEAN_STEPS)
+
+# Read the current state from the file, if present.
+# Will set CURRENT_CLEAN_BUILD_VERSION and CURRENT_CLEAN_STEPS.
+#
+clean_steps_file := $(PRODUCT_OUT)/clean_steps.mk
+-include $(clean_steps_file)
+
+ifneq ($(CURRENT_CLEAN_BUILD_VERSION),$(INTERNAL_CLEAN_BUILD_VERSION))
+  # The major clean version is out-of-date.  Do a full clean, and
+  # don't even bother with the clean steps.
+  $(info *** A clean build is required because of a recent change.)
+  $(shell rm -rf $(OUT_DIR))
+  $(info *** Done with the cleaning, now starting the real build.)
+else
+  # The major clean version is correct.  Find the list of clean steps
+  # that we need to execute to get up-to-date.
+  steps := \
+      $(filter-out $(CURRENT_CLEAN_STEPS),$(INTERNAL_CLEAN_STEPS))
+  $(foreach step,$(steps), \
+    $(info Clean step: $(INTERNAL_CLEAN_STEP.$(step))) \
+    $(shell $(INTERNAL_CLEAN_STEP.$(step))) \
+   )
+  steps :=
+endif
+CURRENT_CLEAN_BUILD_VERSION :=
+CURRENT_CLEAN_STEPS :=
+
+# Write the new state to the file.
+#
+$(shell \
+  mkdir -p $(dir $(clean_steps_file)) && \
+  echo "CURRENT_CLEAN_BUILD_VERSION := $(INTERNAL_CLEAN_BUILD_VERSION)" > \
+      $(clean_steps_file) ;\
+  echo "CURRENT_CLEAN_STEPS := $(INTERNAL_CLEAN_STEPS)" >> \
+      $(clean_steps_file) \
+ )
+
+clean_steps_file :=
+INTERNAL_CLEAN_STEPS :=
+INTERNAL_CLEAN_BUILD_VERSION :=