diff --git a/core/version_defaults.mk b/core/version_defaults.mk
index 8eac1ac..1366a85 100644
--- a/core/version_defaults.mk
+++ b/core/version_defaults.mk
@@ -40,51 +40,10 @@
 endif
 
 DEFAULT_PLATFORM_VERSION := TP1A
+.KATI_READONLY := DEFAULT_PLATFORM_VERSION
 MIN_PLATFORM_VERSION := TP1A
 MAX_PLATFORM_VERSION := TP1A
 
-ALLOWED_VERSIONS := $(call allowed-platform-versions,\
-  $(MIN_PLATFORM_VERSION),\
-  $(MAX_PLATFORM_VERSION),\
-  $(DEFAULT_PLATFORM_VERSION))
-
-ifndef TARGET_PLATFORM_VERSION
-  TARGET_PLATFORM_VERSION := $(DEFAULT_PLATFORM_VERSION)
-endif
-
-ifeq (,$(filter $(ALLOWED_VERSIONS), $(TARGET_PLATFORM_VERSION)))
-  $(warning Invalid TARGET_PLATFORM_VERSION '$(TARGET_PLATFORM_VERSION)', must be one of)
-  $(error $(ALLOWED_VERSIONS))
-endif
-ALLOWED_VERSIONS :=
-MIN_PLATFORM_VERSION :=
-MAX_PLATFORM_VERSION :=
-
-.KATI_READONLY := \
-  DEFAULT_PLATFORM_VERSION \
-  TARGET_PLATFORM_VERSION
-
-# Default versions for each TARGET_PLATFORM_VERSION
-# TODO: PLATFORM_VERSION, PLATFORM_SDK_VERSION, etc. should be conditional
-# on this
-
-# This is the canonical definition of the platform version,
-# which is the version that we reveal to the end user.
-# Update this value when the platform version changes (rather
-# than overriding it somewhere else).  Can be an arbitrary string.
-
-# When you change PLATFORM_VERSION for a given PLATFORM_SDK_VERSION
-# please add that PLATFORM_VERSION as well as clean up obsolete PLATFORM_VERSION's
-# in the following text file:
-# cts/tests/tests/os/assets/platform_versions.txt
-
-# Note that there should be one PLATFORM_VERSION and PLATFORM_VERSION_CODENAME
-# entry for each unreleased API level, regardless of
-# MIN_PLATFORM_VERSION/MAX_PLATFORM_VERSION. PLATFORM_VERSION is used to
-# generate the range of allowed SDK versions, so it must have an entry for every
-# unreleased API level targetable by this branch, not just those that are valid
-# lunch targets for this branch.
-
 # The last stable version name of the platform that was released.  During
 # development, this stays at that previous version, while the codename indicates
 # further work based on the previous version.
@@ -95,49 +54,6 @@
 # release build.  If this is a final release build, it is simply "REL".
 PLATFORM_VERSION_CODENAME.TP1A := Tiramisu
 
-ifndef PLATFORM_VERSION_CODENAME
-  PLATFORM_VERSION_CODENAME := $(PLATFORM_VERSION_CODENAME.$(TARGET_PLATFORM_VERSION))
-  ifndef PLATFORM_VERSION_CODENAME
-    # PLATFORM_VERSION_CODENAME falls back to TARGET_PLATFORM_VERSION
-    PLATFORM_VERSION_CODENAME := $(TARGET_PLATFORM_VERSION)
-  endif
-
-  # This is all of the *active* development codenames.
-  # This confusing name is needed because
-  # all_codenames has been baked into build.prop for ages.
-  #
-  # Should be either the same as PLATFORM_VERSION_CODENAME or a comma-separated
-  # list of additional codenames after PLATFORM_VERSION_CODENAME.
-  PLATFORM_VERSION_ALL_CODENAMES :=
-
-  # Build a list of all active code names. Avoid duplicates, and stop when we
-  # reach a codename that matches PLATFORM_VERSION_CODENAME (anything beyond
-  # that is not included in our build).
-  _versions_in_target := \
-    $(call find_and_earlier,$(ALL_VERSIONS),$(TARGET_PLATFORM_VERSION))
-  $(foreach version,$(_versions_in_target),\
-    $(eval _codename := $(PLATFORM_VERSION_CODENAME.$(version)))\
-    $(if $(filter $(_codename),$(PLATFORM_VERSION_ALL_CODENAMES)),,\
-      $(eval PLATFORM_VERSION_ALL_CODENAMES += $(_codename))))
-
-  # And convert from space separated to comma separated.
-  PLATFORM_VERSION_ALL_CODENAMES := \
-    $(subst $(space),$(comma),$(strip $(PLATFORM_VERSION_ALL_CODENAMES)))
-
-endif
-.KATI_READONLY := \
-  PLATFORM_VERSION_CODENAME \
-  PLATFORM_VERSION_ALL_CODENAMES
-
-ifndef PLATFORM_VERSION
-  ifeq (REL,$(PLATFORM_VERSION_CODENAME))
-      PLATFORM_VERSION := $(PLATFORM_VERSION_LAST_STABLE)
-  else
-      PLATFORM_VERSION := $(PLATFORM_VERSION_CODENAME)
-  endif
-endif
-.KATI_READONLY := PLATFORM_VERSION
-
 ifndef PLATFORM_SDK_VERSION
   # This is the canonical definition of the SDK version, which defines
   # the set of APIs and functionality available in the platform.  It
@@ -156,89 +72,12 @@
 .KATI_READONLY := PLATFORM_SDK_VERSION
 
 # This is the sdk extension version of this tree.
-PLATFORM_SDK_EXTENSION_VERSION :=$= 1
+PLATFORM_SDK_EXTENSION_VERSION := 1
+.KATI_READONLY := PLATFORM_SDK_EXTENSION_VERSION
 
 # This is the sdk extension version that PLATFORM_SDK_VERSION ships with.
-PLATFORM_BASE_SDK_EXTENSION_VERSION :=$= 0
-
-ifeq (REL,$(PLATFORM_VERSION_CODENAME))
-  PLATFORM_PREVIEW_SDK_VERSION := 0
-else
-  ifndef PLATFORM_PREVIEW_SDK_VERSION
-    # This is the definition of a preview SDK version over and above the current
-    # platform SDK version. Unlike the platform SDK version, a higher value
-    # for preview SDK version does NOT mean that all prior preview APIs are
-    # included. Packages reading this value to determine compatibility with
-    # known APIs should check that this value is precisely equal to the preview
-    # SDK version the package was built for, otherwise it should fall back to
-    # assuming the device can only support APIs as of the previous official
-    # public release.
-    # This value will always be forced to 0 for release builds by the logic
-    # in the "ifeq" block above, so the value below will be used on any
-    # non-release builds, and it should always be at least 1, to indicate that
-    # APIs may have changed since the claimed PLATFORM_SDK_VERSION.
-    PLATFORM_PREVIEW_SDK_VERSION := 1
-  endif
-endif
-.KATI_READONLY := PLATFORM_PREVIEW_SDK_VERSION
-
-ifndef DEFAULT_APP_TARGET_SDK
-  # This is the default minSdkVersion and targetSdkVersion to use for
-  # all .apks created by the build system.  It can be overridden by explicitly
-  # setting these in the .apk's AndroidManifest.xml.  It is either the code
-  # name of the development build or, if this is a release build, the official
-  # SDK version of this release.
-  ifeq (REL,$(PLATFORM_VERSION_CODENAME))
-    DEFAULT_APP_TARGET_SDK := $(PLATFORM_SDK_VERSION)
-  else
-    DEFAULT_APP_TARGET_SDK := $(PLATFORM_VERSION_CODENAME)
-  endif
-endif
-.KATI_READONLY := DEFAULT_APP_TARGET_SDK
-
-ifndef PLATFORM_VNDK_VERSION
-  # This is the definition of the VNDK version for the current VNDK libraries.
-  # The version is only available when PLATFORM_VERSION_CODENAME == REL.
-  # Otherwise, it will be set to a CODENAME version. The ABI is allowed to be
-  # changed only before the Android version is released. Once
-  # PLATFORM_VNDK_VERSION is set to actual version, the ABI for this version
-  # will be frozon and emit build errors if any ABI for the VNDK libs are
-  # changed.
-  # After that the snapshot of the VNDK with this version will be generated.
-  #
-  # The VNDK version follows PLATFORM_SDK_VERSION.
-  ifeq (REL,$(PLATFORM_VERSION_CODENAME))
-    PLATFORM_VNDK_VERSION := $(PLATFORM_SDK_VERSION)
-  else
-    PLATFORM_VNDK_VERSION := $(PLATFORM_VERSION_CODENAME)
-  endif
-endif
-.KATI_READONLY := PLATFORM_VNDK_VERSION
-
-ifndef PLATFORM_SYSTEMSDK_MIN_VERSION
-  # This is the oldest version of system SDK that the platform supports. Contrary
-  # to the public SDK where platform essentially supports all previous SDK versions,
-  # platform supports only a few number of recent system SDK versions as some of
-  # old system APIs are gradually deprecated, removed and then deleted.
-  PLATFORM_SYSTEMSDK_MIN_VERSION := 28
-endif
-.KATI_READONLY := PLATFORM_SYSTEMSDK_MIN_VERSION
-
-# This is the list of system SDK versions that the current platform supports.
-PLATFORM_SYSTEMSDK_VERSIONS :=
-ifneq (,$(PLATFORM_SYSTEMSDK_MIN_VERSION))
-  $(if $(call math_is_number,$(PLATFORM_SYSTEMSDK_MIN_VERSION)),,\
-    $(error PLATFORM_SYSTEMSDK_MIN_VERSION must be a number, but was $(PLATFORM_SYSTEMSDK_MIN_VERSION)))
-  PLATFORM_SYSTEMSDK_VERSIONS := $(call int_range_list,$(PLATFORM_SYSTEMSDK_MIN_VERSION),$(PLATFORM_SDK_VERSION))
-endif
-# Platform always supports the current version
-ifeq (REL,$(PLATFORM_VERSION_CODENAME))
-  PLATFORM_SYSTEMSDK_VERSIONS += $(PLATFORM_SDK_VERSION)
-else
-  PLATFORM_SYSTEMSDK_VERSIONS += $(subst $(comma),$(space),$(PLATFORM_VERSION_ALL_CODENAMES))
-endif
-PLATFORM_SYSTEMSDK_VERSIONS := $(strip $(sort $(PLATFORM_SYSTEMSDK_VERSIONS)))
-.KATI_READONLY := PLATFORM_SYSTEMSDK_VERSIONS
+PLATFORM_BASE_SDK_EXTENSION_VERSION := 0
+.KATI_READONLY := PLATFORM_BASE_SDK_EXTENSION_VERSION
 
 ifndef PLATFORM_SECURITY_PATCH
     #  Used to indicate the security patch that has been applied to the device.
@@ -246,69 +85,9 @@
     #  It must be of the form "YYYY-MM-DD" on production devices.
     #  It must match one of the Android Security Patch Level strings of the Public Security Bulletins.
     #  If there is no $PLATFORM_SECURITY_PATCH set, keep it empty.
-      PLATFORM_SECURITY_PATCH := 2021-10-05
+    PLATFORM_SECURITY_PATCH := 2021-10-05
 endif
 .KATI_READONLY := PLATFORM_SECURITY_PATCH
 
-ifndef PLATFORM_SECURITY_PATCH_TIMESTAMP
-  # Used to indicate the matching timestamp for the security patch string in PLATFORM_SECURITY_PATCH.
-  PLATFORM_SECURITY_PATCH_TIMESTAMP := $(shell date -d 'TZ="GMT" $(PLATFORM_SECURITY_PATCH)' +%s)
-endif
-.KATI_READONLY := PLATFORM_SECURITY_PATCH_TIMESTAMP
+include $(BUILD_SYSTEM)/version_util.mk
 
-ifndef PLATFORM_BASE_OS
-  # Used to indicate the base os applied to the device.
-  # Can be an arbitrary string, but must be a single word.
-  #
-  # If there is no $PLATFORM_BASE_OS set, keep it empty.
-  PLATFORM_BASE_OS :=
-endif
-.KATI_READONLY := PLATFORM_BASE_OS
-
-ifndef BUILD_ID
-  # Used to signify special builds.  E.g., branches and/or releases,
-  # like "M5-RC7".  Can be an arbitrary string, but must be a single
-  # word and a valid file name.
-  #
-  # If there is no BUILD_ID set, make it obvious.
-  BUILD_ID := UNKNOWN
-endif
-.KATI_READONLY := BUILD_ID
-
-ifndef BUILD_DATETIME
-  # Used to reproduce builds by setting the same time. Must be the number
-  # of seconds since the Epoch.
-  BUILD_DATETIME := $(shell date +%s)
-endif
-
-DATE := date -d @$(BUILD_DATETIME)
-.KATI_READONLY := DATE
-
-# Everything should be using BUILD_DATETIME_FROM_FILE instead.
-# BUILD_DATETIME and DATE can be removed once BUILD_NUMBER moves
-# to soong_ui.
-$(KATI_obsolete_var BUILD_DATETIME,Use BUILD_DATETIME_FROM_FILE)
-
-HAS_BUILD_NUMBER := true
-ifndef BUILD_NUMBER
-  # BUILD_NUMBER should be set to the source control value that
-  # represents the current state of the source code.  E.g., a
-  # perforce changelist number or a git hash.  Can be an arbitrary string
-  # (to allow for source control that uses something other than numbers),
-  # but must be a single word and a valid file name.
-  #
-  # If no BUILD_NUMBER is set, create a useful "I am an engineering build
-  # from this date/time" value.  Make it start with a non-digit so that
-  # anyone trying to parse it as an integer will probably get "0".
-  BUILD_NUMBER := eng.$(shell echo $${BUILD_USERNAME:0:6}).$(shell $(DATE) +%Y%m%d.%H%M%S)
-  HAS_BUILD_NUMBER := false
-endif
-.KATI_READONLY := BUILD_NUMBER HAS_BUILD_NUMBER
-
-ifndef PLATFORM_MIN_SUPPORTED_TARGET_SDK_VERSION
-  # Used to set minimum supported target sdk version. Apps targeting sdk
-  # version lower than the set value will result in a warning being shown
-  # when any activity from the app is started.
-  PLATFORM_MIN_SUPPORTED_TARGET_SDK_VERSION := 23
-endif
-.KATI_READONLY := PLATFORM_MIN_SUPPORTED_TARGET_SDK_VERSION
diff --git a/core/version_util.mk b/core/version_util.mk
new file mode 100644
index 0000000..b7c4e48
--- /dev/null
+++ b/core/version_util.mk
@@ -0,0 +1,245 @@
+#
+# Copyright (C) 2008 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.
+#
+
+#
+
+ALLOWED_VERSIONS := $(call allowed-platform-versions,\
+  $(MIN_PLATFORM_VERSION),\
+  $(MAX_PLATFORM_VERSION),\
+  $(DEFAULT_PLATFORM_VERSION))
+
+ifndef TARGET_PLATFORM_VERSION
+  TARGET_PLATFORM_VERSION := $(DEFAULT_PLATFORM_VERSION)
+endif
+
+ifeq (,$(filter $(ALLOWED_VERSIONS), $(TARGET_PLATFORM_VERSION)))
+  $(warning Invalid TARGET_PLATFORM_VERSION '$(TARGET_PLATFORM_VERSION)', must be one of)
+  $(error $(ALLOWED_VERSIONS))
+endif
+ALLOWED_VERSIONS :=
+MIN_PLATFORM_VERSION :=
+MAX_PLATFORM_VERSION :=
+
+.KATI_READONLY := TARGET_PLATFORM_VERSION
+
+# Default versions for each TARGET_PLATFORM_VERSION
+# TODO: PLATFORM_VERSION, PLATFORM_SDK_VERSION, etc. should be conditional
+# on this
+
+# This is the canonical definition of the platform version,
+# which is the version that we reveal to the end user.
+# Update this value when the platform version changes (rather
+# than overriding it somewhere else).  Can be an arbitrary string.
+
+# When you change PLATFORM_VERSION for a given PLATFORM_SDK_VERSION
+# please add that PLATFORM_VERSION as well as clean up obsolete PLATFORM_VERSION's
+# in the following text file:
+# cts/tests/tests/os/assets/platform_versions.txt
+
+# Note that there should be one PLATFORM_VERSION and PLATFORM_VERSION_CODENAME
+# entry for each unreleased API level, regardless of
+# MIN_PLATFORM_VERSION/MAX_PLATFORM_VERSION. PLATFORM_VERSION is used to
+# generate the range of allowed SDK versions, so it must have an entry for every
+# unreleased API level targetable by this branch, not just those that are valid
+# lunch targets for this branch.
+
+ifndef PLATFORM_VERSION_CODENAME
+  PLATFORM_VERSION_CODENAME := $(PLATFORM_VERSION_CODENAME.$(TARGET_PLATFORM_VERSION))
+  ifndef PLATFORM_VERSION_CODENAME
+    # PLATFORM_VERSION_CODENAME falls back to TARGET_PLATFORM_VERSION
+    PLATFORM_VERSION_CODENAME := $(TARGET_PLATFORM_VERSION)
+  endif
+
+  # This is all of the *active* development codenames.
+  # This confusing name is needed because
+  # all_codenames has been baked into build.prop for ages.
+  #
+  # Should be either the same as PLATFORM_VERSION_CODENAME or a comma-separated
+  # list of additional codenames after PLATFORM_VERSION_CODENAME.
+  PLATFORM_VERSION_ALL_CODENAMES :=
+
+  # Build a list of all active code names. Avoid duplicates, and stop when we
+  # reach a codename that matches PLATFORM_VERSION_CODENAME (anything beyond
+  # that is not included in our build).
+  _versions_in_target := \
+    $(call find_and_earlier,$(ALL_VERSIONS),$(TARGET_PLATFORM_VERSION))
+  $(foreach version,$(_versions_in_target),\
+    $(eval _codename := $(PLATFORM_VERSION_CODENAME.$(version)))\
+    $(if $(filter $(_codename),$(PLATFORM_VERSION_ALL_CODENAMES)),,\
+      $(eval PLATFORM_VERSION_ALL_CODENAMES += $(_codename))))
+
+  # And convert from space separated to comma separated.
+  PLATFORM_VERSION_ALL_CODENAMES := \
+    $(subst $(space),$(comma),$(strip $(PLATFORM_VERSION_ALL_CODENAMES)))
+
+endif
+.KATI_READONLY := \
+  PLATFORM_VERSION_CODENAME \
+  PLATFORM_VERSION_ALL_CODENAMES
+
+ifndef PLATFORM_VERSION
+  ifeq (REL,$(PLATFORM_VERSION_CODENAME))
+      PLATFORM_VERSION := $(PLATFORM_VERSION_LAST_STABLE)
+  else
+      PLATFORM_VERSION := $(PLATFORM_VERSION_CODENAME)
+  endif
+endif
+.KATI_READONLY := PLATFORM_VERSION
+
+
+ifeq (REL,$(PLATFORM_VERSION_CODENAME))
+  PLATFORM_PREVIEW_SDK_VERSION := 0
+else
+  ifndef PLATFORM_PREVIEW_SDK_VERSION
+    # This is the definition of a preview SDK version over and above the current
+    # platform SDK version. Unlike the platform SDK version, a higher value
+    # for preview SDK version does NOT mean that all prior preview APIs are
+    # included. Packages reading this value to determine compatibility with
+    # known APIs should check that this value is precisely equal to the preview
+    # SDK version the package was built for, otherwise it should fall back to
+    # assuming the device can only support APIs as of the previous official
+    # public release.
+    # This value will always be forced to 0 for release builds by the logic
+    # in the "ifeq" block above, so the value below will be used on any
+    # non-release builds, and it should always be at least 1, to indicate that
+    # APIs may have changed since the claimed PLATFORM_SDK_VERSION.
+    PLATFORM_PREVIEW_SDK_VERSION := 1
+  endif
+endif
+.KATI_READONLY := PLATFORM_PREVIEW_SDK_VERSION
+
+ifndef DEFAULT_APP_TARGET_SDK
+  # This is the default minSdkVersion and targetSdkVersion to use for
+  # all .apks created by the build system.  It can be overridden by explicitly
+  # setting these in the .apk's AndroidManifest.xml.  It is either the code
+  # name of the development build or, if this is a release build, the official
+  # SDK version of this release.
+  ifeq (REL,$(PLATFORM_VERSION_CODENAME))
+    DEFAULT_APP_TARGET_SDK := $(PLATFORM_SDK_VERSION)
+  else
+    DEFAULT_APP_TARGET_SDK := $(PLATFORM_VERSION_CODENAME)
+  endif
+endif
+.KATI_READONLY := DEFAULT_APP_TARGET_SDK
+
+ifndef PLATFORM_VNDK_VERSION
+  # This is the definition of the VNDK version for the current VNDK libraries.
+  # The version is only available when PLATFORM_VERSION_CODENAME == REL.
+  # Otherwise, it will be set to a CODENAME version. The ABI is allowed to be
+  # changed only before the Android version is released. Once
+  # PLATFORM_VNDK_VERSION is set to actual version, the ABI for this version
+  # will be frozon and emit build errors if any ABI for the VNDK libs are
+  # changed.
+  # After that the snapshot of the VNDK with this version will be generated.
+  #
+  # The VNDK version follows PLATFORM_SDK_VERSION.
+  ifeq (REL,$(PLATFORM_VERSION_CODENAME))
+    PLATFORM_VNDK_VERSION := $(PLATFORM_SDK_VERSION)
+  else
+    PLATFORM_VNDK_VERSION := $(PLATFORM_VERSION_CODENAME)
+  endif
+endif
+.KATI_READONLY := PLATFORM_VNDK_VERSION
+
+ifndef PLATFORM_SYSTEMSDK_MIN_VERSION
+  # This is the oldest version of system SDK that the platform supports. Contrary
+  # to the public SDK where platform essentially supports all previous SDK versions,
+  # platform supports only a few number of recent system SDK versions as some of
+  # old system APIs are gradually deprecated, removed and then deleted.
+  PLATFORM_SYSTEMSDK_MIN_VERSION := 28
+endif
+.KATI_READONLY := PLATFORM_SYSTEMSDK_MIN_VERSION
+
+# This is the list of system SDK versions that the current platform supports.
+PLATFORM_SYSTEMSDK_VERSIONS :=
+ifneq (,$(PLATFORM_SYSTEMSDK_MIN_VERSION))
+  $(if $(call math_is_number,$(PLATFORM_SYSTEMSDK_MIN_VERSION)),,\
+    $(error PLATFORM_SYSTEMSDK_MIN_VERSION must be a number, but was $(PLATFORM_SYSTEMSDK_MIN_VERSION)))
+  PLATFORM_SYSTEMSDK_VERSIONS := $(call int_range_list,$(PLATFORM_SYSTEMSDK_MIN_VERSION),$(PLATFORM_SDK_VERSION))
+endif
+# Platform always supports the current version
+ifeq (REL,$(PLATFORM_VERSION_CODENAME))
+  PLATFORM_SYSTEMSDK_VERSIONS += $(PLATFORM_SDK_VERSION)
+else
+  PLATFORM_SYSTEMSDK_VERSIONS += $(subst $(comma),$(space),$(PLATFORM_VERSION_ALL_CODENAMES))
+endif
+PLATFORM_SYSTEMSDK_VERSIONS := $(strip $(sort $(PLATFORM_SYSTEMSDK_VERSIONS)))
+.KATI_READONLY := PLATFORM_SYSTEMSDK_VERSIONS
+
+.KATI_READONLY := PLATFORM_SECURITY_PATCH
+
+ifndef PLATFORM_SECURITY_PATCH_TIMESTAMP
+  # Used to indicate the matching timestamp for the security patch string in PLATFORM_SECURITY_PATCH.
+  PLATFORM_SECURITY_PATCH_TIMESTAMP := $(shell date -d 'TZ="GMT" $(PLATFORM_SECURITY_PATCH)' +%s)
+endif
+.KATI_READONLY := PLATFORM_SECURITY_PATCH_TIMESTAMP
+
+ifndef PLATFORM_BASE_OS
+  # Used to indicate the base os applied to the device.
+  # Can be an arbitrary string, but must be a single word.
+  #
+  # If there is no $PLATFORM_BASE_OS set, keep it empty.
+  PLATFORM_BASE_OS :=
+endif
+.KATI_READONLY := PLATFORM_BASE_OS
+
+ifndef BUILD_ID
+  # Used to signify special builds.  E.g., branches and/or releases,
+  # like "M5-RC7".  Can be an arbitrary string, but must be a single
+  # word and a valid file name.
+  #
+  # If there is no BUILD_ID set, make it obvious.
+  BUILD_ID := UNKNOWN
+endif
+.KATI_READONLY := BUILD_ID
+
+ifndef BUILD_DATETIME
+  # Used to reproduce builds by setting the same time. Must be the number
+  # of seconds since the Epoch.
+  BUILD_DATETIME := $(shell date +%s)
+endif
+
+DATE := date -d @$(BUILD_DATETIME)
+.KATI_READONLY := DATE
+
+# Everything should be using BUILD_DATETIME_FROM_FILE instead.
+# BUILD_DATETIME and DATE can be removed once BUILD_NUMBER moves
+# to soong_ui.
+$(KATI_obsolete_var BUILD_DATETIME,Use BUILD_DATETIME_FROM_FILE)
+
+HAS_BUILD_NUMBER := true
+ifndef BUILD_NUMBER
+  # BUILD_NUMBER should be set to the source control value that
+  # represents the current state of the source code.  E.g., a
+  # perforce changelist number or a git hash.  Can be an arbitrary string
+  # (to allow for source control that uses something other than numbers),
+  # but must be a single word and a valid file name.
+  #
+  # If no BUILD_NUMBER is set, create a useful "I am an engineering build
+  # from this date/time" value.  Make it start with a non-digit so that
+  # anyone trying to parse it as an integer will probably get "0".
+  BUILD_NUMBER := eng.$(shell echo $${BUILD_USERNAME:0:6}).$(shell $(DATE) +%Y%m%d.%H%M%S)
+  HAS_BUILD_NUMBER := false
+endif
+.KATI_READONLY := BUILD_NUMBER HAS_BUILD_NUMBER
+
+ifndef PLATFORM_MIN_SUPPORTED_TARGET_SDK_VERSION
+  # Used to set minimum supported target sdk version. Apps targeting sdk
+  # version lower than the set value will result in a warning being shown
+  # when any activity from the app is started.
+  PLATFORM_MIN_SUPPORTED_TARGET_SDK_VERSION := 23
+endif
+.KATI_READONLY := PLATFORM_MIN_SUPPORTED_TARGET_SDK_VERSION