diff --git a/common/core.mk b/common/core.mk
index e5264b0..7d505c0 100644
--- a/common/core.mk
+++ b/common/core.mk
@@ -42,6 +42,9 @@
 backslash := \a
 backslash := $(patsubst %a,%,$(backslash))
 
+TOP :=$= .
+TOPDIR :=$=
+
 # Prevent accidentally changing these variables
 .KATI_READONLY := SHELL empty space comma newline pound backslash
 
diff --git a/core/binary.mk b/core/binary.mk
index 4709e8e..e916164 100644
--- a/core/binary.mk
+++ b/core/binary.mk
@@ -119,6 +119,8 @@
     $(error $(LOCAL_PATH): LOCAL_SDK_VERSION cannot be used in host module)
   endif
 
+  my_cflags += -D__ANDROID_NDK__
+
   # Make sure we've built the NDK.
   my_additional_dependencies += $(SOONG_OUT_DIR)/ndk_base.timestamp
 
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index 3cc8594..2e24eb9 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -221,6 +221,7 @@
 LOCAL_PROGUARD_ENABLED:=
 LOCAL_PROGUARD_FLAG_FILES:=
 LOCAL_PROGUARD_FLAGS:=
+LOCAL_PROGUARD_FLAGS_DEPS:=
 LOCAL_PROPRIETARY_MODULE:=
 LOCAL_PROTOC_FLAGS:=
 # lite(default),micro,nano,stream,full,nanopb-c,nanopb-c-enable_malloc,nanopb-c-16bit,nanopb-c-enable_malloc-16bit,nanopb-c-32bit,nanopb-c-enable_malloc-32bit
diff --git a/core/java.mk b/core/java.mk
index b463037..d080450 100644
--- a/core/java.mk
+++ b/core/java.mk
@@ -470,6 +470,8 @@
 proguard_flag_files := $(addprefix $(LOCAL_PATH)/, $(LOCAL_PROGUARD_FLAG_FILES))
 proguard_flag_files += $(addprefix $(LOCAL_PATH)/, $(LOCAL_R8_FLAG_FILES))
 LOCAL_PROGUARD_FLAGS += $(addprefix -include , $(proguard_flag_files))
+LOCAL_PROGUARD_FLAGS_DEPS += $(proguard_flag_files)
+proguard_flag_files :=
 
 ifdef LOCAL_TEST_MODULE_TO_PROGUARD_WITH
 extra_input_jar := $(call intermediates-dir-for,APPS,$(LOCAL_TEST_MODULE_TO_PROGUARD_WITH),,COMMON)/classes.jar
@@ -481,8 +483,6 @@
   $(built_dex_intermediate): .KATI_IMPLICIT_OUTPUTS := $(proguard_dictionary) $(proguard_configuration)
 endif
 
-else  # LOCAL_PROGUARD_ENABLED not defined
-proguard_flag_files :=
 endif # LOCAL_PROGUARD_ENABLED defined
 
 ifneq ($(LOCAL_IS_STATIC_JAVA_LIBRARY),true)
@@ -492,7 +492,7 @@
   $(built_dex_intermediate): PRIVATE_EXTRA_INPUT_JAR := $(extra_input_jar)
   $(built_dex_intermediate): PRIVATE_PROGUARD_FLAGS := $(legacy_proguard_flags) $(common_proguard_flags) $(LOCAL_PROGUARD_FLAGS)
   $(built_dex_intermediate): PRIVATE_PROGUARD_DICTIONARY := $(proguard_dictionary)
-  $(built_dex_intermediate) : $(full_classes_pre_proguard_jar) $(extra_input_jar) $(my_proguard_sdk_raise) $(common_proguard_flag_files) $(proguard_flag_files) $(legacy_proguard_lib_deps) $(R8_COMPAT_PROGUARD)
+  $(built_dex_intermediate) : $(full_classes_pre_proguard_jar) $(extra_input_jar) $(my_proguard_sdk_raise) $(common_proguard_flag_files) $(legacy_proguard_lib_deps) $(R8_COMPAT_PROGUARD) $(LOCAL_PROGUARD_FLAGS_DEPS)
 	$(transform-jar-to-dex-r8)
 else # !LOCAL_PROGUARD_ENABLED
   $(built_dex_intermediate): PRIVATE_D8_LIBS := $(full_java_bootclasspath_libs) $(full_shared_java_header_libs)
diff --git a/core/java_library.mk b/core/java_library.mk
index 34e4874..4734eaf 100644
--- a/core/java_library.mk
+++ b/core/java_library.mk
@@ -44,6 +44,7 @@
 LOCAL_STATIC_JAVA_LIBRARIES += jacocoagent
 # Exclude jacoco classes from proguard
 LOCAL_PROGUARD_FLAGS += -include $(BUILD_SYSTEM)/proguard.jacoco.flags
+LOCAL_PROGUARD_FLAGS_DEPS += $(BUILD_SYSTEM)/proguard.jacoco.flags
 endif # LOCAL_EMMA_INSTRUMENT
 endif # EMMA_INSTRUMENT_STATIC
 else
diff --git a/core/main.mk b/core/main.mk
index a240b35..5e25af4 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -1,14 +1,3 @@
-# Only use ANDROID_BUILD_SHELL to wrap around bash.
-# DO NOT use other shells such as zsh.
-ifdef ANDROID_BUILD_SHELL
-SHELL := $(ANDROID_BUILD_SHELL)
-else
-# Use bash, not whatever shell somebody has installed as /bin/sh
-# This is repeated in config.mk, since envsetup.sh runs that file
-# directly.
-SHELL := /bin/bash
-endif
-
 ifndef KATI
 $(warning Calling make directly is no longer supported.)
 $(warning Either use 'envsetup.sh; m' or 'build/soong/soong_ui.bash --make-mode')
@@ -22,9 +11,6 @@
 # the top of the source tree, for example when "make -C" is used in m/mm/mmm.
 PWD := $(shell pwd)
 
-TOP := .
-TOPDIR :=
-
 # This is the default target.  It must be the first declared target.
 .PHONY: droid
 DEFAULT_GOAL := droid
diff --git a/core/package_internal.mk b/core/package_internal.mk
index 2130058..b80ccb3 100644
--- a/core/package_internal.mk
+++ b/core/package_internal.mk
@@ -253,6 +253,7 @@
 endif # need_compile_res
 endif # !custom
 LOCAL_PROGUARD_FLAGS := $(addprefix -include ,$(proguard_options_file)) $(LOCAL_PROGUARD_FLAGS)
+LOCAL_PROGUARD_FLAGS_DEPS += $(proguard_options_file)
 
 ifeq (true,$(EMMA_INSTRUMENT))
 ifndef LOCAL_EMMA_INSTRUMENT
@@ -272,6 +273,7 @@
 LOCAL_STATIC_JAVA_LIBRARIES += jacocoagent
 # Exclude jacoco classes from proguard
 LOCAL_PROGUARD_FLAGS += -include $(BUILD_SYSTEM)/proguard.jacoco.flags
+LOCAL_PROGUARD_FLAGS_DEPS += $(BUILD_SYSTEM)/proguard.jacoco.flags
 endif # Contains java code
 else
 ifdef LOCAL_SDK_VERSION
@@ -282,6 +284,7 @@
 LOCAL_STATIC_JAVA_LIBRARIES += jacocoagent
 # Exclude jacoco classes from proguard
 LOCAL_PROGUARD_FLAGS += -include $(BUILD_SYSTEM)/proguard.jacoco.flags
+LOCAL_PROGUARD_FLAGS_DEPS += $(BUILD_SYSTEM)/proguard.jacoco.flags
 endif # Contains java code
 endif # TARGET_BUILD_APPS
 endif # LOCAL_SDK_VERSION
diff --git a/core/product.mk b/core/product.mk
index c54583d..3d54719 100644
--- a/core/product.mk
+++ b/core/product.mk
@@ -368,6 +368,12 @@
 # Whether the product would like to check prebuilt ELF files.
 _product_single_value_vars += PRODUCT_CHECK_ELF_FILES
 
+# If set, device uses virtual A/B.
+_product_single_value_vars += PRODUCT_VIRTUAL_AB_OTA
+
+# If set, device retrofits virtual A/B.
+_product_single_value_vars += PRODUCT_VIRTUAL_AB_OTA_RETROFIT
+
 .KATI_READONLY := _product_single_value_vars _product_list_vars
 _product_var_list :=$= $(_product_single_value_vars) $(_product_list_vars)
 
diff --git a/core/static_java_library.mk b/core/static_java_library.mk
index cb3281a..7eef167 100644
--- a/core/static_java_library.mk
+++ b/core/static_java_library.mk
@@ -74,6 +74,7 @@
 endif
 
 LOCAL_PROGUARD_FLAGS := $(addprefix -include ,$(proguard_options_file)) $(LOCAL_PROGUARD_FLAGS)
+LOCAL_PROGUARD_FLAGS_DEPS += $(proguard_options_file)
 
 R_file_stamp := $(intermediates.COMMON)/src/R.stamp
 LOCAL_INTERMEDIATE_TARGETS += $(R_file_stamp)
diff --git a/target/product/base_system.mk b/target/product/base_system.mk
index c256641..60646c3 100644
--- a/target/product/base_system.mk
+++ b/target/product/base_system.mk
@@ -54,6 +54,7 @@
     charger \
     cmd \
     com.android.conscrypt \
+    com.android.i18n \
     com.android.location.provider \
     com.android.resolv \
     com.android.neuralnetworks \
@@ -289,7 +290,7 @@
     e2fsck \
     fastboot \
     flags_health_check \
-    icu-data_host_runtime_apex \
+    icu-data_host_i18n_apex \
     icu_tzdata.dat_host_tzdata_apex \
     incident_report \
     ld.mc \
diff --git a/target/product/base_vendor.mk b/target/product/base_vendor.mk
index 4233c1c..c57cc3f 100644
--- a/target/product/base_vendor.mk
+++ b/target/product/base_vendor.mk
@@ -36,7 +36,7 @@
     make_f2fs \
 
 PRODUCT_HOST_PACKAGES += \
-    icu-data_host_runtime_apex
+    icu-data_host_i18n_apex
 
 # Base modules and settings for the vendor partition.
 PRODUCT_PACKAGES += \
diff --git a/target/product/virtual_ab_ota.mk b/target/product/virtual_ab_ota.mk
new file mode 100644
index 0000000..c00b0ed
--- /dev/null
+++ b/target/product/virtual_ab_ota.mk
@@ -0,0 +1,19 @@
+#
+# Copyright (C) 2019 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.
+#
+
+PRODUCT_VIRTUAL_AB_OTA := true
+
+PRODUCT_PRODUCT_PROPERTIES += ro.virtual_ab.enabled=true
diff --git a/target/product/virtual_ab_ota_retrofit.mk b/target/product/virtual_ab_ota_retrofit.mk
new file mode 100644
index 0000000..b492fad
--- /dev/null
+++ b/target/product/virtual_ab_ota_retrofit.mk
@@ -0,0 +1,21 @@
+#
+# Copyright (C) 2019 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.
+#
+
+$(call inherit-product, $(SRC_TARGET_DIR)/product/virtual_ab_ota.mk)
+
+PRODUCT_VIRTUAL_AB_OTA_RETROFIT := true
+
+PRODUCT_PRODUCT_PROPERTIES += ro.virtual_ab.retrofit=true
diff --git a/tools/releasetools/ota_from_target_files.py b/tools/releasetools/ota_from_target_files.py
index 1a4f7e1..9715aa1 100755
--- a/tools/releasetools/ota_from_target_files.py
+++ b/tools/releasetools/ota_from_target_files.py
@@ -241,6 +241,9 @@
 DYNAMIC_PARTITION_INFO = 'META/dynamic_partitions_info.txt'
 AB_PARTITIONS = 'META/ab_partitions.txt'
 UNZIP_PATTERN = ['IMAGES/*', 'META/*', 'OTA/*', 'RADIO/*']
+# Files to be unzipped for target diffing purpose.
+TARGET_DIFFING_UNZIP_PATTERN = ['BOOT', 'RECOVERY', 'SYSTEM/*', 'VENDOR/*',
+                                'PRODUCT/*', 'SYSTEM_EXT/*', 'ODM/*']
 RETROFIT_DAP_UNZIP_PATTERN = ['OTA/super_*.img', AB_PARTITIONS]
 
 
@@ -539,7 +542,7 @@
     self.payload_properties = None
     self.secondary = secondary
 
-  def _Run(self, cmd):
+  def _Run(self, cmd):  # pylint: disable=no-self-use
     # Don't pipe (buffer) the output if verbose is set. Let
     # brillo_update_payload write to stdout/stderr directly, so its progress can
     # be monitored.
@@ -2005,8 +2008,7 @@
   return target_file
 
 
-def WriteABOTAPackageWithBrilloScript(target_file, output_file,
-                                      source_file=None):
+def GenerateAbOtaPackage(target_file, output_file, source_file=None):
   """Generates an Android OTA package that has A/B update payload."""
   # Stage the output zip package for package signing.
   if not OPTIONS.no_signing:
@@ -2104,6 +2106,66 @@
   FinalizeMetadata(metadata, staging_file, output_file, needed_property_files)
 
 
+def GenerateNonAbOtaPackage(target_file, output_file, source_file=None):
+  """Generates a non-A/B OTA package."""
+  # Sanity check the loaded info dicts first.
+  if OPTIONS.info_dict.get("no_recovery") == "true":
+    raise common.ExternalError(
+        "--- target build has specified no recovery ---")
+
+  # Non-A/B OTAs rely on /cache partition to store temporary files.
+  cache_size = OPTIONS.info_dict.get("cache_size")
+  if cache_size is None:
+    logger.warning("--- can't determine the cache partition size ---")
+  OPTIONS.cache_size = cache_size
+
+  if OPTIONS.extra_script is not None:
+    with open(OPTIONS.extra_script) as fp:
+      OPTIONS.extra_script = fp.read()
+
+  if OPTIONS.extracted_input is not None:
+    OPTIONS.input_tmp = OPTIONS.extracted_input
+  else:
+    logger.info("unzipping target target-files...")
+    OPTIONS.input_tmp = common.UnzipTemp(target_file, UNZIP_PATTERN)
+  OPTIONS.target_tmp = OPTIONS.input_tmp
+
+  # If the caller explicitly specified the device-specific extensions path via
+  # -s / --device_specific, use that. Otherwise, use META/releasetools.py if it
+  # is present in the target target_files. Otherwise, take the path of the file
+  # from 'tool_extensions' in the info dict and look for that in the local
+  # filesystem, relative to the current directory.
+  if OPTIONS.device_specific is None:
+    from_input = os.path.join(OPTIONS.input_tmp, "META", "releasetools.py")
+    if os.path.exists(from_input):
+      logger.info("(using device-specific extensions from target_files)")
+      OPTIONS.device_specific = from_input
+    else:
+      OPTIONS.device_specific = OPTIONS.info_dict.get("tool_extensions")
+
+  if OPTIONS.device_specific is not None:
+    OPTIONS.device_specific = os.path.abspath(OPTIONS.device_specific)
+
+  # Generate a full OTA.
+  if source_file is None:
+    with zipfile.ZipFile(target_file) as input_zip:
+      WriteFullOTAPackage(
+          input_zip,
+          output_file)
+
+  # Generate an incremental OTA.
+  else:
+    logger.info("unzipping source target-files...")
+    OPTIONS.source_tmp = common.UnzipTemp(
+        OPTIONS.incremental_source, UNZIP_PATTERN)
+    with zipfile.ZipFile(target_file) as input_zip, \
+        zipfile.ZipFile(source_file) as source_zip:
+      WriteBlockIncrementalOTAPackage(
+          input_zip,
+          source_zip,
+          output_file)
+
+
 def main(argv):
 
   def option_handler(o, a):
@@ -2278,76 +2340,29 @@
     OPTIONS.key_passwords = common.GetKeyPasswords([OPTIONS.package_key])
 
   if ab_update:
-    WriteABOTAPackageWithBrilloScript(
+    GenerateAbOtaPackage(
         target_file=args[0],
         output_file=args[1],
         source_file=OPTIONS.incremental_source)
 
-    logger.info("done.")
-    return
-
-  # Sanity check the loaded info dicts first.
-  if OPTIONS.info_dict.get("no_recovery") == "true":
-    raise common.ExternalError(
-        "--- target build has specified no recovery ---")
-
-  # Non-A/B OTAs rely on /cache partition to store temporary files.
-  cache_size = OPTIONS.info_dict.get("cache_size")
-  if cache_size is None:
-    logger.warning("--- can't determine the cache partition size ---")
-  OPTIONS.cache_size = cache_size
-
-  if OPTIONS.extra_script is not None:
-    with open(OPTIONS.extra_script) as fp:
-      OPTIONS.extra_script = fp.read()
-
-  if OPTIONS.extracted_input is not None:
-    OPTIONS.input_tmp = OPTIONS.extracted_input
   else:
-    logger.info("unzipping target target-files...")
-    OPTIONS.input_tmp = common.UnzipTemp(args[0], UNZIP_PATTERN)
-  OPTIONS.target_tmp = OPTIONS.input_tmp
+    GenerateNonAbOtaPackage(
+        target_file=args[0],
+        output_file=args[1],
+        source_file=OPTIONS.incremental_source)
 
-  # If the caller explicitly specified the device-specific extensions path via
-  # -s / --device_specific, use that. Otherwise, use META/releasetools.py if it
-  # is present in the target target_files. Otherwise, take the path of the file
-  # from 'tool_extensions' in the info dict and look for that in the local
-  # filesystem, relative to the current directory.
-  if OPTIONS.device_specific is None:
-    from_input = os.path.join(OPTIONS.input_tmp, "META", "releasetools.py")
-    if os.path.exists(from_input):
-      logger.info("(using device-specific extensions from target_files)")
-      OPTIONS.device_specific = from_input
-    else:
-      OPTIONS.device_specific = OPTIONS.info_dict.get("tool_extensions")
+  # Post OTA generation works.
+  if OPTIONS.incremental_source is not None and OPTIONS.log_diff:
+    logger.info("Generating diff logs...")
+    logger.info("Unzipping target-files for diffing...")
+    target_dir = common.UnzipTemp(args[0], TARGET_DIFFING_UNZIP_PATTERN)
+    source_dir = common.UnzipTemp(
+        OPTIONS.incremental_source, TARGET_DIFFING_UNZIP_PATTERN)
 
-  if OPTIONS.device_specific is not None:
-    OPTIONS.device_specific = os.path.abspath(OPTIONS.device_specific)
-
-  # Generate a full OTA.
-  if OPTIONS.incremental_source is None:
-    with zipfile.ZipFile(args[0], 'r') as input_zip:
-      WriteFullOTAPackage(
-          input_zip,
-          output_file=args[1])
-
-  # Generate an incremental OTA.
-  else:
-    logger.info("unzipping source target-files...")
-    OPTIONS.source_tmp = common.UnzipTemp(
-        OPTIONS.incremental_source, UNZIP_PATTERN)
-    with zipfile.ZipFile(args[0], 'r') as input_zip, \
-        zipfile.ZipFile(OPTIONS.incremental_source, 'r') as source_zip:
-      WriteBlockIncrementalOTAPackage(
-          input_zip,
-          source_zip,
-          output_file=args[1])
-
-    if OPTIONS.log_diff:
-      with open(OPTIONS.log_diff, 'w') as out_file:
-        import target_files_diff
-        target_files_diff.recursiveDiff(
-            '', OPTIONS.source_tmp, OPTIONS.input_tmp, out_file)
+    with open(OPTIONS.log_diff, 'w') as out_file:
+      import target_files_diff
+      target_files_diff.recursiveDiff(
+          '', source_dir, target_dir, out_file)
 
   logger.info("done.")