diff --git a/Changes.md b/Changes.md
index 3e48bad..37bbad0 100644
--- a/Changes.md
+++ b/Changes.md
@@ -92,6 +92,11 @@
 attribute to the root element `<manifest>`. If `PRODUCT_COMPATIBILITY_MATRIX_LEVEL_OVERRIDE`
 is 26 or 27, you can add `"target-level"="1"` to your device manifest instead.
 
+### Stop using USE_CLANG_PLATFORM_BUILD {#USE_CLANG_PLATFORM_BUILD}
+
+Clang is the default and only supported Android compiler, so there is no reason
+for this option to exist.
+
 ### Other envsetup.sh variables  {#other_envsetup_variables}
 
 * ANDROID_TOOLCHAIN
diff --git a/core/binary.mk b/core/binary.mk
index a4fd8e3..e3da7d2 100644
--- a/core/binary.mk
+++ b/core/binary.mk
@@ -354,11 +354,6 @@
             my_clang := true
         endif
     endif
-# Add option to make gcc the default for device build
-else ifeq ($(USE_CLANG_PLATFORM_BUILD),false)
-    ifeq ($(my_clang),)
-        my_clang := false
-    endif
 else ifeq ($(my_clang),)
     my_clang := true
 endif
diff --git a/core/config.mk b/core/config.mk
index 1a6ac47..255c848 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -76,6 +76,7 @@
   ANDROID_PRE_BUILD_PATHS \
   ,See $(CHANGES_URL)#other_envsetup_variables)
 $(KATI_obsolete_var PRODUCT_COMPATIBILITY_MATRIX_LEVEL_OVERRIDE,Set FCM Version in device manifest instead. See $(CHANGES_URL)#PRODUCT_COMPATIBILITY_MATRIX_LEVEL_OVERRIDE)
+$(KATI_obsolete_var USE_CLANG_PLATFORM_BUILD,Clang is the only supported Android compiler. See $(CHANGES_URL)#USE_CLANG_PLATFORM_BUILD)
 
 CHANGES_URL :=
 
diff --git a/core/cxx_stl_setup.mk b/core/cxx_stl_setup.mk
index f07659d..5171b8a 100644
--- a/core/cxx_stl_setup.mk
+++ b/core/cxx_stl_setup.mk
@@ -74,6 +74,16 @@
 ifneq ($(filter $(my_cxx_stl),libc++ libc++_static),)
     my_cflags += -D_USING_LIBCXX
 
+    ifeq ($($(my_prefix)OS),darwin)
+        # libc++'s headers are annotated with availability macros that indicate
+        # which version of Mac OS was the first to ship with a libc++ feature
+        # available in its *system's* libc++.dylib. We do not use the system's
+        # library, but rather ship our own. As such, these availability
+        # attributes are meaningless for us but cause build breaks when we try
+        # to use code that would not be available in the system's dylib.
+        my_cppflags += -D_LIBCPP_DISABLE_AVAILABILITY
+    endif
+
     # Note that the structure of this means that LOCAL_CXX_STL := libc++ will
     # use the static libc++ for static executables.
     ifeq ($(my_link_type),dynamic)
diff --git a/core/dex_preopt_libart.mk b/core/dex_preopt_libart.mk
index 79e72c1..20d43dc 100644
--- a/core/dex_preopt_libart.mk
+++ b/core/dex_preopt_libart.mk
@@ -93,8 +93,11 @@
 # If we use a boot image profile.
 my_use_profile_for_boot_image := $(PRODUCT_USE_PROFILE_FOR_BOOT_IMAGE)
 ifeq (,$(my_use_profile_for_boot_image))
-# If not set, use the default.
-my_use_profile_for_boot_image := false
+# If not set, set the default to true if we are not a PDK build. PDK builds
+# can't build the profile since they don't have frameworks/base.
+ifneq (true,$(TARGET_BUILD_PDK))
+my_use_profile_for_boot_image := true
+endif
 endif
 
 ifeq (true,$(my_use_profile_for_boot_image))
diff --git a/core/envsetup.mk b/core/envsetup.mk
index 255c02b..05add60 100644
--- a/core/envsetup.mk
+++ b/core/envsetup.mk
@@ -657,13 +657,3 @@
 ifeq ($(CALLED_FROM_SETUP),true)
 PRINT_BUILD_CONFIG ?= true
 endif
-
-ifeq ($(USE_CLANG_PLATFORM_BUILD),)
-USE_CLANG_PLATFORM_BUILD := true
-endif
-
-ifneq ($(USE_CLANG_PLATFORM_BUILD),true)
-ifneq ($(USE_CLANG_PLATFORM_BUILD),false)
-$(error USE_CLANG_PLATFORM_BUILD must be true or false)
-endif
-endif
diff --git a/core/soong_config.mk b/core/soong_config.mk
index bbad4c8..c7eefc9 100644
--- a/core/soong_config.mk
+++ b/core/soong_config.mk
@@ -110,7 +110,6 @@
 $(call add_json_bool, Device_uses_hwc2,                  $(filter true,$(TARGET_USES_HWC2)))
 $(call add_json_list, DeviceKernelHeaders,               $(TARGET_PROJECT_SYSTEM_INCLUDES))
 $(call add_json_bool, DevicePrefer32BitExecutables,      $(filter true,$(TARGET_PREFER_32_BIT_EXECUTABLES)))
-$(call add_json_val,  DeviceUsesClang,                   $(if $(USE_CLANG_PLATFORM_BUILD),$(USE_CLANG_PLATFORM_BUILD),false))
 $(call add_json_str,  DeviceVndkVersion,                 $(BOARD_VNDK_VERSION))
 $(call add_json_str,  Platform_vndk_version,             $(PLATFORM_VNDK_VERSION))
 $(call add_json_list, ExtraVndkVersions,                 $(PRODUCT_EXTRA_VNDK_VERSIONS))
diff --git a/tools/releasetools/blockimgdiff.py b/tools/releasetools/blockimgdiff.py
index 2b2e6d9..f366853 100644
--- a/tools/releasetools/blockimgdiff.py
+++ b/tools/releasetools/blockimgdiff.py
@@ -1467,7 +1467,7 @@
     max_blocks_per_transfer = int(cache_size * split_threshold /
                                   self.tgt.blocksize)
     empty = RangeSet()
-    for tgt_fn, tgt_ranges in self.tgt.file_map.items():
+    for tgt_fn, tgt_ranges in sorted(self.tgt.file_map.items()):
       if tgt_fn == "__ZERO":
         # the special "__ZERO" domain is all the blocks not contained
         # in any file and that are filled with zeros.  We have a
diff --git a/tools/releasetools/check_target_files_signatures.py b/tools/releasetools/check_target_files_signatures.py
index c4877e0..db63fd3 100755
--- a/tools/releasetools/check_target_files_signatures.py
+++ b/tools/releasetools/check_target_files_signatures.py
@@ -53,11 +53,13 @@
 
 import common
 
-# Work around a bug in python's zipfile module that prevents opening
-# of zipfiles if any entry has an extra field of between 1 and 3 bytes
-# (which is common with zipaligned APKs).  This overrides the
-# ZipInfo._decodeExtra() method (which contains the bug) with an empty
-# version (since we don't need to decode the extra field anyway).
+# Work around a bug in Python's zipfile module that prevents opening of zipfiles
+# if any entry has an extra field of between 1 and 3 bytes (which is common with
+# zipaligned APKs). This overrides the ZipInfo._decodeExtra() method (which
+# contains the bug) with an empty version (since we don't need to decode the
+# extra field anyway).
+# Issue #14315: https://bugs.python.org/issue14315, fixed in Python 2.7.8 and
+# Python 3.5.0 alpha 1.
 class MyZipInfo(zipfile.ZipInfo):
   def _decodeExtra(self):
     pass
diff --git a/tools/releasetools/ota_from_target_files.py b/tools/releasetools/ota_from_target_files.py
index f474a6c..d6c50dc 100755
--- a/tools/releasetools/ota_from_target_files.py
+++ b/tools/releasetools/ota_from_target_files.py
@@ -527,12 +527,7 @@
   if target_info.oem_props and not OPTIONS.oem_no_mount:
     target_info.WriteMountOemScript(script)
 
-  metadata = {
-      "post-build": target_info.fingerprint,
-      "pre-device": target_info.device,
-      "post-timestamp": target_info.GetBuildProp("ro.build.date.utc"),
-      "ota-type" : "BLOCK",
-  }
+  metadata = GetPackageMetadata(target_info)
 
   device_specific = common.DeviceSpecificParams(
       input_zip=input_zip,
@@ -711,6 +706,57 @@
     metadata["post-timestamp"] = post_timestamp
 
 
+def GetPackageMetadata(target_info, source_info=None):
+  """Generates and returns the metadata dict.
+
+  It generates a dict() that contains the info to be written into an OTA
+  package (META-INF/com/android/metadata). It also handles the detection of
+  downgrade / timestamp override / data wipe based on the global options.
+
+  Args:
+    target_info: The BuildInfo instance that holds the target build info.
+    source_info: The BuildInfo instance that holds the source build info, or
+        None if generating full OTA.
+
+  Returns:
+    A dict to be written into package metadata entry.
+  """
+  assert isinstance(target_info, BuildInfo)
+  assert source_info is None or isinstance(source_info, BuildInfo)
+
+  metadata = {
+      'post-build' : target_info.fingerprint,
+      'post-build-incremental' : target_info.GetBuildProp(
+          'ro.build.version.incremental'),
+  }
+
+  if target_info.is_ab:
+    metadata['ota-type'] = 'AB'
+    metadata['ota-required-cache'] = '0'
+  else:
+    metadata['ota-type'] = 'BLOCK'
+
+  if OPTIONS.wipe_user_data:
+    metadata['ota-wipe'] = 'yes'
+
+  is_incremental = source_info is not None
+  if is_incremental:
+    metadata['pre-build'] = source_info.fingerprint
+    metadata['pre-build-incremental'] = source_info.GetBuildProp(
+        'ro.build.version.incremental')
+    metadata['pre-device'] = source_info.device
+  else:
+    metadata['pre-device'] = target_info.device
+
+  # Detect downgrades, or fill in the post-timestamp.
+  if is_incremental:
+    HandleDowngradeMetadata(metadata, target_info, source_info)
+  else:
+    metadata['post-timestamp'] = target_info.GetBuildProp('ro.build.date.utc')
+
+  return metadata
+
+
 def WriteBlockIncrementalOTAPackage(target_zip, source_zip, output_zip):
   target_info = BuildInfo(OPTIONS.target_info_dict, OPTIONS.oem_dicts)
   source_info = BuildInfo(OPTIONS.source_info_dict, OPTIONS.oem_dicts)
@@ -728,12 +774,7 @@
     if not OPTIONS.oem_no_mount:
       source_info.WriteMountOemScript(script)
 
-  metadata = {
-      "pre-device": source_info.device,
-      "ota-type": "BLOCK",
-  }
-
-  HandleDowngradeMetadata(metadata, target_info, source_info)
+  metadata = GetPackageMetadata(target_info, source_info)
 
   device_specific = common.DeviceSpecificParams(
       source_zip=source_zip,
@@ -745,13 +786,6 @@
       metadata=metadata,
       info_dict=source_info)
 
-  metadata["pre-build"] = source_info.fingerprint
-  metadata["post-build"] = target_info.fingerprint
-  metadata["pre-build-incremental"] = source_info.GetBuildProp(
-      "ro.build.version.incremental")
-  metadata["post-build-incremental"] = target_info.GetBuildProp(
-      "ro.build.version.incremental")
-
   source_boot = common.GetBootableImage(
       "/tmp/boot.img", "boot.img", OPTIONS.source_tmp, "BOOT", source_info)
   target_boot = common.GetBootableImage(
@@ -1070,24 +1104,7 @@
     source_info = None
 
   # Metadata to comply with Android OTA package format.
-  metadata = {
-      "post-build" : target_info.fingerprint,
-      "post-build-incremental" : target_info.GetBuildProp(
-          "ro.build.version.incremental"),
-      "ota-required-cache" : "0",
-      "ota-type" : "AB",
-  }
-
-  if source_file is not None:
-    metadata["pre-device"] = source_info.device
-    metadata["pre-build"] = source_info.fingerprint
-    metadata["pre-build-incremental"] = source_info.GetBuildProp(
-        "ro.build.version.incremental")
-
-    HandleDowngradeMetadata(metadata, target_info, source_info)
-  else:
-    metadata["pre-device"] = target_info.device
-    metadata["post-timestamp"] = target_info.GetBuildProp("ro.build.date.utc")
+  metadata = GetPackageMetadata(target_info, source_info)
 
   # 1. Generate payload.
   payload_file = common.MakeTempFile(prefix="payload-", suffix=".bin")
diff --git a/tools/releasetools/test_ota_from_target_files.py b/tools/releasetools/test_ota_from_target_files.py
index 0948c61..5f6c5d0 100644
--- a/tools/releasetools/test_ota_from_target_files.py
+++ b/tools/releasetools/test_ota_from_target_files.py
@@ -19,7 +19,7 @@
 
 import common
 from ota_from_target_files import (
-    _LoadOemDicts, BuildInfo, WriteFingerprintAssertion)
+    _LoadOemDicts, BuildInfo, GetPackageMetadata, WriteFingerprintAssertion)
 
 
 class MockScriptWriter(object):
@@ -300,3 +300,179 @@
       self.assertEqual('foo', oem_dict['xyz'])
       self.assertEqual('bar', oem_dict['a.b.c'])
       self.assertEqual('{}'.format(i), oem_dict['ro.build.index'])
+
+
+class OtaFromTargetFilesTest(unittest.TestCase):
+
+  TEST_TARGET_INFO_DICT = {
+      'build.prop' : {
+          'ro.product.device' : 'product-device',
+          'ro.build.fingerprint' : 'build-fingerprint-target',
+          'ro.build.version.incremental' : 'build-version-incremental-target',
+          'ro.build.date.utc' : '1500000000',
+      },
+  }
+
+  TEST_SOURCE_INFO_DICT = {
+      'build.prop' : {
+          'ro.product.device' : 'product-device',
+          'ro.build.fingerprint' : 'build-fingerprint-source',
+          'ro.build.version.incremental' : 'build-version-incremental-source',
+          'ro.build.date.utc' : '1400000000',
+      },
+  }
+
+  def setUp(self):
+    # Reset the global options as in ota_from_target_files.py.
+    common.OPTIONS.incremental_source = None
+    common.OPTIONS.downgrade = False
+    common.OPTIONS.timestamp = False
+    common.OPTIONS.wipe_user_data = False
+
+  def test_GetPackageMetadata_abOta_full(self):
+    target_info_dict = copy.deepcopy(self.TEST_TARGET_INFO_DICT)
+    target_info_dict['ab_update'] = 'true'
+    target_info = BuildInfo(target_info_dict, None)
+    metadata = GetPackageMetadata(target_info)
+    self.assertDictEqual(
+        {
+            'ota-type' : 'AB',
+            'ota-required-cache' : '0',
+            'post-build' : 'build-fingerprint-target',
+            'post-build-incremental' : 'build-version-incremental-target',
+            'post-timestamp' : '1500000000',
+            'pre-device' : 'product-device',
+        },
+        metadata)
+
+  def test_GetPackageMetadata_abOta_incremental(self):
+    target_info_dict = copy.deepcopy(self.TEST_TARGET_INFO_DICT)
+    target_info_dict['ab_update'] = 'true'
+    target_info = BuildInfo(target_info_dict, None)
+    source_info = BuildInfo(self.TEST_SOURCE_INFO_DICT, None)
+    common.OPTIONS.incremental_source = ''
+    metadata = GetPackageMetadata(target_info, source_info)
+    self.assertDictEqual(
+        {
+            'ota-type' : 'AB',
+            'ota-required-cache' : '0',
+            'post-build' : 'build-fingerprint-target',
+            'post-build-incremental' : 'build-version-incremental-target',
+            'post-timestamp' : '1500000000',
+            'pre-device' : 'product-device',
+            'pre-build' : 'build-fingerprint-source',
+            'pre-build-incremental' : 'build-version-incremental-source',
+        },
+        metadata)
+
+  def test_GetPackageMetadata_nonAbOta_full(self):
+    target_info = BuildInfo(self.TEST_TARGET_INFO_DICT, None)
+    metadata = GetPackageMetadata(target_info)
+    self.assertDictEqual(
+        {
+            'ota-type' : 'BLOCK',
+            'post-build' : 'build-fingerprint-target',
+            'post-build-incremental' : 'build-version-incremental-target',
+            'post-timestamp' : '1500000000',
+            'pre-device' : 'product-device',
+        },
+        metadata)
+
+  def test_GetPackageMetadata_nonAbOta_incremental(self):
+    target_info = BuildInfo(self.TEST_TARGET_INFO_DICT, None)
+    source_info = BuildInfo(self.TEST_SOURCE_INFO_DICT, None)
+    common.OPTIONS.incremental_source = ''
+    metadata = GetPackageMetadata(target_info, source_info)
+    self.assertDictEqual(
+        {
+            'ota-type' : 'BLOCK',
+            'post-build' : 'build-fingerprint-target',
+            'post-build-incremental' : 'build-version-incremental-target',
+            'post-timestamp' : '1500000000',
+            'pre-device' : 'product-device',
+            'pre-build' : 'build-fingerprint-source',
+            'pre-build-incremental' : 'build-version-incremental-source',
+        },
+        metadata)
+
+  def test_GetPackageMetadata_wipe(self):
+    target_info = BuildInfo(self.TEST_TARGET_INFO_DICT, None)
+    common.OPTIONS.wipe_user_data = True
+    metadata = GetPackageMetadata(target_info)
+    self.assertDictEqual(
+        {
+            'ota-type' : 'BLOCK',
+            'ota-wipe' : 'yes',
+            'post-build' : 'build-fingerprint-target',
+            'post-build-incremental' : 'build-version-incremental-target',
+            'post-timestamp' : '1500000000',
+            'pre-device' : 'product-device',
+        },
+        metadata)
+
+  @staticmethod
+  def _test_GetPackageMetadata_swapBuildTimestamps(target_info, source_info):
+    (target_info['build.prop']['ro.build.date.utc'],
+     source_info['build.prop']['ro.build.date.utc']) = (
+         source_info['build.prop']['ro.build.date.utc'],
+         target_info['build.prop']['ro.build.date.utc'])
+
+  def test_GetPackageMetadata_unintentionalDowngradeDetected(self):
+    target_info_dict = copy.deepcopy(self.TEST_TARGET_INFO_DICT)
+    source_info_dict = copy.deepcopy(self.TEST_SOURCE_INFO_DICT)
+    self._test_GetPackageMetadata_swapBuildTimestamps(
+        target_info_dict, source_info_dict)
+
+    target_info = BuildInfo(target_info_dict, None)
+    source_info = BuildInfo(source_info_dict, None)
+    common.OPTIONS.incremental_source = ''
+    self.assertRaises(RuntimeError, GetPackageMetadata, target_info,
+                      source_info)
+
+  def test_GetPackageMetadata_downgrade(self):
+    target_info_dict = copy.deepcopy(self.TEST_TARGET_INFO_DICT)
+    source_info_dict = copy.deepcopy(self.TEST_SOURCE_INFO_DICT)
+    self._test_GetPackageMetadata_swapBuildTimestamps(
+        target_info_dict, source_info_dict)
+
+    target_info = BuildInfo(target_info_dict, None)
+    source_info = BuildInfo(source_info_dict, None)
+    common.OPTIONS.incremental_source = ''
+    common.OPTIONS.downgrade = True
+    common.OPTIONS.wipe_user_data = True
+    metadata = GetPackageMetadata(target_info, source_info)
+    self.assertDictEqual(
+        {
+            'ota-downgrade' : 'yes',
+            'ota-type' : 'BLOCK',
+            'ota-wipe' : 'yes',
+            'post-build' : 'build-fingerprint-target',
+            'post-build-incremental' : 'build-version-incremental-target',
+            'pre-device' : 'product-device',
+            'pre-build' : 'build-fingerprint-source',
+            'pre-build-incremental' : 'build-version-incremental-source',
+        },
+        metadata)
+
+  def test_GetPackageMetadata_overrideTimestamp(self):
+    target_info_dict = copy.deepcopy(self.TEST_TARGET_INFO_DICT)
+    source_info_dict = copy.deepcopy(self.TEST_SOURCE_INFO_DICT)
+    self._test_GetPackageMetadata_swapBuildTimestamps(
+        target_info_dict, source_info_dict)
+
+    target_info = BuildInfo(target_info_dict, None)
+    source_info = BuildInfo(source_info_dict, None)
+    common.OPTIONS.incremental_source = ''
+    common.OPTIONS.timestamp = True
+    metadata = GetPackageMetadata(target_info, source_info)
+    self.assertDictEqual(
+        {
+            'ota-type' : 'BLOCK',
+            'post-build' : 'build-fingerprint-target',
+            'post-build-incremental' : 'build-version-incremental-target',
+            'post-timestamp' : '1500000001',
+            'pre-device' : 'product-device',
+            'pre-build' : 'build-fingerprint-source',
+            'pre-build-incremental' : 'build-version-incremental-source',
+        },
+        metadata)