diff --git a/core/base_rules.mk b/core/base_rules.mk
index 6722af4..6fc2935 100644
--- a/core/base_rules.mk
+++ b/core/base_rules.mk
@@ -210,7 +210,10 @@
   # Apk and its attachments reside in its own subdir.
   ifeq ($(LOCAL_MODULE_CLASS),APPS)
   # framework-res.apk doesn't like the additional layer.
-  ifneq ($(LOCAL_NO_STANDARD_LIBRARIES),true)
+  ifeq ($(LOCAL_NO_STANDARD_LIBRARIES),true)
+  # Neither do Runtime Resource Overlay apks, which contain just the overlaid resources.
+  else ifeq ($(LOCAL_IS_RUNTIME_RESOURCE_OVERLAY),true)
+  else
     my_module_path := $(my_module_path)/$(LOCAL_MODULE)
   endif
   endif
diff --git a/core/build_rro_package.mk b/core/build_rro_package.mk
new file mode 100644
index 0000000..24cd9a3
--- /dev/null
+++ b/core/build_rro_package.mk
@@ -0,0 +1,22 @@
+#########################################################################
+## Standard rules for installing runtime resouce overlay APKs.
+##
+## Set LOCAL_RRO_SKU to the SKU name if the package should apply only to
+## a particular SKU as set by ro.boot.vendor.overlay.sku system property.
+##
+#########################################################################
+
+LOCAL_IS_RUNTIME_RESOURCE_OVERLAY := true
+
+ifneq ($(LOCAL_SRC_FILES),)
+  $(error runtime resource overlay package should not contain sources)
+endif
+
+ifeq (S(LOCAL_RRO_SKU),)
+  LOCAL_MODULE_PATH := $(TARGET_OUT_VENDOR)/overlay
+else
+  LOCAL_MODULE_PATH := $(TARGET_OUT_VENDOR)/overlay/$(LOCAL_RRO_SKU)
+endif
+
+include $(BUILD_SYSTEM)/package.mk
+
diff --git a/core/clang/HOST_x86_common.mk b/core/clang/HOST_x86_common.mk
index 9e71750..690c0f6 100644
--- a/core/clang/HOST_x86_common.mk
+++ b/core/clang/HOST_x86_common.mk
@@ -13,7 +13,8 @@
 ifeq ($(HOST_OS),linux)
 CLANG_CONFIG_x86_LINUX_HOST_EXTRA_ASFLAGS := \
   --gcc-toolchain=$($(clang_2nd_arch_prefix)HOST_TOOLCHAIN_FOR_CLANG) \
-  --sysroot $($(clang_2nd_arch_prefix)HOST_TOOLCHAIN_FOR_CLANG)/sysroot
+  --sysroot $($(clang_2nd_arch_prefix)HOST_TOOLCHAIN_FOR_CLANG)/sysroot \
+  -B$($(clang_2nd_arch_prefix)HOST_TOOLCHAIN_FOR_CLANG)/x86_64-linux/bin
 
 CLANG_CONFIG_x86_LINUX_HOST_EXTRA_CFLAGS := \
   --gcc-toolchain=$($(clang_2nd_arch_prefix)HOST_TOOLCHAIN_FOR_CLANG)
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index 5886610..fdaa624 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -363,6 +363,8 @@
 LOCAL_INIT_RC_32:=
 LOCAL_INIT_RC_64:=
 LOCAL_JAVA_LANGUAGE_VERSION:=
+LOCAL_IS_RUNTIME_RESOURCE_OVERLAY:=
+LOCAL_RRO_SKU:=
 
 # Trim MAKEFILE_LIST so that $(call my-dir) doesn't need to
 # iterate over thousands of entries every time.
diff --git a/core/config.mk b/core/config.mk
index 94c880f..6152060 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -85,6 +85,7 @@
 BUILD_HOST_EXECUTABLE:= $(BUILD_SYSTEM)/host_executable.mk
 BUILD_PACKAGE:= $(BUILD_SYSTEM)/package.mk
 BUILD_PHONY_PACKAGE:= $(BUILD_SYSTEM)/phony_package.mk
+BUILD_RRO_PACKAGE:= $(BUILD_SYSTEM)/build_rro_package.mk
 BUILD_HOST_PREBUILT:= $(BUILD_SYSTEM)/host_prebuilt.mk
 BUILD_PREBUILT:= $(BUILD_SYSTEM)/prebuilt.mk
 BUILD_MULTI_PREBUILT:= $(BUILD_SYSTEM)/multi_prebuilt.mk
diff --git a/tools/releasetools/add_img_to_target_files.py b/tools/releasetools/add_img_to_target_files.py
index 6acc69d..446b94f 100755
--- a/tools/releasetools/add_img_to_target_files.py
+++ b/tools/releasetools/add_img_to_target_files.py
@@ -19,7 +19,31 @@
 not have an IMAGES/ top-level subdirectory), produce the images and
 add them to the zipfile.
 
-Usage:  add_img_to_target_files target_files
+Usage:  add_img_to_target_files [flag] target_files
+
+  -a  (--add_missing)
+      Build and add missing images to "IMAGES/". If this option is
+      not specified, this script will simply exit when "IMAGES/"
+      directory exists in the target file.
+
+  -r  (--rebuild_recovery)
+      Rebuild the recovery patch and write it to the system image. Only
+      meaningful when system image needs to be rebuilt.
+
+  --replace_verity_private_key
+      Replace the private key used for verity signing. (same as the option
+      in sign_target_files_apks)
+
+  --replace_verity_public_key
+       Replace the certificate (public key) used for verity verification. (same
+       as the option in sign_target_files_apks)
+
+  --is_signing
+      Skip building & adding the images for "userdata" and "cache" if we
+      are signing the target files.
+
+  --verity_signer_path
+      Specify the signer path to build verity metadata.
 """
 
 import sys
@@ -45,6 +69,7 @@
 OPTIONS.rebuild_recovery = False
 OPTIONS.replace_verity_public_key = False
 OPTIONS.replace_verity_private_key = False
+OPTIONS.is_signing = False
 OPTIONS.verity_signer_path = None
 
 def GetCareMap(which, imgname):
@@ -356,10 +381,11 @@
   if has_system_other:
     banner("system_other")
     AddSystemOther(output_zip)
-  banner("userdata")
-  AddUserdata(output_zip)
-  banner("cache")
-  AddCache(output_zip)
+  if not OPTIONS.is_signing:
+    banner("userdata")
+    AddUserdata(output_zip)
+    banner("cache")
+    AddCache(output_zip)
 
   # For devices using A/B update, copy over images from RADIO/ to IMAGES/ and
   # make sure we have all the needed images ready under IMAGES/.
@@ -406,6 +432,8 @@
       OPTIONS.replace_verity_private_key = (True, a)
     elif o == "--replace_verity_public_key":
       OPTIONS.replace_verity_public_key = (True, a)
+    elif o == "--is_signing":
+      OPTIONS.is_signing = True
     elif o == "--verity_signer_path":
       OPTIONS.verity_signer_path = a
     else:
@@ -417,6 +445,7 @@
       extra_long_opts=["add_missing", "rebuild_recovery",
                        "replace_verity_public_key=",
                        "replace_verity_private_key=",
+                       "is_signing",
                        "verity_signer_path="],
       extra_option_handler=option_handler)
 
diff --git a/tools/releasetools/sign_target_files_apks.py b/tools/releasetools/sign_target_files_apks.py
index 0f20f82..6d68be1 100755
--- a/tools/releasetools/sign_target_files_apks.py
+++ b/tools/releasetools/sign_target_files_apks.py
@@ -713,7 +713,9 @@
   common.ZipClose(input_zip)
   common.ZipClose(output_zip)
 
-  add_img_to_target_files.AddImagesToTargetFiles(args[1])
+  # Skip building userdata.img and cache.img when signing the target files.
+  new_args = ["--is_signing", args[1]]
+  add_img_to_target_files.main(new_args)
 
   print "done."