Parse <overlay> and abstract resource mapping

This change introduces idmap parsing of <overlay> tags.

The <overlay> tag allows one to explicitly map resources in the target
to either a resource in the overlay or an inline attribute value.

Use the android:resourcesMap atttribute on the <overlay> tag in the
android manifest to specify a file to provide the resource mapping.

Bug: 135943783
Bug: 135051420
Test: idmap2_tests
Change-Id: I1740dcdc01849c43b1f2cb8c6645d666dbb05dba

25 files changed, 1060 insertions, 211 deletions

diff --git a/cmds/idmap2/Android.bp b/cmds/idmap2/Android.bp
index 60d64149510c..41a17064c3ba 100644
--- a/cmds/idmap2/Android.bp
+++ b/cmds/idmap2/Android.bp
@@ -43,6 +43,7 @@ cc_library {
         "libidmap2/Policies.cpp",
         "libidmap2/PrettyPrintVisitor.cpp",
         "libidmap2/RawPrintVisitor.cpp",
+        "libidmap2/ResourceMapping.cpp",
         "libidmap2/ResourceUtils.cpp",
         "libidmap2/Result.cpp",
         "libidmap2/XmlParser.cpp",
@@ -97,6 +98,7 @@ cc_test {
         "tests/PoliciesTests.cpp",
         "tests/PrettyPrintVisitorTests.cpp",
         "tests/RawPrintVisitorTests.cpp",
+        "tests/ResourceMappingTests.cpp",
         "tests/ResourceUtilsTests.cpp",
         "tests/ResultTests.cpp",
         "tests/XmlParserTests.cpp",
diff --git a/cmds/idmap2/idmap2/Create.cpp b/cmds/idmap2/idmap2/Create.cpp
index f482191b09a8..3ff6d3514331 100644
--- a/cmds/idmap2/idmap2/Create.cpp
+++ b/cmds/idmap2/idmap2/Create.cpp
@@ -99,8 +99,8 @@ Result<Unit> Create(const std::vector<std::string>& args) {
     return Error("failed to load apk %s", overlay_apk_path.c_str());
   }
 
-  const auto idmap = Idmap::FromApkAssets(target_apk_path, *target_apk, overlay_apk_path,
-                                          *overlay_apk, fulfilled_policies, !ignore_overlayable);
+  const auto idmap =
+      Idmap::FromApkAssets(*target_apk, *overlay_apk, fulfilled_policies, !ignore_overlayable);
   if (!idmap) {
     return Error(idmap.GetError(), "failed to create idmap");
   }
diff --git a/cmds/idmap2/idmap2d/Idmap2Service.cpp b/cmds/idmap2/idmap2d/Idmap2Service.cpp
index 8ee79f61520a..4aabf8399a25 100644
--- a/cmds/idmap2/idmap2d/Idmap2Service.cpp
+++ b/cmds/idmap2/idmap2d/Idmap2Service.cpp
@@ -137,8 +137,8 @@ Status Idmap2Service::createIdmap(const std::string& target_apk_path,
     return error("failed to load apk " + overlay_apk_path);
   }
 
-  const auto idmap = Idmap::FromApkAssets(target_apk_path, *target_apk, overlay_apk_path,
-                                          *overlay_apk, policy_bitmask, enforce_overlayable);
+  const auto idmap =
+      Idmap::FromApkAssets(*target_apk, *overlay_apk, policy_bitmask, enforce_overlayable);
   if (!idmap) {
     return error(idmap.GetErrorMessage());
   }
diff --git a/cmds/idmap2/include/idmap2/Idmap.h b/cmds/idmap2/include/idmap2/Idmap.h
index ebbb5ffc989d..f2cae58b910a 100644
--- a/cmds/idmap2/include/idmap2/Idmap.h
+++ b/cmds/idmap2/include/idmap2/Idmap.h
@@ -56,20 +56,14 @@
 #include "androidfw/ResourceTypes.h"
 #include "androidfw/StringPiece.h"
 #include "idmap2/Policies.h"
+#include "idmap2/ResourceMapping.h"
 
 namespace android::idmap2 {
 
 class Idmap;
 class Visitor;
 
-// use typedefs to let the compiler warn us about implicit casts
-typedef uint32_t ResourceId;  // 0xpptteeee
-typedef uint8_t PackageId;    // pp in 0xpptteeee
-typedef uint8_t TypeId;       // tt in 0xpptteeee
-typedef uint16_t EntryId;     // eeee in 0xpptteeee
-
 static constexpr const ResourceId kPadding = 0xffffffffu;
-
 static constexpr const EntryId kNoEntry = 0xffffu;
 
 // magic number: all idmap files start with this
@@ -155,7 +149,7 @@ class IdmapData {
     PackageId target_package_id_;
     uint16_t type_count_;
 
-    friend Idmap;
+    friend IdmapData;
     DISALLOW_COPY_AND_ASSIGN(Header);
   };
 
@@ -194,12 +188,15 @@ class IdmapData {
     uint16_t entry_offset_;
     std::vector<EntryId> entries_;
 
-    friend Idmap;
+    friend IdmapData;
     DISALLOW_COPY_AND_ASSIGN(TypeEntry);
   };
 
   static std::unique_ptr<const IdmapData> FromBinaryStream(std::istream& stream);
 
+  static Result<std::unique_ptr<const IdmapData>> FromResourceMapping(
+      const ResourceMapping& resource_mapping);
+
   inline const std::unique_ptr<const Header>& GetHeader() const {
     return header_;
   }
@@ -232,9 +229,7 @@ class Idmap {
   // file is used; change this in the next version of idmap to use a named
   // package instead; also update FromApkAssets to take additional parameters:
   // the target and overlay package names
-  static Result<std::unique_ptr<const Idmap>> FromApkAssets(const std::string& target_apk_path,
-                                                            const ApkAssets& target_apk_assets,
-                                                            const std::string& overlay_apk_path,
+  static Result<std::unique_ptr<const Idmap>> FromApkAssets(const ApkAssets& target_apk_assets,
                                                             const ApkAssets& overlay_apk_assets,
                                                             const PolicyBitmask& fulfilled_policies,
                                                             bool enforce_overlayable);
diff --git a/cmds/idmap2/include/idmap2/ResourceMapping.h b/cmds/idmap2/include/idmap2/ResourceMapping.h
new file mode 100644
index 000000000000..c3e1ef06c20f
--- /dev/null
+++ b/cmds/idmap2/include/idmap2/ResourceMapping.h
@@ -0,0 +1,132 @@
+/*
+ * 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.
+ */
+
+#ifndef IDMAP2_INCLUDE_IDMAP2_RESOURCEMAPPING_H_
+#define IDMAP2_INCLUDE_IDMAP2_RESOURCEMAPPING_H_
+
+#include <map>
+#include <memory>
+#include <utility>
+
+#include "androidfw/ApkAssets.h"
+#include "idmap2/Policies.h"
+#include "idmap2/ResourceUtils.h"
+#include "idmap2/Result.h"
+#include "idmap2/XmlParser.h"
+
+using android::idmap2::utils::OverlayManifestInfo;
+
+namespace android::idmap2 {
+
+struct TargetValue {
+  typedef uint8_t DataType;
+  typedef uint32_t DataValue;
+  DataType data_type;
+  DataValue data_value;
+};
+
+using TargetResourceMap = std::map<ResourceId, TargetValue>;
+using OverlayResourceMap = std::map<ResourceId, ResourceId>;
+
+class ResourceMapping {
+ public:
+  // Creates a ResourceMapping using the target and overlay APKs. Setting enforce_overlayable to
+  // `false` disables all overlayable and policy enforcement: this is intended for backwards
+  // compatibility pre-Q and unit tests.
+  static Result<ResourceMapping> FromApkAssets(const ApkAssets& target_apk_assets,
+                                               const ApkAssets& overlay_apk_assets,
+                                               const OverlayManifestInfo& overlay_info,
+                                               const PolicyBitmask& fulfilled_policies,
+                                               bool enforce_overlayable);
+
+  // Retrieves the mapping of target resource id to overlay value.
+  inline TargetResourceMap GetTargetToOverlayMap() const {
+    return target_map_;
+  }
+
+  // Retrieves the mapping of overlay resource id to target resource id. This allows a reference to
+  // an overlay resource to appear as a reference to its corresponding target resource at runtime.
+  OverlayResourceMap GetOverlayToTargetMap() const;
+
+  // Retrieves the build-time package id of the target package.
+  inline uint32_t GetTargetPackageId() const {
+    return target_package_id_;
+  }
+
+  // Retrieves the build-time package id of the overlay package.
+  inline uint32_t GetOverlayPackageId() const {
+    return overlay_package_id_;
+  }
+
+  // Retrieves the offset that was added to the index of inline string overlay values so the indices
+  // do not collide with the indices of the overlay resource table string pool.
+  inline uint32_t GetStringPoolOffset() const {
+    return string_pool_offset_;
+  }
+
+  // Retrieves the raw string pool data from the xml referenced in android:resourcesMap.
+  inline const std::pair<const uint8_t*, uint32_t> GetStringPoolData() const {
+    return std::make_pair(string_pool_data_.get(), string_pool_data_length_);
+  }
+
+ private:
+  ResourceMapping() = default;
+
+  // Apps a mapping of target resource id to the type and value of the data that overlays the
+  // target resource. The data_type is the runtime format of the data value (see
+  // Res_value::dataType). If rewrite_overlay_reference is `true` then references to an overlay
+  // resource should appear as a reference to its corresponding target resource at runtime.
+  Result<Unit> AddMapping(ResourceId target_resource, TargetValue::DataType data_type,
+                          TargetValue::DataValue data_value, bool rewrite_overlay_reference);
+
+  // Removes the overlay value mapping for the target resource.
+  void RemoveMapping(ResourceId target_resource);
+
+  // Parses the mapping of target resources to overlay resources to generate a ResourceMapping.
+  static Result<ResourceMapping> CreateResourceMapping(const AssetManager2* target_am,
+                                                       const LoadedPackage* target_package,
+                                                       const LoadedPackage* overlay_package,
+                                                       size_t string_pool_offset,
+                                                       const XmlParser& overlay_parser);
+
+  // Generates a ResourceMapping that maps target resources to overlay resources by name. To overlay
+  // a target resource, a resource must exist in the overlay with the same type and entry name as
+  // the target resource.
+  static Result<ResourceMapping> CreateResourceMappingLegacy(const AssetManager2* target_am,
+                                                             const AssetManager2* overlay_am,
+                                                             const LoadedPackage* target_package,
+                                                             const LoadedPackage* overlay_package);
+
+  // Removes resources that do not pass policy or overlayable checks of the target package.
+  void FilterOverlayableResources(const AssetManager2* target_am,
+                                  const LoadedPackage* target_package,
+                                  const LoadedPackage* overlay_package,
+                                  const OverlayManifestInfo& overlay_info,
+                                  const PolicyBitmask& fulfilled_policies);
+
+  TargetResourceMap target_map_;
+  std::multimap<ResourceId, ResourceId> overlay_map_;
+
+  uint32_t target_package_id_ = 0;
+  uint32_t overlay_package_id_ = 0;
+  uint32_t string_pool_offset_ = 0;
+  uint32_t string_pool_data_length_ = 0;
+  std::unique_ptr<uint8_t[]> string_pool_data_ = nullptr;
+};
+
+}  // namespace android::idmap2
+
+#endif  // IDMAP2_INCLUDE_IDMAP2_RESOURCEMAPPING_H_
diff --git a/cmds/idmap2/include/idmap2/ResourceUtils.h b/cmds/idmap2/include/idmap2/ResourceUtils.h
index 9a0c2abced5a..abc2df1a147f 100644
--- a/cmds/idmap2/include/idmap2/ResourceUtils.h
+++ b/cmds/idmap2/include/idmap2/ResourceUtils.h
@@ -21,17 +21,28 @@
 #include <string>
 
 #include "androidfw/AssetManager2.h"
-#include "idmap2/Idmap.h"
 #include "idmap2/Result.h"
 #include "idmap2/ZipFile.h"
 
-namespace android::idmap2::utils {
+namespace android::idmap2 {
+
+// use typedefs to let the compiler warn us about implicit casts
+typedef uint32_t ResourceId;  // 0xpptteeee
+typedef uint8_t PackageId;    // pp in 0xpptteeee
+typedef uint8_t TypeId;       // tt in 0xpptteeee
+typedef uint16_t EntryId;     // eeee in 0xpptteeee
+
+#define EXTRACT_TYPE(resid) ((0x00ff0000 & (resid)) >> 16)
+#define EXTRACT_ENTRY(resid) (0x0000ffff & (resid))
+
+namespace utils {
 
 struct OverlayManifestInfo {
   std::string target_package;  // NOLINT(misc-non-private-member-variables-in-classes)
   std::string target_name;     // NOLINT(misc-non-private-member-variables-in-classes)
   std::string requiredSystemPropertyName;  // NOLINT(misc-non-private-member-variables-in-classes)
   std::string requiredSystemPropertyValue;  // NOLINT(misc-non-private-member-variables-in-classes)
+  uint32_t resource_mapping;   // NOLINT(misc-non-private-member-variables-in-classes)
   bool is_static;              // NOLINT(misc-non-private-member-variables-in-classes)
   int priority = -1;           // NOLINT(misc-non-private-member-variables-in-classes)
 };
@@ -41,6 +52,8 @@ Result<OverlayManifestInfo> ExtractOverlayManifestInfo(const std::string& path,
 
 Result<std::string> ResToTypeEntryName(const AssetManager2& am, ResourceId resid);
 
-}  // namespace android::idmap2::utils
+}  // namespace utils
+
+}  // namespace android::idmap2
 
 #endif  // IDMAP2_INCLUDE_IDMAP2_RESOURCEUTILS_H_
diff --git a/cmds/idmap2/libidmap2/Idmap.cpp b/cmds/idmap2/libidmap2/Idmap.cpp
index 4649675965db..389ade59200c 100644
--- a/cmds/idmap2/libidmap2/Idmap.cpp
+++ b/cmds/idmap2/libidmap2/Idmap.cpp
@@ -30,6 +30,7 @@
 #include "android-base/macros.h"
 #include "android-base/stringprintf.h"
 #include "androidfw/AssetManager2.h"
+#include "idmap2/ResourceMapping.h"
 #include "idmap2/ResourceUtils.h"
 #include "idmap2/Result.h"
 #include "idmap2/SysTrace.h"
@@ -41,10 +42,6 @@ namespace android::idmap2 {
 
 namespace {
 
-#define EXTRACT_TYPE(resid) ((0x00ff0000 & (resid)) >> 16)
-
-#define EXTRACT_ENTRY(resid) (0x0000ffff & (resid))
-
 class MatchingResources {
  public:
   void Add(ResourceId target_resid, ResourceId overlay_resid) {
@@ -97,28 +94,6 @@ bool WARN_UNUSED ReadString(std::istream& stream, char out[kIdmapStringLength])
   return true;
 }
 
-ResourceId NameToResid(const AssetManager2& am, const std::string& name) {
-  return am.GetResourceId(name);
-}
-
-// TODO(martenkongstad): scan for package name instead of assuming package at index 0
-//
-// idmap version 0x01 naively assumes that the package to use is always the first ResTable_package
-// in the resources.arsc blob. In most cases, there is only a single ResTable_package anyway, so
-// this assumption tends to work out. That said, the correct thing to do is to scan
-// resources.arsc for a package with a given name as read from the package manifest instead of
-// relying on a hard-coded index. This however requires storing the package name in the idmap
-// header, which in turn requires incrementing the idmap version. Because the initial version of
-// idmap2 is compatible with idmap, this will have to wait for now.
-const LoadedPackage* GetPackageAtIndex0(const LoadedArsc& loaded_arsc) {
-  const std::vector<std::unique_ptr<const LoadedPackage>>& packages = loaded_arsc.GetPackages();
-  if (packages.empty()) {
-    return nullptr;
-  }
-  int id = packages[0]->GetPackageId();
-  return loaded_arsc.GetPackageById(id);
-}
-
 Result<uint32_t> GetCrc(const ZipFile& zip) {
   const Result<uint32_t> a = zip.Crc("resources.arsc");
   const Result<uint32_t> b = zip.Crc("AndroidManifest.xml");
@@ -266,95 +241,57 @@ Result<std::unique_ptr<const Idmap>> Idmap::FromBinaryStream(std::istream& strea
   return {std::move(idmap)};
 }
 
-std::string ConcatPolicies(const std::vector<std::string>& policies) {
-  std::string message;
-  for (const std::string& policy : policies) {
-    if (!message.empty()) {
-      message.append("|");
-    }
-    message.append(policy);
+Result<std::unique_ptr<const IdmapData>> IdmapData::FromResourceMapping(
+    const ResourceMapping& resource_mapping) {
+  if (resource_mapping.GetTargetToOverlayMap().empty()) {
+    return Error("no resources were overlaid");
   }
 
-  return message;
-}
-
-Result<Unit> CheckOverlayable(const LoadedPackage& target_package,
-                              const utils::OverlayManifestInfo& overlay_info,
-                              const PolicyBitmask& fulfilled_policies, const ResourceId& resid) {
-  static constexpr const PolicyBitmask sDefaultPolicies =
-      PolicyFlags::POLICY_ODM_PARTITION | PolicyFlags::POLICY_OEM_PARTITION |
-      PolicyFlags::POLICY_SYSTEM_PARTITION | PolicyFlags::POLICY_VENDOR_PARTITION |
-      PolicyFlags::POLICY_PRODUCT_PARTITION | PolicyFlags::POLICY_SIGNATURE;
-
-  // If the resource does not have an overlayable definition, allow the resource to be overlaid if
-  // the overlay is preinstalled or signed with the same signature as the target.
-  if (!target_package.DefinesOverlayable()) {
-    return (sDefaultPolicies & fulfilled_policies) != 0
-               ? Result<Unit>({})
-               : Error(
-                     "overlay must be preinstalled or signed with the same signature as the "
-                     "target");
-  }
-
-  const OverlayableInfo* overlayable_info = target_package.GetOverlayableInfo(resid);
-  if (overlayable_info == nullptr) {
-    // Do not allow non-overlayable resources to be overlaid.
-    return Error("resource has no overlayable declaration");
-  }
+  MatchingResources matching_resources;
+  for (const auto mapping : resource_mapping.GetTargetToOverlayMap()) {
+    if (mapping.second.data_type != Res_value::TYPE_REFERENCE) {
+      // The idmap format must change to support non-references.
+      continue;
+    }
 
-  if (overlay_info.target_name != overlayable_info->name) {
-    // If the overlay supplies a target overlayable name, the resource must belong to the
-    // overlayable defined with the specified name to be overlaid.
-    return Error("<overlay> android:targetName '%s' does not match overlayable name '%s'",
-                 overlay_info.target_name.c_str(), overlayable_info->name.c_str());
+    matching_resources.Add(mapping.first, mapping.second.data_value);
   }
 
-  // Enforce policy restrictions if the resource is declared as overlayable.
-  if ((overlayable_info->policy_flags & fulfilled_policies) == 0) {
-    return Error("overlay with policies '%s' does not fulfill any overlayable policies '%s'",
-                 ConcatPolicies(BitmaskToPolicies(fulfilled_policies)).c_str(),
-                 ConcatPolicies(BitmaskToPolicies(overlayable_info->policy_flags)).c_str());
+  // encode idmap data
+  std::unique_ptr<IdmapData> data(new IdmapData());
+  const auto types_end = matching_resources.Map().cend();
+  for (auto ti = matching_resources.Map().cbegin(); ti != types_end; ++ti) {
+    auto ei = ti->second.cbegin();
+    std::unique_ptr<IdmapData::TypeEntry> type(new IdmapData::TypeEntry());
+    type->target_type_id_ = EXTRACT_TYPE(ei->first);
+    type->overlay_type_id_ = EXTRACT_TYPE(ei->second);
+    type->entry_offset_ = EXTRACT_ENTRY(ei->first);
+    EntryId last_target_entry = kNoEntry;
+    for (; ei != ti->second.cend(); ++ei) {
+      if (last_target_entry != kNoEntry) {
+        int count = EXTRACT_ENTRY(ei->first) - last_target_entry - 1;
+        type->entries_.insert(type->entries_.end(), count, kNoEntry);
+      }
+      type->entries_.push_back(EXTRACT_ENTRY(ei->second));
+      last_target_entry = EXTRACT_ENTRY(ei->first);
+    }
+    data->type_entries_.push_back(std::move(type));
   }
 
-  return Result<Unit>({});
+  std::unique_ptr<IdmapData::Header> data_header(new IdmapData::Header());
+  data_header->target_package_id_ = resource_mapping.GetTargetPackageId();
+  data_header->type_count_ = data->type_entries_.size();
+  data->header_ = std::move(data_header);
+  return {std::move(data)};
 }
 
-Result<std::unique_ptr<const Idmap>> Idmap::FromApkAssets(const std::string& target_apk_path,
-                                                          const ApkAssets& target_apk_assets,
-                                                          const std::string& overlay_apk_path,
+Result<std::unique_ptr<const Idmap>> Idmap::FromApkAssets(const ApkAssets& target_apk_assets,
                                                           const ApkAssets& overlay_apk_assets,
                                                           const PolicyBitmask& fulfilled_policies,
                                                           bool enforce_overlayable) {
   SYSTRACE << "Idmap::FromApkAssets";
-  AssetManager2 target_asset_manager;
-  if (!target_asset_manager.SetApkAssets({&target_apk_assets}, true, false)) {
-    return Error("failed to create target asset manager");
-  }
-
-  AssetManager2 overlay_asset_manager;
-  if (!overlay_asset_manager.SetApkAssets({&overlay_apk_assets}, true, false)) {
-    return Error("failed to create overlay asset manager");
-  }
-
-  const LoadedArsc* target_arsc = target_apk_assets.GetLoadedArsc();
-  if (target_arsc == nullptr) {
-    return Error("failed to load target resources.arsc");
-  }
-
-  const LoadedArsc* overlay_arsc = overlay_apk_assets.GetLoadedArsc();
-  if (overlay_arsc == nullptr) {
-    return Error("failed to load overlay resources.arsc");
-  }
-
-  const LoadedPackage* target_pkg = GetPackageAtIndex0(*target_arsc);
-  if (target_pkg == nullptr) {
-    return Error("failed to load target package from resources.arsc");
-  }
-
-  const LoadedPackage* overlay_pkg = GetPackageAtIndex0(*overlay_arsc);
-  if (overlay_pkg == nullptr) {
-    return Error("failed to load overlay package from resources.arsc");
-  }
+  const std::string& target_apk_path = target_apk_assets.GetPath();
+  const std::string& overlay_apk_path = overlay_apk_assets.GetPath();
 
   const std::unique_ptr<const ZipFile> target_zip = ZipFile::Open(target_apk_path);
   if (!target_zip) {
@@ -366,11 +303,6 @@ Result<std::unique_ptr<const Idmap>> Idmap::FromApkAssets(const std::string& tar
     return Error("failed to open overlay as zip");
   }
 
-  auto overlay_info = utils::ExtractOverlayManifestInfo(overlay_apk_path);
-  if (!overlay_info) {
-    return overlay_info.GetError();
-  }
-
   std::unique_ptr<IdmapHeader> header(new IdmapHeader());
   header->magic_ = kIdmapMagic;
   header->version_ = kIdmapCurrentVersion;
@@ -395,7 +327,7 @@ Result<std::unique_ptr<const Idmap>> Idmap::FromApkAssets(const std::string& tar
   memcpy(header->target_path_, target_apk_path.data(), target_apk_path.size());
 
   if (overlay_apk_path.size() > sizeof(header->overlay_path_)) {
-    return Error("overlay apk path \"%s\" longer than maximum size %zu", target_apk_path.c_str(),
+    return Error("overlay apk path \"%s\" longer than maximum size %zu", overlay_apk_path.c_str(),
                  sizeof(header->target_path_));
   }
   memset(header->overlay_path_, 0, sizeof(header->overlay_path_));
@@ -404,70 +336,24 @@ Result<std::unique_ptr<const Idmap>> Idmap::FromApkAssets(const std::string& tar
   std::unique_ptr<Idmap> idmap(new Idmap());
   idmap->header_ = std::move(header);
 
-  // find the resources that exist in both packages
-  MatchingResources matching_resources;
-  const auto end = overlay_pkg->end();
-  for (auto iter = overlay_pkg->begin(); iter != end; ++iter) {
-    const ResourceId overlay_resid = *iter;
-    Result<std::string> name = utils::ResToTypeEntryName(overlay_asset_manager, overlay_resid);
-    if (!name) {
-      continue;
-    }
-    // prepend "<package>:" to turn name into "<package>:<type>/<name>"
-    const std::string full_name =
-        base::StringPrintf("%s:%s", target_pkg->GetPackageName().c_str(), name->c_str());
-    const ResourceId target_resid = NameToResid(target_asset_manager, full_name);
-    if (target_resid == 0) {
-      continue;
-    }
-
-    if (enforce_overlayable) {
-      Result<Unit> success =
-          CheckOverlayable(*target_pkg, *overlay_info, fulfilled_policies, target_resid);
-      if (!success) {
-        LOG(WARNING) << "overlay \"" << overlay_apk_path
-                     << "\" is not allowed to overlay resource \"" << full_name
-                     << "\": " << success.GetErrorMessage();
-        continue;
-      }
-    }
-
-    matching_resources.Add(target_resid, overlay_resid);
+  auto overlay_info = utils::ExtractOverlayManifestInfo(overlay_apk_path);
+  if (!overlay_info) {
+    return overlay_info.GetError();
   }
 
-  if (matching_resources.Map().empty()) {
-    return Error("overlay \"%s\" does not successfully overlay any resource",
-                 overlay_apk_path.c_str());
+  auto resource_mapping =
+      ResourceMapping::FromApkAssets(target_apk_assets, overlay_apk_assets, *overlay_info,
+                                     fulfilled_policies, enforce_overlayable);
+  if (!resource_mapping) {
+    return resource_mapping.GetError();
   }
 
-  // encode idmap data
-  std::unique_ptr<IdmapData> data(new IdmapData());
-  const auto types_end = matching_resources.Map().cend();
-  for (auto ti = matching_resources.Map().cbegin(); ti != types_end; ++ti) {
-    auto ei = ti->second.cbegin();
-    std::unique_ptr<IdmapData::TypeEntry> type(new IdmapData::TypeEntry());
-    type->target_type_id_ = EXTRACT_TYPE(ei->first);
-    type->overlay_type_id_ = EXTRACT_TYPE(ei->second);
-    type->entry_offset_ = EXTRACT_ENTRY(ei->first);
-    EntryId last_target_entry = kNoEntry;
-    for (; ei != ti->second.cend(); ++ei) {
-      if (last_target_entry != kNoEntry) {
-        int count = EXTRACT_ENTRY(ei->first) - last_target_entry - 1;
-        type->entries_.insert(type->entries_.end(), count, kNoEntry);
-      }
-      type->entries_.push_back(EXTRACT_ENTRY(ei->second));
-      last_target_entry = EXTRACT_ENTRY(ei->first);
-    }
-    data->type_entries_.push_back(std::move(type));
+  auto idmap_data = IdmapData::FromResourceMapping(*resource_mapping);
+  if (!idmap_data) {
+    return idmap_data.GetError();
   }
 
-  std::unique_ptr<IdmapData::Header> data_header(new IdmapData::Header());
-  data_header->target_package_id_ = target_pkg->GetPackageId();
-  data_header->type_count_ = data->type_entries_.size();
-  data->header_ = std::move(data_header);
-
-  idmap->data_.push_back(std::move(data));
-
+  idmap->data_.push_back(std::move(*idmap_data));
   return {std::move(idmap)};
 }
 
diff --git a/cmds/idmap2/libidmap2/ResourceMapping.cpp b/cmds/idmap2/libidmap2/ResourceMapping.cpp
new file mode 100644
index 000000000000..95ae626664dd
--- /dev/null
+++ b/cmds/idmap2/libidmap2/ResourceMapping.cpp
@@ -0,0 +1,411 @@
+/*
+ * 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.
+ */
+
+#include "idmap2/ResourceMapping.h"
+
+#include <map>
+#include <memory>
+#include <set>
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "android-base/stringprintf.h"
+#include "idmap2/ResourceUtils.h"
+
+using android::base::StringPrintf;
+using android::idmap2::utils::ResToTypeEntryName;
+
+namespace android::idmap2 {
+
+namespace {
+
+#define EXTRACT_PACKAGE(resid) ((0xff000000 & (resid)) >> 24)
+
+std::string ConcatPolicies(const std::vector<std::string>& policies) {
+  std::string message;
+  for (const std::string& policy : policies) {
+    if (!message.empty()) {
+      message.append("|");
+    }
+    message.append(policy);
+  }
+
+  return message;
+}
+
+Result<Unit> CheckOverlayable(const LoadedPackage& target_package,
+                              const OverlayManifestInfo& overlay_info,
+                              const PolicyBitmask& fulfilled_policies,
+                              const ResourceId& target_resource) {
+  static constexpr const PolicyBitmask sDefaultPolicies =
+      PolicyFlags::POLICY_ODM_PARTITION | PolicyFlags::POLICY_OEM_PARTITION |
+      PolicyFlags::POLICY_SYSTEM_PARTITION | PolicyFlags::POLICY_VENDOR_PARTITION |
+      PolicyFlags::POLICY_PRODUCT_PARTITION | PolicyFlags::POLICY_SIGNATURE;
+
+  // If the resource does not have an overlayable definition, allow the resource to be overlaid if
+  // the overlay is preinstalled or signed with the same signature as the target.
+  if (!target_package.DefinesOverlayable()) {
+    return (sDefaultPolicies & fulfilled_policies) != 0
+               ? Result<Unit>({})
+               : Error(
+                     "overlay must be preinstalled or signed with the same signature as the "
+                     "target");
+  }
+
+  const OverlayableInfo* overlayable_info = target_package.GetOverlayableInfo(target_resource);
+  if (overlayable_info == nullptr) {
+    // Do not allow non-overlayable resources to be overlaid.
+    return Error("target resource has no overlayable declaration");
+  }
+
+  if (overlay_info.target_name != overlayable_info->name) {
+    // If the overlay supplies a target overlayable name, the resource must belong to the
+    // overlayable defined with the specified name to be overlaid.
+    return Error(R"(<overlay> android:targetName "%s" does not match overlayable name "%s")",
+                 overlay_info.target_name.c_str(), overlayable_info->name.c_str());
+  }
+
+  // Enforce policy restrictions if the resource is declared as overlayable.
+  if ((overlayable_info->policy_flags & fulfilled_policies) == 0) {
+    return Error(R"(overlay with policies "%s" does not fulfill any overlayable policies "%s")",
+                 ConcatPolicies(BitmaskToPolicies(fulfilled_policies)).c_str(),
+                 ConcatPolicies(BitmaskToPolicies(overlayable_info->policy_flags)).c_str());
+  }
+
+  return Result<Unit>({});
+}
+
+// TODO(martenkongstad): scan for package name instead of assuming package at index 0
+//
+// idmap version 0x01 naively assumes that the package to use is always the first ResTable_package
+// in the resources.arsc blob. In most cases, there is only a single ResTable_package anyway, so
+// this assumption tends to work out. That said, the correct thing to do is to scan
+// resources.arsc for a package with a given name as read from the package manifest instead of
+// relying on a hard-coded index. This however requires storing the package name in the idmap
+// header, which in turn requires incrementing the idmap version. Because the initial version of
+// idmap2 is compatible with idmap, this will have to wait for now.
+const LoadedPackage* GetPackageAtIndex0(const LoadedArsc& loaded_arsc) {
+  const std::vector<std::unique_ptr<const LoadedPackage>>& packages = loaded_arsc.GetPackages();
+  if (packages.empty()) {
+    return nullptr;
+  }
+  int id = packages[0]->GetPackageId();
+  return loaded_arsc.GetPackageById(id);
+}
+
+Result<std::unique_ptr<Asset>> OpenNonAssetFromResource(const ResourceId& resource_id,
+                                                        const AssetManager2& asset_manager) {
+  Res_value value{};
+  ResTable_config selected_config{};
+  uint32_t flags;
+  auto cookie =
+      asset_manager.GetResource(resource_id, /* may_be_bag */ false,
+                                /* density_override */ 0U, &value, &selected_config, &flags);
+  if (cookie == kInvalidCookie) {
+    return Error("failed to find resource for id 0x%08x", resource_id);
+  }
+
+  if (value.dataType != Res_value::TYPE_STRING) {
+    return Error("resource for is 0x%08x is not a file", resource_id);
+  }
+
+  auto string_pool = asset_manager.GetStringPoolForCookie(cookie);
+  size_t len;
+  auto file_path16 = string_pool->stringAt(value.data, &len);
+  if (file_path16 == nullptr) {
+    return Error("failed to find string for index %d", value.data);
+  }
+
+  // Load the overlay resource mappings from the file specified using android:resourcesMap.
+  auto file_path = String8(String16(file_path16));
+  auto asset = asset_manager.OpenNonAsset(file_path.c_str(), Asset::AccessMode::ACCESS_BUFFER);
+  if (asset == nullptr) {
+    return Error("file \"%s\" not found", file_path.c_str());
+  }
+
+  return asset;
+}
+
+}  // namespace
+
+Result<ResourceMapping> ResourceMapping::CreateResourceMapping(const AssetManager2* target_am,
+                                                               const LoadedPackage* target_package,
+                                                               const LoadedPackage* overlay_package,
+                                                               size_t string_pool_offset,
+                                                               const XmlParser& overlay_parser) {
+  ResourceMapping resource_mapping;
+  auto root_it = overlay_parser.tree_iterator();
+  if (root_it->event() != XmlParser::Event::START_TAG || root_it->name() != "overlay") {
+    return Error("root element is not <overlay> tag");
+  }
+
+  const uint8_t overlay_package_id = overlay_package->GetPackageId();
+  auto overlay_it_end = root_it.end();
+  for (auto overlay_it = root_it.begin(); overlay_it != overlay_it_end; ++overlay_it) {
+    if (overlay_it->event() == XmlParser::Event::BAD_DOCUMENT) {
+      return Error("failed to parse overlay xml document");
+    }
+
+    if (overlay_it->event() != XmlParser::Event::START_TAG) {
+      continue;
+    }
+
+    if (overlay_it->name() != "item") {
+      return Error("unexpected tag <%s> in <overlay>", overlay_it->name().c_str());
+    }
+
+    Result<std::string> target_resource = overlay_it->GetAttributeStringValue("target");
+    if (!target_resource) {
+      return Error(R"(<item> tag missing expected attribute "target")");
+    }
+
+    Result<android::Res_value> overlay_resource = overlay_it->GetAttributeValue("value");
+    if (!overlay_resource) {
+      return Error(R"(<item> tag missing expected attribute "value")");
+    }
+
+    ResourceId target_id =
+        target_am->GetResourceId(*target_resource, "", target_package->GetPackageName());
+    if (target_id == 0U) {
+      LOG(WARNING) << "failed to find resource \"" << *target_resource << "\" in target resources";
+      continue;
+    }
+
+    if (overlay_resource->dataType == Res_value::TYPE_STRING) {
+      overlay_resource->data += string_pool_offset;
+    }
+
+    // Only rewrite resources defined within the overlay package to their corresponding target
+    // resource ids at runtime.
+    bool rewrite_overlay_reference =
+        (overlay_resource->dataType == Res_value::TYPE_REFERENCE)
+            ? overlay_package_id == EXTRACT_PACKAGE(overlay_resource->data)
+            : false;
+
+    resource_mapping.AddMapping(target_id, overlay_resource->dataType, overlay_resource->data,
+                                rewrite_overlay_reference);
+  }
+
+  return resource_mapping;
+}
+
+Result<ResourceMapping> ResourceMapping::CreateResourceMappingLegacy(
+    const AssetManager2* target_am, const AssetManager2* overlay_am,
+    const LoadedPackage* target_package, const LoadedPackage* overlay_package) {
+  ResourceMapping resource_mapping;
+  const auto end = overlay_package->end();
+  for (auto iter = overlay_package->begin(); iter != end; ++iter) {
+    const ResourceId overlay_resid = *iter;
+    Result<std::string> name = utils::ResToTypeEntryName(*overlay_am, overlay_resid);
+    if (!name) {
+      continue;
+    }
+
+    // Find the resource with the same type and entry name within the target package.
+    const std::string full_name =
+        base::StringPrintf("%s:%s", target_package->GetPackageName().c_str(), name->c_str());
+    const ResourceId target_resource = target_am->GetResourceId(full_name);
+    if (target_resource == 0U) {
+      continue;
+    }
+
+    resource_mapping.AddMapping(target_resource, Res_value::TYPE_REFERENCE, overlay_resid,
+                                /* rewrite_overlay_reference */ true);
+  }
+
+  return resource_mapping;
+}
+
+void ResourceMapping::FilterOverlayableResources(const AssetManager2* target_am,
+                                                 const LoadedPackage* target_package,
+                                                 const LoadedPackage* overlay_package,
+                                                 const OverlayManifestInfo& overlay_info,
+                                                 const PolicyBitmask& fulfilled_policies) {
+  std::set<ResourceId> remove_ids;
+  for (const auto& target_map : target_map_) {
+    const ResourceId target_resid = target_map.first;
+    Result<Unit> success =
+        CheckOverlayable(*target_package, overlay_info, fulfilled_policies, target_resid);
+    if (success) {
+      continue;
+    }
+
+    // Attempting to overlay a resource that is not allowed to be overlaid is treated as a
+    // warning.
+    Result<std::string> name = utils::ResToTypeEntryName(*target_am, target_resid);
+    if (!name) {
+      name = StringPrintf("0x%08x", target_resid);
+    }
+
+    LOG(WARNING) << "overlay \"" << overlay_package->GetPackageName()
+                 << "\" is not allowed to overlay resource \"" << *name
+                 << "\" in target: " << success.GetErrorMessage();
+
+    remove_ids.insert(target_resid);
+  }
+
+  for (const ResourceId target_resid : remove_ids) {
+    RemoveMapping(target_resid);
+  }
+}
+
+Result<ResourceMapping> ResourceMapping::FromApkAssets(const ApkAssets& target_apk_assets,
+                                                       const ApkAssets& overlay_apk_assets,
+                                                       const OverlayManifestInfo& overlay_info,
+                                                       const PolicyBitmask& fulfilled_policies,
+                                                       bool enforce_overlayable) {
+  AssetManager2 target_asset_manager;
+  if (!target_asset_manager.SetApkAssets({&target_apk_assets}, true /* invalidate_caches */,
+                                         false /* filter_incompatible_configs*/)) {
+    return Error("failed to create target asset manager");
+  }
+
+  AssetManager2 overlay_asset_manager;
+  if (!overlay_asset_manager.SetApkAssets({&overlay_apk_assets}, true /* invalidate_caches */,
+                                          false /* filter_incompatible_configs */)) {
+    return Error("failed to create overlay asset manager");
+  }
+
+  const LoadedArsc* target_arsc = target_apk_assets.GetLoadedArsc();
+  if (target_arsc == nullptr) {
+    return Error("failed to load target resources.arsc");
+  }
+
+  const LoadedArsc* overlay_arsc = overlay_apk_assets.GetLoadedArsc();
+  if (overlay_arsc == nullptr) {
+    return Error("failed to load overlay resources.arsc");
+  }
+
+  const LoadedPackage* target_pkg = GetPackageAtIndex0(*target_arsc);
+  if (target_pkg == nullptr) {
+    return Error("failed to load target package from resources.arsc");
+  }
+
+  const LoadedPackage* overlay_pkg = GetPackageAtIndex0(*overlay_arsc);
+  if (overlay_pkg == nullptr) {
+    return Error("failed to load overlay package from resources.arsc");
+  }
+
+  size_t string_pool_data_length = 0U;
+  size_t string_pool_offset = 0U;
+  std::unique_ptr<uint8_t[]> string_pool_data;
+  Result<ResourceMapping> resource_mapping = {{}};
+  if (overlay_info.resource_mapping != 0U) {
+    // Load the overlay resource mappings from the file specified using android:resourcesMap.
+    auto asset = OpenNonAssetFromResource(overlay_info.resource_mapping, overlay_asset_manager);
+    if (!asset) {
+      return Error("failed opening xml for android:resourcesMap: %s",
+                   asset.GetErrorMessage().c_str());
+    }
+
+    auto parser =
+        XmlParser::Create((*asset)->getBuffer(true /* wordAligned*/), (*asset)->getLength());
+    if (!parser) {
+      return Error("failed opening ResXMLTree");
+    }
+
+    // Copy the xml string pool data before the parse goes out of scope.
+    auto& string_pool = (*parser)->get_strings();
+    string_pool_data_length = string_pool.bytes();
+    string_pool_data.reset(new uint8_t[string_pool_data_length]);
+    memcpy(string_pool_data.get(), string_pool.data(), string_pool_data_length);
+
+    // Offset string indices by the size of the overlay resource table string pool.
+    string_pool_offset = overlay_arsc->GetStringPool()->size();
+
+    resource_mapping = CreateResourceMapping(&target_asset_manager, target_pkg, overlay_pkg,
+                                             string_pool_offset, *(*parser));
+  } else {
+    // If no file is specified using android:resourcesMap, it is assumed that the overlay only
+    // defines resources intended to override target resources of the same type and name.
+    resource_mapping = CreateResourceMappingLegacy(&target_asset_manager, &overlay_asset_manager,
+                                                   target_pkg, overlay_pkg);
+  }
+
+  if (!resource_mapping) {
+    return resource_mapping.GetError();
+  }
+
+  if (enforce_overlayable) {
+    // Filter out resources the overlay is not allowed to override.
+    (*resource_mapping)
+        .FilterOverlayableResources(&target_asset_manager, target_pkg, overlay_pkg, overlay_info,
+                                    fulfilled_policies);
+  }
+
+  resource_mapping->target_package_id_ = target_pkg->GetPackageId();
+  resource_mapping->overlay_package_id_ = overlay_pkg->GetPackageId();
+  resource_mapping->string_pool_offset_ = string_pool_offset;
+  resource_mapping->string_pool_data_ = std::move(string_pool_data);
+  resource_mapping->string_pool_data_length_ = string_pool_data_length;
+  return std::move(*resource_mapping);
+}
+
+OverlayResourceMap ResourceMapping::GetOverlayToTargetMap() const {
+  // An overlay resource can override multiple target resources at once. Rewrite the overlay
+  // resource as the first target resource it overrides.
+  OverlayResourceMap map;
+  for (const auto& mappings : overlay_map_) {
+    map.insert(std::make_pair(mappings.first, mappings.second));
+  }
+  return map;
+}
+
+Result<Unit> ResourceMapping::AddMapping(ResourceId target_resource,
+                                         TargetValue::DataType data_type,
+                                         TargetValue::DataValue data_value,
+                                         bool rewrite_overlay_reference) {
+  if (target_map_.find(target_resource) != target_map_.end()) {
+    return Error(R"(target resource id "0x%08x" mapped to multiple values)", target_resource);
+  }
+
+  // TODO(141485591): Ensure that the overlay type is compatible with the target type. If the
+  // runtime types are not compatible, it could cause runtime crashes when the resource is resolved.
+
+  target_map_.insert(std::make_pair(target_resource, TargetValue{data_type, data_value}));
+
+  if (rewrite_overlay_reference && data_type == Res_value::TYPE_REFERENCE) {
+    overlay_map_.insert(std::make_pair(data_value, target_resource));
+  }
+
+  return Result<Unit>({});
+}
+
+void ResourceMapping::RemoveMapping(ResourceId target_resource) {
+  auto target_iter = target_map_.find(target_resource);
+  if (target_iter == target_map_.end()) {
+    return;
+  }
+
+  const TargetValue value = target_iter->second;
+  target_map_.erase(target_iter);
+
+  // Remove rewriting of overlay resource id to target resource id.
+  if (value.data_type != Res_value::TYPE_REFERENCE) {
+    return;
+  }
+
+  auto overlay_iter = overlay_map_.equal_range(value.data_value);
+  for (auto i = overlay_iter.first; i != overlay_iter.second; ++i) {
+    if (i->second == target_resource) {
+      overlay_map_.erase(i);
+      return;
+    }
+  }
+}
+
+}  // namespace android::idmap2
diff --git a/cmds/idmap2/libidmap2/ResourceUtils.cpp b/cmds/idmap2/libidmap2/ResourceUtils.cpp
index d9c97e19399b..9d3269207c91 100644
--- a/cmds/idmap2/libidmap2/ResourceUtils.cpp
+++ b/cmds/idmap2/libidmap2/ResourceUtils.cpp
@@ -98,6 +98,15 @@ Result<OverlayManifestInfo> ExtractOverlayManifestInfo(const std::string& path,
     info.target_name = *result_str;
   }
 
+  if (auto result_value = overlay_it->GetAttributeValue("resourcesMap")) {
+    if ((*result_value).dataType == Res_value::TYPE_REFERENCE) {
+      info.resource_mapping = (*result_value).data;
+    } else {
+      return Error("android:resourcesMap is not a reference in AndroidManifest.xml of %s",
+                   path.c_str());
+    }
+  }
+
   if (auto result_value = overlay_it->GetAttributeValue("isStatic")) {
     if ((*result_value).dataType >= Res_value::TYPE_FIRST_INT &&
         (*result_value).dataType <= Res_value::TYPE_LAST_INT) {
@@ -116,14 +125,12 @@ Result<OverlayManifestInfo> ExtractOverlayManifestInfo(const std::string& path,
     }
   }
 
-  iter = tag->find("requiredSystemPropertyName");
-  if (iter != tag->end()) {
-    info.requiredSystemPropertyName = iter->second;
+  if (auto result_str = overlay_it->GetAttributeStringValue("requiredSystemPropertyName")) {
+    info.requiredSystemPropertyName = *result_str;
   }
 
-  iter = tag->find("requiredSystemPropertyValue");
-  if (iter != tag->end()) {
-    info.requiredSystemPropertyValue = iter->second;
+   if (auto result_str = overlay_it->GetAttributeStringValue("requiredSystemPropertyValue")) {
+    info.requiredSystemPropertyValue = *result_str;
   }
 
   return info;
diff --git a/cmds/idmap2/tests/BinaryStreamVisitorTests.cpp b/cmds/idmap2/tests/BinaryStreamVisitorTests.cpp
index 9348ab721493..43fdc9a78186 100644
--- a/cmds/idmap2/tests/BinaryStreamVisitorTests.cpp
+++ b/cmds/idmap2/tests/BinaryStreamVisitorTests.cpp
@@ -75,9 +75,8 @@ TEST(BinaryStreamVisitorTests, CreateIdmapFromApkAssetsInteropWithLoadedIdmap) {
   std::unique_ptr<const ApkAssets> overlay_apk = ApkAssets::Load(overlay_apk_path);
   ASSERT_THAT(overlay_apk, NotNull());
 
-  const auto idmap =
-      Idmap::FromApkAssets(target_apk_path, *target_apk, overlay_apk_path, *overlay_apk,
-                           PolicyFlags::POLICY_PUBLIC, /* enforce_overlayable */ true);
+  const auto idmap = Idmap::FromApkAssets(*target_apk, *overlay_apk, PolicyFlags::POLICY_PUBLIC,
+                                          /* enforce_overlayable */ true);
   ASSERT_TRUE(idmap);
 
   std::stringstream stream;
diff --git a/cmds/idmap2/tests/IdmapTests.cpp b/cmds/idmap2/tests/IdmapTests.cpp
index 0f47f1e77d7b..47e5b17f4a98 100644
--- a/cmds/idmap2/tests/IdmapTests.cpp
+++ b/cmds/idmap2/tests/IdmapTests.cpp
@@ -179,8 +179,7 @@ void CreateIdmap(const StringPiece& target_apk_path, const StringPiece& overlay_
   ASSERT_THAT(overlay_apk, NotNull());
 
   auto result =
-      Idmap::FromApkAssets(target_apk_path.to_string(), *target_apk, overlay_apk_path.to_string(),
-                           *overlay_apk, fulfilled_policies, enforce_overlayable);
+      Idmap::FromApkAssets(*target_apk, *overlay_apk, fulfilled_policies, enforce_overlayable);
   *out_idmap = result ? std::move(*result) : nullptr;
 }
 
@@ -195,7 +194,7 @@ TEST(IdmapTests, CreateIdmapFromApkAssets) {
   ASSERT_EQ(idmap->GetHeader()->GetMagic(), 0x504d4449U);
   ASSERT_EQ(idmap->GetHeader()->GetVersion(), 0x01U);
   ASSERT_EQ(idmap->GetHeader()->GetTargetCrc(), 0x76a20829);
-  ASSERT_EQ(idmap->GetHeader()->GetOverlayCrc(), 0x8635c2ed);
+  ASSERT_EQ(idmap->GetHeader()->GetOverlayCrc(), 0xc054fb26);
   ASSERT_EQ(idmap->GetHeader()->GetTargetPath().to_string(), target_apk_path);
   ASSERT_EQ(idmap->GetHeader()->GetOverlayPath(), overlay_apk_path);
   ASSERT_EQ(idmap->GetHeader()->GetOverlayPath(), overlay_apk_path);
@@ -480,9 +479,8 @@ TEST(IdmapTests, FailToCreateIdmapFromApkAssetsIfPathTooLong) {
   std::unique_ptr<const ApkAssets> overlay_apk = ApkAssets::Load(overlay_apk_path);
   ASSERT_THAT(overlay_apk, NotNull());
 
-  const auto result =
-      Idmap::FromApkAssets(target_apk_path, *target_apk, overlay_apk_path, *overlay_apk,
-                           PolicyFlags::POLICY_PUBLIC, /* enforce_overlayable */ true);
+  const auto result = Idmap::FromApkAssets(*target_apk, *overlay_apk, PolicyFlags::POLICY_PUBLIC,
+                                           /* enforce_overlayable */ true);
   ASSERT_FALSE(result);
 }
 
@@ -497,8 +495,7 @@ TEST(IdmapTests, IdmapHeaderIsUpToDate) {
   std::unique_ptr<const ApkAssets> overlay_apk = ApkAssets::Load(overlay_apk_path);
   ASSERT_THAT(overlay_apk, NotNull());
 
-  auto result = Idmap::FromApkAssets(target_apk_path, *target_apk, overlay_apk_path, *overlay_apk,
-                                     PolicyFlags::POLICY_PUBLIC,
+  auto result = Idmap::FromApkAssets(*target_apk, *overlay_apk, PolicyFlags::POLICY_PUBLIC,
                                      /* enforce_overlayable */ true);
   ASSERT_TRUE(result);
   const auto idmap = std::move(*result);
diff --git a/cmds/idmap2/tests/PrettyPrintVisitorTests.cpp b/cmds/idmap2/tests/PrettyPrintVisitorTests.cpp
index c41250457678..1d34e42e188d 100644
--- a/cmds/idmap2/tests/PrettyPrintVisitorTests.cpp
+++ b/cmds/idmap2/tests/PrettyPrintVisitorTests.cpp
@@ -43,9 +43,8 @@ TEST(PrettyPrintVisitorTests, CreatePrettyPrintVisitor) {
   std::unique_ptr<const ApkAssets> overlay_apk = ApkAssets::Load(overlay_apk_path);
   ASSERT_THAT(overlay_apk, NotNull());
 
-  const auto idmap =
-      Idmap::FromApkAssets(target_apk_path, *target_apk, overlay_apk_path, *overlay_apk,
-                           PolicyFlags::POLICY_PUBLIC, /* enforce_overlayable */ true);
+  const auto idmap = Idmap::FromApkAssets(*target_apk, *overlay_apk, PolicyFlags::POLICY_PUBLIC,
+                                          /* enforce_overlayable */ true);
   ASSERT_TRUE(idmap);
 
   std::stringstream stream;
diff --git a/cmds/idmap2/tests/RawPrintVisitorTests.cpp b/cmds/idmap2/tests/RawPrintVisitorTests.cpp
index 26951763cd66..c243d745e568 100644
--- a/cmds/idmap2/tests/RawPrintVisitorTests.cpp
+++ b/cmds/idmap2/tests/RawPrintVisitorTests.cpp
@@ -38,9 +38,8 @@ TEST(RawPrintVisitorTests, CreateRawPrintVisitor) {
   std::unique_ptr<const ApkAssets> overlay_apk = ApkAssets::Load(overlay_apk_path);
   ASSERT_THAT(overlay_apk, NotNull());
 
-  const auto idmap =
-      Idmap::FromApkAssets(target_apk_path, *target_apk, overlay_apk_path, *overlay_apk,
-                           PolicyFlags::POLICY_PUBLIC, /* enforce_overlayable */ true);
+  const auto idmap = Idmap::FromApkAssets(*target_apk, *overlay_apk, PolicyFlags::POLICY_PUBLIC,
+                                          /* enforce_overlayable */ true);
   ASSERT_TRUE(idmap);
 
   std::stringstream stream;
@@ -50,7 +49,7 @@ TEST(RawPrintVisitorTests, CreateRawPrintVisitor) {
   ASSERT_NE(stream.str().find("00000000: 504d4449  magic\n"), std::string::npos);
   ASSERT_NE(stream.str().find("00000004: 00000001  version\n"), std::string::npos);
   ASSERT_NE(stream.str().find("00000008: 76a20829  target crc\n"), std::string::npos);
-  ASSERT_NE(stream.str().find("0000000c: 8635c2ed  overlay crc\n"), std::string::npos);
+  ASSERT_NE(stream.str().find("0000000c: c054fb26  overlay crc\n"), std::string::npos);
   ASSERT_NE(stream.str().find("0000021c: 00000000  0x7f010000 -> 0x7f010000 integer/int1\n"),
             std::string::npos);
 }
diff --git a/cmds/idmap2/tests/ResourceMappingTests.cpp b/cmds/idmap2/tests/ResourceMappingTests.cpp
new file mode 100644
index 000000000000..1ef41de4410d
--- /dev/null
+++ b/cmds/idmap2/tests/ResourceMappingTests.cpp
@@ -0,0 +1,322 @@
+/*
+ * Copyright (C) 2018 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.
+ */
+
+#include <cstdio>  // fclose
+#include <fstream>
+#include <memory>
+#include <sstream>
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "TestHelpers.h"
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include "idmap2/ResourceMapping.h"
+
+using android::idmap2::utils::ExtractOverlayManifestInfo;
+
+namespace android::idmap2 {
+
+#define ASSERT_RESULT(r)                             \
+  do {                                               \
+    auto result = r;                                 \
+    ASSERT_TRUE(result) << result.GetErrorMessage(); \
+  } while (0)
+
+Result<ResourceMapping> TestGetResourceMapping(const android::StringPiece& local_target_apk_path,
+                                               const android::StringPiece& local_overlay_apk_path,
+                                               const OverlayManifestInfo& overlay_info,
+                                               const PolicyBitmask& fulfilled_policies,
+                                               bool enforce_overlayable) {
+  const std::string target_apk_path(GetTestDataPath() + local_target_apk_path.data());
+  std::unique_ptr<const ApkAssets> target_apk = ApkAssets::Load(target_apk_path);
+  if (!target_apk) {
+    return Error(R"(Failed to load target apk "%s")", target_apk_path.data());
+  }
+
+  const std::string overlay_apk_path(GetTestDataPath() + local_overlay_apk_path.data());
+  std::unique_ptr<const ApkAssets> overlay_apk = ApkAssets::Load(overlay_apk_path);
+  if (!overlay_apk) {
+    return Error(R"(Failed to load overlay apk "%s")", overlay_apk_path.data());
+  }
+
+  return ResourceMapping::FromApkAssets(*target_apk, *overlay_apk, overlay_info, fulfilled_policies,
+                                        enforce_overlayable);
+}
+
+Result<ResourceMapping> TestGetResourceMapping(const android::StringPiece& local_target_apk_path,
+                                               const android::StringPiece& local_overlay_apk_path,
+                                               const PolicyBitmask& fulfilled_policies,
+                                               bool enforce_overlayable) {
+  auto overlay_info = ExtractOverlayManifestInfo(GetTestDataPath() + local_overlay_apk_path.data());
+  if (!overlay_info) {
+    return overlay_info.GetError();
+  }
+  return TestGetResourceMapping(local_target_apk_path, local_overlay_apk_path, *overlay_info,
+                                fulfilled_policies, enforce_overlayable);
+}
+
+Result<Unit> MappingExists(const ResourceMapping& mapping, const ResourceId& target_resource,
+                           const uint8_t type, const uint32_t value, bool rewrite) {
+  auto target_map = mapping.GetTargetToOverlayMap();
+  auto entry_map = target_map.find(target_resource);
+  if (entry_map == target_map.end()) {
+    return Error("Failed to find mapping for target resource");
+  }
+
+  if (entry_map->second.data_type != type) {
+    return Error(R"(Expected type: "0x%02x" Actual type: "0x%02x")", type,
+                 entry_map->second.data_type);
+  }
+
+  if (entry_map->second.data_value != value) {
+    return Error(R"(Expected value: "0x%08x" Actual value: "0x%08x")", type,
+                 entry_map->second.data_value);
+  }
+
+  auto overlay_map = mapping.GetOverlayToTargetMap();
+  auto overlay_iter = overlay_map.find(entry_map->second.data_value);
+  if ((overlay_iter != overlay_map.end()) != rewrite) {
+    return Error(R"(Expected rewriting: "%s")", rewrite ? "true" : "false");
+  }
+
+  return Result<Unit>({});
+}
+
+TEST(ResourceMappingTests, ResourcesFromApkAssetsLegacy) {
+  OverlayManifestInfo info{};
+  info.target_package = "test.target";
+  info.target_name = "TestResources";
+  info.resource_mapping = 0U;  // no xml
+  auto resources = TestGetResourceMapping("/target/target.apk", "/overlay/overlay.apk", info,
+                                          PolicyFlags::POLICY_PUBLIC,
+                                          /* enforce_overlayable */ false);
+
+  ASSERT_TRUE(resources) << resources.GetErrorMessage();
+  auto& res = *resources;
+  ASSERT_EQ(res.GetTargetToOverlayMap().size(), 4U);
+  ASSERT_RESULT(MappingExists(res, 0x7f010000, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f010000,
+                              true /* rewrite */));  // integer/int1
+  ASSERT_RESULT(MappingExists(res, 0x7f02000c, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f020000,
+                              true /* rewrite */));  // string/str1
+  ASSERT_RESULT(MappingExists(res, 0x7f02000e, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f020001,
+                              true /* rewrite */));  // string/str3
+  ASSERT_RESULT(MappingExists(res, 0x7f02000f, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f020002,
+                              true /* rewrite */));  // string/str4
+}
+
+TEST(ResourceMappingTests, ResourcesFromApkAssetsNonMatchingNames) {
+  OverlayManifestInfo info{};
+  info.target_package = "test.target";
+  info.target_name = "TestResources";
+  info.resource_mapping = 0x7f030003;  // xml/overlays_swap
+  auto resources = TestGetResourceMapping("/target/target.apk", "/overlay/overlay.apk", info,
+                                          PolicyFlags::POLICY_PUBLIC,
+                                          /* enforce_overlayable */ false);
+
+  ASSERT_TRUE(resources) << resources.GetErrorMessage();
+  auto& res = *resources;
+  ASSERT_EQ(res.GetTargetToOverlayMap().size(), 3U);
+  ASSERT_RESULT(MappingExists(res, 0x7f02000c, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f020002,
+                              true /* rewrite */));  // string/str1 -> string/str4
+  ASSERT_RESULT(MappingExists(res, 0x7f02000e, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f020000,
+                              true /* rewrite */));  // string/str3 -> string/str1
+  ASSERT_RESULT(MappingExists(res, 0x7f02000f, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f020001,
+                              true /* rewrite */));  // string/str4 -> string/str3
+}
+
+TEST(ResourceMappingTests, DoNotRewriteNonResourceMapping) {
+  OverlayManifestInfo info{};
+  info.target_package = "test.target";
+  info.target_name = "TestResources";
+  info.resource_mapping = 0x7f030001;  // xml/overlays_different_packages
+  auto resources = TestGetResourceMapping("/target/target.apk", "/overlay/overlay.apk", info,
+                                          PolicyFlags::POLICY_PUBLIC,
+                                          /* enforce_overlayable */ false);
+
+  ASSERT_TRUE(resources) << resources.GetErrorMessage();
+  auto& res = *resources;
+  ASSERT_EQ(res.GetTargetToOverlayMap().size(), 2U);
+  ASSERT_EQ(res.GetOverlayToTargetMap().size(), 1U);
+  ASSERT_RESULT(MappingExists(res, 0x7f02000c, 0x01 /* Res_value::TYPE_REFERENCE */, 0x0104000a,
+                              false /* rewrite */));  // string/str1 -> android:string/ok
+  ASSERT_RESULT(MappingExists(res, 0x7f02000e, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f020001,
+                              true /* rewrite */));  // string/str3 -> string/str4
+}
+
+TEST(ResourceMappingTests, InlineResources) {
+  OverlayManifestInfo info{};
+  info.target_package = "test.target";
+  info.target_name = "TestResources";
+  info.resource_mapping = 0x7f030002;  // xml/overlays_inline
+  auto resources = TestGetResourceMapping("/target/target.apk", "/overlay/overlay.apk", info,
+                                          PolicyFlags::POLICY_PUBLIC,
+                                          /* enforce_overlayable */ false);
+
+  constexpr size_t overlay_string_pool_size = 8U;
+  ASSERT_TRUE(resources) << resources.GetErrorMessage();
+  auto& res = *resources;
+  ASSERT_EQ(res.GetTargetToOverlayMap().size(), 2U);
+  ASSERT_EQ(res.GetOverlayToTargetMap().size(), 0U);
+  ASSERT_RESULT(MappingExists(res, 0x7f02000c, 0x03 /* Res_value::TYPE_STRING */,
+                              overlay_string_pool_size + 0U,
+                              false /* rewrite */));  // string/str1 -> "Hello World"
+  ASSERT_RESULT(MappingExists(res, 0x7f010000, 0x10 /* Res_value::TYPE_INT_DEC */, 73U,
+                              false /* rewrite */));  // string/str1 -> "Hello World"
+}
+
+TEST(ResourceMappingTests, CreateIdmapFromApkAssetsPolicySystemPublic) {
+  auto resources =
+      TestGetResourceMapping("/target/target.apk", "/system-overlay/system-overlay.apk",
+                             PolicyFlags::POLICY_SYSTEM_PARTITION | PolicyFlags::POLICY_PUBLIC,
+                             /* enforce_overlayable */ true);
+
+  ASSERT_TRUE(resources) << resources.GetErrorMessage();
+  auto& res = *resources;
+  ASSERT_EQ(res.GetTargetToOverlayMap().size(), 3U);
+  ASSERT_RESULT(MappingExists(res, 0x7f020008, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f010000,
+                              true /* rewrite */));  // string/policy_public
+  ASSERT_RESULT(MappingExists(res, 0x7f02000a, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f010001,
+                              true /* rewrite */));  // string/policy_system
+  ASSERT_RESULT(MappingExists(res, 0x7f02000b, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f010002,
+                              true /* rewrite */));  // string/policy_system_vendor
+}
+
+// Resources that are not declared as overlayable and resources that a protected by policies the
+// overlay does not fulfill must not map to overlay resources.
+TEST(ResourceMappingTests, CreateIdmapFromApkAssetsPolicySystemPublicInvalid) {
+  auto resources = TestGetResourceMapping(
+      "/target/target.apk", "/system-overlay-invalid/system-overlay-invalid.apk",
+      PolicyFlags::POLICY_SYSTEM_PARTITION | PolicyFlags::POLICY_PUBLIC,
+      /* enforce_overlayable */ true);
+
+  ASSERT_TRUE(resources) << resources.GetErrorMessage();
+  auto& res = *resources;
+  ASSERT_EQ(res.GetTargetToOverlayMap().size(), 3U);
+  ASSERT_RESULT(MappingExists(res, 0x7f020008, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f010005,
+                              true /* rewrite */));  // string/policy_public
+  ASSERT_RESULT(MappingExists(res, 0x7f02000a, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f010007,
+                              true /* rewrite */));  // string/policy_system
+  ASSERT_RESULT(MappingExists(res, 0x7f02000b, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f010008,
+                              true /* rewrite */));  // string/policy_system_vendor
+}
+
+// Resources that are not declared as overlayable and resources that a protected by policies the
+// overlay does not fulfilled can map to overlay resources when overlayable enforcement is turned
+// off.
+TEST(ResourceMappingTests, ResourcesFromApkAssetsPolicySystemPublicInvalidIgnoreOverlayable) {
+  auto resources = TestGetResourceMapping(
+      "/target/target.apk", "/system-overlay-invalid/system-overlay-invalid.apk",
+      PolicyFlags::POLICY_SYSTEM_PARTITION | PolicyFlags::POLICY_PUBLIC,
+      /* enforce_overlayable */ false);
+
+  ASSERT_TRUE(resources) << resources.GetErrorMessage();
+  auto& res = *resources;
+  ASSERT_EQ(res.GetTargetToOverlayMap().size(), 9U);
+  ASSERT_RESULT(MappingExists(res, 0x7f020003, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f010000,
+                              true /* rewrite */));  // string/not_overlayable
+  ASSERT_RESULT(MappingExists(res, 0x7f020004, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f010001,
+                              true /* rewrite */));  // string/other
+  ASSERT_RESULT(MappingExists(res, 0x7f020005, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f010002,
+                              true /* rewrite */));  // string/policy_odm
+  ASSERT_RESULT(MappingExists(res, 0x7f020006, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f010003,
+                              true /* rewrite */));  // string/policy_oem
+  ASSERT_RESULT(MappingExists(res, 0x7f020007, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f010004,
+                              true /* rewrite */));  // string/policy_product
+  ASSERT_RESULT(MappingExists(res, 0x7f020008, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f010005,
+                              true /* rewrite */));  // string/policy_public
+  ASSERT_RESULT(MappingExists(res, 0x7f020009, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f010006,
+                              true /* rewrite */));  // string/policy_signature
+  ASSERT_RESULT(MappingExists(res, 0x7f02000a, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f010007,
+                              true /* rewrite */));  // string/policy_system
+  ASSERT_RESULT(MappingExists(res, 0x7f02000b, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f010008,
+                              true /* rewrite */));  // string/policy_system_vendor
+}
+
+// Overlays that do not target an <overlayable> tag can overlay resources defined within any
+// <overlayable> tag.
+TEST(ResourceMappingTests, ResourcesFromApkAssetsNoDefinedOverlayableAndNoTargetName) {
+  auto resources = TestGetResourceMapping("/target/target.apk", "/overlay/overlay-no-name.apk",
+                                          PolicyFlags::POLICY_PUBLIC,
+                                          /* enforce_overlayable */ false);
+
+  ASSERT_TRUE(resources) << resources.GetErrorMessage();
+  auto& res = *resources;
+  ASSERT_EQ(res.GetTargetToOverlayMap().size(), 4U);
+  ASSERT_RESULT(MappingExists(res, 0x7f010000, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f010000,
+                              true /* rewrite */));  // integer/int1
+  ASSERT_RESULT(MappingExists(res, 0x7f02000c, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f020000,
+                              true /* rewrite */));  // string/str1
+  ASSERT_RESULT(MappingExists(res, 0x7f02000e, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f020001,
+                              true /* rewrite */));  // string/str3
+  ASSERT_RESULT(MappingExists(res, 0x7f02000f, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f020002,
+                              true /* rewrite */));  // string/str4
+}
+
+// Overlays that are neither pre-installed nor signed with the same signature as the target cannot
+// overlay packages that have not defined overlayable resources.
+TEST(ResourceMappingTests, ResourcesFromApkAssetsDefaultPoliciesPublicFail) {
+  auto resources =
+      TestGetResourceMapping("/target/target-no-overlayable.apk", "/overlay/overlay-no-name.apk",
+                             PolicyFlags::POLICY_PUBLIC,
+                             /* enforce_overlayable */ true);
+
+  ASSERT_TRUE(resources) << resources.GetErrorMessage();
+  ASSERT_EQ(resources->GetTargetToOverlayMap().size(), 0U);
+}
+
+// Overlays that are pre-installed or are signed with the same signature as the target can overlay
+// packages that have not defined overlayable resources.
+TEST(ResourceMappingTests, ResourcesFromApkAssetsDefaultPolicies) {
+  auto CheckEntries = [&](const PolicyBitmask& fulfilled_policies) -> void {
+    auto resources = TestGetResourceMapping("/target/target-no-overlayable.apk",
+                                            "/system-overlay-invalid/system-overlay-invalid.apk",
+                                            fulfilled_policies,
+                                            /* enforce_overlayable */ true);
+
+    ASSERT_TRUE(resources) << resources.GetErrorMessage();
+    auto& res = *resources;
+    ASSERT_EQ(resources->GetTargetToOverlayMap().size(), 9U);
+    ASSERT_RESULT(MappingExists(res, 0x7f020003, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f010000,
+                                true /* rewrite */));  // string/not_overlayable
+    ASSERT_RESULT(MappingExists(res, 0x7f020004, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f010001,
+                                true /* rewrite */));  // string/other
+    ASSERT_RESULT(MappingExists(res, 0x7f020005, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f010002,
+                                true /* rewrite */));  // string/policy_odm
+    ASSERT_RESULT(MappingExists(res, 0x7f020006, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f010003,
+                                true /* rewrite */));  // string/policy_oem
+    ASSERT_RESULT(MappingExists(res, 0x7f020007, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f010004,
+                                true /* rewrite */));  // string/policy_product
+    ASSERT_RESULT(MappingExists(res, 0x7f020008, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f010005,
+                                true /* rewrite */));  // string/policy_public
+    ASSERT_RESULT(MappingExists(res, 0x7f020009, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f010006,
+                                true /* rewrite */));  // string/policy_signature
+    ASSERT_RESULT(MappingExists(res, 0x7f02000a, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f010007,
+                                true /* rewrite */));  // string/policy_system
+    ASSERT_RESULT(MappingExists(res, 0x7f02000b, 0x01 /* Res_value::TYPE_REFERENCE */, 0x7f010008,
+                                true /* rewrite */));  // string/policy_system_vendor
+  };
+
+  CheckEntries(PolicyFlags::POLICY_SIGNATURE);
+  CheckEntries(PolicyFlags::POLICY_PRODUCT_PARTITION);
+  CheckEntries(PolicyFlags::POLICY_SYSTEM_PARTITION);
+  CheckEntries(PolicyFlags::POLICY_VENDOR_PARTITION);
+  CheckEntries(PolicyFlags::POLICY_ODM_PARTITION);
+  CheckEntries(PolicyFlags::POLICY_OEM_PARTITION);
+}
+
+}  // namespace android::idmap2
diff --git a/cmds/idmap2/tests/data/overlay/AndroidManifest.xml b/cmds/idmap2/tests/data/overlay/AndroidManifest.xml
index 619bb6ce0f25..cf3691c3b3cf 100644
--- a/cmds/idmap2/tests/data/overlay/AndroidManifest.xml
+++ b/cmds/idmap2/tests/data/overlay/AndroidManifest.xml
@@ -16,8 +16,11 @@
 <manifest
     xmlns:android="http://schemas.android.com/apk/res/android"
     package="test.overlay">
+
     <application android:hasCode="false"/>
+
     <overlay
         android:targetPackage="test.target"
-        android:targetName="TestResources"/>
+        android:targetName="TestResources"
+        android:resourcesMap="@xml/overlays"/>
 </manifest>
diff --git a/cmds/idmap2/tests/data/overlay/build b/cmds/idmap2/tests/data/overlay/build
index 68b9f507a11d..b921b0d3d3ad 100755
--- a/cmds/idmap2/tests/data/overlay/build
+++ b/cmds/idmap2/tests/data/overlay/build
@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-FRAMEWORK_RES_APK=${ANDROID_BUILD_TOP}/prebuilts/sdk/current/public/android.jar
+FRAMEWORK_RES_APK=${ANDROID_PRODUCT_OUT}/system/framework/framework-res.apk
 
 aapt2 compile --dir res -o compiled.flata
 
diff --git a/cmds/idmap2/tests/data/overlay/overlay-no-name-static.apk b/cmds/idmap2/tests/data/overlay/overlay-no-name-static.apk
index 18ee43dc57a4..7c25985e5a61 100644
--- a/cmds/idmap2/tests/data/overlay/overlay-no-name-static.apk
+++ b/cmds/idmap2/tests/data/overlay/overlay-no-name-static.apk
diff --git a/cmds/idmap2/tests/data/overlay/overlay-no-name.apk b/cmds/idmap2/tests/data/overlay/overlay-no-name.apk
index 642519008b15..c75f3e1dbddf 100644
--- a/cmds/idmap2/tests/data/overlay/overlay-no-name.apk
+++ b/cmds/idmap2/tests/data/overlay/overlay-no-name.apk
diff --git a/cmds/idmap2/tests/data/overlay/overlay-static-1.apk b/cmds/idmap2/tests/data/overlay/overlay-static-1.apk
index 642ab90d00ae..5b8a6e4a90ed 100644
--- a/cmds/idmap2/tests/data/overlay/overlay-static-1.apk
+++ b/cmds/idmap2/tests/data/overlay/overlay-static-1.apk
diff --git a/cmds/idmap2/tests/data/overlay/overlay-static-2.apk b/cmds/idmap2/tests/data/overlay/overlay-static-2.apk
index 2ec56020c4aa..698a1fd6e702 100644
--- a/cmds/idmap2/tests/data/overlay/overlay-static-2.apk
+++ b/cmds/idmap2/tests/data/overlay/overlay-static-2.apk
diff --git a/cmds/idmap2/tests/data/overlay/overlay.apk b/cmds/idmap2/tests/data/overlay/overlay.apk
index 5842da4f432e..1db303ff05b5 100644
--- a/cmds/idmap2/tests/data/overlay/overlay.apk
+++ b/cmds/idmap2/tests/data/overlay/overlay.apk
diff --git a/cmds/idmap2/tests/data/overlay/res/xml/overlays.xml b/cmds/idmap2/tests/data/overlay/res/xml/overlays.xml
new file mode 100644
index 000000000000..edd33f7dc90d
--- /dev/null
+++ b/cmds/idmap2/tests/data/overlay/res/xml/overlays.xml
@@ -0,0 +1,23 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- 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.
+-->
+<overlay>
+    <item target="string/str1" value="@string/str1"/>
+    <item target="string/str3" value="@string/str3" />
+    <item target="string/str4" value="@string/str4" />
+    <item target="integer/int1" value="@integer/int1" />
+    <item target="integer/not_in_target" value="@integer/not_in_target" />
+</overlay>
+
diff --git a/cmds/idmap2/tests/data/overlay/res/xml/overlays_different_package.xml b/cmds/idmap2/tests/data/overlay/res/xml/overlays_different_package.xml
new file mode 100644
index 000000000000..aa7fefaa305e
--- /dev/null
+++ b/cmds/idmap2/tests/data/overlay/res/xml/overlays_different_package.xml
@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- 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.
+-->
+<overlay>
+    <item target="string/str1" value="@android:string/ok"/>
+    <item target="string/str3" value="@string/str3" />
+</overlay>
+
diff --git a/cmds/idmap2/tests/data/overlay/res/xml/overlays_inline.xml b/cmds/idmap2/tests/data/overlay/res/xml/overlays_inline.xml
new file mode 100644
index 000000000000..e12b823ff50d
--- /dev/null
+++ b/cmds/idmap2/tests/data/overlay/res/xml/overlays_inline.xml
@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- 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.
+-->
+<overlay>
+    <item target="string/str1" value="Hello World"/>
+    <item target="integer/int1" value="73" />
+</overlay>
+
diff --git a/cmds/idmap2/tests/data/overlay/res/xml/overlays_swap.xml b/cmds/idmap2/tests/data/overlay/res/xml/overlays_swap.xml
new file mode 100644
index 000000000000..5728e672d94a
--- /dev/null
+++ b/cmds/idmap2/tests/data/overlay/res/xml/overlays_swap.xml
@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- 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.
+-->
+<overlay>
+    <item target="string/str1" value="@string/str4"/>
+    <item target="string/str3" value="@string/str1" />
+    <item target="string/str4" value="@string/str3" />
+    <item target="integer/int_not_in_target" value="@integer/int1" />
+</overlay>