diff --git a/libs/androidfw/ApkAssets.cpp b/libs/androidfw/ApkAssets.cpp
index ca5981c0..9c743ce 100755
--- a/libs/androidfw/ApkAssets.cpp
+++ b/libs/androidfw/ApkAssets.cpp
@@ -83,8 +83,16 @@
     return {};
   }
 
+  std::unique_ptr<AssetsProvider> overlay_assets;
   const std::string overlay_path(loaded_idmap->OverlayApkPath());
-  auto overlay_assets = ZipAssetsProvider::Create(overlay_path);
+  if (IsFabricatedOverlay(overlay_path)) {
+    // Fabricated overlays do not contain resource definitions. All of the overlay resource values
+    // are defined inline in the idmap.
+    overlay_assets = EmptyAssetsProvider::Create();
+  } else {
+    // The overlay should be an APK.
+    overlay_assets = ZipAssetsProvider::Create(overlay_path);
+  }
   if (overlay_assets == nullptr) {
     return {};
   }
diff --git a/libs/androidfw/AssetManager2.cpp b/libs/androidfw/AssetManager2.cpp
index 03ab62f..36bde5c 100644
--- a/libs/androidfw/AssetManager2.cpp
+++ b/libs/androidfw/AssetManager2.cpp
@@ -102,9 +102,8 @@
   memset(&configuration_, 0, sizeof(configuration_));
 }
 
-bool AssetManager2::SetApkAssets(const std::vector<const ApkAssets*>& apk_assets,
-                                 bool invalidate_caches) {
-  apk_assets_ = apk_assets;
+bool AssetManager2::SetApkAssets(std::vector<const ApkAssets*> apk_assets, bool invalidate_caches) {
+  apk_assets_ = std::move(apk_assets);
   BuildDynamicRefTable();
   RebuildFilterList();
   if (invalidate_caches) {
@@ -137,6 +136,36 @@
   // 0x01 is reserved for the android package.
   int next_package_id = 0x02;
   for (const ApkAssets* apk_assets : sorted_apk_assets) {
+    std::shared_ptr<OverlayDynamicRefTable> overlay_ref_table;
+    if (auto loaded_idmap = apk_assets->GetLoadedIdmap(); loaded_idmap != nullptr) {
+      // The target package must precede the overlay package in the apk assets paths in order
+      // to take effect.
+      auto iter = apk_assets_package_ids.find(std::string(loaded_idmap->TargetApkPath()));
+      if (iter == apk_assets_package_ids.end()) {
+         LOG(INFO) << "failed to find target package for overlay "
+                   << loaded_idmap->OverlayApkPath();
+      } else {
+        uint8_t target_package_id = iter->second;
+
+        // Create a special dynamic reference table for the overlay to rewrite references to
+        // overlay resources as references to the target resources they overlay.
+        overlay_ref_table = std::make_shared<OverlayDynamicRefTable>(
+            loaded_idmap->GetOverlayDynamicRefTable(target_package_id));
+
+        // Add the overlay resource map to the target package's set of overlays.
+        const uint8_t target_idx = package_ids_[target_package_id];
+        CHECK(target_idx != 0xff) << "overlay target '" << loaded_idmap->TargetApkPath()
+                                  << "'added to apk_assets_package_ids but does not have an"
+                                  << " assigned package group";
+
+        PackageGroup& target_package_group = package_groups_[target_idx];
+        target_package_group.overlays_.push_back(
+            ConfiguredOverlay{loaded_idmap->GetTargetResourcesMap(target_package_id,
+                                                                  overlay_ref_table.get()),
+                              apk_assets_cookies[apk_assets]});
+      }
+    }
+
     const LoadedArsc* loaded_arsc = apk_assets->GetLoadedArsc();
     for (const std::unique_ptr<const LoadedPackage>& package : loaded_arsc->GetPackages()) {
       // Get the package ID or assign one if a shared library.
@@ -147,50 +176,25 @@
         package_id = package->GetPackageId();
       }
 
-      // Add the mapping for package ID to index if not present.
       uint8_t idx = package_ids_[package_id];
       if (idx == 0xff) {
+        // Add the mapping for package ID to index if not present.
         package_ids_[package_id] = idx = static_cast<uint8_t>(package_groups_.size());
-        package_groups_.push_back({});
+        PackageGroup& new_group = package_groups_.emplace_back();
 
-        if (apk_assets->IsOverlay()) {
-          // The target package must precede the overlay package in the apk assets paths in order
-          // to take effect.
-          const auto& loaded_idmap = apk_assets->GetLoadedIdmap();
-          auto target_package_iter = apk_assets_package_ids.find(
-              std::string(loaded_idmap->TargetApkPath()));
-          if (target_package_iter == apk_assets_package_ids.end()) {
-             LOG(INFO) << "failed to find target package for overlay "
-                       << loaded_idmap->OverlayApkPath();
-          } else {
-            const uint8_t target_package_id = target_package_iter->second;
-            const uint8_t target_idx = package_ids_[target_package_id];
-            CHECK(target_idx != 0xff) << "overlay added to apk_assets_package_ids but does not"
-                                      << " have an assigned package group";
-
-            PackageGroup& target_package_group = package_groups_[target_idx];
-
-            // Create a special dynamic reference table for the overlay to rewrite references to
-            // overlay resources as references to the target resources they overlay.
-            auto overlay_table = std::make_shared<OverlayDynamicRefTable>(
-                loaded_idmap->GetOverlayDynamicRefTable(target_package_id));
-            package_groups_.back().dynamic_ref_table = overlay_table;
-
-            // Add the overlay resource map to the target package's set of overlays.
-            target_package_group.overlays_.push_back(
-                ConfiguredOverlay{loaded_idmap->GetTargetResourcesMap(target_package_id,
-                                                                      overlay_table.get()),
-                                  apk_assets_cookies[apk_assets]});
-          }
+        if (overlay_ref_table != nullptr) {
+          // If this package is from an overlay, use a dynamic reference table that can rewrite
+          // overlay resource ids to their corresponding target resource ids.
+          new_group.dynamic_ref_table = overlay_ref_table;
         }
 
-        DynamicRefTable* ref_table = package_groups_.back().dynamic_ref_table.get();
+        DynamicRefTable* ref_table = new_group.dynamic_ref_table.get();
         ref_table->mAssignedPackageId = package_id;
         ref_table->mAppAsLib = package->IsDynamic() && package->GetPackageId() == 0x7f;
       }
-      PackageGroup* package_group = &package_groups_[idx];
 
       // Add the package and to the set of packages with the same ID.
+      PackageGroup* package_group = &package_groups_[idx];
       package_group->packages_.push_back(ConfiguredPackage{package.get(), {}});
       package_group->cookies_.push_back(apk_assets_cookies[apk_assets]);
 
@@ -578,7 +582,7 @@
 
   const PackageGroup& package_group = package_groups_[package_idx];
   auto result = FindEntryInternal(package_group, type_idx, entry_idx, *desired_config,
-                                 stop_at_first_match, ignore_configuration);
+                                  stop_at_first_match, ignore_configuration);
   if (UNLIKELY(!result.has_value())) {
     return base::unexpected(result.error());
   }
diff --git a/libs/androidfw/AssetsProvider.cpp b/libs/androidfw/AssetsProvider.cpp
index 23cacf8..f3c48f7 100644
--- a/libs/androidfw/AssetsProvider.cpp
+++ b/libs/androidfw/AssetsProvider.cpp
@@ -84,7 +84,7 @@
   return value_;
 }
 
-ZipAssetsProvider::ZipAssetsProvider(ZipArchive* handle, PathOrDebugName&& path,
+ZipAssetsProvider::ZipAssetsProvider(ZipArchiveHandle handle, PathOrDebugName&& path,
                                      time_t last_mod_time)
     : zip_handle_(handle, ::CloseArchive),
       name_(std::forward<PathOrDebugName>(path)),
@@ -93,7 +93,7 @@
 std::unique_ptr<ZipAssetsProvider> ZipAssetsProvider::Create(std::string path) {
   ZipArchiveHandle handle;
   if (int32_t result = OpenArchive(path.c_str(), &handle); result != 0) {
-    LOG(ERROR) << "Failed to open APK '" << path << "' " << ::ErrorCodeString(result);
+    LOG(ERROR) << "Failed to open APK '" << path << "': " << ::ErrorCodeString(result);
     CloseArchive(handle);
     return {};
   }
@@ -253,6 +253,14 @@
     return result == -1;
 }
 
+std::optional<uint32_t> ZipAssetsProvider::GetCrc(std::string_view path) const {
+  ::ZipEntry entry;
+  if (FindEntry(zip_handle_.get(), path, &entry) != 0) {
+    return {};
+  }
+  return entry.crc32;
+}
+
 const std::string& ZipAssetsProvider::GetDebugName() const {
   return name_.GetDebugName();
 }
diff --git a/libs/androidfw/Idmap.cpp b/libs/androidfw/Idmap.cpp
index f216f55..efd1f6a 100644
--- a/libs/androidfw/Idmap.cpp
+++ b/libs/androidfw/Idmap.cpp
@@ -54,12 +54,6 @@
 };
 
 struct Idmap_data_header {
-  uint8_t target_package_id;
-  uint8_t overlay_package_id;
-
-  // Padding to ensure 4 byte alignment for target_entry_count
-  uint16_t p0;
-
   uint32_t target_entry_count;
   uint32_t target_inline_entry_count;
   uint32_t overlay_entry_count;
@@ -158,19 +152,19 @@
     return {};
   }
 
-  // The resource ids encoded within the idmap are build-time resource ids.
-  target_res_id = (0x00FFFFFFU & target_res_id)
-      | (((uint32_t) data_header_->target_package_id) << 24U);
+  // The resource ids encoded within the idmap are build-time resource ids so do not consider the
+  // package id when determining if the resource in the target package is overlaid.
+  target_res_id &= 0x00FFFFFFU;
 
   // Check if the target resource is mapped to an overlay resource.
   auto first_entry = entries_;
   auto end_entry = entries_ + dtohl(data_header_->target_entry_count);
   auto entry = std::lower_bound(first_entry, end_entry, target_res_id,
-                                [](const Idmap_target_entry &e, const uint32_t target_id) {
-    return dtohl(e.target_id) < target_id;
+                                [](const Idmap_target_entry& e, const uint32_t target_id) {
+    return (0x00FFFFFFU & dtohl(e.target_id)) < target_id;
   });
 
-  if (entry != end_entry && dtohl(entry->target_id) == target_res_id) {
+  if (entry != end_entry && (0x00FFFFFFU & dtohl(entry->target_id)) == target_res_id) {
     uint32_t overlay_resource_id = dtohl(entry->overlay_id);
     // Lookup the resource without rewriting the overlay resource id back to the target resource id
     // being looked up.
@@ -182,12 +176,13 @@
   auto first_inline_entry = inline_entries_;
   auto end_inline_entry = inline_entries_ + dtohl(data_header_->target_inline_entry_count);
   auto inline_entry = std::lower_bound(first_inline_entry, end_inline_entry, target_res_id,
-                                       [](const Idmap_target_entry_inline &e,
+                                       [](const Idmap_target_entry_inline& e,
                                           const uint32_t target_id) {
-    return dtohl(e.target_id) < target_id;
+    return (0x00FFFFFFU & dtohl(e.target_id)) < target_id;
   });
 
-  if (inline_entry != end_inline_entry && dtohl(inline_entry->target_id) == target_res_id) {
+  if (inline_entry != end_inline_entry &&
+      (0x00FFFFFFU & dtohl(inline_entry->target_id)) == target_res_id) {
     return Result(inline_entry->value);
   }
   return {};
@@ -235,7 +230,7 @@
   }
   return std::string_view(data, *len);
 }
-}
+} // namespace
 
 LoadedIdmap::LoadedIdmap(std::string&& idmap_path,
                          const Idmap_header* header,
diff --git a/libs/androidfw/ResourceTypes.cpp b/libs/androidfw/ResourceTypes.cpp
index 2233827..30500ab 100644
--- a/libs/androidfw/ResourceTypes.cpp
+++ b/libs/androidfw/ResourceTypes.cpp
@@ -25,6 +25,7 @@
 #include <string.h>
 
 #include <algorithm>
+#include <fstream>
 #include <limits>
 #include <map>
 #include <memory>
@@ -44,6 +45,7 @@
 
 #ifdef __ANDROID__
 #include <binder/TextOutput.h>
+
 #endif
 
 #ifndef INT32_MAX
@@ -233,6 +235,15 @@
     fill9patchOffsets(reinterpret_cast<Res_png_9patch*>(outData));
 }
 
+bool IsFabricatedOverlay(const std::string& path) {
+  std::ifstream fin(path);
+  uint32_t magic;
+  if (fin.read(reinterpret_cast<char*>(&magic), sizeof(uint32_t))) {
+    return magic == kFabricatedOverlayMagic;
+  }
+  return false;
+}
+
 static bool assertIdmapHeader(const void* idmap, size_t size) {
     if (reinterpret_cast<uintptr_t>(idmap) & 0x03) {
         ALOGE("idmap: header is not word aligned");
diff --git a/libs/androidfw/include/androidfw/AssetManager2.h b/libs/androidfw/include/androidfw/AssetManager2.h
index 6fbd6aa..2255973f 100644
--- a/libs/androidfw/include/androidfw/AssetManager2.h
+++ b/libs/androidfw/include/androidfw/AssetManager2.h
@@ -101,7 +101,7 @@
   // Only pass invalidate_caches=false when it is known that the structure
   // change in ApkAssets is due to a safe addition of resources with completely
   // new resource IDs.
-  bool SetApkAssets(const std::vector<const ApkAssets*>& apk_assets, bool invalidate_caches = true);
+  bool SetApkAssets(std::vector<const ApkAssets*> apk_assets, bool invalidate_caches = true);
 
   inline const std::vector<const ApkAssets*> GetApkAssets() const {
     return apk_assets_;
diff --git a/libs/androidfw/include/androidfw/AssetsProvider.h b/libs/androidfw/include/androidfw/AssetsProvider.h
index 7b06947..6f16ff4 100644
--- a/libs/androidfw/include/androidfw/AssetsProvider.h
+++ b/libs/androidfw/include/androidfw/AssetsProvider.h
@@ -88,6 +88,8 @@
   WARN_UNUSED const std::string& GetDebugName() const override;
   WARN_UNUSED bool IsUpToDate() const override;
 
+  WARN_UNUSED std::optional<uint32_t> GetCrc(std::string_view path) const;
+
   ~ZipAssetsProvider() override = default;
  protected:
   std::unique_ptr<Asset> OpenInternal(const std::string& path, Asset::AccessMode mode,
diff --git a/libs/androidfw/include/androidfw/Idmap.h b/libs/androidfw/include/androidfw/Idmap.h
index 0ded793..6804472 100644
--- a/libs/androidfw/include/androidfw/Idmap.h
+++ b/libs/androidfw/include/androidfw/Idmap.h
@@ -168,15 +168,14 @@
   }
 
   // Returns a mapping from target resource ids to overlay values.
-  const IdmapResMap GetTargetResourcesMap(
-      uint8_t target_assigned_package_id, const OverlayDynamicRefTable* overlay_ref_table) const {
+  const IdmapResMap GetTargetResourcesMap(uint8_t target_assigned_package_id,
+                                          const OverlayDynamicRefTable* overlay_ref_table) const {
     return IdmapResMap(data_header_, target_entries_, target_inline_entries_,
                        target_assigned_package_id, overlay_ref_table);
   }
 
   // Returns a dynamic reference table for a loaded overlay package.
-  const OverlayDynamicRefTable GetOverlayDynamicRefTable(
-      uint8_t target_assigned_package_id) const {
+  const OverlayDynamicRefTable GetOverlayDynamicRefTable(uint8_t target_assigned_package_id) const {
     return OverlayDynamicRefTable(data_header_, overlay_entries_, target_assigned_package_id);
   }
 
diff --git a/libs/androidfw/include/androidfw/ResourceTypes.h b/libs/androidfw/include/androidfw/ResourceTypes.h
index bfd564c..168a863 100644
--- a/libs/androidfw/include/androidfw/ResourceTypes.h
+++ b/libs/androidfw/include/androidfw/ResourceTypes.h
@@ -43,8 +43,19 @@
 
 namespace android {
 
-constexpr const static uint32_t kIdmapMagic = 0x504D4449u;
-constexpr const static uint32_t kIdmapCurrentVersion = 0x00000007u;
+constexpr const uint32_t kIdmapMagic = 0x504D4449u;
+constexpr const uint32_t kIdmapCurrentVersion = 0x00000008u;
+
+// This must never change.
+constexpr const uint32_t kFabricatedOverlayMagic = 0x4f525246; // FRRO (big endian)
+
+// The version should only be changed when a backwards-incompatible change must be made to the
+// fabricated overlay file format. Old fabricated overlays must be migrated to the new file format
+// to prevent losing fabricated overlay data.
+constexpr const uint32_t kFabricatedOverlayCurrentVersion = 1;
+
+// Returns whether or not the path represents a fabricated overlay.
+bool IsFabricatedOverlay(const std::string& path);
 
 /**
  * In C++11, char16_t is defined as *at least* 16 bits. We do a lot of
diff --git a/libs/androidfw/tests/data/overlay/overlay.idmap b/libs/androidfw/tests/data/overlay/overlay.idmap
index 723413c..88eadcc 100644
--- a/libs/androidfw/tests/data/overlay/overlay.idmap
+++ b/libs/androidfw/tests/data/overlay/overlay.idmap
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