Merge changes from topic "invalidate_idmap" into rvc-dev am: 6cb79cdfb7

Change-Id: Iec3d0e3bab28964442c5aada00c2586e284feb92

38 files changed, 429 insertions, 119 deletions

diff --git a/cmds/idmap2/TEST_MAPPING b/cmds/idmap2/TEST_MAPPING
index 26ccf038cba2..9e0fb84c7949 100644
--- a/cmds/idmap2/TEST_MAPPING
+++ b/cmds/idmap2/TEST_MAPPING
@@ -3,5 +3,10 @@
     {
       "name" : "idmap2_tests"
     }
+  ],
+  "imports": [
+    {
+      "path": "frameworks/base/services/core/java/com/android/server/om"
+    }
   ]
 }
diff --git a/cmds/idmap2/idmap2d/Idmap2Service.cpp b/cmds/idmap2/idmap2d/Idmap2Service.cpp
index 9cae926d56d7..b8f1a1c0ee72 100644
--- a/cmds/idmap2/idmap2d/Idmap2Service.cpp
+++ b/cmds/idmap2/idmap2d/Idmap2Service.cpp
@@ -149,15 +149,21 @@ Status Idmap2Service::createIdmap(const std::string& target_apk_path,
     return error(idmap.GetErrorMessage());
   }
 
+  // idmap files are mapped with mmap in libandroidfw. Deleting and recreating the idmap guarantees
+  // that existing memory maps will continue to be valid and unaffected.
+  unlink(idmap_path.c_str());
+
   umask(kIdmapFilePermissionMask);
   std::ofstream fout(idmap_path);
   if (fout.fail()) {
     return error("failed to open idmap path " + idmap_path);
   }
+
   BinaryStreamVisitor visitor(fout);
   (*idmap)->accept(&visitor);
   fout.close();
   if (fout.fail()) {
+    unlink(idmap_path.c_str());
     return error("failed to write to idmap path " + idmap_path);
   }
 
diff --git a/core/java/android/app/ResourcesManager.java b/core/java/android/app/ResourcesManager.java
index d2e848b9562a..47ccc2f0badb 100644
--- a/core/java/android/app/ResourcesManager.java
+++ b/core/java/android/app/ResourcesManager.java
@@ -344,7 +344,7 @@ public class ResourcesManager {
         ApkAssets apkAssets = null;
         if (mLoadedApkAssets != null) {
             apkAssets = mLoadedApkAssets.get(newKey);
-            if (apkAssets != null) {
+            if (apkAssets != null && apkAssets.isUpToDate()) {
                 return apkAssets;
             }
         }
@@ -353,7 +353,7 @@ public class ResourcesManager {
         final WeakReference<ApkAssets> apkAssetsRef = mCachedApkAssets.get(newKey);
         if (apkAssetsRef != null) {
             apkAssets = apkAssetsRef.get();
-            if (apkAssets != null) {
+            if (apkAssets != null && apkAssets.isUpToDate()) {
                 if (mLoadedApkAssets != null) {
                     mLoadedApkAssets.put(newKey, apkAssets);
                 }
diff --git a/core/tests/overlaytests/host/Android.bp b/core/tests/overlaytests/host/Android.bp
index a2fcef56b780..2b38cca2db36 100644
--- a/core/tests/overlaytests/host/Android.bp
+++ b/core/tests/overlaytests/host/Android.bp
@@ -16,7 +16,7 @@ java_test_host {
     name: "OverlayHostTests",
     srcs: ["src/**/*.java"],
     libs: ["tradefed"],
-    test_suites: ["general-tests"],
+    test_suites: ["device-tests"],
     target_required: [
         "OverlayHostTests_NonPlatformSignatureOverlay",
         "OverlayHostTests_PlatformSignatureStaticOverlay",
diff --git a/core/tests/overlaytests/host/src/com/android/server/om/hosttest/InstallOverlayTests.java b/core/tests/overlaytests/host/src/com/android/server/om/hosttest/InstallOverlayTests.java
index eec7be22c78b..d898d222b8de 100644
--- a/core/tests/overlaytests/host/src/com/android/server/om/hosttest/InstallOverlayTests.java
+++ b/core/tests/overlaytests/host/src/com/android/server/om/hosttest/InstallOverlayTests.java
@@ -78,14 +78,9 @@ public class InstallOverlayTests extends BaseHostJUnit4Test {
     }
 
     @Test
-    public void failToInstallPlatformSignedStaticOverlay() throws Exception {
-        try {
-            installPackage("OverlayHostTests_PlatformSignatureStaticOverlay.apk");
-            fail("installed a static overlay");
-        } catch (Exception e) {
-            // Expected.
-        }
-        assertFalse(overlayManagerContainsPackage(SIG_OVERLAY_PACKAGE_NAME));
+    public void installedIsStaticOverlayIsMutable() throws Exception {
+        installPackage("OverlayHostTests_PlatformSignatureStaticOverlay.apk");
+        assertTrue(isOverlayMutable(SIG_OVERLAY_PACKAGE_NAME));
     }
 
     @Test
@@ -229,6 +224,10 @@ public class InstallOverlayTests extends BaseHostJUnit4Test {
         return shell("cmd overlay list").contains(pkg);
     }
 
+    private boolean isOverlayMutable(String pkg) throws Exception {
+        return shell("cmd overlay dump ismutable " + pkg).contains("true");
+    }
+
     private String shell(final String cmd) throws Exception {
         return getDevice().executeShellCommand(cmd);
     }
diff --git a/core/tests/overlaytests/host/test-apps/SignatureOverlay/Android.mk b/core/tests/overlaytests/host/test-apps/SignatureOverlay/Android.mk
index cc7704b0ce98..f3c0abd8293f 100644
--- a/core/tests/overlaytests/host/test-apps/SignatureOverlay/Android.mk
+++ b/core/tests/overlaytests/host/test-apps/SignatureOverlay/Android.mk
@@ -20,7 +20,7 @@ include $(CLEAR_VARS)
 LOCAL_MODULE_TAGS := tests
 LOCAL_PACKAGE_NAME := OverlayHostTests_NonPlatformSignatureOverlay
 LOCAL_SDK_VERSION := current
-LOCAL_COMPATIBILITY_SUITE := general-tests
+LOCAL_COMPATIBILITY_SUITE := device-tests
 LOCAL_AAPT_FLAGS := --custom-package $(my_package_prefix)_bad
 include $(BUILD_PACKAGE)
 
@@ -28,7 +28,8 @@ include $(CLEAR_VARS)
 LOCAL_MODULE_TAGS := tests
 LOCAL_PACKAGE_NAME := OverlayHostTests_PlatformSignatureStaticOverlay
 LOCAL_SDK_VERSION := current
-LOCAL_COMPATIBILITY_SUITE := general-tests
+LOCAL_COMPATIBILITY_SUITE := device-tests
+LOCAL_CERTIFICATE := platform
 LOCAL_MANIFEST_FILE := static/AndroidManifest.xml
 LOCAL_AAPT_FLAGS := --custom-package $(my_package_prefix)_static
 include $(BUILD_PACKAGE)
@@ -37,7 +38,7 @@ include $(CLEAR_VARS)
 LOCAL_MODULE_TAGS := tests
 LOCAL_PACKAGE_NAME := OverlayHostTests_PlatformSignatureOverlay
 LOCAL_SDK_VERSION := current
-LOCAL_COMPATIBILITY_SUITE := general-tests
+LOCAL_COMPATIBILITY_SUITE := device-tests
 LOCAL_CERTIFICATE := platform
 LOCAL_AAPT_FLAGS := --custom-package $(my_package_prefix)_v1
 LOCAL_AAPT_FLAGS += --version-code 1 --version-name v1
diff --git a/core/tests/overlaytests/host/test-apps/UpdateOverlay/Android.mk b/core/tests/overlaytests/host/test-apps/UpdateOverlay/Android.mk
index f8607f44bda6..878f05d57662 100644
--- a/core/tests/overlaytests/host/test-apps/UpdateOverlay/Android.mk
+++ b/core/tests/overlaytests/host/test-apps/UpdateOverlay/Android.mk
@@ -19,7 +19,7 @@ LOCAL_MODULE_TAGS := tests
 LOCAL_SRC_FILES := $(call all-java-files-under,src)
 LOCAL_PACKAGE_NAME := OverlayHostTests_UpdateOverlay
 LOCAL_SDK_VERSION := current
-LOCAL_COMPATIBILITY_SUITE := general-tests
+LOCAL_COMPATIBILITY_SUITE := device-tests
 LOCAL_STATIC_JAVA_LIBRARIES := androidx.test.rules
 LOCAL_USE_AAPT2 := true
 LOCAL_AAPT_FLAGS := --no-resource-removal
@@ -31,7 +31,7 @@ include $(CLEAR_VARS)
 LOCAL_MODULE_TAGS := tests
 LOCAL_PACKAGE_NAME := OverlayHostTests_FrameworkOverlayV1
 LOCAL_SDK_VERSION := current
-LOCAL_COMPATIBILITY_SUITE := general-tests
+LOCAL_COMPATIBILITY_SUITE := device-tests
 LOCAL_CERTIFICATE := platform
 LOCAL_AAPT_FLAGS := --custom-package $(my_package_prefix)_v1
 LOCAL_AAPT_FLAGS += --version-code 1 --version-name v1
@@ -43,7 +43,7 @@ include $(CLEAR_VARS)
 LOCAL_MODULE_TAGS := tests
 LOCAL_PACKAGE_NAME := OverlayHostTests_FrameworkOverlayV2
 LOCAL_SDK_VERSION := current
-LOCAL_COMPATIBILITY_SUITE := general-tests
+LOCAL_COMPATIBILITY_SUITE := device-tests
 LOCAL_CERTIFICATE := platform
 LOCAL_AAPT_FLAGS := --custom-package $(my_package_prefix)_v2
 LOCAL_AAPT_FLAGS += --version-code 2 --version-name v2
@@ -57,7 +57,7 @@ include $(CLEAR_VARS)
 LOCAL_MODULE_TAGS := tests
 LOCAL_PACKAGE_NAME := OverlayHostTests_AppOverlayV1
 LOCAL_SDK_VERSION := current
-LOCAL_COMPATIBILITY_SUITE := general-tests
+LOCAL_COMPATIBILITY_SUITE := device-tests
 LOCAL_AAPT_FLAGS := --custom-package $(my_package_prefix)_v1
 LOCAL_AAPT_FLAGS += --version-code 1 --version-name v1
 LOCAL_RESOURCE_DIR := $(LOCAL_PATH)/app/v1/res
@@ -68,7 +68,7 @@ include $(CLEAR_VARS)
 LOCAL_MODULE_TAGS := tests
 LOCAL_PACKAGE_NAME := OverlayHostTests_AppOverlayV2
 LOCAL_SDK_VERSION := current
-LOCAL_COMPATIBILITY_SUITE := general-tests
+LOCAL_COMPATIBILITY_SUITE := device-tests
 LOCAL_AAPT_FLAGS := --custom-package $(my_package_prefix)_v2
 LOCAL_AAPT_FLAGS += --version-code 2 --version-name v2
 LOCAL_RESOURCE_DIR := $(LOCAL_PATH)/app/v2/res
diff --git a/core/tests/overlaytests/remount/host/Android.bp b/core/tests/overlaytests/remount/Android.bp
index 3825c55f3b4b..9baedf81d6e0 100644
--- a/core/tests/overlaytests/remount/host/Android.bp
+++ b/core/tests/overlaytests/remount/Android.bp
@@ -24,5 +24,7 @@ java_test_host {
         ":OverlayRemountedTest_SharedLibrary",
         ":OverlayRemountedTest_SharedLibraryOverlay",
         ":OverlayRemountedTest_Target",
+        ":OverlayRemountedTest_TargetUpgrade",
+        ":OverlayRemountedTest_Overlay",
     ],
 }
diff --git a/core/tests/overlaytests/remount/host/AndroidTest.xml b/core/tests/overlaytests/remount/AndroidTest.xml
index 087b7313693d..087b7313693d 100644
--- a/core/tests/overlaytests/remount/host/AndroidTest.xml
+++ b/core/tests/overlaytests/remount/AndroidTest.xml
diff --git a/core/tests/overlaytests/remount/src/com/android/overlaytest/remounted/OverlayRemountedTestBase.java b/core/tests/overlaytests/remount/src/com/android/overlaytest/remounted/OverlayRemountedTestBase.java
new file mode 100644
index 000000000000..00a53c45d797
--- /dev/null
+++ b/core/tests/overlaytests/remount/src/com/android/overlaytest/remounted/OverlayRemountedTestBase.java
@@ -0,0 +1,84 @@
+/*
+ * Copyright (C) 2020 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.
+ */
+
+package com.android.overlaytest.remounted;
+
+import static org.junit.Assert.fail;
+
+import com.android.tradefed.device.DeviceNotAvailableException;
+import com.android.tradefed.testtype.junit4.BaseHostJUnit4Test;
+
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.rules.RuleChain;
+import org.junit.rules.TemporaryFolder;
+
+public class OverlayRemountedTestBase extends BaseHostJUnit4Test {
+    static final long ASSERT_RESOURCE_TIMEOUT_MS = 30000;
+
+    static final String TARGET_APK = "OverlayRemountedTest_Target.apk";
+    static final String TARGET_PACKAGE = "com.android.overlaytest.remounted.target";
+    static final String TARGET_UPGRADE_APK = "OverlayRemountedTest_TargetUpgrade.apk";
+    static final String OVERLAY_APK = "OverlayRemountedTest_Overlay.apk";
+    static final String OVERLAY_PACKAGE = "com.android.overlaytest.remounted.target.overlay";
+    static final String SHARED_LIBRARY_APK =
+            "OverlayRemountedTest_SharedLibrary.apk";
+    static final String SHARED_LIBRARY_PACKAGE =
+            "com.android.overlaytest.remounted.shared_library";
+    static final String SHARED_LIBRARY_OVERLAY_APK =
+            "OverlayRemountedTest_SharedLibraryOverlay.apk";
+    static final String SHARED_LIBRARY_OVERLAY_PACKAGE =
+            "com.android.overlaytest.remounted.shared_library.overlay";
+
+    private final TemporaryFolder mTemporaryFolder = new TemporaryFolder();
+    protected final SystemPreparer mPreparer = new SystemPreparer(mTemporaryFolder,
+            this::getDevice);
+
+    @Rule
+    public final RuleChain ruleChain = RuleChain.outerRule(mTemporaryFolder).around(mPreparer);
+
+    @Before
+    public void startBefore() throws DeviceNotAvailableException {
+        getDevice().waitForDeviceAvailable();
+    }
+
+    /** Builds the full name of a resource in the form package:type/entry. */
+    String resourceName(String pkg, String type, String entry) {
+        return String.format("%s:%s/%s", pkg, type, entry);
+    }
+
+    void assertResource(String resourceName, String expectedValue)
+            throws DeviceNotAvailableException {
+        String result = null;
+
+        final long endMillis = System.currentTimeMillis() + ASSERT_RESOURCE_TIMEOUT_MS;
+        while (System.currentTimeMillis() <= endMillis) {
+            result = getDevice().executeShellCommand(
+                    String.format("cmd overlay lookup %s %s", TARGET_PACKAGE, resourceName));
+            if (result.equals(expectedValue + "\n") ||
+                    result.endsWith("-> " + expectedValue + "\n")) {
+                return;
+            }
+
+            try {
+                Thread.sleep(200);
+            } catch (InterruptedException ignore) {
+            }
+        }
+
+        fail(String.format("expected: <[%s]> in: <[%s]>", expectedValue, result));
+    }
+}
diff --git a/core/tests/overlaytests/remount/host/src/com/android/overlaytest/remounted/OverlaySharedLibraryTest.java b/core/tests/overlaytests/remount/src/com/android/overlaytest/remounted/OverlaySharedLibraryTest.java
index 06b2ac8f9e22..49d1894c9bae 100644
--- a/core/tests/overlaytests/remount/host/src/com/android/overlaytest/remounted/OverlaySharedLibraryTest.java
+++ b/core/tests/overlaytests/remount/src/com/android/overlaytest/remounted/OverlaySharedLibraryTest.java
@@ -16,42 +16,13 @@
 
 package com.android.overlaytest.remounted;
 
-import static org.junit.Assert.assertTrue;
-
-import com.android.tradefed.device.DeviceNotAvailableException;
 import com.android.tradefed.testtype.DeviceJUnit4ClassRunner;
-import com.android.tradefed.testtype.junit4.BaseHostJUnit4Test;
 
-import org.junit.Before;
-import org.junit.Rule;
 import org.junit.Test;
-import org.junit.rules.RuleChain;
-import org.junit.rules.TemporaryFolder;
 import org.junit.runner.RunWith;
 
 @RunWith(DeviceJUnit4ClassRunner.class)
-public class OverlaySharedLibraryTest extends BaseHostJUnit4Test {
-    private static final String TARGET_APK = "OverlayRemountedTest_Target.apk";
-    private static final String TARGET_PACKAGE = "com.android.overlaytest.remounted.target";
-    private static final String SHARED_LIBRARY_APK =
-            "OverlayRemountedTest_SharedLibrary.apk";
-    private static final String SHARED_LIBRARY_PACKAGE =
-            "com.android.overlaytest.remounted.shared_library";
-    private static final String SHARED_LIBRARY_OVERLAY_APK =
-            "OverlayRemountedTest_SharedLibraryOverlay.apk";
-    private static final String SHARED_LIBRARY_OVERLAY_PACKAGE =
-            "com.android.overlaytest.remounted.shared_library.overlay";
-
-    public final TemporaryFolder temporaryFolder = new TemporaryFolder();
-    public final SystemPreparer preparer = new SystemPreparer(temporaryFolder, this::getDevice);
-
-    @Rule
-    public final RuleChain ruleChain = RuleChain.outerRule(temporaryFolder).around(preparer);
-
-    @Before
-    public void startBefore() throws DeviceNotAvailableException {
-        getDevice().waitForDeviceAvailable();
-    }
+public class OverlaySharedLibraryTest extends OverlayRemountedTestBase {
 
     @Test
     public void testSharedLibrary() throws Exception {
@@ -60,7 +31,7 @@ public class OverlaySharedLibraryTest extends BaseHostJUnit4Test {
         final String libraryResource = resourceName(SHARED_LIBRARY_PACKAGE, "bool",
                 "shared_library_overlaid");
 
-        preparer.pushResourceFile(SHARED_LIBRARY_APK, "/product/app/SharedLibrary.apk")
+        mPreparer.pushResourceFile(SHARED_LIBRARY_APK, "/product/app/SharedLibrary.apk")
                 .installResourceApk(SHARED_LIBRARY_OVERLAY_APK, SHARED_LIBRARY_OVERLAY_PACKAGE)
                 .reboot()
                 .setOverlayEnabled(SHARED_LIBRARY_OVERLAY_PACKAGE, false)
@@ -71,7 +42,7 @@ public class OverlaySharedLibraryTest extends BaseHostJUnit4Test {
         assertResource(libraryResource, "false");
 
         // Overlay the shared library resource.
-        preparer.setOverlayEnabled(SHARED_LIBRARY_OVERLAY_PACKAGE, true);
+        mPreparer.setOverlayEnabled(SHARED_LIBRARY_OVERLAY_PACKAGE, true);
         assertResource(targetResource, "true");
         assertResource(libraryResource, "true");
     }
@@ -83,7 +54,7 @@ public class OverlaySharedLibraryTest extends BaseHostJUnit4Test {
         final String libraryResource = resourceName(SHARED_LIBRARY_PACKAGE, "bool",
                 "shared_library_overlaid");
 
-        preparer.pushResourceFile(SHARED_LIBRARY_APK, "/product/app/SharedLibrary.apk")
+        mPreparer.pushResourceFile(SHARED_LIBRARY_APK, "/product/app/SharedLibrary.apk")
                 .installResourceApk(SHARED_LIBRARY_OVERLAY_APK, SHARED_LIBRARY_OVERLAY_PACKAGE)
                 .setOverlayEnabled(SHARED_LIBRARY_OVERLAY_PACKAGE, true)
                 .reboot()
@@ -92,18 +63,4 @@ public class OverlaySharedLibraryTest extends BaseHostJUnit4Test {
         assertResource(targetResource, "true");
         assertResource(libraryResource, "true");
     }
-
-    /** Builds the full name of a resource in the form package:type/entry. */
-    String resourceName(String pkg, String type, String entry) {
-        return String.format("%s:%s/%s", pkg, type, entry);
-    }
-
-    void assertResource(String resourceName, String expectedValue)
-            throws DeviceNotAvailableException {
-        final String result = getDevice().executeShellCommand(
-                String.format("cmd overlay lookup %s %s", TARGET_PACKAGE, resourceName));
-        assertTrue(String.format("expected: <[%s]> in: <[%s]>", expectedValue, result),
-                result.equals(expectedValue + "\n") ||
-                result.endsWith("-> " + expectedValue + "\n"));
-    }
 }
diff --git a/core/tests/overlaytests/remount/src/com/android/overlaytest/remounted/PackagedUpgradedTest.java b/core/tests/overlaytests/remount/src/com/android/overlaytest/remounted/PackagedUpgradedTest.java
new file mode 100644
index 000000000000..f685ec1580ad
--- /dev/null
+++ b/core/tests/overlaytests/remount/src/com/android/overlaytest/remounted/PackagedUpgradedTest.java
@@ -0,0 +1,65 @@
+/*
+ * Copyright (C) 2020 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.
+ */
+
+package com.android.overlaytest.remounted;
+
+import com.android.tradefed.testtype.DeviceJUnit4ClassRunner;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+@RunWith(DeviceJUnit4ClassRunner.class)
+public class PackagedUpgradedTest extends OverlayRemountedTestBase {
+
+    @Test
+    public void testTargetUpgrade() throws Exception {
+        final String targetOverlaid = resourceName(TARGET_PACKAGE, "bool", "target_overlaid");
+        final String targetReference = resourceName(TARGET_PACKAGE, "bool", "target_reference");
+
+        mPreparer.pushResourceFile(TARGET_APK, "/product/app/OverlayTarget.apk")
+                .reboot()
+                .installResourceApk(OVERLAY_APK, OVERLAY_PACKAGE)
+                .setOverlayEnabled(OVERLAY_PACKAGE, true);
+
+        assertResource(targetReference, "@" + 0x7f010000 + " -> true");
+        assertResource(targetOverlaid, "true");
+
+        mPreparer.installResourceApk(TARGET_UPGRADE_APK, TARGET_PACKAGE);
+
+        assertResource(targetReference, "@" + 0x7f0100ff + " -> true");
+        assertResource(targetOverlaid, "true");
+    }
+
+    @Test
+    public void testTargetRelocated() throws Exception {
+        final String targetOverlaid = resourceName(TARGET_PACKAGE, "bool", "target_overlaid");
+        final String originalPath = "/product/app/OverlayTarget.apk";
+
+        mPreparer.pushResourceFile(TARGET_APK, originalPath)
+                .reboot()
+                .installResourceApk(OVERLAY_APK, OVERLAY_PACKAGE)
+                .setOverlayEnabled(OVERLAY_PACKAGE, true);
+
+        assertResource(targetOverlaid, "true");
+
+        mPreparer.remount();
+        getDevice().deleteFile(originalPath);
+        mPreparer.pushResourceFile(TARGET_UPGRADE_APK, "/product/app/OverlayTarget2.apk")
+                .reboot();
+
+        assertResource(targetOverlaid, "true");
+    }
+}
diff --git a/core/tests/overlaytests/remount/host/src/com/android/overlaytest/remounted/SystemPreparer.java b/core/tests/overlaytests/remount/src/com/android/overlaytest/remounted/SystemPreparer.java
index 8696091239c2..b45b8eabf7c0 100644
--- a/core/tests/overlaytests/remount/host/src/com/android/overlaytest/remounted/SystemPreparer.java
+++ b/core/tests/overlaytests/remount/src/com/android/overlaytest/remounted/SystemPreparer.java
@@ -18,8 +18,6 @@ package com.android.overlaytest.remounted;
 
 import static org.junit.Assert.assertTrue;
 
-import static java.util.concurrent.TimeUnit.MILLISECONDS;
-
 import com.android.tradefed.device.DeviceNotAvailableException;
 import com.android.tradefed.device.ITestDevice;
 
@@ -32,10 +30,6 @@ import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.util.ArrayList;
-import java.util.concurrent.ExecutionException;
-import java.util.concurrent.Executor;
-import java.util.concurrent.FutureTask;
-import java.util.concurrent.TimeoutException;
 
 class SystemPreparer extends ExternalResource {
     private static final long OVERLAY_ENABLE_TIMEOUT_MS = 30000;
@@ -58,7 +52,7 @@ class SystemPreparer extends ExternalResource {
     SystemPreparer pushResourceFile(String resourcePath,
             String outputPath) throws DeviceNotAvailableException, IOException {
         final ITestDevice device = mDeviceProvider.getDevice();
-        device.executeAdbCommand("remount");
+        remount();
         assertTrue(device.pushFile(copyResourceToTemp(resourcePath), outputPath));
         mPushedFiles.add(outputPath);
         return this;
@@ -69,7 +63,7 @@ class SystemPreparer extends ExternalResource {
             throws DeviceNotAvailableException, IOException {
         final ITestDevice device = mDeviceProvider.getDevice();
         final File tmpFile = copyResourceToTemp(resourcePath);
-        final String result = device.installPackage(tmpFile, true);
+        final String result = device.installPackage(tmpFile, true /* reinstall */);
         Assert.assertNull(result);
         mInstalledPackages.add(packageName);
         return this;
@@ -77,34 +71,29 @@ class SystemPreparer extends ExternalResource {
 
     /** Sets the enable state of an overlay pacakage. */
     SystemPreparer setOverlayEnabled(String packageName, boolean enabled)
-            throws ExecutionException, DeviceNotAvailableException {
+            throws DeviceNotAvailableException {
         final ITestDevice device = mDeviceProvider.getDevice();
+        final String enable = enabled ? "enable" : "disable";
 
         // Wait for the overlay to change its enabled state.
-        final FutureTask<Boolean> enabledListener = new FutureTask<>(() -> {
-            while (true) {
-                device.executeShellCommand(String.format("cmd overlay %s %s",
-                        enabled ? "enable" : "disable", packageName));
-
-                final String result = device.executeShellCommand("cmd overlay dump " + packageName);
-                final int startIndex = result.indexOf("mIsEnabled");
-                final int endIndex = result.indexOf('\n', startIndex);
-                if (result.substring(startIndex, endIndex).contains((enabled) ? "true" : "false")) {
-                    return true;
-                }
+        final long endMillis = System.currentTimeMillis() + OVERLAY_ENABLE_TIMEOUT_MS;
+        String result;
+        while (System.currentTimeMillis() <= endMillis) {
+            device.executeShellCommand(String.format("cmd overlay %s %s", enable, packageName));
+            result = device.executeShellCommand("cmd overlay dump isenabled "
+                    + packageName);
+            if (((enabled) ? "true\n" : "false\n").equals(result)) {
+                return this;
             }
-        });
 
-        final Executor executor = (cmd) -> new Thread(cmd).start();
-        executor.execute(enabledListener);
-        try {
-            enabledListener.get(OVERLAY_ENABLE_TIMEOUT_MS, MILLISECONDS);
-        } catch (InterruptedException ignored) {
-        } catch (TimeoutException e) {
-            throw new IllegalStateException(device.executeShellCommand("cmd overlay list"));
+            try {
+                Thread.sleep(200);
+            } catch (InterruptedException ignore) {
+            }
         }
 
-        return this;
+        throw new IllegalStateException(String.format("Failed to %s overlay %s:\n%s", enable,
+                packageName, device.executeShellCommand("cmd overlay list")));
     }
 
     /** Restarts the device and waits until after boot is completed. */
@@ -114,6 +103,11 @@ class SystemPreparer extends ExternalResource {
         return this;
     }
 
+    SystemPreparer remount() throws DeviceNotAvailableException {
+        mDeviceProvider.getDevice().executeAdbCommand("remount");
+        return this;
+    }
+
     /** Copies a file within the host test jar to a temporary file on the host machine. */
     private File copyResourceToTemp(String resourcePath) throws IOException {
         final File tempFile = mHostTempFolder.newFile(resourcePath);
@@ -138,7 +132,7 @@ class SystemPreparer extends ExternalResource {
     protected void after() {
         final ITestDevice device = mDeviceProvider.getDevice();
         try {
-            device.executeAdbCommand("remount");
+            remount();
             for (final String file : mPushedFiles) {
                 device.deleteFile(file);
             }
diff --git a/core/tests/overlaytests/remount/test-apps/Overlay/Android.bp b/core/tests/overlaytests/remount/test-apps/Overlay/Android.bp
new file mode 100644
index 000000000000..447601972f78
--- /dev/null
+++ b/core/tests/overlaytests/remount/test-apps/Overlay/Android.bp
@@ -0,0 +1,18 @@
+// 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.
+
+android_test_helper_app {
+    name: "OverlayRemountedTest_Overlay",
+    sdk_version: "current",
+}
diff --git a/core/tests/overlaytests/remount/test-apps/Overlay/AndroidManifest.xml b/core/tests/overlaytests/remount/test-apps/Overlay/AndroidManifest.xml
new file mode 100644
index 000000000000..d6d706c2da62
--- /dev/null
+++ b/core/tests/overlaytests/remount/test-apps/Overlay/AndroidManifest.xml
@@ -0,0 +1,23 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+  ~ Copyright (C) 2020 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.
+  -->
+
+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+    package="com.android.overlaytest.remounted.target.overlay">
+    <application android:hasCode="false" />
+    <overlay android:targetPackage="com.android.overlaytest.remounted.target"
+             android:targetName="TestResources" />
+</manifest>
\ No newline at end of file
diff --git a/core/tests/overlaytests/remount/test-apps/Overlay/res/values/values.xml b/core/tests/overlaytests/remount/test-apps/Overlay/res/values/values.xml
new file mode 100644
index 000000000000..675e44f19f95
--- /dev/null
+++ b/core/tests/overlaytests/remount/test-apps/Overlay/res/values/values.xml
@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+  ~ Copyright (C) 2020 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.
+  -->
+
+<resources>
+    <bool name="target_overlaid">true</bool>
+</resources>
diff --git a/core/tests/overlaytests/remount/host/test-apps/SharedLibrary/Android.bp b/core/tests/overlaytests/remount/test-apps/SharedLibrary/Android.bp
index ffb0572c3fd0..ffb0572c3fd0 100644
--- a/core/tests/overlaytests/remount/host/test-apps/SharedLibrary/Android.bp
+++ b/core/tests/overlaytests/remount/test-apps/SharedLibrary/Android.bp
diff --git a/core/tests/overlaytests/remount/host/test-apps/SharedLibrary/AndroidManifest.xml b/core/tests/overlaytests/remount/test-apps/SharedLibrary/AndroidManifest.xml
index 06e3f6a99410..06e3f6a99410 100644
--- a/core/tests/overlaytests/remount/host/test-apps/SharedLibrary/AndroidManifest.xml
+++ b/core/tests/overlaytests/remount/test-apps/SharedLibrary/AndroidManifest.xml
diff --git a/core/tests/overlaytests/remount/host/test-apps/SharedLibrary/res/values/overlayable.xml b/core/tests/overlaytests/remount/test-apps/SharedLibrary/res/values/overlayable.xml
index 1b06f6d7530b..1b06f6d7530b 100644
--- a/core/tests/overlaytests/remount/host/test-apps/SharedLibrary/res/values/overlayable.xml
+++ b/core/tests/overlaytests/remount/test-apps/SharedLibrary/res/values/overlayable.xml
diff --git a/core/tests/overlaytests/remount/host/test-apps/SharedLibrary/res/values/public.xml b/core/tests/overlaytests/remount/test-apps/SharedLibrary/res/values/public.xml
index 5b9db163a274..5b9db163a274 100644
--- a/core/tests/overlaytests/remount/host/test-apps/SharedLibrary/res/values/public.xml
+++ b/core/tests/overlaytests/remount/test-apps/SharedLibrary/res/values/public.xml
diff --git a/core/tests/overlaytests/remount/host/test-apps/SharedLibrary/res/values/values.xml b/core/tests/overlaytests/remount/test-apps/SharedLibrary/res/values/values.xml
index 2dc47a7ecf61..2dc47a7ecf61 100644
--- a/core/tests/overlaytests/remount/host/test-apps/SharedLibrary/res/values/values.xml
+++ b/core/tests/overlaytests/remount/test-apps/SharedLibrary/res/values/values.xml
diff --git a/core/tests/overlaytests/remount/host/test-apps/SharedLibraryOverlay/Android.bp b/core/tests/overlaytests/remount/test-apps/SharedLibraryOverlay/Android.bp
index 0d29aec909d5..0d29aec909d5 100644
--- a/core/tests/overlaytests/remount/host/test-apps/SharedLibraryOverlay/Android.bp
+++ b/core/tests/overlaytests/remount/test-apps/SharedLibraryOverlay/Android.bp
diff --git a/core/tests/overlaytests/remount/host/test-apps/SharedLibraryOverlay/AndroidManifest.xml b/core/tests/overlaytests/remount/test-apps/SharedLibraryOverlay/AndroidManifest.xml
index 53a4e61949da..53a4e61949da 100644
--- a/core/tests/overlaytests/remount/host/test-apps/SharedLibraryOverlay/AndroidManifest.xml
+++ b/core/tests/overlaytests/remount/test-apps/SharedLibraryOverlay/AndroidManifest.xml
diff --git a/core/tests/overlaytests/remount/host/test-apps/SharedLibraryOverlay/res/values/values.xml b/core/tests/overlaytests/remount/test-apps/SharedLibraryOverlay/res/values/values.xml
index f66448a8d991..f66448a8d991 100644
--- a/core/tests/overlaytests/remount/host/test-apps/SharedLibraryOverlay/res/values/values.xml
+++ b/core/tests/overlaytests/remount/test-apps/SharedLibraryOverlay/res/values/values.xml
diff --git a/core/tests/overlaytests/remount/target/Android.bp b/core/tests/overlaytests/remount/test-apps/Target/Android.bp
index 83f9f28b3f48..a8910eb8dae2 100644
--- a/core/tests/overlaytests/remount/target/Android.bp
+++ b/core/tests/overlaytests/remount/test-apps/Target/Android.bp
@@ -1,4 +1,4 @@
-// Copyright (C) 2018 The Android Open Source Project
+// 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.
@@ -14,7 +14,12 @@
 
 android_test_helper_app {
     name: "OverlayRemountedTest_Target",
-    srcs: ["src/**/*.java"],
     sdk_version: "test_current",
     libs: ["OverlayRemountedTest_SharedLibrary"],
 }
+
+android_test_helper_app {
+    name: "OverlayRemountedTest_TargetUpgrade",
+    resource_dirs: ["res_upgrade"],
+    sdk_version: "test_current",
+}
diff --git a/core/tests/overlaytests/remount/target/AndroidManifest.xml b/core/tests/overlaytests/remount/test-apps/Target/AndroidManifest.xml
index dc07dca16718..d1c7b7e8bb9d 100644
--- a/core/tests/overlaytests/remount/target/AndroidManifest.xml
+++ b/core/tests/overlaytests/remount/test-apps/Target/AndroidManifest.xml
@@ -19,8 +19,7 @@
           package="com.android.overlaytest.remounted.target">
 
     <application>
-        <uses-library android:name="android.test.runner" />
         <uses-library android:name="com.android.overlaytest.remounted.shared_library"
-                      android:required="true" />
+                      android:required="false" />
     </application>
 </manifest>
diff --git a/core/tests/overlaytests/remount/test-apps/Target/res/values/overlayable.xml b/core/tests/overlaytests/remount/test-apps/Target/res/values/overlayable.xml
new file mode 100644
index 000000000000..4aa5bcee8f3d
--- /dev/null
+++ b/core/tests/overlaytests/remount/test-apps/Target/res/values/overlayable.xml
@@ -0,0 +1,24 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+  ~ Copyright (C) 2020 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.
+  -->
+
+<resources>
+    <overlayable name="TestResources">
+        <policy type="public">
+            <item type="bool" name="target_overlaid" />
+        </policy>
+    </overlayable>
+</resources>
diff --git a/core/tests/overlaytests/remount/target/res/values/values.xml b/core/tests/overlaytests/remount/test-apps/Target/res/values/values.xml
index b5f444a5eb72..76253a95b766 100644
--- a/core/tests/overlaytests/remount/target/res/values/values.xml
+++ b/core/tests/overlaytests/remount/test-apps/Target/res/values/values.xml
@@ -17,4 +17,10 @@
 
 <resources xmlns:sharedlib="http://schemas.android.com/apk/res/com.android.overlaytest.remounted.shared_library">
     <bool name="uses_shared_library_overlaid">@sharedlib:bool/shared_library_overlaid</bool>
+
+    <!-- This resource has a different id in the updated version of this target app to test that the
+         idmap is regenerated when the target is updated. -->
+    <bool name="target_overlaid">false</bool>
+    <public type="bool" name="target_overlaid" id="0x7f010000" />
+    <bool name="target_reference">@bool/target_overlaid</bool>
 </resources>
diff --git a/core/tests/overlaytests/remount/test-apps/Target/res_upgrade/values/overlayable.xml b/core/tests/overlaytests/remount/test-apps/Target/res_upgrade/values/overlayable.xml
new file mode 100644
index 000000000000..4aa5bcee8f3d
--- /dev/null
+++ b/core/tests/overlaytests/remount/test-apps/Target/res_upgrade/values/overlayable.xml
@@ -0,0 +1,24 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+  ~ Copyright (C) 2020 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.
+  -->
+
+<resources>
+    <overlayable name="TestResources">
+        <policy type="public">
+            <item type="bool" name="target_overlaid" />
+        </policy>
+    </overlayable>
+</resources>
diff --git a/core/tests/overlaytests/remount/test-apps/Target/res_upgrade/values/values.xml b/core/tests/overlaytests/remount/test-apps/Target/res_upgrade/values/values.xml
new file mode 100644
index 000000000000..f552cb0776ab
--- /dev/null
+++ b/core/tests/overlaytests/remount/test-apps/Target/res_upgrade/values/values.xml
@@ -0,0 +1,23 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+  ~ Copyright (C) 2020 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.
+  -->
+<resources>
+    <!-- This resource has a different id in the updated target app than the base target app to test
+         that the idmap is regenerated when the target is updated. -->
+    <bool name="target_overlaid">false</bool>
+    <public type="bool" name="target_overlaid" id="0x7f0100ff" />
+    <bool name="target_reference">@bool/target_overlaid</bool>
+</resources>
\ No newline at end of file
diff --git a/libs/androidfw/ApkAssets.cpp b/libs/androidfw/ApkAssets.cpp
index 918e7af12d31..05f4d6b63a4c 100644
--- a/libs/androidfw/ApkAssets.cpp
+++ b/libs/androidfw/ApkAssets.cpp
@@ -385,7 +385,7 @@ std::unique_ptr<const ApkAssets> ApkAssets::LoadOverlay(const std::string& idmap
   const StringPiece idmap_data(
       reinterpret_cast<const char*>(idmap_asset->getBuffer(true /*wordAligned*/)),
       static_cast<size_t>(idmap_asset->getLength()));
-  std::unique_ptr<const LoadedIdmap> loaded_idmap = LoadedIdmap::Load(idmap_data);
+  std::unique_ptr<const LoadedIdmap> loaded_idmap = LoadedIdmap::Load(idmap_path, idmap_data);
   if (loaded_idmap == nullptr) {
     LOG(ERROR) << "failed to load IDMAP " << idmap_path;
     return {};
@@ -538,8 +538,9 @@ bool ApkAssets::IsUpToDate() const {
     // Loaders are invalidated by the app, not the system, so assume they are up to date.
     return true;
   }
+  return (!loaded_idmap_ || loaded_idmap_->IsUpToDate()) &&
+      last_mod_time_ == getFileModDate(path_.c_str());
 
-  return last_mod_time_ == getFileModDate(path_.c_str());
 }
 
 }  // namespace android
diff --git a/libs/androidfw/Idmap.cpp b/libs/androidfw/Idmap.cpp
index 0b2fd9ec982d..eb6ee9525bb9 100644
--- a/libs/androidfw/Idmap.cpp
+++ b/libs/androidfw/Idmap.cpp
@@ -20,6 +20,7 @@
 
 #include "android-base/logging.h"
 #include "android-base/stringprintf.h"
+#include "androidfw/misc.h"
 #include "androidfw/ResourceTypes.h"
 #include "androidfw/Util.h"
 #include "utils/ByteOrder.h"
@@ -192,7 +193,9 @@ static bool IsValidIdmapHeader(const StringPiece& data) {
   return true;
 }
 
-LoadedIdmap::LoadedIdmap(const Idmap_header* header,
+LoadedIdmap::LoadedIdmap(std::string&& idmap_path,
+                         const time_t last_mod_time,
+                         const Idmap_header* header,
                          const Idmap_data_header* data_header,
                          const Idmap_target_entry* target_entries,
                          const Idmap_overlay_entry* overlay_entries,
@@ -201,7 +204,9 @@ LoadedIdmap::LoadedIdmap(const Idmap_header* header,
        data_header_(data_header),
        target_entries_(target_entries),
        overlay_entries_(overlay_entries),
-       string_pool_(string_pool) {
+       string_pool_(string_pool),
+       idmap_path_(std::move(idmap_path)),
+       idmap_last_mod_time_(last_mod_time) {
 
   size_t length = strnlen(reinterpret_cast<const char*>(header_->overlay_path),
                           arraysize(header_->overlay_path));
@@ -212,7 +217,8 @@ LoadedIdmap::LoadedIdmap(const Idmap_header* header,
   target_apk_path_.assign(reinterpret_cast<const char*>(header_->target_path), length);
 }
 
-std::unique_ptr<const LoadedIdmap> LoadedIdmap::Load(const StringPiece& idmap_data) {
+std::unique_ptr<const LoadedIdmap> LoadedIdmap::Load(const StringPiece& idmap_path,
+                                                     const StringPiece& idmap_data) {
   ATRACE_CALL();
   if (!IsValidIdmapHeader(idmap_data)) {
     return {};
@@ -275,10 +281,14 @@ std::unique_ptr<const LoadedIdmap> LoadedIdmap::Load(const StringPiece& idmap_da
 
   // Can't use make_unique because LoadedIdmap constructor is private.
   std::unique_ptr<LoadedIdmap> loaded_idmap = std::unique_ptr<LoadedIdmap>(
-      new LoadedIdmap(header, data_header, target_entries, overlay_entries,
-                      idmap_string_pool.release()));
+      new LoadedIdmap(idmap_path.to_string(), getFileModDate(idmap_path.data()), header,
+                      data_header, target_entries, overlay_entries, idmap_string_pool.release()));
 
   return std::move(loaded_idmap);
 }
 
+bool LoadedIdmap::IsUpToDate() const {
+  return idmap_last_mod_time_ == getFileModDate(idmap_path_.c_str());
+}
+
 }  // namespace android
diff --git a/libs/androidfw/include/androidfw/Idmap.h b/libs/androidfw/include/androidfw/Idmap.h
index ccb57f373473..ecc1ce65d124 100644
--- a/libs/androidfw/include/androidfw/Idmap.h
+++ b/libs/androidfw/include/androidfw/Idmap.h
@@ -142,7 +142,13 @@ class IdmapResMap {
 class LoadedIdmap {
  public:
   // Loads an IDMAP from a chunk of memory. Returns nullptr if the IDMAP data was malformed.
-  static std::unique_ptr<const LoadedIdmap> Load(const StringPiece& idmap_data);
+  static std::unique_ptr<const LoadedIdmap> Load(const StringPiece& idmap_path,
+                                                 const StringPiece& idmap_data);
+
+  // Returns the path to the IDMAP.
+  inline const std::string& IdmapPath() const {
+    return idmap_path_;
+  }
 
   // Returns the path to the RRO (Runtime Resource Overlay) APK for which this IDMAP was generated.
   inline const std::string& OverlayApkPath() const {
@@ -167,6 +173,10 @@ class LoadedIdmap {
     return OverlayDynamicRefTable(data_header_, overlay_entries_, target_assigned_package_id);
   }
 
+  // Returns whether the idmap file on disk has not been modified since the construction of this
+  // LoadedIdmap.
+  bool IsUpToDate() const;
+
  protected:
   // Exposed as protected so that tests can subclass and mock this class out.
   LoadedIdmap() = default;
@@ -177,13 +187,17 @@ class LoadedIdmap {
   const Idmap_overlay_entry* overlay_entries_;
   const std::unique_ptr<ResStringPool> string_pool_;
 
+  const std::string idmap_path_;
   std::string overlay_apk_path_;
   std::string target_apk_path_;
+  const time_t idmap_last_mod_time_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(LoadedIdmap);
 
-  explicit LoadedIdmap(const Idmap_header* header,
+  explicit LoadedIdmap(std::string&& idmap_path,
+                       time_t last_mod_time,
+                       const Idmap_header* header,
                        const Idmap_data_header* data_header,
                        const Idmap_target_entry* target_entries,
                        const Idmap_overlay_entry* overlay_entries,
diff --git a/libs/androidfw/tests/Idmap_test.cpp b/libs/androidfw/tests/Idmap_test.cpp
index 41ba637da5d7..7aa0dbbafab3 100644
--- a/libs/androidfw/tests/Idmap_test.cpp
+++ b/libs/androidfw/tests/Idmap_test.cpp
@@ -38,7 +38,7 @@ class IdmapTest : public ::testing::Test {
  protected:
   void SetUp() override {
     // Move to the test data directory so the idmap can locate the overlay APK.
-    std::string original_path = base::GetExecutableDirectory();
+    original_path = base::GetExecutableDirectory();
     chdir(GetTestDataPath().c_str());
 
     system_assets_ = ApkAssets::Load("system/system.apk");
@@ -49,10 +49,14 @@ class IdmapTest : public ::testing::Test {
 
     overlayable_assets_ = ApkAssets::Load("overlayable/overlayable.apk");
     ASSERT_NE(nullptr, overlayable_assets_);
+  }
+
+  void TearDown() override {
     chdir(original_path.c_str());
   }
 
  protected:
+  std::string original_path;
   std::unique_ptr<const ApkAssets> system_assets_;
   std::unique_ptr<const ApkAssets> overlay_assets_;
   std::unique_ptr<const ApkAssets> overlayable_assets_;
@@ -221,8 +225,7 @@ TEST_F(IdmapTest, OverlaidResourceHasSameName) {
 
 TEST_F(IdmapTest, OverlayLoaderInterop) {
   std::string contents;
-  auto loader_assets = ApkAssets::LoadTable(GetTestDataPath() + "/loader/resources.arsc",
-                                            PROPERTY_LOADER);
+  auto loader_assets = ApkAssets::LoadTable("loader/resources.arsc", PROPERTY_LOADER);
 
   AssetManager2 asset_manager;
   asset_manager.SetApkAssets({overlayable_assets_.get(), loader_assets.get(),
@@ -241,4 +244,25 @@ TEST_F(IdmapTest, OverlayLoaderInterop) {
   ASSERT_EQ(GetStringFromApkAssets(asset_manager, val, cookie), "loader");
 }
 
+TEST_F(IdmapTest, OverlayAssetsIsUpToDate) {
+  std::string idmap_contents;
+  ASSERT_TRUE(base::ReadFileToString("overlay/overlay.idmap", &idmap_contents));
+
+  TemporaryFile temp_file;
+  ASSERT_TRUE(base::WriteStringToFile(idmap_contents, temp_file.path));
+
+  auto apk_assets = ApkAssets::LoadOverlay(temp_file.path);
+  ASSERT_NE(nullptr, apk_assets);
+  ASSERT_TRUE(apk_assets->IsUpToDate());
+
+  unlink(temp_file.path);
+  ASSERT_FALSE(apk_assets->IsUpToDate());
+  sleep(2);
+
+  base::WriteStringToFile("hello", temp_file.path);
+  sleep(2);
+
+  ASSERT_FALSE(apk_assets->IsUpToDate());
+}
+
 }  // namespace
diff --git a/services/core/java/com/android/server/om/IdmapManager.java b/services/core/java/com/android/server/om/IdmapManager.java
index 43fc7ed0e39d..90c85ada9def 100644
--- a/services/core/java/com/android/server/om/IdmapManager.java
+++ b/services/core/java/com/android/server/om/IdmapManager.java
@@ -63,20 +63,23 @@ class IdmapManager {
         mIdmapDaemon = IdmapDaemon.getInstance();
     }
 
+    /**
+     * Creates the idmap for the target/overlay combination and returns whether the idmap file was
+     * modified.
+     */
     boolean createIdmap(@NonNull final PackageInfo targetPackage,
             @NonNull final PackageInfo overlayPackage, int userId) {
         if (DEBUG) {
             Slog.d(TAG, "create idmap for " + targetPackage.packageName + " and "
                     + overlayPackage.packageName);
         }
-        final int sharedGid = UserHandle.getSharedAppGid(targetPackage.applicationInfo.uid);
         final String targetPath = targetPackage.applicationInfo.getBaseCodePath();
         final String overlayPath = overlayPackage.applicationInfo.getBaseCodePath();
         try {
             int policies = calculateFulfilledPolicies(targetPackage, overlayPackage, userId);
             boolean enforce = enforceOverlayable(overlayPackage);
             if (mIdmapDaemon.verifyIdmap(targetPath, overlayPath, policies, enforce, userId)) {
-                return true;
+                return false;
             }
             return mIdmapDaemon.createIdmap(targetPath, overlayPath, policies,
                     enforce, userId) != null;
diff --git a/services/core/java/com/android/server/om/OverlayManagerServiceImpl.java b/services/core/java/com/android/server/om/OverlayManagerServiceImpl.java
index d108e76e37df..05a4a38feef1 100644
--- a/services/core/java/com/android/server/om/OverlayManagerServiceImpl.java
+++ b/services/core/java/com/android/server/om/OverlayManagerServiceImpl.java
@@ -700,14 +700,15 @@ final class OverlayManagerServiceImpl {
         final PackageInfo overlayPackage = mPackageManager.getPackageInfo(overlayPackageName,
                 userId);
 
-        // Immutable RROs targeting to "android", ie framework-res.apk, are handled by native layers.
+        // Immutable RROs targeting to "android", ie framework-res.apk, are handled by native
+        // layers.
+        boolean modified = false;
         if (targetPackage != null && overlayPackage != null
                 && !("android".equals(targetPackageName)
                     && !isPackageConfiguredMutable(overlayPackageName))) {
-            mIdmapManager.createIdmap(targetPackage, overlayPackage, userId);
+            modified |= mIdmapManager.createIdmap(targetPackage, overlayPackage, userId);
         }
 
-        boolean modified = false;
         if (overlayPackage != null) {
             modified |= mSettings.setBaseCodePath(overlayPackageName, userId,
                     overlayPackage.applicationInfo.getBaseCodePath());
diff --git a/services/core/java/com/android/server/om/TEST_MAPPING b/services/core/java/com/android/server/om/TEST_MAPPING
index 75229a1adccc..6edd76f1810a 100644
--- a/services/core/java/com/android/server/om/TEST_MAPPING
+++ b/services/core/java/com/android/server/om/TEST_MAPPING
@@ -15,6 +15,9 @@
       "name": "OverlayHostTests"
     },
     {
+      "name": "OverlayRemountedTest"
+    },
+    {
       "name": "CtsAppSecurityHostTestCases",
       "options": [
         {
diff --git a/services/tests/servicestests/src/com/android/server/om/OverlayManagerServiceImplTestsBase.java b/services/tests/servicestests/src/com/android/server/om/OverlayManagerServiceImplTestsBase.java
index 820e61cb0a08..9eda718ed922 100644
--- a/services/tests/servicestests/src/com/android/server/om/OverlayManagerServiceImplTestsBase.java
+++ b/services/tests/servicestests/src/com/android/server/om/OverlayManagerServiceImplTestsBase.java
@@ -377,8 +377,7 @@ class OverlayManagerServiceImplTestsBase {
                 return false;
             }
             final String key = createKey(overlayPackage.packageName, userId);
-            mIdmapFiles.add(key);
-            return true;
+            return mIdmapFiles.add(key);
         }
 
         @Override