android: Make a special ZygotePreload for Trichrome

This is needed to avoid hardcoding "libmonochrome" in //content, as
discussed in http://crrev.com/c/3165931.

Also pull the guard flag from the main change to make it clear how the
two preloads are going to differ.

Bug: 1154224
Change-Id: If4b2606fe3e2c902854f235d6e83a85d4d0805ce
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3172621
Reviewed-by: Bo <boliu@chromium.org>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Egor Pasko <pasko@chromium.org>
Cr-Commit-Position: refs/heads/main@{#924392}

base/android/java/src/org/chromium/base/library_loader/LibraryLoader.java

@@ -71,6 +71,10 @@ public class LibraryLoader {
     private static final String REACHED_CODE_SAMPLING_INTERVAL_KEY =
             "reached_code_sampling_interval";
 
+    // Compile time switch for sharing RELRO between the browser and the app zygote.
+    // TODO(crbug.com/1154224): remove when the issue is closed.
+    private static final boolean ALLOW_CHROMIUM_LINKER_IN_ZYGOTE = false;
+
     // Default sampling interval for reached code profiler in microseconds.
     private static final int DEFAULT_REACHED_CODE_SAMPLING_INTERVAL_US = 10000;
 
@@ -155,6 +159,12 @@ public class LibraryLoader {
         int CHILD_WITHOUT_ZYGOTE = 2;
     }
 
+    // Returns true when sharing RELRO between the browser process and the app zygote should *not*
+    // be attempted.
+    public static boolean mainProcessIntendsToProvideRelroFd() {
+        return !ALLOW_CHROMIUM_LINKER_IN_ZYGOTE || Build.VERSION.SDK_INT <= Build.VERSION_CODES.R;
+    }
+
     /**
      * Inner class encapsulating points of communication between instances of LibraryLoader in
      * different processes.

chrome/android/BUILD.gn

@@ -2456,6 +2456,7 @@ android_library("base_module_java") {
   sources = [
     "../browser/attribution_reporting/android/java/src/org/chromium/chrome/browser/attribution_reporting/AttributionReportingProvider.java",
     "java/src/com/google/ipc/invalidation/ticl/android2/channel/GcmRegistrationTaskService.java",
+    "java/src/org/chromium/chrome/app/TrichromeZygotePreload.java",
     "java/src/org/chromium/chrome/browser/ChromeBackgroundService.java",
     "java/src/org/chromium/chrome/browser/ChromeBackupAgent.java",
     "java/src/org/chromium/chrome/browser/DeferredStartupHandler.java",

chrome/android/chrome_public_apk_tmpl.gni

@@ -22,6 +22,7 @@ default_chrome_public_jinja_variables = [
   "channel=$android_channel",
   "enable_vr=$enable_vr",
   "include_arcore_manifest_flag=false",
+  "zygote_preload_class=org.chromium.content_public.app.ZygotePreload",
 ]
 
 # Enable stack unwinding only on official build with specific channels. It is

chrome/android/expectations/monochrome_public_bundle.AndroidManifest.expected

@@ -85,7 +85,7 @@
       android:roundIcon="@drawable/ic_launcher_round"
       android:supportsRtl="true"
       android:use32bitAbi="true"
-      android:zygotePreloadName="org.chromium.content.app.ZygotePreload">
+      android:zygotePreloadName="org.chromium.content_public.app.ZygotePreload">
     <activity  # DIFF-ANCHOR: ea1a94af
         android:name="com.google.android.gms.common.api.GoogleApiActivity"
         android:exported="false"

chrome/android/expectations/trichrome_chrome_bundle.AndroidManifest.expected

@@ -85,7 +85,7 @@
       android:roundIcon="@drawable/ic_launcher_round"
       android:supportsRtl="true"
       android:use32bitAbi="true"
-      android:zygotePreloadName="org.chromium.content.app.ZygotePreload">
+      android:zygotePreloadName="org.chromium.chrome.app.TrichromeZygotePreload">
     <activity  # DIFF-ANCHOR: ea1a94af
         android:name="com.google.android.gms.common.api.GoogleApiActivity"
         android:exported="false"

chrome/android/java/AndroidManifest.xml

@@ -177,7 +177,7 @@ by a child template that "extends" this file.
         android:largeHeap="false"
         android:manageSpaceActivity="@string/manage_space_activity"
         android:supportsRtl="true"
-        android:zygotePreloadName="org.chromium.content.app.ZygotePreload"
+        android:zygotePreloadName="{{ zygote_preload_class }}"
         {% if backup_key is defined %}
         android:allowBackup="true"
         android:backupAgent="org.chromium.chrome.browser.ChromeBackupAgent"

chrome/android/java/src/org/chromium/chrome/app/TrichromeZygotePreload.java

@@ -0,0 +1,24 @@
+// Copyright 2021 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.chrome.app;
+
+import android.content.pm.ApplicationInfo;
+
+import org.chromium.base.library_loader.LibraryLoader;
+import org.chromium.chrome.browser.ProductConfig;
+import org.chromium.content_public.app.ZygotePreload;
+
+/**
+ * The {@link ZygotePreload} allowing to use the ModernLinker when running Trichrome.
+ */
+public class TrichromeZygotePreload extends ZygotePreload {
+    @Override
+    public void doPreload(ApplicationInfo appInfo) {
+        // The ModernLinker is only needed when the App Zygote intends to create the RELRO region.
+        boolean useModernLinker = ProductConfig.USE_MODERN_LINKER
+                && !LibraryLoader.mainProcessIntendsToProvideRelroFd();
+        doPreloadCommon(appInfo, useModernLinker);
+    }
+}

chrome/android/trichrome.gni

@@ -35,6 +35,7 @@ trichrome_jinja_variables = [
   "trichrome_library=$trichrome_library_package",
   "trichrome_certdigest=$trichrome_certdigest",
   "use32bitAbi=android:use32bitAbi=\"true\"",
+  "zygote_preload_class=org.chromium.chrome.app.TrichromeZygotePreload",
 ]
 
 trichrome_synchronized_proguard =

content/public/android/BUILD.gn

@@ -99,7 +99,6 @@ android_library("content_main_dex_java") {
     "java/src/org/chromium/content/app/PrivilegedProcessService3.java",
     "java/src/org/chromium/content/app/PrivilegedProcessService4.java",
     "java/src/org/chromium/content/app/SandboxedProcessService.java",
-    "java/src/org/chromium/content/app/ZygotePreload.java",
     "java/src/org/chromium/content/browser/BrowserStartupControllerImpl.java",
     "java/src/org/chromium/content/browser/ChildProcessCreationParamsImpl.java",
     "java/src/org/chromium/content/browser/ContentChildProcessConstants.java",
@@ -110,6 +109,7 @@ android_library("content_main_dex_java") {
     "java/src/org/chromium/content/common/ContentSwitchUtils.java",
     "java/src/org/chromium/content/common/SurfaceWrapper.java",
     "java/src/org/chromium/content_public/app/ChildProcessServiceFactory.java",
+    "java/src/org/chromium/content_public/app/ZygotePreload.java",
     "java/src/org/chromium/content_public/browser/BrowserStartupController.java",
     "java/src/org/chromium/content_public/browser/BrowserTaskExecutor.java",
     "java/src/org/chromium/content_public/browser/ChildProcessCreationParams.java",

content/public/android/java/src/org/chromium/content/app/ZygotePreload.java → content/public/android/java/src/org/chromium/content_public/app/ZygotePreload.java

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-package org.chromium.content.app;
+package org.chromium.content_public.app;
 
 import android.annotation.SuppressLint;
 import android.annotation.TargetApi;
@@ -32,13 +32,19 @@ public class ZygotePreload implements android.app.ZygotePreload {
     @SuppressLint("Override")
     @Override
     public void doPreload(ApplicationInfo appInfo) {
-        try {
-            // Using concatenation rather than %s to allow values to be inlined by R8.
-            Log.i(TAG,
-                    "Loaded Zygote. version=" + VersionConstants.PRODUCT_VERSION
-                            + " minSdkVersion=" + BuildConfig.MIN_SDK_VERSION
-                            + " isBundle=" + BuildConfig.BUNDLES_SUPPORTED);
+        // Non-trichrome zygotes always use the system linker.
+        doPreloadCommon(appInfo, /* useModernLinker= */ false);
+    }
 
+    protected final void doPreloadCommon(ApplicationInfo appInfo, boolean useModernLinker) {
+        // Using concatenation rather than %s to allow values to be inlined by R8.
+        Log.i(TAG,
+                "Loaded Zygote. version=" + VersionConstants.PRODUCT_VERSION
+                        + " minSdkVersion=" + BuildConfig.MIN_SDK_VERSION
+                        + " isBundle=" + BuildConfig.BUNDLES_SUPPORTED);
+        try {
+            LibraryLoader.getInstance().setLinkerImplementation(
+                    /* useChromiumLinker= */ useModernLinker, useModernLinker);
             // The current thread time is the best approximation we have of the zygote start time
             // since Process.getStartUptimeMillis() is not reliable in the zygote process. This will
             // be the total CPU time the current thread has been running, and is reset on fork so

content/shell/android/shell_apk/AndroidManifest.xml.jinja2

@@ -24,7 +24,7 @@
 
     <application android:name="org.chromium.content_shell_apk.ContentShellApplication"
             android:icon="@mipmap/app_icon"
-            android:zygotePreloadName="org.chromium.content.app.ZygotePreload"
+            android:zygotePreloadName="org.chromium.content_public.app.ZygotePreload"
             android:label="{% block application_label %}Content Shell{% endblock %}">
         <activity android:name="org.chromium.content_shell_apk.ContentShellActivity"
                   android:launchMode="singleTask"