Enable flutter engine to also work with .*so files on android (#4298)

* Enable flutter engine to also work with .*so files on android

We would like to be able to use native tools (e.g. simpleperf, gdb) with
precompiled flutter apps.  The native tools work much better with *.so
files instead of the custom formats the Dart VM uses by default.

This CL adds support for being able to load the flutter app from an *.so
file on Android.

* Add sanity check to ensure we have either shared library or instruction snapshot (but not both)

common/settings.h

@@ -26,6 +26,7 @@ struct Settings {
   bool dart_non_checked_mode = false;
   bool enable_software_rendering = false;
   bool using_blink = true;
+  std::string aot_shared_library_path;
   std::string aot_snapshot_path;
   std::string aot_vm_snapshot_data_filename;
   std::string aot_vm_snapshot_instr_filename;

shell/common/engine.cc

@@ -163,20 +163,40 @@ void Engine::Init(const std::string& bundle_path) {
       dlsym(library_handle, "kDartIsolateSnapshotInstructions"));
 #elif OS(ANDROID)
   const blink::Settings& settings = blink::Settings::Get();
+  const std::string& aot_shared_library_path = settings.aot_shared_library_path;
   const std::string& aot_snapshot_path = settings.aot_snapshot_path;
-  FXL_CHECK(!aot_snapshot_path.empty());
-  vm_snapshot_data =
-      MemMapSnapshot(aot_snapshot_path, "vm_snapshot_data",
-                     settings.aot_vm_snapshot_data_filename, false);
-  vm_snapshot_instr =
-      MemMapSnapshot(aot_snapshot_path, "vm_snapshot_instr",
-                     settings.aot_vm_snapshot_instr_filename, true);
-  default_isolate_snapshot_data =
-      MemMapSnapshot(aot_snapshot_path, "isolate_snapshot_data",
-                     settings.aot_isolate_snapshot_data_filename, false);
-  default_isolate_snapshot_instr =
-      MemMapSnapshot(aot_snapshot_path, "isolate_snapshot_instr",
-                     settings.aot_isolate_snapshot_instr_filename, true);
+
+  if (!aot_shared_library_path.empty()) {
+    FXL_CHECK(aot_snapshot_path.empty());
+    dlerror();  // clear previous errors on thread
+    void* library_handle = dlopen(aot_shared_library_path.c_str(), RTLD_NOW);
+    const char* err = dlerror();
+    if (err != nullptr) {
+      FXL_LOG(FATAL) << "dlopen failed: " << err;
+    }
+    vm_snapshot_data = reinterpret_cast<const uint8_t*>(
+        dlsym(library_handle, "_kDartVmSnapshotData"));
+    vm_snapshot_instr = reinterpret_cast<const uint8_t*>(
+        dlsym(library_handle, "_kDartVmSnapshotInstructions"));
+    default_isolate_snapshot_data = reinterpret_cast<const uint8_t*>(
+        dlsym(library_handle, "_kDartIsolateSnapshotData"));
+    default_isolate_snapshot_instr = reinterpret_cast<const uint8_t*>(
+        dlsym(library_handle, "_kDartIsolateSnapshotInstructions"));
+  } else {
+    FXL_CHECK(!aot_snapshot_path.empty());
+    vm_snapshot_data =
+        MemMapSnapshot(aot_snapshot_path, "vm_snapshot_data",
+                       settings.aot_vm_snapshot_data_filename, false);
+    vm_snapshot_instr =
+        MemMapSnapshot(aot_snapshot_path, "vm_snapshot_instr",
+                       settings.aot_vm_snapshot_instr_filename, true);
+    default_isolate_snapshot_data =
+        MemMapSnapshot(aot_snapshot_path, "isolate_snapshot_data",
+                       settings.aot_isolate_snapshot_data_filename, false);
+    default_isolate_snapshot_instr =
+        MemMapSnapshot(aot_snapshot_path, "isolate_snapshot_instr",
+                       settings.aot_isolate_snapshot_instr_filename, true);
+  }
 #else
 #error Unknown OS
 #endif

shell/common/shell.cc

@@ -139,6 +139,9 @@ void Shell::InitStandalone(fxl::CommandLine command_line,
   command_line.GetOptionValue(FlagForSwitch(Switch::AotIsolateSnapshotData),
                               &settings.aot_isolate_snapshot_data_filename);
 
+  command_line.GetOptionValue(FlagForSwitch(Switch::AotSharedLibraryPath),
+                              &settings.aot_shared_library_path);
+
   command_line.GetOptionValue(
       FlagForSwitch(Switch::AotIsolateSnapshotInstructions),
       &settings.aot_isolate_snapshot_instr_filename);

shell/common/switches.h

@@ -22,6 +22,7 @@ namespace shell {
 // clang-format on
 
 DEF_SWITCHES_START
+DEF_SWITCH(AotSharedLibraryPath, "aot-shared-library-path", "Path to the *.so.")
 DEF_SWITCH(AotSnapshotPath, "aot-snapshot-path", "Path to the AOT snapshot.")
 DEF_SWITCH(AotVmSnapshotData, "vm-snapshot-data", "")
 DEF_SWITCH(AotVmSnapshotInstructions, "vm-snapshot-instr", "")

shell/platform/android/io/flutter/view/FlutterMain.java

@@ -30,6 +30,7 @@ public class FlutterMain {
     private static final String TAG = "FlutterMain";
 
     // Must match values in sky::shell::switches
+    private static final String AOT_SHARED_LIBRARY_PATH = "aot-shared-library-path";
     private static final String AOT_SNAPSHOT_PATH_KEY = "aot-snapshot-path";
     private static final String AOT_VM_SNAPSHOT_DATA_KEY = "vm-snapshot-data";
     private static final String AOT_VM_SNAPSHOT_INSTR_KEY = "vm-snapshot-instr";
@@ -39,6 +40,8 @@ public class FlutterMain {
     private static final String SNAPSHOT_BLOB_KEY = "snapshot-blob";
 
     // XML Attribute keys supported in AndroidManifest.xml
+    public static final String PUBLIC_AOT_AOT_SHARED_LIBRARY_PATH =
+        FlutterMain.class.getName() + '.' + AOT_SHARED_LIBRARY_PATH;
     public static final String PUBLIC_AOT_VM_SNAPSHOT_DATA_KEY =
         FlutterMain.class.getName() + '.' + AOT_VM_SNAPSHOT_DATA_KEY;
     public static final String PUBLIC_AOT_VM_SNAPSHOT_INSTR_KEY =
@@ -53,6 +56,7 @@ public class FlutterMain {
         FlutterMain.class.getName() + '.' + SNAPSHOT_BLOB_KEY;
 
     // Resource names used for components of the precompiled snapshot.
+    private static final String DEFAULT_AOT_SHARED_LIBRARY_PATH= "app.so";
     private static final String DEFAULT_AOT_VM_SNAPSHOT_DATA = "vm_snapshot_data";
     private static final String DEFAULT_AOT_VM_SNAPSHOT_INSTR = "vm_snapshot_instr";
     private static final String DEFAULT_AOT_ISOLATE_SNAPSHOT_DATA = "isolate_snapshot_data";
@@ -68,6 +72,7 @@ public class FlutterMain {
         .build();
 
     // Mutable because default values can be overridden via config properties
+    private static String sAotSharedLibraryPath = DEFAULT_AOT_SHARED_LIBRARY_PATH;
     private static String sAotVmSnapshotData = DEFAULT_AOT_VM_SNAPSHOT_DATA;
     private static String sAotVmSnapshotInstr = DEFAULT_AOT_VM_SNAPSHOT_INSTR;
     private static String sAotIsolateSnapshotData = DEFAULT_AOT_ISOLATE_SNAPSHOT_DATA;
@@ -78,6 +83,7 @@ public class FlutterMain {
     private static boolean sInitialized = false;
     private static ResourceExtractor sResourceExtractor;
     private static boolean sIsPrecompiled;
+    private static boolean sIsPrecompiledAsSharedLibrary;
     private static Settings sSettings;
 
     private static final class ImmutableSetBuilder<T> {
@@ -141,9 +147,9 @@ public class FlutterMain {
 
         long initStartTimestampMillis = SystemClock.uptimeMillis();
         initConfig(applicationContext);
+        initAot(applicationContext);
         initResources(applicationContext);
         System.loadLibrary("flutter");
-        initAot(applicationContext);
 
         // We record the initialization time using SystemClock because at the start of the
         // initialization we have not yet loaded the native library to call into dart_tools_api.h.
@@ -179,6 +185,9 @@ public class FlutterMain {
                 shellArgs.add("--" + AOT_VM_SNAPSHOT_INSTR_KEY + "=" + sAotVmSnapshotInstr);
                 shellArgs.add("--" + AOT_ISOLATE_SNAPSHOT_DATA_KEY + "=" + sAotIsolateSnapshotData);
                 shellArgs.add("--" + AOT_ISOLATE_SNAPSHOT_INSTR_KEY + "=" + sAotIsolateSnapshotInstr);
+            } else if (sIsPrecompiledAsSharedLibrary) {
+                shellArgs.add("--" + AOT_SHARED_LIBRARY_PATH + "=" +
+                    new File(PathUtils.getDataDirectory(applicationContext), sAotSharedLibraryPath));
             } else {
                 shellArgs.add("--cache-dir-path=" +
                     PathUtils.getCacheDirectory(applicationContext));
@@ -211,6 +220,7 @@ public class FlutterMain {
             Bundle metadata = applicationContext.getPackageManager().getApplicationInfo(
                 applicationContext.getPackageName(), PackageManager.GET_META_DATA).metaData;
             if (metadata != null) {
+                sAotSharedLibraryPath = metadata.getString(PUBLIC_AOT_AOT_SHARED_LIBRARY_PATH, DEFAULT_AOT_SHARED_LIBRARY_PATH);
                 sAotVmSnapshotData = metadata.getString(PUBLIC_AOT_VM_SNAPSHOT_DATA_KEY, DEFAULT_AOT_VM_SNAPSHOT_DATA);
                 sAotVmSnapshotInstr = metadata.getString(PUBLIC_AOT_VM_SNAPSHOT_INSTR_KEY, DEFAULT_AOT_VM_SNAPSHOT_INSTR);
                 sAotIsolateSnapshotData = metadata.getString(PUBLIC_AOT_ISOLATE_SNAPSHOT_DATA_KEY, DEFAULT_AOT_ISOLATE_SNAPSHOT_DATA);
@@ -228,13 +238,19 @@ public class FlutterMain {
         new ResourceCleaner(context).start();
         sResourceExtractor = new ResourceExtractor(context)
             .addResources(SKY_RESOURCES)
+            .addResource(sFlx);
+        if (sIsPrecompiledAsSharedLibrary) {
+          sResourceExtractor
+            .addResource(sAotSharedLibraryPath);
+        } else {
+          sResourceExtractor
             .addResource(sAotVmSnapshotData)
             .addResource(sAotVmSnapshotInstr)
             .addResource(sAotIsolateSnapshotData)
             .addResource(sAotIsolateSnapshotInstr)
-            .addResource(sFlx)
-            .addResource(sSnapshotBlob)
-            .start();
+            .addResource(sSnapshotBlob);
+        }
+        sResourceExtractor.start();
     }
 
     /**
@@ -261,10 +277,15 @@ public class FlutterMain {
             sAotIsolateSnapshotData,
             sAotIsolateSnapshotInstr
         ));
+        sIsPrecompiledAsSharedLibrary = assets.contains(sAotSharedLibraryPath);
+        if (sIsPrecompiled && sIsPrecompiledAsSharedLibrary) {
+          throw new RuntimeException(
+              "Found precompiled app as shared library and as Dart VM snapshots.");
+        }
     }
 
     public static boolean isRunningPrecompiledCode() {
-        return sIsPrecompiled;
+        return sIsPrecompiled || sIsPrecompiledAsSharedLibrary;
     }
 
     public static String findAppBundlePath(Context applicationContext) {