Use Dart's new direct ELF generator to package AOT blobs as shared libraries...

Use Dart's new direct ELF generator to package AOT blobs as shared libraries in Android APKs (#33611)

This is a replacement for the old implementation of --build-shared-library
that emits an AOT assembly snapshot and feeds it to the Android NDK toolchain.

packages/flutter_tools/lib/src/android/gradle.dart

@@ -429,7 +429,7 @@ Future<void> _buildGradleProjectV2(
     command.add('-Pfilesystem-roots=${buildInfo.fileSystemRoots.join('|')}');
   if (buildInfo.fileSystemScheme != null)
     command.add('-Pfilesystem-scheme=${buildInfo.fileSystemScheme}');
-  if (buildInfo.buildSharedLibrary && androidSdk.ndk != null) {
+  if (buildInfo.buildSharedLibrary) {
     command.add('-Pbuild-shared-library=true');
   }
   if (buildInfo.targetPlatform != null)

packages/flutter_tools/lib/src/base/build.dart

@@ -6,7 +6,6 @@ import 'dart:async';
 
 import 'package:meta/meta.dart';
 
-import '../android/android_sdk.dart';
 import '../artifacts.dart';
 import '../build_info.dart';
 import '../bundle.dart';
@@ -101,19 +100,6 @@ class AOTSnapshotter {
     if (platform == TargetPlatform.ios)
       buildSharedLibrary = false;
 
-    if (buildSharedLibrary && androidSdk.ndk == null) {
-      final String explanation = AndroidNdk.explainMissingNdk(androidSdk.directory);
-      printError(
-        'Could not find NDK in Android SDK at ${androidSdk.directory}:\n'
-        '\n'
-        '  $explanation\n'
-        '\n'
-        'Unable to build with --build-shared-library\n'
-        'To install the NDK, see instructions at https://developer.android.com/ndk/guides/'
-      );
-      return 1;
-    }
-
     final PackageMap packageMap = PackageMap(packagesPath);
     final String packageMapError = packageMap.checkValid();
     if (packageMapError != null) {
@@ -141,11 +127,16 @@ class AOTSnapshotter {
     }
 
     final String assembly = fs.path.join(outputDir.path, 'snapshot_assembly.S');
-    if (buildSharedLibrary || platform == TargetPlatform.ios) {
+    if (platform == TargetPlatform.ios) {
       // Assembly AOT snapshot.
       outputPaths.add(assembly);
       genSnapshotArgs.add('--snapshot_kind=app-aot-assembly');
       genSnapshotArgs.add('--assembly=$assembly');
+    } else if (buildSharedLibrary) {
+      final String aotSharedLibrary = fs.path.join(outputDir.path, 'app.so');
+      outputPaths.add(aotSharedLibrary);
+      genSnapshotArgs.add('--snapshot_kind=app-aot-elf');
+      genSnapshotArgs.add('--assembly=$aotSharedLibrary');
     } else {
       // Blob AOT snapshot.
       final String vmSnapshotData = fs.path.join(outputDir.path, 'vm_snapshot_data');
@@ -224,12 +215,6 @@ class AOTSnapshotter {
       final RunResult result = await _buildIosFramework(iosArch: iosArch, assemblyPath: assembly, outputPath: outputDir.path);
       if (result.exitCode != 0)
         return result.exitCode;
-    } else if (buildSharedLibrary) {
-      final RunResult result = await _buildAndroidSharedLibrary(assemblyPath: assembly, outputPath: outputDir.path);
-      if (result.exitCode != 0) {
-        printError('Failed to build AOT snapshot. Compiler terminated with exit code ${result.exitCode}');
-        return result.exitCode;
-      }
     }
 
     // Compute and record build fingerprint.
@@ -273,25 +258,6 @@ class AOTSnapshotter {
     return linkResult;
   }
 
-  /// Builds an Android shared library at [outputPath]/app.so from the assembly
-  /// source at [assemblyPath].
-  Future<RunResult> _buildAndroidSharedLibrary({
-    @required String assemblyPath,
-    @required String outputPath,
-  }) async {
-    // A word of warning: Instead of compiling via two steps, to a .o file and
-    // then to a .so file we use only one command. When using two commands
-    // gcc will end up putting a .eh_frame and a .debug_frame into the shared
-    // library. Without stripping .debug_frame afterwards, unwinding tools
-    // based upon libunwind use just one and ignore the contents of the other
-    // (which causes it to not look into the other section and therefore not
-    // find the correct unwinding information).
-    final String assemblySo = fs.path.join(outputPath, 'app.so');
-    return await runCheckedAsync(<String>[androidSdk.ndk.compiler]
-        ..addAll(androidSdk.ndk.compilerArgs)
-        ..addAll(<String>[ '-shared', '-nostdlib', '-o', assemblySo, assemblyPath ]));
-  }
-
   /// Compiles a Dart file to kernel.
   ///
   /// Returns the output kernel file path, or null on failure.