Cross-compile from x64 to arm64 (#20)

lib/commands/build.dart

@@ -44,6 +44,21 @@ class BuildPackageCommand extends BuildSubCommand with ELinuxExtension {
       allowed: <String>['wayland', 'gbm', 'eglstream', 'x11'],
       help: 'Target backend type that the app will run on devices.',
     );
+    argParser.addOption(
+      'target-sysroot',
+      defaultsTo: '/',
+      help: 'The root filesystem path of target platform for which '
+          'the app is compiled. This option is valid only '
+          'if the current host and target architectures are different.',
+    );
+    argParser.addOption(
+      'system-include-directories',
+      defaultsTo: null,
+      help:
+          'The additional system include paths to cross-compile for target platform. '
+          'This option is valid only '
+          'if the current host and target architectures are different.',
+    );
   }
 
   @override
@@ -70,12 +85,21 @@ class BuildPackageCommand extends BuildSubCommand with ELinuxExtension {
   /// See: [BuildApkCommand.runCommand] in `build_apk.dart`
   @override
   Future<FlutterCommandResult> runCommand() async {
+    // Not supported cross-building for x64 on arm64.
+    final String targetArch = stringArg('target-arch');
+    final String hostArch = _getCurrentHostPlatformArchName();
+    if (hostArch != targetArch && hostArch == 'arm64') {
+      globals.logger
+          .printError('Not supported cross-building for x64 on arm64.');
+      return FlutterCommandResult.fail();
+    }
+
     final BuildInfo buildInfo = await getBuildInfo();
-    final ELinuxBuildInfo eLinuxBuildInfo = ELinuxBuildInfo(
-      buildInfo,
-      targetArch: stringArg('target-arch'),
-      targetBackendType: stringArg('target-backend-type'),
-    );
+    final ELinuxBuildInfo eLinuxBuildInfo = ELinuxBuildInfo(buildInfo,
+        targetArch: targetArch,
+        targetBackendType: stringArg('target-backend-type'),
+        targetSysroot: stringArg('target-sysroot'),
+        systemIncludeDirectories: stringArg('system-include-directories'));
     validateBuild(eLinuxBuildInfo);
     displayNullSafetyMode(buildInfo);
 

lib/elinux_build_target.dart

@@ -12,6 +12,7 @@ import 'package:file/file.dart';
 import 'package:flutter_tools/src/artifacts.dart';
 import 'package:flutter_tools/src/base/common.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
+import 'package:flutter_tools/src/base/os.dart';
 import 'package:flutter_tools/src/base/process.dart';
 import 'package:flutter_tools/src/build_info.dart';
 import 'package:flutter_tools/src/build_system/build_system.dart';
@@ -68,7 +69,7 @@ abstract class ELinuxAssetBundle extends Target {
         getBuildModeForName(environment.defines[kBuildMode]);
     final Directory outputDirectory = environment.outputDir
         .childDirectory('flutter_assets')
-          ..createSync(recursive: true);
+      ..createSync(recursive: true);
 
     // Only copy the prebuilt runtimes and kernel blob in debug mode.
     if (buildMode == BuildMode.debug) {
@@ -348,11 +349,24 @@ class NativeBundle {
 
     // Run the native build.
     final String cmakeBuildType = buildMode.isPrecompiled ? 'Release' : 'Debug';
+    final String targetArch = buildInfo.targetArch;
+    final String hostArch = _getCurrentHostPlatformArchName();
+    final String targetSysroot = buildInfo.targetSysroot;
+    final String systemIncludeDirectories = buildInfo.systemIncludeDirectories;
+    final bool needCrossBuild = targetArch != hostArch;
+    final bool needCrossBuildOptionsForArm64 = targetArch == 'arm64';
     RunResult result = await _processUtils.run(
       <String>[
         'cmake',
         '-DCMAKE_BUILD_TYPE=$cmakeBuildType',
         '-DFLUTTER_TARGET_BACKEND_TYPE=${buildInfo.targetBackendType}',
+        if (needCrossBuild) '-DFLUTTER_TARGET_PLATFORM_SYSROOT=$targetSysroot',
+        if (needCrossBuild && systemIncludeDirectories != null)
+          '-DFLUTTER_SYSTEM_INCLUDE_DIRECTORIES=$systemIncludeDirectories',
+        if (needCrossBuildOptionsForArm64)
+          '-DCMAKE_C_COMPILER_TARGET=aarch64-linux-gnu',
+        if (needCrossBuildOptionsForArm64)
+          '-DCMAKE_CXX_COMPILER_TARGET=aarch64-linux-gnu',
         eLinuxDir.path,
       ],
       workingDirectory: outputDir.path,
@@ -389,6 +403,11 @@ class NativeBundle {
   }
 }
 
+String _getCurrentHostPlatformArchName() {
+  final HostPlatform hostPlatform = getCurrentHostPlatform();
+  return getNameForHostPlatformArch(hostPlatform);
+}
+
 /// Converts [targetArch] to an arch name that corresponds to the `BUILD_ARCH`
 /// value used by the eLinux native builder.
 String getELinuxBuildArch(String targetArch) {

lib/elinux_builder.dart

@@ -34,12 +34,16 @@ class ELinuxBuildInfo {
     this.buildInfo, {
     @required this.targetArch,
     @required this.targetBackendType,
+    @required this.targetSysroot,
+    @required this.systemIncludeDirectories,
   })  : assert(targetArch != null),
         assert(targetBackendType != null);
 
   final BuildInfo buildInfo;
   final String targetArch;
   final String targetBackendType;
+  final String targetSysroot;
+  final String systemIncludeDirectories;
 }
 
 /// See:

lib/elinux_device.dart

@@ -224,10 +224,14 @@ class ELinuxDevice extends Device {
     BuildInfo buildInfo,
   }) async {
     final FlutterProject project = FlutterProject.current();
+    // TODO(hidenori): change the fixed values (|targetSysroot| and |systemIncludeDirectories|)
+    //  to the values from user-specified custom-devices feilds.
     final ELinuxBuildInfo eLinuxBuildInfo = ELinuxBuildInfo(
       buildInfo,
       targetArch: _targetArch,
       targetBackendType: _backendType,
+      targetSysroot: '/',
+      systemIncludeDirectories: null,
     );
     await ELinuxBuilder.buildBundle(
       project: project,

lib/elinux_doctor.dart

@@ -219,7 +219,8 @@ class ELinuxWorkflow extends Workflow {
 
   @override
   bool get appliesToHostPlatform =>
-      _operatingSystemUtils.hostPlatform != HostPlatform.linux_arm64;
+      (_operatingSystemUtils.hostPlatform == HostPlatform.linux_x64) ||
+      (_operatingSystemUtils.hostPlatform == HostPlatform.linux_arm64);
 
   @override
   bool get canLaunchDevices => true;

templates/app/CMakeLists.txt.tmpl

@@ -15,6 +15,12 @@ if(FLUTTER_TARGET_PLATFORM_SYSROOT)
   set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)
   set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
   set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
+
+  # Basically we use this include when we got the following error:
+  #  fatal error: 'bits/c++config.h' file not found
+  if(FLUTTER_TARGET_PLATFORM_SYSROOT)
+    include_directories(SYSTEM ${FLUTTER_SYSTEM_INCLUDE_DIRECTORIES})
+  endif()
 endif()
 
 # Configure build options.