Add support of cross-building the engine for ARM64 Linux Host

[HidenoriMatsubayashi]

Description

Added cross-building Flutter Engine for ARM64 Linux platforms. This PR is part of ARM64 Linux support in the Flutter SDK.

Related PRs

• [flutter_tools] Add ARM64 Linux host and cross-building option support flutter#61221
• Add support of cross-building the engine for ARM64 Linux Host buildroot#390

Related Issues

• [flutter_tools] Add support for Linux host ARM flutter#56992
• support linux arm/aarch64 target platform flutter#60678

Tests

1. Build Test

First, I confirmed that Flutter Engine can be built for x64 and arm64. The procedure is as follows. All are operations on x64 Linux Host.

Get source code and setup build enviroment.

create .gclient file.
$ gclient sync
$ cd src

Cross-build for ARM64 Linux

$ ./flutter/tools/gn --target-os linux --linux-cpu arm64 --runtime-mode release
$ ninja -C out/linux_release_arm64
-> Passed!

$ ./flutter/tools/gn --target-os linux --linux-cpu arm64 --runtime-mode debug
$ ninja -C out/linux_debug_arm64
-> Passed!

Build for x64 Linux and Regression test.

$ ./flutter/tools/gn --unoptimized
$ ninja -C out/host_debug_unopt
-> Passed!

$ ./flutter/testing/run_tests.sh
-> All Tests Passed!

2. Run Flutter SDK and app on ARM64 Linux (Jetson Nano)

Second, using the artifacts for ARM64 built by the above procedure, I have confirmed that the Flutter SDK and Flutter app can work fine on Jetson Nano (ARM64 CPU).

All are operations on ARM64 Linux Host (Jetson Nano).

$ git clone https://github.com/flutter/flutter.git
$ export PATH=$PATH:{your working dir path}/flutter/bin
$ flutter doctor
   ... Error happened.

Copy dart-sdk which was locally built to ${your installpath}/bin/cache/.

$ flutter doctor
$ flutter config --enable-linux-desktop
$ flutter create sample
$ cd sample
$ flutter build linux
   ... Error happened.

Copy the Flutter SDK artifacts (build data) to ${your installpath}/bin/cache/artifacts/engine directory manually.

• out/linux_debug_arm64/flutter_patched_sdk to ${your installpath}/bin/cache/artifacts/engine/common/flutter_patched_sdk

• out/linux_debug_arm64/flutter_linux, gen/const_finder.dart.snapshot, flutter_tester, font-subset, gen/frontend_server.dart.snapshot, icudtl.dat, libflutter_linux_gtk.so, gen/flutter/lib/snapshot/isolate_snapshot.bin, gen/flutter/lib/snapshot/vm_isolate_snapshot.bin to ${your installpath}/bin/cache/artifacts/engine/artifacts/engine/linux-x64

• out/linux_release_arm64/flutter_patched_sdk to ${your installpath}/bin/cache/artifacts/engine/common/flutter_patched_sdk_product

• out/linux_release_arm64/flutter_linux, libflutter_linux_gtk.so to ${your installpath}/bin/cache/artifacts/engine/artifacts/engine/linux-x64-release

• out/linux_release_arm64/clang_x64/gen_snapshot to ${your installpath}/bin/cache/artifacts/engine/artifacts/engine/linux-x64-release

• For simple operation check, ${your installpath}/bin/cache/artifacts/engine/artifacts/engine/linux-x64-profile is omitted.

( $ flutter build linux --verbose )
$ flutter run -d linux

Checklist

Before you create this PR confirm that it meets all requirements listed below by checking the relevant checkboxes ([x]). This will ensure a smooth and quick review process.

• I read the contributor guide and followed the process outlined there for submitting PRs.
• I signed the CLA.
• I read and followed the C++, Objective-C, Java style guides for the engine.
• I read the tree hygiene wiki page, which explains my responsibilities.
• I updated/added relevant documentation.
• All existing and new tests are passing.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

Did any tests fail when you ran them? Please read handling breaking changes.

• No, no existing tests failed, so this is not a breaking change.
• Yes, this is a breaking change. If not, delete the remainder of this section.
  • I wrote a design doc: https://flutter.dev/go/template Replace this with a link to your design doc's short link
  • I got input from the developer relations team, specifically from: Replace with the names of who gave advice
  • I wrote a migration guide: https://flutter.dev/go/breaking-changes-template Replace this with a link to a pull request that adds the migration guide to https://flutter.dev/docs/release/breaking-changes

[iskakaushik]

@christopherfujino to route to the right reviewer for this.

[stuartmorgan-g]

This condition no longer matches the comment. Aren't these host tools? It's not clear to me why you are cross-compiling them.

[HidenoriMatsubayashi]

Yes, I have to modify the comment.

But I couldn't understand why if (current_toolchain == host_toolchain) was necessary. In order to run the Flutter SDK and Flutter Apps on ARM64 Linux platforms, we need to build dart-sdk, frontend_server.dart.snapshot and const_finder.dart.snapshot and so on. This condition is not necessary for cross build.

I think I got it for now. But I think you need to build the following in order to run Flutter SDK on ARM64 Linux. Correct?

• //flutter/flutter_frontend_server:frontend_server
• //third_party/dart:create_sdk
• //flutter/web_sdk
• //flutter/shell/testing
• //flutter/tools/const_finder
• //flutter/tools/font-subset

[stuartmorgan-g]

I don't know the answer to that offhand.

Are they uploaded as artifacts and then downloaded and run by the flutter tool? If so, then you are correct that they aren't host tools, in which case we should instead be deciding when to build them based on support Flutter SDK environments.

[HidenoriMatsubayashi]

@stuartmorgan
(cc: @christopherfujino please support me.)

Thank you for your reply.

Are they uploaded as artifacts and then downloaded and run by the flutter tool?

That's right.
I think that it is not necessary in the case where only cross build like Android and iOS, however it is necessary when running as Flutter SDK on Host.

I think that all can be built for ARM64 without problems.

//third_party/dart:create_sdk

This is dart-sdk and download to ${INSTALL_PATH}/flutter/bin/cache/dart-sdk. ARM64 is already supported (link)

//flutter/flutter_frontend_server:frontend_server

This is the Dart project, it can be built for ARM64.
It's downloaded to ${INSTALL_PATH}/flutter/bin/cache/artifacts/engine/linux-${arch}/frontend_server.dart.snapshot

//flutter/web_sdk

I'm not sure about this.

//flutter/shell/testing

This is the C++ source code for flutter_test?
It's downloaded to ${INSTALL_PATH}/flutter/bin/cache/artifacts/engine/linux-${arch}/flutter_tester

//flutter/tools/const_finder

This is the Dart project.
It's downloaded to ${INSTALL_PATH}/flutter/bin/cache/artifacts/engine/linux-${arch}/const_finder.dart.snapshot

//flutter/tools/font-subset

This is the C++ source code.
It's downloaded to ${INSTALL_PATH}/flutter/bin/cache/artifacts/engine/linux-${arch}/font-subset

[stuartmorgan-g]

Makes sense; I thought "host" in the comment meant build host, rather that "Flutter host". I think you'll want (is_linux && !is_chromeos) though.

The comment should probably be something like:

# Flutter SDK artifacts should only be built when either doing host builds, or
# for cross-compiled desktop targets.

(I wouldn't mention Linux since macOS and/or Windows could be done this way in the future.)

Also, you should extract this to a variable like build_engine_artifacts since it's used in two places.

[HidenoriMatsubayashi]

Thank you so much. I fixed it. Could you review my change?

[incon]

Description

Added cross-building Flutter Engine for ARM64 Linux platforms. This PR is part of ARM64 Linux support in the Flutter SDK.

Related PRs

• flutter/flutter#61221
• flutter/buildroot#390

Related Issues

• flutter/flutter#56992
• flutter/flutter#60678

Tests

1. Build Test

First, I confirmed that Flutter Engine can be built for x64 and arm64. The procedure is as follows. All are operations on x64 Linux Host.

Get source code and setup build enviroment.

create .gclient file.
$ gclient sync
$ cd src

Cross-build for ARM64 Linux

$ ./flutter/tools/gn --target-os linux --linux-cpu arm64 --runtime-mode release
$ ninja -C out/linux_release_arm64
-> Passed!

$ ./flutter/tools/gn --target-os linux --linux-cpu arm64 --runtime-mode debug
$ ninja -C out/linux_debug_arm64
-> Passed!

Build for x64 Linux and Regression test.

$ ./flutter/tools/gn --unoptimized
$ ninja -C out/host_debug_unopt
-> Passed!

$ ./flutter/testing/run_tests.sh
-> All Tests Passed!

2. Run Flutter SDK and app on ARM64 Linux (Jetson Nano)

Second, using the artifacts for ARM64 built by the above procedure, I have confirmed that the Flutter SDK and Flutter app can work fine on Jetson Nano (ARM64 CPU).

All are operations on ARM64 Linux Host (Jetson Nano).

$ git clone https://github.com/flutter/flutter.git
$ export PATH=$PATH:{your working dir path}/flutter/bin
$ flutter doctor
   ... Error happened.
Copy the dart-sdk which was locally built to ${your installpath}/bin/cache/.
$ flutter doctor
$ flutter config --enable-linux-desktop
$ flutter create sample
$ cd sample
$ flutter build linux
   ... Error happened.
Copy the build data to built to ${your installpath}/bin/cache/artifacts/engine/common/flutter_patched_sdk, ${your installpath}/bin/cache/artifacts/engine/common/flutter_patched_sdk_product, ${your installpath}/bin/cache/artifacts/engine/artifacts/engine/linux-x64, ${your installpath}/bin/cache/artifacts/engine/artifacts/engine/linux-x64-release and ${your installpath}/bin/cache/artifacts/engine/artifacts/engine/linux-x64-profile.
( $ flutter build linux --verbose )
$ flutter run -d linux

Checklist

Before you create this PR confirm that it meets all requirements listed below by checking the relevant checkboxes ([x]). This will ensure a smooth and quick review process.

• I read the contributor guide and followed the process outlined there for submitting PRs.
• I signed the CLA.
• I read and followed the C++, Objective-C, Java style guides for the engine.
• I read the tree hygiene wiki page, which explains my responsibilities.
• I updated/added relevant documentation.
• All existing and new tests are passing.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

Did any tests fail when you ran them? Please read handling breaking changes.

• No, no existing tests failed, so this is not a breaking change.

• Yes, this is a breaking change. If not, delete the remainder of this section.

  • I wrote a design doc: https://flutter.dev/go/template Replace this with a link to your design doc's short link
  • I got input from the developer relations team, specifically from: Replace with the names of who gave advice
  • I wrote a migration guide: https://flutter.dev/go/breaking-changes-template Replace this with a link to a pull request that adds the migration guide to https://flutter.dev/docs/release/breaking-changes

I've been able to complete the build step on my Linux x86 Host machine.
I'm unsure on what files I need copy over to my Raspberry Pi in this step Copy the build data to built to ${your installpath}/bin/cache/artifacts/engine/common/flutter_patched_sdk, ${your installpath}/bin/cache/artifacts/engine/common/flutter_patched_sdk_product, ${your installpath}/bin/cache/artifacts/engine/artifacts/engine/linux-x64, ${your installpath}/bin/cache/artifacts/engine/artifacts/engine/linux-x64-release and ${your installpath}/bin/cache/artifacts/engine/artifacts/engine/linux-x64-profile.
Could you please need me know what files I need to copy and to where, thank you.

[HidenoriMatsubayashi]

@incon
I updated the description.

[stuartmorgan-g]

Needs GN formatting so it passes CI, but otherwise LGTM. @chinmaygarde should review as well since he's more familiar with the engine artifacts though, to make sure that new logic makes sense to him as well.

[HidenoriMatsubayashi]

@stuartmorgan Thank you so much. I fixed the formatting error.

[cthurston]

Using these instructions to run on pi 4. The debug works and I can run and debug the sample application on the pi. Very nice.

However, I can't build a release. It seems that the clang_x64/gen_snapshot executable is still x86.

Update: I copied gen_snapshot_product to the gen_snapshot and it successfully built a release bundle. Wahoo!

Really nice write up has been created here:
https://wiki.loliot.net/docs/lang/flutter/engine/flutter-engine-for-linux-arm64/
https://wiki.loliot.net/docs/lang/flutter/engine/flutter-app-for-linux-arm64

[jwinarske]

I don't understand why this PR claims cross compilation for aarch64. I was able to cross compile the engine for arrch64 long before this PR.

[cthurston]

I believe this PR is so that you can compile and run inside of a linux desktop that is running on arm64, a raspberry pi running raspberry pi OS for example.

[jwinarske]

Yes I see the build on host, it also claims cross compilation. Imagine trying to build the engine on a raspberry pi? That would take an enternity... Hence why cross compiling is preferred, which already worked for ~2 years.