Linux on aarch64 support for Flutter

[leclairem]

Description

Submitted per Ian Ward's request.
Working on a project using a Raspberry pi4 to run a flutter application that requires realm with flexible sync to retrieve data and persist transactions.
Installation steps to build and load application:

1. Application directory is opened in a docker container with balenalib/raspberrypi4-64 base image
2. App is built with "flutter build linux"
3. Release folder is uploaded to rpi4

When the app is started it immediately crashes with the following:
[ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: Invalid argument(s): Failed to load dynamic library 'librealm_dart.so': librealm_dart.so: cannot open shared object file: No such file or directory
#0 _openRealmLib (package:realm/src/init.dart:81)
#1 initRealm (package:realm/src/init.dart:105)
#2 new RealmCore. (package:realm/src/native/realm_core.dart:68)
#3 new _RealmCore (package:realm/src/native/realm_core.dart:76)
#4 realmCore (package:realm/src/native/realm_core.dart:49)

The .so file packaged in the release folder is x86_64
~/Desktop/release/bundle/lib $ file librealm_dart.so
librealm_dart.so: ELF 64-bit LSB shared object, x86-64, version 1 (GNU/Linux), dynamically linked, BuildID[sha1]=e82f6eae35d31178157e461cd12e7dc9fdedce11, not stripped

Our project requires a aarch64 librealm_dart.so

How important is this improvement for you?

Dealbreaker

[fealebenpae]

Hey @leclairem,

AFAICT Flutter doesn't support Raspberry Pi (or Linux cross-compilation in general). But it should be possible to compile the Realm SDK for aarch64. I'm not familiar with the balenalib/raspberrypi4-64 image, but a cursory search through their documentation reveals that there are extra steps necessary to enable cross-compilation.

In any case, I don't know enough about the Balena images to be able to offer specific guidance, but if you use something like https://github.com/Pro/raspi-toolchain to build the Realm SDK from source then it's just a matter of setting the CMAKE_TOOLCHAIN_FILE environment variable to point to the toolchain file and then run scripts/build-linux.sh to manually produce the aarch64 librealm_dart.so you need.