Cross‑Compiling Flutter Apps for RISC‑V Boards

Introduction

Cross-compiling Flutter apps for RISC-V boards unlocks embedded use cases and custom hardware acceleration. As RISC-V architectures gain traction in edge devices, enabling Flutter on RISC-V empowers developers to deliver rich, Dart-driven interfaces on open-source silicon. This tutorial dives into setting up a RISC-V toolchain, patching the Flutter engine, building your app, and optimizing performance for RISC-V Flutter deployments.

Setting Up the RISC-V Toolchain

First, install a cross-compile toolchain targeting your board’s ABI (RV32IMAC, RV64GC, etc.). On Ubuntu:

sudo apt update
sudo apt install gcc-riscv64-unknown-elf binutils-riscv64-unknown-elf

Clone and build a glibc or musl sysroot matching your board:

git clone https://github.com/riscv/riscv-glibc
cd riscv-glibc
mkdir build && cd build
../configure --host=riscv64-unknown-linux-gnu --prefix=$HOME/riscv-sysroot
make -j$(nproc) && make

Set environment variables:

export RISCV_TOOLCHAIN=$HOME/riscv-toolchain
export SYSROOT=$HOME/riscv-sysroot
export PATH=$RISCV_TOOLCHAIN/bin:$PATH

Ensure you can compile a “Hello World” C program before proceeding.

Configuring the Flutter Engine for RISC-V

Flutter’s engine must be recompiled to target RISC-V Linux. Clone the engine repo:

git clone https://github.com/flutter/engine.git
cd

Modify flutter/tools/gn to recognize a riscv64 target:

if (target_cpu == "riscv64") {
  toolchain("riscv64-linux") {
    cc = "${ENV_PATH}/riscv64-unknown-linux-gnu-gcc"
    cxx = "${ENV_PATH}/riscv64-unknown-linux-gnu-g++"
    ar = "${ENV_PATH}/riscv64-unknown-linux-gnu-ar"
    sysroot = "${SYSROOT}"
  }
}

Generate build files with GN:

gn gen out/android_riscv64 --args='target_os="linux" target_cpu="riscv64" is_debug=false use_x11=false'

Build libflutter_engine.so:

ninja -C out/android_riscv64 flutter_engine

Copy the resulting .so and headers into a Flutter plugin or embed them directly into your Flutter project under linux/riscv64.

Cross-Compiling and Deploying the App

In your Flutter project, create a custom Linux desktop target in linux/CMakeLists.txt. Add:

if(CMAKE_SYSTEM_PROCESSOR STREQUAL "riscv64")
  set(FLUTTER_ENGINE_PATH "${CMAKE_SOURCE_DIR}/../engine/linux/riscv64")
endif()

Point the build to your cross toolchain:

cmake -S linux -B linux/build_riscv64 \
  -DCMAKE_TOOLCHAIN_FILE=$SYSROOT/usr/share/cmake-riscv64-linux.cmake \
  -DCMAKE_BUILD_TYPE=Release
cmake --build linux/build_riscv64 -j

Bundle assets and the RISC-V engine library into the linux/build_riscv64 directory. Finally, transfer the build artifact to your board via SCP or flash tools:

scp -r linux/build_riscv64 user@riscv-board:/home/user/my_flutter_app
ssh user@riscv-board "~/my_flutter_app/my_flutter_app"

App output should render using your board’s display driver or frame buffer.

Optimizing Performance on RISC-V

Performance tuning is critical on resource-constrained boards. Key strategies:

• Enable ThinLTO in GN args (is_official_build=true, use_thin_lto=true).

• Strip symbols from engine and app binaries:

riscv64-unknown-linux-gnu-strip --strip-unneeded libflutter_engine.so

• Use Flutter’s deferred components or dynamic streaming of asset bundles to reduce startup time.

• Leverage SIMD extensions (e.g., RISC-V Vector extension) by patching the engine’s target_cpu flags with -march=rv64gcv.

• Profile with perf:

sudo perf record -p $(pidof my_flutter_app) -g
sudo perf report

Tackle hotspots by offloading computations to native C or Rust modules via FFI, reducing Dart overhead where heavy loops or floating-point math occur.

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Conclusion

Cross-compiling Flutter apps for RISC-V boards involves careful setup of a RISC-V toolchain, patching and building the Flutter engine, integrating the engine into your Flutter project, and optimizing for performance. By following these steps, you can achieve a fully native, high-performance Flutter experience on emerging RISC-V hardware.