ettom / flutter-ci

flutter engine binaries

flutter engine binaries for armv7, aarch64

This repo contains flutter engine binaries (in the https://github.com/ardera/flutter-engine-binaries-for-arm filesystem layout) for armv7 and aarch64. The binaries come in 2 variants: generic, and tuned for the Pi 4 CPU.

📦 Downloads

See Releases.

🛠️ Build Config and Compiler Invocation

Build Config

The engine build is configured with:

$ ./src/flutter/tools/gn \
  --runtime-mode <debug / profile / release> \
  --target-os linux \
  --linux-cpu <arm / arm64> \
  --arm-float-abi hard \
  --target-dir build \
  --embedder-for-target \
  --disable-desktop-embeddings \
  --no-build-glfw-shell \
  --no-build-embedder-examples \
  --no-goma

--arm-float-abi hard is only specified when building for armv7.

After that, the following args are added to the args.gn file for the generic flavor:

arm_cpu = "generic"
arm_tune = "generic"

When tuning for pi 4, the following args are specified instead:

arm_cpu = "cortex-a72+nocrypto"
arm_tune = "cortex-a72"

For both armv7 and aarch64, the engine is built against the sysroot provided by the engine build scripts, which is some debian sid sysroot from 2020. (See https://github.com/flutter/buildroot/blob/master/build/linux/sysroot_scripts/install-sysroot.py)

Compiler Invocation

This will result in the clang compiler being invoked with the following args:

artifact	compiler arguments
armv7-generic	--target=armv7-linux-gnueabihf -mcpu=generic -mtune=generic
pi4	--target=armv7-linux-gnueabihf -mcpu=cortex-a72+nocrypto -mtune=cortex-a721
aarch64-generic	--target=aarch64-linux-gnu -mcpu=generic -mtune=generic
pi4-64	--target=aarch64-linux-gnu -mcpu=cortex-a72+nocrypto -mtune=cortex-a721

Footnotes

1. The CPU of the Raspberry Pi 4 is a Cortex-A72. +nocrypto is specified for -mcpu because the A72 in the Pi 4 is (apparently) the only A72 in the world that doesn't support cryptography instructions: https://github.com/ardera/flutter-ci/issues/3#issuecomment-1272330857 ↩ ↩²