sdlamp2/docs/TOOLCHAIN.md

Cross-Compilation Toolchain

This document describes the target device and the arm64 Docker build container used to produce binaries for it.

Target Device

Hardware

• Device: Anbernic RG35XX Plus
• SoC: Allwinner H700 — quad-core ARM Cortex-A53 @ 1.5 GHz (AArch64 / ARMv8-A)
• GPU: Mali G31 MP2
• RAM: 1 GB LPDDR4
• Display: 640×480 IPS

Software

• OS: Ubuntu 22.04 LTS (Jammy Jellyfish) — modified stock firmware
• Kernel: Linux 4.9.170 aarch64 (proprietary, no source released by Anbernic)
• Architecture: aarch64 / arm64 (confirmed via dpkg --print-architecture)
• glibc: 2.35

Libraries on Device

All required shared libraries are pre-installed. Most are at /usr/lib/, some at /usr/lib/aarch64-linux-gnu/ (Debian multiarch path):

Library	Soname	Notes
SDL2	libSDL2-2.0.so.0.12.0	SDL 2.0.12
SDL2_image	libSDL2_image-2.0.so.0.900.0	SDL2_image 2.0.9, at multiarch path
libavcodec	libavcodec.so.58	FFmpeg ~4.x
libavformat	libavformat.so.58	FFmpeg ~4.x
libavutil	libavutil.so.56	FFmpeg ~4.x
libswresample	libswresample.so.3	FFmpeg ~4.x

Implications for Cross-Compilation

• The device userland is Debian/Ubuntu-based (has dpkg, apt-get, systemd)
• Shared libraries are already present — no need to bundle or build them via Buildroot
• A native aarch64 compile (e.g. inside an arm64 Docker container) produces working binaries
• Must link against glibc ≤ 2.35 (use GCC ≤ 12 to avoid GLIBCXX version mismatches)

Build Container

The docker-arm64/ directory contains a Docker setup that runs an arm64 Ubuntu 22.04 container via QEMU user-mode emulation. This matches the target device exactly — same distro, same glibc 2.35, same library versions. The project's native make (using pkg-config) works as-is inside the container, no cross-compilation flags needed.

Prerequisites

QEMU binfmt handlers must be registered on the host (one-time setup, persists across reboots):

docker run --privileged --rm tonistiigi/binfmt --install arm64

Usage

From the docker-arm64/ directory:

make build              # one-shot: build sdlamp2 inside the container
make shell              # interactive bash shell for development
make clean              # remove the Docker image

The container mounts the project root at /workspace. Output binary is build/sdlamp2 (ELF 64-bit ARM aarch64).

Image Contents

• Base: ubuntu:22.04 (arm64)
• Build tools: build-essential, pkg-config
• SDL2: libsdl2-dev, libsdl2-image-dev
• FFmpeg: libavformat-dev, libavcodec-dev, libavutil-dev, libswresample-dev

The image is tagged arm64-dev and is generic enough to reuse for other projects targeting the same device.