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Barebox Bootloader – QEMU (ARM) Learning Setup

This repository documents how to build, configure, and test the Barebox bootloader using QEMU on Linux, targeting a generic ARM (multi_v7) platform.

The goal is to learn Barebox fundamentals without real hardware constraints (such as SRAM limits, complex ROM boot stages, or vendor-specific quirks).

📌 What is Barebox?

Barebox is a modern, flexible bootloader for embedded Linux systems. It sits between the SoC ROM code and the Linux kernel.

It provides:

  • A Linux-like shell context
  • Scriptable boot logic (via /env)
  • A clean device model
  • Strong support for custom boards

🧠 Why Use multi_v7?

While Barebox supports many real hardware boards, those targets often have strict SRAM size limits, require multi-stage boot mechanisms (PBL/X-Load), and can be difficult for beginners to debug.

The multi_v7_defconfig target is ideal for learning because it:

  • Works seamlessly with QEMU.
  • Has no strict SRAM overflow limits.
  • Uses a simple single-stage boot process.
  • Fully supports Linux boot testing.

🛠️ Prerequisites

Host System

  • OS: Linux (Ubuntu/Debian recommended)

Install Packages

Run the following to install the cross-compiler, QEMU, and build dependencies:

sudo apt update
sudo apt install \
  gcc-arm-linux-gnueabihf \
  qemu-system-arm \
  bison flex \
  libssl-dev \
  bc \
  device-tree-compiler

🏗️ Build Steps

1. Verify Toolchain

Ensure the ARM cross-compiler is accessible:

arm-linux-gnueabihf-gcc --version

2. Get Barebox Source

git clone [https://github.com/barebox/barebox.git](https://github.com/barebox/barebox.git)
cd barebox

3. Configure Barebox

Set the architecture and cross-compiler environment variables, then clean and configure the project.

# Set environment variables
export ARCH=arm
export CROSS_COMPILE=arm-linux-gnueabihf-

# Clean previous builds
make distclean

# Configure for QEMU (ARMv7 generic)
make multi_v7_defconfig

Optional: To customize the build (e.g., enable debugging or specific drivers), run:

make menuconfig

4. Compile

Build the bootloader using all available processor cores.

make -j$(nproc)

Expected Artifact: The build process should produce the binary image at: images/barebox.bin

▶️ Run Barebox in QEMU

Execute the following command to boot the generated image in QEMU.

qemu-system-arm \
  -M virt \
  -cpu cortex-a15 \
  -m 512M \
  -nographic \
  -kernel images/barebox.bin

Expected Output

You should see the Barebox startup log and shell prompt:

barebox 20xx.xx
barebox@multi-v7:/

🧪 Basic Barebox Commands

Once inside the shell, try these commands to explore the environment:

  • help - List available commands.
  • ls - List files in the virtual filesystem.
  • devinfo - Display device information.
  • printenv - Show current environment variables.