Buildroot for TinyEMU

This repo is a quick getting started guide on how to build kernel and rootfs using Buildroot for TinyEMU

The current configuration is a minimal kernel with no networking, though it should be easy to change.

If you're not ready to build your own, you can start get a ready made kernel, rootfs and bbl from TinyEMU, at the bottom there's diskimage-linux-riscv-2018-09-23.tar.gz.

BBL - Berkely boot loader

To build BBL, you'll find the patches needed for RISC-V Proxy Kernel in diskimage-linux-riscv-2018-09-23.tar.gz.

Getting Started

Building the docker image

docker build -t buildroot .

Running the docker image

docker run -it buildroot

At this point you have a ready made machine to start building your rootfs and kernel:

make -j 5

Once its done, you'll find 2 files in output/images:

~/buildroot-2022.05# ls -l output/images
total 10252
-rw-r--r-- 1 root root  2172016 Jul 12 11:36 Image
-rw-r--r-- 1 root root 20971520 Jul 12 11:36 rootfs.ext2

Now we want to copy them into our virtual riscv machine:

docker cp <container id>:/root/buildroot-2022.05/output/images/Image kernel32.bin
docker cp <container id>:/root/buildroot-2022.05/output/images/rootfs.ext2 rootfs32.bin

Make sure you have bbl32.bin and TinyEMU configuration file:

/* VM configuration file */
{
    version: 1,
    machine: "riscv32",
    memory_size: 12,
    bios: "bbl32.bin",
    kernel: "kernel32.bin",
    cmdline: "console=hvc0 debug ignore_loglevel earlycon=sbi root=/dev/vda rw",
    drive0: { file: "rootfs32.bin" }
}

And you're ready to go, either copy it to your SD card under /emu or run tinyemu from the command line

<tinyemu executable> riscv32.cfg

If you choose to run it on ESP32 through my esp32-tinyemu, you'll see something very similar to this:

Quick Cheat Sheet for Buildroot

configure buildroot:

make menuconfig

configure busybox:

make busybox-menuconfig

configure kernel:

make linux-menuconfig

rebuild whole system:

make clean all -j 5

persist your buildroot configuration:

make savedefconfig
docker cp <container id>:/root/buildroot-2022.05/buildroot_rv32_config buildroot_config/buildroot_rv32_config

persist your kernel configuration:

make linux-update-defconfig
docker cp <container id>:/root/buildroot-2022.05/linux_rv32_config buildroot_config/linux_rv32_config

persist your busybox configuration:

make busybox-update-config
docker cp <container id>:/root/buildroot-2022.05/busybox_config buildroot_config/busybox_config

Notes

• This docker image was customized to use axel for downloading dependencies with multiple connections, you might not need it on your network.
• The configured overlay skips init and goes straight to bash, you'll need to remove it to work with getty (BR2_ROOTFS_OVERLAY and BR2_TARGET_GENERIC_GETTY_OPTIONS)