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Kernel.md

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Kernel

Warning Replacing the default kernel package should be avoided unless you really know what you're doing or you need kernel drivers that we don't provide in the default images.

This section describes in detail how to build kernel packages that will be compatible with this action.

Firstly, it is worth mentioning that what we call the kernel package is actually a tar.xz archive containing initramfs and firmware for the emulated system.

Available default images

We currently provide the following kernel configurations:

  • riscv64:

    • kernel-riscv64-hifive_unleashed.tar.xz

  • arm32:

    • kernel-arm32-zynq_7000.tar.xz

The packages contain a Busybox with essential commands, drivers essential for these boards, and other drivers:

  • vivid for Video4Linux
  • i2c-stub
  • gpio-mockup

Required image components

Your custom kernel package should include:

  • A vmlinux or Image file - a compiled kernel for the selected architecture, and a bootloader and firmware for vmlinux kernels
  • fw_payload.elf - a bootloader and firmware for Image kernels
  • rootfs.cpio - a packaged initramfs compiled for the selected architecture
  • .dtb file - a device tree binary file for the specified board.

rootfs.cpio should contain:

  • /init, an executable script that redirects output to the ttyS0 device and starts an interactive shell session.
  • basic programs like: sh, mount, chroot, dmesg, date.
  • the ip command and a network stack, should you want to use networking.

Create your own custom kernel package

You can build the kernel package using any method you like, but we recommend using buildroot. It provides many configuration options and will produce the file structure that this action requires. To start, you can download the default kernel package configuration and modify it. The configuration is stored in the kernel/<arch-board> directory.

Adding Devices and Modifying Other Components

If you want to add devices that we currently do not offer in our build, take a look at the configs/linux.config.fragment file. You can add the necessary drivers there. You may also want to change the kernel version in configs/board_defconfig or add/delete kernel patches in patches/linux.

Preparing the archive

Download the latest buildroot from GitHub and apply your configuration with:

make BR2_EXTERNAL=path/to/configuration board_name_defconfig

Start compiling:

make -j$(nproc)

This will take some time.

You should end up with files in the buildroot/output/images directory. Create a new tar.xz archive with the required files. The resulting archive is ready for use with the action.

Use your kernel

- uses: antmicro/renode-linux-runner-action@v1
  with:
    arch: your-arch (i.e. riscv64)
    kernel: path/to/kernel or URL
    renode-run: sh --help