Tutorial, part 1: Starting from scratch

This tutorial will guide you through the process of setting up a working coreboot toolchain. In same cases you will find specific instructions for Debian (apt-get), Fedora (dnf) and Arch Linux (pacman) based package management systems. Use the instructions according to your system.

To test the toolchain and make sure it works, we will build coreboot for an emulated system provided by QEMU. This allows you to get familiar with the general process of configuring and building coreboot without needing to flash any hardware.

IMPORTANT: Do not attempt to flash the coreboot ROM built here to a real board

coreboot is board specific, so a ROM built for one board model (such as the QEMU emulation boards) cannot be expected to work on a different board. You must reconfigure coreboot for your board and rebuild the ROM before flashing it to a physical system.

Note: Summaries of each of the steps are at the end of the document.

Download, configure, and build coreboot

Step 1 - Install tools and libraries needed for coreboot

Debian based distros: sudo apt-get install -y bison build-essential curl flex git gnat libncurses5-dev libssl-dev m4 zlib1g-dev pkg-config

Arch based distros: sudo pacman -S base-devel curl git gcc-ada ncurses zlib

Redhat based distros: sudo dnf install git make gcc-gnat flex bison xz bzip2 gcc g++ ncurses-devel wget zlib-devel patch

Step 2 - Download coreboot source tree

git clone https://review.coreboot.org/coreboot
cd coreboot

Step 3 - Build the coreboot toolchain

Please note that this can take a significant amount of time. Use CPUS= to specify number of make jobs to run in parallel.

This will list toolchain options and supported architectures:

make help_toolchain

Here are some examples:

make crossgcc-i386 CPUS=$(nproc)       # build i386 toolchain
make crossgcc-aarch64 CPUS=$(nproc)    # build Aarch64 toolchain
make crossgcc-riscv CPUS=$(nproc)      # build RISC-V toolchain

Note that the i386 toolchain is currently used for all x86 platforms, including x86_64. For this tutorial we only need the i386 toolchain.

Also note that you can possibly use your system toolchain, but the results are not reproducible, and may have issues, so this is not recommended. See step 5 to use your system toolchain.

Step 4 - Build the payload - coreinfo

make -C payloads/coreinfo olddefconfig
make -C payloads/coreinfo

Step 5 - Configure the build

Configure your mainboard

make menuconfig

Do the next steps in the menu:

select 'Mainboard' menu
Beside 'Mainboard vendor' should be '(Emulation)'
Beside 'Mainboard model' should be 'QEMU x86 i440fx/piix4'
select < Exit >

These should be the default selections, so if anything else was set, run make distclean to remove your old config file and start over.

Select the payload

select 'Payload' menu
select 'Payload to add (SeaBIOS) --->'
choose 'An ELF executable payload'
select 'Payload path and filename'
enter 'payloads/coreinfo/build/coreinfo.elf'
select < Exit >
select < Exit >
select < Yes >

Check your configuration (optional step):

make savedefconfig
cat defconfig

There should only be 9 lines (or 10 if you’re using the system toolchain):


Note that this may differ depending on the revision of the coreboot source you are building from and should not be taken as the required contents of defconfig.

Step 6 - Build coreboot


At the end of the build, you should see:

Built emulation/qemu-i440fx (QEMU x86 i440fx/piix4)

This means your build was successful. The output from the build is in the build directory. build/coreboot.rom is the full rom file.

Test the image using QEMU

Step 7 - Install QEMU

  • Debian: sudo apt-get install -y qemu-system
  • Arch: sudo pacman -S qemu
  • Redhat: sudo dnf install qemu

Step 8 - Run QEMU

Start QEMU, and point it to the ROM you just built:

qemu-system-x86_64 -bios build/coreboot.rom -serial stdio

You should see the serial output of coreboot in the original console window, and a new window will appear running the coreinfo payload.


Step 1 summary - Install tools and libraries needed for coreboot

Depending on your distribution you have installed the minimum additional software requirements to continue with downloading and building coreboot. Not every distribution has the tools, that would be required, installed by default. In the following we shortly introduce the purpose of the installed packages:

  • build-essential or base-devel are the basic tools for building software.
  • git is needed to download coreboot from the coreboot git repository.
  • libncurses5-dev or ncurses is needed to build the menu for ‘make menuconfig’
  • m4, bison, curl, flex, zlib1g-dev, gcc, gnat and g++ or clang are needed to build the coreboot toolchain. gcc and gnat have to be of the same version.
  • libssl-dev, pkg-config are needed to build coreboot image (Step 6). In particular, libcrypto provided by libssl-dev package.

If you started with a different distribution or package management system you might need to install other packages. Most likely they are named slightly different. If that is the case for you, we’d like to encourage you to contribute to the project and submit a pull request with an update for this documentation for your system.

Step 2 summary - Download coreboot source tree

This will download a ‘read-only’ copy of the coreboot tree. This just means that if you made changes to the coreboot tree, you couldn’t immediately contribute them back to the community. To pull a copy of coreboot that would allow you to contribute back, you would first need to sign up for an account on gerrit.

Step 3 summary - Build the coreboot toolchain.

This builds one of the coreboot cross-compiler toolchains for X86 platforms. Because of the variability of compilers and the other required tools between the various operating systems that coreboot can be built on, coreboot supplies and uses its own cross-compiler toolchain to build the binaries that end up as part of the coreboot ROM. The toolchain provided by the operating system (the ‘host toolchain’) is used to build various tools that will run on the local system during the build process.

Step 4 summary - Build the payload

To actually do anything useful with coreboot, you need to build a payload to include into the rom. The idea behind coreboot is that it does the minimum amount possible before passing control of the machine to a payload. There are various payloads such as grub or SeaBIOS that are typically used to boot the operating system. Instead, we used coreinfo, a small demonstration payload that allows the user to look at various things such as memory and the contents of the coreboot file system (CBFS) - the pieces that make up the coreboot rom.

Usually, the coreboot build system automatically builds the payload selected in the “Payload to add” menu and sets it as the default payload (also known as the “primary payload”). Such payloads are able to boot an operating system and may be able to load another payload. Although coreinfo can be found in the “Secondary Payloads” menu, in which case it would be handled automatically, it is not available as a primary payload since it cannot load an OS or another payload. Secondary payloads must be loaded from other primary or secondary payloads and will not be run when coreboot hands off execution after initializing hardware. Thus, to get coreinfo to run as if it were a primary payload, it must be manually built and explicitly set as the primary payload using the “ELF executable payload” option.

Step 5 summary - Configure the build

This step configures coreboot’s build options using the menuconfig interface to Kconfig. Kconfig is the same configuration program used by the linux kernel. It allows you to enable, disable, and change various values to control the coreboot build process, including which mainboard(motherboard) to use, which toolchain to use, and how the runtime debug console should be presented and saved. Anytime you change mainboards in Kconfig, you should always run make distclean before running make menuconfig. Due to the way that Kconfig works, values will be kept from the previous mainboard if you skip the clean step. This leads to a hybrid configuration which may or may not work as expected.

Step 6 summary - Build coreboot

You may notice that a number of other pieces are downloaded at the beginning of the build process. These are the git submodules used in various coreboot builds. By default, the blobs submodule is not downloaded. This git submodule may be required for other builds for microcode or other binaries. To enable downloading this submodule, select the option “Allow use of binary-only repository” in the “General Setup” menu of Kconfig This attempts to build the coreboot rom. The rom file itself ends up in the build directory as ‘coreboot.rom’. At the end of the build process, the build displayed the contents of the rom file.

Step 7 summary - Install QEMU

QEMU is a processor emulator which we can use to show the coreboot boot process in a virtualised environment.

Step 8 summary - Run QEMU

Here’s the command line instruction broken down:

  • qemu-system-x86_64 This starts the QEMU emulator with the i440FX host PCI bridge and PIIX3 PCI to ISA bridge.
  • -bios build/coreboot.rom Use the coreboot rom image that we just built. If this flag is left out, the standard SeaBIOS image that comes with QEMU is used.
  • -serial stdio Send the serial output to the console. This allows you to view the coreboot boot log.