beanEFI is a project i made to learn about the bootloader and how my linux boots up.
The project is written entirely in C and compiled with Clang targeting the PE/COFF executable format (BOOTX64.EFI), which is the executable format required by UEFI firmware.
Instead of using the full EDK II build system, beanEFI only uses the EDK II header files. These headers provide the UEFI data structures, protocols, GUIDs, and function definitions needed to communicate with the firmware while keeping the build process simple and transparent.
During development, the project runs inside QEMU using the OVMF (Open Virtual Machine Firmware) UEFI firmware image. OVMF is an open-source implementation of the UEFI specification, allowing the bootloader to be tested without requiring physical hardware.
Here is beanEFI in action, drawing a custom font rendering "beanie" in a shifting rainbow color palette:
The build process is kept pretty simple because the goal of this project was to actually understand how UEFI works instead of hiding everything behind a huge build system.
The code is written in C and compiled using Clang targeting x86_64-pc-win32-coff, which makes the output a PE32+ (PE/COFF) executable (BOOTX64.EFI). This is the format that 64-bit UEFI firmware expects. The binary is then linked using LLD.
When the machine starts, OVMF looks for EFI/BOOT/BOOTX64.EFI, loads it into memory, and jumps into the efi_main() function. It also gives the program an EFI_SYSTEM_TABLE, which contains all the interfaces provided by the firmware.
Ensure you have the following packages installed on your Linux system:
# On Debian/Ubuntu based systems:
sudo apt install clang lld qemu-system-x86_64 mtools dosfstools# On Arch:
yay -S clang lld qemu-desktop mtools dosfstools-
Clone the repository:
git clone https://github.com/BeanieMen/beanEFI.git cd beanEFI -
Build and launch in QEMU:
make run
ai was used in the making of this application