uefi-elf-bootloader

This repository contains a simple UEFI ELF bootloader which loads a simple demonstration kernel. It provides an extremely basic example implementation of a UEFI bootloader for a bare-metal x86-64 system, though this example should be portable to other architectures.

The aim of this repository is to serve as a basic teachable example of how to implement a UEFI bootloader.

Build instructions

This bootloader assumes a GCC cross-compiler toolchain targeting the bare-metal x86_64-elf architecture. Instructions for building and obtaining a valid cross-compiler toolchain can be found here.

This bootloader can be built simply by running make within the src directory. This will create the build/kernel.img file, which is a bootable disk image containing the bootloader loading a demonstration kernel. There is a run script within the root directory containing a script for testing the bootloader/kernel combination using QEMU.

Build dependencies

• GNU Make
• GNU EFI
• An x86_64-elf-gcc cross-compiler toolchain present in PATH

Project structure

This project is broken down into two distinct components: The bootloader, and the example kernel. These can be found in the src/bootloder and src/kernel directories respectively. These can be built and tested individually using the makefiles within their individual directories. Running the makefile within the top level src directory will build the entire project.

Bootloader

The bootloader component of this repository, contained within the src/bootloader directory, contains the basic implementation of a UEFI ELF bootloader for the x86-64 platform. The bootloader is hardcoded to load and execute a bare-metal x86-64 application located at /kernel.elf on the boot media. This path can be modifid from within the src/bootloader/src/include/bootloader.h file by modifying the KERNEL_INCLUDE_PATH preprocessor directive.

The bootloader will output debugging information over the system's serial port, if present. Otherwise VGA output will be used.

The bootloader passes a Kernel_Boot_Info struct to the loaded kernel containing basic system information, such as the memory map. This struct is defined within the src/bootloader/src/include/bootloader.h header file. This implementation is not tied to any specific architecture.

The bootloader will open the Graphics Output Protocol and Serial Protocol. A routine has been provided for drawing a test screen to demonstrate that the graphics output protocol has been loaded correctly. This can be toggled by setting the DRAW_TEST_SCREEN preprocessor directive at the top of the src/bootloader/src/main.c file.

Kernel

This repository contains a minimal x86-64 kernel for testing purposes. This is located within the src/kernel directory. It contains a basic UART implementation suitable for testing that the kernel has been correctly loaded.

Feedback

Feel free to direct any questions or feedback to me directly at ajxs [at] panoptic.online