Printing a welcome message on the screen using UEFI (Unified Extensible Firmware Interface) involves writing a UEFI application. UEFI provides a set of runtime and boot-time services accessible through a standardized interface. We can use these services to interact with the system's hardware, including the console output.
Prerequisites
Development Environment: You need a development environment set up with a UEFI toolchain. The GNU-EFI or EDK2 (EFI Development Kit) toolchain can be used.
We will be using GNU-EFI
sudo apt-get install build-essential uuid-dev git nasm
// Install the GNU-EFI library:
sudo apt-get install gnu-efi
Compiler: A C compiler like gcc or clang.
UEFI Shell: An environment where you can test the UEFI application, such as QEMU (emulator) with OVMF firmware or a real UEFI-capable machine.
Write the UEFI Application:
boot.c:
#include <efi.h>
#include <efilib.h>
EFI_STATUS
EFIAPI
efi_main (EFI_HANDLE ImageHandle, EFI_SYSTEM_TABLE *SystemTable) {
InitializeLib(ImageHandle, SystemTable);
Print(L"Welcome to UEFI!\n");
// Wait for a key press before exiting
EFI_INPUT_KEY Key;
SystemTable->ConIn->Reset(SystemTable->ConIn, FALSE);
SystemTable->ConIn->ReadKeyStroke(SystemTable->ConIn, &Key);
return EFI_SUCCESS;
}
2 Compile the UEFI Application:
# Compile the C source file to an object file
gcc -I /usr/include/efi -I /usr/include/efi/x86_64 -O2 -fpic -fshort-wchar -ffreestanding -c hello.c -o hello.o
# Link the object file to create the EFI executable
ld -nostdlib -znocombreloc -T /usr/lib/elf_x86_64_efi.lds -shared -Bsymbolic -L /usr/lib /usr/lib/crt0-efi-x86_64.o hello.o -o hello.efi -lefi -lgnuefi
3 Test the UEFI Application:
3.1 Create a Disk Image:
qemu-img create -f raw disk.img 200M
mkfs.vfat disk.img
3.2 Mount the Disk Image and Copy the Application:
sudo mount -o loop disk.img /mnt
mkdir -p /mnt/EFI/BOOT
cp hello.efi /mnt/EFI/BOOT/BOOTX64.EFI
sudo umount /mnt
3.3 Run the Application in QEMU:
qemu-system-x86_64 -drive file=disk.img,format=raw -bios /usr/share/ovmf/OVMF.fd