First UEFI application

UEFI boots PE/COFF .efi executables linked for the firmware subsystem, not DOS or Linux ELF. A minimal app locates EFI_SYSTEM_TABLE, then calls ConOut->OutputString to print text in UTF-16. For example, GNU-EFI's InitializeLib macro stores the table pointer your efi_main receives in registers per the calling convention.

Entry and console output

c
Loading…

Link with -nostdlib -e efi_main against libefi/libgnuefi
Strings to the console must be CHAR16 (wide) with L prefix
Boot services stay available until ExitBootServices is called
Firmware loads .efi from the EFI System Partition (FAT32)

Toolchain and loading

GNU-EFI or EDK2-style builds produce a PE32+ image with subsystem EFI_APPLICATION. Copy the .efi to EFI/BOOT/BOOTX64.EFI on a FAT ESP for firmware to auto-run it. OVMF in QEMU boots that path when you point -drive at a vfat disk image. If the screen stays blank, confirm you passed wide strings to ConOut and returned EFI_SUCCESS so firmware does not hang waiting for exit.

Why for this exercise

You will build a UEFI application that prints a greeting through the ConOut protocol. This exercise requires using the system table's boot services instead of BIOS interrupts or libc printf.

Create a minimal UEFI Hello World application.

Requirements:

Use UEFI API to print text
Include proper UEFI headers
Implement UEFI entry point (UefiMain or efi_main)
Use EFI_SYSTEM_TABLE for console output
Compile to .efi executable format
Display multiple lines of text
Show UEFI firmware vendor and version
Print memory map information
Demonstrate understanding of UEFI architecture
Include build instructions

First UEFI application

Entry and console output

c
Loading…

Link with -nostdlib -e efi_main against libefi/libgnuefi
Strings to the console must be CHAR16 (wide) with L prefix
Boot services stay available until ExitBootServices is called
Firmware loads .efi from the EFI System Partition (FAT32)

Toolchain and loading

Why for this exercise

You will build a UEFI application that prints a greeting through the ConOut protocol. This exercise requires using the system table's boot services instead of BIOS interrupts or libc printf.

Create a minimal UEFI Hello World application.

Requirements:

Use UEFI API to print text
Include proper UEFI headers
Implement UEFI entry point (UefiMain or efi_main)
Use EFI_SYSTEM_TABLE for console output
Compile to .efi executable format
Display multiple lines of text
Show UEFI firmware vendor and version
Print memory map information
Demonstrate understanding of UEFI architecture
Include build instructions

Create Simple UEFI Application that Prints Hello World

Topic Overview

First UEFI application

Entry and console output

Toolchain and loading

Why for this exercise

Implementation Task

Progressive Hints

Resources

Learn by building

Create Simple UEFI Application that Prints Hello World

Topic Overview

First UEFI application

Entry and console output

Toolchain and loading

Why for this exercise

Implementation Task

Progressive Hints

Resources

Learn by building