loader.s

    global loader                   ; the entry symbol for ELF

    MAGIC_NUMBER equ 0x1BADB002     ; define the magic number constant
    FLAGS        equ 0x0            ; multiboot flags
    CHECKSUM     equ -MAGIC_NUMBER  ; calculate the checksum
                                    ; (magic number + checksum + flags should equal 0)
        KERNEL_STACK_SIZE equ 4096                  ; size of stack in bytes

    section .bss
    align 4                                     ; align at 4 bytes
    kernel_stack:                               ; label points to beginning of memory
        resb KERNEL_STACK_SIZE                  ; reserve stack for the kernel

    section .text:                  ; start of the text (code) section
    align 4                         ; the code must be 4 byte aligned
        dd MAGIC_NUMBER             ; write the magic number to the machine code,
        dd FLAGS                    ; the flags,
        dd CHECKSUM                 ; and the checksum

    loader:                         ; the loader label (defined as entry point in linker script)
        mov eax, 0xCAFEBABE         ; place the number 0xCAFEBABE in the register eax
        mov esp, kernel_stack + KERNEL_STACK_SIZE   ; point esp to the start of the
                                                ; stack (end of memory area)
            ; The assembly code
        extern sum_of_three   ; the function sum_of_three is defined elsewhere

        push dword 3            ; arg3
        push dword 2            ; arg2
        push dword 1            ; arg1
        call sum_of_three       ; call the function, the result will be in eax
    .loop:
        jmp .loop                   ; loop forever