loader.s

global loader                   ; the entry symbol for ELF

extern main

section .__mbHeader
align 0x4
mboot:
    MODULEALIGN  equ  1<<0                   ; align loaded modules on page boundaries
    MEMINFO      equ  1<<1                   ; provide memory map
    MAGIC_NUMBER equ 0x1BADB002              ; define the magic number constant
    FLAGS        equ MODULEALIGN | MEMINFO   ; multiboot flags
    CHECKSUM     equ -(MAGIC_NUMBER + FLAGS) ; calculate the checksum
                                            ; (magic number + checksum + flags should equal 0)
    KERNEL_STACK_SIZE equ 4096               ; size of stack in bytes
                      ; 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



section .text                   ; start of the text (code) section
loader:                                       ; the loader label (defined as entry point in linker script)
    mov esp, kernel_stack + KERNEL_STACK_SIZE ; point esp to the start of the stack (end of memory area)
    call main

.loop:
    jmp .loop                   ; loop forever


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