boot.S

.intel_syntax noprefix

# ----------------------------------------------------------------------
# .multiboot: declare header in mutliboot standard

.section .multiboot
.align 4

    # some constants for multiboot header:
    .set ALIGN, 1<<0                # align loaded modules on page boundaries
    .set MEMINFO, 1<<1              # provide memory map
    .set FLAGS, ALIGN | MEMINFO     # mutliboot flags
    .set MAGIC, 0x1BADB002          # 'magic number' lets bootloader find header
    .set CHECKSUM, -(MAGIC + FLAGS) # checksum of the mboot header

    .long MAGIC
    .long FLAGS
    .long CHECKSUM

# ----------------------------------------------------------------------
# allocate some stack space

.section .bootstrap_stack, "aw", @nobits

stack_bottom:
    .skip 16384    # 16 KB
stack_top:

# ----------------------------------------------------------------------
# .text: the global function _start represents our kernel entry point in
#        our .text segment

.section .text

    .globl _start
    .type _start, @function

_start:
    # first, setup a stack:
    mov esp, stack_top

    call _init

    call k_early_init

    call k_main

endless:
    jmp endless

# ----------------------------------------------------------------------
# signalize end of module: size of the code -- for debugging purposes:

.size _start, . - _start