boot.s

# build instructions i686-elf-as boot.s -o boot.o
# the multiboot header constants.
.set ALIGN,    1<<0             # align loaded modules on page boundaries
.set MEMINFO,  1<<1             # provide memory map
.set FLAGS,    ALIGN | MEMINFO  # this is the Multiboot 'flag' field
.set MAGIC,    0x1BADB002       # 'magic number' lets bootloader find the header
.set CHECKSUM, -(MAGIC + FLAGS) # checksum of above, to prove we are multiboot


# this has to be in the 1st 8KiB os the kernel file
.section .multiboot
.align 4
.long MAGIC
.long FLAGS
.long CHECKSUM

# The stack on x86 must be 16-byte aligned according to the
# System V ABI standard and de-facto extensions.
# stack initialization and alignment 
.section .bss
.align 16
stack_bottom:
.skip 16384 # 16 KiB
stack_top:


# starting the actual program settings for some linker magic
.section .text
.global _start
.type _start, @function
_start:
    mov $stack_top, %esp
    call kernel_main
    cli
1:	hlt
	jmp 1b

# Set the size of the _start symbol to the current location '.' minus its start.
# This is useful when debugging or when you implement call tracing.
.size _start, . - _start