# https://www.gnu.org/software/grub/manual/multiboot/multiboot.html#Boot-information-format
# http://wiki.osdev.org/Bare_Bones

# Fill Multiboot Haeder, init stack and call kernel_main passing to params:
# eax - magic number
# ebx - multiboot structure

# Declare constants used for creating a multiboot header.
.set ALIGN,    1<<0             # align loaded modules on page boundaries
.set MEMINFO,  1<<1             # provide memory map
.set GFXINFO,  1<<2             # provide gfx info
.set FLAGS,    ALIGN | MEMINFO | GFXINFO  # 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

# Declare a header as in the Multiboot Standard. We put this into a special
# section so we can force the header to be in the start of the final program.
# You don't need to understand all these details as it is just magic values that
# is documented in the multiboot standard. The bootloader will search for this
# magic sequence and recognize us as a multiboot kernel.

.section .multiboot
.align 4
.long MAGIC
.long FLAGS
.long CHECKSUM

.long 0	# we dont need this for ELF
.long 0
.long 0
.long 0
.long 0

.long 0		#gfx_stuff 0=enable!
.long 1280
.long 1024
.long 32

# Currently the stack pointer register (esp) points at anything and using it may
# cause massive harm. Instead, we'll provide our own stack. We will allocate
# room for a small temporary stack by creating a symbol at the bottom of it,
# then allocating 16384 bytes for it, and finally creating a symbol at the top.
.section .bootstrap_stack, "aw", @nobits
stack_bottom:
.skip 16384 # 16 KiB
stack_top:

# The linker script specifies _start as the entry point to the kernel and the
# bootloader will jump to this position once the kernel has been loaded. It
# doesn't make sense to return from this function as the bootloader is gone.
.section .text
.global _start
.global stack_top 
.global stack_bottom
.type _start, @function
_start:


	# To set up a stack, we simply set the esp register to point to the top of
	# our stack (as it grows downwards).
	movl $stack_top, %esp

	push %ebx #pass address of the multiboot information data structure
	push %eax #pass eax, so kernel can check for magic number

	call kernel_main

	# should never be reached

	cli
	hlt
.Lhang:
	jmp .Lhang

# 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