Question about loader.s script in Bare Bones tutorial
Posted: Sun Jan 06, 2013 5:27 pm
Here is the loader.s script from the Bare Bones tutorial:
For the following two lines, I'm assuming we're putting the magic value and the mbd data structure starting address in the the correct variables to be later used in kmain. But when were the eax and ebx registers set to those values? Or am I misunderstanding what's going on?
Code: Select all
global loader ; making entry point visible to linker
global magic ; we will use this in kmain
global mbd ; we will use this in kmain
extern kmain ; kmain is defined in kmain.cpp
; setting up the Multiboot header - see GRUB docs for details
MODULEALIGN equ 1<<0 ; align loaded modules on page boundaries
MEMINFO equ 1<<1 ; provide memory map
FLAGS equ MODULEALIGN | MEMINFO ; this is the Multiboot 'flag' field
MAGIC equ 0x1BADB002 ; 'magic number' lets bootloader find the header
CHECKSUM equ -(MAGIC + FLAGS) ; checksum required
section .text
align 4
dd MAGIC
dd FLAGS
dd CHECKSUM
; reserve initial kernel stack space
STACKSIZE equ 0x4000 ; that's 16k.
loader:
mov esp, stack + STACKSIZE ; set up the stack
mov [magic], eax ; Multiboot magic number
mov [mbd], ebx ; Multiboot info structure
call kmain ; call kernel proper
cli
.hang:
hlt ; halt machine should kernel return
jmp .hang
section .bss
align 4
stack: resb STACKSIZE ; reserve 16k stack on a doubleword boundary
magic: resd 1
mbd: resd 1Code: Select all
mov [magic], eax ; Multiboot magic number
mov [mbd], ebx ; Multiboot info structure