Luigi Capogrosso
90 lines
2.8 KiB
NASM
90 lines
2.8 KiB
NASM
; MentOS, The Mentoring Operating system project
|
|
; @file boot.asm
|
|
; @brief Kernel start location, multiboot header
|
|
; @copyright (c) 2019 This file is distributed under the MIT License.
|
|
; See LICENSE.md for details.
|
|
|
|
[BITS 32] ; All instructions should be 32-bit.
|
|
[EXTERN kmain] ; The start point of our C code
|
|
|
|
; Grub is informed with this flag to load
|
|
; the kernel and kernel modules on a page boundary.
|
|
MBOOT_PAGE_ALIGN equ 1<<0
|
|
; Grub is informed with this flag to provide the kernel
|
|
; with memory information.
|
|
MBOOT_MEM_INFO equ 1<<1
|
|
; This is the multiboot magic value.
|
|
MBOOT_HEADER_MAGIC equ 0x1BADB002
|
|
; This is the flag combination that we prepare for Grub
|
|
; to read at kernel load time.
|
|
MBOOT_HEADER_FLAGS equ MBOOT_PAGE_ALIGN | MBOOT_MEM_INFO
|
|
; Grub reads this value to make sure it loads a kernel
|
|
; and not just garbage.
|
|
MBOOT_CHECKSUM equ - (MBOOT_HEADER_MAGIC + MBOOT_HEADER_FLAGS)
|
|
|
|
LOAD_MEMORY_ADDRESS equ 0x00000000
|
|
; reserve (1024*1024) for the stack on a doubleword boundary
|
|
KERNEL_STACK_SIZE equ 0x100000
|
|
|
|
; -----------------------------------------------------------------------------
|
|
; SECTION (multiboot_header)
|
|
; -----------------------------------------------------------------------------
|
|
section .multiboot_header
|
|
align 4
|
|
; This is the GRUB Multiboot header.
|
|
multiboot_header:
|
|
dd MBOOT_HEADER_MAGIC
|
|
dd MBOOT_HEADER_FLAGS
|
|
dd MBOOT_CHECKSUM
|
|
|
|
; -----------------------------------------------------------------------------
|
|
; SECTION (data)
|
|
; -----------------------------------------------------------------------------
|
|
section .data, nobits
|
|
align 4096
|
|
[GLOBAL boot_page_dir]
|
|
boot_page_dir:
|
|
resb 0x1000
|
|
boot_page_tabl:
|
|
resb 0x1000
|
|
|
|
; -----------------------------------------------------------------------------
|
|
; SECTION (text)
|
|
; -----------------------------------------------------------------------------
|
|
section .text
|
|
[GLOBAL kernel_entry]
|
|
kernel_entry:
|
|
; Clear interrupt flag [IF = 0]; 0xFA
|
|
cli
|
|
; To set up a stack, we simply set the esp register to point to the top of
|
|
; our stack (as it grows downwards).
|
|
mov esp, stack_top
|
|
; pass the initial ESP
|
|
push esp
|
|
;mov ebp, esp
|
|
; pass Multiboot info structure
|
|
push ebx
|
|
; pass Multiboot magic number
|
|
push eax
|
|
; Call the kmain() function inside kernel.c
|
|
call kmain
|
|
; Set interrupt flag [IF = 1]; 0xFA
|
|
; Clear interrupts and hang if we return from kmain
|
|
cli
|
|
hang:
|
|
hlt
|
|
jmp hang
|
|
|
|
|
|
; -----------------------------------------------------------------------------
|
|
; SECTION (bss)
|
|
; -----------------------------------------------------------------------------
|
|
section .bss
|
|
[GLOBAL stack_bottom]
|
|
[GLOBAL stack_top]
|
|
align 16
|
|
stack_bottom:
|
|
resb KERNEL_STACK_SIZE
|
|
stack_top:
|
|
; the top of the stack is the bottom because the stack counts down
|