Enrico Fraccaroli
104 lines
3.3 KiB
ArmAsm
104 lines
3.3 KiB
ArmAsm
; MentOS, The Mentoring Operating system project
|
|
; @file boot.asm
|
|
; @brief Kernel start location, multiboot header
|
|
; @copyright (c) 2014-2021 This file is distributed under the MIT License.
|
|
; See LICENSE.md for details.
|
|
|
|
bits 32 ; All instructions should be 32-bit.
|
|
extern boot_main ; The start point of our C code
|
|
|
|
; The magic field should contain this.
|
|
MULTIBOOT_HEADER_MAGIC equ 0x1BADB002
|
|
; This should be in %eax.
|
|
MULTIBOOT_BOOTLOADER_MAGIC equ 0x2BADB002
|
|
|
|
; = Specify what GRUB should PROVIDE =========================================
|
|
; Align the kernel and kernel modules on i386 page (4KB) boundaries.
|
|
MULTIBOOT_PAGE_ALIGN equ 0x00000001
|
|
; Provide the kernel with memory information.
|
|
MULTIBOOT_MEMORY_INFO equ 0x00000002
|
|
; Must pass video information to OS.
|
|
MULTIBOOT_VIDEO_MODE equ 0x00000004
|
|
; -----------------------------------------------------------------------------
|
|
|
|
; This is the flag combination that we prepare for Grub
|
|
; to read at kernel load time.
|
|
MULTIBOOT_HEADER_FLAGS equ (MULTIBOOT_PAGE_ALIGN | MULTIBOOT_MEMORY_INFO | MULTIBOOT_VIDEO_MODE)
|
|
; Grub reads this value to make sure it loads a kernel
|
|
; and not just garbage.
|
|
MULTIBOOT_CHECKSUM equ -(MULTIBOOT_HEADER_MAGIC + MULTIBOOT_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:
|
|
; magic
|
|
dd MULTIBOOT_HEADER_MAGIC
|
|
; flags
|
|
dd MULTIBOOT_HEADER_FLAGS
|
|
; checksum
|
|
dd MULTIBOOT_CHECKSUM
|
|
|
|
; -----------------------------------------------------------------------------
|
|
; SECTION (data)
|
|
; -----------------------------------------------------------------------------
|
|
; section .data nobits
|
|
; align 4096
|
|
|
|
; -----------------------------------------------------------------------------
|
|
; SECTION (text)
|
|
; -----------------------------------------------------------------------------
|
|
section .text
|
|
global boot_entry
|
|
boot_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
|
|
; pass Multiboot info structure
|
|
push ebx
|
|
; pass Multiboot magic number
|
|
push eax
|
|
; Call the boot_main() function inside boot.c
|
|
call boot_main
|
|
; Set interrupt flag [IF = 1]; 0xFA
|
|
; Clear interrupts and hang if we return from boot_main
|
|
cli
|
|
hang:
|
|
hlt
|
|
jmp hang
|
|
|
|
global boot_kernel
|
|
boot_kernel:
|
|
mov edx, [esp + 4] ; stack_pointer
|
|
mov ebx, [esp + 8] ; entry
|
|
mov eax, [esp + 12] ; boot info
|
|
mov esp, edx ; set stack pointer
|
|
push eax ; push the boot info
|
|
call ebx ; call the kernel main
|
|
|
|
|
|
; -----------------------------------------------------------------------------
|
|
; SECTION (bss)
|
|
; -----------------------------------------------------------------------------
|
|
section .bss
|
|
align 16
|
|
|
|
global stack_bottom
|
|
stack_bottom:
|
|
resb KERNEL_STACK_SIZE
|
|
|
|
global stack_top
|
|
stack_top:
|
|
; the top of the stack is the bottom because the stack counts down
|