Enrico Fraccaroli
98 lines
3.2 KiB
NASM
98 lines
3.2 KiB
NASM
; MentOS, The Mentoring Operating system project
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; @file boot.asm
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; @brief Kernel start location, multiboot header
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; @copyright (c) 2019 This file is distributed under the MIT License.
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; See LICENSE.md for details.
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[BITS 32] ; All instructions should be 32-bit.
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[EXTERN kmain] ; The start point of our C code
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; The magic field should contain this.
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MULTIBOOT_HEADER_MAGIC equ 0x1BADB002
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; This should be in %eax.
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MULTIBOOT_BOOTLOADER_MAGIC equ 0x2BADB002
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; = Specify what GRUB should PROVIDE =========================================
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; Align the kernel and kernel modules on i386 page (4KB) boundaries.
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MULTIBOOT_PAGE_ALIGN equ 0x00000001
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; Provide the kernel with memory information.
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MULTIBOOT_MEMORY_INFO equ 0x00000002
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; Must pass video information to OS.
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MULTIBOOT_VIDEO_MODE equ 0x00000004
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; -----------------------------------------------------------------------------
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; This is the flag combination that we prepare for Grub
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; to read at kernel load time.
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MULTIBOOT_HEADER_FLAGS equ (MULTIBOOT_PAGE_ALIGN | MULTIBOOT_MEMORY_INFO | MULTIBOOT_VIDEO_MODE)
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; Grub reads this value to make sure it loads a kernel
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; and not just garbage.
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MULTIBOOT_CHECKSUM equ -(MULTIBOOT_HEADER_MAGIC + MULTIBOOT_HEADER_FLAGS)
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LOAD_MEMORY_ADDRESS equ 0x00000000
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; reserve (1024*1024) for the stack on a doubleword boundary
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KERNEL_STACK_SIZE equ 0x100000
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; -----------------------------------------------------------------------------
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; SECTION (multiboot_header)
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; -----------------------------------------------------------------------------
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section .multiboot_header
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align 4
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; This is the GRUB Multiboot header.
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multiboot_header:
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; magic
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dd MULTIBOOT_HEADER_MAGIC
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; flags
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dd MULTIBOOT_HEADER_FLAGS
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; checksum
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dd MULTIBOOT_CHECKSUM
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; -----------------------------------------------------------------------------
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; SECTION (data)
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; -----------------------------------------------------------------------------
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section .data, nobits
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align 4096
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[GLOBAL boot_page_dir]
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boot_page_dir:
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resb 0x1000
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boot_page_tabl:
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resb 0x1000
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; -----------------------------------------------------------------------------
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; SECTION (text)
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; -----------------------------------------------------------------------------
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section .text
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[GLOBAL kernel_entry]
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kernel_entry:
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; Clear interrupt flag [IF = 0]; 0xFA
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cli
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; To set up a stack, we simply set the esp register to point to the top of
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; our stack (as it grows downwards).
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mov esp, stack_top
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; pass the initial ESP
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push esp
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; pass Multiboot info structure
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push ebx
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; pass Multiboot magic number
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push eax
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; Call the kmain() function inside kernel.c
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call kmain
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; Set interrupt flag [IF = 1]; 0xFA
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; Clear interrupts and hang if we return from kmain
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cli
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hang:
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hlt
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jmp hang
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; -----------------------------------------------------------------------------
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; SECTION (bss)
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; -----------------------------------------------------------------------------
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section .bss
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[GLOBAL stack_bottom]
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[GLOBAL stack_top]
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align 16
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stack_bottom:
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resb KERNEL_STACK_SIZE
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stack_top:
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; the top of the stack is the bottom because the stack counts down
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