Peter Ross
c31a678075
We do not populate the video mode fields in the multiboot header, therefore we should not request the boot loader to go looking for this information. This is required to boot MentOS using GRUB. Tested with v2.04.
104 lines
3.3 KiB
ArmAsm
104 lines
3.3 KiB
ArmAsm
; 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) 2014-2021 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 boot_main ; 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)
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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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; -----------------------------------------------------------------------------
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; SECTION (text)
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; -----------------------------------------------------------------------------
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section .text
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global boot_entry
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boot_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 boot_main() function inside boot.c
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call boot_main
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; Set interrupt flag [IF = 1]; 0xFA
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; Clear interrupts and hang if we return from boot_main
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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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global boot_kernel
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boot_kernel:
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mov edx, [esp + 4] ; stack_pointer
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mov ebx, [esp + 8] ; entry
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mov eax, [esp + 12] ; boot info
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mov esp, edx ; set stack pointer
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push eax ; push the boot info
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call ebx ; call the kernel main
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; -----------------------------------------------------------------------------
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; SECTION (bss)
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; -----------------------------------------------------------------------------
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section .bss
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align 16
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global stack_bottom
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stack_bottom:
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resb KERNEL_STACK_SIZE
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global stack_top
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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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