100 lines
1.7 KiB
NASM
100 lines
1.7 KiB
NASM
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bits 32
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global start
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; multiboot header
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MODULEALIGN equ 1<<0
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MEMINFO equ 1<<1
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VIDEOINFO equ 1<<2
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FLAGS equ MODULEALIGN | MEMINFO | VIDEOINFO
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MAGIC equ 0x1BADB002
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CHECKSUM equ -(MAGIC + FLAGS)
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section .__mbHeader
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align 4
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MultiBootHeader:
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dd MAGIC
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dd FLAGS
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dd CHECKSUM
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section .text
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STACKSIZE equ 0x4000 ; that's 16k.
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start:
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XCHG BX, BX ; magic breakpoint
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mov ecx, eax
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; lgdt [trickgdt]
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; mov ax, 0x10;
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; mov ds, ax
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; mov es, ax
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; mov fs, ax
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; mov gs, ax
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; mov ss, ax
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; jmp 0x08:HigherHalf ; NOTE: Must be absolute jump!
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HigherHalf:
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; Verify booted with multiboot compliant bootloader
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mov esp, stack+STACKSIZE
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cmp ecx, 0x2BADB002
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jne .bad
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push ebx
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extern k_main
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call k_main
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; Show error message, and halt system
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.bad:
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extern ConsoleClear
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extern ConsoleWrite
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extern CommandOsver
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call ConsoleClear
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call CommandOsver
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mov eax, [ErrorColor]
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push eax
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push ErrorString
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call ConsoleWrite
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cli
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hlt
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; some variables
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ErrorString db 0xA, "%#! Fatal error: Not booted with multiboot compliant bootloader (e.g. GRUB).", 0x0
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ErrorColor db 0x0C
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; tells the assembler to include this data in the '.setup' section
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section .setup
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trickgdt:
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dw gdt_end - gdt - 1 ; size of the GDT
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dd gdt ; linear address of GDT
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gdt:
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dd 0, 0 ; null gate
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db 0xFF, 0xFF, 0, 0, 0, 10011010b, 11001111b, 0x40 ; code selector 0x08: base 0x40000000, limit 0xFFFFFFFF, type 0x9A, granularity 0xCF
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db 0xFF, 0xFF, 0, 0, 0, 10010010b, 11001111b, 0x40 ; data selector 0x10: base 0x40000000, limit 0xFFFFFFFF, type 0x92, granularity 0xCF
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gdt_end:
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; stack
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section .bss
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align 32
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stack:
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resb STACKSIZE ; This reserves 64KBytes of memory here
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