94 lines
1.2 KiB
NASM
94 lines
1.2 KiB
NASM
; http://stackoverflow.com/a/28645943/895245
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[bits 16]
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[org 0x7c00]
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mov ax, 0
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mov ss, ax
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mov sp, 0xFFFC
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mov ax, 0
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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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cli
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lgdt[gdt_descriptor]
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mov eax, cr0
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or eax, 0x1
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mov cr0, eax
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; TODO why is this needed?
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jmp CODE_SEG:b32
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[bits 32]
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print32:
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pusha
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; Video memory address.
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mov edx, 0xb8000
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.loop:
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mov al, [ebx]
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; White on black.
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mov ah, 0x0f
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cmp al, 0
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je .done
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mov [edx], ax
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add ebx, 1
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add edx, 2
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jmp .loop
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.done:
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popa
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ret
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b32:
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mov ax, DATA_SEG
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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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mov ebp, 0x2000
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mov esp, ebp
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mov ebx, message
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call print32
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jmp $
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gdt_start:
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gdt_null:
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dd 0x0
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dd 0x0
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gdt_code:
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dw 0xffff
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dw 0x0
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db 0x0
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db 10011010b
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db 11001111b
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db 0x0
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gdt_data:
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dw 0xffff
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dw 0x0
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db 0x0
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db 10010010b
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db 11001111b
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db 0x0
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gdt_end:
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gdt_descriptor:
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dw gdt_end - gdt_start
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dd gdt_start
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CODE_SEG equ gdt_code - gdt_start
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DATA_SEG equ gdt_data - gdt_start
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message db 'hello world', 0
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[SECTION signature start=0x7dfe]
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dw 0AA55h
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