add kernel
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62
src/kernel.asm
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62
src/kernel.asm
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; vim: ft=nasm
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org 0x7C00
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bits 16
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%define ENDL 0x0D, 0x0A
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start:
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jmp main
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;
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; echo:
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; print something to the screen
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; - ds:si points to string
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;
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echo:
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; save the registers we want to modify
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push si
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push ax
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push bx
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mov ah, 0xe
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mov bh, 0
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.loop:
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lodsb ; load byte from ds:si to al
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or al, al ; check if next char is null
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jz .done
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int 0x10
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jmp .loop
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.done:
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pop bx
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pop ax
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pop si
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ret
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main:
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; setup data segments
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; use ax as and intermediary as we can't write to es/ds directly
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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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; setup stack
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mov ss, ax
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mov sp, 0x7C00 ; stack grows downward from where we are loaded in memory
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; print the hello world
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mov si, msg_hello
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call echo
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hlt
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.halt:
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jmp .halt
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msg_hello: db 'Hello, world!', ENDL, 0
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times 510-($-$$) db 0
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dw 0AA55h
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