159 lines
2.3 KiB
NASM
159 lines
2.3 KiB
NASM
; bootler
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; legacy bootloader in nasm-flavoured asm
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; 2026 Andromeda
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; GPL licensed
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[bits 16]
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[org 0x7C00] ; address where bootloader is loaded
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xor ax, ax
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mov ds, ax
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mov es, ax
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mov ss, ax
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mov sp, 0x7C00
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mov ah, 0x0E
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mov al, 'R'
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int 0x10
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mov al, 'e'
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int 0x10
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mov al, 'a'
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int 0x10
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mov al, 'l'
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int 0x10
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mov al, 0x0D
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int 0x10
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mov al, 0x0A
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int 0x10
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mov al, 0x00 ; stops serial and bios output from overlapping in qemu -nographic
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int 0x10 ; output
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; activate a20
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mov ax, 0x2401
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int 0x15
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jc error
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; load kernel
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; 'docs' from https://www.ctyme.com/intr/rb-0607.htm
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mov ah, 0x02
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mov al, 1 ; number of sectors to read (must be nonzero)
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mov ch, 0 ; low eight bits of cylinder number
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mov cl, 2 ; sector number 1-63 (bits 0-5); high two bits of cylinder (bits 6-7,
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; hard disk only)
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mov dh, 0 ; head number
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; dl is already set by bios
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mov bx, 0x1000 ; data buffer
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mov es, bx
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xor bx, bx
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int 0x13 ; read disk
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jc error
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; load gdt
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lgdt [gdt_descriptor]
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; jump to pm
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cli
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mov eax, cr0
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or eax, 1
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mov cr0, eax
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jmp 0x08:pm_start
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error:
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mov al, 'e'
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int 0x10
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mov al, 'r'
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int 0x10
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mov al, 'r'
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int 0x10
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mov al, 'o'
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int 0x10
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mov al, 'r'
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int 0x10
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jmp $
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gdt_data:
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; null segment
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dq 0x0000000000000000
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; code segment
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dw 0xFFFF
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dw 0x0000
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db 0x00
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db 10011010b ; 32-bit code segment, present, ring 0
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db 11001111b ; limit bits 16-19
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db 0x00
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; data segment
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dw 0xFFFF
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dw 0x0000
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db 0x00
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db 10010010b ; 32-bit data segment, present, ring 0
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db 11001111b ; limit bits 16-19
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db 0x00
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gdt_descriptor:
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dw $ - gdt_data - 1 ; size
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dd gdt_data ; start
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[bits 32]
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; entry point
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pm_start:
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; data segment registers
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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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mov esp, 0x80000
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; TODO actually configure COM1
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mov dx, 0x3F8 ; COM1
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mov al, 'P'
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out dx, al
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mov al, 'r'
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out dx, al
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mov al, 'o'
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out dx, al
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mov al, 't'
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out dx, al
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mov al, 'e'
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out dx, al
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mov al, 'c'
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out dx, al
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mov al, 't'
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out dx, al
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mov al, 'e'
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out dx, al
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mov al, 'd'
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out dx, al
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mov al, 0x0D
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out dx, al
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mov al, 0x0A
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out dx, al
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jmp 0x08:0x10000
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pm_error:
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mov al, 'p'
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out dx, al
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mov al, 'm'
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out dx, al
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mov al, 'e'
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out dx, al
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mov al, 'r'
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out dx, al
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mov al, 'r'
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out dx, al
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mov al, 'o'
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out dx, al
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mov al, 'r'
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out dx, al
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jmp $
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times 510-($-$$) db 0 ; 2 bytes less now
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db 0x55
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db 0xAA
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