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use16
org 0x7c00
 
    ; Set stack
    mov bp, 0x8000
    mov sp, bp
 
    ; Load 2nd stage
    mov bx, 0x07E0
    mov es, bx
    mov ds, bx
    xor bx, bx
 
    mov al, 0x01    ; number of sectors to read
    mov ch, 0x00    ; cylinder number
    mov cl, 0x02    ; sector number
    mov dh, 0x00    ; head number
    mov dl, 0x80    ; drive number (using a disk drive in qemu)
 
    clc
    mov ah, 0x02
    int 0x13
    jc error        ; error handling is omitted, not important & doesnt cause problems
 
    jmp 0x07E0:0x00
 
times 510 - ($-$$) db 0
dw 0xaa55
 
 
 
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; second stage code
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
use16
org 0x7E00
 
bootsect_second_stage:
    ; WITHOUT THIS BIT IT DOESNT WORK...
    ; WHY DO I NEED TO SET THE SEGMENT REGISTERS to 0... (and not 0x07E0 for example)?
    mov bx, 0
    mov ds, bx
    mov es, bx
    mov fs, bx
    mov gs, bx
    mov ss, bx
 
    call switch_to_protected_mode
 
    cli
    hlt
 
gdt_start:
gdd_null:
    dq 0
gdt_code:
    dw 0xFFFF
    dw 0
    db 0
    db 10011010b
    db 11001111b
    db 0
gdt_data:
    dw 0xFFFF
    dw 0
    db 0
    db 10010010b
    db 11001111b
    db 0
gdt_end:
 
gdt_descriptor:
    dw gdt_end - gdt_start - 1
    dd gdt_start
 
CODE_SEG equ gdt_code - gdt_start
DATA_SEG equ gdt_data - gdt_start
 
switch_to_protected_mode:
    mov bx, switching_to_protected_mode
    call print_str
 
    cli
    lgdt [gdt_descriptor]
    mov eax, cr0
    or eax, 1
    mov cr0, eax
 
    jmp CODE_SEG:protected_mode_start
    ret ; Should never be reached
 
use32
protected_mode_start:
    mov ax, DATA_SEG
    mov ds, ax
    mov es, ax
    mov fs, ax
    mov gs, ax
    mov ss, ax
    mov esp, 090000h
 
    ; Write 'A' to the middle of the screen (beginning of the video memory is at 0xB8000)
    mov edi, 0xB85EC
    mov byte [edi], 'A'
    mov edi, 0xB85ED
    mov byte [edi], 4
 
    hlt
 
times 512 - ($ - $$) db 0

prog.s: Assembler messages:
prog.s: Warning: end of file not at end of a line; newline inserted
prog.s:1: Error: no such instruction: `use16'
prog.s:2: Error: no such instruction: `org 0x7c00'
prog.s:4: Error: no such instruction: `set stack'
prog.s:5: Error: too many memory references for `mov'
prog.s:6: Error: too many memory references for `mov'
prog.s:8: Error: no such instruction: `load 2nd stage'
prog.s:9: Error: too many memory references for `mov'
prog.s:10: Error: too many memory references for `mov'
prog.s:11: Error: too many memory references for `mov'
prog.s:12: Error: too many memory references for `xor'
prog.s:14: Error: too many memory references for `mov'
prog.s:14: Error: no such instruction: `number of sectors to read'
prog.s:15: Error: too many memory references for `mov'
prog.s:15: Error: no such instruction: `cylinder number'
prog.s:16: Error: too many memory references for `mov'
prog.s:16: Error: no such instruction: `sector number'
prog.s:17: Error: too many memory references for `mov'
prog.s:17: Error: no such instruction: `head number'
prog.s:18: Error: too many memory references for `mov'
prog.s:18: Error: no such instruction: `drive number (using a disk drive in qemu)'
prog.s:21: Error: too many memory references for `mov'
prog.s:22: Error: operand size mismatch for `int'
prog.s:23: Error: no such instruction: `error handling is omitted,not important&doesnt cause problems'
prog.s:25: Error: junk `:0x00' after expression
prog.s:27: Error: no such instruction: `times 510 - ($-$$)db 0'
prog.s:28: Error: no such instruction: `dw 0xaa55'
prog.s:33: Error: no such instruction: `second stage code'
prog.s:36: Error: no such instruction: `use16'
prog.s:37: Error: no such instruction: `org 0x7E00'
prog.s:40: Error: no such instruction: `without THIS BIT IT DOESN84WORK...'
prog.s:41: Error: no such instruction: `why DO I NEED TO SET THE SEGMENT REGISTERS to 0... (and not 0x07E0 for example)?'
prog.s:42: Error: too many memory references for `mov'
prog.s:43: Error: too many memory references for `mov'
prog.s:44: Error: too many memory references for `mov'
prog.s:45: Error: too many memory references for `mov'
prog.s:46: Error: too many memory references for `mov'
prog.s:47: Error: too many memory references for `mov'
prog.s:56: Error: no such instruction: `dq 0'
prog.s:58: Error: no such instruction: `dw 0xFFFF'
prog.s:59: Error: no such instruction: `dw 0'
prog.s:60: Error: no such instruction: `db 0'
prog.s:61: Error: no such instruction: `db 10011010b'
prog.s:62: Error: no such instruction: `db 11001111b'
prog.s:63: Error: no such instruction: `db 0'
prog.s:65: Error: no such instruction: `dw 0xFFFF'
prog.s:66: Error: no such instruction: `dw 0'
prog.s:67: Error: no such instruction: `db 0'
prog.s:68: Error: no such instruction: `db 10010010b'
prog.s:69: Error: no such instruction: `db 11001111b'
prog.s:70: Error: no such instruction: `db 0'
prog.s:74: Error: no such instruction: `dw gdt_end - gdt_start - 1'
prog.s:75: Error: no such instruction: `dd gdt_start'
prog.s:77: Error: no such instruction: `code_seg equ gdt_code - gdt_start'
prog.s:78: Error: no such instruction: `data_seg equ gdt_data - gdt_start'
prog.s:81: Error: too many memory references for `mov'
prog.s:85: Error: invalid char '[' beginning operand 1 `[gdt_descriptor]'
prog.s:86: Error: too many memory references for `mov'
prog.s:87: Error: too many memory references for `or'
prog.s:88: Error: too many memory references for `mov'
prog.s:90: Error: junk `:protected_mode_start' after expression
prog.s:91: Error: no such instruction: `should never be reached'
prog.s:93: Error: no such instruction: `use32'
prog.s:95: Error: too many memory references for `mov'
prog.s:96: Error: too many memory references for `mov'
prog.s:97: Error: too many memory references for `mov'
prog.s:98: Error: too many memory references for `mov'
prog.s:99: Error: too many memory references for `mov'
prog.s:100: Error: too many memory references for `mov'
prog.s:101: Error: too many memory references for `mov'
prog.s:103: Error: no such instruction: `write 65to the middle of the screen (beginning of the video memory is at 0xB8000)'
prog.s:104: Error: too many memory references for `mov'
prog.s:105: Error: junk `[edi]' after expression
prog.s:105: Error: too many memory references for `mov'
prog.s:106: Error: too many memory references for `mov'
prog.s:107: Error: junk `[edi]' after expression
prog.s:107: Error: too many memory references for `mov'
prog.s:111: Error: no such instruction: `times 512 - ($ - $$)db 0'

Standard output is empty