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161 lines
3.4 KiB
161 lines
3.4 KiB
section .boot
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bits 16
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global boot
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boot:
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jmp main
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display_enable:
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push bp
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mov bp, sp
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mov ah, 0h ; 00h Set Video Mode
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mov al, 07h ; Txt, monochrome, 80x25
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int 10h
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mov sp, bp
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pop bp
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ret
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print:
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push bp
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mov bp, sp
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mov si, [bp + 4]; put first function arg in si. sp is stask pointer
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.loop:
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lodsb ; load si content into al then inc si
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cmp al, 0;
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je .end
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mov ah, 0eh
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mov bx, 0
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int 10h
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jmp .loop
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.end:
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mov sp, bp
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pop bp
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ret
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println:
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push bp
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mov bp, sp
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push word [bp + 4]
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call print
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add sp, 2
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mov ah, 03h ; read cursor position
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int 10h ; row number in dh. Col in dl
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inc dh ; goto next line
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mov dl, 0
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mov ah, 02h ; Set Cursor Position
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int 10h
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mov sp, bp
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pop bp
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ret
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hello db 'Booting matOs', 0
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main:
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sti ; enable virtual interupts
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mov [disk],dl ; save disk used to boot by bios
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call display_enable
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push hello
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call println
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add sp, 2
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; Switch in 32bits Protected mode
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; Activate A20 http://wiki.osdev.org/A20_Line to be able to access more than 1Mb memory
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mov ah, 0h
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mov ax, 0x2401
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int 0x15
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; Change video mode to display VGA
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mov ax, 0x3
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int 0x10
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; http://www.ctyme.com/intr/rb-0607.htm
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; Bios read first 512 bytes, read next disk sector
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mov ah, 0x2 ;read sectors
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mov al, 15 ;sectors to read
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mov ch, 0 ;cylinder idx
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mov dh, 0 ;head idx
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mov cl, 2 ;sector idx
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mov dl, [disk] ;disk idx
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mov bx, copy_target;target pointer
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int 0x13
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cli ; disable interruption when setting GDT
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; switch in 32 bits
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lgdt [gdt_pointer] ; switch in 32bits here
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mov eax, cr0
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or eax,0x1; set the protected mode bit on special CPU reg cr0
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mov cr0, eax
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jmp CODE_SEG:boot2 ; In protected mode we need to add the segment selector
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; GDT table desciption could be found http://wiki.osdev.org/Global_Descriptor_Table
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; here we define the 3 64bits segment needed: null segment, code segment and data segment
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gdt_start: ;null segment
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dq 0x0
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gdt_code: ;code segment
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dw 0xFFFF ; limit [0:15]
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dw 0x0 ; base [0:15]
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db 0x0 ; base [16:23]
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db 10011010b ; access byte: Present(1)| Priv(2) 0 ->kernel 3->userspace | 1 | Executable(1) | Direction/Conformity (1) | RW(1) | Accessed(1)
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db 11001111b ; Granularity(1) | Size (1) 0-> 16bit mode 1->32protected mode | 0 | 0 | Limit [16:19]
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db 0x0 ; base [24:31]
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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_pointer:
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dw gdt_end - gdt_start
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dd gdt_start
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disk:
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db 0x0
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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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times 510 - ($-$$) db 0
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dw 0xaa55
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copy_target:
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bits 32
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boot2:
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mov ax, DATA_SEG ; set all segments to point to DATA_SEG https://en.wikipedia.org/wiki/X86_memory_segmentation
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mov ds, ax ; Data segment
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mov es, ax ; Extra Segment (for string operation)
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mov fs, ax ; No Specific use
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mov gs, ax ; No Specific use
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mov ss, ax ; stack segment
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mov esi,hello32
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mov ebx,0xb8000 ; Cannot use BIOS anymore, use VGA Text buffer instead
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.loop32:
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lodsb
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or al,al
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jz halt
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or eax,0x0100 ; blue bg
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mov word [ebx], ax
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add ebx,2
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jmp .loop32
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halt:
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mov esp,kernel_stack_top
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extern kmain
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call kmain
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cli
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hlt
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hello32: db "Hello 32 bits world!",0
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section .bss
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align 4
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kernel_stack_bottom: equ $
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resb 16384 ; 16 KB
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kernel_stack_top:
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