Initial commit
This commit is contained in:
Freywar Ulvnaudgari
@@ -0,0 +1,337 @@
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bits 16
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org 0x8000
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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, 0x7000
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FIRST_PARTITION_SECTOR equ 2048 ; TODO Read MBR.
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STAGE_BUFFER_SEGMENT equ 0x0900
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STAGE_BUFFER_OFFSET equ 0x0000
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KERNEL_BUFFER_SEGMENT equ 0x2000
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jmp prepare_kernel
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dap:
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.dap_size: db 16
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.reserved: db 0
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.src_sectors: dw 1
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.dst_offset: dw 0
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.dst_segment: dw 0
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.src_lba: dq 0
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dap_end:
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bpb:
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.bytes_per_sector: dw 0
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.sectors_per_cluster: db 0
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.reserved_sectors: dw 0
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.fats_count: db 0
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.root_entry_count: dw 0
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.total_sectors_16: dw 0
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.media_type: db 0
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.sectors_per_fat: dw 0
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bpb_end:
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fat_start: dw 0
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root_start: dw 0
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root_size: dw 0
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data_start: dw 0
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kernel_filename: db 'KERNEL BIN'
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kernel_cluster: dw 0
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kernel_buffer_offset: dw 0
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read_sectors:
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xor bx, bx
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mov ds, bx
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mov [dap.src_lba], eax
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mov [dap.src_sectors], cx
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mov [dap.dst_segment], es
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mov [dap.dst_offset], di
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mov ah, 0x42
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mov dl, 0x80
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mov si, dap
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int 0x13
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jc disk_error
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ret
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disk_error:
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mov ah, 0x0E
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mov al, 'E'
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int 0x10
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jmp $
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prepare_kernel:
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load_bpb:
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xor bx, bx
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mov ds, bx
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mov eax, FIRST_PARTITION_SECTOR
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mov cx, 1
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mov bx, STAGE_BUFFER_SEGMENT
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mov es, bx
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mov di, STAGE_BUFFER_OFFSET
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call read_sectors
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mov bx, STAGE_BUFFER_SEGMENT
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mov ds, bx
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mov si, STAGE_BUFFER_OFFSET + 11
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xor bx, bx
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mov es, bx
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mov di, bpb
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mov cx, bpb_end - bpb
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rep movsb
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find_data_start:
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xor bx, bx
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mov ds, bx
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mov ax, FIRST_PARTITION_SECTOR
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add ax, [bpb.reserved_sectors]
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mov [fat_start], ax
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xor ax, ax
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mov al, [bpb.fats_count]
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mul word [bpb.sectors_per_fat]
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add ax, [fat_start]
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mov [root_start], ax ; dx should be zero for sane FAT16 values
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mov ax, [bpb.root_entry_count]
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shl ax, 5 ; * 32
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shr ax, 9 ; / 512 ; there should be at least 512 entries, so safe
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mov [root_size], ax
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mov ax, [root_start]
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add ax, [root_size]
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mov [data_start], ax
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find_kernel:
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xor bx, bx
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mov ds, bx
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xor eax, eax
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mov ax, [root_start]
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mov cx, [root_size]
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mov bx, STAGE_BUFFER_SEGMENT
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mov es, bx
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mov di, STAGE_BUFFER_OFFSET
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call read_sectors
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mov cx, [bpb.root_entry_count]
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mov bx, STAGE_BUFFER_SEGMENT
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mov ds, bx
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mov si, STAGE_BUFFER_OFFSET
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.check_entry:
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mov bx, STAGE_BUFFER_SEGMENT
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mov ds, bx
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cmp byte [si], 0x00
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je .no_more_entries
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cmp byte [si], 0xE5
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je .continue
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push si
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push cx
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xor bx, bx
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mov es, bx
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mov di, kernel_filename
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mov cx, 11
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rep cmpsb
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pop cx
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pop si
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je .found
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.continue:
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add si, 32
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loop .check_entry
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.no_more_entries:
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mov ah, 0x0E
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mov al, 'K'
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int 0x10
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jmp $
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.found:
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mov bx, STAGE_BUFFER_SEGMENT
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mov ds, bx
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mov ax, [si + 26]
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xor bx, bx
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mov ds, bx
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mov [kernel_cluster], ax
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load_fat:
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xor bx, bx
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mov ds, bx
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xor eax, eax
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mov ax, [fat_start]
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mov cx, [bpb.sectors_per_fat]
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mov bx, STAGE_BUFFER_SEGMENT
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mov es, bx
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mov di, STAGE_BUFFER_OFFSET
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call read_sectors
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load_kernel_cluster:
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xor bx, bx
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mov ds, bx
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xor eax, eax
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mov ax, [kernel_cluster]
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sub ax, 2
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xor bx, bx
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mov bl, [bpb.sectors_per_cluster]
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mul bx
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add ax, [data_start]
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xor cx, cx
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mov cl, [bpb.sectors_per_cluster]
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mov bx, KERNEL_BUFFER_SEGMENT
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mov es, bx
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mov di, [kernel_buffer_offset]
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call read_sectors
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mov ax, [bpb.sectors_per_cluster]
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shl ax, 9 ; * 512
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add ax, [kernel_buffer_offset]
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mov [kernel_buffer_offset], ax
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find_next_kernel_cluster:
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xor bx, bx
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mov ds, bx
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mov si, [kernel_cluster]
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shl si, 1 ; * 2
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add si, STAGE_BUFFER_OFFSET
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mov bx, STAGE_BUFFER_SEGMENT
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mov ds, bx
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mov ax, [si]
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xor bx, bx
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mov ds, bx
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mov [kernel_cluster], ax
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cmp ax, 0xFFF8
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jb load_kernel_cluster
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; ------------------------------------------------------------------------------
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jmp load_gdt
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gdt_start:
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gdt_0: dq 0x0000000000000000
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gdt_1:
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.limit_low: dw 0xFFFF
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.base_low: dw 0x0000
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.base_middle: db 0x00
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.access: db 10011010b ; present, ring 0, code, executable, readable
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.flags: db 11001111b ; 32-bit, 4KB granularity
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.base_high: db 0x00
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gdt_1_end:
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gdt_2:
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.limit_low: dw 0xFFFF
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.base_low: dw 0x0000
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.base_middle: db 0x00
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.access: db 10011010b ; present, ring 0, code, executable, readable
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.flags: db 10101111b ; long mode (L bit)
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.base_high: db 0x00
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gdt_2_end:
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gdt_3:
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.limit_low: dw 0xFFFF
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.base_low: dw 0x0000
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.base_middle: db 0x00
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.access: db 10010010b ; present, ring 0, data, writable
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.flags: db 00000000b
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.base_high: db 0x00
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gdt_3_end:
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gdt_end:
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gdt_descriptor:
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.size: dw gdt_end - gdt_start - 1
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.offset: dd gdt_start
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gdt_descriptor_end:
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load_gdt:
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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, 0x00000001
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mov cr0, eax
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jmp 0x0008:protected_mode
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; ------------------------------------------------------------------------------
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bits 32
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protected_mode:
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mov ax, 0x0018 ; data segment is now third entry = 0x18
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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 esp, 0x00090000
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; zero page table memory at 0x00010000 (3 pages = 768 dwords)
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mov edi, 0x00010000
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mov ecx, 768
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xor eax, eax
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rep stosd
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; PML4[0] -> PDPT at 0x00011000
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mov dword [0x00010000], 0x00011003
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; PDPT[0] -> PD at 0x00012000
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mov dword [0x00011000], 0x00012003
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; PD: fill 64 entries, each mapping 2MB
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mov edi, 0x00012000
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mov eax, 0x00000083 ; present, writable, huge page, base 0
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mov ecx, 64
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.fill_pd:
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mov dword [edi], eax
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add edi, 8
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add eax, 0x00200000 ; next 2MB
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loop .fill_pd
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; load PML4 into CR3
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mov eax, 0x00010000
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mov cr3, eax
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; enable PAE
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mov eax, cr4
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or eax, 0x00000020
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mov cr4, eax
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; enable long mode in EFER MSR
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mov ecx, 0xC0000080
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rdmsr
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or eax, 0x00000100
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wrmsr
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; enable paging (and keep protection enabled)
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mov eax, cr0
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or eax, 0x80000000
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mov cr0, eax
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jmp 0x0010:long_mode ; 0x10 = second entry = 64-bit code segment
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; ------------------------------------------------------------------------------
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bits 64
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long_mode:
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mov ax, 0x0018 ; data segment
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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 rsp, 0x0000000000090000
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xor rax, rax
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xor rbx, rbx
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xor rcx, rcx
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xor rdx, rdx
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jmp 0x00020000
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