mirror of
https://github.com/wichtounet/thor-os.git
synced 2025-09-12 14:10:36 -04:00
Optimization and cleanup
Do string comparison two byte at a time Output error messages for unsupported FAT32 features
This commit is contained in:
Baptiste Wicht
parent
c21164d102
commit
8d8bfc3ea1
@ -10,7 +10,6 @@
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jmp second_step
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%include "intel_16.asm"
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%include "sectors.asm"
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FREE_BASE equ 0x4500
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KERNEL_BASE equ 0x600 ; 0x600:0x0 (0x6000)
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@ -24,6 +23,18 @@ DAP:
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.lba dd 0
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.lba48 dd 0
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; Perform an extended read using BIOS
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; On error, jump to read_failed and never returns
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extended_read:
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mov ah, 0x42
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mov si, DAP
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mov dl, 0x80
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int 0x13
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jc read_failed
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ret
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; Loaded at 0x410:0x0 (0x4100)
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second_step:
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; Set data segment
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@ -44,12 +55,7 @@ second_step:
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mov word [DAP.segment], 0
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mov dword [DAP.lba], 0
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mov ah, 0x42
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mov si, DAP
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mov dl, 0x80
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int 0x13
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jc read_failed
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call extended_read
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mov ax, [gs:(FREE_BASE + 446 + 8)]
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mov [partition_start], ax
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@ -63,12 +69,7 @@ second_step:
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mov di, [partition_start]
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mov word [DAP.lba], di
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mov ah, 0x42
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mov si, DAP
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mov dl, 0x80
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int 0x13
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jc read_failed
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call extended_read
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mov ah, [gs:(FREE_BASE + 13)]
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mov [sectors_per_cluster], ah
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@ -79,6 +80,11 @@ second_step:
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mov ah, [gs:(FREE_BASE + 16)]
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mov [number_of_fat], ah
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mov ax, [gs:(FREE_BASE + 38)]
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test ax, ax
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jne sectors_per_fat_too_high
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; sectors_per_fat (only low part)
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mov ax, [gs:(FREE_BASE + 36)]
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mov [sectors_per_fat], ax
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@ -100,9 +106,8 @@ second_step:
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mov [cluster_begin], ax
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; entries per cluster = (512/32) * sectors_per_cluster
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mov ax, 32
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movzx bx, byte [sectors_per_cluster]
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mul bx
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movzx ax, byte [sectors_per_cluster]
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shl ax, 4
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mov [entries_per_cluster], ax
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; 3. Read the root directory to find the kernel executable
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@ -122,12 +127,7 @@ second_step:
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mov word [DAP.lba], ax
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mov ah, 0x42
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mov si, DAP
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mov dl, 0x80
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int 0x13
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jc read_failed
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call extended_read
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mov si, FREE_BASE
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xor cx, cx
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@ -139,48 +139,28 @@ second_step:
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test ah, ah
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je .end_of_directory
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; Verify char by char if it is KERNEL.BIN
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cmp ah, 75
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mov ax, [gs:si]
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cmp ax, 0x454B ; EK
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jne .continue
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mov ah, [gs:(si+1)]
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cmp ah, 69
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mov ax, [gs:(si+2)]
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cmp ax, 0x4E52 ; NR
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jne .continue
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mov ah, [gs:(si+2)]
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cmp ah, 82
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mov ax, [gs:(si+4)]
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cmp ax, 0x4C45 ; LE
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jne .continue
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mov ah, [gs:(si+3)]
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cmp ah, 78
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mov ax, [gs:(si+6)]
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cmp ax, 0x2020 ; space space
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jne .continue
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mov ah, [gs:(si+4)]
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cmp ah, 69
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jne .continue
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mov ah, [gs:(si+5)]
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cmp ah, 76
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jne .continue
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mov ah, [gs:(si+6)]
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cmp ah, 32
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jne .continue
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mov ah, [gs:(si+7)]
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cmp ah, 32
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jne .continue
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mov ah, [gs:(si+8)]
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cmp ah, 66
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jne .continue
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mov ah, [gs:(si+9)]
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cmp ah, 73
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mov ax, [gs:(si+8)]
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cmp ax, 0x4942; IB
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jne .continue
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mov ah, [gs:(si+10)]
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cmp ah, 78
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cmp ah, 0x4E ; N
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jne .continue
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; cluster high
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@ -191,14 +171,6 @@ second_step:
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mov ax, [gs:(si+26)]
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mov [cluster_low], ax
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; file_size low
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mov ax, [gs:(si+28)]
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mov [size_low], ax
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; file_size high
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mov ax, [gs:(si+30)]
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mov [size_high], ax
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jmp .found
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.continue:
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@ -210,6 +182,11 @@ second_step:
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jne .next
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.end_of_cluster:
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mov si, multicluster_directory
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call print_line_16
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jmp error_end
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.end_of_directory:
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mov si, kernel_not_found
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call print_line_16
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@ -223,6 +200,10 @@ second_step:
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; 4. Load the kernel into memory
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mov ax, [cluster_high]
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test ax, ax
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jne cluster_too_high
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mov ax, [cluster_low]
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mov [current_cluster], ax
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mov word [current_segment], KERNEL_BASE
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@ -248,12 +229,7 @@ second_step:
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mov word [DAP.lba], ax
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mov ah, 0x42
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mov si, DAP
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mov dl, 0x80
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int 0x13
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jc read_failed
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call extended_read
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; Compute next cluster
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@ -270,12 +246,7 @@ second_step:
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mov word [DAP.segment], 0x0
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mov word [DAP.lba], ax
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mov ah, 0x42
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mov si, DAP
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mov dl, 0x80
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int 0x13
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jc read_failed
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call extended_read
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mov si, [current_cluster]
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and si, 512 - 1 ; current_cluster % 512
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@ -296,6 +267,9 @@ second_step:
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jge .fully_loaded
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.ok:
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test bx, bx
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jne cluster_too_high
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mov [current_cluster], ax
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movzx ax, byte [sectors_per_cluster]
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@ -314,6 +288,18 @@ second_step:
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jmp $
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cluster_too_high:
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mov si, cluster_too_high_msg
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call print_line_16
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jmp error_end
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sectors_per_fat_too_high:
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mov si, sectors_per_fat_too_high_msg
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call print_line_16
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jmp error_end
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corrupted:
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mov si, corrupted_disk
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call print_line_16
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@ -344,8 +330,6 @@ error_end:
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cluster_high dw 0
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cluster_low dw 0
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size_high dw 0
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size_low dw 0
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current_cluster dw 0
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current_segment dw 0
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@ -354,15 +338,17 @@ error_end:
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load_kernel db 'Attempt to load the kernel...', 0
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kernel_found db 'Kernel found. Starting kernel loading...', 0
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kernel_not_found db 'Kernel not found...', 0
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kernel_loaded db 'Kernel fully loaded', 0
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corrupted_disk db 'The disk seeems to be corrupted', 0
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star db '*', 0
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dix db '|', 0
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kernel_not_found db 'Kernel not found...', 0
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corrupted_disk db 'The disk seeems to be corrupted', 0
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sectors_per_fat_too_high_msg db 'Error 1. The disk is probably too big', 0
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multicluster_directory db 'Error 2. Multicluster directory not supported', 0
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cluster_too_high_msg db 'Error 3. Only 16bit cluster are supported', 0
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read_failed_msg db 'Read disk failed', 0
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load_failed db 'Kernel loading failed', 0
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; Make it two sectors exactly
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; Make it sector-aligned
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times 1024-($-$$) db 0
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