mirror of
https://github.com/reactos/reactos.git
synced 2024-12-28 18:15:11 +00:00
174 lines
5.8 KiB
NASM
174 lines
5.8 KiB
NASM
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segment .text
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bits 16
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start:
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jmp short main
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nop
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OEMName db 'FreeLDR!'
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BytesPerSector dw 512
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SectsPerCluster db 1
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ReservedSectors dw 1
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NumberOfFats db 2
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MaxRootEntries dw 0 ;512 - Always zero for FAT32 volumes
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TotalSectors dw 0 ;2880 - Always zero for FAT32 volumes
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MediaDescriptor db 0f8h
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SectorsPerFat dw 0 ;9 - Always zero for FAT32 volumes
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SectorsPerTrack dw 18
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NumberOfHeads dw 2
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HiddenSectors dd 0
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TotalSectorsBig dd 0
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; FAT32 Inserted Info
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SectorsPerFatBig dd 0
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ExtendedFlags dw 0
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FSVersion dw 0
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RootDirStartCluster dd 0
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FSInfoSector dw 0
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BackupBootSector dw 6
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Reserved1 times 12 db 0
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; End FAT32 Inserted Info
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BootDrive db 0
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Reserved db 0
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ExtendSig db 29h
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SerialNumber dd 00000000h
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VolumeLabel db 'FreeLoader!'
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FileSystem db 'FAT12 '
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main:
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00007C5A 33C9 xor cx,cx
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00007C5C 8ED1 mov ss,cx
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00007C5E BCF47B mov sp,0x7bf4
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00007C61 8EC1 mov es,cx
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00007C63 8ED9 mov ds,cx
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00007C65 BD007C mov bp,0x7c00
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00007C68 884E02 mov [bp+0x2],cl
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00007C6B 8A5640 mov dl,[bp+BootDrive]
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00007C6E B408 mov ah,0x8
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00007C70 CD13 int 0x13 ; Int 13, func 8 - Get Drive Parameters
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00007C72 7305 jnc 0x7c79 ; If no error jmp
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00007C74 B9FFFF mov cx,0xffff
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00007C77 8AF1 mov dh,cl
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00007C79 660FB6C6 movzx eax,dh
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00007C7D 40 inc ax
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00007C7E 660FB6D1 movzx edx,cl
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00007C82 80E23F and dl,0x3f
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00007C85 F7E2 mul dx
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00007C87 86CD xchg cl,ch
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00007C89 C0ED06 shr ch,0x6
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00007C8C 41 inc cx
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00007C8D 660FB7C9 movzx ecx,cx
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00007C91 66F7E1 mul ecx
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00007C94 668946F8 mov [bp-0x8],eax
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00007C98 837E1600 cmp word [bp+TotalSectors],byte +0x0
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00007C9C 7538 jnz print_ntldr_error_message
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00007C9E 837E2A00 cmp word [bp+FSVersion],byte +0x0
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00007CA2 7732 ja print_ntldr_error_message
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00007CA4 668B461C mov eax,[bp+0x1c]
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00007CA8 6683C00C add eax,byte +0xc
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00007CAC BB0080 mov bx,0x8000
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00007CAF B90100 mov cx,0x1
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00007CB2 E82B00 call read_sectors
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00007CB5 E94803 jmp 0x8000
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print_disk_error_message:
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00007CB8 A0FA7D mov al,[DISK_ERR_offset_from_0x7d00]
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putchars:
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00007CBB B47D mov ah,0x7d
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00007CBD 8BF0 mov si,ax
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get_another_char:
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00007CBF AC lodsb
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00007CC0 84C0 test al,al
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00007CC2 7417 jz reboot
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00007CC4 3CFF cmp al,0xff
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00007CC6 7409 jz print_reboot_message
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00007CC8 B40E mov ah,0xe
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00007CCA BB0700 mov bx,0x7
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00007CCD CD10 int 0x10
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00007CCF EBEE jmp short get_another_char
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print_reboot_message:
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00007CD1 A0FB7D mov al,[RESTART_ERR_offset_from_0x7d00]
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00007CD4 EBE5 jmp short putchars
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print_ntldr_error_message:
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00007CD6 A0F97D mov al,[NTLDR_ERR_offset_from_0x7d00]
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00007CD9 EBE0 jmp short putchars
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reboot:
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00007CDB 98 cbw
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00007CDC CD16 int 0x16
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00007CDE CD19 int 0x19
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read_sectors:
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00007CE0 6660 pushad
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00007CE2 663B46F8 cmp eax,[bp-0x8]
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00007CE6 0F824A00 jc near 0x7d34
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00007CEA 666A00 o32 push byte +0x0
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00007CED 6650 push eax
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00007CEF 06 push es
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00007CF0 53 push bx
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00007CF1 666810000100 push dword 0x10010
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00007CF7 807E0200 cmp byte [bp+0x2],0x0
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00007CFB 0F852000 jnz near 0x7d1f
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00007CFF B441 mov ah,0x41
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00007D01 BBAA55 mov bx,0x55aa
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00007D04 8A5640 mov dl,[bp+BootDrive]
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00007D07 CD13 int 0x13
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00007D09 0F821C00 jc near 0x7d29
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00007D0D 81FB55AA cmp bx,0xaa55
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00007D11 0F851400 jnz near 0x7d29
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00007D15 F6C101 test cl,0x1
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00007D18 0F840D00 jz near 0x7d29
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00007D1C FE4602 inc byte [bp+0x2]
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00007D1F B442 mov ah,0x42
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00007D21 8A5640 mov dl,[bp+BootDrive]
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00007D24 8BF4 mov si,sp
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00007D26 CD13 int 0x13
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00007D28 B0F9 mov al,0xf9
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00007D2A 6658 pop eax
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00007D2C 6658 pop eax
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00007D2E 6658 pop eax
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00007D30 6658 pop eax
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00007D32 EB2A jmp short 0x7d5e
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00007D34 6633D2 xor edx,edx
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00007D37 660FB74E18 movzx ecx,word [bp+SectorsPerTrack]
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00007D3C 66F7F1 div ecx
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00007D3F FEC2 inc dl
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00007D41 8ACA mov cl,dl
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00007D43 668BD0 mov edx,eax
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00007D46 66C1EA10 shr edx,0x10
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00007D4A F7761A div word [bp+NumberOfHeads]
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00007D4D 86D6 xchg dl,dh
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00007D4F 8A5640 mov dl,[bp+BootDrive]
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00007D52 8AE8 mov ch,al
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00007D54 C0E406 shl ah,0x6
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00007D57 0ACC or cl,ah
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00007D59 B80102 mov ax,0x201
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00007D5C CD13 int 0x13
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00007D5E 6661 popad
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00007D60 0F8254FF jc near print_disk_error_message
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00007D64 81C30002 add bx,0x200
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00007D68 6640 inc eax
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00007D6A 49 dec cx
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00007D6B 0F8571FF jnz near read_sectors
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00007D6F C3 ret
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NTLDR db 'NTLDR '
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filler times 49 db 0
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NTLDR_ERR db 0dh,0ah,'NTLDR is missing',0ffh
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DISK_ERR db 0dh,0ah,'Disk error',0ffh
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RESTART_ERR db 0dh,0ah,'Press any key to restart',0dh,0ah
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more_filler times 16 db 0
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NTLDR_offset_from_0x7d00 db 0
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NTLDR_ERR_offset_from_0x7d00 db 0ach
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DISK_ERR_offset_from_0x7d00 db 0bfh
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RESTART_ERR_offset_from_0x7d00 db 0cch
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dw 0
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dw 0aa55h
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