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