+++ /dev/null
-;
-; Win2k FAT32 Boot Sector
-;
-; Brian Palmer <brianp@sginet.com>
-;
-
-;
-; The BP register is initialized to 0x7c00, the start of
-; the boot sector. The SP register is initialized to
-; 0x7bf4, leaving 12 bytes of data storage space above
-; the stack.
-;
-; The DWORD that gets stored at 0x7bf4 is 0xffffffff ??
-;
-; The DWORD that gets stored at 0x7bf8 is the count of
-; total sectors of the volume, calculated from the BPB.
-;
-; The DWORD that gets stored at 0x7bfc is the logical
-; sector number of the start of the data area.
-;
-
-org 7c00h
-
-segment .text
-
-bits 16
-
-start:
- jmp short main
- nop
-
-OEMName db 'MSWIN4.0'
-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 80h
-Reserved db 0
-ExtendSig db 29h
-SerialNumber dd 00000000h
-VolumeLabel db 'NO NAME '
-FileSystem db 'FAT32 '
-
-main:
-00007C5A 33C9 xor cx,cx
-00007C5C 8ED1 mov ss,cx ; Setup the stack
-00007C5E BCF47B mov sp,0x7bf4 ; Give us 12 bytes of space above the stack
-00007C61 8EC1 mov es,cx
-00007C63 8ED9 mov ds,cx
-00007C65 BD007C mov bp,0x7c00
-00007C68 884E02 mov [bp+0x2],cl ; Zero out the nop instruction?? (3rd byte of the boot sector)
-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 drive_param_ok ; If no error jmp
-
-drive_param_error:
-00007C74 B9FFFF mov cx,0xffff ; We couldn't determine the drive parameters
-00007C77 8AF1 mov dh,cl ; So just set the CHS to 0xff
-
-drive_param_ok:
-00007C79 660FB6C6 movzx eax,dh ; Store the number of heads in eax
-00007C7D 40 inc ax ; Make it one-based because the bios returns it zero-based
-00007C7E 660FB6D1 movzx edx,cl ; Store the sectors per track in edx
-00007C82 80E23F and dl,0x3f ; Mask off the cylinder bits
-00007C85 F7E2 mul dx ; Multiply the sectors per track with the heads, result in dx:ax
-00007C87 86CD xchg cl,ch ; Switch the cylinder with the sectors
-00007C89 C0ED06 shr ch,0x6 ; Move the top two cylinder bits down where they should be
-00007C8C 41 inc cx ; Make it one-based because the bios returns it zero-based
-00007C8D 660FB7C9 movzx ecx,cx
-00007C91 66F7E1 mul ecx ; Multiply the cylinders with (heads * sectors) [stored in dx:ax already]
-00007C94 668946F8 mov [bp-0x8],eax ; This value is the number of total sectors on the disk, so save it for later
-00007C98 837E1600 cmp word [bp+TotalSectors],byte +0x0 ; Check the old 16-bit value of TotalSectors
-00007C9C 7538 jnz print_ntldr_error_message ; If it is non-zero then exit with an error
-
-00007C9E 837E2A00 cmp word [bp+FSVersion],byte +0x0 ; Check the file system version word
-00007CA2 7732 ja print_ntldr_error_message ; If it is not zero then exit with an error
-
-
- ;
- ; We are now ready to load our second sector of boot code
- ; But first, a bit of undocumented information about how
- ; Win2k stores it's second sector of boot code.
- ;
- ; The FAT32 filesystem was designed so that you can store
- ; multiple sectors of boot code. The boot sector of a FAT32
- ; volume is actually three sectors long. Microsoft extended
- ; the BPB so much that you can't fit enough code in the
- ; boot sector to make it work. So they extended it. Sector 0
- ; is the traditional boot sector, sector 1 is the FSInfo sector,
- ; and sector 2 is used to store extra boot code to make up
- ; for the lost space the BPB takes.
- ;
- ; Now this creates an interesting problem. Suppose for example
- ; that the user has Win98 and Win2k installed. The Win2k
- ; boot sector is stored at sector 0 and the Win98 boot sector is
- ; stored as BOOTSECT.DOS on the file system. Now if Win2k were
- ; to store it's second sector of boot code in sector 2 like
- ; the fat spec says to do then when you try to dual boot back
- ; to Win98 the Win98 boot sector will load Win2k's second
- ; sector of boot code. Understand? ;-)
- ;
- ; To get around this problem Win2k stores it's second sector
- ; of boot code elsewhere. This sector is always stored at sector 13
- ; on the file system. Now don't ask me what happens when you don't
- ; have enough reserved sectors to store it, but I've never seen a
- ; FAT32 volume that didn't have at least 32 reserved sectors.
- ;
-
-00007CA4 668B461C mov eax,[bp+HiddenSectors] ; Get the count of hidden sectors
-00007CA8 6683C00C add eax,byte +0xc ; Add 12 to that value so that we are loading the 13th sector of the volume
-00007CAC BB0080 mov bx,0x8000 ; Read the sector to address 0x8000
-00007CAF B90100 mov cx,0x1 ; Read just one sector
-00007CB2 E82B00 call read_sectors ; Read it
-00007CB5 E94803 jmp 0x8000 ; Jump to the next sector of boot code
-
-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
-
-
-
-
-
-
-;
-; And that ends the code that makes up the traditional boot sector
-; From here on out is a disassembly of the extra sector of boot
-; code required for a FAT32 volume. Win2k stores this code at
-; sector 13 on the file system.
-;
-
-
-
-
-00008000 660FB64610 movzx eax,byte [bp+NumberOfFats] ; Put the number of fats into eax
-00008005 668B4E24 mov ecx,[bp+SectorsPerFatBig] ; Put the count of sectors per fat into ecx
-00008009 66F7E1 mul ecx ; Multiply them, edx:eax = (eax * ecx)
-0000800C 6603461C add eax,[bp+HiddenSectors] ; Add the hidden sectors to eax
-00008010 660FB7560E movzx edx,word [bp+ReservedSectors] ; Put the count of reserved sectors into edx
-00008015 6603C2 add eax,edx ; Add it to eax
-00008018 668946FC mov [bp-0x4],eax ; eax now contains the start of the data area, so save it for later
-0000801C 66C746F4FFFFFFFF mov dword [bp-0xc],0xffffffff ; Save 0xffffffff for later??
-00008024 668B462C mov eax,[bp+RootDirStartCluster] ; Put the starting cluster of the root directory into eax
-00008028 6683F802 cmp eax,byte +0x2 ; Check and see if the root directory starts at cluster 2 or above
-0000802C 0F82A6FC jc near print_ntldr_error_message ; If not exit with error
-00008030 663DF8FFFF0F cmp eax,0xffffff8 ; Check and see if the root directory start cluster is and end of cluster chain indicator
-00008036 0F839CFC jnc near print_ntldr_error_message ; If so exit with error
-
-search_root_directory_cluster:
-0000803A 6650 push eax ; Save root directory start cluster on stack
-0000803C 6683E802 sub eax,byte +0x2 ; Adjust it because the first two fat entries are unused so the third entry marks the first data area cluster
-00008040 660FB65E0D movzx ebx,byte [bp+SectsPerCluster] ; Put the number of sectors per cluster in ebx
-00008045 8BF3 mov si,bx ; Now store it also in si register
-00008047 66F7E3 mul ebx ; Multiply sectors per cluster with root directory start cluster
-0000804A 660346FC add eax,[bp-0x4] ; Add the start sector of the data area
-
-read_directory_sector:
-0000804E BB0082 mov bx,0x8200 ; We now have the start sector of the root directory, so load it to 0x8200
-00008051 8BFB mov di,bx ; Put the address of the root directory sector in di also
-00008053 B90100 mov cx,0x1 ; Read one sector
-00008056 E887FC call read_sectors ; Perform the read
-
-check_entry_for_ntldr:
-00008059 382D cmp [di],ch ; Check the first byte of the root directory entry for zero
-0000805B 741E jz ntldr_not_found ; If so then NTLDR is missing so exit with error
-0000805D B10B mov cl,0xb ; Put the value 11 in cl so we can compare an 11-byte filename
-0000805F 56 push si ; Save si (which contains the number of sectors per cluster)
-00008060 BE707D mov si,NTLDR ;0x7d70 ; Check and see if "NTLDR" is the first file entry
-00008063 F3A6 repe cmpsb ; Do the compare
-00008065 5E pop si ; Restore sectors per cluster into si
-00008066 741B jz ntldr_found ; If we found it then continue, else check next entry
-00008068 03F9 add di,cx ; Add 0 to di? the next entry is 0x15 bytes away
-0000806A 83C715 add di,byte +0x15 ; Add 0x15 to di
-0000806D 3BFB cmp di,bx ; Check to see if we have reached the end of our sector we loaded, read_sectors sets bx = end address of data loaded
-0000806F 72E8 jc check_entry_for_ntldr ; If we haven't reached the end then check the next entry
-00008071 4E dec si ; decrement si, si holds the number of sectors per cluster
-00008072 75DA jnz read_directory_sector ; If it's not zero then search the next sector for NTLDR
-00008074 6658 pop eax ; If we got here that means we didn't find NTLDR in the previous root directory cluster, so restore eax with the start cluster
-00008076 E86500 call get_fat_entry ; Get the next cluster in the fat chain
-00008079 72BF jc search_root_directory_cluster ; If we reached end-of-file marker then don't jump, otherwise continue search
-
-ntldr_not_found:
-0000807B 83C404 add sp,byte +0x4
-0000807E E955FC jmp print_ntldr_error_message
-
-ntldr_load_segment_address dw 0x2000
-
-ntldr_found:
-00008083 83C404 add sp,byte +0x4 ; Adjust stack to remove root directory start cluster
-00008086 8B7509 mov si,[di+0x9] ; Put start cluster high word in si
-00008089 8B7D0F mov di,[di+0xf] ; Put start cluster low word in di
-0000808C 8BC6 mov ax,si ; Put high word in ax
-0000808E 66C1E010 shl eax,0x10 ; Shift it into position
-00008092 8BC7 mov ax,di ; Put low word in ax, now eax contains start cluster of NTLDR
-00008094 6683F802 cmp eax,byte +0x2 ; Check and see if the start cluster of NTLDR starts at cluster 2 or above
-00008098 0F823AFC jc near print_ntldr_error_message ; If not exit with error
-0000809C 663DF8FFFF0F cmp eax,0xffffff8 ; Check and see if the start cluster of NTLDR is and end of cluster chain indicator
-000080A2 0F8330FC jnc near print_ntldr_error_message ; If so exit with error
-
-load_next_ntldr_cluster:
-000080A6 6650 push eax ; Save NTLDR start cluster for later
-000080A8 6683E802 sub eax,byte +0x2 ; Adjust it because the first two fat entries are unused so the third entry marks the first data area cluster
-000080AC 660FB64E0D movzx ecx,byte [bp+SectsPerCluster] ; Put the sectors per cluster into ecx
-000080B1 66F7E1 mul ecx ; Multiply sectors per cluster by the start cluster, we now have the logical start sector
-000080B4 660346FC add eax,[bp-0x4] ; Add the start of the data area logical sector
-000080B8 BB0000 mov bx,0x0 ; Load NTLDR to offset zero
-000080BB 06 push es ; Save es
-000080BC 8E068180 mov es,[ntldr_load_segment_address] ; Get the segment address to load NTLDR to
-000080C0 E81DFC call read_sectors ; Load the first cluster
-000080C3 07 pop es ; Restore es
-000080C4 6658 pop eax ; Restore eax to NTLDR start cluster
-000080C6 C1EB04 shr bx,0x4 ; bx contains the amount of data we transferred, so divide it by 16
-000080C9 011E8180 add [ntldr_load_segment_address],bx ; Add that value to the segment
-000080CD E80E00 call get_fat_entry ; Get the next cluster in eax
-000080D0 0F830200 jnc near jump_to_ntldr ; If we have reached the end of file then lets get to NTLDR
-000080D4 72D0 jc load_next_ntldr_cluster ; If not, then load another cluster
-
-jump_to_ntldr:
-000080D6 8A5640 mov dl,[bp+BootDrive] ; Put the boot drive in dl
-000080D9 EA00000020 jmp 0x2000:0x0 ; Jump to NTLDR
-
-get_fat_entry:
-000080DE 66C1E002 shl eax,0x2 ; Multiply cluster by 4
-000080E2 E81100 call load_fat_sector ; Load the fat sector
-000080E5 26668B01 mov eax,[es:bx+di] ; Get the fat entry
-000080E9 6625FFFFFF0F and eax,0xfffffff ; Mask off the most significant 4 bits
-000080EF 663DF8FFFF0F cmp eax,0xffffff8 ; Compare it to end of file marker to set the flags correctly
-000080F5 C3 ret ; Return to caller
-
-load_fat_sector:
-000080F6 BF007E mov di,0x7e00 ; We will load the fat sector to 0x7e00
-000080F9 660FB74E0B movzx ecx,word [bp+SectsPerCluster] ; Get the sectors per cluster
-000080FE 6633D2 xor edx,edx ; We will divide (cluster * 4) / sectorspercluster
-00008101 66F7F1 div ecx ; eax is already set before we get to this routine
-00008104 663B46F4 cmp eax,[bp-0xc] ; Compare eax to 0xffffffff (initially, we set this value later)
-00008108 743A jz load_fat_sector_end ; If it is the same return
-0000810A 668946F4 mov [bp-0xc],eax ; Update that value
-0000810E 6603461C add eax,[bp+HiddenSectors] ; Add the hidden sectors
-00008112 660FB74E0E movzx ecx,word [bp+ReservedSectors] ; Add the reserved sectors
-00008117 6603C1 add eax,ecx ; To the hidden sectors + the value we computed earlier
-0000811A 660FB75E28 movzx ebx,word [bp+ExtendedFlags] ; Get extended flags and put into ebx
-0000811F 83E30F and bx,byte +0xf ; Mask off upper 8 bits
-00008122 7416 jz load_fat_sector_into_memory ; If fat is mirrored then skip fat calcs
-00008124 3A5E10 cmp bl,[bp+NumberOfFats] ; Compare bl to number of fats
-00008127 0F83ABFB jnc near print_ntldr_error_message ; If bl is bigger than numfats exit with error
-0000812B 52 push dx ; Save dx
-0000812C 668BC8 mov ecx,eax ; Put the current fat sector offset into ecx
-0000812F 668B4624 mov eax,[bp+SectorsPerFatBig] ; Get the number of sectors occupied by one fat
-00008133 66F7E3 mul ebx ; Multiplied by the active fat index
-00008136 6603C1 add eax,ecx ; Add the current fat sector offset
-00008139 5A pop dx ; Restore dx
-load_fat_sector_into_memory:
-0000813A 52 push dx ; Save dx, what is so important in dx??
-0000813B 8BDF mov bx,di ; Put 0x7e00 in bx
-0000813D B90100 mov cx,0x1 ; Load one sector
-00008140 E89DFB call read_sectors ; Perform the read
-00008143 5A pop dx ; Restore dx
-load_fat_sector_end:
-00008144 8BDA mov bx,dx ; Put it into bx, what is this value??
-00008146 C3 ret ; Return
-
-
-00008147 0000 add [bx+si],al
-00008149 0000 add [bx+si],al
-0000814B 0000 add [bx+si],al
-0000814D 0000 add [bx+si],al
-0000814F 0000 add [bx+si],al
-00008151 0000 add [bx+si],al
-00008153 0000 add [bx+si],al
-00008155 0000 add [bx+si],al
-00008157 0000 add [bx+si],al
-00008159 0000 add [bx+si],al
-0000815B 0000 add [bx+si],al
-0000815D 0000 add [bx+si],al
-0000815F 0000 add [bx+si],al
-00008161 0000 add [bx+si],al
-00008163 0000 add [bx+si],al
-00008165 0000 add [bx+si],al
-00008167 0000 add [bx+si],al
-00008169 0000 add [bx+si],al
-0000816B 0000 add [bx+si],al
-0000816D 0000 add [bx+si],al
-0000816F 0000 add [bx+si],al
-00008171 0000 add [bx+si],al
-00008173 0000 add [bx+si],al
-00008175 0000 add [bx+si],al
-00008177 0000 add [bx+si],al
-00008179 0000 add [bx+si],al
-0000817B 0000 add [bx+si],al
-0000817D 0000 add [bx+si],al
-0000817F 0000 add [bx+si],al
-00008181 0000 add [bx+si],al
-00008183 0000 add [bx+si],al
-00008185 0000 add [bx+si],al
-00008187 0000 add [bx+si],al
-00008189 0000 add [bx+si],al
-0000818B 0000 add [bx+si],al
-0000818D 0000 add [bx+si],al
-0000818F 0000 add [bx+si],al
-00008191 0000 add [bx+si],al
-00008193 0000 add [bx+si],al
-00008195 0000 add [bx+si],al
-00008197 0000 add [bx+si],al
-00008199 0000 add [bx+si],al
-0000819B 0000 add [bx+si],al
-0000819D 0000 add [bx+si],al
-0000819F 0000 add [bx+si],al
-000081A1 0000 add [bx+si],al
-000081A3 0000 add [bx+si],al
-000081A5 0000 add [bx+si],al
-000081A7 0000 add [bx+si],al
-000081A9 0000 add [bx+si],al
-000081AB 0000 add [bx+si],al
-000081AD 0000 add [bx+si],al
-000081AF 0000 add [bx+si],al
-000081B1 0000 add [bx+si],al
-000081B3 0000 add [bx+si],al
-000081B5 0000 add [bx+si],al
-000081B7 0000 add [bx+si],al
-000081B9 0000 add [bx+si],al
-000081BB 0000 add [bx+si],al
-000081BD 0000 add [bx+si],al
-000081BF 0000 add [bx+si],al
-000081C1 0000 add [bx+si],al
-000081C3 0000 add [bx+si],al
-000081C5 0000 add [bx+si],al
-000081C7 0000 add [bx+si],al
-000081C9 0000 add [bx+si],al
-000081CB 0000 add [bx+si],al
-000081CD 0000 add [bx+si],al
-000081CF 0000 add [bx+si],al
-000081D1 0000 add [bx+si],al
-000081D3 0000 add [bx+si],al
-000081D5 0000 add [bx+si],al
-000081D7 0000 add [bx+si],al
-000081D9 0000 add [bx+si],al
-000081DB 0000 add [bx+si],al
-000081DD 0000 add [bx+si],al
-000081DF 0000 add [bx+si],al
-000081E1 0000 add [bx+si],al
-000081E3 0000 add [bx+si],al
-000081E5 0000 add [bx+si],al
-000081E7 0000 add [bx+si],al
-000081E9 0000 add [bx+si],al
-000081EB 0000 add [bx+si],al
-000081ED 0000 add [bx+si],al
-000081EF 0000 add [bx+si],al
-000081F1 0000 add [bx+si],al
-000081F3 0000 add [bx+si],al
-000081F5 0000 add [bx+si],al
-000081F7 0000 add [bx+si],al
-000081F9 0000 add [bx+si],al
-000081FB 0000 add [bx+si],al
-000081FD 0055AA add [di-0x56],dl ; We can't forget the infamous boot signature
projects / reactos.git / blobdiff