580 lines
21 KiB
NASM
580 lines
21 KiB
NASM
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Page ,132
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TITLE BOOT SECTOR 1 OF TRACK 0 - BOOT LOADER
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;/*
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; * Microsoft Confidential
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; * Copyright (C) Microsoft Corporation 1991
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; * All Rights Reserved.
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; */
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; Rev 1.0 ChrisP, AaronR and others. 2.0 format boot
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;
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; Rev 3.0 MarkZ PC/AT enhancements
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; 2.50 in label
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; Rev 3.1 MarkZ 3.1 in label due to vagaries of SYSing to IBM drive D's
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; This resulted in the BPB being off by 1. So we now trust
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; 2.0 and 3.1 boot sectors and disbelieve 3.0.
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;
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; Rev 3.2 LeeAc Modify layout of extended BPB for >32M support
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; Move PHYDRV to 3rd byte from end of sector
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; so that it won't have to be moved again
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; FORMAT and SYS count on PHYDRV being in a known location
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;
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; Rev 3.3 D.C.L. Changed Sec 9 EOT field from 15 to 18. May 29, 1986.
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;
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; Rev 3.31 MarkT The COUNT value has a bogus check (JBE????) to determine
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; if we've loaded in all the sectors of IBMBIO. This will
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; cause too big of a load if the sectors per track is high
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; enough, causing either a stack overflow or the boot code
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; to be overwritten.
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;
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; Rev 4.00 J. K. For DOS 4.00 Modified to handle the extended BPB, and
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; 32 bit sector number calculation to enable the primary
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; partition be started beyond 32 MB boundary.
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;
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; Rev 7.0 JeffPar Loads WINBOOT.SYS from anywhere in the root of the boot
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; drive. WINBOOT.SYS must be an EXE with exactly 1 sector
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; of header information, followed by a series of binary
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; images imbedded in the EXE, as follows:
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;
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; 1. WINLOAD module (ORGed at 200h, loaded at 70:200h)
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; 2. IO.SYS module
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; 3. MSDOS.SYS module
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;
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; The WINLOAD module should fit within WINLOAD_SIZE sectors,
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; which includes 1 sector for the EXE header, so the code
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; and data for the WINLOAD bootstrap should fit in 3 sectors.
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;
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; Rev 7.1 ScottQ removed Winboot.sys stuff, add support for extended int 13
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; MSliger bootable partitions implemented by scanning the MBR.
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;
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; Rev 8.0 ScottQ re-implement winboot.sys dual-boot as JO.SYS dual boot
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; MSliger
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;
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; The ROM in the IBM PC starts the boot process by performing a hardware
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; initialization and a verification of all external devices. If all goes
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; well, it will then load from the boot drive the sector from track 0, head 0,
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; sector 1. This sector is placed at physical address 07C00h. The initial
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; registers are presumably set up as follows: CS=DS=ES=SS=0, IP=7C00h, and
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; SP=0400h. But all we rely on is the BIOS being loaded at linear 07C00h.
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;
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; If IO.SYS is not found, an error message is displayed and the user is
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; prompted to insert another disk. If there is a disk error during the
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; process, a message is displayed and things are halted.
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;
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; At the beginning of the boot sector, there is a table which describes the
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; MSDOS structure of the media. This is equivalent to the BPB with some
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; additional information describing the physical layout of the driver (heads,
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; tracks, sectors)
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;
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;==============================================================================
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;REALLY OLD REVISION HISTORY which has no meaning but hey its nostalgic
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;AN000 - New for DOS Version 4.00 - J.K.
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;AC000 - Changed for DOS Version 4.00 - J.K.
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;AN00x - PTM number for DOS Version 4.00 - J.K.
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;==============================================================================
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;AN001; d52 Make the fixed positioned variable "CURHD" to be local. 7/6/87 J.K.
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;AN002; d48 Change head settle at boot time. 7/7/87 J.K.
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;AN003; P1820 New message SKL file 10/20/87 J.K.
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;AN004; D304 New structrue of Boot record for OS2. 11/09/87 J.K.
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;AN005; Changed version to 5.0 03/08/90 E.A.
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;AN006; Changed to remove MSLOAD in first cluster restriction 04/23/90 J.H.
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;==============================================================================
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.xlist
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include bpb.inc
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include bootsec.inc
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include dirent.inc
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;include version.inc
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.list
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; ==========================================================================
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ORIGIN EQU 7C00H ; Origin of bootstrap LOADER
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BIO_SEG EQU 2000H ; Destination segment of ntldr
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BIO_OFFSET EQU 0 ; Offset of ntldr
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SECTOR_SIZE EQU 512 ; Sector size in bytes
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DIR_ENTRY_SIZE EQU SIZE DIR_ENTRY ; Size of directory entry in bytes
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DSK_PARMS EQU 1EH*4 ; POINTER TO DRIVE PARMS
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SEC9 EQU 522h ; ADDRESS OF NEW DRIVE PARM TABLE
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ROM_DISKRD EQU 2
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ROM_DISKRDX EQU 42h
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; ==========================================================================
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;
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; This little set of directives establishes the address
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; where we'll jump to once the first sector of ntldr has been
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; loaded. The first 3 bytes of that sector are used for non-FAT
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; filesystems, so we must skip over them.
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;
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SEGBIOS SEGMENT AT BIO_SEG
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ORG 3
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NTLOAD LABEL BYTE
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SEGBIOS ENDS
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; ==========================================================================
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; Data storage between temp. stack and start of boot sector
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pReadClustersO EQU -16
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pReadClustersS EQU -14
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pReadSectorsO EQU -12
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pReadSectorsS EQU -10
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SectorBase EQU -8
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DataSecL EQU -4 ; absolute sector # of first sector in data area
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DataSecH EQU -2
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; ==========================================================================
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CODE SEGMENT
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ASSUME CS:CODE,DS:NOTHING,ES:NOTHING,SS:NOTHING
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ORG ORIGIN
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Public $START
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$START Label byte
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jmp short Main
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PartitionType: ;the in-memory copy of this will leave
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nop ;the partition type in this NOP's place
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;so IO.SYS can tell if it needs x13
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PartitionTypeOffset = (offset PartitionType - offset $START)
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; ==========================================================================
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; Start of BPB area of the boot record
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OsName DB "MSWIN"
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OsVersion DB "4.1" ; Windows version number
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CoreBpb label byte
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BytesPerSector DW SECTOR_SIZE ; Size of a physical sector
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SecsPerClust DB 8 ; Sectors per allocation unit
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ReservedSecs DW 1 ; Number of reserved sectors
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NumFats DB 2 ; Number of fats
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NumDirEntries DW 512 ; Number of direc entries
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TotalSectors DW 4*17*305-1 ; Number of sectors - number of hidden
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; sectors (0 when 32 bit sector number)
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MediaByte DB 0F8H ; MediaByte byte
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NumFatSecs DW 8 ; Number of fat sectors
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SecPerTrack DW 17 ; Sectors per track
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NumHeads DW 4 ; Number of drive heads
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HiddenSecs DD 1 ; Number of hidden sectors
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BigTotalSecs DD 0 ; 32 bit version of number of sectors
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.errnz ($-BytesPerSector) NE SIZE BPB
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BootDrv DB 80h
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CurrentHead DB 0h ; Current Head
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ExtBootSig DB 41
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SerialNum DD 0
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VolumeLabel DB 'NO NAME '
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FatId DB 'FAT12 '
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.errnz ($-$START) NE SIZE BOOTSEC
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; =========================================================================
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;
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; First thing is to reset the stack to a better and more known
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; place. The ROM may change, but we'd like to get the stack
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; in the correct place.
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;
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Main:
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xor CX,CX
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mov SS,CX ;Work in stack just below this routine
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mov SP,ORIGIN+pReadClustersO
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ASSUME SS:CODE
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mov ds,cx
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assume DS:CODE
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;
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; Set up es for sector reads
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;
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mov ax,BIO_SEG
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mov es,ax
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ASSUME ES:NOTHING
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cld
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mov BP,ORIGIN
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; The system is now prepared for us to begin reading.
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; First we read the master boot record (MBR) if this is a
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; harddisk so we can get our partion type. Types E and C
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; need extended int13 calls.
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cmp [BP].bsDriveNumber,cl ;assert cl == 0 from above
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jnl failed ;dont check for MBR on floppies!
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mov ax,cx ;read sector zero
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cwd
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call DoReadOne ;note! assume cx==0 for DoReadOne
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jc failed
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sub bx,(42h - 12 +4) ;bx comes back point it end of sector,
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;we want hidden sector field of first
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;partition entry
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.386
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mov eax,dword ptr HiddenSecs;get the hidden sectors for us
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scan:
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cmp eax,dword ptr es:[bx] ;is it the same as this partition entry?
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.286
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mov dl,byte ptr es:[bx-4] ;put the entry's type in dl
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jne short dontgotit ;its our partition, go write it down
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or dl,2 ;turn C's into E's
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mov [bp+2],dl ;put our partition type at byte 2's nop
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dontgotit:
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add bl,10h ; 8CA - 8DA - 8EA - 8FA - 90A : carry
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jnc short scan ; we scan 4 partition entries
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failed:
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;if we failed, leave nop alone; we
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;will use old int13 and so will IO.SYS
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xor cx,cx ;later code needs CX to still be zero
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.286
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; Next, determine logical sector numbers of the start of the
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; directory and the start of the data area.
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;
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DirRead:
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mov AL,[BP].bsBPB.BPB_NumberOfFATs ; Determine sector dir starts on (NumFats)
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cbw ;
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mul [BP].bsBPB.BPB_SectorsPerFAT ; DX:AX (NumFatSecs)
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add AX,[BP].bsBPB.BPB_HiddenSectors ; (HiddenSecs)
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adc DX,[BP].bsBPB.BPB_HiddenSectorsHigh
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add AX,[BP].bsBPB.BPB_ReservedSectors;(ReservedSecs)
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adc DX,CX
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;
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; DX:AX = NumFats * NumFatSecs + ReservedSecs + cSecHid
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;
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mov SI,[BP].bsBPB.BPB_RootEntries
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pusha
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mov [BP].DataSecL,AX
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mov [BP].DataSecH,DX
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mov AX,DIR_ENTRY_SIZE ; bytes per directory entry
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mul SI ; convert to bytes in directory (NumDirEntries)
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mov BX,[BP].bsBPB.BPB_BytesPerSector; add in sector size
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add AX,BX
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dec AX ; decrement so that we round up
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div BX ; convert to sector number
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add [BP].DataSecL,AX ; Start sector # of Data area
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adc [BP].DataSecH,CX ;
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popa
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DirSector:
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mov DI,BIO_OFFSET ; address in DI for comparisons
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call DoReadOne ;NOTE assumes CX==0!
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DiskErrorJump:
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jc DiskError ; if errors try to recover
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DirEntry:
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cmp byte ptr es:[di],ch ; empty directory entry?
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je MissingFile ; yes, that's the end
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pusha
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mov cl,11
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mov si,offset BootFilename
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repz cmpsb ; see if the same
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popa
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jz DoLoad ; if so, continue booting
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dec SI ; decrement # root entries
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jz MissingFile ; hmmm, file doesn't exist in root
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next_entry:
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add DI,DIR_ENTRY_SIZE
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cmp DI,BX ; exhausted this root dir sector yet?
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jb DirEntry ; no, check next entry
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jmp DirSector ; yes, check next sector
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MissingFile:
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mov al,byte ptr [MSGOFF_NOSYS] ; point to no system file message
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;
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; There has been some recoverable error. Display a message
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; and wait for a keystroke. Al is the offset - 256 of the
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; message within the boot sector. So we first calculate
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; the real segment-based offset to the message and stick it in si
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; so lodsb will work later.
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;
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DisplayError:
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.ERRNZ ORIGIN MOD 256
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mov ah,(ORIGIN / 256) + 1
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mov si,ax
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DisplayError1:
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lodsb ; get next character
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cbw ; make 00->0000, FF->FFFF
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inc ax ; end of sub-message? (0xFF?)
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jz DisplayWait ; if so, get tail
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dec ax ; end of message? (0x00?)
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jz WaitForKey ; if so, get key
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mov AH,14 ; write character & attribute
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mov BX,7 ; attribute (white char on black)
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int 10h ; print the character
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jmp short DisplayError1
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DisplayWait:
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mov al,byte ptr [MSGOFF_COMMON]
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jmp short DisplayError
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DiskError:
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mov al,byte ptr [MSGOFF_IOERROR]
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jmp short DisplayError
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WaitForKey:
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;we know ax is zero, thats how we got here
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int 16h ; get character from keyboard
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int 19h ; Continue in loop till good disk
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;
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; We now load the first sector of ntldr.
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;
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; All we have to do is multiply the file's starting cluster
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; (whose directory entry is at ES:DI-11) by sectors per cluster and
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; add that to the disk's starting data sector.
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;
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; Note that after we're read the sector into 2000:0 the directory sector
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; will get blown away. So we need to save the starting cluster number.
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;
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DoLoad:
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mov dx,es:[di].dir_first ; dx = ntldr starting cluster
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push dx ; save for later
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mov al,1 ; 1 sector
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mov bx,BIO_OFFSET ; into 2000:0
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call NtldrClusterRead
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jc DiskError
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; =========================================================================
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;
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; NTLDR requires the following input conditions:
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;
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|
; BX == starting cluster number of NTLDR
|
||
|
|
; DL == int13 unit number of boot drive
|
||
|
|
; DS:SI -> BPB
|
||
|
|
; DS:DI -> arg structure
|
||
|
|
;
|
||
|
|
; =========================================================================
|
||
|
|
|
||
|
|
pop bx ; starting cluster number
|
||
|
|
mov dl,[bp].bsDriveNumber
|
||
|
|
mov si,OFFSET CoreBpb
|
||
|
|
mov di,sp ; we should be at TOS now
|
||
|
|
|
||
|
|
mov [bp].pReadClustersO,OFFSET NtldrClusterRead
|
||
|
|
mov [bp].pReadSectorsO,OFFSET NtldrSectorRead
|
||
|
|
mov cx,ds
|
||
|
|
mov [bp].pReadClustersS,cx
|
||
|
|
mov [bp].pReadSectorsS,cx
|
||
|
|
|
||
|
|
;
|
||
|
|
; We do something nasty. Ntldr is expecting the readcluster and readsector
|
||
|
|
; routines to do a far return. Since ntldr is now the only guy who will be
|
||
|
|
; reading via those routines, we patch the return instruction from a near
|
||
|
|
; return to a far return.
|
||
|
|
;
|
||
|
|
mov byte ptr DoReadExit,0cbh ; retf
|
||
|
|
jmp FAR PTR NTLOAD ; Crank up NTLDR
|
||
|
|
|
||
|
|
;
|
||
|
|
; Sector read routine required by ntldr
|
||
|
|
;
|
||
|
|
; Read al sectors into es:bx starting from sector SectorBase
|
||
|
|
; (SectorBase is logical sector # from start of partition)
|
||
|
|
;
|
||
|
|
NtldrSectorRead label near
|
||
|
|
.386
|
||
|
|
movzx cx,al
|
||
|
|
mov eax,[bp].SectorBase
|
||
|
|
add eax,dword ptr [bp].bsBPB.BPB_HiddenSectors
|
||
|
|
mov edx,eax
|
||
|
|
shr edx,16
|
||
|
|
.286
|
||
|
|
jmp short DoReadMore
|
||
|
|
|
||
|
|
;
|
||
|
|
; Cluster read routine required by ntldr
|
||
|
|
;
|
||
|
|
; Read al sectors into es:bx starting from cluster dx
|
||
|
|
;
|
||
|
|
NtldrClusterRead label near
|
||
|
|
.386
|
||
|
|
movzx cx,al ; cx = # of sectors to read
|
||
|
|
.286
|
||
|
|
dec dx
|
||
|
|
dec dx ; adjust for reserved clusters 0 and 1
|
||
|
|
mov al,[BP].bsBPB.BPB_SectorsPerCluster
|
||
|
|
xor ah,ah
|
||
|
|
mul dx ; DX:AX = starting sector number
|
||
|
|
add ax,[bp].DataSecL ; adjust for FATs, root dir, boot sec.
|
||
|
|
adc dx,[bp].DataSecH
|
||
|
|
DoPush:
|
||
|
|
jmp short DoReadMore
|
||
|
|
|
||
|
|
; =========================================================================
|
||
|
|
;
|
||
|
|
; Read disk sector(s).
|
||
|
|
;
|
||
|
|
; Inputs: DX:AX == logical sector #
|
||
|
|
; CL == # sectors (CH == 0)
|
||
|
|
; ES:BX == transfer address
|
||
|
|
;
|
||
|
|
; Outputs: DX:AX next logical sector #
|
||
|
|
; CX == 0 (assuming no errors)
|
||
|
|
; ES:BX -> byte after last byte of read
|
||
|
|
; Carry set if error, else clear if success
|
||
|
|
;
|
||
|
|
; Preserves: BP, SI, DI
|
||
|
|
;
|
||
|
|
; New Notes: This function will now use extended int 13 if
|
||
|
|
; necessary. The next note is correct for standard int 13
|
||
|
|
;
|
||
|
|
; Notes: Reads sectors one at a time in case they straddle a
|
||
|
|
; track boundary. Performs full 32-bit division on the
|
||
|
|
; first decomposition (of logical sector into track+sector)
|
||
|
|
; but not on the second (of track into cylinder+head),
|
||
|
|
; since (A) we don't have room for it, and (B) the results
|
||
|
|
; of that division must yield a quotient < 1024 anyway, because
|
||
|
|
; the CHS-style INT 13h interface can't deal with cylinders
|
||
|
|
; larger than that.
|
||
|
|
;
|
||
|
|
; =========================================================================
|
||
|
|
|
||
|
|
switchx13: ;setup for x13 read, and switch to old if not needed
|
||
|
|
|
||
|
|
push dx ;
|
||
|
|
push ax ; block number
|
||
|
|
push es
|
||
|
|
push bx ; transfer address
|
||
|
|
push 1 ; count of one, because we're looping
|
||
|
|
push 16 ; packet size
|
||
|
|
|
||
|
|
xchg AX,CX ; AX -> CX
|
||
|
|
|
||
|
|
mov ax,[bp].bsBPB.BPB_SectorsPerTrack ; get sectors/track
|
||
|
|
xchg ax,si ; save for divides
|
||
|
|
|
||
|
|
xchg AX,DX ; DX -> AX
|
||
|
|
xor DX,DX ; divide 0:AX
|
||
|
|
div si ; AX = high word of track
|
||
|
|
|
||
|
|
xchg AX,CX ; save AX in CX and restore old AX
|
||
|
|
div si ; CX:AX = track, DX = sector
|
||
|
|
|
||
|
|
inc DX ; sector is 1-based
|
||
|
|
xchg CX,DX ; CX = sector, DX = high word of track
|
||
|
|
div [BP].bsBPB.BPB_Heads ; AX = cylinder, DX = head
|
||
|
|
|
||
|
|
mov DH,DL ; head # < 255
|
||
|
|
|
||
|
|
mov CH,AL ; CH = cyl #
|
||
|
|
ror AH,2 ; move bits 8,9 of AX to bits 14,15
|
||
|
|
; (the rest has to be zero, since
|
||
|
|
; cyls cannot be more than 10 bits)
|
||
|
|
or CL,AH ; CL = sector # plus high bits of cyl #
|
||
|
|
mov AX,(ROM_DISKRD SHL 8)+1 ; disk read 1 sector
|
||
|
|
|
||
|
|
cmp byte ptr [bp].PartitionTypeOffset,0Eh ;set flag to be tested
|
||
|
|
jne short doio ;use extended calls if E (or C)
|
||
|
|
mov ah,ROM_DISKRDX ;x13, we're ready to rock
|
||
|
|
mov si,sp ; DS:SI -> X13 packet
|
||
|
|
doio:
|
||
|
|
mov dl,[bp].bsDriveNumber ; DL == drive #
|
||
|
|
int 13h
|
||
|
|
|
||
|
|
popa ; throw away packet on stack (8 words)
|
||
|
|
popa ; get real registers back
|
||
|
|
|
||
|
|
jc DoReadExit ; disk error
|
||
|
|
|
||
|
|
inc ax
|
||
|
|
jnz DoReadNext
|
||
|
|
inc dx
|
||
|
|
|
||
|
|
DoReadNext: ; Adjust buffer address
|
||
|
|
add BX,[BP].bsBPB.BPB_BytesPerSector
|
||
|
|
|
||
|
|
dec cx
|
||
|
|
jnz DoReadMore
|
||
|
|
clc
|
||
|
|
|
||
|
|
DoReadExit:
|
||
|
|
|
||
|
|
ret
|
||
|
|
|
||
|
|
DoReadOne:
|
||
|
|
inc cx ;assumes cx == 0! to set to 1 sector read
|
||
|
|
DoRead:
|
||
|
|
mov bx,BIO_OFFSET
|
||
|
|
DoReadMore:
|
||
|
|
|
||
|
|
pusha
|
||
|
|
.386
|
||
|
|
db 66h ;push a dword of 0 on the stack
|
||
|
|
push 0 ;hand coded for 386
|
||
|
|
.286
|
||
|
|
jmp switchx13
|
||
|
|
|
||
|
|
;
|
||
|
|
; This string can go anywhere. NT and NT Setup are not picky about it.
|
||
|
|
;
|
||
|
|
Public BootFilename
|
||
|
|
|
||
|
|
BootFilename db "NTLDR ";
|
||
|
|
|
||
|
|
;
|
||
|
|
; Message table.
|
||
|
|
;
|
||
|
|
; We put English messages here as a placeholder only, so that in case
|
||
|
|
; anyone uses bootfat.h without patching new messages in, things will
|
||
|
|
; still be correct (in English, but at least functional).
|
||
|
|
;
|
||
|
|
include msgstub.inc
|
||
|
|
|
||
|
|
;
|
||
|
|
; Now build a table with the low byte of the offset to each message.
|
||
|
|
; Code that patches the boot sector messages updates this table.
|
||
|
|
;
|
||
|
|
.errnz ($-$START) GT (SECTOR_SIZE-5)
|
||
|
|
ORG ORIGIN + SECTOR_SIZE - 5
|
||
|
|
MSGOFF_NOSYS:
|
||
|
|
db OFFSET (MSG_NOSYS - ORIGIN) - 256
|
||
|
|
MSGOFF_IOERROR:
|
||
|
|
db OFFSET (MSG_IOERROR - ORIGIN) - 256
|
||
|
|
MSGOFF_COMMON:
|
||
|
|
db OFFSET (MSG_COMMON - ORIGIN) - 256
|
||
|
|
|
||
|
|
.errnz ($-$START) NE (SECTOR_SIZE-2)
|
||
|
|
DB 55h,0AAh ; Boot sector signature
|
||
|
|
|
||
|
|
|
||
|
|
CODE ENDS
|
||
|
|
|
||
|
|
END
|
||
|
|
|
||
|
|
|
||
|
|
|