.386C
CODE SEGMENT USE16
ASSUME CS:CODE, DS:CODE, SS:NOTHING
; BOOT RECORD - PART I - MAIN BOOT SECTOR CODE
; Just so I've said it - ASM opcodes are only readable when capitalized,
; but I forgot to set the option in sourcer... so I wrote a small TP program
; that capitalized everything but what's after the semicolon...
Win95b PROC FAR
JMP SkipData ; 0000h
brINT13Flag DB 90H ; 0002h - 0EH for INT13 AH=42 READ
brOEM DB 'MSWIN4.1' ; 0003h - OEM ID - Windows 95B
brBPS DW 512 ; 000Bh - Bytes per sector
brSPC DB 8 ; 000Dh - Sector per cluster
brResCount DW 32 ; 000Eh - Reserved sectors
brFATs DB 2 ; 0010h - FAT copies
brRootEntries DW 0 ; 0011h - Root directory entries
brSectorCount DW 0 ; 0013h - Sectors in volume, < 32MB
brMedia DB 0F8H ; 0015h - Media descriptor
brSPF DW 0 ; 0016h - Sectors per FAT
brSPH DW 63 ; 0018h - Sectors per head/track
brHPC DW 128 ; 001Ah - Heads per cylinder
brHidden DD 63 ; 001Ch - Hidden sectors
brSectors DD 6305985 ; 0020h - Total number of sectors
brSPF32 DD 6153 ; 0024h - Sector per FAT (FAT32)
brFlags DW 0 ; 0028h - Flags (FAT32)
brVersion DW 0 ; 002Ah - FS Version (FAT32)
brRootCluster DD 2 ; 002Ch - Root start cluster (FAT32)
brFSInfoSector DW 1 ; 0030h - FS Info Sector (FAT32)
brBackupBoot DW 6 ; 0032h - Backup Boot Record
brReserved DB 6 DUP (0) ; 0038h - Reserved
brShitter DB 6 DUP (0) ; 003Bh - Unused filler??
brDrive DB 80H ; 0040h - BIOS drive number
brHeadTemp DB 00H ; 0041h - Head/temp number????
brSignature DB 29H ; 0042h - Extended Boot Record sig.
brSerialNum DD 404418EAH ; 0043h - Volume serial number
brLabel DB 'HARDDISK ' ; 0047h - Volume label
brFSID DB 'FAT32 ' ; 0052h - File System ID
SkipData:
CLI
XOR CX,CX
MOV SS,CX ; SS=CX=0
; Set up stack 8 bytes below us, do you know why???
; Yes, it's because somewhere in this code, the shitter who
; wrote this... save the start of data area DWORD at 7C00H - 4 and
; the value -1 at 7C00H - 8... cool?
MOV SP,7C00H - 8
MOV ES,CX ; ES=CX=0
MOV BP,78H
; Point DS:SI to INT 1E - DISKETTE PARAMS structure...
LDS SI,DWORD PTR SS:[BP]
PUSHDS
PUSHSI
PUSHSS
PUSHBP
MOV DI,522H
MOV SS:[BP],DI ; setup our INT 1E
MOV SS:[BP+2],CX
; copy 11 bytes from old diskette parameter table into
; es:522h, that is 0000:0522 or 0050:0022 - into the PrtScr/DOS area.
; I assume that 0001-0021 is used for something else 0050:0000 I know
; is the PrtScr flag byte.
MOV CL,11
CLD
REP MOVSB
MOV DS,CX ; DS=CX=0
MOV BP,7C00H ; point BP to start of us
MOV BYTE PTR [DI-2],0FH ; modify head settle time
MOV AX,SS:[BP+18H]
MOV [DI-7],AL ; modify sectors per track
; compare drive number with 0...
; if greater than or equal... go to MBRReadError
; I guess that lower than zero... must be -1 .. -128 (80H..FFH)
; Which would mean Harddisk boot...
CMP SS:[BP+40H],CL ; Boot from diskette?
JGE MBRReadError
MOV AX,CX ; AX=CX=0
CWD ; DX=AX[15]-> (ZerO)
MOV BX,0700H ; Use 0000:0700 for sector
; read buffer
CALL ReadSector ; load Master Boot Record
JC MBRReadError ; error?
SUB BX,58 ; BX = 08C6h (700h - 3Ah)
; point to "start" field
MOV EAX,DS:[7C1CH] ; load hidden sectors
CheckMBR:
CMP EAX,[BX] ; Is this our entry??
MOV DL,[BX-4] ; Put System ID in DL
JNZ NotOurs ; Jump if not our entry
; If system ID or "partition type", is 0Ch or 0Eh, ReadSector
; will use INT13/42H...
OR DL,2 ; set bit 1, to allow for
; types 0Ch or 0Eh to be
; thought of as both 0Eh.
MOV SS:[BP+2],DL ; set brINT13Flag
NotOurs:
ADD BL,16 ; skip to next entry...
JNB CheckMBR ; More entries?
MBRReadError:
MOV DI,2
; FAT32 - Is sector per FAT zero?
CMP WORD PTR SS:[BP+16H],0
JNE ShowErrMsg1
; Put number of hidden sectors in DX:AX
MOV AX,WORD PTR SS:[BP+1CH]
MOV DX,WORD PTR SS:[BP+1EH]
MOV CX,3 ; Boot Record is 3 sectors...
; Start loading reminder of Boot Record for FAT32
LoadIt:
DEC CX
INC AX ; next Boot Record sector
JNZ Skipper ; AX wrap-around?
INC DX ; Yes, inc DX too
Skipper:
MOV BX,7E00H ; into 0000:7E00
CALL ReadSectorX ; Read Sector
JNC ReadOK ; no error?
MOV AL,0F8H ; what's this????
DECDI
JZ NoMore ; Jump if no more sectors
MOV AX,SS:[BP+32H] ; get backup boot sector
XOR DX,DX
MOV CX,3
CMP CX,AX ; compare backup BS num
JA ShowErrMsg1 ; with 3 (or vice versa)
; if 3 is higher than
; backup sector number,
; Bill's oooutta here...
MOV SI,SS:[BP+0EH] ; SI = # of reserved sectors
CMP CX,SI
JAE ShowErrMsg1 ; same thing here... if 3 is
; higher then the number of
; reserved sectors... Bill's
; gone
SUB SI,CX ; get number reserved sectors
; excluding the three boot
; sectors...
; add number of hidden sectors to DX:AX
ADD AX,WORD PTR SS:[BP+1CH]
ADC DX,WORD PTR SS:[BP+1EH]
JMP LoadIt
NoMore:
JNC ShowErrMsg1 ; Jump if carry=0
JMP ShowErrMsg2
ReadOK:
CMP WORD PTR SS:[BP+2AH],0
JA ShowErrMsg1 ; Jump if not version 0.0?
JMP GOFAT32
ShowErrMsg1:
MOV SI,OFFSET ErrMsg1 + 7C00H
PrintMessage:
LODSB ; get msg Skip length
CBW
ADD SI,AX ; Skip control data
NextChar:
LODSB ; get chacacter
TESTAL,AL
JZ LastChar ; End of string?
CMP AL,-1
JE SkipChar ; End of first part?
MOV AH,0EH ; TTY write character
MOV BX,7
INT 10H
JMP NextChar ; repeat write...
SkipChar:
MOV SI,OFFSET ErrMsg4 + 7C00H ; point to tail message
JMP PrintMessage
ShowErrMsg2:
MOV SI,OFFSET ErrMsg2 + 7C00H
JMP PrintMessage
LastChar:
CBW ; Ah, clever... save one byte, take
; advantage of the fact that LODSB
INT 16H ; returns the null-terminator.
POP SI ; restore the stack... why???
POP DS ; the stack is killed at startup...
POP DWORD PTR [SI]
INT 19H ; BIOS bootstrap loader...
Win95b ENDP
;==========================================================================
; READ SECTOR
;==========================================================================
ReadSector PROC NEAR
INC CX ; increase SECTOR COUNT
ReadSectorX:
rsReadMore:
PUSHSI
PUSHDWORD PTR 0
PUSH DX
PUSH AX
PUSHES
PUSH BX
PUSH1
PUSH10H
MOV SI,SP ; save stack pointer
; for later use by LEA
PUSHA ; Save "all" registers
CMP BYTE PTR SS:[BP+2],0EH ; Use INT13 extensions?
JNE rsOldINT13
MOV AH,42H ; Do ext INT13 READ
JMP RSDiskIO
rsOldINT13:
XCHG CX,AX ; swap CX and AX
XCHG DX,AX ; swap DX and AX
XOR DX,DX ; clear DX
DIV WORD PTR SS:[BP+18H] ; div LBA_HI by sectors/track
XCHG CX,AX ; save result in CX and put
; the LBA_LO in AX
DIV WORD PTR SS:[BP+18H] ; divide reminder and LBA_LO
; by sectors/track too
INC DX ; make sector 1-based
XCHG CX,DX ; save it in CX and get the
; result of the 1st division
; in DX
DIV WORD PTR SS:[BP+1AH] ; divide this new result by
; heads per cylinder
MOV DH,DL ; save Head of CHS in DH
; head was in the reminder
; after the division above
MOV CH,AL ; save LO cylinder in CH
; cylinder was in the result
; after the division above
ROR AH,2 ; rotate AH to make bits 8-9
; of cylinder appear as bits
; 6-7 in AH and...
OR CL,AH ; or it with the sector num
MOV AX,201H ; setup for READ - 1 sector
rsDiskIO:
MOV DL,SS:[BP+40H] ; load drive number
INT 13H ; call INT13
POPA ; Restore "all" registers
; the entry code pushed 12h bytes on the stack...
; the last word pushed was 0001h, restore SP to point to it...
LEASP,[SI+10H]; Load effective addr
; Now, SI should contain 0001h
POPSI
; was there an error from INT13?
JC RSDone
INC AX ; increment LBA sector num
JNZ rsSkip ; wrap-around?
INC DX ; yes raise high word too
rsSkip:
ADD BX,SS:[BP+0BH] ; increment by sector size
DEC CX ; decrement SECTOR COUNT
JNZ rsReadMore ; Jump if more to read
rsDone:
RET
ReadSector ENDP
;============================================================================
; DATA AREA FOR MESSAGES - IN "NORSK" NORWEGIAN
;============================================================================
ErrMsg1 DB 03H ; Skip counter for message1
ErrMsg2 DB 18H ; Skip counter for message2
ErrMsg3 DB 01H ; Skip counter for message3
ErrMsg4 DB 27H ; Skip counter for message4
DB 13,10,'Ugyldig systemdisk ',-1
DB 13,10,'Disk I/U-feil ',-1
DB 13,10,'Sett inn en annen disk, og trykk en tast',13,10,0
;============================================================================
DB 0,0 ; Padding?
; ROOT file names to search for...?
IO_SYS DB 'IO SYS'
MSDOS_SYS DB 'MSDOS SYS'
DB 7EH,1,0 ; What is this?
WINBOOT_SYS DB 'WINBOOT SYS' ; When is this used?
DB 0,0 ; Padding?
DW 0AA55H ; 1st Boot Signature
;
; BOOT RECORD - PART II - FSINFO sector
;
DB 'RRaA' ; FAT32 Extension Signature
DB480 DUP (0)
; FSINFO information...
DB 'rrAa' ; FAT32 FSINFO Signature
brFreeClusters DD 56990 ; I have 233431040 bytes free!
brNextFree DD 466175 ; My next free cluster!
DD 3 DUP (0) ; Reserved, acroding to FAT32API.HLP
DW ? ; word padding
DW 0AA55H ; 2nd Boot Signature
;
; BOOT RECORD - PART III - FAT32 specific code, I think? only Bill knows?
;
GOFAT32:
CLI
; calculate total size of FAT area
MOVZX EAX,BYTE PTR SS:[BP+10H] ; number of FATs
MOV ECX,SS:[BP+24H] ; sectors per FAT
MUL ECX ; mul'em
; add hidden sectors
ADD EAX,SS:[BP+1CH]
; add reserved sectors
MOVZX EDX,WORD PTR SS:[BP+0EH]
ADD EAX,EDX
XOR CX,CX ; clear CX for some reason...
; By looking down the code, I can't
; seem to find out why CX is cleared
; It's set to 1 down there...
; before it's ever used...
; EAX will now point to the start of the data area (cluster 2)
; save start of data area below us at 0000:7BFC, or there around...
MOV SS:[BP-4],EAX
; Save another value to... This one is checked by GetFAT32Sector
MOV DWORD PTR SS:[BP-8],0FFFFFFFFH
; Oh... at Microsoft they take no chances... disable INTs again!
; This is what I call proper software writing! Hail M$
CLI
; load Root Start Cluster in EAX
MOV EAX,SS:[BP+2CH]
; Is it cluster 2?
CMP EAX,2
JB ShowErrMsg1 ; error if less than 2
; Is it an EOF marker or something above?
CMP EAX,0FFFFFF8H
JAE ShowErrMsg1 ; error if it is
; Put upper 16-bits of cluster number into DX??
SHLD EDX,EAX,16
STI ; Puh. Safe again.
GetRootCluster:
PUSH DX
PUSH AX
CLI ; Eh?
; clear upper 16-bits of cluster number, and of course move up the
; lower bits...
SHL EAX,16
; shift lower 16-bits of cluster number back down, and at the same
; time shift in the high 16-bits in top of EAX?
SHRD EAX,EDX,16
; make cluster number 0-based... "the way it's supposed to be"
SUB EAX,2
; put Sectors Per Cluster in EBX
MOVZX EBX,BYTE PTR SS:[BP+0DH]
; save it in SI too! Yippi
MOV SI,BX
; calculate relative sector of first part of root... right?
MUL EBX
; add the "start of data area" value we saved below us!
ADD EAX,SS:[BP-4]
; Maybe now, some shitter is trying to make DX:AX what EAX is??
; Shift upper 16-bits of EAX into DX... and AX is lower bits...
SHLD EDX,EAX,10H
STI; Enable interrupts
GetRootSector:
; Use 0070:0000 as a directory buffer...
MOV BX,0700H
MOV DI,BX
; read 1 sector
MOV CX,1
CALL ReadSectorX ; this shit should be pretty
JC ShowErrMsg2 ; obvious...
CheckEntry:
CMP [DI],CH ; is the first entry of the
JE EndOfRoot ; root empty???
MOV CL,11 ; the stupid CP/M filenames
; are 11 bytes...
PUSHSI
MOV SI,OFFSET IO_SYS + 7C00H
REPE CMPSB ; Is it IO.SYS?
POPSI
JZ FoundOS ; Yeah...
ADD DI,CX ; add what's left after CMPSB
ADD DI,15H ; and then 21 more...
; Yeah, yeah, anyway... point to the next dir entry...
; and check if it is above the last entry... INT13 increments
; BX with 512 on the sector read, so it points past the sector.
CMP DI,BX
JB CheckEntry ; Jump if below
; are there any more sectors in this cluster???
DECSI
JNZ GetRootSector ; yeap, read more
POP AX ; restore cluster number
POP DX
; Get FAT value... "GetFAT32value" will compare the value with
; -8, and the JB below continues if below... that is, non-EOF/BAD
; the "previous cluster" value is taken from DX:AX (as restored
; above with POP).
CALL GetFAT32value
JB GetRootCluster
; if not end of root... go to GetRootCluster..
EndOfRoot: ; EOF/BAD cluster...
ADD SP,4 ; clean up stack...
JMP ShowErrMsg1 ; and print error message
FoundOS:
ADD SP,4 ; clean up...
; Now... DI should point just above the IO.SYS name...
; SI would be set to DirEntry[14H] - starting cluster (HI)
; DI would be set to DirEntry[1AH] - starting cluster (LO)
MOV SI,[DI+09H]
MOVDI,[DI+0FH]
; copy FAT32 starting cluster upper 16-bits to AX
MOV AX,SI
CLI; Disable interrupts
; shift cluster high into upper half of EAX and store lower half
; from DI into AX
SHL EAX,10H
MOV AX,DI
; cluster out of range??
CMP EAX,2 ; clusters start with 2
JB InvalidCluster
CMP EAX,0FFFFFF8H ; cluster 0FFFFFF8 is EOF
JAE InvalidCluster
DEC EAX ; make it 0-based...
DEC EAX
; Multiply cluster number with "sectors per cluster"
MOVZX ECX,BYTE PTR SS:[BP+0DH]
MUL ECX
; Add the "start of data area" value that was saved back there...
ADD EAX,SS:[BP-4]
; And for the N'th time, make DX:AX same as EAX - sector number.
SHLD EDX,EAX,10H
STI ; aha...
MOV BX,0700H ; IO.SYS loads here!
PUSH BX
MOV CX,4 ; load 4 IO.SYS sectors
CALL ReadSectorX ; 2K is minimum FAT32 cluster
POP BX ; size anyway...
JC ShowErrMsg2 ; error...???
; COMMENT:
;
; Now, there is enough code here... to read the entire IO.SYS
; file into memory. This code has code to go through the FAT,
; there is code to read cluster... bla bla. And still only 2K
; of IO.SYS is read. If the entire file was read... IO.SYS would
; not have to do this... well well.
; Is there a Mark Zibikowski in the room?
CMP WORD PTR [BX],'ZM' ; EXE signature...
JNE InvalidCluster
; Is there a Barabara Jones in the room?
CMP WORD PTR DS:[0200H][BX],'JB' ; IO.SYS signature?
JE ExecutIOSYS
; The above shit appear in the IO.SYS file at offsets 0 and 200h
; The MZ is the usual EXE signature while the "BJ" is unknown to
; me. Maybe they chose it because it translates to harmless code:
;
; INC DX - DEC DX, pretty dull if you ask me
;
InvalidCluster:
MOV SI,OFFSET ErrMsg3 + 7C00H
JMP PrintMessage
ExecutIOSYS:
DB 0EAH ; Jump to IO.SYS at 0070:0200
DW 0200H, 0070H
;==========================================================================
; GET FAT32 value
;==========================================================================
GetFAT32value PROC NEAR
ADD AX,AX ; Multiply DX:AX by 4,
ADC DX,DX
ADD AX,AX ; convert DX:AX from FAT32
ADC DX,DX ; index value to offset
; DX:AX is passed on as the FAT offset to lookup...
CALL GetFAT32Sector ; read FAT sector
; the correct sector is returned... with DI as index...??
; At least that's what the MOV below assumes...
CLI
MOV EAX,ES:[BX+DI] ; EAX = cluster value
; mask of top 4 bits of because Microsoft say it's reserved.
AND EAX,0FFFFFFFH
; Make DX:AX the cluster number too...
SHLD EDX,EAX,16 ; EAX[HI] into EDX[LO]
; Check for EOF/BAD
CMP EAX,0FFFFFF8H ; Is it the EOF marker?
STI ; return with ZF=1 if the
; last cluster was read??
RET
GetFAT32value ENDP
;==========================================================================
; GET FAT32 SECTOR
;==========================================================================
; On entry DX:AX is the FAT offset in bytes...
GetFAT32Sector PROC NEAR
; When this is called 0070:0200 seems to be the buffer in ES:BX
; but, the code below uses the DI value set down under here...
MOV DI,7E00H
CLI; Disable interrupts
; make EAX the sector number again... move DX into top of EAX...
SHL EAX,16
SHRD EAX,EDX,16
; move bytes per sector into ECX
MOVZX ECX,WORD PTR SS:[BP+0BH]
; divide EDX:EAX by BPS... EAX = sector, EDX = offset in sector...
XOR EDX,EDX
DIV ECX
; Check FAT sector number agains... saved value on stack...
; This one is initially -1 (also known as 0FFFFFFFFH)
CMP EAX,SS:[BP-8]
JE LOC_30
; If sector is <> from -1, save this sector at 0000:7BF8
MOV SS:[BP-8],EAX
; add hidden sectors...
ADD EAX,SS:[BP+1CH]
; add reserved sectors too...
MOVZX ECX,WORD PTR SS:[BP+0EH]
ADD EAX,ECX
; get FAT32 flags into EBX
MOVZX EBX,WORD PTR SS:[BP+28H]
; keep "Active FAT" bits 0-3
AND BX,0FH
; If zero, we're at the correct FAT
JZ CorrectFAT
; compare active FAT with number of FATs...
CMP BL,SS:[BP+10H]
JAE ShowErrMsg1 ; oops... invalid active FAT
PUSH DX ; save DX for a while...
; save FAT sector in ECX
MOV ECX,EAX
; Put sectors per fat in EAX
MOV EAX,SS:[BP+24H]
; Multiply active FAT number with sectors per FAT
MUL EBX
; Add to first FAT sector number we already had...
ADD EAX,ECX
; NOW, EAX contains the correct FAT sector number.
POP DX
CorrectFAT:
PUSH DX
; And for the N'th time, make DX:AX same as EAX - sector number.
SHLD EDX,EAX,16
STI; Enable interrupts
MOV BX,DI ; read FAT sector into
; 0000:7E00
; They sucker who wrote this could have saved 1 byte by
; saying XOR CX,CX instead of MOV CX,1 and called ReadSector
; instead of ReadSectorX, because there is an INC CX at
; ReadSector... haha...
MOV CX,1 ; 1 sector
CALL ReadSectorX
POP DX
JC ShowErrMsg2
LOC_30:
STI; Enable interrupts
MOV BX,DX
RET
GetFAT32Sector ENDP
; Properly align the sector's boot signature at the end of
; the 3rd boot sect0r.
ORG 512 * 3 - 2
DW 0AA55H ; 3rd Boot Signature
CODE ENDS
END
; - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
;
; CONCLUSION - THE END - HASTA LA VISTA - SLUTT - DET VAR ALT FOR I DAG.
;
; OK, Folks. that was quite a bit of work. It got pretty simple after some
; hours.
;
; I would like to thank the following people...
;
; * V Communications for Sourcer.
; * Ralf Brown for the Interrupt List.
; * Uriah Heep, The Who and Blind Guardian, for providing music.
;
; - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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