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https://github.com/vxunderground/MalwareSourceCode
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374 lines
9.1 KiB
NASM
374 lines
9.1 KiB
NASM
page ,132
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title BootThru - v1.05
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;------------------------------------------------------------------------
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;
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; BootThru - Copyright (c) Bill Gibson - 1987
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; Lathrup Village, Mi 48076
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;
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; Ver. 1.00 - Initial version (not rlsd) - 01/11/87
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; 1.01 - revised code structure " - 01/25/87
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; 1.02 - revised Modify Proc " - 02/01/87
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; 1.03 - enhanced error message output " - 02/06/87
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; 1.04 - revised Print Proc released - 02/07/87
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; 1.05 - fix incompatibility plbm - 02/09/87
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;
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;
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; For Public Domain Use. Not for Sale or Hire.
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;------------------------------------------------------------------------
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COMMENT *
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Routine to modify diskette boot record, using drive A: or B:,
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thus circumventing DOS' non-system disk display error.
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Usage:
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BT A: -> transfer new boot record to drive A:
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BT B: -> transfer new boot record to drive B:
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BT -> starts program, default is drive A:
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*
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;------------------------------------------------------------------------
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code SEGMENT BYTE PUBLIC 'code'
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ASSUME CS:code,DS:code,SS:code
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ORG 5Ch ;drive id
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param1 LABEL BYTE
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ORG 5Dh ;elim spurrious characters
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param2 LABEL BYTE
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ORG 100h
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BootThru PROC FAR
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MOV CS:stk_ptr,SP ;save stack ptr to ensure ret
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CALL Chk_Ver ;dos 2.0 or greater
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CALL Scan
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CALL Dwrite
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JMP SHORT exit
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error:
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MOV SP,stk_ptr ;insure proper return
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CALL Print ;print error messages
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MOV AL,1 ;set errorlevel to 1
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exit:
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MOV AH,4Ch
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INT 21h
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;------------------------------------------------------------------------
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; Work Area - constants,equates,messages
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;------------------------------------------------------------------------
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drive DB 0
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stk_ptr DW 0
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blank EQU 020h ;ascii space code
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cr EQU 0Dh ;carriage return
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lf EQU 0Ah ;line feed
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esc EQU 01Bh ;escape char
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stopper EQU 255 ;end of display line indicator
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logo DB cr,lf,'BootThru - The Diskette Modifier'
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DB cr,lf,'Version 1.05 - Bill Gibson 1987',cr,lf,stopper
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usage DB cr,lf,'Usage: BT [drive A: or B:]',cr,lf,stopper
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sorry DB cr,lf,'Wrong PC DOS Version',cr,lf,stopper
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msg1 DB cr,lf,'Insert diskette in drive A, and press ENTER'
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DB ' when ready ...',stopper
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msg2 DB cr,lf,'Insert diskette in drive B, and press ENTER'
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DB ' when ready ...',stopper
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msg3 DB cr,lf,'Press ENTER to modify another disk',cr,lf
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DB 'or ESCape to quit...',stopper
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msg4 DB cr,lf,cr,lf,'Transferring New Boot Sector',cr,lf,stopper
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msg5 DB cr,lf,'Transfer Completed',cr,lf,stopper
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msg80h DB cr,lf,cr,lf,'* Error * Drive failed to respond.',cr,lf,cr,lf,stopper
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msg40h DB cr,lf,cr,lf,'* Error * Seek operation failed.',cr,lf,cr,lf,stopper
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msg20h DB cr,lf,cr,lf,'* Error * Controller failure.',cr,lf,cr,lf,stopper
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msg10h DB cr,lf,cr,lf,'* Error * Bad CRC on diskette write.',cr,lf,cr,lf,stopper
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msg08h DB cr,lf,cr,lf,'* Error * DMA overrun on operation.',cr,lf,cr,lf,stopper
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msg04h DB cr,lf,cr,lf,'* Error * Requested sector not found.',cr,lf,cr,lf,stopper
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msg03h DB cr,lf,cr,lf,'* Error * Write protected diskette.',cr,lf,cr,lf,stopper
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msg02h DB cr,lf,cr,lf,'* Error * Address mark not found.',cr,lf,cr,lf,stopper
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msggen DB cr,lf,cr,lf,'* Unknown Error *',cr,lf,cr,lf,stopper
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;--------------------------------------------------------------------------
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; Sub-Routines:
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;--------------------------------------------------------------------------
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Chk_Ver PROC NEAR
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MOV AH,30h ;verify DOS 2.0 or later
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INT 21h
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CMP AL,2
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JAE SHORT chk_ok
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MOV DX,OFFSET sorry
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JMP error
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chk_ok:
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RET
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Chk_Ver ENDP
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;--------------
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Scan PROC NEAR ;check for any spurrious chars
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MOV AL,[param2]
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CMP AL,blank ;anything ?
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JNZ shlp ;yes, give error msg
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s1:
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MOV AL,[param1] ;check for drive parameters
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OR AL,AL ;anything ?
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JNZ s2 ;jump and test
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MOV DX,OFFSET logo ;setup default drive A:
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CALL Print
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MOV drive,0
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MOV DX,OFFSET msg1
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RET
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s2:
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CMP AL,01 ;setup for drive A:
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JZ SHORT sdrvA
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CMP AL,02 ;for drive B:
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JZ SHORT sdrvB
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shlp:
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MOV DX,OFFSET usage ;display for invalid drives
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JMP error
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sdrvA:
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MOV DX,OFFSET logo
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CALL Print
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MOV drive,0
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MOV DX,OFFSET msg1
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RET
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sdrvB:
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MOV DX,OFFSET logo
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CALL Print
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MOV drive,1
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MOV DX,OFFSET msg2
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RET
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Scan ENDP
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;--------------
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Dwrite PROC NEAR ;transfer new disk boot sector
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CALL Print ;get ready
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d1:
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MOV AH,8 ;use function 8 in order to detect
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INT 21h ;ctrl-breaks
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CMP AL,esc ;ESC & Ctrl-Break aborts process
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JZ d5
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CMP AL,cr
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JNZ d1
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d2:
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MOV DX,OFFSET msg4 ;setup for disk write
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CALL Print
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MOV AL,drive
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LEA BX,head
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MOV CX,0001
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MOV DX,0000
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drite: ;more setups
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PUSH AX
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PUSH BX
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PUSH CX
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PUSH DX
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INT 26h
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JC derror ;processing error ?
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POPF ;done
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POP DX
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POP CX
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POP BX
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POP AX
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d3:
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MOV DX,OFFSET msg5 ;transfer complete
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CALL Print
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JMP d4
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derror: ;display disk errror
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CALL ErrorList
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dend_of:
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CALL Print
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POPF ;done
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POP DX
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POP CX
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POP BX
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POP AX
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d4:
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MOV DX,OFFSET msg3 ;another ?
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CALL Print
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JMP d1 ;loop
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d5:
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RET
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Dwrite ENDP
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;--------------
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Print PROC NEAR ;a Great idea from Vern Buerg !
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PUSH SI
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PUSH BX
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PUSH CX
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MOV SI,DX ;DX has the offset to string
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SUB CX,CX ;set to zero for count
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p1:
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LODSB
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CMP AL,stopper ;string ends in FFh
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JE p9
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INC CX ;increment text length
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JMP p1
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p9:
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MOV AH,40h ;write using file handles
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MOV BX,1
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INT 21h
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POP CX
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POP BX ;recover registers
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POP SI
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RET
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Print ENDP
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;--------------
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ErrorList PROC NEAR ;error code interpretation
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;the upper byte (AH) contains error
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err80h: CMP AH,080h ;attachment failed to respond
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JNZ err40h
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MOV DX,OFFSET msg80h
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RET
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err40h:
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CMP AH,040h ;seek operation failed
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JNZ err20h
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MOV DX,OFFSET msg40h
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RET
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err20h:
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CMP AH,020h ;controller failed
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JNZ err10h
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MOV DX,OFFSET msg20h
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RET
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err10h:
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CMP AH,010h ;data error (bad CRC)
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JNZ err08h
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MOV DX,OFFSET msg10h
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RET
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err08h:
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CMP AH,08h ;direct memory access failure
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JNZ err04h
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MOV DX,OFFSET msg08h
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RET
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err04h:
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CMP AH,04h ;requested sector not found
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JNZ err03h
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MOV DX,OFFSET msg04h
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RET
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err03h:
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CMP AH,03h ;write-protect fault
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JNZ err02h
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MOV DX,OFFSET msg03h
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RET
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err02h:
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CMP AH,02h ;bad address mark
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JNZ errgen
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MOV DX,OFFSET msg02h
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RET
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errgen:
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MOV DX,OFFSET msggen ;something new ? (Unknown)
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RET
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ErrorList ENDP
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;--------------
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Modify PROC FAR
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head:
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cr EQU 0Dh ;carriage return
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lf EQU 0Ah ;line feed
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stopper EQU 255 ;end of display line indicator
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boot_area EQU 0000h ;setup boot area
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bogus_drv EQU 0080h ;setup bogus drive
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loc2 EQU 01FEh ;last two bytes of boot sector
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eof_bootsec EQU 0AA55h ;end of boot sector (reversed)
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bulc EQU 0DAh ;box upper left corner
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burc EQU 0BFh ;box upper right corner
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bllc EQU 0C0h ;box lower left corner
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blrc EQU 0D9h ;box lower right corner
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bver EQU 0B3h ;vertical
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bhor EQU 0C4h ;horizontal
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JMP start ;1st byte of the sector must be a jmp
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DB 'BootThru' ;8-byte system id
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DW 512 ;sector size in bytes
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DB 2 ;sectors per cluster
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DW 1 ;reserved clusters
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DB 2 ;number of fats
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DW 112 ;root directory entries
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DW 720 ;total sectors
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DB 0FDh ;format id (2 sided, 9 sector)
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DW 2 ;sectors per fat
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DW 9 ;sectors per track
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DW 2 ;sides
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DW 0 ;special hidden sectors
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DB 0 ;filler
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DB 0 ;head
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DB 0Ah ;length of BIOS file
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DB 0DFh ;disk parameter table
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DB 02 ; "
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DB 25h ; "
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DB 02 ; "
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DB 09 ; "
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DB 02Ah ;Int 1Eh points to this table,
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DB 0FFh ;the disk parameter table.
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DB 050h ;contents of this vector (1Eh)
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DB 0F6h ;are used as a pointer only,
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DB 0Fh ;Int 1Eh is not executed
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DB 02 ;directly
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intro_beg:
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DB cr,lf,
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DB cr,lf,bulc,46 DUP(bhor),burc
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DB cr,lf,bver,' This disk was modified by BootThru ',bver
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DB cr,lf,bver,' Version 1.05 by Bill Gibson 1987 ',bver
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DB cr,lf,bllc,46 DUP(bhor),blrc
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DB cr,lf,stopper
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intro_offset EQU intro_beg - head
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start:
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MOV AX,07C0h ;boot record location
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MOV ES,AX
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MOV DS,AX
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MOV SI,intro_offset
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strt1:
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MOV AH,0Eh ;write teletype
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MOV AL,[SI]
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CMP AL,stopper
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JE SHORT strt2
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PUSH SI
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INT 10h
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POP SI
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INC SI
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JMP SHORT strt1
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strt2:
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CLD ;setup to bypass drive A:
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MOV SI,OFFSET strt3 - OFFSET head
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MOV DI,0200h ;boot sector size
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MOV CX,0200h
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REPZ MOVSB
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JMP head + 200h
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strt3:
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MOV AH,2 ;function 02h - read floppy disk
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MOV BX,boot_area ;boot area
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MOV CH,0 ;track number
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MOV CL,1 ;sector
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MOV DH,0 ;head
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MOV DL,bogus_drv ;bogus drive
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MOV AL,1 ;number of sectors
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INT 13h
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strt4:
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MOV BX,loc2 ;setup to pull ROM Basic in
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MOV AX,[BX] ;if an error occurs
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CMP AX,eof_bootsec
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JNZ strt9
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JMP strt3 - 200h
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strt9:
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INT 18h
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DB 'BootThru, Copyright (c) Bill Gibson, 02.09.87'
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tail:
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filler_amount EQU 512 - (tail - head) - 2
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DB filler_amount dup (0) ; filler
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boot_id DB 055h,0AAh ; boot id
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Modify ENDP
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BootThru ENDP
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code ENDS
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END BootThru
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