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https://github.com/vxunderground/MalwareSourceCode
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247 lines
7.0 KiB
NASM
247 lines
7.0 KiB
NASM
; KEY-FAKE.ASM -- Fakes keystrokes from internal keyboard buffer.
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; ============
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CSEG Segment
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Assume CS:CSEG
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Org 0100h
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Entry: Jmp Initialize
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; Most Resident Data
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; ------------------
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db 'KEY-FAKE (C) Copyright Charles Petzold, 1985'
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SearchLabelEnd Label Byte
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OldInterrupt16 dd 0
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Pointer dw Offset KeyStrokeBuffer
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Counter db 0
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; New Interrupt 16 (Keyboard)
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; ---------------------------
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NewInterrupt16 Proc Far
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Sti ; Allow futher interrupts
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Cmp CS:[Counter],0 ; See if characters in buffer
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Jz DoOldInterrupt ; If not, just do regular interrupt
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Or AH,AH ; Check if AH is zero
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Jz GetCharacter ; If so, call is to get character
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Cmp AH,1 ; Check if AH is one
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Jz GetStatus ; If so, call is for status
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DoOldInterrupt: Jmp CS:[OldInterrupt16] ; Otherwise, go away
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GetCharacter: Push BX
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Mov BX,CS:[Pointer] ; BX points to current buffer position
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Mov AX,CS:[BX] ; Get ASCII code and scan code
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Inc BX ; Move buffer pointer ahead
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Inc BX
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Mov CS:[Pointer],BX ; Save new pointer
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Dec CS:[Counter] ; One less character in counter
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Pop BX
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Or AX,AX ; See if 0 returned
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Jz NewInterrupt16 ; If so, take it from the top again
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IRet ; Return to calling program
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GetStatus: Push BX
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Mov BX,CS:[Pointer] ; BX points to current buffer position
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Mov AX,CS:[BX] ; Get ASCII code and scan code
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Pop BX
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Or AX,AX ; See if special 0 keystroke
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Jnz StatusReturn ; If not, return non-zero flag
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Add CS:[Pointer],2 ; If so, skip over it
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Dec CS:[Counter] ; One less character
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Or AX,AX ; Will set zero flag
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StatusReturn: Ret 2 ; Do not pop flags
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NewInterrupt16 EndP
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; Beginning of Key Stroke Buffer
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; ------------------------------
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KeyStrokeBuffer Label Byte ; 256 Byte Buffer for keystrokes
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; Initialization -- Search through Memory and see if label matches
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; ----------------------------------------------------------------
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;
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; If so, use the loaded program; if not, create a new interrupt
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Assume DS:CSEG, ES:CSEG, SS:CSEG
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Initialize: Mov Word Ptr [Entry],0 ; Slightly modify search label
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Mov Byte Ptr [Entry + 2],0 ; so no false matches
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Cld
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Mov DX,CS ; This segment
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Sub AX,AX ; Beginning of search
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Mov ES,AX ; Search segment
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SearchLoop: Mov SI,100h ; Address to search
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Mov DI,SI ; Set pointers to same address
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Mov CX,Offset SearchLabelEnd - Offset Entry
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Repz Cmpsb ; Check for match
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Jz ReadyForDecode ; If label matches
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Inc AX ; Still the search segment
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Mov ES,AX ; ES to next segment
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Cmp AX,DX ; Check if it's this segment
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Jnz SearchLoop ; Try another compare
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Mov Byte Ptr DS:[1],27h ; Since no match found,
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; set up PSP for Terminate &
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; remain resident.
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; Save and Set Interupt 16 if Staying Resident
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; --------------------------------------------
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Sub AX,AX ; Set AX to zero
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Mov DS,AX ; To access vector segment
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Assume DS:Nothing ; Tell the assembler
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Mov AX,Word Ptr DS:[16h * 4] ; Get vector offset
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Mov Word Ptr CS:[OldInterrupt16],AX ; Save it
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Mov AX,Word Ptr DS:[16h * 4 + 2] ; Get vector segment
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Mov Word Ptr CS:[OldInterrupt16 + 2],AX ; and save it
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Cli ; Don't interrupt me
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Mov DS:[16h * 4],Offset NewInterrupt16 ; Store new
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Mov DS:[16h * 4 + 2],CS ; address
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Sti ; Now you can talk
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Push CS
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Pop DS ; Restore DS
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Assume DS:CSEG
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; Parameter decoding when program segment has been found
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; ------------------------------------------------------
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;
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; ES = segment of loaded program (could be CS)
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ReadyForDecode: Mov SI,80h ; SI points to parameter area
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Mov DI,Offset KeyStrokeBuffer
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Mov ES:[Pointer],DI ; ES:DI points to buffer area
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Mov ES:[Counter],0 ; Set keystroke counter to zero
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Lodsb ; Get parameter count
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Cbw ; Convert to word
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Mov CX,AX ; CX = parameter count
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Inc CX ; So catch last delimiter (0D)
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Or AX,AX ; Check if parameter present
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Jnz GoDecodeLoop ; If so, continue
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Jmp EndDecode ; If not, cut out
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GoDecodeLoop: Jmp DecodeLoop
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; End of Residence is end of Key Stroke Buffer
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; --------------------------------------------
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Org 256 + Offset KeyStrokeBuffer
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EndResidence Label Byte
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; Data for Parameter Decoding
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; ---------------------------
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QuoteSign db 0 ; Flag for quoted strings
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DoingNumber db 0 ; Flag for doing a number
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DoingExtended db 0 ; Flag for doing extended ASCII
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CalcNumber db 0 ; A calculated number
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Ten db 10 ; For MUL convenience
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; Routine for doing quoted text
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; -----------------------------
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DecodeLoop: Lodsb ; Get character
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Cmp [QuoteSign],0 ; Check if doing quoted text
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Jz NotDoingQuote ; If not, continue checks
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Cmp AL,[QuoteSign] ; Check first if character is quote
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Jz EndQuote ; If so, finish quoted text
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Sub AH,AH ; Set scan code to zero
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Stosw ; Save it in buffer
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Inc ES:[Counter] ; One more character
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Jmp DoNextCharacter ; Go to bottom of routine
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EndQuote: Mov [QuoteSign],0 ; End of quoted text
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Jmp DoNextCharacter ; Get the next character
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; Routine for Extended Ascii Character (@)
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; ----------------------------------------
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NotDoingQuote: Cmp AL,'@' ; See if character is for extended
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Jnz NotExtended ; If not, hop over a little code
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Mov [DoingExtended],1 ; Flag for extended ASCII
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Jmp Delimiter ; To possibly dump number
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; Routine for Quote Sign ' or "
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; -----------------------------
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NotExtended: Cmp AL,'"' ; Check for a double quote sign
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Jz Quote
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Cmp AL,"'" ; Check for a single quote sign
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Jnz NotAQuote
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Quote: Mov [QuoteSign],AL ; Save the quote sign
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Jmp Delimiter ; To possibly dump number
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; Routine for decimal number
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; --------------------------
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NotAQuote: Cmp AL,'0' ; See if character >= 0
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Jb Delimiter
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Cmp AL,'9' ; See if character <= 9
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Ja Delimiter
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Mov [DoingNumber],1 ; If so, doing number
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Sub AL,'0' ; Convert to binary
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Xchg AL,[CalcNumber] ; Get previously calculated
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Mul [Ten] ; Multiply by 10
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Add [CalcNumber],AL ; Add it to new digit
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Jmp DoNextCharacter ; And continue
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; Anything else is considered a delimiter
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; ---------------------------------------
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Delimiter: Cmp [DoingNumber],1 ; Check if doing a number
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Jnz DoNextCharacter ; If not, do not dump
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Mov AL,[CalcNumber] ; Set AX to ASCII number
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Sub AH,AH ; Zero out scan code part
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Cmp [DoingExtended],1 ; Check if doing scan code
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Jnz NumberOK
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Xchg AL,AH ; Switch ASCII and scan code
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NumberOK: Stosw ; Store the two codes
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Inc ES:[Counter] ; One more character in buffer
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Mov [DoingNumber],0 ; Clear out all flags
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Mov [DoingExtended],0
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Mov [CalcNumber],0
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DoNextCharacter:Dec CX ; One less character to do
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Jz EndDecode ; If no more, we're done
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Jmp DecodeLoop ; Otherwise, get next one
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; End Decode -- Ready to terminate (and possibly stay resident)
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; -------------------------------------------------------------
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EndDecode: Mov DX,Offset EndResidence ; End of resident part
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Ret ; Int 20h or 27h
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CSEG EndS
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End Entry
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