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Assembly Source File | 1998-01-14 | 11.0 KB | 312 lines

; NO.ASM -- Hides specified files from command that follows ; ====== CSEG Segment Assume CS:CSEG, DS:CSEG, ES:CSEG, SS:CSEG Org 002Ch Environment Label Word ; Segment of Environment is here Org 0080h Parameter Label Byte ; Parameter is here Org 0100h Entry: Jmp Begin ; Entry Point ; Most Data (some more at end of program) ; --------------------------------------- db "Copyright 1986 Ziff-Davis Publishing Co.",1Ah db " Programmed by Charles Petzold ",1Ah SyntaxMsg db "Syntax: NO filespec command [parameters]$" DosVersMsg db "NO: Needs DOS 2.0 +$" FileSpecMsg db "NO: Incorrect File Spec$" TooManyMsg db "NO: Too many files to hide$" MemAllocMsg db "NO: Allocation Problem$" CommandMsg db "NO: COMMAND Problem$" Delimiters db 9,' ,;=' FileList dw ? ; Storage of found files FileCount dw 0 ; Count of found files FileListEnd dw ? ; End of storage of found files BreakState db ? ; Store original break state here Comspec db 'COMSPEC=' ; String for Environment search ParamBlock dw ? ; Parameter block for EXEC call dw ?, ? dw 5Ch, ? dw 6Ch, ? StackPointer dw ? ; Save SP during EXEC call ; Check DOS Version ; ----------------- Begin: Mov AH, 30h ; Check for DOS Version Int 21h ; through DOS call Cmp AL, 2 ; See if it's 2.0 or above Jae DosVersOK ; If so, continue Mov DX, Offset DosVersMsg ; Error message ErrorExit: Mov AH, 9 ; Print String function call Int 21h ; Do it Int 20h ; And exit prematurely ; Parse Command Line to get NO File specification ; ----------------------------------------------- ScanParam: Lodsb ; SUBROUTINE: Get byte Cmp AL, 13 ; See if end of parameter Je ErrorExit ; If so, exit Mov DI, Offset Delimiters ; Check if delimiter Mov CX, 5 ; There are 5 of them Repne Scasb ; Scan the string Ret ; And return DosVersOK: Mov DX, Offset SyntaxMsg ; Possible error msg Mov SI, 1+Offset Parameter ; NO Parameter string Cld ; Directions forward BegSearch: Call ScanParam ; Check byte in subroutine Je BegSearch ; If delimiter, keep searching Mov BX, SI ; Save pointer in BX Dec BX ; BX points to NO file spec EndSearch: Call ScanParam ; Check byte in subroutine Jne EndSearch ; If not delimiter, keep going ; Construct full FilePath and save down at end of program ; ------------------------------------------------------- Dec SI ; Points after NO file spec Xchg SI, BX ; SI points to beg, BX to end Mov DI, Offset FullPath ; Points to destination Cmp Byte Ptr [SI + 1], ':' ; See if drive spec included Jnz GetDrive ; If not, must get the drive Lodsw ; Otherwise, grab drive spec And AL, 0DFh ; Capitalize drive letter Jmp Short SaveDrive ; And skip next section GetDrive: Mov AH, 19h ; Get current drive Int 21h ; through DOS Add AL, 'A' ; Convert to letter Mov AH, ':' ; Colon after drive letter SaveDrive: Stosw ; Save drive spec and colon Mov AL, '\' ; Directory divider byte Cmp [SI], AL ; See if spec starts at root Jz HaveFullPath ; If so, no need to get path Stosb ; Store that character Push SI ; Save pointer to parameter Mov SI, DI ; Destination of current path Mov DL, [SI - 3] ; Drive letter specification Sub DL, '@' ; Convert to number Mov AH, 47h ; Get current directory Int 21h ; through DOS Mov DX, Offset FileSpecMsg ; Possible error message Jc ErrorExit ; Exit if error Sub AL, AL ; Search for terminating zero Cmp [SI], AL ; Check if Root Directory Jz RootDir ; If so, don't use it Mov CX, 64 ; Number of bytes to search Repnz Scasb ; Do the search Dec DI ; DI points to last zero Mov AL, '\' ; Put a backslash in there Stosb ; So filespec can follow RootDir: Pop SI ; Get back SI HaveFullPath: Mov CX, BX ; End of NO file spec Sub CX, SI ; Number of bytes to transfer Rep Movsb ; Transfer them Sub AL, AL ; Terminating zero Stosb ; Save it Mov [FileList], DI ; Repository for found files ; Fix up parameter and ParamBlock for eventual COMMAND load ; --------------------------------------------------------- Sub BX, 4 ; Points to new param begin Mov AL, [Parameter] ; Old byte count of parameter Add AL, 80h ; Add beginning of old param Sub AL, BL ; Subtract beginning of new Mov AH, ' ' ; Space separator Mov Word Ptr [BX], AX ; Store it Mov Word Ptr [BX + 2], 'C/' ; Add /C to beginning of rest Mov AX, [Environment] ; Get environment segment Mov [ParamBlock], AX ; Save it Mov [ParamBlock + 2], BX ; Save parameter pointer Mov [ParamBlock + 4], CS ; Save segment of ParamBlock Mov [ParamBlock + 8], CS Mov [ParamBlock + 10], CS ; Find Files from NO File Specification ; ------------------------------------- Mov DX, Offset DTABuffer ; Set File Find buffer Mov AH, 1Ah ; by calling DOS Int 21h Mov DI, [FileList] ; Address of destination Mov DX, Offset FullPath ; Search string Sub CX, CX ; Search Normal files only Mov AH, 4Eh ; Find first file FindFile: Int 21h ; Call DOS to find file Jnc Continue ; If no error continue Cmp AX, 18 ; If no more files Jz NoMoreFiles ; get out of the loop Mov DX, Offset FileSpecMsg ; Error message otherwise Jmp ErrorExit ; Exit and print message Continue: Mov AX, DI ; Address of destination Add AX, 512 ; See if near top of segment Jc TooManyFiles ; If so, too many files Cmp AX, SP ; See if getting too many Jb StillOK ; If not, continue TooManyFiles: Mov DX, Offset TooManyMsg ; Otherwise error message Jmp ErrorExit ; And terminate StillOK: Mov SI, 30+Offset DTABuffer ; Points to filename Call AsciizTransfer ; Transfer it to list Inc [FileCount] ; Kick up counter Mov AH, 4Fh ; Find next file Jmp FindFile ; By looping around NoMoreFiles: Mov [FileListEnd], DI ; Points after last file Mov DI, [FileList] ; Points to end of find string Mov CX, 64 ; Search up to 64 bytes Mov AL, '\' ; For the backslash Std ; Search backwards Repnz Scasb ; Do the search Mov Byte Ptr [DI + 2], 0 ; Stick zero in there Cld ; Fix up direction flag ; Stop Ctrl-Break Exits and Hide the files ; ---------------------------------------- Mov AX,3300h ; Get Break State Int 21h ; By calling DOS Mov [BreakState],DL ; Save it Sub DL,DL ; Set it to OFF Mov AX,3301h ; Set Break State Int 21h ; By calling DOS Mov BL, 0FFh ; Value to AND attribute Mov BH, 02h ; Value to OR attribute Call ChangeFileMode ; Hide all the files ; Un-allocate rest of memory ; -------------------------- Mov BX, [FileListEnd] ; Beyond this we don't need Add BX, 512 ; Allow 512 bytes for stack Mov SP, BX ; Set new stack pointer Add BX, 15 ; Prepare for truncation Mov CL,4 ; Prepare for shift Shr BX,CL ; Convert to segment form Mov AH,4Ah ; Shrink allocated memory Int 21h ; By calling DOS Mov DX,Offset MemAllocMsg ; Possible Error Message Jc ErrorExit2 ; Print it and terminate ; Search for Comspec in Environment ; --------------------------------- Push ES ; We'll be changing this Mov ES, [Environment] ; Set ES to Environment Sub DI, DI ; Start at the beginning Mov SI, Offset ComSpec ; String to search for Mov DX, Offset CommandMsg ; Possible error message TryThis: Cmp Byte Ptr ES:[DI], 0 ; See if points to zero Jz ErrorExit2 ; If so, we can't go on Push SI ; Temporarily save these Push DI Mov CX, 8 ; Search string has 8 chars Repz Cmpsb ; Do the string compare Pop DI ; Get back the registers Pop SI Jz LoadCommand ; If equals, we've found it Sub AL, AL ; Otherwise search for zero Mov CX, -1 ; For 'infinite' bytes Repnz Scasb ; Do the search Jmp TryThis ; And try the next string ; Load COMMAND.COM ; ----------------- LoadCommand: Add DI, 8 ; so points after 'COMSPEC=' Push DS ; Switch DS and ES registers Push ES Pop DS Pop ES Mov [StackPointer],SP ; Save Stack Pointer Mov DX, DI ; DS:DX = Asciiz of COMMAND Mov BX, Offset ParamBlock ; ES:BX = parameter block Mov AX, 4B00h ; EXEC function call Int 21h ; Load command processor ; Return from COMMAND.COM ; ----------------------- Mov AX, CS ; Current code segment Mov DS, AX ; Reset DS to this segment Mov ES, AX ; Reset ES to this segment Mov SS, AX ; Reset stack segment to it Mov SP, [StackPointer] ; Reset SP Pushf ; Save error flag Sub DL,DL ; Set Ctrl Break to OFF Mov AX,3301h Int 21h ; By calling DOS Popf ; Get back error flag Mov DX,Offset CommandMsg ; Set up possible error msg Jnc Terminate ; And print if EXEC error ; Unhide the Files, restore Ctrl-Break state, and exit ; ---------------------------------------------------- ErrorExit2: Mov AH,9 ; Will print the string Int 21h ; Print it Terminate: Mov BL, 0FDh ; AND value for change Mov BH, 00h ; OR value for change Call ChangeFileMode ; Change file attributes Mov DL,[BreakState] ; Original break-state Mov AX,3301h ; Change the break-state Int 21h ; by calling DOS Int 20h ; Terminate ; SUBROUTINE: Change File Mode (All files, BL = AND, BH = OR) ; ----------------------------------------------------------- ChangeFileMode: Mov CX, [FileCount] ; Number of files Jcxz EndOfChange ; If no files, do nothing Mov SI, [FileList] ; Beginning of list Mov DX, [FileListEnd] ; End of List ChangeLoop: Push SI ; Save pointer Mov SI, Offset FullPath ; Preceeding path string Mov DI, DX ; Destination of full name Call AsciizTransfer ; Transfer it Dec DI ; Back up to end zero Pop SI ; Get back pointer to filename Call AsciizTransfer ; Transfer it Push CX ; Save the counter Mov AX, 4300h ; Get attribute Int 21h ; by calling DOS And CL, BL ; AND with BL Or CL, BH ; OR with BH Mov AX, 4301h ; Now set attribute Int 21h ; by calling DOS Pop CX ; Get back counter Loop ChangeLoop ; And do it again if necessary EndOfChange: Ret ; End of subroutine ; SUBROUTINE: Asciiz String Transfer (SI, DI in, returned incremented) ; -------------------------------------------------------------------- AsciizTransfer: Movsb ; Transfer Byte Cmp Byte Ptr [DI - 1], 0 ; See if it was end Jnz AsciizTransfer ; If not, loop Ret ; Or leave subroutine ; Variable length data stored at end ; ---------------------------------- DTABuffer Label Byte ; For file find calls FullPath equ DTABuffer + 43 ; For file path and names CSEG EndS ; End of the segment End Entry ; Denotes entry point