04/07/97

             How to make XCOPY work with all versions of DOS

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Notes - My version of XCOPY is dated 30-Dec-85 (12-30-85), 12.00 PM.
        The filesize is 11200 bytes.
        If your copy is identical, the numbers which I give may be used in
        the patch.  If not, follow the entire procedure, in order to find
        the correct locations.

        I have been using the patched version with DOS 3.1 for several
        months.  It should also work with 3.0.
        I DO NOT recommend using the patched program with any version of DOS
        before 3.0 (ie, 1.0 2.0, 2.1...)  I doubt that the former versions
        have certain necessary functions for XCOPY's use.  Try it on a scratch
        disk - if it works, be happy - if it doesn't, invest in a copy of 3.1.

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Follow the procesure shown below, using SYMDEB (or DEBUG, or your favorite)
to patch the program file.

I have used ANSI sequences to highlight what the you type. The computer's
output will appear in normal text, yours will be in inverse-video.  All
segment addresses are for my computer only, and will probably change,
depending on weather, trip distance, an how many resident programs you
have in memory.  The offsets, however, should remain constant.  After
the procedure is illustrated, I give an explanation of what's been done.



    C:>ren XCOPY.EXE XCOPY.XXX
    C:>symdeb xcopy.xxx
    Microsoft (R) Symbolic Debug Utility  Version 4.00
    Copyright (C) Microsoft Corp 1984, 1985.  All rights reserved.

    Processor is [80286]
    -s ds:0000 ds:cx B4 30
    2CFB:292A
    -u 2CFB:292A
    2CFB:292A B430           MOV    AH,30
    2CFB:292C CD21           INT    21
    2CFB:292E 86E0           XCHG   AH,AL
    2CFB:2930 3D1403         CMP    AX,0314
    2CFB:2933 7410           JZ     2945
    2CFB:2935 8D16B022       LEA    DX,[22B0]
    2CFB:2939 B409           MOV    AH,09
    2CFB:293B CD21           INT    21
    -a 2CFB:2933
    2CFB:2933 jmp short 2945
    2CFB:2935 <return>
    -u 2CFB:292A
    2CFB:292A B430           MOV    AH,30
    2CFB:292C CD21           INT    21
    2CFB:292E 86E0           XCHG   AH,AL
    2CFB:2930 3D1403         CMP    AX,0314
    2CFB:2933 EB10           JMP    2945
    2CFB:2935 8D16B022       LEA    DX,[22B0]
    2CFB:2939 B409           MOV    AH,09
    2CFB:293B CD21           INT    21
    -w
    Writing 2CB0 bytes
    -q
    C:>ren XCOPY.XXX XCOPY.EXE

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What this procedure actually does

    A - REN XCOPY.EXE XOPY.XXX
        The rename is needed to fool SYMDEB (or DEBUG or whatever) into
        thinking that we are patching a text file.  Without the rename, it
        would think that we are debugging the file, fix all memory references,
        and later use would be impossible.
    B - The "s" and "u" commands:
        You are searching for the command MOV AH,30.  This is the call to DOS
        which returns the version number.  After you dissassemble the returned
        location, you can see that this version number is checked agains the
        the value 3.20 (high byte is 3, low byte is 20).  If it is correct, a
        jump (JZ, Jump if Zero) skips the code which displays a nasty message
        and exits.
    C - The "a" command:
        With this, we replace the conditional jump by an unconditional jump.
        We then do another dissassembly, to confirm that we haven't trashed
        anything important.
    D - REN XCOPY.XXX XCOPY.EXE
        Makes it usable.