GW-BAS to QB 2 of 2

 BBS: Inland Empire Archive
Date: 03-15-92 (16:54)             Number: 140
From: TOM HAMMOND                  Refer#: NONE
  To: ALL                           Recvd: NO  
Subj: GW-BAS to QB  2 of 2           Conf: (2) Quik_Bas
Part 2, continued from part 1 (wow, what a concept!)

I did not conceive of this patch, but it does seem to work quite well.

>> NOTE:  These pages detail how to use DEBUG to PATCH a copy of IBM
          (or GW) BASICA.EXE or BASIC.COM to permit that program to
          remove PROTection from a BASIC program when it is LOADed.  A
          patched version of BASIC is created.

Unprotecting BASICA (or GW Basic) files is a fairly simple task, if you
have the right tools and know what to look for.  The following sequence
is the procedure for creating a copy of BASICA, version 2.0, that will
NOT test the protect flag when you ask for a LIST, LLIST, SAVE, etc.
This procedure is possible as the BasicA LOAD or implied (command line)
program load both convert the program to BasicA's normal tokenized
internal format and just relies on an internal flag to disallow those
commands.  This patch changes that flag test to always return

In the following we patch the main version of BASICA (in this version,
three programs make up the BASIC set, they are named BASIC.COM,
BASICA.COM and BASICA.EXE.  The first two are just loaders for the
latter, which we'll patch).

Note, finally, that the search pattern I used is for the OR AL,AL JMP
+2 POPF RET and JMP opcodes, which makes the search version independent
(where the exact addresses may vary).

The comments following the "*" character have been added as an

A> copy basica.exe                * Make an editable copy to
        1 File(s) copied                * (DEBUG won't edit .EXE

A> DEBUG                          * Invoke DEBUG b.XXX

-s cs:0 ffff 0a c0 75 02 9d c3 e9       * Search for the test, NO
786B:A557                               * DEBUG only found the right
-u cs:a554                              * Now, UNASSEMBLE 3 bytes
                                          BEFORE that.
786B:A554 A00C06         MOV    AL,[060C]
786B:A557 0AC0           OR     AL,AL
786B:A559 7502           JNZ    A55D
786B:A55B 9D             POPF
786B:A55C C3             RET
786B:A55D E95068         JMP    0DB0
786B:A560 807C2800       CMP    Byte Ptr [SI+28],00
786B:A564 7403           JZ     A569
                                        * NOTE in the above that the
                                        * address of the first
                                        * instruction may vary slightly
                                        * with the BASICA version.
-a cs:a554                              * ASSEMBLE the following patch:
786B:A554 mov al,0                      *   Put a zero into AL,
786B:A556 nop                           *   NOP for the correct code
786B:A557                               * RETURN only to stop ASSEMBLE.
-u cs:a554                              * UNASSEMBLE the code to check
786B:A554 B000           MOV    AL,00
786B:A556 90             NOP
786B:A557 0AC0           OR     AL,AL
786B:A559 7502           JNZ    A55D
786B:A55B 9D             POPF
786B:A55C C3             RET
786B:A55D E95068         JMP    0DB0
786B:A560 807C2800       CMP    Byte Ptr [SI+28],00
-w                                      * Looks good, WRITE it to disk,
Writing FF90 bytes                      * this may vary slightly on
                                        * yours,
-q                                      * and QUIT the DEBUG.

A> Ren b-unprot.exe               * REName the file to use it.

That does it.  You now have a program named B-UnProt that will allow
you to LOAD a protected file and then LIST, SAVE, edit, etc, it to your
heart's content.

--- WM v2.00/91-0231
 * Origin: The Modem Zone BBS (314) 893-5106 (1:289/2)
Outer Court
Echo Basic Postings

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Moths in the Machine: The Power and Perils of Programming

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