Xref: utzoo comp.sys.ibm.pc:33682 comp.lang.fortran:2386
Path: utzoo!attcan!uunet!dino!uxc.cso.uiuc.edu!tank!uwvax!astroatc!brown
From: brown@astroatc.UUCP (Vidiot)
Newsgroups: comp.sys.ibm.pc,comp.lang.fortran
Subject: Re: modifying executables
Keywords: exe
Message-ID: <2686@astroatc.UUCP>
Date: 24 Aug 89 19:35:24 GMT
References: <1984@leah.Albany.Edu>
Reply-To: brown@astroatc.UUCP (Vidiot)
Organization: Vidiot's Hangout
Lines: 44

In article <1984@leah.Albany.Edu> ppd491@leah.Albany.Edu (Peter P. Donohue @ nowheresville) writes:
<
<   Where my brother works, they have some software that has an error in
<it that they would like to fix (nor do I know what fortran compiler they
<used).  The program was written in Fortran but they don't have the
<source code. Is there a way to modify the executable?
<   The change fix should be relatively easy, just switching a number
<around. The program does something with wind direction, which the
<machine reads as being off by 180 degrees. It would be an easy fix if
<they had the source, but they don't. 
<   DOS has a utility called EXE2BIN.EXE, and from Turbo Pascal I have a
<utility called BINOBJ.EXE. Would these be of any help in modifying the
<program? If the binary or objective files were modified, how would you
<get back to executable?

Having modified some PC programs myself (removing copy protection from
programs that were in the way [the programs were legit]), there are ways
to do it.  But you better know PC machine (8088) code.  The programs you
mentioned have nothing to do with debugging code.

You use the program tool called DEBUG.  By running that against the .EXE
program, you can run the program under the debugger and figure out where in
the code the offending area lies.  This is not as easy as it sound, since
you don't have any source to know how the code flows or where any constants
are.

Also, if you do find the offending area, you cannot modify a .EXE file that
is brought into DEBUG.  That is because DEBUG actually loads up the program,
ie, fixes up all of the relocatable addresses.  Once you find the area,
you need to make a note about the area.  You then get out of DEBUG, without
saving any changes.  You have to then rename the .EXE program to a different
extention name.  For example: LOTUS.EXE to LOTUS.XXX.  Then you start up
DEBUG again, using the changed name.  This keeps DEBUG from loading the
program, so that you can change it.  You will not be able to execute it
while running DEBUG.  Do your changes, save the file and rename it back.

After telling you all this, I have an easier way of getting it fixed:
call the original programming source and have them send you an update with
the bug fixed.  You are probably not the only ones to notice the problem.
-- 
	        harvard\     att!nicmad\
Vidiot            ucbvax!uwvax..........!astroatc!brown
	        rutgers/  decvax!nicmad/
	ARPA/INTERNET: brown%astroatc.UUCP@spool.cs.wisc.edu