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From: klute@heike.informatik.uni-dortmund.de (Rainer Klute)
Newsgroups: comp.sys.atari.st.tech
Subject: Re: Location of variables in executable files.
Message-ID: <2796@laura.UUCP>
Date: 15 Nov 90 07:47:12 GMT
References: <1990Nov11.013428.4566@cs.utk.edu>
Sender: news@laura.UUCP
Reply-To: klute@heike.informatik.uni-dortmund.de (Rainer Klute)
Organization: University of Dortmund, Germany
Lines: 54

In article <1990Nov11.013428.4566@cs.utk.edu>, andrew@.cs.utk.edu (Andrew
Krzywdzinski) writes:
|> I want to be able to write setup information directly to a program
|> file.

I once posted a fundamental (as I think) article against self-modifying
code to this newsgroup. Here it is again - slightly generalized and of
course open to consideration and discussion:

------------------------------ cut here ------------------------------

	No, no, no! Never write self-modifying code!

	Self-modifying code is very bad style. It is difficult to write and even
more difficult to understand. Programs that modify itself tend to be
unmaintainable.

	A lot of machines do not allow you to modify a program file for security
aspects. Consider everyone on a multiuser system would be
allowed to modify any file. Sure, this is not true for the Atari ST, but
one should learn to do it the right way. Spend some time to figure out how
to do it on e. g. a Unix system and you can to it equivalently on the ST.
(Slight simplification here, but you got the idea, right?)

	On a related topic: Several systems do not even allow you to modify your
executing program while it is located in memory. You will only be allowed
to write to the data portion of the program. This is due to the fact that
on a multitasking system several tasks can execute one single program
simultaneously. Now, if the program code can not be modified by the
executing task it is sufficient to load the program into core only once,
thus gaining a lot of efficiency. (Of course each program get it's
individual data section.)

	If you are afraid of virusses don't modify your program file. You (the
average user) can never tell whether the program has been modified by a
virus or not. There are programs on the market (including the PD market)
that estimate a certain checksum for each program and alarm you if this
number changes. How could such a program tell if the change is due to a
virus or not?

	If you are afraid of virusses write protect your media as far as possible.
A program that writes to its program file needs to be run from a not write
protected disk. This a unnessary and an avoidable security hole.

	In most cases it is fully sufficient to maintain a configuration file.
Keep an entry for every variable that needs to be modified permanently.
Upon startup of the program the whole stuff is read in again and the
program's variables are set accordingly. Simple, isn't it?

-- 
  Dipl.-Inform. Rainer Klute      klute@irb.informatik.uni-dortmund.de
  Univ. Dortmund, IRB             klute@unido.uucp, klute@unido.bitnet
  Postfach 500500         |)|/    Tel.: +49 231 755-4663
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