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Date:	Thu, 22 Apr 2004 08:50:37 PDT7
From:	Peter Skye <pskye@peterskye.com >
Reply-To:	scoug-programming@scoug.com
To:	scoug-programming@scoug.com
Subject:	SCOUG-Programming: Onward software soldiers

Content Type: text/plain

Lynn H. Maxson wrote:
>
> At the last meeting someone raised the question of converting
> existing programs to PL/E, later named to SL/I. I responded
> that it would not involve a source to source conversion, but
> instead one of an executable to source. In that manner you
> needed only one conversion program regardless of the source
> language(s) used. In effect to "reverse engineer" or
> "disassemble" the executable whether .exe, .sys, or .whatever
> to PL/E source.
>
> ...
>
> I would like to address that at some point in the future.
> Having had some experience in disassembling PL/I and COBOL
> executables into their PL/I and COBOL source for clients who
> had "lost" their source, I would like to demonstrate the
> process. In that manner also illustrate its automation.

I've disassembled a wide variety of binaries (machine code programs) and
I wrote an assembler-to-PL/I translator a number of years ago.

There are problems with this approach. Not insurmountable problems, but
it's not easy.

Your output, whether discrete statements or specifications, is lacking
in all of the creative thought which went into the software. You've
lost any "why I used QuickSort instead of Shell-Metzner" comments or
insights. It's like going down to the adult store and buying a
life-size inflatable doll. It looks about right, but there's something
_missing_ here.

There are some tricks. The library code which is in the executables
need only be disassembled and analyzed once, and all other users of the
same library can partake of those results; thus, you can create a
disassembly library containing these often-used routines. Your
disassembler can include blocking so it's easier to figure out the major
sections of the .exe.

But what do you do with things like error codes? The library routine
can return a -17 error code but the program you are disassembling
doesn't have a handler for -17 and you don't have any documentation that
tells you what -17 means. Now what do you do?

Not insurmountable, but it's not going to be easy.

As for PL/E, the syntactically closest open source compiler I can think
of is Ada. Do you think the PL/E tool development effort should start
from scratch, or do you think it should modify an existing tool?

- Peter

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