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Path: utzoo!decvax!decwrl!glacier!well!few
From: few@well.UUCP
Newsgroups: net.micro.pc
Subject: Re: Query: can MS C generate .COM files?
Message-ID: <1012@well.UUCP>
Date: Wed, 30-Apr-86 03:27:50 EDT
Article-I.D.: well.1012
Posted: Wed Apr 30 03:27:50 1986
Date-Received: Wed, 30-Apr-86 23:47:48 EDT
References: <2479@pogo.UUCP>
Reply-To: few@well.UUCP (Frank Whaley)
Distribution: na
Organization: Whole Earth Lectronic Link, Sausalito CA
Lines: 42
Keywords: C, .COM, Query

In article <2479@pogo.UUCP> maybee@pogo.UUCP (Joe Maybee) writes:
>It is possible, using MS C, to generate an .EXE
>file that can be converted to a .COM file?
>If you KNOW it to be impossible, would you please
>explain why?

As far as I have been able to uncover, it is mostly impossible.

microsoft's small-model run-time code makes at least (the smallest I
have produced) four references to DGROUP, which is (in essence) the
address of the data segment used while the program is running.  This value
is determined at load time (by the EXE file loader), and the references
are "fixed-up" by the loader.  The presence of "fix-ups" is noted by
EXE2BIN, who complains that the file cannot be converted (as the program
cannot simply be read into memory).  Clever library coders can get around
these references.  [Begin Horn-tooting] I was one of the first to
produce COM files with Lattice C, and still use it to produce Device
Drivers and other Binary Goodies.  [End Horn-tooting].

Note also that msc does not require that a run-time startup module
be linked first (ala crt0.o), thus insuring that the program will
"begin at the beginning".  Instead, the Starting Address will occur
at some address other than the CS:0100H required of COM files.  Again,
EXE2BIN will squawk.

Finally, (oops, a fuzzy part here -- where's that damn manual...)
COM files must be built with no stack segment (the linker should
always complain), but I forget why (too many late hours).

Some enterprising individual may write a run-time startup for msc
(including all of the undocumented Flags and Gizmos, not to mention
new versions of some library routines) which would allow COM files
to be produced, but I have to charge money for that kind of stuff.

Bon Compute!
-- 
Frank Whaley
EFS Management Software, Inc.
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