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From: whm@arizona.edu (Bill Mitchell)
Newsgroups: comp.unix.wizards
Subject: multiple-machine executables for Suns?
Message-ID: <1853@megaron.arizona.edu>
Date: Tue, 4-Aug-87 04:02:53 EDT
Article-I.D.: megaron.1853
Posted: Tue Aug  4 04:02:53 1987
Date-Received: Thu, 6-Aug-87 01:03:07 EDT
Organization: U of Arizona CS Dept, Tucson
Lines: 49

I find myself frequently inconvenienced by the incompatibilities between
different Sun binaries.  Sun-2 binaries will work on a Sun-3, but not
vice-versa and I expect that Sun-4 binaries work iff they're on a Sun-4.
A fairly straightforward solution to this problem seems to be to extend
the executable format so that multiple executables can be contained in a
single file.  Thus, if you've got Sun-2s and Sun-3s lying around, it'd be
nice to have an executable that contains both Sun-2 and Sun-3 versions of
the same program.  If you run it on a Sun-3, it fishes out the Sun-3 code
and if you run it on a Sun-2, it fishes out the Sun-2 code.

I asked someone at Sun about this and they said that although Sun had talked
about it there were no plans for doing it at the current time.  As the only
specific reason for not doing this, he cited the extra disk space required for
such a format.  Here, disk space is much cheaper than programmer time and I'd
gladly have binaries that are twice as big if I didn't have to worry about two
different executables.

As far as I've thought about it, it seems that it really wouldn't be hard to
implement this.  I might go so far as to say that it would make a good
independent study project for a sharp student.

A possible plan of attack:

	Fix the kernel to recognize the multiple format and ignore portions
	 of the file intended for other machines.

	As with the kernel, fix programs that read a.out files to ignore
	 portions for other machines.

	Produce a utility that will take one or more regular executables of
	 different machine types and produce a multiple-machine executable.

There's also the problem of object files, but since they're also a.out files,
a lot of the stuff for them would just fall out.  As far as production of
multiple-machine object files is concerned, just modify the language front
ends to accept a list of machines to compile for and then do each one in turn,
adding each to the object file.

Has anyone else done much thinking about this?  Any implementation attempts?

In some ways the current incompatibilities help Sun -- they provides some
motivation to roll out Sun-2s and roll in Sun-3s, but on the other hand, it
lessens (to near-zero for me) the motivation to roll in a Sun-4.

					Bill Mitchell
					whm@arizona.edu
					{allegra,cmcl2,ihnp4,noao}!arizona!whm
p.s.
If you've got something to say of interest -- post it; don't just mail it to me.