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From: jans@mako.UUCP (Jan Steinman)
Newsgroups: net.unix-wizards
Subject: Re: Do you believe in MAGIC?
Message-ID: <814@mako.UUCP>
Date: Mon, 10-Jun-85 18:30:28 EDT
Article-I.D.: mako.814
Posted: Mon Jun 10 18:30:28 1985
Date-Received: Wed, 12-Jun-85 07:04:37 EDT
References: <821@unmvax.UUCP> <490@usl.UUCP> <82@decvax.UUCP> <106@aplvax.UUCP>
Reply-To: jans@mako.UUCP (Jan Steinman)
Distribution: net
Organization: Tektronix, Wilsonville OR
Lines: 26
Summary: 

In article <106@aplvax.UUCP> ded@aplvax.UUCP (Don E. Davis) writes:
>What is going on here?  Is there an easy way to determine which files
>are running shared text?  What are the tradeoffs?  Why not make all programs
>shared text?  Thanks?

As Chris Torek points out in another article, both NMAGIC (0410) and ZMAGIC
(0413) files are sharable.  The remaining need for "impure" OMAGIC (0407)
files has not been addressed.

OMAGIC files are not sharable because their code space is writable.  Two uses
are old binaries, and new programs that, for some reason, require writes to
code space.  Until the mmap() calls become generally available (4.3?) there is
a need for OMAGIC files.

We are currently writing extremely fast assembly code for the NS32000 under
UNIX, and want to take advantage of the short abslolute addresses starting at
location zero.  The only way we know to have writable data below the code
space is to use OMAGIC format.  Note that I am not advocating dynamic code
modification; I simply need more control over data - code layout than UNIX
gives me.

When facilities for explicit control of memory management are available,
OMAGIC can probably be put to bed, at least for new code.
-- 
:::::: Jan Steinman		Box 1000, MS 61-161	(w)503/685-2843 ::::::
:::::: tektronix!tekecs!jans	Wilsonville, OR 97070	(h)503/657-7703 ::::::