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From: jfh@killer.UUCP
Newsgroups: comp.lang.c
Subject: Re: Shared run-time libraries
Message-ID: <737@killer.UUCP>
Date: Fri, 3-Apr-87 15:33:47 EST
Article-I.D.: killer.737
Posted: Fri Apr  3 15:33:47 1987
Date-Received: Sun, 5-Apr-87 12:44:12 EST
References: <6644@brl-adm.ARPA>
Organization: The Unix(tm) Connection, Dallas, Texas
Lines: 25
Summary: How we did it...


While at Pinnacle Systems in Dallas America, John Bremsteller and I played
with the idea of shared libraries.  The method we used was quite simple.
(simple methods for simple minds :-)  We created a shared memory segment into
which we copied a file containing an array of pointers to the routines and
the routines themselves.  The offsets into the array were predefined.

The file was created by relocating the base of the text segment to some
address and linking all of the parts together.  We then wrote a program
that would extract the text segment of this a.out file.  The text was
copied into the shared memory segment.

Then, we wrote stub routines in /lib/libc.a that called these routines.
When you linked with these routines, you got a stub with an indirect call
to a procedure in the library.

The only problem was that you had to attach to the shared memory segment
yourself.  And you couldn't do much until you did.  The big advantage of
this was that it was very simple to implement and could probably be
implemented on any system that has shared memory without having to make
any modifications to the kernel.

- john.		(jfh@killer.UUCP)

No disclaimer.  Whatcha gonna do, sue me?