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From: peterc@suite.sw.oz.au.sw.oz.au (Peter Chubb,-x27,6982322,3982735)
Newsgroups: comp.os.minix
Subject: Re: Shared libraries with minix
Message-ID: <1991Jun5.001444.13267@softway.sw.oz.au>
Date: 5 Jun 91 00:14:44 GMT
References: <1991Jun4.041033.20792@dvorak.amd.com>
Sender: news@softway.sw.oz.au (Usenet)
Organization: Softway Pty Ltd
Lines: 29
Originator: peterc@suite.sw.oz.au

From article <1991Jun4.041033.20792@dvorak.amd.com>, by tim@proton.amd.com (Tim Olson):
> 
> Another (albeit grungy!) possibility for non-PIC systems is to fix the
> library's virtual addresses to well-known, otherwise unused virtual
> memory locations, and compile the library to use those addresses (e.g.
> printf() exists at 0xa0001234 in every process' address space).  Then,
> the one physical copy of the library gets mapped to the same virtual
> address in each process at runtime.  However, this type of
> shared-library mapping quickly becomes impossible to use when frequent
> changes to the libraries occur.

Alternatively, have a vector of addresses of routines at some standard place 
in the system -- rather like the way AmigaDOS does things now.  It
goes (almost) without saying that the shared library code itself has
to be written to be reentrant.  The data area used has to be that
appropriate for the process calling the function.  In a MMU-based
system that's easy: data virtual addresses can start at zero (separate
i/d); in a non-MMU based system,  the calling convention will have to
include setting a pointer to the base of the process's data segment.
All data references by the library routine will then have to be
indirected off this pointer, preferably automatically by the compiler.

			Regards,

				- Peter Chubb

Softway Pty Ltd, P.O. Box 305, Strawberry Hills, NSW 2012, AUSTRALIA
Phone: +61 2 698 2322;       Fax: +61 2 699 9174;     Telex: AA27987
Internet: peterc@softway.oz.au	   UUCP: ...!uunet!softway.oz!peterc