Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!think.com!spool.mu.edu!uunet!auspex!guy
From: guy@auspex.auspex.com (Guy Harris)
Newsgroups: comp.unix.internals
Subject: Re: Fundamental defect of the concept of shared libraries
Keywords: ISC i386 shared libraries
Message-ID: <7916@auspex.auspex.com>
Date: 19 May 91 18:15:40 GMT
Article-I.D.: auspex.7916
References: <184@titccy.cc.titech.ac.jp> <1991May16.002617.15386@ladc.bull.com> <197@titccy.cc.titech.ac.jp>
Organization: Auspex Systems, Santa Clara
Lines: 26

>If we take 1), the hardware architecture must support PC relative jump,
>of course. Moreover, to access library private data, it must also
>address data PC relative. Aside from effeciency, not all architechture
>support this.

Are there any architectures of interest in this discussion that can't
support PC-relative references?

>Even worse, with some architechture, it is impossible to map several virtual
>addresses to a physical address. Virtually tagged cache and inverted
>page tables are notable examples.

If you believe that a system with a virtual-address cache, or a system
with inverted page tables, cannot map several virtual addresses to a
physical address, you're wrong.  Proof by counterexample:

	1) various flavors of Suns with virtual address caches, which
	   all support mapping several virtual addresses to a physical
	   address;

	2) the IBM ROMP and RIOS architectures, which have inverted page
	   tables and support mapping several virtual addresses to a
	   physical address.

They may have to go through some amount of pain to do so, but they *do*
manage to do it.