Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!think.com!paperboy!meissner
From: meissner@osf.org (Michael Meissner)
Newsgroups: comp.arch
Subject: Re: addressing on Mips (Was: 64 Bit addressing on R4000?)
Message-ID: <MEISSNER.91Jun30214219@curley.osf.org>
Date: 1 Jul 91 01:42:19 GMT
References: <14900025@hpdmd48.boi.hp.com> <880@taniwha.UUCP>
	<MEISSNER.91Jun28105156@tiktok.osf.org> <5240@spim.mips.COM>
Sender: news@OSF.ORG
Organization: Open Software Foundation
Lines: 26
In-reply-to: keith@mips.com's message of 29 Jun 91 18:26:51 GMT

In article <5240@spim.mips.COM> keith@mips.com (Keith Garrett) writes:

| [discussion of possible differences between 32 & 64 bit instructions deleted]
| In article <MEISSNER.91Jun28105156@tiktok.osf.org> meissner@osf.org (Michael Meissner) writes:
| >The other thing I've thought about is how do you do generalized
| >external references.  On the current R[236]000's a normal (non-GP)
| >reference is two instructions:
| >
| >	lui	$at,addr>>16
| >	<lw/sw>	<reg>,addr&0xffff($at)
| this won't work in the general case. the offset is sign-extended before
| it is added to the base register contents. here is the general solution:
| 	lui	$at,(addr>>16)&0xffff
| 	ori	$at,addr&0xffff
| 	<lw/sw>	<reg>,0($at)

Umm, the optimal solution is to have a new relocation type that
corrects the lui, so that only two instructions are needed.  In fact,
that's what MIPS currently uses.  However, you can't get that
relocation from the assembler as two discreete instructions, you have
to use one macro instruction, and let the assembler generate the code.
--
Michael Meissner	email: meissner@osf.org		phone: 617-621-8861
Open Software Foundation, 11 Cambridge Center, Cambridge, MA, 02142

You are in a twisty little passage of standards, all conflicting.