Path: utzoo!mnetor!uunet!husc6!cmcl2!brl-adm!umd5!purdue!i.cc.purdue.edu!j.cc.purdue.edu!pur-ee!uiucdcs!uxc.cso.uiuc.edu!ccvaxa!aglew
From: aglew@ccvaxa.UUCP
Newsgroups: comp.arch
Subject: Re: Condition Codes in General Regi
Message-ID: <28200106@ccvaxa>
Date: 20 Feb 88 21:44:00 GMT
References: <7446@apple.UUCP>
Lines: 30
Nf-ID: #R:apple.UUCP:7446:ccvaxa:28200106:000:1453
Nf-From: ccvaxa.UUCP!aglew    Feb 20 15:44:00 1988


..> Memory mapping the register file.

Sure, you can do it already! Reserve an address range for the register
file. Make these pages invalid, so you fault whenever you try to touch
them. In your page fault handler, go and actually fetch from the 
register file (which you have probably saved on the stack when you took
the exception).
    Clunky? Yes, but not much more so than other techniques for mapping
the register file, and probably with less impact on performance if you
don't access through maps often.

By the way, this is also a technique for guaranteeing semantics of
pointers to auto variables on machines with multiple register sets.
I mean, it doesn't *look* like an auto variable is being accessed
through a pointer, it probably isn't, and you'd like to put the auto
in a register for speed. But there is one teensy little indirection,
on an extremely infrequently used path, that you have to worry about...



Andy "Krazy" Glew. Gould CSD-Urbana.    1101 E. University, Urbana, IL 61801   
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