Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!nic.csu.net!csun!kithrup!sef
From: sef@kithrup.COM (Sean Eric Fagan)
Newsgroups: comp.unix.sysv386
Subject: Re: Weitek under unix (was Re: SECURITY BUG)
Keywords: BAD BUG
Message-ID: <1991Feb15.195340.26903@kithrup.COM>
Date: 15 Feb 91 19:53:40 GMT
References: <54428@bigtex.cactus.org> <1991Feb13.050417.10170@rfengr.com> <54602@bigtex.cactus.org>
Organization: Kithrup Enterprises, Ltd.
Lines: 25

In article <54602@bigtex.cactus.org> james@bigtex.cactus.org (James Van Artsdalen) writes:
>there is no
>reason for 387 support (real or emulated) to need the u block to be
>writable.

Yes, there is, unless you want to make the emulated fpu even slower.
Currently, the fp emulator runs in ring 3, just like user processes.  When
you try to execute an fp instruction (and don't have an fpu), after some
inital setting up, you go directly from your process (in ring 3) to the fp
emulator (also in ring three).  This is *tons* faster than going to another
ring.  Since you might have hundreds of fp instructions, an additional 60+
clocks for each emulated instruction *would* be noticeable.

>> Here, here's a simple yes or no question: "Does Dell Unix allow user
>> processes to overwrite the u block?"
>It does not allow it on my 486.  I have no 386 to try it on.

Try booting with 'ignorefpu' (I think that's the option).  That will tell
the kernel to run the fp emulator anyway.

-- 
Sean Eric Fagan  | "I made the universe, but please don't blame me for it;
sef@kithrup.COM  |  I had a bellyache at the time."
-----------------+           -- The Turtle (Stephen King, _It_)
Any opinions expressed are my own, and generally unpopular with others.