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From: Terry Lambert <terry@lambert.org>
Message-Id: <199707162141.OAA01599@phaeton.artisoft.com>
Subject: Re: self modifying kernel code
To: smp@csn.net (Steve Passe)
Date: Wed, 16 Jul 1997 14:41:26 -0700 (MST)
Cc: smp@FreeBSD.ORG, current@FreeBSD.ORG
In-Reply-To: <199707162042.OAA09705@Ilsa.StevesCafe.com> from "Steve Passe" at Jul 16, 97 02:42:55 pm
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> I see the possible usefullness for "self-modifying-code" in several places in
> the SMP kernel.

[ ... discussion of patch vectors vs. indirected jump tables ... ]

> So what is the policy/reality of self-modifying code in the -current source?
> The 1st example above can be handled during boot, so I suspect that the
> modifications should be easy enough.  The second involves modification of the
> kernel code space after going multi-user (probaly dozens of times b4 its
> finished), I'm not so sure about modifying kernel code-space at that point...
> 
> Comments?

Are we assuming that the processors will be Pentium only?  The icache
is not written back prior to the P5.  This takes a significant number
of NOP's to flush the pipeline (as discussed in Van Guilluwe's "The
Undocumented PC" in the section where he investigates instruction cache
depth using self-modifying code).

Note that these patches would have to be done for 386/486 in the UP case.


					Regards,
					Terry Lambert
					terry@lambert.org
---
Any opinions in this posting are my own and not those of my present
or previous employers.