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From: Steve Passe <smp@csn.net>
To: smp@freebsd.org
cc: current@freebsd.org
Subject: self modifying kernel code
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Date: Wed, 16 Jul 1997 14:42:55 -0600
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Hi,

I see the possible usefullness for "self-modifying-code" in several places in
the SMP kernel.  I currently am doing some "redirected calls" for INT
resumption routines because we don't know till run time where several of the
vectors will be.  Peter pointed out a technique where another SMP kernel
puts calls in the kernel to a pseudo-lock routine.  This routine then
determines whether it is running on a UP or SMP motherboard.  If UP it replaces
the call with a near jump to the return address.  If SMP it replaces the call
TARGET address with the address of the real lock routine.  Note that this
means a modification the 1st time EACH call to a lock/unlock routine is
encountered, NOT "just once".  This is a win for both UP and SMP, while
allowing one kernel to support both.

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?

--
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