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Date:      Sun, 26 Nov 2000 17:50:06 -0800
From:      Jake Burkholder <jburkhol@home.com>
To:        Greg Lehey <grog@lemis.com>
Cc:        smp@FreeBSD.ORG
Subject:   Re: BSD/OS interrupt code 
Message-ID:  <20001127015006.5B7BDBA7A@io.yi.org>
In-Reply-To: Message from Greg Lehey <grog@lemis.com>  of "Mon, 27 Nov 2000 10:41:48 %2B1030." <20001127104147.B27186@echunga.lemis.com> 

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> On Sunday, 26 November 2000 at 14:07:49 -0800, Jake Burkholder wrote:
> > Hi,
> >
> > If anyone with access to the BSD/OS code is interested, I've written
> > a little program that runs their interrupt stub code generator in
> > userland.  You can then abort(); and disassemble the stub from
> > the core dump to look at the code all in one piece.  Makes it much
> > easier to follow.
> >
> > In case you haven't looked, their interrupt handlers are generated
> > by bcopy-ing various blocks of assembler code into an array at
> > runtime, and then poking in arguments and relocating branches.
> 
> Interesting.  I was wondering whether something similar would be a
> good idea.  On the other hand, We don't waste much space by having
> multiple alternate stubs.  What's your feeling?

I suspect that it would be hard to do this for architectures
other than x86, which has a relatively simple instruction format.

I also think that BSD/OS went a little too far with this, and
have produced code that is very difficult to understand, let
alone maintain.  I think its cool what they did, I'm humbled
and amazed that they made it work, but I don't know that its
right for FreeBSD.



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