Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uunet!aplcen!samsung!zaphod.mps.ohio-state.edu!rpi!crdgw1!crdos1!davidsen
From: davidsen@crdos1.crd.ge.COM (Wm E Davidsen Jr)
Newsgroups: comp.arch
Subject: Re: ABI and growth
Keywords: ABI expansion
Message-ID: <2020@crdos1.crd.ge.COM>
Date: 16 Jan 90 14:00:42 GMT
References: <6186@celit.fps.com>
Reply-To: davidsen@crdos1.crd.ge.com (bill davidsen)
Organization: GE Corp R&D Center, Schenectady NY
Lines: 32

In article <6186@celit.fps.com> hutch@fps.com (Jim Hutchison) writes:

| Now, here we have the ABI(s) and people already want them to grow to include
| FPAs, Application Processors, and such.  Sounds good.  Unfortunately it seems
| that to add these neat things, and it gets called a "new" ABI.

  That is the problem in a nutshell.

| So here is a thought I was toying with.  How about allowing for library calls
| to trap and re-write there calls as the appropriate instruction?  I can see
| some problems right away with handling shared pages neatly, and having space
| and parameters to re-write the call with.  

  It could work if you have copy on write. Or maybe not, since the page
will still be valid for all processes using it. I think this requires
some careful though about doing stuff with the MMU and paging. The usual
practice is to overwrite a code page rather than swap it, since it
(usually) hasn't been modified. I suppose this wouldn't be a problem,
since if a new, unmodified, copy came back in it would become a modified
copy quickly.

  You would need to lock the page which writing it in a multi-CPU
system, which might require a lot of MMU extensions.

  This is an old problem. The VAX gets around some of it by allowing
"writable control store" (users defined microcode for certain
instructions). A friend did a master's thesis based on implementing an
FFT instruction in microcode. It was almost twice as fast as doing it
with discrete instructions.
-- 
bill davidsen	(davidsen@crdos1.crd.GE.COM -or- uunet!crdgw1!crdos1!davidsen)
            "Stupidity, like virtue, is its own reward" -me