From owner-freebsd-arch  Mon Jan  7 12: 2:43 2002
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Date: Mon, 7 Jan 2002 15:01:32 -0500 (EST)
From: Daniel Eischen <eischen@pcnet1.pcnet.com>
To: Nate Williams <nate@yogotech.com>
Cc: Dan Eischen <eischen@vigrid.com>, Peter Wemm <peter@wemm.org>,
	Archie Cobbs <archie@dellroad.org>, Alfred Perlstein <bright@mu.org>,
	arch@FreeBSD.ORG
Subject: Re: Request for review: getcontext, setcontext, etc
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On Mon, 7 Jan 2002, Nate Williams wrote:
> > > 
> > > Nope, but you need to be able to get the FPU context saved in setcontext.
> > 
> > Well, that's what I mean.  If somewhere else in the application
> > there was a setcontext that returned to the getcontext above...
> 
> I think I understand what you are asking.  Are you asking if there is
> application specific context that needs to be saved, such as GC state or
> somesuch?  Or, am I truly confused?
> 
> > What I'm asking is, is there any FP state (other than the FP
> > control word which does get saved/restored), from before the
> > getcontext call that needs to be reloaded after the call, or
> > does the compiler assume that state may have been changed
> > by the call itself?

  Thread 1:
  ---------
  /* munch some FP stuff */
  pthread_yield();  /* allow thread 2 to run */
  /* munch some more FP stuff */

Assume that pthread_yield only saves the FP control word (which
is what it does currently in libc_r).

  Thread 2:
  ---------
  /* FP munchy munchy */
  pthread_yield();   /* allow thread 1 to run */
  /* FP munchy munch munch */


What FP state exists in registers across the call to
pthread_yield().

-- 
Dan Eischen

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