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Date: Fri, 31 May 2002 18:54:41 -0700 (PDT)
From: Julian Elischer <julian@elischer.org>
To: Jake Burkholder <jake@locore.ca>
Cc: FreeBSD current users <current@FreeBSD.ORG>
Subject: Re: Seeking OK to commit KSE MIII-again
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On Fri, 31 May 2002, Jake Burkholder wrote:

> Apparently, On Fri, May 31, 2002 at 05:49:59PM -0700,
> 	Julian Elischer said words to the effect of;
> 
> > interesting but not exactly brief.. :-)
> > 
> > 
> > On Fri, 31 May 2002, Jake Burkholder wrote:
> > 
> > > 
> > > The system call stubs in libc are leaf functions; basically just a
> > > trap instruction followed by a return.  They do not touch the stack
> > > at all, or change the stack pointer.  One of the first few instructions
> > > on entry to the kernel is a save, which rotates the register window
> > > and logically saves the call-safe registers onto the user stack
> > > (the outs become the ins, and the kernel gets new ins and locals,
> > > with the old ones being saved to the user stack once a flush is
> > > performed or they get spilled out).
> > 
> > the question is "when does it switch to the kernel stack?"
> > (and back?)
> 
> This is not done by the hardware.  Its done by the trap code after
> the save is executed.

so if the software did it in the opposite order,
you'd save to the kernel stack?
(I doubt it but I have to ask..)


> 
> > 
> > 
> > > 
> > > Here is a reference:  http://www.sparc.com/standards/v9.ps.Z
> > 
> > downloaded... 300+ pages.. hmm.
> > 
> > 
> > > 
> > > Jake
> > > 
> 
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