From owner-freebsd-current  Wed Feb 28  3:38:47 2001
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Date: Wed, 28 Feb 2001 22:38:32 +1100 (EST)
From: Bruce Evans <bde@zeta.org.au>
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To: Julian Elischer <julian@elischer.org>
Cc: John Baldwin <jhb@FreeBSD.ORG>, Leif Neland <leifn@neland.dk>,
	freebsd-current@FreeBSD.ORG, Gary Jennejohn <garyj@jennejohn.org>
Subject: Re: make kernel failure: pecoff: machine/lock.h
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On Tue, 27 Feb 2001, Julian Elischer wrote:

> Bruce Evans wrote:
> > Most of the pcb actually has the same persistence as the kernel stack
> > (both mainly store the process's context while the process is in the
> > kernel).  But it is silly to put the pcb below the stack instead of
> > above it.  Perhaps the idea is to get a panic sooner when something
> > is corrupted.
> 
> I have never understood why the context is not ON the stack.

At least on i386's, it is because the context is not all saved in LIFO
order.  The pcb gets the non-LIFO stuff.  E.g., the FP state is saved
lazily, not pushed on every entry to the kernel.

Bruce


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