Re: Using memory above TOS (Mark Tillotson)
29 May 1996 21:04:05 -0400

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From: (Mark Tillotson)
Newsgroups: comp.arch,comp.compilers
Date: 29 May 1996 21:04:05 -0400
Organization: Harlequin Limited, Cambridge, England
References: <> 96-05-012 96-05-100 96-05-105 96-05-132
Keywords: architecture

> P.S. -- Actually, now that I think about it, the main reason I
> avoided memory above TOS is that I wasn't sure that UNIX
> promised to keep pages above TOS backed up in VM; i.e., if TOS
> was sitting at a page boundary, the page above might be paged
> out at an arbitrary time, and then be reallocated zero-filled
> when next referenced, losing the contents of words above TOS.

I've never heard of that - the pager isn't going to check which
user-mode register was responsible for generating a virtual address,
it will just deal with the fault and restart the instruction. You
certainly wouldn't be able to implement thread-libraries if the kernel
looked at the stack pointer!!

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