linux-kernel - Re: Assignment of GDT entries

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Date:	Wed, 13 Sep 2006 21:16:41 +0200
From:	Arjan van de Ven <arjan@...radead.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Linus Torvalds <torvalds@...l.org>, Ingo Molnar <mingo@...e.hu>,
	Andi Kleen <ak@...e.de>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Zachary Amsden <zach@...are.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Michael A Fetterman <Michael.Fetterman@...cam.ac.uk>
Subject: Re: Assignment of GDT entries

On Wed, 2006-09-13 at 11:58 -0700, Jeremy Fitzhardinge wrote:
> What's the rationale for the current assignment of GDT entries?  In 
> particular, this section:
> 
>  *   0 - null
>  *   1 - reserved
>  *   2 - reserved
>  *   3 - reserved
>  *
>  *   4 - unused			<==== new cacheline
>  *   5 - unused
>  *
>  *  ------- start of TLS (Thread-Local Storage) segments:
>  *
>  *   6 - TLS segment #1			[ glibc's TLS segment ]
>  *   7 - TLS segment #2			[ Wine's %fs Win32 segment ]
>  *   8 - TLS segment #3
>  *   9 - reserved
>  *  10 - reserved
>  *  11 - reserved
> 
> 
> What are entries 1-3 and 9-11 reserved for?  Must they be unused for 
> some reason, or is there some proposed use that has not been impemented yet?


I don't know the exact details on these; I do know that several GDT
entries tend to be used by BIOSes in their APM implementations and thus
are better of not being used. That might be the underlying reason
here....


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