Message-ID: <49BE7C57.6060100@goop.org>
Date: Mon, 16 Mar 2009 09:20:39 -0700
From: Jeremy Fitzhardinge <jeremy@goop.org>
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To: Avi Kivity <avi@redhat.com>
CC: Sergio Luis <eeeesti@gmail.com>, Ingo Molnar <mingo@elte.hu>,
       "Rafael J. Wysocki" <rjw@sisk.pl>, Pavel Machek <pavel@suse.cz>,
       Linux-kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: x86: asm doubt
References: <ce0170d90903150716t14033a9dr3b3bf028933dde7c@mail.gmail.com> <49BD2FC7.5050903@goop.org> <49BE5E4E.1070209@redhat.com>
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Avi Kivity wrote:
> Jeremy Fitzhardinge wrote:
>> In 32-bit mode, moving to a segment register can fault if the 
>> underlying GDT/LDT entry is invalid.  In 64-bit mode, segment 
>> registers are mostly decorative and have no function, and moving 
>> arbitrary values into them doesn't fault, making the exception 
>> catching unnecessary.
>
> 64-bit mode will in fact fault if an access is made outside the 
> GDT/LDT, or of the descriptor is invalid.

Oh, I didn't think it bothered.  I guess I'm conflating that with the 
fact that it doesn't apply any of the segment properties to memory 
accesses.  Anyway, in that case the 64-bit code should definitely be 
using the standard segment accessors.

    J

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