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From: Eric Lacombe <goretux@gmail.com>
To: Jeremy Fitzhardinge <jeremy@goop.org>
Subject: Re: [x86] do_arch_prctl
Date: Thu, 20 Nov 2008 00:35:57 +0100
User-Agent: KMail/1.10.3 (Linux/2.6.27.5; KDE/4.1.3; x86_64; ; )
Cc: Arjan van de Ven <arjan@infradead.org>, Ingo Molnar <mingo@elte.hu>,
       linux-kernel@vger.kernel.org
References: <200811181835.07360.goretux@gmail.com> <200811191023.16358.goretux@gmail.com> <49247FC6.8080201@goop.org>
In-Reply-To: <49247FC6.8080201@goop.org>
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Thanks for your answer, I've got one last question ;)
In the ARCH_GET_GS, can you explain the line 834 to 838?

In fact, at first sight I thought that just the line 836 was sufficient, but I 
obviously miss the case where MSR_KERNEL_GS_BASE does not reflect the value 
requested, hence my question.

828 case ARCH_GET_GS: {
829                 unsigned long base;
830                 unsigned gsindex;
831                 if (task->thread.gsindex == GS_TLS_SEL)
832                         base = read_32bit_tls(task, GS_TLS);
833                 else if (doit) {
834                         asm("movl %%gs,%0" : "=r" (gsindex));
835                         if (gsindex)
836                                 rdmsrl(MSR_KERNEL_GS_BASE, base);
837                         else
838                                 base = task->thread.gs;
839                 }
840                 else
841                         base = task->thread.gs;

Thanks,

	Eric


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