linux-kernel - Re: [x86] do_arch

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Message-Id: <200811200035.57509.goretux@gmail.com>
Date:	Thu, 20 Nov 2008 00:35:57 +0100
From:	Eric Lacombe <goretux@...il.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [x86] do_arch_prctl

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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