Message-ID: <474F449B.70603@redhat.com>
Date: Thu, 29 Nov 2007 18:00:43 -0500
From: Chuck Ebbert <cebbert@redhat.com>
Organization: Red Hat
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To: Roland McGrath <roland@redhat.com>
CC: Andrew Morton <akpm@linux-foundation.org>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
       Ingo Molnar <mingo@elte.hu>, "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH x86/mm 6/6] x86-64 ia32 ptrace get/putreg32 current task
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On 11/29/2007 05:21 PM, Roland McGrath wrote:
>>>  	case offsetof(struct user32, regs.gs):
>>>  		*val = child->thread.gsindex;
>>> +		if (child == current)
>>> +			asm("movl %%gs,%0" : "=r" (*val));
>> Won't this return the kernel's GS instead of the user's?
> [...]
>> But this is x86_64, where swapgs is done on kernel entry.
> 
> As I understand it, and from what the documentation I have says, swapgs has
> nothing to do with the %gs selector.  It affects the "GS base register",
> i.e. the MSR.
> 

Yep, I confused the GS selector with the base address in the descriptor.
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