linux-kernel - Re: [PATCH x86/mm 6/6] x86-64 ia32 ptrace get/putreg32 current task

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Message-Id: <20071129222157.1120B26F8E7@magilla.localdomain>
Date:	Thu, 29 Nov 2007 14:21:57 -0800 (PST)
From:	Roland McGrath <roland@...hat.com>
To:	Chuck Ebbert <cebbert@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH x86/mm 6/6] x86-64 ia32 ptrace get/putreg32 current task

> >  	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.


Thanks,
Roland
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