linux-kernel - Re: [patch] paravirt: VDSO page is essential

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Date:	Mon, 05 Mar 2007 14:01:43 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Roland McGrath <roland@...hat.com>
CC:	Andi Kleen <ak@...e.de>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	Jan Beulich <jbeulich@...ell.com>
Subject: Re: [patch] paravirt: VDSO page is essential

Roland McGrath wrote:
> Does the old userland compatibility you're concerned about really need the
> vdso to be at 0xfffffe000 in particular, or just need it to be at a fixed
> address that matches the phdrs inside the image?  My recollection of the old
> glibc's limitation was that it expected the image's phdrs to match its load
> address.  The xen kernels used to change this to 0xffffd000 or something,
> and AFAIK that was fine.  If that's all that's needed, it is not so hard to
> adjust the vDSO contents at boot time (phdrs, shdrs, and symbols; no code
> contents use the absolute address).  Under CONFIG_COMPAT_VDSO, it can see
> where the paravirt moved the fixmap to, and apply adjustments.
>   

Jan Beulich just posted a patch to do just this - relocate the vdso's
ELF header.  If that's all that's really required to keep COMPAT_VDSO
viable under PARAVIRT, then it seems like the way to go.

    J
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