linux-kernel - Re: [PATCH 6/6] Add 32 bit VDSO support for 32 and 64 bit kernels

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Message-ID: <CAMe9rOoxTqF3PpvhS-+K40e-3fCELJUQhCjRPenZOi=Df895fg@mail.gmail.com>
Date:	Thu, 20 Dec 2012 10:23:39 -0800
From:	"H.J. Lu" <hjl.tools@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Stefani Seibold <stefani@...bold.net>,
	Andy Lutomirski <luto@...capital.net>,
	linux-kernel@...r.kernel.org, x86@...nel.org, tglx@...utronix.de,
	mingo@...hat.com, ak@...ux.intel.com, aarcange@...hat.com,
	john.stultz@...aro.org, xemul@...allels.com, gorcunov@...nvz.org,
	andriy.shevchenko@...ux.intel.com,
	Roland McGrath <mcgrathr@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 6/6] Add 32 bit VDSO support for 32 and 64 bit kernels

On Thu, Dec 20, 2012 at 10:21 AM, H. Peter Anvin <hpa@...or.com> wrote:
> On 12/20/2012 09:53 AM, Stefani Seibold wrote:
>>
>> In a 32 bit kernel a VDSO can mapped on an fix address VDSO_HIGH_BASE
>> (kernel parameter vdso32=2 or CONFIG_COMPAT_VDSO), which is 0xffffe000.
>> There is no available page BEFORE nor AFTER the page, so it is not
>> possible to have VVAR or HPET as a part of that list!!!!
>>
>
> [Cc: Roland, Linus, H.J.]
>
> The pages before it are safe to use, because they are kernel internal
> and hence not ABI (and in fact depend on the kernel configuration
> parameters.)  So pushing down the start of the fixmap region is not a
> problem.  This means that to retain this compatibility the existing
> entry points need to be at the end, which is more painful than we'd
> like, but nevertheless there.
>
> Do we know what actually used these fixed address, if anything, ever?
>

Glibc gets VDSO address from AT_* vector. I think glibc is
safe.


-- 
H.J.
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