linux-kernel - Re: [CRIU] [PATCH] Add VDSO time function support for x86 32-bit kernel

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Date:	Fri, 14 Dec 2012 14:46:57 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Pavel Emelyanov <xemul@...allels.com>
CC:	Andy Lutomirski <luto@...capital.net>, aarcange@...hat.com,
	ak@...ux.intel.com, Stefani Seibold <stefani@...bold.net>,
	x86@...nel.org, linux-kernel@...r.kernel.org, criu@...nvz.org,
	mingo@...hat.com, john.stultz@...aro.org, tglx@...utronix.de
Subject: Re: [CRIU] [PATCH] Add VDSO time function support for x86 32-bit
 kernel

On 12/14/2012 12:34 AM, Pavel Emelyanov wrote:
> On 12/14/2012 06:20 AM, Andy Lutomirski wrote:
>> On Thu, Dec 13, 2012 at 6:18 PM, H. Peter Anvin <hpa@...or.com> wrote:
>>> Wouldn't the vdso get mapped already and could be mremap()'d.  If we
>> really need more control I'd almost push for a device/filesystem node
>> that could be mmapped the usual way.
>>
>> Hmm.  That may work, but it'll still break ABI.  I'm not sure that
>> criu is stable enough yet that we should care.  Criu people?
> 
> It's not yet, but we'd still appreciate the criu-friendly vdso redesign.
> 
>> (In brief summary: how annoying would it be if the vdso was no longer
>> just a bunch of constant bytes that lived somewhere?)
> 
> It depends on what vdso is going to be. In the perfect case it should
> a) be mremap-able to any address (or be at fixed address _forever_, but
>    I assume this is not feasible);
> b) have entry points at fixed (or somehow movable) places.
> 
> I admit that I didn't understand your question properly, if I did,
> please correct me.
> 

Either way... criu on the side, we should proceed with this vdso
redesign and get support for the 32-bit entry points including compat
mode on x86-64.

	-hpa


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