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

From: H. Peter Anvin
Date: Mon Dec 17 2012 - 10:22:23 EST

Because it is almost impossible to do right?

Pavel Emelyanov <xemul@xxxxxxxxxxxxx> wrote:

>On 12/14/2012 10:44 PM, Andy Lutomirski wrote:
>> On Fri, Dec 14, 2012 at 10:35 AM, H. Peter Anvin <hpa@xxxxxxxxx>
>>> 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@xxxxxxxxx>
>>>>>> Wouldn't the vdso get mapped already and could be mremap()'d. If
>>>>> really need more control I'd almost push for a device/filesystem
>>>>> 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
>>>>> (In brief summary: how annoying would it be if the vdso was no
>>>>> just a bunch of constant bytes that lived somewhere?)
>>>> It depends on what vdso is going to be. In the perfect case it
>>>> a) be mremap-able to any address (or be at fixed address _forever_,
>>>> 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.
>>> mremap() should work. At the same time, the code itself is not
>going to
>>> have any stability guarantees between kernel versions -- it
>>> cannot.
>> We could guarantee that the symbols in the vdso resolve to particular
>> offsets within the vdso. (Yes, this is ugly.)
>> Does criu support checkpointing with one version of a shared library
>> and restoring with another?
>No, neither we have this in plans.
>However, if somebody needs this and implements -- why not?!

Sent from my mobile phone. Please excuse brevity and lack of formatting.
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