[Devel] Re: [RFC PATCH 0/2] cr: Introduce s390x checkpoint/restart code

[Serge E. Hallyn]

Quoting Martin Schwidefsky (schwidefsky at de.ibm.com):
> On Wed, 2009-01-14 at 23:05 -0600, Serge E. Hallyn wrote:
> > Hi,
> > 
> > here is a first stab at extending Oren's application c/r patchset
> > (http://lkml.org/lkml/2008/12/29/38) to s390.  I pretty much spent a day
> > or two looking through the s390 include and .S files and then took a
> > stab, so I won't be surprised to find these patches (and myself) the
> > subject of ridicule.  For instance, I'm really not *sure* whether I
> > should be backing up the acrs registers (some s390 docs suggested
> > userspace could use them), the ksp, or the vdso_base.  But one thing
> > I've got going for me at least...  it works!
> 
> The access registers need to be saved, a0/a1 contain the TLS pointer and
> the user can store anything to a2-a15. The ksp does not have to be
> stored as it cannot contain an important value. If it would then we'd

Ok, will drop the kso part.

> have kernel state which would break checkpoint/restart. The restart code
> needs to come up with a sensible initial value for ksp though. The
> vdso_base code needs to be stored as well. 

But the vdso is set up at exec() time, right?  So if I reset vdso_base
to the checkpointed value, might it actually end up at the wrong place,
since the exec() of the 'restart' program might have placed the vdso
at a different location than where it was at checkpoint time?

I also notice that on s390 vdso_base seems to always be either
20000020000 or 20000000000, and so far my checkpointed and restart
programs have always had 20000000000, so testing doesn't really help :)

-serge
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