RE: [Xen-users] xen and different ARCH

[Jason <fearthepenguin@xxxxxxxxxxxxxxxxx>]

Ah, the ssh idea is a good one!   Have you tried doing anything along 
the lines of making the machine think it is an i386 instead of a 686?  I 
do most of my builds for boxes that are 486 compatible (Soekris, ELan 
chips).
HAWKER, Dan wrote:
> > hey gang, just an odd question. I do a lot of cross compiling of 
> > software, all for x86, and got to thinking. It would be a LOT 
> > easier to 
> > setup a VM that thinks it's an i(3|4|5|)86 instead of 
> > building separate 
> > tool chains. Does anyone know if I can make a xen machine think it is 
> > something other then what the host is, within x86 that is.
> >     
> Hi Jason,
>
> Kind of :)
>
> I'm the sys admin for a software development team of around 70 or so. We
> have a series of server(s) that the guys build software on directly. Its all
> Linux (FC) based Java, C & C++ stuff.
>
> Recently, we've been getting new x86_64 boxes in the door and I had the same
> ?problem/idea?. My experiences so far...
>
> Xen won't allow you to run say a 64bit DomO and have a 32bit DomU beneath
> it. They all have to be 64 or 32bit. Don't know the true intricacies of why,
> (IIRC to do with how 64 and 32bit machines access memory) but you can't.
> Haven't tested VMware properly regarding this yet, but due to its different
> approach to virtualisation, it may be possible (if so I could be doing some
> serious migration work soon :).
>
> Subsequently, no, you can't have a DomU think its something different
> (arch-wise). The kernels (DomO & DomU) have to be of the same arch so if the
> DomO is 64bit, your DomU has to be too. This is a problem for us when
> building apps (all of ours are for embedded 32bit targets).
>
> To get around these issues, I presently...
>
> # Generally run 64bit. Most of my DomO's are x64_64 FC4/5 boxes. 
> # Use a SSH startup hack (introduce setarch into the initscript) so that all
> clients that connect get a 32bit session. This works surprisingly well and
> stops nasty uname issues (their session always (presuming access via SSH)
> thinks its 32bit).
> # Create a 32bit template DomU. I have a series of *clean* DomU templates
> (created using yum into a chroot on a 32bit machine), that I use when
> creating a new 32bit DomU. I just copy the lot across to a new LVM based
> VBD, copy across the appropriate 64bit kernel and modules from the DomO (I
> keep kernels and modules for both on my DomO just in case), change the usual
> settings and light it up. Add in the SSH hack and you have to all intents
> and purposes, a 32bit DomU beneath a 64bit DomO.
>
> That's about it. Its kind of messy, but it works. It would be nice to just
> use any architecture, but...
>
> (Wonder if VT based Xen Doms can be mixed and matched... Hmmmm....)
>
> HTH
>
> Dan
> --
>
> Dan Hawker
> Linux System Administrator
> Astrium
>
>   

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