I had this problem too a couple of days back (2.6.32.9 dom0 on Xen 3.4.2 
- screen blank on boot). I didn't try 3.4.3rc3 but went straight to 
4.0.0-rc6 and it booted ok.

Yasir
> On Mon, Mar 08, 2010 at 03:16:15PM -0800, Jeremy Fitzhardinge wrote:
>    
>> On 03/07/2010 03:31 PM, Josip Rodin wrote:
>>      
>>>> but when you update the dom0 kernel to current xen/master 2.6.31.6, it crashes?
>>>>
>>>>          
>>> When I update it to current xen/stable 2.6.32.9. (I put that bit in the
>>> subject only, sorry.)
>>>        
>> So 2.6.31.6 is OK on the 3.4.3rc3?  It's just the new dom0 which fails?
>>      
> Yes.
>
> (Sorry for the delay in further testing, I'm still waiting for users to
> ACK a new downtime.)
>
>    
>
>
>
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