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Re: [Xen-users] Debugging DomU

On Wed, 2015-05-13 at 21:37 +0000, Chris (Christopher) Brand wrote:
> Hi Ian,
> I did end up writing some code to do what you suggested (trap to the 
> hypervisor on an early exception), but never got it to succeed.
> I have now got a JTAG on the system, which allows me to look at the page 
> tables when it's in the locked up state, and I see that address 0 isn't 
> mapped to any RAM at all, which would seem to be a problem because the 
> vmlinux includes exception table code that should live there.
> Can you point me towards the code that populates the page table for a new 
> DomU ?

In the hypervisor side maddr hack it would be the:
        p2m_populate_ram(d, 0x0, 0x1000 - 1);

As I mentioned before the userspace equivalent of that is
xc_domain_populate_physmap_exact, what I didn't make clear (sorry) was
that you would need to add that call in order to populate a page of
memory at address 0, since by default there is no RAM at address 0 in a
Xen domU.

Although if you have a JTAG I suspect all this is rather moot now ;-)


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