32bit libxc with 64bit guest

[Mukesh Rathor <mukesh.rathor@oracle.com>]

Hi Folks,
   I am somewhat new to xen, and have been looking into making 32bit libxc
work with 64bit guests which would allow gdbserver on a 32bit dom0 to attach 
to a 64bit guest.

   I have gotten some of the data structures expanded for 32bit, however, I'm
currently trying to figure out the flow of address look up from ioctl down.
Somewhere down this path, I'm getting incorrect results translating a
64bit address. The first lookup (using cr3) returns a value that seems OK, but 
  the l3 look up results in 0x0. I am looking for any help or
high level writeup that might shed some light on  direct_remap_pfn_range()
and below, basically trying to figure out vm_area_struct's, what the dom0 is
trying to fill, why is it going down to pte all the way when i'm just looking
for pml4 (so it appears from libxc:map_domain_va_64().

For 32bit pae, the above works fine.

Thanks a lot,
Mukesh