| I was able to rebuild xen& tools with only one line modified in Config.mk :- 
 PYTHON      ?= /usr/bin/python2.5
 PYTHON_PREFIX_ARG ?= --prefix="$(PREFIX)"
 # make clean
 # make uninstall
 # make install-xen
 # make install-tools
 
 IF  PYTHON_PREFIX_ARG ?=''
 OR
 PYTHON_PREFIX_ARG ?= --prefix=''
 # make tools
 fails.
 Xen 3.4 Dom0 with 2.6.30-rc3-tip loads fine. Xend starts fine.
 Reports bellow :-
 # xm info
 # brctl show
 # ifconfig
 Demonstrate normal Xen Host state.
 However, working in same Xen environment and same kernel , been built on top of Ubuntu Server 8.10, F10 PV DomU fails to start:-
 
 root@ServerJaunty:/home/boris/vm# cat f10.pyrun
 name="F10PV"
 memory=2048
 disk = ['phy:/dev/sdb7,xvda,w' ]
 vif = [ 'bridge=eth1' ]
 bootloader =
 "/usr/bin/pygrub"
 vcpus=2
 root@ServerJaunty:/home/boris/vm# xm create -c f10.pyrun
 Using config file "./f10.pyrun".
 Traceback (most recent call last):
 File "/usr/bin/pygrub", line 684, in <module>
 chosencfg = run_grub(file,
 entry, fs, incfg["args"])
 File "/usr/bin/pygrub", line 521, in run_grub
 curses.wrapper(run_main)
 File "/usr/lib/python2.5/curses/wrapper.py", line 47, in wrapper
 root@ServerJaunty:/home/boris/vm# Error: Boot loader didn't return any data!
 
 root@ServerJaunty:/home/boris/vm# xm create -c f10.pyrun
 Using config file "./f10.pyrun".
 Error: Boot loader didn't return any
 data!
 root@ServerJaunty:/home/boris/vm# xm create -c rhel.pyrun
 Using config file "./rhel.pyrun".
 Error: Boot loader didn't return any data!
 root@ServerJaunty:/home/boris/vm#
 
 Boris
 
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