I don't know why the pid_hash debug info is not getting
 included in your vmlinux file, i.e., when built with -g.
 I note that your kernel was built with gcc 4.0.0, whereas
 my non-xen 2.6.16 kernel above was built with gcc 4.1.0,
 and the 2.6.17 xen kernel above was built with gcc 4.1.1.
 Perhaps there's an issue with the 4.0.0 compiler?
 I don't know -- I give up.
 Anyway, I guess the only way around it is going to
 have to be a hack.  The "pid_hash" symbol is there,
 and the size of the array can be determined by looking
 at the symbol value of the next sequential symbol, and
 dividing the address difference by the size of a pointer.
 
Ah, neat.  I will either upgrade gcc or use the hack - but given the
bug, it will not be surprising if there are more symbols missing.
Thanks for triaging the problem.
-- 
Thanks
-Tejasvi