xsplice,symbols: Implement symbol name resolution on address.

xsplice,symbols: Implement symbol name resolution on address.

If in the payload we do not have the old_addr we can resolve
the virtual address based on the UNDEFined symbols.

We also use an boolean flag: new_symbol to track symbols. The usual
case this is used is by:

* A payload may introduce a new symbol
* A payload may override an existing symbol (introduced in Xen or another
  payload)
* Overriding symbols must exist in the symtab for backtraces.
* A payload must always link against the object which defines the new symbol.

Considering that payloads may be loaded in any order it would be incorrect to
link against a payload which simply overrides a symbol because you could end
up with a chain of jumps which is inefficient and may result in the expected
function not being executed.

Since the payload we get is an relocatable image (partial linked ELF file)
we have to match up the symbols. We follow the ELF visibility rules for that
and for local symbols do what bintutils ld does.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Release-acked-by: Wei Liu <wei.liu2@citrix.com>