This patch solves a number of problems related to variables with Dwarf2 
location expressions - which these days, means just about every local in 
optimized code. :-)  Perhaps the most interesting part is that I finally 
got tired of working blind and filled out description location 
functions, so now both "info scope" and "info address" have quite a lot 
of say about variables.  Try things like "info scope 
handle_inferior_event" to get some truly awesome verbiage. :-)

Since there's a lot of new code here, I'll leave it up for a couple days 
before committing.

Stan

2010-04-15  Stan Shebs  <stan@codesourcery.com>
        Nathan Sidwell  <nathan@codesourcery.com>

    * dwarf2loc.c (struct axs_var_loc): New struct.
    (dwarf2_tracepoint_var_loc): New function.
    (dwarf2_tracepoint_var_access): New function.
    (dwarf2_tracepoint_var_ref): Use dwarf2_tracepoint_var_loc, deal
    with DW_OP_piece.
    (locexpr_describe_location_piece): New function.
    (locexpr_describe_location_1): New function.
    (locexpr_describe_location): Call it, update signature.
    (loclist_describe_location): Rewrite to loop over locations,
    update signature.
    * symtab.h (struct symbol_computed_ops): Add address to
    describe_location arguments, return void.
    * printcmd.c (address_info): Get context PC, pass to computed
    location description.
    * tracepoint.c (scope_info): Ditto.
    * ax-gdb.c (trace_kludge): Export.