Re: Modifies vs. Replaces

[Michael Eager <eager at eagercon dot com>]

Ron 603-884-2088 wrote:
> 
> Of the original three alternatives, I strongly support #1 as the better
> interpretation for a location attribute on a non-defining declaration:
> 
>     Ignore location information in the defining entry, and
>     only use the location information provided in the non-defining
>     entry [within the scope of the non-defining entry].

As mentioned before, this requires duplication of information 
in the defining declaration.  This seems unnecessary and wasteful.

In most (all?) cases this would require a location list to be 
used in the non-defining entry, since both the location of the
a global and any the locations of any copies would normally be 
specified.  The location of the global would be a relocatable 
reference, adding to the size and complexity of the Dwarf data.

I have a question about what a compiler would put in the range list
for a non-defining entry.  Using Todd's examples, he would put in
the start and end locations of the compilation unit containing
the non-defining declaration.  Why he selected those numbers, 
I can't guess, but I know that globals have valid lifetimes 
outside that range.  How should this range list be specified?

What is a debugger expected to do?  Keep a list of all of the 
many location lists which are created by non-defining declarations,
each tagged with a scope?  

If Compaq's compilers generate code which has lifetime holes for 
global variables, could you provide a reasonable example?  Perhaps
with both the source and assembly code for the example?

-- 
Michael Eager	 Eager Consulting     eager@eagercon.com
1960 Park Blvd., Palo Alto, CA 94306  650-325-8077