Re: DW_AT_specification and partial symtabs

[Daniel Jacobowitz <drow@mvista.com>]

On Thu, Jun 12, 2003 at 10:01:38AM -0700, David Carlton wrote:
> One of the main issues that I'm dealing with on my branch is getting
> nested types to work right in C++ (with DWARF 2): these have the
> characteristic that they depend on the hierarchical structure of the
> debug info to a greater extent than, as far as I can tell, anything
> that mainline GDB currently does.  The reason for this is that, to
> deduce a nested type's name, you really have to know where it lives in
> the hierarchical structure, so you can add whatever prefixes are
> appropriate to its DW_AT_name.  (With non-types, we (over)use mangled
> names for this sort of thing, so it's not such a big deal there.)

> Unfortunately, there's no way to get at that information at all with
> the current psymtab reader: it tries to march from top-level DIE to
> top-level DIE without building up a tree of DIEs.  So it seems to me
> that I have no choice but to have the psymtab reader build up a tree
> of DIEs before it starts reading, just like the symtab reader does.
> 
> Comments?  Suggestions?  Ideas for how to make the tree that the
> psymtab reader builds to be as small as possible?  I'm a little
> worried about weird cases like local classes: if I have

I'll answer this in more depth in a bit.  For now, something to
consider: I would like to add .debug_typenames (spelling?) to GCC -
it's an SGI extension, IIRC.  This plus .debug_pubnames should allow us
to implement psymtabs entirely without mapping .debug_info.  I believe
it handles your case too, since it should have fully qualified
typenames.

The implementation may need a little tweaking for space efficiency...

>   void foo ()
>   {
>     class Local {
>     public:
>       int mem() {return 1;}
>     };
> 
>     ...
>   }
> 
> then is the compiler allowed to put a definition of Local::mem as a
> child of the comp unit die (with a DW_AT_specification pointing to a
> DIE inside of foo somewhere)?

I believe so.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer