Re: Dwarf expertise needed

[Roland McGrath <roland@redhat.com>]

> First of all thank you for the thorough reply. I now see issues that I 
> have not seen before.

I think I'll have that on my tombstone. ;-)

> If it turns out that frame_base is the only instance then how about a 
> function get_framebase that is smart enough to figure out where the 
> correct frame base is. That way you help the client not make that 
> mistake. Or get_* for each attribute that needs the abstract instance of 
> the function.

For attributes in general it's easy, you just use dwarf_attr_integrate.
For elided children I don't have a handy helper yet, but it is
straightforward to follow the abstract_origin reference and go from there.

The frame_base case is on the other side of exactly the distinction I
pointed out.  It has nothing to do with the abstract instance, and only to
do with the physical parent of the particular concrete instance.  Figuring
it out requires a tree walk to find the parent.  

It makes sense to fetch that as part of the same operation as something
like getscopes primarily because that same tree walk is already being done.
I've imagined there might in future be some libdw optimizations that would
preserve some back-pointers to make it efficient to go up the tree, though
I certainly haven't figured out all the details of that.  So it might make
sense to use a separate call for this with the expectation that its
expensive repeat of the tree walk will be optimized in the future, but I'm
not quite sure.  I'd still like to contemplate the potential related cases
a bit more.

> That will do, although I think there might be a bug there :(. Let me 
> double check.

There is certainly a bug hit by Stan's test case, since it gets an error.


Thanks,
Roland