Re: [PATCH v3] Bug 28191 - Interpret DWARF 5 addrx locations

[Giuliano Procida <gprocida@google.com>]

Hi Dodji.

On Tue, 23 Nov 2021 at 17:15, Dodji Seketeli <dodji@seketeli.org> wrote:
>
> [I am adding Mark to the list recipients as I am going to ask him a
> question below]
>

Indeed, I forgot to CC him on the patch. Hi Mark.

>
> Hello,
>
> Giuliano Procida <gprocida@google.com> a écrit:
>
> > This change uses libdw facilities to interpret location expressions
> > instead of using libabigail's own mini-interpreter. With the fix for
> > elfutils https://sourceware.org/bugzilla/show_bug.cgi?id=28220 in
> > elfutils-0.186, abidw will correctly interpret Clang DWARF 5 symbol
> > addresses. Without that fix many declarations will not be linked to
> > their corresponding symbols due to the incorrect interpretation of
> > location attribute data.
> >
> >       * src/abg-dwarf-reader.cc (die_location_address): Use
> >       dwarf_attr_integrate, dwarf_getlocation and
> >       dwarf_getlocation_attr to decode addreses, instead of
> >       die_location_expr and eval_last_constant_dwarf_sub_expr.
> >       * tests/data/test-read-dwarf/PR25042-libgdbm-clang-dwarf5.so.6.0.0.abi:
> >       Refresh test reference output; two more symbols have types.
>
> Thanks for looking into that.
>
> It seems to me that we can also do away with the use of eval_last_constant_dwarf_sub_expr from
> die_member_offset.  Would that work on your testing binaries?
>

I think I originally wrote the code just before a trip away and didn't
have the time to look into the other callers then.

>
> From what I am seeing, dwarf_getlocation_attr and dwarf_getlocation are
> present in elfutils 0.176 which is the oldest version that we need to
> support, so we should be able to ditch eval_last_constant_dwarf_sub_expr
> and its dependencies altogether.
>
> Or what am I missing?
>

I think it would be good if we could rely on elfutils for this functionality.

I've had a go at die_member_offset and I think I have it working (at
least with the test suite). I'll clean up what I have and post it.
There is considerable overlap with the address function.

I haven't been able to get die_virtual_function_index to work as
dwarf_getlocation_attr fails.  There may be a simpler recipe to follow
here.

If/when the 3 existing callers are working, there may be some code in
common to factor out as a new die_location_expr function.

Regards,
Giuliano.

>
> [...]
>
> Cheers,
>
> --
>                 Dodji