Re: [RFA/DWARF] constant class of DW_AT_high_pc is offset for version >=4 only.

[Mark Wielaard <mjw@redhat.com>]

On Tue, 2014-02-18 at 14:30 +0100, Joel Brobecker wrote:
>   1. The introduction of attr_value_as_address, to be used
>      in place of DW_ADDR when dealing with address attributes.
>      I left a few uses of this macro in the situations where
>      we actually know that the form is an address form.

This accepts any form as address/unsigned. I would at least check that
it is either DW_FORM_data4 or DW_FORM_data8 (even better would be to
check the CU address width too, although that would require to pass
around cu too, which might not be practical). Also I would add a comment
that this is really to work around buggy producers.

>   2. Instead of duplicating everywhere the conditions for
>      non-address forms in the handling of DW_AT_high_pc
>      attributes, I used the attr_form_is_constant function
>      instead.  It's not stricly the same, but I think it is
>      closer to the DWARF reference.

It is closer when used like you do, combined with a check for
cu->header.version >= 4.

> @@ -4201,7 +4217,7 @@ dwarf2_find_base_address (struct die_info *die, struct dwarf2_cu *cu)
>    attr = dwarf2_attr (die, DW_AT_entry_pc, cu);
>    if (attr)
>      {
> -      cu->base_address = DW_ADDR (attr);
> +      cu->base_address = attr_value_as_address (attr);
>        cu->base_known = 1;
>      }

Note that this might break for DWARF5. See http://dwarfstd.org/ShowIssue.php?issue=120719.1

In general I would only use attr_value_as_address for attributes (low_pc
and high_pc) which you know a buggy producer might encode with
DW_FORM_data[48].

Cheers,

Mark.