[PATCH] Handle DW_FORM_implicit_const for DW_AT_decl_line

[Mark Wielaard]

Hi Tom,

On Sun, 2021-02-14 at 09:52 +0100, Tom de Vries wrote:
> due to the DW_AT_decl_line attribute having different forms,
> DW_FORM_data1 and
> DW_FORM_implicit_const.
> 
> Fix this in checksum_die and die_eq_1 by adding dedicated handling for
> DW_AT_decl_line, similar to how that's done for DW_AT_decl_file.
> 
> Any comments?

Yes, this makes sense. Like you said, we do something like this already
for decl/call_file. I think technically the die_eq_1 part could be put
under the same switch case. But maybe you find it clearer to do it
separately to mirror the checksum_die part?

Together with your DW_LANG_C_plus_plus_{03,11,14} patch it fixes the --
odr testsuite failures I was seeing.

As a follow up this might actually make sense for more attributes.
Where we know the attribute value is interpreted as an signed or
unsigned value (so we know what data[124] represents). This is actually
slightly tricky, because it isn't always immediately clear which
attribute values DWARF intends to be signed/unsigned, and it might even
differ per language (or whether or not an attribute is associated with
a [referenced] signed or unsigned type).

But the following seem to be always be unsigned values that might
qualify because they have unsigned constants assigned:

DW_AT_encoding
DW_AT_decimal_sign
DW_AT_endianity
DW_AT_accessibility
DW_AT_visibility
DW_AT_virtuality
DW_AT_language
DW_AT_address_class
DW_AT_identifier_case
DW_AT_calling_convention
DW_AT_inline
DW_AT_ordering
DW_AT_discr_list
DW_AT_defaulted

And the following qualify because they describe sizes, or counts, when
constant class:
DW_AT_byte_size
DW_AT_bit_size
DW_AT_count
DW_AT_digit_count
DW_AT_rank
DW_AT_string_length_bit_size
DW_AT_string_length_byte_size
DW_AT_alignment

As are these when constant class, indicating positive offsets
DW_AT_high_pc
DW_AT_start_scope
DW_AT_data_member_location
DW_AT_data_bit_offset

Cheers,

Mark