[Dwarf-discuss] Question on Clang 18.1.8 and DW_IDX_parent

[David Blaikie]

Some context:
https://discourse.llvm.org/t/rfc-improve-dwarf-5-debug-names-type-lookup-parsing-speed/74151/44
https://github.com/llvm/llvm-project/pull/77457

Essentially clang/llvm produces DW_IDX_parent with DW_FORM_flag_present
when the entry has a parent, but that parent isn't indexed (I think this
mostly comes up for the entities that are direct children of the unit DIE).

This is designed to make it more efficient for consumers (lldb, in
particular) to do quicker comparisons from the index for qualified names.

My vague recollection is the idea that the consumer needs that info to know
the difference between "this thing may or may not have a parent" and "this
thing has an unnamed/unindexed parent".

On Sat, Aug 31, 2024 at 1:03 PM David Anderson via Dwarf-discuss <
dwarf-discuss@lists.dwarfstd.org> wrote:

> Dwarf5. The Name Table .debug_names
>
> Background:
> 6.1.1.2, page 141
> Parent debugging information entry, a reference to the
> index entry for the parent. This is represented as the
> offset of the entry relative to the start of the entry
> pool.
>
> Table 7.232 Name index attribute encodings
>        DW_IDX_parent constant
>
>
> However clang version 18.1.8 generates
>
> DW_IDX_parent      DW_FORM_flag_present
> when there is no parent entry to refer to.
>
> And that does not seem to match what DWARF5
> says to do.
>
> So what is 'true' supposed to mean for DW_IDX_parent?
>
> A bit puzzled here.
> Thanks for any insight.
> David Anderson
>
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