[Dwarf-discuss] .debug_cu_index question

David Blaikie dblaikie@gmail.com
Fri Dec 20 18:05:47 GMT 2024


On Fri, Dec 20, 2024 at 9:36 AM David Anderson via Dwarf-discuss <
dwarf-discuss@lists.dwarfstd.org> wrote:

>
> The examples of .debug_tu_index in DWARF5 Section F.2.3
> show the hash as computed  by Type Signature Computation
> Section 7.32 and referenced by DW_AT_LOCATION DW_FORM_ref_sig8.
>

do you mean DW_AT_signature, rather than DW_AT_location? (I don't think
I've seen/heard of DW_AT_location+DW_FORM_ref_sig8)


> Ok. I was thinking of this incorrectly before. It's not
> visible as a whole-CU index.  I think.
> See pages 412, 413.
>

I'm not sure what you mean by "visible as a whole-CU index" - could you
speak more to this?


> The examples of .debug_cu_index in DWARF5 Section F.2.3
> do not really show where/how a calculated hash is used.
>

If you're looking for info on the cu/tu_index, the wording you're looking
for is "package files" (F.3 DWARF package file example, and 7.3.5 for
instance).


> Text on page 411, line 6 is relevant.
>
> One example object I have on hand (not a recent
> one) shows a CU header  signature
> of   0x60ff5d2827dca832
> and that same signature in a hash field in .debug_cu_index.
> (the examples in DWARF5 do not mention the connection to
> the CU header signature).
>

I believe they all refer to it as the "compilation unit ID" both in the
description of the dwo_id field in the (skeleton and split full) unit
header and in the documentation for the index/packaging format


>
> Would that mean .debug_cu_index just uses the CU header signature
> by borrowing  a precomputed hash from the CU header?
>
> That means      .debug_cu_index is a whole-CU index?
>

.debug_cu_index provides an index for all CUs in the .dwp file, yes. (which
should contain split full units for all the skeleton units in the matched
binary)


>
>
>
>
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