https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94450
Tom de Vries <vries at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |tromey at gcc dot gnu.org
--- Comment #13 from Tom de Vries <vries at gcc dot gnu.org> ---
(In reply to rguent...@suse.de from comment #11)
> Note that as I read the DWARF spec changing the
> early CUs to DW_TAG_partial_unit and then again importing those
> (the spec suggests you need to import DW_TAG_partial_units) would
> not reflect documented semantics either.
It's not my understanding from the spec that DW_TAG_partial_units are required
to be imported. AFAIU, it's just that in all the use-cases there using
DW_TAG_partial_unit, an import happens to be required.
OK, so lets look at the use cases described in the spec at E.1.
I. classic dwz: factor out into partial unit, add imports:
...
DW_TAG_compile_unit
DW_AT_name cu1
L1: DIEx
DIEy
DW_AT_type L1
DW_TAG_compile_unit
DW_AT_name cu2
L2: DIEx
DIEz
DW_AT_type L2
->
L3: DW_TAG_partial_unit
L4: DIEx
DW_TAG_compile_unit
DW_TAG_imported_unit
DW_AT_import L3
DW_AT_name cu1
DIEy
DW_AT_type L4
DW_TAG_compile_unit
DW_TAG_imported_unit
DW_AT_import L3
DW_AT_name cu2
DIEz
DW_AT_type L4
...
II. dwz --devel-uni-lang --devel-gen-cu: factor out into DW_TAG_compile_unit,
no imports, exploit global namespace:
...
DW_TAG_compile_unit
DW_AT_name cu1
L1: DIEx
DIEy
DW_AT_type L1
DW_TAG_compile_unit
DW_AT_name cu2
L2: DIEx
DIEz
DW_AT_type L2
->
DW_TAG_compile_unit
L4: DIEx
DW_TAG_compile_unit
DW_AT_name cu1
DIEy
DW_AT_type L4
DW_TAG_compile_unit
DW_AT_name cu2
DIEz
DW_AT_type L4
...
III. #include in namespace:
...
DW_TAG_compile_unit
DW_AT_name cu1
DW_TAG_namespace bla1
L1: DIEx
DIEy
DW_AT_type L1
DW_TAG_compile_unit
DW_AT_name cu2
DW_TAG_namespace bla2
L2: DIEx
DIEz
DW_AT_type L2
->
L3: DW_TAG_partial_unit
L4: DIEx
DW_TAG_compile_unit
DW_AT_name cu1
DW_TAG_namespace bla1
DW_TAG_imported_unit
DW_AT_import L3
DIEy
DW_AT_type L4
DW_TAG_compile_unit
DW_AT_name cu2
DW_TAG_namespace bla2
DW_TAG_imported_unit
DW_AT_import L3
DIEz
DW_AT_type L4
...
So indeed, in all cases where DW_TAG_partial_unit is used, we use an import,
but that's because it's applicable to the transformation, and we're just doing
an entirely different transformation here:
...
DW_TAG_compile_unit
DW_AT_name cu1
DW_TAG_variable
DW_AT_name var1
DW_AT_location
->
DW_TAG_partial_unit
L1: DW_TAG_variable
DW_AT_name var1
DW_TAG_compile_unit
DW_AT_name cu1
DW_TAG_variable
DW_AT_abstract_origin L1
DW_AT_location
...
We fabricate a new abstract DW_TAG_variable DIE out of thin air, then try to
hide that fact by placing it in a DW_TAG_partial_unit, much like is done at
III. Only in contrast to III, we don't want to reintroduce it in another
context, we want it to keep hidden, so there's no import.
