jankratochvil added a comment.
In https://reviews.llvm.org/D32167#1062618, @clayborg wrote:
> we should be using the AST importer to import the type from that file into
> the AST for the current DWARF file. We do have done this with -gmodules
> already, so DWZ shouldn't be that different.
Is AST usable for imported declarations of `DW_TAG_variable`,
`DW_TAG_subprogram`, `DW_TAG_enumeration_type`+`DW_TAG_enumerator`s etc.? Still
imported `DW_TAG_partial_unit` cannot contain any code or data addresses which
may make it easier for AST.
================
Comment at: source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp:595
+ uint64_t debug_info_size = get_debug_info_data().GetByteSize();
+ data_segment.m_data.OffsetData(debug_info_size);
+ }
----------------
clayborg wrote:
> jankratochvil wrote:
> > I do not like this `DWARFDataExtractor::m_start` modification, it sort of
> > corrupts the `DataExtractor` and various operations stop working then -
> > such as `DWARFDataExtractor::GetByteSize()`. DWZ patch makes from current
> > `dw_offset_t` a virtual (remapped) offset and introduces new physical file
> > section offset which is looked up for data extraction. The file offset is
> > represented as `DWARFFileOffset` in D40474, instead of `bool m_is_dwz;`
> > there could be some `enum { DEBUG_INFO, DEBUG_TYPES, DWZ_DEBUG_INFO }
> > m_where;` instead.
> This means that this diff doesn't affect all of the other DWARF code. Nothing
> in .debug_types will refer to anything else (not DW_FORM_ref_addr, or any
> external references). So this trick allows us to just treat .debug_info as if
> .debug_types was appended to the end since nothing in .debug_types refers to
> any DIE outside of its type unit. This also mirrors what will actually happen
> with DWARF5 when all of the data is contained inside of the .debug_info
> section. This allows each DIE to have a unique "ID". Any other change
> requires a lot of changes to the DWARF parser and logic. So I actually like
> this feature. We can fix the GetByteSize() if needed. Basically every object
> in DWARf right now must be able to make a unique 64 bit unsigned integer ID
> in some way that we can get back to that info and partially parse more. These
> are handed out as lldb::user_id_t values for types, functions and more. Each
> flavor of DWARF will encode what they want into here. The normal DWARF it is
> just the absolute offset within the .debug_info. With .debug_types we just
> add the size of the .debug_info to the ID. For DWARF in .o files on Darwin,
> we encode the compile unit index into the top 32 bits and the DIE offset into
> the lower, DWO does something just as DWZ will need to. DWARFFileOffset
> doesn't mean much if there are multiple files. We have many competing type
> uniquing/debug info size reduction strategies being employed here. I can't
> believe we have DWO, DWZ, and debug types... But we have to make them all
> work. We can't just use the absolute file offset because DWO used external
> files where the file offsets could be the same in the external .o files...
> Not sure how this works with DWZ or what the best option is. I will read up
> on DWZ so I can propose some viable options. But each new flavor of the day
> that gets added the DWARF parser is adding a bunch of logic and edge cases.
> If two technologies (DWZ + DWO, DWZ + debug_types, etc) are used together, we
> need to ensure they can.
> Any other change requires a lot of changes to the DWARF parser and logic. So
> I actually like this feature.
I agree it is a fine quick&dirty hack. Just if my DWZ support gets accepted
later anyway then this `.debug_types` feature could be implemented by its
framework in a clean way (as a regular DIEs remapping which is required for DWZ
anyway).
> If two technologies (DWZ + DWO, DWZ + debug_types, etc) are used together, we
> need to ensure they can.
`DWZ + DWO` do not make sense to me. I haven't tried to use DWZ for DWO but
DWZ finds common DWARF subtrees typically across CUs so it would not find much.
`DWZ + debug_types` is explicitly supported by the DWZ tool although that is
IMO for compatibility only, DWZ can make the common type references slightly
smaller than debug_types. I will sure need to implement debug_types support
into my DWZ-for-LLDB patchset later.
https://reviews.llvm.org/D32167
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