[Lldb-commits] [PATCH] D63428: DWARF: Add "dwo_num" field to the DIERef class

[Pavel Labath via Phabricator via lldb-commits]

labath created this revision.
labath added reviewers: JDevlieghere, clayborg, aprantl.
Herald added subscribers: arphaman, dexonsmith, mehdi_amini.

When dwo support was introduced, it used a trick where debug info
entries were referenced by the offset of the compile unit in the main
file, but the die offset was relative to the dwo file. Although there
was some elegance to it, this representation was starting to reach its
breaking point:

- the fact that the skeleton compile unit owned the DWO file meant that it was impossible (or at least hard and unintuitive) to support DWO files containing more than one compile unit. These kinds of files are produced by LTO for example.
- it made it impossible to reference any DIEs in the skeleton compile unit (although the skeleton units are generally empty, clang still puts some info into them with -fsplit-dwarf-inlining).
- (current motivation) it made it very hard to support type units placed in DWO files, as type units don't have any skeleton units which could be referenced in the main file

This patch addresses this problem by introducing an additional
"dwo_num" field to the DIERef class, whose purpose is to identify the
dwo file. It's kind of similar to the dwo_id field in DWARF5 unit
headers, but while this is a 64bit hash whose main purpose is to catch
file mismatches, this is just a smaller integer used to indentify a
loaded dwo file. Currently, this is based on the index of the skeleton
compile unit which owns the dwo file, but it is intended to be
eventually independent of that (to support the LTO use case).

Simultaneously the unit_offset field is changed to reference the compile
unit containing the referenced die instead of the main unit. This means
we can remove the "BaseObjectOffset" field from the DWARFUnit class. It
also means we can remove some of the workarounds put in place to support
the skeleton-unit+dwo-die combo. More work is needed to remove all of
them, which is out of scope of this patch.


https://reviews.llvm.org/D63428

Files:
  source/Plugins/SymbolFile/DWARF/AppleDWARFIndex.cpp
  source/Plugins/SymbolFile/DWARF/AppleDWARFIndex.h
  source/Plugins/SymbolFile/DWARF/DIERef.cpp
  source/Plugins/SymbolFile/DWARF/DIERef.h
  source/Plugins/SymbolFile/DWARF/DWARFBaseDIE.cpp
  source/Plugins/SymbolFile/DWARF/DWARFDIE.cpp
  source/Plugins/SymbolFile/DWARF/DWARFDebugInfoEntry.cpp
  source/Plugins/SymbolFile/DWARF/DWARFIndex.cpp
  source/Plugins/SymbolFile/DWARF/DWARFIndex.h
  source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp
  source/Plugins/SymbolFile/DWARF/DWARFUnit.h
  source/Plugins/SymbolFile/DWARF/DebugNamesDWARFIndex.cpp
  source/Plugins/SymbolFile/DWARF/DebugNamesDWARFIndex.h
  source/Plugins/SymbolFile/DWARF/HashedNameToDIE.h
  source/Plugins/SymbolFile/DWARF/ManualDWARFIndex.cpp
  source/Plugins/SymbolFile/DWARF/ManualDWARFIndex.h
  source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
  source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.h
  source/Plugins/SymbolFile/DWARF/SymbolFileDWARFDwo.cpp
  source/Plugins/SymbolFile/DWARF/SymbolFileDWARFDwo.h

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