[DWARF] Add an api to get "interpreted" location lists

Summary:
This patch adds DWARFDie::getLocations, which returns the location
expressions for a given attribute (typically DW_AT_location). It handles
both "inline" locations and references to the external location list
sections (currently only of the DW_FORM_sec_offset type). It is
implemented on top of DWARFUnit::findLoclistFromOffset, which is also
added in this patch. I tried to make their signatures similar to the
equivalent range list functionality.

The actual location list interpretation logic is in
DWARFLocationTable::visitAbsoluteLocationList. This part is not
equivalent to the range list code, but this deviation is motivated by a
desire to reuse the same location list parsing code within lldb.

The functionality is tested via a c++ unit test of the DWARFDie API.

Reviewers: dblaikie, JDevlieghere, SouraVX

Subscribers: mgorny, hiraditya, cmtice, probinson, llvm-commits, aprantl

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D70394

1 files changed, 4 insertions, 1 deletions

diff --git a/llvm/lib/ObjectYAML/DWARFEmitter.cpp b/llvm/lib/ObjectYAML/DWARFEmitter.cpp
index 2ae66997cf5..b410fed16f0 100644
--- a/llvm/lib/ObjectYAML/DWARFEmitter.cpp
+++ b/llvm/lib/ObjectYAML/DWARFEmitter.cpp
@@ -314,7 +314,10 @@ public:
   DIEFixupVisitor(DWARFYAML::Data &DI) : DWARFYAML::Visitor(DI){};
 
 private:
-  virtual void onStartCompileUnit(DWARFYAML::Unit &CU) { Length = 7; }
+  virtual void onStartCompileUnit(DWARFYAML::Unit &CU) {
+    // Size of the unit header, excluding the length field itself.
+    Length = CU.Version >= 5 ? 8 : 7;
+  }
 
   virtual void onEndCompileUnit(DWARFYAML::Unit &CU) {
     CU.Length.setLength(Length);