[dsymutil] Emit label at the begin of a CU

When emitting a CU, store the MCSymbol pointing to the beginning of the
CU. We'll need this information later when emitting the .debug_names
section (DWARF5 accelerator table).

llvm-svn: 336433

2 files changed, 9 insertions, 0 deletions

diff --git a/llvm/tools/dsymutil/CompileUnit.h b/llvm/tools/dsymutil/CompileUnit.h
index d56f298360b..0f5efdd6805 100644
--- a/llvm/tools/dsymutil/CompileUnit.h
+++ b/llvm/tools/dsymutil/CompileUnit.h
@@ -247,11 +247,15 @@ public:
     ResolvedPaths[FileNum] = Path;
   }
 
+  MCSymbol *getLabelBegin() { return LabelBegin; }
+  void setLabelBegin(MCSymbol *S) { LabelBegin = S; }
+
 private:
   DWARFUnit &OrigUnit;
   unsigned ID;
   std::vector<DIEInfo> Info; ///< DIE info indexed by DIE index.
   Optional<BasicDIEUnit> NewUnit;
+  MCSymbol *LabelBegin = nullptr;
 
   uint64_t StartOffset;
   uint64_t NextUnitOffset;
diff --git a/llvm/tools/dsymutil/DwarfStreamer.cpp b/llvm/tools/dsymutil/DwarfStreamer.cpp
index 05034673e20..5bf23820dec 100644
--- a/llvm/tools/dsymutil/DwarfStreamer.cpp
+++ b/llvm/tools/dsymutil/DwarfStreamer.cpp
@@ -136,11 +136,16 @@ void DwarfStreamer::emitCompileUnitHeader(CompileUnit &Unit) {
   unsigned Version = Unit.getOrigUnit().getVersion();
   switchToDebugInfoSection(Version);
 
+  /// The start of the unit within its section.
+  Unit.setLabelBegin(Asm->createTempSymbol("cu_begin"));
+  Asm->OutStreamer->EmitLabel(Unit.getLabelBegin());
+
   // Emit size of content not including length itself. The size has already
   // been computed in CompileUnit::computeOffsets(). Subtract 4 to that size to
   // account for the length field.
   Asm->emitInt32(Unit.getNextUnitOffset() - Unit.getStartOffset() - 4);
   Asm->emitInt16(Version);
+
   // We share one abbreviations table across all units so it's always at the
   // start of the section.
   Asm->emitInt32(0);