[codeview] Make obj2yaml/yaml2obj support .debug$S/T sections.

This allows us to use yaml2obj and obj2yaml to round-trip CodeView
symbol and type information without having to manually specify the bytes
of the section. This makes for much easier to maintain tests. See the
tests under lld/COFF in this patch for example. Before they just said
SectionData: <blob> whereas now we can use meaningful record
descriptions. Note that it still supports the SectionData yaml field,
which could be useful for initializing a section to invalid bytes for
testing, for example.

Differential Revision: https://reviews.llvm.org/D34127

llvm-svn: 305366

10 files changed, 268 insertions, 198 deletions

diff --git a/llvm/lib/DebugInfo/CodeView/CMakeLists.txt b/llvm/lib/DebugInfo/CodeView/CMakeLists.txt
index 2f9e8981b69..f916695a843 100644
--- a/llvm/lib/DebugInfo/CodeView/CMakeLists.txt
+++ b/llvm/lib/DebugInfo/CodeView/CMakeLists.txt
@@ -20,6 +20,7 @@ add_llvm_library(LLVMDebugInfoCodeView
   LazyRandomTypeCollection.cpp
   Line.cpp
   RecordSerialization.cpp
+  StringsAndChecksums.cpp
   SymbolRecordMapping.cpp
   SymbolDumper.cpp
   SymbolSerializer.cpp
@@ -32,7 +33,7 @@ add_llvm_library(LLVMDebugInfoCodeView
   TypeSerializer.cpp
   TypeStreamMerger.cpp
   TypeTableCollection.cpp
-  
+
   ADDITIONAL_HEADER_DIRS
   ${LLVM_MAIN_INCLUDE_DIR}/llvm/DebugInfo/CodeView
   )
diff --git a/llvm/lib/DebugInfo/CodeView/DebugStringTableSubsection.cpp b/llvm/lib/DebugInfo/CodeView/DebugStringTableSubsection.cpp
index 6e647c4b976..de02525270c 100644
--- a/llvm/lib/DebugInfo/CodeView/DebugStringTableSubsection.cpp
+++ b/llvm/lib/DebugInfo/CodeView/DebugStringTableSubsection.cpp
@@ -58,6 +58,10 @@ Error DebugStringTableSubsection::commit(BinaryStreamWriter &Writer) const {
   uint32_t Begin = Writer.getOffset();
   uint32_t End = Begin + StringSize;
 
+  // Write a null string at the beginning.
+  if (auto EC = Writer.writeCString(StringRef()))
+    return EC;
+
   for (auto &Pair : Strings) {
     StringRef S = Pair.getKey();
     uint32_t Offset = Begin + Pair.getValue();
@@ -68,6 +72,7 @@ Error DebugStringTableSubsection::commit(BinaryStreamWriter &Writer) const {
   }
 
   Writer.setOffset(End);
+  assert((End - Begin) == StringSize);
   return Error::success();
 }
 
diff --git a/llvm/lib/DebugInfo/CodeView/DebugSubsectionRecord.cpp b/llvm/lib/DebugInfo/CodeView/DebugSubsectionRecord.cpp
index e9124e68fe8..334c5e002bb 100644
--- a/llvm/lib/DebugInfo/CodeView/DebugSubsectionRecord.cpp
+++ b/llvm/lib/DebugInfo/CodeView/DebugSubsectionRecord.cpp
@@ -50,7 +50,7 @@ DebugSubsectionKind DebugSubsectionRecord::kind() const { return Kind; }
 BinaryStreamRef DebugSubsectionRecord::getRecordData() const { return Data; }
 
 DebugSubsectionRecordBuilder::DebugSubsectionRecordBuilder(
-    std::unique_ptr<DebugSubsection> Subsection, CodeViewContainer Container)
+    std::shared_ptr<DebugSubsection> Subsection, CodeViewContainer Container)
     : Subsection(std::move(Subsection)), Container(Container) {}
 
 uint32_t DebugSubsectionRecordBuilder::calculateSerializedLength() {
diff --git a/llvm/lib/DebugInfo/CodeView/DebugSubsectionVisitor.cpp b/llvm/lib/DebugInfo/CodeView/DebugSubsectionVisitor.cpp
index 8550107741c..9b824333369 100644
--- a/llvm/lib/DebugInfo/CodeView/DebugSubsectionVisitor.cpp
+++ b/llvm/lib/DebugInfo/CodeView/DebugSubsectionVisitor.cpp
@@ -26,40 +26,9 @@
 using namespace llvm;
 using namespace llvm::codeview;
 
-DebugSubsectionState::DebugSubsectionState() {}
-
-DebugSubsectionState::DebugSubsectionState(
-    const DebugStringTableSubsectionRef &Strings)
-    : Strings(&Strings) {}
-
-DebugSubsectionState::DebugSubsectionState(
-    const DebugStringTableSubsectionRef &Strings,
-    const DebugChecksumsSubsectionRef &Checksums)
-    : Strings(&Strings), Checksums(&Checksums) {}
-
-void DebugSubsectionState::initializeStrings(const DebugSubsectionRecord &SR) {
-  assert(SR.kind() == DebugSubsectionKind::StringTable);
-  assert(!Strings && "Found a string table even though we already have one!");
-
-  OwnedStrings = llvm::make_unique<DebugStringTableSubsectionRef>();
-  consumeError(OwnedStrings->initialize(SR.getRecordData()));
-  Strings = OwnedStrings.get();
-}
-
-void DebugSubsectionState::initializeChecksums(
-    const DebugSubsectionRecord &FCR) {
-  assert(FCR.kind() == DebugSubsectionKind::FileChecksums);
-  if (Checksums)
-    return;
-
-  OwnedChecksums = llvm::make_unique<DebugChecksumsSubsectionRef>();
-  consumeError(OwnedChecksums->initialize(FCR.getRecordData()));
-  Checksums = OwnedChecksums.get();
-}
-
-Error llvm::codeview::visitDebugSubsection(const DebugSubsectionRecord &R,
-                                           DebugSubsectionVisitor &V,
-                                           const DebugSubsectionState &State) {
+Error llvm::codeview::visitDebugSubsection(
+    const DebugSubsectionRecord &R, DebugSubsectionVisitor &V,
+    const StringsAndChecksumsRef &State) {
   BinaryStreamReader Reader(R.getRecordData());
   switch (R.kind()) {
   case DebugSubsectionKind::Lines: {
diff --git a/llvm/lib/DebugInfo/CodeView/StringsAndChecksums.cpp b/llvm/lib/DebugInfo/CodeView/StringsAndChecksums.cpp
new file mode 100644
index 00000000000..ccd9aba45ea
--- /dev/null
+++ b/llvm/lib/DebugInfo/CodeView/StringsAndChecksums.cpp
@@ -0,0 +1,48 @@
+//===- StringsAndChecksums.cpp ----------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/DebugInfo/CodeView/StringsAndChecksums.h"
+#include "llvm/DebugInfo/CodeView/DebugChecksumsSubsection.h"
+#include "llvm/DebugInfo/CodeView/DebugStringTableSubsection.h"
+#include "llvm/DebugInfo/CodeView/DebugSubsectionRecord.h"
+
+using namespace llvm;
+using namespace llvm::codeview;
+
+StringsAndChecksumsRef::StringsAndChecksumsRef() {}
+
+StringsAndChecksumsRef::StringsAndChecksumsRef(
+    const DebugStringTableSubsectionRef &Strings)
+    : Strings(&Strings) {}
+
+StringsAndChecksumsRef::StringsAndChecksumsRef(
+    const DebugStringTableSubsectionRef &Strings,
+    const DebugChecksumsSubsectionRef &Checksums)
+    : Strings(&Strings), Checksums(&Checksums) {}
+
+void StringsAndChecksumsRef::initializeStrings(
+    const DebugSubsectionRecord &SR) {
+  assert(SR.kind() == DebugSubsectionKind::StringTable);
+  assert(!Strings && "Found a string table even though we already have one!");
+
+  OwnedStrings = llvm::make_unique<DebugStringTableSubsectionRef>();
+  consumeError(OwnedStrings->initialize(SR.getRecordData()));
+  Strings = OwnedStrings.get();
+}
+
+void StringsAndChecksumsRef::initializeChecksums(
+    const DebugSubsectionRecord &FCR) {
+  assert(FCR.kind() == DebugSubsectionKind::FileChecksums);
+  if (Checksums)
+    return;
+
+  OwnedChecksums = llvm::make_unique<DebugChecksumsSubsectionRef>();
+  consumeError(OwnedChecksums->initialize(FCR.getRecordData()));
+  Checksums = OwnedChecksums.get();
+}
diff --git a/llvm/lib/DebugInfo/PDB/Native/DbiModuleDescriptorBuilder.cpp b/llvm/lib/DebugInfo/PDB/Native/DbiModuleDescriptorBuilder.cpp
index 396dffaa68b..81a9d3eeec6 100644
--- a/llvm/lib/DebugInfo/PDB/Native/DbiModuleDescriptorBuilder.cpp
+++ b/llvm/lib/DebugInfo/PDB/Native/DbiModuleDescriptorBuilder.cpp
@@ -177,7 +177,7 @@ Error DbiModuleDescriptorBuilder::commit(BinaryStreamWriter &ModiWriter,
 }
 
 void DbiModuleDescriptorBuilder::addDebugSubsection(
-    std::unique_ptr<DebugSubsection> Subsection) {
+    std::shared_ptr<DebugSubsection> Subsection) {
   assert(Subsection);
   C13Builders.push_back(llvm::make_unique<DebugSubsectionRecordBuilder>(
       std::move(Subsection), CodeViewContainer::Pdb));
diff --git a/llvm/lib/DebugInfo/PDB/Native/PDBStringTableBuilder.cpp b/llvm/lib/DebugInfo/PDB/Native/PDBStringTableBuilder.cpp
index a472181a489..90acfadd311 100644
--- a/llvm/lib/DebugInfo/PDB/Native/PDBStringTableBuilder.cpp
+++ b/llvm/lib/DebugInfo/PDB/Native/PDBStringTableBuilder.cpp
@@ -52,6 +52,11 @@ uint32_t PDBStringTableBuilder::calculateSerializedSize() const {
   return Size;
 }
 
+void PDBStringTableBuilder::setStrings(
+    const codeview::DebugStringTableSubsection &Strings) {
+  this->Strings = Strings;
+}
+
 Error PDBStringTableBuilder::writeHeader(BinaryStreamWriter &Writer) const {
   // Write a header
   PDBStringTableHeader H;
diff --git a/llvm/lib/ObjectYAML/COFFYAML.cpp b/llvm/lib/ObjectYAML/COFFYAML.cpp
index 7f9f4c1f8c2..c8cbea1490f 100644
--- a/llvm/lib/ObjectYAML/COFFYAML.cpp
+++ b/llvm/lib/ObjectYAML/COFFYAML.cpp
@@ -488,7 +488,16 @@ void MappingTraits<COFFYAML::Section>::mapping(IO &IO, COFFYAML::Section &Sec) {
   IO.mapOptional("VirtualAddress", Sec.Header.VirtualAddress, 0U);
   IO.mapOptional("VirtualSize", Sec.Header.VirtualSize, 0U);
   IO.mapOptional("Alignment", Sec.Alignment, 0U);
-  IO.mapRequired("SectionData", Sec.SectionData);
+
+  // If this is a .debug$S or .debug$T section parse the semantic representation
+  // of the symbols/types.  If it is any other kind of section, just deal in raw
+  // bytes.
+  IO.mapOptional("SectionData", Sec.SectionData);
+  if (Sec.Name == ".debug$S")
+    IO.mapOptional("Subsections", Sec.DebugS);
+  else if (Sec.Name == ".debug$T")
+    IO.mapOptional("Types", Sec.DebugT);
+
   IO.mapOptional("Relocations", Sec.Relocations);
 }
 
diff --git a/llvm/lib/ObjectYAML/CodeViewYAMLDebugSections.cpp b/llvm/lib/ObjectYAML/CodeViewYAMLDebugSections.cpp
index 08a4bb715fa..aa5f3cca10f 100644
--- a/llvm/lib/ObjectYAML/CodeViewYAMLDebugSections.cpp
+++ b/llvm/lib/ObjectYAML/CodeViewYAMLDebugSections.cpp
@@ -28,6 +28,7 @@
 #include "llvm/DebugInfo/CodeView/DebugSymbolRVASubsection.h"
 #include "llvm/DebugInfo/CodeView/DebugSymbolsSubsection.h"
 #include "llvm/DebugInfo/CodeView/EnumTables.h"
+#include "llvm/DebugInfo/CodeView/StringsAndChecksums.h"
 #include "llvm/DebugInfo/CodeView/SymbolRecord.h"
 #include "llvm/DebugInfo/CodeView/SymbolSerializer.h"
 #include "llvm/ObjectYAML/CodeViewYAMLSymbols.h"
@@ -75,10 +76,9 @@ struct YAMLSubsectionBase {
   virtual ~YAMLSubsectionBase() {}
 
   virtual void map(IO &IO) = 0;
-  virtual std::unique_ptr<DebugSubsection>
+  virtual std::shared_ptr<DebugSubsection>
   toCodeViewSubsection(BumpPtrAllocator &Allocator,
-                       DebugStringTableSubsection *UseStrings,
-                       DebugChecksumsSubsection *UseChecksums) const = 0;
+                       const codeview::StringsAndChecksums &SC) const = 0;
 };
 }
 }
@@ -90,10 +90,9 @@ struct YAMLChecksumsSubsection : public YAMLSubsectionBase {
       : YAMLSubsectionBase(DebugSubsectionKind::FileChecksums) {}
 
   void map(IO &IO) override;
-  std::unique_ptr<DebugSubsection>
+  std::shared_ptr<DebugSubsection>
   toCodeViewSubsection(BumpPtrAllocator &Allocator,
-                       DebugStringTableSubsection *Strings,
-                       DebugChecksumsSubsection *Checksums) const override;
+                       const codeview::StringsAndChecksums &SC) const override;
   static Expected<std::shared_ptr<YAMLChecksumsSubsection>>
   fromCodeViewSubsection(const DebugStringTableSubsectionRef &Strings,
                          const DebugChecksumsSubsectionRef &FC);
@@ -105,10 +104,9 @@ struct YAMLLinesSubsection : public YAMLSubsectionBase {
   YAMLLinesSubsection() : YAMLSubsectionBase(DebugSubsectionKind::Lines) {}
 
   void map(IO &IO) override;
-  std::unique_ptr<DebugSubsection>
+  std::shared_ptr<DebugSubsection>
   toCodeViewSubsection(BumpPtrAllocator &Allocator,
-                       DebugStringTableSubsection *Strings,
-                       DebugChecksumsSubsection *Checksums) const override;
+                       const codeview::StringsAndChecksums &SC) const override;
   static Expected<std::shared_ptr<YAMLLinesSubsection>>
   fromCodeViewSubsection(const DebugStringTableSubsectionRef &Strings,
                          const DebugChecksumsSubsectionRef &Checksums,
@@ -122,10 +120,9 @@ struct YAMLInlineeLinesSubsection : public YAMLSubsectionBase {
       : YAMLSubsectionBase(DebugSubsectionKind::InlineeLines) {}
 
   void map(IO &IO) override;
-  std::unique_ptr<DebugSubsection>
+  std::shared_ptr<DebugSubsection>
   toCodeViewSubsection(BumpPtrAllocator &Allocator,
-                       DebugStringTableSubsection *Strings,
-                       DebugChecksumsSubsection *Checksums) const override;
+                       const codeview::StringsAndChecksums &SC) const override;
   static Expected<std::shared_ptr<YAMLInlineeLinesSubsection>>
   fromCodeViewSubsection(const DebugStringTableSubsectionRef &Strings,
                          const DebugChecksumsSubsectionRef &Checksums,
@@ -139,10 +136,9 @@ struct YAMLCrossModuleExportsSubsection : public YAMLSubsectionBase {
       : YAMLSubsectionBase(DebugSubsectionKind::CrossScopeExports) {}
 
   void map(IO &IO) override;
-  std::unique_ptr<DebugSubsection>
+  std::shared_ptr<DebugSubsection>
   toCodeViewSubsection(BumpPtrAllocator &Allocator,
-                       DebugStringTableSubsection *Strings,
-                       DebugChecksumsSubsection *Checksums) const override;
+                       const codeview::StringsAndChecksums &SC) const override;
   static Expected<std::shared_ptr<YAMLCrossModuleExportsSubsection>>
   fromCodeViewSubsection(const DebugCrossModuleExportsSubsectionRef &Exports);
 
@@ -154,10 +150,9 @@ struct YAMLCrossModuleImportsSubsection : public YAMLSubsectionBase {
       : YAMLSubsectionBase(DebugSubsectionKind::CrossScopeImports) {}
 
   void map(IO &IO) override;
-  std::unique_ptr<DebugSubsection>
+  std::shared_ptr<DebugSubsection>
   toCodeViewSubsection(BumpPtrAllocator &Allocator,
-                       DebugStringTableSubsection *Strings,
-                       DebugChecksumsSubsection *Checksums) const override;
+                       const codeview::StringsAndChecksums &SC) const override;
   static Expected<std::shared_ptr<YAMLCrossModuleImportsSubsection>>
   fromCodeViewSubsection(const DebugStringTableSubsectionRef &Strings,
                          const DebugCrossModuleImportsSubsectionRef &Imports);
@@ -169,10 +164,9 @@ struct YAMLSymbolsSubsection : public YAMLSubsectionBase {
   YAMLSymbolsSubsection() : YAMLSubsectionBase(DebugSubsectionKind::Symbols) {}
 
   void map(IO &IO) override;
-  std::unique_ptr<DebugSubsection>
+  std::shared_ptr<DebugSubsection>
   toCodeViewSubsection(BumpPtrAllocator &Allocator,
-                       DebugStringTableSubsection *Strings,
-                       DebugChecksumsSubsection *Checksums) const override;
+                       const codeview::StringsAndChecksums &SC) const override;
   static Expected<std::shared_ptr<YAMLSymbolsSubsection>>
   fromCodeViewSubsection(const DebugSymbolsSubsectionRef &Symbols);
 
@@ -184,10 +178,9 @@ struct YAMLStringTableSubsection : public YAMLSubsectionBase {
       : YAMLSubsectionBase(DebugSubsectionKind::StringTable) {}
 
   void map(IO &IO) override;
-  std::unique_ptr<DebugSubsection>
+  std::shared_ptr<DebugSubsection>
   toCodeViewSubsection(BumpPtrAllocator &Allocator,
-                       DebugStringTableSubsection *Strings,
-                       DebugChecksumsSubsection *Checksums) const override;
+                       const codeview::StringsAndChecksums &SC) const override;
   static Expected<std::shared_ptr<YAMLStringTableSubsection>>
   fromCodeViewSubsection(const DebugStringTableSubsectionRef &Strings);
 
@@ -199,10 +192,9 @@ struct YAMLFrameDataSubsection : public YAMLSubsectionBase {
       : YAMLSubsectionBase(DebugSubsectionKind::FrameData) {}
 
   void map(IO &IO) override;
-  std::unique_ptr<DebugSubsection>
+  std::shared_ptr<DebugSubsection>
   toCodeViewSubsection(BumpPtrAllocator &Allocator,
-                       DebugStringTableSubsection *Strings,
-                       DebugChecksumsSubsection *Checksums) const override;
+                       const codeview::StringsAndChecksums &SC) const override;
   static Expected<std::shared_ptr<YAMLFrameDataSubsection>>
   fromCodeViewSubsection(const DebugStringTableSubsectionRef &Strings,
                          const DebugFrameDataSubsectionRef &Frames);
@@ -215,10 +207,9 @@ struct YAMLCoffSymbolRVASubsection : public YAMLSubsectionBase {
       : YAMLSubsectionBase(DebugSubsectionKind::CoffSymbolRVA) {}
 
   void map(IO &IO) override;
-  std::unique_ptr<DebugSubsection>
+  std::shared_ptr<DebugSubsection>
   toCodeViewSubsection(BumpPtrAllocator &Allocator,
-                       DebugStringTableSubsection *Strings,
-                       DebugChecksumsSubsection *Checksums) const override;
+                       const codeview::StringsAndChecksums &SC) const override;
   static Expected<std::shared_ptr<YAMLCoffSymbolRVASubsection>>
   fromCodeViewSubsection(const DebugSymbolRVASubsectionRef &RVAs);
 
@@ -400,23 +391,23 @@ findChecksums(ArrayRef<YAMLDebugSubsection> Subsections) {
   return nullptr;
 }
 
-std::unique_ptr<DebugSubsection> YAMLChecksumsSubsection::toCodeViewSubsection(
-    BumpPtrAllocator &Allocator, DebugStringTableSubsection *UseStrings,
-    DebugChecksumsSubsection *UseChecksums) const {
-  assert(UseStrings && !UseChecksums);
-  auto Result = llvm::make_unique<DebugChecksumsSubsection>(*UseStrings);
+std::shared_ptr<DebugSubsection> YAMLChecksumsSubsection::toCodeViewSubsection(
+    BumpPtrAllocator &Allocator,
+    const codeview::StringsAndChecksums &SC) const {
+  assert(SC.hasStrings());
+  auto Result = std::make_shared<DebugChecksumsSubsection>(*SC.strings());
   for (const auto &CS : Checksums) {
     Result->addChecksum(CS.FileName, CS.Kind, CS.ChecksumBytes.Bytes);
   }
   return std::move(Result);
 }
 
-std::unique_ptr<DebugSubsection> YAMLLinesSubsection::toCodeViewSubsection(
-    BumpPtrAllocator &Allocator, DebugStringTableSubsection *UseStrings,
-    DebugChecksumsSubsection *UseChecksums) const {
-  assert(UseStrings && UseChecksums);
+std::shared_ptr<DebugSubsection> YAMLLinesSubsection::toCodeViewSubsection(
+    BumpPtrAllocator &Allocator,
+    const codeview::StringsAndChecksums &SC) const {
+  assert(SC.hasStrings() && SC.hasChecksums());
   auto Result =
-      llvm::make_unique<DebugLinesSubsection>(*UseChecksums, *UseStrings);
+      std::make_shared<DebugLinesSubsection>(*SC.checksums(), *SC.strings());
   Result->setCodeSize(Lines.CodeSize);
   Result->setRelocationAddress(Lines.RelocSegment, Lines.RelocOffset);
   Result->setFlags(Lines.Flags);
@@ -438,16 +429,16 @@ std::unique_ptr<DebugSubsection> YAMLLinesSubsection::toCodeViewSubsection(
       }
     }
   }
-  return llvm::cast<DebugSubsection>(std::move(Result));
+  return std::move(Result);
 }
 
-std::unique_ptr<DebugSubsection>
+std::shared_ptr<DebugSubsection>
 YAMLInlineeLinesSubsection::toCodeViewSubsection(
-    BumpPtrAllocator &Allocator, DebugStringTableSubsection *UseStrings,
-    DebugChecksumsSubsection *UseChecksums) const {
-  assert(UseChecksums);
-  auto Result = llvm::make_unique<DebugInlineeLinesSubsection>(
-      *UseChecksums, InlineeLines.HasExtraFiles);
+    BumpPtrAllocator &Allocator,
+    const codeview::StringsAndChecksums &SC) const {
+  assert(SC.hasChecksums());
+  auto Result = std::make_shared<DebugInlineeLinesSubsection>(
+      *SC.checksums(), InlineeLines.HasExtraFiles);
 
   for (const auto &Site : InlineeLines.Sites) {
     Result->addInlineSite(TypeIndex(Site.Inlinee), Site.FileName,
@@ -459,55 +450,59 @@ YAMLInlineeLinesSubsection::toCodeViewSubsection(
       Result->addExtraFile(EF);
     }
   }
-  return llvm::cast<DebugSubsection>(std::move(Result));
+  return std::move(Result);
 }
 
-std::unique_ptr<DebugSubsection>
+std::shared_ptr<DebugSubsection>
 YAMLCrossModuleExportsSubsection::toCodeViewSubsection(
-    BumpPtrAllocator &Allocator, DebugStringTableSubsection *Strings,
-    DebugChecksumsSubsection *Checksums) const {
-  auto Result = llvm::make_unique<DebugCrossModuleExportsSubsection>();
+    BumpPtrAllocator &Allocator,
+    const codeview::StringsAndChecksums &SC) const {
+  auto Result = std::make_shared<DebugCrossModuleExportsSubsection>();
   for (const auto &M : Exports)
     Result->addMapping(M.Local, M.Global);
-  return llvm::cast<DebugSubsection>(std::move(Result));
+  return std::move(Result);
 }
 
-std::unique_ptr<DebugSubsection>
+std::shared_ptr<DebugSubsection>
 YAMLCrossModuleImportsSubsection::toCodeViewSubsection(
-    BumpPtrAllocator &Allocator, DebugStringTableSubsection *Strings,
-    DebugChecksumsSubsection *Checksums) const {
-  auto Result = llvm::make_unique<DebugCrossModuleImportsSubsection>(*Strings);
+    BumpPtrAllocator &Allocator,
+    const codeview::StringsAndChecksums &SC) const {
+  assert(SC.hasStrings());
+
+  auto Result =
+      std::make_shared<DebugCrossModuleImportsSubsection>(*SC.strings());
   for (const auto &M : Imports) {
     for (const auto Id : M.ImportIds)
       Result->addImport(M.ModuleName, Id);
   }
-  return llvm::cast<DebugSubsection>(std::move(Result));
+  return std::move(Result);
 }
 
-std::unique_ptr<DebugSubsection> YAMLSymbolsSubsection::toCodeViewSubsection(
-    BumpPtrAllocator &Allocator, DebugStringTableSubsection *Strings,
-    DebugChecksumsSubsection *Checksums) const {
-  auto Result = llvm::make_unique<DebugSymbolsSubsection>();
+std::shared_ptr<DebugSubsection> YAMLSymbolsSubsection::toCodeViewSubsection(
+    BumpPtrAllocator &Allocator,
+    const codeview::StringsAndChecksums &SC) const {
+  auto Result = std::make_shared<DebugSymbolsSubsection>();
   for (const auto &Sym : Symbols)
     Result->addSymbol(
         Sym.toCodeViewSymbol(Allocator, CodeViewContainer::ObjectFile));
   return std::move(Result);
 }
 
-std::unique_ptr<DebugSubsection>
+std::shared_ptr<DebugSubsection>
 YAMLStringTableSubsection::toCodeViewSubsection(
-    BumpPtrAllocator &Allocator, DebugStringTableSubsection *Strings,
-    DebugChecksumsSubsection *Checksums) const {
-  auto Result = llvm::make_unique<DebugStringTableSubsection>();
+    BumpPtrAllocator &Allocator,
+    const codeview::StringsAndChecksums &SC) const {
+  auto Result = std::make_shared<DebugStringTableSubsection>();
   for (const auto &Str : this->Strings)
     Result->insert(Str);
   return std::move(Result);
 }
 
-std::unique_ptr<DebugSubsection> YAMLFrameDataSubsection::toCodeViewSubsection(
-    BumpPtrAllocator &Allocator, DebugStringTableSubsection *Strings,
-    DebugChecksumsSubsection *Checksums) const {
-  assert(Strings);
+std::shared_ptr<DebugSubsection> YAMLFrameDataSubsection::toCodeViewSubsection(
+    BumpPtrAllocator &Allocator,
+    const codeview::StringsAndChecksums &SC) const {
+  assert(SC.hasStrings());
+
   auto Result = llvm::make_unique<DebugFrameDataSubsection>();
   for (const auto &YF : Frames) {
     codeview::FrameData F;
@@ -519,16 +514,16 @@ std::unique_ptr<DebugSubsection> YAMLFrameDataSubsection::toCodeViewSubsection(
     F.PrologSize = YF.PrologSize;
     F.RvaStart = YF.RvaStart;
     F.SavedRegsSize = YF.SavedRegsSize;
-    F.FrameFunc = Strings->insert(YF.FrameFunc);
+    F.FrameFunc = SC.strings()->insert(YF.FrameFunc);
     Result->addFrameData(F);
   }
   return std::move(Result);
 }
 
-std::unique_ptr<DebugSubsection>
+std::shared_ptr<DebugSubsection>
 YAMLCoffSymbolRVASubsection::toCodeViewSubsection(
-    BumpPtrAllocator &Allocator, DebugStringTableSubsection *Strings,
-    DebugChecksumsSubsection *Checksums) const {
+    BumpPtrAllocator &Allocator,
+    const codeview::StringsAndChecksums &SC) const {
   auto Result = llvm::make_unique<DebugSymbolRVASubsection>();
   for (const auto &RVA : RVAs)
     Result->addRVA(RVA);
@@ -741,63 +736,17 @@ YAMLCoffSymbolRVASubsection::fromCodeViewSubsection(
   return Result;
 }
 
-Expected<std::vector<std::unique_ptr<DebugSubsection>>>
-llvm::CodeViewYAML::toCodeViewSubsectionList(
-    BumpPtrAllocator &Allocator, ArrayRef<YAMLDebugSubsection> Subsections,
-    DebugStringTableSubsection &Strings) {
-  std::vector<std::unique_ptr<DebugSubsection>> Result;
-  if (Subsections.empty())
-    return std::move(Result);
-
-  auto Checksums = findChecksums(Subsections);
-  std::unique_ptr<DebugSubsection> ChecksumsBase;
-  if (Checksums)
-    ChecksumsBase =
-        Checksums->toCodeViewSubsection(Allocator, &Strings, nullptr);
-  DebugChecksumsSubsection *CS =
-      static_cast<DebugChecksumsSubsection *>(ChecksumsBase.get());
-  for (const auto &SS : Subsections) {
-    // We've already converted the checksums subsection, don't do it
-    // twice.
-    std::unique_ptr<DebugSubsection> CVS;
-    if (SS.Subsection->Kind == DebugSubsectionKind::FileChecksums)
-      CVS = std::move(ChecksumsBase);
-    else
-      CVS = SS.Subsection->toCodeViewSubsection(Allocator, &Strings, CS);
-    assert(CVS != nullptr);
-    Result.push_back(std::move(CVS));
-  }
-  return std::move(Result);
-}
-
-Expected<std::vector<std::unique_ptr<codeview::DebugSubsection>>>
+Expected<std::vector<std::shared_ptr<DebugSubsection>>>
 llvm::CodeViewYAML::toCodeViewSubsectionList(
     BumpPtrAllocator &Allocator, ArrayRef<YAMLDebugSubsection> Subsections,
-    std::unique_ptr<DebugStringTableSubsection> &TakeStrings,
-    DebugStringTableSubsection *StringsRef) {
-  std::vector<std::unique_ptr<DebugSubsection>> Result;
+    const codeview::StringsAndChecksums &SC) {
+  std::vector<std::shared_ptr<DebugSubsection>> Result;
   if (Subsections.empty())
     return std::move(Result);
 
-  auto Checksums = findChecksums(Subsections);
-
-  std::unique_ptr<DebugSubsection> ChecksumsBase;
-  if (Checksums)
-    ChecksumsBase =
-        Checksums->toCodeViewSubsection(Allocator, StringsRef, nullptr);
-  DebugChecksumsSubsection *CS =
-      static_cast<DebugChecksumsSubsection *>(ChecksumsBase.get());
   for (const auto &SS : Subsections) {
-    // We've already converted the checksums and string table subsection, don't
-    // do it twice.
-    std::unique_ptr<DebugSubsection> CVS;
-    if (SS.Subsection->Kind == DebugSubsectionKind::FileChecksums)
-      CVS = std::move(ChecksumsBase);
-    else if (SS.Subsection->Kind == DebugSubsectionKind::StringTable) {
-      assert(TakeStrings && "No string table!");
-      CVS = std::move(TakeStrings);
-    } else
-      CVS = SS.Subsection->toCodeViewSubsection(Allocator, StringsRef, CS);
+    std::shared_ptr<DebugSubsection> CVS;
+    CVS = SS.Subsection->toCodeViewSubsection(Allocator, SC);
     assert(CVS != nullptr);
     Result.push_back(std::move(CVS));
   }
@@ -810,23 +759,23 @@ struct SubsectionConversionVisitor : public DebugSubsectionVisitor {
 
   Error visitUnknown(DebugUnknownSubsectionRef &Unknown) override;
   Error visitLines(DebugLinesSubsectionRef &Lines,
-                   const DebugSubsectionState &State) override;
+                   const StringsAndChecksumsRef &State) override;
   Error visitFileChecksums(DebugChecksumsSubsectionRef &Checksums,
-                           const DebugSubsectionState &State) override;
+                           const StringsAndChecksumsRef &State) override;
   Error visitInlineeLines(DebugInlineeLinesSubsectionRef &Inlinees,
-                          const DebugSubsectionState &State) override;
+                          const StringsAndChecksumsRef &State) override;
   Error visitCrossModuleExports(DebugCrossModuleExportsSubsectionRef &Checksums,
-                                const DebugSubsectionState &State) override;
+                                const StringsAndChecksumsRef &State) override;
   Error visitCrossModuleImports(DebugCrossModuleImportsSubsectionRef &Inlinees,
-                                const DebugSubsectionState &State) override;
+                                const StringsAndChecksumsRef &State) override;
   Error visitStringTable(DebugStringTableSubsectionRef &ST,
-                         const DebugSubsectionState &State) override;
+                         const StringsAndChecksumsRef &State) override;
   Error visitSymbols(DebugSymbolsSubsectionRef &Symbols,
-                     const DebugSubsectionState &State) override;
+                     const StringsAndChecksumsRef &State) override;
   Error visitFrameData(DebugFrameDataSubsectionRef &Symbols,
-                       const DebugSubsectionState &State) override;
+                       const StringsAndChecksumsRef &State) override;
   Error visitCOFFSymbolRVAs(DebugSymbolRVASubsectionRef &Symbols,
-                            const DebugSubsectionState &State) override;
+                            const StringsAndChecksumsRef &State) override;
 
   YAMLDebugSubsection Subsection;
 };
@@ -837,7 +786,7 @@ Error SubsectionConversionVisitor::visitUnknown(
 }
 
 Error SubsectionConversionVisitor::visitLines(
-    DebugLinesSubsectionRef &Lines, const DebugSubsectionState &State) {
+    DebugLinesSubsectionRef &Lines, const StringsAndChecksumsRef &State) {
   auto Result = YAMLLinesSubsection::fromCodeViewSubsection(
       State.strings(), State.checksums(), Lines);
   if (!Result)
@@ -847,7 +796,8 @@ Error SubsectionConversionVisitor::visitLines(
 }
 
 Error SubsectionConversionVisitor::visitFileChecksums(
-    DebugChecksumsSubsectionRef &Checksums, const DebugSubsectionState &State) {
+    DebugChecksumsSubsectionRef &Checksums,
+    const StringsAndChecksumsRef &State) {
   auto Result = YAMLChecksumsSubsection::fromCodeViewSubsection(State.strings(),
                                                                 Checksums);
   if (!Result)
@@ -858,7 +808,7 @@ Error SubsectionConversionVisitor::visitFileChecksums(
 
 Error SubsectionConversionVisitor::visitInlineeLines(
     DebugInlineeLinesSubsectionRef &Inlinees,
-    const DebugSubsectionState &State) {
+    const StringsAndChecksumsRef &State) {
   auto Result = YAMLInlineeLinesSubsection::fromCodeViewSubsection(
       State.strings(), State.checksums(), Inlinees);
   if (!Result)
@@ -869,7 +819,7 @@ Error SubsectionConversionVisitor::visitInlineeLines(
 
 Error SubsectionConversionVisitor::visitCrossModuleExports(
     DebugCrossModuleExportsSubsectionRef &Exports,
-    const DebugSubsectionState &State) {
+    const StringsAndChecksumsRef &State) {
   auto Result =
       YAMLCrossModuleExportsSubsection::fromCodeViewSubsection(Exports);
   if (!Result)
@@ -880,7 +830,7 @@ Error SubsectionConversionVisitor::visitCrossModuleExports(
 
 Error SubsectionConversionVisitor::visitCrossModuleImports(
     DebugCrossModuleImportsSubsectionRef &Imports,
-    const DebugSubsectionState &State) {
+    const StringsAndChecksumsRef &State) {
   auto Result = YAMLCrossModuleImportsSubsection::fromCodeViewSubsection(
       State.strings(), Imports);
   if (!Result)
@@ -890,7 +840,8 @@ Error SubsectionConversionVisitor::visitCrossModuleImports(
 }
 
 Error SubsectionConversionVisitor::visitStringTable(
-    DebugStringTableSubsectionRef &Strings, const DebugSubsectionState &State) {
+    DebugStringTableSubsectionRef &Strings,
+    const StringsAndChecksumsRef &State) {
   auto Result = YAMLStringTableSubsection::fromCodeViewSubsection(Strings);
   if (!Result)
     return Result.takeError();
@@ -899,7 +850,7 @@ Error SubsectionConversionVisitor::visitStringTable(
 }
 
 Error SubsectionConversionVisitor::visitSymbols(
-    DebugSymbolsSubsectionRef &Symbols, const DebugSubsectionState &State) {
+    DebugSymbolsSubsectionRef &Symbols, const StringsAndChecksumsRef &State) {
   auto Result = YAMLSymbolsSubsection::fromCodeViewSubsection(Symbols);
   if (!Result)
     return Result.takeError();
@@ -908,7 +859,7 @@ Error SubsectionConversionVisitor::visitSymbols(
 }
 
 Error SubsectionConversionVisitor::visitFrameData(
-    DebugFrameDataSubsectionRef &Frames, const DebugSubsectionState &State) {
+    DebugFrameDataSubsectionRef &Frames, const StringsAndChecksumsRef &State) {
   auto Result =
       YAMLFrameDataSubsection::fromCodeViewSubsection(State.strings(), Frames);
   if (!Result)
@@ -918,7 +869,7 @@ Error SubsectionConversionVisitor::visitFrameData(
 }
 
 Error SubsectionConversionVisitor::visitCOFFSymbolRVAs(
-    DebugSymbolRVASubsectionRef &RVAs, const DebugSubsectionState &State) {
+    DebugSymbolRVASubsectionRef &RVAs, const StringsAndChecksumsRef &State) {
   auto Result = YAMLCoffSymbolRVASubsection::fromCodeViewSubsection(RVAs);
   if (!Result)
     return Result.takeError();
@@ -927,29 +878,71 @@ Error SubsectionConversionVisitor::visitCOFFSymbolRVAs(
 }
 }
 
-Expected<YAMLDebugSubsection> YAMLDebugSubsection::fromCodeViewSubection(
-    const DebugStringTableSubsectionRef &Strings,
-    const DebugChecksumsSubsectionRef &Checksums,
-    const DebugSubsectionRecord &SS) {
-  DebugSubsectionState State(Strings, Checksums);
+Expected<YAMLDebugSubsection>
+YAMLDebugSubsection::fromCodeViewSubection(const StringsAndChecksumsRef &SC,
+                                           const DebugSubsectionRecord &SS) {
   SubsectionConversionVisitor V;
-  if (auto EC = visitDebugSubsection(SS, V, State))
+  if (auto EC = visitDebugSubsection(SS, V, SC))
     return std::move(EC);
 
   return V.Subsection;
 }
 
-std::unique_ptr<DebugStringTableSubsection>
-llvm::CodeViewYAML::findStringTable(ArrayRef<YAMLDebugSubsection> Sections) {
-  for (const auto &SS : Sections) {
-    if (SS.Subsection->Kind != DebugSubsectionKind::StringTable)
-      continue;
+std::vector<YAMLDebugSubsection>
+llvm::CodeViewYAML::fromDebugS(ArrayRef<uint8_t> Data,
+                               const StringsAndChecksumsRef &SC) {
+  BinaryStreamReader Reader(Data, support::little);
+  uint32_t Magic;
+
+  ExitOnError Err("Invalid .debug$S section!");
+  Err(Reader.readInteger(Magic));
+  assert(Magic == COFF::DEBUG_SECTION_MAGIC && "Invalid .debug$S section!");
+
+  DebugSubsectionArray Subsections;
+  Err(Reader.readArray(Subsections, Reader.bytesRemaining()));
 
-    // String Table doesn't use the allocator.
-    BumpPtrAllocator Allocator;
-    auto Result =
-        SS.Subsection->toCodeViewSubsection(Allocator, nullptr, nullptr);
-    return llvm::cast<DebugStringTableSubsection>(std::move(Result));
+  std::vector<YAMLDebugSubsection> Result;
+
+  for (const auto &SS : Subsections) {
+    auto YamlSS = Err(YAMLDebugSubsection::fromCodeViewSubection(SC, SS));
+    Result.push_back(YamlSS);
+  }
+  return std::move(Result);
+}
+
+void llvm::CodeViewYAML::initializeStringsAndChecksums(
+    ArrayRef<YAMLDebugSubsection> Sections, codeview::StringsAndChecksums &SC) {
+  // String Table and Checksums subsections don't use the allocator.
+  BumpPtrAllocator Allocator;
+
+  // It's possible for checksums and strings to even appear in different debug$S
+  // sections, so we have to make this a stateful function that can build up
+  // the strings and checksums field over multiple iterations.
+
+  // File Checksums require the string table, but may become before it, so we
+  // have to scan for strings first, then scan for checksums again from the
+  // beginning.
+  if (!SC.hasStrings()) {
+    for (const auto &SS : Sections) {
+      if (SS.Subsection->Kind != DebugSubsectionKind::StringTable)
+        continue;
+
+      auto Result = SS.Subsection->toCodeViewSubsection(Allocator, SC);
+      SC.setStrings(
+          std::static_pointer_cast<DebugStringTableSubsection>(Result));
+      break;
+    }
+  }
+
+  if (SC.hasStrings() && !SC.hasChecksums()) {
+    for (const auto &SS : Sections) {
+      if (SS.Subsection->Kind != DebugSubsectionKind::FileChecksums)
+        continue;
+
+      auto Result = SS.Subsection->toCodeViewSubsection(Allocator, SC);
+      SC.setChecksums(
+          std::static_pointer_cast<DebugChecksumsSubsection>(Result));
+      break;
+    }
   }
-  return nullptr;
 }
diff --git a/llvm/lib/ObjectYAML/CodeViewYAMLTypes.cpp b/llvm/lib/ObjectYAML/CodeViewYAMLTypes.cpp
index 1302b0713d0..aa8653d7e88 100644
--- a/llvm/lib/ObjectYAML/CodeViewYAMLTypes.cpp
+++ b/llvm/lib/ObjectYAML/CodeViewYAMLTypes.cpp
@@ -714,3 +714,43 @@ void MappingTraits<MemberRecord>::mapping(IO &IO, MemberRecord &Obj) {
   default: { llvm_unreachable("Unknown member kind!"); }
   }
 }
+
+std::vector<LeafRecord>
+llvm::CodeViewYAML::fromDebugT(ArrayRef<uint8_t> DebugT) {
+  ExitOnError Err("Invalid .debug$T section!");
+  BinaryStreamReader Reader(DebugT, support::little);
+  CVTypeArray Types;
+  uint32_t Magic;
+
+  Err(Reader.readInteger(Magic));
+  assert(Magic == COFF::DEBUG_SECTION_MAGIC && "Invalid .debug$T section!");
+
+  std::vector<LeafRecord> Result;
+  Err(Reader.readArray(Types, Reader.bytesRemaining()));
+  for (const auto &T : Types) {
+    auto CVT = Err(LeafRecord::fromCodeViewRecord(T));
+    Result.push_back(CVT);
+  }
+  return std::move(Result);
+}
+
+ArrayRef<uint8_t> llvm::CodeViewYAML::toDebugT(ArrayRef<LeafRecord> Leafs,
+                                               BumpPtrAllocator &Alloc) {
+  TypeTableBuilder TTB(Alloc, false);
+  uint32_t Size = sizeof(uint32_t);
+  for (const auto &Leaf : Leafs) {
+    CVType T = Leaf.toCodeViewRecord(TTB);
+    Size += T.length();
+    assert(T.length() % 4 == 0 && "Improper type record alignment!");
+  }
+  uint8_t *ResultBuffer = Alloc.Allocate<uint8_t>(Size);
+  MutableArrayRef<uint8_t> Output(ResultBuffer, Size);
+  BinaryStreamWriter Writer(Output, support::little);
+  ExitOnError Err("Error writing type record to .debug$T section");
+  Err(Writer.writeInteger<uint32_t>(COFF::DEBUG_SECTION_MAGIC));
+  for (const auto &R : TTB.records()) {
+    Err(Writer.writeBytes(R));
+  }
+  assert(Writer.bytesRemaining() == 0 && "Didn't write all type record bytes!");
+  return Output;
+}