[ObjectYAML] Add ability for DWARFYAML to calculate DIE lengths

This patch adds the ability for the ObjectYAML DWARFEmitter to calculate
the lengths of DIEs. This is accomplished by creating a DIEFixupVisitor
class which traverses the DWARF DIEs to calculate and fix up the lengths
in the Compile Unit header.

The DIEFixupVisitor can be extended in the future to enable more complex
fix ups which will enable simplified YAML string representations.

This is also very useful when using the YAML format in unit tests
because you no longer need to know the length of the compile unit when
writing the YAML string.

Differential commandeered from Chris Bieneman (beanz)

Differential revision: https://reviews.llvm.org/D30666

llvm-svn: 330421

include/llvm/ObjectYAML/DWARFEmitter.h

@@ -39,11 +39,12 @@ void EmitDebugInfo(raw_ostream &OS, const Data &DI);
 void EmitDebugLine(raw_ostream &OS, const Data &DI);
 
 Expected<StringMap<std::unique_ptr<MemoryBuffer>>>
-EmitDebugSections(StringRef YAMLString,
+EmitDebugSections(StringRef YAMLString, bool ApplyFixups = false,
                   bool IsLittleEndian = sys::IsLittleEndianHost);
+StringMap<std::unique_ptr<MemoryBuffer>>
+EmitDebugSections(llvm::DWARFYAML::Data &DI, bool ApplyFixups);
 
 } // end namespace DWARFYAML
-
 } // end namespace llvm
 
 #endif // LLVM_OBJECTYAML_DWARFEMITTER_H

lib/ObjectYAML/DWARFEmitter.cpp

@@ -149,7 +149,6 @@ protected:
       writeInteger((uint32_t)CU.AbbrOffset, OS, DebugInfo.IsLittleEndian);
       writeInteger((uint8_t)CU.AddrSize, OS, DebugInfo.IsLittleEndian);
     }
-    
   }
 
   void onStartDIE(const DWARFYAML::Unit &CU,
@@ -308,11 +307,48 @@ EmitDebugSectionImpl(const DWARFYAML::Data &DI, EmitFuncType EmitFunc,
     OutputBuffers[Sec] = MemoryBuffer::getMemBufferCopy(Data);
 }
 
-Expected<StringMap<std::unique_ptr<MemoryBuffer>>>
+class DIEFixupVisitor : public DWARFYAML::Visitor {
-DWARFYAML::EmitDebugSections(StringRef YAMLString,
+  uint64_t Length;
-                             bool IsLittleEndian) {
-  StringMap<std::unique_ptr<MemoryBuffer>> DebugSections;
 
+public:
+  DIEFixupVisitor(DWARFYAML::Data &DI) : DWARFYAML::Visitor(DI){};
+
+private:
+  virtual void onStartCompileUnit(DWARFYAML::Unit &CU) { Length = 7; }
+
+  virtual void onEndCompileUnit(DWARFYAML::Unit &CU) {
+    CU.Length.setLength(Length);
+  }
+
+  virtual void onStartDIE(DWARFYAML::Unit &CU, DWARFYAML::Entry &DIE) {
+    Length += getULEB128Size(DIE.AbbrCode);
+  }
+
+  virtual void onValue(const uint8_t U) { Length += 1; }
+  virtual void onValue(const uint16_t U) { Length += 2; }
+  virtual void onValue(const uint32_t U) { Length += 4; }
+  virtual void onValue(const uint64_t U, const bool LEB = false) {
+    if (LEB)
+      Length += getULEB128Size(U);
+    else
+      Length += 8;
+  }
+  virtual void onValue(const int64_t S, const bool LEB = false) {
+    if (LEB)
+      Length += getSLEB128Size(S);
+    else
+      Length += 8;
+  }
+  virtual void onValue(const StringRef String) { Length += String.size() + 1; }
+
+  virtual void onValue(const MemoryBufferRef MBR) {
+    Length += MBR.getBufferSize();
+  }
+};
+
+Expected<StringMap<std::unique_ptr<MemoryBuffer>>>
+DWARFYAML::EmitDebugSections(StringRef YAMLString, bool ApplyFixups,
+                             bool IsLittleEndian) {
   yaml::Input YIn(YAMLString);
 
   DWARFYAML::Data DI;
@@ -321,6 +357,12 @@ DWARFYAML::EmitDebugSections(StringRef YAMLString,
   if (YIn.error())
     return errorCodeToError(YIn.error());
 
+  if (ApplyFixups) {
+    DIEFixupVisitor DIFixer(DI);
+    DIFixer.traverseDebugInfo();
+  }
+
+  StringMap<std::unique_ptr<MemoryBuffer>> DebugSections;
   EmitDebugSectionImpl(DI, &DWARFYAML::EmitDebugInfo, "debug_info",
                        DebugSections);
   EmitDebugSectionImpl(DI, &DWARFYAML::EmitDebugLine, "debug_line",

unittests/DebugInfo/DWARF/DWARFDebugInfoTest.cpp

@@ -1166,7 +1166,7 @@ TEST(DWARFDebugInfo, TestEmptyChildren) {
                          "    Attributes:\n"
                          "debug_info:\n"
                          "  - Length:\n"
-                         "      TotalLength:          9\n"
+                         "      TotalLength:          0\n"
                          "    Version:         4\n"
                          "    AbbrOffset:      0\n"
                          "    AddrSize:        8\n"
@@ -1176,7 +1176,7 @@ TEST(DWARFDebugInfo, TestEmptyChildren) {
                          "      - AbbrCode:        0x00000000\n"
                          "        Values:\n";
 
-  auto ErrOrSections = DWARFYAML::EmitDebugSections(StringRef(yamldata));
+  auto ErrOrSections = DWARFYAML::EmitDebugSections(StringRef(yamldata), true);
   ASSERT_TRUE((bool)ErrOrSections);
   std::unique_ptr<DWARFContext> DwarfContext =
       DWARFContext::create(*ErrOrSections, 8);