lib/DebugInfo/DWARFContext.cpp

//===-- DWARFContext.cpp --------------------------------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#include "DWARFContext.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/StringSwitch.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Support/Compression.h"
#include "llvm/Support/Dwarf.h"
#include "llvm/Support/Format.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
using namespace llvm;
using namespace dwarf;
using namespace object;

typedef DWARFDebugLine::LineTable DWARFLineTable;

DWARFContext::~DWARFContext() {
  DeleteContainerPointers(CUs);
  DeleteContainerPointers(DWOCUs);
}

void DWARFContext::dump(raw_ostream &OS, DIDumpType DumpType) {
  if (DumpType == DIDT_All || DumpType == DIDT_Abbrev) {
    OS << ".debug_abbrev contents:\n";
    getDebugAbbrev()->dump(OS);
  }

  if (DumpType == DIDT_All || DumpType == DIDT_Info) {
    OS << "\n.debug_info contents:\n";
    for (unsigned i = 0, e = getNumCompileUnits(); i != e; ++i)
      getCompileUnitAtIndex(i)->dump(OS);
  }

  if (DumpType == DIDT_All || DumpType == DIDT_Loc) {
    OS << ".debug_loc contents:\n";
    getDebugLoc()->dump(OS);
  }

  if (DumpType == DIDT_All || DumpType == DIDT_Frames) {
    OS << "\n.debug_frame contents:\n";
    getDebugFrame()->dump(OS);
  }

  uint32_t offset = 0;
  if (DumpType == DIDT_All || DumpType == DIDT_Aranges) {
    OS << "\n.debug_aranges contents:\n";
    DataExtractor arangesData(getARangeSection(), isLittleEndian(), 0);
    DWARFDebugArangeSet set;
    while (set.extract(arangesData, &offset))
      set.dump(OS);
  }

  uint8_t savedAddressByteSize = 0;
  if (DumpType == DIDT_All || DumpType == DIDT_Line) {
    OS << "\n.debug_line contents:\n";
    for (unsigned i = 0, e = getNumCompileUnits(); i != e; ++i) {
      DWARFCompileUnit *cu = getCompileUnitAtIndex(i);
      savedAddressByteSize = cu->getAddressByteSize();
      unsigned stmtOffset =
        cu->getCompileUnitDIE()->getAttributeValueAsUnsigned(cu, DW_AT_stmt_list,
                                                             -1U);
      if (stmtOffset != -1U) {
        DataExtractor lineData(getLineSection(), isLittleEndian(),
                               savedAddressByteSize);
        DWARFDebugLine::DumpingState state(OS);
        DWARFDebugLine::parseStatementTable(lineData, &lineRelocMap(), &stmtOffset, state);
      }
    }
  }

  if (DumpType == DIDT_All || DumpType == DIDT_Str) {
    OS << "\n.debug_str contents:\n";
    DataExtractor strData(getStringSection(), isLittleEndian(), 0);
    offset = 0;
    uint32_t strOffset = 0;
    while (const char *s = strData.getCStr(&offset)) {
      OS << format("0x%8.8x: \"%s\"\n", strOffset, s);
      strOffset = offset;
    }
  }

  if (DumpType == DIDT_All || DumpType == DIDT_Ranges) {
    OS << "\n.debug_ranges contents:\n";
    // In fact, different compile units may have different address byte
    // sizes, but for simplicity we just use the address byte size of the last
    // compile unit (there is no easy and fast way to associate address range
    // list and the compile unit it describes).
    DataExtractor rangesData(getRangeSection(), isLittleEndian(),
                             savedAddressByteSize);
    offset = 0;
    DWARFDebugRangeList rangeList;
    while (rangeList.extract(rangesData, &offset))
      rangeList.dump(OS);
  }

  if (DumpType == DIDT_All || DumpType == DIDT_Pubnames) {
    OS << "\n.debug_pubnames contents:\n";
    DataExtractor pubNames(getPubNamesSection(), isLittleEndian(), 0);
    offset = 0;
    OS << "Length:                " << pubNames.getU32(&offset) << "\n";
    OS << "Version:               " << pubNames.getU16(&offset) << "\n";
    OS << "Offset in .debug_info: " << pubNames.getU32(&offset) << "\n";
    OS << "Size:                  " << pubNames.getU32(&offset) << "\n";
    OS << "\n  Offset    Name\n";
    while (offset < getPubNamesSection().size()) {
      uint32_t n = pubNames.getU32(&offset);
      if (n == 0)
        break;
      OS << format("%8x    ", n);
      OS << pubNames.getCStr(&offset) << "\n";
    }
  }

  if (DumpType == DIDT_All || DumpType == DIDT_AbbrevDwo) {
    const DWARFDebugAbbrev *D = getDebugAbbrevDWO();
    if (D) {
      OS << "\n.debug_abbrev.dwo contents:\n";
      getDebugAbbrevDWO()->dump(OS);
    }
  }

  if (DumpType == DIDT_All || DumpType == DIDT_InfoDwo)
    if (getNumDWOCompileUnits()) {
      OS << "\n.debug_info.dwo contents:\n";
      for (unsigned i = 0, e = getNumDWOCompileUnits(); i != e; ++i)
        getDWOCompileUnitAtIndex(i)->dump(OS);
    }

  if (DumpType == DIDT_All || DumpType == DIDT_StrDwo)
    if (!getStringDWOSection().empty()) {
      OS << "\n.debug_str.dwo contents:\n";
      DataExtractor strDWOData(getStringDWOSection(), isLittleEndian(), 0);
      offset = 0;
      uint32_t strDWOOffset = 0;
      while (const char *s = strDWOData.getCStr(&offset)) {
        OS << format("0x%8.8x: \"%s\"\n", strDWOOffset, s);
        strDWOOffset = offset;
      }
    }

  if (DumpType == DIDT_All || DumpType == DIDT_StrOffsetsDwo)
    if (!getStringOffsetDWOSection().empty()) {
      OS << "\n.debug_str_offsets.dwo contents:\n";
      DataExtractor strOffsetExt(getStringOffsetDWOSection(), isLittleEndian(), 0);
      offset = 0;
      uint64_t size = getStringOffsetDWOSection().size();
      while (offset < size) {
        OS << format("0x%8.8x: ", offset);
        OS << format("%8.8x\n", strOffsetExt.getU32(&offset));
      }
    }
}

const DWARFDebugAbbrev *DWARFContext::getDebugAbbrev() {
  if (Abbrev)
    return Abbrev.get();

  DataExtractor abbrData(getAbbrevSection(), isLittleEndian(), 0);

  Abbrev.reset(new DWARFDebugAbbrev());
  Abbrev->parse(abbrData);
  return Abbrev.get();
}

const DWARFDebugAbbrev *DWARFContext::getDebugAbbrevDWO() {
  if (AbbrevDWO)
    return AbbrevDWO.get();

  DataExtractor abbrData(getAbbrevDWOSection(), isLittleEndian(), 0);
  AbbrevDWO.reset(new DWARFDebugAbbrev());
  AbbrevDWO->parse(abbrData);
  return AbbrevDWO.get();
}

const DWARFDebugLoc *DWARFContext::getDebugLoc() {
  if (Loc)
    return Loc.get();

  DataExtractor LocData(getLocSection(), isLittleEndian(), 0);
  Loc.reset(new DWARFDebugLoc(locRelocMap()));
  // assume all compile units have the same address byte size
  if (getNumCompileUnits())
    Loc->parse(LocData, getCompileUnitAtIndex(0)->getAddressByteSize());
  return Loc.get();
}

const DWARFDebugAranges *DWARFContext::getDebugAranges() {
  if (Aranges)
    return Aranges.get();

  DataExtractor arangesData(getARangeSection(), isLittleEndian(), 0);

  Aranges.reset(new DWARFDebugAranges());
  Aranges->extract(arangesData);
  // Generate aranges from DIEs: even if .debug_aranges section is present,
  // it may describe only a small subset of compilation units, so we need to
  // manually build aranges for the rest of them.
  Aranges->generate(this);
  return Aranges.get();
}

const DWARFDebugFrame *DWARFContext::getDebugFrame() {
  if (DebugFrame)
    return DebugFrame.get();

  // There's a "bug" in the DWARFv3 standard with respect to the target address
  // size within debug frame sections. While DWARF is supposed to be independent
  // of its container, FDEs have fields with size being "target address size",
  // which isn't specified in DWARF in general. It's only specified for CUs, but
  // .eh_frame can appear without a .debug_info section. Follow the example of
  // other tools (libdwarf) and extract this from the container (ObjectFile
  // provides this information). This problem is fixed in DWARFv4
  // See this dwarf-discuss discussion for more details:
  // http://lists.dwarfstd.org/htdig.cgi/dwarf-discuss-dwarfstd.org/2011-December/001173.html
  DataExtractor debugFrameData(getDebugFrameSection(), isLittleEndian(),
                               getAddressSize());
  DebugFrame.reset(new DWARFDebugFrame());
  DebugFrame->parse(debugFrameData);
  return DebugFrame.get();
}

const DWARFLineTable *
DWARFContext::getLineTableForCompileUnit(DWARFCompileUnit *cu) {
  if (!Line)
    Line.reset(new DWARFDebugLine(&lineRelocMap()));

  unsigned stmtOffset =
    cu->getCompileUnitDIE()->getAttributeValueAsUnsigned(cu, DW_AT_stmt_list,
                                                         -1U);
  if (stmtOffset == -1U)
    return 0; // No line table for this compile unit.

  // See if the line table is cached.
  if (const DWARFLineTable *lt = Line->getLineTable(stmtOffset))
    return lt;

  // We have to parse it first.
  DataExtractor lineData(getLineSection(), isLittleEndian(),
                         cu->getAddressByteSize());
  return Line->getOrParseLineTable(lineData, stmtOffset);
}

void DWARFContext::parseCompileUnits() {
  uint32_t offset = 0;
  const DataExtractor &DIData = DataExtractor(getInfoSection(),
                                              isLittleEndian(), 0);
  while (DIData.isValidOffset(offset)) {
    OwningPtr<DWARFCompileUnit> CU(new DWARFCompileUnit(
        getDebugAbbrev(), getInfoSection(), getAbbrevSection(),
        getRangeSection(), getStringSection(), StringRef(), getAddrSection(),
        &infoRelocMap(), isLittleEndian()));
    if (!CU->extract(DIData, &offset)) {
      break;
    }
    CUs.push_back(CU.take());
    offset = CUs.back()->getNextCompileUnitOffset();
  }
}

void DWARFContext::parseDWOCompileUnits() {
  uint32_t offset = 0;
  const DataExtractor &DIData = DataExtractor(getInfoDWOSection(),
                                              isLittleEndian(), 0);
  while (DIData.isValidOffset(offset)) {
    OwningPtr<DWARFCompileUnit> DWOCU(new DWARFCompileUnit(
        getDebugAbbrevDWO(), getInfoDWOSection(), getAbbrevDWOSection(),
        getRangeDWOSection(), getStringDWOSection(),
        getStringOffsetDWOSection(), getAddrSection(), &infoDWORelocMap(),
        isLittleEndian()));
    if (!DWOCU->extract(DIData, &offset)) {
      break;
    }
    DWOCUs.push_back(DWOCU.take());
    offset = DWOCUs.back()->getNextCompileUnitOffset();
  }
}

namespace {
  struct OffsetComparator {
    bool operator()(const DWARFCompileUnit *LHS,
                    const DWARFCompileUnit *RHS) const {
      return LHS->getOffset() < RHS->getOffset();
    }
    bool operator()(const DWARFCompileUnit *LHS, uint32_t RHS) const {
      return LHS->getOffset() < RHS;
    }
    bool operator()(uint32_t LHS, const DWARFCompileUnit *RHS) const {
      return LHS < RHS->getOffset();
    }
  };
}

DWARFCompileUnit *DWARFContext::getCompileUnitForOffset(uint32_t Offset) {
  if (CUs.empty())
    parseCompileUnits();

  DWARFCompileUnit **CU =
      std::lower_bound(CUs.begin(), CUs.end(), Offset, OffsetComparator());
  if (CU != CUs.end()) {
    return *CU;
  }
  return 0;
}

DWARFCompileUnit *DWARFContext::getCompileUnitForAddress(uint64_t Address) {
  // First, get the offset of the compile unit.
  uint32_t CUOffset = getDebugAranges()->findAddress(Address);
  // Retrieve the compile unit.
  return getCompileUnitForOffset(CUOffset);
}

static bool getFileNameForCompileUnit(DWARFCompileUnit *CU,
                                      const DWARFLineTable *LineTable,
                                      uint64_t FileIndex,
                                      bool NeedsAbsoluteFilePath,
                                      std::string &FileName) {
  if (CU == 0 ||
      LineTable == 0 ||
      !LineTable->getFileNameByIndex(FileIndex, NeedsAbsoluteFilePath,
                                     FileName))
    return false;
  if (NeedsAbsoluteFilePath && sys::path::is_relative(FileName)) {
    // We may still need to append compilation directory of compile unit.
    SmallString<16> AbsolutePath;
    if (const char *CompilationDir = CU->getCompilationDir()) {
      sys::path::append(AbsolutePath, CompilationDir);
    }
    sys::path::append(AbsolutePath, FileName);
    FileName = AbsolutePath.str();
  }
  return true;
}

static bool getFileLineInfoForCompileUnit(DWARFCompileUnit *CU,
                                          const DWARFLineTable *LineTable,
                                          uint64_t Address,
                                          bool NeedsAbsoluteFilePath,
                                          std::string &FileName,
                                          uint32_t &Line, uint32_t &Column) {
  if (CU == 0 || LineTable == 0)
    return false;
  // Get the index of row we're looking for in the line table.
  uint32_t RowIndex = LineTable->lookupAddress(Address);
  if (RowIndex == -1U)
    return false;
  // Take file number and line/column from the row.
  const DWARFDebugLine::Row &Row = LineTable->Rows[RowIndex];
  if (!getFileNameForCompileUnit(CU, LineTable, Row.File,
                                 NeedsAbsoluteFilePath, FileName))
    return false;
  Line = Row.Line;
  Column = Row.Column;
  return true;
}

DILineInfo DWARFContext::getLineInfoForAddress(uint64_t Address,
    DILineInfoSpecifier Specifier) {
  DWARFCompileUnit *CU = getCompileUnitForAddress(Address);
  if (!CU)
    return DILineInfo();
  std::string FileName = "<invalid>";
  std::string FunctionName = "<invalid>";
  uint32_t Line = 0;
  uint32_t Column = 0;
  if (Specifier.needs(DILineInfoSpecifier::FunctionName)) {
    // The address may correspond to instruction in some inlined function,
    // so we have to build the chain of inlined functions and take the
    // name of the topmost function in it.
    const DWARFDebugInfoEntryInlinedChain &InlinedChain =
        CU->getInlinedChainForAddress(Address);
    if (InlinedChain.DIEs.size() > 0) {
      const DWARFDebugInfoEntryMinimal &TopFunctionDIE = InlinedChain.DIEs[0];
      if (const char *Name = TopFunctionDIE.getSubroutineName(InlinedChain.CU))
        FunctionName = Name;
    }
  }
  if (Specifier.needs(DILineInfoSpecifier::FileLineInfo)) {
    const DWARFLineTable *LineTable = getLineTableForCompileUnit(CU);
    const bool NeedsAbsoluteFilePath =
        Specifier.needs(DILineInfoSpecifier::AbsoluteFilePath);
    getFileLineInfoForCompileUnit(CU, LineTable, Address,
                                  NeedsAbsoluteFilePath,
                                  FileName, Line, Column);
  }
  return DILineInfo(StringRef(FileName), StringRef(FunctionName),
                    Line, Column);
}

DILineInfoTable DWARFContext::getLineInfoForAddressRange(uint64_t Address,
    uint64_t Size,
    DILineInfoSpecifier Specifier) {
  DILineInfoTable  Lines;
  DWARFCompileUnit *CU = getCompileUnitForAddress(Address);
  if (!CU)
    return Lines;

  std::string FunctionName = "<invalid>";
  if (Specifier.needs(DILineInfoSpecifier::FunctionName)) {
    // The address may correspond to instruction in some inlined function,
    // so we have to build the chain of inlined functions and take the
    // name of the topmost function in it.
    const DWARFDebugInfoEntryInlinedChain &InlinedChain =
        CU->getInlinedChainForAddress(Address);
    if (InlinedChain.DIEs.size() > 0) {
      const DWARFDebugInfoEntryMinimal &TopFunctionDIE = InlinedChain.DIEs[0];
      if (const char *Name = TopFunctionDIE.getSubroutineName(InlinedChain.CU))
        FunctionName = Name;
    }
  }

  StringRef  FuncNameRef = StringRef(FunctionName);

  // If the Specifier says we don't need FileLineInfo, just
  // return the top-most function at the starting address.
  if (!Specifier.needs(DILineInfoSpecifier::FileLineInfo)) {
    Lines.push_back(std::make_pair(Address,
                                   DILineInfo(StringRef("<invalid>"),
                                              FuncNameRef, 0, 0)));
    return Lines;
  }

  const DWARFLineTable *LineTable = getLineTableForCompileUnit(CU);
  const bool NeedsAbsoluteFilePath =
      Specifier.needs(DILineInfoSpecifier::AbsoluteFilePath);

  // Get the index of row we're looking for in the line table.
  std::vector<uint32_t> RowVector;
  if (!LineTable->lookupAddressRange(Address, Size, RowVector))
    return Lines;

  uint32_t NumRows = RowVector.size();
  for (uint32_t i = 0; i < NumRows; ++i) {
    uint32_t RowIndex = RowVector[i];
    // Take file number and line/column from the row.
    const DWARFDebugLine::Row &Row = LineTable->Rows[RowIndex];
    std::string FileName = "<invalid>";
    getFileNameForCompileUnit(CU, LineTable, Row.File,
                              NeedsAbsoluteFilePath, FileName);
    Lines.push_back(std::make_pair(Row.Address,
                                   DILineInfo(StringRef(FileName),
                                         FuncNameRef, Row.Line, Row.Column)));
  }

  return Lines;
}

DIInliningInfo DWARFContext::getInliningInfoForAddress(uint64_t Address,
    DILineInfoSpecifier Specifier) {
  DWARFCompileUnit *CU = getCompileUnitForAddress(Address);
  if (!CU)
    return DIInliningInfo();

  const DWARFDebugInfoEntryInlinedChain &InlinedChain =
      CU->getInlinedChainForAddress(Address);
  if (InlinedChain.DIEs.size() == 0)
    return DIInliningInfo();

  DIInliningInfo InliningInfo;
  uint32_t CallFile = 0, CallLine = 0, CallColumn = 0;
  const DWARFLineTable *LineTable = 0;
  for (uint32_t i = 0, n = InlinedChain.DIEs.size(); i != n; i++) {
    const DWARFDebugInfoEntryMinimal &FunctionDIE = InlinedChain.DIEs[i];
    std::string FileName = "<invalid>";
    std::string FunctionName = "<invalid>";
    uint32_t Line = 0;
    uint32_t Column = 0;
    // Get function name if necessary.
    if (Specifier.needs(DILineInfoSpecifier::FunctionName)) {
      if (const char *Name = FunctionDIE.getSubroutineName(InlinedChain.CU))
        FunctionName = Name;
    }
    if (Specifier.needs(DILineInfoSpecifier::FileLineInfo)) {
      const bool NeedsAbsoluteFilePath =
          Specifier.needs(DILineInfoSpecifier::AbsoluteFilePath);
      if (i == 0) {
        // For the topmost frame, initialize the line table of this
        // compile unit and fetch file/line info from it.
        LineTable = getLineTableForCompileUnit(CU);
        // For the topmost routine, get file/line info from line table.
        getFileLineInfoForCompileUnit(CU, LineTable, Address,
                                      NeedsAbsoluteFilePath,
                                      FileName, Line, Column);
      } else {
        // Otherwise, use call file, call line and call column from
        // previous DIE in inlined chain.
        getFileNameForCompileUnit(CU, LineTable, CallFile,
                                  NeedsAbsoluteFilePath, FileName);
        Line = CallLine;
        Column = CallColumn;
      }
      // Get call file/line/column of a current DIE.
      if (i + 1 < n) {
        FunctionDIE.getCallerFrame(InlinedChain.CU, CallFile, CallLine,
                                   CallColumn);
      }
    }
    DILineInfo Frame(StringRef(FileName), StringRef(FunctionName),
                     Line, Column);
    InliningInfo.addFrame(Frame);
  }
  return InliningInfo;
}

static bool consumeCompressedDebugSectionHeader(StringRef &data,
                                                uint64_t &OriginalSize) {
  // Consume "ZLIB" prefix.
  if (!data.startswith("ZLIB"))
    return false;
  data = data.substr(4);
  // Consume uncompressed section size (big-endian 8 bytes).
  DataExtractor extractor(data, false, 8);
  uint32_t Offset = 0;
  OriginalSize = extractor.getU64(&Offset);
  if (Offset == 0)
    return false;
  data = data.substr(Offset);
  return true;
}

DWARFContextInMemory::DWARFContextInMemory(object::ObjectFile *Obj) :
  IsLittleEndian(Obj->isLittleEndian()),
  AddressSize(Obj->getBytesInAddress()) {
  error_code ec;
  for (object::section_iterator i = Obj->begin_sections(),
         e = Obj->end_sections();
       i != e; i.increment(ec)) {
    StringRef name;
    i->getName(name);
    StringRef data;
    i->getContents(data);

    name = name.substr(name.find_first_not_of("._")); // Skip . and _ prefixes.

    // Check if debug info section is compressed with zlib.
    if (name.startswith("zdebug_")) {
      uint64_t OriginalSize;
      if (!zlib::isAvailable() ||
          !consumeCompressedDebugSectionHeader(data, OriginalSize))
        continue;
      OwningPtr<MemoryBuffer> UncompressedSection;
      if (zlib::uncompress(data, UncompressedSection, OriginalSize) !=
          zlib::StatusOK)
        continue;
      // Make data point to uncompressed section contents and save its contents.
      name = name.substr(1);
      data = UncompressedSection->getBuffer();
      UncompressedSections.push_back(UncompressedSection.take());
    }

    StringRef *Section = StringSwitch<StringRef*>(name)
        .Case("debug_info", &InfoSection)
        .Case("debug_abbrev", &AbbrevSection)
        .Case("debug_loc", &LocSection)
        .Case("debug_line", &LineSection)
        .Case("debug_aranges", &ARangeSection)
        .Case("debug_frame", &DebugFrameSection)
        .Case("debug_str", &StringSection)
        .Case("debug_ranges", &RangeSection)
        .Case("debug_pubnames", &PubNamesSection)
        .Case("debug_info.dwo", &InfoDWOSection)
        .Case("debug_abbrev.dwo", &AbbrevDWOSection)
        .Case("debug_str.dwo", &StringDWOSection)
        .Case("debug_str_offsets.dwo", &StringOffsetDWOSection)
        .Case("debug_addr", &AddrSection)
        // Any more debug info sections go here.
        .Default(0);
    if (Section) {
      *Section = data;
      if (name == "debug_ranges") {
        // FIXME: Use the other dwo range section when we emit it.
        RangeDWOSection = data;
      }
    }

    section_iterator RelocatedSection = i->getRelocatedSection();
    if (RelocatedSection == Obj->end_sections())
      continue;

    StringRef RelSecName;
    RelocatedSection->getName(RelSecName);
    RelSecName = RelSecName.substr(
        RelSecName.find_first_not_of("._")); // Skip . and _ prefixes.

    // TODO: Add support for relocations in other sections as needed.
    // Record relocations for the debug_info and debug_line sections.
    RelocAddrMap *Map = StringSwitch<RelocAddrMap*>(RelSecName)
        .Case("debug_info", &InfoRelocMap)
        .Case("debug_loc", &LocRelocMap)
        .Case("debug_info.dwo", &InfoDWORelocMap)
        .Case("debug_line", &LineRelocMap)
        .Default(0);
    if (!Map)
      continue;

    if (i->begin_relocations() != i->end_relocations()) {
      uint64_t SectionSize;
      RelocatedSection->getSize(SectionSize);
      for (object::relocation_iterator reloc_i = i->begin_relocations(),
             reloc_e = i->end_relocations();
           reloc_i != reloc_e; reloc_i.increment(ec)) {
        uint64_t Address;
        reloc_i->getOffset(Address);
        uint64_t Type;
        reloc_i->getType(Type);
        uint64_t SymAddr = 0;
        // ELF relocations may need the symbol address
        if (Obj->isELF()) {
          object::symbol_iterator Sym = reloc_i->getSymbol();
          Sym->getAddress(SymAddr);
        }

        object::RelocVisitor V(Obj->getFileFormatName());
        // The section address is always 0 for debug sections.
        object::RelocToApply R(V.visit(Type, *reloc_i, 0, SymAddr));
        if (V.error()) {
          SmallString<32> Name;
          error_code ec(reloc_i->getTypeName(Name));
          if (ec) {
            errs() << "Aaaaaa! Nameless relocation! Aaaaaa!\n";
          }
          errs() << "error: failed to compute relocation: "
                 << Name << "\n";
          continue;
        }

        if (Address + R.Width > SectionSize) {
          errs() << "error: " << R.Width << "-byte relocation starting "
                 << Address << " bytes into section " << name << " which is "
                 << SectionSize << " bytes long.\n";
          continue;
        }
        if (R.Width > 8) {
          errs() << "error: can't handle a relocation of more than 8 bytes at "
                    "a time.\n";
          continue;
        }
        DEBUG(dbgs() << "Writing " << format("%p", R.Value)
                     << " at " << format("%p", Address)
                     << " with width " << format("%d", R.Width)
                     << "\n");
        Map->insert(std::make_pair(Address, std::make_pair(R.Width, R.Value)));
      }
    }
  }
}

DWARFContextInMemory::~DWARFContextInMemory() {
  DeleteContainerPointers(UncompressedSections);
}

void DWARFContextInMemory::anchor() { }