lib/MC/MCContext.cpp

//===- lib/MC/MCContext.cpp - Machine Code Context ------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#include "llvm/MC/MCContext.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/Twine.h"
#include "llvm/BinaryFormat/COFF.h"
#include "llvm/BinaryFormat/ELF.h"
#include "llvm/BinaryFormat/XCOFF.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MCCodeView.h"
#include "llvm/MC/MCDwarf.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCFragment.h"
#include "llvm/MC/MCLabel.h"
#include "llvm/MC/MCObjectFileInfo.h"
#include "llvm/MC/MCSectionCOFF.h"
#include "llvm/MC/MCSectionELF.h"
#include "llvm/MC/MCSectionMachO.h"
#include "llvm/MC/MCSectionWasm.h"
#include "llvm/MC/MCSectionXCOFF.h"
#include "llvm/MC/MCStreamer.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/MC/MCSymbolCOFF.h"
#include "llvm/MC/MCSymbolELF.h"
#include "llvm/MC/MCSymbolMachO.h"
#include "llvm/MC/MCSymbolWasm.h"
#include "llvm/MC/MCSymbolXCOFF.h"
#include "llvm/MC/SectionKind.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/Signals.h"
#include "llvm/Support/SourceMgr.h"
#include "llvm/Support/raw_ostream.h"
#include <cassert>
#include <cstdlib>
#include <tuple>
#include <utility>

using namespace llvm;

static cl::opt<char*>
AsSecureLogFileName("as-secure-log-file-name",
        cl::desc("As secure log file name (initialized from "
                 "AS_SECURE_LOG_FILE env variable)"),
        cl::init(getenv("AS_SECURE_LOG_FILE")), cl::Hidden);

MCContext::MCContext(const MCAsmInfo *mai, const MCRegisterInfo *mri,
                     const MCObjectFileInfo *mofi, const SourceMgr *mgr,
                     MCTargetOptions const *TargetOpts, bool DoAutoReset)
    : SrcMgr(mgr), InlineSrcMgr(nullptr), MAI(mai), MRI(mri), MOFI(mofi),
      Symbols(Allocator), UsedNames(Allocator),
      InlineAsmUsedLabelNames(Allocator),
      CurrentDwarfLoc(0, 0, 0, DWARF2_FLAG_IS_STMT, 0, 0),
      AutoReset(DoAutoReset), TargetOptions(TargetOpts) {
  SecureLogFile = AsSecureLogFileName;

  if (SrcMgr && SrcMgr->getNumBuffers())
    MainFileName = std::string(SrcMgr->getMemoryBuffer(SrcMgr->getMainFileID())
                                   ->getBufferIdentifier());
}

MCContext::~MCContext() {
  if (AutoReset)
    reset();

  // NOTE: The symbols are all allocated out of a bump pointer allocator,
  // we don't need to free them here.
}

//===----------------------------------------------------------------------===//
// Module Lifetime Management
//===----------------------------------------------------------------------===//

void MCContext::reset() {
  // Call the destructors so the fragments are freed
  COFFAllocator.DestroyAll();
  ELFAllocator.DestroyAll();
  MachOAllocator.DestroyAll();
  XCOFFAllocator.DestroyAll();

  MCSubtargetAllocator.DestroyAll();
  InlineAsmUsedLabelNames.clear();
  UsedNames.clear();
  Symbols.clear();
  Allocator.Reset();
  Instances.clear();
  CompilationDir.clear();
  MainFileName.clear();
  MCDwarfLineTablesCUMap.clear();
  SectionsForRanges.clear();
  MCGenDwarfLabelEntries.clear();
  DwarfDebugFlags = StringRef();
  DwarfCompileUnitID = 0;
  CurrentDwarfLoc = MCDwarfLoc(0, 0, 0, DWARF2_FLAG_IS_STMT, 0, 0);

  CVContext.reset();

  MachOUniquingMap.clear();
  ELFUniquingMap.clear();
  COFFUniquingMap.clear();
  WasmUniquingMap.clear();
  XCOFFUniquingMap.clear();

  ELFEntrySizeMap.clear();
  ELFSeenGenericMergeableSections.clear();

  NextID.clear();
  AllowTemporaryLabels = true;
  DwarfLocSeen = false;
  GenDwarfForAssembly = false;
  GenDwarfFileNumber = 0;

  HadError = false;
}

//===----------------------------------------------------------------------===//
// Symbol Manipulation
//===----------------------------------------------------------------------===//

MCSymbol *MCContext::getOrCreateSymbol(const Twine &Name) {
  SmallString<128> NameSV;
  StringRef NameRef = Name.toStringRef(NameSV);

  assert(!NameRef.empty() && "Normal symbols cannot be unnamed!");

  MCSymbol *&Sym = Symbols[NameRef];
  if (!Sym)
    Sym = createSymbol(NameRef, false, false);

  return Sym;
}

MCSymbol *MCContext::getOrCreateFrameAllocSymbol(StringRef FuncName,
                                                 unsigned Idx) {
  return getOrCreateSymbol(Twine(MAI->getPrivateGlobalPrefix()) + FuncName +
                           "$frame_escape_" + Twine(Idx));
}

MCSymbol *MCContext::getOrCreateParentFrameOffsetSymbol(StringRef FuncName) {
  return getOrCreateSymbol(Twine(MAI->getPrivateGlobalPrefix()) + FuncName +
                           "$parent_frame_offset");
}

MCSymbol *MCContext::getOrCreateLSDASymbol(StringRef FuncName) {
  return getOrCreateSymbol(Twine(MAI->getPrivateGlobalPrefix()) + "__ehtable$" +
                           FuncName);
}

MCSymbol *MCContext::createSymbolImpl(const StringMapEntry<bool> *Name,
                                      bool IsTemporary) {
  static_assert(std::is_trivially_destructible<MCSymbolCOFF>(),
                "MCSymbol classes must be trivially destructible");
  static_assert(std::is_trivially_destructible<MCSymbolELF>(),
                "MCSymbol classes must be trivially destructible");
  static_assert(std::is_trivially_destructible<MCSymbolMachO>(),
                "MCSymbol classes must be trivially destructible");
  static_assert(std::is_trivially_destructible<MCSymbolWasm>(),
                "MCSymbol classes must be trivially destructible");
  static_assert(std::is_trivially_destructible<MCSymbolXCOFF>(),
                "MCSymbol classes must be trivially destructible");
  if (MOFI) {
    switch (MOFI->getObjectFileType()) {
    case MCObjectFileInfo::IsCOFF:
      return new (Name, *this) MCSymbolCOFF(Name, IsTemporary);
    case MCObjectFileInfo::IsELF:
      return new (Name, *this) MCSymbolELF(Name, IsTemporary);
    case MCObjectFileInfo::IsMachO:
      return new (Name, *this) MCSymbolMachO(Name, IsTemporary);
    case MCObjectFileInfo::IsWasm:
      return new (Name, *this) MCSymbolWasm(Name, IsTemporary);
    case MCObjectFileInfo::IsXCOFF:
      return createXCOFFSymbolImpl(Name, IsTemporary);
    }
  }
  return new (Name, *this) MCSymbol(MCSymbol::SymbolKindUnset, Name,
                                    IsTemporary);
}

MCSymbol *MCContext::createSymbol(StringRef Name, bool AlwaysAddSuffix,
                                  bool CanBeUnnamed) {
  if (CanBeUnnamed && !UseNamesOnTempLabels)
    return createSymbolImpl(nullptr, true);

  // Determine whether this is a user written assembler temporary or normal
  // label, if used.
  bool IsTemporary = CanBeUnnamed;
  if (AllowTemporaryLabels && !IsTemporary)
    IsTemporary = Name.startswith(MAI->getPrivateGlobalPrefix());

  SmallString<128> NewName = Name;
  bool AddSuffix = AlwaysAddSuffix;
  unsigned &NextUniqueID = NextID[Name];
  while (true) {
    if (AddSuffix) {
      NewName.resize(Name.size());
      raw_svector_ostream(NewName) << NextUniqueID++;
    }
    auto NameEntry = UsedNames.insert(std::make_pair(NewName, true));
    if (NameEntry.second || !NameEntry.first->second) {
      // Ok, we found a name.
      // Mark it as used for a non-section symbol.
      NameEntry.first->second = true;
      // Have the MCSymbol object itself refer to the copy of the string that is
      // embedded in the UsedNames entry.
      return createSymbolImpl(&*NameEntry.first, IsTemporary);
    }
    assert(IsTemporary && "Cannot rename non-temporary symbols");
    AddSuffix = true;
  }
  llvm_unreachable("Infinite loop");
}

MCSymbol *MCContext::createTempSymbol(const Twine &Name, bool AlwaysAddSuffix,
                                      bool CanBeUnnamed) {
  SmallString<128> NameSV;
  raw_svector_ostream(NameSV) << MAI->getPrivateGlobalPrefix() << Name;
  return createSymbol(NameSV, AlwaysAddSuffix, CanBeUnnamed);
}

MCSymbol *MCContext::createLinkerPrivateTempSymbol() {
  SmallString<128> NameSV;
  raw_svector_ostream(NameSV) << MAI->getLinkerPrivateGlobalPrefix() << "tmp";
  return createSymbol(NameSV, true, false);
}

MCSymbol *MCContext::createTempSymbol(bool CanBeUnnamed) {
  return createTempSymbol("tmp", true, CanBeUnnamed);
}

unsigned MCContext::NextInstance(unsigned LocalLabelVal) {
  MCLabel *&Label = Instances[LocalLabelVal];
  if (!Label)
    Label = new (*this) MCLabel(0);
  return Label->incInstance();
}

unsigned MCContext::GetInstance(unsigned LocalLabelVal) {
  MCLabel *&Label = Instances[LocalLabelVal];
  if (!Label)
    Label = new (*this) MCLabel(0);
  return Label->getInstance();
}

MCSymbol *MCContext::getOrCreateDirectionalLocalSymbol(unsigned LocalLabelVal,
                                                       unsigned Instance) {
  MCSymbol *&Sym = LocalSymbols[std::make_pair(LocalLabelVal, Instance)];
  if (!Sym)
    Sym = createTempSymbol(false);
  return Sym;
}

MCSymbol *MCContext::createDirectionalLocalSymbol(unsigned LocalLabelVal) {
  unsigned Instance = NextInstance(LocalLabelVal);
  return getOrCreateDirectionalLocalSymbol(LocalLabelVal, Instance);
}

MCSymbol *MCContext::getDirectionalLocalSymbol(unsigned LocalLabelVal,
                                               bool Before) {
  unsigned Instance = GetInstance(LocalLabelVal);
  if (!Before)
    ++Instance;
  return getOrCreateDirectionalLocalSymbol(LocalLabelVal, Instance);
}

MCSymbol *MCContext::lookupSymbol(const Twine &Name) const {
  SmallString<128> NameSV;
  StringRef NameRef = Name.toStringRef(NameSV);
  return Symbols.lookup(NameRef);
}

void MCContext::setSymbolValue(MCStreamer &Streamer,
                              StringRef Sym,
                              uint64_t Val) {
  auto Symbol = getOrCreateSymbol(Sym);
  Streamer.emitAssignment(Symbol, MCConstantExpr::create(Val, *this));
}

void MCContext::registerInlineAsmLabel(MCSymbol *Sym) {
  InlineAsmUsedLabelNames[Sym->getName()] = Sym;
}

MCSymbolXCOFF *
MCContext::createXCOFFSymbolImpl(const StringMapEntry<bool> *Name,
                                 bool IsTemporary) {
  if (!Name)
    return new (nullptr, *this) MCSymbolXCOFF(nullptr, IsTemporary);

  StringRef OriginalName = Name->first();
  if (OriginalName.startswith("._Renamed..") ||
      OriginalName.startswith("_Renamed.."))
    reportError(SMLoc(), "invalid symbol name from source");

  if (MAI->isValidUnquotedName(OriginalName))
    return new (Name, *this) MCSymbolXCOFF(Name, IsTemporary);

  // Now we have a name that contains invalid character(s) for XCOFF symbol.
  // Let's replace with something valid, but save the original name so that
  // we could still use the original name in the symbol table.
  SmallString<128> InvalidName(OriginalName);

  // If it's an entry point symbol, we will keep the '.'
  // in front for the convention purpose. Otherwise, add "_Renamed.."
  // as prefix to signal this is an renamed symbol.
  const bool IsEntryPoint = !InvalidName.empty() && InvalidName[0] == '.';
  SmallString<128> ValidName =
      StringRef(IsEntryPoint ? "._Renamed.." : "_Renamed..");

  // Append the hex values of '_' and invalid characters with "_Renamed..";
  // at the same time replace invalid characters with '_'.
  for (size_t I = 0; I < InvalidName.size(); ++I) {
    if (!MAI->isAcceptableChar(InvalidName[I]) || InvalidName[I] == '_') {
      raw_svector_ostream(ValidName).write_hex(InvalidName[I]);
      InvalidName[I] = '_';
    }
  }

  // Skip entry point symbol's '.' as we already have a '.' in front of
  // "_Renamed".
  if (IsEntryPoint)
    ValidName.append(InvalidName.substr(1, InvalidName.size() - 1));
  else
    ValidName.append(InvalidName);

  auto NameEntry = UsedNames.insert(std::make_pair(ValidName, true));
  assert((NameEntry.second || !NameEntry.first->second) &&
         "This name is used somewhere else.");
  // Mark the name as used for a non-section symbol.
  NameEntry.first->second = true;
  // Have the MCSymbol object itself refer to the copy of the string
  // that is embedded in the UsedNames entry.
  MCSymbolXCOFF *XSym = new (&*NameEntry.first, *this)
      MCSymbolXCOFF(&*NameEntry.first, IsTemporary);
  XSym->setSymbolTableName(MCSymbolXCOFF::getUnqualifiedName(OriginalName));
  return XSym;
}

//===----------------------------------------------------------------------===//
// Section Management
//===----------------------------------------------------------------------===//

MCSectionMachO *MCContext::getMachOSection(StringRef Segment, StringRef Section,
                                           unsigned TypeAndAttributes,
                                           unsigned Reserved2, SectionKind Kind,
                                           const char *BeginSymName) {
  // We unique sections by their segment/section pair.  The returned section
  // may not have the same flags as the requested section, if so this should be
  // diagnosed by the client as an error.

  // Form the name to look up.
  assert(Section.size() <= 16 && "section name is too long");
  assert(!memchr(Section.data(), '\0', Section.size()) &&
         "section name cannot contain NUL");

  // Do the lookup, if we have a hit, return it.
  auto R = MachOUniquingMap.try_emplace((Segment + Twine(',') + Section).str());
  if (!R.second)
    return R.first->second;

  MCSymbol *Begin = nullptr;
  if (BeginSymName)
    Begin = createTempSymbol(BeginSymName, false);

  // Otherwise, return a new section.
  StringRef Name = R.first->first();
  R.first->second = new (MachOAllocator.Allocate())
      MCSectionMachO(Segment, Name.substr(Name.size() - Section.size()),
                     TypeAndAttributes, Reserved2, Kind, Begin);
  return R.first->second;
}

void MCContext::renameELFSection(MCSectionELF *Section, StringRef Name) {
  StringRef GroupName;
  if (const MCSymbol *Group = Section->getGroup())
    GroupName = Group->getName();

  // This function is only used by .debug*, which should not have the
  // SHF_LINK_ORDER flag.
  unsigned UniqueID = Section->getUniqueID();
  ELFUniquingMap.erase(
      ELFSectionKey{Section->getName(), GroupName, "", UniqueID});
  auto I = ELFUniquingMap
               .insert(std::make_pair(
                   ELFSectionKey{Name, GroupName, "", UniqueID}, Section))
               .first;
  StringRef CachedName = I->first.SectionName;
  const_cast<MCSectionELF *>(Section)->setSectionName(CachedName);
}

MCSectionELF *MCContext::createELFSectionImpl(StringRef Section, unsigned Type,
                                              unsigned Flags, SectionKind K,
                                              unsigned EntrySize,
                                              const MCSymbolELF *Group,
                                              unsigned UniqueID,
                                              const MCSymbolELF *LinkedToSym) {
  MCSymbolELF *R;
  MCSymbol *&Sym = Symbols[Section];
  // A section symbol can not redefine regular symbols. There may be multiple
  // sections with the same name, in which case the first such section wins.
  if (Sym && Sym->isDefined() &&
      (!Sym->isInSection() || Sym->getSection().getBeginSymbol() != Sym))
    reportError(SMLoc(), "invalid symbol redefinition");
  if (Sym && Sym->isUndefined()) {
    R = cast<MCSymbolELF>(Sym);
  } else {
    auto NameIter = UsedNames.insert(std::make_pair(Section, false)).first;
    R = new (&*NameIter, *this) MCSymbolELF(&*NameIter, /*isTemporary*/ false);
    if (!Sym)
      Sym = R;
  }
  R->setBinding(ELF::STB_LOCAL);
  R->setType(ELF::STT_SECTION);

  auto *Ret = new (ELFAllocator.Allocate()) MCSectionELF(
      Section, Type, Flags, K, EntrySize, Group, UniqueID, R, LinkedToSym);

  auto *F = new MCDataFragment();
  Ret->getFragmentList().insert(Ret->begin(), F);
  F->setParent(Ret);
  R->setFragment(F);

  return Ret;
}

MCSectionELF *MCContext::createELFRelSection(const Twine &Name, unsigned Type,
                                             unsigned Flags, unsigned EntrySize,
                                             const MCSymbolELF *Group,
                                             const MCSectionELF *RelInfoSection) {
  StringMap<bool>::iterator I;
  bool Inserted;
  std::tie(I, Inserted) =
      RelSecNames.insert(std::make_pair(Name.str(), true));

  return createELFSectionImpl(
      I->getKey(), Type, Flags, SectionKind::getReadOnly(), EntrySize, Group,
      true, cast<MCSymbolELF>(RelInfoSection->getBeginSymbol()));
}

MCSectionELF *MCContext::getELFNamedSection(const Twine &Prefix,
                                            const Twine &Suffix, unsigned Type,
                                            unsigned Flags,
                                            unsigned EntrySize) {
  return getELFSection(Prefix + "." + Suffix, Type, Flags, EntrySize, Suffix);
}

MCSectionELF *MCContext::getELFSection(const Twine &Section, unsigned Type,
                                       unsigned Flags, unsigned EntrySize,
                                       const Twine &Group, unsigned UniqueID,
                                       const MCSymbolELF *LinkedToSym) {
  MCSymbolELF *GroupSym = nullptr;
  if (!Group.isTriviallyEmpty() && !Group.str().empty())
    GroupSym = cast<MCSymbolELF>(getOrCreateSymbol(Group));

  return getELFSection(Section, Type, Flags, EntrySize, GroupSym, UniqueID,
                       LinkedToSym);
}

MCSectionELF *MCContext::getELFSection(const Twine &Section, unsigned Type,
                                       unsigned Flags, unsigned EntrySize,
                                       const MCSymbolELF *GroupSym,
                                       unsigned UniqueID,
                                       const MCSymbolELF *LinkedToSym) {
  StringRef Group = "";
  if (GroupSym)
    Group = GroupSym->getName();
  assert(!(LinkedToSym && LinkedToSym->getName().empty()));
  // Do the lookup, if we have a hit, return it.
  auto IterBool = ELFUniquingMap.insert(std::make_pair(
      ELFSectionKey{Section.str(), Group,
                    LinkedToSym ? LinkedToSym->getName() : "", UniqueID},
      nullptr));
  auto &Entry = *IterBool.first;
  if (!IterBool.second)
    return Entry.second;

  StringRef CachedName = Entry.first.SectionName;

  SectionKind Kind;
  if (Flags & ELF::SHF_ARM_PURECODE)
    Kind = SectionKind::getExecuteOnly();
  else if (Flags & ELF::SHF_EXECINSTR)
    Kind = SectionKind::getText();
  else
    Kind = SectionKind::getReadOnly();

  MCSectionELF *Result =
      createELFSectionImpl(CachedName, Type, Flags, Kind, EntrySize, GroupSym,
                           UniqueID, LinkedToSym);
  Entry.second = Result;

  recordELFMergeableSectionInfo(Result->getName(), Result->getFlags(),
                                Result->getUniqueID(), Result->getEntrySize());

  return Result;
}

MCSectionELF *MCContext::createELFGroupSection(const MCSymbolELF *Group) {
  return createELFSectionImpl(".group", ELF::SHT_GROUP, 0,
                              SectionKind::getReadOnly(), 4, Group,
                              MCSection::NonUniqueID, nullptr);
}

void MCContext::recordELFMergeableSectionInfo(StringRef SectionName,
                                              unsigned Flags, unsigned UniqueID,
                                              unsigned EntrySize) {
  bool IsMergeable = Flags & ELF::SHF_MERGE;
  if (IsMergeable && (UniqueID == GenericSectionID))
    ELFSeenGenericMergeableSections.insert(SectionName);

  // For mergeable sections or non-mergeable sections with a generic mergeable
  // section name we enter their Unique ID into the ELFEntrySizeMap so that
  // compatible globals can be assigned to the same section.
  if (IsMergeable || isELFGenericMergeableSection(SectionName)) {
    ELFEntrySizeMap.insert(std::make_pair(
        ELFEntrySizeKey{SectionName, Flags, EntrySize}, UniqueID));
  }
}

bool MCContext::isELFImplicitMergeableSectionNamePrefix(StringRef SectionName) {
  return SectionName.startswith(".rodata.str") ||
         SectionName.startswith(".rodata.cst");
}

bool MCContext::isELFGenericMergeableSection(StringRef SectionName) {
  return isELFImplicitMergeableSectionNamePrefix(SectionName) ||
         ELFSeenGenericMergeableSections.count(SectionName);
}

Optional<unsigned> MCContext::getELFUniqueIDForEntsize(StringRef SectionName,
                                                       unsigned Flags,
                                                       unsigned EntrySize) {
  auto I = ELFEntrySizeMap.find(
      MCContext::ELFEntrySizeKey{SectionName, Flags, EntrySize});
  return (I != ELFEntrySizeMap.end()) ? Optional<unsigned>(I->second) : None;
}

MCSectionCOFF *MCContext::getCOFFSection(StringRef Section,
                                         unsigned Characteristics,
                                         SectionKind Kind,
                                         StringRef COMDATSymName, int Selection,
                                         unsigned UniqueID,
                                         const char *BeginSymName) {
  MCSymbol *COMDATSymbol = nullptr;
  if (!COMDATSymName.empty()) {
    COMDATSymbol = getOrCreateSymbol(COMDATSymName);
    COMDATSymName = COMDATSymbol->getName();
  }


  // Do the lookup, if we have a hit, return it.
  COFFSectionKey T{Section, COMDATSymName, Selection, UniqueID};
  auto IterBool = COFFUniquingMap.insert(std::make_pair(T, nullptr));
  auto Iter = IterBool.first;
  if (!IterBool.second)
    return Iter->second;

  MCSymbol *Begin = nullptr;
  if (BeginSymName)
    Begin = createTempSymbol(BeginSymName, false);

  StringRef CachedName = Iter->first.SectionName;
  MCSectionCOFF *Result = new (COFFAllocator.Allocate()) MCSectionCOFF(
      CachedName, Characteristics, COMDATSymbol, Selection, Kind, Begin);

  Iter->second = Result;
  return Result;
}

MCSectionCOFF *MCContext::getCOFFSection(StringRef Section,
                                         unsigned Characteristics,
                                         SectionKind Kind,
                                         const char *BeginSymName) {
  return getCOFFSection(Section, Characteristics, Kind, "", 0, GenericSectionID,
                        BeginSymName);
}

MCSectionCOFF *MCContext::getAssociativeCOFFSection(MCSectionCOFF *Sec,
                                                    const MCSymbol *KeySym,
                                                    unsigned UniqueID) {
  // Return the normal section if we don't have to be associative or unique.
  if (!KeySym && UniqueID == GenericSectionID)
    return Sec;

  // If we have a key symbol, make an associative section with the same name and
  // kind as the normal section.
  unsigned Characteristics = Sec->getCharacteristics();
  if (KeySym) {
    Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
    return getCOFFSection(Sec->getName(), Characteristics, Sec->getKind(),
                          KeySym->getName(),
                          COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE, UniqueID);
  }

  return getCOFFSection(Sec->getName(), Characteristics, Sec->getKind(), "", 0,
                        UniqueID);
}

MCSectionWasm *MCContext::getWasmSection(const Twine &Section, SectionKind K,
                                         const Twine &Group, unsigned UniqueID,
                                         const char *BeginSymName) {
  MCSymbolWasm *GroupSym = nullptr;
  if (!Group.isTriviallyEmpty() && !Group.str().empty()) {
    GroupSym = cast<MCSymbolWasm>(getOrCreateSymbol(Group));
    GroupSym->setComdat(true);
  }

  return getWasmSection(Section, K, GroupSym, UniqueID, BeginSymName);
}

MCSectionWasm *MCContext::getWasmSection(const Twine &Section, SectionKind Kind,
                                         const MCSymbolWasm *GroupSym,
                                         unsigned UniqueID,
                                         const char *BeginSymName) {
  StringRef Group = "";
  if (GroupSym)
    Group = GroupSym->getName();
  // Do the lookup, if we have a hit, return it.
  auto IterBool = WasmUniquingMap.insert(
      std::make_pair(WasmSectionKey{Section.str(), Group, UniqueID}, nullptr));
  auto &Entry = *IterBool.first;
  if (!IterBool.second)
    return Entry.second;

  StringRef CachedName = Entry.first.SectionName;

  MCSymbol *Begin = createSymbol(CachedName, false, false);
  cast<MCSymbolWasm>(Begin)->setType(wasm::WASM_SYMBOL_TYPE_SECTION);

  MCSectionWasm *Result = new (WasmAllocator.Allocate())
      MCSectionWasm(CachedName, Kind, GroupSym, UniqueID, Begin);
  Entry.second = Result;

  auto *F = new MCDataFragment();
  Result->getFragmentList().insert(Result->begin(), F);
  F->setParent(Result);
  Begin->setFragment(F);

  return Result;
}

MCSectionXCOFF *MCContext::getXCOFFSection(StringRef Section,
                                           XCOFF::StorageMappingClass SMC,
                                           XCOFF::SymbolType Type,
                                           XCOFF::StorageClass SC,
                                           SectionKind Kind,
                                           const char *BeginSymName) {
  // Do the lookup. If we have a hit, return it.
  auto IterBool = XCOFFUniquingMap.insert(
      std::make_pair(XCOFFSectionKey{Section.str(), SMC}, nullptr));
  auto &Entry = *IterBool.first;
  if (!IterBool.second)
    return Entry.second;

  // Otherwise, return a new section.
  StringRef CachedName = Entry.first.SectionName;
  MCSymbolXCOFF *QualName = cast<MCSymbolXCOFF>(getOrCreateSymbol(
      CachedName + "[" + XCOFF::getMappingClassString(SMC) + "]"));

  MCSymbol *Begin = nullptr;
  if (BeginSymName)
    Begin = createTempSymbol(BeginSymName, false);

  // QualName->getUnqualifiedName() and CachedName are the same except when
  // CachedName contains invalid character(s) such as '$' for an XCOFF symbol.
  MCSectionXCOFF *Result = new (XCOFFAllocator.Allocate())
      MCSectionXCOFF(QualName->getUnqualifiedName(), SMC, Type, SC, Kind,
                     QualName, Begin, CachedName);
  Entry.second = Result;

  auto *F = new MCDataFragment();
  Result->getFragmentList().insert(Result->begin(), F);
  F->setParent(Result);

  if (Begin)
    Begin->setFragment(F);

  return Result;
}

MCSubtargetInfo &MCContext::getSubtargetCopy(const MCSubtargetInfo &STI) {
  return *new (MCSubtargetAllocator.Allocate()) MCSubtargetInfo(STI);
}

void MCContext::addDebugPrefixMapEntry(const std::string &From,
                                       const std::string &To) {
  DebugPrefixMap.insert(std::make_pair(From, To));
}

void MCContext::RemapDebugPaths() {
  const auto &DebugPrefixMap = this->DebugPrefixMap;
  if (DebugPrefixMap.empty())
    return;

  const auto RemapDebugPath = [&DebugPrefixMap](std::string &Path) {
    SmallString<256> P(Path);
    for (const auto &Entry : DebugPrefixMap) {
      if (llvm::sys::path::replace_path_prefix(P, Entry.first, Entry.second)) {
        Path = P.str().str();
        break;
      }
    }
  };

  // Remap compilation directory.
  std::string CompDir = std::string(CompilationDir.str());
  RemapDebugPath(CompDir);
  CompilationDir = CompDir;

  // Remap MCDwarfDirs in all compilation units.
  for (auto &CUIDTablePair : MCDwarfLineTablesCUMap)
    for (auto &Dir : CUIDTablePair.second.getMCDwarfDirs())
      RemapDebugPath(Dir);
}

//===----------------------------------------------------------------------===//
// Dwarf Management
//===----------------------------------------------------------------------===//

void MCContext::setGenDwarfRootFile(StringRef InputFileName, StringRef Buffer) {
  // MCDwarf needs the root file as well as the compilation directory.
  // If we find a '.file 0' directive that will supersede these values.
  Optional<MD5::MD5Result> Cksum;
  if (getDwarfVersion() >= 5) {
    MD5 Hash;
    MD5::MD5Result Sum;
    Hash.update(Buffer);
    Hash.final(Sum);
    Cksum = Sum;
  }
  // Canonicalize the root filename. It cannot be empty, and should not
  // repeat the compilation dir.
  // The MCContext ctor initializes MainFileName to the name associated with
  // the SrcMgr's main file ID, which might be the same as InputFileName (and
  // possibly include directory components).
  // Or, MainFileName might have been overridden by a -main-file-name option,
  // which is supposed to be just a base filename with no directory component.
  // So, if the InputFileName and MainFileName are not equal, assume
  // MainFileName is a substitute basename and replace the last component.
  SmallString<1024> FileNameBuf = InputFileName;
  if (FileNameBuf.empty() || FileNameBuf == "-")
    FileNameBuf = "<stdin>";
  if (!getMainFileName().empty() && FileNameBuf != getMainFileName()) {
    llvm::sys::path::remove_filename(FileNameBuf);
    llvm::sys::path::append(FileNameBuf, getMainFileName());
  }
  StringRef FileName = FileNameBuf;
  if (FileName.consume_front(getCompilationDir()))
    if (llvm::sys::path::is_separator(FileName.front()))
      FileName = FileName.drop_front();
  assert(!FileName.empty());
  setMCLineTableRootFile(
      /*CUID=*/0, getCompilationDir(), FileName, Cksum, None);
}

/// getDwarfFile - takes a file name and number to place in the dwarf file and
/// directory tables.  If the file number has already been allocated it is an
/// error and zero is returned and the client reports the error, else the
/// allocated file number is returned.  The file numbers may be in any order.
Expected<unsigned> MCContext::getDwarfFile(StringRef Directory,
                                           StringRef FileName,
                                           unsigned FileNumber,
                                           Optional<MD5::MD5Result> Checksum,
                                           Optional<StringRef> Source,
                                           unsigned CUID) {
  MCDwarfLineTable &Table = MCDwarfLineTablesCUMap[CUID];
  return Table.tryGetFile(Directory, FileName, Checksum, Source, DwarfVersion,
                          FileNumber);
}

/// isValidDwarfFileNumber - takes a dwarf file number and returns true if it
/// currently is assigned and false otherwise.
bool MCContext::isValidDwarfFileNumber(unsigned FileNumber, unsigned CUID) {
  const MCDwarfLineTable &LineTable = getMCDwarfLineTable(CUID);
  if (FileNumber == 0)
    return getDwarfVersion() >= 5;
  if (FileNumber >= LineTable.getMCDwarfFiles().size())
    return false;

  return !LineTable.getMCDwarfFiles()[FileNumber].Name.empty();
}

/// Remove empty sections from SectionsForRanges, to avoid generating
/// useless debug info for them.
void MCContext::finalizeDwarfSections(MCStreamer &MCOS) {
  SectionsForRanges.remove_if(
      [&](MCSection *Sec) { return !MCOS.mayHaveInstructions(*Sec); });
}

CodeViewContext &MCContext::getCVContext() {
  if (!CVContext.get())
    CVContext.reset(new CodeViewContext);
  return *CVContext.get();
}

//===----------------------------------------------------------------------===//
// Error Reporting
//===----------------------------------------------------------------------===//

void MCContext::reportError(SMLoc Loc, const Twine &Msg) {
  HadError = true;

  // If we have a source manager use it. Otherwise, try using the inline source
  // manager.
  // If that fails, use the generic report_fatal_error().
  if (SrcMgr)
    SrcMgr->PrintMessage(Loc, SourceMgr::DK_Error, Msg);
  else if (InlineSrcMgr)
    InlineSrcMgr->PrintMessage(Loc, SourceMgr::DK_Error, Msg);
  else
    report_fatal_error(Msg, false);
}

void MCContext::reportWarning(SMLoc Loc, const Twine &Msg) {
  if (TargetOptions && TargetOptions->MCNoWarn)
    return;
  if (TargetOptions && TargetOptions->MCFatalWarnings)
    reportError(Loc, Msg);
  else {
    // If we have a source manager use it. Otherwise, try using the inline
    // source manager.
    if (SrcMgr)
      SrcMgr->PrintMessage(Loc, SourceMgr::DK_Warning, Msg);
    else if (InlineSrcMgr)
      InlineSrcMgr->PrintMessage(Loc, SourceMgr::DK_Warning, Msg);
  }
}

void MCContext::reportFatalError(SMLoc Loc, const Twine &Msg) {
  reportError(Loc, Msg);

  // If we reached here, we are failing ungracefully. Run the interrupt handlers
  // to make sure any special cleanups get done, in particular that we remove
  // files registered with RemoveFileOnSignal.
  sys::RunInterruptHandlers();
  exit(1);
}