//===- InputFiles.cpp -----------------------------------------------------===//

//

// 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 "InputFiles.h"

#include "Chunks.h"

#include "Config.h"

#include "DebugTypes.h"

#include "Driver.h"

#include "SymbolTable.h"

#include "Symbols.h"

#include "lld/Common/ErrorHandler.h"

#include "lld/Common/Memory.h"

#include "llvm-c/lto.h"

#include "llvm/ADT/SmallVector.h"

#include "llvm/ADT/Triple.h"

#include "llvm/ADT/Twine.h"

#include "llvm/BinaryFormat/COFF.h"

#include "llvm/DebugInfo/CodeView/DebugSubsectionRecord.h"

#include "llvm/DebugInfo/CodeView/SymbolDeserializer.h"

#include "llvm/DebugInfo/CodeView/SymbolRecord.h"

#include "llvm/DebugInfo/CodeView/TypeDeserializer.h"

#include "llvm/Object/Binary.h"

#include "llvm/Object/COFF.h"

#include "llvm/Support/Casting.h"

#include "llvm/Support/Endian.h"

#include "llvm/Support/Error.h"

#include "llvm/Support/ErrorOr.h"

#include "llvm/Support/FileSystem.h"

#include "llvm/Support/Path.h"

#include "llvm/Target/TargetOptions.h"

#include <cstring>

#include <system_error>

#include <utility>

using namespace llvm;

using namespace llvm::COFF;

using namespace llvm::codeview;

using namespace llvm::object;

using namespace llvm::support::endian;

using llvm::Triple;

using llvm::support::ulittle32_t;

namespace lld {

namespace coff {

std::vector<ObjFile *> ObjFile::instances;

std::vector<ImportFile *> ImportFile::instances;

std::vector<BitcodeFile *> BitcodeFile::instances;

/// Checks that Source is compatible with being a weak alias to Target.

/// If Source is Undefined and has no weak alias set, makes it a weak

/// alias to Target.

static void checkAndSetWeakAlias(SymbolTable *symtab, InputFile *f,

                                 Symbol *source, Symbol *target) {

  if (auto *u = dyn_cast<Undefined>(source)) {

    if (u->weakAlias && 
u->weakAlias != target2
) {

      // Weak aliases as produced by GCC are named in the form

      // .weak.<weaksymbol>.<othersymbol>, where <othersymbol> is the name

      // of another symbol emitted near the weak symbol.

      // Just use the definition from the first object file that defined

      // this weak symbol.

      if (config->mingw)

        return;

      symtab->reportDuplicate(source, f);

    }

    u->weakAlias = target;

  }

}

ArchiveFile::ArchiveFile(MemoryBufferRef m) : InputFile(ArchiveKind, m) {}

void ArchiveFile::parse() {

  // Parse a MemoryBufferRef as an archive file.

  file = CHECK(Archive::create(mb), this);

  // Read the symbol table to construct Lazy objects.

  for (const Archive::Symbol &sym : file->symbols())

    symtab->addLazy(this, sym);

}

// Returns a buffer pointing to a member file containing a given symbol.

void ArchiveFile::addMember(const Archive::Symbol &sym) {

  const Archive::Child &c =

      CHECK(sym.getMember(),

            "could not get the member for symbol " + toCOFFString(sym));

  // Return an empty buffer if we have already returned the same buffer.

  if (!seen.insert(c.getChildOffset()).second)

    return;

  driver->enqueueArchiveMember(c, sym, getName());

}

std::vector<MemoryBufferRef> getArchiveMembers(Archive *file) {

  std::vector<MemoryBufferRef> v;

  Error err = Error::success();

  for (const ErrorOr<Archive::Child> &cOrErr : file->children(err)) {

    Archive::Child c =

        CHECK(cOrErr,

              file->getFileName() + ": could not get the child of the archive");

    MemoryBufferRef mbref =

        CHECK(c.getMemoryBufferRef(),

              file->getFileName() +

                  ": could not get the buffer for a child of the archive");

    v.push_back(mbref);

  }

  if (err)

    fatal(file->getFileName() +

          ": Archive::children failed: " + toString(std::move(err)));

  return v;

}

void ObjFile::parse() {

  // Parse a memory buffer as a COFF file.

  std::unique_ptr<Binary> bin = CHECK(createBinary(mb), this);

  if (auto *obj = dyn_cast<COFFObjectFile>(bin.get())) {

    bin.release();

    coffObj.reset(obj);

  } else {

    fatal(toString(this) + " is not a COFF file");

  }

  // Read section and symbol tables.

  initializeChunks();

  initializeSymbols();

  initializeFlags();

  initializeDependencies();

}

const coff_section* ObjFile::getSection(uint32_t i) {

  const coff_section *sec;

  if (auto ec = coffObj->getSection(i, sec))

    fatal("getSection failed: #" + Twine(i) + ": " + ec.message());

  return sec;

}

// We set SectionChunk pointers in the SparseChunks vector to this value

// temporarily to mark comdat sections as having an unknown resolution. As we

// walk the object file's symbol table, once we visit either a leader symbol or

// an associative section definition together with the parent comdat's leader,

// we set the pointer to either nullptr (to mark the section as discarded) or a

// valid SectionChunk for that section.

static SectionChunk *const pendingComdat = reinterpret_cast<SectionChunk *>(1);

void ObjFile::initializeChunks() {

  uint32_t numSections = coffObj->getNumberOfSections();

  chunks.reserve(numSections);

  sparseChunks.resize(numSections + 1);

  for (uint32_t i = 1; i < numSections + 1; 
++i3.03k
) {

    const coff_section *sec = getSection(i);

    if (sec->Characteristics & IMAGE_SCN_LNK_COMDAT)

      sparseChunks[i] = pendingComdat;

    else

      sparseChunks[i] = readSection(i, nullptr, "");

  }

}

SectionChunk *ObjFile::readSection(uint32_t sectionNumber,

                                   const coff_aux_section_definition *def,

                                   StringRef leaderName) {

  const coff_section *sec = getSection(sectionNumber);

  StringRef name;

  if (Expected<StringRef> e = coffObj->getSectionName(sec))

    name = *e;

  else

    fatal("getSectionName failed: #" + Twine(sectionNumber) + ": " +

          toString(e.takeError()));

  if (name == ".drectve") {

    ArrayRef<uint8_t> data;

    cantFail(coffObj->getSectionContents(sec, data));

    directives = StringRef((const char *)data.data(), data.size());

    return nullptr;

  }

  if (name == ".llvm_addrsig") {

    addrsigSec = sec;

    return nullptr;

  }

  // Object files may have DWARF debug info or MS CodeView debug info

  // (or both).

  //

  // DWARF sections don't need any special handling from the perspective

  // of the linker; they are just a data section containing relocations.

  // We can just link them to complete debug info.

  //

  // CodeView needs linker support. We need to interpret debug info,

  // and then write it to a separate .pdb file.

  // Ignore DWARF debug info unless /debug is given.

  if (!config->debug && 
name.startswith(".debug_")2.07k
)

    return nullptr;

  if (sec->Characteristics & llvm::COFF::IMAGE_SCN_LNK_REMOVE)

    return nullptr;

  auto *c = make<SectionChunk>(this, sec);

  if (def)

    c->checksum = def->CheckSum;

  // link.exe uses the presence of .rsrc$01 for LNK4078, so match that.

  if (name == ".rsrc$01")

    isResourceObjFile = true;

  // CodeView sections are stored to a different vector because they are not

  // linked in the regular manner.

  if (c->isCodeView())

    debugChunks.push_back(c);

  else if (name == ".gfids$y")

    guardFidChunks.push_back(c);

  else if (name == ".gljmp$y")

    guardLJmpChunks.push_back(c);

  else if (name == ".sxdata")

    sXDataChunks.push_back(c);

  else if (config->tailMerge && 
sec->NumberOfRelocations == 01.85k
 &&

           
name == ".rdata"1.51k
 && 
leaderName.startswith("??_C@")44
)

    // COFF sections that look like string literal sections (i.e. no

    // relocations, in .rdata, leader symbol name matches the MSVC name mangling

    // for string literals) are subject to string tail merging.

    MergeChunk::addSection(c);

  else

    chunks.push_back(c);

  return c;

}

void ObjFile::readAssociativeDefinition(

    COFFSymbolRef sym, const coff_aux_section_definition *def) {

  readAssociativeDefinition(sym, def, def->getNumber(sym.isBigObj()));

}

void ObjFile::readAssociativeDefinition(COFFSymbolRef sym,

                                        const coff_aux_section_definition *def,

                                        uint32_t parentIndex) {

  SectionChunk *parent = sparseChunks[parentIndex];

  int32_t sectionNumber = sym.getSectionNumber();

  auto diag = [&]() {

    StringRef name, parentName;

    coffObj->getSymbolName(sym, name);

    const coff_section *parentSec = getSection(parentIndex);

    if (Expected<StringRef> e = coffObj->getSectionName(parentSec))

      parentName = *e;

    error(toString(this) + ": associative comdat " + name + " (sec " +

          Twine(sectionNumber) + ") has invalid reference to section " +

          parentName + " (sec " + Twine(parentIndex) + ")");

  };

  if (parent == pendingComdat) {

    // This can happen if an associative comdat refers to another associative

    // comdat that appears after it (invalid per COFF spec) or to a section

    // without any symbols.

    diag();

    return;

  }

  // Check whether the parent is prevailing. If it is, so are we, and we read

  // the section; otherwise mark it as discarded.

  if (parent) {

    SectionChunk *c = readSection(sectionNumber, def, "");

    sparseChunks[sectionNumber] = c;

    if (c) {

      c->selection = IMAGE_COMDAT_SELECT_ASSOCIATIVE;

      parent->addAssociative(c);

    }

  } else {

    sparseChunks[sectionNumber] = nullptr;

  }

}

void ObjFile::recordPrevailingSymbolForMingw(

    COFFSymbolRef sym, DenseMap<StringRef, uint32_t> &prevailingSectionMap) {

  // For comdat symbols in executable sections, where this is the copy

  // of the section chunk we actually include instead of discarding it,

  // add the symbol to a map to allow using it for implicitly

  // associating .[px]data$<func> sections to it.

  int32_t sectionNumber = sym.getSectionNumber();

  SectionChunk *sc = sparseChunks[sectionNumber];

  if (sc && sc->getOutputCharacteristics() & IMAGE_SCN_MEM_EXECUTE) {

    StringRef name;

    coffObj->getSymbolName(sym, name);

    if (getMachineType() == I386)

      name.consume_front("_");

    prevailingSectionMap[name] = sectionNumber;

  }

}

void ObjFile::maybeAssociateSEHForMingw(

    COFFSymbolRef sym, const coff_aux_section_definition *def,

    const DenseMap<StringRef, uint32_t> &prevailingSectionMap) {

  StringRef name;

  coffObj->getSymbolName(sym, name);

  if (name.consume_front(".pdata$") || 
name.consume_front(".xdata$")26
 ||

      
name.consume_front(".eh_frame$")18
) {

    // For MinGW, treat .[px]data$<func> and .eh_frame$<func> as implicitly

    // associative to the symbol <func>.

    auto parentSym = prevailingSectionMap.find(name);

    if (parentSym != prevailingSectionMap.end())

      readAssociativeDefinition(sym, def, parentSym->second);

  }

}

Symbol *ObjFile::createRegular(COFFSymbolRef sym) {

  SectionChunk *sc = sparseChunks[sym.getSectionNumber()];

  if (sym.isExternal()) {

    StringRef name;

    coffObj->getSymbolName(sym, name);

    if (sc)

      return symtab->addRegular(this, name, sym.getGeneric(), sc);

    // For MinGW symbols named .weak.* that point to a discarded section,

    // don't create an Undefined symbol. If nothing ever refers to the symbol,

    // everything should be fine. If something actually refers to the symbol

    // (e.g. the undefined weak alias), linking will fail due to undefined

    // references at the end.

    if (config->mingw && name.startswith(".weak."))

      return nullptr;

    return symtab->addUndefined(name, this, false);

  }

  if (sc)

    return make<DefinedRegular>(this, /*Name*/ "", /*IsCOMDAT*/ false,

                                /*IsExternal*/ false, sym.getGeneric(), sc);

  return nullptr;

}

void ObjFile::initializeSymbols() {

  uint32_t numSymbols = coffObj->getNumberOfSymbols();

  symbols.resize(numSymbols);

  SmallVector<std::pair<Symbol *, uint32_t>, 8> weakAliases;

  std::vector<uint32_t> pendingIndexes;

  pendingIndexes.reserve(numSymbols);

  DenseMap<StringRef, uint32_t> prevailingSectionMap;

  std::vector<const coff_aux_section_definition *> comdatDefs(

      coffObj->getNumberOfSections() + 1);

  for (uint32_t i = 0; i < numSymbols; 
++i5.72k
) {

    COFFSymbolRef coffSym = check(coffObj->getSymbol(i));

    bool prevailingComdat;

    if (coffSym.isUndefined()) {

      symbols[i] = createUndefined(coffSym);

    } else if (coffSym.isWeakExternal()) {

      symbols[i] = createUndefined(coffSym);

      uint32_t tagIndex = coffSym.getAux<coff_aux_weak_external>()->TagIndex;

      weakAliases.emplace_back(symbols[i], tagIndex);

    } else if (Optional<Symbol *> optSym =

                   createDefined(coffSym, comdatDefs, prevailingComdat)) {

      symbols[i] = *optSym;

      if (config->mingw && 
prevailingComdat452
)

        recordPrevailingSymbolForMingw(coffSym, prevailingSectionMap);

    } else {

      // createDefined() returns None if a symbol belongs to a section that

      // was pending at the point when the symbol was read. This can happen in

      // two cases:

      // 1) section definition symbol for a comdat leader;

      // 2) symbol belongs to a comdat section associated with another section.

      // In both of these cases, we can expect the section to be resolved by

      // the time we finish visiting the remaining symbols in the symbol

      // table. So we postpone the handling of this symbol until that time.

      pendingIndexes.push_back(i);

    }

    i += coffSym.getNumberOfAuxSymbols();

  }

  for (uint32_t i : pendingIndexes) {

    COFFSymbolRef sym = check(coffObj->getSymbol(i));

    if (const coff_aux_section_definition *def = sym.getSectionDefinition()) {

      if (def->Selection == IMAGE_COMDAT_SELECT_ASSOCIATIVE)

        readAssociativeDefinition(sym, def);

      else if (config->mingw)

        maybeAssociateSEHForMingw(sym, def, prevailingSectionMap);

    }

    if (sparseChunks[sym.getSectionNumber()] == pendingComdat) {

      StringRef name;

      coffObj->getSymbolName(sym, name);

      log("comdat section " + name +

          " without leader and unassociated, discarding");

      continue;

    }

    symbols[i] = createRegular(sym);

  }

  for (auto &kv : weakAliases) {

    Symbol *sym = kv.first;

    uint32_t idx = kv.second;

    checkAndSetWeakAlias(symtab, this, sym, symbols[idx]);

  }

}

Symbol *ObjFile::createUndefined(COFFSymbolRef sym) {

  StringRef name;

  coffObj->getSymbolName(sym, name);

  return symtab->addUndefined(name, this, sym.isWeakExternal());

}

void ObjFile::handleComdatSelection(COFFSymbolRef sym, COMDATType &selection,

                                    bool &prevailing, DefinedRegular *leader) {

  if (prevailing)

    return;

  // There's already an existing comdat for this symbol: `Leader`.

  // Use the comdats's selection field to determine if the new

  // symbol in `Sym` should be discarded, produce a duplicate symbol

  // error, etc.

  SectionChunk *leaderChunk = nullptr;

  COMDATType leaderSelection = IMAGE_COMDAT_SELECT_ANY;

  if (leader->data) {

    leaderChunk = leader->getChunk();

    leaderSelection = leaderChunk->selection;

  } else {

    // FIXME: comdats from LTO files don't know their selection; treat them

    // as "any".

    selection = leaderSelection;

  }

  if ((selection == IMAGE_COMDAT_SELECT_ANY &&

       
leaderSelection == IMAGE_COMDAT_SELECT_LARGEST20
) ||

      
(40
selection == IMAGE_COMDAT_SELECT_LARGEST40
 &&

       
leaderSelection == IMAGE_COMDAT_SELECT_ANY11
)) {

    // cl.exe picks "any" for vftables when building with /GR- and

    // "largest" when building with /GR. To be able to link object files

    // compiled with each flag, "any" and "largest" are merged as "largest".

    leaderSelection = selection = IMAGE_COMDAT_SELECT_LARGEST;

  }

  // Other than that, comdat selections must match.  This is a bit more

  // strict than link.exe which allows merging "any" and "largest" if "any"

  // is the first symbol the linker sees, and it allows merging "largest"

  // with everything (!) if "largest" is the first symbol the linker sees.

  // Making this symmetric independent of which selection is seen first

  // seems better though.

  // (This behavior matches ModuleLinker::getComdatResult().)

  if (selection != leaderSelection) {

    log(("conflicting comdat type for " + toString(*leader) + ": " +

         Twine((int)leaderSelection) + " in " + toString(leader->getFile()) +

         " and " + Twine((int)selection) + " in " + toString(this))

            .str());

    symtab->reportDuplicate(leader, this);

    return;

  }

  switch (selection) {

  case IMAGE_COMDAT_SELECT_NODUPLICATES:

    symtab->reportDuplicate(leader, this);

    break;

  case IMAGE_COMDAT_SELECT_ANY:

    // Nothing to do.

    break;

  case IMAGE_COMDAT_SELECT_SAME_SIZE:

    if (leaderChunk->getSize() != getSection(sym)->SizeOfRawData)

      symtab->reportDuplicate(leader, this);

    break;

  case IMAGE_COMDAT_SELECT_EXACT_MATCH: {

    SectionChunk newChunk(this, getSection(sym));

    // link.exe only compares section contents here and doesn't complain

    // if the two comdat sections have e.g. different alignment.

    // Match that.

    if (leaderChunk->getContents() != newChunk.getContents())

      symtab->reportDuplicate(leader, this);

    break;

  }

  case IMAGE_COMDAT_SELECT_ASSOCIATIVE:

    // createDefined() is never called for IMAGE_COMDAT_SELECT_ASSOCIATIVE.

    // (This means lld-link doesn't produce duplicate symbol errors for

    // associative comdats while link.exe does, but associate comdats

    // are never extern in practice.)

    llvm_unreachable("createDefined not called for associative comdats");

  case IMAGE_COMDAT_SELECT_LARGEST:

    if (leaderChunk->getSize() < getSection(sym)->SizeOfRawData) {

      // Replace the existing comdat symbol with the new one.

      StringRef name;

      coffObj->getSymbolName(sym, name);

      // FIXME: This is incorrect: With /opt:noref, the previous sections

      // make it into the final executable as well. Correct handling would

      // be to undo reading of the whole old section that's being replaced,

      // or doing one pass that determines what the final largest comdat

      // is for all IMAGE_COMDAT_SELECT_LARGEST comdats and then reading

      // only the largest one.

      replaceSymbol<DefinedRegular>(leader, this, name, /*IsCOMDAT*/ true,

                                    /*IsExternal*/ true, sym.getGeneric(),

                                    nullptr);

      prevailing = true;

    }

    break;

  case IMAGE_COMDAT_SELECT_NEWEST:

    llvm_unreachable("should have been rejected earlier");

  }

}

Optional<Symbol *> ObjFile::createDefined(

    COFFSymbolRef sym,

    std::vector<const coff_aux_section_definition *> &comdatDefs,

    bool &prevailing) {

  prevailing = false;

  auto getName = [&]() {

    StringRef s;

    coffObj->getSymbolName(sym, s);

    return s;

  };

  if (sym.isCommon()) {

    auto *c = make<CommonChunk>(sym);

    chunks.push_back(c);

    return symtab->addCommon(this, getName(), sym.getValue(), sym.getGeneric(),

                             c);

  }

  if (sym.isAbsolute()) {

    StringRef name = getName();

    // Skip special symbols.

    if (name == "@comp.id")

      return nullptr;

    if (name == "@feat.00") {

      feat00Flags = sym.getValue();

      return nullptr;

    }

    if (sym.isExternal())

      return symtab->addAbsolute(name, sym);

    return make<DefinedAbsolute>(name, sym);

  }

  int32_t sectionNumber = sym.getSectionNumber();

  if (sectionNumber == llvm::COFF::IMAGE_SYM_DEBUG)

    return nullptr;

  if (llvm::COFF::isReservedSectionNumber(sectionNumber))

    fatal(toString(this) + ": " + getName() +

          " should not refer to special section " + Twine(sectionNumber));

  if ((uint32_t)sectionNumber >= sparseChunks.size())

    fatal(toString(this) + ": " + getName() +

          " should not refer to non-existent section " + Twine(sectionNumber));

  // Comdat handling.

  // A comdat symbol consists of two symbol table entries.

  // The first symbol entry has the name of the section (e.g. .text), fixed

  // values for the other fields, and one auxilliary record.

  // The second symbol entry has the name of the comdat symbol, called the

  // "comdat leader".

  // When this function is called for the first symbol entry of a comdat,

  // it sets comdatDefs and returns None, and when it's called for the second

  // symbol entry it reads comdatDefs and then sets it back to nullptr.

  // Handle comdat leader.

  if (const coff_aux_section_definition *def = comdatDefs[sectionNumber]) {

    comdatDefs[sectionNumber] = nullptr;

    DefinedRegular *leader;

    if (sym.isExternal()) {

      std::tie(leader, prevailing) =

          symtab->addComdat(this, getName(), sym.getGeneric());

    } else {

      leader = make<DefinedRegular>(this, /*Name*/ "", /*IsCOMDAT*/ false,

                                    /*IsExternal*/ false, sym.getGeneric());

      prevailing = true;

    }

    if (def->Selection < (int)IMAGE_COMDAT_SELECT_NODUPLICATES ||

        // Intentionally ends at IMAGE_COMDAT_SELECT_LARGEST: link.exe

        // doesn't understand IMAGE_COMDAT_SELECT_NEWEST either.

        def->Selection > (int)IMAGE_COMDAT_SELECT_LARGEST) {

      fatal("unknown comdat type " + std::to_string((int)def->Selection) +

            " for " + getName() + " in " + toString(this));

    }

    COMDATType selection = (COMDATType)def->Selection;

    if (leader->isCOMDAT)

      handleComdatSelection(sym, selection, prevailing, leader);

    if (prevailing) {

      SectionChunk *c = readSection(sectionNumber, def, getName());

      sparseChunks[sectionNumber] = c;

      c->sym = cast<DefinedRegular>(leader);

      c->selection = selection;

      cast<DefinedRegular>(leader)->data = &c->repl;

    } else {

      sparseChunks[sectionNumber] = nullptr;

    }

    return leader;

  }

  // Prepare to handle the comdat leader symbol by setting the section's

  // ComdatDefs pointer if we encounter a non-associative comdat.

  if (sparseChunks[sectionNumber] == pendingComdat) {

    if (const coff_aux_section_definition *def = sym.getSectionDefinition()) {

      if (def->Selection != IMAGE_COMDAT_SELECT_ASSOCIATIVE)

        comdatDefs[sectionNumber] = def;

    }

    return None;

  }

  return createRegular(sym);

}

MachineTypes ObjFile::getMachineType() {

  if (coffObj)

    return static_cast<MachineTypes>(coffObj->getMachine());

  return IMAGE_FILE_MACHINE_UNKNOWN;

}

ArrayRef<uint8_t> ObjFile::getDebugSection(StringRef secName) {

  if (SectionChunk *sec = SectionChunk::findByName(debugChunks, secName))

    return sec->consumeDebugMagic();

  return {};

}

// OBJ files systematically store critical informations in a .debug$S stream,

// even if the TU was compiled with no debug info. At least two records are

// always there. S_OBJNAME stores a 32-bit signature, which is loaded into the

// PCHSignature member. S_COMPILE3 stores compile-time cmd-line flags. This is

// currently used to initialize the hotPatchable member.

void ObjFile::initializeFlags() {

  ArrayRef<uint8_t> data = getDebugSection(".debug$S");

  if (data.empty())

    return;

  DebugSubsectionArray subsections;

  BinaryStreamReader reader(data, support::little);

  ExitOnError exitOnErr;

  exitOnErr(reader.readArray(subsections, data.size()));

  for (const DebugSubsectionRecord &ss : subsections) {

    if (ss.kind() != DebugSubsectionKind::Symbols)

      continue;

    unsigned offset = 0;

    // Only parse the first two records. We are only looking for S_OBJNAME

    // and S_COMPILE3, and they usually appear at the beginning of the

    // stream.

    for (unsigned i = 0; i < 2; 
++i489
) {

      Expected<CVSymbol> sym = readSymbolFromStream(ss.getRecordData(), offset);

      if (!sym) {

        consumeError(sym.takeError());

        return;

      }

      if (sym->kind() == SymbolKind::S_COMPILE3) {

        auto cs =

            cantFail(SymbolDeserializer::deserializeAs<Compile3Sym>(sym.get()));

        hotPatchable =

            (cs.Flags & CompileSym3Flags::HotPatch) != CompileSym3Flags::None;

      }

      if (sym->kind() == SymbolKind::S_OBJNAME) {

        auto objName = cantFail(SymbolDeserializer::deserializeAs<ObjNameSym>(

            sym.get()));

        pchSignature = objName.Signature;

      }

      offset += sym->length();

    }

  }

}

// Depending on the compilation flags, OBJs can refer to external files,

// necessary to merge this OBJ into the final PDB. We currently support two

// types of external files: Precomp/PCH OBJs, when compiling with /Yc and /Yu.

// And PDB type servers, when compiling with /Zi. This function extracts these

// dependencies and makes them available as a TpiSource interface (see

// DebugTypes.h). Both cases only happen with cl.exe: clang-cl produces regular

// output even with /Yc and /Yu and with /Zi.

void ObjFile::initializeDependencies() {

  if (!config->debug)

    return;

  bool isPCH = false;

  ArrayRef<uint8_t> data = getDebugSection(".debug$P");

  if (!data.empty())

    isPCH = true;

  else

    data = getDebugSection(".debug$T");

  if (data.empty())

    return;

  CVTypeArray types;

  BinaryStreamReader reader(data, support::little);

  cantFail(reader.readArray(types, reader.getLength()));

  CVTypeArray::Iterator firstType = types.begin();

  if (firstType == types.end())

    return;

  debugTypes.emplace(types);

  if (isPCH) {

    debugTypesObj = makePrecompSource(this);

    return;

  }

  if (firstType->kind() == LF_TYPESERVER2) {

    TypeServer2Record ts = cantFail(

        TypeDeserializer::deserializeAs<TypeServer2Record>(firstType->data()));

    debugTypesObj = makeUseTypeServerSource(this, &ts);

    return;

  }

  if (firstType->kind() == LF_PRECOMP) {

    PrecompRecord precomp = cantFail(

        TypeDeserializer::deserializeAs<PrecompRecord>(firstType->data()));

    debugTypesObj = makeUsePrecompSource(this, &precomp);

    return;

  }

  debugTypesObj = makeTpiSource(this);

}

StringRef ltrim1(StringRef s, const char *chars) {

  if (!s.empty() && strchr(chars, s[0]))

    return s.substr(1);

  return s;

}

void ImportFile::parse() {

  const char *buf = mb.getBufferStart();

  const auto *hdr = reinterpret_cast<const coff_import_header *>(buf);

  // Check if the total size is valid.

  if (mb.getBufferSize() != sizeof(*hdr) + hdr->SizeOfData)

    fatal("broken import library");

  // Read names and create an __imp_ symbol.

  StringRef name = saver.save(StringRef(buf + sizeof(*hdr)));

  StringRef impName = saver.save("__imp_" + name);

  const char *nameStart = buf + sizeof(coff_import_header) + name.size() + 1;

  dllName = StringRef(nameStart);

  StringRef extName;

  switch (hdr->getNameType()) {

  case IMPORT_ORDINAL:

    extName = "";

    break;

  case IMPORT_NAME:

    extName = name;

    break;

  case IMPORT_NAME_NOPREFIX:

    extName = ltrim1(name, "?@_");

    break;

  case IMPORT_NAME_UNDECORATE:

    extName = ltrim1(name, "?@_");

    extName = extName.substr(0, extName.find('@'));

    break;

  }

  this->hdr = hdr;

  externalName = extName;

  impSym = symtab->addImportData(impName, this);

  // If this was a duplicate, we logged an error but may continue;

  // in this case, impSym is nullptr.

  if (!impSym)

    return;

  if (hdr->getType() == llvm::COFF::IMPORT_CONST)

    static_cast<void>(symtab->addImportData(name, this));

  // If type is function, we need to create a thunk which jump to an

  // address pointed by the __imp_ symbol. (This allows you to call

  // DLL functions just like regular non-DLL functions.)

  if (hdr->getType() == llvm::COFF::IMPORT_CODE)

    thunkSym = symtab->addImportThunk(

        name, cast_or_null<DefinedImportData>(impSym), hdr->Machine);

}

BitcodeFile::BitcodeFile(MemoryBufferRef mb, StringRef archiveName,

                         uint64_t offsetInArchive)

    : InputFile(BitcodeKind, mb) {

  std::string path = mb.getBufferIdentifier().str();

  if (config->thinLTOIndexOnly)

    path = replaceThinLTOSuffix(mb.getBufferIdentifier());

  // ThinLTO assumes that all MemoryBufferRefs given to it have a unique

  // name. If two archives define two members with the same name, this

  // causes a collision which result in only one of the objects being taken

  // into consideration at LTO time (which very likely causes undefined

  // symbols later in the link stage). So we append file offset to make

  // filename unique.

  MemoryBufferRef mbref(

      mb.getBuffer(),

      saver.save(archiveName + path +

                 (archiveName.empty() ? 
""65
 : 
utostr(offsetInArchive)12
)));

  obj = check(lto::InputFile::create(mbref));

}

void BitcodeFile::parse() {

  std::vector<std::pair<Symbol *, bool>> comdat(obj->getComdatTable().size());

  for (size_t i = 0; i != obj->getComdatTable().size(); 
++i29
)

    // FIXME: lto::InputFile doesn't keep enough data to do correct comdat

    // selection handling.

    comdat[i] = symtab->addComdat(this, saver.save(obj->getComdatTable()[i]));

  for (const lto::InputFile::Symbol &objSym : obj->symbols()) {

    StringRef symName = saver.save(objSym.getName());

    int comdatIndex = objSym.getComdatIndex();

    Symbol *sym;

    if (objSym.isUndefined()) {

      sym = symtab->addUndefined(symName, this, false);

    } else if (objSym.isCommon()) {

      sym = symtab->addCommon(this, symName, objSym.getCommonSize());

    } else if (objSym.isWeak() && 
objSym.isIndirect()22
) {

      // Weak external.

      sym = symtab->addUndefined(symName, this, true);

      std::string fallback = objSym.getCOFFWeakExternalFallback();

      Symbol *alias = symtab->addUndefined(saver.save(fallback));

      checkAndSetWeakAlias(symtab, this, sym, alias);

    } else if (comdatIndex != -1) {

      if (symName == obj->getComdatTable()[comdatIndex])

        sym = comdat[comdatIndex].first;

      else if (comdat[comdatIndex].second)

        sym = symtab->addRegular(this, symName);

      else

        sym = symtab->addUndefined(symName, this, false);

    } else {

      sym = symtab->addRegular(this, symName);

    }

    symbols.push_back(sym);

    if (objSym.isUsed())

      config->gcroot.push_back(sym);

  }

  directives = obj->getCOFFLinkerOpts();

}

MachineTypes BitcodeFile::getMachineType() {

  switch (Triple(obj->getTargetTriple()).getArch()) {

  case Triple::x86_64:

    return AMD64;

  case Triple::x86:

    return I386;

  case Triple::arm:

    return ARMNT;

  case Triple::aarch64:

    return ARM64;

  default:

    return IMAGE_FILE_MACHINE_UNKNOWN;

  }

}

std::string replaceThinLTOSuffix(StringRef path) {

  StringRef suffix = config->thinLTOObjectSuffixReplace.first;

  StringRef repl = config->thinLTOObjectSuffixReplace.second;

  if (path.consume_back(suffix))

    return (path + repl).str();

  return path;

}

} // namespace coff

} // namespace lld

// Returns the last element of a path, which is supposed to be a filename.

static StringRef getBasename(StringRef path) {

  return sys::path::filename(path, sys::path::Style::windows);

}

// Returns a string in the format of "foo.obj" or "foo.obj(bar.lib)".

std::string lld::toString(const coff::InputFile *file) {

  if (!file)

    return "<internal>";

  if (file->parentName.empty() || 
file->kind() == coff::InputFile::ImportKind228
)

    return file->getName();

  return (getBasename(file->parentName) + "(" + getBasename(file->getName()) +

          ")")

      .str();

}