xref: /llvm-project-15.0.7/lld/ELF/SymbolTable.cpp (revision f05b42e9)

//===- SymbolTable.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
//
//===----------------------------------------------------------------------===//
//
// Symbol table is a bag of all known symbols. We put all symbols of
// all input files to the symbol table. The symbol table is basically
// a hash table with the logic to resolve symbol name conflicts using
// the symbol types.
//
//===----------------------------------------------------------------------===//

#include "SymbolTable.h"
#include "Config.h"
#include "LinkerScript.h"
#include "Symbols.h"
#include "SyntheticSections.h"
#include "lld/Common/ErrorHandler.h"
#include "lld/Common/Memory.h"
#include "lld/Common/Strings.h"
#include "llvm/ADT/STLExtras.h"

using namespace llvm;
using namespace llvm::object;
using namespace llvm::ELF;

using namespace lld;
using namespace lld::elf;

SymbolTable *elf::Symtab;

static InputFile *getFirstElf() {
  if (!ObjectFiles.empty())
    return ObjectFiles[0];
  if (!SharedFiles.empty())
    return SharedFiles[0];
  return BitcodeFiles[0];
}

// All input object files must be for the same architecture
// (e.g. it does not make sense to link x86 object files with
// MIPS object files.) This function checks for that error.
static bool isCompatible(InputFile *F) {
  if (!F->isElf() && !isa<BitcodeFile>(F))
    return true;

  if (F->EKind == Config->EKind && F->EMachine == Config->EMachine) {
    if (Config->EMachine != EM_MIPS)
      return true;
    if (isMipsN32Abi(F) == Config->MipsN32Abi)
      return true;
  }

  if (!Config->Emulation.empty())
    error(toString(F) + " is incompatible with " + Config->Emulation);
  else
    error(toString(F) + " is incompatible with " + toString(getFirstElf()));
  return false;
}

// Add symbols in File to the symbol table.
template <class ELFT> void SymbolTable::addFile(InputFile *File) {
  if (!isCompatible(File))
    return;

  // Binary file
  if (auto *F = dyn_cast<BinaryFile>(File)) {
    BinaryFiles.push_back(F);
    F->parse();
    return;
  }

  // .a file
  if (auto *F = dyn_cast<ArchiveFile>(File)) {
    F->parse<ELFT>();
    return;
  }

  // Lazy object file
  if (auto *F = dyn_cast<LazyObjFile>(File)) {
    LazyObjFiles.push_back(F);
    F->parse<ELFT>();
    return;
  }

  if (Config->Trace)
    message(toString(File));

  // .so file
  if (auto *F = dyn_cast<SharedFile<ELFT>>(File)) {
    // DSOs are uniquified not by filename but by soname.
    F->parseDynamic();
    if (errorCount())
      return;

    // If a DSO appears more than once on the command line with and without
    // --as-needed, --no-as-needed takes precedence over --as-needed because a
    // user can add an extra DSO with --no-as-needed to force it to be added to
    // the dependency list.
    DenseMap<StringRef, InputFile *>::iterator It;
    bool WasInserted;
    std::tie(It, WasInserted) = SoNames.try_emplace(F->SoName, F);
    cast<SharedFile<ELFT>>(It->second)->IsNeeded |= F->IsNeeded;
    if (!WasInserted)
      return;

    SharedFiles.push_back(F);
    F->parseRest();
    return;
  }

  // LLVM bitcode file
  if (auto *F = dyn_cast<BitcodeFile>(File)) {
    BitcodeFiles.push_back(F);
    F->parse<ELFT>(ComdatGroups);
    return;
  }

  // Regular object file
  ObjectFiles.push_back(File);
  cast<ObjFile<ELFT>>(File)->parse(ComdatGroups);
}

// This function is where all the optimizations of link-time
// optimization happens. When LTO is in use, some input files are
// not in native object file format but in the LLVM bitcode format.
// This function compiles bitcode files into a few big native files
// using LLVM functions and replaces bitcode symbols with the results.
// Because all bitcode files that the program consists of are passed
// to the compiler at once, it can do whole-program optimization.
template <class ELFT> void SymbolTable::addCombinedLTOObject() {
  if (BitcodeFiles.empty())
    return;

  // Compile bitcode files and replace bitcode symbols.
  LTO.reset(new BitcodeCompiler);
  for (BitcodeFile *F : BitcodeFiles)
    LTO->add(*F);

  for (InputFile *File : LTO->compile()) {
    DenseSet<CachedHashStringRef> DummyGroups;
    auto *Obj = cast<ObjFile<ELFT>>(File);
    Obj->parse(DummyGroups);
    for (Symbol *Sym : Obj->getGlobalSymbols())
      Sym->parseSymbolVersion();
    ObjectFiles.push_back(File);
  }
}

// Set a flag for --trace-symbol so that we can print out a log message
// if a new symbol with the same name is inserted into the symbol table.
void SymbolTable::trace(StringRef Name) {
  SymMap.insert({CachedHashStringRef(Name), -1});
}

void SymbolTable::wrap(Symbol *Sym, Symbol *Real, Symbol *Wrap) {
  // Swap symbols as instructed by -wrap.
  int &Idx1 = SymMap[CachedHashStringRef(Sym->getName())];
  int &Idx2 = SymMap[CachedHashStringRef(Real->getName())];
  int &Idx3 = SymMap[CachedHashStringRef(Wrap->getName())];

  Idx2 = Idx1;
  Idx1 = Idx3;

  // Now renaming is complete. No one refers Real symbol. We could leave
  // Real as-is, but if Real is written to the symbol table, that may
  // contain irrelevant values. So, we copy all values from Sym to Real.
  StringRef S = Real->getName();
  memcpy(Real, Sym, sizeof(SymbolUnion));
  Real->setName(S);
}

static uint8_t getMinVisibility(uint8_t VA, uint8_t VB) {
  if (VA == STV_DEFAULT)
    return VB;
  if (VB == STV_DEFAULT)
    return VA;
  return std::min(VA, VB);
}

// Find an existing symbol or create and insert a new one.
std::pair<Symbol *, bool> SymbolTable::insertName(StringRef Name) {
  // <name>@@<version> means the symbol is the default version. In that
  // case <name>@@<version> will be used to resolve references to <name>.
  //
  // Since this is a hot path, the following string search code is
  // optimized for speed. StringRef::find(char) is much faster than
  // StringRef::find(StringRef).
  size_t Pos = Name.find('@');
  if (Pos != StringRef::npos && Pos + 1 < Name.size() && Name[Pos + 1] == '@')
    Name = Name.take_front(Pos);

  auto P = SymMap.insert({CachedHashStringRef(Name), (int)SymVector.size()});
  int &SymIndex = P.first->second;
  bool IsNew = P.second;
  bool Traced = false;

  if (SymIndex == -1) {
    SymIndex = SymVector.size();
    IsNew = true;
    Traced = true;
  }

  if (!IsNew)
    return {SymVector[SymIndex], false};

  auto *Sym = reinterpret_cast<Symbol *>(make<SymbolUnion>());
  Sym->SymbolKind = Symbol::PlaceholderKind;
  Sym->Visibility = STV_DEFAULT;
  Sym->IsUsedInRegularObj = false;
  Sym->ExportDynamic = false;
  Sym->CanInline = true;
  Sym->Traced = Traced;
  Sym->VersionId = Config->DefaultSymbolVersion;
  SymVector.push_back(Sym);
  return {Sym, true};
}

// Find an existing symbol or create and insert a new one, then apply the given
// attributes.
std::pair<Symbol *, bool> SymbolTable::insert(StringRef Name,
                                              uint8_t Visibility,
                                              bool CanOmitFromDynSym,
                                              InputFile *File) {
  Symbol *S;
  bool WasInserted;
  std::tie(S, WasInserted) = insertName(Name);

  // Merge in the new symbol's visibility.
  S->Visibility = getMinVisibility(S->Visibility, Visibility);

  if (!CanOmitFromDynSym && (Config->Shared || Config->ExportDynamic))
    S->ExportDynamic = true;

  if (!File || File->kind() == InputFile::ObjKind)
    S->IsUsedInRegularObj = true;

  return {S, WasInserted};
}

static uint8_t getVisibility(uint8_t StOther) { return StOther & 3; }

template <class ELFT>
Symbol *SymbolTable::addUndefined(StringRef Name, uint8_t Binding,
                                  uint8_t StOther, uint8_t Type,
                                  bool CanOmitFromDynSym, InputFile *File) {
  Symbol *S;
  bool WasInserted;
  uint8_t Visibility = getVisibility(StOther);
  std::tie(S, WasInserted) = insert(Name, Visibility, CanOmitFromDynSym, File);

  // An undefined symbol with non default visibility must be satisfied
  // in the same DSO.
  if (WasInserted || (isa<SharedSymbol>(S) && Visibility != STV_DEFAULT)) {
    replaceSymbol<Undefined>(S, File, Name, Binding, StOther, Type);
    return S;
  }

  if (S->isShared() || S->isLazy() || (S->isUndefined() && Binding != STB_WEAK))
    S->Binding = Binding;

  if (S->isLazy()) {
    // An undefined weak will not fetch archive members. See comment on Lazy in
    // Symbols.h for the details.
    if (Binding == STB_WEAK) {
      S->Type = Type;
      return S;
    }

    // Do extra check for --warn-backrefs.
    //
    // --warn-backrefs is an option to prevent an undefined reference from
    // fetching an archive member written earlier in the command line. It can be
    // used to keep compatibility with GNU linkers to some degree.
    // I'll explain the feature and why you may find it useful in this comment.
    //
    // lld's symbol resolution semantics is more relaxed than traditional Unix
    // linkers. For example,
    //
    //   ld.lld foo.a bar.o
    //
    // succeeds even if bar.o contains an undefined symbol that has to be
    // resolved by some object file in foo.a. Traditional Unix linkers don't
    // allow this kind of backward reference, as they visit each file only once
    // from left to right in the command line while resolving all undefined
    // symbols at the moment of visiting.
    //
    // In the above case, since there's no undefined symbol when a linker visits
    // foo.a, no files are pulled out from foo.a, and because the linker forgets
    // about foo.a after visiting, it can't resolve undefined symbols in bar.o
    // that could have been resolved otherwise.
    //
    // That lld accepts more relaxed form means that (besides it'd make more
    // sense) you can accidentally write a command line or a build file that
    // works only with lld, even if you have a plan to distribute it to wider
    // users who may be using GNU linkers. With --warn-backrefs, you can detect
    // a library order that doesn't work with other Unix linkers.
    //
    // The option is also useful to detect cyclic dependencies between static
    // archives. Again, lld accepts
    //
    //   ld.lld foo.a bar.a
    //
    // even if foo.a and bar.a depend on each other. With --warn-backrefs, it is
    // handled as an error.
    //
    // Here is how the option works. We assign a group ID to each file. A file
    // with a smaller group ID can pull out object files from an archive file
    // with an equal or greater group ID. Otherwise, it is a reverse dependency
    // and an error.
    //
    // A file outside --{start,end}-group gets a fresh ID when instantiated. All
    // files within the same --{start,end}-group get the same group ID. E.g.
    //
    //   ld.lld A B --start-group C D --end-group E
    //
    // A forms group 0. B form group 1. C and D (including their member object
    // files) form group 2. E forms group 3. I think that you can see how this
    // group assignment rule simulates the traditional linker's semantics.
    bool Backref =
        Config->WarnBackrefs && File && S->File->GroupId < File->GroupId;
    fetchLazy<ELFT>(S);

    // We don't report backward references to weak symbols as they can be
    // overridden later.
    if (Backref && !S->isWeak())
      warn("backward reference detected: " + Name + " in " + toString(File) +
           " refers to " + toString(S->File));
  }
  return S;
}

// Using .symver foo,foo@@VER unfortunately creates two symbols: foo and
// foo@@VER. We want to effectively ignore foo, so give precedence to
// foo@@VER.
// FIXME: If users can transition to using
// .symver foo,foo@@@VER
// we can delete this hack.
static int compareVersion(Symbol *S, StringRef Name) {
  bool A = Name.contains("@@");
  bool B = S->getName().contains("@@");
  if (A && !B)
    return 1;
  if (!A && B)
    return -1;
  return 0;
}

// We have a new defined symbol with the specified binding. Return 1 if the new
// symbol should win, -1 if the new symbol should lose, or 0 if both symbols are
// strong defined symbols.
static int compareDefined(Symbol *S, bool WasInserted, uint8_t Binding,
                          StringRef Name) {
  if (WasInserted)
    return 1;
  if (!S->isDefined())
    return 1;
  if (int R = compareVersion(S, Name))
    return R;
  if (Binding == STB_WEAK)
    return -1;
  if (S->isWeak())
    return 1;
  return 0;
}

// We have a new non-common defined symbol with the specified binding. Return 1
// if the new symbol should win, -1 if the new symbol should lose, or 0 if there
// is a conflict. If the new symbol wins, also update the binding.
static int compareDefinedNonCommon(Symbol *S, bool WasInserted, uint8_t Binding,
                                   bool IsAbsolute, uint64_t Value,
                                   StringRef Name) {
  if (int Cmp = compareDefined(S, WasInserted, Binding, Name))
    return Cmp;
  if (auto *R = dyn_cast<Defined>(S)) {
    if (R->Section && isa<BssSection>(R->Section)) {
      // Non-common symbols take precedence over common symbols.
      if (Config->WarnCommon)
        warn("common " + S->getName() + " is overridden");
      return 1;
    }
    if (R->Section == nullptr && Binding == STB_GLOBAL && IsAbsolute &&
        R->Value == Value)
      return -1;
  }
  return 0;
}

Symbol *SymbolTable::addCommon(StringRef N, uint64_t Size, uint32_t Alignment,
                               uint8_t Binding, uint8_t StOther, uint8_t Type,
                               InputFile &File) {
  Symbol *S;
  bool WasInserted;
  std::tie(S, WasInserted) = insert(N, getVisibility(StOther),
                                    /*CanOmitFromDynSym*/ false, &File);

  int Cmp = compareDefined(S, WasInserted, Binding, N);
  if (Cmp < 0)
    return S;

  if (Cmp > 0) {
    auto *Bss = make<BssSection>("COMMON", Size, Alignment);
    Bss->File = &File;
    Bss->Live = !Config->GcSections;
    InputSections.push_back(Bss);

    replaceSymbol<Defined>(S, &File, N, Binding, StOther, Type, 0, Size, Bss);
    return S;
  }

  auto *D = cast<Defined>(S);
  auto *Bss = dyn_cast_or_null<BssSection>(D->Section);
  if (!Bss) {
    // Non-common symbols take precedence over common symbols.
    if (Config->WarnCommon)
      warn("common " + S->getName() + " is overridden");
    return S;
  }

  if (Config->WarnCommon)
    warn("multiple common of " + D->getName());

  Bss->Alignment = std::max(Bss->Alignment, Alignment);
  if (Size > Bss->Size) {
    D->File = Bss->File = &File;
    D->Size = Bss->Size = Size;
  }
  return S;
}

static void reportDuplicate(Symbol *Sym, InputFile *NewFile,
                            InputSectionBase *ErrSec, uint64_t ErrOffset) {
  if (Config->AllowMultipleDefinition)
    return;

  Defined *D = cast<Defined>(Sym);
  if (!D->Section || !ErrSec) {
    error("duplicate symbol: " + toString(*Sym) + "\n>>> defined in " +
          toString(Sym->File) + "\n>>> defined in " + toString(NewFile));
    return;
  }

  // Construct and print an error message in the form of:
  //
  //   ld.lld: error: duplicate symbol: foo
  //   >>> defined at bar.c:30
  //   >>>            bar.o (/home/alice/src/bar.o)
  //   >>> defined at baz.c:563
  //   >>>            baz.o in archive libbaz.a
  auto *Sec1 = cast<InputSectionBase>(D->Section);
  std::string Src1 = Sec1->getSrcMsg(*Sym, D->Value);
  std::string Obj1 = Sec1->getObjMsg(D->Value);
  std::string Src2 = ErrSec->getSrcMsg(*Sym, ErrOffset);
  std::string Obj2 = ErrSec->getObjMsg(ErrOffset);

  std::string Msg = "duplicate symbol: " + toString(*Sym) + "\n>>> defined at ";
  if (!Src1.empty())
    Msg += Src1 + "\n>>>            ";
  Msg += Obj1 + "\n>>> defined at ";
  if (!Src2.empty())
    Msg += Src2 + "\n>>>            ";
  Msg += Obj2;
  error(Msg);
}

Defined *SymbolTable::addDefined(StringRef Name, uint8_t StOther, uint8_t Type,
                                 uint64_t Value, uint64_t Size, uint8_t Binding,
                                 SectionBase *Section, InputFile *File) {
  Symbol *S;
  bool WasInserted;
  std::tie(S, WasInserted) = insert(Name, getVisibility(StOther),
                                    /*CanOmitFromDynSym*/ false, File);
  int Cmp = compareDefinedNonCommon(S, WasInserted, Binding, Section == nullptr,
                                    Value, Name);
  if (Cmp > 0)
    replaceSymbol<Defined>(S, File, Name, Binding, StOther, Type, Value, Size,
                           Section);
  else if (Cmp == 0)
    reportDuplicate(S, File, dyn_cast_or_null<InputSectionBase>(Section),
                    Value);
  return cast<Defined>(S);
}

template <typename ELFT>
void SymbolTable::addShared(StringRef Name, SharedFile<ELFT> &File,
                            const typename ELFT::Sym &Sym, uint32_t Alignment,
                            uint32_t VerdefIndex) {
  // DSO symbols do not affect visibility in the output, so we pass STV_DEFAULT
  // as the visibility, which will leave the visibility in the symbol table
  // unchanged.
  Symbol *S;
  bool WasInserted;
  std::tie(S, WasInserted) = insert(Name, STV_DEFAULT,
                                    /*CanOmitFromDynSym*/ true, &File);
  // Make sure we preempt DSO symbols with default visibility.
  if (Sym.getVisibility() == STV_DEFAULT)
    S->ExportDynamic = true;

  // An undefined symbol with non default visibility must be satisfied
  // in the same DSO.
  auto Replace = [&](uint8_t Binding) {
    replaceSymbol<SharedSymbol>(S, File, Name, Binding, Sym.st_other,
                                Sym.getType(), Sym.st_value, Sym.st_size,
                                Alignment, VerdefIndex);
  };

  if (WasInserted)
    Replace(Sym.getBinding());
  else if (S->Visibility == STV_DEFAULT && (S->isUndefined() || S->isLazy()))
    Replace(S->Binding);
}

Symbol *SymbolTable::addBitcode(StringRef Name, uint8_t Binding,
                                uint8_t StOther, uint8_t Type,
                                bool CanOmitFromDynSym, BitcodeFile &F) {
  Symbol *S;
  bool WasInserted;
  std::tie(S, WasInserted) =
      insert(Name, getVisibility(StOther), CanOmitFromDynSym, &F);
  int Cmp = compareDefinedNonCommon(S, WasInserted, Binding,
                                    /*IsAbs*/ false, /*Value*/ 0, Name);
  if (Cmp > 0)
    replaceSymbol<Defined>(S, &F, Name, Binding, StOther, Type, 0, 0, nullptr);
  else if (Cmp == 0)
    reportDuplicate(S, &F, nullptr, 0);
  return S;
}

Symbol *SymbolTable::find(StringRef Name) {
  auto It = SymMap.find(CachedHashStringRef(Name));
  if (It == SymMap.end())
    return nullptr;
  if (It->second == -1)
    return nullptr;
  return SymVector[It->second];
}

template <class ELFT>
void SymbolTable::addLazyArchive(StringRef Name, ArchiveFile &File,
                                 const object::Archive::Symbol Sym) {
  Symbol *S;
  bool WasInserted;
  std::tie(S, WasInserted) = insertName(Name);
  if (WasInserted) {
    replaceSymbol<LazyArchive>(S, File, STT_NOTYPE, Sym);
    return;
  }
  if (!S->isUndefined())
    return;

  // An undefined weak will not fetch archive members. See comment on Lazy in
  // Symbols.h for the details.
  if (S->isWeak()) {
    replaceSymbol<LazyArchive>(S, File, S->Type, Sym);
    S->Binding = STB_WEAK;
    return;
  }

  if (InputFile *F = File.fetch(Sym))
    addFile<ELFT>(F);
}

template <class ELFT>
void SymbolTable::addLazyObject(StringRef Name, LazyObjFile &File) {
  Symbol *S;
  bool WasInserted;
  std::tie(S, WasInserted) = insertName(Name);
  if (WasInserted) {
    replaceSymbol<LazyObject>(S, File, STT_NOTYPE, Name);
    return;
  }
  if (!S->isUndefined())
    return;

  // An undefined weak will not fetch archive members. See comment on Lazy in
  // Symbols.h for the details.
  if (S->isWeak()) {
    replaceSymbol<LazyObject>(S, File, S->Type, Name);
    S->Binding = STB_WEAK;
    return;
  }

  if (InputFile *F = File.fetch())
    addFile<ELFT>(F);
}

template <class ELFT> void SymbolTable::fetchLazy(Symbol *Sym) {
  if (auto *S = dyn_cast<LazyArchive>(Sym)) {
    if (InputFile *File = S->fetch())
      addFile<ELFT>(File);
    return;
  }

  auto *S = cast<LazyObject>(Sym);
  if (InputFile *File = cast<LazyObjFile>(S->File)->fetch())
    addFile<ELFT>(File);
}

// Initialize DemangledSyms with a map from demangled symbols to symbol
// objects. Used to handle "extern C++" directive in version scripts.
//
// The map will contain all demangled symbols. That can be very large,
// and in LLD we generally want to avoid do anything for each symbol.
// Then, why are we doing this? Here's why.
//
// Users can use "extern C++ {}" directive to match against demangled
// C++ symbols. For example, you can write a pattern such as
// "llvm::*::foo(int, ?)". Obviously, there's no way to handle this
// other than trying to match a pattern against all demangled symbols.
// So, if "extern C++" feature is used, we need to demangle all known
// symbols.
StringMap<std::vector<Symbol *>> &SymbolTable::getDemangledSyms() {
  if (!DemangledSyms) {
    DemangledSyms.emplace();
    for (Symbol *Sym : SymVector) {
      if (!Sym->isDefined())
        continue;
      if (Optional<std::string> S = demangleItanium(Sym->getName()))
        (*DemangledSyms)[*S].push_back(Sym);
      else
        (*DemangledSyms)[Sym->getName()].push_back(Sym);
    }
  }
  return *DemangledSyms;
}

std::vector<Symbol *> SymbolTable::findByVersion(SymbolVersion Ver) {
  if (Ver.IsExternCpp)
    return getDemangledSyms().lookup(Ver.Name);
  if (Symbol *B = find(Ver.Name))
    if (B->isDefined())
      return {B};
  return {};
}

std::vector<Symbol *> SymbolTable::findAllByVersion(SymbolVersion Ver) {
  std::vector<Symbol *> Res;
  StringMatcher M(Ver.Name);

  if (Ver.IsExternCpp) {
    for (auto &P : getDemangledSyms())
      if (M.match(P.first()))
        Res.insert(Res.end(), P.second.begin(), P.second.end());
    return Res;
  }

  for (Symbol *Sym : SymVector)
    if (Sym->isDefined() && M.match(Sym->getName()))
      Res.push_back(Sym);
  return Res;
}

// If there's only one anonymous version definition in a version
// script file, the script does not actually define any symbol version,
// but just specifies symbols visibilities.
void SymbolTable::handleAnonymousVersion() {
  for (SymbolVersion &Ver : Config->VersionScriptGlobals)
    assignExactVersion(Ver, VER_NDX_GLOBAL, "global");
  for (SymbolVersion &Ver : Config->VersionScriptGlobals)
    assignWildcardVersion(Ver, VER_NDX_GLOBAL);
  for (SymbolVersion &Ver : Config->VersionScriptLocals)
    assignExactVersion(Ver, VER_NDX_LOCAL, "local");
  for (SymbolVersion &Ver : Config->VersionScriptLocals)
    assignWildcardVersion(Ver, VER_NDX_LOCAL);
}

// Handles -dynamic-list.
void SymbolTable::handleDynamicList() {
  for (SymbolVersion &Ver : Config->DynamicList) {
    std::vector<Symbol *> Syms;
    if (Ver.HasWildcard)
      Syms = findAllByVersion(Ver);
    else
      Syms = findByVersion(Ver);

    for (Symbol *B : Syms) {
      if (!Config->Shared)
        B->ExportDynamic = true;
      else if (B->includeInDynsym())
        B->IsPreemptible = true;
    }
  }
}

// Set symbol versions to symbols. This function handles patterns
// containing no wildcard characters.
void SymbolTable::assignExactVersion(SymbolVersion Ver, uint16_t VersionId,
                                     StringRef VersionName) {
  if (Ver.HasWildcard)
    return;

  // Get a list of symbols which we need to assign the version to.
  std::vector<Symbol *> Syms = findByVersion(Ver);
  if (Syms.empty()) {
    if (!Config->UndefinedVersion)
      error("version script assignment of '" + VersionName + "' to symbol '" +
            Ver.Name + "' failed: symbol not defined");
    return;
  }

  // Assign the version.
  for (Symbol *Sym : Syms) {
    // Skip symbols containing version info because symbol versions
    // specified by symbol names take precedence over version scripts.
    // See parseSymbolVersion().
    if (Sym->getName().contains('@'))
      continue;

    if (Sym->VersionId != Config->DefaultSymbolVersion &&
        Sym->VersionId != VersionId)
      error("duplicate symbol '" + Ver.Name + "' in version script");
    Sym->VersionId = VersionId;
  }
}

void SymbolTable::assignWildcardVersion(SymbolVersion Ver, uint16_t VersionId) {
  if (!Ver.HasWildcard)
    return;

  // Exact matching takes precendence over fuzzy matching,
  // so we set a version to a symbol only if no version has been assigned
  // to the symbol. This behavior is compatible with GNU.
  for (Symbol *B : findAllByVersion(Ver))
    if (B->VersionId == Config->DefaultSymbolVersion)
      B->VersionId = VersionId;
}

// This function processes version scripts by updating VersionId
// member of symbols.
void SymbolTable::scanVersionScript() {
  // Handle edge cases first.
  handleAnonymousVersion();
  handleDynamicList();

  // Now we have version definitions, so we need to set version ids to symbols.
  // Each version definition has a glob pattern, and all symbols that match
  // with the pattern get that version.

  // First, we assign versions to exact matching symbols,
  // i.e. version definitions not containing any glob meta-characters.
  for (VersionDefinition &V : Config->VersionDefinitions)
    for (SymbolVersion &Ver : V.Globals)
      assignExactVersion(Ver, V.Id, V.Name);

  // Next, we assign versions to fuzzy matching symbols,
  // i.e. version definitions containing glob meta-characters.
  // Note that because the last match takes precedence over previous matches,
  // we iterate over the definitions in the reverse order.
  for (VersionDefinition &V : llvm::reverse(Config->VersionDefinitions))
    for (SymbolVersion &Ver : V.Globals)
      assignWildcardVersion(Ver, V.Id);

  // Symbol themselves might know their versions because symbols
  // can contain versions in the form of <name>@<version>.
  // Let them parse and update their names to exclude version suffix.
  for (Symbol *Sym : SymVector)
    Sym->parseSymbolVersion();
}

template void SymbolTable::addFile<ELF32LE>(InputFile *);
template void SymbolTable::addFile<ELF32BE>(InputFile *);
template void SymbolTable::addFile<ELF64LE>(InputFile *);
template void SymbolTable::addFile<ELF64BE>(InputFile *);

template Symbol *SymbolTable::addUndefined<ELF32LE>(StringRef, uint8_t, uint8_t,
                                                    uint8_t, bool, InputFile *);
template Symbol *SymbolTable::addUndefined<ELF32BE>(StringRef, uint8_t, uint8_t,
                                                    uint8_t, bool, InputFile *);
template Symbol *SymbolTable::addUndefined<ELF64LE>(StringRef, uint8_t, uint8_t,
                                                    uint8_t, bool, InputFile *);
template Symbol *SymbolTable::addUndefined<ELF64BE>(StringRef, uint8_t, uint8_t,
                                                    uint8_t, bool, InputFile *);

template void SymbolTable::addCombinedLTOObject<ELF32LE>();
template void SymbolTable::addCombinedLTOObject<ELF32BE>();
template void SymbolTable::addCombinedLTOObject<ELF64LE>();
template void SymbolTable::addCombinedLTOObject<ELF64BE>();

template void
SymbolTable::addLazyArchive<ELF32LE>(StringRef, ArchiveFile &,
                                     const object::Archive::Symbol);
template void
SymbolTable::addLazyArchive<ELF32BE>(StringRef, ArchiveFile &,
                                     const object::Archive::Symbol);
template void
SymbolTable::addLazyArchive<ELF64LE>(StringRef, ArchiveFile &,
                                     const object::Archive::Symbol);
template void
SymbolTable::addLazyArchive<ELF64BE>(StringRef, ArchiveFile &,
                                     const object::Archive::Symbol);

template void SymbolTable::addLazyObject<ELF32LE>(StringRef, LazyObjFile &);
template void SymbolTable::addLazyObject<ELF32BE>(StringRef, LazyObjFile &);
template void SymbolTable::addLazyObject<ELF64LE>(StringRef, LazyObjFile &);
template void SymbolTable::addLazyObject<ELF64BE>(StringRef, LazyObjFile &);

template void SymbolTable::fetchLazy<ELF32LE>(Symbol *);
template void SymbolTable::fetchLazy<ELF32BE>(Symbol *);
template void SymbolTable::fetchLazy<ELF64LE>(Symbol *);
template void SymbolTable::fetchLazy<ELF64BE>(Symbol *);

template void SymbolTable::addShared<ELF32LE>(StringRef, SharedFile<ELF32LE> &,
                                              const typename ELF32LE::Sym &,
                                              uint32_t Alignment, uint32_t);
template void SymbolTable::addShared<ELF32BE>(StringRef, SharedFile<ELF32BE> &,
                                              const typename ELF32BE::Sym &,
                                              uint32_t Alignment, uint32_t);
template void SymbolTable::addShared<ELF64LE>(StringRef, SharedFile<ELF64LE> &,
                                              const typename ELF64LE::Sym &,
                                              uint32_t Alignment, uint32_t);
template void SymbolTable::addShared<ELF64BE>(StringRef, SharedFile<ELF64BE> &,
                                              const typename ELF64BE::Sym &,
                                              uint32_t Alignment, uint32_t);