llvm-project/lld/ELF/InputFiles.h

//===- InputFiles.h ---------------------------------------------*- C++ -*-===//
//
//                             The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#ifndef LLD_ELF_INPUT_FILES_H
#define LLD_ELF_INPUT_FILES_H

#include "Config.h"
#include "lld/Common/ErrorHandler.h"
#include "lld/Common/LLVM.h"
#include "lld/Common/Reproduce.h"
#include "llvm/ADT/CachedHashString.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/DebugInfo/DWARF/DWARFDebugLine.h"
#include "llvm/IR/Comdat.h"
#include "llvm/Object/Archive.h"
#include "llvm/Object/ELF.h"
#include "llvm/Object/IRObjectFile.h"
#include "llvm/Support/Threading.h"
#include <map>

namespace llvm {
class TarWriter;
struct DILineInfo;
namespace lto {
class InputFile;
}
} // namespace llvm

namespace lld {
namespace elf {
class InputFile;
class InputSectionBase;
}

// Returns "<internal>", "foo.a(bar.o)" or "baz.o".
std::string toString(const elf::InputFile *F);

namespace elf {

using llvm::object::Archive;

class Symbol;

// If -reproduce option is given, all input files are written
// to this tar archive.
extern llvm::TarWriter *Tar;

// Opens a given file.
llvm::Optional<MemoryBufferRef> readFile(StringRef Path);

// The root class of input files.
class InputFile {
public:
  enum Kind {
    ObjKind,
    SharedKind,
    LazyObjKind,
    ArchiveKind,
    BitcodeKind,
    BinaryKind,
  };

  Kind kind() const { return FileKind; }

  bool isElf() const {
    Kind K = kind();
    return K == ObjKind || K == SharedKind;
  }

  StringRef getName() const { return MB.getBufferIdentifier(); }
  MemoryBufferRef MB;

  // Returns sections. It is a runtime error to call this function
  // on files that don't have the notion of sections.
  ArrayRef<InputSectionBase *> getSections() const {
    assert(FileKind == ObjKind || FileKind == BinaryKind);
    return Sections;
  }

  // Returns object file symbols. It is a runtime error to call this
  // function on files of other types.
  ArrayRef<Symbol *> getSymbols() {
    assert(FileKind == BinaryKind || FileKind == ObjKind ||
           FileKind == BitcodeKind);
    return Symbols;
  }

  // Filename of .a which contained this file. If this file was
  // not in an archive file, it is the empty string. We use this
  // string for creating error messages.
  std::string ArchiveName;

  // If this is an architecture-specific file, the following members
  // have ELF type (i.e. ELF{32,64}{LE,BE}) and target machine type.
  ELFKind EKind = ELFNoneKind;
  uint16_t EMachine = llvm::ELF::EM_NONE;
  uint8_t OSABI = 0;

  // Cache for toString(). Only toString() should use this member.
  mutable std::string ToStringCache;

  std::string getSrcMsg(const Symbol &Sym, InputSectionBase &Sec,
                        uint64_t Offset);

  // True if this is an argument for --just-symbols. Usually false.
  bool JustSymbols = false;

  // GroupId is used for --warn-backrefs which is an optional error
  // checking feature. All files within the same --{start,end}-group or
  // --{start,end}-lib get the same group ID. Otherwise, each file gets a new
  // group ID. For more info, see checkDependency() in SymbolTable.cpp.
  uint32_t GroupId;
  static bool IsInGroup;
  static uint32_t NextGroupId;

  // Index of MIPS GOT built for this file.
  llvm::Optional<size_t> MipsGotIndex;

protected:
  InputFile(Kind K, MemoryBufferRef M);
  std::vector<InputSectionBase *> Sections;
  std::vector<Symbol *> Symbols;

private:
  const Kind FileKind;
};

template <typename ELFT> class ELFFileBase : public InputFile {
public:
  typedef typename ELFT::Shdr Elf_Shdr;
  typedef typename ELFT::Sym Elf_Sym;
  typedef typename ELFT::Word Elf_Word;
  typedef typename ELFT::SymRange Elf_Sym_Range;

  ELFFileBase(Kind K, MemoryBufferRef M);
  static bool classof(const InputFile *F) { return F->isElf(); }

  llvm::object::ELFFile<ELFT> getObj() const {
    return check(llvm::object::ELFFile<ELFT>::create(MB.getBuffer()));
  }

  StringRef getStringTable() const { return StringTable; }

  uint32_t getSectionIndex(const Elf_Sym &Sym) const;

  Elf_Sym_Range getGlobalELFSyms();
  Elf_Sym_Range getELFSyms() const { return ELFSyms; }

protected:
  ArrayRef<Elf_Sym> ELFSyms;
  uint32_t FirstGlobal = 0;
  ArrayRef<Elf_Word> SymtabSHNDX;
  StringRef StringTable;
  void initSymtab(ArrayRef<Elf_Shdr> Sections, const Elf_Shdr *Symtab);
};

// .o file.
template <class ELFT> class ObjFile : public ELFFileBase<ELFT> {
  typedef ELFFileBase<ELFT> Base;
  typedef typename ELFT::Rel Elf_Rel;
  typedef typename ELFT::Rela Elf_Rela;
  typedef typename ELFT::Sym Elf_Sym;
  typedef typename ELFT::Shdr Elf_Shdr;
  typedef typename ELFT::Word Elf_Word;

  StringRef getShtGroupSignature(ArrayRef<Elf_Shdr> Sections,
                                 const Elf_Shdr &Sec);
  ArrayRef<Elf_Word> getShtGroupEntries(const Elf_Shdr &Sec);

public:
  static bool classof(const InputFile *F) { return F->kind() == Base::ObjKind; }

  ArrayRef<Symbol *> getLocalSymbols();
  ArrayRef<Symbol *> getGlobalSymbols();

  ObjFile(MemoryBufferRef M, StringRef ArchiveName);
  void parse(llvm::DenseSet<llvm::CachedHashStringRef> &ComdatGroups);

  Symbol &getSymbol(uint32_t SymbolIndex) const {
    if (SymbolIndex >= this->Symbols.size())
      fatal(toString(this) + ": invalid symbol index");
    return *this->Symbols[SymbolIndex];
  }

  template <typename RelT> Symbol &getRelocTargetSym(const RelT &Rel) const {
    uint32_t SymIndex = Rel.getSymbol(Config->IsMips64EL);
    return getSymbol(SymIndex);
  }

  // Returns source line information for a given offset.
  // If no information is available, returns "".
  std::string getLineInfo(InputSectionBase *S, uint64_t Offset);
  llvm::Optional<llvm::DILineInfo> getDILineInfo(InputSectionBase *, uint64_t);
  llvm::Optional<std::pair<std::string, unsigned>> getVariableLoc(StringRef Name);

  // MIPS GP0 value defined by this file. This value represents the gp value
  // used to create the relocatable object and required to support
  // R_MIPS_GPREL16 / R_MIPS_GPREL32 relocations.
  uint32_t MipsGp0 = 0;

  // Name of source file obtained from STT_FILE symbol value,
  // or empty string if there is no such symbol in object file
  // symbol table.
  StringRef SourceFile;

private:
  void
  initializeSections(llvm::DenseSet<llvm::CachedHashStringRef> &ComdatGroups);
  void initializeSymbols();
  void initializeJustSymbols();
  void initializeDwarf();
  InputSectionBase *getRelocTarget(const Elf_Shdr &Sec);
  InputSectionBase *createInputSection(const Elf_Shdr &Sec);
  StringRef getSectionName(const Elf_Shdr &Sec);

  bool shouldMerge(const Elf_Shdr &Sec);
  Symbol *createSymbol(const Elf_Sym *Sym);

  // .shstrtab contents.
  StringRef SectionStringTable;

  // Debugging information to retrieve source file and line for error
  // reporting. Linker may find reasonable number of errors in a
  // single object file, so we cache debugging information in order to
  // parse it only once for each object file we link.
  std::unique_ptr<llvm::DWARFContext> Dwarf;
  std::vector<const llvm::DWARFDebugLine::LineTable *> LineTables;
  struct VarLoc {
    const llvm::DWARFDebugLine::LineTable *LT;
    unsigned File;
    unsigned Line;
  };
  llvm::DenseMap<StringRef, VarLoc> VariableLoc;
  llvm::once_flag InitDwarfLine;
};

// LazyObjFile is analogous to ArchiveFile in the sense that
// the file contains lazy symbols. The difference is that
// LazyObjFile wraps a single file instead of multiple files.
//
// This class is used for --start-lib and --end-lib options which
// instruct the linker to link object files between them with the
// archive file semantics.
class LazyObjFile : public InputFile {
public:
  LazyObjFile(MemoryBufferRef M, StringRef ArchiveName,
              uint64_t OffsetInArchive)
      : InputFile(LazyObjKind, M), OffsetInArchive(OffsetInArchive) {
    this->ArchiveName = ArchiveName;
  }

  static bool classof(const InputFile *F) { return F->kind() == LazyObjKind; }

  template <class ELFT> void parse();
  MemoryBufferRef getBuffer();
  InputFile *fetch();
  bool AddedToLink = false;

private:
  template <class ELFT> void addElfSymbols();

  uint64_t OffsetInArchive;
};

// An ArchiveFile object represents a .a file.
class ArchiveFile : public InputFile {
public:
  explicit ArchiveFile(std::unique_ptr<Archive> &&File);
  static bool classof(const InputFile *F) { return F->kind() == ArchiveKind; }
  template <class ELFT> void parse();

  // Pulls out an object file that contains a definition for Sym and
  // returns it. If the same file was instantiated before, this
  // function returns a nullptr (so we don't instantiate the same file
  // more than once.)
  InputFile *fetch(const Archive::Symbol &Sym);

private:
  std::unique_ptr<Archive> File;
  llvm::DenseSet<uint64_t> Seen;
};

class BitcodeFile : public InputFile {
public:
  BitcodeFile(MemoryBufferRef M, StringRef ArchiveName,
              uint64_t OffsetInArchive);
  static bool classof(const InputFile *F) { return F->kind() == BitcodeKind; }
  template <class ELFT>
  void parse(llvm::DenseSet<llvm::CachedHashStringRef> &ComdatGroups);
  std::unique_ptr<llvm::lto::InputFile> Obj;
};

// .so file.
template <class ELFT> class SharedFile : public ELFFileBase<ELFT> {
  typedef ELFFileBase<ELFT> Base;
  typedef typename ELFT::Dyn Elf_Dyn;
  typedef typename ELFT::Shdr Elf_Shdr;
  typedef typename ELFT::Sym Elf_Sym;
  typedef typename ELFT::SymRange Elf_Sym_Range;
  typedef typename ELFT::Verdef Elf_Verdef;
  typedef typename ELFT::Versym Elf_Versym;

  const Elf_Shdr *VersymSec = nullptr;
  const Elf_Shdr *VerdefSec = nullptr;

public:
  std::vector<const Elf_Verdef *> Verdefs;
  std::string SoName;

  static bool classof(const InputFile *F) {
    return F->kind() == Base::SharedKind;
  }

  SharedFile(MemoryBufferRef M, StringRef DefaultSoName);

  void parseSoName();
  void parseRest();
  uint32_t getAlignment(ArrayRef<Elf_Shdr> Sections, const Elf_Sym &Sym);
  std::vector<const Elf_Verdef *> parseVerdefs();
  std::vector<uint32_t> parseVersyms();

  struct NeededVer {
    // The string table offset of the version name in the output file.
    size_t StrTab;

    // The version identifier for this version name.
    uint16_t Index;
  };

  // Mapping from Elf_Verdef data structures to information about Elf_Vernaux
  // data structures in the output file.
  std::map<const Elf_Verdef *, NeededVer> VerdefMap;

  // Used for --as-needed
  bool IsNeeded;
};

class BinaryFile : public InputFile {
public:
  explicit BinaryFile(MemoryBufferRef M) : InputFile(BinaryKind, M) {}
  static bool classof(const InputFile *F) { return F->kind() == BinaryKind; }
  void parse();
};

InputFile *createObjectFile(MemoryBufferRef MB, StringRef ArchiveName = "",
                            uint64_t OffsetInArchive = 0);
InputFile *createSharedFile(MemoryBufferRef MB, StringRef DefaultSoName);

inline bool isBitcode(MemoryBufferRef MB) {
  return identify_magic(MB.getBuffer()) == llvm::file_magic::bitcode;
}

std::string replaceThinLTOSuffix(StringRef Path);

extern std::vector<BinaryFile *> BinaryFiles;
extern std::vector<BitcodeFile *> BitcodeFiles;
extern std::vector<LazyObjFile *> LazyObjFiles;
extern std::vector<InputFile *> ObjectFiles;
extern std::vector<InputFile *> SharedFiles;

} // namespace elf
} // namespace lld

#endif