MCDwarf.h

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//===- MCDwarf.h - Machine Code Dwarf support -------------------*- C++ -*-===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// This file contains the declaration of the MCDwarfFile to support the dwarf
// .file directive and the .loc directive.
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_MC_MCDWARF_H
#define LLVM_MC_MCDWARF_H
 
#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/MC/StringTableBuilder.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/MD5.h"
#include "llvm/Support/SMLoc.h"
#include "llvm/Support/StringSaver.h"
#include <cassert>
#include <cstdint>
#include <optional>
#include <string>
#include <utility>
#include <variant>
#include <vector>
 
namespace llvm {
 
template <typename T> class ArrayRef;
class MCAsmBackend;
class MCContext;
class MCObjectStreamer;
class MCSection;
class MCStreamer;
class MCSymbol;
class raw_ostream;
class SourceMgr;
 
namespace mcdwarf {
// Emit the common part of the DWARF 5 range/locations list tables header.
LLVM_ABI MCSymbol *emitListsTableHeaderStart(MCStreamer &S);
} // namespace mcdwarf
 
/// Manage the .debug_line_str section contents, if we use it.
class MCDwarfLineStr {
  BumpPtrAllocator Alloc;
  StringSaver Saver{Alloc};
  MCSymbol *LineStrLabel = nullptr;
  StringTableBuilder LineStrings{StringTableBuilder::DWARF};
  bool UseRelocs = false;
 
public:
  /// Construct an instance that can emit .debug_line_str (for use in a normal
  /// v5 line table).
  LLVM_ABI explicit MCDwarfLineStr(MCContext &Ctx);
 
  StringSaver &getSaver() { return Saver; }
 
  /// Emit a reference to the string.
  LLVM_ABI void emitRef(MCStreamer *MCOS, StringRef Path);
 
  /// Emit the .debug_line_str section if appropriate.
  LLVM_ABI void emitSection(MCStreamer *MCOS);
 
  /// Returns finalized section.
  LLVM_ABI SmallString<0> getFinalizedData();
 
  /// Adds path \p Path to the line string. Returns offset in the
  /// .debug_line_str section.
  LLVM_ABI size_t addString(StringRef Path);
};
 
/// Instances of this class represent the name of the dwarf .file directive and
/// its associated dwarf file number in the MC file. MCDwarfFile's are created
/// and uniqued by the MCContext class. In Dwarf 4 file numbers start from 1;
/// i.e. the entry with file number 1 is the first element in the vector of
/// DwarfFiles and there is no MCDwarfFile with file number 0. In Dwarf 5 file
/// numbers start from 0, with the MCDwarfFile with file number 0 being the
/// primary source file, and file numbers correspond to their index in the
/// vector.
struct MCDwarfFile {
  // The base name of the file without its directory path.
  std::string Name;
 
  // The index into the list of directory names for this file name.
  unsigned DirIndex = 0;
 
  /// The MD5 checksum, if there is one. Non-owning pointer to data allocated
  /// in MCContext.
  std::optional<MD5::MD5Result> Checksum;
 
  /// The source code of the file. Non-owning reference to data allocated in
  /// MCContext.
  std::optional<StringRef> Source;
};
 
/// Instances of this class represent the information from a
/// dwarf .loc directive.
class MCDwarfLoc {
  uint32_t FileNum;
  uint32_t Line;
  uint16_t Column;
  // Flags (see #define's below)
  uint8_t Flags;
  uint8_t Isa;
  uint32_t Discriminator;
 
// Flag that indicates the initial value of the is_stmt_start flag.
#define DWARF2_LINE_DEFAULT_IS_STMT 1
 
#define DWARF2_FLAG_IS_STMT (1 << 0)
#define DWARF2_FLAG_BASIC_BLOCK (1 << 1)
#define DWARF2_FLAG_PROLOGUE_END (1 << 2)
#define DWARF2_FLAG_EPILOGUE_BEGIN (1 << 3)
 
private: // MCContext manages these
  friend class MCContext;
  friend class MCDwarfLineEntry;
 
  MCDwarfLoc(unsigned fileNum, unsigned line, unsigned column, unsigned flags,
             unsigned isa, unsigned discriminator)
      : FileNum(fileNum), Line(line), Column(column), Flags(flags), Isa(isa),
        Discriminator(discriminator) {}
 
  // Allow the default copy constructor and assignment operator to be used
  // for an MCDwarfLoc object.
 
public:
  /// Get the FileNum of this MCDwarfLoc.
  unsigned getFileNum() const { return FileNum; }
 
  /// Get the Line of this MCDwarfLoc.
  unsigned getLine() const { return Line; }
 
  /// Get the Column of this MCDwarfLoc.
  unsigned getColumn() const { return Column; }
 
  /// Get the Flags of this MCDwarfLoc.
  unsigned getFlags() const { return Flags; }
 
  /// Get the Isa of this MCDwarfLoc.
  unsigned getIsa() const { return Isa; }
 
  /// Get the Discriminator of this MCDwarfLoc.
  unsigned getDiscriminator() const { return Discriminator; }
 
  /// Set the FileNum of this MCDwarfLoc.
  void setFileNum(unsigned fileNum) { FileNum = fileNum; }
 
  /// Set the Line of this MCDwarfLoc.
  void setLine(unsigned line) { Line = line; }
 
  /// Set the Column of this MCDwarfLoc.
  void setColumn(unsigned column) {
    assert(column <= UINT16_MAX);
    Column = column;
  }
 
  /// Set the Flags of this MCDwarfLoc.
  void setFlags(unsigned flags) {
    assert(flags <= UINT8_MAX);
    Flags = flags;
  }
 
  /// Set the Isa of this MCDwarfLoc.
  void setIsa(unsigned isa) {
    assert(isa <= UINT8_MAX);
    Isa = isa;
  }
 
  /// Set the Discriminator of this MCDwarfLoc.
  void setDiscriminator(unsigned discriminator) {
    Discriminator = discriminator;
  }
};
 
/// Instances of this class represent the line information for
/// the dwarf line table entries.  Which is created after a machine
/// instruction is assembled and uses an address from a temporary label
/// created at the current address in the current section and the info from
/// the last .loc directive seen as stored in the context.
class MCDwarfLineEntry : public MCDwarfLoc {
  MCSymbol *Label;
 
private:
  // Allow the default copy constructor and assignment operator to be used
  // for an MCDwarfLineEntry object.
 
public:
  // Constructor to create an MCDwarfLineEntry given a symbol and the dwarf loc.
  MCDwarfLineEntry(MCSymbol *label, const MCDwarfLoc loc,
                   MCSymbol *lineStreamLabel = nullptr,
                   SMLoc streamLabelDefLoc = {})
      : MCDwarfLoc(loc), Label(label), LineStreamLabel(lineStreamLabel),
        StreamLabelDefLoc(streamLabelDefLoc) {}
 
  MCSymbol *getLabel() const { return Label; }
 
  // This is the label that is to be emitted into the line stream. If this is
  // non-null and we need to emit a label, also make sure to restart the current
  // line sequence.
  MCSymbol *LineStreamLabel;
 
  // Location where LineStreamLabel was defined. If there is an error emitting
  // LineStreamLabel, we can use the SMLoc to report an error.
  SMLoc StreamLabelDefLoc;
 
  // This indicates the line entry is synthesized for an end entry.
  bool IsEndEntry = false;
 
  // Override the label with the given EndLabel.
  void setEndLabel(MCSymbol *EndLabel) {
    // If we're setting this to be an end entry, make sure we don't have
    // LineStreamLabel set.
    assert(LineStreamLabel == nullptr);
    Label = EndLabel;
    IsEndEntry = true;
  }
 
  // This is called when an instruction is assembled into the specified
  // section and if there is information from the last .loc directive that
  // has yet to have a line entry made for it is made.
  LLVM_ABI static void make(MCStreamer *MCOS, MCSection *Section);
};
 
/// Instances of this class represent the line information for a compile
/// unit where machine instructions have been assembled after seeing .loc
/// directives.  This is the information used to build the dwarf line
/// table for a section.
class MCLineSection {
public:
  // Add an entry to this MCLineSection's line entries.
  void addLineEntry(const MCDwarfLineEntry &LineEntry, MCSection *Sec) {
    MCLineDivisions[Sec].push_back(LineEntry);
  }
 
  // Add an end entry by cloning the last entry, if exists, for the section
  // the given EndLabel belongs to. The label is replaced by the given EndLabel.
  LLVM_ABI void addEndEntry(MCSymbol *EndLabel);
 
  using MCDwarfLineEntryCollection = std::vector<MCDwarfLineEntry>;
  using iterator = MCDwarfLineEntryCollection::iterator;
  using const_iterator = MCDwarfLineEntryCollection::const_iterator;
  using MCLineDivisionMap = MapVector<MCSection *, MCDwarfLineEntryCollection>;
 
private:
  // A collection of MCDwarfLineEntry for each section.
  MCLineDivisionMap MCLineDivisions;
 
public:
  // Returns the collection of MCDwarfLineEntry for a given Compile Unit ID.
  const MCLineDivisionMap &getMCLineEntries() const {
    return MCLineDivisions;
  }
};
 
struct MCDwarfLineTableParams {
  /// First special line opcode - leave room for the standard opcodes.
  /// Note: If you want to change this, you'll have to update the
  /// "StandardOpcodeLengths" table that is emitted in
  /// \c Emit().
  uint8_t DWARF2LineOpcodeBase = 13;
  /// Minimum line offset in a special line info. opcode.  The value
  /// -5 was chosen to give a reasonable range of values.
  int8_t DWARF2LineBase = -5;
  /// Range of line offsets in a special line info. opcode.
  uint8_t DWARF2LineRange = 14;
};
 
struct MCDwarfLineTableHeader {
  MCSymbol *Label = nullptr;
  SmallVector<std::string, 3> MCDwarfDirs;
  SmallVector<MCDwarfFile, 3> MCDwarfFiles;
  StringMap<unsigned> SourceIdMap;
  std::string CompilationDir;
  MCDwarfFile RootFile;
  bool HasAnySource = false;
 
private:
  bool HasAllMD5 = true;
  bool HasAnyMD5 = false;
 
public:
  MCDwarfLineTableHeader() = default;
 
  LLVM_ABI Expected<unsigned> tryGetFile(StringRef &Directory,
                                         StringRef &FileName,
                                         std::optional<MD5::MD5Result> Checksum,
                                         std::optional<StringRef> Source,
                                         uint16_t DwarfVersion,
                                         unsigned FileNumber = 0);
  LLVM_ABI std::pair<MCSymbol *, MCSymbol *>
  Emit(MCStreamer *MCOS, MCDwarfLineTableParams Params,
       std::optional<MCDwarfLineStr> &LineStr) const;
  LLVM_ABI std::pair<MCSymbol *, MCSymbol *>
  Emit(MCStreamer *MCOS, MCDwarfLineTableParams Params,
       ArrayRef<char> SpecialOpcodeLengths,
       std::optional<MCDwarfLineStr> &LineStr) const;
  void resetMD5Usage() {
    HasAllMD5 = true;
    HasAnyMD5 = false;
  }
  void trackMD5Usage(bool MD5Used) {
    HasAllMD5 &= MD5Used;
    HasAnyMD5 |= MD5Used;
  }
  bool isMD5UsageConsistent() const {
    return MCDwarfFiles.empty() || (HasAllMD5 == HasAnyMD5);
  }
 
  void setRootFile(StringRef Directory, StringRef FileName,
                   std::optional<MD5::MD5Result> Checksum,
                   std::optional<StringRef> Source) {
    CompilationDir = std::string(Directory);
    RootFile.Name = std::string(FileName);
    RootFile.DirIndex = 0;
    RootFile.Checksum = Checksum;
    RootFile.Source = Source;
    trackMD5Usage(Checksum.has_value());
    HasAnySource |= Source.has_value();
  }
 
  void resetFileTable() {
    MCDwarfDirs.clear();
    MCDwarfFiles.clear();
    RootFile.Name.clear();
    resetMD5Usage();
    HasAnySource = false;
  }
 
private:
  void emitV2FileDirTables(MCStreamer *MCOS) const;
  void emitV5FileDirTables(MCStreamer *MCOS,
                           std::optional<MCDwarfLineStr> &LineStr) const;
};
 
class MCDwarfDwoLineTable {
  MCDwarfLineTableHeader Header;
  bool HasSplitLineTable = false;
 
public:
  void maybeSetRootFile(StringRef Directory, StringRef FileName,
                        std::optional<MD5::MD5Result> Checksum,
                        std::optional<StringRef> Source) {
    if (!Header.RootFile.Name.empty())
      return;
    Header.setRootFile(Directory, FileName, Checksum, Source);
  }
 
  unsigned getFile(StringRef Directory, StringRef FileName,
                   std::optional<MD5::MD5Result> Checksum,
                   uint16_t DwarfVersion, std::optional<StringRef> Source) {
    HasSplitLineTable = true;
    return cantFail(Header.tryGetFile(Directory, FileName, Checksum, Source,
                                      DwarfVersion));
  }
 
  LLVM_ABI void Emit(MCStreamer &MCOS, MCDwarfLineTableParams Params,
                     MCSection *Section) const;
};
 
class MCDwarfLineTable {
  MCDwarfLineTableHeader Header;
  MCLineSection MCLineSections;
 
public:
  // This emits the Dwarf file and the line tables for all Compile Units.
  LLVM_ABI static void emit(MCStreamer *MCOS, MCDwarfLineTableParams Params);
 
  // This emits the Dwarf file and the line tables for a given Compile Unit.
  LLVM_ABI void emitCU(MCStreamer *MCOS, MCDwarfLineTableParams Params,
                       std::optional<MCDwarfLineStr> &LineStr) const;
 
  // This emits a single line table associated with a given Section.
  LLVM_ABI static void
  emitOne(MCStreamer *MCOS, MCSection *Section,
          const MCLineSection::MCDwarfLineEntryCollection &LineEntries);
 
  LLVM_ABI void endCurrentSeqAndEmitLineStreamLabel(MCStreamer *MCOS,
                                                    SMLoc DefLoc,
                                                    StringRef Name);
 
  LLVM_ABI Expected<unsigned> tryGetFile(StringRef &Directory,
                                         StringRef &FileName,
                                         std::optional<MD5::MD5Result> Checksum,
                                         std::optional<StringRef> Source,
                                         uint16_t DwarfVersion,
                                         unsigned FileNumber = 0);
  unsigned getFile(StringRef &Directory, StringRef &FileName,
                   std::optional<MD5::MD5Result> Checksum,
                   std::optional<StringRef> Source, uint16_t DwarfVersion,
                   unsigned FileNumber = 0) {
    return cantFail(tryGetFile(Directory, FileName, Checksum, Source,
                               DwarfVersion, FileNumber));
  }
 
  void setRootFile(StringRef Directory, StringRef FileName,
                   std::optional<MD5::MD5Result> Checksum,
                   std::optional<StringRef> Source) {
    Header.CompilationDir = std::string(Directory);
    Header.RootFile.Name = std::string(FileName);
    Header.RootFile.DirIndex = 0;
    Header.RootFile.Checksum = Checksum;
    Header.RootFile.Source = Source;
    Header.trackMD5Usage(Checksum.has_value());
    Header.HasAnySource |= Source.has_value();
  }
 
  void resetFileTable() { Header.resetFileTable(); }
 
  bool hasRootFile() const { return !Header.RootFile.Name.empty(); }
 
  MCDwarfFile &getRootFile() { return Header.RootFile; }
  const MCDwarfFile &getRootFile() const { return Header.RootFile; }
 
  // Report whether MD5 usage has been consistent (all-or-none).
  bool isMD5UsageConsistent() const { return Header.isMD5UsageConsistent(); }
 
  MCSymbol *getLabel() const {
    return Header.Label;
  }
 
  void setLabel(MCSymbol *Label) {
    Header.Label = Label;
  }
 
  const SmallVectorImpl<std::string> &getMCDwarfDirs() const {
    return Header.MCDwarfDirs;
  }
 
  SmallVectorImpl<std::string> &getMCDwarfDirs() {
    return Header.MCDwarfDirs;
  }
 
  const SmallVectorImpl<MCDwarfFile> &getMCDwarfFiles() const {
    return Header.MCDwarfFiles;
  }
 
  SmallVectorImpl<MCDwarfFile> &getMCDwarfFiles() {
    return Header.MCDwarfFiles;
  }
 
  const MCLineSection &getMCLineSections() const {
    return MCLineSections;
  }
  MCLineSection &getMCLineSections() {
    return MCLineSections;
  }
};
 
class MCDwarfLineAddr {
public:
  /// Utility function to encode a Dwarf pair of LineDelta and AddrDeltas.
  LLVM_ABI static void encode(MCContext &Context, MCDwarfLineTableParams Params,
                              int64_t LineDelta, uint64_t AddrDelta,
                              SmallVectorImpl<char> &OS);
 
  /// Utility function to emit the encoding to a streamer.
  LLVM_ABI static void Emit(MCStreamer *MCOS, MCDwarfLineTableParams Params,
                            int64_t LineDelta, uint64_t AddrDelta);
};
 
class MCGenDwarfInfo {
public:
  //
  // When generating dwarf for assembly source files this emits the Dwarf
  // sections.
  //
  LLVM_ABI static void Emit(MCStreamer *MCOS);
};
 
// When generating dwarf for assembly source files this is the info that is
// needed to be gathered for each symbol that will have a dwarf label.
class MCGenDwarfLabelEntry {
private:
  // Name of the symbol without a leading underbar, if any.
  StringRef Name;
  // The dwarf file number this symbol is in.
  unsigned FileNumber;
  // The line number this symbol is at.
  unsigned LineNumber;
  // The low_pc for the dwarf label is taken from this symbol.
  MCSymbol *Label;
 
public:
  MCGenDwarfLabelEntry(StringRef name, unsigned fileNumber, unsigned lineNumber,
                       MCSymbol *label)
      : Name(name), FileNumber(fileNumber), LineNumber(lineNumber),
        Label(label) {}
 
  StringRef getName() const { return Name; }
  unsigned getFileNumber() const { return FileNumber; }
  unsigned getLineNumber() const { return LineNumber; }
  MCSymbol *getLabel() const { return Label; }
 
  // This is called when label is created when we are generating dwarf for
  // assembly source files.
  LLVM_ABI static void Make(MCSymbol *Symbol, MCStreamer *MCOS,
                            SourceMgr &SrcMgr, SMLoc &Loc);
};
 
class MCCFIInstruction {
public:
  enum OpType : uint8_t {
    OpSameValue,
    OpRememberState,
    OpRestoreState,
    OpOffset,
    OpLLVMDefAspaceCfa,
    OpDefCfaRegister,
    OpDefCfaOffset,
    OpDefCfa,
    OpRelOffset,
    OpAdjustCfaOffset,
    OpEscape,
    OpRestore,
    OpUndefined,
    OpRegister,
    OpWindowSave,
    OpNegateRAState,
    OpNegateRAStateWithPC,
    OpGnuArgsSize,
    OpLabel,
    OpValOffset,
  };
 
  // Held in ExtraFields for most common OpTypes, exceptions follow.
  struct CommonFields {
    unsigned Register;
    int64_t Offset;
    unsigned Register2;
    unsigned AddressSpace;
    // FIXME: Workaround for GCC7 bug with nested class used as std::variant
    // alternative where the compiler really wants a user-defined default
    // constructor. Once we no longer support GCC7 these constructors can be
    // replaced with default member initializers and aggregate initialization.
    CommonFields(unsigned Reg, int64_t Off = 0,
                 unsigned Reg2 = std::numeric_limits<unsigned>::max(),
                 unsigned AddrSpace = 0)
        : Register(Reg), Offset(Off), Register2(Reg2), AddressSpace(AddrSpace) {
    }
    CommonFields() : CommonFields(std::numeric_limits<unsigned>::max()) {}
  };
  // Held in ExtraFields when OpEscape.
  struct EscapeFields {
    std::vector<char> Values;
    std::string Comment;
  };
  // Held in ExtraFields when OpLabel.
  struct LabelFields {
    MCSymbol *CfiLabel = nullptr;
  };
 
private:
  MCSymbol *Label;
  std::variant<CommonFields, EscapeFields, LabelFields> ExtraFields;
  OpType Operation;
  SMLoc Loc;
 
  template <class FieldsType>
  MCCFIInstruction(OpType Op, MCSymbol *L, FieldsType &&EF, SMLoc Loc)
      : Label(L), ExtraFields(std::forward<FieldsType>(EF)), Operation(Op),
        Loc(Loc) {}
 
public:
  /// .cfi_def_cfa defines a rule for computing CFA as: take address from
  /// Register and add Offset to it.
  static MCCFIInstruction cfiDefCfa(MCSymbol *L, unsigned Register,
                                    int64_t Offset, SMLoc Loc = {}) {
    return {OpDefCfa, L, CommonFields{Register, Offset}, Loc};
  }
 
  /// .cfi_def_cfa_register modifies a rule for computing CFA. From now
  /// on Register will be used instead of the old one. Offset remains the same.
  static MCCFIInstruction createDefCfaRegister(MCSymbol *L, unsigned Register,
                                               SMLoc Loc = {}) {
    return {OpDefCfaRegister, L, CommonFields{Register}, Loc};
  }
 
  /// .cfi_def_cfa_offset modifies a rule for computing CFA. Register
  /// remains the same, but offset is new. Note that it is the absolute offset
  /// that will be added to a defined register to the compute CFA address.
  static MCCFIInstruction cfiDefCfaOffset(MCSymbol *L, int64_t Offset,
                                          SMLoc Loc = {}) {
    return {OpDefCfaOffset, L, CommonFields{0, Offset}, Loc};
  }
 
  /// .cfi_adjust_cfa_offset Same as .cfi_def_cfa_offset, but
  /// Offset is a relative value that is added/subtracted from the previous
  /// offset.
  static MCCFIInstruction createAdjustCfaOffset(MCSymbol *L, int64_t Adjustment,
                                                SMLoc Loc = {}) {
    return {OpAdjustCfaOffset, L, CommonFields{0, Adjustment}, Loc};
  }
 
  // FIXME: Update the remaining docs to use the new proposal wording.
  /// .cfi_llvm_def_aspace_cfa defines the rule for computing the CFA to
  /// be the result of evaluating the DWARF operation expression
  /// `DW_OP_constu AS; DW_OP_aspace_bregx R, B` as a location description.
  static MCCFIInstruction createLLVMDefAspaceCfa(MCSymbol *L, unsigned Register,
                                                 int64_t Offset,
                                                 unsigned AddressSpace,
                                                 SMLoc Loc) {
    return {OpLLVMDefAspaceCfa, L,
            CommonFields{Register, Offset, 0, AddressSpace}, Loc};
  }
 
  /// .cfi_offset Previous value of Register is saved at offset Offset
  /// from CFA.
  static MCCFIInstruction createOffset(MCSymbol *L, unsigned Register,
                                       int64_t Offset, SMLoc Loc = {}) {
    return {OpOffset, L, CommonFields{Register, Offset}, Loc};
  }
 
  /// .cfi_rel_offset Previous value of Register is saved at offset
  /// Offset from the current CFA register. This is transformed to .cfi_offset
  /// using the known displacement of the CFA register from the CFA.
  static MCCFIInstruction createRelOffset(MCSymbol *L, unsigned Register,
                                          int64_t Offset, SMLoc Loc = {}) {
    return {OpRelOffset, L, CommonFields{Register, Offset}, Loc};
  }
 
  /// .cfi_register Previous value of Register1 is saved in
  /// register Register2.
  static MCCFIInstruction createRegister(MCSymbol *L, unsigned Register1,
                                         unsigned Register2, SMLoc Loc = {}) {
    return {OpRegister, L, CommonFields{Register1, 0, Register2}, Loc};
  }
 
  /// .cfi_window_save SPARC register window is saved.
  static MCCFIInstruction createWindowSave(MCSymbol *L, SMLoc Loc = {}) {
    return {OpWindowSave, L, CommonFields{}, Loc};
  }
 
  /// .cfi_negate_ra_state AArch64 negate RA state.
  static MCCFIInstruction createNegateRAState(MCSymbol *L, SMLoc Loc = {}) {
    return {OpNegateRAState, L, CommonFields{}, Loc};
  }
 
  /// .cfi_negate_ra_state_with_pc AArch64 negate RA state with PC.
  static MCCFIInstruction createNegateRAStateWithPC(MCSymbol *L,
                                                    SMLoc Loc = {}) {
    return {OpNegateRAStateWithPC, L, CommonFields{}, Loc};
  }
 
  /// .cfi_restore says that the rule for Register is now the same as it
  /// was at the beginning of the function, after all initial instructions added
  /// by .cfi_startproc were executed.
  static MCCFIInstruction createRestore(MCSymbol *L, unsigned Register,
                                        SMLoc Loc = {}) {
    return {OpRestore, L, CommonFields{Register}, Loc};
  }
 
  /// .cfi_undefined From now on the previous value of Register can't be
  /// restored anymore.
  static MCCFIInstruction createUndefined(MCSymbol *L, unsigned Register,
                                          SMLoc Loc = {}) {
    return {OpUndefined, L, CommonFields{Register}, Loc};
  }
 
  /// .cfi_same_value Current value of Register is the same as in the
  /// previous frame. I.e., no restoration is needed.
  static MCCFIInstruction createSameValue(MCSymbol *L, unsigned Register,
                                          SMLoc Loc = {}) {
    return {OpSameValue, L, CommonFields{Register}, Loc};
  }
 
  /// .cfi_remember_state Save all current rules for all registers.
  static MCCFIInstruction createRememberState(MCSymbol *L, SMLoc Loc = {}) {
    return {OpRememberState, L, CommonFields{}, Loc};
  }
 
  /// .cfi_restore_state Restore the previously saved state.
  static MCCFIInstruction createRestoreState(MCSymbol *L, SMLoc Loc = {}) {
    return {OpRestoreState, L, CommonFields{}, Loc};
  }
 
  /// .cfi_escape Allows the user to add arbitrary bytes to the unwind
  /// info.
  static MCCFIInstruction createEscape(MCSymbol *L, StringRef Vals,
                                       SMLoc Loc = {}, StringRef Comment = "") {
    return {OpEscape, L,
            EscapeFields{std::vector<char>(Vals.begin(), Vals.end()),
                         Comment.str()},
            Loc};
  }
 
  /// A special wrapper for .cfi_escape that indicates GNU_ARGS_SIZE
  static MCCFIInstruction createGnuArgsSize(MCSymbol *L, int64_t Size,
                                            SMLoc Loc = {}) {
    return {OpGnuArgsSize, L, CommonFields{0, Size}, Loc};
  }
 
  static MCCFIInstruction createLabel(MCSymbol *L, MCSymbol *CfiLabel,
                                      SMLoc Loc) {
    return {OpLabel, L, LabelFields{CfiLabel}, Loc};
  }
 
  /// .cfi_val_offset Previous value of Register is offset Offset from the
  /// current CFA register.
  static MCCFIInstruction createValOffset(MCSymbol *L, unsigned Register,
                                          int64_t Offset, SMLoc Loc = {}) {
    return {OpValOffset, L, CommonFields{Register, Offset}, Loc};
  }
 
  OpType getOperation() const { return Operation; }
  MCSymbol *getLabel() const { return Label; }
 
  unsigned getRegister() const {
    assert(Operation == OpDefCfa || Operation == OpOffset ||
           Operation == OpRestore || Operation == OpUndefined ||
           Operation == OpSameValue || Operation == OpDefCfaRegister ||
           Operation == OpRelOffset || Operation == OpValOffset ||
           Operation == OpRegister || Operation == OpLLVMDefAspaceCfa);
    return std::get<CommonFields>(ExtraFields).Register;
  }
 
  unsigned getRegister2() const {
    assert(Operation == OpRegister);
    return std::get<CommonFields>(ExtraFields).Register2;
  }
 
  unsigned getAddressSpace() const {
    assert(Operation == OpLLVMDefAspaceCfa);
    return std::get<CommonFields>(ExtraFields).AddressSpace;
  }
 
  int64_t getOffset() const {
    assert(Operation == OpDefCfa || Operation == OpOffset ||
           Operation == OpRelOffset || Operation == OpDefCfaOffset ||
           Operation == OpAdjustCfaOffset || Operation == OpGnuArgsSize ||
           Operation == OpValOffset || Operation == OpLLVMDefAspaceCfa);
    return std::get<CommonFields>(ExtraFields).Offset;
  }
 
  MCSymbol *getCfiLabel() const {
    assert(Operation == OpLabel);
    return std::get<LabelFields>(ExtraFields).CfiLabel;
  }
 
  StringRef getValues() const {
    assert(Operation == OpEscape);
    auto &Values = std::get<EscapeFields>(ExtraFields).Values;
    return StringRef(&Values[0], Values.size());
  }
 
  StringRef getComment() const {
    assert(Operation == OpEscape);
    return std::get<EscapeFields>(ExtraFields).Comment;
  }
  SMLoc getLoc() const { return Loc; }
};
 
struct MCDwarfFrameInfo {
  MCDwarfFrameInfo() = default;
 
  MCSymbol *Begin = nullptr;
  MCSymbol *End = nullptr;
  const MCSymbol *Personality = nullptr;
  const MCSymbol *Lsda = nullptr;
  std::vector<MCCFIInstruction> Instructions;
  unsigned CurrentCfaRegister = 0;
  unsigned PersonalityEncoding = 0;
  unsigned LsdaEncoding = 0;
  uint64_t CompactUnwindEncoding = 0;
  bool IsSignalFrame = false;
  bool IsSimple = false;
  unsigned RAReg = static_cast<unsigned>(INT_MAX);
  bool IsBKeyFrame = false;
  bool IsMTETaggedFrame = false;
};
 
class MCDwarfFrameEmitter {
public:
  //
  // This emits the frame info section.
  //
  LLVM_ABI static void Emit(MCObjectStreamer &streamer, MCAsmBackend *MAB,
                            bool isEH);
  LLVM_ABI static void encodeAdvanceLoc(MCContext &Context, uint64_t AddrDelta,
                                        SmallVectorImpl<char> &OS);
};
 
} // end namespace llvm
 
#endif // LLVM_MC_MCDWARF_H