Subversion Repositories QNX 8.QNX8 LLVM/Clang compiler suite

//===- MCStreamer.h - High-level Streaming Machine Code Output --*- 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 declares the MCStreamer class.

//

//===----------------------------------------------------------------------===//

#ifndef LLVM_MC_MCSTREAMER_H

#define LLVM_MC_MCSTREAMER_H

#include "llvm/ADT/ArrayRef.h"

#include "llvm/ADT/DenseMap.h"

#include "llvm/ADT/SmallVector.h"

#include "llvm/ADT/StringRef.h"

#include "llvm/MC/MCDirectives.h"

#include "llvm/MC/MCDwarf.h"

#include "llvm/MC/MCLinkerOptimizationHint.h"

#include "llvm/MC/MCPseudoProbe.h"

#include "llvm/MC/MCWinEH.h"

#include "llvm/Support/ARMTargetParser.h"

#include "llvm/Support/Error.h"

#include "llvm/Support/MD5.h"

#include "llvm/Support/SMLoc.h"

#include "llvm/Support/VersionTuple.h"

#include <cassert>

#include <cstdint>

#include <memory>

#include <optional>

#include <string>

#include <utility>

#include <vector>

namespace llvm {

class APInt;

class AssemblerConstantPools;

class MCAsmBackend;

class MCAssembler;

class MCContext;

class MCExpr;

class MCFragment;

class MCInst;

class MCInstPrinter;

class MCRegister;

class MCSection;

class MCStreamer;

class MCSubtargetInfo;

class MCSymbol;

class MCSymbolRefExpr;

class Triple;

class Twine;

class raw_ostream;

namespace codeview {

struct DefRangeRegisterRelHeader;

struct DefRangeSubfieldRegisterHeader;

struct DefRangeRegisterHeader;

struct DefRangeFramePointerRelHeader;

}

using MCSectionSubPair = std::pair<MCSection *, const MCExpr *>;

/// Target specific streamer interface. This is used so that targets can

/// implement support for target specific assembly directives.

///

/// If target foo wants to use this, it should implement 3 classes:

/// * FooTargetStreamer : public MCTargetStreamer

/// * FooTargetAsmStreamer : public FooTargetStreamer

/// * FooTargetELFStreamer : public FooTargetStreamer

///

/// FooTargetStreamer should have a pure virtual method for each directive. For

/// example, for a ".bar symbol_name" directive, it should have

/// virtual emitBar(const MCSymbol &Symbol) = 0;

///

/// The FooTargetAsmStreamer and FooTargetELFStreamer classes implement the

/// method. The assembly streamer just prints ".bar symbol_name". The object

/// streamer does whatever is needed to implement .bar in the object file.

///

/// In the assembly printer and parser the target streamer can be used by

/// calling getTargetStreamer and casting it to FooTargetStreamer:

///

/// MCTargetStreamer &TS = OutStreamer.getTargetStreamer();

/// FooTargetStreamer &ATS = static_cast<FooTargetStreamer &>(TS);

///

/// The base classes FooTargetAsmStreamer and FooTargetELFStreamer should

/// *never* be treated differently. Callers should always talk to a

/// FooTargetStreamer.

class MCTargetStreamer {

protected:

  MCStreamer &Streamer;

public:

  MCTargetStreamer(MCStreamer &S);

  virtual ~MCTargetStreamer();

  MCStreamer &getStreamer() { return Streamer; }

  // Allow a target to add behavior to the EmitLabel of MCStreamer.

  virtual void emitLabel(MCSymbol *Symbol);

  // Allow a target to add behavior to the emitAssignment of MCStreamer.

  virtual void emitAssignment(MCSymbol *Symbol, const MCExpr *Value);

  virtual void prettyPrintAsm(MCInstPrinter &InstPrinter, uint64_t Address,

                              const MCInst &Inst, const MCSubtargetInfo &STI,

                              raw_ostream &OS);

  virtual void emitDwarfFileDirective(StringRef Directive);

  /// Update streamer for a new active section.

  ///

  /// This is called by popSection and switchSection, if the current

  /// section changes.

  virtual void changeSection(const MCSection *CurSection, MCSection *Section,

                             const MCExpr *SubSection, raw_ostream &OS);

  virtual void emitValue(const MCExpr *Value);

  /// Emit the bytes in \p Data into the output.

  ///

  /// This is used to emit bytes in \p Data as sequence of .byte directives.

  virtual void emitRawBytes(StringRef Data);

  virtual void emitConstantPools();

  virtual void finish();

};

// FIXME: declared here because it is used from

// lib/CodeGen/AsmPrinter/ARMException.cpp.

class ARMTargetStreamer : public MCTargetStreamer {

public:

  ARMTargetStreamer(MCStreamer &S);

  ~ARMTargetStreamer() override;

  virtual void emitFnStart();

  virtual void emitFnEnd();

  virtual void emitCantUnwind();

  virtual void emitPersonality(const MCSymbol *Personality);

  virtual void emitPersonalityIndex(unsigned Index);

  virtual void emitHandlerData();

  virtual void emitSetFP(unsigned FpReg, unsigned SpReg,

                         int64_t Offset = 0);

  virtual void emitMovSP(unsigned Reg, int64_t Offset = 0);

  virtual void emitPad(int64_t Offset);

  virtual void emitRegSave(const SmallVectorImpl<unsigned> &RegList,

                           bool isVector);

  virtual void emitUnwindRaw(int64_t StackOffset,

                             const SmallVectorImpl<uint8_t> &Opcodes);

  virtual void switchVendor(StringRef Vendor);

  virtual void emitAttribute(unsigned Attribute, unsigned Value);

  virtual void emitTextAttribute(unsigned Attribute, StringRef String);

  virtual void emitIntTextAttribute(unsigned Attribute, unsigned IntValue,

                                    StringRef StringValue = "");

  virtual void emitFPU(unsigned FPU);

  virtual void emitArch(ARM::ArchKind Arch);

  virtual void emitArchExtension(uint64_t ArchExt);

  virtual void emitObjectArch(ARM::ArchKind Arch);

  void emitTargetAttributes(const MCSubtargetInfo &STI);

  virtual void finishAttributeSection();

  virtual void emitInst(uint32_t Inst, char Suffix = '\0');

  virtual void annotateTLSDescriptorSequence(const MCSymbolRefExpr *SRE);

  virtual void emitThumbSet(MCSymbol *Symbol, const MCExpr *Value);

  void emitConstantPools() override;

  virtual void emitARMWinCFIAllocStack(unsigned Size, bool Wide);

  virtual void emitARMWinCFISaveRegMask(unsigned Mask, bool Wide);

  virtual void emitARMWinCFISaveSP(unsigned Reg);

  virtual void emitARMWinCFISaveFRegs(unsigned First, unsigned Last);

  virtual void emitARMWinCFISaveLR(unsigned Offset);

  virtual void emitARMWinCFIPrologEnd(bool Fragment);

  virtual void emitARMWinCFINop(bool Wide);

  virtual void emitARMWinCFIEpilogStart(unsigned Condition);

  virtual void emitARMWinCFIEpilogEnd();

  virtual void emitARMWinCFICustom(unsigned Opcode);

  /// Reset any state between object emissions, i.e. the equivalent of

  /// MCStreamer's reset method.

  virtual void reset();

  /// Callback used to implement the ldr= pseudo.

  /// Add a new entry to the constant pool for the current section and return an

  /// MCExpr that can be used to refer to the constant pool location.

  const MCExpr *addConstantPoolEntry(const MCExpr *, SMLoc Loc);

  /// Callback used to implement the .ltorg directive.

  /// Emit contents of constant pool for the current section.

  void emitCurrentConstantPool();

private:

  std::unique_ptr<AssemblerConstantPools> ConstantPools;

};

/// Streaming machine code generation interface.

///

/// This interface is intended to provide a programmatic interface that is very

/// similar to the level that an assembler .s file provides.  It has callbacks

/// to emit bytes, handle directives, etc.  The implementation of this interface

/// retains state to know what the current section is etc.

///

/// There are multiple implementations of this interface: one for writing out

/// a .s file, and implementations that write out .o files of various formats.

///

class MCStreamer {

  MCContext &Context;

  std::unique_ptr<MCTargetStreamer> TargetStreamer;

  std::vector<MCDwarfFrameInfo> DwarfFrameInfos;

  MCDwarfFrameInfo *getCurrentDwarfFrameInfo();

  /// Similar to DwarfFrameInfos, but for SEH unwind info. Chained frames may

  /// refer to each other, so use std::unique_ptr to provide pointer stability.

  std::vector<std::unique_ptr<WinEH::FrameInfo>> WinFrameInfos;

  WinEH::FrameInfo *CurrentWinFrameInfo;

  size_t CurrentProcWinFrameInfoStartIndex;

  /// Tracks an index to represent the order a symbol was emitted in.

  /// Zero means we did not emit that symbol.

  DenseMap<const MCSymbol *, unsigned> SymbolOrdering;

  /// This is stack of current and previous section values saved by

  /// pushSection.

  SmallVector<std::pair<MCSectionSubPair, MCSectionSubPair>, 4> SectionStack;

  /// Pointer to the parser's SMLoc if available. This is used to provide

  /// locations for diagnostics.

  const SMLoc *StartTokLocPtr = nullptr;

  /// The next unique ID to use when creating a WinCFI-related section (.pdata

  /// or .xdata). This ID ensures that we have a one-to-one mapping from

  /// code section to unwind info section, which MSVC's incremental linker

  /// requires.

  unsigned NextWinCFIID = 0;

  bool UseAssemblerInfoForParsing;

  /// Is the assembler allowed to insert padding automatically?  For

  /// correctness reasons, we sometimes need to ensure instructions aren't

  /// separated in unexpected ways.  At the moment, this feature is only

  /// useable from an integrated assembler, but assembly syntax is under

  /// discussion for future inclusion.

  bool AllowAutoPadding = false;

protected:

  MCStreamer(MCContext &Ctx);

  virtual void emitCFIStartProcImpl(MCDwarfFrameInfo &Frame);

  virtual void emitCFIEndProcImpl(MCDwarfFrameInfo &CurFrame);

  WinEH::FrameInfo *getCurrentWinFrameInfo() {

    return CurrentWinFrameInfo;

  }

  virtual void emitWindowsUnwindTables(WinEH::FrameInfo *Frame);

  virtual void emitWindowsUnwindTables();

  virtual void emitRawTextImpl(StringRef String);

  /// Returns true if the the .cv_loc directive is in the right section.

  bool checkCVLocSection(unsigned FuncId, unsigned FileNo, SMLoc Loc);

public:

  MCStreamer(const MCStreamer &) = delete;

  MCStreamer &operator=(const MCStreamer &) = delete;

  virtual ~MCStreamer();

  void visitUsedExpr(const MCExpr &Expr);

  virtual void visitUsedSymbol(const MCSymbol &Sym);

  void setTargetStreamer(MCTargetStreamer *TS) {

    TargetStreamer.reset(TS);

  }

  void setStartTokLocPtr(const SMLoc *Loc) { StartTokLocPtr = Loc; }

  SMLoc getStartTokLoc() const {

    return StartTokLocPtr ? *StartTokLocPtr : SMLoc();

  }

  /// State management

  ///

  virtual void reset();

  MCContext &getContext() const { return Context; }

  virtual MCAssembler *getAssemblerPtr() { return nullptr; }

  void setUseAssemblerInfoForParsing(bool v) { UseAssemblerInfoForParsing = v; }

  bool getUseAssemblerInfoForParsing() { return UseAssemblerInfoForParsing; }

  MCTargetStreamer *getTargetStreamer() {

    return TargetStreamer.get();

  }

  void setAllowAutoPadding(bool v) { AllowAutoPadding = v; }

  bool getAllowAutoPadding() const { return AllowAutoPadding; }

  /// When emitting an object file, create and emit a real label. When emitting

  /// textual assembly, this should do nothing to avoid polluting our output.

  virtual MCSymbol *emitCFILabel();

  /// Retrieve the current frame info if one is available and it is not yet

  /// closed. Otherwise, issue an error and return null.

  WinEH::FrameInfo *EnsureValidWinFrameInfo(SMLoc Loc);

  unsigned getNumFrameInfos();

  ArrayRef<MCDwarfFrameInfo> getDwarfFrameInfos() const;

  bool hasUnfinishedDwarfFrameInfo();

  unsigned getNumWinFrameInfos() { return WinFrameInfos.size(); }

  ArrayRef<std::unique_ptr<WinEH::FrameInfo>> getWinFrameInfos() const {

    return WinFrameInfos;

  }

  void generateCompactUnwindEncodings(MCAsmBackend *MAB);

  /// \name Assembly File Formatting.

  /// @{

  /// Return true if this streamer supports verbose assembly and if it is

  /// enabled.

  virtual bool isVerboseAsm() const { return false; }

  /// Return true if this asm streamer supports emitting unformatted text

  /// to the .s file with EmitRawText.

  virtual bool hasRawTextSupport() const { return false; }

  /// Is the integrated assembler required for this streamer to function

  /// correctly?

  virtual bool isIntegratedAssemblerRequired() const { return false; }

  /// Add a textual comment.

  ///

  /// Typically for comments that can be emitted to the generated .s

  /// file if applicable as a QoI issue to make the output of the compiler

  /// more readable.  This only affects the MCAsmStreamer, and only when

  /// verbose assembly output is enabled.

  ///

  /// If the comment includes embedded \n's, they will each get the comment

  /// prefix as appropriate.  The added comment should not end with a \n.

  /// By default, each comment is terminated with an end of line, i.e. the

  /// EOL param is set to true by default. If one prefers not to end the

  /// comment with a new line then the EOL param should be passed

  /// with a false value.

  virtual void AddComment(const Twine &T, bool EOL = true) {}

  /// Return a raw_ostream that comments can be written to. Unlike

  /// AddComment, you are required to terminate comments with \n if you use this

  /// method.

  virtual raw_ostream &getCommentOS();

  /// Print T and prefix it with the comment string (normally #) and

  /// optionally a tab. This prints the comment immediately, not at the end of

  /// the current line. It is basically a safe version of EmitRawText: since it

  /// only prints comments, the object streamer ignores it instead of asserting.

  virtual void emitRawComment(const Twine &T, bool TabPrefix = true);

  /// Add explicit comment T. T is required to be a valid

  /// comment in the output and does not need to be escaped.

  virtual void addExplicitComment(const Twine &T);

  /// Emit added explicit comments.

  virtual void emitExplicitComments();

  /// Emit a blank line to a .s file to pretty it up.

  virtual void addBlankLine() {}

  /// @}

  /// \name Symbol & Section Management

  /// @{

  /// Return the current section that the streamer is emitting code to.

  MCSectionSubPair getCurrentSection() const {

    if (!SectionStack.empty())

      return SectionStack.back().first;

    return MCSectionSubPair();

  }

  MCSection *getCurrentSectionOnly() const { return getCurrentSection().first; }

  /// Return the previous section that the streamer is emitting code to.

  MCSectionSubPair getPreviousSection() const {

    if (!SectionStack.empty())

      return SectionStack.back().second;

    return MCSectionSubPair();

  }

  /// Returns an index to represent the order a symbol was emitted in.

  /// (zero if we did not emit that symbol)

  unsigned getSymbolOrder(const MCSymbol *Sym) const {

    return SymbolOrdering.lookup(Sym);

  }

  /// Update streamer for a new active section.

  ///

  /// This is called by popSection and switchSection, if the current

  /// section changes.

  virtual void changeSection(MCSection *, const MCExpr *);

  /// Save the current and previous section on the section stack.

  void pushSection() {

    SectionStack.push_back(

        std::make_pair(getCurrentSection(), getPreviousSection()));

  }

  /// Restore the current and previous section from the section stack.

  /// Calls changeSection as needed.

  ///

  /// Returns false if the stack was empty.

  bool popSection() {

    if (SectionStack.size() <= 1)

      return false;

    auto I = SectionStack.end();

    --I;

    MCSectionSubPair OldSection = I->first;

    --I;

    MCSectionSubPair NewSection = I->first;

    if (NewSection.first && OldSection != NewSection)

      changeSection(NewSection.first, NewSection.second);

    SectionStack.pop_back();

    return true;

  }

  bool subSection(const MCExpr *Subsection) {

    if (SectionStack.empty())

      return false;

    switchSection(SectionStack.back().first.first, Subsection);

    return true;

  }

  /// Set the current section where code is being emitted to \p Section.  This

  /// is required to update CurSection.

  ///

  /// This corresponds to assembler directives like .section, .text, etc.

  virtual void switchSection(MCSection *Section,

                             const MCExpr *Subsection = nullptr);

  /// Set the current section where code is being emitted to \p Section.

  /// This is required to update CurSection. This version does not call

  /// changeSection.

  void switchSectionNoChange(MCSection *Section,

                             const MCExpr *Subsection = nullptr) {

    assert(Section && "Cannot switch to a null section!");

    MCSectionSubPair curSection = SectionStack.back().first;

    SectionStack.back().second = curSection;

    if (MCSectionSubPair(Section, Subsection) != curSection)

      SectionStack.back().first = MCSectionSubPair(Section, Subsection);

  }

  /// Create the default sections and set the initial one.

  virtual void initSections(bool NoExecStack, const MCSubtargetInfo &STI);

  MCSymbol *endSection(MCSection *Section);

  /// Sets the symbol's section.

  ///

  /// Each emitted symbol will be tracked in the ordering table,

  /// so we can sort on them later.

  void assignFragment(MCSymbol *Symbol, MCFragment *Fragment);

  /// Returns the mnemonic for \p MI, if the streamer has access to a

  /// instruction printer and returns an empty string otherwise.

  virtual StringRef getMnemonic(MCInst &MI) { return ""; }

  /// Emit a label for \p Symbol into the current section.

  ///

  /// This corresponds to an assembler statement such as:

  ///   foo:

  ///

  /// \param Symbol - The symbol to emit. A given symbol should only be

  /// emitted as a label once, and symbols emitted as a label should never be

  /// used in an assignment.

  // FIXME: These emission are non-const because we mutate the symbol to

  // add the section we're emitting it to later.

  virtual void emitLabel(MCSymbol *Symbol, SMLoc Loc = SMLoc());

  virtual void emitEHSymAttributes(const MCSymbol *Symbol, MCSymbol *EHSymbol);

  /// Note in the output the specified \p Flag.

  virtual void emitAssemblerFlag(MCAssemblerFlag Flag);

  /// Emit the given list \p Options of strings as linker

  /// options into the output.

  virtual void emitLinkerOptions(ArrayRef<std::string> Kind) {}

  /// Note in the output the specified region \p Kind.

  virtual void emitDataRegion(MCDataRegionType Kind) {}

  /// Specify the Mach-O minimum deployment target version.

  virtual void emitVersionMin(MCVersionMinType Type, unsigned Major,

                              unsigned Minor, unsigned Update,

                              VersionTuple SDKVersion) {}

  /// Emit/Specify Mach-O build version command.

  /// \p Platform should be one of MachO::PlatformType.

  virtual void emitBuildVersion(unsigned Platform, unsigned Major,

                                unsigned Minor, unsigned Update,

                                VersionTuple SDKVersion) {}

  virtual void emitDarwinTargetVariantBuildVersion(unsigned Platform,

                                                   unsigned Major,

                                                   unsigned Minor,

                                                   unsigned Update,

                                                   VersionTuple SDKVersion) {}

  void emitVersionForTarget(const Triple &Target,

                            const VersionTuple &SDKVersion,

                            const Triple *DarwinTargetVariantTriple,

                            const VersionTuple &DarwinTargetVariantSDKVersion);

  /// Note in the output that the specified \p Func is a Thumb mode

  /// function (ARM target only).

  virtual void emitThumbFunc(MCSymbol *Func);

  /// Emit an assignment of \p Value to \p Symbol.

  ///

  /// This corresponds to an assembler statement such as:

  ///  symbol = value

  ///

  /// The assignment generates no code, but has the side effect of binding the

  /// value in the current context. For the assembly streamer, this prints the

  /// binding into the .s file.

  ///

  /// \param Symbol - The symbol being assigned to.

  /// \param Value - The value for the symbol.

  virtual void emitAssignment(MCSymbol *Symbol, const MCExpr *Value);

  /// Emit an assignment of \p Value to \p Symbol, but only if \p Value is also

  /// emitted.

  virtual void emitConditionalAssignment(MCSymbol *Symbol, const MCExpr *Value);

  /// Emit an weak reference from \p Alias to \p Symbol.

  ///

  /// This corresponds to an assembler statement such as:

  ///  .weakref alias, symbol

  ///

  /// \param Alias - The alias that is being created.

  /// \param Symbol - The symbol being aliased.

  virtual void emitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol);

  /// Add the given \p Attribute to \p Symbol.

  virtual bool emitSymbolAttribute(MCSymbol *Symbol,

                                   MCSymbolAttr Attribute) = 0;

  /// Set the \p DescValue for the \p Symbol.

  ///

  /// \param Symbol - The symbol to have its n_desc field set.

  /// \param DescValue - The value to set into the n_desc field.

  virtual void emitSymbolDesc(MCSymbol *Symbol, unsigned DescValue);

  /// Start emitting COFF symbol definition

  ///

  /// \param Symbol - The symbol to have its External & Type fields set.

  virtual void beginCOFFSymbolDef(const MCSymbol *Symbol);

  /// Emit the storage class of the symbol.

  ///

  /// \param StorageClass - The storage class the symbol should have.

  virtual void emitCOFFSymbolStorageClass(int StorageClass);

  /// Emit the type of the symbol.

  ///

  /// \param Type - A COFF type identifier (see COFF::SymbolType in X86COFF.h)

  virtual void emitCOFFSymbolType(int Type);

  /// Marks the end of the symbol definition.

  virtual void endCOFFSymbolDef();

  virtual void emitCOFFSafeSEH(MCSymbol const *Symbol);

  /// Emits the symbol table index of a Symbol into the current section.

  virtual void emitCOFFSymbolIndex(MCSymbol const *Symbol);

  /// Emits a COFF section index.

  ///

  /// \param Symbol - Symbol the section number relocation should point to.

  virtual void emitCOFFSectionIndex(MCSymbol const *Symbol);

  /// Emits a COFF section relative relocation.

  ///

  /// \param Symbol - Symbol the section relative relocation should point to.

  virtual void emitCOFFSecRel32(MCSymbol const *Symbol, uint64_t Offset);

  /// Emits a COFF image relative relocation.

  ///

  /// \param Symbol - Symbol the image relative relocation should point to.

  virtual void emitCOFFImgRel32(MCSymbol const *Symbol, int64_t Offset);

  /// Emits an lcomm directive with XCOFF csect information.

  ///

  /// \param LabelSym - Label on the block of storage.

  /// \param Size - The size of the block of storage.

  /// \param CsectSym - Csect name for the block of storage.

  /// \param Alignment - The alignment of the symbol in bytes.

  virtual void emitXCOFFLocalCommonSymbol(MCSymbol *LabelSym, uint64_t Size,

                                          MCSymbol *CsectSym, Align Alignment);

  /// Emit a symbol's linkage and visibility with a linkage directive for XCOFF.

  ///

  /// \param Symbol - The symbol to emit.

  /// \param Linkage - The linkage of the symbol to emit.

  /// \param Visibility - The visibility of the symbol to emit or MCSA_Invalid

  /// if the symbol does not have an explicit visibility.

  virtual void emitXCOFFSymbolLinkageWithVisibility(MCSymbol *Symbol,

                                                    MCSymbolAttr Linkage,

                                                    MCSymbolAttr Visibility);

  /// Emit a XCOFF .rename directive which creates a synonym for an illegal or

  /// undesirable name.

  ///

  /// \param Name - The name used internally in the assembly for references to

  /// the symbol.

  /// \param Rename - The value to which the Name parameter is

  /// changed at the end of assembly.

  virtual void emitXCOFFRenameDirective(const MCSymbol *Name, StringRef Rename);

  /// Emit an XCOFF .except directive which adds information about

  /// a trap instruction to the object file exception section

  ///

  /// \param Symbol - The function containing the trap.

  /// \param Lang - The language code for the exception entry.

  /// \param Reason - The reason code for the exception entry.

  virtual void emitXCOFFExceptDirective(const MCSymbol *Symbol,

                                        const MCSymbol *Trap,

                                        unsigned Lang, unsigned Reason,

                                        unsigned FunctionSize, bool hasDebug);

  /// Emit a XCOFF .ref directive which creates R_REF type entry in the

  /// relocation table for one or more symbols.

  ///

  /// \param Sym - The symbol on the .ref directive.

  virtual void emitXCOFFRefDirective(StringRef Sym);

  /// Emit an ELF .size directive.

  ///

  /// This corresponds to an assembler statement such as:

  ///  .size symbol, expression

  virtual void emitELFSize(MCSymbol *Symbol, const MCExpr *Value);

  /// Emit an ELF .symver directive.

  ///

  /// This corresponds to an assembler statement such as:

  ///  .symver _start, foo@@SOME_VERSION

  virtual void emitELFSymverDirective(const MCSymbol *OriginalSym,

                                      StringRef Name, bool KeepOriginalSym);

  /// Emit a Linker Optimization Hint (LOH) directive.

  /// \param Args - Arguments of the LOH.

  virtual void emitLOHDirective(MCLOHType Kind, const MCLOHArgs &Args) {}

  /// Emit a .gnu_attribute directive.

  virtual void emitGNUAttribute(unsigned Tag, unsigned Value) {}

  /// Emit a common symbol.

  ///

  /// \param Symbol - The common symbol to emit.

  /// \param Size - The size of the common symbol.

  /// \param ByteAlignment - The alignment of the symbol.

  virtual void emitCommonSymbol(MCSymbol *Symbol, uint64_t Size,

                                Align ByteAlignment) = 0;

  /// Emit a local common (.lcomm) symbol.

  ///

  /// \param Symbol - The common symbol to emit.

  /// \param Size - The size of the common symbol.

  /// \param ByteAlignment - The alignment of the common symbol in bytes.

  virtual void emitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,

                                     Align ByteAlignment);

  /// Emit the zerofill section and an optional symbol.

  ///

  /// \param Section - The zerofill section to create and or to put the symbol

  /// \param Symbol - The zerofill symbol to emit, if non-NULL.

  /// \param Size - The size of the zerofill symbol.

  /// \param ByteAlignment - The alignment of the zerofill symbol.

  virtual void emitZerofill(MCSection *Section, MCSymbol *Symbol = nullptr,

                            uint64_t Size = 0, Align ByteAlignment = Align(1),

                            SMLoc Loc = SMLoc()) = 0;

  /// Emit a thread local bss (.tbss) symbol.

  ///

  /// \param Section - The thread local common section.

  /// \param Symbol - The thread local common symbol to emit.

  /// \param Size - The size of the symbol.

  /// \param ByteAlignment - The alignment of the thread local common symbol.

  virtual void emitTBSSSymbol(MCSection *Section, MCSymbol *Symbol,

                              uint64_t Size, Align ByteAlignment = Align(1));

  /// @}

  /// \name Generating Data

  /// @{

  /// Emit the bytes in \p Data into the output.

  ///

  /// This is used to implement assembler directives such as .byte, .ascii,

  /// etc.

  virtual void emitBytes(StringRef Data);

  /// Functionally identical to EmitBytes. When emitting textual assembly, this

  /// method uses .byte directives instead of .ascii or .asciz for readability.

  virtual void emitBinaryData(StringRef Data);

  /// Emit the expression \p Value into the output as a native

  /// integer of the given \p Size bytes.

  ///

  /// This is used to implement assembler directives such as .word, .quad,

  /// etc.

  ///

  /// \param Value - The value to emit.

  /// \param Size - The size of the integer (in bytes) to emit. This must

  /// match a native machine width.

  /// \param Loc - The location of the expression for error reporting.

  virtual void emitValueImpl(const MCExpr *Value, unsigned Size,

                             SMLoc Loc = SMLoc());

  void emitValue(const MCExpr *Value, unsigned Size, SMLoc Loc = SMLoc());

  /// Special case of EmitValue that avoids the client having

  /// to pass in a MCExpr for constant integers.

  virtual void emitIntValue(uint64_t Value, unsigned Size);

  virtual void emitIntValue(APInt Value);

  /// Special case of EmitValue that avoids the client having to pass

  /// in a MCExpr for constant integers & prints in Hex format for certain

  /// modes.

  virtual void emitIntValueInHex(uint64_t Value, unsigned Size) {

    emitIntValue(Value, Size);

  }

  void emitInt8(uint64_t Value) { emitIntValue(Value, 1); }

  void emitInt16(uint64_t Value) { emitIntValue(Value, 2); }

  void emitInt32(uint64_t Value) { emitIntValue(Value, 4); }

  void emitInt64(uint64_t Value) { emitIntValue(Value, 8); }

  /// Special case of EmitValue that avoids the client having to pass

  /// in a MCExpr for constant integers & prints in Hex format for certain

  /// modes, pads the field with leading zeros to Size width

  virtual void emitIntValueInHexWithPadding(uint64_t Value, unsigned Size) {

    emitIntValue(Value, Size);

  }

  virtual void emitULEB128Value(const MCExpr *Value);

  virtual void emitSLEB128Value(const MCExpr *Value);

  /// Special case of EmitULEB128Value that avoids the client having to

  /// pass in a MCExpr for constant integers.

  unsigned emitULEB128IntValue(uint64_t Value, unsigned PadTo = 0);

  /// Special case of EmitSLEB128Value that avoids the client having to

  /// pass in a MCExpr for constant integers.

  unsigned emitSLEB128IntValue(int64_t Value);

  /// Special case of EmitValue that avoids the client having to pass in

  /// a MCExpr for MCSymbols.

  void emitSymbolValue(const MCSymbol *Sym, unsigned Size,

                       bool IsSectionRelative = false);

  /// Emit the expression \p Value into the output as a dtprel

  /// (64-bit DTP relative) value.

  ///

  /// This is used to implement assembler directives such as .dtpreldword on

  /// targets that support them.

  virtual void emitDTPRel64Value(const MCExpr *Value);

  /// Emit the expression \p Value into the output as a dtprel

  /// (32-bit DTP relative) value.

  ///

  /// This is used to implement assembler directives such as .dtprelword on

  /// targets that support them.

  virtual void emitDTPRel32Value(const MCExpr *Value);

  /// Emit the expression \p Value into the output as a tprel

  /// (64-bit TP relative) value.

  ///

  /// This is used to implement assembler directives such as .tpreldword on

  /// targets that support them.

  virtual void emitTPRel64Value(const MCExpr *Value);

  /// Emit the expression \p Value into the output as a tprel

  /// (32-bit TP relative) value.

  ///

  /// This is used to implement assembler directives such as .tprelword on

  /// targets that support them.

  virtual void emitTPRel32Value(const MCExpr *Value);

  /// Emit the expression \p Value into the output as a gprel64 (64-bit

  /// GP relative) value.

  ///

  /// This is used to implement assembler directives such as .gpdword on

  /// targets that support them.

  virtual void emitGPRel64Value(const MCExpr *Value);

  /// Emit the expression \p Value into the output as a gprel32 (32-bit

  /// GP relative) value.

  ///

  /// This is used to implement assembler directives such as .gprel32 on

  /// targets that support them.

  virtual void emitGPRel32Value(const MCExpr *Value);

  /// Emit NumBytes bytes worth of the value specified by FillValue.

  /// This implements directives such as '.space'.

  void emitFill(uint64_t NumBytes, uint8_t FillValue);

  /// Emit \p Size bytes worth of the value specified by \p FillValue.

  ///

  /// This is used to implement assembler directives such as .space or .skip.

  ///

  /// \param NumBytes - The number of bytes to emit.

  /// \param FillValue - The value to use when filling bytes.

  /// \param Loc - The location of the expression for error reporting.

  virtual void emitFill(const MCExpr &NumBytes, uint64_t FillValue,

                        SMLoc Loc = SMLoc());

  /// Emit \p NumValues copies of \p Size bytes. Each \p Size bytes is

  /// taken from the lowest order 4 bytes of \p Expr expression.

  ///

  /// This is used to implement assembler directives such as .fill.

  ///

  /// \param NumValues - The number of copies of \p Size bytes to emit.

  /// \param Size - The size (in bytes) of each repeated value.

  /// \param Expr - The expression from which \p Size bytes are used.

  virtual void emitFill(const MCExpr &NumValues, int64_t Size, int64_t Expr,

                        SMLoc Loc = SMLoc());

  virtual void emitNops(int64_t NumBytes, int64_t ControlledNopLength,

                        SMLoc Loc, const MCSubtargetInfo& STI);

  /// Emit NumBytes worth of zeros.

  /// This function properly handles data in virtual sections.

  void emitZeros(uint64_t NumBytes);

  /// Emit some number of copies of \p Value until the byte alignment \p

  /// ByteAlignment is reached.

  ///

  /// If the number of bytes need to emit for the alignment is not a multiple

  /// of \p ValueSize, then the contents of the emitted fill bytes is

  /// undefined.