MCSection.h

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//===- MCSection.h - Machine Code Sections ----------------------*- 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 MCSection class.
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_MC_MCSECTION_H
#define LLVM_MC_MCSECTION_H
 
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/MC/MCFixup.h"
#include "llvm/MC/MCInst.h"
#include "llvm/MC/SectionKind.h"
#include "llvm/Support/Alignment.h"
#include "llvm/Support/Compiler.h"
#include <cassert>
#include <utility>
 
namespace llvm {
 
class MCAsmInfo;
class MCAssembler;
class MCContext;
class MCExpr;
class MCFragment;
class MCObjectStreamer;
class MCSymbol;
class MCSection;
class MCSubtargetInfo;
class raw_ostream;
class Triple;
 
// Represents a contiguous piece of code or data within a section. Its size is
// determined by MCAssembler::layout. All subclasses must have trivial
// destructors.
class MCFragment {
  friend class MCAssembler;
  friend class MCStreamer;
  friend class MCObjectStreamer;
  friend class MCSection;
 
public:
  enum FragmentType : uint8_t {
    FT_Data,
    FT_Relaxable,
    FT_Align,
    FT_Fill,
    FT_LEB,
    FT_Nops,
    FT_Org,
    FT_Dwarf,
    FT_DwarfFrame,
    FT_BoundaryAlign,
    FT_SymbolId,
    FT_CVInlineLines,
    FT_CVDefRange,
  };
 
private:
  // The next fragment within the section.
  MCFragment *Next = nullptr;
 
  /// The data for the section this fragment is in.
  MCSection *Parent = nullptr;
 
  /// The offset of this fragment in its section.
  uint64_t Offset = 0;
 
  /// The layout order of this fragment.
  unsigned LayoutOrder = 0;
 
  FragmentType Kind;
 
  //== Used by certain fragment types for better packing.
 
  // The number of fixups for the optional variable-size tail must be small.
  uint8_t VarFixupSize = 0;
 
  bool LinkerRelaxable : 1;
 
  /// FT_Data, FT_Relaxable
  bool HasInstructions : 1;
  /// FT_Relaxable, x86-specific
  bool AllowAutoPadding : 1;
 
  // Track content and fixups for the fixed-size part as fragments are
  // appended to the section. The content is stored as trailing data of the
  // MCFragment. The content remains immutable, except when modified by
  // applyFixup.
  uint32_t FixedSize = 0;
  uint32_t FixupStart = 0;
  uint32_t FixupEnd = 0;
 
  // Track content and fixups for the optional variable-size tail part,
  // typically modified during relaxation.
  uint32_t VarContentStart = 0;
  uint32_t VarContentEnd = 0;
  uint32_t VarFixupStart = 0;
 
  const MCSubtargetInfo *STI = nullptr;
 
  // Optional variable-size tail used by various fragment types.
  union Tail {
    struct {
      uint32_t Opcode;
      uint32_t Flags;
      uint32_t OperandStart;
      uint32_t OperandSize;
    } relax;
    struct {
      // The alignment to ensure, in bytes.
      Align Alignment;
      // The size of the integer (in bytes) of \p Value.
      uint8_t FillLen;
      // If true, fill with target-specific nop instructions.
      bool EmitNops;
      // The maximum number of bytes to emit; if the alignment
      // cannot be satisfied in this width then this fragment is ignored.
      unsigned MaxBytesToEmit;
      // Value to use for filling padding bytes.
      int64_t Fill;
    } align;
    struct {
      // True if this is a sleb128, false if uleb128.
      bool IsSigned;
      // The value this fragment should contain.
      const MCExpr *Value;
    } leb;
    // Used by .debug_frame and .debug_line to encode an address difference.
    struct {
      // The address difference between two labels.
      const MCExpr *AddrDelta;
      // The value of the difference between the two line numbers between two
      // .loc dwarf directives.
      int64_t LineDelta;
    } dwarf;
  } u{};
 
public:
  LLVM_ABI MCFragment(FragmentType Kind = MCFragment::FT_Data,
                      bool HasInstructions = false);
  MCFragment(const MCFragment &) = delete;
  MCFragment &operator=(const MCFragment &) = delete;
 
  MCFragment *getNext() const { return Next; }
 
  FragmentType getKind() const { return Kind; }
 
  MCSection *getParent() const { return Parent; }
  void setParent(MCSection *Value) { Parent = Value; }
 
  LLVM_ABI const MCSymbol *getAtom() const;
 
  unsigned getLayoutOrder() const { return LayoutOrder; }
  void setLayoutOrder(unsigned Value) { LayoutOrder = Value; }
 
  /// Does this fragment have instructions emitted into it? By default
  /// this is false, but specific fragment types may set it to true.
  bool hasInstructions() const { return HasInstructions; }
 
  LLVM_ABI void dump() const;
 
  /// Retrieve the MCSubTargetInfo in effect when the instruction was encoded.
  /// Guaranteed to be non-null if hasInstructions() == true
  const MCSubtargetInfo *getSubtargetInfo() const { return STI; }
 
  /// Record that the fragment contains instructions with the MCSubtargetInfo in
  /// effect when the instruction was encoded.
  void setHasInstructions(const MCSubtargetInfo &STI) {
    HasInstructions = true;
    this->STI = &STI;
  }
 
  bool isLinkerRelaxable() const { return LinkerRelaxable; }
  void setLinkerRelaxable() { LinkerRelaxable = true; }
 
  bool getAllowAutoPadding() const { return AllowAutoPadding; }
  void setAllowAutoPadding(bool V) { AllowAutoPadding = V; }
 
  //== Content-related functions manage parent's storage using ContentStart and
  // ContentSize.
 
  MutableArrayRef<char> getContents();
  ArrayRef<char> getContents() const;
 
  LLVM_ABI void setVarContents(ArrayRef<char> Contents);
  void clearVarContents() { setVarContents({}); }
  MutableArrayRef<char> getVarContents();
  ArrayRef<char> getVarContents() const;
 
  size_t getFixedSize() const { return FixedSize; }
  size_t getVarSize() const { return VarContentEnd - VarContentStart; }
  size_t getSize() const {
    return FixedSize + (VarContentEnd - VarContentStart);
  }
 
  //== Fixup-related functions manage parent's storage using FixupStart and
  // FixupSize.
  void clearFixups() { FixupEnd = FixupStart; }
  LLVM_ABI void addFixup(MCFixup Fixup);
  LLVM_ABI void appendFixups(ArrayRef<MCFixup> Fixups);
  MutableArrayRef<MCFixup> getFixups();
  ArrayRef<MCFixup> getFixups() const;
 
  // Source fixup offsets are relative to the variable part's start.
  // Stored fixup offsets are relative to the fixed part's start.
  LLVM_ABI void setVarFixups(ArrayRef<MCFixup> Fixups);
  void clearVarFixups() { setVarFixups({}); }
  MutableArrayRef<MCFixup> getVarFixups();
  ArrayRef<MCFixup> getVarFixups() const;
 
  //== FT_Relaxable functions
  unsigned getOpcode() const {
    assert(Kind == FT_Relaxable);
    return u.relax.Opcode;
  }
  ArrayRef<MCOperand> getOperands() const;
  MCInst getInst() const;
  void setInst(const MCInst &Inst);
 
  //== FT_Align functions
  void makeAlign(Align Alignment, int64_t Fill, uint8_t FillLen,
                 unsigned MaxBytesToEmit) {
    Kind = FT_Align;
    u.align.EmitNops = false;
    u.align.Alignment = Alignment;
    u.align.Fill = Fill;
    u.align.FillLen = FillLen;
    u.align.MaxBytesToEmit = MaxBytesToEmit;
  }
 
  Align getAlignment() const {
    assert(Kind == FT_Align);
    return u.align.Alignment;
  }
  int64_t getAlignFill() const {
    assert(Kind == FT_Align);
    return u.align.Fill;
  }
  uint8_t getAlignFillLen() const {
    assert(Kind == FT_Align);
    return u.align.FillLen;
  }
  unsigned getAlignMaxBytesToEmit() const {
    assert(Kind == FT_Align);
    return u.align.MaxBytesToEmit;
  }
  bool hasAlignEmitNops() const {
    assert(Kind == FT_Align);
    return u.align.EmitNops;
  }
 
  //== FT_LEB functions
  void makeLEB(bool IsSigned, const MCExpr *Value) {
    assert(Kind == FT_Data);
    Kind = MCFragment::FT_LEB;
    u.leb.IsSigned = IsSigned;
    u.leb.Value = Value;
  }
  const MCExpr &getLEBValue() const {
    assert(Kind == FT_LEB);
    return *u.leb.Value;
  }
  void setLEBValue(const MCExpr *Expr) {
    assert(Kind == FT_LEB);
    u.leb.Value = Expr;
  }
  bool isLEBSigned() const {
    assert(Kind == FT_LEB);
    return u.leb.IsSigned;
  }
 
  //== FT_DwarfFrame functions
  const MCExpr &getDwarfAddrDelta() const {
    assert(Kind == FT_Dwarf || Kind == FT_DwarfFrame);
    return *u.dwarf.AddrDelta;
  }
  void setDwarfAddrDelta(const MCExpr *E) {
    assert(Kind == FT_Dwarf || Kind == FT_DwarfFrame);
    u.dwarf.AddrDelta = E;
  }
  int64_t getDwarfLineDelta() const {
    assert(Kind == FT_Dwarf);
    return u.dwarf.LineDelta;
  }
  void setDwarfLineDelta(int64_t LineDelta) {
    assert(Kind == FT_Dwarf);
    u.dwarf.LineDelta = LineDelta;
  }
};
 
// MCFragment subclasses do not use the fixed-size part or variable-size tail of
// MCFragment. Instead, they encode content in a specialized way.
 
class MCFillFragment : public MCFragment {
  uint8_t ValueSize;
  /// Value to use for filling bytes.
  uint64_t Value;
  /// The number of bytes to insert.
  const MCExpr &NumValues;
 
  /// Source location of the directive that this fragment was created for.
  SMLoc Loc;
 
public:
  MCFillFragment(uint64_t Value, uint8_t VSize, const MCExpr &NumValues,
                 SMLoc Loc)
      : MCFragment(FT_Fill), ValueSize(VSize), Value(Value),
        NumValues(NumValues), Loc(Loc) {}
 
  uint64_t getValue() const { return Value; }
  uint8_t getValueSize() const { return ValueSize; }
  const MCExpr &getNumValues() const { return NumValues; }
 
  SMLoc getLoc() const { return Loc; }
 
  static bool classof(const MCFragment *F) {
    return F->getKind() == MCFragment::FT_Fill;
  }
};
 
class MCNopsFragment : public MCFragment {
  /// The number of bytes to insert.
  int64_t Size;
  /// Maximum number of bytes allowed in each NOP instruction.
  int64_t ControlledNopLength;
 
  /// Source location of the directive that this fragment was created for.
  SMLoc Loc;
 
  /// When emitting Nops some subtargets have specific nop encodings.
  const MCSubtargetInfo &STI;
 
public:
  MCNopsFragment(int64_t NumBytes, int64_t ControlledNopLength, SMLoc L,
                 const MCSubtargetInfo &STI)
      : MCFragment(FT_Nops), Size(NumBytes),
        ControlledNopLength(ControlledNopLength), Loc(L), STI(STI) {}
 
  int64_t getNumBytes() const { return Size; }
  int64_t getControlledNopLength() const { return ControlledNopLength; }
 
  SMLoc getLoc() const { return Loc; }
 
  const MCSubtargetInfo *getSubtargetInfo() const { return &STI; }
 
  static bool classof(const MCFragment *F) {
    return F->getKind() == MCFragment::FT_Nops;
  }
};
 
class MCOrgFragment : public MCFragment {
  /// Value to use for filling bytes.
  int8_t Value;
 
  /// The offset this fragment should start at.
  const MCExpr *Offset;
 
  /// Source location of the directive that this fragment was created for.
  SMLoc Loc;
 
public:
  MCOrgFragment(const MCExpr &Offset, int8_t Value, SMLoc Loc)
      : MCFragment(FT_Org), Value(Value), Offset(&Offset), Loc(Loc) {}
 
  const MCExpr &getOffset() const { return *Offset; }
  uint8_t getValue() const { return Value; }
 
  SMLoc getLoc() const { return Loc; }
 
  static bool classof(const MCFragment *F) {
    return F->getKind() == MCFragment::FT_Org;
  }
};
 
/// Represents a symbol table index fragment.
class MCSymbolIdFragment : public MCFragment {
  const MCSymbol *Sym;
 
public:
  MCSymbolIdFragment(const MCSymbol *Sym) : MCFragment(FT_SymbolId), Sym(Sym) {}
 
  const MCSymbol *getSymbol() { return Sym; }
  const MCSymbol *getSymbol() const { return Sym; }
 
  static bool classof(const MCFragment *F) {
    return F->getKind() == MCFragment::FT_SymbolId;
  }
};
 
/// Fragment representing the binary annotations produced by the
/// .cv_inline_linetable directive.
class MCCVInlineLineTableFragment : public MCFragment {
  unsigned SiteFuncId;
  unsigned StartFileId;
  unsigned StartLineNum;
  const MCSymbol *FnStartSym;
  const MCSymbol *FnEndSym;
 
  /// CodeViewContext has the real knowledge about this format, so let it access
  /// our members.
  friend class CodeViewContext;
 
public:
  MCCVInlineLineTableFragment(unsigned SiteFuncId, unsigned StartFileId,
                              unsigned StartLineNum, const MCSymbol *FnStartSym,
                              const MCSymbol *FnEndSym)
      : MCFragment(FT_CVInlineLines), SiteFuncId(SiteFuncId),
        StartFileId(StartFileId), StartLineNum(StartLineNum),
        FnStartSym(FnStartSym), FnEndSym(FnEndSym) {}
 
  const MCSymbol *getFnStartSym() const { return FnStartSym; }
  const MCSymbol *getFnEndSym() const { return FnEndSym; }
 
  static bool classof(const MCFragment *F) {
    return F->getKind() == MCFragment::FT_CVInlineLines;
  }
};
 
/// Fragment representing the .cv_def_range directive.
class MCCVDefRangeFragment : public MCFragment {
  ArrayRef<std::pair<const MCSymbol *, const MCSymbol *>> Ranges;
  StringRef FixedSizePortion;
 
  /// CodeViewContext has the real knowledge about this format, so let it access
  /// our members.
  friend class CodeViewContext;
 
public:
  MCCVDefRangeFragment(
      ArrayRef<std::pair<const MCSymbol *, const MCSymbol *>> Ranges,
      StringRef FixedSizePortion)
      : MCFragment(FT_CVDefRange), Ranges(Ranges.begin(), Ranges.end()),
        FixedSizePortion(FixedSizePortion) {}
 
  ArrayRef<std::pair<const MCSymbol *, const MCSymbol *>> getRanges() const {
    return Ranges;
  }
 
  StringRef getFixedSizePortion() const { return FixedSizePortion; }
 
  static bool classof(const MCFragment *F) {
    return F->getKind() == MCFragment::FT_CVDefRange;
  }
};
 
/// Represents required padding such that a particular other set of fragments
/// does not cross a particular power-of-two boundary. The other fragments must
/// follow this one within the same section.
class MCBoundaryAlignFragment : public MCFragment {
  /// The alignment requirement of the branch to be aligned.
  Align AlignBoundary;
  /// The last fragment in the set of fragments to be aligned.
  const MCFragment *LastFragment = nullptr;
  /// The size of the fragment.  The size is lazily set during relaxation, and
  /// is not meaningful before that.
  uint64_t Size = 0;
 
  /// When emitting Nops some subtargets have specific nop encodings.
  const MCSubtargetInfo &STI;
 
public:
  MCBoundaryAlignFragment(Align AlignBoundary, const MCSubtargetInfo &STI)
      : MCFragment(FT_BoundaryAlign), AlignBoundary(AlignBoundary), STI(STI) {}
 
  uint64_t getSize() const { return Size; }
  void setSize(uint64_t Value) { Size = Value; }
 
  Align getAlignment() const { return AlignBoundary; }
  void setAlignment(Align Value) { AlignBoundary = Value; }
 
  const MCFragment *getLastFragment() const { return LastFragment; }
  void setLastFragment(const MCFragment *F) {
    assert(!F || getParent() == F->getParent());
    LastFragment = F;
  }
 
  const MCSubtargetInfo *getSubtargetInfo() const { return &STI; }
 
  static bool classof(const MCFragment *F) {
    return F->getKind() == MCFragment::FT_BoundaryAlign;
  }
};
 
/// Instances of this class represent a uniqued identifier for a section in the
/// current translation unit.  The MCContext class uniques and creates these.
class LLVM_ABI MCSection {
public:
  friend MCAssembler;
  friend MCObjectStreamer;
  friend class MCFragment;
  static constexpr unsigned NonUniqueID = ~0U;
 
  struct iterator {
    MCFragment *F = nullptr;
    iterator() = default;
    explicit iterator(MCFragment *F) : F(F) {}
    MCFragment &operator*() const { return *F; }
    bool operator==(const iterator &O) const { return F == O.F; }
    bool operator!=(const iterator &O) const { return F != O.F; }
    iterator &operator++();
  };
 
  struct FragList {
    MCFragment *Head = nullptr;
    MCFragment *Tail = nullptr;
  };
 
private:
  // At parse time, this holds the fragment list of the current subsection. At
  // layout time, this holds the concatenated fragment lists of all subsections.
  FragList *CurFragList;
  // In many object file formats, this denotes the section symbol. In Mach-O,
  // this denotes an optional temporary label at the section start.
  MCSymbol *Begin;
  MCSymbol *End = nullptr;
  /// The alignment requirement of this section.
  Align Alignment;
  /// The section index in the assemblers section list.
  unsigned Ordinal = 0;
  // If not -1u, the first linker-relaxable fragment's order within the
  // subsection. When present, the offset between two locations crossing this
  // fragment may not be fully resolved.
  unsigned FirstLinkerRelaxable = -1u;
 
  /// Whether this section has had instructions emitted into it.
  bool HasInstructions : 1;
 
  bool IsRegistered : 1;
 
  bool IsText : 1;
  bool IsBss : 1;
 
  MCFragment DummyFragment;
 
  // Mapping from subsection number to fragment list. At layout time, the
  // subsection 0 list is replaced with concatenated fragments from all
  // subsections.
  SmallVector<std::pair<unsigned, FragList>, 1> Subsections;
 
  // Content and fixup storage for fragments
  SmallVector<char, 0> ContentStorage;
  SmallVector<MCFixup, 0> FixupStorage;
  SmallVector<MCOperand, 0> MCOperandStorage;
 
protected:
  // TODO Make Name private when possible.
  StringRef Name;
 
  MCSection(StringRef Name, bool IsText, bool IsBss, MCSymbol *Begin);
 
public:
  MCSection(const MCSection &) = delete;
  MCSection &operator=(const MCSection &) = delete;
 
  StringRef getName() const { return Name; }
  bool isText() const { return IsText; }
 
  MCSymbol *getBeginSymbol() { return Begin; }
  const MCSymbol *getBeginSymbol() const {
    return const_cast<MCSection *>(this)->getBeginSymbol();
  }
  void setBeginSymbol(MCSymbol *Sym) {
    assert(!Begin);
    Begin = Sym;
  }
  MCSymbol *getEndSymbol(MCContext &Ctx);
  bool hasEnded() const;
 
  Align getAlign() const { return Alignment; }
  void setAlignment(Align Value) { Alignment = Value; }
 
  /// Makes sure that Alignment is at least MinAlignment.
  void ensureMinAlignment(Align MinAlignment) {
    if (Alignment < MinAlignment)
      Alignment = MinAlignment;
  }
 
  unsigned getOrdinal() const { return Ordinal; }
  void setOrdinal(unsigned Value) { Ordinal = Value; }
 
  bool hasInstructions() const { return HasInstructions; }
  void setHasInstructions(bool Value) { HasInstructions = Value; }
 
  bool isRegistered() const { return IsRegistered; }
  void setIsRegistered(bool Value) { IsRegistered = Value; }
 
  unsigned firstLinkerRelaxable() const { return FirstLinkerRelaxable; }
  bool isLinkerRelaxable() const { return FirstLinkerRelaxable != -1u; }
  void setFirstLinkerRelaxable(unsigned Order) { FirstLinkerRelaxable = Order; }
 
  MCFragment &getDummyFragment() { return DummyFragment; }
 
  FragList *curFragList() const { return CurFragList; }
  iterator begin() const { return iterator(CurFragList->Head); }
  iterator end() const { return {}; }
 
  void dump(DenseMap<const MCFragment *, SmallVector<const MCSymbol *, 0>>
                *FragToSyms = nullptr) const;
 
  /// Check whether this section is "virtual", that is has no actual object
  /// file contents.
  bool isBssSection() const { return IsBss; }
};
 
inline MutableArrayRef<char> MCFragment::getContents() {
  return {reinterpret_cast<char *>(this + 1), FixedSize};
}
inline ArrayRef<char> MCFragment::getContents() const {
  return {reinterpret_cast<const char *>(this + 1), FixedSize};
}
 
inline MutableArrayRef<char> MCFragment::getVarContents() {
  return MutableArrayRef(getParent()->ContentStorage)
      .slice(VarContentStart, VarContentEnd - VarContentStart);
}
inline ArrayRef<char> MCFragment::getVarContents() const {
  return ArrayRef(getParent()->ContentStorage)
      .slice(VarContentStart, VarContentEnd - VarContentStart);
}
 
//== Fixup-related functions manage parent's storage using FixupStart and
// FixupSize.
inline MutableArrayRef<MCFixup> MCFragment::getFixups() {
  return MutableArrayRef(getParent()->FixupStorage)
      .slice(FixupStart, FixupEnd - FixupStart);
}
inline ArrayRef<MCFixup> MCFragment::getFixups() const {
  return ArrayRef(getParent()->FixupStorage)
      .slice(FixupStart, FixupEnd - FixupStart);
}
 
inline MutableArrayRef<MCFixup> MCFragment::getVarFixups() {
  return MutableArrayRef(getParent()->FixupStorage)
      .slice(VarFixupStart, VarFixupSize);
}
inline ArrayRef<MCFixup> MCFragment::getVarFixups() const {
  return ArrayRef(getParent()->FixupStorage).slice(VarFixupStart, VarFixupSize);
}
 
//== FT_Relaxable functions
inline ArrayRef<MCOperand> MCFragment::getOperands() const {
  assert(Kind == FT_Relaxable);
  return MutableArrayRef(getParent()->MCOperandStorage)
      .slice(u.relax.OperandStart, u.relax.OperandSize);
}
inline MCInst MCFragment::getInst() const {
  assert(Kind == FT_Relaxable);
  MCInst Inst;
  Inst.setOpcode(u.relax.Opcode);
  Inst.setFlags(u.relax.Flags);
  Inst.setOperands(ArrayRef(getParent()->MCOperandStorage)
                       .slice(u.relax.OperandStart, u.relax.OperandSize));
  return Inst;
}
inline void MCFragment::setInst(const MCInst &Inst) {
  assert(Kind == FT_Relaxable);
  u.relax.Opcode = Inst.getOpcode();
  u.relax.Flags = Inst.getFlags();
  auto &S = getParent()->MCOperandStorage;
  if (Inst.getNumOperands() > u.relax.OperandSize) {
    u.relax.OperandStart = S.size();
    S.resize_for_overwrite(S.size() + Inst.getNumOperands());
  }
  u.relax.OperandSize = Inst.getNumOperands();
  llvm::copy(Inst, S.begin() + u.relax.OperandStart);
}
 
inline MCSection::iterator &MCSection::iterator::operator++() {
  F = F->Next;
  return *this;
}
 
} // end namespace llvm
 
#endif // LLVM_MC_MCSECTION_H