MCSection.h

Go to the documentation of this file.

//===- 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/SmallVector.h"
#include "llvm/ADT/ilist.h"
#include "llvm/MC/MCFragment.h"
#include "llvm/MC/SectionKind.h"
#include "llvm/Support/Alignment.h"
#include <cassert>
#include <utility>
 
namespace llvm {
 
class MCAsmInfo;
class MCContext;
class MCExpr;
class MCSymbol;
class raw_ostream;
class Triple;
 
template <> struct ilist_alloc_traits<MCFragment> {
  static void deleteNode(MCFragment *V);
};
 
/// Instances of this class represent a uniqued identifier for a section in the
/// current translation unit.  The MCContext class uniques and creates these.
class MCSection {
public:
  static constexpr unsigned NonUniqueID = ~0U;
 
  enum SectionVariant { SV_COFF = 0, SV_ELF, SV_MachO, SV_Wasm, SV_XCOFF };
 
  /// Express the state of bundle locked groups while emitting code.
  enum BundleLockStateType {
    NotBundleLocked,
    BundleLocked,
    BundleLockedAlignToEnd
  };
 
  using FragmentListType = iplist<MCFragment>;
 
  using const_iterator = FragmentListType::const_iterator;
  using iterator = FragmentListType::iterator;
 
  using const_reverse_iterator = FragmentListType::const_reverse_iterator;
  using reverse_iterator = FragmentListType::reverse_iterator;
 
private:
  MCSymbol *Begin;
  MCSymbol *End = nullptr;
  /// The alignment requirement of this section.
  Align Alignment;
  /// The section index in the assemblers section list.
  unsigned Ordinal = 0;
  /// The index of this section in the layout order.
  unsigned LayoutOrder;
 
  /// Keeping track of bundle-locked state.
  BundleLockStateType BundleLockState = NotBundleLocked;
 
  /// Current nesting depth of bundle_lock directives.
  unsigned BundleLockNestingDepth = 0;
 
  /// We've seen a bundle_lock directive but not its first instruction
  /// yet.
  bool BundleGroupBeforeFirstInst : 1;
 
  /// Whether this section has had instructions emitted into it.
  bool HasInstructions : 1;
 
  bool IsRegistered : 1;
 
  MCDummyFragment DummyFragment;
 
  FragmentListType Fragments;
 
  /// Mapping from subsection number to insertion point for subsection numbers
  /// below that number.
  SmallVector<std::pair<unsigned, MCFragment *>, 1> SubsectionFragmentMap;
 
  /// State for tracking labels that don't yet have Fragments
  struct PendingLabel {
    MCSymbol* Sym;
    unsigned Subsection;
    PendingLabel(MCSymbol* Sym, unsigned Subsection = 0)
      : Sym(Sym), Subsection(Subsection) {}
  };
  SmallVector<PendingLabel, 2> PendingLabels;
 
protected:
  // TODO Make Name private when possible.
  StringRef Name;
  SectionVariant Variant;
  SectionKind Kind;
 
  MCSection(SectionVariant V, StringRef Name, SectionKind K, MCSymbol *Begin);
  ~MCSection();
 
public:
  MCSection(const MCSection &) = delete;
  MCSection &operator=(const MCSection &) = delete;
 
  StringRef getName() const { return Name; }
  SectionKind getKind() const { return Kind; }
 
  SectionVariant getVariant() const { return Variant; }
 
  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;
 
  unsigned getAlignment() const { return Alignment.value(); }
  void setAlignment(Align Value) { Alignment = Value; }
 
  unsigned getOrdinal() const { return Ordinal; }
  void setOrdinal(unsigned Value) { Ordinal = Value; }
 
  unsigned getLayoutOrder() const { return LayoutOrder; }
  void setLayoutOrder(unsigned Value) { LayoutOrder = Value; }
 
  BundleLockStateType getBundleLockState() const { return BundleLockState; }
  void setBundleLockState(BundleLockStateType NewState);
  bool isBundleLocked() const { return BundleLockState != NotBundleLocked; }
 
  bool isBundleGroupBeforeFirstInst() const {
    return BundleGroupBeforeFirstInst;
  }
  void setBundleGroupBeforeFirstInst(bool IsFirst) {
    BundleGroupBeforeFirstInst = IsFirst;
  }
 
  bool hasInstructions() const { return HasInstructions; }
  void setHasInstructions(bool Value) { HasInstructions = Value; }
 
  bool isRegistered() const { return IsRegistered; }
  void setIsRegistered(bool Value) { IsRegistered = Value; }
 
  MCSection::FragmentListType &getFragmentList() { return Fragments; }
  const MCSection::FragmentListType &getFragmentList() const {
    return const_cast<MCSection *>(this)->getFragmentList();
  }
 
  /// Support for MCFragment::getNextNode().
  static FragmentListType MCSection::*getSublistAccess(MCFragment *) {
    return &MCSection::Fragments;
  }
 
  const MCDummyFragment &getDummyFragment() const { return DummyFragment; }
  MCDummyFragment &getDummyFragment() { return DummyFragment; }
 
  iterator begin() { return Fragments.begin(); }
  const_iterator begin() const { return Fragments.begin(); }
 
  iterator end() { return Fragments.end(); }
  const_iterator end() const { return Fragments.end(); }
 
  MCSection::iterator getSubsectionInsertionPoint(unsigned Subsection);
 
  void dump() const;
 
  virtual void PrintSwitchToSection(const MCAsmInfo &MAI, const Triple &T,
                                    raw_ostream &OS,
                                    const MCExpr *Subsection) const = 0;
 
  /// Return true if a .align directive should use "optimized nops" to fill
  /// instead of 0s.
  virtual bool UseCodeAlign() const = 0;
 
  /// Check whether this section is "virtual", that is has no actual object
  /// file contents.
  virtual bool isVirtualSection() const = 0;
 
  virtual StringRef getVirtualSectionKind() const;
 
  /// Add a pending label for the requested subsection. This label will be
  /// associated with a fragment in flushPendingLabels()
  void addPendingLabel(MCSymbol* label, unsigned Subsection = 0);
 
  /// Associate all pending labels in a subsection with a fragment.
  void flushPendingLabels(MCFragment *F, uint64_t FOffset = 0,
        unsigned Subsection = 0);
 
  /// Associate all pending labels with empty data fragments. One fragment
  /// will be created for each subsection as necessary.
  void flushPendingLabels();
};
 
} // end namespace llvm
 
#endif // LLVM_MC_MCSECTION_H