MCAssembler.h

Go to the documentation of this file.

//===- MCAssembler.h - Object File Generation -------------------*- 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
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_MC_MCASSEMBLER_H
#define LLVM_MC_MCASSEMBLER_H
 
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/iterator.h"
#include "llvm/ADT/iterator_range.h"
#include "llvm/MC/MCDwarf.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/Support/SMLoc.h"
#include <algorithm>
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <memory>
#include <string>
#include <tuple>
#include <utility>
#include <vector>
 
namespace llvm {
 
class MCBoundaryAlignFragment;
class MCCVDefRangeFragment;
class MCCVInlineLineTableFragment;
class MCDwarfCallFrameFragment;
class MCDwarfLineAddrFragment;
class MCEncodedFragment;
class MCFixup;
class MCLEBFragment;
class MCPseudoProbeAddrFragment;
class MCRelaxableFragment;
class MCSymbolRefExpr;
class raw_ostream;
class MCAsmBackend;
class MCContext;
class MCCodeEmitter;
class MCFragment;
class MCObjectWriter;
class MCSection;
class MCValue;
 
class MCAssembler {
public:
  friend class MCObjectWriter;
  using SectionListType = SmallVector<MCSection *, 0>;
  using const_iterator = pointee_iterator<SectionListType::const_iterator>;
 
private:
  MCContext &Context;
 
  std::unique_ptr<MCAsmBackend> Backend;
  std::unique_ptr<MCCodeEmitter> Emitter;
  std::unique_ptr<MCObjectWriter> Writer;
 
  bool HasLayout = false;
  bool RelaxAll = false;
 
  SectionListType Sections;
 
  SmallVector<const MCSymbol *, 0> Symbols;
 
  MCDwarfLineTableParams LTParams;
 
  /// The set of function symbols for which a .thumb_func directive has
  /// been seen.
  //
  // FIXME: We really would like this in target specific code rather than
  // here. Maybe when the relocation stuff moves to target specific,
  // this can go with it? The streamer would need some target specific
  // refactoring too.
  mutable SmallPtrSet<const MCSymbol *, 32> ThumbFuncs;
 
  /// The bundle alignment size currently set in the assembler.
  ///
  /// By default it's 0, which means bundling is disabled.
  unsigned BundleAlignSize = 0;
 
  /// Evaluate a fixup to a relocatable expression and the value which should be
  /// placed into the fixup.
  ///
  /// \param Fixup The fixup to evaluate.
  /// \param DF The fragment the fixup is inside.
  /// \param Target [out] On return, the relocatable expression the fixup
  /// evaluates to.
  /// \param Value [out] On return, the value of the fixup as currently laid
  /// out.
  /// \param WasForced [out] On return, the value in the fixup is set to the
  /// correct value if WasForced is true, even if evaluateFixup returns false.
  /// \return Whether the fixup value was fully resolved. This is true if the
  /// \p Value result is fixed, otherwise the value may change due to
  /// relocation.
  bool evaluateFixup(const MCFixup &Fixup, const MCFragment *DF,
                     MCValue &Target, const MCSubtargetInfo *STI,
                     uint64_t &Value, bool &WasForced) const;
 
  /// Check whether a fixup can be satisfied, or whether it needs to be relaxed
  /// (increased in size, in order to hold its value correctly).
  bool fixupNeedsRelaxation(const MCFixup &Fixup, const MCRelaxableFragment *DF) const;
 
  /// Check whether the given fragment needs relaxation.
  bool fragmentNeedsRelaxation(const MCRelaxableFragment *IF) const;
 
  /// Perform one layout iteration and return true if any offsets
  /// were adjusted.
  bool layoutOnce();
 
  /// Perform relaxation on a single fragment - returns true if the fragment
  /// changes as a result of relaxation.
  bool relaxFragment(MCFragment &F);
  bool relaxInstruction(MCRelaxableFragment &IF);
  bool relaxLEB(MCLEBFragment &IF);
  bool relaxBoundaryAlign(MCBoundaryAlignFragment &BF);
  bool relaxDwarfLineAddr(MCDwarfLineAddrFragment &DF);
  bool relaxDwarfCallFrameFragment(MCDwarfCallFrameFragment &DF);
  bool relaxCVInlineLineTable(MCCVInlineLineTableFragment &DF);
  bool relaxCVDefRange(MCCVDefRangeFragment &DF);
  bool relaxPseudoProbeAddr(MCPseudoProbeAddrFragment &DF);
 
  std::tuple<MCValue, uint64_t, bool>
  handleFixup(MCFragment &F, const MCFixup &Fixup, const MCSubtargetInfo *STI);
 
public:
  /// Construct a new assembler instance.
  //
  // FIXME: How are we going to parameterize this? Two obvious options are stay
  // concrete and require clients to pass in a target like object. The other
  // option is to make this abstract, and have targets provide concrete
  // implementations as we do with AsmParser.
  MCAssembler(MCContext &Context, std::unique_ptr<MCAsmBackend> Backend,
              std::unique_ptr<MCCodeEmitter> Emitter,
              std::unique_ptr<MCObjectWriter> Writer);
  MCAssembler(const MCAssembler &) = delete;
  MCAssembler &operator=(const MCAssembler &) = delete;
 
  /// Compute the effective fragment size.
  uint64_t computeFragmentSize(const MCFragment &F) const;
 
  void layoutBundle(MCFragment *Prev, MCFragment *F) const;
  void ensureValid(MCSection &Sec) const;
 
  // Get the offset of the given fragment inside its containing section.
  uint64_t getFragmentOffset(const MCFragment &F) const;
 
  uint64_t getSectionAddressSize(const MCSection &Sec) const;
  uint64_t getSectionFileSize(const MCSection &Sec) const;
 
  // Get the offset of the given symbol, as computed in the current
  // layout.
  // \return True on success.
  bool getSymbolOffset(const MCSymbol &S, uint64_t &Val) const;
 
  // Variant that reports a fatal error if the offset is not computable.
  uint64_t getSymbolOffset(const MCSymbol &S) const;
 
  // If this symbol is equivalent to A + Constant, return A.
  const MCSymbol *getBaseSymbol(const MCSymbol &Symbol) const;
 
  /// Emit the section contents to \p OS.
  void writeSectionData(raw_ostream &OS, const MCSection *Section) const;
 
  /// Check whether a given symbol has been flagged with .thumb_func.
  bool isThumbFunc(const MCSymbol *Func) const;
 
  /// Flag a function symbol as the target of a .thumb_func directive.
  void setIsThumbFunc(const MCSymbol *Func) { ThumbFuncs.insert(Func); }
 
  /// Reuse an assembler instance
  ///
  void reset();
 
  MCContext &getContext() const { return Context; }
 
  MCAsmBackend *getBackendPtr() const { return Backend.get(); }
 
  MCCodeEmitter *getEmitterPtr() const { return Emitter.get(); }
 
  MCAsmBackend &getBackend() const { return *Backend; }
 
  MCCodeEmitter &getEmitter() const { return *Emitter; }
 
  MCObjectWriter &getWriter() const { return *Writer; }
 
  MCDwarfLineTableParams getDWARFLinetableParams() const { return LTParams; }
 
  /// Finish - Do final processing and write the object to the output stream.
  /// \p Writer is used for custom object writer (as the MCJIT does),
  /// if not specified it is automatically created from backend.
  void Finish();
 
  // Layout all section and prepare them for emission.
  void layout();
 
  bool hasLayout() const { return HasLayout; }
  bool getRelaxAll() const { return RelaxAll; }
  void setRelaxAll(bool Value) { RelaxAll = Value; }
 
  bool isBundlingEnabled() const { return BundleAlignSize != 0; }
 
  unsigned getBundleAlignSize() const { return BundleAlignSize; }
 
  void setBundleAlignSize(unsigned Size) {
    assert((Size == 0 || !(Size & (Size - 1))) &&
           "Expect a power-of-two bundle align size");
    BundleAlignSize = Size;
  }
 
  const_iterator begin() const { return Sections.begin(); }
  const_iterator end() const { return Sections.end(); }
 
  SmallVectorImpl<const MCSymbol *> &getSymbols() { return Symbols; }
  iterator_range<pointee_iterator<
      typename SmallVector<const MCSymbol *, 0>::const_iterator>>
  symbols() const {
    return make_pointee_range(Symbols);
  }
 
  bool registerSection(MCSection &Section);
  bool registerSymbol(const MCSymbol &Symbol);
 
  /// Write the necessary bundle padding to \p OS.
  /// Expects a fragment \p F containing instructions and its size \p FSize.
  void writeFragmentPadding(raw_ostream &OS, const MCEncodedFragment &F,
                            uint64_t FSize) const;
 
  void dump() const;
};
 
} // end namespace llvm
 
#endif // LLVM_MC_MCASSEMBLER_H