MCAssembler.h

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//===- 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/Alignment.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/SMLoc.h"
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <memory>
#include <string>
#include <utility>
 
namespace llvm {
 
class MCBoundaryAlignFragment;
class MCCVDefRangeFragment;
class MCCVInlineLineTableFragment;
class MCFragment;
class MCFixup;
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 HasFinalLayout = false;
  bool RelaxAll = false;
 
  // Cumulative upstream size change during `relaxOnce`. Used to compensate
  // forward-reference displacements in `evaluateFixup`.
  int64_t Stretch = 0;
 
  /// Non-empty when aligned instruction bundling is enabled.
  MaybeAlign BundleAlign;
 
  SectionListType Sections;
 
  SmallVector<const MCSymbol *, 0> Symbols;
 
  struct RelocDirective {
    const MCExpr &Offset;
    const MCExpr *Expr;
    uint32_t Kind;
  };
  SmallVector<RelocDirective, 0> relocDirectives;
 
  mutable SmallVector<std::pair<SMLoc, std::string>, 0> PendingErrors;
 
  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;
 
  /// Evaluate a fixup to a relocatable expression and the value which should be
  /// placed into the fixup.
  ///
  /// \param F The fragment the fixup is inside.
  /// \param Fixup The fixup to evaluate.
  /// \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 RecordReloc Record relocation if needed.
  /// relocation.
  bool evaluateFixup(const MCFragment &F, MCFixup &Fixup, MCValue &Target,
                     uint64_t &Value, bool RecordReloc, uint8_t *Data) 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 MCFragment &, const MCFixup &) const;
 
  void layoutSection(MCSection &Sec);
  /// Perform one layout iteration and return the index of the first stable
  /// section for subsequent optimization.
  unsigned relaxOnce(unsigned FirstStable);
 
  /// Perform relaxation on a single fragment.
  void relaxFragment(MCFragment &F);
  void relaxAlign(MCFragment &F);
  void relaxPrefAlign(MCFragment &F);
  void relaxInstruction(MCFragment &F);
  void relaxLEB(MCFragment &F);
  void relaxBoundaryAlign(MCBoundaryAlignFragment &BF);
  void relaxDwarfLineAddr(MCFragment &F);
  void relaxDwarfCallFrameFragment(MCFragment &F);
  void relaxSFrameFragment(MCFragment &DF);
 
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.
  LLVM_ABI 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.
  LLVM_ABI uint64_t computeFragmentSize(const MCFragment &F) const;
 
  // Get the offset of the given fragment inside its containing section.
  uint64_t getFragmentOffset(const MCFragment &F) const { return F.Offset; }
 
  LLVM_ABI uint64_t getSectionAddressSize(const MCSection &Sec) const;
  LLVM_ABI uint64_t getSectionFileSize(const MCSection &Sec) const;
 
  // Get the offset of the given symbol, as computed in the current
  // layout.
  // \return True on success.
  LLVM_ABI bool getSymbolOffset(const MCSymbol &S, uint64_t &Val) const;
 
  // Variant that reports a fatal error if the offset is not computable.
  LLVM_ABI uint64_t getSymbolOffset(const MCSymbol &S) const;
 
  // If this symbol is equivalent to A + Constant, return A.
  LLVM_ABI const MCSymbol *getBaseSymbol(const MCSymbol &Symbol) const;
 
  /// Emit the section contents to \p OS.
  LLVM_ABI void writeSectionData(raw_ostream &OS,
                                 const MCSection *Section) const;
 
  /// Check whether a given symbol has been flagged with .thumb_func.
  LLVM_ABI 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
  ///
  LLVM_ABI 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.
  LLVM_ABI void Finish();
 
  // Layout all section and prepare them for emission.
  LLVM_ABI void layout();
 
  bool hasLayout() const { return HasLayout; }
  bool hasFinalLayout() const { return HasFinalLayout; }
  bool getRelaxAll() const { return RelaxAll; }
  void setRelaxAll(bool Value) { RelaxAll = Value; }
  int64_t getStretch() const { return Stretch; }
 
  bool isBundlingEnabled() const { return bool(BundleAlign); }
  Align getBundleAlign() const {
    assert(BundleAlign && "bundling is not enabled");
    return *BundleAlign;
  }
  void setBundleAlign(Align Value) { BundleAlign = Value; }
 
  const_iterator begin() const { return Sections.begin(); }
  const_iterator end() const { return Sections.end(); }
 
  SmallVectorImpl<const MCSymbol *> &getSymbols() { return Symbols; }
  iterator_range<
      pointee_iterator<SmallVector<const MCSymbol *, 0>::const_iterator>>
  symbols() const {
    return make_pointee_range(Symbols);
  }
 
  LLVM_ABI bool registerSection(MCSection &Section);
  LLVM_ABI bool registerSymbol(const MCSymbol &Symbol);
  LLVM_ABI void addRelocDirective(RelocDirective RD);
 
  LLVM_ABI void reportError(SMLoc L, const Twine &Msg) const;
  // Record pending errors during layout iteration, as they may go away once the
  // layout is finalized.
  LLVM_ABI void recordError(SMLoc L, const Twine &Msg) const;
  LLVM_ABI void flushPendingErrors() const;
 
  LLVM_ABI void dump() const;
};
 
} // end namespace llvm
 
#endif // LLVM_MC_MCASSEMBLER_H