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      1 //===-- llvm/MC/MCObjectWriter.h - Object File Writer Interface -*- C++ -*-===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 
     10 #ifndef LLVM_MC_MCOBJECTWRITER_H
     11 #define LLVM_MC_MCOBJECTWRITER_H
     12 
     13 #include "llvm/ADT/SmallVector.h"
     14 #include "llvm/Support/Compiler.h"
     15 #include "llvm/Support/DataTypes.h"
     16 #include "llvm/Support/raw_ostream.h"
     17 #include <cassert>
     18 
     19 namespace llvm {
     20 class MCAsmLayout;
     21 class MCAssembler;
     22 class MCFixup;
     23 class MCFragment;
     24 class MCSymbolData;
     25 class MCSymbolRefExpr;
     26 class MCValue;
     27 
     28 /// MCObjectWriter - Defines the object file and target independent interfaces
     29 /// used by the assembler backend to write native file format object files.
     30 ///
     31 /// The object writer contains a few callbacks used by the assembler to allow
     32 /// the object writer to modify the assembler data structures at appropriate
     33 /// points. Once assembly is complete, the object writer is given the
     34 /// MCAssembler instance, which contains all the symbol and section data which
     35 /// should be emitted as part of WriteObject().
     36 ///
     37 /// The object writer also contains a number of helper methods for writing
     38 /// binary data to the output stream.
     39 class MCObjectWriter {
     40   MCObjectWriter(const MCObjectWriter &) LLVM_DELETED_FUNCTION;
     41   void operator=(const MCObjectWriter &) LLVM_DELETED_FUNCTION;
     42 
     43 protected:
     44   raw_ostream &OS;
     45 
     46   unsigned IsLittleEndian : 1;
     47 
     48 protected: // Can only create subclasses.
     49   MCObjectWriter(raw_ostream &_OS, bool _IsLittleEndian)
     50     : OS(_OS), IsLittleEndian(_IsLittleEndian) {}
     51 
     52 public:
     53   virtual ~MCObjectWriter();
     54 
     55   /// lifetime management
     56   virtual void reset() { }
     57 
     58   bool isLittleEndian() const { return IsLittleEndian; }
     59 
     60   raw_ostream &getStream() { return OS; }
     61 
     62   /// @name High-Level API
     63   /// @{
     64 
     65   /// \brief Perform any late binding of symbols (for example, to assign symbol
     66   /// indices for use when generating relocations).
     67   ///
     68   /// This routine is called by the assembler after layout and relaxation is
     69   /// complete.
     70   virtual void ExecutePostLayoutBinding(MCAssembler &Asm,
     71                                         const MCAsmLayout &Layout) = 0;
     72 
     73   /// \brief Record a relocation entry.
     74   ///
     75   /// This routine is called by the assembler after layout and relaxation, and
     76   /// post layout binding. The implementation is responsible for storing
     77   /// information about the relocation so that it can be emitted during
     78   /// WriteObject().
     79   virtual void RecordRelocation(const MCAssembler &Asm,
     80                                 const MCAsmLayout &Layout,
     81                                 const MCFragment *Fragment,
     82                                 const MCFixup &Fixup, MCValue Target,
     83                                 bool &IsPCRel,
     84                                 uint64_t &FixedValue) = 0;
     85 
     86   /// \brief Check whether the difference (A - B) between two symbol
     87   /// references is fully resolved.
     88   ///
     89   /// Clients are not required to answer precisely and may conservatively return
     90   /// false, even when a difference is fully resolved.
     91   bool
     92   IsSymbolRefDifferenceFullyResolved(const MCAssembler &Asm,
     93                                      const MCSymbolRefExpr *A,
     94                                      const MCSymbolRefExpr *B,
     95                                      bool InSet) const;
     96 
     97   virtual bool
     98   IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
     99                                          const MCSymbolData &DataA,
    100                                          const MCFragment &FB,
    101                                          bool InSet,
    102                                          bool IsPCRel) const;
    103 
    104   /// \brief Write the object file.
    105   ///
    106   /// This routine is called by the assembler after layout and relaxation is
    107   /// complete, fixups have been evaluated and applied, and relocations
    108   /// generated.
    109   virtual void WriteObject(MCAssembler &Asm,
    110                            const MCAsmLayout &Layout) = 0;
    111 
    112   /// @}
    113   /// @name Binary Output
    114   /// @{
    115 
    116   void Write8(uint8_t Value) {
    117     OS << char(Value);
    118   }
    119 
    120   void WriteLE16(uint16_t Value) {
    121     Write8(uint8_t(Value >> 0));
    122     Write8(uint8_t(Value >> 8));
    123   }
    124 
    125   void WriteLE32(uint32_t Value) {
    126     WriteLE16(uint16_t(Value >> 0));
    127     WriteLE16(uint16_t(Value >> 16));
    128   }
    129 
    130   void WriteLE64(uint64_t Value) {
    131     WriteLE32(uint32_t(Value >> 0));
    132     WriteLE32(uint32_t(Value >> 32));
    133   }
    134 
    135   void WriteBE16(uint16_t Value) {
    136     Write8(uint8_t(Value >> 8));
    137     Write8(uint8_t(Value >> 0));
    138   }
    139 
    140   void WriteBE32(uint32_t Value) {
    141     WriteBE16(uint16_t(Value >> 16));
    142     WriteBE16(uint16_t(Value >> 0));
    143   }
    144 
    145   void WriteBE64(uint64_t Value) {
    146     WriteBE32(uint32_t(Value >> 32));
    147     WriteBE32(uint32_t(Value >> 0));
    148   }
    149 
    150   void Write16(uint16_t Value) {
    151     if (IsLittleEndian)
    152       WriteLE16(Value);
    153     else
    154       WriteBE16(Value);
    155   }
    156 
    157   void Write32(uint32_t Value) {
    158     if (IsLittleEndian)
    159       WriteLE32(Value);
    160     else
    161       WriteBE32(Value);
    162   }
    163 
    164   void Write64(uint64_t Value) {
    165     if (IsLittleEndian)
    166       WriteLE64(Value);
    167     else
    168       WriteBE64(Value);
    169   }
    170 
    171   void WriteZeros(unsigned N) {
    172     const char Zeros[16] = { 0 };
    173 
    174     for (unsigned i = 0, e = N / 16; i != e; ++i)
    175       OS << StringRef(Zeros, 16);
    176 
    177     OS << StringRef(Zeros, N % 16);
    178   }
    179 
    180   void WriteBytes(const SmallVectorImpl<char> &ByteVec, unsigned ZeroFillSize = 0) {
    181     WriteBytes(StringRef(ByteVec.data(), ByteVec.size()), ZeroFillSize);
    182   }
    183 
    184   void WriteBytes(StringRef Str, unsigned ZeroFillSize = 0) {
    185     // TODO: this version may need to go away once all fragment contents are
    186     // converted to SmallVector<char, N>
    187     assert((ZeroFillSize == 0 || Str.size () <= ZeroFillSize) &&
    188       "data size greater than fill size, unexpected large write will occur");
    189     OS << Str;
    190     if (ZeroFillSize)
    191       WriteZeros(ZeroFillSize - Str.size());
    192   }
    193 
    194   /// @}
    195 
    196 };
    197 
    198 } // End llvm namespace
    199 
    200 #endif
    201