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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/Support/raw_ostream.h"
     14 #include "llvm/Support/DataTypes.h"
     15 #include <cassert>
     16 
     17 namespace llvm {
     18 class MCAsmLayout;
     19 class MCAssembler;
     20 class MCFixup;
     21 class MCFragment;
     22 class MCSymbolData;
     23 class MCSymbolRefExpr;
     24 class MCValue;
     25 
     26 /// MCObjectWriter - Defines the object file and target independent interfaces
     27 /// used by the assembler backend to write native file format object files.
     28 ///
     29 /// The object writer contains a few callbacks used by the assembler to allow
     30 /// the object writer to modify the assembler data structures at appropriate
     31 /// points. Once assembly is complete, the object writer is given the
     32 /// MCAssembler instance, which contains all the symbol and section data which
     33 /// should be emitted as part of WriteObject().
     34 ///
     35 /// The object writer also contains a number of helper methods for writing
     36 /// binary data to the output stream.
     37 class MCObjectWriter {
     38   MCObjectWriter(const MCObjectWriter &); // DO NOT IMPLEMENT
     39   void operator=(const MCObjectWriter &); // DO NOT IMPLEMENT
     40 
     41 protected:
     42   raw_ostream &OS;
     43 
     44   unsigned IsLittleEndian : 1;
     45 
     46 protected: // Can only create subclasses.
     47   MCObjectWriter(raw_ostream &_OS, bool _IsLittleEndian)
     48     : OS(_OS), IsLittleEndian(_IsLittleEndian) {}
     49 
     50 public:
     51   virtual ~MCObjectWriter();
     52 
     53   bool isLittleEndian() const { return IsLittleEndian; }
     54 
     55   raw_ostream &getStream() { return OS; }
     56 
     57   /// @name High-Level API
     58   /// @{
     59 
     60   /// Perform any late binding of symbols (for example, to assign symbol indices
     61   /// for use when generating relocations).
     62   ///
     63   /// This routine is called by the assembler after layout and relaxation is
     64   /// complete.
     65   virtual void ExecutePostLayoutBinding(MCAssembler &Asm,
     66                                         const MCAsmLayout &Layout) = 0;
     67 
     68   /// Record a relocation entry.
     69   ///
     70   /// This routine is called by the assembler after layout and relaxation, and
     71   /// post layout binding. The implementation is responsible for storing
     72   /// information about the relocation so that it can be emitted during
     73   /// WriteObject().
     74   virtual void RecordRelocation(const MCAssembler &Asm,
     75                                 const MCAsmLayout &Layout,
     76                                 const MCFragment *Fragment,
     77                                 const MCFixup &Fixup, MCValue Target,
     78                                 uint64_t &FixedValue) = 0;
     79 
     80   /// \brief Check whether the difference (A - B) between two symbol
     81   /// references is fully resolved.
     82   ///
     83   /// Clients are not required to answer precisely and may conservatively return
     84   /// false, even when a difference is fully resolved.
     85   bool
     86   IsSymbolRefDifferenceFullyResolved(const MCAssembler &Asm,
     87                                      const MCSymbolRefExpr *A,
     88                                      const MCSymbolRefExpr *B,
     89                                      bool InSet) const;
     90 
     91   virtual bool
     92   IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
     93                                          const MCSymbolData &DataA,
     94                                          const MCFragment &FB,
     95                                          bool InSet,
     96                                          bool IsPCRel) const;
     97 
     98 
     99   /// Write the object file.
    100   ///
    101   /// This routine is called by the assembler after layout and relaxation is
    102   /// complete, fixups have been evaluated and applied, and relocations
    103   /// generated.
    104   virtual void WriteObject(MCAssembler &Asm,
    105                            const MCAsmLayout &Layout) = 0;
    106 
    107   /// @}
    108   /// @name Binary Output
    109   /// @{
    110 
    111   void Write8(uint8_t Value) {
    112     OS << char(Value);
    113   }
    114 
    115   void WriteLE16(uint16_t Value) {
    116     Write8(uint8_t(Value >> 0));
    117     Write8(uint8_t(Value >> 8));
    118   }
    119 
    120   void WriteLE32(uint32_t Value) {
    121     WriteLE16(uint16_t(Value >> 0));
    122     WriteLE16(uint16_t(Value >> 16));
    123   }
    124 
    125   void WriteLE64(uint64_t Value) {
    126     WriteLE32(uint32_t(Value >> 0));
    127     WriteLE32(uint32_t(Value >> 32));
    128   }
    129 
    130   void WriteBE16(uint16_t Value) {
    131     Write8(uint8_t(Value >> 8));
    132     Write8(uint8_t(Value >> 0));
    133   }
    134 
    135   void WriteBE32(uint32_t Value) {
    136     WriteBE16(uint16_t(Value >> 16));
    137     WriteBE16(uint16_t(Value >> 0));
    138   }
    139 
    140   void WriteBE64(uint64_t Value) {
    141     WriteBE32(uint32_t(Value >> 32));
    142     WriteBE32(uint32_t(Value >> 0));
    143   }
    144 
    145   void Write16(uint16_t Value) {
    146     if (IsLittleEndian)
    147       WriteLE16(Value);
    148     else
    149       WriteBE16(Value);
    150   }
    151 
    152   void Write32(uint32_t Value) {
    153     if (IsLittleEndian)
    154       WriteLE32(Value);
    155     else
    156       WriteBE32(Value);
    157   }
    158 
    159   void Write64(uint64_t Value) {
    160     if (IsLittleEndian)
    161       WriteLE64(Value);
    162     else
    163       WriteBE64(Value);
    164   }
    165 
    166   void WriteZeros(unsigned N) {
    167     const char Zeros[16] = { 0 };
    168 
    169     for (unsigned i = 0, e = N / 16; i != e; ++i)
    170       OS << StringRef(Zeros, 16);
    171 
    172     OS << StringRef(Zeros, N % 16);
    173   }
    174 
    175   void WriteBytes(StringRef Str, unsigned ZeroFillSize = 0) {
    176     assert((ZeroFillSize == 0 || Str.size () <= ZeroFillSize) &&
    177       "data size greater than fill size, unexpected large write will occur");
    178     OS << Str;
    179     if (ZeroFillSize)
    180       WriteZeros(ZeroFillSize - Str.size());
    181   }
    182 
    183   /// @}
    184 
    185   /// Utility function to encode a SLEB128 value.
    186   static void EncodeSLEB128(int64_t Value, raw_ostream &OS);
    187   /// Utility function to encode a ULEB128 value.
    188   static void EncodeULEB128(uint64_t Value, raw_ostream &OS,
    189                             unsigned Padding = 0);
    190 };
    191 
    192 } // End llvm namespace
    193 
    194 #endif
    195