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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                                 uint64_t &FixedValue) = 0;
     84 
     85   /// \brief Check whether the difference (A - B) between two symbol
     86   /// references is fully resolved.
     87   ///
     88   /// Clients are not required to answer precisely and may conservatively return
     89   /// false, even when a difference is fully resolved.
     90   bool
     91   IsSymbolRefDifferenceFullyResolved(const MCAssembler &Asm,
     92                                      const MCSymbolRefExpr *A,
     93                                      const MCSymbolRefExpr *B,
     94                                      bool InSet) const;
     95 
     96   virtual bool
     97   IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
     98                                          const MCSymbolData &DataA,
     99                                          const MCFragment &FB,
    100                                          bool InSet,
    101                                          bool IsPCRel) const;
    102 
    103   /// \brief Write the object file.
    104   ///
    105   /// This routine is called by the assembler after layout and relaxation is
    106   /// complete, fixups have been evaluated and applied, and relocations
    107   /// generated.
    108   virtual void WriteObject(MCAssembler &Asm,
    109                            const MCAsmLayout &Layout) = 0;
    110 
    111   /// @}
    112   /// @name Binary Output
    113   /// @{
    114 
    115   void Write8(uint8_t Value) {
    116     OS << char(Value);
    117   }
    118 
    119   void WriteLE16(uint16_t Value) {
    120     Write8(uint8_t(Value >> 0));
    121     Write8(uint8_t(Value >> 8));
    122   }
    123 
    124   void WriteLE32(uint32_t Value) {
    125     WriteLE16(uint16_t(Value >> 0));
    126     WriteLE16(uint16_t(Value >> 16));
    127   }
    128 
    129   void WriteLE64(uint64_t Value) {
    130     WriteLE32(uint32_t(Value >> 0));
    131     WriteLE32(uint32_t(Value >> 32));
    132   }
    133 
    134   void WriteBE16(uint16_t Value) {
    135     Write8(uint8_t(Value >> 8));
    136     Write8(uint8_t(Value >> 0));
    137   }
    138 
    139   void WriteBE32(uint32_t Value) {
    140     WriteBE16(uint16_t(Value >> 16));
    141     WriteBE16(uint16_t(Value >> 0));
    142   }
    143 
    144   void WriteBE64(uint64_t Value) {
    145     WriteBE32(uint32_t(Value >> 32));
    146     WriteBE32(uint32_t(Value >> 0));
    147   }
    148 
    149   void Write16(uint16_t Value) {
    150     if (IsLittleEndian)
    151       WriteLE16(Value);
    152     else
    153       WriteBE16(Value);
    154   }
    155 
    156   void Write32(uint32_t Value) {
    157     if (IsLittleEndian)
    158       WriteLE32(Value);
    159     else
    160       WriteBE32(Value);
    161   }
    162 
    163   void Write64(uint64_t Value) {
    164     if (IsLittleEndian)
    165       WriteLE64(Value);
    166     else
    167       WriteBE64(Value);
    168   }
    169 
    170   void WriteZeros(unsigned N) {
    171     const char Zeros[16] = { 0 };
    172 
    173     for (unsigned i = 0, e = N / 16; i != e; ++i)
    174       OS << StringRef(Zeros, 16);
    175 
    176     OS << StringRef(Zeros, N % 16);
    177   }
    178 
    179   void WriteBytes(const SmallVectorImpl<char> &ByteVec, unsigned ZeroFillSize = 0) {
    180     WriteBytes(StringRef(ByteVec.data(), ByteVec.size()), ZeroFillSize);
    181   }
    182 
    183   void WriteBytes(StringRef Str, unsigned ZeroFillSize = 0) {
    184     // TODO: this version may need to go away once all fragment contents are
    185     // converted to SmallVector<char, N>
    186     assert((ZeroFillSize == 0 || Str.size () <= ZeroFillSize) &&
    187       "data size greater than fill size, unexpected large write will occur");
    188     OS << Str;
    189     if (ZeroFillSize)
    190       WriteZeros(ZeroFillSize - Str.size());
    191   }
    192 
    193   /// @}
    194 
    195 };
    196 
    197 } // End llvm namespace
    198 
    199 #endif
    200