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/EndianStream.h" 17 #include "llvm/Support/raw_ostream.h" 18 #include <cassert> 19 20 namespace llvm { 21 class MCAsmLayout; 22 class MCAssembler; 23 class MCFixup; 24 class MCFragment; 25 class MCSymbolRefExpr; 26 class MCValue; 27 28 /// Defines the object file and target independent interfaces used by the 29 /// 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 &) = delete; 41 void operator=(const MCObjectWriter &) = delete; 42 43 protected: 44 raw_pwrite_stream &OS; 45 46 unsigned IsLittleEndian : 1; 47 48 protected: // Can only create subclasses. MCObjectWriter(raw_pwrite_stream & OS,bool IsLittleEndian)49 MCObjectWriter(raw_pwrite_stream &OS, bool IsLittleEndian) 50 : OS(OS), IsLittleEndian(IsLittleEndian) {} 51 52 public: 53 virtual ~MCObjectWriter(); 54 55 /// lifetime management reset()56 virtual void reset() {} 57 isLittleEndian()58 bool isLittleEndian() const { return IsLittleEndian; } 59 getStream()60 raw_ostream &getStream() { return OS; } 61 62 /// \name High-Level API 63 /// @{ 64 65 /// 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 /// 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(MCAssembler &Asm, const MCAsmLayout &Layout, 80 const MCFragment *Fragment, 81 const MCFixup &Fixup, MCValue Target, 82 bool &IsPCRel, uint64_t &FixedValue) = 0; 83 84 /// Check whether the difference (A - B) between two symbol references is 85 /// fully resolved. 86 /// 87 /// Clients are not required to answer precisely and may conservatively return 88 /// false, even when a difference is fully resolved. 89 bool isSymbolRefDifferenceFullyResolved(const MCAssembler &Asm, 90 const MCSymbolRefExpr *A, 91 const MCSymbolRefExpr *B, 92 bool InSet) const; 93 94 virtual bool isSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm, 95 const MCSymbol &SymA, 96 const MCFragment &FB, 97 bool InSet, 98 bool IsPCRel) const; 99 100 /// True if this symbol (which is a variable) is weak. This is not 101 /// just STB_WEAK, but more generally whether or not we can evaluate 102 /// past it. 103 virtual bool isWeak(const MCSymbol &Sym) const; 104 105 /// Write the object file. 106 /// 107 /// This routine is called by the assembler after layout and relaxation is 108 /// complete, fixups have been evaluated and applied, and relocations 109 /// generated. 110 virtual void writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) = 0; 111 112 /// @} 113 /// \name Binary Output 114 /// @{ 115 write8(uint8_t Value)116 void write8(uint8_t Value) { OS << char(Value); } 117 writeLE16(uint16_t Value)118 void writeLE16(uint16_t Value) { 119 support::endian::Writer<support::little>(OS).write(Value); 120 } 121 writeLE32(uint32_t Value)122 void writeLE32(uint32_t Value) { 123 support::endian::Writer<support::little>(OS).write(Value); 124 } 125 writeLE64(uint64_t Value)126 void writeLE64(uint64_t Value) { 127 support::endian::Writer<support::little>(OS).write(Value); 128 } 129 writeBE16(uint16_t Value)130 void writeBE16(uint16_t Value) { 131 support::endian::Writer<support::big>(OS).write(Value); 132 } 133 writeBE32(uint32_t Value)134 void writeBE32(uint32_t Value) { 135 support::endian::Writer<support::big>(OS).write(Value); 136 } 137 writeBE64(uint64_t Value)138 void writeBE64(uint64_t Value) { 139 support::endian::Writer<support::big>(OS).write(Value); 140 } 141 write16(uint16_t Value)142 void write16(uint16_t Value) { 143 if (IsLittleEndian) 144 writeLE16(Value); 145 else 146 writeBE16(Value); 147 } 148 write32(uint32_t Value)149 void write32(uint32_t Value) { 150 if (IsLittleEndian) 151 writeLE32(Value); 152 else 153 writeBE32(Value); 154 } 155 write64(uint64_t Value)156 void write64(uint64_t Value) { 157 if (IsLittleEndian) 158 writeLE64(Value); 159 else 160 writeBE64(Value); 161 } 162 WriteZeros(unsigned N)163 void WriteZeros(unsigned N) { 164 const char Zeros[16] = {0}; 165 166 for (unsigned i = 0, e = N / 16; i != e; ++i) 167 OS << StringRef(Zeros, 16); 168 169 OS << StringRef(Zeros, N % 16); 170 } 171 172 void writeBytes(const SmallVectorImpl<char> &ByteVec, 173 unsigned ZeroFillSize = 0) { 174 writeBytes(StringRef(ByteVec.data(), ByteVec.size()), ZeroFillSize); 175 } 176 177 void writeBytes(StringRef Str, unsigned ZeroFillSize = 0) { 178 // TODO: this version may need to go away once all fragment contents are 179 // converted to SmallVector<char, N> 180 assert( 181 (ZeroFillSize == 0 || Str.size() <= ZeroFillSize) && 182 "data size greater than fill size, unexpected large write will occur"); 183 OS << Str; 184 if (ZeroFillSize) 185 WriteZeros(ZeroFillSize - Str.size()); 186 } 187 188 /// @} 189 }; 190 191 } // End llvm namespace 192 193 #endif 194