1 //===-- llvm/MC/MCAsmBack.h - MC Asm Backend --------------------*- 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_MCASMBACKEND_H 11 #define LLVM_MC_MCASMBACKEND_H 12 13 #include "llvm/MC/MCDirectives.h" 14 #include "llvm/MC/MCFixup.h" 15 #include "llvm/Support/DataTypes.h" 16 #include "llvm/Support/ErrorHandling.h" 17 18 namespace llvm { 19 class MCAsmLayout; 20 class MCAssembler; 21 class MCELFObjectTargetWriter; 22 struct MCFixupKindInfo; 23 class MCFragment; 24 class MCInst; 25 class MCRelaxableFragment; 26 class MCObjectWriter; 27 class MCSection; 28 class MCValue; 29 class raw_ostream; 30 31 /// MCAsmBackend - Generic interface to target specific assembler backends. 32 class MCAsmBackend { 33 MCAsmBackend(const MCAsmBackend &) LLVM_DELETED_FUNCTION; 34 void operator=(const MCAsmBackend &) LLVM_DELETED_FUNCTION; 35 protected: // Can only create subclasses. 36 MCAsmBackend(); 37 38 unsigned HasReliableSymbolDifference : 1; 39 unsigned HasDataInCodeSupport : 1; 40 41 public: 42 virtual ~MCAsmBackend(); 43 44 /// lifetime management 45 virtual void reset() { } 46 47 /// createObjectWriter - Create a new MCObjectWriter instance for use by the 48 /// assembler backend to emit the final object file. 49 virtual MCObjectWriter *createObjectWriter(raw_ostream &OS) const = 0; 50 51 /// createELFObjectTargetWriter - Create a new ELFObjectTargetWriter to enable 52 /// non-standard ELFObjectWriters. 53 virtual MCELFObjectTargetWriter *createELFObjectTargetWriter() const { 54 llvm_unreachable("createELFObjectTargetWriter is not supported by asm " 55 "backend"); 56 } 57 58 /// hasReliableSymbolDifference - Check whether this target implements 59 /// accurate relocations for differences between symbols. If not, differences 60 /// between symbols will always be relocatable expressions and any references 61 /// to temporary symbols will be assumed to be in the same atom, unless they 62 /// reside in a different section. 63 /// 64 /// This should always be true (since it results in fewer relocations with no 65 /// loss of functionality), but is currently supported as a way to maintain 66 /// exact object compatibility with Darwin 'as' (on non-x86_64). It should 67 /// eventually should be eliminated. 68 bool hasReliableSymbolDifference() const { 69 return HasReliableSymbolDifference; 70 } 71 72 /// hasDataInCodeSupport - Check whether this target implements data-in-code 73 /// markers. If not, data region directives will be ignored. 74 bool hasDataInCodeSupport() const { 75 return HasDataInCodeSupport; 76 } 77 78 /// doesSectionRequireSymbols - Check whether the given section requires that 79 /// all symbols (even temporaries) have symbol table entries. 80 virtual bool doesSectionRequireSymbols(const MCSection &Section) const { 81 return false; 82 } 83 84 /// isSectionAtomizable - Check whether the given section can be split into 85 /// atoms. 86 /// 87 /// \see MCAssembler::isSymbolLinkerVisible(). 88 virtual bool isSectionAtomizable(const MCSection &Section) const { 89 return true; 90 } 91 92 /// @name Target Fixup Interfaces 93 /// @{ 94 95 /// getNumFixupKinds - Get the number of target specific fixup kinds. 96 virtual unsigned getNumFixupKinds() const = 0; 97 98 /// getFixupKindInfo - Get information on a fixup kind. 99 virtual const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const; 100 101 /// processFixupValue - Target hook to adjust the literal value of a fixup 102 /// if necessary. IsResolved signals whether the caller believes a relocation 103 /// is needed; the target can modify the value. The default does nothing. 104 virtual void processFixupValue(const MCAssembler &Asm, 105 const MCAsmLayout &Layout, 106 const MCFixup &Fixup, const MCFragment *DF, 107 MCValue &Target, uint64_t &Value, 108 bool &IsResolved) {} 109 110 /// @} 111 112 /// applyFixup - Apply the \p Value for given \p Fixup into the provided 113 /// data fragment, at the offset specified by the fixup and following the 114 /// fixup kind as appropriate. 115 virtual void applyFixup(const MCFixup &Fixup, char *Data, unsigned DataSize, 116 uint64_t Value) const = 0; 117 118 /// @} 119 120 /// @name Target Relaxation Interfaces 121 /// @{ 122 123 /// mayNeedRelaxation - Check whether the given instruction may need 124 /// relaxation. 125 /// 126 /// \param Inst - The instruction to test. 127 virtual bool mayNeedRelaxation(const MCInst &Inst) const = 0; 128 129 /// fixupNeedsRelaxation - Target specific predicate for whether a given 130 /// fixup requires the associated instruction to be relaxed. 131 virtual bool fixupNeedsRelaxation(const MCFixup &Fixup, 132 uint64_t Value, 133 const MCRelaxableFragment *DF, 134 const MCAsmLayout &Layout) const = 0; 135 136 /// RelaxInstruction - Relax the instruction in the given fragment to the next 137 /// wider instruction. 138 /// 139 /// \param Inst The instruction to relax, which may be the same as the 140 /// output. 141 /// \param [out] Res On return, the relaxed instruction. 142 virtual void relaxInstruction(const MCInst &Inst, MCInst &Res) const = 0; 143 144 /// @} 145 146 /// getMinimumNopSize - Returns the minimum size of a nop in bytes on this 147 /// target. The assembler will use this to emit excess padding in situations 148 /// where the padding required for simple alignment would be less than the 149 /// minimum nop size. 150 /// 151 virtual unsigned getMinimumNopSize() const { return 1; } 152 153 /// writeNopData - Write an (optimal) nop sequence of Count bytes to the given 154 /// output. If the target cannot generate such a sequence, it should return an 155 /// error. 156 /// 157 /// \return - True on success. 158 virtual bool writeNopData(uint64_t Count, MCObjectWriter *OW) const = 0; 159 160 /// handleAssemblerFlag - Handle any target-specific assembler flags. 161 /// By default, do nothing. 162 virtual void handleAssemblerFlag(MCAssemblerFlag Flag) {} 163 }; 164 165 } // End llvm namespace 166 167 #endif 168
