1 //===-- llvm/MC/MCAsmBackend.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/ADT/ArrayRef.h" 14 #include "llvm/MC/MCDirectives.h" 15 #include "llvm/MC/MCDwarf.h" 16 #include "llvm/MC/MCFixup.h" 17 #include "llvm/Support/DataTypes.h" 18 #include "llvm/Support/ErrorHandling.h" 19 20 namespace llvm { 21 class MCAsmLayout; 22 class MCAssembler; 23 class MCELFObjectTargetWriter; 24 struct MCFixupKindInfo; 25 class MCFragment; 26 class MCInst; 27 class MCRelaxableFragment; 28 class MCObjectWriter; 29 class MCSection; 30 class MCValue; 31 class raw_ostream; 32 33 /// Generic interface to target specific assembler backends. 34 class MCAsmBackend { 35 MCAsmBackend(const MCAsmBackend &) = delete; 36 void operator=(const MCAsmBackend &) = delete; 37 38 protected: // Can only create subclasses. 39 MCAsmBackend(); 40 41 unsigned HasDataInCodeSupport : 1; 42 43 public: 44 virtual ~MCAsmBackend(); 45 46 /// lifetime management reset()47 virtual void reset() {} 48 49 /// Create a new MCObjectWriter instance for use by the assembler backend to 50 /// emit the final object file. 51 virtual MCObjectWriter *createObjectWriter(raw_pwrite_stream &OS) const = 0; 52 53 /// Create a new ELFObjectTargetWriter to enable non-standard 54 /// ELFObjectWriters. createELFObjectTargetWriter()55 virtual MCELFObjectTargetWriter *createELFObjectTargetWriter() const { 56 llvm_unreachable("createELFObjectTargetWriter is not supported by asm " 57 "backend"); 58 } 59 60 /// Check whether this target implements data-in-code markers. If not, data 61 /// region directives will be ignored. hasDataInCodeSupport()62 bool hasDataInCodeSupport() const { return HasDataInCodeSupport; } 63 64 /// \name Target Fixup Interfaces 65 /// @{ 66 67 /// Get the number of target specific fixup kinds. 68 virtual unsigned getNumFixupKinds() const = 0; 69 70 /// Map a relocation name used in .reloc to a fixup kind. 71 /// Returns true and sets MappedKind if Name is successfully mapped. 72 /// Otherwise returns false and leaves MappedKind unchanged. 73 virtual bool getFixupKind(StringRef Name, MCFixupKind &MappedKind) const; 74 75 /// Get information on a fixup kind. 76 virtual const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const; 77 78 /// Target hook to adjust the literal value of a fixup if necessary. 79 /// IsResolved signals whether the caller believes a relocation is needed; the 80 /// target can modify the value. The default does nothing. processFixupValue(const MCAssembler & Asm,const MCAsmLayout & Layout,const MCFixup & Fixup,const MCFragment * DF,const MCValue & Target,uint64_t & Value,bool & IsResolved)81 virtual void processFixupValue(const MCAssembler &Asm, 82 const MCAsmLayout &Layout, 83 const MCFixup &Fixup, const MCFragment *DF, 84 const MCValue &Target, uint64_t &Value, 85 bool &IsResolved) {} 86 87 /// Apply the \p Value for given \p Fixup into the provided data fragment, at 88 /// the offset specified by the fixup and following the fixup kind as 89 /// appropriate. 90 virtual void applyFixup(const MCFixup &Fixup, char *Data, unsigned DataSize, 91 uint64_t Value, bool IsPCRel) const = 0; 92 93 /// @} 94 95 /// \name Target Relaxation Interfaces 96 /// @{ 97 98 /// Check whether the given instruction may need relaxation. 99 /// 100 /// \param Inst - The instruction to test. 101 virtual bool mayNeedRelaxation(const MCInst &Inst) const = 0; 102 103 /// Target specific predicate for whether a given fixup requires the 104 /// associated instruction to be relaxed. 105 virtual bool fixupNeedsRelaxationAdvanced(const MCFixup &Fixup, bool Resolved, 106 uint64_t Value, 107 const MCRelaxableFragment *DF, 108 const MCAsmLayout &Layout) const; 109 110 /// Simple predicate for targets where !Resolved implies requiring relaxation 111 virtual bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value, 112 const MCRelaxableFragment *DF, 113 const MCAsmLayout &Layout) const = 0; 114 115 /// Relax the instruction in the given fragment to the next wider instruction. 116 /// 117 /// \param Inst The instruction to relax, which may be the same as the 118 /// output. 119 /// \param [out] Res On return, the relaxed instruction. 120 virtual void relaxInstruction(const MCInst &Inst, MCInst &Res) const = 0; 121 122 /// @} 123 124 /// Returns the minimum size of a nop in bytes on this target. The assembler 125 /// will use this to emit excess padding in situations where the padding 126 /// required for simple alignment would be less than the minimum nop size. 127 /// getMinimumNopSize()128 virtual unsigned getMinimumNopSize() const { return 1; } 129 130 /// Write an (optimal) nop sequence of Count bytes to the given output. If the 131 /// target cannot generate such a sequence, it should return an error. 132 /// 133 /// \return - True on success. 134 virtual bool writeNopData(uint64_t Count, MCObjectWriter *OW) const = 0; 135 136 /// Handle any target-specific assembler flags. By default, do nothing. handleAssemblerFlag(MCAssemblerFlag Flag)137 virtual void handleAssemblerFlag(MCAssemblerFlag Flag) {} 138 139 /// \brief Generate the compact unwind encoding for the CFI instructions. 140 virtual uint32_t generateCompactUnwindEncoding(ArrayRef<MCCFIInstruction>)141 generateCompactUnwindEncoding(ArrayRef<MCCFIInstruction>) const { 142 return 0; 143 } 144 }; 145 146 } // End llvm namespace 147 148 #endif 149