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