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 20namespace llvm { 21class MCAsmLayout; 22class MCAssembler; 23class MCELFObjectTargetWriter; 24struct MCFixupKindInfo; 25class MCFragment; 26class MCInst; 27class MCRelaxableFragment; 28class MCObjectWriter; 29class MCSection; 30class MCValue; 31class raw_ostream; 32 33/// Generic interface to target specific assembler backends. 34class MCAsmBackend { 35 MCAsmBackend(const MCAsmBackend &) = delete; 36 void operator=(const MCAsmBackend &) = delete; 37 38protected: // Can only create subclasses. 39 MCAsmBackend(); 40 41 unsigned HasDataInCodeSupport : 1; 42 43public: 44 virtual ~MCAsmBackend(); 45 46 /// lifetime management 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. 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. 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 /// Get information on a fixup kind. 71 virtual const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const; 72 73 /// Target hook to adjust the literal value of a fixup if necessary. 74 /// IsResolved signals whether the caller believes a relocation is needed; the 75 /// target can modify the value. The default does nothing. 76 virtual void processFixupValue(const MCAssembler &Asm, 77 const MCAsmLayout &Layout, 78 const MCFixup &Fixup, const MCFragment *DF, 79 const MCValue &Target, uint64_t &Value, 80 bool &IsResolved) {} 81 82 /// Apply the \p Value for given \p Fixup into the provided data fragment, at 83 /// the offset specified by the fixup and following the fixup kind as 84 /// appropriate. 85 virtual void applyFixup(const MCFixup &Fixup, char *Data, unsigned DataSize, 86 uint64_t Value, bool IsPCRel) const = 0; 87 88 /// @} 89 90 /// @name Target Relaxation Interfaces 91 /// @{ 92 93 /// Check whether the given instruction may need relaxation. 94 /// 95 /// \param Inst - The instruction to test. 96 virtual bool mayNeedRelaxation(const MCInst &Inst) const = 0; 97 98 /// Target specific predicate for whether a given fixup requires the 99 /// associated instruction to be relaxed. 100 virtual bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value, 101 const MCRelaxableFragment *DF, 102 const MCAsmLayout &Layout) const = 0; 103 104 /// Relax the instruction in the given fragment to the next wider instruction. 105 /// 106 /// \param Inst The instruction to relax, which may be the same as the 107 /// output. 108 /// \param [out] Res On return, the relaxed instruction. 109 virtual void relaxInstruction(const MCInst &Inst, 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 /// Handle any target-specific assembler flags. By default, do nothing. 126 virtual void handleAssemblerFlag(MCAssemblerFlag Flag) {} 127 128 /// \brief Generate the compact unwind encoding for the CFI instructions. 129 virtual uint32_t 130 generateCompactUnwindEncoding(ArrayRef<MCCFIInstruction>) const { 131 return 0; 132 } 133}; 134 135} // End llvm namespace 136 137#endif 138