1 //===-- llvm/MC/MCFixup.h - Instruction Relocation and Patching -*- 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_MCFIXUP_H 11 #define LLVM_MC_MCFIXUP_H 12 13 #include "llvm/MC/MCExpr.h" 14 #include "llvm/Support/DataTypes.h" 15 #include "llvm/Support/ErrorHandling.h" 16 #include "llvm/Support/SMLoc.h" 17 #include <cassert> 18 19 namespace llvm { 20 class MCExpr; 21 22 /// Extensible enumeration to represent the type of a fixup. 23 enum MCFixupKind { 24 FK_Data_1 = 0, ///< A one-byte fixup. 25 FK_Data_2, ///< A two-byte fixup. 26 FK_Data_4, ///< A four-byte fixup. 27 FK_Data_8, ///< A eight-byte fixup. 28 FK_PCRel_1, ///< A one-byte pc relative fixup. 29 FK_PCRel_2, ///< A two-byte pc relative fixup. 30 FK_PCRel_4, ///< A four-byte pc relative fixup. 31 FK_PCRel_8, ///< A eight-byte pc relative fixup. 32 FK_GPRel_1, ///< A one-byte gp relative fixup. 33 FK_GPRel_2, ///< A two-byte gp relative fixup. 34 FK_GPRel_4, ///< A four-byte gp relative fixup. 35 FK_GPRel_8, ///< A eight-byte gp relative fixup. 36 FK_DTPRel_4, ///< A four-byte dtp relative fixup. 37 FK_DTPRel_8, ///< A eight-byte dtp relative fixup. 38 FK_TPRel_4, ///< A four-byte tp relative fixup. 39 FK_TPRel_8, ///< A eight-byte tp relative fixup. 40 FK_SecRel_1, ///< A one-byte section relative fixup. 41 FK_SecRel_2, ///< A two-byte section relative fixup. 42 FK_SecRel_4, ///< A four-byte section relative fixup. 43 FK_SecRel_8, ///< A eight-byte section relative fixup. 44 FK_Data_Add_1, ///< A one-byte add fixup. 45 FK_Data_Add_2, ///< A two-byte add fixup. 46 FK_Data_Add_4, ///< A four-byte add fixup. 47 FK_Data_Add_8, ///< A eight-byte add fixup. 48 FK_Data_Sub_1, ///< A one-byte sub fixup. 49 FK_Data_Sub_2, ///< A two-byte sub fixup. 50 FK_Data_Sub_4, ///< A four-byte sub fixup. 51 FK_Data_Sub_8, ///< A eight-byte sub fixup. 52 53 FirstTargetFixupKind = 128, 54 55 // Limit range of target fixups, in case we want to pack more efficiently 56 // later. 57 MaxTargetFixupKind = (1 << 8) 58 }; 59 60 /// Encode information on a single operation to perform on a byte 61 /// sequence (e.g., an encoded instruction) which requires assemble- or run- 62 /// time patching. 63 /// 64 /// Fixups are used any time the target instruction encoder needs to represent 65 /// some value in an instruction which is not yet concrete. The encoder will 66 /// encode the instruction assuming the value is 0, and emit a fixup which 67 /// communicates to the assembler backend how it should rewrite the encoded 68 /// value. 69 /// 70 /// During the process of relaxation, the assembler will apply fixups as 71 /// symbolic values become concrete. When relaxation is complete, any remaining 72 /// fixups become relocations in the object file (or errors, if the fixup cannot 73 /// be encoded on the target). 74 class MCFixup { 75 /// The value to put into the fixup location. The exact interpretation of the 76 /// expression is target dependent, usually it will be one of the operands to 77 /// an instruction or an assembler directive. 78 const MCExpr *Value; 79 80 /// The byte index of start of the relocation inside the MCFragment. 81 uint32_t Offset; 82 83 /// The target dependent kind of fixup item this is. The kind is used to 84 /// determine how the operand value should be encoded into the instruction. 85 unsigned Kind; 86 87 /// The source location which gave rise to the fixup, if any. 88 SMLoc Loc; 89 public: 90 static MCFixup create(uint32_t Offset, const MCExpr *Value, 91 MCFixupKind Kind, SMLoc Loc = SMLoc()) { 92 assert(unsigned(Kind) < MaxTargetFixupKind && "Kind out of range!"); 93 MCFixup FI; 94 FI.Value = Value; 95 FI.Offset = Offset; 96 FI.Kind = unsigned(Kind); 97 FI.Loc = Loc; 98 return FI; 99 } 100 101 /// Return a fixup corresponding to the add half of a add/sub fixup pair for 102 /// the given Fixup. createAddFor(const MCFixup & Fixup)103 static MCFixup createAddFor(const MCFixup &Fixup) { 104 MCFixup FI; 105 FI.Value = Fixup.getValue(); 106 FI.Offset = Fixup.getOffset(); 107 FI.Kind = (unsigned)getAddKindForKind(Fixup.getKind()); 108 FI.Loc = Fixup.getLoc(); 109 return FI; 110 } 111 112 /// Return a fixup corresponding to the sub half of a add/sub fixup pair for 113 /// the given Fixup. createSubFor(const MCFixup & Fixup)114 static MCFixup createSubFor(const MCFixup &Fixup) { 115 MCFixup FI; 116 FI.Value = Fixup.getValue(); 117 FI.Offset = Fixup.getOffset(); 118 FI.Kind = (unsigned)getSubKindForKind(Fixup.getKind()); 119 FI.Loc = Fixup.getLoc(); 120 return FI; 121 } 122 getKind()123 MCFixupKind getKind() const { return MCFixupKind(Kind); } 124 getOffset()125 uint32_t getOffset() const { return Offset; } setOffset(uint32_t Value)126 void setOffset(uint32_t Value) { Offset = Value; } 127 getValue()128 const MCExpr *getValue() const { return Value; } 129 130 /// Return the generic fixup kind for a value with the given size. It 131 /// is an error to pass an unsupported size. getKindForSize(unsigned Size,bool isPCRel)132 static MCFixupKind getKindForSize(unsigned Size, bool isPCRel) { 133 switch (Size) { 134 default: llvm_unreachable("Invalid generic fixup size!"); 135 case 1: return isPCRel ? FK_PCRel_1 : FK_Data_1; 136 case 2: return isPCRel ? FK_PCRel_2 : FK_Data_2; 137 case 4: return isPCRel ? FK_PCRel_4 : FK_Data_4; 138 case 8: return isPCRel ? FK_PCRel_8 : FK_Data_8; 139 } 140 } 141 142 /// Return the generic fixup kind for an addition with a given size. It 143 /// is an error to pass an unsupported size. getAddKindForKind(unsigned Kind)144 static MCFixupKind getAddKindForKind(unsigned Kind) { 145 switch (Kind) { 146 default: llvm_unreachable("Unknown type to convert!"); 147 case FK_Data_1: return FK_Data_Add_1; 148 case FK_Data_2: return FK_Data_Add_2; 149 case FK_Data_4: return FK_Data_Add_4; 150 case FK_Data_8: return FK_Data_Add_8; 151 } 152 } 153 154 /// Return the generic fixup kind for an subtraction with a given size. It 155 /// is an error to pass an unsupported size. getSubKindForKind(unsigned Kind)156 static MCFixupKind getSubKindForKind(unsigned Kind) { 157 switch (Kind) { 158 default: llvm_unreachable("Unknown type to convert!"); 159 case FK_Data_1: return FK_Data_Sub_1; 160 case FK_Data_2: return FK_Data_Sub_2; 161 case FK_Data_4: return FK_Data_Sub_4; 162 case FK_Data_8: return FK_Data_Sub_8; 163 } 164 } 165 getLoc()166 SMLoc getLoc() const { return Loc; } 167 }; 168 169 } // End llvm namespace 170 171 #endif 172