1 //===-- llvm/MC/MCFixup.h - Instruction Relocation and Patching -*- C++ -*-===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 9 #ifndef LLVM_MC_MCFIXUP_H 10 #define LLVM_MC_MCFIXUP_H 11 12 #include "llvm/MC/MCExpr.h" 13 #include "llvm/Support/DataTypes.h" 14 #include "llvm/Support/ErrorHandling.h" 15 #include "llvm/Support/SMLoc.h" 16 #include <cassert> 17 18 namespace llvm { 19 class MCExpr; 20 21 /// Extensible enumeration to represent the type of a fixup. 22 enum MCFixupKind { 23 FK_NONE = 0, ///< A no-op fixup. 24 FK_Data_1, ///< 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_Data_6b, ///< A six-bits fixup. 29 FK_PCRel_1, ///< A one-byte pc relative fixup. 30 FK_PCRel_2, ///< A two-byte pc relative fixup. 31 FK_PCRel_4, ///< A four-byte pc relative fixup. 32 FK_PCRel_8, ///< A eight-byte pc relative fixup. 33 FK_GPRel_1, ///< A one-byte gp relative fixup. 34 FK_GPRel_2, ///< A two-byte gp relative fixup. 35 FK_GPRel_4, ///< A four-byte gp relative fixup. 36 FK_GPRel_8, ///< A eight-byte gp relative fixup. 37 FK_DTPRel_4, ///< A four-byte dtp relative fixup. 38 FK_DTPRel_8, ///< A eight-byte dtp relative fixup. 39 FK_TPRel_4, ///< A four-byte tp relative fixup. 40 FK_TPRel_8, ///< A eight-byte tp relative fixup. 41 FK_SecRel_1, ///< A one-byte section relative fixup. 42 FK_SecRel_2, ///< A two-byte section relative fixup. 43 FK_SecRel_4, ///< A four-byte section relative fixup. 44 FK_SecRel_8, ///< A eight-byte section relative fixup. 45 FK_Data_Add_1, ///< A one-byte add fixup. 46 FK_Data_Add_2, ///< A two-byte add fixup. 47 FK_Data_Add_4, ///< A four-byte add fixup. 48 FK_Data_Add_8, ///< A eight-byte add fixup. 49 FK_Data_Add_6b, ///< A six-bits add fixup. 50 FK_Data_Sub_1, ///< A one-byte sub fixup. 51 FK_Data_Sub_2, ///< A two-byte sub fixup. 52 FK_Data_Sub_4, ///< A four-byte sub fixup. 53 FK_Data_Sub_8, ///< A eight-byte sub fixup. 54 FK_Data_Sub_6b, ///< A six-bits sub fixup. 55 56 FirstTargetFixupKind = 128, 57 58 // Limit range of target fixups, in case we want to pack more efficiently 59 // later. 60 MaxTargetFixupKind = (1 << 8) 61 }; 62 63 /// Encode information on a single operation to perform on a byte 64 /// sequence (e.g., an encoded instruction) which requires assemble- or run- 65 /// time patching. 66 /// 67 /// Fixups are used any time the target instruction encoder needs to represent 68 /// some value in an instruction which is not yet concrete. The encoder will 69 /// encode the instruction assuming the value is 0, and emit a fixup which 70 /// communicates to the assembler backend how it should rewrite the encoded 71 /// value. 72 /// 73 /// During the process of relaxation, the assembler will apply fixups as 74 /// symbolic values become concrete. When relaxation is complete, any remaining 75 /// fixups become relocations in the object file (or errors, if the fixup cannot 76 /// be encoded on the target). 77 class MCFixup { 78 /// The value to put into the fixup location. The exact interpretation of the 79 /// expression is target dependent, usually it will be one of the operands to 80 /// an instruction or an assembler directive. 81 const MCExpr *Value = nullptr; 82 83 /// The byte index of start of the relocation inside the MCFragment. 84 uint32_t Offset = 0; 85 86 /// The target dependent kind of fixup item this is. The kind is used to 87 /// determine how the operand value should be encoded into the instruction. 88 MCFixupKind Kind = FK_NONE; 89 90 /// The source location which gave rise to the fixup, if any. 91 SMLoc Loc; 92 public: 93 static MCFixup create(uint32_t Offset, const MCExpr *Value, 94 MCFixupKind Kind, SMLoc Loc = SMLoc()) { 95 assert(Kind < MaxTargetFixupKind && "Kind out of range!"); 96 MCFixup FI; 97 FI.Value = Value; 98 FI.Offset = Offset; 99 FI.Kind = Kind; 100 FI.Loc = Loc; 101 return FI; 102 } 103 104 /// Return a fixup corresponding to the add half of a add/sub fixup pair for 105 /// the given Fixup. createAddFor(const MCFixup & Fixup)106 static MCFixup createAddFor(const MCFixup &Fixup) { 107 MCFixup FI; 108 FI.Value = Fixup.getValue(); 109 FI.Offset = Fixup.getOffset(); 110 FI.Kind = getAddKindForKind(Fixup.getKind()); 111 FI.Loc = Fixup.getLoc(); 112 return FI; 113 } 114 115 /// Return a fixup corresponding to the sub half of a add/sub fixup pair for 116 /// the given Fixup. createSubFor(const MCFixup & Fixup)117 static MCFixup createSubFor(const MCFixup &Fixup) { 118 MCFixup FI; 119 FI.Value = Fixup.getValue(); 120 FI.Offset = Fixup.getOffset(); 121 FI.Kind = getSubKindForKind(Fixup.getKind()); 122 FI.Loc = Fixup.getLoc(); 123 return FI; 124 } 125 getKind()126 MCFixupKind getKind() const { return Kind; } 127 getTargetKind()128 unsigned getTargetKind() const { return Kind; } 129 getOffset()130 uint32_t getOffset() const { return Offset; } setOffset(uint32_t Value)131 void setOffset(uint32_t Value) { Offset = Value; } 132 getValue()133 const MCExpr *getValue() const { return Value; } 134 135 /// Return the generic fixup kind for a value with the given size. It 136 /// is an error to pass an unsupported size. getKindForSize(unsigned Size,bool IsPCRel)137 static MCFixupKind getKindForSize(unsigned Size, bool IsPCRel) { 138 switch (Size) { 139 default: llvm_unreachable("Invalid generic fixup size!"); 140 case 1: 141 return IsPCRel ? FK_PCRel_1 : FK_Data_1; 142 case 2: 143 return IsPCRel ? FK_PCRel_2 : FK_Data_2; 144 case 4: 145 return IsPCRel ? FK_PCRel_4 : FK_Data_4; 146 case 8: 147 return IsPCRel ? FK_PCRel_8 : FK_Data_8; 148 } 149 } 150 151 /// Return the generic fixup kind for a value with the given size in bits. 152 /// It is an error to pass an unsupported size. getKindForSizeInBits(unsigned Size,bool IsPCRel)153 static MCFixupKind getKindForSizeInBits(unsigned Size, bool IsPCRel) { 154 switch (Size) { 155 default: 156 llvm_unreachable("Invalid generic fixup size!"); 157 case 6: 158 assert(!IsPCRel && "Invalid pc-relative fixup size!"); 159 return FK_Data_6b; 160 case 8: 161 return IsPCRel ? FK_PCRel_1 : FK_Data_1; 162 case 16: 163 return IsPCRel ? FK_PCRel_2 : FK_Data_2; 164 case 32: 165 return IsPCRel ? FK_PCRel_4 : FK_Data_4; 166 case 64: 167 return IsPCRel ? FK_PCRel_8 : FK_Data_8; 168 } 169 } 170 171 /// Return the generic fixup kind for an addition with a given size. It 172 /// is an error to pass an unsupported size. getAddKindForKind(MCFixupKind Kind)173 static MCFixupKind getAddKindForKind(MCFixupKind Kind) { 174 switch (Kind) { 175 default: llvm_unreachable("Unknown type to convert!"); 176 case FK_Data_1: return FK_Data_Add_1; 177 case FK_Data_2: return FK_Data_Add_2; 178 case FK_Data_4: return FK_Data_Add_4; 179 case FK_Data_8: return FK_Data_Add_8; 180 case FK_Data_6b: return FK_Data_Add_6b; 181 } 182 } 183 184 /// Return the generic fixup kind for an subtraction with a given size. It 185 /// is an error to pass an unsupported size. getSubKindForKind(MCFixupKind Kind)186 static MCFixupKind getSubKindForKind(MCFixupKind Kind) { 187 switch (Kind) { 188 default: llvm_unreachable("Unknown type to convert!"); 189 case FK_Data_1: return FK_Data_Sub_1; 190 case FK_Data_2: return FK_Data_Sub_2; 191 case FK_Data_4: return FK_Data_Sub_4; 192 case FK_Data_8: return FK_Data_Sub_8; 193 case FK_Data_6b: return FK_Data_Sub_6b; 194 } 195 } 196 getLoc()197 SMLoc getLoc() const { return Loc; } 198 }; 199 200 } // End llvm namespace 201 202 #endif 203