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/Support/DataTypes.h" 13 #include "llvm/Support/ErrorHandling.h" 14 #include "llvm/Support/SMLoc.h" 15 #include <cassert> 16 17 namespace llvm { 18 class MCExpr; 19 20 /// Extensible enumeration to represent the type of a fixup. 21 enum MCFixupKind { 22 FK_NONE = 0, ///< A no-op fixup. 23 FK_Data_1, ///< A one-byte fixup. 24 FK_Data_2, ///< A two-byte fixup. 25 FK_Data_4, ///< A four-byte fixup. 26 FK_Data_8, ///< A eight-byte fixup. 27 FK_Data_6b, ///< A six-bits 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 45 FirstTargetFixupKind = 128, 46 47 /// The range [FirstLiteralRelocationKind, MaxTargetFixupKind) is used for 48 /// relocations coming from .reloc directive. Fixup kind 49 /// FirstLiteralRelocationKind+V represents the relocation type with number V. 50 FirstLiteralRelocationKind = 256, 51 52 /// Set limit to accommodate the highest reloc type in use for all Targets, 53 /// currently R_AARCH64_IRELATIVE at 1032, including room for expansion. 54 MaxFixupKind = FirstLiteralRelocationKind + 1032 + 32, 55 }; 56 57 /// Encode information on a single operation to perform on a byte 58 /// sequence (e.g., an encoded instruction) which requires assemble- or run- 59 /// time patching. 60 /// 61 /// Fixups are used any time the target instruction encoder needs to represent 62 /// some value in an instruction which is not yet concrete. The encoder will 63 /// encode the instruction assuming the value is 0, and emit a fixup which 64 /// communicates to the assembler backend how it should rewrite the encoded 65 /// value. 66 /// 67 /// During the process of relaxation, the assembler will apply fixups as 68 /// symbolic values become concrete. When relaxation is complete, any remaining 69 /// fixups become relocations in the object file (or errors, if the fixup cannot 70 /// be encoded on the target). 71 class MCFixup { 72 /// The value to put into the fixup location. The exact interpretation of the 73 /// expression is target dependent, usually it will be one of the operands to 74 /// an instruction or an assembler directive. 75 const MCExpr *Value = nullptr; 76 77 /// The byte index of start of the relocation inside the MCFragment. 78 uint32_t Offset = 0; 79 80 /// The target dependent kind of fixup item this is. The kind is used to 81 /// determine how the operand value should be encoded into the instruction. 82 MCFixupKind Kind = FK_NONE; 83 84 /// The source location which gave rise to the fixup, if any. 85 SMLoc Loc; 86 public: 87 static MCFixup create(uint32_t Offset, const MCExpr *Value, 88 MCFixupKind Kind, SMLoc Loc = SMLoc()) { 89 assert(Kind <= MaxFixupKind && "Kind out of range!"); 90 MCFixup FI; 91 FI.Value = Value; 92 FI.Offset = Offset; 93 FI.Kind = Kind; 94 FI.Loc = Loc; 95 return FI; 96 } 97 getKind()98 MCFixupKind getKind() const { return Kind; } 99 getTargetKind()100 unsigned getTargetKind() const { return Kind; } 101 getOffset()102 uint32_t getOffset() const { return Offset; } setOffset(uint32_t Value)103 void setOffset(uint32_t Value) { Offset = Value; } 104 getValue()105 const MCExpr *getValue() const { return Value; } 106 107 /// Return the generic fixup kind for a value with the given size. It 108 /// is an error to pass an unsupported size. getKindForSize(unsigned Size,bool IsPCRel)109 static MCFixupKind getKindForSize(unsigned Size, bool IsPCRel) { 110 switch (Size) { 111 default: llvm_unreachable("Invalid generic fixup size!"); 112 case 1: 113 return IsPCRel ? FK_PCRel_1 : FK_Data_1; 114 case 2: 115 return IsPCRel ? FK_PCRel_2 : FK_Data_2; 116 case 4: 117 return IsPCRel ? FK_PCRel_4 : FK_Data_4; 118 case 8: 119 return IsPCRel ? FK_PCRel_8 : FK_Data_8; 120 } 121 } 122 123 /// Return the generic fixup kind for a value with the given size in bits. 124 /// It is an error to pass an unsupported size. getKindForSizeInBits(unsigned Size,bool IsPCRel)125 static MCFixupKind getKindForSizeInBits(unsigned Size, bool IsPCRel) { 126 switch (Size) { 127 default: 128 llvm_unreachable("Invalid generic fixup size!"); 129 case 6: 130 assert(!IsPCRel && "Invalid pc-relative fixup size!"); 131 return FK_Data_6b; 132 case 8: 133 return IsPCRel ? FK_PCRel_1 : FK_Data_1; 134 case 16: 135 return IsPCRel ? FK_PCRel_2 : FK_Data_2; 136 case 32: 137 return IsPCRel ? FK_PCRel_4 : FK_Data_4; 138 case 64: 139 return IsPCRel ? FK_PCRel_8 : FK_Data_8; 140 } 141 } 142 getLoc()143 SMLoc getLoc() const { return Loc; } 144 }; 145 146 } // End llvm namespace 147 148 #endif 149