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 /// \brief 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 45 FirstTargetFixupKind = 128, 46 47 // Limit range of target fixups, in case we want to pack more efficiently 48 // later. 49 MaxTargetFixupKind = (1 << 8) 50 }; 51 52 /// \brief Encode information on a single operation to perform on a byte 53 /// sequence (e.g., an encoded instruction) which requires assemble- or run- 54 /// time patching. 55 /// 56 /// Fixups are used any time the target instruction encoder needs to represent 57 /// some value in an instruction which is not yet concrete. The encoder will 58 /// encode the instruction assuming the value is 0, and emit a fixup which 59 /// communicates to the assembler backend how it should rewrite the encoded 60 /// value. 61 /// 62 /// During the process of relaxation, the assembler will apply fixups as 63 /// symbolic values become concrete. When relaxation is complete, any remaining 64 /// fixups become relocations in the object file (or errors, if the fixup cannot 65 /// be encoded on the target). 66 class MCFixup { 67 /// The value to put into the fixup location. The exact interpretation of the 68 /// expression is target dependent, usually it will be one of the operands to 69 /// an instruction or an assembler directive. 70 const MCExpr *Value; 71 72 /// The byte index of start of the relocation inside the encoded instruction. 73 uint32_t Offset; 74 75 /// The target dependent kind of fixup item this is. The kind is used to 76 /// determine how the operand value should be encoded into the instruction. 77 unsigned Kind; 78 79 /// The source location which gave rise to the fixup, if any. 80 SMLoc Loc; 81 public: 82 static MCFixup create(uint32_t Offset, const MCExpr *Value, 83 MCFixupKind Kind, SMLoc Loc = SMLoc()) { 84 assert(unsigned(Kind) < MaxTargetFixupKind && "Kind out of range!"); 85 MCFixup FI; 86 FI.Value = Value; 87 FI.Offset = Offset; 88 FI.Kind = unsigned(Kind); 89 FI.Loc = Loc; 90 return FI; 91 } 92 93 MCFixupKind getKind() const { return MCFixupKind(Kind); } 94 95 uint32_t getOffset() const { return Offset; } 96 void setOffset(uint32_t Value) { Offset = Value; } 97 98 const MCExpr *getValue() const { return Value; } 99 100 /// \brief Return the generic fixup kind for a value with the given size. It 101 /// is an error to pass an unsupported size. 102 static MCFixupKind getKindForSize(unsigned Size, bool isPCRel) { 103 switch (Size) { 104 default: llvm_unreachable("Invalid generic fixup size!"); 105 case 1: return isPCRel ? FK_PCRel_1 : FK_Data_1; 106 case 2: return isPCRel ? FK_PCRel_2 : FK_Data_2; 107 case 4: return isPCRel ? FK_PCRel_4 : FK_Data_4; 108 case 8: return isPCRel ? FK_PCRel_8 : FK_Data_8; 109 } 110 } 111 112 SMLoc getLoc() const { return Loc; } 113 }; 114 115 } // End llvm namespace 116 117 #endif 118
