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/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 /// MCFixupKind - Extensible enumeration to represent the type of a fixup. 22 enum MCFixupKind { 23 FK_Data_1 = 0, ///< 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_PCRel_1, ///< A one-byte pc relative fixup. 28 FK_PCRel_2, ///< A two-byte pc relative fixup. 29 FK_PCRel_4, ///< A four-byte pc relative fixup. 30 FK_PCRel_8, ///< A eight-byte pc relative fixup. 31 FK_GPRel_1, ///< A one-byte gp relative fixup. 32 FK_GPRel_2, ///< A two-byte gp relative fixup. 33 FK_GPRel_4, ///< A four-byte gp relative fixup. 34 FK_GPRel_8, ///< A eight-byte gp relative fixup. 35 FK_SecRel_1, ///< A one-byte section relative fixup. 36 FK_SecRel_2, ///< A two-byte section relative fixup. 37 FK_SecRel_4, ///< A four-byte section relative fixup. 38 FK_SecRel_8, ///< A eight-byte section relative fixup. 39 40 FirstTargetFixupKind = 128, 41 42 // Limit range of target fixups, in case we want to pack more efficiently 43 // later. 44 MaxTargetFixupKind = (1 << 8) 45 }; 46 47 /// MCFixup - Encode information on a single operation to perform on a byte 48 /// sequence (e.g., an encoded instruction) which requires assemble- or run- 49 /// time patching. 50 /// 51 /// Fixups are used any time the target instruction encoder needs to represent 52 /// some value in an instruction which is not yet concrete. The encoder will 53 /// encode the instruction assuming the value is 0, and emit a fixup which 54 /// communicates to the assembler backend how it should rewrite the encoded 55 /// value. 56 /// 57 /// During the process of relaxation, the assembler will apply fixups as 58 /// symbolic values become concrete. When relaxation is complete, any remaining 59 /// fixups become relocations in the object file (or errors, if the fixup cannot 60 /// be encoded on the target). 61 class MCFixup { 62 /// The value to put into the fixup location. The exact interpretation of the 63 /// expression is target dependent, usually it will be one of the operands to 64 /// an instruction or an assembler directive. 65 const MCExpr *Value; 66 67 /// The byte index of start of the relocation inside the encoded instruction. 68 uint32_t Offset; 69 70 /// The target dependent kind of fixup item this is. The kind is used to 71 /// determine how the operand value should be encoded into the instruction. 72 unsigned Kind; 73 74 /// The source location which gave rise to the fixup, if any. 75 SMLoc Loc; 76 public: 77 static MCFixup Create(uint32_t Offset, const MCExpr *Value, 78 MCFixupKind Kind, SMLoc Loc = SMLoc()) { 79 assert(unsigned(Kind) < MaxTargetFixupKind && "Kind out of range!"); 80 MCFixup FI; 81 FI.Value = Value; 82 FI.Offset = Offset; 83 FI.Kind = unsigned(Kind); 84 FI.Loc = Loc; 85 return FI; 86 } 87 88 MCFixupKind getKind() const { return MCFixupKind(Kind); } 89 90 uint32_t getOffset() const { return Offset; } 91 void setOffset(uint32_t Value) { Offset = Value; } 92 93 const MCExpr *getValue() const { return Value; } 94 95 /// getKindForSize - Return the generic fixup kind for a value with the given 96 /// size. It is an error to pass an unsupported size. 97 static MCFixupKind getKindForSize(unsigned Size, bool isPCRel) { 98 switch (Size) { 99 default: llvm_unreachable("Invalid generic fixup size!"); 100 case 1: return isPCRel ? FK_PCRel_1 : FK_Data_1; 101 case 2: return isPCRel ? FK_PCRel_2 : FK_Data_2; 102 case 4: return isPCRel ? FK_PCRel_4 : FK_Data_4; 103 case 8: return isPCRel ? FK_PCRel_8 : FK_Data_8; 104 } 105 } 106 107 SMLoc getLoc() const { return Loc; } 108 }; 109 110 } // End llvm namespace 111 112 #endif 113
