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 <cassert> 15 16 namespace llvm { 17 class MCExpr; 18 19 /// MCFixupKind - Extensible enumeration to represent the type of a fixup. 20 enum MCFixupKind { 21 FK_Data_1 = 0, ///< A one-byte fixup. 22 FK_Data_2, ///< A two-byte fixup. 23 FK_Data_4, ///< A four-byte fixup. 24 FK_Data_8, ///< A eight-byte fixup. 25 FK_PCRel_1, ///< A one-byte pc relative fixup. 26 FK_PCRel_2, ///< A two-byte pc relative fixup. 27 FK_PCRel_4, ///< A four-byte pc relative fixup. 28 FK_PCRel_8, ///< A eight-byte pc relative fixup. 29 30 FirstTargetFixupKind = 128, 31 32 // Limit range of target fixups, in case we want to pack more efficiently 33 // later. 34 MaxTargetFixupKind = (1 << 8) 35 }; 36 37 /// MCFixup - Encode information on a single operation to perform on a byte 38 /// sequence (e.g., an encoded instruction) which requires assemble- or run- 39 /// time patching. 40 /// 41 /// Fixups are used any time the target instruction encoder needs to represent 42 /// some value in an instruction which is not yet concrete. The encoder will 43 /// encode the instruction assuming the value is 0, and emit a fixup which 44 /// communicates to the assembler backend how it should rewrite the encoded 45 /// value. 46 /// 47 /// During the process of relaxation, the assembler will apply fixups as 48 /// symbolic values become concrete. When relaxation is complete, any remaining 49 /// fixups become relocations in the object file (or errors, if the fixup cannot 50 /// be encoded on the target). 51 class MCFixup { 52 /// The value to put into the fixup location. The exact interpretation of the 53 /// expression is target dependent, usually it will be one of the operands to 54 /// an instruction or an assembler directive. 55 const MCExpr *Value; 56 57 /// The byte index of start of the relocation inside the encoded instruction. 58 uint32_t Offset; 59 60 /// The target dependent kind of fixup item this is. The kind is used to 61 /// determine how the operand value should be encoded into the instruction. 62 unsigned Kind; 63 64 public: 65 static MCFixup Create(uint32_t Offset, const MCExpr *Value, 66 MCFixupKind Kind) { 67 assert(unsigned(Kind) < MaxTargetFixupKind && "Kind out of range!"); 68 MCFixup FI; 69 FI.Value = Value; 70 FI.Offset = Offset; 71 FI.Kind = unsigned(Kind); 72 return FI; 73 } 74 75 MCFixupKind getKind() const { return MCFixupKind(Kind); } 76 77 uint32_t getOffset() const { return Offset; } 78 void setOffset(uint32_t Value) { Offset = Value; } 79 80 const MCExpr *getValue() const { return Value; } 81 82 /// getKindForSize - Return the generic fixup kind for a value with the given 83 /// size. It is an error to pass an unsupported size. 84 static MCFixupKind getKindForSize(unsigned Size, bool isPCRel) { 85 switch (Size) { 86 default: assert(0 && "Invalid generic fixup size!"); 87 case 1: return isPCRel ? FK_PCRel_1 : FK_Data_1; 88 case 2: return isPCRel ? FK_PCRel_2 : FK_Data_2; 89 case 4: return isPCRel ? FK_PCRel_4 : FK_Data_4; 90 case 8: return isPCRel ? FK_PCRel_8 : FK_Data_8; 91 } 92 } 93 }; 94 95 } // End llvm namespace 96 97 #endif 98
