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