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 19namespace llvm { 20class MCExpr; 21 22/// \brief Extensible enumeration to represent the type of a fixup. 23enum 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_SecRel_1, ///< A one-byte section relative fixup. 37 FK_SecRel_2, ///< A two-byte section relative fixup. 38 FK_SecRel_4, ///< A four-byte section relative fixup. 39 FK_SecRel_8, ///< A eight-byte section relative fixup. 40 41 FirstTargetFixupKind = 128, 42 43 // Limit range of target fixups, in case we want to pack more efficiently 44 // later. 45 MaxTargetFixupKind = (1 << 8) 46}; 47 48/// \brief Encode information on a single operation to perform on a byte 49/// sequence (e.g., an encoded instruction) which requires assemble- or run- 50/// time patching. 51/// 52/// Fixups are used any time the target instruction encoder needs to represent 53/// some value in an instruction which is not yet concrete. The encoder will 54/// encode the instruction assuming the value is 0, and emit a fixup which 55/// communicates to the assembler backend how it should rewrite the encoded 56/// value. 57/// 58/// During the process of relaxation, the assembler will apply fixups as 59/// symbolic values become concrete. When relaxation is complete, any remaining 60/// fixups become relocations in the object file (or errors, if the fixup cannot 61/// be encoded on the target). 62class MCFixup { 63 /// The value to put into the fixup location. The exact interpretation of the 64 /// expression is target dependent, usually it will be one of the operands to 65 /// an instruction or an assembler directive. 66 const MCExpr *Value; 67 68 /// The byte index of start of the relocation inside the encoded instruction. 69 uint32_t Offset; 70 71 /// The target dependent kind of fixup item this is. The kind is used to 72 /// determine how the operand value should be encoded into the instruction. 73 unsigned Kind; 74 75 /// The source location which gave rise to the fixup, if any. 76 SMLoc Loc; 77public: 78 static MCFixup create(uint32_t Offset, const MCExpr *Value, 79 MCFixupKind Kind, SMLoc Loc = SMLoc()) { 80 assert(unsigned(Kind) < MaxTargetFixupKind && "Kind out of range!"); 81 MCFixup FI; 82 FI.Value = Value; 83 FI.Offset = Offset; 84 FI.Kind = unsigned(Kind); 85 FI.Loc = Loc; 86 return FI; 87 } 88 89 MCFixupKind getKind() const { return MCFixupKind(Kind); } 90 91 uint32_t getOffset() const { return Offset; } 92 void setOffset(uint32_t Value) { Offset = Value; } 93 94 const MCExpr *getValue() const { return Value; } 95 96 /// \brief Return the generic fixup kind for a value with the given size. It 97 /// is an error to pass an unsupported size. 98 static MCFixupKind getKindForSize(unsigned Size, bool isPCRel) { 99 switch (Size) { 100 default: llvm_unreachable("Invalid generic fixup size!"); 101 case 1: return isPCRel ? FK_PCRel_1 : FK_Data_1; 102 case 2: return isPCRel ? FK_PCRel_2 : FK_Data_2; 103 case 4: return isPCRel ? FK_PCRel_4 : FK_Data_4; 104 case 8: return isPCRel ? FK_PCRel_8 : FK_Data_8; 105 } 106 } 107 108 SMLoc getLoc() const { return Loc; } 109}; 110 111} // End llvm namespace 112 113#endif 114