include/llvm/MC/MCFixup.h

   1 //===-- llvm/MC/MCFixup.h - Instruction Relocation and Patching -*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef LLVM_MC_MCFIXUP_H
  10 #define LLVM_MC_MCFIXUP_H
  11
  12 #include "llvm/MC/MCExpr.h"
  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 /// 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_DTPRel_4,   ///< A four-byte dtp relative fixup.
  36   FK_DTPRel_8,   ///< A eight-byte dtp relative fixup.
  37   FK_TPRel_4,    ///< A four-byte tp relative fixup.
  38   FK_TPRel_8,    ///< A eight-byte tp relative fixup.
  39   FK_SecRel_1,   ///< A one-byte section relative fixup.
  40   FK_SecRel_2,   ///< A two-byte section relative fixup.
  41   FK_SecRel_4,   ///< A four-byte section relative fixup.
  42   FK_SecRel_8,   ///< A eight-byte section relative fixup.
  43   FK_Data_Add_1, ///< A one-byte add fixup.
  44   FK_Data_Add_2, ///< A two-byte add fixup.
  45   FK_Data_Add_4, ///< A four-byte add fixup.
  46   FK_Data_Add_8, ///< A eight-byte add fixup.
  47   FK_Data_Sub_1, ///< A one-byte sub fixup.
  48   FK_Data_Sub_2, ///< A two-byte sub fixup.
  49   FK_Data_Sub_4, ///< A four-byte sub fixup.
  50   FK_Data_Sub_8, ///< A eight-byte sub fixup.
  51
  52   FirstTargetFixupKind = 128,
  53
  54   // Limit range of target fixups, in case we want to pack more efficiently
  55   // later.
  56   MaxTargetFixupKind = (1 << 8)
  57 };
  58
  59 /// Encode information on a single operation to perform on a byte
  60 /// sequence (e.g., an encoded instruction) which requires assemble- or run-
  61 /// time patching.
  62 ///
  63 /// Fixups are used any time the target instruction encoder needs to represent
  64 /// some value in an instruction which is not yet concrete. The encoder will
  65 /// encode the instruction assuming the value is 0, and emit a fixup which
  66 /// communicates to the assembler backend how it should rewrite the encoded
  67 /// value.
  68 ///
  69 /// During the process of relaxation, the assembler will apply fixups as
  70 /// symbolic values become concrete. When relaxation is complete, any remaining
  71 /// fixups become relocations in the object file (or errors, if the fixup cannot
  72 /// be encoded on the target).
  73 class MCFixup {
  74   /// The value to put into the fixup location. The exact interpretation of the
  75   /// expression is target dependent, usually it will be one of the operands to
  76   /// an instruction or an assembler directive.
  77   const MCExpr *Value;
  78
  79   /// The byte index of start of the relocation inside the MCFragment.
  80   uint32_t Offset;
  81
  82   /// The target dependent kind of fixup item this is. The kind is used to
  83   /// determine how the operand value should be encoded into the instruction.
  84   unsigned Kind;
  85
  86   /// The source location which gave rise to the fixup, if any.
  87   SMLoc Loc;
  88 public:
  89   static MCFixup create(uint32_t Offset, const MCExpr *Value,
  90                         MCFixupKind Kind, SMLoc Loc = SMLoc()) {
  91     assert(unsigned(Kind) < MaxTargetFixupKind && "Kind out of range!");
  92     MCFixup FI;
  93     FI.Value = Value;
  94     FI.Offset = Offset;
  95     FI.Kind = unsigned(Kind);
  96     FI.Loc = Loc;
  97     return FI;
  98   }
  99
 100   /// Return a fixup corresponding to the add half of a add/sub fixup pair for
 101   /// the given Fixup.
 102   static MCFixup createAddFor(const MCFixup &Fixup) {
 103     MCFixup FI;
 104     FI.Value = Fixup.getValue();
 105     FI.Offset = Fixup.getOffset();
 106     FI.Kind = (unsigned)getAddKindForKind(Fixup.getKind());
 107     FI.Loc = Fixup.getLoc();
 108     return FI;
 109   }
 110
 111   /// Return a fixup corresponding to the sub half of a add/sub fixup pair for
 112   /// the given Fixup.
 113   static MCFixup createSubFor(const MCFixup &Fixup) {
 114     MCFixup FI;
 115     FI.Value = Fixup.getValue();
 116     FI.Offset = Fixup.getOffset();
 117     FI.Kind = (unsigned)getSubKindForKind(Fixup.getKind());
 118     FI.Loc = Fixup.getLoc();
 119     return FI;
 120   }
 121
 122   MCFixupKind getKind() const { return MCFixupKind(Kind); }
 123
 124   uint32_t getOffset() const { return Offset; }
 125   void setOffset(uint32_t Value) { Offset = Value; }
 126
 127   const MCExpr *getValue() const { return Value; }
 128
 129   /// Return the generic fixup kind for a value with the given size. It
 130   /// is an error to pass an unsupported size.
 131   static MCFixupKind getKindForSize(unsigned Size, bool isPCRel) {
 132     switch (Size) {
 133     default: llvm_unreachable("Invalid generic fixup size!");
 134     case 1: return isPCRel ? FK_PCRel_1 : FK_Data_1;
 135     case 2: return isPCRel ? FK_PCRel_2 : FK_Data_2;
 136     case 4: return isPCRel ? FK_PCRel_4 : FK_Data_4;
 137     case 8: return isPCRel ? FK_PCRel_8 : FK_Data_8;
 138     }
 139   }
 140
 141   /// Return the generic fixup kind for an addition with a given size. It
 142   /// is an error to pass an unsupported size.
 143   static MCFixupKind getAddKindForKind(unsigned Kind) {
 144     switch (Kind) {
 145     default: llvm_unreachable("Unknown type to convert!");
 146     case FK_Data_1: return FK_Data_Add_1;
 147     case FK_Data_2: return FK_Data_Add_2;
 148     case FK_Data_4: return FK_Data_Add_4;
 149     case FK_Data_8: return FK_Data_Add_8;
 150     }
 151   }
 152
 153   /// Return the generic fixup kind for an subtraction with a given size. It
 154   /// is an error to pass an unsupported size.
 155   static MCFixupKind getSubKindForKind(unsigned Kind) {
 156     switch (Kind) {
 157     default: llvm_unreachable("Unknown type to convert!");
 158     case FK_Data_1: return FK_Data_Sub_1;
 159     case FK_Data_2: return FK_Data_Sub_2;
 160     case FK_Data_4: return FK_Data_Sub_4;
 161     case FK_Data_8: return FK_Data_Sub_8;
 162     }
 163   }
 164
 165   SMLoc getLoc() const { return Loc; }
 166 };
 167
 168 } // End llvm namespace
 169
 170 #endif