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_NONE = 0,    ///< A no-op fixup.
  24   FK_Data_1,      ///< 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_Data_6b,     ///< A six-bits fixup.
  29   FK_PCRel_1,     ///< A one-byte pc relative fixup.
  30   FK_PCRel_2,     ///< A two-byte pc relative fixup.
  31   FK_PCRel_4,     ///< A four-byte pc relative fixup.
  32   FK_PCRel_8,     ///< A eight-byte pc relative fixup.
  33   FK_GPRel_1,     ///< A one-byte gp relative fixup.
  34   FK_GPRel_2,     ///< A two-byte gp relative fixup.
  35   FK_GPRel_4,     ///< A four-byte gp relative fixup.
  36   FK_GPRel_8,     ///< A eight-byte gp relative fixup.
  37   FK_DTPRel_4,    ///< A four-byte dtp relative fixup.
  38   FK_DTPRel_8,    ///< A eight-byte dtp relative fixup.
  39   FK_TPRel_4,     ///< A four-byte tp relative fixup.
  40   FK_TPRel_8,     ///< A eight-byte tp relative fixup.
  41   FK_SecRel_1,    ///< A one-byte section relative fixup.
  42   FK_SecRel_2,    ///< A two-byte section relative fixup.
  43   FK_SecRel_4,    ///< A four-byte section relative fixup.
  44   FK_SecRel_8,    ///< A eight-byte section relative fixup.
  45   FK_Data_Add_1,  ///< A one-byte add fixup.
  46   FK_Data_Add_2,  ///< A two-byte add fixup.
  47   FK_Data_Add_4,  ///< A four-byte add fixup.
  48   FK_Data_Add_8,  ///< A eight-byte add fixup.
  49   FK_Data_Add_6b, ///< A six-bits add fixup.
  50   FK_Data_Sub_1,  ///< A one-byte sub fixup.
  51   FK_Data_Sub_2,  ///< A two-byte sub fixup.
  52   FK_Data_Sub_4,  ///< A four-byte sub fixup.
  53   FK_Data_Sub_8,  ///< A eight-byte sub fixup.
  54   FK_Data_Sub_6b, ///< A six-bits sub fixup.
  55
  56   FirstTargetFixupKind = 128,
  57
  58   // Limit range of target fixups, in case we want to pack more efficiently
  59   // later.
  60   MaxTargetFixupKind = (1 << 8)
  61 };
  62
  63 /// Encode information on a single operation to perform on a byte
  64 /// sequence (e.g., an encoded instruction) which requires assemble- or run-
  65 /// time patching.
  66 ///
  67 /// Fixups are used any time the target instruction encoder needs to represent
  68 /// some value in an instruction which is not yet concrete. The encoder will
  69 /// encode the instruction assuming the value is 0, and emit a fixup which
  70 /// communicates to the assembler backend how it should rewrite the encoded
  71 /// value.
  72 ///
  73 /// During the process of relaxation, the assembler will apply fixups as
  74 /// symbolic values become concrete. When relaxation is complete, any remaining
  75 /// fixups become relocations in the object file (or errors, if the fixup cannot
  76 /// be encoded on the target).
  77 class MCFixup {
  78   /// The value to put into the fixup location. The exact interpretation of the
  79   /// expression is target dependent, usually it will be one of the operands to
  80   /// an instruction or an assembler directive.
  81   const MCExpr *Value = nullptr;
  82
  83   /// The byte index of start of the relocation inside the MCFragment.
  84   uint32_t Offset = 0;
  85
  86   /// The target dependent kind of fixup item this is. The kind is used to
  87   /// determine how the operand value should be encoded into the instruction.
  88   MCFixupKind Kind = FK_NONE;
  89
  90   /// The source location which gave rise to the fixup, if any.
  91   SMLoc Loc;
  92 public:
  93   static MCFixup create(uint32_t Offset, const MCExpr *Value,
  94                         MCFixupKind Kind, SMLoc Loc = SMLoc()) {
  95     assert(Kind < MaxTargetFixupKind && "Kind out of range!");
  96     MCFixup FI;
  97     FI.Value = Value;
  98     FI.Offset = Offset;
  99     FI.Kind = Kind;
 100     FI.Loc = Loc;
 101     return FI;
 102   }
 103
 104   /// Return a fixup corresponding to the add half of a add/sub fixup pair for
 105   /// the given Fixup.
 106   static MCFixup createAddFor(const MCFixup &Fixup) {
 107     MCFixup FI;
 108     FI.Value = Fixup.getValue();
 109     FI.Offset = Fixup.getOffset();
 110     FI.Kind = getAddKindForKind(Fixup.getKind());
 111     FI.Loc = Fixup.getLoc();
 112     return FI;
 113   }
 114
 115   /// Return a fixup corresponding to the sub half of a add/sub fixup pair for
 116   /// the given Fixup.
 117   static MCFixup createSubFor(const MCFixup &Fixup) {
 118     MCFixup FI;
 119     FI.Value = Fixup.getValue();
 120     FI.Offset = Fixup.getOffset();
 121     FI.Kind = getSubKindForKind(Fixup.getKind());
 122     FI.Loc = Fixup.getLoc();
 123     return FI;
 124   }
 125
 126   MCFixupKind getKind() const { return Kind; }
 127
 128   unsigned getTargetKind() const { return Kind; }
 129
 130   uint32_t getOffset() const { return Offset; }
 131   void setOffset(uint32_t Value) { Offset = Value; }
 132
 133   const MCExpr *getValue() const { return Value; }
 134
 135   /// Return the generic fixup kind for a value with the given size. It
 136   /// is an error to pass an unsupported size.
 137   static MCFixupKind getKindForSize(unsigned Size, bool IsPCRel) {
 138     switch (Size) {
 139     default: llvm_unreachable("Invalid generic fixup size!");
 140     case 1:
 141       return IsPCRel ? FK_PCRel_1 : FK_Data_1;
 142     case 2:
 143       return IsPCRel ? FK_PCRel_2 : FK_Data_2;
 144     case 4:
 145       return IsPCRel ? FK_PCRel_4 : FK_Data_4;
 146     case 8:
 147       return IsPCRel ? FK_PCRel_8 : FK_Data_8;
 148     }
 149   }
 150
 151   /// Return the generic fixup kind for a value with the given size in bits.
 152   /// It is an error to pass an unsupported size.
 153   static MCFixupKind getKindForSizeInBits(unsigned Size, bool IsPCRel) {
 154     switch (Size) {
 155     default:
 156       llvm_unreachable("Invalid generic fixup size!");
 157     case 6:
 158       assert(!IsPCRel && "Invalid pc-relative fixup size!");
 159       return FK_Data_6b;
 160     case 8:
 161       return IsPCRel ? FK_PCRel_1 : FK_Data_1;
 162     case 16:
 163       return IsPCRel ? FK_PCRel_2 : FK_Data_2;
 164     case 32:
 165       return IsPCRel ? FK_PCRel_4 : FK_Data_4;
 166     case 64:
 167       return IsPCRel ? FK_PCRel_8 : FK_Data_8;
 168     }
 169   }
 170
 171   /// Return the generic fixup kind for an addition with a given size. It
 172   /// is an error to pass an unsupported size.
 173   static MCFixupKind getAddKindForKind(MCFixupKind Kind) {
 174     switch (Kind) {
 175     default: llvm_unreachable("Unknown type to convert!");
 176     case FK_Data_1: return FK_Data_Add_1;
 177     case FK_Data_2: return FK_Data_Add_2;
 178     case FK_Data_4: return FK_Data_Add_4;
 179     case FK_Data_8: return FK_Data_Add_8;
 180     case FK_Data_6b: return FK_Data_Add_6b;
 181     }
 182   }
 183
 184   /// Return the generic fixup kind for an subtraction with a given size. It
 185   /// is an error to pass an unsupported size.
 186   static MCFixupKind getSubKindForKind(MCFixupKind Kind) {
 187     switch (Kind) {
 188     default: llvm_unreachable("Unknown type to convert!");
 189     case FK_Data_1: return FK_Data_Sub_1;
 190     case FK_Data_2: return FK_Data_Sub_2;
 191     case FK_Data_4: return FK_Data_Sub_4;
 192     case FK_Data_8: return FK_Data_Sub_8;
 193     case FK_Data_6b: return FK_Data_Sub_6b;
 194     }
 195   }
 196
 197   SMLoc getLoc() const { return Loc; }
 198 };
 199
 200 } // End llvm namespace
 201
 202 #endif