src/llvm/include/llvm/MC/MCFixup.h

   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
  19 namespace llvm {
  20 class MCExpr;
  21
  22 /// MCFixupKind - Extensible enumeration to represent the type of a fixup.
  23 enum 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 /// MCFixup - 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).
  62 class 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;
  77 public:
  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   /// getKindForSize - Return the generic fixup kind for a value with the given
  97   /// size. It 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