MCFixup.h revision 50bee42b54cd9aec5f49566307df2b0cf23afcf6 
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/Support/DataTypes.h"
14#include "llvm/Support/ErrorHandling.h"
15#include "llvm/Support/SMLoc.h"
16#include <cassert>
17
18namespace llvm {
19class MCExpr;
20
21/// MCFixupKind - Extensible enumeration to represent the type of a fixup.
22enum 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_SecRel_1,   ///< A one-byte section relative fixup.
36  FK_SecRel_2,   ///< A two-byte section relative fixup.
37  FK_SecRel_4,   ///< A four-byte section relative fixup.
38  FK_SecRel_8,   ///< A eight-byte section relative fixup.
39
40  FirstTargetFixupKind = 128,
41
42  // Limit range of target fixups, in case we want to pack more efficiently
43  // later.
44  MaxTargetFixupKind = (1 << 8)
45};
46
47/// MCFixup - Encode information on a single operation to perform on a byte
48/// sequence (e.g., an encoded instruction) which requires assemble- or run-
49/// time patching.
50///
51/// Fixups are used any time the target instruction encoder needs to represent
52/// some value in an instruction which is not yet concrete. The encoder will
53/// encode the instruction assuming the value is 0, and emit a fixup which
54/// communicates to the assembler backend how it should rewrite the encoded
55/// value.
56///
57/// During the process of relaxation, the assembler will apply fixups as
58/// symbolic values become concrete. When relaxation is complete, any remaining
59/// fixups become relocations in the object file (or errors, if the fixup cannot
60/// be encoded on the target).
61class MCFixup {
62  /// The value to put into the fixup location. The exact interpretation of the
63  /// expression is target dependent, usually it will be one of the operands to
64  /// an instruction or an assembler directive.
65  const MCExpr *Value;
66
67  /// The byte index of start of the relocation inside the encoded instruction.
68  uint32_t Offset;
69
70  /// The target dependent kind of fixup item this is. The kind is used to
71  /// determine how the operand value should be encoded into the instruction.
72  unsigned Kind;
73
74  /// The source location which gave rise to the fixup, if any.
75  SMLoc Loc;
76public:
77  static MCFixup Create(uint32_t Offset, const MCExpr *Value,
78                        MCFixupKind Kind, SMLoc Loc = SMLoc()) {
79    assert(unsigned(Kind) < MaxTargetFixupKind && "Kind out of range!");
80    MCFixup FI;
81    FI.Value = Value;
82    FI.Offset = Offset;
83    FI.Kind = unsigned(Kind);
84    FI.Loc = Loc;
85    return FI;
86  }
87
88  MCFixupKind getKind() const { return MCFixupKind(Kind); }
89
90  uint32_t getOffset() const { return Offset; }
91  void setOffset(uint32_t Value) { Offset = Value; }
92
93  const MCExpr *getValue() const { return Value; }
94
95  /// getKindForSize - Return the generic fixup kind for a value with the given
96  /// size. It is an error to pass an unsupported size.
97  static MCFixupKind getKindForSize(unsigned Size, bool isPCRel) {
98    switch (Size) {
99    default: llvm_unreachable("Invalid generic fixup size!");
100    case 1: return isPCRel ? FK_PCRel_1 : FK_Data_1;
101    case 2: return isPCRel ? FK_PCRel_2 : FK_Data_2;
102    case 4: return isPCRel ? FK_PCRel_4 : FK_Data_4;
103    case 8: return isPCRel ? FK_PCRel_8 : FK_Data_8;
104    }
105  }
106
107  SMLoc getLoc() const { return Loc; }
108};
109
110} // End llvm namespace
111
112#endif
113