MCFixup.h revision 82f4ce5081fc9cfbf34bbe61eb0412e7ca4dc3df 
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/SMLoc.h"
15#include <cassert>
16
17namespace llvm {
18class MCExpr;
19
20/// MCFixupKind - Extensible enumeration to represent the type of a fixup.
21enum MCFixupKind {
22  FK_Data_1 = 0, ///< A one-byte fixup.
23  FK_Data_2,     ///< A two-byte fixup.
24  FK_Data_4,     ///< A four-byte fixup.
25  FK_Data_8,     ///< A eight-byte fixup.
26  FK_PCRel_1,    ///< A one-byte pc relative fixup.
27  FK_PCRel_2,    ///< A two-byte pc relative fixup.
28  FK_PCRel_4,    ///< A four-byte pc relative fixup.
29  FK_PCRel_8,    ///< A eight-byte pc relative fixup.
30  FK_GPRel_1,    ///< A one-byte gp relative fixup.
31  FK_GPRel_2,    ///< A two-byte gp relative fixup.
32  FK_GPRel_4,    ///< A four-byte gp relative fixup.
33  FK_GPRel_8,    ///< A eight-byte gp relative fixup.
34  FK_SecRel_1,   ///< A one-byte section relative fixup.
35  FK_SecRel_2,   ///< A two-byte section relative fixup.
36  FK_SecRel_4,   ///< A four-byte section relative fixup.
37  FK_SecRel_8,   ///< A eight-byte section relative fixup.
38
39  FirstTargetFixupKind = 128,
40
41  // Limit range of target fixups, in case we want to pack more efficiently
42  // later.
43  MaxTargetFixupKind = (1 << 8)
44};
45
46/// MCFixup - Encode information on a single operation to perform on a byte
47/// sequence (e.g., an encoded instruction) which requires assemble- or run-
48/// time patching.
49///
50/// Fixups are used any time the target instruction encoder needs to represent
51/// some value in an instruction which is not yet concrete. The encoder will
52/// encode the instruction assuming the value is 0, and emit a fixup which
53/// communicates to the assembler backend how it should rewrite the encoded
54/// value.
55///
56/// During the process of relaxation, the assembler will apply fixups as
57/// symbolic values become concrete. When relaxation is complete, any remaining
58/// fixups become relocations in the object file (or errors, if the fixup cannot
59/// be encoded on the target).
60class MCFixup {
61  /// The value to put into the fixup location. The exact interpretation of the
62  /// expression is target dependent, usually it will be one of the operands to
63  /// an instruction or an assembler directive.
64  const MCExpr *Value;
65
66  /// The byte index of start of the relocation inside the encoded instruction.
67  uint32_t Offset;
68
69  /// The target dependent kind of fixup item this is. The kind is used to
70  /// determine how the operand value should be encoded into the instruction.
71  unsigned Kind;
72
73  /// The source location which gave rise to the fixup, if any.
74  SMLoc Loc;
75public:
76  static MCFixup Create(uint32_t Offset, const MCExpr *Value,
77                        MCFixupKind Kind, SMLoc Loc = SMLoc()) {
78    assert(unsigned(Kind) < MaxTargetFixupKind && "Kind out of range!");
79    MCFixup FI;
80    FI.Value = Value;
81    FI.Offset = Offset;
82    FI.Kind = unsigned(Kind);
83    FI.Loc = Loc;
84    return FI;
85  }
86
87  MCFixupKind getKind() const { return MCFixupKind(Kind); }
88
89  uint32_t getOffset() const { return Offset; }
90  void setOffset(uint32_t Value) { Offset = Value; }
91
92  const MCExpr *getValue() const { return Value; }
93
94  /// getKindForSize - Return the generic fixup kind for a value with the given
95  /// size. It is an error to pass an unsupported size.
96  static MCFixupKind getKindForSize(unsigned Size, bool isPCRel) {
97    switch (Size) {
98    default: assert(0 && "Invalid generic fixup size!");
99    case 1: return isPCRel ? FK_PCRel_1 : FK_Data_1;
100    case 2: return isPCRel ? FK_PCRel_2 : FK_Data_2;
101    case 4: return isPCRel ? FK_PCRel_4 : FK_Data_4;
102    case 8: return isPCRel ? FK_PCRel_8 : FK_Data_8;
103    }
104  }
105
106  SMLoc getLoc() const { return Loc; }
107};
108
109} // End llvm namespace
110
111#endif
112