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