LLVM  3.7.0
MCFixup.h
Go to the documentation of this file.
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"
16 #include "llvm/Support/SMLoc.h"
17 #include <cassert>
18 
19 namespace llvm {
20 class MCExpr;
21 
22 /// \brief Extensible enumeration to represent the type of a fixup.
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 
42 
43  // Limit range of target fixups, in case we want to pack more efficiently
44  // later.
45  MaxTargetFixupKind = (1 << 8)
46 };
47 
48 /// \brief 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  /// \brief Return the generic fixup kind for a value with the given size. It
97  /// 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
A eight-byte pc relative fixup.
Definition: MCFixup.h:31
SMLoc getLoc() const
Definition: MCFixup.h:108
static MCFixupKind getKindForSize(unsigned Size, bool isPCRel)
Return the generic fixup kind for a value with the given size.
Definition: MCFixup.h:98
Encode information on a single operation to perform on a byte sequence (e.g., an encoded instruction)...
Definition: MCFixup.h:62
A one-byte pc relative fixup.
Definition: MCFixup.h:28
#define llvm_unreachable(msg)
Marks that the current location is not supposed to be reachable.
Definition: ErrorHandling.h:98
Base class for the full range of assembler expressions which are needed for parsing.
Definition: MCExpr.h:33
A four-byte section relative fixup.
Definition: MCFixup.h:38
A four-byte fixup.
Definition: MCFixup.h:26
A four-byte gp relative fixup.
Definition: MCFixup.h:34
A two-byte section relative fixup.
Definition: MCFixup.h:37
uint32_t getOffset() const
Definition: MCFixup.h:91
const MCExpr * getValue() const
Definition: MCFixup.h:94
void setOffset(uint32_t Value)
Definition: MCFixup.h:92
MCFixupKind
Extensible enumeration to represent the type of a fixup.
Definition: MCFixup.h:23
MCFixupKind getKind() const
Definition: MCFixup.h:89
static MCFixup create(uint32_t Offset, const MCExpr *Value, MCFixupKind Kind, SMLoc Loc=SMLoc())
Definition: MCFixup.h:78
A one-byte fixup.
Definition: MCFixup.h:24
A two-byte pc relative fixup.
Definition: MCFixup.h:29
A four-byte pc relative fixup.
Definition: MCFixup.h:30
A two-byte gp relative fixup.
Definition: MCFixup.h:33
A one-byte section relative fixup.
Definition: MCFixup.h:36
A eight-byte gp relative fixup.
Definition: MCFixup.h:35
A eight-byte section relative fixup.
Definition: MCFixup.h:39
A eight-byte fixup.
Definition: MCFixup.h:27
A one-byte gp relative fixup.
Definition: MCFixup.h:32
LLVM Value Representation.
Definition: Value.h:69
Represents a location in source code.
Definition: SMLoc.h:23
A two-byte fixup.
Definition: MCFixup.h:25