xref: /freebsd/contrib/llvm-project/llvm/include/llvm/MC/MCFixup.h (revision 5f757f3ff9144b609b3c433dfd370cc6bdc191ad)
1 //===-- llvm/MC/MCFixup.h - Instruction Relocation and Patching -*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #ifndef LLVM_MC_MCFIXUP_H
10 #define LLVM_MC_MCFIXUP_H
11 
12 #include "llvm/Support/DataTypes.h"
13 #include "llvm/Support/ErrorHandling.h"
14 #include "llvm/Support/SMLoc.h"
15 #include <cassert>
16 
17 namespace llvm {
18 class MCExpr;
19 
20 /// Extensible enumeration to represent the type of a fixup.
21 enum MCFixupKind {
22   FK_NONE = 0,    ///< A no-op fixup.
23   FK_Data_1,      ///< 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_Data_leb128, ///< A leb128 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_DTPRel_4,    ///< A four-byte dtp relative fixup.
37   FK_DTPRel_8,    ///< A eight-byte dtp relative fixup.
38   FK_TPRel_4,     ///< A four-byte tp relative fixup.
39   FK_TPRel_8,     ///< A eight-byte tp relative fixup.
40   FK_SecRel_1,    ///< A one-byte section relative fixup.
41   FK_SecRel_2,    ///< A two-byte section relative fixup.
42   FK_SecRel_4,    ///< A four-byte section relative fixup.
43   FK_SecRel_8,    ///< A eight-byte section relative fixup.
44 
45   FirstTargetFixupKind = 128,
46 
47   /// The range [FirstLiteralRelocationKind, MaxTargetFixupKind) is used for
48   /// relocations coming from .reloc directive. Fixup kind
49   /// FirstLiteralRelocationKind+V represents the relocation type with number V.
50   FirstLiteralRelocationKind = 256,
51 
52   /// Set limit to accommodate the highest reloc type in use for all Targets,
53   /// currently R_AARCH64_IRELATIVE at 1032, including room for expansion.
54   MaxFixupKind = FirstLiteralRelocationKind + 1032 + 32,
55 };
56 
57 /// Encode information on a single operation to perform on a byte
58 /// sequence (e.g., an encoded instruction) which requires assemble- or run-
59 /// time patching.
60 ///
61 /// Fixups are used any time the target instruction encoder needs to represent
62 /// some value in an instruction which is not yet concrete. The encoder will
63 /// encode the instruction assuming the value is 0, and emit a fixup which
64 /// communicates to the assembler backend how it should rewrite the encoded
65 /// value.
66 ///
67 /// During the process of relaxation, the assembler will apply fixups as
68 /// symbolic values become concrete. When relaxation is complete, any remaining
69 /// fixups become relocations in the object file (or errors, if the fixup cannot
70 /// be encoded on the target).
71 class MCFixup {
72   /// The value to put into the fixup location. The exact interpretation of the
73   /// expression is target dependent, usually it will be one of the operands to
74   /// an instruction or an assembler directive.
75   const MCExpr *Value = nullptr;
76 
77   /// The byte index of start of the relocation inside the MCFragment.
78   uint32_t Offset = 0;
79 
80   /// The target dependent kind of fixup item this is. The kind is used to
81   /// determine how the operand value should be encoded into the instruction.
82   MCFixupKind Kind = FK_NONE;
83 
84   /// The source location which gave rise to the fixup, if any.
85   SMLoc Loc;
86 public:
87   static MCFixup create(uint32_t Offset, const MCExpr *Value,
88                         MCFixupKind Kind, SMLoc Loc = SMLoc()) {
89     assert(Kind <= MaxFixupKind && "Kind out of range!");
90     MCFixup FI;
91     FI.Value = Value;
92     FI.Offset = Offset;
93     FI.Kind = Kind;
94     FI.Loc = Loc;
95     return FI;
96   }
97 
98   MCFixupKind getKind() const { return Kind; }
99 
100   unsigned getTargetKind() const { return Kind; }
101 
102   uint32_t getOffset() const { return Offset; }
103   void setOffset(uint32_t Value) { Offset = Value; }
104 
105   const MCExpr *getValue() const { return Value; }
106 
107   /// Return the generic fixup kind for a value with the given size. It
108   /// is an error to pass an unsupported size.
109   static MCFixupKind getKindForSize(unsigned Size, bool IsPCRel) {
110     switch (Size) {
111     default: llvm_unreachable("Invalid generic fixup size!");
112     case 1:
113       return IsPCRel ? FK_PCRel_1 : FK_Data_1;
114     case 2:
115       return IsPCRel ? FK_PCRel_2 : FK_Data_2;
116     case 4:
117       return IsPCRel ? FK_PCRel_4 : FK_Data_4;
118     case 8:
119       return IsPCRel ? FK_PCRel_8 : FK_Data_8;
120     }
121   }
122 
123   SMLoc getLoc() const { return Loc; }
124 };
125 
126 } // End llvm namespace
127 
128 #endif
129