1 //===-- llvm/MC/MCFixup.h - Instruction Relocation and Patching -*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 #ifndef LLVM_MC_MCFIXUP_H
11 #define LLVM_MC_MCFIXUP_H
13 #include "llvm/System/DataTypes.h"
19 /// MCFixupKind - Extensible enumeration to represent the type of a fixup.
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.
26 FirstTargetFixupKind = 128,
28 // Limit range of target fixups, in case we want to pack more efficiently
30 MaxTargetFixupKind = (1 << 8)
33 /// MCFixup - Encode information on a single operation to perform on a byte
34 /// sequence (e.g., an encoded instruction) which requires assemble- or run-
37 /// Fixups are used any time the target instruction encoder needs to represent
38 /// some value in an instruction which is not yet concrete. The encoder will
39 /// encode the instruction assuming the value is 0, and emit a fixup which
40 /// communicates to the assembler backend how it should rewrite the encoded
43 /// During the process of relaxation, the assembler will apply fixups as
44 /// symbolic values become concrete. When relaxation is complete, any remaining
45 /// fixups become relocations in the object file (or errors, if the fixup cannot
46 /// be encoded on the target).
48 /// The value to put into the fixup location. The exact interpretation of the
49 /// expression is target dependent, usually it will be one of the operands to
50 /// an instruction or an assembler directive.
53 /// The byte index of start of the relocation inside the encoded instruction.
56 /// The target dependent kind of fixup item this is. The kind is used to
57 /// determine how the operand value should be encoded into the instruction.
61 static MCFixup Create(uint32_t Offset, const MCExpr *Value,
63 assert(unsigned(Kind) < MaxTargetFixupKind && "Kind out of range!");
67 FI.Kind = unsigned(Kind);
71 MCFixupKind getKind() const { return MCFixupKind(Kind); }
73 uint32_t getOffset() const { return Offset; }
74 void setOffset(uint32_t Value) { Offset = Value; }
76 const MCExpr *getValue() const { return Value; }
78 /// getKindForSize - Return the generic fixup kind for a value with the given
79 /// size. It is an error to pass an unsupported size.
80 static MCFixupKind getKindForSize(unsigned Size) {
82 default: assert(0 && "Invalid generic fixup size!");
83 case 1: return FK_Data_1;
84 case 2: return FK_Data_2;
85 case 4: return FK_Data_4;
86 case 8: return FK_Data_8;
91 } // End llvm namespace