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/Support/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.
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.
29 FirstTargetFixupKind = 128,
31 // Limit range of target fixups, in case we want to pack more efficiently
33 MaxTargetFixupKind = (1 << 8)
36 /// MCFixup - Encode information on a single operation to perform on a byte
37 /// sequence (e.g., an encoded instruction) which requires assemble- or run-
40 /// Fixups are used any time the target instruction encoder needs to represent
41 /// some value in an instruction which is not yet concrete. The encoder will
42 /// encode the instruction assuming the value is 0, and emit a fixup which
43 /// communicates to the assembler backend how it should rewrite the encoded
46 /// During the process of relaxation, the assembler will apply fixups as
47 /// symbolic values become concrete. When relaxation is complete, any remaining
48 /// fixups become relocations in the object file (or errors, if the fixup cannot
49 /// be encoded on the target).
51 /// The value to put into the fixup location. The exact interpretation of the
52 /// expression is target dependent, usually it will be one of the operands to
53 /// an instruction or an assembler directive.
56 /// The byte index of start of the relocation inside the encoded instruction.
59 /// The target dependent kind of fixup item this is. The kind is used to
60 /// determine how the operand value should be encoded into the instruction.
64 static MCFixup Create(uint32_t Offset, const MCExpr *Value,
66 assert(unsigned(Kind) < MaxTargetFixupKind && "Kind out of range!");
70 FI.Kind = unsigned(Kind);
74 MCFixupKind getKind() const { return MCFixupKind(Kind); }
76 uint32_t getOffset() const { return Offset; }
77 void setOffset(uint32_t Value) { Offset = Value; }
79 const MCExpr *getValue() const { return Value; }
81 /// getKindForSize - Return the generic fixup kind for a value with the given
82 /// size. It is an error to pass an unsupported size.
83 static MCFixupKind getKindForSize(unsigned Size, bool isPCRel) {
85 default: assert(0 && "Invalid generic fixup size!");
86 case 1: return isPCRel ? FK_PCRel_1 : FK_Data_1;
87 case 2: return isPCRel ? FK_PCRel_2 : FK_Data_2;
88 case 4: return isPCRel ? FK_PCRel_4 : FK_Data_4;
90 assert(!isPCRel && "8 byte pc relative fixup is not supported.");
96 } // End llvm namespace