| //===-- llvm/MC/MCFixup.h - Instruction Relocation and Patching -*- C++ -*-===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #ifndef LLVM_MC_MCFIXUP_H |
| #define LLVM_MC_MCFIXUP_H |
| |
| #include "llvm/Support/DataTypes.h" |
| #include <cassert> |
| |
| namespace llvm { |
| class MCExpr; |
| |
| /// MCFixupKind - Extensible enumeration to represent the type of a fixup. |
| enum MCFixupKind { |
| FK_Data_1 = 0, ///< A one-byte fixup. |
| FK_Data_2, ///< A two-byte fixup. |
| FK_Data_4, ///< A four-byte fixup. |
| FK_Data_8, ///< A eight-byte fixup. |
| FK_PCRel_1, ///< A one-byte pc relative fixup. |
| FK_PCRel_2, ///< A two-byte pc relative fixup. |
| FK_PCRel_4, ///< A four-byte pc relative fixup. |
| FK_PCRel_8, ///< A eight-byte pc relative fixup. |
| |
| FirstTargetFixupKind = 128, |
| |
| // Limit range of target fixups, in case we want to pack more efficiently |
| // later. |
| MaxTargetFixupKind = (1 << 8) |
| }; |
| |
| /// MCFixup - Encode information on a single operation to perform on a byte |
| /// sequence (e.g., an encoded instruction) which requires assemble- or run- |
| /// time patching. |
| /// |
| /// Fixups are used any time the target instruction encoder needs to represent |
| /// some value in an instruction which is not yet concrete. The encoder will |
| /// encode the instruction assuming the value is 0, and emit a fixup which |
| /// communicates to the assembler backend how it should rewrite the encoded |
| /// value. |
| /// |
| /// During the process of relaxation, the assembler will apply fixups as |
| /// symbolic values become concrete. When relaxation is complete, any remaining |
| /// fixups become relocations in the object file (or errors, if the fixup cannot |
| /// be encoded on the target). |
| class MCFixup { |
| /// The value to put into the fixup location. The exact interpretation of the |
| /// expression is target dependent, usually it will be one of the operands to |
| /// an instruction or an assembler directive. |
| const MCExpr *Value; |
| |
| /// The byte index of start of the relocation inside the encoded instruction. |
| uint32_t Offset; |
| |
| /// The target dependent kind of fixup item this is. The kind is used to |
| /// determine how the operand value should be encoded into the instruction. |
| unsigned Kind; |
| |
| public: |
| static MCFixup Create(uint32_t Offset, const MCExpr *Value, |
| MCFixupKind Kind) { |
| assert(unsigned(Kind) < MaxTargetFixupKind && "Kind out of range!"); |
| MCFixup FI; |
| FI.Value = Value; |
| FI.Offset = Offset; |
| FI.Kind = unsigned(Kind); |
| return FI; |
| } |
| |
| MCFixupKind getKind() const { return MCFixupKind(Kind); } |
| |
| uint32_t getOffset() const { return Offset; } |
| void setOffset(uint32_t Value) { Offset = Value; } |
| |
| const MCExpr *getValue() const { return Value; } |
| |
| /// getKindForSize - Return the generic fixup kind for a value with the given |
| /// size. It is an error to pass an unsupported size. |
| static MCFixupKind getKindForSize(unsigned Size, bool isPCRel) { |
| switch (Size) { |
| default: assert(0 && "Invalid generic fixup size!"); |
| case 1: return isPCRel ? FK_PCRel_1 : FK_Data_1; |
| case 2: return isPCRel ? FK_PCRel_2 : FK_Data_2; |
| case 4: return isPCRel ? FK_PCRel_4 : FK_Data_4; |
| case 8: return isPCRel ? FK_PCRel_8 : FK_Data_8; |
| } |
| } |
| }; |
| |
| } // End llvm namespace |
| |
| #endif |