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//===-- 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.
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:
assert(!isPCRel && "8 byte pc relative fixup is not supported.");
return FK_Data_8;
}
}
};
} // End llvm namespace
#endif
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