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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 <cassert>
namespace llvm {
// Private constants, do not use.
//
// This is currently layed out so that the MCFixup fields can be efficiently
// accessed, while keeping the offset field large enought that the assembler
// backend can reasonably use the MCFixup representation for an entire fragment
// (splitting any overly large fragments).
//
// The division of bits between the kind and the opindex can be tweaked if we
// end up needing more bits for target dependent kinds.
enum {
MCFIXUP_NUM_GENERIC_KINDS = 128,
MCFIXUP_NUM_KIND_BITS = 8,
MCFIXUP_NUM_OPINDEX_BITS = 8,
MCFIXUP_NUM_OFFSET_BITS = (32 - MCFIXUP_NUM_OPINDEX_BITS -
MCFIXUP_NUM_OPINDEX_BITS)
};
/// 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.
FirstTargetFixupKind = MCFIXUP_NUM_GENERIC_KINDS,
MaxTargetFixupKind = (1 << MCFIXUP_NUM_KIND_BITS)
};
/// MCFixup - Encode information on a single operation to perform on an 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 {
static const unsigned MaxOffset = 1 << MCFIXUP_NUM_KIND_BITS;
/// The byte index of start of the relocation inside the encoded instruction.
unsigned Offset : MCFIXUP_NUM_OFFSET_BITS;
/// The index of the operand to encode into the instruction.
unsigned OpIndex : MCFIXUP_NUM_OPINDEX_BITS;
/// 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 : MCFIXUP_NUM_KIND_BITS;
public:
static MCFixup Create(unsigned Offset, unsigned OpIndex, MCFixupKind Kind) {
MCFixup FI;
FI.Offset = Offset;
FI.OpIndex = OpIndex;
FI.Kind = unsigned(Kind);
assert(Offset == FI.Offset && "Offset out of range!");
assert(OpIndex == FI.OpIndex && "Operand index out of range!");
assert(Kind == FI.Kind && "Kind out of range!");
return FI;
}
unsigned getOffset() const { return Offset; }
unsigned getOpIndex() const { return OpIndex; }
MCFixupKind getKind() const { return MCFixupKind(Kind); }
};
} // End llvm namespace
#endif
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