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//===-- llvm/Target/TargetAsmBackend.h - Target Asm Backend -----*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_TARGET_TARGETASMBACKEND_H
#define LLVM_TARGET_TARGETASMBACKEND_H
#include "llvm/System/DataTypes.h"
namespace llvm {
class MCAsmFixup;
class MCDataFragment;
class MCInst;
class MCInstFragment;
class MCObjectWriter;
class MCSection;
template<typename T>
class SmallVectorImpl;
class Target;
class raw_ostream;
/// TargetAsmBackend - Generic interface to target specific assembler backends.
class TargetAsmBackend {
TargetAsmBackend(const TargetAsmBackend &); // DO NOT IMPLEMENT
void operator=(const TargetAsmBackend &); // DO NOT IMPLEMENT
protected: // Can only create subclasses.
TargetAsmBackend(const Target &);
/// TheTarget - The Target that this machine was created for.
const Target &TheTarget;
unsigned HasAbsolutizedSet : 1;
unsigned HasReliableSymbolDifference : 1;
unsigned HasScatteredSymbols : 1;
public:
virtual ~TargetAsmBackend();
const Target &getTarget() const { return TheTarget; }
/// createObjectWriter - Create a new MCObjectWriter instance for use by the
/// assembler backend to emit the final object file.
virtual MCObjectWriter *createObjectWriter(raw_ostream &OS) const = 0;
/// hasAbsolutizedSet - Check whether this target "absolutizes"
/// assignments. That is, given code like:
/// a:
/// ...
/// b:
/// tmp = a - b
/// .long tmp
/// will the value of 'tmp' be a relocatable expression, or the assembly time
/// value of L0 - L1. This distinction is only relevant for platforms that
/// support scattered symbols, since in the absence of scattered symbols (a -
/// b) cannot change after assembly.
bool hasAbsolutizedSet() const { return HasAbsolutizedSet; }
/// hasReliableSymbolDifference - Check whether this target implements
/// accurate relocations for differences between symbols. If not, differences
/// between symbols will always be relocatable expressions and any references
/// to temporary symbols will be assumed to be in the same atom, unless they
/// reside in a different section.
///
/// This should always be true (since it results in fewer relocations with no
/// loss of functionality), but is currently supported as a way to maintain
/// exact object compatibility with Darwin 'as' (on non-x86_64). It should
/// eventually should be eliminated. See also \see hasAbsolutizedSet.
bool hasReliableSymbolDifference() const {
return HasReliableSymbolDifference;
}
/// hasScatteredSymbols - Check whether this target supports scattered
/// symbols. If so, the assembler should assume that atoms can be scattered by
/// the linker. In particular, this means that the offsets between symbols
/// which are in distinct atoms is not known at link time, and the assembler
/// must generate fixups and relocations appropriately.
///
/// Note that the assembler currently does not reason about atoms, instead it
/// assumes all temporary symbols reside in the "current atom".
bool hasScatteredSymbols() const { return HasScatteredSymbols; }
/// doesSectionRequireSymbols - Check whether the given section requires that
/// all symbols (even temporaries) have symbol table entries.
virtual bool doesSectionRequireSymbols(const MCSection &Section) const {
return false;
}
/// isVirtualSection - Check whether the given section is "virtual", that is
/// has no actual object file contents.
virtual bool isVirtualSection(const MCSection &Section) const = 0;
/// ApplyFixup - Apply the \arg Value for given \arg Fixup into the provided
/// data fragment, at the offset specified by the fixup and following the
/// fixup kind as appropriate.
virtual void ApplyFixup(const MCAsmFixup &Fixup, MCDataFragment &Fragment,
uint64_t Value) const = 0;
/// MayNeedRelaxation - Check whether the given instruction may need
/// relaxation.
///
/// \arg Inst - The instruction to test.
/// \arg Fixups - The actual fixups this instruction encoded to, for potential
/// use by the target backend.
virtual bool MayNeedRelaxation(const MCInst &Inst,
const SmallVectorImpl<MCAsmFixup> &Fixups) const = 0;
/// RelaxInstruction - Relax the instruction in the given fragment to the next
/// wider instruction.
virtual void RelaxInstruction(const MCInstFragment *IF,
MCInst &Res) const = 0;
/// WriteNopData - Write an (optimal) nop sequence of Count bytes to the given
/// output. If the target cannot generate such a sequence, it should return an
/// error.
///
/// \return - True on success.
virtual bool WriteNopData(uint64_t Count, MCObjectWriter *OW) const = 0;
};
} // End llvm namespace
#endif
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