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//===-- llvm/MC/MCAsmBack.h - MC 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_MC_MCASMBACKEND_H
#define LLVM_MC_MCASMBACKEND_H
#include "llvm/MC/MCDirectives.h"
#include "llvm/MC/MCFixup.h"
#include "llvm/Support/DataTypes.h"
#include "llvm/Support/ErrorHandling.h"
namespace llvm {
class MCAsmLayout;
class MCAssembler;
class MCELFObjectTargetWriter;
struct MCFixupKindInfo;
class MCFragment;
class MCInst;
class MCInstFragment;
class MCObjectWriter;
class MCSection;
class MCValue;
class raw_ostream;
/// MCAsmBackend - Generic interface to target specific assembler backends.
class MCAsmBackend {
MCAsmBackend(const MCAsmBackend &) LLVM_DELETED_FUNCTION;
void operator=(const MCAsmBackend &) LLVM_DELETED_FUNCTION;
protected: // Can only create subclasses.
MCAsmBackend();
unsigned HasReliableSymbolDifference : 1;
unsigned HasDataInCodeSupport : 1;
public:
virtual ~MCAsmBackend();
/// 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;
/// createELFObjectTargetWriter - Create a new ELFObjectTargetWriter to enable
/// non-standard ELFObjectWriters.
virtual MCELFObjectTargetWriter *createELFObjectTargetWriter() const {
llvm_unreachable("createELFObjectTargetWriter is not supported by asm "
"backend");
}
/// 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.
bool hasReliableSymbolDifference() const {
return HasReliableSymbolDifference;
}
/// hasDataInCodeSupport - Check whether this target implements data-in-code
/// markers. If not, data region directives will be ignored.
bool hasDataInCodeSupport() const {
return HasDataInCodeSupport;
}
/// 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;
}
/// isSectionAtomizable - Check whether the given section can be split into
/// atoms.
///
/// \see MCAssembler::isSymbolLinkerVisible().
virtual bool isSectionAtomizable(const MCSection &Section) const {
return true;
}
/// @name Target Fixup Interfaces
/// @{
/// getNumFixupKinds - Get the number of target specific fixup kinds.
virtual unsigned getNumFixupKinds() const = 0;
/// getFixupKindInfo - Get information on a fixup kind.
virtual const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const;
/// processFixupValue - Target hook to adjust the literal value of a fixup
/// if necessary. IsResolved signals whether the caller believes a relocation
/// is needed; the target can modify the value. The default does nothing.
virtual void processFixupValue(const MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCFixup &Fixup, const MCFragment *DF,
MCValue &Target, uint64_t &Value,
bool &IsResolved) {}
/// @}
/// applyFixup - Apply the \p Value for given \p Fixup into the provided
/// data fragment, at the offset specified by the fixup and following the
/// fixup kind as appropriate.
virtual void applyFixup(const MCFixup &Fixup, char *Data, unsigned DataSize,
uint64_t Value) const = 0;
/// @}
/// @name Target Relaxation Interfaces
/// @{
/// mayNeedRelaxation - Check whether the given instruction may need
/// relaxation.
///
/// \param Inst - The instruction to test.
virtual bool mayNeedRelaxation(const MCInst &Inst) const = 0;
/// fixupNeedsRelaxation - Target specific predicate for whether a given
/// fixup requires the associated instruction to be relaxed.
virtual bool fixupNeedsRelaxation(const MCFixup &Fixup,
uint64_t Value,
const MCInstFragment *DF,
const MCAsmLayout &Layout) const = 0;
/// RelaxInstruction - Relax the instruction in the given fragment to the next
/// wider instruction.
///
/// \param Inst The instruction to relax, which may be the same as the
/// output.
/// \param [out] Res On return, the relaxed instruction.
virtual void relaxInstruction(const MCInst &Inst, MCInst &Res) const = 0;
/// @}
/// getMinimumNopSize - Returns the minimum size of a nop in bytes on this
/// target. The assembler will use this to emit excess padding in situations
/// where the padding required for simple alignment would be less than the
/// minimum nop size.
///
virtual unsigned getMinimumNopSize() const { return 1; }
/// 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;
/// handleAssemblerFlag - Handle any target-specific assembler flags.
/// By default, do nothing.
virtual void handleAssemblerFlag(MCAssemblerFlag Flag) {}
};
} // End llvm namespace
#endif
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