212 lines
8.2 KiB
C
212 lines
8.2 KiB
C
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//===- llvm/MC/MCAsmBackend.h - MC Asm Backend ------------------*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_MC_MCASMBACKEND_H
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#define LLVM_MC_MCASMBACKEND_H
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#include "llvm/ADT/ArrayRef.h"
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#include "llvm/ADT/Optional.h"
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#include "llvm/MC/MCDirectives.h"
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#include "llvm/MC/MCFixup.h"
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#include "llvm/MC/MCFragment.h"
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#include "llvm/Support/Endian.h"
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#include <cstdint>
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namespace llvm {
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class MCAsmLayout;
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class MCAssembler;
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class MCCFIInstruction;
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struct MCFixupKindInfo;
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class MCInst;
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class MCObjectStreamer;
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class MCObjectTargetWriter;
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class MCObjectWriter;
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class MCSubtargetInfo;
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class MCValue;
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class raw_pwrite_stream;
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class StringRef;
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/// Generic interface to target specific assembler backends.
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class MCAsmBackend {
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protected: // Can only create subclasses.
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MCAsmBackend(support::endianness Endian);
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public:
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MCAsmBackend(const MCAsmBackend &) = delete;
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MCAsmBackend &operator=(const MCAsmBackend &) = delete;
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virtual ~MCAsmBackend();
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const support::endianness Endian;
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/// Return true if this target might automatically pad instructions and thus
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/// need to emit padding enable/disable directives around sensative code.
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virtual bool allowAutoPadding() const { return false; }
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/// Return true if this target allows an unrelaxable instruction to be
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/// emitted into RelaxableFragment and then we can increase its size in a
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/// tricky way for optimization.
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virtual bool allowEnhancedRelaxation() const { return false; }
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/// Give the target a chance to manipulate state related to instruction
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/// alignment (e.g. padding for optimization), instruction relaxablility, etc.
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/// before and after actually emitting the instruction.
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virtual void emitInstructionBegin(MCObjectStreamer &OS, const MCInst &Inst) {}
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virtual void emitInstructionEnd(MCObjectStreamer &OS, const MCInst &Inst) {}
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/// lifetime management
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virtual void reset() {}
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/// Create a new MCObjectWriter instance for use by the assembler backend to
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/// emit the final object file.
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std::unique_ptr<MCObjectWriter>
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createObjectWriter(raw_pwrite_stream &OS) const;
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/// Create an MCObjectWriter that writes two object files: a .o file which is
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/// linked into the final program and a .dwo file which is used by debuggers.
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/// This function is only supported with ELF targets.
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std::unique_ptr<MCObjectWriter>
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createDwoObjectWriter(raw_pwrite_stream &OS, raw_pwrite_stream &DwoOS) const;
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virtual std::unique_ptr<MCObjectTargetWriter>
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createObjectTargetWriter() const = 0;
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/// \name Target Fixup Interfaces
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/// @{
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/// Get the number of target specific fixup kinds.
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virtual unsigned getNumFixupKinds() const = 0;
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/// Map a relocation name used in .reloc to a fixup kind.
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virtual Optional<MCFixupKind> getFixupKind(StringRef Name) const;
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/// Get information on a fixup kind.
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virtual const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const;
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/// Hook to check if a relocation is needed for some target specific reason.
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virtual bool shouldForceRelocation(const MCAssembler &Asm,
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const MCFixup &Fixup,
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const MCValue &Target) {
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return false;
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}
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/// Hook to check if extra nop bytes must be inserted for alignment directive.
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/// For some targets this may be necessary in order to support linker
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/// relaxation. The number of bytes to insert are returned in Size.
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virtual bool shouldInsertExtraNopBytesForCodeAlign(const MCAlignFragment &AF,
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unsigned &Size) {
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return false;
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}
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/// Hook which indicates if the target requires a fixup to be generated when
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/// handling an align directive in an executable section
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virtual bool shouldInsertFixupForCodeAlign(MCAssembler &Asm,
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const MCAsmLayout &Layout,
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MCAlignFragment &AF) {
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return false;
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}
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virtual bool evaluateTargetFixup(const MCAssembler &Asm,
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const MCAsmLayout &Layout,
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const MCFixup &Fixup, const MCFragment *DF,
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const MCValue &Target, uint64_t &Value,
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bool &WasForced) {
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llvm_unreachable("Need to implement hook if target has custom fixups");
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}
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/// Apply the \p Value for given \p Fixup into the provided data fragment, at
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/// the offset specified by the fixup and following the fixup kind as
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/// appropriate. Errors (such as an out of range fixup value) should be
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/// reported via \p Ctx.
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/// The \p STI is present only for fragments of type MCRelaxableFragment and
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/// MCDataFragment with hasInstructions() == true.
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virtual void applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
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const MCValue &Target, MutableArrayRef<char> Data,
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uint64_t Value, bool IsResolved,
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const MCSubtargetInfo *STI) const = 0;
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/// Check whether the given target requires emitting differences of two
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/// symbols as a set of relocations.
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virtual bool requiresDiffExpressionRelocations() const { return false; }
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/// @}
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/// \name Target Relaxation Interfaces
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/// @{
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/// Check whether the given instruction may need relaxation.
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///
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/// \param Inst - The instruction to test.
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/// \param STI - The MCSubtargetInfo in effect when the instruction was
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/// encoded.
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virtual bool mayNeedRelaxation(const MCInst &Inst,
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const MCSubtargetInfo &STI) const {
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return false;
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}
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/// Target specific predicate for whether a given fixup requires the
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/// associated instruction to be relaxed.
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virtual bool fixupNeedsRelaxationAdvanced(const MCFixup &Fixup, bool Resolved,
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uint64_t Value,
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const MCRelaxableFragment *DF,
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const MCAsmLayout &Layout,
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const bool WasForced) const;
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/// Simple predicate for targets where !Resolved implies requiring relaxation
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virtual bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,
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const MCRelaxableFragment *DF,
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const MCAsmLayout &Layout) const = 0;
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/// Relax the instruction in the given fragment to the next wider instruction.
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///
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/// \param [out] Inst The instruction to relax, which is also the relaxed
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/// instruction.
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/// \param STI the subtarget information for the associated instruction.
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virtual void relaxInstruction(MCInst &Inst,
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const MCSubtargetInfo &STI) const {};
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/// @}
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/// Returns the minimum size of a nop in bytes on this target. The assembler
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/// will use this to emit excess padding in situations where the padding
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/// required for simple alignment would be less than the minimum nop size.
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///
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virtual unsigned getMinimumNopSize() const { return 1; }
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/// Returns the maximum size of a nop in bytes on this target.
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///
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virtual unsigned getMaximumNopSize() const { return 0; }
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/// Write an (optimal) nop sequence of Count bytes to the given output. If the
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/// target cannot generate such a sequence, it should return an error.
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///
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/// \return - True on success.
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virtual bool writeNopData(raw_ostream &OS, uint64_t Count) const = 0;
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/// Give backend an opportunity to finish layout after relaxation
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virtual void finishLayout(MCAssembler const &Asm,
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MCAsmLayout &Layout) const {}
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/// Handle any target-specific assembler flags. By default, do nothing.
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virtual void handleAssemblerFlag(MCAssemblerFlag Flag) {}
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/// Generate the compact unwind encoding for the CFI instructions.
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virtual uint32_t
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generateCompactUnwindEncoding(ArrayRef<MCCFIInstruction>) const {
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return 0;
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}
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/// Check whether a given symbol has been flagged with MICROMIPS flag.
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virtual bool isMicroMips(const MCSymbol *Sym) const {
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return false;
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}
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};
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} // end namespace llvm
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#endif // LLVM_MC_MCASMBACKEND_H
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