212 lines
7.5 KiB
C++
212 lines
7.5 KiB
C++
//===- 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/MC/MCDirectives.h"
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#include "llvm/MC/MCFixup.h"
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#include "llvm/Support/Compiler.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 MCFragment;
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class MCSymbol;
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class MCAssembler;
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class MCContext;
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struct MCDwarfFrameInfo;
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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 MCOperand;
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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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class raw_ostream;
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/// Target independent information on a fixup kind.
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struct MCFixupKindInfo {
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/// A target specific name for the fixup kind. The names will be unique for
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/// distinct kinds on any given target.
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const char *Name;
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/// The bit offset to write the relocation into.
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uint8_t TargetOffset;
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/// The number of bits written by this fixup. The bits are assumed to be
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/// contiguous.
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uint8_t TargetSize;
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/// Flags describing additional information on this fixup kind.
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unsigned Flags;
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};
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/// Generic interface to target specific assembler backends.
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class LLVM_ABI MCAsmBackend {
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protected: // Can only create subclasses.
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MCAsmBackend(llvm::endianness Endian) : Endian(Endian) {}
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MCAssembler *Asm = nullptr;
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bool AllowAutoPadding = false;
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bool AllowEnhancedRelaxation = false;
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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 llvm::endianness Endian;
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void setAssembler(MCAssembler *A) { Asm = A; }
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MCContext &getContext() const;
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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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bool allowAutoPadding() const { return AllowAutoPadding; }
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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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bool allowEnhancedRelaxation() const { return AllowEnhancedRelaxation; }
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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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/// Map a relocation name used in .reloc to a fixup kind.
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virtual std::optional<MCFixupKind> getFixupKind(StringRef Name) const;
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/// Get information on a fixup kind.
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virtual MCFixupKindInfo getFixupKindInfo(MCFixupKind Kind) const;
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// Evaluate a fixup, returning std::nullopt to use default handling for
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// `Value` and `IsResolved`. Otherwise, returns `IsResolved` with the
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// expectation that the hook updates `Value`.
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virtual std::optional<bool> evaluateFixup(const MCFragment &, MCFixup &,
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MCValue &, uint64_t &) {
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return {};
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}
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void maybeAddReloc(const MCFragment &, const MCFixup &, const MCValue &,
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uint64_t &Value, bool IsResolved);
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// Determine if a relocation is required. In addition, apply `Value` to the
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// `Data` fragment at the specified fixup offset if applicable. `Data` points
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// to the first byte of the fixup offset, which may be at the content's end if
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// the fixup is zero-sized.
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virtual void applyFixup(const MCFragment &, const MCFixup &,
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const MCValue &Target, uint8_t *Data, uint64_t Value,
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bool IsResolved) = 0;
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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 (encoded as Opcode+Operands) may need
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/// relaxation.
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virtual bool mayNeedRelaxation(unsigned Opcode, ArrayRef<MCOperand> Operands,
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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 MCFragment &, const MCFixup &,
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const MCValue &, uint64_t,
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bool Resolved) const;
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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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llvm_unreachable("Needed if fixupNeedsRelaxationAdvanced may return true");
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}
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// Defined by linker relaxation targets.
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// Return false to use default handling. Otherwise, set `Size` to the number
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// of padding bytes.
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virtual bool relaxAlign(MCFragment &F, unsigned &Size) { return false; }
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virtual bool relaxDwarfLineAddr(MCFragment &) const { return false; }
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virtual bool relaxDwarfCFA(MCFragment &) const { return false; }
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virtual bool relaxSFrameCFA(MCFragment &) const { return false; }
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// Defined by linker relaxation targets to possibly emit LEB128 relocations
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// and set Value at the relocated location.
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virtual std::pair<bool, bool> relaxLEB128(MCFragment &,
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int64_t &Value) const {
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return std::make_pair(false, false);
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}
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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 MCSubtargetInfo &STI) const {
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return 0;
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}
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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,
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const MCSubtargetInfo *STI) const = 0;
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// Return true if fragment offsets have been adjusted and an extra layout
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// iteration is needed.
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virtual bool finishLayout() const { return false; }
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/// Generate the compact unwind encoding for the CFI instructions.
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virtual uint64_t generateCompactUnwindEncoding(const MCDwarfFrameInfo *FI,
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const MCContext *Ctxt) const {
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return 0;
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}
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bool isDarwinCanonicalPersonality(const MCSymbol *Sym) const;
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// Return STI for fragments with hasInstructions() == true.
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static const MCSubtargetInfo *getSubtargetInfo(const MCFragment &F);
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};
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} // end namespace llvm
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#endif // LLVM_MC_MCASMBACKEND_H
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