1 //===-- llvm/MC/MCAsmBackend.h - MC Asm Backend -----------------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 #ifndef LLVM_MC_MCASMBACKEND_H
11 #define LLVM_MC_MCASMBACKEND_H
13 #include "llvm/ADT/ArrayRef.h"
14 #include "llvm/ADT/Optional.h"
15 #include "llvm/MC/MCDirectives.h"
16 #include "llvm/MC/MCDwarf.h"
17 #include "llvm/MC/MCFixup.h"
18 #include "llvm/Support/DataTypes.h"
19 #include "llvm/Support/ErrorHandling.h"
24 class MCELFObjectTargetWriter;
25 struct MCFixupKindInfo;
28 class MCRelaxableFragment;
32 class raw_pwrite_stream;
34 /// Generic interface to target specific assembler backends.
36 MCAsmBackend(const MCAsmBackend &) = delete;
37 void operator=(const MCAsmBackend &) = delete;
39 protected: // Can only create subclasses.
43 virtual ~MCAsmBackend();
45 /// lifetime management
46 virtual void reset() {}
48 /// Create a new MCObjectWriter instance for use by the assembler backend to
49 /// emit the final object file.
50 virtual MCObjectWriter *createObjectWriter(raw_pwrite_stream &OS) const = 0;
52 /// \name Target Fixup Interfaces
55 /// Get the number of target specific fixup kinds.
56 virtual unsigned getNumFixupKinds() const = 0;
58 /// Map a relocation name used in .reloc to a fixup kind.
59 virtual Optional<MCFixupKind> getFixupKind(StringRef Name) const;
61 /// Get information on a fixup kind.
62 virtual const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const;
64 /// Target hook to adjust the literal value of a fixup if necessary.
65 /// IsResolved signals whether the caller believes a relocation is needed; the
66 /// target can modify the value. The default does nothing.
67 virtual void processFixupValue(const MCAssembler &Asm,
68 const MCAsmLayout &Layout,
69 const MCFixup &Fixup, const MCFragment *DF,
70 const MCValue &Target, uint64_t &Value,
73 /// Apply the \p Value for given \p Fixup into the provided data fragment, at
74 /// the offset specified by the fixup and following the fixup kind as
76 virtual void applyFixup(const MCFixup &Fixup, char *Data, unsigned DataSize,
77 uint64_t Value, bool IsPCRel) const = 0;
81 /// \name Target Relaxation Interfaces
84 /// Check whether the given instruction may need relaxation.
86 /// \param Inst - The instruction to test.
87 virtual bool mayNeedRelaxation(const MCInst &Inst) const = 0;
89 /// Target specific predicate for whether a given fixup requires the
90 /// associated instruction to be relaxed.
91 virtual bool fixupNeedsRelaxationAdvanced(const MCFixup &Fixup, bool Resolved,
93 const MCRelaxableFragment *DF,
94 const MCAsmLayout &Layout) const;
96 /// Simple predicate for targets where !Resolved implies requiring relaxation
97 virtual bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,
98 const MCRelaxableFragment *DF,
99 const MCAsmLayout &Layout) const = 0;
101 /// Relax the instruction in the given fragment to the next wider instruction.
103 /// \param Inst The instruction to relax, which may be the same as the
105 /// \param STI the subtarget information for the associated instruction.
106 /// \param [out] Res On return, the relaxed instruction.
107 virtual void relaxInstruction(const MCInst &Inst, const MCSubtargetInfo &STI,
108 MCInst &Res) const = 0;
112 /// Returns the minimum size of a nop in bytes on this target. The assembler
113 /// will use this to emit excess padding in situations where the padding
114 /// required for simple alignment would be less than the minimum nop size.
116 virtual unsigned getMinimumNopSize() const { return 1; }
118 /// Write an (optimal) nop sequence of Count bytes to the given output. If the
119 /// target cannot generate such a sequence, it should return an error.
121 /// \return - True on success.
122 virtual bool writeNopData(uint64_t Count, MCObjectWriter *OW) const = 0;
124 /// Give backend an opportunity to finish layout after relaxation
125 virtual void finishLayout(MCAssembler const &Asm,
126 MCAsmLayout &Layout) const {}
128 /// Handle any target-specific assembler flags. By default, do nothing.
129 virtual void handleAssemblerFlag(MCAssemblerFlag Flag) {}
131 /// \brief Generate the compact unwind encoding for the CFI instructions.
133 generateCompactUnwindEncoding(ArrayRef<MCCFIInstruction>) const {
138 } // End llvm namespace