1//===- llvm/MC/MCAsmBackend.h - MC Asm Backend ------------------*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9
10#ifndef LLVM_MC_MCASMBACKEND_H
11#define LLVM_MC_MCASMBACKEND_H
12
13#include "llvm/ADT/ArrayRef.h"
14#include "llvm/ADT/Optional.h"
15#include "llvm/ADT/StringRef.h"
16#include "llvm/MC/MCDirectives.h"
17#include "llvm/MC/MCFixup.h"
18#include <cstdint>
19
20namespace llvm {
21
22class MCAsmLayout;
23class MCAssembler;
24class MCCFIInstruction;
25struct MCFixupKindInfo;
26class MCFragment;
27class MCInst;
28class MCObjectWriter;
29class MCRelaxableFragment;
30class MCSubtargetInfo;
31class MCValue;
32class raw_pwrite_stream;
33
34/// Generic interface to target specific assembler backends.
35class MCAsmBackend {
36protected: // Can only create subclasses.
37  MCAsmBackend();
38
39public:
40  MCAsmBackend(const MCAsmBackend &) = delete;
41  MCAsmBackend &operator=(const MCAsmBackend &) = delete;
42  virtual ~MCAsmBackend();
43
44  /// lifetime management
45  virtual void reset() {}
46
47  /// Create a new MCObjectWriter instance for use by the assembler backend to
48  /// emit the final object file.
49  virtual std::unique_ptr<MCObjectWriter>
50  createObjectWriter(raw_pwrite_stream &OS) const = 0;
51
52  /// \name Target Fixup Interfaces
53  /// @{
54
55  /// Get the number of target specific fixup kinds.
56  virtual unsigned getNumFixupKinds() const = 0;
57
58  /// Map a relocation name used in .reloc to a fixup kind.
59  virtual Optional<MCFixupKind> getFixupKind(StringRef Name) const;
60
61  /// Get information on a fixup kind.
62  virtual const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const;
63
64  /// Hook to check if a relocation is needed for some target specific reason.
65  virtual bool shouldForceRelocation(const MCAssembler &Asm,
66                                     const MCFixup &Fixup,
67                                     const MCValue &Target) {
68    return false;
69  }
70
71  /// Apply the \p Value for given \p Fixup into the provided data fragment, at
72  /// the offset specified by the fixup and following the fixup kind as
73  /// appropriate. Errors (such as an out of range fixup value) should be
74  /// reported via \p Ctx.
75  virtual void applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
76                          const MCValue &Target, MutableArrayRef<char> Data,
77                          uint64_t Value, bool IsResolved) const = 0;
78
79  /// @}
80
81  /// \name Target Relaxation Interfaces
82  /// @{
83
84  /// Check whether the given instruction may need relaxation.
85  ///
86  /// \param Inst - The instruction to test.
87  virtual bool mayNeedRelaxation(const MCInst &Inst) const = 0;
88
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,
92                                            uint64_t Value,
93                                            const MCRelaxableFragment *DF,
94                                            const MCAsmLayout &Layout) const;
95
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;
100
101  /// Relax the instruction in the given fragment to the next wider instruction.
102  ///
103  /// \param Inst The instruction to relax, which may be the same as the
104  /// output.
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;
109
110  /// @}
111
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.
115  ///
116  virtual unsigned getMinimumNopSize() const { return 1; }
117
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.
120  ///
121  /// \return - True on success.
122  virtual bool writeNopData(uint64_t Count, MCObjectWriter *OW) const = 0;
123
124  /// Give backend an opportunity to finish layout after relaxation
125  virtual void finishLayout(MCAssembler const &Asm,
126                            MCAsmLayout &Layout) const {}
127
128  /// Handle any target-specific assembler flags. By default, do nothing.
129  virtual void handleAssemblerFlag(MCAssemblerFlag Flag) {}
130
131  /// \brief Generate the compact unwind encoding for the CFI instructions.
132  virtual uint32_t
133      generateCompactUnwindEncoding(ArrayRef<MCCFIInstruction>) const {
134    return 0;
135  }
136};
137
138} // end namespace llvm
139
140#endif // LLVM_MC_MCASMBACKEND_H
141