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/MC/MCDirectives.h"
15#include "llvm/MC/MCDwarf.h"
16#include "llvm/MC/MCFixup.h"
17#include "llvm/Support/DataTypes.h"
18#include "llvm/Support/ErrorHandling.h"
19
20namespace llvm {
21class MCAsmLayout;
22class MCAssembler;
23class MCELFObjectTargetWriter;
24struct MCFixupKindInfo;
25class MCFragment;
26class MCInst;
27class MCRelaxableFragment;
28class MCObjectWriter;
29class MCSection;
30class MCValue;
31class raw_ostream;
32
33/// Generic interface to target specific assembler backends.
34class MCAsmBackend {
35  MCAsmBackend(const MCAsmBackend &) = delete;
36  void operator=(const MCAsmBackend &) = delete;
37
38protected: // Can only create subclasses.
39  MCAsmBackend();
40
41  unsigned HasDataInCodeSupport : 1;
42
43public:
44  virtual ~MCAsmBackend();
45
46  /// lifetime management
47  virtual void reset() {}
48
49  /// Create a new MCObjectWriter instance for use by the assembler backend to
50  /// emit the final object file.
51  virtual MCObjectWriter *createObjectWriter(raw_pwrite_stream &OS) const = 0;
52
53  /// Create a new ELFObjectTargetWriter to enable non-standard
54  /// ELFObjectWriters.
55  virtual MCELFObjectTargetWriter *createELFObjectTargetWriter() const {
56    llvm_unreachable("createELFObjectTargetWriter is not supported by asm "
57                     "backend");
58  }
59
60  /// Check whether this target implements data-in-code markers. If not, data
61  /// region directives will be ignored.
62  bool hasDataInCodeSupport() const { return HasDataInCodeSupport; }
63
64  /// @name Target Fixup Interfaces
65  /// @{
66
67  /// Get the number of target specific fixup kinds.
68  virtual unsigned getNumFixupKinds() const = 0;
69
70  /// Get information on a fixup kind.
71  virtual const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const;
72
73  /// Target hook to adjust the literal value of a fixup if necessary.
74  /// IsResolved signals whether the caller believes a relocation is needed; the
75  /// target can modify the value. The default does nothing.
76  virtual void processFixupValue(const MCAssembler &Asm,
77                                 const MCAsmLayout &Layout,
78                                 const MCFixup &Fixup, const MCFragment *DF,
79                                 const MCValue &Target, uint64_t &Value,
80                                 bool &IsResolved) {}
81
82  /// Apply the \p Value for given \p Fixup into the provided data fragment, at
83  /// the offset specified by the fixup and following the fixup kind as
84  /// appropriate.
85  virtual void applyFixup(const MCFixup &Fixup, char *Data, unsigned DataSize,
86                          uint64_t Value, bool IsPCRel) const = 0;
87
88  /// @}
89
90  /// @name Target Relaxation Interfaces
91  /// @{
92
93  /// Check whether the given instruction may need relaxation.
94  ///
95  /// \param Inst - The instruction to test.
96  virtual bool mayNeedRelaxation(const MCInst &Inst) const = 0;
97
98  /// Target specific predicate for whether a given fixup requires the
99  /// associated instruction to be relaxed.
100  virtual bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,
101                                    const MCRelaxableFragment *DF,
102                                    const MCAsmLayout &Layout) const = 0;
103
104  /// Relax the instruction in the given fragment to the next wider instruction.
105  ///
106  /// \param Inst The instruction to relax, which may be the same as the
107  /// output.
108  /// \param [out] Res On return, the relaxed instruction.
109  virtual void relaxInstruction(const MCInst &Inst, MCInst &Res) const = 0;
110
111  /// @}
112
113  /// Returns the minimum size of a nop in bytes on this target. The assembler
114  /// will use this to emit excess padding in situations where the padding
115  /// required for simple alignment would be less than the minimum nop size.
116  ///
117  virtual unsigned getMinimumNopSize() const { return 1; }
118
119  /// Write an (optimal) nop sequence of Count bytes to the given output. If the
120  /// target cannot generate such a sequence, it should return an error.
121  ///
122  /// \return - True on success.
123  virtual bool writeNopData(uint64_t Count, MCObjectWriter *OW) const = 0;
124
125  /// Handle any target-specific assembler flags. By default, do nothing.
126  virtual void handleAssemblerFlag(MCAssemblerFlag Flag) {}
127
128  /// \brief Generate the compact unwind encoding for the CFI instructions.
129  virtual uint32_t
130      generateCompactUnwindEncoding(ArrayRef<MCCFIInstruction>) const {
131    return 0;
132  }
133};
134
135} // End llvm namespace
136
137#endif
138