1//===-- llvm/MC/MCAsmBack.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/// MCAsmBackend - Generic interface to target specific assembler backends.
34class MCAsmBackend {
35  MCAsmBackend(const MCAsmBackend &) LLVM_DELETED_FUNCTION;
36  void operator=(const MCAsmBackend &) LLVM_DELETED_FUNCTION;
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  /// createObjectWriter - Create a new MCObjectWriter instance for use by the
50  /// assembler backend to emit the final object file.
51  virtual MCObjectWriter *createObjectWriter(raw_ostream &OS) const = 0;
52
53  /// createELFObjectTargetWriter - Create a new ELFObjectTargetWriter to enable
54  /// non-standard ELFObjectWriters.
55  virtual MCELFObjectTargetWriter *createELFObjectTargetWriter() const {
56    llvm_unreachable("createELFObjectTargetWriter is not supported by asm "
57                     "backend");
58  }
59
60  /// hasDataInCodeSupport - Check whether this target implements data-in-code
61  /// markers. If not, data region directives will be ignored.
62  bool hasDataInCodeSupport() const { return HasDataInCodeSupport; }
63
64  /// doesSectionRequireSymbols - Check whether the given section requires that
65  /// all symbols (even temporaries) have symbol table entries.
66  virtual bool doesSectionRequireSymbols(const MCSection &Section) const {
67    return false;
68  }
69
70  /// isSectionAtomizable - Check whether the given section can be split into
71  /// atoms.
72  ///
73  /// \see MCAssembler::isSymbolLinkerVisible().
74  virtual bool isSectionAtomizable(const MCSection &Section) const {
75    return true;
76  }
77
78  /// @name Target Fixup Interfaces
79  /// @{
80
81  /// getNumFixupKinds - Get the number of target specific fixup kinds.
82  virtual unsigned getNumFixupKinds() const = 0;
83
84  /// getFixupKindInfo - Get information on a fixup kind.
85  virtual const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const;
86
87  /// processFixupValue - Target hook to adjust the literal value of a fixup
88  /// if necessary. IsResolved signals whether the caller believes a relocation
89  /// is needed; the target can modify the value. The default does nothing.
90  virtual void processFixupValue(const MCAssembler &Asm,
91                                 const MCAsmLayout &Layout,
92                                 const MCFixup &Fixup, const MCFragment *DF,
93                                 const MCValue &Target, uint64_t &Value,
94                                 bool &IsResolved) {}
95
96  /// applyFixup - Apply the \p Value for given \p Fixup into the provided
97  /// data fragment, at the offset specified by the fixup and following the
98  /// fixup kind as appropriate.
99  virtual void applyFixup(const MCFixup &Fixup, char *Data, unsigned DataSize,
100                          uint64_t Value, bool IsPCRel) const = 0;
101
102  /// @}
103
104  /// @name Target Relaxation Interfaces
105  /// @{
106
107  /// mayNeedRelaxation - Check whether the given instruction may need
108  /// relaxation.
109  ///
110  /// \param Inst - The instruction to test.
111  virtual bool mayNeedRelaxation(const MCInst &Inst) const = 0;
112
113  /// fixupNeedsRelaxation - Target specific predicate for whether a given
114  /// fixup requires the associated instruction to be relaxed.
115  virtual bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,
116                                    const MCRelaxableFragment *DF,
117                                    const MCAsmLayout &Layout) const = 0;
118
119  /// RelaxInstruction - Relax the instruction in the given fragment to the next
120  /// wider instruction.
121  ///
122  /// \param Inst The instruction to relax, which may be the same as the
123  /// output.
124  /// \param [out] Res On return, the relaxed instruction.
125  virtual void relaxInstruction(const MCInst &Inst, MCInst &Res) const = 0;
126
127  /// @}
128
129  /// getMinimumNopSize - Returns the minimum size of a nop in bytes on this
130  /// target. The assembler will use this to emit excess padding in situations
131  /// where the padding required for simple alignment would be less than the
132  /// minimum nop size.
133  ///
134  virtual unsigned getMinimumNopSize() const { return 1; }
135
136  /// writeNopData - Write an (optimal) nop sequence of Count bytes to the given
137  /// output. If the target cannot generate such a sequence, it should return an
138  /// error.
139  ///
140  /// \return - True on success.
141  virtual bool writeNopData(uint64_t Count, MCObjectWriter *OW) const = 0;
142
143  /// handleAssemblerFlag - Handle any target-specific assembler flags.
144  /// By default, do nothing.
145  virtual void handleAssemblerFlag(MCAssemblerFlag Flag) {}
146
147  /// \brief Generate the compact unwind encoding for the CFI instructions.
148  virtual uint32_t
149  generateCompactUnwindEncoding(ArrayRef<MCCFIInstruction>) const {
150    return 0;
151  }
152};
153
154} // End llvm namespace
155
156#endif
157