MCAsmBackend.h revision c3cee57f7d20f69a84fd88464ed8cf050e63c7ad 
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 HasReliableSymbolDifference : 1;
42  unsigned HasDataInCodeSupport : 1;
43
44public:
45  virtual ~MCAsmBackend();
46
47  /// lifetime management
48  virtual void reset() {}
49
50  /// createObjectWriter - Create a new MCObjectWriter instance for use by the
51  /// assembler backend to emit the final object file.
52  virtual MCObjectWriter *createObjectWriter(raw_ostream &OS) const = 0;
53
54  /// createELFObjectTargetWriter - Create a new ELFObjectTargetWriter to enable
55  /// non-standard ELFObjectWriters.
56  virtual MCELFObjectTargetWriter *createELFObjectTargetWriter() const {
57    llvm_unreachable("createELFObjectTargetWriter is not supported by asm "
58                     "backend");
59  }
60
61  /// hasReliableSymbolDifference - Check whether this target implements
62  /// accurate relocations for differences between symbols. If not, differences
63  /// between symbols will always be relocatable expressions and any references
64  /// to temporary symbols will be assumed to be in the same atom, unless they
65  /// reside in a different section.
66  ///
67  /// This should always be true (since it results in fewer relocations with no
68  /// loss of functionality), but is currently supported as a way to maintain
69  /// exact object compatibility with Darwin 'as' (on non-x86_64). It should
70  /// eventually should be eliminated.
71  bool hasReliableSymbolDifference() const {
72    return HasReliableSymbolDifference;
73  }
74
75  /// hasDataInCodeSupport - Check whether this target implements data-in-code
76  /// markers. If not, data region directives will be ignored.
77  bool hasDataInCodeSupport() const { return HasDataInCodeSupport; }
78
79  /// doesSectionRequireSymbols - Check whether the given section requires that
80  /// all symbols (even temporaries) have symbol table entries.
81  virtual bool doesSectionRequireSymbols(const MCSection &Section) const {
82    return false;
83  }
84
85  /// isSectionAtomizable - Check whether the given section can be split into
86  /// atoms.
87  ///
88  /// \see MCAssembler::isSymbolLinkerVisible().
89  virtual bool isSectionAtomizable(const MCSection &Section) const {
90    return true;
91  }
92
93  /// @name Target Fixup Interfaces
94  /// @{
95
96  /// getNumFixupKinds - Get the number of target specific fixup kinds.
97  virtual unsigned getNumFixupKinds() const = 0;
98
99  /// getFixupKindInfo - Get information on a fixup kind.
100  virtual const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const;
101
102  /// processFixupValue - Target hook to adjust the literal value of a fixup
103  /// if necessary. IsResolved signals whether the caller believes a relocation
104  /// is needed; the target can modify the value. The default does nothing.
105  virtual void processFixupValue(const MCAssembler &Asm,
106                                 const MCAsmLayout &Layout,
107                                 const MCFixup &Fixup, const MCFragment *DF,
108                                 MCValue &Target, uint64_t &Value,
109                                 bool &IsResolved) {}
110
111  /// @}
112
113  /// applyFixup - Apply the \p Value for given \p Fixup into the provided
114  /// data fragment, at the offset specified by the fixup and following the
115  /// fixup kind as appropriate.
116  virtual void applyFixup(const MCFixup &Fixup, char *Data, unsigned DataSize,
117                          uint64_t Value) const = 0;
118
119  /// @}
120
121  /// @name Target Relaxation Interfaces
122  /// @{
123
124  /// mayNeedRelaxation - Check whether the given instruction may need
125  /// relaxation.
126  ///
127  /// \param Inst - The instruction to test.
128  virtual bool mayNeedRelaxation(const MCInst &Inst) const = 0;
129
130  /// fixupNeedsRelaxation - Target specific predicate for whether a given
131  /// fixup requires the associated instruction to be relaxed.
132  virtual bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,
133                                    const MCRelaxableFragment *DF,
134                                    const MCAsmLayout &Layout) const = 0;
135
136  /// RelaxInstruction - Relax the instruction in the given fragment to the next
137  /// wider instruction.
138  ///
139  /// \param Inst The instruction to relax, which may be the same as the
140  /// output.
141  /// \param [out] Res On return, the relaxed instruction.
142  virtual void relaxInstruction(const MCInst &Inst, MCInst &Res) const = 0;
143
144  /// @}
145
146  /// getMinimumNopSize - Returns the minimum size of a nop in bytes on this
147  /// target. The assembler will use this to emit excess padding in situations
148  /// where the padding required for simple alignment would be less than the
149  /// minimum nop size.
150  ///
151  virtual unsigned getMinimumNopSize() const { return 1; }
152
153  /// writeNopData - Write an (optimal) nop sequence of Count bytes to the given
154  /// output. If the target cannot generate such a sequence, it should return an
155  /// error.
156  ///
157  /// \return - True on success.
158  virtual bool writeNopData(uint64_t Count, MCObjectWriter *OW) const = 0;
159
160  /// handleAssemblerFlag - Handle any target-specific assembler flags.
161  /// By default, do nothing.
162  virtual void handleAssemblerFlag(MCAssemblerFlag Flag) {}
163
164  /// \brief Generate the compact unwind encoding for the CFI instructions.
165  virtual unsigned
166  generateCompactUnwindEncoding(ArrayRef<MCCFIInstruction>) const {
167    return 0;
168  }
169};
170
171} // End llvm namespace
172
173#endif
174