MCAsmBackend.h revision 251040bc18eedfa56d01fe92836e55cfd8c5d990 
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/MC/MCDirectives.h"
14#include "llvm/MC/MCFixup.h"
15#include "llvm/Support/DataTypes.h"
16#include "llvm/Support/ErrorHandling.h"
17
18namespace llvm {
19class MCAsmLayout;
20class MCAssembler;
21class MCELFObjectTargetWriter;
22struct MCFixupKindInfo;
23class MCFragment;
24class MCInst;
25class MCRelaxableFragment;
26class MCObjectWriter;
27class MCSection;
28class MCValue;
29class raw_ostream;
30
31/// MCAsmBackend - Generic interface to target specific assembler backends.
32class MCAsmBackend {
33  MCAsmBackend(const MCAsmBackend &) LLVM_DELETED_FUNCTION;
34  void operator=(const MCAsmBackend &) LLVM_DELETED_FUNCTION;
35protected: // Can only create subclasses.
36  MCAsmBackend();
37
38  unsigned HasReliableSymbolDifference : 1;
39  unsigned HasDataInCodeSupport : 1;
40
41public:
42  virtual ~MCAsmBackend();
43
44  /// lifetime management
45  virtual void reset() { }
46
47  /// createObjectWriter - Create a new MCObjectWriter instance for use by the
48  /// assembler backend to emit the final object file.
49  virtual MCObjectWriter *createObjectWriter(raw_ostream &OS) const = 0;
50
51  /// createELFObjectTargetWriter - Create a new ELFObjectTargetWriter to enable
52  /// non-standard ELFObjectWriters.
53  virtual  MCELFObjectTargetWriter *createELFObjectTargetWriter() const {
54    llvm_unreachable("createELFObjectTargetWriter is not supported by asm "
55                     "backend");
56  }
57
58  /// hasReliableSymbolDifference - Check whether this target implements
59  /// accurate relocations for differences between symbols. If not, differences
60  /// between symbols will always be relocatable expressions and any references
61  /// to temporary symbols will be assumed to be in the same atom, unless they
62  /// reside in a different section.
63  ///
64  /// This should always be true (since it results in fewer relocations with no
65  /// loss of functionality), but is currently supported as a way to maintain
66  /// exact object compatibility with Darwin 'as' (on non-x86_64). It should
67  /// eventually should be eliminated.
68  bool hasReliableSymbolDifference() const {
69    return HasReliableSymbolDifference;
70  }
71
72  /// hasDataInCodeSupport - Check whether this target implements data-in-code
73  /// markers. If not, data region directives will be ignored.
74  bool hasDataInCodeSupport() const {
75    return HasDataInCodeSupport;
76  }
77
78  /// doesSectionRequireSymbols - Check whether the given section requires that
79  /// all symbols (even temporaries) have symbol table entries.
80  virtual bool doesSectionRequireSymbols(const MCSection &Section) const {
81    return false;
82  }
83
84  /// isSectionAtomizable - Check whether the given section can be split into
85  /// atoms.
86  ///
87  /// \see MCAssembler::isSymbolLinkerVisible().
88  virtual bool isSectionAtomizable(const MCSection &Section) const {
89    return true;
90  }
91
92  /// @name Target Fixup Interfaces
93  /// @{
94
95  /// getNumFixupKinds - Get the number of target specific fixup kinds.
96  virtual unsigned getNumFixupKinds() const = 0;
97
98  /// getFixupKindInfo - Get information on a fixup kind.
99  virtual const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const;
100
101  /// processFixupValue - Target hook to adjust the literal value of a fixup
102  /// if necessary. IsResolved signals whether the caller believes a relocation
103  /// is needed; the target can modify the value. The default does nothing.
104  virtual void processFixupValue(const MCAssembler &Asm,
105                                 const MCAsmLayout &Layout,
106                                 const MCFixup &Fixup, const MCFragment *DF,
107                                 MCValue &Target, uint64_t &Value,
108                                 bool &IsResolved) {}
109
110  /// @}
111
112  /// applyFixup - Apply the \p Value for given \p Fixup into the provided
113  /// data fragment, at the offset specified by the fixup and following the
114  /// fixup kind as appropriate.
115  virtual void applyFixup(const MCFixup &Fixup, char *Data, unsigned DataSize,
116                          uint64_t Value) const = 0;
117
118  /// @}
119
120  /// @name Target Relaxation Interfaces
121  /// @{
122
123  /// mayNeedRelaxation - Check whether the given instruction may need
124  /// relaxation.
125  ///
126  /// \param Inst - The instruction to test.
127  virtual bool mayNeedRelaxation(const MCInst &Inst) const = 0;
128
129  /// fixupNeedsRelaxation - Target specific predicate for whether a given
130  /// fixup requires the associated instruction to be relaxed.
131  virtual bool fixupNeedsRelaxation(const MCFixup &Fixup,
132                                    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
165} // End llvm namespace
166
167#endif
168