MCAsmBackend.h revision 78c10eeaa57d1c6c4b7781d3c0bcb0cfbbc43b5c 
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/MC/MCFixupKindInfo.h"
16#include "llvm/Support/DataTypes.h"
17
18namespace llvm {
19class MCELFObjectTargetWriter;
20class MCFixup;
21class MCInst;
22class MCObjectWriter;
23class MCSection;
24template<typename T>
25class SmallVectorImpl;
26class raw_ostream;
27
28/// MCAsmBackend - Generic interface to target specific assembler backends.
29class MCAsmBackend {
30  MCAsmBackend(const MCAsmBackend &);   // DO NOT IMPLEMENT
31  void operator=(const MCAsmBackend &);  // DO NOT IMPLEMENT
32protected: // Can only create subclasses.
33  MCAsmBackend();
34
35  unsigned HasReliableSymbolDifference : 1;
36
37public:
38  virtual ~MCAsmBackend();
39
40  /// createObjectWriter - Create a new MCObjectWriter instance for use by the
41  /// assembler backend to emit the final object file.
42  virtual MCObjectWriter *createObjectWriter(raw_ostream &OS) const = 0;
43
44  /// createELFObjectTargetWriter - Create a new ELFObjectTargetWriter to enable
45  /// non-standard ELFObjectWriters.
46  virtual  MCELFObjectTargetWriter *createELFObjectTargetWriter() const {
47    assert(0 && "createELFObjectTargetWriter is not supported by asm backend");
48    return 0;
49  }
50
51  /// hasReliableSymbolDifference - Check whether this target implements
52  /// accurate relocations for differences between symbols. If not, differences
53  /// between symbols will always be relocatable expressions and any references
54  /// to temporary symbols will be assumed to be in the same atom, unless they
55  /// reside in a different section.
56  ///
57  /// This should always be true (since it results in fewer relocations with no
58  /// loss of functionality), but is currently supported as a way to maintain
59  /// exact object compatibility with Darwin 'as' (on non-x86_64). It should
60  /// eventually should be eliminated.
61  bool hasReliableSymbolDifference() const {
62    return HasReliableSymbolDifference;
63  }
64
65  /// doesSectionRequireSymbols - Check whether the given section requires that
66  /// all symbols (even temporaries) have symbol table entries.
67  virtual bool doesSectionRequireSymbols(const MCSection &Section) const {
68    return false;
69  }
70
71  /// isSectionAtomizable - Check whether the given section can be split into
72  /// atoms.
73  ///
74  /// \see MCAssembler::isSymbolLinkerVisible().
75  virtual bool isSectionAtomizable(const MCSection &Section) const {
76    return true;
77  }
78
79  /// @name Target Fixup Interfaces
80  /// @{
81
82  /// getNumFixupKinds - Get the number of target specific fixup kinds.
83  virtual unsigned getNumFixupKinds() const = 0;
84
85  /// getFixupKindInfo - Get information on a fixup kind.
86  virtual const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const;
87
88  /// @}
89
90  /// ApplyFixup - Apply the \arg Value for given \arg Fixup into the provided
91  /// data fragment, at the offset specified by the fixup and following the
92  /// fixup kind as appropriate.
93  virtual void ApplyFixup(const MCFixup &Fixup, char *Data, unsigned DataSize,
94                          uint64_t Value) const = 0;
95
96  /// @}
97
98  /// @name Target Relaxation Interfaces
99  /// @{
100
101  /// MayNeedRelaxation - Check whether the given instruction may need
102  /// relaxation.
103  ///
104  /// \param Inst - The instruction to test.
105  virtual bool MayNeedRelaxation(const MCInst &Inst) const = 0;
106
107  /// RelaxInstruction - Relax the instruction in the given fragment to the next
108  /// wider instruction.
109  ///
110  /// \param Inst - The instruction to relax, which may be the same as the
111  /// output.
112  /// \parm Res [output] - On return, the relaxed instruction.
113  virtual void RelaxInstruction(const MCInst &Inst, MCInst &Res) const = 0;
114
115  /// @}
116
117  /// WriteNopData - Write an (optimal) nop sequence of Count bytes to the given
118  /// output. If the target cannot generate such a sequence, it should return an
119  /// error.
120  ///
121  /// \return - True on success.
122  virtual bool WriteNopData(uint64_t Count, MCObjectWriter *OW) const = 0;
123
124  /// HandleAssemblerFlag - Handle any target-specific assembler flags.
125  /// By default, do nothing.
126  virtual void HandleAssemblerFlag(MCAssemblerFlag Flag) {}
127};
128
129} // End llvm namespace
130
131#endif
132