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 MCInstFragment;
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
40public:
41  virtual ~MCAsmBackend();
42
43  /// createObjectWriter - Create a new MCObjectWriter instance for use by the
44  /// assembler backend to emit the final object file.
45  virtual MCObjectWriter *createObjectWriter(raw_ostream &OS) const = 0;
46
47  /// createELFObjectTargetWriter - Create a new ELFObjectTargetWriter to enable
48  /// non-standard ELFObjectWriters.
49  virtual  MCELFObjectTargetWriter *createELFObjectTargetWriter() const {
50    llvm_unreachable("createELFObjectTargetWriter is not supported by asm "
51                     "backend");
52  }
53
54  /// hasReliableSymbolDifference - Check whether this target implements
55  /// accurate relocations for differences between symbols. If not, differences
56  /// between symbols will always be relocatable expressions and any references
57  /// to temporary symbols will be assumed to be in the same atom, unless they
58  /// reside in a different section.
59  ///
60  /// This should always be true (since it results in fewer relocations with no
61  /// loss of functionality), but is currently supported as a way to maintain
62  /// exact object compatibility with Darwin 'as' (on non-x86_64). It should
63  /// eventually should be eliminated.
64  bool hasReliableSymbolDifference() const {
65    return HasReliableSymbolDifference;
66  }
67
68  /// doesSectionRequireSymbols - Check whether the given section requires that
69  /// all symbols (even temporaries) have symbol table entries.
70  virtual bool doesSectionRequireSymbols(const MCSection &Section) const {
71    return false;
72  }
73
74  /// isSectionAtomizable - Check whether the given section can be split into
75  /// atoms.
76  ///
77  /// \see MCAssembler::isSymbolLinkerVisible().
78  virtual bool isSectionAtomizable(const MCSection &Section) const {
79    return true;
80  }
81
82  /// @name Target Fixup Interfaces
83  /// @{
84
85  /// getNumFixupKinds - Get the number of target specific fixup kinds.
86  virtual unsigned getNumFixupKinds() const = 0;
87
88  /// getFixupKindInfo - Get information on a fixup kind.
89  virtual const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const;
90
91  /// processFixupValue - Target hook to adjust the literal value of a fixup
92  /// if necessary. IsResolved signals whether the caller believes a relocation
93  /// is needed; the target can modify the value. The default does nothing.
94  virtual void processFixupValue(const MCAssembler &Asm,
95                                 const MCAsmLayout &Layout,
96                                 const MCFixup &Fixup, const MCFragment *DF,
97                                 MCValue &Target, uint64_t &Value,
98                                 bool &IsResolved) {}
99
100  /// @}
101
102  /// applyFixup - Apply the \arg Value for given \arg Fixup into the provided
103  /// data fragment, at the offset specified by the fixup and following the
104  /// fixup kind as appropriate.
105  virtual void applyFixup(const MCFixup &Fixup, char *Data, unsigned DataSize,
106                          uint64_t Value) const = 0;
107
108  /// @}
109
110  /// @name Target Relaxation Interfaces
111  /// @{
112
113  /// mayNeedRelaxation - Check whether the given instruction may need
114  /// relaxation.
115  ///
116  /// \param Inst - The instruction to test.
117  virtual bool mayNeedRelaxation(const MCInst &Inst) const = 0;
118
119  /// fixupNeedsRelaxation - Target specific predicate for whether a given
120  /// fixup requires the associated instruction to be relaxed.
121  virtual bool fixupNeedsRelaxation(const MCFixup &Fixup,
122                                    uint64_t Value,
123                                    const MCInstFragment *DF,
124                                    const MCAsmLayout &Layout) const = 0;
125
126  /// RelaxInstruction - Relax the instruction in the given fragment to the next
127  /// wider instruction.
128  ///
129  /// \param Inst - The instruction to relax, which may be the same as the
130  /// output.
131  /// \parm Res [output] - On return, the relaxed instruction.
132  virtual void relaxInstruction(const MCInst &Inst, MCInst &Res) const = 0;
133
134  /// @}
135
136  /// getMinimumNopSize - Returns the minimum size of a nop in bytes on this
137  /// target. The assembler will use this to emit excess padding in situations
138  /// where the padding required for simple alignment would be less than the
139  /// minimum nop size.
140  ///
141  virtual unsigned getMinimumNopSize() const { return 1; }
142
143  /// writeNopData - Write an (optimal) nop sequence of Count bytes to the given
144  /// output. If the target cannot generate such a sequence, it should return an
145  /// error.
146  ///
147  /// \return - True on success.
148  virtual bool writeNopData(uint64_t Count, MCObjectWriter *OW) const = 0;
149
150  /// handleAssemblerFlag - Handle any target-specific assembler flags.
151  /// By default, do nothing.
152  virtual void handleAssemblerFlag(MCAssemblerFlag Flag) {}
153};
154
155} // End llvm namespace
156
157#endif
158