1 //===-- llvm/MC/MCAsmBackend.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 
20 namespace llvm {
21 class MCAsmLayout;
22 class MCAssembler;
23 class MCELFObjectTargetWriter;
24 struct MCFixupKindInfo;
25 class MCFragment;
26 class MCInst;
27 class MCRelaxableFragment;
28 class MCObjectWriter;
29 class MCSection;
30 class MCValue;
31 class raw_ostream;
32 
33 /// Generic interface to target specific assembler backends.
34 class MCAsmBackend {
35   MCAsmBackend(const MCAsmBackend &) = delete;
36   void operator=(const MCAsmBackend &) = delete;
37 
38 protected: // Can only create subclasses.
39   MCAsmBackend();
40 
41   unsigned HasDataInCodeSupport : 1;
42 
43 public:
44   virtual ~MCAsmBackend();
45 
46   /// lifetime management
reset()47   virtual void reset() {}
48 
49   /// Create a new MCObjectWriter instance for use by the assembler backend to
50   /// emit the final object file.
51   virtual MCObjectWriter *createObjectWriter(raw_pwrite_stream &OS) const = 0;
52 
53   /// Create a new ELFObjectTargetWriter to enable non-standard
54   /// ELFObjectWriters.
createELFObjectTargetWriter()55   virtual MCELFObjectTargetWriter *createELFObjectTargetWriter() const {
56     llvm_unreachable("createELFObjectTargetWriter is not supported by asm "
57                      "backend");
58   }
59 
60   /// Check whether this target implements data-in-code markers. If not, data
61   /// region directives will be ignored.
hasDataInCodeSupport()62   bool hasDataInCodeSupport() const { return HasDataInCodeSupport; }
63 
64   /// @name Target Fixup Interfaces
65   /// @{
66 
67   /// Get the number of target specific fixup kinds.
68   virtual unsigned getNumFixupKinds() const = 0;
69 
70   /// Get information on a fixup kind.
71   virtual const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const;
72 
73   /// Target hook to adjust the literal value of a fixup if necessary.
74   /// IsResolved signals whether the caller believes a relocation is needed; the
75   /// target can modify the value. The default does nothing.
processFixupValue(const MCAssembler & Asm,const MCAsmLayout & Layout,const MCFixup & Fixup,const MCFragment * DF,const MCValue & Target,uint64_t & Value,bool & IsResolved)76   virtual void processFixupValue(const MCAssembler &Asm,
77                                  const MCAsmLayout &Layout,
78                                  const MCFixup &Fixup, const MCFragment *DF,
79                                  const MCValue &Target, uint64_t &Value,
80                                  bool &IsResolved) {}
81 
82   /// Apply the \p Value for given \p Fixup into the provided data fragment, at
83   /// the offset specified by the fixup and following the fixup kind as
84   /// appropriate.
85   virtual void applyFixup(const MCFixup &Fixup, char *Data, unsigned DataSize,
86                           uint64_t Value, bool IsPCRel) const = 0;
87 
88   /// @}
89 
90   /// @name Target Relaxation Interfaces
91   /// @{
92 
93   /// Check whether the given instruction may need relaxation.
94   ///
95   /// \param Inst - The instruction to test.
96   virtual bool mayNeedRelaxation(const MCInst &Inst) const = 0;
97 
98   /// Target specific predicate for whether a given fixup requires the
99   /// associated instruction to be relaxed.
100   virtual bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,
101                                     const MCRelaxableFragment *DF,
102                                     const MCAsmLayout &Layout) const = 0;
103 
104   /// Relax the instruction in the given fragment to the next wider instruction.
105   ///
106   /// \param Inst The instruction to relax, which may be the same as the
107   /// output.
108   /// \param [out] Res On return, the relaxed instruction.
109   virtual void relaxInstruction(const MCInst &Inst, MCInst &Res) const = 0;
110 
111   /// @}
112 
113   /// Returns the minimum size of a nop in bytes on this target. The assembler
114   /// will use this to emit excess padding in situations where the padding
115   /// required for simple alignment would be less than the minimum nop size.
116   ///
getMinimumNopSize()117   virtual unsigned getMinimumNopSize() const { return 1; }
118 
119   /// Write an (optimal) nop sequence of Count bytes to the given output. If the
120   /// target cannot generate such a sequence, it should return an error.
121   ///
122   /// \return - True on success.
123   virtual bool writeNopData(uint64_t Count, MCObjectWriter *OW) const = 0;
124 
125   /// Handle any target-specific assembler flags. By default, do nothing.
handleAssemblerFlag(MCAssemblerFlag Flag)126   virtual void handleAssemblerFlag(MCAssemblerFlag Flag) {}
127 
128   /// \brief Generate the compact unwind encoding for the CFI instructions.
129   virtual uint32_t
generateCompactUnwindEncoding(ArrayRef<MCCFIInstruction>)130       generateCompactUnwindEncoding(ArrayRef<MCCFIInstruction>) const {
131     return 0;
132   }
133 };
134 
135 } // End llvm namespace
136 
137 #endif
138