1 //===-- llvm/MC/MCMachObjectWriter.h - Mach Object Writer -------*- 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_MCMACHOBJECTWRITER_H
11 #define LLVM_MC_MCMACHOBJECTWRITER_H
12 
13 #include "llvm/ADT/DenseMap.h"
14 #include "llvm/ADT/SmallString.h"
15 #include "llvm/MC/MCExpr.h"
16 #include "llvm/MC/MCObjectWriter.h"
17 #include "llvm/MC/StringTableBuilder.h"
18 #include "llvm/Support/DataTypes.h"
19 #include "llvm/Support/MachO.h"
20 #include <vector>
21 
22 namespace llvm {
23 
24 class MachObjectWriter;
25 
26 class MCMachObjectTargetWriter {
27   const unsigned Is64Bit : 1;
28   const uint32_t CPUType;
29   const uint32_t CPUSubtype;
30   unsigned LocalDifference_RIT;
31 
32 protected:
33   MCMachObjectTargetWriter(bool Is64Bit_, uint32_t CPUType_,
34                            uint32_t CPUSubtype_);
35 
setLocalDifferenceRelocationType(unsigned Type)36   void setLocalDifferenceRelocationType(unsigned Type) {
37     LocalDifference_RIT = Type;
38   }
39 
40 public:
41   virtual ~MCMachObjectTargetWriter();
42 
43   /// \name Lifetime Management
44   /// @{
45 
reset()46   virtual void reset() {}
47 
48   /// @}
49 
50   /// \name Accessors
51   /// @{
52 
is64Bit()53   bool is64Bit() const { return Is64Bit; }
getCPUType()54   uint32_t getCPUType() const { return CPUType; }
getCPUSubtype()55   uint32_t getCPUSubtype() const { return CPUSubtype; }
getLocalDifferenceRelocationType()56   unsigned getLocalDifferenceRelocationType() const {
57     return LocalDifference_RIT;
58   }
59 
60   /// @}
61 
62   /// \name API
63   /// @{
64 
65   virtual void recordRelocation(MachObjectWriter *Writer, MCAssembler &Asm,
66                                 const MCAsmLayout &Layout,
67                                 const MCFragment *Fragment,
68                                 const MCFixup &Fixup, MCValue Target,
69                                 uint64_t &FixedValue) = 0;
70 
71   /// @}
72 };
73 
74 class MachObjectWriter : public MCObjectWriter {
75   /// Helper struct for containing some precomputed information on symbols.
76   struct MachSymbolData {
77     const MCSymbol *Symbol;
78     uint64_t StringIndex;
79     uint8_t SectionIndex;
80 
81     // Support lexicographic sorting.
82     bool operator<(const MachSymbolData &RHS) const;
83   };
84 
85   /// The target specific Mach-O writer instance.
86   std::unique_ptr<MCMachObjectTargetWriter> TargetObjectWriter;
87 
88   /// \name Relocation Data
89   /// @{
90 
91   struct RelAndSymbol {
92     const MCSymbol *Sym;
93     MachO::any_relocation_info MRE;
RelAndSymbolRelAndSymbol94     RelAndSymbol(const MCSymbol *Sym, const MachO::any_relocation_info &MRE)
95         : Sym(Sym), MRE(MRE) {}
96   };
97 
98   llvm::DenseMap<const MCSection *, std::vector<RelAndSymbol>> Relocations;
99   llvm::DenseMap<const MCSection *, unsigned> IndirectSymBase;
100 
101   SectionAddrMap SectionAddress;
102 
103   /// @}
104   /// \name Symbol Table Data
105   /// @{
106 
107   StringTableBuilder StringTable{StringTableBuilder::MachO};
108   std::vector<MachSymbolData> LocalSymbolData;
109   std::vector<MachSymbolData> ExternalSymbolData;
110   std::vector<MachSymbolData> UndefinedSymbolData;
111 
112   /// @}
113 
114   MachSymbolData *findSymbolData(const MCSymbol &Sym);
115 
116 public:
MachObjectWriter(MCMachObjectTargetWriter * MOTW,raw_pwrite_stream & OS,bool IsLittleEndian)117   MachObjectWriter(MCMachObjectTargetWriter *MOTW, raw_pwrite_stream &OS,
118                    bool IsLittleEndian)
119       : MCObjectWriter(OS, IsLittleEndian), TargetObjectWriter(MOTW) {}
120 
121   const MCSymbol &findAliasedSymbol(const MCSymbol &Sym) const;
122 
123   /// \name Lifetime management Methods
124   /// @{
125 
126   void reset() override;
127 
128   /// @}
129 
130   /// \name Utility Methods
131   /// @{
132 
133   bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind);
134 
getSectionAddressMap()135   SectionAddrMap &getSectionAddressMap() { return SectionAddress; }
136 
getSectionAddress(const MCSection * Sec)137   uint64_t getSectionAddress(const MCSection *Sec) const {
138     return SectionAddress.lookup(Sec);
139   }
140   uint64_t getSymbolAddress(const MCSymbol &S, const MCAsmLayout &Layout) const;
141 
142   uint64_t getFragmentAddress(const MCFragment *Fragment,
143                               const MCAsmLayout &Layout) const;
144 
145   uint64_t getPaddingSize(const MCSection *SD, const MCAsmLayout &Layout) const;
146 
147   bool doesSymbolRequireExternRelocation(const MCSymbol &S);
148 
149   /// @}
150 
151   /// \name Target Writer Proxy Accessors
152   /// @{
153 
is64Bit()154   bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
isX86_64()155   bool isX86_64() const {
156     uint32_t CPUType = TargetObjectWriter->getCPUType();
157     return CPUType == MachO::CPU_TYPE_X86_64;
158   }
159 
160   /// @}
161 
162   void writeHeader(MachO::HeaderFileType Type, unsigned NumLoadCommands,
163                    unsigned LoadCommandsSize, bool SubsectionsViaSymbols);
164 
165   /// Write a segment load command.
166   ///
167   /// \param NumSections The number of sections in this segment.
168   /// \param SectionDataSize The total size of the sections.
169   void writeSegmentLoadCommand(StringRef Name, unsigned NumSections,
170                                uint64_t VMAddr, uint64_t VMSize,
171                                uint64_t SectionDataStartOffset,
172                                uint64_t SectionDataSize, uint32_t MaxProt,
173                                uint32_t InitProt);
174 
175   void writeSection(const MCAsmLayout &Layout, const MCSection &Sec,
176                     uint64_t VMAddr, uint64_t FileOffset, unsigned Flags,
177                     uint64_t RelocationsStart, unsigned NumRelocations);
178 
179   void writeSymtabLoadCommand(uint32_t SymbolOffset, uint32_t NumSymbols,
180                               uint32_t StringTableOffset,
181                               uint32_t StringTableSize);
182 
183   void writeDysymtabLoadCommand(
184       uint32_t FirstLocalSymbol, uint32_t NumLocalSymbols,
185       uint32_t FirstExternalSymbol, uint32_t NumExternalSymbols,
186       uint32_t FirstUndefinedSymbol, uint32_t NumUndefinedSymbols,
187       uint32_t IndirectSymbolOffset, uint32_t NumIndirectSymbols);
188 
189   void writeNlist(MachSymbolData &MSD, const MCAsmLayout &Layout);
190 
191   void writeLinkeditLoadCommand(uint32_t Type, uint32_t DataOffset,
192                                 uint32_t DataSize);
193 
194   void writeLinkerOptionsLoadCommand(const std::vector<std::string> &Options);
195 
196   // FIXME: We really need to improve the relocation validation. Basically, we
197   // want to implement a separate computation which evaluates the relocation
198   // entry as the linker would, and verifies that the resultant fixup value is
199   // exactly what the encoder wanted. This will catch several classes of
200   // problems:
201   //
202   //  - Relocation entry bugs, the two algorithms are unlikely to have the same
203   //    exact bug.
204   //
205   //  - Relaxation issues, where we forget to relax something.
206   //
207   //  - Input errors, where something cannot be correctly encoded. 'as' allows
208   //    these through in many cases.
209 
210   // Add a relocation to be output in the object file. At the time this is
211   // called, the symbol indexes are not know, so if the relocation refers
212   // to a symbol it should be passed as \p RelSymbol so that it can be updated
213   // afterwards. If the relocation doesn't refer to a symbol, nullptr should be
214   // used.
addRelocation(const MCSymbol * RelSymbol,const MCSection * Sec,MachO::any_relocation_info & MRE)215   void addRelocation(const MCSymbol *RelSymbol, const MCSection *Sec,
216                      MachO::any_relocation_info &MRE) {
217     RelAndSymbol P(RelSymbol, MRE);
218     Relocations[Sec].push_back(P);
219   }
220 
221   void recordScatteredRelocation(const MCAssembler &Asm,
222                                  const MCAsmLayout &Layout,
223                                  const MCFragment *Fragment,
224                                  const MCFixup &Fixup, MCValue Target,
225                                  unsigned Log2Size, uint64_t &FixedValue);
226 
227   void recordTLVPRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout,
228                             const MCFragment *Fragment, const MCFixup &Fixup,
229                             MCValue Target, uint64_t &FixedValue);
230 
231   void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
232                         const MCFragment *Fragment, const MCFixup &Fixup,
233                         MCValue Target, bool &IsPCRel,
234                         uint64_t &FixedValue) override;
235 
236   void bindIndirectSymbols(MCAssembler &Asm);
237 
238   /// Compute the symbol table data.
239   void computeSymbolTable(MCAssembler &Asm,
240                           std::vector<MachSymbolData> &LocalSymbolData,
241                           std::vector<MachSymbolData> &ExternalSymbolData,
242                           std::vector<MachSymbolData> &UndefinedSymbolData);
243 
244   void computeSectionAddresses(const MCAssembler &Asm,
245                                const MCAsmLayout &Layout);
246 
247   void executePostLayoutBinding(MCAssembler &Asm,
248                                 const MCAsmLayout &Layout) override;
249 
250   bool isSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
251                                               const MCSymbol &A,
252                                               const MCSymbol &B,
253                                               bool InSet) const override;
254 
255   bool isSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
256                                               const MCSymbol &SymA,
257                                               const MCFragment &FB, bool InSet,
258                                               bool IsPCRel) const override;
259 
260   void writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
261 };
262 
263 /// Construct a new Mach-O writer instance.
264 ///
265 /// This routine takes ownership of the target writer subclass.
266 ///
267 /// \param MOTW - The target specific Mach-O writer subclass.
268 /// \param OS - The stream to write to.
269 /// \returns The constructed object writer.
270 MCObjectWriter *createMachObjectWriter(MCMachObjectTargetWriter *MOTW,
271                                        raw_pwrite_stream &OS,
272                                        bool IsLittleEndian);
273 
274 } // End llvm namespace
275 
276 #endif
277