MCMachObjectWriter.h revision 360784 
1//===- llvm/MC/MCMachObjectWriter.h - Mach Object Writer --------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#ifndef LLVM_MC_MCMACHOBJECTWRITER_H
10#define LLVM_MC_MCMACHOBJECTWRITER_H
11
12#include "llvm/ADT/DenseMap.h"
13#include "llvm/ADT/StringRef.h"
14#include "llvm/BinaryFormat/MachO.h"
15#include "llvm/MC/MCExpr.h"
16#include "llvm/MC/MCObjectWriter.h"
17#include "llvm/MC/MCSection.h"
18#include "llvm/MC/StringTableBuilder.h"
19#include <cstdint>
20#include <memory>
21#include <string>
22#include <vector>
23
24namespace llvm {
25
26class MachObjectWriter;
27
28class MCMachObjectTargetWriter : public MCObjectTargetWriter {
29  const unsigned Is64Bit : 1;
30  const uint32_t CPUType;
31protected:
32  uint32_t CPUSubtype;
33public:
34  unsigned LocalDifference_RIT;
35
36protected:
37  MCMachObjectTargetWriter(bool Is64Bit_, uint32_t CPUType_,
38                           uint32_t CPUSubtype_);
39
40  void setLocalDifferenceRelocationType(unsigned Type) {
41    LocalDifference_RIT = Type;
42  }
43
44public:
45  virtual ~MCMachObjectTargetWriter();
46
47  virtual Triple::ObjectFormatType getFormat() const { return Triple::MachO; }
48  static bool classof(const MCObjectTargetWriter *W) {
49    return W->getFormat() == Triple::MachO;
50  }
51
52  /// \name Lifetime Management
53  /// @{
54
55  virtual void reset() {}
56
57  /// @}
58
59  /// \name Accessors
60  /// @{
61
62  bool is64Bit() const { return Is64Bit; }
63  uint32_t getCPUType() const { return CPUType; }
64  uint32_t getCPUSubtype() const { return CPUSubtype; }
65  unsigned getLocalDifferenceRelocationType() const {
66    return LocalDifference_RIT;
67  }
68
69  /// @}
70
71  /// \name API
72  /// @{
73
74  virtual void recordRelocation(MachObjectWriter *Writer, MCAssembler &Asm,
75                                const MCAsmLayout &Layout,
76                                const MCFragment *Fragment,
77                                const MCFixup &Fixup, MCValue Target,
78                                uint64_t &FixedValue) = 0;
79
80  /// @}
81};
82
83class MachObjectWriter : public MCObjectWriter {
84  /// Helper struct for containing some precomputed information on symbols.
85  struct MachSymbolData {
86    const MCSymbol *Symbol;
87    uint64_t StringIndex;
88    uint8_t SectionIndex;
89
90    // Support lexicographic sorting.
91    bool operator<(const MachSymbolData &RHS) const;
92  };
93
94  /// The target specific Mach-O writer instance.
95  std::unique_ptr<MCMachObjectTargetWriter> TargetObjectWriter;
96
97  /// \name Relocation Data
98  /// @{
99
100  struct RelAndSymbol {
101    const MCSymbol *Sym;
102    MachO::any_relocation_info MRE;
103    RelAndSymbol(const MCSymbol *Sym, const MachO::any_relocation_info &MRE)
104        : Sym(Sym), MRE(MRE) {}
105  };
106
107  DenseMap<const MCSection *, std::vector<RelAndSymbol>> Relocations;
108  DenseMap<const MCSection *, unsigned> IndirectSymBase;
109
110  SectionAddrMap SectionAddress;
111
112  /// @}
113  /// \name Symbol Table Data
114  /// @{
115
116  StringTableBuilder StringTable{StringTableBuilder::MachO};
117  std::vector<MachSymbolData> LocalSymbolData;
118  std::vector<MachSymbolData> ExternalSymbolData;
119  std::vector<MachSymbolData> UndefinedSymbolData;
120
121  /// @}
122
123  MachSymbolData *findSymbolData(const MCSymbol &Sym);
124
125  void writeWithPadding(StringRef Str, uint64_t Size);
126
127public:
128  MachObjectWriter(std::unique_ptr<MCMachObjectTargetWriter> MOTW,
129                   raw_pwrite_stream &OS, bool IsLittleEndian)
130      : TargetObjectWriter(std::move(MOTW)),
131        W(OS, IsLittleEndian ? support::little : support::big) {}
132
133  support::endian::Writer W;
134
135  const MCSymbol &findAliasedSymbol(const MCSymbol &Sym) const;
136
137  /// \name Lifetime management Methods
138  /// @{
139
140  void reset() override;
141
142  /// @}
143
144  /// \name Utility Methods
145  /// @{
146
147  bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind);
148
149  SectionAddrMap &getSectionAddressMap() { return SectionAddress; }
150
151  uint64_t getSectionAddress(const MCSection *Sec) const {
152    return SectionAddress.lookup(Sec);
153  }
154  uint64_t getSymbolAddress(const MCSymbol &S, const MCAsmLayout &Layout) const;
155
156  uint64_t getFragmentAddress(const MCFragment *Fragment,
157                              const MCAsmLayout &Layout) const;
158
159  uint64_t getPaddingSize(const MCSection *SD, const MCAsmLayout &Layout) const;
160
161  bool doesSymbolRequireExternRelocation(const MCSymbol &S);
162
163  /// @}
164
165  /// \name Target Writer Proxy Accessors
166  /// @{
167
168  bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
169  bool isX86_64() const {
170    uint32_t CPUType = TargetObjectWriter->getCPUType();
171    return CPUType == MachO::CPU_TYPE_X86_64;
172  }
173
174  /// @}
175
176  void writeHeader(MachO::HeaderFileType Type, unsigned NumLoadCommands,
177                   unsigned LoadCommandsSize, bool SubsectionsViaSymbols);
178
179  /// Write a segment load command.
180  ///
181  /// \param NumSections The number of sections in this segment.
182  /// \param SectionDataSize The total size of the sections.
183  void writeSegmentLoadCommand(StringRef Name, unsigned NumSections,
184                               uint64_t VMAddr, uint64_t VMSize,
185                               uint64_t SectionDataStartOffset,
186                               uint64_t SectionDataSize, uint32_t MaxProt,
187                               uint32_t InitProt);
188
189  void writeSection(const MCAsmLayout &Layout, const MCSection &Sec,
190                    uint64_t VMAddr, uint64_t FileOffset, unsigned Flags,
191                    uint64_t RelocationsStart, unsigned NumRelocations);
192
193  void writeSymtabLoadCommand(uint32_t SymbolOffset, uint32_t NumSymbols,
194                              uint32_t StringTableOffset,
195                              uint32_t StringTableSize);
196
197  void writeDysymtabLoadCommand(
198      uint32_t FirstLocalSymbol, uint32_t NumLocalSymbols,
199      uint32_t FirstExternalSymbol, uint32_t NumExternalSymbols,
200      uint32_t FirstUndefinedSymbol, uint32_t NumUndefinedSymbols,
201      uint32_t IndirectSymbolOffset, uint32_t NumIndirectSymbols);
202
203  void writeNlist(MachSymbolData &MSD, const MCAsmLayout &Layout);
204
205  void writeLinkeditLoadCommand(uint32_t Type, uint32_t DataOffset,
206                                uint32_t DataSize);
207
208  void writeLinkerOptionsLoadCommand(const std::vector<std::string> &Options);
209
210  // FIXME: We really need to improve the relocation validation. Basically, we
211  // want to implement a separate computation which evaluates the relocation
212  // entry as the linker would, and verifies that the resultant fixup value is
213  // exactly what the encoder wanted. This will catch several classes of
214  // problems:
215  //
216  //  - Relocation entry bugs, the two algorithms are unlikely to have the same
217  //    exact bug.
218  //
219  //  - Relaxation issues, where we forget to relax something.
220  //
221  //  - Input errors, where something cannot be correctly encoded. 'as' allows
222  //    these through in many cases.
223
224  // Add a relocation to be output in the object file. At the time this is
225  // called, the symbol indexes are not know, so if the relocation refers
226  // to a symbol it should be passed as \p RelSymbol so that it can be updated
227  // afterwards. If the relocation doesn't refer to a symbol, nullptr should be
228  // used.
229  void addRelocation(const MCSymbol *RelSymbol, const MCSection *Sec,
230                     MachO::any_relocation_info &MRE) {
231    RelAndSymbol P(RelSymbol, MRE);
232    Relocations[Sec].push_back(P);
233  }
234
235  void recordScatteredRelocation(const MCAssembler &Asm,
236                                 const MCAsmLayout &Layout,
237                                 const MCFragment *Fragment,
238                                 const MCFixup &Fixup, MCValue Target,
239                                 unsigned Log2Size, uint64_t &FixedValue);
240
241  void recordTLVPRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout,
242                            const MCFragment *Fragment, const MCFixup &Fixup,
243                            MCValue Target, uint64_t &FixedValue);
244
245  void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
246                        const MCFragment *Fragment, const MCFixup &Fixup,
247                        MCValue Target, uint64_t &FixedValue) override;
248
249  void bindIndirectSymbols(MCAssembler &Asm);
250
251  /// Compute the symbol table data.
252  void computeSymbolTable(MCAssembler &Asm,
253                          std::vector<MachSymbolData> &LocalSymbolData,
254                          std::vector<MachSymbolData> &ExternalSymbolData,
255                          std::vector<MachSymbolData> &UndefinedSymbolData);
256
257  void computeSectionAddresses(const MCAssembler &Asm,
258                               const MCAsmLayout &Layout);
259
260  void executePostLayoutBinding(MCAssembler &Asm,
261                                const MCAsmLayout &Layout) override;
262
263  bool isSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
264                                              const MCSymbol &A,
265                                              const MCSymbol &B,
266                                              bool InSet) const override;
267
268  bool isSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
269                                              const MCSymbol &SymA,
270                                              const MCFragment &FB, bool InSet,
271                                              bool IsPCRel) const override;
272
273  uint64_t writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
274};
275
276/// Construct a new Mach-O writer instance.
277///
278/// This routine takes ownership of the target writer subclass.
279///
280/// \param MOTW - The target specific Mach-O writer subclass.
281/// \param OS - The stream to write to.
282/// \returns The constructed object writer.
283std::unique_ptr<MCObjectWriter>
284createMachObjectWriter(std::unique_ptr<MCMachObjectTargetWriter> MOTW,
285                       raw_pwrite_stream &OS, bool IsLittleEndian);
286
287} // end namespace llvm
288
289#endif // LLVM_MC_MCMACHOBJECTWRITER_H
290