1//===- lib/MC/MachObjectWriter.cpp - Mach-O File Writer -------------------===//
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#include "llvm/MC/MCMachObjectWriter.h"
11#include "llvm/ADT/StringMap.h"
12#include "llvm/ADT/Twine.h"
13#include "llvm/MC/MCAsmBackend.h"
14#include "llvm/MC/MCAsmLayout.h"
15#include "llvm/MC/MCAssembler.h"
16#include "llvm/MC/MCExpr.h"
17#include "llvm/MC/MCFixupKindInfo.h"
18#include "llvm/MC/MCMachOSymbolFlags.h"
19#include "llvm/MC/MCObjectWriter.h"
20#include "llvm/MC/MCSectionMachO.h"
21#include "llvm/MC/MCSymbol.h"
22#include "llvm/MC/MCValue.h"
23#include "llvm/Support/Debug.h"
24#include "llvm/Support/ErrorHandling.h"
25#include "llvm/Support/MachO.h"
26#include <vector>
27using namespace llvm;
28
29#define DEBUG_TYPE "mc"
30
31void MachObjectWriter::reset() {
32  Relocations.clear();
33  IndirectSymBase.clear();
34  StringTable.clear();
35  LocalSymbolData.clear();
36  ExternalSymbolData.clear();
37  UndefinedSymbolData.clear();
38  MCObjectWriter::reset();
39}
40
41bool MachObjectWriter::
42doesSymbolRequireExternRelocation(const MCSymbolData *SD) {
43  // Undefined symbols are always extern.
44  if (SD->Symbol->isUndefined())
45    return true;
46
47  // References to weak definitions require external relocation entries; the
48  // definition may not always be the one in the same object file.
49  if (SD->getFlags() & SF_WeakDefinition)
50    return true;
51
52  // Otherwise, we can use an internal relocation.
53  return false;
54}
55
56bool MachObjectWriter::
57MachSymbolData::operator<(const MachSymbolData &RHS) const {
58  return SymbolData->getSymbol().getName() <
59    RHS.SymbolData->getSymbol().getName();
60}
61
62bool MachObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
63  const MCFixupKindInfo &FKI = Asm.getBackend().getFixupKindInfo(
64    (MCFixupKind) Kind);
65
66  return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
67}
68
69uint64_t MachObjectWriter::getFragmentAddress(const MCFragment *Fragment,
70                                              const MCAsmLayout &Layout) const {
71  return getSectionAddress(Fragment->getParent()) +
72    Layout.getFragmentOffset(Fragment);
73}
74
75uint64_t MachObjectWriter::getSymbolAddress(const MCSymbolData* SD,
76                                            const MCAsmLayout &Layout) const {
77  const MCSymbol &S = SD->getSymbol();
78
79  // If this is a variable, then recursively evaluate now.
80  if (S.isVariable()) {
81    if (const MCConstantExpr *C =
82          dyn_cast<const MCConstantExpr>(S.getVariableValue()))
83      return C->getValue();
84
85
86    MCValue Target;
87    if (!S.getVariableValue()->EvaluateAsRelocatable(Target, &Layout))
88      report_fatal_error("unable to evaluate offset for variable '" +
89                         S.getName() + "'");
90
91    // Verify that any used symbols are defined.
92    if (Target.getSymA() && Target.getSymA()->getSymbol().isUndefined())
93      report_fatal_error("unable to evaluate offset to undefined symbol '" +
94                         Target.getSymA()->getSymbol().getName() + "'");
95    if (Target.getSymB() && Target.getSymB()->getSymbol().isUndefined())
96      report_fatal_error("unable to evaluate offset to undefined symbol '" +
97                         Target.getSymB()->getSymbol().getName() + "'");
98
99    uint64_t Address = Target.getConstant();
100    if (Target.getSymA())
101      Address += getSymbolAddress(&Layout.getAssembler().getSymbolData(
102                                    Target.getSymA()->getSymbol()), Layout);
103    if (Target.getSymB())
104      Address += getSymbolAddress(&Layout.getAssembler().getSymbolData(
105                                    Target.getSymB()->getSymbol()), Layout);
106    return Address;
107  }
108
109  return getSectionAddress(SD->getFragment()->getParent()) +
110    Layout.getSymbolOffset(SD);
111}
112
113uint64_t MachObjectWriter::getPaddingSize(const MCSectionData *SD,
114                                          const MCAsmLayout &Layout) const {
115  uint64_t EndAddr = getSectionAddress(SD) + Layout.getSectionAddressSize(SD);
116  unsigned Next = SD->getLayoutOrder() + 1;
117  if (Next >= Layout.getSectionOrder().size())
118    return 0;
119
120  const MCSectionData &NextSD = *Layout.getSectionOrder()[Next];
121  if (NextSD.getSection().isVirtualSection())
122    return 0;
123  return OffsetToAlignment(EndAddr, NextSD.getAlignment());
124}
125
126void MachObjectWriter::WriteHeader(unsigned NumLoadCommands,
127                                   unsigned LoadCommandsSize,
128                                   bool SubsectionsViaSymbols) {
129  uint32_t Flags = 0;
130
131  if (SubsectionsViaSymbols)
132    Flags |= MachO::MH_SUBSECTIONS_VIA_SYMBOLS;
133
134  // struct mach_header (28 bytes) or
135  // struct mach_header_64 (32 bytes)
136
137  uint64_t Start = OS.tell();
138  (void) Start;
139
140  Write32(is64Bit() ? MachO::MH_MAGIC_64 : MachO::MH_MAGIC);
141
142  Write32(TargetObjectWriter->getCPUType());
143  Write32(TargetObjectWriter->getCPUSubtype());
144
145  Write32(MachO::MH_OBJECT);
146  Write32(NumLoadCommands);
147  Write32(LoadCommandsSize);
148  Write32(Flags);
149  if (is64Bit())
150    Write32(0); // reserved
151
152  assert(OS.tell() - Start ==
153         (is64Bit()?sizeof(MachO::mach_header_64): sizeof(MachO::mach_header)));
154}
155
156/// WriteSegmentLoadCommand - Write a segment load command.
157///
158/// \param NumSections The number of sections in this segment.
159/// \param SectionDataSize The total size of the sections.
160void MachObjectWriter::WriteSegmentLoadCommand(unsigned NumSections,
161                                               uint64_t VMSize,
162                                               uint64_t SectionDataStartOffset,
163                                               uint64_t SectionDataSize) {
164  // struct segment_command (56 bytes) or
165  // struct segment_command_64 (72 bytes)
166
167  uint64_t Start = OS.tell();
168  (void) Start;
169
170  unsigned SegmentLoadCommandSize =
171    is64Bit() ? sizeof(MachO::segment_command_64):
172    sizeof(MachO::segment_command);
173  Write32(is64Bit() ? MachO::LC_SEGMENT_64 : MachO::LC_SEGMENT);
174  Write32(SegmentLoadCommandSize +
175          NumSections * (is64Bit() ? sizeof(MachO::section_64) :
176                         sizeof(MachO::section)));
177
178  WriteBytes("", 16);
179  if (is64Bit()) {
180    Write64(0); // vmaddr
181    Write64(VMSize); // vmsize
182    Write64(SectionDataStartOffset); // file offset
183    Write64(SectionDataSize); // file size
184  } else {
185    Write32(0); // vmaddr
186    Write32(VMSize); // vmsize
187    Write32(SectionDataStartOffset); // file offset
188    Write32(SectionDataSize); // file size
189  }
190  // maxprot
191  Write32(MachO::VM_PROT_READ | MachO::VM_PROT_WRITE | MachO::VM_PROT_EXECUTE);
192  // initprot
193  Write32(MachO::VM_PROT_READ | MachO::VM_PROT_WRITE | MachO::VM_PROT_EXECUTE);
194  Write32(NumSections);
195  Write32(0); // flags
196
197  assert(OS.tell() - Start == SegmentLoadCommandSize);
198}
199
200void MachObjectWriter::WriteSection(const MCAssembler &Asm,
201                                    const MCAsmLayout &Layout,
202                                    const MCSectionData &SD,
203                                    uint64_t FileOffset,
204                                    uint64_t RelocationsStart,
205                                    unsigned NumRelocations) {
206  uint64_t SectionSize = Layout.getSectionAddressSize(&SD);
207
208  // The offset is unused for virtual sections.
209  if (SD.getSection().isVirtualSection()) {
210    assert(Layout.getSectionFileSize(&SD) == 0 && "Invalid file size!");
211    FileOffset = 0;
212  }
213
214  // struct section (68 bytes) or
215  // struct section_64 (80 bytes)
216
217  uint64_t Start = OS.tell();
218  (void) Start;
219
220  const MCSectionMachO &Section = cast<MCSectionMachO>(SD.getSection());
221  WriteBytes(Section.getSectionName(), 16);
222  WriteBytes(Section.getSegmentName(), 16);
223  if (is64Bit()) {
224    Write64(getSectionAddress(&SD)); // address
225    Write64(SectionSize); // size
226  } else {
227    Write32(getSectionAddress(&SD)); // address
228    Write32(SectionSize); // size
229  }
230  Write32(FileOffset);
231
232  unsigned Flags = Section.getTypeAndAttributes();
233  if (SD.hasInstructions())
234    Flags |= MachO::S_ATTR_SOME_INSTRUCTIONS;
235
236  assert(isPowerOf2_32(SD.getAlignment()) && "Invalid alignment!");
237  Write32(Log2_32(SD.getAlignment()));
238  Write32(NumRelocations ? RelocationsStart : 0);
239  Write32(NumRelocations);
240  Write32(Flags);
241  Write32(IndirectSymBase.lookup(&SD)); // reserved1
242  Write32(Section.getStubSize()); // reserved2
243  if (is64Bit())
244    Write32(0); // reserved3
245
246  assert(OS.tell() - Start == (is64Bit() ? sizeof(MachO::section_64) :
247                               sizeof(MachO::section)));
248}
249
250void MachObjectWriter::WriteSymtabLoadCommand(uint32_t SymbolOffset,
251                                              uint32_t NumSymbols,
252                                              uint32_t StringTableOffset,
253                                              uint32_t StringTableSize) {
254  // struct symtab_command (24 bytes)
255
256  uint64_t Start = OS.tell();
257  (void) Start;
258
259  Write32(MachO::LC_SYMTAB);
260  Write32(sizeof(MachO::symtab_command));
261  Write32(SymbolOffset);
262  Write32(NumSymbols);
263  Write32(StringTableOffset);
264  Write32(StringTableSize);
265
266  assert(OS.tell() - Start == sizeof(MachO::symtab_command));
267}
268
269void MachObjectWriter::WriteDysymtabLoadCommand(uint32_t FirstLocalSymbol,
270                                                uint32_t NumLocalSymbols,
271                                                uint32_t FirstExternalSymbol,
272                                                uint32_t NumExternalSymbols,
273                                                uint32_t FirstUndefinedSymbol,
274                                                uint32_t NumUndefinedSymbols,
275                                                uint32_t IndirectSymbolOffset,
276                                                uint32_t NumIndirectSymbols) {
277  // struct dysymtab_command (80 bytes)
278
279  uint64_t Start = OS.tell();
280  (void) Start;
281
282  Write32(MachO::LC_DYSYMTAB);
283  Write32(sizeof(MachO::dysymtab_command));
284  Write32(FirstLocalSymbol);
285  Write32(NumLocalSymbols);
286  Write32(FirstExternalSymbol);
287  Write32(NumExternalSymbols);
288  Write32(FirstUndefinedSymbol);
289  Write32(NumUndefinedSymbols);
290  Write32(0); // tocoff
291  Write32(0); // ntoc
292  Write32(0); // modtaboff
293  Write32(0); // nmodtab
294  Write32(0); // extrefsymoff
295  Write32(0); // nextrefsyms
296  Write32(IndirectSymbolOffset);
297  Write32(NumIndirectSymbols);
298  Write32(0); // extreloff
299  Write32(0); // nextrel
300  Write32(0); // locreloff
301  Write32(0); // nlocrel
302
303  assert(OS.tell() - Start == sizeof(MachO::dysymtab_command));
304}
305
306MachObjectWriter::MachSymbolData *
307MachObjectWriter::findSymbolData(const MCSymbol &Sym) {
308  for (auto &Entry : LocalSymbolData)
309    if (&Entry.SymbolData->getSymbol() == &Sym)
310      return &Entry;
311
312  for (auto &Entry : ExternalSymbolData)
313    if (&Entry.SymbolData->getSymbol() == &Sym)
314      return &Entry;
315
316  for (auto &Entry : UndefinedSymbolData)
317    if (&Entry.SymbolData->getSymbol() == &Sym)
318      return &Entry;
319
320  return nullptr;
321}
322
323void MachObjectWriter::WriteNlist(MachSymbolData &MSD,
324                                  const MCAsmLayout &Layout) {
325  MCSymbolData &Data = *MSD.SymbolData;
326  const MCSymbol *Symbol = &Data.getSymbol();
327  const MCSymbol *AliasedSymbol = &Symbol->AliasedSymbol();
328  uint8_t SectionIndex = MSD.SectionIndex;
329  uint8_t Type = 0;
330  uint16_t Flags = Data.getFlags();
331  uint64_t Address = 0;
332  bool IsAlias = Symbol != AliasedSymbol;
333
334  MachSymbolData *AliaseeInfo;
335  if (IsAlias) {
336    AliaseeInfo = findSymbolData(*AliasedSymbol);
337    if (AliaseeInfo)
338      SectionIndex = AliaseeInfo->SectionIndex;
339    Symbol = AliasedSymbol;
340  }
341
342  // Set the N_TYPE bits. See <mach-o/nlist.h>.
343  //
344  // FIXME: Are the prebound or indirect fields possible here?
345  if (IsAlias && Symbol->isUndefined())
346    Type = MachO::N_INDR;
347  else if (Symbol->isUndefined())
348    Type = MachO::N_UNDF;
349  else if (Symbol->isAbsolute())
350    Type = MachO::N_ABS;
351  else
352    Type = MachO::N_SECT;
353
354  // FIXME: Set STAB bits.
355
356  if (Data.isPrivateExtern())
357    Type |= MachO::N_PEXT;
358
359  // Set external bit.
360  if (Data.isExternal() || (!IsAlias && Symbol->isUndefined()))
361    Type |= MachO::N_EXT;
362
363  // Compute the symbol address.
364  if (IsAlias && Symbol->isUndefined())
365    Address = AliaseeInfo->StringIndex;
366  else if (Symbol->isDefined())
367    Address = getSymbolAddress(&Data, Layout);
368  else if (Data.isCommon()) {
369    // Common symbols are encoded with the size in the address
370    // field, and their alignment in the flags.
371    Address = Data.getCommonSize();
372
373    // Common alignment is packed into the 'desc' bits.
374    if (unsigned Align = Data.getCommonAlignment()) {
375      unsigned Log2Size = Log2_32(Align);
376      assert((1U << Log2Size) == Align && "Invalid 'common' alignment!");
377      if (Log2Size > 15)
378        report_fatal_error("invalid 'common' alignment '" +
379                           Twine(Align) + "' for '" + Symbol->getName() + "'",
380                           false);
381      // FIXME: Keep this mask with the SymbolFlags enumeration.
382      Flags = (Flags & 0xF0FF) | (Log2Size << 8);
383    }
384  }
385
386  if (Layout.getAssembler().isThumbFunc(Symbol))
387    Flags |= SF_ThumbFunc;
388
389  // struct nlist (12 bytes)
390
391  Write32(MSD.StringIndex);
392  Write8(Type);
393  Write8(SectionIndex);
394
395  // The Mach-O streamer uses the lowest 16-bits of the flags for the 'desc'
396  // value.
397  Write16(Flags);
398  if (is64Bit())
399    Write64(Address);
400  else
401    Write32(Address);
402}
403
404void MachObjectWriter::WriteLinkeditLoadCommand(uint32_t Type,
405                                                uint32_t DataOffset,
406                                                uint32_t DataSize) {
407  uint64_t Start = OS.tell();
408  (void) Start;
409
410  Write32(Type);
411  Write32(sizeof(MachO::linkedit_data_command));
412  Write32(DataOffset);
413  Write32(DataSize);
414
415  assert(OS.tell() - Start == sizeof(MachO::linkedit_data_command));
416}
417
418static unsigned ComputeLinkerOptionsLoadCommandSize(
419  const std::vector<std::string> &Options, bool is64Bit)
420{
421  unsigned Size = sizeof(MachO::linker_options_command);
422  for (unsigned i = 0, e = Options.size(); i != e; ++i)
423    Size += Options[i].size() + 1;
424  return RoundUpToAlignment(Size, is64Bit ? 8 : 4);
425}
426
427void MachObjectWriter::WriteLinkerOptionsLoadCommand(
428  const std::vector<std::string> &Options)
429{
430  unsigned Size = ComputeLinkerOptionsLoadCommandSize(Options, is64Bit());
431  uint64_t Start = OS.tell();
432  (void) Start;
433
434  Write32(MachO::LC_LINKER_OPTIONS);
435  Write32(Size);
436  Write32(Options.size());
437  uint64_t BytesWritten = sizeof(MachO::linker_options_command);
438  for (unsigned i = 0, e = Options.size(); i != e; ++i) {
439    // Write each string, including the null byte.
440    const std::string &Option = Options[i];
441    WriteBytes(Option.c_str(), Option.size() + 1);
442    BytesWritten += Option.size() + 1;
443  }
444
445  // Pad to a multiple of the pointer size.
446  WriteBytes("", OffsetToAlignment(BytesWritten, is64Bit() ? 8 : 4));
447
448  assert(OS.tell() - Start == Size);
449}
450
451
452void MachObjectWriter::RecordRelocation(const MCAssembler &Asm,
453                                        const MCAsmLayout &Layout,
454                                        const MCFragment *Fragment,
455                                        const MCFixup &Fixup,
456                                        MCValue Target,
457                                        bool &IsPCRel,
458                                        uint64_t &FixedValue) {
459  TargetObjectWriter->RecordRelocation(this, Asm, Layout, Fragment, Fixup,
460                                       Target, FixedValue);
461}
462
463void MachObjectWriter::BindIndirectSymbols(MCAssembler &Asm) {
464  // This is the point where 'as' creates actual symbols for indirect symbols
465  // (in the following two passes). It would be easier for us to do this sooner
466  // when we see the attribute, but that makes getting the order in the symbol
467  // table much more complicated than it is worth.
468  //
469  // FIXME: Revisit this when the dust settles.
470
471  // Report errors for use of .indirect_symbol not in a symbol pointer section
472  // or stub section.
473  for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
474         ie = Asm.indirect_symbol_end(); it != ie; ++it) {
475    const MCSectionMachO &Section =
476      cast<MCSectionMachO>(it->SectionData->getSection());
477
478    if (Section.getType() != MachO::S_NON_LAZY_SYMBOL_POINTERS &&
479        Section.getType() != MachO::S_LAZY_SYMBOL_POINTERS &&
480        Section.getType() != MachO::S_SYMBOL_STUBS) {
481	MCSymbol &Symbol = *it->Symbol;
482	report_fatal_error("indirect symbol '" + Symbol.getName() +
483                           "' not in a symbol pointer or stub section");
484    }
485  }
486
487  // Bind non-lazy symbol pointers first.
488  unsigned IndirectIndex = 0;
489  for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
490         ie = Asm.indirect_symbol_end(); it != ie; ++it, ++IndirectIndex) {
491    const MCSectionMachO &Section =
492      cast<MCSectionMachO>(it->SectionData->getSection());
493
494    if (Section.getType() != MachO::S_NON_LAZY_SYMBOL_POINTERS)
495      continue;
496
497    // Initialize the section indirect symbol base, if necessary.
498    IndirectSymBase.insert(std::make_pair(it->SectionData, IndirectIndex));
499
500    Asm.getOrCreateSymbolData(*it->Symbol);
501  }
502
503  // Then lazy symbol pointers and symbol stubs.
504  IndirectIndex = 0;
505  for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
506         ie = Asm.indirect_symbol_end(); it != ie; ++it, ++IndirectIndex) {
507    const MCSectionMachO &Section =
508      cast<MCSectionMachO>(it->SectionData->getSection());
509
510    if (Section.getType() != MachO::S_LAZY_SYMBOL_POINTERS &&
511        Section.getType() != MachO::S_SYMBOL_STUBS)
512      continue;
513
514    // Initialize the section indirect symbol base, if necessary.
515    IndirectSymBase.insert(std::make_pair(it->SectionData, IndirectIndex));
516
517    // Set the symbol type to undefined lazy, but only on construction.
518    //
519    // FIXME: Do not hardcode.
520    bool Created;
521    MCSymbolData &Entry = Asm.getOrCreateSymbolData(*it->Symbol, &Created);
522    if (Created)
523      Entry.setFlags(Entry.getFlags() | 0x0001);
524  }
525}
526
527/// ComputeSymbolTable - Compute the symbol table data
528///
529/// \param StringTable [out] - The string table data.
530/// \param StringIndexMap [out] - Map from symbol names to offsets in the
531/// string table.
532void MachObjectWriter::
533ComputeSymbolTable(MCAssembler &Asm, SmallString<256> &StringTable,
534                   std::vector<MachSymbolData> &LocalSymbolData,
535                   std::vector<MachSymbolData> &ExternalSymbolData,
536                   std::vector<MachSymbolData> &UndefinedSymbolData) {
537  // Build section lookup table.
538  DenseMap<const MCSection*, uint8_t> SectionIndexMap;
539  unsigned Index = 1;
540  for (MCAssembler::iterator it = Asm.begin(),
541         ie = Asm.end(); it != ie; ++it, ++Index)
542    SectionIndexMap[&it->getSection()] = Index;
543  assert(Index <= 256 && "Too many sections!");
544
545  // Index 0 is always the empty string.
546  StringMap<uint64_t> StringIndexMap;
547  StringTable += '\x00';
548
549  // Build the symbol arrays and the string table, but only for non-local
550  // symbols.
551  //
552  // The particular order that we collect the symbols and create the string
553  // table, then sort the symbols is chosen to match 'as'. Even though it
554  // doesn't matter for correctness, this is important for letting us diff .o
555  // files.
556  for (MCSymbolData &SD : Asm.symbols()) {
557    const MCSymbol &Symbol = SD.getSymbol();
558
559    // Ignore non-linker visible symbols.
560    if (!Asm.isSymbolLinkerVisible(SD.getSymbol()))
561      continue;
562
563    if (!SD.isExternal() && !Symbol.isUndefined())
564      continue;
565
566    uint64_t &Entry = StringIndexMap[Symbol.getName()];
567    if (!Entry) {
568      Entry = StringTable.size();
569      StringTable += Symbol.getName();
570      StringTable += '\x00';
571    }
572
573    MachSymbolData MSD;
574    MSD.SymbolData = &SD;
575    MSD.StringIndex = Entry;
576
577    if (Symbol.isUndefined()) {
578      MSD.SectionIndex = 0;
579      UndefinedSymbolData.push_back(MSD);
580    } else if (Symbol.isAbsolute()) {
581      MSD.SectionIndex = 0;
582      ExternalSymbolData.push_back(MSD);
583    } else {
584      MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
585      assert(MSD.SectionIndex && "Invalid section index!");
586      ExternalSymbolData.push_back(MSD);
587    }
588  }
589
590  // Now add the data for local symbols.
591  for (MCSymbolData &SD : Asm.symbols()) {
592    const MCSymbol &Symbol = SD.getSymbol();
593
594    // Ignore non-linker visible symbols.
595    if (!Asm.isSymbolLinkerVisible(SD.getSymbol()))
596      continue;
597
598    if (SD.isExternal() || Symbol.isUndefined())
599      continue;
600
601    uint64_t &Entry = StringIndexMap[Symbol.getName()];
602    if (!Entry) {
603      Entry = StringTable.size();
604      StringTable += Symbol.getName();
605      StringTable += '\x00';
606    }
607
608    MachSymbolData MSD;
609    MSD.SymbolData = &SD;
610    MSD.StringIndex = Entry;
611
612    if (Symbol.isAbsolute()) {
613      MSD.SectionIndex = 0;
614      LocalSymbolData.push_back(MSD);
615    } else {
616      MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
617      assert(MSD.SectionIndex && "Invalid section index!");
618      LocalSymbolData.push_back(MSD);
619    }
620  }
621
622  // External and undefined symbols are required to be in lexicographic order.
623  std::sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
624  std::sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
625
626  // Set the symbol indices.
627  Index = 0;
628  for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
629    LocalSymbolData[i].SymbolData->setIndex(Index++);
630  for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
631    ExternalSymbolData[i].SymbolData->setIndex(Index++);
632  for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
633    UndefinedSymbolData[i].SymbolData->setIndex(Index++);
634
635  // The string table is padded to a multiple of 4.
636  while (StringTable.size() % 4)
637    StringTable += '\x00';
638}
639
640void MachObjectWriter::computeSectionAddresses(const MCAssembler &Asm,
641                                               const MCAsmLayout &Layout) {
642  uint64_t StartAddress = 0;
643  const SmallVectorImpl<MCSectionData*> &Order = Layout.getSectionOrder();
644  for (int i = 0, n = Order.size(); i != n ; ++i) {
645    const MCSectionData *SD = Order[i];
646    StartAddress = RoundUpToAlignment(StartAddress, SD->getAlignment());
647    SectionAddress[SD] = StartAddress;
648    StartAddress += Layout.getSectionAddressSize(SD);
649
650    // Explicitly pad the section to match the alignment requirements of the
651    // following one. This is for 'gas' compatibility, it shouldn't
652    /// strictly be necessary.
653    StartAddress += getPaddingSize(SD, Layout);
654  }
655}
656
657void MachObjectWriter::markAbsoluteVariableSymbols(MCAssembler &Asm,
658                                                   const MCAsmLayout &Layout) {
659  for (MCSymbolData &SD : Asm.symbols()) {
660    if (!SD.getSymbol().isVariable())
661      continue;
662
663    // Is the variable is a symbol difference (SA - SB + C) expression,
664    // and neither symbol is external, mark the variable as absolute.
665    const MCExpr *Expr = SD.getSymbol().getVariableValue();
666    MCValue Value;
667    if (Expr->EvaluateAsRelocatable(Value, &Layout)) {
668      if (Value.getSymA() && Value.getSymB())
669        const_cast<MCSymbol*>(&SD.getSymbol())->setAbsolute();
670    }
671  }
672}
673
674void MachObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
675                                                const MCAsmLayout &Layout) {
676  computeSectionAddresses(Asm, Layout);
677
678  // Create symbol data for any indirect symbols.
679  BindIndirectSymbols(Asm);
680
681  // Mark symbol difference expressions in variables (from .set or = directives)
682  // as absolute.
683  markAbsoluteVariableSymbols(Asm, Layout);
684
685  // Compute symbol table information and bind symbol indices.
686  ComputeSymbolTable(Asm, StringTable, LocalSymbolData, ExternalSymbolData,
687                     UndefinedSymbolData);
688}
689
690bool MachObjectWriter::
691IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
692                                       const MCSymbolData &DataA,
693                                       const MCFragment &FB,
694                                       bool InSet,
695                                       bool IsPCRel) const {
696  if (InSet)
697    return true;
698
699  // The effective address is
700  //     addr(atom(A)) + offset(A)
701  //   - addr(atom(B)) - offset(B)
702  // and the offsets are not relocatable, so the fixup is fully resolved when
703  //  addr(atom(A)) - addr(atom(B)) == 0.
704  const MCSymbolData *A_Base = nullptr, *B_Base = nullptr;
705
706  const MCSymbol &SA = DataA.getSymbol().AliasedSymbol();
707  const MCSection &SecA = SA.getSection();
708  const MCSection &SecB = FB.getParent()->getSection();
709
710  if (IsPCRel) {
711    // The simple (Darwin, except on x86_64) way of dealing with this was to
712    // assume that any reference to a temporary symbol *must* be a temporary
713    // symbol in the same atom, unless the sections differ. Therefore, any PCrel
714    // relocation to a temporary symbol (in the same section) is fully
715    // resolved. This also works in conjunction with absolutized .set, which
716    // requires the compiler to use .set to absolutize the differences between
717    // symbols which the compiler knows to be assembly time constants, so we
718    // don't need to worry about considering symbol differences fully resolved.
719    //
720    // If the file isn't using sub-sections-via-symbols, we can make the
721    // same assumptions about any symbol that we normally make about
722    // assembler locals.
723
724    bool hasReliableSymbolDifference = isX86_64();
725    if (!hasReliableSymbolDifference) {
726      if (!SA.isInSection() || &SecA != &SecB ||
727          (!SA.isTemporary() &&
728           FB.getAtom() != Asm.getSymbolData(SA).getFragment()->getAtom() &&
729           Asm.getSubsectionsViaSymbols()))
730        return false;
731      return true;
732    }
733    // For Darwin x86_64, there is one special case when the reference IsPCRel.
734    // If the fragment with the reference does not have a base symbol but meets
735    // the simple way of dealing with this, in that it is a temporary symbol in
736    // the same atom then it is assumed to be fully resolved.  This is needed so
737    // a relocation entry is not created and so the static linker does not
738    // mess up the reference later.
739    else if(!FB.getAtom() &&
740            SA.isTemporary() && SA.isInSection() && &SecA == &SecB){
741      return true;
742    }
743  } else {
744    if (!TargetObjectWriter->useAggressiveSymbolFolding())
745      return false;
746  }
747
748  const MCFragment *FA = Asm.getSymbolData(SA).getFragment();
749
750  // Bail if the symbol has no fragment.
751  if (!FA)
752    return false;
753
754  A_Base = FA->getAtom();
755  if (!A_Base)
756    return false;
757
758  B_Base = FB.getAtom();
759  if (!B_Base)
760    return false;
761
762  // If the atoms are the same, they are guaranteed to have the same address.
763  if (A_Base == B_Base)
764    return true;
765
766  // Otherwise, we can't prove this is fully resolved.
767  return false;
768}
769
770void MachObjectWriter::WriteObject(MCAssembler &Asm,
771                                   const MCAsmLayout &Layout) {
772  unsigned NumSections = Asm.size();
773  const MCAssembler::VersionMinInfoType &VersionInfo =
774    Layout.getAssembler().getVersionMinInfo();
775
776  // The section data starts after the header, the segment load command (and
777  // section headers) and the symbol table.
778  unsigned NumLoadCommands = 1;
779  uint64_t LoadCommandsSize = is64Bit() ?
780    sizeof(MachO::segment_command_64) + NumSections * sizeof(MachO::section_64):
781    sizeof(MachO::segment_command) + NumSections * sizeof(MachO::section);
782
783  // Add the deployment target version info load command size, if used.
784  if (VersionInfo.Major != 0) {
785    ++NumLoadCommands;
786    LoadCommandsSize += sizeof(MachO::version_min_command);
787  }
788
789  // Add the data-in-code load command size, if used.
790  unsigned NumDataRegions = Asm.getDataRegions().size();
791  if (NumDataRegions) {
792    ++NumLoadCommands;
793    LoadCommandsSize += sizeof(MachO::linkedit_data_command);
794  }
795
796  // Add the loh load command size, if used.
797  uint64_t LOHRawSize = Asm.getLOHContainer().getEmitSize(*this, Layout);
798  uint64_t LOHSize = RoundUpToAlignment(LOHRawSize, is64Bit() ? 8 : 4);
799  if (LOHSize) {
800    ++NumLoadCommands;
801    LoadCommandsSize += sizeof(MachO::linkedit_data_command);
802  }
803
804  // Add the symbol table load command sizes, if used.
805  unsigned NumSymbols = LocalSymbolData.size() + ExternalSymbolData.size() +
806    UndefinedSymbolData.size();
807  if (NumSymbols) {
808    NumLoadCommands += 2;
809    LoadCommandsSize += (sizeof(MachO::symtab_command) +
810                         sizeof(MachO::dysymtab_command));
811  }
812
813  // Add the linker option load commands sizes.
814  const std::vector<std::vector<std::string> > &LinkerOptions =
815    Asm.getLinkerOptions();
816  for (unsigned i = 0, e = LinkerOptions.size(); i != e; ++i) {
817    ++NumLoadCommands;
818    LoadCommandsSize += ComputeLinkerOptionsLoadCommandSize(LinkerOptions[i],
819                                                            is64Bit());
820  }
821
822  // Compute the total size of the section data, as well as its file size and vm
823  // size.
824  uint64_t SectionDataStart = (is64Bit() ? sizeof(MachO::mach_header_64) :
825                               sizeof(MachO::mach_header)) + LoadCommandsSize;
826  uint64_t SectionDataSize = 0;
827  uint64_t SectionDataFileSize = 0;
828  uint64_t VMSize = 0;
829  for (MCAssembler::const_iterator it = Asm.begin(),
830         ie = Asm.end(); it != ie; ++it) {
831    const MCSectionData &SD = *it;
832    uint64_t Address = getSectionAddress(&SD);
833    uint64_t Size = Layout.getSectionAddressSize(&SD);
834    uint64_t FileSize = Layout.getSectionFileSize(&SD);
835    FileSize += getPaddingSize(&SD, Layout);
836
837    VMSize = std::max(VMSize, Address + Size);
838
839    if (SD.getSection().isVirtualSection())
840      continue;
841
842    SectionDataSize = std::max(SectionDataSize, Address + Size);
843    SectionDataFileSize = std::max(SectionDataFileSize, Address + FileSize);
844  }
845
846  // The section data is padded to 4 bytes.
847  //
848  // FIXME: Is this machine dependent?
849  unsigned SectionDataPadding = OffsetToAlignment(SectionDataFileSize, 4);
850  SectionDataFileSize += SectionDataPadding;
851
852  // Write the prolog, starting with the header and load command...
853  WriteHeader(NumLoadCommands, LoadCommandsSize,
854              Asm.getSubsectionsViaSymbols());
855  WriteSegmentLoadCommand(NumSections, VMSize,
856                          SectionDataStart, SectionDataSize);
857
858  // ... and then the section headers.
859  uint64_t RelocTableEnd = SectionDataStart + SectionDataFileSize;
860  for (MCAssembler::const_iterator it = Asm.begin(),
861         ie = Asm.end(); it != ie; ++it) {
862    std::vector<MachO::any_relocation_info> &Relocs = Relocations[it];
863    unsigned NumRelocs = Relocs.size();
864    uint64_t SectionStart = SectionDataStart + getSectionAddress(it);
865    WriteSection(Asm, Layout, *it, SectionStart, RelocTableEnd, NumRelocs);
866    RelocTableEnd += NumRelocs * sizeof(MachO::any_relocation_info);
867  }
868
869  // Write out the deployment target information, if it's available.
870  if (VersionInfo.Major != 0) {
871    assert(VersionInfo.Update < 256 && "unencodable update target version");
872    assert(VersionInfo.Minor < 256 && "unencodable minor target version");
873    assert(VersionInfo.Major < 65536 && "unencodable major target version");
874    uint32_t EncodedVersion = VersionInfo.Update | (VersionInfo.Minor << 8) |
875      (VersionInfo.Major << 16);
876    Write32(VersionInfo.Kind == MCVM_OSXVersionMin ? MachO::LC_VERSION_MIN_MACOSX :
877            MachO::LC_VERSION_MIN_IPHONEOS);
878    Write32(sizeof(MachO::version_min_command));
879    Write32(EncodedVersion);
880    Write32(0);         // reserved.
881  }
882
883  // Write the data-in-code load command, if used.
884  uint64_t DataInCodeTableEnd = RelocTableEnd + NumDataRegions * 8;
885  if (NumDataRegions) {
886    uint64_t DataRegionsOffset = RelocTableEnd;
887    uint64_t DataRegionsSize = NumDataRegions * 8;
888    WriteLinkeditLoadCommand(MachO::LC_DATA_IN_CODE, DataRegionsOffset,
889                             DataRegionsSize);
890  }
891
892  // Write the loh load command, if used.
893  uint64_t LOHTableEnd = DataInCodeTableEnd + LOHSize;
894  if (LOHSize)
895    WriteLinkeditLoadCommand(MachO::LC_LINKER_OPTIMIZATION_HINT,
896                             DataInCodeTableEnd, LOHSize);
897
898  // Write the symbol table load command, if used.
899  if (NumSymbols) {
900    unsigned FirstLocalSymbol = 0;
901    unsigned NumLocalSymbols = LocalSymbolData.size();
902    unsigned FirstExternalSymbol = FirstLocalSymbol + NumLocalSymbols;
903    unsigned NumExternalSymbols = ExternalSymbolData.size();
904    unsigned FirstUndefinedSymbol = FirstExternalSymbol + NumExternalSymbols;
905    unsigned NumUndefinedSymbols = UndefinedSymbolData.size();
906    unsigned NumIndirectSymbols = Asm.indirect_symbol_size();
907    unsigned NumSymTabSymbols =
908      NumLocalSymbols + NumExternalSymbols + NumUndefinedSymbols;
909    uint64_t IndirectSymbolSize = NumIndirectSymbols * 4;
910    uint64_t IndirectSymbolOffset = 0;
911
912    // If used, the indirect symbols are written after the section data.
913    if (NumIndirectSymbols)
914      IndirectSymbolOffset = LOHTableEnd;
915
916    // The symbol table is written after the indirect symbol data.
917    uint64_t SymbolTableOffset = LOHTableEnd + IndirectSymbolSize;
918
919    // The string table is written after symbol table.
920    uint64_t StringTableOffset =
921      SymbolTableOffset + NumSymTabSymbols * (is64Bit() ?
922                                              sizeof(MachO::nlist_64) :
923                                              sizeof(MachO::nlist));
924    WriteSymtabLoadCommand(SymbolTableOffset, NumSymTabSymbols,
925                           StringTableOffset, StringTable.size());
926
927    WriteDysymtabLoadCommand(FirstLocalSymbol, NumLocalSymbols,
928                             FirstExternalSymbol, NumExternalSymbols,
929                             FirstUndefinedSymbol, NumUndefinedSymbols,
930                             IndirectSymbolOffset, NumIndirectSymbols);
931  }
932
933  // Write the linker options load commands.
934  for (unsigned i = 0, e = LinkerOptions.size(); i != e; ++i) {
935    WriteLinkerOptionsLoadCommand(LinkerOptions[i]);
936  }
937
938  // Write the actual section data.
939  for (MCAssembler::const_iterator it = Asm.begin(),
940         ie = Asm.end(); it != ie; ++it) {
941    Asm.writeSectionData(it, Layout);
942
943    uint64_t Pad = getPaddingSize(it, Layout);
944    for (unsigned int i = 0; i < Pad; ++i)
945      Write8(0);
946  }
947
948  // Write the extra padding.
949  WriteZeros(SectionDataPadding);
950
951  // Write the relocation entries.
952  for (MCAssembler::const_iterator it = Asm.begin(),
953         ie = Asm.end(); it != ie; ++it) {
954    // Write the section relocation entries, in reverse order to match 'as'
955    // (approximately, the exact algorithm is more complicated than this).
956    std::vector<MachO::any_relocation_info> &Relocs = Relocations[it];
957    for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
958      Write32(Relocs[e - i - 1].r_word0);
959      Write32(Relocs[e - i - 1].r_word1);
960    }
961  }
962
963  // Write out the data-in-code region payload, if there is one.
964  for (MCAssembler::const_data_region_iterator
965         it = Asm.data_region_begin(), ie = Asm.data_region_end();
966         it != ie; ++it) {
967    const DataRegionData *Data = &(*it);
968    uint64_t Start =
969      getSymbolAddress(&Layout.getAssembler().getSymbolData(*Data->Start),
970                       Layout);
971    uint64_t End =
972      getSymbolAddress(&Layout.getAssembler().getSymbolData(*Data->End),
973                       Layout);
974    DEBUG(dbgs() << "data in code region-- kind: " << Data->Kind
975                 << "  start: " << Start << "(" << Data->Start->getName() << ")"
976                 << "  end: " << End << "(" << Data->End->getName() << ")"
977                 << "  size: " << End - Start
978                 << "\n");
979    Write32(Start);
980    Write16(End - Start);
981    Write16(Data->Kind);
982  }
983
984  // Write out the loh commands, if there is one.
985  if (LOHSize) {
986#ifndef NDEBUG
987    unsigned Start = OS.tell();
988#endif
989    Asm.getLOHContainer().Emit(*this, Layout);
990    // Pad to a multiple of the pointer size.
991    WriteBytes("", OffsetToAlignment(LOHRawSize, is64Bit() ? 8 : 4));
992    assert(OS.tell() - Start == LOHSize);
993  }
994
995  // Write the symbol table data, if used.
996  if (NumSymbols) {
997    // Write the indirect symbol entries.
998    for (MCAssembler::const_indirect_symbol_iterator
999           it = Asm.indirect_symbol_begin(),
1000           ie = Asm.indirect_symbol_end(); it != ie; ++it) {
1001      // Indirect symbols in the non-lazy symbol pointer section have some
1002      // special handling.
1003      const MCSectionMachO &Section =
1004        static_cast<const MCSectionMachO&>(it->SectionData->getSection());
1005      if (Section.getType() == MachO::S_NON_LAZY_SYMBOL_POINTERS) {
1006        // If this symbol is defined and internal, mark it as such.
1007        if (it->Symbol->isDefined() &&
1008            !Asm.getSymbolData(*it->Symbol).isExternal()) {
1009          uint32_t Flags = MachO::INDIRECT_SYMBOL_LOCAL;
1010          if (it->Symbol->isAbsolute())
1011            Flags |= MachO::INDIRECT_SYMBOL_ABS;
1012          Write32(Flags);
1013          continue;
1014        }
1015      }
1016
1017      Write32(Asm.getSymbolData(*it->Symbol).getIndex());
1018    }
1019
1020    // FIXME: Check that offsets match computed ones.
1021
1022    // Write the symbol table entries.
1023    for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1024      WriteNlist(LocalSymbolData[i], Layout);
1025    for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1026      WriteNlist(ExternalSymbolData[i], Layout);
1027    for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1028      WriteNlist(UndefinedSymbolData[i], Layout);
1029
1030    // Write the string table.
1031    OS << StringTable.str();
1032  }
1033}
1034
1035MCObjectWriter *llvm::createMachObjectWriter(MCMachObjectTargetWriter *MOTW,
1036                                             raw_ostream &OS,
1037                                             bool IsLittleEndian) {
1038  return new MachObjectWriter(MOTW, OS, IsLittleEndian);
1039}
1040