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/MCObjectWriter.h"
19#include "llvm/MC/MCSectionMachO.h"
20#include "llvm/MC/MCSymbolMachO.h"
21#include "llvm/MC/MCValue.h"
22#include "llvm/Support/Debug.h"
23#include "llvm/Support/ErrorHandling.h"
24#include "llvm/Support/MachO.h"
25#include "llvm/Support/raw_ostream.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::doesSymbolRequireExternRelocation(const MCSymbol &S) {
42  // Undefined symbols are always extern.
43  if (S.isUndefined())
44    return true;
45
46  // References to weak definitions require external relocation entries; the
47  // definition may not always be the one in the same object file.
48  if (cast<MCSymbolMachO>(S).isWeakDefinition())
49    return true;
50
51  // Otherwise, we can use an internal relocation.
52  return false;
53}
54
55bool MachObjectWriter::
56MachSymbolData::operator<(const MachSymbolData &RHS) const {
57  return Symbol->getName() < RHS.Symbol->getName();
58}
59
60bool MachObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
61  const MCFixupKindInfo &FKI = Asm.getBackend().getFixupKindInfo(
62    (MCFixupKind) Kind);
63
64  return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
65}
66
67uint64_t MachObjectWriter::getFragmentAddress(const MCFragment *Fragment,
68                                              const MCAsmLayout &Layout) const {
69  return getSectionAddress(Fragment->getParent()) +
70         Layout.getFragmentOffset(Fragment);
71}
72
73uint64_t MachObjectWriter::getSymbolAddress(const MCSymbol &S,
74                                            const MCAsmLayout &Layout) const {
75  // If this is a variable, then recursively evaluate now.
76  if (S.isVariable()) {
77    if (const MCConstantExpr *C =
78          dyn_cast<const MCConstantExpr>(S.getVariableValue()))
79      return C->getValue();
80
81    MCValue Target;
82    if (!S.getVariableValue()->evaluateAsRelocatable(Target, &Layout, nullptr))
83      report_fatal_error("unable to evaluate offset for variable '" +
84                         S.getName() + "'");
85
86    // Verify that any used symbols are defined.
87    if (Target.getSymA() && Target.getSymA()->getSymbol().isUndefined())
88      report_fatal_error("unable to evaluate offset to undefined symbol '" +
89                         Target.getSymA()->getSymbol().getName() + "'");
90    if (Target.getSymB() && Target.getSymB()->getSymbol().isUndefined())
91      report_fatal_error("unable to evaluate offset to undefined symbol '" +
92                         Target.getSymB()->getSymbol().getName() + "'");
93
94    uint64_t Address = Target.getConstant();
95    if (Target.getSymA())
96      Address += getSymbolAddress(Target.getSymA()->getSymbol(), Layout);
97    if (Target.getSymB())
98      Address += getSymbolAddress(Target.getSymB()->getSymbol(), Layout);
99    return Address;
100  }
101
102  return getSectionAddress(S.getFragment()->getParent()) +
103         Layout.getSymbolOffset(S);
104}
105
106uint64_t MachObjectWriter::getPaddingSize(const MCSection *Sec,
107                                          const MCAsmLayout &Layout) const {
108  uint64_t EndAddr = getSectionAddress(Sec) + Layout.getSectionAddressSize(Sec);
109  unsigned Next = Sec->getLayoutOrder() + 1;
110  if (Next >= Layout.getSectionOrder().size())
111    return 0;
112
113  const MCSection &NextSec = *Layout.getSectionOrder()[Next];
114  if (NextSec.isVirtualSection())
115    return 0;
116  return OffsetToAlignment(EndAddr, NextSec.getAlignment());
117}
118
119void MachObjectWriter::writeHeader(MachO::HeaderFileType Type,
120                                   unsigned NumLoadCommands,
121                                   unsigned LoadCommandsSize,
122                                   bool SubsectionsViaSymbols) {
123  uint32_t Flags = 0;
124
125  if (SubsectionsViaSymbols)
126    Flags |= MachO::MH_SUBSECTIONS_VIA_SYMBOLS;
127
128  // struct mach_header (28 bytes) or
129  // struct mach_header_64 (32 bytes)
130
131  uint64_t Start = getStream().tell();
132  (void) Start;
133
134  write32(is64Bit() ? MachO::MH_MAGIC_64 : MachO::MH_MAGIC);
135
136  write32(TargetObjectWriter->getCPUType());
137  write32(TargetObjectWriter->getCPUSubtype());
138
139  write32(Type);
140  write32(NumLoadCommands);
141  write32(LoadCommandsSize);
142  write32(Flags);
143  if (is64Bit())
144    write32(0); // reserved
145
146  assert(
147      getStream().tell() - Start ==
148      (is64Bit() ? sizeof(MachO::mach_header_64) : sizeof(MachO::mach_header)));
149}
150
151/// writeSegmentLoadCommand - Write a segment load command.
152///
153/// \param NumSections The number of sections in this segment.
154/// \param SectionDataSize The total size of the sections.
155void MachObjectWriter::writeSegmentLoadCommand(
156    StringRef Name, unsigned NumSections, uint64_t VMAddr, uint64_t VMSize,
157    uint64_t SectionDataStartOffset, uint64_t SectionDataSize, uint32_t MaxProt,
158    uint32_t InitProt) {
159  // struct segment_command (56 bytes) or
160  // struct segment_command_64 (72 bytes)
161
162  uint64_t Start = getStream().tell();
163  (void) Start;
164
165  unsigned SegmentLoadCommandSize =
166    is64Bit() ? sizeof(MachO::segment_command_64):
167    sizeof(MachO::segment_command);
168  write32(is64Bit() ? MachO::LC_SEGMENT_64 : MachO::LC_SEGMENT);
169  write32(SegmentLoadCommandSize +
170          NumSections * (is64Bit() ? sizeof(MachO::section_64) :
171                         sizeof(MachO::section)));
172
173  assert(Name.size() <= 16);
174  writeBytes(Name, 16);
175  if (is64Bit()) {
176    write64(VMAddr);                 // vmaddr
177    write64(VMSize); // vmsize
178    write64(SectionDataStartOffset); // file offset
179    write64(SectionDataSize); // file size
180  } else {
181    write32(VMAddr);                 // vmaddr
182    write32(VMSize); // vmsize
183    write32(SectionDataStartOffset); // file offset
184    write32(SectionDataSize); // file size
185  }
186  // maxprot
187  write32(MaxProt);
188  // initprot
189  write32(InitProt);
190  write32(NumSections);
191  write32(0); // flags
192
193  assert(getStream().tell() - Start == SegmentLoadCommandSize);
194}
195
196void MachObjectWriter::writeSection(const MCAsmLayout &Layout,
197                                    const MCSection &Sec, uint64_t VMAddr,
198                                    uint64_t FileOffset, unsigned Flags,
199                                    uint64_t RelocationsStart,
200                                    unsigned NumRelocations) {
201  uint64_t SectionSize = Layout.getSectionAddressSize(&Sec);
202  const MCSectionMachO &Section = cast<MCSectionMachO>(Sec);
203
204  // The offset is unused for virtual sections.
205  if (Section.isVirtualSection()) {
206    assert(Layout.getSectionFileSize(&Sec) == 0 && "Invalid file size!");
207    FileOffset = 0;
208  }
209
210  // struct section (68 bytes) or
211  // struct section_64 (80 bytes)
212
213  uint64_t Start = getStream().tell();
214  (void) Start;
215
216  writeBytes(Section.getSectionName(), 16);
217  writeBytes(Section.getSegmentName(), 16);
218  if (is64Bit()) {
219    write64(VMAddr);      // address
220    write64(SectionSize); // size
221  } else {
222    write32(VMAddr);      // address
223    write32(SectionSize); // size
224  }
225  write32(FileOffset);
226
227  assert(isPowerOf2_32(Section.getAlignment()) && "Invalid alignment!");
228  write32(Log2_32(Section.getAlignment()));
229  write32(NumRelocations ? RelocationsStart : 0);
230  write32(NumRelocations);
231  write32(Flags);
232  write32(IndirectSymBase.lookup(&Sec)); // reserved1
233  write32(Section.getStubSize()); // reserved2
234  if (is64Bit())
235    write32(0); // reserved3
236
237  assert(getStream().tell() - Start ==
238         (is64Bit() ? sizeof(MachO::section_64) : sizeof(MachO::section)));
239}
240
241void MachObjectWriter::writeSymtabLoadCommand(uint32_t SymbolOffset,
242                                              uint32_t NumSymbols,
243                                              uint32_t StringTableOffset,
244                                              uint32_t StringTableSize) {
245  // struct symtab_command (24 bytes)
246
247  uint64_t Start = getStream().tell();
248  (void) Start;
249
250  write32(MachO::LC_SYMTAB);
251  write32(sizeof(MachO::symtab_command));
252  write32(SymbolOffset);
253  write32(NumSymbols);
254  write32(StringTableOffset);
255  write32(StringTableSize);
256
257  assert(getStream().tell() - Start == sizeof(MachO::symtab_command));
258}
259
260void MachObjectWriter::writeDysymtabLoadCommand(uint32_t FirstLocalSymbol,
261                                                uint32_t NumLocalSymbols,
262                                                uint32_t FirstExternalSymbol,
263                                                uint32_t NumExternalSymbols,
264                                                uint32_t FirstUndefinedSymbol,
265                                                uint32_t NumUndefinedSymbols,
266                                                uint32_t IndirectSymbolOffset,
267                                                uint32_t NumIndirectSymbols) {
268  // struct dysymtab_command (80 bytes)
269
270  uint64_t Start = getStream().tell();
271  (void) Start;
272
273  write32(MachO::LC_DYSYMTAB);
274  write32(sizeof(MachO::dysymtab_command));
275  write32(FirstLocalSymbol);
276  write32(NumLocalSymbols);
277  write32(FirstExternalSymbol);
278  write32(NumExternalSymbols);
279  write32(FirstUndefinedSymbol);
280  write32(NumUndefinedSymbols);
281  write32(0); // tocoff
282  write32(0); // ntoc
283  write32(0); // modtaboff
284  write32(0); // nmodtab
285  write32(0); // extrefsymoff
286  write32(0); // nextrefsyms
287  write32(IndirectSymbolOffset);
288  write32(NumIndirectSymbols);
289  write32(0); // extreloff
290  write32(0); // nextrel
291  write32(0); // locreloff
292  write32(0); // nlocrel
293
294  assert(getStream().tell() - Start == sizeof(MachO::dysymtab_command));
295}
296
297MachObjectWriter::MachSymbolData *
298MachObjectWriter::findSymbolData(const MCSymbol &Sym) {
299  for (auto *SymbolData :
300       {&LocalSymbolData, &ExternalSymbolData, &UndefinedSymbolData})
301    for (MachSymbolData &Entry : *SymbolData)
302      if (Entry.Symbol == &Sym)
303        return &Entry;
304
305  return nullptr;
306}
307
308const MCSymbol &MachObjectWriter::findAliasedSymbol(const MCSymbol &Sym) const {
309  const MCSymbol *S = &Sym;
310  while (S->isVariable()) {
311    const MCExpr *Value = S->getVariableValue();
312    const auto *Ref = dyn_cast<MCSymbolRefExpr>(Value);
313    if (!Ref)
314      return *S;
315    S = &Ref->getSymbol();
316  }
317  return *S;
318}
319
320void MachObjectWriter::writeNlist(MachSymbolData &MSD,
321                                  const MCAsmLayout &Layout) {
322  const MCSymbol *Symbol = MSD.Symbol;
323  const MCSymbol &Data = *Symbol;
324  const MCSymbol *AliasedSymbol = &findAliasedSymbol(*Symbol);
325  uint8_t SectionIndex = MSD.SectionIndex;
326  uint8_t Type = 0;
327  uint64_t Address = 0;
328  bool IsAlias = Symbol != AliasedSymbol;
329
330  const MCSymbol &OrigSymbol = *Symbol;
331  MachSymbolData *AliaseeInfo;
332  if (IsAlias) {
333    AliaseeInfo = findSymbolData(*AliasedSymbol);
334    if (AliaseeInfo)
335      SectionIndex = AliaseeInfo->SectionIndex;
336    Symbol = AliasedSymbol;
337    // FIXME: Should this update Data as well?  Do we need OrigSymbol at all?
338  }
339
340  // Set the N_TYPE bits. See <mach-o/nlist.h>.
341  //
342  // FIXME: Are the prebound or indirect fields possible here?
343  if (IsAlias && Symbol->isUndefined())
344    Type = MachO::N_INDR;
345  else if (Symbol->isUndefined())
346    Type = MachO::N_UNDF;
347  else if (Symbol->isAbsolute())
348    Type = MachO::N_ABS;
349  else
350    Type = MachO::N_SECT;
351
352  // FIXME: Set STAB bits.
353
354  if (Data.isPrivateExtern())
355    Type |= MachO::N_PEXT;
356
357  // Set external bit.
358  if (Data.isExternal() || (!IsAlias && Symbol->isUndefined()))
359    Type |= MachO::N_EXT;
360
361  // Compute the symbol address.
362  if (IsAlias && Symbol->isUndefined())
363    Address = AliaseeInfo->StringIndex;
364  else if (Symbol->isDefined())
365    Address = getSymbolAddress(OrigSymbol, Layout);
366  else if (Symbol->isCommon()) {
367    // Common symbols are encoded with the size in the address
368    // field, and their alignment in the flags.
369    Address = Symbol->getCommonSize();
370  }
371
372  // struct nlist (12 bytes)
373
374  write32(MSD.StringIndex);
375  write8(Type);
376  write8(SectionIndex);
377
378  // The Mach-O streamer uses the lowest 16-bits of the flags for the 'desc'
379  // value.
380  write16(cast<MCSymbolMachO>(Symbol)->getEncodedFlags());
381  if (is64Bit())
382    write64(Address);
383  else
384    write32(Address);
385}
386
387void MachObjectWriter::writeLinkeditLoadCommand(uint32_t Type,
388                                                uint32_t DataOffset,
389                                                uint32_t DataSize) {
390  uint64_t Start = getStream().tell();
391  (void) Start;
392
393  write32(Type);
394  write32(sizeof(MachO::linkedit_data_command));
395  write32(DataOffset);
396  write32(DataSize);
397
398  assert(getStream().tell() - Start == sizeof(MachO::linkedit_data_command));
399}
400
401static unsigned ComputeLinkerOptionsLoadCommandSize(
402  const std::vector<std::string> &Options, bool is64Bit)
403{
404  unsigned Size = sizeof(MachO::linker_option_command);
405  for (const std::string &Option : Options)
406    Size += Option.size() + 1;
407  return RoundUpToAlignment(Size, is64Bit ? 8 : 4);
408}
409
410void MachObjectWriter::writeLinkerOptionsLoadCommand(
411  const std::vector<std::string> &Options)
412{
413  unsigned Size = ComputeLinkerOptionsLoadCommandSize(Options, is64Bit());
414  uint64_t Start = getStream().tell();
415  (void) Start;
416
417  write32(MachO::LC_LINKER_OPTION);
418  write32(Size);
419  write32(Options.size());
420  uint64_t BytesWritten = sizeof(MachO::linker_option_command);
421  for (const std::string &Option : Options) {
422    // Write each string, including the null byte.
423    writeBytes(Option.c_str(), Option.size() + 1);
424    BytesWritten += Option.size() + 1;
425  }
426
427  // Pad to a multiple of the pointer size.
428  writeBytes("", OffsetToAlignment(BytesWritten, is64Bit() ? 8 : 4));
429
430  assert(getStream().tell() - Start == Size);
431}
432
433void MachObjectWriter::recordRelocation(MCAssembler &Asm,
434                                        const MCAsmLayout &Layout,
435                                        const MCFragment *Fragment,
436                                        const MCFixup &Fixup, MCValue Target,
437                                        bool &IsPCRel, uint64_t &FixedValue) {
438  TargetObjectWriter->recordRelocation(this, Asm, Layout, Fragment, Fixup,
439                                       Target, FixedValue);
440}
441
442void MachObjectWriter::bindIndirectSymbols(MCAssembler &Asm) {
443  // This is the point where 'as' creates actual symbols for indirect symbols
444  // (in the following two passes). It would be easier for us to do this sooner
445  // when we see the attribute, but that makes getting the order in the symbol
446  // table much more complicated than it is worth.
447  //
448  // FIXME: Revisit this when the dust settles.
449
450  // Report errors for use of .indirect_symbol not in a symbol pointer section
451  // or stub section.
452  for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
453         ie = Asm.indirect_symbol_end(); it != ie; ++it) {
454    const MCSectionMachO &Section = cast<MCSectionMachO>(*it->Section);
455
456    if (Section.getType() != MachO::S_NON_LAZY_SYMBOL_POINTERS &&
457        Section.getType() != MachO::S_LAZY_SYMBOL_POINTERS &&
458        Section.getType() != MachO::S_SYMBOL_STUBS) {
459      MCSymbol &Symbol = *it->Symbol;
460      report_fatal_error("indirect symbol '" + Symbol.getName() +
461                         "' not in a symbol pointer or stub section");
462    }
463  }
464
465  // Bind non-lazy symbol pointers first.
466  unsigned IndirectIndex = 0;
467  for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
468         ie = Asm.indirect_symbol_end(); it != ie; ++it, ++IndirectIndex) {
469    const MCSectionMachO &Section = cast<MCSectionMachO>(*it->Section);
470
471    if (Section.getType() != MachO::S_NON_LAZY_SYMBOL_POINTERS)
472      continue;
473
474    // Initialize the section indirect symbol base, if necessary.
475    IndirectSymBase.insert(std::make_pair(it->Section, IndirectIndex));
476
477    Asm.registerSymbol(*it->Symbol);
478  }
479
480  // Then lazy symbol pointers and symbol stubs.
481  IndirectIndex = 0;
482  for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
483         ie = Asm.indirect_symbol_end(); it != ie; ++it, ++IndirectIndex) {
484    const MCSectionMachO &Section = cast<MCSectionMachO>(*it->Section);
485
486    if (Section.getType() != MachO::S_LAZY_SYMBOL_POINTERS &&
487        Section.getType() != MachO::S_SYMBOL_STUBS)
488      continue;
489
490    // Initialize the section indirect symbol base, if necessary.
491    IndirectSymBase.insert(std::make_pair(it->Section, IndirectIndex));
492
493    // Set the symbol type to undefined lazy, but only on construction.
494    //
495    // FIXME: Do not hardcode.
496    bool Created;
497    Asm.registerSymbol(*it->Symbol, &Created);
498    if (Created)
499      cast<MCSymbolMachO>(it->Symbol)->setReferenceTypeUndefinedLazy(true);
500  }
501}
502
503/// computeSymbolTable - Compute the symbol table data
504void MachObjectWriter::computeSymbolTable(
505    MCAssembler &Asm, std::vector<MachSymbolData> &LocalSymbolData,
506    std::vector<MachSymbolData> &ExternalSymbolData,
507    std::vector<MachSymbolData> &UndefinedSymbolData) {
508  // Build section lookup table.
509  DenseMap<const MCSection*, uint8_t> SectionIndexMap;
510  unsigned Index = 1;
511  for (MCAssembler::iterator it = Asm.begin(),
512         ie = Asm.end(); it != ie; ++it, ++Index)
513    SectionIndexMap[&*it] = Index;
514  assert(Index <= 256 && "Too many sections!");
515
516  // Build the string table.
517  for (const MCSymbol &Symbol : Asm.symbols()) {
518    if (!Asm.isSymbolLinkerVisible(Symbol))
519      continue;
520
521    StringTable.add(Symbol.getName());
522  }
523  StringTable.finalize();
524
525  // Build the symbol arrays but only for non-local symbols.
526  //
527  // The particular order that we collect and then sort the symbols is chosen to
528  // match 'as'. Even though it doesn't matter for correctness, this is
529  // important for letting us diff .o files.
530  for (const MCSymbol &Symbol : Asm.symbols()) {
531    // Ignore non-linker visible symbols.
532    if (!Asm.isSymbolLinkerVisible(Symbol))
533      continue;
534
535    if (!Symbol.isExternal() && !Symbol.isUndefined())
536      continue;
537
538    MachSymbolData MSD;
539    MSD.Symbol = &Symbol;
540    MSD.StringIndex = StringTable.getOffset(Symbol.getName());
541
542    if (Symbol.isUndefined()) {
543      MSD.SectionIndex = 0;
544      UndefinedSymbolData.push_back(MSD);
545    } else if (Symbol.isAbsolute()) {
546      MSD.SectionIndex = 0;
547      ExternalSymbolData.push_back(MSD);
548    } else {
549      MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
550      assert(MSD.SectionIndex && "Invalid section index!");
551      ExternalSymbolData.push_back(MSD);
552    }
553  }
554
555  // Now add the data for local symbols.
556  for (const MCSymbol &Symbol : Asm.symbols()) {
557    // Ignore non-linker visible symbols.
558    if (!Asm.isSymbolLinkerVisible(Symbol))
559      continue;
560
561    if (Symbol.isExternal() || Symbol.isUndefined())
562      continue;
563
564    MachSymbolData MSD;
565    MSD.Symbol = &Symbol;
566    MSD.StringIndex = StringTable.getOffset(Symbol.getName());
567
568    if (Symbol.isAbsolute()) {
569      MSD.SectionIndex = 0;
570      LocalSymbolData.push_back(MSD);
571    } else {
572      MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
573      assert(MSD.SectionIndex && "Invalid section index!");
574      LocalSymbolData.push_back(MSD);
575    }
576  }
577
578  // External and undefined symbols are required to be in lexicographic order.
579  std::sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
580  std::sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
581
582  // Set the symbol indices.
583  Index = 0;
584  for (auto *SymbolData :
585       {&LocalSymbolData, &ExternalSymbolData, &UndefinedSymbolData})
586    for (MachSymbolData &Entry : *SymbolData)
587      Entry.Symbol->setIndex(Index++);
588
589  for (const MCSection &Section : Asm) {
590    for (RelAndSymbol &Rel : Relocations[&Section]) {
591      if (!Rel.Sym)
592        continue;
593
594      // Set the Index and the IsExtern bit.
595      unsigned Index = Rel.Sym->getIndex();
596      assert(isInt<24>(Index));
597      if (IsLittleEndian)
598        Rel.MRE.r_word1 = (Rel.MRE.r_word1 & (~0U << 24)) | Index | (1 << 27);
599      else
600        Rel.MRE.r_word1 = (Rel.MRE.r_word1 & 0xff) | Index << 8 | (1 << 4);
601    }
602  }
603}
604
605void MachObjectWriter::computeSectionAddresses(const MCAssembler &Asm,
606                                               const MCAsmLayout &Layout) {
607  uint64_t StartAddress = 0;
608  for (const MCSection *Sec : Layout.getSectionOrder()) {
609    StartAddress = RoundUpToAlignment(StartAddress, Sec->getAlignment());
610    SectionAddress[Sec] = StartAddress;
611    StartAddress += Layout.getSectionAddressSize(Sec);
612
613    // Explicitly pad the section to match the alignment requirements of the
614    // following one. This is for 'gas' compatibility, it shouldn't
615    /// strictly be necessary.
616    StartAddress += getPaddingSize(Sec, Layout);
617  }
618}
619
620void MachObjectWriter::executePostLayoutBinding(MCAssembler &Asm,
621                                                const MCAsmLayout &Layout) {
622  computeSectionAddresses(Asm, Layout);
623
624  // Create symbol data for any indirect symbols.
625  bindIndirectSymbols(Asm);
626}
627
628bool MachObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(
629    const MCAssembler &Asm, const MCSymbol &A, const MCSymbol &B,
630    bool InSet) const {
631  // FIXME: We don't handle things like
632  // foo = .
633  // creating atoms.
634  if (A.isVariable() || B.isVariable())
635    return false;
636  return MCObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(Asm, A, B,
637                                                                InSet);
638}
639
640bool MachObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(
641    const MCAssembler &Asm, const MCSymbol &SymA, const MCFragment &FB,
642    bool InSet, bool IsPCRel) const {
643  if (InSet)
644    return true;
645
646  // The effective address is
647  //     addr(atom(A)) + offset(A)
648  //   - addr(atom(B)) - offset(B)
649  // and the offsets are not relocatable, so the fixup is fully resolved when
650  //  addr(atom(A)) - addr(atom(B)) == 0.
651  const MCSymbol &SA = findAliasedSymbol(SymA);
652  const MCSection &SecA = SA.getSection();
653  const MCSection &SecB = *FB.getParent();
654
655  if (IsPCRel) {
656    // The simple (Darwin, except on x86_64) way of dealing with this was to
657    // assume that any reference to a temporary symbol *must* be a temporary
658    // symbol in the same atom, unless the sections differ. Therefore, any PCrel
659    // relocation to a temporary symbol (in the same section) is fully
660    // resolved. This also works in conjunction with absolutized .set, which
661    // requires the compiler to use .set to absolutize the differences between
662    // symbols which the compiler knows to be assembly time constants, so we
663    // don't need to worry about considering symbol differences fully resolved.
664    //
665    // If the file isn't using sub-sections-via-symbols, we can make the
666    // same assumptions about any symbol that we normally make about
667    // assembler locals.
668
669    bool hasReliableSymbolDifference = isX86_64();
670    if (!hasReliableSymbolDifference) {
671      if (!SA.isInSection() || &SecA != &SecB ||
672          (!SA.isTemporary() && FB.getAtom() != SA.getFragment()->getAtom() &&
673           Asm.getSubsectionsViaSymbols()))
674        return false;
675      return true;
676    }
677    // For Darwin x86_64, there is one special case when the reference IsPCRel.
678    // If the fragment with the reference does not have a base symbol but meets
679    // the simple way of dealing with this, in that it is a temporary symbol in
680    // the same atom then it is assumed to be fully resolved.  This is needed so
681    // a relocation entry is not created and so the static linker does not
682    // mess up the reference later.
683    else if(!FB.getAtom() &&
684            SA.isTemporary() && SA.isInSection() && &SecA == &SecB){
685      return true;
686    }
687  }
688
689  // If they are not in the same section, we can't compute the diff.
690  if (&SecA != &SecB)
691    return false;
692
693  const MCFragment *FA = SA.getFragment();
694
695  // Bail if the symbol has no fragment.
696  if (!FA)
697    return false;
698
699  // If the atoms are the same, they are guaranteed to have the same address.
700  if (FA->getAtom() == FB.getAtom())
701    return true;
702
703  // Otherwise, we can't prove this is fully resolved.
704  return false;
705}
706
707void MachObjectWriter::writeObject(MCAssembler &Asm,
708                                   const MCAsmLayout &Layout) {
709  // Compute symbol table information and bind symbol indices.
710  computeSymbolTable(Asm, LocalSymbolData, ExternalSymbolData,
711                     UndefinedSymbolData);
712
713  unsigned NumSections = Asm.size();
714  const MCAssembler::VersionMinInfoType &VersionInfo =
715    Layout.getAssembler().getVersionMinInfo();
716
717  // The section data starts after the header, the segment load command (and
718  // section headers) and the symbol table.
719  unsigned NumLoadCommands = 1;
720  uint64_t LoadCommandsSize = is64Bit() ?
721    sizeof(MachO::segment_command_64) + NumSections * sizeof(MachO::section_64):
722    sizeof(MachO::segment_command) + NumSections * sizeof(MachO::section);
723
724  // Add the deployment target version info load command size, if used.
725  if (VersionInfo.Major != 0) {
726    ++NumLoadCommands;
727    LoadCommandsSize += sizeof(MachO::version_min_command);
728  }
729
730  // Add the data-in-code load command size, if used.
731  unsigned NumDataRegions = Asm.getDataRegions().size();
732  if (NumDataRegions) {
733    ++NumLoadCommands;
734    LoadCommandsSize += sizeof(MachO::linkedit_data_command);
735  }
736
737  // Add the loh load command size, if used.
738  uint64_t LOHRawSize = Asm.getLOHContainer().getEmitSize(*this, Layout);
739  uint64_t LOHSize = RoundUpToAlignment(LOHRawSize, is64Bit() ? 8 : 4);
740  if (LOHSize) {
741    ++NumLoadCommands;
742    LoadCommandsSize += sizeof(MachO::linkedit_data_command);
743  }
744
745  // Add the symbol table load command sizes, if used.
746  unsigned NumSymbols = LocalSymbolData.size() + ExternalSymbolData.size() +
747    UndefinedSymbolData.size();
748  if (NumSymbols) {
749    NumLoadCommands += 2;
750    LoadCommandsSize += (sizeof(MachO::symtab_command) +
751                         sizeof(MachO::dysymtab_command));
752  }
753
754  // Add the linker option load commands sizes.
755  for (const auto &Option : Asm.getLinkerOptions()) {
756    ++NumLoadCommands;
757    LoadCommandsSize += ComputeLinkerOptionsLoadCommandSize(Option, is64Bit());
758  }
759
760  // Compute the total size of the section data, as well as its file size and vm
761  // size.
762  uint64_t SectionDataStart = (is64Bit() ? sizeof(MachO::mach_header_64) :
763                               sizeof(MachO::mach_header)) + LoadCommandsSize;
764  uint64_t SectionDataSize = 0;
765  uint64_t SectionDataFileSize = 0;
766  uint64_t VMSize = 0;
767  for (const MCSection &Sec : Asm) {
768    uint64_t Address = getSectionAddress(&Sec);
769    uint64_t Size = Layout.getSectionAddressSize(&Sec);
770    uint64_t FileSize = Layout.getSectionFileSize(&Sec);
771    FileSize += getPaddingSize(&Sec, Layout);
772
773    VMSize = std::max(VMSize, Address + Size);
774
775    if (Sec.isVirtualSection())
776      continue;
777
778    SectionDataSize = std::max(SectionDataSize, Address + Size);
779    SectionDataFileSize = std::max(SectionDataFileSize, Address + FileSize);
780  }
781
782  // The section data is padded to 4 bytes.
783  //
784  // FIXME: Is this machine dependent?
785  unsigned SectionDataPadding = OffsetToAlignment(SectionDataFileSize, 4);
786  SectionDataFileSize += SectionDataPadding;
787
788  // Write the prolog, starting with the header and load command...
789  writeHeader(MachO::MH_OBJECT, NumLoadCommands, LoadCommandsSize,
790              Asm.getSubsectionsViaSymbols());
791  uint32_t Prot =
792      MachO::VM_PROT_READ | MachO::VM_PROT_WRITE | MachO::VM_PROT_EXECUTE;
793  writeSegmentLoadCommand("", NumSections, 0, VMSize, SectionDataStart,
794                          SectionDataSize, Prot, Prot);
795
796  // ... and then the section headers.
797  uint64_t RelocTableEnd = SectionDataStart + SectionDataFileSize;
798  for (const MCSection &Section : Asm) {
799    const auto &Sec = cast<MCSectionMachO>(Section);
800    std::vector<RelAndSymbol> &Relocs = Relocations[&Sec];
801    unsigned NumRelocs = Relocs.size();
802    uint64_t SectionStart = SectionDataStart + getSectionAddress(&Sec);
803    unsigned Flags = Sec.getTypeAndAttributes();
804    if (Sec.hasInstructions())
805      Flags |= MachO::S_ATTR_SOME_INSTRUCTIONS;
806    writeSection(Layout, Sec, getSectionAddress(&Sec), SectionStart, Flags,
807                 RelocTableEnd, NumRelocs);
808    RelocTableEnd += NumRelocs * sizeof(MachO::any_relocation_info);
809  }
810
811  // Write out the deployment target information, if it's available.
812  if (VersionInfo.Major != 0) {
813    assert(VersionInfo.Update < 256 && "unencodable update target version");
814    assert(VersionInfo.Minor < 256 && "unencodable minor target version");
815    assert(VersionInfo.Major < 65536 && "unencodable major target version");
816    uint32_t EncodedVersion = VersionInfo.Update | (VersionInfo.Minor << 8) |
817      (VersionInfo.Major << 16);
818    MachO::LoadCommandType LCType;
819    switch (VersionInfo.Kind) {
820    case MCVM_OSXVersionMin:
821      LCType = MachO::LC_VERSION_MIN_MACOSX;
822      break;
823    case MCVM_IOSVersionMin:
824      LCType = MachO::LC_VERSION_MIN_IPHONEOS;
825      break;
826    case MCVM_TvOSVersionMin:
827      LCType = MachO::LC_VERSION_MIN_TVOS;
828      break;
829    case MCVM_WatchOSVersionMin:
830      LCType = MachO::LC_VERSION_MIN_WATCHOS;
831      break;
832    }
833    write32(LCType);
834    write32(sizeof(MachO::version_min_command));
835    write32(EncodedVersion);
836    write32(0);         // reserved.
837  }
838
839  // Write the data-in-code load command, if used.
840  uint64_t DataInCodeTableEnd = RelocTableEnd + NumDataRegions * 8;
841  if (NumDataRegions) {
842    uint64_t DataRegionsOffset = RelocTableEnd;
843    uint64_t DataRegionsSize = NumDataRegions * 8;
844    writeLinkeditLoadCommand(MachO::LC_DATA_IN_CODE, DataRegionsOffset,
845                             DataRegionsSize);
846  }
847
848  // Write the loh load command, if used.
849  uint64_t LOHTableEnd = DataInCodeTableEnd + LOHSize;
850  if (LOHSize)
851    writeLinkeditLoadCommand(MachO::LC_LINKER_OPTIMIZATION_HINT,
852                             DataInCodeTableEnd, LOHSize);
853
854  // Write the symbol table load command, if used.
855  if (NumSymbols) {
856    unsigned FirstLocalSymbol = 0;
857    unsigned NumLocalSymbols = LocalSymbolData.size();
858    unsigned FirstExternalSymbol = FirstLocalSymbol + NumLocalSymbols;
859    unsigned NumExternalSymbols = ExternalSymbolData.size();
860    unsigned FirstUndefinedSymbol = FirstExternalSymbol + NumExternalSymbols;
861    unsigned NumUndefinedSymbols = UndefinedSymbolData.size();
862    unsigned NumIndirectSymbols = Asm.indirect_symbol_size();
863    unsigned NumSymTabSymbols =
864      NumLocalSymbols + NumExternalSymbols + NumUndefinedSymbols;
865    uint64_t IndirectSymbolSize = NumIndirectSymbols * 4;
866    uint64_t IndirectSymbolOffset = 0;
867
868    // If used, the indirect symbols are written after the section data.
869    if (NumIndirectSymbols)
870      IndirectSymbolOffset = LOHTableEnd;
871
872    // The symbol table is written after the indirect symbol data.
873    uint64_t SymbolTableOffset = LOHTableEnd + IndirectSymbolSize;
874
875    // The string table is written after symbol table.
876    uint64_t StringTableOffset =
877      SymbolTableOffset + NumSymTabSymbols * (is64Bit() ?
878                                              sizeof(MachO::nlist_64) :
879                                              sizeof(MachO::nlist));
880    writeSymtabLoadCommand(SymbolTableOffset, NumSymTabSymbols,
881                           StringTableOffset, StringTable.data().size());
882
883    writeDysymtabLoadCommand(FirstLocalSymbol, NumLocalSymbols,
884                             FirstExternalSymbol, NumExternalSymbols,
885                             FirstUndefinedSymbol, NumUndefinedSymbols,
886                             IndirectSymbolOffset, NumIndirectSymbols);
887  }
888
889  // Write the linker options load commands.
890  for (const auto &Option : Asm.getLinkerOptions())
891    writeLinkerOptionsLoadCommand(Option);
892
893  // Write the actual section data.
894  for (const MCSection &Sec : Asm) {
895    Asm.writeSectionData(&Sec, Layout);
896
897    uint64_t Pad = getPaddingSize(&Sec, Layout);
898    WriteZeros(Pad);
899  }
900
901  // Write the extra padding.
902  WriteZeros(SectionDataPadding);
903
904  // Write the relocation entries.
905  for (const MCSection &Sec : Asm) {
906    // Write the section relocation entries, in reverse order to match 'as'
907    // (approximately, the exact algorithm is more complicated than this).
908    std::vector<RelAndSymbol> &Relocs = Relocations[&Sec];
909    for (const RelAndSymbol &Rel : make_range(Relocs.rbegin(), Relocs.rend())) {
910      write32(Rel.MRE.r_word0);
911      write32(Rel.MRE.r_word1);
912    }
913  }
914
915  // Write out the data-in-code region payload, if there is one.
916  for (MCAssembler::const_data_region_iterator
917         it = Asm.data_region_begin(), ie = Asm.data_region_end();
918         it != ie; ++it) {
919    const DataRegionData *Data = &(*it);
920    uint64_t Start = getSymbolAddress(*Data->Start, Layout);
921    uint64_t End = getSymbolAddress(*Data->End, Layout);
922    DEBUG(dbgs() << "data in code region-- kind: " << Data->Kind
923                 << "  start: " << Start << "(" << Data->Start->getName() << ")"
924                 << "  end: " << End << "(" << Data->End->getName() << ")"
925                 << "  size: " << End - Start
926                 << "\n");
927    write32(Start);
928    write16(End - Start);
929    write16(Data->Kind);
930  }
931
932  // Write out the loh commands, if there is one.
933  if (LOHSize) {
934#ifndef NDEBUG
935    unsigned Start = getStream().tell();
936#endif
937    Asm.getLOHContainer().emit(*this, Layout);
938    // Pad to a multiple of the pointer size.
939    writeBytes("", OffsetToAlignment(LOHRawSize, is64Bit() ? 8 : 4));
940    assert(getStream().tell() - Start == LOHSize);
941  }
942
943  // Write the symbol table data, if used.
944  if (NumSymbols) {
945    // Write the indirect symbol entries.
946    for (MCAssembler::const_indirect_symbol_iterator
947           it = Asm.indirect_symbol_begin(),
948           ie = Asm.indirect_symbol_end(); it != ie; ++it) {
949      // Indirect symbols in the non-lazy symbol pointer section have some
950      // special handling.
951      const MCSectionMachO &Section =
952          static_cast<const MCSectionMachO &>(*it->Section);
953      if (Section.getType() == MachO::S_NON_LAZY_SYMBOL_POINTERS) {
954        // If this symbol is defined and internal, mark it as such.
955        if (it->Symbol->isDefined() && !it->Symbol->isExternal()) {
956          uint32_t Flags = MachO::INDIRECT_SYMBOL_LOCAL;
957          if (it->Symbol->isAbsolute())
958            Flags |= MachO::INDIRECT_SYMBOL_ABS;
959          write32(Flags);
960          continue;
961        }
962      }
963
964      write32(it->Symbol->getIndex());
965    }
966
967    // FIXME: Check that offsets match computed ones.
968
969    // Write the symbol table entries.
970    for (auto *SymbolData :
971         {&LocalSymbolData, &ExternalSymbolData, &UndefinedSymbolData})
972      for (MachSymbolData &Entry : *SymbolData)
973        writeNlist(Entry, Layout);
974
975    // Write the string table.
976    getStream() << StringTable.data();
977  }
978}
979
980MCObjectWriter *llvm::createMachObjectWriter(MCMachObjectTargetWriter *MOTW,
981                                             raw_pwrite_stream &OS,
982                                             bool IsLittleEndian) {
983  return new MachObjectWriter(MOTW, OS, IsLittleEndian);
984}
985