MachObjectWriter.cpp revision dce4a407a24b04eebc6a376f8e62b41aaa7b071f 
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
306void MachObjectWriter::WriteNlist(MachSymbolData &MSD,
307                                  const MCAsmLayout &Layout) {
308  MCSymbolData &Data = *MSD.SymbolData;
309  const MCSymbol &Symbol = Data.getSymbol();
310  uint8_t Type = 0;
311  uint16_t Flags = Data.getFlags();
312  uint64_t Address = 0;
313
314  // Set the N_TYPE bits. See <mach-o/nlist.h>.
315  //
316  // FIXME: Are the prebound or indirect fields possible here?
317  if (Symbol.isUndefined())
318    Type = MachO::N_UNDF;
319  else if (Symbol.isAbsolute())
320    Type = MachO::N_ABS;
321  else
322    Type = MachO::N_SECT;
323
324  // FIXME: Set STAB bits.
325
326  if (Data.isPrivateExtern())
327    Type |= MachO::N_PEXT;
328
329  // Set external bit.
330  if (Data.isExternal() || Symbol.isUndefined())
331    Type |= MachO::N_EXT;
332
333  // Compute the symbol address.
334  if (Symbol.isDefined()) {
335    Address = getSymbolAddress(&Data, Layout);
336  } else if (Data.isCommon()) {
337    // Common symbols are encoded with the size in the address
338    // field, and their alignment in the flags.
339    Address = Data.getCommonSize();
340
341    // Common alignment is packed into the 'desc' bits.
342    if (unsigned Align = Data.getCommonAlignment()) {
343      unsigned Log2Size = Log2_32(Align);
344      assert((1U << Log2Size) == Align && "Invalid 'common' alignment!");
345      if (Log2Size > 15)
346        report_fatal_error("invalid 'common' alignment '" +
347                           Twine(Align) + "' for '" + Symbol.getName() + "'",
348                           false);
349      // FIXME: Keep this mask with the SymbolFlags enumeration.
350      Flags = (Flags & 0xF0FF) | (Log2Size << 8);
351    }
352  }
353
354  if (Layout.getAssembler().isThumbFunc(&Symbol))
355    Flags |= SF_ThumbFunc;
356
357  // struct nlist (12 bytes)
358
359  Write32(MSD.StringIndex);
360  Write8(Type);
361  Write8(MSD.SectionIndex);
362
363  // The Mach-O streamer uses the lowest 16-bits of the flags for the 'desc'
364  // value.
365  Write16(Flags);
366  if (is64Bit())
367    Write64(Address);
368  else
369    Write32(Address);
370}
371
372void MachObjectWriter::WriteLinkeditLoadCommand(uint32_t Type,
373                                                uint32_t DataOffset,
374                                                uint32_t DataSize) {
375  uint64_t Start = OS.tell();
376  (void) Start;
377
378  Write32(Type);
379  Write32(sizeof(MachO::linkedit_data_command));
380  Write32(DataOffset);
381  Write32(DataSize);
382
383  assert(OS.tell() - Start == sizeof(MachO::linkedit_data_command));
384}
385
386static unsigned ComputeLinkerOptionsLoadCommandSize(
387  const std::vector<std::string> &Options, bool is64Bit)
388{
389  unsigned Size = sizeof(MachO::linker_options_command);
390  for (unsigned i = 0, e = Options.size(); i != e; ++i)
391    Size += Options[i].size() + 1;
392  return RoundUpToAlignment(Size, is64Bit ? 8 : 4);
393}
394
395void MachObjectWriter::WriteLinkerOptionsLoadCommand(
396  const std::vector<std::string> &Options)
397{
398  unsigned Size = ComputeLinkerOptionsLoadCommandSize(Options, is64Bit());
399  uint64_t Start = OS.tell();
400  (void) Start;
401
402  Write32(MachO::LC_LINKER_OPTIONS);
403  Write32(Size);
404  Write32(Options.size());
405  uint64_t BytesWritten = sizeof(MachO::linker_options_command);
406  for (unsigned i = 0, e = Options.size(); i != e; ++i) {
407    // Write each string, including the null byte.
408    const std::string &Option = Options[i];
409    WriteBytes(Option.c_str(), Option.size() + 1);
410    BytesWritten += Option.size() + 1;
411  }
412
413  // Pad to a multiple of the pointer size.
414  WriteBytes("", OffsetToAlignment(BytesWritten, is64Bit() ? 8 : 4));
415
416  assert(OS.tell() - Start == Size);
417}
418
419
420void MachObjectWriter::RecordRelocation(const MCAssembler &Asm,
421                                        const MCAsmLayout &Layout,
422                                        const MCFragment *Fragment,
423                                        const MCFixup &Fixup,
424                                        MCValue Target,
425                                        bool &IsPCRel,
426                                        uint64_t &FixedValue) {
427  TargetObjectWriter->RecordRelocation(this, Asm, Layout, Fragment, Fixup,
428                                       Target, FixedValue);
429}
430
431void MachObjectWriter::BindIndirectSymbols(MCAssembler &Asm) {
432  // This is the point where 'as' creates actual symbols for indirect symbols
433  // (in the following two passes). It would be easier for us to do this sooner
434  // when we see the attribute, but that makes getting the order in the symbol
435  // table much more complicated than it is worth.
436  //
437  // FIXME: Revisit this when the dust settles.
438
439  // Report errors for use of .indirect_symbol not in a symbol pointer section
440  // or stub section.
441  for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
442         ie = Asm.indirect_symbol_end(); it != ie; ++it) {
443    const MCSectionMachO &Section =
444      cast<MCSectionMachO>(it->SectionData->getSection());
445
446    if (Section.getType() != MachO::S_NON_LAZY_SYMBOL_POINTERS &&
447        Section.getType() != MachO::S_LAZY_SYMBOL_POINTERS &&
448        Section.getType() != MachO::S_SYMBOL_STUBS) {
449	MCSymbol &Symbol = *it->Symbol;
450	report_fatal_error("indirect symbol '" + Symbol.getName() +
451                           "' not in a symbol pointer or stub section");
452    }
453  }
454
455  // Bind non-lazy symbol pointers first.
456  unsigned IndirectIndex = 0;
457  for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
458         ie = Asm.indirect_symbol_end(); it != ie; ++it, ++IndirectIndex) {
459    const MCSectionMachO &Section =
460      cast<MCSectionMachO>(it->SectionData->getSection());
461
462    if (Section.getType() != MachO::S_NON_LAZY_SYMBOL_POINTERS)
463      continue;
464
465    // Initialize the section indirect symbol base, if necessary.
466    IndirectSymBase.insert(std::make_pair(it->SectionData, IndirectIndex));
467
468    Asm.getOrCreateSymbolData(*it->Symbol);
469  }
470
471  // Then lazy symbol pointers and symbol stubs.
472  IndirectIndex = 0;
473  for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
474         ie = Asm.indirect_symbol_end(); it != ie; ++it, ++IndirectIndex) {
475    const MCSectionMachO &Section =
476      cast<MCSectionMachO>(it->SectionData->getSection());
477
478    if (Section.getType() != MachO::S_LAZY_SYMBOL_POINTERS &&
479        Section.getType() != MachO::S_SYMBOL_STUBS)
480      continue;
481
482    // Initialize the section indirect symbol base, if necessary.
483    IndirectSymBase.insert(std::make_pair(it->SectionData, IndirectIndex));
484
485    // Set the symbol type to undefined lazy, but only on construction.
486    //
487    // FIXME: Do not hardcode.
488    bool Created;
489    MCSymbolData &Entry = Asm.getOrCreateSymbolData(*it->Symbol, &Created);
490    if (Created)
491      Entry.setFlags(Entry.getFlags() | 0x0001);
492  }
493}
494
495/// ComputeSymbolTable - Compute the symbol table data
496///
497/// \param StringTable [out] - The string table data.
498/// \param StringIndexMap [out] - Map from symbol names to offsets in the
499/// string table.
500void MachObjectWriter::
501ComputeSymbolTable(MCAssembler &Asm, SmallString<256> &StringTable,
502                   std::vector<MachSymbolData> &LocalSymbolData,
503                   std::vector<MachSymbolData> &ExternalSymbolData,
504                   std::vector<MachSymbolData> &UndefinedSymbolData) {
505  // Build section lookup table.
506  DenseMap<const MCSection*, uint8_t> SectionIndexMap;
507  unsigned Index = 1;
508  for (MCAssembler::iterator it = Asm.begin(),
509         ie = Asm.end(); it != ie; ++it, ++Index)
510    SectionIndexMap[&it->getSection()] = Index;
511  assert(Index <= 256 && "Too many sections!");
512
513  // Index 0 is always the empty string.
514  StringMap<uint64_t> StringIndexMap;
515  StringTable += '\x00';
516
517  // Build the symbol arrays and the string table, but only for non-local
518  // symbols.
519  //
520  // The particular order that we collect the symbols and create the string
521  // table, then sort the symbols is chosen to match 'as'. Even though it
522  // doesn't matter for correctness, this is important for letting us diff .o
523  // files.
524  for (MCSymbolData &SD : Asm.symbols()) {
525    const MCSymbol &Symbol = SD.getSymbol();
526
527    // Ignore non-linker visible symbols.
528    if (!Asm.isSymbolLinkerVisible(SD.getSymbol()))
529      continue;
530
531    if (!SD.isExternal() && !Symbol.isUndefined())
532      continue;
533
534    uint64_t &Entry = StringIndexMap[Symbol.getName()];
535    if (!Entry) {
536      Entry = StringTable.size();
537      StringTable += Symbol.getName();
538      StringTable += '\x00';
539    }
540
541    MachSymbolData MSD;
542    MSD.SymbolData = &SD;
543    MSD.StringIndex = Entry;
544
545    if (Symbol.isUndefined()) {
546      MSD.SectionIndex = 0;
547      UndefinedSymbolData.push_back(MSD);
548    } else if (Symbol.isAbsolute()) {
549      MSD.SectionIndex = 0;
550      ExternalSymbolData.push_back(MSD);
551    } else {
552      MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
553      assert(MSD.SectionIndex && "Invalid section index!");
554      ExternalSymbolData.push_back(MSD);
555    }
556  }
557
558  // Now add the data for local symbols.
559  for (MCSymbolData &SD : Asm.symbols()) {
560    const MCSymbol &Symbol = SD.getSymbol();
561
562    // Ignore non-linker visible symbols.
563    if (!Asm.isSymbolLinkerVisible(SD.getSymbol()))
564      continue;
565
566    if (SD.isExternal() || Symbol.isUndefined())
567      continue;
568
569    uint64_t &Entry = StringIndexMap[Symbol.getName()];
570    if (!Entry) {
571      Entry = StringTable.size();
572      StringTable += Symbol.getName();
573      StringTable += '\x00';
574    }
575
576    MachSymbolData MSD;
577    MSD.SymbolData = &SD;
578    MSD.StringIndex = Entry;
579
580    if (Symbol.isAbsolute()) {
581      MSD.SectionIndex = 0;
582      LocalSymbolData.push_back(MSD);
583    } else {
584      MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
585      assert(MSD.SectionIndex && "Invalid section index!");
586      LocalSymbolData.push_back(MSD);
587    }
588  }
589
590  // External and undefined symbols are required to be in lexicographic order.
591  std::sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
592  std::sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
593
594  // Set the symbol indices.
595  Index = 0;
596  for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
597    LocalSymbolData[i].SymbolData->setIndex(Index++);
598  for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
599    ExternalSymbolData[i].SymbolData->setIndex(Index++);
600  for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
601    UndefinedSymbolData[i].SymbolData->setIndex(Index++);
602
603  // The string table is padded to a multiple of 4.
604  while (StringTable.size() % 4)
605    StringTable += '\x00';
606}
607
608void MachObjectWriter::computeSectionAddresses(const MCAssembler &Asm,
609                                               const MCAsmLayout &Layout) {
610  uint64_t StartAddress = 0;
611  const SmallVectorImpl<MCSectionData*> &Order = Layout.getSectionOrder();
612  for (int i = 0, n = Order.size(); i != n ; ++i) {
613    const MCSectionData *SD = Order[i];
614    StartAddress = RoundUpToAlignment(StartAddress, SD->getAlignment());
615    SectionAddress[SD] = StartAddress;
616    StartAddress += Layout.getSectionAddressSize(SD);
617
618    // Explicitly pad the section to match the alignment requirements of the
619    // following one. This is for 'gas' compatibility, it shouldn't
620    /// strictly be necessary.
621    StartAddress += getPaddingSize(SD, Layout);
622  }
623}
624
625void MachObjectWriter::markAbsoluteVariableSymbols(MCAssembler &Asm,
626                                                   const MCAsmLayout &Layout) {
627  for (MCSymbolData &SD : Asm.symbols()) {
628    if (!SD.getSymbol().isVariable())
629      continue;
630
631    // Is the variable is a symbol difference (SA - SB + C) expression,
632    // and neither symbol is external, mark the variable as absolute.
633    const MCExpr *Expr = SD.getSymbol().getVariableValue();
634    MCValue Value;
635    if (Expr->EvaluateAsRelocatable(Value, &Layout)) {
636      if (Value.getSymA() && Value.getSymB())
637        const_cast<MCSymbol*>(&SD.getSymbol())->setAbsolute();
638    }
639  }
640}
641
642void MachObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
643                                                const MCAsmLayout &Layout) {
644  computeSectionAddresses(Asm, Layout);
645
646  // Create symbol data for any indirect symbols.
647  BindIndirectSymbols(Asm);
648
649  // Mark symbol difference expressions in variables (from .set or = directives)
650  // as absolute.
651  markAbsoluteVariableSymbols(Asm, Layout);
652
653  // Compute symbol table information and bind symbol indices.
654  ComputeSymbolTable(Asm, StringTable, LocalSymbolData, ExternalSymbolData,
655                     UndefinedSymbolData);
656}
657
658bool MachObjectWriter::
659IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
660                                       const MCSymbolData &DataA,
661                                       const MCFragment &FB,
662                                       bool InSet,
663                                       bool IsPCRel) const {
664  if (InSet)
665    return true;
666
667  // The effective address is
668  //     addr(atom(A)) + offset(A)
669  //   - addr(atom(B)) - offset(B)
670  // and the offsets are not relocatable, so the fixup is fully resolved when
671  //  addr(atom(A)) - addr(atom(B)) == 0.
672  const MCSymbolData *A_Base = nullptr, *B_Base = nullptr;
673
674  const MCSymbol &SA = DataA.getSymbol().AliasedSymbol();
675  const MCSection &SecA = SA.getSection();
676  const MCSection &SecB = FB.getParent()->getSection();
677
678  if (IsPCRel) {
679    // The simple (Darwin, except on x86_64) way of dealing with this was to
680    // assume that any reference to a temporary symbol *must* be a temporary
681    // symbol in the same atom, unless the sections differ. Therefore, any PCrel
682    // relocation to a temporary symbol (in the same section) is fully
683    // resolved. This also works in conjunction with absolutized .set, which
684    // requires the compiler to use .set to absolutize the differences between
685    // symbols which the compiler knows to be assembly time constants, so we
686    // don't need to worry about considering symbol differences fully resolved.
687    //
688    // If the file isn't using sub-sections-via-symbols, we can make the
689    // same assumptions about any symbol that we normally make about
690    // assembler locals.
691
692    bool hasReliableSymbolDifference = isX86_64();
693    if (!hasReliableSymbolDifference) {
694      if (!SA.isInSection() || &SecA != &SecB ||
695          (!SA.isTemporary() &&
696           FB.getAtom() != Asm.getSymbolData(SA).getFragment()->getAtom() &&
697           Asm.getSubsectionsViaSymbols()))
698        return false;
699      return true;
700    }
701    // For Darwin x86_64, there is one special case when the reference IsPCRel.
702    // If the fragment with the reference does not have a base symbol but meets
703    // the simple way of dealing with this, in that it is a temporary symbol in
704    // the same atom then it is assumed to be fully resolved.  This is needed so
705    // a relocation entry is not created and so the static linker does not
706    // mess up the reference later.
707    else if(!FB.getAtom() &&
708            SA.isTemporary() && SA.isInSection() && &SecA == &SecB){
709      return true;
710    }
711  } else {
712    if (!TargetObjectWriter->useAggressiveSymbolFolding())
713      return false;
714  }
715
716  const MCFragment *FA = Asm.getSymbolData(SA).getFragment();
717
718  // Bail if the symbol has no fragment.
719  if (!FA)
720    return false;
721
722  A_Base = FA->getAtom();
723  if (!A_Base)
724    return false;
725
726  B_Base = FB.getAtom();
727  if (!B_Base)
728    return false;
729
730  // If the atoms are the same, they are guaranteed to have the same address.
731  if (A_Base == B_Base)
732    return true;
733
734  // Otherwise, we can't prove this is fully resolved.
735  return false;
736}
737
738void MachObjectWriter::WriteObject(MCAssembler &Asm,
739                                   const MCAsmLayout &Layout) {
740  unsigned NumSections = Asm.size();
741  const MCAssembler::VersionMinInfoType &VersionInfo =
742    Layout.getAssembler().getVersionMinInfo();
743
744  // The section data starts after the header, the segment load command (and
745  // section headers) and the symbol table.
746  unsigned NumLoadCommands = 1;
747  uint64_t LoadCommandsSize = is64Bit() ?
748    sizeof(MachO::segment_command_64) + NumSections * sizeof(MachO::section_64):
749    sizeof(MachO::segment_command) + NumSections * sizeof(MachO::section);
750
751  // Add the deployment target version info load command size, if used.
752  if (VersionInfo.Major != 0) {
753    ++NumLoadCommands;
754    LoadCommandsSize += sizeof(MachO::version_min_command);
755  }
756
757  // Add the data-in-code load command size, if used.
758  unsigned NumDataRegions = Asm.getDataRegions().size();
759  if (NumDataRegions) {
760    ++NumLoadCommands;
761    LoadCommandsSize += sizeof(MachO::linkedit_data_command);
762  }
763
764  // Add the loh load command size, if used.
765  uint64_t LOHRawSize = Asm.getLOHContainer().getEmitSize(*this, Layout);
766  uint64_t LOHSize = RoundUpToAlignment(LOHRawSize, is64Bit() ? 8 : 4);
767  if (LOHSize) {
768    ++NumLoadCommands;
769    LoadCommandsSize += sizeof(MachO::linkedit_data_command);
770  }
771
772  // Add the symbol table load command sizes, if used.
773  unsigned NumSymbols = LocalSymbolData.size() + ExternalSymbolData.size() +
774    UndefinedSymbolData.size();
775  if (NumSymbols) {
776    NumLoadCommands += 2;
777    LoadCommandsSize += (sizeof(MachO::symtab_command) +
778                         sizeof(MachO::dysymtab_command));
779  }
780
781  // Add the linker option load commands sizes.
782  const std::vector<std::vector<std::string> > &LinkerOptions =
783    Asm.getLinkerOptions();
784  for (unsigned i = 0, e = LinkerOptions.size(); i != e; ++i) {
785    ++NumLoadCommands;
786    LoadCommandsSize += ComputeLinkerOptionsLoadCommandSize(LinkerOptions[i],
787                                                            is64Bit());
788  }
789
790  // Compute the total size of the section data, as well as its file size and vm
791  // size.
792  uint64_t SectionDataStart = (is64Bit() ? sizeof(MachO::mach_header_64) :
793                               sizeof(MachO::mach_header)) + LoadCommandsSize;
794  uint64_t SectionDataSize = 0;
795  uint64_t SectionDataFileSize = 0;
796  uint64_t VMSize = 0;
797  for (MCAssembler::const_iterator it = Asm.begin(),
798         ie = Asm.end(); it != ie; ++it) {
799    const MCSectionData &SD = *it;
800    uint64_t Address = getSectionAddress(&SD);
801    uint64_t Size = Layout.getSectionAddressSize(&SD);
802    uint64_t FileSize = Layout.getSectionFileSize(&SD);
803    FileSize += getPaddingSize(&SD, Layout);
804
805    VMSize = std::max(VMSize, Address + Size);
806
807    if (SD.getSection().isVirtualSection())
808      continue;
809
810    SectionDataSize = std::max(SectionDataSize, Address + Size);
811    SectionDataFileSize = std::max(SectionDataFileSize, Address + FileSize);
812  }
813
814  // The section data is padded to 4 bytes.
815  //
816  // FIXME: Is this machine dependent?
817  unsigned SectionDataPadding = OffsetToAlignment(SectionDataFileSize, 4);
818  SectionDataFileSize += SectionDataPadding;
819
820  // Write the prolog, starting with the header and load command...
821  WriteHeader(NumLoadCommands, LoadCommandsSize,
822              Asm.getSubsectionsViaSymbols());
823  WriteSegmentLoadCommand(NumSections, VMSize,
824                          SectionDataStart, SectionDataSize);
825
826  // ... and then the section headers.
827  uint64_t RelocTableEnd = SectionDataStart + SectionDataFileSize;
828  for (MCAssembler::const_iterator it = Asm.begin(),
829         ie = Asm.end(); it != ie; ++it) {
830    std::vector<MachO::any_relocation_info> &Relocs = Relocations[it];
831    unsigned NumRelocs = Relocs.size();
832    uint64_t SectionStart = SectionDataStart + getSectionAddress(it);
833    WriteSection(Asm, Layout, *it, SectionStart, RelocTableEnd, NumRelocs);
834    RelocTableEnd += NumRelocs * sizeof(MachO::any_relocation_info);
835  }
836
837  // Write out the deployment target information, if it's available.
838  if (VersionInfo.Major != 0) {
839    assert(VersionInfo.Update < 256 && "unencodable update target version");
840    assert(VersionInfo.Minor < 256 && "unencodable minor target version");
841    assert(VersionInfo.Major < 65536 && "unencodable major target version");
842    uint32_t EncodedVersion = VersionInfo.Update | (VersionInfo.Minor << 8) |
843      (VersionInfo.Major << 16);
844    Write32(VersionInfo.Kind == MCVM_OSXVersionMin ? MachO::LC_VERSION_MIN_MACOSX :
845            MachO::LC_VERSION_MIN_IPHONEOS);
846    Write32(sizeof(MachO::version_min_command));
847    Write32(EncodedVersion);
848    Write32(0);         // reserved.
849  }
850
851  // Write the data-in-code load command, if used.
852  uint64_t DataInCodeTableEnd = RelocTableEnd + NumDataRegions * 8;
853  if (NumDataRegions) {
854    uint64_t DataRegionsOffset = RelocTableEnd;
855    uint64_t DataRegionsSize = NumDataRegions * 8;
856    WriteLinkeditLoadCommand(MachO::LC_DATA_IN_CODE, DataRegionsOffset,
857                             DataRegionsSize);
858  }
859
860  // Write the loh load command, if used.
861  uint64_t LOHTableEnd = DataInCodeTableEnd + LOHSize;
862  if (LOHSize)
863    WriteLinkeditLoadCommand(MachO::LC_LINKER_OPTIMIZATION_HINT,
864                             DataInCodeTableEnd, LOHSize);
865
866  // Write the symbol table load command, if used.
867  if (NumSymbols) {
868    unsigned FirstLocalSymbol = 0;
869    unsigned NumLocalSymbols = LocalSymbolData.size();
870    unsigned FirstExternalSymbol = FirstLocalSymbol + NumLocalSymbols;
871    unsigned NumExternalSymbols = ExternalSymbolData.size();
872    unsigned FirstUndefinedSymbol = FirstExternalSymbol + NumExternalSymbols;
873    unsigned NumUndefinedSymbols = UndefinedSymbolData.size();
874    unsigned NumIndirectSymbols = Asm.indirect_symbol_size();
875    unsigned NumSymTabSymbols =
876      NumLocalSymbols + NumExternalSymbols + NumUndefinedSymbols;
877    uint64_t IndirectSymbolSize = NumIndirectSymbols * 4;
878    uint64_t IndirectSymbolOffset = 0;
879
880    // If used, the indirect symbols are written after the section data.
881    if (NumIndirectSymbols)
882      IndirectSymbolOffset = LOHTableEnd;
883
884    // The symbol table is written after the indirect symbol data.
885    uint64_t SymbolTableOffset = LOHTableEnd + IndirectSymbolSize;
886
887    // The string table is written after symbol table.
888    uint64_t StringTableOffset =
889      SymbolTableOffset + NumSymTabSymbols * (is64Bit() ?
890                                              sizeof(MachO::nlist_64) :
891                                              sizeof(MachO::nlist));
892    WriteSymtabLoadCommand(SymbolTableOffset, NumSymTabSymbols,
893                           StringTableOffset, StringTable.size());
894
895    WriteDysymtabLoadCommand(FirstLocalSymbol, NumLocalSymbols,
896                             FirstExternalSymbol, NumExternalSymbols,
897                             FirstUndefinedSymbol, NumUndefinedSymbols,
898                             IndirectSymbolOffset, NumIndirectSymbols);
899  }
900
901  // Write the linker options load commands.
902  for (unsigned i = 0, e = LinkerOptions.size(); i != e; ++i) {
903    WriteLinkerOptionsLoadCommand(LinkerOptions[i]);
904  }
905
906  // Write the actual section data.
907  for (MCAssembler::const_iterator it = Asm.begin(),
908         ie = Asm.end(); it != ie; ++it) {
909    Asm.writeSectionData(it, Layout);
910
911    uint64_t Pad = getPaddingSize(it, Layout);
912    for (unsigned int i = 0; i < Pad; ++i)
913      Write8(0);
914  }
915
916  // Write the extra padding.
917  WriteZeros(SectionDataPadding);
918
919  // Write the relocation entries.
920  for (MCAssembler::const_iterator it = Asm.begin(),
921         ie = Asm.end(); it != ie; ++it) {
922    // Write the section relocation entries, in reverse order to match 'as'
923    // (approximately, the exact algorithm is more complicated than this).
924    std::vector<MachO::any_relocation_info> &Relocs = Relocations[it];
925    for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
926      Write32(Relocs[e - i - 1].r_word0);
927      Write32(Relocs[e - i - 1].r_word1);
928    }
929  }
930
931  // Write out the data-in-code region payload, if there is one.
932  for (MCAssembler::const_data_region_iterator
933         it = Asm.data_region_begin(), ie = Asm.data_region_end();
934         it != ie; ++it) {
935    const DataRegionData *Data = &(*it);
936    uint64_t Start =
937      getSymbolAddress(&Layout.getAssembler().getSymbolData(*Data->Start),
938                       Layout);
939    uint64_t End =
940      getSymbolAddress(&Layout.getAssembler().getSymbolData(*Data->End),
941                       Layout);
942    DEBUG(dbgs() << "data in code region-- kind: " << Data->Kind
943                 << "  start: " << Start << "(" << Data->Start->getName() << ")"
944                 << "  end: " << End << "(" << Data->End->getName() << ")"
945                 << "  size: " << End - Start
946                 << "\n");
947    Write32(Start);
948    Write16(End - Start);
949    Write16(Data->Kind);
950  }
951
952  // Write out the loh commands, if there is one.
953  if (LOHSize) {
954#ifndef NDEBUG
955    unsigned Start = OS.tell();
956#endif
957    Asm.getLOHContainer().Emit(*this, Layout);
958    // Pad to a multiple of the pointer size.
959    WriteBytes("", OffsetToAlignment(LOHRawSize, is64Bit() ? 8 : 4));
960    assert(OS.tell() - Start == LOHSize);
961  }
962
963  // Write the symbol table data, if used.
964  if (NumSymbols) {
965    // Write the indirect symbol entries.
966    for (MCAssembler::const_indirect_symbol_iterator
967           it = Asm.indirect_symbol_begin(),
968           ie = Asm.indirect_symbol_end(); it != ie; ++it) {
969      // Indirect symbols in the non-lazy symbol pointer section have some
970      // special handling.
971      const MCSectionMachO &Section =
972        static_cast<const MCSectionMachO&>(it->SectionData->getSection());
973      if (Section.getType() == MachO::S_NON_LAZY_SYMBOL_POINTERS) {
974        // If this symbol is defined and internal, mark it as such.
975        if (it->Symbol->isDefined() &&
976            !Asm.getSymbolData(*it->Symbol).isExternal()) {
977          uint32_t Flags = MachO::INDIRECT_SYMBOL_LOCAL;
978          if (it->Symbol->isAbsolute())
979            Flags |= MachO::INDIRECT_SYMBOL_ABS;
980          Write32(Flags);
981          continue;
982        }
983      }
984
985      Write32(Asm.getSymbolData(*it->Symbol).getIndex());
986    }
987
988    // FIXME: Check that offsets match computed ones.
989
990    // Write the symbol table entries.
991    for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
992      WriteNlist(LocalSymbolData[i], Layout);
993    for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
994      WriteNlist(ExternalSymbolData[i], Layout);
995    for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
996      WriteNlist(UndefinedSymbolData[i], Layout);
997
998    // Write the string table.
999    OS << StringTable.str();
1000  }
1001}
1002
1003MCObjectWriter *llvm::createMachObjectWriter(MCMachObjectTargetWriter *MOTW,
1004                                             raw_ostream &OS,
1005                                             bool IsLittleEndian) {
1006  return new MachObjectWriter(MOTW, OS, IsLittleEndian);
1007}
1008