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      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>
     27 using namespace llvm;
     28 
     29 #define DEBUG_TYPE "mc"
     30 
     31 void 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 
     41 bool 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 
     55 bool MachObjectWriter::
     56 MachSymbolData::operator<(const MachSymbolData &RHS) const {
     57   return Symbol->getName() < RHS.Symbol->getName();
     58 }
     59 
     60 bool 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 
     67 uint64_t MachObjectWriter::getFragmentAddress(const MCFragment *Fragment,
     68                                               const MCAsmLayout &Layout) const {
     69   return getSectionAddress(Fragment->getParent()) +
     70          Layout.getFragmentOffset(Fragment);
     71 }
     72 
     73 uint64_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 
    106 uint64_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 
    119 void 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.
    155 void 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 
    196 void 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 
    241 void 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 
    260 void 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 
    297 MachObjectWriter::MachSymbolData *
    298 MachObjectWriter::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 
    308 const 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 
    320 void 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?
    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   bool EncodeAsAltEntry =
    381     IsAlias && cast<MCSymbolMachO>(OrigSymbol).isAltEntry();
    382   write16(cast<MCSymbolMachO>(Symbol)->getEncodedFlags(EncodeAsAltEntry));
    383   if (is64Bit())
    384     write64(Address);
    385   else
    386     write32(Address);
    387 }
    388 
    389 void MachObjectWriter::writeLinkeditLoadCommand(uint32_t Type,
    390                                                 uint32_t DataOffset,
    391                                                 uint32_t DataSize) {
    392   uint64_t Start = getStream().tell();
    393   (void) Start;
    394 
    395   write32(Type);
    396   write32(sizeof(MachO::linkedit_data_command));
    397   write32(DataOffset);
    398   write32(DataSize);
    399 
    400   assert(getStream().tell() - Start == sizeof(MachO::linkedit_data_command));
    401 }
    402 
    403 static unsigned ComputeLinkerOptionsLoadCommandSize(
    404   const std::vector<std::string> &Options, bool is64Bit)
    405 {
    406   unsigned Size = sizeof(MachO::linker_option_command);
    407   for (const std::string &Option : Options)
    408     Size += Option.size() + 1;
    409   return alignTo(Size, is64Bit ? 8 : 4);
    410 }
    411 
    412 void MachObjectWriter::writeLinkerOptionsLoadCommand(
    413   const std::vector<std::string> &Options)
    414 {
    415   unsigned Size = ComputeLinkerOptionsLoadCommandSize(Options, is64Bit());
    416   uint64_t Start = getStream().tell();
    417   (void) Start;
    418 
    419   write32(MachO::LC_LINKER_OPTION);
    420   write32(Size);
    421   write32(Options.size());
    422   uint64_t BytesWritten = sizeof(MachO::linker_option_command);
    423   for (const std::string &Option : Options) {
    424     // Write each string, including the null byte.
    425     writeBytes(Option.c_str(), Option.size() + 1);
    426     BytesWritten += Option.size() + 1;
    427   }
    428 
    429   // Pad to a multiple of the pointer size.
    430   writeBytes("", OffsetToAlignment(BytesWritten, is64Bit() ? 8 : 4));
    431 
    432   assert(getStream().tell() - Start == Size);
    433 }
    434 
    435 void MachObjectWriter::recordRelocation(MCAssembler &Asm,
    436                                         const MCAsmLayout &Layout,
    437                                         const MCFragment *Fragment,
    438                                         const MCFixup &Fixup, MCValue Target,
    439                                         bool &IsPCRel, uint64_t &FixedValue) {
    440   TargetObjectWriter->recordRelocation(this, Asm, Layout, Fragment, Fixup,
    441                                        Target, FixedValue);
    442 }
    443 
    444 void MachObjectWriter::bindIndirectSymbols(MCAssembler &Asm) {
    445   // This is the point where 'as' creates actual symbols for indirect symbols
    446   // (in the following two passes). It would be easier for us to do this sooner
    447   // when we see the attribute, but that makes getting the order in the symbol
    448   // table much more complicated than it is worth.
    449   //
    450   // FIXME: Revisit this when the dust settles.
    451 
    452   // Report errors for use of .indirect_symbol not in a symbol pointer section
    453   // or stub section.
    454   for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
    455          ie = Asm.indirect_symbol_end(); it != ie; ++it) {
    456     const MCSectionMachO &Section = cast<MCSectionMachO>(*it->Section);
    457 
    458     if (Section.getType() != MachO::S_NON_LAZY_SYMBOL_POINTERS &&
    459         Section.getType() != MachO::S_LAZY_SYMBOL_POINTERS &&
    460         Section.getType() != MachO::S_THREAD_LOCAL_VARIABLE_POINTERS &&
    461         Section.getType() != MachO::S_SYMBOL_STUBS) {
    462       MCSymbol &Symbol = *it->Symbol;
    463       report_fatal_error("indirect symbol '" + Symbol.getName() +
    464                          "' not in a symbol pointer or stub section");
    465     }
    466   }
    467 
    468   // Bind non-lazy symbol pointers first.
    469   unsigned IndirectIndex = 0;
    470   for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
    471          ie = Asm.indirect_symbol_end(); it != ie; ++it, ++IndirectIndex) {
    472     const MCSectionMachO &Section = cast<MCSectionMachO>(*it->Section);
    473 
    474     if (Section.getType() != MachO::S_NON_LAZY_SYMBOL_POINTERS &&
    475         Section.getType() !=  MachO::S_THREAD_LOCAL_VARIABLE_POINTERS)
    476       continue;
    477 
    478     // Initialize the section indirect symbol base, if necessary.
    479     IndirectSymBase.insert(std::make_pair(it->Section, IndirectIndex));
    480 
    481     Asm.registerSymbol(*it->Symbol);
    482   }
    483 
    484   // Then lazy symbol pointers and symbol stubs.
    485   IndirectIndex = 0;
    486   for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
    487          ie = Asm.indirect_symbol_end(); it != ie; ++it, ++IndirectIndex) {
    488     const MCSectionMachO &Section = cast<MCSectionMachO>(*it->Section);
    489 
    490     if (Section.getType() != MachO::S_LAZY_SYMBOL_POINTERS &&
    491         Section.getType() != MachO::S_SYMBOL_STUBS)
    492       continue;
    493 
    494     // Initialize the section indirect symbol base, if necessary.
    495     IndirectSymBase.insert(std::make_pair(it->Section, IndirectIndex));
    496 
    497     // Set the symbol type to undefined lazy, but only on construction.
    498     //
    499     // FIXME: Do not hardcode.
    500     bool Created;
    501     Asm.registerSymbol(*it->Symbol, &Created);
    502     if (Created)
    503       cast<MCSymbolMachO>(it->Symbol)->setReferenceTypeUndefinedLazy(true);
    504   }
    505 }
    506 
    507 /// computeSymbolTable - Compute the symbol table data
    508 void MachObjectWriter::computeSymbolTable(
    509     MCAssembler &Asm, std::vector<MachSymbolData> &LocalSymbolData,
    510     std::vector<MachSymbolData> &ExternalSymbolData,
    511     std::vector<MachSymbolData> &UndefinedSymbolData) {
    512   // Build section lookup table.
    513   DenseMap<const MCSection*, uint8_t> SectionIndexMap;
    514   unsigned Index = 1;
    515   for (MCAssembler::iterator it = Asm.begin(),
    516          ie = Asm.end(); it != ie; ++it, ++Index)
    517     SectionIndexMap[&*it] = Index;
    518   assert(Index <= 256 && "Too many sections!");
    519 
    520   // Build the string table.
    521   for (const MCSymbol &Symbol : Asm.symbols()) {
    522     if (!Asm.isSymbolLinkerVisible(Symbol))
    523       continue;
    524 
    525     StringTable.add(Symbol.getName());
    526   }
    527   StringTable.finalize();
    528 
    529   // Build the symbol arrays but only for non-local symbols.
    530   //
    531   // The particular order that we collect and then sort the symbols is chosen to
    532   // match 'as'. Even though it doesn't matter for correctness, this is
    533   // important for letting us diff .o files.
    534   for (const MCSymbol &Symbol : Asm.symbols()) {
    535     // Ignore non-linker visible symbols.
    536     if (!Asm.isSymbolLinkerVisible(Symbol))
    537       continue;
    538 
    539     if (!Symbol.isExternal() && !Symbol.isUndefined())
    540       continue;
    541 
    542     MachSymbolData MSD;
    543     MSD.Symbol = &Symbol;
    544     MSD.StringIndex = StringTable.getOffset(Symbol.getName());
    545 
    546     if (Symbol.isUndefined()) {
    547       MSD.SectionIndex = 0;
    548       UndefinedSymbolData.push_back(MSD);
    549     } else if (Symbol.isAbsolute()) {
    550       MSD.SectionIndex = 0;
    551       ExternalSymbolData.push_back(MSD);
    552     } else {
    553       MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
    554       assert(MSD.SectionIndex && "Invalid section index!");
    555       ExternalSymbolData.push_back(MSD);
    556     }
    557   }
    558 
    559   // Now add the data for local symbols.
    560   for (const MCSymbol &Symbol : Asm.symbols()) {
    561     // Ignore non-linker visible symbols.
    562     if (!Asm.isSymbolLinkerVisible(Symbol))
    563       continue;
    564 
    565     if (Symbol.isExternal() || Symbol.isUndefined())
    566       continue;
    567 
    568     MachSymbolData MSD;
    569     MSD.Symbol = &Symbol;
    570     MSD.StringIndex = StringTable.getOffset(Symbol.getName());
    571 
    572     if (Symbol.isAbsolute()) {
    573       MSD.SectionIndex = 0;
    574       LocalSymbolData.push_back(MSD);
    575     } else {
    576       MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
    577       assert(MSD.SectionIndex && "Invalid section index!");
    578       LocalSymbolData.push_back(MSD);
    579     }
    580   }
    581 
    582   // External and undefined symbols are required to be in lexicographic order.
    583   std::sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
    584   std::sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
    585 
    586   // Set the symbol indices.
    587   Index = 0;
    588   for (auto *SymbolData :
    589        {&LocalSymbolData, &ExternalSymbolData, &UndefinedSymbolData})
    590     for (MachSymbolData &Entry : *SymbolData)
    591       Entry.Symbol->setIndex(Index++);
    592 
    593   for (const MCSection &Section : Asm) {
    594     for (RelAndSymbol &Rel : Relocations[&Section]) {
    595       if (!Rel.Sym)
    596         continue;
    597 
    598       // Set the Index and the IsExtern bit.
    599       unsigned Index = Rel.Sym->getIndex();
    600       assert(isInt<24>(Index));
    601       if (IsLittleEndian)
    602         Rel.MRE.r_word1 = (Rel.MRE.r_word1 & (~0U << 24)) | Index | (1 << 27);
    603       else
    604         Rel.MRE.r_word1 = (Rel.MRE.r_word1 & 0xff) | Index << 8 | (1 << 4);
    605     }
    606   }
    607 }
    608 
    609 void MachObjectWriter::computeSectionAddresses(const MCAssembler &Asm,
    610                                                const MCAsmLayout &Layout) {
    611   uint64_t StartAddress = 0;
    612   for (const MCSection *Sec : Layout.getSectionOrder()) {
    613     StartAddress = alignTo(StartAddress, Sec->getAlignment());
    614     SectionAddress[Sec] = StartAddress;
    615     StartAddress += Layout.getSectionAddressSize(Sec);
    616 
    617     // Explicitly pad the section to match the alignment requirements of the
    618     // following one. This is for 'gas' compatibility, it shouldn't
    619     /// strictly be necessary.
    620     StartAddress += getPaddingSize(Sec, Layout);
    621   }
    622 }
    623 
    624 void MachObjectWriter::executePostLayoutBinding(MCAssembler &Asm,
    625                                                 const MCAsmLayout &Layout) {
    626   computeSectionAddresses(Asm, Layout);
    627 
    628   // Create symbol data for any indirect symbols.
    629   bindIndirectSymbols(Asm);
    630 }
    631 
    632 bool MachObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(
    633     const MCAssembler &Asm, const MCSymbol &A, const MCSymbol &B,
    634     bool InSet) const {
    635   // FIXME: We don't handle things like
    636   // foo = .
    637   // creating atoms.
    638   if (A.isVariable() || B.isVariable())
    639     return false;
    640   return MCObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(Asm, A, B,
    641                                                                 InSet);
    642 }
    643 
    644 bool MachObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(
    645     const MCAssembler &Asm, const MCSymbol &SymA, const MCFragment &FB,
    646     bool InSet, bool IsPCRel) const {
    647   if (InSet)
    648     return true;
    649 
    650   // The effective address is
    651   //     addr(atom(A)) + offset(A)
    652   //   - addr(atom(B)) - offset(B)
    653   // and the offsets are not relocatable, so the fixup is fully resolved when
    654   //  addr(atom(A)) - addr(atom(B)) == 0.
    655   const MCSymbol &SA = findAliasedSymbol(SymA);
    656   const MCSection &SecA = SA.getSection();
    657   const MCSection &SecB = *FB.getParent();
    658 
    659   if (IsPCRel) {
    660     // The simple (Darwin, except on x86_64) way of dealing with this was to
    661     // assume that any reference to a temporary symbol *must* be a temporary
    662     // symbol in the same atom, unless the sections differ. Therefore, any PCrel
    663     // relocation to a temporary symbol (in the same section) is fully
    664     // resolved. This also works in conjunction with absolutized .set, which
    665     // requires the compiler to use .set to absolutize the differences between
    666     // symbols which the compiler knows to be assembly time constants, so we
    667     // don't need to worry about considering symbol differences fully resolved.
    668     //
    669     // If the file isn't using sub-sections-via-symbols, we can make the
    670     // same assumptions about any symbol that we normally make about
    671     // assembler locals.
    672 
    673     bool hasReliableSymbolDifference = isX86_64();
    674     if (!hasReliableSymbolDifference) {
    675       if (!SA.isInSection() || &SecA != &SecB ||
    676           (!SA.isTemporary() && FB.getAtom() != SA.getFragment()->getAtom() &&
    677            Asm.getSubsectionsViaSymbols()))
    678         return false;
    679       return true;
    680     }
    681     // For Darwin x86_64, there is one special case when the reference IsPCRel.
    682     // If the fragment with the reference does not have a base symbol but meets
    683     // the simple way of dealing with this, in that it is a temporary symbol in
    684     // the same atom then it is assumed to be fully resolved.  This is needed so
    685     // a relocation entry is not created and so the static linker does not
    686     // mess up the reference later.
    687     else if(!FB.getAtom() &&
    688             SA.isTemporary() && SA.isInSection() && &SecA == &SecB){
    689       return true;
    690     }
    691   }
    692 
    693   // If they are not in the same section, we can't compute the diff.
    694   if (&SecA != &SecB)
    695     return false;
    696 
    697   const MCFragment *FA = SA.getFragment();
    698 
    699   // Bail if the symbol has no fragment.
    700   if (!FA)
    701     return false;
    702 
    703   // If the atoms are the same, they are guaranteed to have the same address.
    704   if (FA->getAtom() == FB.getAtom())
    705     return true;
    706 
    707   // Otherwise, we can't prove this is fully resolved.
    708   return false;
    709 }
    710 
    711 void MachObjectWriter::writeObject(MCAssembler &Asm,
    712                                    const MCAsmLayout &Layout) {
    713   // Compute symbol table information and bind symbol indices.
    714   computeSymbolTable(Asm, LocalSymbolData, ExternalSymbolData,
    715                      UndefinedSymbolData);
    716 
    717   unsigned NumSections = Asm.size();
    718   const MCAssembler::VersionMinInfoType &VersionInfo =
    719     Layout.getAssembler().getVersionMinInfo();
    720 
    721   // The section data starts after the header, the segment load command (and
    722   // section headers) and the symbol table.
    723   unsigned NumLoadCommands = 1;
    724   uint64_t LoadCommandsSize = is64Bit() ?
    725     sizeof(MachO::segment_command_64) + NumSections * sizeof(MachO::section_64):
    726     sizeof(MachO::segment_command) + NumSections * sizeof(MachO::section);
    727 
    728   // Add the deployment target version info load command size, if used.
    729   if (VersionInfo.Major != 0) {
    730     ++NumLoadCommands;
    731     LoadCommandsSize += sizeof(MachO::version_min_command);
    732   }
    733 
    734   // Add the data-in-code load command size, if used.
    735   unsigned NumDataRegions = Asm.getDataRegions().size();
    736   if (NumDataRegions) {
    737     ++NumLoadCommands;
    738     LoadCommandsSize += sizeof(MachO::linkedit_data_command);
    739   }
    740 
    741   // Add the loh load command size, if used.
    742   uint64_t LOHRawSize = Asm.getLOHContainer().getEmitSize(*this, Layout);
    743   uint64_t LOHSize = alignTo(LOHRawSize, is64Bit() ? 8 : 4);
    744   if (LOHSize) {
    745     ++NumLoadCommands;
    746     LoadCommandsSize += sizeof(MachO::linkedit_data_command);
    747   }
    748 
    749   // Add the symbol table load command sizes, if used.
    750   unsigned NumSymbols = LocalSymbolData.size() + ExternalSymbolData.size() +
    751     UndefinedSymbolData.size();
    752   if (NumSymbols) {
    753     NumLoadCommands += 2;
    754     LoadCommandsSize += (sizeof(MachO::symtab_command) +
    755                          sizeof(MachO::dysymtab_command));
    756   }
    757 
    758   // Add the linker option load commands sizes.
    759   for (const auto &Option : Asm.getLinkerOptions()) {
    760     ++NumLoadCommands;
    761     LoadCommandsSize += ComputeLinkerOptionsLoadCommandSize(Option, is64Bit());
    762   }
    763 
    764   // Compute the total size of the section data, as well as its file size and vm
    765   // size.
    766   uint64_t SectionDataStart = (is64Bit() ? sizeof(MachO::mach_header_64) :
    767                                sizeof(MachO::mach_header)) + LoadCommandsSize;
    768   uint64_t SectionDataSize = 0;
    769   uint64_t SectionDataFileSize = 0;
    770   uint64_t VMSize = 0;
    771   for (const MCSection &Sec : Asm) {
    772     uint64_t Address = getSectionAddress(&Sec);
    773     uint64_t Size = Layout.getSectionAddressSize(&Sec);
    774     uint64_t FileSize = Layout.getSectionFileSize(&Sec);
    775     FileSize += getPaddingSize(&Sec, Layout);
    776 
    777     VMSize = std::max(VMSize, Address + Size);
    778 
    779     if (Sec.isVirtualSection())
    780       continue;
    781 
    782     SectionDataSize = std::max(SectionDataSize, Address + Size);
    783     SectionDataFileSize = std::max(SectionDataFileSize, Address + FileSize);
    784   }
    785 
    786   // The section data is padded to 4 bytes.
    787   //
    788   // FIXME: Is this machine dependent?
    789   unsigned SectionDataPadding = OffsetToAlignment(SectionDataFileSize, 4);
    790   SectionDataFileSize += SectionDataPadding;
    791 
    792   // Write the prolog, starting with the header and load command...
    793   writeHeader(MachO::MH_OBJECT, NumLoadCommands, LoadCommandsSize,
    794               Asm.getSubsectionsViaSymbols());
    795   uint32_t Prot =
    796       MachO::VM_PROT_READ | MachO::VM_PROT_WRITE | MachO::VM_PROT_EXECUTE;
    797   writeSegmentLoadCommand("", NumSections, 0, VMSize, SectionDataStart,
    798                           SectionDataSize, Prot, Prot);
    799 
    800   // ... and then the section headers.
    801   uint64_t RelocTableEnd = SectionDataStart + SectionDataFileSize;
    802   for (const MCSection &Section : Asm) {
    803     const auto &Sec = cast<MCSectionMachO>(Section);
    804     std::vector<RelAndSymbol> &Relocs = Relocations[&Sec];
    805     unsigned NumRelocs = Relocs.size();
    806     uint64_t SectionStart = SectionDataStart + getSectionAddress(&Sec);
    807     unsigned Flags = Sec.getTypeAndAttributes();
    808     if (Sec.hasInstructions())
    809       Flags |= MachO::S_ATTR_SOME_INSTRUCTIONS;
    810     writeSection(Layout, Sec, getSectionAddress(&Sec), SectionStart, Flags,
    811                  RelocTableEnd, NumRelocs);
    812     RelocTableEnd += NumRelocs * sizeof(MachO::any_relocation_info);
    813   }
    814 
    815   // Write out the deployment target information, if it's available.
    816   if (VersionInfo.Major != 0) {
    817     assert(VersionInfo.Update < 256 && "unencodable update target version");
    818     assert(VersionInfo.Minor < 256 && "unencodable minor target version");
    819     assert(VersionInfo.Major < 65536 && "unencodable major target version");
    820     uint32_t EncodedVersion = VersionInfo.Update | (VersionInfo.Minor << 8) |
    821       (VersionInfo.Major << 16);
    822     MachO::LoadCommandType LCType;
    823     switch (VersionInfo.Kind) {
    824     case MCVM_OSXVersionMin:
    825       LCType = MachO::LC_VERSION_MIN_MACOSX;
    826       break;
    827     case MCVM_IOSVersionMin:
    828       LCType = MachO::LC_VERSION_MIN_IPHONEOS;
    829       break;
    830     case MCVM_TvOSVersionMin:
    831       LCType = MachO::LC_VERSION_MIN_TVOS;
    832       break;
    833     case MCVM_WatchOSVersionMin:
    834       LCType = MachO::LC_VERSION_MIN_WATCHOS;
    835       break;
    836     }
    837     write32(LCType);
    838     write32(sizeof(MachO::version_min_command));
    839     write32(EncodedVersion);
    840     write32(0);         // reserved.
    841   }
    842 
    843   // Write the data-in-code load command, if used.
    844   uint64_t DataInCodeTableEnd = RelocTableEnd + NumDataRegions * 8;
    845   if (NumDataRegions) {
    846     uint64_t DataRegionsOffset = RelocTableEnd;
    847     uint64_t DataRegionsSize = NumDataRegions * 8;
    848     writeLinkeditLoadCommand(MachO::LC_DATA_IN_CODE, DataRegionsOffset,
    849                              DataRegionsSize);
    850   }
    851 
    852   // Write the loh load command, if used.
    853   uint64_t LOHTableEnd = DataInCodeTableEnd + LOHSize;
    854   if (LOHSize)
    855     writeLinkeditLoadCommand(MachO::LC_LINKER_OPTIMIZATION_HINT,
    856                              DataInCodeTableEnd, LOHSize);
    857 
    858   // Write the symbol table load command, if used.
    859   if (NumSymbols) {
    860     unsigned FirstLocalSymbol = 0;
    861     unsigned NumLocalSymbols = LocalSymbolData.size();
    862     unsigned FirstExternalSymbol = FirstLocalSymbol + NumLocalSymbols;
    863     unsigned NumExternalSymbols = ExternalSymbolData.size();
    864     unsigned FirstUndefinedSymbol = FirstExternalSymbol + NumExternalSymbols;
    865     unsigned NumUndefinedSymbols = UndefinedSymbolData.size();
    866     unsigned NumIndirectSymbols = Asm.indirect_symbol_size();
    867     unsigned NumSymTabSymbols =
    868       NumLocalSymbols + NumExternalSymbols + NumUndefinedSymbols;
    869     uint64_t IndirectSymbolSize = NumIndirectSymbols * 4;
    870     uint64_t IndirectSymbolOffset = 0;
    871 
    872     // If used, the indirect symbols are written after the section data.
    873     if (NumIndirectSymbols)
    874       IndirectSymbolOffset = LOHTableEnd;
    875 
    876     // The symbol table is written after the indirect symbol data.
    877     uint64_t SymbolTableOffset = LOHTableEnd + IndirectSymbolSize;
    878 
    879     // The string table is written after symbol table.
    880     uint64_t StringTableOffset =
    881       SymbolTableOffset + NumSymTabSymbols * (is64Bit() ?
    882                                               sizeof(MachO::nlist_64) :
    883                                               sizeof(MachO::nlist));
    884     writeSymtabLoadCommand(SymbolTableOffset, NumSymTabSymbols,
    885                            StringTableOffset, StringTable.data().size());
    886 
    887     writeDysymtabLoadCommand(FirstLocalSymbol, NumLocalSymbols,
    888                              FirstExternalSymbol, NumExternalSymbols,
    889                              FirstUndefinedSymbol, NumUndefinedSymbols,
    890                              IndirectSymbolOffset, NumIndirectSymbols);
    891   }
    892 
    893   // Write the linker options load commands.
    894   for (const auto &Option : Asm.getLinkerOptions())
    895     writeLinkerOptionsLoadCommand(Option);
    896 
    897   // Write the actual section data.
    898   for (const MCSection &Sec : Asm) {
    899     Asm.writeSectionData(&Sec, Layout);
    900 
    901     uint64_t Pad = getPaddingSize(&Sec, Layout);
    902     WriteZeros(Pad);
    903   }
    904 
    905   // Write the extra padding.
    906   WriteZeros(SectionDataPadding);
    907 
    908   // Write the relocation entries.
    909   for (const MCSection &Sec : Asm) {
    910     // Write the section relocation entries, in reverse order to match 'as'
    911     // (approximately, the exact algorithm is more complicated than this).
    912     std::vector<RelAndSymbol> &Relocs = Relocations[&Sec];
    913     for (const RelAndSymbol &Rel : make_range(Relocs.rbegin(), Relocs.rend())) {
    914       write32(Rel.MRE.r_word0);
    915       write32(Rel.MRE.r_word1);
    916     }
    917   }
    918 
    919   // Write out the data-in-code region payload, if there is one.
    920   for (MCAssembler::const_data_region_iterator
    921          it = Asm.data_region_begin(), ie = Asm.data_region_end();
    922          it != ie; ++it) {
    923     const DataRegionData *Data = &(*it);
    924     uint64_t Start = getSymbolAddress(*Data->Start, Layout);
    925     uint64_t End = getSymbolAddress(*Data->End, Layout);
    926     DEBUG(dbgs() << "data in code region-- kind: " << Data->Kind
    927                  << "  start: " << Start << "(" << Data->Start->getName() << ")"
    928                  << "  end: " << End << "(" << Data->End->getName() << ")"
    929                  << "  size: " << End - Start
    930                  << "\n");
    931     write32(Start);
    932     write16(End - Start);
    933     write16(Data->Kind);
    934   }
    935 
    936   // Write out the loh commands, if there is one.
    937   if (LOHSize) {
    938 #ifndef NDEBUG
    939     unsigned Start = getStream().tell();
    940 #endif
    941     Asm.getLOHContainer().emit(*this, Layout);
    942     // Pad to a multiple of the pointer size.
    943     writeBytes("", OffsetToAlignment(LOHRawSize, is64Bit() ? 8 : 4));
    944     assert(getStream().tell() - Start == LOHSize);
    945   }
    946 
    947   // Write the symbol table data, if used.
    948   if (NumSymbols) {
    949     // Write the indirect symbol entries.
    950     for (MCAssembler::const_indirect_symbol_iterator
    951            it = Asm.indirect_symbol_begin(),
    952            ie = Asm.indirect_symbol_end(); it != ie; ++it) {
    953       // Indirect symbols in the non-lazy symbol pointer section have some
    954       // special handling.
    955       const MCSectionMachO &Section =
    956           static_cast<const MCSectionMachO &>(*it->Section);
    957       if (Section.getType() == MachO::S_NON_LAZY_SYMBOL_POINTERS) {
    958         // If this symbol is defined and internal, mark it as such.
    959         if (it->Symbol->isDefined() && !it->Symbol->isExternal()) {
    960           uint32_t Flags = MachO::INDIRECT_SYMBOL_LOCAL;
    961           if (it->Symbol->isAbsolute())
    962             Flags |= MachO::INDIRECT_SYMBOL_ABS;
    963           write32(Flags);
    964           continue;
    965         }
    966       }
    967 
    968       write32(it->Symbol->getIndex());
    969     }
    970 
    971     // FIXME: Check that offsets match computed ones.
    972 
    973     // Write the symbol table entries.
    974     for (auto *SymbolData :
    975          {&LocalSymbolData, &ExternalSymbolData, &UndefinedSymbolData})
    976       for (MachSymbolData &Entry : *SymbolData)
    977         writeNlist(Entry, Layout);
    978 
    979     // Write the string table.
    980     getStream() << StringTable.data();
    981   }
    982 }
    983 
    984 MCObjectWriter *llvm::createMachObjectWriter(MCMachObjectTargetWriter *MOTW,
    985                                              raw_pwrite_stream &OS,
    986                                              bool IsLittleEndian) {
    987   return new MachObjectWriter(MOTW, OS, IsLittleEndian);
    988 }
    989