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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 
reset()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 
doesSymbolRequireExternRelocation(const MCSymbol & S)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::
operator <(const MachSymbolData & RHS) const56 MachSymbolData::operator<(const MachSymbolData &RHS) const {
57   return Symbol->getName() < RHS.Symbol->getName();
58 }
59 
isFixupKindPCRel(const MCAssembler & Asm,unsigned Kind)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 
getFragmentAddress(const MCFragment * Fragment,const MCAsmLayout & Layout) const67 uint64_t MachObjectWriter::getFragmentAddress(const MCFragment *Fragment,
68                                               const MCAsmLayout &Layout) const {
69   return getSectionAddress(Fragment->getParent()) +
70          Layout.getFragmentOffset(Fragment);
71 }
72 
getSymbolAddress(const MCSymbol & S,const MCAsmLayout & Layout) const73 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 
getPaddingSize(const MCSection * Sec,const MCAsmLayout & Layout) const106 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 
writeHeader(MachO::HeaderFileType Type,unsigned NumLoadCommands,unsigned LoadCommandsSize,bool SubsectionsViaSymbols)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.
writeSegmentLoadCommand(StringRef Name,unsigned NumSections,uint64_t VMAddr,uint64_t VMSize,uint64_t SectionDataStartOffset,uint64_t SectionDataSize,uint32_t MaxProt,uint32_t InitProt)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 
writeSection(const MCAsmLayout & Layout,const MCSection & Sec,uint64_t VMAddr,uint64_t FileOffset,unsigned Flags,uint64_t RelocationsStart,unsigned NumRelocations)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 
writeSymtabLoadCommand(uint32_t SymbolOffset,uint32_t NumSymbols,uint32_t StringTableOffset,uint32_t StringTableSize)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 
writeDysymtabLoadCommand(uint32_t FirstLocalSymbol,uint32_t NumLocalSymbols,uint32_t FirstExternalSymbol,uint32_t NumExternalSymbols,uint32_t FirstUndefinedSymbol,uint32_t NumUndefinedSymbols,uint32_t IndirectSymbolOffset,uint32_t NumIndirectSymbols)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 *
findSymbolData(const MCSymbol & Sym)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 
findAliasedSymbol(const MCSymbol & Sym) const308 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 
writeNlist(MachSymbolData & MSD,const MCAsmLayout & Layout)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 
writeLinkeditLoadCommand(uint32_t Type,uint32_t DataOffset,uint32_t DataSize)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 
ComputeLinkerOptionsLoadCommandSize(const std::vector<std::string> & Options,bool is64Bit)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 
writeLinkerOptionsLoadCommand(const std::vector<std::string> & Options)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 
recordRelocation(MCAssembler & Asm,const MCAsmLayout & Layout,const MCFragment * Fragment,const MCFixup & Fixup,MCValue Target,bool & IsPCRel,uint64_t & FixedValue)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 
bindIndirectSymbols(MCAssembler & Asm)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
computeSymbolTable(MCAssembler & Asm,std::vector<MachSymbolData> & LocalSymbolData,std::vector<MachSymbolData> & ExternalSymbolData,std::vector<MachSymbolData> & UndefinedSymbolData)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 
computeSectionAddresses(const MCAssembler & Asm,const MCAsmLayout & Layout)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 
executePostLayoutBinding(MCAssembler & Asm,const MCAsmLayout & Layout)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 
isSymbolRefDifferenceFullyResolvedImpl(const MCAssembler & Asm,const MCSymbol & A,const MCSymbol & B,bool InSet) const632 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 
isSymbolRefDifferenceFullyResolvedImpl(const MCAssembler & Asm,const MCSymbol & SymA,const MCFragment & FB,bool InSet,bool IsPCRel) const644 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 
writeObject(MCAssembler & Asm,const MCAsmLayout & Layout)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 
createMachObjectWriter(MCMachObjectTargetWriter * MOTW,raw_pwrite_stream & OS,bool IsLittleEndian)984 MCObjectWriter *llvm::createMachObjectWriter(MCMachObjectTargetWriter *MOTW,
985                                              raw_pwrite_stream &OS,
986                                              bool IsLittleEndian) {
987   return new MachObjectWriter(MOTW, OS, IsLittleEndian);
988 }
989