MCAssembler.cpp revision f8b8ad77a8b5632886a4cfe41d798bae7277efcb 
1//===- lib/MC/MCAssembler.cpp - Assembler Backend Implementation ----------===//
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#define DEBUG_TYPE "assembler"
11#include "llvm/MC/MCAssembler.h"
12#include "llvm/MC/MCExpr.h"
13#include "llvm/MC/MCSectionMachO.h"
14#include "llvm/MC/MCSymbol.h"
15#include "llvm/MC/MCValue.h"
16#include "llvm/ADT/DenseMap.h"
17#include "llvm/ADT/SmallString.h"
18#include "llvm/ADT/Statistic.h"
19#include "llvm/ADT/StringExtras.h"
20#include "llvm/ADT/StringMap.h"
21#include "llvm/ADT/Twine.h"
22#include "llvm/Support/ErrorHandling.h"
23#include "llvm/Support/MachO.h"
24#include "llvm/Support/raw_ostream.h"
25#include "llvm/Support/Debug.h"
26
27// FIXME: Gross.
28#include "../Target/X86/X86FixupKinds.h"
29
30#include <vector>
31using namespace llvm;
32
33class MachObjectWriter;
34
35STATISTIC(EmittedFragments, "Number of emitted assembler fragments");
36
37// FIXME FIXME FIXME: There are number of places in this file where we convert
38// what is a 64-bit assembler value used for computation into a value in the
39// object file, which may truncate it. We should detect that truncation where
40// invalid and report errors back.
41
42static void WriteFileData(raw_ostream &OS, const MCSectionData &SD,
43                          MachObjectWriter &MOW);
44
45static uint64_t WriteNopData(uint64_t Count, MachObjectWriter &MOW);
46
47/// isVirtualSection - Check if this is a section which does not actually exist
48/// in the object file.
49static bool isVirtualSection(const MCSection &Section) {
50  // FIXME: Lame.
51  const MCSectionMachO &SMO = static_cast<const MCSectionMachO&>(Section);
52  unsigned Type = SMO.getTypeAndAttributes() & MCSectionMachO::SECTION_TYPE;
53  return (Type == MCSectionMachO::S_ZEROFILL);
54}
55
56static unsigned getFixupKindLog2Size(unsigned Kind) {
57  switch (Kind) {
58  default: llvm_unreachable("invalid fixup kind!");
59  case X86::reloc_pcrel_1byte:
60  case FK_Data_1: return 0;
61  case FK_Data_2: return 1;
62  case X86::reloc_pcrel_4byte:
63  case X86::reloc_riprel_4byte:
64  case FK_Data_4: return 2;
65  case FK_Data_8: return 3;
66  }
67}
68
69static bool isFixupKindPCRel(unsigned Kind) {
70  switch (Kind) {
71  default:
72    return false;
73  case X86::reloc_pcrel_1byte:
74  case X86::reloc_pcrel_4byte:
75  case X86::reloc_riprel_4byte:
76    return true;
77  }
78}
79
80class MachObjectWriter {
81  // See <mach-o/loader.h>.
82  enum {
83    Header_Magic32 = 0xFEEDFACE,
84    Header_Magic64 = 0xFEEDFACF
85  };
86
87  static const unsigned Header32Size = 28;
88  static const unsigned Header64Size = 32;
89  static const unsigned SegmentLoadCommand32Size = 56;
90  static const unsigned Section32Size = 68;
91  static const unsigned SymtabLoadCommandSize = 24;
92  static const unsigned DysymtabLoadCommandSize = 80;
93  static const unsigned Nlist32Size = 12;
94  static const unsigned RelocationInfoSize = 8;
95
96  enum HeaderFileType {
97    HFT_Object = 0x1
98  };
99
100  enum HeaderFlags {
101    HF_SubsectionsViaSymbols = 0x2000
102  };
103
104  enum LoadCommandType {
105    LCT_Segment = 0x1,
106    LCT_Symtab = 0x2,
107    LCT_Dysymtab = 0xb
108  };
109
110  // See <mach-o/nlist.h>.
111  enum SymbolTypeType {
112    STT_Undefined = 0x00,
113    STT_Absolute  = 0x02,
114    STT_Section   = 0x0e
115  };
116
117  enum SymbolTypeFlags {
118    // If any of these bits are set, then the entry is a stab entry number (see
119    // <mach-o/stab.h>. Otherwise the other masks apply.
120    STF_StabsEntryMask = 0xe0,
121
122    STF_TypeMask       = 0x0e,
123    STF_External       = 0x01,
124    STF_PrivateExtern  = 0x10
125  };
126
127  /// IndirectSymbolFlags - Flags for encoding special values in the indirect
128  /// symbol entry.
129  enum IndirectSymbolFlags {
130    ISF_Local    = 0x80000000,
131    ISF_Absolute = 0x40000000
132  };
133
134  /// RelocationFlags - Special flags for addresses.
135  enum RelocationFlags {
136    RF_Scattered = 0x80000000
137  };
138
139  enum RelocationInfoType {
140    RIT_Vanilla             = 0,
141    RIT_Pair                = 1,
142    RIT_Difference          = 2,
143    RIT_PreboundLazyPointer = 3,
144    RIT_LocalDifference     = 4
145  };
146
147  /// MachSymbolData - Helper struct for containing some precomputed information
148  /// on symbols.
149  struct MachSymbolData {
150    MCSymbolData *SymbolData;
151    uint64_t StringIndex;
152    uint8_t SectionIndex;
153
154    // Support lexicographic sorting.
155    bool operator<(const MachSymbolData &RHS) const {
156      const std::string &Name = SymbolData->getSymbol().getName();
157      return Name < RHS.SymbolData->getSymbol().getName();
158    }
159  };
160
161  raw_ostream &OS;
162  bool IsLSB;
163
164public:
165  MachObjectWriter(raw_ostream &_OS, bool _IsLSB = true)
166    : OS(_OS), IsLSB(_IsLSB) {
167  }
168
169  /// @name Helper Methods
170  /// @{
171
172  void Write8(uint8_t Value) {
173    OS << char(Value);
174  }
175
176  void Write16(uint16_t Value) {
177    if (IsLSB) {
178      Write8(uint8_t(Value >> 0));
179      Write8(uint8_t(Value >> 8));
180    } else {
181      Write8(uint8_t(Value >> 8));
182      Write8(uint8_t(Value >> 0));
183    }
184  }
185
186  void Write32(uint32_t Value) {
187    if (IsLSB) {
188      Write16(uint16_t(Value >> 0));
189      Write16(uint16_t(Value >> 16));
190    } else {
191      Write16(uint16_t(Value >> 16));
192      Write16(uint16_t(Value >> 0));
193    }
194  }
195
196  void Write64(uint64_t Value) {
197    if (IsLSB) {
198      Write32(uint32_t(Value >> 0));
199      Write32(uint32_t(Value >> 32));
200    } else {
201      Write32(uint32_t(Value >> 32));
202      Write32(uint32_t(Value >> 0));
203    }
204  }
205
206  void WriteZeros(unsigned N) {
207    const char Zeros[16] = { 0 };
208
209    for (unsigned i = 0, e = N / 16; i != e; ++i)
210      OS << StringRef(Zeros, 16);
211
212    OS << StringRef(Zeros, N % 16);
213  }
214
215  void WriteString(StringRef Str, unsigned ZeroFillSize = 0) {
216    OS << Str;
217    if (ZeroFillSize)
218      WriteZeros(ZeroFillSize - Str.size());
219  }
220
221  /// @}
222
223  void WriteHeader32(unsigned NumLoadCommands, unsigned LoadCommandsSize,
224                     bool SubsectionsViaSymbols) {
225    uint32_t Flags = 0;
226
227    if (SubsectionsViaSymbols)
228      Flags |= HF_SubsectionsViaSymbols;
229
230    // struct mach_header (28 bytes)
231
232    uint64_t Start = OS.tell();
233    (void) Start;
234
235    Write32(Header_Magic32);
236
237    // FIXME: Support cputype.
238    Write32(MachO::CPUTypeI386);
239    // FIXME: Support cpusubtype.
240    Write32(MachO::CPUSubType_I386_ALL);
241    Write32(HFT_Object);
242    Write32(NumLoadCommands);    // Object files have a single load command, the
243                                 // segment.
244    Write32(LoadCommandsSize);
245    Write32(Flags);
246
247    assert(OS.tell() - Start == Header32Size);
248  }
249
250  /// WriteSegmentLoadCommand32 - Write a 32-bit segment load command.
251  ///
252  /// \arg NumSections - The number of sections in this segment.
253  /// \arg SectionDataSize - The total size of the sections.
254  void WriteSegmentLoadCommand32(unsigned NumSections,
255                                 uint64_t VMSize,
256                                 uint64_t SectionDataStartOffset,
257                                 uint64_t SectionDataSize) {
258    // struct segment_command (56 bytes)
259
260    uint64_t Start = OS.tell();
261    (void) Start;
262
263    Write32(LCT_Segment);
264    Write32(SegmentLoadCommand32Size + NumSections * Section32Size);
265
266    WriteString("", 16);
267    Write32(0); // vmaddr
268    Write32(VMSize); // vmsize
269    Write32(SectionDataStartOffset); // file offset
270    Write32(SectionDataSize); // file size
271    Write32(0x7); // maxprot
272    Write32(0x7); // initprot
273    Write32(NumSections);
274    Write32(0); // flags
275
276    assert(OS.tell() - Start == SegmentLoadCommand32Size);
277  }
278
279  void WriteSection32(const MCSectionData &SD, uint64_t FileOffset,
280                      uint64_t RelocationsStart, unsigned NumRelocations) {
281    // The offset is unused for virtual sections.
282    if (isVirtualSection(SD.getSection())) {
283      assert(SD.getFileSize() == 0 && "Invalid file size!");
284      FileOffset = 0;
285    }
286
287    // struct section (68 bytes)
288
289    uint64_t Start = OS.tell();
290    (void) Start;
291
292    // FIXME: cast<> support!
293    const MCSectionMachO &Section =
294      static_cast<const MCSectionMachO&>(SD.getSection());
295    WriteString(Section.getSectionName(), 16);
296    WriteString(Section.getSegmentName(), 16);
297    Write32(SD.getAddress()); // address
298    Write32(SD.getSize()); // size
299    Write32(FileOffset);
300
301    unsigned Flags = Section.getTypeAndAttributes();
302    if (SD.hasInstructions())
303      Flags |= MCSectionMachO::S_ATTR_SOME_INSTRUCTIONS;
304
305    assert(isPowerOf2_32(SD.getAlignment()) && "Invalid alignment!");
306    Write32(Log2_32(SD.getAlignment()));
307    Write32(NumRelocations ? RelocationsStart : 0);
308    Write32(NumRelocations);
309    Write32(Flags);
310    Write32(0); // reserved1
311    Write32(Section.getStubSize()); // reserved2
312
313    assert(OS.tell() - Start == Section32Size);
314  }
315
316  void WriteSymtabLoadCommand(uint32_t SymbolOffset, uint32_t NumSymbols,
317                              uint32_t StringTableOffset,
318                              uint32_t StringTableSize) {
319    // struct symtab_command (24 bytes)
320
321    uint64_t Start = OS.tell();
322    (void) Start;
323
324    Write32(LCT_Symtab);
325    Write32(SymtabLoadCommandSize);
326    Write32(SymbolOffset);
327    Write32(NumSymbols);
328    Write32(StringTableOffset);
329    Write32(StringTableSize);
330
331    assert(OS.tell() - Start == SymtabLoadCommandSize);
332  }
333
334  void WriteDysymtabLoadCommand(uint32_t FirstLocalSymbol,
335                                uint32_t NumLocalSymbols,
336                                uint32_t FirstExternalSymbol,
337                                uint32_t NumExternalSymbols,
338                                uint32_t FirstUndefinedSymbol,
339                                uint32_t NumUndefinedSymbols,
340                                uint32_t IndirectSymbolOffset,
341                                uint32_t NumIndirectSymbols) {
342    // struct dysymtab_command (80 bytes)
343
344    uint64_t Start = OS.tell();
345    (void) Start;
346
347    Write32(LCT_Dysymtab);
348    Write32(DysymtabLoadCommandSize);
349    Write32(FirstLocalSymbol);
350    Write32(NumLocalSymbols);
351    Write32(FirstExternalSymbol);
352    Write32(NumExternalSymbols);
353    Write32(FirstUndefinedSymbol);
354    Write32(NumUndefinedSymbols);
355    Write32(0); // tocoff
356    Write32(0); // ntoc
357    Write32(0); // modtaboff
358    Write32(0); // nmodtab
359    Write32(0); // extrefsymoff
360    Write32(0); // nextrefsyms
361    Write32(IndirectSymbolOffset);
362    Write32(NumIndirectSymbols);
363    Write32(0); // extreloff
364    Write32(0); // nextrel
365    Write32(0); // locreloff
366    Write32(0); // nlocrel
367
368    assert(OS.tell() - Start == DysymtabLoadCommandSize);
369  }
370
371  void WriteNlist32(MachSymbolData &MSD) {
372    MCSymbolData &Data = *MSD.SymbolData;
373    const MCSymbol &Symbol = Data.getSymbol();
374    uint8_t Type = 0;
375    uint16_t Flags = Data.getFlags();
376    uint32_t Address = 0;
377
378    // Set the N_TYPE bits. See <mach-o/nlist.h>.
379    //
380    // FIXME: Are the prebound or indirect fields possible here?
381    if (Symbol.isUndefined())
382      Type = STT_Undefined;
383    else if (Symbol.isAbsolute())
384      Type = STT_Absolute;
385    else
386      Type = STT_Section;
387
388    // FIXME: Set STAB bits.
389
390    if (Data.isPrivateExtern())
391      Type |= STF_PrivateExtern;
392
393    // Set external bit.
394    if (Data.isExternal() || Symbol.isUndefined())
395      Type |= STF_External;
396
397    // Compute the symbol address.
398    if (Symbol.isDefined()) {
399      if (Symbol.isAbsolute()) {
400        llvm_unreachable("FIXME: Not yet implemented!");
401      } else {
402        Address = Data.getFragment()->getAddress() + Data.getOffset();
403      }
404    } else if (Data.isCommon()) {
405      // Common symbols are encoded with the size in the address
406      // field, and their alignment in the flags.
407      Address = Data.getCommonSize();
408
409      // Common alignment is packed into the 'desc' bits.
410      if (unsigned Align = Data.getCommonAlignment()) {
411        unsigned Log2Size = Log2_32(Align);
412        assert((1U << Log2Size) == Align && "Invalid 'common' alignment!");
413        if (Log2Size > 15)
414          llvm_report_error("invalid 'common' alignment '" +
415                            Twine(Align) + "'");
416        // FIXME: Keep this mask with the SymbolFlags enumeration.
417        Flags = (Flags & 0xF0FF) | (Log2Size << 8);
418      }
419    }
420
421    // struct nlist (12 bytes)
422
423    Write32(MSD.StringIndex);
424    Write8(Type);
425    Write8(MSD.SectionIndex);
426
427    // The Mach-O streamer uses the lowest 16-bits of the flags for the 'desc'
428    // value.
429    Write16(Flags);
430    Write32(Address);
431  }
432
433  struct MachRelocationEntry {
434    uint32_t Word0;
435    uint32_t Word1;
436  };
437  void ComputeScatteredRelocationInfo(MCAssembler &Asm, MCFragment &Fragment,
438                                      MCAsmFixup &Fixup,
439                                      const MCValue &Target,
440                             DenseMap<const MCSymbol*,MCSymbolData*> &SymbolMap,
441                                     std::vector<MachRelocationEntry> &Relocs) {
442    uint32_t Address = Fragment.getOffset() + Fixup.Offset;
443    unsigned IsPCRel = 0;
444    unsigned Log2Size = getFixupKindLog2Size(Fixup.Kind);
445    unsigned Type = RIT_Vanilla;
446
447    // See <reloc.h>.
448    const MCSymbol *A = Target.getSymA();
449    MCSymbolData *SD = SymbolMap.lookup(A);
450
451    if (!SD->getFragment())
452      llvm_report_error("symbol '" + A->getName() +
453                        "' can not be undefined in a subtraction expression");
454
455    uint32_t Value = SD->getFragment()->getAddress() + SD->getOffset();
456    uint32_t Value2 = 0;
457
458    if (const MCSymbol *B = Target.getSymB()) {
459      MCSymbolData *SD = SymbolMap.lookup(B);
460
461      if (!SD->getFragment())
462        llvm_report_error("symbol '" + B->getName() +
463                          "' can not be undefined in a subtraction expression");
464
465      Type = RIT_LocalDifference;
466      Value2 = SD->getFragment()->getAddress() + SD->getOffset();
467    }
468
469    // The value which goes in the fixup is current value of the expression.
470    Fixup.FixedValue = Value - Value2 + Target.getConstant();
471    if (isFixupKindPCRel(Fixup.Kind)) {
472      Fixup.FixedValue -= Address;
473      IsPCRel = 1;
474    }
475
476    MachRelocationEntry MRE;
477    MRE.Word0 = ((Address   <<  0) |
478                 (Type      << 24) |
479                 (Log2Size  << 28) |
480                 (IsPCRel   << 30) |
481                 RF_Scattered);
482    MRE.Word1 = Value;
483    Relocs.push_back(MRE);
484
485    if (Type == RIT_LocalDifference) {
486      Type = RIT_Pair;
487
488      MachRelocationEntry MRE;
489      MRE.Word0 = ((0         <<  0) |
490                   (Type      << 24) |
491                   (Log2Size  << 28) |
492                   (0   << 30) |
493                   RF_Scattered);
494      MRE.Word1 = Value2;
495      Relocs.push_back(MRE);
496    }
497  }
498
499  void ComputeRelocationInfo(MCAssembler &Asm, MCDataFragment &Fragment,
500                             MCAsmFixup &Fixup,
501                             DenseMap<const MCSymbol*,MCSymbolData*> &SymbolMap,
502                             std::vector<MachRelocationEntry> &Relocs) {
503    MCValue Target;
504    if (!Fixup.Value->EvaluateAsRelocatable(Target))
505      llvm_report_error("expected relocatable expression");
506
507    // If this is a difference or a local symbol plus an offset, then we need a
508    // scattered relocation entry.
509    if (Target.getSymB() ||
510        (Target.getSymA() && !Target.getSymA()->isUndefined() &&
511         Target.getConstant()))
512      return ComputeScatteredRelocationInfo(Asm, Fragment, Fixup, Target,
513                                            SymbolMap, Relocs);
514
515    // See <reloc.h>.
516    uint32_t Address = Fragment.getOffset() + Fixup.Offset;
517    uint32_t Value = 0;
518    unsigned Index = 0;
519    unsigned IsPCRel = 0;
520    unsigned Log2Size = getFixupKindLog2Size(Fixup.Kind);
521    unsigned IsExtern = 0;
522    unsigned Type = 0;
523
524    if (Target.isAbsolute()) { // constant
525      // SymbolNum of 0 indicates the absolute section.
526      //
527      // FIXME: When is this generated?
528      Type = RIT_Vanilla;
529      Value = 0;
530      llvm_unreachable("FIXME: Not yet implemented!");
531    } else {
532      const MCSymbol *Symbol = Target.getSymA();
533      MCSymbolData *SD = SymbolMap.lookup(Symbol);
534
535      if (Symbol->isUndefined()) {
536        IsExtern = 1;
537        Index = SD->getIndex();
538        Value = 0;
539      } else {
540        // The index is the section ordinal.
541        //
542        // FIXME: O(N)
543        Index = 1;
544        MCAssembler::iterator it = Asm.begin(), ie = Asm.end();
545        for (; it != ie; ++it, ++Index)
546          if (&*it == SD->getFragment()->getParent())
547            break;
548        assert(it != ie && "Unable to find section index!");
549        Value = SD->getFragment()->getAddress() + SD->getOffset();
550      }
551
552      Type = RIT_Vanilla;
553    }
554
555    // The value which goes in the fixup is current value of the expression.
556    Fixup.FixedValue = Value + Target.getConstant();
557
558    if (isFixupKindPCRel(Fixup.Kind)) {
559      Fixup.FixedValue -= Address;
560      IsPCRel = 1;
561    }
562
563    // struct relocation_info (8 bytes)
564    MachRelocationEntry MRE;
565    MRE.Word0 = Address;
566    MRE.Word1 = ((Index     <<  0) |
567                 (IsPCRel   << 24) |
568                 (Log2Size  << 25) |
569                 (IsExtern  << 27) |
570                 (Type      << 28));
571    Relocs.push_back(MRE);
572  }
573
574  void BindIndirectSymbols(MCAssembler &Asm,
575                           DenseMap<const MCSymbol*,MCSymbolData*> &SymbolMap) {
576    // This is the point where 'as' creates actual symbols for indirect symbols
577    // (in the following two passes). It would be easier for us to do this
578    // sooner when we see the attribute, but that makes getting the order in the
579    // symbol table much more complicated than it is worth.
580    //
581    // FIXME: Revisit this when the dust settles.
582
583    // Bind non lazy symbol pointers first.
584    for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
585           ie = Asm.indirect_symbol_end(); it != ie; ++it) {
586      // FIXME: cast<> support!
587      const MCSectionMachO &Section =
588        static_cast<const MCSectionMachO&>(it->SectionData->getSection());
589
590      unsigned Type =
591        Section.getTypeAndAttributes() & MCSectionMachO::SECTION_TYPE;
592      if (Type != MCSectionMachO::S_NON_LAZY_SYMBOL_POINTERS)
593        continue;
594
595      MCSymbolData *&Entry = SymbolMap[it->Symbol];
596      if (!Entry)
597        Entry = new MCSymbolData(*it->Symbol, 0, 0, &Asm);
598    }
599
600    // Then lazy symbol pointers and symbol stubs.
601    for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
602           ie = Asm.indirect_symbol_end(); it != ie; ++it) {
603      // FIXME: cast<> support!
604      const MCSectionMachO &Section =
605        static_cast<const MCSectionMachO&>(it->SectionData->getSection());
606
607      unsigned Type =
608        Section.getTypeAndAttributes() & MCSectionMachO::SECTION_TYPE;
609      if (Type != MCSectionMachO::S_LAZY_SYMBOL_POINTERS &&
610          Type != MCSectionMachO::S_SYMBOL_STUBS)
611        continue;
612
613      MCSymbolData *&Entry = SymbolMap[it->Symbol];
614      if (!Entry) {
615        Entry = new MCSymbolData(*it->Symbol, 0, 0, &Asm);
616
617        // Set the symbol type to undefined lazy, but only on construction.
618        //
619        // FIXME: Do not hardcode.
620        Entry->setFlags(Entry->getFlags() | 0x0001);
621      }
622    }
623  }
624
625  /// ComputeSymbolTable - Compute the symbol table data
626  ///
627  /// \param StringTable [out] - The string table data.
628  /// \param StringIndexMap [out] - Map from symbol names to offsets in the
629  /// string table.
630  void ComputeSymbolTable(MCAssembler &Asm, SmallString<256> &StringTable,
631                          std::vector<MachSymbolData> &LocalSymbolData,
632                          std::vector<MachSymbolData> &ExternalSymbolData,
633                          std::vector<MachSymbolData> &UndefinedSymbolData) {
634    // Build section lookup table.
635    DenseMap<const MCSection*, uint8_t> SectionIndexMap;
636    unsigned Index = 1;
637    for (MCAssembler::iterator it = Asm.begin(),
638           ie = Asm.end(); it != ie; ++it, ++Index)
639      SectionIndexMap[&it->getSection()] = Index;
640    assert(Index <= 256 && "Too many sections!");
641
642    // Index 0 is always the empty string.
643    StringMap<uint64_t> StringIndexMap;
644    StringTable += '\x00';
645
646    // Build the symbol arrays and the string table, but only for non-local
647    // symbols.
648    //
649    // The particular order that we collect the symbols and create the string
650    // table, then sort the symbols is chosen to match 'as'. Even though it
651    // doesn't matter for correctness, this is important for letting us diff .o
652    // files.
653    for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
654           ie = Asm.symbol_end(); it != ie; ++it) {
655      const MCSymbol &Symbol = it->getSymbol();
656
657      // Ignore assembler temporaries.
658      if (it->getSymbol().isTemporary())
659        continue;
660
661      if (!it->isExternal() && !Symbol.isUndefined())
662        continue;
663
664      uint64_t &Entry = StringIndexMap[Symbol.getName()];
665      if (!Entry) {
666        Entry = StringTable.size();
667        StringTable += Symbol.getName();
668        StringTable += '\x00';
669      }
670
671      MachSymbolData MSD;
672      MSD.SymbolData = it;
673      MSD.StringIndex = Entry;
674
675      if (Symbol.isUndefined()) {
676        MSD.SectionIndex = 0;
677        UndefinedSymbolData.push_back(MSD);
678      } else if (Symbol.isAbsolute()) {
679        MSD.SectionIndex = 0;
680        ExternalSymbolData.push_back(MSD);
681      } else {
682        MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
683        assert(MSD.SectionIndex && "Invalid section index!");
684        ExternalSymbolData.push_back(MSD);
685      }
686    }
687
688    // Now add the data for local symbols.
689    for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
690           ie = Asm.symbol_end(); it != ie; ++it) {
691      const MCSymbol &Symbol = it->getSymbol();
692
693      // Ignore assembler temporaries.
694      if (it->getSymbol().isTemporary())
695        continue;
696
697      if (it->isExternal() || Symbol.isUndefined())
698        continue;
699
700      uint64_t &Entry = StringIndexMap[Symbol.getName()];
701      if (!Entry) {
702        Entry = StringTable.size();
703        StringTable += Symbol.getName();
704        StringTable += '\x00';
705      }
706
707      MachSymbolData MSD;
708      MSD.SymbolData = it;
709      MSD.StringIndex = Entry;
710
711      if (Symbol.isAbsolute()) {
712        MSD.SectionIndex = 0;
713        LocalSymbolData.push_back(MSD);
714      } else {
715        MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
716        assert(MSD.SectionIndex && "Invalid section index!");
717        LocalSymbolData.push_back(MSD);
718      }
719    }
720
721    // External and undefined symbols are required to be in lexicographic order.
722    std::sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
723    std::sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
724
725    // Set the symbol indices.
726    Index = 0;
727    for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
728      LocalSymbolData[i].SymbolData->setIndex(Index++);
729    for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
730      ExternalSymbolData[i].SymbolData->setIndex(Index++);
731    for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
732      UndefinedSymbolData[i].SymbolData->setIndex(Index++);
733
734    // The string table is padded to a multiple of 4.
735    while (StringTable.size() % 4)
736      StringTable += '\x00';
737  }
738
739  void WriteObject(MCAssembler &Asm) {
740    unsigned NumSections = Asm.size();
741
742    // Compute the symbol -> symbol data map.
743    //
744    // FIXME: This should not be here.
745    DenseMap<const MCSymbol*, MCSymbolData *> SymbolMap;
746    for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
747           ie = Asm.symbol_end(); it != ie; ++it)
748      SymbolMap[&it->getSymbol()] = it;
749
750    // Create symbol data for any indirect symbols.
751    BindIndirectSymbols(Asm, SymbolMap);
752
753    // Compute symbol table information.
754    SmallString<256> StringTable;
755    std::vector<MachSymbolData> LocalSymbolData;
756    std::vector<MachSymbolData> ExternalSymbolData;
757    std::vector<MachSymbolData> UndefinedSymbolData;
758    unsigned NumSymbols = Asm.symbol_size();
759
760    // No symbol table command is written if there are no symbols.
761    if (NumSymbols)
762      ComputeSymbolTable(Asm, StringTable, LocalSymbolData, ExternalSymbolData,
763                         UndefinedSymbolData);
764
765    // The section data starts after the header, the segment load command (and
766    // section headers) and the symbol table.
767    unsigned NumLoadCommands = 1;
768    uint64_t LoadCommandsSize =
769      SegmentLoadCommand32Size + NumSections * Section32Size;
770
771    // Add the symbol table load command sizes, if used.
772    if (NumSymbols) {
773      NumLoadCommands += 2;
774      LoadCommandsSize += SymtabLoadCommandSize + DysymtabLoadCommandSize;
775    }
776
777    // Compute the total size of the section data, as well as its file size and
778    // vm size.
779    uint64_t SectionDataStart = Header32Size + LoadCommandsSize;
780    uint64_t SectionDataSize = 0;
781    uint64_t SectionDataFileSize = 0;
782    uint64_t VMSize = 0;
783    for (MCAssembler::iterator it = Asm.begin(),
784           ie = Asm.end(); it != ie; ++it) {
785      MCSectionData &SD = *it;
786
787      VMSize = std::max(VMSize, SD.getAddress() + SD.getSize());
788
789      if (isVirtualSection(SD.getSection()))
790        continue;
791
792      SectionDataSize = std::max(SectionDataSize,
793                                 SD.getAddress() + SD.getSize());
794      SectionDataFileSize = std::max(SectionDataFileSize,
795                                     SD.getAddress() + SD.getFileSize());
796    }
797
798    // The section data is padded to 4 bytes.
799    //
800    // FIXME: Is this machine dependent?
801    unsigned SectionDataPadding = OffsetToAlignment(SectionDataFileSize, 4);
802    SectionDataFileSize += SectionDataPadding;
803
804    // Write the prolog, starting with the header and load command...
805    WriteHeader32(NumLoadCommands, LoadCommandsSize,
806                  Asm.getSubsectionsViaSymbols());
807    WriteSegmentLoadCommand32(NumSections, VMSize,
808                              SectionDataStart, SectionDataSize);
809
810    // ... and then the section headers.
811    //
812    // We also compute the section relocations while we do this. Note that
813    // computing relocation info will also update the fixup to have the correct
814    // value; this will overwrite the appropriate data in the fragment when it
815    // is written.
816    std::vector<MachRelocationEntry> RelocInfos;
817    uint64_t RelocTableEnd = SectionDataStart + SectionDataFileSize;
818    for (MCAssembler::iterator it = Asm.begin(),
819           ie = Asm.end(); it != ie; ++it) {
820      MCSectionData &SD = *it;
821
822      // The assembler writes relocations in the reverse order they were seen.
823      //
824      // FIXME: It is probably more complicated than this.
825      unsigned NumRelocsStart = RelocInfos.size();
826      for (MCSectionData::reverse_iterator it2 = SD.rbegin(),
827             ie2 = SD.rend(); it2 != ie2; ++it2)
828        if (MCDataFragment *DF = dyn_cast<MCDataFragment>(&*it2))
829          for (unsigned i = 0, e = DF->fixup_size(); i != e; ++i)
830            ComputeRelocationInfo(Asm, *DF, DF->getFixups()[e - i - 1],
831                                  SymbolMap, RelocInfos);
832
833      unsigned NumRelocs = RelocInfos.size() - NumRelocsStart;
834      uint64_t SectionStart = SectionDataStart + SD.getAddress();
835      WriteSection32(SD, SectionStart, RelocTableEnd, NumRelocs);
836      RelocTableEnd += NumRelocs * RelocationInfoSize;
837    }
838
839    // Write the symbol table load command, if used.
840    if (NumSymbols) {
841      unsigned FirstLocalSymbol = 0;
842      unsigned NumLocalSymbols = LocalSymbolData.size();
843      unsigned FirstExternalSymbol = FirstLocalSymbol + NumLocalSymbols;
844      unsigned NumExternalSymbols = ExternalSymbolData.size();
845      unsigned FirstUndefinedSymbol = FirstExternalSymbol + NumExternalSymbols;
846      unsigned NumUndefinedSymbols = UndefinedSymbolData.size();
847      unsigned NumIndirectSymbols = Asm.indirect_symbol_size();
848      unsigned NumSymTabSymbols =
849        NumLocalSymbols + NumExternalSymbols + NumUndefinedSymbols;
850      uint64_t IndirectSymbolSize = NumIndirectSymbols * 4;
851      uint64_t IndirectSymbolOffset = 0;
852
853      // If used, the indirect symbols are written after the section data.
854      if (NumIndirectSymbols)
855        IndirectSymbolOffset = RelocTableEnd;
856
857      // The symbol table is written after the indirect symbol data.
858      uint64_t SymbolTableOffset = RelocTableEnd + IndirectSymbolSize;
859
860      // The string table is written after symbol table.
861      uint64_t StringTableOffset =
862        SymbolTableOffset + NumSymTabSymbols * Nlist32Size;
863      WriteSymtabLoadCommand(SymbolTableOffset, NumSymTabSymbols,
864                             StringTableOffset, StringTable.size());
865
866      WriteDysymtabLoadCommand(FirstLocalSymbol, NumLocalSymbols,
867                               FirstExternalSymbol, NumExternalSymbols,
868                               FirstUndefinedSymbol, NumUndefinedSymbols,
869                               IndirectSymbolOffset, NumIndirectSymbols);
870    }
871
872    // Write the actual section data.
873    for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
874      WriteFileData(OS, *it, *this);
875
876    // Write the extra padding.
877    WriteZeros(SectionDataPadding);
878
879    // Write the relocation entries.
880    for (unsigned i = 0, e = RelocInfos.size(); i != e; ++i) {
881      Write32(RelocInfos[i].Word0);
882      Write32(RelocInfos[i].Word1);
883    }
884
885    // Write the symbol table data, if used.
886    if (NumSymbols) {
887      // Write the indirect symbol entries.
888      for (MCAssembler::indirect_symbol_iterator
889             it = Asm.indirect_symbol_begin(),
890             ie = Asm.indirect_symbol_end(); it != ie; ++it) {
891        // Indirect symbols in the non lazy symbol pointer section have some
892        // special handling.
893        const MCSectionMachO &Section =
894          static_cast<const MCSectionMachO&>(it->SectionData->getSection());
895        unsigned Type =
896          Section.getTypeAndAttributes() & MCSectionMachO::SECTION_TYPE;
897        if (Type == MCSectionMachO::S_NON_LAZY_SYMBOL_POINTERS) {
898          // If this symbol is defined and internal, mark it as such.
899          if (it->Symbol->isDefined() &&
900              !SymbolMap.lookup(it->Symbol)->isExternal()) {
901            uint32_t Flags = ISF_Local;
902            if (it->Symbol->isAbsolute())
903              Flags |= ISF_Absolute;
904            Write32(Flags);
905            continue;
906          }
907        }
908
909        Write32(SymbolMap[it->Symbol]->getIndex());
910      }
911
912      // FIXME: Check that offsets match computed ones.
913
914      // Write the symbol table entries.
915      for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
916        WriteNlist32(LocalSymbolData[i]);
917      for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
918        WriteNlist32(ExternalSymbolData[i]);
919      for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
920        WriteNlist32(UndefinedSymbolData[i]);
921
922      // Write the string table.
923      OS << StringTable.str();
924    }
925  }
926
927  void ApplyFixup(const MCAsmFixup &Fixup, MCDataFragment &DF) {
928    unsigned Size = 1 << getFixupKindLog2Size(Fixup.Kind);
929
930    // FIXME: Endianness assumption.
931    assert(Fixup.Offset + Size <= DF.getContents().size() &&
932           "Invalid fixup offset!");
933    for (unsigned i = 0; i != Size; ++i)
934      DF.getContents()[Fixup.Offset + i] = uint8_t(Fixup.FixedValue >> (i * 8));
935  }
936};
937
938/* *** */
939
940MCFragment::MCFragment() : Kind(FragmentType(~0)) {
941}
942
943MCFragment::MCFragment(FragmentType _Kind, MCSectionData *_Parent)
944  : Kind(_Kind),
945    Parent(_Parent),
946    FileSize(~UINT64_C(0))
947{
948  if (Parent)
949    Parent->getFragmentList().push_back(this);
950}
951
952MCFragment::~MCFragment() {
953}
954
955uint64_t MCFragment::getAddress() const {
956  assert(getParent() && "Missing Section!");
957  return getParent()->getAddress() + Offset;
958}
959
960/* *** */
961
962MCSectionData::MCSectionData() : Section(0) {}
963
964MCSectionData::MCSectionData(const MCSection &_Section, MCAssembler *A)
965  : Section(&_Section),
966    Alignment(1),
967    Address(~UINT64_C(0)),
968    Size(~UINT64_C(0)),
969    FileSize(~UINT64_C(0)),
970    HasInstructions(false)
971{
972  if (A)
973    A->getSectionList().push_back(this);
974}
975
976/* *** */
977
978MCSymbolData::MCSymbolData() : Symbol(0) {}
979
980MCSymbolData::MCSymbolData(const MCSymbol &_Symbol, MCFragment *_Fragment,
981                           uint64_t _Offset, MCAssembler *A)
982  : Symbol(&_Symbol), Fragment(_Fragment), Offset(_Offset),
983    IsExternal(false), IsPrivateExtern(false),
984    CommonSize(0), CommonAlign(0), Flags(0), Index(0)
985{
986  if (A)
987    A->getSymbolList().push_back(this);
988}
989
990/* *** */
991
992MCAssembler::MCAssembler(MCContext &_Context, raw_ostream &_OS)
993  : Context(_Context), OS(_OS), SubsectionsViaSymbols(false)
994{
995}
996
997MCAssembler::~MCAssembler() {
998}
999
1000void MCAssembler::LayoutSection(MCSectionData &SD) {
1001  uint64_t Address = SD.getAddress();
1002
1003  for (MCSectionData::iterator it = SD.begin(), ie = SD.end(); it != ie; ++it) {
1004    MCFragment &F = *it;
1005
1006    F.setOffset(Address - SD.getAddress());
1007
1008    // Evaluate fragment size.
1009    switch (F.getKind()) {
1010    case MCFragment::FT_Align: {
1011      MCAlignFragment &AF = cast<MCAlignFragment>(F);
1012
1013      uint64_t Size = OffsetToAlignment(Address, AF.getAlignment());
1014      if (Size > AF.getMaxBytesToEmit())
1015        AF.setFileSize(0);
1016      else
1017        AF.setFileSize(Size);
1018      break;
1019    }
1020
1021    case MCFragment::FT_Data:
1022    case MCFragment::FT_Fill:
1023      F.setFileSize(F.getMaxFileSize());
1024      break;
1025
1026    case MCFragment::FT_Org: {
1027      MCOrgFragment &OF = cast<MCOrgFragment>(F);
1028
1029      MCValue Target;
1030      if (!OF.getOffset().EvaluateAsRelocatable(Target))
1031        llvm_report_error("expected relocatable expression");
1032
1033      if (!Target.isAbsolute())
1034        llvm_unreachable("FIXME: Not yet implemented!");
1035      uint64_t OrgOffset = Target.getConstant();
1036      uint64_t Offset = Address - SD.getAddress();
1037
1038      // FIXME: We need a way to communicate this error.
1039      if (OrgOffset < Offset)
1040        llvm_report_error("invalid .org offset '" + Twine(OrgOffset) +
1041                          "' (at offset '" + Twine(Offset) + "'");
1042
1043      F.setFileSize(OrgOffset - Offset);
1044      break;
1045    }
1046
1047    case MCFragment::FT_ZeroFill: {
1048      MCZeroFillFragment &ZFF = cast<MCZeroFillFragment>(F);
1049
1050      // Align the fragment offset; it is safe to adjust the offset freely since
1051      // this is only in virtual sections.
1052      Address = RoundUpToAlignment(Address, ZFF.getAlignment());
1053      F.setOffset(Address - SD.getAddress());
1054
1055      // FIXME: This is misnamed.
1056      F.setFileSize(ZFF.getSize());
1057      break;
1058    }
1059    }
1060
1061    Address += F.getFileSize();
1062  }
1063
1064  // Set the section sizes.
1065  SD.setSize(Address - SD.getAddress());
1066  if (isVirtualSection(SD.getSection()))
1067    SD.setFileSize(0);
1068  else
1069    SD.setFileSize(Address - SD.getAddress());
1070}
1071
1072/// WriteNopData - Write optimal nops to the output file for the \arg Count
1073/// bytes.  This returns the number of bytes written.  It may return 0 if
1074/// the \arg Count is more than the maximum optimal nops.
1075///
1076/// FIXME this is X86 32-bit specific and should move to a better place.
1077static uint64_t WriteNopData(uint64_t Count, MachObjectWriter &MOW) {
1078  static const uint8_t Nops[16][16] = {
1079    // nop
1080    {0x90},
1081    // xchg %ax,%ax
1082    {0x66, 0x90},
1083    // nopl (%[re]ax)
1084    {0x0f, 0x1f, 0x00},
1085    // nopl 0(%[re]ax)
1086    {0x0f, 0x1f, 0x40, 0x00},
1087    // nopl 0(%[re]ax,%[re]ax,1)
1088    {0x0f, 0x1f, 0x44, 0x00, 0x00},
1089    // nopw 0(%[re]ax,%[re]ax,1)
1090    {0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00},
1091    // nopl 0L(%[re]ax)
1092    {0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00},
1093    // nopl 0L(%[re]ax,%[re]ax,1)
1094    {0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00},
1095    // nopw 0L(%[re]ax,%[re]ax,1)
1096    {0x66, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00},
1097    // nopw %cs:0L(%[re]ax,%[re]ax,1)
1098    {0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00},
1099    // nopl 0(%[re]ax,%[re]ax,1)
1100    // nopw 0(%[re]ax,%[re]ax,1)
1101    {0x0f, 0x1f, 0x44, 0x00, 0x00,
1102     0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00},
1103    // nopw 0(%[re]ax,%[re]ax,1)
1104    // nopw 0(%[re]ax,%[re]ax,1)
1105    {0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00,
1106     0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00},
1107    // nopw 0(%[re]ax,%[re]ax,1)
1108    // nopl 0L(%[re]ax) */
1109    {0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00,
1110     0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00},
1111    // nopl 0L(%[re]ax)
1112    // nopl 0L(%[re]ax)
1113    {0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00,
1114     0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00},
1115    // nopl 0L(%[re]ax)
1116    // nopl 0L(%[re]ax,%[re]ax,1)
1117    {0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00,
1118     0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00}
1119  };
1120
1121  if (Count > 15)
1122    return 0;
1123
1124  for (uint64_t i = 0; i < Count; i++)
1125    MOW.Write8 (uint8_t(Nops[Count - 1][i]));
1126
1127  return Count;
1128}
1129
1130/// WriteFileData - Write the \arg F data to the output file.
1131static void WriteFileData(raw_ostream &OS, const MCFragment &F,
1132                          MachObjectWriter &MOW) {
1133  uint64_t Start = OS.tell();
1134  (void) Start;
1135
1136  ++EmittedFragments;
1137
1138  // FIXME: Embed in fragments instead?
1139  switch (F.getKind()) {
1140  case MCFragment::FT_Align: {
1141    MCAlignFragment &AF = cast<MCAlignFragment>(F);
1142    uint64_t Count = AF.getFileSize() / AF.getValueSize();
1143
1144    // FIXME: This error shouldn't actually occur (the front end should emit
1145    // multiple .align directives to enforce the semantics it wants), but is
1146    // severe enough that we want to report it. How to handle this?
1147    if (Count * AF.getValueSize() != AF.getFileSize())
1148      llvm_report_error("undefined .align directive, value size '" +
1149                        Twine(AF.getValueSize()) +
1150                        "' is not a divisor of padding size '" +
1151                        Twine(AF.getFileSize()) + "'");
1152
1153    // See if we are aligning with nops, and if so do that first to try to fill
1154    // the Count bytes.  Then if that did not fill any bytes or there are any
1155    // bytes left to fill use the the Value and ValueSize to fill the rest.
1156    if (AF.getEmitNops()) {
1157      uint64_t NopByteCount = WriteNopData(Count, MOW);
1158      Count -= NopByteCount;
1159    }
1160
1161    for (uint64_t i = 0; i != Count; ++i) {
1162      switch (AF.getValueSize()) {
1163      default:
1164        assert(0 && "Invalid size!");
1165      case 1: MOW.Write8 (uint8_t (AF.getValue())); break;
1166      case 2: MOW.Write16(uint16_t(AF.getValue())); break;
1167      case 4: MOW.Write32(uint32_t(AF.getValue())); break;
1168      case 8: MOW.Write64(uint64_t(AF.getValue())); break;
1169      }
1170    }
1171    break;
1172  }
1173
1174  case MCFragment::FT_Data: {
1175    MCDataFragment &DF = cast<MCDataFragment>(F);
1176
1177    // Apply the fixups.
1178    //
1179    // FIXME: Move elsewhere.
1180    for (MCDataFragment::const_fixup_iterator it = DF.fixup_begin(),
1181           ie = DF.fixup_end(); it != ie; ++it)
1182      MOW.ApplyFixup(*it, DF);
1183
1184    OS << cast<MCDataFragment>(F).getContents().str();
1185    break;
1186  }
1187
1188  case MCFragment::FT_Fill: {
1189    MCFillFragment &FF = cast<MCFillFragment>(F);
1190    for (uint64_t i = 0, e = FF.getCount(); i != e; ++i) {
1191      switch (FF.getValueSize()) {
1192      default:
1193        assert(0 && "Invalid size!");
1194      case 1: MOW.Write8 (uint8_t (FF.getValue())); break;
1195      case 2: MOW.Write16(uint16_t(FF.getValue())); break;
1196      case 4: MOW.Write32(uint32_t(FF.getValue())); break;
1197      case 8: MOW.Write64(uint64_t(FF.getValue())); break;
1198      }
1199    }
1200    break;
1201  }
1202
1203  case MCFragment::FT_Org: {
1204    MCOrgFragment &OF = cast<MCOrgFragment>(F);
1205
1206    for (uint64_t i = 0, e = OF.getFileSize(); i != e; ++i)
1207      MOW.Write8(uint8_t(OF.getValue()));
1208
1209    break;
1210  }
1211
1212  case MCFragment::FT_ZeroFill: {
1213    assert(0 && "Invalid zero fill fragment in concrete section!");
1214    break;
1215  }
1216  }
1217
1218  assert(OS.tell() - Start == F.getFileSize());
1219}
1220
1221/// WriteFileData - Write the \arg SD data to the output file.
1222static void WriteFileData(raw_ostream &OS, const MCSectionData &SD,
1223                          MachObjectWriter &MOW) {
1224  // Ignore virtual sections.
1225  if (isVirtualSection(SD.getSection())) {
1226    assert(SD.getFileSize() == 0);
1227    return;
1228  }
1229
1230  uint64_t Start = OS.tell();
1231  (void) Start;
1232
1233  for (MCSectionData::const_iterator it = SD.begin(),
1234         ie = SD.end(); it != ie; ++it)
1235    WriteFileData(OS, *it, MOW);
1236
1237  // Add section padding.
1238  assert(SD.getFileSize() >= SD.getSize() && "Invalid section sizes!");
1239  MOW.WriteZeros(SD.getFileSize() - SD.getSize());
1240
1241  assert(OS.tell() - Start == SD.getFileSize());
1242}
1243
1244void MCAssembler::Finish() {
1245  DEBUG_WITH_TYPE("mc-dump", {
1246      llvm::errs() << "assembler backend - pre-layout\n--\n";
1247      dump(); });
1248
1249  // Layout the concrete sections and fragments.
1250  uint64_t Address = 0;
1251  MCSectionData *Prev = 0;
1252  for (iterator it = begin(), ie = end(); it != ie; ++it) {
1253    MCSectionData &SD = *it;
1254
1255    // Skip virtual sections.
1256    if (isVirtualSection(SD.getSection()))
1257      continue;
1258
1259    // Align this section if necessary by adding padding bytes to the previous
1260    // section.
1261    if (uint64_t Pad = OffsetToAlignment(Address, it->getAlignment())) {
1262      assert(Prev && "Missing prev section!");
1263      Prev->setFileSize(Prev->getFileSize() + Pad);
1264      Address += Pad;
1265    }
1266
1267    // Layout the section fragments and its size.
1268    SD.setAddress(Address);
1269    LayoutSection(SD);
1270    Address += SD.getFileSize();
1271
1272    Prev = &SD;
1273  }
1274
1275  // Layout the virtual sections.
1276  for (iterator it = begin(), ie = end(); it != ie; ++it) {
1277    MCSectionData &SD = *it;
1278
1279    if (!isVirtualSection(SD.getSection()))
1280      continue;
1281
1282    // Align this section if necessary by adding padding bytes to the previous
1283    // section.
1284    if (uint64_t Pad = OffsetToAlignment(Address, it->getAlignment()))
1285      Address += Pad;
1286
1287    SD.setAddress(Address);
1288    LayoutSection(SD);
1289    Address += SD.getSize();
1290
1291  }
1292
1293  DEBUG_WITH_TYPE("mc-dump", {
1294      llvm::errs() << "assembler backend - post-layout\n--\n";
1295      dump(); });
1296
1297  // Write the object file.
1298  MachObjectWriter MOW(OS);
1299  MOW.WriteObject(*this);
1300
1301  OS.flush();
1302}
1303
1304
1305// Debugging methods
1306
1307namespace llvm {
1308
1309raw_ostream &operator<<(raw_ostream &OS, const MCAsmFixup &AF) {
1310  OS << "<MCAsmFixup" << " Offset:" << AF.Offset << " Value:" << *AF.Value
1311     << " Kind:" << AF.Kind << ">";
1312  return OS;
1313}
1314
1315}
1316
1317void MCFragment::dump() {
1318  raw_ostream &OS = llvm::errs();
1319
1320  OS << "<MCFragment " << (void*) this << " Offset:" << Offset
1321     << " FileSize:" << FileSize;
1322
1323  OS << ">";
1324}
1325
1326void MCAlignFragment::dump() {
1327  raw_ostream &OS = llvm::errs();
1328
1329  OS << "<MCAlignFragment ";
1330  this->MCFragment::dump();
1331  OS << "\n       ";
1332  OS << " Alignment:" << getAlignment()
1333     << " Value:" << getValue() << " ValueSize:" << getValueSize()
1334     << " MaxBytesToEmit:" << getMaxBytesToEmit() << ">";
1335}
1336
1337void MCDataFragment::dump() {
1338  raw_ostream &OS = llvm::errs();
1339
1340  OS << "<MCDataFragment ";
1341  this->MCFragment::dump();
1342  OS << "\n       ";
1343  OS << " Contents:[";
1344  for (unsigned i = 0, e = getContents().size(); i != e; ++i) {
1345    if (i) OS << ",";
1346    OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
1347  }
1348  OS << "] (" << getContents().size() << " bytes)";
1349
1350  if (!getFixups().empty()) {
1351    OS << ",\n       ";
1352    OS << " Fixups:[";
1353    for (fixup_iterator it = fixup_begin(), ie = fixup_end(); it != ie; ++it) {
1354      if (it != fixup_begin()) OS << ",\n            ";
1355      OS << *it;
1356    }
1357    OS << "]";
1358  }
1359
1360  OS << ">";
1361}
1362
1363void MCFillFragment::dump() {
1364  raw_ostream &OS = llvm::errs();
1365
1366  OS << "<MCFillFragment ";
1367  this->MCFragment::dump();
1368  OS << "\n       ";
1369  OS << " Value:" << getValue() << " ValueSize:" << getValueSize()
1370     << " Count:" << getCount() << ">";
1371}
1372
1373void MCOrgFragment::dump() {
1374  raw_ostream &OS = llvm::errs();
1375
1376  OS << "<MCOrgFragment ";
1377  this->MCFragment::dump();
1378  OS << "\n       ";
1379  OS << " Offset:" << getOffset() << " Value:" << getValue() << ">";
1380}
1381
1382void MCZeroFillFragment::dump() {
1383  raw_ostream &OS = llvm::errs();
1384
1385  OS << "<MCZeroFillFragment ";
1386  this->MCFragment::dump();
1387  OS << "\n       ";
1388  OS << " Size:" << getSize() << " Alignment:" << getAlignment() << ">";
1389}
1390
1391void MCSectionData::dump() {
1392  raw_ostream &OS = llvm::errs();
1393
1394  OS << "<MCSectionData";
1395  OS << " Alignment:" << getAlignment() << " Address:" << Address
1396     << " Size:" << Size << " FileSize:" << FileSize
1397     << " Fragments:[";
1398  for (iterator it = begin(), ie = end(); it != ie; ++it) {
1399    if (it != begin()) OS << ",\n      ";
1400    it->dump();
1401  }
1402  OS << "]>";
1403}
1404
1405void MCSymbolData::dump() {
1406  raw_ostream &OS = llvm::errs();
1407
1408  OS << "<MCSymbolData Symbol:" << getSymbol()
1409     << " Fragment:" << getFragment() << " Offset:" << getOffset()
1410     << " Flags:" << getFlags() << " Index:" << getIndex();
1411  if (isCommon())
1412    OS << " (common, size:" << getCommonSize()
1413       << " align: " << getCommonAlignment() << ")";
1414  if (isExternal())
1415    OS << " (external)";
1416  if (isPrivateExtern())
1417    OS << " (private extern)";
1418  OS << ">";
1419}
1420
1421void MCAssembler::dump() {
1422  raw_ostream &OS = llvm::errs();
1423
1424  OS << "<MCAssembler\n";
1425  OS << "  Sections:[";
1426  for (iterator it = begin(), ie = end(); it != ie; ++it) {
1427    if (it != begin()) OS << ",\n    ";
1428    it->dump();
1429  }
1430  OS << "],\n";
1431  OS << "  Symbols:[";
1432
1433  for (symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) {
1434    if (it != symbol_begin()) OS << ",\n    ";
1435    it->dump();
1436  }
1437  OS << "]>\n";
1438}
1439