lib/Target/X86/X86MachObjectWriter.cpp

   1 //===-- X86MachObjectWriter.cpp - X86 Mach-O 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 "X86.h"
  11 #include "X86FixupKinds.h"
  12 #include "llvm/ADT/Twine.h"
  13 #include "llvm/MC/MCAssembler.h"
  14 #include "llvm/MC/MCAsmLayout.h"
  15 #include "llvm/MC/MCMachObjectWriter.h"
  16 #include "llvm/MC/MCSectionMachO.h"
  17 #include "llvm/MC/MCValue.h"
  18 #include "llvm/Support/ErrorHandling.h"
  19 #include "llvm/Object/MachOFormat.h"
  20
  21 using namespace llvm;
  22 using namespace llvm::object;
  23
  24 namespace {
  25 class X86MachObjectWriter : public MCMachObjectTargetWriter {
  26   void RecordScatteredRelocation(MachObjectWriter *Writer,
  27                                  const MCAssembler &Asm,
  28                                  const MCAsmLayout &Layout,
  29                                  const MCFragment *Fragment,
  30                                  const MCFixup &Fixup,
  31                                  MCValue Target,
  32                                  unsigned Log2Size,
  33                                  uint64_t &FixedValue);
  34   void RecordTLVPRelocation(MachObjectWriter *Writer,
  35                             const MCAssembler &Asm,
  36                             const MCAsmLayout &Layout,
  37                             const MCFragment *Fragment,
  38                             const MCFixup &Fixup,
  39                             MCValue Target,
  40                             uint64_t &FixedValue);
  41
  42   void RecordX86Relocation(MachObjectWriter *Writer,
  43                               const MCAssembler &Asm,
  44                               const MCAsmLayout &Layout,
  45                               const MCFragment *Fragment,
  46                               const MCFixup &Fixup,
  47                               MCValue Target,
  48                               uint64_t &FixedValue);
  49   void RecordX86_64Relocation(MachObjectWriter *Writer,
  50                               const MCAssembler &Asm,
  51                               const MCAsmLayout &Layout,
  52                               const MCFragment *Fragment,
  53                               const MCFixup &Fixup,
  54                               MCValue Target,
  55                               uint64_t &FixedValue);
  56 public:
  57   X86MachObjectWriter(bool Is64Bit, uint32_t CPUType,
  58                       uint32_t CPUSubtype)
  59     : MCMachObjectTargetWriter(Is64Bit, CPUType, CPUSubtype,
  60                                /*UseAggressiveSymbolFolding=*/Is64Bit) {}
  61
  62   void RecordRelocation(MachObjectWriter *Writer,
  63                         const MCAssembler &Asm, const MCAsmLayout &Layout,
  64                         const MCFragment *Fragment, const MCFixup &Fixup,
  65                         MCValue Target, uint64_t &FixedValue) {
  66     if (Writer->is64Bit())
  67       RecordX86_64Relocation(Writer, Asm, Layout, Fragment, Fixup, Target,
  68                              FixedValue);
  69     else
  70       RecordX86Relocation(Writer, Asm, Layout, Fragment, Fixup, Target,
  71                           FixedValue);
  72   }
  73 };
  74 }
  75
  76 static bool isFixupKindRIPRel(unsigned Kind) {
  77   return Kind == X86::reloc_riprel_4byte ||
  78     Kind == X86::reloc_riprel_4byte_movq_load;
  79 }
  80
  81 static unsigned getFixupKindLog2Size(unsigned Kind) {
  82   switch (Kind) {
  83   default:
  84     llvm_unreachable("invalid fixup kind!");
  85   case FK_PCRel_1:
  86   case FK_Data_1: return 0;
  87   case FK_PCRel_2:
  88   case FK_Data_2: return 1;
  89   case FK_PCRel_4:
  90     // FIXME: Remove these!!!
  91   case X86::reloc_riprel_4byte:
  92   case X86::reloc_riprel_4byte_movq_load:
  93   case X86::reloc_signed_4byte:
  94   case FK_Data_4: return 2;
  95   case FK_Data_8: return 3;
  96   }
  97 }
  98
  99 void X86MachObjectWriter::RecordX86_64Relocation(MachObjectWriter *Writer,
 100                                                  const MCAssembler &Asm,
 101                                                  const MCAsmLayout &Layout,
 102                                                  const MCFragment *Fragment,
 103                                                  const MCFixup &Fixup,
 104                                                  MCValue Target,
 105                                                  uint64_t &FixedValue) {
 106   unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
 107   unsigned IsRIPRel = isFixupKindRIPRel(Fixup.getKind());
 108   unsigned Log2Size = getFixupKindLog2Size(Fixup.getKind());
 109
 110   // See <reloc.h>.
 111   uint32_t FixupOffset =
 112     Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
 113   uint32_t FixupAddress =
 114     Writer->getFragmentAddress(Fragment, Layout) + Fixup.getOffset();
 115   int64_t Value = 0;
 116   unsigned Index = 0;
 117   unsigned IsExtern = 0;
 118   unsigned Type = 0;
 119
 120   Value = Target.getConstant();
 121
 122   if (IsPCRel) {
 123     // Compensate for the relocation offset, Darwin x86_64 relocations only have
 124     // the addend and appear to have attempted to define it to be the actual
 125     // expression addend without the PCrel bias. However, instructions with data
 126     // following the relocation are not accommodated for (see comment below
 127     // regarding SIGNED{1,2,4}), so it isn't exactly that either.
 128     Value += 1LL << Log2Size;
 129   }
 130
 131   if (Target.isAbsolute()) { // constant
 132     // SymbolNum of 0 indicates the absolute section.
 133     Type = macho::RIT_X86_64_Unsigned;
 134     Index = 0;
 135
 136     // FIXME: I believe this is broken, I don't think the linker can understand
 137     // it. I think it would require a local relocation, but I'm not sure if that
 138     // would work either. The official way to get an absolute PCrel relocation
 139     // is to use an absolute symbol (which we don't support yet).
 140     if (IsPCRel) {
 141       IsExtern = 1;
 142       Type = macho::RIT_X86_64_Branch;
 143     }
 144   } else if (Target.getSymB()) { // A - B + constant
 145     const MCSymbol *A = &Target.getSymA()->getSymbol();
 146     MCSymbolData &A_SD = Asm.getSymbolData(*A);
 147     const MCSymbolData *A_Base = Asm.getAtom(&A_SD);
 148
 149     const MCSymbol *B = &Target.getSymB()->getSymbol();
 150     MCSymbolData &B_SD = Asm.getSymbolData(*B);
 151     const MCSymbolData *B_Base = Asm.getAtom(&B_SD);
 152
 153     // Neither symbol can be modified.
 154     if (Target.getSymA()->getKind() != MCSymbolRefExpr::VK_None ||
 155         Target.getSymB()->getKind() != MCSymbolRefExpr::VK_None)
 156       report_fatal_error("unsupported relocation of modified symbol");
 157
 158     // We don't support PCrel relocations of differences. Darwin 'as' doesn't
 159     // implement most of these correctly.
 160     if (IsPCRel)
 161       report_fatal_error("unsupported pc-relative relocation of difference");
 162
 163     // The support for the situation where one or both of the symbols would
 164     // require a local relocation is handled just like if the symbols were
 165     // external.  This is certainly used in the case of debug sections where the
 166     // section has only temporary symbols and thus the symbols don't have base
 167     // symbols.  This is encoded using the section ordinal and non-extern
 168     // relocation entries.
 169
 170     // Darwin 'as' doesn't emit correct relocations for this (it ends up with a
 171     // single SIGNED relocation); reject it for now.  Except the case where both
 172     // symbols don't have a base, equal but both NULL.
 173     if (A_Base == B_Base && A_Base)
 174       report_fatal_error("unsupported relocation with identical base");
 175
 176     Value += Writer->getSymbolAddress(&A_SD, Layout) -
 177       (A_Base == NULL ? 0 : Writer->getSymbolAddress(A_Base, Layout));
 178     Value -= Writer->getSymbolAddress(&B_SD, Layout) -
 179       (B_Base == NULL ? 0 : Writer->getSymbolAddress(B_Base, Layout));
 180
 181     if (A_Base) {
 182       Index = A_Base->getIndex();
 183       IsExtern = 1;
 184     }
 185     else {
 186       Index = A_SD.getFragment()->getParent()->getOrdinal() + 1;
 187       IsExtern = 0;
 188     }
 189     Type = macho::RIT_X86_64_Unsigned;
 190
 191     macho::RelocationEntry MRE;
 192     MRE.Word0 = FixupOffset;
 193     MRE.Word1 = ((Index     <<  0) |
 194                  (IsPCRel   << 24) |
 195                  (Log2Size  << 25) |
 196                  (IsExtern  << 27) |
 197                  (Type      << 28));
 198     Writer->addRelocation(Fragment->getParent(), MRE);
 199
 200     if (B_Base) {
 201       Index = B_Base->getIndex();
 202       IsExtern = 1;
 203     }
 204     else {
 205       Index = B_SD.getFragment()->getParent()->getOrdinal() + 1;
 206       IsExtern = 0;
 207     }
 208     Type = macho::RIT_X86_64_Subtractor;
 209   } else {
 210     const MCSymbol *Symbol = &Target.getSymA()->getSymbol();
 211     MCSymbolData &SD = Asm.getSymbolData(*Symbol);
 212     const MCSymbolData *Base = Asm.getAtom(&SD);
 213
 214     // Relocations inside debug sections always use local relocations when
 215     // possible. This seems to be done because the debugger doesn't fully
 216     // understand x86_64 relocation entries, and expects to find values that
 217     // have already been fixed up.
 218     if (Symbol->isInSection()) {
 219       const MCSectionMachO &Section = static_cast<const MCSectionMachO&>(
 220         Fragment->getParent()->getSection());
 221       if (Section.hasAttribute(MCSectionMachO::S_ATTR_DEBUG))
 222         Base = 0;
 223     }
 224
 225     // x86_64 almost always uses external relocations, except when there is no
 226     // symbol to use as a base address (a local symbol with no preceding
 227     // non-local symbol).
 228     if (Base) {
 229       Index = Base->getIndex();
 230       IsExtern = 1;
 231
 232       // Add the local offset, if needed.
 233       if (Base != &SD)
 234         Value += Layout.getSymbolOffset(&SD) - Layout.getSymbolOffset(Base);
 235     } else if (Symbol->isInSection() && !Symbol->isVariable()) {
 236       // The index is the section ordinal (1-based).
 237       Index = SD.getFragment()->getParent()->getOrdinal() + 1;
 238       IsExtern = 0;
 239       Value += Writer->getSymbolAddress(&SD, Layout);
 240
 241       if (IsPCRel)
 242         Value -= FixupAddress + (1 << Log2Size);
 243     } else if (Symbol->isVariable()) {
 244       const MCExpr *Value = Symbol->getVariableValue();
 245       int64_t Res;
 246       bool isAbs = Value->EvaluateAsAbsolute(Res, Layout,
 247                                              Writer->getSectionAddressMap());
 248       if (isAbs) {
 249         FixedValue = Res;
 250         return;
 251       } else {
 252         report_fatal_error("unsupported relocation of variable '" +
 253                            Symbol->getName() + "'");
 254       }
 255     } else {
 256       report_fatal_error("unsupported relocation of undefined symbol '" +
 257                          Symbol->getName() + "'");
 258     }
 259
 260     MCSymbolRefExpr::VariantKind Modifier = Target.getSymA()->getKind();
 261     if (IsPCRel) {
 262       if (IsRIPRel) {
 263         if (Modifier == MCSymbolRefExpr::VK_GOTPCREL) {
 264           // x86_64 distinguishes movq foo@GOTPCREL so that the linker can
 265           // rewrite the movq to an leaq at link time if the symbol ends up in
 266           // the same linkage unit.
 267           if (unsigned(Fixup.getKind()) == X86::reloc_riprel_4byte_movq_load)
 268             Type = macho::RIT_X86_64_GOTLoad;
 269           else
 270             Type = macho::RIT_X86_64_GOT;
 271         }  else if (Modifier == MCSymbolRefExpr::VK_TLVP) {
 272           Type = macho::RIT_X86_64_TLV;
 273         }  else if (Modifier != MCSymbolRefExpr::VK_None) {
 274           report_fatal_error("unsupported symbol modifier in relocation");
 275         } else {
 276           Type = macho::RIT_X86_64_Signed;
 277
 278           // The Darwin x86_64 relocation format has a problem where it cannot
 279           // encode an address (L<foo> + <constant>) which is outside the atom
 280           // containing L<foo>. Generally, this shouldn't occur but it does
 281           // happen when we have a RIPrel instruction with data following the
 282           // relocation entry (e.g., movb $012, L0(%rip)). Even with the PCrel
 283           // adjustment Darwin x86_64 uses, the offset is still negative and the
 284           // linker has no way to recognize this.
 285           //
 286           // To work around this, Darwin uses several special relocation types
 287           // to indicate the offsets. However, the specification or
 288           // implementation of these seems to also be incomplete; they should
 289           // adjust the addend as well based on the actual encoded instruction
 290           // (the additional bias), but instead appear to just look at the final
 291           // offset.
 292           switch (-(Target.getConstant() + (1LL << Log2Size))) {
 293           case 1: Type = macho::RIT_X86_64_Signed1; break;
 294           case 2: Type = macho::RIT_X86_64_Signed2; break;
 295           case 4: Type = macho::RIT_X86_64_Signed4; break;
 296           }
 297         }
 298       } else {
 299         if (Modifier != MCSymbolRefExpr::VK_None)
 300           report_fatal_error("unsupported symbol modifier in branch "
 301                              "relocation");
 302
 303         Type = macho::RIT_X86_64_Branch;
 304       }
 305     } else {
 306       if (Modifier == MCSymbolRefExpr::VK_GOT) {
 307         Type = macho::RIT_X86_64_GOT;
 308       } else if (Modifier == MCSymbolRefExpr::VK_GOTPCREL) {
 309         // GOTPCREL is allowed as a modifier on non-PCrel instructions, in which
 310         // case all we do is set the PCrel bit in the relocation entry; this is
 311         // used with exception handling, for example. The source is required to
 312         // include any necessary offset directly.
 313         Type = macho::RIT_X86_64_GOT;
 314         IsPCRel = 1;
 315       } else if (Modifier == MCSymbolRefExpr::VK_TLVP) {
 316         report_fatal_error("TLVP symbol modifier should have been rip-rel");
 317       } else if (Modifier != MCSymbolRefExpr::VK_None)
 318         report_fatal_error("unsupported symbol modifier in relocation");
 319       else
 320         Type = macho::RIT_X86_64_Unsigned;
 321     }
 322   }
 323
 324   // x86_64 always writes custom values into the fixups.
 325   FixedValue = Value;
 326
 327   // struct relocation_info (8 bytes)
 328   macho::RelocationEntry MRE;
 329   MRE.Word0 = FixupOffset;
 330   MRE.Word1 = ((Index     <<  0) |
 331                (IsPCRel   << 24) |
 332                (Log2Size  << 25) |
 333                (IsExtern  << 27) |
 334                (Type      << 28));
 335   Writer->addRelocation(Fragment->getParent(), MRE);
 336 }
 337
 338 void X86MachObjectWriter::RecordScatteredRelocation(MachObjectWriter *Writer,
 339                                                     const MCAssembler &Asm,
 340                                                     const MCAsmLayout &Layout,
 341                                                     const MCFragment *Fragment,
 342                                                     const MCFixup &Fixup,
 343                                                     MCValue Target,
 344                                                     unsigned Log2Size,
 345                                                     uint64_t &FixedValue) {
 346   uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
 347   unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
 348   unsigned Type = macho::RIT_Vanilla;
 349
 350   // See <reloc.h>.
 351   const MCSymbol *A = &Target.getSymA()->getSymbol();
 352   MCSymbolData *A_SD = &Asm.getSymbolData(*A);
 353
 354   if (!A_SD->getFragment())
 355     report_fatal_error("symbol '" + A->getName() +
 356                        "' can not be undefined in a subtraction expression");
 357
 358   uint32_t Value = Writer->getSymbolAddress(A_SD, Layout);
 359   uint64_t SecAddr = Writer->getSectionAddress(A_SD->getFragment()->getParent());
 360   FixedValue += SecAddr;
 361   uint32_t Value2 = 0;
 362
 363   if (const MCSymbolRefExpr *B = Target.getSymB()) {
 364     MCSymbolData *B_SD = &Asm.getSymbolData(B->getSymbol());
 365
 366     if (!B_SD->getFragment())
 367       report_fatal_error("symbol '" + B->getSymbol().getName() +
 368                          "' can not be undefined in a subtraction expression");
 369
 370     // Select the appropriate difference relocation type.
 371     //
 372     // Note that there is no longer any semantic difference between these two
 373     // relocation types from the linkers point of view, this is done solely for
 374     // pedantic compatibility with 'as'.
 375     Type = A_SD->isExternal() ? (unsigned)macho::RIT_Difference :
 376       (unsigned)macho::RIT_Generic_LocalDifference;
 377     Value2 = Writer->getSymbolAddress(B_SD, Layout);
 378     FixedValue -= Writer->getSectionAddress(B_SD->getFragment()->getParent());
 379   }
 380
 381   // Relocations are written out in reverse order, so the PAIR comes first.
 382   if (Type == macho::RIT_Difference ||
 383       Type == macho::RIT_Generic_LocalDifference) {
 384     macho::RelocationEntry MRE;
 385     MRE.Word0 = ((0         <<  0) |
 386                  (macho::RIT_Pair  << 24) |
 387                  (Log2Size  << 28) |
 388                  (IsPCRel   << 30) |
 389                  macho::RF_Scattered);
 390     MRE.Word1 = Value2;
 391     Writer->addRelocation(Fragment->getParent(), MRE);
 392   }
 393
 394   macho::RelocationEntry MRE;
 395   MRE.Word0 = ((FixupOffset <<  0) |
 396                (Type        << 24) |
 397                (Log2Size    << 28) |
 398                (IsPCRel     << 30) |
 399                macho::RF_Scattered);
 400   MRE.Word1 = Value;
 401   Writer->addRelocation(Fragment->getParent(), MRE);
 402 }
 403
 404 void X86MachObjectWriter::RecordTLVPRelocation(MachObjectWriter *Writer,
 405                                                const MCAssembler &Asm,
 406                                                const MCAsmLayout &Layout,
 407                                                const MCFragment *Fragment,
 408                                                const MCFixup &Fixup,
 409                                                MCValue Target,
 410                                                uint64_t &FixedValue) {
 411   assert(Target.getSymA()->getKind() == MCSymbolRefExpr::VK_TLVP &&
 412          !is64Bit() &&
 413          "Should only be called with a 32-bit TLVP relocation!");
 414
 415   unsigned Log2Size = getFixupKindLog2Size(Fixup.getKind());
 416   uint32_t Value = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
 417   unsigned IsPCRel = 0;
 418
 419   // Get the symbol data.
 420   MCSymbolData *SD_A = &Asm.getSymbolData(Target.getSymA()->getSymbol());
 421   unsigned Index = SD_A->getIndex();
 422
 423   // We're only going to have a second symbol in pic mode and it'll be a
 424   // subtraction from the picbase. For 32-bit pic the addend is the difference
 425   // between the picbase and the next address.  For 32-bit static the addend is
 426   // zero.
 427   if (Target.getSymB()) {
 428     // If this is a subtraction then we're pcrel.
 429     uint32_t FixupAddress =
 430       Writer->getFragmentAddress(Fragment, Layout) + Fixup.getOffset();
 431     MCSymbolData *SD_B = &Asm.getSymbolData(Target.getSymB()->getSymbol());
 432     IsPCRel = 1;
 433     FixedValue = (FixupAddress - Writer->getSymbolAddress(SD_B, Layout) +
 434                   Target.getConstant());
 435     FixedValue += 1ULL << Log2Size;
 436   } else {
 437     FixedValue = 0;
 438   }
 439
 440   // struct relocation_info (8 bytes)
 441   macho::RelocationEntry MRE;
 442   MRE.Word0 = Value;
 443   MRE.Word1 = ((Index                  <<  0) |
 444                (IsPCRel                << 24) |
 445                (Log2Size               << 25) |
 446                (1                      << 27) | // Extern
 447                (macho::RIT_Generic_TLV << 28)); // Type
 448   Writer->addRelocation(Fragment->getParent(), MRE);
 449 }
 450
 451 void X86MachObjectWriter::RecordX86Relocation(MachObjectWriter *Writer,
 452                                               const MCAssembler &Asm,
 453                                               const MCAsmLayout &Layout,
 454                                               const MCFragment *Fragment,
 455                                               const MCFixup &Fixup,
 456                                               MCValue Target,
 457                                               uint64_t &FixedValue) {
 458   unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
 459   unsigned Log2Size = getFixupKindLog2Size(Fixup.getKind());
 460
 461   // If this is a 32-bit TLVP reloc it's handled a bit differently.
 462   if (Target.getSymA() &&
 463       Target.getSymA()->getKind() == MCSymbolRefExpr::VK_TLVP) {
 464     RecordTLVPRelocation(Writer, Asm, Layout, Fragment, Fixup, Target,
 465                          FixedValue);
 466     return;
 467   }
 468
 469   // If this is a difference or a defined symbol plus an offset, then we need a
 470   // scattered relocation entry. Differences always require scattered
 471   // relocations.
 472   if (Target.getSymB())
 473     return RecordScatteredRelocation(Writer, Asm, Layout, Fragment, Fixup,
 474                                      Target, Log2Size, FixedValue);
 475
 476   // Get the symbol data, if any.
 477   MCSymbolData *SD = 0;
 478   if (Target.getSymA())
 479     SD = &Asm.getSymbolData(Target.getSymA()->getSymbol());
 480
 481   // If this is an internal relocation with an offset, it also needs a scattered
 482   // relocation entry.
 483   uint32_t Offset = Target.getConstant();
 484   if (IsPCRel)
 485     Offset += 1 << Log2Size;
 486   if (Offset && SD && !Writer->doesSymbolRequireExternRelocation(SD))
 487     return RecordScatteredRelocation(Writer, Asm, Layout, Fragment, Fixup,
 488                                      Target, Log2Size, FixedValue);
 489
 490   // See <reloc.h>.
 491   uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
 492   unsigned Index = 0;
 493   unsigned IsExtern = 0;
 494   unsigned Type = 0;
 495
 496   if (Target.isAbsolute()) { // constant
 497     // SymbolNum of 0 indicates the absolute section.
 498     //
 499     // FIXME: Currently, these are never generated (see code below). I cannot
 500     // find a case where they are actually emitted.
 501     Type = macho::RIT_Vanilla;
 502   } else {
 503     // Resolve constant variables.
 504     if (SD->getSymbol().isVariable()) {
 505       int64_t Res;
 506       if (SD->getSymbol().getVariableValue()->EvaluateAsAbsolute(
 507             Res, Layout, Writer->getSectionAddressMap())) {
 508         FixedValue = Res;
 509         return;
 510       }
 511     }
 512
 513     // Check whether we need an external or internal relocation.
 514     if (Writer->doesSymbolRequireExternRelocation(SD)) {
 515       IsExtern = 1;
 516       Index = SD->getIndex();
 517       // For external relocations, make sure to offset the fixup value to
 518       // compensate for the addend of the symbol address, if it was
 519       // undefined. This occurs with weak definitions, for example.
 520       if (!SD->Symbol->isUndefined())
 521         FixedValue -= Layout.getSymbolOffset(SD);
 522     } else {
 523       // The index is the section ordinal (1-based).
 524       const MCSectionData &SymSD = Asm.getSectionData(
 525         SD->getSymbol().getSection());
 526       Index = SymSD.getOrdinal() + 1;
 527       FixedValue += Writer->getSectionAddress(&SymSD);
 528     }
 529     if (IsPCRel)
 530       FixedValue -= Writer->getSectionAddress(Fragment->getParent());
 531
 532     Type = macho::RIT_Vanilla;
 533   }
 534
 535   // struct relocation_info (8 bytes)
 536   macho::RelocationEntry MRE;
 537   MRE.Word0 = FixupOffset;
 538   MRE.Word1 = ((Index     <<  0) |
 539                (IsPCRel   << 24) |
 540                (Log2Size  << 25) |
 541                (IsExtern  << 27) |
 542                (Type      << 28));
 543   Writer->addRelocation(Fragment->getParent(), MRE);
 544 }
 545
 546 MCObjectWriter *llvm::createX86MachObjectWriter(raw_ostream &OS,
 547                                                 bool Is64Bit,
 548                                                 uint32_t CPUType,
 549                                                 uint32_t CPUSubtype) {
 550   return createMachObjectWriter(new X86MachObjectWriter(Is64Bit,
 551                                                         CPUType,
 552                                                         CPUSubtype),
 553                                 OS, /*IsLittleEndian=*/true);
 554 }