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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 "MCTargetDesc/X86MCTargetDesc.h"
11 #include "MCTargetDesc/X86FixupKinds.h"
12 #include "llvm/ADT/Twine.h"
13 #include "llvm/MC/MCAsmLayout.h"
14 #include "llvm/MC/MCAssembler.h"
15 #include "llvm/MC/MCContext.h"
16 #include "llvm/MC/MCMachObjectWriter.h"
17 #include "llvm/MC/MCSectionMachO.h"
18 #include "llvm/MC/MCValue.h"
19 #include "llvm/Object/MachOFormat.h"
20 #include "llvm/Support/ErrorHandling.h"
21 #include "llvm/Support/Format.h"
22 
23 using namespace llvm;
24 using namespace llvm::object;
25 
26 namespace {
27 class X86MachObjectWriter : public MCMachObjectTargetWriter {
28   bool RecordScatteredRelocation(MachObjectWriter *Writer,
29                                  const MCAssembler &Asm,
30                                  const MCAsmLayout &Layout,
31                                  const MCFragment *Fragment,
32                                  const MCFixup &Fixup,
33                                  MCValue Target,
34                                  unsigned Log2Size,
35                                  uint64_t &FixedValue);
36   void RecordTLVPRelocation(MachObjectWriter *Writer,
37                             const MCAssembler &Asm,
38                             const MCAsmLayout &Layout,
39                             const MCFragment *Fragment,
40                             const MCFixup &Fixup,
41                             MCValue Target,
42                             uint64_t &FixedValue);
43 
44   void RecordX86Relocation(MachObjectWriter *Writer,
45                               const MCAssembler &Asm,
46                               const MCAsmLayout &Layout,
47                               const MCFragment *Fragment,
48                               const MCFixup &Fixup,
49                               MCValue Target,
50                               uint64_t &FixedValue);
51   void RecordX86_64Relocation(MachObjectWriter *Writer,
52                               const MCAssembler &Asm,
53                               const MCAsmLayout &Layout,
54                               const MCFragment *Fragment,
55                               const MCFixup &Fixup,
56                               MCValue Target,
57                               uint64_t &FixedValue);
58 public:
X86MachObjectWriter(bool Is64Bit,uint32_t CPUType,uint32_t CPUSubtype)59   X86MachObjectWriter(bool Is64Bit, uint32_t CPUType,
60                       uint32_t CPUSubtype)
61     : MCMachObjectTargetWriter(Is64Bit, CPUType, CPUSubtype,
62                                /*UseAggressiveSymbolFolding=*/Is64Bit) {}
63 
RecordRelocation(MachObjectWriter * Writer,const MCAssembler & Asm,const MCAsmLayout & Layout,const MCFragment * Fragment,const MCFixup & Fixup,MCValue Target,uint64_t & FixedValue)64   void RecordRelocation(MachObjectWriter *Writer,
65                         const MCAssembler &Asm, const MCAsmLayout &Layout,
66                         const MCFragment *Fragment, const MCFixup &Fixup,
67                         MCValue Target, uint64_t &FixedValue) {
68     if (Writer->is64Bit())
69       RecordX86_64Relocation(Writer, Asm, Layout, Fragment, Fixup, Target,
70                              FixedValue);
71     else
72       RecordX86Relocation(Writer, Asm, Layout, Fragment, Fixup, Target,
73                           FixedValue);
74   }
75 };
76 }
77 
isFixupKindRIPRel(unsigned Kind)78 static bool isFixupKindRIPRel(unsigned Kind) {
79   return Kind == X86::reloc_riprel_4byte ||
80     Kind == X86::reloc_riprel_4byte_movq_load;
81 }
82 
getFixupKindLog2Size(unsigned Kind)83 static unsigned getFixupKindLog2Size(unsigned Kind) {
84   switch (Kind) {
85   default:
86     llvm_unreachable("invalid fixup kind!");
87   case FK_PCRel_1:
88   case FK_Data_1: return 0;
89   case FK_PCRel_2:
90   case FK_Data_2: return 1;
91   case FK_PCRel_4:
92     // FIXME: Remove these!!!
93   case X86::reloc_riprel_4byte:
94   case X86::reloc_riprel_4byte_movq_load:
95   case X86::reloc_signed_4byte:
96   case FK_Data_4: return 2;
97   case FK_Data_8: return 3;
98   }
99 }
100 
RecordX86_64Relocation(MachObjectWriter * Writer,const MCAssembler & Asm,const MCAsmLayout & Layout,const MCFragment * Fragment,const MCFixup & Fixup,MCValue Target,uint64_t & FixedValue)101 void X86MachObjectWriter::RecordX86_64Relocation(MachObjectWriter *Writer,
102                                                  const MCAssembler &Asm,
103                                                  const MCAsmLayout &Layout,
104                                                  const MCFragment *Fragment,
105                                                  const MCFixup &Fixup,
106                                                  MCValue Target,
107                                                  uint64_t &FixedValue) {
108   unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
109   unsigned IsRIPRel = isFixupKindRIPRel(Fixup.getKind());
110   unsigned Log2Size = getFixupKindLog2Size(Fixup.getKind());
111 
112   // See <reloc.h>.
113   uint32_t FixupOffset =
114     Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
115   uint32_t FixupAddress =
116     Writer->getFragmentAddress(Fragment, Layout) + Fixup.getOffset();
117   int64_t Value = 0;
118   unsigned Index = 0;
119   unsigned IsExtern = 0;
120   unsigned Type = 0;
121 
122   Value = Target.getConstant();
123 
124   if (IsPCRel) {
125     // Compensate for the relocation offset, Darwin x86_64 relocations only have
126     // the addend and appear to have attempted to define it to be the actual
127     // expression addend without the PCrel bias. However, instructions with data
128     // following the relocation are not accommodated for (see comment below
129     // regarding SIGNED{1,2,4}), so it isn't exactly that either.
130     Value += 1LL << Log2Size;
131   }
132 
133   if (Target.isAbsolute()) { // constant
134     // SymbolNum of 0 indicates the absolute section.
135     Type = macho::RIT_X86_64_Unsigned;
136     Index = 0;
137 
138     // FIXME: I believe this is broken, I don't think the linker can understand
139     // it. I think it would require a local relocation, but I'm not sure if that
140     // would work either. The official way to get an absolute PCrel relocation
141     // is to use an absolute symbol (which we don't support yet).
142     if (IsPCRel) {
143       IsExtern = 1;
144       Type = macho::RIT_X86_64_Branch;
145     }
146   } else if (Target.getSymB()) { // A - B + constant
147     const MCSymbol *A = &Target.getSymA()->getSymbol();
148     MCSymbolData &A_SD = Asm.getSymbolData(*A);
149     const MCSymbolData *A_Base = Asm.getAtom(&A_SD);
150 
151     const MCSymbol *B = &Target.getSymB()->getSymbol();
152     MCSymbolData &B_SD = Asm.getSymbolData(*B);
153     const MCSymbolData *B_Base = Asm.getAtom(&B_SD);
154 
155     // Neither symbol can be modified.
156     if (Target.getSymA()->getKind() != MCSymbolRefExpr::VK_None ||
157         Target.getSymB()->getKind() != MCSymbolRefExpr::VK_None)
158       report_fatal_error("unsupported relocation of modified symbol");
159 
160     // We don't support PCrel relocations of differences. Darwin 'as' doesn't
161     // implement most of these correctly.
162     if (IsPCRel)
163       report_fatal_error("unsupported pc-relative relocation of difference");
164 
165     // The support for the situation where one or both of the symbols would
166     // require a local relocation is handled just like if the symbols were
167     // external.  This is certainly used in the case of debug sections where the
168     // section has only temporary symbols and thus the symbols don't have base
169     // symbols.  This is encoded using the section ordinal and non-extern
170     // relocation entries.
171 
172     // Darwin 'as' doesn't emit correct relocations for this (it ends up with a
173     // single SIGNED relocation); reject it for now.  Except the case where both
174     // symbols don't have a base, equal but both NULL.
175     if (A_Base == B_Base && A_Base)
176       report_fatal_error("unsupported relocation with identical base");
177 
178     Value += Writer->getSymbolAddress(&A_SD, Layout) -
179       (A_Base == NULL ? 0 : Writer->getSymbolAddress(A_Base, Layout));
180     Value -= Writer->getSymbolAddress(&B_SD, Layout) -
181       (B_Base == NULL ? 0 : Writer->getSymbolAddress(B_Base, Layout));
182 
183     if (A_Base) {
184       Index = A_Base->getIndex();
185       IsExtern = 1;
186     }
187     else {
188       Index = A_SD.getFragment()->getParent()->getOrdinal() + 1;
189       IsExtern = 0;
190     }
191     Type = macho::RIT_X86_64_Unsigned;
192 
193     macho::RelocationEntry MRE;
194     MRE.Word0 = FixupOffset;
195     MRE.Word1 = ((Index     <<  0) |
196                  (IsPCRel   << 24) |
197                  (Log2Size  << 25) |
198                  (IsExtern  << 27) |
199                  (Type      << 28));
200     Writer->addRelocation(Fragment->getParent(), MRE);
201 
202     if (B_Base) {
203       Index = B_Base->getIndex();
204       IsExtern = 1;
205     }
206     else {
207       Index = B_SD.getFragment()->getParent()->getOrdinal() + 1;
208       IsExtern = 0;
209     }
210     Type = macho::RIT_X86_64_Subtractor;
211   } else {
212     const MCSymbol *Symbol = &Target.getSymA()->getSymbol();
213     MCSymbolData &SD = Asm.getSymbolData(*Symbol);
214     const MCSymbolData *Base = Asm.getAtom(&SD);
215 
216     // Relocations inside debug sections always use local relocations when
217     // possible. This seems to be done because the debugger doesn't fully
218     // understand x86_64 relocation entries, and expects to find values that
219     // have already been fixed up.
220     if (Symbol->isInSection()) {
221       const MCSectionMachO &Section = static_cast<const MCSectionMachO&>(
222         Fragment->getParent()->getSection());
223       if (Section.hasAttribute(MCSectionMachO::S_ATTR_DEBUG))
224         Base = 0;
225     }
226 
227     // x86_64 almost always uses external relocations, except when there is no
228     // symbol to use as a base address (a local symbol with no preceding
229     // non-local symbol).
230     if (Base) {
231       Index = Base->getIndex();
232       IsExtern = 1;
233 
234       // Add the local offset, if needed.
235       if (Base != &SD)
236         Value += Layout.getSymbolOffset(&SD) - Layout.getSymbolOffset(Base);
237     } else if (Symbol->isInSection() && !Symbol->isVariable()) {
238       // The index is the section ordinal (1-based).
239       Index = SD.getFragment()->getParent()->getOrdinal() + 1;
240       IsExtern = 0;
241       Value += Writer->getSymbolAddress(&SD, Layout);
242 
243       if (IsPCRel)
244         Value -= FixupAddress + (1 << Log2Size);
245     } else if (Symbol->isVariable()) {
246       const MCExpr *Value = Symbol->getVariableValue();
247       int64_t Res;
248       bool isAbs = Value->EvaluateAsAbsolute(Res, Layout,
249                                              Writer->getSectionAddressMap());
250       if (isAbs) {
251         FixedValue = Res;
252         return;
253       } else {
254         report_fatal_error("unsupported relocation of variable '" +
255                            Symbol->getName() + "'");
256       }
257     } else {
258       report_fatal_error("unsupported relocation of undefined symbol '" +
259                          Symbol->getName() + "'");
260     }
261 
262     MCSymbolRefExpr::VariantKind Modifier = Target.getSymA()->getKind();
263     if (IsPCRel) {
264       if (IsRIPRel) {
265         if (Modifier == MCSymbolRefExpr::VK_GOTPCREL) {
266           // x86_64 distinguishes movq foo@GOTPCREL so that the linker can
267           // rewrite the movq to an leaq at link time if the symbol ends up in
268           // the same linkage unit.
269           if (unsigned(Fixup.getKind()) == X86::reloc_riprel_4byte_movq_load)
270             Type = macho::RIT_X86_64_GOTLoad;
271           else
272             Type = macho::RIT_X86_64_GOT;
273         }  else if (Modifier == MCSymbolRefExpr::VK_TLVP) {
274           Type = macho::RIT_X86_64_TLV;
275         }  else if (Modifier != MCSymbolRefExpr::VK_None) {
276           report_fatal_error("unsupported symbol modifier in relocation");
277         } else {
278           Type = macho::RIT_X86_64_Signed;
279 
280           // The Darwin x86_64 relocation format has a problem where it cannot
281           // encode an address (L<foo> + <constant>) which is outside the atom
282           // containing L<foo>. Generally, this shouldn't occur but it does
283           // happen when we have a RIPrel instruction with data following the
284           // relocation entry (e.g., movb $012, L0(%rip)). Even with the PCrel
285           // adjustment Darwin x86_64 uses, the offset is still negative and the
286           // linker has no way to recognize this.
287           //
288           // To work around this, Darwin uses several special relocation types
289           // to indicate the offsets. However, the specification or
290           // implementation of these seems to also be incomplete; they should
291           // adjust the addend as well based on the actual encoded instruction
292           // (the additional bias), but instead appear to just look at the final
293           // offset.
294           switch (-(Target.getConstant() + (1LL << Log2Size))) {
295           case 1: Type = macho::RIT_X86_64_Signed1; break;
296           case 2: Type = macho::RIT_X86_64_Signed2; break;
297           case 4: Type = macho::RIT_X86_64_Signed4; break;
298           }
299         }
300       } else {
301         if (Modifier != MCSymbolRefExpr::VK_None)
302           report_fatal_error("unsupported symbol modifier in branch "
303                              "relocation");
304 
305         Type = macho::RIT_X86_64_Branch;
306       }
307     } else {
308       if (Modifier == MCSymbolRefExpr::VK_GOT) {
309         Type = macho::RIT_X86_64_GOT;
310       } else if (Modifier == MCSymbolRefExpr::VK_GOTPCREL) {
311         // GOTPCREL is allowed as a modifier on non-PCrel instructions, in which
312         // case all we do is set the PCrel bit in the relocation entry; this is
313         // used with exception handling, for example. The source is required to
314         // include any necessary offset directly.
315         Type = macho::RIT_X86_64_GOT;
316         IsPCRel = 1;
317       } else if (Modifier == MCSymbolRefExpr::VK_TLVP) {
318         report_fatal_error("TLVP symbol modifier should have been rip-rel");
319       } else if (Modifier != MCSymbolRefExpr::VK_None)
320         report_fatal_error("unsupported symbol modifier in relocation");
321       else
322         Type = macho::RIT_X86_64_Unsigned;
323     }
324   }
325 
326   // x86_64 always writes custom values into the fixups.
327   FixedValue = Value;
328 
329   // struct relocation_info (8 bytes)
330   macho::RelocationEntry MRE;
331   MRE.Word0 = FixupOffset;
332   MRE.Word1 = ((Index     <<  0) |
333                (IsPCRel   << 24) |
334                (Log2Size  << 25) |
335                (IsExtern  << 27) |
336                (Type      << 28));
337   Writer->addRelocation(Fragment->getParent(), MRE);
338 }
339 
RecordScatteredRelocation(MachObjectWriter * Writer,const MCAssembler & Asm,const MCAsmLayout & Layout,const MCFragment * Fragment,const MCFixup & Fixup,MCValue Target,unsigned Log2Size,uint64_t & FixedValue)340 bool X86MachObjectWriter::RecordScatteredRelocation(MachObjectWriter *Writer,
341                                                     const MCAssembler &Asm,
342                                                     const MCAsmLayout &Layout,
343                                                     const MCFragment *Fragment,
344                                                     const MCFixup &Fixup,
345                                                     MCValue Target,
346                                                     unsigned Log2Size,
347                                                     uint64_t &FixedValue) {
348   uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
349   unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
350   unsigned Type = macho::RIT_Vanilla;
351 
352   // See <reloc.h>.
353   const MCSymbol *A = &Target.getSymA()->getSymbol();
354   MCSymbolData *A_SD = &Asm.getSymbolData(*A);
355 
356   if (!A_SD->getFragment())
357     report_fatal_error("symbol '" + A->getName() +
358                        "' can not be undefined in a subtraction expression");
359 
360   uint32_t Value = Writer->getSymbolAddress(A_SD, Layout);
361   uint64_t SecAddr = Writer->getSectionAddress(A_SD->getFragment()->getParent());
362   FixedValue += SecAddr;
363   uint32_t Value2 = 0;
364 
365   if (const MCSymbolRefExpr *B = Target.getSymB()) {
366     MCSymbolData *B_SD = &Asm.getSymbolData(B->getSymbol());
367 
368     if (!B_SD->getFragment())
369       report_fatal_error("symbol '" + B->getSymbol().getName() +
370                          "' can not be undefined in a subtraction expression");
371 
372     // Select the appropriate difference relocation type.
373     //
374     // Note that there is no longer any semantic difference between these two
375     // relocation types from the linkers point of view, this is done solely for
376     // pedantic compatibility with 'as'.
377     Type = A_SD->isExternal() ? (unsigned)macho::RIT_Difference :
378       (unsigned)macho::RIT_Generic_LocalDifference;
379     Value2 = Writer->getSymbolAddress(B_SD, Layout);
380     FixedValue -= Writer->getSectionAddress(B_SD->getFragment()->getParent());
381   }
382 
383   // Relocations are written out in reverse order, so the PAIR comes first.
384   if (Type == macho::RIT_Difference ||
385       Type == macho::RIT_Generic_LocalDifference) {
386     // If the offset is too large to fit in a scattered relocation,
387     // we're hosed. It's an unfortunate limitation of the MachO format.
388     if (FixupOffset > 0xffffff) {
389       char Buffer[32];
390       format("0x%x", FixupOffset).print(Buffer, sizeof(Buffer));
391       Asm.getContext().FatalError(Fixup.getLoc(),
392                          Twine("Section too large, can't encode "
393                                 "r_address (") + Buffer +
394                          ") into 24 bits of scattered "
395                          "relocation entry.");
396       llvm_unreachable("fatal error returned?!");
397     }
398 
399     macho::RelocationEntry MRE;
400     MRE.Word0 = ((0         <<  0) |
401                  (macho::RIT_Pair  << 24) |
402                  (Log2Size  << 28) |
403                  (IsPCRel   << 30) |
404                  macho::RF_Scattered);
405     MRE.Word1 = Value2;
406     Writer->addRelocation(Fragment->getParent(), MRE);
407   } else {
408     // If the offset is more than 24-bits, it won't fit in a scattered
409     // relocation offset field, so we fall back to using a non-scattered
410     // relocation. This is a bit risky, as if the offset reaches out of
411     // the block and the linker is doing scattered loading on this
412     // symbol, things can go badly.
413     //
414     // Required for 'as' compatibility.
415     if (FixupOffset > 0xffffff)
416       return false;
417   }
418 
419   macho::RelocationEntry MRE;
420   MRE.Word0 = ((FixupOffset <<  0) |
421                (Type        << 24) |
422                (Log2Size    << 28) |
423                (IsPCRel     << 30) |
424                macho::RF_Scattered);
425   MRE.Word1 = Value;
426   Writer->addRelocation(Fragment->getParent(), MRE);
427   return true;
428 }
429 
RecordTLVPRelocation(MachObjectWriter * Writer,const MCAssembler & Asm,const MCAsmLayout & Layout,const MCFragment * Fragment,const MCFixup & Fixup,MCValue Target,uint64_t & FixedValue)430 void X86MachObjectWriter::RecordTLVPRelocation(MachObjectWriter *Writer,
431                                                const MCAssembler &Asm,
432                                                const MCAsmLayout &Layout,
433                                                const MCFragment *Fragment,
434                                                const MCFixup &Fixup,
435                                                MCValue Target,
436                                                uint64_t &FixedValue) {
437   assert(Target.getSymA()->getKind() == MCSymbolRefExpr::VK_TLVP &&
438          !is64Bit() &&
439          "Should only be called with a 32-bit TLVP relocation!");
440 
441   unsigned Log2Size = getFixupKindLog2Size(Fixup.getKind());
442   uint32_t Value = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
443   unsigned IsPCRel = 0;
444 
445   // Get the symbol data.
446   MCSymbolData *SD_A = &Asm.getSymbolData(Target.getSymA()->getSymbol());
447   unsigned Index = SD_A->getIndex();
448 
449   // We're only going to have a second symbol in pic mode and it'll be a
450   // subtraction from the picbase. For 32-bit pic the addend is the difference
451   // between the picbase and the next address.  For 32-bit static the addend is
452   // zero.
453   if (Target.getSymB()) {
454     // If this is a subtraction then we're pcrel.
455     uint32_t FixupAddress =
456       Writer->getFragmentAddress(Fragment, Layout) + Fixup.getOffset();
457     MCSymbolData *SD_B = &Asm.getSymbolData(Target.getSymB()->getSymbol());
458     IsPCRel = 1;
459     FixedValue = (FixupAddress - Writer->getSymbolAddress(SD_B, Layout) +
460                   Target.getConstant());
461     FixedValue += 1ULL << Log2Size;
462   } else {
463     FixedValue = 0;
464   }
465 
466   // struct relocation_info (8 bytes)
467   macho::RelocationEntry MRE;
468   MRE.Word0 = Value;
469   MRE.Word1 = ((Index                  <<  0) |
470                (IsPCRel                << 24) |
471                (Log2Size               << 25) |
472                (1                      << 27) | // Extern
473                (macho::RIT_Generic_TLV << 28)); // Type
474   Writer->addRelocation(Fragment->getParent(), MRE);
475 }
476 
RecordX86Relocation(MachObjectWriter * Writer,const MCAssembler & Asm,const MCAsmLayout & Layout,const MCFragment * Fragment,const MCFixup & Fixup,MCValue Target,uint64_t & FixedValue)477 void X86MachObjectWriter::RecordX86Relocation(MachObjectWriter *Writer,
478                                               const MCAssembler &Asm,
479                                               const MCAsmLayout &Layout,
480                                               const MCFragment *Fragment,
481                                               const MCFixup &Fixup,
482                                               MCValue Target,
483                                               uint64_t &FixedValue) {
484   unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
485   unsigned Log2Size = getFixupKindLog2Size(Fixup.getKind());
486 
487   // If this is a 32-bit TLVP reloc it's handled a bit differently.
488   if (Target.getSymA() &&
489       Target.getSymA()->getKind() == MCSymbolRefExpr::VK_TLVP) {
490     RecordTLVPRelocation(Writer, Asm, Layout, Fragment, Fixup, Target,
491                          FixedValue);
492     return;
493   }
494 
495   // If this is a difference or a defined symbol plus an offset, then we need a
496   // scattered relocation entry. Differences always require scattered
497   // relocations.
498   if (Target.getSymB()) {
499     RecordScatteredRelocation(Writer, Asm, Layout, Fragment, Fixup,
500                               Target, Log2Size, FixedValue);
501     return;
502   }
503 
504   // Get the symbol data, if any.
505   MCSymbolData *SD = 0;
506   if (Target.getSymA())
507     SD = &Asm.getSymbolData(Target.getSymA()->getSymbol());
508 
509   // If this is an internal relocation with an offset, it also needs a scattered
510   // relocation entry.
511   uint32_t Offset = Target.getConstant();
512   if (IsPCRel)
513     Offset += 1 << Log2Size;
514   // Try to record the scattered relocation if needed. Fall back to non
515   // scattered if necessary (see comments in RecordScatteredRelocation()
516   // for details).
517   if (Offset && SD && !Writer->doesSymbolRequireExternRelocation(SD) &&
518       RecordScatteredRelocation(Writer, Asm, Layout, Fragment, Fixup,
519                                 Target, Log2Size, FixedValue))
520     return;
521 
522   // See <reloc.h>.
523   uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
524   unsigned Index = 0;
525   unsigned IsExtern = 0;
526   unsigned Type = 0;
527 
528   if (Target.isAbsolute()) { // constant
529     // SymbolNum of 0 indicates the absolute section.
530     //
531     // FIXME: Currently, these are never generated (see code below). I cannot
532     // find a case where they are actually emitted.
533     Type = macho::RIT_Vanilla;
534   } else {
535     // Resolve constant variables.
536     if (SD->getSymbol().isVariable()) {
537       int64_t Res;
538       if (SD->getSymbol().getVariableValue()->EvaluateAsAbsolute(
539             Res, Layout, Writer->getSectionAddressMap())) {
540         FixedValue = Res;
541         return;
542       }
543     }
544 
545     // Check whether we need an external or internal relocation.
546     if (Writer->doesSymbolRequireExternRelocation(SD)) {
547       IsExtern = 1;
548       Index = SD->getIndex();
549       // For external relocations, make sure to offset the fixup value to
550       // compensate for the addend of the symbol address, if it was
551       // undefined. This occurs with weak definitions, for example.
552       if (!SD->Symbol->isUndefined())
553         FixedValue -= Layout.getSymbolOffset(SD);
554     } else {
555       // The index is the section ordinal (1-based).
556       const MCSectionData &SymSD = Asm.getSectionData(
557         SD->getSymbol().getSection());
558       Index = SymSD.getOrdinal() + 1;
559       FixedValue += Writer->getSectionAddress(&SymSD);
560     }
561     if (IsPCRel)
562       FixedValue -= Writer->getSectionAddress(Fragment->getParent());
563 
564     Type = macho::RIT_Vanilla;
565   }
566 
567   // struct relocation_info (8 bytes)
568   macho::RelocationEntry MRE;
569   MRE.Word0 = FixupOffset;
570   MRE.Word1 = ((Index     <<  0) |
571                (IsPCRel   << 24) |
572                (Log2Size  << 25) |
573                (IsExtern  << 27) |
574                (Type      << 28));
575   Writer->addRelocation(Fragment->getParent(), MRE);
576 }
577 
createX86MachObjectWriter(raw_ostream & OS,bool Is64Bit,uint32_t CPUType,uint32_t CPUSubtype)578 MCObjectWriter *llvm::createX86MachObjectWriter(raw_ostream &OS,
579                                                 bool Is64Bit,
580                                                 uint32_t CPUType,
581                                                 uint32_t CPUSubtype) {
582   return createMachObjectWriter(new X86MachObjectWriter(Is64Bit,
583                                                         CPUType,
584                                                         CPUSubtype),
585                                 OS, /*IsLittleEndian=*/true);
586 }
587