1 //===-- LTOModule.cpp - LLVM Link Time Optimizer --------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements the Link Time Optimization library. This library is
10 // intended to be used by linker to optimize code at link time.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "llvm/LTO/legacy/LTOModule.h"
15 #include "llvm/ADT/Triple.h"
16 #include "llvm/Bitcode/BitcodeReader.h"
17 #include "llvm/CodeGen/TargetSubtargetInfo.h"
18 #include "llvm/IR/Constants.h"
19 #include "llvm/IR/LLVMContext.h"
20 #include "llvm/IR/Mangler.h"
21 #include "llvm/IR/Metadata.h"
22 #include "llvm/IR/Module.h"
23 #include "llvm/MC/MCExpr.h"
24 #include "llvm/MC/MCInst.h"
25 #include "llvm/MC/MCParser/MCAsmParser.h"
26 #include "llvm/MC/MCSection.h"
27 #include "llvm/MC/MCSubtargetInfo.h"
28 #include "llvm/MC/MCSymbol.h"
29 #include "llvm/MC/SubtargetFeature.h"
30 #include "llvm/MC/TargetRegistry.h"
31 #include "llvm/Object/IRObjectFile.h"
32 #include "llvm/Object/MachO.h"
33 #include "llvm/Object/ObjectFile.h"
34 #include "llvm/Support/FileSystem.h"
35 #include "llvm/Support/Host.h"
36 #include "llvm/Support/MemoryBuffer.h"
37 #include "llvm/Support/Path.h"
38 #include "llvm/Support/SourceMgr.h"
39 #include "llvm/Support/TargetSelect.h"
40 #include "llvm/Target/TargetLoweringObjectFile.h"
41 #include "llvm/Transforms/Utils/GlobalStatus.h"
42 #include <system_error>
43 using namespace llvm;
44 using namespace llvm::object;
45 
46 LTOModule::LTOModule(std::unique_ptr<Module> M, MemoryBufferRef MBRef,
47                      llvm::TargetMachine *TM)
48     : Mod(std::move(M)), MBRef(MBRef), _target(TM) {
49   assert(_target && "target machine is null");
50   SymTab.addModule(Mod.get());
51 }
52 
53 LTOModule::~LTOModule() = default;
54 
55 /// isBitcodeFile - Returns 'true' if the file (or memory contents) is LLVM
56 /// bitcode.
57 bool LTOModule::isBitcodeFile(const void *Mem, size_t Length) {
58   Expected<MemoryBufferRef> BCData = IRObjectFile::findBitcodeInMemBuffer(
59       MemoryBufferRef(StringRef((const char *)Mem, Length), "<mem>"));
60   return !errorToBool(BCData.takeError());
61 }
62 
63 bool LTOModule::isBitcodeFile(StringRef Path) {
64   ErrorOr<std::unique_ptr<MemoryBuffer>> BufferOrErr =
65       MemoryBuffer::getFile(Path);
66   if (!BufferOrErr)
67     return false;
68 
69   Expected<MemoryBufferRef> BCData = IRObjectFile::findBitcodeInMemBuffer(
70       BufferOrErr.get()->getMemBufferRef());
71   return !errorToBool(BCData.takeError());
72 }
73 
74 bool LTOModule::isThinLTO() {
75   Expected<BitcodeLTOInfo> Result = getBitcodeLTOInfo(MBRef);
76   if (!Result) {
77     logAllUnhandledErrors(Result.takeError(), errs());
78     return false;
79   }
80   return Result->IsThinLTO;
81 }
82 
83 bool LTOModule::isBitcodeForTarget(MemoryBuffer *Buffer,
84                                    StringRef TriplePrefix) {
85   Expected<MemoryBufferRef> BCOrErr =
86       IRObjectFile::findBitcodeInMemBuffer(Buffer->getMemBufferRef());
87   if (errorToBool(BCOrErr.takeError()))
88     return false;
89   LLVMContext Context;
90   ErrorOr<std::string> TripleOrErr =
91       expectedToErrorOrAndEmitErrors(Context, getBitcodeTargetTriple(*BCOrErr));
92   if (!TripleOrErr)
93     return false;
94   return StringRef(*TripleOrErr).startswith(TriplePrefix);
95 }
96 
97 std::string LTOModule::getProducerString(MemoryBuffer *Buffer) {
98   Expected<MemoryBufferRef> BCOrErr =
99       IRObjectFile::findBitcodeInMemBuffer(Buffer->getMemBufferRef());
100   if (errorToBool(BCOrErr.takeError()))
101     return "";
102   LLVMContext Context;
103   ErrorOr<std::string> ProducerOrErr = expectedToErrorOrAndEmitErrors(
104       Context, getBitcodeProducerString(*BCOrErr));
105   if (!ProducerOrErr)
106     return "";
107   return *ProducerOrErr;
108 }
109 
110 ErrorOr<std::unique_ptr<LTOModule>>
111 LTOModule::createFromFile(LLVMContext &Context, StringRef path,
112                           const TargetOptions &options) {
113   ErrorOr<std::unique_ptr<MemoryBuffer>> BufferOrErr =
114       MemoryBuffer::getFile(path);
115   if (std::error_code EC = BufferOrErr.getError()) {
116     Context.emitError(EC.message());
117     return EC;
118   }
119   std::unique_ptr<MemoryBuffer> Buffer = std::move(BufferOrErr.get());
120   return makeLTOModule(Buffer->getMemBufferRef(), options, Context,
121                        /* ShouldBeLazy*/ false);
122 }
123 
124 ErrorOr<std::unique_ptr<LTOModule>>
125 LTOModule::createFromOpenFile(LLVMContext &Context, int fd, StringRef path,
126                               size_t size, const TargetOptions &options) {
127   return createFromOpenFileSlice(Context, fd, path, size, 0, options);
128 }
129 
130 ErrorOr<std::unique_ptr<LTOModule>>
131 LTOModule::createFromOpenFileSlice(LLVMContext &Context, int fd, StringRef path,
132                                    size_t map_size, off_t offset,
133                                    const TargetOptions &options) {
134   ErrorOr<std::unique_ptr<MemoryBuffer>> BufferOrErr =
135       MemoryBuffer::getOpenFileSlice(sys::fs::convertFDToNativeFile(fd), path,
136                                      map_size, offset);
137   if (std::error_code EC = BufferOrErr.getError()) {
138     Context.emitError(EC.message());
139     return EC;
140   }
141   std::unique_ptr<MemoryBuffer> Buffer = std::move(BufferOrErr.get());
142   return makeLTOModule(Buffer->getMemBufferRef(), options, Context,
143                        /* ShouldBeLazy */ false);
144 }
145 
146 ErrorOr<std::unique_ptr<LTOModule>>
147 LTOModule::createFromBuffer(LLVMContext &Context, const void *mem,
148                             size_t length, const TargetOptions &options,
149                             StringRef path) {
150   StringRef Data((const char *)mem, length);
151   MemoryBufferRef Buffer(Data, path);
152   return makeLTOModule(Buffer, options, Context, /* ShouldBeLazy */ false);
153 }
154 
155 ErrorOr<std::unique_ptr<LTOModule>>
156 LTOModule::createInLocalContext(std::unique_ptr<LLVMContext> Context,
157                                 const void *mem, size_t length,
158                                 const TargetOptions &options, StringRef path) {
159   StringRef Data((const char *)mem, length);
160   MemoryBufferRef Buffer(Data, path);
161   // If we own a context, we know this is being used only for symbol extraction,
162   // not linking.  Be lazy in that case.
163   ErrorOr<std::unique_ptr<LTOModule>> Ret =
164       makeLTOModule(Buffer, options, *Context, /* ShouldBeLazy */ true);
165   if (Ret)
166     (*Ret)->OwnedContext = std::move(Context);
167   return Ret;
168 }
169 
170 static ErrorOr<std::unique_ptr<Module>>
171 parseBitcodeFileImpl(MemoryBufferRef Buffer, LLVMContext &Context,
172                      bool ShouldBeLazy) {
173   // Find the buffer.
174   Expected<MemoryBufferRef> MBOrErr =
175       IRObjectFile::findBitcodeInMemBuffer(Buffer);
176   if (Error E = MBOrErr.takeError()) {
177     std::error_code EC = errorToErrorCode(std::move(E));
178     Context.emitError(EC.message());
179     return EC;
180   }
181 
182   if (!ShouldBeLazy) {
183     // Parse the full file.
184     return expectedToErrorOrAndEmitErrors(Context,
185                                           parseBitcodeFile(*MBOrErr, Context));
186   }
187 
188   // Parse lazily.
189   return expectedToErrorOrAndEmitErrors(
190       Context,
191       getLazyBitcodeModule(*MBOrErr, Context, true /*ShouldLazyLoadMetadata*/));
192 }
193 
194 ErrorOr<std::unique_ptr<LTOModule>>
195 LTOModule::makeLTOModule(MemoryBufferRef Buffer, const TargetOptions &options,
196                          LLVMContext &Context, bool ShouldBeLazy) {
197   ErrorOr<std::unique_ptr<Module>> MOrErr =
198       parseBitcodeFileImpl(Buffer, Context, ShouldBeLazy);
199   if (std::error_code EC = MOrErr.getError())
200     return EC;
201   std::unique_ptr<Module> &M = *MOrErr;
202 
203   std::string TripleStr = M->getTargetTriple();
204   if (TripleStr.empty())
205     TripleStr = sys::getDefaultTargetTriple();
206   llvm::Triple Triple(TripleStr);
207 
208   // find machine architecture for this module
209   std::string errMsg;
210   const Target *march = TargetRegistry::lookupTarget(TripleStr, errMsg);
211   if (!march)
212     return make_error_code(object::object_error::arch_not_found);
213 
214   // construct LTOModule, hand over ownership of module and target
215   SubtargetFeatures Features;
216   Features.getDefaultSubtargetFeatures(Triple);
217   std::string FeatureStr = Features.getString();
218   // Set a default CPU for Darwin triples.
219   std::string CPU;
220   if (Triple.isOSDarwin()) {
221     if (Triple.getArch() == llvm::Triple::x86_64)
222       CPU = "core2";
223     else if (Triple.getArch() == llvm::Triple::x86)
224       CPU = "yonah";
225     else if (Triple.isArm64e())
226       CPU = "apple-a12";
227     else if (Triple.getArch() == llvm::Triple::aarch64 ||
228              Triple.getArch() == llvm::Triple::aarch64_32)
229       CPU = "cyclone";
230   }
231 
232   TargetMachine *target =
233       march->createTargetMachine(TripleStr, CPU, FeatureStr, options, None);
234 
235   std::unique_ptr<LTOModule> Ret(new LTOModule(std::move(M), Buffer, target));
236   Ret->parseSymbols();
237   Ret->parseMetadata();
238 
239   return std::move(Ret);
240 }
241 
242 /// Create a MemoryBuffer from a memory range with an optional name.
243 std::unique_ptr<MemoryBuffer>
244 LTOModule::makeBuffer(const void *mem, size_t length, StringRef name) {
245   const char *startPtr = (const char*)mem;
246   return MemoryBuffer::getMemBuffer(StringRef(startPtr, length), name, false);
247 }
248 
249 /// objcClassNameFromExpression - Get string that the data pointer points to.
250 bool
251 LTOModule::objcClassNameFromExpression(const Constant *c, std::string &name) {
252   if (const ConstantExpr *ce = dyn_cast<ConstantExpr>(c)) {
253     Constant *op = ce->getOperand(0);
254     if (GlobalVariable *gvn = dyn_cast<GlobalVariable>(op)) {
255       Constant *cn = gvn->getInitializer();
256       if (ConstantDataArray *ca = dyn_cast<ConstantDataArray>(cn)) {
257         if (ca->isCString()) {
258           name = (".objc_class_name_" + ca->getAsCString()).str();
259           return true;
260         }
261       }
262     }
263   }
264   return false;
265 }
266 
267 /// addObjCClass - Parse i386/ppc ObjC class data structure.
268 void LTOModule::addObjCClass(const GlobalVariable *clgv) {
269   const ConstantStruct *c = dyn_cast<ConstantStruct>(clgv->getInitializer());
270   if (!c) return;
271 
272   // second slot in __OBJC,__class is pointer to superclass name
273   std::string superclassName;
274   if (objcClassNameFromExpression(c->getOperand(1), superclassName)) {
275     auto IterBool =
276         _undefines.insert(std::make_pair(superclassName, NameAndAttributes()));
277     if (IterBool.second) {
278       NameAndAttributes &info = IterBool.first->second;
279       info.name = IterBool.first->first();
280       info.attributes = LTO_SYMBOL_DEFINITION_UNDEFINED;
281       info.isFunction = false;
282       info.symbol = clgv;
283     }
284   }
285 
286   // third slot in __OBJC,__class is pointer to class name
287   std::string className;
288   if (objcClassNameFromExpression(c->getOperand(2), className)) {
289     auto Iter = _defines.insert(className).first;
290 
291     NameAndAttributes info;
292     info.name = Iter->first();
293     info.attributes = LTO_SYMBOL_PERMISSIONS_DATA |
294       LTO_SYMBOL_DEFINITION_REGULAR | LTO_SYMBOL_SCOPE_DEFAULT;
295     info.isFunction = false;
296     info.symbol = clgv;
297     _symbols.push_back(info);
298   }
299 }
300 
301 /// addObjCCategory - Parse i386/ppc ObjC category data structure.
302 void LTOModule::addObjCCategory(const GlobalVariable *clgv) {
303   const ConstantStruct *c = dyn_cast<ConstantStruct>(clgv->getInitializer());
304   if (!c) return;
305 
306   // second slot in __OBJC,__category is pointer to target class name
307   std::string targetclassName;
308   if (!objcClassNameFromExpression(c->getOperand(1), targetclassName))
309     return;
310 
311   auto IterBool =
312       _undefines.insert(std::make_pair(targetclassName, NameAndAttributes()));
313 
314   if (!IterBool.second)
315     return;
316 
317   NameAndAttributes &info = IterBool.first->second;
318   info.name = IterBool.first->first();
319   info.attributes = LTO_SYMBOL_DEFINITION_UNDEFINED;
320   info.isFunction = false;
321   info.symbol = clgv;
322 }
323 
324 /// addObjCClassRef - Parse i386/ppc ObjC class list data structure.
325 void LTOModule::addObjCClassRef(const GlobalVariable *clgv) {
326   std::string targetclassName;
327   if (!objcClassNameFromExpression(clgv->getInitializer(), targetclassName))
328     return;
329 
330   auto IterBool =
331       _undefines.insert(std::make_pair(targetclassName, NameAndAttributes()));
332 
333   if (!IterBool.second)
334     return;
335 
336   NameAndAttributes &info = IterBool.first->second;
337   info.name = IterBool.first->first();
338   info.attributes = LTO_SYMBOL_DEFINITION_UNDEFINED;
339   info.isFunction = false;
340   info.symbol = clgv;
341 }
342 
343 void LTOModule::addDefinedDataSymbol(ModuleSymbolTable::Symbol Sym) {
344   SmallString<64> Buffer;
345   {
346     raw_svector_ostream OS(Buffer);
347     SymTab.printSymbolName(OS, Sym);
348     Buffer.c_str();
349   }
350 
351   const GlobalValue *V = Sym.get<GlobalValue *>();
352   addDefinedDataSymbol(Buffer, V);
353 }
354 
355 void LTOModule::addDefinedDataSymbol(StringRef Name, const GlobalValue *v) {
356   // Add to list of defined symbols.
357   addDefinedSymbol(Name, v, false);
358 
359   if (!v->hasSection() /* || !isTargetDarwin */)
360     return;
361 
362   // Special case i386/ppc ObjC data structures in magic sections:
363   // The issue is that the old ObjC object format did some strange
364   // contortions to avoid real linker symbols.  For instance, the
365   // ObjC class data structure is allocated statically in the executable
366   // that defines that class.  That data structures contains a pointer to
367   // its superclass.  But instead of just initializing that part of the
368   // struct to the address of its superclass, and letting the static and
369   // dynamic linkers do the rest, the runtime works by having that field
370   // instead point to a C-string that is the name of the superclass.
371   // At runtime the objc initialization updates that pointer and sets
372   // it to point to the actual super class.  As far as the linker
373   // knows it is just a pointer to a string.  But then someone wanted the
374   // linker to issue errors at build time if the superclass was not found.
375   // So they figured out a way in mach-o object format to use an absolute
376   // symbols (.objc_class_name_Foo = 0) and a floating reference
377   // (.reference .objc_class_name_Bar) to cause the linker into erroring when
378   // a class was missing.
379   // The following synthesizes the implicit .objc_* symbols for the linker
380   // from the ObjC data structures generated by the front end.
381 
382   // special case if this data blob is an ObjC class definition
383   if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(v)) {
384     StringRef Section = GV->getSection();
385     if (Section.startswith("__OBJC,__class,")) {
386       addObjCClass(GV);
387     }
388 
389     // special case if this data blob is an ObjC category definition
390     else if (Section.startswith("__OBJC,__category,")) {
391       addObjCCategory(GV);
392     }
393 
394     // special case if this data blob is the list of referenced classes
395     else if (Section.startswith("__OBJC,__cls_refs,")) {
396       addObjCClassRef(GV);
397     }
398   }
399 }
400 
401 void LTOModule::addDefinedFunctionSymbol(ModuleSymbolTable::Symbol Sym) {
402   SmallString<64> Buffer;
403   {
404     raw_svector_ostream OS(Buffer);
405     SymTab.printSymbolName(OS, Sym);
406     Buffer.c_str();
407   }
408 
409   const Function *F = cast<Function>(Sym.get<GlobalValue *>());
410   addDefinedFunctionSymbol(Buffer, F);
411 }
412 
413 void LTOModule::addDefinedFunctionSymbol(StringRef Name, const Function *F) {
414   // add to list of defined symbols
415   addDefinedSymbol(Name, F, true);
416 }
417 
418 void LTOModule::addDefinedSymbol(StringRef Name, const GlobalValue *def,
419                                  bool isFunction) {
420   const GlobalObject *go = dyn_cast<GlobalObject>(def);
421   uint32_t attr = go ? Log2(go->getAlign().valueOrOne()) : 0;
422 
423   // set permissions part
424   if (isFunction) {
425     attr |= LTO_SYMBOL_PERMISSIONS_CODE;
426   } else {
427     const GlobalVariable *gv = dyn_cast<GlobalVariable>(def);
428     if (gv && gv->isConstant())
429       attr |= LTO_SYMBOL_PERMISSIONS_RODATA;
430     else
431       attr |= LTO_SYMBOL_PERMISSIONS_DATA;
432   }
433 
434   // set definition part
435   if (def->hasWeakLinkage() || def->hasLinkOnceLinkage())
436     attr |= LTO_SYMBOL_DEFINITION_WEAK;
437   else if (def->hasCommonLinkage())
438     attr |= LTO_SYMBOL_DEFINITION_TENTATIVE;
439   else
440     attr |= LTO_SYMBOL_DEFINITION_REGULAR;
441 
442   // set scope part
443   if (def->hasLocalLinkage())
444     // Ignore visibility if linkage is local.
445     attr |= LTO_SYMBOL_SCOPE_INTERNAL;
446   else if (def->hasHiddenVisibility())
447     attr |= LTO_SYMBOL_SCOPE_HIDDEN;
448   else if (def->hasProtectedVisibility())
449     attr |= LTO_SYMBOL_SCOPE_PROTECTED;
450   else if (def->canBeOmittedFromSymbolTable())
451     attr |= LTO_SYMBOL_SCOPE_DEFAULT_CAN_BE_HIDDEN;
452   else
453     attr |= LTO_SYMBOL_SCOPE_DEFAULT;
454 
455   if (def->hasComdat())
456     attr |= LTO_SYMBOL_COMDAT;
457 
458   if (isa<GlobalAlias>(def))
459     attr |= LTO_SYMBOL_ALIAS;
460 
461   auto Iter = _defines.insert(Name).first;
462 
463   // fill information structure
464   NameAndAttributes info;
465   StringRef NameRef = Iter->first();
466   info.name = NameRef;
467   assert(NameRef.data()[NameRef.size()] == '\0');
468   info.attributes = attr;
469   info.isFunction = isFunction;
470   info.symbol = def;
471 
472   // add to table of symbols
473   _symbols.push_back(info);
474 }
475 
476 /// addAsmGlobalSymbol - Add a global symbol from module-level ASM to the
477 /// defined list.
478 void LTOModule::addAsmGlobalSymbol(StringRef name,
479                                    lto_symbol_attributes scope) {
480   auto IterBool = _defines.insert(name);
481 
482   // only add new define if not already defined
483   if (!IterBool.second)
484     return;
485 
486   NameAndAttributes &info = _undefines[IterBool.first->first()];
487 
488   if (info.symbol == nullptr) {
489     // FIXME: This is trying to take care of module ASM like this:
490     //
491     //   module asm ".zerofill __FOO, __foo, _bar_baz_qux, 0"
492     //
493     // but is gross and its mother dresses it funny. Have the ASM parser give us
494     // more details for this type of situation so that we're not guessing so
495     // much.
496 
497     // fill information structure
498     info.name = IterBool.first->first();
499     info.attributes =
500       LTO_SYMBOL_PERMISSIONS_DATA | LTO_SYMBOL_DEFINITION_REGULAR | scope;
501     info.isFunction = false;
502     info.symbol = nullptr;
503 
504     // add to table of symbols
505     _symbols.push_back(info);
506     return;
507   }
508 
509   if (info.isFunction)
510     addDefinedFunctionSymbol(info.name, cast<Function>(info.symbol));
511   else
512     addDefinedDataSymbol(info.name, info.symbol);
513 
514   _symbols.back().attributes &= ~LTO_SYMBOL_SCOPE_MASK;
515   _symbols.back().attributes |= scope;
516 }
517 
518 /// addAsmGlobalSymbolUndef - Add a global symbol from module-level ASM to the
519 /// undefined list.
520 void LTOModule::addAsmGlobalSymbolUndef(StringRef name) {
521   auto IterBool = _undefines.insert(std::make_pair(name, NameAndAttributes()));
522 
523   _asm_undefines.push_back(IterBool.first->first());
524 
525   // we already have the symbol
526   if (!IterBool.second)
527     return;
528 
529   uint32_t attr = LTO_SYMBOL_DEFINITION_UNDEFINED;
530   attr |= LTO_SYMBOL_SCOPE_DEFAULT;
531   NameAndAttributes &info = IterBool.first->second;
532   info.name = IterBool.first->first();
533   info.attributes = attr;
534   info.isFunction = false;
535   info.symbol = nullptr;
536 }
537 
538 /// Add a symbol which isn't defined just yet to a list to be resolved later.
539 void LTOModule::addPotentialUndefinedSymbol(ModuleSymbolTable::Symbol Sym,
540                                             bool isFunc) {
541   SmallString<64> name;
542   {
543     raw_svector_ostream OS(name);
544     SymTab.printSymbolName(OS, Sym);
545     name.c_str();
546   }
547 
548   auto IterBool =
549       _undefines.insert(std::make_pair(name.str(), NameAndAttributes()));
550 
551   // we already have the symbol
552   if (!IterBool.second)
553     return;
554 
555   NameAndAttributes &info = IterBool.first->second;
556 
557   info.name = IterBool.first->first();
558 
559   const GlobalValue *decl = Sym.dyn_cast<GlobalValue *>();
560 
561   if (decl->hasExternalWeakLinkage())
562     info.attributes = LTO_SYMBOL_DEFINITION_WEAKUNDEF;
563   else
564     info.attributes = LTO_SYMBOL_DEFINITION_UNDEFINED;
565 
566   info.isFunction = isFunc;
567   info.symbol = decl;
568 }
569 
570 void LTOModule::parseSymbols() {
571   for (auto Sym : SymTab.symbols()) {
572     auto *GV = Sym.dyn_cast<GlobalValue *>();
573     uint32_t Flags = SymTab.getSymbolFlags(Sym);
574     if (Flags & object::BasicSymbolRef::SF_FormatSpecific)
575       continue;
576 
577     bool IsUndefined = Flags & object::BasicSymbolRef::SF_Undefined;
578 
579     if (!GV) {
580       SmallString<64> Buffer;
581       {
582         raw_svector_ostream OS(Buffer);
583         SymTab.printSymbolName(OS, Sym);
584         Buffer.c_str();
585       }
586       StringRef Name = Buffer;
587 
588       if (IsUndefined)
589         addAsmGlobalSymbolUndef(Name);
590       else if (Flags & object::BasicSymbolRef::SF_Global)
591         addAsmGlobalSymbol(Name, LTO_SYMBOL_SCOPE_DEFAULT);
592       else
593         addAsmGlobalSymbol(Name, LTO_SYMBOL_SCOPE_INTERNAL);
594       continue;
595     }
596 
597     auto *F = dyn_cast<Function>(GV);
598     if (IsUndefined) {
599       addPotentialUndefinedSymbol(Sym, F != nullptr);
600       continue;
601     }
602 
603     if (F) {
604       addDefinedFunctionSymbol(Sym);
605       continue;
606     }
607 
608     if (isa<GlobalVariable>(GV)) {
609       addDefinedDataSymbol(Sym);
610       continue;
611     }
612 
613     assert(isa<GlobalAlias>(GV));
614     addDefinedDataSymbol(Sym);
615   }
616 
617   // make symbols for all undefines
618   for (StringMap<NameAndAttributes>::iterator u =_undefines.begin(),
619          e = _undefines.end(); u != e; ++u) {
620     // If this symbol also has a definition, then don't make an undefine because
621     // it is a tentative definition.
622     if (_defines.count(u->getKey())) continue;
623     NameAndAttributes info = u->getValue();
624     _symbols.push_back(info);
625   }
626 }
627 
628 /// parseMetadata - Parse metadata from the module
629 void LTOModule::parseMetadata() {
630   raw_string_ostream OS(LinkerOpts);
631 
632   // Linker Options
633   if (NamedMDNode *LinkerOptions =
634           getModule().getNamedMetadata("llvm.linker.options")) {
635     for (unsigned i = 0, e = LinkerOptions->getNumOperands(); i != e; ++i) {
636       MDNode *MDOptions = LinkerOptions->getOperand(i);
637       for (unsigned ii = 0, ie = MDOptions->getNumOperands(); ii != ie; ++ii) {
638         MDString *MDOption = cast<MDString>(MDOptions->getOperand(ii));
639         OS << " " << MDOption->getString();
640       }
641     }
642   }
643 
644   // Globals - we only need to do this for COFF.
645   const Triple TT(_target->getTargetTriple());
646   if (!TT.isOSBinFormatCOFF())
647     return;
648   Mangler M;
649   for (const NameAndAttributes &Sym : _symbols) {
650     if (!Sym.symbol)
651       continue;
652     emitLinkerFlagsForGlobalCOFF(OS, Sym.symbol, TT, M);
653   }
654 }
655 
656 lto::InputFile *LTOModule::createInputFile(const void *buffer,
657                                            size_t buffer_size, const char *path,
658                                            std::string &outErr) {
659   StringRef Data((const char *)buffer, buffer_size);
660   MemoryBufferRef BufferRef(Data, path);
661 
662   Expected<std::unique_ptr<lto::InputFile>> ObjOrErr =
663       lto::InputFile::create(BufferRef);
664 
665   if (ObjOrErr)
666     return ObjOrErr->release();
667 
668   outErr = std::string(path) +
669            ": Could not read LTO input file: " + toString(ObjOrErr.takeError());
670   return nullptr;
671 }
672 
673 size_t LTOModule::getDependentLibraryCount(lto::InputFile *input) {
674   return input->getDependentLibraries().size();
675 }
676 
677 const char *LTOModule::getDependentLibrary(lto::InputFile *input, size_t index,
678                                            size_t *size) {
679   StringRef S = input->getDependentLibraries()[index];
680   *size = S.size();
681   return S.data();
682 }
683 
684 Expected<uint32_t> LTOModule::getMachOCPUType() const {
685   return MachO::getCPUType(Triple(Mod->getTargetTriple()));
686 }
687 
688 Expected<uint32_t> LTOModule::getMachOCPUSubType() const {
689   return MachO::getCPUSubType(Triple(Mod->getTargetTriple()));
690 }
691 
692 bool LTOModule::hasCtorDtor() const {
693   for (auto Sym : SymTab.symbols()) {
694     if (auto *GV = Sym.dyn_cast<GlobalValue *>()) {
695       StringRef Name = GV->getName();
696       if (Name.consume_front("llvm.global_")) {
697         if (Name.equals("ctors") || Name.equals("dtors"))
698           return true;
699       }
700     }
701   }
702   return false;
703 }
704