1 //===-- LLVMSymbolize.cpp -------------------------------------------------===//
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 // Implementation for LLVM symbolization library.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "llvm/DebugInfo/Symbolize/Symbolize.h"
14 
15 #include "SymbolizableObjectFile.h"
16 
17 #include "llvm/ADT/STLExtras.h"
18 #include "llvm/BinaryFormat/COFF.h"
19 #include "llvm/DebugInfo/DWARF/DWARFContext.h"
20 #include "llvm/DebugInfo/PDB/PDB.h"
21 #include "llvm/DebugInfo/PDB/PDBContext.h"
22 #include "llvm/Demangle/Demangle.h"
23 #include "llvm/Object/COFF.h"
24 #include "llvm/Object/MachO.h"
25 #include "llvm/Object/MachOUniversal.h"
26 #include "llvm/Support/CRC.h"
27 #include "llvm/Support/Casting.h"
28 #include "llvm/Support/Compression.h"
29 #include "llvm/Support/DataExtractor.h"
30 #include "llvm/Support/Errc.h"
31 #include "llvm/Support/FileSystem.h"
32 #include "llvm/Support/MemoryBuffer.h"
33 #include "llvm/Support/Path.h"
34 #include <algorithm>
35 #include <cassert>
36 #include <cstring>
37 
38 namespace llvm {
39 namespace symbolize {
40 
41 Expected<DILineInfo>
42 LLVMSymbolizer::symbolizeCodeCommon(SymbolizableModule *Info,
43                                     object::SectionedAddress ModuleOffset) {
44   // A null module means an error has already been reported. Return an empty
45   // result.
46   if (!Info)
47     return DILineInfo();
48 
49   // If the user is giving us relative addresses, add the preferred base of the
50   // object to the offset before we do the query. It's what DIContext expects.
51   if (Opts.RelativeAddresses)
52     ModuleOffset.Address += Info->getModulePreferredBase();
53 
54   DILineInfo LineInfo = Info->symbolizeCode(ModuleOffset, Opts.PrintFunctions,
55                                             Opts.UseSymbolTable);
56   if (Opts.Demangle)
57     LineInfo.FunctionName = DemangleName(LineInfo.FunctionName, Info);
58   return LineInfo;
59 }
60 
61 Expected<DILineInfo>
62 LLVMSymbolizer::symbolizeCode(const ObjectFile &Obj,
63                               object::SectionedAddress ModuleOffset) {
64   StringRef ModuleName = Obj.getFileName();
65   auto I = Modules.find(ModuleName);
66   if (I != Modules.end())
67     return symbolizeCodeCommon(I->second.get(), ModuleOffset);
68 
69   std::unique_ptr<DIContext> Context =
70         DWARFContext::create(Obj, nullptr, DWARFContext::defaultErrorHandler);
71   Expected<SymbolizableModule *> InfoOrErr =
72                      createModuleInfo(&Obj, std::move(Context), ModuleName);
73   if (!InfoOrErr)
74     return InfoOrErr.takeError();
75   return symbolizeCodeCommon(*InfoOrErr, ModuleOffset);
76 }
77 
78 Expected<DILineInfo>
79 LLVMSymbolizer::symbolizeCode(const std::string &ModuleName,
80                               object::SectionedAddress ModuleOffset) {
81   Expected<SymbolizableModule *> InfoOrErr = getOrCreateModuleInfo(ModuleName);
82   if (!InfoOrErr)
83     return InfoOrErr.takeError();
84   return symbolizeCodeCommon(*InfoOrErr, ModuleOffset);
85 }
86 
87 Expected<DIInliningInfo>
88 LLVMSymbolizer::symbolizeInlinedCode(const std::string &ModuleName,
89                                      object::SectionedAddress ModuleOffset) {
90   SymbolizableModule *Info;
91   if (auto InfoOrErr = getOrCreateModuleInfo(ModuleName))
92     Info = InfoOrErr.get();
93   else
94     return InfoOrErr.takeError();
95 
96   // A null module means an error has already been reported. Return an empty
97   // result.
98   if (!Info)
99     return DIInliningInfo();
100 
101   // If the user is giving us relative addresses, add the preferred base of the
102   // object to the offset before we do the query. It's what DIContext expects.
103   if (Opts.RelativeAddresses)
104     ModuleOffset.Address += Info->getModulePreferredBase();
105 
106   DIInliningInfo InlinedContext = Info->symbolizeInlinedCode(
107       ModuleOffset, Opts.PrintFunctions, Opts.UseSymbolTable);
108   if (Opts.Demangle) {
109     for (int i = 0, n = InlinedContext.getNumberOfFrames(); i < n; i++) {
110       auto *Frame = InlinedContext.getMutableFrame(i);
111       Frame->FunctionName = DemangleName(Frame->FunctionName, Info);
112     }
113   }
114   return InlinedContext;
115 }
116 
117 Expected<DIGlobal>
118 LLVMSymbolizer::symbolizeData(const std::string &ModuleName,
119                               object::SectionedAddress ModuleOffset) {
120   SymbolizableModule *Info;
121   if (auto InfoOrErr = getOrCreateModuleInfo(ModuleName))
122     Info = InfoOrErr.get();
123   else
124     return InfoOrErr.takeError();
125 
126   // A null module means an error has already been reported. Return an empty
127   // result.
128   if (!Info)
129     return DIGlobal();
130 
131   // If the user is giving us relative addresses, add the preferred base of
132   // the object to the offset before we do the query. It's what DIContext
133   // expects.
134   if (Opts.RelativeAddresses)
135     ModuleOffset.Address += Info->getModulePreferredBase();
136 
137   DIGlobal Global = Info->symbolizeData(ModuleOffset);
138   if (Opts.Demangle)
139     Global.Name = DemangleName(Global.Name, Info);
140   return Global;
141 }
142 
143 Expected<std::vector<DILocal>>
144 LLVMSymbolizer::symbolizeFrame(const std::string &ModuleName,
145                                object::SectionedAddress ModuleOffset) {
146   SymbolizableModule *Info;
147   if (auto InfoOrErr = getOrCreateModuleInfo(ModuleName))
148     Info = InfoOrErr.get();
149   else
150     return InfoOrErr.takeError();
151 
152   // A null module means an error has already been reported. Return an empty
153   // result.
154   if (!Info)
155     return std::vector<DILocal>();
156 
157   // If the user is giving us relative addresses, add the preferred base of
158   // the object to the offset before we do the query. It's what DIContext
159   // expects.
160   if (Opts.RelativeAddresses)
161     ModuleOffset.Address += Info->getModulePreferredBase();
162 
163   return Info->symbolizeFrame(ModuleOffset);
164 }
165 
166 void LLVMSymbolizer::flush() {
167   ObjectForUBPathAndArch.clear();
168   BinaryForPath.clear();
169   ObjectPairForPathArch.clear();
170   Modules.clear();
171 }
172 
173 namespace {
174 
175 // For Path="/path/to/foo" and Basename="foo" assume that debug info is in
176 // /path/to/foo.dSYM/Contents/Resources/DWARF/foo.
177 // For Path="/path/to/bar.dSYM" and Basename="foo" assume that debug info is in
178 // /path/to/bar.dSYM/Contents/Resources/DWARF/foo.
179 std::string getDarwinDWARFResourceForPath(
180     const std::string &Path, const std::string &Basename) {
181   SmallString<16> ResourceName = StringRef(Path);
182   if (sys::path::extension(Path) != ".dSYM") {
183     ResourceName += ".dSYM";
184   }
185   sys::path::append(ResourceName, "Contents", "Resources", "DWARF");
186   sys::path::append(ResourceName, Basename);
187   return std::string(ResourceName.str());
188 }
189 
190 bool checkFileCRC(StringRef Path, uint32_t CRCHash) {
191   ErrorOr<std::unique_ptr<MemoryBuffer>> MB =
192       MemoryBuffer::getFileOrSTDIN(Path);
193   if (!MB)
194     return false;
195   return CRCHash == llvm::crc32(arrayRefFromStringRef(MB.get()->getBuffer()));
196 }
197 
198 bool findDebugBinary(const std::string &OrigPath,
199                      const std::string &DebuglinkName, uint32_t CRCHash,
200                      const std::string &FallbackDebugPath,
201                      std::string &Result) {
202   SmallString<16> OrigDir(OrigPath);
203   llvm::sys::path::remove_filename(OrigDir);
204   SmallString<16> DebugPath = OrigDir;
205   // Try relative/path/to/original_binary/debuglink_name
206   llvm::sys::path::append(DebugPath, DebuglinkName);
207   if (checkFileCRC(DebugPath, CRCHash)) {
208     Result = std::string(DebugPath.str());
209     return true;
210   }
211   // Try relative/path/to/original_binary/.debug/debuglink_name
212   DebugPath = OrigDir;
213   llvm::sys::path::append(DebugPath, ".debug", DebuglinkName);
214   if (checkFileCRC(DebugPath, CRCHash)) {
215     Result = std::string(DebugPath.str());
216     return true;
217   }
218   // Make the path absolute so that lookups will go to
219   // "/usr/lib/debug/full/path/to/debug", not
220   // "/usr/lib/debug/to/debug"
221   llvm::sys::fs::make_absolute(OrigDir);
222   if (!FallbackDebugPath.empty()) {
223     // Try <FallbackDebugPath>/absolute/path/to/original_binary/debuglink_name
224     DebugPath = FallbackDebugPath;
225   } else {
226 #if defined(__NetBSD__)
227     // Try /usr/libdata/debug/absolute/path/to/original_binary/debuglink_name
228     DebugPath = "/usr/libdata/debug";
229 #else
230     // Try /usr/lib/debug/absolute/path/to/original_binary/debuglink_name
231     DebugPath = "/usr/lib/debug";
232 #endif
233   }
234   llvm::sys::path::append(DebugPath, llvm::sys::path::relative_path(OrigDir),
235                           DebuglinkName);
236   if (checkFileCRC(DebugPath, CRCHash)) {
237     Result = std::string(DebugPath.str());
238     return true;
239   }
240   return false;
241 }
242 
243 bool getGNUDebuglinkContents(const ObjectFile *Obj, std::string &DebugName,
244                              uint32_t &CRCHash) {
245   if (!Obj)
246     return false;
247   for (const SectionRef &Section : Obj->sections()) {
248     StringRef Name;
249     if (Expected<StringRef> NameOrErr = Section.getName())
250       Name = *NameOrErr;
251     else
252       consumeError(NameOrErr.takeError());
253 
254     Name = Name.substr(Name.find_first_not_of("._"));
255     if (Name == "gnu_debuglink") {
256       Expected<StringRef> ContentsOrErr = Section.getContents();
257       if (!ContentsOrErr) {
258         consumeError(ContentsOrErr.takeError());
259         return false;
260       }
261       DataExtractor DE(*ContentsOrErr, Obj->isLittleEndian(), 0);
262       uint64_t Offset = 0;
263       if (const char *DebugNameStr = DE.getCStr(&Offset)) {
264         // 4-byte align the offset.
265         Offset = (Offset + 3) & ~0x3;
266         if (DE.isValidOffsetForDataOfSize(Offset, 4)) {
267           DebugName = DebugNameStr;
268           CRCHash = DE.getU32(&Offset);
269           return true;
270         }
271       }
272       break;
273     }
274   }
275   return false;
276 }
277 
278 bool darwinDsymMatchesBinary(const MachOObjectFile *DbgObj,
279                              const MachOObjectFile *Obj) {
280   ArrayRef<uint8_t> dbg_uuid = DbgObj->getUuid();
281   ArrayRef<uint8_t> bin_uuid = Obj->getUuid();
282   if (dbg_uuid.empty() || bin_uuid.empty())
283     return false;
284   return !memcmp(dbg_uuid.data(), bin_uuid.data(), dbg_uuid.size());
285 }
286 
287 template <typename ELFT>
288 Optional<ArrayRef<uint8_t>> getBuildID(const ELFFile<ELFT> *Obj) {
289   if (!Obj)
290     return {};
291   auto PhdrsOrErr = Obj->program_headers();
292   if (!PhdrsOrErr) {
293     consumeError(PhdrsOrErr.takeError());
294     return {};
295   }
296   for (const auto &P : *PhdrsOrErr) {
297     if (P.p_type != ELF::PT_NOTE)
298       continue;
299     Error Err = Error::success();
300     for (auto N : Obj->notes(P, Err))
301       if (N.getType() == ELF::NT_GNU_BUILD_ID && N.getName() == ELF::ELF_NOTE_GNU)
302         return N.getDesc();
303     consumeError(std::move(Err));
304   }
305   return {};
306 }
307 
308 Optional<ArrayRef<uint8_t>> getBuildID(const ELFObjectFileBase *Obj) {
309   Optional<ArrayRef<uint8_t>> BuildID;
310   if (auto *O = dyn_cast<ELFObjectFile<ELF32LE>>(Obj))
311     BuildID = getBuildID(O->getELFFile());
312   else if (auto *O = dyn_cast<ELFObjectFile<ELF32BE>>(Obj))
313     BuildID = getBuildID(O->getELFFile());
314   else if (auto *O = dyn_cast<ELFObjectFile<ELF64LE>>(Obj))
315     BuildID = getBuildID(O->getELFFile());
316   else if (auto *O = dyn_cast<ELFObjectFile<ELF64BE>>(Obj))
317     BuildID = getBuildID(O->getELFFile());
318   else
319     llvm_unreachable("unsupported file format");
320   return BuildID;
321 }
322 
323 bool findDebugBinary(const std::vector<std::string> &DebugFileDirectory,
324                      const ArrayRef<uint8_t> BuildID,
325                      std::string &Result) {
326   auto getDebugPath = [&](StringRef Directory) {
327     SmallString<128> Path{Directory};
328     sys::path::append(Path, ".build-id",
329                       llvm::toHex(BuildID[0], /*LowerCase=*/true),
330                       llvm::toHex(BuildID.slice(1), /*LowerCase=*/true));
331     Path += ".debug";
332     return Path;
333   };
334   if (DebugFileDirectory.empty()) {
335     SmallString<128> Path = getDebugPath(
336 #if defined(__NetBSD__)
337       // Try /usr/libdata/debug/.build-id/../...
338       "/usr/libdata/debug"
339 #else
340       // Try /usr/lib/debug/.build-id/../...
341       "/usr/lib/debug"
342 #endif
343     );
344     if (llvm::sys::fs::exists(Path)) {
345       Result = std::string(Path.str());
346       return true;
347     }
348   } else {
349     for (const auto &Directory : DebugFileDirectory) {
350       // Try <debug-file-directory>/.build-id/../...
351       SmallString<128> Path = getDebugPath(Directory);
352       if (llvm::sys::fs::exists(Path)) {
353         Result = std::string(Path.str());
354         return true;
355       }
356     }
357   }
358   return false;
359 }
360 
361 } // end anonymous namespace
362 
363 ObjectFile *LLVMSymbolizer::lookUpDsymFile(const std::string &ExePath,
364     const MachOObjectFile *MachExeObj, const std::string &ArchName) {
365   // On Darwin we may find DWARF in separate object file in
366   // resource directory.
367   std::vector<std::string> DsymPaths;
368   StringRef Filename = sys::path::filename(ExePath);
369   DsymPaths.push_back(
370       getDarwinDWARFResourceForPath(ExePath, std::string(Filename)));
371   for (const auto &Path : Opts.DsymHints) {
372     DsymPaths.push_back(
373         getDarwinDWARFResourceForPath(Path, std::string(Filename)));
374   }
375   for (const auto &Path : DsymPaths) {
376     auto DbgObjOrErr = getOrCreateObject(Path, ArchName);
377     if (!DbgObjOrErr) {
378       // Ignore errors, the file might not exist.
379       consumeError(DbgObjOrErr.takeError());
380       continue;
381     }
382     ObjectFile *DbgObj = DbgObjOrErr.get();
383     if (!DbgObj)
384       continue;
385     const MachOObjectFile *MachDbgObj = dyn_cast<const MachOObjectFile>(DbgObj);
386     if (!MachDbgObj)
387       continue;
388     if (darwinDsymMatchesBinary(MachDbgObj, MachExeObj))
389       return DbgObj;
390   }
391   return nullptr;
392 }
393 
394 ObjectFile *LLVMSymbolizer::lookUpDebuglinkObject(const std::string &Path,
395                                                   const ObjectFile *Obj,
396                                                   const std::string &ArchName) {
397   std::string DebuglinkName;
398   uint32_t CRCHash;
399   std::string DebugBinaryPath;
400   if (!getGNUDebuglinkContents(Obj, DebuglinkName, CRCHash))
401     return nullptr;
402   if (!findDebugBinary(Path, DebuglinkName, CRCHash, Opts.FallbackDebugPath,
403                        DebugBinaryPath))
404     return nullptr;
405   auto DbgObjOrErr = getOrCreateObject(DebugBinaryPath, ArchName);
406   if (!DbgObjOrErr) {
407     // Ignore errors, the file might not exist.
408     consumeError(DbgObjOrErr.takeError());
409     return nullptr;
410   }
411   return DbgObjOrErr.get();
412 }
413 
414 ObjectFile *LLVMSymbolizer::lookUpBuildIDObject(const std::string &Path,
415                                                 const ELFObjectFileBase *Obj,
416                                                 const std::string &ArchName) {
417   auto BuildID = getBuildID(Obj);
418   if (!BuildID)
419     return nullptr;
420   if (BuildID->size() < 2)
421     return nullptr;
422   std::string DebugBinaryPath;
423   if (!findDebugBinary(Opts.DebugFileDirectory, *BuildID, DebugBinaryPath))
424     return nullptr;
425   auto DbgObjOrErr = getOrCreateObject(DebugBinaryPath, ArchName);
426   if (!DbgObjOrErr) {
427     consumeError(DbgObjOrErr.takeError());
428     return nullptr;
429   }
430   return DbgObjOrErr.get();
431 }
432 
433 Expected<LLVMSymbolizer::ObjectPair>
434 LLVMSymbolizer::getOrCreateObjectPair(const std::string &Path,
435                                       const std::string &ArchName) {
436   auto I = ObjectPairForPathArch.find(std::make_pair(Path, ArchName));
437   if (I != ObjectPairForPathArch.end())
438     return I->second;
439 
440   auto ObjOrErr = getOrCreateObject(Path, ArchName);
441   if (!ObjOrErr) {
442     ObjectPairForPathArch.emplace(std::make_pair(Path, ArchName),
443                                   ObjectPair(nullptr, nullptr));
444     return ObjOrErr.takeError();
445   }
446 
447   ObjectFile *Obj = ObjOrErr.get();
448   assert(Obj != nullptr);
449   ObjectFile *DbgObj = nullptr;
450 
451   if (auto MachObj = dyn_cast<const MachOObjectFile>(Obj))
452     DbgObj = lookUpDsymFile(Path, MachObj, ArchName);
453   else if (auto ELFObj = dyn_cast<const ELFObjectFileBase>(Obj))
454     DbgObj = lookUpBuildIDObject(Path, ELFObj, ArchName);
455   if (!DbgObj)
456     DbgObj = lookUpDebuglinkObject(Path, Obj, ArchName);
457   if (!DbgObj)
458     DbgObj = Obj;
459   ObjectPair Res = std::make_pair(Obj, DbgObj);
460   ObjectPairForPathArch.emplace(std::make_pair(Path, ArchName), Res);
461   return Res;
462 }
463 
464 Expected<ObjectFile *>
465 LLVMSymbolizer::getOrCreateObject(const std::string &Path,
466                                   const std::string &ArchName) {
467   Binary *Bin;
468   auto Pair = BinaryForPath.emplace(Path, OwningBinary<Binary>());
469   if (!Pair.second) {
470     Bin = Pair.first->second.getBinary();
471   } else {
472     Expected<OwningBinary<Binary>> BinOrErr = createBinary(Path);
473     if (!BinOrErr)
474       return BinOrErr.takeError();
475     Pair.first->second = std::move(BinOrErr.get());
476     Bin = Pair.first->second.getBinary();
477   }
478 
479   if (!Bin)
480     return static_cast<ObjectFile *>(nullptr);
481 
482   if (MachOUniversalBinary *UB = dyn_cast_or_null<MachOUniversalBinary>(Bin)) {
483     auto I = ObjectForUBPathAndArch.find(std::make_pair(Path, ArchName));
484     if (I != ObjectForUBPathAndArch.end())
485       return I->second.get();
486 
487     Expected<std::unique_ptr<ObjectFile>> ObjOrErr =
488         UB->getMachOObjectForArch(ArchName);
489     if (!ObjOrErr) {
490       ObjectForUBPathAndArch.emplace(std::make_pair(Path, ArchName),
491                                      std::unique_ptr<ObjectFile>());
492       return ObjOrErr.takeError();
493     }
494     ObjectFile *Res = ObjOrErr->get();
495     ObjectForUBPathAndArch.emplace(std::make_pair(Path, ArchName),
496                                    std::move(ObjOrErr.get()));
497     return Res;
498   }
499   if (Bin->isObject()) {
500     return cast<ObjectFile>(Bin);
501   }
502   return errorCodeToError(object_error::arch_not_found);
503 }
504 
505 Expected<SymbolizableModule *>
506 LLVMSymbolizer::createModuleInfo(const ObjectFile *Obj,
507                                  std::unique_ptr<DIContext> Context,
508                                  StringRef ModuleName) {
509   auto InfoOrErr = SymbolizableObjectFile::create(Obj, std::move(Context),
510                                                   Opts.UntagAddresses);
511   std::unique_ptr<SymbolizableModule> SymMod;
512   if (InfoOrErr)
513     SymMod = std::move(*InfoOrErr);
514   auto InsertResult = Modules.insert(
515       std::make_pair(std::string(ModuleName), std::move(SymMod)));
516   assert(InsertResult.second);
517   if (std::error_code EC = InfoOrErr.getError())
518     return errorCodeToError(EC);
519   return InsertResult.first->second.get();
520 }
521 
522 Expected<SymbolizableModule *>
523 LLVMSymbolizer::getOrCreateModuleInfo(const std::string &ModuleName) {
524   auto I = Modules.find(ModuleName);
525   if (I != Modules.end())
526     return I->second.get();
527 
528   std::string BinaryName = ModuleName;
529   std::string ArchName = Opts.DefaultArch;
530   size_t ColonPos = ModuleName.find_last_of(':');
531   // Verify that substring after colon form a valid arch name.
532   if (ColonPos != std::string::npos) {
533     std::string ArchStr = ModuleName.substr(ColonPos + 1);
534     if (Triple(ArchStr).getArch() != Triple::UnknownArch) {
535       BinaryName = ModuleName.substr(0, ColonPos);
536       ArchName = ArchStr;
537     }
538   }
539   auto ObjectsOrErr = getOrCreateObjectPair(BinaryName, ArchName);
540   if (!ObjectsOrErr) {
541     // Failed to find valid object file.
542     Modules.emplace(ModuleName, std::unique_ptr<SymbolizableModule>());
543     return ObjectsOrErr.takeError();
544   }
545   ObjectPair Objects = ObjectsOrErr.get();
546 
547   std::unique_ptr<DIContext> Context;
548   // If this is a COFF object containing PDB info, use a PDBContext to
549   // symbolize. Otherwise, use DWARF.
550   if (auto CoffObject = dyn_cast<COFFObjectFile>(Objects.first)) {
551     const codeview::DebugInfo *DebugInfo;
552     StringRef PDBFileName;
553     auto EC = CoffObject->getDebugPDBInfo(DebugInfo, PDBFileName);
554     if (!EC && DebugInfo != nullptr && !PDBFileName.empty()) {
555       using namespace pdb;
556       std::unique_ptr<IPDBSession> Session;
557       if (auto Err = loadDataForEXE(PDB_ReaderType::DIA,
558                                     Objects.first->getFileName(), Session)) {
559         Modules.emplace(ModuleName, std::unique_ptr<SymbolizableModule>());
560         // Return along the PDB filename to provide more context
561         return createFileError(PDBFileName, std::move(Err));
562       }
563       Context.reset(new PDBContext(*CoffObject, std::move(Session)));
564     }
565   }
566   if (!Context)
567     Context =
568         DWARFContext::create(*Objects.second, nullptr,
569                              DWARFContext::defaultErrorHandler, Opts.DWPName);
570   return createModuleInfo(Objects.first, std::move(Context), ModuleName);
571 }
572 
573 namespace {
574 
575 // Undo these various manglings for Win32 extern "C" functions:
576 // cdecl       - _foo
577 // stdcall     - _foo@12
578 // fastcall    - @foo@12
579 // vectorcall  - foo@@12
580 // These are all different linkage names for 'foo'.
581 StringRef demanglePE32ExternCFunc(StringRef SymbolName) {
582   // Remove any '_' or '@' prefix.
583   char Front = SymbolName.empty() ? '\0' : SymbolName[0];
584   if (Front == '_' || Front == '@')
585     SymbolName = SymbolName.drop_front();
586 
587   // Remove any '@[0-9]+' suffix.
588   if (Front != '?') {
589     size_t AtPos = SymbolName.rfind('@');
590     if (AtPos != StringRef::npos &&
591         std::all_of(SymbolName.begin() + AtPos + 1, SymbolName.end(),
592                     [](char C) { return C >= '0' && C <= '9'; })) {
593       SymbolName = SymbolName.substr(0, AtPos);
594     }
595   }
596 
597   // Remove any ending '@' for vectorcall.
598   if (SymbolName.endswith("@"))
599     SymbolName = SymbolName.drop_back();
600 
601   return SymbolName;
602 }
603 
604 } // end anonymous namespace
605 
606 std::string
607 LLVMSymbolizer::DemangleName(const std::string &Name,
608                              const SymbolizableModule *DbiModuleDescriptor) {
609   // We can spoil names of symbols with C linkage, so use an heuristic
610   // approach to check if the name should be demangled.
611   if (Name.substr(0, 2) == "_Z") {
612     int status = 0;
613     char *DemangledName = itaniumDemangle(Name.c_str(), nullptr, nullptr, &status);
614     if (status != 0)
615       return Name;
616     std::string Result = DemangledName;
617     free(DemangledName);
618     return Result;
619   }
620 
621   if (!Name.empty() && Name.front() == '?') {
622     // Only do MSVC C++ demangling on symbols starting with '?'.
623     int status = 0;
624     char *DemangledName = microsoftDemangle(
625         Name.c_str(), nullptr, nullptr, &status,
626         MSDemangleFlags(MSDF_NoAccessSpecifier | MSDF_NoCallingConvention |
627                         MSDF_NoMemberType | MSDF_NoReturnType));
628     if (status != 0)
629       return Name;
630     std::string Result = DemangledName;
631     free(DemangledName);
632     return Result;
633   }
634 
635   if (DbiModuleDescriptor && DbiModuleDescriptor->isWin32Module())
636     return std::string(demanglePE32ExternCFunc(Name));
637   return Name;
638 }
639 
640 } // namespace symbolize
641 } // namespace llvm
642