1 //===- SymbolTable.cpp ----------------------------------------------------===//
2 //
3 //                             The LLVM Linker
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 "SymbolTable.h"
11 
12 #include "Config.h"
13 #include "InputChunks.h"
14 #include "WriterUtils.h"
15 #include "lld/Common/ErrorHandler.h"
16 #include "lld/Common/Memory.h"
17 
18 #include <unordered_set>
19 
20 #define DEBUG_TYPE "lld"
21 
22 using namespace llvm;
23 using namespace llvm::wasm;
24 using namespace lld;
25 using namespace lld::wasm;
26 
27 SymbolTable *lld::wasm::Symtab;
28 
29 void SymbolTable::addFile(InputFile *File) {
30   log("Processing: " + toString(File));
31   File->parse();
32 
33   if (auto *F = dyn_cast<ObjFile>(File))
34     ObjectFiles.push_back(F);
35 }
36 
37 void SymbolTable::reportRemainingUndefines() {
38   std::unordered_set<Symbol *> Undefs;
39   for (Symbol *Sym : SymVector) {
40     if (Sym->isUndefined() && !Sym->isWeak() &&
41         Config->AllowUndefinedSymbols.count(Sym->getName()) == 0) {
42       Undefs.insert(Sym);
43     }
44   }
45 
46   if (Undefs.empty())
47     return;
48 
49   for (ObjFile *File : ObjectFiles)
50     for (Symbol *Sym : File->getSymbols())
51       if (Undefs.count(Sym))
52         error(toString(File) + ": undefined symbol: " + toString(*Sym));
53 
54   for (Symbol *Sym : Undefs)
55     if (!Sym->getFile())
56       error("undefined symbol: " + toString(*Sym));
57 }
58 
59 Symbol *SymbolTable::find(StringRef Name) {
60   auto It = SymMap.find(CachedHashStringRef(Name));
61   if (It == SymMap.end())
62     return nullptr;
63   return It->second;
64 }
65 
66 std::pair<Symbol *, bool> SymbolTable::insert(StringRef Name) {
67   Symbol *&Sym = SymMap[CachedHashStringRef(Name)];
68   if (Sym)
69     return {Sym, false};
70   Sym = make<Symbol>(Name, false);
71   SymVector.emplace_back(Sym);
72   return {Sym, true};
73 }
74 
75 void SymbolTable::reportDuplicate(Symbol *Existing, InputFile *NewFile) {
76   error("duplicate symbol: " + toString(*Existing) + "\n>>> defined in " +
77         toString(Existing->getFile()) + "\n>>> defined in " +
78         toString(NewFile));
79 }
80 
81 // Check the type of new symbol matches that of the symbol is replacing.
82 // For functions this can also involve verifying that the signatures match.
83 static void checkSymbolTypes(const Symbol &Existing, const InputFile &F,
84                              Symbol::Kind Kind, const WasmSignature *NewSig) {
85   if (Existing.isLazy())
86     return;
87 
88   bool NewIsFunction = Kind == Symbol::Kind::UndefinedFunctionKind ||
89                        Kind == Symbol::Kind::DefinedFunctionKind;
90 
91   // First check the symbol types match (i.e. either both are function
92   // symbols or both are data symbols).
93   if (Existing.isFunction() != NewIsFunction) {
94     error("symbol type mismatch: " + Existing.getName() + "\n>>> defined as " +
95           (Existing.isFunction() ? "Function" : "Global") + " in " +
96           toString(Existing.getFile()) + "\n>>> defined as " +
97           (NewIsFunction ? "Function" : "Global") + " in " + F.getName());
98     return;
99   }
100 
101   // For function symbols, optionally check the function signature matches too.
102   if (!NewIsFunction || !Config->CheckSignatures)
103     return;
104   // Skip the signature check if the existing function has no signature (e.g.
105   // if it is an undefined symbol generated by --undefined command line flag).
106   if (!Existing.hasFunctionType())
107     return;
108 
109   DEBUG(dbgs() << "checkSymbolTypes: " << Existing.getName() << "\n");
110   assert(NewSig);
111 
112   const WasmSignature &OldSig = Existing.getFunctionType();
113   if (*NewSig == OldSig)
114     return;
115 
116   error("function signature mismatch: " + Existing.getName() +
117         "\n>>> defined as " + toString(OldSig) + " in " +
118         toString(Existing.getFile()) + "\n>>> defined as " + toString(*NewSig) +
119         " in " + F.getName());
120 }
121 
122 Symbol *SymbolTable::addDefinedFunction(StringRef Name,
123                                         const WasmSignature *Type,
124                                         uint32_t Flags) {
125   DEBUG(dbgs() << "addDefinedFunction: " << Name << "\n");
126   Symbol *S;
127   bool WasInserted;
128   std::tie(S, WasInserted) = insert(Name);
129   if (WasInserted) {
130     S->update(Symbol::DefinedFunctionKind, nullptr, Flags);
131     S->setFunctionType(Type);
132   } else if (!S->isFunction()) {
133     error("symbol type mismatch: " + Name);
134   }
135   return S;
136 }
137 
138 Symbol *SymbolTable::addDefinedGlobal(StringRef Name) {
139   DEBUG(dbgs() << "addDefinedGlobal: " << Name << "\n");
140   Symbol *S;
141   bool WasInserted;
142   std::tie(S, WasInserted) = insert(Name);
143   if (WasInserted)
144     S->update(Symbol::DefinedGlobalKind);
145   else if (!S->isGlobal())
146     error("symbol type mismatch: " + Name);
147   return S;
148 }
149 
150 Symbol *SymbolTable::addDefined(StringRef Name, Symbol::Kind Kind,
151                                 uint32_t Flags, InputFile *F,
152                                 const InputSegment *Segment,
153                                 InputFunction *Function, uint32_t Address) {
154   DEBUG(dbgs() << "addDefined: " << Name << " addr:" << Address << "\n");
155   Symbol *S;
156   bool WasInserted;
157 
158   std::tie(S, WasInserted) = insert(Name);
159   if (WasInserted) {
160     S->update(Kind, F, Flags, Segment, Function, Address);
161   } else if (S->isLazy()) {
162     // The existing symbol is lazy. Replace it without checking types since
163     // lazy symbols don't have any type information.
164     DEBUG(dbgs() << "replacing existing lazy symbol: " << Name << "\n");
165     S->update(Kind, F, Flags, Segment, Function, Address);
166   } else if (!S->isDefined()) {
167     // The existing symbol table entry is undefined. The new symbol replaces
168     // it, after checking the type matches
169     DEBUG(dbgs() << "resolving existing undefined symbol: " << Name << "\n");
170     checkSymbolTypes(*S, *F, Kind, Function ? &Function->Signature : nullptr);
171     S->update(Kind, F, Flags, Segment, Function, Address);
172   } else if ((Flags & WASM_SYMBOL_BINDING_MASK) == WASM_SYMBOL_BINDING_WEAK) {
173     // the new symbol is weak we can ignore it
174     DEBUG(dbgs() << "existing symbol takes precedence\n");
175   } else if (S->isWeak()) {
176     // the new symbol is not weak and the existing symbol is, so we replace
177     // it
178     DEBUG(dbgs() << "replacing existing weak symbol\n");
179     checkSymbolTypes(*S, *F, Kind, Function ? &Function->Signature : nullptr);
180     S->update(Kind, F, Flags, Segment, Function, Address);
181   } else {
182     // neither symbol is week. They conflict.
183     reportDuplicate(S, F);
184   }
185   return S;
186 }
187 
188 Symbol *SymbolTable::addUndefinedFunction(StringRef Name,
189                                           const WasmSignature *Type) {
190   Symbol *S;
191   bool WasInserted;
192   std::tie(S, WasInserted) = insert(Name);
193   if (WasInserted) {
194     S->update(Symbol::UndefinedFunctionKind);
195     S->setFunctionType(Type);
196   } else if (!S->isFunction()) {
197     error("symbol type mismatch: " + Name);
198   }
199   return S;
200 }
201 
202 Symbol *SymbolTable::addUndefined(StringRef Name, Symbol::Kind Kind,
203                                   uint32_t Flags, InputFile *F,
204                                   const WasmSignature *Type) {
205   DEBUG(dbgs() << "addUndefined: " << Name << "\n");
206   Symbol *S;
207   bool WasInserted;
208   std::tie(S, WasInserted) = insert(Name);
209   if (WasInserted) {
210     S->update(Kind, F, Flags);
211     if (Type)
212       S->setFunctionType(Type);
213   } else if (S->isLazy()) {
214     DEBUG(dbgs() << "resolved by existing lazy\n");
215     auto *AF = cast<ArchiveFile>(S->getFile());
216     AF->addMember(&S->getArchiveSymbol());
217   } else if (S->isDefined()) {
218     DEBUG(dbgs() << "resolved by existing\n");
219     checkSymbolTypes(*S, *F, Kind, Type);
220   }
221   return S;
222 }
223 
224 void SymbolTable::addLazy(ArchiveFile *F, const Archive::Symbol *Sym) {
225   DEBUG(dbgs() << "addLazy: " << Sym->getName() << "\n");
226   StringRef Name = Sym->getName();
227   Symbol *S;
228   bool WasInserted;
229   std::tie(S, WasInserted) = insert(Name);
230   if (WasInserted) {
231     S->update(Symbol::LazyKind, F);
232     S->setArchiveSymbol(*Sym);
233   } else if (S->isUndefined()) {
234     // There is an existing undefined symbol.  The can load from the
235     // archive.
236     DEBUG(dbgs() << "replacing existing undefined\n");
237     F->addMember(Sym);
238   }
239 }
240 
241 bool SymbolTable::addComdat(StringRef Name, ObjFile *F) {
242   DEBUG(dbgs() << "addComdat: " << Name << "\n");
243   ObjFile *&File = ComdatMap[CachedHashStringRef(Name)];
244   if (File) {
245     DEBUG(dbgs() << "COMDAT already defined\n");
246     return false;
247   }
248   File = F;
249   return true;
250 }
251 
252 ObjFile *SymbolTable::findComdat(StringRef Name) const {
253   auto It = ComdatMap.find(CachedHashStringRef(Name));
254   return It == ComdatMap.end() ? nullptr : It->second;
255 }
256