1 //===- SymbolTable.h --------------------------------------------*- C++ -*-===// 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 #ifndef LLD_ELF_SYMBOL_TABLE_H 10 #define LLD_ELF_SYMBOL_TABLE_H 11 12 #include "InputFiles.h" 13 #include "Symbols.h" 14 #include "lld/Common/Strings.h" 15 #include "llvm/ADT/CachedHashString.h" 16 #include "llvm/ADT/DenseMap.h" 17 #include "llvm/ADT/STLExtras.h" 18 19 namespace lld { 20 namespace elf { 21 22 // SymbolTable is a bucket of all known symbols, including defined, 23 // undefined, or lazy symbols (the last one is symbols in archive 24 // files whose archive members are not yet loaded). 25 // 26 // We put all symbols of all files to a SymbolTable, and the 27 // SymbolTable selects the "best" symbols if there are name 28 // conflicts. For example, obviously, a defined symbol is better than 29 // an undefined symbol. Or, if there's a conflict between a lazy and a 30 // undefined, it'll read an archive member to read a real definition 31 // to replace the lazy symbol. The logic is implemented in the 32 // add*() functions, which are called by input files as they are parsed. There 33 // is one add* function per symbol type. 34 class SymbolTable { 35 struct FilterOutPlaceholder { operatorFilterOutPlaceholder36 bool operator()(Symbol *S) const { return !S->isPlaceholder(); } 37 }; 38 using iterator = llvm::filter_iterator<std::vector<Symbol *>::const_iterator, 39 FilterOutPlaceholder>; 40 41 public: symbols()42 llvm::iterator_range<iterator> symbols() const { 43 return llvm::make_filter_range(symVector, FilterOutPlaceholder()); 44 } 45 46 void wrap(Symbol *sym, Symbol *real, Symbol *wrap); 47 48 Symbol *insert(StringRef name); 49 50 Symbol *addSymbol(const Symbol &newSym); 51 52 void scanVersionScript(); 53 54 Symbol *find(StringRef name); 55 56 void handleDynamicList(); 57 58 // Set of .so files to not link the same shared object file more than once. 59 llvm::DenseMap<StringRef, SharedFile *> soNames; 60 61 // Comdat groups define "link once" sections. If two comdat groups have the 62 // same name, only one of them is linked, and the other is ignored. This map 63 // is used to uniquify them. 64 llvm::DenseMap<llvm::CachedHashStringRef, const InputFile *> comdatGroups; 65 66 private: 67 std::vector<Symbol *> findByVersion(SymbolVersion ver); 68 std::vector<Symbol *> findAllByVersion(SymbolVersion ver); 69 70 llvm::StringMap<std::vector<Symbol *>> &getDemangledSyms(); 71 void assignExactVersion(SymbolVersion ver, uint16_t versionId, 72 StringRef versionName); 73 void assignWildcardVersion(SymbolVersion ver, uint16_t versionId); 74 75 // The order the global symbols are in is not defined. We can use an arbitrary 76 // order, but it has to be reproducible. That is true even when cross linking. 77 // The default hashing of StringRef produces different results on 32 and 64 78 // bit systems so we use a map to a vector. That is arbitrary, deterministic 79 // but a bit inefficient. 80 // FIXME: Experiment with passing in a custom hashing or sorting the symbols 81 // once symbol resolution is finished. 82 llvm::DenseMap<llvm::CachedHashStringRef, int> symMap; 83 std::vector<Symbol *> symVector; 84 85 // A map from demangled symbol names to their symbol objects. 86 // This mapping is 1:N because two symbols with different versions 87 // can have the same name. We use this map to handle "extern C++ {}" 88 // directive in version scripts. 89 llvm::Optional<llvm::StringMap<std::vector<Symbol *>>> demangledSyms; 90 }; 91 92 extern SymbolTable *symtab; 93 94 } // namespace elf 95 } // namespace lld 96 97 #endif 98