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1 //===- SymbolTable.h --------------------------------------------*- C++ -*-===//
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2 //
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3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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4 // See https://llvm.org/LICENSE.txt for license information.
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5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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6 //
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7 //===----------------------------------------------------------------------===//
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8
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9 #ifndef LLD_ELF_SYMBOL_TABLE_H
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10 #define LLD_ELF_SYMBOL_TABLE_H
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11
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12 #include "InputFiles.h"
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13 #include "Symbols.h"
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14 #include "lld/Common/Strings.h"
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15 #include "llvm/ADT/CachedHashString.h"
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16 #include "llvm/ADT/DenseMap.h"
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17 #include "llvm/ADT/STLExtras.h"
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18
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19 namespace lld {
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20 namespace elf {
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21
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22 // SymbolTable is a bucket of all known symbols, including defined,
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23 // undefined, or lazy symbols (the last one is symbols in archive
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24 // files whose archive members are not yet loaded).
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25 //
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26 // We put all symbols of all files to a SymbolTable, and the
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27 // SymbolTable selects the "best" symbols if there are name
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28 // conflicts. For example, obviously, a defined symbol is better than
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29 // an undefined symbol. Or, if there's a conflict between a lazy and a
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30 // undefined, it'll read an archive member to read a real definition
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31 // to replace the lazy symbol. The logic is implemented in the
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32 // add*() functions, which are called by input files as they are parsed. There
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33 // is one add* function per symbol type.
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34 class SymbolTable {
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35 struct FilterOutPlaceholder {
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36 bool operator()(Symbol *S) const { return !S->isPlaceholder(); }
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37 };
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38 using iterator = llvm::filter_iterator<std::vector<Symbol *>::const_iterator,
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39 FilterOutPlaceholder>;
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40
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41 public:
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42 llvm::iterator_range<iterator> symbols() const {
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43 return llvm::make_filter_range(symVector, FilterOutPlaceholder());
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44 }
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45
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46 void wrap(Symbol *sym, Symbol *real, Symbol *wrap);
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47
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48 Symbol *insert(StringRef name);
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49
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50 Symbol *addSymbol(const Symbol &newSym);
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51
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52 void scanVersionScript();
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53
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54 Symbol *find(StringRef name);
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55
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56 void handleDynamicList();
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57
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58 // Set of .so files to not link the same shared object file more than once.
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59 llvm::DenseMap<StringRef, SharedFile *> soNames;
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60
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61 // Comdat groups define "link once" sections. If two comdat groups have the
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62 // same name, only one of them is linked, and the other is ignored. This map
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63 // is used to uniquify them.
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64 llvm::DenseMap<llvm::CachedHashStringRef, const InputFile *> comdatGroups;
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65
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66 private:
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67 std::vector<Symbol *> findByVersion(SymbolVersion ver);
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68 std::vector<Symbol *> findAllByVersion(SymbolVersion ver);
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69
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70 llvm::StringMap<std::vector<Symbol *>> &getDemangledSyms();
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71 void assignExactVersion(SymbolVersion ver, uint16_t versionId,
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72 StringRef versionName);
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73 void assignWildcardVersion(SymbolVersion ver, uint16_t versionId);
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74
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75 // The order the global symbols are in is not defined. We can use an arbitrary
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76 // order, but it has to be reproducible. That is true even when cross linking.
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77 // The default hashing of StringRef produces different results on 32 and 64
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78 // bit systems so we use a map to a vector. That is arbitrary, deterministic
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79 // but a bit inefficient.
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80 // FIXME: Experiment with passing in a custom hashing or sorting the symbols
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81 // once symbol resolution is finished.
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82 llvm::DenseMap<llvm::CachedHashStringRef, int> symMap;
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83 std::vector<Symbol *> symVector;
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84
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85 // A map from demangled symbol names to their symbol objects.
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86 // This mapping is 1:N because two symbols with different versions
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87 // can have the same name. We use this map to handle "extern C++ {}"
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88 // directive in version scripts.
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89 llvm::Optional<llvm::StringMap<std::vector<Symbol *>>> demangledSyms;
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90 };
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91
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92 extern SymbolTable *symtab;
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93
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94 } // namespace elf
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95 } // namespace lld
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96
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97 #endif
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