lld/ELF/SymbolTable.h

   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 "Symbols.h"
  13 #include "llvm/ADT/CachedHashString.h"
  14 #include "llvm/ADT/DenseMap.h"
  15 #include "llvm/Support/Compiler.h"
  16
  17 namespace lld::elf {
  18
  19 class InputFile;
  20 class SharedFile;
  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 public:
  36   ArrayRef<Symbol *> getSymbols() const { return symVector; }
  37
  38   void wrap(Symbol *sym, Symbol *real, Symbol *wrap);
  39
  40   Symbol *insert(StringRef name);
  41
  42   template <typename T> Symbol *addSymbol(const T &newSym) {
  43     Symbol *sym = insert(newSym.getName());
  44     sym->resolve(newSym);
  45     return sym;
  46   }
  47   Symbol *addAndCheckDuplicate(const Defined &newSym);
  48
  49   void scanVersionScript();
  50
  51   Symbol *find(StringRef name);
  52
  53   void handleDynamicList();
  54
  55   // Set of .so files to not link the same shared object file more than once.
  56   llvm::DenseMap<llvm::CachedHashStringRef, SharedFile *> soNames;
  57
  58   // Comdat groups define "link once" sections. If two comdat groups have the
  59   // same name, only one of them is linked, and the other is ignored. This map
  60   // is used to uniquify them.
  61   llvm::DenseMap<llvm::CachedHashStringRef, const InputFile *> comdatGroups;
  62
  63 private:
  64   SmallVector<Symbol *, 0> findByVersion(SymbolVersion ver);
  65   SmallVector<Symbol *, 0> findAllByVersion(SymbolVersion ver,
  66                                             bool includeNonDefault);
  67
  68   llvm::StringMap<SmallVector<Symbol *, 0>> &getDemangledSyms();
  69   bool assignExactVersion(SymbolVersion ver, uint16_t versionId,
  70                           StringRef versionName, bool includeNonDefault);
  71   void assignWildcardVersion(SymbolVersion ver, uint16_t versionId,
  72                              bool includeNonDefault);
  73
  74   // The order the global symbols are in is not defined. We can use an arbitrary
  75   // order, but it has to be reproducible. That is true even when cross linking.
  76   // The default hashing of StringRef produces different results on 32 and 64
  77   // bit systems so we use a map to a vector. That is arbitrary, deterministic
  78   // but a bit inefficient.
  79   // FIXME: Experiment with passing in a custom hashing or sorting the symbols
  80   // once symbol resolution is finished.
  81   llvm::DenseMap<llvm::CachedHashStringRef, int> symMap;
  82   SmallVector<Symbol *, 0> symVector;
  83
  84   // A map from demangled symbol names to their symbol objects.
  85   // This mapping is 1:N because two symbols with different versions
  86   // can have the same name. We use this map to handle "extern C++ {}"
  87   // directive in version scripts.
  88   std::optional<llvm::StringMap<SmallVector<Symbol *, 0>>> demangledSyms;
  89 };
  90
  91 LLVM_LIBRARY_VISIBILITY extern SymbolTable symtab;
  92
  93 } // namespace lld::elf
  94
  95 #endif