mozglue/linker/BaseElf.h

   1 /* This Source Code Form is subject to the terms of the Mozilla Public
   2  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
   3  * You can obtain one at http://mozilla.org/MPL/2.0/. */
   4
   5 #ifndef BaseElf_h
   6 #define BaseElf_h
   7
   8 #include "ElfLoader.h"
   9 #include "Elfxx.h"
  10
  11 /**
  12  * Base class for ELF libraries. This class includes things that will be
  13  * common between SystemElfs and CustomElfs.
  14  */
  15 class BaseElf : public LibHandle {
  16  public:
  17   /**
  18    * Hash function for symbol lookup, as defined in ELF standard for System V.
  19    */
  20   static unsigned long Hash(const char* symbol);
  21
  22   /**
  23    * Returns the address corresponding to the given symbol name (with a
  24    * pre-computed hash).
  25    */
  26   void* GetSymbolPtr(const char* symbol, unsigned long hash) const;
  27
  28   /**
  29    * Returns a pointer to the Elf Symbol in the Dynamic Symbol table
  30    * corresponding to the given symbol name (with a pre-computed hash).
  31    */
  32   const Elf::Sym* GetSymbol(const char* symbol, unsigned long hash) const;
  33
  34   explicit BaseElf(const char* path, Mappable* mappable = nullptr)
  35       : LibHandle(path), mappable(mappable) {}
  36
  37  protected:
  38   /**
  39    * Inherited from LibHandle. Those are temporary and are not supposed to
  40    * be used.
  41    */
  42   virtual void* GetSymbolPtr(const char* symbol) const;
  43   virtual bool Contains(void* addr) const;
  44   virtual void* GetBase() const { return GetPtr(0); }
  45
  46 #ifdef __ARM_EABI__
  47   virtual const void* FindExidx(int* pcount) const;
  48 #endif
  49
  50   virtual Mappable* GetMappable() const { return NULL; };
  51
  52  public:
  53   /* private: */
  54   /**
  55    * Returns a pointer relative to the base address where the library is
  56    * loaded.
  57    */
  58   void* GetPtr(const Elf::Addr offset) const {
  59     if (reinterpret_cast<void*>(offset) > base)
  60       return reinterpret_cast<void*>(offset);
  61     return base + offset;
  62   }
  63
  64   /**
  65    * Like the above, but returns a typed (const) pointer
  66    */
  67   template <typename T>
  68   const T* GetPtr(const Elf::Addr offset) const {
  69     if (reinterpret_cast<void*>(offset) > base)
  70       return reinterpret_cast<const T*>(offset);
  71     return reinterpret_cast<const T*>(base + offset);
  72   }
  73
  74   /* Appropriated Mappable */
  75   /* /!\ we rely on this being nullptr for BaseElf instances, but not
  76    * CustomElf instances. */
  77   RefPtr<Mappable> mappable;
  78
  79   /* Base address where the library is loaded */
  80   MappedPtr base;
  81
  82   /* Buckets and chains for the System V symbol hash table */
  83   Array<Elf::Word> buckets;
  84   UnsizedArray<Elf::Word> chains;
  85
  86   /* protected: */
  87   /* String table */
  88   Elf::Strtab strtab;
  89
  90   /* Symbol table */
  91   UnsizedArray<Elf::Sym> symtab;
  92
  93 #ifdef __ARM_EABI__
  94   /* ARM.exidx information used by FindExidx */
  95   Array<uint32_t[2]> arm_exidx;
  96 #endif
  97 };
  98
  99 /**
 100  * Class for ELF libraries that already loaded in memory.
 101  */
 102 class LoadedElf : public BaseElf {
 103  public:
 104   /**
 105    * Returns a LoadedElf corresponding to the already loaded ELF
 106    * at the given base address.
 107    */
 108   static already_AddRefed<LibHandle> Create(const char* path, void* base_addr);
 109
 110  private:
 111   explicit LoadedElf(const char* path) : BaseElf(path) {}
 112
 113   ~LoadedElf() {
 114     /* Avoid base's destructor unmapping something that doesn't actually
 115      * belong to it. */
 116     base.release();
 117     ElfLoader::Singleton.Forget(this);
 118   }
 119
 120   /**
 121    * Initializes the library according to information found in the given
 122    * PT_DYNAMIC header.
 123    * Returns whether this succeeded or failed.
 124    */
 125   bool InitDyn(const Elf::Phdr* pt_dyn);
 126 };
 127
 128 #endif /* BaseElf_h */