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  public:
  51   /* private: */
  52   /**
  53    * Returns a pointer relative to the base address where the library is
  54    * loaded.
  55    */
  56   void* GetPtr(const Elf::Addr offset) const {
  57     if (reinterpret_cast<void*>(offset) > base)
  58       return reinterpret_cast<void*>(offset);
  59     return base + offset;
  60   }
  61
  62   /**
  63    * Like the above, but returns a typed (const) pointer
  64    */
  65   template <typename T>
  66   const T* GetPtr(const Elf::Addr offset) const {
  67     if (reinterpret_cast<void*>(offset) > base)
  68       return reinterpret_cast<const T*>(offset);
  69     return reinterpret_cast<const T*>(base + offset);
  70   }
  71
  72   /* Appropriated Mappable */
  73   /* /!\ we rely on this being nullptr for BaseElf instances, but not
  74    * CustomElf instances. */
  75   RefPtr<Mappable> mappable;
  76
  77   /* Base address where the library is loaded */
  78   MappedPtr base;
  79
  80   /* Buckets and chains for the System V symbol hash table */
  81   Array<Elf::Word> buckets;
  82   UnsizedArray<Elf::Word> chains;
  83
  84   /* protected: */
  85   /* String table */
  86   Elf::Strtab strtab;
  87
  88   /* Symbol table */
  89   UnsizedArray<Elf::Sym> symtab;
  90
  91 #ifdef __ARM_EABI__
  92   /* ARM.exidx information used by FindExidx */
  93   Array<uint32_t[2]> arm_exidx;
  94 #endif
  95 };
  96
  97 /**
  98  * Class for ELF libraries that already loaded in memory.
  99  */
 100 class LoadedElf : public BaseElf {
 101  public:
 102   /**
 103    * Returns a LoadedElf corresponding to the already loaded ELF
 104    * at the given base address.
 105    */
 106   static already_AddRefed<LibHandle> Create(const char* path, void* base_addr);
 107
 108  private:
 109   explicit LoadedElf(const char* path) : BaseElf(path) {}
 110
 111   ~LoadedElf() {
 112     /* Avoid base's destructor unmapping something that doesn't actually
 113      * belong to it. */
 114     base.release();
 115     ElfLoader::Singleton.Forget(this);
 116   }
 117
 118   /**
 119    * Initializes the library according to information found in the given
 120    * PT_DYNAMIC header.
 121    * Returns whether this succeeded or failed.
 122    */
 123   bool InitDyn(const Elf::Phdr* pt_dyn);
 124 };
 125
 126 #endif /* BaseElf_h */