gecko-dev/mozglue/linker/BaseElf.h

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this file,
 * You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef BaseElf_h
#define BaseElf_h

#include "ElfLoader.h"
#include "Elfxx.h"

/**
 * Base class for ELF libraries. This class includes things that will be
 * common between SystemElfs and CustomElfs.
 */
class BaseElf : public LibHandle {
 public:
  /**
   * Hash function for symbol lookup, as defined in ELF standard for System V.
   */
  static unsigned long Hash(const char* symbol);

  /**
   * Returns the address corresponding to the given symbol name (with a
   * pre-computed hash).
   */
  void* GetSymbolPtr(const char* symbol, unsigned long hash) const;

  /**
   * Returns a pointer to the Elf Symbol in the Dynamic Symbol table
   * corresponding to the given symbol name (with a pre-computed hash).
   */
  const Elf::Sym* GetSymbol(const char* symbol, unsigned long hash) const;

  explicit BaseElf(const char* path, Mappable* mappable = nullptr)
      : LibHandle(path), mappable(mappable) {}

 protected:
  /**
   * Inherited from LibHandle. Those are temporary and are not supposed to
   * be used.
   */
  virtual void* GetSymbolPtr(const char* symbol) const;
  virtual bool Contains(void* addr) const;
  virtual void* GetBase() const { return GetPtr(0); }

#ifdef __ARM_EABI__
  virtual const void* FindExidx(int* pcount) const;
#endif

  virtual Mappable* GetMappable() const { return NULL; };

 public:
  /* private: */
  /**
   * Returns a pointer relative to the base address where the library is
   * loaded.
   */
  void* GetPtr(const Elf::Addr offset) const {
    if (reinterpret_cast<void*>(offset) > base)
      return reinterpret_cast<void*>(offset);
    return base + offset;
  }

  /**
   * Like the above, but returns a typed (const) pointer
   */
  template <typename T>
  const T* GetPtr(const Elf::Addr offset) const {
    if (reinterpret_cast<void*>(offset) > base)
      return reinterpret_cast<const T*>(offset);
    return reinterpret_cast<const T*>(base + offset);
  }

  /* Appropriated Mappable */
  /* /!\ we rely on this being nullptr for BaseElf instances, but not
   * CustomElf instances. */
  RefPtr<Mappable> mappable;

  /* Base address where the library is loaded */
  MappedPtr base;

  /* Buckets and chains for the System V symbol hash table */
  Array<Elf::Word> buckets;
  UnsizedArray<Elf::Word> chains;

  /* protected: */
  /* String table */
  Elf::Strtab strtab;

  /* Symbol table */
  UnsizedArray<Elf::Sym> symtab;

#ifdef __ARM_EABI__
  /* ARM.exidx information used by FindExidx */
  Array<uint32_t[2]> arm_exidx;
#endif
};

/**
 * Class for ELF libraries that already loaded in memory.
 */
class LoadedElf : public BaseElf {
 public:
  /**
   * Returns a LoadedElf corresponding to the already loaded ELF
   * at the given base address.
   */
  static already_AddRefed<LibHandle> Create(const char* path, void* base_addr);

 private:
  explicit LoadedElf(const char* path) : BaseElf(path) {}

  ~LoadedElf() {
    /* Avoid base's destructor unmapping something that doesn't actually
     * belong to it. */
    base.release();
    ElfLoader::Singleton.Forget(this);
  }

  /**
   * Initializes the library according to information found in the given
   * PT_DYNAMIC header.
   * Returns whether this succeeded or failed.
   */
  bool InitDyn(const Elf::Phdr* pt_dyn);
};

#endif /* BaseElf_h */