mozglue/linker/CustomElf.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 CustomElf_h
   6 #define CustomElf_h
   7
   8 #include "ElfLoader.h"
   9 #include "BaseElf.h"
  10 #include "Logging.h"
  11 #include "Elfxx.h"
  12
  13 /**
  14  * Library Handle class for ELF libraries we don't let the system linker
  15  * handle.
  16  */
  17 class CustomElf : public BaseElf, private ElfLoader::link_map {
  18   friend class ElfLoader;
  19   friend class SEGVHandler;
  20
  21  public:
  22   /**
  23    * Returns a new CustomElf using the given file descriptor to map ELF
  24    * content. The file descriptor ownership is stolen, and it will be closed
  25    * in CustomElf's destructor if an instance is created, or by the Load
  26    * method otherwise. The path corresponds to the file descriptor, and flags
  27    * are the same kind of flags that would be given to dlopen(), though
  28    * currently, none are supported and the behaviour is more or less that of
  29    * RTLD_GLOBAL | RTLD_BIND_NOW.
  30    */
  31   static already_AddRefed<LibHandle> Load(Mappable* mappable, const char* path,
  32                                           int flags);
  33
  34   /**
  35    * Inherited from LibHandle/BaseElf
  36    */
  37   virtual ~CustomElf();
  38
  39  public:
  40   /**
  41    * Returns the instance, casted as BaseElf. (short of a better way to do
  42    * this without RTTI)
  43    */
  44   virtual BaseElf* AsBaseElf() { return this; }
  45
  46  private:
  47   /**
  48    * Scan dependent libraries to find the address corresponding to the
  49    * given symbol name. This is used to find symbols that are undefined
  50    * in the Elf object.
  51    */
  52   void* GetSymbolPtrInDeps(const char* symbol) const;
  53
  54   /**
  55    * Private constructor
  56    */
  57   CustomElf(Mappable* mappable, const char* path)
  58       : BaseElf(path, mappable),
  59         link_map(),
  60         init(0),
  61         fini(0),
  62         initialized(false),
  63         has_text_relocs(false) {}
  64
  65   /**
  66    * Loads an Elf segment defined by the given PT_LOAD header.
  67    * Returns whether this succeeded or failed.
  68    */
  69   bool LoadSegment(const Elf::Phdr* pt_load) const;
  70
  71   /**
  72    * Initializes the library according to information found in the given
  73    * PT_DYNAMIC header.
  74    * Returns whether this succeeded or failed.
  75    */
  76   bool InitDyn(const Elf::Phdr* pt_dyn);
  77
  78   /**
  79    * Apply .rel.dyn/.rela.dyn relocations.
  80    * Returns whether this succeeded or failed.
  81    */
  82   bool Relocate();
  83
  84   /**
  85    * Apply .rel.plt/.rela.plt relocations.
  86    * Returns whether this succeeded or failed.
  87    */
  88   bool RelocateJumps();
  89
  90   /**
  91    * Call initialization functions (.init/.init_array)
  92    * Returns true;
  93    */
  94   bool CallInit();
  95
  96   /**
  97    * Call destructor functions (.fini_array/.fini)
  98    * Returns whether this succeeded or failed.
  99    */
 100   void CallFini();
 101
 102   /**
 103    * Call a function given a pointer to its location.
 104    */
 105   void CallFunction(void* ptr) const {
 106     /* C++ doesn't allow direct conversion between pointer-to-object
 107      * and pointer-to-function. */
 108     union {
 109       void* ptr;
 110       void (*func)(void);
 111     } f;
 112     f.ptr = ptr;
 113     DEBUG_LOG("%s: Calling function @%p", GetPath(), ptr);
 114     f.func();
 115   }
 116
 117   /**
 118    * Call a function given a an address relative to the library base
 119    */
 120   void CallFunction(Elf::Addr addr) const { return CallFunction(GetPtr(addr)); }
 121
 122   /* List of dependent libraries */
 123   std::vector<RefPtr<LibHandle> > dependencies;
 124
 125   /* List of .rel.dyn/.rela.dyn relocations */
 126   Array<Elf::Reloc> relocations;
 127
 128   /* List of .rel.plt/.rela.plt relocation */
 129   Array<Elf::Reloc> jumprels;
 130
 131   /* Relative address of the initialization and destruction functions
 132    * (.init/.fini) */
 133   Elf::Addr init, fini;
 134
 135   /* List of initialization and destruction functions
 136    * (.init_array/.fini_array) */
 137   Array<void*> init_array, fini_array;
 138
 139   bool initialized;
 140
 141   bool has_text_relocs;
 142 };
 143
 144 #endif /* CustomElf_h */