mozglue/interposers/InterposerHelper.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
   3  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   4
   5 #ifndef InterposerHelper_h
   6 #define InterposerHelper_h
   7
   8 #include <type_traits>
   9
  10 #ifdef MOZ_LINKER
  11 #  include "Linker.h"
  12 #else
  13 #  include <dlfcn.h>
  14 #endif
  15
  16 #include "mozilla/Assertions.h"
  17
  18 template <typename T>
  19 static inline T dlsym_wrapper(void* aHandle, const char* aName) {
  20 #ifdef MOZ_LINKER
  21   return reinterpret_cast<T>(__wrap_dlsym(aHandle, aName));
  22 #else
  23   return reinterpret_cast<T>(dlsym(aHandle, aName));
  24 #endif  // MOZ_LINKER
  25 }
  26
  27 static inline void* dlopen_wrapper(const char* aPath, int flags) {
  28 #ifdef MOZ_LINKER
  29   return __wrap_dlopen(aPath, flags);
  30 #else
  31   return dlopen(aPath, flags);
  32 #endif  // MOZ_LINKER
  33 }
  34
  35 template <typename T>
  36 static T get_real_symbol(const char* aName, T aReplacementSymbol) {
  37   // T can only be a function pointer
  38   static_assert(std::is_function<typename std::remove_pointer<T>::type>::value);
  39
  40   // Find the corresponding function in the linked libraries
  41   T real_symbol = dlsym_wrapper<T>(RTLD_NEXT, aName);
  42
  43 #if defined(ANDROID)
  44   if (real_symbol == nullptr) {
  45     // On old versions of Android the application runtime links in libc before
  46     // we get a chance to link libmozglue, so its symbols don't appear when
  47     // resolving them with RTLD_NEXT. This behavior differ between the
  48     // different versions of Android so we'll just look for them directly into
  49     // libc.so. Note that this won't work if we're trying to interpose
  50     // functions that are in other libraries, but hopefully we'll never have
  51     // to do that.
  52     void* handle = dlopen_wrapper("libc.so", RTLD_LAZY);
  53
  54     if (handle) {
  55       real_symbol = dlsym_wrapper<T>(handle, aName);
  56     }
  57   }
  58 #endif
  59
  60   if (real_symbol == nullptr) {
  61     MOZ_CRASH_UNSAFE_PRINTF(
  62         "%s() interposition failed but the interposer function is "
  63         "still being called, this won't work!",
  64         aName);
  65   }
  66
  67   if (real_symbol == aReplacementSymbol) {
  68     MOZ_CRASH_UNSAFE_PRINTF(
  69         "We could not obtain the real %s(). Calling the symbol we "
  70         "got would make us enter an infinite loop so stop here instead.",
  71         aName);
  72   }
  73
  74   return real_symbol;
  75 }
  76
  77 #define GET_REAL_SYMBOL(name) get_real_symbol(#name, name)
  78
  79 #endif  // InterposerHelper_h