1 files changed, 79 insertions, 0 deletions
diff --git a/mozglue/interposers/InterposerHelper.h b/mozglue/interposers/InterposerHelper.h
new file mode 100644
index 0000000000..58e55d081e
--- /dev/null
+++ b/mozglue/interposers/InterposerHelper.h
@@ -0,0 +1,79 @@
+/* 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 InterposerHelper_h
+#define InterposerHelper_h
+
+#include <type_traits>
+
+#ifdef MOZ_LINKER
+#  include "Linker.h"
+#else
+#  include <dlfcn.h>
+#endif
+
+#include "mozilla/Assertions.h"
+
+template <typename T>
+static inline T dlsym_wrapper(void* aHandle, const char* aName) {
+#ifdef MOZ_LINKER
+  return reinterpret_cast<T>(__wrap_dlsym(aHandle, aName));
+#else
+  return reinterpret_cast<T>(dlsym(aHandle, aName));
+#endif  // MOZ_LINKER
+}
+
+static inline void* dlopen_wrapper(const char* aPath, int flags) {
+#ifdef MOZ_LINKER
+  return __wrap_dlopen(aPath, flags);
+#else
+  return dlopen(aPath, flags);
+#endif  // MOZ_LINKER
+}
+
+template <typename T>
+static T get_real_symbol(const char* aName, T aReplacementSymbol) {
+  // T can only be a function pointer
+  static_assert(std::is_function<typename std::remove_pointer<T>::type>::value);
+
+  // Find the corresponding function in the linked libraries
+  T real_symbol = dlsym_wrapper<T>(RTLD_NEXT, aName);
+
+#if defined(ANDROID)
+  if ((real_symbol == nullptr) || (real_symbol == aReplacementSymbol)) {
+    // On old versions of Android the application runtime links in libc before
+    // we get a chance to link libmozglue, so its symbols don't appear when
+    // resolving them with RTLD_NEXT. This behavior differs between the
+    // different versions of Android so we'll just look for them directly into
+    // libc.so. Note that this won't work if we're trying to interpose
+    // functions that are in other libraries, but hopefully we'll never have
+    // to do that.
+    void* handle = dlopen_wrapper("libc.so", RTLD_LAZY);
+
+    if (handle) {
+      real_symbol = dlsym_wrapper<T>(handle, aName);
+    }
+  }
+#endif
+
+  if (real_symbol == nullptr) {
+    MOZ_CRASH_UNSAFE_PRINTF(
+        "%s() interposition failed but the interposer function is "
+        "still being called, this won't work!",
+        aName);
+  }
+
+  if (real_symbol == aReplacementSymbol) {
+    MOZ_CRASH_UNSAFE_PRINTF(
+        "We could not obtain the real %s(). Calling the symbol we "
+        "got would make us enter an infinite loop so stop here instead.",
+        aName);
+  }
+
+  return real_symbol;
+}
+
+#define GET_REAL_SYMBOL(name) get_real_symbol(#name, name)
+
+#endif  // InterposerHelper_h