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-rw-r--r--mozglue/interposers/InterposerHelper.h79
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diff --git a/mozglue/interposers/InterposerHelper.h b/mozglue/interposers/InterposerHelper.h
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+/* 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