libnativeloader/native_loader.cpp - platform/art - Git at Google

 /*
  * Copyright (C) 2015 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 #define LOG_TAG "nativeloader"

 #include "nativeloader/native_loader.h"

 #include <dlfcn.h>
 #include <sys/types.h>

 #include <algorithm>
 #include <memory>
 #include <mutex>
 #include <string>
 #include <vector>

 #include <android-base/file.h>
 #include <android-base/macros.h>
 #include <android-base/strings.h>
 #include <android-base/thread_annotations.h>
 #include <nativebridge/native_bridge.h>
 #include <nativehelper/scoped_utf_chars.h>

 #ifdef ART_TARGET_ANDROID
 #include <log/log.h>
 #include "library_namespaces.h"
 #include "nativeloader/dlext_namespaces.h"
 #endif

 namespace android {

 namespace {

 #if defined(ART_TARGET_ANDROID)

 // NATIVELOADER_DEFAULT_NAMESPACE_LIBS is an environment variable that can be
 // used to list extra libraries (separated by ":") that libnativeloader will
 // load from the default namespace. The libraries must be listed without paths,
 // and then LD_LIBRARY_PATH is typically set to the directories to load them
 // from. The libraries will be available in all classloader namespaces, and also
 // in the fallback namespace used when no classloader is given.
 //
 // kNativeloaderExtraLibs is the name of that fallback namespace.
 //
 // NATIVELOADER_DEFAULT_NAMESPACE_LIBS is intended to be used for testing only,
 // and in particular in the ART run tests that are executed through dalvikvm in
 // the APEX. In that case the default namespace links to the ART namespace
 // (com_android_art) for all libraries, which means this can be used to load
 // test libraries that depend on ART internal libraries.
 constexpr const char* kNativeloaderExtraLibs = "nativeloader-extra-libs";

 using android::nativeloader::LibraryNamespaces;

 std::mutex g_namespaces_mutex;
 LibraryNamespaces* g_namespaces = new LibraryNamespaces;
 NativeLoaderNamespace* g_nativeloader_extra_libs_namespace = nullptr;

 android_namespace_t* FindExportedNamespace(const char* caller_location) {
   auto name = nativeloader::FindApexNamespaceName(caller_location);
   if (name.ok()) {
     android_namespace_t* boot_namespace = android_get_exported_namespace(name->c_str());
     LOG_ALWAYS_FATAL_IF((boot_namespace == nullptr),
                         "Error finding namespace of apex: no namespace called %s", name->c_str());
     return boot_namespace;
   }
   return nullptr;
 }

 Result<void> CreateNativeloaderDefaultNamespaceLibsLink(NativeLoaderNamespace& ns)
     REQUIRES(g_namespaces_mutex) {
   const char* links = getenv("NATIVELOADER_DEFAULT_NAMESPACE_LIBS");
   if (links == nullptr || *links == 0) {
     return {};
   }
   // Pass nullptr to Link() to create a link to the default namespace without
   // requiring it to be visible.
   return ns.Link(nullptr, links);
 }

 Result<NativeLoaderNamespace*> GetNativeloaderExtraLibsNamespace() REQUIRES(g_namespaces_mutex) {
   if (g_nativeloader_extra_libs_namespace != nullptr) {
     return g_nativeloader_extra_libs_namespace;
   }

   Result<NativeLoaderNamespace> ns =
       NativeLoaderNamespace::Create(kNativeloaderExtraLibs,
                                     /*search_paths=*/"",
                                     /*permitted_paths=*/"",
                                     /*parent=*/nullptr,
                                     /*is_shared=*/false,
                                     /*is_exempt_list_enabled=*/false,
                                     /*also_used_as_anonymous=*/false);
   if (!ns.ok()) {
     return ns.error();
   }
   g_nativeloader_extra_libs_namespace = new NativeLoaderNamespace(std::move(ns.value()));
   Result<void> linked =
       CreateNativeloaderDefaultNamespaceLibsLink(*g_nativeloader_extra_libs_namespace);
   if (!linked.ok()) {
     return linked.error();
   }
   return g_nativeloader_extra_libs_namespace;
 }

 // If the given path matches a library in NATIVELOADER_DEFAULT_NAMESPACE_LIBS
 // then load it in the nativeloader-extra-libs namespace, otherwise return
 // nullptr without error.
 Result<void*> TryLoadNativeloaderExtraLib(const char* path) {
   const char* links = getenv("NATIVELOADER_DEFAULT_NAMESPACE_LIBS");
   if (links == nullptr || *links == 0) {
     return nullptr;
   }
   std::vector<std::string> lib_list = base::Split(links, ":");
   if (std::find(lib_list.begin(), lib_list.end(), path) == lib_list.end()) {
     return nullptr;
   }

   std::lock_guard<std::mutex> guard(g_namespaces_mutex);
   Result<NativeLoaderNamespace*> ns = GetNativeloaderExtraLibsNamespace();
   if (!ns.ok()) {
     return ns.error();
   }
   return ns.value()->Load(path);
 }

 Result<NativeLoaderNamespace*> CreateClassLoaderNamespaceLocked(JNIEnv* env,
                                                                 int32_t target_sdk_version,
                                                                 jobject class_loader,
                                                                 bool is_shared,
                                                                 jstring dex_path,
                                                                 jstring library_path,
                                                                 jstring permitted_path,
                                                                 jstring uses_library_list)
     REQUIRES(g_namespaces_mutex) {
   Result<NativeLoaderNamespace*> ns = g_namespaces->Create(env,
                                                            target_sdk_version,
                                                            class_loader,
                                                            is_shared,
                                                            dex_path,
                                                            library_path,
                                                            permitted_path,
                                                            uses_library_list);
   if (!ns.ok()) {
     return ns;
   }
   Result<void> linked = CreateNativeloaderDefaultNamespaceLibsLink(*ns.value());
   if (!linked.ok()) {
     return linked.error();
   }
   return ns;
 }

 #endif  // #if defined(ART_TARGET_ANDROID)

 }  // namespace

 void InitializeNativeLoader() {
 #if defined(ART_TARGET_ANDROID)
   std::lock_guard<std::mutex> guard(g_namespaces_mutex);
   g_namespaces->Initialize();
 #endif
 }

 void ResetNativeLoader() {
 #if defined(ART_TARGET_ANDROID)
   std::lock_guard<std::mutex> guard(g_namespaces_mutex);
   g_namespaces->Reset();
   delete g_nativeloader_extra_libs_namespace;
   g_nativeloader_extra_libs_namespace = nullptr;
 #endif
 }

 jstring CreateClassLoaderNamespace(JNIEnv* env, int32_t target_sdk_version, jobject class_loader,
                                    bool is_shared, jstring dex_path, jstring library_path,
                                    jstring permitted_path, jstring uses_library_list) {
 #if defined(ART_TARGET_ANDROID)
   std::lock_guard<std::mutex> guard(g_namespaces_mutex);
   Result<NativeLoaderNamespace*> ns = CreateClassLoaderNamespaceLocked(env,
                                                                        target_sdk_version,
                                                                        class_loader,
                                                                        is_shared,
                                                                        dex_path,
                                                                        library_path,
                                                                        permitted_path,
                                                                        uses_library_list);
   if (!ns.ok()) {
     return env->NewStringUTF(ns.error().message().c_str());
   }
 #else
   UNUSED(env, target_sdk_version, class_loader, is_shared, dex_path, library_path, permitted_path,
          uses_library_list);
 #endif
   return nullptr;
 }

 void* OpenNativeLibrary(JNIEnv* env, int32_t target_sdk_version, const char* path,
                         jobject class_loader, const char* caller_location, jstring library_path,
                         bool* needs_native_bridge, char** error_msg) {
 #if defined(ART_TARGET_ANDROID)
   UNUSED(target_sdk_version);

   if (class_loader == nullptr) {
     *needs_native_bridge = false;
     if (caller_location != nullptr) {
       android_namespace_t* boot_namespace = FindExportedNamespace(caller_location);
       if (boot_namespace != nullptr) {
         const android_dlextinfo dlextinfo = {
             .flags = ANDROID_DLEXT_USE_NAMESPACE,
             .library_namespace = boot_namespace,
         };
         void* handle = android_dlopen_ext(path, RTLD_NOW, &dlextinfo);
         if (handle == nullptr) {
           *error_msg = strdup(dlerror());
         }
         return handle;
       }
     }

     // Check if the library is in NATIVELOADER_DEFAULT_NAMESPACE_LIBS and should
     // be loaded from the kNativeloaderExtraLibs namespace.
     {
       Result<void*> handle = TryLoadNativeloaderExtraLib(path);
       if (!handle.ok()) {
         *error_msg = strdup(handle.error().message().c_str());
         return nullptr;
       }
       if (handle.value() != nullptr) {
         return handle.value();
       }
     }

     // Fall back to the system namespace. This happens for preloaded JNI
     // libraries in the zygote.
     // TODO(b/185833744): Investigate if this should fall back to the app main
     // namespace (aka anonymous namespace) instead.
     void* handle = OpenSystemLibrary(path, RTLD_NOW);
     if (handle == nullptr) {
       *error_msg = strdup(dlerror());
     }
     return handle;
   }

   std::lock_guard<std::mutex> guard(g_namespaces_mutex);
   NativeLoaderNamespace* ns;

   if ((ns = g_namespaces->FindNamespaceByClassLoader(env, class_loader)) == nullptr) {
     // This is the case where the classloader was not created by ApplicationLoaders
     // In this case we create an isolated not-shared namespace for it.
     Result<NativeLoaderNamespace*> isolated_ns =
         CreateClassLoaderNamespaceLocked(env,
                                          target_sdk_version,
                                          class_loader,
                                          /*is_shared=*/false,
                                          /*dex_path=*/nullptr,
                                          library_path,
                                          /*permitted_path=*/nullptr,
                                          /*uses_library_list=*/nullptr);
     if (!isolated_ns.ok()) {
       *error_msg = strdup(isolated_ns.error().message().c_str());
       return nullptr;
     } else {
       ns = *isolated_ns;
     }
   }

   return OpenNativeLibraryInNamespace(ns, path, needs_native_bridge, error_msg);
 #else
   UNUSED(env, target_sdk_version, class_loader, caller_location);

   // Do some best effort to emulate library-path support. It will not
   // work for dependencies.
   //
   // Note: null has a special meaning and must be preserved.
   std::string c_library_path;  // Empty string by default.
   if (library_path != nullptr && path != nullptr && path[0] != '/') {
     ScopedUtfChars library_path_utf_chars(env, library_path);
     c_library_path = library_path_utf_chars.c_str();
   }

   std::vector<std::string> library_paths = base::Split(c_library_path, ":");

   for (const std::string& lib_path : library_paths) {
     *needs_native_bridge = false;
     const char* path_arg;
     std::string complete_path;
     if (path == nullptr) {
       // Preserve null.
       path_arg = nullptr;
     } else {
       complete_path = lib_path;
       if (!complete_path.empty()) {
         complete_path.append("/");
       }
       complete_path.append(path);
       path_arg = complete_path.c_str();
     }
     void* handle = dlopen(path_arg, RTLD_NOW);
     if (handle != nullptr) {
       return handle;
     }
     if (NativeBridgeIsSupported(path_arg)) {
       *needs_native_bridge = true;
       handle = NativeBridgeLoadLibrary(path_arg, RTLD_NOW);
       if (handle != nullptr) {
         return handle;
       }
       *error_msg = strdup(NativeBridgeGetError());
     } else {
       *error_msg = strdup(dlerror());
     }
   }
   return nullptr;
 #endif
 }

 bool CloseNativeLibrary(void* handle, const bool needs_native_bridge, char** error_msg) {
   bool success;
   if (needs_native_bridge) {
     success = (NativeBridgeUnloadLibrary(handle) == 0);
     if (!success) {
       *error_msg = strdup(NativeBridgeGetError());
     }
   } else {
     success = (dlclose(handle) == 0);
     if (!success) {
       *error_msg = strdup(dlerror());
     }
   }

   return success;
 }

 void NativeLoaderFreeErrorMessage(char* msg) {
   // The error messages get allocated through strdup, so we must call free on them.
   free(msg);
 }

 #if defined(ART_TARGET_ANDROID)
 void* OpenNativeLibraryInNamespace(NativeLoaderNamespace* ns, const char* path,
                                    bool* needs_native_bridge, char** error_msg) {
   auto handle = ns->Load(path);
   if (!handle.ok() && error_msg != nullptr) {
     *error_msg = strdup(handle.error().message().c_str());
   }
   if (needs_native_bridge != nullptr) {
     *needs_native_bridge = ns->IsBridged();
   }
   return handle.ok() ? *handle : nullptr;
 }

 // native_bridge_namespaces are not supported for callers of this function.
 // This function will return nullptr in the case when application is running
 // on native bridge.
 android_namespace_t* FindNamespaceByClassLoader(JNIEnv* env, jobject class_loader) {
   std::lock_guard<std::mutex> guard(g_namespaces_mutex);
   NativeLoaderNamespace* ns = g_namespaces->FindNamespaceByClassLoader(env, class_loader);
   if (ns != nullptr && !ns->IsBridged()) {
     return ns->ToRawAndroidNamespace();
   }
   return nullptr;
 }

 NativeLoaderNamespace* FindNativeLoaderNamespaceByClassLoader(JNIEnv* env, jobject class_loader) {
   std::lock_guard<std::mutex> guard(g_namespaces_mutex);
   return g_namespaces->FindNamespaceByClassLoader(env, class_loader);
 }

 void LinkNativeLoaderNamespaceToExportedNamespaceLibrary(struct NativeLoaderNamespace* ns,
                                                          const char* exported_ns_name,
                                                          const char* library_name,
                                                          char** error_msg) {
   Result<NativeLoaderNamespace> exported_ns =
       NativeLoaderNamespace::GetExportedNamespace(exported_ns_name, ns->IsBridged());
   if (!exported_ns.ok()) {
     *error_msg = strdup(exported_ns.error().message().c_str());
     return;
   }

   Result<void> linked = ns->Link(&exported_ns.value(), std::string(library_name));
   if (!linked.ok()) {
     *error_msg = strdup(linked.error().message().c_str());
   }
 }

 #endif  // ART_TARGET_ANDROID

 };  // namespace android
	/*
	* Copyright (C) 2015 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	#define LOG_TAG "nativeloader"

	#include "nativeloader/native_loader.h"

	#include <dlfcn.h>
	#include <sys/types.h>

	#include <algorithm>
	#include <memory>
	#include <mutex>
	#include <string>
	#include <vector>

	#include <android-base/file.h>
	#include <android-base/macros.h>
	#include <android-base/strings.h>
	#include <android-base/thread_annotations.h>
	#include <nativebridge/native_bridge.h>
	#include <nativehelper/scoped_utf_chars.h>

	#ifdef ART_TARGET_ANDROID
	#include <log/log.h>
	#include "library_namespaces.h"
	#include "nativeloader/dlext_namespaces.h"
	#endif

	namespace android {

	namespace {

	#if defined(ART_TARGET_ANDROID)

	// NATIVELOADER_DEFAULT_NAMESPACE_LIBS is an environment variable that can be
	// used to list extra libraries (separated by ":") that libnativeloader will
	// load from the default namespace. The libraries must be listed without paths,
	// and then LD_LIBRARY_PATH is typically set to the directories to load them
	// from. The libraries will be available in all classloader namespaces, and also
	// in the fallback namespace used when no classloader is given.
	//
	// kNativeloaderExtraLibs is the name of that fallback namespace.
	//
	// NATIVELOADER_DEFAULT_NAMESPACE_LIBS is intended to be used for testing only,
	// and in particular in the ART run tests that are executed through dalvikvm in
	// the APEX. In that case the default namespace links to the ART namespace
	// (com_android_art) for all libraries, which means this can be used to load
	// test libraries that depend on ART internal libraries.
	constexpr const char* kNativeloaderExtraLibs = "nativeloader-extra-libs";

	using android::nativeloader::LibraryNamespaces;

	std::mutex g_namespaces_mutex;
	LibraryNamespaces* g_namespaces = new LibraryNamespaces;
	NativeLoaderNamespace* g_nativeloader_extra_libs_namespace = nullptr;

	android_namespace_t* FindExportedNamespace(const char* caller_location) {
	auto name = nativeloader::FindApexNamespaceName(caller_location);
	if (name.ok()) {
	android_namespace_t* boot_namespace = android_get_exported_namespace(name->c_str());
	LOG_ALWAYS_FATAL_IF((boot_namespace == nullptr),
	"Error finding namespace of apex: no namespace called %s", name->c_str());
	return boot_namespace;
	}
	return nullptr;
	}

	Result<void> CreateNativeloaderDefaultNamespaceLibsLink(NativeLoaderNamespace& ns)
	REQUIRES(g_namespaces_mutex) {
	const char* links = getenv("NATIVELOADER_DEFAULT_NAMESPACE_LIBS");
	if (links == nullptr \|\| *links == 0) {
	return {};
	}
	// Pass nullptr to Link() to create a link to the default namespace without
	// requiring it to be visible.
	return ns.Link(nullptr, links);
	}

	Result<NativeLoaderNamespace*> GetNativeloaderExtraLibsNamespace() REQUIRES(g_namespaces_mutex) {
	if (g_nativeloader_extra_libs_namespace != nullptr) {
	return g_nativeloader_extra_libs_namespace;
	}

	Result<NativeLoaderNamespace> ns =
	NativeLoaderNamespace::Create(kNativeloaderExtraLibs,
	/search_paths=/"",
	/permitted_paths=/"",
	/parent=/nullptr,
	/is_shared=/false,
	/is_exempt_list_enabled=/false,
	/also_used_as_anonymous=/false);
	if (!ns.ok()) {
	return ns.error();
	}
	g_nativeloader_extra_libs_namespace = new NativeLoaderNamespace(std::move(ns.value()));
	Result<void> linked =
	CreateNativeloaderDefaultNamespaceLibsLink(*g_nativeloader_extra_libs_namespace);
	if (!linked.ok()) {
	return linked.error();
	}
	return g_nativeloader_extra_libs_namespace;
	}

	// If the given path matches a library in NATIVELOADER_DEFAULT_NAMESPACE_LIBS
	// then load it in the nativeloader-extra-libs namespace, otherwise return
	// nullptr without error.
	Result<void> TryLoadNativeloaderExtraLib(const char path) {
	const char* links = getenv("NATIVELOADER_DEFAULT_NAMESPACE_LIBS");
	if (links == nullptr \|\| *links == 0) {
	return nullptr;
	}
	std::vector<std::string> lib_list = base::Split(links, ":");
	if (std::find(lib_list.begin(), lib_list.end(), path) == lib_list.end()) {
	return nullptr;
	}

	std::lock_guard<std::mutex> guard(g_namespaces_mutex);
	Result<NativeLoaderNamespace*> ns = GetNativeloaderExtraLibsNamespace();
	if (!ns.ok()) {
	return ns.error();
	}
	return ns.value()->Load(path);
	}

	Result<NativeLoaderNamespace> CreateClassLoaderNamespaceLocked(JNIEnv env,
	int32_t target_sdk_version,
	jobject class_loader,
	bool is_shared,
	jstring dex_path,
	jstring library_path,
	jstring permitted_path,
	jstring uses_library_list)
	REQUIRES(g_namespaces_mutex) {
	Result<NativeLoaderNamespace*> ns = g_namespaces->Create(env,
	target_sdk_version,
	class_loader,
	is_shared,
	dex_path,
	library_path,
	permitted_path,
	uses_library_list);
	if (!ns.ok()) {
	return ns;
	}
	Result<void> linked = CreateNativeloaderDefaultNamespaceLibsLink(*ns.value());
	if (!linked.ok()) {
	return linked.error();
	}
	return ns;
	}

	#endif // #if defined(ART_TARGET_ANDROID)

	} // namespace

	void InitializeNativeLoader() {
	#if defined(ART_TARGET_ANDROID)
	std::lock_guard<std::mutex> guard(g_namespaces_mutex);
	g_namespaces->Initialize();
	#endif
	}

	void ResetNativeLoader() {
	#if defined(ART_TARGET_ANDROID)
	std::lock_guard<std::mutex> guard(g_namespaces_mutex);
	g_namespaces->Reset();
	delete g_nativeloader_extra_libs_namespace;
	g_nativeloader_extra_libs_namespace = nullptr;
	#endif
	}

	jstring CreateClassLoaderNamespace(JNIEnv* env, int32_t target_sdk_version, jobject class_loader,
	bool is_shared, jstring dex_path, jstring library_path,
	jstring permitted_path, jstring uses_library_list) {
	#if defined(ART_TARGET_ANDROID)
	std::lock_guard<std::mutex> guard(g_namespaces_mutex);
	Result<NativeLoaderNamespace*> ns = CreateClassLoaderNamespaceLocked(env,
	target_sdk_version,
	class_loader,
	is_shared,
	dex_path,
	library_path,
	permitted_path,
	uses_library_list);
	if (!ns.ok()) {
	return env->NewStringUTF(ns.error().message().c_str());
	}
	#else
	UNUSED(env, target_sdk_version, class_loader, is_shared, dex_path, library_path, permitted_path,
	uses_library_list);
	#endif
	return nullptr;
	}

	void* OpenNativeLibrary(JNIEnv* env, int32_t target_sdk_version, const char* path,
	jobject class_loader, const char* caller_location, jstring library_path,
	bool* needs_native_bridge, char** error_msg) {
	#if defined(ART_TARGET_ANDROID)
	UNUSED(target_sdk_version);

	if (class_loader == nullptr) {
	*needs_native_bridge = false;
	if (caller_location != nullptr) {
	android_namespace_t* boot_namespace = FindExportedNamespace(caller_location);
	if (boot_namespace != nullptr) {
	const android_dlextinfo dlextinfo = {
	.flags = ANDROID_DLEXT_USE_NAMESPACE,
	.library_namespace = boot_namespace,
	};
	void* handle = android_dlopen_ext(path, RTLD_NOW, &dlextinfo);
	if (handle == nullptr) {
	*error_msg = strdup(dlerror());
	}
	return handle;
	}
	}

	// Check if the library is in NATIVELOADER_DEFAULT_NAMESPACE_LIBS and should
	// be loaded from the kNativeloaderExtraLibs namespace.
	{
	Result<void*> handle = TryLoadNativeloaderExtraLib(path);
	if (!handle.ok()) {
	*error_msg = strdup(handle.error().message().c_str());
	return nullptr;
	}
	if (handle.value() != nullptr) {
	return handle.value();
	}
	}

	// Fall back to the system namespace. This happens for preloaded JNI
	// libraries in the zygote.
	// TODO(b/185833744): Investigate if this should fall back to the app main
	// namespace (aka anonymous namespace) instead.
	void* handle = OpenSystemLibrary(path, RTLD_NOW);
	if (handle == nullptr) {
	*error_msg = strdup(dlerror());
	}
	return handle;
	}

	std::lock_guard<std::mutex> guard(g_namespaces_mutex);
	NativeLoaderNamespace* ns;

	if ((ns = g_namespaces->FindNamespaceByClassLoader(env, class_loader)) == nullptr) {
	// This is the case where the classloader was not created by ApplicationLoaders
	// In this case we create an isolated not-shared namespace for it.
	Result<NativeLoaderNamespace*> isolated_ns =
	CreateClassLoaderNamespaceLocked(env,
	target_sdk_version,
	class_loader,
	/is_shared=/false,
	/dex_path=/nullptr,
	library_path,
	/permitted_path=/nullptr,
	/uses_library_list=/nullptr);
	if (!isolated_ns.ok()) {
	*error_msg = strdup(isolated_ns.error().message().c_str());
	return nullptr;
	} else {
	ns = *isolated_ns;
	}
	}

	return OpenNativeLibraryInNamespace(ns, path, needs_native_bridge, error_msg);
	#else
	UNUSED(env, target_sdk_version, class_loader, caller_location);

	// Do some best effort to emulate library-path support. It will not
	// work for dependencies.
	//
	// Note: null has a special meaning and must be preserved.
	std::string c_library_path; // Empty string by default.
	if (library_path != nullptr && path != nullptr && path[0] != '/') {
	ScopedUtfChars library_path_utf_chars(env, library_path);
	c_library_path = library_path_utf_chars.c_str();
	}

	std::vector<std::string> library_paths = base::Split(c_library_path, ":");

	for (const std::string& lib_path : library_paths) {
	*needs_native_bridge = false;
	const char* path_arg;
	std::string complete_path;
	if (path == nullptr) {
	// Preserve null.
	path_arg = nullptr;
	} else {
	complete_path = lib_path;
	if (!complete_path.empty()) {
	complete_path.append("/");
	}
	complete_path.append(path);
	path_arg = complete_path.c_str();
	}
	void* handle = dlopen(path_arg, RTLD_NOW);
	if (handle != nullptr) {
	return handle;
	}
	if (NativeBridgeIsSupported(path_arg)) {
	*needs_native_bridge = true;
	handle = NativeBridgeLoadLibrary(path_arg, RTLD_NOW);
	if (handle != nullptr) {
	return handle;
	}
	*error_msg = strdup(NativeBridgeGetError());
	} else {
	*error_msg = strdup(dlerror());
	}
	}
	return nullptr;
	#endif
	}

	bool CloseNativeLibrary(void* handle, const bool needs_native_bridge, char** error_msg) {
	bool success;
	if (needs_native_bridge) {
	success = (NativeBridgeUnloadLibrary(handle) == 0);
	if (!success) {
	*error_msg = strdup(NativeBridgeGetError());
	}
	} else {
	success = (dlclose(handle) == 0);
	if (!success) {
	*error_msg = strdup(dlerror());
	}
	}

	return success;
	}

	void NativeLoaderFreeErrorMessage(char* msg) {
	// The error messages get allocated through strdup, so we must call free on them.
	free(msg);
	}

	#if defined(ART_TARGET_ANDROID)
	void* OpenNativeLibraryInNamespace(NativeLoaderNamespace* ns, const char* path,
	bool* needs_native_bridge, char** error_msg) {
	auto handle = ns->Load(path);
	if (!handle.ok() && error_msg != nullptr) {
	*error_msg = strdup(handle.error().message().c_str());
	}
	if (needs_native_bridge != nullptr) {
	*needs_native_bridge = ns->IsBridged();
	}
	return handle.ok() ? *handle : nullptr;
	}

	// native_bridge_namespaces are not supported for callers of this function.
	// This function will return nullptr in the case when application is running
	// on native bridge.
	android_namespace_t* FindNamespaceByClassLoader(JNIEnv* env, jobject class_loader) {
	std::lock_guard<std::mutex> guard(g_namespaces_mutex);
	NativeLoaderNamespace* ns = g_namespaces->FindNamespaceByClassLoader(env, class_loader);
	if (ns != nullptr && !ns->IsBridged()) {
	return ns->ToRawAndroidNamespace();
	}
	return nullptr;
	}

	NativeLoaderNamespace* FindNativeLoaderNamespaceByClassLoader(JNIEnv* env, jobject class_loader) {
	std::lock_guard<std::mutex> guard(g_namespaces_mutex);
	return g_namespaces->FindNamespaceByClassLoader(env, class_loader);
	}

	void LinkNativeLoaderNamespaceToExportedNamespaceLibrary(struct NativeLoaderNamespace* ns,
	const char* exported_ns_name,
	const char* library_name,
	char** error_msg) {
	Result<NativeLoaderNamespace> exported_ns =
	NativeLoaderNamespace::GetExportedNamespace(exported_ns_name, ns->IsBridged());
	if (!exported_ns.ok()) {
	*error_msg = strdup(exported_ns.error().message().c_str());
	return;
	}

	Result<void> linked = ns->Link(&exported_ns.value(), std::string(library_name));
	if (!linked.ok()) {
	*error_msg = strdup(linked.error().message().c_str());
	}
	}

	#endif // ART_TARGET_ANDROID

	}; // namespace android