libc: pthread TLS optimizations

Fixes #4024

repos/base/include/base/thread.h

@@ -50,9 +50,8 @@ class Genode::Thread
 		typedef Cpu_session::Name   Name;
 		typedef Cpu_session::Weight Weight;
 
-		struct Stack_info { addr_t base; addr_t top; };
-
-		struct Tls { struct Base; Base *ptr; };
+		struct Stack_info { addr_t base; addr_t top;
+		                    addr_t libc_tls_pointer_offset; };
 
 	private:
 
@@ -152,17 +151,6 @@ class Genode::Thread
 		 */
 		static Trace::Logger *_logger();
 
-		/**
-		 * Base pointer to thread-local storage
-		 *
-		 * The opaque pointer allows higher-level thread libraries (i.e.,
-		 * pthread) to implement TLS. It should never be used outside such
-		 * libraries.
-		 */
-		Tls _tls { };
-
-		friend class Tls::Base;
-
 		/**
 		 * Hook for platform-specific constructor supplements
 		 *

repos/base/src/include/base/internal/stack.h

@@ -86,6 +86,11 @@ class Genode::Stack
 		 */
 		addr_t _stack[1];
 
+		/*
+		 * TLS pointer for libc pthreads
+		 */
+		addr_t _libc_tls_pointer { };
+
 		/**
 		 * Thread name, used for debugging
 		 */
@@ -152,6 +157,15 @@ class Genode::Stack
 		 */
 		addr_t base() const { return _base; }
 
+		/**
+		 * Return libc TLS pointer offset relative to end of stack
+		 */
+		addr_t libc_tls_pointer_offset()
+		{
+			return (addr_t)this + sizeof(Stack) -
+			       (addr_t)&_libc_tls_pointer;
+		}
+
 		/**
 		 * Ensure that the stack has a given minimum size
 		 *

repos/base/src/lib/base/thread.cc

@@ -175,7 +175,8 @@ Thread::Stack_info Thread::mystack()
 {
 	addr_t base = Stack_allocator::addr_to_base(&base);
 	Stack *stack = Stack_allocator::base_to_stack(base);
-	return { stack->base(), stack->top() };
+	return { stack->base(), stack->top(),
+	         stack_virtual_size() - stack->libc_tls_pointer_offset() };
 }
 
 

repos/libports/lib/symbols/libc

@@ -973,14 +973,10 @@ _ZN4Libc19Select_handler_baseC2Ev T
 _ZN4Libc19Select_handler_baseD1Ev T
 _ZN4Libc19Select_handler_baseD2Ev T
 _ZN4Libc10resume_allEv T
+_ZN4Libc7PthreadC2ERN6Genode6ThreadEPv T
 _ZN4Libc7suspendERNS_15Suspend_functorEm T
-_Z16pthread_registryv T
-_ZN4Libc16Pthread_registry6insertERNS_7PthreadE T
-_ZN4Libc16Pthread_registry6removeERNS_7PthreadE T
-_ZN4Libc16Pthread_registry7cleanupEPNS_7PthreadE T
-_ZN4Libc16Pthread_registry8containsERNS_7PthreadE T
 _ZN4Libc14pthread_createEPP7pthreadPFPvS3_ES3_mPKcPN6Genode11Cpu_sessionENS8_8Affinity8LocationE T
-_ZN4Libc14pthread_createEPP7pthreadRN6Genode6ThreadE T
+_ZN4Libc14pthread_createEPP7pthreadRN6Genode6ThreadEPv T
 
 #
 # Libc plugin interface

repos/libports/src/lib/libc/internal/pthread.h

@@ -34,42 +34,28 @@
 namespace Libc {
 
 	struct Pthread;
-	struct Pthread_registry;
 	struct Pthread_blockade;
+	struct Pthread_cleanup;
 	struct Pthread_job;
 	struct Pthread_mutex;
 }
 
 
-/*
- * Used by 'pthread_self()' to find out if the current thread is an alien
- * thread.
- */
-class Libc::Pthread_registry
+class Libc::Pthread_cleanup
 {
 	private:
 
-		enum { MAX_NUM_PTHREADS = 128 };
-
-		Pthread *_array[MAX_NUM_PTHREADS] = { 0 };
-
 		/* thread to be destroyed on next 'cleanup()' call */
 		Pthread *_cleanup_thread { nullptr };
 
 	public:
 
-		void insert(Pthread &thread);
-
-		void remove(Pthread &thread);
-
-		bool contains(Pthread &thread);
-
 		/* destroy '_cleanup_thread' and register another one if given */
 		void cleanup(Pthread *new_cleanup_thread = nullptr);
 };
 
 
-Libc::Pthread_registry &pthread_registry();
+Libc::Pthread_cleanup &pthread_cleanup();
 
 
 extern "C" {
@@ -89,36 +75,7 @@ extern "C" {
 }
 
 
-struct Genode::Thread::Tls::Base
-{
-	/**
-	 * Register thread-local-storage object at Genode thread
-	 */
-	static void tls(Thread &thread, Tls::Base &tls)
-	{
-		thread._tls = Tls { &tls };
-	}
-
-	struct Undefined : Exception { };
-
-	/**
-	 * Obtain thread-local-storage object for the calling thread
-	 *
-	 * \throw Undefined
-	 */
-	static Tls::Base &tls()
-	{
-		Thread &myself = *Thread::myself();
-
-		if (!myself._tls.ptr)
-			throw Undefined();
-
-		return *myself._tls.ptr;
-	}
-};
-
-
-struct Libc::Pthread : Noncopyable, Thread::Tls::Base
+struct Libc::Pthread : Noncopyable
 {
 	typedef void *(*start_routine_t) (void *);
 
@@ -132,6 +89,8 @@ struct Libc::Pthread : Noncopyable, Thread::Tls::Base
 			void          *&_stack_addr;
 			size_t         &_stack_size;
 
+			Pthread        *_pthread;
+
 			enum { WEIGHT = Cpu_session::Weight::DEFAULT_WEIGHT };
 
 			/* 'stack_addr_out' and 'stack_size_out' are written when the thread starts */
@@ -139,11 +98,13 @@ struct Libc::Pthread : Noncopyable, Thread::Tls::Base
 			              Cpu_session *cpu,
 			              Affinity::Location location,
 			              start_routine_t start_routine, void *arg,
-			              void *&stack_addr_out, size_t &stack_size_out)
+			              void *&stack_addr_out, size_t &stack_size_out,
+			              Pthread *pthread)
 			:
 				Thread(WEIGHT, name, stack_size, Type::NORMAL, cpu, location),
 				_start_routine(start_routine), _arg(arg),
-				_stack_addr(stack_addr_out), _stack_size(stack_size_out)
+				_stack_addr(stack_addr_out), _stack_size(stack_size_out),
+				_pthread(pthread)
 			{ }
 
 			void entry() override;
@@ -166,13 +127,6 @@ struct Libc::Pthread : Noncopyable, Thread::Tls::Base
 		 */
 		Thread &_thread;
 
-		void _associate_thread_with_pthread()
-		{
-			Thread::Tls::Base::tls(_thread, *this);
-			pthread_registry().cleanup();
-			pthread_registry().insert(*this);
-		}
-
 		bool _exiting = false;
 
 		/*
@@ -212,6 +166,22 @@ struct Libc::Pthread : Noncopyable, Thread::Tls::Base
 
 		List<Cleanup_handler> _cleanup_handlers;
 
+		/* TLS support */
+
+		/* mask to obtain stack virtual base from address of stack variable */
+		static size_t _stack_virtual_base_mask;
+
+		/*
+		 * Offset of TLS pointer relative to base address of a thread's
+		 * virtual stack area.
+		 */
+		static size_t _tls_pointer_offset;
+
+		/* initialize TLS pointer on given stack */
+		static void _tls_pointer(void *stack_address, Pthread *pthread);
+
+		void const *_tls_data[PTHREAD_KEYS_MAX] { };
+
 	public:
 
 		int thread_local_errno = 0;
@@ -225,31 +195,32 @@ struct Libc::Pthread : Noncopyable, Thread::Tls::Base
 		:
 			_thread(_construct_thread_object(name, stack_size, cpu, location,
 			                                 start_routine, arg,
-			                                 _stack_addr, _stack_size))
+			                                 _stack_addr, _stack_size, this))
 		{
-			_associate_thread_with_pthread();
+			pthread_cleanup().cleanup();
 		}
 
 		/**
 		 * Constructor to create pthread object out of existing thread,
-		 * i.e., the main thread
+		 * i.e., the main thread or a VirtualBox thread
+		 *
+		 * The 'stack_address' argument can be any address on the stack
+		 * of 'existing_thread'. It is needed to locate the correct
+		 * TLS pointer to initialize, because
+		 *
+		 * - the main thread uses a secondary stack, so
+		 *   'existing_thread.stack_top()' would be the
+		 *   wrong stack for the main thread
+		 *
+		 * - VirtualBox EMT threads have this constructor called
+		 *   from a different thread than 'existing_thread', so
+		 *   the address of a local stack variable would belong to
+		 *   the wrong stack for those threads
+		 *
 		 */
-		Pthread(Thread &existing_thread)
-		:
-			_thread(existing_thread)
-		{
-			/* obtain stack attributes of main thread */
-			Thread::Stack_info info = Thread::mystack();
-			_stack_addr = (void *)info.base;
-			_stack_size = info.top - info.base;
+		Pthread(Thread &existing_thread, void *stack_address);
 
-			_associate_thread_with_pthread();
-		}
-
-		~Pthread()
-		{
-			pthread_registry().remove(*this);
-		}
+		static void init_tls_support();
 
 		void start() { _thread.start(); }
 
@@ -276,13 +247,15 @@ struct Libc::Pthread : Noncopyable, Thread::Tls::Base
 
 			_detach_blockade.block();
 
-			pthread_registry().cleanup(this);
+			pthread_cleanup().cleanup(this);
 			sleep_forever();
 		}
 
 		void   *stack_addr() const { return _stack_addr; }
 		size_t  stack_size() const { return _stack_size; }
 
+		static Pthread *myself();
+
 		/*
 		 * Push a cleanup handler to the cancellation cleanup stack.
 		 */
@@ -312,6 +285,16 @@ struct Libc::Pthread : Noncopyable, Thread::Tls::Base
 
 			return true;
 		}
+
+		void setspecific(pthread_key_t key, void const *value)
+		{
+			_tls_data[key] = value;
+		}
+
+		void const *getspecific(pthread_key_t key)
+		{
+			return _tls_data[key];
+		}
 };
 
 

repos/libports/src/lib/libc/internal/thread_create.h

@@ -32,7 +32,7 @@ namespace Libc {
 	                   size_t stack_size, char const * name,
 	                   Cpu_session * cpu, Affinity::Location location);
 
-	int pthread_create(pthread_t *, Thread &);
+	int pthread_create(pthread_t *, Thread &, void *stack_address);
 }
 
 #endif /* _LIBC__INTERNAL__THREAD_CREATE_H_ */

repos/libports/src/lib/libc/pthread.cc

@@ -49,6 +49,8 @@ void Libc::init_pthread_support(Monitor &monitor, Timer_accessor &timer_accessor
 	_main_thread_ptr    = Thread::myself();
 	_monitor_ptr        = &monitor;
 	_timer_accessor_ptr = &timer_accessor;
+
+	Pthread::init_tls_support();
 }
 
 
@@ -66,17 +68,73 @@ namespace { using Fn = Libc::Monitor::Function_result; }
  ** Pthread **
  *************/
 
+size_t Pthread::_stack_virtual_base_mask;
+size_t Pthread::_tls_pointer_offset;
+
+
 void Libc::Pthread::Thread_object::entry()
 {
-	/* obtain stack attributes of new thread */
+	/*
+	 * Obtain stack attributes of new thread for
+	 * 'pthread_attr_get_np()'
+	 */
 	Thread::Stack_info info = Thread::mystack();
 	_stack_addr = (void *)info.base;
 	_stack_size = info.top - info.base;
 
+	_tls_pointer(&info, _pthread);
+
 	pthread_exit(_start_routine(_arg));
 }
 
 
+void Libc::Pthread::_tls_pointer(void *stack_address, Pthread *pthread)
+{
+	addr_t stack_virtual_base = (addr_t)stack_address &
+	                            _stack_virtual_base_mask;
+	*(Pthread**)(stack_virtual_base + _tls_pointer_offset) = pthread;
+}
+
+
+Libc::Pthread::Pthread(Thread &existing_thread, void *stack_address)
+:
+	_thread(existing_thread)
+{
+	/* 
+	 * Obtain stack attributes for 'pthread_attr_get_np()'
+	 *
+	 * Note: the values might be incorrect for VirtualBox EMT threads,
+	 *       which have this constructor called from a different thread
+	 *       than 'existing_thread'.
+	 *
+	 */
+	Thread::Stack_info info = Thread::mystack();
+	_stack_addr = (void *)info.base;
+	_stack_size = info.top - info.base;
+
+	_tls_pointer(stack_address, this);
+
+	pthread_cleanup().cleanup();
+}
+
+
+void Libc::Pthread::init_tls_support()
+{
+	Thread::Stack_info info = Thread::mystack();
+	_tls_pointer_offset = info.libc_tls_pointer_offset;
+	_stack_virtual_base_mask = ~(Thread::stack_virtual_size() - 1);
+}
+
+
+Pthread *Libc::Pthread::myself()
+{
+	int stack_variable;
+	addr_t stack_virtual_base = (addr_t)&stack_variable &
+	                            _stack_virtual_base_mask;
+	return *(Pthread**)(stack_virtual_base + _tls_pointer_offset);
+}
+
+
 void Libc::Pthread::join(void **retval)
 {
 	monitor().monitor([&] {
@@ -110,50 +168,10 @@ void Libc::Pthread::cancel()
 
 
 /*
- * Registry
+ * Cleanup
  */
 
-void Libc::Pthread_registry::insert(Pthread &thread)
-{
-	/* prevent multiple insertions at the same location */
-	static Mutex insert_mutex;
-	Mutex::Guard guard(insert_mutex);
-
-	for (unsigned int i = 0; i < MAX_NUM_PTHREADS; i++) {
-		if (_array[i] == 0) {
-			_array[i] = &thread;
-			return;
-		}
-	}
-
-	error("pthread registry overflow, pthread_self() might fail");
-}
-
-
-void Libc::Pthread_registry::remove(Pthread &thread)
-{
-	for (unsigned int i = 0; i < MAX_NUM_PTHREADS; i++) {
-		if (_array[i] == &thread) {
-			_array[i] = 0;
-			return;
-		}
-	}
-
-	error("could not remove unknown pthread from registry");
-}
-
-
-bool Libc::Pthread_registry::contains(Pthread &thread)
-{
-	for (unsigned int i = 0; i < MAX_NUM_PTHREADS; i++)
-		if (_array[i] == &thread)
-			return true;
-
-	return false;
-}
-
-
-void Libc::Pthread_registry::cleanup(Pthread *new_cleanup_thread)
+void Libc::Pthread_cleanup::cleanup(Pthread *new_cleanup_thread)
 {
 	static Mutex cleanup_mutex;
 	Mutex::Guard guard(cleanup_mutex);
@@ -167,9 +185,9 @@ void Libc::Pthread_registry::cleanup(Pthread *new_cleanup_thread)
 }
 
 
-Libc::Pthread_registry &pthread_registry()
+Libc::Pthread_cleanup &pthread_cleanup()
 {
-	static Libc::Pthread_registry instance;
+	static Libc::Pthread_cleanup instance;
 	return instance;
 }
 
@@ -519,8 +537,100 @@ struct Libc::Pthread_mutex_recursive : pthread_mutex
 extern "C" int sem_set_clock(sem_t *sem, clockid_t clock_id);
 
 
+/* TLS */
+
+class Key_allocator : public Genode::Bit_allocator<PTHREAD_KEYS_MAX>
+{
+	private:
+
+		Mutex _mutex;
+
+	public:
+
+		addr_t alloc_key()
+		{
+			Mutex::Guard guard(_mutex);
+			return alloc();
+		}
+
+		void free_key(addr_t key)
+		{
+			Mutex::Guard guard(_mutex);
+			free(key);
+		}
+};
+
+
+static Key_allocator &key_allocator()
+{
+	static Key_allocator inst;
+	return inst;
+}
+
+typedef void (*key_destructor_func)(void*);
+static key_destructor_func key_destructors[PTHREAD_KEYS_MAX];
+
 extern "C" {
 
+	int pthread_key_create(pthread_key_t *key, void (*destructor)(void*))
+	{
+		if (!key)
+			return EINVAL;
+
+		try {
+			*key = key_allocator().alloc_key();
+			key_destructors[*key] = destructor;
+			return 0;
+		} catch (Key_allocator::Out_of_indices) {
+			return EAGAIN;
+		}
+	}
+
+	typeof(pthread_key_create) _pthread_key_create
+		__attribute__((alias("pthread_key_create")));
+
+
+	int pthread_key_delete(pthread_key_t key)
+	{
+		if (key < 0 || key >= PTHREAD_KEYS_MAX)
+			return EINVAL;
+
+		key_destructors[key] = nullptr;
+		key_allocator().free_key(key);
+		return 0;
+	}
+
+	typeof(pthread_key_delete) _pthread_key_delete
+		__attribute__((alias("pthread_key_delete")));
+
+
+	int pthread_setspecific(pthread_key_t key, const void *value)
+	{
+		if (key < 0 || key >= PTHREAD_KEYS_MAX)
+			return EINVAL;
+
+		pthread_t pthread_myself = pthread_self();
+		pthread_myself->setspecific(key, value);
+		return 0;
+	}
+
+	typeof(pthread_setspecific) _pthread_setspecific
+		__attribute__((alias("pthread_setspecific")));
+
+
+	void *pthread_getspecific(pthread_key_t key)
+	{
+		if (key < 0 || key >= PTHREAD_KEYS_MAX)
+			return nullptr;
+
+		pthread_t pthread_myself = pthread_self();
+		return (void*)pthread_myself->getspecific(key);
+	}
+
+	typeof(pthread_getspecific) _pthread_getspecific
+		__attribute__((alias("pthread_getspecific")));
+
+
 	/* Thread */
 
 	int pthread_join(pthread_t thread, void **retval)
@@ -577,6 +687,24 @@ extern "C" {
 
 	void pthread_exit(void *value_ptr)
 	{
+		/* call TLS key destructors */
+
+		bool at_least_one_destructor_called;
+
+		do {
+			at_least_one_destructor_called = false;
+			for (pthread_key_t key = 0; key < PTHREAD_KEYS_MAX; key++) {
+				if (key_destructors[key]) {
+					void *value = pthread_getspecific(key);
+					if (value) {
+						pthread_setspecific(key, nullptr);
+						key_destructors[key](value);
+						at_least_one_destructor_called = true;
+					}
+				}
+			}
+		} while (at_least_one_destructor_called);
+
 		pthread_self()->exit(value_ptr);
 	}
 
@@ -593,14 +721,10 @@ extern "C" {
 
 	pthread_t pthread_self(void)
 	{
-		try {
-			pthread_t pthread_myself =
-				static_cast<pthread_t>(&Thread::Tls::Base::tls());
+		pthread_t pthread_myself = static_cast<pthread_t>(Pthread::myself());
 
-			if (pthread_registry().contains(*pthread_myself))
+		if (pthread_myself)
 			return pthread_myself;
-		}
-		catch (Thread::Tls::Base::Undefined) { }
 
 		/*
 		 * We pass here if the main thread or an alien thread calls
@@ -620,7 +744,7 @@ extern "C" {
 		 * destruction of the pthread object would also destruct the 'Thread'
 		 * of the main thread.
 		 */
-		return unmanaged_singleton<pthread>(*Thread::myself());
+		return unmanaged_singleton<pthread>(*Thread::myself(), &pthread_myself);
 	}
 
 	typeof(pthread_self) _pthread_self
@@ -1168,136 +1292,6 @@ extern "C" {
 		__attribute__((alias("pthread_cond_broadcast")));
 
 
-	/* TLS */
-
-
-	struct Key_element : List<Key_element>::Element
-	{
-		const void *thread_base;
-		const void *value;
-
-		Key_element(const void *thread_base, const void *value)
-		: thread_base(thread_base),
-		  value(value) { }
-	};
-
-
-	static Mutex &key_list_mutex()
-	{
-		static Mutex inst { };
-		return inst;
-	}
-
-
-	struct Keys
-	{
-		List<Key_element> key[PTHREAD_KEYS_MAX];
-	};
-
-
-	static Keys &keys()
-	{
-		static Keys inst { };
-		return inst;
-	}
-
-
-	int pthread_key_create(pthread_key_t *key, void (*destructor)(void*))
-	{
-		if (!key)
-			return EINVAL;
-
-		Mutex::Guard guard(key_list_mutex());
-
-		for (int k = 0; k < PTHREAD_KEYS_MAX; k++) {
-			/*
-			 * Find an empty key slot and insert an element for the current
-			 * thread to mark the key slot as used.
-			 */
-			if (!keys().key[k].first()) {
-				Libc::Allocator alloc { };
-				Key_element *key_element = new (alloc) Key_element(Thread::myself(), 0);
-				keys().key[k].insert(key_element);
-				*key = k;
-				return 0;
-			}
-		}
-
-		return EAGAIN;
-	}
-
-	typeof(pthread_key_create) _pthread_key_create
-		__attribute__((alias("pthread_key_create")));
-
-
-	int pthread_key_delete(pthread_key_t key)
-	{
-		if (key < 0 || key >= PTHREAD_KEYS_MAX || !keys().key[key].first())
-			return EINVAL;
-
-		Mutex::Guard guard(key_list_mutex());
-
-		while (Key_element * element = keys().key[key].first()) {
-			keys().key[key].remove(element);
-			Libc::Allocator alloc { };
-			destroy(alloc, element);
-		}
-
-		return 0;
-	}
-
-	typeof(pthread_key_delete) _pthread_key_delete
-		__attribute__((alias("pthread_key_delete")));
-
-
-	int pthread_setspecific(pthread_key_t key, const void *value)
-	{
-		if (key < 0 || key >= PTHREAD_KEYS_MAX)
-			return EINVAL;
-
-		void *myself = Thread::myself();
-
-		Mutex::Guard guard(key_list_mutex());
-
-		for (Key_element *key_element = keys().key[key].first(); key_element;
-		     key_element = key_element->next())
-			if (key_element->thread_base == myself) {
-				key_element->value = value;
-				return 0;
-			}
-
-		/* key element does not exist yet - create a new one */
-		Libc::Allocator alloc { };
-		Key_element *key_element = new (alloc) Key_element(Thread::myself(), value);
-		keys().key[key].insert(key_element);
-		return 0;
-	}
-
-	typeof(pthread_setspecific) _pthread_setspecific
-		__attribute__((alias("pthread_setspecific")));
-
-
-	void *pthread_getspecific(pthread_key_t key)
-	{
-		if (key < 0 || key >= PTHREAD_KEYS_MAX)
-			return nullptr;
-
-		void *myself = Thread::myself();
-
-		Mutex::Guard guard(key_list_mutex());
-
-		for (Key_element *key_element = keys().key[key].first(); key_element;
-		     key_element = key_element->next())
-			if (key_element->thread_base == myself)
-				return (void*)(key_element->value);
-
-		return 0;
-	}
-
-	typeof(pthread_getspecific) _pthread_getspecific
-		__attribute__((alias("pthread_getspecific")));
-
-
 	int pthread_once(pthread_once_t *once, void (*init_once)(void))
 	{
 		if (!once || ((once->state != PTHREAD_NEEDS_INIT) &&

repos/libports/src/lib/libc/pthread_create.cc

@@ -104,10 +104,11 @@ int Libc::pthread_create(pthread_t *thread,
 }
 
 
-int Libc::pthread_create(pthread_t *thread, Thread &t)
+int Libc::pthread_create(pthread_t *thread, Thread &t, void *stack_address)
 {
 	Libc::Allocator alloc { };
-	pthread_t thread_obj = new (alloc) pthread(t);
+
+	pthread_t thread_obj = new (alloc) pthread(t, stack_address);
 
 	if (!thread_obj)
 		return EAGAIN;

repos/ports/src/virtualbox5/devxhci.cc

@@ -456,7 +456,7 @@ struct Usb_ep : Genode::Entrypoint
 	void _handle_pthread_registration()
 	{
 		Genode::Thread *myself = Genode::Thread::myself();
-		if (!myself || Libc::pthread_create(&_pthread, *myself)) {
+		if (!myself || Libc::pthread_create(&_pthread, *myself, &myself)) {
 			Genode::error("USB passthough will not work - thread for "
 			              "pthread registration invalid");
 		}

repos/ports/src/virtualbox5/network.cpp

@@ -186,7 +186,7 @@ class Nic_client
 		void _handle_pthread_registration()
 		{
 			Genode::Thread *myself = Genode::Thread::myself();
-			if (!myself || Libc::pthread_create(&_pthread, *myself)) {
+			if (!myself || Libc::pthread_create(&_pthread, *myself, &myself)) {
 				Genode::error("network will not work - thread for pthread "
 				              "registration invalid");
 				return;

repos/ports/src/virtualbox5/spec/nova/vcpu.h

@@ -857,7 +857,7 @@ class Vcpu_handler : public Vmm::Vcpu_dispatcher<Genode::Thread>,
 		:
 			Vmm::Vcpu_dispatcher<Genode::Thread>(env, stack_size, cpu_connection,
 			                                     location, name),
-			_pthread(*this),
+			_pthread(*this, stack_top()),
 			_start_routine(start_routine),
 			_start_routine_arg(arg),
 			_vcpu(cpu_connection, location, pd_vcpu),