Use POSIX threads in Linux/Genode hybrids

- Let hybrid Linux/Genode programs use POSIX threads for the
  implementation of the Thread API.
- Prevent linkage of cxx library to hybrid Linux/Genode programs because
  the cxx functionality is covered by glibc.

base-linux/src/platform/lx_hybrid.cc

@@ -18,13 +18,16 @@
 
 extern "C" int raw_write_str(const char *str);
 
+enum { verbose_atexit = false };
+
 
 /**
  * Dummy for symbol that is normally provided by '_main.cc'
  */
 int genode___cxa_atexit(void (*func)(void*), void *arg, void *dso)
 {
-	raw_write_str("genode___cxa_atexit called, not implemented\n");
+	if (verbose_atexit)
+		raw_write_str("genode___cxa_atexit called, not implemented\n");
 	return 0;
 }
 
@@ -45,3 +48,199 @@ __attribute__((constructor(101))) void lx_hybrid_init()
 	main_thread_bootstrap();
 	lx_environ = environ;
 }
+
+
+/************
+ ** Thread **
+ ************/
+
+/*
+ * For hybrid Linux/Genode programs, Genode's thread API is implemented via
+ * POSIX threads.
+ *
+ * Hybrid Linux/Genode programs are linked against the glibc along with other
+ * native Linux libraries. Such libraries may use the 'pthread' API to spawn
+ * threads, which then may call Genode code. Vice versa, Genode threads may
+ * interact with code of a native Linux libraries. Hence, both worlds Genode
+ * and native Linux libraries should use the same underlying threading API.
+ * Furthermore, using the pthread API is a precondition to satisfy the glibc's
+ * assumption about thread-local storage, which is particularly important
+ * for the correct thread-local handling of 'errno'. As another benefit of
+ * using the pthread API over the normal Genode thread implementation, hybrid
+ * Linux/Genode programs comply with the GNU debugger's expectations. Such
+ * programs can be debugged as normal Linux programs.
+ *
+ * Genode's normal thread API for Linux was introduced to decouple Genode
+ * from the glibc. This is especially important when using Genode's libc
+ * Mixing both Genode's libc and glibc won't work.
+ */
+
+/* Genode includes */
+#include <base/thread.h>
+
+/* libc includes */
+#include <pthread.h>
+#include <stdio.h>
+#include <errno.h>
+
+using namespace Genode;
+
+
+/**
+ * Return TLS key used to storing the thread meta data
+ */
+static pthread_key_t tls_key()
+{
+	struct Tls_key
+	{
+		pthread_key_t key;
+
+		Tls_key()
+		{
+			pthread_key_create(&key, 0);
+		}
+	};
+
+	static Tls_key inst;
+	return inst.key;
+}
+
+
+namespace Genode {
+
+	struct Thread_meta_data
+	{
+		/**
+		 * Used to block the constructor until the new thread has initialized
+		 * 'id'
+		 */
+		Lock construct_lock;
+
+		/**
+		 * Used to block the new thread until 'start' is called
+		 */
+		Lock start_lock;
+
+		/**
+		 * Filled out by 'thread_start' function in the context of the new
+		 * thread
+		 */
+		Thread_base * const thread_base;
+
+		/**
+		 * POSIX thread handle
+		 */
+		pthread_t pt;
+
+		/**
+		 * Constructor
+		 *
+		 * \param thread_base  associated 'Thread_base' object
+		 */
+		Thread_meta_data(Thread_base *thread_base)
+		:
+			construct_lock(Lock::LOCKED), start_lock(Lock::LOCKED),
+			thread_base(thread_base)
+		{ }
+	};
+}
+
+
+static void empty_signal_handler(int) { }
+
+
+static void *thread_start(void *arg)
+{
+	/*
+	 * Set signal handler such that canceled system calls get not
+	 * transparently retried after a signal gets received.
+	 */
+	lx_sigaction(LX_SIGUSR1, empty_signal_handler);
+
+	/* assign 'Thread_meta_data' pointer to TLS entry */
+	pthread_setspecific(tls_key(), arg);
+
+	/* enable immediate cancellation when calling 'pthread_cancel' */
+	pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, 0);
+
+	/*
+	 * Initialize thread meta data
+	 */
+	Thread_meta_data *meta_data = (Thread_meta_data *)arg;
+	meta_data->thread_base->tid().tid = lx_gettid();
+	meta_data->thread_base->tid().pid = lx_getpid();
+
+	/* unblock 'Thread_base' constructor */
+	meta_data->construct_lock.unlock();
+
+	/* block until the 'Thread_base::start' gets called */
+	meta_data->start_lock.lock();
+
+	Thread_base::myself()->entry();
+	return 0;
+}
+
+
+Thread_base *Thread_base::myself()
+{
+	void *tls = pthread_getspecific(tls_key());
+
+	bool const is_main_thread = (tls == 0);
+
+	return is_main_thread ? 0 : ((Thread_meta_data *)tls)->thread_base;
+}
+
+
+void Thread_base::start()
+{
+	/*
+	 * Unblock thread that is supposed to slumber in 'thread_start'.
+	 */
+	_tid.meta_data->start_lock.unlock();
+}
+
+
+Thread_base::Thread_base(const char *name, size_t stack_size)
+: _list_element(this)
+{
+	_tid.meta_data = new Thread_meta_data(this);
+
+	int const ret = pthread_create(&_tid.meta_data->pt, 0, thread_start,
+	                              _tid.meta_data);
+	if (ret) {
+		PERR("pthread_create failed (returned %d, errno=%d)",
+		     ret, errno);
+		delete _tid.meta_data;
+		throw Context_alloc_failed();
+	}
+
+	_tid.meta_data->construct_lock.lock();
+}
+
+
+void Thread_base::cancel_blocking()
+{
+	/*
+	 * XXX implement interaction with CPU session
+	 */
+}
+
+
+Thread_base::~Thread_base()
+{
+	{
+		int const ret = pthread_cancel(_tid.meta_data->pt);
+		if (ret)
+			PWRN("pthread_cancel unexpectedly returned with %d", ret);
+	}
+
+	{
+		int const ret = pthread_join(_tid.meta_data->pt, 0);
+		if (ret)
+			PWRN("pthread_join unexpectedly returned with %d (errno=%d)",
+			     ret, errno);
+	}
+
+	delete _tid.meta_data;
+	_tid.meta_data = 0;
+}