hw: don't use assertions in Kernel::get_thread

ref #589

base-hw/include/kernel/syscalls.h

@@ -317,14 +317,19 @@ namespace Kernel
 
 
 	/**
-	 * Get platform thread by ID or 0 if target is "core main" or "idle"
+	 * Get platform thread by the kernel name of a thread
 	 *
-	 * \param id  ID of the targeted thread or 0 if caller targets itself
+	 * \param id  kernel name of the thread or 0 if the caller targets itself
+	 *
+	 * \retval  0  thread doesn't exist or has no platform thread
+	 * \retval >0  core local address of platform thread
 	 *
 	 * Restricted to core threads.
 	 */
-	inline Platform_thread * get_thread(unsigned const id = 0) {
-		return (Platform_thread *)syscall(GET_THREAD, id); }
+	inline Platform_thread * get_thread(unsigned const id)
+	{
+		return (Platform_thread *)syscall(GET_THREAD, id);
+	}
 
 
 	/**

base-hw/src/core/kernel.cc

@@ -444,21 +444,21 @@ namespace Kernel
 	void do_get_thread(Thread * const user)
 	{
 		/* check permissions */
-		assert(user->pd_id() == core_id());
-
-		/* get target */
-		unsigned const tid = (unsigned)user->user_arg_1();
+		if (user->pd_id() != core_id()) {
+			PERR("not entitled to read address of platform thread");
+			user->user_arg_0(0);
+			return;
+		}
+		/* lookup thread */
+		unsigned const id = user->user_arg_1();
 		Thread * t;
-
-		/* user targets a thread by ID */
-		if (tid) {
-			t = Thread::pool()->object(tid);
-			assert(t);
-
-		/* user targets itself */
-		} else t = user;
-
-		/* return target platform thread */
+		if (id) {
+			t = Thread::pool()->object(id);
+			if (!t) {
+				PERR("unknown thread");
+				user->user_arg_0(0);
+			}
+		} else { t = user; }
 		user->user_arg_0((Syscall_ret)t->platform_thread());
 	}
 

base-hw/src/core/thread.cc

@@ -42,12 +42,9 @@ Native_utcb * Thread_base::utcb()
  */
 Thread_base * Thread_base::myself()
 {
-	/* get our platform thread wich holds our thread base or 0 */
-	Platform_thread * const pt = Kernel::get_thread();
-	if (pt) return pt->thread_base();
-
-	/* we are core main, the only thread beside idle with no platform thread */
-	else return 0;
+	Platform_thread * const t = Kernel::get_thread(0);
+	if (t) { return t->thread_base(); }
+	return 0;
 }