base/core: use references instead of pointers

This patch replaces the former prominent use of pointers by references
wherever feasible. This has the following benefits:

* The contract between caller and callee becomes more obvious. When
  passing a reference, the contract says that the argument cannot be
  a null pointer. The caller is responsible to ensure that. Therefore,
  the use of reference eliminates the need to add defensive null-pointer
  checks at the callee site, which sometimes merely exist to be on the
  safe side. The bottom line is that the code becomes easier to follow.

* Reference members must be initialized via an object initializer,
  which promotes a programming style that avoids intermediate object-
  construction states. Within core, there are still a few pointers
  as member variables left though. E.g., caused by the late association
  of 'Platform_thread' objects with their 'Platform_pd' objects.

* If no pointers are present as member variables, we don't need to
  manually provide declarations of a private copy constructor and
  an assignment operator to avoid -Weffc++ errors "class ... has
  pointer data members [-Werror=effc++]".

This patch also changes a few system bindings on NOVA and Fiasco.OC,
e.g., the return value of the global 'cap_map' accessor has become a
reference. Hence, the patch touches a few places outside of core.

Fixes #3135

repos/base-nova/src/lib/base/cap_map.cc

@@ -21,10 +21,10 @@
 using namespace Genode;
 
 
-Capability_map *Genode::cap_map()
+Capability_map &Genode::cap_map()
 {
 	static Genode::Capability_map map;
-	return ↦
+	return map;
 }
 
 

repos/base-nova/src/lib/base/capability.cc

@@ -29,14 +29,14 @@ Native_capability::Native_capability()
 
 void Native_capability::_inc()
 {
-	Cap_index idx(cap_map()->find(local_name()));
+	Cap_index idx(cap_map().find(local_name()));
 	idx.inc();
 }
 
 
 void Native_capability::_dec()
 {
-	Cap_index idx(cap_map()->find(local_name()));
+	Cap_index idx(cap_map().find(local_name()));
 	idx.dec();
 }
 

repos/base-nova/src/lib/base/ipc.cc

@@ -154,7 +154,7 @@ bool Receive_window::rcv_cleanup(bool keep, unsigned short const new_max)
 
 			/* free rest of indexes if new_max is smaller then last window */
 			if (i >= new_max && _rcv_pt_cap_free[i] == FREE_SEL)
-				cap_map()->remove(_rcv_pt_base + i, 0, false);
+				cap_map().remove(_rcv_pt_base + i, 0, false);
 		}
 
 		return false;
@@ -164,7 +164,7 @@ bool Receive_window::rcv_cleanup(bool keep, unsigned short const new_max)
 	for (unsigned i = 0; i < MAX_CAP_ARGS; i++) {
 		if (_rcv_pt_cap_free[i] == FREE_INVALID)
 			continue;
-		cap_map()->remove(_rcv_pt_base + i, 0, _rcv_pt_cap_free[i] != FREE_SEL);
+		cap_map().remove(_rcv_pt_base + i, 0, _rcv_pt_cap_free[i] != FREE_SEL);
 	}
 
 	return true;
@@ -191,7 +191,7 @@ bool Receive_window::prepare_rcv_window(Nova::Utcb &utcb, addr_t rcv_window)
 	/* allocate receive window if necessary, otherwise use old one */
 	if (rcv_invalid() || rcv_cleanup(true, 1U << _rcv_wnd_log2))
 	{
-		_rcv_pt_base = cap_map()->insert(_rcv_wnd_log2);
+		_rcv_pt_base = cap_map().insert(_rcv_wnd_log2);
 
 		if (_rcv_pt_base == INVALID_INDEX) {
 			/* no mappings can be received */

repos/base-nova/src/lib/base/stack.cc

@@ -61,10 +61,10 @@ class Initial_cap_range : public Cap_range
 };
 
 
-Initial_cap_range * initial_cap_range()
+Initial_cap_range &initial_cap_range()
 {
 	static Initial_cap_range s;
-	return &s;
+	return s;
 }
 
 
@@ -76,26 +76,26 @@ void prepare_init_main_thread()
 {
 	using namespace Genode;
 
-	cap_map()->insert(initial_cap_range());
+	cap_map().insert(initial_cap_range());
 
 	/* for Core we can't perform the following code so early */
 	if (!__initial_sp) {
 
 		enum { CAP_RANGES = 32 };
 
-		unsigned index = initial_cap_range()->base() +
-		                 initial_cap_range()->elements();
+		unsigned index = initial_cap_range().base() +
+		                 initial_cap_range().elements();
 
 		static char local[CAP_RANGES][sizeof(Cap_range)];
 
 		for (unsigned i = 0; i < CAP_RANGES; i++) {
 
-			Cap_range * range = reinterpret_cast<Cap_range *>(local[i]);
-			construct_at<Cap_range>(range, index);
+			Cap_range &range = *reinterpret_cast<Cap_range *>(local[i]);
+			construct_at<Cap_range>(&range, index);
 
-			cap_map()->insert(range);
+			cap_map().insert(range);
 
-			index = range->base() + range->elements();
+			index = range.base() + range.elements();
 		}
 	}
 }
@@ -103,8 +103,8 @@ void prepare_init_main_thread()
 void prepare_reinit_main_thread()
 {
 	using namespace Genode;
-	construct_at<Capability_map>(cap_map());
-	construct_at<Initial_cap_range>(initial_cap_range());
+	construct_at<Capability_map>(&cap_map());
+	construct_at<Initial_cap_range>(&initial_cap_range());
 	prepare_init_main_thread();
 }
 

repos/base-nova/src/lib/base/thread_start.cc

@@ -103,7 +103,7 @@ void Thread::_init_platform_thread(size_t weight, Type type)
 	addr_t utcb = reinterpret_cast<addr_t>(&_stack->utcb());
 	revoke(Mem_crd(utcb >> 12, 0, rwx));
 
-	native_thread().exc_pt_sel = cap_map()->insert(NUM_INITIAL_PT_LOG2);
+	native_thread().exc_pt_sel = cap_map().insert(NUM_INITIAL_PT_LOG2);
 	if (native_thread().exc_pt_sel == Native_thread::INVALID_INDEX)
 		throw Cpu_session::Thread_creation_failed();
 
@@ -124,14 +124,14 @@ void Thread::_deinit_platform_thread()
 
 	if (native_thread().ec_sel != Native_thread::INVALID_INDEX) {
 		revoke(Obj_crd(native_thread().ec_sel, 0));
-		cap_map()->remove(native_thread().ec_sel, 0, false);
+		cap_map().remove(native_thread().ec_sel, 0, false);
 	}
 
 	/* de-announce thread */
 	if (_thread_cap.valid())
 		_cpu_session->kill_thread(_thread_cap);
 
-	cap_map()->remove(native_thread().exc_pt_sel, NUM_INITIAL_PT_LOG2);
+	cap_map().remove(native_thread().exc_pt_sel, NUM_INITIAL_PT_LOG2);
 }
 
 
@@ -173,7 +173,7 @@ void Thread::start()
 	cpu_thread.start(thread_ip, _stack->top());
 
 	/* request native EC thread cap */ 
-	native_thread().ec_sel = cap_map()->insert();
+	native_thread().ec_sel = cap_map().insert();
 	if (native_thread().ec_sel == Native_thread::INVALID_INDEX)
 		throw Cpu_session::Thread_creation_failed();