thread: rearrange thread context management

Use a bit allocator for the allocation management of thread contexts,
instead of holding allocation information within the Thread_base objects,
which lead to race conditions in the past.

Moreover, extend the Thread_base class interface with the ability to
to add additional stacks to a thread, and associate the context they're
located in with the corresponding Thread_base object. Additional stacks
can be used to do user-level scheduling with stack switching, without breaking
Genode's API.

Fixes #1024
Fixes #1036

base-foc/include/x86/base/native_config.h

@@ -0,0 +1,38 @@
+/*
+ * \brief  Platform-specific context area definitions
+ * \author Stefan Kalkowski
+ * \date   2014-01-24
+ */
+
+/*
+ * Copyright (C) 2014 Genode Labs GmbH
+ *
+ * This file is part of the Genode OS framework, which is distributed
+ * under the terms of the GNU General Public License version 2.
+ */
+
+#ifndef _INCLUDE__BASE__NATIVE_CONFIG_H_
+#define _INCLUDE__BASE__NATIVE_CONFIG_H_
+
+#include <base/stdint.h>
+
+namespace Genode {
+
+	struct Native_config
+	{
+		/**
+		 * Thread-context area configuration
+		 */
+		static constexpr addr_t context_area_virtual_base() {
+			return 0x40000000UL; }
+		static constexpr addr_t context_area_virtual_size() {
+			return 0x10000000UL; }
+
+		/**
+		 * Size of virtual address region holding the context of one thread
+		 */
+		static constexpr addr_t context_virtual_size() { return 0x00100000UL; }
+	};
+}
+
+#endif /* _INCLUDE__BASE__NATIVE_CONFIG_H_ */