hw_x86_64: Add Tss class

The class Genode::Tss represents a 64-bit Task State Segment (TSS) as
specified by Intel SDM Vol. 3A, section 7.7.

The setup function sets the stack pointers for privilege levels 0-2 to
the kernel stack address. The load function loads the TSS segment
selector into the task register.

repos/base-hw/lib/mk/x86_64/core.mk

@@ -17,6 +17,7 @@ SRC_S += spec/x86_64/isr.s
 # add C++ sources
 SRC_CC += spec/x86_64/kernel/thread_base.cc
 SRC_CC += spec/x86_64/idt.cc
+SRC_CC += spec/x86_64/tss.cc
 
 # include less specific configuration
 include $(REP_DIR)/lib/mk/x86/core.inc

repos/base-hw/src/core/include/spec/x86_64/tss.h

@@ -0,0 +1,53 @@
+#ifndef _TSS_H_
+#define _TSS_H_
+
+#include <base/stdint.h>
+
+namespace Genode
+{
+	/**
+	 * Task State Segment (TSS)
+	 *
+	 * See Intel SDM Vol. 3A, section 7.7
+	 */
+	class Tss;
+}
+
+class Genode::Tss
+{
+	private:
+
+		enum {
+			TSS_SELECTOR = 0x28,
+		};
+
+		uint32_t : 32;
+		addr_t rsp0;
+		addr_t rsp1;
+		addr_t rsp2;
+		uint64_t : 64;
+		addr_t ist[7];
+		uint64_t : 64;
+		uint16_t : 16;
+		uint16_t iomap_base;
+
+		/**
+		 * TSS
+		 */
+		static Tss _tss asm ("_tss");
+
+	public:
+
+		/**
+		 * Setup TSS.
+		 */
+		static void setup();
+
+		/**
+		 * Load TSS into TR.
+		 */
+		static void load();
+
+}__attribute__((packed));
+
+#endif /* _TSS_H_ */

repos/base-hw/src/core/spec/x86_64/tss.cc

@@ -0,0 +1,20 @@
+#include "tss.h"
+
+using namespace Genode;
+
+extern char kernel_stack[];
+
+__attribute__((aligned(8))) Tss Tss::_tss;
+
+void Tss::setup()
+{
+	_tss.rsp0 = (addr_t)kernel_stack;
+	_tss.rsp1 = (addr_t)kernel_stack;
+	_tss.rsp2 = (addr_t)kernel_stack;
+}
+
+
+void Tss::load()
+{
+	asm volatile ("ltr %w0" : : "r" (TSS_SELECTOR));
+}