kvm: Introduce IVT handling

Introduce procedures for handling IVT (Interrupt Vector Table) to be used int
real mode bootstrap procedure.

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>

Makefile

@@ -4,6 +4,7 @@ OBJS	+= cpu.o
 OBJS	+= kvm.o
 OBJS	+= main.o
 OBJS	+= util.o
+OBJS	+= ivt.o
 
 CFLAGS	+= $(CPPFLAGS) -Iinclude
 

ivt.c

@@ -0,0 +1,38 @@
+#include <stdbool.h>
+#include <limits.h>
+#include <stdarg.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <stdio.h>
+
+#include "util.h"
+#include "ivt.h"
+
+static struct ivt_entry ivt_table[IVT_VECTORS];
+
+void ivt_reset(void)
+{
+	memset(ivt_table, 0x0, sizeof(ivt_table));
+}
+
+void ivt_copy_table(void *dst, unsigned int size)
+{
+	if (size < sizeof(ivt_table))
+		die("An attempt to overwrite host memory");
+	memcpy(dst, ivt_table, sizeof(ivt_table));
+}
+
+struct ivt_entry * const ivt_get_entry(unsigned int n)
+{
+	struct ivt_entry *v = NULL;
+	if (n < IVT_VECTORS)
+		v = &ivt_table[n];
+	return (struct ivt_entry * const)v;
+}
+
+void ivt_set_entry(struct ivt_entry e, unsigned int n)
+{
+	if (n < IVT_VECTORS)
+		ivt_table[n] = e;
+}

ivt.h

@@ -0,0 +1,15 @@
+#include <inttypes.h>
+#include <stdbool.h>
+
+#define IVT_BASE	0x0000
+#define IVT_VECTORS	256
+
+struct ivt_entry {
+	uint16_t segment;
+	uint16_t offset;
+} __attribute__((packed));
+
+void ivt_reset(void);
+void ivt_copy_table(void *dst, unsigned int size);
+struct ivt_entry * const ivt_get_entry(unsigned int n);
+void ivt_set_entry(struct ivt_entry e, unsigned int n);