exec: Save CPUState::exception_index field

This patch adds a subsection with exception_index field to the VMState for
correct saving the CPU state.
Without this patch, simulator could miss the pending exception in the saved
virtual machine state.
Signed-off-by: NPavel Dovgalyuk <pavel.dovgaluk@ispras.ru>
Cc: qemu-stable@nongnu.org
Signed-off-by: NAndreas Färber <afaerber@suse.de>

exec.c

@@ -430,15 +430,50 @@ static int cpu_common_post_load(void *opaque, int version_id)
     return 0;
 }
 
+static int cpu_common_pre_load(void *opaque)
+{
+    CPUState *cpu = opaque;
+
+    cpu->exception_index = 0;
+
+    return 0;
+}
+
+static bool cpu_common_exception_index_needed(void *opaque)
+{
+    CPUState *cpu = opaque;
+
+    return cpu->exception_index != 0;
+}
+
+static const VMStateDescription vmstate_cpu_common_exception_index = {
+    .name = "cpu_common/exception_index",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .fields = (VMStateField[]) {
+        VMSTATE_INT32(exception_index, CPUState),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
 const VMStateDescription vmstate_cpu_common = {
     .name = "cpu_common",
     .version_id = 1,
     .minimum_version_id = 1,
+    .pre_load = cpu_common_pre_load,
     .post_load = cpu_common_post_load,
     .fields = (VMStateField[]) {
         VMSTATE_UINT32(halted, CPUState),
         VMSTATE_UINT32(interrupt_request, CPUState),
         VMSTATE_END_OF_LIST()
+    },
+    .subsections = (VMStateSubsection[]) {
+        {
+            .vmsd = &vmstate_cpu_common_exception_index,
+            .needed = cpu_common_exception_index_needed,
+        } , {
+            /* empty */
+        }
     }
 };