vmport_register() is also called from other modules such as vmmouse.
Therefore, these modules rely that vmport is realized before those call
sites. If this is violated, vmport_register() will NULL-deref.

To make such issues easier to debug, assert in vmport_register() that
vmport is already realized.

Reviewed-by: Nikita Leshenko <nikita.leshchenko@oracle.com>
Signed-off-by: Liran Alon <liran.alon@oracle.com>
---
 hw/i386/vmport.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/hw/i386/vmport.c b/hw/i386/vmport.c
index 76fd49c52058..8d3d268bfd7e 100644
--- a/hw/i386/vmport.c
+++ b/hw/i386/vmport.c
@@ -72,6 +72,8 @@ static VMPortState *port_state;
 void vmport_register(VMPortCommand command, VMPortReadFunc *func, void *opaque)
 {
     assert(command < VMPORT_ENTRIES);
+    assert(port_state);
+
     trace_vmport_register(command, func, opaque);
     port_state->func[command] = func;
     port_state->opaque[command] = opaque;
-- 
2.20.1