MEM: Fatal when no port can be found for an address

This patch adds a check in the findPort method to ensure that an
invalid port id is never returned. Previously this could happen if no
default port was set, and no address matched the request, in which
case -1 was returned causing a SEGFAULT when using the id to index in
the port array. To clean things up further a symbolic name is added
for the invalid port id.

1 files changed, 4 insertions, 1 deletions

diff --git a/src/mem/bus.hh b/src/mem/bus.hh
index 3117bf4e1..f7f69e08e 100644
--- a/src/mem/bus.hh
+++ b/src/mem/bus.hh
@@ -220,7 +220,7 @@ class Bus : public MemObject
             return portCache[2].id;
         }
 
-        return -1;
+        return INVALID_PORT_ID;
     }
 
     // Clears the earliest entry of the cache and inserts a new port entry
@@ -317,6 +317,9 @@ class Bus : public MemObject
     /** Port that handles requests that don't match any of the interfaces.*/
     short defaultPortId;
 
+    /** A symbolic name for a port id that denotes no port. */
+    static const short INVALID_PORT_ID = -1;
+
     /** If true, use address range provided by default device.  Any
        address not handled by another port and not in default device's
        range will cause a fatal error.  If false, just send all