mem: Add predecessor to SenderState base class

This patch adds a predecessor field to the SenderState base class to
make the process of linking them up more uniform, and enable a
traversal of the stack without knowing the specific type of the
subclasses.

There are a number of simplifications done as part of changing the
SenderState, particularly in the RubyTest.

3 files changed, 10 insertions, 13 deletions

diff --git a/src/mem/ruby/system/RubyPort.cc b/src/mem/ruby/system/RubyPort.cc
index 2f1cc622d..5e9e8cdd4 100644
--- a/src/mem/ruby/system/RubyPort.cc
+++ b/src/mem/ruby/system/RubyPort.cc
@@ -151,12 +151,9 @@ RubyPort::PioPort::recvTimingResp(PacketPtr pkt)
 
     // First we must retrieve the request port from the sender State
     RubyPort::SenderState *senderState =
-      safe_cast<RubyPort::SenderState *>(pkt->senderState);
+        safe_cast<RubyPort::SenderState *>(pkt->popSenderState());
     M5Port *port = senderState->port;
     assert(port != NULL);
-
-    // pop the sender state from the packet
-    pkt->senderState = senderState->saved;
     delete senderState;
 
     port->sendTimingResp(pkt);
@@ -187,7 +184,7 @@ RubyPort::M5Port::recvTimingReq(PacketPtr pkt)
 
     // Save the port in the sender state object to be used later to
     // route the response
-    pkt->senderState = new SenderState(this, pkt->senderState);
+    pkt->pushSenderState(new SenderState(this));
 
     // Check for pio requests and directly send them to the dedicated
     // pio port.
@@ -230,7 +227,7 @@ RubyPort::M5Port::recvTimingReq(PacketPtr pkt)
             pkt->getAddr(), RequestStatus_to_string(requestStatus));
 
     SenderState* senderState = safe_cast<SenderState*>(pkt->senderState);
-    pkt->senderState = senderState->saved;
+    pkt->senderState = senderState->predecessor;
     delete senderState;
     return false;
 }
@@ -305,7 +302,7 @@ RubyPort::ruby_hit_callback(PacketPtr pkt)
     assert(port != NULL);
 
     // pop the sender state from the packet
-    pkt->senderState = senderState->saved;
+    pkt->senderState = senderState->predecessor;
     delete senderState;
 
     port->hitCallback(pkt);
diff --git a/src/mem/ruby/system/RubyPort.hh b/src/mem/ruby/system/RubyPort.hh
index cec356edb..3c61eb522 100644
--- a/src/mem/ruby/system/RubyPort.hh
+++ b/src/mem/ruby/system/RubyPort.hh
@@ -113,10 +113,8 @@ class RubyPort : public MemObject
     struct SenderState : public Packet::SenderState
     {
         M5Port* port;
-        Packet::SenderState *saved;
 
-        SenderState(M5Port* _port, Packet::SenderState *sender_state = NULL)
-            : port(_port), saved(sender_state)
+        SenderState(M5Port* _port) : port(_port)
         {}
     };
 
diff --git a/src/mem/ruby/system/Sequencer.cc b/src/mem/ruby/system/Sequencer.cc
index 1cdd6d806..f00f8407a 100644
--- a/src/mem/ruby/system/Sequencer.cc
+++ b/src/mem/ruby/system/Sequencer.cc
@@ -530,11 +530,13 @@ Sequencer::hitCallback(SequencerRequest* srequest,
     // Note: RubyPort will access it's sender state before the
     // RubyTester.
     if (m_usingRubyTester) {
-        RubyPort::SenderState *requestSenderState =
+        RubyPort::SenderState *reqSenderState =
             safe_cast<RubyPort::SenderState*>(pkt->senderState);
+        // @todo This is a dangerous assumption on nothing else
+        // modifying the senderState
         RubyTester::SenderState* testerSenderState =
-            safe_cast<RubyTester::SenderState*>(requestSenderState->saved);
-        testerSenderState->subBlock->mergeFrom(data);
+            safe_cast<RubyTester::SenderState*>(reqSenderState->predecessor);
+        testerSenderState->subBlock.mergeFrom(data);
     }
 
     delete srequest;