mem: Add PacketInfo to be used for packet probe points

This patch fixes a use-after-delete issue in the packet probe points
by adding a PacketInfo struct to retain the key fields before passing
the packet onwards. We want to probe the packet after it is
successfully sent, but by that time the fields may be modified, and
the packet may even be deleted.

Amazingly enough the issue has gone undetected for months, and only
recently popped up in our regressions.

1 files changed, 19 insertions, 1 deletions

diff --git a/src/sim/probe/mem.hh b/src/sim/probe/mem.hh
index 506287140..2d4b9aeec 100644
--- a/src/sim/probe/mem.hh
+++ b/src/sim/probe/mem.hh
@@ -47,6 +47,24 @@
 namespace ProbePoints {
 
 /**
+ * A struct to hold on to the essential fields from a packet, so that
+ * the packet and underlying request can be safely passed on, and
+ * consequently modified or even deleted.
+ */
+struct PacketInfo {
+    MemCmd cmd;
+    Addr addr;
+    uint32_t size;
+    Request::FlagsType flags;
+
+    explicit PacketInfo(const PacketPtr& pkt) :
+        cmd(pkt->cmd),
+        addr(pkt->getAddr()),
+        size(pkt->getSize()),
+        flags(pkt->req->getFlags()) { }
+};
+
+/**
  * Packet probe point
  *
  * This probe point provides a unified interface for components that
@@ -79,7 +97,7 @@ namespace ProbePoints {
  * </ul>
  *
  */
-typedef ProbePointArg< ::PacketPtr> Packet;
+typedef ProbePointArg<PacketInfo> Packet;
 typedef std::unique_ptr<Packet> PacketUPtr;
 
 }