From: Brian Norris <banorris@uci.edu>
Date: Tue, 16 Apr 2013 16:46:58 +0000 (-0700)
Subject: action: bugfix - use non-zero fence "location"
X-Git-Url: http://plrg.eecs.uci.edu/git/?p=cdsspec-compiler.git;a=commitdiff_plain;h=b5d7d602016a4640c31b79ba9598dceefa778ab6

action: bugfix - use non-zero fence "location"

Our HashTable does not support zero-based keys (e.g., NULL pointer as a
key). So as a hack, switch to use a small, arbitrary, non-zero location
instead of NULL (0).
---

diff --git a/action.h b/action.h
index dc56017..ad34c83 100644
--- a/action.h
+++ b/action.h
@@ -37,6 +37,15 @@ using std::memory_order_seq_cst;
  */
 #define VALUE_NONE 0xdeadbeef
 
+/**
+ * @brief The "location" at which a fence occurs
+ *
+ * We need a non-zero memory location to associate with fences, since our hash
+ * tables don't handle NULL-pointer keys. HACK: Hopefully this doesn't collide
+ * with any legitimate memory locations.
+ */
+#define FENCE_LOCATION ((void *)0x7)
+
 /** @brief Represents an action type, identifying one of several types of
  * ModelAction */
 typedef enum action_type {
diff --git a/cmodelint.cc b/cmodelint.cc
index 47aef05..1632581 100644
--- a/cmodelint.cc
+++ b/cmodelint.cc
@@ -39,5 +39,5 @@ void model_rmwc_action(void *obj, memory_order ord) {
 
 /** Issues a fence operation. */
 void model_fence_action(memory_order ord) {
-	model->switch_to_master(new ModelAction(ATOMIC_FENCE, ord, NULL));
+	model->switch_to_master(new ModelAction(ATOMIC_FENCE, ord, FENCE_LOCATION));
 }
diff --git a/execution.cc b/execution.cc
index 8b50771..17ea954 100644
--- a/execution.cc
+++ b/execution.cc
@@ -2215,8 +2215,8 @@ ModelAction * ModelExecution::get_last_seq_cst_write(ModelAction *curr) const
  */
 ModelAction * ModelExecution::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
 {
-	/* All fences should have NULL location */
-	action_list_t *list = get_safe_ptr_action(obj_map, NULL);
+	/* All fences should have location FENCE_LOCATION */
+	action_list_t *list = get_safe_ptr_action(obj_map, FENCE_LOCATION);
 	action_list_t::reverse_iterator rit = list->rbegin();
 
 	if (before_fence) {