Set up initial task link-register to point to 'task_end' function.

Change-Id: Id1b122d789b84eebd75feb3bdb7e1ca222e6d76e
Reviewed-on: http://gfw160.austin.ibm.com:8080/gerrit/147
Reviewed-by: Nicholas E. Bofferding <bofferdn@us.ibm.com>
Tested-by: Jenkins Server
Reviewed-by: Mark W. Wenning <wenning@us.ibm.com>

2 files changed, 14 insertions, 3 deletions

diff --git a/src/include/sys/task.h b/src/include/sys/task.h
index 265f175fb..901f938ea 100644
--- a/src/include/sys/task.h
+++ b/src/include/sys/task.h
@@ -36,9 +36,11 @@ tid_t task_create(void(*start_routine)(void*), void* arg);
  *
  *  See POSIX pthread_exit.
  *
- *  @note A thread must call task_end when it wishes to exit.  It is not
- *        acceptable to simply return from the 'start_routine' and may result
- *        in unexpected behavior.
+ *  @note A task must call task_end when it wishes to exit.  If a task were
+ *        to simply return from its entry point function, the kernel sets up
+ *        the initial task structure with the link-register pointing to this
+ *        function.  Therefore, returning from the entry point function will
+ *        also cause the task to end cleanly using this function.
  */
 void task_end();
 
diff --git a/src/kernel/taskmgr.C b/src/kernel/taskmgr.C
index 8225b7da3..0573bab7d 100644
--- a/src/kernel/taskmgr.C
+++ b/src/kernel/taskmgr.C
@@ -3,8 +3,10 @@
 #include <kernel/task.H>
 #include <kernel/pagemgr.H>
 #include <kernel/cpumgr.H>
+#include <sys/task.h>
 #include <arch/ppc.H>
 #include <string.h>
+#include <limits.h>
 
 void TaskManager::idleTaskLoop(void* unused)
 {
@@ -60,6 +62,11 @@ task_t* TaskManager::_createTask(TaskManager::task_fn_t t,
     task->context.nip = (void*) ((uint64_t*) t)[0];
     task->context.gprs[2] = ((uint64_t*)t)[1];
 
+    // Set up LR to be the entry point for task_end in case a task 
+    // 'returns' from its entry point.  By the Power ABI, the entry
+    // point address is in (func_ptr)[0].
+    task->context.lr = reinterpret_cast<uint64_t*>(&task_end)[0];
+
     // Set up GRP[13] as task structure reserved.
     task->context.gprs[13] = (uint64_t)task;
 
@@ -71,6 +78,8 @@ task_t* TaskManager::_createTask(TaskManager::task_fn_t t,
     {
 	task->context.stack_ptr = 
 	    PageManager::allocatePage(TASK_DEFAULT_STACK_SIZE);
+        memset(task->context.stack_ptr, '\0', 
+               TASK_DEFAULT_STACK_SIZE * PAGE_SIZE);
 	task->context.gprs[1] = ((uint64_t)task->context.stack_ptr) + 16320;
     }
     else