[blight] 18967: Optimize NtGetContextThread a bit and fix use of unitinialized memory if PreviousMode == KernelMode and Thread ==

Optimize NtGetContextThread a bit and fix use of unitinialized memory if
PreviousMode == KernelMode and Thread == 
CurrentThread (thanks to Thomas for spotting!)
Modified: trunk/reactos/ntoskrnl/ps/debug.c
  _____  

Modified: trunk/reactos/ntoskrnl/ps/debug.c
--- trunk/reactos/ntoskrnl/ps/debug.c	2005-11-03 00:17:55 UTC (rev
18966)
+++ trunk/reactos/ntoskrnl/ps/debug.c	2005-11-03 00:34:09 UTC (rev
18967)
@@ -86,6 +86,7 @@

     KPROCESSOR_MODE PreviousMode = ExGetPreviousMode();
     GET_SET_CTX_CONTEXT GetSetContext;
     NTSTATUS Status = STATUS_SUCCESS;
+    PCONTEXT SafeThreadContext = NULL;
 
     PAGED_CODE();
 
@@ -98,6 +99,7 @@
                           sizeof(CONTEXT),
                           sizeof(ULONG));
             GetSetContext.Context = *ThreadContext;
+            SafeThreadContext = &GetSetContext.Context;
 
         } _SEH_HANDLE {
 
@@ -106,6 +108,8 @@
         } _SEH_END;
 
         if(!NT_SUCCESS(Status)) return Status;
+    } else {
+        SafeThreadContext = ThreadContext;
     }
 
     /* Get the Thread Object */
@@ -121,15 +125,20 @@
 
         /* Check if we're running in the same thread */
         if(Thread == PsGetCurrentThread()) {
-
             /*
              * I don't know if trying to get your own context makes
much
              * sense but we can handle it more efficently.
              */
-            KeTrapFrameToContext(Thread->Tcb.TrapFrame, NULL,
&GetSetContext.Context);
+            KeTrapFrameToContext(Thread->Tcb.TrapFrame, NULL,
SafeThreadContext);
 
         } else {
 
+            /* Copy context into GetSetContext if not already done */
+            if(PreviousMode == KernelMode) {
+                GetSetContext.Context = *ThreadContext;
+                SafeThreadContext = &GetSetContext.Context;
+            }
+
             /* Use an APC... Initialize the Event */
             KeInitializeEvent(&GetSetContext.Event,
                               NotificationEvent,
@@ -173,7 +182,7 @@
         ObDereferenceObject(Thread);
 
         /* Check for success and return the Context */
-        if(NT_SUCCESS(Status)) {
+        if(NT_SUCCESS(Status) && SafeThreadContext != ThreadContext) {
             _SEH_TRY {
 
                 *ThreadContext = GetSetContext.Context;