From ffce5f4f66ae25ec29a68fae6b76f5e73c27af6e Mon Sep 17 00:00:00 2001
From: Aleksey Bragin <aleksey@reactos.org>
Date: Sat, 30 Jun 2007 18:58:09 +0000
Subject: [PATCH] - Commit a fix for KDBG's attach to process problem. See
 issue #1263 for more details.

svn path=/trunk/; revision=27348
---
 reactos/ntoskrnl/kdbg/kdb.c | 46 +++++++++++++++++++++++++++----------
 1 file changed, 34 insertions(+), 12 deletions(-)

diff --git a/reactos/ntoskrnl/kdbg/kdb.c b/reactos/ntoskrnl/kdbg/kdb.c
index a2bab606a96..4bbd0cfbfd8 100644
--- a/reactos/ntoskrnl/kdbg/kdb.c
+++ b/reactos/ntoskrnl/kdbg/kdb.c
@@ -168,6 +168,29 @@ KdbpKdbTrapFrameToTrapFrame(PKDB_KTRAP_FRAME KdbTrapFrame, PKTRAP_FRAME TrapFram
    /* FIXME: copy v86 registers if TrapFrame is a V86 trapframe */
 }
 
+STATIC VOID
+KdbpKdbTrapFrameFromKernelStack(PVOID KernelStack,
+                                PKDB_KTRAP_FRAME KdbTrapFrame)
+{
+   ULONG_PTR *StackPtr;
+
+   RtlZeroMemory(KdbTrapFrame, sizeof(KDB_KTRAP_FRAME));
+   StackPtr = (ULONG_PTR *) KernelStack;
+   KdbTrapFrame->Tf.Ebp = StackPtr[3];
+   KdbTrapFrame->Tf.Edi = StackPtr[4];
+   KdbTrapFrame->Tf.Esi = StackPtr[5];
+   KdbTrapFrame->Tf.Ebx = StackPtr[6];
+   KdbTrapFrame->Tf.Eip = StackPtr[7];
+   KdbTrapFrame->Tf.HardwareEsp = (ULONG) (StackPtr + 8);
+   KdbTrapFrame->Tf.HardwareSegSs = KGDT_R0_DATA;
+   KdbTrapFrame->Tf.SegCs = KGDT_R0_CODE;
+   KdbTrapFrame->Tf.SegDs = KGDT_R0_DATA;
+   KdbTrapFrame->Tf.SegEs = KGDT_R0_DATA;
+   KdbTrapFrame->Tf.SegGs = KGDT_R0_DATA;
+
+   /* FIXME: what about the other registers??? */
+}
+
 /*!\brief Overwrites the instruction at \a Address with \a NewInst and stores
  *        the old instruction in *OldInst.
  *
@@ -1040,7 +1063,8 @@ KdbpAttachToThread(
    if (KdbCurrentThread != KdbOriginalThread)
    {
       ASSERT(KdbCurrentTrapFrame == &KdbThreadTrapFrame);
-      KdbpKdbTrapFrameToTrapFrame(KdbCurrentTrapFrame, KdbCurrentThread->Tcb.TrapFrame);
+      /* Actually, we can't save the context, there's no guarantee that there
+       * was a trap frame */
    }
    else
    {
@@ -1050,12 +1074,13 @@ KdbpAttachToThread(
    /* Switch to the thread's context */
    if (Thread != KdbOriginalThread)
    {
-      if (Thread->Tcb.TrapFrame == NULL)
-      {
-         KdbpPrint("Threads TrapFrame is NULL! Cannot attach.\n");
-         return FALSE;
-      }
-      KdbpTrapFrameToKdbTrapFrame(Thread->Tcb.TrapFrame, &KdbThreadTrapFrame);
+      /* The thread we're attaching to isn't the thread on which we entered
+       * kdb and so the thread we're attaching to is not running. There
+       * is no guarantee that it actually has a trap frame. So we have to
+       * peek directly at the registers which were saved on the stack when the
+       * thread was preempted in the scheduler */
+      KdbpKdbTrapFrameFromKernelStack(Thread->Tcb.KernelStack,
+                                      &KdbThreadTrapFrame);
       KdbCurrentTrapFrame = &KdbThreadTrapFrame;
    }
    else /* Switching back to original thread */
@@ -1529,11 +1554,8 @@ KdbEnterDebuggerException(
       }
    }
 
-   /* Save the current thread's trapframe */
-   if (KdbCurrentTrapFrame == &KdbThreadTrapFrame)
-   {
-      KdbpKdbTrapFrameToTrapFrame(KdbCurrentTrapFrame, KdbCurrentThread->Tcb.TrapFrame);
-   }
+   /* We can't update the current thread's trapframe 'cause it might not
+      have one */
 
    /* Detach from attached process */
    if (KdbCurrentProcess != KdbOriginalProcess)