--- trunk/reactos/ntoskrnl/ke/i386/syscall.S 2005-09-24 23:45:05 UTC (rev 18037)
+++ trunk/reactos/ntoskrnl/ke/i386/syscall.S 2005-09-25 00:00:03 UTC (rev 18038)
@@ -255,6 +255,22 @@
mov ebx, [ebp+KTRAP_FRAME_EBP]
mov edi, [ebp+KTRAP_FRAME_EIP]
+#ifdef DBG
+ /*
+ * We want to know the address from where the syscall stub was called.
+ * If PrevMode is KernelMode, that address is stored in our own (kernel)
+ * stack, at location KTRAP_FRAME_ESP.
+ * If we're coming from UserMode, we load the usermode stack pointer
+ * and go back two frames (first frame is the syscall stub, second call
+ * is the caller of the stub).
+ */
+ mov edi, [ebp+KTRAP_FRAME_ESP]
+ test byte ptr [esi+KTHREAD_PREVIOUS_MODE], 0x01
+ jz PrevWasKernelMode
+ mov edi, [edi+4]
+PrevWasKernelMode:
+#endif
+
/* Write the debug data */
mov [ebp+KTRAP_FRAME_DEBUGPOINTER], edx
mov dword ptr [ebp+KTRAP_FRAME_DEBUGARGMARK], 0xBADB0D00
@@ -334,6 +350,22 @@
mov edi, esp
rep movsd
+#ifdef DBG
+ /*
+ * The following lines are for the benefit of GDB. It will see the return
+ * address of the "call ebx" below, find the last label before it and
+ * thinks that that's the start of the function. It will then check to see
+ * if it starts with a standard function prolog (push ebp, mov ebp,esp).
+ * When that standard function prolog is not found, it will stop the
+ * stack backtrace. Since we do want to backtrace into usermode, let's
+ * make GDB happy and create a standard prolog.
+ */
+KiSystemService:
+ push ebp
+ mov ebp,esp
+ pop ebp
+#endif
+
/* Do the System Call */
call ebx