Fix bug when reserve stack space to fill exception context.

Signed-off-by: Jeff Fan <jeff.fan@intel.com>
Reviewed-by: Feng Tian <feng.tian@intel.com>












git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15086 6f19259b-4bc3-4df7-8a09-765794883524

UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ExceptionHandlerAsm.asm

@@ -1,5 +1,5 @@
 ;------------------------------------------------------------------------------ ;
-; Copyright (c) 2012 - 2013, Intel Corporation. All rights reserved.<BR>
+; Copyright (c) 2012 - 2014, Intel Corporation. All rights reserved.<BR>
 ; This program and the accompanying materials
 ; are licensed and made available under the terms and conditions of the BSD License
 ; which accompanies this distribution.  The full text of the license may be found at
@@ -53,12 +53,12 @@ HookAfterStubHeaderBegin:
     jmp     rax
 HookAfterStubHeaderEnd:
     mov     rax, rsp
-    sub     rsp, 8h
-    and     sp, 0fff0h
+    and     sp,  0fff0h        ; make sure 16-byte aligned for exception context
+    sub     rsp, 18h           ; reserve room for filling exception data later
     push    rcx
     mov     rcx, [rax + 8]
     bt      mErrorCodeFlag, ecx
-    jc      @F
+    jnc     @F
     push    [rsp]             ; push additional rcx to make stack alignment
 @@:
     xchg    rcx, [rsp]        ; restore rcx, save Exception Number in stack