[PATCH 3/6] MdeModulePkg/Tpl: Fix negative value left shift

[Hao Wu <hao.a.wu@intel.com>]

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=695

Within function CoreRestoreTpl(), left shift a negative value -2 is used
in:
"while (((-2 << NewTpl) & gEventPending) != 0) {"

which involves undefined behavior.

According to the C11 spec, Section 6.5.7:
> 4 The result of E1 << E2 is E1 left-shifted E2 bit positions; vacated
>   bits are filled with zeros. If E1 has an unsigned type, the value
>   of the result is E1 * 2^E2 , reduced modulo one more than the
>   maximum value representable in the result type. If E1 has a signed
>   type and nonnegative value, and E1 * 2^E2 is representable in the
>   result type, then that is the resulting value; otherwise, the
>   behavior is undefined.

This commit explicitly cast '-2' with UINTN to resolve this issue.

Cc: Steven Shi <steven.shi@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
---
 MdeModulePkg/Core/Dxe/Event/Tpl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/MdeModulePkg/Core/Dxe/Event/Tpl.c b/MdeModulePkg/Core/Dxe/Event/Tpl.c
index 8ad0a33701..8c50f61117 100644
--- a/MdeModulePkg/Core/Dxe/Event/Tpl.c
+++ b/MdeModulePkg/Core/Dxe/Event/Tpl.c
@@ -123,7 +123,7 @@ CoreRestoreTpl (
   //
   // Dispatch any pending events
   //
-  while (((-2 << NewTpl) & gEventPending) != 0) {
+  while (((((UINTN)-2) << NewTpl) & gEventPending) != 0) {
     gEfiCurrentTpl = (UINTN) HighBitSet64 (gEventPending);
     if (gEfiCurrentTpl < TPL_HIGH_LEVEL) {
       CoreSetInterruptState (TRUE);
-- 
2.12.0.windows.1