MdePkg/BaseLib: Let CpuDeadLoop() be breakable in debugger

Starting from certain version of Visual Studio  C compiler (I don’t
have the exact version. I am using VS2019), CpuDeadLoop is optimized
quite well by compiler.
The compiler does not generate instructions that jump out of the loop
when the "Index" is non-zero.
It becomes harder/impossible for developers to break out of the dead-loop
in debugger.

The new version of CpuDeadLoop() compares a volatile global to a volatile
local. This forces 2 reads and a comparison on every loop iteration.
The local variable can be set to 1 to exit the loop without modifying the
global variable.
Using VS2019 with max opt enabled, The dead-loop can be exit by setting
Index to 1 in a debugger.

Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/MdePkg/Library/BaseLib/CpuDeadLoop.c b/MdePkg/Library/BaseLib/CpuDeadLoop.c
index b3b7548..01e7b4d 100644
--- a/MdePkg/Library/BaseLib/CpuDeadLoop.c
+++ b/MdePkg/Library/BaseLib/CpuDeadLoop.c
@@ -1,7 +1,7 @@
 /** @file

   Base Library CPU Functions for all architectures.

 

-  Copyright (c) 2006 - 2008, Intel Corporation. All rights reserved.<BR>

+  Copyright (c) 2006 - 2024, Intel Corporation. All rights reserved.<BR>

   SPDX-License-Identifier: BSD-2-Clause-Patent

 

 **/

@@ -9,6 +9,8 @@
 #include <Base.h>

 #include <Library/BaseLib.h>

 

+static volatile UINTN  mDeadLoopComparator = 0;

+

 /**

   Executes an infinite loop.

 

@@ -26,7 +28,7 @@ CpuDeadLoop (
 {

   volatile UINTN  Index;

 

-  for (Index = 0; Index == 0;) {

+  for (Index = mDeadLoopComparator; Index == mDeadLoopComparator;) {

     CpuPause ();

   }

 }