ArmPkg: Introduce the PCD PcdDebuggerExceptionSupport

The Exception Vector can be set before installing the CPU DXE driver to add
debugger support at the early stage of the firmware initialization.
If no one has touched the exception vector prior to the CPU DXE then the Vector
might contain non zero data.



git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@11733 6f19259b-4bc3-4df7-8a09-765794883524

ArmPkg/Drivers/CpuDxe/CpuDxe.inf

@@ -73,6 +73,7 @@
 [FeaturePcd.common]
   gArmTokenSpaceGuid.PcdCpuDxeProduceDebugSupport
   gArmTokenSpaceGuid.PcdRelocateVectorTable
+  gArmTokenSpaceGuid.PcdDebuggerExceptionSupport
   gArmTokenSpaceGuid.PcdEfiUncachedMemoryToStronglyOrdered
 
 [depex]

ArmPkg/Drivers/CpuDxe/Exception.c

@@ -162,8 +162,10 @@ InitializeExceptions (
         ASSERT_EFI_ERROR (Status);
       }
     
+    if (FeaturePcdGet(PcdDebuggerExceptionSupport) == TRUE) {
       // Save existing vector table, in case debugger is already hooked in
       CopyMem ((VOID *)gDebuggerExceptionHandlers, (VOID *)VectorBase, sizeof (gDebuggerExceptionHandlers));
+    }
     
       // Copy our assembly code into the page that contains the exception vectors. 
       CopyMem ((VOID *)VectorBase, (VOID *)ExceptionHandlersStart, Length);
@@ -178,7 +180,8 @@ InitializeExceptions (
       // Initialize the C entry points for interrupts
       //
       for (Index = 0; Index <= MAX_ARM_EXCEPTION; Index++) {
-        if ((gDebuggerExceptionHandlers[Index] == 0) || (gDebuggerExceptionHandlers[Index] == (VOID *)(UINTN)0xEAFFFFFE)) {
+      if (!FeaturePcdGet(PcdDebuggerExceptionSupport) ||
+          (gDebuggerExceptionHandlers[Index] == 0) || (gDebuggerExceptionHandlers[Index] == (VOID *)(UINTN)0xEAFFFFFE)) {
           // Exception handler contains branch to vector location (jmp $) so no handler
           // NOTE: This code assumes vectors are ARM and not Thumb code
           Status = RegisterInterruptHandler (Index, NULL);