[PATCH V6 27/42] OvmfPkg/Sec: Declare local variable as volatile in SecCoreStartupWithStack

["Min Xu" <min.m.xu@intel.com>]

RFC: https://bugzilla.tianocore.org/show_bug.cgi?id=3429

Declare the local variables in SecCoreStartupWithStack that actually
move the data elements as volatile to prevent the optimizer from
replacing this function with the intrinsic memcpy().

Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Erdem Aktas <erdemaktas@google.com>
Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Min Xu <min.m.xu@intel.com>
---
 OvmfPkg/Sec/SecMain.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/OvmfPkg/Sec/SecMain.c b/OvmfPkg/Sec/SecMain.c
index 2c5561661ef3..02520e25ab9a 100644
--- a/OvmfPkg/Sec/SecMain.c
+++ b/OvmfPkg/Sec/SecMain.c
@@ -757,12 +757,17 @@ SecCoreStartupWithStack (
   //
   IdtTableInStack.PeiService = NULL;
   for (Index = 0; Index < SEC_IDT_ENTRY_COUNT; Index++) {
-    UINT8  *Src;
-    UINT8  *Dst;
-    UINTN  Byte;
+    //
+    // Declare the local variables that actually move the data elements as
+    // volatile to prevent the optimizer from replacing this function with
+    // the intrinsic memcpy()
+    //
+    CONST UINT8     *Src;
+    volatile UINT8  *Dst;
+    UINTN           Byte;
 
-    Src = (UINT8 *)&mIdtEntryTemplate;
-    Dst = (UINT8 *)&IdtTableInStack.IdtTable[Index];
+    Src = (CONST UINT8 *)&mIdtEntryTemplate;
+    Dst = (volatile UINT8 *)&IdtTableInStack.IdtTable[Index];
     for (Byte = 0; Byte < sizeof (mIdtEntryTemplate); Byte++) {
       Dst[Byte] = Src[Byte];
     }
-- 
2.29.2.windows.2