OvmfPkg/Sec: Declare local variable as volatile in SecCoreStartupWithStack

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>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
Signed-off-by: Min Xu <min.m.xu@intel.com>

1 files changed, 10 insertions, 5 deletions

diff --git a/OvmfPkg/Sec/SecMain.c b/OvmfPkg/Sec/SecMain.c
index 2c55616..02520e2 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];

     }