Re: [edk2-devel] [RFC] Remove PI spec TemporaryRamSupport PPI from PEI Core

["Ni, Ray" <ray.ni@intel.com>]

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Nate,
GCC generates assembly code that uses `RBP` to store `Private` local variable for below C code in PeiCore/Dispatcher.c

```c
      if (StackOffsetPositive) {
        SecCoreData = (CONST EFI_SEC_PEI_HAND_OFF *)((UINTN)(VOID *)SecCoreData + StackOffset);
        Private     = (PEI_CORE_INSTANCE *)((UINTN)(VOID *)Private + StackOffset);
      } else {
        SecCoreData = (CONST EFI_SEC_PEI_HAND_OFF *)((UINTN)(VOID *)SecCoreData - StackOffset);
        Private     = (PEI_CORE_INSTANCE *)((UINTN)(VOID *)Private - StackOffset);
      }

      TemporaryRamSupportPpi->TemporaryRamMigration (
                                PeiServices,
                                TemporaryRamBase,
                                (EFI_PHYSICAL_ADDRESS)(UINTN)(TopOfNewStack - TemporaryStackSize),
                                TemporaryRamSize
                                );

      PeiCore (SecCoreData, NULL, Private);
```

If `TemporaryRamMigration()` updates the `RBP` to point to physical memory by adding/subtracting
the `StackOffset`, that results the Private is added/subtracted by `StackOffset` twice: One in the C code before calling
TemporayRamSupport PPI, the other in `TemporaryRamMigration ()`.

Since `FspSecMain.SecSwitchStack()` does update the `RBP`, have you met the similar issue?

The issue doesn't always happen. It depends on whether `RBP` is used to store either `SecCoreData` or `Private`.

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