Re: [PATCH 0/4] MdeModulePkg: add support for dispatching foreign arch PE/COFF images

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On 13 September 2018 at 19:20, Kinney, Michael D
<michael.d.kinney@intel.com> wrote:
> Ard,
>
> I think there is a fundamental assumption that
> the sizeof(UINTN) and size of pointers of
> the native CPU are the same as the emulated CPU.
> If that is not the case, then I would like to see
> more details.  Otherwise that is a significant
> restriction that needs to be clearly documented.
>

There is no such assumption. The PE/COFF emulator protocol is an
abstract protocol that leaves it fully up to the implementation to
decide whether it can support images of machine type X and image type
Y.

> Protocols that only allow a single instance need to
> clearly document that assumption.
>

I will remove that restriction.

> If we decide to treat EBC as an emulated CPU, then
> we would want to support multiple instances of the
> protocol.  The updates to the DXE Core are a bit
> confusing because it has separate handling of EBC
> and emulated CPUs.  I think it would make the DXE
> Core logic simpler and easier to understand if they
> were combined.
>

Yes, excellent idea, and it results in a nice cleanup as well

> I asked about the startup case because if we do EBC,
> then we may need more services in the protocol because
> of the thunk code between native and EBC code.  At the
> time EBC was originally implemented, we did not have
> paging enabled and the EBC interpreter work without
> depending on a page fault handler.
>
> The way the protocol is currently defined, I believe it
> fundamentally assumes paging is enabled.  If paging is
> not enabled, then the current protocol services are not
> sufficient for any emulated CPU.  Do we want this to work
> for paging disabled cases?  If not, another assumption
> to clearly document.
>

The paging disabled case is interesting. Does the UEFI spec even
permit running in DXE with paging disabled?

In any case, I will send out a v2 as the basis for further discussion.
We can also sit down and discuss it in Vancouver the coming week.