Re: Can OVMF run on an emulated QEMU ARM vexpress-a9?

[Laszlo Ersek <lersek@redhat.com>]

CC Ard & Leif

On 06/12/17 08:44, Andre wrote:
> Hi,
> 
> this might be a silly question, as I am learning as I go about the topic,
> but is it possible to emulate UEFI on QEMU when setting the emulated
> machine to an ARM vexpress-a9?
> 
> I was able to emulate it on QEMU's virt machine, but I don't care as much
> about the vexpress-a9, but as to know whether OVMF can only run against
> QEMU's virt machine or if it can run against some other emulated board.
> 
> Are there too many differences between the virt machine to other boards
> that make providing images for different emulated boards impractical?
> 
> I really don't know enough even to know if my question is sensible, so any
> pointers on the topic are really appreciated!

Your question is fully justified and to the point.

The answer is that, yes, there's a *whole lot* of integration between
QEMU machine type and firmware. This is reflected by several things:

- The kinds of firmware drivers we include the firmware build follows
the QEMU machine type. Under "driver", understand both software drivers
(i.e. something that produces ACPI tables and SMBIOS tables -- because
QEMU exports those in a particular format), and hardware drivers (for
the kinds of emulated hardware that we know the targeted QEMU machine
type will, or can, provide).

- The way we customize or control generic (= platform-independent)
firmware drivers.

- The things we assume about hardware in the lowest-level / earliest
firmware modules (for example, what parts of the address space are known
to map to system RAM / MMIO / platform devices; what IO ports belong to
what platform devices, etc)

There *is* a bunch of stuff we try to abstract even between QEMU and
firmware, for enabling incremental development & compat, but then again
those abstractions rest upon virtual hardware specifics (DTB pre-filled
into RAM, fw_cfg, virtio, ...).

So, a quick summary about virtual platform support (that I know of) in edk2:

- ArmVirtPkg/ArmVirtQemu.dsc:

  - qemu-system-arm and qemu-system-aarch64, with the "virt" machine
    type (the higher-versioned "virt" machine types you use, the better
    integration you get)

- ArmVirtPkg/ArmVirtQemuKernel.dsc:

  - Not really sure about the QEMU configuration for this, but see
    commit 8de84d424221 ("ArmVirtPkg: implement ArmVirtQemuKernel",
    2016-02-05) for the intended use. I think Ard can explain it better.

- ArmVirtPkg/ArmVirtXen.dsc:

  - Xen, with HVM (fullvirt) guests, potentially using the XenPV block
    device. Both arm/aarch64. (I'm not a Xen user myself, hence the
    scant details -- I'm sorry.)

- OvmfPkg/*dsc:

  - qemu-system-i386 and qemu-system-x86_64, with the "pc" and "q35"
    machine types (the higher-versioned machine types you use, the
    better integration you get)

  - Xen, with HVM (fullvirt) guests, potentially using the XenPV block
    device

There used to be ArmPlatformPkg/ArmVExpressPkg (now defunct I think?),
and there's
<https://git.linaro.org/uefi/OpenPlatformPkg.git/tree/Platforms/ARM/VExpress>
as well.

I think the latter might just give you what you want.

You might get away running builds of existent firmware platforms (DSC
files) in non-matching environments, but the platform integration will
suffer. This ranges from "crashes without a single log message" to "some
optional UEFI protocols are missing".

Thanks
Laszlo