Re: PciBusDxe: PCI-Express bug with dynamic PcdPciExpressBaseAddress

[Nikita Leshenko <nikita.leshchenko@oracle.com>]

> On 11 Sep 2018, at 15:34, Laszlo Ersek <lersek@redhat.com> wrote:
> 
> "BasePciExpressLib" has the prefix "Base", meaning that it is supposed
> to be usable in all types of firmware modules, even in SEC and PEIMs --
> which may not have access to writeable memory except stack (i.e.
> writeable global variables). Therefore modifying the original lib
> instance so that it depend on writeable globals wouldn't have been right.
> 
> We could have attempted to add the new library instance under MdePkg,
> and not ArmVirtPkg, but that's just a (more difficult) special case of
> point (1).
> 
> (Obviously if you try to apply the nomenclature I describe above to
> "BaseCachingPciExpressLib" as well, you'll see that it doesn't match.
> And that's because, when I invented the name for that lib instance, in
> 2015, I didn't know about the naming rules myself. :) In reality the lib
> instance should be called "DxePciExpressLibCaching" -- with "Dxe" for
> prefix, and "Caching" for suffix.)

Thanks for the detailed explanation. I guess we have no choice
but to copy BaseCachingPciExpressLib (renamed to
DxePciExpressLibCaching) from ArmVirt to OVMF as well.

In order to prevent such bugs in the future, what do you think
about changing the PCD reference in BasePciExpressLib.inf (in
MdePkg) from [Pcd] to [FixedPcd]? This way a module that has a
dynamic PcdPciExpressBaseAddress will fail to link with the
default PCIE library. Is it practical to get such change into
MdePkg despite their strict change policy?

Nikita

> 
> Thanks
> Laszlo
>