RE: [PATCH 20/37] xen: introduce CONFIG_EFI to stub API for non-EFI architecture

[Wei Chen <Wei.Chen@xxxxxxx>]

Hi Julien, Stefano,

> -----Original Message-----
> From: Xen-devel <xen-devel-bounces@xxxxxxxxxxxxxxxxxxxx> On Behalf Of Wei
> Chen
> Sent: 2021年9月26日 18:25
> To: Jan Beulich <jbeulich@xxxxxxxx>
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; julien@xxxxxxx; Bertrand Marquis
> <Bertrand.Marquis@xxxxxxx>; Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Subject: RE: [PATCH 20/37] xen: introduce CONFIG_EFI to stub API for non-
> EFI architecture
> 
> Hi Jan,
> 
> > -----Original Message-----
> > From: Xen-devel <xen-devel-bounces@xxxxxxxxxxxxxxxxxxxx> On Behalf Of
> Jan
> > Beulich
> > Sent: 2021年9月24日 18:49
> > To: Wei Chen <Wei.Chen@xxxxxxx>
> > Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; julien@xxxxxxx; Bertrand Marquis
> > <Bertrand.Marquis@xxxxxxx>; Stefano Stabellini <sstabellini@xxxxxxxxxx>
> > Subject: Re: [PATCH 20/37] xen: introduce CONFIG_EFI to stub API for
> non-
> > EFI architecture
> >
> > On 24.09.2021 12:31, Wei Chen wrote:
> > >> From: Jan Beulich <jbeulich@xxxxxxxx>
> > >> Sent: 2021年9月24日 15:59
> > >>
> > >> On 24.09.2021 06:34, Wei Chen wrote:
> > >>>> From: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> > >>>> Sent: 2021年9月24日 9:15
> > >>>>
> > >>>> On Thu, 23 Sep 2021, Wei Chen wrote:
> > >>>>> --- a/xen/common/Kconfig
> > >>>>> +++ b/xen/common/Kconfig
> > >>>>> @@ -11,6 +11,16 @@ config COMPAT
> > >>>>>  config CORE_PARKING
> > >>>>>       bool
> > >>>>>
> > >>>>> +config EFI
> > >>>>> +     bool
> > >>>>
> > >>>> Without the title the option is not user-selectable (or de-
> > selectable).
> > >>>> So the help message below can never be seen.
> > >>>>
> > >>>> Either add a title, e.g.:
> > >>>>
> > >>>> bool "EFI support"
> > >>>>
> > >>>> Or fully make the option a silent option by removing the help text.
> > >>>
> > >>> OK, in current Xen code, EFI is unconditionally compiled. Before
> > >>> we change related code, I prefer to remove the help text.
> > >>
> > >> But that's not true: At least on x86 EFI gets compiled depending on
> > >> tool chain capabilities. Ultimately we may indeed want a user
> > >> selectable option here, but until then I'm afraid having this option
> > >> at all may be misleading on x86.
> > >>
> > >
> > > I check the build scripts, yes, you're right. For x86, EFI is not a
> > > selectable option in Kconfig. I agree with you, we can't use Kconfig
> > > system to decide to enable EFI build for x86 or not.
> > >
> > > So how about we just use this EFI option for Arm only? Because on Arm,
> > > we do not have such toolchain dependency.
> >
> > To be honest - don't know. That's because I don't know what you want
> > to use the option for subsequently.
> >
> 
> In last version, I had introduced an arch-helper to stub EFI_BOOT
> in Arm's common code for Arm32. Because Arm32 doesn't support EFI.
> So Julien suggested me to introduce a CONFIG_EFI option for non-EFI
> supported architectures to stub in EFI layer.
> 
> [1] https://lists.xenproject.org/archives/html/xen-devel/2021-
> 08/msg00808.html
> 

As Jan' reminded, x86 doesn't depend on Kconfig to build EFI code.
So, if we CONFIG_EFI to stub EFI API's for x86, we will encounter
that toolchains enable EFI, but Kconfig disable EFI. Or Kconfig
enable EFI but toolchain doesn't provide EFI build supports. And
then x86 could not work well.

If we use CONFIG_EFI for Arm only, that means CONFIG_EFI for x86
is off, this will also cause problem.

So, can we still use previous arch_helpers to stub for Arm32?
until x86 can use this selectable option?

> > Jan
> >