Re: [PATCH] meson.build: fix building of Xen support for aarch64

[Jason Andryuk <jandryuk@xxxxxxxxx>]

On Thu, Oct 29, 2020 at 6:01 AM Alex Bennée <alex.bennee@xxxxxxxxxx> wrote:
>
>
> Stefano Stabellini <sstabellini@xxxxxxxxxx> writes:
>
> > On Wed, 28 Oct 2020, Alex Bennée wrote:
> >> Xen is supported on aarch64 although weirdly using the i386-softmmu
> >> model. Checking based on the host CPU meant we never enabled Xen
> >> support. It would be nice to enable CONFIG_XEN for aarch64-softmmu to
> >> make it not seem weird but that will require further build surgery.
> >>
> >> Signed-off-by: Alex Bennée <alex.bennee@xxxxxxxxxx>
> >> Cc: Masami Hiramatsu <masami.hiramatsu@xxxxxxxxxx>
> >> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> >> Cc: Anthony Perard <anthony.perard@xxxxxxxxxx>
> >> Cc: Paul Durrant <paul@xxxxxxx>
> >> Fixes: 8a19980e3f ("configure: move accelerator logic to meson")
> >> ---
> >>  meson.build | 2 ++
> >>  1 file changed, 2 insertions(+)
> >>
> >> diff --git a/meson.build b/meson.build
> >> index 835424999d..f1fcbfed4c 100644
> >> --- a/meson.build
> >> +++ b/meson.build
> >> @@ -81,6 +81,8 @@ if cpu in ['x86', 'x86_64']
> >>      'CONFIG_HVF': ['x86_64-softmmu'],
> >>      'CONFIG_WHPX': ['i386-softmmu', 'x86_64-softmmu'],
> >>    }
> >> +elif cpu in [ 'arm', 'aarch64' ]
> >> +  accelerator_targets += { 'CONFIG_XEN': ['i386-softmmu'] }
> >>  endif
> >
> > This looks very reasonable -- the patch makes sense.

A comment would be useful to explain that Arm needs i386-softmmu for
the xenpv machine.

> >
> > However I have two questions, mostly for my own understanding. I tried
> > to repro the aarch64 build problem but it works at my end, even without
> > this patch.
>
> Building on a x86 host or with cross compiler?
>
> > I wonder why. I suspect it works thanks to these lines in
> > meson.build:

I think it's a runtime and not a build problem.  In osstest, Xen
support was detected and configured, but CONFIG_XEN wasn't set for
Arm.  So at runtime xen_available() returns 0, and QEMU doesn't start
with "qemu-system-i386: -xen-domid 1: Option not supported for this
target"

I posted my investigation here:
https://lore.kernel.org/xen-devel/CAKf6xpss8KpGOvZrKiTPz63bhBVbjxRTYWdHEkzUo2q1KEMjhg@xxxxxxxxxxxxxx/

Regards,
Jason