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

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 29 Oct 2020, Jason Andryuk wrote:
> 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/

Right, but strangely I cannot reproduce it here. I am natively building
(qemu-user) on aarch64 and for me CONFIG_XEN gets set.