Re: [Xen-devel] [PATCH] enable QEMU for ARM builds

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Wed, 16 Jul 2014, Ian Campbell wrote:
> On Thu, 2014-07-10 at 17:26 +0100, Stefano Stabellini wrote:
> > On Thu, 10 Jul 2014, Ian Campbell wrote:
> > > On Thu, 2014-07-10 at 15:04 +0100, Stefano Stabellini wrote:
> > > > On Thu, 10 Jul 2014, Ian Campbell wrote:
> > > > > On Thu, 2014-07-10 at 12:18 +0100, Stefano Stabellini wrote:
> > > > > > Build qemu-xen on ARM and ARM64: it is used to provide the PV 
> > > > > > backends,
> > > > > > disk and framebuffer in particular.
> > > > > > 
> > > > > > Ideally we would also modify the configure options to only build 
> > > > > > what is
> > > > > > necessary: a machine just for PV backends. However that is a work in
> > > > > > progress and not yet available in QEMU (see
> > > > > > http://marc.info/?l=qemu-devel&m=139082425718379&w=2). So we just 
> > > > > > build
> > > > > > the usual i386 target, even though no i386 emulation is going to be 
> > > > > > done
> > > > > > by qemu-xen on ARM.
> > > > > 
> > > > > As I mentioned IRL we need to confirm that this doesn't end up 
> > > > > exposing
> > > > > a protocol property in the xenstore backend dir of
> > > > > XEN_IO_PROTO_ABI_X86_* instead of XEN_IO_PROTO_ABI_ARM.
> > > > 
> > > > QEMU doesn't write the protocol to xenstore. In fact the protocol is
> > > > written to xenstore by the frontend so this shouldn't be a problem. 
> > > 
> > > Oh good, I was misremembering which way round it was.
> > > 
> > > > > Likewise we need to be sure that the code actually implements the ARM
> > > > > protocol, not one of the x86 ones.
> > > > 
> > > > Sure. No matter the QEMU target architecture,  qdisk and xenfb implement
> > > > NATIVE as well as x86 protocols.
> > > 
> > > When built as an ARM binary with x86 as the target architecture what
> > > does it consider to be the NATIVE protocol?
> > 
> > ARM
> > 
> >  
> > > You didn't mention the ARM protocol, hopefully just an oversight?
> > 
> > NATIVE is defined as ARM when building on arm:
> > 
> > xen/include/public/io/protocols.h
> > 
> > and because aarch64 and arm use the same protocol qemu don't need to
> > special case them.
> 
> Arguably that's a bug in Qemu when building for target!=arm, but I
> suppose it works in our favour right now, but bear it in mind for when
> you review the patch to "fix" this bug ;-)
> 
> Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> 
> I think application of this patch is dependent on the headers movement
> one, right?

Yep. Once the following series is applied, it can go in:

<alpine.DEB.2.02.1407181831070.2295@xxxxxxxxxxxxxxxxxxxxxxx>

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