Re: [PATCH] fix qemu build with xen-4.18.0

[Stefan Hajnoczi]

On Tue, 12 Dec 2023 at 10:36, Volodymyr Babchuk
<Volodymyr_Babchuk@epam.com> wrote:
>
> Hi Anthony
>
> Anthony PERARD <anthony.perard@citrix.com> writes:
>
> > On Fri, Dec 08, 2023 at 02:49:27PM -0800, Stefano Stabellini wrote:
> >> On Fri, 8 Dec 2023, Daniel P. Berrangé wrote:
> >> > On Thu, Dec 07, 2023 at 11:12:48PM +0000, Michael Young wrote:
> >> > > Builds of qemu-8.2.0rc2 with xen-4.18.0 are currently failing
> >> > > with errors like
> >> > > ../hw/arm/xen_arm.c:74:5: error: ‘GUEST_VIRTIO_MMIO_SPI_LAST’ 
> >> > > undeclared (first use in this function)
> >> > >    74 |    (GUEST_VIRTIO_MMIO_SPI_LAST - GUEST_VIRTIO_MMIO_SPI_FIRST)
> >> > >       |     ^~~~~~~~~~~~~~~~~~~~~~~~~~
> >> > >
> >> > > as there is an incorrect comparision in include/hw/xen/xen_native.h
> >> > > which means that settings like GUEST_VIRTIO_MMIO_SPI_LAST
> >> > > aren't being defined for xen-4.18.0
> >> >
> >> > The conditions in arch-arm.h for xen 4.18 show:
> >> >
> >> > $ cppi arch-arm.h | grep -E '(#.*if)|MMIO'
> >> > #ifndef __XEN_PUBLIC_ARCH_ARM_H__
> >> > # if defined(__XEN__) || defined(__XEN_TOOLS__) || defined(__GNUC__)
> >> > # endif
> >> > # ifndef __ASSEMBLY__
> >> > #  if defined(__XEN__) || defined(__XEN_TOOLS__)
> >> > #   if defined(__GNUC__) && !defined(__STRICT_ANSI__)
> >> > #   endif
> >> > #  endif /* __XEN__ || __XEN_TOOLS__ */
> >> > # endif
> >> > # if defined(__XEN__) || defined(__XEN_TOOLS__)
> >> > #  define PSR_MODE_BIT  0x10U /* Set iff AArch32 */
> >> > /* Virtio MMIO mappings */
> >> > #  define GUEST_VIRTIO_MMIO_BASE   xen_mk_ullong(0x02000000)
> >> > #  define GUEST_VIRTIO_MMIO_SIZE   xen_mk_ullong(0x00100000)
> >> > #  define GUEST_VIRTIO_MMIO_SPI_FIRST   33
> >> > #  define GUEST_VIRTIO_MMIO_SPI_LAST    43
> >> > # endif
> >> > # ifndef __ASSEMBLY__
> >> > # endif
> >> > #endif /*  __XEN_PUBLIC_ARCH_ARM_H__ */
> >> >
> >> > So the MMIO constants are available if __XEN__ or __XEN_TOOLS__
> >> > are defined. This is no different to the condition that was
> >> > present in Xen 4.17.
> >> >
> >> > What you didn't mention was that the Fedora build failure is
> >> > seen on an x86_64 host, when building the aarch64 target QEMU,
> >> > and I think this is the key issue.
> >>
> >> Hi Daniel, thanks for looking into it.
> >>
> >> - you are building on a x86_64 host
> >> - the target is aarch64
> >> - the target is the aarch64 Xen PVH machine (xen_arm.c)
> >>
> >> But is the resulting QEMU binary expected to be an x86 binary? Or are
> >> you cross compiling ARM binaries on a x86 host?
> >>
> >> In other word, is the resulting QEMU binary expected to run on ARM or
> >> x86?
> >>
> >>
> >> > Are we expecting to build Xen support for non-arch native QEMU
> >> > system binaries or not ?
> >>
> >> The ARM xenpvh machine (xen_arm.c) is meant to work with Xen on ARM, not
> >> Xen on x86.  So this is only expected to work if you are
> >> cross-compiling. But you can cross-compile both Xen and QEMU, and I am
> >> pretty sure that Yocto is able to build Xen, Xen userspace tools, and
> >> QEMU for Xen/ARM on an x86 host today.
> >>
> >>
> >> > The constants are defined in arch-arm.h, which is only included
> >> > under:
> >> >
> >> >   #if defined(__i386__) || defined(__x86_64__)
> >> >   #include "arch-x86/xen.h"
> >> >   #elif defined(__arm__) || defined (__aarch64__)
> >> >   #include "arch-arm.h"
> >> >   #else
> >> >   #error "Unsupported architecture"
> >> >   #endif
> >> >
> >> >
> >> > When we are building on an x86_64 host, we not going to get
> >> > arch-arm.h included, even if we're trying to build the aarch64
> >> > system emulator.
> >> >
> >> > I don't know how this is supposed to work ?
> >>
> >> It looks like a host vs. target architecture mismatch: the #if defined
> >> (__aarch64__) check should pass I think.
> >
> >
> > Building qemu with something like:
> >     ./configure --enable-xen --cpu=x86_64
> > used to work. Can we fix that? It still works with v8.1.0.
> > At least, it works on x86, I never really try to build qemu for arm.
> > Notice that there's no "--target-list" on the configure command line.
> > I don't know if --cpu is useful here.
> >
> > Looks like the first commit where the build doesn't work is
> > 7899f6589b78 ("xen_arm: Add virtual PCIe host bridge support").
>
> I am currently trying to upstream this patch. It is in the QEMU mailing
> list but it was never accepted. It is not reviewed in fact. I'll take a
> look at it, but I don't understand how did you get in the first place.

Hi Volodymyr,
Paolo Bonzini sent a pull request with similar code changes this
morning and I have merged it into the qemu.git/staging branch:
https://gitlab.com/qemu-project/qemu/-/commit/eaae59af4035770975b0ce9364b587223a909501

If you spot something that is not correct, please reply here.

Thanks!

Stefan

>
> --
> WBR, Volodymyr