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

[Volodymyr Babchuk]

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.

-- 
WBR, Volodymyr