[v2,1/9] configure: change CONFIG_XEN_BACKEND to be a target property

On Tue, 14 Mar 2017, Stefano Stabellini wrote:
> On Tue, 14 Mar 2017, Paolo Bonzini wrote:
> > On 14/03/2017 00:55, Stefano Stabellini wrote:
> > > CONFIG_XEN_BACKEND is currently set when the host supports Xen,
> > > regardless of the chosen targets. As a consequence, Xen backends can be
> > > enabled even on targets that don't support Xen.
> > > 
> > > Fix the issue by setting CONFIG_XEN_BACKEND only for targets that
> > > support Xen.
> > > 
> > > Signed-off-by: Stefano Stabellini <stefano@aporeto.com>
> > > CC: groug@kaod.org
> > > CC: groug@kaod.org
> > > CC: pbonzini@redhat.com
> > > CC: peter.maydell@linaro.org
> > > CC: rth@twiddle.net
> > > CC: stefanha@redhat.com
> > > ---
> > >  configure | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/configure b/configure
> > > index 6c21975..6d8f752 100755
> > > --- a/configure
> > > +++ b/configure
> > > @@ -5442,7 +5442,6 @@ if test "$virglrenderer" = "yes" ; then
> > >    echo "VIRGL_LIBS=$virgl_libs" >> $config_host_mak
> > >  fi
> > >  if test "$xen" = "yes" ; then
> > > -  echo "CONFIG_XEN_BACKEND=y" >> $config_host_mak
> > >    echo "CONFIG_XEN_CTRL_INTERFACE_VERSION=$xen_ctrl_version" >> $config_host_mak
> > >    if test "$xen_pv_domain_build" = "yes" ; then
> > >      echo "CONFIG_XEN_PV_DOMAIN_BUILD=y" >> $config_host_mak
> > > @@ -6028,6 +6027,7 @@ case "$target_name" in
> > >    i386|x86_64)
> > >      if test "$xen" = "yes" -a "$target_softmmu" = "yes" ; then
> > >        echo "CONFIG_XEN=y" >> $config_target_mak
> > > +      echo "CONFIG_XEN_BACKEND=y" >> $config_target_mak
> > >        if test "$xen_pci_passthrough" = yes; then
> > >          echo "CONFIG_XEN_PCI_PASSTHROUGH=y" >> "$config_target_mak"
> > >        fi
> > > 
> > 
> > This messes up a bit the way xen_nic.o and friends are compiled, I
> > think, because they are common-obj-y but they are only found when
> > compiling in the target subdirectories.  So you end up building
> > x86_64-softmmu/../hw/net/xen_nic.o
> > 
> > If you're unlucky, I believe this can lead to a link failure where a
> > target is building xen_nic.o, while the other tries to link to a
> > partially written object file.
> > 
> > I think the files should be changed from
> > common-obj-$(CONFIG_XEN_BACKEND) to common-obj-$(CONFIG_XEN).
> >
> > The Makefile.objs change ensures that Xen backends are not enabled on
> > targets that support Xen.
> 
> Actually I thought about doing that instead of the configure change. It
> makes sense to me.
> 
> 
> > Then you add to Makefile:
> > 
> >  CONFIG_SOFTMMU := $(if $(filter %-softmmu,$(TARGET_DIRS)),y)
> >  CONFIG_USER_ONLY := $(if $(filter %-user,$(TARGET_DIRS)),y)
> > +CONFIG_XEN := $(CONFIG_XEN_BACKEND)
> >  CONFIG_ALL=y
> >  -include config-all-devices.mak
> >  -include config-all-disas.mak
> > 
> > The Makefile change ensures that they are built before descending in the
> > target-specific directories.
> 
> But I don't understand this. Please correct me if I am wrong, but this
> change looks like it would end up setting CONFIG_XEN every time that
> CONFIG_XEN_BACKEND is set. Without the configure change at the top, it
> would end up setting CONFIG_XEN whenever the host supports Xen, even for
> non-x86 and non-ARM targets. What am I missing?

FYI I made the following changes:

I applied the rest of the series and did

  ./configure --enable-virtfs --enable-xen; make -j5

I got the following error:

  LINK    aarch64-softmmu/qemu-system-aarch64
../hw/9pfs/xen-9p-backend.o: In function `xen_9pfs_alloc':
/local/qemu/hw/9pfs/xen-9p-backend.c:387: undefined reference to `xenstore_write_be_str'
/local/qemu/hw/9pfs/xen-9p-backend.c:388: undefined reference to `xenstore_write_be_int'
../hw/9pfs/xen-9p-backend.o: In function `xen_9pfs_connect':
/local/qemu/hw/9pfs/xen-9p-backend.c:292: undefined reference to `xenstore_read_fe_int'
/local/qemu/hw/9pfs/xen-9p-backend.c:313: undefined reference to `xenstore_read_fe_int'
/local/qemu/hw/9pfs/xen-9p-backend.c:357: undefined reference to `xen_pv_printf'
/local/qemu/hw/9pfs/xen-9p-backend.c:307: undefined reference to `xenstore_read_fe_int'
/local/qemu/hw/9pfs/xen-9p-backend.c:362: undefined reference to `xenstore_read_be_str'
/local/qemu/hw/9pfs/xen-9p-backend.c:363: undefined reference to `xenstore_read_be_str'
/local/qemu/hw/9pfs/xen-9p-backend.c:366: undefined reference to `xenstore_read_fe_str'
/local/qemu/hw/9pfs/xen-9p-backend.c:353: undefined reference to `xen_pv_printf'
../hw/9pfs/xen-9p-backend.o: In function `xen_9pfs_alloc':
/local/qemu/hw/9pfs/xen-9p-backend.c:389: undefined reference to `xenstore_write_be_int'
collect2: error: ld returned 1 exit status
make[1]: *** [qemu-system-arm] Error 1
make: *** [subdir-arm-softmmu] Error 2
../hw/9pfs/xen-9p-backend.o: In function `xen_9pfs_alloc':
/local/qemu/hw/9pfs/xen-9p-backend.c:387: undefined reference to `xenstore_write_be_str'
/local/qemu/hw/9pfs/xen-9p-backend.c:388: undefined reference to `xenstore_write_be_int'
../hw/9pfs/xen-9p-backend.o: In function `xen_9pfs_connect':
/local/qemu/hw/9pfs/xen-9p-backend.c:292: undefined reference to `xenstore_read_fe_int'
/local/qemu/hw/9pfs/xen-9p-backend.c:313: undefined reference to `xenstore_read_fe_int'
/local/qemu/hw/9pfs/xen-9p-backend.c:357: undefined reference to `xen_pv_printf'
/local/qemu/hw/9pfs/xen-9p-backend.c:307: undefined reference to `xenstore_read_fe_int'
/local/qemu/hw/9pfs/xen-9p-backend.c:362: undefined reference to `xenstore_read_be_str'
/local/qemu/hw/9pfs/xen-9p-backend.c:363: undefined reference to `xenstore_read_be_str'
/local/qemu/hw/9pfs/xen-9p-backend.c:366: undefined reference to `xenstore_read_fe_str'
/local/qemu/hw/9pfs/xen-9p-backend.c:353: undefined reference to `xen_pv_printf'
../hw/9pfs/xen-9p-backend.o: In function `xen_9pfs_alloc':
/local/qemu/hw/9pfs/xen-9p-backend.c:389: undefined reference to `xenstore_write_be_int'
collect2: error: ld returned 1 exit status
make[1]: *** [qemu-system-aarch64] Error 1
make: *** [subdir-aarch64-softmmu] Error 2

[v2,1/9] configure: change CONFIG_XEN_BACKEND to be a target property

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