Re: [Qemu-devel] [PATCH v2 1/9] configure: change CONFIG_XEN_BACKEND to be a target property

[Stefano Stabellini <sstabellini@kernel.org>]

On Wed, 15 Mar 2017, Paolo Bonzini wrote:
> On 14/03/2017 21:23, Stefano Stabellini wrote:
> > On Tue, 14 Mar 2017, Stefano Stabellini wrote:
> >>> Then you add to Makefile:
> >>>
> >>>  CONFIG_SOFTMMU := $(if $(filter %-softmmu,$(TARGET_DIRS)),y)
> >>>  CONFIG_USER_ONLY := $(if $(filter %-user,$(TARGET_DIRS)),y)
> >>> +CONFIG_XEN := $(CONFIG_XEN_BACKEND)
> >>>  CONFIG_ALL=y
> >>>  -include config-all-devices.mak
> >>>  -include config-all-disas.mak
> >>>
> >>> The Makefile change ensures that they are built before descending in the
> >>> target-specific directories.
> >>
> >> But I don't understand this. Please correct me if I am wrong, but this
> >> change looks like it would end up setting CONFIG_XEN every time that
> >> CONFIG_XEN_BACKEND is set. Without the configure change at the top, it
> >> would end up setting CONFIG_XEN whenever the host supports Xen, even for
> >> non-x86 and non-ARM targets. What am I missing?
> 
> This CONFIG_XEN assignment applies to the toplevel only, i.e. to files
> that are built once.  Targets will still take CONFIG_XEN from
> config-target.mak, and it will not be set for non-x86/non-ARM targets.
> This CONFIG_XEN assignment applies to files that are compiled once.
> 
> The issue you reported here:
> 
> >   LINK    aarch64-softmmu/qemu-system-aarch64
> > ../hw/9pfs/xen-9p-backend.o: In function `xen_9pfs_alloc':
> > /local/qemu/hw/9pfs/xen-9p-backend.c:387: undefined reference to `xenstore_write_be_str'
> > /local/qemu/hw/9pfs/xen-9p-backend.c:388: undefined reference to `xenstore_write_be_int'
> 
> is because you need this in patch 9:
> 
> -common-obj-$(CONFIG_XEN_BACKEND) += xen-9p-backend.o
> +common-obj-$(CONFIG_XEN) += xen-9p-backend.o
> 

/me shakes his head in shame.
Thank you for the explanation!