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From: Eric Blake <eblake@redhat.com>
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Date: Thu, 15 Nov 2018 16:43:02 -0600
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Subject: Re: [Qemu-devel] [PATCH] qapi: Reduce Makefile boilerplate
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Cc: qemu-trivial@nongnu.org, armbru@redhat.com, xiezhide@huawei.com, Paolo Bonzini <pbonzini@redhat.com>

On 11/15/18 4:37 PM, Eric Blake wrote:
> I'm trying to do the same thing to Makefile.objs, but when I use:
>=20
> common-obj-y +=3D $(QAPI_MODULES:%=3Dqapi/qapi-commands-%.o)
>=20
> or the longer $(patsubst %,qapi,qapi-commands-%.o,$(QAPI_MODULES))
>=20
> both before and after the change, 'make print-common-obj-y | grep qapi'=
=20
> returns identical content, but after the change, the linker fails with:
>=20

>=20
> So something about variable expansions is NOT playing nicely with our
>=20
> dummy :=3D $(call unnest-vars,, \
>  =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0 stub-obj-y \
>  =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0 chardev-obj-y \
> ...
>  =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0 common-obj-y \

Aha - the problem is that $(QAPI_MODULES) is empty at the time=20
unnest-vars tries to slurp in Makefile.objs, while it was non-empty at=20
the time that Makefile directly includes it. Moving the definition of=20
QAPI_MODULES into Makefile.objs solves that. v2 coming up.

--=20
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org