Re: [Qemu-devel] [PATCH v2] kvm: workaround build break on gcc-7.1.1 / fedora26

[Cornelia Huck <cohuck@redhat.com>]

On Mon, 07 Aug 2017 13:36:44 +0200
Greg Kurz <groug@kaod.org> wrote:

> Building QEMU on fedora26 with the latest gcc package fails:
> 
>   CC      ppc64-softmmu/target/ppc/kvm.o
> In file included from include/sysemu/hw_accel.h:16:0,
>                  from target/ppc/kvm.c:31:
> target/ppc/kvm.c: In function ‘kvmppc_booke_watchdog_enable’:
> include/sysemu/kvm.h:449:35: error: ‘args_tmp[i]’ may be used uninitialized
>  in this function [-Werror=maybe-uninitialized]
>              cap.args[i] = args_tmp[i];                               \
>                                    ^
> target/ppc/kvm.c: In function ‘kvmppc_set_papr’:
> include/sysemu/kvm.h:449:35: error: ‘args_tmp[i]’ may be used uninitialized
>  in this function [-Werror=maybe-uninitialized]
> cc1: all warnings being treated as errors
> 
> $ rpm -q gcc
> gcc-7.1.1-3.fc26.ppc64le
> 
> The compiler should obviously optimize this code away when no extra
> agument is passed to kvm_vm_enable_cap() and kvm_vcpu_enable_cap(),
> but it doesn't. This bug should be fixed one day in gcc, but we can
> also change our code pattern so that we don't hit the issue anymore.
> We workaround this, by using memcpy() instead of open-coding the copy.
> 
> Signed-off-by: Greg Kurz <groug@kaod.org>
> ---
> v2: - use memcpy()
> ---
>  include/sysemu/kvm.h |   14 ++++----------
>  1 file changed, 4 insertions(+), 10 deletions(-)

Acked-by: Cornelia Huck <cohuck@redhat.com>