Re: [Qemu-devel] [PATCH] pc-bios/s390-ccw: struct tpi_info must be declared as aligned(4)

[Cornelia Huck <cohuck@redhat.com>]

On Tue, 8 May 2018 12:49:59 +0200
Thomas Huth <thuth@redhat.com> wrote:

> On 08.05.2018 12:44, Cornelia Huck wrote:
> > On Tue,  8 May 2018 12:17:52 +0200
> > Thomas Huth <thuth@redhat.com> wrote:
> >   
> >> I've run into a compilation error today with the current version of GCC 8:
> >>
> >> In file included from s390-ccw.h:49,
> >>                  from main.c:12:
> >> cio.h:128:1: error: alignment 1 of 'struct tpi_info' is less than 4 [-Werror=packed-not-aligned]
> >>  } __attribute__ ((packed));
> >>  ^
> >> cc1: all warnings being treated as errors
> >>
> >> Since the struct tpi_info contains an element ("struct subchannel_id schid")
> >> which is marked as aligned(4), we've got to mark the struct tpi_info as
> >> aligned(4), too.
> >>
> >> Signed-off-by: Thomas Huth <thuth@redhat.com>
> >> ---
> >>  pc-bios/s390-ccw/cio.h | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/pc-bios/s390-ccw/cio.h b/pc-bios/s390-ccw/cio.h
> >> index 55eaeee..1a0795f 100644
> >> --- a/pc-bios/s390-ccw/cio.h
> >> +++ b/pc-bios/s390-ccw/cio.h
> >> @@ -125,7 +125,7 @@ struct tpi_info {
> >>      __u32 reserved3  : 12;
> >>      __u32 int_type   : 3;
> >>      __u32 reserved4  : 12;
> >> -} __attribute__ ((packed));
> >> +} __attribute__ ((packed, aligned(4)));
> >>  
> >>  /* channel command word (type 1) */
> >>  struct ccw1 {  
> > 
> > Reviewed-by: Cornelia Huck <cohuck@redhat.com>
> > 
> > Alternatively, we could also ditch this struct and the tpi function...
> > but I have not given up hope yet that we might someday handle channel
> > I/O more canonically in the bios :)  
> 
> Yes, it's currently unused (so I think you could also pick up the patch
> directly, without the need for recompiling the s390-ccw.img just because
> of this) ... I don't mind too much if we fix it or remove it, but since
> you've said that it might be useful in the future again, I think we can
> simply keep it for now.

Related question: Should this be cc:stable (without a rebuild)? The
same logic as for the just-merged e500 patch probably applies.