Re: [Qemu-devel] [qemu-s390x] [PATCH 12/14] hw/s390/css: avoid taking address members in packed structs

[Halil Pasic <pasic@linux.ibm.com>]

On Fri, 29 Mar 2019 11:11:02 +0000
Daniel P. Berrangé <berrange@redhat.com> wrote:

> The GCC 9 compiler complains about many places in s390 code
> that take the address of members of the 'struct SCHIB' which
> is marked packed:
> 
> hw/s390x/css.c: In function ‘sch_handle_clear_func’:
> hw/s390x/css.c:698:15: warning: taking address of packed member of ‘struct SCHIB’ may result in an unaligned pointer val\
> ue [-Waddress-of-packed-member]
>   698 |     PMCW *p = &sch->curr_status.pmcw;
>       |               ^~~~~~~~~~~~~~~~~~~~~~
> hw/s390x/css.c:699:15: warning: taking address of packed member of ‘struct SCHIB’ may result in an unaligned pointer val\
> ue [-Waddress-of-packed-member]
>   699 |     SCSW *s = &sch->curr_status.scsw;
>       |               ^~~~~~~~~~~~~~~~~~~~~~
> 
> ...snip many more...
> 
> Almost all of these are just done for convenience to avoid
> typing out long variable/field names when referencing struct
> members. We can get most of this convenience by taking the
> address of the 'struct SCHIB' instead, avoiding triggering
> the compiler warnings.
> 
> In a couple of places we copy via a local variable which is
> a technique already applied elsewhere in s390 code for this
> problem.
> 
> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

Reviewed-by: Halil Pasic <pasic@linux.ibm.com>

Thanks!