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

[Thomas Huth <thuth@redhat.com>]

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.

 Thomas