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

[Thomas Huth]

On 08.05.2018 13:06, Cornelia Huck wrote:
> On Tue, 8 May 2018 12:49:59 +0200
> Thomas Huth <address@hidden> wrote:
> 
>> On 08.05.2018 12:44, Cornelia Huck wrote:
>>> On Tue,  8 May 2018 12:17:52 +0200
>>> Thomas Huth <address@hidden> 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 <address@hidden>
>>>> ---
>>>>  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 <address@hidden>
>>>
>>> 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.

Since the stable releases are normally not built with -Werror, I think
it's ok to not include it there. OTOH it also does not hurt and silences
an annoying warning, and in case somebody tries to build a stable
release with -Werror, it also fixes the build there. So why not, please
add a "Cc: stable" when you pick up the patch.

 Thomas