Re: sparse and anonymous unions

[Hans Verkuil <hverkuil@xs4all.nl>]

On 03/31/2014 09:51 AM, Hans Verkuil wrote:
> On 03/15/2014 11:26 AM, Hans Verkuil wrote:
>> Hi!
>>
>> I'm trying to cut down the list of sparse warnings and errors I get when
>> compiling drivers/media. Most of them are obviously our problem, but there
>> is one that seems to be a sparse bug:
>>
>> drivers/media/v4l2-core/v4l2-dv-timings.c:30:9: error: unknown field name in initializer
>>
>> This uses the v4l2_dv_timings type which is defined here:
>>
>> include/uapi/linux/videodev2.h
>>
>> and which has an anonymous union:
>>
>> struct v4l2_dv_timings {
>>         __u32 type;
>>         union {
>>                 struct v4l2_bt_timings  bt;
>>                 __u32   reserved[32];
>>         };
>> } __attribute__ ((packed));
>>
>> The macro used in the source above comes from this header:
>>
>> include/uapi/linux/v4l2-dv-timings.h
>>
>> and is defined as follows:
>>
>> #if __GNUC__ < 4 || (__GNUC__ == 4 && (__GNUC_MINOR__ < 6))
>> /* Sadly gcc versions older than 4.6 have a bug in how they initialize
>>    anonymous unions where they require additional curly brackets.
>>    This violates the C1x standard. This workaround adds the curly brackets
>>    if needed. */
>> #define V4L2_INIT_BT_TIMINGS(_width, args...) \
>>         { .bt = { _width , ## args } }
>> #else
>> #define V4L2_INIT_BT_TIMINGS(_width, args...) \
>>         .bt = { _width , ## args }
>> #endif
>>
>> /* CEA-861-E timings (i.e. standard HDTV timings) */
>>         
>> #define V4L2_DV_BT_CEA_640X480P59_94 { \
>>         .type = V4L2_DV_BT_656_1120, \
>>         V4L2_INIT_BT_TIMINGS(640, 480, 0, 0, \
>>                 25175000, 16, 96, 48, 10, 2, 33, 0, 0, 0, \
>>                 V4L2_DV_BT_STD_DMT | V4L2_DV_BT_STD_CEA861, 0) \
>> }
>>
>> The problem is that it seems that sparse follows the old pre-4.6 rules for
>> initializing anonymous unions instead of what is actually in the C standard.
>>
>> If I add ' || defined(__CHECKER__)' to the #if above it will pass without
>> generating sparse errors.
>>
>> Is this something that can be fixed in sparse, or am I forced to add the
>> 'defined(__CHECKER__)' to the #if condition?
> 
> Here is a simple test case for this problem:
> 
> ====== anon-union.c ======
> struct s {
>         union {
>                 int val;
>         };
> };
> 
> static struct s foo = { .val = 5, };
> /*
>  * check-name: duplicate extern array

Oops: that should be:

check-name: test anonymous union initializer

>  *
>  * check-error-start
>  * check-error-end
>  */
> ====== anon-union.c ======
> 
> Running sparse gives:
> 
> anon-union.c:7:26: error: unknown field name in initializer
> 
> Regards,
> 
> 	Hans
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