Re: sparse and anonymous unions

[Hans Verkuil <hverkuil@xs4all.nl>]

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
 *
 * 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