Re: sparse: ARRAY_SIZE and sparse array initialization

[Hans Verkuil <hverkuil@xs4all.nl>]

For the record: all these tests were done with a 3.14-rc5 kernel and sparse
compiled from the git tree as of today (version v0.5.0). The gcc version is 4.8.2.

Regards,

	Hans

On 03/15/2014 01:09 PM, Hans Verkuil wrote:
> Hmm, interesting. Twice 'sparse' in the same subject line with different meanings :-)
> 
> This is another sparse error I get with drivers/media/v4l2-core/v4l2-ioctl.c:
> 
> drivers/media/v4l2-core/v4l2-ioctl.c:424:9: error: cannot size expression
> 
> (there are more of those in drivers/media, all with the same cause).
> 
> This sparse (the tool) error occurs because of sparse (C language) array initialization
> in combination with ARRAY_SIZE:
> 
> static const char *v4l2_memory_names[] = {
>         [V4L2_MEMORY_MMAP]    = "mmap",
>         [V4L2_MEMORY_USERPTR] = "userptr",
>         [V4L2_MEMORY_OVERLAY] = "overlay",
>         [V4L2_MEMORY_DMABUF] = "dmabuf",
> };
> 
> #define prt_names(a, arr) (((unsigned)(a)) < ARRAY_SIZE(arr) ? arr[a] : "unknown")
> 
> static void v4l_print_requestbuffers(const void *arg, bool write_only)
> {
>         const struct v4l2_requestbuffers *p = arg;
> 
>         pr_cont("count=%d, type=%s, memory=%s\n",
>                 p->count,
>                 prt_names(p->type, v4l2_type_names),
>                 prt_names(p->memory, v4l2_memory_names));
> }
> 
> I could change v4l2_memory_names to:
> 
> static const char *v4l2_memory_names[V4L2_MEMORY_DMABUF + 1] = {
> 
> and the error goes away.
> 
> I'm actually not sure if this is a sparse bug or a feature.
> 
> If it is a feature then the error message is definitely wrong, since the size is
> perfectly well defined. As an aside: the error message is pretty vague IMHO.
> 
> Regards,
> 
> 	Hans
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