On 08/21/2015 11:50 AM, Andrzej Hajda wrote:
> Union v4l2_event::u is aligned to 8 bytes on arm32. On arm64 v4l2_event32::u
> is aligned to 4 bytes. As a result structures v4l2_event and v4l2_event32 have
> different sizes and VIDOC_DQEVENT ioctl does not work from arm32 apps running
> on arm64 kernel. The patch fixes it.
>
> Signed-off-by: Andrzej Hajda <a.hajda@xxxxxxxxxxx>
> ---
> Hi Hans,
>
> It seems there is problem with VIDIOC_DQEVENT called from arm32 apps on arm64
> kernel. After tracking down the issue it seems v4l2_event32 on arm64 have
> different field alignment/size than v4l2_event on arm32. The patch fixes it.
> But i guess it can break ABI on other architectures. Simple tests shows:
>
> i386:
> sizeof(struct v4l2_event)=0x78
> offsetof(struct v4l2_event::u)=0x4
>
> amd64:
> sizeof(struct v4l2_event)=0x88
> offsetof(struct v4l2_event::u)=0x8
>
> arm:
> sizeof(struct v4l2_event)=0x80
> offsetof(struct v4l2_event::u)=0x8
>
> arm64:
> sizeof(struct v4l2_event)=0x88
> offsetof(struct v4l2_event::u)=0x8
>
> Any advices how to fix it in arch compatible way?
I noticed a compat_s64 type that knows about the 4-byte alignment on i386.
So I think this can be solved by declaring v4l2_event32 as follows:
struct v4l2_event32 {
__u32 type;
union {
compat_s64 value64;
__u8 data[64];
} u;
__u32 pending;
__u32 sequence;
struct compat_timespec timestamp;
__u32 id;
__u32 reserved[8];
};
I think that this will force the correct alignment. Can you check this?
Good catch BTW.
Looking at v4l2-compat-ioctl32.c I suspect that compat_u/s64 will need to be
used in more places: v4l2_standard32 (replace the id[2] array by compat_u64 id)
and v4l2_ext_control32 are both almost certainly wrong for arm64. I would check
those two.
Regards,
Hans
>
> Regards
> Andrzej
> ---
> drivers/media/v4l2-core/v4l2-compat-ioctl32.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
> index af63543..a4a1856 100644
> --- a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
> +++ b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
> @@ -739,7 +739,7 @@ struct v4l2_event32 {
> __u32 type;
> union {
> __u8 data[64];
> - } u;
> + } u __attribute__((aligned(8)));
> __u32 pending;
> __u32 sequence;
> struct compat_timespec timestamp;
>
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