[Spice-devel] [PATCH] server/red_dispatcher: fix memset params

[Christophe Fergeau]

Hey Uri,

Good catch! How did you find it? valgrind? static analysis? Code
review?

On Tue, Aug 02, 2011 at 11:05:11AM +0300, Uri Lublin wrote:
>      update_client_mouse_allowed();
> -    memset(&dispatcher->surface_create, sizeof(QXLDevSurfaceCreate), 0);
> +    memset(&dispatcher->surface_create, 0, sizeof(QXLDevSurfaceCreate));

It's interesting that the problematic structure is QXLDevSurfaceCreate
because valgrind had issues with it in test_display_streaming too (patch
coming). However, what is interesting is that the QXLDevSurfaceCreate has
4 bytes of padding adding by the compiler on x86_64:

struct QXLDevSurfaceCreate {
        uint32_t                   width;                /*     0     4 */
        uint32_t                   height;               /*     4     4 */
        int32_t                    stride;               /*     8     4 */
        uint32_t                   format;               /*    12     4 */
        uint32_t                   position;             /*    16     4 */
        uint32_t                   mouse_mode;           /*    20     4 */
        uint32_t                   flags;                /*    24     4 */
        uint32_t                   type;                 /*    28     4 */
        uint64_t                   mem;                  /*    32     8 */
        uint32_t                   group_id;             /*    40     4 */

        /* size: 48, cachelines: 1, members: 10 */
        /* padding: 4 */
        /* last cacheline: 48 bytes */
};

As far as I understand, the whole structure is sent on the wire
(for example send_data(dispatcher->channel, surface,
sizeof(QXLDevSurfaceCreate)); in
RedDispatcher::handle_dev_create_primary_surface ), which these 4 bytes
part of the protocol. So I was wondering if we should document somewhere
these 4 bytes of padding? I also haven't checked what size this structure
gets on x86.

Christophe


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