[PATCH] DRM: 64-bit warning in compilation: wrong param size in DRM or harmless?

From: Blaisorblade (blaisorblade_at_yahoo.it)
Date: 10/30/05

  • Next message: Pavel Machek: "Re: [patch 2/5] Core HW RNG support" 
    To: LKML <linux-kernel@vger.kernel.org>
Date:	Sun, 30 Oct 2005 13:53:02 +0100

    I got a warning and while going to fix it, I discovered some issues with the
    code (including raciness).

    While compiling 2.6.14 for x86_64, I got:

      CC [M] drivers/char/drm/drm_bufs.o
    /home/paolo/Admin/kernel/6/VCS/linux-2.6.14/drivers/char/drm/drm_bufs.c: In
    function `drm_addmap_ioctl':
    /home/paolo/Admin/kernel/6/VCS/linux-2.6.14/drivers/char/drm/drm_bufs.c:309:
    warning: cast to pointer from integer of different size
    /home/paolo/Admin/kernel/6/VCS/linux-2.6.14/drivers/char/drm/drm_bufs.c:309:
    warning: cast to pointer from integer of different size
    /home/paolo/Admin/kernel/6/VCS/linux-2.6.14/drivers/char/drm/drm_bufs.c:309:
    warning: cast to pointer from integer of different size
    /home/paolo/Admin/kernel/6/VCS/linux-2.6.14/drivers/char/drm/drm_bufs.c:309:
    warning: cast to pointer from integer of different size

    All these warnings are generated by:
            if (put_user(maplist->user_token, &argp->handle))
                    return -EFAULT;

    Given the decls:
           drm_map_list_t *maplist;
           drm_map_t __user *argp = (void __user *)arg;

    typedef struct drm_map {
    ...
            void *handle;
            /**< User-space: "Handle" to pass to mmap()*/
            /**< Kernel-space: kernel-virtual address */
    ...
    } drm_map_t;

    maplist->user_token is an unsigned int, instead.

    It seems that even if handle is overloaded, the two roles are totally
    different and never interchanged, but I'm unsure.

    In this case, the warning is totally harmless, so the attached patch avoids
    the warning and fixes everything (compile-tested).

    BUT:

    * If we _ever_ have more drm_device_t, the call to HandleId() would be racy.
    Right? 

    -- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade

            

            
                    
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