[PATCH] tomoyo: fix clang pointer arithmetic warning

[Arnd Bergmann]

On Wed, Oct 28, 2020 at 2:22 PM Tetsuo Handa
<penguin-kernel at i-love.sakura.ne.jp> wrote:
>
> Thank you for a patch. I have two questions.
>
> On 2020/10/27 6:52, Arnd Bergmann wrote:
> > From: Arnd Bergmann <arnd at arndb.de>
> >
> > clang warns about additions on NULL pointers being undefined in C:
> >
> > security/tomoyo/securityfs_if.c:226:59: warning: arithmetic on a null pointer treated as a cast from integer to pointer is a GNU extension [-Wnull-pointer-arithmetic]
> >         securityfs_create_file(name, mode, parent, ((u8 *) NULL) + key,
> >
> > Change the code to instead use a cast through uintptr_t to avoid
> > the warning.
> >
>
> > -     securityfs_create_file(name, mode, parent, ((u8 *) NULL) + key,
> > +     securityfs_create_file(name, mode, parent, (u8 *)(uintptr_t)key,
> >                              &tomoyo_operations);
>
> (1) Does clang warn if "(void *)key" is used instead of "(u8 *)(uintptr_t)key" ?

Yes, both clang and gcc warn when you cast between a pointer and
an integer of a different size.

> (2) tomoyo_open() has
>
>         const int key = ((u8 *) file_inode(file)->i_private) - ((u8 *) NULL);
>
>     which decodes the "u8 key" passed to tomoyo_create_entry(). For symmetry,
>     I'd like to remove NULL from tomoyo_open() as well. Does clang warn if
>
>         const int key = (u8) (file_inode(file)->i_private);
>
>     is used?

Yes, same thing, but

   const int key = (uintptr_t)file_inode(file)->i_private;

works without warnings and seems clearer.

       Arnd