Thank you for a patch. I have two questions.

On 2020/10/27 6:52, Arnd Bergmann wrote:

From: Arnd Bergmann <arnd@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" ?

(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?