On Mon, Oct 26, 2020 at 10:52:56PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
>
> Clang points out that adding something to NULL is notallowed
> in standard C:
>
> fs/kernfs/file.c:127:15: warning: performing pointer arithmetic on a
> null pointer has undefined behavior [-Wnull-pointer-arithmetic]
> return NULL + !*ppos;
> ~~~~ ^
> fs/seq_file.c:529:14: warning: performing pointer arithmetic on a
> null pointer has undefined behavior [-Wnull-pointer-arithmetic]
> return NULL + (*pos == 0);
>
> Rephrase the function to do the same thing without triggering that
> warning. Linux already relies on a specific binary representation
> of NULL, so it makes no real difference here. The instance in
> kernfs was copied from single_start, so fix both at once.
>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Fixes: c2b19daf6760 ("sysfs, kernfs: prepare read path for kernfs")
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
Reviewed-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
> ---
> fs/kernfs/file.c | 2 +-
> fs/seq_file.c | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
> index f277d023ebcd..b55e6ef4d677 100644
> --- a/fs/kernfs/file.c
> +++ b/fs/kernfs/file.c
> @@ -124,7 +124,7 @@ static void *kernfs_seq_start(struct seq_file *sf, loff_t *ppos)
> * The same behavior and code as single_open(). Returns
> * !NULL if pos is at the beginning; otherwise, NULL.
> */
> - return NULL + !*ppos;
> + return (void *)(uintptr_t)!*ppos;
> }
> }
>
> diff --git a/fs/seq_file.c b/fs/seq_file.c
> index 31219c1db17d..d456468eb934 100644
> --- a/fs/seq_file.c
> +++ b/fs/seq_file.c
> @@ -526,7 +526,7 @@ EXPORT_SYMBOL(seq_dentry);
>
> static void *single_start(struct seq_file *p, loff_t *pos)
> {
> - return NULL + (*pos == 0);
> + return (void *)(uintptr_t)(*pos == 0);
> }
>
> static void *single_next(struct seq_file *p, void *v, loff_t *pos)
> --
> 2.27.0
>
