linux-kernel - Re: [PATCH] cb710: avoid NULL pointer subtraction

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Date:   Mon, 27 Sep 2021 17:31:56 +0200
From:   Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Pierre Ossman <pierre@...man.eu>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] cb710: avoid NULL pointer subtraction

On Mon, Sep 27, 2021 at 02:13:57PM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> clang-14 complains about an unusual way of converting a pointer to
> an integer:
> 
> drivers/misc/cb710/sgbuf2.c:50:15: error: performing pointer subtraction with a null pointer has undefined behavior [-Werror,-Wnull-pointer-subtraction]
>         return ((ptr - NULL) & 3) != 0;
> 
> Replace this with a normal cast to uintptr_t.
> 
> Fixes: 5f5bac8272be ("mmc: Driver for CB710/720 memory card reader (MMC part)")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/misc/cb710/sgbuf2.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/misc/cb710/sgbuf2.c b/drivers/misc/cb710/sgbuf2.c
> index e5a4ed3701eb..a798fad5f03c 100644
> --- a/drivers/misc/cb710/sgbuf2.c
> +++ b/drivers/misc/cb710/sgbuf2.c
> @@ -47,7 +47,7 @@ static inline bool needs_unaligned_copy(const void *ptr)
>  #ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
>  	return false;
>  #else
> -	return ((ptr - NULL) & 3) != 0;
> +	return ((uintptr_t)ptr & 3) != 0;
>  #endif
>  }
>  

Acked-by: Michał Mirosław <mirq-linux@...e.qmqmq.pl>