linux-kernel - Re: [PATCH] peak_usb: fix clang build warning

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Date:   Thu, 7 Mar 2019 08:31:43 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Wolfgang Grandegger <wg@...ndegger.com>,
        Marc Kleine-Budde <mkl@...gutronix.de>,
        "David S. Miller" <davem@...emloft.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        linux-can@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] peak_usb: fix clang build warning

On Thu, Mar 07, 2019 at 11:31:55AM +0100, Arnd Bergmann wrote:
> Clang points out undefined behavior when building the pcan_usb_pro driver:
> 
> drivers/net/can/usb/peak_usb/pcan_usb_pro.c:136:15: error: passing an object that undergoes default argument promotion to 'va_start' has undefined behavior [-Werror,-Wvarargs]
> 
> Changing the function prototype to avoid argument promotion in the
> varargs call avoids the warning, and should make this well-defined.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Link: https://github.com/ClangBuiltLinux/linux/issues/109
Reviewed-by: Nathan Chancellor <natechancellor@...il.com>

I wonder if the format specifier in the pr_err statement at the end of
this function should be updated.

> ---
>  drivers/net/can/usb/peak_usb/pcan_usb_pro.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/can/usb/peak_usb/pcan_usb_pro.c b/drivers/net/can/usb/peak_usb/pcan_usb_pro.c
> index d516def846ab..b388406ac0f5 100644
> --- a/drivers/net/can/usb/peak_usb/pcan_usb_pro.c
> +++ b/drivers/net/can/usb/peak_usb/pcan_usb_pro.c
> @@ -127,7 +127,7 @@ static u8 *pcan_msg_init_empty(struct pcan_usb_pro_msg *pm,
>  /*
>   * add one record to a message being built
>   */
> -static int pcan_msg_add_rec(struct pcan_usb_pro_msg *pm, u8 id, ...)
> +static int pcan_msg_add_rec(struct pcan_usb_pro_msg *pm, int id, ...)
>  {
>  	int len, i;
>  	u8 *pc;
> -- 
> 2.20.0
>