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

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Date:   Thu, 7 Mar 2019 16:38:53 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Nathan Chancellor <natechancellor@...il.com>
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, Networking <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] peak_usb: fix clang build warning

On Thu, Mar 7, 2019 at 4:31 PM Nathan Chancellor
<natechancellor@...il.com> wrote:
>
> 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>

Thanks!

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

I think it's still ok as it is.

      Arnd