linux-kernel - Re: [PATCH] net: amd-xgbe: fix clang -Wformat warning

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Message-ID: <CAKwvOdkHb9W1dePaKAuSKv2D0e0uMGLGCZGeakzgD3ZWxf-2iA@mail.gmail.com>
Date:   Tue, 7 Jun 2022 13:44:50 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Justin Stitt <jstitt007@...il.com>
Cc:     Tom Lendacky <thomas.lendacky@....com>, llvm@...ts.linux.dev,
        Nathan Chancellor <nathan@...nel.org>, netdev@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>, pabeni@...hat.com,
        Tom Rix <trix@...hat.com>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: amd-xgbe: fix clang -Wformat warning

On Tue, Jun 7, 2022 at 12:11 PM Justin Stitt <jstitt007@...il.com> wrote:
>
> see warning:
> | drivers/net/ethernet/amd/xgbe/xgbe-drv.c:2787:43: warning: format specifies
> | type 'unsigned short' but the argument has type 'int' [-Wformat]
> |        netdev_dbg(netdev, "Protocol: %#06hx\n", ntohs(eth->h_proto));
> |                                      ~~~~~~     ^~~~~~~~~~~~~~~~~~~
>
> Variadic functions (printf-like) undergo default argument promotion.
> Documentation/core-api/printk-formats.rst specifically recommends
> using the promoted-to-type's format flag.
>
> Also, as per C11 6.3.1.1:
> (https://www.open-std.org/jtc1/sc22/wg14/www/docs/n1548.pdf)
> `If an int can represent all values of the original type ..., the
> value is converted to an int; otherwise, it is converted to an
> unsigned int. These are called the integer promotions.`
>
> Since the argument is a u16 it will get promoted to an int and thus it is
> most accurate to use the %x format specifier here. It should be noted that the
> `#06` formatting sugar does not alter the promotion rules.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/378
> Signed-off-by: Justin Stitt <jstitt007@...il.com>

LGTM; thanks for the patch!
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

Don't forget to cc everyone from ./scripts/get_maintainer.pl!
$ /scripts/get_maintainer.pl
20220607_jstitt007_net_amd_xgbe_fix_clang_wformat_warning.mbx
Tom Lendacky <thomas.lendacky@....com> (supporter:AMD XGBE DRIVER)
"David S. Miller" <davem@...emloft.net> (maintainer:NETWORKING DRIVERS)
Eric Dumazet <edumazet@...gle.com> (maintainer:NETWORKING DRIVERS)
Jakub Kicinski <kuba@...nel.org> (maintainer:NETWORKING DRIVERS)
Paolo Abeni <pabeni@...hat.com> (maintainer:NETWORKING DRIVERS)
Nathan Chancellor <nathan@...nel.org> (supporter:CLANG/LLVM BUILD SUPPORT)
Nick Desaulniers <ndesaulniers@...gle.com> (supporter:CLANG/LLVM BUILD SUPPORT)
Tom Rix <trix@...hat.com> (reviewer:CLANG/LLVM BUILD SUPPORT)
netdev@...r.kernel.org (open list:AMD XGBE DRIVER)
linux-kernel@...r.kernel.org (open list)
llvm@...ts.linux.dev (open list:CLANG/LLVM BUILD SUPPORT)

> ---
>  drivers/net/ethernet/amd/xgbe/xgbe-drv.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/net/ethernet/amd/xgbe/xgbe-drv.c b/drivers/net/ethernet/amd/xgbe/xgbe-drv.c
> index a3593290886f..4d46780fad13 100644
> --- a/drivers/net/ethernet/amd/xgbe/xgbe-drv.c
> +++ b/drivers/net/ethernet/amd/xgbe/xgbe-drv.c
> @@ -2784,7 +2784,7 @@ void xgbe_print_pkt(struct net_device *netdev, struct sk_buff *skb, bool tx_rx)
>
>         netdev_dbg(netdev, "Dst MAC addr: %pM\n", eth->h_dest);
>         netdev_dbg(netdev, "Src MAC addr: %pM\n", eth->h_source);
> -       netdev_dbg(netdev, "Protocol: %#06hx\n", ntohs(eth->h_proto));
> +       netdev_dbg(netdev, "Protocol: %#06x\n", ntohs(eth->h_proto));
>
>         for (i = 0; i < skb->len; i += 32) {
>                 unsigned int len = min(skb->len - i, 32U);
> --
> 2.30.2
>


-- 
Thanks,
~Nick Desaulniers