linux-kernel - Re: wifi: mt7601u: fix clang -Wformat warning

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Date:   Mon, 18 Jul 2022 11:54:29 +0000 (UTC)
From:   Kalle Valo <kvalo@...nel.org>
To:     Justin Stitt <justinstitt@...gle.com>
Cc:     Jakub Kicinski <kubakici@...pl>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, linux-wireless@...r.kernel.org,
        netdev@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, Justin Stitt <justinstitt@...gle.com>
Subject: Re: wifi: mt7601u: fix clang -Wformat warning

Justin Stitt <justinstitt@...gle.com> wrote:

> When building with Clang we encounter this warning:
> | drivers/net/wireless/mediatek/mt7601u/debugfs.c:92:6: error: format
> | specifies type 'unsigned char' but the argument has type 'int'
> | [-Werror,-Wformat] dev->ee->reg.start + dev->ee->reg.num - 1);
> 
> The format specifier used is `%hhu` which describes a u8. Both
> `dev->ee->reg.start` and `.num` are u8 as well. However, the expression
> as a whole is promoted to an int as you cannot get smaller-than-int from
> addition. Therefore, to fix the warning, use the promoted-to-type's
> format specifier -- in this case `%d`.
> 
> example:
> ```
> uint8_t a = 4, b = 7;
> int size = sizeof(a + b - 1);
> printf("%d\n", size);
> // output: 4
> ```
> 
> See more:
> (https://wiki.sei.cmu.edu/confluence/display/c/INT02-C.+Understand+integer+conversion+rules)
> "Integer types smaller than int are promoted when an operation is
> performed on them. If all values of the original type can be represented
> as an int, the value of the smaller type is converted to an int;
> otherwise, it is converted to an unsigned int."
> 
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>
> Acked-by: Jakub Kicinski <kubakici@...pl>

Patch applied to wireless-next.git, thanks.

68204a696505 wifi: mt7601u: fix clang -Wformat warning

-- 
https://patchwork.kernel.org/project/linux-wireless/patch/20220711212932.1501592-1-justinstitt@google.com/

https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches