linux-kernel - Re: [PATCH v2] drivers: lkdtm: fix clang -Wformat warning

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Message-ID: <YtnNlZYZCEVUiuaE@dev-arch.thelio-3990X>
Date:   Thu, 21 Jul 2022 15:05:09 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Justin Stitt <justinstitt@...gle.com>
Cc:     ndesaulniers@...gle.com, arnd@...db.de, gregkh@...uxfoundation.org,
        keescook@...omium.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, trix@...hat.com
Subject: Re: [PATCH v2] drivers: lkdtm: fix clang -Wformat warning

On Thu, Jul 21, 2022 at 02:57:06PM -0700, Justin Stitt wrote:
> When building with Clang we encounter the following warning
> (ARCH=hexagon + CONFIG_FRAME_WARN=0):
> | ../drivers/misc/lkdtm/bugs.c:107:3: error: format specifies type
> | 'unsigned long' but the argument has type 'int' [-Werror,-Wformat]
> |                 REC_STACK_SIZE, recur_count);
> |                 ^~~~~~~~~~~~~~
> 
> Cast REC_STACK_SIZE to `unsigned long` to match format specifier `%lu`
> as well as maintain symmetry with `#define REC_STACK_SIZE
> (_AC(CONFIG_FRAME_WARN, UL) / 2)`.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/378
> Reported-by: Nathan Chancellor <nathan@...nel.org>
> Suggested-by: Nathan Chancellor <nathan@...nel.org>

Personally, I would drop this; my suggestion was the cast, which we are
not going with anymore. Not worth a v3 unless there are other changes
requested.

> Suggested-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>

Reviewed-by: Nathan Chancellor <nathan@...nel.org>
Tested-by: Nathan Chancellor <nathan@...nel.org>

> ---
> Reported by Nathan here:
> https://lore.kernel.org/all/YtmrCJjQrSbv8Aj1@dev-arch.thelio-3990X/
> 
> changes from v1 -> v2:
> * Use implicit division conversion with `/ nUL` instead of verbose
> `(unsigned long)` ~ Thanks Nick
> 
>  drivers/misc/lkdtm/bugs.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c
> index 009239ad1d8a..48821f4c2b21 100644
> --- a/drivers/misc/lkdtm/bugs.c
> +++ b/drivers/misc/lkdtm/bugs.c
> @@ -29,7 +29,7 @@ struct lkdtm_list {
>  #if defined(CONFIG_FRAME_WARN) && (CONFIG_FRAME_WARN > 0)
>  #define REC_STACK_SIZE (_AC(CONFIG_FRAME_WARN, UL) / 2)
>  #else
> -#define REC_STACK_SIZE (THREAD_SIZE / 8)
> +#define REC_STACK_SIZE (THREAD_SIZE / 8UL)
>  #endif
>  #define REC_NUM_DEFAULT ((THREAD_SIZE / REC_STACK_SIZE) * 2)
>  
> -- 
> 2.37.1.359.gd136c6c3e2-goog
> 
>