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

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Date:   Thu, 21 Jul 2022 14:34:52 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Justin Stitt <justinstitt@...gle.com>
Cc:     Kees Cook <keescook@...omium.org>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH] drivers: lkdtm: fix clang -Wformat warning

On Thu, Jul 21, 2022 at 02:20:12PM -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`.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/378
> Reported-by: Nathan Chancellor <nathan@...nel.org>
> Suggested-by: Nathan Chancellor <nathan@...nel.org>
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>

I think this is the right fix, as REC_STACK_SIZE will be 'unsigned long'
when CONFIG_FRAME_WARN is greater than 0 due to the _AC(..., UL) macro,
so the other one should match too. THREAD_SIZE might not be an unsigned
long; I see at least hexagon, microblaze, m68k, powerpc, and sh that
define it as either a regular integer literal with no suffix or
'1 << THREAD_SHIFT', which will both be of type 'int'.

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

> ---
> Reported by Nathan here:
> https://lore.kernel.org/all/YtmrCJjQrSbv8Aj1@dev-arch.thelio-3990X/
> 
>  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..6381255aaecc 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 ((unsigned long)(THREAD_SIZE / 8))
>  #endif
>  #define REC_NUM_DEFAULT ((THREAD_SIZE / REC_STACK_SIZE) * 2)
>  
> -- 
> 2.37.1.359.gd136c6c3e2-goog
>