linux-kernel - Re: [PATCH 4/9] kcov: avoid clang out-of-range warning

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Message-ID: <CAFhGd8qDCMkP6rZ6A6i3b7DuJ0Rzem=V0TxAkvmMTsZM3NH43A@mail.gmail.com>
Date: Thu, 28 Mar 2024 15:22:16 -0700
From: Justin Stitt <justinstitt@...gle.com>
To: Arnd Bergmann <arnd@...nel.org>
Cc: linux-kernel@...r.kernel.org, Nathan Chancellor <nathan@...nel.org>, 
	Arnd Bergmann <arnd@...db.de>, Dmitry Vyukov <dvyukov@...gle.com>, 
	Andrey Konovalov <andreyknvl@...il.com>, Nick Desaulniers <ndesaulniers@...gle.com>, 
	Bill Wendling <morbo@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>, kasan-dev@...glegroups.com, 
	llvm@...ts.linux.dev
Subject: Re: [PATCH 4/9] kcov: avoid clang out-of-range warning

On Thu, Mar 28, 2024 at 7:31 AM Arnd Bergmann <arnd@...nel.org> wrote:
>
> From: Arnd Bergmann <arnd@...db.de>
>
> The area_size is never larger than the maximum on 64-bit architectutes:
>
> kernel/kcov.c:634:29: error: result of comparison of constant 1152921504606846975 with expression of type '__u32' (aka 'unsigned int') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
>                 if (remote_arg->area_size > LONG_MAX / sizeof(unsigned long))
>                     ~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> The compiler can correctly optimize the check away and the code appears
> correct to me, so just add a cast to avoid the warning.
>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Reviewed-by: Justin Stitt <justinstitt@...gle.com>

> ---
>  kernel/kcov.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/kcov.c b/kernel/kcov.c
> index f9ac2e9e460f..c3124f6d5536 100644
> --- a/kernel/kcov.c
> +++ b/kernel/kcov.c
> @@ -627,7 +627,8 @@ static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
>                 mode = kcov_get_mode(remote_arg->trace_mode);
>                 if (mode < 0)
>                         return mode;
> -               if (remote_arg->area_size > LONG_MAX / sizeof(unsigned long))
> +               if ((unsigned long)remote_arg->area_size >
> +                   LONG_MAX / sizeof(unsigned long))
>                         return -EINVAL;
>                 kcov->mode = mode;
>                 t->kcov = kcov;
> --
> 2.39.2
>