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

From: Justin Stitt <justinstitt@google.com>
To: Arnd Bergmann <arnd@kernel.org>
Cc: linux-kernel@vger.kernel.org,
	Nathan Chancellor <nathan@kernel.org>,
	 Arnd Bergmann <arnd@arndb.de>,
	Dmitry Vyukov <dvyukov@google.com>,
	 Andrey Konovalov <andreyknvl@gmail.com>,
	Nick Desaulniers <ndesaulniers@google.com>,
	 Bill Wendling <morbo@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	kasan-dev@googlegroups.com,  llvm@lists.linux.dev
Subject: Re: [PATCH 4/9] kcov: avoid clang out-of-range warning
Date: Thu, 28 Mar 2024 15:22:16 -0700	[thread overview]
Message-ID: <CAFhGd8qDCMkP6rZ6A6i3b7DuJ0Rzem=V0TxAkvmMTsZM3NH43A@mail.gmail.com> (raw)
In-Reply-To: <20240328143051.1069575-5-arnd@kernel.org>

On Thu, Mar 28, 2024 at 7:31 AM Arnd Bergmann <arnd@kernel.org> wrote:
>
> From: Arnd Bergmann <arnd@arndb.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@arndb.de>

Reviewed-by: Justin Stitt <justinstitt@google.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
>