address remaining -Wtautological-constant-out-of-range-compare

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

Posted by Arnd Bergmann 1 year, 10 months ago

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>
---
 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

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

Posted by Justin Stitt 1 year, 10 months ago

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
>