Re: [PATCH] drm/xe/hwmon: Restrict LONG_MAX overflow check to 32-bit builds

[Jani Nikula <jani.nikula@linux.intel.com>]

On Fri, 23 Oct 2026, Mallesh Koujalagi <mallesh.koujalagi@intel.com> wrote:
> The temperature decoding code stores the intermediate result in an
> s64 and checks it against LONG_MAX before assigning it to a long.
>
> This check is only needed on 32-bit architectures, where long is
> narrower than s64. On 64-bit systems, long and s64 are both 64 bits,
> so the condition can never be true.
>
> Wrap the check with BITS_PER_LONG == 32 so it is only compiled where
> it is needed, preserving the existing overflow protection on 32-bit
> architectures while eliminating the dead branch on 64-bit builds.

Why would it matter? Why make the code harder to read with the inline
#ifdef?

>
> Fixes: 24ec15d64617 ("drm/xe/hwmon: Decode CRI temperature registers as IEEE-754")
> Signed-off-by: Mallesh Koujalagi <mallesh.koujalagi@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_hwmon.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/xe/xe_hwmon.c b/drivers/gpu/drm/xe/xe_hwmon.c
> index 42acfeb8818c..2ee51921acf5 100644
> --- a/drivers/gpu/drm/xe/xe_hwmon.c
> +++ b/drivers/gpu/drm/xe/xe_hwmon.c
> @@ -1322,9 +1322,14 @@ static int xe_hwmon_temperature_decode(u32 reg_val, long *temperature)
>  		value = 0;
>  	}
>  
> -	/* Ensure the magnitude fits in long, which is 32-bit on some arches. */
> +#if BITS_PER_LONG == 32
> +	/*
> +	 * On 32-bit systems, long is smaller than s64, so the value may
> +	 * still overflow long even if it fits in s64.
> +	 */
>  	if (value > LONG_MAX)
>  		return -ERANGE;
> +#endif
>  
>  	if (reg_val & IEEE754_SIGN)
>  		value = -value;

-- 
Jani Nikula, Intel