Re: [PATCH 2/2] hwmon: (cros_ec) Handle temperature conversion overflows

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] Using `BUILD_BUG()` with runtime variables introduces build fragility because it relies on compiler Value Range Propagation (VRP) to eliminate the branch.
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commit a22cd7f1036247302ddc232e1cbd36ceb641e202
Author: Thomas Weißschuh <linux@weissschuh.net>

hwmon: (cros_ec) Handle temperature conversion overflows

The calculations converting between the different temperature units can
overflow, resulting in incorrect data. Detect these overflows and report them.

> diff --git a/drivers/hwmon/cros_ec_hwmon.c b/drivers/hwmon/cros_ec_hwmon.c
> index 44291799dd8e4..4b402142b46f3 100644
> --- a/drivers/hwmon/cros_ec_hwmon.c
> +++ b/drivers/hwmon/cros_ec_hwmon.c

[ ... ]

> @@ -150,14 +152,28 @@ static bool cros_ec_hwmon_is_error_temp(u8 temp)
>  /* This differs slightly from the variant in units.h to avoid rounding inconsistencies. */
>  #define CROS_EC_HWMON_ABSOLUTE_ZERO_MILLICELSIUS (-273000)

[ ... ]

> -static long cros_ec_hwmon_temp_to_millicelsius(u8 temp)
> +static long __flatten cros_ec_hwmon_temp_to_millicelsius(u8 temp)
>  {
> -	return cros_ec_hwmon_kelvin_to_millicelsius((((long)temp) + EC_TEMP_SENSOR_OFFSET));
> +	long ret;
> +
> +	if (check_add_overflow(temp, EC_TEMP_SENSOR_OFFSET, &ret))
> +		BUILD_BUG();

[Severity: Low]
Does the use of BUILD_BUG() with the runtime variable temp risk spurious build
failures?

Relying on the compiler's Value Range Propagation (VRP) to eliminate the
check_add_overflow() branch can lead to broken builds when compiling with
CONFIG_CC_OPTIMIZE_FOR_DEBUGGING (which uses -Og) or on older toolchains where
VRP fails to eliminate the branch.

> +
> +	if (cros_ec_hwmon_kelvin_to_millicelsius_overflow(ret, &ret))
> +		BUILD_BUG();
> +
> +	return ret;
>  }

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Sashiko AI review · https://sashiko.dev/#/patchset/20260630-cros_ec-hwmon-overflow-v1-0-3d2ecd3eb0f2@weissschuh.net?part=2