Re: [PATCH v1 1/1] thermal: sysfs: switch to use scnprintf() to suppress truncation warning

[David Laight <david.laight.linux@gmail.com>]

On Mon, 17 Aug 2026 12:33:24 +0200
Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote:

> Switch the sysfs code to use scnprintf() to avoid warnings about potential
> truncation of the names of the sysfs attributes.

It has to be a 'bug' that 'format overflow' warnings are generated for
snprintf() but not for scnprintf().
They really shouldn't behave differently.

I did some tests a while back and the warning goes away if you do
'some things' with the result (like comparing against the buffer size),
but even explicitly ignoring it with a (void) cast isn't enough.

Using OPTIMIZER_HIDE_VAR() (or an _VAL variant) on the buffer size does
stop the error, but I expect gcc to start checking sizeof(buf) as well.
So both arguments might need hiding to get the warning ignored.

David

> We can't increase the buffer
> size because the size is the part of an ABI for some reason. Note, with
> the current size of buffer the affected attributes have a room for up to
> 1000 names, which ought to be enough for all cases. There is no functional
> change, as the same limitation was implied before.
> 
> Fixes: c56f5c0342df ("Thermal: Make Thermal trip points writeable")
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> ---
>  drivers/thermal/thermal_sysfs.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/thermal/thermal_sysfs.c b/drivers/thermal/thermal_sysfs.c
> index b44abfc997ed..44bd7c50e4ac 100644
> --- a/drivers/thermal/thermal_sysfs.c
> +++ b/drivers/thermal/thermal_sysfs.c
> @@ -400,8 +400,8 @@ static int create_trip_attrs(struct thermal_zone_device *tz)
>  		struct thermal_trip_attrs *trip_attrs = &td->trip_attrs;
>  
>  		/* create trip type attribute */
> -		snprintf(trip_attrs->type.name, THERMAL_NAME_LENGTH,
> -			 "trip_point_%d_type", i);
> +		scnprintf(trip_attrs->type.name, sizeof(trip_attrs->type.name),
> +			  "trip_point_%d_type", i);
>  
>  		sysfs_attr_init(&trip_attrs->type.attr.attr);
>  		trip_attrs->type.attr.attr.name = trip_attrs->type.name;
> @@ -410,8 +410,8 @@ static int create_trip_attrs(struct thermal_zone_device *tz)
>  		attrs[i] = &trip_attrs->type.attr.attr;
>  
>  		/* create trip temp attribute */
> -		snprintf(trip_attrs->temp.name, THERMAL_NAME_LENGTH,
> -			 "trip_point_%d_temp", i);
> +		scnprintf(trip_attrs->temp.name, sizeof(trip_attrs->temp.name),
> +			  "trip_point_%d_temp", i);
>  
>  		sysfs_attr_init(&trip_attrs->temp.attr.attr);
>  		trip_attrs->temp.attr.attr.name = trip_attrs->temp.name;
> @@ -423,8 +423,8 @@ static int create_trip_attrs(struct thermal_zone_device *tz)
>  		}
>  		attrs[i + tz->num_trips] = &trip_attrs->temp.attr.attr;
>  
> -		snprintf(trip_attrs->hyst.name, THERMAL_NAME_LENGTH,
> -			 "trip_point_%d_hyst", i);
> +		scnprintf(trip_attrs->hyst.name, sizeof(trip_attrs->hyst.name),
> +			  "trip_point_%d_hyst", i);
>  
>  		sysfs_attr_init(&trip_attrs->hyst.attr.attr);
>  		trip_attrs->hyst.attr.attr.name = trip_attrs->hyst.name;