Re: [PATCH v2 2/2] net: macb: fix format-truncation warning

[Andrew Lunn]

On Tue, Feb 17, 2026 at 01:49:50AM +0800, Sean Chang wrote:
> Use a precision specifier in snprintf to ensure the generated
> string fits within the ETH_GSTRING_LEN (32 bytes) buffer.
> 
> Signed-off-by: Sean Chang <seanwascoding@xxxxxxxxx>
> ---
> v2:
> - Split the original treewide patch into subsystem-specific commits.
> - Added more detailed commit descriptions to satisfy checkpatch.
> 
>  drivers/net/ethernet/cadence/macb_main.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
> index 43cd013bb70e..26f9ccadd9f6 100644
> --- a/drivers/net/ethernet/cadence/macb_main.c
> +++ b/drivers/net/ethernet/cadence/macb_main.c
> @@ -3159,8 +3159,8 @@ static void gem_get_ethtool_strings(struct net_device *dev, u32 sset, u8 *p)
>  
>  		for (q = 0, queue = bp->queues; q < bp->num_queues; ++q, ++queue) {
>  			for (i = 0; i < QUEUE_STATS_LEN; i++, p += ETH_GSTRING_LEN) {
> -				snprintf(stat_string, ETH_GSTRING_LEN, "q%d_%s",
> -						q, queue_statistics[i].stat_string);
> +				snprintf(stat_string, ETH_GSTRING_LEN, "q%u_%.19s",
> +					 q, queue_statistics[i].stat_string);

These strings are special, in that they are fixed length, 32 bytes
long, and not \0 terminated. There are some helpers at the end of
linux/ethtool.h for dealing with these strings. You might want to use
them.

>  				memcpy(p, stat_string, ETH_GSTRING_LEN);

Also, it looks like stat_string might be one byte too
short. snprintf() will \0 terminate, so you need it big enough to hold
the \0, and then this memcpy() will discard it.

I also wounder, why is just one architecture complaining about this?

    Andrew