Re: [PATCH bpf-next 2/2] bpf: Avoid redundant min()/max() in cnum signed bounds

[Shung-Hsi Yu <shung-hsi.yu@suse.com>]

On Tue, Jul 28, 2026 at 01:57:18AM +0000, Vinicius Sampaio wrote:
> This patch simplifies the smin() and smax() calculation by removing the
> integer min and max calculation on the non-overflowing branch. This is a
> valid simplification because when the arc does not cross the signed
> ST_MAX/ST_MIN boundary, the signed order of the endpoints is preserved,
> so base is the signed minimum and base + size is the signed maximum.
> Therefore, the min()/max() calls are redundant.
[...]
> --- a/kernel/bpf/cnum_defs.h
> +++ b/kernel/bpf/cnum_defs.h
> @@ -44,6 +44,9 @@ static inline bool FN(urange_overflow)(struct cnum_t cnum)
>   * cnum{T}_umin / cnum{T}_umax query an unsigned range represented by this cnum.
>   * If cnum represents a range crossing the UT_MAX/0 boundary, the unbound range
>   * [0..UT_MAX] is returned.
> + *
> + * The empty cnum doesn't produce any meaningful value, so you should avoid
> + * calling cnum{T}_umin / cnum{T}_umax with it.
>   */
>  ut FN(umin)(struct cnum_t cnum)
>  {
> @@ -67,19 +70,18 @@ static inline bool FN(srange_overflow)(struct cnum_t cnum)
>   * cnum{T}_smin / cnum{T}_smax query a signed range represented by this cnum.
>   * If cnum represents a range crossing the ST_MAX/ST_MIN boundary, the unbound range
>   * [ST_MIN..ST_MAX] is returned.
> + *
> + * The empty cnum doesn't produce any meaningful value, so you should avoid
> + * calling cnum{T}_smin / cnum{T}_smax with it.

Nit: if we are adding these it would perhaps be helpful to add similar
comment to {u,s}range_overflow as well. AFAICT
{u,s}{min,max,range_overflow} should be the only cnum function that is
not expected to take on an empty cnum.

Thought I'd prefer something along the lines of

  caller should ensure !is_empty(cnum) holds when calling

>   */
>  st FN(smin)(struct cnum_t cnum)
>  {
> -	return FN(srange_overflow)(cnum)
> -	       ? ST_MIN
> -	       : min((st)cnum.base, (st)(cnum.base + cnum.size));
> +	return FN(srange_overflow)(cnum) ? ST_MIN : (st)cnum.base;
>  }
>  
>  st FN(smax)(struct cnum_t cnum)
>  {
> -	return FN(srange_overflow)(cnum)
> -	       ? ST_MAX
> -	       : max((st)cnum.base, (st)(cnum.base + cnum.size));
> +	return FN(srange_overflow)(cnum) ? ST_MAX : (st)(cnum.base + cnum.size);
>  }

Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>