Re: [PATCH bpf-next 1/8] bpf: Add UHMUL and SHMUL instructions

["Alexei Starovoitov" <alexei.starovoitov@gmail.com>]

On Thu, Sep 17, 2026 at 12:17 PM Yazhou Tang <tangyazhou@zju.edu.cn> wrote:
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 732b35cc08d1..845eee536198 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -34,6 +34,16 @@
>  #define BPF_FROM_LE	BPF_TO_LE
>  #define BPF_FROM_BE	BPF_TO_BE
>
> +/*
> + * BPF_MUL variants selected by the off field.
> + * UHMUL and SHMUL are only valid for BPF_ALU64.
> + */
> +enum bpf_mul_variant {
> +	BPF_MUL_VARIANT_LO    = 0,
> +	BPF_MUL_VARIANT_UHMUL = 1,
> +	BPF_MUL_VARIANT_SHMUL = 2,
> +};

Slept on it and imo it's too verbose for uapi.
Maybe just BPF_UHMUL = 1, BPF_SHMUL = 2 ?
No need to name zero, sdiv doesn't.

> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index 4e208cc94752..4f746973481b 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c

[...]

> +	ALU_MUL_X:
> +		if (OFF != BPF_MUL_VARIANT_LO)
> +			goto default_label;
> +		DST = (u32) DST * (u32)
 SRC;
> +		CONT;

The verifier already rejected these. Interpreter doesn't
need to re-validate.

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