Re: [RFC bpf-next 02/15] libbpf: Add support for BTF kinds LOC_PARAM, LOC_PROTO and LOCSEC

[Eduard Zingerman <eddyz87@gmail.com>]

On Wed, 2025-10-08 at 18:34 +0100, Alan Maguire wrote:

[...]

> diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> index 18907f0fcf9f..0abd7831d6b4 100644
> --- a/tools/lib/bpf/btf.c
> +++ b/tools/lib/bpf/btf.c

[...]

> @@ -588,6 +621,34 @@ static int btf_validate_type(const struct btf *btf, const struct btf_type *t, __
>  		}
>  		break;
>  	}
> +	case BTF_KIND_LOC_PARAM:
> +		break;
> +	case BTF_KIND_LOC_PROTO: {
> +		__u32 *p = btf_loc_proto_params(t);
> +
> +		n = btf_vlen(t);
> +		for (i = 0; i < n; i++, p++) {
> +			err = btf_validate_id(btf, *p, id);
> +			if (err)
> +				return err;
> +		}
> +		break;
> +	}
> +	case BTF_KIND_LOCSEC: {
> +		const struct btf_loc *l = btf_locsec_locs(t);
> +
> +		n = btf_vlen(t);
> +		for (i = 0; i < n; i++, l++) {
> +			err = btf_validate_str(btf, l->name_off, "loc name", id);
> +			if (!err)
> +				err = btf_validate_id(btf, l->func_proto, id);
> +			if (!err)
> +				btf_validate_id(btf, l->loc_proto, id);
> +			if (err)
> +				return err;
> +		}
> +		break;

Do we want to also check that number of parameters in loc_proto is the
same (or less then) number of parameters in func_proto?
Also, would it make sense to support a case when e.g. parameters #1
and #3 are in known locations, but parameter #2 is absent?

> +	}
>  	default:
>  		pr_warn("btf: type [%u]: unrecognized kind %u\n", id, kind);
>  		return -EINVAL;

[...]