Re: [PATCH v8 bpf-next 04/10] libbpf: Add kind layout encoding support

[Eduard Zingerman <eddyz87@gmail.com>]

On Mon, 2025-12-15 at 09:17 +0000, Alan Maguire wrote:

[...]

> @@ -1106,6 +1137,8 @@ static struct btf *btf_new_empty(struct btf *base_btf)
>  
>  	/* +1 for empty string at offset 0 */
>  	btf->raw_size = sizeof(struct btf_header) + (base_btf ? 0 : 1);
> +	if (add_kind_layout)
> +		btf->raw_size = roundup(btf->raw_size, 4) + sizeof(kind_layouts);
>  	btf->raw_data = calloc(1, btf->raw_size);
>  	if (!btf->raw_data) {
>  		free(btf);
> @@ -1126,6 +1159,13 @@ static struct btf *btf_new_empty(struct btf *base_btf)
>  		free(btf);
>  		return ERR_PTR(-ENOMEM);
>  	}
> +
> +	if (add_kind_layout) {
> +		hdr->kind_layout_len = sizeof(kind_layouts);
> +		hdr->kind_layout_off = roundup(hdr->str_len, 4);

btf_add_str() adjusts btf->hdr->str_len w/o moving hdr->kind_layout_off.
This should make hdr->kind_layout_off obsolete after each string addition.
btf_get_raw_data() does not seem to have any logic to adjust kind_layout_off.
Is this a problem, or do I miss something?

> +		btf->kind_layout = btf->raw_data + hdr->hdr_len + hdr->kind_layout_off;
> +		memcpy(btf->kind_layout, kind_layouts, sizeof(kind_layouts));
> +	}
>  	memcpy(btf->hdr, hdr, sizeof(*hdr));
>  
>  	return btf;
> @@ -1133,12 +1173,26 @@ static struct btf *btf_new_empty(struct btf *base_btf)
>  
>  struct btf *btf__new_empty(void)
>  {
> -	return libbpf_ptr(btf_new_empty(NULL));
> +	LIBBPF_OPTS(btf_new_opts, opts);
> +
> +	return libbpf_ptr(btf_new_empty(&opts));

Nit: btf_new_empty(NULL) should work fine because of OPTS_GET.

>  }
>  

[...]