Re: [PATCH bpf-next v2 4/6] libbpf: Resolve typeless ksyms via KALLSYMS_QUERY ioctl

[Jiri Olsa]

On Thu, Oct 22, 2026 at 05:16:05PM -0700, Samuel Wu wrote:

SNIP

> +static int bpf_object__query_ksyms(struct bpf_object *obj)
> +{
> +	struct kallsyms_query q;
> +	struct extern_desc *ext;
> +	int err = 0;
> +	int fd;
> +	int i;
> +
> +	fd = open("/proc/kallsyms", O_RDONLY | O_CLOEXEC);
> +	if (fd < 0)
> +		return -errno;
> +
> +	for (i = 0; i < obj->nr_extern; i++) {
> +		ext = &obj->externs[i];
> +		if (ext->type != EXT_KSYM || ext->ksym.type_id)
> +			continue;
> +
> +		q = (struct kallsyms_query){
> +			.size = sizeof(q),
> +			.query_flags = KALLSYMS_QUERY_BY_SYMBOL,
> +			.sym_name_addr = ptr_to_u64(ext->name),
> +		};
> +
> +			err = -errno;
> +			if (err == -ENOENT) {
> +				err = 0;
> +				continue;
> +			}
> +			if (err == -EADDRNOTAVAIL)
> +				pr_warn("extern (ksym) '%s': resolution is ambiguous\n",
> +					ext->name);
> +			break;
> +		}
> +		ext->is_set = true;
> +		ext->ksym.addr = q.sym_addr;
> +		pr_debug("extern (ksym) '%s': resolved in kernel to 0x%llx\n",
> +			 ext->name, ext->ksym.addr);
> +	}
> +	close(fd);
> +	return err;
> +}
> +
> +static int bpf_object__resolve_typeless_ksyms(struct bpf_object *obj)
>  {
> +	int err;
> +
> +	err = bpf_object__query_ksyms(obj);

hi,
we could also add similar support for libbpf_available_kallsyms_parse and
probably in some other places like bpf_get_ksyms.. which makes me think it
could be useful to have KALLSYMS_QUERY support for multiple symbols

thanks,
jirka


> +	/*
> +	 * Fall back to parsing /proc/kallsyms only if the ioctl is not
> +	 * accessible: not present (-ENOTTY on older kernels) or kallsyms
> +	 * addresses hidden from this opener (-EPERM, e.g. kptr_restrict).
> +	 */
> +	if (err != -ENOTTY && err != -EPERM)
> +		return err;
> +
> +	pr_debug("KALLSYMS_QUERY unavailable (%s), falling back to /proc/kallsyms\n",
> +		 errstr(err));
>  	return libbpf_kallsyms_parse(kallsyms_cb, obj);
>  }
>  
> @@ -9922,7 +9996,7 @@ static int bpf_object__resolve_externs(struct bpf_object *obj,
>  			return -EINVAL;
>  	}
>  	if (need_kallsyms) {
> -		err = bpf_object__read_kallsyms_file(obj);
> +		err = bpf_object__resolve_typeless_ksyms(obj);
>  		if (err)
>  			return -EINVAL;
>  	}
> -- 
> 2.56.0.257.gf7497c7d27-goog
>