From patchwork Sat Jul 11 21:53:27 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jiri Olsa X-Patchwork-Id: 1327405 X-Patchwork-Delegate: bpf@iogearbox.net Return-Path: X-Original-To: patchwork-incoming-netdev@ozlabs.org Delivered-To: patchwork-incoming-netdev@ozlabs.org Authentication-Results: ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=vger.kernel.org (client-ip=23.128.96.18; helo=vger.kernel.org; envelope-from=netdev-owner@vger.kernel.org; receiver=) Authentication-Results: ozlabs.org; dmarc=pass (p=none dis=none) header.from=kernel.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by ozlabs.org (Postfix) with ESMTP id 4B43Zm2lVjz9sRN for ; Sun, 12 Jul 2020 07:53:52 +1000 (AEST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728223AbgGKVxv convert rfc822-to-8bit (ORCPT ); Sat, 11 Jul 2020 17:53:51 -0400 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:33924 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728180AbgGKVxt (ORCPT ); Sat, 11 Jul 2020 17:53:49 -0400 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-361-wwaWyGBKMPutCB8ThLphvA-1; Sat, 11 Jul 2020 17:53:46 -0400 X-MC-Unique: wwaWyGBKMPutCB8ThLphvA-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 3DC021083; Sat, 11 Jul 2020 21:53:45 +0000 (UTC) Received: from krava.redhat.com (unknown [10.40.192.15]) by smtp.corp.redhat.com (Postfix) with ESMTP id C85FE60BEC; Sat, 11 Jul 2020 21:53:43 +0000 (UTC) From: Jiri Olsa To: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko Cc: netdev@vger.kernel.org, bpf@vger.kernel.org Subject: [PATCH v7 bpf-next 7/9] bpf: Add info about .BTF_ids section to btf.rst Date: Sat, 11 Jul 2020 23:53:27 +0200 Message-Id: <20200711215329.41165-8-jolsa@kernel.org> In-Reply-To: <20200711215329.41165-1-jolsa@kernel.org> References: <20200711215329.41165-1-jolsa@kernel.org> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: kernel.org Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Updating btf.rst doc with info about .BTF_ids section Acked-by: Andrii Nakryiko Tested-by: Andrii Nakryiko Signed-off-by: Jiri Olsa --- Documentation/bpf/btf.rst | 36 ++++++++++++++++++++++++++++++++++++ 1 file changed, 36 insertions(+) diff --git a/Documentation/bpf/btf.rst b/Documentation/bpf/btf.rst index 4d565d202ce3..b5361b8621c9 100644 --- a/Documentation/bpf/btf.rst +++ b/Documentation/bpf/btf.rst @@ -691,6 +691,42 @@ kernel API, the ``insn_off`` is the instruction offset in the unit of ``struct bpf_insn``. For ELF API, the ``insn_off`` is the byte offset from the beginning of section (``btf_ext_info_sec->sec_name_off``). +4.2 .BTF_ids section +==================== + +The .BTF_ids section encodes BTF ID values that are used within the kernel. + +This section is created during the kernel compilation with the help of +macros defined in ``include/linux/btf_ids.h`` header file. Kernel code can +use them to create lists and sets (sorted lists) of BTF ID values. + +The ``BTF_ID_LIST`` and ``BTF_ID`` macros define unsorted list of BTF ID values, +with following syntax:: + + BTF_ID_LIST(list) + BTF_ID(type1, name1) + BTF_ID(type2, name2) + +resulting in following layout in .BTF_ids section:: + + __BTF_ID__type1__name1__1: + .zero 4 + __BTF_ID__type2__name2__2: + .zero 4 + +The ``u32 list[];`` variable is defined to access the list. + +The ``BTF_ID_UNUSED`` macro defines 4 zero bytes. It's used when we +want to define unused entry in BTF_ID_LIST, like:: + + BTF_ID_LIST(bpf_skb_output_btf_ids) + BTF_ID(struct, sk_buff) + BTF_ID_UNUSED + BTF_ID(struct, task_struct) + +All the BTF ID lists and sets are compiled in the .BTF_ids section and +resolved during the linking phase of kernel build by ``resolve_btfids`` tool. + 5. Using BTF ************