From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2C80AC433ED for ; Fri, 10 Jul 2020 19:38:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EECF12078B for ; Fri, 10 Jul 2020 19:38:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1594409901; bh=GN+WCVKo5ynWcGLI/vbl8Mu1RTWOTnu212vdno1Omss=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=C/FWfiInZehW1mneovykQKvjerAuKmdySBDy7jX/q6ZO7oyRFJbMjQbxyvTvlm2FS yzFAx+IfKHY4066/SKGl7MJ8Zs+mWuVMMeBl4P987PYZPqPUmKGSZ0SRRjIzl4COWM OnWd6JjNaZO5bW+JlkIwGBbwZpaWfd4Hp3hXOrfc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728430AbgGJTiT convert rfc822-to-8bit (ORCPT ); Fri, 10 Jul 2020 15:38:19 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:49065 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728402AbgGJTiO (ORCPT ); Fri, 10 Jul 2020 15:38:14 -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-287-kzUhjEaDN-6g3bVtLVEAZw-1; Fri, 10 Jul 2020 15:38:11 -0400 X-MC-Unique: kzUhjEaDN-6g3bVtLVEAZw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 77217100CCC0; Fri, 10 Jul 2020 19:38:10 +0000 (UTC) Received: from krava.redhat.com (unknown [10.40.192.98]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0F73D100EBA9; Fri, 10 Jul 2020 19:38:08 +0000 (UTC) From: Jiri Olsa To: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko Cc: netdev@vger.kernel.org, bpf@vger.kernel.org Subject: [PATCH v6 bpf-next 7/9] bpf: Add info about .BTF_ids section to btf.rst Date: Fri, 10 Jul 2020 21:37:52 +0200 Message-Id: <20200710193754.3821104-8-jolsa@kernel.org> In-Reply-To: <20200710193754.3821104-1-jolsa@kernel.org> References: <20200710193754.3821104-1-jolsa@kernel.org> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: kernel.org Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: 8BIT 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 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..c9dec7a565e8 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 ``int 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 ************ -- 2.25.4