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=-13.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT 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 A861CC433E3 for ; Mon, 13 Jul 2020 23:25:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 84B6220DD4 for ; Mon, 13 Jul 2020 23:25:03 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=fb.com header.i=@fb.com header.b="cfpj6Lfu" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726600AbgGMXZA (ORCPT ); Mon, 13 Jul 2020 19:25:00 -0400 Received: from mx0b-00082601.pphosted.com ([67.231.153.30]:32210 "EHLO mx0b-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726356AbgGMXZA (ORCPT ); Mon, 13 Jul 2020 19:25:00 -0400 Received: from pps.filterd (m0109332.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id 06DNJo3v000406 for ; Mon, 13 Jul 2020 16:24:59 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.com; h=from : to : cc : subject : date : message-id : in-reply-to : references : mime-version : content-transfer-encoding : content-type; s=facebook; bh=iO6Z0rbAmQVRyf6UvboOnbNBq/HdRiy1eI3jgGDd/Rc=; b=cfpj6LfuWImMP8XTnnfufB6ULlp14Z0j+v8zGWF81kBQBYiOl6fHJAu/JV12SXcuxd7V uyBa6SXm146gBGrmBHdYOKsF7BtMBYDeH80DQXpXJhLoTUGYmCLshehVOVF3K2ytEK56 UMkJxcx/xLIAv8xMZJOu/0tWavhyvYsVjWg= Received: from mail.thefacebook.com ([163.114.132.120]) by mx0a-00082601.pphosted.com with ESMTP id 327b5p26f7-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Mon, 13 Jul 2020 16:24:58 -0700 Received: from intmgw001.03.ash8.facebook.com (2620:10d:c085:208::f) by mail.thefacebook.com (2620:10d:c085:21d::4) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.1979.3; Mon, 13 Jul 2020 16:24:57 -0700 Received: by devbig012.ftw2.facebook.com (Postfix, from userid 137359) id 0BAC42EC4105; Mon, 13 Jul 2020 16:24:45 -0700 (PDT) Smtp-Origin-Hostprefix: devbig From: Andrii Nakryiko Smtp-Origin-Hostname: devbig012.ftw2.facebook.com To: , , , CC: , , Andrii Nakryiko , Anton Protopopov Smtp-Origin-Cluster: ftw2c04 Subject: [PATCH v2 bpf-next 1/2] libbpf: support stripping modifiers for btf_dump Date: Mon, 13 Jul 2020 16:24:08 -0700 Message-ID: <20200713232409.3062144-2-andriin@fb.com> X-Mailer: git-send-email 2.24.1 In-Reply-To: <20200713232409.3062144-1-andriin@fb.com> References: <20200713232409.3062144-1-andriin@fb.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-FB-Internal: Safe Content-Type: text/plain X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235,18.0.687 definitions=2020-07-13_17:2020-07-13,2020-07-13 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 malwarescore=0 bulkscore=0 mlxlogscore=999 priorityscore=1501 suspectscore=8 adultscore=0 spamscore=0 phishscore=0 mlxscore=0 lowpriorityscore=0 impostorscore=0 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2007130170 X-FB-Internal: deliver Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org One important use case when emitting const/volatile/restrict is undesirab= le is BPF skeleton generation of DATASEC layout. These are further memory-mappe= d and can be written/read from user-space directly. For important case of .rodata variables, bpftool strips away first-level modifiers, to make their use on user-space side simple and not requiring = extra type casts to override compiler complaining about writing to const variab= les. This logic works mostly fine, but breaks in some more complicated cases. = E.g.: const volatile int params[10]; Because in BTF it's a chain of ARRAY -> CONST -> VOLATILE -> INT, bpftool stops at ARRAY and doesn't strip CONST and VOLATILE. In skeleton this var= iable will be emitted as is. So when used from user-space, compiler will compla= in about writing to const array. This is problematic, as also mentioned in [= 0]. To solve this for arrays and other non-trivial cases (e.g., inner const/volatile fields inside the struct), teach btf_dump to strip away an= y modifier, when requested. This is done as an extra option on btf_dump__emit_type_decl() API. Reported-by: Anton Protopopov Signed-off-by: Andrii Nakryiko --- tools/lib/bpf/btf.h | 2 ++ tools/lib/bpf/btf_dump.c | 10 ++++++++-- 2 files changed, 10 insertions(+), 2 deletions(-) diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h index 70c1b7ec2bd0..be98dd75b791 100644 --- a/tools/lib/bpf/btf.h +++ b/tools/lib/bpf/btf.h @@ -143,6 +143,8 @@ struct btf_dump_emit_type_decl_opts { * necessary indentation already */ int indent_level; + /* strip all the const/volatile/restrict mods */ + bool strip_mods; }; #define btf_dump_emit_type_decl_opts__last_field indent_level =20 diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c index bbb430317260..e1c344504cae 100644 --- a/tools/lib/bpf/btf_dump.c +++ b/tools/lib/bpf/btf_dump.c @@ -60,6 +60,7 @@ struct btf_dump { const struct btf_ext *btf_ext; btf_dump_printf_fn_t printf_fn; struct btf_dump_opts opts; + bool strip_mods; =20 /* per-type auxiliary state */ struct btf_dump_type_aux_state *type_states; @@ -1032,7 +1033,9 @@ int btf_dump__emit_type_decl(struct btf_dump *d, __= u32 id, =20 fname =3D OPTS_GET(opts, field_name, ""); lvl =3D OPTS_GET(opts, indent_level, 0); + d->strip_mods =3D OPTS_GET(opts, strip_mods, false); btf_dump_emit_type_decl(d, id, fname, lvl); + d->strip_mods =3D false; return 0; } =20 @@ -1045,6 +1048,10 @@ static void btf_dump_emit_type_decl(struct btf_dum= p *d, __u32 id, =20 stack_start =3D d->decl_stack_cnt; for (;;) { + t =3D btf__type_by_id(d->btf, id); + if (d->strip_mods && btf_is_mod(t)) + goto skip_mod; + err =3D btf_dump_push_decl_stack_id(d, id); if (err < 0) { /* @@ -1056,12 +1063,11 @@ static void btf_dump_emit_type_decl(struct btf_du= mp *d, __u32 id, d->decl_stack_cnt =3D stack_start; return; } - +skip_mod: /* VOID */ if (id =3D=3D 0) break; =20 - t =3D btf__type_by_id(d->btf, id); switch (btf_kind(t)) { case BTF_KIND_PTR: case BTF_KIND_VOLATILE: --=20 2.24.1