From patchwork Wed Jul 1 06:45:23 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrii Nakryiko X-Patchwork-Id: 1320271 X-Patchwork-Delegate: bpf@iogearbox.net Return-Path: X-Original-To: incoming-bpf@patchwork.ozlabs.org Delivered-To: patchwork-incoming-bpf@bilbo.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=bpf-owner@vger.kernel.org; receiver=) Authentication-Results: ozlabs.org; dmarc=pass (p=reject dis=none) header.from=fb.com Authentication-Results: ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=fb.com header.i=@fb.com header.a=rsa-sha256 header.s=facebook header.b=JF6ayrA9; dkim-atps=neutral Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by ozlabs.org (Postfix) with ESMTP id 49xWvS2SNzz9s1x for ; Wed, 1 Jul 2020 16:45:40 +1000 (AEST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727970AbgGAGpi (ORCPT ); Wed, 1 Jul 2020 02:45:38 -0400 Received: from mx0a-00082601.pphosted.com ([67.231.145.42]:54778 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727968AbgGAGpi (ORCPT ); Wed, 1 Jul 2020 02:45:38 -0400 Received: from pps.filterd (m0044012.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id 0616fAYl008221 for ; Tue, 30 Jun 2020 23:45:37 -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=jqUwwYpFA1EqVwoHCCH4zCzzCGaoLEOB4aLchWeaIEY=; b=JF6ayrA9dM8n9z0IJdbWUqE2INztKhQPTWn0OzyLHCv29zKyzO3BwG5LD0PSujpsK02E T5ybzBRfbQpnL2RsypR3gmbnVyIFXF6+AaKON7F17SaJDjq/HcKfbo5VA64sOo4/tT7A q2B0J3Z4sGwD2JWjCtTz65IO0Oo4HAY0WQ0= Received: from maileast.thefacebook.com ([163.114.130.16]) by mx0a-00082601.pphosted.com with ESMTP id 320bcdta11-2 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Tue, 30 Jun 2020 23:45:37 -0700 Received: from intmgw002.03.ash8.facebook.com (2620:10d:c0a8:1b::d) by mail.thefacebook.com (2620:10d:c0a8:82::d) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.1979.3; Tue, 30 Jun 2020 23:45:35 -0700 Received: by devbig012.ftw2.facebook.com (Postfix, from userid 137359) id 3ADA72EC3A2B; Tue, 30 Jun 2020 23:45:31 -0700 (PDT) Smtp-Origin-Hostprefix: devbig From: Andrii Nakryiko Smtp-Origin-Hostname: devbig012.ftw2.facebook.com To: , , , CC: , , Andrii Nakryiko , Anton Protopopov , Daniel Xu Smtp-Origin-Cluster: ftw2c04 Subject: [PATCH bpf-next 1/3] libbpf: support stripping modifiers for btf_dump Date: Tue, 30 Jun 2020 23:45:23 -0700 Message-ID: <20200701064527.3158178-2-andriin@fb.com> X-Mailer: git-send-email 2.24.1 In-Reply-To: <20200701064527.3158178-1-andriin@fb.com> References: <20200701064527.3158178-1-andriin@fb.com> MIME-Version: 1.0 X-FB-Internal: Safe X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235, 18.0.687 definitions=2020-07-01_03:2020-07-01,2020-07-01 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 mlxscore=0 lowpriorityscore=0 malwarescore=0 bulkscore=0 mlxlogscore=999 impostorscore=0 adultscore=0 cotscore=-2147483648 spamscore=0 suspectscore=0 phishscore=0 clxscore=1015 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2007010047 X-FB-Internal: deliver Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org One important use case when emitting const/volatile/restrict is undesirable is BPF skeleton generation of DATASEC layout. These are further memory-mapped 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 variables. 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 variable will be emitted as is. So when used from user-space, compiler will complain 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 any modifier, when requested. This patch converts existing struct btf_dump_opts to modern opts "framework" with size field and easily extensible in the future with backwards/forward compatibility. While this is a breaking change, there are only two known clients of this API: bpftool and bpftrace. bpftool hasn't used opts and just passed NULL, so is not affected and subsequent patch makes it use using DECLARE_LIBBPF_OPTS() macro. bpftrace does use opts and I'll work with bpftrace maintainers to adopt to a new opts style. While a bit painful, it seems like a better strategy long-term, instead of maintaining two sets of btf_dump opts and constructors. [0] https://github.com/iovisor/bcc/pull/2994#issuecomment-650588533 Cc: Daniel Xu Reported-by: Anton Protopopov Signed-off-by: Andrii Nakryiko --- tools/lib/bpf/btf.h | 6 ++++++ tools/lib/bpf/btf_dump.c | 18 +++++++++++++----- 2 files changed, 19 insertions(+), 5 deletions(-) diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h index 06cd1731c154..5c2acca8d7f4 100644 --- a/tools/lib/bpf/btf.h +++ b/tools/lib/bpf/btf.h @@ -115,8 +115,14 @@ LIBBPF_API int btf__dedup(struct btf *btf, struct btf_ext *btf_ext, struct btf_dump; struct btf_dump_opts { + /* size of this struct, for backward/forward compatibility */ + size_t sz; + /* extra context passed to print callback */ void *ctx; + /* strip all the const/volatile/restrict mods */ + bool strip_mods; }; +#define btf_dump_opts__last_field strip_mods typedef void (*btf_dump_printf_fn_t)(void *ctx, const char *fmt, va_list args); diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c index bbb430317260..4b843bbd8657 100644 --- a/tools/lib/bpf/btf_dump.c +++ b/tools/lib/bpf/btf_dump.c @@ -59,7 +59,8 @@ struct btf_dump { const struct btf *btf; const struct btf_ext *btf_ext; btf_dump_printf_fn_t printf_fn; - struct btf_dump_opts opts; + void *print_ctx; + bool strip_mods; /* per-type auxiliary state */ struct btf_dump_type_aux_state *type_states; @@ -115,7 +116,7 @@ static void btf_dump_printf(const struct btf_dump *d, const char *fmt, ...) va_list args; va_start(args, fmt); - d->printf_fn(d->opts.ctx, fmt, args); + d->printf_fn(d->print_ctx, fmt, args); va_end(args); } @@ -129,6 +130,9 @@ struct btf_dump *btf_dump__new(const struct btf *btf, struct btf_dump *d; int err; + if (!OPTS_VALID(opts, btf_dump_opts)) + return ERR_PTR(-EINVAL); + d = calloc(1, sizeof(struct btf_dump)); if (!d) return ERR_PTR(-ENOMEM); @@ -136,7 +140,8 @@ struct btf_dump *btf_dump__new(const struct btf *btf, d->btf = btf; d->btf_ext = btf_ext; d->printf_fn = printf_fn; - d->opts.ctx = opts ? opts->ctx : NULL; + d->print_ctx = OPTS_GET(opts, ctx, NULL); + d->strip_mods = OPTS_GET(opts, strip_mods, false); d->type_names = hashmap__new(str_hash_fn, str_equal_fn, NULL); if (IS_ERR(d->type_names)) { @@ -1045,6 +1050,10 @@ static void btf_dump_emit_type_decl(struct btf_dump *d, __u32 id, stack_start = d->decl_stack_cnt; for (;;) { + t = btf__type_by_id(d->btf, id); + if (d->strip_mods && btf_is_mod(t)) + goto skip_mod; + err = btf_dump_push_decl_stack_id(d, id); if (err < 0) { /* @@ -1056,12 +1065,11 @@ static void btf_dump_emit_type_decl(struct btf_dump *d, __u32 id, d->decl_stack_cnt = stack_start; return; } - +skip_mod: /* VOID */ if (id == 0) break; - t = btf__type_by_id(d->btf, id); switch (btf_kind(t)) { case BTF_KIND_PTR: case BTF_KIND_VOLATILE: