From patchwork Tue Sep 1 01:49:52 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrii Nakryiko X-Patchwork-Id: 1354693 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=msH69ByE; dkim-atps=neutral Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by ozlabs.org (Postfix) with ESMTP id 4BgVQM26cJz9sVS for ; Tue, 1 Sep 2020 11:50:35 +1000 (AEST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726192AbgIABue (ORCPT ); Mon, 31 Aug 2020 21:50:34 -0400 Received: from mx0b-00082601.pphosted.com ([67.231.153.30]:18642 "EHLO mx0b-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726224AbgIABuR (ORCPT ); Mon, 31 Aug 2020 21:50:17 -0400 Received: from pps.filterd (m0109331.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id 0811n8cU002042 for ; Mon, 31 Aug 2020 18:50:14 -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=ebvfNM5tAkOSSBvFArksu3q6Rpb9v1j/Zzhz/TosMmo=; b=msH69ByEPUTDZI/WXk4vyVHgH7jRnCf9werLwzzk6tNnP8WyYSPVGpDRx7hsDDs42XEo xgMl7q0JoEqvctBphoiDgK/1xnrAQQXq6M8RXx+wVrz8fJR9uqWDmmqQ3lHgO0txUfJf UVfBg1S/pvi6bLN38wMApf06ufZsrEYQcPE= Received: from mail.thefacebook.com ([163.114.132.120]) by mx0a-00082601.pphosted.com with ESMTP id 337muh2y02-3 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Mon, 31 Aug 2020 18:50:14 -0700 Received: from intmgw004.03.ash8.facebook.com (2620:10d:c085:208::11) by mail.thefacebook.com (2620:10d:c085:11d::5) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.1979.3; Mon, 31 Aug 2020 18:50:13 -0700 Received: by devbig012.ftw2.facebook.com (Postfix, from userid 137359) id A69752EC663B; Mon, 31 Aug 2020 18:50:11 -0700 (PDT) From: Andrii Nakryiko To: , , , CC: , , Andrii Nakryiko Subject: [PATCH v2 bpf-next 03/14] libbpf: support CO-RE relocations for multi-prog sections Date: Mon, 31 Aug 2020 18:49:52 -0700 Message-ID: <20200901015003.2871861-4-andriin@fb.com> X-Mailer: git-send-email 2.24.1 In-Reply-To: <20200901015003.2871861-1-andriin@fb.com> References: <20200901015003.2871861-1-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=2020-09-01_01:2020-08-31,2020-09-01 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 mlxscore=0 lowpriorityscore=0 priorityscore=1501 mlxlogscore=999 suspectscore=8 phishscore=0 adultscore=0 malwarescore=0 spamscore=0 clxscore=1015 impostorscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2009010014 X-FB-Internal: deliver Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Fix up CO-RE relocation code to handle relocations against ELF sections containing multiple BPF programs. This requires lookup of a BPF program by its section name and instruction index it contains. While it could have been done as a simple loop, it could run into performance issues pretty quickly, as number of CO-RE relocations can be quite large in real-world applications, and each CO-RE relocation incurs BPF program look up now. So instead of simple loop, implement a binary search by section name + insn offset. Signed-off-by: Andrii Nakryiko Acked-by: John Fastabend --- tools/lib/bpf/libbpf.c | 82 +++++++++++++++++++++++++++++++++++++----- 1 file changed, 74 insertions(+), 8 deletions(-) diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index 57f87eee5be5..11ad230ec20c 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -2753,6 +2753,18 @@ static bool ignore_elf_section(GElf_Shdr *hdr, const char *name) return false; } +static int cmp_progs(const void *_a, const void *_b) +{ + const struct bpf_program *a = _a; + const struct bpf_program *b = _b; + + if (a->sec_idx != b->sec_idx) + return a->sec_idx < b->sec_idx ? -1 : 1; + + /* sec_insn_off can't be the same within the section */ + return a->sec_insn_off < b->sec_insn_off ? -1 : 1; +} + static int bpf_object__elf_collect(struct bpf_object *obj) { Elf *elf = obj->efile.elf; @@ -2887,6 +2899,11 @@ static int bpf_object__elf_collect(struct bpf_object *obj) pr_warn("elf: symbol strings section missing or invalid in %s\n", obj->path); return -LIBBPF_ERRNO__FORMAT; } + + /* sort BPF programs by section name and in-section instruction offset + * for faster search */ + qsort(obj->programs, obj->nr_programs, sizeof(*obj->programs), cmp_progs); + return bpf_object__init_btf(obj, btf_data, btf_ext_data); } @@ -3415,6 +3432,37 @@ static int bpf_program__record_reloc(struct bpf_program *prog, return 0; } +static bool prog_contains_insn(const struct bpf_program *prog, size_t insn_idx) +{ + return insn_idx >= prog->sec_insn_off && + insn_idx < prog->sec_insn_off + prog->sec_insn_cnt; +} + +static struct bpf_program *find_prog_by_sec_insn(const struct bpf_object *obj, + size_t sec_idx, size_t insn_idx) +{ + int l = 0, r = obj->nr_programs - 1, m; + struct bpf_program *prog; + + while (l < r) { + m = l + (r - l + 1) / 2; + prog = &obj->programs[m]; + + if (prog->sec_idx < sec_idx || + (prog->sec_idx == sec_idx && prog->sec_insn_off <= insn_idx)) + l = m; + else + r = m - 1; + } + /* matching program could be at index l, but it still might be the + * wrong one, so we need to double check conditions for the last time + */ + prog = &obj->programs[l]; + if (prog->sec_idx == sec_idx && prog_contains_insn(prog, insn_idx)) + return prog; + return NULL; +} + static int bpf_program__collect_reloc(struct bpf_program *prog, GElf_Shdr *shdr, Elf_Data *data, struct bpf_object *obj) @@ -5229,6 +5277,11 @@ static int bpf_core_patch_insn(struct bpf_program *prog, if (relo->insn_off % BPF_INSN_SZ) return -EINVAL; insn_idx = relo->insn_off / BPF_INSN_SZ; + /* adjust insn_idx from section frame of reference to the local + * program's frame of reference; (sub-)program code is not yet + * relocated, so it's enough to just subtract in-section offset + */ + insn_idx = insn_idx - prog->sec_insn_off; insn = &prog->insns[insn_idx]; class = BPF_CLASS(insn->code); @@ -5619,7 +5672,7 @@ bpf_object__relocate_core(struct bpf_object *obj, const char *targ_btf_path) struct bpf_program *prog; struct btf *targ_btf; const char *sec_name; - int i, err = 0; + int i, err = 0, insn_idx, sec_idx; if (obj->btf_ext->core_relo_info.len == 0) return 0; @@ -5646,24 +5699,37 @@ bpf_object__relocate_core(struct bpf_object *obj, const char *targ_btf_path) err = -EINVAL; goto out; } + /* bpf_object's ELF is gone by now so it's not easy to find + * section index by section name, but we can find *any* + * bpf_program within desired section name and use it's + * prog->sec_idx to do a proper search by section index and + * instruction offset + */ prog = NULL; for (i = 0; i < obj->nr_programs; i++) { - if (!strcmp(obj->programs[i].section_name, sec_name)) { - prog = &obj->programs[i]; + prog = &obj->programs[i]; + if (strcmp(prog->section_name, sec_name) == 0) break; - } } if (!prog) { - pr_warn("failed to find program '%s' for CO-RE offset relocation\n", - sec_name); - err = -EINVAL; - goto out; + pr_warn("sec '%s': failed to find a BPF program\n", sec_name); + return -ENOENT; } + sec_idx = prog->sec_idx; pr_debug("sec '%s': found %d CO-RE relocations\n", sec_name, sec->num_info); for_each_btf_ext_rec(seg, sec, i, rec) { + insn_idx = rec->insn_off / BPF_INSN_SZ; + prog = find_prog_by_sec_insn(obj, sec_idx, insn_idx); + if (!prog) { + pr_warn("sec '%s': failed to find program at insn #%d for CO-RE offset relocation #%d\n", + sec_name, insn_idx, i); + err = -EINVAL; + goto out; + } + err = bpf_core_apply_relo(prog, rec, i, obj->btf, targ_btf, cand_cache); if (err) {