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=-6.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no 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 0349BC4708D for ; Fri, 28 May 2021 13:01:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D3CA261378 for ; Fri, 28 May 2021 13:01:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234618AbhE1ND2 (ORCPT ); Fri, 28 May 2021 09:03:28 -0400 Received: from mail.kernel.org ([198.145.29.99]:48136 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230080AbhE1ND0 (ORCPT ); Fri, 28 May 2021 09:03:26 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id CF09761001; Fri, 28 May 2021 13:01:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1622206912; bh=FNx7PuKOW6IqJOgQcEMKBCcMzoBUxAFP70kRxG5nUgk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=BtQCL3mEOsr3bzTNeYB0hmSZ2K2oOXmVgRFfj3P89ZhmG0J0Ww4/h9vBc6YKmgJYs +YmcOhk7WRYTqH5UohfZCDH0lEMt+Ss+srVImaFJ82AFSmrokBCf6M8yv/Z7Y5hNpD OSrA5Ac0MTrnZuVFr4QDKDl/EgyFSwwA4PiOnkBU0CMnlvXozG9Iki53DVywZixyAh 0b6Cx1GrCwSjAwfDvoxZt+5N7LcrynM0scJqlRzRaY0YEYHvc/bbphkWCZ5gMe/91V KyfgebpBBJ7cq98WLpIMD4Gp2JfcQOssZxnt+Bj451M8YvA8x15qUCT4njZQL1A1Xq gvBM9NcOCZtfQ== Received: by quaco.ghostprotocols.net (Postfix, from userid 1000) id B47634011C; Fri, 28 May 2021 10:01:48 -0300 (-03) Date: Fri, 28 May 2021 10:01:48 -0300 From: Arnaldo Carvalho de Melo To: Thomas Richter , Andrii Nakryiko , bpf@vger.kernel.org Cc: "linux-perf-use." , Ilya Leoshkevich Subject: Re: perf test 40 Basic BPF llvm compile dumps core (x86 and s390) Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Url: http://acmel.wordpress.com Precedence: bulk List-ID: X-Mailing-List: linux-perf-users@vger.kernel.org Em Fri, May 28, 2021 at 12:48:56PM +0200, Thomas Richter escreveu: > I noticed perf test 40.1 dumps core on 5.13.0rc2 and rc3: > > [root@f34 perf]# ./perf test -F 40 > 40: LLVM search and compile : > 40.1: Basic BPF llvm compile : > libbpf: elf: skipping unrecognized data section(8) .eh_frame > libbpf: elf: skipping relo section(9) .rel.eh_frame for section(8) .eh_frame > Segmentation fault (core dumped) > [root@f34 perf]# > The root cause is a NULL pointer reference in function btf__get_nr_types() > as can be seen with gdb: This looks like a bug in libbpf: static int bpf_object__collect_externs(struct bpf_object *obj) { struct btf_type *sec, *kcfg_sec = NULL, *ksym_sec = NULL; const struct btf_type *t; struct extern_desc *ext; int i, n, off, dummy_var_btf_id; const char *ext_name, *sec_name; Elf_Scn *scn; GElf_Shdr sh; if (!obj->efile.symbols) return 0; scn = elf_sec_by_idx(obj, obj->efile.symbols_shndx); if (elf_sec_hdr(obj, scn, &sh)) return -LIBBPF_ERRNO__FORMAT; dummy_var_btf_id = add_dummy_ksym_var(obj->btf); if (dummy_var_btf_id < 0) return dummy_var_btf_id; obj->btf is NULL, so probably btf__find_by_name_kind() should check that and return an error, Andrii? - Arnaldo > Breakpoint 1, 0x000000000065f4b1 in btf__get_nr_types > (btf=btf@entry=0x0) at btf.c:425 > 425 return btf->start_id + btf->nr_types - 1; > > This is the same function and reason why test case 42.1 Basic BPF filtering > fails and dumps core too. > > The call chain is: > (gdb) where > #0 0x000000000065f4b1 in btf__get_nr_types (btf=btf@entry=0x0) at btf.c:425 > #1 btf__find_by_name_kind (btf=btf@entry=0x0, > type_name=type_name@entry=0x928ab2 ".ksyms", > kind=kind@entry=15) at btf.c:696 > #2 0x00000000006527fe in add_dummy_ksym_var (btf=0x0) at libbpf.c:3219 > #3 bpf_object__collect_externs (obj=0xd0ea20) at libbpf.c:3266 > #4 __bpf_object__open (path=, path@entry=0x0, > obj_buf=obj_buf@entry=0xd12fa0, > obj_buf_sz=obj_buf_sz@entry=1520, > opts=opts@entry=0x7fffffffdb30) at libbpf.c:7372 > #5 0x0000000000655415 in __bpf_object__open (opts=0x7fffffffdb30, > obj_buf_sz=1520, obj_buf=0xd12fa0, path=0x0) at libbpf.c:7337 > #6 bpf_object__open_mem (opts=0x7fffffffdb30, obj_buf_sz=1520, > obj_buf=0xd12fa0) at libbpf.c:7454 > #7 bpf_object__open_mem (opts=0x7fffffffdb30, obj_buf_sz=1520, > obj_buf=0xd12fa0) at libbpf.c:7448 > #8 bpf_object__open_buffer (obj_buf=0xd12fa0, obj_buf_sz=1520, > name=) at libbpf.c:7471 > #9 0x00000000004c8c6e in test__bpf_parsing (obj_buf=0xd12fa0, > obj_buf_sz=1520) at tests/llvm.c:16 > #10 0x00000000004c8fe2 in test__llvm (test=0xac7d20 , > subtest=0) at tests/llvm.c:142 > ... > > I have no knowledge about BPF and why the core dump happens. Before > I start digging into this has anybody some hints on where to look? > > Thanks a lot. > > -- > Thomas Richter, Dept 3303, IBM s390 Linux Development, Boeblingen, Germany > -- > Vorsitzender des Aufsichtsrats: Gregor Pillen > Geschäftsführung: Dirk Wittkopp > Sitz der Gesellschaft: Böblingen / Registergericht: Amtsgericht Stuttgart, HRB 243294 -- - Arnaldo