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=-16.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 1964FC4332D for ; Wed, 20 Jan 2021 11:30:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D003E2332B for ; Wed, 20 Jan 2021 11:30:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389451AbhATLXu (ORCPT ); Wed, 20 Jan 2021 06:23:50 -0500 Received: from mail.kernel.org ([198.145.29.99]:57938 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731608AbhATLN2 (ORCPT ); Wed, 20 Jan 2021 06:13:28 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 5272D2250E; Wed, 20 Jan 2021 11:12:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1611141134; bh=WirnMIqg9sdoD42HDZbb17JLEdR68OdowIbN6i1LK7A=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ZJs5vNidFmCeW6AA+2g7IZ2O04HTHwacKOwlJzd6IUhXLPTOAVnfZOs1+rVzxKkJd Bjni9c0uRVTWqFtQUQslKNpXMaxEFOprFeFRjX3T/Br1eyvEQPSAMicd+okZHrAGsD 7BGMKYxebTKHVrwro4ri2XOdK+RLD7360KOQS3amqOuJIXVbCnoPywK1RveWpCPZ5V 4o2aIgmTPpUtmCQmmNVCqZERgAoMzyUBoApa2KiGN9ziV6syJcO6Y5818SFsa411tB 6WhT0e6RbQMuKWXZ/6eEaMDTI70TYrUQZLnYFJGG+aPSThOfI7K2EoYXeHz9Xl22XH HraoRQGklJ2Sg== Received: by quaco.ghostprotocols.net (Postfix, from userid 1000) id 0176940CE2; Wed, 20 Jan 2021 08:12:11 -0300 (-03) Date: Wed, 20 Jan 2021 08:12:11 -0300 From: Arnaldo Carvalho de Melo To: Andrii Nakryiko Cc: Jiri Olsa , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , dwarves@vger.kernel.org, Networking , bpf , Yonghong Song , Hao Luo , Martin KaFai Lau , Song Liu , John Fastabend , KP Singh , Joe Lawrence , Mark Wielaard Subject: Re: [PATCH bpf-next 3/3] libbpf: Use string table index from index table if needed Message-ID: <20210120111211.GP12699@kernel.org> References: <20210119221220.1745061-1-jolsa@kernel.org> <20210119221220.1745061-4-jolsa@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Url: http://acmel.wordpress.com Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Em Tue, Jan 19, 2021 at 05:22:08PM -0800, Andrii Nakryiko escreveu: > On Tue, Jan 19, 2021 at 2:15 PM Jiri Olsa wrote: > > > > For very large ELF objects (with many sections), we could > > get special value SHN_XINDEX (65535) for elf object's string > > table index - e_shstrndx. > > > > In such case we need to call elf_getshdrstrndx to get the > > proper string table index. > > > > Signed-off-by: Jiri Olsa > > --- > > tools/lib/bpf/btf.c | 14 ++++++++++++-- > > 1 file changed, 12 insertions(+), 2 deletions(-) > > > > diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c > > index 3c3f2bc6c652..4fe987846bc0 100644 > > --- a/tools/lib/bpf/btf.c > > +++ b/tools/lib/bpf/btf.c > > @@ -863,6 +863,7 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf, > > Elf_Scn *scn = NULL; > > Elf *elf = NULL; > > GElf_Ehdr ehdr; > > + size_t shstrndx; > > > > if (elf_version(EV_CURRENT) == EV_NONE) { > > pr_warn("failed to init libelf for %s\n", path); > > @@ -887,7 +888,16 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf, > > pr_warn("failed to get EHDR from %s\n", path); > > goto done; > > } > > - if (!elf_rawdata(elf_getscn(elf, ehdr.e_shstrndx), NULL)) { > > + > > + /* > > + * Get string table index from extended section index > > + * table if needed. > > + */ > > + shstrndx = ehdr.e_shstrndx; > > + if (shstrndx == SHN_XINDEX && elf_getshdrstrndx(elf, &shstrndx)) > > + goto done; > > just use elf_getshdrstrndx() unconditionally, it works for extended > and non-extended numbering (see libbpf.c). Yeah, we even have this in tools/perf/util/symbol-elf.c: #ifndef HAVE_ELF_GETSHDRSTRNDX_SUPPORT static int elf_getshdrstrndx(Elf *elf __maybe_unused, size_t *dst __maybe_unused) { pr_err("%s: update your libelf to > 0.140, this one lacks elf_getshdrstrndx().\n", __func__); return -1; } #endif And a feature detection for that: [acme@five perf]$ cat tools/build/feature/test-libelf-getshdrstrndx.c // SPDX-License-Identifier: GPL-2.0 #include int main(void) { size_t dst; return elf_getshdrstrndx(0, &dst); } [acme@five perf]$ Your implementation would provide a good fallback tho to avoid requiring updating to 0.140 :-) - Arnaldo > > + > > + if (!elf_rawdata(elf_getscn(elf, shstrndx), NULL)) { > > pr_warn("failed to get e_shstrndx from %s\n", path); > > goto done; > > } > > @@ -902,7 +912,7 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf, > > idx, path); > > goto done; > > } > > - name = elf_strptr(elf, ehdr.e_shstrndx, sh.sh_name); > > + name = elf_strptr(elf, shstrndx, sh.sh_name); > > if (!name) { > > pr_warn("failed to get section(%d) name from %s\n", > > idx, path); > > -- > > 2.27.0 > > -- - Arnaldo