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=-14.0 required=3.0 tests=BAYES_00,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 3BE8AC433E0 for ; Tue, 19 Jan 2021 22:15:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1775222E01 for ; Tue, 19 Jan 2021 22:15:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726049AbhASWPT convert rfc822-to-8bit (ORCPT ); Tue, 19 Jan 2021 17:15:19 -0500 Received: from us-smtp-delivery-44.mimecast.com ([207.211.30.44]:32255 "EHLO us-smtp-delivery-44.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389101AbhASWNg (ORCPT ); Tue, 19 Jan 2021 17:13:36 -0500 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-91-pESdaNy3OP-4R8EIVaHF8w-1; Tue, 19 Jan 2021 17:12:39 -0500 X-MC-Unique: pESdaNy3OP-4R8EIVaHF8w-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id A44CF10054FF; Tue, 19 Jan 2021 22:12:37 +0000 (UTC) Received: from krava.redhat.com (unknown [10.40.195.212]) by smtp.corp.redhat.com (Postfix) with ESMTP id 745F19CA0; Tue, 19 Jan 2021 22:12:34 +0000 (UTC) From: Jiri Olsa To: Arnaldo Carvalho de Melo , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko Cc: dwarves@vger.kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org, Yonghong Song , Hao Luo , Martin KaFai Lau , Song Liu , John Fastabend , KP Singh , Joe Lawrence , Mark Wielaard Subject: [PATCH 2/3] bpf_encoder: Translate SHN_XINDEX in symbol's st_shndx values Date: Tue, 19 Jan 2021 23:12:19 +0100 Message-Id: <20210119221220.1745061-3-jolsa@kernel.org> In-Reply-To: <20210119221220.1745061-1-jolsa@kernel.org> References: <20210119221220.1745061-1-jolsa@kernel.org> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=jolsa@kernel.org X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: kernel.org Content-Transfer-Encoding: 8BIT Content-Type: text/plain; charset=WINDOWS-1252 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org For very large ELF objects (with many sections), we could get special value SHN_XINDEX (65535) for symbol's st_shndx. This patch is adding code to detect the optional extended section index table and use it to resolve symbol's section index id needed. Signed-off-by: Jiri Olsa --- btf_encoder.c | 18 ++++++++++++++++++ elf_symtab.c | 31 ++++++++++++++++++++++++++++++- elf_symtab.h | 1 + 3 files changed, 49 insertions(+), 1 deletion(-) diff --git a/btf_encoder.c b/btf_encoder.c index 5557c9efd365..2ab6815dc2b3 100644 --- a/btf_encoder.c +++ b/btf_encoder.c @@ -609,6 +609,24 @@ static int collect_symbols(struct btf_elf *btfe, bool collect_percpu_vars) /* search within symtab for percpu variables */ elf_symtab__for_each_symbol(btfe->symtab, core_id, sym) { + struct elf_symtab *symtab = btfe->symtab; + + /* + * Symbol's st_shndx needs to be translated with the + * extended section index table. + */ + if (sym.st_shndx == SHN_XINDEX) { + Elf32_Word xndx; + + if (!symtab->syms_shndx) { + fprintf(stderr, "SHN_XINDEX found, but no symtab shndx section.\n"); + return -1; + } + + if (gelf_getsymshndx(symtab->syms, symtab->syms_shndx, core_id, &sym, &xndx)) + sym.st_shndx = xndx; + } + if (collect_percpu_vars && collect_percpu_var(btfe, &sym)) return -1; if (collect_function(btfe, &sym)) diff --git a/elf_symtab.c b/elf_symtab.c index 741990ea3ed9..c1def0189652 100644 --- a/elf_symtab.c +++ b/elf_symtab.c @@ -17,11 +17,13 @@ struct elf_symtab *elf_symtab__new(const char *name, Elf *elf, GElf_Ehdr *ehdr) { + size_t index; + if (name == NULL) name = ".symtab"; GElf_Shdr shdr; - Elf_Scn *sec = elf_section_by_name(elf, ehdr, &shdr, name, NULL); + Elf_Scn *sec = elf_section_by_name(elf, ehdr, &shdr, name, &index); if (sec == NULL) return NULL; @@ -29,6 +31,8 @@ struct elf_symtab *elf_symtab__new(const char *name, Elf *elf, GElf_Ehdr *ehdr) if (gelf_getshdr(sec, &shdr) == NULL) return NULL; + int xindex = elf_scnshndx(sec); + struct elf_symtab *symtab = malloc(sizeof(*symtab)); if (symtab == NULL) return NULL; @@ -49,6 +53,31 @@ struct elf_symtab *elf_symtab__new(const char *name, Elf *elf, GElf_Ehdr *ehdr) if (symtab->symstrs == NULL) goto out_free_name; + /* + * The .symtab section has optional extended section index + * table, load its data so it can be used to resolve symbol's + * section index. + **/ + if (xindex > 0) { + GElf_Shdr shdr_shndx; + Elf_Scn *sec_shndx; + + sec_shndx = elf_getscn(elf, xindex); + if (sec_shndx == NULL) + goto out_free_name; + + if (gelf_getshdr(sec_shndx, &shdr_shndx) == NULL) + goto out_free_name; + + /* Extra check to verify it belongs to the .symtab */ + if (index != shdr_shndx.sh_link) + goto out_free_name; + + symtab->syms_shndx = elf_getdata(elf_getscn(elf, xindex), NULL); + if (symtab->syms_shndx == NULL) + goto out_free_name; + } + symtab->nr_syms = shdr.sh_size / shdr.sh_entsize; return symtab; diff --git a/elf_symtab.h b/elf_symtab.h index 359add69c8ab..f9277a48ed4c 100644 --- a/elf_symtab.h +++ b/elf_symtab.h @@ -16,6 +16,7 @@ struct elf_symtab { uint32_t nr_syms; Elf_Data *syms; Elf_Data *symstrs; + Elf_Data *syms_shndx; char *name; }; -- 2.27.0