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 16C93C433E0 for ; Sun, 24 Jan 2021 22:16:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DC1F022CA2 for ; Sun, 24 Jan 2021 22:16:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726583AbhAXWQy convert rfc822-to-8bit (ORCPT ); Sun, 24 Jan 2021 17:16:54 -0500 Received: from us-smtp-delivery-44.mimecast.com ([205.139.111.44]:46609 "EHLO us-smtp-delivery-44.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726608AbhAXWQn (ORCPT ); Sun, 24 Jan 2021 17:16:43 -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-366-5AiBYZKkMmqhuJK12LSdWg-1; Sun, 24 Jan 2021 17:15:40 -0500 X-MC-Unique: 5AiBYZKkMmqhuJK12LSdWg-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 A5ED1192FDA0; Sun, 24 Jan 2021 22:15:38 +0000 (UTC) Received: from krava.redhat.com (unknown [10.40.192.64]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7DCE65B4D1; Sun, 24 Jan 2021 22:15:35 +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 2/2] bpf_encoder: Translate SHN_XINDEX in symbol's st_shndx values Date: Sun, 24 Jan 2021 23:15:19 +0100 Message-Id: <20210124221519.219750-3-jolsa@kernel.org> In-Reply-To: <20210124221519.219750-1-jolsa@kernel.org> References: <20210124221519.219750-1-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: netdev@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. Adding elf_symtab__for_each_symbol_index macro that returns symbol's section index and usign it in collect functions. Tested by running pahole on kernel compiled with: make KCFLAGS="-ffunction-sections -fdata-sections" -j$(nproc) vmlinux and ensure FUNC records are generated and match normal build (without above KCFLAGS). Also bpf selftest passed and generated kernel BTF, is same as without the patch. Signed-off-by: Jiri Olsa --- btf_encoder.c | 33 +++++++++++++++++---------------- elf_symtab.c | 41 +++++++++++++++++++++++++++++++++++++++-- elf_symtab.h | 29 +++++++++++++++++++++++++++++ 3 files changed, 85 insertions(+), 18 deletions(-) diff --git a/btf_encoder.c b/btf_encoder.c index 5557c9efd365..b124ec20a689 100644 --- a/btf_encoder.c +++ b/btf_encoder.c @@ -63,13 +63,13 @@ static void delete_functions(void) #define max(x, y) ((x) < (y) ? (y) : (x)) #endif -static int collect_function(struct btf_elf *btfe, GElf_Sym *sym) +static int collect_function(struct btf_elf *btfe, GElf_Sym *sym, + size_t sym_sec_idx) { struct elf_function *new; static GElf_Shdr sh; - static int last_idx; + static size_t last_idx; const char *name; - int idx; if (elf_sym__type(sym) != STT_FUNC) return 0; @@ -90,12 +90,10 @@ static int collect_function(struct btf_elf *btfe, GElf_Sym *sym) functions = new; } - idx = elf_sym__section(sym); - - if (idx != last_idx) { - if (!elf_section_by_idx(btfe->elf, &sh, idx)) + if (sym_sec_idx != last_idx) { + if (!elf_section_by_idx(btfe->elf, &sh, sym_sec_idx)) return 0; - last_idx = idx; + last_idx = sym_sec_idx; } functions[functions_cnt].name = name; @@ -542,14 +540,15 @@ static bool percpu_var_exists(uint64_t addr, uint32_t *sz, const char **name) return true; } -static int collect_percpu_var(struct btf_elf *btfe, GElf_Sym *sym) +static int collect_percpu_var(struct btf_elf *btfe, GElf_Sym *sym, + size_t sym_sec_idx) { const char *sym_name; uint64_t addr; uint32_t size; /* compare a symbol's shndx to determine if it's a percpu variable */ - if (elf_sym__section(sym) != btfe->percpu_shndx) + if (sym_sec_idx != btfe->percpu_shndx) return 0; if (elf_sym__type(sym) != STT_OBJECT) return 0; @@ -585,12 +584,13 @@ static int collect_percpu_var(struct btf_elf *btfe, GElf_Sym *sym) return 0; } -static void collect_symbol(GElf_Sym *sym, struct funcs_layout *fl) +static void collect_symbol(GElf_Sym *sym, struct funcs_layout *fl, + size_t sym_sec_idx) { if (!fl->mcount_start && !strcmp("__start_mcount_loc", elf_sym__name(sym, btfe->symtab))) { fl->mcount_start = sym->st_value; - fl->mcount_sec_idx = sym->st_shndx; + fl->mcount_sec_idx = sym_sec_idx; } if (!fl->mcount_stop && @@ -601,6 +601,7 @@ static void collect_symbol(GElf_Sym *sym, struct funcs_layout *fl) static int collect_symbols(struct btf_elf *btfe, bool collect_percpu_vars) { struct funcs_layout fl = { }; + Elf32_Word sym_sec_idx; uint32_t core_id; GElf_Sym sym; @@ -608,12 +609,12 @@ static int collect_symbols(struct btf_elf *btfe, bool collect_percpu_vars) percpu_var_cnt = 0; /* search within symtab for percpu variables */ - elf_symtab__for_each_symbol(btfe->symtab, core_id, sym) { - if (collect_percpu_vars && collect_percpu_var(btfe, &sym)) + elf_symtab__for_each_symbol_index(btfe->symtab, core_id, sym, sym_sec_idx) { + if (collect_percpu_vars && collect_percpu_var(btfe, &sym, sym_sec_idx)) return -1; - if (collect_function(btfe, &sym)) + if (collect_function(btfe, &sym, sym_sec_idx)) return -1; - collect_symbol(&sym, &fl); + collect_symbol(&sym, &fl, sym_sec_idx); } if (collect_percpu_vars) { diff --git a/elf_symtab.c b/elf_symtab.c index 741990ea3ed9..77c5dc423c56 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 symtab_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, &symtab_index); if (sec == NULL) return NULL; @@ -29,7 +31,7 @@ struct elf_symtab *elf_symtab__new(const char *name, Elf *elf, GElf_Ehdr *ehdr) if (gelf_getshdr(sec, &shdr) == NULL) return NULL; - struct elf_symtab *symtab = malloc(sizeof(*symtab)); + struct elf_symtab *symtab = zalloc(sizeof(*symtab)); if (symtab == NULL) return NULL; @@ -41,6 +43,12 @@ struct elf_symtab *elf_symtab__new(const char *name, Elf *elf, GElf_Ehdr *ehdr) if (symtab->syms == NULL) goto out_free_name; + /* + * This returns extended section index table's + * section index, if it exists. + */ + int symtab_xindex = elf_scnshndx(sec); + sec = elf_getscn(elf, shdr.sh_link); if (sec == NULL) goto out_free_name; @@ -49,6 +57,35 @@ 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 (symtab_xindex > 0) { + GElf_Shdr shdr_xindex; + Elf_Scn *sec_xindex; + + sec_xindex = elf_getscn(elf, symtab_xindex); + if (sec_xindex == NULL) + goto out_free_name; + + if (gelf_getshdr(sec_xindex, &shdr_xindex) == NULL) + goto out_free_name; + + /* Extra check to verify it's correct type */ + if (shdr_xindex.sh_type != SHT_SYMTAB_SHNDX) + goto out_free_name; + + /* Extra check to verify it belongs to the .symtab */ + if (symtab_index != shdr_xindex.sh_link) + goto out_free_name; + + symtab->syms_sec_idx_table = elf_getdata(elf_getscn(elf, symtab_xindex), NULL); + if (symtab->syms_sec_idx_table == 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..489e2b1a3505 100644 --- a/elf_symtab.h +++ b/elf_symtab.h @@ -16,6 +16,8 @@ struct elf_symtab { uint32_t nr_syms; Elf_Data *syms; Elf_Data *symstrs; + /* Data of SHT_SYMTAB_SHNDX section. */ + Elf_Data *syms_sec_idx_table; char *name; }; @@ -77,6 +79,19 @@ static inline bool elf_sym__is_local_object(const GElf_Sym *sym) sym->st_shndx != SHN_UNDEF; } +static inline bool +elf_sym__get(Elf_Data *syms, Elf_Data *syms_sec_idx_table, + int id, GElf_Sym *sym, Elf32_Word *sym_sec_idx) +{ + if (!gelf_getsymshndx(syms, syms_sec_idx_table, id, sym, sym_sec_idx)) + return false; + + if (sym->st_shndx != SHN_XINDEX) + *sym_sec_idx = sym->st_shndx; + + return true; +} + /** * elf_symtab__for_each_symbol - iterate thru all the symbols * @@ -89,4 +104,18 @@ static inline bool elf_sym__is_local_object(const GElf_Sym *sym) index < symtab->nr_syms; \ index++, gelf_getsym(symtab->syms, index, &sym)) +/** + * elf_symtab__for_each_symbol_index - iterate through all the symbols, + * that takes extended symbols indexes into account + * + * @symtab: struct elf_symtab instance to iterate + * @index: uint32_t index + * @sym: GElf_Sym iterator + * @sym_sec_idx: symbol's index + */ +#define elf_symtab__for_each_symbol_index(symtab, id, sym, sym_sec_idx) \ + for (id = 0; id < symtab->nr_syms; id++) \ + if (elf_sym__get(symtab->syms, symtab->syms_sec_idx_table, \ + id, &sym, &sym_sec_idx)) + #endif /* _ELF_SYMTAB_H_ */ -- 2.26.2