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=-16.3 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 A0596C433E6 for ; Mon, 25 Jan 2021 17:38:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 68CD722B3B for ; Mon, 25 Jan 2021 17:38:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731040AbhAYRiV (ORCPT ); Mon, 25 Jan 2021 12:38:21 -0500 Received: from mail.kernel.org ([198.145.29.99]:35102 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730605AbhAYRiB (ORCPT ); Mon, 25 Jan 2021 12:38:01 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 7A50222583; Mon, 25 Jan 2021 17:37:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1611596234; bh=6sAHpexwV3E1wMY3f2ODMH4HeE/GvpgftiTgGfYZgOY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=iFHm38L+28trlPkwfAFWJs0EJXo1UIstTLOJZ1R57Lbh1b4bFCQhMFWqEKq1NW9m4 e0tYmtMPbc07uh79aMLuHGJHM+gWT4AOMGvmz1tPnesZjT68R9c8/Lppu0dSOT/Hpg toG/Wu0tXExkaz54gha7mgahhCJ6vqZ2CBDVKZqjLgTUEGe0wrgzNW5pd8oBDVfHgG xEvO4GX2Z3xuewhq8fEBKjih/OQuCXFAfcg2dlCMQZO66ezfsS8O4YJXpxBk0W5w1V YgQpRYBBRpG/diUUeh7b/uRLDevuPijqB5tMcGQ/oofpKyG5uOHKH1OHgh5Wu2gyZH IZ7Wgifj8IjFg== Received: by quaco.ghostprotocols.net (Postfix, from userid 1000) id 983E740513; Mon, 25 Jan 2021 14:37:11 -0300 (-03) Date: Mon, 25 Jan 2021 14:37:11 -0300 From: Arnaldo Carvalho de Melo To: Jiri Olsa Cc: Andrii Nakryiko , 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 2/2] bpf_encoder: Translate SHN_XINDEX in symbol's st_shndx values Message-ID: <20210125173711.GE617095@kernel.org> References: <20210122163920.59177-1-jolsa@kernel.org> <20210122163920.59177-3-jolsa@kernel.org> <20210122203748.GA70760@krava> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210122203748.GA70760@krava> X-Url: http://acmel.wordpress.com Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Em Fri, Jan 22, 2021 at 09:37:48PM +0100, Jiri Olsa escreveu: > On Fri, Jan 22, 2021 at 12:16:42PM -0800, Andrii Nakryiko wrote: > > On Fri, Jan 22, 2021 at 8:46 AM Jiri Olsa wrote: > > > > > > 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. > > > > > > Signed-off-by: Jiri Olsa > > > --- > > > btf_encoder.c | 59 +++++++++++++++++++++++++++++++++++++-------------- > > > elf_symtab.c | 39 +++++++++++++++++++++++++++++++++- > > > elf_symtab.h | 2 ++ > > > 3 files changed, 83 insertions(+), 17 deletions(-) > > > > > > diff --git a/btf_encoder.c b/btf_encoder.c > > > index 5557c9efd365..56ee55965093 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, > > > + Elf32_Word sym_sec_idx) > > > > nit: we use size_t or int for this, no need for libelf types here, imo > > ok I think it is because this patch ends up calling extern GElf_Sym *gelf_getsymshndx (Elf_Data *__symdata, Elf_Data *__shndxdata, int __ndx, GElf_Sym *__sym, Elf32_Word *__xshndx); Which expects a pointer to a Elf32_Word, right Jiri? Jiri, are you going to submit a new version of this patch? I processed the first one, collecting Andrii's Acked-by, if you're busy I can try to address the other concerns from Andrii, please let me know. - Arnaldo > > > > > > > > > { > > > struct elf_function *new; > > > static GElf_Shdr sh; > > > - static int last_idx; > > > + static Elf32_Word 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, > > > + Elf32_Word sym_sec_idx) > > > > nit: same, size_t or just int would be fine > > > > > { > > > 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, > > > + Elf32_Word 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 && > > > @@ -598,9 +598,36 @@ static void collect_symbol(GElf_Sym *sym, struct funcs_layout *fl) > > > fl->mcount_stop = sym->st_value; > > > } > > > > > > +static bool elf_sym__get(Elf_Data *syms, Elf_Data *syms_sec_idx_table, > > > + int id, GElf_Sym *sym, Elf32_Word *sym_sec_idx) > > > > This is a generic function, why don't you want to move it into elf_symtab.h? > > > > > +{ > > > + if (!gelf_getsym(syms, id, sym)) > > > + return false; > > > + > > > + *sym_sec_idx = sym->st_shndx; > > > + > > > + if (sym->st_shndx == SHN_XINDEX) { > > > + if (!syms_sec_idx_table) > > > + return false; > > > + if (!gelf_getsymshndx(syms, syms_sec_idx_table, > > > + id, sym, sym_sec_idx)) > > > + return false; > > > > You also ignored my feedback about not fetching symbol twice. Why? > > ugh, I did not read your last 2 comments.. let me check that, sry > > > > > > + } > > > + > > > + return true; > > > +} > > > + > > > +#define elf_symtab__for_each_symbol_index(symtab, id, sym, sym_sec_idx) \ > > > + for (id = 0; \ > > > + id < symtab->nr_syms && \ > > > + elf_sym__get(symtab->syms, symtab->syms_sec_idx_table, \ > > > + id, &sym, &sym_sec_idx); \ > > > + id++) > > > > This should be in elf_symtab.h next to elf_symtab__for_each_symbol. > > > > And thinking a bit more, the variant with just ignoring symbols that > > we failed to get is probably a safer alternative. I.e., currently > > there is no way to communicate that we terminated iteration with > > error, so it's probably better to skip failed symbols and still get > > the rest, no? I was hoping to discuss stuff like this on the previous > > version of the patch... > > I was thinking of that, but then I thought it's better to fail, > than have possibly wrong data in BTF, because the ELF data is > possibly damaged? no idea.. so I took the safer way > > jirka > -- - Arnaldo