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=-13.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 D98EDC43331 for ; Fri, 3 Apr 2020 08:58:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B723420B1F for ; Fri, 3 Apr 2020 08:58:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390559AbgDCI6X (ORCPT ); Fri, 3 Apr 2020 04:58:23 -0400 Received: from mx2.suse.de ([195.135.220.15]:58060 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390474AbgDCI6X (ORCPT ); Fri, 3 Apr 2020 04:58:23 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id C3EBFAC65; Fri, 3 Apr 2020 08:58:20 +0000 (UTC) Date: Fri, 3 Apr 2020 10:58:20 +0200 (CEST) From: Miroslav Benes To: Josh Poimboeuf cc: x86@kernel.org, linux-kernel@vger.kernel.org, Peter Zijlstra , Julien Thierry , Nick Desaulniers , Dmitry Golovin , Nathan Chancellor Subject: Re: [PATCH 3/5] objtool: Support Clang non-section symbols in ORC generation In-Reply-To: <9a9cae7fcf628843aabe5a086b1a3c5bf50f42e8.1585761021.git.jpoimboe@redhat.com> Message-ID: References: <9a9cae7fcf628843aabe5a086b1a3c5bf50f42e8.1585761021.git.jpoimboe@redhat.com> User-Agent: Alpine 2.21 (LSU 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 1 Apr 2020, Josh Poimboeuf wrote: > When compiling the kernel with AS=clang, objtool produces a lot of > warnings: > > warning: objtool: missing symbol for section .text > warning: objtool: missing symbol for section .init.text > warning: objtool: missing symbol for section .ref.text > > It then fails to generate the ORC table. > > The problem is that objtool assumes text section symbols always exist. > But the Clang assembler is aggressive about removing them. > > When generating relocations for the ORC table, objtool always tries to > reference instructions by their section symbol offset. If the section > symbol doesn't exist, it bails. > > Do a fallback: when a section symbol isn't available, reference a > function symbol instead. > > Link: https://github.com/ClangBuiltLinux/linux/issues/669 > Cc: Nick Desaulniers > Reported-by: Dmitry Golovin > Tested-by: Nathan Chancellor > Signed-off-by: Josh Poimboeuf > --- > tools/objtool/orc_gen.c | 33 ++++++++++++++++++++++++++------- > 1 file changed, 26 insertions(+), 7 deletions(-) > > diff --git a/tools/objtool/orc_gen.c b/tools/objtool/orc_gen.c > index 41e4a2754da4..4c0dabd28000 100644 > --- a/tools/objtool/orc_gen.c > +++ b/tools/objtool/orc_gen.c > @@ -88,11 +88,6 @@ static int create_orc_entry(struct elf *elf, struct section *u_sec, struct secti > struct orc_entry *orc; > struct rela *rela; > > - if (!insn_sec->sym) { > - WARN("missing symbol for section %s", insn_sec->name); > - return -1; > - } > - > /* populate ORC data */ > orc = (struct orc_entry *)u_sec->data->d_buf + idx; > memcpy(orc, o, sizeof(*orc)); > @@ -105,8 +100,32 @@ static int create_orc_entry(struct elf *elf, struct section *u_sec, struct secti > } > memset(rela, 0, sizeof(*rela)); > > - rela->sym = insn_sec->sym; > - rela->addend = insn_off; > + if (insn_sec->sym) { > + rela->sym = insn_sec->sym; > + rela->addend = insn_off; > + } else { > + /* > + * The Clang assembler doesn't produce section symbols, so we > + * have to reference the function symbol instead: > + */ > + rela->sym = find_symbol_containing(insn_sec, insn_off); > + if (!rela->sym) { > + /* > + * Hack alert. This happens when we need to reference > + * the NOP pad insn immediately after the function. > + */ > + rela->sym = find_symbol_containing(insn_sec, > + insn_off - 1); > + } I suppose there is always just one NOP pad insn, right? Anyway, it would be better to get rid of it as you proposed. > + if (!rela->sym) { > + WARN("missing symbol for insn at offset 0x%lx\n", > + insn_off); > + return -1; > + } > + > + rela->addend = insn_off - rela->sym->offset; > + } > + > rela->type = R_X86_64_PC32; > rela->offset = idx * sizeof(int); > rela->sec = ip_relasec; Miroslav