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=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,USER_AGENT_MUTT 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 8A264C0044C for ; Wed, 7 Nov 2018 18:42:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5CDBB2086C for ; Wed, 7 Nov 2018 18:42:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5CDBB2086C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729002AbeKHEOY (ORCPT ); Wed, 7 Nov 2018 23:14:24 -0500 Received: from mx1.redhat.com ([209.132.183.28]:49964 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726915AbeKHEOY (ORCPT ); Wed, 7 Nov 2018 23:14:24 -0500 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 97D063001DCC; Wed, 7 Nov 2018 18:42:47 +0000 (UTC) Received: from shodan.usersys.redhat.com (unknown [10.43.17.28]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5F12F5D6A6; Wed, 7 Nov 2018 18:42:47 +0000 (UTC) Received: by shodan.usersys.redhat.com (Postfix, from userid 1000) id B1BF42C1A13; Wed, 7 Nov 2018 19:42:46 +0100 (CET) Date: Wed, 7 Nov 2018 19:42:46 +0100 From: Artem Savkov To: Josh Poimboeuf Cc: Peter Zijlstra , linux-kernel@vger.kernel.org Subject: Re: [PATCH] objtool: fix .cold. functions parent symbols search Message-ID: <20181107184246.GC11183@shodan.usersys.redhat.com> References: <20181107140559.28504-1-asavkov@redhat.com> <20181107170856.usgyzckfirem5qh7@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20181107170856.usgyzckfirem5qh7@treble> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.44]); Wed, 07 Nov 2018 18:42:47 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 07, 2018 at 11:08:56AM -0600, Josh Poimboeuf wrote: > On Wed, Nov 07, 2018 at 03:05:59PM +0100, Artem Savkov wrote: > > The way it is currently done it is possible for read_symbols() to find the > > same symbol as parent for ".cold" functions. > > I seem to remember having this discussion for kpatch-build, but I forget > the details. Can you explain how this can happen (and also add that > detail to the commit message)? find_symbol_by_name() traverses the same lists as read_symbols and when we change sym->name in place without copying it it changes in the list as well. So if child function is before parent in sec->symbol_list the same function will be returned as "parent". It is hard for me to put it into words worthy to be included into commit message. > I haven't seen any bug reports, is it purely theoretical? No, 4.20-rc1 (actually anything after 4a60aa05a063 "objtool: Support per-function rodata sections", before that add_switch_table() doesn't seem to be called for those .cold. funcs) fails to build for mewith KCFLAGS="-ffunction-sections -fdata-sections" because objtool is segfaulting. > > This leads to a bunch of > > complications such as func length being set to 0 and a segfault in > > add_switch_table(). Fix by copying the search string instead of modifying > > it in place. > > > > Signed-off-by: Artem Savkov > > --- > > tools/objtool/elf.c | 7 ++++--- > > 1 file changed, 4 insertions(+), 3 deletions(-) > > > > diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c > > index 6dbb9fae0f9d..781c8afb29b9 100644 > > --- a/tools/objtool/elf.c > > +++ b/tools/objtool/elf.c > > @@ -298,6 +298,7 @@ static int read_symbols(struct elf *elf) > > /* Create parent/child links for any cold subfunctions */ > > list_for_each_entry(sec, &elf->sections, list) { > > list_for_each_entry(sym, &sec->symbol_list, list) { > > + char *pname; > > if (sym->type != STT_FUNC) > > continue; > > sym->pfunc = sym->cfunc = sym; > > @@ -305,9 +306,9 @@ static int read_symbols(struct elf *elf) > > if (!coldstr) > > continue; > > > > - coldstr[0] = '\0'; > > - pfunc = find_symbol_by_name(elf, sym->name); > > - coldstr[0] = '.'; > > + pname = strndup(sym->name, coldstr - sym->name); > > + pfunc = find_symbol_by_name(elf, pname); > > + free(pname); > > > > if (!pfunc) { > > WARN("%s(): can't find parent function", > > -- > > 2.17.2 > > > > -- > Josh -- Regards, Artem