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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 79BF4C433E0 for ; Mon, 15 Mar 2021 23:54:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 46AB564F5E for ; Mon, 15 Mar 2021 23:54:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232717AbhCOXxn (ORCPT ); Mon, 15 Mar 2021 19:53:43 -0400 Received: from gate.crashing.org ([63.228.1.57]:44877 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232029AbhCOXxO (ORCPT ); Mon, 15 Mar 2021 19:53:14 -0400 Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id 12FNlGwa003537; Mon, 15 Mar 2021 18:47:16 -0500 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id 12FNlEh4003533; Mon, 15 Mar 2021 18:47:14 -0500 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Mon, 15 Mar 2021 18:47:14 -0500 From: Segher Boessenkool To: Rasmus Villemoes Cc: Christophe Leroy , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH] powerpc/vdso32: Add missing _restgpr_31_x to fix build failure Message-ID: <20210315234714.GC16691@gate.crashing.org> References: <20210312022940.GO29191@gate.crashing.org> <023afd0c-dc61-5891-5145-5bcdce8227be@prevas.dk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <023afd0c-dc61-5891-5145-5bcdce8227be@prevas.dk> User-Agent: Mutt/1.4.2.3i Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 15, 2021 at 05:23:44PM +0100, Rasmus Villemoes wrote: > On 12/03/2021 03.29, Segher Boessenkool wrote: > > On Tue, Mar 09, 2021 at 06:19:30AM +0000, Christophe Leroy wrote: > >> With some defconfig including CONFIG_CC_OPTIMIZE_FOR_SIZE, > >> (for instance mvme5100_defconfig and ps3_defconfig), gcc 5 > >> generates a call to _restgpr_31_x. > > > >> I don't know if there is a way to tell GCC not to emit that call, because at the end we get more instructions than needed. > > > > The function is required by the ABI, you need to have it. > > > > You get *fewer* insns statically, and that is what -Os is about: reduce > > the size of the binaries. > > Is there any reason to not just always build the vdso with -O2? It's one > page/one VMA either way, and the vdso is about making certain system > calls cheaper, so if unconditional -O2 could save a few cycles compared > to -Os, why not? (And if, as it seems, there's only one user within the > DSO of _restgpr_31_x, yes, the overall size of the .text segment > probably increases slightly). You can use exactly the same reasoning for using -O2 instead of -Os anywhere else. -Os doesn't mean "smaller code, but only where that is reasonable". It means "smaller code". Segher