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=-2.3 required=3.0 tests=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 57AE9CA9EA0 for ; Tue, 22 Oct 2019 08:57:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 26B2720640 for ; Tue, 22 Oct 2019 08:57:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731272AbfJVI5h (ORCPT ); Tue, 22 Oct 2019 04:57:37 -0400 Received: from gate.crashing.org ([63.228.1.57]:42736 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731223AbfJVI5g (ORCPT ); Tue, 22 Oct 2019 04:57:36 -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 x9M8vAi3013910; Tue, 22 Oct 2019 03:57:10 -0500 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id x9M8v9Dv013909; Tue, 22 Oct 2019 03:57:09 -0500 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Tue, 22 Oct 2019 03:57:09 -0500 From: Segher Boessenkool To: Nathan Chancellor Cc: Nick Desaulniers , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , clang-built-linux , linuxppc-dev , LKML Subject: Re: [PATCH v4 3/3] powerpc/prom_init: Use -ffreestanding to avoid a reference to bcmp Message-ID: <20191022085709.GI28442@gate.crashing.org> References: <20190911182049.77853-1-natechancellor@gmail.com> <20191014025101.18567-1-natechancellor@gmail.com> <20191014025101.18567-4-natechancellor@gmail.com> <20191014093501.GE28442@gate.crashing.org> <20191014191141.GK28442@gate.crashing.org> <20191018190022.GA1292@ubuntu-m2-xlarge-x86> <20191018200210.GR28442@gate.crashing.org> <20191022051529.GA44041@ubuntu-m2-xlarge-x86> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191022051529.GA44041@ubuntu-m2-xlarge-x86> User-Agent: Mutt/1.4.2.3i Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 21, 2019 at 10:15:29PM -0700, Nathan Chancellor wrote: > On Fri, Oct 18, 2019 at 03:02:10PM -0500, Segher Boessenkool wrote: > > I think the proper solution is for the kernel to *do* use -ffreestanding, > > and then somehow tell the kernel that memcpy etc. are the standard > > functions. A freestanding GCC already requires memcpy, memmove, memset, > > memcmp, and sometimes abort to exist and do the standard thing; why cannot > > programs then also rely on it to be the standard functions. > > > > What exact functions are the reason the kernel does not use -ffreestanding? > > Is it just memcpy? Is more wanted? > > I think Linus summarized it pretty well here: > > https://lore.kernel.org/lkml/CAHk-=wi-epJZfBHDbKKDZ64us7WkF=LpUfhvYBmZSteO8Q0RAg@mail.gmail.com/ GCC recognises __builtin_memcpy (or any other __builtin) just fine even with -ffreestanding. So the kernel wants a warning (or error) whenever a call to one of these library functions is generated by the compiler without the user asking for it directly (via a __builtin)? And that is all that is needed for the kernel to use -ffreestanding? That shouldn't be hard. Anything missing here? Segher