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=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 D0027C433E1 for ; Wed, 19 Aug 2020 00:20:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A878C20738 for ; Wed, 19 Aug 2020 00:20:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="czQqdKt7" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726751AbgHSAU6 (ORCPT ); Tue, 18 Aug 2020 20:20:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59820 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726367AbgHSAU5 (ORCPT ); Tue, 18 Aug 2020 20:20:57 -0400 Received: from mail-qk1-x743.google.com (mail-qk1-x743.google.com [IPv6:2607:f8b0:4864:20::743]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 246BAC061389; Tue, 18 Aug 2020 17:20:57 -0700 (PDT) Received: by mail-qk1-x743.google.com with SMTP id p25so20159810qkp.2; Tue, 18 Aug 2020 17:20:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:from:date:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=7YNr0/jQBoOjMJ1GJxHc4XuPsYwYYSpKoFcUKAuCANQ=; b=czQqdKt7Ca9NxyEtTkZJKnoqff5S2PCADfuwPj54uAEzngcgpvq2sEK0//1InPOnun 6csXn+aZtRq81zUu7dEhrTqTSsYS0ApQtZGsRRG06A+90t8P4d6DmR+6pN0qRpqS/Ngp uiWqojUedgWVouv+216Z3jWhDdl0EjUCp1ZWSJJJYoljM+nNRR5oTyzWVrrq4YUzxQVP +1lTKMiL/QBddxKqDQtlksBF+LmRqSOZb2R4ijdvgQnVaWEtRkmPCKkCF1uZUhWm4xhr yD99SKjUDq6YwmQvK/o8xspQ/xISBL0rVPKZNfmBScbOmF6VRW2iDaF2/0Bw9U6gtGXi LS3w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:from:date:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to; bh=7YNr0/jQBoOjMJ1GJxHc4XuPsYwYYSpKoFcUKAuCANQ=; b=FkzC2dJdFEGLVWuu8uTzht+4EMRlJVrUI3883xvK47Q7BM5mw+W0DCy1LJE/p7SLHK GVg613vCnIEDGBiJCUQrshCij3XsuzRaqIVMetIR9Rb1xA2wAMxZlGHBxThAQpeldvoJ cGSq1EN5bSmBMg3KKf0WGD97FBlbsUTBBl7XiKXvbADuK229BFYtW4wFTbpX4pLzqN6H hKiDj441NGYSTztYgGtfz3OvKuun7aOdgF39fGTpbM1+60vo/6tHUhRl8qp74DuZRAt/ pMPbhY5STMOwZKtP4TjjytQwjF6gamk9G/7ppBMTpOX+eaPknNEpVXt8TmDt2AvBYLYP ZTJA== X-Gm-Message-State: AOAM531XiuW6d0aMnvUPTPK978BaykqYGTVe22OMzjOYX9j6tRoRqSng A4sgfp2mSqwUEg58I3jA25M= X-Google-Smtp-Source: ABdhPJxGWqcfe5RiBveI6ga7nnllhDQGBRudEemfUBLCJQnu4+nLDHKaZMXMVuHsjKW+7EtPKiaC6Q== X-Received: by 2002:a37:397:: with SMTP id 145mr20144568qkd.258.1597796455589; Tue, 18 Aug 2020 17:20:55 -0700 (PDT) Received: from rani.riverdale.lan ([2001:470:1f07:5f3::b55f]) by smtp.gmail.com with ESMTPSA id j72sm22657625qke.20.2020.08.18.17.20.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 18 Aug 2020 17:20:54 -0700 (PDT) From: Arvind Sankar X-Google-Original-From: Arvind Sankar Date: Tue, 18 Aug 2020 20:20:52 -0400 To: Nick Desaulniers Cc: Arvind Sankar , Eli Friedman , Masahiro Yamada , Andrew Morton , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Michal Marek , Linux Kbuild mailing list , LKML , Kees Cook , Tony Luck , Dmitry Vyukov , Michael Ellerman , Joe Perches , Joel Fernandes , Daniel Axtens , Andy Shevchenko , Alexandru Ardelean , Yury Norov , "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , "H . Peter Anvin" , Ard Biesheuvel , "Paul E . McKenney" , Daniel Kiper , Bruce Ashfield , Marco Elver , Vamshi K Sthambamkadi , Andi Kleen , Linus Torvalds , =?utf-8?B?RMOhdmlkIEJvbHZhbnNrw70=?= Subject: Re: [PATCH 0/4] -ffreestanding/-fno-builtin-* patches Message-ID: <20200819002052.GA3397377@rani.riverdale.lan> References: <20200817220212.338670-1-ndesaulniers@google.com> <20200818222542.GA3254379@rani.riverdale.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 18, 2020 at 03:59:45PM -0700, Nick Desaulniers wrote: > On Tue, Aug 18, 2020 at 3:25 PM Arvind Sankar wrote: > > > > Another thing that needs to be fixed is that at least lib/string.c needs > > to be compiled with -ffreestanding. > > > > gcc-10 optimizes the generic memset implementation in there into a call > > to memset. Now that's on x86 which doesn't use the generic > > implementation, but this is just waiting to bite us. > > > > https://godbolt.org/z/6EhG15 > > Admittedly, we've had the same shenanigans with memcpy implemented in > terms of calls to __builtin_memcpy being lowered to infinitely > recursive calls...which feels like the same kind of bug. ("You wanted > infinite recursion in the kexec purgatory image, right?" "No, > compiler, I did not.") example: https://godbolt.org/z/MzrTaM > (probably should fix this in both implementations; at the least I feel > like Clang's -Winfinite-recursion should try to help us out here). > What's the other implementation we need to worry about? purgatory (at least on x86) has freestanding already.