From patchwork Mon Aug 17 22:02:08 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Nick Desaulniers X-Patchwork-Id: 11719331 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 4BBF313B1 for ; Mon, 17 Aug 2020 22:02:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 332682075B for ; Mon, 17 Aug 2020 22:02:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="ImA5y6OS" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728131AbgHQWCW (ORCPT ); Mon, 17 Aug 2020 18:02:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38726 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729256AbgHQWCS (ORCPT ); Mon, 17 Aug 2020 18:02:18 -0400 Received: from mail-pj1-x1049.google.com (mail-pj1-x1049.google.com [IPv6:2607:f8b0:4864:20::1049]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D1E33C061343 for ; Mon, 17 Aug 2020 15:02:18 -0700 (PDT) Received: by mail-pj1-x1049.google.com with SMTP id s4so11581312pjq.8 for ; Mon, 17 Aug 2020 15:02:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:message-id:mime-version:subject:from:to:cc; bh=SCGP1B0GabBPIIHG5VJ2o7cUGzZ8S7iKHRNNa+xeYyE=; b=ImA5y6OSZJsSxIPHsXDdYNsmOWF03t/GCF1wydDTkMNPnwFYHmAoquiUE1s1V7h8jH UXrSnaNxxzBdcEXBZ2qo9Qw+m9RgBQRony04zbdg/4XMUNjpbSmAUDgMqTmRtowMDeGJ kewoEMjj+PZYqbE9CSY+3R4Cg7XUc+y5DEPvMt22tvVMtoJS1y9zcahOkuDtmU+eVBQd cUjgV6APd8twafZwkYF+WYlhVyFPKtSEVN6aqA2n6/C5tzcICXlukjmNMzL9NRiRIMmt fcouD5X6n88sMsMTcROVsdKKWRTxpSeWeFuALYEGTrJYLJFF1ez8g5m6ZZJUFKsWVr1Y Q9lA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:message-id:mime-version:subject:from:to:cc; bh=SCGP1B0GabBPIIHG5VJ2o7cUGzZ8S7iKHRNNa+xeYyE=; b=p4z0v0XxFKoCyPlqKINeBWhpvyoXBtv8mq/ZrEDL13PWXcM/hwEXAMKlzMtBoFHaJv lqtRj31uTwUZs6GuTKJxuQIgunSLjDJoNSJMAOdCb2c4tJyQ0fLnjfv+07tdgOunK2NQ dTKFuQTzBtAFuKBXUZ2ghHiU5O7RUuLCHwe6zoZsgPNAlaXtYf/a31zjLazV6S+eG79o pnCy39MBwB0sCDhvg0a5KJC1k5bArGbE6NUkfPEDGRWC9z13pZO4cIj019+si8IavBhX MvIEE5P9eoxesuqAI9K5xse4W18atr1PElP1DLkiESCSSWOJO7R4kC5zYZmyRYDmIFmp YkVQ== X-Gm-Message-State: AOAM532TLvJQk0+UQSFJGBbRylnEEsOi3W67s3VXX0dgSXVPaV/jvBBm YTFjmY3SHWUD6/VssRq+ZL1wepUog/y9kIerzNM= X-Google-Smtp-Source: ABdhPJz+qTv6DNAPpLl1NNFe6vUzEWyhgMT8911arSjyrAqqr+1/c8Xk2osiyz6NvqgiYJnN1HAimTN3fhEsKUXGFR8= X-Received: by 2002:a62:6142:: with SMTP id v63mr13080841pfb.179.1597701737995; Mon, 17 Aug 2020 15:02:17 -0700 (PDT) Date: Mon, 17 Aug 2020 15:02:08 -0700 Message-Id: <20200817220212.338670-1-ndesaulniers@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.28.0.220.ged08abb693-goog Subject: [PATCH 0/4] -ffreestanding/-fno-builtin-* patches From: Nick Desaulniers To: Masahiro Yamada , Andrew Morton , Thomas Gleixner , Ingo Molnar , Borislav Petkov Cc: Michal Marek , linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, Kees Cook , Tony Luck , Dmitry Vyukov , Michael Ellerman , Joe Perches , Joel Fernandes , Daniel Axtens , Arvind Sankar , Andy Shevchenko , Alexandru Ardelean , Yury Norov , x86@kernel.org, "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=?= " , Eli Friedman , Nick Desaulniers Sender: linux-kbuild-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kbuild@vger.kernel.org -ffreestanding typically inhibits "libcall optimizations" where calls to certain library functions can be replaced by the compiler in certain cases to calls to other library functions that may be more efficient. This can be problematic for embedded targets that don't provide full libc implementations. -ffreestanding inhibits all such optimizations, which is the safe choice, but generally we want the optimizations that are performed. The Linux kernel does implement a fair amount of libc routines. Instead of -ffreestanding (which makes more sense in smaller images like kexec's purgatory image), prefer -fno-builtin-* flags to disable the compiler from emitting calls to functions which may not be defined. If you see a linkage failure due to a missing symbol that's typically defined in a libc, and not explicitly called from the source code, then the compiler may have done such a transform. You can either implement such a function (ie. in lib/string.c) or disable the transform outright via -fno-builtin-* flag (where * is the name of the library routine, ie. -fno-builtin-bcmp). Patch 1 unbreaks the build with ToT clang, which has been red all weekend, by adding -fno-builtin-stpcpy. Patch 2 is a revert but adds -fno-builtin-bcmp. Patch 3 does the same for x86 purgatory. Patch 4 removes -ffreestanding from i386. The first patch makes sense for Kbuild, the second maybe akpm@, the third and forth for x86. Not sure who should pick up the series (they can be merged out of order, technically) but I really need the first patch soon. The 3 latter patches are cleanups. Nick Desaulniers (4): Makefile: add -fno-builtin-stpcpy Revert "lib/string.c: implement a basic bcmp" x86/boot: use -fno-builtin-bcmp x86: don't build CONFIG_X86_32 as -ffreestanding Makefile | 7 +++++++ arch/x86/Makefile | 3 --- arch/x86/boot/Makefile | 1 + arch/x86/boot/string.c | 8 -------- include/linux/string.h | 3 --- lib/string.c | 20 -------------------- 6 files changed, 8 insertions(+), 34 deletions(-)