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=-18.2 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_IN_DEF_DKIM_WL autolearn=unavailable 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 AA5EFC2BB48 for ; Tue, 8 Dec 2020 16:44:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8D8C923A79 for ; Tue, 8 Dec 2020 16:44:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730574AbgLHQn7 (ORCPT ); Tue, 8 Dec 2020 11:43:59 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58426 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730507AbgLHQn7 (ORCPT ); Tue, 8 Dec 2020 11:43:59 -0500 Received: from mail-vk1-xa41.google.com (mail-vk1-xa41.google.com [IPv6:2607:f8b0:4864:20::a41]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B890DC061749 for ; Tue, 8 Dec 2020 08:43:18 -0800 (PST) Received: by mail-vk1-xa41.google.com with SMTP id i62so4072386vkb.7 for ; Tue, 08 Dec 2020 08:43:18 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=/l23vYzjhD/UMOBSQH+RJul+Bc4oeAA+Y4sxIdjxioI=; b=RAfcD6E7qB/m1g1h+JuwuaF/uflP8i26lZi2phJ6ivM8bTCfjLivQI5OCQ8w6QpWtz GhVbzW0KThpwLDlWvoq6XvuUahnRfW3XWYFEP3/KfbbcE6Mt0xbOSz4rsOQD6EhU4ccb VgjGN1rWqxhd0C0yDGCAAFPp62C56jQyUmdWbq0BO+l5ksMgtWC/hcVK5I++oQFHI7TD XTg5FqhImVrlmWEKuWWtjpLEzGXazHJq+Y3ZsMs6xviYy+OURLB+T+cRV4zeKAJEWHxV mb8QfrCr9XZREmLpj3q8g1+b/aiqk3TuelL46dokcNrd8oTPrJGo9iUQrKDPY1BNYMDM rA1A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=/l23vYzjhD/UMOBSQH+RJul+Bc4oeAA+Y4sxIdjxioI=; b=X2OZia+cDlASlrTTH/Jim7NWG6Nm8OujWM/2Js5Smheawl0uvKZVEVc81R+qOYtOag Q6hf1/M/WkBcSW0RMyO+44zWXc+LIge9yQSYHmQZ3sB4ow5jM21IY07u45kVs5O5y2Nz OmqX4cShWKkEMOfwndfG6NvpOL3WfceVszscjrwjpWySNUoQQ+8f22s9ypKLXn403sYu dqthhUONenyIKoHVL4tpVMb5UMf/oH04UtdRPjMzDrMCwLB1gsWjdYnfmAbx5jhgFR9V t3V4bA2OwFNcmbUjJOmb6Jd5mO1Qdx9/46U0BpSSkfrqNy+z63O4F9mi6ubWCqb5IeXZ Q/Fw== X-Gm-Message-State: AOAM533chix/IOJz4249bg1O670OYhNQBSBFdDTg/Tp04n13dezHD7cJ mgxfjM8Si/mm7pnksbORKi/50q6axbzaJcWAWVhTVw== X-Google-Smtp-Source: ABdhPJzj58Nc2qNmGYOW78LxSHKIESqV6GNFn6VDhGIrOTLcDC2d6Ia7wDNo0+77MjZ0A6JkVLbP9FXkxnngbqbRKfM= X-Received: by 2002:a1f:304a:: with SMTP id w71mr17359481vkw.3.1607445797616; Tue, 08 Dec 2020 08:43:17 -0800 (PST) MIME-Version: 1.0 References: <20201201213707.541432-1-samitolvanen@google.com> In-Reply-To: From: Sami Tolvanen Date: Tue, 8 Dec 2020 08:43:06 -0800 Message-ID: Subject: Re: [PATCH v8 00/16] Add support for Clang LTO To: Arnd Bergmann Cc: Masahiro Yamada , Steven Rostedt , Will Deacon , Josh Poimboeuf , Peter Zijlstra , Greg Kroah-Hartman , "Paul E. McKenney" , Kees Cook , Nick Desaulniers , clang-built-linux , Kernel Hardening , linux-arch , Linux ARM , Linux Kbuild mailing list , "linux-kernel@vger.kernel.org" , linux-pci Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 8, 2020 at 4:15 AM Arnd Bergmann wrote: > > On Tue, Dec 1, 2020 at 10:37 PM 'Sami Tolvanen' via Clang Built Linux > wrote: > > > > This patch series adds support for building the kernel with Clang's > > Link Time Optimization (LTO). In addition to performance, the primary > > motivation for LTO is to allow Clang's Control-Flow Integrity (CFI) > > to be used in the kernel. Google has shipped millions of Pixel > > devices running three major kernel versions with LTO+CFI since 2018. > > > > Most of the patches are build system changes for handling LLVM > > bitcode, which Clang produces with LTO instead of ELF object files, > > postponing ELF processing until a later stage, and ensuring initcall > > ordering. > > > > Note that arm64 support depends on Will's memory ordering patches > > [1]. I will post x86_64 patches separately after we have fixed the > > remaining objtool warnings [2][3]. > > > > [1] https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/log/?h=for-next/lto > > [2] https://lore.kernel.org/lkml/20201120040424.a3wctajzft4ufoiw@treble/ > > [3] https://git.kernel.org/pub/scm/linux/kernel/git/jpoimboe/linux.git/log/?h=objtool-vmlinux > > > > You can also pull this series from > > > > https://github.com/samitolvanen/linux.git lto-v8 > > I've tried pull this into my randconfig test tree to give it a spin. Great, thank you for testing this! > So far I have > not managed to get a working build out of it, the main problem so far being > that it is really slow to build because the link stage only uses one CPU. > These are the other issues I've seen so far: You may want to limit your testing only to ThinLTO at first, because full LTO is going to be extremely slow with larger configs, especially when building arm64 kernels. > - one build seems to take even longer to link. It's currently at 35GB RAM > usage and 40 minutes into the final link, but I'm worried it might > not complete > before it runs out of memory. I only have 128GB installed, and google-chrome > uses another 30GB of that, and I'm also doing some other builds in parallel. > Is there a minimum recommended amount of memory for doing LTO builds? When building arm64 defconfig, the maximum memory usage I measured with ThinLTO was 3.5 GB, and with full LTO 20.3 GB. I haven't measured larger configurations, but I believe LLD can easily consume 3-4x that much with full LTO allyesconfig. > - One build failed with > ld.lld -EL -maarch64elf -mllvm -import-instr-limit=5 -r -o vmlinux.o > -T .tmp_initcalls.lds --whole-archive arch/arm64/kernel/head.o > init/built-in.a usr/built-in.a arch/arm64/built-in.a kernel/built-in.a > certs/built-in.a mm/built-in.a fs/built-in.a ipc/built-in.a > security/built-in.a crypto/built-in.a block/built-in.a > arch/arm64/lib/built-in.a lib/built-in.a drivers/built-in.a > sound/built-in.a net/built-in.a virt/built-in.a --no-whole-archive > --start-group arch/arm64/lib/lib.a lib/lib.a > ./drivers/firmware/efi/libstub/lib.a --end-group > "ld.lld: error: arch/arm64/kernel/head.o: invalid symbol index" > after about 30 minutes That's interesting. Did you use LLVM_IAS=1? > - CONFIG_CPU_BIG_ENDIAN doesn't seem to work with lld, and LTO > doesn't work with ld.bfd. > I've added a CPU_LITTLE_ENDIAN dependency to > ARCH_SUPPORTS_LTO_CLANG{,THIN} Ah, good point. I'll fix this in v9. [...] > Not sure if these are all known issues. If there is one you'd like me try > take a closer look at for finding which config options break it, I can try No, none of these are known issues. I would be happy to take a closer look if you can share configs that reproduce these. Sami