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=-10.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 BF9E9C2BBD0 for ; Sat, 5 Sep 2020 20:18:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 83A422073B for ; Sat, 5 Sep 2020 20:18:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1599337111; bh=JJsATsMVElGjYABsb0vWB2hqBGkj04Smv3z/n38lfv4=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=VGtNB5G8mRRxvbzKosQaj5cy8ibTLaGZkOS38YJB5TAPGvObIT8v0Grdm78917Rtl m0bfet+gxu8RK8X6BNnsWNuD9FhAja1uO9YaaireCkUDRu8VdbGRBnrFF2rJ0z9s+G plKjFoNHKeZ+u0kJ0UYM/VpTTYJe2FwXVPKp5dtM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728627AbgIEUSa (ORCPT ); Sat, 5 Sep 2020 16:18:30 -0400 Received: from conssluserg-01.nifty.com ([210.131.2.80]:52079 "EHLO conssluserg-01.nifty.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727875AbgIEUSZ (ORCPT ); Sat, 5 Sep 2020 16:18:25 -0400 X-Greylist: delayed 110455 seconds by postgrey-1.27 at vger.kernel.org; Sat, 05 Sep 2020 16:18:23 EDT Received: from mail-pf1-f179.google.com (mail-pf1-f179.google.com [209.85.210.179]) (authenticated) by conssluserg-01.nifty.com with ESMTP id 085KIAXe008998; Sun, 6 Sep 2020 05:18:11 +0900 DKIM-Filter: OpenDKIM Filter v2.10.3 conssluserg-01.nifty.com 085KIAXe008998 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nifty.com; s=dec2015msa; t=1599337091; bh=AM99QzFxxKGBKlEOzZ//FGYuWqlVjObjhMrW0TXZ1vI=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=2mT3GBG1wE8G/yhfLSiGJrSIlfMwrbNAUJKfC8gZ3etoILU0Zt8SumIhqPwfSULnc NiTXPP6y+jVKTSdF52qblNj8+Erwe44OAi3+JvNj3bnz1xnxKFq7ODs67zco8o0vN/ 3TsC6sQGntZygvez3VSOoQd+9TJdtVBzKLn31Tii+GMykpZKux2BYRxCt7WzqItnhf gQF8087kfcTGYy6+HQH8Nm7HxU9Soano2FeVeXwfbVYa1sktzUe5OKbi1/IDSFfoRv AQGmR5q2uh4wolJFo7NXbJsHPQOtZZYon5wxO3OEc6anfYAFK6QTSLvUTvWKMtN4DG SLh9BXK/ERc5Q== X-Nifty-SrcIP: [209.85.210.179] Received: by mail-pf1-f179.google.com with SMTP id k15so6467835pfc.12; Sat, 05 Sep 2020 13:18:11 -0700 (PDT) X-Gm-Message-State: AOAM533M+KOq3mFmd0jb1/ESVUCxpW0tDyvpKFOIZgBluRINYk59EXaY RAVvkRAEokIuKgEPToF2gs+W40wYJInEP73EgFA= X-Google-Smtp-Source: ABdhPJyNsnmMbyAG66fOWmKiovR25YJyERnRLtPM25a82Zl3RS3nL26piTxmNQ2uNI60/yqc3rOaDVz5VEX2fwwCiOI= X-Received: by 2002:a62:8007:0:b029:13c:1611:6533 with SMTP id j7-20020a6280070000b029013c16116533mr12182097pfd.5.1599337089871; Sat, 05 Sep 2020 13:18:09 -0700 (PDT) MIME-Version: 1.0 References: <20200624203200.78870-1-samitolvanen@google.com> <20200903203053.3411268-1-samitolvanen@google.com> <20200903203053.3411268-10-samitolvanen@google.com> In-Reply-To: <20200903203053.3411268-10-samitolvanen@google.com> From: Masahiro Yamada Date: Sun, 6 Sep 2020 05:17:32 +0900 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v2 09/28] kbuild: add support for Clang LTO To: Sami Tolvanen Cc: Will Deacon , Peter Zijlstra , Steven Rostedt , Greg Kroah-Hartman , "Paul E. McKenney" , Kees Cook , Nick Desaulniers , clang-built-linux , Kernel Hardening , linux-arch , linux-arm-kernel , Linux Kbuild mailing list , Linux Kernel Mailing List , linux-pci@vger.kernel.org, X86 ML Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 4, 2020 at 5:31 AM Sami Tolvanen wrote: > > This change adds build system support for Clang's Link Time > Optimization (LTO). With -flto, instead of ELF object files, Clang > produces LLVM bitcode, which is compiled into native code at link > time, allowing the final binary to be optimized globally. For more > details, see: > > https://llvm.org/docs/LinkTimeOptimization.html > > The Kconfig option CONFIG_LTO_CLANG is implemented as a choice, > which defaults to LTO being disabled. To use LTO, the architecture > must select ARCH_SUPPORTS_LTO_CLANG and support: > > - compiling with Clang, > - compiling inline assembly with Clang's integrated assembler, > - and linking with LLD. > > While using full LTO results in the best runtime performance, the > compilation is not scalable in time or memory. CONFIG_THINLTO > enables ThinLTO, which allows parallel optimization and faster > incremental builds. ThinLTO is used by default if the architecture > also selects ARCH_SUPPORTS_THINLTO: > > https://clang.llvm.org/docs/ThinLTO.html > > To enable LTO, LLVM tools must be used to handle bitcode files. The > easiest way is to pass the LLVM=1 option to make: > > $ make LLVM=1 defconfig > $ scripts/config -e LTO_CLANG > $ make LLVM=1 > > Alternatively, at least the following LLVM tools must be used: > > CC=clang LD=ld.lld AR=llvm-ar NM=llvm-nm > > To prepare for LTO support with other compilers, common parts are > gated behind the CONFIG_LTO option, and LTO can be disabled for > specific files by filtering out CC_FLAGS_LTO. > > Note that support for DYNAMIC_FTRACE and MODVERSIONS are added in > follow-up patches. > > Signed-off-by: Sami Tolvanen > --- > Makefile | 18 +++++++- > arch/Kconfig | 68 +++++++++++++++++++++++++++++++ > include/asm-generic/vmlinux.lds.h | 11 +++-- > scripts/Makefile.build | 9 +++- > scripts/Makefile.modfinal | 9 +++- > scripts/Makefile.modpost | 24 ++++++++++- > scripts/link-vmlinux.sh | 32 +++++++++++---- > 7 files changed, 154 insertions(+), 17 deletions(-) > > diff --git a/Makefile b/Makefile > index a9dae26c93b5..dd49eaea7c25 100644 > --- a/Makefile > +++ b/Makefile > @@ -909,6 +909,22 @@ KBUILD_CFLAGS += $(CC_FLAGS_SCS) > export CC_FLAGS_SCS > endif > > +ifdef CONFIG_LTO_CLANG > +ifdef CONFIG_THINLTO > +CC_FLAGS_LTO_CLANG := -flto=thin -fsplit-lto-unit > +KBUILD_LDFLAGS += --thinlto-cache-dir=.thinlto-cache > +else > +CC_FLAGS_LTO_CLANG := -flto > +endif > +CC_FLAGS_LTO_CLANG += -fvisibility=default > +endif > + > +ifdef CONFIG_LTO > +CC_FLAGS_LTO := $(CC_FLAGS_LTO_CLANG) $(CC_FLAGS_LTO_CLANG) is not used elsewhere. Why didn't you add the flags to CC_FLAGS_LTO directly? Will it be useful if LTO_GCC is supported ? > +KBUILD_CFLAGS += $(CC_FLAGS_LTO) > +export CC_FLAGS_LTO > +endif -- Best Regards Masahiro Yamada