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=-22.4 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT,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 CA639C11D30 for ; Mon, 24 Feb 2020 17:41:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9763E20838 for ; Mon, 24 Feb 2020 17:41:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="RVEFVPgU" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728085AbgBXRlm (ORCPT ); Mon, 24 Feb 2020 12:41:42 -0500 Received: from mail-pg1-f201.google.com ([209.85.215.201]:54549 "EHLO mail-pg1-f201.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728043AbgBXRll (ORCPT ); Mon, 24 Feb 2020 12:41:41 -0500 Received: by mail-pg1-f201.google.com with SMTP id l17so7077741pgh.21 for ; Mon, 24 Feb 2020 09:41:41 -0800 (PST) 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=5nz7K/9gLs7EaewmF2wRn410ngVKaW83QWECedJma1o=; b=RVEFVPgU+ScpyMwz7WfaB+ItQ1JnmyRVQdauoq5Hla6qBbUseznXc4uAFG7Bn9wDIQ xN27LFJFYWTi2nwnRc4n2jIIiBUA8AKjhSKIsI2w6L+MLGraE8CBzpoNAY+jQj142T2c GbsQkJys39l//NmYke/Dl3qt8pWth1ivhTFGoSuRmWOi7ZTEiuEwu6uqmf2+EAbN4Xwj yGcx48yYsSLTF7Fs/bk88t2dE9K/MNFltYl2jSGsjdtuAIUIy3NePMj0qin8WcxIsvMK KuM4AmzgvD5/9sbPJ652/5IesJ6rdo9giLLcRyRm2CxhsY9OnV2nuczIFHaSA+kRg/W7 /IdA== 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=5nz7K/9gLs7EaewmF2wRn410ngVKaW83QWECedJma1o=; b=RNgdMIvylS+1+1IMIoljhTh4OvpRViD37z8WEuA11hjqSwtf5vfkmT8oQ8c2aTdivS kuSIIyp1y+9oR1Gkw3bQD8zJNlLnV1Apl+siFyYVu38LcAeFlFt7xBZeM5RDYgGYS/FB IqVMSPoXwhQJRV32lF2h5tLIJSt3Z5TcudCUvY2rB0iuT3CNgi3HXwXJbGMRyXoaB2ti +9GoxohuiIW2SkZ4CKszBBVN9HxP6N6tyntPcXA2Jv1dT/HsTap2edWw+fvCkbVCU4Wj dpcx+mFIjUHj2I4k3xXMJNEJCxaLKjr6fkFOQoaSYXFP/rzvXgSkSCksZPT7TBXo2mYC i3vA== X-Gm-Message-State: APjAAAU/I6xHiDQXR89Xm5e/4/NmVCTI5yArz8G4LRBKe7LV/bmqjaKX 3VDtvIomCDPfDVnkfeIQvXNbccGcQXPAtDYTKBM= X-Google-Smtp-Source: APXvYqyH8QxNwAutG1ZN9iCwc4/0fjrPF2jacaW4sjYkH4gbhT4P+UST1Yofs3uM/wUc87c1owiFJwJcD3WtXXPUqY0= X-Received: by 2002:a63:ae0a:: with SMTP id q10mr53967461pgf.178.1582566100948; Mon, 24 Feb 2020 09:41:40 -0800 (PST) Date: Mon, 24 Feb 2020 09:41:28 -0800 Message-Id: <20200224174129.2664-1-ndesaulniers@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.25.0.265.gbab2e86ba0-goog Subject: [PATCH] Documentation/llvm: add documentation on building w/ Clang/LLVM From: Nick Desaulniers To: corbet@lwn.net, masahiroy@kernel.org Cc: Nick Desaulniers , Kees Cook , Nathan Chancellor , Michal Marek , linux-kbuild@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com 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 Added to kbuild documentation. Provides more official info on building kernels with Clang and LLVM than our wiki. Suggested-by: Kees Cook Reviewed-by: Nathan Chancellor Signed-off-by: Nick Desaulniers --- Documentation/kbuild/index.rst | 1 + Documentation/kbuild/llvm.rst | 80 ++++++++++++++++++++++++++++++++++ 2 files changed, 81 insertions(+) create mode 100644 Documentation/kbuild/llvm.rst diff --git a/Documentation/kbuild/index.rst b/Documentation/kbuild/index.rst index 0f144fad99a6..3882bd5f7728 100644 --- a/Documentation/kbuild/index.rst +++ b/Documentation/kbuild/index.rst @@ -19,6 +19,7 @@ Kernel Build System issues reproducible-builds + llvm .. only:: subproject and html diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst new file mode 100644 index 000000000000..68ae022aebc0 --- /dev/null +++ b/Documentation/kbuild/llvm.rst @@ -0,0 +1,80 @@ +============================== +Building Linux with Clang/LLVM +============================== + +This document covers how to build the Linux kernel with Clang and LLVM +utilities. + +About +----- + +The Linux kernel has always traditionally been compiled with GNU toolchains +such as GCC and binutils. On going work has allowed for `Clang +`_ and `LLVM `_ utilities to be +used as viable substitutes. Distributions such as `Android +`_, `ChromeOS +`_, and `OpenMandriva +`_ use Clang built kernels. `LLVM is a +collection of toolchain components implemented in terms of C++ objects +`_. Clang is a front-end to LLVM that +supports C and the GNU C extensions required by the kernel, and is pronounced +"klang," not "see-lang." + +Clang +----- + +The compiler used can be swapped out via `CC=` command line argument to `make`. +`CC=` should be set when selecting a config and during a build. + + make CC=clang defconfig + + make CC=clang + +Cross Compiling +--------------- + +A single Clang compiler binary will typically contain all supported backends, +which can help simplify cross compiling. + + ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make CC=clang + +`CROSS_COMPILE` is not used to suffix the Clang compiler binary, instead +`CROSS_COMPILE` is used to set a command line flag: `--target `. For +example: + + clang --target aarch64-linux-gnu foo.c + +LLVM Utilities +-------------- + +LLVM has substitutes for GNU binutils utilities. These can be invoked as +additional parameters to `make`. + + make CC=clang AS=clang LD=ld.lld AR=llvm-ar NM=llvm-nm STRIP=llvm-strip \\ + OBJCOPY=llvm-objcopy OBJDUMP=llvm-objdump OBJSIZE=llvm-objsize \\ + READELF=llvm-readelf HOSTCC=clang HOSTCXX=clang++ HOSTAR=llvm-ar \\ + HOSTLD=ld.lld + +Getting Help +------------ + +- `Website `_ +- `Mailing List `_: +- `Issue Tracker `_ +- IRC: #clangbuiltlinux on chat.freenode.net +- `Telegram `_: @ClangBuiltLinux +- `Wiki `_ +- `Beginner Bugs `_ + +Getting LLVM +------------- + +- http://releases.llvm.org/download.html +- https://github.com/llvm/llvm-project +- https://llvm.org/docs/GettingStarted.html +- https://llvm.org/docs/CMake.html +- https://apt.llvm.org/ +- https://www.archlinux.org/packages/extra/x86_64/llvm/ +- https://github.com/ClangBuiltLinux/tc-build +- https://github.com/ClangBuiltLinux/linux/wiki/Building-Clang-from-source +- https://android.googlesource.com/platform/prebuilts/clang/host/linux-x86/ -- 2.25.0.265.gbab2e86ba0-goog