From patchwork Tue Feb 25 21:02:49 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Nick Desaulniers X-Patchwork-Id: 11404605 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 EC46313A4 for ; Tue, 25 Feb 2020 21:02:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C95CA20675 for ; Tue, 25 Feb 2020 21:02:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="az9/lEQ6" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728383AbgBYVC7 (ORCPT ); Tue, 25 Feb 2020 16:02:59 -0500 Received: from mail-qk1-f201.google.com ([209.85.222.201]:47760 "EHLO mail-qk1-f201.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728618AbgBYVC7 (ORCPT ); Tue, 25 Feb 2020 16:02:59 -0500 Received: by mail-qk1-f201.google.com with SMTP id h6so541266qkj.14 for ; Tue, 25 Feb 2020 13:02:58 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=vWB3la6MZAcuUeVOqIcp281F5LSfjcobFajXxwkFi6A=; b=az9/lEQ6wwXYJyI3Gy29nxJIfWaxkNA++/xMMPhGH9Bp55F58tIoAVd2evBeCT3IlI KKgT00uOWJLWB6jM4tMv/BPZk2IBrtNGq1UX9hERFKv4CE6BDLW/6YKDNoqRugx0oOT1 JFEPhPT7z9F67zo+gQk9nVxt8J2a//vG9eP1UplMOqDnWzcoXl0qqUpUbhow29LFFsDn reHM0SO7vQWbTfc/yOUJLSXO7dgd9DEpCrAc4RVQU0ltXVvkKgrYgYLltwqnerD/XmQS /3lvr+TKKjaUhwe/wV9rXCo1vDnYLQPRPVlKZHfsvP2A00O5Bpk2Anzs0X1WZLoKap6w wzAQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=vWB3la6MZAcuUeVOqIcp281F5LSfjcobFajXxwkFi6A=; b=iJPiyWfkcyhGUcZT8J+/ACHOBEKDZC9PZ6YkjztYeSTgBLS5ZVFTULeKvRnDLSEEzl Pj9tCL01LTa4Dn4Nywe0T1TAg28rxAngm2OLXU0YY8KIfUPXs7mKUz31p/lUGbvrDjCb WluSvIwahrL9DFbOjgN7gJuHEzYVQIXRx5n9pHXwsvkl8sQEFeYTnMqYxqzfgX3bdBZW 10OnotfShq1OlAkCdvk83iWFvrm9iiGMwP7uUeR4fRVSJd5fh9FNfe1mMZrydQ7nngrr zdEGSnrisshCCYPLvj9aEsMDehxHVClr5ayZskiMkjSpf1GGHVIJLibpcp1qjGWQaoiz GsXg== X-Gm-Message-State: APjAAAXfoCQrrX6JsK9i40f1rRshxPl5RW2q4Ls6KZyJgzQnmsNwS3aZ XF/48PXLKjWpA6HjiI1VqhGDMKZ/YsI9/G/wY/U= X-Google-Smtp-Source: APXvYqw9j4SjKcqy0U3A0k0fMjgQj/y1SE9wLfZHXsZM0aTr3GyALCU9cgEB1u7akUo3JkjTfFIOLdEo4I2R8DIwtHE= X-Received: by 2002:ad4:48c6:: with SMTP id v6mr930719qvx.207.1582664577840; Tue, 25 Feb 2020 13:02:57 -0800 (PST) Date: Tue, 25 Feb 2020 13:02:49 -0800 In-Reply-To: <20200224174129.2664-1-ndesaulniers@google.com> Message-Id: <20200225210250.64366-1-ndesaulniers@google.com> Mime-Version: 1.0 References: <20200224174129.2664-1-ndesaulniers@google.com> X-Mailer: git-send-email 2.25.0.265.gbab2e86ba0-goog Subject: [PATCH v2] Documentation/llvm: add documentation on building w/ Clang/LLVM From: Nick Desaulniers To: corbet@lwn.net, masahiroy@kernel.org Cc: Nick Desaulniers , Randy Dunlap , Kees Cook , Nathan Chancellor , Sedat Dilek , Michal Marek , linux-kbuild@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com Sender: linux-kbuild-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kbuild@vger.kernel.org Added to kbuild documentation. Provides more official info on building kernels with Clang and LLVM than our wiki. Suggested-by: Randy Dunlap Reviewed-by: Kees Cook Reviewed-by: Nathan Chancellor Reviewed-by: Sedat Dilek Signed-off-by: Nick Desaulniers Reviewed-by: Kees Cook --- Changes V1 -> V2: * s/On going/ongoing/ * add Randy's Suggested-by * add Nathan and Sedat's Reviewed-by * Upgrade Kees' Sugguested-by to Reviewed-by * s/suffix/prefix/ 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..d6c79eb4e23e --- /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. Ongoing 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 prefix 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/