From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-6.1 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=ham autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id 259277D04D for ; Tue, 5 Mar 2019 16:27:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726535AbfCEQ1D (ORCPT ); Tue, 5 Mar 2019 11:27:03 -0500 Received: from mail-qk1-f194.google.com ([209.85.222.194]:38399 "EHLO mail-qk1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726561AbfCEQ1D (ORCPT ); Tue, 5 Mar 2019 11:27:03 -0500 Received: by mail-qk1-f194.google.com with SMTP id p15so5088582qkl.5 for ; Tue, 05 Mar 2019 08:27:02 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=d/RWTJYqTpuZTyuFKaESBOTYVSFBlzsLQJKVAB32I58=; b=hvmEqbCdYzsIqNYNZhPSlod6L2/r1WLETDpIHrXsLekgc9v1El22InXdQfaxdlU6v/ khZCqUzFW4O/b3Go6GnU9s8Y5OI31FCwvUVUQprsQHxYJPniY4bmNkUN1LOSwm6GkARA KzV3HrL5yIAEDapL21jvW8tIpAklee/viHBK8= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=d/RWTJYqTpuZTyuFKaESBOTYVSFBlzsLQJKVAB32I58=; b=lNY+NvHW78vIgwC+1K4O6jmmmgjSW7dLLbRnEFqUuZwglOpVfdwdKxUPQnxkkBs9C+ 8CwVOh3tuxxD1ZQJqbluJQg1dEHrMzp9NPG1ZLHzoNbSGAaU6BHdZLe7FAC/0xtagqy+ uuJjDxJKvcKCYE436SpuQ+8JsM8LgU27KUfy/kYYMXHDJGASji8Fg1U94TPnfKl77qQK FxPGGzuRlq1F/UGYaGUG9S7cSXvdh55iixcl+Zis1sMwZF2xsVimSgBV4WIyBUjqN2hS xLN5Ax94aWKv4dXLVsdc9I7oWcfXYOeI4Q0hW789Wdd+FKYR5oCbhVhAWJzbu1dgevNV wQyw== X-Gm-Message-State: APjAAAWVcmZO0xz8wabw0S4Yog0IatkKyEm7MAirj5tujhNUJpamHZhD 5EKfRgGyRZH10gFVcy+5m1BJ7g== X-Google-Smtp-Source: APXvYqw4rGj9VsJbXrMjYMyf9dK6MwNKmsds+4gEH8EbhNT6/YBj/DaGJvHtB0iYoSFX4uCsxsgrqQ== X-Received: by 2002:ae9:f112:: with SMTP id k18mr2291507qkg.231.1551803221801; Tue, 05 Mar 2019 08:27:01 -0800 (PST) Received: from localhost ([2620:0:1004:1100:cca9:fccc:8667:9bdc]) by smtp.gmail.com with ESMTPSA id v26sm5798571qtk.22.2019.03.05.08.27.00 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 05 Mar 2019 08:27:00 -0800 (PST) Date: Tue, 5 Mar 2019 11:27:00 -0500 From: Joel Fernandes To: Qais Yousef Cc: linux-kernel@vger.kernel.org, Andrew Morton , ast@kernel.org, atishp04@gmail.com, dancol@google.com, Dan Williams , dietmar.eggemann@arm.com, gregkh@linuxfoundation.org, Guenter Roeck , Jonathan Corbet , karim.yaghmour@opersys.com, Kees Cook , kernel-team@android.com, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-trace-devel@vger.kernel.org, Manoj Rao , Masahiro Yamada , mhiramat@kernel.org, rdunlap@infradead.org, rostedt@goodmis.org, Shuah Khan , yhs@fb.com Subject: Re: [PATCH v4 1/2] Provide in-kernel headers for making it easy to extend the kernel Message-ID: <20190305162700.GB78911@google.com> References: <20190301160856.129678-1-joel@joelfernandes.org> <20190304140059.5t2bhq7x27jbiuqx@e107158-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190304140059.5t2bhq7x27jbiuqx@e107158-lin.cambridge.arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Mon, Mar 04, 2019 at 02:00:59PM +0000, Qais Yousef wrote: > On 03/01/19 11:08, Joel Fernandes (Google) wrote: > > Introduce in-kernel headers and other artifacts which are made available > > as an archive through proc (/proc/kheaders.tar.xz file). This archive makes > > it possible to build kernel modules, run eBPF programs, and other > > tracing programs that need to extend the kernel for tracing purposes > > without any dependency on the file system having headers and build > > artifacts. > > > > On Android and embedded systems, it is common to switch kernels but not > > have kernel headers available on the file system. Raw kernel headers > > also cannot be copied into the filesystem like they can be on other > > distros, due to licensing and other issues. There's no linux-headers > > package on Android. Further once a different kernel is booted, any > > headers stored on the file system will no longer be useful. By storing > > the headers as a compressed archive within the kernel, we can avoid these > > issues that have been a hindrance for a long time. > > > > The feature is also buildable as a module just in case the user desires > > it not being part of the kernel image. This makes it possible to load > > and unload the headers on demand. A tracing program, or a kernel module > > builder can load the module, do its operations, and then unload the > > module to save kernel memory. The total memory needed is 3.8MB. > > > > The code to read the headers is based on /proc/config.gz code and uses > > the same technique to embed the headers. > > > > To build a module, the below steps have been tested on an x86 machine: > > modprobe kheaders > > rm -rf $HOME/headers > > mkdir -p $HOME/headers > > tar -xvf /proc/kheaders.tar.xz -C $HOME/headers >/dev/null > > cd my-kernel-module > > make -C $HOME/headers M=$(pwd) modules > > rmmod kheaders > > > > Additional notes: > > (1) external modules must be built on the same arch as the host that > > built vmlinux. This can be done either in a qemu emulated chroot on the > > target, or natively. This is due to host arch dependency of kernel > > scripts. > > > > (2) > > A limitation of module building with this is, since Module.symvers is > > not available in the archive due to a cyclic dependency with building of > > the archive into the kernel or module binaries, the modules built using > > the archive will not contain symbol versioning (modversion). This is > > usually not an issue since the idea of this patch is to build a kernel > > module on the fly and load it into the same kernel. An appropriate > > warning is already printed by the kernel to alert the user of modules > > not having modversions when built using the archive. For building with > > modversions, the user can use traditional header packages. For our > > tracing usecases, we build modules on the fly with this so it is not a > > concern. > > > > (3) I have left IKHD_ST and IKHD_ED markers as is to facilitate > > future patches that would extract the headers from a kernel or module > > image. > > > > Signed-off-by: Joel Fernandes (Google) > > I could get the headers using this patch in both built-in and modules options. > > You can add my tested-and-reviewed-by: Qais Yousef > > I am not familiar with running kselftests so didn't get a chance to try the > next patch. Thanks a lot for testing! Will repost with the tags soon. - Joel