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=-1.0 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 1305CC10F03 for ; Sat, 2 Mar 2019 02:13:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D37ED20838 for ; Sat, 2 Mar 2019 02:13:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=nifty.com header.i=@nifty.com header.b="JDYOPLMI" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727697AbfCBCNv (ORCPT ); Fri, 1 Mar 2019 21:13:51 -0500 Received: from conssluserg-05.nifty.com ([210.131.2.90]:64263 "EHLO conssluserg-05.nifty.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726968AbfCBCNv (ORCPT ); Fri, 1 Mar 2019 21:13:51 -0500 Received: from mail-vk1-f181.google.com (mail-vk1-f181.google.com [209.85.221.181]) (authenticated) by conssluserg-05.nifty.com with ESMTP id x222Di3H013972; Sat, 2 Mar 2019 11:13:44 +0900 DKIM-Filter: OpenDKIM Filter v2.10.3 conssluserg-05.nifty.com x222Di3H013972 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nifty.com; s=dec2015msa; t=1551492825; bh=XbXan2AURT+UfKxn+6S042gHQGOknCAdduMwYMBjJM4=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=JDYOPLMIGZd1krPxT2Y2vIuqEZuky15ly+gQsFy2YwTyLTmOmHPjRjg4UxMHHhgaO +oRluAjIyA8pxGHfbRbmoBjTO/DwmMaEZ4/fUoYmN4WmvZ34RuRH0gUMIntpBQOMTf 2YG7JLBlQjcEqeueDPy1ooF77DzWMK0mYOQemvpO/klUSFAdfe7MIXmjw5cop8kKhC kONMwDPTqLK/mWbuxeUrM9CrWp+s6f8SHMEs/634y1eVL8x1VGekP21MPskIxZZkTu gmTBG5QjYa23xH3lb4zQqfYNJAKQsm7DoHLmgdoUlcq37jzlLCO76cuftoHxo5Pf1R O2jXytJIuh0pw== X-Nifty-SrcIP: [209.85.221.181] Received: by mail-vk1-f181.google.com with SMTP id l62so6135257vkh.0; Fri, 01 Mar 2019 18:13:44 -0800 (PST) X-Gm-Message-State: APjAAAUVaPecn6Qs1xoyLsCE9JE9xBm5/agVAwY3ExhPEkNeA9dlj7Av BgTjZ5Jb0S/ZO4N7/sIDvpoEub1WU5MZREOQTaU= X-Google-Smtp-Source: APXvYqxJSj4E6d2FxisV/Gt0QMyXD3cUgk6pVEEQqAlHRoDu8/Am7aez5bzltKvKoynh/lWF4nFWLMkiCgbgZASpzcg= X-Received: by 2002:a1f:9788:: with SMTP id z130mr4633346vkd.0.1551492823456; Fri, 01 Mar 2019 18:13:43 -0800 (PST) MIME-Version: 1.0 References: <20190227193748.132301-1-joel@joelfernandes.org> <20190228144306.GA138215@google.com> <20190301171954.GA217990@google.com> In-Reply-To: <20190301171954.GA217990@google.com> From: Masahiro Yamada Date: Sat, 2 Mar 2019 11:13:07 +0900 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v3 1/2] Provide in-kernel headers for making it easy to extend the kernel To: Joel Fernandes Cc: Linux Kernel Mailing List , Andrew Morton , Alexei Starovoitov , atish patra , Daniel Colascione , Dan Williams , Greg Kroah-Hartman , Guenter Roeck , Jonathan Corbet , Karim Yaghmour , Kees Cook , kernel-team@android.com, "open list:DOCUMENTATION" , "open list:KERNEL SELFTEST FRAMEWORK" , linux-trace-devel@vger.kernel.org, Manoj Rao , Masami Hiramatsu , Paul McKenney , "Peter Zijlstra (Intel)" , qais.yousef@arm.com, Randy Dunlap , Steven Rostedt , Shuah Khan , Thomas Gleixner , Yonghong Song 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 Sat, Mar 2, 2019 at 3:03 AM Joel Fernandes wrote: > > On Fri, Mar 01, 2019 at 03:25:05PM +0900, Masahiro Yamada wrote: > [...] > > > > I am guessing the user will run these commands > > > > on the target system. > > > > In other words, external modules are native-compiled. > > > > So, > > > > > > > > target-arch: arm64 > > > > host-arch: arm64 > > > > > > > > > > > > Is this correct? > > > > > > > > > > > > If I understood the assumed use-case correctly, > > > > kheaders.tar.xw will contain host-programs compiled for x86, > > > > which will not work on the target system. > > > > > > > > > > You are right, the above commands in the commit message work only if the > > > host/target are same arch due to scripts. > > > > > > However we can build with arm64 device connected to a host, like this (which > > > I tested): > > > > > > adb shell modprobe kheaders; adb pull /proc/kheaders.tar.xz > > > 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) ARCH=arm64 CROSS_COMPILE=aarch64- modules > > > adb push test.ko /data/; adb shell rmmod kheaders > > > > > > The other way we can make this work is using x86 usermode emulation inside a > > > chroot on the Android device which will make the earlier commands work. One > > > thing to note is that Android also runs on x86 hardware so the commands in > > > the commit message will work even for x86 Android targets already. > > > > > > Also note that this the "module building" part is really only one of the > > > usecases. eBPF is another which needs the headers - and the headers are vast > > > majority of the archive. Headers take 3.1MB out of 3.6MB of the archive on > > > arm64 builds. > > > > > > How do you want to proceed here, should I mention these points in the commit > > > message? > > > > > > > > I do not request a re-spin just for a matter of commit log, > > but this version produces an empty tarball. > > So, you will have a chance to update the patch anyway. > > > > In the next version, it would be nice to note that > > "external modules must be built on the same host arch > > as built vmlinux". > > Ok, I respun it with 1 more minor nit for arm64 building. Please take a look. I have not checked code-diff in v3 yet. Anyway, I will add comments to v4 if I notice something. > > Let me ask one more question. > > > > I guess this patch is motivated by > > how difficult to convey kernel headers > > from vendors to users. > > > > In that situation, how will the user find > > the right compiler to use for building external modules? > > > > > > > > > > Greg KH said: > > > > We don't ever support the system of loading a module built with anything > > other than the _exact_ same compiler than the kernel was. > > > > > > For the full context, see this: > > https://lore.kernel.org/patchwork/patch/836247/#1031547 > > IMO this issue is not related to this patch but is just an issue with > building external modules in general. I do not think it is an issue of the build system, at least. As far as I understood Greg's comment, it is troublesome without the assumption that vmlinux and modules are built by the same compiler. It is related to this patch since this patch assumes use-cases where external modules are built in a completely different environment, where a different compiler is probably installed. > It is up to the user to use the right > compiler, etc. I will let Greg comment more on that. > thanks, > > - Joel > -- Best Regards Masahiro Yamada