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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT 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 955D9C4321D for ; Thu, 23 Aug 2018 19:07:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 15F49208E8 for ; Thu, 23 Aug 2018 19:07:11 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 15F49208E8 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=1wt.eu Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727482AbeHWWiM (ORCPT ); Thu, 23 Aug 2018 18:38:12 -0400 Received: from wtarreau.pck.nerim.net ([62.212.114.60]:32904 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726081AbeHWWiM (ORCPT ); Thu, 23 Aug 2018 18:38:12 -0400 Received: (from willy@localhost) by pcw.home.local (8.15.2/8.15.2/Submit) id w7NJ6vIk012063; Thu, 23 Aug 2018 21:06:57 +0200 Date: Thu, 23 Aug 2018 21:06:57 +0200 From: Willy Tarreau To: Adam Borowski Cc: "Paul E. McKenney" , nicolas.pitre@linaro.org, josh@joshtriplett.org, linux-kernel@vger.kernel.org Subject: Re: Kernel-only deployments? Message-ID: <20180823190657.GA12057@1wt.eu> References: <20180823174359.GA13033@linux.vnet.ibm.com> <20180823185417.y3ung3b553f2d24a@angband.pl> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180823185417.y3ung3b553f2d24a@angband.pl> User-Agent: Mutt/1.6.1 (2016-04-27) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 23, 2018 at 08:54:17PM +0200, Adam Borowski wrote: > .globl _start > .data > req: .8byte 999999999, 999999999 > .text > _start: > mov $35, %rax # syscall: nanosleep > mov $req, %rdi > xor %rsi, %rsi > syscall > jmp _start > > > as sl.s -o sl.o > ld sl.o -o init > > 'Ere you go, no libc needed. If your arch is not amd64, just say so. > > If you want to do anything more complex, though -- you really want musl > or another lightweight libc instead. Glibc is utterly unfit for static > linking. Since there seems to be some interest about this, I'll repost this here. I've developed a "nolibc" include file which implements most common syscalls and string functions (those I use in early boot) as static inlines so the resulting executable only contains the code you really use : http://git.formilux.org/?p=people/willy/nolibc.git;a=tree Example : $ echo "int main() { return sleep(3);}" | gcc -Os -nostdlib -include ../nolibc/nolibc.h -s -fno-exceptions -fno-asynchronous-unwind-tables -fno-unwind-tables -lgcc -o sleep -xc - $ ls -l sleep -rwxr-xr-x 1 willy users 664 Aug 23 20:37 sleep It's actually used by my pre-init loader that is embedded into the initramfs of all my kernels, to untar the modules and switch to the initrd or rootfs. This way all my modules are contained into the kernel image and I can easily use many different kernels with rootfs without having to install modules. Just in case someone curious would want to know more about it, the (old and horrible) preinit is here : http://git.formilux.org/?p=dist/src/flxutils.git;a=tree;f=init;h=9dc8fbae6383d9b4d56d34cc6c3d59585318bef8;hb=HEAD And the (old and ugly) build script is here : http://git.formilux.org/?p=dist/techno.git;a=tree;f=scripts/kernel;hb=HEAD Yes it's aging a lot now but it's still very convenient ;-) Willy