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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A175DC61DA4 for ; Wed, 15 Feb 2023 02:37:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232822AbjBOChe (ORCPT ); Tue, 14 Feb 2023 21:37:34 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57940 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232779AbjBOChc (ORCPT ); Tue, 14 Feb 2023 21:37:32 -0500 Received: from bg4.exmail.qq.com (bg4.exmail.qq.com [43.154.221.58]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1F89F31E14 for ; Tue, 14 Feb 2023 18:37:27 -0800 (PST) X-QQ-mid: bizesmtp90t1676428611tg2aeyqf Received: from localhost.localdomain ( [116.30.131.224]) by bizesmtp.qq.com (ESMTP) with id ; Wed, 15 Feb 2023 10:36:50 +0800 (CST) X-QQ-SSF: 01200000000000C0S000000A0000000 X-QQ-FEAT: 5q30pvLz2id9OWHmZBHyel5Z+VxupIKX8tOxdUvJ2Sm6Ur1eW4eOqxmdiDkP7 0u4dxNhC02Uy4qQ3nA0pC/pXD+mrRi9omPGwtK7z8STNWm55MKr3JcdRy/dWr+HC7sclqNo PC5Rl+2jSvmgYkc1xaWX7ZoNvObbdFn5Am6UNKfUfufdCk6+7vm0BSeKRJxqlxDDJqkaywv 74Pm/NKm2OFplkWphNzS0vjjuy7oo6aJcWUAASTVLmy6A5DyZ6xzSV7yYNYxl/NbjrIwM0U A6d84LukKidn2n+/37SVdmFRUBmJ126P4iR0iZMRSyRKxdwH5OUU3gmpEQv3nv/eloD+4gu YrySkNpOEzYts7/9HunA8MEne/FTn95BXYQn33o X-QQ-GoodBg: 0 From: Zhangjin Wu To: Willy Tarreau , "Paul E . McKenney" Cc: Zhangjin Wu , nicolas.pitre@linaro.org, josh@joshtriplett.org, linux-kernel@vger.kernel.org, Adam Borowski , Paul Burton Subject: Re: Re: Kernel-only deployments? Date: Wed, 15 Feb 2023 10:35:57 +0800 Message-Id: <20230215023557.7241-1-falcon@tinylab.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20180823190657.GA12057@1wt.eu> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-QQ-SENDSIZE: 520 Feedback-ID: bizesmtp:tinylab.org:qybglogicsvr:qybglogicsvr7 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Willy & Paul Thanks very much for your work on nolibc, based on the nolibc feature and the gc-sections feature from Paul Burton, I have tried to 'gc' the dead system calls not used in the nolibc applications. Tests shows, the gc-sections shrinks a minimal config of RISC-V 64 by ~10% and the gc-sections for syscalls shrinks another ~4.6% (~200k). Since nolibc has been added into tools/include/nolibc, it may be possible to auto 'gc' the dead syscalls automatically while building the nolibc based initrd, but it requires to auto update the architecture specific system call table after building the nolibc application: 1. Eliminate the unused functions and syscalls of the nolibc application add -ffunction-sections -fdata-sections and -Wl,--gc-sections to compile the nolibc application 2. Dump the used syscalls with the help of objdump This is architecture dependent, a RISC-V 64 example: riscv64-linux-gnu-objdump -d $nolibc_bin | \ egrep "li[[:space:]]*a7|ecall" | \ egrep -B1 ecall | \ egrep "li[[:space:]]*a7" | \ rev | cut -d ' ' -f1 | rev | cut -d ',' -f2 | \ sort -u -g Use a simple hello.c with reboot() at the end as an example, the dumped syscall numbers are: 64 93 142 3. Update architecture specific system call table Use RISC-V 64 as an example, arch/riscv/kernel/syscall_table.c: diff --git a/arch/riscv/kernel/syscall_table.c b/arch/riscv/kernel/syscall_table.c index 44b1420a2270..3b48a94c0ae8 100644 --- a/arch/riscv/kernel/syscall_table.c +++ b/arch/riscv/kernel/syscall_table.c @@ -14,5 +14,10 @@ void * const sys_call_table[__NR_syscalls] = { [0 ... __NR_syscalls - 1] = sys_ni_syscall, -#include +// AUTO INSERT START + [64] = sys_write, + [93] = sys_exit, + [142] = sys_reboot, +// AUTO INSERT END +// #include }; 4. Build kernel with gc-sections, the unused syscalls will be eliminated It is not that complicated, but to mainline such a feature and let it support more architectures, it is not that easy. I have written more about this here: https://lore.kernel.org/linux-riscv/20230214084229.42623-1-falcon@tinylab.org/ So, is such a feature really useful? does anyone in the deep embedded space already do this? welcome your suggestion. Thanks - Zhangjin Wu On Thu, 23 Aug 2018 18:38:12 -0400, Willy Tarreau wrote: > > 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