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 52055C7EE2A for ; Sun, 4 Jun 2023 11:28:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230422AbjFDL2H (ORCPT ); Sun, 4 Jun 2023 07:28:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34002 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229462AbjFDL2G (ORCPT ); Sun, 4 Jun 2023 07:28:06 -0400 Received: from 1wt.eu (ded1.1wt.eu [163.172.96.212]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 2BE17DA; Sun, 4 Jun 2023 04:28:04 -0700 (PDT) Received: (from willy@localhost) by mail.home.local (8.17.1/8.17.1/Submit) id 354BRs1j001843; Sun, 4 Jun 2023 13:27:54 +0200 Date: Sun, 4 Jun 2023 13:27:54 +0200 From: Willy Tarreau To: Arnd Bergmann Cc: Zhangjin Wu , Thomas =?iso-8859-1?Q?Wei=DFschuh?= , linux-kernel , linux-kselftest , linux-riscv Subject: Re: [PATCH v3 11/12] selftests/nolibc: add new gettimeofday test cases Message-ID: References: <68dace9e2532316ff454894697ecfd99e419a523.1685777982.git.falcon@tinylab.org> <2fccaff5-2354-4ac0-8389-1004d47d8dc9@t-8ch.de> <51e1db37-3981-4ea5-9348-b6f6b31ecc8a@app.fastmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <51e1db37-3981-4ea5-9348-b6f6b31ecc8a@app.fastmail.com> Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org On Sun, Jun 04, 2023 at 11:24:39AM +0200, Arnd Bergmann wrote: > On Sun, Jun 4, 2023, at 10:29, ??? wrote: > > > > Sorry for missing part of your feedbacks, I will check if -nostdlib > > stops the linking of libgcc_s or my own separated test script forgot > > linking the libgcc_s manually. > > According to the gcc documentation, -nostdlib drops libgcc.a, but > adding -lgcc is the recommended way to bring it back. > > > And as suggestion from Thomas' reply, > > > >>> Perhaps we really need to add the missing __divdi3 and __aeabi_ldivmod and the > >>> ones for the other architectures, or get one from lib/math/div64.c. > > > >>No, these ones come from the compiler via libgcc_s, we must not try to > > reimplement them. And we should do our best to avoid depending on them > > to avoid the error you got above. > > > > So, the explicit conversion is used instead in the patch. > > I think a cast to a 32-bit type is ideal when converting the > clock_gettime() result into microseconds, since the kernel guarantees > that the timespec value is normalized, with all zeroes in the > upper 34 bits. Going through __aeabi_ldivmod would make the > conversion much slower. > > For user supplied non-normalized timeval values, it's not obvious > whether we need the full 64-bit division We don't have to care about these here for the microsecond part, because for decades these were exclusively 32-bit. Also the only one consuming this field would have been settimeofday() and it's already documented as returning EINVAL if tv_usec is not within the expected 0..999999 range. And when in doubt we should keep in mind that nolibc's purpose is not to become a yet-another full-blown libc alternative but just a small piece of software allowing to produce portable and compact binaries for testing or booting. Being a bit stricter than other libcs for the sake of code compactness is better here. Originally for example it was necessary to always pass the 3 arguments to open(). Over time we managed to make simple code compile with both glibc and nolibc, but when it comes at the cost of adding size and burden for the developers, such as forcing them to add libgcc, I prefer that we slightly limit the domain of application instead. Thanks! Willy