From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on gnuweeb.org X-Spam-Level: X-Spam-Status: No, score=-2.0 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, NICE_REPLY_A,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.6 Received: from mail-il1-f180.google.com (mail-il1-f180.google.com [209.85.166.180]) by gnuweeb.org (Postfix) with ESMTPS id E13507E3B7 for ; Mon, 18 Apr 2022 15:24:00 +0000 (UTC) Authentication-Results: gnuweeb.org; dkim=pass (2048-bit key; unprotected) header.d=kernel-dk.20210112.gappssmtp.com header.i=@kernel-dk.20210112.gappssmtp.com header.a=rsa-sha256 header.s=20210112 header.b=nMGP++Wl; dkim-atps=neutral Received: by mail-il1-f180.google.com with SMTP id i8so3713633ila.5 for ; Mon, 18 Apr 2022 08:24:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20210112.gappssmtp.com; s=20210112; h=message-id:date:mime-version:user-agent:subject:content-language:to :cc:references:from:in-reply-to:content-transfer-encoding; bh=8Iqyww9DEAjB3MOyihAAT+JyYCPpbthvKoltZeSNRvY=; b=nMGP++WlkRp99/ZjYg8u+sOuqyVU1QHCB0jlQzUD9THnztmbZpLnmVLti2V/OlV10p sxeUE+l3dDxxK/AnBxpMmTMf5hKWC2yWqnSpKmKO7Q7di1vHGurnQ23+U73Iacw1O7M8 pGNdG6GCwLTxl8yhUSDpP4kiP+luwNLv+LsaAUxBN3EkRzNk3T7fzRc5KxFdUlEa0TN3 cCypOF25q2kDEd7kNyV3Yz/QP6ptQyf//L4k/DCW+PmKBmap8BT6EBqS0i54UBeG1gvi 0yya9i0ERbJJ5DwdAejx0us4M283u1aMRCeN6lItyo6JaBPEw2h8nZ/HpOqJcmCU1bQg 9L6w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:message-id:date:mime-version:user-agent:subject :content-language:to:cc:references:from:in-reply-to :content-transfer-encoding; bh=8Iqyww9DEAjB3MOyihAAT+JyYCPpbthvKoltZeSNRvY=; b=cGH7g82kiouMDEBj2hJwuSkORRZ2iF6qMRzBMFDMue+PNdOvn/C3s1x7TqakFkLg8C 30TyDG6bueUdd2FKlS0hpDa0XCnpepxaDMRbZuox947GBLcZ7wwLPq0R7ksyTe6gKvyI HKGz+LkMR1etQunjulnbkaiv4ZBS1oKpYworZrd+DqBH7t4kjxbFOGwMQ6IH5E/NnKRM /SLs/k8a0fZnAk+do1jSQiAIAZRFZzphI4FSRMyvrrwGqF55CgLBTU1pcC/jkS3NyV4F ozkhkdpvzClksu3te0tdm45S1lhF3SBDNol9aTQ1Txs2R68k6bC2W+z773wzdtk4a3+j 44Pg== X-Gm-Message-State: AOAM5304Gfr5EinJUbYD53ekF2H0EPuwNqemHoI/NrTt6nQh3ajJDLkb dudxOqmR+o4MYywli84OrTpkoA== X-Google-Smtp-Source: ABdhPJzc3MYBXf0nS9rSsOhkX2uF3P8CgB4ABhopWCSjnRflFnucUE7kG8V469ZIv6jQI+rgjRFrFA== X-Received: by 2002:a92:ca06:0:b0:2cc:3a47:e5d with SMTP id j6-20020a92ca06000000b002cc3a470e5dmr909372ils.115.1650295439766; Mon, 18 Apr 2022 08:23:59 -0700 (PDT) Received: from [192.168.1.172] ([207.135.234.126]) by smtp.gmail.com with ESMTPSA id p66-20020a6bbf45000000b006499925f1f1sm8483460iof.19.2022.04.18.08.23.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 18 Apr 2022 08:23:58 -0700 (PDT) Message-ID: Date: Mon, 18 Apr 2022 09:23:57 -0600 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0 Subject: Re: [PATCH liburing 0/3] Add x86 32-bit support for the nolibc build Content-Language: en-US To: Ammar Faizi Cc: io-uring Mailing List , GNU/Weeb Mailing List , Pavel Begunkov , Alviro Iskandar Setiawan References: <20220414224001.187778-1-ammar.faizi@intel.com> <459a2922-55cd-aec1-f4f2-bf037844017f@kernel.dk> From: Jens Axboe In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit List-Id: On 4/18/22 8:14 AM, Ammar Faizi wrote: > On 4/18/22 9:01 AM, Jens Axboe wrote: >> On 4/14/22 4:41 PM, Ammar Faizi wrote: >>> Hi, >>> >>> This series adds nolibc support for x86 32-bit. There are 3 patches in >>> this series: >>> >>> 1) Use `__NR_mmap2` instead of `__NR_mmap` for x86 32-bit. >>> 2) Provide `get_page_size()` function for x86 32-bit. >>> 3) Add x86 32-bit native syscall support. >>> >>> The most noticeable changes is the patch 3. Unlike x86-64, only >>> use native syscall from the __do_syscall macros when CONFIG_NOLIBC is >>> enabled for 32-bit build. The reason is because the libc syscall >>> wrapper can do better in 32-bit. The libc syscall wrapper can dispatch >>> the best syscall instruction that the environment is supported, there >>> are at least two variants syscall instruction for x86 32-bit, they are: >>> `int $0x80` and `sysenter`. The `int $0x80` instruction is always >>> available, but `sysenter` is not, it relies on VDSO. liburing always >>> uses `int $0x80` for syscall if it's compiled with CONFIG_NOLIBC, >>> otherwise it uses whatever the libc provides. >>> >>> Extra notes for __do_syscall6() macro: >>> On i386, the 6th argument of syscall goes in %ebp. However, both Clang >>> and GCC cannot use %ebp in the clobber list and in the "r" constraint >>> without using -fomit-frame-pointer. To make it always available for >>> any kind of compilation, the below workaround is implemented: >>> >>> 1) Push the 6-th argument. >>> 2) Push %ebp. >>> 3) Load the 6-th argument from 4(%esp) to %ebp. >>> 4) Do the syscall (int $0x80). >>> 5) Pop %ebp (restore the old value of %ebp). >>> 6) Add %esp by 4 (undo the stack pointer). >>> >>> WARNING: >>> Don't use register variables for __do_syscall6(), there is a known >>> GCC bug that results in an endless loop. >>> >>> BugLink: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105032 >>> >>> >>> ===== How is this tested? ===== >>> >>> This has been tested on x86-64 Linux (compiled with 32-bit bin support) >>> with the following commands: >>> >>> sudo apt-get install gcc-i686-linux-gnu g++-i686-linux-gnu -y; >>> ./configure --cc=i686-linux-gnu-gcc --cxx=i686-linux-gnu-g++ --nolibc; >>> sudo make -j8 runtests; >> >> Looks reasonable to me, even with the warts. I keep threatening to do a >> 2.2 release, and I do want to do that soon, so question is if we defer >> this patchset until after that has happened? >> >> I'm looking for a gauge of confidence on the series. > > I personally love not to defer this patchset. I understand that if we > were adding something like this to the Linux kernel, it's pretty sure > that it is not acceptable time. But liburing. > > Several things that you may want to consider: > > 1) Previously, `--nolibc` build on x86 32-bit will throw a compile > error, "Arch doesn't support building liburing without libc". > After this patchset, it compiles just fine. > > 2) This series doesn't have any effect for x86 32-bit that uses libc, > and that is what we do by default. > > 3) I believe x86 32-bit users are not that many. So having this one > earlier gives sometime to get it mature without much chaos (if > we ever found a bug). > > Not to say it's buggy. But younger code tend to be buggier. If we > ever hit that bug due to this patchset, some of them may fallback > to the libc build while waiting for the next stable liburing. > > But anyway, I don't think it's that urgent seeing that we don't have > visible users that are actively using nolibc x86 32-bit. So if you > prefer to defer this, please defer it. What do you think? All good points, let's just get it done. -- Jens Axboe