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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 EFC65C433FE for ; Sat, 12 Dec 2020 19:23:45 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 4ACE722257 for ; Sat, 12 Dec 2020 19:23:44 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4ACE722257 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=nocrew.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:55350 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1koAUZ-0000jc-U1 for qemu-devel@archiver.kernel.org; Sat, 12 Dec 2020 14:23:43 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:59518) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ko9YB-0006MN-Rz for qemu-devel@nongnu.org; Sat, 12 Dec 2020 13:23:25 -0500 Received: from ste-pvt-msa1.bahnhof.se ([213.80.101.70]:60775) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ko9YA-0003bh-4D for qemu-devel@nongnu.org; Sat, 12 Dec 2020 13:23:23 -0500 Received: from localhost (localhost [127.0.0.1]) by ste-pvt-msa1.bahnhof.se (Postfix) with ESMTP id DD92140CA2; Sat, 12 Dec 2020 18:03:51 +0100 (CET) X-Virus-Scanned: Debian amavisd-new at bahnhof.se Received: from ste-pvt-msa1.bahnhof.se ([127.0.0.1]) by localhost (ste-pvt-msa1.bahnhof.se [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id f9khAWnkFLcs; Sat, 12 Dec 2020 18:03:51 +0100 (CET) Received: by ste-pvt-msa1.bahnhof.se (Postfix) with ESMTPA id 06E4D3FA44; Sat, 12 Dec 2020 18:03:49 +0100 (CET) Date: Sat, 12 Dec 2020 18:03:49 +0100 From: Fredrik Noring To: "Maciej W. Rozycki" Subject: Re: [PATCH 3/4] default-configs: Support o32 ABI with 64-bit MIPS CPUs Message-ID: References: <20201119161710.1985083-1-f4bug@amsat.org> <20201119161710.1985083-4-f4bug@amsat.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Received-SPF: softfail client-ip=213.80.101.70; envelope-from=noring@nocrew.org; helo=ste-pvt-msa1.bahnhof.se X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_LOW=-0.7, SPF_HELO_NONE=0.001, SPF_SOFTFAIL=0.665 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-devel@nongnu.org, Richard Henderson , Laurent Vivier , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Mathieu Malaterre , YunQiang Su , James Cowgill , David Daney , =?utf-8?Q?J=C3=BCrgen?= Urban , Aurelien Jarno Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Nov 19, 2020 at 04:45:29PM +0000, Maciej W. Rozycki wrote: > On Thu, 19 Nov 2020, Philippe Mathieu-Daudé wrote: > > > MIPS o32 ABI on 64-bit CPUs looks like a ILP32-on-64bit data > > model, allowing 64-bit arithmetic and data movement instructions. > > > > This is the default ABI used by the "Sony Linux Toolkit for > > Playstation 2". > > Please don't, not at least with a generic configuration (i.e. make it > unambiguous that this is R5900-specific). This only works with R5900 > because it does not implement the MIPS ISA correctly (e.g. see what $ra is > set to with JAL/JALR/etc. in the kernel mode), and it is not supported by > the standard Linux ABI. Use n32 instead, which has the same functionality > and is standard (and is also a better ABI in terms of performance). > > You'd probably need to implement all the R5900 addressing quirks for your > proposed hack to match hardware, or otherwise you'll end up with emulation > that creates its own reality. I agree. Modern Linux kernel and GCC are important too. It seems both o32 and n32, with quirks, are generally accepted, but R5900 MMIs and other special features are less clear: For example, given the fact that the 128-bit MMIs are unconditionally executable on R5900 hardware, a user may be forgiven to believe that they always work. But unless the Linux kernel restores 128-bit registers in its operating mode switches, which could be o32, there will be silent data corruption (and ensuing frustration). (For this reason I favour full register restores in all operating modes.) Fredrik