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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 DF96AC2D0DB for ; Wed, 29 Jan 2020 17:53:03 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (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 52D7D206D4 for ; Wed, 29 Jan 2020 17:53:03 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 52D7D206D4 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 487B0Y0P0GzDqTM for ; Thu, 30 Jan 2020 04:53:01 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=permerror (SPF Permanent Error: Unknown mechanism found: ip:192.40.192.88/32) smtp.mailfrom=kernel.crashing.org (client-ip=63.228.1.57; helo=gate.crashing.org; envelope-from=segher@kernel.crashing.org; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4879yV00hczDqQy for ; Thu, 30 Jan 2020 04:51:11 +1100 (AEDT) Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id 00THp595024193; Wed, 29 Jan 2020 11:51:05 -0600 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id 00THp4Aj024192; Wed, 29 Jan 2020 11:51:04 -0600 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Wed, 29 Jan 2020 11:51:04 -0600 From: Segher Boessenkool To: Florian Weimer Subject: Re: powerpc Linux scv support and scv system call ABI proposal Message-ID: <20200129175104.GO22482@gate.crashing.org> References: <1580207907.c96c1lh9t0.astroid@bobo.none> <87tv4fd8wp.fsf@oldenburg2.str.redhat.com> <1580218232.2tezmthp1x.astroid@bobo.none> <20200128154026.GI22482@gate.crashing.org> <87o8unbm8u.fsf@oldenburg2.str.redhat.com> <20200128200133.GJ22482@gate.crashing.org> <87wo9a8cc8.fsf@oldenburg2.str.redhat.com> <20200129162947.GN22482@gate.crashing.org> <87imku8ac5.fsf@oldenburg2.str.redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87imku8ac5.fsf@oldenburg2.str.redhat.com> User-Agent: Mutt/1.4.2.3i X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: libc-alpha@sourceware.org, Tulio Magno Quites Machado Filho , linuxppc-dev@lists.ozlabs.org, Nicholas Piggin Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Wed, Jan 29, 2020 at 06:02:34PM +0100, Florian Weimer wrote: > * Segher Boessenkool: > > > On Wed, Jan 29, 2020 at 05:19:19PM +0100, Florian Weimer wrote: > >> * Segher Boessenkool: > >> >> But GCC doesn't expose them as integers to C code, so you can't do much > >> >> without them. > >> > > >> > Sure, it doesn't expose any other registers directly, either. > >> > >> I can use r0 & 1 with a register variable r0 to check a bit. > > > > That is not reliable, or supported, and it *will* break. This is > > explicit for local register asm, and global register asm is > > underdefined. > > Ugh. I did not know that. And neither did the person who wrote > powerpc64/sysdep.h because it uses register variables in regular C > expressions. 8-( Other architectures are affected as well. Where? I don't see any? Ah, the other one, heh (there are two). No, that *is* supported: as input to or output from an asm, a local register asm variable *is* guaranteed to live in the specified register. This is the *only* supported use. Other uses may sometimes still work, but they never worked reliably, and it cannot be made reliable; it has been documented as not supported since ages, and it will not work at all anymore some day. Segher