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 B219EC433DF for ; Thu, 11 Jun 2020 21:02:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8D9B82073E for ; Thu, 11 Jun 2020 21:02:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726153AbgFKVCx (ORCPT ); Thu, 11 Jun 2020 17:02:53 -0400 Received: from gate.crashing.org ([63.228.1.57]:52027 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725869AbgFKVCx (ORCPT ); Thu, 11 Jun 2020 17:02:53 -0400 Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id 05BL2WSL021038; Thu, 11 Jun 2020 16:02:32 -0500 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id 05BL2UHa021034; Thu, 11 Jun 2020 16:02:30 -0500 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Thu, 11 Jun 2020 16:02:30 -0500 From: Segher Boessenkool To: Nicholas Piggin Cc: linuxppc-dev@lists.ozlabs.org, libc-dev@lists.llvm.org, musl@lists.openwall.com, linux-api@vger.kernel.org Subject: Re: Linux powerpc new system call instruction and ABI Message-ID: <20200611210230.GH31009@gate.crashing.org> References: <20200611081203.995112-1-npiggin@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200611081203.995112-1-npiggin@gmail.com> User-Agent: Mutt/1.4.2.3i Sender: linux-api-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org Hi! On Thu, Jun 11, 2020 at 06:12:01PM +1000, Nicholas Piggin wrote: > Calling convention > ------------------ > The proposal is for scv 0 to provide the standard Linux system call ABI > with the following differences from sc convention[1]: > > - lr is to be volatile across scv calls. This is necessary because the > scv instruction clobbers lr. From previous discussion, this should be > possible to deal with in GCC clobbers and CFI. > > - cr1 and cr5-cr7 are volatile. This matches the C ABI and would allow the > kernel system call exit to avoid restoring the volatile cr registers > (although we probably still would anyway to avoid information leaks). > > - Error handling: The consensus among kernel, glibc, and musl is to move to > using negative return values in r3 rather than CR0[SO]=1 to indicate error, > which matches most other architectures, and is closer to a function call. What about cr0 then? Will it be volatile as well (exactly like for function calls)? > Notes > ----- > - r0,r4-r8 are documented as volatile in the ABI, but the kernel patch as > submitted currently preserves them. This is to leave room for deciding > which way to go with these. The kernel has to set it to *something* that doesn't leak information ;-) Segher