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 1BD9DC43331 for ; Thu, 5 Sep 2019 14:47:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 63B0D206CD for ; Thu, 5 Sep 2019 14:47:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390013AbfIEOrj (ORCPT ); Thu, 5 Sep 2019 10:47:39 -0400 Received: from gate.crashing.org ([63.228.1.57]:48300 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728590AbfIEOri (ORCPT ); Thu, 5 Sep 2019 10:47:38 -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 x85ElRDl031452; Thu, 5 Sep 2019 09:47:27 -0500 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id x85ElQoY031451; Thu, 5 Sep 2019 09:47:26 -0500 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Thu, 5 Sep 2019 09:47:25 -0500 From: Segher Boessenkool To: Rasmus Villemoes Cc: Nick Desaulniers , "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , LKML , Miguel Ojeda , "gcc-patches@gcc.gnu.org" Subject: Re: [PATCH v2 4/6] compiler-gcc.h: add asm_inline definition Message-ID: <20190905144725.GQ9749@gate.crashing.org> References: <20190829083233.24162-1-linux@rasmusvillemoes.dk> <20190830231527.22304-1-linux@rasmusvillemoes.dk> <20190830231527.22304-5-linux@rasmusvillemoes.dk> <20190905134535.GP9749@gate.crashing.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.3i Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 05, 2019 at 04:23:11PM +0200, Rasmus Villemoes wrote: > On 05/09/2019 15.45, Segher Boessenkool wrote: > > On Thu, Sep 05, 2019 at 01:07:11PM +0200, Rasmus Villemoes wrote: > >> Perhaps something like below, though that > >> won't affect the already released gcc 9.1 and 9.2, of course. > > > > That is one reason to not want such a predefined macro. Another reason > > is that you usually need to compile some test programs *anyway*, to see if > > some bug is present for example, or to see if the exact implementation of > > the feature is beneficial (or harmful) to your program in some way. > > OK, I think I'll just use a version check for now, and then switch to a > Kconfig test if and when clang grows support. > > >> gcc maintainers, WDYT? Can we add a feature test macro for asm inline()? > > > > Why would GCC want to have macros for all features it has? > > Well, gcc has implemented __has_attribute() which is similar - one could > detect support by compiling a trivial test program. It is not a macro, it doesn't spill over the place, and it is for detecting things that are already fixed strings, much easier to do :-) > Or the same could be > said for many of the predefined macros that are conditionally defined, > e.g. __HAVE_SPECULATION_SAFE_VALUE. That one happened because of the Great Security Scare of 2017/2018, it's not a good precedent. And, how it is set is target-specific, it can depend on CPU model selected, target code generation options, or whatnot. > But I was just throwing the question into the air, I won't pursue this > further. Maybe GCC should have a has_feature thing, it might fit in well there. As preprocessor macros, not so much, IMO. Segher