Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753180AbbGAUJf (ORCPT ); Wed, 1 Jul 2015 16:09:35 -0400 Received: from mail-la0-f47.google.com ([209.85.215.47]:33497 "EHLO mail-la0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752407AbbGAUJ1 (ORCPT ); Wed, 1 Jul 2015 16:09:27 -0400 MIME-Version: 1.0 In-Reply-To: <20150701174333.GA10247@tucnak.redhat.com> References: <20150630213736.GQ10247@tucnak.redhat.com> <559405E5.7000405@redhat.com> <20150701153133.GY10247@tucnak.redhat.com> <559424D4.6010908@redhat.com> <20150701174333.GA10247@tucnak.redhat.com> From: Andy Lutomirski Date: Wed, 1 Jul 2015 13:09:06 -0700 Message-ID: Subject: Re: gcc feature request / RFC: extra clobbered regs To: Jakub Jelinek Cc: Vladimir Makarov , Andy Lutomirski , gcc@gcc.gnu.org, "linux-kernel@vger.kernel.org" , Linus Torvalds , "H. Peter Anvin" , Ingo Molnar , Thomas Gleixner Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1673 Lines: 39 On Wed, Jul 1, 2015 at 10:43 AM, Jakub Jelinek wrote: > On Wed, Jul 01, 2015 at 01:35:16PM -0400, Vladimir Makarov wrote: >> Actually it raise a question for me. If we describe that a function >> clobbers more than calling convention and then use it as a value (assigning >> a variable or passing as an argument) and loosing a track of it and than >> call it. How can RA know what the call clobbers actually. So for the >> function with the attributes we should prohibit use it as a value or make >> the attributes as a part of the function type, or at least say it is unsafe. >> So now I see this as a *bigger problem* with this extension. Although I >> guess it already exists as we have description of different ABI as an >> extension. > > Unfortunately target attribute is function decl attribute rather than > function type. And having more attributes affect switchable targets will be > non-fun. Just to make sure we're on the same page here, if I write: extern void normal_func(void); void weird_func(void) __attribute__((used_regs("r12"))) { // do something normal_func(); // do something } I'd want the code that calls normal_func() to be understand that normal_func() *will* preserve r12 despite the fact that weird_func is allowed to clobber r12. I think this means that the attribute would have to be an attribute of a function, not of the RA while compiling the function. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/