From mboxrd@z Thu Jan 1 00:00:00 1970 From: "H. Peter Anvin" Subject: Re: [PATCH 1/2] UNREACHABLE() macro Date: Fri, 11 Sep 2009 21:43:42 -0700 Message-ID: <4AAB26FE.7010309@kernel.org> References: <20090910015923.8FB628AE5F@magilla.sf.frob.com> <20090910020031.87DC68BF6E@magilla.sf.frob.com> <20090911134528.cd1782d9.akpm@linux-foundation.org> <20090911215525.12B366A98F@magilla.sf.frob.com> <20090912054906.22b05848@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: Received: from terminus.zytor.com ([198.137.202.10]:51258 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750705AbZILFMq (ORCPT ); Sat, 12 Sep 2009 01:12:46 -0400 In-Reply-To: <20090912054906.22b05848@infradead.org> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Arjan van de Ven Cc: Roland McGrath , Andrew Morton , torvalds@linux-foundation.org, jakub@redhat.com, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, x86@kernel.org On 09/11/2009 08:49 PM, Arjan van de Ven wrote: > On Fri, 11 Sep 2009 14:55:25 -0700 (PDT) > Roland McGrath wrote: > >>> That's a bit of a mouthful. Did you consider a runtime probe with >>> scripts/Kbuild.include's try-run, cc-option, etc? >> >> I did not see any precedent in the sources for using those to test for >> features by compiling particular test sources (i.e. in autoconf > > look at the stackprotector flags.. they work this way already. > It gets done once per kernel build... > That works for flags, but not for the presence of builtin functions. You can't even just try compiling something, since it will turn into an ordinary function if not present... not obvious until link. -hpa