Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752427AbdJAAj2 (ORCPT ); Sat, 30 Sep 2017 20:39:28 -0400 Received: from gate.crashing.org ([63.228.1.57]:49797 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752020AbdJAAj1 (ORCPT ); Sat, 30 Sep 2017 20:39:27 -0400 Date: Sat, 30 Sep 2017 19:38:53 -0500 From: Segher Boessenkool To: Nick Desaulniers Cc: Masahiro Yamada , Behan Webster , dl9pf@gmx.de, Mark Charlebois , Matthias Kaehlcke , Greg Hackmann , Michael Davidson , Michal Marek , Linux Kbuild mailing list , Linux Kernel Mailing List , llvmlinux@lists.linuxfoundation.org Subject: Re: [PATCH] kbuild: clang: remove crufty HOSTCFLAGS Message-ID: <20171001003853.GX8421@gate.crashing.org> References: <20170926022835.30916-1-nick.desaulniers@gmail.com> <20170930231450.cggvysrt4zedsbkq@lostoracle.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170930231450.cggvysrt4zedsbkq@lostoracle.net> User-Agent: Mutt/1.4.2.3i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1228 Lines: 27 On Sat, Sep 30, 2017 at 04:14:50PM -0700, Nick Desaulniers wrote: > On Thu, Sep 28, 2017 at 07:52:35PM +0900, Masahiro Yamada wrote: > > 2017-09-26 11:28 GMT+09:00 Nick Desaulniers : > > > HOSTCFLAGS := -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 \ > > > + $(call hostcc-option,-fno-delete-null-pointer-checks) \ > > > -fomit-frame-pointer -std=gnu89 $(HOST_LFS_CFLAGS) > > > > You call hostcc-option > > before Kbuild.include is included around line 341. > > > > So, $(call hostcc-option, ...) returns always an empty string here > > whether the compiler supports the option or not. > > So calling a yet-to-be defined variable results in an empty string > rather than a loud failure? Chalk that up there with language features > no one ever asked for. That kind of implicit conversion gets languages > like JavaScript (with its loose type system, not that C is without its > own implicit type conversions/promotions) in a lot of hot water. make --warn-undefined-variables (and it warns all over the place during a kernel build -- having undefined variables expand to the empty string is a useful feature, too, not just a trap for the unwary). Segher