From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754959AbYKSTHA (ORCPT ); Wed, 19 Nov 2008 14:07:00 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754122AbYKSTGk (ORCPT ); Wed, 19 Nov 2008 14:06:40 -0500 Received: from zeniv.linux.org.uk ([195.92.253.2]:39382 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753975AbYKSTGj (ORCPT ); Wed, 19 Nov 2008 14:06:39 -0500 Date: Wed, 19 Nov 2008 19:06:36 +0000 From: Al Viro To: Am??rico Wang Cc: LKML , Andrew Morton , Jeff Dike , user-mode-linux-devel@lists.sourceforge.net Subject: Re: [Patch] uml: fix undeclared variables Message-ID: <20081119190636.GW28946@ZenIV.linux.org.uk> References: <20081118174250.GE3185@hack.voiplan.pt> <20081118192626.GU28946@ZenIV.linux.org.uk> <20081119184014.GD22898@hack.voiplan.pt> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20081119184014.GD22898@hack.voiplan.pt> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 19, 2008 at 06:40:14PM +0000, Am??rico Wang wrote: > On Tue, Nov 18, 2008 at 07:26:26PM +0000, Al Viro wrote: > >On Tue, Nov 18, 2008 at 05:42:51PM +0000, Am??rico Wang wrote: > >> > >> Fix three compile errors about undeclared variables in > >> arch/um/kernel/mem.c. > > > >And what, pray tell, would initialize it? > > Sorry, I can't fully understand you. I got the following error: > > arch/um/kernel/mem.c: In function ???init_highmem???: > arch/um/kernel/mem.c:177: error: ???pkmap_page_table??? undeclared (first > use in this function) > arch/um/kernel/mem.c:177: error: (Each undeclared identifier is > reported only once > arch/um/kernel/mem.c:177: error: for each function it appears in.) The error is there, all right. However, proposed patch only hides the real problem. Building uml/i386 with CONFIG_HIGHMEM will result in a badly broken kernel with that patch, with no visible hints at the cause of problems. You've got it to link, but that's not enough. The problems you are seeing come from arch/x86/mm/highmem_32.c. It uses several variables from arch/x86/mm/init_32.c and you have copied them to arch/um. However, getting these variable defined is not going to make it work - the code that used to set it had been in init_32.c too and you've just left your copy initialized to NULL. Which will *not* work. IOW, it's still broken, but now you have lost all indications regarding the source of problem. Folks, "it doesn't build in that config" is _better_ than "it builds with no complaints, but resulting binary is FUBAR". As a short-term solution - make HIGHMEM in arch/um/Kconfig.um depend on BROKEN. The proper fix, of course, is to try and make it _work_, not just compile, but that's going to take a fair amount of digging in uml and x86 low-level VM guts.