From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932703AbaFUH3A (ORCPT ); Sat, 21 Jun 2014 03:29:00 -0400 Received: from mail-pd0-f176.google.com ([209.85.192.176]:60904 "EHLO mail-pd0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757660AbaFUH27 (ORCPT ); Sat, 21 Jun 2014 03:28:59 -0400 Date: Sat, 21 Jun 2014 15:28:52 +0800 From: Real Name To: Richard Weinberger Cc: user-mode-linux-devel@lists.sourceforge.net, user-mode-linux-user@lists.sourceforge.net, linux-kernel@vger.kernel.org Subject: Re: [PATCH] remove csum_partial_copy_generic_i386 to clean up exception table Message-ID: <20140621072852.GA6538@name> References: <538F275B.7000508@nod.at> <1401941724-6703-1-git-send-email-enjoymindful@gmail.com> <1401941724-6703-2-git-send-email-enjoymindful@gmail.com> <5390E5FD.5030400@nod.at> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5390E5FD.5030400@nod.at> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 05, 2014 at 11:49:49PM +0200, Richard Weinberger wrote: > Am 05.06.2014 06:15, schrieb Honggang Li: > > arch/x86/um/checksum_32.S had been copy & paste from x86. When build > > x86 uml, csum_partial_copy_generic_i386 mess up the exception table. > > In fact, exception table dose not work in uml kernel. > > Are you sure that exception tables do not work on UML? > I said, I'm not sure. Can you please find out? Hi, After traced i386 uml kernel with gdb , I'm sure exception tables do *not* work. When csum_partial_copy_generic_i386 read user space memory, an access error exception arises, however, the segv function always return zero. So, the fixup nerver executed. The uml system hang (not kernel panic). thanks. > > In arch/um/kernel/trap.c:segv() we have the mechanism for it: > else if (!is_user && arch_fixup(ip, regs)) > goto out; > > The interesting question is, is this by design or was it just copy&pasted from x86 > many moons ago? :) > > > And csum_partial_copy_generic_i386 never been called. So, delete it. > > I like such clean ups. :-) > > Thanks, > //richard