From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: [PATCH] stop gcc warning about uninitialized 'dev' in ata_scsi_scan_host Date: Thu, 16 Oct 2008 15:08:55 +0900 Message-ID: <48F6DA77.7090303@kernel.org> References: <20081015232505.GB9272@ldl.fc.hp.com> <48F6A2E7.5090005@kernel.org> <20081016034042.GA27621@ldl.fc.hp.com> <48F6BAFE.6080106@kernel.org> <87r66hjcwv.fsf@denkblock.local> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from hera.kernel.org ([140.211.167.34]:56786 "EHLO hera.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751826AbYJPGLh (ORCPT ); Thu, 16 Oct 2008 02:11:37 -0400 In-Reply-To: <87r66hjcwv.fsf@denkblock.local> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Elias Oltmanns Cc: Alex Chiang , jeff@redhat.com, linux-ide@vger.kernel.org, linux-kernel Elias Oltmanns wrote: >> I think the current policy is blaming gcc but I also added quite a few >> bogus NULL initializations here and there and caught several bugs thanks >> to those warnings. We can think about adding an additional annotation >> with leading double underbars which indicate that certain pointer >> arguments to functions expect (or are okay with) pointers to >> uninitialized variables which should be able to remove many of those >> spurious warnings (on the caller side, the compiler can ignore the >> warning and on the callee side the compiler can check whether it's being >> dereferenced without being written to). Does anyone know whether gcc >> already has that type of annotation? > > Well, I don't know of this particular kind of annotation. However, I > don't quite see how that would solve the reported issue. I was thinking about the warning in sata_via.c and for such cases the compiler doesn't have any other way of figuring out whether it's okay or not (the sata_via case, the compiler can actually do as the callee is in the same file but you know what I mean). > Here, dev is a local variable and the warning is generated due to > the line > > if (dev != last_failed_dev) { > > For this sort of thing we have: > > struct ata_device *uninitialized_var(dev); Ah.. thanks. > Or is that precisely the thing you did *not* want? I don't know. Later versions of gcc doesn't issue warning because it knows "if (!link)" always triggers if dev is not initialized. I don't think we should be adding those annotations if the current gen compiler can already figure that out as it only decreases debuggability when something actually gets broken there. Thanks. -- tejun