From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS31976 209.132.180.0/23 X-Spam-Status: No, score=-3.6 required=3.0 tests=AWL,BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,RCVD_IN_DNSWL_HI,RP_MATCHES_RCVD shortcircuit=no autolearn=ham autolearn_force=no version=3.4.0 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by dcvr.yhbt.net (Postfix) with ESMTP id E3170202DD for ; Mon, 2 Oct 2017 05:08:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750929AbdJBFIN (ORCPT ); Mon, 2 Oct 2017 01:08:13 -0400 Received: from cloud.peff.net ([104.130.231.41]:57008 "HELO cloud.peff.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1750763AbdJBFIN (ORCPT ); Mon, 2 Oct 2017 01:08:13 -0400 Received: (qmail 5655 invoked by uid 109); 2 Oct 2017 05:08:13 -0000 Received: from Unknown (HELO peff.net) (10.0.1.2) by cloud.peff.net (qpsmtpd/0.94) with SMTP; Mon, 02 Oct 2017 05:08:13 +0000 Authentication-Results: cloud.peff.net; auth=none Received: (qmail 25045 invoked by uid 111); 2 Oct 2017 05:08:53 -0000 Received: from sigill.intra.peff.net (HELO sigill.intra.peff.net) (10.0.0.7) by peff.net (qpsmtpd/0.94) with SMTP; Mon, 02 Oct 2017 01:08:53 -0400 Authentication-Results: peff.net; auth=none Received: by sigill.intra.peff.net (sSMTP sendmail emulation); Mon, 02 Oct 2017 01:08:11 -0400 Date: Mon, 2 Oct 2017 01:08:11 -0400 From: Jeff King To: =?utf-8?B?UmVuw6k=?= Scharfe Cc: Git List , Junio C Hamano Subject: Re: [PATCH] tag: avoid NULL pointer arithmetic Message-ID: <20171002050810.ryj4nv3nwqp7gb7p@sigill.intra.peff.net> References: <99e56671-bdf9-a59f-ae7b-758f1b7a8f14@web.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <99e56671-bdf9-a59f-ae7b-758f1b7a8f14@web.de> Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org On Sun, Oct 01, 2017 at 04:45:13PM +0200, René Scharfe wrote: > lookup_blob() etc. can return NULL if the referenced object isn't of the > expected type. In theory it's wrong to reference the object member in > that case. In practice it's OK because it's located at offset 0 for all > types, so the pointer arithmetic (NULL + 0) is optimized out by the > compiler. The issue is reported by Clang's AddressSanitizer, though. > > Avoid the ASan error by casting the results of the lookup functions to > struct object pointers. That works fine with NULL pointers as well. We > already rely on the object member being first in all object types in > other places in the code. Out of curiosity, did you have to do anything to coax this out of ASan (e.g., a specific version)? I've been running it pretty regularly and didn't see this one (I did switch from clang to gcc a month or two ago, but this code is pretty old, I think). -Peff