From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS31976 209.132.180.0/23 X-Spam-Status: No, score=-4.0 required=3.0 tests=AWL,BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by dcvr.yhbt.net (Postfix) with ESMTP id 9C5021F803 for ; Thu, 10 Jan 2019 06:40:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727220AbfAJGkd (ORCPT ); Thu, 10 Jan 2019 01:40:33 -0500 Received: from cloud.peff.net ([104.130.231.41]:60386 "HELO cloud.peff.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1726776AbfAJGkd (ORCPT ); Thu, 10 Jan 2019 01:40:33 -0500 Received: (qmail 2054 invoked by uid 109); 10 Jan 2019 06:40:33 -0000 Received: from Unknown (HELO peff.net) (10.0.1.2) by cloud.peff.net (qpsmtpd/0.94) with SMTP; Thu, 10 Jan 2019 06:40:33 +0000 Authentication-Results: cloud.peff.net; auth=none Received: (qmail 29402 invoked by uid 111); 10 Jan 2019 06:40:32 -0000 Received: from sigill.intra.peff.net (HELO sigill.intra.peff.net) (10.0.0.7) by peff.net (qpsmtpd/0.94) with (ECDHE-RSA-AES256-GCM-SHA384 encrypted) SMTP; Thu, 10 Jan 2019 01:40:32 -0500 Authentication-Results: peff.net; auth=none Received: by sigill.intra.peff.net (sSMTP sendmail emulation); Thu, 10 Jan 2019 01:40:31 -0500 Date: Thu, 10 Jan 2019 01:40:31 -0500 From: Jeff King To: "brian m. carlson" Cc: git@vger.kernel.org, Martin =?utf-8?B?w4VncmVu?= , Junio C Hamano Subject: Re: [PATCH 0/5] tree-walk object_id refactor Message-ID: <20190110064030.GB20497@sigill.intra.peff.net> References: <20190110042551.915769-1-sandals@crustytoothpaste.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190110042551.915769-1-sandals@crustytoothpaste.net> Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org On Thu, Jan 10, 2019 at 04:25:46AM +0000, brian m. carlson wrote: > There are a small number of places in our codebase where we cast a > buffer of unsigned char to a struct object_id pointer. When we have > GIT_MAX_RAWSZ set to 32 (because we have SHA-256), one of these places > (the buffer for tree objects) can lead to us copying too much data when > using SHA-1 as the hash, since there are only 20 bytes to read. > > This was not expected to be a problem before future code was introduced, > but due to a combination of series the issue became noticeable. > > This series introduces a refactor to avoid referencing the struct > object_id directly from a buffer and instead storing an additional > struct object_id (and an int) in struct name_entry and referring to > that. I think this is really the only safe and sane solution. We resisted it because of the cost of the extra copies (especially the update_tree_entry() one). But I don't know that anybody actually measured it. Do you have any performance numbers before/after this series? -Peff