From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 55007 invoked by alias); 22 Feb 2019 15:47:14 -0000 Mailing-List: contact gcc-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-owner@gcc.gnu.org Received: (qmail 54988 invoked by uid 89); 22 Feb 2019 15:47:14 -0000 Authentication-Results: sourceware.org; auth=none X-Spam-SWARE-Status: No, score=-1.9 required=5.0 tests=BAYES_00,SPF_HELO_PASS autolearn=ham version=3.3.2 spammy= X-HELO: mx1.redhat.com Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Fri, 22 Feb 2019 15:47:12 +0000 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 9A0BF3091D7F; Fri, 22 Feb 2019 15:47:11 +0000 (UTC) Received: from localhost.localdomain (ovpn-112-17.rdu2.redhat.com [10.10.112.17]) by smtp.corp.redhat.com (Postfix) with ESMTP id C258B600CD; Fri, 22 Feb 2019 15:47:10 +0000 (UTC) Subject: Re: [RFC] Change PCH "checksum" To: Richard Biener , gcc@gcc.gnu.org References: From: Jeff Law Openpgp: preference=signencrypt Message-ID: <4e1e43f2-f944-7067-d4ba-71b42ae3f2c8@redhat.com> Date: Fri, 22 Feb 2019 15:47:00 -0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-IsSubscribed: yes X-SW-Source: 2019-02/txt/msg00123.txt.bz2 On 2/22/19 4:29 AM, Richard Biener wrote: > > GCC builds are currently not reproducible because for one the checksum > we compute for PCH purposes (by genchecksum) nowaways includes checksums > of archives (since we switched from checksumming a dummy executable > to checksumming object files). That includes dates (unless built with > -D which we don't do). > > Then later we switched to do thin archives so for example libbackend.a > we checksum doesn't contain the actual code anymore... > > A pragmatic approach to "fix" things would be to just checksum > gtype-desc.o which should have enough state to cover PCH dependences > if I understand the workings correctly (patch below - a single > checksum would suffice so more simplifications are possible). > > Another solution working on ELF systems with build-id support is > simply forgo checksumming anything and rely on the executable > build-id instead (pat^whack below as well). > > Does anybody think that just checksumming gtype-desc.o is a > degradation over the current state (which checksums thin archives)? > > Thanks, > Richard. > > 2019-02-22 Richard Biener > > c/ > * Make-lang.in (cc1-checksum.c): Checksum only gtype-desc.o. > > cp/ > * Make-lang.in (cc1plus-checksum.c): Checksum only gtype-desc.o. > > objc/ > * Make-lang.in (cc1obj-checksum.c): Checksum only gtype-desc.o. > > objcp/ > * Make-lang.in (cc1objplus-checksum.c): Checksum only gtype-desc.o. ISTM that gtype-desc effectively describes the structure of all the GC data. Given we're summing the thin-archives, we're already missing things like a change in static data. So I don't think your patch is a degradation over the current state. I'm not 100% sure the current state is correct though :-) jeff