From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg1-x543.google.com (mail-pg1-x543.google.com [IPv6:2607:f8b0:4864:20::543]) by sourceware.org (Postfix) with ESMTPS id 259873857C5A for ; Thu, 3 Sep 2020 06:07:58 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 259873857C5A Received: by mail-pg1-x543.google.com with SMTP id m5so1237126pgj.9 for ; Wed, 02 Sep 2020 23:07:58 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=yacjZiWHRZTXyG/ooFArh5HUkfxw/DcVSRKZcW6LEi4=; b=qDjJBXZ74ZYLUe14Dpk+YcSdHXFmR7NuOwseY5jXck3PUWRyU5WR8evCwrJ/Stay+K okcM1PfpcLu4Iq/DE3mNHLvsmzKMQ6y6svTHbSPYskocqlMNYHVma+wEfwHN3sIX0pT+ rLiF5/LglpHorbqsf1NGOCnvtmNgnlOBpRlc6hQIgnXpn81cfWBxYjfH8D/qGUbWZ4f/ X9C7dtBljMUirQU1AhzMY6MU+c2vyxeGgmxM3PKhL77pHaS3qsuJAsQCd+qlGS0KjgNm CEt9lvcIaMvLMa4vA97TMI3j06TAcKBh8oZUo+TjljD7Ao0rWcb7WnSZ9HogtPo224zn 3cjA== X-Gm-Message-State: AOAM532ewiTDiTxVYVb7am4Z81ZL8hGn6+YB+3BYtW4adSQewCuaVO1i k1eiYOOcNebvzEwW7/+GeHI= X-Google-Smtp-Source: ABdhPJzgDbU0rcyiQeBmUAIqi79RZKsPKcYkkulz2Gtlilp7gYbyW2EbiSFZbYiv6H2PdgDN5q9vUQ== X-Received: by 2002:a17:902:8c84:: with SMTP id t4mr2077506plo.99.1599113277319; Wed, 02 Sep 2020 23:07:57 -0700 (PDT) Received: from bubble.grove.modra.org ([2406:3400:51d:8cc0:d197:c5ae:484a:3c93]) by smtp.gmail.com with ESMTPSA id t63sm1222223pgt.50.2020.09.02.23.07.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 02 Sep 2020 23:07:56 -0700 (PDT) Received: by bubble.grove.modra.org (Postfix, from userid 1000) id 7504387AB1; Thu, 3 Sep 2020 15:37:52 +0930 (ACST) Date: Thu, 3 Sep 2020 15:37:52 +0930 From: Alan Modra To: "H.J. Lu" Cc: Martin =?utf-8?B?TGnFoWth?= , Binutils Subject: Re: [PATCH] elf: Don't load archive element after dynamic definition Message-ID: <20200903060752.GO15695@bubble.grove.modra.org> References: <20200902081225.GH15695@bubble.grove.modra.org> <20200902130522.GI15695@bubble.grove.modra.org> <20200902142930.GJ15695@bubble.grove.modra.org> <20200903013137.GM15695@bubble.grove.modra.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) X-Spam-Status: No, score=-4.5 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: binutils@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Binutils mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 03 Sep 2020 06:07:59 -0000 On Wed, Sep 02, 2020 at 07:16:14PM -0700, H.J. Lu wrote: > On Wed, Sep 2, 2020 at 6:31 PM Alan Modra wrote: > > > > On Wed, Sep 02, 2020 at 07:35:58AM -0700, H.J. Lu wrote: > > > On Wed, Sep 2, 2020 at 7:29 AM Alan Modra wrote: > > > > > > > > On Wed, Sep 02, 2020 at 06:22:08AM -0700, H.J. Lu wrote: > > > > > > It's reasonably obvious that we need to load archive elements when > > > > > > they define IR referenced symbols, because the archive element might > > > > > > be an LTO object. What's not so obvious is whether loading of shared > > > > > > libraries should follow the same rule. I think they should, in order > > > > > > for LTO to get symbol resolution correct in corner cases. Basically > > > > > > LTO needs to know what shared libraries are loaded before > > > > > > recompilation. See commit a896df97b952 log comments. > > > > > > > > > > There is dynamic_def for this purpose. > > > > > > > > Your patch doesn't make changes to ld/plugin.c to inform LTO of the > > > > availability of these symbols. And if you did, then how does the > > > > linker work out whether or not the LTO recompilation depended on those > > > > symbols? If it did change LTO recompilation then you had better > > > > ensure the library really is loaded. By the time you work all of that > > > > out, if it is even possible, your patch will likely be very > > > > complicated indeed. > > > > > > A testcase? > > > > What don't you understand from my emails in this thread? I suggest > > you look at what happened with the testcase in PR26314, in regard to > > my comment > > The lto recompilation didn't see symbol references from libbfd.so and > > variables like _xexit_cleanup are made local in the recompiled > > objects. Oops, two copies of them. > > A testcase? You kindly provided it yourself. https://sourceware.org/bugzilla/show_bug.cgi?id=26314#c4 It takes only a small amount of digging to see the _xexit_cleanup problem. > > > That's critical in understanding why LTO needs to know about symbols > > from shared libraries before LTO recompilation. > > > > Linker is complicated and LTO makes it even more complicated. > Without a testcase, we can't be sure that the bug is really fixed > nor we can be sure it won't regress. > > > -- > H.J. -- Alan Modra Australia Development Lab, IBM