From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io1-xd42.google.com (mail-io1-xd42.google.com [IPv6:2607:f8b0:4864:20::d42]) by sourceware.org (Postfix) with ESMTPS id 962943857C7C for ; Thu, 3 Sep 2020 02:16:50 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 962943857C7C Received: by mail-io1-xd42.google.com with SMTP id j2so1068190ioj.7 for ; Wed, 02 Sep 2020 19:16:50 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=gerKeq8xAzYwT1bLI1bMICGRPBVsDGG6PnCURBT8i4o=; b=JNneUVmdRn1wUgUczpUzOUw7eQSvGApvW3Zjr8y27oyJi9ImjJjNYF/Xo13xlR7FI6 HNxWNOQhusIINxBHryKczdRYyy2IWzhbSwLmZmIzqwERKatpVhCb5halRyfai9PJH/bB wDrnDJapiHcd6PlyusGSLUEp1ZD/IK9OkX2p0c3/1G9zXGCWZiSdzSKeP+oBG49qOG9d aikLEldDBdvQJ7S7hMFg7gkMsAIHWtbw8ZOlJaFhPOSD1AafMY1fTnb5bbf84HNqpudb UWHyKzSDDt9GQbGZ2mkq1bRQ2LuvuQ35HH/u5zytziDnLDrlpfnKxAqtFNJeuW3qAx7j B8UQ== X-Gm-Message-State: AOAM533DHZklwkHX3bBSxA1YqMs2Qa1HFGFh5iV0MVXkS0TuzrT2k+0f 1j/5l57fu8fBB6Sv/oGBLr9feWsjjX3X4c2nzrw= X-Google-Smtp-Source: ABdhPJwmM2BQEI5lHLSbbWIgJyhRQa/HhoOuaPwfT80uSh47vHuWPIAIpa2wBPQvE8FFZTToqBtUeGMI7eGqa4ImXEs= X-Received: by 2002:a5e:881a:: with SMTP id l26mr1095364ioj.51.1599099410071; Wed, 02 Sep 2020 19:16:50 -0700 (PDT) MIME-Version: 1.0 References: <20200828144914.GP15695@bubble.grove.modra.org> <20200902081225.GH15695@bubble.grove.modra.org> <20200902130522.GI15695@bubble.grove.modra.org> <20200902142930.GJ15695@bubble.grove.modra.org> <20200903013137.GM15695@bubble.grove.modra.org> In-Reply-To: <20200903013137.GM15695@bubble.grove.modra.org> From: "H.J. Lu" Date: Wed, 2 Sep 2020 19:16:14 -0700 Message-ID: Subject: Re: [PATCH] elf: Don't load archive element after dynamic definition To: Alan Modra Cc: =?UTF-8?Q?Martin_Li=C5=A1ka?= , Binutils Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-3.0 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 02:16:51 -0000 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? > 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.