From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-il1-x141.google.com (mail-il1-x141.google.com [IPv6:2607:f8b0:4864:20::141]) by sourceware.org (Postfix) with ESMTPS id CB1833860C3E for ; Thu, 3 Sep 2020 11:34:59 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org CB1833860C3E Received: by mail-il1-x141.google.com with SMTP id t4so2193337iln.1 for ; Thu, 03 Sep 2020 04:34:59 -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=zu4aB0PPdRkD0kghsF4ghaKNa2UNiPomvDnIpMQQD7U=; b=gQCpQrndrMAmpBpet2YsL8gScTykd13Hqpwyzy9Fi/Dd9Bs3JJ3KwwyRuJ205QJQv+ Abkm4nyQoulBaXUewe3nFfjC4Gg6ly6czzhCYKJ+YNng+SElRAH+0yqhvWh7klpLDbGx uF/dmoM9etbPyPZvHhZ5DwVzv2EKFD7c9fi4WX0AhfwbqKxu0TsnWASPk3sxBBy8voqW lAV1s7PnxDoyGfVtj8KDo53RB5bE4NfXUPXBrBZqKYnTRrmje94dH2ra6uYOKyB7cydc mc9SM+meBA3YW0+26/WhU1MOeZB8w9U9Tu5cK5hIsv/y/V/ItdoDonPJlnJ3tDbSE7nZ 6t+Q== X-Gm-Message-State: AOAM531fD5CTXjmwg4x3uhA44RepMznHaBNrjOBKe00JGA1VC+Z0gmms +X9NH4hJ3B4vCiebyExL9CO3wM49gwm7+oaNf2E16u7FIkE= X-Google-Smtp-Source: ABdhPJzKRIljOoPoOtXsCQlFO/FJWZD0rsjZjbJ56YmNnxbFQfvtAsGFyWzlb/0jfQqHxvSTUNpKGhmGjcHnMnj+w08= X-Received: by 2002:a92:6a0c:: with SMTP id f12mr2586641ilc.213.1599132899215; Thu, 03 Sep 2020 04:34:59 -0700 (PDT) MIME-Version: 1.0 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> <20200903060752.GO15695@bubble.grove.modra.org> In-Reply-To: <20200903060752.GO15695@bubble.grove.modra.org> From: "H.J. Lu" Date: Thu, 3 Sep 2020 04:34:23 -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=-3.1 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, KAM_SHORT, 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 11:35:01 -0000 On Wed, Sep 2, 2020 at 11:07 PM Alan Modra wrote: > > 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. This particular problem came from: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96385 where GCC generated incorrect output and I do have a mitigation patch. -- H.J.