From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by sourceware.org (Postfix) with ESMTP id B0C313939C01 for ; Wed, 28 Apr 2021 08:35:00 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org B0C313939C01 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-110-Ldv4WOp7Ng-NKlqJSJrhQg-1; Wed, 28 Apr 2021 04:34:58 -0400 X-MC-Unique: Ldv4WOp7Ng-NKlqJSJrhQg-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id EB36F10054F6; Wed, 28 Apr 2021 08:34:56 +0000 (UTC) Received: from oldenburg.str.redhat.com (ovpn-113-20.ams2.redhat.com [10.36.113.20]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0104F70580; Wed, 28 Apr 2021 08:34:54 +0000 (UTC) From: Florian Weimer To: "H.J. Lu via Libc-alpha" Cc: Bruno Haible , "H.J. Lu" , Andreas Schwab , bug-gnulib@gnu.org, Binutils Subject: Re: Undefined use of weak symbols in gnulib References: <87o8e0p92r.fsf@oldenburg.str.redhat.com> <87fszc8a1z.fsf@igel.home> <87eeewnfzw.fsf@oldenburg.str.redhat.com> <1680226.UWtE2gOZdF@omega> Date: Wed, 28 Apr 2021 10:35:24 +0200 In-Reply-To: (H. J. Lu via Libc-alpha's message of "Tue, 27 Apr 2021 19:10:56 -0700") Message-ID: <87h7jqkdrn.fsf@oldenburg.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Spam-Status: No, score=-6.6 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H4, RCVD_IN_MSPIKE_WL, 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: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 28 Apr 2021 08:35:02 -0000 * H. J. Lu via Libc-alpha: > Alan extended the fix to PPC: > > commit 954b63d4c8645f86e40c7ef6c6d60acd2bf019de > Author: Alan Modra > Date: Wed Apr 19 01:26:57 2017 +0930 > > Implement -z dynamic-undefined-weak > > -z nodynamic-undefined-weak is only implemented for x86. (The sparc > backend has some support code but doesn't enable the option by > including ld/emulparams/dynamic_undefined_weak.sh, and since the > support looks like it may be broken I haven't enabled it.) This patch > adds the complementary -z dynamic-undefined-weak, extends both options > to affect building of shared libraries as well as executables, and > adds support for the option on powerpc. I'm not sure if this option is compatible with all compilers on POWER. The old binutils behavior allowed the compiler to optimize this common pattern void f1 (void) __attribute__ ((weak)); void f2 (void) { if (f1 != 0) f1 (); } into an unconditional call to f1 because the linker would replace the call with a NOP if the symbol is undefined, reproducing the effect of the if condition. However, GCC 10 does not appear to perform this optimization on powerpc64le. Thanks, Florian