From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS17314 8.43.84.0/22 X-Spam-Status: No, score=-4.3 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI,SPF_HELO_PASS,SPF_PASS shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from sourceware.org (server2.sourceware.org [8.43.85.97]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by dcvr.yhbt.net (Postfix) with ESMTPS id 505B61F5AE for ; Wed, 28 Apr 2021 08:35:11 +0000 (UTC) Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id C3650393A41F; Wed, 28 Apr 2021 08:35:05 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org C3650393A41F DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1619598905; bh=Z9/hZ6krZKYTXq6vXFYjr/hwj0qEF73f7m0JHhtli7Y=; h=To:Subject:References:Date:In-Reply-To:List-Id:List-Unsubscribe: List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To:Cc: From; b=VGF1UyXlgOIgyHXMPpfVcQTKWabU+Y47RyRfZm5412NnPWt6q4Y62mTxjaqqkWcZd Lsz1Aby24SRbyiQjNUK8yGDuP4UxhuzHAlBSp+ZkEdjtzvgTUBR3Uxaby3hMfFNMMy 2H/BSQwiVRyVRivGvWqy6jPFrlhiGZIBU8pZaCYU= 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) To: "H.J. Lu via Libc-alpha" 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-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: , From: Florian Weimer via Libc-alpha Reply-To: Florian Weimer Cc: Andreas Schwab , bug-gnulib@gnu.org, Bruno Haible , Binutils Errors-To: libc-alpha-bounces@sourceware.org Sender: "Libc-alpha" * 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