From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_2 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6863EC35679 for ; Mon, 24 Feb 2020 10:32:36 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 2305820828 for ; Mon, 24 Feb 2020 10:32:36 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2305820828 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 48Qz0K5g5FzDqV9 for ; Mon, 24 Feb 2020 21:32:33 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=permerror (SPF Permanent Error: Unknown mechanism found: ip:192.40.192.88/32) smtp.mailfrom=kernel.crashing.org (client-ip=76.164.61.194; helo=kernel.crashing.org; envelope-from=benh@kernel.crashing.org; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org X-Greylist: delayed 771 seconds by postgrey-1.36 at bilbo; Mon, 24 Feb 2020 21:30:28 AEDT Received: from kernel.crashing.org (kernel.crashing.org [76.164.61.194]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 48Qyxw0L3hzDqPl for ; Mon, 24 Feb 2020 21:30:27 +1100 (AEDT) Received: from localhost (gate.crashing.org [63.228.1.57]) (authenticated bits=0) by kernel.crashing.org (8.14.7/8.14.7) with ESMTP id 01OAHKrN026076 (version=TLSv1/SSLv3 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Mon, 24 Feb 2020 04:17:27 -0600 Message-ID: <587a0a1765ba1264b92044f7b1f9937eb40731f1.camel@kernel.crashing.org> Subject: Re: vdso function descriptors (VDS64_HAS_DESCRIPTORS)? From: Benjamin Herrenschmidt To: Segher Boessenkool , Joe Lawrence Date: Mon, 24 Feb 2020 21:17:19 +1100 In-Reply-To: <20200223000715.GW22482@gate.crashing.org> References: <20200217160852.GA9557@redhat.com> <20200223000715.GW22482@gate.crashing.org> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.5-0ubuntu0.18.04.1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Sat, 2020-02-22 at 18:07 -0600, Segher Boessenkool wrote: > > > > so I don't believe they are ever used by default -- in this case > > V_FUNCTION_BEGIN doesn't add to the .opd section with .name, .TOC base, > > etc. > > > > Manually setting VDS64_HAS_DESCRIPTORS results in a vdso64.so in which > > binutils tools like readelf properly report functions with symbol type > > FUNC instead of NOTYPE. > > > > Are there pieces of the build/etc toolchain unprepared for function > > descriptors? I'm just trying to figure out why the code defaults to > > unsetting them. > > Because direct calls are faster than indirect calls? Ben might have a > fuller explanation, cc:ing him. I don't remember why :-) I think I didn't want to mess with the OPD fixup in glibc back then. Ben.