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=-4.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 5EED4C433E0 for ; Mon, 3 Aug 2020 16:59:23 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (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 2B3E320A8B for ; Mon, 3 Aug 2020 16:59:23 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="WPUwiBuO" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2B3E320A8B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=ACULAB.COM Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:MIME-Version:In-Reply-To:References:Message-ID:Date: Subject:To:From:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=Wv5HRudhYq8wHDmp7iREB3YMUtlbehnkGfxzUn4z83U=; b=WPUwiBuOR8MQ9aiJI5lNsrIth gu12CMH43Dpu6wcXSLGgr6hoxl3QquYdeliOo9QtV7Shshr4m3Qio3y7ZQc/aXGHlZNpN7J12SG26 MmfvTl1uGlJiBNanqjtsAXRy3oyH7a+7syGX/GETAza8oZxfZfvalDxf5QJRKGnxP3eFx0BhiKJKd C7tkuST6zw6ehESxDAk/Xs2nfWrSCPQC8nzdNLZpatCOjXXbhhJ9ev8b4VR6SuTTFTFm1nT5udjnO jVMBkoeNm1Je/UlKYmiSDcAk7paRkG5iZvQZYg/TNdKYCARPrGP2cEq7sOwzJq8/MVtQUeGvpNJpo g/ekHnlzw==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1k2dmd-0003m8-N3; Mon, 03 Aug 2020 16:57:55 +0000 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.86.151]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1k2dma-0003l8-Jf for linux-arm-kernel@lists.infradead.org; Mon, 03 Aug 2020 16:57:53 +0000 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-167-AfxWu5hnN66AhufCIfqZ2Q-1; Mon, 03 Aug 2020 17:57:48 +0100 X-MC-Unique: AfxWu5hnN66AhufCIfqZ2Q-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Mon, 3 Aug 2020 17:57:47 +0100 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Mon, 3 Aug 2020 17:57:47 +0100 From: David Laight To: "'Madhavan T. Venkataraman'" , "'Mark Rutland'" Subject: RE: [PATCH v1 0/4] [RFC] Implement Trampoline File Descriptor Thread-Topic: [PATCH v1 0/4] [RFC] Implement Trampoline File Descriptor Thread-Index: AQHWZ2jYT+e4gDrzGEmP/30MMvDTCqkmD9qggABvyICAAB4gEA== Date: Mon, 3 Aug 2020 16:57:47 +0000 Message-ID: References: <20200728131050.24443-1-madvenka@linux.microsoft.com> <6540b4b7-3f70-adbf-c922-43886599713a@linux.microsoft.com> <46a1adef-65f0-bd5e-0b17-54856fb7e7ee@linux.microsoft.com> <20200731183146.GD67415@C02TD0UTHF1T.local> <7fdc102e-75ea-6d91-d2a3-7fe8c91802ce@linux.microsoft.com> In-Reply-To: <7fdc102e-75ea-6d91-d2a3-7fe8c91802ce@linux.microsoft.com> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200803_125752_844995_C7856FD9 X-CRM114-Status: GOOD ( 15.81 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kernel Hardening , Linux API , X86 ML , LKML , Oleg Nesterov , LSM List , Andy Lutomirski , Linux FS Devel , linux-integrity , linux-arm-kernel Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org From: Madhavan T. Venkataraman > Sent: 03 August 2020 17:03 > > On 8/3/20 3:27 AM, David Laight wrote: > > From: Mark Rutland > >> Sent: 31 July 2020 19:32 > > ... > >>> It requires PC-relative data references. I have not worked on all architectures. > >>> So, I need to study this. But do all ISAs support PC-relative data references? > >> Not all do, but pretty much any recent ISA will as it's a practical > >> necessity for fast position-independent code. > > i386 has neither PC-relative addressing nor moves from %pc. > > The cpu architecture knows that the sequence: > > call 1f > > 1: pop %reg > > is used to get the %pc value so is treated specially so that > > it doesn't 'trash' the return stack. > > > > So PIC code isn't too bad, but you have to use the correct > > sequence. > > Is that true only for 32-bit systems only? I thought RIP-relative addressing was > introduced in 64-bit mode. Please confirm. I said i386 not amd64 or x86-64. So yes, 64bit code has PC-relative addressing. But I'm pretty sure it has no other way to get the PC itself except using call - certainly nothing in the 'usual' instructions. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales) _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel