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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D44B4C7EE23 for ; Thu, 1 Jun 2023 08:04:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231732AbjFAIE6 convert rfc822-to-8bit (ORCPT ); Thu, 1 Jun 2023 04:04:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59190 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232042AbjFAIEu (ORCPT ); Thu, 1 Jun 2023 04:04:50 -0400 Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.85.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 196A197 for ; Thu, 1 Jun 2023 01:04:48 -0700 (PDT) Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) by relay.mimecast.com with ESMTP with both STARTTLS and AUTH (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id uk-mta-12-ZZ_0crTpOS2e4R0wAwNCcQ-1; Thu, 01 Jun 2023 09:04:46 +0100 X-MC-Unique: ZZ_0crTpOS2e4R0wAwNCcQ-1 Received: from AcuMS.Aculab.com (10.202.163.6) by AcuMS.aculab.com (10.202.163.6) with Microsoft SMTP Server (TLS) id 15.0.1497.48; Thu, 1 Jun 2023 09:04:43 +0100 Received: from AcuMS.Aculab.com ([::1]) by AcuMS.aculab.com ([::1]) with mapi id 15.00.1497.048; Thu, 1 Jun 2023 09:04:43 +0100 From: David Laight To: "'Preble, Adam C'" , Pavel Machek CC: "linux-kernel@vger.kernel.org" Subject: RE: How do I force an IBT trap in a demo kernel module? Thread-Topic: How do I force an IBT trap in a demo kernel module? Thread-Index: AdmNrJN/HBQNXQy0RfSVuasMlQAruQAaPVaQALWt3oAAybiRcAAStlQg Date: Thu, 1 Jun 2023 08:04:43 +0000 Message-ID: <8ee1b8453e614b5b930d13c2f3747221@AcuMS.aculab.com> References: <82034ea784e44c5b929f519ceac6c4e0@AcuMS.aculab.com> In-Reply-To: Accept-Language: en-GB, 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 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Preble, Adam C > Sent: 01 June 2023 00:02 > > It looked to me like I was getting the indirect jump just fine with what I already was doing. Sure, I > made the instruction pointer volatile and static, but nothing changed just from that. This ought to compile to code that does what you want.. void func(void) {} void (*func_ptr)(void) = func; void test(void) { void (*ptr)(void) = (void *)func_ptr + 4; ptr(); } See https://godbolt.org/z/o8cedv3d4 but that doesn't have the option that generated the endbra. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)