Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751289Ab3HFE2e (ORCPT ); Tue, 6 Aug 2013 00:28:34 -0400 Received: from mga09.intel.com ([134.134.136.24]:64146 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750982Ab3HFE2d (ORCPT ); Tue, 6 Aug 2013 00:28:33 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.89,823,1367996400"; d="scan'208";a="382469824" Message-ID: <52007B70.9070504@linux.intel.com> Date: Mon, 05 Aug 2013 21:28:32 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130625 Thunderbird/17.0.7 MIME-Version: 1.0 To: Mathieu Desnoyers CC: Linus Torvalds , Steven Rostedt , LKML , gcc , Ingo Molnar , Thomas Gleixner , David Daney , Behan Webster , Peter Zijlstra , Herbert Xu Subject: Re: [RFC] gcc feature request: Moving blocks into sections References: <51FFEC56.6040206@linux.intel.com> <1375727010.22073.110.camel@gandalf.local.home> <51FFEEEC.5060902@linux.intel.com> <1375728583.22073.118.camel@gandalf.local.home> <51FFF430.1060701@linux.intel.com> <20130805195446.GA22359@Krystal> <20130805212855.GA23044@Krystal> <52001C92.3070209@linux.intel.com> <20130806041437.GA30449@Krystal> In-Reply-To: <20130806041437.GA30449@Krystal> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1106 Lines: 33 On 08/05/2013 09:14 PM, Mathieu Desnoyers wrote: >> >> For unconditional jmp that should be pretty safe barring any fundamental >> changes to the instruction set, in which case we can enable it as >> needed, but for extra robustness it probably should skip prefix bytes. > > On x86-32, some prefixes are actually meaningful. AFAIK, the 0x66 prefix > is used for: > > E9 cw jmp rel16 relative jump, only in 32-bit > > Other prefixes can probably be safely skipped. > Yes. Some of them are used as hints or for MPX. > Another question is whether anything prevents the assembler from > generating a jump near (absolute indirect), or far jump. The code above > seems to assume that we have either a short or near relative jump. Absolutely something prevents! It would be a very serious error for the assembler to generate such instructions. -hpa -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/