From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753924AbaHKPIS (ORCPT ); Mon, 11 Aug 2014 11:08:18 -0400 Received: from mail.emea.novell.com ([130.57.118.101]:50436 "EHLO mail.emea.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753465AbaHKPIR convert rfc822-to-8bit (ORCPT ); Mon, 11 Aug 2014 11:08:17 -0400 Message-Id: <53E8F87B020000780002B41D@mail.emea.novell.com> X-Mailer: Novell GroupWise Internet Agent 14.0.0 Date: Mon, 11 Aug 2014 16:08:11 +0100 From: "Jan Beulich" To: "H. Peter Anvin" Cc: "Andy Lutomirski" , "Kees Cook" , "Will Drewry" , "Frederic Weisbecker" , "Denys Vlasenko" , "X86 ML" , "Alexei Starovoitov" , "Denys Vlasenko" , "Oleg Nesterov" , "Linux Kernel Mailing List" Subject: Re: [PATCH 4/5] x86: entry_64.S: always allocate complete "struct pt_regs" References: <1406904498-21647-1-git-send-email-dvlasenk@redhat.com> <1406904498-21647-4-git-send-email-dvlasenk@redhat.com> <20140801231929.GB26491@localhost.localdomain> <20140811004559.GA2656@lerouge> <53E89DA3020000780002B00B@mail.emea.novell.com> <53E8C476.8000800@redhat.com> <53E8EC9F020000780002B383@mail.emea.novell.com> <53E8D905.7030809@zytor.com> In-Reply-To: <53E8D905.7030809@zytor.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8BIT Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org >>> On 11.08.14 at 16:53, wrote: > On 08/11/2014 07:17 AM, Jan Beulich wrote: >>> >>> The existing comments explain what every byte means. >>> They are useful if CFI-literate reader wants to check correctness >>> of the encoding of this annotation. >>> >>> There is no overall comment what this CFI annotation >>> *achieves*. In human language, what do we say >>> to DWARF decoder here? >> >> Short answer: DW_CFA_def_cfa_expression. >> >> Longer response: Just like I said before, what you're asking for is >> identical to ask for each other CFI annotation to get a comment >> associated to tell you what it's doing, which I don't think you >> really mean to ask for. (Our main problem here is that we can't >> specify expressions with the .cfi_* gas directives, and hence have >> to resort to .cfi_escape.) >> > > No, in *human language*. What does the DW_CFA_def_cfa_expression > actually aim to accomplish? If you don't know the innards of the DWARF > spec, the whole thing might as well be Hungarian. Just like the other DW_CFA_def_cfa_* ones it sets the current frame address (CFA), just not via one of the pre-canned shortcuts, but via an expression (in the case here de-referencing the stack pointer to read the top of stack, and then adding the necessary offset). So it indeed is similar enough to other .cfi_* annotations we use without further comments. And btw., Hungarian isn't _that_ bad. Jan