From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752214AbaHKJHj (ORCPT ); Mon, 11 Aug 2014 05:07:39 -0400 Received: from mail-lb0-f174.google.com ([209.85.217.174]:55742 "EHLO mail-lb0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751370AbaHKJHi (ORCPT ); Mon, 11 Aug 2014 05:07:38 -0400 MIME-Version: 1.0 In-Reply-To: <53E89DA3020000780002B00B@mail.emea.novell.com> 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> From: Andy Lutomirski Date: Mon, 11 Aug 2014 18:07:16 +0900 Message-ID: Subject: Re: [PATCH 4/5] x86: entry_64.S: always allocate complete "struct pt_regs" To: Jan Beulich Cc: Frederic Weisbecker , Denys Vlasenko , Kees Cook , Will Drewry , X86 ML , Alexei Starovoitov , Denys Vlasenko , Oleg Nesterov , Linux Kernel Mailing List , "H. Peter Anvin" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 11, 2014 at 5:40 PM, Jan Beulich wrote: >>>> On 11.08.14 at 02:46, wrote: >> On Mon, Aug 04, 2014 at 05:03:42AM +0200, Denys Vlasenko wrote: >>> On Sat, Aug 2, 2014 at 1:19 AM, Frederic Weisbecker >> wrote: >>> >> CFI_ESCAPE 0x0f /* DW_CFA_def_cfa_expression */, 6, \ >>> >> 0x77 /* DW_OP_breg7 */, 0, \ >>> >> 0x06 /* DW_OP_deref */, \ >>> >> - 0x08 /* DW_OP_const1u */, SS+8-RBP, \ >>> >> + 0x08 /* DW_OP_const1u */, SS+8, \ >>> >> 0x22 /* DW_OP_plus */ >>> >> /* We entered an interrupt context - irqs are off: */ >>> >> TRACE_IRQS_OFF >>> >> - >>> >> call \func >>> >> .endm >>> >> >>> >> @@ -749,10 +719,9 @@ ret_from_intr: >>> >> >>> >> /* Restore saved previous stack */ >>> >> popq %rsi >>> > >>> > And then you pop to rsi. Ok that indeed works but perhaps we should keep it symetrical >>> > just for clarity? Any reason why we can't reuse rdi here? >>> >>> I changed this entire area in v2: basically, I will not change the logic, >>> but will add comments explaining what are we doing here, and why. >>> (Some minor code changes will be done, not affecting the logic). >>> >>> While we are at it, what this CFI_ESCAPE thing does here? >>> As usual, it has no comment :/ > > Each of its lines has a comment; with other CFI annotations not > each having comments, I don't see what else is needed here. > >> I don't know, only Jan Beulich understands those CFI black magic. > > That would be very said if true. > > In any case: This needs to be a CFI_ESCAPE because there's no > other way I know of to emit the DW_CFA_def_cfa_expression. > And the change to it looks correct to me. > How does one test the entry CFI annotations? The best that I know of is to single-step through using gdb attached to qemu and see whether backtraces seem to work. --Andy