From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: Re: [PATCH 2/2] Xen/x86: Improve information from domain_crash_synchronous Date: Thu, 5 Sep 2013 10:44:39 +0100 Message-ID: <52285287.2070208@citrix.com> References: <1378318727-29518-1-git-send-email-andrew.cooper3@citrix.com> <1378318727-29518-3-git-send-email-andrew.cooper3@citrix.com> <522859C402000078000F0AF8@nat28.tlf.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta14.messagelabs.com ([193.109.254.103]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1VHW7d-0002Xb-Qw for xen-devel@lists.xenproject.org; Thu, 05 Sep 2013 09:45:06 +0000 In-Reply-To: <522859C402000078000F0AF8@nat28.tlf.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Jan Beulich Cc: xen-devel , Keir Fraser List-Id: xen-devel@lists.xenproject.org On 05/09/13 09:15, Jan Beulich wrote: >>>> On 04.09.13 at 20:18, Andrew Cooper wrote: >> As it currently stands, the string "domain_crash_sync called from entry.S" is >> not helpful at identifying why the domain was crashed, and a debug build of >> Xen doesn't help the matter >> >> This patch improves the information printed, by pointing to where the crash >> decision was made. > Looks quite useful. > >> --- a/xen/arch/x86/x86_64/compat/entry.S >> +++ b/xen/arch/x86/x86_64/compat/entry.S >> @@ -263,6 +263,7 @@ ENTRY(compat_int80_direct_trap) >> /* {[ERRCODE,] EIP, CS, EFLAGS, [ESP, SS]} */ >> /* %rdx: trap_bounce, %rbx: struct vcpu */ >> /* On return only %rbx and %rdx are guaranteed non-clobbered. */ >> +.globl compat_create_bounce_frame >> compat_create_bounce_frame: > Is the addition above a left-over? I don't see any use of the > label outside of this file. This is for the benifit of print_symbol(), which will now give create_bounce_frame()+some rather than trap_nop()+loads. > >> @@ -329,7 +330,12 @@ UNLIKELY_END(compat_bounce_failsafe) >> movzwl TRAPBOUNCE_cs(%rdx),%eax >> /* Null selectors (0-3) are not allowed. */ >> testl $~3,%eax >> - jz domain_crash_synchronous >> +.Lcompat_bounce_null_selector: >> +UNLIKELY_START(z, compat_bounce_null_selector) >> + lea .Lcompat_bounce_null_selector(%rip), %rdi >> + jmp asm_domain_crash_synchronous >> + ud2a >> +UNLIKELY_END(compat_bounce_null_selector) > Here and further down you don't really need the label at the > start of the unlikely section - the place can as well be identified > by using > > lea (%rip), %rdi > > inside that section (the place is still unique, just outside the > original code stream, i.e. just slightly more difficult to > re-associate). > > Jan > But in an unlikely section, %rip is shifted quite a lot from %rip of the code immediately before. This is also for the benefit of print_symbol() which will pick up the {compat_,}create_bounce_frame rather than the global symbol surrounding the unlikely section. ~Andrew