From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S968263AbcA1UUs (ORCPT ); Thu, 28 Jan 2016 15:20:48 -0500 Received: from terminus.zytor.com ([198.137.202.10]:50003 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S967401AbcA1UUq (ORCPT ); Thu, 28 Jan 2016 15:20:46 -0500 Subject: Re: [PATCH 02/31] Add debugger entry points for X86 To: Jeffrey Merkey , linux-kernel@vger.kernel.org References: <1454010374-28459-1-git-send-email-jeffmerkey@gmail.com> Cc: tglx@linutronix.de, mingo@redhat.com, x86@kernel.org, akpm@linux-foundation.org, linux.mdb@gmail.com, dzickus@redhat.com, dyoung@redhat.com, mnfhuang@gmail.com From: "H. Peter Anvin" Message-ID: <56AA780E.7000002@zytor.com> Date: Thu, 28 Jan 2016 12:20:30 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.0 MIME-Version: 1.0 In-Reply-To: <1454010374-28459-1-git-send-email-jeffmerkey@gmail.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/28/16 11:46, Jeffrey Merkey wrote: > This patch series adds an export which can be set by system debuggers to > direct the hard lockup and soft lockup detector to trigger a breakpoint > exception and enter a debugger if one is active. It is assumed that if > someone sets this variable, then an breakpoint handler of some sort will > be actively loaded or registered via the notify die handler chain. > > This addition is extremely useful for debugging hard and soft lockups > real time and quickly from a console debugger. > > Signed-off-by: Jeffrey Merkey > --- > arch/x86/include/asm/kdebug.h | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/arch/x86/include/asm/kdebug.h b/arch/x86/include/asm/kdebug.h > index e5f5dc9..cbe9004 100644 > --- a/arch/x86/include/asm/kdebug.h > +++ b/arch/x86/include/asm/kdebug.h > @@ -3,6 +3,11 @@ > > #include > > +static inline void arch_breakpoint(void) > +{ > + asm(" int $3"); > +} > + > struct pt_regs; > Even though apparently gas changed "int $3" to "int3" the latter is actually a different instruction (with subtly different behavior) and this may very well be corrected in gas at a future date. So please encode this as "int3". It should also be "asm volatile" since it has side effects unbeknownst to the compiler. -hpa