From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756453AbbAPOzm (ORCPT ); Fri, 16 Jan 2015 09:55:42 -0500 Received: from mx1.redhat.com ([209.132.183.28]:43402 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756337AbbAPOzl (ORCPT ); Fri, 16 Jan 2015 09:55:41 -0500 Message-ID: <54B92649.6030009@redhat.com> Date: Fri, 16 Jan 2015 20:25:05 +0530 From: Pratyush Anand User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0 MIME-Version: 1.0 To: Will Deacon CC: Catalin Marinas , Steve Capper , Oleg Nesterov , "linux-kernel@vger.kernel.org" , David Long , William Cohen , "linux-arm-kernel@lists.infradead.org" Subject: Re: Query: ARM64: Behavior of el1_dbg exception while executing el0_dbg References: <54AE830E.1090000@redhat.com> <20150108162312.GO11583@arm.com> <54AEBE45.9080203@redhat.com> <20150109154635.GG11258@arm.com> <54B00C39.1070809@redhat.com> <20150112173005.GK13360@arm.com> <54B4BF4C.2030009@redhat.com> <20150113155221.GG16524@e104818-lin.cambridge.arm.com> <54B55B95.1070402@redhat.com> <54B7EF3C.8060909@redhat.com> <54B8FD49.2060503@redhat.com> In-Reply-To: <54B8FD49.2060503@redhat.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Sorry for writing so many mails...But I have one more closer information which could help to further explain the behavior. See below. On Friday 16 January 2015 05:30 PM, Pratyush Anand wrote: > Hi Will, > > > On Thursday 15 January 2015 10:17 PM, Pratyush Anand wrote: >> Hi Will / Catalin, >> >> On Tuesday 13 January 2015 11:23 PM, Pratyush Anand wrote: >>> I will still try to find some way to capture enable_dbg macro path.H >> >> I did instrumented debug tap points at all the location from where >> enable_debug macro is called(see attached debug patch). But, I do not >> see that, execution reaches to any of those tap points between el0_dbg >> and el1_dbg, and tap points debug log also confirms that el1_dbg is >> raised before el0_dbg is returned. > > Probably we all missed this, ARMv8 specs is very clear about it. In > section "D2.1 About debug exceptions" it says: > > Software Breakpoint Instruction exceptions cannot be masked. The PE > takes Software Breakpoint Instruction exceptions regardless of both of > the following: > • The current Exception level. > • The current Security state. > > So, reception of el1_dbg while executing el0_dbg seems perfectly normal > to me. If you agree then I am back with the original query which I asked > in the beginning of the > thread,(http://permalink.gmane.org/gmane.linux.ports.arm.kernel/383672) > ie how can instruction_pointer be wrong when second el1_dbg is called > recursively(as follows). > > [1]-> el0_dbg (After executing BRK instruction by user) > [2] -> el1_dbg (when uprobe break handler at [1] executes BRK > instruction) > (At the end of this ELR_EL1 is programmed with fffffdfffc000004) With new tap point debug of entry.S, I see that: After this we are receiving one more exception and that is el1_inv. Now, as soon as enable_dbg is called in el1_inv, we receive next single step exception, with ELR_EL1 value as next instruction address after enable_dbg of el1_inv. EC value of ESR_EL1(0x86000007) in el1_inv is 0x21 ie ESR_EL1_EC_IABT_EL1 and IFSC is 0x07 Hummmm..So, why did we receive here, an instruction abort in EL1 due to Translation fault, third level??? I do not have that much knowledge yet, to decipher it... :( > [3] -> el1_dbg (when kprobe break handler at [2] enables single > stepping) > (Here ELR_EL1 was found fffffe0000092470).So When this el1_dbg > was received, then regs->pc values are not same what was programmed in > ELR_EL1 at the return of [2]. > ~Pratyush PS: Debug code is here: https://github.com/pratyushanand/linux.git : ml_arm64_uprobe_devel_debug_el1_inv_while_kprobe_insertion_at_uprobe_breakpoint_handler