From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 64245 invoked by alias); 24 Feb 2016 13:21:20 -0000 Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org Received: (qmail 64225 invoked by uid 89); 24 Feb 2016 13:21:19 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.9 required=5.0 tests=AWL,BAYES_00,RCVD_IN_DNSWL_NONE,SPF_PASS autolearn=ham version=3.3.2 spammy=cell, Cell, watchpoint X-HELO: relay1.mentorg.com Received: from relay1.mentorg.com (HELO relay1.mentorg.com) (192.94.38.131) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Wed, 24 Feb 2016 13:21:13 +0000 Received: from svr-orw-fem-03.mgc.mentorg.com ([147.34.97.39]) by relay1.mentorg.com with esmtp id 1aYZNN-00069N-Hl from Luis_Gustavo@mentor.com ; Wed, 24 Feb 2016 05:21:09 -0800 Received: from [172.30.1.130] (147.34.91.1) by svr-orw-fem-03.mgc.mentorg.com (147.34.97.39) with Microsoft SMTP Server id 14.3.224.2; Wed, 24 Feb 2016 05:21:09 -0800 Reply-To: Luis Machado Subject: Re: [PATCH, v3] Expect SI_KERNEL or TRAP_BRKPT si_code values for MIPS breakpoint traps References: <1456179628-14249-1-git-send-email-lgustavo@codesourcery.com> <56CB8E9D.70605@redhat.com> <56CBBD44.8020808@codesourcery.com> <56CDA835.7030903@redhat.com> To: Pedro Alves , CC: From: Luis Machado Message-ID: <56CDAE41.2050609@codesourcery.com> Date: Wed, 24 Feb 2016 13:21:00 -0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 MIME-Version: 1.0 In-Reply-To: <56CDA835.7030903@redhat.com> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit X-IsSubscribed: yes X-SW-Source: 2016-02/txt/msg00725.txt.bz2 On 02/24/2016 09:55 AM, Pedro Alves wrote: > On 02/23/2016 02:00 AM, Luis Machado wrote: >> On 02/22/2016 07:41 PM, Pedro Alves wrote: >>> On 02/22/2016 10:20 PM, Luis Machado wrote: >>> >>>> diff --git a/gdb/nat/linux-ptrace.h b/gdb/nat/linux-ptrace.h >>>> index ba58717..72b32b1 100644 >>>> --- a/gdb/nat/linux-ptrace.h >>>> +++ b/gdb/nat/linux-ptrace.h >>>> @@ -140,11 +140,16 @@ struct buffer; >>>> in SPU code on a Cell/B.E. However, SI_KERNEL is never seen >>>> on a SIGTRAP for any other reason. >>>> >>>> + The MIPS kernel uses the default si_code of SI_KERNEL for software >>>> + breakpoints, hardware watchpoints and SIGTRAP's in general. >>> >>> If we get this for both software breakpoints and hardware watchpoints, >>> then it seems to me that this change still leaves watchpoints broken, >>> as I can't see how check_stopped_by_watchpoint is reached, in either >>> gdb/linux-nat.c or gdbserver/linux-low.c. >> >> With or without this specific breakpoint fix, hardware watchpoints are >> already broken for MIPS AFAICS. > > Yep, hence my "still". ;-) > >> >> MIPS' kernel has never set si_code to anything other than SI_KERNEL. >> When the change to expect TRAP_HWBKPT was committed, then hardware >> watchpoints stopped working properly for MIPS. >> >> Now all hardware watchpoints produce are breakpoint-like traps that get >> silently ignored by GDB as "delayed software breakpoint trap". Neither >> GDB nor GDBserver can tell when a hardware watchpoint really happened by >> using si_code information. >> >> But this seems to be a different issue and i think it should be handle >> separately. > > I think it's all the same, and that we'll need to change > linux-nat.c:save_sigtrap and the equivalent bits in gdbserver/linux-low.c. > > So if we pick the table I added for x86, and fill it in > for MIPS, this is what we get: > > | what | si_code | > |------------------------------------------+----------------| > | software breakpoints | SI_KERNEL | > | single-steps | N/A | > | single-stepping a syscall | N/A | > | user sent SIGTRAP | 0 | > | exec SIGTRAP (when no PTRACE_EVENT_EXEC) | doesn't matter | > | hardware breakpoints | N/A | > | hardware watchpoints | SI_KERNEL | > Should i add that table explicitly or will v4 with the most meaningful bits of that table cut it? It seems we will eventually move from SI_KERNEL to something more appropriate for MIPS. > So the only distinction we need to make is between software > breakpoints SI_KERNEL, and hardware watchpoints SI_KERNEL. > > And we can accurately do that with > mips_linux_stopped_by_watchpoint / mips_stopped_by_watchpoint. > > Is my understanding correct? > Yes. We need to check the MIPS debug registers unconditionally and not just when a meaningful si_code of TRAP_HWBKPT shows up. Did you want that in the same patch or in a separate one? I was attempting to address the software breakpoint issue for now, but it seems i ended up with 2 problems now. :-)