From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 61637 invoked by alias); 17 Jun 2016 15:10:52 -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 61625 invoked by uid 89); 17 Jun 2016 15:10:51 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-3.3 required=5.0 tests=BAYES_00,RP_MATCHES_RCVD,SPF_HELO_PASS autolearn=ham version=3.3.2 spammy= X-HELO: mx1.redhat.com Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (AES256-GCM-SHA384 encrypted) ESMTPS; Fri, 17 Jun 2016 15:10:46 +0000 Received: from int-mx13.intmail.prod.int.phx2.redhat.com (int-mx13.intmail.prod.int.phx2.redhat.com [10.5.11.26]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id C637E1393C0; Fri, 17 Jun 2016 15:10:45 +0000 (UTC) Received: from [127.0.0.1] (ovpn01.gateway.prod.ext.ams2.redhat.com [10.39.146.11]) by int-mx13.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id u5HFAixG023717; Fri, 17 Jun 2016 11:10:45 -0400 Subject: Re: [PATCH 11/12] Use reinsert_breakpoint for vCont;s To: Yao Qi References: <1464859846-15619-1-git-send-email-yao.qi@linaro.org> <1464859846-15619-12-git-send-email-yao.qi@linaro.org> <61835b69-a4bf-a912-4eb3-b223c2a16614@redhat.com> <86h9cvud2z.fsf@gmail.com> <1cec772e-a659-3f2f-1eae-67d27fdbd9e0@redhat.com> <86a8imtnf7.fsf@gmail.com> Cc: gdb-patches@sourceware.org From: Pedro Alves Message-ID: Date: Fri, 17 Jun 2016 15:10:00 -0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1 MIME-Version: 1.0 In-Reply-To: <86a8imtnf7.fsf@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-SW-Source: 2016-06/txt/msg00305.txt.bz2 On 06/15/2016 05:41 PM, Yao Qi wrote: > Pedro Alves writes: > >> That doesn't tell the reader why we need to stop _all_ threads. The >> threads that are about to be resumed are obviously stopped, and >> thus we could already _access_ inferior memory through them. > > GDB may only resume some threads, and leave other threads running. In > order to access inferior memory safely, we must stop all threads. But what do you mean by "safely" ? What goes wrong if we don't stop all threads? > >> >> I guess this is about flushing instruction caches? >> > > No, it is not about flushing instruction caches. Then what is it about? > >>>>> @@ -5176,6 +5241,30 @@ proceed_all_lwps (void) >>>>> if (debug_threads) >>>>> debug_printf ("Proceeding, no step-over needed\n"); >>>>> >>>>> + /* Re-install the reinsert breakpoints on software single step target >>>>> + if the client wants it step. */ >>>>> + if (can_software_single_step ()) >>>> >>>> Not immediately obvious to why is this necessary. Where were they >>>> removed in the first place? I'm it must be necessary, but maybe >>>> extending the comment helps. >>> >>> How about this >>> >>> /* On software single step target, we removed reinsert breakpoints >>> after we get any events from the inferior. >> >> Is that all events, even internal events? From the patch, it seemed >> like it was only before reporting an event to gdb. >> > > You are right, I though too much about supporting range-stepping. > I rewrite the comments in the patch below, > >>> If the client wants >>> thread step, re-install these reinsert breakpoints. */ >>> >> >> If we only remove before reporting an event to gdb, then I don't >> understand this. We already insert single-step breakpoints when >> we process the resume request from gdb, no? > > We insert single-step breakpoints when we process the resume requests > and threads are about to be resumed. If threads still have pending > status, single-step breakpoints are not installed, so we need to install > them in proceed_all_lwps. > > @@ -3518,6 +3521,23 @@ linux_wait_1 (ptid_t ptid, > return ignore_event (ourstatus); > } > > + /* Remove reinsert breakpoints ... */ > + if (can_software_single_step () > + && has_reinsert_breakpoints (current_thread) > + /*... if GDB requests this thread doing resume_step or ...*/ > + && (current_thread->last_resume_kind == resume_step > + /* GDBserver has already started the step-over for vCont;s, > + but it gets some other signal, like SIGSTOP sent by > + GDBserver for vCont;t or other signal program received. */ > + || !maybe_internal_trap)) > + { > + stop_all_lwps (1, event_child); > + > + delete_reinsert_breakpoints (current_thread); > + > + unstop_all_lwps (1, event_child); > + } I'm re-looking at this and wondering if this is really the right place to do this. If the thread hits a breakpoint that ends up not reported to gdb (e.g., condition evals false), then we'll remove the reinsert breakpoints here, and then later reinsert them in proceed_all_lwps. The extra stopping/unstopping everything is best avoided if possible. Thus, couldn't we move this to after: /* We found no reason GDB would want us to stop. We either hit one of our own breakpoints, or finished an internal step GDB shouldn't know about. */ if (!report_to_gdb) { ... } ? - Also, if in all-stop mode, if gdb does: vCont;s:1;c thus setting thread 1 stepping, and all others continuing, and then some other thread but thread 1 hits a breakpoint, what is removing the reinsert breakpoint of thread 1? > + > /* Note that all addresses are always "out of the step range" when > there's no range to begin with. */ > in_step_range = lwp_in_step_range (event_child); > @@ -4281,12 +4301,6 @@ linux_resume_one_lwp_throw (struct lwp_info *lwp, > > step = maybe_hw_step (thread); > } > - else > - { > - /* If the thread isn't doing step-over, there shouldn't be any > - reinsert breakpoints. */ > - gdb_assert (!has_reinsert_breakpoints (thread)); > - } > > if (fast_tp_collecting == 1) > { > @@ -4841,7 +4855,6 @@ linux_resume_one_thread (struct inferior_list_entry *entry, void *arg) > { > struct thread_info *thread = (struct thread_info *) entry; > struct lwp_info *lwp = get_thread_lwp (thread); > - int step; > int leave_all_stopped = * (int *) arg; > int leave_pending; > > @@ -4910,10 +4923,14 @@ linux_resume_one_thread (struct inferior_list_entry *entry, void *arg) > > if (!leave_pending) > { > + int step = 0; > + > if (debug_threads) > debug_printf ("resuming LWP %ld\n", lwpid_of (thread)); > > - step = (lwp->resume->kind == resume_step); > + if (lwp->resume->kind == resume_step) > + step = maybe_hw_step (thread); > + > linux_resume_one_lwp (lwp, step, lwp->resume->sig, NULL); > } > else > @@ -4954,6 +4971,7 @@ linux_resume (struct thread_resume *resume_info, size_t n) > struct thread_info *need_step_over = NULL; > int any_pending; > int leave_all_stopped; > + int resume_step_is_handled = 0; > > if (debug_threads) > { > @@ -4997,12 +5015,55 @@ linux_resume (struct thread_resume *resume_info, size_t n) > debug_printf ("Resuming, no pending status or step over needed\n"); > } > > + /* If resume_step is requested by GDB, install reinsert breakpoints > + when the thread is about to be actually resumed. IOW, we don't > + insert reinsert breakpoints if any thread has pending status. */ > + if (!leave_all_stopped && can_software_single_step ()) > + { > + struct inferior_list_entry *inf, *tmp; > + > + if (debug_threads) > + debug_printf ("Handle resume_step.\n"); > + > + ALL_INFERIORS (&all_threads, inf, tmp) > + { > + struct thread_info *thread = (struct thread_info *) inf; > + struct lwp_info *lwp = get_thread_lwp (thread); > + > + if (lwp->resume != NULL && lwp->resume->kind == resume_step) > + { > + if (!resume_step_is_handled) > + { > + /* We need to access the inferior memory to install > + reinsert breakpoints, so stop all threads. */ > + stop_all_lwps (0, NULL); > + > + if (debug_threads) > + debug_printf ("Done stopping all threads.\n"); > + > + resume_step_is_handled = 1; > + } > + > + install_software_single_step_breakpoints (lwp); > + > + if (debug_threads) > + debug_printf ("Insert breakpoint for resume_step LWP %ld\n", > + lwpid_of (thread)); > + } > + } > + > + if (debug_threads) > + debug_printf ("Handle resume_step. Done\n"); > + } > + > /* Even if we're leaving threads stopped, queue all signals we'd > otherwise deliver. */ > find_inferior (&all_threads, linux_resume_one_thread, &leave_all_stopped); > > if (need_step_over) > start_step_over (get_thread_lwp (need_step_over)); > + else if (resume_step_is_handled) > + unstop_all_lwps (0, NULL); > > if (debug_threads) > { > @@ -5098,7 +5159,8 @@ proceed_one_lwp (struct inferior_list_entry *entry, void *except) > if (debug_threads) > debug_printf (" stepping LWP %ld, client wants it stepping\n", > lwpid_of (thread)); > - step = 1; > + > + step = maybe_hw_step (thread); > } > else if (lwp->bp_reinsert != 0) > { > @@ -5164,6 +5226,33 @@ proceed_all_lwps (void) > if (debug_threads) > debug_printf ("Proceeding, no step-over needed\n"); > > + if (can_software_single_step ()) > + { > + struct inferior_list_entry *inf, *tmp; > + > + ALL_INFERIORS (&all_threads, inf, tmp) > + { > + struct thread_info *thread = (struct thread_info *) inf; > + > + /* On software single step target, we insert reinsert > + breakpoints when the threads are about to be actually > + resumed. IOW, we don't insert them if any thread has > + pending status. Before we proceed threads, insert > + reinsert breakpoints if the client wants it step. */ > + if (thread->last_resume_kind == resume_step) > + { > + struct lwp_info *lwp = get_thread_lwp (thread); > + > + if (!has_reinsert_breakpoints (thread)) > + install_software_single_step_breakpoints (lwp); > + > + if (debug_threads) > + debug_printf ("Insert breakpoint for resume_step LWP %ld\n", > + lwpid_of (thread)); > + } > + } > + } > + > find_inferior (&all_threads, proceed_one_lwp, NULL); > } > Hmm, seeing that we need to handle installing the breakpoints in both places, I wonder about making linux_resume just handle setting up the last resume kind and queue signals, and then end up calling proceed_all_lwps. If that works, I suspect it would simplify things a good deal. Thanks, Pedro Alves