Fix PR18360 - internal error when using "interrupt -a"

If you do "interrupt -a" just while some thread is stepping over a
breakpoint, gdb trips on an internal error.

The test added by this patch manages to trigger this consistently by
spawning a few threads that are constantly tripping on a conditional
breakpoint whose condition always evaluates to false.  With current
gdb, you get:

~~~
 interrupt -a
 .../src/gdb/inline-frame.c:343: internal-error: void skip_inline_frames(ptid_t): Assertion `find_inline_frame_state (ptid) == NULL' failed.
 A problem internal to GDB has been detected,
 further debugging may prove unreliable.
 Quit this debugging session? (y or n) FAIL: gdb.threads/interrupt-while-step-over.exp: displaced-stepping=on: iter=0: interrupt -a (GDB internal error)
[...]
 .../src/gdb/inline-frame.c:343: internal-error: void skip_inline_frames(ptid_t): Assertion `find_inline_frame_state (ptid) == NULL' failed.
 A problem internal to GDB has been detected,
 further debugging may prove unreliable.
 Quit this debugging session? (y or n) FAIL: gdb.threads/interrupt-while-step-over.exp: displaced-stepping=off: iter=0: wait for stops (GDB internal error)
~~~

The assertion triggers because we're processing a stop for a thread
that had already stopped before and thus had already its inline-frame
state filled in.

Calling handle_inferior_event_1 directly within a
"thread_stop_requested" observer is something that I've wanted to get
rid of before, for being fragile.  Nowadays, infrun is aware of
threads with pending events, so we can use that instead, and let the
normal fetch_inferior_event -> handle_inferior_event code path handle
the forced stop.

The change to finish_step_over is necessary because sometimes a thread
that was told to PTRACE_SINGLESTEP reports back a SIGSTOP instead of a
SIGTRAP (i.e., we tell it to single-step, and then interrupt it quick
enough that on the kernel side the thread dequeues the SIGTOP before
ever having had a chance of executing the instruction to be stepped).
SIGSTOP gets translated to a GDB_SIGNAL_0.  And then finish_step_over
would miss calling clear_step_over_info, and thus miss restarting the
other threads (which in this case of threads with pending events,
means setting their "resumed" flag, so their pending events can be
consumed).

And now that we always restart threads in finish_step_over, we no
longer need to do that in handle_signal_stop.

Tested on x86_64 Fedora 23, native and gdbserver.

gdb/ChangeLog:
2017-03-08  Pedro Alves  <palves@redhat.com>

	PR gdb/18360
	* infrun.c (start_step_over, do_target_resume, resume)
	(restart_threads): Assert we're not resuming a thread that is
	meant to be stopped.
	(infrun_thread_stop_requested_callback): Delete.
	(infrun_thread_stop_requested): If the thread is internally
	stopped, queue a pending stop event and clear the thread's
	inline-frame state.
	(handle_stop_requested): New function.
	(handle_syscall_event, handle_inferior_event_1): Use
	handle_stop_requested.
	(handle_stop_requested): New function.
	(handle_signal_stop): Set the thread's stop_signal here instead of
	at caller.
	(finish_step_over): Clear step over info unconditionally.
	(handle_signal_stop): If the user had interrupted the event
	thread, consider the stop a random signal.
	(handle_signal_stop) <signal arrived while stepping over
	breakpoint>: Don't restart threads here.
	(stop_waiting): Don't clear step-over info here.

gdb/testsuite/ChangeLog:
2017-03-08  Pedro Alves  <palves@redhat.com>

	PR gdb/18360
	* gdb.threads/interrupt-while-step-over.c: New file.
	* gdb.threads/interrupt-while-step-over.exp: New file.
This commit is contained in:
Pedro Alves 2017-03-08 18:54:34 +00:00
parent 15c22686d0
commit c65d6b55b3
6 changed files with 410 additions and 95 deletions

View File

@ -1,3 +1,26 @@
2017-03-08 Pedro Alves <palves@redhat.com>
PR gdb/18360
* infrun.c (start_step_over, do_target_resume, resume)
(restart_threads): Assert we're not resuming a thread that is
meant to be stopped.
(infrun_thread_stop_requested_callback): Delete.
(infrun_thread_stop_requested): If the thread is internally
stopped, queue a pending stop event and clear the thread's
inline-frame state.
(handle_stop_requested): New function.
(handle_syscall_event, handle_inferior_event_1): Use
handle_stop_requested.
(handle_stop_requested): New function.
(handle_signal_stop): Set the thread's stop_signal here instead of
at caller.
(finish_step_over): Clear step over info unconditionally.
(handle_signal_stop): If the user had interrupted the event
thread, consider the stop a random signal.
(handle_signal_stop) <signal arrived while stepping over
breakpoint>: Don't restart threads here.
(stop_waiting): Don't clear step-over info here.
2017-03-08 Pedro Alves <palves@redhat.com>
PR 21206

View File

@ -2083,6 +2083,8 @@ start_step_over (void)
step_over_what step_what;
int must_be_in_line;
gdb_assert (!tp->stop_requested);
next = thread_step_over_chain_next (tp);
/* If this inferior already has a displaced step in process,
@ -2331,6 +2333,8 @@ do_target_resume (ptid_t resume_ptid, int step, enum gdb_signal sig)
{
struct thread_info *tp = inferior_thread ();
gdb_assert (!tp->stop_requested);
/* Install inferior's terminal modes. */
target_terminal_inferior ();
@ -2395,6 +2399,7 @@ resume (enum gdb_signal sig)
single-step). */
int step;
gdb_assert (!tp->stop_requested);
gdb_assert (!thread_is_in_step_over_chain (tp));
QUIT;
@ -3276,65 +3281,6 @@ static void keep_going (struct execution_control_state *ecs);
static void process_event_stop_test (struct execution_control_state *ecs);
static int switch_back_to_stepped_thread (struct execution_control_state *ecs);
/* Callback for iterate over threads. If the thread is stopped, but
the user/frontend doesn't know about that yet, go through
normal_stop, as if the thread had just stopped now. ARG points at
a ptid. If PTID is MINUS_ONE_PTID, applies to all threads. If
ptid_is_pid(PTID) is true, applies to all threads of the process
pointed at by PTID. Otherwise, apply only to the thread pointed by
PTID. */
static int
infrun_thread_stop_requested_callback (struct thread_info *info, void *arg)
{
ptid_t ptid = * (ptid_t *) arg;
if ((ptid_equal (info->ptid, ptid)
|| ptid_equal (minus_one_ptid, ptid)
|| (ptid_is_pid (ptid)
&& ptid_get_pid (ptid) == ptid_get_pid (info->ptid)))
&& is_running (info->ptid)
&& !is_executing (info->ptid))
{
struct cleanup *old_chain;
struct execution_control_state ecss;
struct execution_control_state *ecs = &ecss;
memset (ecs, 0, sizeof (*ecs));
old_chain = make_cleanup_restore_current_thread ();
overlay_cache_invalid = 1;
/* Flush target cache before starting to handle each event.
Target was running and cache could be stale. This is just a
heuristic. Running threads may modify target memory, but we
don't get any event. */
target_dcache_invalidate ();
/* Go through handle_inferior_event/normal_stop, so we always
have consistent output as if the stop event had been
reported. */
ecs->ptid = info->ptid;
ecs->event_thread = info;
ecs->ws.kind = TARGET_WAITKIND_STOPPED;
ecs->ws.value.sig = GDB_SIGNAL_0;
handle_inferior_event (ecs);
if (!ecs->wait_some_more)
{
/* Cancel any running execution command. */
thread_cancel_execution_command (info);
normal_stop ();
}
do_cleanups (old_chain);
}
return 0;
}
/* This function is attached as a "thread_stop_requested" observer.
Cleanup local state that assumed the PTID was to be resumed, and
report the stop to the frontend. */
@ -3344,17 +3290,51 @@ infrun_thread_stop_requested (ptid_t ptid)
{
struct thread_info *tp;
/* PTID was requested to stop. Remove matching threads from the
step-over queue, so we don't try to resume them
automatically. */
/* PTID was requested to stop. If the thread was already stopped,
but the user/frontend doesn't know about that yet (e.g., the
thread had been temporarily paused for some step-over), set up
for reporting the stop now. */
ALL_NON_EXITED_THREADS (tp)
if (ptid_match (tp->ptid, ptid))
{
if (tp->state != THREAD_RUNNING)
continue;
if (tp->executing)
continue;
/* Remove matching threads from the step-over queue, so
start_step_over doesn't try to resume them
automatically. */
if (thread_is_in_step_over_chain (tp))
thread_step_over_chain_remove (tp);
}
iterate_over_threads (infrun_thread_stop_requested_callback, &ptid);
/* If the thread is stopped, but the user/frontend doesn't
know about that yet, queue a pending event, as if the
thread had just stopped now. Unless the thread already had
a pending event. */
if (!tp->suspend.waitstatus_pending_p)
{
tp->suspend.waitstatus_pending_p = 1;
tp->suspend.waitstatus.kind = TARGET_WAITKIND_STOPPED;
tp->suspend.waitstatus.value.sig = GDB_SIGNAL_0;
}
/* Clear the inline-frame state, since we're re-processing the
stop. */
clear_inline_frame_state (tp->ptid);
/* If this thread was paused because some other thread was
doing an inline-step over, let that finish first. Once
that happens, we'll restart all threads and consume pending
stop events then. */
if (step_over_info_valid_p ())
continue;
/* Otherwise we can process the (new) pending event now. Set
it so this pending event is considered by
do_target_wait. */
tp->resumed = 1;
}
}
static void
@ -4248,6 +4228,23 @@ stepped_in_from (struct frame_info *frame, struct frame_id step_frame_id)
return 0;
}
/* If the event thread has the stop requested flag set, pretend it
stopped for a GDB_SIGNAL_0 (i.e., as if it stopped due to
target_stop). */
static bool
handle_stop_requested (struct execution_control_state *ecs)
{
if (ecs->event_thread->stop_requested)
{
ecs->ws.kind = TARGET_WAITKIND_STOPPED;
ecs->ws.value.sig = GDB_SIGNAL_0;
handle_signal_stop (ecs);
return true;
}
return false;
}
/* Auxiliary function that handles syscall entry/return events.
It returns 1 if the inferior should keep going (and GDB
should ignore the event), or 0 if the event deserves to be
@ -4277,6 +4274,9 @@ handle_syscall_event (struct execution_control_state *ecs)
= bpstat_stop_status (get_regcache_aspace (regcache),
stop_pc, ecs->ptid, &ecs->ws);
if (handle_stop_requested (ecs))
return 0;
if (bpstat_causes_stop (ecs->event_thread->control.stop_bpstat))
{
/* Catchpoint hit. */
@ -4284,6 +4284,9 @@ handle_syscall_event (struct execution_control_state *ecs)
}
}
if (handle_stop_requested (ecs))
return 0;
/* If no catchpoint triggered for this, then keep going. */
keep_going (ecs);
return 1;
@ -4974,6 +4977,9 @@ handle_inferior_event_1 (struct execution_control_state *ecs)
= bpstat_stop_status (get_regcache_aspace (regcache),
stop_pc, ecs->ptid, &ecs->ws);
if (handle_stop_requested (ecs))
return;
if (bpstat_causes_stop (ecs->event_thread->control.stop_bpstat))
{
/* A catchpoint triggered. */
@ -5028,6 +5034,8 @@ handle_inferior_event_1 (struct execution_control_state *ecs)
case TARGET_WAITKIND_SPURIOUS:
if (debug_infrun)
fprintf_unfiltered (gdb_stdlog, "infrun: TARGET_WAITKIND_SPURIOUS\n");
if (handle_stop_requested (ecs))
return;
if (!ptid_equal (ecs->ptid, inferior_ptid))
context_switch (ecs->ptid);
resume (GDB_SIGNAL_0);
@ -5037,6 +5045,8 @@ handle_inferior_event_1 (struct execution_control_state *ecs)
case TARGET_WAITKIND_THREAD_CREATED:
if (debug_infrun)
fprintf_unfiltered (gdb_stdlog, "infrun: TARGET_WAITKIND_THREAD_CREATED\n");
if (handle_stop_requested (ecs))
return;
if (!ptid_equal (ecs->ptid, inferior_ptid))
context_switch (ecs->ptid);
if (!switch_back_to_stepped_thread (ecs))
@ -5221,6 +5231,9 @@ Cannot fill $_exitsignal with the correct signal number.\n"));
= bpstat_stop_status (get_regcache_aspace (get_current_regcache ()),
stop_pc, ecs->ptid, &ecs->ws);
if (handle_stop_requested (ecs))
return;
/* If no catchpoint triggered for this, then keep going. Note
that we're interested in knowing the bpstat actually causes a
stop, not just if it may explain the signal. Software
@ -5295,6 +5308,10 @@ Cannot fill $_exitsignal with the correct signal number.\n"));
current_inferior ()->waiting_for_vfork_done = 0;
current_inferior ()->pspace->breakpoints_not_allowed = 0;
if (handle_stop_requested (ecs))
return;
/* This also takes care of reinserting breakpoints in the
previously locked inferior. */
keep_going (ecs);
@ -5331,6 +5348,9 @@ Cannot fill $_exitsignal with the correct signal number.\n"));
xfree (ecs->ws.value.execd_pathname);
ecs->ws.value.execd_pathname = NULL;
if (handle_stop_requested (ecs))
return;
/* If no catchpoint triggered for this, then keep going. */
if (!bpstat_causes_stop (ecs->event_thread->control.stop_bpstat))
{
@ -5368,7 +5388,6 @@ Cannot fill $_exitsignal with the correct signal number.\n"));
case TARGET_WAITKIND_STOPPED:
if (debug_infrun)
fprintf_unfiltered (gdb_stdlog, "infrun: TARGET_WAITKIND_STOPPED\n");
ecs->event_thread->suspend.stop_signal = ecs->ws.value.sig;
handle_signal_stop (ecs);
return;
@ -5385,6 +5404,10 @@ Cannot fill $_exitsignal with the correct signal number.\n"));
delete_just_stopped_threads_single_step_breakpoints ();
stop_pc = regcache_read_pc (get_thread_regcache (inferior_ptid));
if (handle_stop_requested (ecs))
return;
observer_notify_no_history ();
stop_waiting (ecs);
return;
@ -5474,6 +5497,8 @@ restart_threads (struct thread_info *event_thread)
continue;
}
gdb_assert (!tp->stop_requested);
/* If some thread needs to start a step-over at this point, it
should still be in the step-over queue, and thus skipped
above. */
@ -5543,8 +5568,7 @@ finish_step_over (struct execution_control_state *ecs)
back an event. */
gdb_assert (ecs->event_thread->control.trap_expected);
if (ecs->event_thread->suspend.stop_signal == GDB_SIGNAL_TRAP)
clear_step_over_info ();
clear_step_over_info ();
}
if (!target_is_non_stop_p ())
@ -5656,6 +5680,8 @@ handle_signal_stop (struct execution_control_state *ecs)
gdb_assert (ecs->ws.kind == TARGET_WAITKIND_STOPPED);
ecs->event_thread->suspend.stop_signal = ecs->ws.value.sig;
/* Do we need to clean up the state of a thread that has
completed a displaced single-step? (Doing so usually affects
the PC, so do it here, before we set stop_pc.) */
@ -6045,6 +6071,15 @@ handle_signal_stop (struct execution_control_state *ecs)
if (random_signal)
random_signal = !stopped_by_watchpoint;
/* Always stop if the user explicitly requested this thread to
remain stopped. */
if (ecs->event_thread->stop_requested)
{
random_signal = 1;
if (debug_infrun)
fprintf_unfiltered (gdb_stdlog, "infrun: user-requested stop\n");
}
/* For the program's own signals, act according to
the signal handling tables. */
@ -6091,8 +6126,6 @@ handle_signal_stop (struct execution_control_state *ecs)
&& ecs->event_thread->control.trap_expected
&& ecs->event_thread->control.step_resume_breakpoint == NULL)
{
int was_in_line;
/* We were just starting a new sequence, attempting to
single-step off of a breakpoint and expecting a SIGTRAP.
Instead this signal arrives. This signal will take us out
@ -6108,34 +6141,11 @@ handle_signal_stop (struct execution_control_state *ecs)
"infrun: signal arrived while stepping over "
"breakpoint\n");
was_in_line = step_over_info_valid_p ();
clear_step_over_info ();
insert_hp_step_resume_breakpoint_at_frame (frame);
ecs->event_thread->step_after_step_resume_breakpoint = 1;
/* Reset trap_expected to ensure breakpoints are re-inserted. */
ecs->event_thread->control.trap_expected = 0;
if (target_is_non_stop_p ())
{
/* Either "set non-stop" is "on", or the target is
always in non-stop mode. In this case, we have a bit
more work to do. Resume the current thread, and if
we had paused all threads, restart them while the
signal handler runs. */
keep_going (ecs);
if (was_in_line)
{
restart_threads (ecs->event_thread);
}
else if (debug_infrun)
{
fprintf_unfiltered (gdb_stdlog,
"infrun: no need to restart threads\n");
}
return;
}
/* If we were nexting/stepping some other thread, switch to
it, so that we don't continue it, losing control. */
if (!switch_back_to_stepped_thread (ecs))
@ -7676,8 +7686,6 @@ stop_waiting (struct execution_control_state *ecs)
if (debug_infrun)
fprintf_unfiltered (gdb_stdlog, "infrun: stop_waiting\n");
clear_step_over_info ();
/* Let callers know we don't want to wait for the inferior anymore. */
ecs->wait_some_more = 0;

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@ -1,3 +1,9 @@
2017-03-08 Pedro Alves <palves@redhat.com>
PR gdb/18360
* gdb.threads/interrupt-while-step-over.c: New file.
* gdb.threads/interrupt-while-step-over.exp: New file.
2017-03-08 Pedro Alves <palves@redhat.com>
* gdb.arch/amd64-entry-value-param-dwarf5.exp: Use with_test_prefix.

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@ -0,0 +1,75 @@
/* This testcase is part of GDB, the GNU debugger.
Copyright 2016-2017 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
#include <pthread.h>
#include <unistd.h>
#include <stdlib.h>
#define NUM_THREADS 20
const int num_threads = NUM_THREADS;
static pthread_t child_thread[NUM_THREADS];
static pthread_barrier_t threads_started_barrier;
volatile int always_zero;
volatile unsigned int dummy;
static void
infinite_loop (void)
{
while (1)
{
dummy++; /* set breakpoint here */
}
}
static void *
child_function (void *arg)
{
pthread_barrier_wait (&threads_started_barrier);
infinite_loop ();
}
void
all_started (void)
{
}
int
main (void)
{
int res;
int i;
alarm (300);
pthread_barrier_init (&threads_started_barrier, NULL, NUM_THREADS + 1);
for (i = 0; i < NUM_THREADS; i++)
{
res = pthread_create (&child_thread[i], NULL, child_function, NULL);
}
/* Wait until all threads have been scheduled. */
pthread_barrier_wait (&threads_started_barrier);
all_started ();
infinite_loop ();
}

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@ -0,0 +1,204 @@
# Copyright (C) 2016-2017 Free Software Foundation, Inc.
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
# Regression test for PR gdb/18360. Test that "interrupt -a" while
# some thread is stepping over a breakpoint behaves as expected.
standard_testfile
if {[prepare_for_testing "failed to prepare" $testfile $srcfile \
{debug pthreads}] == -1} {
return -1
}
if {![runto_main]} {
fail "can't run to main"
return -1
}
# Read the number of threads out of the inferior.
set NUM_THREADS [get_integer_valueof "num_threads" -1]
# Account for the main thread.
incr NUM_THREADS
# Run command and wait for the prompt, without end anchor.
proc gdb_test_no_anchor {cmd} {
global gdb_prompt
gdb_test_multiple $cmd $cmd {
-re "$gdb_prompt " {
pass $cmd
}
-re "infrun:" {
exp_continue
}
}
}
# Enable/disable debugging.
proc enable_debug {enable} {
# Comment out to debug problems with the test.
return
gdb_test_no_anchor "set debug infrun $enable"
gdb_test_no_anchor "set debug displaced $enable"
}
# If RESULT is not zero, make the caller return RESULT.
proc return_if_nonzero { result } {
if {$result != 0} {
return -code return $result
}
}
# Do one iteration of "c -a& -> interrupt -a". Return zero on sucess,
# and non-zero if some test fails.
proc test_one_iteration {} {
global gdb_prompt
global NUM_THREADS
global decimal
set saw_continuing 0
set test "continue -a &"
return_if_nonzero [gdb_test_multiple $test $test {
-re "Continuing.\r\n" {
set saw_continuing 1
exp_continue
}
-re "$gdb_prompt " {
if ![gdb_assert $saw_continuing $test] {
return 1
}
}
-re "infrun:" {
exp_continue
}
}]
set running_count 0
set test "all threads are running"
return_if_nonzero [gdb_test_multiple "info threads" $test {
-re "Thread \[^\r\n\]* \\(running\\)" {
incr running_count
exp_continue
}
-re "$gdb_prompt " {
if ![gdb_assert {$running_count == $NUM_THREADS} $test] {
return 1
}
}
-re "infrun:" {
exp_continue
}
}]
set test "interrupt -a"
return_if_nonzero [gdb_test_multiple $test $test {
-re "$gdb_prompt " {
pass $test
}
-re "infrun:" {
exp_continue
}
}]
set stopped_count 0
set test "wait for stops"
# Don't return on failure here, in order to let "info threads" put
# useful info in gdb.log.
gdb_test_multiple "" $test {
-re "Thread $decimal \[^\r\n\]*stopped" {
incr stopped_count
if {$stopped_count != $NUM_THREADS} {
exp_continue
}
}
-re "$gdb_prompt " {
gdb_assert {$stopped_count == $NUM_THREADS} $test
}
-re "infrun:" {
exp_continue
}
}
# Check if all threads are seen as stopped with "info
# threads". It's a bit redundant with the test above, but
# it's useful to have this in the gdb.log if the above ever
# happens to fail.
set running_count 0
set test "all threads are stopped"
return_if_nonzero [gdb_test_multiple "info threads" $test {
-re "Thread \[^\r\n\]* \\(running\\)" {
incr running_count
exp_continue
}
-re "$gdb_prompt " {
if ![gdb_assert {$running_count == 0} $test] {
return 1
}
}
}]
return 0
}
# The test driver proper. If DISPLACED is "on", turn on displaced
# stepping. If "off", turn it off.
proc testdriver {displaced} {
global binfile
global GDBFLAGS
save_vars { GDBFLAGS } {
append GDBFLAGS " -ex \"set non-stop on\""
clean_restart $binfile
}
gdb_test_no_output "set displaced-stepping $displaced"
if ![runto all_started] {
fail "couldn't run to all_started"
return
}
set break_line [gdb_get_line_number "set breakpoint here"]
gdb_test "break $break_line if always_zero" "Breakpoint .*" "set breakpoint"
enable_debug 1
for {set iter 0} {$iter < 20} {incr iter} {
with_test_prefix "iter=$iter" {
# Return early if some test fails, to avoid cascading
# timeouts if something goes wrong.
if {[test_one_iteration] != 0} {
return
}
}
}
}
foreach_with_prefix displaced-stepping {"on" "off"} {
if { ${displaced-stepping} != "off" && ![support_displaced_stepping] } {
continue
}
testdriver ${displaced-stepping}
}

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@ -100,7 +100,6 @@ gdb_test_sequence $test $test {
"need to step-over"
"resume \\(step=1"
"signal arrived while stepping over breakpoint"
"(restart threads|switching back to stepped thread)"
"stepped to a different line"
"callme"
}