RE: [PATCH v2] gdb/infrun: do not restart a stepped thread if not running (was: gdb/infrun: reset thread control's step info in end_stepping_range)

["Aktemur, Tankut Baris" <tankut.baris.aktemur@intel.com>]

Kindly pinging.

Thanks,
-Baris


On Tuesday, November 21, 2023 9:01 PM, Aktemur, Tankut Baris wrote:
> Kindly pinging.
> 
> (The patch was Tested-By: Guinevere Larsen <blarsen@redhat.com> )
> 
> Regards
> -Baris
> 
> On Tuesday, June 20, 2023 5:25 PM, Aktemur, Tankut Baris wrote:
> > ======
> > Changes in V2:
> >
> > * Changed the thread state check to `(tp->state != THREAD_RUNNING)`.
> > * Rebased on the current master.
> >
> > The latest discussion was
> > https://sourceware.org/pipermail/gdb-patches/2023-May/199613.html
> >
> > ======
> >
> > Suppose we have two inferiors on an all-stop target with schedule-multi
> > set on:
> >
> >   $ gdb -q
> >   (gdb) target extended-remote | gdbserver --multi -
> >   Remote debugging using | gdbserver --multi -
> >   Remote debugging using stdio
> >   (gdb) file /temp/test
> >   Reading symbols from /temp/test...
> >   (gdb) set remote exec-file /temp/test
> >   (gdb) start
> >   Temporary breakpoint 1 at 0x115c: file test.c, line 8.
> >   Starting program: /temp/test
> >   stdin/stdout redirected
> >   Process /temp/test created; pid = 864027
> >   ...
> >
> >   Temporary breakpoint 1, main (argc=1, argv=0x7fffffffd218) at test.c:8
> >   8         foo();
> >   (gdb) add-inferior
> >   [New inferior 2]
> >   Added inferior 2 on connection 1 (extended-remote | gdbserver --multi -)
> >   (gdb) inferior 2
> >   [Switching to inferior 2 [<null>] (<noexec>)]
> >   (gdb) file /temp/test
> >   Reading symbols from /temp/test...
> >   (gdb) set remote exec-file /temp/test
> >   (gdb) tbreak 2
> >   Temporary breakpoint 2 at 0x555555555131: /temp/test.c:2. (2 locations)
> >   (gdb) run
> >   Starting program: /temp/test
> >   stdin/stdout redirected
> >   Process /temp/test created; pid = 864430
> >   ...
> >
> >   Thread 2.1 "test" hit Temporary breakpoint 2, foo () at test.c:2
> >   2         int a = 42;
> >   (gdb) set schedule-multi on
> >   (gdb)
> >
> > At this point, detaching the first inferior works fine:
> >
> >   (gdb) detach inferiors 1
> >   Detaching from program: /temp/test, process 858904
> >   Detaching from process 858904
> >   [Inferior 1 (process 858904) detached]
> >   (gdb) info inferiors
> >     Num  Description       Connection                                Executable
> >     1    <null>            1 (extended-remote | gdbserver --multi -) /temp/test
> >   * 2    process 858925    1 (extended-remote | gdbserver --multi -) /temp/test
> >   (gdb)
> >
> > Let us now repeat exactly the same scenario, but before detaching, we
> > make the current thread single-step an instruction:
> >
> >   ...
> >   Thread 2.1 "test" hit Temporary breakpoint 2, foo () at test.c:2
> >   2         int a = 42;
> >   (gdb) stepi
> >   3         int b = 43;
> >   (gdb) detach inferiors 1
> >   Detaching from program: /temp/test, process 876580
> >   Detaching from process 876580
> >   gdbserver: Couldn't reap LWP 876580 while detaching: No child processes
> >   [Inferior 1 (process 876580) detached]
> >   (gdb) 3   int b = 43;
> >
> > There is a mysterious line info output.  Running the scenario with
> > infrun debug logs reveals more information.
> >
> >   ...
> >   Thread 2.1 "test" hit Temporary breakpoint 2, foo () at test.c:2
> >   2         int a = 42;
> >   (gdb) stepi
> >   3         int b = 43;
> >   (gdb) set debug infrun on
> >   (gdb) detach inferiors 1
> >   [infrun] scoped_disable_commit_resumed: reason=detaching
> >   Detaching from program: /temp/test, process 872445
> >   Detaching from process 872445
> >   gdbserver: Couldn't reap LWP 872445 while detaching: No child processes
> >   [Inferior 1 (process 872445) detached]
> >   [infrun] start_step_over: enter
> >     [infrun] start_step_over: stealing global queue of threads to step, length = 0
> >     [infrun] operator(): step-over queue now empty
> >   [infrun] start_step_over: exit
> >   [infrun] restart_stepped_thread: switching back to stepped thread (stepping)
> >   [infrun] keep_going_stepped_thread: resuming previously stepped thread
> >   [infrun] keep_going_stepped_thread: expected thread advanced also (0x555555555131 -
> > > 0x555555555138)
> >   [infrun] clear_step_over_info: clearing step over info
> >   [infrun] do_target_resume: resume_ptid=-1.0.0, step=0, sig=GDB_SIGNAL_0
> >   [infrun] infrun_async: enable=1
> >   [infrun] reset: reason=detaching
> >   [infrun] maybe_set_commit_resumed_all_targets: enabling commit-resumed for target
> > extended-remote
> >   [infrun] maybe_call_commit_resumed_all_targets: calling commit_resumed for target
> > extended-remote
> >   (gdb) [infrun] fetch_inferior_event: enter
> >     [infrun] scoped_disable_commit_resumed: reason=handling event
> >     [infrun] do_target_wait: Found 2 inferiors, starting at #0
> >     [infrun] random_pending_event_thread: None found.
> >     [infrun] print_target_wait_results: target_wait (-1.0.0 [process -1], status) =
> >     [infrun] print_target_wait_results:   872464.872464.0 [Thread 872464.872464],
> >     [infrun] print_target_wait_results:   status->kind = STOPPED, sig =
> > GDB_SIGNAL_TRAP
> >     [infrun] handle_inferior_event: status->kind = STOPPED, sig = GDB_SIGNAL_TRAP
> >     [infrun] context_switch: Switching context from 0.0.0 to 872464.872464.0
> >     [infrun] handle_signal_stop: stop_pc=0x555555555138
> >     [infrun] handle_signal_stop: [872464.872464.0] hit its single-step breakpoint
> >     [infrun] handle_signal_stop: delayed software breakpoint trap, ignoring
> >     [infrun] process_event_stop_test: stepi/nexti
> >     [infrun] stop_waiting: stop_waiting
> >   3         int b = 43;
> >     [infrun] infrun_async: enable=0
> >     [infrun] reset: reason=handling event
> >     [infrun] maybe_set_commit_resumed_all_targets: not requesting commit-resumed for
> > target extended-remote, no resumed threads
> >   [infrun] fetch_inferior_event: exit
> >
> > GDB attempted to do a step-over for the current thread.  This takes us
> > to the commit that introduced restarting step-overs:
> >
> >   commit 408f66864a1a823591b26420410c982174c239a2
> >   Author: Pedro Alves <pedro@palves.net>
> >   Date:   Mon Jan 11 20:01:58 2021 +0000
> >
> >     detach in all-stop with threads running
> >
> >     A following patch will add a testcase that has a number of threads
> >     constantly stepping over a breakpoint, and then has GDB detach the
> >     process, while threads are running.  If we have more than one inferior
> >     running, and we detach from just one of the inferiors, we expect that
> >     the remaining inferior continues running.  However, in all-stop, if
> >     GDB needs to pause the target for the detach, nothing is re-resuming
> >     the other inferiors after the detach.  "info threads" shows the
> >     threads as running, but they really aren't.  This fixes it.
> >
> > However, the thread that was resumed for step-over in our scenario did
> > not have an interrupted step-over; it had completed its stepi already.
> > More debugging reveals that the thread is resumed because of the
> > following two conditions in `restart_stepped_thread`:
> >
> >       if (tp->control.trap_expected)
> >         {
> >           infrun_debug_printf ("switching back to stepped thread (step-over)");
> >
> >           if (keep_going_stepped_thread (tp))
> >             return true;
> >         }
> >
> > and
> >
> >       if (tp->control.step_range_end)
> >         {
> >           infrun_debug_printf ("switching back to stepped thread (stepping)");
> >
> >           if (keep_going_stepped_thread (tp))
> >             return true;
> >         }
> >
> > The root cause of the problem is, `restart_stepped_thread` checks for
> > the thread state as
> >
> >     if (tp->state == THREAD_EXITED)
> >       continue;
> >
> > but the thread's state is THREAD_STOPPED.  To fix, we change the state
> > check to
> >
> >     if (tp->state != THREAD_RUNNING)
> >
> > Additionally, the 'trap_expected' and the 'step_range_end' fields of
> > the thread's control remain set even after the "stepi" command
> > completes, creating a half-baked internal state that can be misleading
> > when debugging.  We address this problem by clearing the control
> > fields when stepping completes.  We also add a regression test.
> >
> > Regression-tested on X86_64 Linux using the default, native-gdbserver,
> > and native-extended-gdbserver board files.
> > ---
> >  gdb/infrun.c                             |  7 ++-
> >  gdb/testsuite/gdb.multi/detach-stepi.c   | 30 +++++++++++
> >  gdb/testsuite/gdb.multi/detach-stepi.exp | 66 ++++++++++++++++++++++++
> >  3 files changed, 101 insertions(+), 2 deletions(-)
> >  create mode 100644 gdb/testsuite/gdb.multi/detach-stepi.c
> >  create mode 100644 gdb/testsuite/gdb.multi/detach-stepi.exp
> >
> > diff --git a/gdb/infrun.c b/gdb/infrun.c
> > index 58da1cef29e..f40d924dc7a 100644
> > --- a/gdb/infrun.c
> > +++ b/gdb/infrun.c
> > @@ -7776,7 +7776,7 @@ restart_stepped_thread (process_stratum_target *resume_target,
> >
> >    for (thread_info *tp : all_threads_safe ())
> >      {
> > -      if (tp->state == THREAD_EXITED)
> > +      if (tp->state != THREAD_RUNNING)
> >  	continue;
> >
> >        if (tp->has_pending_waitstatus ())
> > @@ -7800,7 +7800,7 @@ restart_stepped_thread (process_stratum_target *resume_target,
> >
> >    for (thread_info *tp : all_threads_safe ())
> >      {
> > -      if (tp->state == THREAD_EXITED)
> > +      if (tp->state != THREAD_RUNNING)
> >  	continue;
> >
> >        if (tp->has_pending_waitstatus ())
> > @@ -8523,6 +8523,9 @@ static void
> >  end_stepping_range (struct execution_control_state *ecs)
> >  {
> >    ecs->event_thread->control.stop_step = 1;
> > +  ecs->event_thread->control.trap_expected = 0;
> > +  ecs->event_thread->control.step_range_start = 0;
> > +  ecs->event_thread->control.step_range_end = 0;
> >    stop_waiting (ecs);
> >  }
> >
> > diff --git a/gdb/testsuite/gdb.multi/detach-stepi.c b/gdb/testsuite/gdb.multi/detach-
> > stepi.c
> > new file mode 100644
> > index 00000000000..d365645fb3f
> > --- /dev/null
> > +++ b/gdb/testsuite/gdb.multi/detach-stepi.c
> > @@ -0,0 +1,30 @@
> > +/* This testcase is part of GDB, the GNU debugger.
> > +
> > +   Copyright 2022 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/>.  */
> > +
> > +void
> > +a_function ()
> > +{
> > +  int a = 42;
> > +}
> > +
> > +int
> > +main ()
> > +{
> > +  int b = 43;
> > +  a_function ();
> > +  return 0;
> > +}
> > diff --git a/gdb/testsuite/gdb.multi/detach-stepi.exp
> > b/gdb/testsuite/gdb.multi/detach-stepi.exp
> > new file mode 100644
> > index 00000000000..28ef8c4f9f7
> > --- /dev/null
> > +++ b/gdb/testsuite/gdb.multi/detach-stepi.exp
> > @@ -0,0 +1,66 @@
> > +# This testcase is part of GDB, the GNU debugger.
> > +
> > +# Copyright 2022 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/>.
> > +
> > +# Test detaching from an inferior after a thread in another inferior
> > +# completes a stepi.  This is a regression test for a bug that was
> > +# causing an inadvertent resume of the just-stepped thread.
> > +
> > +standard_testfile
> > +
> > +if {[use_gdb_stub]} {
> > +    untested "using gdb stub"
> > +    return 0
> > +}
> > +
> > +if {[prepare_for_testing "failed to prepare" $testfile $srcfile]} {
> > +    return -1
> > +}
> > +
> > +if {![runto_main]} {
> > +    return -1
> > +}
> > +
> > +delete_breakpoints
> > +
> > +# Setup inferior 2.
> > +gdb_test "add-inferior" "Added inferior .*" \
> > +    "add empty inferior"
> > +gdb_test "inferior 2" "Switching to inferior .*" \
> > +    "switch to inferior"
> > +
> > +gdb_load $binfile
> > +runto "a_function"
> > +gdb_test "info inferiors"
> > +
> > +# The bug for which this regression test is written appears in
> > +# schedule-multi mode.
> > +gdb_test_no_output "set schedule-multiple on"
> > +
> > +# Single-step the thread in Inferior 2, then detach Inferior 1.
> > +gdb_test "info threads" ".*" "threads before stepi"
> > +gdb_test "stepi"
> > +gdb_test "info threads" ".*" "threads after stepi"
> > +
> > +gdb_test "set debug infrun on"
> > +gdb_test_multiple "detach inferior 1" "" {
> > +    -re "resuming previously stepped thread.*$gdb_prompt" {
> > +	fail $gdb_test_name
> > +    }
> > +    -re "$gdb_prompt $" {
> > +	pass $gdb_test_name
> > +    }
> > +}
> > --
> > 2.25.1

Intel Deutschland GmbH
Registered Address: Am Campeon 10, 85579 Neubiberg, Germany
Tel: +49 89 99 8853-0, www.intel.de
Managing Directors: Sean Fennelly, Jeffrey Schneiderman, Tiffany Doon Silva
Chairperson of the Supervisory Board: Nicole Lau
Registered Office: Munich
Commercial Register: Amtsgericht Muenchen HRB 186928