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.
The patch still applies smoothly.

Regards,
-Baris

On Wednesday, April 23, 2025 9:59 AM, Aktemur, Tankut Baris wrote:
> 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: Dornacher Straße 1, 85622 Feldkirchen, Germany
Tel: +49 89 991 430, www.intel.de
Managing Directors: Harry Demas, Jeffrey Schneiderman, Yin Chong Sorrell
Chairperson of the Supervisory Board: Nicole Lau
Registered Seat: Munich
Commercial Register: Amtsgericht München HRB 186928