gdb/testsuite/gdb.threads/main-thread-exit-during-detach.exp

# Copyright 2023-2024 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/>.

# Check for a race condition where in non-stop mode, the user might
# have a thread other than the main (original) thread selected and use
# the 'detach' command.
#
# As GDB tries to detach it is possible that the main thread might
# exit, the main thread is still running due to non-stop mode.
#
# GDB used to assume that the main thread would always exist when
# processing the detach, clearly this isn't the case, and this
# assumption would lead to assertion failures and segfaults.
#
# Triggering the precise timing is pretty hard, we need the main
# thread to exit after the user has entered the 'detach' command, but
# before GDB enters the detach implementation and stops all threads,
# the window of opportunity for this bug is actually tiny.
#
# However, we can trigger this bug 100% from Python, as GDB's
# event-loop only kicks in once we return from a Python function.
# Thus, if we have a single Python function that causes the main
# thread to exit, and then calls detach GDB will not have a chance to
# handle the main thread exiting before entering the detach code.

standard_testfile

require allow_python_tests

if {[build_executable "failed to prepare" $testfile $srcfile \
	 {debug pthreads}] == -1} {
    return -1
}

# Run the test.  When SPAWN_INFERIOR is true the inferior is started
# as a separate process which GDB then attaches too.  When
# SPAWN_INFERIOR is false the inferior is started directly within GDB.

proc run_test { spawn_inferior } {
    save_vars { ::GDBFLAGS } {
	append ::GDBFLAGS " -ex \"set non-stop on\""
	clean_restart $::binfile
    }

    # Setup the inferior.  When complete the main thread (#1) will
    # still be running (due to non-stop mode), while the worker thread
    # (#2) will be stopped.
    #
    # There are two setup modes, when SPAWN_INFERIOR is true we span a
    # separate process and attach to it, after the attach both threads
    # are stopped, so it is necessary to resume thread #1.
    #
    # When SPAWN_INFERIOR is false we just start the inferior within
    # GDB, in this case we place a breakpoint that will be hit by
    # thread #2.  When the breakpoint is hit thread #1 will remain
    # running.
    if {$spawn_inferior} {
	set test_spawn_id [spawn_wait_for_attach $::binfile]
	set testpid [spawn_id_get_pid $test_spawn_id]

	set escapedbinfile  [string_to_regexp $::binfile]
	gdb_test -no-prompt-anchor "attach $testpid" \
	    "Attaching to program.*`?$escapedbinfile'?, process $testpid.*" \
	    "attach to the inferior"

	# Attaching to a multi-threaded application in non-stop mode
	# can result in thread stops being reported after the prompt
	# is displayed.
	#
	# Send a simple command now just to resync the command prompt.
	gdb_test "p 1 + 2" " = 3"

	# Set thread 1 (the current thread) running again.
	gdb_test "continue&"
    } else {
	if {![runto_main]} {
	    return -1
	}

	gdb_breakpoint "breakpt"
	gdb_continue_to_breakpoint "run to breakpoint"
    }

    # Switch to thread 2.
    gdb_test "thread 2" \
	[multi_line \
	     "Switching to thread 2\[^\r\n\]*" \
	     "#0\\s+.*"]

    # Create a Python function that sets a variable in the inferior and
    # then detaches.  Setting the variable in the inferior will allow the
    # main thread to exit, we even sleep for a short while in order to
    # give the inferior a chance to exit.
    #
    # However, we don't want GDB to notice the exit before we call detach,
    # which is why we perform both these actions from a Python function.
    gdb_test_multiline "Create worker function" \
	"python" "" \
	"import time" "" \
	"def set_and_detach():" "" \
	"   gdb.execute(\"set variable dont_exit_just_yet=0\")" "" \
	"   time.sleep(1)" "" \
	"   gdb.execute(\"detach\")" "" \
	"end" ""

    # The Python function performs two actions, the first causes the
    # main thread to exit, while the second detaches from the inferior.
    #
    # In both cases the stop arrives while GDB is processing the
    # detach, however, for remote targets GDB doesn't report the stop,
    # while for local targets GDB does report the stop.
    if {![gdb_is_target_remote]} {
	set stop_re "\\\[Thread.*exited\\\]\r\n"
    } else {
	set stop_re ""
    }
    gdb_test "python set_and_detach()" \
	"${stop_re}\\\[Inferior.*detached\\\]"
}

foreach_with_prefix spawn_inferior { true false } {
    if {$spawn_inferior && ![can_spawn_for_attach]} {
	# If spawning (and attaching too) a separate inferior is not
	# supported for the current board, then skip this test.
	continue
    }

    run_test $spawn_inferior
}