binutils-gdb/gdb/testsuite/gdb.python/py-events.py
Magne Hov df5bc734f2 gdb: fix eval.c assert during inferior exit event
Evaluating expressions from within an inferior exit event handler can
cause a crash:

    echo "int main() { return 0; }" > repro.c
    gcc -g repro.c -o repro
    ./gdb -q --ex "set language c++" --ex "python gdb.events.exited.connect(lambda _: gdb.execute('set \$_a=0'))" --ex "run" repro

    Reading symbols from repro...
    Starting program: /home/mhov/repos/binutils-gdb-master/install-bad/bin/repro
    [Inferior 1 (process 1974779) exited normally]
    ../../gdb/thread.c:72: internal-error: thread_info* inferior_thread(): Assertion `current_thread_ != nullptr' failed.
    A problem internal to GDB has been detected,
    further debugging may prove unreliable.
    Quit this debugging session? (y or n) [answered Y; input not from terminal]

    This is a bug, please report it.  For instructions, see:
    <https://www.gnu.org/software/gdb/bugs/>.

Backtrace
    0  in internal_error of ../../gdbsupport/errors.cc:51
    1  in inferior_thread of ../../gdb/thread.c:72
    2  in expression::evaluate of ../../gdb/eval.c:98
    3  in evaluate_expression of ../../gdb/eval.c:115
    4  in set_command of ../../gdb/printcmd.c:1502
    5  in do_const_cfunc of ../../gdb/cli/cli-decode.c:101
    6  in cmd_func of ../../gdb/cli/cli-decode.c:2181
    7  in execute_command of ../../gdb/top.c:670
    ...
    22 in python_inferior_exit of ../../gdb/python/py-inferior.c:182

In `expression::evaluate (...)' there is a call to `inferior_thread
()' that is guarded by `target_has_execution ()':

    struct value *
    expression::evaluate (struct type *expect_type, enum noside noside)
    {
      gdb::optional<enable_thread_stack_temporaries> stack_temporaries;
      if (target_has_execution ()
          && language_defn->la_language == language_cplus
          && !thread_stack_temporaries_enabled_p (inferior_thread ()))
        stack_temporaries.emplace (inferior_thread ());

The `target_has_execution ()' guard maps onto `inf->pid' and the
`inferior_thread ()' call assumes that `current_thread_' is set to
something meaningful:

    struct thread_info*
    inferior_thread (void)
    {
      gdb_assert (current_thread_ != nullptr);
      return current_thread_;
    }

In other words, it is assumed that if `inf->pid' is set then
`current_thread_' must also be set. This does not hold at the point
where inferior exit observers are notified:
- `generic_mourn_inferior (...)'
  - `switch_to_no_thread ()'
    - `current_thread_ = nullptr;'
  - `exit_inferior (...)'
    - `gdb::observers::inferior_exit.notify (...)'
    - `inf->pid = 0'

The inferior exit notification means that a Python handler can get a
chance to run while `current_thread' has been cleared and the
`inf->pid' has not been cleared. Since the Python handler can call any
GDB command with `gdb.execute(...)' (in my case `gdb.execute("set
$_a=0")' we can end up evaluating expressions and asserting in
`evaluate_subexp (...)'.

This patch adds a test in `evaluate_subexp (...)' to check the global
`inferior_ptid' which is reset at the same time as `current_thread_'.
Checking `inferior_ptid' at the same time as `target_has_execution ()'
seems to be a common pattern:

    $ git grep -n -e inferior_ptid --and -e target_has_execution
    gdb/breakpoint.c:2998:    && (inferior_ptid == null_ptid || !target_has_execution ()))
    gdb/breakpoint.c:3054:    && (inferior_ptid == null_ptid || !target_has_execution ()))
    gdb/breakpoint.c:4587:  if (inferior_ptid == null_ptid || !target_has_execution ())
    gdb/infcmd.c:360:  if (inferior_ptid != null_ptid && target_has_execution ())
    gdb/infcmd.c:2380:  /* FIXME:  This should not really be inferior_ptid (or target_has_execution).
    gdb/infrun.c:3438:  if (!target_has_execution () || inferior_ptid == null_ptid)
    gdb/remote.c:11961:  if (!target_has_execution () || inferior_ptid == null_ptid)
    gdb/solib.c:725:  if (target_has_execution () && inferior_ptid != null_ptid)

The testsuite has been run on 5.4.0-59-generic x86_64 GNU/Linux:
- Ubuntu 20.04.1 LTS
- gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0
- DejaGnu version 1.6.2
  - Expect version 5.45.4
  - Tcl version 8.6
- Native configuration: x86_64-pc-linux-gnu
- Target: unix

Results show a few XFAIL in
gdb.threads/attach-many-short-lived-threads.exp. The existing
py-events.exp tests are skipped for native-gdbserver and fail for
native-extended-gdbserver, but the new tests pass with
native-extended-gdbserver when run without the existing tests.

gdb/ChangeLog:

2021-06-03  Magne Hov  <mhov@undo.io>

	PR python/27841
	* eval.c (expression::evaluate): Check inferior_ptid.

gdb/testsuite/ChangeLog:

2021-06-03  Magne Hov  <mhov@undo.io>

	PR python/27841
	* gdb.python/py-events.exp: Extend inferior exit tests.
	* gdb.python/py-events.py: Print inferior exit PID.
2021-06-03 21:22:08 +01:00

131 lines
4.3 KiB
Python

# Copyright (C) 2010-2021 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/>.
# This file is part of the GDB testsuite. It tests python pretty
# printers.
import gdb
def signal_stop_handler(event):
if isinstance(event, gdb.StopEvent):
print("event type: stop")
if isinstance(event, gdb.SignalEvent):
print("stop reason: signal")
print("stop signal: %s" % (event.stop_signal))
if event.inferior_thread is not None:
print("thread num: %s" % (event.inferior_thread.num))
def breakpoint_stop_handler(event):
if isinstance(event, gdb.StopEvent):
print("event type: stop")
if isinstance(event, gdb.BreakpointEvent):
print("stop reason: breakpoint")
print("first breakpoint number: %s" % (event.breakpoint.number))
for bp in event.breakpoints:
print("breakpoint number: %s" % (bp.number))
if event.inferior_thread is not None:
print("thread num: %s" % (event.inferior_thread.num))
else:
print("all threads stopped")
def exit_handler(event):
assert isinstance(event, gdb.ExitedEvent)
print("event type: exit")
print("exit code: %d" % (event.exit_code))
print("exit inf: %d" % (event.inferior.num))
print("exit pid: %d" % (event.inferior.pid))
print("dir ok: %s" % str("exit_code" in dir(event)))
def continue_handler(event):
assert isinstance(event, gdb.ContinueEvent)
print("event type: continue")
if event.inferior_thread is not None:
print("thread num: %s" % (event.inferior_thread.num))
def new_objfile_handler(event):
assert isinstance(event, gdb.NewObjFileEvent)
print("event type: new_objfile")
print("new objfile name: %s" % (event.new_objfile.filename))
def clear_objfiles_handler(event):
assert isinstance(event, gdb.ClearObjFilesEvent)
print("event type: clear_objfiles")
print("progspace: %s" % (event.progspace.filename))
def inferior_call_handler(event):
if isinstance(event, gdb.InferiorCallPreEvent):
print("event type: pre-call")
elif isinstance(event, gdb.InferiorCallPostEvent):
print("event type: post-call")
else:
assert False
print("ptid: %s" % (event.ptid,))
print("address: 0x%x" % (event.address))
def register_changed_handler(event):
assert isinstance(event, gdb.RegisterChangedEvent)
print("event type: register-changed")
assert isinstance(event.frame, gdb.Frame)
print("frame: %s" % (event.frame))
print("num: %s" % (event.regnum))
def memory_changed_handler(event):
assert isinstance(event, gdb.MemoryChangedEvent)
print("event type: memory-changed")
print("address: %s" % (event.address))
print("length: %s" % (event.length))
class test_events(gdb.Command):
"""Test events."""
def __init__(self):
gdb.Command.__init__(self, "test-events", gdb.COMMAND_STACK)
def invoke(self, arg, from_tty):
gdb.events.stop.connect(signal_stop_handler)
gdb.events.stop.connect(breakpoint_stop_handler)
gdb.events.exited.connect(exit_handler)
gdb.events.cont.connect(continue_handler)
gdb.events.inferior_call.connect(inferior_call_handler)
gdb.events.memory_changed.connect(memory_changed_handler)
gdb.events.register_changed.connect(register_changed_handler)
print("Event testers registered.")
test_events()
class test_newobj_events(gdb.Command):
"""NewObj events."""
def __init__(self):
gdb.Command.__init__(self, "test-objfile-events", gdb.COMMAND_STACK)
def invoke(self, arg, from_tty):
gdb.events.new_objfile.connect(new_objfile_handler)
gdb.events.clear_objfiles.connect(clear_objfiles_handler)
print("Object file events registered.")
test_newobj_events()