
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.
131 lines
4.3 KiB
Python
131 lines
4.3 KiB
Python
# Copyright (C) 2010-2021 Free Software Foundation, Inc.
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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# This file is part of the GDB testsuite. It tests python pretty
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# printers.
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import gdb
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def signal_stop_handler(event):
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if isinstance(event, gdb.StopEvent):
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print("event type: stop")
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if isinstance(event, gdb.SignalEvent):
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print("stop reason: signal")
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print("stop signal: %s" % (event.stop_signal))
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if event.inferior_thread is not None:
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print("thread num: %s" % (event.inferior_thread.num))
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def breakpoint_stop_handler(event):
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if isinstance(event, gdb.StopEvent):
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print("event type: stop")
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if isinstance(event, gdb.BreakpointEvent):
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print("stop reason: breakpoint")
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print("first breakpoint number: %s" % (event.breakpoint.number))
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for bp in event.breakpoints:
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print("breakpoint number: %s" % (bp.number))
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if event.inferior_thread is not None:
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print("thread num: %s" % (event.inferior_thread.num))
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else:
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print("all threads stopped")
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def exit_handler(event):
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assert isinstance(event, gdb.ExitedEvent)
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print("event type: exit")
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print("exit code: %d" % (event.exit_code))
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print("exit inf: %d" % (event.inferior.num))
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print("exit pid: %d" % (event.inferior.pid))
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print("dir ok: %s" % str("exit_code" in dir(event)))
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def continue_handler(event):
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assert isinstance(event, gdb.ContinueEvent)
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print("event type: continue")
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if event.inferior_thread is not None:
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print("thread num: %s" % (event.inferior_thread.num))
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def new_objfile_handler(event):
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assert isinstance(event, gdb.NewObjFileEvent)
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print("event type: new_objfile")
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print("new objfile name: %s" % (event.new_objfile.filename))
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def clear_objfiles_handler(event):
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assert isinstance(event, gdb.ClearObjFilesEvent)
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print("event type: clear_objfiles")
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print("progspace: %s" % (event.progspace.filename))
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def inferior_call_handler(event):
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if isinstance(event, gdb.InferiorCallPreEvent):
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print("event type: pre-call")
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elif isinstance(event, gdb.InferiorCallPostEvent):
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print("event type: post-call")
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else:
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assert False
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print("ptid: %s" % (event.ptid,))
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print("address: 0x%x" % (event.address))
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def register_changed_handler(event):
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assert isinstance(event, gdb.RegisterChangedEvent)
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print("event type: register-changed")
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assert isinstance(event.frame, gdb.Frame)
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print("frame: %s" % (event.frame))
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print("num: %s" % (event.regnum))
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def memory_changed_handler(event):
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assert isinstance(event, gdb.MemoryChangedEvent)
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print("event type: memory-changed")
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print("address: %s" % (event.address))
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print("length: %s" % (event.length))
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class test_events(gdb.Command):
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"""Test events."""
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def __init__(self):
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gdb.Command.__init__(self, "test-events", gdb.COMMAND_STACK)
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def invoke(self, arg, from_tty):
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gdb.events.stop.connect(signal_stop_handler)
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gdb.events.stop.connect(breakpoint_stop_handler)
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gdb.events.exited.connect(exit_handler)
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gdb.events.cont.connect(continue_handler)
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gdb.events.inferior_call.connect(inferior_call_handler)
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gdb.events.memory_changed.connect(memory_changed_handler)
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gdb.events.register_changed.connect(register_changed_handler)
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print("Event testers registered.")
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test_events()
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class test_newobj_events(gdb.Command):
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"""NewObj events."""
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def __init__(self):
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gdb.Command.__init__(self, "test-objfile-events", gdb.COMMAND_STACK)
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def invoke(self, arg, from_tty):
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gdb.events.new_objfile.connect(new_objfile_handler)
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gdb.events.clear_objfiles.connect(clear_objfiles_handler)
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print("Object file events registered.")
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test_newobj_events()
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