[PATCH v3] gdb, python: selectively omit enabling stdin in gdb.execute exception
Aktemur, Tankut Baris
tankut.baris.aktemur@intel.com
Tue Jun 20 13:04:04 GMT 2023
Kindly pinging.
Regards
-Baris
On Friday, March 31, 2023 10:11 AM, Aktemur, Tankut Baris wrote:
> From the Python API, we can execute GDB commands via gdb.execute. If
> the command gives an exception, however, we need to recover the GDB
> prompt and enable stdin, because the exception does not reach
> top-level GDB or normal_stop. This was done in commit
>
> commit 1ba1ac88011703abcd0271e4f5d00927dc69a09a
> Author: Andrew Burgess <andrew.burgess@embecosm.com>
> Date: Tue Nov 19 11:17:20 2019 +0000
>
> gdb: Enable stdin on exception in execute_gdb_command
>
> However, we face a glitch if the Python side executes the command in a
> context where GDB had already disabled stdin, because it was running a
> synchronous execution command such as "continue" or "run". As an
> example, suppose we have the following objfile event listener,
> specified in a file named file.py:
>
> ~~~
> import gdb
>
> class MyListener:
> def __init__(self):
> gdb.events.new_objfile.connect(self.handle_new_objfile_event)
> self.processed_objfile = False
>
> def handle_new_objfile_event(self, event):
> if self.processed_objfile:
> return
>
> print("loading " + event.new_objfile.filename)
> self.processed_objfile = True
> gdb.execute("print a")
>
> the_listener = MyListener()
> ~~~
>
> The executed command "print a", gives an error because "a" is not
> defined. We use the listener as follows:
>
> $ gdb -q -ex "source file.py" -ex "run" --args a.out
> Reading symbols from /tmp/a.out...
> Starting program: /tmp/a.out
> loading /lib64/ld-linux-x86-64.so.2
> Python Exception <class 'gdb.error'>: No symbol "a" in current context.
> (gdb) [Inferior 1 (process 3980401) exited normally]
>
> Note how the GDB prompt comes inbetween the exception message and the
> inferior's exit message. We have this obscure behavior, because GDB
> continues to execute its flow after emitting the Python event. In
> this case, GDB would enable stdin in the normal way. Hence, we do not
> need to explicitly enable stdin in execute_gdb_command when an
> exception occurs.
>
> As a solution, we track whether the prompt was already blocked. If so,
> we leave enabling stdin to GDB.
>
> With this patch, we see
>
> $ gdb -q -ex "source file.py" -ex "run" --args a.out
> Reading symbols from /tmp/a.out...
> Starting program: /tmp/a.out
> loading /lib64/ld-linux-x86-64.so.2
> Python Exception <class 'gdb.error'>: No symbol "a" in current context.
> [Inferior 1 (process 3984511) exited normally]
> (gdb)
>
> Regression-tested on X86_64 Linux using the default board file (i.e. unix).
>
> Co-Authored-By: Oguzhan Karakaya <oguzhan.karakaya@intel.com>
> Reviewed-By: Bruno Larsen <blarsen@redhat.com>
> ---
> gdb/python/python.c | 29 +++++++++++--
> gdb/testsuite/gdb.python/py-cmd-exception.c | 22 ++++++++++
> gdb/testsuite/gdb.python/py-cmd-exception.exp | 43 +++++++++++++++++++
> gdb/testsuite/gdb.python/py-cmd-exception.py | 33 ++++++++++++++
> 4 files changed, 123 insertions(+), 4 deletions(-)
> create mode 100644 gdb/testsuite/gdb.python/py-cmd-exception.c
> create mode 100644 gdb/testsuite/gdb.python/py-cmd-exception.exp
> create mode 100644 gdb/testsuite/gdb.python/py-cmd-exception.py
>
> diff --git a/gdb/python/python.c b/gdb/python/python.c
> index b295ff88743..5b34d142d1d 100644
> --- a/gdb/python/python.c
> +++ b/gdb/python/python.c
> @@ -653,6 +653,11 @@ execute_gdb_command (PyObject *self, PyObject *args, PyObject *kw)
>
> scoped_restore preventer = prevent_dont_repeat ();
>
> + /* If the executed command raises an exception, we may have to
> + enable stdin and recover the GDB prompt. Check the current
> + state. */
> + bool prompt_was_blocked = (current_ui->prompt_state == PROMPT_BLOCKED);
> +
> try
> {
> gdbpy_allow_threads allow_threads;
> @@ -698,10 +703,26 @@ execute_gdb_command (PyObject *self, PyObject *args, PyObject *kw)
> {
> /* If an exception occurred then we won't hit normal_stop (), or have
> an exception reach the top level of the event loop, which are the
> - two usual places in which stdin would be re-enabled. So, before we
> - convert the exception and continue back in Python, we should
> - re-enable stdin here. */
> - async_enable_stdin ();
> + two usual places in which stdin would be re-enabled. So, we check
> + here if stdin should be re-enabled, and do so if it is the case.
> + Stdin should not be re-enabled if it is already blocked because,
> + for example, we are running a command in the context of a
> + synchronous execution command ("run", "continue", etc.). Like
> + this:
> +
> + User runs "continue"
> + --> command blocks the prompt
> + --> Python API is invoked, e.g. via events
> + --> gdb.execute(C) invoked inside Python
> + --> command C raises an exception
> + --> this location
> +
> + In this case case, GDB would go back to the top "continue" command
> + and move on with its normal course of execution. That is, it
> + would enable stdin in the way it normally does. */
> + if (!prompt_was_blocked)
> + async_enable_stdin ();
> +
> GDB_PY_HANDLE_EXCEPTION (except);
> }
>
> diff --git a/gdb/testsuite/gdb.python/py-cmd-exception.c b/gdb/testsuite/gdb.python/py-cmd-
> exception.c
> new file mode 100644
> index 00000000000..f151960ce3a
> --- /dev/null
> +++ b/gdb/testsuite/gdb.python/py-cmd-exception.c
> @@ -0,0 +1,22 @@
> +/* This testcase is part of GDB, the GNU debugger.
> +
> + Copyright 2023 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/>. */
> +
> +int
> +main ()
> +{
> + return 0;
> +}
> diff --git a/gdb/testsuite/gdb.python/py-cmd-exception.exp b/gdb/testsuite/gdb.python/py-
> cmd-exception.exp
> new file mode 100644
> index 00000000000..3b81131ee08
> --- /dev/null
> +++ b/gdb/testsuite/gdb.python/py-cmd-exception.exp
> @@ -0,0 +1,43 @@
> +# Copyright (C) 2023 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 a corner case where
> +# the executed GDB command gives an exception and enabling the stdin would
> +# cause the GDB prompt to be displayed prematurely.
> +
> +load_lib gdb-python.exp
> +
> +require !use_gdb_stub allow_python_tests
> +
> +standard_testfile
> +
> +if { [prepare_for_testing "failed to prepare" ${testfile} ${srcfile}] } {
> + return -1
> +}
> +
> +set pyfile [gdb_remote_download host ${srcdir}/${subdir}/${testfile}.py]
> +gdb_test_no_output "source $pyfile" "source the script"
> +
> +gdb_start_cmd
> +
> +gdb_test_multiple "" "check the prompt" {
> + -re "breakpoint $decimal, main .*\r\n$gdb_prompt $" {
> + # The prompt is positioned correctly.
> + pass $gdb_test_name
> + }
> + -re "No symbol \"a\" in current context.\r\n$gdb_prompt " {
> + fail $gdb_test_name
> + }
> +}
> diff --git a/gdb/testsuite/gdb.python/py-cmd-exception.py b/gdb/testsuite/gdb.python/py-cmd-
> exception.py
> new file mode 100644
> index 00000000000..51199bd3fe3
> --- /dev/null
> +++ b/gdb/testsuite/gdb.python/py-cmd-exception.py
> @@ -0,0 +1,33 @@
> +# Copyright (C) 2023 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/>.
> +
> +import gdb
> +
> +class MyListener:
> + def __init__(self):
> + gdb.events.new_objfile.connect(self.handle_new_objfile_event)
> + self.processed_objfile = False
> +
> + def handle_new_objfile_event(self, event):
> + if self.processed_objfile:
> + return
> +
> + print('loading ' + event.new_objfile.filename)
> + self.processed_objfile = True
> +
> + # There is no variable 'a'. The command raises an exception.
> + gdb.execute('print a')
> +
> +the_listener = MyListener()
> --
> 2.25.1
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