[v3] gdb, python: selectively omit enabling stdin in gdb.execute exception

Message ID 20230331081114.1319992-1-tankut.baris.aktemur@intel.com
State New
Headers
Series [v3] gdb, python: selectively omit enabling stdin in gdb.execute exception |

Commit Message

Aktemur, Tankut Baris March 31, 2023, 8:11 a.m. UTC
  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
  

Comments

Terekhov, Mikhail via Gdb-patches June 20, 2023, 1:04 p.m. UTC | #1
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

Intel Deutschland GmbH
Registered Address: Am Campeon 10, 85579 Neubiberg, Germany
Tel: +49 89 99 8853-0, www.intel.de <http://www.intel.de>
Managing Directors: Christin Eisenschmid, Sharon Heck, Tiffany Doon Silva  
Chairperson of the Supervisory Board: Nicole Lau
Registered Office: Munich
Commercial Register: Amtsgericht Muenchen HRB 186928
  

Patch

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()