gdb/python/mi: create MI commands using python

This commit allows a user to create custom MI commands using Python
similarly to what is possible for Python CLI commands.

A new subclass of mi_command is defined for Python MI commands,
mi_command_py. A new file, gdb/python/py-micmd.c contains the logic
for Python MI commands.

This commit is based on work linked too from this mailing list thread:

  https://sourceware.org/pipermail/gdb/2021-November/049774.html

Which has also been previously posted to the mailing list here:

  https://sourceware.org/pipermail/gdb-patches/2019-May/158010.html

And was recently reposted here:

  https://sourceware.org/pipermail/gdb-patches/2022-January/185190.html

The version in this patch takes some core code from the previously
posted patches, but also has some significant differences, especially
after the feedback given here:

  https://sourceware.org/pipermail/gdb-patches/2022-February/185767.html

A new MI command can be implemented in Python like this:

  class echo_args(gdb.MICommand):
      def invoke(self, args):
          return { 'args': args }

  echo_args("-echo-args")

The 'args' parameter (to the invoke method) is a list
containing (almost) all command line arguments passed to the MI
command (--thread and --frame are handled before the Python code is
called, and removed from the args list).  This list can be empty if
the MI command was passed no arguments.

When used within gdb the above command produced output like this:

  (gdb)
  -echo-args a b c
  ^done,args=["a","b","c"]
  (gdb)

The 'invoke' method of the new command must return a dictionary.  The
keys of this dictionary are then used as the field names in the mi
command output (e.g. 'args' in the above).

The values of the result returned by invoke can be dictionaries,
lists, iterators, or an object that can be converted to a string.
These are processed recursively to create the mi output.  And so, this
is valid:

  class new_command(gdb.MICommand):
      def invoke(self,args):
          return { 'result_one': { 'abc': 123, 'def': 'Hello' },
                   'result_two': [ { 'a': 1, 'b': 2 },
                                   { 'c': 3, 'd': 4 } ] }

Which produces output like:

  (gdb)
  -new-command
  ^done,result_one={abc="123",def="Hello"},result_two=[{a="1",b="2"},{c="3",d="4"}]
  (gdb)

I have required that the fields names used in mi result output must
match the regexp: "^[a-zA-Z][-_a-zA-Z0-9]*$" (without the quotes).
This restriction was never written down anywhere before, but seems
sensible to me, and we can always loosen this rule later if it proves
to be a problem.  Much harder to try and add a restriction later, once
people are already using the API.

What follows are some details about how this implementation differs
from the original patch that was posted to the mailing list.

In this patch, I have changed how the lifetime of the Python
gdb.MICommand objects is managed.  In the original patch, these object
were kept alive by an owned reference within the mi_command_py object.
As such, the Python object would not be deleted until the
mi_command_py object itself was deleted.

This caused a problem, the mi_command_py were held in the global mi
command table (in mi/mi-cmds.c), which, as a global, was not cleared
until program shutdown.  By this point the Python interpreter has
already been shutdown.  Attempting to delete the mi_command_py object
at this point was causing GDB to try and invoke Python code after
finalising the Python interpreter, and we would crash.

To work around this problem, the original patch added code in
python/python.c that would search the mi command table, and delete the
mi_command_py objects before the Python environment was finalised.

In contrast, in this patch, I have added a new global dictionary to
the gdb module, gdb._mi_commands.  We already have several such global
data stores related to pretty printers, and frame unwinders.

The MICommand objects are placed into the new gdb.mi_commands
dictionary, and it is this reference that keeps the objects alive.
When GDB's Python interpreter is shut down gdb._mi_commands is deleted,
and any MICommand objects within it are deleted at this point.

This change avoids having to make the mi_cmd_table global, and walk
over it from within GDB's python related code.

This patch handles command redefinition entirely within GDB's python
code, though this does impose one small restriction which is not
present in the original code (detailed below), I don't think this is a
big issue.  However, the original patch relied on being able to
finish executing the mi_command::do_invoke member function after the
mi_command object had been deleted.  Though continuing to execute a
member function after an object is deleted is well defined, it is
also (IMHO) risky, its too easy for someone to later add a use of the
object without realising that the object might sometimes, have been
deleted.  The new patch avoids this issue.

The one restriction that is added to avoid this, is that an MICommand
object can't be reinitialised with a different command name, so:

  (gdb) python cmd = MyMICommand("-abc")
  (gdb) python cmd.__init__("-def")
  can't reinitialize object with a different command name

This feels like a pretty weird edge case, and I'm happy to live with
this restriction.

I have also changed how the memory is managed for the command name.
In the most recently posted patch series, the command name is moved
into a subclass of mi_command, the python mi_command_py, which
inherits from mi_command is then free to use a smart pointer to manage
the memory for the name.

In this patch, I leave the mi_command class unchanged, and instead
hold the memory for the name within the Python object, as the lifetime
of the Python object always exceeds the c++ object stored in the
mi_cmd_table.  This adds a little more complexity in py-micmd.c, but
leaves the mi_command class nice and simple.

Next, this patch adds some extra functionality, there's a
MICommand.name read-only attribute containing the name of the command,
and a read-write MICommand.installed attribute that can be used to
install (make the command available for use) and uninstall (remove the
command from the mi_cmd_table so it can't be used) the command.  This
attribute will be automatically updated if a second command replaces
an earlier command.

This patch adds additional error handling, and makes more use the
gdbpy_handle_exception function.

Co-Authored-By: Jan Vrany <jan.vrany@labware.com>

12 files changed, 1553 insertions, 18 deletions

diff --git a/gdb/Makefile.in b/gdb/Makefile.in
index db0125b..9bca9b0 100644
--- a/gdb/Makefile.in
+++ b/gdb/Makefile.in
@@ -409,6 +409,7 @@ SUBDIR_PYTHON_SRCS = \
 	python/py-lazy-string.c \
 	python/py-linetable.c \
 	python/py-membuf.c \
+	python/py-micmd.c \
 	python/py-newobjfileevent.c \
 	python/py-objfile.c \
 	python/py-param.c \
diff --git a/gdb/NEWS b/gdb/NEWS
index c9b6f42..bfa6b63 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -250,6 +250,8 @@ GNU/Linux/LoongArch    loongarch*-*-linux*
      for signed types, and False for all other types.  Attempting to
      read this attribute for non-scalar types will raise a ValueError.
 
+  ** It is now possible to add GDB/MI commands implemented in Python.
+
 * New features in the GDB remote stub, GDBserver
 
   ** GDBserver is now supported on OpenRISC GNU/Linux.
diff --git a/gdb/doc/python.texi b/gdb/doc/python.texi
index b6acda4..918418b 100644
--- a/gdb/doc/python.texi
+++ b/gdb/doc/python.texi
@@ -95,6 +95,7 @@ containing @code{end}.  For example:
 23
 @end smallexample
 
+@anchor{set_python_print_stack}
 @kindex set python print-stack
 @item set python print-stack
 By default, @value{GDBN} will print only the message component of a
@@ -204,7 +205,8 @@ optional arguments while skipping others.  Example:
 * Events In Python::            Listening for events from @value{GDBN}.
 * Threads In Python::           Accessing inferior threads from Python.
 * Recordings In Python::        Accessing recordings from Python.
-* Commands In Python::          Implementing new commands in Python.
+* CLI Commands In Python::      Implementing new CLI commands in Python.
+* GDB/MI Commands In Python::   Implementing new @sc{GDB/MI} commands in Python.
 * Parameters In Python::        Adding new @value{GDBN} parameters.
 * Functions In Python::         Writing new convenience functions.
 * Progspaces In Python::        Program spaces.
@@ -419,7 +421,8 @@ the current language, evaluate it, and return the result as a
 @code{gdb.Value}.
 
 This function can be useful when implementing a new command
-(@pxref{Commands In Python}), as it provides a way to parse the
+(@pxref{CLI Commands In Python}, @pxref{GDB/MI Commands In Python}),
+as it provides a way to parse the
 command's argument as an expression.  It is also useful simply to
 compute values.
 @end defun
@@ -2162,7 +2165,7 @@ must contain the frames that are being elided wrapped in a suitable
 frame decorator.  If no frames are being elided this function may
 return an empty iterable, or @code{None}.  Elided frames are indented
 from normal frames in a @code{CLI} backtrace, or in the case of
-@code{GDB/MI}, are placed in the @code{children} field of the eliding
+@sc{GDB/MI}, are placed in the @code{children} field of the eliding
 frame.
 
 It is the frame filter's task to also filter out the elided frames from
@@ -3883,11 +3886,12 @@ def countrange (filename, linerange):
     return count
 @end smallexample
 
-@node Commands In Python
-@subsubsection Commands In Python
+@node CLI Commands In Python
+@subsubsection CLI Commands In Python
 
-@cindex commands in python
-@cindex python commands
+@cindex CLI commands in python
+@cindex commands in python, CLI
+@cindex python commands, CLI
 You can implement new @value{GDBN} CLI commands in Python.  A CLI
 command is implemented using an instance of the @code{gdb.Command}
 class, most commonly using a subclass.
@@ -4166,6 +4170,154 @@ registration of the command with @value{GDBN}.  Depending on how the
 Python code is read into @value{GDBN}, you may need to import the
 @code{gdb} module explicitly.
 
+@node GDB/MI Commands In Python
+@subsubsection @sc{GDB/MI} Commands In Python
+
+@cindex MI commands in python
+@cindex commands in python, GDB/MI
+@cindex python commands, GDB/MI
+It is possible to add @sc{GDB/MI} (@pxref{GDB/MI}) commands
+implemented in Python.  A @sc{GDB/MI} command is implemented using an
+instance of the @code{gdb.MICommand} class, most commonly using a
+subclass.
+
+@defun MICommand.__init__ (name)
+The object initializer for @code{MICommand} registers the new command
+with @value{GDBN}.  This initializer is normally invoked from the
+subclass' own @code{__init__} method.
+
+@var{name} is the name of the command.  It must be a valid name of a
+@sc{GDB/MI} command, and in particular must start with a hyphen
+(@code{-}).  Reusing the name of a built-in @sc{GDB/MI} is not
+allowed, and a @code{RuntimeError} will be raised.  Using the name
+of an @sc{GDB/MI} command previously defined in Python is allowed, the
+previous command will be replaced with the new command.
+@end defun
+
+@defun MICommand.invoke (arguments)
+This method is called by @value{GDBN} when the new MI command is
+invoked.
+
+@var{arguments} is a list of strings.  Note, that @code{--thread}
+and @code{--frame} arguments are handled by @value{GDBN} itself therefore
+they do not show up in @code{arguments}.
+
+If this method raises an exception, then it is turned into a
+@sc{GDB/MI} @code{^error} response.  Only @code{gdb.GdbError}
+exceptions (or its sub-classes) should be used for reporting errors to
+users, any other exception type is treated as a failure of the
+@code{invoke} method, and the exception will be printed to the error
+stream according to the @kbd{set python print-stack} setting
+(@pxref{set_python_print_stack,,@kbd{set python print-stack}}).
+
+If this method returns @code{None}, then the @sc{GDB/MI} command will
+return a @code{^done} response with no additional values.
+
+Otherwise, the return value must be a dictionary, which is converted
+to a @sc{GDB/MI} @var{result-record} (@pxref{GDB/MI Output Syntax}).
+The keys of this dictionary must be strings, and are used as
+@var{variable} names in the @var{result-record}, these strings must
+comply with the naming rules detailed below.  The values of this
+dictionary are recursively handled as follows:
+
+@itemize
+@item
+If the value is Python sequence or iterator, it is converted to
+@sc{GDB/MI} @var{list} with elements converted recursively.
+
+@item
+If the value is Python dictionary, it is converted to
+@sc{GDB/MI} @var{tuple}.  Keys in that dictionary must be strings,
+which comply with the @var{variable} naming rules detailed below.
+Values are converted recursively.
+
+@item
+Otherwise, value is first converted to a Python string using
+@code{str ()} and then converted to @sc{GDB/MI} @var{const}.
+@end itemize
+
+The strings used for @var{variable} names in the @sc{GDB/MI} output
+must follow the following rules; the string must be at least one
+character long, the first character must be in the set
+@code{[a-zA-Z]}, while every subsequent character must be in the set
+@code{[-_a-zA-Z0-9]}.
+@end defun
+
+An instance of @code{MICommand} has the following attributes:
+
+@defvar MICommand.name
+A string, the name of this @sc{GDB/MI} command, as was passed to the
+@code{__init__} method.  This attribute is read-only.
+@end defvar
+
+@defvar MICommand.installed
+A boolean value indicating if this command is installed ready for a
+user to call from the command line.  Commands are automatically
+installed when they are instantiated, after which this attribute will
+be @code{True}.
+
+If later, a new command is created with the same name, then the
+original command will become uninstalled, and this attribute will be
+@code{False}.
+
+This attribute is read-write, setting this attribute to @code{False}
+will uninstall the command, removing it from the set of available
+commands.  Setting this attribute to @code{True} will install the
+command for use.  If there is already a Python command with this name
+installed, the currently installed command will be uninstalled, and
+this command installed in its place.
+@end defvar
+
+The following code snippet shows how a two trivial MI command can be
+implemented in Python:
+
+@smallexample
+class MIEcho(gdb.MICommand):
+    """Echo arguments passed to the command."""
+
+    def __init__(self, name, mode):
+        self._mode = mode
+        super(MIEcho, self).__init__(name)
+
+    def invoke(self, argv):
+        if self._mode == 'dict':
+            return @{ 'dict': @{ 'argv' : argv @} @}
+        elif self._mode == 'list':
+            return @{ 'list': argv @}
+        else:
+            return @{ 'string': ", ".join(argv) @}
+
+
+MIEcho("-echo-dict", "dict")
+MIEcho("-echo-list", "list")
+MIEcho("-echo-string", "string")
+@end smallexample
+
+The last three lines instantiate the class three times, creating three
+new @sc{GDB/MI} commands @code{-echo-dict}, @code{-echo-list}, and
+@code{-echo-string}.  Each time a subclass of @code{gdb.MICommand} is
+instantiated, the new command is automatically registered with
+@value{GDBN}.
+
+Depending on how the Python code is read into @value{GDBN}, you may
+need to import the @code{gdb} module explicitly.
+
+The following example shows a @value{GDBN} session in which the above
+commands have been added:
+
+@smallexample
+(@value{GDBP})
+-echo-dict abc def ghi
+^done,dict=@{argv=["abc","def","ghi"]@}
+(@value{GDBP})
+-echo-list abc def ghi
+^done,list=["abc","def","ghi"]
+(@value{GDBP})
+-echo-string abc def ghi
+^done,string="abc, def, ghi"
+(@value{GDBP})
+@end smallexample
+
 @node Parameters In Python
 @subsubsection Parameters In Python
 
@@ -4203,7 +4355,7 @@ If @var{name} consists of multiple words, and no prefix parameter group
 can be found, an exception is raised.
 
 @var{command-class} should be one of the @samp{COMMAND_} constants
-(@pxref{Commands In Python}).  This argument tells @value{GDBN} how to
+(@pxref{CLI Commands In Python}).  This argument tells @value{GDBN} how to
 categorize the new parameter in the help system.
 
 @var{parameter-class} should be one of the @samp{PARAM_} constants
diff --git a/gdb/mi/mi-cmds.c b/gdb/mi/mi-cmds.c
index cd7cabd..38fbe0d 100644
--- a/gdb/mi/mi-cmds.c
+++ b/gdb/mi/mi-cmds.c
@@ -26,10 +26,6 @@
 #include <map>
 #include <string>
 
-/* A command held in the MI_CMD_TABLE.  */
-
-using mi_command_up = std::unique_ptr<struct mi_command>;
-
 /* MI command table (built at run time). */
 
 static std::map<std::string, mi_command_up> mi_cmd_table;
@@ -108,12 +104,9 @@ private:
   bool m_args_p;
 };
 
-/* Insert COMMAND into the global mi_cmd_table.  Return false if
-   COMMAND->name already exists in mi_cmd_table, in which case COMMAND will
-   not have been added to mi_cmd_table.  Otherwise, return true, and
-   COMMAND was added to mi_cmd_table.  */
+/* See mi-cmds.h.  */
 
-static bool
+bool
 insert_mi_cmd_entry (mi_command_up command)
 {
   gdb_assert (command != nullptr);
@@ -127,6 +120,18 @@ insert_mi_cmd_entry (mi_command_up command)
   return true;
 }
 
+/* See mi-cmds.h.  */
+
+bool
+remove_mi_cmd_entry (const std::string &name)
+{
+  if (mi_cmd_table.find (name) == mi_cmd_table.end ())
+    return false;
+
+  mi_cmd_table.erase (name);
+  return true;
+}
+
 /* Create and register a new MI command with an MI specific implementation.
    NAME must name an MI command that does not already exist, otherwise an
    assertion will trigger.  */
diff --git a/gdb/mi/mi-cmds.h b/gdb/mi/mi-cmds.h
index 785652e..47b90a2 100644
--- a/gdb/mi/mi-cmds.h
+++ b/gdb/mi/mi-cmds.h
@@ -199,6 +199,10 @@ private:
   int *m_suppress_notification;
 };
 
+/* A command held in the global mi_cmd_table.  */
+
+using mi_command_up = std::unique_ptr<struct mi_command>;
+
 /* Lookup a command in the MI command table, returns nullptr if COMMAND is
    not found.  */
 
@@ -206,4 +210,18 @@ extern mi_command *mi_cmd_lookup (const char *command);
 
 extern void mi_execute_command (const char *cmd, int from_tty);
 
+/* Insert COMMAND into the global mi_cmd_table.  Return false if
+   COMMAND->name already exists in mi_cmd_table, in which case COMMAND will
+   not have been added to mi_cmd_table.  Otherwise, return true, and
+   COMMAND was added to mi_cmd_table.  */
+
+extern bool insert_mi_cmd_entry (mi_command_up command);
+
+/* Remove the command called NAME from the global mi_cmd_table.  Return
+   true if the removal was a success, otherwise return false, which
+   indicates no command called NAME was found in the mi_cmd_table. */
+
+extern bool remove_mi_cmd_entry (const std::string &name);
+
+
 #endif /* MI_MI_CMDS_H */
diff --git a/gdb/python/lib/gdb/__init__.py b/gdb/python/lib/gdb/__init__.py
index 5f63bce..3294583 100644
--- a/gdb/python/lib/gdb/__init__.py
+++ b/gdb/python/lib/gdb/__init__.py
@@ -82,6 +82,10 @@ frame_filters = {}
 # Initial frame unwinders.
 frame_unwinders = []
 
+# Dictionary containing all user created MI commands, the key is the
+# command name, and the value is the gdb.MICommand object.
+_mi_commands = {}
+
 
 def _execute_unwinders(pending_frame):
     """Internal function called from GDB to execute all unwinders.
diff --git a/gdb/python/py-micmd.c b/gdb/python/py-micmd.c
new file mode 100644
index 0000000..4665fcc
--- /dev/null
+++ b/gdb/python/py-micmd.c
@@ -0,0 +1,812 @@
+/* MI Command Set for GDB, the GNU debugger.
+
+   Copyright (C) 2019-2022 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   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/>.  */
+
+/* GDB/MI commands implemented in Python.  */
+
+#include "defs.h"
+#include "python-internal.h"
+#include "arch-utils.h"
+#include "charset.h"
+#include "language.h"
+#include "mi/mi-cmds.h"
+#include "mi/mi-parse.h"
+#include "cli/cli-cmds.h"
+#include <string>
+
+/* Debugging of Python MI commands.  */
+
+static bool pymicmd_debug;
+
+/* Implementation of "show debug py-micmd".  */
+
+static void
+show_pymicmd_debug (struct ui_file *file, int from_tty,
+		    struct cmd_list_element *c, const char *value)
+{
+  fprintf_filtered (file, _("Python MI command debugging is %s.\n"), value);
+}
+
+/* Print a "py-micmd" debug statement.  */
+
+#define pymicmd_debug_printf(fmt, ...) \
+  debug_prefixed_printf_cond (pymicmd_debug, "py-micmd", fmt, ##__VA_ARGS__)
+
+/* Print a "py-micmd" enter/exit debug statements.  */
+
+#define PYMICMD_SCOPED_DEBUG_ENTER_EXIT \
+  scoped_debug_enter_exit (pymicmd_debug, "py-micmd")
+
+struct mi_command_py;
+
+/* Representation of a Python gdb.MICommand object.  */
+
+struct micmdpy_object
+{
+  PyObject_HEAD
+
+  /* The object representing this command in the MI command table.  This
+     pointer can be nullptr if the command is not currently installed into
+     the MI command table (see gdb.MICommand.installed property).  */
+  struct mi_command_py *mi_command;
+
+  /* The string representing the name of this command, without the leading
+     dash.  This string is never nullptr once the Python object has been
+     initialised.
+
+     The memory for this string was allocated with malloc, and needs to be
+     deallocated with free when the Python object is deallocated.
+
+     When the MI_COMMAND field is not nullptr, then the mi_command_py
+     object's name will point back to this string.  */
+  char *mi_command_name;
+};
+
+/* The MI command implemented in Python.  */
+
+struct mi_command_py : public mi_command
+{
+  /* Constructs a new mi_command_py object.  NAME is command name without
+     leading dash.  OBJECT is a reference to a Python object implementing
+     the command.  This object must inherit from gdb.MICommand and must
+     implement the invoke method.  */
+
+  mi_command_py (const char *name, micmdpy_object *object)
+    : mi_command (name, nullptr),
+      m_pyobj (object)
+  {
+    pymicmd_debug_printf ("this = %p", this);
+  }
+
+  ~mi_command_py ()
+  {
+    /* The Python object representing a MI command contains a pointer back
+       to this c++ object.  We can safely set this pointer back to nullptr
+       now, to indicate the Python object no longer references a valid c++
+       object.
+
+       However, the Python object also holds the storage for our name
+       string.  We can't clear that here as our parent's destructor might
+       still want to reference that string.  Instead we rely on the Python
+       object deallocator to free that memory, and reset the pointer.  */
+    m_pyobj->mi_command = nullptr;
+
+    pymicmd_debug_printf ("this = %p", this);
+  };
+
+  /* Validate that CMD_OBJ, a non-nullptr pointer, is installed into the MI
+     command table correctly.  This function looks up the command in the MI
+     command table and checks that the object we get back references
+     CMD_OBJ.  This function is only intended for calling within a
+     gdb_assert.  This function performs many assertions internally, and
+     then always returns true.  */
+  static void validate_installation (micmdpy_object *cmd_obj);
+
+  /* Update m_pyobj to NEW_PYOBJ.  The pointer from M_PYOBJ that points
+     back to this object is swapped with the pointer in NEW_PYOBJ, which
+     must be nullptr, so that NEW_PYOBJ now points back to this object.
+     Additionally our parent's name string is stored in m_pyobj, so we
+     swap the name string with NEW_PYOBJ.
+
+     Before this call m_pyobj is the Python object representing this MI
+     command object.  After this call has completed, NEW_PYOBJ now
+     represents this MI command object.  */
+  void swap_python_object (micmdpy_object *new_pyobj)
+  {
+    gdb_assert (new_pyobj->mi_command == nullptr);
+    std::swap (new_pyobj->mi_command, m_pyobj->mi_command);
+    std::swap (new_pyobj->mi_command_name, m_pyobj->mi_command_name);
+    m_pyobj = new_pyobj;
+  }
+
+protected:
+  /* Called when the MI command is invoked.  */
+  virtual void do_invoke(struct mi_parse *parse) const override;
+
+private:
+  /* The Python object representing this MI command.  */
+  micmdpy_object *m_pyobj;
+};
+
+extern PyTypeObject micmdpy_object_type
+	CPYCHECKER_TYPE_OBJECT_FOR_TYPEDEF ("micmdpy_object");
+
+/* Holds a Python object containing the string 'invoke'.  */
+
+static PyObject *invoke_cst;
+
+/* Convert KEY_OBJ into a string that can be used as a field name in MI
+   output.  KEY_OBJ must be a Python string object, and must only contain
+   characters suitable for use as an MI field name.
+
+   If KEY_OBJ is not a string, or if KEY_OBJ contains invalid characters,
+   then an error is thrown.  Otherwise, KEY_OBJ is converted to a string
+   and returned.  */
+
+static gdb::unique_xmalloc_ptr<char>
+py_object_to_mi_key (PyObject *key_obj)
+{
+  /* The key must be a string.  */
+  if (!PyString_Check (key_obj))
+    {
+      gdbpy_ref<> key_repr (PyObject_Repr (key_obj));
+      gdb::unique_xmalloc_ptr<char> key_repr_string;
+      if (key_repr != nullptr)
+	key_repr_string = python_string_to_target_string (key_repr.get ());
+      if (key_repr_string == nullptr)
+	gdbpy_handle_exception ();
+
+      gdbpy_error (_("non-string object used as key: %s"),
+		   key_repr_string.get ());
+    }
+
+  gdb::unique_xmalloc_ptr<char> key_string
+    = python_string_to_target_string (key_obj);
+  if (key_string == nullptr)
+    gdbpy_handle_exception ();
+
+  /* Predicate function, returns true if NAME is a valid field name for use
+     in MI result output, otherwise, returns false.  */
+  auto is_valid_key_name = [] (const char *name) -> bool
+  {
+    gdb_assert (name != nullptr);
+
+    if (*name == '\0' || !isalpha (*name))
+      return false;
+
+    for (; *name != '\0'; ++name)
+      if (!isalnum (*name) && *name != '_' && *name != '-')
+	return false;
+
+    return true;
+  };
+
+  if (!is_valid_key_name (key_string.get ()))
+    {
+      if (*key_string.get () == '\0')
+	gdbpy_error (_("Invalid empty key in MI result"));
+      else
+	gdbpy_error (_("Invalid key in MI result: %s"), key_string.get ());
+    }
+
+  return key_string;
+}
+
+/* Serialize RESULT and print it in MI format to the current_uiout.
+   FIELD_NAME is used as the name of this result field.
+
+   RESULT can be a dictionary, a sequence, an iterator, or an object that
+   can be converted to a string, these are converted to the matching MI
+   output format (dictionaries as tuples, sequences and iterators as lists,
+   and strings as named fields).
+
+   If anything goes wrong while formatting the output then an error is
+   thrown.
+
+   This function is the recursive inner core of serialize_mi_result, and
+   should only be called from that function.  */
+
+static void
+serialize_mi_result_1 (PyObject *result, const char *field_name)
+{
+  struct ui_out *uiout = current_uiout;
+
+  if (PyDict_Check (result))
+    {
+      PyObject *key, *value;
+      Py_ssize_t pos = 0;
+      ui_out_emit_tuple tuple_emitter (uiout, field_name);
+      while (PyDict_Next (result, &pos, &key, &value))
+	{
+	  gdb::unique_xmalloc_ptr<char> key_string
+	    (py_object_to_mi_key (key));
+	  serialize_mi_result_1 (value, key_string.get ());
+	}
+    }
+  else if (PySequence_Check (result) && !PyString_Check (result))
+    {
+      ui_out_emit_list list_emitter (uiout, field_name);
+      Py_ssize_t len = PySequence_Size (result);
+      if (len == -1)
+	gdbpy_handle_exception ();
+      for (Py_ssize_t i = 0; i < len; ++i)
+	{
+          gdbpy_ref<> item (PySequence_ITEM (result, i));
+	  if (item == nullptr)
+	    gdbpy_handle_exception ();
+	  serialize_mi_result_1 (item.get (), nullptr);
+	}
+    }
+  else if (PyIter_Check (result))
+    {
+      gdbpy_ref<> item;
+      ui_out_emit_list list_emitter (uiout, field_name);
+      while (true)
+	{
+	  item.reset (PyIter_Next (result));
+	  if (item == nullptr)
+	    {
+	      if (PyErr_Occurred () != nullptr)
+		gdbpy_handle_exception ();
+	      break;
+	    }
+	  serialize_mi_result_1 (item.get (), nullptr);
+	}
+    }
+  else
+    {
+      gdb::unique_xmalloc_ptr<char> string (gdbpy_obj_to_string (result));
+      if (string == nullptr)
+	gdbpy_handle_exception ();
+      uiout->field_string (field_name, string.get ());
+    }
+}
+
+/* Serialize RESULT and print it in MI format to the current_uiout.
+
+   This function handles the top-level result initially returned from the
+   invoke method of the Python command implementation.  At the top-level
+   the result must be a dictionary.  The values within this dictionary can
+   be a wider range of types.  Handling the values of the top-level
+   dictionary is done by serialize_mi_result_1, see that function for more
+   details.
+
+   If anything goes wrong while parsing and printing the MI output then an
+   error is thrown.  */
+
+static void
+serialize_mi_result (PyObject *result)
+{
+  /* At the top-level, the result must be a dictionary.  */
+
+  if (!PyDict_Check (result))
+    gdbpy_error (_("Result from invoke must be a dictionary"));
+
+  PyObject *key, *value;
+  Py_ssize_t pos = 0;
+  while (PyDict_Next (result, &pos, &key, &value))
+    {
+      gdb::unique_xmalloc_ptr<char> key_string
+	(py_object_to_mi_key (key));
+      serialize_mi_result_1 (value, key_string.get ());
+    }
+}
+
+/* Called when the MI command is invoked.  PARSE contains the parsed
+   command line arguments from the user.  */
+
+void
+mi_command_py::do_invoke (struct mi_parse *parse) const
+{
+  PYMICMD_SCOPED_DEBUG_ENTER_EXIT;
+
+  pymicmd_debug_printf ("this = %p, name = %s", this, name ());
+
+  mi_parse_argv (parse->args, parse);
+
+  if (parse->argv == nullptr)
+    error (_("Problem parsing arguments: %s %s"), parse->command, parse->args);
+
+  PyObject *obj = (PyObject *) this->m_pyobj;
+  gdb_assert (obj != nullptr);
+
+  gdbpy_enter enter_py;
+
+  /* Place all the arguments into a list which we pass as a single argument
+     to the MI command's invoke method.  */
+  gdbpy_ref<> argobj (PyList_New (parse->argc));
+  if (argobj == nullptr)
+    gdbpy_handle_exception ();
+
+  for (int i = 0; i < parse->argc; ++i)
+    {
+      gdbpy_ref<> str (PyUnicode_Decode (parse->argv[i],
+					 strlen (parse->argv[i]),
+					 host_charset (), nullptr));
+      if (PyList_SetItem (argobj.get (), i, str.release ()) < 0)
+	gdbpy_handle_exception ();
+    }
+
+  gdb_assert (PyErr_Occurred () == nullptr);
+  gdbpy_ref<> result (PyObject_CallMethodObjArgs (obj, invoke_cst,
+						  argobj.get (), nullptr));
+  if (result == nullptr)
+    gdbpy_handle_exception ();
+
+  if (result != Py_None)
+    serialize_mi_result (result.get ());
+}
+
+/* See declaration above.  */
+
+void
+mi_command_py::validate_installation (micmdpy_object *cmd_obj)
+{
+  gdb_assert (cmd_obj != nullptr);
+  mi_command_py *cmd = cmd_obj->mi_command;
+  gdb_assert (cmd != nullptr);
+  const char *name = cmd_obj->mi_command_name;
+  gdb_assert (name != nullptr);
+  gdb_assert (name == cmd->name ());
+  mi_command *mi_cmd = mi_cmd_lookup (name);
+  gdb_assert (mi_cmd == cmd);
+  gdb_assert (cmd->m_pyobj == cmd_obj);
+}
+
+/* Return a reference to the gdb._mi_commands dictionary.  If the
+   dictionary can't be found for any reason then nullptr is returned, and
+   a Python exception will be set.  */
+
+static gdbpy_ref<>
+micmdpy_global_command_dictionary ()
+{
+  if (gdb_python_module == nullptr)
+    {
+      PyErr_SetString (PyExc_RuntimeError, _("unable to find gdb module"));
+      return nullptr;
+    }
+
+  gdbpy_ref<> mi_cmd_dict (PyObject_GetAttrString (gdb_python_module,
+						   "_mi_commands"));
+  if (mi_cmd_dict == nullptr)
+    return nullptr;
+
+  if (!PyDict_Check (mi_cmd_dict.get ()))
+    {
+      PyErr_SetString (PyExc_RuntimeError,
+		       _("gdb._mi_commands is not a dictionary as expected"));
+      return nullptr;
+    }
+
+  return mi_cmd_dict;
+}
+
+/* Uninstall OBJ, making the MI command represented by OBJ unavailable for
+   use by the user.  On success 0 is returned, otherwise -1 is returned
+   and a Python exception will be set.  */
+
+static int
+micmdpy_uninstall_command (micmdpy_object *obj)
+{
+  PYMICMD_SCOPED_DEBUG_ENTER_EXIT;
+
+  gdb_assert (obj->mi_command != nullptr);
+  gdb_assert (obj->mi_command_name != nullptr);
+
+  pymicmd_debug_printf ("name = %s", obj->mi_command_name);
+
+  /* Remove the command from the internal MI table of commands, this will
+     cause the c++ object to be deleted, which will clear the mi_command
+     member variable within the Python object.  */
+  remove_mi_cmd_entry (obj->mi_command->name ());
+  gdb_assert (obj->mi_command == nullptr);
+
+  gdbpy_ref<> mi_cmd_dict = micmdpy_global_command_dictionary ();
+  if (mi_cmd_dict == nullptr)
+    return -1;
+
+  /* Grab the name for this command.  */
+  gdbpy_ref<> name_obj
+    = host_string_to_python_string (obj->mi_command_name);
+  if (name_obj == nullptr)
+    return -1;
+
+  /* Lookup the gdb.MICommand object in the dictionary of all Python MI
+     commands, this is gdb._mi_command, and remove it.  */
+  PyObject *curr = PyDict_GetItemWithError (mi_cmd_dict.get (),
+					    name_obj.get ());
+
+  /* Did we encounter an error?  Failing to find the object in the
+     dictionary isn't an error, that's fine.  */
+  if (curr == nullptr && PyErr_Occurred ())
+    return -1;
+
+  /* Did we find this command in the gdb._mi_commands dictionary?  If so,
+     then remove it.  */
+  if (curr != nullptr)
+    {
+      /* Yes we did!  Remove it.  */
+      if (PyDict_DelItem (mi_cmd_dict.get (), name_obj.get ()) < 0)
+	return -1;
+    }
+
+  return 0;
+}
+
+/* Install OBJ as a usable MI command.  Return 0 on success, and -1 on
+   error, in which case, a Python error will have been set.
+
+   After successful completion the command name associated with OBJ will
+   be installed in the MI command table (so it can be found if the user
+   enters that command name), additionally, OBJ will have been added to
+   the gdb._mi_commands dictionary (using the command name as its key),
+   this will ensure that OBJ remains live even if the user gives up all
+   references.  */
+
+static int
+micmdpy_install_command (micmdpy_object *obj)
+{
+  PYMICMD_SCOPED_DEBUG_ENTER_EXIT;
+
+  gdb_assert (obj->mi_command == nullptr);
+  gdb_assert (obj->mi_command_name != nullptr);
+
+  pymicmd_debug_printf ("name = %s", obj->mi_command_name);
+
+  gdbpy_ref<> mi_cmd_dict = micmdpy_global_command_dictionary ();
+  if (mi_cmd_dict == nullptr)
+    return -1;
+
+  /* Look up this command name in the gdb._mi_commands dictionary, a
+     command with this name may already exist.  */
+  gdbpy_ref<> name_obj
+    = host_string_to_python_string (obj->mi_command_name);
+
+  PyObject *curr = PyDict_GetItemWithError (mi_cmd_dict.get (),
+					    name_obj.get ());
+  if (curr == nullptr && PyErr_Occurred ())
+    return -1;
+  if (curr != nullptr)
+    {
+      /* There is a command with this name already in the gdb._mi_commands
+	 dictionary.  First, validate that the object in the dictionary is
+	 of the expected type, just in case something weird has happened.  */
+      if (!PyObject_IsInstance (curr, (PyObject *) &micmdpy_object_type))
+	{
+	  PyErr_SetString (PyExc_RuntimeError,
+			   _("unexpected object in gdb._mi_commands dictionary"));
+	  return -1;
+	}
+
+      /* To get to this function OBJ should not be installed, which should
+	 mean OBJ is not in the gdb._mi_commands dictionary.  If we find
+	 that OBJ is the thing in the dictionary, then something weird is
+	 going on, we should throw an error.  */
+      micmdpy_object *other = (micmdpy_object *) curr;
+      if (other == obj || other->mi_command == nullptr)
+	{
+	  PyErr_SetString (PyExc_RuntimeError,
+			   _("uninstalled command found in gdb._mi_commands dictionary"));
+	  return -1;
+	}
+
+      /* All Python mi command object should always have a name set.  */
+      gdb_assert (other->mi_command_name != nullptr);
+
+      /* We always insert commands into the gdb._mi_commands dictionary
+	 using their name as a key, if this check fails then the dictionary
+	 is in some weird state.  */
+      if (other->mi_command_name != other->mi_command->name ()
+	  || strcmp (other->mi_command_name, obj->mi_command_name) != 0)
+	{
+	  PyErr_SetString (PyExc_RuntimeError,
+			   _("gdb._mi_commands dictionary is corrupted"));
+	  return -1;
+	}
+
+      /* Switch the state of the c++ object held in the MI command table
+	 so that it now references OBJ.  After this action the old Python
+	 object that used to be referenced from the MI command table will
+	 now show as uninstalled, while the new Python object will show as
+	 installed.  */
+      other->mi_command->swap_python_object (obj);
+
+      gdb_assert (other->mi_command == nullptr);
+      gdb_assert (obj->mi_command != nullptr);
+      gdb_assert (obj->mi_command->name () == obj->mi_command_name);
+
+      /* Remove the previous Python object from the gdb._mi_commands
+	 dictionary, we'll install the new object below.  */
+      if (PyDict_DelItem (mi_cmd_dict.get (), name_obj.get ()) < 0)
+       return -1;
+    }
+  else
+    {
+      /* There's no Python object for this command name in the
+	 gdb._mi_commands dictionary from which we can steal an existing
+	 object already held in the MI commands table, and so, we now
+	 create a new c++ object, and install it into the MI table.  */
+      obj->mi_command = new mi_command_py (obj->mi_command_name, obj);
+      mi_command_up micommand (obj->mi_command);
+
+      /* Add the command to the gdb internal MI command table.  */
+      bool result = insert_mi_cmd_entry (std::move (micommand));
+      if (!result)
+	{
+	  PyErr_SetString (PyExc_RuntimeError,
+			   _("unable to add command, name may already be in use"));
+	  return -1;
+	}
+    }
+
+  /* Finally, add the Python object to the gdb._mi_commands dictionary.  */
+  if (PyDict_SetItem (mi_cmd_dict.get (), name_obj.get (), (PyObject *) obj) < 0)
+    return -1;
+
+  return 0;
+}
+
+/* Implement gdb.MICommand.__init__.  The init method takes the name of
+   the MI command as the first argument, which must be a string, starting
+   with a single dash.  */
+
+static int
+micmdpy_init (PyObject *self, PyObject *args, PyObject *kwargs)
+{
+  PYMICMD_SCOPED_DEBUG_ENTER_EXIT;
+
+  micmdpy_object *cmd = (micmdpy_object *) self;
+
+  static const char *keywords[] = { "name", nullptr };
+  const char *name;
+
+  if (!gdb_PyArg_ParseTupleAndKeywords (args, kwargs, "s", keywords,
+					&name))
+    return -1;
+
+  /* Validate command name */
+  const int name_len = strlen (name);
+  if (name_len == 0)
+    {
+      PyErr_SetString (PyExc_ValueError, _("MI command name is empty."));
+      return -1;
+    }
+  else if ((name_len < 2) || (name[0] != '-') || !isalnum (name[1]))
+    {
+      PyErr_SetString (PyExc_ValueError,
+		       _("MI command name does not start with '-'"
+			 " followed by at least one letter or digit."));
+      return -1;
+    }
+  else
+    {
+      for (int i = 2; i < name_len; i++)
+	{
+	  if (!isalnum (name[i]) && name[i] != '-')
+	    {
+	      PyErr_Format
+		(PyExc_ValueError,
+		 _("MI command name contains invalid character: %c."),
+		 name[i]);
+	      return -1;
+	    }
+	}
+
+      /* Skip over the leading dash.  For the rest of this function the
+	 dash is not important.  */
+      ++name;
+    }
+
+  /* If this object already has a name set, then this object has been
+     initialized before.  We handle this case a little differently.  */
+  if (cmd->mi_command_name != nullptr)
+    {
+      /* First, we don't allow the user to change the MI command name.
+	 Supporting this would be tricky as we would need to delete the
+	 mi_command_py from the MI command table, however, the user might
+	 be trying to perform this reinitialization from within the very
+	 command we're about to delete... it all gets very messy.
+
+	 So, for now at least, we don't allow this.  This doesn't seem like
+	 an excessive restriction.  */
+      if (strcmp (cmd->mi_command_name, name) != 0)
+	{
+	  PyErr_SetString
+	    (PyExc_ValueError,
+	     _("can't reinitialize object with a different command name"));
+	  return -1;
+	}
+
+      /* If there's already an object registered with the MI command table,
+	 then we're done.  That object must be a mi_command_py, which
+	 should reference back to this micmdpy_object.  */
+      if (cmd->mi_command != nullptr)
+	{
+	  mi_command_py::validate_installation (cmd);
+	  return 0;
+	}
+    }
+  else
+    cmd->mi_command_name = xstrdup (name);
+
+  /* Now we can install this mi_command_py in the MI command table.  */
+  return micmdpy_install_command (cmd);
+}
+
+/* Called when a gdb.MICommand object is deallocated.  */
+
+static void
+micmdpy_dealloc (PyObject *obj)
+{
+  PYMICMD_SCOPED_DEBUG_ENTER_EXIT;
+
+  micmdpy_object *cmd = (micmdpy_object *) obj;
+
+  /* If the Python object failed to initialize, then the name field might
+     be nullptr.  */
+  pymicmd_debug_printf ("obj = %p, name = %s", cmd,
+			(cmd->mi_command_name == nullptr
+			 ? "(null)" : cmd->mi_command_name));
+
+  /* Remove the command from the MI command table if needed.  This will
+     cause the mi_command_py object to be deleted, which, in turn, will
+     clear the cmd->mi_command member variable, hence the assert.  */
+  if (cmd->mi_command != nullptr)
+    remove_mi_cmd_entry (cmd->mi_command->name ());
+  gdb_assert (cmd->mi_command == nullptr);
+
+  /* Free the memory that holds the command name.  */
+  xfree (cmd->mi_command_name);
+  cmd->mi_command_name = nullptr;
+
+  /* Finally, free the memory for this Python object.  */
+  Py_TYPE (obj)->tp_free (obj);
+}
+
+/* Python initialization for the MI commands components.  */
+
+int
+gdbpy_initialize_micommands ()
+{
+  micmdpy_object_type.tp_new = PyType_GenericNew;
+  if (PyType_Ready (&micmdpy_object_type) < 0)
+    return -1;
+
+  if (gdb_pymodule_addobject (gdb_module, "MICommand",
+			      (PyObject *) &micmdpy_object_type)
+      < 0)
+    return -1;
+
+  invoke_cst = PyString_FromString ("invoke");
+  if (invoke_cst == nullptr)
+    return -1;
+
+  return 0;
+}
+
+/* Get the gdb.MICommand.name attribute, returns a string, the name of this
+   MI command.  */
+
+static PyObject *
+micmdpy_get_name (PyObject *self, void *closure)
+{
+  struct micmdpy_object *micmd_obj = (struct micmdpy_object *) self;
+
+  gdb_assert (micmd_obj->mi_command_name != nullptr);
+  std::string name_str = string_printf ("-%s", micmd_obj->mi_command_name);
+  return PyString_FromString (name_str.c_str ());
+}
+
+/* Get the gdb.MICommand.installed property.  Returns true if this MI
+   command is installed into the MI command table, otherwise returns
+   false.  */
+
+static PyObject *
+micmdpy_get_installed (PyObject *self, void *closure)
+{
+  struct micmdpy_object *micmd_obj = (struct micmdpy_object *) self;
+
+  if (micmd_obj->mi_command == nullptr)
+    Py_RETURN_FALSE;
+  Py_RETURN_TRUE;
+}
+
+/* Set the gdb.MICommand.installed property.  The property can be set to
+   either true or false.  Setting the property to true will cause the
+   command to be installed into the MI command table (if it isn't
+   already), while setting this property to false will cause the command
+   to be removed from the MI command table (if it is present).  */
+
+static int
+micmdpy_set_installed (PyObject *self, PyObject *newvalue, void *closure)
+{
+  struct micmdpy_object *micmd_obj = (struct micmdpy_object *) self;
+
+  bool installed_p = PyObject_IsTrue (newvalue);
+  if (installed_p == (micmd_obj->mi_command != nullptr))
+    return 0;
+
+  if (installed_p)
+    return micmdpy_install_command (micmd_obj);
+  else
+    return micmdpy_uninstall_command (micmd_obj);
+}
+
+/* The gdb.MICommand properties.   */
+
+static gdb_PyGetSetDef micmdpy_object_getset[] = {
+  { "name", micmdpy_get_name, nullptr, "The command's name.", nullptr },
+  { "installed", micmdpy_get_installed, micmdpy_set_installed,
+    "Is this command installed for use.", nullptr },
+  { nullptr }	/* Sentinel.  */
+};
+
+/* The gdb.MICommand descriptor.  */
+
+PyTypeObject micmdpy_object_type = {
+  PyVarObject_HEAD_INIT (nullptr, 0) "gdb.MICommand", /*tp_name */
+  sizeof (micmdpy_object),			   /*tp_basicsize */
+  0,						   /*tp_itemsize */
+  micmdpy_dealloc,				   /*tp_dealloc */
+  0,						   /*tp_print */
+  0,						   /*tp_getattr */
+  0,						   /*tp_setattr */
+  0,						   /*tp_compare */
+  0,						   /*tp_repr */
+  0,						   /*tp_as_number */
+  0,						   /*tp_as_sequence */
+  0,						   /*tp_as_mapping */
+  0,						   /*tp_hash */
+  0,						   /*tp_call */
+  0,						   /*tp_str */
+  0,						   /*tp_getattro */
+  0,						   /*tp_setattro */
+  0,						   /*tp_as_buffer */
+  Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,	/*tp_flags */
+  "GDB mi-command object",			   /* tp_doc */
+  0,						   /* tp_traverse */
+  0,						   /* tp_clear */
+  0,						   /* tp_richcompare */
+  0,						   /* tp_weaklistoffset */
+  0,						   /* tp_iter */
+  0,						   /* tp_iternext */
+  0,						   /* tp_methods */
+  0,						   /* tp_members */
+  micmdpy_object_getset,			   /* tp_getset */
+  0,						   /* tp_base */
+  0,						   /* tp_dict */
+  0,						   /* tp_descr_get */
+  0,						   /* tp_descr_set */
+  0,						   /* tp_dictoffset */
+  micmdpy_init,					   /* tp_init */
+  0,						   /* tp_alloc */
+};
+
+void _initialize_py_micmd ();
+void
+_initialize_py_micmd ()
+{
+  add_setshow_boolean_cmd
+    ("py-micmd", class_maintenance, &pymicmd_debug,
+     _("Set Python micmd debugging."),
+     _("Show Python micmd debugging."),
+     _("When on, Python micmd debugging is enabled."),
+     nullptr,
+     show_pymicmd_debug,
+     &setdebuglist, &showdebuglist);
+}
diff --git a/gdb/python/py-utils.c b/gdb/python/py-utils.c
index 73c860b..838853c 100644
--- a/gdb/python/py-utils.c
+++ b/gdb/python/py-utils.c
@@ -382,6 +382,23 @@ gdb_pymodule_addobject (PyObject *module, const char *name, PyObject *object)
   return result;
 }
 
+/* See python-internal.h.  */
+
+void
+gdbpy_error (const char *fmt, ...)
+{
+  va_list ap;
+  va_start (ap, fmt);
+  std::string str = string_vprintf (fmt, ap);
+  va_end (ap);
+
+  const char *msg = str.c_str ();
+  if (msg != nullptr && *msg != '\0')
+    error (_("Error occurred in Python: %s"), msg);
+  else
+    error (_("Error occurred in Python."));
+}
+
 /* Handle a Python exception when the special gdb.GdbError treatment
    is desired.  This should only be called when an exception is set.
    If the exception is a gdb.GdbError, throw a gdb exception with the
diff --git a/gdb/python/python-internal.h b/gdb/python/python-internal.h
index 5e15f62..083c4db 100644
--- a/gdb/python/python-internal.h
+++ b/gdb/python/python-internal.h
@@ -562,6 +562,8 @@ int gdbpy_initialize_membuf ()
   CPYCHECKER_NEGATIVE_RESULT_SETS_EXCEPTION;
 int gdbpy_initialize_connection ()
   CPYCHECKER_NEGATIVE_RESULT_SETS_EXCEPTION;
+int gdbpy_initialize_micommands (void)
+  CPYCHECKER_NEGATIVE_RESULT_SETS_EXCEPTION;
 
 /* A wrapper for PyErr_Fetch that handles reference counting for the
    caller.  */
@@ -730,6 +732,17 @@ void gdbpy_print_stack (void);
 void gdbpy_print_stack_or_quit ();
 void gdbpy_handle_exception () ATTRIBUTE_NORETURN;
 
+/* A wrapper around calling 'error'.  Prefixes the error message with an
+   'Error occurred in Python' string.  Use this in C++ code if we spot
+   something wrong with an object returned from Python code.  The prefix
+   string gives the user a hint that the mistake is within Python code,
+   rather than some other part of GDB.
+
+   This always calls error, and never returns.  */
+
+void gdbpy_error (const char *fmt, ...)
+  ATTRIBUTE_NORETURN ATTRIBUTE_PRINTF (1, 2);
+
 gdbpy_ref<> python_string_to_unicode (PyObject *obj);
 gdb::unique_xmalloc_ptr<char> unicode_to_target_string (PyObject *unicode_str);
 gdb::unique_xmalloc_ptr<char> python_string_to_target_string (PyObject *obj);
diff --git a/gdb/python/python.c b/gdb/python/python.c
index 79f9826..9795588 100644
--- a/gdb/python/python.c
+++ b/gdb/python/python.c
@@ -1983,7 +1983,8 @@ do_start_initialization ()
       || gdbpy_initialize_unwind () < 0
       || gdbpy_initialize_membuf () < 0
       || gdbpy_initialize_connection () < 0
-      || gdbpy_initialize_tui () < 0)
+      || gdbpy_initialize_tui () < 0
+      || gdbpy_initialize_micommands () < 0)
     return false;
 
 #define GDB_PY_DEFINE_EVENT_TYPE(name, py_name, doc, base)	\
diff --git a/gdb/testsuite/gdb.python/py-mi-cmd.exp b/gdb/testsuite/gdb.python/py-mi-cmd.exp
new file mode 100644
index 0000000..c102efb
--- /dev/null
+++ b/gdb/testsuite/gdb.python/py-mi-cmd.exp
@@ -0,0 +1,390 @@
+# Copyright (C) 2019-2022 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/>.
+
+# Test custom MI commands implemented in Python.
+
+load_lib gdb-python.exp
+load_lib mi-support.exp
+set MIFLAGS "-i=mi"
+
+gdb_exit
+if {[mi_gdb_start]} {
+    continue
+}
+
+if {[lsearch -exact [mi_get_features] python] < 0} {
+    unsupported "python support is disabled"
+    return -1
+}
+
+standard_testfile
+
+mi_gdb_test "set python print-stack full" \
+    ".*\\^done" \
+    "set python print-stack full"
+
+mi_gdb_test "source ${srcdir}/${subdir}/${testfile}.py" \
+    ".*\\^done" \
+    "load python file"
+
+mi_gdb_test "python pycmd1('-pycmd')" \
+    ".*\\^done" \
+    "define -pycmd MI command"
+
+mi_gdb_test "-pycmd int" \
+    "\\^done,result=\"42\"" \
+    "-pycmd int"
+
+mi_gdb_test "-pycmd str" \
+    "\\^done,result=\"Hello world!\"" \
+    "-pycmd str"
+
+mi_gdb_test "-pycmd ary" \
+    "\\^done,result=\\\[\"Hello\",\"42\"\\\]" \
+    "-pycmd ary"
+
+mi_gdb_test "-pycmd dct" \
+    "\\^done,result={hello=\"world\",times=\"42\"}" \
+    "-pycmd dct"
+
+mi_gdb_test "-pycmd bk1" \
+    "\\^error,msg=\"Error occurred in Python: non-string object used as key: Bad Key\"" \
+    "-pycmd bk1"
+
+mi_gdb_test "-pycmd bk2" \
+    "\\^error,msg=\"Error occurred in Python: non-string object used as key: 1\"" \
+    "-pycmd bk2"
+
+mi_gdb_test "-pycmd bk3" \
+    [multi_line \
+	 "&\"TypeError: __repr__ returned non-string \\(type BadKey\\)..\"" \
+	 "\\^error,msg=\"Error occurred in Python: __repr__ returned non-string \\(type BadKey\\)\""] \
+    "-pycmd bk3"
+
+mi_gdb_test "-pycmd tpl" \
+    "\\^done,result=\\\[\"42\",\"Hello\"\\\]" \
+    "-pycmd tpl"
+
+mi_gdb_test "-pycmd itr" \
+    "\\^done,result=\\\[\"1\",\"2\",\"3\"\\\]" \
+    "-pycmd itr"
+
+mi_gdb_test "-pycmd nn1" \
+    "\\^done" \
+    "-pycmd nn1"
+
+mi_gdb_test "-pycmd nn2" \
+    "\\^done,result=\\\[\"None\"\\\]" \
+    "-pycmd nn2"
+
+mi_gdb_test "-pycmd bogus" \
+    "\\^error,msg=\"Invalid parameter: bogus\"" \
+    "-pycmd bogus"
+
+# Check that the top-level result from 'invoke' must be a dictionary.
+foreach test_name { nd1 nd2 nd3 } {
+    mi_gdb_test "-pycmd ${test_name}" \
+	"\\^error,msg=\"Error occurred in Python: Result from invoke must be a dictionary\""
+}
+
+# Check for invalid strings in the result.
+foreach test_desc { {ik1 "xxx yyy"} {ik2 "xxx yyy"} {ik3 "xxx\\+yyy"} \
+			{ik4 "xxx\\.yyy"} {ik5 "123xxxyyy"} } {
+    lassign $test_desc name pattern
+
+    mi_gdb_test "-pycmd ${name}" \
+	"\\^error,msg=\"Error occurred in Python: Invalid key in MI result: ${pattern}\""
+}
+
+mi_gdb_test "-pycmd empty_key" \
+    "\\^error,msg=\"Error occurred in Python: Invalid empty key in MI result\""
+
+# Check that a dash ('-') can be used in a key name.
+mi_gdb_test "-pycmd dash-key" \
+    "\\^done,the-key=\"123\""
+
+# With this argument the command raises a gdb.GdbError with no message
+# string.  GDB considers this a bug in the user program, so prints a
+# backtrace, and a generic error message.
+mi_gdb_test "-pycmd exp" \
+    [multi_line ".*&\"Traceback \\(most recent call last\\):..\"" \
+	 "&\"\[^\r\n\]+${testfile}.py\[^\r\n\]+\"" \
+	 "&\"\[^\r\n\]+raise gdb.GdbError\\(\\)..\"" \
+	 "&\"gdb.GdbError..\"" \
+	 "\\^error,msg=\"Error occurred in Python\\.\""] \
+    "-pycmd exp"
+
+mi_gdb_test "python pycmd2('-pycmd')" \
+    ".*\\^done" \
+    "redefine -pycmd MI command from CLI command"
+
+mi_gdb_test "-pycmd str" \
+    "\\^done,result=\"Ciao!\"" \
+    "-pycmd str - redefined from CLI"
+
+mi_gdb_test "-pycmd int" \
+    "\\^error,msg=\"Invalid parameter: int\"" \
+    "-pycmd int - redefined from CLI"
+
+mi_gdb_test "-pycmd new" \
+    "\\^done" \
+    "Define new command -pycmd-new MI command from Python MI command"
+
+mi_gdb_test "-pycmd red" \
+    "\\^error,msg=\"Command redefined but we failing anyway\"" \
+    "redefine -pycmd MI command from Python MI command"
+
+mi_gdb_test "-pycmd int" \
+    "\\^done,result=\"42\"" \
+    "-pycmd int - redefined from MI"
+
+mi_gdb_test "-pycmd-new int" \
+    "\\^done,result=\"42\"" \
+    "-pycmd-new int - defined from MI"
+
+mi_gdb_test "python pycmd1('')" \
+    ".*&\"ValueError: MI command name is empty\\...\".*\\^error,msg=\"Error while executing Python code\\.\"" \
+    "empty MI command name"
+
+mi_gdb_test "python pycmd1('-')" \
+    [multi_line \
+	 ".*" \
+	 "&\"ValueError: MI command name does not start with '-' followed by at least one letter or digit\\...\"" \
+	 "&\"Error while executing Python code\\...\"" \
+	 "\\^error,msg=\"Error while executing Python code\\.\""] \
+    "invalid MI command name"
+
+mi_gdb_test "python pycmd1('-bad-character-@')" \
+    [multi_line \
+	 ".*" \
+	 "&\"ValueError: MI command name contains invalid character: @\\...\"" \
+	 "&\"Error while executing Python code\\...\"" \
+	 "\\^error,msg=\"Error while executing Python code\\.\""] \
+    "invalid character in MI command name"
+
+mi_gdb_test "python cmd=pycmd1('-abc')" \
+    ".*\\^done" \
+    "create command -abc, stored in a python variable"
+
+mi_gdb_test "python print(cmd.name)" \
+    ".*\r\n~\"-abc\\\\n\"\r\n\\^done" \
+    "print the name of the stored mi command"
+
+mi_gdb_test "python print(cmd.installed)" \
+    ".*\r\n~\"True\\\\n\"\r\n\\^done" \
+    "print the installed status of the stored mi command"
+
+mi_gdb_test "-abc str" \
+    "\\^done,result=\"Hello world!\"" \
+    "-abc str"
+
+mi_gdb_test "python cmd.installed = False" \
+    ".*\\^done" \
+    "uninstall the mi command"
+
+mi_gdb_test "-abc str" \
+    "\\^error,msg=\"Undefined MI command: abc\",code=\"undefined-command\"" \
+    "-abc str, but now the command is gone"
+
+mi_gdb_test "python cmd.installed = True" \
+    ".*\\^done" \
+    "re-install the mi command"
+
+mi_gdb_test "-abc str" \
+    "\\^done,result=\"Hello world!\"" \
+    "-abc str, the command is back again"
+
+mi_gdb_test "python other=pycmd2('-abc')" \
+    ".*\\^done" \
+    "create another command called -abc, stored in a separate python variable"
+
+mi_gdb_test "python print(other.installed)" \
+    ".*\r\n~\"True\\\\n\"\r\n\\^done" \
+    "print the installed status of the other stored mi command"
+
+mi_gdb_test "python print(cmd.installed)" \
+    ".*\r\n~\"False\\\\n\"\r\n\\^done" \
+    "print the installed status of the original stored mi command"
+
+mi_gdb_test "-abc str" \
+    "\\^done,result=\"Ciao!\"" \
+    "-abc str, when the other command is in place"
+
+mi_gdb_test "python cmd.installed = True" \
+    ".*\\^done" \
+    "re-install the original mi command"
+
+mi_gdb_test "-abc str" \
+    "\\^done,result=\"Hello world!\"" \
+    "-abc str, the original command is back again"
+
+mi_gdb_test "python print(other.installed)" \
+    ".*\r\n~\"False\\\\n\"\r\n\\^done" \
+    "the other command is now not installed"
+
+mi_gdb_test "python print(cmd.installed)" \
+    ".*\r\n~\"True\\\\n\"\r\n\\^done" \
+    "the original command is now installed"
+
+mi_gdb_test "python aa = pycmd3('-aa', 'message one', 'xxx')" \
+    ".*\\^done" \
+    "created a new -aa command"
+
+mi_gdb_test "-aa" \
+    ".*\\^done,xxx={msg=\"message one\"}" \
+    "call the -aa command"
+
+mi_gdb_test "python aa.__init__('-aa', 'message two', 'yyy')" \
+    ".*\\^done" \
+    "reinitialise -aa command with a new message"
+
+mi_gdb_test "-aa" \
+    ".*\\^done,yyy={msg=\"message two\"}" \
+    "call the -aa command, get the new message"
+
+mi_gdb_test "python aa.__init__('-bb', 'message three', 'zzz')" \
+    [multi_line \
+	 ".*" \
+	 "&\"ValueError: can't reinitialize object with a different command name..\"" \
+	 "&\"Error while executing Python code\\...\"" \
+	 "\\^error,msg=\"Error while executing Python code\\.\""] \
+    "attempt to reinitialise aa variable to a new command name"
+
+mi_gdb_test "-aa" \
+    ".*\\^done,yyy={msg=\"message two\"}" \
+    "check the aa object has not changed after failed initialization"
+
+mi_gdb_test "python aa.installed = False" \
+    ".*\\^done" \
+    "uninstall the -aa command"
+
+mi_gdb_test "python aa.__init__('-bb', 'message three', 'zzz')" \
+    [multi_line \
+	 ".*" \
+	 "&\"ValueError: can't reinitialize object with a different command name..\"" \
+	 "&\"Error while executing Python code\\...\"" \
+	 "\\^error,msg=\"Error while executing Python code\\.\""] \
+    "attempt to reinitialise aa variable to a new command name while uninstalled"
+
+mi_gdb_test "python aa.__init__('-aa', 'message three', 'zzz')" \
+    ".*\\^done" \
+    "reinitialise -aa command with a new message while uninstalled"
+
+mi_gdb_test "python aa.installed = True" \
+    ".*\\^done" \
+    "install the -aa command"
+
+mi_gdb_test "-aa" \
+    ".*\\^done,zzz={msg=\"message three\"}" \
+    "call the -aa command looking for message three"
+
+# Remove the gdb._mi_commands dictionary, then try to register a new
+# command.
+mi_gdb_test "python del(gdb._mi_commands)" ".*\\^done"
+mi_gdb_test "python pycmd3('-hello', 'Hello', 'msg')" \
+    [multi_line \
+	 ".*" \
+	 "&\"AttributeError: module 'gdb' has no attribute '_mi_commands'..\"" \
+	 "&\"Error while executing Python code\\...\"" \
+	 "\\^error,msg=\"Error while executing Python code\\.\""] \
+    "register a command with no gdb._mi_commands available"
+
+# Set gdb._mi_commands to be something other than a dictionary, and
+# try to register a command.
+mi_gdb_test "python gdb._mi_commands = 'string'" ".*\\^done"
+mi_gdb_test "python pycmd3('-hello', 'Hello', 'msg')" \
+    [multi_line \
+	 ".*" \
+	 "&\"RuntimeError: gdb._mi_commands is not a dictionary as expected..\"" \
+	 "&\"Error while executing Python code\\...\"" \
+	 "\\^error,msg=\"Error while executing Python code\\.\""] \
+    "register a command when gdb._mi_commands is not a dictionary"
+
+# Restore gdb._mi_commands to a dictionary.
+mi_gdb_test "python gdb._mi_commands = {}" ".*\\^done"
+
+# Try to register a command object that is missing an invoke method.
+# This is accepted, but will give an error when the user tries to run
+# the command.
+mi_gdb_test "python no_invoke('-no-invoke')" ".*\\^done" \
+    "attempt to register command with no invoke method"
+mi_gdb_test "-no-invoke" \
+    [multi_line \
+	 ".*" \
+	 "&\"AttributeError: 'no_invoke' object has no attribute 'invoke'..\"" \
+	 "\\^error,msg=\"Error occurred in Python: 'no_invoke' object has no attribute 'invoke'\""] \
+    "execute -no-invoke command, which is missing the invoke method"
+
+# Register a command, then delete its invoke method.  What is the user thinking!!
+mi_gdb_test "python setattr(no_invoke, 'invoke', free_invoke)" ".*\\^done"
+mi_gdb_test "python cmd = no_invoke('-hello')" ".*\\^done"
+mi_gdb_test "-hello" ".*\\^done,result=\\\[\\\]" \
+    "execute no_invoke command, while it still has an invoke attribute"
+mi_gdb_test "python delattr(no_invoke, 'invoke')" ".*\\^done"
+mi_gdb_test "-hello" \
+    [multi_line \
+	 ".*" \
+	 "&\"AttributeError: 'no_invoke' object has no attribute 'invoke'..\"" \
+	 "\\^error,msg=\"Error occurred in Python: 'no_invoke' object has no attribute 'invoke'\""] \
+    "execute -hello command, that had its invoke method removed"
+mi_gdb_test "python cmd.invoke = 'string'" ".*\\^done"
+mi_gdb_test "-hello" \
+    [multi_line \
+	 ".*" \
+	 "&\"TypeError: 'str' object is not callable..\"" \
+	 "\\^error,msg=\"Error occurred in Python: 'str' object is not callable\""] \
+    "execute command with invoke set to a string"
+
+# Further checking of corruption to the gdb._mi_commands dictionary.
+#
+# First, insert an object of the wrong type, then try to register an
+# MI command that will go into that same dictionary slot.
+mi_gdb_test "python gdb._mi_commands\['blah'\] = 'blah blah blah'" ".*\\^done"
+mi_gdb_test "python pycmd2('-blah')" \
+    [multi_line \
+	 ".*" \
+	 "&\"RuntimeError: unexpected object in gdb\\._mi_commands dictionary..\"" \
+	 "&\"Error while executing Python code\\...\"" \
+	 "\\^error,msg=\"Error while executing Python code\\.\""] \
+    "hit unexpected object in gdb._mi_commands dictionary"
+
+# Next, create a command, uninstall it, then force the command back
+# into the dictionary.
+mi_gdb_test "python cmd = pycmd2('-foo')" ".*\\^done"
+mi_gdb_test "python cmd.installed = False" ".*\\^done"
+mi_gdb_test "python gdb._mi_commands\['foo'\] = cmd" ".*\\^done"
+mi_gdb_test "python cmd.installed = True" \
+    [multi_line \
+	 ".*" \
+	 "&\"RuntimeError: uninstalled command found in gdb\\._mi_commands dictionary..\"" \
+	 "&\"Error while executing Python code\\...\"" \
+	 "\\^error,msg=\"Error while executing Python code\\.\""] \
+    "found uninstalled command in gdb._mi_commands dictionary"
+
+# Try to create a new MI command that uses the name of a builtin MI command.
+mi_gdb_test "python cmd = pycmd2('-data-disassemble')" \
+    [multi_line \
+	 ".*" \
+	 "&\"RuntimeError: unable to add command, name may already be in use..\"" \
+	 "&\"Error while executing Python code\\...\"" \
+	 "\\^error,msg=\"Error while executing Python code\\.\""] \
+    "try to register a command that replaces -data-disassemble"
+
+
+
+mi_gdb_test "python run_exception_tests()" \
+    [multi_line \
+	 ".*" \
+	 "~\"PASS..\"" \
+	 "\\^done"]
diff --git a/gdb/testsuite/gdb.python/py-mi-cmd.py b/gdb/testsuite/gdb.python/py-mi-cmd.py
new file mode 100644
index 0000000..ffe27c5
--- /dev/null
+++ b/gdb/testsuite/gdb.python/py-mi-cmd.py
@@ -0,0 +1,120 @@
+# Copyright (C) 2019-2022 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 BadKey:
+    def __repr__(self):
+        return "Bad Key"
+
+
+class ReallyBadKey:
+    def __repr__(self):
+        return BadKey()
+
+
+class pycmd1(gdb.MICommand):
+    def invoke(self, argv):
+        if argv[0] == "int":
+            return {"result": 42}
+        elif argv[0] == "str":
+            return {"result": "Hello world!"}
+        elif argv[0] == "ary":
+            return {"result": ["Hello", 42]}
+        elif argv[0] == "dct":
+            return {"result": {"hello": "world", "times": 42}}
+        elif argv[0] == "bk1":
+            return {"result": {BadKey(): "world"}}
+        elif argv[0] == "bk2":
+            return {"result": {1: "world"}}
+        elif argv[0] == "bk3":
+            return {"result": {ReallyBadKey(): "world"}}
+        elif argv[0] == "tpl":
+            return {"result": (42, "Hello")}
+        elif argv[0] == "itr":
+            return {"result": iter([1, 2, 3])}
+        elif argv[0] == "nn1":
+            return None
+        elif argv[0] == "nn2":
+            return {"result": [None]}
+        elif argv[0] == "red":
+            pycmd2("-pycmd")
+            return None
+        elif argv[0] == "nd1":
+            return [1, 2, 3]
+        elif argv[0] == "nd2":
+            return 123
+        elif argv[0] == "nd3":
+            return "abc"
+        elif argv[0] == "ik1":
+            return {"xxx yyy": 123}
+        elif argv[0] == "ik2":
+            return {"result": {"xxx yyy": 123}}
+        elif argv[0] == "ik3":
+            return {"xxx+yyy": 123}
+        elif argv[0] == "ik4":
+            return {"xxx.yyy": 123}
+        elif argv[0] == "ik5":
+            return {"123xxxyyy": 123}
+        elif argv[0] == "empty_key":
+            return {"": 123}
+        elif argv[0] == "dash-key":
+            return {"the-key": 123}
+        elif argv[0] == "exp":
+            raise gdb.GdbError()
+        else:
+            raise gdb.GdbError("Invalid parameter: %s" % argv[0])
+
+
+class pycmd2(gdb.MICommand):
+    def invoke(self, argv):
+        if argv[0] == "str":
+            return {"result": "Ciao!"}
+        elif argv[0] == "red":
+            pycmd1("-pycmd")
+            raise gdb.GdbError("Command redefined but we failing anyway")
+        elif argv[0] == "new":
+            pycmd1("-pycmd-new")
+            return None
+        else:
+            raise gdb.GdbError("Invalid parameter: %s" % argv[0])
+
+
+# This class creates a command that returns a string, which is passed
+# when the command is created.
+class pycmd3(gdb.MICommand):
+    def __init__(self, name, msg, top_level):
+        super(pycmd3, self).__init__(name)
+        self._msg = msg
+        self._top_level = top_level
+
+    def invoke(self, args):
+        return {self._top_level: {"msg": self._msg}}
+
+
+# A command that is missing it's invoke method.
+class no_invoke(gdb.MICommand):
+    def __init__(self, name):
+        super(no_invoke, self).__init__(name)
+
+
+def free_invoke(obj, args):
+    return {"result": args}
+
+
+# Run some test involving catching exceptions.  It's easier to write
+# these as a Python function which is then called from the exp script.
+def run_exception_tests():
+    print("PASS")