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   (a) The FSF's Back-Cover Text is: "You are free to copy and modify
this GNU Manual.  Buying copies from GNU Press supports the FSF in
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INFO-DIR-SECTION Software development
START-INFO-DIR-ENTRY
* Gdb: (gdb).                     The GNU debugger.
* gdbserver: (gdb) Server.        The GNU debugging server.
END-INFO-DIR-ENTRY

   This file documents the GNU debugger GDB.

   This is the Tenth Edition, of 'Debugging with GDB: the GNU
Source-Level Debugger' for GDB (GDB) Version 7.8.1.

   Copyright (C) 1988-2014 Free Software Foundation, Inc.

   Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "Free Software" and "Free Software Needs Free
Documentation", with the Front-Cover Texts being "A GNU Manual," and
with the Back-Cover Texts as in (a) below.

   (a) The FSF's Back-Cover Text is: "You are free to copy and modify
this GNU Manual.  Buying copies from GNU Press supports the FSF in
developing GNU and promoting software freedom."

\1f
File: gdb.info,  Node: Xmethods In Python,  Next: Xmethod API,  Prev: Writing a Frame Filter,  Up: Python API

23.2.2.12 Xmethods In Python
............................

"Xmethods" are additional methods or replacements for existing methods
of a C++ class.  This feature is useful for those cases where a method
defined in C++ source code could be inlined or optimized out by the
compiler, making it unavailable to GDB.  For such cases, one can define
an xmethod to serve as a replacement for the method defined in the C++
source code.  GDB will then invoke the xmethod, instead of the C++
method, to evaluate expressions.  One can also use xmethods when
debugging with core files.  Moreover, when debugging live programs,
invoking an xmethod need not involve running the inferior (which can
potentially perturb its state).  Hence, even if the C++ method is
available, it is better to use its replacement xmethod if one is
defined.

   The xmethods feature in Python is available via the concepts of an
"xmethod matcher" and an "xmethod worker".  To implement an xmethod, one
has to implement a matcher and a corresponding worker for it (more than
one worker can be implemented, each catering to a different overloaded
instance of the method).  Internally, GDB invokes the 'match' method of
a matcher to match the class type and method name.  On a match, the
'match' method returns a list of matching _worker_ objects.  Each worker
object typically corresponds to an overloaded instance of the xmethod.
They implement a 'get_arg_types' method which returns a sequence of
types corresponding to the arguments the xmethod requires.  GDB uses
this sequence of types to perform overload resolution and picks a
winning xmethod worker.  A winner is also selected from among the
methods GDB finds in the C++ source code.  Next, the winning xmethod
worker and the winning C++ method are compared to select an overall
winner.  In case of a tie between a xmethod worker and a C++ method, the
xmethod worker is selected as the winner.  That is, if a winning xmethod
worker is found to be equivalent to the winning C++ method, then the
xmethod worker is treated as a replacement for the C++ method.  GDB uses
the overall winner to invoke the method.  If the winning xmethod worker
is the overall winner, then the corresponding xmethod is invoked via the
'invoke' method of the worker object.

   If one wants to implement an xmethod as a replacement for an existing
C++ method, then they have to implement an equivalent xmethod which has
exactly the same name and takes arguments of exactly the same type as
the C++ method.  If the user wants to invoke the C++ method even though
a replacement xmethod is available for that method, then they can
disable the xmethod.

   *Note Xmethod API::, for API to implement xmethods in Python.  *Note
Writing an Xmethod::, for implementing xmethods in Python.

\1f
File: gdb.info,  Node: Xmethod API,  Next: Writing an Xmethod,  Prev: Xmethods In Python,  Up: Python API

23.2.2.13 Xmethod API
.....................

The GDB Python API provides classes, interfaces and functions to
implement, register and manipulate xmethods.  *Note Xmethods In
Python::.

   An xmethod matcher should be an instance of a class derived from
'XMethodMatcher' defined in the module 'gdb.xmethod', or an object with
similar interface and attributes.  An instance of 'XMethodMatcher' has
the following attributes:

 -- Variable: name
     The name of the matcher.

 -- Variable: enabled
     A boolean value indicating whether the matcher is enabled or
     disabled.

 -- Variable: methods
     A list of named methods managed by the matcher.  Each object in the
     list is an instance of the class 'XMethod' defined in the module
     'gdb.xmethod', or any object with the following attributes:

     'name'
          Name of the xmethod which should be unique for each xmethod
          managed by the matcher.

     'enabled'
          A boolean value indicating whether the xmethod is enabled or
          disabled.

     The class 'XMethod' is a convenience class with same attributes as
     above along with the following constructor:

      -- Function: XMethod.__init__ (self, name)
          Constructs an enabled xmethod with name NAME.

The 'XMethodMatcher' class has the following methods:

 -- Function: XMethodMatcher.__init__ (self, name)
     Constructs an enabled xmethod matcher with name NAME.  The
     'methods' attribute is initialized to 'None'.

 -- Function: XMethodMatcher.match (self, class_type, method_name)
     Derived classes should override this method.  It should return a
     xmethod worker object (or a sequence of xmethod worker objects)
     matching the CLASS_TYPE and METHOD_NAME.  CLASS_TYPE is a
     'gdb.Type' object, and METHOD_NAME is a string value.  If the
     matcher manages named methods as listed in its 'methods' attribute,
     then only those worker objects whose corresponding entries in the
     'methods' list are enabled should be returned.

   An xmethod worker should be an instance of a class derived from
'XMethodWorker' defined in the module 'gdb.xmethod', or support the
following interface:

 -- Function: XMethodWorker.get_arg_types (self)
     This method returns a sequence of 'gdb.Type' objects corresponding
     to the arguments that the xmethod takes.  It can return an empty
     sequence or 'None' if the xmethod does not take any arguments.  If
     the xmethod takes a single argument, then a single 'gdb.Type'
     object corresponding to it can be returned.

 -- Function: XMethodWorker.__call__ (self, *args)
     This is the method which does the _work_ of the xmethod.  The ARGS
     arguments is the tuple of arguments to the xmethod.  Each element
     in this tuple is a gdb.Value object.  The first element is always
     the 'this' pointer value.

   For GDB to lookup xmethods, the xmethod matchers should be registered
using the following function defined in the module 'gdb.xmethod':

 -- Function: register_xmethod_matcher (locus, matcher, replace=False)
     The 'matcher' is registered with 'locus', replacing an existing
     matcher with the same name as 'matcher' if 'replace' is 'True'.
     'locus' can be a 'gdb.Objfile' object (*note Objfiles In Python::),
     or a 'gdb.Progspace' object (*note Progspaces In Python::), or
     'None'.  If it is 'None', then 'matcher' is registered globally.

\1f
File: gdb.info,  Node: Writing an Xmethod,  Next: Inferiors In Python,  Prev: Xmethod API,  Up: Python API

23.2.2.14 Writing an Xmethod
............................

Implementing xmethods in Python will require implementing xmethod
matchers and xmethod workers (*note Xmethods In Python::).  Consider the
following C++ class:

     class MyClass
     {
     public:
       MyClass (int a) : a_(a) { }

       int geta (void) { return a_; }
       int operator+ (int b);

     private:
       int a_;
     };

     int
     MyClass::operator+ (int b)
     {
       return a_ + b;
     }

Let us define two xmethods for the class 'MyClass', one replacing the
method 'geta', and another adding an overloaded flavor of 'operator+'
which takes a 'MyClass' argument (the C++ code above already has an
overloaded 'operator+' which takes an 'int' argument).  The xmethod
matcher can be defined as follows:

     class MyClass_geta(gdb.xmethod.XMethod):
         def __init__(self):
             gdb.xmethod.XMethod.__init__(self, 'geta')

         def get_worker(self, method_name):
             if method_name == 'geta':
                 return MyClassWorker_geta()


     class MyClass_sum(gdb.xmethod.XMethod):
         def __init__(self):
             gdb.xmethod.XMethod.__init__(self, 'sum')

         def get_worker(self, method_name):
             if method_name == 'operator+':
                 return MyClassWorker_plus()


     class MyClassMatcher(gdb.xmethod.XMethodMatcher):
         def __init__(self):
             gdb.xmethod.XMethodMatcher.__init__(self, 'MyClassMatcher')
             # List of methods 'managed' by this matcher
             self.methods = [MyClass_geta(), MyClass_sum()]

         def match(self, class_type, method_name):
             if class_type.tag != 'MyClass':
                 return None
             workers = []
             for method in self.methods:
                 if method.enabled:
                     worker = method.get_worker(method_name)
                     if worker:
                         workers.append(worker)

             return workers

Notice that the 'match' method of 'MyClassMatcher' returns a worker
object of type 'MyClassWorker_geta' for the 'geta' method, and a worker
object of type 'MyClassWorker_plus' for the 'operator+' method.  This is
done indirectly via helper classes derived from 'gdb.xmethod.XMethod'.
One does not need to use the 'methods' attribute in a matcher as it is
optional.  However, if a matcher manages more than one xmethod, it is a
good practice to list the xmethods in the 'methods' attribute of the
matcher.  This will then facilitate enabling and disabling individual
xmethods via the 'enable/disable' commands.  Notice also that a worker
object is returned only if the corresponding entry in the 'methods'
attribute of the matcher is enabled.

   The implementation of the worker classes returned by the matcher
setup above is as follows:

     class MyClassWorker_geta(gdb.xmethod.XMethodWorker):
         def get_arg_types(self):
             return None

         def __call__(self, obj):
             return obj['a_']


     class MyClassWorker_plus(gdb.xmethod.XMethodWorker):
         def get_arg_types(self):
             return gdb.lookup_type('MyClass')

         def __call__(self, obj, other):
             return obj['a_'] + other['a_']

   For GDB to actually lookup a xmethod, it has to be registered with
it.  The matcher defined above is registered with GDB globally as
follows:

     gdb.xmethod.register_xmethod_matcher(None, MyClassMatcher())

   If an object 'obj' of type 'MyClass' is initialized in C++ code as
follows:

     MyClass obj(5);

then, after loading the Python script defining the xmethod matchers and
workers into 'GDBN', invoking the method 'geta' or using the operator
'+' on 'obj' will invoke the xmethods defined above:

     (gdb) p obj.geta()
     $1 = 5

     (gdb) p obj + obj
     $2 = 10

   Consider another example with a C++ template class:

     template <class T>
     class MyTemplate
     {
     public:
       MyTemplate () : dsize_(10), data_ (new T [10]) { }
       ~MyTemplate () { delete [] data_; }

       int footprint (void)
       {
         return sizeof (T) * dsize_ + sizeof (MyTemplate<T>);
       }

     private:
       int dsize_;
       T *data_;
     };

   Let us implement an xmethod for the above class which serves as a
replacement for the 'footprint' method.  The full code listing of the
xmethod workers and xmethod matchers is as follows:

     class MyTemplateWorker_footprint(gdb.xmethod.XMethodWorker):
         def __init__(self, class_type):
             self.class_type = class_type

         def get_arg_types(self):
             return None

         def __call__(self, obj):
             return (self.class_type.sizeof +
                     obj['dsize_'] *
                     self.class_type.template_argument(0).sizeof)


     class MyTemplateMatcher_footprint(gdb.xmethod.XMethodMatcher):
         def __init__(self):
             gdb.xmethod.XMethodMatcher.__init__(self, 'MyTemplateMatcher')

         def match(self, class_type, method_name):
             if (re.match('MyTemplate<[ \t\n]*[_a-zA-Z][ _a-zA-Z0-9]*>',
                          class_type.tag) and
                 method_name == 'footprint'):
                 return MyTemplateWorker_footprint(class_type)

   Notice that, in this example, we have not used the 'methods'
attribute of the matcher as the matcher manages only one xmethod.  The
user can enable/disable this xmethod by enabling/disabling the matcher
itself.

\1f
File: gdb.info,  Node: Inferiors In Python,  Next: Events In Python,  Prev: Writing an Xmethod,  Up: Python API

23.2.2.15 Inferiors In Python
.............................

Programs which are being run under GDB are called inferiors (*note
Inferiors and Programs::).  Python scripts can access information about
and manipulate inferiors controlled by GDB via objects of the
'gdb.Inferior' class.

   The following inferior-related functions are available in the 'gdb'
module:

 -- Function: gdb.inferiors ()
     Return a tuple containing all inferior objects.

 -- Function: gdb.selected_inferior ()
     Return an object representing the current inferior.

   A 'gdb.Inferior' object has the following attributes:

 -- Variable: Inferior.num
     ID of inferior, as assigned by GDB.

 -- Variable: Inferior.pid
     Process ID of the inferior, as assigned by the underlying operating
     system.

 -- Variable: Inferior.was_attached
     Boolean signaling whether the inferior was created using 'attach',
     or started by GDB itself.

   A 'gdb.Inferior' object has the following methods:

 -- Function: Inferior.is_valid ()
     Returns 'True' if the 'gdb.Inferior' object is valid, 'False' if
     not.  A 'gdb.Inferior' object will become invalid if the inferior
     no longer exists within GDB.  All other 'gdb.Inferior' methods will
     throw an exception if it is invalid at the time the method is
     called.

 -- Function: Inferior.threads ()
     This method returns a tuple holding all the threads which are valid
     when it is called.  If there are no valid threads, the method will
     return an empty tuple.

 -- Function: Inferior.read_memory (address, length)
     Read LENGTH bytes of memory from the inferior, starting at ADDRESS.
     Returns a buffer object, which behaves much like an array or a
     string.  It can be modified and given to the
     'Inferior.write_memory' function.  In 'Python' 3, the return value
     is a 'memoryview' object.

 -- Function: Inferior.write_memory (address, buffer [, length])
     Write the contents of BUFFER to the inferior, starting at ADDRESS.
     The BUFFER parameter must be a Python object which supports the
     buffer protocol, i.e., a string, an array or the object returned
     from 'Inferior.read_memory'.  If given, LENGTH determines the
     number of bytes from BUFFER to be written.

 -- Function: Inferior.search_memory (address, length, pattern)
     Search a region of the inferior memory starting at ADDRESS with the
     given LENGTH using the search pattern supplied in PATTERN.  The
     PATTERN parameter must be a Python object which supports the buffer
     protocol, i.e., a string, an array or the object returned from
     'gdb.read_memory'.  Returns a Python 'Long' containing the address
     where the pattern was found, or 'None' if the pattern could not be
     found.

\1f
File: gdb.info,  Node: Events In Python,  Next: Threads In Python,  Prev: Inferiors In Python,  Up: Python API

23.2.2.16 Events In Python
..........................

GDB provides a general event facility so that Python code can be
notified of various state changes, particularly changes that occur in
the inferior.

   An "event" is just an object that describes some state change.  The
type of the object and its attributes will vary depending on the details
of the change.  All the existing events are described below.

   In order to be notified of an event, you must register an event
handler with an "event registry".  An event registry is an object in the
'gdb.events' module which dispatches particular events.  A registry
provides methods to register and unregister event handlers:

 -- Function: EventRegistry.connect (object)
     Add the given callable OBJECT to the registry.  This object will be
     called when an event corresponding to this registry occurs.

 -- Function: EventRegistry.disconnect (object)
     Remove the given OBJECT from the registry.  Once removed, the
     object will no longer receive notifications of events.

   Here is an example:

     def exit_handler (event):
         print "event type: exit"
         print "exit code: %d" % (event.exit_code)

     gdb.events.exited.connect (exit_handler)

   In the above example we connect our handler 'exit_handler' to the
registry 'events.exited'.  Once connected, 'exit_handler' gets called
when the inferior exits.  The argument "event" in this example is of
type 'gdb.ExitedEvent'.  As you can see in the example the 'ExitedEvent'
object has an attribute which indicates the exit code of the inferior.

   The following is a listing of the event registries that are available
and details of the events they emit:

'events.cont'
     Emits 'gdb.ThreadEvent'.

     Some events can be thread specific when GDB is running in non-stop
     mode.  When represented in Python, these events all extend
     'gdb.ThreadEvent'.  Note, this event is not emitted directly;
     instead, events which are emitted by this or other modules might
     extend this event.  Examples of these events are
     'gdb.BreakpointEvent' and 'gdb.ContinueEvent'.

      -- Variable: ThreadEvent.inferior_thread
          In non-stop mode this attribute will be set to the specific
          thread which was involved in the emitted event.  Otherwise, it
          will be set to 'None'.

     Emits 'gdb.ContinueEvent' which extends 'gdb.ThreadEvent'.

     This event indicates that the inferior has been continued after a
     stop.  For inherited attribute refer to 'gdb.ThreadEvent' above.

'events.exited'
     Emits 'events.ExitedEvent' which indicates that the inferior has
     exited.  'events.ExitedEvent' has two attributes:
      -- Variable: ExitedEvent.exit_code
          An integer representing the exit code, if available, which the
          inferior has returned.  (The exit code could be unavailable
          if, for example, GDB detaches from the inferior.)  If the exit
          code is unavailable, the attribute does not exist.
      -- Variable: ExitedEvent inferior
          A reference to the inferior which triggered the 'exited'
          event.

'events.stop'
     Emits 'gdb.StopEvent' which extends 'gdb.ThreadEvent'.

     Indicates that the inferior has stopped.  All events emitted by
     this registry extend StopEvent.  As a child of 'gdb.ThreadEvent',
     'gdb.StopEvent' will indicate the stopped thread when GDB is
     running in non-stop mode.  Refer to 'gdb.ThreadEvent' above for
     more details.

     Emits 'gdb.SignalEvent' which extends 'gdb.StopEvent'.

     This event indicates that the inferior or one of its threads has
     received as signal.  'gdb.SignalEvent' has the following
     attributes:

      -- Variable: SignalEvent.stop_signal
          A string representing the signal received by the inferior.  A
          list of possible signal values can be obtained by running the
          command 'info signals' in the GDB command prompt.

     Also emits 'gdb.BreakpointEvent' which extends 'gdb.StopEvent'.

     'gdb.BreakpointEvent' event indicates that one or more breakpoints
     have been hit, and has the following attributes:

      -- Variable: BreakpointEvent.breakpoints
          A sequence containing references to all the breakpoints (type
          'gdb.Breakpoint') that were hit.  *Note Breakpoints In
          Python::, for details of the 'gdb.Breakpoint' object.
      -- Variable: BreakpointEvent.breakpoint
          A reference to the first breakpoint that was hit.  This
          function is maintained for backward compatibility and is now
          deprecated in favor of the 'gdb.BreakpointEvent.breakpoints'
          attribute.

'events.new_objfile'
     Emits 'gdb.NewObjFileEvent' which indicates that a new object file
     has been loaded by GDB.  'gdb.NewObjFileEvent' has one attribute:

      -- Variable: NewObjFileEvent.new_objfile
          A reference to the object file ('gdb.Objfile') which has been
          loaded.  *Note Objfiles In Python::, for details of the
          'gdb.Objfile' object.

\1f
File: gdb.info,  Node: Threads In Python,  Next: Commands In Python,  Prev: Events In Python,  Up: Python API

23.2.2.17 Threads In Python
...........................

Python scripts can access information about, and manipulate inferior
threads controlled by GDB, via objects of the 'gdb.InferiorThread'
class.

   The following thread-related functions are available in the 'gdb'
module:

 -- Function: gdb.selected_thread ()
     This function returns the thread object for the selected thread.
     If there is no selected thread, this will return 'None'.

   A 'gdb.InferiorThread' object has the following attributes:

 -- Variable: InferiorThread.name
     The name of the thread.  If the user specified a name using 'thread
     name', then this returns that name.  Otherwise, if an OS-supplied
     name is available, then it is returned.  Otherwise, this returns
     'None'.

     This attribute can be assigned to.  The new value must be a string
     object, which sets the new name, or 'None', which removes any
     user-specified thread name.

 -- Variable: InferiorThread.num
     ID of the thread, as assigned by GDB.

 -- Variable: InferiorThread.ptid
     ID of the thread, as assigned by the operating system.  This
     attribute is a tuple containing three integers.  The first is the
     Process ID (PID); the second is the Lightweight Process ID (LWPID),
     and the third is the Thread ID (TID). Either the LWPID or TID may
     be 0, which indicates that the operating system does not use that
     identifier.

   A 'gdb.InferiorThread' object has the following methods:

 -- Function: InferiorThread.is_valid ()
     Returns 'True' if the 'gdb.InferiorThread' object is valid, 'False'
     if not.  A 'gdb.InferiorThread' object will become invalid if the
     thread exits, or the inferior that the thread belongs is deleted.
     All other 'gdb.InferiorThread' methods will throw an exception if
     it is invalid at the time the method is called.

 -- Function: InferiorThread.switch ()
     This changes GDB's currently selected thread to the one represented
     by this object.

 -- Function: InferiorThread.is_stopped ()
     Return a Boolean indicating whether the thread is stopped.

 -- Function: InferiorThread.is_running ()
     Return a Boolean indicating whether the thread is running.

 -- Function: InferiorThread.is_exited ()
     Return a Boolean indicating whether the thread is exited.

\1f
File: gdb.info,  Node: Commands In Python,  Next: Parameters In Python,  Prev: Threads In Python,  Up: Python API

23.2.2.18 Commands In Python
............................

You can implement new GDB CLI commands in Python.  A CLI command is
implemented using an instance of the 'gdb.Command' class, most commonly
using a subclass.

 -- Function: Command.__init__ (name, COMMAND_CLASS [, COMPLETER_CLASS
          [, PREFIX]])
     The object initializer for 'Command' registers the new command with
     GDB.  This initializer is normally invoked from the subclass' own
     '__init__' method.

     NAME is the name of the command.  If NAME consists of multiple
     words, then the initial words are looked for as prefix commands.
     In this case, if one of the prefix commands does not exist, an
     exception is raised.

     There is no support for multi-line commands.

     COMMAND_CLASS should be one of the 'COMMAND_' constants defined
     below.  This argument tells GDB how to categorize the new command
     in the help system.

     COMPLETER_CLASS is an optional argument.  If given, it should be
     one of the 'COMPLETE_' constants defined below.  This argument
     tells GDB how to perform completion for this command.  If not
     given, GDB will attempt to complete using the object's 'complete'
     method (see below); if no such method is found, an error will occur
     when completion is attempted.

     PREFIX is an optional argument.  If 'True', then the new command is
     a prefix command; sub-commands of this command may be registered.

     The help text for the new command is taken from the Python
     documentation string for the command's class, if there is one.  If
     no documentation string is provided, the default value "This
     command is not documented."  is used.

 -- Function: Command.dont_repeat ()
     By default, a GDB command is repeated when the user enters a blank
     line at the command prompt.  A command can suppress this behavior
     by invoking the 'dont_repeat' method.  This is similar to the user
     command 'dont-repeat', see *note dont-repeat: Define.

 -- Function: Command.invoke (argument, from_tty)
     This method is called by GDB when this command is invoked.

     ARGUMENT is a string.  It is the argument to the command, after
     leading and trailing whitespace has been stripped.

     FROM_TTY is a boolean argument.  When true, this means that the
     command was entered by the user at the terminal; when false it
     means that the command came from elsewhere.

     If this method throws an exception, it is turned into a GDB 'error'
     call.  Otherwise, the return value is ignored.

     To break ARGUMENT up into an argv-like string use
     'gdb.string_to_argv'.  This function behaves identically to GDB's
     internal argument lexer 'buildargv'.  It is recommended to use this
     for consistency.  Arguments are separated by spaces and may be
     quoted.  Example:

          print gdb.string_to_argv ("1 2\ \\\"3 '4 \"5' \"6 '7\"")
          ['1', '2 "3', '4 "5', "6 '7"]

 -- Function: Command.complete (text, word)
     This method is called by GDB when the user attempts completion on
     this command.  All forms of completion are handled by this method,
     that is, the <TAB> and <M-?> key bindings (*note Completion::), and
     the 'complete' command (*note complete: Help.).

     The arguments TEXT and WORD are both strings; TEXT holds the
     complete command line up to the cursor's location, while WORD holds
     the last word of the command line; this is computed using a
     word-breaking heuristic.

     The 'complete' method can return several values:
        * If the return value is a sequence, the contents of the
          sequence are used as the completions.  It is up to 'complete'
          to ensure that the contents actually do complete the word.  A
          zero-length sequence is allowed, it means that there were no
          completions available.  Only string elements of the sequence
          are used; other elements in the sequence are ignored.

        * If the return value is one of the 'COMPLETE_' constants
          defined below, then the corresponding GDB-internal completion
          function is invoked, and its result is used.

        * All other results are treated as though there were no
          available completions.

   When a new command is registered, it must be declared as a member of
some general class of commands.  This is used to classify top-level
commands in the on-line help system; note that prefix commands are not
listed under their own category but rather that of their top-level
command.  The available classifications are represented by constants
defined in the 'gdb' module:

'gdb.COMMAND_NONE'
     The command does not belong to any particular class.  A command in
     this category will not be displayed in any of the help categories.

'gdb.COMMAND_RUNNING'
     The command is related to running the inferior.  For example,
     'start', 'step', and 'continue' are in this category.  Type 'help
     running' at the GDB prompt to see a list of commands in this
     category.

'gdb.COMMAND_DATA'
     The command is related to data or variables.  For example, 'call',
     'find', and 'print' are in this category.  Type 'help data' at the
     GDB prompt to see a list of commands in this category.

'gdb.COMMAND_STACK'
     The command has to do with manipulation of the stack.  For example,
     'backtrace', 'frame', and 'return' are in this category.  Type
     'help stack' at the GDB prompt to see a list of commands in this
     category.

'gdb.COMMAND_FILES'
     This class is used for file-related commands.  For example, 'file',
     'list' and 'section' are in this category.  Type 'help files' at
     the GDB prompt to see a list of commands in this category.

'gdb.COMMAND_SUPPORT'
     This should be used for "support facilities", generally meaning
     things that are useful to the user when interacting with GDB, but
     not related to the state of the inferior.  For example, 'help',
     'make', and 'shell' are in this category.  Type 'help support' at
     the GDB prompt to see a list of commands in this category.

'gdb.COMMAND_STATUS'
     The command is an 'info'-related command, that is, related to the
     state of GDB itself.  For example, 'info', 'macro', and 'show' are
     in this category.  Type 'help status' at the GDB prompt to see a
     list of commands in this category.

'gdb.COMMAND_BREAKPOINTS'
     The command has to do with breakpoints.  For example, 'break',
     'clear', and 'delete' are in this category.  Type 'help
     breakpoints' at the GDB prompt to see a list of commands in this
     category.

'gdb.COMMAND_TRACEPOINTS'
     The command has to do with tracepoints.  For example, 'trace',
     'actions', and 'tfind' are in this category.  Type 'help
     tracepoints' at the GDB prompt to see a list of commands in this
     category.

'gdb.COMMAND_USER'
     The command is a general purpose command for the user, and
     typically does not fit in one of the other categories.  Type 'help
     user-defined' at the GDB prompt to see a list of commands in this
     category, as well as the list of gdb macros (*note Sequences::).

'gdb.COMMAND_OBSCURE'
     The command is only used in unusual circumstances, or is not of
     general interest to users.  For example, 'checkpoint', 'fork', and
     'stop' are in this category.  Type 'help obscure' at the GDB prompt
     to see a list of commands in this category.

'gdb.COMMAND_MAINTENANCE'
     The command is only useful to GDB maintainers.  The 'maintenance'
     and 'flushregs' commands are in this category.  Type 'help
     internals' at the GDB prompt to see a list of commands in this
     category.

   A new command can use a predefined completion function, either by
specifying it via an argument at initialization, or by returning it from
the 'complete' method.  These predefined completion constants are all
defined in the 'gdb' module:

'gdb.COMPLETE_NONE'
     This constant means that no completion should be done.

'gdb.COMPLETE_FILENAME'
     This constant means that filename completion should be performed.

'gdb.COMPLETE_LOCATION'
     This constant means that location completion should be done.  *Note
     Specify Location::.

'gdb.COMPLETE_COMMAND'
     This constant means that completion should examine GDB command
     names.

'gdb.COMPLETE_SYMBOL'
     This constant means that completion should be done using symbol
     names as the source.

'gdb.COMPLETE_EXPRESSION'
     This constant means that completion should be done on expressions.
     Often this means completing on symbol names, but some language
     parsers also have support for completing on field names.

   The following code snippet shows how a trivial CLI command can be
implemented in Python:

     class HelloWorld (gdb.Command):
       """Greet the whole world."""

       def __init__ (self):
         super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)

       def invoke (self, arg, from_tty):
         print "Hello, World!"

     HelloWorld ()

   The last line instantiates the class, and is necessary to trigger the
registration of the command with GDB.  Depending on how the Python code
is read into GDB, you may need to import the 'gdb' module explicitly.

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File: gdb.info,  Node: Parameters In Python,  Next: Functions In Python,  Prev: Commands In Python,  Up: Python API

23.2.2.19 Parameters In Python
..............................

You can implement new GDB parameters using Python.  A new parameter is
implemented as an instance of the 'gdb.Parameter' class.

   Parameters are exposed to the user via the 'set' and 'show' commands.
*Note Help::.

   There are many parameters that already exist and can be set in GDB.
Two examples are: 'set follow fork' and 'set charset'.  Setting these
parameters influences certain behavior in GDB.  Similarly, you can
define parameters that can be used to influence behavior in custom
Python scripts and commands.

 -- Function: Parameter.__init__ (name, COMMAND-CLASS, PARAMETER-CLASS
          [, ENUM-SEQUENCE])
     The object initializer for 'Parameter' registers the new parameter
     with GDB.  This initializer is normally invoked from the subclass'
     own '__init__' method.

     NAME is the name of the new parameter.  If NAME consists of
     multiple words, then the initial words are looked for as prefix
     parameters.  An example of this can be illustrated with the 'set
     print' set of parameters.  If NAME is 'print foo', then 'print'
     will be searched as the prefix parameter.  In this case the
     parameter can subsequently be accessed in GDB as 'set print foo'.

     If NAME consists of multiple words, and no prefix parameter group
     can be found, an exception is raised.

     COMMAND-CLASS should be one of the 'COMMAND_' constants (*note
     Commands In Python::).  This argument tells GDB how to categorize
     the new parameter in the help system.

     PARAMETER-CLASS should be one of the 'PARAM_' constants defined
     below.  This argument tells GDB the type of the new parameter; this
     information is used for input validation and completion.

     If PARAMETER-CLASS is 'PARAM_ENUM', then ENUM-SEQUENCE must be a
     sequence of strings.  These strings represent the possible values
     for the parameter.

     If PARAMETER-CLASS is not 'PARAM_ENUM', then the presence of a
     fourth argument will cause an exception to be thrown.

     The help text for the new parameter is taken from the Python
     documentation string for the parameter's class, if there is one.
     If there is no documentation string, a default value is used.

 -- Variable: Parameter.set_doc
     If this attribute exists, and is a string, then its value is used
     as the help text for this parameter's 'set' command.  The value is
     examined when 'Parameter.__init__' is invoked; subsequent changes
     have no effect.

 -- Variable: Parameter.show_doc
     If this attribute exists, and is a string, then its value is used
     as the help text for this parameter's 'show' command.  The value is
     examined when 'Parameter.__init__' is invoked; subsequent changes
     have no effect.

 -- Variable: Parameter.value
     The 'value' attribute holds the underlying value of the parameter.
     It can be read and assigned to just as any other attribute.  GDB
     does validation when assignments are made.

   There are two methods that should be implemented in any 'Parameter'
class.  These are:

 -- Function: Parameter.get_set_string (self)
     GDB will call this method when a PARAMETER's value has been changed
     via the 'set' API (for example, 'set foo off').  The 'value'
     attribute has already been populated with the new value and may be
     used in output.  This method must return a string.

 -- Function: Parameter.get_show_string (self, svalue)
     GDB will call this method when a PARAMETER's 'show' API has been
     invoked (for example, 'show foo').  The argument 'svalue' receives
     the string representation of the current value.  This method must
     return a string.

   When a new parameter is defined, its type must be specified.  The
available types are represented by constants defined in the 'gdb'
module:

'gdb.PARAM_BOOLEAN'
     The value is a plain boolean.  The Python boolean values, 'True'
     and 'False' are the only valid values.

'gdb.PARAM_AUTO_BOOLEAN'
     The value has three possible states: true, false, and 'auto'.  In
     Python, true and false are represented using boolean constants, and
     'auto' is represented using 'None'.

'gdb.PARAM_UINTEGER'
     The value is an unsigned integer.  The value of 0 should be
     interpreted to mean "unlimited".

'gdb.PARAM_INTEGER'
     The value is a signed integer.  The value of 0 should be
     interpreted to mean "unlimited".

'gdb.PARAM_STRING'
     The value is a string.  When the user modifies the string, any
     escape sequences, such as '\t', '\f', and octal escapes, are
     translated into corresponding characters and encoded into the
     current host charset.

'gdb.PARAM_STRING_NOESCAPE'
     The value is a string.  When the user modifies the string, escapes
     are passed through untranslated.

'gdb.PARAM_OPTIONAL_FILENAME'
     The value is a either a filename (a string), or 'None'.

'gdb.PARAM_FILENAME'
     The value is a filename.  This is just like
     'PARAM_STRING_NOESCAPE', but uses file names for completion.

'gdb.PARAM_ZINTEGER'
     The value is an integer.  This is like 'PARAM_INTEGER', except 0 is
     interpreted as itself.

'gdb.PARAM_ENUM'
     The value is a string, which must be one of a collection string
     constants provided when the parameter is created.

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File: gdb.info,  Node: Functions In Python,  Next: Progspaces In Python,  Prev: Parameters In Python,  Up: Python API

23.2.2.20 Writing new convenience functions
...........................................

You can implement new convenience functions (*note Convenience Vars::)
in Python.  A convenience function is an instance of a subclass of the
class 'gdb.Function'.

 -- Function: Function.__init__ (name)
     The initializer for 'Function' registers the new function with GDB.
     The argument NAME is the name of the function, a string.  The
     function will be visible to the user as a convenience variable of
     type 'internal function', whose name is the same as the given NAME.

     The documentation for the new function is taken from the
     documentation string for the new class.

 -- Function: Function.invoke (*ARGS)
     When a convenience function is evaluated, its arguments are
     converted to instances of 'gdb.Value', and then the function's
     'invoke' method is called.  Note that GDB does not predetermine the
     arity of convenience functions.  Instead, all available arguments
     are passed to 'invoke', following the standard Python calling
     convention.  In particular, a convenience function can have default
     values for parameters without ill effect.

     The return value of this method is used as its value in the
     enclosing expression.  If an ordinary Python value is returned, it
     is converted to a 'gdb.Value' following the usual rules.

   The following code snippet shows how a trivial convenience function
can be implemented in Python:

     class Greet (gdb.Function):
       """Return string to greet someone.
     Takes a name as argument."""

       def __init__ (self):
         super (Greet, self).__init__ ("greet")

       def invoke (self, name):
         return "Hello, %s!" % name.string ()

     Greet ()

   The last line instantiates the class, and is necessary to trigger the
registration of the function with GDB.  Depending on how the Python code
is read into GDB, you may need to import the 'gdb' module explicitly.

   Now you can use the function in an expression:

     (gdb) print $greet("Bob")
     $1 = "Hello, Bob!"

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File: gdb.info,  Node: Progspaces In Python,  Next: Objfiles In Python,  Prev: Functions In Python,  Up: Python API

23.2.2.21 Program Spaces In Python
..................................

A program space, or "progspace", represents a symbolic view of an
address space.  It consists of all of the objfiles of the program.
*Note Objfiles In Python::.  *Note program spaces: Inferiors and
Programs, for more details about program spaces.

   The following progspace-related functions are available in the 'gdb'
module:

 -- Function: gdb.current_progspace ()
     This function returns the program space of the currently selected
     inferior.  *Note Inferiors and Programs::.

 -- Function: gdb.progspaces ()
     Return a sequence of all the progspaces currently known to GDB.

   Each progspace is represented by an instance of the 'gdb.Progspace'
class.

 -- Variable: Progspace.filename
     The file name of the progspace as a string.

 -- Variable: Progspace.pretty_printers
     The 'pretty_printers' attribute is a list of functions.  It is used
     to look up pretty-printers.  A 'Value' is passed to each function
     in order; if the function returns 'None', then the search
     continues.  Otherwise, the return value should be an object which
     is used to format the value.  *Note Pretty Printing API::, for more
     information.

 -- Variable: Progspace.type_printers
     The 'type_printers' attribute is a list of type printer objects.
     *Note Type Printing API::, for more information.

 -- Variable: Progspace.frame_filters
     The 'frame_filters' attribute is a dictionary of frame filter
     objects.  *Note Frame Filter API::, for more information.

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File: gdb.info,  Node: Objfiles In Python,  Next: Frames In Python,  Prev: Progspaces In Python,  Up: Python API

23.2.2.22 Objfiles In Python
............................

GDB loads symbols for an inferior from various symbol-containing files
(*note Files::).  These include the primary executable file, any shared
libraries used by the inferior, and any separate debug info files (*note
Separate Debug Files::).  GDB calls these symbol-containing files
"objfiles".

   The following objfile-related functions are available in the 'gdb'
module:

 -- Function: gdb.current_objfile ()
     When auto-loading a Python script (*note Python Auto-loading::),
     GDB sets the "current objfile" to the corresponding objfile.  This
     function returns the current objfile.  If there is no current
     objfile, this function returns 'None'.

 -- Function: gdb.objfiles ()
     Return a sequence of all the objfiles current known to GDB.  *Note
     Objfiles In Python::.

   Each objfile is represented by an instance of the 'gdb.Objfile'
class.

 -- Variable: Objfile.filename
     The file name of the objfile as a string.

 -- Variable: Objfile.pretty_printers
     The 'pretty_printers' attribute is a list of functions.  It is used
     to look up pretty-printers.  A 'Value' is passed to each function
     in order; if the function returns 'None', then the search
     continues.  Otherwise, the return value should be an object which
     is used to format the value.  *Note Pretty Printing API::, for more
     information.

 -- Variable: Objfile.type_printers
     The 'type_printers' attribute is a list of type printer objects.
     *Note Type Printing API::, for more information.

 -- Variable: Objfile.frame_filters
     The 'frame_filters' attribute is a dictionary of frame filter
     objects.  *Note Frame Filter API::, for more information.

   A 'gdb.Objfile' object has the following methods:

 -- Function: Objfile.is_valid ()
     Returns 'True' if the 'gdb.Objfile' object is valid, 'False' if
     not.  A 'gdb.Objfile' object can become invalid if the object file
     it refers to is not loaded in GDB any longer.  All other
     'gdb.Objfile' methods will throw an exception if it is invalid at
     the time the method is called.

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File: gdb.info,  Node: Frames In Python,  Next: Blocks In Python,  Prev: Objfiles In Python,  Up: Python API

23.2.2.23 Accessing inferior stack frames from Python.
......................................................

When the debugged program stops, GDB is able to analyze its call stack
(*note Stack frames: Frames.).  The 'gdb.Frame' class represents a frame
in the stack.  A 'gdb.Frame' object is only valid while its
corresponding frame exists in the inferior's stack.  If you try to use
an invalid frame object, GDB will throw a 'gdb.error' exception (*note
Exception Handling::).

   Two 'gdb.Frame' objects can be compared for equality with the '=='
operator, like:

     (gdb) python print gdb.newest_frame() == gdb.selected_frame ()
     True

   The following frame-related functions are available in the 'gdb'
module:

 -- Function: gdb.selected_frame ()
     Return the selected frame object.  (*note Selecting a Frame:
     Selection.).

 -- Function: gdb.newest_frame ()
     Return the newest frame object for the selected thread.

 -- Function: gdb.frame_stop_reason_string (reason)
     Return a string explaining the reason why GDB stopped unwinding
     frames, as expressed by the given REASON code (an integer, see the
     'unwind_stop_reason' method further down in this section).

   A 'gdb.Frame' object has the following methods:

 -- Function: Frame.is_valid ()
     Returns true if the 'gdb.Frame' object is valid, false if not.  A
     frame object can become invalid if the frame it refers to doesn't
     exist anymore in the inferior.  All 'gdb.Frame' methods will throw
     an exception if it is invalid at the time the method is called.

 -- Function: Frame.name ()
     Returns the function name of the frame, or 'None' if it can't be
     obtained.

 -- Function: Frame.architecture ()
     Returns the 'gdb.Architecture' object corresponding to the frame's
     architecture.  *Note Architectures In Python::.

 -- Function: Frame.type ()
     Returns the type of the frame.  The value can be one of:
     'gdb.NORMAL_FRAME'
          An ordinary stack frame.

     'gdb.DUMMY_FRAME'
          A fake stack frame that was created by GDB when performing an
          inferior function call.

     'gdb.INLINE_FRAME'
          A frame representing an inlined function.  The function was
          inlined into a 'gdb.NORMAL_FRAME' that is older than this one.

     'gdb.TAILCALL_FRAME'
          A frame representing a tail call.  *Note Tail Call Frames::.

     'gdb.SIGTRAMP_FRAME'
          A signal trampoline frame.  This is the frame created by the
          OS when it calls into a signal handler.

     'gdb.ARCH_FRAME'
          A fake stack frame representing a cross-architecture call.

     'gdb.SENTINEL_FRAME'
          This is like 'gdb.NORMAL_FRAME', but it is only used for the
          newest frame.

 -- Function: Frame.unwind_stop_reason ()
     Return an integer representing the reason why it's not possible to
     find more frames toward the outermost frame.  Use
     'gdb.frame_stop_reason_string' to convert the value returned by
     this function to a string.  The value can be one of:

     'gdb.FRAME_UNWIND_NO_REASON'
          No particular reason (older frames should be available).

     'gdb.FRAME_UNWIND_NULL_ID'
          The previous frame's analyzer returns an invalid result.  This
          is no longer used by GDB, and is kept only for backward
          compatibility.

     'gdb.FRAME_UNWIND_OUTERMOST'
          This frame is the outermost.

     'gdb.FRAME_UNWIND_UNAVAILABLE'
          Cannot unwind further, because that would require knowing the
          values of registers or memory that have not been collected.

     'gdb.FRAME_UNWIND_INNER_ID'
          This frame ID looks like it ought to belong to a NEXT frame,
          but we got it for a PREV frame.  Normally, this is a sign of
          unwinder failure.  It could also indicate stack corruption.

     'gdb.FRAME_UNWIND_SAME_ID'
          This frame has the same ID as the previous one.  That means
          that unwinding further would almost certainly give us another
          frame with exactly the same ID, so break the chain.  Normally,
          this is a sign of unwinder failure.  It could also indicate
          stack corruption.

     'gdb.FRAME_UNWIND_NO_SAVED_PC'
          The frame unwinder did not find any saved PC, but we needed
          one to unwind further.

     'gdb.FRAME_UNWIND_MEMORY_ERROR'
          The frame unwinder caused an error while trying to access
          memory.

     'gdb.FRAME_UNWIND_FIRST_ERROR'
          Any stop reason greater or equal to this value indicates some
          kind of error.  This special value facilitates writing code
          that tests for errors in unwinding in a way that will work
          correctly even if the list of the other values is modified in
          future GDB versions.  Using it, you could write:
               reason = gdb.selected_frame().unwind_stop_reason ()
               reason_str =  gdb.frame_stop_reason_string (reason)
               if reason >=  gdb.FRAME_UNWIND_FIRST_ERROR:
                   print "An error occured: %s" % reason_str

 -- Function: Frame.pc ()
     Returns the frame's resume address.

 -- Function: Frame.block ()
     Return the frame's code block.  *Note Blocks In Python::.

 -- Function: Frame.function ()
     Return the symbol for the function corresponding to this frame.
     *Note Symbols In Python::.

 -- Function: Frame.older ()
     Return the frame that called this frame.

 -- Function: Frame.newer ()
     Return the frame called by this frame.

 -- Function: Frame.find_sal ()
     Return the frame's symtab and line object.  *Note Symbol Tables In
     Python::.

 -- Function: Frame.read_var (variable [, block])
     Return the value of VARIABLE in this frame.  If the optional
     argument BLOCK is provided, search for the variable from that
     block; otherwise start at the frame's current block (which is
     determined by the frame's current program counter).  The VARIABLE
     argument must be a string or a 'gdb.Symbol' object; BLOCK must be a
     'gdb.Block' object.

 -- Function: Frame.select ()
     Set this frame to be the selected frame.  *Note Examining the
     Stack: Stack.

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File: gdb.info,  Node: Blocks In Python,  Next: Symbols In Python,  Prev: Frames In Python,  Up: Python API

23.2.2.24 Accessing blocks from Python.
.......................................

In GDB, symbols are stored in blocks.  A block corresponds roughly to a
scope in the source code.  Blocks are organized hierarchically, and are
represented individually in Python as a 'gdb.Block'.  Blocks rely on
debugging information being available.

   A frame has a block.  Please see *note Frames In Python::, for a more
in-depth discussion of frames.

   The outermost block is known as the "global block".  The global block
typically holds public global variables and functions.

   The block nested just inside the global block is the "static block".
The static block typically holds file-scoped variables and functions.

   GDB provides a method to get a block's superblock, but there is
currently no way to examine the sub-blocks of a block, or to iterate
over all the blocks in a symbol table (*note Symbol Tables In Python::).

   Here is a short example that should help explain blocks:

     /* This is in the global block.  */
     int global;

     /* This is in the static block.  */
     static int file_scope;

     /* 'function' is in the global block, and 'argument' is
        in a block nested inside of 'function'.  */
     int function (int argument)
     {
       /* 'local' is in a block inside 'function'.  It may or may
          not be in the same block as 'argument'.  */
       int local;

       {
          /* 'inner' is in a block whose superblock is the one holding
             'local'.  */
          int inner;

          /* If this call is expanded by the compiler, you may see
             a nested block here whose function is 'inline_function'
             and whose superblock is the one holding 'inner'.  */
          inline_function ();
       }
     }

   A 'gdb.Block' is iterable.  The iterator returns the symbols (*note
Symbols In Python::) local to the block.  Python programs should not
assume that a specific block object will always contain a given symbol,
since changes in GDB features and infrastructure may cause symbols move
across blocks in a symbol table.

   The following block-related functions are available in the 'gdb'
module:

 -- Function: gdb.block_for_pc (pc)
     Return the innermost 'gdb.Block' containing the given PC value.  If
     the block cannot be found for the PC value specified, the function
     will return 'None'.

   A 'gdb.Block' object has the following methods:

 -- Function: Block.is_valid ()
     Returns 'True' if the 'gdb.Block' object is valid, 'False' if not.
     A block object can become invalid if the block it refers to doesn't
     exist anymore in the inferior.  All other 'gdb.Block' methods will
     throw an exception if it is invalid at the time the method is
     called.  The block's validity is also checked during iteration over
     symbols of the block.

   A 'gdb.Block' object has the following attributes:

 -- Variable: Block.start
     The start address of the block.  This attribute is not writable.

 -- Variable: Block.end
     The end address of the block.  This attribute is not writable.

 -- Variable: Block.function
     The name of the block represented as a 'gdb.Symbol'.  If the block
     is not named, then this attribute holds 'None'.  This attribute is
     not writable.

     For ordinary function blocks, the superblock is the static block.
     However, you should note that it is possible for a function block
     to have a superblock that is not the static block - for instance
     this happens for an inlined function.

 -- Variable: Block.superblock
     The block containing this block.  If this parent block does not
     exist, this attribute holds 'None'.  This attribute is not
     writable.

 -- Variable: Block.global_block
     The global block associated with this block.  This attribute is not
     writable.

 -- Variable: Block.static_block
     The static block associated with this block.  This attribute is not
     writable.

 -- Variable: Block.is_global
     'True' if the 'gdb.Block' object is a global block, 'False' if not.
     This attribute is not writable.

 -- Variable: Block.is_static
     'True' if the 'gdb.Block' object is a static block, 'False' if not.
     This attribute is not writable.

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File: gdb.info,  Node: Symbols In Python,  Next: Symbol Tables In Python,  Prev: Blocks In Python,  Up: Python API

23.2.2.25 Python representation of Symbols.
...........................................

GDB represents every variable, function and type as an entry in a symbol
table.  *Note Examining the Symbol Table: Symbols.  Similarly, Python
represents these symbols in GDB with the 'gdb.Symbol' object.

   The following symbol-related functions are available in the 'gdb'
module:

 -- Function: gdb.lookup_symbol (name [, block [, domain]])
     This function searches for a symbol by name.  The search scope can
     be restricted to the parameters defined in the optional domain and
     block arguments.

     NAME is the name of the symbol.  It must be a string.  The optional
     BLOCK argument restricts the search to symbols visible in that
     BLOCK.  The BLOCK argument must be a 'gdb.Block' object.  If
     omitted, the block for the current frame is used.  The optional
     DOMAIN argument restricts the search to the domain type.  The
     DOMAIN argument must be a domain constant defined in the 'gdb'
     module and described later in this chapter.

     The result is a tuple of two elements.  The first element is a
     'gdb.Symbol' object or 'None' if the symbol is not found.  If the
     symbol is found, the second element is 'True' if the symbol is a
     field of a method's object (e.g., 'this' in C++), otherwise it is
     'False'.  If the symbol is not found, the second element is
     'False'.

 -- Function: gdb.lookup_global_symbol (name [, domain])
     This function searches for a global symbol by name.  The search
     scope can be restricted to by the domain argument.

     NAME is the name of the symbol.  It must be a string.  The optional
     DOMAIN argument restricts the search to the domain type.  The
     DOMAIN argument must be a domain constant defined in the 'gdb'
     module and described later in this chapter.

     The result is a 'gdb.Symbol' object or 'None' if the symbol is not
     found.

   A 'gdb.Symbol' object has the following attributes:

 -- Variable: Symbol.type
     The type of the symbol or 'None' if no type is recorded.  This
     attribute is represented as a 'gdb.Type' object.  *Note Types In
     Python::.  This attribute is not writable.

 -- Variable: Symbol.symtab
     The symbol table in which the symbol appears.  This attribute is
     represented as a 'gdb.Symtab' object.  *Note Symbol Tables In
     Python::.  This attribute is not writable.

 -- Variable: Symbol.line
     The line number in the source code at which the symbol was defined.
     This is an integer.

 -- Variable: Symbol.name
     The name of the symbol as a string.  This attribute is not
     writable.

 -- Variable: Symbol.linkage_name
     The name of the symbol, as used by the linker (i.e., may be
     mangled).  This attribute is not writable.

 -- Variable: Symbol.print_name
     The name of the symbol in a form suitable for output.  This is
     either 'name' or 'linkage_name', depending on whether the user
     asked GDB to display demangled or mangled names.

 -- Variable: Symbol.addr_class
     The address class of the symbol.  This classifies how to find the
     value of a symbol.  Each address class is a constant defined in the
     'gdb' module and described later in this chapter.

 -- Variable: Symbol.needs_frame
     This is 'True' if evaluating this symbol's value requires a frame
     (*note Frames In Python::) and 'False' otherwise.  Typically, local
     variables will require a frame, but other symbols will not.

 -- Variable: Symbol.is_argument
     'True' if the symbol is an argument of a function.

 -- Variable: Symbol.is_constant
     'True' if the symbol is a constant.

 -- Variable: Symbol.is_function
     'True' if the symbol is a function or a method.

 -- Variable: Symbol.is_variable
     'True' if the symbol is a variable.

   A 'gdb.Symbol' object has the following methods:

 -- Function: Symbol.is_valid ()
     Returns 'True' if the 'gdb.Symbol' object is valid, 'False' if not.
     A 'gdb.Symbol' object can become invalid if the symbol it refers to
     does not exist in GDB any longer.  All other 'gdb.Symbol' methods
     will throw an exception if it is invalid at the time the method is
     called.

 -- Function: Symbol.value ([frame])
     Compute the value of the symbol, as a 'gdb.Value'.  For functions,
     this computes the address of the function, cast to the appropriate
     type.  If the symbol requires a frame in order to compute its
     value, then FRAME must be given.  If FRAME is not given, or if
     FRAME is invalid, then this method will throw an exception.

   The available domain categories in 'gdb.Symbol' are represented as
constants in the 'gdb' module:

'gdb.SYMBOL_UNDEF_DOMAIN'
     This is used when a domain has not been discovered or none of the
     following domains apply.  This usually indicates an error either in
     the symbol information or in GDB's handling of symbols.

'gdb.SYMBOL_VAR_DOMAIN'
     This domain contains variables, function names, typedef names and
     enum type values.

'gdb.SYMBOL_STRUCT_DOMAIN'
     This domain holds struct, union and enum type names.

'gdb.SYMBOL_LABEL_DOMAIN'
     This domain contains names of labels (for gotos).

'gdb.SYMBOL_VARIABLES_DOMAIN'
     This domain holds a subset of the 'SYMBOLS_VAR_DOMAIN'; it contains
     everything minus functions and types.

'gdb.SYMBOL_FUNCTION_DOMAIN'
     This domain contains all functions.

'gdb.SYMBOL_TYPES_DOMAIN'
     This domain contains all types.

   The available address class categories in 'gdb.Symbol' are
represented as constants in the 'gdb' module:

'gdb.SYMBOL_LOC_UNDEF'
     If this is returned by address class, it indicates an error either
     in the symbol information or in GDB's handling of symbols.

'gdb.SYMBOL_LOC_CONST'
     Value is constant int.

'gdb.SYMBOL_LOC_STATIC'
     Value is at a fixed address.

'gdb.SYMBOL_LOC_REGISTER'
     Value is in a register.

'gdb.SYMBOL_LOC_ARG'
     Value is an argument.  This value is at the offset stored within
     the symbol inside the frame's argument list.

'gdb.SYMBOL_LOC_REF_ARG'
     Value address is stored in the frame's argument list.  Just like
     'LOC_ARG' except that the value's address is stored at the offset,
     not the value itself.

'gdb.SYMBOL_LOC_REGPARM_ADDR'
     Value is a specified register.  Just like 'LOC_REGISTER' except the
     register holds the address of the argument instead of the argument
     itself.

'gdb.SYMBOL_LOC_LOCAL'
     Value is a local variable.

'gdb.SYMBOL_LOC_TYPEDEF'
     Value not used.  Symbols in the domain 'SYMBOL_STRUCT_DOMAIN' all
     have this class.

'gdb.SYMBOL_LOC_BLOCK'
     Value is a block.

'gdb.SYMBOL_LOC_CONST_BYTES'
     Value is a byte-sequence.

'gdb.SYMBOL_LOC_UNRESOLVED'
     Value is at a fixed address, but the address of the variable has to
     be determined from the minimal symbol table whenever the variable
     is referenced.

'gdb.SYMBOL_LOC_OPTIMIZED_OUT'
     The value does not actually exist in the program.

'gdb.SYMBOL_LOC_COMPUTED'
     The value's address is a computed location.

\1f
File: gdb.info,  Node: Symbol Tables In Python,  Next: Line Tables In Python,  Prev: Symbols In Python,  Up: Python API

23.2.2.26 Symbol table representation in Python.
................................................

Access to symbol table data maintained by GDB on the inferior is exposed
to Python via two objects: 'gdb.Symtab_and_line' and 'gdb.Symtab'.
Symbol table and line data for a frame is returned from the 'find_sal'
method in 'gdb.Frame' object.  *Note Frames In Python::.

   For more information on GDB's symbol table management, see *note
Examining the Symbol Table: Symbols, for more information.

   A 'gdb.Symtab_and_line' object has the following attributes:

 -- Variable: Symtab_and_line.symtab
     The symbol table object ('gdb.Symtab') for this frame.  This
     attribute is not writable.

 -- Variable: Symtab_and_line.pc
     Indicates the start of the address range occupied by code for the
     current source line.  This attribute is not writable.

 -- Variable: Symtab_and_line.last
     Indicates the end of the address range occupied by code for the
     current source line.  This attribute is not writable.

 -- Variable: Symtab_and_line.line
     Indicates the current line number for this object.  This attribute
     is not writable.

   A 'gdb.Symtab_and_line' object has the following methods:

 -- Function: Symtab_and_line.is_valid ()
     Returns 'True' if the 'gdb.Symtab_and_line' object is valid,
     'False' if not.  A 'gdb.Symtab_and_line' object can become invalid
     if the Symbol table and line object it refers to does not exist in
     GDB any longer.  All other 'gdb.Symtab_and_line' methods will throw
     an exception if it is invalid at the time the method is called.

   A 'gdb.Symtab' object has the following attributes:

 -- Variable: Symtab.filename
     The symbol table's source filename.  This attribute is not
     writable.

 -- Variable: Symtab.objfile
     The symbol table's backing object file.  *Note Objfiles In
     Python::.  This attribute is not writable.

   A 'gdb.Symtab' object has the following methods:

 -- Function: Symtab.is_valid ()
     Returns 'True' if the 'gdb.Symtab' object is valid, 'False' if not.
     A 'gdb.Symtab' object can become invalid if the symbol table it
     refers to does not exist in GDB any longer.  All other 'gdb.Symtab'
     methods will throw an exception if it is invalid at the time the
     method is called.

 -- Function: Symtab.fullname ()
     Return the symbol table's source absolute file name.

 -- Function: Symtab.global_block ()
     Return the global block of the underlying symbol table.  *Note
     Blocks In Python::.

 -- Function: Symtab.static_block ()
     Return the static block of the underlying symbol table.  *Note
     Blocks In Python::.

 -- Function: Symtab.linetable ()
     Return the line table associated with the symbol table.  *Note Line
     Tables In Python::.

\1f
File: gdb.info,  Node: Line Tables In Python,  Next: Breakpoints In Python,  Prev: Symbol Tables In Python,  Up: Python API

23.2.2.27 Manipulating line tables using Python
...............................................

Python code can request and inspect line table information from a symbol
table that is loaded in GDB.  A line table is a mapping of source lines
to their executable locations in memory.  To acquire the line table
information for a particular symbol table, use the 'linetable' function
(*note Symbol Tables In Python::).

   A 'gdb.LineTable' is iterable.  The iterator returns 'LineTableEntry'
objects that correspond to the source line and address for each line
table entry.  'LineTableEntry' objects have the following attributes:

 -- Variable: LineTableEntry.line
     The source line number for this line table entry.  This number
     corresponds to the actual line of source.  This attribute is not
     writable.

 -- Variable: LineTableEntry.pc
     The address that is associated with the line table entry where the
     executable code for that source line resides in memory.  This
     attribute is not writable.

   As there can be multiple addresses for a single source line, you may
receive multiple 'LineTableEntry' objects with matching 'line'
attributes, but with different 'pc' attributes.  The iterator is sorted
in ascending 'pc' order.  Here is a small example illustrating iterating
over a line table.

     symtab = gdb.selected_frame().find_sal().symtab
     linetable = symtab.linetable()
     for line in linetable:
        print "Line: "+str(line.line)+" Address: "+hex(line.pc)

   This will have the following output:

     Line: 33 Address: 0x4005c8L
     Line: 37 Address: 0x4005caL
     Line: 39 Address: 0x4005d2L
     Line: 40 Address: 0x4005f8L
     Line: 42 Address: 0x4005ffL
     Line: 44 Address: 0x400608L
     Line: 42 Address: 0x40060cL
     Line: 45 Address: 0x400615L

   In addition to being able to iterate over a 'LineTable', it also has
the following direct access methods:

 -- Function: LineTable.line (line)
     Return a Python 'Tuple' of 'LineTableEntry' objects for any entries
     in the line table for the given LINE, which specifies the source
     code line.  If there are no entries for that source code LINE, the
     Python 'None' is returned.

 -- Function: LineTable.has_line (line)
     Return a Python 'Boolean' indicating whether there is an entry in
     the line table for this source line.  Return 'True' if an entry is
     found, or 'False' if not.

 -- Function: LineTable.source_lines ()
     Return a Python 'List' of the source line numbers in the symbol
     table.  Only lines with executable code locations are returned.
     The contents of the 'List' will just be the source line entries
     represented as Python 'Long' values.

\1f
File: gdb.info,  Node: Breakpoints In Python,  Next: Finish Breakpoints in Python,  Prev: Line Tables In Python,  Up: Python API

23.2.2.28 Manipulating breakpoints using Python
...............................................

Python code can manipulate breakpoints via the 'gdb.Breakpoint' class.

 -- Function: Breakpoint.__init__ (spec [, type [, wp_class [,internal
          [,temporary]]]])
     Create a new breakpoint according to SPEC, which is a string naming
     the location of the breakpoint, or an expression that defines a
     watchpoint.  The contents can be any location recognized by the
     'break' command, or in the case of a watchpoint, by the 'watch'
     command.  The optional TYPE denotes the breakpoint to create from
     the types defined later in this chapter.  This argument can be
     either 'gdb.BP_BREAKPOINT' or 'gdb.BP_WATCHPOINT'; it defaults to
     'gdb.BP_BREAKPOINT'.  The optional INTERNAL argument allows the
     breakpoint to become invisible to the user.  The breakpoint will
     neither be reported when created, nor will it be listed in the
     output from 'info breakpoints' (but will be listed with the 'maint
     info breakpoints' command).  The optional TEMPORARY argument makes
     the breakpoint a temporary breakpoint.  Temporary breakpoints are
     deleted after they have been hit.  Any further access to the Python
     breakpoint after it has been hit will result in a runtime error (as
     that breakpoint has now been automatically deleted).  The optional
     WP_CLASS argument defines the class of watchpoint to create, if
     TYPE is 'gdb.BP_WATCHPOINT'.  If a watchpoint class is not
     provided, it is assumed to be a 'gdb.WP_WRITE' class.

 -- Function: Breakpoint.stop (self)
     The 'gdb.Breakpoint' class can be sub-classed and, in particular,
     you may choose to implement the 'stop' method.  If this method is
     defined in a sub-class of 'gdb.Breakpoint', it will be called when
     the inferior reaches any location of a breakpoint which
     instantiates that sub-class.  If the method returns 'True', the
     inferior will be stopped at the location of the breakpoint,
     otherwise the inferior will continue.

     If there are multiple breakpoints at the same location with a
     'stop' method, each one will be called regardless of the return
     status of the previous.  This ensures that all 'stop' methods have
     a chance to execute at that location.  In this scenario if one of
     the methods returns 'True' but the others return 'False', the
     inferior will still be stopped.

     You should not alter the execution state of the inferior (i.e.,
     step, next, etc.), alter the current frame context (i.e., change
     the current active frame), or alter, add or delete any breakpoint.
     As a general rule, you should not alter any data within GDB or the
     inferior at this time.

     Example 'stop' implementation:

          class MyBreakpoint (gdb.Breakpoint):
                def stop (self):
                  inf_val = gdb.parse_and_eval("foo")
                  if inf_val == 3:
                    return True
                  return False

   The available watchpoint types represented by constants are defined
in the 'gdb' module:

'gdb.WP_READ'
     Read only watchpoint.

'gdb.WP_WRITE'
     Write only watchpoint.

'gdb.WP_ACCESS'
     Read/Write watchpoint.

 -- Function: Breakpoint.is_valid ()
     Return 'True' if this 'Breakpoint' object is valid, 'False'
     otherwise.  A 'Breakpoint' object can become invalid if the user
     deletes the breakpoint.  In this case, the object still exists, but
     the underlying breakpoint does not.  In the cases of watchpoint
     scope, the watchpoint remains valid even if execution of the
     inferior leaves the scope of that watchpoint.

 -- Function: Breakpoint.delete
     Permanently deletes the GDB breakpoint.  This also invalidates the
     Python 'Breakpoint' object.  Any further access to this object's
     attributes or methods will raise an error.

 -- Variable: Breakpoint.enabled
     This attribute is 'True' if the breakpoint is enabled, and 'False'
     otherwise.  This attribute is writable.

 -- Variable: Breakpoint.silent
     This attribute is 'True' if the breakpoint is silent, and 'False'
     otherwise.  This attribute is writable.

     Note that a breakpoint can also be silent if it has commands and
     the first command is 'silent'.  This is not reported by the
     'silent' attribute.

 -- Variable: Breakpoint.thread
     If the breakpoint is thread-specific, this attribute holds the
     thread id.  If the breakpoint is not thread-specific, this
     attribute is 'None'.  This attribute is writable.

 -- Variable: Breakpoint.task
     If the breakpoint is Ada task-specific, this attribute holds the
     Ada task id.  If the breakpoint is not task-specific (or the
     underlying language is not Ada), this attribute is 'None'.  This
     attribute is writable.

 -- Variable: Breakpoint.ignore_count
     This attribute holds the ignore count for the breakpoint, an
     integer.  This attribute is writable.

 -- Variable: Breakpoint.number
     This attribute holds the breakpoint's number -- the identifier used
     by the user to manipulate the breakpoint.  This attribute is not
     writable.

 -- Variable: Breakpoint.type
     This attribute holds the breakpoint's type -- the identifier used
     to determine the actual breakpoint type or use-case.  This
     attribute is not writable.

 -- Variable: Breakpoint.visible
     This attribute tells whether the breakpoint is visible to the user
     when set, or when the 'info breakpoints' command is run.  This
     attribute is not writable.

 -- Variable: Breakpoint.temporary
     This attribute indicates whether the breakpoint was created as a
     temporary breakpoint.  Temporary breakpoints are automatically
     deleted after that breakpoint has been hit.  Access to this
     attribute, and all other attributes and functions other than the
     'is_valid' function, will result in an error after the breakpoint
     has been hit (as it has been automatically deleted).  This
     attribute is not writable.

   The available types are represented by constants defined in the 'gdb'
module:

'gdb.BP_BREAKPOINT'
     Normal code breakpoint.

'gdb.BP_WATCHPOINT'
     Watchpoint breakpoint.

'gdb.BP_HARDWARE_WATCHPOINT'
     Hardware assisted watchpoint.

'gdb.BP_READ_WATCHPOINT'
     Hardware assisted read watchpoint.

'gdb.BP_ACCESS_WATCHPOINT'
     Hardware assisted access watchpoint.

 -- Variable: Breakpoint.hit_count
     This attribute holds the hit count for the breakpoint, an integer.
     This attribute is writable, but currently it can only be set to
     zero.

 -- Variable: Breakpoint.location
     This attribute holds the location of the breakpoint, as specified
     by the user.  It is a string.  If the breakpoint does not have a
     location (that is, it is a watchpoint) the attribute's value is
     'None'.  This attribute is not writable.

 -- Variable: Breakpoint.expression
     This attribute holds a breakpoint expression, as specified by the
     user.  It is a string.  If the breakpoint does not have an
     expression (the breakpoint is not a watchpoint) the attribute's
     value is 'None'.  This attribute is not writable.

 -- Variable: Breakpoint.condition
     This attribute holds the condition of the breakpoint, as specified
     by the user.  It is a string.  If there is no condition, this
     attribute's value is 'None'.  This attribute is writable.

 -- Variable: Breakpoint.commands
     This attribute holds the commands attached to the breakpoint.  If
     there are commands, this attribute's value is a string holding all
     the commands, separated by newlines.  If there are no commands,
     this attribute is 'None'.  This attribute is not writable.

\1f
File: gdb.info,  Node: Finish Breakpoints in Python,  Next: Lazy Strings In Python,  Prev: Breakpoints In Python,  Up: Python API

23.2.2.29 Finish Breakpoints
............................

A finish breakpoint is a temporary breakpoint set at the return address
of a frame, based on the 'finish' command.  'gdb.FinishBreakpoint'
extends 'gdb.Breakpoint'.  The underlying breakpoint will be disabled
and deleted when the execution will run out of the breakpoint scope
(i.e. 'Breakpoint.stop' or 'FinishBreakpoint.out_of_scope' triggered).
Finish breakpoints are thread specific and must be create with the right
thread selected.

 -- Function: FinishBreakpoint.__init__ ([frame] [, internal])
     Create a finish breakpoint at the return address of the 'gdb.Frame'
     object FRAME.  If FRAME is not provided, this defaults to the
     newest frame.  The optional INTERNAL argument allows the breakpoint
     to become invisible to the user.  *Note Breakpoints In Python::,
     for further details about this argument.

 -- Function: FinishBreakpoint.out_of_scope (self)
     In some circumstances (e.g. 'longjmp', C++ exceptions, GDB 'return'
     command, ...), a function may not properly terminate, and thus
     never hit the finish breakpoint.  When GDB notices such a
     situation, the 'out_of_scope' callback will be triggered.

     You may want to sub-class 'gdb.FinishBreakpoint' and override this
     method:

          class MyFinishBreakpoint (gdb.FinishBreakpoint)
              def stop (self):
                  print "normal finish"
                  return True

              def out_of_scope ():
                  print "abnormal finish"

 -- Variable: FinishBreakpoint.return_value
     When GDB is stopped at a finish breakpoint and the frame used to
     build the 'gdb.FinishBreakpoint' object had debug symbols, this
     attribute will contain a 'gdb.Value' object corresponding to the
     return value of the function.  The value will be 'None' if the
     function return type is 'void' or if the return value was not
     computable.  This attribute is not writable.

\1f
File: gdb.info,  Node: Lazy Strings In Python,  Next: Architectures In Python,  Prev: Finish Breakpoints in Python,  Up: Python API

23.2.2.30 Python representation of lazy strings.
................................................

A "lazy string" is a string whose contents is not retrieved or encoded
until it is needed.

   A 'gdb.LazyString' is represented in GDB as an 'address' that points
to a region of memory, an 'encoding' that will be used to encode that
region of memory, and a 'length' to delimit the region of memory that
represents the string.  The difference between a 'gdb.LazyString' and a
string wrapped within a 'gdb.Value' is that a 'gdb.LazyString' will be
treated differently by GDB when printing.  A 'gdb.LazyString' is
retrieved and encoded during printing, while a 'gdb.Value' wrapping a
string is immediately retrieved and encoded on creation.

   A 'gdb.LazyString' object has the following functions:

 -- Function: LazyString.value ()
     Convert the 'gdb.LazyString' to a 'gdb.Value'.  This value will
     point to the string in memory, but will lose all the delayed
     retrieval, encoding and handling that GDB applies to a
     'gdb.LazyString'.

 -- Variable: LazyString.address
     This attribute holds the address of the string.  This attribute is
     not writable.

 -- Variable: LazyString.length
     This attribute holds the length of the string in characters.  If
     the length is -1, then the string will be fetched and encoded up to
     the first null of appropriate width.  This attribute is not
     writable.

 -- Variable: LazyString.encoding
     This attribute holds the encoding that will be applied to the
     string when the string is printed by GDB.  If the encoding is not
     set, or contains an empty string, then GDB will select the most
     appropriate encoding when the string is printed.  This attribute is
     not writable.

 -- Variable: LazyString.type
     This attribute holds the type that is represented by the lazy
     string's type.  For a lazy string this will always be a pointer
     type.  To resolve this to the lazy string's character type, use the
     type's 'target' method.  *Note Types In Python::.  This attribute
     is not writable.

\1f
File: gdb.info,  Node: Architectures In Python,  Prev: Lazy Strings In Python,  Up: Python API

23.2.2.31 Python representation of architectures
................................................

GDB uses architecture specific parameters and artifacts in a number of
its various computations.  An architecture is represented by an instance
of the 'gdb.Architecture' class.

   A 'gdb.Architecture' class has the following methods:

 -- Function: Architecture.name ()
     Return the name (string value) of the architecture.

 -- Function: Architecture.disassemble (START_PC [, END_PC [, COUNT]])
     Return a list of disassembled instructions starting from the memory
     address START_PC.  The optional arguments END_PC and COUNT
     determine the number of instructions in the returned list.  If both
     the optional arguments END_PC and COUNT are specified, then a list
     of at most COUNT disassembled instructions whose start address
     falls in the closed memory address interval from START_PC to END_PC
     are returned.  If END_PC is not specified, but COUNT is specified,
     then COUNT number of instructions starting from the address
     START_PC are returned.  If COUNT is not specified but END_PC is
     specified, then all instructions whose start address falls in the
     closed memory address interval from START_PC to END_PC are
     returned.  If neither END_PC nor COUNT are specified, then a single
     instruction at START_PC is returned.  For all of these cases, each
     element of the returned list is a Python 'dict' with the following
     string keys:

     'addr'
          The value corresponding to this key is a Python long integer
          capturing the memory address of the instruction.

     'asm'
          The value corresponding to this key is a string value which
          represents the instruction with assembly language mnemonics.
          The assembly language flavor used is the same as that
          specified by the current CLI variable 'disassembly-flavor'.
          *Note Machine Code::.

     'length'
          The value corresponding to this key is the length (integer
          value) of the instruction in bytes.

\1f
File: gdb.info,  Node: Python Auto-loading,  Next: Python modules,  Prev: Python API,  Up: Python

23.2.3 Python Auto-loading
--------------------------

When a new object file is read (for example, due to the 'file' command,
or because the inferior has loaded a shared library), GDB will look for
Python support scripts in several ways: 'OBJFILE-gdb.py' and
'.debug_gdb_scripts' section.  *Note Auto-loading extensions::.

   The auto-loading feature is useful for supplying application-specific
debugging commands and scripts.

   Auto-loading can be enabled or disabled, and the list of auto-loaded
scripts can be printed.

'set auto-load python-scripts [on|off]'
     Enable or disable the auto-loading of Python scripts.

'show auto-load python-scripts'
     Show whether auto-loading of Python scripts is enabled or disabled.

'info auto-load python-scripts [REGEXP]'
     Print the list of all Python scripts that GDB auto-loaded.

     Also printed is the list of Python scripts that were mentioned in
     the '.debug_gdb_scripts' section and were not found (*note
     dotdebug_gdb_scripts section::).  This is useful because their
     names are not printed when GDB tries to load them and fails.  There
     may be many of them, and printing an error message for each one is
     problematic.

     If REGEXP is supplied only Python scripts with matching names are
     printed.

     Example:

          (gdb) info auto-load python-scripts
          Loaded Script
          Yes    py-section-script.py
                 full name: /tmp/py-section-script.py
          No     my-foo-pretty-printers.py

   When reading an auto-loaded file, GDB sets the "current objfile".
This is available via the 'gdb.current_objfile' function (*note Objfiles
In Python::).  This can be useful for registering objfile-specific
pretty-printers and frame-filters.

\1f
File: gdb.info,  Node: Python modules,  Prev: Python Auto-loading,  Up: Python

23.2.4 Python modules
---------------------

GDB comes with several modules to assist writing Python code.

* Menu:

* gdb.printing::       Building and registering pretty-printers.
* gdb.types::          Utilities for working with types.
* gdb.prompt::         Utilities for prompt value substitution.

\1f
File: gdb.info,  Node: gdb.printing,  Next: gdb.types,  Up: Python modules

23.2.4.1 gdb.printing
.....................

This module provides a collection of utilities for working with
pretty-printers.

'PrettyPrinter (NAME, SUBPRINTERS=None)'
     This class specifies the API that makes 'info pretty-printer',
     'enable pretty-printer' and 'disable pretty-printer' work.
     Pretty-printers should generally inherit from this class.

'SubPrettyPrinter (NAME)'
     For printers that handle multiple types, this class specifies the
     corresponding API for the subprinters.

'RegexpCollectionPrettyPrinter (NAME)'
     Utility class for handling multiple printers, all recognized via
     regular expressions.  *Note Writing a Pretty-Printer::, for an
     example.

'FlagEnumerationPrinter (NAME)'
     A pretty-printer which handles printing of 'enum' values.  Unlike
     GDB's built-in 'enum' printing, this printer attempts to work
     properly when there is some overlap between the enumeration
     constants.  The argument NAME is the name of the printer and also
     the name of the 'enum' type to look up.

'register_pretty_printer (OBJ, PRINTER, REPLACE=False)'
     Register PRINTER with the pretty-printer list of OBJ.  If REPLACE
     is 'True' then any existing copy of the printer is replaced.
     Otherwise a 'RuntimeError' exception is raised if a printer with
     the same name already exists.

\1f
File: gdb.info,  Node: gdb.types,  Next: gdb.prompt,  Prev: gdb.printing,  Up: Python modules

23.2.4.2 gdb.types
..................

This module provides a collection of utilities for working with
'gdb.Type' objects.

'get_basic_type (TYPE)'
     Return TYPE with const and volatile qualifiers stripped, and with
     typedefs and C++ references converted to the underlying type.

     C++ example:

          typedef const int const_int;
          const_int foo (3);
          const_int& foo_ref (foo);
          int main () { return 0; }

     Then in gdb:

          (gdb) start
          (gdb) python import gdb.types
          (gdb) python foo_ref = gdb.parse_and_eval("foo_ref")
          (gdb) python print gdb.types.get_basic_type(foo_ref.type)
          int

'has_field (TYPE, FIELD)'
     Return 'True' if TYPE, assumed to be a type with fields (e.g., a
     structure or union), has field FIELD.

'make_enum_dict (ENUM_TYPE)'
     Return a Python 'dictionary' type produced from ENUM_TYPE.

'deep_items (TYPE)'
     Returns a Python iterator similar to the standard
     'gdb.Type.iteritems' method, except that the iterator returned by
     'deep_items' will recursively traverse anonymous struct or union
     fields.  For example:

          struct A
          {
              int a;
              union {
                  int b0;
                  int b1;
              };
          };

     Then in GDB:
          (gdb) python import gdb.types
          (gdb) python struct_a = gdb.lookup_type("struct A")
          (gdb) python print struct_a.keys ()
          {['a', '']}
          (gdb) python print [k for k,v in gdb.types.deep_items(struct_a)]
          {['a', 'b0', 'b1']}

'get_type_recognizers ()'
     Return a list of the enabled type recognizers for the current
     context.  This is called by GDB during the type-printing process
     (*note Type Printing API::).

'apply_type_recognizers (recognizers, type_obj)'
     Apply the type recognizers, RECOGNIZERS, to the type object
     TYPE_OBJ.  If any recognizer returns a string, return that string.
     Otherwise, return 'None'.  This is called by GDB during the
     type-printing process (*note Type Printing API::).

'register_type_printer (locus, printer)'
     This is a convenience function to register a type printer PRINTER.
     The printer must implement the type printer protocol.  The LOCUS
     argument is either a 'gdb.Objfile', in which case the printer is
     registered with that objfile; a 'gdb.Progspace', in which case the
     printer is registered with that progspace; or 'None', in which case
     the printer is registered globally.

'TypePrinter'
     This is a base class that implements the type printer protocol.
     Type printers are encouraged, but not required, to derive from this
     class.  It defines a constructor:

      -- Method on TypePrinter: __init__ (self, name)
          Initialize the type printer with the given name.  The new
          printer starts in the enabled state.

\1f
File: gdb.info,  Node: gdb.prompt,  Prev: gdb.types,  Up: Python modules

23.2.4.3 gdb.prompt
...................

This module provides a method for prompt value-substitution.

'substitute_prompt (STRING)'
     Return STRING with escape sequences substituted by values.  Some
     escape sequences take arguments.  You can specify arguments inside
     "{}" immediately following the escape sequence.

     The escape sequences you can pass to this function are:

     '\\'
          Substitute a backslash.
     '\e'
          Substitute an ESC character.
     '\f'
          Substitute the selected frame; an argument names a frame
          parameter.
     '\n'
          Substitute a newline.
     '\p'
          Substitute a parameter's value; the argument names the
          parameter.
     '\r'
          Substitute a carriage return.
     '\t'
          Substitute the selected thread; an argument names a thread
          parameter.
     '\v'
          Substitute the version of GDB.
     '\w'
          Substitute the current working directory.
     '\['
          Begin a sequence of non-printing characters.  These sequences
          are typically used with the ESC character, and are not counted
          in the string length.  Example: "\[\e[0;34m\](gdb)\[\e[0m\]"
          will return a blue-colored "(gdb)" prompt where the length is
          five.
     '\]'
          End a sequence of non-printing characters.

     For example:

          substitute_prompt (``frame: \f,
                             print arguments: \p{print frame-arguments}'')

will return the string:

          "frame: main, print arguments: scalars"

\1f
File: gdb.info,  Node: Guile,  Next: Auto-loading extensions,  Prev: Python,  Up: Extending GDB

23.3 Extending GDB using Guile
==============================

You can extend GDB using the Guile implementation of the Scheme
programming language (http://www.gnu.org/software/guile/).  This feature
is available only if GDB was configured using '--with-guile'.

* Menu:

* Guile Introduction::     Introduction to Guile scripting in GDB
* Guile Commands::         Accessing Guile from GDB
* Guile API::              Accessing GDB from Guile
* Guile Auto-loading::     Automatically loading Guile code
* Guile Modules::          Guile modules provided by GDB

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File: gdb.info,  Node: Guile Introduction,  Next: Guile Commands,  Up: Guile

23.3.1 Guile Introduction
-------------------------

Guile is an implementation of the Scheme programming language and is the
GNU project's official extension language.

   Guile support in GDB follows the Python support in GDB reasonably
closely, so concepts there should carry over.  However, some things are
done differently where it makes sense.

   GDB requires Guile version 2.0 or greater.  Older versions are not
supported.

   Guile scripts used by GDB should be installed in
'DATA-DIRECTORY/guile', where DATA-DIRECTORY is the data directory as
determined at GDB startup (*note Data Files::).  This directory, known
as the "guile directory", is automatically added to the Guile Search
Path in order to allow the Guile interpreter to locate all scripts
installed at this location.

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File: gdb.info,  Node: Guile Commands,  Next: Guile API,  Prev: Guile Introduction,  Up: Guile

23.3.2 Guile Commands
---------------------

GDB provides two commands for accessing the Guile interpreter:

'guile-repl'
'gr'
     The 'guile-repl' command can be used to start an interactive Guile
     prompt or "repl".  To return to GDB, type ',q' or the 'EOF'
     character (e.g., 'Ctrl-D' on an empty prompt).  These commands do
     not take any arguments.

'guile [SCHEME-EXPRESSION]'
'gu [SCHEME-EXPRESSION]'
     The 'guile' command can be used to evaluate a Scheme expression.

     If given an argument, GDB will pass the argument to the Guile
     interpreter for evaluation.

          (gdb) guile (display (+ 20 3)) (newline)
          23

     The result of the Scheme expression is displayed using normal Guile
     rules.

          (gdb) guile (+ 20 3)
          23

     If you do not provide an argument to 'guile', it will act as a
     multi-line command, like 'define'.  In this case, the Guile script
     is made up of subsequent command lines, given after the 'guile'
     command.  This command list is terminated using a line containing
     'end'.  For example:

          (gdb) guile
          >(display 23)
          >(newline)
          >end
          23

   It is also possible to execute a Guile script from the GDB
interpreter:

'source script-name'
     The script name must end with '.scm' and GDB must be configured to
     recognize the script language based on filename extension using the
     'script-extension' setting.  *Note Extending GDB: Extending GDB.

'guile (load "script-name")'
     This method uses the 'load' Guile function.  It takes a string
     argument that is the name of the script to load.  See the Guile
     documentation for a description of this function.  (*note
     (guile)Loading::).

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File: gdb.info,  Node: Guile API,  Next: Guile Auto-loading,  Prev: Guile Commands,  Up: Guile

23.3.3 Guile API
----------------

You can get quick online help for GDB's Guile API by issuing the command
'help guile', or by issuing the command ',help' from an interactive
Guile session.  Furthermore, most Guile procedures provided by GDB have
doc strings which can be obtained with ',describe PROCEDURE-NAME' or ',d
PROCEDURE-NAME' from the Guile interactive prompt.

* Menu:

* Basic Guile::              Basic Guile Functions
* Guile Configuration::      Guile configuration variables
* GDB Scheme Data Types::    Scheme representations of GDB objects
* Guile Exception Handling:: How Guile exceptions are translated
* Values From Inferior In Guile:: Guile representation of values
* Arithmetic In Guile::      Arithmetic in Guile
* Types In Guile::           Guile representation of types
* Guile Pretty Printing API:: Pretty-printing values with Guile
* Selecting Guile Pretty-Printers:: How GDB chooses a pretty-printer
* Writing a Guile Pretty-Printer:: Writing a pretty-printer
* Commands In Guile::        Implementing new commands in Guile
* Parameters In Guile::      Adding new GDB parameters
* Progspaces In Guile::      Program spaces
* Objfiles In Guile::        Object files in Guile
* Frames In Guile::          Accessing inferior stack frames from Guile
* Blocks In Guile::          Accessing blocks from Guile
* Symbols In Guile::         Guile representation of symbols
* Symbol Tables In Guile::   Guile representation of symbol tables
* Breakpoints In Guile::     Manipulating breakpoints using Guile
* Lazy Strings In Guile::    Guile representation of lazy strings
* Architectures In Guile::   Guile representation of architectures
* Disassembly In Guile::     Disassembling instructions from Guile
* I/O Ports in Guile::       GDB I/O ports
* Memory Ports in Guile::    Accessing memory through ports and bytevectors
* Iterators In Guile::       Basic iterator support

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File: gdb.info,  Node: Basic Guile,  Next: Guile Configuration,  Up: Guile API

23.3.3.1 Basic Guile
....................

At startup, GDB overrides Guile's 'current-output-port' and
'current-error-port' to print using GDB's output-paging streams.  A
Guile program which outputs to one of these streams may have its output
interrupted by the user (*note Screen Size::).  In this situation, a
Guile 'signal' exception is thrown with value 'SIGINT'.

   Guile's history mechanism uses the same naming as GDB's, namely the
user of dollar-variables (e.g., $1, $2, etc.).  The results of
evaluations in Guile and in GDB are counted separately, '$1' in Guile is
not the same value as '$1' in GDB.

   GDB is not thread-safe.  If your Guile program uses multiple threads,
you must be careful to only call GDB-specific functions in the GDB
thread.

   Some care must be taken when writing Guile code to run in GDB.  Two
things are worth noting in particular:

   * GDB installs handlers for 'SIGCHLD' and 'SIGINT'.  Guile code must
     not override these, or even change the options using 'sigaction'.
     If your program changes the handling of these signals, GDB will
     most likely stop working correctly.  Note that it is unfortunately
     common for GUI toolkits to install a 'SIGCHLD' handler.

   * GDB takes care to mark its internal file descriptors as
     close-on-exec.  However, this cannot be done in a thread-safe way
     on all platforms.  Your Guile programs should be aware of this and
     should both create new file descriptors with the close-on-exec flag
     set and arrange to close unneeded file descriptors before starting
     a child process.

   GDB introduces a new Guile module, named 'gdb'.  All methods and
classes added by GDB are placed in this module.  GDB does not
automatically 'import' the 'gdb' module, scripts must do this
themselves.  There are various options for how to import a module, so
GDB leaves the choice of how the 'gdb' module is imported to the user.
To simplify interactive use, it is recommended to add one of the
following to your ~/.gdbinit.

     guile (use-modules (gdb))

     guile (use-modules ((gdb) #:renamer (symbol-prefix-proc 'gdb:)))

   Which one to choose depends on your preference.  The second one adds
'gdb:' as a prefix to all module functions and variables.

   The rest of this manual assumes the 'gdb' module has been imported
without any prefix.  See the Guile documentation for 'use-modules' for
more information (*note (guile)Using Guile Modules::).

   Example:

     (gdb) guile (value-type (make-value 1))
     ERROR: Unbound variable: value-type
     Error while executing Scheme code.
     (gdb) guile (use-modules (gdb))
     (gdb) guile (value-type (make-value 1))
     int
     (gdb)

   The '(gdb)' module provides these basic Guile functions.

 -- Scheme Procedure: execute command [#:from-tty boolean] [#:to-string
          boolean]
     Evaluate COMMAND, a string, as a GDB CLI command.  If a GDB
     exception happens while COMMAND runs, it is translated as described
     in *note Guile Exception Handling: Guile Exception Handling.

     FROM-TTY specifies whether GDB ought to consider this command as
     having originated from the user invoking it interactively.  It must
     be a boolean value.  If omitted, it defaults to '#f'.

     By default, any output produced by COMMAND is sent to GDB's
     standard output (and to the log output if logging is turned on).
     If the TO-STRING parameter is '#t', then output will be collected
     by 'execute' and returned as a string.  The default is '#f', in
     which case the return value is unspecified.  If TO-STRING is '#t',
     the GDB virtual terminal will be temporarily set to unlimited width
     and height, and its pagination will be disabled; *note Screen
     Size::.

 -- Scheme Procedure: history-ref number
     Return a value from GDB's value history (*note Value History::).
     The NUMBER argument indicates which history element to return.  If
     NUMBER is negative, then GDB will take its absolute value and count
     backward from the last element (i.e., the most recent element) to
     find the value to return.  If NUMBER is zero, then GDB will return
     the most recent element.  If the element specified by NUMBER
     doesn't exist in the value history, a 'gdb:error' exception will be
     raised.

     If no exception is raised, the return value is always an instance
     of '<gdb:value>' (*note Values From Inferior In Guile::).

     _Note:_ GDB's value history is independent of Guile's.  '$1' in
     GDB's value history contains the result of evaluating an expression
     from GDB's command line and '$1' from Guile's history contains the
     result of evaluating an expression from Guile's command line.

 -- Scheme Procedure: history-append! value
     Append VALUE, an instance of '<gdb:value>', to GDB's value history.
     Return its index in the history.

     Putting into history values returned by Guile extensions will allow
     the user convenient access to those values via CLI history
     facilities.

 -- Scheme Procedure: parse-and-eval expression
     Parse EXPRESSION as an expression in the current language, evaluate
     it, and return the result as a '<gdb:value>'.  The EXPRESSION must
     be a string.

     This function can be useful when implementing a new command (*note
     Commands In Guile::), as it provides a way to parse the command's
     arguments as an expression.  It is also is useful when computing
     values.  For example, it is the only way to get the value of a
     convenience variable (*note Convenience Vars::) as a '<gdb:value>'.

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File: gdb.info,  Node: Guile Configuration,  Next: GDB Scheme Data Types,  Prev: Basic Guile,  Up: Guile API

23.3.3.2 Guile Configuration
............................

GDB provides these Scheme functions to access various configuration
parameters.

 -- Scheme Procedure: data-directory
     Return a string containing GDB's data directory.  This directory
     contains GDB's ancillary files.

 -- Scheme Procedure: guile-data-directory
     Return a string containing GDB's Guile data directory.  This
     directory contains the Guile modules provided by GDB.

 -- Scheme Procedure: gdb-version
     Return a string containing the GDB version.

 -- Scheme Procedure: host-config
     Return a string containing the host configuration.  This is the
     string passed to '--host' when GDB was configured.

 -- Scheme Procedure: target-config
     Return a string containing the target configuration.  This is the
     string passed to '--target' when GDB was configured.

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File: gdb.info,  Node: GDB Scheme Data Types,  Next: Guile Exception Handling,  Prev: Guile Configuration,  Up: Guile API

23.3.3.3 GDB Scheme Data Types
..............................

The values exposed by GDB to Guile are known as "GDB objects".  There
are several kinds of GDB object, and each is disjoint from all other
types known to Guile.

 -- Scheme Procedure: gdb-object-kind object
     Return the kind of the GDB object, e.g., '<gdb:breakpoint>', as a
     symbol.

   GDB defines the following object types:

'<gdb:arch>'
     *Note Architectures In Guile::.

'<gdb:block>'
     *Note Blocks In Guile::.

'<gdb:block-symbols-iterator>'
     *Note Blocks In Guile::.

'<gdb:breakpoint>'
     *Note Breakpoints In Guile::.

'<gdb:command>'
     *Note Commands In Guile::.

'<gdb:exception>'
     *Note Guile Exception Handling::.

'<gdb:frame>'
     *Note Frames In Guile::.

'<gdb:iterator>'
     *Note Iterators In Guile::.

'<gdb:lazy-string>'
     *Note Lazy Strings In Guile::.

'<gdb:objfile>'
     *Note Objfiles In Guile::.

'<gdb:parameter>'
     *Note Parameters In Guile::.

'<gdb:pretty-printer>'
     *Note Guile Pretty Printing API::.

'<gdb:pretty-printer-worker>'
     *Note Guile Pretty Printing API::.

'<gdb:progspace>'
     *Note Progspaces In Guile::.

'<gdb:symbol>'
     *Note Symbols In Guile::.

'<gdb:symtab>'
     *Note Symbol Tables In Guile::.

'<gdb:sal>'
     *Note Symbol Tables In Guile::.

'<gdb:type>'
     *Note Types In Guile::.

'<gdb:field>'
     *Note Types In Guile::.

'<gdb:value>'
     *Note Values From Inferior In Guile::.

   The following GDB objects are managed internally so that the Scheme
function 'eq?' may be applied to them.

'<gdb:arch>'
'<gdb:block>'
'<gdb:breakpoint>'
'<gdb:frame>'
'<gdb:objfile>'
'<gdb:progspace>'
'<gdb:symbol>'
'<gdb:symtab>'
'<gdb:type>'

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File: gdb.info,  Node: Guile Exception Handling,  Next: Values From Inferior In Guile,  Prev: GDB Scheme Data Types,  Up: Guile API

23.3.3.4 Guile Exception Handling
.................................

When executing the 'guile' command, Guile exceptions uncaught within the
Guile code are translated to calls to the GDB error-reporting mechanism.
If the command that called 'guile' does not handle the error, GDB will
terminate it and report the error according to the setting of the 'guile
print-stack' parameter.

   The 'guile print-stack' parameter has three settings:

'none'
     Nothing is printed.

'message'
     An error message is printed containing the Guile exception name,
     the associated value, and the Guile call stack backtrace at the
     point where the exception was raised.  Example:

          (gdb) guile (display foo)
          ERROR: In procedure memoize-variable-access!:
          ERROR: Unbound variable: foo
          Error while executing Scheme code.

'full'
     In addition to an error message a full backtrace is printed.

          (gdb) set guile print-stack full
          (gdb) guile (display foo)
          Guile Backtrace:
          In ice-9/boot-9.scm:
           157: 10 [catch #t #<catch-closure 2c76e20> ...]
          In unknown file:
             ?: 9 [apply-smob/1 #<catch-closure 2c76e20>]
          In ice-9/boot-9.scm:
           157: 8 [catch #t #<catch-closure 2c76d20> ...]
          In unknown file:
             ?: 7 [apply-smob/1 #<catch-closure 2c76d20>]
             ?: 6 [call-with-input-string "(display foo)" ...]
          In ice-9/boot-9.scm:
          2320: 5 [save-module-excursion #<procedure 2c2dc30 ... ()>]
          In ice-9/eval-string.scm:
            44: 4 [read-and-eval #<input: string 27cb410> #:lang ...]
            37: 3 [lp (display foo)]
          In ice-9/eval.scm:
           387: 2 [eval # ()]
           393: 1 [eval #<memoized foo> ()]
          In unknown file:
             ?: 0 [memoize-variable-access! #<memoized foo> ...]

          ERROR: In procedure memoize-variable-access!:
          ERROR: Unbound variable: foo
          Error while executing Scheme code.

   GDB errors that happen in GDB commands invoked by Guile code are
converted to Guile exceptions.  The type of the Guile exception depends
on the error.

   Guile procedures provided by GDB can throw the standard Guile
exceptions like 'wrong-type-arg' and 'out-of-range'.

   User interrupt (via 'C-c' or by typing 'q' at a pagination prompt) is
translated to a Guile 'signal' exception with value 'SIGINT'.

   GDB Guile procedures can also throw these exceptions:

'gdb:error'
     This exception is a catch-all for errors generated from within GDB.

'gdb:invalid-object'
     This exception is thrown when accessing Guile objects that wrap
     underlying GDB objects have become invalid.  For example, a
     '<gdb:breakpoint>' object becomes invalid if the user deletes it
     from the command line.  The object still exists in Guile, but the
     object it represents is gone.  Further operations on this
     breakpoint will throw this exception.

'gdb:memory-error'
     This exception is thrown when an operation tried to access invalid
     memory in the inferior.

'gdb:pp-type-error'
     This exception is thrown when a Guile pretty-printer passes a bad
     object to GDB.

   The following exception-related procedures are provided by the
'(gdb)' module.

 -- Scheme Procedure: make-exception key args
     Return a '<gdb:exception>' object given by its KEY and ARGS, which
     are the standard Guile parameters of an exception.  See the Guile
     documentation for more information (*note (guile)Exceptions::).

 -- Scheme Procedure: exception? object
     Return '#t' if OBJECT is a '<gdb:exception>' object.  Otherwise
     return '#f'.

 -- Scheme Procedure: exception-key exception
     Return the ARGS field of a '<gdb:exception>' object.

 -- Scheme Procedure: exception-args exception
     Return the ARGS field of a '<gdb:exception>' object.

\1f
File: gdb.info,  Node: Values From Inferior In Guile,  Next: Arithmetic In Guile,  Prev: Guile Exception Handling,  Up: Guile API

23.3.3.5 Values From Inferior In Guile
......................................

GDB provides values it obtains from the inferior program in an object of
type '<gdb:value>'.  GDB uses this object for its internal bookkeeping
of the inferior's values, and for fetching values when necessary.

   GDB does not memoize '<gdb:value>' objects.  'make-value' always
returns a fresh object.

     (gdb) guile (eq? (make-value 1) (make-value 1))
     $1 = #f
     (gdb) guile (equal? (make-value 1) (make-value 1))
     $1 = #t

   A '<gdb:value>' that represents a function can be executed via
inferior function call with 'value-call'.  Any arguments provided to the
call must match the function's prototype, and must be provided in the
order specified by that prototype.

   For example, 'some-val' is a '<gdb:value>' instance representing a
function that takes two integers as arguments.  To execute this
function, call it like so:

     (define result (value-call some-val 10 20))

   Any values returned from a function call are '<gdb:value>' objects.

   Note: Unlike Python scripting in GDB, inferior values that are simple
scalars cannot be used directly in Scheme expressions that are valid for
the value's data type.  For example, '(+ (parse-and-eval "int_variable")
2)' does not work.  And inferior values that are structures or instances
of some class cannot be accessed using any special syntax, instead
'value-field' must be used.

   The following value-related procedures are provided by the '(gdb)'
module.

 -- Scheme Procedure: value? object
     Return '#t' if OBJECT is a '<gdb:value>' object.  Otherwise return
     '#f'.

 -- Scheme Procedure: make-value value [#:type type]
     Many Scheme values can be converted directly to a '<gdb:value>'
     with this procedure.  If TYPE is specified, the result is a value
     of this type, and if VALUE can't be represented with this type an
     exception is thrown.  Otherwise the type of the result is
     determined from VALUE as described below.

     *Note Architectures In Guile::, for a list of the builtin types for
     an architecture.

     Here's how Scheme values are converted when TYPE argument to
     'make-value' is not specified:

     Scheme boolean
          A Scheme boolean is converted the boolean type for the current
          language.

     Scheme integer
          A Scheme integer is converted to the first of a C 'int',
          'unsigned int', 'long', 'unsigned long', 'long long' or
          'unsigned long long' type for the current architecture that
          can represent the value.

          If the Scheme integer cannot be represented as a target
          integer an 'out-of-range' exception is thrown.

     Scheme real
          A Scheme real is converted to the C 'double' type for the
          current architecture.

     Scheme string
          A Scheme string is converted to a string in the current target
          language using the current target encoding.  Characters that
          cannot be represented in the current target encoding are
          replaced with the corresponding escape sequence.  This is
          Guile's 'SCM_FAILED_CONVERSION_ESCAPE_SEQUENCE' conversion
          strategy (*note (guile)Strings::).

          Passing TYPE is not supported in this case, if it is provided
          a 'wrong-type-arg' exception is thrown.

     '<gdb:lazy-string>'
          If VALUE is a '<gdb:lazy-string>' object (*note Lazy Strings
          In Guile::), then the 'lazy-string->value' procedure is
          called, and its result is used.

          Passing TYPE is not supported in this case, if it is provided
          a 'wrong-type-arg' exception is thrown.

     Scheme bytevector
          If VALUE is a Scheme bytevector and TYPE is provided, VALUE
          must be the same size, in bytes, of values of type TYPE, and
          the result is essentially created by using 'memcpy'.

          If VALUE is a Scheme bytevector and TYPE is not provided, the
          result is an array of type 'uint8' of the same length.

 -- Scheme Procedure: value-optimized-out? value
     Return '#t' if the compiler optimized out VALUE, thus it is not
     available for fetching from the inferior.  Otherwise return '#f'.

 -- Scheme Procedure: value-address value
     If VALUE is addressable, returns a '<gdb:value>' object
     representing the address.  Otherwise, '#f' is returned.

 -- Scheme Procedure: value-type value
     Return the type of VALUE as a '<gdb:type>' object (*note Types In
     Guile::).

 -- Scheme Procedure: value-dynamic-type value
     Return the dynamic type of VALUE.  This uses C++ run-time type
     information (RTTI) to determine the dynamic type of the value.  If
     the value is of class type, it will return the class in which the
     value is embedded, if any.  If the value is of pointer or reference
     to a class type, it will compute the dynamic type of the referenced
     object, and return a pointer or reference to that type,
     respectively.  In all other cases, it will return the value's
     static type.

     Note that this feature will only work when debugging a C++ program
     that includes RTTI for the object in question.  Otherwise, it will
     just return the static type of the value as in 'ptype foo'.  *Note
     ptype: Symbols.

 -- Scheme Procedure: value-cast value type
     Return a new instance of '<gdb:value>' that is the result of
     casting VALUE to the type described by TYPE, which must be a
     '<gdb:type>' object.  If the cast cannot be performed for some
     reason, this method throws an exception.

 -- Scheme Procedure: value-dynamic-cast value type
     Like 'value-cast', but works as if the C++ 'dynamic_cast' operator
     were used.  Consult a C++ reference for details.

 -- Scheme Procedure: value-reinterpret-cast value type
     Like 'value-cast', but works as if the C++ 'reinterpret_cast'
     operator were used.  Consult a C++ reference for details.

 -- Scheme Procedure: value-dereference value
     For pointer data types, this method returns a new '<gdb:value>'
     object whose contents is the object pointed to by VALUE.  For
     example, if 'foo' is a C pointer to an 'int', declared in your C
     program as

          int *foo;

     then you can use the corresponding '<gdb:value>' to access what
     'foo' points to like this:

          (define bar (value-dereference foo))

     The result 'bar' will be a '<gdb:value>' object holding the value
     pointed to by 'foo'.

     A similar function 'value-referenced-value' exists which also
     returns '<gdb:value>' objects corresonding to the values pointed to
     by pointer values (and additionally, values referenced by reference
     values).  However, the behavior of 'value-dereference' differs from
     'value-referenced-value' by the fact that the behavior of
     'value-dereference' is identical to applying the C unary operator
     '*' on a given value.  For example, consider a reference to a
     pointer 'ptrref', declared in your C++ program as

          typedef int *intptr;
          ...
          int val = 10;
          intptr ptr = &val;
          intptr &ptrref = ptr;

     Though 'ptrref' is a reference value, one can apply the method
     'value-dereference' to the '<gdb:value>' object corresponding to it
     and obtain a '<gdb:value>' which is identical to that corresponding
     to 'val'.  However, if you apply the method
     'value-referenced-value', the result would be a '<gdb:value>'
     object identical to that corresponding to 'ptr'.

          (define scm-ptrref (parse-and-eval "ptrref"))
          (define scm-val (value-dereference scm-ptrref))
          (define scm-ptr (value-referenced-value scm-ptrref))

     The '<gdb:value>' object 'scm-val' is identical to that
     corresponding to 'val', and 'scm-ptr' is identical to that
     corresponding to 'ptr'.  In general, 'value-dereference' can be
     applied whenever the C unary operator '*' can be applied to the
     corresponding C value.  For those cases where applying both
     'value-dereference' and 'value-referenced-value' is allowed, the
     results obtained need not be identical (as we have seen in the
     above example).  The results are however identical when applied on
     '<gdb:value>' objects corresponding to pointers ('<gdb:value>'
     objects with type code 'TYPE_CODE_PTR') in a C/C++ program.

 -- Scheme Procedure: value-referenced-value value
     For pointer or reference data types, this method returns a new
     '<gdb:value>' object corresponding to the value referenced by the
     pointer/reference value.  For pointer data types,
     'value-dereference' and 'value-referenced-value' produce identical
     results.  The difference between these methods is that
     'value-dereference' cannot get the values referenced by reference
     values.  For example, consider a reference to an 'int', declared in
     your C++ program as

          int val = 10;
          int &ref = val;

     then applying 'value-dereference' to the '<gdb:value>' object
     corresponding to 'ref' will result in an error, while applying
     'value-referenced-value' will result in a '<gdb:value>' object
     identical to that corresponding to 'val'.

          (define scm-ref (parse-and-eval "ref"))
          (define err-ref (value-dereference scm-ref))      ;; error
          (define scm-val (value-referenced-value scm-ref)) ;; ok

     The '<gdb:value>' object 'scm-val' is identical to that
     corresponding to 'val'.

 -- Scheme Procedure: value-field value field-name
     Return field FIELD-NAME from '<gdb:value>' object VALUE.

 -- Scheme Procedure: value-subscript value index
     Return the value of array VALUE at index INDEX.  The VALUE argument
     must be a subscriptable '<gdb:value>' object.

 -- Scheme Procedure: value-call value arg-list
     Perform an inferior function call, taking VALUE as a pointer to the
     function to call.  Each element of list ARG-LIST must be a
     <gdb:value> object or an object that can be converted to a value.
     The result is the value returned by the function.

 -- Scheme Procedure: value->bool value
     Return the Scheme boolean representing '<gdb:value>' VALUE.  The
     value must be "integer like".  Pointers are ok.

 -- Scheme Procedure: value->integer
     Return the Scheme integer representing '<gdb:value>' VALUE.  The
     value must be "integer like".  Pointers are ok.

 -- Scheme Procedure: value->real
     Return the Scheme real number representing '<gdb:value>' VALUE.
     The value must be a number.

 -- Scheme Procedure: value->bytevector
     Return a Scheme bytevector with the raw contents of '<gdb:value>'
     VALUE.  No transformation, endian or otherwise, is performed.

 -- Scheme Procedure: value->string value [#:encoding encoding]
          [#:errors errors] [#:length length]
     If VALUE> represents a string, then this method converts the
     contents to a Guile string.  Otherwise, this method will throw an
     exception.

     Values are interpreted as strings according to the rules of the
     current language.  If the optional length argument is given, the
     string will be converted to that length, and will include any
     embedded zeroes that the string may contain.  Otherwise, for
     languages where the string is zero-terminated, the entire string
     will be converted.

     For example, in C-like languages, a value is a string if it is a
     pointer to or an array of characters or ints of type 'wchar_t',
     'char16_t', or 'char32_t'.

     If the optional ENCODING argument is given, it must be a string
     naming the encoding of the string in the '<gdb:value>', such as
     '"ascii"', '"iso-8859-6"' or '"utf-8"'.  It accepts the same
     encodings as the corresponding argument to Guile's
     'scm_from_stringn' function, and the Guile codec machinery will be
     used to convert the string.  If ENCODING is not given, or if
     ENCODING is the empty string, then either the 'target-charset'
     (*note Character Sets::) will be used, or a language-specific
     encoding will be used, if the current language is able to supply
     one.

     The optional ERRORS argument is one of '#f', 'error' or
     'substitute'.  'error' and 'substitute' must be symbols.  If ERRORS
     is not specified, or if its value is '#f', then the default
     conversion strategy is used, which is set with the Scheme function
     'set-port-conversion-strategy!'.  If the value is ''error' then an
     exception is thrown if there is any conversion error.  If the value
     is ''substitute' then any conversion error is replaced with
     question marks.  *Note (guile)Strings::.

     If the optional LENGTH argument is given, the string will be
     fetched and converted to the given length.  The length must be a
     Scheme integer and not a '<gdb:value>' integer.

 -- Scheme Procedure: value->lazy-string value [#:encoding encoding]
          [#:length length]
     If this '<gdb:value>' represents a string, then this method
     converts VALUE to a '<gdb:lazy-string' (*note Lazy Strings In
     Guile::).  Otherwise, this method will throw an exception.

     If the optional ENCODING argument is given, it must be a string
     naming the encoding of the '<gdb:lazy-string'.  Some examples are:
     '"ascii"', '"iso-8859-6"' or '"utf-8"'.  If the ENCODING argument
     is an encoding that GDB does not recognize, GDB will raise an
     error.

     When a lazy string is printed, the GDB encoding machinery is used
     to convert the string during printing.  If the optional ENCODING
     argument is not provided, or is an empty string, GDB will
     automatically select the encoding most suitable for the string
     type.  For further information on encoding in GDB please see *note
     Character Sets::.

     If the optional LENGTH argument is given, the string will be
     fetched and encoded to the length of characters specified.  If the
     LENGTH argument is not provided, the string will be fetched and
     encoded until a null of appropriate width is found.  The length
     must be a Scheme integer and not a '<gdb:value>' integer.

 -- Scheme Procedure: value-lazy? value
     Return '#t' if VALUE has not yet been fetched from the inferior.
     Otherwise return '#f'.  GDB does not fetch values until necessary,
     for efficiency.  For example:

          (define myval (parse-and-eval "somevar"))

     The value of 'somevar' is not fetched at this time.  It will be
     fetched when the value is needed, or when the 'fetch-lazy'
     procedure is invoked.

 -- Scheme Procedure: make-lazy-value type address
     Return a '<gdb:value>' that will be lazily fetched from the target.
     The object of type '<gdb:type>' whose value to fetch is specified
     by its TYPE and its target memory ADDRESS, which is a Scheme
     integer.

 -- Scheme Procedure: value-fetch-lazy! value
     If VALUE is a lazy value ('(value-lazy? value)' is '#t'), then the
     value is fetched from the inferior.  Any errors that occur in the
     process will produce a Guile exception.

     If VALUE is not a lazy value, this method has no effect.

     The result of this function is unspecified.

 -- Scheme Procedure: value-print value
     Return the string representation (print form) of '<gdb:value>'
     VALUE.

\1f
File: gdb.info,  Node: Arithmetic In Guile,  Next: Types In Guile,  Prev: Values From Inferior In Guile,  Up: Guile API

23.3.3.6 Arithmetic In Guile
............................

The '(gdb)' module provides several functions for performing arithmetic
on '<gdb:value>' objects.  The arithmetic is performed as if it were
done by the target, and therefore has target semantics which are not
necessarily those of Scheme.  For example operations work with a fixed
precision, not the arbitrary precision of Scheme.

   Wherever a function takes an integer or pointer as an operand, GDB
will convert appropriate Scheme values to perform the operation.

 -- Scheme Procedure: value-add a b

 -- Scheme Procedure: value-sub a b

 -- Scheme Procedure: value-mul a b

 -- Scheme Procedure: value-div a b

 -- Scheme Procedure: value-rem a b

 -- Scheme Procedure: value-mod a b

 -- Scheme Procedure: value-pow a b

 -- Scheme Procedure: value-not a

 -- Scheme Procedure: value-neg a

 -- Scheme Procedure: value-pos a

 -- Scheme Procedure: value-abs a

 -- Scheme Procedure: value-lsh a b

 -- Scheme Procedure: value-rsh a b

 -- Scheme Procedure: value-min a b

 -- Scheme Procedure: value-max a b

 -- Scheme Procedure: value-lognot a

 -- Scheme Procedure: value-logand a b

 -- Scheme Procedure: value-logior a b

 -- Scheme Procedure: value-logxor a b

 -- Scheme Procedure: value=? a b

 -- Scheme Procedure: value<? a b

 -- Scheme Procedure: value<=? a b

 -- Scheme Procedure: value>? a b

 -- Scheme Procedure: value>=? a b

   Scheme does not provide a 'not-equal' function, and thus Guile
support in GDB does not either.

\1f
File: gdb.info,  Node: Types In Guile,  Next: Guile Pretty Printing API,  Prev: Arithmetic In Guile,  Up: Guile API

23.3.3.7 Types In Guile
.......................

GDB represents types from the inferior in objects of type '<gdb:type>'.

   The following type-related procedures are provided by the '(gdb)'
module.

 -- Scheme Procedure: type? object
     Return '#t' if OBJECT is an object of type '<gdb:type>'.  Otherwise
     return '#f'.

 -- Scheme Procedure: lookup-type name [#:block block]
     This function looks up a type by its NAME, which must be a string.

     If BLOCK is given, it is an object of type '<gdb:block>', and NAME
     is looked up in that scope.  Otherwise, it is searched for
     globally.

     Ordinarily, this function will return an instance of '<gdb:type>'.
     If the named type cannot be found, it will throw an exception.

 -- Scheme Procedure: type-code type
     Return the type code of TYPE.  The type code will be one of the
     'TYPE_CODE_' constants defined below.

 -- Scheme Procedure: type-tag type
     Return the tag name of TYPE.  The tag name is the name after
     'struct', 'union', or 'enum' in C and C++; not all languages have
     this concept.  If this type has no tag name, then '#f' is returned.

 -- Scheme Procedure: type-name type
     Return the name of TYPE.  If this type has no name, then '#f' is
     returned.

 -- Scheme Procedure: type-print-name type
     Return the print name of TYPE.  This returns something even for
     anonymous types.  For example, for an anonymous C struct '"struct
     {...}"' is returned.

 -- Scheme Procedure: type-sizeof type
     Return the size of this type, in target 'char' units.  Usually, a
     target's 'char' type will be an 8-bit byte.  However, on some
     unusual platforms, this type may have a different size.

 -- Scheme Procedure: type-strip-typedefs type
     Return a new '<gdb:type>' that represents the real type of TYPE,
     after removing all layers of typedefs.

 -- Scheme Procedure: type-array type n1 [n2]
     Return a new '<gdb:type>' object which represents an array of this
     type.  If one argument is given, it is the inclusive upper bound of
     the array; in this case the lower bound is zero.  If two arguments
     are given, the first argument is the lower bound of the array, and
     the second argument is the upper bound of the array.  An array's
     length must not be negative, but the bounds can be.

 -- Scheme Procedure: type-vector type n1 [n2]
     Return a new '<gdb:type>' object which represents a vector of this
     type.  If one argument is given, it is the inclusive upper bound of
     the vector; in this case the lower bound is zero.  If two arguments
     are given, the first argument is the lower bound of the vector, and
     the second argument is the upper bound of the vector.  A vector's
     length must not be negative, but the bounds can be.

     The difference between an 'array' and a 'vector' is that arrays
     behave like in C: when used in expressions they decay to a pointer
     to the first element whereas vectors are treated as first class
     values.

 -- Scheme Procedure: type-pointer type
     Return a new '<gdb:type>' object which represents a pointer to
     TYPE.

 -- Scheme Procedure: type-range type
     Return a list of two elements: the low bound and high bound of
     TYPE.  If TYPE does not have a range, an exception is thrown.

 -- Scheme Procedure: type-reference type
     Return a new '<gdb:type>' object which represents a reference to
     TYPE.

 -- Scheme Procedure: type-target type
     Return a new '<gdb:type>' object which represents the target type
     of TYPE.

     For a pointer type, the target type is the type of the pointed-to
     object.  For an array type (meaning C-like arrays), the target type
     is the type of the elements of the array.  For a function or method
     type, the target type is the type of the return value.  For a
     complex type, the target type is the type of the elements.  For a
     typedef, the target type is the aliased type.

     If the type does not have a target, this method will throw an
     exception.

 -- Scheme Procedure: type-const type
     Return a new '<gdb:type>' object which represents a
     'const'-qualified variant of TYPE.

 -- Scheme Procedure: type-volatile type
     Return a new '<gdb:type>' object which represents a
     'volatile'-qualified variant of TYPE.

 -- Scheme Procedure: type-unqualified type
     Return a new '<gdb:type>' object which represents an unqualified
     variant of TYPE.  That is, the result is neither 'const' nor
     'volatile'.

 -- Scheme Procedure: type-num-fields
     Return the number of fields of '<gdb:type>' TYPE.

 -- Scheme Procedure: type-fields type
     Return the fields of TYPE as a list.  For structure and union
     types, 'fields' has the usual meaning.  Range types have two
     fields, the minimum and maximum values.  Enum types have one field
     per enum constant.  Function and method types have one field per
     parameter.  The base types of C++ classes are also represented as
     fields.  If the type has no fields, or does not fit into one of
     these categories, an empty list will be returned.  *Note Fields of
     a type in Guile::.

 -- Scheme Procedure: make-field-iterator type
     Return the fields of TYPE as a <gdb:iterator> object.  *Note
     Iterators In Guile::.

 -- Scheme Procedure: type-field type field-name
     Return field named FIELD-NAME in TYPE.  The result is an object of
     type '<gdb:field>'.  *Note Fields of a type in Guile::.  If the
     type does not have fields, or FIELD-NAME is not a field of TYPE, an
     exception is thrown.

     For example, if 'some-type' is a '<gdb:type>' instance holding a
     structure type, you can access its 'foo' field with:

          (define bar (type-field some-type "foo"))

     'bar' will be a '<gdb:field>' object.

 -- Scheme Procedure: type-has-field? type name
     Return '#t' if '<gdb:type>' TYPE has field named NAME.  Otherwise
     return '#f'.

   Each type has a code, which indicates what category this type falls
into.  The available type categories are represented by constants
defined in the '(gdb)' module:

'TYPE_CODE_PTR'
     The type is a pointer.

'TYPE_CODE_ARRAY'
     The type is an array.

'TYPE_CODE_STRUCT'
     The type is a structure.

'TYPE_CODE_UNION'
     The type is a union.

'TYPE_CODE_ENUM'
     The type is an enum.

'TYPE_CODE_FLAGS'
     A bit flags type, used for things such as status registers.

'TYPE_CODE_FUNC'
     The type is a function.

'TYPE_CODE_INT'
     The type is an integer type.

'TYPE_CODE_FLT'
     A floating point type.

'TYPE_CODE_VOID'
     The special type 'void'.

'TYPE_CODE_SET'
     A Pascal set type.

'TYPE_CODE_RANGE'
     A range type, that is, an integer type with bounds.

'TYPE_CODE_STRING'
     A string type.  Note that this is only used for certain languages
     with language-defined string types; C strings are not represented
     this way.

'TYPE_CODE_BITSTRING'
     A string of bits.  It is deprecated.

'TYPE_CODE_ERROR'
     An unknown or erroneous type.

'TYPE_CODE_METHOD'
     A method type, as found in C++ or Java.

'TYPE_CODE_METHODPTR'
     A pointer-to-member-function.

'TYPE_CODE_MEMBERPTR'
     A pointer-to-member.

'TYPE_CODE_REF'
     A reference type.

'TYPE_CODE_CHAR'
     A character type.

'TYPE_CODE_BOOL'
     A boolean type.

'TYPE_CODE_COMPLEX'
     A complex float type.

'TYPE_CODE_TYPEDEF'
     A typedef to some other type.

'TYPE_CODE_NAMESPACE'
     A C++ namespace.

'TYPE_CODE_DECFLOAT'
     A decimal floating point type.

'TYPE_CODE_INTERNAL_FUNCTION'
     A function internal to GDB.  This is the type used to represent
     convenience functions (*note Convenience Funs::).

   Further support for types is provided in the '(gdb types)' Guile
module (*note Guile Types Module::).

   Each field is represented as an object of type '<gdb:field>'.

   The following field-related procedures are provided by the '(gdb)'
module:

 -- Scheme Procedure: field? object
     Return '#t' if OBJECT is an object of type '<gdb:field>'.
     Otherwise return '#f'.

 -- Scheme Procedure: field-name field
     Return the name of the field, or '#f' for anonymous fields.

 -- Scheme Procedure: field-type field
     Return the type of the field.  This is usually an instance of
     '<gdb:type>', but it can be '#f' in some situations.

 -- Scheme Procedure: field-enumval field
     Return the enum value represented by '<gdb:field>' FIELD.

 -- Scheme Procedure: field-bitpos field
     Return the bit position of '<gdb:field>' FIELD.  This attribute is
     not available for 'static' fields (as in C++ or Java).

 -- Scheme Procedure: field-bitsize field
     If the field is packed, or is a bitfield, return the size of
     '<gdb:field>' FIELD in bits.  Otherwise, zero is returned; in which
     case the field's size is given by its type.

 -- Scheme Procedure: field-artificial? field
     Return '#t' if the field is artificial, usually meaning that it was
     provided by the compiler and not the user.  Otherwise return '#f'.

 -- Scheme Procedure: field-base-class? field
     Return '#t' if the field represents a base class of a C++
     structure.  Otherwise return '#f'.

\1f
File: gdb.info,  Node: Guile Pretty Printing API,  Next: Selecting Guile Pretty-Printers,  Prev: Types In Guile,  Up: Guile API

23.3.3.8 Guile Pretty Printing API
..................................

An example output is provided (*note Pretty Printing::).

   A pretty-printer is represented by an object of type
<gdb:pretty-printer>.  Pretty-printer objects are created with
'make-pretty-printer'.

   The following pretty-printer-related procedures are provided by the
'(gdb)' module:

 -- Scheme Procedure: make-pretty-printer name lookup-function
     Return a '<gdb:pretty-printer>' object named NAME.

     LOOKUP-FUNCTION is a function of one parameter: the value to be
     printed.  If the value is handled by this pretty-printer, then
     LOOKUP-FUNCTION returns an object of type
     <gdb:pretty-printer-worker> to perform the actual pretty-printing.
     Otherwise LOOKUP-FUNCTION returns '#f'.

 -- Scheme Procedure: pretty-printer? object
     Return '#t' if OBJECT is a '<gdb:pretty-printer>' object.
     Otherwise return '#f'.

 -- Scheme Procedure: pretty-printer-enabled? pretty-printer
     Return '#t' if PRETTY-PRINTER is enabled.  Otherwise return '#f'.

 -- Scheme Procedure: set-pretty-printer-enabled! pretty-printer flag
     Set the enabled flag of PRETTY-PRINTER to FLAG.  The value returned
     is unspecified.

 -- Scheme Procedure: pretty-printers
     Return the list of global pretty-printers.

 -- Scheme Procedure: set-pretty-printers! pretty-printers
     Set the list of global pretty-printers to PRETTY-PRINTERS.  The
     value returned is unspecified.

 -- Scheme Procedure: make-pretty-printer-worker display-hint to-string
          children
     Return an object of type '<gdb:pretty-printer-worker>'.

     This function takes three parameters:

     'display-hint'
          DISPLAY-HINT provides a hint to GDB or GDB front end via MI to
          change the formatting of the value being printed.  The value
          must be a string or '#f' (meaning there is no hint).  Several
          values for DISPLAY-HINT are predefined by GDB:

          'array'
               Indicate that the object being printed is "array-like".
               The CLI uses this to respect parameters such as 'set
               print elements' and 'set print array'.

          'map'
               Indicate that the object being printed is "map-like", and
               that the children of this value can be assumed to
               alternate between keys and values.

          'string'
               Indicate that the object being printed is "string-like".
               If the printer's 'to-string' function returns a Guile
               string of some kind, then GDB will call its internal
               language-specific string-printing function to format the
               string.  For the CLI this means adding quotation marks,
               possibly escaping some characters, respecting 'set print
               elements', and the like.

     'to-string'
          TO-STRING is either a function of one parameter, the
          '<gdb:pretty-printer-worker>' object, or '#f'.

          When printing from the CLI, if the 'to-string' method exists,
          then GDB will prepend its result to the values returned by
          'children'.  Exactly how this formatting is done is dependent
          on the display hint, and may change as more hints are added.
          Also, depending on the print settings (*note Print
          Settings::), the CLI may print just the result of 'to-string'
          in a stack trace, omitting the result of 'children'.

          If this method returns a string, it is printed verbatim.

          Otherwise, if this method returns an instance of
          '<gdb:value>', then GDB prints this value.  This may result in
          a call to another pretty-printer.

          If instead the method returns a Guile value which is
          convertible to a '<gdb:value>', then GDB performs the
          conversion and prints the resulting value.  Again, this may
          result in a call to another pretty-printer.  Guile scalars
          (integers, floats, and booleans) and strings are convertible
          to '<gdb:value>'; other types are not.

          Finally, if this method returns '#f' then no further
          operations are peformed in this method and nothing is printed.

          If the result is not one of these types, an exception is
          raised.

          TO-STRING may also be '#f' in which case it is left to
          CHILDREN to print the value.

     'children'
          CHILDREN is either a function of one parameter, the
          '<gdb:pretty-printer-worker>' object, or '#f'.

          GDB will call this function on a pretty-printer to compute the
          children of the pretty-printer's value.

          This function must return a <gdb:iterator> object.  Each item
          returned by the iterator must be a tuple holding two elements.
          The first element is the "name" of the child; the second
          element is the child's value.  The value can be any Guile
          object which is convertible to a GDB value.

          If CHILDREN is '#f', GDB will act as though the value has no
          children.

   GDB provides a function which can be used to look up the default
pretty-printer for a '<gdb:value>':

 -- Scheme Procedure: default-visualizer value
     This function takes a '<gdb:value>' object as an argument.  If a
     pretty-printer for this value exists, then it is returned.  If no
     such printer exists, then this returns '#f'.

\1f
File: gdb.info,  Node: Selecting Guile Pretty-Printers,  Next: Writing a Guile Pretty-Printer,  Prev: Guile Pretty Printing API,  Up: Guile API

23.3.3.9 Selecting Guile Pretty-Printers
........................................

There are three sets of pretty-printers that GDB searches:

   * Per-objfile list of pretty-printers (*note Objfiles In Guile::).
   * Per-progspace list of pretty-printers (*note Progspaces In
     Guile::).
   * The global list of pretty-printers (*note Guile Pretty Printing
     API::).  These printers are available when debugging any inferior.

   Pretty-printer lookup is done by passing the value to be printed to
the lookup function of each enabled object in turn.  Lookup stops when a
lookup function returns a non-'#f' value or when the list is exhausted.
Lookup functions must return either a '<gdb:pretty-printer-worker>'
object or '#f'.  Otherwise an exception is thrown.

   GDB first checks the result of 'objfile-pretty-printers' of each
'<gdb:objfile>' in the current program space and iteratively calls each
enabled lookup function in the list for that '<gdb:objfile>' until a
non-'#f' object is returned.  If no pretty-printer is found in the
objfile lists, GDB then searches the result of
'progspace-pretty-printers' of the current program space, calling each
enabled function until a non-'#f' object is returned.  After these lists
have been exhausted, it tries the global pretty-printers list, obtained
with 'pretty-printers', again calling each enabled function until a
non-'#f' object is returned.

   The order in which the objfiles are searched is not specified.  For a
given list, functions are always invoked from the head of the list, and
iterated over sequentially until the end of the list, or a
'<gdb:pretty-printer-worker>' object is returned.

   For various reasons a pretty-printer may not work.  For example, the
underlying data structure may have changed and the pretty-printer is out
of date.

   The consequences of a broken pretty-printer are severe enough that
GDB provides support for enabling and disabling individual printers.
For example, if 'print frame-arguments' is on, a backtrace can become
highly illegible if any argument is printed with a broken printer.

   Pretty-printers are enabled and disabled from Scheme by calling
'set-pretty-printer-enabled!'.  *Note Guile Pretty Printing API::.

\1f
File: gdb.info,  Node: Writing a Guile Pretty-Printer,  Next: Commands In Guile,  Prev: Selecting Guile Pretty-Printers,  Up: Guile API

23.3.3.10 Writing a Guile Pretty-Printer
........................................

A pretty-printer consists of two basic parts: a lookup function to
determine if the type is supported, and the printer itself.

   Here is an example showing how a 'std::string' printer might be
written.  *Note Guile Pretty Printing API::, for details.

     (define (make-my-string-printer value)
       "Print a my::string string"
       (make-pretty-printer-worker
        "string"
        (lambda (printer)
          (value-field value "_data"))
        #f))

   And here is an example showing how a lookup function for the printer
example above might be written.

     (define (str-lookup-function pretty-printer value)
       (let ((tag (type-tag (value-type value))))
         (and tag
              (string-prefix? "std::string<" tag)
              (make-my-string-printer value))))

   Then to register this printer in the global printer list:

     (append-pretty-printer!
      (make-pretty-printer "my-string" str-lookup-function))

   The example lookup function extracts the value's type, and attempts
to match it to a type that it can pretty-print.  If it is a type the
printer can pretty-print, it will return a <gdb:pretty-printer-worker>
object.  If not, it returns '#f'.

   We recommend that you put your core pretty-printers into a Guile
package.  If your pretty-printers are for use with a library, we further
recommend embedding a version number into the package name.  This
practice will enable GDB to load multiple versions of your
pretty-printers at the same time, because they will have different
names.

   You should write auto-loaded code (*note Guile Auto-loading::) such
that it can be evaluated multiple times without changing its meaning.
An ideal auto-load file will consist solely of 'import's of your printer
modules, followed by a call to a register pretty-printers with the
current objfile.

   Taken as a whole, this approach will scale nicely to multiple
inferiors, each potentially using a different library version.
Embedding a version number in the Guile package name will ensure that
GDB is able to load both sets of printers simultaneously.  Then, because
the search for pretty-printers is done by objfile, and because your
auto-loaded code took care to register your library's printers with a
specific objfile, GDB will find the correct printers for the specific
version of the library used by each inferior.

   To continue the 'my::string' example, this code might appear in
'(my-project my-library v1)':

     (use-modules (gdb))
     (define (register-printers objfile)
       (append-objfile-pretty-printer!
        (make-pretty-printer "my-string" str-lookup-function)))

And then the corresponding contents of the auto-load file would be:

     (use-modules (gdb) (my-project my-library v1))
     (register-printers (current-objfile))

   The previous example illustrates a basic pretty-printer.  There are a
few things that can be improved on.  The printer only handles one type,
whereas a library typically has several types.  One could install a
lookup function for each desired type in the library, but one could also
have a single lookup function recognize several types.  The latter is
the conventional way this is handled.  If a pretty-printer can handle
multiple data types, then its "subprinters" are the printers for the
individual data types.

   The '(gdb printing)' module provides a formal way of solving this
problem (*note Guile Printing Module::).  Here is another example that
handles multiple types.

   These are the types we are going to pretty-print:

     struct foo { int a, b; };
     struct bar { struct foo x, y; };

   Here are the printers:

     (define (make-foo-printer value)
       "Print a foo object"
       (make-pretty-printer-worker
        "foo"
        (lambda (printer)
          (format #f "a=<~a> b=<~a>"
                  (value-field value "a") (value-field value "a")))
        #f))

     (define (make-bar-printer value)
       "Print a bar object"
       (make-pretty-printer-worker
        "foo"
        (lambda (printer)
          (format #f "x=<~a> y=<~a>"
                  (value-field value "x") (value-field value "y")))
        #f))

   This example doesn't need a lookup function, that is handled by the
'(gdb printing)' module.  Instead a function is provided to build up the
object that handles the lookup.

     (use-modules (gdb printing))

     (define (build-pretty-printer)
       (let ((pp (make-pretty-printer-collection "my-library")))
         (pp-collection-add-tag-printer "foo" make-foo-printer)
         (pp-collection-add-tag-printer "bar" make-bar-printer)
         pp))

   And here is the autoload support:

     (use-modules (gdb) (my-library))
     (append-objfile-pretty-printer! (current-objfile) (build-pretty-printer))

   Finally, when this printer is loaded into GDB, here is the
corresponding output of 'info pretty-printer':

     (gdb) info pretty-printer
     my_library.so:
       my-library
         foo
         bar

\1f
File: gdb.info,  Node: Commands In Guile,  Next: Parameters In Guile,  Prev: Writing a Guile Pretty-Printer,  Up: Guile API

23.3.3.11 Commands In Guile
...........................

You can implement new GDB CLI commands in Guile.  A CLI command object
is created with the 'make-command' Guile function, and added to GDB with
the 'register-command!' Guile function.  This two-step approach is taken
to separate out the side-effect of adding the command to GDB from
'make-command'.

   There is no support for multi-line commands, that is commands that
consist of multiple lines and are terminated with 'end'.

 -- Scheme Procedure: (make-command name [#:invoke invoke]
          [#:command-class command-class] [#:completer-class completer]
          [#:prefix? prefix] [#:doc doc-string])

     The argument NAME is the name of the command.  If NAME consists of
     multiple words, then the initial words are looked for as prefix
     commands.  In this case, if one of the prefix commands does not
     exist, an exception is raised.

     The result is the '<gdb:command>' object representing the command.
     The command is not usable until it has been registered with GDB
     with 'register-command!'.

     The rest of the arguments are optional.

     The argument INVOKE is a procedure of three arguments: SELF, ARGS
     and FROM-TTY.  The argument SELF is the '<gdb:command>' object
     representing the command.  The argument ARGS is a string
     representing the arguments passed to the command, after leading and
     trailing whitespace has been stripped.  The argument FROM-TTY is a
     boolean flag and specifies whether the command should consider
     itself to have been originated from the user invoking it
     interactively.  If this function throws an exception, it is turned
     into a GDB 'error' call.  Otherwise, the return value is ignored.

     The argument COMMAND-CLASS is one of the 'COMMAND_' constants
     defined below.  This argument tells GDB how to categorize the new
     command in the help system.  The default is 'COMMAND_NONE'.

     The argument COMPLETER is either '#f', one of the 'COMPLETE_'
     constants defined below, or a procedure, also defined below.  This
     argument tells GDB how to perform completion for this command.  If
     not provided or if the value is '#f', then no completion is
     performed on the command.

     The argument PREFIX is a boolean flag indicating whether the new
     command is a prefix command; sub-commands of this command may be
     registered.

     The argument DOC-STRING is help text for the new command.  If no
     documentation string is provided, the default value "This command
     is not documented."  is used.

 -- Scheme Procedure: register-command! command
     Add COMMAND, a '<gdb:command>' object, to GDB's list of commands.
     It is an error to register a command more than once.  The result is
     unspecified.

 -- Scheme Procedure: command? object
     Return '#t' if OBJECT is a '<gdb:command>' object.  Otherwise
     return '#f'.

 -- Scheme Procedure: dont-repeat
     By default, a GDB command is repeated when the user enters a blank
     line at the command prompt.  A command can suppress this behavior
     by invoking the 'dont-repeat' function.  This is similar to the
     user command 'dont-repeat', see *note dont-repeat: Define.

 -- Scheme Procedure: string->argv string
     Convert a string to a list of strings split up according to GDB's
     argv parsing rules.  It is recommended to use this for consistency.
     Arguments are separated by spaces and may be quoted.  Example:

          scheme@(guile-user)> (string->argv "1 2\\ \\\"3 '4 \"5' \"6 '7\"")
          $1 = ("1" "2 \"3" "4 \"5" "6 '7")

 -- Scheme Procedure: throw-user-error message . args
     Throw a 'gdb:user-error' exception.  The argument MESSAGE is the
     error message as a format string, like the FMT argument to the
     'format' Scheme function.  *Note (guile)Formatted Output::.  The
     argument ARGS is a list of the optional arguments of MESSAGE.

     This is used when the command detects a user error of some kind,
     say a bad command argument.

          (gdb) guile (use-modules (gdb))
          (gdb) guile
          (register-command! (make-command "test-user-error"
            #:command-class COMMAND_OBSCURE
            #:invoke (lambda (self arg from-tty)
              (throw-user-error "Bad argument ~a" arg))))
          end
          (gdb) test-user-error ugh
          ERROR: Bad argument ugh

 -- completer: self text word
     If the COMPLETER option to 'make-command' is a procedure, it takes
     three arguments: SELF which is the '<gdb:command>' object, and TEXT
     and WORD which are both strings.  The argument TEXT holds the
     complete command line up to the cursor's location.  The argument
     WORD holds the last word of the command line; this is computed
     using a word-breaking heuristic.

     All forms of completion are handled by this function, that is, the
     <TAB> and <M-?> key bindings (*note Completion::), and the
     'complete' command (*note complete: Help.).

     This procedure can return several kinds of values:

        * If the return value is a list, the contents of the list are
          used as the completions.  It is up to COMPLETER to ensure that
          the contents actually do complete the word.  An empty list is
          allowed, it means that there were no completions available.
          Only string elements of the list are used; other elements in
          the list are ignored.

        * If the return value is a '<gdb:iterator>' object, it is
          iterated over to obtain the completions.  It is up to
          'completer-procedure' to ensure that the results actually do
          complete the word.  Only string elements of the result are
          used; other elements in the sequence are ignored.

        * All other results are treated as though there were no
          available completions.

   When a new command is registered, it will have been declared as a
member of some general class of commands.  This is used to classify
top-level commands in the on-line help system; note that prefix commands
are not listed under their own category but rather that of their
top-level command.  The available classifications are represented by
constants defined in the 'gdb' module:

'COMMAND_NONE'
     The command does not belong to any particular class.  A command in
     this category will not be displayed in any of the help categories.
     This is the default.

'COMMAND_RUNNING'
     The command is related to running the inferior.  For example,
     'start', 'step', and 'continue' are in this category.  Type 'help
     running' at the GDB prompt to see a list of commands in this
     category.

'COMMAND_DATA'
     The command is related to data or variables.  For example, 'call',
     'find', and 'print' are in this category.  Type 'help data' at the
     GDB prompt to see a list of commands in this category.

'COMMAND_STACK'
     The command has to do with manipulation of the stack.  For example,
     'backtrace', 'frame', and 'return' are in this category.  Type
     'help stack' at the GDB prompt to see a list of commands in this
     category.

'COMMAND_FILES'
     This class is used for file-related commands.  For example, 'file',
     'list' and 'section' are in this category.  Type 'help files' at
     the GDB prompt to see a list of commands in this category.

'COMMAND_SUPPORT'
     This should be used for "support facilities", generally meaning
     things that are useful to the user when interacting with GDB, but
     not related to the state of the inferior.  For example, 'help',
     'make', and 'shell' are in this category.  Type 'help support' at
     the GDB prompt to see a list of commands in this category.

'COMMAND_STATUS'
     The command is an 'info'-related command, that is, related to the
     state of GDB itself.  For example, 'info', 'macro', and 'show' are
     in this category.  Type 'help status' at the GDB prompt to see a
     list of commands in this category.

'COMMAND_BREAKPOINTS'
     The command has to do with breakpoints.  For example, 'break',
     'clear', and 'delete' are in this category.  Type 'help
     breakpoints' at the GDB prompt to see a list of commands in this
     category.

'COMMAND_TRACEPOINTS'
     The command has to do with tracepoints.  For example, 'trace',
     'actions', and 'tfind' are in this category.  Type 'help
     tracepoints' at the GDB prompt to see a list of commands in this
     category.

'COMMAND_USER'
     The command is a general purpose command for the user, and
     typically does not fit in one of the other categories.  Type 'help
     user-defined' at the GDB prompt to see a list of commands in this
     category, as well as the list of gdb macros (*note Sequences::).

'COMMAND_OBSCURE'
     The command is only used in unusual circumstances, or is not of
     general interest to users.  For example, 'checkpoint', 'fork', and
     'stop' are in this category.  Type 'help obscure' at the GDB prompt
     to see a list of commands in this category.

'COMMAND_MAINTENANCE'
     The command is only useful to GDB maintainers.  The 'maintenance'
     and 'flushregs' commands are in this category.  Type 'help
     internals' at the GDB prompt to see a list of commands in this
     category.

   A new command can use a predefined completion function, either by
specifying it via an argument at initialization, or by returning it from
the 'completer' procedure.  These predefined completion constants are
all defined in the 'gdb' module:

'COMPLETE_NONE'
     This constant means that no completion should be done.

'COMPLETE_FILENAME'
     This constant means that filename completion should be performed.

'COMPLETE_LOCATION'
     This constant means that location completion should be done.  *Note
     Specify Location::.

'COMPLETE_COMMAND'
     This constant means that completion should examine GDB command
     names.

'COMPLETE_SYMBOL'
     This constant means that completion should be done using symbol
     names as the source.

'COMPLETE_EXPRESSION'
     This constant means that completion should be done on expressions.
     Often this means completing on symbol names, but some language
     parsers also have support for completing on field names.

   The following code snippet shows how a trivial CLI command can be
implemented in Guile:

     (gdb) guile
     (register-command! (make-command "hello-world"
       #:command-class COMMAND_USER
       #:doc "Greet the whole world."
       #:invoke (lambda (self args from-tty) (display "Hello, World!\n"))))
     end
     (gdb) hello-world
     Hello, World!

\1f
File: gdb.info,  Node: Parameters In Guile,  Next: Progspaces In Guile,  Prev: Commands In Guile,  Up: Guile API

23.3.3.12 Parameters In Guile
.............................

You can implement new GDB "parameters" using Guile (1).

   There are many parameters that already exist and can be set in GDB.
Two examples are: 'set follow-fork' and 'set charset'.  Setting these
parameters influences certain behavior in GDB.  Similarly, you can
define parameters that can be used to influence behavior in custom Guile
scripts and commands.

   A new parameter is defined with the 'make-parameter' Guile function,
and added to GDB with the 'register-parameter!' Guile function.  This
two-step approach is taken to separate out the side-effect of adding the
parameter to GDB from 'make-parameter'.

   Parameters are exposed to the user via the 'set' and 'show' commands.
*Note Help::.

 -- Scheme Procedure: (make-parameter name [#:command-class
          command-class] [#:parameter-type parameter-type] [#:enum-list
          enum-list] [#:set-func set-func] [#:show-func show-func]
          [#:doc doc] [#:set-doc set-doc] [#:show-doc show-doc]
          [#:initial-value initial-value])

     The argument NAME is the name of the new parameter.  If NAME
     consists of multiple words, then the initial words are looked for
     as prefix parameters.  An example of this can be illustrated with
     the 'set print' set of parameters.  If NAME is 'print foo', then
     'print' will be searched as the prefix parameter.  In this case the
     parameter can subsequently be accessed in GDB as 'set print foo'.
     If NAME consists of multiple words, and no prefix parameter group
     can be found, an exception is raised.

     The result is the '<gdb:parameter>' object representing the
     parameter.  The parameter is not usable until it has been
     registered with GDB with 'register-parameter!'.

     The rest of the arguments are optional.

     The argument COMMAND-CLASS should be one of the 'COMMAND_'
     constants (*note Commands In Guile::).  This argument tells GDB how
     to categorize the new parameter in the help system.  The default is
     'COMMAND_NONE'.

     The argument PARAMETER-TYPE should be one of the 'PARAM_' constants
     defined below.  This argument tells GDB the type of the new
     parameter; this information is used for input validation and
     completion.  The default is 'PARAM_BOOLEAN'.

     If PARAMETER-TYPE is 'PARAM_ENUM', then ENUM-LIST must be a list of
     strings.  These strings represent the possible values for the
     parameter.

     If PARAMETER-TYPE is not 'PARAM_ENUM', then the presence of
     ENUM-LIST will cause an exception to be thrown.

     The argument SET-FUNC is a function of one argument: SELF which is
     the '<gdb:parameter>' object representing the parameter.  GDB will
     call this function when a PARAMETER's value has been changed via
     the 'set' API (for example, 'set foo off').  The value of the
     parameter has already been set to the new value.  This function
     must return a string to be displayed to the user.  GDB will add a
     trailing newline if the string is non-empty.  GDB generally doesn't
     print anything when a parameter is set, thus typically this
     function should return '""'.  A non-empty string result should
     typically be used for displaying warnings and errors.

     The argument SHOW-FUNC is a function of two arguments: SELF which
     is the '<gdb:parameter>' object representing the parameter, and
     SVALUE which is the string representation of the current value.
     GDB will call this function when a PARAMETER's 'show' API has been
     invoked (for example, 'show foo').  This function must return a
     string, and will be displayed to the user.  GDB will add a trailing
     newline.

     The argument DOC is the help text for the new parameter.  If there
     is no documentation string, a default value is used.

     The argument SET-DOC is the help text for this parameter's 'set'
     command.

     The argument SHOW-DOC is the help text for this parameter's 'show'
     command.

     The argument INITIAL-VALUE specifies the initial value of the
     parameter.  If it is a function, it takes one parameter, the
     '<gdb:parameter>' object and its result is used as the initial
     value of the parameter.  The initial value must be valid for the
     parameter type, otherwise an exception is thrown.

 -- Scheme Procedure: register-parameter! parameter
     Add PARAMETER, a '<gdb:parameter>' object, to GDB's list of
     parameters.  It is an error to register a parameter more than once.
     The result is unspecified.

 -- Scheme Procedure: parameter? object
     Return '#t' if OBJECT is a '<gdb:parameter>' object.  Otherwise
     return '#f'.

 -- Scheme Procedure: parameter-value parameter
     Return the value of PARAMETER which may either be a
     '<gdb:parameter>' object or a string naming the parameter.

 -- Scheme Procedure: set-parameter-value! parameter new-value
     Assign PARAMETER the value of NEW-VALUE.  The argument PARAMETER
     must be an object of type '<gdb:parameter>'.  GDB does validation
     when assignments are made.

   When a new parameter is defined, its type must be specified.  The
available types are represented by constants defined in the 'gdb'
module:

'PARAM_BOOLEAN'
     The value is a plain boolean.  The Guile boolean values, '#t' and
     '#f' are the only valid values.

'PARAM_AUTO_BOOLEAN'
     The value has three possible states: true, false, and 'auto'.  In
     Guile, true and false are represented using boolean constants, and
     'auto' is represented using '#:auto'.

'PARAM_UINTEGER'
     The value is an unsigned integer.  The value of 0 should be
     interpreted to mean "unlimited".

'PARAM_ZINTEGER'
     The value is an integer.

'PARAM_ZUINTEGER'
     The value is an unsigned integer.

'PARAM_ZUINTEGER_UNLIMITED'
     The value is an integer in the range '[0, INT_MAX]'.  A value of
     '-1' means "unlimited", and other negative numbers are not allowed.

'PARAM_STRING'
     The value is a string.  When the user modifies the string, any
     escape sequences, such as '\t', '\f', and octal escapes, are
     translated into corresponding characters and encoded into the
     current host charset.

'PARAM_STRING_NOESCAPE'
     The value is a string.  When the user modifies the string, escapes
     are passed through untranslated.

'PARAM_OPTIONAL_FILENAME'
     The value is a either a filename (a string), or '#f'.

'PARAM_FILENAME'
     The value is a filename.  This is just like
     'PARAM_STRING_NOESCAPE', but uses file names for completion.

'PARAM_ENUM'
     The value is a string, which must be one of a collection of string
     constants provided when the parameter is created.

   ---------- Footnotes ----------

   (1) Note that GDB parameters must not be confused with Guile’s
parameter objects (*note (guile)Parameters::).

\1f
File: gdb.info,  Node: Progspaces In Guile,  Next: Objfiles In Guile,  Prev: Parameters In Guile,  Up: Guile API

23.3.3.13 Program Spaces In Guile
.................................

A program space, or "progspace", represents a symbolic view of an
address space.  It consists of all of the objfiles of the program.
*Note Objfiles In Guile::.  *Note program spaces: Inferiors and
Programs, for more details about program spaces.

   Each progspace is represented by an instance of the '<gdb:progspace>'
smob.  *Note GDB Scheme Data Types::.

   The following progspace-related functions are available in the
'(gdb)' module:

 -- Scheme Procedure: progspace? object
     Return '#t' if OBJECT is a '<gdb:progspace>' object.  Otherwise
     return '#f'.

 -- Scheme Procedure: progspace-valid? progspace
     Return '#t' if PROGSPACE is valid, '#f' if not.  A
     '<gdb:progspace>' object can become invalid if the program it
     refers to is not loaded in GDB any longer.

 -- Scheme Procedure: current-progspace
     This function returns the program space of the currently selected
     inferior.  There is always a current progspace, this never returns
     '#f'.  *Note Inferiors and Programs::.

 -- Scheme Procedure: progspaces
     Return a list of all the progspaces currently known to GDB.

 -- Scheme Procedure: progspace-filename progspace
     Return the absolute file name of PROGSPACE as a string.  This is
     the name of the file passed as the argument to the 'file' or
     'symbol-file' commands.  If the program space does not have an
     associated file name, then '#f' is returned.  This occurs, for
     example, when GDB is started without a program to debug.

     A 'gdb:invalid-object-error' exception is thrown if PROGSPACE is
     invalid.

 -- Scheme Procedure: progspace-objfiles progspace
     Return the list of objfiles of PROGSPACE.  The order of objfiles in
     the result is arbitrary.  Each element is an object of type
     '<gdb:objfile>'.  *Note Objfiles In Guile::.

     A 'gdb:invalid-object-error' exception is thrown if PROGSPACE is
     invalid.

 -- Scheme Procedure: progspace-pretty-printers progspace
     Return the list of pretty-printers of PROGSPACE.  Each element is
     an object of type '<gdb:pretty-printer>'.  *Note Guile Pretty
     Printing API::, for more information.

 -- Scheme Procedure: set-progspace-pretty-printers! progspace
          printer-list
     Set the list of registered '<gdb:pretty-printer>' objects for
     PROGSPACE to PRINTER-LIST.  *Note Guile Pretty Printing API::, for
     more information.

\1f
File: gdb.info,  Node: Objfiles In Guile,  Next: Frames In Guile,  Prev: Progspaces In Guile,  Up: Guile API

23.3.3.14 Objfiles In Guile
...........................

GDB loads symbols for an inferior from various symbol-containing files
(*note Files::).  These include the primary executable file, any shared
libraries used by the inferior, and any separate debug info files (*note
Separate Debug Files::).  GDB calls these symbol-containing files
"objfiles".

   Each objfile is represented as an object of type '<gdb:objfile>'.

   The following objfile-related procedures are provided by the '(gdb)'
module:

 -- Scheme Procedure: objfile? object
     Return '#t' if OBJECT is a '<gdb:objfile>' object.  Otherwise
     return '#f'.

 -- Scheme Procedure: objfile-valid? objfile
     Return '#t' if OBJFILE is valid, '#f' if not.  A '<gdb:objfile>'
     object can become invalid if the object file it refers to is not
     loaded in GDB any longer.  All other '<gdb:objfile>' procedures
     will throw an exception if it is invalid at the time the procedure
     is called.

 -- Scheme Procedure: objfile-filename objfile
     Return the file name of OBJFILE as a string.

 -- Scheme Procedure: objfile-pretty-printers objfile
     Return the list of registered '<gdb:pretty-printer>' objects for
     OBJFILE.  *Note Guile Pretty Printing API::, for more information.

 -- Scheme Procedure: set-objfile-pretty-printers! objfile printer-list
     Set the list of registered '<gdb:pretty-printer>' objects for
     OBJFILE to PRINTER-LIST.  The PRINTER-LIST must be a list of
     '<gdb:pretty-printer>' objects.  *Note Guile Pretty Printing API::,
     for more information.

 -- Scheme Procedure: current-objfile
     When auto-loading a Guile script (*note Guile Auto-loading::), GDB
     sets the "current objfile" to the corresponding objfile.  This
     function returns the current objfile.  If there is no current
     objfile, this function returns '#f'.

 -- Scheme Procedure: objfiles
     Return a list of all the objfiles in the current program space.

\1f
File: gdb.info,  Node: Frames In Guile,  Next: Blocks In Guile,  Prev: Objfiles In Guile,  Up: Guile API

23.3.3.15 Accessing inferior stack frames from Guile.
.....................................................

When the debugged program stops, GDB is able to analyze its call stack
(*note Stack frames: Frames.).  The '<gdb:frame>' class represents a
frame in the stack.  A '<gdb:frame>' object is only valid while its
corresponding frame exists in the inferior's stack.  If you try to use
an invalid frame object, GDB will throw a 'gdb:invalid-object' exception
(*note Guile Exception Handling::).

   Two '<gdb:frame>' objects can be compared for equality with the
'equal?' function, like:

     (gdb) guile (equal? (newest-frame) (selected-frame))
     #t

   The following frame-related procedures are provided by the '(gdb)'
module:

 -- Scheme Procedure: frame? object
     Return '#t' if OBJECT is a '<gdb:frame>' object.  Otherwise return
     '#f'.

 -- Scheme Procedure: frame-valid? frame
     Returns '#t' if FRAME is valid, '#f' if not.  A frame object can
     become invalid if the frame it refers to doesn't exist anymore in
     the inferior.  All '<gdb:frame>' procedures will throw an exception
     if the frame is invalid at the time the procedure is called.

 -- Scheme Procedure: frame-name frame
     Return the function name of FRAME, or '#f' if it can't be obtained.

 -- Scheme Procedure: frame-arch frame
     Return the '<gdb:architecture>' object corresponding to FRAME's
     architecture.  *Note Architectures In Guile::.

 -- Scheme Procedure: frame-type frame
     Return the type of FRAME.  The value can be one of:

     'NORMAL_FRAME'
          An ordinary stack frame.

     'DUMMY_FRAME'
          A fake stack frame that was created by GDB when performing an
          inferior function call.

     'INLINE_FRAME'
          A frame representing an inlined function.  The function was
          inlined into a 'NORMAL_FRAME' that is older than this one.

     'TAILCALL_FRAME'
          A frame representing a tail call.  *Note Tail Call Frames::.

     'SIGTRAMP_FRAME'
          A signal trampoline frame.  This is the frame created by the
          OS when it calls into a signal handler.

     'ARCH_FRAME'
          A fake stack frame representing a cross-architecture call.

     'SENTINEL_FRAME'
          This is like 'NORMAL_FRAME', but it is only used for the
          newest frame.

 -- Scheme Procedure: frame-unwind-stop-reason frame
     Return an integer representing the reason why it's not possible to
     find more frames toward the outermost frame.  Use
     'unwind-stop-reason-string' to convert the value returned by this
     function to a string.  The value can be one of:

     'FRAME_UNWIND_NO_REASON'
          No particular reason (older frames should be available).

     'FRAME_UNWIND_NULL_ID'
          The previous frame's analyzer returns an invalid result.

     'FRAME_UNWIND_OUTERMOST'
          This frame is the outermost.

     'FRAME_UNWIND_UNAVAILABLE'
          Cannot unwind further, because that would require knowing the
          values of registers or memory that have not been collected.

     'FRAME_UNWIND_INNER_ID'
          This frame ID looks like it ought to belong to a NEXT frame,
          but we got it for a PREV frame.  Normally, this is a sign of
          unwinder failure.  It could also indicate stack corruption.

     'FRAME_UNWIND_SAME_ID'
          This frame has the same ID as the previous one.  That means
          that unwinding further would almost certainly give us another
          frame with exactly the same ID, so break the chain.  Normally,
          this is a sign of unwinder failure.  It could also indicate
          stack corruption.

     'FRAME_UNWIND_NO_SAVED_PC'
          The frame unwinder did not find any saved PC, but we needed
          one to unwind further.

     'FRAME_UNWIND_MEMORY_ERROR'
          The frame unwinder caused an error while trying to access
          memory.

     'FRAME_UNWIND_FIRST_ERROR'
          Any stop reason greater or equal to this value indicates some
          kind of error.  This special value facilitates writing code
          that tests for errors in unwinding in a way that will work
          correctly even if the list of the other values is modified in
          future GDB versions.  Using it, you could write:

               (define reason (frame-unwind-stop-readon (selected-frame)))
               (define reason-str (unwind-stop-reason-string reason))
               (if (>= reason FRAME_UNWIND_FIRST_ERROR)
                   (format #t "An error occured: ~s\n" reason-str))

 -- Scheme Procedure: frame-pc frame
     Return the frame's resume address.

 -- Scheme Procedure: frame-block frame
     Return the frame's code block as a '<gdb:block>' object.  *Note
     Blocks In Guile::.

 -- Scheme Procedure: frame-function frame
     Return the symbol for the function corresponding to this frame as a
     '<gdb:symbol>' object, or '#f' if there isn't one.  *Note Symbols
     In Guile::.

 -- Scheme Procedure: frame-older frame
     Return the frame that called FRAME.

 -- Scheme Procedure: frame-newer frame
     Return the frame called by FRAME.

 -- Scheme Procedure: frame-sal frame
     Return the frame's '<gdb:sal>' (symtab and line) object.  *Note
     Symbol Tables In Guile::.

 -- Scheme Procedure: frame-read-var frame variable [#:block block]
     Return the value of VARIABLE in FRAME.  If the optional argument
     BLOCK is provided, search for the variable from that block;
     otherwise start at the frame's current block (which is determined
     by the frame's current program counter).  The VARIABLE must be
     given as a string or a '<gdb:symbol>' object, and BLOCK must be a
     '<gdb:block>' object.

 -- Scheme Procedure: frame-select frame
     Set FRAME to be the selected frame.  *Note Examining the Stack:
     Stack.

 -- Scheme Procedure: selected-frame
     Return the selected frame object.  *Note Selecting a Frame:
     Selection.

 -- Scheme Procedure: newest-frame
     Return the newest frame object for the selected thread.

 -- Scheme Procedure: unwind-stop-reason-string reason
     Return a string explaining the reason why GDB stopped unwinding
     frames, as expressed by the given REASON code (an integer, see the
     'frame-unwind-stop-reason' procedure above in this section).

\1f
File: gdb.info,  Node: Blocks In Guile,  Next: Symbols In Guile,  Prev: Frames In Guile,  Up: Guile API

23.3.3.16 Accessing blocks from Guile.
......................................

In GDB, symbols are stored in blocks.  A block corresponds roughly to a
scope in the source code.  Blocks are organized hierarchically, and are
represented individually in Guile as an object of type '<gdb:block>'.
Blocks rely on debugging information being available.

   A frame has a block.  Please see *note Frames In Guile::, for a more
in-depth discussion of frames.

   The outermost block is known as the "global block".  The global block
typically holds public global variables and functions.

   The block nested just inside the global block is the "static block".
The static block typically holds file-scoped variables and functions.

   GDB provides a method to get a block's superblock, but there is
currently no way to examine the sub-blocks of a block, or to iterate
over all the blocks in a symbol table (*note Symbol Tables In Guile::).

   Here is a short example that should help explain blocks:

     /* This is in the global block.  */
     int global;

     /* This is in the static block.  */
     static int file_scope;

     /* 'function' is in the global block, and 'argument' is
        in a block nested inside of 'function'.  */
     int function (int argument)
     {
       /* 'local' is in a block inside 'function'.  It may or may
          not be in the same block as 'argument'.  */
       int local;

       {
          /* 'inner' is in a block whose superblock is the one holding
             'local'.  */
          int inner;

          /* If this call is expanded by the compiler, you may see
             a nested block here whose function is 'inline_function'
             and whose superblock is the one holding 'inner'.  */
          inline_function ();
       }
     }

   The following block-related procedures are provided by the '(gdb)'
module:

 -- Scheme Procedure: block? object
     Return '#t' if OBJECT is a '<gdb:block>' object.  Otherwise return
     '#f'.

 -- Scheme Procedure: block-valid? block
     Returns '#t' if '<gdb:block>' BLOCK is valid, '#f' if not.  A block
     object can become invalid if the block it refers to doesn't exist
     anymore in the inferior.  All other '<gdb:block>' methods will
     throw an exception if it is invalid at the time the procedure is
     called.  The block's validity is also checked during iteration over
     symbols of the block.

 -- Scheme Procedure: block-start block
     Return the start address of '<gdb:block>' BLOCK.

 -- Scheme Procedure: block-end block
     Return the end address of '<gdb:block>' BLOCK.

 -- Scheme Procedure: block-function block
     Return the name of '<gdb:block>' BLOCK represented as a
     '<gdb:symbol>' object.  If the block is not named, then '#f' is
     returned.

     For ordinary function blocks, the superblock is the static block.
     However, you should note that it is possible for a function block
     to have a superblock that is not the static block - for instance
     this happens for an inlined function.

 -- Scheme Procedure: block-superblock block
     Return the block containing '<gdb:block>' BLOCK.  If the parent
     block does not exist, then '#f' is returned.

 -- Scheme Procedure: block-global-block block
     Return the global block associated with '<gdb:block>' BLOCK.

 -- Scheme Procedure: block-static-block block
     Return the static block associated with '<gdb:block>' BLOCK.

 -- Scheme Procedure: block-global? block
     Return '#t' if '<gdb:block>' BLOCK is a global block.  Otherwise
     return '#f'.

 -- Scheme Procedure: block-static? block
     Return '#t' if '<gdb:block>' BLOCK is a static block.  Otherwise
     return '#f'.

 -- Scheme Procedure: block-symbols
     Return a list of all symbols (as <gdb:symbol> objects) in
     '<gdb:block>' BLOCK.

 -- Scheme Procedure: make-block-symbols-iterator block
     Return an object of type '<gdb:iterator>' that will iterate over
     all symbols of the block.  Guile programs should not assume that a
     specific block object will always contain a given symbol, since
     changes in GDB features and infrastructure may cause symbols move
     across blocks in a symbol table.  *Note Iterators In Guile::.

 -- Scheme Procedure: block-symbols-progress?
     Return #t if the object is a <gdb:block-symbols-progress> object.
     This object would be obtained from the 'progress' element of the
     '<gdb:iterator>' object returned by 'make-block-symbols-iterator'.

 -- Scheme Procedure: lookup-block pc
     Return the innermost '<gdb:block>' containing the given PC value.
     If the block cannot be found for the PC value specified, the
     function will return '#f'.

\1f
File: gdb.info,  Node: Symbols In Guile,  Next: Symbol Tables In Guile,  Prev: Blocks In Guile,  Up: Guile API

23.3.3.17 Guile representation of Symbols.
..........................................

GDB represents every variable, function and type as an entry in a symbol
table.  *Note Examining the Symbol Table: Symbols.  Guile represents
these symbols in GDB with the '<gdb:symbol>' object.

   The following symbol-related procedures are provided by the '(gdb)'
module:

 -- Scheme Procedure: symbol? object
     Return '#t' if OBJECT is an object of type '<gdb:symbol>'.
     Otherwise return '#f'.

 -- Scheme Procedure: symbol-valid? symbol
     Return '#t' if the '<gdb:symbol>' object is valid, '#f' if not.  A
     '<gdb:symbol>' object can become invalid if the symbol it refers to
     does not exist in GDB any longer.  All other '<gdb:symbol>'
     procedures will throw an exception if it is invalid at the time the
     procedure is called.

 -- Scheme Procedure: symbol-type symbol
     Return the type of SYMBOL or '#f' if no type is recorded.  The
     result is an object of type '<gdb:type>'.  *Note Types In Guile::.

 -- Scheme Procedure: symbol-symtab symbol
     Return the symbol table in which SYMBOL appears.  The result is an
     object of type '<gdb:symtab>'.  *Note Symbol Tables In Guile::.

 -- Scheme Procedure: symbol-line symbol
     Return the line number in the source code at which SYMBOL was
     defined.  This is an integer.

 -- Scheme Procedure: symbol-name symbol
     Return the name of SYMBOL as a string.

 -- Scheme Procedure: symbol-linkage-name symbol
     Return the name of SYMBOL, as used by the linker (i.e., may be
     mangled).

 -- Scheme Procedure: symbol-print-name symbol
     Return the name of SYMBOL in a form suitable for output.  This is
     either 'name' or 'linkage_name', depending on whether the user
     asked GDB to display demangled or mangled names.

 -- Scheme Procedure: symbol-addr-class symbol
     Return the address class of the symbol.  This classifies how to
     find the value of a symbol.  Each address class is a constant
     defined in the '(gdb)' module and described later in this chapter.

 -- Scheme Procedure: symbol-needs-frame? symbol
     Return '#t' if evaluating SYMBOL's value requires a frame (*note
     Frames In Guile::) and '#f' otherwise.  Typically, local variables
     will require a frame, but other symbols will not.

 -- Scheme Procedure: symbol-argument? symbol
     Return '#t' if SYMBOL is an argument of a function.  Otherwise
     return '#f'.

 -- Scheme Procedure: symbol-constant? symbol
     Return '#t' if SYMBOL is a constant.  Otherwise return '#f'.

 -- Scheme Procedure: symbol-function? symbol
     Return '#t' if SYMBOL is a function or a method.  Otherwise return
     '#f'.

 -- Scheme Procedure: symbol-variable? symbol
     Return '#t' if SYMBOL is a variable.  Otherwise return '#f'.

 -- Scheme Procedure: symbol-value symbol [#:frame frame]
     Compute the value of SYMBOL, as a '<gdb:value>'.  For functions,
     this computes the address of the function, cast to the appropriate
     type.  If the symbol requires a frame in order to compute its
     value, then FRAME must be given.  If FRAME is not given, or if
     FRAME is invalid, then an exception is thrown.

 -- Scheme Procedure: lookup-symbol name [#:block block] [#:domain
          domain]
     This function searches for a symbol by name.  The search scope can
     be restricted to the parameters defined in the optional domain and
     block arguments.

     NAME is the name of the symbol.  It must be a string.  The optional
     BLOCK argument restricts the search to symbols visible in that
     BLOCK.  The BLOCK argument must be a '<gdb:block>' object.  If
     omitted, the block for the current frame is used.  The optional
     DOMAIN argument restricts the search to the domain type.  The
     DOMAIN argument must be a domain constant defined in the '(gdb)'
     module and described later in this chapter.

     The result is a list of two elements.  The first element is a
     '<gdb:symbol>' object or '#f' if the symbol is not found.  If the
     symbol is found, the second element is '#t' if the symbol is a
     field of a method's object (e.g., 'this' in C++), otherwise it is
     '#f'.  If the symbol is not found, the second element is '#f'.

 -- Scheme Procedure: lookup-global-symbol name [#:domain domain]
     This function searches for a global symbol by name.  The search
     scope can be restricted by the domain argument.

     NAME is the name of the symbol.  It must be a string.  The optional
     DOMAIN argument restricts the search to the domain type.  The
     DOMAIN argument must be a domain constant defined in the '(gdb)'
     module and described later in this chapter.

     The result is a '<gdb:symbol>' object or '#f' if the symbol is not
     found.

   The available domain categories in '<gdb:symbol>' are represented as
constants in the '(gdb)' module:

'SYMBOL_UNDEF_DOMAIN'
     This is used when a domain has not been discovered or none of the
     following domains apply.  This usually indicates an error either in
     the symbol information or in GDB's handling of symbols.

'SYMBOL_VAR_DOMAIN'
     This domain contains variables, function names, typedef names and
     enum type values.

'SYMBOL_STRUCT_DOMAIN'
     This domain holds struct, union and enum type names.

'SYMBOL_LABEL_DOMAIN'
     This domain contains names of labels (for gotos).

'SYMBOL_VARIABLES_DOMAIN'
     This domain holds a subset of the 'SYMBOLS_VAR_DOMAIN'; it contains
     everything minus functions and types.

'SYMBOL_FUNCTION_DOMAIN'
     This domain contains all functions.

'SYMBOL_TYPES_DOMAIN'
     This domain contains all types.

   The available address class categories in '<gdb:symbol>' are
represented as constants in the 'gdb' module:

'SYMBOL_LOC_UNDEF'
     If this is returned by address class, it indicates an error either
     in the symbol information or in GDB's handling of symbols.

'SYMBOL_LOC_CONST'
     Value is constant int.

'SYMBOL_LOC_STATIC'
     Value is at a fixed address.

'SYMBOL_LOC_REGISTER'
     Value is in a register.

'SYMBOL_LOC_ARG'
     Value is an argument.  This value is at the offset stored within
     the symbol inside the frame's argument list.

'SYMBOL_LOC_REF_ARG'
     Value address is stored in the frame's argument list.  Just like
     'LOC_ARG' except that the value's address is stored at the offset,
     not the value itself.

'SYMBOL_LOC_REGPARM_ADDR'
     Value is a specified register.  Just like 'LOC_REGISTER' except the
     register holds the address of the argument instead of the argument
     itself.

'SYMBOL_LOC_LOCAL'
     Value is a local variable.

'SYMBOL_LOC_TYPEDEF'
     Value not used.  Symbols in the domain 'SYMBOL_STRUCT_DOMAIN' all
     have this class.

'SYMBOL_LOC_BLOCK'
     Value is a block.

'SYMBOL_LOC_CONST_BYTES'
     Value is a byte-sequence.

'SYMBOL_LOC_UNRESOLVED'
     Value is at a fixed address, but the address of the variable has to
     be determined from the minimal symbol table whenever the variable
     is referenced.

'SYMBOL_LOC_OPTIMIZED_OUT'
     The value does not actually exist in the program.

'SYMBOL_LOC_COMPUTED'
     The value's address is a computed location.

\1f
File: gdb.info,  Node: Symbol Tables In Guile,  Next: Breakpoints In Guile,  Prev: Symbols In Guile,  Up: Guile API

23.3.3.18 Symbol table representation in Guile.
...............................................

Access to symbol table data maintained by GDB on the inferior is exposed
to Guile via two objects: '<gdb:sal>' (symtab-and-line) and
'<gdb:symtab>'.  Symbol table and line data for a frame is returned from
the 'frame-find-sal' '<gdb:frame>' procedure.  *Note Frames In Guile::.

   For more information on GDB's symbol table management, see *note
Examining the Symbol Table: Symbols.

   The following symtab-related procedures are provided by the '(gdb)'
module:

 -- Scheme Procedure: symtab? object
     Return '#t' if OBJECT is an object of type '<gdb:symtab>'.
     Otherwise return '#f'.

 -- Scheme Procedure: symtab-valid? symtab
     Return '#t' if the '<gdb:symtab>' object is valid, '#f' if not.  A
     '<gdb:symtab>' object becomes invalid when the symbol table it
     refers to no longer exists in GDB.  All other '<gdb:symtab>'
     procedures will throw an exception if it is invalid at the time the
     procedure is called.

 -- Scheme Procedure: symtab-filename symtab
     Return the symbol table's source filename.

 -- Scheme Procedure: symtab-fullname symtab
     Return the symbol table's source absolute file name.

 -- Scheme Procedure: symtab-objfile symtab
     Return the symbol table's backing object file.  *Note Objfiles In
     Guile::.

 -- Scheme Procedure: symtab-global-block symtab
     Return the global block of the underlying symbol table.  *Note
     Blocks In Guile::.

 -- Scheme Procedure: symtab-static-block symtab
     Return the static block of the underlying symbol table.  *Note
     Blocks In Guile::.

   The following symtab-and-line-related procedures are provided by the
'(gdb)' module:

 -- Scheme Procedure: sal? object
     Return '#t' if OBJECT is an object of type '<gdb:sal>'.  Otherwise
     return '#f'.

 -- Scheme Procedure: sal-valid? sal
     Return '#t' if SAL is valid, '#f' if not.  A '<gdb:sal>' object
     becomes invalid when the Symbol table object it refers to no longer
     exists in GDB.  All other '<gdb:sal>' procedures will throw an
     exception if it is invalid at the time the procedure is called.

 -- Scheme Procedure: sal-symtab sal
     Return the symbol table object ('<gdb:symtab>') for SAL.

 -- Scheme Procedure: sal-line sal
     Return the line number for SAL.

 -- Scheme Procedure: sal-pc sal
     Return the start of the address range occupied by code for SAL.

 -- Scheme Procedure: sal-last sal
     Return the end of the address range occupied by code for SAL.

 -- Scheme Procedure: find-pc-line pc
     Return the '<gdb:sal>' object corresponding to the PC value.  If an
     invalid value of PC is passed as an argument, then the 'symtab' and
     'line' attributes of the returned '<gdb:sal>' object will be '#f'
     and 0 respectively.

\1f
File: gdb.info,  Node: Breakpoints In Guile,  Next: Lazy Strings In Guile,  Prev: Symbol Tables In Guile,  Up: Guile API

23.3.3.19 Manipulating breakpoints using Guile
..............................................

Breakpoints in Guile are represented by objects of type
'<gdb:breakpoint>'.  New breakpoints can be created with the
'make-breakpoint' Guile function, and then added to GDB with the
'register-breakpoint!' Guile function.  This two-step approach is taken
to separate out the side-effect of adding the breakpoint to GDB from
'make-breakpoint'.

   Support is also provided to view and manipulate breakpoints created
outside of Guile.

   The following breakpoint-related procedures are provided by the
'(gdb)' module:

 -- Scheme Procedure: make-breakpoint location [#:type type] [#:wp-class
          wp-class] [#:internal internal]
     Create a new breakpoint at LOCATION, a string naming the location
     of the breakpoint, or an expression that defines a watchpoint.  The
     contents can be any location recognized by the 'break' command, or
     in the case of a watchpoint, by the 'watch' command.

     The breakpoint is initially marked as 'invalid'.  The breakpoint is
     not usable until it has been registered with GDB with
     'register-breakpoint!', at which point it becomes 'valid'.  The
     result is the '<gdb:breakpoint>' object representing the
     breakpoint.

     The optional TYPE denotes the breakpoint to create.  This argument
     can be either 'BP_BREAKPOINT' or 'BP_WATCHPOINT', and defaults to
     'BP_BREAKPOINT'.

     The optional WP-CLASS argument defines the class of watchpoint to
     create, if TYPE is 'BP_WATCHPOINT'.  If a watchpoint class is not
     provided, it is assumed to be a 'WP_WRITE' class.

     The optional INTERNAL argument allows the breakpoint to become
     invisible to the user.  The breakpoint will neither be reported
     when registered, nor will it be listed in the output from 'info
     breakpoints' (but will be listed with the 'maint info breakpoints'
     command).  If an internal flag is not provided, the breakpoint is
     visible (non-internal).

     When a watchpoint is created, GDB will try to create a hardware
     assisted watchpoint.  If successful, the type of the watchpoint is
     changed from 'BP_WATCHPOINT' to 'BP_HARDWARE_WATCHPOINT' for
     'WP_WRITE', 'BP_READ_WATCHPOINT' for 'WP_READ', and
     'BP_ACCESS_WATCHPOINT' for 'WP_ACCESS'.  If not successful, the
     type of the watchpoint is left as 'WP_WATCHPOINT'.

     The available types are represented by constants defined in the
     'gdb' module:

     'BP_BREAKPOINT'
          Normal code breakpoint.

     'BP_WATCHPOINT'
          Watchpoint breakpoint.

     'BP_HARDWARE_WATCHPOINT'
          Hardware assisted watchpoint.  This value cannot be specified
          when creating the breakpoint.

     'BP_READ_WATCHPOINT'
          Hardware assisted read watchpoint.  This value cannot be
          specified when creating the breakpoint.

     'BP_ACCESS_WATCHPOINT'
          Hardware assisted access watchpoint.  This value cannot be
          specified when creating the breakpoint.

     The available watchpoint types represented by constants are defined
     in the '(gdb)' module:

     'WP_READ'
          Read only watchpoint.

     'WP_WRITE'
          Write only watchpoint.

     'WP_ACCESS'
          Read/Write watchpoint.

 -- Scheme Procedure: register-breakpoint! breakpoint
     Add BREAKPOINT, a '<gdb:breakpoint>' object, to GDB's list of
     breakpoints.  The breakpoint must have been created with
     'make-breakpoint'.  One cannot register breakpoints that have been
     created outside of Guile.  Once a breakpoint is registered it
     becomes 'valid'.  It is an error to register an already registered
     breakpoint.  The result is unspecified.

 -- Scheme Procedure: delete-breakpoint! breakpoint
     Remove BREAKPOINT from GDB's list of breakpoints.  This also
     invalidates the Guile BREAKPOINT object.  Any further attempt to
     access the object will throw an exception.

     If BREAKPOINT was created from Guile with 'make-breakpoint' it may
     be re-registered with GDB, in which case the breakpoint becomes
     valid again.

 -- Scheme Procedure: breakpoints
     Return a list of all breakpoints.  Each element of the list is a
     '<gdb:breakpoint>' object.

 -- Scheme Procedure: breakpoint? object
     Return '#t' if OBJECT is a '<gdb:breakpoint>' object, and '#f'
     otherwise.

 -- Scheme Procedure: breakpoint-valid? breakpoint
     Return '#t' if BREAKPOINT is valid, '#f' otherwise.  Breakpoints
     created with 'make-breakpoint' are marked as invalid until they are
     registered with GDB with 'register-breakpoint!'.  A
     '<gdb:breakpoint>' object can become invalid if the user deletes
     the breakpoint.  In this case, the object still exists, but the
     underlying breakpoint does not.  In the cases of watchpoint scope,
     the watchpoint remains valid even if execution of the inferior
     leaves the scope of that watchpoint.

 -- Scheme Procedure: breakpoint-number breakpoint
     Return the breakpoint's number -- the identifier used by the user
     to manipulate the breakpoint.

 -- Scheme Procedure: breakpoint-type breakpoint
     Return the breakpoint's type -- the identifier used to determine
     the actual breakpoint type or use-case.

 -- Scheme Procedure: breakpoint-visible? breakpoint
     Return '#t' if the breakpoint is visible to the user when hit, or
     when the 'info breakpoints' command is run.  Otherwise return '#f'.

 -- Scheme Procedure: breakpoint-location breakpoint
     Return the location of the breakpoint, as specified by the user.
     It is a string.  If the breakpoint does not have a location (that
     is, it is a watchpoint) return '#f'.

 -- Scheme Procedure: breakpoint-expression breakpoint
     Return the breakpoint expression, as specified by the user.  It is
     a string.  If the breakpoint does not have an expression (the
     breakpoint is not a watchpoint) return '#f'.

 -- Scheme Procedure: breakpoint-enabled? breakpoint
     Return '#t' if the breakpoint is enabled, and '#f' otherwise.

 -- Scheme Procedure: set-breakpoint-enabled! breakpoint flag
     Set the enabled state of BREAKPOINT to FLAG.  If flag is '#f' it is
     disabled, otherwise it is enabled.

 -- Scheme Procedure: breakpoint-silent? breakpoint
     Return '#t' if the breakpoint is silent, and '#f' otherwise.

     Note that a breakpoint can also be silent if it has commands and
     the first command is 'silent'.  This is not reported by the
     'silent' attribute.

 -- Scheme Procedure: set-breakpoint-silent! breakpoint flag
     Set the silent state of BREAKPOINT to FLAG.  If flag is '#f' the
     breakpoint is made silent, otherwise it is made non-silent (or
     noisy).

 -- Scheme Procedure: breakpoint-ignore-count breakpoint
     Return the ignore count for BREAKPOINT.

 -- Scheme Procedure: set-breakpoint-ignore-count! breakpoint count
     Set the ignore count for BREAKPOINT to COUNT.

 -- Scheme Procedure: breakpoint-hit-count breakpoint
     Return hit count of BREAKPOINT.

 -- Scheme Procedure: set-breakpoint-hit-count! breakpoint count
     Set the hit count of BREAKPOINT to COUNT.  At present, COUNT must
     be zero.

 -- Scheme Procedure: breakpoint-thread breakpoint
     Return the thread-id for thread-specific breakpoint BREAKPOINT.
     Return #f if BREAKPOINT is not thread-specific.

 -- Scheme Procedure: set-breakpoint-thread! breakpoint thread-id|#f
     Set the thread-id for BREAKPOINT to THREAD-ID.  If set to '#f', the
     breakpoint is no longer thread-specific.

 -- Scheme Procedure: breakpoint-task breakpoint
     If the breakpoint is Ada task-specific, return the Ada task id.  If
     the breakpoint is not task-specific (or the underlying language is
     not Ada), return '#f'.

 -- Scheme Procedure: set-breakpoint-task! breakpoint task
     Set the Ada task of BREAKPOINT to TASK.  If set to '#f', the
     breakpoint is no longer task-specific.

 -- Scheme Procedure: breakpoint-condition breakpoint
     Return the condition of BREAKPOINT, as specified by the user.  It
     is a string.  If there is no condition, return '#f'.

 -- Scheme Procedure: set-breakpoint-condition! breakpoint condition
     Set the condition of BREAKPOINT to CONDITION, which must be a
     string.  If set to '#f' then the breakpoint becomes unconditional.

 -- Scheme Procedure: breakpoint-stop breakpoint
     Return the stop predicate of BREAKPOINT.  See
     'set-breakpoint-stop!' below in this section.

 -- Scheme Procedure: set-breakpoint-stop! breakpoint procedure|#f
     Set the stop predicate of BREAKPOINT.  The predicate PROCEDURE
     takes one argument: the <gdb:breakpoint> object.  If this predicate
     is set to a procedure then it is invoked whenever the inferior
     reaches this breakpoint.  If it returns '#t', or any non-'#f'
     value, then the inferior is stopped, otherwise the inferior will
     continue.

     If there are multiple breakpoints at the same location with a
     'stop' predicate, each one will be called regardless of the return
     status of the previous.  This ensures that all 'stop' predicates
     have a chance to execute at that location.  In this scenario if one
     of the methods returns '#t' but the others return '#f', the
     inferior will still be stopped.

     You should not alter the execution state of the inferior (i.e.,
     step, next, etc.), alter the current frame context (i.e., change
     the current active frame), or alter, add or delete any breakpoint.
     As a general rule, you should not alter any data within GDB or the
     inferior at this time.

     Example 'stop' implementation:

          (define (my-stop? bkpt)
            (let ((int-val (parse-and-eval "foo")))
              (value=? int-val 3)))
          (define bkpt (make-breakpoint "main.c:42"))
          (register-breakpoint! bkpt)
          (set-breakpoint-stop! bkpt my-stop?)

 -- Scheme Procedure: breakpoint-commands breakpoint
     Return the commands attached to BREAKPOINT as a string, or '#f' if
     there are none.

\1f
File: gdb.info,  Node: Lazy Strings In Guile,  Next: Architectures In Guile,  Prev: Breakpoints In Guile,  Up: Guile API

23.3.3.20 Guile representation of lazy strings.
...............................................

A "lazy string" is a string whose contents is not retrieved or encoded
until it is needed.

   A '<gdb:lazy-string>' is represented in GDB as an 'address' that
points to a region of memory, an 'encoding' that will be used to encode
that region of memory, and a 'length' to delimit the region of memory
that represents the string.  The difference between a
'<gdb:lazy-string>' and a string wrapped within a '<gdb:value>' is that
a '<gdb:lazy-string>' will be treated differently by GDB when printing.
A '<gdb:lazy-string>' is retrieved and encoded during printing, while a
'<gdb:value>' wrapping a string is immediately retrieved and encoded on
creation.

   The following lazy-string-related procedures are provided by the
'(gdb)' module:

 -- Scheme Procedure: lazy-string? object
     Return '#t' if OBJECT is an object of type '<gdb:lazy-string>'.
     Otherwise return '#f'.

 -- Scheme Procedure: lazy-string-address lazy-sring
     Return the address of LAZY-STRING.

 -- Scheme Procedure: lazy-string-length lazy-string
     Return the length of LAZY-STRING in characters.  If the length is
     -1, then the string will be fetched and encoded up to the first
     null of appropriate width.

 -- Scheme Procedure: lazy-string-encoding lazy-string
     Return the encoding that will be applied to LAZY-STRING when the
     string is printed by GDB.  If the encoding is not set, or contains
     an empty string, then GDB will select the most appropriate encoding
     when the string is printed.

 -- Scheme Procedure: lazy-string-type lazy-string
     Return the type that is represented by LAZY-STRING's type.  For a
     lazy string this will always be a pointer type.  To resolve this to
     the lazy string's character type, use 'type-target-type'.  *Note
     Types In Guile::.

 -- Scheme Procedure: lazy-string->value lazy-string
     Convert the '<gdb:lazy-string>' to a '<gdb:value>'.  This value
     will point to the string in memory, but will lose all the delayed
     retrieval, encoding and handling that GDB applies to a
     '<gdb:lazy-string>'.

\1f
File: gdb.info,  Node: Architectures In Guile,  Next: Disassembly In Guile,  Prev: Lazy Strings In Guile,  Up: Guile API

23.3.3.21 Guile representation of architectures
...............................................

GDB uses architecture specific parameters and artifacts in a number of
its various computations.  An architecture is represented by an instance
of the '<gdb:arch>' class.

   The following architecture-related procedures are provided by the
'(gdb)' module:

 -- Scheme Procedure: arch? object
     Return '#t' if OBJECT is an object of type '<gdb:arch>'.  Otherwise
     return '#f'.

 -- Scheme Procedure: current-arch
     Return the current architecture as a '<gdb:arch>' object.

 -- Scheme Procedure: arch-name arch
     Return the name (string value) of '<gdb:arch>' ARCH.

 -- Scheme Procedure: arch-charset arch
     Return name of target character set of '<gdb:arch>' ARCH.

 -- Scheme Procedure: arch-wide-charset
     Return name of target wide character set of '<gdb:arch>' ARCH.

   Each architecture provides a set of predefined types, obtained by the
following functions.

 -- Scheme Procedure: arch-void-type arch
     Return the '<gdb:type>' object for a 'void' type of architecture
     ARCH.

 -- Scheme Procedure: arch-char-type arch
     Return the '<gdb:type>' object for a 'char' type of architecture
     ARCH.

 -- Scheme Procedure: arch-short-type arch
     Return the '<gdb:type>' object for a 'short' type of architecture
     ARCH.

 -- Scheme Procedure: arch-int-type arch
     Return the '<gdb:type>' object for an 'int' type of architecture
     ARCH.

 -- Scheme Procedure: arch-long-type arch
     Return the '<gdb:type>' object for a 'long' type of architecture
     ARCH.

 -- Scheme Procedure: arch-schar-type arch
     Return the '<gdb:type>' object for a 'signed char' type of
     architecture ARCH.

 -- Scheme Procedure: arch-uchar-type arch
     Return the '<gdb:type>' object for an 'unsigned char' type of
     architecture ARCH.

 -- Scheme Procedure: arch-ushort-type arch
     Return the '<gdb:type>' object for an 'unsigned short' type of
     architecture ARCH.

 -- Scheme Procedure: arch-uint-type arch
     Return the '<gdb:type>' object for an 'unsigned int' type of
     architecture ARCH.

 -- Scheme Procedure: arch-ulong-type arch
     Return the '<gdb:type>' object for an 'unsigned long' type of
     architecture ARCH.

 -- Scheme Procedure: arch-float-type arch
     Return the '<gdb:type>' object for a 'float' type of architecture
     ARCH.

 -- Scheme Procedure: arch-double-type arch
     Return the '<gdb:type>' object for a 'double' type of architecture
     ARCH.

 -- Scheme Procedure: arch-longdouble-type arch
     Return the '<gdb:type>' object for a 'long double' type of
     architecture ARCH.

 -- Scheme Procedure: arch-bool-type arch
     Return the '<gdb:type>' object for a 'bool' type of architecture
     ARCH.

 -- Scheme Procedure: arch-longlong-type arch
     Return the '<gdb:type>' object for a 'long long' type of
     architecture ARCH.

 -- Scheme Procedure: arch-ulonglong-type arch
     Return the '<gdb:type>' object for an 'unsigned long long' type of
     architecture ARCH.

 -- Scheme Procedure: arch-int8-type arch
     Return the '<gdb:type>' object for an 'int8' type of architecture
     ARCH.

 -- Scheme Procedure: arch-uint8-type arch
     Return the '<gdb:type>' object for a 'uint8' type of architecture
     ARCH.

 -- Scheme Procedure: arch-int16-type arch
     Return the '<gdb:type>' object for an 'int16' type of architecture
     ARCH.

 -- Scheme Procedure: arch-uint16-type arch
     Return the '<gdb:type>' object for a 'uint16' type of architecture
     ARCH.

 -- Scheme Procedure: arch-int32-type arch
     Return the '<gdb:type>' object for an 'int32' type of architecture
     ARCH.

 -- Scheme Procedure: arch-uint32-type arch
     Return the '<gdb:type>' object for a 'uint32' type of architecture
     ARCH.

 -- Scheme Procedure: arch-int64-type arch
     Return the '<gdb:type>' object for an 'int64' type of architecture
     ARCH.

 -- Scheme Procedure: arch-uint64-type arch
     Return the '<gdb:type>' object for a 'uint64' type of architecture
     ARCH.

   Example:

     (gdb) guile (type-name (arch-uchar-type (current-arch)))
     "unsigned char"

\1f
File: gdb.info,  Node: Disassembly In Guile,  Next: I/O Ports in Guile,  Prev: Architectures In Guile,  Up: Guile API

23.3.3.22 Disassembly In Guile
..............................

The disassembler can be invoked from Scheme code.  Furthermore, the
disassembler can take a Guile port as input, allowing one to disassemble
from any source, and not just target memory.

 -- Scheme Procedure: arch-disassemble arch start-pc [#:port port]
          [#:offset offset] [#:size size] [#:count count]
     Return a list of disassembled instructions starting from the memory
     address START-PC.

     The optional argument PORT specifies the input port to read bytes
     from.  If PORT is '#f' then bytes are read from target memory.

     The optional argument OFFSET specifies the address offset of the
     first byte in PORT.  This is useful, for example, when PORT
     specifies a 'bytevector' and you want the bytevector to be
     disassembled as if it came from that address.  The START-PC passed
     to the reader for PORT is offset by the same amount.

     Example:
          (gdb) guile (use-modules (rnrs io ports))
          (gdb) guile (define pc (value->integer (parse-and-eval "$pc")))
          (gdb) guile (define mem (open-memory #:start pc))
          (gdb) guile (define bv (get-bytevector-n mem 10))
          (gdb) guile (define bv-port (open-bytevector-input-port bv))
          (gdb) guile (define arch (current-arch))
          (gdb) guile (arch-disassemble arch pc #:port bv-port #:offset pc)
          (((address . 4195516) (asm . "mov    $0x4005c8,%edi") (length . 5)))

     The optional arguments SIZE and COUNT determine the number of
     instructions in the returned list.  If either SIZE or COUNT is
     specified as zero, then no instructions are disassembled and an
     empty list is returned.  If both the optional arguments SIZE and
     COUNT are specified, then a list of at most COUNT disassembled
     instructions whose start address falls in the closed memory address
     interval from START-PC to (START-PC + SIZE - 1) are returned.  If
     SIZE is not specified, but COUNT is specified, then COUNT number of
     instructions starting from the address START-PC are returned.  If
     COUNT is not specified but SIZE is specified, then all instructions
     whose start address falls in the closed memory address interval
     from START-PC to (START-PC + SIZE - 1) are returned.  If neither
     SIZE nor COUNT are specified, then a single instruction at START-PC
     is returned.

     Each element of the returned list is an alist (associative list)
     with the following keys:

     'address'
          The value corresponding to this key is a Guile integer of the
          memory address of the instruction.

     'asm'
          The value corresponding to this key is a string value which
          represents the instruction with assembly language mnemonics.
          The assembly language flavor used is the same as that
          specified by the current CLI variable 'disassembly-flavor'.
          *Note Machine Code::.

     'length'
          The value corresponding to this key is the length of the
          instruction in bytes.

\1f
File: gdb.info,  Node: I/O Ports in Guile,  Next: Memory Ports in Guile,  Prev: Disassembly In Guile,  Up: Guile API

23.3.3.23 I/O Ports in Guile
............................

 -- Scheme Procedure: input-port
     Return GDB's input port as a Guile port object.

 -- Scheme Procedure: output-port
     Return GDB's output port as a Guile port object.

 -- Scheme Procedure: error-port
     Return GDB's error port as a Guile port object.

 -- Scheme Procedure: stdio-port? object
     Return '#t' if OBJECT is a GDB stdio port.  Otherwise return '#f'.

\1f
File: gdb.info,  Node: Memory Ports in Guile,  Next: Iterators In Guile,  Prev: I/O Ports in Guile,  Up: Guile API

23.3.3.24 Memory Ports in Guile
...............................

GDB provides a 'port' interface to target memory.  This allows Guile
code to read/write target memory using Guile's port and bytevector
functionality.  The main routine is 'open-memory' which returns a port
object.  One can then read/write memory using that object.

 -- Scheme Procedure: open-memory [#:mode mode] [#:start address]
          [#:size size]
     Return a port object that can be used for reading and writing
     memory.  The port will be open according to MODE, which is the
     standard mode argument to Guile port open routines, except that it
     is restricted to one of '"r"', '"w"', or '"r+"'.  For compatibility
     '"b"' (binary) may also be present, but we ignore it: memory ports
     are binary only.  The default is '"r"', read-only.

     The chunk of memory that can be accessed can be bounded.  If both
     START and SIZE are unspecified, all of memory can be accessed.  If
     only START is specified, all of memory from that point on can be
     accessed.  If only SIZE if specified, all memory in the range
     [0,SIZE) can be accessed.  If both are specified, all memory in the
     rane [START,START+SIZE) can be accessed.

 -- Scheme Procedure: memory-port?
     Return '#t' if OBJECT is an object of type '<gdb:memory-port>'.
     Otherwise return '#f'.

 -- Scheme Procedure: memory-port-range memory-port
     Return the range of '<gdb:memory-port>' MEMORY-PORT as a list of
     two elements: '(start end)'.  The range is START to END inclusive.

 -- Scheme Procedure: memory-port-read-buffer-size memory-port
     Return the size of the read buffer of '<gdb:memory-port>'
     MEMORY-PORT.

 -- Scheme Procedure: set-memory-port-read-buffer-size! memory-port size
     Set the size of the read buffer of '<gdb:memory-port>' MEMORY-PORT
     to SIZE.  The result is unspecified.

 -- Scheme Procedure: memory-port-write-buffer-size memory-port
     Return the size of the write buffer of '<gdb:memory-port>'
     MEMORY-PORT.

 -- Scheme Procedure: set-memory-port-write-buffer-size! memory-port
          size
     Set the size of the write buffer of '<gdb:memory-port>' MEMORY-PORT
     to SIZE.  The result is unspecified.

   A memory port is closed like any other port, with 'close-port'.

   Combined with Guile's 'bytevectors', memory ports provide a lot of
utility.  For example, to fill a buffer of 10 integers in memory, one
can do something like the following.

     ;; In the program: int buffer[10];
     (use-modules (rnrs bytevectors))
     (use-modules (rnrs io ports))
     (define addr (parse-and-eval "buffer"))
     (define n 10)
     (define byte-size (* n 4))
     (define mem-port (open-memory #:mode "r+" #:start
                                   (value->integer addr) #:size byte-size))
     (define byte-vec (make-bytevector byte-size))
     (do ((i 0 (+ i 1)))
         ((>= i n))
         (bytevector-s32-native-set! byte-vec (* i 4) (* i 42)))
     (put-bytevector mem-port byte-vec)
     (close-port mem-port)

\1f
File: gdb.info,  Node: Iterators In Guile,  Prev: Memory Ports in Guile,  Up: Guile API

23.3.3.25 Iterators In Guile
............................

A simple iterator facility is provided to allow, for example, iterating
over the set of program symbols without having to first construct a list
of all of them.  A useful contribution would be to add support for SRFI
41 and SRFI 45.

 -- Scheme Procedure: make-iterator object progress next!
     A '<gdb:iterator>' object is constructed with the 'make-iterator'
     procedure.  It takes three arguments: the object to be iterated
     over, an object to record the progress of the iteration, and a
     procedure to return the next element in the iteration, or an
     implementation chosen value to denote the end of iteration.

     By convention, end of iteration is marked with
     '(end-of-iteration)', and may be tested with the
     'end-of-iteration?' predicate.  The result of '(end-of-iteration)'
     is chosen so that it is not otherwise used by the '(gdb)' module.
     If you are using '<gdb:iterator>' in your own code it is your
     responsibility to maintain this invariant.

     A trivial example for illustration's sake:

          (use-modules (gdb iterator))
          (define my-list (list 1 2 3))
          (define iter
            (make-iterator my-list my-list
                           (lambda (iter)
                             (let ((l (iterator-progress iter)))
                               (if (eq? l '())
                                   (end-of-iteration)
                                   (begin
                                     (set-iterator-progress! iter (cdr l))
                                     (car l)))))))

     Here is a slightly more realistic example, which computes a list of
     all the functions in 'my-global-block'.

          (use-modules (gdb iterator))
          (define this-sal (find-pc-line (frame-pc (selected-frame))))
          (define this-symtab (sal-symtab this-sal))
          (define this-global-block (symtab-global-block this-symtab))
          (define syms-iter (make-block-symbols-iterator this-global-block))
          (define functions (iterator-filter symbol-function? syms-iter))

 -- Scheme Procedure: iterator? object
     Return '#t' if OBJECT is a '<gdb:iterator>' object.  Otherwise
     return '#f'.

 -- Scheme Procedure: iterator-object iterator
     Return the first argument that was passed to 'make-iterator'.  This
     is the object being iterated over.

 -- Scheme Procedure: iterator-progress iterator
     Return the object tracking iteration progress.

 -- Scheme Procedure: set-iterator-progress! iterator new-value
     Set the object tracking iteration progress.

 -- Scheme Procedure: iterator-next! iterator
     Invoke the procedure that was the third argument to
     'make-iterator', passing it one argument, the '<gdb:iterator>'
     object.  The result is either the next element in the iteration, or
     an end marker as implemented by the 'next!' procedure.  By
     convention the end marker is the result of '(end-of-iteration)'.

 -- Scheme Procedure: end-of-iteration
     Return the Scheme object that denotes end of iteration.

 -- Scheme Procedure: end-of-iteration? object
     Return '#t' if OBJECT is the end of iteration marker.  Otherwise
     return '#f'.

   These functions are provided by the '(gdb iterator)' module to assist
in using iterators.

 -- Scheme Procedure: make-list-iterator list
     Return a '<gdb:iterator>' object that will iterate over LIST.

 -- Scheme Procedure: iterator->list iterator
     Return the elements pointed to by ITERATOR as a list.

 -- Scheme Procedure: iterator-map proc iterator
     Return the list of objects obtained by applying PROC to the object
     pointed to by ITERATOR and to each subsequent object.

 -- Scheme Procedure: iterator-for-each proc iterator
     Apply PROC to each element pointed to by ITERATOR.  The result is
     unspecified.

 -- Scheme Procedure: iterator-filter pred iterator
     Return the list of elements pointed to by ITERATOR that satisfy
     PRED.

 -- Scheme Procedure: iterator-until pred iterator
     Run ITERATOR until the result of '(pred element)' is true and
     return that as the result.  Otherwise return '#f'.

\1f
File: gdb.info,  Node: Guile Auto-loading,  Next: Guile Modules,  Prev: Guile API,  Up: Guile

23.3.4 Guile Auto-loading
-------------------------

When a new object file is read (for example, due to the 'file' command,
or because the inferior has loaded a shared library), GDB will look for
Guile support scripts in two ways: 'OBJFILE-gdb.scm' and the
'.debug_gdb_scripts' section.  *Note Auto-loading extensions::.

   The auto-loading feature is useful for supplying application-specific
debugging commands and scripts.

   Auto-loading can be enabled or disabled, and the list of auto-loaded
scripts can be printed.

'set auto-load guile-scripts [on|off]'
     Enable or disable the auto-loading of Guile scripts.

'show auto-load guile-scripts'
     Show whether auto-loading of Guile scripts is enabled or disabled.

'info auto-load guile-scripts [REGEXP]'
     Print the list of all Guile scripts that GDB auto-loaded.

     Also printed is the list of Guile scripts that were mentioned in
     the '.debug_gdb_scripts' section and were not found.  This is
     useful because their names are not printed when GDB tries to load
     them and fails.  There may be many of them, and printing an error
     message for each one is problematic.

     If REGEXP is supplied only Guile scripts with matching names are
     printed.

     Example:

          (gdb) info auto-load guile-scripts
          Loaded Script
          Yes    scm-section-script.scm
                 full name: /tmp/scm-section-script.scm
          No     my-foo-pretty-printers.scm

   When reading an auto-loaded file, GDB sets the "current objfile".
This is available via the 'current-objfile' procedure (*note Objfiles In
Guile::).  This can be useful for registering objfile-specific
pretty-printers.

\1f
File: gdb.info,  Node: Guile Modules,  Prev: Guile Auto-loading,  Up: Guile

23.3.5 Guile Modules
--------------------

GDB comes with several modules to assist writing Guile code.

* Menu:

* Guile Printing Module::  Building and registering pretty-printers
* Guile Types Module::     Utilities for working with types

\1f
File: gdb.info,  Node: Guile Printing Module,  Next: Guile Types Module,  Up: Guile Modules

23.3.5.1 Guile Printing Module
..............................

This module provides a collection of utilities for working with
pretty-printers.

   Usage:

     (use-modules (gdb printing))

 -- Scheme Procedure: prepend-pretty-printer! object printer
     Add PRINTER to the front of the list of pretty-printers for OBJECT.
     The OBJECT must either be a '<gdb:objfile>' object, or '#f' in
     which case PRINTER is added to the global list of printers.

 -- Scheme Procecure: append-pretty-printer! object printer
     Add PRINTER to the end of the list of pretty-printers for OBJECT.
     The OBJECT must either be a '<gdb:objfile>' object, or '#f' in
     which case PRINTER is added to the global list of printers.

\1f
File: gdb.info,  Node: Guile Types Module,  Prev: Guile Printing Module,  Up: Guile Modules

23.3.5.2 Guile Types Module
...........................

This module provides a collection of utilities for working with
'<gdb:type>' objects.

   Usage:

     (use-modules (gdb types))

 -- Scheme Procedure: get-basic-type type
     Return TYPE with const and volatile qualifiers stripped, and with
     typedefs and C++ references converted to the underlying type.

     C++ example:

          typedef const int const_int;
          const_int foo (3);
          const_int& foo_ref (foo);
          int main () { return 0; }

     Then in gdb:

          (gdb) start
          (gdb) guile (use-modules (gdb) (gdb types))
          (gdb) guile (define foo-ref (parse-and-eval "foo_ref"))
          (gdb) guile (get-basic-type (value-type foo-ref))
          int

 -- Scheme Procedure: type-has-field-deep? type field
     Return '#t' if TYPE, assumed to be a type with fields (e.g., a
     structure or union), has field FIELD.  Otherwise return '#f'.  This
     searches baseclasses, whereas 'type-has-field?' does not.

 -- Scheme Procedure: make-enum-hashtable enum-type
     Return a Guile hash table produced from ENUM-TYPE.  Elements in the
     hash table are referenced with 'hashq-ref'.

\1f
File: gdb.info,  Node: Auto-loading extensions,  Next: Multiple Extension Languages,  Prev: Guile,  Up: Extending GDB

23.4 Auto-loading extensions
============================

GDB provides two mechanisms for automatically loading extensions when a
new object file is read (for example, due to the 'file' command, or
because the inferior has loaded a shared library): 'OBJFILE-gdb.EXT' and
the '.debug_gdb_scripts' section of modern file formats like ELF.

* Menu:

* objfile-gdb.ext file: objfile-gdbdotext file.  The 'OBJFILE-gdb.EXT' file
* .debug_gdb_scripts section: dotdebug_gdb_scripts section.  The '.debug_gdb_scripts' section
* Which flavor to choose?::

   The auto-loading feature is useful for supplying application-specific
debugging commands and features.

   Auto-loading can be enabled or disabled, and the list of auto-loaded
scripts can be printed.  See the 'auto-loading' section of each
extension language for more information.  For GDB command files see
*note Auto-loading sequences::.  For Python files see *note Python
Auto-loading::.

   Note that loading of this script file also requires accordingly
configured 'auto-load safe-path' (*note Auto-loading safe path::).

\1f
File: gdb.info,  Node: objfile-gdbdotext file,  Next: dotdebug_gdb_scripts section,  Up: Auto-loading extensions

23.4.1 The 'OBJFILE-gdb.EXT' file
---------------------------------

When a new object file is read, GDB looks for a file named
'OBJFILE-gdb.EXT' (we call it SCRIPT-NAME below), where OBJFILE is the
object file's name and where EXT is the file extension for the extension
language:

'OBJFILE-gdb.gdb'
     GDB's own command language
'OBJFILE-gdb.py'
     Python
'OBJFILE-gdb.scm'
     Guile

   SCRIPT-NAME is formed by ensuring that the file name of OBJFILE is
absolute, following all symlinks, and resolving '.' and '..' components,
and appending the '-gdb.EXT' suffix.  If this file exists and is
readable, GDB will evaluate it as a script in the specified extension
language.

   If this file does not exist, then GDB will look for SCRIPT-NAME file
in all of the directories as specified below.

   Note that loading of these files requires an accordingly configured
'auto-load safe-path' (*note Auto-loading safe path::).

   For object files using '.exe' suffix GDB tries to load first the
scripts normally according to its '.exe' filename.  But if no scripts
are found GDB also tries script filenames matching the object file
without its '.exe' suffix.  This '.exe' stripping is case insensitive
and it is attempted on any platform.  This makes the script filenames
compatible between Unix and MS-Windows hosts.

'set auto-load scripts-directory [DIRECTORIES]'
     Control GDB auto-loaded scripts location.  Multiple directory
     entries may be delimited by the host platform path separator in use
     (':' on Unix, ';' on MS-Windows and MS-DOS).

     Each entry here needs to be covered also by the security setting
     'set auto-load safe-path' (*note set auto-load safe-path::).

     This variable defaults to '$debugdir:$datadir/auto-load'.  The
     default 'set auto-load safe-path' value can be also overriden by
     GDB configuration option '--with-auto-load-dir'.

     Any reference to '$debugdir' will get replaced by
     DEBUG-FILE-DIRECTORY value (*note Separate Debug Files::) and any
     reference to '$datadir' will get replaced by DATA-DIRECTORY which
     is determined at GDB startup (*note Data Files::).  '$debugdir' and
     '$datadir' must be placed as a directory component -- either alone
     or delimited by '/' or '\' directory separators, depending on the
     host platform.

     The list of directories uses path separator (':' on GNU and Unix
     systems, ';' on MS-Windows and MS-DOS) to separate directories,
     similarly to the 'PATH' environment variable.

'show auto-load scripts-directory'
     Show GDB auto-loaded scripts location.

   GDB does not track which files it has already auto-loaded this way.
GDB will load the associated script every time the corresponding OBJFILE
is opened.  So your '-gdb.EXT' file should be careful to avoid errors if
it is evaluated more than once.

\1f
File: gdb.info,  Node: dotdebug_gdb_scripts section,  Next: Which flavor to choose?,  Prev: objfile-gdbdotext file,  Up: Auto-loading extensions

23.4.2 The '.debug_gdb_scripts' section
---------------------------------------

For systems using file formats like ELF and COFF, when GDB loads a new
object file it will look for a special section named
'.debug_gdb_scripts'.  If this section exists, its contents is a list of
NUL-terminated names of scripts to load.  Each entry begins with a
non-NULL prefix byte that specifies the kind of entry, typically the
extension language.

   GDB will look for each specified script file first in the current
directory and then along the source search path (*note Specifying Source
Directories: Source Path.), except that '$cdir' is not searched, since
the compilation directory is not relevant to scripts.

   Entries can be placed in section '.debug_gdb_scripts' with, for
example, this GCC macro for Python scripts.

     /* Note: The "MS" section flags are to remove duplicates.  */
     #define DEFINE_GDB_PY_SCRIPT(script_name) \
       asm("\
     .pushsection \".debug_gdb_scripts\", \"MS\",@progbits,1\n\
     .byte 1 /* Python */\n\
     .asciz \"" script_name "\"\n\
     .popsection \n\
     ");

For Guile scripts, replace '.byte 1' with '.byte 3'.  Then one can
reference the macro in a header or source file like this:

     DEFINE_GDB_PY_SCRIPT ("my-app-scripts.py")

   The script name may include directories if desired.

   Note that loading of this script file also requires accordingly
configured 'auto-load safe-path' (*note Auto-loading safe path::).

   If the macro invocation is put in a header, any application or
library using this header will get a reference to the specified script,
and with the use of '"MS"' attributes on the section, the linker will
remove duplicates.

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File: gdb.info,  Node: Which flavor to choose?,  Prev: dotdebug_gdb_scripts section,  Up: Auto-loading extensions

23.4.3 Which flavor to choose?
------------------------------

Given the multiple ways of auto-loading extensions, it might not always
be clear which one to choose.  This section provides some guidance.

Benefits of the '-gdb.EXT' way:

   * Can be used with file formats that don't support multiple sections.

   * Ease of finding scripts for public libraries.

     Scripts specified in the '.debug_gdb_scripts' section are searched
     for in the source search path.  For publicly installed libraries,
     e.g., 'libstdc++', there typically isn't a source directory in
     which to find the script.

   * Doesn't require source code additions.

Benefits of the '.debug_gdb_scripts' way:

   * Works with static linking.

     Scripts for libraries done the '-gdb.EXT' way require an objfile to
     trigger their loading.  When an application is statically linked
     the only objfile available is the executable, and it is cumbersome
     to attach all the scripts from all the input libraries to the
     executable's '-gdb.EXT' script.

   * Works with classes that are entirely inlined.

     Some classes can be entirely inlined, and thus there may not be an
     associated shared library to attach a '-gdb.EXT' script to.

   * Scripts needn't be copied out of the source tree.

     In some circumstances, apps can be built out of large collections
     of internal libraries, and the build infrastructure necessary to
     install the '-gdb.EXT' scripts in a place where GDB can find them
     is cumbersome.  It may be easier to specify the scripts in the
     '.debug_gdb_scripts' section as relative paths, and add a path to
     the top of the source tree to the source search path.

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File: gdb.info,  Node: Multiple Extension Languages,  Next: Aliases,  Prev: Auto-loading extensions,  Up: Extending GDB

23.5 Multiple Extension Languages
=================================

The Guile and Python extension languages do not share any state, and
generally do not interfere with each other.  There are some things to be
aware of, however.

23.5.1 Python comes first
-------------------------

Python was GDB's first extension language, and to avoid breaking
existing behaviour Python comes first.  This is generally solved by the
"first one wins" principle.  GDB maintains a list of enabled extension
languages, and when it makes a call to an extension language, (say to
pretty-print a value), it tries each in turn until an extension language
indicates it has performed the request (e.g., has returned the
pretty-printed form of a value).  This extends to errors while
performing such requests: If an error happens while, for example, trying
to pretty-print an object then the error is reported and any following
extension languages are not tried.

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File: gdb.info,  Node: Aliases,  Prev: Multiple Extension Languages,  Up: Extending GDB

23.6 Creating new spellings of existing commands
================================================

It is often useful to define alternate spellings of existing commands.
For example, if a new GDB command defined in Python has a long name to
type, it is handy to have an abbreviated version of it that involves
less typing.

   GDB itself uses aliases.  For example 's' is an alias of the 'step'
command even though it is otherwise an ambiguous abbreviation of other
commands like 'set' and 'show'.

   Aliases are also used to provide shortened or more common versions of
multi-word commands.  For example, GDB provides the 'tty' alias of the
'set inferior-tty' command.

   You can define a new alias with the 'alias' command.

'alias [-a] [--] ALIAS = COMMAND'

   ALIAS specifies the name of the new alias.  Each word of ALIAS must
consist of letters, numbers, dashes and underscores.

   COMMAND specifies the name of an existing command that is being
aliased.

   The '-a' option specifies that the new alias is an abbreviation of
the command.  Abbreviations are not shown in command lists displayed by
the 'help' command.

   The '--' option specifies the end of options, and is useful when
ALIAS begins with a dash.

   Here is a simple example showing how to make an abbreviation of a
command so that there is less to type.  Suppose you were tired of typing
'disas', the current shortest unambiguous abbreviation of the
'disassemble' command and you wanted an even shorter version named 'di'.
The following will accomplish this.

     (gdb) alias -a di = disas

   Note that aliases are different from user-defined commands.  With a
user-defined command, you also need to write documentation for it with
the 'document' command.  An alias automatically picks up the
documentation of the existing command.

   Here is an example where we make 'elms' an abbreviation of 'elements'
in the 'set print elements' command.  This is to show that you can make
an abbreviation of any part of a command.

     (gdb) alias -a set print elms = set print elements
     (gdb) alias -a show print elms = show print elements
     (gdb) set p elms 20
     (gdb) show p elms
     Limit on string chars or array elements to print is 200.

   Note that if you are defining an alias of a 'set' command, and you
want to have an alias for the corresponding 'show' command, then you
need to define the latter separately.

   Unambiguously abbreviated commands are allowed in COMMAND and ALIAS,
just as they are normally.

     (gdb) alias -a set pr elms = set p ele

   Finally, here is an example showing the creation of a one word alias
for a more complex command.  This creates alias 'spe' of the command
'set print elements'.

     (gdb) alias spe = set print elements
     (gdb) spe 20

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File: gdb.info,  Node: Interpreters,  Next: TUI,  Prev: Extending GDB,  Up: Top

24 Command Interpreters
***********************

GDB supports multiple command interpreters, and some command
infrastructure to allow users or user interface writers to switch
between interpreters or run commands in other interpreters.

   GDB currently supports two command interpreters, the console
interpreter (sometimes called the command-line interpreter or CLI) and
the machine interface interpreter (or GDB/MI).  This manual describes
both of these interfaces in great detail.

   By default, GDB will start with the console interpreter.  However,
the user may choose to start GDB with another interpreter by specifying
the '-i' or '--interpreter' startup options.  Defined interpreters
include:

'console'
     The traditional console or command-line interpreter.  This is the
     most often used interpreter with GDB.  With no interpreter
     specified at runtime, GDB will use this interpreter.

'mi'
     The newest GDB/MI interface (currently 'mi2').  Used primarily by
     programs wishing to use GDB as a backend for a debugger GUI or an
     IDE. For more information, see *note The GDB/MI Interface: GDB/MI.

'mi2'
     The current GDB/MI interface.

'mi1'
     The GDB/MI interface included in GDB 5.1, 5.2, and 5.3.

   The interpreter being used by GDB may not be dynamically switched at
runtime.  Although possible, this could lead to a very precarious
situation.  Consider an IDE using GDB/MI.  If a user enters the command
"interpreter-set console" in a console view, GDB would switch to using
the console interpreter, rendering the IDE inoperable!

   Although you may only choose a single interpreter at startup, you may
execute commands in any interpreter from the current interpreter using
the appropriate command.  If you are running the console interpreter,
simply use the 'interpreter-exec' command:

     interpreter-exec mi "-data-list-register-names"

   GDB/MI has a similar command, although it is only available in
versions of GDB which support GDB/MI version 2 (or greater).

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File: gdb.info,  Node: TUI,  Next: Emacs,  Prev: Interpreters,  Up: Top

25 GDB Text User Interface
**************************

* Menu:

* TUI Overview::                TUI overview
* TUI Keys::                    TUI key bindings
* TUI Single Key Mode::         TUI single key mode
* TUI Commands::                TUI-specific commands
* TUI Configuration::           TUI configuration variables

The GDB Text User Interface (TUI) is a terminal interface which uses the
'curses' library to show the source file, the assembly output, the
program registers and GDB commands in separate text windows.  The TUI
mode is supported only on platforms where a suitable version of the
'curses' library is available.

   The TUI mode is enabled by default when you invoke GDB as 'gdb -tui'.
You can also switch in and out of TUI mode while GDB runs by using
various TUI commands and key bindings, such as 'C-x C-a'.  *Note TUI Key
Bindings: TUI Keys.

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File: gdb.info,  Node: TUI Overview,  Next: TUI Keys,  Up: TUI

25.1 TUI Overview
=================

In TUI mode, GDB can display several text windows:

_command_
     This window is the GDB command window with the GDB prompt and the
     GDB output.  The GDB input is still managed using readline.

_source_
     The source window shows the source file of the program.  The
     current line and active breakpoints are displayed in this window.

_assembly_
     The assembly window shows the disassembly output of the program.

_register_
     This window shows the processor registers.  Registers are
     highlighted when their values change.

   The source and assembly windows show the current program position by
highlighting the current line and marking it with a '>' marker.
Breakpoints are indicated with two markers.  The first marker indicates
the breakpoint type:

'B'
     Breakpoint which was hit at least once.

'b'
     Breakpoint which was never hit.

'H'
     Hardware breakpoint which was hit at least once.

'h'
     Hardware breakpoint which was never hit.

   The second marker indicates whether the breakpoint is enabled or not:

'+'
     Breakpoint is enabled.

'-'
     Breakpoint is disabled.

   The source, assembly and register windows are updated when the
current thread changes, when the frame changes, or when the program
counter changes.

   These windows are not all visible at the same time.  The command
window is always visible.  The others can be arranged in several
layouts:

   * source only,

   * assembly only,

   * source and assembly,

   * source and registers, or

   * assembly and registers.

   A status line above the command window shows the following
information:

_target_
     Indicates the current GDB target.  (*note Specifying a Debugging
     Target: Targets.).

_process_
     Gives the current process or thread number.  When no process is
     being debugged, this field is set to 'No process'.

_function_
     Gives the current function name for the selected frame.  The name
     is demangled if demangling is turned on (*note Print Settings::).
     When there is no symbol corresponding to the current program
     counter, the string '??' is displayed.

_line_
     Indicates the current line number for the selected frame.  When the
     current line number is not known, the string '??' is displayed.

_pc_
     Indicates the current program counter address.

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File: gdb.info,  Node: TUI Keys,  Next: TUI Single Key Mode,  Prev: TUI Overview,  Up: TUI

25.2 TUI Key Bindings
=====================

The TUI installs several key bindings in the readline keymaps (*note
Command Line Editing::).  The following key bindings are installed for
both TUI mode and the GDB standard mode.

'C-x C-a'
'C-x a'
'C-x A'
     Enter or leave the TUI mode.  When leaving the TUI mode, the curses
     window management stops and GDB operates using its standard mode,
     writing on the terminal directly.  When reentering the TUI mode,
     control is given back to the curses windows.  The screen is then
     refreshed.

'C-x 1'
     Use a TUI layout with only one window.  The layout will either be
     'source' or 'assembly'.  When the TUI mode is not active, it will
     switch to the TUI mode.

     Think of this key binding as the Emacs 'C-x 1' binding.

'C-x 2'
     Use a TUI layout with at least two windows.  When the current
     layout already has two windows, the next layout with two windows is
     used.  When a new layout is chosen, one window will always be
     common to the previous layout and the new one.

     Think of it as the Emacs 'C-x 2' binding.

'C-x o'
     Change the active window.  The TUI associates several key bindings
     (like scrolling and arrow keys) with the active window.  This
     command gives the focus to the next TUI window.

     Think of it as the Emacs 'C-x o' binding.

'C-x s'
     Switch in and out of the TUI SingleKey mode that binds single keys
     to GDB commands (*note TUI Single Key Mode::).

   The following key bindings only work in the TUI mode:

<PgUp>
     Scroll the active window one page up.

<PgDn>
     Scroll the active window one page down.

<Up>
     Scroll the active window one line up.

<Down>
     Scroll the active window one line down.

<Left>
     Scroll the active window one column left.

<Right>
     Scroll the active window one column right.

'C-L'
     Refresh the screen.

   Because the arrow keys scroll the active window in the TUI mode, they
are not available for their normal use by readline unless the command
window has the focus.  When another window is active, you must use other
readline key bindings such as 'C-p', 'C-n', 'C-b' and 'C-f' to control
the command window.

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File: gdb.info,  Node: TUI Single Key Mode,  Next: TUI Commands,  Prev: TUI Keys,  Up: TUI

25.3 TUI Single Key Mode
========================

The TUI also provides a "SingleKey" mode, which binds several frequently
used GDB commands to single keys.  Type 'C-x s' to switch into this
mode, where the following key bindings are used:

'c'
     continue

'd'
     down

'f'
     finish

'n'
     next

'q'
     exit the SingleKey mode.

'r'
     run

's'
     step

'u'
     up

'v'
     info locals

'w'
     where

   Other keys temporarily switch to the GDB command prompt.  The key
that was pressed is inserted in the editing buffer so that it is
possible to type most GDB commands without interaction with the TUI
SingleKey mode.  Once the command is entered the TUI SingleKey mode is
restored.  The only way to permanently leave this mode is by typing 'q'
or 'C-x s'.

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File: gdb.info,  Node: TUI Commands,  Next: TUI Configuration,  Prev: TUI Single Key Mode,  Up: TUI

25.4 TUI-specific Commands
==========================

The TUI has specific commands to control the text windows.  These
commands are always available, even when GDB is not in the TUI mode.
When GDB is in the standard mode, most of these commands will
automatically switch to the TUI mode.

   Note that if GDB's 'stdout' is not connected to a terminal, or GDB
has been started with the machine interface interpreter (*note The
GDB/MI Interface: GDB/MI.), most of these commands will fail with an
error, because it would not be possible or desirable to enable curses
window management.

'info win'
     List and give the size of all displayed windows.

'layout next'
     Display the next layout.

'layout prev'
     Display the previous layout.

'layout src'
     Display the source window only.

'layout asm'
     Display the assembly window only.

'layout split'
     Display the source and assembly window.

'layout regs'
     Display the register window together with the source or assembly
     window.

'focus next'
     Make the next window active for scrolling.

'focus prev'
     Make the previous window active for scrolling.

'focus src'
     Make the source window active for scrolling.

'focus asm'
     Make the assembly window active for scrolling.

'focus regs'
     Make the register window active for scrolling.

'focus cmd'
     Make the command window active for scrolling.

'refresh'
     Refresh the screen.  This is similar to typing 'C-L'.

'tui reg float'
     Show the floating point registers in the register window.

'tui reg general'
     Show the general registers in the register window.

'tui reg next'
     Show the next register group.  The list of register groups as well
     as their order is target specific.  The predefined register groups
     are the following: 'general', 'float', 'system', 'vector', 'all',
     'save', 'restore'.

'tui reg system'
     Show the system registers in the register window.

'update'
     Update the source window and the current execution point.

'winheight NAME +COUNT'
'winheight NAME -COUNT'
     Change the height of the window NAME by COUNT lines.  Positive
     counts increase the height, while negative counts decrease it.

'tabset NCHARS'
     Set the width of tab stops to be NCHARS characters.

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File: gdb.info,  Node: TUI Configuration,  Prev: TUI Commands,  Up: TUI

25.5 TUI Configuration Variables
================================

Several configuration variables control the appearance of TUI windows.

'set tui border-kind KIND'
     Select the border appearance for the source, assembly and register
     windows.  The possible values are the following:
     'space'
          Use a space character to draw the border.

     'ascii'
          Use ASCII characters '+', '-' and '|' to draw the border.

     'acs'
          Use the Alternate Character Set to draw the border.  The
          border is drawn using character line graphics if the terminal
          supports them.

'set tui border-mode MODE'
'set tui active-border-mode MODE'
     Select the display attributes for the borders of the inactive
     windows or the active window.  The MODE can be one of the
     following:
     'normal'
          Use normal attributes to display the border.

     'standout'
          Use standout mode.

     'reverse'
          Use reverse video mode.

     'half'
          Use half bright mode.

     'half-standout'
          Use half bright and standout mode.

     'bold'
          Use extra bright or bold mode.

     'bold-standout'
          Use extra bright or bold and standout mode.

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File: gdb.info,  Node: Emacs,  Next: GDB/MI,  Prev: TUI,  Up: Top

26 Using GDB under GNU Emacs
****************************

A special interface allows you to use GNU Emacs to view (and edit) the
source files for the program you are debugging with GDB.

   To use this interface, use the command 'M-x gdb' in Emacs.  Give the
executable file you want to debug as an argument.  This command starts
GDB as a subprocess of Emacs, with input and output through a newly
created Emacs buffer.

   Running GDB under Emacs can be just like running GDB normally except
for two things:

   * All "terminal" input and output goes through an Emacs buffer,
     called the GUD buffer.

     This applies both to GDB commands and their output, and to the
     input and output done by the program you are debugging.

     This is useful because it means that you can copy the text of
     previous commands and input them again; you can even use parts of
     the output in this way.

     All the facilities of Emacs' Shell mode are available for
     interacting with your program.  In particular, you can send signals
     the usual way--for example, 'C-c C-c' for an interrupt, 'C-c C-z'
     for a stop.

   * GDB displays source code through Emacs.

     Each time GDB displays a stack frame, Emacs automatically finds the
     source file for that frame and puts an arrow ('=>') at the left
     margin of the current line.  Emacs uses a separate buffer for
     source display, and splits the screen to show both your GDB session
     and the source.

     Explicit GDB 'list' or search commands still produce output as
     usual, but you probably have no reason to use them from Emacs.

   We call this "text command mode".  Emacs 22.1, and later, also uses a
graphical mode, enabled by default, which provides further buffers that
can control the execution and describe the state of your program.  *Note
(Emacs)GDB Graphical Interface::.

   If you specify an absolute file name when prompted for the 'M-x gdb'
argument, then Emacs sets your current working directory to where your
program resides.  If you only specify the file name, then Emacs sets
your current working directory to the directory associated with the
previous buffer.  In this case, GDB may find your program by searching
your environment's 'PATH' variable, but on some operating systems it
might not find the source.  So, although the GDB input and output
session proceeds normally, the auxiliary buffer does not display the
current source and line of execution.

   The initial working directory of GDB is printed on the top line of
the GUD buffer and this serves as a default for the commands that
specify files for GDB to operate on.  *Note Commands to Specify Files:
Files.

   By default, 'M-x gdb' calls the program called 'gdb'.  If you need to
call GDB by a different name (for example, if you keep several
configurations around, with different names) you can customize the Emacs
variable 'gud-gdb-command-name' to run the one you want.

   In the GUD buffer, you can use these special Emacs commands in
addition to the standard Shell mode commands:

'C-h m'
     Describe the features of Emacs' GUD Mode.

'C-c C-s'
     Execute to another source line, like the GDB 'step' command; also
     update the display window to show the current file and location.

'C-c C-n'
     Execute to next source line in this function, skipping all function
     calls, like the GDB 'next' command.  Then update the display window
     to show the current file and location.

'C-c C-i'
     Execute one instruction, like the GDB 'stepi' command; update
     display window accordingly.

'C-c C-f'
     Execute until exit from the selected stack frame, like the GDB
     'finish' command.

'C-c C-r'
     Continue execution of your program, like the GDB 'continue'
     command.

'C-c <'
     Go up the number of frames indicated by the numeric argument (*note
     Numeric Arguments: (Emacs)Arguments.), like the GDB 'up' command.

'C-c >'
     Go down the number of frames indicated by the numeric argument,
     like the GDB 'down' command.

   In any source file, the Emacs command 'C-x <SPC>' ('gud-break') tells
GDB to set a breakpoint on the source line point is on.

   In text command mode, if you type 'M-x speedbar', Emacs displays a
separate frame which shows a backtrace when the GUD buffer is current.
Move point to any frame in the stack and type <RET> to make it become
the current frame and display the associated source in the source
buffer.  Alternatively, click 'Mouse-2' to make the selected frame
become the current one.  In graphical mode, the speedbar displays watch
expressions.

   If you accidentally delete the source-display buffer, an easy way to
get it back is to type the command 'f' in the GDB buffer, to request a
frame display; when you run under Emacs, this recreates the source
buffer if necessary to show you the context of the current frame.

   The source files displayed in Emacs are in ordinary Emacs buffers
which are visiting the source files in the usual way.  You can edit the
files with these buffers if you wish; but keep in mind that GDB
communicates with Emacs in terms of line numbers.  If you add or delete
lines from the text, the line numbers that GDB knows cease to correspond
properly with the code.

   A more detailed description of Emacs' interaction with GDB is given
in the Emacs manual (*note (Emacs)Debuggers::).

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File: gdb.info,  Node: GDB/MI,  Next: Annotations,  Prev: Emacs,  Up: Top

27 The GDB/MI Interface
***********************

Function and Purpose
====================

GDB/MI is a line based machine oriented text interface to GDB and is
activated by specifying using the '--interpreter' command line option
(*note Mode Options::).  It is specifically intended to support the
development of systems which use the debugger as just one small
component of a larger system.

   This chapter is a specification of the GDB/MI interface.  It is
written in the form of a reference manual.

   Note that GDB/MI is still under construction, so some of the features
described below are incomplete and subject to change (*note GDB/MI
Development and Front Ends: GDB/MI Development and Front Ends.).

Notation and Terminology
========================

This chapter uses the following notation:

   * '|' separates two alternatives.

   * '[ SOMETHING ]' indicates that SOMETHING is optional: it may or may
     not be given.

   * '( GROUP )*' means that GROUP inside the parentheses may repeat
     zero or more times.

   * '( GROUP )+' means that GROUP inside the parentheses may repeat one
     or more times.

   * '"STRING"' means a literal STRING.

* Menu:

* GDB/MI General Design::
* GDB/MI Command Syntax::
* GDB/MI Compatibility with CLI::
* GDB/MI Development and Front Ends::
* GDB/MI Output Records::
* GDB/MI Simple Examples::
* GDB/MI Command Description Format::
* GDB/MI Breakpoint Commands::
* GDB/MI Catchpoint Commands::
* GDB/MI Program Context::
* GDB/MI Thread Commands::
* GDB/MI Ada Tasking Commands::
* GDB/MI Program Execution::
* GDB/MI Stack Manipulation::
* GDB/MI Variable Objects::
* GDB/MI Data Manipulation::
* GDB/MI Tracepoint Commands::
* GDB/MI Symbol Query::
* GDB/MI File Commands::
* GDB/MI Target Manipulation::
* GDB/MI File Transfer Commands::
* GDB/MI Ada Exceptions Commands::
* GDB/MI Support Commands::
* GDB/MI Miscellaneous Commands::

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File: gdb.info,  Node: GDB/MI General Design,  Next: GDB/MI Command Syntax,  Up: GDB/MI

27.1 GDB/MI General Design
==========================

Interaction of a GDB/MI frontend with GDB involves three parts--commands
sent to GDB, responses to those commands and notifications.  Each
command results in exactly one response, indicating either successful
completion of the command, or an error.  For the commands that do not
resume the target, the response contains the requested information.  For
the commands that resume the target, the response only indicates whether
the target was successfully resumed.  Notifications is the mechanism for
reporting changes in the state of the target, or in GDB state, that
cannot conveniently be associated with a command and reported as part of
that command response.

   The important examples of notifications are:

   * Exec notifications.  These are used to report changes in target
     state--when a target is resumed, or stopped.  It would not be
     feasible to include this information in response of resuming
     commands, because one resume commands can result in multiple events
     in different threads.  Also, quite some time may pass before any
     event happens in the target, while a frontend needs to know whether
     the resuming command itself was successfully executed.

   * Console output, and status notifications.  Console output
     notifications are used to report output of CLI commands, as well as
     diagnostics for other commands.  Status notifications are used to
     report the progress of a long-running operation.  Naturally,
     including this information in command response would mean no output
     is produced until the command is finished, which is undesirable.

   * General notifications.  Commands may have various side effects on
     the GDB or target state beyond their official purpose.  For
     example, a command may change the selected thread.  Although such
     changes can be included in command response, using notification
     allows for more orthogonal frontend design.

   There's no guarantee that whenever an MI command reports an error,
GDB or the target are in any specific state, and especially, the state
is not reverted to the state before the MI command was processed.
Therefore, whenever an MI command results in an error, we recommend that
the frontend refreshes all the information shown in the user interface.

* Menu:

* Context management::
* Asynchronous and non-stop modes::
* Thread groups::

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File: gdb.info,  Node: Context management,  Next: Asynchronous and non-stop modes,  Up: GDB/MI General Design

27.1.1 Context management
-------------------------

27.1.1.1 Threads and Frames
...........................

In most cases when GDB accesses the target, this access is done in
context of a specific thread and frame (*note Frames::).  Often, even
when accessing global data, the target requires that a thread be
specified.  The CLI interface maintains the selected thread and frame,
and supplies them to target on each command.  This is convenient,
because a command line user would not want to specify that information
explicitly on each command, and because user interacts with GDB via a
single terminal, so no confusion is possible as to what thread and frame
are the current ones.

   In the case of MI, the concept of selected thread and frame is less
useful.  First, a frontend can easily remember this information itself.
Second, a graphical frontend can have more than one window, each one
used for debugging a different thread, and the frontend might want to
access additional threads for internal purposes.  This increases the
risk that by relying on implicitly selected thread, the frontend may be
operating on a wrong one.  Therefore, each MI command should explicitly
specify which thread and frame to operate on.  To make it possible, each
MI command accepts the '--thread' and '--frame' options, the value to
each is GDB identifier for thread and frame to operate on.

   Usually, each top-level window in a frontend allows the user to
select a thread and a frame, and remembers the user selection for
further operations.  However, in some cases GDB may suggest that the
current thread be changed.  For example, when stopping on a breakpoint
it is reasonable to switch to the thread where breakpoint is hit.  For
another example, if the user issues the CLI 'thread' command via the
frontend, it is desirable to change the frontend's selected thread to
the one specified by user.  GDB communicates the suggestion to change
current thread using the '=thread-selected' notification.  No such
notification is available for the selected frame at the moment.

   Note that historically, MI shares the selected thread with CLI, so
frontends used the '-thread-select' to execute commands in the right
context.  However, getting this to work right is cumbersome.  The
simplest way is for frontend to emit '-thread-select' command before
every command.  This doubles the number of commands that need to be
sent.  The alternative approach is to suppress '-thread-select' if the
selected thread in GDB is supposed to be identical to the thread the
frontend wants to operate on.  However, getting this optimization right
can be tricky.  In particular, if the frontend sends several commands to
GDB, and one of the commands changes the selected thread, then the
behaviour of subsequent commands will change.  So, a frontend should
either wait for response from such problematic commands, or explicitly
add '-thread-select' for all subsequent commands.  No frontend is known
to do this exactly right, so it is suggested to just always pass the
'--thread' and '--frame' options.

27.1.1.2 Language
.................

The execution of several commands depends on which language is selected.
By default, the current language (*note show language::) is used.  But
for commands known to be language-sensitive, it is recommended to use
the '--language' option.  This option takes one argument, which is the
name of the language to use while executing the command.  For instance:

     -data-evaluate-expression --language c "sizeof (void*)"
     ^done,value="4"
     (gdb)

   The valid language names are the same names accepted by the 'set
language' command (*note Manually::), excluding 'auto', 'local' or
'unknown'.

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File: gdb.info,  Node: Asynchronous and non-stop modes,  Next: Thread groups,  Prev: Context management,  Up: GDB/MI General Design

27.1.2 Asynchronous command execution and non-stop mode
-------------------------------------------------------

On some targets, GDB is capable of processing MI commands even while the
target is running.  This is called "asynchronous command execution"
(*note Background Execution::).  The frontend may specify a preferrence
for asynchronous execution using the '-gdb-set mi-async 1' command,
which should be emitted before either running the executable or
attaching to the target.  After the frontend has started the executable
or attached to the target, it can find if asynchronous execution is
enabled using the '-list-target-features' command.

'-gdb-set mi-async on'
'-gdb-set mi-async off'
     Set whether MI is in asynchronous mode.

     When 'off', which is the default, MI execution commands (e.g.,
     '-exec-continue') are foreground commands, and GDB waits for the
     program to stop before processing further commands.

     When 'on', MI execution commands are background execution commands
     (e.g., '-exec-continue' becomes the equivalent of the 'c&' CLI
     command), and so GDB is capable of processing MI commands even
     while the target is running.

'-gdb-show mi-async'
     Show whether MI asynchronous mode is enabled.

   Note: In GDB version 7.7 and earlier, this option was called
'target-async' instead of 'mi-async', and it had the effect of both
putting MI in asynchronous mode and making CLI background commands
possible.  CLI background commands are now always possible "out of the
box" if the target supports them.  The old spelling is kept as a
deprecated alias for backwards compatibility.

   Even if GDB can accept a command while target is running, many
commands that access the target do not work when the target is running.
Therefore, asynchronous command execution is most useful when combined
with non-stop mode (*note Non-Stop Mode::).  Then, it is possible to
examine the state of one thread, while other threads are running.

   When a given thread is running, MI commands that try to access the
target in the context of that thread may not work, or may work only on
some targets.  In particular, commands that try to operate on thread's
stack will not work, on any target.  Commands that read memory, or
modify breakpoints, may work or not work, depending on the target.  Note
that even commands that operate on global state, such as 'print', 'set',
and breakpoint commands, still access the target in the context of a
specific thread, so frontend should try to find a stopped thread and
perform the operation on that thread (using the '--thread' option).

   Which commands will work in the context of a running thread is highly
target dependent.  However, the two commands '-exec-interrupt', to stop
a thread, and '-thread-info', to find the state of a thread, will always
work.

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File: gdb.info,  Node: Thread groups,  Prev: Asynchronous and non-stop modes,  Up: GDB/MI General Design

27.1.3 Thread groups
--------------------

GDB may be used to debug several processes at the same time.  On some
platfroms, GDB may support debugging of several hardware systems, each
one having several cores with several different processes running on
each core.  This section describes the MI mechanism to support such
debugging scenarios.

   The key observation is that regardless of the structure of the
target, MI can have a global list of threads, because most commands that
accept the '--thread' option do not need to know what process that
thread belongs to.  Therefore, it is not necessary to introduce neither
additional '--process' option, nor an notion of the current process in
the MI interface.  The only strictly new feature that is required is the
ability to find how the threads are grouped into processes.

   To allow the user to discover such grouping, and to support arbitrary
hierarchy of machines/cores/processes, MI introduces the concept of a
"thread group".  Thread group is a collection of threads and other
thread groups.  A thread group always has a string identifier, a type,
and may have additional attributes specific to the type.  A new command,
'-list-thread-groups', returns the list of top-level thread groups,
which correspond to processes that GDB is debugging at the moment.  By
passing an identifier of a thread group to the '-list-thread-groups'
command, it is possible to obtain the members of specific thread group.

   To allow the user to easily discover processes, and other objects, he
wishes to debug, a concept of "available thread group" is introduced.
Available thread group is an thread group that GDB is not debugging, but
that can be attached to, using the '-target-attach' command.  The list
of available top-level thread groups can be obtained using
'-list-thread-groups --available'.  In general, the content of a thread
group may be only retrieved only after attaching to that thread group.

   Thread groups are related to inferiors (*note Inferiors and
Programs::).  Each inferior corresponds to a thread group of a special
type 'process', and some additional operations are permitted on such
thread groups.

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File: gdb.info,  Node: GDB/MI Command Syntax,  Next: GDB/MI Compatibility with CLI,  Prev: GDB/MI General Design,  Up: GDB/MI

27.2 GDB/MI Command Syntax
==========================

* Menu:

* GDB/MI Input Syntax::
* GDB/MI Output Syntax::

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File: gdb.info,  Node: GDB/MI Input Syntax,  Next: GDB/MI Output Syntax,  Up: GDB/MI Command Syntax

27.2.1 GDB/MI Input Syntax
--------------------------

'COMMAND ==>'
     'CLI-COMMAND | MI-COMMAND'

'CLI-COMMAND ==>'
     '[ TOKEN ] CLI-COMMAND NL', where CLI-COMMAND is any existing GDB
     CLI command.

'MI-COMMAND ==>'
     '[ TOKEN ] "-" OPERATION ( " " OPTION )* [ " --" ] ( " " PARAMETER
     )* NL'

'TOKEN ==>'
     "any sequence of digits"

'OPTION ==>'
     '"-" PARAMETER [ " " PARAMETER ]'

'PARAMETER ==>'
     'NON-BLANK-SEQUENCE | C-STRING'

'OPERATION ==>'
     _any of the operations described in this chapter_

'NON-BLANK-SEQUENCE ==>'
     _anything, provided it doesn't contain special characters such as
     "-", NL, """ and of course " "_

'C-STRING ==>'
     '""" SEVEN-BIT-ISO-C-STRING-CONTENT """'

'NL ==>'
     'CR | CR-LF'

Notes:

   * The CLI commands are still handled by the MI interpreter; their
     output is described below.

   * The 'TOKEN', when present, is passed back when the command
     finishes.

   * Some MI commands accept optional arguments as part of the parameter
     list.  Each option is identified by a leading '-' (dash) and may be
     followed by an optional argument parameter.  Options occur first in
     the parameter list and can be delimited from normal parameters
     using '--' (this is useful when some parameters begin with a dash).

   Pragmatics:

   * We want easy access to the existing CLI syntax (for debugging).

   * We want it to be easy to spot a MI operation.

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File: gdb.info,  Node: GDB/MI Output Syntax,  Prev: GDB/MI Input Syntax,  Up: GDB/MI Command Syntax

27.2.2 GDB/MI Output Syntax
---------------------------

The output from GDB/MI consists of zero or more out-of-band records
followed, optionally, by a single result record.  This result record is
for the most recent command.  The sequence of output records is
terminated by '(gdb)'.

   If an input command was prefixed with a 'TOKEN' then the
corresponding output for that command will also be prefixed by that same
TOKEN.

'OUTPUT ==>'
     '( OUT-OF-BAND-RECORD )* [ RESULT-RECORD ] "(gdb)" NL'

'RESULT-RECORD ==>'
     ' [ TOKEN ] "^" RESULT-CLASS ( "," RESULT )* NL'

'OUT-OF-BAND-RECORD ==>'
     'ASYNC-RECORD | STREAM-RECORD'

'ASYNC-RECORD ==>'
     'EXEC-ASYNC-OUTPUT | STATUS-ASYNC-OUTPUT | NOTIFY-ASYNC-OUTPUT'

'EXEC-ASYNC-OUTPUT ==>'
     '[ TOKEN ] "*" ASYNC-OUTPUT NL'

'STATUS-ASYNC-OUTPUT ==>'
     '[ TOKEN ] "+" ASYNC-OUTPUT NL'

'NOTIFY-ASYNC-OUTPUT ==>'
     '[ TOKEN ] "=" ASYNC-OUTPUT NL'

'ASYNC-OUTPUT ==>'
     'ASYNC-CLASS ( "," RESULT )*'

'RESULT-CLASS ==>'
     '"done" | "running" | "connected" | "error" | "exit"'

'ASYNC-CLASS ==>'
     '"stopped" | OTHERS' (where OTHERS will be added depending on the
     needs--this is still in development).

'RESULT ==>'
     ' VARIABLE "=" VALUE'

'VARIABLE ==>'
     ' STRING '

'VALUE ==>'
     ' CONST | TUPLE | LIST '

'CONST ==>'
     'C-STRING'

'TUPLE ==>'
     ' "{}" | "{" RESULT ( "," RESULT )* "}" '

'LIST ==>'
     ' "[]" | "[" VALUE ( "," VALUE )* "]" | "[" RESULT ( "," RESULT )*
     "]" '

'STREAM-RECORD ==>'
     'CONSOLE-STREAM-OUTPUT | TARGET-STREAM-OUTPUT | LOG-STREAM-OUTPUT'

'CONSOLE-STREAM-OUTPUT ==>'
     '"~" C-STRING NL'

'TARGET-STREAM-OUTPUT ==>'
     '"@" C-STRING NL'

'LOG-STREAM-OUTPUT ==>'
     '"&" C-STRING NL'

'NL ==>'
     'CR | CR-LF'

'TOKEN ==>'
     _any sequence of digits_.

Notes:

   * All output sequences end in a single line containing a period.

   * The 'TOKEN' is from the corresponding request.  Note that for all
     async output, while the token is allowed by the grammar and may be
     output by future versions of GDB for select async output messages,
     it is generally omitted.  Frontends should treat all async output
     as reporting general changes in the state of the target and there
     should be no need to associate async output to any prior command.

   * STATUS-ASYNC-OUTPUT contains on-going status information about the
     progress of a slow operation.  It can be discarded.  All status
     output is prefixed by '+'.

   * EXEC-ASYNC-OUTPUT contains asynchronous state change on the target
     (stopped, started, disappeared).  All async output is prefixed by
     '*'.

   * NOTIFY-ASYNC-OUTPUT contains supplementary information that the
     client should handle (e.g., a new breakpoint information).  All
     notify output is prefixed by '='.

   * CONSOLE-STREAM-OUTPUT is output that should be displayed as is in
     the console.  It is the textual response to a CLI command.  All the
     console output is prefixed by '~'.

   * TARGET-STREAM-OUTPUT is the output produced by the target program.
     All the target output is prefixed by '@'.

   * LOG-STREAM-OUTPUT is output text coming from GDB's internals, for
     instance messages that should be displayed as part of an error log.
     All the log output is prefixed by '&'.

   * New GDB/MI commands should only output LISTS containing VALUES.

   *Note GDB/MI Stream Records: GDB/MI Stream Records, for more details
about the various output records.

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File: gdb.info,  Node: GDB/MI Compatibility with CLI,  Next: GDB/MI Development and Front Ends,  Prev: GDB/MI Command Syntax,  Up: GDB/MI

27.3 GDB/MI Compatibility with CLI
==================================

For the developers convenience CLI commands can be entered directly, but
there may be some unexpected behaviour.  For example, commands that
query the user will behave as if the user replied yes, breakpoint
command lists are not executed and some CLI commands, such as 'if',
'when' and 'define', prompt for further input with '>', which is not
valid MI output.

   This feature may be removed at some stage in the future and it is
recommended that front ends use the '-interpreter-exec' command (*note
-interpreter-exec::).

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File: gdb.info,  Node: GDB/MI Development and Front Ends,  Next: GDB/MI Output Records,  Prev: GDB/MI Compatibility with CLI,  Up: GDB/MI

27.4 GDB/MI Development and Front Ends
======================================

The application which takes the MI output and presents the state of the
program being debugged to the user is called a "front end".

   Although GDB/MI is still incomplete, it is currently being used by a
variety of front ends to GDB.  This makes it difficult to introduce new
functionality without breaking existing usage.  This section tries to
minimize the problems by describing how the protocol might change.

   Some changes in MI need not break a carefully designed front end, and
for these the MI version will remain unchanged.  The following is a list
of changes that may occur within one level, so front ends should parse
MI output in a way that can handle them:

   * New MI commands may be added.

   * New fields may be added to the output of any MI command.

   * The range of values for fields with specified values, e.g.,
     'in_scope' (*note -var-update::) may be extended.

   If the changes are likely to break front ends, the MI version level
will be increased by one.  This will allow the front end to parse the
output according to the MI version.  Apart from mi0, new versions of GDB
will not support old versions of MI and it will be the responsibility of
the front end to work with the new one.

   The best way to avoid unexpected changes in MI that might break your
front end is to make your project known to GDB developers and follow
development on <gdb@sourceware.org> and <gdb-patches@sourceware.org>.

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File: gdb.info,  Node: GDB/MI Output Records,  Next: GDB/MI Simple Examples,  Prev: GDB/MI Development and Front Ends,  Up: GDB/MI

27.5 GDB/MI Output Records
==========================

* Menu:

* GDB/MI Result Records::
* GDB/MI Stream Records::
* GDB/MI Async Records::
* GDB/MI Breakpoint Information::
* GDB/MI Frame Information::
* GDB/MI Thread Information::
* GDB/MI Ada Exception Information::

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File: gdb.info,  Node: GDB/MI Result Records,  Next: GDB/MI Stream Records,  Up: GDB/MI Output Records

27.5.1 GDB/MI Result Records
----------------------------

In addition to a number of out-of-band notifications, the response to a
GDB/MI command includes one of the following result indications:

'"^done" [ "," RESULTS ]'
     The synchronous operation was successful, 'RESULTS' are the return
     values.

'"^running"'
     This result record is equivalent to '^done'.  Historically, it was
     output instead of '^done' if the command has resumed the target.
     This behaviour is maintained for backward compatibility, but all
     frontends should treat '^done' and '^running' identically and rely
     on the '*running' output record to determine which threads are
     resumed.

'"^connected"'
     GDB has connected to a remote target.

'"^error" "," "msg=" C-STRING [ "," "code=" C-STRING ]'
     The operation failed.  The 'msg=C-STRING' variable contains the
     corresponding error message.

     If present, the 'code=C-STRING' variable provides an error code on
     which consumers can rely on to detect the corresponding error
     condition.  At present, only one error code is defined:

     '"undefined-command"'
          Indicates that the command causing the error does not exist.

'"^exit"'
     GDB has terminated.

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File: gdb.info,  Node: GDB/MI Stream Records,  Next: GDB/MI Async Records,  Prev: GDB/MI Result Records,  Up: GDB/MI Output Records

27.5.2 GDB/MI Stream Records
----------------------------

GDB internally maintains a number of output streams: the console, the
target, and the log.  The output intended for each of these streams is
funneled through the GDB/MI interface using "stream records".

   Each stream record begins with a unique "prefix character" which
identifies its stream (*note GDB/MI Output Syntax: GDB/MI Output
Syntax.).  In addition to the prefix, each stream record contains a
'STRING-OUTPUT'.  This is either raw text (with an implicit new line) or
a quoted C string (which does not contain an implicit newline).

'"~" STRING-OUTPUT'
     The console output stream contains text that should be displayed in
     the CLI console window.  It contains the textual responses to CLI
     commands.

'"@" STRING-OUTPUT'
     The target output stream contains any textual output from the
     running target.  This is only present when GDB's event loop is
     truly asynchronous, which is currently only the case for remote
     targets.

'"&" STRING-OUTPUT'
     The log stream contains debugging messages being produced by GDB's
     internals.

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File: gdb.info,  Node: GDB/MI Async Records,  Next: GDB/MI Breakpoint Information,  Prev: GDB/MI Stream Records,  Up: GDB/MI Output Records

27.5.3 GDB/MI Async Records
---------------------------

"Async" records are used to notify the GDB/MI client of additional
changes that have occurred.  Those changes can either be a consequence
of GDB/MI commands (e.g., a breakpoint modified) or a result of target
activity (e.g., target stopped).

   The following is the list of possible async records:

'*running,thread-id="THREAD"'
     The target is now running.  The THREAD field tells which specific
     thread is now running, and can be 'all' if all threads are running.
     The frontend should assume that no interaction with a running
     thread is possible after this notification is produced.  The
     frontend should not assume that this notification is output only
     once for any command.  GDB may emit this notification several
     times, either for different threads, because it cannot resume all
     threads together, or even for a single thread, if the thread must
     be stepped though some code before letting it run freely.

'*stopped,reason="REASON",thread-id="ID",stopped-threads="STOPPED",core="CORE"'
     The target has stopped.  The REASON field can have one of the
     following values:

     'breakpoint-hit'
          A breakpoint was reached.
     'watchpoint-trigger'
          A watchpoint was triggered.
     'read-watchpoint-trigger'
          A read watchpoint was triggered.
     'access-watchpoint-trigger'
          An access watchpoint was triggered.
     'function-finished'
          An -exec-finish or similar CLI command was accomplished.
     'location-reached'
          An -exec-until or similar CLI command was accomplished.
     'watchpoint-scope'
          A watchpoint has gone out of scope.
     'end-stepping-range'
          An -exec-next, -exec-next-instruction, -exec-step,
          -exec-step-instruction or similar CLI command was
          accomplished.
     'exited-signalled'
          The inferior exited because of a signal.
     'exited'
          The inferior exited.
     'exited-normally'
          The inferior exited normally.
     'signal-received'
          A signal was received by the inferior.
     'solib-event'
          The inferior has stopped due to a library being loaded or
          unloaded.  This can happen when 'stop-on-solib-events' (*note
          Files::) is set or when a 'catch load' or 'catch unload'
          catchpoint is in use (*note Set Catchpoints::).
     'fork'
          The inferior has forked.  This is reported when 'catch fork'
          (*note Set Catchpoints::) has been used.
     'vfork'
          The inferior has vforked.  This is reported in when 'catch
          vfork' (*note Set Catchpoints::) has been used.
     'syscall-entry'
          The inferior entered a system call.  This is reported when
          'catch syscall' (*note Set Catchpoints::) has been used.
     'syscall-entry'
          The inferior returned from a system call.  This is reported
          when 'catch syscall' (*note Set Catchpoints::) has been used.
     'exec'
          The inferior called 'exec'.  This is reported when 'catch
          exec' (*note Set Catchpoints::) has been used.

     The ID field identifies the thread that directly caused the stop -
     for example by hitting a breakpoint.  Depending on whether all-stop
     mode is in effect (*note All-Stop Mode::), GDB may either stop all
     threads, or only the thread that directly triggered the stop.  If
     all threads are stopped, the STOPPED field will have the value of
     '"all"'.  Otherwise, the value of the STOPPED field will be a list
     of thread identifiers.  Presently, this list will always include a
     single thread, but frontend should be prepared to see several
     threads in the list.  The CORE field reports the processor core on
     which the stop event has happened.  This field may be absent if
     such information is not available.

'=thread-group-added,id="ID"'
'=thread-group-removed,id="ID"'
     A thread group was either added or removed.  The ID field contains
     the GDB identifier of the thread group.  When a thread group is
     added, it generally might not be associated with a running process.
     When a thread group is removed, its id becomes invalid and cannot
     be used in any way.

'=thread-group-started,id="ID",pid="PID"'
     A thread group became associated with a running program, either
     because the program was just started or the thread group was
     attached to a program.  The ID field contains the GDB identifier of
     the thread group.  The PID field contains process identifier,
     specific to the operating system.

'=thread-group-exited,id="ID"[,exit-code="CODE"]'
     A thread group is no longer associated with a running program,
     either because the program has exited, or because it was detached
     from.  The ID field contains the GDB identifier of the thread
     group.  The CODE field is the exit code of the inferior; it exists
     only when the inferior exited with some code.

'=thread-created,id="ID",group-id="GID"'
'=thread-exited,id="ID",group-id="GID"'
     A thread either was created, or has exited.  The ID field contains
     the GDB identifier of the thread.  The GID field identifies the
     thread group this thread belongs to.

'=thread-selected,id="ID"'
     Informs that the selected thread was changed as result of the last
     command.  This notification is not emitted as result of
     '-thread-select' command but is emitted whenever an MI command that
     is not documented to change the selected thread actually changes
     it.  In particular, invoking, directly or indirectly (via
     user-defined command), the CLI 'thread' command, will generate this
     notification.

     We suggest that in response to this notification, front ends
     highlight the selected thread and cause subsequent commands to
     apply to that thread.

'=library-loaded,...'
     Reports that a new library file was loaded by the program.  This
     notification has 4 fields--ID, TARGET-NAME, HOST-NAME, and
     SYMBOLS-LOADED.  The ID field is an opaque identifier of the
     library.  For remote debugging case, TARGET-NAME and HOST-NAME
     fields give the name of the library file on the target, and on the
     host respectively.  For native debugging, both those fields have
     the same value.  The SYMBOLS-LOADED field is emitted only for
     backward compatibility and should not be relied on to convey any
     useful information.  The THREAD-GROUP field, if present, specifies
     the id of the thread group in whose context the library was loaded.
     If the field is absent, it means the library was loaded in the
     context of all present thread groups.

'=library-unloaded,...'
     Reports that a library was unloaded by the program.  This
     notification has 3 fields--ID, TARGET-NAME and HOST-NAME with the
     same meaning as for the '=library-loaded' notification.  The
     THREAD-GROUP field, if present, specifies the id of the thread
     group in whose context the library was unloaded.  If the field is
     absent, it means the library was unloaded in the context of all
     present thread groups.

'=traceframe-changed,num=TFNUM,tracepoint=TPNUM'
'=traceframe-changed,end'
     Reports that the trace frame was changed and its new number is
     TFNUM.  The number of the tracepoint associated with this trace
     frame is TPNUM.

'=tsv-created,name=NAME,initial=INITIAL'
     Reports that the new trace state variable NAME is created with
     initial value INITIAL.

'=tsv-deleted,name=NAME'
'=tsv-deleted'
     Reports that the trace state variable NAME is deleted or all trace
     state variables are deleted.

'=tsv-modified,name=NAME,initial=INITIAL[,current=CURRENT]'
     Reports that the trace state variable NAME is modified with the
     initial value INITIAL.  The current value CURRENT of trace state
     variable is optional and is reported if the current value of trace
     state variable is known.

'=breakpoint-created,bkpt={...}'
'=breakpoint-modified,bkpt={...}'
'=breakpoint-deleted,id=NUMBER'
     Reports that a breakpoint was created, modified, or deleted,
     respectively.  Only user-visible breakpoints are reported to the MI
     user.

     The BKPT argument is of the same form as returned by the various
     breakpoint commands; *Note GDB/MI Breakpoint Commands::.  The
     NUMBER is the ordinal number of the breakpoint.

     Note that if a breakpoint is emitted in the result record of a
     command, then it will not also be emitted in an async record.

'=record-started,thread-group="ID"'
'=record-stopped,thread-group="ID"'
     Execution log recording was either started or stopped on an
     inferior.  The ID is the GDB identifier of the thread group
     corresponding to the affected inferior.

'=cmd-param-changed,param=PARAM,value=VALUE'
     Reports that a parameter of the command 'set PARAM' is changed to
     VALUE.  In the multi-word 'set' command, the PARAM is the whole
     parameter list to 'set' command.  For example, In command 'set
     check type on', PARAM is 'check type' and VALUE is 'on'.

'=memory-changed,thread-group=ID,addr=ADDR,len=LEN[,type="code"]'
     Reports that bytes from ADDR to DATA + LEN were written in an
     inferior.  The ID is the identifier of the thread group
     corresponding to the affected inferior.  The optional 'type="code"'
     part is reported if the memory written to holds executable code.