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14 @section Extending @value{GDBN} using Python
15 @cindex python scripting
16 @cindex scripting with python
18 You can extend @value{GDBN} using the @uref{http://www.python.org/,
19 Python programming language}. This feature is available only if
20 @value{GDBN} was configured using @option{--with-python}.
21 @value{GDBN} can be built against either Python 2 or Python 3; which
22 one you have depends on this configure-time option.
24 @cindex python directory
25 Python scripts used by @value{GDBN} should be installed in
26 @file{@var{data-directory}/python}, where @var{data-directory} is
27 the data directory as determined at @value{GDBN} startup (@pxref{Data Files}).
28 This directory, known as the @dfn{python directory},
29 is automatically added to the Python Search Path in order to allow
30 the Python interpreter to locate all scripts installed at this location.
32 Additionally, @value{GDBN} commands and convenience functions which
33 are written in Python and are located in the
34 @file{@var{data-directory}/python/gdb/command} or
35 @file{@var{data-directory}/python/gdb/function} directories are
36 automatically imported when @value{GDBN} starts.
39 * Python Commands:: Accessing Python from @value{GDBN}.
40 * Python API:: Accessing @value{GDBN} from Python.
41 * Python Auto-loading:: Automatically loading Python code.
42 * Python modules:: Python modules provided by @value{GDBN}.
46 @subsection Python Commands
47 @cindex python commands
48 @cindex commands to access python
50 @value{GDBN} provides two commands for accessing the Python interpreter,
51 and one related setting:
54 @kindex python-interactive
56 @item python-interactive @r{[}@var{command}@r{]}
57 @itemx pi @r{[}@var{command}@r{]}
58 Without an argument, the @code{python-interactive} command can be used
59 to start an interactive Python prompt. To return to @value{GDBN},
60 type the @code{EOF} character (e.g., @kbd{Ctrl-D} on an empty prompt).
62 Alternatively, a single-line Python command can be given as an
63 argument and evaluated. If the command is an expression, the result
64 will be printed; otherwise, nothing will be printed. For example:
67 (@value{GDBP}) python-interactive 2 + 3
73 @item python @r{[}@var{command}@r{]}
74 @itemx py @r{[}@var{command}@r{]}
75 The @code{python} command can be used to evaluate Python code.
77 If given an argument, the @code{python} command will evaluate the
78 argument as a Python command. For example:
81 (@value{GDBP}) python print 23
85 If you do not provide an argument to @code{python}, it will act as a
86 multi-line command, like @code{define}. In this case, the Python
87 script is made up of subsequent command lines, given after the
88 @code{python} command. This command list is terminated using a line
89 containing @code{end}. For example:
98 @kindex set python print-stack
99 @item set python print-stack
100 By default, @value{GDBN} will print only the message component of a
101 Python exception when an error occurs in a Python script. This can be
102 controlled using @code{set python print-stack}: if @code{full}, then
103 full Python stack printing is enabled; if @code{none}, then Python stack
104 and message printing is disabled; if @code{message}, the default, only
105 the message component of the error is printed.
107 @kindex set python ignore-environment
108 @item set python ignore-environment @r{[}on@r{|}off@r{]}
109 By default this option is @samp{off}, and, when @value{GDBN}
110 initializes its internal Python interpreter, the Python interpreter
111 will check the environment for variables that will effect how it
112 behaves, for example @env{PYTHONHOME}, and
113 @env{PYTHONPATH}@footnote{See the ENVIRONMENT VARIABLES section of
114 @command{man 1 python} for a comprehensive list.}.
116 If this option is set to @samp{on} before Python is initialized then
117 Python will ignore all such environment variables. As Python is
118 initialized early during @value{GDBN}'s startup process, then this
119 option must be placed into the early initialization file
120 (@pxref{Initialization Files}) to have the desired effect.
122 This option is equivalent to passing @option{-E} to the real
123 @command{python} executable.
125 @kindex set python dont-write-bytecode
126 @item set python dont-write-bytecode @r{[}auto@r{|}on@r{|}off@r{]}
127 When this option is @samp{off}, then, once @value{GDBN} has
128 initialized the Python interpreter, the interpreter will byte-compile
129 any Python modules that it imports and write the byte code to disk in
132 If this option is set to @samp{on} before Python is initialized then
133 Python will no longer write the byte code to disk. As Python is
134 initialized early during @value{GDBN}'s startup process, then this
135 option must be placed into the early initialization file
136 (@pxref{Initialization Files}) to have the desired effect.
138 By default this option is set to @samp{auto}, in this mode Python will
139 check the environment variable @env{PYTHONDONTWRITEBYTECODE} to see
140 if it should write out byte-code or not.
142 This option is equivalent to passing @option{-B} to the real
143 @command{python} executable.
146 It is also possible to execute a Python script from the @value{GDBN}
150 @item source @file{script-name}
151 The script name must end with @samp{.py} and @value{GDBN} must be configured
152 to recognize the script language based on filename extension using
153 the @code{script-extension} setting. @xref{Extending GDB, ,Extending GDB}.
156 The following commands are intended to help debug @value{GDBN} itself:
159 @kindex set debug py-breakpoint
160 @kindex show debug py-breakpoint
161 @item set debug py-breakpoint on@r{|}off
162 @itemx show debug py-breakpoint
163 When @samp{on}, @value{GDBN} prints debug messages related to the
164 Python breakpoint API. This is @samp{off} by default.
166 @kindex set debug py-unwind
167 @kindex show debug py-unwind
168 @item set debug py-unwind on@r{|}off
169 @itemx show debug py-unwind
170 When @samp{on}, @value{GDBN} prints debug messages related to the
171 Python unwinder API. This is @samp{off} by default.
175 @subsection Python API
177 @cindex programming in python
179 You can get quick online help for @value{GDBN}'s Python API by issuing
180 the command @w{@kbd{python help (gdb)}}.
182 Functions and methods which have two or more optional arguments allow
183 them to be specified using keyword syntax. This allows passing some
184 optional arguments while skipping others. Example:
185 @w{@code{gdb.some_function ('foo', bar = 1, baz = 2)}}.
188 * Basic Python:: Basic Python Functions.
189 * Exception Handling:: How Python exceptions are translated.
190 * Values From Inferior:: Python representation of values.
191 * Types In Python:: Python representation of types.
192 * Pretty Printing API:: Pretty-printing values.
193 * Selecting Pretty-Printers:: How GDB chooses a pretty-printer.
194 * Writing a Pretty-Printer:: Writing a Pretty-Printer.
195 * Type Printing API:: Pretty-printing types.
196 * Frame Filter API:: Filtering Frames.
197 * Frame Decorator API:: Decorating Frames.
198 * Writing a Frame Filter:: Writing a Frame Filter.
199 * Unwinding Frames in Python:: Writing frame unwinder.
200 * Xmethods In Python:: Adding and replacing methods of C++ classes.
201 * Xmethod API:: Xmethod types.
202 * Writing an Xmethod:: Writing an xmethod.
203 * Inferiors In Python:: Python representation of inferiors (processes)
204 * Events In Python:: Listening for events from @value{GDBN}.
205 * Threads In Python:: Accessing inferior threads from Python.
206 * Recordings In Python:: Accessing recordings from Python.
207 * Commands In Python:: Implementing new commands in Python.
208 * Parameters In Python:: Adding new @value{GDBN} parameters.
209 * Functions In Python:: Writing new convenience functions.
210 * Progspaces In Python:: Program spaces.
211 * Objfiles In Python:: Object files.
212 * Frames In Python:: Accessing inferior stack frames from Python.
213 * Blocks In Python:: Accessing blocks from Python.
214 * Symbols In Python:: Python representation of symbols.
215 * Symbol Tables In Python:: Python representation of symbol tables.
216 * Line Tables In Python:: Python representation of line tables.
217 * Breakpoints In Python:: Manipulating breakpoints using Python.
218 * Finish Breakpoints in Python:: Setting Breakpoints on function return
220 * Lazy Strings In Python:: Python representation of lazy strings.
221 * Architectures In Python:: Python representation of architectures.
222 * Registers In Python:: Python representation of registers.
223 * Connections In Python:: Python representation of connections.
224 * TUI Windows In Python:: Implementing new TUI windows.
228 @subsubsection Basic Python
230 @cindex python stdout
231 @cindex python pagination
232 At startup, @value{GDBN} overrides Python's @code{sys.stdout} and
233 @code{sys.stderr} to print using @value{GDBN}'s output-paging streams.
234 A Python program which outputs to one of these streams may have its
235 output interrupted by the user (@pxref{Screen Size}). In this
236 situation, a Python @code{KeyboardInterrupt} exception is thrown.
238 Some care must be taken when writing Python code to run in
239 @value{GDBN}. Two things worth noting in particular:
243 @value{GDBN} install handlers for @code{SIGCHLD} and @code{SIGINT}.
244 Python code must not override these, or even change the options using
245 @code{sigaction}. If your program changes the handling of these
246 signals, @value{GDBN} will most likely stop working correctly. Note
247 that it is unfortunately common for GUI toolkits to install a
248 @code{SIGCHLD} handler.
251 @value{GDBN} takes care to mark its internal file descriptors as
252 close-on-exec. However, this cannot be done in a thread-safe way on
253 all platforms. Your Python programs should be aware of this and
254 should both create new file descriptors with the close-on-exec flag
255 set and arrange to close unneeded file descriptors before starting a
259 @cindex python functions
260 @cindex python module
262 @value{GDBN} introduces a new Python module, named @code{gdb}. All
263 methods and classes added by @value{GDBN} are placed in this module.
264 @value{GDBN} automatically @code{import}s the @code{gdb} module for
265 use in all scripts evaluated by the @code{python} command.
267 Some types of the @code{gdb} module come with a textual representation
268 (accessible through the @code{repr} or @code{str} functions). These are
269 offered for debugging purposes only, expect them to change over time.
271 @findex gdb.PYTHONDIR
272 @defvar gdb.PYTHONDIR
273 A string containing the python directory (@pxref{Python}).
277 @defun gdb.execute (command @r{[}, from_tty @r{[}, to_string@r{]]})
278 Evaluate @var{command}, a string, as a @value{GDBN} CLI command.
279 If a GDB exception happens while @var{command} runs, it is
280 translated as described in @ref{Exception Handling,,Exception Handling}.
282 The @var{from_tty} flag specifies whether @value{GDBN} ought to consider this
283 command as having originated from the user invoking it interactively.
284 It must be a boolean value. If omitted, it defaults to @code{False}.
286 By default, any output produced by @var{command} is sent to
287 @value{GDBN}'s standard output (and to the log output if logging is
288 turned on). If the @var{to_string} parameter is
289 @code{True}, then output will be collected by @code{gdb.execute} and
290 returned as a string. The default is @code{False}, in which case the
291 return value is @code{None}. If @var{to_string} is @code{True}, the
292 @value{GDBN} virtual terminal will be temporarily set to unlimited width
293 and height, and its pagination will be disabled; @pxref{Screen Size}.
296 @findex gdb.breakpoints
297 @defun gdb.breakpoints ()
298 Return a sequence holding all of @value{GDBN}'s breakpoints.
299 @xref{Breakpoints In Python}, for more information. In @value{GDBN}
300 version 7.11 and earlier, this function returned @code{None} if there
301 were no breakpoints. This peculiarity was subsequently fixed, and now
302 @code{gdb.breakpoints} returns an empty sequence in this case.
305 @defun gdb.rbreak (regex @r{[}, minsyms @r{[}, throttle, @r{[}, symtabs @r{]]]})
306 Return a Python list holding a collection of newly set
307 @code{gdb.Breakpoint} objects matching function names defined by the
308 @var{regex} pattern. If the @var{minsyms} keyword is @code{True}, all
309 system functions (those not explicitly defined in the inferior) will
310 also be included in the match. The @var{throttle} keyword takes an
311 integer that defines the maximum number of pattern matches for
312 functions matched by the @var{regex} pattern. If the number of
313 matches exceeds the integer value of @var{throttle}, a
314 @code{RuntimeError} will be raised and no breakpoints will be created.
315 If @var{throttle} is not defined then there is no imposed limit on the
316 maximum number of matches and breakpoints to be created. The
317 @var{symtabs} keyword takes a Python iterable that yields a collection
318 of @code{gdb.Symtab} objects and will restrict the search to those
319 functions only contained within the @code{gdb.Symtab} objects.
322 @findex gdb.parameter
323 @defun gdb.parameter (parameter)
324 Return the value of a @value{GDBN} @var{parameter} given by its name,
325 a string; the parameter name string may contain spaces if the parameter has a
326 multi-part name. For example, @samp{print object} is a valid
329 If the named parameter does not exist, this function throws a
330 @code{gdb.error} (@pxref{Exception Handling}). Otherwise, the
331 parameter's value is converted to a Python value of the appropriate
336 @defun gdb.history (number)
337 Return a value from @value{GDBN}'s value history (@pxref{Value
338 History}). The @var{number} argument indicates which history element to return.
339 If @var{number} is negative, then @value{GDBN} will take its absolute value
340 and count backward from the last element (i.e., the most recent element) to
341 find the value to return. If @var{number} is zero, then @value{GDBN} will
342 return the most recent element. If the element specified by @var{number}
343 doesn't exist in the value history, a @code{gdb.error} exception will be
346 If no exception is raised, the return value is always an instance of
347 @code{gdb.Value} (@pxref{Values From Inferior}).
350 @defun gdb.add_history (value)
351 Takes @var{value}, an instance of @code{gdb.Value} (@pxref{Values From
352 Inferior}), and appends the value this object represents to
353 @value{GDBN}'s value history (@pxref{Value History}), and return an
354 integer, its history number. If @var{value} is not a
355 @code{gdb.Value}, it is is converted using the @code{gdb.Value}
356 constructor. If @var{value} can't be converted to a @code{gdb.Value}
357 then a @code{TypeError} is raised.
359 When a command implemented in Python prints a single @code{gdb.Value}
360 as its result, then placing the value into the history will allow the
361 user convenient access to those values via CLI history facilities.
364 @findex gdb.convenience_variable
365 @defun gdb.convenience_variable (name)
366 Return the value of the convenience variable (@pxref{Convenience
367 Vars}) named @var{name}. @var{name} must be a string. The name
368 should not include the @samp{$} that is used to mark a convenience
369 variable in an expression. If the convenience variable does not
370 exist, then @code{None} is returned.
373 @findex gdb.set_convenience_variable
374 @defun gdb.set_convenience_variable (name, value)
375 Set the value of the convenience variable (@pxref{Convenience Vars})
376 named @var{name}. @var{name} must be a string. The name should not
377 include the @samp{$} that is used to mark a convenience variable in an
378 expression. If @var{value} is @code{None}, then the convenience
379 variable is removed. Otherwise, if @var{value} is not a
380 @code{gdb.Value} (@pxref{Values From Inferior}), it is is converted
381 using the @code{gdb.Value} constructor.
384 @findex gdb.parse_and_eval
385 @defun gdb.parse_and_eval (expression)
386 Parse @var{expression}, which must be a string, as an expression in
387 the current language, evaluate it, and return the result as a
390 This function can be useful when implementing a new command
391 (@pxref{Commands In Python}), as it provides a way to parse the
392 command's argument as an expression. It is also useful simply to
396 @findex gdb.find_pc_line
397 @defun gdb.find_pc_line (pc)
398 Return the @code{gdb.Symtab_and_line} object corresponding to the
399 @var{pc} value. @xref{Symbol Tables In Python}. If an invalid
400 value of @var{pc} is passed as an argument, then the @code{symtab} and
401 @code{line} attributes of the returned @code{gdb.Symtab_and_line} object
402 will be @code{None} and 0 respectively. This is identical to
403 @code{gdb.current_progspace().find_pc_line(pc)} and is included for
404 historical compatibility.
407 @findex gdb.post_event
408 @defun gdb.post_event (event)
409 Put @var{event}, a callable object taking no arguments, into
410 @value{GDBN}'s internal event queue. This callable will be invoked at
411 some later point, during @value{GDBN}'s event processing. Events
412 posted using @code{post_event} will be run in the order in which they
413 were posted; however, there is no way to know when they will be
414 processed relative to other events inside @value{GDBN}.
416 @value{GDBN} is not thread-safe. If your Python program uses multiple
417 threads, you must be careful to only call @value{GDBN}-specific
418 functions in the @value{GDBN} thread. @code{post_event} ensures
422 (@value{GDBP}) python
426 > def __init__(self, message):
427 > self.message = message;
428 > def __call__(self):
429 > gdb.write(self.message)
431 >class MyThread1 (threading.Thread):
433 > gdb.post_event(Writer("Hello "))
435 >class MyThread2 (threading.Thread):
437 > gdb.post_event(Writer("World\n"))
442 (@value{GDBP}) Hello World
447 @defun gdb.write (string @r{[}, stream{]})
448 Print a string to @value{GDBN}'s paginated output stream. The
449 optional @var{stream} determines the stream to print to. The default
450 stream is @value{GDBN}'s standard output stream. Possible stream
457 @value{GDBN}'s standard output stream.
462 @value{GDBN}'s standard error stream.
467 @value{GDBN}'s log stream (@pxref{Logging Output}).
470 Writing to @code{sys.stdout} or @code{sys.stderr} will automatically
471 call this function and will automatically direct the output to the
477 Flush the buffer of a @value{GDBN} paginated stream so that the
478 contents are displayed immediately. @value{GDBN} will flush the
479 contents of a stream automatically when it encounters a newline in the
480 buffer. The optional @var{stream} determines the stream to flush. The
481 default stream is @value{GDBN}'s standard output stream. Possible
488 @value{GDBN}'s standard output stream.
493 @value{GDBN}'s standard error stream.
498 @value{GDBN}'s log stream (@pxref{Logging Output}).
502 Flushing @code{sys.stdout} or @code{sys.stderr} will automatically
503 call this function for the relevant stream.
506 @findex gdb.target_charset
507 @defun gdb.target_charset ()
508 Return the name of the current target character set (@pxref{Character
509 Sets}). This differs from @code{gdb.parameter('target-charset')} in
510 that @samp{auto} is never returned.
513 @findex gdb.target_wide_charset
514 @defun gdb.target_wide_charset ()
515 Return the name of the current target wide character set
516 (@pxref{Character Sets}). This differs from
517 @code{gdb.parameter('target-wide-charset')} in that @samp{auto} is
521 @findex gdb.host_charset
522 @defun gdb.host_charset ()
523 Return a string, the name of the current host character set
524 (@pxref{Character Sets}). This differs from
525 @code{gdb.parameter('host-charset')} in that @samp{auto} is never
529 @findex gdb.solib_name
530 @defun gdb.solib_name (address)
531 Return the name of the shared library holding the given @var{address}
532 as a string, or @code{None}. This is identical to
533 @code{gdb.current_progspace().solib_name(address)} and is included for
534 historical compatibility.
537 @findex gdb.decode_line
538 @defun gdb.decode_line (@r{[}expression@r{]})
539 Return locations of the line specified by @var{expression}, or of the
540 current line if no argument was given. This function returns a Python
541 tuple containing two elements. The first element contains a string
542 holding any unparsed section of @var{expression} (or @code{None} if
543 the expression has been fully parsed). The second element contains
544 either @code{None} or another tuple that contains all the locations
545 that match the expression represented as @code{gdb.Symtab_and_line}
546 objects (@pxref{Symbol Tables In Python}). If @var{expression} is
547 provided, it is decoded the way that @value{GDBN}'s inbuilt
548 @code{break} or @code{edit} commands do (@pxref{Specify Location}).
551 @defun gdb.prompt_hook (current_prompt)
554 If @var{prompt_hook} is callable, @value{GDBN} will call the method
555 assigned to this operation before a prompt is displayed by
558 The parameter @code{current_prompt} contains the current @value{GDBN}
559 prompt. This method must return a Python string, or @code{None}. If
560 a string is returned, the @value{GDBN} prompt will be set to that
561 string. If @code{None} is returned, @value{GDBN} will continue to use
564 Some prompts cannot be substituted in @value{GDBN}. Secondary prompts
565 such as those used by readline for command input, and annotation
566 related prompts are prohibited from being changed.
569 @defun gdb.architecture_names ()
570 Return a list containing all of the architecture names that the
571 current build of @value{GDBN} supports. Each architecture name is a
572 string. The names returned in this list are the same names as are
573 returned from @code{gdb.Architecture.name}
574 (@pxref{gdbpy_architecture_name,,Architecture.name}).
577 @anchor{gdbpy_connections}
578 @defun gdb.connections
579 Return a list of @code{gdb.TargetConnection} objects, one for each
580 currently active connection (@pxref{Connections In Python}). The
581 connection objects are in no particular order in the returned list.
584 @node Exception Handling
585 @subsubsection Exception Handling
586 @cindex python exceptions
587 @cindex exceptions, python
589 When executing the @code{python} command, Python exceptions
590 uncaught within the Python code are translated to calls to
591 @value{GDBN} error-reporting mechanism. If the command that called
592 @code{python} does not handle the error, @value{GDBN} will
593 terminate it and print an error message containing the Python
594 exception name, the associated value, and the Python call stack
595 backtrace at the point where the exception was raised. Example:
598 (@value{GDBP}) python print foo
599 Traceback (most recent call last):
600 File "<string>", line 1, in <module>
601 NameError: name 'foo' is not defined
604 @value{GDBN} errors that happen in @value{GDBN} commands invoked by
605 Python code are converted to Python exceptions. The type of the
606 Python exception depends on the error.
610 This is the base class for most exceptions generated by @value{GDBN}.
611 It is derived from @code{RuntimeError}, for compatibility with earlier
612 versions of @value{GDBN}.
614 If an error occurring in @value{GDBN} does not fit into some more
615 specific category, then the generated exception will have this type.
617 @item gdb.MemoryError
618 This is a subclass of @code{gdb.error} which is thrown when an
619 operation tried to access invalid memory in the inferior.
621 @item KeyboardInterrupt
622 User interrupt (via @kbd{C-c} or by typing @kbd{q} at a pagination
623 prompt) is translated to a Python @code{KeyboardInterrupt} exception.
626 In all cases, your exception handler will see the @value{GDBN} error
627 message as its value and the Python call stack backtrace at the Python
628 statement closest to where the @value{GDBN} error occured as the
632 When implementing @value{GDBN} commands in Python via
633 @code{gdb.Command}, or functions via @code{gdb.Function}, it is useful
634 to be able to throw an exception that doesn't cause a traceback to be
635 printed. For example, the user may have invoked the command
636 incorrectly. @value{GDBN} provides a special exception class that can
637 be used for this purpose.
641 When thrown from a command or function, this exception will cause the
642 command or function to fail, but the Python stack will not be
643 displayed. @value{GDBN} does not throw this exception itself, but
644 rather recognizes it when thrown from user Python code. Example:
648 >class HelloWorld (gdb.Command):
649 > """Greet the whole world."""
650 > def __init__ (self):
651 > super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)
652 > def invoke (self, args, from_tty):
653 > argv = gdb.string_to_argv (args)
654 > if len (argv) != 0:
655 > raise gdb.GdbError ("hello-world takes no arguments")
656 > print ("Hello, World!")
660 hello-world takes no arguments
664 @node Values From Inferior
665 @subsubsection Values From Inferior
666 @cindex values from inferior, with Python
667 @cindex python, working with values from inferior
669 @cindex @code{gdb.Value}
670 @value{GDBN} provides values it obtains from the inferior program in
671 an object of type @code{gdb.Value}. @value{GDBN} uses this object
672 for its internal bookkeeping of the inferior's values, and for
673 fetching values when necessary.
675 Inferior values that are simple scalars can be used directly in
676 Python expressions that are valid for the value's data type. Here's
677 an example for an integer or floating-point value @code{some_val}:
684 As result of this, @code{bar} will also be a @code{gdb.Value} object
685 whose values are of the same type as those of @code{some_val}. Valid
686 Python operations can also be performed on @code{gdb.Value} objects
687 representing a @code{struct} or @code{class} object. For such cases,
688 the overloaded operator (if present), is used to perform the operation.
689 For example, if @code{val1} and @code{val2} are @code{gdb.Value} objects
690 representing instances of a @code{class} which overloads the @code{+}
691 operator, then one can use the @code{+} operator in their Python script
699 The result of the operation @code{val3} is also a @code{gdb.Value}
700 object corresponding to the value returned by the overloaded @code{+}
701 operator. In general, overloaded operators are invoked for the
702 following operations: @code{+} (binary addition), @code{-} (binary
703 subtraction), @code{*} (multiplication), @code{/}, @code{%}, @code{<<},
704 @code{>>}, @code{|}, @code{&}, @code{^}.
706 Inferior values that are structures or instances of some class can
707 be accessed using the Python @dfn{dictionary syntax}. For example, if
708 @code{some_val} is a @code{gdb.Value} instance holding a structure, you
709 can access its @code{foo} element with:
712 bar = some_val['foo']
715 @cindex getting structure elements using gdb.Field objects as subscripts
716 Again, @code{bar} will also be a @code{gdb.Value} object. Structure
717 elements can also be accessed by using @code{gdb.Field} objects as
718 subscripts (@pxref{Types In Python}, for more information on
719 @code{gdb.Field} objects). For example, if @code{foo_field} is a
720 @code{gdb.Field} object corresponding to element @code{foo} of the above
721 structure, then @code{bar} can also be accessed as follows:
724 bar = some_val[foo_field]
727 A @code{gdb.Value} that represents a function can be executed via
728 inferior function call. Any arguments provided to the call must match
729 the function's prototype, and must be provided in the order specified
732 For example, @code{some_val} is a @code{gdb.Value} instance
733 representing a function that takes two integers as arguments. To
734 execute this function, call it like so:
737 result = some_val (10,20)
740 Any values returned from a function call will be stored as a
743 The following attributes are provided:
745 @defvar Value.address
746 If this object is addressable, this read-only attribute holds a
747 @code{gdb.Value} object representing the address. Otherwise,
748 this attribute holds @code{None}.
751 @cindex optimized out value in Python
752 @defvar Value.is_optimized_out
753 This read-only boolean attribute is true if the compiler optimized out
754 this value, thus it is not available for fetching from the inferior.
758 The type of this @code{gdb.Value}. The value of this attribute is a
759 @code{gdb.Type} object (@pxref{Types In Python}).
762 @defvar Value.dynamic_type
763 The dynamic type of this @code{gdb.Value}. This uses the object's
764 virtual table and the C@t{++} run-time type information
765 (@acronym{RTTI}) to determine the dynamic type of the value. If this
766 value is of class type, it will return the class in which the value is
767 embedded, if any. If this value is of pointer or reference to a class
768 type, it will compute the dynamic type of the referenced object, and
769 return a pointer or reference to that type, respectively. In all
770 other cases, it will return the value's static type.
772 Note that this feature will only work when debugging a C@t{++} program
773 that includes @acronym{RTTI} for the object in question. Otherwise,
774 it will just return the static type of the value as in @kbd{ptype foo}
775 (@pxref{Symbols, ptype}).
778 @defvar Value.is_lazy
779 The value of this read-only boolean attribute is @code{True} if this
780 @code{gdb.Value} has not yet been fetched from the inferior.
781 @value{GDBN} does not fetch values until necessary, for efficiency.
785 myval = gdb.parse_and_eval ('somevar')
788 The value of @code{somevar} is not fetched at this time. It will be
789 fetched when the value is needed, or when the @code{fetch_lazy}
793 The following methods are provided:
795 @defun Value.__init__ (@var{val})
796 Many Python values can be converted directly to a @code{gdb.Value} via
797 this object initializer. Specifically:
801 A Python boolean is converted to the boolean type from the current
805 A Python integer is converted to the C @code{long} type for the
806 current architecture.
809 A Python long is converted to the C @code{long long} type for the
810 current architecture.
813 A Python float is converted to the C @code{double} type for the
814 current architecture.
817 A Python string is converted to a target string in the current target
818 language using the current target encoding.
819 If a character cannot be represented in the current target encoding,
820 then an exception is thrown.
822 @item @code{gdb.Value}
823 If @code{val} is a @code{gdb.Value}, then a copy of the value is made.
825 @item @code{gdb.LazyString}
826 If @code{val} is a @code{gdb.LazyString} (@pxref{Lazy Strings In
827 Python}), then the lazy string's @code{value} method is called, and
832 @defun Value.__init__ (@var{val}, @var{type})
833 This second form of the @code{gdb.Value} constructor returns a
834 @code{gdb.Value} of type @var{type} where the value contents are taken
835 from the Python buffer object specified by @var{val}. The number of
836 bytes in the Python buffer object must be greater than or equal to the
839 If @var{type} is @code{None} then this version of @code{__init__}
840 behaves as though @var{type} was not passed at all.
843 @defun Value.cast (type)
844 Return a new instance of @code{gdb.Value} that is the result of
845 casting this instance to the type described by @var{type}, which must
846 be a @code{gdb.Type} object. If the cast cannot be performed for some
847 reason, this method throws an exception.
850 @defun Value.dereference ()
851 For pointer data types, this method returns a new @code{gdb.Value} object
852 whose contents is the object pointed to by the pointer. For example, if
853 @code{foo} is a C pointer to an @code{int}, declared in your C program as
860 then you can use the corresponding @code{gdb.Value} to access what
861 @code{foo} points to like this:
864 bar = foo.dereference ()
867 The result @code{bar} will be a @code{gdb.Value} object holding the
868 value pointed to by @code{foo}.
870 A similar function @code{Value.referenced_value} exists which also
871 returns @code{gdb.Value} objects corresponding to the values pointed to
872 by pointer values (and additionally, values referenced by reference
873 values). However, the behavior of @code{Value.dereference}
874 differs from @code{Value.referenced_value} by the fact that the
875 behavior of @code{Value.dereference} is identical to applying the C
876 unary operator @code{*} on a given value. For example, consider a
877 reference to a pointer @code{ptrref}, declared in your C@t{++} program
885 intptr &ptrref = ptr;
888 Though @code{ptrref} is a reference value, one can apply the method
889 @code{Value.dereference} to the @code{gdb.Value} object corresponding
890 to it and obtain a @code{gdb.Value} which is identical to that
891 corresponding to @code{val}. However, if you apply the method
892 @code{Value.referenced_value}, the result would be a @code{gdb.Value}
893 object identical to that corresponding to @code{ptr}.
896 py_ptrref = gdb.parse_and_eval ("ptrref")
897 py_val = py_ptrref.dereference ()
898 py_ptr = py_ptrref.referenced_value ()
901 The @code{gdb.Value} object @code{py_val} is identical to that
902 corresponding to @code{val}, and @code{py_ptr} is identical to that
903 corresponding to @code{ptr}. In general, @code{Value.dereference} can
904 be applied whenever the C unary operator @code{*} can be applied
905 to the corresponding C value. For those cases where applying both
906 @code{Value.dereference} and @code{Value.referenced_value} is allowed,
907 the results obtained need not be identical (as we have seen in the above
908 example). The results are however identical when applied on
909 @code{gdb.Value} objects corresponding to pointers (@code{gdb.Value}
910 objects with type code @code{TYPE_CODE_PTR}) in a C/C@t{++} program.
913 @defun Value.referenced_value ()
914 For pointer or reference data types, this method returns a new
915 @code{gdb.Value} object corresponding to the value referenced by the
916 pointer/reference value. For pointer data types,
917 @code{Value.dereference} and @code{Value.referenced_value} produce
918 identical results. The difference between these methods is that
919 @code{Value.dereference} cannot get the values referenced by reference
920 values. For example, consider a reference to an @code{int}, declared
921 in your C@t{++} program as
929 then applying @code{Value.dereference} to the @code{gdb.Value} object
930 corresponding to @code{ref} will result in an error, while applying
931 @code{Value.referenced_value} will result in a @code{gdb.Value} object
932 identical to that corresponding to @code{val}.
935 py_ref = gdb.parse_and_eval ("ref")
936 er_ref = py_ref.dereference () # Results in error
937 py_val = py_ref.referenced_value () # Returns the referenced value
940 The @code{gdb.Value} object @code{py_val} is identical to that
941 corresponding to @code{val}.
944 @defun Value.reference_value ()
945 Return a @code{gdb.Value} object which is a reference to the value
946 encapsulated by this instance.
949 @defun Value.const_value ()
950 Return a @code{gdb.Value} object which is a @code{const} version of the
951 value encapsulated by this instance.
954 @defun Value.dynamic_cast (type)
955 Like @code{Value.cast}, but works as if the C@t{++} @code{dynamic_cast}
956 operator were used. Consult a C@t{++} reference for details.
959 @defun Value.reinterpret_cast (type)
960 Like @code{Value.cast}, but works as if the C@t{++} @code{reinterpret_cast}
961 operator were used. Consult a C@t{++} reference for details.
964 @defun Value.format_string (...)
965 Convert a @code{gdb.Value} to a string, similarly to what the @code{print}
966 command does. Invoked with no arguments, this is equivalent to calling
967 the @code{str} function on the @code{gdb.Value}. The representation of
968 the same value may change across different versions of @value{GDBN}, so
969 you shouldn't, for instance, parse the strings returned by this method.
971 All the arguments are keyword only. If an argument is not specified, the
972 current global default setting is used.
976 @code{True} if pretty-printers (@pxref{Pretty Printing}) should not be
977 used to format the value. @code{False} if enabled pretty-printers
978 matching the type represented by the @code{gdb.Value} should be used to
982 @code{True} if arrays should be pretty printed to be more convenient to
983 read, @code{False} if they shouldn't (see @code{set print array} in
984 @ref{Print Settings}).
987 @code{True} if structs should be pretty printed to be more convenient to
988 read, @code{False} if they shouldn't (see @code{set print pretty} in
989 @ref{Print Settings}).
992 @code{True} if array indexes should be included in the string
993 representation of arrays, @code{False} if they shouldn't (see @code{set
994 print array-indexes} in @ref{Print Settings}).
997 @code{True} if the string representation of a pointer should include the
998 corresponding symbol name (if one exists), @code{False} if it shouldn't
999 (see @code{set print symbol} in @ref{Print Settings}).
1002 @code{True} if unions which are contained in other structures or unions
1003 should be expanded, @code{False} if they shouldn't (see @code{set print
1004 union} in @ref{Print Settings}).
1007 @code{True} if the string representation of a pointer should include the
1008 address, @code{False} if it shouldn't (see @code{set print address} in
1009 @ref{Print Settings}).
1012 @code{True} if C@t{++} references should be resolved to the value they
1013 refer to, @code{False} (the default) if they shouldn't. Note that, unlike
1014 for the @code{print} command, references are not automatically expanded
1015 when using the @code{format_string} method or the @code{str}
1016 function. There is no global @code{print} setting to change the default
1019 @item actual_objects
1020 @code{True} if the representation of a pointer to an object should
1021 identify the @emph{actual} (derived) type of the object rather than the
1022 @emph{declared} type, using the virtual function table. @code{False} if
1023 the @emph{declared} type should be used. (See @code{set print object} in
1024 @ref{Print Settings}).
1026 @item static_members
1027 @code{True} if static members should be included in the string
1028 representation of a C@t{++} object, @code{False} if they shouldn't (see
1029 @code{set print static-members} in @ref{Print Settings}).
1032 Number of array elements to print, or @code{0} to print an unlimited
1033 number of elements (see @code{set print elements} in @ref{Print
1037 The maximum depth to print for nested structs and unions, or @code{-1}
1038 to print an unlimited number of elements (see @code{set print
1039 max-depth} in @ref{Print Settings}).
1041 @item repeat_threshold
1042 Set the threshold for suppressing display of repeated array elements, or
1043 @code{0} to represent all elements, even if repeated. (See @code{set
1044 print repeats} in @ref{Print Settings}).
1047 A string containing a single character representing the format to use for
1048 the returned string. For instance, @code{'x'} is equivalent to using the
1049 @value{GDBN} command @code{print} with the @code{/x} option and formats
1050 the value as a hexadecimal number.
1054 @defun Value.string (@r{[}encoding@r{[}, errors@r{[}, length@r{]]]})
1055 If this @code{gdb.Value} represents a string, then this method
1056 converts the contents to a Python string. Otherwise, this method will
1059 Values are interpreted as strings according to the rules of the
1060 current language. If the optional length argument is given, the
1061 string will be converted to that length, and will include any embedded
1062 zeroes that the string may contain. Otherwise, for languages
1063 where the string is zero-terminated, the entire string will be
1066 For example, in C-like languages, a value is a string if it is a pointer
1067 to or an array of characters or ints of type @code{wchar_t}, @code{char16_t},
1070 If the optional @var{encoding} argument is given, it must be a string
1071 naming the encoding of the string in the @code{gdb.Value}, such as
1072 @code{"ascii"}, @code{"iso-8859-6"} or @code{"utf-8"}. It accepts
1073 the same encodings as the corresponding argument to Python's
1074 @code{string.decode} method, and the Python codec machinery will be used
1075 to convert the string. If @var{encoding} is not given, or if
1076 @var{encoding} is the empty string, then either the @code{target-charset}
1077 (@pxref{Character Sets}) will be used, or a language-specific encoding
1078 will be used, if the current language is able to supply one.
1080 The optional @var{errors} argument is the same as the corresponding
1081 argument to Python's @code{string.decode} method.
1083 If the optional @var{length} argument is given, the string will be
1084 fetched and converted to the given length.
1087 @defun Value.lazy_string (@r{[}encoding @r{[}, length@r{]]})
1088 If this @code{gdb.Value} represents a string, then this method
1089 converts the contents to a @code{gdb.LazyString} (@pxref{Lazy Strings
1090 In Python}). Otherwise, this method will throw an exception.
1092 If the optional @var{encoding} argument is given, it must be a string
1093 naming the encoding of the @code{gdb.LazyString}. Some examples are:
1094 @samp{ascii}, @samp{iso-8859-6} or @samp{utf-8}. If the
1095 @var{encoding} argument is an encoding that @value{GDBN} does
1096 recognize, @value{GDBN} will raise an error.
1098 When a lazy string is printed, the @value{GDBN} encoding machinery is
1099 used to convert the string during printing. If the optional
1100 @var{encoding} argument is not provided, or is an empty string,
1101 @value{GDBN} will automatically select the encoding most suitable for
1102 the string type. For further information on encoding in @value{GDBN}
1103 please see @ref{Character Sets}.
1105 If the optional @var{length} argument is given, the string will be
1106 fetched and encoded to the length of characters specified. If
1107 the @var{length} argument is not provided, the string will be fetched
1108 and encoded until a null of appropriate width is found.
1111 @defun Value.fetch_lazy ()
1112 If the @code{gdb.Value} object is currently a lazy value
1113 (@code{gdb.Value.is_lazy} is @code{True}), then the value is
1114 fetched from the inferior. Any errors that occur in the process
1115 will produce a Python exception.
1117 If the @code{gdb.Value} object is not a lazy value, this method
1120 This method does not return a value.
1124 @node Types In Python
1125 @subsubsection Types In Python
1126 @cindex types in Python
1127 @cindex Python, working with types
1130 @value{GDBN} represents types from the inferior using the class
1133 The following type-related functions are available in the @code{gdb}
1136 @findex gdb.lookup_type
1137 @defun gdb.lookup_type (name @r{[}, block@r{]})
1138 This function looks up a type by its @var{name}, which must be a string.
1140 If @var{block} is given, then @var{name} is looked up in that scope.
1141 Otherwise, it is searched for globally.
1143 Ordinarily, this function will return an instance of @code{gdb.Type}.
1144 If the named type cannot be found, it will throw an exception.
1147 Integer types can be found without looking them up by name.
1148 @xref{Architectures In Python}, for the @code{integer_type} method.
1150 If the type is a structure or class type, or an enum type, the fields
1151 of that type can be accessed using the Python @dfn{dictionary syntax}.
1152 For example, if @code{some_type} is a @code{gdb.Type} instance holding
1153 a structure type, you can access its @code{foo} field with:
1156 bar = some_type['foo']
1159 @code{bar} will be a @code{gdb.Field} object; see below under the
1160 description of the @code{Type.fields} method for a description of the
1161 @code{gdb.Field} class.
1163 An instance of @code{Type} has the following attributes:
1165 @defvar Type.alignof
1166 The alignment of this type, in bytes. Type alignment comes from the
1167 debugging information; if it was not specified, then @value{GDBN} will
1168 use the relevant ABI to try to determine the alignment. In some
1169 cases, even this is not possible, and zero will be returned.
1173 The type code for this type. The type code will be one of the
1174 @code{TYPE_CODE_} constants defined below.
1177 @defvar Type.dynamic
1178 A boolean indicating whether this type is dynamic. In some
1179 situations, such as Rust @code{enum} types or Ada variant records, the
1180 concrete type of a value may vary depending on its contents. That is,
1181 the declared type of a variable, or the type returned by
1182 @code{gdb.lookup_type} may be dynamic; while the type of the
1183 variable's value will be a concrete instance of that dynamic type.
1185 For example, consider this code:
1191 Here, at least conceptually (whether your compiler actually does this
1192 is a separate issue), examining @w{@code{gdb.lookup_symbol("array", ...).type}}
1193 could yield a @code{gdb.Type} which reports a size of @code{None}.
1194 This is the dynamic type.
1196 However, examining @code{gdb.parse_and_eval("array").type} would yield
1197 a concrete type, whose length would be known.
1201 The name of this type. If this type has no name, then @code{None}
1206 The size of this type, in target @code{char} units. Usually, a
1207 target's @code{char} type will be an 8-bit byte. However, on some
1208 unusual platforms, this type may have a different size. A dynamic
1209 type may not have a fixed size; in this case, this attribute's value
1210 will be @code{None}.
1214 The tag name for this type. The tag name is the name after
1215 @code{struct}, @code{union}, or @code{enum} in C and C@t{++}; not all
1216 languages have this concept. If this type has no tag name, then
1217 @code{None} is returned.
1220 @defvar Type.objfile
1221 The @code{gdb.Objfile} that this type was defined in, or @code{None} if
1222 there is no associated objfile.
1225 The following methods are provided:
1227 @defun Type.fields ()
1229 Return the fields of this type. The behavior depends on the type code:
1234 For structure and union types, this method returns the fields.
1237 Range types have two fields, the minimum and maximum values.
1240 Enum types have one field per enum constant.
1243 Function and method types have one field per parameter. The base types of
1244 C@t{++} classes are also represented as fields.
1247 Array types have one field representing the array's range.
1250 If the type does not fit into one of these categories, a @code{TypeError}
1255 Each field is a @code{gdb.Field} object, with some pre-defined attributes:
1258 This attribute is not available for @code{enum} or @code{static}
1259 (as in C@t{++}) fields. The value is the position, counting
1260 in bits, from the start of the containing type. Note that, in a
1261 dynamic type, the position of a field may not be constant. In this
1262 case, the value will be @code{None}. Also, a dynamic type may have
1263 fields that do not appear in a corresponding concrete type.
1266 This attribute is only available for @code{enum} fields, and its value
1267 is the enumeration member's integer representation.
1270 The name of the field, or @code{None} for anonymous fields.
1273 This is @code{True} if the field is artificial, usually meaning that
1274 it was provided by the compiler and not the user. This attribute is
1275 always provided, and is @code{False} if the field is not artificial.
1278 This is @code{True} if the field represents a base class of a C@t{++}
1279 structure. This attribute is always provided, and is @code{False}
1280 if the field is not a base class of the type that is the argument of
1281 @code{fields}, or if that type was not a C@t{++} class.
1284 If the field is packed, or is a bitfield, then this will have a
1285 non-zero value, which is the size of the field in bits. Otherwise,
1286 this will be zero; in this case the field's size is given by its type.
1289 The type of the field. This is usually an instance of @code{Type},
1290 but it can be @code{None} in some situations.
1293 The type which contains this field. This is an instance of
1298 @defun Type.array (@var{n1} @r{[}, @var{n2}@r{]})
1299 Return a new @code{gdb.Type} object which represents an array of this
1300 type. If one argument is given, it is the inclusive upper bound of
1301 the array; in this case the lower bound is zero. If two arguments are
1302 given, the first argument is the lower bound of the array, and the
1303 second argument is the upper bound of the array. An array's length
1304 must not be negative, but the bounds can be.
1307 @defun Type.vector (@var{n1} @r{[}, @var{n2}@r{]})
1308 Return a new @code{gdb.Type} object which represents a vector of this
1309 type. If one argument is given, it is the inclusive upper bound of
1310 the vector; in this case the lower bound is zero. If two arguments are
1311 given, the first argument is the lower bound of the vector, and the
1312 second argument is the upper bound of the vector. A vector's length
1313 must not be negative, but the bounds can be.
1315 The difference between an @code{array} and a @code{vector} is that
1316 arrays behave like in C: when used in expressions they decay to a pointer
1317 to the first element whereas vectors are treated as first class values.
1320 @defun Type.const ()
1321 Return a new @code{gdb.Type} object which represents a
1322 @code{const}-qualified variant of this type.
1325 @defun Type.volatile ()
1326 Return a new @code{gdb.Type} object which represents a
1327 @code{volatile}-qualified variant of this type.
1330 @defun Type.unqualified ()
1331 Return a new @code{gdb.Type} object which represents an unqualified
1332 variant of this type. That is, the result is neither @code{const} nor
1336 @defun Type.range ()
1337 Return a Python @code{Tuple} object that contains two elements: the
1338 low bound of the argument type and the high bound of that type. If
1339 the type does not have a range, @value{GDBN} will raise a
1340 @code{gdb.error} exception (@pxref{Exception Handling}).
1343 @defun Type.reference ()
1344 Return a new @code{gdb.Type} object which represents a reference to this
1348 @defun Type.pointer ()
1349 Return a new @code{gdb.Type} object which represents a pointer to this
1353 @defun Type.strip_typedefs ()
1354 Return a new @code{gdb.Type} that represents the real type,
1355 after removing all layers of typedefs.
1358 @defun Type.target ()
1359 Return a new @code{gdb.Type} object which represents the target type
1362 For a pointer type, the target type is the type of the pointed-to
1363 object. For an array type (meaning C-like arrays), the target type is
1364 the type of the elements of the array. For a function or method type,
1365 the target type is the type of the return value. For a complex type,
1366 the target type is the type of the elements. For a typedef, the
1367 target type is the aliased type.
1369 If the type does not have a target, this method will throw an
1373 @defun Type.template_argument (n @r{[}, block@r{]})
1374 If this @code{gdb.Type} is an instantiation of a template, this will
1375 return a new @code{gdb.Value} or @code{gdb.Type} which represents the
1376 value of the @var{n}th template argument (indexed starting at 0).
1378 If this @code{gdb.Type} is not a template type, or if the type has fewer
1379 than @var{n} template arguments, this will throw an exception.
1380 Ordinarily, only C@t{++} code will have template types.
1382 If @var{block} is given, then @var{name} is looked up in that scope.
1383 Otherwise, it is searched for globally.
1386 @defun Type.optimized_out ()
1387 Return @code{gdb.Value} instance of this type whose value is optimized
1388 out. This allows a frame decorator to indicate that the value of an
1389 argument or a local variable is not known.
1392 Each type has a code, which indicates what category this type falls
1393 into. The available type categories are represented by constants
1394 defined in the @code{gdb} module:
1397 @vindex TYPE_CODE_PTR
1398 @item gdb.TYPE_CODE_PTR
1399 The type is a pointer.
1401 @vindex TYPE_CODE_ARRAY
1402 @item gdb.TYPE_CODE_ARRAY
1403 The type is an array.
1405 @vindex TYPE_CODE_STRUCT
1406 @item gdb.TYPE_CODE_STRUCT
1407 The type is a structure.
1409 @vindex TYPE_CODE_UNION
1410 @item gdb.TYPE_CODE_UNION
1411 The type is a union.
1413 @vindex TYPE_CODE_ENUM
1414 @item gdb.TYPE_CODE_ENUM
1415 The type is an enum.
1417 @vindex TYPE_CODE_FLAGS
1418 @item gdb.TYPE_CODE_FLAGS
1419 A bit flags type, used for things such as status registers.
1421 @vindex TYPE_CODE_FUNC
1422 @item gdb.TYPE_CODE_FUNC
1423 The type is a function.
1425 @vindex TYPE_CODE_INT
1426 @item gdb.TYPE_CODE_INT
1427 The type is an integer type.
1429 @vindex TYPE_CODE_FLT
1430 @item gdb.TYPE_CODE_FLT
1431 A floating point type.
1433 @vindex TYPE_CODE_VOID
1434 @item gdb.TYPE_CODE_VOID
1435 The special type @code{void}.
1437 @vindex TYPE_CODE_SET
1438 @item gdb.TYPE_CODE_SET
1441 @vindex TYPE_CODE_RANGE
1442 @item gdb.TYPE_CODE_RANGE
1443 A range type, that is, an integer type with bounds.
1445 @vindex TYPE_CODE_STRING
1446 @item gdb.TYPE_CODE_STRING
1447 A string type. Note that this is only used for certain languages with
1448 language-defined string types; C strings are not represented this way.
1450 @vindex TYPE_CODE_BITSTRING
1451 @item gdb.TYPE_CODE_BITSTRING
1452 A string of bits. It is deprecated.
1454 @vindex TYPE_CODE_ERROR
1455 @item gdb.TYPE_CODE_ERROR
1456 An unknown or erroneous type.
1458 @vindex TYPE_CODE_METHOD
1459 @item gdb.TYPE_CODE_METHOD
1460 A method type, as found in C@t{++}.
1462 @vindex TYPE_CODE_METHODPTR
1463 @item gdb.TYPE_CODE_METHODPTR
1464 A pointer-to-member-function.
1466 @vindex TYPE_CODE_MEMBERPTR
1467 @item gdb.TYPE_CODE_MEMBERPTR
1468 A pointer-to-member.
1470 @vindex TYPE_CODE_REF
1471 @item gdb.TYPE_CODE_REF
1474 @vindex TYPE_CODE_RVALUE_REF
1475 @item gdb.TYPE_CODE_RVALUE_REF
1476 A C@t{++}11 rvalue reference type.
1478 @vindex TYPE_CODE_CHAR
1479 @item gdb.TYPE_CODE_CHAR
1482 @vindex TYPE_CODE_BOOL
1483 @item gdb.TYPE_CODE_BOOL
1486 @vindex TYPE_CODE_COMPLEX
1487 @item gdb.TYPE_CODE_COMPLEX
1488 A complex float type.
1490 @vindex TYPE_CODE_TYPEDEF
1491 @item gdb.TYPE_CODE_TYPEDEF
1492 A typedef to some other type.
1494 @vindex TYPE_CODE_NAMESPACE
1495 @item gdb.TYPE_CODE_NAMESPACE
1496 A C@t{++} namespace.
1498 @vindex TYPE_CODE_DECFLOAT
1499 @item gdb.TYPE_CODE_DECFLOAT
1500 A decimal floating point type.
1502 @vindex TYPE_CODE_INTERNAL_FUNCTION
1503 @item gdb.TYPE_CODE_INTERNAL_FUNCTION
1504 A function internal to @value{GDBN}. This is the type used to represent
1505 convenience functions.
1508 Further support for types is provided in the @code{gdb.types}
1509 Python module (@pxref{gdb.types}).
1511 @node Pretty Printing API
1512 @subsubsection Pretty Printing API
1513 @cindex python pretty printing api
1515 A pretty-printer is just an object that holds a value and implements a
1516 specific interface, defined here. An example output is provided
1517 (@pxref{Pretty Printing}).
1519 @defun pretty_printer.children (self)
1520 @value{GDBN} will call this method on a pretty-printer to compute the
1521 children of the pretty-printer's value.
1523 This method must return an object conforming to the Python iterator
1524 protocol. Each item returned by the iterator must be a tuple holding
1525 two elements. The first element is the ``name'' of the child; the
1526 second element is the child's value. The value can be any Python
1527 object which is convertible to a @value{GDBN} value.
1529 This method is optional. If it does not exist, @value{GDBN} will act
1530 as though the value has no children.
1532 For efficiency, the @code{children} method should lazily compute its
1533 results. This will let @value{GDBN} read as few elements as
1534 necessary, for example when various print settings (@pxref{Print
1535 Settings}) or @code{-var-list-children} (@pxref{GDB/MI Variable
1536 Objects}) limit the number of elements to be displayed.
1538 Children may be hidden from display based on the value of @samp{set
1539 print max-depth} (@pxref{Print Settings}).
1542 @defun pretty_printer.display_hint (self)
1543 The CLI may call this method and use its result to change the
1544 formatting of a value. The result will also be supplied to an MI
1545 consumer as a @samp{displayhint} attribute of the variable being
1548 This method is optional. If it does exist, this method must return a
1549 string or the special value @code{None}.
1551 Some display hints are predefined by @value{GDBN}:
1555 Indicate that the object being printed is ``array-like''. The CLI
1556 uses this to respect parameters such as @code{set print elements} and
1557 @code{set print array}.
1560 Indicate that the object being printed is ``map-like'', and that the
1561 children of this value can be assumed to alternate between keys and
1565 Indicate that the object being printed is ``string-like''. If the
1566 printer's @code{to_string} method returns a Python string of some
1567 kind, then @value{GDBN} will call its internal language-specific
1568 string-printing function to format the string. For the CLI this means
1569 adding quotation marks, possibly escaping some characters, respecting
1570 @code{set print elements}, and the like.
1573 The special value @code{None} causes @value{GDBN} to apply the default
1577 @defun pretty_printer.to_string (self)
1578 @value{GDBN} will call this method to display the string
1579 representation of the value passed to the object's constructor.
1581 When printing from the CLI, if the @code{to_string} method exists,
1582 then @value{GDBN} will prepend its result to the values returned by
1583 @code{children}. Exactly how this formatting is done is dependent on
1584 the display hint, and may change as more hints are added. Also,
1585 depending on the print settings (@pxref{Print Settings}), the CLI may
1586 print just the result of @code{to_string} in a stack trace, omitting
1587 the result of @code{children}.
1589 If this method returns a string, it is printed verbatim.
1591 Otherwise, if this method returns an instance of @code{gdb.Value},
1592 then @value{GDBN} prints this value. This may result in a call to
1593 another pretty-printer.
1595 If instead the method returns a Python value which is convertible to a
1596 @code{gdb.Value}, then @value{GDBN} performs the conversion and prints
1597 the resulting value. Again, this may result in a call to another
1598 pretty-printer. Python scalars (integers, floats, and booleans) and
1599 strings are convertible to @code{gdb.Value}; other types are not.
1601 Finally, if this method returns @code{None} then no further operations
1602 are peformed in this method and nothing is printed.
1604 If the result is not one of these types, an exception is raised.
1607 @value{GDBN} provides a function which can be used to look up the
1608 default pretty-printer for a @code{gdb.Value}:
1610 @findex gdb.default_visualizer
1611 @defun gdb.default_visualizer (value)
1612 This function takes a @code{gdb.Value} object as an argument. If a
1613 pretty-printer for this value exists, then it is returned. If no such
1614 printer exists, then this returns @code{None}.
1617 @node Selecting Pretty-Printers
1618 @subsubsection Selecting Pretty-Printers
1619 @cindex selecting python pretty-printers
1621 @value{GDBN} provides several ways to register a pretty-printer:
1622 globally, per program space, and per objfile. When choosing how to
1623 register your pretty-printer, a good rule is to register it with the
1624 smallest scope possible: that is prefer a specific objfile first, then
1625 a program space, and only register a printer globally as a last
1628 @findex gdb.pretty_printers
1629 @defvar gdb.pretty_printers
1630 The Python list @code{gdb.pretty_printers} contains an array of
1631 functions or callable objects that have been registered via addition
1632 as a pretty-printer. Printers in this list are called @code{global}
1633 printers, they're available when debugging all inferiors.
1636 Each @code{gdb.Progspace} contains a @code{pretty_printers} attribute.
1637 Each @code{gdb.Objfile} also contains a @code{pretty_printers}
1640 Each function on these lists is passed a single @code{gdb.Value}
1641 argument and should return a pretty-printer object conforming to the
1642 interface definition above (@pxref{Pretty Printing API}). If a function
1643 cannot create a pretty-printer for the value, it should return
1646 @value{GDBN} first checks the @code{pretty_printers} attribute of each
1647 @code{gdb.Objfile} in the current program space and iteratively calls
1648 each enabled lookup routine in the list for that @code{gdb.Objfile}
1649 until it receives a pretty-printer object.
1650 If no pretty-printer is found in the objfile lists, @value{GDBN} then
1651 searches the pretty-printer list of the current program space,
1652 calling each enabled function until an object is returned.
1653 After these lists have been exhausted, it tries the global
1654 @code{gdb.pretty_printers} list, again calling each enabled function until an
1657 The order in which the objfiles are searched is not specified. For a
1658 given list, functions are always invoked from the head of the list,
1659 and iterated over sequentially until the end of the list, or a printer
1662 For various reasons a pretty-printer may not work.
1663 For example, the underlying data structure may have changed and
1664 the pretty-printer is out of date.
1666 The consequences of a broken pretty-printer are severe enough that
1667 @value{GDBN} provides support for enabling and disabling individual
1668 printers. For example, if @code{print frame-arguments} is on,
1669 a backtrace can become highly illegible if any argument is printed
1670 with a broken printer.
1672 Pretty-printers are enabled and disabled by attaching an @code{enabled}
1673 attribute to the registered function or callable object. If this attribute
1674 is present and its value is @code{False}, the printer is disabled, otherwise
1675 the printer is enabled.
1677 @node Writing a Pretty-Printer
1678 @subsubsection Writing a Pretty-Printer
1679 @cindex writing a pretty-printer
1681 A pretty-printer consists of two parts: a lookup function to detect
1682 if the type is supported, and the printer itself.
1684 Here is an example showing how a @code{std::string} printer might be
1685 written. @xref{Pretty Printing API}, for details on the API this class
1689 class StdStringPrinter(object):
1690 "Print a std::string"
1692 def __init__(self, val):
1695 def to_string(self):
1696 return self.val['_M_dataplus']['_M_p']
1698 def display_hint(self):
1702 And here is an example showing how a lookup function for the printer
1703 example above might be written.
1706 def str_lookup_function(val):
1707 lookup_tag = val.type.tag
1708 if lookup_tag is None:
1710 regex = re.compile("^std::basic_string<char,.*>$")
1711 if regex.match(lookup_tag):
1712 return StdStringPrinter(val)
1716 The example lookup function extracts the value's type, and attempts to
1717 match it to a type that it can pretty-print. If it is a type the
1718 printer can pretty-print, it will return a printer object. If not, it
1719 returns @code{None}.
1721 We recommend that you put your core pretty-printers into a Python
1722 package. If your pretty-printers are for use with a library, we
1723 further recommend embedding a version number into the package name.
1724 This practice will enable @value{GDBN} to load multiple versions of
1725 your pretty-printers at the same time, because they will have
1728 You should write auto-loaded code (@pxref{Python Auto-loading}) such that it
1729 can be evaluated multiple times without changing its meaning. An
1730 ideal auto-load file will consist solely of @code{import}s of your
1731 printer modules, followed by a call to a register pretty-printers with
1732 the current objfile.
1734 Taken as a whole, this approach will scale nicely to multiple
1735 inferiors, each potentially using a different library version.
1736 Embedding a version number in the Python package name will ensure that
1737 @value{GDBN} is able to load both sets of printers simultaneously.
1738 Then, because the search for pretty-printers is done by objfile, and
1739 because your auto-loaded code took care to register your library's
1740 printers with a specific objfile, @value{GDBN} will find the correct
1741 printers for the specific version of the library used by each
1744 To continue the @code{std::string} example (@pxref{Pretty Printing API}),
1745 this code might appear in @code{gdb.libstdcxx.v6}:
1748 def register_printers(objfile):
1749 objfile.pretty_printers.append(str_lookup_function)
1753 And then the corresponding contents of the auto-load file would be:
1756 import gdb.libstdcxx.v6
1757 gdb.libstdcxx.v6.register_printers(gdb.current_objfile())
1760 The previous example illustrates a basic pretty-printer.
1761 There are a few things that can be improved on.
1762 The printer doesn't have a name, making it hard to identify in a
1763 list of installed printers. The lookup function has a name, but
1764 lookup functions can have arbitrary, even identical, names.
1766 Second, the printer only handles one type, whereas a library typically has
1767 several types. One could install a lookup function for each desired type
1768 in the library, but one could also have a single lookup function recognize
1769 several types. The latter is the conventional way this is handled.
1770 If a pretty-printer can handle multiple data types, then its
1771 @dfn{subprinters} are the printers for the individual data types.
1773 The @code{gdb.printing} module provides a formal way of solving these
1774 problems (@pxref{gdb.printing}).
1775 Here is another example that handles multiple types.
1777 These are the types we are going to pretty-print:
1780 struct foo @{ int a, b; @};
1781 struct bar @{ struct foo x, y; @};
1784 Here are the printers:
1788 """Print a foo object."""
1790 def __init__(self, val):
1793 def to_string(self):
1794 return ("a=<" + str(self.val["a"]) +
1795 "> b=<" + str(self.val["b"]) + ">")
1798 """Print a bar object."""
1800 def __init__(self, val):
1803 def to_string(self):
1804 return ("x=<" + str(self.val["x"]) +
1805 "> y=<" + str(self.val["y"]) + ">")
1808 This example doesn't need a lookup function, that is handled by the
1809 @code{gdb.printing} module. Instead a function is provided to build up
1810 the object that handles the lookup.
1815 def build_pretty_printer():
1816 pp = gdb.printing.RegexpCollectionPrettyPrinter(
1818 pp.add_printer('foo', '^foo$', fooPrinter)
1819 pp.add_printer('bar', '^bar$', barPrinter)
1823 And here is the autoload support:
1828 gdb.printing.register_pretty_printer(
1829 gdb.current_objfile(),
1830 my_library.build_pretty_printer())
1833 Finally, when this printer is loaded into @value{GDBN}, here is the
1834 corresponding output of @samp{info pretty-printer}:
1837 (gdb) info pretty-printer
1844 @node Type Printing API
1845 @subsubsection Type Printing API
1846 @cindex type printing API for Python
1848 @value{GDBN} provides a way for Python code to customize type display.
1849 This is mainly useful for substituting canonical typedef names for
1852 @cindex type printer
1853 A @dfn{type printer} is just a Python object conforming to a certain
1854 protocol. A simple base class implementing the protocol is provided;
1855 see @ref{gdb.types}. A type printer must supply at least:
1857 @defivar type_printer enabled
1858 A boolean which is True if the printer is enabled, and False
1859 otherwise. This is manipulated by the @code{enable type-printer}
1860 and @code{disable type-printer} commands.
1863 @defivar type_printer name
1864 The name of the type printer. This must be a string. This is used by
1865 the @code{enable type-printer} and @code{disable type-printer}
1869 @defmethod type_printer instantiate (self)
1870 This is called by @value{GDBN} at the start of type-printing. It is
1871 only called if the type printer is enabled. This method must return a
1872 new object that supplies a @code{recognize} method, as described below.
1876 When displaying a type, say via the @code{ptype} command, @value{GDBN}
1877 will compute a list of type recognizers. This is done by iterating
1878 first over the per-objfile type printers (@pxref{Objfiles In Python}),
1879 followed by the per-progspace type printers (@pxref{Progspaces In
1880 Python}), and finally the global type printers.
1882 @value{GDBN} will call the @code{instantiate} method of each enabled
1883 type printer. If this method returns @code{None}, then the result is
1884 ignored; otherwise, it is appended to the list of recognizers.
1886 Then, when @value{GDBN} is going to display a type name, it iterates
1887 over the list of recognizers. For each one, it calls the recognition
1888 function, stopping if the function returns a non-@code{None} value.
1889 The recognition function is defined as:
1891 @defmethod type_recognizer recognize (self, type)
1892 If @var{type} is not recognized, return @code{None}. Otherwise,
1893 return a string which is to be printed as the name of @var{type}.
1894 The @var{type} argument will be an instance of @code{gdb.Type}
1895 (@pxref{Types In Python}).
1898 @value{GDBN} uses this two-pass approach so that type printers can
1899 efficiently cache information without holding on to it too long. For
1900 example, it can be convenient to look up type information in a type
1901 printer and hold it for a recognizer's lifetime; if a single pass were
1902 done then type printers would have to make use of the event system in
1903 order to avoid holding information that could become stale as the
1906 @node Frame Filter API
1907 @subsubsection Filtering Frames
1908 @cindex frame filters api
1910 Frame filters are Python objects that manipulate the visibility of a
1911 frame or frames when a backtrace (@pxref{Backtrace}) is printed by
1914 Only commands that print a backtrace, or, in the case of @sc{gdb/mi}
1915 commands (@pxref{GDB/MI}), those that return a collection of frames
1916 are affected. The commands that work with frame filters are:
1918 @code{backtrace} (@pxref{backtrace-command,, The backtrace command}),
1919 @code{-stack-list-frames}
1920 (@pxref{-stack-list-frames,, The -stack-list-frames command}),
1921 @code{-stack-list-variables} (@pxref{-stack-list-variables,, The
1922 -stack-list-variables command}), @code{-stack-list-arguments}
1923 @pxref{-stack-list-arguments,, The -stack-list-arguments command}) and
1924 @code{-stack-list-locals} (@pxref{-stack-list-locals,, The
1925 -stack-list-locals command}).
1927 A frame filter works by taking an iterator as an argument, applying
1928 actions to the contents of that iterator, and returning another
1929 iterator (or, possibly, the same iterator it was provided in the case
1930 where the filter does not perform any operations). Typically, frame
1931 filters utilize tools such as the Python's @code{itertools} module to
1932 work with and create new iterators from the source iterator.
1933 Regardless of how a filter chooses to apply actions, it must not alter
1934 the underlying @value{GDBN} frame or frames, or attempt to alter the
1935 call-stack within @value{GDBN}. This preserves data integrity within
1936 @value{GDBN}. Frame filters are executed on a priority basis and care
1937 should be taken that some frame filters may have been executed before,
1938 and that some frame filters will be executed after.
1940 An important consideration when designing frame filters, and well
1941 worth reflecting upon, is that frame filters should avoid unwinding
1942 the call stack if possible. Some stacks can run very deep, into the
1943 tens of thousands in some cases. To search every frame when a frame
1944 filter executes may be too expensive at that step. The frame filter
1945 cannot know how many frames it has to iterate over, and it may have to
1946 iterate through them all. This ends up duplicating effort as
1947 @value{GDBN} performs this iteration when it prints the frames. If
1948 the filter can defer unwinding frames until frame decorators are
1949 executed, after the last filter has executed, it should. @xref{Frame
1950 Decorator API}, for more information on decorators. Also, there are
1951 examples for both frame decorators and filters in later chapters.
1952 @xref{Writing a Frame Filter}, for more information.
1954 The Python dictionary @code{gdb.frame_filters} contains key/object
1955 pairings that comprise a frame filter. Frame filters in this
1956 dictionary are called @code{global} frame filters, and they are
1957 available when debugging all inferiors. These frame filters must
1958 register with the dictionary directly. In addition to the
1959 @code{global} dictionary, there are other dictionaries that are loaded
1960 with different inferiors via auto-loading (@pxref{Python
1961 Auto-loading}). The two other areas where frame filter dictionaries
1962 can be found are: @code{gdb.Progspace} which contains a
1963 @code{frame_filters} dictionary attribute, and each @code{gdb.Objfile}
1964 object which also contains a @code{frame_filters} dictionary
1967 When a command is executed from @value{GDBN} that is compatible with
1968 frame filters, @value{GDBN} combines the @code{global},
1969 @code{gdb.Progspace} and all @code{gdb.Objfile} dictionaries currently
1970 loaded. All of the @code{gdb.Objfile} dictionaries are combined, as
1971 several frames, and thus several object files, might be in use.
1972 @value{GDBN} then prunes any frame filter whose @code{enabled}
1973 attribute is @code{False}. This pruned list is then sorted according
1974 to the @code{priority} attribute in each filter.
1976 Once the dictionaries are combined, pruned and sorted, @value{GDBN}
1977 creates an iterator which wraps each frame in the call stack in a
1978 @code{FrameDecorator} object, and calls each filter in order. The
1979 output from the previous filter will always be the input to the next
1982 Frame filters have a mandatory interface which each frame filter must
1983 implement, defined here:
1985 @defun FrameFilter.filter (iterator)
1986 @value{GDBN} will call this method on a frame filter when it has
1987 reached the order in the priority list for that filter.
1989 For example, if there are four frame filters:
2000 The order that the frame filters will be called is:
2003 Filter3 -> Filter2 -> Filter1 -> Filter4
2006 Note that the output from @code{Filter3} is passed to the input of
2007 @code{Filter2}, and so on.
2009 This @code{filter} method is passed a Python iterator. This iterator
2010 contains a sequence of frame decorators that wrap each
2011 @code{gdb.Frame}, or a frame decorator that wraps another frame
2012 decorator. The first filter that is executed in the sequence of frame
2013 filters will receive an iterator entirely comprised of default
2014 @code{FrameDecorator} objects. However, after each frame filter is
2015 executed, the previous frame filter may have wrapped some or all of
2016 the frame decorators with their own frame decorator. As frame
2017 decorators must also conform to a mandatory interface, these
2018 decorators can be assumed to act in a uniform manner (@pxref{Frame
2021 This method must return an object conforming to the Python iterator
2022 protocol. Each item in the iterator must be an object conforming to
2023 the frame decorator interface. If a frame filter does not wish to
2024 perform any operations on this iterator, it should return that
2027 This method is not optional. If it does not exist, @value{GDBN} will
2028 raise and print an error.
2031 @defvar FrameFilter.name
2032 The @code{name} attribute must be Python string which contains the
2033 name of the filter displayed by @value{GDBN} (@pxref{Frame Filter
2034 Management}). This attribute may contain any combination of letters
2035 or numbers. Care should be taken to ensure that it is unique. This
2036 attribute is mandatory.
2039 @defvar FrameFilter.enabled
2040 The @code{enabled} attribute must be Python boolean. This attribute
2041 indicates to @value{GDBN} whether the frame filter is enabled, and
2042 should be considered when frame filters are executed. If
2043 @code{enabled} is @code{True}, then the frame filter will be executed
2044 when any of the backtrace commands detailed earlier in this chapter
2045 are executed. If @code{enabled} is @code{False}, then the frame
2046 filter will not be executed. This attribute is mandatory.
2049 @defvar FrameFilter.priority
2050 The @code{priority} attribute must be Python integer. This attribute
2051 controls the order of execution in relation to other frame filters.
2052 There are no imposed limits on the range of @code{priority} other than
2053 it must be a valid integer. The higher the @code{priority} attribute,
2054 the sooner the frame filter will be executed in relation to other
2055 frame filters. Although @code{priority} can be negative, it is
2056 recommended practice to assume zero is the lowest priority that a
2057 frame filter can be assigned. Frame filters that have the same
2058 priority are executed in unsorted order in that priority slot. This
2059 attribute is mandatory. 100 is a good default priority.
2062 @node Frame Decorator API
2063 @subsubsection Decorating Frames
2064 @cindex frame decorator api
2066 Frame decorators are sister objects to frame filters (@pxref{Frame
2067 Filter API}). Frame decorators are applied by a frame filter and can
2068 only be used in conjunction with frame filters.
2070 The purpose of a frame decorator is to customize the printed content
2071 of each @code{gdb.Frame} in commands where frame filters are executed.
2072 This concept is called decorating a frame. Frame decorators decorate
2073 a @code{gdb.Frame} with Python code contained within each API call.
2074 This separates the actual data contained in a @code{gdb.Frame} from
2075 the decorated data produced by a frame decorator. This abstraction is
2076 necessary to maintain integrity of the data contained in each
2079 Frame decorators have a mandatory interface, defined below.
2081 @value{GDBN} already contains a frame decorator called
2082 @code{FrameDecorator}. This contains substantial amounts of
2083 boilerplate code to decorate the content of a @code{gdb.Frame}. It is
2084 recommended that other frame decorators inherit and extend this
2085 object, and only to override the methods needed.
2087 @tindex gdb.FrameDecorator
2088 @code{FrameDecorator} is defined in the Python module
2089 @code{gdb.FrameDecorator}, so your code can import it like:
2091 from gdb.FrameDecorator import FrameDecorator
2094 @defun FrameDecorator.elided (self)
2096 The @code{elided} method groups frames together in a hierarchical
2097 system. An example would be an interpreter, where multiple low-level
2098 frames make up a single call in the interpreted language. In this
2099 example, the frame filter would elide the low-level frames and present
2100 a single high-level frame, representing the call in the interpreted
2101 language, to the user.
2103 The @code{elided} function must return an iterable and this iterable
2104 must contain the frames that are being elided wrapped in a suitable
2105 frame decorator. If no frames are being elided this function may
2106 return an empty iterable, or @code{None}. Elided frames are indented
2107 from normal frames in a @code{CLI} backtrace, or in the case of
2108 @code{GDB/MI}, are placed in the @code{children} field of the eliding
2111 It is the frame filter's task to also filter out the elided frames from
2112 the source iterator. This will avoid printing the frame twice.
2115 @defun FrameDecorator.function (self)
2117 This method returns the name of the function in the frame that is to
2120 This method must return a Python string describing the function, or
2123 If this function returns @code{None}, @value{GDBN} will not print any
2124 data for this field.
2127 @defun FrameDecorator.address (self)
2129 This method returns the address of the frame that is to be printed.
2131 This method must return a Python numeric integer type of sufficient
2132 size to describe the address of the frame, or @code{None}.
2134 If this function returns a @code{None}, @value{GDBN} will not print
2135 any data for this field.
2138 @defun FrameDecorator.filename (self)
2140 This method returns the filename and path associated with this frame.
2142 This method must return a Python string containing the filename and
2143 the path to the object file backing the frame, or @code{None}.
2145 If this function returns a @code{None}, @value{GDBN} will not print
2146 any data for this field.
2149 @defun FrameDecorator.line (self):
2151 This method returns the line number associated with the current
2152 position within the function addressed by this frame.
2154 This method must return a Python integer type, or @code{None}.
2156 If this function returns a @code{None}, @value{GDBN} will not print
2157 any data for this field.
2160 @defun FrameDecorator.frame_args (self)
2163 This method must return an iterable, or @code{None}. Returning an
2164 empty iterable, or @code{None} means frame arguments will not be
2165 printed for this frame. This iterable must contain objects that
2166 implement two methods, described here.
2168 This object must implement a @code{symbol} method which takes a
2169 single @code{self} parameter and must return a @code{gdb.Symbol}
2170 (@pxref{Symbols In Python}), or a Python string. The object must also
2171 implement a @code{value} method which takes a single @code{self}
2172 parameter and must return a @code{gdb.Value} (@pxref{Values From
2173 Inferior}), a Python value, or @code{None}. If the @code{value}
2174 method returns @code{None}, and the @code{argument} method returns a
2175 @code{gdb.Symbol}, @value{GDBN} will look-up and print the value of
2176 the @code{gdb.Symbol} automatically.
2181 class SymValueWrapper():
2183 def __init__(self, symbol, value):
2193 class SomeFrameDecorator()
2196 def frame_args(self):
2199 block = self.inferior_frame.block()
2203 # Iterate over all symbols in a block. Only add
2204 # symbols that are arguments.
2206 if not sym.is_argument:
2208 args.append(SymValueWrapper(sym,None))
2210 # Add example synthetic argument.
2211 args.append(SymValueWrapper(``foo'', 42))
2217 @defun FrameDecorator.frame_locals (self)
2219 This method must return an iterable or @code{None}. Returning an
2220 empty iterable, or @code{None} means frame local arguments will not be
2221 printed for this frame.
2223 The object interface, the description of the various strategies for
2224 reading frame locals, and the example are largely similar to those
2225 described in the @code{frame_args} function, (@pxref{frame_args,,The
2226 frame filter frame_args function}). Below is a modified example:
2229 class SomeFrameDecorator()
2232 def frame_locals(self):
2235 block = self.inferior_frame.block()
2239 # Iterate over all symbols in a block. Add all
2240 # symbols, except arguments.
2244 vars.append(SymValueWrapper(sym,None))
2246 # Add an example of a synthetic local variable.
2247 vars.append(SymValueWrapper(``bar'', 99))
2253 @defun FrameDecorator.inferior_frame (self):
2255 This method must return the underlying @code{gdb.Frame} that this
2256 frame decorator is decorating. @value{GDBN} requires the underlying
2257 frame for internal frame information to determine how to print certain
2258 values when printing a frame.
2261 @node Writing a Frame Filter
2262 @subsubsection Writing a Frame Filter
2263 @cindex writing a frame filter
2265 There are three basic elements that a frame filter must implement: it
2266 must correctly implement the documented interface (@pxref{Frame Filter
2267 API}), it must register itself with @value{GDBN}, and finally, it must
2268 decide if it is to work on the data provided by @value{GDBN}. In all
2269 cases, whether it works on the iterator or not, each frame filter must
2270 return an iterator. A bare-bones frame filter follows the pattern in
2271 the following example.
2276 class FrameFilter():
2279 # Frame filter attribute creation.
2281 # 'name' is the name of the filter that GDB will display.
2283 # 'priority' is the priority of the filter relative to other
2286 # 'enabled' is a boolean that indicates whether this filter is
2287 # enabled and should be executed.
2293 # Register this frame filter with the global frame_filters
2295 gdb.frame_filters[self.name] = self
2297 def filter(self, frame_iter):
2298 # Just return the iterator.
2302 The frame filter in the example above implements the three
2303 requirements for all frame filters. It implements the API, self
2304 registers, and makes a decision on the iterator (in this case, it just
2305 returns the iterator untouched).
2307 The first step is attribute creation and assignment, and as shown in
2308 the comments the filter assigns the following attributes: @code{name},
2309 @code{priority} and whether the filter should be enabled with the
2310 @code{enabled} attribute.
2312 The second step is registering the frame filter with the dictionary or
2313 dictionaries that the frame filter has interest in. As shown in the
2314 comments, this filter just registers itself with the global dictionary
2315 @code{gdb.frame_filters}. As noted earlier, @code{gdb.frame_filters}
2316 is a dictionary that is initialized in the @code{gdb} module when
2317 @value{GDBN} starts. What dictionary a filter registers with is an
2318 important consideration. Generally, if a filter is specific to a set
2319 of code, it should be registered either in the @code{objfile} or
2320 @code{progspace} dictionaries as they are specific to the program
2321 currently loaded in @value{GDBN}. The global dictionary is always
2322 present in @value{GDBN} and is never unloaded. Any filters registered
2323 with the global dictionary will exist until @value{GDBN} exits. To
2324 avoid filters that may conflict, it is generally better to register
2325 frame filters against the dictionaries that more closely align with
2326 the usage of the filter currently in question. @xref{Python
2327 Auto-loading}, for further information on auto-loading Python scripts.
2329 @value{GDBN} takes a hands-off approach to frame filter registration,
2330 therefore it is the frame filter's responsibility to ensure
2331 registration has occurred, and that any exceptions are handled
2332 appropriately. In particular, you may wish to handle exceptions
2333 relating to Python dictionary key uniqueness. It is mandatory that
2334 the dictionary key is the same as frame filter's @code{name}
2335 attribute. When a user manages frame filters (@pxref{Frame Filter
2336 Management}), the names @value{GDBN} will display are those contained
2337 in the @code{name} attribute.
2339 The final step of this example is the implementation of the
2340 @code{filter} method. As shown in the example comments, we define the
2341 @code{filter} method and note that the method must take an iterator,
2342 and also must return an iterator. In this bare-bones example, the
2343 frame filter is not very useful as it just returns the iterator
2344 untouched. However this is a valid operation for frame filters that
2345 have the @code{enabled} attribute set, but decide not to operate on
2348 In the next example, the frame filter operates on all frames and
2349 utilizes a frame decorator to perform some work on the frames.
2350 @xref{Frame Decorator API}, for further information on the frame
2351 decorator interface.
2353 This example works on inlined frames. It highlights frames which are
2354 inlined by tagging them with an ``[inlined]'' tag. By applying a
2355 frame decorator to all frames with the Python @code{itertools imap}
2356 method, the example defers actions to the frame decorator. Frame
2357 decorators are only processed when @value{GDBN} prints the backtrace.
2359 This introduces a new decision making topic: whether to perform
2360 decision making operations at the filtering step, or at the printing
2361 step. In this example's approach, it does not perform any filtering
2362 decisions at the filtering step beyond mapping a frame decorator to
2363 each frame. This allows the actual decision making to be performed
2364 when each frame is printed. This is an important consideration, and
2365 well worth reflecting upon when designing a frame filter. An issue
2366 that frame filters should avoid is unwinding the stack if possible.
2367 Some stacks can run very deep, into the tens of thousands in some
2368 cases. To search every frame to determine if it is inlined ahead of
2369 time may be too expensive at the filtering step. The frame filter
2370 cannot know how many frames it has to iterate over, and it would have
2371 to iterate through them all. This ends up duplicating effort as
2372 @value{GDBN} performs this iteration when it prints the frames.
2374 In this example decision making can be deferred to the printing step.
2375 As each frame is printed, the frame decorator can examine each frame
2376 in turn when @value{GDBN} iterates. From a performance viewpoint,
2377 this is the most appropriate decision to make as it avoids duplicating
2378 the effort that the printing step would undertake anyway. Also, if
2379 there are many frame filters unwinding the stack during filtering, it
2380 can substantially delay the printing of the backtrace which will
2381 result in large memory usage, and a poor user experience.
2384 class InlineFilter():
2387 self.name = "InlinedFrameFilter"
2390 gdb.frame_filters[self.name] = self
2392 def filter(self, frame_iter):
2393 frame_iter = itertools.imap(InlinedFrameDecorator,
2398 This frame filter is somewhat similar to the earlier example, except
2399 that the @code{filter} method applies a frame decorator object called
2400 @code{InlinedFrameDecorator} to each element in the iterator. The
2401 @code{imap} Python method is light-weight. It does not proactively
2402 iterate over the iterator, but rather creates a new iterator which
2403 wraps the existing one.
2405 Below is the frame decorator for this example.
2408 class InlinedFrameDecorator(FrameDecorator):
2410 def __init__(self, fobj):
2411 super(InlinedFrameDecorator, self).__init__(fobj)
2414 frame = self.inferior_frame()
2415 name = str(frame.name())
2417 if frame.type() == gdb.INLINE_FRAME:
2418 name = name + " [inlined]"
2423 This frame decorator only defines and overrides the @code{function}
2424 method. It lets the supplied @code{FrameDecorator}, which is shipped
2425 with @value{GDBN}, perform the other work associated with printing
2428 The combination of these two objects create this output from a
2432 #0 0x004004e0 in bar () at inline.c:11
2433 #1 0x00400566 in max [inlined] (b=6, a=12) at inline.c:21
2434 #2 0x00400566 in main () at inline.c:31
2437 So in the case of this example, a frame decorator is applied to all
2438 frames, regardless of whether they may be inlined or not. As
2439 @value{GDBN} iterates over the iterator produced by the frame filters,
2440 @value{GDBN} executes each frame decorator which then makes a decision
2441 on what to print in the @code{function} callback. Using a strategy
2442 like this is a way to defer decisions on the frame content to printing
2445 @subheading Eliding Frames
2447 It might be that the above example is not desirable for representing
2448 inlined frames, and a hierarchical approach may be preferred. If we
2449 want to hierarchically represent frames, the @code{elided} frame
2450 decorator interface might be preferable.
2452 This example approaches the issue with the @code{elided} method. This
2453 example is quite long, but very simplistic. It is out-of-scope for
2454 this section to write a complete example that comprehensively covers
2455 all approaches of finding and printing inlined frames. However, this
2456 example illustrates the approach an author might use.
2458 This example comprises of three sections.
2461 class InlineFrameFilter():
2464 self.name = "InlinedFrameFilter"
2467 gdb.frame_filters[self.name] = self
2469 def filter(self, frame_iter):
2470 return ElidingInlineIterator(frame_iter)
2473 This frame filter is very similar to the other examples. The only
2474 difference is this frame filter is wrapping the iterator provided to
2475 it (@code{frame_iter}) with a custom iterator called
2476 @code{ElidingInlineIterator}. This again defers actions to when
2477 @value{GDBN} prints the backtrace, as the iterator is not traversed
2480 The iterator for this example is as follows. It is in this section of
2481 the example where decisions are made on the content of the backtrace.
2484 class ElidingInlineIterator:
2485 def __init__(self, ii):
2486 self.input_iterator = ii
2492 frame = next(self.input_iterator)
2494 if frame.inferior_frame().type() != gdb.INLINE_FRAME:
2498 eliding_frame = next(self.input_iterator)
2499 except StopIteration:
2501 return ElidingFrameDecorator(eliding_frame, [frame])
2504 This iterator implements the Python iterator protocol. When the
2505 @code{next} function is called (when @value{GDBN} prints each frame),
2506 the iterator checks if this frame decorator, @code{frame}, is wrapping
2507 an inlined frame. If it is not, it returns the existing frame decorator
2508 untouched. If it is wrapping an inlined frame, it assumes that the
2509 inlined frame was contained within the next oldest frame,
2510 @code{eliding_frame}, which it fetches. It then creates and returns a
2511 frame decorator, @code{ElidingFrameDecorator}, which contains both the
2512 elided frame, and the eliding frame.
2515 class ElidingInlineDecorator(FrameDecorator):
2517 def __init__(self, frame, elided_frames):
2518 super(ElidingInlineDecorator, self).__init__(frame)
2520 self.elided_frames = elided_frames
2523 return iter(self.elided_frames)
2526 This frame decorator overrides one function and returns the inlined
2527 frame in the @code{elided} method. As before it lets
2528 @code{FrameDecorator} do the rest of the work involved in printing
2529 this frame. This produces the following output.
2532 #0 0x004004e0 in bar () at inline.c:11
2533 #2 0x00400529 in main () at inline.c:25
2534 #1 0x00400529 in max (b=6, a=12) at inline.c:15
2537 In that output, @code{max} which has been inlined into @code{main} is
2538 printed hierarchically. Another approach would be to combine the
2539 @code{function} method, and the @code{elided} method to both print a
2540 marker in the inlined frame, and also show the hierarchical
2543 @node Unwinding Frames in Python
2544 @subsubsection Unwinding Frames in Python
2545 @cindex unwinding frames in Python
2547 In @value{GDBN} terminology ``unwinding'' is the process of finding
2548 the previous frame (that is, caller's) from the current one. An
2549 unwinder has three methods. The first one checks if it can handle
2550 given frame (``sniff'' it). For the frames it can sniff an unwinder
2551 provides two additional methods: it can return frame's ID, and it can
2552 fetch registers from the previous frame. A running @value{GDBN}
2553 mantains a list of the unwinders and calls each unwinder's sniffer in
2554 turn until it finds the one that recognizes the current frame. There
2555 is an API to register an unwinder.
2557 The unwinders that come with @value{GDBN} handle standard frames.
2558 However, mixed language applications (for example, an application
2559 running Java Virtual Machine) sometimes use frame layouts that cannot
2560 be handled by the @value{GDBN} unwinders. You can write Python code
2561 that can handle such custom frames.
2563 You implement a frame unwinder in Python as a class with which has two
2564 attributes, @code{name} and @code{enabled}, with obvious meanings, and
2565 a single method @code{__call__}, which examines a given frame and
2566 returns an object (an instance of @code{gdb.UnwindInfo class)}
2567 describing it. If an unwinder does not recognize a frame, it should
2568 return @code{None}. The code in @value{GDBN} that enables writing
2569 unwinders in Python uses this object to return frame's ID and previous
2570 frame registers when @value{GDBN} core asks for them.
2572 An unwinder should do as little work as possible. Some otherwise
2573 innocuous operations can cause problems (even crashes, as this code is
2574 not not well-hardened yet). For example, making an inferior call from
2575 an unwinder is unadvisable, as an inferior call will reset
2576 @value{GDBN}'s stack unwinding process, potentially causing re-entrant
2579 @subheading Unwinder Input
2581 An object passed to an unwinder (a @code{gdb.PendingFrame} instance)
2582 provides a method to read frame's registers:
2584 @defun PendingFrame.read_register (reg)
2585 This method returns the contents of the register @var{reg} in the
2586 frame as a @code{gdb.Value} object. For a description of the
2587 acceptable values of @var{reg} see
2588 @ref{gdbpy_frame_read_register,,Frame.read_register}. If @var{reg}
2589 does not name a register for the current architecture, this method
2590 will throw an exception.
2592 Note that this method will always return a @code{gdb.Value} for a
2593 valid register name. This does not mean that the value will be valid.
2594 For example, you may request a register that an earlier unwinder could
2595 not unwind---the value will be unavailable. Instead, the
2596 @code{gdb.Value} returned from this method will be lazy; that is, its
2597 underlying bits will not be fetched until it is first used. So,
2598 attempting to use such a value will cause an exception at the point of
2601 The type of the returned @code{gdb.Value} depends on the register and
2602 the architecture. It is common for registers to have a scalar type,
2603 like @code{long long}; but many other types are possible, such as
2604 pointer, pointer-to-function, floating point or vector types.
2607 It also provides a factory method to create a @code{gdb.UnwindInfo}
2608 instance to be returned to @value{GDBN}:
2610 @defun PendingFrame.create_unwind_info (frame_id)
2611 Returns a new @code{gdb.UnwindInfo} instance identified by given
2612 @var{frame_id}. The argument is used to build @value{GDBN}'s frame ID
2613 using one of functions provided by @value{GDBN}. @var{frame_id}'s attributes
2614 determine which function will be used, as follows:
2618 The frame is identified by the given stack address and PC. The stack
2619 address must be chosen so that it is constant throughout the lifetime
2620 of the frame, so a typical choice is the value of the stack pointer at
2621 the start of the function---in the DWARF standard, this would be the
2622 ``Call Frame Address''.
2624 This is the most common case by far. The other cases are documented
2625 for completeness but are only useful in specialized situations.
2627 @item sp, pc, special
2628 The frame is identified by the stack address, the PC, and a
2629 ``special'' address. The special address is used on architectures
2630 that can have frames that do not change the stack, but which are still
2631 distinct, for example the IA-64, which has a second stack for
2632 registers. Both @var{sp} and @var{special} must be constant
2633 throughout the lifetime of the frame.
2636 The frame is identified by the stack address only. Any other stack
2637 frame with a matching @var{sp} will be considered to match this frame.
2638 Inside gdb, this is called a ``wild frame''. You will never need
2642 Each attribute value should be an instance of @code{gdb.Value}.
2646 @defun PendingFrame.architecture ()
2647 Return the @code{gdb.Architecture} (@pxref{Architectures In Python})
2648 for this @code{gdb.PendingFrame}. This represents the architecture of
2649 the particular frame being unwound.
2652 @defun PendingFrame.level ()
2653 Return an integer, the stack frame level for this frame.
2654 @xref{Frames, ,Stack Frames}.
2657 @subheading Unwinder Output: UnwindInfo
2659 Use @code{PendingFrame.create_unwind_info} method described above to
2660 create a @code{gdb.UnwindInfo} instance. Use the following method to
2661 specify caller registers that have been saved in this frame:
2663 @defun gdb.UnwindInfo.add_saved_register (reg, value)
2664 @var{reg} identifies the register, for a description of the acceptable
2665 values see @ref{gdbpy_frame_read_register,,Frame.read_register}.
2666 @var{value} is a register value (a @code{gdb.Value} object).
2669 @subheading Unwinder Skeleton Code
2671 @value{GDBN} comes with the module containing the base @code{Unwinder}
2672 class. Derive your unwinder class from it and structure the code as
2676 from gdb.unwinders import Unwinder
2678 class FrameId(object):
2679 def __init__(self, sp, pc):
2684 class MyUnwinder(Unwinder):
2686 super(MyUnwinder, self).__init___(<expects unwinder name argument>)
2688 def __call__(pending_frame):
2689 if not <we recognize frame>:
2691 # Create UnwindInfo. Usually the frame is identified by the stack
2692 # pointer and the program counter.
2693 sp = pending_frame.read_register(<SP number>)
2694 pc = pending_frame.read_register(<PC number>)
2695 unwind_info = pending_frame.create_unwind_info(FrameId(sp, pc))
2697 # Find the values of the registers in the caller's frame and
2698 # save them in the result:
2699 unwind_info.add_saved_register(<register>, <value>)
2702 # Return the result:
2707 @subheading Registering a Unwinder
2709 An object file, a program space, and the @value{GDBN} proper can have
2710 unwinders registered with it.
2712 The @code{gdb.unwinders} module provides the function to register a
2715 @defun gdb.unwinder.register_unwinder (locus, unwinder, replace=False)
2716 @var{locus} is specifies an object file or a program space to which
2717 @var{unwinder} is added. Passing @code{None} or @code{gdb} adds
2718 @var{unwinder} to the @value{GDBN}'s global unwinder list. The newly
2719 added @var{unwinder} will be called before any other unwinder from the
2720 same locus. Two unwinders in the same locus cannot have the same
2721 name. An attempt to add a unwinder with already existing name raises
2722 an exception unless @var{replace} is @code{True}, in which case the
2723 old unwinder is deleted.
2726 @subheading Unwinder Precedence
2728 @value{GDBN} first calls the unwinders from all the object files in no
2729 particular order, then the unwinders from the current program space,
2730 and finally the unwinders from @value{GDBN}.
2732 @node Xmethods In Python
2733 @subsubsection Xmethods In Python
2734 @cindex xmethods in Python
2736 @dfn{Xmethods} are additional methods or replacements for existing
2737 methods of a C@t{++} class. This feature is useful for those cases
2738 where a method defined in C@t{++} source code could be inlined or
2739 optimized out by the compiler, making it unavailable to @value{GDBN}.
2740 For such cases, one can define an xmethod to serve as a replacement
2741 for the method defined in the C@t{++} source code. @value{GDBN} will
2742 then invoke the xmethod, instead of the C@t{++} method, to
2743 evaluate expressions. One can also use xmethods when debugging
2744 with core files. Moreover, when debugging live programs, invoking an
2745 xmethod need not involve running the inferior (which can potentially
2746 perturb its state). Hence, even if the C@t{++} method is available, it
2747 is better to use its replacement xmethod if one is defined.
2749 The xmethods feature in Python is available via the concepts of an
2750 @dfn{xmethod matcher} and an @dfn{xmethod worker}. To
2751 implement an xmethod, one has to implement a matcher and a
2752 corresponding worker for it (more than one worker can be
2753 implemented, each catering to a different overloaded instance of the
2754 method). Internally, @value{GDBN} invokes the @code{match} method of a
2755 matcher to match the class type and method name. On a match, the
2756 @code{match} method returns a list of matching @emph{worker} objects.
2757 Each worker object typically corresponds to an overloaded instance of
2758 the xmethod. They implement a @code{get_arg_types} method which
2759 returns a sequence of types corresponding to the arguments the xmethod
2760 requires. @value{GDBN} uses this sequence of types to perform
2761 overload resolution and picks a winning xmethod worker. A winner
2762 is also selected from among the methods @value{GDBN} finds in the
2763 C@t{++} source code. Next, the winning xmethod worker and the
2764 winning C@t{++} method are compared to select an overall winner. In
2765 case of a tie between a xmethod worker and a C@t{++} method, the
2766 xmethod worker is selected as the winner. That is, if a winning
2767 xmethod worker is found to be equivalent to the winning C@t{++}
2768 method, then the xmethod worker is treated as a replacement for
2769 the C@t{++} method. @value{GDBN} uses the overall winner to invoke the
2770 method. If the winning xmethod worker is the overall winner, then
2771 the corresponding xmethod is invoked via the @code{__call__} method
2772 of the worker object.
2774 If one wants to implement an xmethod as a replacement for an
2775 existing C@t{++} method, then they have to implement an equivalent
2776 xmethod which has exactly the same name and takes arguments of
2777 exactly the same type as the C@t{++} method. If the user wants to
2778 invoke the C@t{++} method even though a replacement xmethod is
2779 available for that method, then they can disable the xmethod.
2781 @xref{Xmethod API}, for API to implement xmethods in Python.
2782 @xref{Writing an Xmethod}, for implementing xmethods in Python.
2785 @subsubsection Xmethod API
2788 The @value{GDBN} Python API provides classes, interfaces and functions
2789 to implement, register and manipulate xmethods.
2790 @xref{Xmethods In Python}.
2792 An xmethod matcher should be an instance of a class derived from
2793 @code{XMethodMatcher} defined in the module @code{gdb.xmethod}, or an
2794 object with similar interface and attributes. An instance of
2795 @code{XMethodMatcher} has the following attributes:
2798 The name of the matcher.
2802 A boolean value indicating whether the matcher is enabled or disabled.
2806 A list of named methods managed by the matcher. Each object in the list
2807 is an instance of the class @code{XMethod} defined in the module
2808 @code{gdb.xmethod}, or any object with the following attributes:
2813 Name of the xmethod which should be unique for each xmethod
2814 managed by the matcher.
2817 A boolean value indicating whether the xmethod is enabled or
2822 The class @code{XMethod} is a convenience class with same
2823 attributes as above along with the following constructor:
2825 @defun XMethod.__init__ (self, name)
2826 Constructs an enabled xmethod with name @var{name}.
2831 The @code{XMethodMatcher} class has the following methods:
2833 @defun XMethodMatcher.__init__ (self, name)
2834 Constructs an enabled xmethod matcher with name @var{name}. The
2835 @code{methods} attribute is initialized to @code{None}.
2838 @defun XMethodMatcher.match (self, class_type, method_name)
2839 Derived classes should override this method. It should return a
2840 xmethod worker object (or a sequence of xmethod worker
2841 objects) matching the @var{class_type} and @var{method_name}.
2842 @var{class_type} is a @code{gdb.Type} object, and @var{method_name}
2843 is a string value. If the matcher manages named methods as listed in
2844 its @code{methods} attribute, then only those worker objects whose
2845 corresponding entries in the @code{methods} list are enabled should be
2849 An xmethod worker should be an instance of a class derived from
2850 @code{XMethodWorker} defined in the module @code{gdb.xmethod},
2851 or support the following interface:
2853 @defun XMethodWorker.get_arg_types (self)
2854 This method returns a sequence of @code{gdb.Type} objects corresponding
2855 to the arguments that the xmethod takes. It can return an empty
2856 sequence or @code{None} if the xmethod does not take any arguments.
2857 If the xmethod takes a single argument, then a single
2858 @code{gdb.Type} object corresponding to it can be returned.
2861 @defun XMethodWorker.get_result_type (self, *args)
2862 This method returns a @code{gdb.Type} object representing the type
2863 of the result of invoking this xmethod.
2864 The @var{args} argument is the same tuple of arguments that would be
2865 passed to the @code{__call__} method of this worker.
2868 @defun XMethodWorker.__call__ (self, *args)
2869 This is the method which does the @emph{work} of the xmethod. The
2870 @var{args} arguments is the tuple of arguments to the xmethod. Each
2871 element in this tuple is a gdb.Value object. The first element is
2872 always the @code{this} pointer value.
2875 For @value{GDBN} to lookup xmethods, the xmethod matchers
2876 should be registered using the following function defined in the module
2879 @defun register_xmethod_matcher (locus, matcher, replace=False)
2880 The @code{matcher} is registered with @code{locus}, replacing an
2881 existing matcher with the same name as @code{matcher} if
2882 @code{replace} is @code{True}. @code{locus} can be a
2883 @code{gdb.Objfile} object (@pxref{Objfiles In Python}), or a
2884 @code{gdb.Progspace} object (@pxref{Progspaces In Python}), or
2885 @code{None}. If it is @code{None}, then @code{matcher} is registered
2889 @node Writing an Xmethod
2890 @subsubsection Writing an Xmethod
2891 @cindex writing xmethods in Python
2893 Implementing xmethods in Python will require implementing xmethod
2894 matchers and xmethod workers (@pxref{Xmethods In Python}). Consider
2895 the following C@t{++} class:
2901 MyClass (int a) : a_(a) @{ @}
2903 int geta (void) @{ return a_; @}
2904 int operator+ (int b);
2911 MyClass::operator+ (int b)
2918 Let us define two xmethods for the class @code{MyClass}, one
2919 replacing the method @code{geta}, and another adding an overloaded
2920 flavor of @code{operator+} which takes a @code{MyClass} argument (the
2921 C@t{++} code above already has an overloaded @code{operator+}
2922 which takes an @code{int} argument). The xmethod matcher can be
2926 class MyClass_geta(gdb.xmethod.XMethod):
2928 gdb.xmethod.XMethod.__init__(self, 'geta')
2930 def get_worker(self, method_name):
2931 if method_name == 'geta':
2932 return MyClassWorker_geta()
2935 class MyClass_sum(gdb.xmethod.XMethod):
2937 gdb.xmethod.XMethod.__init__(self, 'sum')
2939 def get_worker(self, method_name):
2940 if method_name == 'operator+':
2941 return MyClassWorker_plus()
2944 class MyClassMatcher(gdb.xmethod.XMethodMatcher):
2946 gdb.xmethod.XMethodMatcher.__init__(self, 'MyClassMatcher')
2947 # List of methods 'managed' by this matcher
2948 self.methods = [MyClass_geta(), MyClass_sum()]
2950 def match(self, class_type, method_name):
2951 if class_type.tag != 'MyClass':
2954 for method in self.methods:
2956 worker = method.get_worker(method_name)
2958 workers.append(worker)
2964 Notice that the @code{match} method of @code{MyClassMatcher} returns
2965 a worker object of type @code{MyClassWorker_geta} for the @code{geta}
2966 method, and a worker object of type @code{MyClassWorker_plus} for the
2967 @code{operator+} method. This is done indirectly via helper classes
2968 derived from @code{gdb.xmethod.XMethod}. One does not need to use the
2969 @code{methods} attribute in a matcher as it is optional. However, if a
2970 matcher manages more than one xmethod, it is a good practice to list the
2971 xmethods in the @code{methods} attribute of the matcher. This will then
2972 facilitate enabling and disabling individual xmethods via the
2973 @code{enable/disable} commands. Notice also that a worker object is
2974 returned only if the corresponding entry in the @code{methods} attribute
2975 of the matcher is enabled.
2977 The implementation of the worker classes returned by the matcher setup
2978 above is as follows:
2981 class MyClassWorker_geta(gdb.xmethod.XMethodWorker):
2982 def get_arg_types(self):
2985 def get_result_type(self, obj):
2986 return gdb.lookup_type('int')
2988 def __call__(self, obj):
2992 class MyClassWorker_plus(gdb.xmethod.XMethodWorker):
2993 def get_arg_types(self):
2994 return gdb.lookup_type('MyClass')
2996 def get_result_type(self, obj):
2997 return gdb.lookup_type('int')
2999 def __call__(self, obj, other):
3000 return obj['a_'] + other['a_']
3003 For @value{GDBN} to actually lookup a xmethod, it has to be
3004 registered with it. The matcher defined above is registered with
3005 @value{GDBN} globally as follows:
3008 gdb.xmethod.register_xmethod_matcher(None, MyClassMatcher())
3011 If an object @code{obj} of type @code{MyClass} is initialized in C@t{++}
3019 then, after loading the Python script defining the xmethod matchers
3020 and workers into @code{GDBN}, invoking the method @code{geta} or using
3021 the operator @code{+} on @code{obj} will invoke the xmethods
3032 Consider another example with a C++ template class:
3039 MyTemplate () : dsize_(10), data_ (new T [10]) @{ @}
3040 ~MyTemplate () @{ delete [] data_; @}
3042 int footprint (void)
3044 return sizeof (T) * dsize_ + sizeof (MyTemplate<T>);
3053 Let us implement an xmethod for the above class which serves as a
3054 replacement for the @code{footprint} method. The full code listing
3055 of the xmethod workers and xmethod matchers is as follows:
3058 class MyTemplateWorker_footprint(gdb.xmethod.XMethodWorker):
3059 def __init__(self, class_type):
3060 self.class_type = class_type
3062 def get_arg_types(self):
3065 def get_result_type(self):
3066 return gdb.lookup_type('int')
3068 def __call__(self, obj):
3069 return (self.class_type.sizeof +
3071 self.class_type.template_argument(0).sizeof)
3074 class MyTemplateMatcher_footprint(gdb.xmethod.XMethodMatcher):
3076 gdb.xmethod.XMethodMatcher.__init__(self, 'MyTemplateMatcher')
3078 def match(self, class_type, method_name):
3079 if (re.match('MyTemplate<[ \t\n]*[_a-zA-Z][ _a-zA-Z0-9]*>',
3081 method_name == 'footprint'):
3082 return MyTemplateWorker_footprint(class_type)
3085 Notice that, in this example, we have not used the @code{methods}
3086 attribute of the matcher as the matcher manages only one xmethod. The
3087 user can enable/disable this xmethod by enabling/disabling the matcher
3090 @node Inferiors In Python
3091 @subsubsection Inferiors In Python
3092 @cindex inferiors in Python
3094 @findex gdb.Inferior
3095 Programs which are being run under @value{GDBN} are called inferiors
3096 (@pxref{Inferiors Connections and Programs}). Python scripts can access
3097 information about and manipulate inferiors controlled by @value{GDBN}
3098 via objects of the @code{gdb.Inferior} class.
3100 The following inferior-related functions are available in the @code{gdb}
3103 @defun gdb.inferiors ()
3104 Return a tuple containing all inferior objects.
3107 @defun gdb.selected_inferior ()
3108 Return an object representing the current inferior.
3111 A @code{gdb.Inferior} object has the following attributes:
3113 @defvar Inferior.num
3114 ID of inferior, as assigned by GDB.
3117 @anchor{gdbpy_inferior_connection}
3118 @defvar Inferior.connection
3119 The @code{gdb.TargetConnection} for this inferior (@pxref{Connections
3120 In Python}), or @code{None} if this inferior has no connection.
3123 @defvar Inferior.connection_num
3124 ID of inferior's connection as assigned by @value{GDBN}, or None if
3125 the inferior is not connected to a target. @xref{Inferiors Connections
3126 and Programs}. This is equivalent to
3127 @code{gdb.Inferior.connection.num} in the case where
3128 @code{gdb.Inferior.connection} is not @code{None}.
3131 @defvar Inferior.pid
3132 Process ID of the inferior, as assigned by the underlying operating
3136 @defvar Inferior.was_attached
3137 Boolean signaling whether the inferior was created using `attach', or
3138 started by @value{GDBN} itself.
3141 @defvar Inferior.progspace
3142 The inferior's program space. @xref{Progspaces In Python}.
3145 A @code{gdb.Inferior} object has the following methods:
3147 @defun Inferior.is_valid ()
3148 Returns @code{True} if the @code{gdb.Inferior} object is valid,
3149 @code{False} if not. A @code{gdb.Inferior} object will become invalid
3150 if the inferior no longer exists within @value{GDBN}. All other
3151 @code{gdb.Inferior} methods will throw an exception if it is invalid
3152 at the time the method is called.
3155 @defun Inferior.threads ()
3156 This method returns a tuple holding all the threads which are valid
3157 when it is called. If there are no valid threads, the method will
3158 return an empty tuple.
3161 @defun Inferior.architecture ()
3162 Return the @code{gdb.Architecture} (@pxref{Architectures In Python})
3163 for this inferior. This represents the architecture of the inferior
3164 as a whole. Some platforms can have multiple architectures in a
3165 single address space, so this may not match the architecture of a
3166 particular frame (@pxref{Frames In Python}).
3169 @findex Inferior.read_memory
3170 @defun Inferior.read_memory (address, length)
3171 Read @var{length} addressable memory units from the inferior, starting at
3172 @var{address}. Returns a buffer object, which behaves much like an array
3173 or a string. It can be modified and given to the
3174 @code{Inferior.write_memory} function. In Python 3, the return
3175 value is a @code{memoryview} object.
3178 @findex Inferior.write_memory
3179 @defun Inferior.write_memory (address, buffer @r{[}, length@r{]})
3180 Write the contents of @var{buffer} to the inferior, starting at
3181 @var{address}. The @var{buffer} parameter must be a Python object
3182 which supports the buffer protocol, i.e., a string, an array or the
3183 object returned from @code{Inferior.read_memory}. If given, @var{length}
3184 determines the number of addressable memory units from @var{buffer} to be
3188 @findex gdb.search_memory
3189 @defun Inferior.search_memory (address, length, pattern)
3190 Search a region of the inferior memory starting at @var{address} with
3191 the given @var{length} using the search pattern supplied in
3192 @var{pattern}. The @var{pattern} parameter must be a Python object
3193 which supports the buffer protocol, i.e., a string, an array or the
3194 object returned from @code{gdb.read_memory}. Returns a Python @code{Long}
3195 containing the address where the pattern was found, or @code{None} if
3196 the pattern could not be found.
3199 @findex Inferior.thread_from_handle
3200 @findex Inferior.thread_from_thread_handle
3201 @defun Inferior.thread_from_handle (handle)
3202 Return the thread object corresponding to @var{handle}, a thread
3203 library specific data structure such as @code{pthread_t} for pthreads
3204 library implementations.
3206 The function @code{Inferior.thread_from_thread_handle} provides
3207 the same functionality, but use of @code{Inferior.thread_from_thread_handle}
3211 @node Events In Python
3212 @subsubsection Events In Python
3213 @cindex inferior events in Python
3215 @value{GDBN} provides a general event facility so that Python code can be
3216 notified of various state changes, particularly changes that occur in
3219 An @dfn{event} is just an object that describes some state change. The
3220 type of the object and its attributes will vary depending on the details
3221 of the change. All the existing events are described below.
3223 In order to be notified of an event, you must register an event handler
3224 with an @dfn{event registry}. An event registry is an object in the
3225 @code{gdb.events} module which dispatches particular events. A registry
3226 provides methods to register and unregister event handlers:
3228 @defun EventRegistry.connect (object)
3229 Add the given callable @var{object} to the registry. This object will be
3230 called when an event corresponding to this registry occurs.
3233 @defun EventRegistry.disconnect (object)
3234 Remove the given @var{object} from the registry. Once removed, the object
3235 will no longer receive notifications of events.
3241 def exit_handler (event):
3242 print ("event type: exit")
3243 if hasattr (event, 'exit_code'):
3244 print ("exit code: %d" % (event.exit_code))
3246 print ("exit code not available")
3248 gdb.events.exited.connect (exit_handler)
3251 In the above example we connect our handler @code{exit_handler} to the
3252 registry @code{events.exited}. Once connected, @code{exit_handler} gets
3253 called when the inferior exits. The argument @dfn{event} in this example is
3254 of type @code{gdb.ExitedEvent}. As you can see in the example the
3255 @code{ExitedEvent} object has an attribute which indicates the exit code of
3258 The following is a listing of the event registries that are available and
3259 details of the events they emit:
3264 Emits @code{gdb.ThreadEvent}.
3266 Some events can be thread specific when @value{GDBN} is running in non-stop
3267 mode. When represented in Python, these events all extend
3268 @code{gdb.ThreadEvent}. Note, this event is not emitted directly; instead,
3269 events which are emitted by this or other modules might extend this event.
3270 Examples of these events are @code{gdb.BreakpointEvent} and
3271 @code{gdb.ContinueEvent}.
3273 @defvar ThreadEvent.inferior_thread
3274 In non-stop mode this attribute will be set to the specific thread which was
3275 involved in the emitted event. Otherwise, it will be set to @code{None}.
3278 Emits @code{gdb.ContinueEvent} which extends @code{gdb.ThreadEvent}.
3280 This event indicates that the inferior has been continued after a stop. For
3281 inherited attribute refer to @code{gdb.ThreadEvent} above.
3284 Emits @code{events.ExitedEvent} which indicates that the inferior has exited.
3285 @code{events.ExitedEvent} has two attributes:
3286 @defvar ExitedEvent.exit_code
3287 An integer representing the exit code, if available, which the inferior
3288 has returned. (The exit code could be unavailable if, for example,
3289 @value{GDBN} detaches from the inferior.) If the exit code is unavailable,
3290 the attribute does not exist.
3292 @defvar ExitedEvent.inferior
3293 A reference to the inferior which triggered the @code{exited} event.
3297 Emits @code{gdb.StopEvent} which extends @code{gdb.ThreadEvent}.
3299 Indicates that the inferior has stopped. All events emitted by this registry
3300 extend StopEvent. As a child of @code{gdb.ThreadEvent}, @code{gdb.StopEvent}
3301 will indicate the stopped thread when @value{GDBN} is running in non-stop
3302 mode. Refer to @code{gdb.ThreadEvent} above for more details.
3304 Emits @code{gdb.SignalEvent} which extends @code{gdb.StopEvent}.
3306 This event indicates that the inferior or one of its threads has received as
3307 signal. @code{gdb.SignalEvent} has the following attributes:
3309 @defvar SignalEvent.stop_signal
3310 A string representing the signal received by the inferior. A list of possible
3311 signal values can be obtained by running the command @code{info signals} in
3312 the @value{GDBN} command prompt.
3315 Also emits @code{gdb.BreakpointEvent} which extends @code{gdb.StopEvent}.
3317 @code{gdb.BreakpointEvent} event indicates that one or more breakpoints have
3318 been hit, and has the following attributes:
3320 @defvar BreakpointEvent.breakpoints
3321 A sequence containing references to all the breakpoints (type
3322 @code{gdb.Breakpoint}) that were hit.
3323 @xref{Breakpoints In Python}, for details of the @code{gdb.Breakpoint} object.
3325 @defvar BreakpointEvent.breakpoint
3326 A reference to the first breakpoint that was hit.
3327 This function is maintained for backward compatibility and is now deprecated
3328 in favor of the @code{gdb.BreakpointEvent.breakpoints} attribute.
3331 @item events.new_objfile
3332 Emits @code{gdb.NewObjFileEvent} which indicates that a new object file has
3333 been loaded by @value{GDBN}. @code{gdb.NewObjFileEvent} has one attribute:
3335 @defvar NewObjFileEvent.new_objfile
3336 A reference to the object file (@code{gdb.Objfile}) which has been loaded.
3337 @xref{Objfiles In Python}, for details of the @code{gdb.Objfile} object.
3340 @item events.clear_objfiles
3341 Emits @code{gdb.ClearObjFilesEvent} which indicates that the list of object
3342 files for a program space has been reset.
3343 @code{gdb.ClearObjFilesEvent} has one attribute:
3345 @defvar ClearObjFilesEvent.progspace
3346 A reference to the program space (@code{gdb.Progspace}) whose objfile list has
3347 been cleared. @xref{Progspaces In Python}.
3350 @item events.inferior_call
3351 Emits events just before and after a function in the inferior is
3352 called by @value{GDBN}. Before an inferior call, this emits an event
3353 of type @code{gdb.InferiorCallPreEvent}, and after an inferior call,
3354 this emits an event of type @code{gdb.InferiorCallPostEvent}.
3357 @tindex gdb.InferiorCallPreEvent
3358 @item @code{gdb.InferiorCallPreEvent}
3359 Indicates that a function in the inferior is about to be called.
3361 @defvar InferiorCallPreEvent.ptid
3362 The thread in which the call will be run.
3365 @defvar InferiorCallPreEvent.address
3366 The location of the function to be called.
3369 @tindex gdb.InferiorCallPostEvent
3370 @item @code{gdb.InferiorCallPostEvent}
3371 Indicates that a function in the inferior has just been called.
3373 @defvar InferiorCallPostEvent.ptid
3374 The thread in which the call was run.
3377 @defvar InferiorCallPostEvent.address
3378 The location of the function that was called.
3382 @item events.memory_changed
3383 Emits @code{gdb.MemoryChangedEvent} which indicates that the memory of the
3384 inferior has been modified by the @value{GDBN} user, for instance via a
3385 command like @w{@code{set *addr = value}}. The event has the following
3388 @defvar MemoryChangedEvent.address
3389 The start address of the changed region.
3392 @defvar MemoryChangedEvent.length
3393 Length in bytes of the changed region.
3396 @item events.register_changed
3397 Emits @code{gdb.RegisterChangedEvent} which indicates that a register in the
3398 inferior has been modified by the @value{GDBN} user.
3400 @defvar RegisterChangedEvent.frame
3401 A gdb.Frame object representing the frame in which the register was modified.
3403 @defvar RegisterChangedEvent.regnum
3404 Denotes which register was modified.
3407 @item events.breakpoint_created
3408 This is emitted when a new breakpoint has been created. The argument
3409 that is passed is the new @code{gdb.Breakpoint} object.
3411 @item events.breakpoint_modified
3412 This is emitted when a breakpoint has been modified in some way. The
3413 argument that is passed is the new @code{gdb.Breakpoint} object.
3415 @item events.breakpoint_deleted
3416 This is emitted when a breakpoint has been deleted. The argument that
3417 is passed is the @code{gdb.Breakpoint} object. When this event is
3418 emitted, the @code{gdb.Breakpoint} object will already be in its
3419 invalid state; that is, the @code{is_valid} method will return
3422 @item events.before_prompt
3423 This event carries no payload. It is emitted each time @value{GDBN}
3424 presents a prompt to the user.
3426 @item events.new_inferior
3427 This is emitted when a new inferior is created. Note that the
3428 inferior is not necessarily running; in fact, it may not even have an
3429 associated executable.
3431 The event is of type @code{gdb.NewInferiorEvent}. This has a single
3434 @defvar NewInferiorEvent.inferior
3435 The new inferior, a @code{gdb.Inferior} object.
3438 @item events.inferior_deleted
3439 This is emitted when an inferior has been deleted. Note that this is
3440 not the same as process exit; it is notified when the inferior itself
3441 is removed, say via @code{remove-inferiors}.
3443 The event is of type @code{gdb.InferiorDeletedEvent}. This has a single
3446 @defvar NewInferiorEvent.inferior
3447 The inferior that is being removed, a @code{gdb.Inferior} object.
3450 @item events.new_thread
3451 This is emitted when @value{GDBN} notices a new thread. The event is of
3452 type @code{gdb.NewThreadEvent}, which extends @code{gdb.ThreadEvent}.
3453 This has a single attribute:
3455 @defvar NewThreadEvent.inferior_thread
3459 @item events.gdb_exiting
3460 This is emitted when @value{GDBN} exits. This event is not emitted if
3461 @value{GDBN} exits as a result of an internal error, or after an
3462 unexpected signal. The event is of type @code{gdb.GdbExitingEvent},
3463 which has a single attribute:
3465 @defvar GdbExitingEvent.exit_code
3466 An integer, the value of the exit code @value{GDBN} will return.
3469 @item events.connection_removed
3470 This is emitted when @value{GDBN} removes a connection
3471 (@pxref{Connections In Python}). The event is of type
3472 @code{gdb.ConnectionEvent}. This has a single read-only attribute:
3474 @defvar ConnectionEvent.connection
3475 The @code{gdb.TargetConnection} that is being removed.
3480 @node Threads In Python
3481 @subsubsection Threads In Python
3482 @cindex threads in python
3484 @findex gdb.InferiorThread
3485 Python scripts can access information about, and manipulate inferior threads
3486 controlled by @value{GDBN}, via objects of the @code{gdb.InferiorThread} class.
3488 The following thread-related functions are available in the @code{gdb}
3491 @findex gdb.selected_thread
3492 @defun gdb.selected_thread ()
3493 This function returns the thread object for the selected thread. If there
3494 is no selected thread, this will return @code{None}.
3497 To get the list of threads for an inferior, use the @code{Inferior.threads()}
3498 method. @xref{Inferiors In Python}.
3500 A @code{gdb.InferiorThread} object has the following attributes:
3502 @defvar InferiorThread.name
3503 The name of the thread. If the user specified a name using
3504 @code{thread name}, then this returns that name. Otherwise, if an
3505 OS-supplied name is available, then it is returned. Otherwise, this
3506 returns @code{None}.
3508 This attribute can be assigned to. The new value must be a string
3509 object, which sets the new name, or @code{None}, which removes any
3510 user-specified thread name.
3513 @defvar InferiorThread.num
3514 The per-inferior number of the thread, as assigned by GDB.
3517 @defvar InferiorThread.global_num
3518 The global ID of the thread, as assigned by GDB. You can use this to
3519 make Python breakpoints thread-specific, for example
3520 (@pxref{python_breakpoint_thread,,The Breakpoint.thread attribute}).
3523 @defvar InferiorThread.ptid
3524 ID of the thread, as assigned by the operating system. This attribute is a
3525 tuple containing three integers. The first is the Process ID (PID); the second
3526 is the Lightweight Process ID (LWPID), and the third is the Thread ID (TID).
3527 Either the LWPID or TID may be 0, which indicates that the operating system
3528 does not use that identifier.
3531 @defvar InferiorThread.inferior
3532 The inferior this thread belongs to. This attribute is represented as
3533 a @code{gdb.Inferior} object. This attribute is not writable.
3536 A @code{gdb.InferiorThread} object has the following methods:
3538 @defun InferiorThread.is_valid ()
3539 Returns @code{True} if the @code{gdb.InferiorThread} object is valid,
3540 @code{False} if not. A @code{gdb.InferiorThread} object will become
3541 invalid if the thread exits, or the inferior that the thread belongs
3542 is deleted. All other @code{gdb.InferiorThread} methods will throw an
3543 exception if it is invalid at the time the method is called.
3546 @defun InferiorThread.switch ()
3547 This changes @value{GDBN}'s currently selected thread to the one represented
3551 @defun InferiorThread.is_stopped ()
3552 Return a Boolean indicating whether the thread is stopped.
3555 @defun InferiorThread.is_running ()
3556 Return a Boolean indicating whether the thread is running.
3559 @defun InferiorThread.is_exited ()
3560 Return a Boolean indicating whether the thread is exited.
3563 @defun InferiorThread.handle ()
3564 Return the thread object's handle, represented as a Python @code{bytes}
3565 object. A @code{gdb.Value} representation of the handle may be
3566 constructed via @code{gdb.Value(bufobj, type)} where @var{bufobj} is
3567 the Python @code{bytes} representation of the handle and @var{type} is
3568 a @code{gdb.Type} for the handle type.
3571 @node Recordings In Python
3572 @subsubsection Recordings In Python
3573 @cindex recordings in python
3575 The following recordings-related functions
3576 (@pxref{Process Record and Replay}) are available in the @code{gdb}
3579 @defun gdb.start_recording (@r{[}method@r{]}, @r{[}format@r{]})
3580 Start a recording using the given @var{method} and @var{format}. If
3581 no @var{format} is given, the default format for the recording method
3582 is used. If no @var{method} is given, the default method will be used.
3583 Returns a @code{gdb.Record} object on success. Throw an exception on
3586 The following strings can be passed as @var{method}:
3592 @code{"btrace"}: Possible values for @var{format}: @code{"pt"},
3593 @code{"bts"} or leave out for default format.
3597 @defun gdb.current_recording ()
3598 Access a currently running recording. Return a @code{gdb.Record}
3599 object on success. Return @code{None} if no recording is currently
3603 @defun gdb.stop_recording ()
3604 Stop the current recording. Throw an exception if no recording is
3605 currently active. All record objects become invalid after this call.
3608 A @code{gdb.Record} object has the following attributes:
3610 @defvar Record.method
3611 A string with the current recording method, e.g.@: @code{full} or
3615 @defvar Record.format
3616 A string with the current recording format, e.g.@: @code{bt}, @code{pts} or
3620 @defvar Record.begin
3621 A method specific instruction object representing the first instruction
3626 A method specific instruction object representing the current
3627 instruction, that is not actually part of the recording.
3630 @defvar Record.replay_position
3631 The instruction representing the current replay position. If there is
3632 no replay active, this will be @code{None}.
3635 @defvar Record.instruction_history
3636 A list with all recorded instructions.
3639 @defvar Record.function_call_history
3640 A list with all recorded function call segments.
3643 A @code{gdb.Record} object has the following methods:
3645 @defun Record.goto (instruction)
3646 Move the replay position to the given @var{instruction}.
3649 The common @code{gdb.Instruction} class that recording method specific
3650 instruction objects inherit from, has the following attributes:
3652 @defvar Instruction.pc
3653 An integer representing this instruction's address.
3656 @defvar Instruction.data
3657 A buffer with the raw instruction data. In Python 3, the return value is a
3658 @code{memoryview} object.
3661 @defvar Instruction.decoded
3662 A human readable string with the disassembled instruction.
3665 @defvar Instruction.size
3666 The size of the instruction in bytes.
3669 Additionally @code{gdb.RecordInstruction} has the following attributes:
3671 @defvar RecordInstruction.number
3672 An integer identifying this instruction. @code{number} corresponds to
3673 the numbers seen in @code{record instruction-history}
3674 (@pxref{Process Record and Replay}).
3677 @defvar RecordInstruction.sal
3678 A @code{gdb.Symtab_and_line} object representing the associated symtab
3679 and line of this instruction. May be @code{None} if no debug information is
3683 @defvar RecordInstruction.is_speculative
3684 A boolean indicating whether the instruction was executed speculatively.
3687 If an error occured during recording or decoding a recording, this error is
3688 represented by a @code{gdb.RecordGap} object in the instruction list. It has
3689 the following attributes:
3691 @defvar RecordGap.number
3692 An integer identifying this gap. @code{number} corresponds to the numbers seen
3693 in @code{record instruction-history} (@pxref{Process Record and Replay}).
3696 @defvar RecordGap.error_code
3697 A numerical representation of the reason for the gap. The value is specific to
3698 the current recording method.
3701 @defvar RecordGap.error_string
3702 A human readable string with the reason for the gap.
3705 A @code{gdb.RecordFunctionSegment} object has the following attributes:
3707 @defvar RecordFunctionSegment.number
3708 An integer identifying this function segment. @code{number} corresponds to
3709 the numbers seen in @code{record function-call-history}
3710 (@pxref{Process Record and Replay}).
3713 @defvar RecordFunctionSegment.symbol
3714 A @code{gdb.Symbol} object representing the associated symbol. May be
3715 @code{None} if no debug information is available.
3718 @defvar RecordFunctionSegment.level
3719 An integer representing the function call's stack level. May be
3720 @code{None} if the function call is a gap.
3723 @defvar RecordFunctionSegment.instructions
3724 A list of @code{gdb.RecordInstruction} or @code{gdb.RecordGap} objects
3725 associated with this function call.
3728 @defvar RecordFunctionSegment.up
3729 A @code{gdb.RecordFunctionSegment} object representing the caller's
3730 function segment. If the call has not been recorded, this will be the
3731 function segment to which control returns. If neither the call nor the
3732 return have been recorded, this will be @code{None}.
3735 @defvar RecordFunctionSegment.prev
3736 A @code{gdb.RecordFunctionSegment} object representing the previous
3737 segment of this function call. May be @code{None}.
3740 @defvar RecordFunctionSegment.next
3741 A @code{gdb.RecordFunctionSegment} object representing the next segment of
3742 this function call. May be @code{None}.
3745 The following example demonstrates the usage of these objects and
3746 functions to create a function that will rewind a record to the last
3747 time a function in a different file was executed. This would typically
3748 be used to track the execution of user provided callback functions in a
3749 library which typically are not visible in a back trace.
3753 rec = gdb.current_recording ()
3757 insn = rec.instruction_history
3762 position = insn.index (rec.replay_position)
3766 filename = insn[position].sal.symtab.fullname ()
3770 for i in reversed (insn[:position]):
3772 current = i.sal.symtab.fullname ()
3776 if filename == current:
3783 Another possible application is to write a function that counts the
3784 number of code executions in a given line range. This line range can
3785 contain parts of functions or span across several functions and is not
3786 limited to be contiguous.
3789 def countrange (filename, linerange):
3792 def filter_only (file_name):
3793 for call in gdb.current_recording ().function_call_history:
3795 if file_name in call.symbol.symtab.fullname ():
3800 for c in filter_only (filename):
3801 for i in c.instructions:
3803 if i.sal.line in linerange:
3812 @node Commands In Python
3813 @subsubsection Commands In Python
3815 @cindex commands in python
3816 @cindex python commands
3817 You can implement new @value{GDBN} CLI commands in Python. A CLI
3818 command is implemented using an instance of the @code{gdb.Command}
3819 class, most commonly using a subclass.
3821 @defun Command.__init__ (name, @var{command_class} @r{[}, @var{completer_class} @r{[}, @var{prefix}@r{]]})
3822 The object initializer for @code{Command} registers the new command
3823 with @value{GDBN}. This initializer is normally invoked from the
3824 subclass' own @code{__init__} method.
3826 @var{name} is the name of the command. If @var{name} consists of
3827 multiple words, then the initial words are looked for as prefix
3828 commands. In this case, if one of the prefix commands does not exist,
3829 an exception is raised.
3831 There is no support for multi-line commands.
3833 @var{command_class} should be one of the @samp{COMMAND_} constants
3834 defined below. This argument tells @value{GDBN} how to categorize the
3835 new command in the help system.
3837 @var{completer_class} is an optional argument. If given, it should be
3838 one of the @samp{COMPLETE_} constants defined below. This argument
3839 tells @value{GDBN} how to perform completion for this command. If not
3840 given, @value{GDBN} will attempt to complete using the object's
3841 @code{complete} method (see below); if no such method is found, an
3842 error will occur when completion is attempted.
3844 @var{prefix} is an optional argument. If @code{True}, then the new
3845 command is a prefix command; sub-commands of this command may be
3848 The help text for the new command is taken from the Python
3849 documentation string for the command's class, if there is one. If no
3850 documentation string is provided, the default value ``This command is
3851 not documented.'' is used.
3854 @cindex don't repeat Python command
3855 @defun Command.dont_repeat ()
3856 By default, a @value{GDBN} command is repeated when the user enters a
3857 blank line at the command prompt. A command can suppress this
3858 behavior by invoking the @code{dont_repeat} method. This is similar
3859 to the user command @code{dont-repeat}, see @ref{Define, dont-repeat}.
3862 @defun Command.invoke (argument, from_tty)
3863 This method is called by @value{GDBN} when this command is invoked.
3865 @var{argument} is a string. It is the argument to the command, after
3866 leading and trailing whitespace has been stripped.
3868 @var{from_tty} is a boolean argument. When true, this means that the
3869 command was entered by the user at the terminal; when false it means
3870 that the command came from elsewhere.
3872 If this method throws an exception, it is turned into a @value{GDBN}
3873 @code{error} call. Otherwise, the return value is ignored.
3875 @findex gdb.string_to_argv
3876 To break @var{argument} up into an argv-like string use
3877 @code{gdb.string_to_argv}. This function behaves identically to
3878 @value{GDBN}'s internal argument lexer @code{buildargv}.
3879 It is recommended to use this for consistency.
3880 Arguments are separated by spaces and may be quoted.
3884 print gdb.string_to_argv ("1 2\ \\\"3 '4 \"5' \"6 '7\"")
3885 ['1', '2 "3', '4 "5', "6 '7"]
3890 @cindex completion of Python commands
3891 @defun Command.complete (text, word)
3892 This method is called by @value{GDBN} when the user attempts
3893 completion on this command. All forms of completion are handled by
3894 this method, that is, the @key{TAB} and @key{M-?} key bindings
3895 (@pxref{Completion}), and the @code{complete} command (@pxref{Help,
3898 The arguments @var{text} and @var{word} are both strings; @var{text}
3899 holds the complete command line up to the cursor's location, while
3900 @var{word} holds the last word of the command line; this is computed
3901 using a word-breaking heuristic.
3903 The @code{complete} method can return several values:
3906 If the return value is a sequence, the contents of the sequence are
3907 used as the completions. It is up to @code{complete} to ensure that the
3908 contents actually do complete the word. A zero-length sequence is
3909 allowed, it means that there were no completions available. Only
3910 string elements of the sequence are used; other elements in the
3911 sequence are ignored.
3914 If the return value is one of the @samp{COMPLETE_} constants defined
3915 below, then the corresponding @value{GDBN}-internal completion
3916 function is invoked, and its result is used.
3919 All other results are treated as though there were no available
3924 When a new command is registered, it must be declared as a member of
3925 some general class of commands. This is used to classify top-level
3926 commands in the on-line help system; note that prefix commands are not
3927 listed under their own category but rather that of their top-level
3928 command. The available classifications are represented by constants
3929 defined in the @code{gdb} module:
3932 @findex COMMAND_NONE
3933 @findex gdb.COMMAND_NONE
3934 @item gdb.COMMAND_NONE
3935 The command does not belong to any particular class. A command in
3936 this category will not be displayed in any of the help categories.
3938 @findex COMMAND_RUNNING
3939 @findex gdb.COMMAND_RUNNING
3940 @item gdb.COMMAND_RUNNING
3941 The command is related to running the inferior. For example,
3942 @code{start}, @code{step}, and @code{continue} are in this category.
3943 Type @kbd{help running} at the @value{GDBN} prompt to see a list of
3944 commands in this category.
3946 @findex COMMAND_DATA
3947 @findex gdb.COMMAND_DATA
3948 @item gdb.COMMAND_DATA
3949 The command is related to data or variables. For example,
3950 @code{call}, @code{find}, and @code{print} are in this category. Type
3951 @kbd{help data} at the @value{GDBN} prompt to see a list of commands
3954 @findex COMMAND_STACK
3955 @findex gdb.COMMAND_STACK
3956 @item gdb.COMMAND_STACK
3957 The command has to do with manipulation of the stack. For example,
3958 @code{backtrace}, @code{frame}, and @code{return} are in this
3959 category. Type @kbd{help stack} at the @value{GDBN} prompt to see a
3960 list of commands in this category.
3962 @findex COMMAND_FILES
3963 @findex gdb.COMMAND_FILES
3964 @item gdb.COMMAND_FILES
3965 This class is used for file-related commands. For example,
3966 @code{file}, @code{list} and @code{section} are in this category.
3967 Type @kbd{help files} at the @value{GDBN} prompt to see a list of
3968 commands in this category.
3970 @findex COMMAND_SUPPORT
3971 @findex gdb.COMMAND_SUPPORT
3972 @item gdb.COMMAND_SUPPORT
3973 This should be used for ``support facilities'', generally meaning
3974 things that are useful to the user when interacting with @value{GDBN},
3975 but not related to the state of the inferior. For example,
3976 @code{help}, @code{make}, and @code{shell} are in this category. Type
3977 @kbd{help support} at the @value{GDBN} prompt to see a list of
3978 commands in this category.
3980 @findex COMMAND_STATUS
3981 @findex gdb.COMMAND_STATUS
3982 @item gdb.COMMAND_STATUS
3983 The command is an @samp{info}-related command, that is, related to the
3984 state of @value{GDBN} itself. For example, @code{info}, @code{macro},
3985 and @code{show} are in this category. Type @kbd{help status} at the
3986 @value{GDBN} prompt to see a list of commands in this category.
3988 @findex COMMAND_BREAKPOINTS
3989 @findex gdb.COMMAND_BREAKPOINTS
3990 @item gdb.COMMAND_BREAKPOINTS
3991 The command has to do with breakpoints. For example, @code{break},
3992 @code{clear}, and @code{delete} are in this category. Type @kbd{help
3993 breakpoints} at the @value{GDBN} prompt to see a list of commands in
3996 @findex COMMAND_TRACEPOINTS
3997 @findex gdb.COMMAND_TRACEPOINTS
3998 @item gdb.COMMAND_TRACEPOINTS
3999 The command has to do with tracepoints. For example, @code{trace},
4000 @code{actions}, and @code{tfind} are in this category. Type
4001 @kbd{help tracepoints} at the @value{GDBN} prompt to see a list of
4002 commands in this category.
4005 @findex gdb.COMMAND_TUI
4006 @item gdb.COMMAND_TUI
4007 The command has to do with the text user interface (@pxref{TUI}).
4008 Type @kbd{help tui} at the @value{GDBN} prompt to see a list of
4009 commands in this category.
4011 @findex COMMAND_USER
4012 @findex gdb.COMMAND_USER
4013 @item gdb.COMMAND_USER
4014 The command is a general purpose command for the user, and typically
4015 does not fit in one of the other categories.
4016 Type @kbd{help user-defined} at the @value{GDBN} prompt to see
4017 a list of commands in this category, as well as the list of gdb macros
4018 (@pxref{Sequences}).
4020 @findex COMMAND_OBSCURE
4021 @findex gdb.COMMAND_OBSCURE
4022 @item gdb.COMMAND_OBSCURE
4023 The command is only used in unusual circumstances, or is not of
4024 general interest to users. For example, @code{checkpoint},
4025 @code{fork}, and @code{stop} are in this category. Type @kbd{help
4026 obscure} at the @value{GDBN} prompt to see a list of commands in this
4029 @findex COMMAND_MAINTENANCE
4030 @findex gdb.COMMAND_MAINTENANCE
4031 @item gdb.COMMAND_MAINTENANCE
4032 The command is only useful to @value{GDBN} maintainers. The
4033 @code{maintenance} and @code{flushregs} commands are in this category.
4034 Type @kbd{help internals} at the @value{GDBN} prompt to see a list of
4035 commands in this category.
4038 A new command can use a predefined completion function, either by
4039 specifying it via an argument at initialization, or by returning it
4040 from the @code{complete} method. These predefined completion
4041 constants are all defined in the @code{gdb} module:
4044 @vindex COMPLETE_NONE
4045 @item gdb.COMPLETE_NONE
4046 This constant means that no completion should be done.
4048 @vindex COMPLETE_FILENAME
4049 @item gdb.COMPLETE_FILENAME
4050 This constant means that filename completion should be performed.
4052 @vindex COMPLETE_LOCATION
4053 @item gdb.COMPLETE_LOCATION
4054 This constant means that location completion should be done.
4055 @xref{Specify Location}.
4057 @vindex COMPLETE_COMMAND
4058 @item gdb.COMPLETE_COMMAND
4059 This constant means that completion should examine @value{GDBN}
4062 @vindex COMPLETE_SYMBOL
4063 @item gdb.COMPLETE_SYMBOL
4064 This constant means that completion should be done using symbol names
4067 @vindex COMPLETE_EXPRESSION
4068 @item gdb.COMPLETE_EXPRESSION
4069 This constant means that completion should be done on expressions.
4070 Often this means completing on symbol names, but some language
4071 parsers also have support for completing on field names.
4074 The following code snippet shows how a trivial CLI command can be
4075 implemented in Python:
4078 class HelloWorld (gdb.Command):
4079 """Greet the whole world."""
4081 def __init__ (self):
4082 super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)
4084 def invoke (self, arg, from_tty):
4085 print ("Hello, World!")
4090 The last line instantiates the class, and is necessary to trigger the
4091 registration of the command with @value{GDBN}. Depending on how the
4092 Python code is read into @value{GDBN}, you may need to import the
4093 @code{gdb} module explicitly.
4095 @node Parameters In Python
4096 @subsubsection Parameters In Python
4098 @cindex parameters in python
4099 @cindex python parameters
4100 @tindex gdb.Parameter
4102 You can implement new @value{GDBN} parameters using Python. A new
4103 parameter is implemented as an instance of the @code{gdb.Parameter}
4106 Parameters are exposed to the user via the @code{set} and
4107 @code{show} commands. @xref{Help}.
4109 There are many parameters that already exist and can be set in
4110 @value{GDBN}. Two examples are: @code{set follow fork} and
4111 @code{set charset}. Setting these parameters influences certain
4112 behavior in @value{GDBN}. Similarly, you can define parameters that
4113 can be used to influence behavior in custom Python scripts and commands.
4115 @defun Parameter.__init__ (name, @var{command-class}, @var{parameter-class} @r{[}, @var{enum-sequence}@r{]})
4116 The object initializer for @code{Parameter} registers the new
4117 parameter with @value{GDBN}. This initializer is normally invoked
4118 from the subclass' own @code{__init__} method.
4120 @var{name} is the name of the new parameter. If @var{name} consists
4121 of multiple words, then the initial words are looked for as prefix
4122 parameters. An example of this can be illustrated with the
4123 @code{set print} set of parameters. If @var{name} is
4124 @code{print foo}, then @code{print} will be searched as the prefix
4125 parameter. In this case the parameter can subsequently be accessed in
4126 @value{GDBN} as @code{set print foo}.
4128 If @var{name} consists of multiple words, and no prefix parameter group
4129 can be found, an exception is raised.
4131 @var{command-class} should be one of the @samp{COMMAND_} constants
4132 (@pxref{Commands In Python}). This argument tells @value{GDBN} how to
4133 categorize the new parameter in the help system.
4135 @var{parameter-class} should be one of the @samp{PARAM_} constants
4136 defined below. This argument tells @value{GDBN} the type of the new
4137 parameter; this information is used for input validation and
4140 If @var{parameter-class} is @code{PARAM_ENUM}, then
4141 @var{enum-sequence} must be a sequence of strings. These strings
4142 represent the possible values for the parameter.
4144 If @var{parameter-class} is not @code{PARAM_ENUM}, then the presence
4145 of a fourth argument will cause an exception to be thrown.
4147 The help text for the new parameter is taken from the Python
4148 documentation string for the parameter's class, if there is one. If
4149 there is no documentation string, a default value is used.
4152 @defvar Parameter.set_doc
4153 If this attribute exists, and is a string, then its value is used as
4154 the help text for this parameter's @code{set} command. The value is
4155 examined when @code{Parameter.__init__} is invoked; subsequent changes
4159 @defvar Parameter.show_doc
4160 If this attribute exists, and is a string, then its value is used as
4161 the help text for this parameter's @code{show} command. The value is
4162 examined when @code{Parameter.__init__} is invoked; subsequent changes
4166 @defvar Parameter.value
4167 The @code{value} attribute holds the underlying value of the
4168 parameter. It can be read and assigned to just as any other
4169 attribute. @value{GDBN} does validation when assignments are made.
4172 There are two methods that may be implemented in any @code{Parameter}
4175 @defun Parameter.get_set_string (self)
4176 If this method exists, @value{GDBN} will call it when a
4177 @var{parameter}'s value has been changed via the @code{set} API (for
4178 example, @kbd{set foo off}). The @code{value} attribute has already
4179 been populated with the new value and may be used in output. This
4180 method must return a string. If the returned string is not empty,
4181 @value{GDBN} will present it to the user.
4183 If this method raises the @code{gdb.GdbError} exception
4184 (@pxref{Exception Handling}), then @value{GDBN} will print the
4185 exception's string and the @code{set} command will fail. Note,
4186 however, that the @code{value} attribute will not be reset in this
4187 case. So, if your parameter must validate values, it should store the
4188 old value internally and reset the exposed value, like so:
4191 class ExampleParam (gdb.Parameter):
4192 def __init__ (self, name):
4193 super (ExampleParam, self).__init__ (name,
4197 self.saved_value = True
4200 def get_set_string (self):
4201 if not self.validate():
4202 self.value = self.saved_value
4203 raise gdb.GdbError('Failed to validate')
4204 self.saved_value = self.value
4209 @defun Parameter.get_show_string (self, svalue)
4210 @value{GDBN} will call this method when a @var{parameter}'s
4211 @code{show} API has been invoked (for example, @kbd{show foo}). The
4212 argument @code{svalue} receives the string representation of the
4213 current value. This method must return a string.
4216 When a new parameter is defined, its type must be specified. The
4217 available types are represented by constants defined in the @code{gdb}
4221 @findex PARAM_BOOLEAN
4222 @findex gdb.PARAM_BOOLEAN
4223 @item gdb.PARAM_BOOLEAN
4224 The value is a plain boolean. The Python boolean values, @code{True}
4225 and @code{False} are the only valid values.
4227 @findex PARAM_AUTO_BOOLEAN
4228 @findex gdb.PARAM_AUTO_BOOLEAN
4229 @item gdb.PARAM_AUTO_BOOLEAN
4230 The value has three possible states: true, false, and @samp{auto}. In
4231 Python, true and false are represented using boolean constants, and
4232 @samp{auto} is represented using @code{None}.
4234 @findex PARAM_UINTEGER
4235 @findex gdb.PARAM_UINTEGER
4236 @item gdb.PARAM_UINTEGER
4237 The value is an unsigned integer. The value of 0 should be
4238 interpreted to mean ``unlimited''.
4240 @findex PARAM_INTEGER
4241 @findex gdb.PARAM_INTEGER
4242 @item gdb.PARAM_INTEGER
4243 The value is a signed integer. The value of 0 should be interpreted
4244 to mean ``unlimited''.
4246 @findex PARAM_STRING
4247 @findex gdb.PARAM_STRING
4248 @item gdb.PARAM_STRING
4249 The value is a string. When the user modifies the string, any escape
4250 sequences, such as @samp{\t}, @samp{\f}, and octal escapes, are
4251 translated into corresponding characters and encoded into the current
4254 @findex PARAM_STRING_NOESCAPE
4255 @findex gdb.PARAM_STRING_NOESCAPE
4256 @item gdb.PARAM_STRING_NOESCAPE
4257 The value is a string. When the user modifies the string, escapes are
4258 passed through untranslated.
4260 @findex PARAM_OPTIONAL_FILENAME
4261 @findex gdb.PARAM_OPTIONAL_FILENAME
4262 @item gdb.PARAM_OPTIONAL_FILENAME
4263 The value is a either a filename (a string), or @code{None}.
4265 @findex PARAM_FILENAME
4266 @findex gdb.PARAM_FILENAME
4267 @item gdb.PARAM_FILENAME
4268 The value is a filename. This is just like
4269 @code{PARAM_STRING_NOESCAPE}, but uses file names for completion.
4271 @findex PARAM_ZINTEGER
4272 @findex gdb.PARAM_ZINTEGER
4273 @item gdb.PARAM_ZINTEGER
4274 The value is an integer. This is like @code{PARAM_INTEGER}, except 0
4275 is interpreted as itself.
4277 @findex PARAM_ZUINTEGER
4278 @findex gdb.PARAM_ZUINTEGER
4279 @item gdb.PARAM_ZUINTEGER
4280 The value is an unsigned integer. This is like @code{PARAM_INTEGER},
4281 except 0 is interpreted as itself, and the value cannot be negative.
4283 @findex PARAM_ZUINTEGER_UNLIMITED
4284 @findex gdb.PARAM_ZUINTEGER_UNLIMITED
4285 @item gdb.PARAM_ZUINTEGER_UNLIMITED
4286 The value is a signed integer. This is like @code{PARAM_ZUINTEGER},
4287 except the special value -1 should be interpreted to mean
4288 ``unlimited''. Other negative values are not allowed.
4291 @findex gdb.PARAM_ENUM
4292 @item gdb.PARAM_ENUM
4293 The value is a string, which must be one of a collection string
4294 constants provided when the parameter is created.
4297 @node Functions In Python
4298 @subsubsection Writing new convenience functions
4300 @cindex writing convenience functions
4301 @cindex convenience functions in python
4302 @cindex python convenience functions
4303 @tindex gdb.Function
4305 You can implement new convenience functions (@pxref{Convenience Vars})
4306 in Python. A convenience function is an instance of a subclass of the
4307 class @code{gdb.Function}.
4309 @defun Function.__init__ (name)
4310 The initializer for @code{Function} registers the new function with
4311 @value{GDBN}. The argument @var{name} is the name of the function,
4312 a string. The function will be visible to the user as a convenience
4313 variable of type @code{internal function}, whose name is the same as
4314 the given @var{name}.
4316 The documentation for the new function is taken from the documentation
4317 string for the new class.
4320 @defun Function.invoke (@var{*args})
4321 When a convenience function is evaluated, its arguments are converted
4322 to instances of @code{gdb.Value}, and then the function's
4323 @code{invoke} method is called. Note that @value{GDBN} does not
4324 predetermine the arity of convenience functions. Instead, all
4325 available arguments are passed to @code{invoke}, following the
4326 standard Python calling convention. In particular, a convenience
4327 function can have default values for parameters without ill effect.
4329 The return value of this method is used as its value in the enclosing
4330 expression. If an ordinary Python value is returned, it is converted
4331 to a @code{gdb.Value} following the usual rules.
4334 The following code snippet shows how a trivial convenience function can
4335 be implemented in Python:
4338 class Greet (gdb.Function):
4339 """Return string to greet someone.
4340 Takes a name as argument."""
4342 def __init__ (self):
4343 super (Greet, self).__init__ ("greet")
4345 def invoke (self, name):
4346 return "Hello, %s!" % name.string ()
4351 The last line instantiates the class, and is necessary to trigger the
4352 registration of the function with @value{GDBN}. Depending on how the
4353 Python code is read into @value{GDBN}, you may need to import the
4354 @code{gdb} module explicitly.
4356 Now you can use the function in an expression:
4359 (gdb) print $greet("Bob")
4363 @node Progspaces In Python
4364 @subsubsection Program Spaces In Python
4366 @cindex progspaces in python
4367 @tindex gdb.Progspace
4369 A program space, or @dfn{progspace}, represents a symbolic view
4370 of an address space.
4371 It consists of all of the objfiles of the program.
4372 @xref{Objfiles In Python}.
4373 @xref{Inferiors Connections and Programs, program spaces}, for more details
4374 about program spaces.
4376 The following progspace-related functions are available in the
4379 @findex gdb.current_progspace
4380 @defun gdb.current_progspace ()
4381 This function returns the program space of the currently selected inferior.
4382 @xref{Inferiors Connections and Programs}. This is identical to
4383 @code{gdb.selected_inferior().progspace} (@pxref{Inferiors In Python}) and is
4384 included for historical compatibility.
4387 @findex gdb.progspaces
4388 @defun gdb.progspaces ()
4389 Return a sequence of all the progspaces currently known to @value{GDBN}.
4392 Each progspace is represented by an instance of the @code{gdb.Progspace}
4395 @defvar Progspace.filename
4396 The file name of the progspace as a string.
4399 @defvar Progspace.pretty_printers
4400 The @code{pretty_printers} attribute is a list of functions. It is
4401 used to look up pretty-printers. A @code{Value} is passed to each
4402 function in order; if the function returns @code{None}, then the
4403 search continues. Otherwise, the return value should be an object
4404 which is used to format the value. @xref{Pretty Printing API}, for more
4408 @defvar Progspace.type_printers
4409 The @code{type_printers} attribute is a list of type printer objects.
4410 @xref{Type Printing API}, for more information.
4413 @defvar Progspace.frame_filters
4414 The @code{frame_filters} attribute is a dictionary of frame filter
4415 objects. @xref{Frame Filter API}, for more information.
4418 A program space has the following methods:
4420 @findex Progspace.block_for_pc
4421 @defun Progspace.block_for_pc (pc)
4422 Return the innermost @code{gdb.Block} containing the given @var{pc}
4423 value. If the block cannot be found for the @var{pc} value specified,
4424 the function will return @code{None}.
4427 @findex Progspace.find_pc_line
4428 @defun Progspace.find_pc_line (pc)
4429 Return the @code{gdb.Symtab_and_line} object corresponding to the
4430 @var{pc} value. @xref{Symbol Tables In Python}. If an invalid value
4431 of @var{pc} is passed as an argument, then the @code{symtab} and
4432 @code{line} attributes of the returned @code{gdb.Symtab_and_line}
4433 object will be @code{None} and 0 respectively.
4436 @findex Progspace.is_valid
4437 @defun Progspace.is_valid ()
4438 Returns @code{True} if the @code{gdb.Progspace} object is valid,
4439 @code{False} if not. A @code{gdb.Progspace} object can become invalid
4440 if the program space file it refers to is not referenced by any
4441 inferior. All other @code{gdb.Progspace} methods will throw an
4442 exception if it is invalid at the time the method is called.
4445 @findex Progspace.objfiles
4446 @defun Progspace.objfiles ()
4447 Return a sequence of all the objfiles referenced by this program
4448 space. @xref{Objfiles In Python}.
4451 @findex Progspace.solib_name
4452 @defun Progspace.solib_name (address)
4453 Return the name of the shared library holding the given @var{address}
4454 as a string, or @code{None}.
4457 One may add arbitrary attributes to @code{gdb.Progspace} objects
4458 in the usual Python way.
4459 This is useful if, for example, one needs to do some extra record keeping
4460 associated with the program space.
4462 In this contrived example, we want to perform some processing when
4463 an objfile with a certain symbol is loaded, but we only want to do
4464 this once because it is expensive. To achieve this we record the results
4465 with the program space because we can't predict when the desired objfile
4470 def clear_objfiles_handler(event):
4471 event.progspace.expensive_computation = None
4472 def expensive(symbol):
4473 """A mock routine to perform an "expensive" computation on symbol."""
4474 print ("Computing the answer to the ultimate question ...")
4476 def new_objfile_handler(event):
4477 objfile = event.new_objfile
4478 progspace = objfile.progspace
4479 if not hasattr(progspace, 'expensive_computation') or \
4480 progspace.expensive_computation is None:
4481 # We use 'main' for the symbol to keep the example simple.
4482 # Note: There's no current way to constrain the lookup
4484 symbol = gdb.lookup_global_symbol('main')
4485 if symbol is not None:
4486 progspace.expensive_computation = expensive(symbol)
4487 gdb.events.clear_objfiles.connect(clear_objfiles_handler)
4488 gdb.events.new_objfile.connect(new_objfile_handler)
4490 (gdb) file /tmp/hello
4491 Reading symbols from /tmp/hello...
4492 Computing the answer to the ultimate question ...
4493 (gdb) python print gdb.current_progspace().expensive_computation
4496 Starting program: /tmp/hello
4498 [Inferior 1 (process 4242) exited normally]
4501 @node Objfiles In Python
4502 @subsubsection Objfiles In Python
4504 @cindex objfiles in python
4507 @value{GDBN} loads symbols for an inferior from various
4508 symbol-containing files (@pxref{Files}). These include the primary
4509 executable file, any shared libraries used by the inferior, and any
4510 separate debug info files (@pxref{Separate Debug Files}).
4511 @value{GDBN} calls these symbol-containing files @dfn{objfiles}.
4513 The following objfile-related functions are available in the
4516 @findex gdb.current_objfile
4517 @defun gdb.current_objfile ()
4518 When auto-loading a Python script (@pxref{Python Auto-loading}), @value{GDBN}
4519 sets the ``current objfile'' to the corresponding objfile. This
4520 function returns the current objfile. If there is no current objfile,
4521 this function returns @code{None}.
4524 @findex gdb.objfiles
4525 @defun gdb.objfiles ()
4526 Return a sequence of objfiles referenced by the current program space.
4527 @xref{Objfiles In Python}, and @ref{Progspaces In Python}. This is identical
4528 to @code{gdb.selected_inferior().progspace.objfiles()} and is included for
4529 historical compatibility.
4532 @findex gdb.lookup_objfile
4533 @defun gdb.lookup_objfile (name @r{[}, by_build_id{]})
4534 Look up @var{name}, a file name or build ID, in the list of objfiles
4535 for the current program space (@pxref{Progspaces In Python}).
4536 If the objfile is not found throw the Python @code{ValueError} exception.
4538 If @var{name} is a relative file name, then it will match any
4539 source file name with the same trailing components. For example, if
4540 @var{name} is @samp{gcc/expr.c}, then it will match source file
4541 name of @file{/build/trunk/gcc/expr.c}, but not
4542 @file{/build/trunk/libcpp/expr.c} or @file{/build/trunk/gcc/x-expr.c}.
4544 If @var{by_build_id} is provided and is @code{True} then @var{name}
4545 is the build ID of the objfile. Otherwise, @var{name} is a file name.
4546 This is supported only on some operating systems, notably those which use
4547 the ELF format for binary files and the @sc{gnu} Binutils. For more details
4548 about this feature, see the description of the @option{--build-id}
4549 command-line option in @ref{Options, , Command Line Options, ld,
4553 Each objfile is represented by an instance of the @code{gdb.Objfile}
4556 @defvar Objfile.filename
4557 The file name of the objfile as a string, with symbolic links resolved.
4559 The value is @code{None} if the objfile is no longer valid.
4560 See the @code{gdb.Objfile.is_valid} method, described below.
4563 @defvar Objfile.username
4564 The file name of the objfile as specified by the user as a string.
4566 The value is @code{None} if the objfile is no longer valid.
4567 See the @code{gdb.Objfile.is_valid} method, described below.
4570 @defvar Objfile.owner
4571 For separate debug info objfiles this is the corresponding @code{gdb.Objfile}
4572 object that debug info is being provided for.
4573 Otherwise this is @code{None}.
4574 Separate debug info objfiles are added with the
4575 @code{gdb.Objfile.add_separate_debug_file} method, described below.
4578 @defvar Objfile.build_id
4579 The build ID of the objfile as a string.
4580 If the objfile does not have a build ID then the value is @code{None}.
4582 This is supported only on some operating systems, notably those which use
4583 the ELF format for binary files and the @sc{gnu} Binutils. For more details
4584 about this feature, see the description of the @option{--build-id}
4585 command-line option in @ref{Options, , Command Line Options, ld,
4589 @defvar Objfile.progspace
4590 The containing program space of the objfile as a @code{gdb.Progspace}
4591 object. @xref{Progspaces In Python}.
4594 @defvar Objfile.pretty_printers
4595 The @code{pretty_printers} attribute is a list of functions. It is
4596 used to look up pretty-printers. A @code{Value} is passed to each
4597 function in order; if the function returns @code{None}, then the
4598 search continues. Otherwise, the return value should be an object
4599 which is used to format the value. @xref{Pretty Printing API}, for more
4603 @defvar Objfile.type_printers
4604 The @code{type_printers} attribute is a list of type printer objects.
4605 @xref{Type Printing API}, for more information.
4608 @defvar Objfile.frame_filters
4609 The @code{frame_filters} attribute is a dictionary of frame filter
4610 objects. @xref{Frame Filter API}, for more information.
4613 One may add arbitrary attributes to @code{gdb.Objfile} objects
4614 in the usual Python way.
4615 This is useful if, for example, one needs to do some extra record keeping
4616 associated with the objfile.
4618 In this contrived example we record the time when @value{GDBN}
4624 def new_objfile_handler(event):
4625 # Set the time_loaded attribute of the new objfile.
4626 event.new_objfile.time_loaded = datetime.datetime.today()
4627 gdb.events.new_objfile.connect(new_objfile_handler)
4630 Reading symbols from ./hello...
4631 (gdb) python print gdb.objfiles()[0].time_loaded
4632 2014-10-09 11:41:36.770345
4635 A @code{gdb.Objfile} object has the following methods:
4637 @defun Objfile.is_valid ()
4638 Returns @code{True} if the @code{gdb.Objfile} object is valid,
4639 @code{False} if not. A @code{gdb.Objfile} object can become invalid
4640 if the object file it refers to is not loaded in @value{GDBN} any
4641 longer. All other @code{gdb.Objfile} methods will throw an exception
4642 if it is invalid at the time the method is called.
4645 @defun Objfile.add_separate_debug_file (file)
4646 Add @var{file} to the list of files that @value{GDBN} will search for
4647 debug information for the objfile.
4648 This is useful when the debug info has been removed from the program
4649 and stored in a separate file. @value{GDBN} has built-in support for
4650 finding separate debug info files (@pxref{Separate Debug Files}), but if
4651 the file doesn't live in one of the standard places that @value{GDBN}
4652 searches then this function can be used to add a debug info file
4653 from a different place.
4656 @defun Objfile.lookup_global_symbol (name @r{[}, domain@r{]})
4657 Search for a global symbol named @var{name} in this objfile. Optionally, the
4658 search scope can be restricted with the @var{domain} argument.
4659 The @var{domain} argument must be a domain constant defined in the @code{gdb}
4660 module and described in @ref{Symbols In Python}. This function is similar to
4661 @code{gdb.lookup_global_symbol}, except that the search is limited to this
4664 The result is a @code{gdb.Symbol} object or @code{None} if the symbol
4668 @defun Objfile.lookup_static_symbol (name @r{[}, domain@r{]})
4669 Like @code{Objfile.lookup_global_symbol}, but searches for a global
4670 symbol with static linkage named @var{name} in this objfile.
4673 @node Frames In Python
4674 @subsubsection Accessing inferior stack frames from Python
4676 @cindex frames in python
4677 When the debugged program stops, @value{GDBN} is able to analyze its call
4678 stack (@pxref{Frames,,Stack frames}). The @code{gdb.Frame} class
4679 represents a frame in the stack. A @code{gdb.Frame} object is only valid
4680 while its corresponding frame exists in the inferior's stack. If you try
4681 to use an invalid frame object, @value{GDBN} will throw a @code{gdb.error}
4682 exception (@pxref{Exception Handling}).
4684 Two @code{gdb.Frame} objects can be compared for equality with the @code{==}
4688 (@value{GDBP}) python print gdb.newest_frame() == gdb.selected_frame ()
4692 The following frame-related functions are available in the @code{gdb} module:
4694 @findex gdb.selected_frame
4695 @defun gdb.selected_frame ()
4696 Return the selected frame object. (@pxref{Selection,,Selecting a Frame}).
4699 @findex gdb.newest_frame
4700 @defun gdb.newest_frame ()
4701 Return the newest frame object for the selected thread.
4704 @defun gdb.frame_stop_reason_string (reason)
4705 Return a string explaining the reason why @value{GDBN} stopped unwinding
4706 frames, as expressed by the given @var{reason} code (an integer, see the
4707 @code{unwind_stop_reason} method further down in this section).
4710 @findex gdb.invalidate_cached_frames
4711 @defun gdb.invalidate_cached_frames
4712 @value{GDBN} internally keeps a cache of the frames that have been
4713 unwound. This function invalidates this cache.
4715 This function should not generally be called by ordinary Python code.
4716 It is documented for the sake of completeness.
4719 A @code{gdb.Frame} object has the following methods:
4721 @defun Frame.is_valid ()
4722 Returns true if the @code{gdb.Frame} object is valid, false if not.
4723 A frame object can become invalid if the frame it refers to doesn't
4724 exist anymore in the inferior. All @code{gdb.Frame} methods will throw
4725 an exception if it is invalid at the time the method is called.
4728 @defun Frame.name ()
4729 Returns the function name of the frame, or @code{None} if it can't be
4733 @defun Frame.architecture ()
4734 Returns the @code{gdb.Architecture} object corresponding to the frame's
4735 architecture. @xref{Architectures In Python}.
4738 @defun Frame.type ()
4739 Returns the type of the frame. The value can be one of:
4741 @item gdb.NORMAL_FRAME
4742 An ordinary stack frame.
4744 @item gdb.DUMMY_FRAME
4745 A fake stack frame that was created by @value{GDBN} when performing an
4746 inferior function call.
4748 @item gdb.INLINE_FRAME
4749 A frame representing an inlined function. The function was inlined
4750 into a @code{gdb.NORMAL_FRAME} that is older than this one.
4752 @item gdb.TAILCALL_FRAME
4753 A frame representing a tail call. @xref{Tail Call Frames}.
4755 @item gdb.SIGTRAMP_FRAME
4756 A signal trampoline frame. This is the frame created by the OS when
4757 it calls into a signal handler.
4759 @item gdb.ARCH_FRAME
4760 A fake stack frame representing a cross-architecture call.
4762 @item gdb.SENTINEL_FRAME
4763 This is like @code{gdb.NORMAL_FRAME}, but it is only used for the
4768 @defun Frame.unwind_stop_reason ()
4769 Return an integer representing the reason why it's not possible to find
4770 more frames toward the outermost frame. Use
4771 @code{gdb.frame_stop_reason_string} to convert the value returned by this
4772 function to a string. The value can be one of:
4775 @item gdb.FRAME_UNWIND_NO_REASON
4776 No particular reason (older frames should be available).
4778 @item gdb.FRAME_UNWIND_NULL_ID
4779 The previous frame's analyzer returns an invalid result. This is no
4780 longer used by @value{GDBN}, and is kept only for backward
4783 @item gdb.FRAME_UNWIND_OUTERMOST
4784 This frame is the outermost.
4786 @item gdb.FRAME_UNWIND_UNAVAILABLE
4787 Cannot unwind further, because that would require knowing the
4788 values of registers or memory that have not been collected.
4790 @item gdb.FRAME_UNWIND_INNER_ID
4791 This frame ID looks like it ought to belong to a NEXT frame,
4792 but we got it for a PREV frame. Normally, this is a sign of
4793 unwinder failure. It could also indicate stack corruption.
4795 @item gdb.FRAME_UNWIND_SAME_ID
4796 This frame has the same ID as the previous one. That means
4797 that unwinding further would almost certainly give us another
4798 frame with exactly the same ID, so break the chain. Normally,
4799 this is a sign of unwinder failure. It could also indicate
4802 @item gdb.FRAME_UNWIND_NO_SAVED_PC
4803 The frame unwinder did not find any saved PC, but we needed
4804 one to unwind further.
4806 @item gdb.FRAME_UNWIND_MEMORY_ERROR
4807 The frame unwinder caused an error while trying to access memory.
4809 @item gdb.FRAME_UNWIND_FIRST_ERROR
4810 Any stop reason greater or equal to this value indicates some kind
4811 of error. This special value facilitates writing code that tests
4812 for errors in unwinding in a way that will work correctly even if
4813 the list of the other values is modified in future @value{GDBN}
4814 versions. Using it, you could write:
4816 reason = gdb.selected_frame().unwind_stop_reason ()
4817 reason_str = gdb.frame_stop_reason_string (reason)
4818 if reason >= gdb.FRAME_UNWIND_FIRST_ERROR:
4819 print ("An error occured: %s" % reason_str)
4826 Returns the frame's resume address.
4829 @defun Frame.block ()
4830 Return the frame's code block. @xref{Blocks In Python}. If the frame
4831 does not have a block -- for example, if there is no debugging
4832 information for the code in question -- then this will throw an
4836 @defun Frame.function ()
4837 Return the symbol for the function corresponding to this frame.
4838 @xref{Symbols In Python}.
4841 @defun Frame.older ()
4842 Return the frame that called this frame.
4845 @defun Frame.newer ()
4846 Return the frame called by this frame.
4849 @defun Frame.find_sal ()
4850 Return the frame's symtab and line object.
4851 @xref{Symbol Tables In Python}.
4854 @anchor{gdbpy_frame_read_register}
4855 @defun Frame.read_register (register)
4856 Return the value of @var{register} in this frame. Returns a
4857 @code{Gdb.Value} object. Throws an exception if @var{register} does
4858 not exist. The @var{register} argument must be one of the following:
4861 A string that is the name of a valid register (e.g., @code{'sp'} or
4864 A @code{gdb.RegisterDescriptor} object (@pxref{Registers In Python}).
4866 A @value{GDBN} internal, platform specific number. Using these
4867 numbers is supported for historic reasons, but is not recommended as
4868 future changes to @value{GDBN} could change the mapping between
4869 numbers and the registers they represent, breaking any Python code
4870 that uses the platform-specific numbers. The numbers are usually
4871 found in the corresponding @file{@var{platform}-tdep.h} file in the
4872 @value{GDBN} source tree.
4874 Using a string to access registers will be slightly slower than the
4875 other two methods as @value{GDBN} must look up the mapping between
4876 name and internal register number. If performance is critical
4877 consider looking up and caching a @code{gdb.RegisterDescriptor}
4881 @defun Frame.read_var (variable @r{[}, block@r{]})
4882 Return the value of @var{variable} in this frame. If the optional
4883 argument @var{block} is provided, search for the variable from that
4884 block; otherwise start at the frame's current block (which is
4885 determined by the frame's current program counter). The @var{variable}
4886 argument must be a string or a @code{gdb.Symbol} object; @var{block} must be a
4887 @code{gdb.Block} object.
4890 @defun Frame.select ()
4891 Set this frame to be the selected frame. @xref{Stack, ,Examining the
4895 @defun Frame.level ()
4896 Return an integer, the stack frame level for this frame. @xref{Frames, ,Stack Frames}.
4899 @node Blocks In Python
4900 @subsubsection Accessing blocks from Python
4902 @cindex blocks in python
4905 In @value{GDBN}, symbols are stored in blocks. A block corresponds
4906 roughly to a scope in the source code. Blocks are organized
4907 hierarchically, and are represented individually in Python as a
4908 @code{gdb.Block}. Blocks rely on debugging information being
4911 A frame has a block. Please see @ref{Frames In Python}, for a more
4912 in-depth discussion of frames.
4914 The outermost block is known as the @dfn{global block}. The global
4915 block typically holds public global variables and functions.
4917 The block nested just inside the global block is the @dfn{static
4918 block}. The static block typically holds file-scoped variables and
4921 @value{GDBN} provides a method to get a block's superblock, but there
4922 is currently no way to examine the sub-blocks of a block, or to
4923 iterate over all the blocks in a symbol table (@pxref{Symbol Tables In
4926 Here is a short example that should help explain blocks:
4929 /* This is in the global block. */
4932 /* This is in the static block. */
4933 static int file_scope;
4935 /* 'function' is in the global block, and 'argument' is
4936 in a block nested inside of 'function'. */
4937 int function (int argument)
4939 /* 'local' is in a block inside 'function'. It may or may
4940 not be in the same block as 'argument'. */
4944 /* 'inner' is in a block whose superblock is the one holding
4948 /* If this call is expanded by the compiler, you may see
4949 a nested block here whose function is 'inline_function'
4950 and whose superblock is the one holding 'inner'. */
4956 A @code{gdb.Block} is iterable. The iterator returns the symbols
4957 (@pxref{Symbols In Python}) local to the block. Python programs
4958 should not assume that a specific block object will always contain a
4959 given symbol, since changes in @value{GDBN} features and
4960 infrastructure may cause symbols move across blocks in a symbol
4961 table. You can also use Python's @dfn{dictionary syntax} to access
4962 variables in this block, e.g.:
4965 symbol = some_block['variable'] # symbol is of type gdb.Symbol
4968 The following block-related functions are available in the @code{gdb}
4971 @findex gdb.block_for_pc
4972 @defun gdb.block_for_pc (pc)
4973 Return the innermost @code{gdb.Block} containing the given @var{pc}
4974 value. If the block cannot be found for the @var{pc} value specified,
4975 the function will return @code{None}. This is identical to
4976 @code{gdb.current_progspace().block_for_pc(pc)} and is included for
4977 historical compatibility.
4980 A @code{gdb.Block} object has the following methods:
4982 @defun Block.is_valid ()
4983 Returns @code{True} if the @code{gdb.Block} object is valid,
4984 @code{False} if not. A block object can become invalid if the block it
4985 refers to doesn't exist anymore in the inferior. All other
4986 @code{gdb.Block} methods will throw an exception if it is invalid at
4987 the time the method is called. The block's validity is also checked
4988 during iteration over symbols of the block.
4991 A @code{gdb.Block} object has the following attributes:
4994 The start address of the block. This attribute is not writable.
4998 One past the last address that appears in the block. This attribute
5002 @defvar Block.function
5003 The name of the block represented as a @code{gdb.Symbol}. If the
5004 block is not named, then this attribute holds @code{None}. This
5005 attribute is not writable.
5007 For ordinary function blocks, the superblock is the static block.
5008 However, you should note that it is possible for a function block to
5009 have a superblock that is not the static block -- for instance this
5010 happens for an inlined function.
5013 @defvar Block.superblock
5014 The block containing this block. If this parent block does not exist,
5015 this attribute holds @code{None}. This attribute is not writable.
5018 @defvar Block.global_block
5019 The global block associated with this block. This attribute is not
5023 @defvar Block.static_block
5024 The static block associated with this block. This attribute is not
5028 @defvar Block.is_global
5029 @code{True} if the @code{gdb.Block} object is a global block,
5030 @code{False} if not. This attribute is not
5034 @defvar Block.is_static
5035 @code{True} if the @code{gdb.Block} object is a static block,
5036 @code{False} if not. This attribute is not writable.
5039 @node Symbols In Python
5040 @subsubsection Python representation of Symbols
5042 @cindex symbols in python
5045 @value{GDBN} represents every variable, function and type as an
5046 entry in a symbol table. @xref{Symbols, ,Examining the Symbol Table}.
5047 Similarly, Python represents these symbols in @value{GDBN} with the
5048 @code{gdb.Symbol} object.
5050 The following symbol-related functions are available in the @code{gdb}
5053 @findex gdb.lookup_symbol
5054 @defun gdb.lookup_symbol (name @r{[}, block @r{[}, domain@r{]]})
5055 This function searches for a symbol by name. The search scope can be
5056 restricted to the parameters defined in the optional domain and block
5059 @var{name} is the name of the symbol. It must be a string. The
5060 optional @var{block} argument restricts the search to symbols visible
5061 in that @var{block}. The @var{block} argument must be a
5062 @code{gdb.Block} object. If omitted, the block for the current frame
5063 is used. The optional @var{domain} argument restricts
5064 the search to the domain type. The @var{domain} argument must be a
5065 domain constant defined in the @code{gdb} module and described later
5068 The result is a tuple of two elements.
5069 The first element is a @code{gdb.Symbol} object or @code{None} if the symbol
5071 If the symbol is found, the second element is @code{True} if the symbol
5072 is a field of a method's object (e.g., @code{this} in C@t{++}),
5073 otherwise it is @code{False}.
5074 If the symbol is not found, the second element is @code{False}.
5077 @findex gdb.lookup_global_symbol
5078 @defun gdb.lookup_global_symbol (name @r{[}, domain@r{]})
5079 This function searches for a global symbol by name.
5080 The search scope can be restricted to by the domain argument.
5082 @var{name} is the name of the symbol. It must be a string.
5083 The optional @var{domain} argument restricts the search to the domain type.
5084 The @var{domain} argument must be a domain constant defined in the @code{gdb}
5085 module and described later in this chapter.
5087 The result is a @code{gdb.Symbol} object or @code{None} if the symbol
5091 @findex gdb.lookup_static_symbol
5092 @defun gdb.lookup_static_symbol (name @r{[}, domain@r{]})
5093 This function searches for a global symbol with static linkage by name.
5094 The search scope can be restricted to by the domain argument.
5096 @var{name} is the name of the symbol. It must be a string.
5097 The optional @var{domain} argument restricts the search to the domain type.
5098 The @var{domain} argument must be a domain constant defined in the @code{gdb}
5099 module and described later in this chapter.
5101 The result is a @code{gdb.Symbol} object or @code{None} if the symbol
5104 Note that this function will not find function-scoped static variables. To look
5105 up such variables, iterate over the variables of the function's
5106 @code{gdb.Block} and check that @code{block.addr_class} is
5107 @code{gdb.SYMBOL_LOC_STATIC}.
5109 There can be multiple global symbols with static linkage with the same
5110 name. This function will only return the first matching symbol that
5111 it finds. Which symbol is found depends on where @value{GDBN} is
5112 currently stopped, as @value{GDBN} will first search for matching
5113 symbols in the current object file, and then search all other object
5114 files. If the application is not yet running then @value{GDBN} will
5115 search all object files in the order they appear in the debug
5119 @findex gdb.lookup_static_symbols
5120 @defun gdb.lookup_static_symbols (name @r{[}, domain@r{]})
5121 Similar to @code{gdb.lookup_static_symbol}, this function searches for
5122 global symbols with static linkage by name, and optionally restricted
5123 by the domain argument. However, this function returns a list of all
5124 matching symbols found, not just the first one.
5126 @var{name} is the name of the symbol. It must be a string.
5127 The optional @var{domain} argument restricts the search to the domain type.
5128 The @var{domain} argument must be a domain constant defined in the @code{gdb}
5129 module and described later in this chapter.
5131 The result is a list of @code{gdb.Symbol} objects which could be empty
5132 if no matching symbols were found.
5134 Note that this function will not find function-scoped static variables. To look
5135 up such variables, iterate over the variables of the function's
5136 @code{gdb.Block} and check that @code{block.addr_class} is
5137 @code{gdb.SYMBOL_LOC_STATIC}.
5140 A @code{gdb.Symbol} object has the following attributes:
5143 The type of the symbol or @code{None} if no type is recorded.
5144 This attribute is represented as a @code{gdb.Type} object.
5145 @xref{Types In Python}. This attribute is not writable.
5148 @defvar Symbol.symtab
5149 The symbol table in which the symbol appears. This attribute is
5150 represented as a @code{gdb.Symtab} object. @xref{Symbol Tables In
5151 Python}. This attribute is not writable.
5155 The line number in the source code at which the symbol was defined.
5160 The name of the symbol as a string. This attribute is not writable.
5163 @defvar Symbol.linkage_name
5164 The name of the symbol, as used by the linker (i.e., may be mangled).
5165 This attribute is not writable.
5168 @defvar Symbol.print_name
5169 The name of the symbol in a form suitable for output. This is either
5170 @code{name} or @code{linkage_name}, depending on whether the user
5171 asked @value{GDBN} to display demangled or mangled names.
5174 @defvar Symbol.addr_class
5175 The address class of the symbol. This classifies how to find the value
5176 of a symbol. Each address class is a constant defined in the
5177 @code{gdb} module and described later in this chapter.
5180 @defvar Symbol.needs_frame
5181 This is @code{True} if evaluating this symbol's value requires a frame
5182 (@pxref{Frames In Python}) and @code{False} otherwise. Typically,
5183 local variables will require a frame, but other symbols will not.
5186 @defvar Symbol.is_argument
5187 @code{True} if the symbol is an argument of a function.
5190 @defvar Symbol.is_constant
5191 @code{True} if the symbol is a constant.
5194 @defvar Symbol.is_function
5195 @code{True} if the symbol is a function or a method.
5198 @defvar Symbol.is_variable
5199 @code{True} if the symbol is a variable.
5202 A @code{gdb.Symbol} object has the following methods:
5204 @defun Symbol.is_valid ()
5205 Returns @code{True} if the @code{gdb.Symbol} object is valid,
5206 @code{False} if not. A @code{gdb.Symbol} object can become invalid if
5207 the symbol it refers to does not exist in @value{GDBN} any longer.
5208 All other @code{gdb.Symbol} methods will throw an exception if it is
5209 invalid at the time the method is called.
5212 @defun Symbol.value (@r{[}frame@r{]})
5213 Compute the value of the symbol, as a @code{gdb.Value}. For
5214 functions, this computes the address of the function, cast to the
5215 appropriate type. If the symbol requires a frame in order to compute
5216 its value, then @var{frame} must be given. If @var{frame} is not
5217 given, or if @var{frame} is invalid, then this method will throw an
5221 The available domain categories in @code{gdb.Symbol} are represented
5222 as constants in the @code{gdb} module:
5225 @vindex SYMBOL_UNDEF_DOMAIN
5226 @item gdb.SYMBOL_UNDEF_DOMAIN
5227 This is used when a domain has not been discovered or none of the
5228 following domains apply. This usually indicates an error either
5229 in the symbol information or in @value{GDBN}'s handling of symbols.
5231 @vindex SYMBOL_VAR_DOMAIN
5232 @item gdb.SYMBOL_VAR_DOMAIN
5233 This domain contains variables, function names, typedef names and enum
5236 @vindex SYMBOL_STRUCT_DOMAIN
5237 @item gdb.SYMBOL_STRUCT_DOMAIN
5238 This domain holds struct, union and enum type names.
5240 @vindex SYMBOL_LABEL_DOMAIN
5241 @item gdb.SYMBOL_LABEL_DOMAIN
5242 This domain contains names of labels (for gotos).
5244 @vindex SYMBOL_MODULE_DOMAIN
5245 @item gdb.SYMBOL_MODULE_DOMAIN
5246 This domain contains names of Fortran module types.
5248 @vindex SYMBOL_COMMON_BLOCK_DOMAIN
5249 @item gdb.SYMBOL_COMMON_BLOCK_DOMAIN
5250 This domain contains names of Fortran common blocks.
5253 The available address class categories in @code{gdb.Symbol} are represented
5254 as constants in the @code{gdb} module:
5257 @vindex SYMBOL_LOC_UNDEF
5258 @item gdb.SYMBOL_LOC_UNDEF
5259 If this is returned by address class, it indicates an error either in
5260 the symbol information or in @value{GDBN}'s handling of symbols.
5262 @vindex SYMBOL_LOC_CONST
5263 @item gdb.SYMBOL_LOC_CONST
5264 Value is constant int.
5266 @vindex SYMBOL_LOC_STATIC
5267 @item gdb.SYMBOL_LOC_STATIC
5268 Value is at a fixed address.
5270 @vindex SYMBOL_LOC_REGISTER
5271 @item gdb.SYMBOL_LOC_REGISTER
5272 Value is in a register.
5274 @vindex SYMBOL_LOC_ARG
5275 @item gdb.SYMBOL_LOC_ARG
5276 Value is an argument. This value is at the offset stored within the
5277 symbol inside the frame's argument list.
5279 @vindex SYMBOL_LOC_REF_ARG
5280 @item gdb.SYMBOL_LOC_REF_ARG
5281 Value address is stored in the frame's argument list. Just like
5282 @code{LOC_ARG} except that the value's address is stored at the
5283 offset, not the value itself.
5285 @vindex SYMBOL_LOC_REGPARM_ADDR
5286 @item gdb.SYMBOL_LOC_REGPARM_ADDR
5287 Value is a specified register. Just like @code{LOC_REGISTER} except
5288 the register holds the address of the argument instead of the argument
5291 @vindex SYMBOL_LOC_LOCAL
5292 @item gdb.SYMBOL_LOC_LOCAL
5293 Value is a local variable.
5295 @vindex SYMBOL_LOC_TYPEDEF
5296 @item gdb.SYMBOL_LOC_TYPEDEF
5297 Value not used. Symbols in the domain @code{SYMBOL_STRUCT_DOMAIN} all
5300 @vindex SYMBOL_LOC_LABEL
5301 @item gdb.SYMBOL_LOC_LABEL
5304 @vindex SYMBOL_LOC_BLOCK
5305 @item gdb.SYMBOL_LOC_BLOCK
5308 @vindex SYMBOL_LOC_CONST_BYTES
5309 @item gdb.SYMBOL_LOC_CONST_BYTES
5310 Value is a byte-sequence.
5312 @vindex SYMBOL_LOC_UNRESOLVED
5313 @item gdb.SYMBOL_LOC_UNRESOLVED
5314 Value is at a fixed address, but the address of the variable has to be
5315 determined from the minimal symbol table whenever the variable is
5318 @vindex SYMBOL_LOC_OPTIMIZED_OUT
5319 @item gdb.SYMBOL_LOC_OPTIMIZED_OUT
5320 The value does not actually exist in the program.
5322 @vindex SYMBOL_LOC_COMPUTED
5323 @item gdb.SYMBOL_LOC_COMPUTED
5324 The value's address is a computed location.
5326 @vindex SYMBOL_LOC_COMMON_BLOCK
5327 @item gdb.SYMBOL_LOC_COMMON_BLOCK
5328 The value's address is a symbol. This is only used for Fortran common
5332 @node Symbol Tables In Python
5333 @subsubsection Symbol table representation in Python
5335 @cindex symbol tables in python
5337 @tindex gdb.Symtab_and_line
5339 Access to symbol table data maintained by @value{GDBN} on the inferior
5340 is exposed to Python via two objects: @code{gdb.Symtab_and_line} and
5341 @code{gdb.Symtab}. Symbol table and line data for a frame is returned
5342 from the @code{find_sal} method in @code{gdb.Frame} object.
5343 @xref{Frames In Python}.
5345 For more information on @value{GDBN}'s symbol table management, see
5346 @ref{Symbols, ,Examining the Symbol Table}, for more information.
5348 A @code{gdb.Symtab_and_line} object has the following attributes:
5350 @defvar Symtab_and_line.symtab
5351 The symbol table object (@code{gdb.Symtab}) for this frame.
5352 This attribute is not writable.
5355 @defvar Symtab_and_line.pc
5356 Indicates the start of the address range occupied by code for the
5357 current source line. This attribute is not writable.
5360 @defvar Symtab_and_line.last
5361 Indicates the end of the address range occupied by code for the current
5362 source line. This attribute is not writable.
5365 @defvar Symtab_and_line.line
5366 Indicates the current line number for this object. This
5367 attribute is not writable.
5370 A @code{gdb.Symtab_and_line} object has the following methods:
5372 @defun Symtab_and_line.is_valid ()
5373 Returns @code{True} if the @code{gdb.Symtab_and_line} object is valid,
5374 @code{False} if not. A @code{gdb.Symtab_and_line} object can become
5375 invalid if the Symbol table and line object it refers to does not
5376 exist in @value{GDBN} any longer. All other
5377 @code{gdb.Symtab_and_line} methods will throw an exception if it is
5378 invalid at the time the method is called.
5381 A @code{gdb.Symtab} object has the following attributes:
5383 @defvar Symtab.filename
5384 The symbol table's source filename. This attribute is not writable.
5387 @defvar Symtab.objfile
5388 The symbol table's backing object file. @xref{Objfiles In Python}.
5389 This attribute is not writable.
5392 @defvar Symtab.producer
5393 The name and possibly version number of the program that
5394 compiled the code in the symbol table.
5395 The contents of this string is up to the compiler.
5396 If no producer information is available then @code{None} is returned.
5397 This attribute is not writable.
5400 A @code{gdb.Symtab} object has the following methods:
5402 @defun Symtab.is_valid ()
5403 Returns @code{True} if the @code{gdb.Symtab} object is valid,
5404 @code{False} if not. A @code{gdb.Symtab} object can become invalid if
5405 the symbol table it refers to does not exist in @value{GDBN} any
5406 longer. All other @code{gdb.Symtab} methods will throw an exception
5407 if it is invalid at the time the method is called.
5410 @defun Symtab.fullname ()
5411 Return the symbol table's source absolute file name.
5414 @defun Symtab.global_block ()
5415 Return the global block of the underlying symbol table.
5416 @xref{Blocks In Python}.
5419 @defun Symtab.static_block ()
5420 Return the static block of the underlying symbol table.
5421 @xref{Blocks In Python}.
5424 @defun Symtab.linetable ()
5425 Return the line table associated with the symbol table.
5426 @xref{Line Tables In Python}.
5429 @node Line Tables In Python
5430 @subsubsection Manipulating line tables using Python
5432 @cindex line tables in python
5433 @tindex gdb.LineTable
5435 Python code can request and inspect line table information from a
5436 symbol table that is loaded in @value{GDBN}. A line table is a
5437 mapping of source lines to their executable locations in memory. To
5438 acquire the line table information for a particular symbol table, use
5439 the @code{linetable} function (@pxref{Symbol Tables In Python}).
5441 A @code{gdb.LineTable} is iterable. The iterator returns
5442 @code{LineTableEntry} objects that correspond to the source line and
5443 address for each line table entry. @code{LineTableEntry} objects have
5444 the following attributes:
5446 @defvar LineTableEntry.line
5447 The source line number for this line table entry. This number
5448 corresponds to the actual line of source. This attribute is not
5452 @defvar LineTableEntry.pc
5453 The address that is associated with the line table entry where the
5454 executable code for that source line resides in memory. This
5455 attribute is not writable.
5458 As there can be multiple addresses for a single source line, you may
5459 receive multiple @code{LineTableEntry} objects with matching
5460 @code{line} attributes, but with different @code{pc} attributes. The
5461 iterator is sorted in ascending @code{pc} order. Here is a small
5462 example illustrating iterating over a line table.
5465 symtab = gdb.selected_frame().find_sal().symtab
5466 linetable = symtab.linetable()
5467 for line in linetable:
5468 print ("Line: "+str(line.line)+" Address: "+hex(line.pc))
5471 This will have the following output:
5474 Line: 33 Address: 0x4005c8L
5475 Line: 37 Address: 0x4005caL
5476 Line: 39 Address: 0x4005d2L
5477 Line: 40 Address: 0x4005f8L
5478 Line: 42 Address: 0x4005ffL
5479 Line: 44 Address: 0x400608L
5480 Line: 42 Address: 0x40060cL
5481 Line: 45 Address: 0x400615L
5484 In addition to being able to iterate over a @code{LineTable}, it also
5485 has the following direct access methods:
5487 @defun LineTable.line (line)
5488 Return a Python @code{Tuple} of @code{LineTableEntry} objects for any
5489 entries in the line table for the given @var{line}, which specifies
5490 the source code line. If there are no entries for that source code
5491 @var{line}, the Python @code{None} is returned.
5494 @defun LineTable.has_line (line)
5495 Return a Python @code{Boolean} indicating whether there is an entry in
5496 the line table for this source line. Return @code{True} if an entry
5497 is found, or @code{False} if not.
5500 @defun LineTable.source_lines ()
5501 Return a Python @code{List} of the source line numbers in the symbol
5502 table. Only lines with executable code locations are returned. The
5503 contents of the @code{List} will just be the source line entries
5504 represented as Python @code{Long} values.
5507 @node Breakpoints In Python
5508 @subsubsection Manipulating breakpoints using Python
5510 @cindex breakpoints in python
5511 @tindex gdb.Breakpoint
5513 Python code can manipulate breakpoints via the @code{gdb.Breakpoint}
5516 A breakpoint can be created using one of the two forms of the
5517 @code{gdb.Breakpoint} constructor. The first one accepts a string
5518 like one would pass to the @code{break}
5519 (@pxref{Set Breaks,,Setting Breakpoints}) and @code{watch}
5520 (@pxref{Set Watchpoints, , Setting Watchpoints}) commands, and can be used to
5521 create both breakpoints and watchpoints. The second accepts separate Python
5522 arguments similar to @ref{Explicit Locations}, and can only be used to create
5525 @defun Breakpoint.__init__ (spec @r{[}, type @r{][}, wp_class @r{][}, internal @r{][}, temporary @r{][}, qualified @r{]})
5526 Create a new breakpoint according to @var{spec}, which is a string naming the
5527 location of a breakpoint, or an expression that defines a watchpoint. The
5528 string should describe a location in a format recognized by the @code{break}
5529 command (@pxref{Set Breaks,,Setting Breakpoints}) or, in the case of a
5530 watchpoint, by the @code{watch} command
5531 (@pxref{Set Watchpoints, , Setting Watchpoints}).
5533 The optional @var{type} argument specifies the type of the breakpoint to create,
5536 The optional @var{wp_class} argument defines the class of watchpoint to create,
5537 if @var{type} is @code{gdb.BP_WATCHPOINT}. If @var{wp_class} is omitted, it
5538 defaults to @code{gdb.WP_WRITE}.
5540 The optional @var{internal} argument allows the breakpoint to become invisible
5541 to the user. The breakpoint will neither be reported when created, nor will it
5542 be listed in the output from @code{info breakpoints} (but will be listed with
5543 the @code{maint info breakpoints} command).
5545 The optional @var{temporary} argument makes the breakpoint a temporary
5546 breakpoint. Temporary breakpoints are deleted after they have been hit. Any
5547 further access to the Python breakpoint after it has been hit will result in a
5548 runtime error (as that breakpoint has now been automatically deleted).
5550 The optional @var{qualified} argument is a boolean that allows interpreting
5551 the function passed in @code{spec} as a fully-qualified name. It is equivalent
5552 to @code{break}'s @code{-qualified} flag (@pxref{Linespec Locations} and
5553 @ref{Explicit Locations}).
5557 @defun Breakpoint.__init__ (@r{[} source @r{][}, function @r{][}, label @r{][}, line @r{]}, @r{][} internal @r{][}, temporary @r{][}, qualified @r{]})
5558 This second form of creating a new breakpoint specifies the explicit
5559 location (@pxref{Explicit Locations}) using keywords. The new breakpoint will
5560 be created in the specified source file @var{source}, at the specified
5561 @var{function}, @var{label} and @var{line}.
5563 @var{internal}, @var{temporary} and @var{qualified} have the same usage as
5564 explained previously.
5567 The available types are represented by constants defined in the @code{gdb}
5571 @vindex BP_BREAKPOINT
5572 @item gdb.BP_BREAKPOINT
5573 Normal code breakpoint.
5575 @vindex BP_HARDWARE_BREAKPOINT
5576 @item gdb.BP_HARDWARE_BREAKPOINT
5577 Hardware assisted code breakpoint.
5579 @vindex BP_WATCHPOINT
5580 @item gdb.BP_WATCHPOINT
5581 Watchpoint breakpoint.
5583 @vindex BP_HARDWARE_WATCHPOINT
5584 @item gdb.BP_HARDWARE_WATCHPOINT
5585 Hardware assisted watchpoint.
5587 @vindex BP_READ_WATCHPOINT
5588 @item gdb.BP_READ_WATCHPOINT
5589 Hardware assisted read watchpoint.
5591 @vindex BP_ACCESS_WATCHPOINT
5592 @item gdb.BP_ACCESS_WATCHPOINT
5593 Hardware assisted access watchpoint.
5595 @vindex BP_CATCHPOINT
5596 @item gdb.BP_CATCHPOINT
5597 Catchpoint. Currently, this type can't be used when creating
5598 @code{gdb.Breakpoint} objects, but will be present in
5599 @code{gdb.Breakpoint} objects reported from
5600 @code{gdb.BreakpointEvent}s (@pxref{Events In Python}).
5603 The available watchpoint types are represented by constants defined in the
5609 Read only watchpoint.
5613 Write only watchpoint.
5617 Read/Write watchpoint.
5620 @defun Breakpoint.stop (self)
5621 The @code{gdb.Breakpoint} class can be sub-classed and, in
5622 particular, you may choose to implement the @code{stop} method.
5623 If this method is defined in a sub-class of @code{gdb.Breakpoint},
5624 it will be called when the inferior reaches any location of a
5625 breakpoint which instantiates that sub-class. If the method returns
5626 @code{True}, the inferior will be stopped at the location of the
5627 breakpoint, otherwise the inferior will continue.
5629 If there are multiple breakpoints at the same location with a
5630 @code{stop} method, each one will be called regardless of the
5631 return status of the previous. This ensures that all @code{stop}
5632 methods have a chance to execute at that location. In this scenario
5633 if one of the methods returns @code{True} but the others return
5634 @code{False}, the inferior will still be stopped.
5636 You should not alter the execution state of the inferior (i.e.@:, step,
5637 next, etc.), alter the current frame context (i.e.@:, change the current
5638 active frame), or alter, add or delete any breakpoint. As a general
5639 rule, you should not alter any data within @value{GDBN} or the inferior
5642 Example @code{stop} implementation:
5645 class MyBreakpoint (gdb.Breakpoint):
5647 inf_val = gdb.parse_and_eval("foo")
5654 @defun Breakpoint.is_valid ()
5655 Return @code{True} if this @code{Breakpoint} object is valid,
5656 @code{False} otherwise. A @code{Breakpoint} object can become invalid
5657 if the user deletes the breakpoint. In this case, the object still
5658 exists, but the underlying breakpoint does not. In the cases of
5659 watchpoint scope, the watchpoint remains valid even if execution of the
5660 inferior leaves the scope of that watchpoint.
5663 @defun Breakpoint.delete ()
5664 Permanently deletes the @value{GDBN} breakpoint. This also
5665 invalidates the Python @code{Breakpoint} object. Any further access
5666 to this object's attributes or methods will raise an error.
5669 @defvar Breakpoint.enabled
5670 This attribute is @code{True} if the breakpoint is enabled, and
5671 @code{False} otherwise. This attribute is writable. You can use it to enable
5672 or disable the breakpoint.
5675 @defvar Breakpoint.silent
5676 This attribute is @code{True} if the breakpoint is silent, and
5677 @code{False} otherwise. This attribute is writable.
5679 Note that a breakpoint can also be silent if it has commands and the
5680 first command is @code{silent}. This is not reported by the
5681 @code{silent} attribute.
5684 @defvar Breakpoint.pending
5685 This attribute is @code{True} if the breakpoint is pending, and
5686 @code{False} otherwise. @xref{Set Breaks}. This attribute is
5690 @anchor{python_breakpoint_thread}
5691 @defvar Breakpoint.thread
5692 If the breakpoint is thread-specific, this attribute holds the
5693 thread's global id. If the breakpoint is not thread-specific, this
5694 attribute is @code{None}. This attribute is writable.
5697 @defvar Breakpoint.task
5698 If the breakpoint is Ada task-specific, this attribute holds the Ada task
5699 id. If the breakpoint is not task-specific (or the underlying
5700 language is not Ada), this attribute is @code{None}. This attribute
5704 @defvar Breakpoint.ignore_count
5705 This attribute holds the ignore count for the breakpoint, an integer.
5706 This attribute is writable.
5709 @defvar Breakpoint.number
5710 This attribute holds the breakpoint's number --- the identifier used by
5711 the user to manipulate the breakpoint. This attribute is not writable.
5714 @defvar Breakpoint.type
5715 This attribute holds the breakpoint's type --- the identifier used to
5716 determine the actual breakpoint type or use-case. This attribute is not
5720 @defvar Breakpoint.visible
5721 This attribute tells whether the breakpoint is visible to the user
5722 when set, or when the @samp{info breakpoints} command is run. This
5723 attribute is not writable.
5726 @defvar Breakpoint.temporary
5727 This attribute indicates whether the breakpoint was created as a
5728 temporary breakpoint. Temporary breakpoints are automatically deleted
5729 after that breakpoint has been hit. Access to this attribute, and all
5730 other attributes and functions other than the @code{is_valid}
5731 function, will result in an error after the breakpoint has been hit
5732 (as it has been automatically deleted). This attribute is not
5736 @defvar Breakpoint.hit_count
5737 This attribute holds the hit count for the breakpoint, an integer.
5738 This attribute is writable, but currently it can only be set to zero.
5741 @defvar Breakpoint.location
5742 This attribute holds the location of the breakpoint, as specified by
5743 the user. It is a string. If the breakpoint does not have a location
5744 (that is, it is a watchpoint) the attribute's value is @code{None}. This
5745 attribute is not writable.
5748 @defvar Breakpoint.expression
5749 This attribute holds a breakpoint expression, as specified by
5750 the user. It is a string. If the breakpoint does not have an
5751 expression (the breakpoint is not a watchpoint) the attribute's value
5752 is @code{None}. This attribute is not writable.
5755 @defvar Breakpoint.condition
5756 This attribute holds the condition of the breakpoint, as specified by
5757 the user. It is a string. If there is no condition, this attribute's
5758 value is @code{None}. This attribute is writable.
5761 @defvar Breakpoint.commands
5762 This attribute holds the commands attached to the breakpoint. If
5763 there are commands, this attribute's value is a string holding all the
5764 commands, separated by newlines. If there are no commands, this
5765 attribute is @code{None}. This attribute is writable.
5768 @node Finish Breakpoints in Python
5769 @subsubsection Finish Breakpoints
5771 @cindex python finish breakpoints
5772 @tindex gdb.FinishBreakpoint
5774 A finish breakpoint is a temporary breakpoint set at the return address of
5775 a frame, based on the @code{finish} command. @code{gdb.FinishBreakpoint}
5776 extends @code{gdb.Breakpoint}. The underlying breakpoint will be disabled
5777 and deleted when the execution will run out of the breakpoint scope (i.e.@:
5778 @code{Breakpoint.stop} or @code{FinishBreakpoint.out_of_scope} triggered).
5779 Finish breakpoints are thread specific and must be create with the right
5782 @defun FinishBreakpoint.__init__ (@r{[}frame@r{]} @r{[}, internal@r{]})
5783 Create a finish breakpoint at the return address of the @code{gdb.Frame}
5784 object @var{frame}. If @var{frame} is not provided, this defaults to the
5785 newest frame. The optional @var{internal} argument allows the breakpoint to
5786 become invisible to the user. @xref{Breakpoints In Python}, for further
5787 details about this argument.
5790 @defun FinishBreakpoint.out_of_scope (self)
5791 In some circumstances (e.g.@: @code{longjmp}, C@t{++} exceptions, @value{GDBN}
5792 @code{return} command, @dots{}), a function may not properly terminate, and
5793 thus never hit the finish breakpoint. When @value{GDBN} notices such a
5794 situation, the @code{out_of_scope} callback will be triggered.
5796 You may want to sub-class @code{gdb.FinishBreakpoint} and override this
5800 class MyFinishBreakpoint (gdb.FinishBreakpoint)
5802 print ("normal finish")
5805 def out_of_scope ():
5806 print ("abnormal finish")
5810 @defvar FinishBreakpoint.return_value
5811 When @value{GDBN} is stopped at a finish breakpoint and the frame
5812 used to build the @code{gdb.FinishBreakpoint} object had debug symbols, this
5813 attribute will contain a @code{gdb.Value} object corresponding to the return
5814 value of the function. The value will be @code{None} if the function return
5815 type is @code{void} or if the return value was not computable. This attribute
5819 @node Lazy Strings In Python
5820 @subsubsection Python representation of lazy strings
5822 @cindex lazy strings in python
5823 @tindex gdb.LazyString
5825 A @dfn{lazy string} is a string whose contents is not retrieved or
5826 encoded until it is needed.
5828 A @code{gdb.LazyString} is represented in @value{GDBN} as an
5829 @code{address} that points to a region of memory, an @code{encoding}
5830 that will be used to encode that region of memory, and a @code{length}
5831 to delimit the region of memory that represents the string. The
5832 difference between a @code{gdb.LazyString} and a string wrapped within
5833 a @code{gdb.Value} is that a @code{gdb.LazyString} will be treated
5834 differently by @value{GDBN} when printing. A @code{gdb.LazyString} is
5835 retrieved and encoded during printing, while a @code{gdb.Value}
5836 wrapping a string is immediately retrieved and encoded on creation.
5838 A @code{gdb.LazyString} object has the following functions:
5840 @defun LazyString.value ()
5841 Convert the @code{gdb.LazyString} to a @code{gdb.Value}. This value
5842 will point to the string in memory, but will lose all the delayed
5843 retrieval, encoding and handling that @value{GDBN} applies to a
5844 @code{gdb.LazyString}.
5847 @defvar LazyString.address
5848 This attribute holds the address of the string. This attribute is not
5852 @defvar LazyString.length
5853 This attribute holds the length of the string in characters. If the
5854 length is -1, then the string will be fetched and encoded up to the
5855 first null of appropriate width. This attribute is not writable.
5858 @defvar LazyString.encoding
5859 This attribute holds the encoding that will be applied to the string
5860 when the string is printed by @value{GDBN}. If the encoding is not
5861 set, or contains an empty string, then @value{GDBN} will select the
5862 most appropriate encoding when the string is printed. This attribute
5866 @defvar LazyString.type
5867 This attribute holds the type that is represented by the lazy string's
5868 type. For a lazy string this is a pointer or array type. To
5869 resolve this to the lazy string's character type, use the type's
5870 @code{target} method. @xref{Types In Python}. This attribute is not
5874 @node Architectures In Python
5875 @subsubsection Python representation of architectures
5876 @cindex Python architectures
5878 @value{GDBN} uses architecture specific parameters and artifacts in a
5879 number of its various computations. An architecture is represented
5880 by an instance of the @code{gdb.Architecture} class.
5882 A @code{gdb.Architecture} class has the following methods:
5884 @anchor{gdbpy_architecture_name}
5885 @defun Architecture.name ()
5886 Return the name (string value) of the architecture.
5889 @defun Architecture.disassemble (@var{start_pc} @r{[}, @var{end_pc} @r{[}, @var{count}@r{]]})
5890 Return a list of disassembled instructions starting from the memory
5891 address @var{start_pc}. The optional arguments @var{end_pc} and
5892 @var{count} determine the number of instructions in the returned list.
5893 If both the optional arguments @var{end_pc} and @var{count} are
5894 specified, then a list of at most @var{count} disassembled instructions
5895 whose start address falls in the closed memory address interval from
5896 @var{start_pc} to @var{end_pc} are returned. If @var{end_pc} is not
5897 specified, but @var{count} is specified, then @var{count} number of
5898 instructions starting from the address @var{start_pc} are returned. If
5899 @var{count} is not specified but @var{end_pc} is specified, then all
5900 instructions whose start address falls in the closed memory address
5901 interval from @var{start_pc} to @var{end_pc} are returned. If neither
5902 @var{end_pc} nor @var{count} are specified, then a single instruction at
5903 @var{start_pc} is returned. For all of these cases, each element of the
5904 returned list is a Python @code{dict} with the following string keys:
5909 The value corresponding to this key is a Python long integer capturing
5910 the memory address of the instruction.
5913 The value corresponding to this key is a string value which represents
5914 the instruction with assembly language mnemonics. The assembly
5915 language flavor used is the same as that specified by the current CLI
5916 variable @code{disassembly-flavor}. @xref{Machine Code}.
5919 The value corresponding to this key is the length (integer value) of the
5920 instruction in bytes.
5925 @findex Architecture.integer_type
5926 @defun Architecture.integer_type (size @r{[}, signed@r{]})
5927 This function looks up an integer type by its @var{size}, and
5928 optionally whether or not it is signed.
5930 @var{size} is the size, in bits, of the desired integer type. Only
5931 certain sizes are currently supported: 0, 8, 16, 24, 32, 64, and 128.
5933 If @var{signed} is not specified, it defaults to @code{True}. If
5934 @var{signed} is @code{False}, the returned type will be unsigned.
5936 If the indicated type cannot be found, this function will throw a
5937 @code{ValueError} exception.
5940 @anchor{gdbpy_architecture_registers}
5941 @defun Architecture.registers (@r{[} @var{reggroup} @r{]})
5942 Return a @code{gdb.RegisterDescriptorIterator} (@pxref{Registers In
5943 Python}) for all of the registers in @var{reggroup}, a string that is
5944 the name of a register group. If @var{reggroup} is omitted, or is the
5945 empty string, then the register group @samp{all} is assumed.
5948 @anchor{gdbpy_architecture_reggroups}
5949 @defun Architecture.register_groups ()
5950 Return a @code{gdb.RegisterGroupsIterator} (@pxref{Registers In
5951 Python}) for all of the register groups available for the
5952 @code{gdb.Architecture}.
5955 @node Registers In Python
5956 @subsubsection Registers In Python
5957 @cindex Registers In Python
5959 Python code can request from a @code{gdb.Architecture} information
5960 about the set of registers available
5961 (@pxref{gdbpy_architecture_registers,,@code{Architecture.registers}}).
5962 The register information is returned as a
5963 @code{gdb.RegisterDescriptorIterator}, which is an iterator that in
5964 turn returns @code{gdb.RegisterDescriptor} objects.
5966 A @code{gdb.RegisterDescriptor} does not provide the value of a
5967 register (@pxref{gdbpy_frame_read_register,,@code{Frame.read_register}}
5968 for reading a register's value), instead the @code{RegisterDescriptor}
5969 is a way to discover which registers are available for a particular
5972 A @code{gdb.RegisterDescriptor} has the following read-only properties:
5974 @defvar RegisterDescriptor.name
5975 The name of this register.
5978 It is also possible to lookup a register descriptor based on its name
5979 using the following @code{gdb.RegisterDescriptorIterator} function:
5981 @defun RegisterDescriptorIterator.find (@var{name})
5982 Takes @var{name} as an argument, which must be a string, and returns a
5983 @code{gdb.RegisterDescriptor} for the register with that name, or
5984 @code{None} if there is no register with that name.
5987 Python code can also request from a @code{gdb.Architecture}
5988 information about the set of register groups available on a given
5990 (@pxref{gdbpy_architecture_reggroups,,@code{Architecture.register_groups}}).
5992 Every register can be a member of zero or more register groups. Some
5993 register groups are used internally within @value{GDBN} to control
5994 things like which registers must be saved when calling into the
5995 program being debugged (@pxref{Calling,,Calling Program Functions}).
5996 Other register groups exist to allow users to easily see related sets
5997 of registers in commands like @code{info registers}
5998 (@pxref{info_registers_reggroup,,@code{info registers
6001 The register groups information is returned as a
6002 @code{gdb.RegisterGroupsIterator}, which is an iterator that in turn
6003 returns @code{gdb.RegisterGroup} objects.
6005 A @code{gdb.RegisterGroup} object has the following read-only
6008 @defvar RegisterGroup.name
6009 A string that is the name of this register group.
6012 @node Connections In Python
6013 @subsubsection Connections In Python
6014 @cindex connections in python
6015 @value{GDBN} lets you run and debug multiple programs in a single
6016 session. Each program being debugged has a connection, the connection
6017 describes how @value{GDBN} controls the program being debugged.
6018 Examples of different connection types are @samp{native} and
6019 @samp{remote}. @xref{Inferiors Connections and Programs}.
6021 Connections in @value{GDBN} are represented as instances of
6022 @code{gdb.TargetConnection}, or as one of its sub-classes. To get a
6023 list of all connections use @code{gdb.connections}
6024 (@pxref{gdbpy_connections,,gdb.connections}).
6026 To get the connection for a single @code{gdb.Inferior} read its
6027 @code{gdb.Inferior.connection} attribute
6028 (@pxref{gdbpy_inferior_connection,,gdb.Inferior.connection}).
6030 Currently there is only a single sub-class of
6031 @code{gdb.TargetConnection}, @code{gdb.RemoteTargetConnection},
6032 however, additional sub-classes may be added in future releases of
6033 @value{GDBN}. As a result you should avoid writing code like:
6036 conn = gdb.selected_inferior().connection
6037 if type(conn) is gdb.RemoteTargetConnection:
6038 print("This is a remote target connection")
6042 as this may fail when more connection types are added. Instead, you
6046 conn = gdb.selected_inferior().connection
6047 if isinstance(conn, gdb.RemoteTargetConnection):
6048 print("This is a remote target connection")
6051 A @code{gdb.TargetConnection} has the following method:
6053 @defun TargetConnection.is_valid ()
6054 Return @code{True} if the @code{gdb.TargetConnection} object is valid,
6055 @code{False} if not. A @code{gdb.TargetConnection} will become
6056 invalid if the connection no longer exists within @value{GDBN}, this
6057 might happen when no inferiors are using the connection, but could be
6058 delayed until the user replaces the current target.
6060 Reading any of the @code{gdb.TargetConnection} properties will throw
6061 an exception if the connection is invalid.
6064 A @code{gdb.TargetConnection} has the following read-only properties:
6066 @defvar TargetConnection.num
6067 An integer assigned by @value{GDBN} to uniquely identify this
6068 connection. This is the same value as displayed in the @samp{Num}
6069 column of the @code{info connections} command output (@pxref{Inferiors
6070 Connections and Programs,,info connections}).
6073 @defvar TargetConnection.type
6074 A string that describes what type of connection this is. This string
6075 will be one of the valid names that can be passed to the @code{target}
6076 command (@pxref{Target Commands,,target command}).
6079 @defvar TargetConnection.description
6080 A string that gives a short description of this target type. This is
6081 the same string that is displayed in the @samp{Description} column of
6082 the @code{info connection} command output (@pxref{Inferiors
6083 Connections and Programs,,info connections}).
6086 @defvar TargetConnection.details
6087 An optional string that gives additional information about this
6088 connection. This attribute can be @code{None} if there are no
6089 additional details for this connection.
6091 An example of a connection type that might have additional details is
6092 the @samp{remote} connection, in this case the details string can
6093 contain the @samp{@var{hostname}:@var{port}} that was used to connect
6094 to the remote target.
6097 The @code{gdb.RemoteTargetConnection} class is a sub-class of
6098 @code{gdb.TargetConnection}, and is used to represent @samp{remote}
6099 and @samp{extended-remote} connections. In addition to the attributes
6100 and methods available from the @code{gdb.TargetConnection} base class,
6101 a @code{gdb.RemoteTargetConnection} has the following method:
6103 @kindex maint packet
6104 @defun RemoteTargetConnection.send_packet (@var{packet})
6105 This method sends @var{packet} to the remote target and returns the
6106 response. The @var{packet} should either be a @code{bytes} object, or
6107 a @code{Unicode} string.
6109 If @var{packet} is a @code{Unicode} string, then the string is encoded
6110 to a @code{bytes} object using the @sc{ascii} codec. If the string
6111 can't be encoded then an @code{UnicodeError} is raised.
6113 If @var{packet} is not a @code{bytes} object, or a @code{Unicode}
6114 string, then a @code{TypeError} is raised. If @var{packet} is empty
6115 then a @code{ValueError} is raised.
6117 The response is returned as a @code{bytes} object. For Python 3 if it
6118 is known that the response can be represented as a string then this
6119 can be decoded from the buffer. For example, if it is known that the
6120 response is an @sc{ascii} string:
6123 remote_connection.send_packet("some_packet").decode("ascii")
6126 In Python 2 @code{bytes} and @code{str} are aliases, so the result is
6127 already a string, if the response includes non-printable characters,
6128 or null characters, then these will be present in the result, care
6129 should be taken when processing the result to handle this case.
6131 The prefix, suffix, and checksum (as required by the remote serial
6132 protocol) are automatically added to the outgoing packet, and removed
6133 from the incoming packet before the contents of the reply are
6136 This is equivalent to the @code{maintenance packet} command
6137 (@pxref{maint packet}).
6140 @node TUI Windows In Python
6141 @subsubsection Implementing new TUI windows
6142 @cindex Python TUI Windows
6144 New TUI (@pxref{TUI}) windows can be implemented in Python.
6146 @findex gdb.register_window_type
6147 @defun gdb.register_window_type (@var{name}, @var{factory})
6148 Because TUI windows are created and destroyed depending on the layout
6149 the user chooses, new window types are implemented by registering a
6150 factory function with @value{GDBN}.
6152 @var{name} is the name of the new window. It's an error to try to
6153 replace one of the built-in windows, but other window types can be
6156 @var{function} is a factory function that is called to create the TUI
6157 window. This is called with a single argument of type
6158 @code{gdb.TuiWindow}, described below. It should return an object
6159 that implements the TUI window protocol, also described below.
6162 As mentioned above, when a factory function is called, it is passed
6163 an object of type @code{gdb.TuiWindow}. This object has these
6164 methods and attributes:
6166 @defun TuiWindow.is_valid ()
6167 This method returns @code{True} when this window is valid. When the
6168 user changes the TUI layout, windows no longer visible in the new
6169 layout will be destroyed. At this point, the @code{gdb.TuiWindow}
6170 will no longer be valid, and methods (and attributes) other than
6171 @code{is_valid} will throw an exception.
6173 When the TUI is disabled using @code{tui disable} (@pxref{TUI
6174 Commands,,tui disable}) the window is hidden rather than destroyed,
6175 but @code{is_valid} will still return @code{False} and other methods
6176 (and attributes) will still throw an exception.
6179 @defvar TuiWindow.width
6180 This attribute holds the width of the window. It is not writable.
6183 @defvar TuiWindow.height
6184 This attribute holds the height of the window. It is not writable.
6187 @defvar TuiWindow.title
6188 This attribute holds the window's title, a string. This is normally
6189 displayed above the window. This attribute can be modified.
6192 @defun TuiWindow.erase ()
6193 Remove all the contents of the window.
6196 @defun TuiWindow.write (@var{string} @r{[}, @var{full_window}@r{]})
6197 Write @var{string} to the window. @var{string} can contain ANSI
6198 terminal escape styling sequences; @value{GDBN} will translate these
6199 as appropriate for the terminal.
6201 If the @var{full_window} parameter is @code{True}, then @var{string}
6202 contains the full contents of the window. This is similar to calling
6203 @code{erase} before @code{write}, but avoids the flickering.
6206 The factory function that you supply should return an object
6207 conforming to the TUI window protocol. These are the method that can
6208 be called on this object, which is referred to below as the ``window
6209 object''. The methods documented below are optional; if the object
6210 does not implement one of these methods, @value{GDBN} will not attempt
6211 to call it. Additional new methods may be added to the window
6212 protocol in the future. @value{GDBN} guarantees that they will begin
6213 with a lower-case letter, so you can start implementation methods with
6214 upper-case letters or underscore to avoid any future conflicts.
6216 @defun Window.close ()
6217 When the TUI window is closed, the @code{gdb.TuiWindow} object will be
6218 put into an invalid state. At this time, @value{GDBN} will call
6219 @code{close} method on the window object.
6221 After this method is called, @value{GDBN} will discard any references
6222 it holds on this window object, and will no longer call methods on
6226 @defun Window.render ()
6227 In some situations, a TUI window can change size. For example, this
6228 can happen if the user resizes the terminal, or changes the layout.
6229 When this happens, @value{GDBN} will call the @code{render} method on
6232 If your window is intended to update in response to changes in the
6233 inferior, you will probably also want to register event listeners and
6234 send output to the @code{gdb.TuiWindow}.
6237 @defun Window.hscroll (@var{num})
6238 This is a request to scroll the window horizontally. @var{num} is the
6239 amount by which to scroll, with negative numbers meaning to scroll
6240 right. In the TUI model, it is the viewport that moves, not the
6241 contents. A positive argument should cause the viewport to move
6242 right, and so the content should appear to move to the left.
6245 @defun Window.vscroll (@var{num})
6246 This is a request to scroll the window vertically. @var{num} is the
6247 amount by which to scroll, with negative numbers meaning to scroll
6248 backward. In the TUI model, it is the viewport that moves, not the
6249 contents. A positive argument should cause the viewport to move down,
6250 and so the content should appear to move up.
6253 @defun Window.click (@var{x}, @var{y}, @var{button})
6254 This is called on a mouse click in this window. @var{x} and @var{y} are
6255 the mouse coordinates inside the window (0-based), and @var{button}
6256 specifies which mouse button was used, whose values can be 1 (left),
6257 2 (middle), or 3 (right).
6260 @node Python Auto-loading
6261 @subsection Python Auto-loading
6262 @cindex Python auto-loading
6264 When a new object file is read (for example, due to the @code{file}
6265 command, or because the inferior has loaded a shared library),
6266 @value{GDBN} will look for Python support scripts in several ways:
6267 @file{@var{objfile}-gdb.py} and @code{.debug_gdb_scripts} section.
6268 @xref{Auto-loading extensions}.
6270 The auto-loading feature is useful for supplying application-specific
6271 debugging commands and scripts.
6273 Auto-loading can be enabled or disabled,
6274 and the list of auto-loaded scripts can be printed.
6277 @anchor{set auto-load python-scripts}
6278 @kindex set auto-load python-scripts
6279 @item set auto-load python-scripts [on|off]
6280 Enable or disable the auto-loading of Python scripts.
6282 @anchor{show auto-load python-scripts}
6283 @kindex show auto-load python-scripts
6284 @item show auto-load python-scripts
6285 Show whether auto-loading of Python scripts is enabled or disabled.
6287 @anchor{info auto-load python-scripts}
6288 @kindex info auto-load python-scripts
6289 @cindex print list of auto-loaded Python scripts
6290 @item info auto-load python-scripts [@var{regexp}]
6291 Print the list of all Python scripts that @value{GDBN} auto-loaded.
6293 Also printed is the list of Python scripts that were mentioned in
6294 the @code{.debug_gdb_scripts} section and were either not found
6295 (@pxref{dotdebug_gdb_scripts section}) or were not auto-loaded due to
6296 @code{auto-load safe-path} rejection (@pxref{Auto-loading}).
6297 This is useful because their names are not printed when @value{GDBN}
6298 tries to load them and fails. There may be many of them, and printing
6299 an error message for each one is problematic.
6301 If @var{regexp} is supplied only Python scripts with matching names are printed.
6306 (gdb) info auto-load python-scripts
6308 Yes py-section-script.py
6309 full name: /tmp/py-section-script.py
6310 No my-foo-pretty-printers.py
6314 When reading an auto-loaded file or script, @value{GDBN} sets the
6315 @dfn{current objfile}. This is available via the @code{gdb.current_objfile}
6316 function (@pxref{Objfiles In Python}). This can be useful for
6317 registering objfile-specific pretty-printers and frame-filters.
6319 @node Python modules
6320 @subsection Python modules
6321 @cindex python modules
6323 @value{GDBN} comes with several modules to assist writing Python code.
6326 * gdb.printing:: Building and registering pretty-printers.
6327 * gdb.types:: Utilities for working with types.
6328 * gdb.prompt:: Utilities for prompt value substitution.
6332 @subsubsection gdb.printing
6333 @cindex gdb.printing
6335 This module provides a collection of utilities for working with
6339 @item PrettyPrinter (@var{name}, @var{subprinters}=None)
6340 This class specifies the API that makes @samp{info pretty-printer},
6341 @samp{enable pretty-printer} and @samp{disable pretty-printer} work.
6342 Pretty-printers should generally inherit from this class.
6344 @item SubPrettyPrinter (@var{name})
6345 For printers that handle multiple types, this class specifies the
6346 corresponding API for the subprinters.
6348 @item RegexpCollectionPrettyPrinter (@var{name})
6349 Utility class for handling multiple printers, all recognized via
6350 regular expressions.
6351 @xref{Writing a Pretty-Printer}, for an example.
6353 @item FlagEnumerationPrinter (@var{name})
6354 A pretty-printer which handles printing of @code{enum} values. Unlike
6355 @value{GDBN}'s built-in @code{enum} printing, this printer attempts to
6356 work properly when there is some overlap between the enumeration
6357 constants. The argument @var{name} is the name of the printer and
6358 also the name of the @code{enum} type to look up.
6360 @item register_pretty_printer (@var{obj}, @var{printer}, @var{replace}=False)
6361 Register @var{printer} with the pretty-printer list of @var{obj}.
6362 If @var{replace} is @code{True} then any existing copy of the printer
6363 is replaced. Otherwise a @code{RuntimeError} exception is raised
6364 if a printer with the same name already exists.
6368 @subsubsection gdb.types
6371 This module provides a collection of utilities for working with
6372 @code{gdb.Type} objects.
6375 @item get_basic_type (@var{type})
6376 Return @var{type} with const and volatile qualifiers stripped,
6377 and with typedefs and C@t{++} references converted to the underlying type.
6382 typedef const int const_int;
6384 const_int& foo_ref (foo);
6385 int main () @{ return 0; @}
6392 (gdb) python import gdb.types
6393 (gdb) python foo_ref = gdb.parse_and_eval("foo_ref")
6394 (gdb) python print gdb.types.get_basic_type(foo_ref.type)
6398 @item has_field (@var{type}, @var{field})
6399 Return @code{True} if @var{type}, assumed to be a type with fields
6400 (e.g., a structure or union), has field @var{field}.
6402 @item make_enum_dict (@var{enum_type})
6403 Return a Python @code{dictionary} type produced from @var{enum_type}.
6405 @item deep_items (@var{type})
6406 Returns a Python iterator similar to the standard
6407 @code{gdb.Type.iteritems} method, except that the iterator returned
6408 by @code{deep_items} will recursively traverse anonymous struct or
6409 union fields. For example:
6423 Then in @value{GDBN}:
6425 (@value{GDBP}) python import gdb.types
6426 (@value{GDBP}) python struct_a = gdb.lookup_type("struct A")
6427 (@value{GDBP}) python print struct_a.keys ()
6429 (@value{GDBP}) python print [k for k,v in gdb.types.deep_items(struct_a)]
6430 @{['a', 'b0', 'b1']@}
6433 @item get_type_recognizers ()
6434 Return a list of the enabled type recognizers for the current context.
6435 This is called by @value{GDBN} during the type-printing process
6436 (@pxref{Type Printing API}).
6438 @item apply_type_recognizers (recognizers, type_obj)
6439 Apply the type recognizers, @var{recognizers}, to the type object
6440 @var{type_obj}. If any recognizer returns a string, return that
6441 string. Otherwise, return @code{None}. This is called by
6442 @value{GDBN} during the type-printing process (@pxref{Type Printing
6445 @item register_type_printer (locus, printer)
6446 This is a convenience function to register a type printer
6447 @var{printer}. The printer must implement the type printer protocol.
6448 The @var{locus} argument is either a @code{gdb.Objfile}, in which case
6449 the printer is registered with that objfile; a @code{gdb.Progspace},
6450 in which case the printer is registered with that progspace; or
6451 @code{None}, in which case the printer is registered globally.
6454 This is a base class that implements the type printer protocol. Type
6455 printers are encouraged, but not required, to derive from this class.
6456 It defines a constructor:
6458 @defmethod TypePrinter __init__ (self, name)
6459 Initialize the type printer with the given name. The new printer
6460 starts in the enabled state.
6466 @subsubsection gdb.prompt
6469 This module provides a method for prompt value-substitution.
6472 @item substitute_prompt (@var{string})
6473 Return @var{string} with escape sequences substituted by values. Some
6474 escape sequences take arguments. You can specify arguments inside
6475 ``@{@}'' immediately following the escape sequence.
6477 The escape sequences you can pass to this function are:
6481 Substitute a backslash.
6483 Substitute an ESC character.
6485 Substitute the selected frame; an argument names a frame parameter.
6487 Substitute a newline.
6489 Substitute a parameter's value; the argument names the parameter.
6491 Substitute a carriage return.
6493 Substitute the selected thread; an argument names a thread parameter.
6495 Substitute the version of GDB.
6497 Substitute the current working directory.
6499 Begin a sequence of non-printing characters. These sequences are
6500 typically used with the ESC character, and are not counted in the string
6501 length. Example: ``\[\e[0;34m\](gdb)\[\e[0m\]'' will return a
6502 blue-colored ``(gdb)'' prompt where the length is five.
6504 End a sequence of non-printing characters.
6510 substitute_prompt ("frame: \f, args: \p@{print frame-arguments@}")
6513 @exdent will return the string:
6516 "frame: main, args: scalars"