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7 @c and with the Back-Cover Texts as in (a) below.
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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.
108 It is also possible to execute a Python script from the @value{GDBN}
112 @item source @file{script-name}
113 The script name must end with @samp{.py} and @value{GDBN} must be configured
114 to recognize the script language based on filename extension using
115 the @code{script-extension} setting. @xref{Extending GDB, ,Extending GDB}.
119 @subsection Python API
121 @cindex programming in python
123 You can get quick online help for @value{GDBN}'s Python API by issuing
124 the command @w{@kbd{python help (gdb)}}.
126 Functions and methods which have two or more optional arguments allow
127 them to be specified using keyword syntax. This allows passing some
128 optional arguments while skipping others. Example:
129 @w{@code{gdb.some_function ('foo', bar = 1, baz = 2)}}.
132 * Basic Python:: Basic Python Functions.
133 * Exception Handling:: How Python exceptions are translated.
134 * Values From Inferior:: Python representation of values.
135 * Types In Python:: Python representation of types.
136 * Pretty Printing API:: Pretty-printing values.
137 * Selecting Pretty-Printers:: How GDB chooses a pretty-printer.
138 * Writing a Pretty-Printer:: Writing a Pretty-Printer.
139 * Type Printing API:: Pretty-printing types.
140 * Frame Filter API:: Filtering Frames.
141 * Frame Decorator API:: Decorating Frames.
142 * Writing a Frame Filter:: Writing a Frame Filter.
143 * Unwinding Frames in Python:: Writing frame unwinder.
144 * Xmethods In Python:: Adding and replacing methods of C++ classes.
145 * Xmethod API:: Xmethod types.
146 * Writing an Xmethod:: Writing an xmethod.
147 * Inferiors In Python:: Python representation of inferiors (processes)
148 * Events In Python:: Listening for events from @value{GDBN}.
149 * Threads In Python:: Accessing inferior threads from Python.
150 * Recordings In Python:: Accessing recordings from Python.
151 * Commands In Python:: Implementing new commands in Python.
152 * Parameters In Python:: Adding new @value{GDBN} parameters.
153 * Functions In Python:: Writing new convenience functions.
154 * Progspaces In Python:: Program spaces.
155 * Objfiles In Python:: Object files.
156 * Frames In Python:: Accessing inferior stack frames from Python.
157 * Blocks In Python:: Accessing blocks from Python.
158 * Symbols In Python:: Python representation of symbols.
159 * Symbol Tables In Python:: Python representation of symbol tables.
160 * Line Tables In Python:: Python representation of line tables.
161 * Breakpoints In Python:: Manipulating breakpoints using Python.
162 * Finish Breakpoints in Python:: Setting Breakpoints on function return
164 * Lazy Strings In Python:: Python representation of lazy strings.
165 * Architectures In Python:: Python representation of architectures.
166 * TUI Windows In Python:: Implementing new TUI windows.
170 @subsubsection Basic Python
172 @cindex python stdout
173 @cindex python pagination
174 At startup, @value{GDBN} overrides Python's @code{sys.stdout} and
175 @code{sys.stderr} to print using @value{GDBN}'s output-paging streams.
176 A Python program which outputs to one of these streams may have its
177 output interrupted by the user (@pxref{Screen Size}). In this
178 situation, a Python @code{KeyboardInterrupt} exception is thrown.
180 Some care must be taken when writing Python code to run in
181 @value{GDBN}. Two things worth noting in particular:
185 @value{GDBN} install handlers for @code{SIGCHLD} and @code{SIGINT}.
186 Python code must not override these, or even change the options using
187 @code{sigaction}. If your program changes the handling of these
188 signals, @value{GDBN} will most likely stop working correctly. Note
189 that it is unfortunately common for GUI toolkits to install a
190 @code{SIGCHLD} handler.
193 @value{GDBN} takes care to mark its internal file descriptors as
194 close-on-exec. However, this cannot be done in a thread-safe way on
195 all platforms. Your Python programs should be aware of this and
196 should both create new file descriptors with the close-on-exec flag
197 set and arrange to close unneeded file descriptors before starting a
201 @cindex python functions
202 @cindex python module
204 @value{GDBN} introduces a new Python module, named @code{gdb}. All
205 methods and classes added by @value{GDBN} are placed in this module.
206 @value{GDBN} automatically @code{import}s the @code{gdb} module for
207 use in all scripts evaluated by the @code{python} command.
209 Some types of the @code{gdb} module come with a textual representation
210 (accessible through the @code{repr} or @code{str} functions). These are
211 offered for debugging purposes only, expect them to change over time.
213 @findex gdb.PYTHONDIR
214 @defvar gdb.PYTHONDIR
215 A string containing the python directory (@pxref{Python}).
219 @defun gdb.execute (command @r{[}, from_tty @r{[}, to_string@r{]]})
220 Evaluate @var{command}, a string, as a @value{GDBN} CLI command.
221 If a GDB exception happens while @var{command} runs, it is
222 translated as described in @ref{Exception Handling,,Exception Handling}.
224 The @var{from_tty} flag specifies whether @value{GDBN} ought to consider this
225 command as having originated from the user invoking it interactively.
226 It must be a boolean value. If omitted, it defaults to @code{False}.
228 By default, any output produced by @var{command} is sent to
229 @value{GDBN}'s standard output (and to the log output if logging is
230 turned on). If the @var{to_string} parameter is
231 @code{True}, then output will be collected by @code{gdb.execute} and
232 returned as a string. The default is @code{False}, in which case the
233 return value is @code{None}. If @var{to_string} is @code{True}, the
234 @value{GDBN} virtual terminal will be temporarily set to unlimited width
235 and height, and its pagination will be disabled; @pxref{Screen Size}.
238 @findex gdb.breakpoints
239 @defun gdb.breakpoints ()
240 Return a sequence holding all of @value{GDBN}'s breakpoints.
241 @xref{Breakpoints In Python}, for more information. In @value{GDBN}
242 version 7.11 and earlier, this function returned @code{None} if there
243 were no breakpoints. This peculiarity was subsequently fixed, and now
244 @code{gdb.breakpoints} returns an empty sequence in this case.
247 @defun gdb.rbreak (regex @r{[}, minsyms @r{[}, throttle, @r{[}, symtabs @r{]]]})
248 Return a Python list holding a collection of newly set
249 @code{gdb.Breakpoint} objects matching function names defined by the
250 @var{regex} pattern. If the @var{minsyms} keyword is @code{True}, all
251 system functions (those not explicitly defined in the inferior) will
252 also be included in the match. The @var{throttle} keyword takes an
253 integer that defines the maximum number of pattern matches for
254 functions matched by the @var{regex} pattern. If the number of
255 matches exceeds the integer value of @var{throttle}, a
256 @code{RuntimeError} will be raised and no breakpoints will be created.
257 If @var{throttle} is not defined then there is no imposed limit on the
258 maximum number of matches and breakpoints to be created. The
259 @var{symtabs} keyword takes a Python iterable that yields a collection
260 of @code{gdb.Symtab} objects and will restrict the search to those
261 functions only contained within the @code{gdb.Symtab} objects.
264 @findex gdb.parameter
265 @defun gdb.parameter (parameter)
266 Return the value of a @value{GDBN} @var{parameter} given by its name,
267 a string; the parameter name string may contain spaces if the parameter has a
268 multi-part name. For example, @samp{print object} is a valid
271 If the named parameter does not exist, this function throws a
272 @code{gdb.error} (@pxref{Exception Handling}). Otherwise, the
273 parameter's value is converted to a Python value of the appropriate
278 @defun gdb.history (number)
279 Return a value from @value{GDBN}'s value history (@pxref{Value
280 History}). The @var{number} argument indicates which history element to return.
281 If @var{number} is negative, then @value{GDBN} will take its absolute value
282 and count backward from the last element (i.e., the most recent element) to
283 find the value to return. If @var{number} is zero, then @value{GDBN} will
284 return the most recent element. If the element specified by @var{number}
285 doesn't exist in the value history, a @code{gdb.error} exception will be
288 If no exception is raised, the return value is always an instance of
289 @code{gdb.Value} (@pxref{Values From Inferior}).
292 @findex gdb.convenience_variable
293 @defun gdb.convenience_variable (name)
294 Return the value of the convenience variable (@pxref{Convenience
295 Vars}) named @var{name}. @var{name} must be a string. The name
296 should not include the @samp{$} that is used to mark a convenience
297 variable in an expression. If the convenience variable does not
298 exist, then @code{None} is returned.
301 @findex gdb.set_convenience_variable
302 @defun gdb.set_convenience_variable (name, value)
303 Set the value of the convenience variable (@pxref{Convenience Vars})
304 named @var{name}. @var{name} must be a string. The name should not
305 include the @samp{$} that is used to mark a convenience variable in an
306 expression. If @var{value} is @code{None}, then the convenience
307 variable is removed. Otherwise, if @var{value} is not a
308 @code{gdb.Value} (@pxref{Values From Inferior}), it is is converted
309 using the @code{gdb.Value} constructor.
312 @findex gdb.parse_and_eval
313 @defun gdb.parse_and_eval (expression)
314 Parse @var{expression}, which must be a string, as an expression in
315 the current language, evaluate it, and return the result as a
318 This function can be useful when implementing a new command
319 (@pxref{Commands In Python}), as it provides a way to parse the
320 command's argument as an expression. It is also useful simply to
324 @findex gdb.find_pc_line
325 @defun gdb.find_pc_line (pc)
326 Return the @code{gdb.Symtab_and_line} object corresponding to the
327 @var{pc} value. @xref{Symbol Tables In Python}. If an invalid
328 value of @var{pc} is passed as an argument, then the @code{symtab} and
329 @code{line} attributes of the returned @code{gdb.Symtab_and_line} object
330 will be @code{None} and 0 respectively. This is identical to
331 @code{gdb.current_progspace().find_pc_line(pc)} and is included for
332 historical compatibility.
335 @findex gdb.post_event
336 @defun gdb.post_event (event)
337 Put @var{event}, a callable object taking no arguments, into
338 @value{GDBN}'s internal event queue. This callable will be invoked at
339 some later point, during @value{GDBN}'s event processing. Events
340 posted using @code{post_event} will be run in the order in which they
341 were posted; however, there is no way to know when they will be
342 processed relative to other events inside @value{GDBN}.
344 @value{GDBN} is not thread-safe. If your Python program uses multiple
345 threads, you must be careful to only call @value{GDBN}-specific
346 functions in the @value{GDBN} thread. @code{post_event} ensures
350 (@value{GDBP}) python
354 > def __init__(self, message):
355 > self.message = message;
356 > def __call__(self):
357 > gdb.write(self.message)
359 >class MyThread1 (threading.Thread):
361 > gdb.post_event(Writer("Hello "))
363 >class MyThread2 (threading.Thread):
365 > gdb.post_event(Writer("World\n"))
370 (@value{GDBP}) Hello World
375 @defun gdb.write (string @r{[}, stream{]})
376 Print a string to @value{GDBN}'s paginated output stream. The
377 optional @var{stream} determines the stream to print to. The default
378 stream is @value{GDBN}'s standard output stream. Possible stream
385 @value{GDBN}'s standard output stream.
390 @value{GDBN}'s standard error stream.
395 @value{GDBN}'s log stream (@pxref{Logging Output}).
398 Writing to @code{sys.stdout} or @code{sys.stderr} will automatically
399 call this function and will automatically direct the output to the
405 Flush the buffer of a @value{GDBN} paginated stream so that the
406 contents are displayed immediately. @value{GDBN} will flush the
407 contents of a stream automatically when it encounters a newline in the
408 buffer. The optional @var{stream} determines the stream to flush. The
409 default stream is @value{GDBN}'s standard output stream. Possible
416 @value{GDBN}'s standard output stream.
421 @value{GDBN}'s standard error stream.
426 @value{GDBN}'s log stream (@pxref{Logging Output}).
430 Flushing @code{sys.stdout} or @code{sys.stderr} will automatically
431 call this function for the relevant stream.
434 @findex gdb.target_charset
435 @defun gdb.target_charset ()
436 Return the name of the current target character set (@pxref{Character
437 Sets}). This differs from @code{gdb.parameter('target-charset')} in
438 that @samp{auto} is never returned.
441 @findex gdb.target_wide_charset
442 @defun gdb.target_wide_charset ()
443 Return the name of the current target wide character set
444 (@pxref{Character Sets}). This differs from
445 @code{gdb.parameter('target-wide-charset')} in that @samp{auto} is
449 @findex gdb.solib_name
450 @defun gdb.solib_name (address)
451 Return the name of the shared library holding the given @var{address}
452 as a string, or @code{None}. This is identical to
453 @code{gdb.current_progspace().solib_name(address)} and is included for
454 historical compatibility.
457 @findex gdb.decode_line
458 @defun gdb.decode_line (@r{[}expression@r{]})
459 Return locations of the line specified by @var{expression}, or of the
460 current line if no argument was given. This function returns a Python
461 tuple containing two elements. The first element contains a string
462 holding any unparsed section of @var{expression} (or @code{None} if
463 the expression has been fully parsed). The second element contains
464 either @code{None} or another tuple that contains all the locations
465 that match the expression represented as @code{gdb.Symtab_and_line}
466 objects (@pxref{Symbol Tables In Python}). If @var{expression} is
467 provided, it is decoded the way that @value{GDBN}'s inbuilt
468 @code{break} or @code{edit} commands do (@pxref{Specify Location}).
471 @defun gdb.prompt_hook (current_prompt)
474 If @var{prompt_hook} is callable, @value{GDBN} will call the method
475 assigned to this operation before a prompt is displayed by
478 The parameter @code{current_prompt} contains the current @value{GDBN}
479 prompt. This method must return a Python string, or @code{None}. If
480 a string is returned, the @value{GDBN} prompt will be set to that
481 string. If @code{None} is returned, @value{GDBN} will continue to use
484 Some prompts cannot be substituted in @value{GDBN}. Secondary prompts
485 such as those used by readline for command input, and annotation
486 related prompts are prohibited from being changed.
489 @node Exception Handling
490 @subsubsection Exception Handling
491 @cindex python exceptions
492 @cindex exceptions, python
494 When executing the @code{python} command, Python exceptions
495 uncaught within the Python code are translated to calls to
496 @value{GDBN} error-reporting mechanism. If the command that called
497 @code{python} does not handle the error, @value{GDBN} will
498 terminate it and print an error message containing the Python
499 exception name, the associated value, and the Python call stack
500 backtrace at the point where the exception was raised. Example:
503 (@value{GDBP}) python print foo
504 Traceback (most recent call last):
505 File "<string>", line 1, in <module>
506 NameError: name 'foo' is not defined
509 @value{GDBN} errors that happen in @value{GDBN} commands invoked by
510 Python code are converted to Python exceptions. The type of the
511 Python exception depends on the error.
515 This is the base class for most exceptions generated by @value{GDBN}.
516 It is derived from @code{RuntimeError}, for compatibility with earlier
517 versions of @value{GDBN}.
519 If an error occurring in @value{GDBN} does not fit into some more
520 specific category, then the generated exception will have this type.
522 @item gdb.MemoryError
523 This is a subclass of @code{gdb.error} which is thrown when an
524 operation tried to access invalid memory in the inferior.
526 @item KeyboardInterrupt
527 User interrupt (via @kbd{C-c} or by typing @kbd{q} at a pagination
528 prompt) is translated to a Python @code{KeyboardInterrupt} exception.
531 In all cases, your exception handler will see the @value{GDBN} error
532 message as its value and the Python call stack backtrace at the Python
533 statement closest to where the @value{GDBN} error occured as the
537 When implementing @value{GDBN} commands in Python via
538 @code{gdb.Command}, or functions via @code{gdb.Function}, it is useful
539 to be able to throw an exception that doesn't cause a traceback to be
540 printed. For example, the user may have invoked the command
541 incorrectly. @value{GDBN} provides a special exception class that can
542 be used for this purpose.
546 When thrown from a command or function, this exception will cause the
547 command or function to fail, but the Python stack will not be
548 displayed. @value{GDBN} does not throw this exception itself, but
549 rather recognizes it when thrown from user Python code. Example:
553 >class HelloWorld (gdb.Command):
554 > """Greet the whole world."""
555 > def __init__ (self):
556 > super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)
557 > def invoke (self, args, from_tty):
558 > argv = gdb.string_to_argv (args)
559 > if len (argv) != 0:
560 > raise gdb.GdbError ("hello-world takes no arguments")
561 > print "Hello, World!"
565 hello-world takes no arguments
569 @node Values From Inferior
570 @subsubsection Values From Inferior
571 @cindex values from inferior, with Python
572 @cindex python, working with values from inferior
574 @cindex @code{gdb.Value}
575 @value{GDBN} provides values it obtains from the inferior program in
576 an object of type @code{gdb.Value}. @value{GDBN} uses this object
577 for its internal bookkeeping of the inferior's values, and for
578 fetching values when necessary.
580 Inferior values that are simple scalars can be used directly in
581 Python expressions that are valid for the value's data type. Here's
582 an example for an integer or floating-point value @code{some_val}:
589 As result of this, @code{bar} will also be a @code{gdb.Value} object
590 whose values are of the same type as those of @code{some_val}. Valid
591 Python operations can also be performed on @code{gdb.Value} objects
592 representing a @code{struct} or @code{class} object. For such cases,
593 the overloaded operator (if present), is used to perform the operation.
594 For example, if @code{val1} and @code{val2} are @code{gdb.Value} objects
595 representing instances of a @code{class} which overloads the @code{+}
596 operator, then one can use the @code{+} operator in their Python script
604 The result of the operation @code{val3} is also a @code{gdb.Value}
605 object corresponding to the value returned by the overloaded @code{+}
606 operator. In general, overloaded operators are invoked for the
607 following operations: @code{+} (binary addition), @code{-} (binary
608 subtraction), @code{*} (multiplication), @code{/}, @code{%}, @code{<<},
609 @code{>>}, @code{|}, @code{&}, @code{^}.
611 Inferior values that are structures or instances of some class can
612 be accessed using the Python @dfn{dictionary syntax}. For example, if
613 @code{some_val} is a @code{gdb.Value} instance holding a structure, you
614 can access its @code{foo} element with:
617 bar = some_val['foo']
620 @cindex getting structure elements using gdb.Field objects as subscripts
621 Again, @code{bar} will also be a @code{gdb.Value} object. Structure
622 elements can also be accessed by using @code{gdb.Field} objects as
623 subscripts (@pxref{Types In Python}, for more information on
624 @code{gdb.Field} objects). For example, if @code{foo_field} is a
625 @code{gdb.Field} object corresponding to element @code{foo} of the above
626 structure, then @code{bar} can also be accessed as follows:
629 bar = some_val[foo_field]
632 A @code{gdb.Value} that represents a function can be executed via
633 inferior function call. Any arguments provided to the call must match
634 the function's prototype, and must be provided in the order specified
637 For example, @code{some_val} is a @code{gdb.Value} instance
638 representing a function that takes two integers as arguments. To
639 execute this function, call it like so:
642 result = some_val (10,20)
645 Any values returned from a function call will be stored as a
648 The following attributes are provided:
650 @defvar Value.address
651 If this object is addressable, this read-only attribute holds a
652 @code{gdb.Value} object representing the address. Otherwise,
653 this attribute holds @code{None}.
656 @cindex optimized out value in Python
657 @defvar Value.is_optimized_out
658 This read-only boolean attribute is true if the compiler optimized out
659 this value, thus it is not available for fetching from the inferior.
663 The type of this @code{gdb.Value}. The value of this attribute is a
664 @code{gdb.Type} object (@pxref{Types In Python}).
667 @defvar Value.dynamic_type
668 The dynamic type of this @code{gdb.Value}. This uses the object's
669 virtual table and the C@t{++} run-time type information
670 (@acronym{RTTI}) to determine the dynamic type of the value. If this
671 value is of class type, it will return the class in which the value is
672 embedded, if any. If this value is of pointer or reference to a class
673 type, it will compute the dynamic type of the referenced object, and
674 return a pointer or reference to that type, respectively. In all
675 other cases, it will return the value's static type.
677 Note that this feature will only work when debugging a C@t{++} program
678 that includes @acronym{RTTI} for the object in question. Otherwise,
679 it will just return the static type of the value as in @kbd{ptype foo}
680 (@pxref{Symbols, ptype}).
683 @defvar Value.is_lazy
684 The value of this read-only boolean attribute is @code{True} if this
685 @code{gdb.Value} has not yet been fetched from the inferior.
686 @value{GDBN} does not fetch values until necessary, for efficiency.
690 myval = gdb.parse_and_eval ('somevar')
693 The value of @code{somevar} is not fetched at this time. It will be
694 fetched when the value is needed, or when the @code{fetch_lazy}
698 The following methods are provided:
700 @defun Value.__init__ (@var{val})
701 Many Python values can be converted directly to a @code{gdb.Value} via
702 this object initializer. Specifically:
706 A Python boolean is converted to the boolean type from the current
710 A Python integer is converted to the C @code{long} type for the
711 current architecture.
714 A Python long is converted to the C @code{long long} type for the
715 current architecture.
718 A Python float is converted to the C @code{double} type for the
719 current architecture.
722 A Python string is converted to a target string in the current target
723 language using the current target encoding.
724 If a character cannot be represented in the current target encoding,
725 then an exception is thrown.
727 @item @code{gdb.Value}
728 If @code{val} is a @code{gdb.Value}, then a copy of the value is made.
730 @item @code{gdb.LazyString}
731 If @code{val} is a @code{gdb.LazyString} (@pxref{Lazy Strings In
732 Python}), then the lazy string's @code{value} method is called, and
737 @defun Value.__init__ (@var{val}, @var{type})
738 This second form of the @code{gdb.Value} constructor returns a
739 @code{gdb.Value} of type @var{type} where the value contents are taken
740 from the Python buffer object specified by @var{val}. The number of
741 bytes in the Python buffer object must be greater than or equal to the
745 @defun Value.cast (type)
746 Return a new instance of @code{gdb.Value} that is the result of
747 casting this instance to the type described by @var{type}, which must
748 be a @code{gdb.Type} object. If the cast cannot be performed for some
749 reason, this method throws an exception.
752 @defun Value.dereference ()
753 For pointer data types, this method returns a new @code{gdb.Value} object
754 whose contents is the object pointed to by the pointer. For example, if
755 @code{foo} is a C pointer to an @code{int}, declared in your C program as
762 then you can use the corresponding @code{gdb.Value} to access what
763 @code{foo} points to like this:
766 bar = foo.dereference ()
769 The result @code{bar} will be a @code{gdb.Value} object holding the
770 value pointed to by @code{foo}.
772 A similar function @code{Value.referenced_value} exists which also
773 returns @code{gdb.Value} objects corresponding to the values pointed to
774 by pointer values (and additionally, values referenced by reference
775 values). However, the behavior of @code{Value.dereference}
776 differs from @code{Value.referenced_value} by the fact that the
777 behavior of @code{Value.dereference} is identical to applying the C
778 unary operator @code{*} on a given value. For example, consider a
779 reference to a pointer @code{ptrref}, declared in your C@t{++} program
787 intptr &ptrref = ptr;
790 Though @code{ptrref} is a reference value, one can apply the method
791 @code{Value.dereference} to the @code{gdb.Value} object corresponding
792 to it and obtain a @code{gdb.Value} which is identical to that
793 corresponding to @code{val}. However, if you apply the method
794 @code{Value.referenced_value}, the result would be a @code{gdb.Value}
795 object identical to that corresponding to @code{ptr}.
798 py_ptrref = gdb.parse_and_eval ("ptrref")
799 py_val = py_ptrref.dereference ()
800 py_ptr = py_ptrref.referenced_value ()
803 The @code{gdb.Value} object @code{py_val} is identical to that
804 corresponding to @code{val}, and @code{py_ptr} is identical to that
805 corresponding to @code{ptr}. In general, @code{Value.dereference} can
806 be applied whenever the C unary operator @code{*} can be applied
807 to the corresponding C value. For those cases where applying both
808 @code{Value.dereference} and @code{Value.referenced_value} is allowed,
809 the results obtained need not be identical (as we have seen in the above
810 example). The results are however identical when applied on
811 @code{gdb.Value} objects corresponding to pointers (@code{gdb.Value}
812 objects with type code @code{TYPE_CODE_PTR}) in a C/C@t{++} program.
815 @defun Value.referenced_value ()
816 For pointer or reference data types, this method returns a new
817 @code{gdb.Value} object corresponding to the value referenced by the
818 pointer/reference value. For pointer data types,
819 @code{Value.dereference} and @code{Value.referenced_value} produce
820 identical results. The difference between these methods is that
821 @code{Value.dereference} cannot get the values referenced by reference
822 values. For example, consider a reference to an @code{int}, declared
823 in your C@t{++} program as
831 then applying @code{Value.dereference} to the @code{gdb.Value} object
832 corresponding to @code{ref} will result in an error, while applying
833 @code{Value.referenced_value} will result in a @code{gdb.Value} object
834 identical to that corresponding to @code{val}.
837 py_ref = gdb.parse_and_eval ("ref")
838 er_ref = py_ref.dereference () # Results in error
839 py_val = py_ref.referenced_value () # Returns the referenced value
842 The @code{gdb.Value} object @code{py_val} is identical to that
843 corresponding to @code{val}.
846 @defun Value.reference_value ()
847 Return a @code{gdb.Value} object which is a reference to the value
848 encapsulated by this instance.
851 @defun Value.const_value ()
852 Return a @code{gdb.Value} object which is a @code{const} version of the
853 value encapsulated by this instance.
856 @defun Value.dynamic_cast (type)
857 Like @code{Value.cast}, but works as if the C@t{++} @code{dynamic_cast}
858 operator were used. Consult a C@t{++} reference for details.
861 @defun Value.reinterpret_cast (type)
862 Like @code{Value.cast}, but works as if the C@t{++} @code{reinterpret_cast}
863 operator were used. Consult a C@t{++} reference for details.
866 @defun Value.format_string (...)
867 Convert a @code{gdb.Value} to a string, similarly to what the @code{print}
868 command does. Invoked with no arguments, this is equivalent to calling
869 the @code{str} function on the @code{gdb.Value}. The representation of
870 the same value may change across different versions of @value{GDBN}, so
871 you shouldn't, for instance, parse the strings returned by this method.
873 All the arguments are keyword only. If an argument is not specified, the
874 current global default setting is used.
878 @code{True} if pretty-printers (@pxref{Pretty Printing}) should not be
879 used to format the value. @code{False} if enabled pretty-printers
880 matching the type represented by the @code{gdb.Value} should be used to
884 @code{True} if arrays should be pretty printed to be more convenient to
885 read, @code{False} if they shouldn't (see @code{set print array} in
886 @ref{Print Settings}).
889 @code{True} if structs should be pretty printed to be more convenient to
890 read, @code{False} if they shouldn't (see @code{set print pretty} in
891 @ref{Print Settings}).
894 @code{True} if array indexes should be included in the string
895 representation of arrays, @code{False} if they shouldn't (see @code{set
896 print array-indexes} in @ref{Print Settings}).
899 @code{True} if the string representation of a pointer should include the
900 corresponding symbol name (if one exists), @code{False} if it shouldn't
901 (see @code{set print symbol} in @ref{Print Settings}).
904 @code{True} if unions which are contained in other structures or unions
905 should be expanded, @code{False} if they shouldn't (see @code{set print
906 union} in @ref{Print Settings}).
909 @code{True} if C@t{++} references should be resolved to the value they
910 refer to, @code{False} (the default) if they shouldn't. Note that, unlike
911 for the @code{print} command, references are not automatically expanded
912 when using the @code{format_string} method or the @code{str}
913 function. There is no global @code{print} setting to change the default
917 @code{True} if the representation of a pointer to an object should
918 identify the @emph{actual} (derived) type of the object rather than the
919 @emph{declared} type, using the virtual function table. @code{False} if
920 the @emph{declared} type should be used. (See @code{set print object} in
921 @ref{Print Settings}).
924 @code{True} if static members should be included in the string
925 representation of a C@t{++} object, @code{False} if they shouldn't (see
926 @code{set print static-members} in @ref{Print Settings}).
929 Number of array elements to print, or @code{0} to print an unlimited
930 number of elements (see @code{set print elements} in @ref{Print
934 The maximum depth to print for nested structs and unions, or @code{-1}
935 to print an unlimited number of elements (see @code{set print
936 max-depth} in @ref{Print Settings}).
938 @item repeat_threshold
939 Set the threshold for suppressing display of repeated array elements, or
940 @code{0} to represent all elements, even if repeated. (See @code{set
941 print repeats} in @ref{Print Settings}).
944 A string containing a single character representing the format to use for
945 the returned string. For instance, @code{'x'} is equivalent to using the
946 @value{GDBN} command @code{print} with the @code{/x} option and formats
947 the value as a hexadecimal number.
951 @defun Value.string (@r{[}encoding@r{[}, errors@r{[}, length@r{]]]})
952 If this @code{gdb.Value} represents a string, then this method
953 converts the contents to a Python string. Otherwise, this method will
956 Values are interpreted as strings according to the rules of the
957 current language. If the optional length argument is given, the
958 string will be converted to that length, and will include any embedded
959 zeroes that the string may contain. Otherwise, for languages
960 where the string is zero-terminated, the entire string will be
963 For example, in C-like languages, a value is a string if it is a pointer
964 to or an array of characters or ints of type @code{wchar_t}, @code{char16_t},
967 If the optional @var{encoding} argument is given, it must be a string
968 naming the encoding of the string in the @code{gdb.Value}, such as
969 @code{"ascii"}, @code{"iso-8859-6"} or @code{"utf-8"}. It accepts
970 the same encodings as the corresponding argument to Python's
971 @code{string.decode} method, and the Python codec machinery will be used
972 to convert the string. If @var{encoding} is not given, or if
973 @var{encoding} is the empty string, then either the @code{target-charset}
974 (@pxref{Character Sets}) will be used, or a language-specific encoding
975 will be used, if the current language is able to supply one.
977 The optional @var{errors} argument is the same as the corresponding
978 argument to Python's @code{string.decode} method.
980 If the optional @var{length} argument is given, the string will be
981 fetched and converted to the given length.
984 @defun Value.lazy_string (@r{[}encoding @r{[}, length@r{]]})
985 If this @code{gdb.Value} represents a string, then this method
986 converts the contents to a @code{gdb.LazyString} (@pxref{Lazy Strings
987 In Python}). Otherwise, this method will throw an exception.
989 If the optional @var{encoding} argument is given, it must be a string
990 naming the encoding of the @code{gdb.LazyString}. Some examples are:
991 @samp{ascii}, @samp{iso-8859-6} or @samp{utf-8}. If the
992 @var{encoding} argument is an encoding that @value{GDBN} does
993 recognize, @value{GDBN} will raise an error.
995 When a lazy string is printed, the @value{GDBN} encoding machinery is
996 used to convert the string during printing. If the optional
997 @var{encoding} argument is not provided, or is an empty string,
998 @value{GDBN} will automatically select the encoding most suitable for
999 the string type. For further information on encoding in @value{GDBN}
1000 please see @ref{Character Sets}.
1002 If the optional @var{length} argument is given, the string will be
1003 fetched and encoded to the length of characters specified. If
1004 the @var{length} argument is not provided, the string will be fetched
1005 and encoded until a null of appropriate width is found.
1008 @defun Value.fetch_lazy ()
1009 If the @code{gdb.Value} object is currently a lazy value
1010 (@code{gdb.Value.is_lazy} is @code{True}), then the value is
1011 fetched from the inferior. Any errors that occur in the process
1012 will produce a Python exception.
1014 If the @code{gdb.Value} object is not a lazy value, this method
1017 This method does not return a value.
1021 @node Types In Python
1022 @subsubsection Types In Python
1023 @cindex types in Python
1024 @cindex Python, working with types
1027 @value{GDBN} represents types from the inferior using the class
1030 The following type-related functions are available in the @code{gdb}
1033 @findex gdb.lookup_type
1034 @defun gdb.lookup_type (name @r{[}, block@r{]})
1035 This function looks up a type by its @var{name}, which must be a string.
1037 If @var{block} is given, then @var{name} is looked up in that scope.
1038 Otherwise, it is searched for globally.
1040 Ordinarily, this function will return an instance of @code{gdb.Type}.
1041 If the named type cannot be found, it will throw an exception.
1044 If the type is a structure or class type, or an enum type, the fields
1045 of that type can be accessed using the Python @dfn{dictionary syntax}.
1046 For example, if @code{some_type} is a @code{gdb.Type} instance holding
1047 a structure type, you can access its @code{foo} field with:
1050 bar = some_type['foo']
1053 @code{bar} will be a @code{gdb.Field} object; see below under the
1054 description of the @code{Type.fields} method for a description of the
1055 @code{gdb.Field} class.
1057 An instance of @code{Type} has the following attributes:
1059 @defvar Type.alignof
1060 The alignment of this type, in bytes. Type alignment comes from the
1061 debugging information; if it was not specified, then @value{GDBN} will
1062 use the relevant ABI to try to determine the alignment. In some
1063 cases, even this is not possible, and zero will be returned.
1067 The type code for this type. The type code will be one of the
1068 @code{TYPE_CODE_} constants defined below.
1071 @defvar Type.dynamic
1072 A boolean indicating whether this type is dynamic. In some
1073 situations, such as Rust @code{enum} types or Ada variant records, the
1074 concrete type of a value may vary depending on its contents.
1078 The name of this type. If this type has no name, then @code{None}
1083 The size of this type, in target @code{char} units. Usually, a
1084 target's @code{char} type will be an 8-bit byte. However, on some
1085 unusual platforms, this type may have a different size. A dynamic
1086 type may not have a fixed size; in this case, this attribute's value
1087 will be @code{None}.
1091 The tag name for this type. The tag name is the name after
1092 @code{struct}, @code{union}, or @code{enum} in C and C@t{++}; not all
1093 languages have this concept. If this type has no tag name, then
1094 @code{None} is returned.
1097 @defvar Type.objfile
1098 The @code{gdb.Objfile} that this type was defined in, or @code{None} if
1099 there is no associated objfile.
1102 The following methods are provided:
1104 @defun Type.fields ()
1105 For structure and union types, this method returns the fields. Range
1106 types have two fields, the minimum and maximum values. Enum types
1107 have one field per enum constant. Function and method types have one
1108 field per parameter. The base types of C@t{++} classes are also
1109 represented as fields. If the type has no fields, or does not fit
1110 into one of these categories, an empty sequence will be returned.
1112 Each field is a @code{gdb.Field} object, with some pre-defined attributes:
1115 This attribute is not available for @code{enum} or @code{static}
1116 (as in C@t{++}) fields. The value is the position, counting
1117 in bits, from the start of the containing type. Note that, in a
1118 dynamic type, the position of a field may not be constant. In this
1119 case, the value will be @code{None}.
1122 This attribute is only available for @code{enum} fields, and its value
1123 is the enumeration member's integer representation.
1126 The name of the field, or @code{None} for anonymous fields.
1129 This is @code{True} if the field is artificial, usually meaning that
1130 it was provided by the compiler and not the user. This attribute is
1131 always provided, and is @code{False} if the field is not artificial.
1134 This is @code{True} if the field represents a base class of a C@t{++}
1135 structure. This attribute is always provided, and is @code{False}
1136 if the field is not a base class of the type that is the argument of
1137 @code{fields}, or if that type was not a C@t{++} class.
1140 If the field is packed, or is a bitfield, then this will have a
1141 non-zero value, which is the size of the field in bits. Otherwise,
1142 this will be zero; in this case the field's size is given by its type.
1145 The type of the field. This is usually an instance of @code{Type},
1146 but it can be @code{None} in some situations.
1149 The type which contains this field. This is an instance of
1154 @defun Type.array (@var{n1} @r{[}, @var{n2}@r{]})
1155 Return a new @code{gdb.Type} object which represents an array of this
1156 type. If one argument is given, it is the inclusive upper bound of
1157 the array; in this case the lower bound is zero. If two arguments are
1158 given, the first argument is the lower bound of the array, and the
1159 second argument is the upper bound of the array. An array's length
1160 must not be negative, but the bounds can be.
1163 @defun Type.vector (@var{n1} @r{[}, @var{n2}@r{]})
1164 Return a new @code{gdb.Type} object which represents a vector of this
1165 type. If one argument is given, it is the inclusive upper bound of
1166 the vector; in this case the lower bound is zero. If two arguments are
1167 given, the first argument is the lower bound of the vector, and the
1168 second argument is the upper bound of the vector. A vector's length
1169 must not be negative, but the bounds can be.
1171 The difference between an @code{array} and a @code{vector} is that
1172 arrays behave like in C: when used in expressions they decay to a pointer
1173 to the first element whereas vectors are treated as first class values.
1176 @defun Type.const ()
1177 Return a new @code{gdb.Type} object which represents a
1178 @code{const}-qualified variant of this type.
1181 @defun Type.volatile ()
1182 Return a new @code{gdb.Type} object which represents a
1183 @code{volatile}-qualified variant of this type.
1186 @defun Type.unqualified ()
1187 Return a new @code{gdb.Type} object which represents an unqualified
1188 variant of this type. That is, the result is neither @code{const} nor
1192 @defun Type.range ()
1193 Return a Python @code{Tuple} object that contains two elements: the
1194 low bound of the argument type and the high bound of that type. If
1195 the type does not have a range, @value{GDBN} will raise a
1196 @code{gdb.error} exception (@pxref{Exception Handling}).
1199 @defun Type.reference ()
1200 Return a new @code{gdb.Type} object which represents a reference to this
1204 @defun Type.pointer ()
1205 Return a new @code{gdb.Type} object which represents a pointer to this
1209 @defun Type.strip_typedefs ()
1210 Return a new @code{gdb.Type} that represents the real type,
1211 after removing all layers of typedefs.
1214 @defun Type.target ()
1215 Return a new @code{gdb.Type} object which represents the target type
1218 For a pointer type, the target type is the type of the pointed-to
1219 object. For an array type (meaning C-like arrays), the target type is
1220 the type of the elements of the array. For a function or method type,
1221 the target type is the type of the return value. For a complex type,
1222 the target type is the type of the elements. For a typedef, the
1223 target type is the aliased type.
1225 If the type does not have a target, this method will throw an
1229 @defun Type.template_argument (n @r{[}, block@r{]})
1230 If this @code{gdb.Type} is an instantiation of a template, this will
1231 return a new @code{gdb.Value} or @code{gdb.Type} which represents the
1232 value of the @var{n}th template argument (indexed starting at 0).
1234 If this @code{gdb.Type} is not a template type, or if the type has fewer
1235 than @var{n} template arguments, this will throw an exception.
1236 Ordinarily, only C@t{++} code will have template types.
1238 If @var{block} is given, then @var{name} is looked up in that scope.
1239 Otherwise, it is searched for globally.
1242 @defun Type.optimized_out ()
1243 Return @code{gdb.Value} instance of this type whose value is optimized
1244 out. This allows a frame decorator to indicate that the value of an
1245 argument or a local variable is not known.
1248 Each type has a code, which indicates what category this type falls
1249 into. The available type categories are represented by constants
1250 defined in the @code{gdb} module:
1253 @vindex TYPE_CODE_PTR
1254 @item gdb.TYPE_CODE_PTR
1255 The type is a pointer.
1257 @vindex TYPE_CODE_ARRAY
1258 @item gdb.TYPE_CODE_ARRAY
1259 The type is an array.
1261 @vindex TYPE_CODE_STRUCT
1262 @item gdb.TYPE_CODE_STRUCT
1263 The type is a structure.
1265 @vindex TYPE_CODE_UNION
1266 @item gdb.TYPE_CODE_UNION
1267 The type is a union.
1269 @vindex TYPE_CODE_ENUM
1270 @item gdb.TYPE_CODE_ENUM
1271 The type is an enum.
1273 @vindex TYPE_CODE_FLAGS
1274 @item gdb.TYPE_CODE_FLAGS
1275 A bit flags type, used for things such as status registers.
1277 @vindex TYPE_CODE_FUNC
1278 @item gdb.TYPE_CODE_FUNC
1279 The type is a function.
1281 @vindex TYPE_CODE_INT
1282 @item gdb.TYPE_CODE_INT
1283 The type is an integer type.
1285 @vindex TYPE_CODE_FLT
1286 @item gdb.TYPE_CODE_FLT
1287 A floating point type.
1289 @vindex TYPE_CODE_VOID
1290 @item gdb.TYPE_CODE_VOID
1291 The special type @code{void}.
1293 @vindex TYPE_CODE_SET
1294 @item gdb.TYPE_CODE_SET
1297 @vindex TYPE_CODE_RANGE
1298 @item gdb.TYPE_CODE_RANGE
1299 A range type, that is, an integer type with bounds.
1301 @vindex TYPE_CODE_STRING
1302 @item gdb.TYPE_CODE_STRING
1303 A string type. Note that this is only used for certain languages with
1304 language-defined string types; C strings are not represented this way.
1306 @vindex TYPE_CODE_BITSTRING
1307 @item gdb.TYPE_CODE_BITSTRING
1308 A string of bits. It is deprecated.
1310 @vindex TYPE_CODE_ERROR
1311 @item gdb.TYPE_CODE_ERROR
1312 An unknown or erroneous type.
1314 @vindex TYPE_CODE_METHOD
1315 @item gdb.TYPE_CODE_METHOD
1316 A method type, as found in C@t{++}.
1318 @vindex TYPE_CODE_METHODPTR
1319 @item gdb.TYPE_CODE_METHODPTR
1320 A pointer-to-member-function.
1322 @vindex TYPE_CODE_MEMBERPTR
1323 @item gdb.TYPE_CODE_MEMBERPTR
1324 A pointer-to-member.
1326 @vindex TYPE_CODE_REF
1327 @item gdb.TYPE_CODE_REF
1330 @vindex TYPE_CODE_RVALUE_REF
1331 @item gdb.TYPE_CODE_RVALUE_REF
1332 A C@t{++}11 rvalue reference type.
1334 @vindex TYPE_CODE_CHAR
1335 @item gdb.TYPE_CODE_CHAR
1338 @vindex TYPE_CODE_BOOL
1339 @item gdb.TYPE_CODE_BOOL
1342 @vindex TYPE_CODE_COMPLEX
1343 @item gdb.TYPE_CODE_COMPLEX
1344 A complex float type.
1346 @vindex TYPE_CODE_TYPEDEF
1347 @item gdb.TYPE_CODE_TYPEDEF
1348 A typedef to some other type.
1350 @vindex TYPE_CODE_NAMESPACE
1351 @item gdb.TYPE_CODE_NAMESPACE
1352 A C@t{++} namespace.
1354 @vindex TYPE_CODE_DECFLOAT
1355 @item gdb.TYPE_CODE_DECFLOAT
1356 A decimal floating point type.
1358 @vindex TYPE_CODE_INTERNAL_FUNCTION
1359 @item gdb.TYPE_CODE_INTERNAL_FUNCTION
1360 A function internal to @value{GDBN}. This is the type used to represent
1361 convenience functions.
1364 Further support for types is provided in the @code{gdb.types}
1365 Python module (@pxref{gdb.types}).
1367 @node Pretty Printing API
1368 @subsubsection Pretty Printing API
1369 @cindex python pretty printing api
1371 A pretty-printer is just an object that holds a value and implements a
1372 specific interface, defined here. An example output is provided
1373 (@pxref{Pretty Printing}).
1375 @defun pretty_printer.children (self)
1376 @value{GDBN} will call this method on a pretty-printer to compute the
1377 children of the pretty-printer's value.
1379 This method must return an object conforming to the Python iterator
1380 protocol. Each item returned by the iterator must be a tuple holding
1381 two elements. The first element is the ``name'' of the child; the
1382 second element is the child's value. The value can be any Python
1383 object which is convertible to a @value{GDBN} value.
1385 This method is optional. If it does not exist, @value{GDBN} will act
1386 as though the value has no children.
1388 For efficiency, the @code{children} method should lazily compute its
1389 results. This will let @value{GDBN} read as few elements as
1390 necessary, for example when various print settings (@pxref{Print
1391 Settings}) or @code{-var-list-children} (@pxref{GDB/MI Variable
1392 Objects}) limit the number of elements to be displayed.
1394 Children may be hidden from display based on the value of @samp{set
1395 print max-depth} (@pxref{Print Settings}).
1398 @defun pretty_printer.display_hint (self)
1399 The CLI may call this method and use its result to change the
1400 formatting of a value. The result will also be supplied to an MI
1401 consumer as a @samp{displayhint} attribute of the variable being
1404 This method is optional. If it does exist, this method must return a
1405 string or the special value @code{None}.
1407 Some display hints are predefined by @value{GDBN}:
1411 Indicate that the object being printed is ``array-like''. The CLI
1412 uses this to respect parameters such as @code{set print elements} and
1413 @code{set print array}.
1416 Indicate that the object being printed is ``map-like'', and that the
1417 children of this value can be assumed to alternate between keys and
1421 Indicate that the object being printed is ``string-like''. If the
1422 printer's @code{to_string} method returns a Python string of some
1423 kind, then @value{GDBN} will call its internal language-specific
1424 string-printing function to format the string. For the CLI this means
1425 adding quotation marks, possibly escaping some characters, respecting
1426 @code{set print elements}, and the like.
1429 The special value @code{None} causes @value{GDBN} to apply the default
1433 @defun pretty_printer.to_string (self)
1434 @value{GDBN} will call this method to display the string
1435 representation of the value passed to the object's constructor.
1437 When printing from the CLI, if the @code{to_string} method exists,
1438 then @value{GDBN} will prepend its result to the values returned by
1439 @code{children}. Exactly how this formatting is done is dependent on
1440 the display hint, and may change as more hints are added. Also,
1441 depending on the print settings (@pxref{Print Settings}), the CLI may
1442 print just the result of @code{to_string} in a stack trace, omitting
1443 the result of @code{children}.
1445 If this method returns a string, it is printed verbatim.
1447 Otherwise, if this method returns an instance of @code{gdb.Value},
1448 then @value{GDBN} prints this value. This may result in a call to
1449 another pretty-printer.
1451 If instead the method returns a Python value which is convertible to a
1452 @code{gdb.Value}, then @value{GDBN} performs the conversion and prints
1453 the resulting value. Again, this may result in a call to another
1454 pretty-printer. Python scalars (integers, floats, and booleans) and
1455 strings are convertible to @code{gdb.Value}; other types are not.
1457 Finally, if this method returns @code{None} then no further operations
1458 are peformed in this method and nothing is printed.
1460 If the result is not one of these types, an exception is raised.
1463 @value{GDBN} provides a function which can be used to look up the
1464 default pretty-printer for a @code{gdb.Value}:
1466 @findex gdb.default_visualizer
1467 @defun gdb.default_visualizer (value)
1468 This function takes a @code{gdb.Value} object as an argument. If a
1469 pretty-printer for this value exists, then it is returned. If no such
1470 printer exists, then this returns @code{None}.
1473 @node Selecting Pretty-Printers
1474 @subsubsection Selecting Pretty-Printers
1475 @cindex selecting python pretty-printers
1477 @value{GDBN} provides several ways to register a pretty-printer:
1478 globally, per program space, and per objfile. When choosing how to
1479 register your pretty-printer, a good rule is to register it with the
1480 smallest scope possible: that is prefer a specific objfile first, then
1481 a program space, and only register a printer globally as a last
1484 @findex gdb.pretty_printers
1485 @defvar gdb.pretty_printers
1486 The Python list @code{gdb.pretty_printers} contains an array of
1487 functions or callable objects that have been registered via addition
1488 as a pretty-printer. Printers in this list are called @code{global}
1489 printers, they're available when debugging all inferiors.
1492 Each @code{gdb.Progspace} contains a @code{pretty_printers} attribute.
1493 Each @code{gdb.Objfile} also contains a @code{pretty_printers}
1496 Each function on these lists is passed a single @code{gdb.Value}
1497 argument and should return a pretty-printer object conforming to the
1498 interface definition above (@pxref{Pretty Printing API}). If a function
1499 cannot create a pretty-printer for the value, it should return
1502 @value{GDBN} first checks the @code{pretty_printers} attribute of each
1503 @code{gdb.Objfile} in the current program space and iteratively calls
1504 each enabled lookup routine in the list for that @code{gdb.Objfile}
1505 until it receives a pretty-printer object.
1506 If no pretty-printer is found in the objfile lists, @value{GDBN} then
1507 searches the pretty-printer list of the current program space,
1508 calling each enabled function until an object is returned.
1509 After these lists have been exhausted, it tries the global
1510 @code{gdb.pretty_printers} list, again calling each enabled function until an
1513 The order in which the objfiles are searched is not specified. For a
1514 given list, functions are always invoked from the head of the list,
1515 and iterated over sequentially until the end of the list, or a printer
1518 For various reasons a pretty-printer may not work.
1519 For example, the underlying data structure may have changed and
1520 the pretty-printer is out of date.
1522 The consequences of a broken pretty-printer are severe enough that
1523 @value{GDBN} provides support for enabling and disabling individual
1524 printers. For example, if @code{print frame-arguments} is on,
1525 a backtrace can become highly illegible if any argument is printed
1526 with a broken printer.
1528 Pretty-printers are enabled and disabled by attaching an @code{enabled}
1529 attribute to the registered function or callable object. If this attribute
1530 is present and its value is @code{False}, the printer is disabled, otherwise
1531 the printer is enabled.
1533 @node Writing a Pretty-Printer
1534 @subsubsection Writing a Pretty-Printer
1535 @cindex writing a pretty-printer
1537 A pretty-printer consists of two parts: a lookup function to detect
1538 if the type is supported, and the printer itself.
1540 Here is an example showing how a @code{std::string} printer might be
1541 written. @xref{Pretty Printing API}, for details on the API this class
1545 class StdStringPrinter(object):
1546 "Print a std::string"
1548 def __init__(self, val):
1551 def to_string(self):
1552 return self.val['_M_dataplus']['_M_p']
1554 def display_hint(self):
1558 And here is an example showing how a lookup function for the printer
1559 example above might be written.
1562 def str_lookup_function(val):
1563 lookup_tag = val.type.tag
1564 if lookup_tag == None:
1566 regex = re.compile("^std::basic_string<char,.*>$")
1567 if regex.match(lookup_tag):
1568 return StdStringPrinter(val)
1572 The example lookup function extracts the value's type, and attempts to
1573 match it to a type that it can pretty-print. If it is a type the
1574 printer can pretty-print, it will return a printer object. If not, it
1575 returns @code{None}.
1577 We recommend that you put your core pretty-printers into a Python
1578 package. If your pretty-printers are for use with a library, we
1579 further recommend embedding a version number into the package name.
1580 This practice will enable @value{GDBN} to load multiple versions of
1581 your pretty-printers at the same time, because they will have
1584 You should write auto-loaded code (@pxref{Python Auto-loading}) such that it
1585 can be evaluated multiple times without changing its meaning. An
1586 ideal auto-load file will consist solely of @code{import}s of your
1587 printer modules, followed by a call to a register pretty-printers with
1588 the current objfile.
1590 Taken as a whole, this approach will scale nicely to multiple
1591 inferiors, each potentially using a different library version.
1592 Embedding a version number in the Python package name will ensure that
1593 @value{GDBN} is able to load both sets of printers simultaneously.
1594 Then, because the search for pretty-printers is done by objfile, and
1595 because your auto-loaded code took care to register your library's
1596 printers with a specific objfile, @value{GDBN} will find the correct
1597 printers for the specific version of the library used by each
1600 To continue the @code{std::string} example (@pxref{Pretty Printing API}),
1601 this code might appear in @code{gdb.libstdcxx.v6}:
1604 def register_printers(objfile):
1605 objfile.pretty_printers.append(str_lookup_function)
1609 And then the corresponding contents of the auto-load file would be:
1612 import gdb.libstdcxx.v6
1613 gdb.libstdcxx.v6.register_printers(gdb.current_objfile())
1616 The previous example illustrates a basic pretty-printer.
1617 There are a few things that can be improved on.
1618 The printer doesn't have a name, making it hard to identify in a
1619 list of installed printers. The lookup function has a name, but
1620 lookup functions can have arbitrary, even identical, names.
1622 Second, the printer only handles one type, whereas a library typically has
1623 several types. One could install a lookup function for each desired type
1624 in the library, but one could also have a single lookup function recognize
1625 several types. The latter is the conventional way this is handled.
1626 If a pretty-printer can handle multiple data types, then its
1627 @dfn{subprinters} are the printers for the individual data types.
1629 The @code{gdb.printing} module provides a formal way of solving these
1630 problems (@pxref{gdb.printing}).
1631 Here is another example that handles multiple types.
1633 These are the types we are going to pretty-print:
1636 struct foo @{ int a, b; @};
1637 struct bar @{ struct foo x, y; @};
1640 Here are the printers:
1644 """Print a foo object."""
1646 def __init__(self, val):
1649 def to_string(self):
1650 return ("a=<" + str(self.val["a"]) +
1651 "> b=<" + str(self.val["b"]) + ">")
1654 """Print a bar object."""
1656 def __init__(self, val):
1659 def to_string(self):
1660 return ("x=<" + str(self.val["x"]) +
1661 "> y=<" + str(self.val["y"]) + ">")
1664 This example doesn't need a lookup function, that is handled by the
1665 @code{gdb.printing} module. Instead a function is provided to build up
1666 the object that handles the lookup.
1671 def build_pretty_printer():
1672 pp = gdb.printing.RegexpCollectionPrettyPrinter(
1674 pp.add_printer('foo', '^foo$', fooPrinter)
1675 pp.add_printer('bar', '^bar$', barPrinter)
1679 And here is the autoload support:
1684 gdb.printing.register_pretty_printer(
1685 gdb.current_objfile(),
1686 my_library.build_pretty_printer())
1689 Finally, when this printer is loaded into @value{GDBN}, here is the
1690 corresponding output of @samp{info pretty-printer}:
1693 (gdb) info pretty-printer
1700 @node Type Printing API
1701 @subsubsection Type Printing API
1702 @cindex type printing API for Python
1704 @value{GDBN} provides a way for Python code to customize type display.
1705 This is mainly useful for substituting canonical typedef names for
1708 @cindex type printer
1709 A @dfn{type printer} is just a Python object conforming to a certain
1710 protocol. A simple base class implementing the protocol is provided;
1711 see @ref{gdb.types}. A type printer must supply at least:
1713 @defivar type_printer enabled
1714 A boolean which is True if the printer is enabled, and False
1715 otherwise. This is manipulated by the @code{enable type-printer}
1716 and @code{disable type-printer} commands.
1719 @defivar type_printer name
1720 The name of the type printer. This must be a string. This is used by
1721 the @code{enable type-printer} and @code{disable type-printer}
1725 @defmethod type_printer instantiate (self)
1726 This is called by @value{GDBN} at the start of type-printing. It is
1727 only called if the type printer is enabled. This method must return a
1728 new object that supplies a @code{recognize} method, as described below.
1732 When displaying a type, say via the @code{ptype} command, @value{GDBN}
1733 will compute a list of type recognizers. This is done by iterating
1734 first over the per-objfile type printers (@pxref{Objfiles In Python}),
1735 followed by the per-progspace type printers (@pxref{Progspaces In
1736 Python}), and finally the global type printers.
1738 @value{GDBN} will call the @code{instantiate} method of each enabled
1739 type printer. If this method returns @code{None}, then the result is
1740 ignored; otherwise, it is appended to the list of recognizers.
1742 Then, when @value{GDBN} is going to display a type name, it iterates
1743 over the list of recognizers. For each one, it calls the recognition
1744 function, stopping if the function returns a non-@code{None} value.
1745 The recognition function is defined as:
1747 @defmethod type_recognizer recognize (self, type)
1748 If @var{type} is not recognized, return @code{None}. Otherwise,
1749 return a string which is to be printed as the name of @var{type}.
1750 The @var{type} argument will be an instance of @code{gdb.Type}
1751 (@pxref{Types In Python}).
1754 @value{GDBN} uses this two-pass approach so that type printers can
1755 efficiently cache information without holding on to it too long. For
1756 example, it can be convenient to look up type information in a type
1757 printer and hold it for a recognizer's lifetime; if a single pass were
1758 done then type printers would have to make use of the event system in
1759 order to avoid holding information that could become stale as the
1762 @node Frame Filter API
1763 @subsubsection Filtering Frames
1764 @cindex frame filters api
1766 Frame filters are Python objects that manipulate the visibility of a
1767 frame or frames when a backtrace (@pxref{Backtrace}) is printed by
1770 Only commands that print a backtrace, or, in the case of @sc{gdb/mi}
1771 commands (@pxref{GDB/MI}), those that return a collection of frames
1772 are affected. The commands that work with frame filters are:
1774 @code{backtrace} (@pxref{backtrace-command,, The backtrace command}),
1775 @code{-stack-list-frames}
1776 (@pxref{-stack-list-frames,, The -stack-list-frames command}),
1777 @code{-stack-list-variables} (@pxref{-stack-list-variables,, The
1778 -stack-list-variables command}), @code{-stack-list-arguments}
1779 @pxref{-stack-list-arguments,, The -stack-list-arguments command}) and
1780 @code{-stack-list-locals} (@pxref{-stack-list-locals,, The
1781 -stack-list-locals command}).
1783 A frame filter works by taking an iterator as an argument, applying
1784 actions to the contents of that iterator, and returning another
1785 iterator (or, possibly, the same iterator it was provided in the case
1786 where the filter does not perform any operations). Typically, frame
1787 filters utilize tools such as the Python's @code{itertools} module to
1788 work with and create new iterators from the source iterator.
1789 Regardless of how a filter chooses to apply actions, it must not alter
1790 the underlying @value{GDBN} frame or frames, or attempt to alter the
1791 call-stack within @value{GDBN}. This preserves data integrity within
1792 @value{GDBN}. Frame filters are executed on a priority basis and care
1793 should be taken that some frame filters may have been executed before,
1794 and that some frame filters will be executed after.
1796 An important consideration when designing frame filters, and well
1797 worth reflecting upon, is that frame filters should avoid unwinding
1798 the call stack if possible. Some stacks can run very deep, into the
1799 tens of thousands in some cases. To search every frame when a frame
1800 filter executes may be too expensive at that step. The frame filter
1801 cannot know how many frames it has to iterate over, and it may have to
1802 iterate through them all. This ends up duplicating effort as
1803 @value{GDBN} performs this iteration when it prints the frames. If
1804 the filter can defer unwinding frames until frame decorators are
1805 executed, after the last filter has executed, it should. @xref{Frame
1806 Decorator API}, for more information on decorators. Also, there are
1807 examples for both frame decorators and filters in later chapters.
1808 @xref{Writing a Frame Filter}, for more information.
1810 The Python dictionary @code{gdb.frame_filters} contains key/object
1811 pairings that comprise a frame filter. Frame filters in this
1812 dictionary are called @code{global} frame filters, and they are
1813 available when debugging all inferiors. These frame filters must
1814 register with the dictionary directly. In addition to the
1815 @code{global} dictionary, there are other dictionaries that are loaded
1816 with different inferiors via auto-loading (@pxref{Python
1817 Auto-loading}). The two other areas where frame filter dictionaries
1818 can be found are: @code{gdb.Progspace} which contains a
1819 @code{frame_filters} dictionary attribute, and each @code{gdb.Objfile}
1820 object which also contains a @code{frame_filters} dictionary
1823 When a command is executed from @value{GDBN} that is compatible with
1824 frame filters, @value{GDBN} combines the @code{global},
1825 @code{gdb.Progspace} and all @code{gdb.Objfile} dictionaries currently
1826 loaded. All of the @code{gdb.Objfile} dictionaries are combined, as
1827 several frames, and thus several object files, might be in use.
1828 @value{GDBN} then prunes any frame filter whose @code{enabled}
1829 attribute is @code{False}. This pruned list is then sorted according
1830 to the @code{priority} attribute in each filter.
1832 Once the dictionaries are combined, pruned and sorted, @value{GDBN}
1833 creates an iterator which wraps each frame in the call stack in a
1834 @code{FrameDecorator} object, and calls each filter in order. The
1835 output from the previous filter will always be the input to the next
1838 Frame filters have a mandatory interface which each frame filter must
1839 implement, defined here:
1841 @defun FrameFilter.filter (iterator)
1842 @value{GDBN} will call this method on a frame filter when it has
1843 reached the order in the priority list for that filter.
1845 For example, if there are four frame filters:
1856 The order that the frame filters will be called is:
1859 Filter3 -> Filter2 -> Filter1 -> Filter4
1862 Note that the output from @code{Filter3} is passed to the input of
1863 @code{Filter2}, and so on.
1865 This @code{filter} method is passed a Python iterator. This iterator
1866 contains a sequence of frame decorators that wrap each
1867 @code{gdb.Frame}, or a frame decorator that wraps another frame
1868 decorator. The first filter that is executed in the sequence of frame
1869 filters will receive an iterator entirely comprised of default
1870 @code{FrameDecorator} objects. However, after each frame filter is
1871 executed, the previous frame filter may have wrapped some or all of
1872 the frame decorators with their own frame decorator. As frame
1873 decorators must also conform to a mandatory interface, these
1874 decorators can be assumed to act in a uniform manner (@pxref{Frame
1877 This method must return an object conforming to the Python iterator
1878 protocol. Each item in the iterator must be an object conforming to
1879 the frame decorator interface. If a frame filter does not wish to
1880 perform any operations on this iterator, it should return that
1883 This method is not optional. If it does not exist, @value{GDBN} will
1884 raise and print an error.
1887 @defvar FrameFilter.name
1888 The @code{name} attribute must be Python string which contains the
1889 name of the filter displayed by @value{GDBN} (@pxref{Frame Filter
1890 Management}). This attribute may contain any combination of letters
1891 or numbers. Care should be taken to ensure that it is unique. This
1892 attribute is mandatory.
1895 @defvar FrameFilter.enabled
1896 The @code{enabled} attribute must be Python boolean. This attribute
1897 indicates to @value{GDBN} whether the frame filter is enabled, and
1898 should be considered when frame filters are executed. If
1899 @code{enabled} is @code{True}, then the frame filter will be executed
1900 when any of the backtrace commands detailed earlier in this chapter
1901 are executed. If @code{enabled} is @code{False}, then the frame
1902 filter will not be executed. This attribute is mandatory.
1905 @defvar FrameFilter.priority
1906 The @code{priority} attribute must be Python integer. This attribute
1907 controls the order of execution in relation to other frame filters.
1908 There are no imposed limits on the range of @code{priority} other than
1909 it must be a valid integer. The higher the @code{priority} attribute,
1910 the sooner the frame filter will be executed in relation to other
1911 frame filters. Although @code{priority} can be negative, it is
1912 recommended practice to assume zero is the lowest priority that a
1913 frame filter can be assigned. Frame filters that have the same
1914 priority are executed in unsorted order in that priority slot. This
1915 attribute is mandatory. 100 is a good default priority.
1918 @node Frame Decorator API
1919 @subsubsection Decorating Frames
1920 @cindex frame decorator api
1922 Frame decorators are sister objects to frame filters (@pxref{Frame
1923 Filter API}). Frame decorators are applied by a frame filter and can
1924 only be used in conjunction with frame filters.
1926 The purpose of a frame decorator is to customize the printed content
1927 of each @code{gdb.Frame} in commands where frame filters are executed.
1928 This concept is called decorating a frame. Frame decorators decorate
1929 a @code{gdb.Frame} with Python code contained within each API call.
1930 This separates the actual data contained in a @code{gdb.Frame} from
1931 the decorated data produced by a frame decorator. This abstraction is
1932 necessary to maintain integrity of the data contained in each
1935 Frame decorators have a mandatory interface, defined below.
1937 @value{GDBN} already contains a frame decorator called
1938 @code{FrameDecorator}. This contains substantial amounts of
1939 boilerplate code to decorate the content of a @code{gdb.Frame}. It is
1940 recommended that other frame decorators inherit and extend this
1941 object, and only to override the methods needed.
1943 @tindex gdb.FrameDecorator
1944 @code{FrameDecorator} is defined in the Python module
1945 @code{gdb.FrameDecorator}, so your code can import it like:
1947 from gdb.FrameDecorator import FrameDecorator
1950 @defun FrameDecorator.elided (self)
1952 The @code{elided} method groups frames together in a hierarchical
1953 system. An example would be an interpreter, where multiple low-level
1954 frames make up a single call in the interpreted language. In this
1955 example, the frame filter would elide the low-level frames and present
1956 a single high-level frame, representing the call in the interpreted
1957 language, to the user.
1959 The @code{elided} function must return an iterable and this iterable
1960 must contain the frames that are being elided wrapped in a suitable
1961 frame decorator. If no frames are being elided this function may
1962 return an empty iterable, or @code{None}. Elided frames are indented
1963 from normal frames in a @code{CLI} backtrace, or in the case of
1964 @code{GDB/MI}, are placed in the @code{children} field of the eliding
1967 It is the frame filter's task to also filter out the elided frames from
1968 the source iterator. This will avoid printing the frame twice.
1971 @defun FrameDecorator.function (self)
1973 This method returns the name of the function in the frame that is to
1976 This method must return a Python string describing the function, or
1979 If this function returns @code{None}, @value{GDBN} will not print any
1980 data for this field.
1983 @defun FrameDecorator.address (self)
1985 This method returns the address of the frame that is to be printed.
1987 This method must return a Python numeric integer type of sufficient
1988 size to describe the address of the frame, or @code{None}.
1990 If this function returns a @code{None}, @value{GDBN} will not print
1991 any data for this field.
1994 @defun FrameDecorator.filename (self)
1996 This method returns the filename and path associated with this frame.
1998 This method must return a Python string containing the filename and
1999 the path to the object file backing the frame, or @code{None}.
2001 If this function returns a @code{None}, @value{GDBN} will not print
2002 any data for this field.
2005 @defun FrameDecorator.line (self):
2007 This method returns the line number associated with the current
2008 position within the function addressed by this frame.
2010 This method must return a Python integer type, or @code{None}.
2012 If this function returns a @code{None}, @value{GDBN} will not print
2013 any data for this field.
2016 @defun FrameDecorator.frame_args (self)
2019 This method must return an iterable, or @code{None}. Returning an
2020 empty iterable, or @code{None} means frame arguments will not be
2021 printed for this frame. This iterable must contain objects that
2022 implement two methods, described here.
2024 This object must implement a @code{argument} method which takes a
2025 single @code{self} parameter and must return a @code{gdb.Symbol}
2026 (@pxref{Symbols In Python}), or a Python string. The object must also
2027 implement a @code{value} method which takes a single @code{self}
2028 parameter and must return a @code{gdb.Value} (@pxref{Values From
2029 Inferior}), a Python value, or @code{None}. If the @code{value}
2030 method returns @code{None}, and the @code{argument} method returns a
2031 @code{gdb.Symbol}, @value{GDBN} will look-up and print the value of
2032 the @code{gdb.Symbol} automatically.
2037 class SymValueWrapper():
2039 def __init__(self, symbol, value):
2049 class SomeFrameDecorator()
2052 def frame_args(self):
2055 block = self.inferior_frame.block()
2059 # Iterate over all symbols in a block. Only add
2060 # symbols that are arguments.
2062 if not sym.is_argument:
2064 args.append(SymValueWrapper(sym,None))
2066 # Add example synthetic argument.
2067 args.append(SymValueWrapper(``foo'', 42))
2073 @defun FrameDecorator.frame_locals (self)
2075 This method must return an iterable or @code{None}. Returning an
2076 empty iterable, or @code{None} means frame local arguments will not be
2077 printed for this frame.
2079 The object interface, the description of the various strategies for
2080 reading frame locals, and the example are largely similar to those
2081 described in the @code{frame_args} function, (@pxref{frame_args,,The
2082 frame filter frame_args function}). Below is a modified example:
2085 class SomeFrameDecorator()
2088 def frame_locals(self):
2091 block = self.inferior_frame.block()
2095 # Iterate over all symbols in a block. Add all
2096 # symbols, except arguments.
2100 vars.append(SymValueWrapper(sym,None))
2102 # Add an example of a synthetic local variable.
2103 vars.append(SymValueWrapper(``bar'', 99))
2109 @defun FrameDecorator.inferior_frame (self):
2111 This method must return the underlying @code{gdb.Frame} that this
2112 frame decorator is decorating. @value{GDBN} requires the underlying
2113 frame for internal frame information to determine how to print certain
2114 values when printing a frame.
2117 @node Writing a Frame Filter
2118 @subsubsection Writing a Frame Filter
2119 @cindex writing a frame filter
2121 There are three basic elements that a frame filter must implement: it
2122 must correctly implement the documented interface (@pxref{Frame Filter
2123 API}), it must register itself with @value{GDBN}, and finally, it must
2124 decide if it is to work on the data provided by @value{GDBN}. In all
2125 cases, whether it works on the iterator or not, each frame filter must
2126 return an iterator. A bare-bones frame filter follows the pattern in
2127 the following example.
2132 class FrameFilter():
2135 # Frame filter attribute creation.
2137 # 'name' is the name of the filter that GDB will display.
2139 # 'priority' is the priority of the filter relative to other
2142 # 'enabled' is a boolean that indicates whether this filter is
2143 # enabled and should be executed.
2149 # Register this frame filter with the global frame_filters
2151 gdb.frame_filters[self.name] = self
2153 def filter(self, frame_iter):
2154 # Just return the iterator.
2158 The frame filter in the example above implements the three
2159 requirements for all frame filters. It implements the API, self
2160 registers, and makes a decision on the iterator (in this case, it just
2161 returns the iterator untouched).
2163 The first step is attribute creation and assignment, and as shown in
2164 the comments the filter assigns the following attributes: @code{name},
2165 @code{priority} and whether the filter should be enabled with the
2166 @code{enabled} attribute.
2168 The second step is registering the frame filter with the dictionary or
2169 dictionaries that the frame filter has interest in. As shown in the
2170 comments, this filter just registers itself with the global dictionary
2171 @code{gdb.frame_filters}. As noted earlier, @code{gdb.frame_filters}
2172 is a dictionary that is initialized in the @code{gdb} module when
2173 @value{GDBN} starts. What dictionary a filter registers with is an
2174 important consideration. Generally, if a filter is specific to a set
2175 of code, it should be registered either in the @code{objfile} or
2176 @code{progspace} dictionaries as they are specific to the program
2177 currently loaded in @value{GDBN}. The global dictionary is always
2178 present in @value{GDBN} and is never unloaded. Any filters registered
2179 with the global dictionary will exist until @value{GDBN} exits. To
2180 avoid filters that may conflict, it is generally better to register
2181 frame filters against the dictionaries that more closely align with
2182 the usage of the filter currently in question. @xref{Python
2183 Auto-loading}, for further information on auto-loading Python scripts.
2185 @value{GDBN} takes a hands-off approach to frame filter registration,
2186 therefore it is the frame filter's responsibility to ensure
2187 registration has occurred, and that any exceptions are handled
2188 appropriately. In particular, you may wish to handle exceptions
2189 relating to Python dictionary key uniqueness. It is mandatory that
2190 the dictionary key is the same as frame filter's @code{name}
2191 attribute. When a user manages frame filters (@pxref{Frame Filter
2192 Management}), the names @value{GDBN} will display are those contained
2193 in the @code{name} attribute.
2195 The final step of this example is the implementation of the
2196 @code{filter} method. As shown in the example comments, we define the
2197 @code{filter} method and note that the method must take an iterator,
2198 and also must return an iterator. In this bare-bones example, the
2199 frame filter is not very useful as it just returns the iterator
2200 untouched. However this is a valid operation for frame filters that
2201 have the @code{enabled} attribute set, but decide not to operate on
2204 In the next example, the frame filter operates on all frames and
2205 utilizes a frame decorator to perform some work on the frames.
2206 @xref{Frame Decorator API}, for further information on the frame
2207 decorator interface.
2209 This example works on inlined frames. It highlights frames which are
2210 inlined by tagging them with an ``[inlined]'' tag. By applying a
2211 frame decorator to all frames with the Python @code{itertools imap}
2212 method, the example defers actions to the frame decorator. Frame
2213 decorators are only processed when @value{GDBN} prints the backtrace.
2215 This introduces a new decision making topic: whether to perform
2216 decision making operations at the filtering step, or at the printing
2217 step. In this example's approach, it does not perform any filtering
2218 decisions at the filtering step beyond mapping a frame decorator to
2219 each frame. This allows the actual decision making to be performed
2220 when each frame is printed. This is an important consideration, and
2221 well worth reflecting upon when designing a frame filter. An issue
2222 that frame filters should avoid is unwinding the stack if possible.
2223 Some stacks can run very deep, into the tens of thousands in some
2224 cases. To search every frame to determine if it is inlined ahead of
2225 time may be too expensive at the filtering step. The frame filter
2226 cannot know how many frames it has to iterate over, and it would have
2227 to iterate through them all. This ends up duplicating effort as
2228 @value{GDBN} performs this iteration when it prints the frames.
2230 In this example decision making can be deferred to the printing step.
2231 As each frame is printed, the frame decorator can examine each frame
2232 in turn when @value{GDBN} iterates. From a performance viewpoint,
2233 this is the most appropriate decision to make as it avoids duplicating
2234 the effort that the printing step would undertake anyway. Also, if
2235 there are many frame filters unwinding the stack during filtering, it
2236 can substantially delay the printing of the backtrace which will
2237 result in large memory usage, and a poor user experience.
2240 class InlineFilter():
2243 self.name = "InlinedFrameFilter"
2246 gdb.frame_filters[self.name] = self
2248 def filter(self, frame_iter):
2249 frame_iter = itertools.imap(InlinedFrameDecorator,
2254 This frame filter is somewhat similar to the earlier example, except
2255 that the @code{filter} method applies a frame decorator object called
2256 @code{InlinedFrameDecorator} to each element in the iterator. The
2257 @code{imap} Python method is light-weight. It does not proactively
2258 iterate over the iterator, but rather creates a new iterator which
2259 wraps the existing one.
2261 Below is the frame decorator for this example.
2264 class InlinedFrameDecorator(FrameDecorator):
2266 def __init__(self, fobj):
2267 super(InlinedFrameDecorator, self).__init__(fobj)
2270 frame = fobj.inferior_frame()
2271 name = str(frame.name())
2273 if frame.type() == gdb.INLINE_FRAME:
2274 name = name + " [inlined]"
2279 This frame decorator only defines and overrides the @code{function}
2280 method. It lets the supplied @code{FrameDecorator}, which is shipped
2281 with @value{GDBN}, perform the other work associated with printing
2284 The combination of these two objects create this output from a
2288 #0 0x004004e0 in bar () at inline.c:11
2289 #1 0x00400566 in max [inlined] (b=6, a=12) at inline.c:21
2290 #2 0x00400566 in main () at inline.c:31
2293 So in the case of this example, a frame decorator is applied to all
2294 frames, regardless of whether they may be inlined or not. As
2295 @value{GDBN} iterates over the iterator produced by the frame filters,
2296 @value{GDBN} executes each frame decorator which then makes a decision
2297 on what to print in the @code{function} callback. Using a strategy
2298 like this is a way to defer decisions on the frame content to printing
2301 @subheading Eliding Frames
2303 It might be that the above example is not desirable for representing
2304 inlined frames, and a hierarchical approach may be preferred. If we
2305 want to hierarchically represent frames, the @code{elided} frame
2306 decorator interface might be preferable.
2308 This example approaches the issue with the @code{elided} method. This
2309 example is quite long, but very simplistic. It is out-of-scope for
2310 this section to write a complete example that comprehensively covers
2311 all approaches of finding and printing inlined frames. However, this
2312 example illustrates the approach an author might use.
2314 This example comprises of three sections.
2317 class InlineFrameFilter():
2320 self.name = "InlinedFrameFilter"
2323 gdb.frame_filters[self.name] = self
2325 def filter(self, frame_iter):
2326 return ElidingInlineIterator(frame_iter)
2329 This frame filter is very similar to the other examples. The only
2330 difference is this frame filter is wrapping the iterator provided to
2331 it (@code{frame_iter}) with a custom iterator called
2332 @code{ElidingInlineIterator}. This again defers actions to when
2333 @value{GDBN} prints the backtrace, as the iterator is not traversed
2336 The iterator for this example is as follows. It is in this section of
2337 the example where decisions are made on the content of the backtrace.
2340 class ElidingInlineIterator:
2341 def __init__(self, ii):
2342 self.input_iterator = ii
2348 frame = next(self.input_iterator)
2350 if frame.inferior_frame().type() != gdb.INLINE_FRAME:
2354 eliding_frame = next(self.input_iterator)
2355 except StopIteration:
2357 return ElidingFrameDecorator(eliding_frame, [frame])
2360 This iterator implements the Python iterator protocol. When the
2361 @code{next} function is called (when @value{GDBN} prints each frame),
2362 the iterator checks if this frame decorator, @code{frame}, is wrapping
2363 an inlined frame. If it is not, it returns the existing frame decorator
2364 untouched. If it is wrapping an inlined frame, it assumes that the
2365 inlined frame was contained within the next oldest frame,
2366 @code{eliding_frame}, which it fetches. It then creates and returns a
2367 frame decorator, @code{ElidingFrameDecorator}, which contains both the
2368 elided frame, and the eliding frame.
2371 class ElidingInlineDecorator(FrameDecorator):
2373 def __init__(self, frame, elided_frames):
2374 super(ElidingInlineDecorator, self).__init__(frame)
2376 self.elided_frames = elided_frames
2379 return iter(self.elided_frames)
2382 This frame decorator overrides one function and returns the inlined
2383 frame in the @code{elided} method. As before it lets
2384 @code{FrameDecorator} do the rest of the work involved in printing
2385 this frame. This produces the following output.
2388 #0 0x004004e0 in bar () at inline.c:11
2389 #2 0x00400529 in main () at inline.c:25
2390 #1 0x00400529 in max (b=6, a=12) at inline.c:15
2393 In that output, @code{max} which has been inlined into @code{main} is
2394 printed hierarchically. Another approach would be to combine the
2395 @code{function} method, and the @code{elided} method to both print a
2396 marker in the inlined frame, and also show the hierarchical
2399 @node Unwinding Frames in Python
2400 @subsubsection Unwinding Frames in Python
2401 @cindex unwinding frames in Python
2403 In @value{GDBN} terminology ``unwinding'' is the process of finding
2404 the previous frame (that is, caller's) from the current one. An
2405 unwinder has three methods. The first one checks if it can handle
2406 given frame (``sniff'' it). For the frames it can sniff an unwinder
2407 provides two additional methods: it can return frame's ID, and it can
2408 fetch registers from the previous frame. A running @value{GDBN}
2409 mantains a list of the unwinders and calls each unwinder's sniffer in
2410 turn until it finds the one that recognizes the current frame. There
2411 is an API to register an unwinder.
2413 The unwinders that come with @value{GDBN} handle standard frames.
2414 However, mixed language applications (for example, an application
2415 running Java Virtual Machine) sometimes use frame layouts that cannot
2416 be handled by the @value{GDBN} unwinders. You can write Python code
2417 that can handle such custom frames.
2419 You implement a frame unwinder in Python as a class with which has two
2420 attributes, @code{name} and @code{enabled}, with obvious meanings, and
2421 a single method @code{__call__}, which examines a given frame and
2422 returns an object (an instance of @code{gdb.UnwindInfo class)}
2423 describing it. If an unwinder does not recognize a frame, it should
2424 return @code{None}. The code in @value{GDBN} that enables writing
2425 unwinders in Python uses this object to return frame's ID and previous
2426 frame registers when @value{GDBN} core asks for them.
2428 An unwinder should do as little work as possible. Some otherwise
2429 innocuous operations can cause problems (even crashes, as this code is
2430 not not well-hardened yet). For example, making an inferior call from
2431 an unwinder is unadvisable, as an inferior call will reset
2432 @value{GDBN}'s stack unwinding process, potentially causing re-entrant
2435 @subheading Unwinder Input
2437 An object passed to an unwinder (a @code{gdb.PendingFrame} instance)
2438 provides a method to read frame's registers:
2440 @defun PendingFrame.read_register (reg)
2441 This method returns the contents of the register @var{reg} in the
2442 frame as a @code{gdb.Value} object. @var{reg} can be either a
2443 register number or a register name; the values are platform-specific.
2444 They are usually found in the corresponding
2445 @file{@var{platform}-tdep.h} file in the @value{GDBN} source tree. If
2446 @var{reg} does not name a register for the current architecture, this
2447 method will throw an exception.
2449 Note that this method will always return a @code{gdb.Value} for a
2450 valid register name. This does not mean that the value will be valid.
2451 For example, you may request a register that an earlier unwinder could
2452 not unwind---the value will be unavailable. Instead, the
2453 @code{gdb.Value} returned from this method will be lazy; that is, its
2454 underlying bits will not be fetched until it is first used. So,
2455 attempting to use such a value will cause an exception at the point of
2458 The type of the returned @code{gdb.Value} depends on the register and
2459 the architecture. It is common for registers to have a scalar type,
2460 like @code{long long}; but many other types are possible, such as
2461 pointer, pointer-to-function, floating point or vector types.
2464 It also provides a factory method to create a @code{gdb.UnwindInfo}
2465 instance to be returned to @value{GDBN}:
2467 @defun PendingFrame.create_unwind_info (frame_id)
2468 Returns a new @code{gdb.UnwindInfo} instance identified by given
2469 @var{frame_id}. The argument is used to build @value{GDBN}'s frame ID
2470 using one of functions provided by @value{GDBN}. @var{frame_id}'s attributes
2471 determine which function will be used, as follows:
2475 The frame is identified by the given stack address and PC. The stack
2476 address must be chosen so that it is constant throughout the lifetime
2477 of the frame, so a typical choice is the value of the stack pointer at
2478 the start of the function---in the DWARF standard, this would be the
2479 ``Call Frame Address''.
2481 This is the most common case by far. The other cases are documented
2482 for completeness but are only useful in specialized situations.
2484 @item sp, pc, special
2485 The frame is identified by the stack address, the PC, and a
2486 ``special'' address. The special address is used on architectures
2487 that can have frames that do not change the stack, but which are still
2488 distinct, for example the IA-64, which has a second stack for
2489 registers. Both @var{sp} and @var{special} must be constant
2490 throughout the lifetime of the frame.
2493 The frame is identified by the stack address only. Any other stack
2494 frame with a matching @var{sp} will be considered to match this frame.
2495 Inside gdb, this is called a ``wild frame''. You will never need
2499 Each attribute value should be an instance of @code{gdb.Value}.
2503 @subheading Unwinder Output: UnwindInfo
2505 Use @code{PendingFrame.create_unwind_info} method described above to
2506 create a @code{gdb.UnwindInfo} instance. Use the following method to
2507 specify caller registers that have been saved in this frame:
2509 @defun gdb.UnwindInfo.add_saved_register (reg, value)
2510 @var{reg} identifies the register. It can be a number or a name, just
2511 as for the @code{PendingFrame.read_register} method above.
2512 @var{value} is a register value (a @code{gdb.Value} object).
2515 @subheading Unwinder Skeleton Code
2517 @value{GDBN} comes with the module containing the base @code{Unwinder}
2518 class. Derive your unwinder class from it and structure the code as
2522 from gdb.unwinders import Unwinder
2524 class FrameId(object):
2525 def __init__(self, sp, pc):
2530 class MyUnwinder(Unwinder):
2532 super(MyUnwinder, self).__init___(<expects unwinder name argument>)
2534 def __call__(pending_frame):
2535 if not <we recognize frame>:
2537 # Create UnwindInfo. Usually the frame is identified by the stack
2538 # pointer and the program counter.
2539 sp = pending_frame.read_register(<SP number>)
2540 pc = pending_frame.read_register(<PC number>)
2541 unwind_info = pending_frame.create_unwind_info(FrameId(sp, pc))
2543 # Find the values of the registers in the caller's frame and
2544 # save them in the result:
2545 unwind_info.add_saved_register(<register>, <value>)
2548 # Return the result:
2553 @subheading Registering a Unwinder
2555 An object file, a program space, and the @value{GDBN} proper can have
2556 unwinders registered with it.
2558 The @code{gdb.unwinders} module provides the function to register a
2561 @defun gdb.unwinder.register_unwinder (locus, unwinder, replace=False)
2562 @var{locus} is specifies an object file or a program space to which
2563 @var{unwinder} is added. Passing @code{None} or @code{gdb} adds
2564 @var{unwinder} to the @value{GDBN}'s global unwinder list. The newly
2565 added @var{unwinder} will be called before any other unwinder from the
2566 same locus. Two unwinders in the same locus cannot have the same
2567 name. An attempt to add a unwinder with already existing name raises
2568 an exception unless @var{replace} is @code{True}, in which case the
2569 old unwinder is deleted.
2572 @subheading Unwinder Precedence
2574 @value{GDBN} first calls the unwinders from all the object files in no
2575 particular order, then the unwinders from the current program space,
2576 and finally the unwinders from @value{GDBN}.
2578 @node Xmethods In Python
2579 @subsubsection Xmethods In Python
2580 @cindex xmethods in Python
2582 @dfn{Xmethods} are additional methods or replacements for existing
2583 methods of a C@t{++} class. This feature is useful for those cases
2584 where a method defined in C@t{++} source code could be inlined or
2585 optimized out by the compiler, making it unavailable to @value{GDBN}.
2586 For such cases, one can define an xmethod to serve as a replacement
2587 for the method defined in the C@t{++} source code. @value{GDBN} will
2588 then invoke the xmethod, instead of the C@t{++} method, to
2589 evaluate expressions. One can also use xmethods when debugging
2590 with core files. Moreover, when debugging live programs, invoking an
2591 xmethod need not involve running the inferior (which can potentially
2592 perturb its state). Hence, even if the C@t{++} method is available, it
2593 is better to use its replacement xmethod if one is defined.
2595 The xmethods feature in Python is available via the concepts of an
2596 @dfn{xmethod matcher} and an @dfn{xmethod worker}. To
2597 implement an xmethod, one has to implement a matcher and a
2598 corresponding worker for it (more than one worker can be
2599 implemented, each catering to a different overloaded instance of the
2600 method). Internally, @value{GDBN} invokes the @code{match} method of a
2601 matcher to match the class type and method name. On a match, the
2602 @code{match} method returns a list of matching @emph{worker} objects.
2603 Each worker object typically corresponds to an overloaded instance of
2604 the xmethod. They implement a @code{get_arg_types} method which
2605 returns a sequence of types corresponding to the arguments the xmethod
2606 requires. @value{GDBN} uses this sequence of types to perform
2607 overload resolution and picks a winning xmethod worker. A winner
2608 is also selected from among the methods @value{GDBN} finds in the
2609 C@t{++} source code. Next, the winning xmethod worker and the
2610 winning C@t{++} method are compared to select an overall winner. In
2611 case of a tie between a xmethod worker and a C@t{++} method, the
2612 xmethod worker is selected as the winner. That is, if a winning
2613 xmethod worker is found to be equivalent to the winning C@t{++}
2614 method, then the xmethod worker is treated as a replacement for
2615 the C@t{++} method. @value{GDBN} uses the overall winner to invoke the
2616 method. If the winning xmethod worker is the overall winner, then
2617 the corresponding xmethod is invoked via the @code{__call__} method
2618 of the worker object.
2620 If one wants to implement an xmethod as a replacement for an
2621 existing C@t{++} method, then they have to implement an equivalent
2622 xmethod which has exactly the same name and takes arguments of
2623 exactly the same type as the C@t{++} method. If the user wants to
2624 invoke the C@t{++} method even though a replacement xmethod is
2625 available for that method, then they can disable the xmethod.
2627 @xref{Xmethod API}, for API to implement xmethods in Python.
2628 @xref{Writing an Xmethod}, for implementing xmethods in Python.
2631 @subsubsection Xmethod API
2634 The @value{GDBN} Python API provides classes, interfaces and functions
2635 to implement, register and manipulate xmethods.
2636 @xref{Xmethods In Python}.
2638 An xmethod matcher should be an instance of a class derived from
2639 @code{XMethodMatcher} defined in the module @code{gdb.xmethod}, or an
2640 object with similar interface and attributes. An instance of
2641 @code{XMethodMatcher} has the following attributes:
2644 The name of the matcher.
2648 A boolean value indicating whether the matcher is enabled or disabled.
2652 A list of named methods managed by the matcher. Each object in the list
2653 is an instance of the class @code{XMethod} defined in the module
2654 @code{gdb.xmethod}, or any object with the following attributes:
2659 Name of the xmethod which should be unique for each xmethod
2660 managed by the matcher.
2663 A boolean value indicating whether the xmethod is enabled or
2668 The class @code{XMethod} is a convenience class with same
2669 attributes as above along with the following constructor:
2671 @defun XMethod.__init__ (self, name)
2672 Constructs an enabled xmethod with name @var{name}.
2677 The @code{XMethodMatcher} class has the following methods:
2679 @defun XMethodMatcher.__init__ (self, name)
2680 Constructs an enabled xmethod matcher with name @var{name}. The
2681 @code{methods} attribute is initialized to @code{None}.
2684 @defun XMethodMatcher.match (self, class_type, method_name)
2685 Derived classes should override this method. It should return a
2686 xmethod worker object (or a sequence of xmethod worker
2687 objects) matching the @var{class_type} and @var{method_name}.
2688 @var{class_type} is a @code{gdb.Type} object, and @var{method_name}
2689 is a string value. If the matcher manages named methods as listed in
2690 its @code{methods} attribute, then only those worker objects whose
2691 corresponding entries in the @code{methods} list are enabled should be
2695 An xmethod worker should be an instance of a class derived from
2696 @code{XMethodWorker} defined in the module @code{gdb.xmethod},
2697 or support the following interface:
2699 @defun XMethodWorker.get_arg_types (self)
2700 This method returns a sequence of @code{gdb.Type} objects corresponding
2701 to the arguments that the xmethod takes. It can return an empty
2702 sequence or @code{None} if the xmethod does not take any arguments.
2703 If the xmethod takes a single argument, then a single
2704 @code{gdb.Type} object corresponding to it can be returned.
2707 @defun XMethodWorker.get_result_type (self, *args)
2708 This method returns a @code{gdb.Type} object representing the type
2709 of the result of invoking this xmethod.
2710 The @var{args} argument is the same tuple of arguments that would be
2711 passed to the @code{__call__} method of this worker.
2714 @defun XMethodWorker.__call__ (self, *args)
2715 This is the method which does the @emph{work} of the xmethod. The
2716 @var{args} arguments is the tuple of arguments to the xmethod. Each
2717 element in this tuple is a gdb.Value object. The first element is
2718 always the @code{this} pointer value.
2721 For @value{GDBN} to lookup xmethods, the xmethod matchers
2722 should be registered using the following function defined in the module
2725 @defun register_xmethod_matcher (locus, matcher, replace=False)
2726 The @code{matcher} is registered with @code{locus}, replacing an
2727 existing matcher with the same name as @code{matcher} if
2728 @code{replace} is @code{True}. @code{locus} can be a
2729 @code{gdb.Objfile} object (@pxref{Objfiles In Python}), or a
2730 @code{gdb.Progspace} object (@pxref{Progspaces In Python}), or
2731 @code{None}. If it is @code{None}, then @code{matcher} is registered
2735 @node Writing an Xmethod
2736 @subsubsection Writing an Xmethod
2737 @cindex writing xmethods in Python
2739 Implementing xmethods in Python will require implementing xmethod
2740 matchers and xmethod workers (@pxref{Xmethods In Python}). Consider
2741 the following C@t{++} class:
2747 MyClass (int a) : a_(a) @{ @}
2749 int geta (void) @{ return a_; @}
2750 int operator+ (int b);
2757 MyClass::operator+ (int b)
2764 Let us define two xmethods for the class @code{MyClass}, one
2765 replacing the method @code{geta}, and another adding an overloaded
2766 flavor of @code{operator+} which takes a @code{MyClass} argument (the
2767 C@t{++} code above already has an overloaded @code{operator+}
2768 which takes an @code{int} argument). The xmethod matcher can be
2772 class MyClass_geta(gdb.xmethod.XMethod):
2774 gdb.xmethod.XMethod.__init__(self, 'geta')
2776 def get_worker(self, method_name):
2777 if method_name == 'geta':
2778 return MyClassWorker_geta()
2781 class MyClass_sum(gdb.xmethod.XMethod):
2783 gdb.xmethod.XMethod.__init__(self, 'sum')
2785 def get_worker(self, method_name):
2786 if method_name == 'operator+':
2787 return MyClassWorker_plus()
2790 class MyClassMatcher(gdb.xmethod.XMethodMatcher):
2792 gdb.xmethod.XMethodMatcher.__init__(self, 'MyClassMatcher')
2793 # List of methods 'managed' by this matcher
2794 self.methods = [MyClass_geta(), MyClass_sum()]
2796 def match(self, class_type, method_name):
2797 if class_type.tag != 'MyClass':
2800 for method in self.methods:
2802 worker = method.get_worker(method_name)
2804 workers.append(worker)
2810 Notice that the @code{match} method of @code{MyClassMatcher} returns
2811 a worker object of type @code{MyClassWorker_geta} for the @code{geta}
2812 method, and a worker object of type @code{MyClassWorker_plus} for the
2813 @code{operator+} method. This is done indirectly via helper classes
2814 derived from @code{gdb.xmethod.XMethod}. One does not need to use the
2815 @code{methods} attribute in a matcher as it is optional. However, if a
2816 matcher manages more than one xmethod, it is a good practice to list the
2817 xmethods in the @code{methods} attribute of the matcher. This will then
2818 facilitate enabling and disabling individual xmethods via the
2819 @code{enable/disable} commands. Notice also that a worker object is
2820 returned only if the corresponding entry in the @code{methods} attribute
2821 of the matcher is enabled.
2823 The implementation of the worker classes returned by the matcher setup
2824 above is as follows:
2827 class MyClassWorker_geta(gdb.xmethod.XMethodWorker):
2828 def get_arg_types(self):
2831 def get_result_type(self, obj):
2832 return gdb.lookup_type('int')
2834 def __call__(self, obj):
2838 class MyClassWorker_plus(gdb.xmethod.XMethodWorker):
2839 def get_arg_types(self):
2840 return gdb.lookup_type('MyClass')
2842 def get_result_type(self, obj):
2843 return gdb.lookup_type('int')
2845 def __call__(self, obj, other):
2846 return obj['a_'] + other['a_']
2849 For @value{GDBN} to actually lookup a xmethod, it has to be
2850 registered with it. The matcher defined above is registered with
2851 @value{GDBN} globally as follows:
2854 gdb.xmethod.register_xmethod_matcher(None, MyClassMatcher())
2857 If an object @code{obj} of type @code{MyClass} is initialized in C@t{++}
2865 then, after loading the Python script defining the xmethod matchers
2866 and workers into @code{GDBN}, invoking the method @code{geta} or using
2867 the operator @code{+} on @code{obj} will invoke the xmethods
2878 Consider another example with a C++ template class:
2885 MyTemplate () : dsize_(10), data_ (new T [10]) @{ @}
2886 ~MyTemplate () @{ delete [] data_; @}
2888 int footprint (void)
2890 return sizeof (T) * dsize_ + sizeof (MyTemplate<T>);
2899 Let us implement an xmethod for the above class which serves as a
2900 replacement for the @code{footprint} method. The full code listing
2901 of the xmethod workers and xmethod matchers is as follows:
2904 class MyTemplateWorker_footprint(gdb.xmethod.XMethodWorker):
2905 def __init__(self, class_type):
2906 self.class_type = class_type
2908 def get_arg_types(self):
2911 def get_result_type(self):
2912 return gdb.lookup_type('int')
2914 def __call__(self, obj):
2915 return (self.class_type.sizeof +
2917 self.class_type.template_argument(0).sizeof)
2920 class MyTemplateMatcher_footprint(gdb.xmethod.XMethodMatcher):
2922 gdb.xmethod.XMethodMatcher.__init__(self, 'MyTemplateMatcher')
2924 def match(self, class_type, method_name):
2925 if (re.match('MyTemplate<[ \t\n]*[_a-zA-Z][ _a-zA-Z0-9]*>',
2927 method_name == 'footprint'):
2928 return MyTemplateWorker_footprint(class_type)
2931 Notice that, in this example, we have not used the @code{methods}
2932 attribute of the matcher as the matcher manages only one xmethod. The
2933 user can enable/disable this xmethod by enabling/disabling the matcher
2936 @node Inferiors In Python
2937 @subsubsection Inferiors In Python
2938 @cindex inferiors in Python
2940 @findex gdb.Inferior
2941 Programs which are being run under @value{GDBN} are called inferiors
2942 (@pxref{Inferiors Connections and Programs}). Python scripts can access
2943 information about and manipulate inferiors controlled by @value{GDBN}
2944 via objects of the @code{gdb.Inferior} class.
2946 The following inferior-related functions are available in the @code{gdb}
2949 @defun gdb.inferiors ()
2950 Return a tuple containing all inferior objects.
2953 @defun gdb.selected_inferior ()
2954 Return an object representing the current inferior.
2957 A @code{gdb.Inferior} object has the following attributes:
2959 @defvar Inferior.num
2960 ID of inferior, as assigned by GDB.
2963 @defvar Inferior.pid
2964 Process ID of the inferior, as assigned by the underlying operating
2968 @defvar Inferior.was_attached
2969 Boolean signaling whether the inferior was created using `attach', or
2970 started by @value{GDBN} itself.
2973 @defvar Inferior.progspace
2974 The inferior's program space. @xref{Progspaces In Python}.
2977 A @code{gdb.Inferior} object has the following methods:
2979 @defun Inferior.is_valid ()
2980 Returns @code{True} if the @code{gdb.Inferior} object is valid,
2981 @code{False} if not. A @code{gdb.Inferior} object will become invalid
2982 if the inferior no longer exists within @value{GDBN}. All other
2983 @code{gdb.Inferior} methods will throw an exception if it is invalid
2984 at the time the method is called.
2987 @defun Inferior.threads ()
2988 This method returns a tuple holding all the threads which are valid
2989 when it is called. If there are no valid threads, the method will
2990 return an empty tuple.
2993 @defun Inferior.architecture ()
2994 Return the @code{gdb.Architecture} (@pxref{Architectures In Python})
2995 for this inferior. This represents the architecture of the inferior
2996 as a whole. Some platforms can have multiple architectures in a
2997 single address space, so this may not match the architecture of a
2998 particular frame (@pxref{Frames In Python}).
3001 @findex Inferior.read_memory
3002 @defun Inferior.read_memory (address, length)
3003 Read @var{length} addressable memory units from the inferior, starting at
3004 @var{address}. Returns a buffer object, which behaves much like an array
3005 or a string. It can be modified and given to the
3006 @code{Inferior.write_memory} function. In Python 3, the return
3007 value is a @code{memoryview} object.
3010 @findex Inferior.write_memory
3011 @defun Inferior.write_memory (address, buffer @r{[}, length@r{]})
3012 Write the contents of @var{buffer} to the inferior, starting at
3013 @var{address}. The @var{buffer} parameter must be a Python object
3014 which supports the buffer protocol, i.e., a string, an array or the
3015 object returned from @code{Inferior.read_memory}. If given, @var{length}
3016 determines the number of addressable memory units from @var{buffer} to be
3020 @findex gdb.search_memory
3021 @defun Inferior.search_memory (address, length, pattern)
3022 Search a region of the inferior memory starting at @var{address} with
3023 the given @var{length} using the search pattern supplied in
3024 @var{pattern}. The @var{pattern} parameter must be a Python object
3025 which supports the buffer protocol, i.e., a string, an array or the
3026 object returned from @code{gdb.read_memory}. Returns a Python @code{Long}
3027 containing the address where the pattern was found, or @code{None} if
3028 the pattern could not be found.
3031 @findex Inferior.thread_from_handle
3032 @findex Inferior.thread_from_thread_handle
3033 @defun Inferior.thread_from_handle (handle)
3034 Return the thread object corresponding to @var{handle}, a thread
3035 library specific data structure such as @code{pthread_t} for pthreads
3036 library implementations.
3038 The function @code{Inferior.thread_from_thread_handle} provides
3039 the same functionality, but use of @code{Inferior.thread_from_thread_handle}
3043 @node Events In Python
3044 @subsubsection Events In Python
3045 @cindex inferior events in Python
3047 @value{GDBN} provides a general event facility so that Python code can be
3048 notified of various state changes, particularly changes that occur in
3051 An @dfn{event} is just an object that describes some state change. The
3052 type of the object and its attributes will vary depending on the details
3053 of the change. All the existing events are described below.
3055 In order to be notified of an event, you must register an event handler
3056 with an @dfn{event registry}. An event registry is an object in the
3057 @code{gdb.events} module which dispatches particular events. A registry
3058 provides methods to register and unregister event handlers:
3060 @defun EventRegistry.connect (object)
3061 Add the given callable @var{object} to the registry. This object will be
3062 called when an event corresponding to this registry occurs.
3065 @defun EventRegistry.disconnect (object)
3066 Remove the given @var{object} from the registry. Once removed, the object
3067 will no longer receive notifications of events.
3073 def exit_handler (event):
3074 print "event type: exit"
3075 print "exit code: %d" % (event.exit_code)
3077 gdb.events.exited.connect (exit_handler)
3080 In the above example we connect our handler @code{exit_handler} to the
3081 registry @code{events.exited}. Once connected, @code{exit_handler} gets
3082 called when the inferior exits. The argument @dfn{event} in this example is
3083 of type @code{gdb.ExitedEvent}. As you can see in the example the
3084 @code{ExitedEvent} object has an attribute which indicates the exit code of
3087 The following is a listing of the event registries that are available and
3088 details of the events they emit:
3093 Emits @code{gdb.ThreadEvent}.
3095 Some events can be thread specific when @value{GDBN} is running in non-stop
3096 mode. When represented in Python, these events all extend
3097 @code{gdb.ThreadEvent}. Note, this event is not emitted directly; instead,
3098 events which are emitted by this or other modules might extend this event.
3099 Examples of these events are @code{gdb.BreakpointEvent} and
3100 @code{gdb.ContinueEvent}.
3102 @defvar ThreadEvent.inferior_thread
3103 In non-stop mode this attribute will be set to the specific thread which was
3104 involved in the emitted event. Otherwise, it will be set to @code{None}.
3107 Emits @code{gdb.ContinueEvent} which extends @code{gdb.ThreadEvent}.
3109 This event indicates that the inferior has been continued after a stop. For
3110 inherited attribute refer to @code{gdb.ThreadEvent} above.
3113 Emits @code{events.ExitedEvent} which indicates that the inferior has exited.
3114 @code{events.ExitedEvent} has two attributes:
3115 @defvar ExitedEvent.exit_code
3116 An integer representing the exit code, if available, which the inferior
3117 has returned. (The exit code could be unavailable if, for example,
3118 @value{GDBN} detaches from the inferior.) If the exit code is unavailable,
3119 the attribute does not exist.
3121 @defvar ExitedEvent.inferior
3122 A reference to the inferior which triggered the @code{exited} event.
3126 Emits @code{gdb.StopEvent} which extends @code{gdb.ThreadEvent}.
3128 Indicates that the inferior has stopped. All events emitted by this registry
3129 extend StopEvent. As a child of @code{gdb.ThreadEvent}, @code{gdb.StopEvent}
3130 will indicate the stopped thread when @value{GDBN} is running in non-stop
3131 mode. Refer to @code{gdb.ThreadEvent} above for more details.
3133 Emits @code{gdb.SignalEvent} which extends @code{gdb.StopEvent}.
3135 This event indicates that the inferior or one of its threads has received as
3136 signal. @code{gdb.SignalEvent} has the following attributes:
3138 @defvar SignalEvent.stop_signal
3139 A string representing the signal received by the inferior. A list of possible
3140 signal values can be obtained by running the command @code{info signals} in
3141 the @value{GDBN} command prompt.
3144 Also emits @code{gdb.BreakpointEvent} which extends @code{gdb.StopEvent}.
3146 @code{gdb.BreakpointEvent} event indicates that one or more breakpoints have
3147 been hit, and has the following attributes:
3149 @defvar BreakpointEvent.breakpoints
3150 A sequence containing references to all the breakpoints (type
3151 @code{gdb.Breakpoint}) that were hit.
3152 @xref{Breakpoints In Python}, for details of the @code{gdb.Breakpoint} object.
3154 @defvar BreakpointEvent.breakpoint
3155 A reference to the first breakpoint that was hit.
3156 This function is maintained for backward compatibility and is now deprecated
3157 in favor of the @code{gdb.BreakpointEvent.breakpoints} attribute.
3160 @item events.new_objfile
3161 Emits @code{gdb.NewObjFileEvent} which indicates that a new object file has
3162 been loaded by @value{GDBN}. @code{gdb.NewObjFileEvent} has one attribute:
3164 @defvar NewObjFileEvent.new_objfile
3165 A reference to the object file (@code{gdb.Objfile}) which has been loaded.
3166 @xref{Objfiles In Python}, for details of the @code{gdb.Objfile} object.
3169 @item events.clear_objfiles
3170 Emits @code{gdb.ClearObjFilesEvent} which indicates that the list of object
3171 files for a program space has been reset.
3172 @code{gdb.ClearObjFilesEvent} has one attribute:
3174 @defvar ClearObjFilesEvent.progspace
3175 A reference to the program space (@code{gdb.Progspace}) whose objfile list has
3176 been cleared. @xref{Progspaces In Python}.
3179 @item events.inferior_call
3180 Emits events just before and after a function in the inferior is
3181 called by @value{GDBN}. Before an inferior call, this emits an event
3182 of type @code{gdb.InferiorCallPreEvent}, and after an inferior call,
3183 this emits an event of type @code{gdb.InferiorCallPostEvent}.
3186 @tindex gdb.InferiorCallPreEvent
3187 @item @code{gdb.InferiorCallPreEvent}
3188 Indicates that a function in the inferior is about to be called.
3190 @defvar InferiorCallPreEvent.ptid
3191 The thread in which the call will be run.
3194 @defvar InferiorCallPreEvent.address
3195 The location of the function to be called.
3198 @tindex gdb.InferiorCallPostEvent
3199 @item @code{gdb.InferiorCallPostEvent}
3200 Indicates that a function in the inferior has just been called.
3202 @defvar InferiorCallPostEvent.ptid
3203 The thread in which the call was run.
3206 @defvar InferiorCallPostEvent.address
3207 The location of the function that was called.
3211 @item events.memory_changed
3212 Emits @code{gdb.MemoryChangedEvent} which indicates that the memory of the
3213 inferior has been modified by the @value{GDBN} user, for instance via a
3214 command like @w{@code{set *addr = value}}. The event has the following
3217 @defvar MemoryChangedEvent.address
3218 The start address of the changed region.
3221 @defvar MemoryChangedEvent.length
3222 Length in bytes of the changed region.
3225 @item events.register_changed
3226 Emits @code{gdb.RegisterChangedEvent} which indicates that a register in the
3227 inferior has been modified by the @value{GDBN} user.
3229 @defvar RegisterChangedEvent.frame
3230 A gdb.Frame object representing the frame in which the register was modified.
3232 @defvar RegisterChangedEvent.regnum
3233 Denotes which register was modified.
3236 @item events.breakpoint_created
3237 This is emitted when a new breakpoint has been created. The argument
3238 that is passed is the new @code{gdb.Breakpoint} object.
3240 @item events.breakpoint_modified
3241 This is emitted when a breakpoint has been modified in some way. The
3242 argument that is passed is the new @code{gdb.Breakpoint} object.
3244 @item events.breakpoint_deleted
3245 This is emitted when a breakpoint has been deleted. The argument that
3246 is passed is the @code{gdb.Breakpoint} object. When this event is
3247 emitted, the @code{gdb.Breakpoint} object will already be in its
3248 invalid state; that is, the @code{is_valid} method will return
3251 @item events.before_prompt
3252 This event carries no payload. It is emitted each time @value{GDBN}
3253 presents a prompt to the user.
3255 @item events.new_inferior
3256 This is emitted when a new inferior is created. Note that the
3257 inferior is not necessarily running; in fact, it may not even have an
3258 associated executable.
3260 The event is of type @code{gdb.NewInferiorEvent}. This has a single
3263 @defvar NewInferiorEvent.inferior
3264 The new inferior, a @code{gdb.Inferior} object.
3267 @item events.inferior_deleted
3268 This is emitted when an inferior has been deleted. Note that this is
3269 not the same as process exit; it is notified when the inferior itself
3270 is removed, say via @code{remove-inferiors}.
3272 The event is of type @code{gdb.InferiorDeletedEvent}. This has a single
3275 @defvar NewInferiorEvent.inferior
3276 The inferior that is being removed, a @code{gdb.Inferior} object.
3279 @item events.new_thread
3280 This is emitted when @value{GDBN} notices a new thread. The event is of
3281 type @code{gdb.NewThreadEvent}, which extends @code{gdb.ThreadEvent}.
3282 This has a single attribute:
3284 @defvar NewThreadEvent.inferior_thread
3290 @node Threads In Python
3291 @subsubsection Threads In Python
3292 @cindex threads in python
3294 @findex gdb.InferiorThread
3295 Python scripts can access information about, and manipulate inferior threads
3296 controlled by @value{GDBN}, via objects of the @code{gdb.InferiorThread} class.
3298 The following thread-related functions are available in the @code{gdb}
3301 @findex gdb.selected_thread
3302 @defun gdb.selected_thread ()
3303 This function returns the thread object for the selected thread. If there
3304 is no selected thread, this will return @code{None}.
3307 To get the list of threads for an inferior, use the @code{Inferior.threads()}
3308 method. @xref{Inferiors In Python}.
3310 A @code{gdb.InferiorThread} object has the following attributes:
3312 @defvar InferiorThread.name
3313 The name of the thread. If the user specified a name using
3314 @code{thread name}, then this returns that name. Otherwise, if an
3315 OS-supplied name is available, then it is returned. Otherwise, this
3316 returns @code{None}.
3318 This attribute can be assigned to. The new value must be a string
3319 object, which sets the new name, or @code{None}, which removes any
3320 user-specified thread name.
3323 @defvar InferiorThread.num
3324 The per-inferior number of the thread, as assigned by GDB.
3327 @defvar InferiorThread.global_num
3328 The global ID of the thread, as assigned by GDB. You can use this to
3329 make Python breakpoints thread-specific, for example
3330 (@pxref{python_breakpoint_thread,,The Breakpoint.thread attribute}).
3333 @defvar InferiorThread.ptid
3334 ID of the thread, as assigned by the operating system. This attribute is a
3335 tuple containing three integers. The first is the Process ID (PID); the second
3336 is the Lightweight Process ID (LWPID), and the third is the Thread ID (TID).
3337 Either the LWPID or TID may be 0, which indicates that the operating system
3338 does not use that identifier.
3341 @defvar InferiorThread.inferior
3342 The inferior this thread belongs to. This attribute is represented as
3343 a @code{gdb.Inferior} object. This attribute is not writable.
3346 A @code{gdb.InferiorThread} object has the following methods:
3348 @defun InferiorThread.is_valid ()
3349 Returns @code{True} if the @code{gdb.InferiorThread} object is valid,
3350 @code{False} if not. A @code{gdb.InferiorThread} object will become
3351 invalid if the thread exits, or the inferior that the thread belongs
3352 is deleted. All other @code{gdb.InferiorThread} methods will throw an
3353 exception if it is invalid at the time the method is called.
3356 @defun InferiorThread.switch ()
3357 This changes @value{GDBN}'s currently selected thread to the one represented
3361 @defun InferiorThread.is_stopped ()
3362 Return a Boolean indicating whether the thread is stopped.
3365 @defun InferiorThread.is_running ()
3366 Return a Boolean indicating whether the thread is running.
3369 @defun InferiorThread.is_exited ()
3370 Return a Boolean indicating whether the thread is exited.
3373 @defun InferiorThread.handle ()
3374 Return the thread object's handle, represented as a Python @code{bytes}
3375 object. A @code{gdb.Value} representation of the handle may be
3376 constructed via @code{gdb.Value(bufobj, type)} where @var{bufobj} is
3377 the Python @code{bytes} representation of the handle and @var{type} is
3378 a @code{gdb.Type} for the handle type.
3381 @node Recordings In Python
3382 @subsubsection Recordings In Python
3383 @cindex recordings in python
3385 The following recordings-related functions
3386 (@pxref{Process Record and Replay}) are available in the @code{gdb}
3389 @defun gdb.start_recording (@r{[}method@r{]}, @r{[}format@r{]})
3390 Start a recording using the given @var{method} and @var{format}. If
3391 no @var{format} is given, the default format for the recording method
3392 is used. If no @var{method} is given, the default method will be used.
3393 Returns a @code{gdb.Record} object on success. Throw an exception on
3396 The following strings can be passed as @var{method}:
3402 @code{"btrace"}: Possible values for @var{format}: @code{"pt"},
3403 @code{"bts"} or leave out for default format.
3407 @defun gdb.current_recording ()
3408 Access a currently running recording. Return a @code{gdb.Record}
3409 object on success. Return @code{None} if no recording is currently
3413 @defun gdb.stop_recording ()
3414 Stop the current recording. Throw an exception if no recording is
3415 currently active. All record objects become invalid after this call.
3418 A @code{gdb.Record} object has the following attributes:
3420 @defvar Record.method
3421 A string with the current recording method, e.g.@: @code{full} or
3425 @defvar Record.format
3426 A string with the current recording format, e.g.@: @code{bt}, @code{pts} or
3430 @defvar Record.begin
3431 A method specific instruction object representing the first instruction
3436 A method specific instruction object representing the current
3437 instruction, that is not actually part of the recording.
3440 @defvar Record.replay_position
3441 The instruction representing the current replay position. If there is
3442 no replay active, this will be @code{None}.
3445 @defvar Record.instruction_history
3446 A list with all recorded instructions.
3449 @defvar Record.function_call_history
3450 A list with all recorded function call segments.
3453 A @code{gdb.Record} object has the following methods:
3455 @defun Record.goto (instruction)
3456 Move the replay position to the given @var{instruction}.
3459 The common @code{gdb.Instruction} class that recording method specific
3460 instruction objects inherit from, has the following attributes:
3462 @defvar Instruction.pc
3463 An integer representing this instruction's address.
3466 @defvar Instruction.data
3467 A buffer with the raw instruction data. In Python 3, the return value is a
3468 @code{memoryview} object.
3471 @defvar Instruction.decoded
3472 A human readable string with the disassembled instruction.
3475 @defvar Instruction.size
3476 The size of the instruction in bytes.
3479 Additionally @code{gdb.RecordInstruction} has the following attributes:
3481 @defvar RecordInstruction.number
3482 An integer identifying this instruction. @code{number} corresponds to
3483 the numbers seen in @code{record instruction-history}
3484 (@pxref{Process Record and Replay}).
3487 @defvar RecordInstruction.sal
3488 A @code{gdb.Symtab_and_line} object representing the associated symtab
3489 and line of this instruction. May be @code{None} if no debug information is
3493 @defvar RecordInstruction.is_speculative
3494 A boolean indicating whether the instruction was executed speculatively.
3497 If an error occured during recording or decoding a recording, this error is
3498 represented by a @code{gdb.RecordGap} object in the instruction list. It has
3499 the following attributes:
3501 @defvar RecordGap.number
3502 An integer identifying this gap. @code{number} corresponds to the numbers seen
3503 in @code{record instruction-history} (@pxref{Process Record and Replay}).
3506 @defvar RecordGap.error_code
3507 A numerical representation of the reason for the gap. The value is specific to
3508 the current recording method.
3511 @defvar RecordGap.error_string
3512 A human readable string with the reason for the gap.
3515 A @code{gdb.RecordFunctionSegment} object has the following attributes:
3517 @defvar RecordFunctionSegment.number
3518 An integer identifying this function segment. @code{number} corresponds to
3519 the numbers seen in @code{record function-call-history}
3520 (@pxref{Process Record and Replay}).
3523 @defvar RecordFunctionSegment.symbol
3524 A @code{gdb.Symbol} object representing the associated symbol. May be
3525 @code{None} if no debug information is available.
3528 @defvar RecordFunctionSegment.level
3529 An integer representing the function call's stack level. May be
3530 @code{None} if the function call is a gap.
3533 @defvar RecordFunctionSegment.instructions
3534 A list of @code{gdb.RecordInstruction} or @code{gdb.RecordGap} objects
3535 associated with this function call.
3538 @defvar RecordFunctionSegment.up
3539 A @code{gdb.RecordFunctionSegment} object representing the caller's
3540 function segment. If the call has not been recorded, this will be the
3541 function segment to which control returns. If neither the call nor the
3542 return have been recorded, this will be @code{None}.
3545 @defvar RecordFunctionSegment.prev
3546 A @code{gdb.RecordFunctionSegment} object representing the previous
3547 segment of this function call. May be @code{None}.
3550 @defvar RecordFunctionSegment.next
3551 A @code{gdb.RecordFunctionSegment} object representing the next segment of
3552 this function call. May be @code{None}.
3555 The following example demonstrates the usage of these objects and
3556 functions to create a function that will rewind a record to the last
3557 time a function in a different file was executed. This would typically
3558 be used to track the execution of user provided callback functions in a
3559 library which typically are not visible in a back trace.
3563 rec = gdb.current_recording ()
3567 insn = rec.instruction_history
3572 position = insn.index (rec.replay_position)
3576 filename = insn[position].sal.symtab.fullname ()
3580 for i in reversed (insn[:position]):
3582 current = i.sal.symtab.fullname ()
3586 if filename == current:
3593 Another possible application is to write a function that counts the
3594 number of code executions in a given line range. This line range can
3595 contain parts of functions or span across several functions and is not
3596 limited to be contiguous.
3599 def countrange (filename, linerange):
3602 def filter_only (file_name):
3603 for call in gdb.current_recording ().function_call_history:
3605 if file_name in call.symbol.symtab.fullname ():
3610 for c in filter_only (filename):
3611 for i in c.instructions:
3613 if i.sal.line in linerange:
3622 @node Commands In Python
3623 @subsubsection Commands In Python
3625 @cindex commands in python
3626 @cindex python commands
3627 You can implement new @value{GDBN} CLI commands in Python. A CLI
3628 command is implemented using an instance of the @code{gdb.Command}
3629 class, most commonly using a subclass.
3631 @defun Command.__init__ (name, @var{command_class} @r{[}, @var{completer_class} @r{[}, @var{prefix}@r{]]})
3632 The object initializer for @code{Command} registers the new command
3633 with @value{GDBN}. This initializer is normally invoked from the
3634 subclass' own @code{__init__} method.
3636 @var{name} is the name of the command. If @var{name} consists of
3637 multiple words, then the initial words are looked for as prefix
3638 commands. In this case, if one of the prefix commands does not exist,
3639 an exception is raised.
3641 There is no support for multi-line commands.
3643 @var{command_class} should be one of the @samp{COMMAND_} constants
3644 defined below. This argument tells @value{GDBN} how to categorize the
3645 new command in the help system.
3647 @var{completer_class} is an optional argument. If given, it should be
3648 one of the @samp{COMPLETE_} constants defined below. This argument
3649 tells @value{GDBN} how to perform completion for this command. If not
3650 given, @value{GDBN} will attempt to complete using the object's
3651 @code{complete} method (see below); if no such method is found, an
3652 error will occur when completion is attempted.
3654 @var{prefix} is an optional argument. If @code{True}, then the new
3655 command is a prefix command; sub-commands of this command may be
3658 The help text for the new command is taken from the Python
3659 documentation string for the command's class, if there is one. If no
3660 documentation string is provided, the default value ``This command is
3661 not documented.'' is used.
3664 @cindex don't repeat Python command
3665 @defun Command.dont_repeat ()
3666 By default, a @value{GDBN} command is repeated when the user enters a
3667 blank line at the command prompt. A command can suppress this
3668 behavior by invoking the @code{dont_repeat} method. This is similar
3669 to the user command @code{dont-repeat}, see @ref{Define, dont-repeat}.
3672 @defun Command.invoke (argument, from_tty)
3673 This method is called by @value{GDBN} when this command is invoked.
3675 @var{argument} is a string. It is the argument to the command, after
3676 leading and trailing whitespace has been stripped.
3678 @var{from_tty} is a boolean argument. When true, this means that the
3679 command was entered by the user at the terminal; when false it means
3680 that the command came from elsewhere.
3682 If this method throws an exception, it is turned into a @value{GDBN}
3683 @code{error} call. Otherwise, the return value is ignored.
3685 @findex gdb.string_to_argv
3686 To break @var{argument} up into an argv-like string use
3687 @code{gdb.string_to_argv}. This function behaves identically to
3688 @value{GDBN}'s internal argument lexer @code{buildargv}.
3689 It is recommended to use this for consistency.
3690 Arguments are separated by spaces and may be quoted.
3694 print gdb.string_to_argv ("1 2\ \\\"3 '4 \"5' \"6 '7\"")
3695 ['1', '2 "3', '4 "5', "6 '7"]
3700 @cindex completion of Python commands
3701 @defun Command.complete (text, word)
3702 This method is called by @value{GDBN} when the user attempts
3703 completion on this command. All forms of completion are handled by
3704 this method, that is, the @key{TAB} and @key{M-?} key bindings
3705 (@pxref{Completion}), and the @code{complete} command (@pxref{Help,
3708 The arguments @var{text} and @var{word} are both strings; @var{text}
3709 holds the complete command line up to the cursor's location, while
3710 @var{word} holds the last word of the command line; this is computed
3711 using a word-breaking heuristic.
3713 The @code{complete} method can return several values:
3716 If the return value is a sequence, the contents of the sequence are
3717 used as the completions. It is up to @code{complete} to ensure that the
3718 contents actually do complete the word. A zero-length sequence is
3719 allowed, it means that there were no completions available. Only
3720 string elements of the sequence are used; other elements in the
3721 sequence are ignored.
3724 If the return value is one of the @samp{COMPLETE_} constants defined
3725 below, then the corresponding @value{GDBN}-internal completion
3726 function is invoked, and its result is used.
3729 All other results are treated as though there were no available
3734 When a new command is registered, it must be declared as a member of
3735 some general class of commands. This is used to classify top-level
3736 commands in the on-line help system; note that prefix commands are not
3737 listed under their own category but rather that of their top-level
3738 command. The available classifications are represented by constants
3739 defined in the @code{gdb} module:
3742 @findex COMMAND_NONE
3743 @findex gdb.COMMAND_NONE
3744 @item gdb.COMMAND_NONE
3745 The command does not belong to any particular class. A command in
3746 this category will not be displayed in any of the help categories.
3748 @findex COMMAND_RUNNING
3749 @findex gdb.COMMAND_RUNNING
3750 @item gdb.COMMAND_RUNNING
3751 The command is related to running the inferior. For example,
3752 @code{start}, @code{step}, and @code{continue} are in this category.
3753 Type @kbd{help running} at the @value{GDBN} prompt to see a list of
3754 commands in this category.
3756 @findex COMMAND_DATA
3757 @findex gdb.COMMAND_DATA
3758 @item gdb.COMMAND_DATA
3759 The command is related to data or variables. For example,
3760 @code{call}, @code{find}, and @code{print} are in this category. Type
3761 @kbd{help data} at the @value{GDBN} prompt to see a list of commands
3764 @findex COMMAND_STACK
3765 @findex gdb.COMMAND_STACK
3766 @item gdb.COMMAND_STACK
3767 The command has to do with manipulation of the stack. For example,
3768 @code{backtrace}, @code{frame}, and @code{return} are in this
3769 category. Type @kbd{help stack} at the @value{GDBN} prompt to see a
3770 list of commands in this category.
3772 @findex COMMAND_FILES
3773 @findex gdb.COMMAND_FILES
3774 @item gdb.COMMAND_FILES
3775 This class is used for file-related commands. For example,
3776 @code{file}, @code{list} and @code{section} are in this category.
3777 Type @kbd{help files} at the @value{GDBN} prompt to see a list of
3778 commands in this category.
3780 @findex COMMAND_SUPPORT
3781 @findex gdb.COMMAND_SUPPORT
3782 @item gdb.COMMAND_SUPPORT
3783 This should be used for ``support facilities'', generally meaning
3784 things that are useful to the user when interacting with @value{GDBN},
3785 but not related to the state of the inferior. For example,
3786 @code{help}, @code{make}, and @code{shell} are in this category. Type
3787 @kbd{help support} at the @value{GDBN} prompt to see a list of
3788 commands in this category.
3790 @findex COMMAND_STATUS
3791 @findex gdb.COMMAND_STATUS
3792 @item gdb.COMMAND_STATUS
3793 The command is an @samp{info}-related command, that is, related to the
3794 state of @value{GDBN} itself. For example, @code{info}, @code{macro},
3795 and @code{show} are in this category. Type @kbd{help status} at the
3796 @value{GDBN} prompt to see a list of commands in this category.
3798 @findex COMMAND_BREAKPOINTS
3799 @findex gdb.COMMAND_BREAKPOINTS
3800 @item gdb.COMMAND_BREAKPOINTS
3801 The command has to do with breakpoints. For example, @code{break},
3802 @code{clear}, and @code{delete} are in this category. Type @kbd{help
3803 breakpoints} at the @value{GDBN} prompt to see a list of commands in
3806 @findex COMMAND_TRACEPOINTS
3807 @findex gdb.COMMAND_TRACEPOINTS
3808 @item gdb.COMMAND_TRACEPOINTS
3809 The command has to do with tracepoints. For example, @code{trace},
3810 @code{actions}, and @code{tfind} are in this category. Type
3811 @kbd{help tracepoints} at the @value{GDBN} prompt to see a list of
3812 commands in this category.
3814 @findex COMMAND_USER
3815 @findex gdb.COMMAND_USER
3816 @item gdb.COMMAND_USER
3817 The command is a general purpose command for the user, and typically
3818 does not fit in one of the other categories.
3819 Type @kbd{help user-defined} at the @value{GDBN} prompt to see
3820 a list of commands in this category, as well as the list of gdb macros
3821 (@pxref{Sequences}).
3823 @findex COMMAND_OBSCURE
3824 @findex gdb.COMMAND_OBSCURE
3825 @item gdb.COMMAND_OBSCURE
3826 The command is only used in unusual circumstances, or is not of
3827 general interest to users. For example, @code{checkpoint},
3828 @code{fork}, and @code{stop} are in this category. Type @kbd{help
3829 obscure} at the @value{GDBN} prompt to see a list of commands in this
3832 @findex COMMAND_MAINTENANCE
3833 @findex gdb.COMMAND_MAINTENANCE
3834 @item gdb.COMMAND_MAINTENANCE
3835 The command is only useful to @value{GDBN} maintainers. The
3836 @code{maintenance} and @code{flushregs} commands are in this category.
3837 Type @kbd{help internals} at the @value{GDBN} prompt to see a list of
3838 commands in this category.
3841 A new command can use a predefined completion function, either by
3842 specifying it via an argument at initialization, or by returning it
3843 from the @code{complete} method. These predefined completion
3844 constants are all defined in the @code{gdb} module:
3847 @vindex COMPLETE_NONE
3848 @item gdb.COMPLETE_NONE
3849 This constant means that no completion should be done.
3851 @vindex COMPLETE_FILENAME
3852 @item gdb.COMPLETE_FILENAME
3853 This constant means that filename completion should be performed.
3855 @vindex COMPLETE_LOCATION
3856 @item gdb.COMPLETE_LOCATION
3857 This constant means that location completion should be done.
3858 @xref{Specify Location}.
3860 @vindex COMPLETE_COMMAND
3861 @item gdb.COMPLETE_COMMAND
3862 This constant means that completion should examine @value{GDBN}
3865 @vindex COMPLETE_SYMBOL
3866 @item gdb.COMPLETE_SYMBOL
3867 This constant means that completion should be done using symbol names
3870 @vindex COMPLETE_EXPRESSION
3871 @item gdb.COMPLETE_EXPRESSION
3872 This constant means that completion should be done on expressions.
3873 Often this means completing on symbol names, but some language
3874 parsers also have support for completing on field names.
3877 The following code snippet shows how a trivial CLI command can be
3878 implemented in Python:
3881 class HelloWorld (gdb.Command):
3882 """Greet the whole world."""
3884 def __init__ (self):
3885 super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)
3887 def invoke (self, arg, from_tty):
3888 print "Hello, World!"
3893 The last line instantiates the class, and is necessary to trigger the
3894 registration of the command with @value{GDBN}. Depending on how the
3895 Python code is read into @value{GDBN}, you may need to import the
3896 @code{gdb} module explicitly.
3898 @node Parameters In Python
3899 @subsubsection Parameters In Python
3901 @cindex parameters in python
3902 @cindex python parameters
3903 @tindex gdb.Parameter
3905 You can implement new @value{GDBN} parameters using Python. A new
3906 parameter is implemented as an instance of the @code{gdb.Parameter}
3909 Parameters are exposed to the user via the @code{set} and
3910 @code{show} commands. @xref{Help}.
3912 There are many parameters that already exist and can be set in
3913 @value{GDBN}. Two examples are: @code{set follow fork} and
3914 @code{set charset}. Setting these parameters influences certain
3915 behavior in @value{GDBN}. Similarly, you can define parameters that
3916 can be used to influence behavior in custom Python scripts and commands.
3918 @defun Parameter.__init__ (name, @var{command-class}, @var{parameter-class} @r{[}, @var{enum-sequence}@r{]})
3919 The object initializer for @code{Parameter} registers the new
3920 parameter with @value{GDBN}. This initializer is normally invoked
3921 from the subclass' own @code{__init__} method.
3923 @var{name} is the name of the new parameter. If @var{name} consists
3924 of multiple words, then the initial words are looked for as prefix
3925 parameters. An example of this can be illustrated with the
3926 @code{set print} set of parameters. If @var{name} is
3927 @code{print foo}, then @code{print} will be searched as the prefix
3928 parameter. In this case the parameter can subsequently be accessed in
3929 @value{GDBN} as @code{set print foo}.
3931 If @var{name} consists of multiple words, and no prefix parameter group
3932 can be found, an exception is raised.
3934 @var{command-class} should be one of the @samp{COMMAND_} constants
3935 (@pxref{Commands In Python}). This argument tells @value{GDBN} how to
3936 categorize the new parameter in the help system.
3938 @var{parameter-class} should be one of the @samp{PARAM_} constants
3939 defined below. This argument tells @value{GDBN} the type of the new
3940 parameter; this information is used for input validation and
3943 If @var{parameter-class} is @code{PARAM_ENUM}, then
3944 @var{enum-sequence} must be a sequence of strings. These strings
3945 represent the possible values for the parameter.
3947 If @var{parameter-class} is not @code{PARAM_ENUM}, then the presence
3948 of a fourth argument will cause an exception to be thrown.
3950 The help text for the new parameter is taken from the Python
3951 documentation string for the parameter's class, if there is one. If
3952 there is no documentation string, a default value is used.
3955 @defvar Parameter.set_doc
3956 If this attribute exists, and is a string, then its value is used as
3957 the help text for this parameter's @code{set} command. The value is
3958 examined when @code{Parameter.__init__} is invoked; subsequent changes
3962 @defvar Parameter.show_doc
3963 If this attribute exists, and is a string, then its value is used as
3964 the help text for this parameter's @code{show} command. The value is
3965 examined when @code{Parameter.__init__} is invoked; subsequent changes
3969 @defvar Parameter.value
3970 The @code{value} attribute holds the underlying value of the
3971 parameter. It can be read and assigned to just as any other
3972 attribute. @value{GDBN} does validation when assignments are made.
3975 There are two methods that may be implemented in any @code{Parameter}
3978 @defun Parameter.get_set_string (self)
3979 If this method exists, @value{GDBN} will call it when a
3980 @var{parameter}'s value has been changed via the @code{set} API (for
3981 example, @kbd{set foo off}). The @code{value} attribute has already
3982 been populated with the new value and may be used in output. This
3983 method must return a string. If the returned string is not empty,
3984 @value{GDBN} will present it to the user.
3986 If this method raises the @code{gdb.GdbError} exception
3987 (@pxref{Exception Handling}), then @value{GDBN} will print the
3988 exception's string and the @code{set} command will fail. Note,
3989 however, that the @code{value} attribute will not be reset in this
3990 case. So, if your parameter must validate values, it should store the
3991 old value internally and reset the exposed value, like so:
3994 class ExampleParam (gdb.Parameter):
3995 def __init__ (self, name):
3996 super (ExampleParam, self).__init__ (name,
4000 self.saved_value = True
4003 def get_set_string (self):
4004 if not self.validate():
4005 self.value = self.saved_value
4006 raise gdb.GdbError('Failed to validate')
4007 self.saved_value = self.value
4011 @defun Parameter.get_show_string (self, svalue)
4012 @value{GDBN} will call this method when a @var{parameter}'s
4013 @code{show} API has been invoked (for example, @kbd{show foo}). The
4014 argument @code{svalue} receives the string representation of the
4015 current value. This method must return a string.
4018 When a new parameter is defined, its type must be specified. The
4019 available types are represented by constants defined in the @code{gdb}
4023 @findex PARAM_BOOLEAN
4024 @findex gdb.PARAM_BOOLEAN
4025 @item gdb.PARAM_BOOLEAN
4026 The value is a plain boolean. The Python boolean values, @code{True}
4027 and @code{False} are the only valid values.
4029 @findex PARAM_AUTO_BOOLEAN
4030 @findex gdb.PARAM_AUTO_BOOLEAN
4031 @item gdb.PARAM_AUTO_BOOLEAN
4032 The value has three possible states: true, false, and @samp{auto}. In
4033 Python, true and false are represented using boolean constants, and
4034 @samp{auto} is represented using @code{None}.
4036 @findex PARAM_UINTEGER
4037 @findex gdb.PARAM_UINTEGER
4038 @item gdb.PARAM_UINTEGER
4039 The value is an unsigned integer. The value of 0 should be
4040 interpreted to mean ``unlimited''.
4042 @findex PARAM_INTEGER
4043 @findex gdb.PARAM_INTEGER
4044 @item gdb.PARAM_INTEGER
4045 The value is a signed integer. The value of 0 should be interpreted
4046 to mean ``unlimited''.
4048 @findex PARAM_STRING
4049 @findex gdb.PARAM_STRING
4050 @item gdb.PARAM_STRING
4051 The value is a string. When the user modifies the string, any escape
4052 sequences, such as @samp{\t}, @samp{\f}, and octal escapes, are
4053 translated into corresponding characters and encoded into the current
4056 @findex PARAM_STRING_NOESCAPE
4057 @findex gdb.PARAM_STRING_NOESCAPE
4058 @item gdb.PARAM_STRING_NOESCAPE
4059 The value is a string. When the user modifies the string, escapes are
4060 passed through untranslated.
4062 @findex PARAM_OPTIONAL_FILENAME
4063 @findex gdb.PARAM_OPTIONAL_FILENAME
4064 @item gdb.PARAM_OPTIONAL_FILENAME
4065 The value is a either a filename (a string), or @code{None}.
4067 @findex PARAM_FILENAME
4068 @findex gdb.PARAM_FILENAME
4069 @item gdb.PARAM_FILENAME
4070 The value is a filename. This is just like
4071 @code{PARAM_STRING_NOESCAPE}, but uses file names for completion.
4073 @findex PARAM_ZINTEGER
4074 @findex gdb.PARAM_ZINTEGER
4075 @item gdb.PARAM_ZINTEGER
4076 The value is an integer. This is like @code{PARAM_INTEGER}, except 0
4077 is interpreted as itself.
4079 @findex PARAM_ZUINTEGER
4080 @findex gdb.PARAM_ZUINTEGER
4081 @item gdb.PARAM_ZUINTEGER
4082 The value is an unsigned integer. This is like @code{PARAM_INTEGER},
4083 except 0 is interpreted as itself, and the value cannot be negative.
4085 @findex PARAM_ZUINTEGER_UNLIMITED
4086 @findex gdb.PARAM_ZUINTEGER_UNLIMITED
4087 @item gdb.PARAM_ZUINTEGER_UNLIMITED
4088 The value is a signed integer. This is like @code{PARAM_ZUINTEGER},
4089 except the special value -1 should be interpreted to mean
4090 ``unlimited''. Other negative values are not allowed.
4093 @findex gdb.PARAM_ENUM
4094 @item gdb.PARAM_ENUM
4095 The value is a string, which must be one of a collection string
4096 constants provided when the parameter is created.
4099 @node Functions In Python
4100 @subsubsection Writing new convenience functions
4102 @cindex writing convenience functions
4103 @cindex convenience functions in python
4104 @cindex python convenience functions
4105 @tindex gdb.Function
4107 You can implement new convenience functions (@pxref{Convenience Vars})
4108 in Python. A convenience function is an instance of a subclass of the
4109 class @code{gdb.Function}.
4111 @defun Function.__init__ (name)
4112 The initializer for @code{Function} registers the new function with
4113 @value{GDBN}. The argument @var{name} is the name of the function,
4114 a string. The function will be visible to the user as a convenience
4115 variable of type @code{internal function}, whose name is the same as
4116 the given @var{name}.
4118 The documentation for the new function is taken from the documentation
4119 string for the new class.
4122 @defun Function.invoke (@var{*args})
4123 When a convenience function is evaluated, its arguments are converted
4124 to instances of @code{gdb.Value}, and then the function's
4125 @code{invoke} method is called. Note that @value{GDBN} does not
4126 predetermine the arity of convenience functions. Instead, all
4127 available arguments are passed to @code{invoke}, following the
4128 standard Python calling convention. In particular, a convenience
4129 function can have default values for parameters without ill effect.
4131 The return value of this method is used as its value in the enclosing
4132 expression. If an ordinary Python value is returned, it is converted
4133 to a @code{gdb.Value} following the usual rules.
4136 The following code snippet shows how a trivial convenience function can
4137 be implemented in Python:
4140 class Greet (gdb.Function):
4141 """Return string to greet someone.
4142 Takes a name as argument."""
4144 def __init__ (self):
4145 super (Greet, self).__init__ ("greet")
4147 def invoke (self, name):
4148 return "Hello, %s!" % name.string ()
4153 The last line instantiates the class, and is necessary to trigger the
4154 registration of the function with @value{GDBN}. Depending on how the
4155 Python code is read into @value{GDBN}, you may need to import the
4156 @code{gdb} module explicitly.
4158 Now you can use the function in an expression:
4161 (gdb) print $greet("Bob")
4165 @node Progspaces In Python
4166 @subsubsection Program Spaces In Python
4168 @cindex progspaces in python
4169 @tindex gdb.Progspace
4171 A program space, or @dfn{progspace}, represents a symbolic view
4172 of an address space.
4173 It consists of all of the objfiles of the program.
4174 @xref{Objfiles In Python}.
4175 @xref{Inferiors Connections and Programs, program spaces}, for more details
4176 about program spaces.
4178 The following progspace-related functions are available in the
4181 @findex gdb.current_progspace
4182 @defun gdb.current_progspace ()
4183 This function returns the program space of the currently selected inferior.
4184 @xref{Inferiors Connections and Programs}. This is identical to
4185 @code{gdb.selected_inferior().progspace} (@pxref{Inferiors In Python}) and is
4186 included for historical compatibility.
4189 @findex gdb.progspaces
4190 @defun gdb.progspaces ()
4191 Return a sequence of all the progspaces currently known to @value{GDBN}.
4194 Each progspace is represented by an instance of the @code{gdb.Progspace}
4197 @defvar Progspace.filename
4198 The file name of the progspace as a string.
4201 @defvar Progspace.pretty_printers
4202 The @code{pretty_printers} attribute is a list of functions. It is
4203 used to look up pretty-printers. A @code{Value} is passed to each
4204 function in order; if the function returns @code{None}, then the
4205 search continues. Otherwise, the return value should be an object
4206 which is used to format the value. @xref{Pretty Printing API}, for more
4210 @defvar Progspace.type_printers
4211 The @code{type_printers} attribute is a list of type printer objects.
4212 @xref{Type Printing API}, for more information.
4215 @defvar Progspace.frame_filters
4216 The @code{frame_filters} attribute is a dictionary of frame filter
4217 objects. @xref{Frame Filter API}, for more information.
4220 A program space has the following methods:
4222 @findex Progspace.block_for_pc
4223 @defun Progspace.block_for_pc (pc)
4224 Return the innermost @code{gdb.Block} containing the given @var{pc}
4225 value. If the block cannot be found for the @var{pc} value specified,
4226 the function will return @code{None}.
4229 @findex Progspace.find_pc_line
4230 @defun Progspace.find_pc_line (pc)
4231 Return the @code{gdb.Symtab_and_line} object corresponding to the
4232 @var{pc} value. @xref{Symbol Tables In Python}. If an invalid value
4233 of @var{pc} is passed as an argument, then the @code{symtab} and
4234 @code{line} attributes of the returned @code{gdb.Symtab_and_line}
4235 object will be @code{None} and 0 respectively.
4238 @findex Progspace.is_valid
4239 @defun Progspace.is_valid ()
4240 Returns @code{True} if the @code{gdb.Progspace} object is valid,
4241 @code{False} if not. A @code{gdb.Progspace} object can become invalid
4242 if the program space file it refers to is not referenced by any
4243 inferior. All other @code{gdb.Progspace} methods will throw an
4244 exception if it is invalid at the time the method is called.
4247 @findex Progspace.objfiles
4248 @defun Progspace.objfiles ()
4249 Return a sequence of all the objfiles referenced by this program
4250 space. @xref{Objfiles In Python}.
4253 @findex Progspace.solib_name
4254 @defun Progspace.solib_name (address)
4255 Return the name of the shared library holding the given @var{address}
4256 as a string, or @code{None}.
4259 One may add arbitrary attributes to @code{gdb.Progspace} objects
4260 in the usual Python way.
4261 This is useful if, for example, one needs to do some extra record keeping
4262 associated with the program space.
4264 In this contrived example, we want to perform some processing when
4265 an objfile with a certain symbol is loaded, but we only want to do
4266 this once because it is expensive. To achieve this we record the results
4267 with the program space because we can't predict when the desired objfile
4272 def clear_objfiles_handler(event):
4273 event.progspace.expensive_computation = None
4274 def expensive(symbol):
4275 """A mock routine to perform an "expensive" computation on symbol."""
4276 print "Computing the answer to the ultimate question ..."
4278 def new_objfile_handler(event):
4279 objfile = event.new_objfile
4280 progspace = objfile.progspace
4281 if not hasattr(progspace, 'expensive_computation') or \
4282 progspace.expensive_computation is None:
4283 # We use 'main' for the symbol to keep the example simple.
4284 # Note: There's no current way to constrain the lookup
4286 symbol = gdb.lookup_global_symbol('main')
4287 if symbol is not None:
4288 progspace.expensive_computation = expensive(symbol)
4289 gdb.events.clear_objfiles.connect(clear_objfiles_handler)
4290 gdb.events.new_objfile.connect(new_objfile_handler)
4292 (gdb) file /tmp/hello
4293 Reading symbols from /tmp/hello...
4294 Computing the answer to the ultimate question ...
4295 (gdb) python print gdb.current_progspace().expensive_computation
4298 Starting program: /tmp/hello
4300 [Inferior 1 (process 4242) exited normally]
4303 @node Objfiles In Python
4304 @subsubsection Objfiles In Python
4306 @cindex objfiles in python
4309 @value{GDBN} loads symbols for an inferior from various
4310 symbol-containing files (@pxref{Files}). These include the primary
4311 executable file, any shared libraries used by the inferior, and any
4312 separate debug info files (@pxref{Separate Debug Files}).
4313 @value{GDBN} calls these symbol-containing files @dfn{objfiles}.
4315 The following objfile-related functions are available in the
4318 @findex gdb.current_objfile
4319 @defun gdb.current_objfile ()
4320 When auto-loading a Python script (@pxref{Python Auto-loading}), @value{GDBN}
4321 sets the ``current objfile'' to the corresponding objfile. This
4322 function returns the current objfile. If there is no current objfile,
4323 this function returns @code{None}.
4326 @findex gdb.objfiles
4327 @defun gdb.objfiles ()
4328 Return a sequence of objfiles referenced by the current program space.
4329 @xref{Objfiles In Python}, and @ref{Progspaces In Python}. This is identical
4330 to @code{gdb.selected_inferior().progspace.objfiles()} and is included for
4331 historical compatibility.
4334 @findex gdb.lookup_objfile
4335 @defun gdb.lookup_objfile (name @r{[}, by_build_id{]})
4336 Look up @var{name}, a file name or build ID, in the list of objfiles
4337 for the current program space (@pxref{Progspaces In Python}).
4338 If the objfile is not found throw the Python @code{ValueError} exception.
4340 If @var{name} is a relative file name, then it will match any
4341 source file name with the same trailing components. For example, if
4342 @var{name} is @samp{gcc/expr.c}, then it will match source file
4343 name of @file{/build/trunk/gcc/expr.c}, but not
4344 @file{/build/trunk/libcpp/expr.c} or @file{/build/trunk/gcc/x-expr.c}.
4346 If @var{by_build_id} is provided and is @code{True} then @var{name}
4347 is the build ID of the objfile. Otherwise, @var{name} is a file name.
4348 This is supported only on some operating systems, notably those which use
4349 the ELF format for binary files and the @sc{gnu} Binutils. For more details
4350 about this feature, see the description of the @option{--build-id}
4351 command-line option in @ref{Options, , Command Line Options, ld,
4355 Each objfile is represented by an instance of the @code{gdb.Objfile}
4358 @defvar Objfile.filename
4359 The file name of the objfile as a string, with symbolic links resolved.
4361 The value is @code{None} if the objfile is no longer valid.
4362 See the @code{gdb.Objfile.is_valid} method, described below.
4365 @defvar Objfile.username
4366 The file name of the objfile as specified by the user as a string.
4368 The value is @code{None} if the objfile is no longer valid.
4369 See the @code{gdb.Objfile.is_valid} method, described below.
4372 @defvar Objfile.owner
4373 For separate debug info objfiles this is the corresponding @code{gdb.Objfile}
4374 object that debug info is being provided for.
4375 Otherwise this is @code{None}.
4376 Separate debug info objfiles are added with the
4377 @code{gdb.Objfile.add_separate_debug_file} method, described below.
4380 @defvar Objfile.build_id
4381 The build ID of the objfile as a string.
4382 If the objfile does not have a build ID then the value is @code{None}.
4384 This is supported only on some operating systems, notably those which use
4385 the ELF format for binary files and the @sc{gnu} Binutils. For more details
4386 about this feature, see the description of the @option{--build-id}
4387 command-line option in @ref{Options, , Command Line Options, ld,
4391 @defvar Objfile.progspace
4392 The containing program space of the objfile as a @code{gdb.Progspace}
4393 object. @xref{Progspaces In Python}.
4396 @defvar Objfile.pretty_printers
4397 The @code{pretty_printers} attribute is a list of functions. It is
4398 used to look up pretty-printers. A @code{Value} is passed to each
4399 function in order; if the function returns @code{None}, then the
4400 search continues. Otherwise, the return value should be an object
4401 which is used to format the value. @xref{Pretty Printing API}, for more
4405 @defvar Objfile.type_printers
4406 The @code{type_printers} attribute is a list of type printer objects.
4407 @xref{Type Printing API}, for more information.
4410 @defvar Objfile.frame_filters
4411 The @code{frame_filters} attribute is a dictionary of frame filter
4412 objects. @xref{Frame Filter API}, for more information.
4415 One may add arbitrary attributes to @code{gdb.Objfile} objects
4416 in the usual Python way.
4417 This is useful if, for example, one needs to do some extra record keeping
4418 associated with the objfile.
4420 In this contrived example we record the time when @value{GDBN}
4426 def new_objfile_handler(event):
4427 # Set the time_loaded attribute of the new objfile.
4428 event.new_objfile.time_loaded = datetime.datetime.today()
4429 gdb.events.new_objfile.connect(new_objfile_handler)
4432 Reading symbols from ./hello...
4433 (gdb) python print gdb.objfiles()[0].time_loaded
4434 2014-10-09 11:41:36.770345
4437 A @code{gdb.Objfile} object has the following methods:
4439 @defun Objfile.is_valid ()
4440 Returns @code{True} if the @code{gdb.Objfile} object is valid,
4441 @code{False} if not. A @code{gdb.Objfile} object can become invalid
4442 if the object file it refers to is not loaded in @value{GDBN} any
4443 longer. All other @code{gdb.Objfile} methods will throw an exception
4444 if it is invalid at the time the method is called.
4447 @defun Objfile.add_separate_debug_file (file)
4448 Add @var{file} to the list of files that @value{GDBN} will search for
4449 debug information for the objfile.
4450 This is useful when the debug info has been removed from the program
4451 and stored in a separate file. @value{GDBN} has built-in support for
4452 finding separate debug info files (@pxref{Separate Debug Files}), but if
4453 the file doesn't live in one of the standard places that @value{GDBN}
4454 searches then this function can be used to add a debug info file
4455 from a different place.
4458 @defun Objfile.lookup_global_symbol (name @r{[}, domain@r{]})
4459 Search for a global symbol named @var{name} in this objfile. Optionally, the
4460 search scope can be restricted with the @var{domain} argument.
4461 The @var{domain} argument must be a domain constant defined in the @code{gdb}
4462 module and described in @ref{Symbols In Python}. This function is similar to
4463 @code{gdb.lookup_global_symbol}, except that the search is limited to this
4466 The result is a @code{gdb.Symbol} object or @code{None} if the symbol
4470 @defun Objfile.lookup_static_symbol (name @r{[}, domain@r{]})
4471 Like @code{Objfile.lookup_global_symbol}, but searches for a global
4472 symbol with static linkage named @var{name} in this objfile.
4475 @node Frames In Python
4476 @subsubsection Accessing inferior stack frames from Python
4478 @cindex frames in python
4479 When the debugged program stops, @value{GDBN} is able to analyze its call
4480 stack (@pxref{Frames,,Stack frames}). The @code{gdb.Frame} class
4481 represents a frame in the stack. A @code{gdb.Frame} object is only valid
4482 while its corresponding frame exists in the inferior's stack. If you try
4483 to use an invalid frame object, @value{GDBN} will throw a @code{gdb.error}
4484 exception (@pxref{Exception Handling}).
4486 Two @code{gdb.Frame} objects can be compared for equality with the @code{==}
4490 (@value{GDBP}) python print gdb.newest_frame() == gdb.selected_frame ()
4494 The following frame-related functions are available in the @code{gdb} module:
4496 @findex gdb.selected_frame
4497 @defun gdb.selected_frame ()
4498 Return the selected frame object. (@pxref{Selection,,Selecting a Frame}).
4501 @findex gdb.newest_frame
4502 @defun gdb.newest_frame ()
4503 Return the newest frame object for the selected thread.
4506 @defun gdb.frame_stop_reason_string (reason)
4507 Return a string explaining the reason why @value{GDBN} stopped unwinding
4508 frames, as expressed by the given @var{reason} code (an integer, see the
4509 @code{unwind_stop_reason} method further down in this section).
4512 @findex gdb.invalidate_cached_frames
4513 @defun gdb.invalidate_cached_frames
4514 @value{GDBN} internally keeps a cache of the frames that have been
4515 unwound. This function invalidates this cache.
4517 This function should not generally be called by ordinary Python code.
4518 It is documented for the sake of completeness.
4521 A @code{gdb.Frame} object has the following methods:
4523 @defun Frame.is_valid ()
4524 Returns true if the @code{gdb.Frame} object is valid, false if not.
4525 A frame object can become invalid if the frame it refers to doesn't
4526 exist anymore in the inferior. All @code{gdb.Frame} methods will throw
4527 an exception if it is invalid at the time the method is called.
4530 @defun Frame.name ()
4531 Returns the function name of the frame, or @code{None} if it can't be
4535 @defun Frame.architecture ()
4536 Returns the @code{gdb.Architecture} object corresponding to the frame's
4537 architecture. @xref{Architectures In Python}.
4540 @defun Frame.type ()
4541 Returns the type of the frame. The value can be one of:
4543 @item gdb.NORMAL_FRAME
4544 An ordinary stack frame.
4546 @item gdb.DUMMY_FRAME
4547 A fake stack frame that was created by @value{GDBN} when performing an
4548 inferior function call.
4550 @item gdb.INLINE_FRAME
4551 A frame representing an inlined function. The function was inlined
4552 into a @code{gdb.NORMAL_FRAME} that is older than this one.
4554 @item gdb.TAILCALL_FRAME
4555 A frame representing a tail call. @xref{Tail Call Frames}.
4557 @item gdb.SIGTRAMP_FRAME
4558 A signal trampoline frame. This is the frame created by the OS when
4559 it calls into a signal handler.
4561 @item gdb.ARCH_FRAME
4562 A fake stack frame representing a cross-architecture call.
4564 @item gdb.SENTINEL_FRAME
4565 This is like @code{gdb.NORMAL_FRAME}, but it is only used for the
4570 @defun Frame.unwind_stop_reason ()
4571 Return an integer representing the reason why it's not possible to find
4572 more frames toward the outermost frame. Use
4573 @code{gdb.frame_stop_reason_string} to convert the value returned by this
4574 function to a string. The value can be one of:
4577 @item gdb.FRAME_UNWIND_NO_REASON
4578 No particular reason (older frames should be available).
4580 @item gdb.FRAME_UNWIND_NULL_ID
4581 The previous frame's analyzer returns an invalid result. This is no
4582 longer used by @value{GDBN}, and is kept only for backward
4585 @item gdb.FRAME_UNWIND_OUTERMOST
4586 This frame is the outermost.
4588 @item gdb.FRAME_UNWIND_UNAVAILABLE
4589 Cannot unwind further, because that would require knowing the
4590 values of registers or memory that have not been collected.
4592 @item gdb.FRAME_UNWIND_INNER_ID
4593 This frame ID looks like it ought to belong to a NEXT frame,
4594 but we got it for a PREV frame. Normally, this is a sign of
4595 unwinder failure. It could also indicate stack corruption.
4597 @item gdb.FRAME_UNWIND_SAME_ID
4598 This frame has the same ID as the previous one. That means
4599 that unwinding further would almost certainly give us another
4600 frame with exactly the same ID, so break the chain. Normally,
4601 this is a sign of unwinder failure. It could also indicate
4604 @item gdb.FRAME_UNWIND_NO_SAVED_PC
4605 The frame unwinder did not find any saved PC, but we needed
4606 one to unwind further.
4608 @item gdb.FRAME_UNWIND_MEMORY_ERROR
4609 The frame unwinder caused an error while trying to access memory.
4611 @item gdb.FRAME_UNWIND_FIRST_ERROR
4612 Any stop reason greater or equal to this value indicates some kind
4613 of error. This special value facilitates writing code that tests
4614 for errors in unwinding in a way that will work correctly even if
4615 the list of the other values is modified in future @value{GDBN}
4616 versions. Using it, you could write:
4618 reason = gdb.selected_frame().unwind_stop_reason ()
4619 reason_str = gdb.frame_stop_reason_string (reason)
4620 if reason >= gdb.FRAME_UNWIND_FIRST_ERROR:
4621 print "An error occured: %s" % reason_str
4628 Returns the frame's resume address.
4631 @defun Frame.block ()
4632 Return the frame's code block. @xref{Blocks In Python}. If the frame
4633 does not have a block -- for example, if there is no debugging
4634 information for the code in question -- then this will throw an
4638 @defun Frame.function ()
4639 Return the symbol for the function corresponding to this frame.
4640 @xref{Symbols In Python}.
4643 @defun Frame.older ()
4644 Return the frame that called this frame.
4647 @defun Frame.newer ()
4648 Return the frame called by this frame.
4651 @defun Frame.find_sal ()
4652 Return the frame's symtab and line object.
4653 @xref{Symbol Tables In Python}.
4656 @defun Frame.read_register (register)
4657 Return the value of @var{register} in this frame. The @var{register}
4658 argument must be a string (e.g., @code{'sp'} or @code{'rax'}).
4659 Returns a @code{Gdb.Value} object. Throws an exception if @var{register}
4663 @defun Frame.read_var (variable @r{[}, block@r{]})
4664 Return the value of @var{variable} in this frame. If the optional
4665 argument @var{block} is provided, search for the variable from that
4666 block; otherwise start at the frame's current block (which is
4667 determined by the frame's current program counter). The @var{variable}
4668 argument must be a string or a @code{gdb.Symbol} object; @var{block} must be a
4669 @code{gdb.Block} object.
4672 @defun Frame.select ()
4673 Set this frame to be the selected frame. @xref{Stack, ,Examining the
4677 @node Blocks In Python
4678 @subsubsection Accessing blocks from Python
4680 @cindex blocks in python
4683 In @value{GDBN}, symbols are stored in blocks. A block corresponds
4684 roughly to a scope in the source code. Blocks are organized
4685 hierarchically, and are represented individually in Python as a
4686 @code{gdb.Block}. Blocks rely on debugging information being
4689 A frame has a block. Please see @ref{Frames In Python}, for a more
4690 in-depth discussion of frames.
4692 The outermost block is known as the @dfn{global block}. The global
4693 block typically holds public global variables and functions.
4695 The block nested just inside the global block is the @dfn{static
4696 block}. The static block typically holds file-scoped variables and
4699 @value{GDBN} provides a method to get a block's superblock, but there
4700 is currently no way to examine the sub-blocks of a block, or to
4701 iterate over all the blocks in a symbol table (@pxref{Symbol Tables In
4704 Here is a short example that should help explain blocks:
4707 /* This is in the global block. */
4710 /* This is in the static block. */
4711 static int file_scope;
4713 /* 'function' is in the global block, and 'argument' is
4714 in a block nested inside of 'function'. */
4715 int function (int argument)
4717 /* 'local' is in a block inside 'function'. It may or may
4718 not be in the same block as 'argument'. */
4722 /* 'inner' is in a block whose superblock is the one holding
4726 /* If this call is expanded by the compiler, you may see
4727 a nested block here whose function is 'inline_function'
4728 and whose superblock is the one holding 'inner'. */
4734 A @code{gdb.Block} is iterable. The iterator returns the symbols
4735 (@pxref{Symbols In Python}) local to the block. Python programs
4736 should not assume that a specific block object will always contain a
4737 given symbol, since changes in @value{GDBN} features and
4738 infrastructure may cause symbols move across blocks in a symbol
4739 table. You can also use Python's @dfn{dictionary syntax} to access
4740 variables in this block, e.g.:
4743 symbol = some_block['variable'] # symbol is of type gdb.Symbol
4746 The following block-related functions are available in the @code{gdb}
4749 @findex gdb.block_for_pc
4750 @defun gdb.block_for_pc (pc)
4751 Return the innermost @code{gdb.Block} containing the given @var{pc}
4752 value. If the block cannot be found for the @var{pc} value specified,
4753 the function will return @code{None}. This is identical to
4754 @code{gdb.current_progspace().block_for_pc(pc)} and is included for
4755 historical compatibility.
4758 A @code{gdb.Block} object has the following methods:
4760 @defun Block.is_valid ()
4761 Returns @code{True} if the @code{gdb.Block} object is valid,
4762 @code{False} if not. A block object can become invalid if the block it
4763 refers to doesn't exist anymore in the inferior. All other
4764 @code{gdb.Block} methods will throw an exception if it is invalid at
4765 the time the method is called. The block's validity is also checked
4766 during iteration over symbols of the block.
4769 A @code{gdb.Block} object has the following attributes:
4772 The start address of the block. This attribute is not writable.
4776 One past the last address that appears in the block. This attribute
4780 @defvar Block.function
4781 The name of the block represented as a @code{gdb.Symbol}. If the
4782 block is not named, then this attribute holds @code{None}. This
4783 attribute is not writable.
4785 For ordinary function blocks, the superblock is the static block.
4786 However, you should note that it is possible for a function block to
4787 have a superblock that is not the static block -- for instance this
4788 happens for an inlined function.
4791 @defvar Block.superblock
4792 The block containing this block. If this parent block does not exist,
4793 this attribute holds @code{None}. This attribute is not writable.
4796 @defvar Block.global_block
4797 The global block associated with this block. This attribute is not
4801 @defvar Block.static_block
4802 The static block associated with this block. This attribute is not
4806 @defvar Block.is_global
4807 @code{True} if the @code{gdb.Block} object is a global block,
4808 @code{False} if not. This attribute is not
4812 @defvar Block.is_static
4813 @code{True} if the @code{gdb.Block} object is a static block,
4814 @code{False} if not. This attribute is not writable.
4817 @node Symbols In Python
4818 @subsubsection Python representation of Symbols
4820 @cindex symbols in python
4823 @value{GDBN} represents every variable, function and type as an
4824 entry in a symbol table. @xref{Symbols, ,Examining the Symbol Table}.
4825 Similarly, Python represents these symbols in @value{GDBN} with the
4826 @code{gdb.Symbol} object.
4828 The following symbol-related functions are available in the @code{gdb}
4831 @findex gdb.lookup_symbol
4832 @defun gdb.lookup_symbol (name @r{[}, block @r{[}, domain@r{]]})
4833 This function searches for a symbol by name. The search scope can be
4834 restricted to the parameters defined in the optional domain and block
4837 @var{name} is the name of the symbol. It must be a string. The
4838 optional @var{block} argument restricts the search to symbols visible
4839 in that @var{block}. The @var{block} argument must be a
4840 @code{gdb.Block} object. If omitted, the block for the current frame
4841 is used. The optional @var{domain} argument restricts
4842 the search to the domain type. The @var{domain} argument must be a
4843 domain constant defined in the @code{gdb} module and described later
4846 The result is a tuple of two elements.
4847 The first element is a @code{gdb.Symbol} object or @code{None} if the symbol
4849 If the symbol is found, the second element is @code{True} if the symbol
4850 is a field of a method's object (e.g., @code{this} in C@t{++}),
4851 otherwise it is @code{False}.
4852 If the symbol is not found, the second element is @code{False}.
4855 @findex gdb.lookup_global_symbol
4856 @defun gdb.lookup_global_symbol (name @r{[}, domain@r{]})
4857 This function searches for a global symbol by name.
4858 The search scope can be restricted to by the domain argument.
4860 @var{name} is the name of the symbol. It must be a string.
4861 The optional @var{domain} argument restricts the search to the domain type.
4862 The @var{domain} argument must be a domain constant defined in the @code{gdb}
4863 module and described later in this chapter.
4865 The result is a @code{gdb.Symbol} object or @code{None} if the symbol
4869 @findex gdb.lookup_static_symbol
4870 @defun gdb.lookup_static_symbol (name @r{[}, domain@r{]})
4871 This function searches for a global symbol with static linkage by name.
4872 The search scope can be restricted to by the domain argument.
4874 @var{name} is the name of the symbol. It must be a string.
4875 The optional @var{domain} argument restricts the search to the domain type.
4876 The @var{domain} argument must be a domain constant defined in the @code{gdb}
4877 module and described later in this chapter.
4879 The result is a @code{gdb.Symbol} object or @code{None} if the symbol
4882 Note that this function will not find function-scoped static variables. To look
4883 up such variables, iterate over the variables of the function's
4884 @code{gdb.Block} and check that @code{block.addr_class} is
4885 @code{gdb.SYMBOL_LOC_STATIC}.
4887 There can be multiple global symbols with static linkage with the same
4888 name. This function will only return the first matching symbol that
4889 it finds. Which symbol is found depends on where @value{GDBN} is
4890 currently stopped, as @value{GDBN} will first search for matching
4891 symbols in the current object file, and then search all other object
4892 files. If the application is not yet running then @value{GDBN} will
4893 search all object files in the order they appear in the debug
4897 @findex gdb.lookup_static_symbols
4898 @defun gdb.lookup_static_symbols (name @r{[}, domain@r{]})
4899 Similar to @code{gdb.lookup_static_symbol}, this function searches for
4900 global symbols with static linkage by name, and optionally restricted
4901 by the domain argument. However, this function returns a list of all
4902 matching symbols found, not just the first one.
4904 @var{name} is the name of the symbol. It must be a string.
4905 The optional @var{domain} argument restricts the search to the domain type.
4906 The @var{domain} argument must be a domain constant defined in the @code{gdb}
4907 module and described later in this chapter.
4909 The result is a list of @code{gdb.Symbol} objects which could be empty
4910 if no matching symbols were found.
4912 Note that this function will not find function-scoped static variables. To look
4913 up such variables, iterate over the variables of the function's
4914 @code{gdb.Block} and check that @code{block.addr_class} is
4915 @code{gdb.SYMBOL_LOC_STATIC}.
4918 A @code{gdb.Symbol} object has the following attributes:
4921 The type of the symbol or @code{None} if no type is recorded.
4922 This attribute is represented as a @code{gdb.Type} object.
4923 @xref{Types In Python}. This attribute is not writable.
4926 @defvar Symbol.symtab
4927 The symbol table in which the symbol appears. This attribute is
4928 represented as a @code{gdb.Symtab} object. @xref{Symbol Tables In
4929 Python}. This attribute is not writable.
4933 The line number in the source code at which the symbol was defined.
4938 The name of the symbol as a string. This attribute is not writable.
4941 @defvar Symbol.linkage_name
4942 The name of the symbol, as used by the linker (i.e., may be mangled).
4943 This attribute is not writable.
4946 @defvar Symbol.print_name
4947 The name of the symbol in a form suitable for output. This is either
4948 @code{name} or @code{linkage_name}, depending on whether the user
4949 asked @value{GDBN} to display demangled or mangled names.
4952 @defvar Symbol.addr_class
4953 The address class of the symbol. This classifies how to find the value
4954 of a symbol. Each address class is a constant defined in the
4955 @code{gdb} module and described later in this chapter.
4958 @defvar Symbol.needs_frame
4959 This is @code{True} if evaluating this symbol's value requires a frame
4960 (@pxref{Frames In Python}) and @code{False} otherwise. Typically,
4961 local variables will require a frame, but other symbols will not.
4964 @defvar Symbol.is_argument
4965 @code{True} if the symbol is an argument of a function.
4968 @defvar Symbol.is_constant
4969 @code{True} if the symbol is a constant.
4972 @defvar Symbol.is_function
4973 @code{True} if the symbol is a function or a method.
4976 @defvar Symbol.is_variable
4977 @code{True} if the symbol is a variable.
4980 A @code{gdb.Symbol} object has the following methods:
4982 @defun Symbol.is_valid ()
4983 Returns @code{True} if the @code{gdb.Symbol} object is valid,
4984 @code{False} if not. A @code{gdb.Symbol} object can become invalid if
4985 the symbol it refers to does not exist in @value{GDBN} any longer.
4986 All other @code{gdb.Symbol} methods will throw an exception if it is
4987 invalid at the time the method is called.
4990 @defun Symbol.value (@r{[}frame@r{]})
4991 Compute the value of the symbol, as a @code{gdb.Value}. For
4992 functions, this computes the address of the function, cast to the
4993 appropriate type. If the symbol requires a frame in order to compute
4994 its value, then @var{frame} must be given. If @var{frame} is not
4995 given, or if @var{frame} is invalid, then this method will throw an
4999 The available domain categories in @code{gdb.Symbol} are represented
5000 as constants in the @code{gdb} module:
5003 @vindex SYMBOL_UNDEF_DOMAIN
5004 @item gdb.SYMBOL_UNDEF_DOMAIN
5005 This is used when a domain has not been discovered or none of the
5006 following domains apply. This usually indicates an error either
5007 in the symbol information or in @value{GDBN}'s handling of symbols.
5009 @vindex SYMBOL_VAR_DOMAIN
5010 @item gdb.SYMBOL_VAR_DOMAIN
5011 This domain contains variables, function names, typedef names and enum
5014 @vindex SYMBOL_STRUCT_DOMAIN
5015 @item gdb.SYMBOL_STRUCT_DOMAIN
5016 This domain holds struct, union and enum type names.
5018 @vindex SYMBOL_LABEL_DOMAIN
5019 @item gdb.SYMBOL_LABEL_DOMAIN
5020 This domain contains names of labels (for gotos).
5022 @vindex SYMBOL_MODULE_DOMAIN
5023 @item gdb.SYMBOL_MODULE_DOMAIN
5024 This domain contains names of Fortran module types.
5026 @vindex SYMBOL_COMMON_BLOCK_DOMAIN
5027 @item gdb.SYMBOL_COMMON_BLOCK_DOMAIN
5028 This domain contains names of Fortran common blocks.
5031 The available address class categories in @code{gdb.Symbol} are represented
5032 as constants in the @code{gdb} module:
5035 @vindex SYMBOL_LOC_UNDEF
5036 @item gdb.SYMBOL_LOC_UNDEF
5037 If this is returned by address class, it indicates an error either in
5038 the symbol information or in @value{GDBN}'s handling of symbols.
5040 @vindex SYMBOL_LOC_CONST
5041 @item gdb.SYMBOL_LOC_CONST
5042 Value is constant int.
5044 @vindex SYMBOL_LOC_STATIC
5045 @item gdb.SYMBOL_LOC_STATIC
5046 Value is at a fixed address.
5048 @vindex SYMBOL_LOC_REGISTER
5049 @item gdb.SYMBOL_LOC_REGISTER
5050 Value is in a register.
5052 @vindex SYMBOL_LOC_ARG
5053 @item gdb.SYMBOL_LOC_ARG
5054 Value is an argument. This value is at the offset stored within the
5055 symbol inside the frame's argument list.
5057 @vindex SYMBOL_LOC_REF_ARG
5058 @item gdb.SYMBOL_LOC_REF_ARG
5059 Value address is stored in the frame's argument list. Just like
5060 @code{LOC_ARG} except that the value's address is stored at the
5061 offset, not the value itself.
5063 @vindex SYMBOL_LOC_REGPARM_ADDR
5064 @item gdb.SYMBOL_LOC_REGPARM_ADDR
5065 Value is a specified register. Just like @code{LOC_REGISTER} except
5066 the register holds the address of the argument instead of the argument
5069 @vindex SYMBOL_LOC_LOCAL
5070 @item gdb.SYMBOL_LOC_LOCAL
5071 Value is a local variable.
5073 @vindex SYMBOL_LOC_TYPEDEF
5074 @item gdb.SYMBOL_LOC_TYPEDEF
5075 Value not used. Symbols in the domain @code{SYMBOL_STRUCT_DOMAIN} all
5078 @vindex SYMBOL_LOC_BLOCK
5079 @item gdb.SYMBOL_LOC_BLOCK
5082 @vindex SYMBOL_LOC_CONST_BYTES
5083 @item gdb.SYMBOL_LOC_CONST_BYTES
5084 Value is a byte-sequence.
5086 @vindex SYMBOL_LOC_UNRESOLVED
5087 @item gdb.SYMBOL_LOC_UNRESOLVED
5088 Value is at a fixed address, but the address of the variable has to be
5089 determined from the minimal symbol table whenever the variable is
5092 @vindex SYMBOL_LOC_OPTIMIZED_OUT
5093 @item gdb.SYMBOL_LOC_OPTIMIZED_OUT
5094 The value does not actually exist in the program.
5096 @vindex SYMBOL_LOC_COMPUTED
5097 @item gdb.SYMBOL_LOC_COMPUTED
5098 The value's address is a computed location.
5100 @vindex SYMBOL_LOC_COMPUTED
5101 @item gdb.SYMBOL_LOC_COMPUTED
5102 The value's address is a symbol. This is only used for Fortran common
5106 @node Symbol Tables In Python
5107 @subsubsection Symbol table representation in Python
5109 @cindex symbol tables in python
5111 @tindex gdb.Symtab_and_line
5113 Access to symbol table data maintained by @value{GDBN} on the inferior
5114 is exposed to Python via two objects: @code{gdb.Symtab_and_line} and
5115 @code{gdb.Symtab}. Symbol table and line data for a frame is returned
5116 from the @code{find_sal} method in @code{gdb.Frame} object.
5117 @xref{Frames In Python}.
5119 For more information on @value{GDBN}'s symbol table management, see
5120 @ref{Symbols, ,Examining the Symbol Table}, for more information.
5122 A @code{gdb.Symtab_and_line} object has the following attributes:
5124 @defvar Symtab_and_line.symtab
5125 The symbol table object (@code{gdb.Symtab}) for this frame.
5126 This attribute is not writable.
5129 @defvar Symtab_and_line.pc
5130 Indicates the start of the address range occupied by code for the
5131 current source line. This attribute is not writable.
5134 @defvar Symtab_and_line.last
5135 Indicates the end of the address range occupied by code for the current
5136 source line. This attribute is not writable.
5139 @defvar Symtab_and_line.line
5140 Indicates the current line number for this object. This
5141 attribute is not writable.
5144 A @code{gdb.Symtab_and_line} object has the following methods:
5146 @defun Symtab_and_line.is_valid ()
5147 Returns @code{True} if the @code{gdb.Symtab_and_line} object is valid,
5148 @code{False} if not. A @code{gdb.Symtab_and_line} object can become
5149 invalid if the Symbol table and line object it refers to does not
5150 exist in @value{GDBN} any longer. All other
5151 @code{gdb.Symtab_and_line} methods will throw an exception if it is
5152 invalid at the time the method is called.
5155 A @code{gdb.Symtab} object has the following attributes:
5157 @defvar Symtab.filename
5158 The symbol table's source filename. This attribute is not writable.
5161 @defvar Symtab.objfile
5162 The symbol table's backing object file. @xref{Objfiles In Python}.
5163 This attribute is not writable.
5166 @defvar Symtab.producer
5167 The name and possibly version number of the program that
5168 compiled the code in the symbol table.
5169 The contents of this string is up to the compiler.
5170 If no producer information is available then @code{None} is returned.
5171 This attribute is not writable.
5174 A @code{gdb.Symtab} object has the following methods:
5176 @defun Symtab.is_valid ()
5177 Returns @code{True} if the @code{gdb.Symtab} object is valid,
5178 @code{False} if not. A @code{gdb.Symtab} object can become invalid if
5179 the symbol table it refers to does not exist in @value{GDBN} any
5180 longer. All other @code{gdb.Symtab} methods will throw an exception
5181 if it is invalid at the time the method is called.
5184 @defun Symtab.fullname ()
5185 Return the symbol table's source absolute file name.
5188 @defun Symtab.global_block ()
5189 Return the global block of the underlying symbol table.
5190 @xref{Blocks In Python}.
5193 @defun Symtab.static_block ()
5194 Return the static block of the underlying symbol table.
5195 @xref{Blocks In Python}.
5198 @defun Symtab.linetable ()
5199 Return the line table associated with the symbol table.
5200 @xref{Line Tables In Python}.
5203 @node Line Tables In Python
5204 @subsubsection Manipulating line tables using Python
5206 @cindex line tables in python
5207 @tindex gdb.LineTable
5209 Python code can request and inspect line table information from a
5210 symbol table that is loaded in @value{GDBN}. A line table is a
5211 mapping of source lines to their executable locations in memory. To
5212 acquire the line table information for a particular symbol table, use
5213 the @code{linetable} function (@pxref{Symbol Tables In Python}).
5215 A @code{gdb.LineTable} is iterable. The iterator returns
5216 @code{LineTableEntry} objects that correspond to the source line and
5217 address for each line table entry. @code{LineTableEntry} objects have
5218 the following attributes:
5220 @defvar LineTableEntry.line
5221 The source line number for this line table entry. This number
5222 corresponds to the actual line of source. This attribute is not
5226 @defvar LineTableEntry.pc
5227 The address that is associated with the line table entry where the
5228 executable code for that source line resides in memory. This
5229 attribute is not writable.
5232 As there can be multiple addresses for a single source line, you may
5233 receive multiple @code{LineTableEntry} objects with matching
5234 @code{line} attributes, but with different @code{pc} attributes. The
5235 iterator is sorted in ascending @code{pc} order. Here is a small
5236 example illustrating iterating over a line table.
5239 symtab = gdb.selected_frame().find_sal().symtab
5240 linetable = symtab.linetable()
5241 for line in linetable:
5242 print "Line: "+str(line.line)+" Address: "+hex(line.pc)
5245 This will have the following output:
5248 Line: 33 Address: 0x4005c8L
5249 Line: 37 Address: 0x4005caL
5250 Line: 39 Address: 0x4005d2L
5251 Line: 40 Address: 0x4005f8L
5252 Line: 42 Address: 0x4005ffL
5253 Line: 44 Address: 0x400608L
5254 Line: 42 Address: 0x40060cL
5255 Line: 45 Address: 0x400615L
5258 In addition to being able to iterate over a @code{LineTable}, it also
5259 has the following direct access methods:
5261 @defun LineTable.line (line)
5262 Return a Python @code{Tuple} of @code{LineTableEntry} objects for any
5263 entries in the line table for the given @var{line}, which specifies
5264 the source code line. If there are no entries for that source code
5265 @var{line}, the Python @code{None} is returned.
5268 @defun LineTable.has_line (line)
5269 Return a Python @code{Boolean} indicating whether there is an entry in
5270 the line table for this source line. Return @code{True} if an entry
5271 is found, or @code{False} if not.
5274 @defun LineTable.source_lines ()
5275 Return a Python @code{List} of the source line numbers in the symbol
5276 table. Only lines with executable code locations are returned. The
5277 contents of the @code{List} will just be the source line entries
5278 represented as Python @code{Long} values.
5281 @node Breakpoints In Python
5282 @subsubsection Manipulating breakpoints using Python
5284 @cindex breakpoints in python
5285 @tindex gdb.Breakpoint
5287 Python code can manipulate breakpoints via the @code{gdb.Breakpoint}
5290 A breakpoint can be created using one of the two forms of the
5291 @code{gdb.Breakpoint} constructor. The first one accepts a string
5292 like one would pass to the @code{break}
5293 (@pxref{Set Breaks,,Setting Breakpoints}) and @code{watch}
5294 (@pxref{Set Watchpoints, , Setting Watchpoints}) commands, and can be used to
5295 create both breakpoints and watchpoints. The second accepts separate Python
5296 arguments similar to @ref{Explicit Locations}, and can only be used to create
5299 @defun Breakpoint.__init__ (spec @r{[}, type @r{][}, wp_class @r{][}, internal @r{][}, temporary @r{][}, qualified @r{]})
5300 Create a new breakpoint according to @var{spec}, which is a string naming the
5301 location of a breakpoint, or an expression that defines a watchpoint. The
5302 string should describe a location in a format recognized by the @code{break}
5303 command (@pxref{Set Breaks,,Setting Breakpoints}) or, in the case of a
5304 watchpoint, by the @code{watch} command
5305 (@pxref{Set Watchpoints, , Setting Watchpoints}).
5307 The optional @var{type} argument specifies the type of the breakpoint to create,
5310 The optional @var{wp_class} argument defines the class of watchpoint to create,
5311 if @var{type} is @code{gdb.BP_WATCHPOINT}. If @var{wp_class} is omitted, it
5312 defaults to @code{gdb.WP_WRITE}.
5314 The optional @var{internal} argument allows the breakpoint to become invisible
5315 to the user. The breakpoint will neither be reported when created, nor will it
5316 be listed in the output from @code{info breakpoints} (but will be listed with
5317 the @code{maint info breakpoints} command).
5319 The optional @var{temporary} argument makes the breakpoint a temporary
5320 breakpoint. Temporary breakpoints are deleted after they have been hit. Any
5321 further access to the Python breakpoint after it has been hit will result in a
5322 runtime error (as that breakpoint has now been automatically deleted).
5324 The optional @var{qualified} argument is a boolean that allows interpreting
5325 the function passed in @code{spec} as a fully-qualified name. It is equivalent
5326 to @code{break}'s @code{-qualified} flag (@pxref{Linespec Locations} and
5327 @ref{Explicit Locations}).
5331 @defun Breakpoint.__init__ (@r{[} source @r{][}, function @r{][}, label @r{][}, line @r{]}, @r{][} internal @r{][}, temporary @r{][}, qualified @r{]})
5332 This second form of creating a new breakpoint specifies the explicit
5333 location (@pxref{Explicit Locations}) using keywords. The new breakpoint will
5334 be created in the specified source file @var{source}, at the specified
5335 @var{function}, @var{label} and @var{line}.
5337 @var{internal}, @var{temporary} and @var{qualified} have the same usage as
5338 explained previously.
5341 The available types are represented by constants defined in the @code{gdb}
5345 @vindex BP_BREAKPOINT
5346 @item gdb.BP_BREAKPOINT
5347 Normal code breakpoint.
5349 @vindex BP_WATCHPOINT
5350 @item gdb.BP_WATCHPOINT
5351 Watchpoint breakpoint.
5353 @vindex BP_HARDWARE_WATCHPOINT
5354 @item gdb.BP_HARDWARE_WATCHPOINT
5355 Hardware assisted watchpoint.
5357 @vindex BP_READ_WATCHPOINT
5358 @item gdb.BP_READ_WATCHPOINT
5359 Hardware assisted read watchpoint.
5361 @vindex BP_ACCESS_WATCHPOINT
5362 @item gdb.BP_ACCESS_WATCHPOINT
5363 Hardware assisted access watchpoint.
5366 The available watchpoint types represented by constants are defined in the
5372 Read only watchpoint.
5376 Write only watchpoint.
5380 Read/Write watchpoint.
5383 @defun Breakpoint.stop (self)
5384 The @code{gdb.Breakpoint} class can be sub-classed and, in
5385 particular, you may choose to implement the @code{stop} method.
5386 If this method is defined in a sub-class of @code{gdb.Breakpoint},
5387 it will be called when the inferior reaches any location of a
5388 breakpoint which instantiates that sub-class. If the method returns
5389 @code{True}, the inferior will be stopped at the location of the
5390 breakpoint, otherwise the inferior will continue.
5392 If there are multiple breakpoints at the same location with a
5393 @code{stop} method, each one will be called regardless of the
5394 return status of the previous. This ensures that all @code{stop}
5395 methods have a chance to execute at that location. In this scenario
5396 if one of the methods returns @code{True} but the others return
5397 @code{False}, the inferior will still be stopped.
5399 You should not alter the execution state of the inferior (i.e.@:, step,
5400 next, etc.), alter the current frame context (i.e.@:, change the current
5401 active frame), or alter, add or delete any breakpoint. As a general
5402 rule, you should not alter any data within @value{GDBN} or the inferior
5405 Example @code{stop} implementation:
5408 class MyBreakpoint (gdb.Breakpoint):
5410 inf_val = gdb.parse_and_eval("foo")
5417 @defun Breakpoint.is_valid ()
5418 Return @code{True} if this @code{Breakpoint} object is valid,
5419 @code{False} otherwise. A @code{Breakpoint} object can become invalid
5420 if the user deletes the breakpoint. In this case, the object still
5421 exists, but the underlying breakpoint does not. In the cases of
5422 watchpoint scope, the watchpoint remains valid even if execution of the
5423 inferior leaves the scope of that watchpoint.
5426 @defun Breakpoint.delete ()
5427 Permanently deletes the @value{GDBN} breakpoint. This also
5428 invalidates the Python @code{Breakpoint} object. Any further access
5429 to this object's attributes or methods will raise an error.
5432 @defvar Breakpoint.enabled
5433 This attribute is @code{True} if the breakpoint is enabled, and
5434 @code{False} otherwise. This attribute is writable. You can use it to enable
5435 or disable the breakpoint.
5438 @defvar Breakpoint.silent
5439 This attribute is @code{True} if the breakpoint is silent, and
5440 @code{False} otherwise. This attribute is writable.
5442 Note that a breakpoint can also be silent if it has commands and the
5443 first command is @code{silent}. This is not reported by the
5444 @code{silent} attribute.
5447 @defvar Breakpoint.pending
5448 This attribute is @code{True} if the breakpoint is pending, and
5449 @code{False} otherwise. @xref{Set Breaks}. This attribute is
5453 @anchor{python_breakpoint_thread}
5454 @defvar Breakpoint.thread
5455 If the breakpoint is thread-specific, this attribute holds the
5456 thread's global id. If the breakpoint is not thread-specific, this
5457 attribute is @code{None}. This attribute is writable.
5460 @defvar Breakpoint.task
5461 If the breakpoint is Ada task-specific, this attribute holds the Ada task
5462 id. If the breakpoint is not task-specific (or the underlying
5463 language is not Ada), this attribute is @code{None}. This attribute
5467 @defvar Breakpoint.ignore_count
5468 This attribute holds the ignore count for the breakpoint, an integer.
5469 This attribute is writable.
5472 @defvar Breakpoint.number
5473 This attribute holds the breakpoint's number --- the identifier used by
5474 the user to manipulate the breakpoint. This attribute is not writable.
5477 @defvar Breakpoint.type
5478 This attribute holds the breakpoint's type --- the identifier used to
5479 determine the actual breakpoint type or use-case. This attribute is not
5483 @defvar Breakpoint.visible
5484 This attribute tells whether the breakpoint is visible to the user
5485 when set, or when the @samp{info breakpoints} command is run. This
5486 attribute is not writable.
5489 @defvar Breakpoint.temporary
5490 This attribute indicates whether the breakpoint was created as a
5491 temporary breakpoint. Temporary breakpoints are automatically deleted
5492 after that breakpoint has been hit. Access to this attribute, and all
5493 other attributes and functions other than the @code{is_valid}
5494 function, will result in an error after the breakpoint has been hit
5495 (as it has been automatically deleted). This attribute is not
5499 @defvar Breakpoint.hit_count
5500 This attribute holds the hit count for the breakpoint, an integer.
5501 This attribute is writable, but currently it can only be set to zero.
5504 @defvar Breakpoint.location
5505 This attribute holds the location of the breakpoint, as specified by
5506 the user. It is a string. If the breakpoint does not have a location
5507 (that is, it is a watchpoint) the attribute's value is @code{None}. This
5508 attribute is not writable.
5511 @defvar Breakpoint.expression
5512 This attribute holds a breakpoint expression, as specified by
5513 the user. It is a string. If the breakpoint does not have an
5514 expression (the breakpoint is not a watchpoint) the attribute's value
5515 is @code{None}. This attribute is not writable.
5518 @defvar Breakpoint.condition
5519 This attribute holds the condition of the breakpoint, as specified by
5520 the user. It is a string. If there is no condition, this attribute's
5521 value is @code{None}. This attribute is writable.
5524 @defvar Breakpoint.commands
5525 This attribute holds the commands attached to the breakpoint. If
5526 there are commands, this attribute's value is a string holding all the
5527 commands, separated by newlines. If there are no commands, this
5528 attribute is @code{None}. This attribute is writable.
5531 @node Finish Breakpoints in Python
5532 @subsubsection Finish Breakpoints
5534 @cindex python finish breakpoints
5535 @tindex gdb.FinishBreakpoint
5537 A finish breakpoint is a temporary breakpoint set at the return address of
5538 a frame, based on the @code{finish} command. @code{gdb.FinishBreakpoint}
5539 extends @code{gdb.Breakpoint}. The underlying breakpoint will be disabled
5540 and deleted when the execution will run out of the breakpoint scope (i.e.@:
5541 @code{Breakpoint.stop} or @code{FinishBreakpoint.out_of_scope} triggered).
5542 Finish breakpoints are thread specific and must be create with the right
5545 @defun FinishBreakpoint.__init__ (@r{[}frame@r{]} @r{[}, internal@r{]})
5546 Create a finish breakpoint at the return address of the @code{gdb.Frame}
5547 object @var{frame}. If @var{frame} is not provided, this defaults to the
5548 newest frame. The optional @var{internal} argument allows the breakpoint to
5549 become invisible to the user. @xref{Breakpoints In Python}, for further
5550 details about this argument.
5553 @defun FinishBreakpoint.out_of_scope (self)
5554 In some circumstances (e.g.@: @code{longjmp}, C@t{++} exceptions, @value{GDBN}
5555 @code{return} command, @dots{}), a function may not properly terminate, and
5556 thus never hit the finish breakpoint. When @value{GDBN} notices such a
5557 situation, the @code{out_of_scope} callback will be triggered.
5559 You may want to sub-class @code{gdb.FinishBreakpoint} and override this
5563 class MyFinishBreakpoint (gdb.FinishBreakpoint)
5565 print "normal finish"
5568 def out_of_scope ():
5569 print "abnormal finish"
5573 @defvar FinishBreakpoint.return_value
5574 When @value{GDBN} is stopped at a finish breakpoint and the frame
5575 used to build the @code{gdb.FinishBreakpoint} object had debug symbols, this
5576 attribute will contain a @code{gdb.Value} object corresponding to the return
5577 value of the function. The value will be @code{None} if the function return
5578 type is @code{void} or if the return value was not computable. This attribute
5582 @node Lazy Strings In Python
5583 @subsubsection Python representation of lazy strings
5585 @cindex lazy strings in python
5586 @tindex gdb.LazyString
5588 A @dfn{lazy string} is a string whose contents is not retrieved or
5589 encoded until it is needed.
5591 A @code{gdb.LazyString} is represented in @value{GDBN} as an
5592 @code{address} that points to a region of memory, an @code{encoding}
5593 that will be used to encode that region of memory, and a @code{length}
5594 to delimit the region of memory that represents the string. The
5595 difference between a @code{gdb.LazyString} and a string wrapped within
5596 a @code{gdb.Value} is that a @code{gdb.LazyString} will be treated
5597 differently by @value{GDBN} when printing. A @code{gdb.LazyString} is
5598 retrieved and encoded during printing, while a @code{gdb.Value}
5599 wrapping a string is immediately retrieved and encoded on creation.
5601 A @code{gdb.LazyString} object has the following functions:
5603 @defun LazyString.value ()
5604 Convert the @code{gdb.LazyString} to a @code{gdb.Value}. This value
5605 will point to the string in memory, but will lose all the delayed
5606 retrieval, encoding and handling that @value{GDBN} applies to a
5607 @code{gdb.LazyString}.
5610 @defvar LazyString.address
5611 This attribute holds the address of the string. This attribute is not
5615 @defvar LazyString.length
5616 This attribute holds the length of the string in characters. If the
5617 length is -1, then the string will be fetched and encoded up to the
5618 first null of appropriate width. This attribute is not writable.
5621 @defvar LazyString.encoding
5622 This attribute holds the encoding that will be applied to the string
5623 when the string is printed by @value{GDBN}. If the encoding is not
5624 set, or contains an empty string, then @value{GDBN} will select the
5625 most appropriate encoding when the string is printed. This attribute
5629 @defvar LazyString.type
5630 This attribute holds the type that is represented by the lazy string's
5631 type. For a lazy string this is a pointer or array type. To
5632 resolve this to the lazy string's character type, use the type's
5633 @code{target} method. @xref{Types In Python}. This attribute is not
5637 @node Architectures In Python
5638 @subsubsection Python representation of architectures
5639 @cindex Python architectures
5641 @value{GDBN} uses architecture specific parameters and artifacts in a
5642 number of its various computations. An architecture is represented
5643 by an instance of the @code{gdb.Architecture} class.
5645 A @code{gdb.Architecture} class has the following methods:
5647 @defun Architecture.name ()
5648 Return the name (string value) of the architecture.
5651 @defun Architecture.disassemble (@var{start_pc} @r{[}, @var{end_pc} @r{[}, @var{count}@r{]]})
5652 Return a list of disassembled instructions starting from the memory
5653 address @var{start_pc}. The optional arguments @var{end_pc} and
5654 @var{count} determine the number of instructions in the returned list.
5655 If both the optional arguments @var{end_pc} and @var{count} are
5656 specified, then a list of at most @var{count} disassembled instructions
5657 whose start address falls in the closed memory address interval from
5658 @var{start_pc} to @var{end_pc} are returned. If @var{end_pc} is not
5659 specified, but @var{count} is specified, then @var{count} number of
5660 instructions starting from the address @var{start_pc} are returned. If
5661 @var{count} is not specified but @var{end_pc} is specified, then all
5662 instructions whose start address falls in the closed memory address
5663 interval from @var{start_pc} to @var{end_pc} are returned. If neither
5664 @var{end_pc} nor @var{count} are specified, then a single instruction at
5665 @var{start_pc} is returned. For all of these cases, each element of the
5666 returned list is a Python @code{dict} with the following string keys:
5671 The value corresponding to this key is a Python long integer capturing
5672 the memory address of the instruction.
5675 The value corresponding to this key is a string value which represents
5676 the instruction with assembly language mnemonics. The assembly
5677 language flavor used is the same as that specified by the current CLI
5678 variable @code{disassembly-flavor}. @xref{Machine Code}.
5681 The value corresponding to this key is the length (integer value) of the
5682 instruction in bytes.
5687 @node TUI Windows In Python
5688 @subsubsection Implementing new TUI windows
5689 @cindex Python TUI Windows
5691 New TUI (@pxref{TUI}) windows can be implemented in Python.
5693 @findex gdb.register_window_type
5694 @defun gdb.register_window_type (@var{name}, @var{factory})
5695 Because TUI windows are created and destroyed depending on the layout
5696 the user chooses, new window types are implemented by registering a
5697 factory function with @value{GDBN}.
5699 @var{name} is the name of the new window. It's an error to try to
5700 replace one of the built-in windows, but other window types can be
5703 @var{function} is a factory function that is called to create the TUI
5704 window. This is called with a single argument of type
5705 @code{gdb.TuiWindow}, described below. It should return an object
5706 that implements the TUI window protocol, also described below.
5709 As mentioned above, when a factory function is called, it is passed a
5710 an object of type @code{gdb.TuiWindow}. This object has these
5711 methods and attributes:
5713 @defun TuiWindow.is_valid ()
5714 This method returns @code{True} when this window is valid. When the
5715 user changes the TUI layout, windows no longer visible in the new
5716 layout will be destroyed. At this point, the @code{gdb.TuiWindow}
5717 will no longer be valid, and methods (and attributes) other than
5718 @code{is_valid} will throw an exception.
5721 @defvar TuiWindow.width
5722 This attribute holds the width of the window. It is not writable.
5725 @defvar TuiWindow.height
5726 This attribute holds the height of the window. It is not writable.
5729 @defvar TuiWindow.title
5730 This attribute holds the window's title, a string. This is normally
5731 displayed above the window. This attribute can be modified.
5734 @defun TuiWindow.erase ()
5735 Remove all the contents of the window.
5738 @defun TuiWindow.write (@var{string})
5739 Write @var{string} to the window. @var{string} can contain ANSI
5740 terminal escape styling sequences; @value{GDBN} will translate these
5741 as appropriate for the terminal.
5744 The factory function that you supply should return an object
5745 conforming to the TUI window protocol. These are the method that can
5746 be called on this object, which is referred to below as the ``window
5747 object''. The methods documented below are optional; if the object
5748 does not implement one of these methods, @value{GDBN} will not attempt
5749 to call it. Additional new methods may be added to the window
5750 protocol in the future. @value{GDBN} guarantees that they will begin
5751 with a lower-case letter, so you can start implementation methods with
5752 upper-case letters or underscore to avoid any future conflicts.
5754 @defun Window.close ()
5755 When the TUI window is closed, the @code{gdb.TuiWindow} object will be
5756 put into an invalid state. At this time, @value{GDBN} will call
5757 @code{close} method on the window object.
5759 After this method is called, @value{GDBN} will discard any references
5760 it holds on this window object, and will no longer call methods on
5764 @defun Window.render ()
5765 In some situations, a TUI window can change size. For example, this
5766 can happen if the user resizes the terminal, or changes the layout.
5767 When this happens, @value{GDBN} will call the @code{render} method on
5770 If your window is intended to update in response to changes in the
5771 inferior, you will probably also want to register event listeners and
5772 send output to the @code{gdb.TuiWindow}.
5775 @defun Window.hscroll (@var{num})
5776 This is a request to scroll the window horizontally. @var{num} is the
5777 amount by which to scroll, with negative numbers meaning to scroll
5778 right. In the TUI model, it is the viewport that moves, not the
5779 contents. A positive argument should cause the viewport to move
5780 right, and so the content should appear to move to the left.
5783 @defun Window.vscroll (@var{num})
5784 This is a request to scroll the window vertically. @var{num} is the
5785 amount by which to scroll, with negative numbers meaning to scroll
5786 backward. In the TUI model, it is the viewport that moves, not the
5787 contents. A positive argument should cause the viewport to move down,
5788 and so the content should appear to move up.
5791 @node Python Auto-loading
5792 @subsection Python Auto-loading
5793 @cindex Python auto-loading
5795 When a new object file is read (for example, due to the @code{file}
5796 command, or because the inferior has loaded a shared library),
5797 @value{GDBN} will look for Python support scripts in several ways:
5798 @file{@var{objfile}-gdb.py} and @code{.debug_gdb_scripts} section.
5799 @xref{Auto-loading extensions}.
5801 The auto-loading feature is useful for supplying application-specific
5802 debugging commands and scripts.
5804 Auto-loading can be enabled or disabled,
5805 and the list of auto-loaded scripts can be printed.
5808 @anchor{set auto-load python-scripts}
5809 @kindex set auto-load python-scripts
5810 @item set auto-load python-scripts [on|off]
5811 Enable or disable the auto-loading of Python scripts.
5813 @anchor{show auto-load python-scripts}
5814 @kindex show auto-load python-scripts
5815 @item show auto-load python-scripts
5816 Show whether auto-loading of Python scripts is enabled or disabled.
5818 @anchor{info auto-load python-scripts}
5819 @kindex info auto-load python-scripts
5820 @cindex print list of auto-loaded Python scripts
5821 @item info auto-load python-scripts [@var{regexp}]
5822 Print the list of all Python scripts that @value{GDBN} auto-loaded.
5824 Also printed is the list of Python scripts that were mentioned in
5825 the @code{.debug_gdb_scripts} section and were either not found
5826 (@pxref{dotdebug_gdb_scripts section}) or were not auto-loaded due to
5827 @code{auto-load safe-path} rejection (@pxref{Auto-loading}).
5828 This is useful because their names are not printed when @value{GDBN}
5829 tries to load them and fails. There may be many of them, and printing
5830 an error message for each one is problematic.
5832 If @var{regexp} is supplied only Python scripts with matching names are printed.
5837 (gdb) info auto-load python-scripts
5839 Yes py-section-script.py
5840 full name: /tmp/py-section-script.py
5841 No my-foo-pretty-printers.py
5845 When reading an auto-loaded file or script, @value{GDBN} sets the
5846 @dfn{current objfile}. This is available via the @code{gdb.current_objfile}
5847 function (@pxref{Objfiles In Python}). This can be useful for
5848 registering objfile-specific pretty-printers and frame-filters.
5850 @node Python modules
5851 @subsection Python modules
5852 @cindex python modules
5854 @value{GDBN} comes with several modules to assist writing Python code.
5857 * gdb.printing:: Building and registering pretty-printers.
5858 * gdb.types:: Utilities for working with types.
5859 * gdb.prompt:: Utilities for prompt value substitution.
5863 @subsubsection gdb.printing
5864 @cindex gdb.printing
5866 This module provides a collection of utilities for working with
5870 @item PrettyPrinter (@var{name}, @var{subprinters}=None)
5871 This class specifies the API that makes @samp{info pretty-printer},
5872 @samp{enable pretty-printer} and @samp{disable pretty-printer} work.
5873 Pretty-printers should generally inherit from this class.
5875 @item SubPrettyPrinter (@var{name})
5876 For printers that handle multiple types, this class specifies the
5877 corresponding API for the subprinters.
5879 @item RegexpCollectionPrettyPrinter (@var{name})
5880 Utility class for handling multiple printers, all recognized via
5881 regular expressions.
5882 @xref{Writing a Pretty-Printer}, for an example.
5884 @item FlagEnumerationPrinter (@var{name})
5885 A pretty-printer which handles printing of @code{enum} values. Unlike
5886 @value{GDBN}'s built-in @code{enum} printing, this printer attempts to
5887 work properly when there is some overlap between the enumeration
5888 constants. The argument @var{name} is the name of the printer and
5889 also the name of the @code{enum} type to look up.
5891 @item register_pretty_printer (@var{obj}, @var{printer}, @var{replace}=False)
5892 Register @var{printer} with the pretty-printer list of @var{obj}.
5893 If @var{replace} is @code{True} then any existing copy of the printer
5894 is replaced. Otherwise a @code{RuntimeError} exception is raised
5895 if a printer with the same name already exists.
5899 @subsubsection gdb.types
5902 This module provides a collection of utilities for working with
5903 @code{gdb.Type} objects.
5906 @item get_basic_type (@var{type})
5907 Return @var{type} with const and volatile qualifiers stripped,
5908 and with typedefs and C@t{++} references converted to the underlying type.
5913 typedef const int const_int;
5915 const_int& foo_ref (foo);
5916 int main () @{ return 0; @}
5923 (gdb) python import gdb.types
5924 (gdb) python foo_ref = gdb.parse_and_eval("foo_ref")
5925 (gdb) python print gdb.types.get_basic_type(foo_ref.type)
5929 @item has_field (@var{type}, @var{field})
5930 Return @code{True} if @var{type}, assumed to be a type with fields
5931 (e.g., a structure or union), has field @var{field}.
5933 @item make_enum_dict (@var{enum_type})
5934 Return a Python @code{dictionary} type produced from @var{enum_type}.
5936 @item deep_items (@var{type})
5937 Returns a Python iterator similar to the standard
5938 @code{gdb.Type.iteritems} method, except that the iterator returned
5939 by @code{deep_items} will recursively traverse anonymous struct or
5940 union fields. For example:
5954 Then in @value{GDBN}:
5956 (@value{GDBP}) python import gdb.types
5957 (@value{GDBP}) python struct_a = gdb.lookup_type("struct A")
5958 (@value{GDBP}) python print struct_a.keys ()
5960 (@value{GDBP}) python print [k for k,v in gdb.types.deep_items(struct_a)]
5961 @{['a', 'b0', 'b1']@}
5964 @item get_type_recognizers ()
5965 Return a list of the enabled type recognizers for the current context.
5966 This is called by @value{GDBN} during the type-printing process
5967 (@pxref{Type Printing API}).
5969 @item apply_type_recognizers (recognizers, type_obj)
5970 Apply the type recognizers, @var{recognizers}, to the type object
5971 @var{type_obj}. If any recognizer returns a string, return that
5972 string. Otherwise, return @code{None}. This is called by
5973 @value{GDBN} during the type-printing process (@pxref{Type Printing
5976 @item register_type_printer (locus, printer)
5977 This is a convenience function to register a type printer
5978 @var{printer}. The printer must implement the type printer protocol.
5979 The @var{locus} argument is either a @code{gdb.Objfile}, in which case
5980 the printer is registered with that objfile; a @code{gdb.Progspace},
5981 in which case the printer is registered with that progspace; or
5982 @code{None}, in which case the printer is registered globally.
5985 This is a base class that implements the type printer protocol. Type
5986 printers are encouraged, but not required, to derive from this class.
5987 It defines a constructor:
5989 @defmethod TypePrinter __init__ (self, name)
5990 Initialize the type printer with the given name. The new printer
5991 starts in the enabled state.
5997 @subsubsection gdb.prompt
6000 This module provides a method for prompt value-substitution.
6003 @item substitute_prompt (@var{string})
6004 Return @var{string} with escape sequences substituted by values. Some
6005 escape sequences take arguments. You can specify arguments inside
6006 ``@{@}'' immediately following the escape sequence.
6008 The escape sequences you can pass to this function are:
6012 Substitute a backslash.
6014 Substitute an ESC character.
6016 Substitute the selected frame; an argument names a frame parameter.
6018 Substitute a newline.
6020 Substitute a parameter's value; the argument names the parameter.
6022 Substitute a carriage return.
6024 Substitute the selected thread; an argument names a thread parameter.
6026 Substitute the version of GDB.
6028 Substitute the current working directory.
6030 Begin a sequence of non-printing characters. These sequences are
6031 typically used with the ESC character, and are not counted in the string
6032 length. Example: ``\[\e[0;34m\](gdb)\[\e[0m\]'' will return a
6033 blue-colored ``(gdb)'' prompt where the length is five.
6035 End a sequence of non-printing characters.
6041 substitute_prompt ("frame: \f, args: \p@{print frame-arguments@}")
6044 @exdent will return the string:
6047 "frame: main, args: scalars"