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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.
1072 The name of this type. If this type has no name, then @code{None}
1077 The size of this type, in target @code{char} units. Usually, a
1078 target's @code{char} type will be an 8-bit byte. However, on some
1079 unusual platforms, this type may have a different size.
1083 The tag name for this type. The tag name is the name after
1084 @code{struct}, @code{union}, or @code{enum} in C and C@t{++}; not all
1085 languages have this concept. If this type has no tag name, then
1086 @code{None} is returned.
1089 @defvar Type.objfile
1090 The @code{gdb.Objfile} that this type was defined in, or @code{None} if
1091 there is no associated objfile.
1094 The following methods are provided:
1096 @defun Type.fields ()
1097 For structure and union types, this method returns the fields. Range
1098 types have two fields, the minimum and maximum values. Enum types
1099 have one field per enum constant. Function and method types have one
1100 field per parameter. The base types of C@t{++} classes are also
1101 represented as fields. If the type has no fields, or does not fit
1102 into one of these categories, an empty sequence will be returned.
1104 Each field is a @code{gdb.Field} object, with some pre-defined attributes:
1107 This attribute is not available for @code{enum} or @code{static}
1108 (as in C@t{++}) fields. The value is the position, counting
1109 in bits, from the start of the containing type.
1112 This attribute is only available for @code{enum} fields, and its value
1113 is the enumeration member's integer representation.
1116 The name of the field, or @code{None} for anonymous fields.
1119 This is @code{True} if the field is artificial, usually meaning that
1120 it was provided by the compiler and not the user. This attribute is
1121 always provided, and is @code{False} if the field is not artificial.
1124 This is @code{True} if the field represents a base class of a C@t{++}
1125 structure. This attribute is always provided, and is @code{False}
1126 if the field is not a base class of the type that is the argument of
1127 @code{fields}, or if that type was not a C@t{++} class.
1130 If the field is packed, or is a bitfield, then this will have a
1131 non-zero value, which is the size of the field in bits. Otherwise,
1132 this will be zero; in this case the field's size is given by its type.
1135 The type of the field. This is usually an instance of @code{Type},
1136 but it can be @code{None} in some situations.
1139 The type which contains this field. This is an instance of
1144 @defun Type.array (@var{n1} @r{[}, @var{n2}@r{]})
1145 Return a new @code{gdb.Type} object which represents an array of this
1146 type. If one argument is given, it is the inclusive upper bound of
1147 the array; in this case the lower bound is zero. If two arguments are
1148 given, the first argument is the lower bound of the array, and the
1149 second argument is the upper bound of the array. An array's length
1150 must not be negative, but the bounds can be.
1153 @defun Type.vector (@var{n1} @r{[}, @var{n2}@r{]})
1154 Return a new @code{gdb.Type} object which represents a vector of this
1155 type. If one argument is given, it is the inclusive upper bound of
1156 the vector; in this case the lower bound is zero. If two arguments are
1157 given, the first argument is the lower bound of the vector, and the
1158 second argument is the upper bound of the vector. A vector's length
1159 must not be negative, but the bounds can be.
1161 The difference between an @code{array} and a @code{vector} is that
1162 arrays behave like in C: when used in expressions they decay to a pointer
1163 to the first element whereas vectors are treated as first class values.
1166 @defun Type.const ()
1167 Return a new @code{gdb.Type} object which represents a
1168 @code{const}-qualified variant of this type.
1171 @defun Type.volatile ()
1172 Return a new @code{gdb.Type} object which represents a
1173 @code{volatile}-qualified variant of this type.
1176 @defun Type.unqualified ()
1177 Return a new @code{gdb.Type} object which represents an unqualified
1178 variant of this type. That is, the result is neither @code{const} nor
1182 @defun Type.range ()
1183 Return a Python @code{Tuple} object that contains two elements: the
1184 low bound of the argument type and the high bound of that type. If
1185 the type does not have a range, @value{GDBN} will raise a
1186 @code{gdb.error} exception (@pxref{Exception Handling}).
1189 @defun Type.reference ()
1190 Return a new @code{gdb.Type} object which represents a reference to this
1194 @defun Type.pointer ()
1195 Return a new @code{gdb.Type} object which represents a pointer to this
1199 @defun Type.strip_typedefs ()
1200 Return a new @code{gdb.Type} that represents the real type,
1201 after removing all layers of typedefs.
1204 @defun Type.target ()
1205 Return a new @code{gdb.Type} object which represents the target type
1208 For a pointer type, the target type is the type of the pointed-to
1209 object. For an array type (meaning C-like arrays), the target type is
1210 the type of the elements of the array. For a function or method type,
1211 the target type is the type of the return value. For a complex type,
1212 the target type is the type of the elements. For a typedef, the
1213 target type is the aliased type.
1215 If the type does not have a target, this method will throw an
1219 @defun Type.template_argument (n @r{[}, block@r{]})
1220 If this @code{gdb.Type} is an instantiation of a template, this will
1221 return a new @code{gdb.Value} or @code{gdb.Type} which represents the
1222 value of the @var{n}th template argument (indexed starting at 0).
1224 If this @code{gdb.Type} is not a template type, or if the type has fewer
1225 than @var{n} template arguments, this will throw an exception.
1226 Ordinarily, only C@t{++} code will have template types.
1228 If @var{block} is given, then @var{name} is looked up in that scope.
1229 Otherwise, it is searched for globally.
1232 @defun Type.optimized_out ()
1233 Return @code{gdb.Value} instance of this type whose value is optimized
1234 out. This allows a frame decorator to indicate that the value of an
1235 argument or a local variable is not known.
1238 Each type has a code, which indicates what category this type falls
1239 into. The available type categories are represented by constants
1240 defined in the @code{gdb} module:
1243 @vindex TYPE_CODE_PTR
1244 @item gdb.TYPE_CODE_PTR
1245 The type is a pointer.
1247 @vindex TYPE_CODE_ARRAY
1248 @item gdb.TYPE_CODE_ARRAY
1249 The type is an array.
1251 @vindex TYPE_CODE_STRUCT
1252 @item gdb.TYPE_CODE_STRUCT
1253 The type is a structure.
1255 @vindex TYPE_CODE_UNION
1256 @item gdb.TYPE_CODE_UNION
1257 The type is a union.
1259 @vindex TYPE_CODE_ENUM
1260 @item gdb.TYPE_CODE_ENUM
1261 The type is an enum.
1263 @vindex TYPE_CODE_FLAGS
1264 @item gdb.TYPE_CODE_FLAGS
1265 A bit flags type, used for things such as status registers.
1267 @vindex TYPE_CODE_FUNC
1268 @item gdb.TYPE_CODE_FUNC
1269 The type is a function.
1271 @vindex TYPE_CODE_INT
1272 @item gdb.TYPE_CODE_INT
1273 The type is an integer type.
1275 @vindex TYPE_CODE_FLT
1276 @item gdb.TYPE_CODE_FLT
1277 A floating point type.
1279 @vindex TYPE_CODE_VOID
1280 @item gdb.TYPE_CODE_VOID
1281 The special type @code{void}.
1283 @vindex TYPE_CODE_SET
1284 @item gdb.TYPE_CODE_SET
1287 @vindex TYPE_CODE_RANGE
1288 @item gdb.TYPE_CODE_RANGE
1289 A range type, that is, an integer type with bounds.
1291 @vindex TYPE_CODE_STRING
1292 @item gdb.TYPE_CODE_STRING
1293 A string type. Note that this is only used for certain languages with
1294 language-defined string types; C strings are not represented this way.
1296 @vindex TYPE_CODE_BITSTRING
1297 @item gdb.TYPE_CODE_BITSTRING
1298 A string of bits. It is deprecated.
1300 @vindex TYPE_CODE_ERROR
1301 @item gdb.TYPE_CODE_ERROR
1302 An unknown or erroneous type.
1304 @vindex TYPE_CODE_METHOD
1305 @item gdb.TYPE_CODE_METHOD
1306 A method type, as found in C@t{++}.
1308 @vindex TYPE_CODE_METHODPTR
1309 @item gdb.TYPE_CODE_METHODPTR
1310 A pointer-to-member-function.
1312 @vindex TYPE_CODE_MEMBERPTR
1313 @item gdb.TYPE_CODE_MEMBERPTR
1314 A pointer-to-member.
1316 @vindex TYPE_CODE_REF
1317 @item gdb.TYPE_CODE_REF
1320 @vindex TYPE_CODE_RVALUE_REF
1321 @item gdb.TYPE_CODE_RVALUE_REF
1322 A C@t{++}11 rvalue reference type.
1324 @vindex TYPE_CODE_CHAR
1325 @item gdb.TYPE_CODE_CHAR
1328 @vindex TYPE_CODE_BOOL
1329 @item gdb.TYPE_CODE_BOOL
1332 @vindex TYPE_CODE_COMPLEX
1333 @item gdb.TYPE_CODE_COMPLEX
1334 A complex float type.
1336 @vindex TYPE_CODE_TYPEDEF
1337 @item gdb.TYPE_CODE_TYPEDEF
1338 A typedef to some other type.
1340 @vindex TYPE_CODE_NAMESPACE
1341 @item gdb.TYPE_CODE_NAMESPACE
1342 A C@t{++} namespace.
1344 @vindex TYPE_CODE_DECFLOAT
1345 @item gdb.TYPE_CODE_DECFLOAT
1346 A decimal floating point type.
1348 @vindex TYPE_CODE_INTERNAL_FUNCTION
1349 @item gdb.TYPE_CODE_INTERNAL_FUNCTION
1350 A function internal to @value{GDBN}. This is the type used to represent
1351 convenience functions.
1354 Further support for types is provided in the @code{gdb.types}
1355 Python module (@pxref{gdb.types}).
1357 @node Pretty Printing API
1358 @subsubsection Pretty Printing API
1359 @cindex python pretty printing api
1361 A pretty-printer is just an object that holds a value and implements a
1362 specific interface, defined here. An example output is provided
1363 (@pxref{Pretty Printing}).
1365 @defun pretty_printer.children (self)
1366 @value{GDBN} will call this method on a pretty-printer to compute the
1367 children of the pretty-printer's value.
1369 This method must return an object conforming to the Python iterator
1370 protocol. Each item returned by the iterator must be a tuple holding
1371 two elements. The first element is the ``name'' of the child; the
1372 second element is the child's value. The value can be any Python
1373 object which is convertible to a @value{GDBN} value.
1375 This method is optional. If it does not exist, @value{GDBN} will act
1376 as though the value has no children.
1378 For efficiency, the @code{children} method should lazily compute its
1379 results. This will let @value{GDBN} read as few elements as
1380 necessary, for example when various print settings (@pxref{Print
1381 Settings}) or @code{-var-list-children} (@pxref{GDB/MI Variable
1382 Objects}) limit the number of elements to be displayed.
1384 Children may be hidden from display based on the value of @samp{set
1385 print max-depth} (@pxref{Print Settings}).
1388 @defun pretty_printer.display_hint (self)
1389 The CLI may call this method and use its result to change the
1390 formatting of a value. The result will also be supplied to an MI
1391 consumer as a @samp{displayhint} attribute of the variable being
1394 This method is optional. If it does exist, this method must return a
1395 string or the special value @code{None}.
1397 Some display hints are predefined by @value{GDBN}:
1401 Indicate that the object being printed is ``array-like''. The CLI
1402 uses this to respect parameters such as @code{set print elements} and
1403 @code{set print array}.
1406 Indicate that the object being printed is ``map-like'', and that the
1407 children of this value can be assumed to alternate between keys and
1411 Indicate that the object being printed is ``string-like''. If the
1412 printer's @code{to_string} method returns a Python string of some
1413 kind, then @value{GDBN} will call its internal language-specific
1414 string-printing function to format the string. For the CLI this means
1415 adding quotation marks, possibly escaping some characters, respecting
1416 @code{set print elements}, and the like.
1419 The special value @code{None} causes @value{GDBN} to apply the default
1423 @defun pretty_printer.to_string (self)
1424 @value{GDBN} will call this method to display the string
1425 representation of the value passed to the object's constructor.
1427 When printing from the CLI, if the @code{to_string} method exists,
1428 then @value{GDBN} will prepend its result to the values returned by
1429 @code{children}. Exactly how this formatting is done is dependent on
1430 the display hint, and may change as more hints are added. Also,
1431 depending on the print settings (@pxref{Print Settings}), the CLI may
1432 print just the result of @code{to_string} in a stack trace, omitting
1433 the result of @code{children}.
1435 If this method returns a string, it is printed verbatim.
1437 Otherwise, if this method returns an instance of @code{gdb.Value},
1438 then @value{GDBN} prints this value. This may result in a call to
1439 another pretty-printer.
1441 If instead the method returns a Python value which is convertible to a
1442 @code{gdb.Value}, then @value{GDBN} performs the conversion and prints
1443 the resulting value. Again, this may result in a call to another
1444 pretty-printer. Python scalars (integers, floats, and booleans) and
1445 strings are convertible to @code{gdb.Value}; other types are not.
1447 Finally, if this method returns @code{None} then no further operations
1448 are peformed in this method and nothing is printed.
1450 If the result is not one of these types, an exception is raised.
1453 @value{GDBN} provides a function which can be used to look up the
1454 default pretty-printer for a @code{gdb.Value}:
1456 @findex gdb.default_visualizer
1457 @defun gdb.default_visualizer (value)
1458 This function takes a @code{gdb.Value} object as an argument. If a
1459 pretty-printer for this value exists, then it is returned. If no such
1460 printer exists, then this returns @code{None}.
1463 @node Selecting Pretty-Printers
1464 @subsubsection Selecting Pretty-Printers
1465 @cindex selecting python pretty-printers
1467 @value{GDBN} provides several ways to register a pretty-printer:
1468 globally, per program space, and per objfile. When choosing how to
1469 register your pretty-printer, a good rule is to register it with the
1470 smallest scope possible: that is prefer a specific objfile first, then
1471 a program space, and only register a printer globally as a last
1474 @findex gdb.pretty_printers
1475 @defvar gdb.pretty_printers
1476 The Python list @code{gdb.pretty_printers} contains an array of
1477 functions or callable objects that have been registered via addition
1478 as a pretty-printer. Printers in this list are called @code{global}
1479 printers, they're available when debugging all inferiors.
1482 Each @code{gdb.Progspace} contains a @code{pretty_printers} attribute.
1483 Each @code{gdb.Objfile} also contains a @code{pretty_printers}
1486 Each function on these lists is passed a single @code{gdb.Value}
1487 argument and should return a pretty-printer object conforming to the
1488 interface definition above (@pxref{Pretty Printing API}). If a function
1489 cannot create a pretty-printer for the value, it should return
1492 @value{GDBN} first checks the @code{pretty_printers} attribute of each
1493 @code{gdb.Objfile} in the current program space and iteratively calls
1494 each enabled lookup routine in the list for that @code{gdb.Objfile}
1495 until it receives a pretty-printer object.
1496 If no pretty-printer is found in the objfile lists, @value{GDBN} then
1497 searches the pretty-printer list of the current program space,
1498 calling each enabled function until an object is returned.
1499 After these lists have been exhausted, it tries the global
1500 @code{gdb.pretty_printers} list, again calling each enabled function until an
1503 The order in which the objfiles are searched is not specified. For a
1504 given list, functions are always invoked from the head of the list,
1505 and iterated over sequentially until the end of the list, or a printer
1508 For various reasons a pretty-printer may not work.
1509 For example, the underlying data structure may have changed and
1510 the pretty-printer is out of date.
1512 The consequences of a broken pretty-printer are severe enough that
1513 @value{GDBN} provides support for enabling and disabling individual
1514 printers. For example, if @code{print frame-arguments} is on,
1515 a backtrace can become highly illegible if any argument is printed
1516 with a broken printer.
1518 Pretty-printers are enabled and disabled by attaching an @code{enabled}
1519 attribute to the registered function or callable object. If this attribute
1520 is present and its value is @code{False}, the printer is disabled, otherwise
1521 the printer is enabled.
1523 @node Writing a Pretty-Printer
1524 @subsubsection Writing a Pretty-Printer
1525 @cindex writing a pretty-printer
1527 A pretty-printer consists of two parts: a lookup function to detect
1528 if the type is supported, and the printer itself.
1530 Here is an example showing how a @code{std::string} printer might be
1531 written. @xref{Pretty Printing API}, for details on the API this class
1535 class StdStringPrinter(object):
1536 "Print a std::string"
1538 def __init__(self, val):
1541 def to_string(self):
1542 return self.val['_M_dataplus']['_M_p']
1544 def display_hint(self):
1548 And here is an example showing how a lookup function for the printer
1549 example above might be written.
1552 def str_lookup_function(val):
1553 lookup_tag = val.type.tag
1554 if lookup_tag == None:
1556 regex = re.compile("^std::basic_string<char,.*>$")
1557 if regex.match(lookup_tag):
1558 return StdStringPrinter(val)
1562 The example lookup function extracts the value's type, and attempts to
1563 match it to a type that it can pretty-print. If it is a type the
1564 printer can pretty-print, it will return a printer object. If not, it
1565 returns @code{None}.
1567 We recommend that you put your core pretty-printers into a Python
1568 package. If your pretty-printers are for use with a library, we
1569 further recommend embedding a version number into the package name.
1570 This practice will enable @value{GDBN} to load multiple versions of
1571 your pretty-printers at the same time, because they will have
1574 You should write auto-loaded code (@pxref{Python Auto-loading}) such that it
1575 can be evaluated multiple times without changing its meaning. An
1576 ideal auto-load file will consist solely of @code{import}s of your
1577 printer modules, followed by a call to a register pretty-printers with
1578 the current objfile.
1580 Taken as a whole, this approach will scale nicely to multiple
1581 inferiors, each potentially using a different library version.
1582 Embedding a version number in the Python package name will ensure that
1583 @value{GDBN} is able to load both sets of printers simultaneously.
1584 Then, because the search for pretty-printers is done by objfile, and
1585 because your auto-loaded code took care to register your library's
1586 printers with a specific objfile, @value{GDBN} will find the correct
1587 printers for the specific version of the library used by each
1590 To continue the @code{std::string} example (@pxref{Pretty Printing API}),
1591 this code might appear in @code{gdb.libstdcxx.v6}:
1594 def register_printers(objfile):
1595 objfile.pretty_printers.append(str_lookup_function)
1599 And then the corresponding contents of the auto-load file would be:
1602 import gdb.libstdcxx.v6
1603 gdb.libstdcxx.v6.register_printers(gdb.current_objfile())
1606 The previous example illustrates a basic pretty-printer.
1607 There are a few things that can be improved on.
1608 The printer doesn't have a name, making it hard to identify in a
1609 list of installed printers. The lookup function has a name, but
1610 lookup functions can have arbitrary, even identical, names.
1612 Second, the printer only handles one type, whereas a library typically has
1613 several types. One could install a lookup function for each desired type
1614 in the library, but one could also have a single lookup function recognize
1615 several types. The latter is the conventional way this is handled.
1616 If a pretty-printer can handle multiple data types, then its
1617 @dfn{subprinters} are the printers for the individual data types.
1619 The @code{gdb.printing} module provides a formal way of solving these
1620 problems (@pxref{gdb.printing}).
1621 Here is another example that handles multiple types.
1623 These are the types we are going to pretty-print:
1626 struct foo @{ int a, b; @};
1627 struct bar @{ struct foo x, y; @};
1630 Here are the printers:
1634 """Print a foo object."""
1636 def __init__(self, val):
1639 def to_string(self):
1640 return ("a=<" + str(self.val["a"]) +
1641 "> b=<" + str(self.val["b"]) + ">")
1644 """Print a bar object."""
1646 def __init__(self, val):
1649 def to_string(self):
1650 return ("x=<" + str(self.val["x"]) +
1651 "> y=<" + str(self.val["y"]) + ">")
1654 This example doesn't need a lookup function, that is handled by the
1655 @code{gdb.printing} module. Instead a function is provided to build up
1656 the object that handles the lookup.
1661 def build_pretty_printer():
1662 pp = gdb.printing.RegexpCollectionPrettyPrinter(
1664 pp.add_printer('foo', '^foo$', fooPrinter)
1665 pp.add_printer('bar', '^bar$', barPrinter)
1669 And here is the autoload support:
1674 gdb.printing.register_pretty_printer(
1675 gdb.current_objfile(),
1676 my_library.build_pretty_printer())
1679 Finally, when this printer is loaded into @value{GDBN}, here is the
1680 corresponding output of @samp{info pretty-printer}:
1683 (gdb) info pretty-printer
1690 @node Type Printing API
1691 @subsubsection Type Printing API
1692 @cindex type printing API for Python
1694 @value{GDBN} provides a way for Python code to customize type display.
1695 This is mainly useful for substituting canonical typedef names for
1698 @cindex type printer
1699 A @dfn{type printer} is just a Python object conforming to a certain
1700 protocol. A simple base class implementing the protocol is provided;
1701 see @ref{gdb.types}. A type printer must supply at least:
1703 @defivar type_printer enabled
1704 A boolean which is True if the printer is enabled, and False
1705 otherwise. This is manipulated by the @code{enable type-printer}
1706 and @code{disable type-printer} commands.
1709 @defivar type_printer name
1710 The name of the type printer. This must be a string. This is used by
1711 the @code{enable type-printer} and @code{disable type-printer}
1715 @defmethod type_printer instantiate (self)
1716 This is called by @value{GDBN} at the start of type-printing. It is
1717 only called if the type printer is enabled. This method must return a
1718 new object that supplies a @code{recognize} method, as described below.
1722 When displaying a type, say via the @code{ptype} command, @value{GDBN}
1723 will compute a list of type recognizers. This is done by iterating
1724 first over the per-objfile type printers (@pxref{Objfiles In Python}),
1725 followed by the per-progspace type printers (@pxref{Progspaces In
1726 Python}), and finally the global type printers.
1728 @value{GDBN} will call the @code{instantiate} method of each enabled
1729 type printer. If this method returns @code{None}, then the result is
1730 ignored; otherwise, it is appended to the list of recognizers.
1732 Then, when @value{GDBN} is going to display a type name, it iterates
1733 over the list of recognizers. For each one, it calls the recognition
1734 function, stopping if the function returns a non-@code{None} value.
1735 The recognition function is defined as:
1737 @defmethod type_recognizer recognize (self, type)
1738 If @var{type} is not recognized, return @code{None}. Otherwise,
1739 return a string which is to be printed as the name of @var{type}.
1740 The @var{type} argument will be an instance of @code{gdb.Type}
1741 (@pxref{Types In Python}).
1744 @value{GDBN} uses this two-pass approach so that type printers can
1745 efficiently cache information without holding on to it too long. For
1746 example, it can be convenient to look up type information in a type
1747 printer and hold it for a recognizer's lifetime; if a single pass were
1748 done then type printers would have to make use of the event system in
1749 order to avoid holding information that could become stale as the
1752 @node Frame Filter API
1753 @subsubsection Filtering Frames
1754 @cindex frame filters api
1756 Frame filters are Python objects that manipulate the visibility of a
1757 frame or frames when a backtrace (@pxref{Backtrace}) is printed by
1760 Only commands that print a backtrace, or, in the case of @sc{gdb/mi}
1761 commands (@pxref{GDB/MI}), those that return a collection of frames
1762 are affected. The commands that work with frame filters are:
1764 @code{backtrace} (@pxref{backtrace-command,, The backtrace command}),
1765 @code{-stack-list-frames}
1766 (@pxref{-stack-list-frames,, The -stack-list-frames command}),
1767 @code{-stack-list-variables} (@pxref{-stack-list-variables,, The
1768 -stack-list-variables command}), @code{-stack-list-arguments}
1769 @pxref{-stack-list-arguments,, The -stack-list-arguments command}) and
1770 @code{-stack-list-locals} (@pxref{-stack-list-locals,, The
1771 -stack-list-locals command}).
1773 A frame filter works by taking an iterator as an argument, applying
1774 actions to the contents of that iterator, and returning another
1775 iterator (or, possibly, the same iterator it was provided in the case
1776 where the filter does not perform any operations). Typically, frame
1777 filters utilize tools such as the Python's @code{itertools} module to
1778 work with and create new iterators from the source iterator.
1779 Regardless of how a filter chooses to apply actions, it must not alter
1780 the underlying @value{GDBN} frame or frames, or attempt to alter the
1781 call-stack within @value{GDBN}. This preserves data integrity within
1782 @value{GDBN}. Frame filters are executed on a priority basis and care
1783 should be taken that some frame filters may have been executed before,
1784 and that some frame filters will be executed after.
1786 An important consideration when designing frame filters, and well
1787 worth reflecting upon, is that frame filters should avoid unwinding
1788 the call stack if possible. Some stacks can run very deep, into the
1789 tens of thousands in some cases. To search every frame when a frame
1790 filter executes may be too expensive at that step. The frame filter
1791 cannot know how many frames it has to iterate over, and it may have to
1792 iterate through them all. This ends up duplicating effort as
1793 @value{GDBN} performs this iteration when it prints the frames. If
1794 the filter can defer unwinding frames until frame decorators are
1795 executed, after the last filter has executed, it should. @xref{Frame
1796 Decorator API}, for more information on decorators. Also, there are
1797 examples for both frame decorators and filters in later chapters.
1798 @xref{Writing a Frame Filter}, for more information.
1800 The Python dictionary @code{gdb.frame_filters} contains key/object
1801 pairings that comprise a frame filter. Frame filters in this
1802 dictionary are called @code{global} frame filters, and they are
1803 available when debugging all inferiors. These frame filters must
1804 register with the dictionary directly. In addition to the
1805 @code{global} dictionary, there are other dictionaries that are loaded
1806 with different inferiors via auto-loading (@pxref{Python
1807 Auto-loading}). The two other areas where frame filter dictionaries
1808 can be found are: @code{gdb.Progspace} which contains a
1809 @code{frame_filters} dictionary attribute, and each @code{gdb.Objfile}
1810 object which also contains a @code{frame_filters} dictionary
1813 When a command is executed from @value{GDBN} that is compatible with
1814 frame filters, @value{GDBN} combines the @code{global},
1815 @code{gdb.Progspace} and all @code{gdb.Objfile} dictionaries currently
1816 loaded. All of the @code{gdb.Objfile} dictionaries are combined, as
1817 several frames, and thus several object files, might be in use.
1818 @value{GDBN} then prunes any frame filter whose @code{enabled}
1819 attribute is @code{False}. This pruned list is then sorted according
1820 to the @code{priority} attribute in each filter.
1822 Once the dictionaries are combined, pruned and sorted, @value{GDBN}
1823 creates an iterator which wraps each frame in the call stack in a
1824 @code{FrameDecorator} object, and calls each filter in order. The
1825 output from the previous filter will always be the input to the next
1828 Frame filters have a mandatory interface which each frame filter must
1829 implement, defined here:
1831 @defun FrameFilter.filter (iterator)
1832 @value{GDBN} will call this method on a frame filter when it has
1833 reached the order in the priority list for that filter.
1835 For example, if there are four frame filters:
1846 The order that the frame filters will be called is:
1849 Filter3 -> Filter2 -> Filter1 -> Filter4
1852 Note that the output from @code{Filter3} is passed to the input of
1853 @code{Filter2}, and so on.
1855 This @code{filter} method is passed a Python iterator. This iterator
1856 contains a sequence of frame decorators that wrap each
1857 @code{gdb.Frame}, or a frame decorator that wraps another frame
1858 decorator. The first filter that is executed in the sequence of frame
1859 filters will receive an iterator entirely comprised of default
1860 @code{FrameDecorator} objects. However, after each frame filter is
1861 executed, the previous frame filter may have wrapped some or all of
1862 the frame decorators with their own frame decorator. As frame
1863 decorators must also conform to a mandatory interface, these
1864 decorators can be assumed to act in a uniform manner (@pxref{Frame
1867 This method must return an object conforming to the Python iterator
1868 protocol. Each item in the iterator must be an object conforming to
1869 the frame decorator interface. If a frame filter does not wish to
1870 perform any operations on this iterator, it should return that
1873 This method is not optional. If it does not exist, @value{GDBN} will
1874 raise and print an error.
1877 @defvar FrameFilter.name
1878 The @code{name} attribute must be Python string which contains the
1879 name of the filter displayed by @value{GDBN} (@pxref{Frame Filter
1880 Management}). This attribute may contain any combination of letters
1881 or numbers. Care should be taken to ensure that it is unique. This
1882 attribute is mandatory.
1885 @defvar FrameFilter.enabled
1886 The @code{enabled} attribute must be Python boolean. This attribute
1887 indicates to @value{GDBN} whether the frame filter is enabled, and
1888 should be considered when frame filters are executed. If
1889 @code{enabled} is @code{True}, then the frame filter will be executed
1890 when any of the backtrace commands detailed earlier in this chapter
1891 are executed. If @code{enabled} is @code{False}, then the frame
1892 filter will not be executed. This attribute is mandatory.
1895 @defvar FrameFilter.priority
1896 The @code{priority} attribute must be Python integer. This attribute
1897 controls the order of execution in relation to other frame filters.
1898 There are no imposed limits on the range of @code{priority} other than
1899 it must be a valid integer. The higher the @code{priority} attribute,
1900 the sooner the frame filter will be executed in relation to other
1901 frame filters. Although @code{priority} can be negative, it is
1902 recommended practice to assume zero is the lowest priority that a
1903 frame filter can be assigned. Frame filters that have the same
1904 priority are executed in unsorted order in that priority slot. This
1905 attribute is mandatory. 100 is a good default priority.
1908 @node Frame Decorator API
1909 @subsubsection Decorating Frames
1910 @cindex frame decorator api
1912 Frame decorators are sister objects to frame filters (@pxref{Frame
1913 Filter API}). Frame decorators are applied by a frame filter and can
1914 only be used in conjunction with frame filters.
1916 The purpose of a frame decorator is to customize the printed content
1917 of each @code{gdb.Frame} in commands where frame filters are executed.
1918 This concept is called decorating a frame. Frame decorators decorate
1919 a @code{gdb.Frame} with Python code contained within each API call.
1920 This separates the actual data contained in a @code{gdb.Frame} from
1921 the decorated data produced by a frame decorator. This abstraction is
1922 necessary to maintain integrity of the data contained in each
1925 Frame decorators have a mandatory interface, defined below.
1927 @value{GDBN} already contains a frame decorator called
1928 @code{FrameDecorator}. This contains substantial amounts of
1929 boilerplate code to decorate the content of a @code{gdb.Frame}. It is
1930 recommended that other frame decorators inherit and extend this
1931 object, and only to override the methods needed.
1933 @tindex gdb.FrameDecorator
1934 @code{FrameDecorator} is defined in the Python module
1935 @code{gdb.FrameDecorator}, so your code can import it like:
1937 from gdb.FrameDecorator import FrameDecorator
1940 @defun FrameDecorator.elided (self)
1942 The @code{elided} method groups frames together in a hierarchical
1943 system. An example would be an interpreter, where multiple low-level
1944 frames make up a single call in the interpreted language. In this
1945 example, the frame filter would elide the low-level frames and present
1946 a single high-level frame, representing the call in the interpreted
1947 language, to the user.
1949 The @code{elided} function must return an iterable and this iterable
1950 must contain the frames that are being elided wrapped in a suitable
1951 frame decorator. If no frames are being elided this function may
1952 return an empty iterable, or @code{None}. Elided frames are indented
1953 from normal frames in a @code{CLI} backtrace, or in the case of
1954 @code{GDB/MI}, are placed in the @code{children} field of the eliding
1957 It is the frame filter's task to also filter out the elided frames from
1958 the source iterator. This will avoid printing the frame twice.
1961 @defun FrameDecorator.function (self)
1963 This method returns the name of the function in the frame that is to
1966 This method must return a Python string describing the function, or
1969 If this function returns @code{None}, @value{GDBN} will not print any
1970 data for this field.
1973 @defun FrameDecorator.address (self)
1975 This method returns the address of the frame that is to be printed.
1977 This method must return a Python numeric integer type of sufficient
1978 size to describe the address of the frame, or @code{None}.
1980 If this function returns a @code{None}, @value{GDBN} will not print
1981 any data for this field.
1984 @defun FrameDecorator.filename (self)
1986 This method returns the filename and path associated with this frame.
1988 This method must return a Python string containing the filename and
1989 the path to the object file backing the frame, or @code{None}.
1991 If this function returns a @code{None}, @value{GDBN} will not print
1992 any data for this field.
1995 @defun FrameDecorator.line (self):
1997 This method returns the line number associated with the current
1998 position within the function addressed by this frame.
2000 This method must return a Python integer type, or @code{None}.
2002 If this function returns a @code{None}, @value{GDBN} will not print
2003 any data for this field.
2006 @defun FrameDecorator.frame_args (self)
2009 This method must return an iterable, or @code{None}. Returning an
2010 empty iterable, or @code{None} means frame arguments will not be
2011 printed for this frame. This iterable must contain objects that
2012 implement two methods, described here.
2014 This object must implement a @code{argument} method which takes a
2015 single @code{self} parameter and must return a @code{gdb.Symbol}
2016 (@pxref{Symbols In Python}), or a Python string. The object must also
2017 implement a @code{value} method which takes a single @code{self}
2018 parameter and must return a @code{gdb.Value} (@pxref{Values From
2019 Inferior}), a Python value, or @code{None}. If the @code{value}
2020 method returns @code{None}, and the @code{argument} method returns a
2021 @code{gdb.Symbol}, @value{GDBN} will look-up and print the value of
2022 the @code{gdb.Symbol} automatically.
2027 class SymValueWrapper():
2029 def __init__(self, symbol, value):
2039 class SomeFrameDecorator()
2042 def frame_args(self):
2045 block = self.inferior_frame.block()
2049 # Iterate over all symbols in a block. Only add
2050 # symbols that are arguments.
2052 if not sym.is_argument:
2054 args.append(SymValueWrapper(sym,None))
2056 # Add example synthetic argument.
2057 args.append(SymValueWrapper(``foo'', 42))
2063 @defun FrameDecorator.frame_locals (self)
2065 This method must return an iterable or @code{None}. Returning an
2066 empty iterable, or @code{None} means frame local arguments will not be
2067 printed for this frame.
2069 The object interface, the description of the various strategies for
2070 reading frame locals, and the example are largely similar to those
2071 described in the @code{frame_args} function, (@pxref{frame_args,,The
2072 frame filter frame_args function}). Below is a modified example:
2075 class SomeFrameDecorator()
2078 def frame_locals(self):
2081 block = self.inferior_frame.block()
2085 # Iterate over all symbols in a block. Add all
2086 # symbols, except arguments.
2090 vars.append(SymValueWrapper(sym,None))
2092 # Add an example of a synthetic local variable.
2093 vars.append(SymValueWrapper(``bar'', 99))
2099 @defun FrameDecorator.inferior_frame (self):
2101 This method must return the underlying @code{gdb.Frame} that this
2102 frame decorator is decorating. @value{GDBN} requires the underlying
2103 frame for internal frame information to determine how to print certain
2104 values when printing a frame.
2107 @node Writing a Frame Filter
2108 @subsubsection Writing a Frame Filter
2109 @cindex writing a frame filter
2111 There are three basic elements that a frame filter must implement: it
2112 must correctly implement the documented interface (@pxref{Frame Filter
2113 API}), it must register itself with @value{GDBN}, and finally, it must
2114 decide if it is to work on the data provided by @value{GDBN}. In all
2115 cases, whether it works on the iterator or not, each frame filter must
2116 return an iterator. A bare-bones frame filter follows the pattern in
2117 the following example.
2122 class FrameFilter():
2125 # Frame filter attribute creation.
2127 # 'name' is the name of the filter that GDB will display.
2129 # 'priority' is the priority of the filter relative to other
2132 # 'enabled' is a boolean that indicates whether this filter is
2133 # enabled and should be executed.
2139 # Register this frame filter with the global frame_filters
2141 gdb.frame_filters[self.name] = self
2143 def filter(self, frame_iter):
2144 # Just return the iterator.
2148 The frame filter in the example above implements the three
2149 requirements for all frame filters. It implements the API, self
2150 registers, and makes a decision on the iterator (in this case, it just
2151 returns the iterator untouched).
2153 The first step is attribute creation and assignment, and as shown in
2154 the comments the filter assigns the following attributes: @code{name},
2155 @code{priority} and whether the filter should be enabled with the
2156 @code{enabled} attribute.
2158 The second step is registering the frame filter with the dictionary or
2159 dictionaries that the frame filter has interest in. As shown in the
2160 comments, this filter just registers itself with the global dictionary
2161 @code{gdb.frame_filters}. As noted earlier, @code{gdb.frame_filters}
2162 is a dictionary that is initialized in the @code{gdb} module when
2163 @value{GDBN} starts. What dictionary a filter registers with is an
2164 important consideration. Generally, if a filter is specific to a set
2165 of code, it should be registered either in the @code{objfile} or
2166 @code{progspace} dictionaries as they are specific to the program
2167 currently loaded in @value{GDBN}. The global dictionary is always
2168 present in @value{GDBN} and is never unloaded. Any filters registered
2169 with the global dictionary will exist until @value{GDBN} exits. To
2170 avoid filters that may conflict, it is generally better to register
2171 frame filters against the dictionaries that more closely align with
2172 the usage of the filter currently in question. @xref{Python
2173 Auto-loading}, for further information on auto-loading Python scripts.
2175 @value{GDBN} takes a hands-off approach to frame filter registration,
2176 therefore it is the frame filter's responsibility to ensure
2177 registration has occurred, and that any exceptions are handled
2178 appropriately. In particular, you may wish to handle exceptions
2179 relating to Python dictionary key uniqueness. It is mandatory that
2180 the dictionary key is the same as frame filter's @code{name}
2181 attribute. When a user manages frame filters (@pxref{Frame Filter
2182 Management}), the names @value{GDBN} will display are those contained
2183 in the @code{name} attribute.
2185 The final step of this example is the implementation of the
2186 @code{filter} method. As shown in the example comments, we define the
2187 @code{filter} method and note that the method must take an iterator,
2188 and also must return an iterator. In this bare-bones example, the
2189 frame filter is not very useful as it just returns the iterator
2190 untouched. However this is a valid operation for frame filters that
2191 have the @code{enabled} attribute set, but decide not to operate on
2194 In the next example, the frame filter operates on all frames and
2195 utilizes a frame decorator to perform some work on the frames.
2196 @xref{Frame Decorator API}, for further information on the frame
2197 decorator interface.
2199 This example works on inlined frames. It highlights frames which are
2200 inlined by tagging them with an ``[inlined]'' tag. By applying a
2201 frame decorator to all frames with the Python @code{itertools imap}
2202 method, the example defers actions to the frame decorator. Frame
2203 decorators are only processed when @value{GDBN} prints the backtrace.
2205 This introduces a new decision making topic: whether to perform
2206 decision making operations at the filtering step, or at the printing
2207 step. In this example's approach, it does not perform any filtering
2208 decisions at the filtering step beyond mapping a frame decorator to
2209 each frame. This allows the actual decision making to be performed
2210 when each frame is printed. This is an important consideration, and
2211 well worth reflecting upon when designing a frame filter. An issue
2212 that frame filters should avoid is unwinding the stack if possible.
2213 Some stacks can run very deep, into the tens of thousands in some
2214 cases. To search every frame to determine if it is inlined ahead of
2215 time may be too expensive at the filtering step. The frame filter
2216 cannot know how many frames it has to iterate over, and it would have
2217 to iterate through them all. This ends up duplicating effort as
2218 @value{GDBN} performs this iteration when it prints the frames.
2220 In this example decision making can be deferred to the printing step.
2221 As each frame is printed, the frame decorator can examine each frame
2222 in turn when @value{GDBN} iterates. From a performance viewpoint,
2223 this is the most appropriate decision to make as it avoids duplicating
2224 the effort that the printing step would undertake anyway. Also, if
2225 there are many frame filters unwinding the stack during filtering, it
2226 can substantially delay the printing of the backtrace which will
2227 result in large memory usage, and a poor user experience.
2230 class InlineFilter():
2233 self.name = "InlinedFrameFilter"
2236 gdb.frame_filters[self.name] = self
2238 def filter(self, frame_iter):
2239 frame_iter = itertools.imap(InlinedFrameDecorator,
2244 This frame filter is somewhat similar to the earlier example, except
2245 that the @code{filter} method applies a frame decorator object called
2246 @code{InlinedFrameDecorator} to each element in the iterator. The
2247 @code{imap} Python method is light-weight. It does not proactively
2248 iterate over the iterator, but rather creates a new iterator which
2249 wraps the existing one.
2251 Below is the frame decorator for this example.
2254 class InlinedFrameDecorator(FrameDecorator):
2256 def __init__(self, fobj):
2257 super(InlinedFrameDecorator, self).__init__(fobj)
2260 frame = fobj.inferior_frame()
2261 name = str(frame.name())
2263 if frame.type() == gdb.INLINE_FRAME:
2264 name = name + " [inlined]"
2269 This frame decorator only defines and overrides the @code{function}
2270 method. It lets the supplied @code{FrameDecorator}, which is shipped
2271 with @value{GDBN}, perform the other work associated with printing
2274 The combination of these two objects create this output from a
2278 #0 0x004004e0 in bar () at inline.c:11
2279 #1 0x00400566 in max [inlined] (b=6, a=12) at inline.c:21
2280 #2 0x00400566 in main () at inline.c:31
2283 So in the case of this example, a frame decorator is applied to all
2284 frames, regardless of whether they may be inlined or not. As
2285 @value{GDBN} iterates over the iterator produced by the frame filters,
2286 @value{GDBN} executes each frame decorator which then makes a decision
2287 on what to print in the @code{function} callback. Using a strategy
2288 like this is a way to defer decisions on the frame content to printing
2291 @subheading Eliding Frames
2293 It might be that the above example is not desirable for representing
2294 inlined frames, and a hierarchical approach may be preferred. If we
2295 want to hierarchically represent frames, the @code{elided} frame
2296 decorator interface might be preferable.
2298 This example approaches the issue with the @code{elided} method. This
2299 example is quite long, but very simplistic. It is out-of-scope for
2300 this section to write a complete example that comprehensively covers
2301 all approaches of finding and printing inlined frames. However, this
2302 example illustrates the approach an author might use.
2304 This example comprises of three sections.
2307 class InlineFrameFilter():
2310 self.name = "InlinedFrameFilter"
2313 gdb.frame_filters[self.name] = self
2315 def filter(self, frame_iter):
2316 return ElidingInlineIterator(frame_iter)
2319 This frame filter is very similar to the other examples. The only
2320 difference is this frame filter is wrapping the iterator provided to
2321 it (@code{frame_iter}) with a custom iterator called
2322 @code{ElidingInlineIterator}. This again defers actions to when
2323 @value{GDBN} prints the backtrace, as the iterator is not traversed
2326 The iterator for this example is as follows. It is in this section of
2327 the example where decisions are made on the content of the backtrace.
2330 class ElidingInlineIterator:
2331 def __init__(self, ii):
2332 self.input_iterator = ii
2338 frame = next(self.input_iterator)
2340 if frame.inferior_frame().type() != gdb.INLINE_FRAME:
2344 eliding_frame = next(self.input_iterator)
2345 except StopIteration:
2347 return ElidingFrameDecorator(eliding_frame, [frame])
2350 This iterator implements the Python iterator protocol. When the
2351 @code{next} function is called (when @value{GDBN} prints each frame),
2352 the iterator checks if this frame decorator, @code{frame}, is wrapping
2353 an inlined frame. If it is not, it returns the existing frame decorator
2354 untouched. If it is wrapping an inlined frame, it assumes that the
2355 inlined frame was contained within the next oldest frame,
2356 @code{eliding_frame}, which it fetches. It then creates and returns a
2357 frame decorator, @code{ElidingFrameDecorator}, which contains both the
2358 elided frame, and the eliding frame.
2361 class ElidingInlineDecorator(FrameDecorator):
2363 def __init__(self, frame, elided_frames):
2364 super(ElidingInlineDecorator, self).__init__(frame)
2366 self.elided_frames = elided_frames
2369 return iter(self.elided_frames)
2372 This frame decorator overrides one function and returns the inlined
2373 frame in the @code{elided} method. As before it lets
2374 @code{FrameDecorator} do the rest of the work involved in printing
2375 this frame. This produces the following output.
2378 #0 0x004004e0 in bar () at inline.c:11
2379 #2 0x00400529 in main () at inline.c:25
2380 #1 0x00400529 in max (b=6, a=12) at inline.c:15
2383 In that output, @code{max} which has been inlined into @code{main} is
2384 printed hierarchically. Another approach would be to combine the
2385 @code{function} method, and the @code{elided} method to both print a
2386 marker in the inlined frame, and also show the hierarchical
2389 @node Unwinding Frames in Python
2390 @subsubsection Unwinding Frames in Python
2391 @cindex unwinding frames in Python
2393 In @value{GDBN} terminology ``unwinding'' is the process of finding
2394 the previous frame (that is, caller's) from the current one. An
2395 unwinder has three methods. The first one checks if it can handle
2396 given frame (``sniff'' it). For the frames it can sniff an unwinder
2397 provides two additional methods: it can return frame's ID, and it can
2398 fetch registers from the previous frame. A running @value{GDBN}
2399 mantains a list of the unwinders and calls each unwinder's sniffer in
2400 turn until it finds the one that recognizes the current frame. There
2401 is an API to register an unwinder.
2403 The unwinders that come with @value{GDBN} handle standard frames.
2404 However, mixed language applications (for example, an application
2405 running Java Virtual Machine) sometimes use frame layouts that cannot
2406 be handled by the @value{GDBN} unwinders. You can write Python code
2407 that can handle such custom frames.
2409 You implement a frame unwinder in Python as a class with which has two
2410 attributes, @code{name} and @code{enabled}, with obvious meanings, and
2411 a single method @code{__call__}, which examines a given frame and
2412 returns an object (an instance of @code{gdb.UnwindInfo class)}
2413 describing it. If an unwinder does not recognize a frame, it should
2414 return @code{None}. The code in @value{GDBN} that enables writing
2415 unwinders in Python uses this object to return frame's ID and previous
2416 frame registers when @value{GDBN} core asks for them.
2418 An unwinder should do as little work as possible. Some otherwise
2419 innocuous operations can cause problems (even crashes, as this code is
2420 not not well-hardened yet). For example, making an inferior call from
2421 an unwinder is unadvisable, as an inferior call will reset
2422 @value{GDBN}'s stack unwinding process, potentially causing re-entrant
2425 @subheading Unwinder Input
2427 An object passed to an unwinder (a @code{gdb.PendingFrame} instance)
2428 provides a method to read frame's registers:
2430 @defun PendingFrame.read_register (reg)
2431 This method returns the contents of the register @var{reg} in the
2432 frame as a @code{gdb.Value} object. @var{reg} can be either a
2433 register number or a register name; the values are platform-specific.
2434 They are usually found in the corresponding
2435 @file{@var{platform}-tdep.h} file in the @value{GDBN} source tree. If
2436 @var{reg} does not name a register for the current architecture, this
2437 method will throw an exception.
2439 Note that this method will always return a @code{gdb.Value} for a
2440 valid register name. This does not mean that the value will be valid.
2441 For example, you may request a register that an earlier unwinder could
2442 not unwind---the value will be unavailable. Instead, the
2443 @code{gdb.Value} returned from this method will be lazy; that is, its
2444 underlying bits will not be fetched until it is first used. So,
2445 attempting to use such a value will cause an exception at the point of
2448 The type of the returned @code{gdb.Value} depends on the register and
2449 the architecture. It is common for registers to have a scalar type,
2450 like @code{long long}; but many other types are possible, such as
2451 pointer, pointer-to-function, floating point or vector types.
2454 It also provides a factory method to create a @code{gdb.UnwindInfo}
2455 instance to be returned to @value{GDBN}:
2457 @defun PendingFrame.create_unwind_info (frame_id)
2458 Returns a new @code{gdb.UnwindInfo} instance identified by given
2459 @var{frame_id}. The argument is used to build @value{GDBN}'s frame ID
2460 using one of functions provided by @value{GDBN}. @var{frame_id}'s attributes
2461 determine which function will be used, as follows:
2465 The frame is identified by the given stack address and PC. The stack
2466 address must be chosen so that it is constant throughout the lifetime
2467 of the frame, so a typical choice is the value of the stack pointer at
2468 the start of the function---in the DWARF standard, this would be the
2469 ``Call Frame Address''.
2471 This is the most common case by far. The other cases are documented
2472 for completeness but are only useful in specialized situations.
2474 @item sp, pc, special
2475 The frame is identified by the stack address, the PC, and a
2476 ``special'' address. The special address is used on architectures
2477 that can have frames that do not change the stack, but which are still
2478 distinct, for example the IA-64, which has a second stack for
2479 registers. Both @var{sp} and @var{special} must be constant
2480 throughout the lifetime of the frame.
2483 The frame is identified by the stack address only. Any other stack
2484 frame with a matching @var{sp} will be considered to match this frame.
2485 Inside gdb, this is called a ``wild frame''. You will never need
2489 Each attribute value should be an instance of @code{gdb.Value}.
2493 @subheading Unwinder Output: UnwindInfo
2495 Use @code{PendingFrame.create_unwind_info} method described above to
2496 create a @code{gdb.UnwindInfo} instance. Use the following method to
2497 specify caller registers that have been saved in this frame:
2499 @defun gdb.UnwindInfo.add_saved_register (reg, value)
2500 @var{reg} identifies the register. It can be a number or a name, just
2501 as for the @code{PendingFrame.read_register} method above.
2502 @var{value} is a register value (a @code{gdb.Value} object).
2505 @subheading Unwinder Skeleton Code
2507 @value{GDBN} comes with the module containing the base @code{Unwinder}
2508 class. Derive your unwinder class from it and structure the code as
2512 from gdb.unwinders import Unwinder
2514 class FrameId(object):
2515 def __init__(self, sp, pc):
2520 class MyUnwinder(Unwinder):
2522 super(MyUnwinder, self).__init___(<expects unwinder name argument>)
2524 def __call__(pending_frame):
2525 if not <we recognize frame>:
2527 # Create UnwindInfo. Usually the frame is identified by the stack
2528 # pointer and the program counter.
2529 sp = pending_frame.read_register(<SP number>)
2530 pc = pending_frame.read_register(<PC number>)
2531 unwind_info = pending_frame.create_unwind_info(FrameId(sp, pc))
2533 # Find the values of the registers in the caller's frame and
2534 # save them in the result:
2535 unwind_info.add_saved_register(<register>, <value>)
2538 # Return the result:
2543 @subheading Registering a Unwinder
2545 An object file, a program space, and the @value{GDBN} proper can have
2546 unwinders registered with it.
2548 The @code{gdb.unwinders} module provides the function to register a
2551 @defun gdb.unwinder.register_unwinder (locus, unwinder, replace=False)
2552 @var{locus} is specifies an object file or a program space to which
2553 @var{unwinder} is added. Passing @code{None} or @code{gdb} adds
2554 @var{unwinder} to the @value{GDBN}'s global unwinder list. The newly
2555 added @var{unwinder} will be called before any other unwinder from the
2556 same locus. Two unwinders in the same locus cannot have the same
2557 name. An attempt to add a unwinder with already existing name raises
2558 an exception unless @var{replace} is @code{True}, in which case the
2559 old unwinder is deleted.
2562 @subheading Unwinder Precedence
2564 @value{GDBN} first calls the unwinders from all the object files in no
2565 particular order, then the unwinders from the current program space,
2566 and finally the unwinders from @value{GDBN}.
2568 @node Xmethods In Python
2569 @subsubsection Xmethods In Python
2570 @cindex xmethods in Python
2572 @dfn{Xmethods} are additional methods or replacements for existing
2573 methods of a C@t{++} class. This feature is useful for those cases
2574 where a method defined in C@t{++} source code could be inlined or
2575 optimized out by the compiler, making it unavailable to @value{GDBN}.
2576 For such cases, one can define an xmethod to serve as a replacement
2577 for the method defined in the C@t{++} source code. @value{GDBN} will
2578 then invoke the xmethod, instead of the C@t{++} method, to
2579 evaluate expressions. One can also use xmethods when debugging
2580 with core files. Moreover, when debugging live programs, invoking an
2581 xmethod need not involve running the inferior (which can potentially
2582 perturb its state). Hence, even if the C@t{++} method is available, it
2583 is better to use its replacement xmethod if one is defined.
2585 The xmethods feature in Python is available via the concepts of an
2586 @dfn{xmethod matcher} and an @dfn{xmethod worker}. To
2587 implement an xmethod, one has to implement a matcher and a
2588 corresponding worker for it (more than one worker can be
2589 implemented, each catering to a different overloaded instance of the
2590 method). Internally, @value{GDBN} invokes the @code{match} method of a
2591 matcher to match the class type and method name. On a match, the
2592 @code{match} method returns a list of matching @emph{worker} objects.
2593 Each worker object typically corresponds to an overloaded instance of
2594 the xmethod. They implement a @code{get_arg_types} method which
2595 returns a sequence of types corresponding to the arguments the xmethod
2596 requires. @value{GDBN} uses this sequence of types to perform
2597 overload resolution and picks a winning xmethod worker. A winner
2598 is also selected from among the methods @value{GDBN} finds in the
2599 C@t{++} source code. Next, the winning xmethod worker and the
2600 winning C@t{++} method are compared to select an overall winner. In
2601 case of a tie between a xmethod worker and a C@t{++} method, the
2602 xmethod worker is selected as the winner. That is, if a winning
2603 xmethod worker is found to be equivalent to the winning C@t{++}
2604 method, then the xmethod worker is treated as a replacement for
2605 the C@t{++} method. @value{GDBN} uses the overall winner to invoke the
2606 method. If the winning xmethod worker is the overall winner, then
2607 the corresponding xmethod is invoked via the @code{__call__} method
2608 of the worker object.
2610 If one wants to implement an xmethod as a replacement for an
2611 existing C@t{++} method, then they have to implement an equivalent
2612 xmethod which has exactly the same name and takes arguments of
2613 exactly the same type as the C@t{++} method. If the user wants to
2614 invoke the C@t{++} method even though a replacement xmethod is
2615 available for that method, then they can disable the xmethod.
2617 @xref{Xmethod API}, for API to implement xmethods in Python.
2618 @xref{Writing an Xmethod}, for implementing xmethods in Python.
2621 @subsubsection Xmethod API
2624 The @value{GDBN} Python API provides classes, interfaces and functions
2625 to implement, register and manipulate xmethods.
2626 @xref{Xmethods In Python}.
2628 An xmethod matcher should be an instance of a class derived from
2629 @code{XMethodMatcher} defined in the module @code{gdb.xmethod}, or an
2630 object with similar interface and attributes. An instance of
2631 @code{XMethodMatcher} has the following attributes:
2634 The name of the matcher.
2638 A boolean value indicating whether the matcher is enabled or disabled.
2642 A list of named methods managed by the matcher. Each object in the list
2643 is an instance of the class @code{XMethod} defined in the module
2644 @code{gdb.xmethod}, or any object with the following attributes:
2649 Name of the xmethod which should be unique for each xmethod
2650 managed by the matcher.
2653 A boolean value indicating whether the xmethod is enabled or
2658 The class @code{XMethod} is a convenience class with same
2659 attributes as above along with the following constructor:
2661 @defun XMethod.__init__ (self, name)
2662 Constructs an enabled xmethod with name @var{name}.
2667 The @code{XMethodMatcher} class has the following methods:
2669 @defun XMethodMatcher.__init__ (self, name)
2670 Constructs an enabled xmethod matcher with name @var{name}. The
2671 @code{methods} attribute is initialized to @code{None}.
2674 @defun XMethodMatcher.match (self, class_type, method_name)
2675 Derived classes should override this method. It should return a
2676 xmethod worker object (or a sequence of xmethod worker
2677 objects) matching the @var{class_type} and @var{method_name}.
2678 @var{class_type} is a @code{gdb.Type} object, and @var{method_name}
2679 is a string value. If the matcher manages named methods as listed in
2680 its @code{methods} attribute, then only those worker objects whose
2681 corresponding entries in the @code{methods} list are enabled should be
2685 An xmethod worker should be an instance of a class derived from
2686 @code{XMethodWorker} defined in the module @code{gdb.xmethod},
2687 or support the following interface:
2689 @defun XMethodWorker.get_arg_types (self)
2690 This method returns a sequence of @code{gdb.Type} objects corresponding
2691 to the arguments that the xmethod takes. It can return an empty
2692 sequence or @code{None} if the xmethod does not take any arguments.
2693 If the xmethod takes a single argument, then a single
2694 @code{gdb.Type} object corresponding to it can be returned.
2697 @defun XMethodWorker.get_result_type (self, *args)
2698 This method returns a @code{gdb.Type} object representing the type
2699 of the result of invoking this xmethod.
2700 The @var{args} argument is the same tuple of arguments that would be
2701 passed to the @code{__call__} method of this worker.
2704 @defun XMethodWorker.__call__ (self, *args)
2705 This is the method which does the @emph{work} of the xmethod. The
2706 @var{args} arguments is the tuple of arguments to the xmethod. Each
2707 element in this tuple is a gdb.Value object. The first element is
2708 always the @code{this} pointer value.
2711 For @value{GDBN} to lookup xmethods, the xmethod matchers
2712 should be registered using the following function defined in the module
2715 @defun register_xmethod_matcher (locus, matcher, replace=False)
2716 The @code{matcher} is registered with @code{locus}, replacing an
2717 existing matcher with the same name as @code{matcher} if
2718 @code{replace} is @code{True}. @code{locus} can be a
2719 @code{gdb.Objfile} object (@pxref{Objfiles In Python}), or a
2720 @code{gdb.Progspace} object (@pxref{Progspaces In Python}), or
2721 @code{None}. If it is @code{None}, then @code{matcher} is registered
2725 @node Writing an Xmethod
2726 @subsubsection Writing an Xmethod
2727 @cindex writing xmethods in Python
2729 Implementing xmethods in Python will require implementing xmethod
2730 matchers and xmethod workers (@pxref{Xmethods In Python}). Consider
2731 the following C@t{++} class:
2737 MyClass (int a) : a_(a) @{ @}
2739 int geta (void) @{ return a_; @}
2740 int operator+ (int b);
2747 MyClass::operator+ (int b)
2754 Let us define two xmethods for the class @code{MyClass}, one
2755 replacing the method @code{geta}, and another adding an overloaded
2756 flavor of @code{operator+} which takes a @code{MyClass} argument (the
2757 C@t{++} code above already has an overloaded @code{operator+}
2758 which takes an @code{int} argument). The xmethod matcher can be
2762 class MyClass_geta(gdb.xmethod.XMethod):
2764 gdb.xmethod.XMethod.__init__(self, 'geta')
2766 def get_worker(self, method_name):
2767 if method_name == 'geta':
2768 return MyClassWorker_geta()
2771 class MyClass_sum(gdb.xmethod.XMethod):
2773 gdb.xmethod.XMethod.__init__(self, 'sum')
2775 def get_worker(self, method_name):
2776 if method_name == 'operator+':
2777 return MyClassWorker_plus()
2780 class MyClassMatcher(gdb.xmethod.XMethodMatcher):
2782 gdb.xmethod.XMethodMatcher.__init__(self, 'MyClassMatcher')
2783 # List of methods 'managed' by this matcher
2784 self.methods = [MyClass_geta(), MyClass_sum()]
2786 def match(self, class_type, method_name):
2787 if class_type.tag != 'MyClass':
2790 for method in self.methods:
2792 worker = method.get_worker(method_name)
2794 workers.append(worker)
2800 Notice that the @code{match} method of @code{MyClassMatcher} returns
2801 a worker object of type @code{MyClassWorker_geta} for the @code{geta}
2802 method, and a worker object of type @code{MyClassWorker_plus} for the
2803 @code{operator+} method. This is done indirectly via helper classes
2804 derived from @code{gdb.xmethod.XMethod}. One does not need to use the
2805 @code{methods} attribute in a matcher as it is optional. However, if a
2806 matcher manages more than one xmethod, it is a good practice to list the
2807 xmethods in the @code{methods} attribute of the matcher. This will then
2808 facilitate enabling and disabling individual xmethods via the
2809 @code{enable/disable} commands. Notice also that a worker object is
2810 returned only if the corresponding entry in the @code{methods} attribute
2811 of the matcher is enabled.
2813 The implementation of the worker classes returned by the matcher setup
2814 above is as follows:
2817 class MyClassWorker_geta(gdb.xmethod.XMethodWorker):
2818 def get_arg_types(self):
2821 def get_result_type(self, obj):
2822 return gdb.lookup_type('int')
2824 def __call__(self, obj):
2828 class MyClassWorker_plus(gdb.xmethod.XMethodWorker):
2829 def get_arg_types(self):
2830 return gdb.lookup_type('MyClass')
2832 def get_result_type(self, obj):
2833 return gdb.lookup_type('int')
2835 def __call__(self, obj, other):
2836 return obj['a_'] + other['a_']
2839 For @value{GDBN} to actually lookup a xmethod, it has to be
2840 registered with it. The matcher defined above is registered with
2841 @value{GDBN} globally as follows:
2844 gdb.xmethod.register_xmethod_matcher(None, MyClassMatcher())
2847 If an object @code{obj} of type @code{MyClass} is initialized in C@t{++}
2855 then, after loading the Python script defining the xmethod matchers
2856 and workers into @code{GDBN}, invoking the method @code{geta} or using
2857 the operator @code{+} on @code{obj} will invoke the xmethods
2868 Consider another example with a C++ template class:
2875 MyTemplate () : dsize_(10), data_ (new T [10]) @{ @}
2876 ~MyTemplate () @{ delete [] data_; @}
2878 int footprint (void)
2880 return sizeof (T) * dsize_ + sizeof (MyTemplate<T>);
2889 Let us implement an xmethod for the above class which serves as a
2890 replacement for the @code{footprint} method. The full code listing
2891 of the xmethod workers and xmethod matchers is as follows:
2894 class MyTemplateWorker_footprint(gdb.xmethod.XMethodWorker):
2895 def __init__(self, class_type):
2896 self.class_type = class_type
2898 def get_arg_types(self):
2901 def get_result_type(self):
2902 return gdb.lookup_type('int')
2904 def __call__(self, obj):
2905 return (self.class_type.sizeof +
2907 self.class_type.template_argument(0).sizeof)
2910 class MyTemplateMatcher_footprint(gdb.xmethod.XMethodMatcher):
2912 gdb.xmethod.XMethodMatcher.__init__(self, 'MyTemplateMatcher')
2914 def match(self, class_type, method_name):
2915 if (re.match('MyTemplate<[ \t\n]*[_a-zA-Z][ _a-zA-Z0-9]*>',
2917 method_name == 'footprint'):
2918 return MyTemplateWorker_footprint(class_type)
2921 Notice that, in this example, we have not used the @code{methods}
2922 attribute of the matcher as the matcher manages only one xmethod. The
2923 user can enable/disable this xmethod by enabling/disabling the matcher
2926 @node Inferiors In Python
2927 @subsubsection Inferiors In Python
2928 @cindex inferiors in Python
2930 @findex gdb.Inferior
2931 Programs which are being run under @value{GDBN} are called inferiors
2932 (@pxref{Inferiors Connections and Programs}). Python scripts can access
2933 information about and manipulate inferiors controlled by @value{GDBN}
2934 via objects of the @code{gdb.Inferior} class.
2936 The following inferior-related functions are available in the @code{gdb}
2939 @defun gdb.inferiors ()
2940 Return a tuple containing all inferior objects.
2943 @defun gdb.selected_inferior ()
2944 Return an object representing the current inferior.
2947 A @code{gdb.Inferior} object has the following attributes:
2949 @defvar Inferior.num
2950 ID of inferior, as assigned by GDB.
2953 @defvar Inferior.pid
2954 Process ID of the inferior, as assigned by the underlying operating
2958 @defvar Inferior.was_attached
2959 Boolean signaling whether the inferior was created using `attach', or
2960 started by @value{GDBN} itself.
2963 @defvar Inferior.progspace
2964 The inferior's program space. @xref{Progspaces In Python}.
2967 A @code{gdb.Inferior} object has the following methods:
2969 @defun Inferior.is_valid ()
2970 Returns @code{True} if the @code{gdb.Inferior} object is valid,
2971 @code{False} if not. A @code{gdb.Inferior} object will become invalid
2972 if the inferior no longer exists within @value{GDBN}. All other
2973 @code{gdb.Inferior} methods will throw an exception if it is invalid
2974 at the time the method is called.
2977 @defun Inferior.threads ()
2978 This method returns a tuple holding all the threads which are valid
2979 when it is called. If there are no valid threads, the method will
2980 return an empty tuple.
2983 @defun Inferior.architecture ()
2984 Return the @code{gdb.Architecture} (@pxref{Architectures In Python})
2985 for this inferior. This represents the architecture of the inferior
2986 as a whole. Some platforms can have multiple architectures in a
2987 single address space, so this may not match the architecture of a
2988 particular frame (@pxref{Frames In Python}).
2991 @findex Inferior.read_memory
2992 @defun Inferior.read_memory (address, length)
2993 Read @var{length} addressable memory units from the inferior, starting at
2994 @var{address}. Returns a buffer object, which behaves much like an array
2995 or a string. It can be modified and given to the
2996 @code{Inferior.write_memory} function. In Python 3, the return
2997 value is a @code{memoryview} object.
3000 @findex Inferior.write_memory
3001 @defun Inferior.write_memory (address, buffer @r{[}, length@r{]})
3002 Write the contents of @var{buffer} to the inferior, starting at
3003 @var{address}. The @var{buffer} parameter must be a Python object
3004 which supports the buffer protocol, i.e., a string, an array or the
3005 object returned from @code{Inferior.read_memory}. If given, @var{length}
3006 determines the number of addressable memory units from @var{buffer} to be
3010 @findex gdb.search_memory
3011 @defun Inferior.search_memory (address, length, pattern)
3012 Search a region of the inferior memory starting at @var{address} with
3013 the given @var{length} using the search pattern supplied in
3014 @var{pattern}. The @var{pattern} parameter must be a Python object
3015 which supports the buffer protocol, i.e., a string, an array or the
3016 object returned from @code{gdb.read_memory}. Returns a Python @code{Long}
3017 containing the address where the pattern was found, or @code{None} if
3018 the pattern could not be found.
3021 @findex Inferior.thread_from_handle
3022 @findex Inferior.thread_from_thread_handle
3023 @defun Inferior.thread_from_handle (handle)
3024 Return the thread object corresponding to @var{handle}, a thread
3025 library specific data structure such as @code{pthread_t} for pthreads
3026 library implementations.
3028 The function @code{Inferior.thread_from_thread_handle} provides
3029 the same functionality, but use of @code{Inferior.thread_from_thread_handle}
3033 @node Events In Python
3034 @subsubsection Events In Python
3035 @cindex inferior events in Python
3037 @value{GDBN} provides a general event facility so that Python code can be
3038 notified of various state changes, particularly changes that occur in
3041 An @dfn{event} is just an object that describes some state change. The
3042 type of the object and its attributes will vary depending on the details
3043 of the change. All the existing events are described below.
3045 In order to be notified of an event, you must register an event handler
3046 with an @dfn{event registry}. An event registry is an object in the
3047 @code{gdb.events} module which dispatches particular events. A registry
3048 provides methods to register and unregister event handlers:
3050 @defun EventRegistry.connect (object)
3051 Add the given callable @var{object} to the registry. This object will be
3052 called when an event corresponding to this registry occurs.
3055 @defun EventRegistry.disconnect (object)
3056 Remove the given @var{object} from the registry. Once removed, the object
3057 will no longer receive notifications of events.
3063 def exit_handler (event):
3064 print "event type: exit"
3065 print "exit code: %d" % (event.exit_code)
3067 gdb.events.exited.connect (exit_handler)
3070 In the above example we connect our handler @code{exit_handler} to the
3071 registry @code{events.exited}. Once connected, @code{exit_handler} gets
3072 called when the inferior exits. The argument @dfn{event} in this example is
3073 of type @code{gdb.ExitedEvent}. As you can see in the example the
3074 @code{ExitedEvent} object has an attribute which indicates the exit code of
3077 The following is a listing of the event registries that are available and
3078 details of the events they emit:
3083 Emits @code{gdb.ThreadEvent}.
3085 Some events can be thread specific when @value{GDBN} is running in non-stop
3086 mode. When represented in Python, these events all extend
3087 @code{gdb.ThreadEvent}. Note, this event is not emitted directly; instead,
3088 events which are emitted by this or other modules might extend this event.
3089 Examples of these events are @code{gdb.BreakpointEvent} and
3090 @code{gdb.ContinueEvent}.
3092 @defvar ThreadEvent.inferior_thread
3093 In non-stop mode this attribute will be set to the specific thread which was
3094 involved in the emitted event. Otherwise, it will be set to @code{None}.
3097 Emits @code{gdb.ContinueEvent} which extends @code{gdb.ThreadEvent}.
3099 This event indicates that the inferior has been continued after a stop. For
3100 inherited attribute refer to @code{gdb.ThreadEvent} above.
3103 Emits @code{events.ExitedEvent} which indicates that the inferior has exited.
3104 @code{events.ExitedEvent} has two attributes:
3105 @defvar ExitedEvent.exit_code
3106 An integer representing the exit code, if available, which the inferior
3107 has returned. (The exit code could be unavailable if, for example,
3108 @value{GDBN} detaches from the inferior.) If the exit code is unavailable,
3109 the attribute does not exist.
3111 @defvar ExitedEvent.inferior
3112 A reference to the inferior which triggered the @code{exited} event.
3116 Emits @code{gdb.StopEvent} which extends @code{gdb.ThreadEvent}.
3118 Indicates that the inferior has stopped. All events emitted by this registry
3119 extend StopEvent. As a child of @code{gdb.ThreadEvent}, @code{gdb.StopEvent}
3120 will indicate the stopped thread when @value{GDBN} is running in non-stop
3121 mode. Refer to @code{gdb.ThreadEvent} above for more details.
3123 Emits @code{gdb.SignalEvent} which extends @code{gdb.StopEvent}.
3125 This event indicates that the inferior or one of its threads has received as
3126 signal. @code{gdb.SignalEvent} has the following attributes:
3128 @defvar SignalEvent.stop_signal
3129 A string representing the signal received by the inferior. A list of possible
3130 signal values can be obtained by running the command @code{info signals} in
3131 the @value{GDBN} command prompt.
3134 Also emits @code{gdb.BreakpointEvent} which extends @code{gdb.StopEvent}.
3136 @code{gdb.BreakpointEvent} event indicates that one or more breakpoints have
3137 been hit, and has the following attributes:
3139 @defvar BreakpointEvent.breakpoints
3140 A sequence containing references to all the breakpoints (type
3141 @code{gdb.Breakpoint}) that were hit.
3142 @xref{Breakpoints In Python}, for details of the @code{gdb.Breakpoint} object.
3144 @defvar BreakpointEvent.breakpoint
3145 A reference to the first breakpoint that was hit.
3146 This function is maintained for backward compatibility and is now deprecated
3147 in favor of the @code{gdb.BreakpointEvent.breakpoints} attribute.
3150 @item events.new_objfile
3151 Emits @code{gdb.NewObjFileEvent} which indicates that a new object file has
3152 been loaded by @value{GDBN}. @code{gdb.NewObjFileEvent} has one attribute:
3154 @defvar NewObjFileEvent.new_objfile
3155 A reference to the object file (@code{gdb.Objfile}) which has been loaded.
3156 @xref{Objfiles In Python}, for details of the @code{gdb.Objfile} object.
3159 @item events.clear_objfiles
3160 Emits @code{gdb.ClearObjFilesEvent} which indicates that the list of object
3161 files for a program space has been reset.
3162 @code{gdb.ClearObjFilesEvent} has one attribute:
3164 @defvar ClearObjFilesEvent.progspace
3165 A reference to the program space (@code{gdb.Progspace}) whose objfile list has
3166 been cleared. @xref{Progspaces In Python}.
3169 @item events.inferior_call
3170 Emits events just before and after a function in the inferior is
3171 called by @value{GDBN}. Before an inferior call, this emits an event
3172 of type @code{gdb.InferiorCallPreEvent}, and after an inferior call,
3173 this emits an event of type @code{gdb.InferiorCallPostEvent}.
3176 @tindex gdb.InferiorCallPreEvent
3177 @item @code{gdb.InferiorCallPreEvent}
3178 Indicates that a function in the inferior is about to be called.
3180 @defvar InferiorCallPreEvent.ptid
3181 The thread in which the call will be run.
3184 @defvar InferiorCallPreEvent.address
3185 The location of the function to be called.
3188 @tindex gdb.InferiorCallPostEvent
3189 @item @code{gdb.InferiorCallPostEvent}
3190 Indicates that a function in the inferior has just been called.
3192 @defvar InferiorCallPostEvent.ptid
3193 The thread in which the call was run.
3196 @defvar InferiorCallPostEvent.address
3197 The location of the function that was called.
3201 @item events.memory_changed
3202 Emits @code{gdb.MemoryChangedEvent} which indicates that the memory of the
3203 inferior has been modified by the @value{GDBN} user, for instance via a
3204 command like @w{@code{set *addr = value}}. The event has the following
3207 @defvar MemoryChangedEvent.address
3208 The start address of the changed region.
3211 @defvar MemoryChangedEvent.length
3212 Length in bytes of the changed region.
3215 @item events.register_changed
3216 Emits @code{gdb.RegisterChangedEvent} which indicates that a register in the
3217 inferior has been modified by the @value{GDBN} user.
3219 @defvar RegisterChangedEvent.frame
3220 A gdb.Frame object representing the frame in which the register was modified.
3222 @defvar RegisterChangedEvent.regnum
3223 Denotes which register was modified.
3226 @item events.breakpoint_created
3227 This is emitted when a new breakpoint has been created. The argument
3228 that is passed is the new @code{gdb.Breakpoint} object.
3230 @item events.breakpoint_modified
3231 This is emitted when a breakpoint has been modified in some way. The
3232 argument that is passed is the new @code{gdb.Breakpoint} object.
3234 @item events.breakpoint_deleted
3235 This is emitted when a breakpoint has been deleted. The argument that
3236 is passed is the @code{gdb.Breakpoint} object. When this event is
3237 emitted, the @code{gdb.Breakpoint} object will already be in its
3238 invalid state; that is, the @code{is_valid} method will return
3241 @item events.before_prompt
3242 This event carries no payload. It is emitted each time @value{GDBN}
3243 presents a prompt to the user.
3245 @item events.new_inferior
3246 This is emitted when a new inferior is created. Note that the
3247 inferior is not necessarily running; in fact, it may not even have an
3248 associated executable.
3250 The event is of type @code{gdb.NewInferiorEvent}. This has a single
3253 @defvar NewInferiorEvent.inferior
3254 The new inferior, a @code{gdb.Inferior} object.
3257 @item events.inferior_deleted
3258 This is emitted when an inferior has been deleted. Note that this is
3259 not the same as process exit; it is notified when the inferior itself
3260 is removed, say via @code{remove-inferiors}.
3262 The event is of type @code{gdb.InferiorDeletedEvent}. This has a single
3265 @defvar NewInferiorEvent.inferior
3266 The inferior that is being removed, a @code{gdb.Inferior} object.
3269 @item events.new_thread
3270 This is emitted when @value{GDBN} notices a new thread. The event is of
3271 type @code{gdb.NewThreadEvent}, which extends @code{gdb.ThreadEvent}.
3272 This has a single attribute:
3274 @defvar NewThreadEvent.inferior_thread
3280 @node Threads In Python
3281 @subsubsection Threads In Python
3282 @cindex threads in python
3284 @findex gdb.InferiorThread
3285 Python scripts can access information about, and manipulate inferior threads
3286 controlled by @value{GDBN}, via objects of the @code{gdb.InferiorThread} class.
3288 The following thread-related functions are available in the @code{gdb}
3291 @findex gdb.selected_thread
3292 @defun gdb.selected_thread ()
3293 This function returns the thread object for the selected thread. If there
3294 is no selected thread, this will return @code{None}.
3297 To get the list of threads for an inferior, use the @code{Inferior.threads()}
3298 method. @xref{Inferiors In Python}
3300 A @code{gdb.InferiorThread} object has the following attributes:
3302 @defvar InferiorThread.name
3303 The name of the thread. If the user specified a name using
3304 @code{thread name}, then this returns that name. Otherwise, if an
3305 OS-supplied name is available, then it is returned. Otherwise, this
3306 returns @code{None}.
3308 This attribute can be assigned to. The new value must be a string
3309 object, which sets the new name, or @code{None}, which removes any
3310 user-specified thread name.
3313 @defvar InferiorThread.num
3314 The per-inferior number of the thread, as assigned by GDB.
3317 @defvar InferiorThread.global_num
3318 The global ID of the thread, as assigned by GDB. You can use this to
3319 make Python breakpoints thread-specific, for example
3320 (@pxref{python_breakpoint_thread,,The Breakpoint.thread attribute}).
3323 @defvar InferiorThread.ptid
3324 ID of the thread, as assigned by the operating system. This attribute is a
3325 tuple containing three integers. The first is the Process ID (PID); the second
3326 is the Lightweight Process ID (LWPID), and the third is the Thread ID (TID).
3327 Either the LWPID or TID may be 0, which indicates that the operating system
3328 does not use that identifier.
3331 @defvar InferiorThread.inferior
3332 The inferior this thread belongs to. This attribute is represented as
3333 a @code{gdb.Inferior} object. This attribute is not writable.
3336 A @code{gdb.InferiorThread} object has the following methods:
3338 @defun InferiorThread.is_valid ()
3339 Returns @code{True} if the @code{gdb.InferiorThread} object is valid,
3340 @code{False} if not. A @code{gdb.InferiorThread} object will become
3341 invalid if the thread exits, or the inferior that the thread belongs
3342 is deleted. All other @code{gdb.InferiorThread} methods will throw an
3343 exception if it is invalid at the time the method is called.
3346 @defun InferiorThread.switch ()
3347 This changes @value{GDBN}'s currently selected thread to the one represented
3351 @defun InferiorThread.is_stopped ()
3352 Return a Boolean indicating whether the thread is stopped.
3355 @defun InferiorThread.is_running ()
3356 Return a Boolean indicating whether the thread is running.
3359 @defun InferiorThread.is_exited ()
3360 Return a Boolean indicating whether the thread is exited.
3363 @defun InferiorThread.handle ()
3364 Return the thread object's handle, represented as a Python @code{bytes}
3365 object. A @code{gdb.Value} representation of the handle may be
3366 constructed via @code{gdb.Value(bufobj, type)} where @var{bufobj} is
3367 the Python @code{bytes} representation of the handle and @var{type} is
3368 a @code{gdb.Type} for the handle type.
3371 @node Recordings In Python
3372 @subsubsection Recordings In Python
3373 @cindex recordings in python
3375 The following recordings-related functions
3376 (@pxref{Process Record and Replay}) are available in the @code{gdb}
3379 @defun gdb.start_recording (@r{[}method@r{]}, @r{[}format@r{]})
3380 Start a recording using the given @var{method} and @var{format}. If
3381 no @var{format} is given, the default format for the recording method
3382 is used. If no @var{method} is given, the default method will be used.
3383 Returns a @code{gdb.Record} object on success. Throw an exception on
3386 The following strings can be passed as @var{method}:
3392 @code{"btrace"}: Possible values for @var{format}: @code{"pt"},
3393 @code{"bts"} or leave out for default format.
3397 @defun gdb.current_recording ()
3398 Access a currently running recording. Return a @code{gdb.Record}
3399 object on success. Return @code{None} if no recording is currently
3403 @defun gdb.stop_recording ()
3404 Stop the current recording. Throw an exception if no recording is
3405 currently active. All record objects become invalid after this call.
3408 A @code{gdb.Record} object has the following attributes:
3410 @defvar Record.method
3411 A string with the current recording method, e.g.@: @code{full} or
3415 @defvar Record.format
3416 A string with the current recording format, e.g.@: @code{bt}, @code{pts} or
3420 @defvar Record.begin
3421 A method specific instruction object representing the first instruction
3426 A method specific instruction object representing the current
3427 instruction, that is not actually part of the recording.
3430 @defvar Record.replay_position
3431 The instruction representing the current replay position. If there is
3432 no replay active, this will be @code{None}.
3435 @defvar Record.instruction_history
3436 A list with all recorded instructions.
3439 @defvar Record.function_call_history
3440 A list with all recorded function call segments.
3443 A @code{gdb.Record} object has the following methods:
3445 @defun Record.goto (instruction)
3446 Move the replay position to the given @var{instruction}.
3449 The common @code{gdb.Instruction} class that recording method specific
3450 instruction objects inherit from, has the following attributes:
3452 @defvar Instruction.pc
3453 An integer representing this instruction's address.
3456 @defvar Instruction.data
3457 A buffer with the raw instruction data. In Python 3, the return value is a
3458 @code{memoryview} object.
3461 @defvar Instruction.decoded
3462 A human readable string with the disassembled instruction.
3465 @defvar Instruction.size
3466 The size of the instruction in bytes.
3469 Additionally @code{gdb.RecordInstruction} has the following attributes:
3471 @defvar RecordInstruction.number
3472 An integer identifying this instruction. @code{number} corresponds to
3473 the numbers seen in @code{record instruction-history}
3474 (@pxref{Process Record and Replay}).
3477 @defvar RecordInstruction.sal
3478 A @code{gdb.Symtab_and_line} object representing the associated symtab
3479 and line of this instruction. May be @code{None} if no debug information is
3483 @defvar RecordInstruction.is_speculative
3484 A boolean indicating whether the instruction was executed speculatively.
3487 If an error occured during recording or decoding a recording, this error is
3488 represented by a @code{gdb.RecordGap} object in the instruction list. It has
3489 the following attributes:
3491 @defvar RecordGap.number
3492 An integer identifying this gap. @code{number} corresponds to the numbers seen
3493 in @code{record instruction-history} (@pxref{Process Record and Replay}).
3496 @defvar RecordGap.error_code
3497 A numerical representation of the reason for the gap. The value is specific to
3498 the current recording method.
3501 @defvar RecordGap.error_string
3502 A human readable string with the reason for the gap.
3505 A @code{gdb.RecordFunctionSegment} object has the following attributes:
3507 @defvar RecordFunctionSegment.number
3508 An integer identifying this function segment. @code{number} corresponds to
3509 the numbers seen in @code{record function-call-history}
3510 (@pxref{Process Record and Replay}).
3513 @defvar RecordFunctionSegment.symbol
3514 A @code{gdb.Symbol} object representing the associated symbol. May be
3515 @code{None} if no debug information is available.
3518 @defvar RecordFunctionSegment.level
3519 An integer representing the function call's stack level. May be
3520 @code{None} if the function call is a gap.
3523 @defvar RecordFunctionSegment.instructions
3524 A list of @code{gdb.RecordInstruction} or @code{gdb.RecordGap} objects
3525 associated with this function call.
3528 @defvar RecordFunctionSegment.up
3529 A @code{gdb.RecordFunctionSegment} object representing the caller's
3530 function segment. If the call has not been recorded, this will be the
3531 function segment to which control returns. If neither the call nor the
3532 return have been recorded, this will be @code{None}.
3535 @defvar RecordFunctionSegment.prev
3536 A @code{gdb.RecordFunctionSegment} object representing the previous
3537 segment of this function call. May be @code{None}.
3540 @defvar RecordFunctionSegment.next
3541 A @code{gdb.RecordFunctionSegment} object representing the next segment of
3542 this function call. May be @code{None}.
3545 The following example demonstrates the usage of these objects and
3546 functions to create a function that will rewind a record to the last
3547 time a function in a different file was executed. This would typically
3548 be used to track the execution of user provided callback functions in a
3549 library which typically are not visible in a back trace.
3553 rec = gdb.current_recording ()
3557 insn = rec.instruction_history
3562 position = insn.index (rec.replay_position)
3566 filename = insn[position].sal.symtab.fullname ()
3570 for i in reversed (insn[:position]):
3572 current = i.sal.symtab.fullname ()
3576 if filename == current:
3583 Another possible application is to write a function that counts the
3584 number of code executions in a given line range. This line range can
3585 contain parts of functions or span across several functions and is not
3586 limited to be contiguous.
3589 def countrange (filename, linerange):
3592 def filter_only (file_name):
3593 for call in gdb.current_recording ().function_call_history:
3595 if file_name in call.symbol.symtab.fullname ():
3600 for c in filter_only (filename):
3601 for i in c.instructions:
3603 if i.sal.line in linerange:
3612 @node Commands In Python
3613 @subsubsection Commands In Python
3615 @cindex commands in python
3616 @cindex python commands
3617 You can implement new @value{GDBN} CLI commands in Python. A CLI
3618 command is implemented using an instance of the @code{gdb.Command}
3619 class, most commonly using a subclass.
3621 @defun Command.__init__ (name, @var{command_class} @r{[}, @var{completer_class} @r{[}, @var{prefix}@r{]]})
3622 The object initializer for @code{Command} registers the new command
3623 with @value{GDBN}. This initializer is normally invoked from the
3624 subclass' own @code{__init__} method.
3626 @var{name} is the name of the command. If @var{name} consists of
3627 multiple words, then the initial words are looked for as prefix
3628 commands. In this case, if one of the prefix commands does not exist,
3629 an exception is raised.
3631 There is no support for multi-line commands.
3633 @var{command_class} should be one of the @samp{COMMAND_} constants
3634 defined below. This argument tells @value{GDBN} how to categorize the
3635 new command in the help system.
3637 @var{completer_class} is an optional argument. If given, it should be
3638 one of the @samp{COMPLETE_} constants defined below. This argument
3639 tells @value{GDBN} how to perform completion for this command. If not
3640 given, @value{GDBN} will attempt to complete using the object's
3641 @code{complete} method (see below); if no such method is found, an
3642 error will occur when completion is attempted.
3644 @var{prefix} is an optional argument. If @code{True}, then the new
3645 command is a prefix command; sub-commands of this command may be
3648 The help text for the new command is taken from the Python
3649 documentation string for the command's class, if there is one. If no
3650 documentation string is provided, the default value ``This command is
3651 not documented.'' is used.
3654 @cindex don't repeat Python command
3655 @defun Command.dont_repeat ()
3656 By default, a @value{GDBN} command is repeated when the user enters a
3657 blank line at the command prompt. A command can suppress this
3658 behavior by invoking the @code{dont_repeat} method. This is similar
3659 to the user command @code{dont-repeat}, see @ref{Define, dont-repeat}.
3662 @defun Command.invoke (argument, from_tty)
3663 This method is called by @value{GDBN} when this command is invoked.
3665 @var{argument} is a string. It is the argument to the command, after
3666 leading and trailing whitespace has been stripped.
3668 @var{from_tty} is a boolean argument. When true, this means that the
3669 command was entered by the user at the terminal; when false it means
3670 that the command came from elsewhere.
3672 If this method throws an exception, it is turned into a @value{GDBN}
3673 @code{error} call. Otherwise, the return value is ignored.
3675 @findex gdb.string_to_argv
3676 To break @var{argument} up into an argv-like string use
3677 @code{gdb.string_to_argv}. This function behaves identically to
3678 @value{GDBN}'s internal argument lexer @code{buildargv}.
3679 It is recommended to use this for consistency.
3680 Arguments are separated by spaces and may be quoted.
3684 print gdb.string_to_argv ("1 2\ \\\"3 '4 \"5' \"6 '7\"")
3685 ['1', '2 "3', '4 "5', "6 '7"]
3690 @cindex completion of Python commands
3691 @defun Command.complete (text, word)
3692 This method is called by @value{GDBN} when the user attempts
3693 completion on this command. All forms of completion are handled by
3694 this method, that is, the @key{TAB} and @key{M-?} key bindings
3695 (@pxref{Completion}), and the @code{complete} command (@pxref{Help,
3698 The arguments @var{text} and @var{word} are both strings; @var{text}
3699 holds the complete command line up to the cursor's location, while
3700 @var{word} holds the last word of the command line; this is computed
3701 using a word-breaking heuristic.
3703 The @code{complete} method can return several values:
3706 If the return value is a sequence, the contents of the sequence are
3707 used as the completions. It is up to @code{complete} to ensure that the
3708 contents actually do complete the word. A zero-length sequence is
3709 allowed, it means that there were no completions available. Only
3710 string elements of the sequence are used; other elements in the
3711 sequence are ignored.
3714 If the return value is one of the @samp{COMPLETE_} constants defined
3715 below, then the corresponding @value{GDBN}-internal completion
3716 function is invoked, and its result is used.
3719 All other results are treated as though there were no available
3724 When a new command is registered, it must be declared as a member of
3725 some general class of commands. This is used to classify top-level
3726 commands in the on-line help system; note that prefix commands are not
3727 listed under their own category but rather that of their top-level
3728 command. The available classifications are represented by constants
3729 defined in the @code{gdb} module:
3732 @findex COMMAND_NONE
3733 @findex gdb.COMMAND_NONE
3734 @item gdb.COMMAND_NONE
3735 The command does not belong to any particular class. A command in
3736 this category will not be displayed in any of the help categories.
3738 @findex COMMAND_RUNNING
3739 @findex gdb.COMMAND_RUNNING
3740 @item gdb.COMMAND_RUNNING
3741 The command is related to running the inferior. For example,
3742 @code{start}, @code{step}, and @code{continue} are in this category.
3743 Type @kbd{help running} at the @value{GDBN} prompt to see a list of
3744 commands in this category.
3746 @findex COMMAND_DATA
3747 @findex gdb.COMMAND_DATA
3748 @item gdb.COMMAND_DATA
3749 The command is related to data or variables. For example,
3750 @code{call}, @code{find}, and @code{print} are in this category. Type
3751 @kbd{help data} at the @value{GDBN} prompt to see a list of commands
3754 @findex COMMAND_STACK
3755 @findex gdb.COMMAND_STACK
3756 @item gdb.COMMAND_STACK
3757 The command has to do with manipulation of the stack. For example,
3758 @code{backtrace}, @code{frame}, and @code{return} are in this
3759 category. Type @kbd{help stack} at the @value{GDBN} prompt to see a
3760 list of commands in this category.
3762 @findex COMMAND_FILES
3763 @findex gdb.COMMAND_FILES
3764 @item gdb.COMMAND_FILES
3765 This class is used for file-related commands. For example,
3766 @code{file}, @code{list} and @code{section} are in this category.
3767 Type @kbd{help files} at the @value{GDBN} prompt to see a list of
3768 commands in this category.
3770 @findex COMMAND_SUPPORT
3771 @findex gdb.COMMAND_SUPPORT
3772 @item gdb.COMMAND_SUPPORT
3773 This should be used for ``support facilities'', generally meaning
3774 things that are useful to the user when interacting with @value{GDBN},
3775 but not related to the state of the inferior. For example,
3776 @code{help}, @code{make}, and @code{shell} are in this category. Type
3777 @kbd{help support} at the @value{GDBN} prompt to see a list of
3778 commands in this category.
3780 @findex COMMAND_STATUS
3781 @findex gdb.COMMAND_STATUS
3782 @item gdb.COMMAND_STATUS
3783 The command is an @samp{info}-related command, that is, related to the
3784 state of @value{GDBN} itself. For example, @code{info}, @code{macro},
3785 and @code{show} are in this category. Type @kbd{help status} at the
3786 @value{GDBN} prompt to see a list of commands in this category.
3788 @findex COMMAND_BREAKPOINTS
3789 @findex gdb.COMMAND_BREAKPOINTS
3790 @item gdb.COMMAND_BREAKPOINTS
3791 The command has to do with breakpoints. For example, @code{break},
3792 @code{clear}, and @code{delete} are in this category. Type @kbd{help
3793 breakpoints} at the @value{GDBN} prompt to see a list of commands in
3796 @findex COMMAND_TRACEPOINTS
3797 @findex gdb.COMMAND_TRACEPOINTS
3798 @item gdb.COMMAND_TRACEPOINTS
3799 The command has to do with tracepoints. For example, @code{trace},
3800 @code{actions}, and @code{tfind} are in this category. Type
3801 @kbd{help tracepoints} at the @value{GDBN} prompt to see a list of
3802 commands in this category.
3804 @findex COMMAND_USER
3805 @findex gdb.COMMAND_USER
3806 @item gdb.COMMAND_USER
3807 The command is a general purpose command for the user, and typically
3808 does not fit in one of the other categories.
3809 Type @kbd{help user-defined} at the @value{GDBN} prompt to see
3810 a list of commands in this category, as well as the list of gdb macros
3811 (@pxref{Sequences}).
3813 @findex COMMAND_OBSCURE
3814 @findex gdb.COMMAND_OBSCURE
3815 @item gdb.COMMAND_OBSCURE
3816 The command is only used in unusual circumstances, or is not of
3817 general interest to users. For example, @code{checkpoint},
3818 @code{fork}, and @code{stop} are in this category. Type @kbd{help
3819 obscure} at the @value{GDBN} prompt to see a list of commands in this
3822 @findex COMMAND_MAINTENANCE
3823 @findex gdb.COMMAND_MAINTENANCE
3824 @item gdb.COMMAND_MAINTENANCE
3825 The command is only useful to @value{GDBN} maintainers. The
3826 @code{maintenance} and @code{flushregs} commands are in this category.
3827 Type @kbd{help internals} at the @value{GDBN} prompt to see a list of
3828 commands in this category.
3831 A new command can use a predefined completion function, either by
3832 specifying it via an argument at initialization, or by returning it
3833 from the @code{complete} method. These predefined completion
3834 constants are all defined in the @code{gdb} module:
3837 @vindex COMPLETE_NONE
3838 @item gdb.COMPLETE_NONE
3839 This constant means that no completion should be done.
3841 @vindex COMPLETE_FILENAME
3842 @item gdb.COMPLETE_FILENAME
3843 This constant means that filename completion should be performed.
3845 @vindex COMPLETE_LOCATION
3846 @item gdb.COMPLETE_LOCATION
3847 This constant means that location completion should be done.
3848 @xref{Specify Location}.
3850 @vindex COMPLETE_COMMAND
3851 @item gdb.COMPLETE_COMMAND
3852 This constant means that completion should examine @value{GDBN}
3855 @vindex COMPLETE_SYMBOL
3856 @item gdb.COMPLETE_SYMBOL
3857 This constant means that completion should be done using symbol names
3860 @vindex COMPLETE_EXPRESSION
3861 @item gdb.COMPLETE_EXPRESSION
3862 This constant means that completion should be done on expressions.
3863 Often this means completing on symbol names, but some language
3864 parsers also have support for completing on field names.
3867 The following code snippet shows how a trivial CLI command can be
3868 implemented in Python:
3871 class HelloWorld (gdb.Command):
3872 """Greet the whole world."""
3874 def __init__ (self):
3875 super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)
3877 def invoke (self, arg, from_tty):
3878 print "Hello, World!"
3883 The last line instantiates the class, and is necessary to trigger the
3884 registration of the command with @value{GDBN}. Depending on how the
3885 Python code is read into @value{GDBN}, you may need to import the
3886 @code{gdb} module explicitly.
3888 @node Parameters In Python
3889 @subsubsection Parameters In Python
3891 @cindex parameters in python
3892 @cindex python parameters
3893 @tindex gdb.Parameter
3895 You can implement new @value{GDBN} parameters using Python. A new
3896 parameter is implemented as an instance of the @code{gdb.Parameter}
3899 Parameters are exposed to the user via the @code{set} and
3900 @code{show} commands. @xref{Help}.
3902 There are many parameters that already exist and can be set in
3903 @value{GDBN}. Two examples are: @code{set follow fork} and
3904 @code{set charset}. Setting these parameters influences certain
3905 behavior in @value{GDBN}. Similarly, you can define parameters that
3906 can be used to influence behavior in custom Python scripts and commands.
3908 @defun Parameter.__init__ (name, @var{command-class}, @var{parameter-class} @r{[}, @var{enum-sequence}@r{]})
3909 The object initializer for @code{Parameter} registers the new
3910 parameter with @value{GDBN}. This initializer is normally invoked
3911 from the subclass' own @code{__init__} method.
3913 @var{name} is the name of the new parameter. If @var{name} consists
3914 of multiple words, then the initial words are looked for as prefix
3915 parameters. An example of this can be illustrated with the
3916 @code{set print} set of parameters. If @var{name} is
3917 @code{print foo}, then @code{print} will be searched as the prefix
3918 parameter. In this case the parameter can subsequently be accessed in
3919 @value{GDBN} as @code{set print foo}.
3921 If @var{name} consists of multiple words, and no prefix parameter group
3922 can be found, an exception is raised.
3924 @var{command-class} should be one of the @samp{COMMAND_} constants
3925 (@pxref{Commands In Python}). This argument tells @value{GDBN} how to
3926 categorize the new parameter in the help system.
3928 @var{parameter-class} should be one of the @samp{PARAM_} constants
3929 defined below. This argument tells @value{GDBN} the type of the new
3930 parameter; this information is used for input validation and
3933 If @var{parameter-class} is @code{PARAM_ENUM}, then
3934 @var{enum-sequence} must be a sequence of strings. These strings
3935 represent the possible values for the parameter.
3937 If @var{parameter-class} is not @code{PARAM_ENUM}, then the presence
3938 of a fourth argument will cause an exception to be thrown.
3940 The help text for the new parameter is taken from the Python
3941 documentation string for the parameter's class, if there is one. If
3942 there is no documentation string, a default value is used.
3945 @defvar Parameter.set_doc
3946 If this attribute exists, and is a string, then its value is used as
3947 the help text for this parameter's @code{set} command. The value is
3948 examined when @code{Parameter.__init__} is invoked; subsequent changes
3952 @defvar Parameter.show_doc
3953 If this attribute exists, and is a string, then its value is used as
3954 the help text for this parameter's @code{show} command. The value is
3955 examined when @code{Parameter.__init__} is invoked; subsequent changes
3959 @defvar Parameter.value
3960 The @code{value} attribute holds the underlying value of the
3961 parameter. It can be read and assigned to just as any other
3962 attribute. @value{GDBN} does validation when assignments are made.
3965 There are two methods that may be implemented in any @code{Parameter}
3968 @defun Parameter.get_set_string (self)
3969 If this method exists, @value{GDBN} will call it when a
3970 @var{parameter}'s value has been changed via the @code{set} API (for
3971 example, @kbd{set foo off}). The @code{value} attribute has already
3972 been populated with the new value and may be used in output. This
3973 method must return a string. If the returned string is not empty,
3974 @value{GDBN} will present it to the user.
3976 If this method raises the @code{gdb.GdbError} exception
3977 (@pxref{Exception Handling}), then @value{GDBN} will print the
3978 exception's string and the @code{set} command will fail. Note,
3979 however, that the @code{value} attribute will not be reset in this
3980 case. So, if your parameter must validate values, it should store the
3981 old value internally and reset the exposed value, like so:
3984 class ExampleParam (gdb.Parameter):
3985 def __init__ (self, name):
3986 super (ExampleParam, self).__init__ (name,
3990 self.saved_value = True
3993 def get_set_string (self):
3994 if not self.validate():
3995 self.value = self.saved_value
3996 raise gdb.GdbError('Failed to validate')
3997 self.saved_value = self.value
4001 @defun Parameter.get_show_string (self, svalue)
4002 @value{GDBN} will call this method when a @var{parameter}'s
4003 @code{show} API has been invoked (for example, @kbd{show foo}). The
4004 argument @code{svalue} receives the string representation of the
4005 current value. This method must return a string.
4008 When a new parameter is defined, its type must be specified. The
4009 available types are represented by constants defined in the @code{gdb}
4013 @findex PARAM_BOOLEAN
4014 @findex gdb.PARAM_BOOLEAN
4015 @item gdb.PARAM_BOOLEAN
4016 The value is a plain boolean. The Python boolean values, @code{True}
4017 and @code{False} are the only valid values.
4019 @findex PARAM_AUTO_BOOLEAN
4020 @findex gdb.PARAM_AUTO_BOOLEAN
4021 @item gdb.PARAM_AUTO_BOOLEAN
4022 The value has three possible states: true, false, and @samp{auto}. In
4023 Python, true and false are represented using boolean constants, and
4024 @samp{auto} is represented using @code{None}.
4026 @findex PARAM_UINTEGER
4027 @findex gdb.PARAM_UINTEGER
4028 @item gdb.PARAM_UINTEGER
4029 The value is an unsigned integer. The value of 0 should be
4030 interpreted to mean ``unlimited''.
4032 @findex PARAM_INTEGER
4033 @findex gdb.PARAM_INTEGER
4034 @item gdb.PARAM_INTEGER
4035 The value is a signed integer. The value of 0 should be interpreted
4036 to mean ``unlimited''.
4038 @findex PARAM_STRING
4039 @findex gdb.PARAM_STRING
4040 @item gdb.PARAM_STRING
4041 The value is a string. When the user modifies the string, any escape
4042 sequences, such as @samp{\t}, @samp{\f}, and octal escapes, are
4043 translated into corresponding characters and encoded into the current
4046 @findex PARAM_STRING_NOESCAPE
4047 @findex gdb.PARAM_STRING_NOESCAPE
4048 @item gdb.PARAM_STRING_NOESCAPE
4049 The value is a string. When the user modifies the string, escapes are
4050 passed through untranslated.
4052 @findex PARAM_OPTIONAL_FILENAME
4053 @findex gdb.PARAM_OPTIONAL_FILENAME
4054 @item gdb.PARAM_OPTIONAL_FILENAME
4055 The value is a either a filename (a string), or @code{None}.
4057 @findex PARAM_FILENAME
4058 @findex gdb.PARAM_FILENAME
4059 @item gdb.PARAM_FILENAME
4060 The value is a filename. This is just like
4061 @code{PARAM_STRING_NOESCAPE}, but uses file names for completion.
4063 @findex PARAM_ZINTEGER
4064 @findex gdb.PARAM_ZINTEGER
4065 @item gdb.PARAM_ZINTEGER
4066 The value is an integer. This is like @code{PARAM_INTEGER}, except 0
4067 is interpreted as itself.
4069 @findex PARAM_ZUINTEGER
4070 @findex gdb.PARAM_ZUINTEGER
4071 @item gdb.PARAM_ZUINTEGER
4072 The value is an unsigned integer. This is like @code{PARAM_INTEGER},
4073 except 0 is interpreted as itself, and the value cannot be negative.
4075 @findex PARAM_ZUINTEGER_UNLIMITED
4076 @findex gdb.PARAM_ZUINTEGER_UNLIMITED
4077 @item gdb.PARAM_ZUINTEGER_UNLIMITED
4078 The value is a signed integer. This is like @code{PARAM_ZUINTEGER},
4079 except the special value -1 should be interpreted to mean
4080 ``unlimited''. Other negative values are not allowed.
4083 @findex gdb.PARAM_ENUM
4084 @item gdb.PARAM_ENUM
4085 The value is a string, which must be one of a collection string
4086 constants provided when the parameter is created.
4089 @node Functions In Python
4090 @subsubsection Writing new convenience functions
4092 @cindex writing convenience functions
4093 @cindex convenience functions in python
4094 @cindex python convenience functions
4095 @tindex gdb.Function
4097 You can implement new convenience functions (@pxref{Convenience Vars})
4098 in Python. A convenience function is an instance of a subclass of the
4099 class @code{gdb.Function}.
4101 @defun Function.__init__ (name)
4102 The initializer for @code{Function} registers the new function with
4103 @value{GDBN}. The argument @var{name} is the name of the function,
4104 a string. The function will be visible to the user as a convenience
4105 variable of type @code{internal function}, whose name is the same as
4106 the given @var{name}.
4108 The documentation for the new function is taken from the documentation
4109 string for the new class.
4112 @defun Function.invoke (@var{*args})
4113 When a convenience function is evaluated, its arguments are converted
4114 to instances of @code{gdb.Value}, and then the function's
4115 @code{invoke} method is called. Note that @value{GDBN} does not
4116 predetermine the arity of convenience functions. Instead, all
4117 available arguments are passed to @code{invoke}, following the
4118 standard Python calling convention. In particular, a convenience
4119 function can have default values for parameters without ill effect.
4121 The return value of this method is used as its value in the enclosing
4122 expression. If an ordinary Python value is returned, it is converted
4123 to a @code{gdb.Value} following the usual rules.
4126 The following code snippet shows how a trivial convenience function can
4127 be implemented in Python:
4130 class Greet (gdb.Function):
4131 """Return string to greet someone.
4132 Takes a name as argument."""
4134 def __init__ (self):
4135 super (Greet, self).__init__ ("greet")
4137 def invoke (self, name):
4138 return "Hello, %s!" % name.string ()
4143 The last line instantiates the class, and is necessary to trigger the
4144 registration of the function with @value{GDBN}. Depending on how the
4145 Python code is read into @value{GDBN}, you may need to import the
4146 @code{gdb} module explicitly.
4148 Now you can use the function in an expression:
4151 (gdb) print $greet("Bob")
4155 @node Progspaces In Python
4156 @subsubsection Program Spaces In Python
4158 @cindex progspaces in python
4159 @tindex gdb.Progspace
4161 A program space, or @dfn{progspace}, represents a symbolic view
4162 of an address space.
4163 It consists of all of the objfiles of the program.
4164 @xref{Objfiles In Python}.
4165 @xref{Inferiors Connections and Programs, program spaces}, for more details
4166 about program spaces.
4168 The following progspace-related functions are available in the
4171 @findex gdb.current_progspace
4172 @defun gdb.current_progspace ()
4173 This function returns the program space of the currently selected inferior.
4174 @xref{Inferiors Connections and Programs}. This is identical to
4175 @code{gdb.selected_inferior().progspace} (@pxref{Inferiors In Python}) and is
4176 included for historical compatibility.
4179 @findex gdb.progspaces
4180 @defun gdb.progspaces ()
4181 Return a sequence of all the progspaces currently known to @value{GDBN}.
4184 Each progspace is represented by an instance of the @code{gdb.Progspace}
4187 @defvar Progspace.filename
4188 The file name of the progspace as a string.
4191 @defvar Progspace.pretty_printers
4192 The @code{pretty_printers} attribute is a list of functions. It is
4193 used to look up pretty-printers. A @code{Value} is passed to each
4194 function in order; if the function returns @code{None}, then the
4195 search continues. Otherwise, the return value should be an object
4196 which is used to format the value. @xref{Pretty Printing API}, for more
4200 @defvar Progspace.type_printers
4201 The @code{type_printers} attribute is a list of type printer objects.
4202 @xref{Type Printing API}, for more information.
4205 @defvar Progspace.frame_filters
4206 The @code{frame_filters} attribute is a dictionary of frame filter
4207 objects. @xref{Frame Filter API}, for more information.
4210 A program space has the following methods:
4212 @findex Progspace.block_for_pc
4213 @defun Progspace.block_for_pc (pc)
4214 Return the innermost @code{gdb.Block} containing the given @var{pc}
4215 value. If the block cannot be found for the @var{pc} value specified,
4216 the function will return @code{None}.
4219 @findex Progspace.find_pc_line
4220 @defun Progspace.find_pc_line (pc)
4221 Return the @code{gdb.Symtab_and_line} object corresponding to the
4222 @var{pc} value. @xref{Symbol Tables In Python}. If an invalid value
4223 of @var{pc} is passed as an argument, then the @code{symtab} and
4224 @code{line} attributes of the returned @code{gdb.Symtab_and_line}
4225 object will be @code{None} and 0 respectively.
4228 @findex Progspace.is_valid
4229 @defun Progspace.is_valid ()
4230 Returns @code{True} if the @code{gdb.Progspace} object is valid,
4231 @code{False} if not. A @code{gdb.Progspace} object can become invalid
4232 if the program space file it refers to is not referenced by any
4233 inferior. All other @code{gdb.Progspace} methods will throw an
4234 exception if it is invalid at the time the method is called.
4237 @findex Progspace.objfiles
4238 @defun Progspace.objfiles ()
4239 Return a sequence of all the objfiles referenced by this program
4240 space. @xref{Objfiles In Python}.
4243 @findex Progspace.solib_name
4244 @defun Progspace.solib_name (address)
4245 Return the name of the shared library holding the given @var{address}
4246 as a string, or @code{None}.
4249 One may add arbitrary attributes to @code{gdb.Progspace} objects
4250 in the usual Python way.
4251 This is useful if, for example, one needs to do some extra record keeping
4252 associated with the program space.
4254 In this contrived example, we want to perform some processing when
4255 an objfile with a certain symbol is loaded, but we only want to do
4256 this once because it is expensive. To achieve this we record the results
4257 with the program space because we can't predict when the desired objfile
4262 def clear_objfiles_handler(event):
4263 event.progspace.expensive_computation = None
4264 def expensive(symbol):
4265 """A mock routine to perform an "expensive" computation on symbol."""
4266 print "Computing the answer to the ultimate question ..."
4268 def new_objfile_handler(event):
4269 objfile = event.new_objfile
4270 progspace = objfile.progspace
4271 if not hasattr(progspace, 'expensive_computation') or \
4272 progspace.expensive_computation is None:
4273 # We use 'main' for the symbol to keep the example simple.
4274 # Note: There's no current way to constrain the lookup
4276 symbol = gdb.lookup_global_symbol('main')
4277 if symbol is not None:
4278 progspace.expensive_computation = expensive(symbol)
4279 gdb.events.clear_objfiles.connect(clear_objfiles_handler)
4280 gdb.events.new_objfile.connect(new_objfile_handler)
4282 (gdb) file /tmp/hello
4283 Reading symbols from /tmp/hello...done.
4284 Computing the answer to the ultimate question ...
4285 (gdb) python print gdb.current_progspace().expensive_computation
4288 Starting program: /tmp/hello
4290 [Inferior 1 (process 4242) exited normally]
4293 @node Objfiles In Python
4294 @subsubsection Objfiles In Python
4296 @cindex objfiles in python
4299 @value{GDBN} loads symbols for an inferior from various
4300 symbol-containing files (@pxref{Files}). These include the primary
4301 executable file, any shared libraries used by the inferior, and any
4302 separate debug info files (@pxref{Separate Debug Files}).
4303 @value{GDBN} calls these symbol-containing files @dfn{objfiles}.
4305 The following objfile-related functions are available in the
4308 @findex gdb.current_objfile
4309 @defun gdb.current_objfile ()
4310 When auto-loading a Python script (@pxref{Python Auto-loading}), @value{GDBN}
4311 sets the ``current objfile'' to the corresponding objfile. This
4312 function returns the current objfile. If there is no current objfile,
4313 this function returns @code{None}.
4316 @findex gdb.objfiles
4317 @defun gdb.objfiles ()
4318 Return a sequence of objfiles referenced by the current program space.
4319 @xref{Objfiles In Python}, and @ref{Progspaces In Python}. This is identical
4320 to @code{gdb.selected_inferior().progspace.objfiles()} and is included for
4321 historical compatibility.
4324 @findex gdb.lookup_objfile
4325 @defun gdb.lookup_objfile (name @r{[}, by_build_id{]})
4326 Look up @var{name}, a file name or build ID, in the list of objfiles
4327 for the current program space (@pxref{Progspaces In Python}).
4328 If the objfile is not found throw the Python @code{ValueError} exception.
4330 If @var{name} is a relative file name, then it will match any
4331 source file name with the same trailing components. For example, if
4332 @var{name} is @samp{gcc/expr.c}, then it will match source file
4333 name of @file{/build/trunk/gcc/expr.c}, but not
4334 @file{/build/trunk/libcpp/expr.c} or @file{/build/trunk/gcc/x-expr.c}.
4336 If @var{by_build_id} is provided and is @code{True} then @var{name}
4337 is the build ID of the objfile. Otherwise, @var{name} is a file name.
4338 This is supported only on some operating systems, notably those which use
4339 the ELF format for binary files and the @sc{gnu} Binutils. For more details
4340 about this feature, see the description of the @option{--build-id}
4341 command-line option in @ref{Options, , Command Line Options, ld,
4345 Each objfile is represented by an instance of the @code{gdb.Objfile}
4348 @defvar Objfile.filename
4349 The file name of the objfile as a string, with symbolic links resolved.
4351 The value is @code{None} if the objfile is no longer valid.
4352 See the @code{gdb.Objfile.is_valid} method, described below.
4355 @defvar Objfile.username
4356 The file name of the objfile as specified by the user as a string.
4358 The value is @code{None} if the objfile is no longer valid.
4359 See the @code{gdb.Objfile.is_valid} method, described below.
4362 @defvar Objfile.owner
4363 For separate debug info objfiles this is the corresponding @code{gdb.Objfile}
4364 object that debug info is being provided for.
4365 Otherwise this is @code{None}.
4366 Separate debug info objfiles are added with the
4367 @code{gdb.Objfile.add_separate_debug_file} method, described below.
4370 @defvar Objfile.build_id
4371 The build ID of the objfile as a string.
4372 If the objfile does not have a build ID then the value is @code{None}.
4374 This is supported only on some operating systems, notably those which use
4375 the ELF format for binary files and the @sc{gnu} Binutils. For more details
4376 about this feature, see the description of the @option{--build-id}
4377 command-line option in @ref{Options, , Command Line Options, ld,
4381 @defvar Objfile.progspace
4382 The containing program space of the objfile as a @code{gdb.Progspace}
4383 object. @xref{Progspaces In Python}.
4386 @defvar Objfile.pretty_printers
4387 The @code{pretty_printers} attribute is a list of functions. It is
4388 used to look up pretty-printers. A @code{Value} is passed to each
4389 function in order; if the function returns @code{None}, then the
4390 search continues. Otherwise, the return value should be an object
4391 which is used to format the value. @xref{Pretty Printing API}, for more
4395 @defvar Objfile.type_printers
4396 The @code{type_printers} attribute is a list of type printer objects.
4397 @xref{Type Printing API}, for more information.
4400 @defvar Objfile.frame_filters
4401 The @code{frame_filters} attribute is a dictionary of frame filter
4402 objects. @xref{Frame Filter API}, for more information.
4405 One may add arbitrary attributes to @code{gdb.Objfile} objects
4406 in the usual Python way.
4407 This is useful if, for example, one needs to do some extra record keeping
4408 associated with the objfile.
4410 In this contrived example we record the time when @value{GDBN}
4416 def new_objfile_handler(event):
4417 # Set the time_loaded attribute of the new objfile.
4418 event.new_objfile.time_loaded = datetime.datetime.today()
4419 gdb.events.new_objfile.connect(new_objfile_handler)
4422 Reading symbols from ./hello...done.
4423 (gdb) python print gdb.objfiles()[0].time_loaded
4424 2014-10-09 11:41:36.770345
4427 A @code{gdb.Objfile} object has the following methods:
4429 @defun Objfile.is_valid ()
4430 Returns @code{True} if the @code{gdb.Objfile} object is valid,
4431 @code{False} if not. A @code{gdb.Objfile} object can become invalid
4432 if the object file it refers to is not loaded in @value{GDBN} any
4433 longer. All other @code{gdb.Objfile} methods will throw an exception
4434 if it is invalid at the time the method is called.
4437 @defun Objfile.add_separate_debug_file (file)
4438 Add @var{file} to the list of files that @value{GDBN} will search for
4439 debug information for the objfile.
4440 This is useful when the debug info has been removed from the program
4441 and stored in a separate file. @value{GDBN} has built-in support for
4442 finding separate debug info files (@pxref{Separate Debug Files}), but if
4443 the file doesn't live in one of the standard places that @value{GDBN}
4444 searches then this function can be used to add a debug info file
4445 from a different place.
4448 @defun Objfile.lookup_global_symbol (name @r{[}, domain@r{]})
4449 Search for a global symbol named @var{name} in this objfile. Optionally, the
4450 search scope can be restricted with the @var{domain} argument.
4451 The @var{domain} argument must be a domain constant defined in the @code{gdb}
4452 module and described in @ref{Symbols In Python}. This function is similar to
4453 @code{gdb.lookup_global_symbol}, except that the search is limited to this
4456 The result is a @code{gdb.Symbol} object or @code{None} if the symbol
4460 @defun Objfile.lookup_static_symbol (name @r{[}, domain@r{]})
4461 Like @code{Objfile.lookup_global_symbol}, but searches for a global
4462 symbol with static linkage named @var{name} in this objfile.
4465 @node Frames In Python
4466 @subsubsection Accessing inferior stack frames from Python
4468 @cindex frames in python
4469 When the debugged program stops, @value{GDBN} is able to analyze its call
4470 stack (@pxref{Frames,,Stack frames}). The @code{gdb.Frame} class
4471 represents a frame in the stack. A @code{gdb.Frame} object is only valid
4472 while its corresponding frame exists in the inferior's stack. If you try
4473 to use an invalid frame object, @value{GDBN} will throw a @code{gdb.error}
4474 exception (@pxref{Exception Handling}).
4476 Two @code{gdb.Frame} objects can be compared for equality with the @code{==}
4480 (@value{GDBP}) python print gdb.newest_frame() == gdb.selected_frame ()
4484 The following frame-related functions are available in the @code{gdb} module:
4486 @findex gdb.selected_frame
4487 @defun gdb.selected_frame ()
4488 Return the selected frame object. (@pxref{Selection,,Selecting a Frame}).
4491 @findex gdb.newest_frame
4492 @defun gdb.newest_frame ()
4493 Return the newest frame object for the selected thread.
4496 @defun gdb.frame_stop_reason_string (reason)
4497 Return a string explaining the reason why @value{GDBN} stopped unwinding
4498 frames, as expressed by the given @var{reason} code (an integer, see the
4499 @code{unwind_stop_reason} method further down in this section).
4502 @findex gdb.invalidate_cached_frames
4503 @defun gdb.invalidate_cached_frames
4504 @value{GDBN} internally keeps a cache of the frames that have been
4505 unwound. This function invalidates this cache.
4507 This function should not generally be called by ordinary Python code.
4508 It is documented for the sake of completeness.
4511 A @code{gdb.Frame} object has the following methods:
4513 @defun Frame.is_valid ()
4514 Returns true if the @code{gdb.Frame} object is valid, false if not.
4515 A frame object can become invalid if the frame it refers to doesn't
4516 exist anymore in the inferior. All @code{gdb.Frame} methods will throw
4517 an exception if it is invalid at the time the method is called.
4520 @defun Frame.name ()
4521 Returns the function name of the frame, or @code{None} if it can't be
4525 @defun Frame.architecture ()
4526 Returns the @code{gdb.Architecture} object corresponding to the frame's
4527 architecture. @xref{Architectures In Python}.
4530 @defun Frame.type ()
4531 Returns the type of the frame. The value can be one of:
4533 @item gdb.NORMAL_FRAME
4534 An ordinary stack frame.
4536 @item gdb.DUMMY_FRAME
4537 A fake stack frame that was created by @value{GDBN} when performing an
4538 inferior function call.
4540 @item gdb.INLINE_FRAME
4541 A frame representing an inlined function. The function was inlined
4542 into a @code{gdb.NORMAL_FRAME} that is older than this one.
4544 @item gdb.TAILCALL_FRAME
4545 A frame representing a tail call. @xref{Tail Call Frames}.
4547 @item gdb.SIGTRAMP_FRAME
4548 A signal trampoline frame. This is the frame created by the OS when
4549 it calls into a signal handler.
4551 @item gdb.ARCH_FRAME
4552 A fake stack frame representing a cross-architecture call.
4554 @item gdb.SENTINEL_FRAME
4555 This is like @code{gdb.NORMAL_FRAME}, but it is only used for the
4560 @defun Frame.unwind_stop_reason ()
4561 Return an integer representing the reason why it's not possible to find
4562 more frames toward the outermost frame. Use
4563 @code{gdb.frame_stop_reason_string} to convert the value returned by this
4564 function to a string. The value can be one of:
4567 @item gdb.FRAME_UNWIND_NO_REASON
4568 No particular reason (older frames should be available).
4570 @item gdb.FRAME_UNWIND_NULL_ID
4571 The previous frame's analyzer returns an invalid result. This is no
4572 longer used by @value{GDBN}, and is kept only for backward
4575 @item gdb.FRAME_UNWIND_OUTERMOST
4576 This frame is the outermost.
4578 @item gdb.FRAME_UNWIND_UNAVAILABLE
4579 Cannot unwind further, because that would require knowing the
4580 values of registers or memory that have not been collected.
4582 @item gdb.FRAME_UNWIND_INNER_ID
4583 This frame ID looks like it ought to belong to a NEXT frame,
4584 but we got it for a PREV frame. Normally, this is a sign of
4585 unwinder failure. It could also indicate stack corruption.
4587 @item gdb.FRAME_UNWIND_SAME_ID
4588 This frame has the same ID as the previous one. That means
4589 that unwinding further would almost certainly give us another
4590 frame with exactly the same ID, so break the chain. Normally,
4591 this is a sign of unwinder failure. It could also indicate
4594 @item gdb.FRAME_UNWIND_NO_SAVED_PC
4595 The frame unwinder did not find any saved PC, but we needed
4596 one to unwind further.
4598 @item gdb.FRAME_UNWIND_MEMORY_ERROR
4599 The frame unwinder caused an error while trying to access memory.
4601 @item gdb.FRAME_UNWIND_FIRST_ERROR
4602 Any stop reason greater or equal to this value indicates some kind
4603 of error. This special value facilitates writing code that tests
4604 for errors in unwinding in a way that will work correctly even if
4605 the list of the other values is modified in future @value{GDBN}
4606 versions. Using it, you could write:
4608 reason = gdb.selected_frame().unwind_stop_reason ()
4609 reason_str = gdb.frame_stop_reason_string (reason)
4610 if reason >= gdb.FRAME_UNWIND_FIRST_ERROR:
4611 print "An error occured: %s" % reason_str
4618 Returns the frame's resume address.
4621 @defun Frame.block ()
4622 Return the frame's code block. @xref{Blocks In Python}. If the frame
4623 does not have a block -- for example, if there is no debugging
4624 information for the code in question -- then this will throw an
4628 @defun Frame.function ()
4629 Return the symbol for the function corresponding to this frame.
4630 @xref{Symbols In Python}.
4633 @defun Frame.older ()
4634 Return the frame that called this frame.
4637 @defun Frame.newer ()
4638 Return the frame called by this frame.
4641 @defun Frame.find_sal ()
4642 Return the frame's symtab and line object.
4643 @xref{Symbol Tables In Python}.
4646 @defun Frame.read_register (register)
4647 Return the value of @var{register} in this frame. The @var{register}
4648 argument must be a string (e.g., @code{'sp'} or @code{'rax'}).
4649 Returns a @code{Gdb.Value} object. Throws an exception if @var{register}
4653 @defun Frame.read_var (variable @r{[}, block@r{]})
4654 Return the value of @var{variable} in this frame. If the optional
4655 argument @var{block} is provided, search for the variable from that
4656 block; otherwise start at the frame's current block (which is
4657 determined by the frame's current program counter). The @var{variable}
4658 argument must be a string or a @code{gdb.Symbol} object; @var{block} must be a
4659 @code{gdb.Block} object.
4662 @defun Frame.select ()
4663 Set this frame to be the selected frame. @xref{Stack, ,Examining the
4667 @node Blocks In Python
4668 @subsubsection Accessing blocks from Python
4670 @cindex blocks in python
4673 In @value{GDBN}, symbols are stored in blocks. A block corresponds
4674 roughly to a scope in the source code. Blocks are organized
4675 hierarchically, and are represented individually in Python as a
4676 @code{gdb.Block}. Blocks rely on debugging information being
4679 A frame has a block. Please see @ref{Frames In Python}, for a more
4680 in-depth discussion of frames.
4682 The outermost block is known as the @dfn{global block}. The global
4683 block typically holds public global variables and functions.
4685 The block nested just inside the global block is the @dfn{static
4686 block}. The static block typically holds file-scoped variables and
4689 @value{GDBN} provides a method to get a block's superblock, but there
4690 is currently no way to examine the sub-blocks of a block, or to
4691 iterate over all the blocks in a symbol table (@pxref{Symbol Tables In
4694 Here is a short example that should help explain blocks:
4697 /* This is in the global block. */
4700 /* This is in the static block. */
4701 static int file_scope;
4703 /* 'function' is in the global block, and 'argument' is
4704 in a block nested inside of 'function'. */
4705 int function (int argument)
4707 /* 'local' is in a block inside 'function'. It may or may
4708 not be in the same block as 'argument'. */
4712 /* 'inner' is in a block whose superblock is the one holding
4716 /* If this call is expanded by the compiler, you may see
4717 a nested block here whose function is 'inline_function'
4718 and whose superblock is the one holding 'inner'. */
4724 A @code{gdb.Block} is iterable. The iterator returns the symbols
4725 (@pxref{Symbols In Python}) local to the block. Python programs
4726 should not assume that a specific block object will always contain a
4727 given symbol, since changes in @value{GDBN} features and
4728 infrastructure may cause symbols move across blocks in a symbol
4729 table. You can also use Python's @dfn{dictionary syntax} to access
4730 variables in this block, e.g.:
4733 symbol = some_block['variable'] # symbol is of type gdb.Symbol
4736 The following block-related functions are available in the @code{gdb}
4739 @findex gdb.block_for_pc
4740 @defun gdb.block_for_pc (pc)
4741 Return the innermost @code{gdb.Block} containing the given @var{pc}
4742 value. If the block cannot be found for the @var{pc} value specified,
4743 the function will return @code{None}. This is identical to
4744 @code{gdb.current_progspace().block_for_pc(pc)} and is included for
4745 historical compatibility.
4748 A @code{gdb.Block} object has the following methods:
4750 @defun Block.is_valid ()
4751 Returns @code{True} if the @code{gdb.Block} object is valid,
4752 @code{False} if not. A block object can become invalid if the block it
4753 refers to doesn't exist anymore in the inferior. All other
4754 @code{gdb.Block} methods will throw an exception if it is invalid at
4755 the time the method is called. The block's validity is also checked
4756 during iteration over symbols of the block.
4759 A @code{gdb.Block} object has the following attributes:
4762 The start address of the block. This attribute is not writable.
4766 One past the last address that appears in the block. This attribute
4770 @defvar Block.function
4771 The name of the block represented as a @code{gdb.Symbol}. If the
4772 block is not named, then this attribute holds @code{None}. This
4773 attribute is not writable.
4775 For ordinary function blocks, the superblock is the static block.
4776 However, you should note that it is possible for a function block to
4777 have a superblock that is not the static block -- for instance this
4778 happens for an inlined function.
4781 @defvar Block.superblock
4782 The block containing this block. If this parent block does not exist,
4783 this attribute holds @code{None}. This attribute is not writable.
4786 @defvar Block.global_block
4787 The global block associated with this block. This attribute is not
4791 @defvar Block.static_block
4792 The static block associated with this block. This attribute is not
4796 @defvar Block.is_global
4797 @code{True} if the @code{gdb.Block} object is a global block,
4798 @code{False} if not. This attribute is not
4802 @defvar Block.is_static
4803 @code{True} if the @code{gdb.Block} object is a static block,
4804 @code{False} if not. This attribute is not writable.
4807 @node Symbols In Python
4808 @subsubsection Python representation of Symbols
4810 @cindex symbols in python
4813 @value{GDBN} represents every variable, function and type as an
4814 entry in a symbol table. @xref{Symbols, ,Examining the Symbol Table}.
4815 Similarly, Python represents these symbols in @value{GDBN} with the
4816 @code{gdb.Symbol} object.
4818 The following symbol-related functions are available in the @code{gdb}
4821 @findex gdb.lookup_symbol
4822 @defun gdb.lookup_symbol (name @r{[}, block @r{[}, domain@r{]]})
4823 This function searches for a symbol by name. The search scope can be
4824 restricted to the parameters defined in the optional domain and block
4827 @var{name} is the name of the symbol. It must be a string. The
4828 optional @var{block} argument restricts the search to symbols visible
4829 in that @var{block}. The @var{block} argument must be a
4830 @code{gdb.Block} object. If omitted, the block for the current frame
4831 is used. The optional @var{domain} argument restricts
4832 the search to the domain type. The @var{domain} argument must be a
4833 domain constant defined in the @code{gdb} module and described later
4836 The result is a tuple of two elements.
4837 The first element is a @code{gdb.Symbol} object or @code{None} if the symbol
4839 If the symbol is found, the second element is @code{True} if the symbol
4840 is a field of a method's object (e.g., @code{this} in C@t{++}),
4841 otherwise it is @code{False}.
4842 If the symbol is not found, the second element is @code{False}.
4845 @findex gdb.lookup_global_symbol
4846 @defun gdb.lookup_global_symbol (name @r{[}, domain@r{]})
4847 This function searches for a global symbol by name.
4848 The search scope can be restricted to by the domain argument.
4850 @var{name} is the name of the symbol. It must be a string.
4851 The optional @var{domain} argument restricts the search to the domain type.
4852 The @var{domain} argument must be a domain constant defined in the @code{gdb}
4853 module and described later in this chapter.
4855 The result is a @code{gdb.Symbol} object or @code{None} if the symbol
4859 @findex gdb.lookup_static_symbol
4860 @defun gdb.lookup_static_symbol (name @r{[}, domain@r{]})
4861 This function searches for a global symbol with static linkage by name.
4862 The search scope can be restricted to by the domain argument.
4864 @var{name} is the name of the symbol. It must be a string.
4865 The optional @var{domain} argument restricts the search to the domain type.
4866 The @var{domain} argument must be a domain constant defined in the @code{gdb}
4867 module and described later in this chapter.
4869 The result is a @code{gdb.Symbol} object or @code{None} if the symbol
4872 Note that this function will not find function-scoped static variables. To look
4873 up such variables, iterate over the variables of the function's
4874 @code{gdb.Block} and check that @code{block.addr_class} is
4875 @code{gdb.SYMBOL_LOC_STATIC}.
4877 There can be multiple global symbols with static linkage with the same
4878 name. This function will only return the first matching symbol that
4879 it finds. Which symbol is found depends on where @value{GDBN} is
4880 currently stopped, as @value{GDBN} will first search for matching
4881 symbols in the current object file, and then search all other object
4882 files. If the application is not yet running then @value{GDBN} will
4883 search all object files in the order they appear in the debug
4887 @findex gdb.lookup_static_symbols
4888 @defun gdb.lookup_static_symbols (name @r{[}, domain@r{]})
4889 Similar to @code{gdb.lookup_static_symbol}, this function searches for
4890 global symbols with static linkage by name, and optionally restricted
4891 by the domain argument. However, this function returns a list of all
4892 matching symbols found, not just the first one.
4894 @var{name} is the name of the symbol. It must be a string.
4895 The optional @var{domain} argument restricts the search to the domain type.
4896 The @var{domain} argument must be a domain constant defined in the @code{gdb}
4897 module and described later in this chapter.
4899 The result is a list of @code{gdb.Symbol} objects which could be empty
4900 if no matching symbols were found.
4902 Note that this function will not find function-scoped static variables. To look
4903 up such variables, iterate over the variables of the function's
4904 @code{gdb.Block} and check that @code{block.addr_class} is
4905 @code{gdb.SYMBOL_LOC_STATIC}.
4908 A @code{gdb.Symbol} object has the following attributes:
4911 The type of the symbol or @code{None} if no type is recorded.
4912 This attribute is represented as a @code{gdb.Type} object.
4913 @xref{Types In Python}. This attribute is not writable.
4916 @defvar Symbol.symtab
4917 The symbol table in which the symbol appears. This attribute is
4918 represented as a @code{gdb.Symtab} object. @xref{Symbol Tables In
4919 Python}. This attribute is not writable.
4923 The line number in the source code at which the symbol was defined.
4928 The name of the symbol as a string. This attribute is not writable.
4931 @defvar Symbol.linkage_name
4932 The name of the symbol, as used by the linker (i.e., may be mangled).
4933 This attribute is not writable.
4936 @defvar Symbol.print_name
4937 The name of the symbol in a form suitable for output. This is either
4938 @code{name} or @code{linkage_name}, depending on whether the user
4939 asked @value{GDBN} to display demangled or mangled names.
4942 @defvar Symbol.addr_class
4943 The address class of the symbol. This classifies how to find the value
4944 of a symbol. Each address class is a constant defined in the
4945 @code{gdb} module and described later in this chapter.
4948 @defvar Symbol.needs_frame
4949 This is @code{True} if evaluating this symbol's value requires a frame
4950 (@pxref{Frames In Python}) and @code{False} otherwise. Typically,
4951 local variables will require a frame, but other symbols will not.
4954 @defvar Symbol.is_argument
4955 @code{True} if the symbol is an argument of a function.
4958 @defvar Symbol.is_constant
4959 @code{True} if the symbol is a constant.
4962 @defvar Symbol.is_function
4963 @code{True} if the symbol is a function or a method.
4966 @defvar Symbol.is_variable
4967 @code{True} if the symbol is a variable.
4970 A @code{gdb.Symbol} object has the following methods:
4972 @defun Symbol.is_valid ()
4973 Returns @code{True} if the @code{gdb.Symbol} object is valid,
4974 @code{False} if not. A @code{gdb.Symbol} object can become invalid if
4975 the symbol it refers to does not exist in @value{GDBN} any longer.
4976 All other @code{gdb.Symbol} methods will throw an exception if it is
4977 invalid at the time the method is called.
4980 @defun Symbol.value (@r{[}frame@r{]})
4981 Compute the value of the symbol, as a @code{gdb.Value}. For
4982 functions, this computes the address of the function, cast to the
4983 appropriate type. If the symbol requires a frame in order to compute
4984 its value, then @var{frame} must be given. If @var{frame} is not
4985 given, or if @var{frame} is invalid, then this method will throw an
4989 The available domain categories in @code{gdb.Symbol} are represented
4990 as constants in the @code{gdb} module:
4993 @vindex SYMBOL_UNDEF_DOMAIN
4994 @item gdb.SYMBOL_UNDEF_DOMAIN
4995 This is used when a domain has not been discovered or none of the
4996 following domains apply. This usually indicates an error either
4997 in the symbol information or in @value{GDBN}'s handling of symbols.
4999 @vindex SYMBOL_VAR_DOMAIN
5000 @item gdb.SYMBOL_VAR_DOMAIN
5001 This domain contains variables, function names, typedef names and enum
5004 @vindex SYMBOL_STRUCT_DOMAIN
5005 @item gdb.SYMBOL_STRUCT_DOMAIN
5006 This domain holds struct, union and enum type names.
5008 @vindex SYMBOL_LABEL_DOMAIN
5009 @item gdb.SYMBOL_LABEL_DOMAIN
5010 This domain contains names of labels (for gotos).
5012 @vindex SYMBOL_MODULE_DOMAIN
5013 @item gdb.SYMBOL_MODULE_DOMAIN
5014 This domain contains names of Fortran module types.
5016 @vindex SYMBOL_COMMON_BLOCK_DOMAIN
5017 @item gdb.SYMBOL_COMMON_BLOCK_DOMAIN
5018 This domain contains names of Fortran common blocks.
5021 The available address class categories in @code{gdb.Symbol} are represented
5022 as constants in the @code{gdb} module:
5025 @vindex SYMBOL_LOC_UNDEF
5026 @item gdb.SYMBOL_LOC_UNDEF
5027 If this is returned by address class, it indicates an error either in
5028 the symbol information or in @value{GDBN}'s handling of symbols.
5030 @vindex SYMBOL_LOC_CONST
5031 @item gdb.SYMBOL_LOC_CONST
5032 Value is constant int.
5034 @vindex SYMBOL_LOC_STATIC
5035 @item gdb.SYMBOL_LOC_STATIC
5036 Value is at a fixed address.
5038 @vindex SYMBOL_LOC_REGISTER
5039 @item gdb.SYMBOL_LOC_REGISTER
5040 Value is in a register.
5042 @vindex SYMBOL_LOC_ARG
5043 @item gdb.SYMBOL_LOC_ARG
5044 Value is an argument. This value is at the offset stored within the
5045 symbol inside the frame's argument list.
5047 @vindex SYMBOL_LOC_REF_ARG
5048 @item gdb.SYMBOL_LOC_REF_ARG
5049 Value address is stored in the frame's argument list. Just like
5050 @code{LOC_ARG} except that the value's address is stored at the
5051 offset, not the value itself.
5053 @vindex SYMBOL_LOC_REGPARM_ADDR
5054 @item gdb.SYMBOL_LOC_REGPARM_ADDR
5055 Value is a specified register. Just like @code{LOC_REGISTER} except
5056 the register holds the address of the argument instead of the argument
5059 @vindex SYMBOL_LOC_LOCAL
5060 @item gdb.SYMBOL_LOC_LOCAL
5061 Value is a local variable.
5063 @vindex SYMBOL_LOC_TYPEDEF
5064 @item gdb.SYMBOL_LOC_TYPEDEF
5065 Value not used. Symbols in the domain @code{SYMBOL_STRUCT_DOMAIN} all
5068 @vindex SYMBOL_LOC_BLOCK
5069 @item gdb.SYMBOL_LOC_BLOCK
5072 @vindex SYMBOL_LOC_CONST_BYTES
5073 @item gdb.SYMBOL_LOC_CONST_BYTES
5074 Value is a byte-sequence.
5076 @vindex SYMBOL_LOC_UNRESOLVED
5077 @item gdb.SYMBOL_LOC_UNRESOLVED
5078 Value is at a fixed address, but the address of the variable has to be
5079 determined from the minimal symbol table whenever the variable is
5082 @vindex SYMBOL_LOC_OPTIMIZED_OUT
5083 @item gdb.SYMBOL_LOC_OPTIMIZED_OUT
5084 The value does not actually exist in the program.
5086 @vindex SYMBOL_LOC_COMPUTED
5087 @item gdb.SYMBOL_LOC_COMPUTED
5088 The value's address is a computed location.
5090 @vindex SYMBOL_LOC_COMPUTED
5091 @item gdb.SYMBOL_LOC_COMPUTED
5092 The value's address is a symbol. This is only used for Fortran common
5096 @node Symbol Tables In Python
5097 @subsubsection Symbol table representation in Python
5099 @cindex symbol tables in python
5101 @tindex gdb.Symtab_and_line
5103 Access to symbol table data maintained by @value{GDBN} on the inferior
5104 is exposed to Python via two objects: @code{gdb.Symtab_and_line} and
5105 @code{gdb.Symtab}. Symbol table and line data for a frame is returned
5106 from the @code{find_sal} method in @code{gdb.Frame} object.
5107 @xref{Frames In Python}.
5109 For more information on @value{GDBN}'s symbol table management, see
5110 @ref{Symbols, ,Examining the Symbol Table}, for more information.
5112 A @code{gdb.Symtab_and_line} object has the following attributes:
5114 @defvar Symtab_and_line.symtab
5115 The symbol table object (@code{gdb.Symtab}) for this frame.
5116 This attribute is not writable.
5119 @defvar Symtab_and_line.pc
5120 Indicates the start of the address range occupied by code for the
5121 current source line. This attribute is not writable.
5124 @defvar Symtab_and_line.last
5125 Indicates the end of the address range occupied by code for the current
5126 source line. This attribute is not writable.
5129 @defvar Symtab_and_line.line
5130 Indicates the current line number for this object. This
5131 attribute is not writable.
5134 A @code{gdb.Symtab_and_line} object has the following methods:
5136 @defun Symtab_and_line.is_valid ()
5137 Returns @code{True} if the @code{gdb.Symtab_and_line} object is valid,
5138 @code{False} if not. A @code{gdb.Symtab_and_line} object can become
5139 invalid if the Symbol table and line object it refers to does not
5140 exist in @value{GDBN} any longer. All other
5141 @code{gdb.Symtab_and_line} methods will throw an exception if it is
5142 invalid at the time the method is called.
5145 A @code{gdb.Symtab} object has the following attributes:
5147 @defvar Symtab.filename
5148 The symbol table's source filename. This attribute is not writable.
5151 @defvar Symtab.objfile
5152 The symbol table's backing object file. @xref{Objfiles In Python}.
5153 This attribute is not writable.
5156 @defvar Symtab.producer
5157 The name and possibly version number of the program that
5158 compiled the code in the symbol table.
5159 The contents of this string is up to the compiler.
5160 If no producer information is available then @code{None} is returned.
5161 This attribute is not writable.
5164 A @code{gdb.Symtab} object has the following methods:
5166 @defun Symtab.is_valid ()
5167 Returns @code{True} if the @code{gdb.Symtab} object is valid,
5168 @code{False} if not. A @code{gdb.Symtab} object can become invalid if
5169 the symbol table it refers to does not exist in @value{GDBN} any
5170 longer. All other @code{gdb.Symtab} methods will throw an exception
5171 if it is invalid at the time the method is called.
5174 @defun Symtab.fullname ()
5175 Return the symbol table's source absolute file name.
5178 @defun Symtab.global_block ()
5179 Return the global block of the underlying symbol table.
5180 @xref{Blocks In Python}.
5183 @defun Symtab.static_block ()
5184 Return the static block of the underlying symbol table.
5185 @xref{Blocks In Python}.
5188 @defun Symtab.linetable ()
5189 Return the line table associated with the symbol table.
5190 @xref{Line Tables In Python}.
5193 @node Line Tables In Python
5194 @subsubsection Manipulating line tables using Python
5196 @cindex line tables in python
5197 @tindex gdb.LineTable
5199 Python code can request and inspect line table information from a
5200 symbol table that is loaded in @value{GDBN}. A line table is a
5201 mapping of source lines to their executable locations in memory. To
5202 acquire the line table information for a particular symbol table, use
5203 the @code{linetable} function (@pxref{Symbol Tables In Python}).
5205 A @code{gdb.LineTable} is iterable. The iterator returns
5206 @code{LineTableEntry} objects that correspond to the source line and
5207 address for each line table entry. @code{LineTableEntry} objects have
5208 the following attributes:
5210 @defvar LineTableEntry.line
5211 The source line number for this line table entry. This number
5212 corresponds to the actual line of source. This attribute is not
5216 @defvar LineTableEntry.pc
5217 The address that is associated with the line table entry where the
5218 executable code for that source line resides in memory. This
5219 attribute is not writable.
5222 As there can be multiple addresses for a single source line, you may
5223 receive multiple @code{LineTableEntry} objects with matching
5224 @code{line} attributes, but with different @code{pc} attributes. The
5225 iterator is sorted in ascending @code{pc} order. Here is a small
5226 example illustrating iterating over a line table.
5229 symtab = gdb.selected_frame().find_sal().symtab
5230 linetable = symtab.linetable()
5231 for line in linetable:
5232 print "Line: "+str(line.line)+" Address: "+hex(line.pc)
5235 This will have the following output:
5238 Line: 33 Address: 0x4005c8L
5239 Line: 37 Address: 0x4005caL
5240 Line: 39 Address: 0x4005d2L
5241 Line: 40 Address: 0x4005f8L
5242 Line: 42 Address: 0x4005ffL
5243 Line: 44 Address: 0x400608L
5244 Line: 42 Address: 0x40060cL
5245 Line: 45 Address: 0x400615L
5248 In addition to being able to iterate over a @code{LineTable}, it also
5249 has the following direct access methods:
5251 @defun LineTable.line (line)
5252 Return a Python @code{Tuple} of @code{LineTableEntry} objects for any
5253 entries in the line table for the given @var{line}, which specifies
5254 the source code line. If there are no entries for that source code
5255 @var{line}, the Python @code{None} is returned.
5258 @defun LineTable.has_line (line)
5259 Return a Python @code{Boolean} indicating whether there is an entry in
5260 the line table for this source line. Return @code{True} if an entry
5261 is found, or @code{False} if not.
5264 @defun LineTable.source_lines ()
5265 Return a Python @code{List} of the source line numbers in the symbol
5266 table. Only lines with executable code locations are returned. The
5267 contents of the @code{List} will just be the source line entries
5268 represented as Python @code{Long} values.
5271 @node Breakpoints In Python
5272 @subsubsection Manipulating breakpoints using Python
5274 @cindex breakpoints in python
5275 @tindex gdb.Breakpoint
5277 Python code can manipulate breakpoints via the @code{gdb.Breakpoint}
5280 A breakpoint can be created using one of the two forms of the
5281 @code{gdb.Breakpoint} constructor. The first one accepts a string
5282 like one would pass to the @code{break}
5283 (@pxref{Set Breaks,,Setting Breakpoints}) and @code{watch}
5284 (@pxref{Set Watchpoints, , Setting Watchpoints}) commands, and can be used to
5285 create both breakpoints and watchpoints. The second accepts separate Python
5286 arguments similar to @ref{Explicit Locations}, and can only be used to create
5289 @defun Breakpoint.__init__ (spec @r{[}, type @r{][}, wp_class @r{][}, internal @r{][}, temporary @r{][}, qualified @r{]})
5290 Create a new breakpoint according to @var{spec}, which is a string naming the
5291 location of a breakpoint, or an expression that defines a watchpoint. The
5292 string should describe a location in a format recognized by the @code{break}
5293 command (@pxref{Set Breaks,,Setting Breakpoints}) or, in the case of a
5294 watchpoint, by the @code{watch} command
5295 (@pxref{Set Watchpoints, , Setting Watchpoints}).
5297 The optional @var{type} argument specifies the type of the breakpoint to create,
5300 The optional @var{wp_class} argument defines the class of watchpoint to create,
5301 if @var{type} is @code{gdb.BP_WATCHPOINT}. If @var{wp_class} is omitted, it
5302 defaults to @code{gdb.WP_WRITE}.
5304 The optional @var{internal} argument allows the breakpoint to become invisible
5305 to the user. The breakpoint will neither be reported when created, nor will it
5306 be listed in the output from @code{info breakpoints} (but will be listed with
5307 the @code{maint info breakpoints} command).
5309 The optional @var{temporary} argument makes the breakpoint a temporary
5310 breakpoint. Temporary breakpoints are deleted after they have been hit. Any
5311 further access to the Python breakpoint after it has been hit will result in a
5312 runtime error (as that breakpoint has now been automatically deleted).
5314 The optional @var{qualified} argument is a boolean that allows interpreting
5315 the function passed in @code{spec} as a fully-qualified name. It is equivalent
5316 to @code{break}'s @code{-qualified} flag (@pxref{Linespec Locations} and
5317 @ref{Explicit Locations}).
5321 @defun Breakpoint.__init__ (@r{[} source @r{][}, function @r{][}, label @r{][}, line @r{]}, @r{][} internal @r{][}, temporary @r{][}, qualified @r{]})
5322 This second form of creating a new breakpoint specifies the explicit
5323 location (@pxref{Explicit Locations}) using keywords. The new breakpoint will
5324 be created in the specified source file @var{source}, at the specified
5325 @var{function}, @var{label} and @var{line}.
5327 @var{internal}, @var{temporary} and @var{qualified} have the same usage as
5328 explained previously.
5331 The available types are represented by constants defined in the @code{gdb}
5335 @vindex BP_BREAKPOINT
5336 @item gdb.BP_BREAKPOINT
5337 Normal code breakpoint.
5339 @vindex BP_WATCHPOINT
5340 @item gdb.BP_WATCHPOINT
5341 Watchpoint breakpoint.
5343 @vindex BP_HARDWARE_WATCHPOINT
5344 @item gdb.BP_HARDWARE_WATCHPOINT
5345 Hardware assisted watchpoint.
5347 @vindex BP_READ_WATCHPOINT
5348 @item gdb.BP_READ_WATCHPOINT
5349 Hardware assisted read watchpoint.
5351 @vindex BP_ACCESS_WATCHPOINT
5352 @item gdb.BP_ACCESS_WATCHPOINT
5353 Hardware assisted access watchpoint.
5356 The available watchpoint types represented by constants are defined in the
5362 Read only watchpoint.
5366 Write only watchpoint.
5370 Read/Write watchpoint.
5373 @defun Breakpoint.stop (self)
5374 The @code{gdb.Breakpoint} class can be sub-classed and, in
5375 particular, you may choose to implement the @code{stop} method.
5376 If this method is defined in a sub-class of @code{gdb.Breakpoint},
5377 it will be called when the inferior reaches any location of a
5378 breakpoint which instantiates that sub-class. If the method returns
5379 @code{True}, the inferior will be stopped at the location of the
5380 breakpoint, otherwise the inferior will continue.
5382 If there are multiple breakpoints at the same location with a
5383 @code{stop} method, each one will be called regardless of the
5384 return status of the previous. This ensures that all @code{stop}
5385 methods have a chance to execute at that location. In this scenario
5386 if one of the methods returns @code{True} but the others return
5387 @code{False}, the inferior will still be stopped.
5389 You should not alter the execution state of the inferior (i.e.@:, step,
5390 next, etc.), alter the current frame context (i.e.@:, change the current
5391 active frame), or alter, add or delete any breakpoint. As a general
5392 rule, you should not alter any data within @value{GDBN} or the inferior
5395 Example @code{stop} implementation:
5398 class MyBreakpoint (gdb.Breakpoint):
5400 inf_val = gdb.parse_and_eval("foo")
5407 @defun Breakpoint.is_valid ()
5408 Return @code{True} if this @code{Breakpoint} object is valid,
5409 @code{False} otherwise. A @code{Breakpoint} object can become invalid
5410 if the user deletes the breakpoint. In this case, the object still
5411 exists, but the underlying breakpoint does not. In the cases of
5412 watchpoint scope, the watchpoint remains valid even if execution of the
5413 inferior leaves the scope of that watchpoint.
5416 @defun Breakpoint.delete ()
5417 Permanently deletes the @value{GDBN} breakpoint. This also
5418 invalidates the Python @code{Breakpoint} object. Any further access
5419 to this object's attributes or methods will raise an error.
5422 @defvar Breakpoint.enabled
5423 This attribute is @code{True} if the breakpoint is enabled, and
5424 @code{False} otherwise. This attribute is writable. You can use it to enable
5425 or disable the breakpoint.
5428 @defvar Breakpoint.silent
5429 This attribute is @code{True} if the breakpoint is silent, and
5430 @code{False} otherwise. This attribute is writable.
5432 Note that a breakpoint can also be silent if it has commands and the
5433 first command is @code{silent}. This is not reported by the
5434 @code{silent} attribute.
5437 @defvar Breakpoint.pending
5438 This attribute is @code{True} if the breakpoint is pending, and
5439 @code{False} otherwise. @xref{Set Breaks}. This attribute is
5443 @anchor{python_breakpoint_thread}
5444 @defvar Breakpoint.thread
5445 If the breakpoint is thread-specific, this attribute holds the
5446 thread's global id. If the breakpoint is not thread-specific, this
5447 attribute is @code{None}. This attribute is writable.
5450 @defvar Breakpoint.task
5451 If the breakpoint is Ada task-specific, this attribute holds the Ada task
5452 id. If the breakpoint is not task-specific (or the underlying
5453 language is not Ada), this attribute is @code{None}. This attribute
5457 @defvar Breakpoint.ignore_count
5458 This attribute holds the ignore count for the breakpoint, an integer.
5459 This attribute is writable.
5462 @defvar Breakpoint.number
5463 This attribute holds the breakpoint's number --- the identifier used by
5464 the user to manipulate the breakpoint. This attribute is not writable.
5467 @defvar Breakpoint.type
5468 This attribute holds the breakpoint's type --- the identifier used to
5469 determine the actual breakpoint type or use-case. This attribute is not
5473 @defvar Breakpoint.visible
5474 This attribute tells whether the breakpoint is visible to the user
5475 when set, or when the @samp{info breakpoints} command is run. This
5476 attribute is not writable.
5479 @defvar Breakpoint.temporary
5480 This attribute indicates whether the breakpoint was created as a
5481 temporary breakpoint. Temporary breakpoints are automatically deleted
5482 after that breakpoint has been hit. Access to this attribute, and all
5483 other attributes and functions other than the @code{is_valid}
5484 function, will result in an error after the breakpoint has been hit
5485 (as it has been automatically deleted). This attribute is not
5489 @defvar Breakpoint.hit_count
5490 This attribute holds the hit count for the breakpoint, an integer.
5491 This attribute is writable, but currently it can only be set to zero.
5494 @defvar Breakpoint.location
5495 This attribute holds the location of the breakpoint, as specified by
5496 the user. It is a string. If the breakpoint does not have a location
5497 (that is, it is a watchpoint) the attribute's value is @code{None}. This
5498 attribute is not writable.
5501 @defvar Breakpoint.expression
5502 This attribute holds a breakpoint expression, as specified by
5503 the user. It is a string. If the breakpoint does not have an
5504 expression (the breakpoint is not a watchpoint) the attribute's value
5505 is @code{None}. This attribute is not writable.
5508 @defvar Breakpoint.condition
5509 This attribute holds the condition of the breakpoint, as specified by
5510 the user. It is a string. If there is no condition, this attribute's
5511 value is @code{None}. This attribute is writable.
5514 @defvar Breakpoint.commands
5515 This attribute holds the commands attached to the breakpoint. If
5516 there are commands, this attribute's value is a string holding all the
5517 commands, separated by newlines. If there are no commands, this
5518 attribute is @code{None}. This attribute is writable.
5521 @node Finish Breakpoints in Python
5522 @subsubsection Finish Breakpoints
5524 @cindex python finish breakpoints
5525 @tindex gdb.FinishBreakpoint
5527 A finish breakpoint is a temporary breakpoint set at the return address of
5528 a frame, based on the @code{finish} command. @code{gdb.FinishBreakpoint}
5529 extends @code{gdb.Breakpoint}. The underlying breakpoint will be disabled
5530 and deleted when the execution will run out of the breakpoint scope (i.e.@:
5531 @code{Breakpoint.stop} or @code{FinishBreakpoint.out_of_scope} triggered).
5532 Finish breakpoints are thread specific and must be create with the right
5535 @defun FinishBreakpoint.__init__ (@r{[}frame@r{]} @r{[}, internal@r{]})
5536 Create a finish breakpoint at the return address of the @code{gdb.Frame}
5537 object @var{frame}. If @var{frame} is not provided, this defaults to the
5538 newest frame. The optional @var{internal} argument allows the breakpoint to
5539 become invisible to the user. @xref{Breakpoints In Python}, for further
5540 details about this argument.
5543 @defun FinishBreakpoint.out_of_scope (self)
5544 In some circumstances (e.g.@: @code{longjmp}, C@t{++} exceptions, @value{GDBN}
5545 @code{return} command, @dots{}), a function may not properly terminate, and
5546 thus never hit the finish breakpoint. When @value{GDBN} notices such a
5547 situation, the @code{out_of_scope} callback will be triggered.
5549 You may want to sub-class @code{gdb.FinishBreakpoint} and override this
5553 class MyFinishBreakpoint (gdb.FinishBreakpoint)
5555 print "normal finish"
5558 def out_of_scope ():
5559 print "abnormal finish"
5563 @defvar FinishBreakpoint.return_value
5564 When @value{GDBN} is stopped at a finish breakpoint and the frame
5565 used to build the @code{gdb.FinishBreakpoint} object had debug symbols, this
5566 attribute will contain a @code{gdb.Value} object corresponding to the return
5567 value of the function. The value will be @code{None} if the function return
5568 type is @code{void} or if the return value was not computable. This attribute
5572 @node Lazy Strings In Python
5573 @subsubsection Python representation of lazy strings
5575 @cindex lazy strings in python
5576 @tindex gdb.LazyString
5578 A @dfn{lazy string} is a string whose contents is not retrieved or
5579 encoded until it is needed.
5581 A @code{gdb.LazyString} is represented in @value{GDBN} as an
5582 @code{address} that points to a region of memory, an @code{encoding}
5583 that will be used to encode that region of memory, and a @code{length}
5584 to delimit the region of memory that represents the string. The
5585 difference between a @code{gdb.LazyString} and a string wrapped within
5586 a @code{gdb.Value} is that a @code{gdb.LazyString} will be treated
5587 differently by @value{GDBN} when printing. A @code{gdb.LazyString} is
5588 retrieved and encoded during printing, while a @code{gdb.Value}
5589 wrapping a string is immediately retrieved and encoded on creation.
5591 A @code{gdb.LazyString} object has the following functions:
5593 @defun LazyString.value ()
5594 Convert the @code{gdb.LazyString} to a @code{gdb.Value}. This value
5595 will point to the string in memory, but will lose all the delayed
5596 retrieval, encoding and handling that @value{GDBN} applies to a
5597 @code{gdb.LazyString}.
5600 @defvar LazyString.address
5601 This attribute holds the address of the string. This attribute is not
5605 @defvar LazyString.length
5606 This attribute holds the length of the string in characters. If the
5607 length is -1, then the string will be fetched and encoded up to the
5608 first null of appropriate width. This attribute is not writable.
5611 @defvar LazyString.encoding
5612 This attribute holds the encoding that will be applied to the string
5613 when the string is printed by @value{GDBN}. If the encoding is not
5614 set, or contains an empty string, then @value{GDBN} will select the
5615 most appropriate encoding when the string is printed. This attribute
5619 @defvar LazyString.type
5620 This attribute holds the type that is represented by the lazy string's
5621 type. For a lazy string this is a pointer or array type. To
5622 resolve this to the lazy string's character type, use the type's
5623 @code{target} method. @xref{Types In Python}. This attribute is not
5627 @node Architectures In Python
5628 @subsubsection Python representation of architectures
5629 @cindex Python architectures
5631 @value{GDBN} uses architecture specific parameters and artifacts in a
5632 number of its various computations. An architecture is represented
5633 by an instance of the @code{gdb.Architecture} class.
5635 A @code{gdb.Architecture} class has the following methods:
5637 @defun Architecture.name ()
5638 Return the name (string value) of the architecture.
5641 @defun Architecture.disassemble (@var{start_pc} @r{[}, @var{end_pc} @r{[}, @var{count}@r{]]})
5642 Return a list of disassembled instructions starting from the memory
5643 address @var{start_pc}. The optional arguments @var{end_pc} and
5644 @var{count} determine the number of instructions in the returned list.
5645 If both the optional arguments @var{end_pc} and @var{count} are
5646 specified, then a list of at most @var{count} disassembled instructions
5647 whose start address falls in the closed memory address interval from
5648 @var{start_pc} to @var{end_pc} are returned. If @var{end_pc} is not
5649 specified, but @var{count} is specified, then @var{count} number of
5650 instructions starting from the address @var{start_pc} are returned. If
5651 @var{count} is not specified but @var{end_pc} is specified, then all
5652 instructions whose start address falls in the closed memory address
5653 interval from @var{start_pc} to @var{end_pc} are returned. If neither
5654 @var{end_pc} nor @var{count} are specified, then a single instruction at
5655 @var{start_pc} is returned. For all of these cases, each element of the
5656 returned list is a Python @code{dict} with the following string keys:
5661 The value corresponding to this key is a Python long integer capturing
5662 the memory address of the instruction.
5665 The value corresponding to this key is a string value which represents
5666 the instruction with assembly language mnemonics. The assembly
5667 language flavor used is the same as that specified by the current CLI
5668 variable @code{disassembly-flavor}. @xref{Machine Code}.
5671 The value corresponding to this key is the length (integer value) of the
5672 instruction in bytes.
5677 @node TUI Windows In Python
5678 @subsubsection Implementing new TUI windows
5679 @cindex Python TUI Windows
5681 New TUI (@pxref{TUI}) windows can be implemented in Python.
5683 @findex gdb.register_window_type
5684 @defun gdb.register_window_type (@var{name}, @var{factory})
5685 Because TUI windows are created and destroyed depending on the layout
5686 the user chooses, new window types are implemented by registering a
5687 factory function with @value{GDBN}.
5689 @var{name} is the name of the new window. It's an error to try to
5690 replace one of the built-in windows, but other window types can be
5693 @var{function} is a factory function that is called to create the TUI
5694 window. This is called with a single argument of type
5695 @code{gdb.TuiWindow}, described below. It should return an object
5696 that implements the TUI window protocol, also described below.
5699 As mentioned above, when a factory function is called, it is passed a
5700 an object of type @code{gdb.TuiWindow}. This object has these
5701 methods and attributes:
5703 @defun TuiWindow.is_valid ()
5704 This method returns @code{True} when this window is valid. When the
5705 user changes the TUI layout, windows no longer visible in the new
5706 layout will be destroyed. At this point, the @code{gdb.TuiWindow}
5707 will no longer be valid, and methods (and attributes) other than
5708 @code{is_valid} will throw an exception.
5711 @defvar TuiWindow.width
5712 This attribute holds the width of the window. It is not writable.
5715 @defvar TuiWindow.height
5716 This attribute holds the height of the window. It is not writable.
5719 @defvar TuiWindow.title
5720 This attribute holds the window's title, a string. This is normally
5721 displayed above the window. This attribute can be modified.
5724 @defun TuiWindow.erase ()
5725 Remove all the contents of the window.
5728 @defun TuiWindow.write (@var{string})
5729 Write @var{string} to the window. @var{string} can contain ANSI
5730 terminal escape styling sequences; @value{GDBN} will translate these
5731 as appropriate for the terminal.
5734 The factory function that you supply should return an object
5735 conforming to the TUI window protocol. These are the method that can
5736 be called on this object, which is referred to below as the ``window
5737 object''. The methods documented below are optional; if the object
5738 does not implement one of these methods, @value{GDBN} will not attempt
5739 to call it. Additional new methods may be added to the window
5740 protocol in the future. @value{GDBN} guarantees that they will begin
5741 with a lower-case letter, so you can start implementation methods with
5742 upper-case letters or underscore to avoid any future conflicts.
5744 @defun Window.close ()
5745 When the TUI window is closed, the @code{gdb.TuiWindow} object will be
5746 put into an invalid state. At this time, @value{GDBN} will call
5747 @code{close} method on the window object.
5749 After this method is called, @value{GDBN} will discard any references
5750 it holds on this window object, and will no longer call methods on
5754 @defun Window.render ()
5755 In some situations, a TUI window can change size. For example, this
5756 can happen if the user resizes the terminal, or changes the layout.
5757 When this happens, @value{GDBN} will call the @code{render} method on
5760 If your window is intended to update in response to changes in the
5761 inferior, you will probably also want to register event listeners and
5762 send output to the @code{gdb.TuiWindow}.
5765 @defun Window.hscroll (@var{num})
5766 This is a request to scroll the window horizontally. @var{num} is the
5767 amount by which to scroll, with negative numbers meaning to scroll
5768 right. In the TUI model, it is the viewport that moves, not the
5769 contents. A positive argument should cause the viewport to move
5770 right, and so the content should appear to move to the left.
5773 @defun Window.vscroll (@var{num})
5774 This is a request to scroll the window vertically. @var{num} is the
5775 amount by which to scroll, with negative numbers meaning to scroll
5776 backward. In the TUI model, it is the viewport that moves, not the
5777 contents. A positive argument should cause the viewport to move down,
5778 and so the content should appear to move up.
5781 @node Python Auto-loading
5782 @subsection Python Auto-loading
5783 @cindex Python auto-loading
5785 When a new object file is read (for example, due to the @code{file}
5786 command, or because the inferior has loaded a shared library),
5787 @value{GDBN} will look for Python support scripts in several ways:
5788 @file{@var{objfile}-gdb.py} and @code{.debug_gdb_scripts} section.
5789 @xref{Auto-loading extensions}.
5791 The auto-loading feature is useful for supplying application-specific
5792 debugging commands and scripts.
5794 Auto-loading can be enabled or disabled,
5795 and the list of auto-loaded scripts can be printed.
5798 @anchor{set auto-load python-scripts}
5799 @kindex set auto-load python-scripts
5800 @item set auto-load python-scripts [on|off]
5801 Enable or disable the auto-loading of Python scripts.
5803 @anchor{show auto-load python-scripts}
5804 @kindex show auto-load python-scripts
5805 @item show auto-load python-scripts
5806 Show whether auto-loading of Python scripts is enabled or disabled.
5808 @anchor{info auto-load python-scripts}
5809 @kindex info auto-load python-scripts
5810 @cindex print list of auto-loaded Python scripts
5811 @item info auto-load python-scripts [@var{regexp}]
5812 Print the list of all Python scripts that @value{GDBN} auto-loaded.
5814 Also printed is the list of Python scripts that were mentioned in
5815 the @code{.debug_gdb_scripts} section and were either not found
5816 (@pxref{dotdebug_gdb_scripts section}) or were not auto-loaded due to
5817 @code{auto-load safe-path} rejection (@pxref{Auto-loading}).
5818 This is useful because their names are not printed when @value{GDBN}
5819 tries to load them and fails. There may be many of them, and printing
5820 an error message for each one is problematic.
5822 If @var{regexp} is supplied only Python scripts with matching names are printed.
5827 (gdb) info auto-load python-scripts
5829 Yes py-section-script.py
5830 full name: /tmp/py-section-script.py
5831 No my-foo-pretty-printers.py
5835 When reading an auto-loaded file or script, @value{GDBN} sets the
5836 @dfn{current objfile}. This is available via the @code{gdb.current_objfile}
5837 function (@pxref{Objfiles In Python}). This can be useful for
5838 registering objfile-specific pretty-printers and frame-filters.
5840 @node Python modules
5841 @subsection Python modules
5842 @cindex python modules
5844 @value{GDBN} comes with several modules to assist writing Python code.
5847 * gdb.printing:: Building and registering pretty-printers.
5848 * gdb.types:: Utilities for working with types.
5849 * gdb.prompt:: Utilities for prompt value substitution.
5853 @subsubsection gdb.printing
5854 @cindex gdb.printing
5856 This module provides a collection of utilities for working with
5860 @item PrettyPrinter (@var{name}, @var{subprinters}=None)
5861 This class specifies the API that makes @samp{info pretty-printer},
5862 @samp{enable pretty-printer} and @samp{disable pretty-printer} work.
5863 Pretty-printers should generally inherit from this class.
5865 @item SubPrettyPrinter (@var{name})
5866 For printers that handle multiple types, this class specifies the
5867 corresponding API for the subprinters.
5869 @item RegexpCollectionPrettyPrinter (@var{name})
5870 Utility class for handling multiple printers, all recognized via
5871 regular expressions.
5872 @xref{Writing a Pretty-Printer}, for an example.
5874 @item FlagEnumerationPrinter (@var{name})
5875 A pretty-printer which handles printing of @code{enum} values. Unlike
5876 @value{GDBN}'s built-in @code{enum} printing, this printer attempts to
5877 work properly when there is some overlap between the enumeration
5878 constants. The argument @var{name} is the name of the printer and
5879 also the name of the @code{enum} type to look up.
5881 @item register_pretty_printer (@var{obj}, @var{printer}, @var{replace}=False)
5882 Register @var{printer} with the pretty-printer list of @var{obj}.
5883 If @var{replace} is @code{True} then any existing copy of the printer
5884 is replaced. Otherwise a @code{RuntimeError} exception is raised
5885 if a printer with the same name already exists.
5889 @subsubsection gdb.types
5892 This module provides a collection of utilities for working with
5893 @code{gdb.Type} objects.
5896 @item get_basic_type (@var{type})
5897 Return @var{type} with const and volatile qualifiers stripped,
5898 and with typedefs and C@t{++} references converted to the underlying type.
5903 typedef const int const_int;
5905 const_int& foo_ref (foo);
5906 int main () @{ return 0; @}
5913 (gdb) python import gdb.types
5914 (gdb) python foo_ref = gdb.parse_and_eval("foo_ref")
5915 (gdb) python print gdb.types.get_basic_type(foo_ref.type)
5919 @item has_field (@var{type}, @var{field})
5920 Return @code{True} if @var{type}, assumed to be a type with fields
5921 (e.g., a structure or union), has field @var{field}.
5923 @item make_enum_dict (@var{enum_type})
5924 Return a Python @code{dictionary} type produced from @var{enum_type}.
5926 @item deep_items (@var{type})
5927 Returns a Python iterator similar to the standard
5928 @code{gdb.Type.iteritems} method, except that the iterator returned
5929 by @code{deep_items} will recursively traverse anonymous struct or
5930 union fields. For example:
5944 Then in @value{GDBN}:
5946 (@value{GDBP}) python import gdb.types
5947 (@value{GDBP}) python struct_a = gdb.lookup_type("struct A")
5948 (@value{GDBP}) python print struct_a.keys ()
5950 (@value{GDBP}) python print [k for k,v in gdb.types.deep_items(struct_a)]
5951 @{['a', 'b0', 'b1']@}
5954 @item get_type_recognizers ()
5955 Return a list of the enabled type recognizers for the current context.
5956 This is called by @value{GDBN} during the type-printing process
5957 (@pxref{Type Printing API}).
5959 @item apply_type_recognizers (recognizers, type_obj)
5960 Apply the type recognizers, @var{recognizers}, to the type object
5961 @var{type_obj}. If any recognizer returns a string, return that
5962 string. Otherwise, return @code{None}. This is called by
5963 @value{GDBN} during the type-printing process (@pxref{Type Printing
5966 @item register_type_printer (locus, printer)
5967 This is a convenience function to register a type printer
5968 @var{printer}. The printer must implement the type printer protocol.
5969 The @var{locus} argument is either a @code{gdb.Objfile}, in which case
5970 the printer is registered with that objfile; a @code{gdb.Progspace},
5971 in which case the printer is registered with that progspace; or
5972 @code{None}, in which case the printer is registered globally.
5975 This is a base class that implements the type printer protocol. Type
5976 printers are encouraged, but not required, to derive from this class.
5977 It defines a constructor:
5979 @defmethod TypePrinter __init__ (self, name)
5980 Initialize the type printer with the given name. The new printer
5981 starts in the enabled state.
5987 @subsubsection gdb.prompt
5990 This module provides a method for prompt value-substitution.
5993 @item substitute_prompt (@var{string})
5994 Return @var{string} with escape sequences substituted by values. Some
5995 escape sequences take arguments. You can specify arguments inside
5996 ``@{@}'' immediately following the escape sequence.
5998 The escape sequences you can pass to this function are:
6002 Substitute a backslash.
6004 Substitute an ESC character.
6006 Substitute the selected frame; an argument names a frame parameter.
6008 Substitute a newline.
6010 Substitute a parameter's value; the argument names the parameter.
6012 Substitute a carriage return.
6014 Substitute the selected thread; an argument names a thread parameter.
6016 Substitute the version of GDB.
6018 Substitute the current working directory.
6020 Begin a sequence of non-printing characters. These sequences are
6021 typically used with the ESC character, and are not counted in the string
6022 length. Example: ``\[\e[0;34m\](gdb)\[\e[0m\]'' will return a
6023 blue-colored ``(gdb)'' prompt where the length is five.
6025 End a sequence of non-printing characters.
6031 substitute_prompt ("frame: \f, args: \p@{print frame-arguments@}")
6034 @exdent will return the string:
6037 "frame: main, args: scalars"