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3 @c under the terms of the GNU Free Documentation License, Version 1.3 or
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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}.
22 @cindex python directory
23 Python scripts used by @value{GDBN} should be installed in
24 @file{@var{data-directory}/python}, where @var{data-directory} is
25 the data directory as determined at @value{GDBN} startup (@pxref{Data Files}).
26 This directory, known as the @dfn{python directory},
27 is automatically added to the Python Search Path in order to allow
28 the Python interpreter to locate all scripts installed at this location.
30 Additionally, @value{GDBN} commands and convenience functions which
31 are written in Python and are located in the
32 @file{@var{data-directory}/python/gdb/command} or
33 @file{@var{data-directory}/python/gdb/function} directories are
34 automatically imported when @value{GDBN} starts.
37 * Python Commands:: Accessing Python from @value{GDBN}.
38 * Python API:: Accessing @value{GDBN} from Python.
39 * Python Auto-loading:: Automatically loading Python code.
40 * Python modules:: Python modules provided by @value{GDBN}.
44 @subsection Python Commands
45 @cindex python commands
46 @cindex commands to access python
48 @value{GDBN} provides two commands for accessing the Python interpreter,
49 and one related setting:
52 @kindex python-interactive
54 @item python-interactive @r{[}@var{command}@r{]}
55 @itemx pi @r{[}@var{command}@r{]}
56 Without an argument, the @code{python-interactive} command can be used
57 to start an interactive Python prompt. To return to @value{GDBN},
58 type the @code{EOF} character (e.g., @kbd{Ctrl-D} on an empty prompt).
60 Alternatively, a single-line Python command can be given as an
61 argument and evaluated. If the command is an expression, the result
62 will be printed; otherwise, nothing will be printed. For example:
65 (@value{GDBP}) python-interactive 2 + 3
71 @item python @r{[}@var{command}@r{]}
72 @itemx py @r{[}@var{command}@r{]}
73 The @code{python} command can be used to evaluate Python code.
75 If given an argument, the @code{python} command will evaluate the
76 argument as a Python command. For example:
79 (@value{GDBP}) python print 23
83 If you do not provide an argument to @code{python}, it will act as a
84 multi-line command, like @code{define}. In this case, the Python
85 script is made up of subsequent command lines, given after the
86 @code{python} command. This command list is terminated using a line
87 containing @code{end}. For example:
92 End with a line saying just "end".
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}.
117 @item python execfile ("script-name")
118 This method is based on the @code{execfile} Python built-in function,
119 and thus is always available.
123 @subsection Python API
125 @cindex programming in python
127 You can get quick online help for @value{GDBN}'s Python API by issuing
128 the command @w{@kbd{python help (gdb)}}.
130 Functions and methods which have two or more optional arguments allow
131 them to be specified using keyword syntax. This allows passing some
132 optional arguments while skipping others. Example:
133 @w{@code{gdb.some_function ('foo', bar = 1, baz = 2)}}.
136 * Basic Python:: Basic Python Functions.
137 * Exception Handling:: How Python exceptions are translated.
138 * Values From Inferior:: Python representation of values.
139 * Types In Python:: Python representation of types.
140 * Pretty Printing API:: Pretty-printing values.
141 * Selecting Pretty-Printers:: How GDB chooses a pretty-printer.
142 * Writing a Pretty-Printer:: Writing a Pretty-Printer.
143 * Type Printing API:: Pretty-printing types.
144 * Frame Filter API:: Filtering Frames.
145 * Frame Decorator API:: Decorating Frames.
146 * Writing a Frame Filter:: Writing a Frame Filter.
147 * Unwinding Frames in Python:: Writing frame unwinder.
148 * Xmethods In Python:: Adding and replacing methods of C++ classes.
149 * Xmethod API:: Xmethod types.
150 * Writing an Xmethod:: Writing an xmethod.
151 * Inferiors In Python:: Python representation of inferiors (processes)
152 * Events In Python:: Listening for events from @value{GDBN}.
153 * Threads In Python:: Accessing inferior threads from Python.
154 * Recordings In Python:: Accessing recordings from Python.
155 * Commands In Python:: Implementing new commands in Python.
156 * Parameters In Python:: Adding new @value{GDBN} parameters.
157 * Functions In Python:: Writing new convenience functions.
158 * Progspaces In Python:: Program spaces.
159 * Objfiles In Python:: Object files.
160 * Frames In Python:: Accessing inferior stack frames from Python.
161 * Blocks In Python:: Accessing blocks from Python.
162 * Symbols In Python:: Python representation of symbols.
163 * Symbol Tables In Python:: Python representation of symbol tables.
164 * Line Tables In Python:: Python representation of line tables.
165 * Breakpoints In Python:: Manipulating breakpoints using Python.
166 * Finish Breakpoints in Python:: Setting Breakpoints on function return
168 * Lazy Strings In Python:: Python representation of lazy strings.
169 * Architectures In Python:: Python representation of architectures.
173 @subsubsection Basic Python
175 @cindex python stdout
176 @cindex python pagination
177 At startup, @value{GDBN} overrides Python's @code{sys.stdout} and
178 @code{sys.stderr} to print using @value{GDBN}'s output-paging streams.
179 A Python program which outputs to one of these streams may have its
180 output interrupted by the user (@pxref{Screen Size}). In this
181 situation, a Python @code{KeyboardInterrupt} exception is thrown.
183 Some care must be taken when writing Python code to run in
184 @value{GDBN}. Two things worth noting in particular:
188 @value{GDBN} install handlers for @code{SIGCHLD} and @code{SIGINT}.
189 Python code must not override these, or even change the options using
190 @code{sigaction}. If your program changes the handling of these
191 signals, @value{GDBN} will most likely stop working correctly. Note
192 that it is unfortunately common for GUI toolkits to install a
193 @code{SIGCHLD} handler.
196 @value{GDBN} takes care to mark its internal file descriptors as
197 close-on-exec. However, this cannot be done in a thread-safe way on
198 all platforms. Your Python programs should be aware of this and
199 should both create new file descriptors with the close-on-exec flag
200 set and arrange to close unneeded file descriptors before starting a
204 @cindex python functions
205 @cindex python module
207 @value{GDBN} introduces a new Python module, named @code{gdb}. All
208 methods and classes added by @value{GDBN} are placed in this module.
209 @value{GDBN} automatically @code{import}s the @code{gdb} module for
210 use in all scripts evaluated by the @code{python} command.
212 @findex gdb.PYTHONDIR
213 @defvar gdb.PYTHONDIR
214 A string containing the python directory (@pxref{Python}).
218 @defun gdb.execute (command @r{[}, from_tty @r{[}, to_string@r{]]})
219 Evaluate @var{command}, a string, as a @value{GDBN} CLI command.
220 If a GDB exception happens while @var{command} runs, it is
221 translated as described in @ref{Exception Handling,,Exception Handling}.
223 The @var{from_tty} flag specifies whether @value{GDBN} ought to consider this
224 command as having originated from the user invoking it interactively.
225 It must be a boolean value. If omitted, it defaults to @code{False}.
227 By default, any output produced by @var{command} is sent to
228 @value{GDBN}'s standard output (and to the log output if logging is
229 turned on). If the @var{to_string} parameter is
230 @code{True}, then output will be collected by @code{gdb.execute} and
231 returned as a string. The default is @code{False}, in which case the
232 return value is @code{None}. If @var{to_string} is @code{True}, the
233 @value{GDBN} virtual terminal will be temporarily set to unlimited width
234 and height, and its pagination will be disabled; @pxref{Screen Size}.
237 @findex gdb.breakpoints
238 @defun gdb.breakpoints ()
239 Return a sequence holding all of @value{GDBN}'s breakpoints.
240 @xref{Breakpoints In Python}, for more information. In @value{GDBN}
241 version 7.11 and earlier, this function returned @code{None} if there
242 were no breakpoints. This peculiarity was subsequently fixed, and now
243 @code{gdb.breakpoints} returns an empty sequence in this case.
246 @findex gdb.parameter
247 @defun gdb.parameter (parameter)
248 Return the value of a @value{GDBN} @var{parameter} given by its name,
249 a string; the parameter name string may contain spaces if the parameter has a
250 multi-part name. For example, @samp{print object} is a valid
253 If the named parameter does not exist, this function throws a
254 @code{gdb.error} (@pxref{Exception Handling}). Otherwise, the
255 parameter's value is converted to a Python value of the appropriate
260 @defun gdb.history (number)
261 Return a value from @value{GDBN}'s value history (@pxref{Value
262 History}). The @var{number} argument indicates which history element to return.
263 If @var{number} is negative, then @value{GDBN} will take its absolute value
264 and count backward from the last element (i.e., the most recent element) to
265 find the value to return. If @var{number} is zero, then @value{GDBN} will
266 return the most recent element. If the element specified by @var{number}
267 doesn't exist in the value history, a @code{gdb.error} exception will be
270 If no exception is raised, the return value is always an instance of
271 @code{gdb.Value} (@pxref{Values From Inferior}).
274 @findex gdb.parse_and_eval
275 @defun gdb.parse_and_eval (expression)
276 Parse @var{expression}, which must be a string, as an expression in
277 the current language, evaluate it, and return the result as a
280 This function can be useful when implementing a new command
281 (@pxref{Commands In Python}), as it provides a way to parse the
282 command's argument as an expression. It is also useful simply to
283 compute values, for example, it is the only way to get the value of a
284 convenience variable (@pxref{Convenience Vars}) as a @code{gdb.Value}.
287 @findex gdb.find_pc_line
288 @defun gdb.find_pc_line (pc)
289 Return the @code{gdb.Symtab_and_line} object corresponding to the
290 @var{pc} value. @xref{Symbol Tables In Python}. If an invalid
291 value of @var{pc} is passed as an argument, then the @code{symtab} and
292 @code{line} attributes of the returned @code{gdb.Symtab_and_line} object
293 will be @code{None} and 0 respectively.
296 @findex gdb.post_event
297 @defun gdb.post_event (event)
298 Put @var{event}, a callable object taking no arguments, into
299 @value{GDBN}'s internal event queue. This callable will be invoked at
300 some later point, during @value{GDBN}'s event processing. Events
301 posted using @code{post_event} will be run in the order in which they
302 were posted; however, there is no way to know when they will be
303 processed relative to other events inside @value{GDBN}.
305 @value{GDBN} is not thread-safe. If your Python program uses multiple
306 threads, you must be careful to only call @value{GDBN}-specific
307 functions in the @value{GDBN} thread. @code{post_event} ensures
311 (@value{GDBP}) python
315 > def __init__(self, message):
316 > self.message = message;
317 > def __call__(self):
318 > gdb.write(self.message)
320 >class MyThread1 (threading.Thread):
322 > gdb.post_event(Writer("Hello "))
324 >class MyThread2 (threading.Thread):
326 > gdb.post_event(Writer("World\n"))
331 (@value{GDBP}) Hello World
336 @defun gdb.write (string @r{[}, stream{]})
337 Print a string to @value{GDBN}'s paginated output stream. The
338 optional @var{stream} determines the stream to print to. The default
339 stream is @value{GDBN}'s standard output stream. Possible stream
346 @value{GDBN}'s standard output stream.
351 @value{GDBN}'s standard error stream.
356 @value{GDBN}'s log stream (@pxref{Logging Output}).
359 Writing to @code{sys.stdout} or @code{sys.stderr} will automatically
360 call this function and will automatically direct the output to the
366 Flush the buffer of a @value{GDBN} paginated stream so that the
367 contents are displayed immediately. @value{GDBN} will flush the
368 contents of a stream automatically when it encounters a newline in the
369 buffer. The optional @var{stream} determines the stream to flush. The
370 default stream is @value{GDBN}'s standard output stream. Possible
377 @value{GDBN}'s standard output stream.
382 @value{GDBN}'s standard error stream.
387 @value{GDBN}'s log stream (@pxref{Logging Output}).
391 Flushing @code{sys.stdout} or @code{sys.stderr} will automatically
392 call this function for the relevant stream.
395 @findex gdb.target_charset
396 @defun gdb.target_charset ()
397 Return the name of the current target character set (@pxref{Character
398 Sets}). This differs from @code{gdb.parameter('target-charset')} in
399 that @samp{auto} is never returned.
402 @findex gdb.target_wide_charset
403 @defun gdb.target_wide_charset ()
404 Return the name of the current target wide character set
405 (@pxref{Character Sets}). This differs from
406 @code{gdb.parameter('target-wide-charset')} in that @samp{auto} is
410 @findex gdb.solib_name
411 @defun gdb.solib_name (address)
412 Return the name of the shared library holding the given @var{address}
413 as a string, or @code{None}.
416 @findex gdb.decode_line
417 @defun gdb.decode_line @r{[}expression@r{]}
418 Return locations of the line specified by @var{expression}, or of the
419 current line if no argument was given. This function returns a Python
420 tuple containing two elements. The first element contains a string
421 holding any unparsed section of @var{expression} (or @code{None} if
422 the expression has been fully parsed). The second element contains
423 either @code{None} or another tuple that contains all the locations
424 that match the expression represented as @code{gdb.Symtab_and_line}
425 objects (@pxref{Symbol Tables In Python}). If @var{expression} is
426 provided, it is decoded the way that @value{GDBN}'s inbuilt
427 @code{break} or @code{edit} commands do (@pxref{Specify Location}).
430 @defun gdb.prompt_hook (current_prompt)
433 If @var{prompt_hook} is callable, @value{GDBN} will call the method
434 assigned to this operation before a prompt is displayed by
437 The parameter @code{current_prompt} contains the current @value{GDBN}
438 prompt. This method must return a Python string, or @code{None}. If
439 a string is returned, the @value{GDBN} prompt will be set to that
440 string. If @code{None} is returned, @value{GDBN} will continue to use
443 Some prompts cannot be substituted in @value{GDBN}. Secondary prompts
444 such as those used by readline for command input, and annotation
445 related prompts are prohibited from being changed.
448 @node Exception Handling
449 @subsubsection Exception Handling
450 @cindex python exceptions
451 @cindex exceptions, python
453 When executing the @code{python} command, Python exceptions
454 uncaught within the Python code are translated to calls to
455 @value{GDBN} error-reporting mechanism. If the command that called
456 @code{python} does not handle the error, @value{GDBN} will
457 terminate it and print an error message containing the Python
458 exception name, the associated value, and the Python call stack
459 backtrace at the point where the exception was raised. Example:
462 (@value{GDBP}) python print foo
463 Traceback (most recent call last):
464 File "<string>", line 1, in <module>
465 NameError: name 'foo' is not defined
468 @value{GDBN} errors that happen in @value{GDBN} commands invoked by
469 Python code are converted to Python exceptions. The type of the
470 Python exception depends on the error.
474 This is the base class for most exceptions generated by @value{GDBN}.
475 It is derived from @code{RuntimeError}, for compatibility with earlier
476 versions of @value{GDBN}.
478 If an error occurring in @value{GDBN} does not fit into some more
479 specific category, then the generated exception will have this type.
481 @item gdb.MemoryError
482 This is a subclass of @code{gdb.error} which is thrown when an
483 operation tried to access invalid memory in the inferior.
485 @item KeyboardInterrupt
486 User interrupt (via @kbd{C-c} or by typing @kbd{q} at a pagination
487 prompt) is translated to a Python @code{KeyboardInterrupt} exception.
490 In all cases, your exception handler will see the @value{GDBN} error
491 message as its value and the Python call stack backtrace at the Python
492 statement closest to where the @value{GDBN} error occured as the
496 When implementing @value{GDBN} commands in Python via @code{gdb.Command},
497 it is useful to be able to throw an exception that doesn't cause a
498 traceback to be printed. For example, the user may have invoked the
499 command incorrectly. Use the @code{gdb.GdbError} exception
500 to handle this case. Example:
504 >class HelloWorld (gdb.Command):
505 > """Greet the whole world."""
506 > def __init__ (self):
507 > super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)
508 > def invoke (self, args, from_tty):
509 > argv = gdb.string_to_argv (args)
510 > if len (argv) != 0:
511 > raise gdb.GdbError ("hello-world takes no arguments")
512 > print "Hello, World!"
516 hello-world takes no arguments
519 @node Values From Inferior
520 @subsubsection Values From Inferior
521 @cindex values from inferior, with Python
522 @cindex python, working with values from inferior
524 @cindex @code{gdb.Value}
525 @value{GDBN} provides values it obtains from the inferior program in
526 an object of type @code{gdb.Value}. @value{GDBN} uses this object
527 for its internal bookkeeping of the inferior's values, and for
528 fetching values when necessary.
530 Inferior values that are simple scalars can be used directly in
531 Python expressions that are valid for the value's data type. Here's
532 an example for an integer or floating-point value @code{some_val}:
539 As result of this, @code{bar} will also be a @code{gdb.Value} object
540 whose values are of the same type as those of @code{some_val}. Valid
541 Python operations can also be performed on @code{gdb.Value} objects
542 representing a @code{struct} or @code{class} object. For such cases,
543 the overloaded operator (if present), is used to perform the operation.
544 For example, if @code{val1} and @code{val2} are @code{gdb.Value} objects
545 representing instances of a @code{class} which overloads the @code{+}
546 operator, then one can use the @code{+} operator in their Python script
554 The result of the operation @code{val3} is also a @code{gdb.Value}
555 object corresponding to the value returned by the overloaded @code{+}
556 operator. In general, overloaded operators are invoked for the
557 following operations: @code{+} (binary addition), @code{-} (binary
558 subtraction), @code{*} (multiplication), @code{/}, @code{%}, @code{<<},
559 @code{>>}, @code{|}, @code{&}, @code{^}.
561 Inferior values that are structures or instances of some class can
562 be accessed using the Python @dfn{dictionary syntax}. For example, if
563 @code{some_val} is a @code{gdb.Value} instance holding a structure, you
564 can access its @code{foo} element with:
567 bar = some_val['foo']
570 @cindex getting structure elements using gdb.Field objects as subscripts
571 Again, @code{bar} will also be a @code{gdb.Value} object. Structure
572 elements can also be accessed by using @code{gdb.Field} objects as
573 subscripts (@pxref{Types In Python}, for more information on
574 @code{gdb.Field} objects). For example, if @code{foo_field} is a
575 @code{gdb.Field} object corresponding to element @code{foo} of the above
576 structure, then @code{bar} can also be accessed as follows:
579 bar = some_val[foo_field]
582 A @code{gdb.Value} that represents a function can be executed via
583 inferior function call. Any arguments provided to the call must match
584 the function's prototype, and must be provided in the order specified
587 For example, @code{some_val} is a @code{gdb.Value} instance
588 representing a function that takes two integers as arguments. To
589 execute this function, call it like so:
592 result = some_val (10,20)
595 Any values returned from a function call will be stored as a
598 The following attributes are provided:
600 @defvar Value.address
601 If this object is addressable, this read-only attribute holds a
602 @code{gdb.Value} object representing the address. Otherwise,
603 this attribute holds @code{None}.
606 @cindex optimized out value in Python
607 @defvar Value.is_optimized_out
608 This read-only boolean attribute is true if the compiler optimized out
609 this value, thus it is not available for fetching from the inferior.
613 The type of this @code{gdb.Value}. The value of this attribute is a
614 @code{gdb.Type} object (@pxref{Types In Python}).
617 @defvar Value.dynamic_type
618 The dynamic type of this @code{gdb.Value}. This uses C@t{++} run-time
619 type information (@acronym{RTTI}) to determine the dynamic type of the
620 value. If this value is of class type, it will return the class in
621 which the value is embedded, if any. If this value is of pointer or
622 reference to a class type, it will compute the dynamic type of the
623 referenced object, and return a pointer or reference to that type,
624 respectively. In all other cases, it will return the value's static
627 Note that this feature will only work when debugging a C@t{++} program
628 that includes @acronym{RTTI} for the object in question. Otherwise,
629 it will just return the static type of the value as in @kbd{ptype foo}
630 (@pxref{Symbols, ptype}).
633 @defvar Value.is_lazy
634 The value of this read-only boolean attribute is @code{True} if this
635 @code{gdb.Value} has not yet been fetched from the inferior.
636 @value{GDBN} does not fetch values until necessary, for efficiency.
640 myval = gdb.parse_and_eval ('somevar')
643 The value of @code{somevar} is not fetched at this time. It will be
644 fetched when the value is needed, or when the @code{fetch_lazy}
648 The following methods are provided:
650 @defun Value.__init__ (@var{val})
651 Many Python values can be converted directly to a @code{gdb.Value} via
652 this object initializer. Specifically:
656 A Python boolean is converted to the boolean type from the current
660 A Python integer is converted to the C @code{long} type for the
661 current architecture.
664 A Python long is converted to the C @code{long long} type for the
665 current architecture.
668 A Python float is converted to the C @code{double} type for the
669 current architecture.
672 A Python string is converted to a target string in the current target
673 language using the current target encoding.
674 If a character cannot be represented in the current target encoding,
675 then an exception is thrown.
677 @item @code{gdb.Value}
678 If @code{val} is a @code{gdb.Value}, then a copy of the value is made.
680 @item @code{gdb.LazyString}
681 If @code{val} is a @code{gdb.LazyString} (@pxref{Lazy Strings In
682 Python}), then the lazy string's @code{value} method is called, and
687 @defun Value.cast (type)
688 Return a new instance of @code{gdb.Value} that is the result of
689 casting this instance to the type described by @var{type}, which must
690 be a @code{gdb.Type} object. If the cast cannot be performed for some
691 reason, this method throws an exception.
694 @defun Value.dereference ()
695 For pointer data types, this method returns a new @code{gdb.Value} object
696 whose contents is the object pointed to by the pointer. For example, if
697 @code{foo} is a C pointer to an @code{int}, declared in your C program as
704 then you can use the corresponding @code{gdb.Value} to access what
705 @code{foo} points to like this:
708 bar = foo.dereference ()
711 The result @code{bar} will be a @code{gdb.Value} object holding the
712 value pointed to by @code{foo}.
714 A similar function @code{Value.referenced_value} exists which also
715 returns @code{gdb.Value} objects corresonding to the values pointed to
716 by pointer values (and additionally, values referenced by reference
717 values). However, the behavior of @code{Value.dereference}
718 differs from @code{Value.referenced_value} by the fact that the
719 behavior of @code{Value.dereference} is identical to applying the C
720 unary operator @code{*} on a given value. For example, consider a
721 reference to a pointer @code{ptrref}, declared in your C@t{++} program
729 intptr &ptrref = ptr;
732 Though @code{ptrref} is a reference value, one can apply the method
733 @code{Value.dereference} to the @code{gdb.Value} object corresponding
734 to it and obtain a @code{gdb.Value} which is identical to that
735 corresponding to @code{val}. However, if you apply the method
736 @code{Value.referenced_value}, the result would be a @code{gdb.Value}
737 object identical to that corresponding to @code{ptr}.
740 py_ptrref = gdb.parse_and_eval ("ptrref")
741 py_val = py_ptrref.dereference ()
742 py_ptr = py_ptrref.referenced_value ()
745 The @code{gdb.Value} object @code{py_val} is identical to that
746 corresponding to @code{val}, and @code{py_ptr} is identical to that
747 corresponding to @code{ptr}. In general, @code{Value.dereference} can
748 be applied whenever the C unary operator @code{*} can be applied
749 to the corresponding C value. For those cases where applying both
750 @code{Value.dereference} and @code{Value.referenced_value} is allowed,
751 the results obtained need not be identical (as we have seen in the above
752 example). The results are however identical when applied on
753 @code{gdb.Value} objects corresponding to pointers (@code{gdb.Value}
754 objects with type code @code{TYPE_CODE_PTR}) in a C/C@t{++} program.
757 @defun Value.referenced_value ()
758 For pointer or reference data types, this method returns a new
759 @code{gdb.Value} object corresponding to the value referenced by the
760 pointer/reference value. For pointer data types,
761 @code{Value.dereference} and @code{Value.referenced_value} produce
762 identical results. The difference between these methods is that
763 @code{Value.dereference} cannot get the values referenced by reference
764 values. For example, consider a reference to an @code{int}, declared
765 in your C@t{++} program as
773 then applying @code{Value.dereference} to the @code{gdb.Value} object
774 corresponding to @code{ref} will result in an error, while applying
775 @code{Value.referenced_value} will result in a @code{gdb.Value} object
776 identical to that corresponding to @code{val}.
779 py_ref = gdb.parse_and_eval ("ref")
780 er_ref = py_ref.dereference () # Results in error
781 py_val = py_ref.referenced_value () # Returns the referenced value
784 The @code{gdb.Value} object @code{py_val} is identical to that
785 corresponding to @code{val}.
788 @defun Value.reference_value ()
789 Return a @code{gdb.Value} object which is a reference to the value
790 encapsulated by this instance.
793 @defun Value.const_value ()
794 Return a @code{gdb.Value} object which is a @code{const} version of the
795 value encapsulated by this instance.
798 @defun Value.dynamic_cast (type)
799 Like @code{Value.cast}, but works as if the C@t{++} @code{dynamic_cast}
800 operator were used. Consult a C@t{++} reference for details.
803 @defun Value.reinterpret_cast (type)
804 Like @code{Value.cast}, but works as if the C@t{++} @code{reinterpret_cast}
805 operator were used. Consult a C@t{++} reference for details.
808 @defun Value.string (@r{[}encoding@r{[}, errors@r{[}, length@r{]]]})
809 If this @code{gdb.Value} represents a string, then this method
810 converts the contents to a Python string. Otherwise, this method will
813 Values are interpreted as strings according to the rules of the
814 current language. If the optional length argument is given, the
815 string will be converted to that length, and will include any embedded
816 zeroes that the string may contain. Otherwise, for languages
817 where the string is zero-terminated, the entire string will be
820 For example, in C-like languages, a value is a string if it is a pointer
821 to or an array of characters or ints of type @code{wchar_t}, @code{char16_t},
824 If the optional @var{encoding} argument is given, it must be a string
825 naming the encoding of the string in the @code{gdb.Value}, such as
826 @code{"ascii"}, @code{"iso-8859-6"} or @code{"utf-8"}. It accepts
827 the same encodings as the corresponding argument to Python's
828 @code{string.decode} method, and the Python codec machinery will be used
829 to convert the string. If @var{encoding} is not given, or if
830 @var{encoding} is the empty string, then either the @code{target-charset}
831 (@pxref{Character Sets}) will be used, or a language-specific encoding
832 will be used, if the current language is able to supply one.
834 The optional @var{errors} argument is the same as the corresponding
835 argument to Python's @code{string.decode} method.
837 If the optional @var{length} argument is given, the string will be
838 fetched and converted to the given length.
841 @defun Value.lazy_string (@r{[}encoding @r{[}, length@r{]]})
842 If this @code{gdb.Value} represents a string, then this method
843 converts the contents to a @code{gdb.LazyString} (@pxref{Lazy Strings
844 In Python}). Otherwise, this method will throw an exception.
846 If the optional @var{encoding} argument is given, it must be a string
847 naming the encoding of the @code{gdb.LazyString}. Some examples are:
848 @samp{ascii}, @samp{iso-8859-6} or @samp{utf-8}. If the
849 @var{encoding} argument is an encoding that @value{GDBN} does
850 recognize, @value{GDBN} will raise an error.
852 When a lazy string is printed, the @value{GDBN} encoding machinery is
853 used to convert the string during printing. If the optional
854 @var{encoding} argument is not provided, or is an empty string,
855 @value{GDBN} will automatically select the encoding most suitable for
856 the string type. For further information on encoding in @value{GDBN}
857 please see @ref{Character Sets}.
859 If the optional @var{length} argument is given, the string will be
860 fetched and encoded to the length of characters specified. If
861 the @var{length} argument is not provided, the string will be fetched
862 and encoded until a null of appropriate width is found.
865 @defun Value.fetch_lazy ()
866 If the @code{gdb.Value} object is currently a lazy value
867 (@code{gdb.Value.is_lazy} is @code{True}), then the value is
868 fetched from the inferior. Any errors that occur in the process
869 will produce a Python exception.
871 If the @code{gdb.Value} object is not a lazy value, this method
874 This method does not return a value.
878 @node Types In Python
879 @subsubsection Types In Python
880 @cindex types in Python
881 @cindex Python, working with types
884 @value{GDBN} represents types from the inferior using the class
887 The following type-related functions are available in the @code{gdb}
890 @findex gdb.lookup_type
891 @defun gdb.lookup_type (name @r{[}, block@r{]})
892 This function looks up a type by its @var{name}, which must be a string.
894 If @var{block} is given, then @var{name} is looked up in that scope.
895 Otherwise, it is searched for globally.
897 Ordinarily, this function will return an instance of @code{gdb.Type}.
898 If the named type cannot be found, it will throw an exception.
901 If the type is a structure or class type, or an enum type, the fields
902 of that type can be accessed using the Python @dfn{dictionary syntax}.
903 For example, if @code{some_type} is a @code{gdb.Type} instance holding
904 a structure type, you can access its @code{foo} field with:
907 bar = some_type['foo']
910 @code{bar} will be a @code{gdb.Field} object; see below under the
911 description of the @code{Type.fields} method for a description of the
912 @code{gdb.Field} class.
914 An instance of @code{Type} has the following attributes:
917 The type code for this type. The type code will be one of the
918 @code{TYPE_CODE_} constants defined below.
922 The name of this type. If this type has no name, then @code{None}
927 The size of this type, in target @code{char} units. Usually, a
928 target's @code{char} type will be an 8-bit byte. However, on some
929 unusual platforms, this type may have a different size.
933 The tag name for this type. The tag name is the name after
934 @code{struct}, @code{union}, or @code{enum} in C and C@t{++}; not all
935 languages have this concept. If this type has no tag name, then
936 @code{None} is returned.
939 The following methods are provided:
941 @defun Type.fields ()
942 For structure and union types, this method returns the fields. Range
943 types have two fields, the minimum and maximum values. Enum types
944 have one field per enum constant. Function and method types have one
945 field per parameter. The base types of C@t{++} classes are also
946 represented as fields. If the type has no fields, or does not fit
947 into one of these categories, an empty sequence will be returned.
949 Each field is a @code{gdb.Field} object, with some pre-defined attributes:
952 This attribute is not available for @code{enum} or @code{static}
953 (as in C@t{++}) fields. The value is the position, counting
954 in bits, from the start of the containing type.
957 This attribute is only available for @code{enum} fields, and its value
958 is the enumeration member's integer representation.
961 The name of the field, or @code{None} for anonymous fields.
964 This is @code{True} if the field is artificial, usually meaning that
965 it was provided by the compiler and not the user. This attribute is
966 always provided, and is @code{False} if the field is not artificial.
969 This is @code{True} if the field represents a base class of a C@t{++}
970 structure. This attribute is always provided, and is @code{False}
971 if the field is not a base class of the type that is the argument of
972 @code{fields}, or if that type was not a C@t{++} class.
975 If the field is packed, or is a bitfield, then this will have a
976 non-zero value, which is the size of the field in bits. Otherwise,
977 this will be zero; in this case the field's size is given by its type.
980 The type of the field. This is usually an instance of @code{Type},
981 but it can be @code{None} in some situations.
984 The type which contains this field. This is an instance of
989 @defun Type.array (@var{n1} @r{[}, @var{n2}@r{]})
990 Return a new @code{gdb.Type} object which represents an array of this
991 type. If one argument is given, it is the inclusive upper bound of
992 the array; in this case the lower bound is zero. If two arguments are
993 given, the first argument is the lower bound of the array, and the
994 second argument is the upper bound of the array. An array's length
995 must not be negative, but the bounds can be.
998 @defun Type.vector (@var{n1} @r{[}, @var{n2}@r{]})
999 Return a new @code{gdb.Type} object which represents a vector of this
1000 type. If one argument is given, it is the inclusive upper bound of
1001 the vector; in this case the lower bound is zero. If two arguments are
1002 given, the first argument is the lower bound of the vector, and the
1003 second argument is the upper bound of the vector. A vector's length
1004 must not be negative, but the bounds can be.
1006 The difference between an @code{array} and a @code{vector} is that
1007 arrays behave like in C: when used in expressions they decay to a pointer
1008 to the first element whereas vectors are treated as first class values.
1011 @defun Type.const ()
1012 Return a new @code{gdb.Type} object which represents a
1013 @code{const}-qualified variant of this type.
1016 @defun Type.volatile ()
1017 Return a new @code{gdb.Type} object which represents a
1018 @code{volatile}-qualified variant of this type.
1021 @defun Type.unqualified ()
1022 Return a new @code{gdb.Type} object which represents an unqualified
1023 variant of this type. That is, the result is neither @code{const} nor
1027 @defun Type.range ()
1028 Return a Python @code{Tuple} object that contains two elements: the
1029 low bound of the argument type and the high bound of that type. If
1030 the type does not have a range, @value{GDBN} will raise a
1031 @code{gdb.error} exception (@pxref{Exception Handling}).
1034 @defun Type.reference ()
1035 Return a new @code{gdb.Type} object which represents a reference to this
1039 @defun Type.pointer ()
1040 Return a new @code{gdb.Type} object which represents a pointer to this
1044 @defun Type.strip_typedefs ()
1045 Return a new @code{gdb.Type} that represents the real type,
1046 after removing all layers of typedefs.
1049 @defun Type.target ()
1050 Return a new @code{gdb.Type} object which represents the target type
1053 For a pointer type, the target type is the type of the pointed-to
1054 object. For an array type (meaning C-like arrays), the target type is
1055 the type of the elements of the array. For a function or method type,
1056 the target type is the type of the return value. For a complex type,
1057 the target type is the type of the elements. For a typedef, the
1058 target type is the aliased type.
1060 If the type does not have a target, this method will throw an
1064 @defun Type.template_argument (n @r{[}, block@r{]})
1065 If this @code{gdb.Type} is an instantiation of a template, this will
1066 return a new @code{gdb.Value} or @code{gdb.Type} which represents the
1067 value of the @var{n}th template argument (indexed starting at 0).
1069 If this @code{gdb.Type} is not a template type, or if the type has fewer
1070 than @var{n} template arguments, this will throw an exception.
1071 Ordinarily, only C@t{++} code will have template types.
1073 If @var{block} is given, then @var{name} is looked up in that scope.
1074 Otherwise, it is searched for globally.
1077 @defun Type.optimized_out ()
1078 Return @code{gdb.Value} instance of this type whose value is optimized
1079 out. This allows a frame decorator to indicate that the value of an
1080 argument or a local variable is not known.
1083 Each type has a code, which indicates what category this type falls
1084 into. The available type categories are represented by constants
1085 defined in the @code{gdb} module:
1088 @vindex TYPE_CODE_PTR
1089 @item gdb.TYPE_CODE_PTR
1090 The type is a pointer.
1092 @vindex TYPE_CODE_ARRAY
1093 @item gdb.TYPE_CODE_ARRAY
1094 The type is an array.
1096 @vindex TYPE_CODE_STRUCT
1097 @item gdb.TYPE_CODE_STRUCT
1098 The type is a structure.
1100 @vindex TYPE_CODE_UNION
1101 @item gdb.TYPE_CODE_UNION
1102 The type is a union.
1104 @vindex TYPE_CODE_ENUM
1105 @item gdb.TYPE_CODE_ENUM
1106 The type is an enum.
1108 @vindex TYPE_CODE_FLAGS
1109 @item gdb.TYPE_CODE_FLAGS
1110 A bit flags type, used for things such as status registers.
1112 @vindex TYPE_CODE_FUNC
1113 @item gdb.TYPE_CODE_FUNC
1114 The type is a function.
1116 @vindex TYPE_CODE_INT
1117 @item gdb.TYPE_CODE_INT
1118 The type is an integer type.
1120 @vindex TYPE_CODE_FLT
1121 @item gdb.TYPE_CODE_FLT
1122 A floating point type.
1124 @vindex TYPE_CODE_VOID
1125 @item gdb.TYPE_CODE_VOID
1126 The special type @code{void}.
1128 @vindex TYPE_CODE_SET
1129 @item gdb.TYPE_CODE_SET
1132 @vindex TYPE_CODE_RANGE
1133 @item gdb.TYPE_CODE_RANGE
1134 A range type, that is, an integer type with bounds.
1136 @vindex TYPE_CODE_STRING
1137 @item gdb.TYPE_CODE_STRING
1138 A string type. Note that this is only used for certain languages with
1139 language-defined string types; C strings are not represented this way.
1141 @vindex TYPE_CODE_BITSTRING
1142 @item gdb.TYPE_CODE_BITSTRING
1143 A string of bits. It is deprecated.
1145 @vindex TYPE_CODE_ERROR
1146 @item gdb.TYPE_CODE_ERROR
1147 An unknown or erroneous type.
1149 @vindex TYPE_CODE_METHOD
1150 @item gdb.TYPE_CODE_METHOD
1151 A method type, as found in C@t{++}.
1153 @vindex TYPE_CODE_METHODPTR
1154 @item gdb.TYPE_CODE_METHODPTR
1155 A pointer-to-member-function.
1157 @vindex TYPE_CODE_MEMBERPTR
1158 @item gdb.TYPE_CODE_MEMBERPTR
1159 A pointer-to-member.
1161 @vindex TYPE_CODE_REF
1162 @item gdb.TYPE_CODE_REF
1165 @vindex TYPE_CODE_CHAR
1166 @item gdb.TYPE_CODE_CHAR
1169 @vindex TYPE_CODE_BOOL
1170 @item gdb.TYPE_CODE_BOOL
1173 @vindex TYPE_CODE_COMPLEX
1174 @item gdb.TYPE_CODE_COMPLEX
1175 A complex float type.
1177 @vindex TYPE_CODE_TYPEDEF
1178 @item gdb.TYPE_CODE_TYPEDEF
1179 A typedef to some other type.
1181 @vindex TYPE_CODE_NAMESPACE
1182 @item gdb.TYPE_CODE_NAMESPACE
1183 A C@t{++} namespace.
1185 @vindex TYPE_CODE_DECFLOAT
1186 @item gdb.TYPE_CODE_DECFLOAT
1187 A decimal floating point type.
1189 @vindex TYPE_CODE_INTERNAL_FUNCTION
1190 @item gdb.TYPE_CODE_INTERNAL_FUNCTION
1191 A function internal to @value{GDBN}. This is the type used to represent
1192 convenience functions.
1195 Further support for types is provided in the @code{gdb.types}
1196 Python module (@pxref{gdb.types}).
1198 @node Pretty Printing API
1199 @subsubsection Pretty Printing API
1200 @cindex python pretty printing api
1202 An example output is provided (@pxref{Pretty Printing}).
1204 A pretty-printer is just an object that holds a value and implements a
1205 specific interface, defined here.
1207 @defun pretty_printer.children (self)
1208 @value{GDBN} will call this method on a pretty-printer to compute the
1209 children of the pretty-printer's value.
1211 This method must return an object conforming to the Python iterator
1212 protocol. Each item returned by the iterator must be a tuple holding
1213 two elements. The first element is the ``name'' of the child; the
1214 second element is the child's value. The value can be any Python
1215 object which is convertible to a @value{GDBN} value.
1217 This method is optional. If it does not exist, @value{GDBN} will act
1218 as though the value has no children.
1221 @defun pretty_printer.display_hint (self)
1222 The CLI may call this method and use its result to change the
1223 formatting of a value. The result will also be supplied to an MI
1224 consumer as a @samp{displayhint} attribute of the variable being
1227 This method is optional. If it does exist, this method must return a
1230 Some display hints are predefined by @value{GDBN}:
1234 Indicate that the object being printed is ``array-like''. The CLI
1235 uses this to respect parameters such as @code{set print elements} and
1236 @code{set print array}.
1239 Indicate that the object being printed is ``map-like'', and that the
1240 children of this value can be assumed to alternate between keys and
1244 Indicate that the object being printed is ``string-like''. If the
1245 printer's @code{to_string} method returns a Python string of some
1246 kind, then @value{GDBN} will call its internal language-specific
1247 string-printing function to format the string. For the CLI this means
1248 adding quotation marks, possibly escaping some characters, respecting
1249 @code{set print elements}, and the like.
1253 @defun pretty_printer.to_string (self)
1254 @value{GDBN} will call this method to display the string
1255 representation of the value passed to the object's constructor.
1257 When printing from the CLI, if the @code{to_string} method exists,
1258 then @value{GDBN} will prepend its result to the values returned by
1259 @code{children}. Exactly how this formatting is done is dependent on
1260 the display hint, and may change as more hints are added. Also,
1261 depending on the print settings (@pxref{Print Settings}), the CLI may
1262 print just the result of @code{to_string} in a stack trace, omitting
1263 the result of @code{children}.
1265 If this method returns a string, it is printed verbatim.
1267 Otherwise, if this method returns an instance of @code{gdb.Value},
1268 then @value{GDBN} prints this value. This may result in a call to
1269 another pretty-printer.
1271 If instead the method returns a Python value which is convertible to a
1272 @code{gdb.Value}, then @value{GDBN} performs the conversion and prints
1273 the resulting value. Again, this may result in a call to another
1274 pretty-printer. Python scalars (integers, floats, and booleans) and
1275 strings are convertible to @code{gdb.Value}; other types are not.
1277 Finally, if this method returns @code{None} then no further operations
1278 are peformed in this method and nothing is printed.
1280 If the result is not one of these types, an exception is raised.
1283 @value{GDBN} provides a function which can be used to look up the
1284 default pretty-printer for a @code{gdb.Value}:
1286 @findex gdb.default_visualizer
1287 @defun gdb.default_visualizer (value)
1288 This function takes a @code{gdb.Value} object as an argument. If a
1289 pretty-printer for this value exists, then it is returned. If no such
1290 printer exists, then this returns @code{None}.
1293 @node Selecting Pretty-Printers
1294 @subsubsection Selecting Pretty-Printers
1295 @cindex selecting python pretty-printers
1297 The Python list @code{gdb.pretty_printers} contains an array of
1298 functions or callable objects that have been registered via addition
1299 as a pretty-printer. Printers in this list are called @code{global}
1300 printers, they're available when debugging all inferiors.
1301 Each @code{gdb.Progspace} contains a @code{pretty_printers} attribute.
1302 Each @code{gdb.Objfile} also contains a @code{pretty_printers}
1305 Each function on these lists is passed a single @code{gdb.Value}
1306 argument and should return a pretty-printer object conforming to the
1307 interface definition above (@pxref{Pretty Printing API}). If a function
1308 cannot create a pretty-printer for the value, it should return
1311 @value{GDBN} first checks the @code{pretty_printers} attribute of each
1312 @code{gdb.Objfile} in the current program space and iteratively calls
1313 each enabled lookup routine in the list for that @code{gdb.Objfile}
1314 until it receives a pretty-printer object.
1315 If no pretty-printer is found in the objfile lists, @value{GDBN} then
1316 searches the pretty-printer list of the current program space,
1317 calling each enabled function until an object is returned.
1318 After these lists have been exhausted, it tries the global
1319 @code{gdb.pretty_printers} list, again calling each enabled function until an
1322 The order in which the objfiles are searched is not specified. For a
1323 given list, functions are always invoked from the head of the list,
1324 and iterated over sequentially until the end of the list, or a printer
1327 For various reasons a pretty-printer may not work.
1328 For example, the underlying data structure may have changed and
1329 the pretty-printer is out of date.
1331 The consequences of a broken pretty-printer are severe enough that
1332 @value{GDBN} provides support for enabling and disabling individual
1333 printers. For example, if @code{print frame-arguments} is on,
1334 a backtrace can become highly illegible if any argument is printed
1335 with a broken printer.
1337 Pretty-printers are enabled and disabled by attaching an @code{enabled}
1338 attribute to the registered function or callable object. If this attribute
1339 is present and its value is @code{False}, the printer is disabled, otherwise
1340 the printer is enabled.
1342 @node Writing a Pretty-Printer
1343 @subsubsection Writing a Pretty-Printer
1344 @cindex writing a pretty-printer
1346 A pretty-printer consists of two parts: a lookup function to detect
1347 if the type is supported, and the printer itself.
1349 Here is an example showing how a @code{std::string} printer might be
1350 written. @xref{Pretty Printing API}, for details on the API this class
1354 class StdStringPrinter(object):
1355 "Print a std::string"
1357 def __init__(self, val):
1360 def to_string(self):
1361 return self.val['_M_dataplus']['_M_p']
1363 def display_hint(self):
1367 And here is an example showing how a lookup function for the printer
1368 example above might be written.
1371 def str_lookup_function(val):
1372 lookup_tag = val.type.tag
1373 if lookup_tag == None:
1375 regex = re.compile("^std::basic_string<char,.*>$")
1376 if regex.match(lookup_tag):
1377 return StdStringPrinter(val)
1381 The example lookup function extracts the value's type, and attempts to
1382 match it to a type that it can pretty-print. If it is a type the
1383 printer can pretty-print, it will return a printer object. If not, it
1384 returns @code{None}.
1386 We recommend that you put your core pretty-printers into a Python
1387 package. If your pretty-printers are for use with a library, we
1388 further recommend embedding a version number into the package name.
1389 This practice will enable @value{GDBN} to load multiple versions of
1390 your pretty-printers at the same time, because they will have
1393 You should write auto-loaded code (@pxref{Python Auto-loading}) such that it
1394 can be evaluated multiple times without changing its meaning. An
1395 ideal auto-load file will consist solely of @code{import}s of your
1396 printer modules, followed by a call to a register pretty-printers with
1397 the current objfile.
1399 Taken as a whole, this approach will scale nicely to multiple
1400 inferiors, each potentially using a different library version.
1401 Embedding a version number in the Python package name will ensure that
1402 @value{GDBN} is able to load both sets of printers simultaneously.
1403 Then, because the search for pretty-printers is done by objfile, and
1404 because your auto-loaded code took care to register your library's
1405 printers with a specific objfile, @value{GDBN} will find the correct
1406 printers for the specific version of the library used by each
1409 To continue the @code{std::string} example (@pxref{Pretty Printing API}),
1410 this code might appear in @code{gdb.libstdcxx.v6}:
1413 def register_printers(objfile):
1414 objfile.pretty_printers.append(str_lookup_function)
1418 And then the corresponding contents of the auto-load file would be:
1421 import gdb.libstdcxx.v6
1422 gdb.libstdcxx.v6.register_printers(gdb.current_objfile())
1425 The previous example illustrates a basic pretty-printer.
1426 There are a few things that can be improved on.
1427 The printer doesn't have a name, making it hard to identify in a
1428 list of installed printers. The lookup function has a name, but
1429 lookup functions can have arbitrary, even identical, names.
1431 Second, the printer only handles one type, whereas a library typically has
1432 several types. One could install a lookup function for each desired type
1433 in the library, but one could also have a single lookup function recognize
1434 several types. The latter is the conventional way this is handled.
1435 If a pretty-printer can handle multiple data types, then its
1436 @dfn{subprinters} are the printers for the individual data types.
1438 The @code{gdb.printing} module provides a formal way of solving these
1439 problems (@pxref{gdb.printing}).
1440 Here is another example that handles multiple types.
1442 These are the types we are going to pretty-print:
1445 struct foo @{ int a, b; @};
1446 struct bar @{ struct foo x, y; @};
1449 Here are the printers:
1453 """Print a foo object."""
1455 def __init__(self, val):
1458 def to_string(self):
1459 return ("a=<" + str(self.val["a"]) +
1460 "> b=<" + str(self.val["b"]) + ">")
1463 """Print a bar object."""
1465 def __init__(self, val):
1468 def to_string(self):
1469 return ("x=<" + str(self.val["x"]) +
1470 "> y=<" + str(self.val["y"]) + ">")
1473 This example doesn't need a lookup function, that is handled by the
1474 @code{gdb.printing} module. Instead a function is provided to build up
1475 the object that handles the lookup.
1480 def build_pretty_printer():
1481 pp = gdb.printing.RegexpCollectionPrettyPrinter(
1483 pp.add_printer('foo', '^foo$', fooPrinter)
1484 pp.add_printer('bar', '^bar$', barPrinter)
1488 And here is the autoload support:
1493 gdb.printing.register_pretty_printer(
1494 gdb.current_objfile(),
1495 my_library.build_pretty_printer())
1498 Finally, when this printer is loaded into @value{GDBN}, here is the
1499 corresponding output of @samp{info pretty-printer}:
1502 (gdb) info pretty-printer
1509 @node Type Printing API
1510 @subsubsection Type Printing API
1511 @cindex type printing API for Python
1513 @value{GDBN} provides a way for Python code to customize type display.
1514 This is mainly useful for substituting canonical typedef names for
1517 @cindex type printer
1518 A @dfn{type printer} is just a Python object conforming to a certain
1519 protocol. A simple base class implementing the protocol is provided;
1520 see @ref{gdb.types}. A type printer must supply at least:
1522 @defivar type_printer enabled
1523 A boolean which is True if the printer is enabled, and False
1524 otherwise. This is manipulated by the @code{enable type-printer}
1525 and @code{disable type-printer} commands.
1528 @defivar type_printer name
1529 The name of the type printer. This must be a string. This is used by
1530 the @code{enable type-printer} and @code{disable type-printer}
1534 @defmethod type_printer instantiate (self)
1535 This is called by @value{GDBN} at the start of type-printing. It is
1536 only called if the type printer is enabled. This method must return a
1537 new object that supplies a @code{recognize} method, as described below.
1541 When displaying a type, say via the @code{ptype} command, @value{GDBN}
1542 will compute a list of type recognizers. This is done by iterating
1543 first over the per-objfile type printers (@pxref{Objfiles In Python}),
1544 followed by the per-progspace type printers (@pxref{Progspaces In
1545 Python}), and finally the global type printers.
1547 @value{GDBN} will call the @code{instantiate} method of each enabled
1548 type printer. If this method returns @code{None}, then the result is
1549 ignored; otherwise, it is appended to the list of recognizers.
1551 Then, when @value{GDBN} is going to display a type name, it iterates
1552 over the list of recognizers. For each one, it calls the recognition
1553 function, stopping if the function returns a non-@code{None} value.
1554 The recognition function is defined as:
1556 @defmethod type_recognizer recognize (self, type)
1557 If @var{type} is not recognized, return @code{None}. Otherwise,
1558 return a string which is to be printed as the name of @var{type}.
1559 The @var{type} argument will be an instance of @code{gdb.Type}
1560 (@pxref{Types In Python}).
1563 @value{GDBN} uses this two-pass approach so that type printers can
1564 efficiently cache information without holding on to it too long. For
1565 example, it can be convenient to look up type information in a type
1566 printer and hold it for a recognizer's lifetime; if a single pass were
1567 done then type printers would have to make use of the event system in
1568 order to avoid holding information that could become stale as the
1571 @node Frame Filter API
1572 @subsubsection Filtering Frames.
1573 @cindex frame filters api
1575 Frame filters are Python objects that manipulate the visibility of a
1576 frame or frames when a backtrace (@pxref{Backtrace}) is printed by
1579 Only commands that print a backtrace, or, in the case of @sc{gdb/mi}
1580 commands (@pxref{GDB/MI}), those that return a collection of frames
1581 are affected. The commands that work with frame filters are:
1583 @code{backtrace} (@pxref{backtrace-command,, The backtrace command}),
1584 @code{-stack-list-frames}
1585 (@pxref{-stack-list-frames,, The -stack-list-frames command}),
1586 @code{-stack-list-variables} (@pxref{-stack-list-variables,, The
1587 -stack-list-variables command}), @code{-stack-list-arguments}
1588 @pxref{-stack-list-arguments,, The -stack-list-arguments command}) and
1589 @code{-stack-list-locals} (@pxref{-stack-list-locals,, The
1590 -stack-list-locals command}).
1592 A frame filter works by taking an iterator as an argument, applying
1593 actions to the contents of that iterator, and returning another
1594 iterator (or, possibly, the same iterator it was provided in the case
1595 where the filter does not perform any operations). Typically, frame
1596 filters utilize tools such as the Python's @code{itertools} module to
1597 work with and create new iterators from the source iterator.
1598 Regardless of how a filter chooses to apply actions, it must not alter
1599 the underlying @value{GDBN} frame or frames, or attempt to alter the
1600 call-stack within @value{GDBN}. This preserves data integrity within
1601 @value{GDBN}. Frame filters are executed on a priority basis and care
1602 should be taken that some frame filters may have been executed before,
1603 and that some frame filters will be executed after.
1605 An important consideration when designing frame filters, and well
1606 worth reflecting upon, is that frame filters should avoid unwinding
1607 the call stack if possible. Some stacks can run very deep, into the
1608 tens of thousands in some cases. To search every frame when a frame
1609 filter executes may be too expensive at that step. The frame filter
1610 cannot know how many frames it has to iterate over, and it may have to
1611 iterate through them all. This ends up duplicating effort as
1612 @value{GDBN} performs this iteration when it prints the frames. If
1613 the filter can defer unwinding frames until frame decorators are
1614 executed, after the last filter has executed, it should. @xref{Frame
1615 Decorator API}, for more information on decorators. Also, there are
1616 examples for both frame decorators and filters in later chapters.
1617 @xref{Writing a Frame Filter}, for more information.
1619 The Python dictionary @code{gdb.frame_filters} contains key/object
1620 pairings that comprise a frame filter. Frame filters in this
1621 dictionary are called @code{global} frame filters, and they are
1622 available when debugging all inferiors. These frame filters must
1623 register with the dictionary directly. In addition to the
1624 @code{global} dictionary, there are other dictionaries that are loaded
1625 with different inferiors via auto-loading (@pxref{Python
1626 Auto-loading}). The two other areas where frame filter dictionaries
1627 can be found are: @code{gdb.Progspace} which contains a
1628 @code{frame_filters} dictionary attribute, and each @code{gdb.Objfile}
1629 object which also contains a @code{frame_filters} dictionary
1632 When a command is executed from @value{GDBN} that is compatible with
1633 frame filters, @value{GDBN} combines the @code{global},
1634 @code{gdb.Progspace} and all @code{gdb.Objfile} dictionaries currently
1635 loaded. All of the @code{gdb.Objfile} dictionaries are combined, as
1636 several frames, and thus several object files, might be in use.
1637 @value{GDBN} then prunes any frame filter whose @code{enabled}
1638 attribute is @code{False}. This pruned list is then sorted according
1639 to the @code{priority} attribute in each filter.
1641 Once the dictionaries are combined, pruned and sorted, @value{GDBN}
1642 creates an iterator which wraps each frame in the call stack in a
1643 @code{FrameDecorator} object, and calls each filter in order. The
1644 output from the previous filter will always be the input to the next
1647 Frame filters have a mandatory interface which each frame filter must
1648 implement, defined here:
1650 @defun FrameFilter.filter (iterator)
1651 @value{GDBN} will call this method on a frame filter when it has
1652 reached the order in the priority list for that filter.
1654 For example, if there are four frame filters:
1665 The order that the frame filters will be called is:
1668 Filter3 -> Filter2 -> Filter1 -> Filter4
1671 Note that the output from @code{Filter3} is passed to the input of
1672 @code{Filter2}, and so on.
1674 This @code{filter} method is passed a Python iterator. This iterator
1675 contains a sequence of frame decorators that wrap each
1676 @code{gdb.Frame}, or a frame decorator that wraps another frame
1677 decorator. The first filter that is executed in the sequence of frame
1678 filters will receive an iterator entirely comprised of default
1679 @code{FrameDecorator} objects. However, after each frame filter is
1680 executed, the previous frame filter may have wrapped some or all of
1681 the frame decorators with their own frame decorator. As frame
1682 decorators must also conform to a mandatory interface, these
1683 decorators can be assumed to act in a uniform manner (@pxref{Frame
1686 This method must return an object conforming to the Python iterator
1687 protocol. Each item in the iterator must be an object conforming to
1688 the frame decorator interface. If a frame filter does not wish to
1689 perform any operations on this iterator, it should return that
1692 This method is not optional. If it does not exist, @value{GDBN} will
1693 raise and print an error.
1696 @defvar FrameFilter.name
1697 The @code{name} attribute must be Python string which contains the
1698 name of the filter displayed by @value{GDBN} (@pxref{Frame Filter
1699 Management}). This attribute may contain any combination of letters
1700 or numbers. Care should be taken to ensure that it is unique. This
1701 attribute is mandatory.
1704 @defvar FrameFilter.enabled
1705 The @code{enabled} attribute must be Python boolean. This attribute
1706 indicates to @value{GDBN} whether the frame filter is enabled, and
1707 should be considered when frame filters are executed. If
1708 @code{enabled} is @code{True}, then the frame filter will be executed
1709 when any of the backtrace commands detailed earlier in this chapter
1710 are executed. If @code{enabled} is @code{False}, then the frame
1711 filter will not be executed. This attribute is mandatory.
1714 @defvar FrameFilter.priority
1715 The @code{priority} attribute must be Python integer. This attribute
1716 controls the order of execution in relation to other frame filters.
1717 There are no imposed limits on the range of @code{priority} other than
1718 it must be a valid integer. The higher the @code{priority} attribute,
1719 the sooner the frame filter will be executed in relation to other
1720 frame filters. Although @code{priority} can be negative, it is
1721 recommended practice to assume zero is the lowest priority that a
1722 frame filter can be assigned. Frame filters that have the same
1723 priority are executed in unsorted order in that priority slot. This
1724 attribute is mandatory.
1727 @node Frame Decorator API
1728 @subsubsection Decorating Frames.
1729 @cindex frame decorator api
1731 Frame decorators are sister objects to frame filters (@pxref{Frame
1732 Filter API}). Frame decorators are applied by a frame filter and can
1733 only be used in conjunction with frame filters.
1735 The purpose of a frame decorator is to customize the printed content
1736 of each @code{gdb.Frame} in commands where frame filters are executed.
1737 This concept is called decorating a frame. Frame decorators decorate
1738 a @code{gdb.Frame} with Python code contained within each API call.
1739 This separates the actual data contained in a @code{gdb.Frame} from
1740 the decorated data produced by a frame decorator. This abstraction is
1741 necessary to maintain integrity of the data contained in each
1744 Frame decorators have a mandatory interface, defined below.
1746 @value{GDBN} already contains a frame decorator called
1747 @code{FrameDecorator}. This contains substantial amounts of
1748 boilerplate code to decorate the content of a @code{gdb.Frame}. It is
1749 recommended that other frame decorators inherit and extend this
1750 object, and only to override the methods needed.
1752 @defun FrameDecorator.elided (self)
1754 The @code{elided} method groups frames together in a hierarchical
1755 system. An example would be an interpreter, where multiple low-level
1756 frames make up a single call in the interpreted language. In this
1757 example, the frame filter would elide the low-level frames and present
1758 a single high-level frame, representing the call in the interpreted
1759 language, to the user.
1761 The @code{elided} function must return an iterable and this iterable
1762 must contain the frames that are being elided wrapped in a suitable
1763 frame decorator. If no frames are being elided this function may
1764 return an empty iterable, or @code{None}. Elided frames are indented
1765 from normal frames in a @code{CLI} backtrace, or in the case of
1766 @code{GDB/MI}, are placed in the @code{children} field of the eliding
1769 It is the frame filter's task to also filter out the elided frames from
1770 the source iterator. This will avoid printing the frame twice.
1773 @defun FrameDecorator.function (self)
1775 This method returns the name of the function in the frame that is to
1778 This method must return a Python string describing the function, or
1781 If this function returns @code{None}, @value{GDBN} will not print any
1782 data for this field.
1785 @defun FrameDecorator.address (self)
1787 This method returns the address of the frame that is to be printed.
1789 This method must return a Python numeric integer type of sufficient
1790 size to describe the address of the frame, or @code{None}.
1792 If this function returns a @code{None}, @value{GDBN} will not print
1793 any data for this field.
1796 @defun FrameDecorator.filename (self)
1798 This method returns the filename and path associated with this frame.
1800 This method must return a Python string containing the filename and
1801 the path to the object file backing the frame, or @code{None}.
1803 If this function returns a @code{None}, @value{GDBN} will not print
1804 any data for this field.
1807 @defun FrameDecorator.line (self):
1809 This method returns the line number associated with the current
1810 position within the function addressed by this frame.
1812 This method must return a Python integer type, or @code{None}.
1814 If this function returns a @code{None}, @value{GDBN} will not print
1815 any data for this field.
1818 @defun FrameDecorator.frame_args (self)
1821 This method must return an iterable, or @code{None}. Returning an
1822 empty iterable, or @code{None} means frame arguments will not be
1823 printed for this frame. This iterable must contain objects that
1824 implement two methods, described here.
1826 This object must implement a @code{argument} method which takes a
1827 single @code{self} parameter and must return a @code{gdb.Symbol}
1828 (@pxref{Symbols In Python}), or a Python string. The object must also
1829 implement a @code{value} method which takes a single @code{self}
1830 parameter and must return a @code{gdb.Value} (@pxref{Values From
1831 Inferior}), a Python value, or @code{None}. If the @code{value}
1832 method returns @code{None}, and the @code{argument} method returns a
1833 @code{gdb.Symbol}, @value{GDBN} will look-up and print the value of
1834 the @code{gdb.Symbol} automatically.
1839 class SymValueWrapper():
1841 def __init__(self, symbol, value):
1851 class SomeFrameDecorator()
1854 def frame_args(self):
1857 block = self.inferior_frame.block()
1861 # Iterate over all symbols in a block. Only add
1862 # symbols that are arguments.
1864 if not sym.is_argument:
1866 args.append(SymValueWrapper(sym,None))
1868 # Add example synthetic argument.
1869 args.append(SymValueWrapper(``foo'', 42))
1875 @defun FrameDecorator.frame_locals (self)
1877 This method must return an iterable or @code{None}. Returning an
1878 empty iterable, or @code{None} means frame local arguments will not be
1879 printed for this frame.
1881 The object interface, the description of the various strategies for
1882 reading frame locals, and the example are largely similar to those
1883 described in the @code{frame_args} function, (@pxref{frame_args,,The
1884 frame filter frame_args function}). Below is a modified example:
1887 class SomeFrameDecorator()
1890 def frame_locals(self):
1893 block = self.inferior_frame.block()
1897 # Iterate over all symbols in a block. Add all
1898 # symbols, except arguments.
1902 vars.append(SymValueWrapper(sym,None))
1904 # Add an example of a synthetic local variable.
1905 vars.append(SymValueWrapper(``bar'', 99))
1911 @defun FrameDecorator.inferior_frame (self):
1913 This method must return the underlying @code{gdb.Frame} that this
1914 frame decorator is decorating. @value{GDBN} requires the underlying
1915 frame for internal frame information to determine how to print certain
1916 values when printing a frame.
1919 @node Writing a Frame Filter
1920 @subsubsection Writing a Frame Filter
1921 @cindex writing a frame filter
1923 There are three basic elements that a frame filter must implement: it
1924 must correctly implement the documented interface (@pxref{Frame Filter
1925 API}), it must register itself with @value{GDBN}, and finally, it must
1926 decide if it is to work on the data provided by @value{GDBN}. In all
1927 cases, whether it works on the iterator or not, each frame filter must
1928 return an iterator. A bare-bones frame filter follows the pattern in
1929 the following example.
1934 class FrameFilter():
1937 # Frame filter attribute creation.
1939 # 'name' is the name of the filter that GDB will display.
1941 # 'priority' is the priority of the filter relative to other
1944 # 'enabled' is a boolean that indicates whether this filter is
1945 # enabled and should be executed.
1951 # Register this frame filter with the global frame_filters
1953 gdb.frame_filters[self.name] = self
1955 def filter(self, frame_iter):
1956 # Just return the iterator.
1960 The frame filter in the example above implements the three
1961 requirements for all frame filters. It implements the API, self
1962 registers, and makes a decision on the iterator (in this case, it just
1963 returns the iterator untouched).
1965 The first step is attribute creation and assignment, and as shown in
1966 the comments the filter assigns the following attributes: @code{name},
1967 @code{priority} and whether the filter should be enabled with the
1968 @code{enabled} attribute.
1970 The second step is registering the frame filter with the dictionary or
1971 dictionaries that the frame filter has interest in. As shown in the
1972 comments, this filter just registers itself with the global dictionary
1973 @code{gdb.frame_filters}. As noted earlier, @code{gdb.frame_filters}
1974 is a dictionary that is initialized in the @code{gdb} module when
1975 @value{GDBN} starts. What dictionary a filter registers with is an
1976 important consideration. Generally, if a filter is specific to a set
1977 of code, it should be registered either in the @code{objfile} or
1978 @code{progspace} dictionaries as they are specific to the program
1979 currently loaded in @value{GDBN}. The global dictionary is always
1980 present in @value{GDBN} and is never unloaded. Any filters registered
1981 with the global dictionary will exist until @value{GDBN} exits. To
1982 avoid filters that may conflict, it is generally better to register
1983 frame filters against the dictionaries that more closely align with
1984 the usage of the filter currently in question. @xref{Python
1985 Auto-loading}, for further information on auto-loading Python scripts.
1987 @value{GDBN} takes a hands-off approach to frame filter registration,
1988 therefore it is the frame filter's responsibility to ensure
1989 registration has occurred, and that any exceptions are handled
1990 appropriately. In particular, you may wish to handle exceptions
1991 relating to Python dictionary key uniqueness. It is mandatory that
1992 the dictionary key is the same as frame filter's @code{name}
1993 attribute. When a user manages frame filters (@pxref{Frame Filter
1994 Management}), the names @value{GDBN} will display are those contained
1995 in the @code{name} attribute.
1997 The final step of this example is the implementation of the
1998 @code{filter} method. As shown in the example comments, we define the
1999 @code{filter} method and note that the method must take an iterator,
2000 and also must return an iterator. In this bare-bones example, the
2001 frame filter is not very useful as it just returns the iterator
2002 untouched. However this is a valid operation for frame filters that
2003 have the @code{enabled} attribute set, but decide not to operate on
2006 In the next example, the frame filter operates on all frames and
2007 utilizes a frame decorator to perform some work on the frames.
2008 @xref{Frame Decorator API}, for further information on the frame
2009 decorator interface.
2011 This example works on inlined frames. It highlights frames which are
2012 inlined by tagging them with an ``[inlined]'' tag. By applying a
2013 frame decorator to all frames with the Python @code{itertools imap}
2014 method, the example defers actions to the frame decorator. Frame
2015 decorators are only processed when @value{GDBN} prints the backtrace.
2017 This introduces a new decision making topic: whether to perform
2018 decision making operations at the filtering step, or at the printing
2019 step. In this example's approach, it does not perform any filtering
2020 decisions at the filtering step beyond mapping a frame decorator to
2021 each frame. This allows the actual decision making to be performed
2022 when each frame is printed. This is an important consideration, and
2023 well worth reflecting upon when designing a frame filter. An issue
2024 that frame filters should avoid is unwinding the stack if possible.
2025 Some stacks can run very deep, into the tens of thousands in some
2026 cases. To search every frame to determine if it is inlined ahead of
2027 time may be too expensive at the filtering step. The frame filter
2028 cannot know how many frames it has to iterate over, and it would have
2029 to iterate through them all. This ends up duplicating effort as
2030 @value{GDBN} performs this iteration when it prints the frames.
2032 In this example decision making can be deferred to the printing step.
2033 As each frame is printed, the frame decorator can examine each frame
2034 in turn when @value{GDBN} iterates. From a performance viewpoint,
2035 this is the most appropriate decision to make as it avoids duplicating
2036 the effort that the printing step would undertake anyway. Also, if
2037 there are many frame filters unwinding the stack during filtering, it
2038 can substantially delay the printing of the backtrace which will
2039 result in large memory usage, and a poor user experience.
2042 class InlineFilter():
2045 self.name = "InlinedFrameFilter"
2048 gdb.frame_filters[self.name] = self
2050 def filter(self, frame_iter):
2051 frame_iter = itertools.imap(InlinedFrameDecorator,
2056 This frame filter is somewhat similar to the earlier example, except
2057 that the @code{filter} method applies a frame decorator object called
2058 @code{InlinedFrameDecorator} to each element in the iterator. The
2059 @code{imap} Python method is light-weight. It does not proactively
2060 iterate over the iterator, but rather creates a new iterator which
2061 wraps the existing one.
2063 Below is the frame decorator for this example.
2066 class InlinedFrameDecorator(FrameDecorator):
2068 def __init__(self, fobj):
2069 super(InlinedFrameDecorator, self).__init__(fobj)
2072 frame = fobj.inferior_frame()
2073 name = str(frame.name())
2075 if frame.type() == gdb.INLINE_FRAME:
2076 name = name + " [inlined]"
2081 This frame decorator only defines and overrides the @code{function}
2082 method. It lets the supplied @code{FrameDecorator}, which is shipped
2083 with @value{GDBN}, perform the other work associated with printing
2086 The combination of these two objects create this output from a
2090 #0 0x004004e0 in bar () at inline.c:11
2091 #1 0x00400566 in max [inlined] (b=6, a=12) at inline.c:21
2092 #2 0x00400566 in main () at inline.c:31
2095 So in the case of this example, a frame decorator is applied to all
2096 frames, regardless of whether they may be inlined or not. As
2097 @value{GDBN} iterates over the iterator produced by the frame filters,
2098 @value{GDBN} executes each frame decorator which then makes a decision
2099 on what to print in the @code{function} callback. Using a strategy
2100 like this is a way to defer decisions on the frame content to printing
2103 @subheading Eliding Frames
2105 It might be that the above example is not desirable for representing
2106 inlined frames, and a hierarchical approach may be preferred. If we
2107 want to hierarchically represent frames, the @code{elided} frame
2108 decorator interface might be preferable.
2110 This example approaches the issue with the @code{elided} method. This
2111 example is quite long, but very simplistic. It is out-of-scope for
2112 this section to write a complete example that comprehensively covers
2113 all approaches of finding and printing inlined frames. However, this
2114 example illustrates the approach an author might use.
2116 This example comprises of three sections.
2119 class InlineFrameFilter():
2122 self.name = "InlinedFrameFilter"
2125 gdb.frame_filters[self.name] = self
2127 def filter(self, frame_iter):
2128 return ElidingInlineIterator(frame_iter)
2131 This frame filter is very similar to the other examples. The only
2132 difference is this frame filter is wrapping the iterator provided to
2133 it (@code{frame_iter}) with a custom iterator called
2134 @code{ElidingInlineIterator}. This again defers actions to when
2135 @value{GDBN} prints the backtrace, as the iterator is not traversed
2138 The iterator for this example is as follows. It is in this section of
2139 the example where decisions are made on the content of the backtrace.
2142 class ElidingInlineIterator:
2143 def __init__(self, ii):
2144 self.input_iterator = ii
2150 frame = next(self.input_iterator)
2152 if frame.inferior_frame().type() != gdb.INLINE_FRAME:
2156 eliding_frame = next(self.input_iterator)
2157 except StopIteration:
2159 return ElidingFrameDecorator(eliding_frame, [frame])
2162 This iterator implements the Python iterator protocol. When the
2163 @code{next} function is called (when @value{GDBN} prints each frame),
2164 the iterator checks if this frame decorator, @code{frame}, is wrapping
2165 an inlined frame. If it is not, it returns the existing frame decorator
2166 untouched. If it is wrapping an inlined frame, it assumes that the
2167 inlined frame was contained within the next oldest frame,
2168 @code{eliding_frame}, which it fetches. It then creates and returns a
2169 frame decorator, @code{ElidingFrameDecorator}, which contains both the
2170 elided frame, and the eliding frame.
2173 class ElidingInlineDecorator(FrameDecorator):
2175 def __init__(self, frame, elided_frames):
2176 super(ElidingInlineDecorator, self).__init__(frame)
2178 self.elided_frames = elided_frames
2181 return iter(self.elided_frames)
2184 This frame decorator overrides one function and returns the inlined
2185 frame in the @code{elided} method. As before it lets
2186 @code{FrameDecorator} do the rest of the work involved in printing
2187 this frame. This produces the following output.
2190 #0 0x004004e0 in bar () at inline.c:11
2191 #2 0x00400529 in main () at inline.c:25
2192 #1 0x00400529 in max (b=6, a=12) at inline.c:15
2195 In that output, @code{max} which has been inlined into @code{main} is
2196 printed hierarchically. Another approach would be to combine the
2197 @code{function} method, and the @code{elided} method to both print a
2198 marker in the inlined frame, and also show the hierarchical
2201 @node Unwinding Frames in Python
2202 @subsubsection Unwinding Frames in Python
2203 @cindex unwinding frames in Python
2205 In @value{GDBN} terminology ``unwinding'' is the process of finding
2206 the previous frame (that is, caller's) from the current one. An
2207 unwinder has three methods. The first one checks if it can handle
2208 given frame (``sniff'' it). For the frames it can sniff an unwinder
2209 provides two additional methods: it can return frame's ID, and it can
2210 fetch registers from the previous frame. A running @value{GDBN}
2211 mantains a list of the unwinders and calls each unwinder's sniffer in
2212 turn until it finds the one that recognizes the current frame. There
2213 is an API to register an unwinder.
2215 The unwinders that come with @value{GDBN} handle standard frames.
2216 However, mixed language applications (for example, an application
2217 running Java Virtual Machine) sometimes use frame layouts that cannot
2218 be handled by the @value{GDBN} unwinders. You can write Python code
2219 that can handle such custom frames.
2221 You implement a frame unwinder in Python as a class with which has two
2222 attributes, @code{name} and @code{enabled}, with obvious meanings, and
2223 a single method @code{__call__}, which examines a given frame and
2224 returns an object (an instance of @code{gdb.UnwindInfo class)}
2225 describing it. If an unwinder does not recognize a frame, it should
2226 return @code{None}. The code in @value{GDBN} that enables writing
2227 unwinders in Python uses this object to return frame's ID and previous
2228 frame registers when @value{GDBN} core asks for them.
2230 @subheading Unwinder Input
2232 An object passed to an unwinder (a @code{gdb.PendingFrame} instance)
2233 provides a method to read frame's registers:
2235 @defun PendingFrame.read_register (reg)
2236 This method returns the contents of the register @var{regn} in the
2237 frame as a @code{gdb.Value} object. @var{reg} can be either a
2238 register number or a register name; the values are platform-specific.
2239 They are usually found in the corresponding
2240 @file{@var{platform}-tdep.h} file in the @value{GDBN} source tree.
2243 It also provides a factory method to create a @code{gdb.UnwindInfo}
2244 instance to be returned to @value{GDBN}:
2246 @defun PendingFrame.create_unwind_info (frame_id)
2247 Returns a new @code{gdb.UnwindInfo} instance identified by given
2248 @var{frame_id}. The argument is used to build @value{GDBN}'s frame ID
2249 using one of functions provided by @value{GDBN}. @var{frame_id}'s attributes
2250 determine which function will be used, as follows:
2253 @item sp, pc, special
2254 @code{frame_id_build_special (@var{frame_id}.sp, @var{frame_id}.pc, @var{frame_id}.special)}
2257 @code{frame_id_build (@var{frame_id}.sp, @var{frame_id}.pc)}
2259 This is the most common case.
2262 @code{frame_id_build_wild (@var{frame_id}.sp)}
2264 The attribute values should be @code{gdb.Value}
2268 @subheading Unwinder Output: UnwindInfo
2270 Use @code{PendingFrame.create_unwind_info} method described above to
2271 create a @code{gdb.UnwindInfo} instance. Use the following method to
2272 specify caller registers that have been saved in this frame:
2274 @defun gdb.UnwindInfo.add_saved_register (reg, value)
2275 @var{reg} identifies the register. It can be a number or a name, just
2276 as for the @code{PendingFrame.read_register} method above.
2277 @var{value} is a register value (a @code{gdb.Value} object).
2280 @subheading Unwinder Skeleton Code
2282 @value{GDBN} comes with the module containing the base @code{Unwinder}
2283 class. Derive your unwinder class from it and structure the code as
2287 from gdb.unwinders import Unwinder
2289 class FrameId(object):
2290 def __init__(self, sp, pc):
2295 class MyUnwinder(Unwinder):
2297 supe(MyUnwinder, self).__init___(<expects unwinder name argument>)
2299 def __call__(pending_frame):
2300 if not <we recognize frame>:
2302 # Create UnwindInfo. Usually the frame is identified by the stack
2303 # pointer and the program counter.
2304 sp = pending_frame.read_register(<SP number>)
2305 pc = pending_frame.read_register(<PC number>)
2306 unwind_info = pending_frame.create_unwind_info(FrameId(sp, pc))
2308 # Find the values of the registers in the caller's frame and
2309 # save them in the result:
2310 unwind_info.add_saved_register(<register>, <value>)
2313 # Return the result:
2318 @subheading Registering a Unwinder
2320 An object file, a program space, and the @value{GDBN} proper can have
2321 unwinders registered with it.
2323 The @code{gdb.unwinders} module provides the function to register a
2326 @defun gdb.unwinder.register_unwinder (locus, unwinder, replace=False)
2327 @var{locus} is specifies an object file or a program space to which
2328 @var{unwinder} is added. Passing @code{None} or @code{gdb} adds
2329 @var{unwinder} to the @value{GDBN}'s global unwinder list. The newly
2330 added @var{unwinder} will be called before any other unwinder from the
2331 same locus. Two unwinders in the same locus cannot have the same
2332 name. An attempt to add a unwinder with already existing name raises
2333 an exception unless @var{replace} is @code{True}, in which case the
2334 old unwinder is deleted.
2337 @subheading Unwinder Precedence
2339 @value{GDBN} first calls the unwinders from all the object files in no
2340 particular order, then the unwinders from the current program space,
2341 and finally the unwinders from @value{GDBN}.
2343 @node Xmethods In Python
2344 @subsubsection Xmethods In Python
2345 @cindex xmethods in Python
2347 @dfn{Xmethods} are additional methods or replacements for existing
2348 methods of a C@t{++} class. This feature is useful for those cases
2349 where a method defined in C@t{++} source code could be inlined or
2350 optimized out by the compiler, making it unavailable to @value{GDBN}.
2351 For such cases, one can define an xmethod to serve as a replacement
2352 for the method defined in the C@t{++} source code. @value{GDBN} will
2353 then invoke the xmethod, instead of the C@t{++} method, to
2354 evaluate expressions. One can also use xmethods when debugging
2355 with core files. Moreover, when debugging live programs, invoking an
2356 xmethod need not involve running the inferior (which can potentially
2357 perturb its state). Hence, even if the C@t{++} method is available, it
2358 is better to use its replacement xmethod if one is defined.
2360 The xmethods feature in Python is available via the concepts of an
2361 @dfn{xmethod matcher} and an @dfn{xmethod worker}. To
2362 implement an xmethod, one has to implement a matcher and a
2363 corresponding worker for it (more than one worker can be
2364 implemented, each catering to a different overloaded instance of the
2365 method). Internally, @value{GDBN} invokes the @code{match} method of a
2366 matcher to match the class type and method name. On a match, the
2367 @code{match} method returns a list of matching @emph{worker} objects.
2368 Each worker object typically corresponds to an overloaded instance of
2369 the xmethod. They implement a @code{get_arg_types} method which
2370 returns a sequence of types corresponding to the arguments the xmethod
2371 requires. @value{GDBN} uses this sequence of types to perform
2372 overload resolution and picks a winning xmethod worker. A winner
2373 is also selected from among the methods @value{GDBN} finds in the
2374 C@t{++} source code. Next, the winning xmethod worker and the
2375 winning C@t{++} method are compared to select an overall winner. In
2376 case of a tie between a xmethod worker and a C@t{++} method, the
2377 xmethod worker is selected as the winner. That is, if a winning
2378 xmethod worker is found to be equivalent to the winning C@t{++}
2379 method, then the xmethod worker is treated as a replacement for
2380 the C@t{++} method. @value{GDBN} uses the overall winner to invoke the
2381 method. If the winning xmethod worker is the overall winner, then
2382 the corresponding xmethod is invoked via the @code{__call__} method
2383 of the worker object.
2385 If one wants to implement an xmethod as a replacement for an
2386 existing C@t{++} method, then they have to implement an equivalent
2387 xmethod which has exactly the same name and takes arguments of
2388 exactly the same type as the C@t{++} method. If the user wants to
2389 invoke the C@t{++} method even though a replacement xmethod is
2390 available for that method, then they can disable the xmethod.
2392 @xref{Xmethod API}, for API to implement xmethods in Python.
2393 @xref{Writing an Xmethod}, for implementing xmethods in Python.
2396 @subsubsection Xmethod API
2399 The @value{GDBN} Python API provides classes, interfaces and functions
2400 to implement, register and manipulate xmethods.
2401 @xref{Xmethods In Python}.
2403 An xmethod matcher should be an instance of a class derived from
2404 @code{XMethodMatcher} defined in the module @code{gdb.xmethod}, or an
2405 object with similar interface and attributes. An instance of
2406 @code{XMethodMatcher} has the following attributes:
2409 The name of the matcher.
2413 A boolean value indicating whether the matcher is enabled or disabled.
2417 A list of named methods managed by the matcher. Each object in the list
2418 is an instance of the class @code{XMethod} defined in the module
2419 @code{gdb.xmethod}, or any object with the following attributes:
2424 Name of the xmethod which should be unique for each xmethod
2425 managed by the matcher.
2428 A boolean value indicating whether the xmethod is enabled or
2433 The class @code{XMethod} is a convenience class with same
2434 attributes as above along with the following constructor:
2436 @defun XMethod.__init__ (self, name)
2437 Constructs an enabled xmethod with name @var{name}.
2442 The @code{XMethodMatcher} class has the following methods:
2444 @defun XMethodMatcher.__init__ (self, name)
2445 Constructs an enabled xmethod matcher with name @var{name}. The
2446 @code{methods} attribute is initialized to @code{None}.
2449 @defun XMethodMatcher.match (self, class_type, method_name)
2450 Derived classes should override this method. It should return a
2451 xmethod worker object (or a sequence of xmethod worker
2452 objects) matching the @var{class_type} and @var{method_name}.
2453 @var{class_type} is a @code{gdb.Type} object, and @var{method_name}
2454 is a string value. If the matcher manages named methods as listed in
2455 its @code{methods} attribute, then only those worker objects whose
2456 corresponding entries in the @code{methods} list are enabled should be
2460 An xmethod worker should be an instance of a class derived from
2461 @code{XMethodWorker} defined in the module @code{gdb.xmethod},
2462 or support the following interface:
2464 @defun XMethodWorker.get_arg_types (self)
2465 This method returns a sequence of @code{gdb.Type} objects corresponding
2466 to the arguments that the xmethod takes. It can return an empty
2467 sequence or @code{None} if the xmethod does not take any arguments.
2468 If the xmethod takes a single argument, then a single
2469 @code{gdb.Type} object corresponding to it can be returned.
2472 @defun XMethodWorker.get_result_type (self, *args)
2473 This method returns a @code{gdb.Type} object representing the type
2474 of the result of invoking this xmethod.
2475 The @var{args} argument is the same tuple of arguments that would be
2476 passed to the @code{__call__} method of this worker.
2479 @defun XMethodWorker.__call__ (self, *args)
2480 This is the method which does the @emph{work} of the xmethod. The
2481 @var{args} arguments is the tuple of arguments to the xmethod. Each
2482 element in this tuple is a gdb.Value object. The first element is
2483 always the @code{this} pointer value.
2486 For @value{GDBN} to lookup xmethods, the xmethod matchers
2487 should be registered using the following function defined in the module
2490 @defun register_xmethod_matcher (locus, matcher, replace=False)
2491 The @code{matcher} is registered with @code{locus}, replacing an
2492 existing matcher with the same name as @code{matcher} if
2493 @code{replace} is @code{True}. @code{locus} can be a
2494 @code{gdb.Objfile} object (@pxref{Objfiles In Python}), or a
2495 @code{gdb.Progspace} object (@pxref{Progspaces In Python}), or
2496 @code{None}. If it is @code{None}, then @code{matcher} is registered
2500 @node Writing an Xmethod
2501 @subsubsection Writing an Xmethod
2502 @cindex writing xmethods in Python
2504 Implementing xmethods in Python will require implementing xmethod
2505 matchers and xmethod workers (@pxref{Xmethods In Python}). Consider
2506 the following C@t{++} class:
2512 MyClass (int a) : a_(a) @{ @}
2514 int geta (void) @{ return a_; @}
2515 int operator+ (int b);
2522 MyClass::operator+ (int b)
2529 Let us define two xmethods for the class @code{MyClass}, one
2530 replacing the method @code{geta}, and another adding an overloaded
2531 flavor of @code{operator+} which takes a @code{MyClass} argument (the
2532 C@t{++} code above already has an overloaded @code{operator+}
2533 which takes an @code{int} argument). The xmethod matcher can be
2537 class MyClass_geta(gdb.xmethod.XMethod):
2539 gdb.xmethod.XMethod.__init__(self, 'geta')
2541 def get_worker(self, method_name):
2542 if method_name == 'geta':
2543 return MyClassWorker_geta()
2546 class MyClass_sum(gdb.xmethod.XMethod):
2548 gdb.xmethod.XMethod.__init__(self, 'sum')
2550 def get_worker(self, method_name):
2551 if method_name == 'operator+':
2552 return MyClassWorker_plus()
2555 class MyClassMatcher(gdb.xmethod.XMethodMatcher):
2557 gdb.xmethod.XMethodMatcher.__init__(self, 'MyClassMatcher')
2558 # List of methods 'managed' by this matcher
2559 self.methods = [MyClass_geta(), MyClass_sum()]
2561 def match(self, class_type, method_name):
2562 if class_type.tag != 'MyClass':
2565 for method in self.methods:
2567 worker = method.get_worker(method_name)
2569 workers.append(worker)
2575 Notice that the @code{match} method of @code{MyClassMatcher} returns
2576 a worker object of type @code{MyClassWorker_geta} for the @code{geta}
2577 method, and a worker object of type @code{MyClassWorker_plus} for the
2578 @code{operator+} method. This is done indirectly via helper classes
2579 derived from @code{gdb.xmethod.XMethod}. One does not need to use the
2580 @code{methods} attribute in a matcher as it is optional. However, if a
2581 matcher manages more than one xmethod, it is a good practice to list the
2582 xmethods in the @code{methods} attribute of the matcher. This will then
2583 facilitate enabling and disabling individual xmethods via the
2584 @code{enable/disable} commands. Notice also that a worker object is
2585 returned only if the corresponding entry in the @code{methods} attribute
2586 of the matcher is enabled.
2588 The implementation of the worker classes returned by the matcher setup
2589 above is as follows:
2592 class MyClassWorker_geta(gdb.xmethod.XMethodWorker):
2593 def get_arg_types(self):
2596 def get_result_type(self, obj):
2597 return gdb.lookup_type('int')
2599 def __call__(self, obj):
2603 class MyClassWorker_plus(gdb.xmethod.XMethodWorker):
2604 def get_arg_types(self):
2605 return gdb.lookup_type('MyClass')
2607 def get_result_type(self, obj):
2608 return gdb.lookup_type('int')
2610 def __call__(self, obj, other):
2611 return obj['a_'] + other['a_']
2614 For @value{GDBN} to actually lookup a xmethod, it has to be
2615 registered with it. The matcher defined above is registered with
2616 @value{GDBN} globally as follows:
2619 gdb.xmethod.register_xmethod_matcher(None, MyClassMatcher())
2622 If an object @code{obj} of type @code{MyClass} is initialized in C@t{++}
2630 then, after loading the Python script defining the xmethod matchers
2631 and workers into @code{GDBN}, invoking the method @code{geta} or using
2632 the operator @code{+} on @code{obj} will invoke the xmethods
2643 Consider another example with a C++ template class:
2650 MyTemplate () : dsize_(10), data_ (new T [10]) @{ @}
2651 ~MyTemplate () @{ delete [] data_; @}
2653 int footprint (void)
2655 return sizeof (T) * dsize_ + sizeof (MyTemplate<T>);
2664 Let us implement an xmethod for the above class which serves as a
2665 replacement for the @code{footprint} method. The full code listing
2666 of the xmethod workers and xmethod matchers is as follows:
2669 class MyTemplateWorker_footprint(gdb.xmethod.XMethodWorker):
2670 def __init__(self, class_type):
2671 self.class_type = class_type
2673 def get_arg_types(self):
2676 def get_result_type(self):
2677 return gdb.lookup_type('int')
2679 def __call__(self, obj):
2680 return (self.class_type.sizeof +
2682 self.class_type.template_argument(0).sizeof)
2685 class MyTemplateMatcher_footprint(gdb.xmethod.XMethodMatcher):
2687 gdb.xmethod.XMethodMatcher.__init__(self, 'MyTemplateMatcher')
2689 def match(self, class_type, method_name):
2690 if (re.match('MyTemplate<[ \t\n]*[_a-zA-Z][ _a-zA-Z0-9]*>',
2692 method_name == 'footprint'):
2693 return MyTemplateWorker_footprint(class_type)
2696 Notice that, in this example, we have not used the @code{methods}
2697 attribute of the matcher as the matcher manages only one xmethod. The
2698 user can enable/disable this xmethod by enabling/disabling the matcher
2701 @node Inferiors In Python
2702 @subsubsection Inferiors In Python
2703 @cindex inferiors in Python
2705 @findex gdb.Inferior
2706 Programs which are being run under @value{GDBN} are called inferiors
2707 (@pxref{Inferiors and Programs}). Python scripts can access
2708 information about and manipulate inferiors controlled by @value{GDBN}
2709 via objects of the @code{gdb.Inferior} class.
2711 The following inferior-related functions are available in the @code{gdb}
2714 @defun gdb.inferiors ()
2715 Return a tuple containing all inferior objects.
2718 @defun gdb.selected_inferior ()
2719 Return an object representing the current inferior.
2722 A @code{gdb.Inferior} object has the following attributes:
2724 @defvar Inferior.num
2725 ID of inferior, as assigned by GDB.
2728 @defvar Inferior.pid
2729 Process ID of the inferior, as assigned by the underlying operating
2733 @defvar Inferior.was_attached
2734 Boolean signaling whether the inferior was created using `attach', or
2735 started by @value{GDBN} itself.
2738 A @code{gdb.Inferior} object has the following methods:
2740 @defun Inferior.is_valid ()
2741 Returns @code{True} if the @code{gdb.Inferior} object is valid,
2742 @code{False} if not. A @code{gdb.Inferior} object will become invalid
2743 if the inferior no longer exists within @value{GDBN}. All other
2744 @code{gdb.Inferior} methods will throw an exception if it is invalid
2745 at the time the method is called.
2748 @defun Inferior.threads ()
2749 This method returns a tuple holding all the threads which are valid
2750 when it is called. If there are no valid threads, the method will
2751 return an empty tuple.
2754 @findex Inferior.read_memory
2755 @defun Inferior.read_memory (address, length)
2756 Read @var{length} addressable memory units from the inferior, starting at
2757 @var{address}. Returns a buffer object, which behaves much like an array
2758 or a string. It can be modified and given to the
2759 @code{Inferior.write_memory} function. In @code{Python} 3, the return
2760 value is a @code{memoryview} object.
2763 @findex Inferior.write_memory
2764 @defun Inferior.write_memory (address, buffer @r{[}, length@r{]})
2765 Write the contents of @var{buffer} to the inferior, starting at
2766 @var{address}. The @var{buffer} parameter must be a Python object
2767 which supports the buffer protocol, i.e., a string, an array or the
2768 object returned from @code{Inferior.read_memory}. If given, @var{length}
2769 determines the number of addressable memory units from @var{buffer} to be
2773 @findex gdb.search_memory
2774 @defun Inferior.search_memory (address, length, pattern)
2775 Search a region of the inferior memory starting at @var{address} with
2776 the given @var{length} using the search pattern supplied in
2777 @var{pattern}. The @var{pattern} parameter must be a Python object
2778 which supports the buffer protocol, i.e., a string, an array or the
2779 object returned from @code{gdb.read_memory}. Returns a Python @code{Long}
2780 containing the address where the pattern was found, or @code{None} if
2781 the pattern could not be found.
2784 @node Events In Python
2785 @subsubsection Events In Python
2786 @cindex inferior events in Python
2788 @value{GDBN} provides a general event facility so that Python code can be
2789 notified of various state changes, particularly changes that occur in
2792 An @dfn{event} is just an object that describes some state change. The
2793 type of the object and its attributes will vary depending on the details
2794 of the change. All the existing events are described below.
2796 In order to be notified of an event, you must register an event handler
2797 with an @dfn{event registry}. An event registry is an object in the
2798 @code{gdb.events} module which dispatches particular events. A registry
2799 provides methods to register and unregister event handlers:
2801 @defun EventRegistry.connect (object)
2802 Add the given callable @var{object} to the registry. This object will be
2803 called when an event corresponding to this registry occurs.
2806 @defun EventRegistry.disconnect (object)
2807 Remove the given @var{object} from the registry. Once removed, the object
2808 will no longer receive notifications of events.
2814 def exit_handler (event):
2815 print "event type: exit"
2816 print "exit code: %d" % (event.exit_code)
2818 gdb.events.exited.connect (exit_handler)
2821 In the above example we connect our handler @code{exit_handler} to the
2822 registry @code{events.exited}. Once connected, @code{exit_handler} gets
2823 called when the inferior exits. The argument @dfn{event} in this example is
2824 of type @code{gdb.ExitedEvent}. As you can see in the example the
2825 @code{ExitedEvent} object has an attribute which indicates the exit code of
2828 The following is a listing of the event registries that are available and
2829 details of the events they emit:
2834 Emits @code{gdb.ThreadEvent}.
2836 Some events can be thread specific when @value{GDBN} is running in non-stop
2837 mode. When represented in Python, these events all extend
2838 @code{gdb.ThreadEvent}. Note, this event is not emitted directly; instead,
2839 events which are emitted by this or other modules might extend this event.
2840 Examples of these events are @code{gdb.BreakpointEvent} and
2841 @code{gdb.ContinueEvent}.
2843 @defvar ThreadEvent.inferior_thread
2844 In non-stop mode this attribute will be set to the specific thread which was
2845 involved in the emitted event. Otherwise, it will be set to @code{None}.
2848 Emits @code{gdb.ContinueEvent} which extends @code{gdb.ThreadEvent}.
2850 This event indicates that the inferior has been continued after a stop. For
2851 inherited attribute refer to @code{gdb.ThreadEvent} above.
2854 Emits @code{events.ExitedEvent} which indicates that the inferior has exited.
2855 @code{events.ExitedEvent} has two attributes:
2856 @defvar ExitedEvent.exit_code
2857 An integer representing the exit code, if available, which the inferior
2858 has returned. (The exit code could be unavailable if, for example,
2859 @value{GDBN} detaches from the inferior.) If the exit code is unavailable,
2860 the attribute does not exist.
2862 @defvar ExitedEvent.inferior
2863 A reference to the inferior which triggered the @code{exited} event.
2867 Emits @code{gdb.StopEvent} which extends @code{gdb.ThreadEvent}.
2869 Indicates that the inferior has stopped. All events emitted by this registry
2870 extend StopEvent. As a child of @code{gdb.ThreadEvent}, @code{gdb.StopEvent}
2871 will indicate the stopped thread when @value{GDBN} is running in non-stop
2872 mode. Refer to @code{gdb.ThreadEvent} above for more details.
2874 Emits @code{gdb.SignalEvent} which extends @code{gdb.StopEvent}.
2876 This event indicates that the inferior or one of its threads has received as
2877 signal. @code{gdb.SignalEvent} has the following attributes:
2879 @defvar SignalEvent.stop_signal
2880 A string representing the signal received by the inferior. A list of possible
2881 signal values can be obtained by running the command @code{info signals} in
2882 the @value{GDBN} command prompt.
2885 Also emits @code{gdb.BreakpointEvent} which extends @code{gdb.StopEvent}.
2887 @code{gdb.BreakpointEvent} event indicates that one or more breakpoints have
2888 been hit, and has the following attributes:
2890 @defvar BreakpointEvent.breakpoints
2891 A sequence containing references to all the breakpoints (type
2892 @code{gdb.Breakpoint}) that were hit.
2893 @xref{Breakpoints In Python}, for details of the @code{gdb.Breakpoint} object.
2895 @defvar BreakpointEvent.breakpoint
2896 A reference to the first breakpoint that was hit.
2897 This function is maintained for backward compatibility and is now deprecated
2898 in favor of the @code{gdb.BreakpointEvent.breakpoints} attribute.
2901 @item events.new_objfile
2902 Emits @code{gdb.NewObjFileEvent} which indicates that a new object file has
2903 been loaded by @value{GDBN}. @code{gdb.NewObjFileEvent} has one attribute:
2905 @defvar NewObjFileEvent.new_objfile
2906 A reference to the object file (@code{gdb.Objfile}) which has been loaded.
2907 @xref{Objfiles In Python}, for details of the @code{gdb.Objfile} object.
2910 @item events.clear_objfiles
2911 Emits @code{gdb.ClearObjFilesEvent} which indicates that the list of object
2912 files for a program space has been reset.
2913 @code{gdb.ClearObjFilesEvent} has one attribute:
2915 @defvar ClearObjFilesEvent.progspace
2916 A reference to the program space (@code{gdb.Progspace}) whose objfile list has
2917 been cleared. @xref{Progspaces In Python}.
2920 @item events.inferior_call_pre
2921 Emits @code{gdb.InferiorCallPreEvent} which indicates that a function in
2922 the inferior is about to be called.
2924 @defvar InferiorCallPreEvent.ptid
2925 The thread in which the call will be run.
2928 @defvar InferiorCallPreEvent.address
2929 The location of the function to be called.
2932 @item events.inferior_call_post
2933 Emits @code{gdb.InferiorCallPostEvent} which indicates that a function in
2934 the inferior has returned.
2936 @defvar InferiorCallPostEvent.ptid
2937 The thread in which the call was run.
2940 @defvar InferiorCallPostEvent.address
2941 The location of the function that was called.
2944 @item events.memory_changed
2945 Emits @code{gdb.MemoryChangedEvent} which indicates that the memory of the
2946 inferior has been modified by the @value{GDBN} user, for instance via a
2947 command like @w{@code{set *addr = value}}. The event has the following
2950 @defvar MemoryChangedEvent.address
2951 The start address of the changed region.
2954 @defvar MemoryChangedEvent.length
2955 Length in bytes of the changed region.
2958 @item events.register_changed
2959 Emits @code{gdb.RegisterChangedEvent} which indicates that a register in the
2960 inferior has been modified by the @value{GDBN} user.
2962 @defvar RegisterChangedEvent.frame
2963 A gdb.Frame object representing the frame in which the register was modified.
2965 @defvar RegisterChangedEvent.regnum
2966 Denotes which register was modified.
2969 @item events.breakpoint_created
2970 This is emitted when a new breakpoint has been created. The argument
2971 that is passed is the new @code{gdb.Breakpoint} object.
2973 @item events.breakpoint_modified
2974 This is emitted when a breakpoint has been modified in some way. The
2975 argument that is passed is the new @code{gdb.Breakpoint} object.
2977 @item events.breakpoint_deleted
2978 This is emitted when a breakpoint has been deleted. The argument that
2979 is passed is the @code{gdb.Breakpoint} object. When this event is
2980 emitted, the @code{gdb.Breakpoint} object will already be in its
2981 invalid state; that is, the @code{is_valid} method will return
2986 @node Threads In Python
2987 @subsubsection Threads In Python
2988 @cindex threads in python
2990 @findex gdb.InferiorThread
2991 Python scripts can access information about, and manipulate inferior threads
2992 controlled by @value{GDBN}, via objects of the @code{gdb.InferiorThread} class.
2994 The following thread-related functions are available in the @code{gdb}
2997 @findex gdb.selected_thread
2998 @defun gdb.selected_thread ()
2999 This function returns the thread object for the selected thread. If there
3000 is no selected thread, this will return @code{None}.
3003 A @code{gdb.InferiorThread} object has the following attributes:
3005 @defvar InferiorThread.name
3006 The name of the thread. If the user specified a name using
3007 @code{thread name}, then this returns that name. Otherwise, if an
3008 OS-supplied name is available, then it is returned. Otherwise, this
3009 returns @code{None}.
3011 This attribute can be assigned to. The new value must be a string
3012 object, which sets the new name, or @code{None}, which removes any
3013 user-specified thread name.
3016 @defvar InferiorThread.num
3017 The per-inferior number of the thread, as assigned by GDB.
3020 @defvar InferiorThread.global_num
3021 The global ID of the thread, as assigned by GDB. You can use this to
3022 make Python breakpoints thread-specific, for example
3023 (@pxref{python_breakpoint_thread,,The Breakpoint.thread attribute}).
3026 @defvar InferiorThread.ptid
3027 ID of the thread, as assigned by the operating system. This attribute is a
3028 tuple containing three integers. The first is the Process ID (PID); the second
3029 is the Lightweight Process ID (LWPID), and the third is the Thread ID (TID).
3030 Either the LWPID or TID may be 0, which indicates that the operating system
3031 does not use that identifier.
3034 @defvar InferiorThread.inferior
3035 The inferior this thread belongs to. This attribute is represented as
3036 a @code{gdb.Inferior} object. This attribute is not writable.
3039 A @code{gdb.InferiorThread} object has the following methods:
3041 @defun InferiorThread.is_valid ()
3042 Returns @code{True} if the @code{gdb.InferiorThread} object is valid,
3043 @code{False} if not. A @code{gdb.InferiorThread} object will become
3044 invalid if the thread exits, or the inferior that the thread belongs
3045 is deleted. All other @code{gdb.InferiorThread} methods will throw an
3046 exception if it is invalid at the time the method is called.
3049 @defun InferiorThread.switch ()
3050 This changes @value{GDBN}'s currently selected thread to the one represented
3054 @defun InferiorThread.is_stopped ()
3055 Return a Boolean indicating whether the thread is stopped.
3058 @defun InferiorThread.is_running ()
3059 Return a Boolean indicating whether the thread is running.
3062 @defun InferiorThread.is_exited ()
3063 Return a Boolean indicating whether the thread is exited.
3066 @node Recordings In Python
3067 @subsubsection Recordings In Python
3068 @cindex recordings in python
3070 The following recordings-related functions
3071 (@pxref{Process Record and Replay}) are available in the @code{gdb}
3074 @defun gdb.start_recording (@r{[}method@r{]}, @r{[}format@r{]})
3075 Start a recording using the given @var{method} and @var{format}. If
3076 no @var{format} is given, the default format for the recording method
3077 is used. If no @var{method} is given, the default method will be used.
3078 Returns a @code{gdb.Record} object on success. Throw an exception on
3081 The following strings can be passed as @var{method}:
3087 @code{"btrace"}: Possible values for @var{format}: @code{"pt"},
3088 @code{"bts"} or leave out for default format.
3092 @defun gdb.current_recording ()
3093 Access a currently running recording. Return a @code{gdb.Record}
3094 object on success. Return @code{None} if no recording is currently
3098 @defun gdb.stop_recording ()
3099 Stop the current recording. Throw an exception if no recording is
3100 currently active. All record objects become invalid after this call.
3103 A @code{gdb.Record} object has the following attributes:
3106 ID of the thread associated with this object as a tuple of three integers. The
3107 first is the Process ID (PID); the second is the Lightweight Process ID (LWPID),
3108 and the third is the Thread ID (TID). Either the LWPID or TID may be 0, which
3109 indicates that the operating system does not use that identifier.
3112 @defvar Record.method
3113 A string with the current recording method, e.g.@: @code{full} or
3117 @defvar Record.format
3118 A string with the current recording format, e.g.@: @code{bt}, @code{pts} or
3122 @defvar Record.begin
3123 A method specific instruction object representing the first instruction
3128 A method specific instruction object representing the current
3129 instruction, that is not actually part of the recording.
3132 @defvar Record.replay_position
3133 The instruction representing the current replay position. If there is
3134 no replay active, this will be @code{None}.
3137 @defvar Record.instruction_history
3138 A list with all recorded instructions.
3141 @defvar Record.function_call_history
3142 A list with all recorded function call segments.
3145 A @code{gdb.Record} object has the following methods:
3147 @defun Record.goto (instruction)
3148 Move the replay position to the given @var{instruction}.
3151 The attributes and methods of instruction objects depend on the current
3152 recording method. Currently, only btrace instructions are supported.
3154 A @code{gdb.BtraceInstruction} object has the following attributes:
3156 @defvar BtraceInstruction.number
3157 An integer identifying this instruction. @var{number} corresponds to
3158 the numbers seen in @code{record instruction-history}
3159 (@pxref{Process Record and Replay}).
3162 @defvar BtraceInstruction.error
3163 An integer identifying the error code for gaps in the history.
3164 @code{None} for regular instructions.
3167 @defvar BtraceInstruction.sal
3168 A @code{gdb.Symtab_and_line} object representing the associated symtab
3169 and line of this instruction. May be @code{None} if the instruction
3173 @defvar BtraceInstruction.pc
3174 An integer representing this instruction's address. May be @code{None}
3175 if the instruction is a gap or the debug symbols could not be read.
3178 @defvar BtraceInstruction.data
3179 A buffer with the raw instruction data. May be @code{None} if the
3180 instruction is a gap.
3183 @defvar BtraceInstruction.decoded
3184 A human readable string with the disassembled instruction. Contains the
3185 error message for gaps.
3188 @defvar BtraceInstruction.size
3189 The size of the instruction in bytes. Will be @code{None} if the
3190 instruction is a gap.
3193 @defvar BtraceInstruction.is_speculative
3194 A boolean indicating whether the instruction was executed
3195 speculatively. Will be @code{None} for gaps.
3198 The attributes and methods of function call objects depend on the
3199 current recording format. Currently, only btrace function calls are
3202 A @code{gdb.BtraceFunctionCall} object has the following attributes:
3204 @defvar BtraceFunctionCall.number
3205 An integer identifying this function call. @var{number} corresponds to
3206 the numbers seen in @code{record function-call-history}
3207 (@pxref{Process Record and Replay}).
3210 @defvar BtraceFunctionCall.symbol
3211 A @code{gdb.Symbol} object representing the associated symbol. May be
3212 @code{None} if the function call is a gap or the debug symbols could
3216 @defvar BtraceFunctionCall.level
3217 An integer representing the function call's stack level. May be
3218 @code{None} if the function call is a gap.
3221 @defvar BtraceFunctionCall.instructions
3222 A list of @code{gdb.BtraceInstruction} objects associated with this function
3226 @defvar BtraceFunctionCall.up
3227 A @code{gdb.BtraceFunctionCall} object representing the caller's
3228 function segment. If the call has not been recorded, this will be the
3229 function segment to which control returns. If neither the call nor the
3230 return have been recorded, this will be @code{None}.
3233 @defvar BtraceFunctionCall.prev_sibling
3234 A @code{gdb.BtraceFunctionCall} object representing the previous
3235 segment of this function call. May be @code{None}.
3238 @defvar BtraceFunctionCall.next_sibling
3239 A @code{gdb.BtraceFunctionCall} object representing the next segment of
3240 this function call. May be @code{None}.
3243 The following example demonstrates the usage of these objects and
3244 functions to create a function that will rewind a record to the last
3245 time a function in a different file was executed. This would typically
3246 be used to track the execution of user provided callback functions in a
3247 library which typically are not visible in a back trace.
3251 rec = gdb.current_recording ()
3255 insn = rec.instruction_history
3260 position = insn.index (rec.replay_position)
3264 filename = insn[position].sal.symtab.fullname ()
3268 for i in reversed (insn[:position]):
3270 current = i.sal.symtab.fullname ()
3274 if filename == current:
3281 Another possible application is to write a function that counts the
3282 number of code executions in a given line range. This line range can
3283 contain parts of functions or span across several functions and is not
3284 limited to be contiguous.
3287 def countrange (filename, linerange):
3290 def filter_only (file_name):
3291 for call in gdb.current_recording ().function_call_history:
3293 if file_name in call.symbol.symtab.fullname ():
3298 for c in filter_only (filename):
3299 for i in c.instructions:
3301 if i.sal.line in linerange:
3310 @node Commands In Python
3311 @subsubsection Commands In Python
3313 @cindex commands in python
3314 @cindex python commands
3315 You can implement new @value{GDBN} CLI commands in Python. A CLI
3316 command is implemented using an instance of the @code{gdb.Command}
3317 class, most commonly using a subclass.
3319 @defun Command.__init__ (name, @var{command_class} @r{[}, @var{completer_class} @r{[}, @var{prefix}@r{]]})
3320 The object initializer for @code{Command} registers the new command
3321 with @value{GDBN}. This initializer is normally invoked from the
3322 subclass' own @code{__init__} method.
3324 @var{name} is the name of the command. If @var{name} consists of
3325 multiple words, then the initial words are looked for as prefix
3326 commands. In this case, if one of the prefix commands does not exist,
3327 an exception is raised.
3329 There is no support for multi-line commands.
3331 @var{command_class} should be one of the @samp{COMMAND_} constants
3332 defined below. This argument tells @value{GDBN} how to categorize the
3333 new command in the help system.
3335 @var{completer_class} is an optional argument. If given, it should be
3336 one of the @samp{COMPLETE_} constants defined below. This argument
3337 tells @value{GDBN} how to perform completion for this command. If not
3338 given, @value{GDBN} will attempt to complete using the object's
3339 @code{complete} method (see below); if no such method is found, an
3340 error will occur when completion is attempted.
3342 @var{prefix} is an optional argument. If @code{True}, then the new
3343 command is a prefix command; sub-commands of this command may be
3346 The help text for the new command is taken from the Python
3347 documentation string for the command's class, if there is one. If no
3348 documentation string is provided, the default value ``This command is
3349 not documented.'' is used.
3352 @cindex don't repeat Python command
3353 @defun Command.dont_repeat ()
3354 By default, a @value{GDBN} command is repeated when the user enters a
3355 blank line at the command prompt. A command can suppress this
3356 behavior by invoking the @code{dont_repeat} method. This is similar
3357 to the user command @code{dont-repeat}, see @ref{Define, dont-repeat}.
3360 @defun Command.invoke (argument, from_tty)
3361 This method is called by @value{GDBN} when this command is invoked.
3363 @var{argument} is a string. It is the argument to the command, after
3364 leading and trailing whitespace has been stripped.
3366 @var{from_tty} is a boolean argument. When true, this means that the
3367 command was entered by the user at the terminal; when false it means
3368 that the command came from elsewhere.
3370 If this method throws an exception, it is turned into a @value{GDBN}
3371 @code{error} call. Otherwise, the return value is ignored.
3373 @findex gdb.string_to_argv
3374 To break @var{argument} up into an argv-like string use
3375 @code{gdb.string_to_argv}. This function behaves identically to
3376 @value{GDBN}'s internal argument lexer @code{buildargv}.
3377 It is recommended to use this for consistency.
3378 Arguments are separated by spaces and may be quoted.
3382 print gdb.string_to_argv ("1 2\ \\\"3 '4 \"5' \"6 '7\"")
3383 ['1', '2 "3', '4 "5', "6 '7"]
3388 @cindex completion of Python commands
3389 @defun Command.complete (text, word)
3390 This method is called by @value{GDBN} when the user attempts
3391 completion on this command. All forms of completion are handled by
3392 this method, that is, the @key{TAB} and @key{M-?} key bindings
3393 (@pxref{Completion}), and the @code{complete} command (@pxref{Help,
3396 The arguments @var{text} and @var{word} are both strings; @var{text}
3397 holds the complete command line up to the cursor's location, while
3398 @var{word} holds the last word of the command line; this is computed
3399 using a word-breaking heuristic.
3401 The @code{complete} method can return several values:
3404 If the return value is a sequence, the contents of the sequence are
3405 used as the completions. It is up to @code{complete} to ensure that the
3406 contents actually do complete the word. A zero-length sequence is
3407 allowed, it means that there were no completions available. Only
3408 string elements of the sequence are used; other elements in the
3409 sequence are ignored.
3412 If the return value is one of the @samp{COMPLETE_} constants defined
3413 below, then the corresponding @value{GDBN}-internal completion
3414 function is invoked, and its result is used.
3417 All other results are treated as though there were no available
3422 When a new command is registered, it must be declared as a member of
3423 some general class of commands. This is used to classify top-level
3424 commands in the on-line help system; note that prefix commands are not
3425 listed under their own category but rather that of their top-level
3426 command. The available classifications are represented by constants
3427 defined in the @code{gdb} module:
3430 @findex COMMAND_NONE
3431 @findex gdb.COMMAND_NONE
3432 @item gdb.COMMAND_NONE
3433 The command does not belong to any particular class. A command in
3434 this category will not be displayed in any of the help categories.
3436 @findex COMMAND_RUNNING
3437 @findex gdb.COMMAND_RUNNING
3438 @item gdb.COMMAND_RUNNING
3439 The command is related to running the inferior. For example,
3440 @code{start}, @code{step}, and @code{continue} are in this category.
3441 Type @kbd{help running} at the @value{GDBN} prompt to see a list of
3442 commands in this category.
3444 @findex COMMAND_DATA
3445 @findex gdb.COMMAND_DATA
3446 @item gdb.COMMAND_DATA
3447 The command is related to data or variables. For example,
3448 @code{call}, @code{find}, and @code{print} are in this category. Type
3449 @kbd{help data} at the @value{GDBN} prompt to see a list of commands
3452 @findex COMMAND_STACK
3453 @findex gdb.COMMAND_STACK
3454 @item gdb.COMMAND_STACK
3455 The command has to do with manipulation of the stack. For example,
3456 @code{backtrace}, @code{frame}, and @code{return} are in this
3457 category. Type @kbd{help stack} at the @value{GDBN} prompt to see a
3458 list of commands in this category.
3460 @findex COMMAND_FILES
3461 @findex gdb.COMMAND_FILES
3462 @item gdb.COMMAND_FILES
3463 This class is used for file-related commands. For example,
3464 @code{file}, @code{list} and @code{section} are in this category.
3465 Type @kbd{help files} at the @value{GDBN} prompt to see a list of
3466 commands in this category.
3468 @findex COMMAND_SUPPORT
3469 @findex gdb.COMMAND_SUPPORT
3470 @item gdb.COMMAND_SUPPORT
3471 This should be used for ``support facilities'', generally meaning
3472 things that are useful to the user when interacting with @value{GDBN},
3473 but not related to the state of the inferior. For example,
3474 @code{help}, @code{make}, and @code{shell} are in this category. Type
3475 @kbd{help support} at the @value{GDBN} prompt to see a list of
3476 commands in this category.
3478 @findex COMMAND_STATUS
3479 @findex gdb.COMMAND_STATUS
3480 @item gdb.COMMAND_STATUS
3481 The command is an @samp{info}-related command, that is, related to the
3482 state of @value{GDBN} itself. For example, @code{info}, @code{macro},
3483 and @code{show} are in this category. Type @kbd{help status} at the
3484 @value{GDBN} prompt to see a list of commands in this category.
3486 @findex COMMAND_BREAKPOINTS
3487 @findex gdb.COMMAND_BREAKPOINTS
3488 @item gdb.COMMAND_BREAKPOINTS
3489 The command has to do with breakpoints. For example, @code{break},
3490 @code{clear}, and @code{delete} are in this category. Type @kbd{help
3491 breakpoints} at the @value{GDBN} prompt to see a list of commands in
3494 @findex COMMAND_TRACEPOINTS
3495 @findex gdb.COMMAND_TRACEPOINTS
3496 @item gdb.COMMAND_TRACEPOINTS
3497 The command has to do with tracepoints. For example, @code{trace},
3498 @code{actions}, and @code{tfind} are in this category. Type
3499 @kbd{help tracepoints} at the @value{GDBN} prompt to see a list of
3500 commands in this category.
3502 @findex COMMAND_USER
3503 @findex gdb.COMMAND_USER
3504 @item gdb.COMMAND_USER
3505 The command is a general purpose command for the user, and typically
3506 does not fit in one of the other categories.
3507 Type @kbd{help user-defined} at the @value{GDBN} prompt to see
3508 a list of commands in this category, as well as the list of gdb macros
3509 (@pxref{Sequences}).
3511 @findex COMMAND_OBSCURE
3512 @findex gdb.COMMAND_OBSCURE
3513 @item gdb.COMMAND_OBSCURE
3514 The command is only used in unusual circumstances, or is not of
3515 general interest to users. For example, @code{checkpoint},
3516 @code{fork}, and @code{stop} are in this category. Type @kbd{help
3517 obscure} at the @value{GDBN} prompt to see a list of commands in this
3520 @findex COMMAND_MAINTENANCE
3521 @findex gdb.COMMAND_MAINTENANCE
3522 @item gdb.COMMAND_MAINTENANCE
3523 The command is only useful to @value{GDBN} maintainers. The
3524 @code{maintenance} and @code{flushregs} commands are in this category.
3525 Type @kbd{help internals} at the @value{GDBN} prompt to see a list of
3526 commands in this category.
3529 A new command can use a predefined completion function, either by
3530 specifying it via an argument at initialization, or by returning it
3531 from the @code{complete} method. These predefined completion
3532 constants are all defined in the @code{gdb} module:
3535 @vindex COMPLETE_NONE
3536 @item gdb.COMPLETE_NONE
3537 This constant means that no completion should be done.
3539 @vindex COMPLETE_FILENAME
3540 @item gdb.COMPLETE_FILENAME
3541 This constant means that filename completion should be performed.
3543 @vindex COMPLETE_LOCATION
3544 @item gdb.COMPLETE_LOCATION
3545 This constant means that location completion should be done.
3546 @xref{Specify Location}.
3548 @vindex COMPLETE_COMMAND
3549 @item gdb.COMPLETE_COMMAND
3550 This constant means that completion should examine @value{GDBN}
3553 @vindex COMPLETE_SYMBOL
3554 @item gdb.COMPLETE_SYMBOL
3555 This constant means that completion should be done using symbol names
3558 @vindex COMPLETE_EXPRESSION
3559 @item gdb.COMPLETE_EXPRESSION
3560 This constant means that completion should be done on expressions.
3561 Often this means completing on symbol names, but some language
3562 parsers also have support for completing on field names.
3565 The following code snippet shows how a trivial CLI command can be
3566 implemented in Python:
3569 class HelloWorld (gdb.Command):
3570 """Greet the whole world."""
3572 def __init__ (self):
3573 super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)
3575 def invoke (self, arg, from_tty):
3576 print "Hello, World!"
3581 The last line instantiates the class, and is necessary to trigger the
3582 registration of the command with @value{GDBN}. Depending on how the
3583 Python code is read into @value{GDBN}, you may need to import the
3584 @code{gdb} module explicitly.
3586 @node Parameters In Python
3587 @subsubsection Parameters In Python
3589 @cindex parameters in python
3590 @cindex python parameters
3591 @tindex gdb.Parameter
3593 You can implement new @value{GDBN} parameters using Python. A new
3594 parameter is implemented as an instance of the @code{gdb.Parameter}
3597 Parameters are exposed to the user via the @code{set} and
3598 @code{show} commands. @xref{Help}.
3600 There are many parameters that already exist and can be set in
3601 @value{GDBN}. Two examples are: @code{set follow fork} and
3602 @code{set charset}. Setting these parameters influences certain
3603 behavior in @value{GDBN}. Similarly, you can define parameters that
3604 can be used to influence behavior in custom Python scripts and commands.
3606 @defun Parameter.__init__ (name, @var{command-class}, @var{parameter-class} @r{[}, @var{enum-sequence}@r{]})
3607 The object initializer for @code{Parameter} registers the new
3608 parameter with @value{GDBN}. This initializer is normally invoked
3609 from the subclass' own @code{__init__} method.
3611 @var{name} is the name of the new parameter. If @var{name} consists
3612 of multiple words, then the initial words are looked for as prefix
3613 parameters. An example of this can be illustrated with the
3614 @code{set print} set of parameters. If @var{name} is
3615 @code{print foo}, then @code{print} will be searched as the prefix
3616 parameter. In this case the parameter can subsequently be accessed in
3617 @value{GDBN} as @code{set print foo}.
3619 If @var{name} consists of multiple words, and no prefix parameter group
3620 can be found, an exception is raised.
3622 @var{command-class} should be one of the @samp{COMMAND_} constants
3623 (@pxref{Commands In Python}). This argument tells @value{GDBN} how to
3624 categorize the new parameter in the help system.
3626 @var{parameter-class} should be one of the @samp{PARAM_} constants
3627 defined below. This argument tells @value{GDBN} the type of the new
3628 parameter; this information is used for input validation and
3631 If @var{parameter-class} is @code{PARAM_ENUM}, then
3632 @var{enum-sequence} must be a sequence of strings. These strings
3633 represent the possible values for the parameter.
3635 If @var{parameter-class} is not @code{PARAM_ENUM}, then the presence
3636 of a fourth argument will cause an exception to be thrown.
3638 The help text for the new parameter is taken from the Python
3639 documentation string for the parameter's class, if there is one. If
3640 there is no documentation string, a default value is used.
3643 @defvar Parameter.set_doc
3644 If this attribute exists, and is a string, then its value is used as
3645 the help text for this parameter's @code{set} command. The value is
3646 examined when @code{Parameter.__init__} is invoked; subsequent changes
3650 @defvar Parameter.show_doc
3651 If this attribute exists, and is a string, then its value is used as
3652 the help text for this parameter's @code{show} command. The value is
3653 examined when @code{Parameter.__init__} is invoked; subsequent changes
3657 @defvar Parameter.value
3658 The @code{value} attribute holds the underlying value of the
3659 parameter. It can be read and assigned to just as any other
3660 attribute. @value{GDBN} does validation when assignments are made.
3663 There are two methods that should be implemented in any
3664 @code{Parameter} class. These are:
3666 @defun Parameter.get_set_string (self)
3667 @value{GDBN} will call this method when a @var{parameter}'s value has
3668 been changed via the @code{set} API (for example, @kbd{set foo off}).
3669 The @code{value} attribute has already been populated with the new
3670 value and may be used in output. This method must return a string.
3673 @defun Parameter.get_show_string (self, svalue)
3674 @value{GDBN} will call this method when a @var{parameter}'s
3675 @code{show} API has been invoked (for example, @kbd{show foo}). The
3676 argument @code{svalue} receives the string representation of the
3677 current value. This method must return a string.
3680 When a new parameter is defined, its type must be specified. The
3681 available types are represented by constants defined in the @code{gdb}
3685 @findex PARAM_BOOLEAN
3686 @findex gdb.PARAM_BOOLEAN
3687 @item gdb.PARAM_BOOLEAN
3688 The value is a plain boolean. The Python boolean values, @code{True}
3689 and @code{False} are the only valid values.
3691 @findex PARAM_AUTO_BOOLEAN
3692 @findex gdb.PARAM_AUTO_BOOLEAN
3693 @item gdb.PARAM_AUTO_BOOLEAN
3694 The value has three possible states: true, false, and @samp{auto}. In
3695 Python, true and false are represented using boolean constants, and
3696 @samp{auto} is represented using @code{None}.
3698 @findex PARAM_UINTEGER
3699 @findex gdb.PARAM_UINTEGER
3700 @item gdb.PARAM_UINTEGER
3701 The value is an unsigned integer. The value of 0 should be
3702 interpreted to mean ``unlimited''.
3704 @findex PARAM_INTEGER
3705 @findex gdb.PARAM_INTEGER
3706 @item gdb.PARAM_INTEGER
3707 The value is a signed integer. The value of 0 should be interpreted
3708 to mean ``unlimited''.
3710 @findex PARAM_STRING
3711 @findex gdb.PARAM_STRING
3712 @item gdb.PARAM_STRING
3713 The value is a string. When the user modifies the string, any escape
3714 sequences, such as @samp{\t}, @samp{\f}, and octal escapes, are
3715 translated into corresponding characters and encoded into the current
3718 @findex PARAM_STRING_NOESCAPE
3719 @findex gdb.PARAM_STRING_NOESCAPE
3720 @item gdb.PARAM_STRING_NOESCAPE
3721 The value is a string. When the user modifies the string, escapes are
3722 passed through untranslated.
3724 @findex PARAM_OPTIONAL_FILENAME
3725 @findex gdb.PARAM_OPTIONAL_FILENAME
3726 @item gdb.PARAM_OPTIONAL_FILENAME
3727 The value is a either a filename (a string), or @code{None}.
3729 @findex PARAM_FILENAME
3730 @findex gdb.PARAM_FILENAME
3731 @item gdb.PARAM_FILENAME
3732 The value is a filename. This is just like
3733 @code{PARAM_STRING_NOESCAPE}, but uses file names for completion.
3735 @findex PARAM_ZINTEGER
3736 @findex gdb.PARAM_ZINTEGER
3737 @item gdb.PARAM_ZINTEGER
3738 The value is an integer. This is like @code{PARAM_INTEGER}, except 0
3739 is interpreted as itself.
3742 @findex gdb.PARAM_ENUM
3743 @item gdb.PARAM_ENUM
3744 The value is a string, which must be one of a collection string
3745 constants provided when the parameter is created.
3748 @node Functions In Python
3749 @subsubsection Writing new convenience functions
3751 @cindex writing convenience functions
3752 @cindex convenience functions in python
3753 @cindex python convenience functions
3754 @tindex gdb.Function
3756 You can implement new convenience functions (@pxref{Convenience Vars})
3757 in Python. A convenience function is an instance of a subclass of the
3758 class @code{gdb.Function}.
3760 @defun Function.__init__ (name)
3761 The initializer for @code{Function} registers the new function with
3762 @value{GDBN}. The argument @var{name} is the name of the function,
3763 a string. The function will be visible to the user as a convenience
3764 variable of type @code{internal function}, whose name is the same as
3765 the given @var{name}.
3767 The documentation for the new function is taken from the documentation
3768 string for the new class.
3771 @defun Function.invoke (@var{*args})
3772 When a convenience function is evaluated, its arguments are converted
3773 to instances of @code{gdb.Value}, and then the function's
3774 @code{invoke} method is called. Note that @value{GDBN} does not
3775 predetermine the arity of convenience functions. Instead, all
3776 available arguments are passed to @code{invoke}, following the
3777 standard Python calling convention. In particular, a convenience
3778 function can have default values for parameters without ill effect.
3780 The return value of this method is used as its value in the enclosing
3781 expression. If an ordinary Python value is returned, it is converted
3782 to a @code{gdb.Value} following the usual rules.
3785 The following code snippet shows how a trivial convenience function can
3786 be implemented in Python:
3789 class Greet (gdb.Function):
3790 """Return string to greet someone.
3791 Takes a name as argument."""
3793 def __init__ (self):
3794 super (Greet, self).__init__ ("greet")
3796 def invoke (self, name):
3797 return "Hello, %s!" % name.string ()
3802 The last line instantiates the class, and is necessary to trigger the
3803 registration of the function with @value{GDBN}. Depending on how the
3804 Python code is read into @value{GDBN}, you may need to import the
3805 @code{gdb} module explicitly.
3807 Now you can use the function in an expression:
3810 (gdb) print $greet("Bob")
3814 @node Progspaces In Python
3815 @subsubsection Program Spaces In Python
3817 @cindex progspaces in python
3818 @tindex gdb.Progspace
3820 A program space, or @dfn{progspace}, represents a symbolic view
3821 of an address space.
3822 It consists of all of the objfiles of the program.
3823 @xref{Objfiles In Python}.
3824 @xref{Inferiors and Programs, program spaces}, for more details
3825 about program spaces.
3827 The following progspace-related functions are available in the
3830 @findex gdb.current_progspace
3831 @defun gdb.current_progspace ()
3832 This function returns the program space of the currently selected inferior.
3833 @xref{Inferiors and Programs}.
3836 @findex gdb.progspaces
3837 @defun gdb.progspaces ()
3838 Return a sequence of all the progspaces currently known to @value{GDBN}.
3841 Each progspace is represented by an instance of the @code{gdb.Progspace}
3844 @defvar Progspace.filename
3845 The file name of the progspace as a string.
3848 @defvar Progspace.pretty_printers
3849 The @code{pretty_printers} attribute is a list of functions. It is
3850 used to look up pretty-printers. A @code{Value} is passed to each
3851 function in order; if the function returns @code{None}, then the
3852 search continues. Otherwise, the return value should be an object
3853 which is used to format the value. @xref{Pretty Printing API}, for more
3857 @defvar Progspace.type_printers
3858 The @code{type_printers} attribute is a list of type printer objects.
3859 @xref{Type Printing API}, for more information.
3862 @defvar Progspace.frame_filters
3863 The @code{frame_filters} attribute is a dictionary of frame filter
3864 objects. @xref{Frame Filter API}, for more information.
3867 One may add arbitrary attributes to @code{gdb.Progspace} objects
3868 in the usual Python way.
3869 This is useful if, for example, one needs to do some extra record keeping
3870 associated with the program space.
3872 In this contrived example, we want to perform some processing when
3873 an objfile with a certain symbol is loaded, but we only want to do
3874 this once because it is expensive. To achieve this we record the results
3875 with the program space because we can't predict when the desired objfile
3880 def clear_objfiles_handler(event):
3881 event.progspace.expensive_computation = None
3882 def expensive(symbol):
3883 """A mock routine to perform an "expensive" computation on symbol."""
3884 print "Computing the answer to the ultimate question ..."
3886 def new_objfile_handler(event):
3887 objfile = event.new_objfile
3888 progspace = objfile.progspace
3889 if not hasattr(progspace, 'expensive_computation') or \
3890 progspace.expensive_computation is None:
3891 # We use 'main' for the symbol to keep the example simple.
3892 # Note: There's no current way to constrain the lookup
3894 symbol = gdb.lookup_global_symbol('main')
3895 if symbol is not None:
3896 progspace.expensive_computation = expensive(symbol)
3897 gdb.events.clear_objfiles.connect(clear_objfiles_handler)
3898 gdb.events.new_objfile.connect(new_objfile_handler)
3900 (gdb) file /tmp/hello
3901 Reading symbols from /tmp/hello...done.
3902 Computing the answer to the ultimate question ...
3903 (gdb) python print gdb.current_progspace().expensive_computation
3906 Starting program: /tmp/hello
3908 [Inferior 1 (process 4242) exited normally]
3911 @node Objfiles In Python
3912 @subsubsection Objfiles In Python
3914 @cindex objfiles in python
3917 @value{GDBN} loads symbols for an inferior from various
3918 symbol-containing files (@pxref{Files}). These include the primary
3919 executable file, any shared libraries used by the inferior, and any
3920 separate debug info files (@pxref{Separate Debug Files}).
3921 @value{GDBN} calls these symbol-containing files @dfn{objfiles}.
3923 The following objfile-related functions are available in the
3926 @findex gdb.current_objfile
3927 @defun gdb.current_objfile ()
3928 When auto-loading a Python script (@pxref{Python Auto-loading}), @value{GDBN}
3929 sets the ``current objfile'' to the corresponding objfile. This
3930 function returns the current objfile. If there is no current objfile,
3931 this function returns @code{None}.
3934 @findex gdb.objfiles
3935 @defun gdb.objfiles ()
3936 Return a sequence of all the objfiles current known to @value{GDBN}.
3937 @xref{Objfiles In Python}.
3940 @findex gdb.lookup_objfile
3941 @defun gdb.lookup_objfile (name @r{[}, by_build_id{]})
3942 Look up @var{name}, a file name or build ID, in the list of objfiles
3943 for the current program space (@pxref{Progspaces In Python}).
3944 If the objfile is not found throw the Python @code{ValueError} exception.
3946 If @var{name} is a relative file name, then it will match any
3947 source file name with the same trailing components. For example, if
3948 @var{name} is @samp{gcc/expr.c}, then it will match source file
3949 name of @file{/build/trunk/gcc/expr.c}, but not
3950 @file{/build/trunk/libcpp/expr.c} or @file{/build/trunk/gcc/x-expr.c}.
3952 If @var{by_build_id} is provided and is @code{True} then @var{name}
3953 is the build ID of the objfile. Otherwise, @var{name} is a file name.
3954 This is supported only on some operating systems, notably those which use
3955 the ELF format for binary files and the @sc{gnu} Binutils. For more details
3956 about this feature, see the description of the @option{--build-id}
3957 command-line option in @ref{Options, , Command Line Options, ld.info,
3961 Each objfile is represented by an instance of the @code{gdb.Objfile}
3964 @defvar Objfile.filename
3965 The file name of the objfile as a string, with symbolic links resolved.
3967 The value is @code{None} if the objfile is no longer valid.
3968 See the @code{gdb.Objfile.is_valid} method, described below.
3971 @defvar Objfile.username
3972 The file name of the objfile as specified by the user as a string.
3974 The value is @code{None} if the objfile is no longer valid.
3975 See the @code{gdb.Objfile.is_valid} method, described below.
3978 @defvar Objfile.owner
3979 For separate debug info objfiles this is the corresponding @code{gdb.Objfile}
3980 object that debug info is being provided for.
3981 Otherwise this is @code{None}.
3982 Separate debug info objfiles are added with the
3983 @code{gdb.Objfile.add_separate_debug_file} method, described below.
3986 @defvar Objfile.build_id
3987 The build ID of the objfile as a string.
3988 If the objfile does not have a build ID then the value is @code{None}.
3990 This is supported only on some operating systems, notably those which use
3991 the ELF format for binary files and the @sc{gnu} Binutils. For more details
3992 about this feature, see the description of the @option{--build-id}
3993 command-line option in @ref{Options, , Command Line Options, ld.info,
3997 @defvar Objfile.progspace
3998 The containing program space of the objfile as a @code{gdb.Progspace}
3999 object. @xref{Progspaces In Python}.
4002 @defvar Objfile.pretty_printers
4003 The @code{pretty_printers} attribute is a list of functions. It is
4004 used to look up pretty-printers. A @code{Value} is passed to each
4005 function in order; if the function returns @code{None}, then the
4006 search continues. Otherwise, the return value should be an object
4007 which is used to format the value. @xref{Pretty Printing API}, for more
4011 @defvar Objfile.type_printers
4012 The @code{type_printers} attribute is a list of type printer objects.
4013 @xref{Type Printing API}, for more information.
4016 @defvar Objfile.frame_filters
4017 The @code{frame_filters} attribute is a dictionary of frame filter
4018 objects. @xref{Frame Filter API}, for more information.
4021 One may add arbitrary attributes to @code{gdb.Objfile} objects
4022 in the usual Python way.
4023 This is useful if, for example, one needs to do some extra record keeping
4024 associated with the objfile.
4026 In this contrived example we record the time when @value{GDBN}
4032 def new_objfile_handler(event):
4033 # Set the time_loaded attribute of the new objfile.
4034 event.new_objfile.time_loaded = datetime.datetime.today()
4035 gdb.events.new_objfile.connect(new_objfile_handler)
4038 Reading symbols from ./hello...done.
4039 (gdb) python print gdb.objfiles()[0].time_loaded
4040 2014-10-09 11:41:36.770345
4043 A @code{gdb.Objfile} object has the following methods:
4045 @defun Objfile.is_valid ()
4046 Returns @code{True} if the @code{gdb.Objfile} object is valid,
4047 @code{False} if not. A @code{gdb.Objfile} object can become invalid
4048 if the object file it refers to is not loaded in @value{GDBN} any
4049 longer. All other @code{gdb.Objfile} methods will throw an exception
4050 if it is invalid at the time the method is called.
4053 @defun Objfile.add_separate_debug_file (file)
4054 Add @var{file} to the list of files that @value{GDBN} will search for
4055 debug information for the objfile.
4056 This is useful when the debug info has been removed from the program
4057 and stored in a separate file. @value{GDBN} has built-in support for
4058 finding separate debug info files (@pxref{Separate Debug Files}), but if
4059 the file doesn't live in one of the standard places that @value{GDBN}
4060 searches then this function can be used to add a debug info file
4061 from a different place.
4064 @node Frames In Python
4065 @subsubsection Accessing inferior stack frames from Python.
4067 @cindex frames in python
4068 When the debugged program stops, @value{GDBN} is able to analyze its call
4069 stack (@pxref{Frames,,Stack frames}). The @code{gdb.Frame} class
4070 represents a frame in the stack. A @code{gdb.Frame} object is only valid
4071 while its corresponding frame exists in the inferior's stack. If you try
4072 to use an invalid frame object, @value{GDBN} will throw a @code{gdb.error}
4073 exception (@pxref{Exception Handling}).
4075 Two @code{gdb.Frame} objects can be compared for equality with the @code{==}
4079 (@value{GDBP}) python print gdb.newest_frame() == gdb.selected_frame ()
4083 The following frame-related functions are available in the @code{gdb} module:
4085 @findex gdb.selected_frame
4086 @defun gdb.selected_frame ()
4087 Return the selected frame object. (@pxref{Selection,,Selecting a Frame}).
4090 @findex gdb.newest_frame
4091 @defun gdb.newest_frame ()
4092 Return the newest frame object for the selected thread.
4095 @defun gdb.frame_stop_reason_string (reason)
4096 Return a string explaining the reason why @value{GDBN} stopped unwinding
4097 frames, as expressed by the given @var{reason} code (an integer, see the
4098 @code{unwind_stop_reason} method further down in this section).
4101 @findex gdb.invalidate_cached_frames
4102 @defun gdb.invalidate_cached_frames
4103 @value{GDBN} internally keeps a cache of the frames that have been
4104 unwound. This function invalidates this cache.
4106 This function should not generally be called by ordinary Python code.
4107 It is documented for the sake of completeness.
4110 A @code{gdb.Frame} object has the following methods:
4112 @defun Frame.is_valid ()
4113 Returns true if the @code{gdb.Frame} object is valid, false if not.
4114 A frame object can become invalid if the frame it refers to doesn't
4115 exist anymore in the inferior. All @code{gdb.Frame} methods will throw
4116 an exception if it is invalid at the time the method is called.
4119 @defun Frame.name ()
4120 Returns the function name of the frame, or @code{None} if it can't be
4124 @defun Frame.architecture ()
4125 Returns the @code{gdb.Architecture} object corresponding to the frame's
4126 architecture. @xref{Architectures In Python}.
4129 @defun Frame.type ()
4130 Returns the type of the frame. The value can be one of:
4132 @item gdb.NORMAL_FRAME
4133 An ordinary stack frame.
4135 @item gdb.DUMMY_FRAME
4136 A fake stack frame that was created by @value{GDBN} when performing an
4137 inferior function call.
4139 @item gdb.INLINE_FRAME
4140 A frame representing an inlined function. The function was inlined
4141 into a @code{gdb.NORMAL_FRAME} that is older than this one.
4143 @item gdb.TAILCALL_FRAME
4144 A frame representing a tail call. @xref{Tail Call Frames}.
4146 @item gdb.SIGTRAMP_FRAME
4147 A signal trampoline frame. This is the frame created by the OS when
4148 it calls into a signal handler.
4150 @item gdb.ARCH_FRAME
4151 A fake stack frame representing a cross-architecture call.
4153 @item gdb.SENTINEL_FRAME
4154 This is like @code{gdb.NORMAL_FRAME}, but it is only used for the
4159 @defun Frame.unwind_stop_reason ()
4160 Return an integer representing the reason why it's not possible to find
4161 more frames toward the outermost frame. Use
4162 @code{gdb.frame_stop_reason_string} to convert the value returned by this
4163 function to a string. The value can be one of:
4166 @item gdb.FRAME_UNWIND_NO_REASON
4167 No particular reason (older frames should be available).
4169 @item gdb.FRAME_UNWIND_NULL_ID
4170 The previous frame's analyzer returns an invalid result. This is no
4171 longer used by @value{GDBN}, and is kept only for backward
4174 @item gdb.FRAME_UNWIND_OUTERMOST
4175 This frame is the outermost.
4177 @item gdb.FRAME_UNWIND_UNAVAILABLE
4178 Cannot unwind further, because that would require knowing the
4179 values of registers or memory that have not been collected.
4181 @item gdb.FRAME_UNWIND_INNER_ID
4182 This frame ID looks like it ought to belong to a NEXT frame,
4183 but we got it for a PREV frame. Normally, this is a sign of
4184 unwinder failure. It could also indicate stack corruption.
4186 @item gdb.FRAME_UNWIND_SAME_ID
4187 This frame has the same ID as the previous one. That means
4188 that unwinding further would almost certainly give us another
4189 frame with exactly the same ID, so break the chain. Normally,
4190 this is a sign of unwinder failure. It could also indicate
4193 @item gdb.FRAME_UNWIND_NO_SAVED_PC
4194 The frame unwinder did not find any saved PC, but we needed
4195 one to unwind further.
4197 @item gdb.FRAME_UNWIND_MEMORY_ERROR
4198 The frame unwinder caused an error while trying to access memory.
4200 @item gdb.FRAME_UNWIND_FIRST_ERROR
4201 Any stop reason greater or equal to this value indicates some kind
4202 of error. This special value facilitates writing code that tests
4203 for errors in unwinding in a way that will work correctly even if
4204 the list of the other values is modified in future @value{GDBN}
4205 versions. Using it, you could write:
4207 reason = gdb.selected_frame().unwind_stop_reason ()
4208 reason_str = gdb.frame_stop_reason_string (reason)
4209 if reason >= gdb.FRAME_UNWIND_FIRST_ERROR:
4210 print "An error occured: %s" % reason_str
4217 Returns the frame's resume address.
4220 @defun Frame.block ()
4221 Return the frame's code block. @xref{Blocks In Python}.
4224 @defun Frame.function ()
4225 Return the symbol for the function corresponding to this frame.
4226 @xref{Symbols In Python}.
4229 @defun Frame.older ()
4230 Return the frame that called this frame.
4233 @defun Frame.newer ()
4234 Return the frame called by this frame.
4237 @defun Frame.find_sal ()
4238 Return the frame's symtab and line object.
4239 @xref{Symbol Tables In Python}.
4242 @defun Frame.read_register (register)
4243 Return the value of @var{register} in this frame. The @var{register}
4244 argument must be a string (e.g., @code{'sp'} or @code{'rax'}).
4245 Returns a @code{Gdb.Value} object. Throws an exception if @var{register}
4249 @defun Frame.read_var (variable @r{[}, block@r{]})
4250 Return the value of @var{variable} in this frame. If the optional
4251 argument @var{block} is provided, search for the variable from that
4252 block; otherwise start at the frame's current block (which is
4253 determined by the frame's current program counter). The @var{variable}
4254 argument must be a string or a @code{gdb.Symbol} object; @var{block} must be a
4255 @code{gdb.Block} object.
4258 @defun Frame.select ()
4259 Set this frame to be the selected frame. @xref{Stack, ,Examining the
4263 @node Blocks In Python
4264 @subsubsection Accessing blocks from Python.
4266 @cindex blocks in python
4269 In @value{GDBN}, symbols are stored in blocks. A block corresponds
4270 roughly to a scope in the source code. Blocks are organized
4271 hierarchically, and are represented individually in Python as a
4272 @code{gdb.Block}. Blocks rely on debugging information being
4275 A frame has a block. Please see @ref{Frames In Python}, for a more
4276 in-depth discussion of frames.
4278 The outermost block is known as the @dfn{global block}. The global
4279 block typically holds public global variables and functions.
4281 The block nested just inside the global block is the @dfn{static
4282 block}. The static block typically holds file-scoped variables and
4285 @value{GDBN} provides a method to get a block's superblock, but there
4286 is currently no way to examine the sub-blocks of a block, or to
4287 iterate over all the blocks in a symbol table (@pxref{Symbol Tables In
4290 Here is a short example that should help explain blocks:
4293 /* This is in the global block. */
4296 /* This is in the static block. */
4297 static int file_scope;
4299 /* 'function' is in the global block, and 'argument' is
4300 in a block nested inside of 'function'. */
4301 int function (int argument)
4303 /* 'local' is in a block inside 'function'. It may or may
4304 not be in the same block as 'argument'. */
4308 /* 'inner' is in a block whose superblock is the one holding
4312 /* If this call is expanded by the compiler, you may see
4313 a nested block here whose function is 'inline_function'
4314 and whose superblock is the one holding 'inner'. */
4320 A @code{gdb.Block} is iterable. The iterator returns the symbols
4321 (@pxref{Symbols In Python}) local to the block. Python programs
4322 should not assume that a specific block object will always contain a
4323 given symbol, since changes in @value{GDBN} features and
4324 infrastructure may cause symbols move across blocks in a symbol
4327 The following block-related functions are available in the @code{gdb}
4330 @findex gdb.block_for_pc
4331 @defun gdb.block_for_pc (pc)
4332 Return the innermost @code{gdb.Block} containing the given @var{pc}
4333 value. If the block cannot be found for the @var{pc} value specified,
4334 the function will return @code{None}.
4337 A @code{gdb.Block} object has the following methods:
4339 @defun Block.is_valid ()
4340 Returns @code{True} if the @code{gdb.Block} object is valid,
4341 @code{False} if not. A block object can become invalid if the block it
4342 refers to doesn't exist anymore in the inferior. All other
4343 @code{gdb.Block} methods will throw an exception if it is invalid at
4344 the time the method is called. The block's validity is also checked
4345 during iteration over symbols of the block.
4348 A @code{gdb.Block} object has the following attributes:
4351 The start address of the block. This attribute is not writable.
4355 The end address of the block. This attribute is not writable.
4358 @defvar Block.function
4359 The name of the block represented as a @code{gdb.Symbol}. If the
4360 block is not named, then this attribute holds @code{None}. This
4361 attribute is not writable.
4363 For ordinary function blocks, the superblock is the static block.
4364 However, you should note that it is possible for a function block to
4365 have a superblock that is not the static block -- for instance this
4366 happens for an inlined function.
4369 @defvar Block.superblock
4370 The block containing this block. If this parent block does not exist,
4371 this attribute holds @code{None}. This attribute is not writable.
4374 @defvar Block.global_block
4375 The global block associated with this block. This attribute is not
4379 @defvar Block.static_block
4380 The static block associated with this block. This attribute is not
4384 @defvar Block.is_global
4385 @code{True} if the @code{gdb.Block} object is a global block,
4386 @code{False} if not. This attribute is not
4390 @defvar Block.is_static
4391 @code{True} if the @code{gdb.Block} object is a static block,
4392 @code{False} if not. This attribute is not writable.
4395 @node Symbols In Python
4396 @subsubsection Python representation of Symbols.
4398 @cindex symbols in python
4401 @value{GDBN} represents every variable, function and type as an
4402 entry in a symbol table. @xref{Symbols, ,Examining the Symbol Table}.
4403 Similarly, Python represents these symbols in @value{GDBN} with the
4404 @code{gdb.Symbol} object.
4406 The following symbol-related functions are available in the @code{gdb}
4409 @findex gdb.lookup_symbol
4410 @defun gdb.lookup_symbol (name @r{[}, block @r{[}, domain@r{]]})
4411 This function searches for a symbol by name. The search scope can be
4412 restricted to the parameters defined in the optional domain and block
4415 @var{name} is the name of the symbol. It must be a string. The
4416 optional @var{block} argument restricts the search to symbols visible
4417 in that @var{block}. The @var{block} argument must be a
4418 @code{gdb.Block} object. If omitted, the block for the current frame
4419 is used. The optional @var{domain} argument restricts
4420 the search to the domain type. The @var{domain} argument must be a
4421 domain constant defined in the @code{gdb} module and described later
4424 The result is a tuple of two elements.
4425 The first element is a @code{gdb.Symbol} object or @code{None} if the symbol
4427 If the symbol is found, the second element is @code{True} if the symbol
4428 is a field of a method's object (e.g., @code{this} in C@t{++}),
4429 otherwise it is @code{False}.
4430 If the symbol is not found, the second element is @code{False}.
4433 @findex gdb.lookup_global_symbol
4434 @defun gdb.lookup_global_symbol (name @r{[}, domain@r{]})
4435 This function searches for a global symbol by name.
4436 The search scope can be restricted to by the domain argument.
4438 @var{name} is the name of the symbol. It must be a string.
4439 The optional @var{domain} argument restricts the search to the domain type.
4440 The @var{domain} argument must be a domain constant defined in the @code{gdb}
4441 module and described later in this chapter.
4443 The result is a @code{gdb.Symbol} object or @code{None} if the symbol
4447 A @code{gdb.Symbol} object has the following attributes:
4450 The type of the symbol or @code{None} if no type is recorded.
4451 This attribute is represented as a @code{gdb.Type} object.
4452 @xref{Types In Python}. This attribute is not writable.
4455 @defvar Symbol.symtab
4456 The symbol table in which the symbol appears. This attribute is
4457 represented as a @code{gdb.Symtab} object. @xref{Symbol Tables In
4458 Python}. This attribute is not writable.
4462 The line number in the source code at which the symbol was defined.
4467 The name of the symbol as a string. This attribute is not writable.
4470 @defvar Symbol.linkage_name
4471 The name of the symbol, as used by the linker (i.e., may be mangled).
4472 This attribute is not writable.
4475 @defvar Symbol.print_name
4476 The name of the symbol in a form suitable for output. This is either
4477 @code{name} or @code{linkage_name}, depending on whether the user
4478 asked @value{GDBN} to display demangled or mangled names.
4481 @defvar Symbol.addr_class
4482 The address class of the symbol. This classifies how to find the value
4483 of a symbol. Each address class is a constant defined in the
4484 @code{gdb} module and described later in this chapter.
4487 @defvar Symbol.needs_frame
4488 This is @code{True} if evaluating this symbol's value requires a frame
4489 (@pxref{Frames In Python}) and @code{False} otherwise. Typically,
4490 local variables will require a frame, but other symbols will not.
4493 @defvar Symbol.is_argument
4494 @code{True} if the symbol is an argument of a function.
4497 @defvar Symbol.is_constant
4498 @code{True} if the symbol is a constant.
4501 @defvar Symbol.is_function
4502 @code{True} if the symbol is a function or a method.
4505 @defvar Symbol.is_variable
4506 @code{True} if the symbol is a variable.
4509 A @code{gdb.Symbol} object has the following methods:
4511 @defun Symbol.is_valid ()
4512 Returns @code{True} if the @code{gdb.Symbol} object is valid,
4513 @code{False} if not. A @code{gdb.Symbol} object can become invalid if
4514 the symbol it refers to does not exist in @value{GDBN} any longer.
4515 All other @code{gdb.Symbol} methods will throw an exception if it is
4516 invalid at the time the method is called.
4519 @defun Symbol.value (@r{[}frame@r{]})
4520 Compute the value of the symbol, as a @code{gdb.Value}. For
4521 functions, this computes the address of the function, cast to the
4522 appropriate type. If the symbol requires a frame in order to compute
4523 its value, then @var{frame} must be given. If @var{frame} is not
4524 given, or if @var{frame} is invalid, then this method will throw an
4528 The available domain categories in @code{gdb.Symbol} are represented
4529 as constants in the @code{gdb} module:
4532 @vindex SYMBOL_UNDEF_DOMAIN
4533 @item gdb.SYMBOL_UNDEF_DOMAIN
4534 This is used when a domain has not been discovered or none of the
4535 following domains apply. This usually indicates an error either
4536 in the symbol information or in @value{GDBN}'s handling of symbols.
4538 @vindex SYMBOL_VAR_DOMAIN
4539 @item gdb.SYMBOL_VAR_DOMAIN
4540 This domain contains variables, function names, typedef names and enum
4543 @vindex SYMBOL_STRUCT_DOMAIN
4544 @item gdb.SYMBOL_STRUCT_DOMAIN
4545 This domain holds struct, union and enum type names.
4547 @vindex SYMBOL_LABEL_DOMAIN
4548 @item gdb.SYMBOL_LABEL_DOMAIN
4549 This domain contains names of labels (for gotos).
4551 @vindex SYMBOL_VARIABLES_DOMAIN
4552 @item gdb.SYMBOL_VARIABLES_DOMAIN
4553 This domain holds a subset of the @code{SYMBOLS_VAR_DOMAIN}; it
4554 contains everything minus functions and types.
4556 @vindex SYMBOL_FUNCTIONS_DOMAIN
4557 @item gdb.SYMBOL_FUNCTION_DOMAIN
4558 This domain contains all functions.
4560 @vindex SYMBOL_TYPES_DOMAIN
4561 @item gdb.SYMBOL_TYPES_DOMAIN
4562 This domain contains all types.
4565 The available address class categories in @code{gdb.Symbol} are represented
4566 as constants in the @code{gdb} module:
4569 @vindex SYMBOL_LOC_UNDEF
4570 @item gdb.SYMBOL_LOC_UNDEF
4571 If this is returned by address class, it indicates an error either in
4572 the symbol information or in @value{GDBN}'s handling of symbols.
4574 @vindex SYMBOL_LOC_CONST
4575 @item gdb.SYMBOL_LOC_CONST
4576 Value is constant int.
4578 @vindex SYMBOL_LOC_STATIC
4579 @item gdb.SYMBOL_LOC_STATIC
4580 Value is at a fixed address.
4582 @vindex SYMBOL_LOC_REGISTER
4583 @item gdb.SYMBOL_LOC_REGISTER
4584 Value is in a register.
4586 @vindex SYMBOL_LOC_ARG
4587 @item gdb.SYMBOL_LOC_ARG
4588 Value is an argument. This value is at the offset stored within the
4589 symbol inside the frame's argument list.
4591 @vindex SYMBOL_LOC_REF_ARG
4592 @item gdb.SYMBOL_LOC_REF_ARG
4593 Value address is stored in the frame's argument list. Just like
4594 @code{LOC_ARG} except that the value's address is stored at the
4595 offset, not the value itself.
4597 @vindex SYMBOL_LOC_REGPARM_ADDR
4598 @item gdb.SYMBOL_LOC_REGPARM_ADDR
4599 Value is a specified register. Just like @code{LOC_REGISTER} except
4600 the register holds the address of the argument instead of the argument
4603 @vindex SYMBOL_LOC_LOCAL
4604 @item gdb.SYMBOL_LOC_LOCAL
4605 Value is a local variable.
4607 @vindex SYMBOL_LOC_TYPEDEF
4608 @item gdb.SYMBOL_LOC_TYPEDEF
4609 Value not used. Symbols in the domain @code{SYMBOL_STRUCT_DOMAIN} all
4612 @vindex SYMBOL_LOC_BLOCK
4613 @item gdb.SYMBOL_LOC_BLOCK
4616 @vindex SYMBOL_LOC_CONST_BYTES
4617 @item gdb.SYMBOL_LOC_CONST_BYTES
4618 Value is a byte-sequence.
4620 @vindex SYMBOL_LOC_UNRESOLVED
4621 @item gdb.SYMBOL_LOC_UNRESOLVED
4622 Value is at a fixed address, but the address of the variable has to be
4623 determined from the minimal symbol table whenever the variable is
4626 @vindex SYMBOL_LOC_OPTIMIZED_OUT
4627 @item gdb.SYMBOL_LOC_OPTIMIZED_OUT
4628 The value does not actually exist in the program.
4630 @vindex SYMBOL_LOC_COMPUTED
4631 @item gdb.SYMBOL_LOC_COMPUTED
4632 The value's address is a computed location.
4635 @node Symbol Tables In Python
4636 @subsubsection Symbol table representation in Python.
4638 @cindex symbol tables in python
4640 @tindex gdb.Symtab_and_line
4642 Access to symbol table data maintained by @value{GDBN} on the inferior
4643 is exposed to Python via two objects: @code{gdb.Symtab_and_line} and
4644 @code{gdb.Symtab}. Symbol table and line data for a frame is returned
4645 from the @code{find_sal} method in @code{gdb.Frame} object.
4646 @xref{Frames In Python}.
4648 For more information on @value{GDBN}'s symbol table management, see
4649 @ref{Symbols, ,Examining the Symbol Table}, for more information.
4651 A @code{gdb.Symtab_and_line} object has the following attributes:
4653 @defvar Symtab_and_line.symtab
4654 The symbol table object (@code{gdb.Symtab}) for this frame.
4655 This attribute is not writable.
4658 @defvar Symtab_and_line.pc
4659 Indicates the start of the address range occupied by code for the
4660 current source line. This attribute is not writable.
4663 @defvar Symtab_and_line.last
4664 Indicates the end of the address range occupied by code for the current
4665 source line. This attribute is not writable.
4668 @defvar Symtab_and_line.line
4669 Indicates the current line number for this object. This
4670 attribute is not writable.
4673 A @code{gdb.Symtab_and_line} object has the following methods:
4675 @defun Symtab_and_line.is_valid ()
4676 Returns @code{True} if the @code{gdb.Symtab_and_line} object is valid,
4677 @code{False} if not. A @code{gdb.Symtab_and_line} object can become
4678 invalid if the Symbol table and line object it refers to does not
4679 exist in @value{GDBN} any longer. All other
4680 @code{gdb.Symtab_and_line} methods will throw an exception if it is
4681 invalid at the time the method is called.
4684 A @code{gdb.Symtab} object has the following attributes:
4686 @defvar Symtab.filename
4687 The symbol table's source filename. This attribute is not writable.
4690 @defvar Symtab.objfile
4691 The symbol table's backing object file. @xref{Objfiles In Python}.
4692 This attribute is not writable.
4695 @defvar Symtab.producer
4696 The name and possibly version number of the program that
4697 compiled the code in the symbol table.
4698 The contents of this string is up to the compiler.
4699 If no producer information is available then @code{None} is returned.
4700 This attribute is not writable.
4703 A @code{gdb.Symtab} object has the following methods:
4705 @defun Symtab.is_valid ()
4706 Returns @code{True} if the @code{gdb.Symtab} object is valid,
4707 @code{False} if not. A @code{gdb.Symtab} object can become invalid if
4708 the symbol table it refers to does not exist in @value{GDBN} any
4709 longer. All other @code{gdb.Symtab} methods will throw an exception
4710 if it is invalid at the time the method is called.
4713 @defun Symtab.fullname ()
4714 Return the symbol table's source absolute file name.
4717 @defun Symtab.global_block ()
4718 Return the global block of the underlying symbol table.
4719 @xref{Blocks In Python}.
4722 @defun Symtab.static_block ()
4723 Return the static block of the underlying symbol table.
4724 @xref{Blocks In Python}.
4727 @defun Symtab.linetable ()
4728 Return the line table associated with the symbol table.
4729 @xref{Line Tables In Python}.
4732 @node Line Tables In Python
4733 @subsubsection Manipulating line tables using Python
4735 @cindex line tables in python
4736 @tindex gdb.LineTable
4738 Python code can request and inspect line table information from a
4739 symbol table that is loaded in @value{GDBN}. A line table is a
4740 mapping of source lines to their executable locations in memory. To
4741 acquire the line table information for a particular symbol table, use
4742 the @code{linetable} function (@pxref{Symbol Tables In Python}).
4744 A @code{gdb.LineTable} is iterable. The iterator returns
4745 @code{LineTableEntry} objects that correspond to the source line and
4746 address for each line table entry. @code{LineTableEntry} objects have
4747 the following attributes:
4749 @defvar LineTableEntry.line
4750 The source line number for this line table entry. This number
4751 corresponds to the actual line of source. This attribute is not
4755 @defvar LineTableEntry.pc
4756 The address that is associated with the line table entry where the
4757 executable code for that source line resides in memory. This
4758 attribute is not writable.
4761 As there can be multiple addresses for a single source line, you may
4762 receive multiple @code{LineTableEntry} objects with matching
4763 @code{line} attributes, but with different @code{pc} attributes. The
4764 iterator is sorted in ascending @code{pc} order. Here is a small
4765 example illustrating iterating over a line table.
4768 symtab = gdb.selected_frame().find_sal().symtab
4769 linetable = symtab.linetable()
4770 for line in linetable:
4771 print "Line: "+str(line.line)+" Address: "+hex(line.pc)
4774 This will have the following output:
4777 Line: 33 Address: 0x4005c8L
4778 Line: 37 Address: 0x4005caL
4779 Line: 39 Address: 0x4005d2L
4780 Line: 40 Address: 0x4005f8L
4781 Line: 42 Address: 0x4005ffL
4782 Line: 44 Address: 0x400608L
4783 Line: 42 Address: 0x40060cL
4784 Line: 45 Address: 0x400615L
4787 In addition to being able to iterate over a @code{LineTable}, it also
4788 has the following direct access methods:
4790 @defun LineTable.line (line)
4791 Return a Python @code{Tuple} of @code{LineTableEntry} objects for any
4792 entries in the line table for the given @var{line}, which specifies
4793 the source code line. If there are no entries for that source code
4794 @var{line}, the Python @code{None} is returned.
4797 @defun LineTable.has_line (line)
4798 Return a Python @code{Boolean} indicating whether there is an entry in
4799 the line table for this source line. Return @code{True} if an entry
4800 is found, or @code{False} if not.
4803 @defun LineTable.source_lines ()
4804 Return a Python @code{List} of the source line numbers in the symbol
4805 table. Only lines with executable code locations are returned. The
4806 contents of the @code{List} will just be the source line entries
4807 represented as Python @code{Long} values.
4810 @node Breakpoints In Python
4811 @subsubsection Manipulating breakpoints using Python
4813 @cindex breakpoints in python
4814 @tindex gdb.Breakpoint
4816 Python code can manipulate breakpoints via the @code{gdb.Breakpoint}
4819 @defun Breakpoint.__init__ (spec @r{[}, type @r{[}, wp_class @r{[},internal @r{[},temporary@r{]]]]})
4820 Create a new breakpoint according to @var{spec}, which is a string
4821 naming the location of the breakpoint, or an expression that defines a
4822 watchpoint. The contents can be any location recognized by the
4823 @code{break} command, or in the case of a watchpoint, by the
4824 @code{watch} command. The optional @var{type} denotes the breakpoint
4825 to create from the types defined later in this chapter. This argument
4826 can be either @code{gdb.BP_BREAKPOINT} or @code{gdb.BP_WATCHPOINT}; it
4827 defaults to @code{gdb.BP_BREAKPOINT}. The optional @var{internal}
4828 argument allows the breakpoint to become invisible to the user. The
4829 breakpoint will neither be reported when created, nor will it be
4830 listed in the output from @code{info breakpoints} (but will be listed
4831 with the @code{maint info breakpoints} command). The optional
4832 @var{temporary} argument makes the breakpoint a temporary breakpoint.
4833 Temporary breakpoints are deleted after they have been hit. Any
4834 further access to the Python breakpoint after it has been hit will
4835 result in a runtime error (as that breakpoint has now been
4836 automatically deleted). The optional @var{wp_class} argument defines
4837 the class of watchpoint to create, if @var{type} is
4838 @code{gdb.BP_WATCHPOINT}. If a watchpoint class is not provided, it
4839 is assumed to be a @code{gdb.WP_WRITE} class.
4842 The available types are represented by constants defined in the @code{gdb}
4846 @vindex BP_BREAKPOINT
4847 @item gdb.BP_BREAKPOINT
4848 Normal code breakpoint.
4850 @vindex BP_WATCHPOINT
4851 @item gdb.BP_WATCHPOINT
4852 Watchpoint breakpoint.
4854 @vindex BP_HARDWARE_WATCHPOINT
4855 @item gdb.BP_HARDWARE_WATCHPOINT
4856 Hardware assisted watchpoint.
4858 @vindex BP_READ_WATCHPOINT
4859 @item gdb.BP_READ_WATCHPOINT
4860 Hardware assisted read watchpoint.
4862 @vindex BP_ACCESS_WATCHPOINT
4863 @item gdb.BP_ACCESS_WATCHPOINT
4864 Hardware assisted access watchpoint.
4867 The available watchpoint types represented by constants are defined in the
4873 Read only watchpoint.
4877 Write only watchpoint.
4881 Read/Write watchpoint.
4884 @defun Breakpoint.stop (self)
4885 The @code{gdb.Breakpoint} class can be sub-classed and, in
4886 particular, you may choose to implement the @code{stop} method.
4887 If this method is defined in a sub-class of @code{gdb.Breakpoint},
4888 it will be called when the inferior reaches any location of a
4889 breakpoint which instantiates that sub-class. If the method returns
4890 @code{True}, the inferior will be stopped at the location of the
4891 breakpoint, otherwise the inferior will continue.
4893 If there are multiple breakpoints at the same location with a
4894 @code{stop} method, each one will be called regardless of the
4895 return status of the previous. This ensures that all @code{stop}
4896 methods have a chance to execute at that location. In this scenario
4897 if one of the methods returns @code{True} but the others return
4898 @code{False}, the inferior will still be stopped.
4900 You should not alter the execution state of the inferior (i.e.@:, step,
4901 next, etc.), alter the current frame context (i.e.@:, change the current
4902 active frame), or alter, add or delete any breakpoint. As a general
4903 rule, you should not alter any data within @value{GDBN} or the inferior
4906 Example @code{stop} implementation:
4909 class MyBreakpoint (gdb.Breakpoint):
4911 inf_val = gdb.parse_and_eval("foo")
4918 @defun Breakpoint.is_valid ()
4919 Return @code{True} if this @code{Breakpoint} object is valid,
4920 @code{False} otherwise. A @code{Breakpoint} object can become invalid
4921 if the user deletes the breakpoint. In this case, the object still
4922 exists, but the underlying breakpoint does not. In the cases of
4923 watchpoint scope, the watchpoint remains valid even if execution of the
4924 inferior leaves the scope of that watchpoint.
4927 @defun Breakpoint.delete ()
4928 Permanently deletes the @value{GDBN} breakpoint. This also
4929 invalidates the Python @code{Breakpoint} object. Any further access
4930 to this object's attributes or methods will raise an error.
4933 @defvar Breakpoint.enabled
4934 This attribute is @code{True} if the breakpoint is enabled, and
4935 @code{False} otherwise. This attribute is writable. You can use it to enable
4936 or disable the breakpoint.
4939 @defvar Breakpoint.silent
4940 This attribute is @code{True} if the breakpoint is silent, and
4941 @code{False} otherwise. This attribute is writable.
4943 Note that a breakpoint can also be silent if it has commands and the
4944 first command is @code{silent}. This is not reported by the
4945 @code{silent} attribute.
4948 @defvar Breakpoint.pending
4949 This attribute is @code{True} if the breakpoint is pending, and
4950 @code{False} otherwise. @xref{Set Breaks}. This attribute is
4954 @anchor{python_breakpoint_thread}
4955 @defvar Breakpoint.thread
4956 If the breakpoint is thread-specific, this attribute holds the
4957 thread's global id. If the breakpoint is not thread-specific, this
4958 attribute is @code{None}. This attribute is writable.
4961 @defvar Breakpoint.task
4962 If the breakpoint is Ada task-specific, this attribute holds the Ada task
4963 id. If the breakpoint is not task-specific (or the underlying
4964 language is not Ada), this attribute is @code{None}. This attribute
4968 @defvar Breakpoint.ignore_count
4969 This attribute holds the ignore count for the breakpoint, an integer.
4970 This attribute is writable.
4973 @defvar Breakpoint.number
4974 This attribute holds the breakpoint's number --- the identifier used by
4975 the user to manipulate the breakpoint. This attribute is not writable.
4978 @defvar Breakpoint.type
4979 This attribute holds the breakpoint's type --- the identifier used to
4980 determine the actual breakpoint type or use-case. This attribute is not
4984 @defvar Breakpoint.visible
4985 This attribute tells whether the breakpoint is visible to the user
4986 when set, or when the @samp{info breakpoints} command is run. This
4987 attribute is not writable.
4990 @defvar Breakpoint.temporary
4991 This attribute indicates whether the breakpoint was created as a
4992 temporary breakpoint. Temporary breakpoints are automatically deleted
4993 after that breakpoint has been hit. Access to this attribute, and all
4994 other attributes and functions other than the @code{is_valid}
4995 function, will result in an error after the breakpoint has been hit
4996 (as it has been automatically deleted). This attribute is not
5000 @defvar Breakpoint.hit_count
5001 This attribute holds the hit count for the breakpoint, an integer.
5002 This attribute is writable, but currently it can only be set to zero.
5005 @defvar Breakpoint.location
5006 This attribute holds the location of the breakpoint, as specified by
5007 the user. It is a string. If the breakpoint does not have a location
5008 (that is, it is a watchpoint) the attribute's value is @code{None}. This
5009 attribute is not writable.
5012 @defvar Breakpoint.expression
5013 This attribute holds a breakpoint expression, as specified by
5014 the user. It is a string. If the breakpoint does not have an
5015 expression (the breakpoint is not a watchpoint) the attribute's value
5016 is @code{None}. This attribute is not writable.
5019 @defvar Breakpoint.condition
5020 This attribute holds the condition of the breakpoint, as specified by
5021 the user. It is a string. If there is no condition, this attribute's
5022 value is @code{None}. This attribute is writable.
5025 @defvar Breakpoint.commands
5026 This attribute holds the commands attached to the breakpoint. If
5027 there are commands, this attribute's value is a string holding all the
5028 commands, separated by newlines. If there are no commands, this
5029 attribute is @code{None}. This attribute is not writable.
5032 @node Finish Breakpoints in Python
5033 @subsubsection Finish Breakpoints
5035 @cindex python finish breakpoints
5036 @tindex gdb.FinishBreakpoint
5038 A finish breakpoint is a temporary breakpoint set at the return address of
5039 a frame, based on the @code{finish} command. @code{gdb.FinishBreakpoint}
5040 extends @code{gdb.Breakpoint}. The underlying breakpoint will be disabled
5041 and deleted when the execution will run out of the breakpoint scope (i.e.@:
5042 @code{Breakpoint.stop} or @code{FinishBreakpoint.out_of_scope} triggered).
5043 Finish breakpoints are thread specific and must be create with the right
5046 @defun FinishBreakpoint.__init__ (@r{[}frame@r{]} @r{[}, internal@r{]})
5047 Create a finish breakpoint at the return address of the @code{gdb.Frame}
5048 object @var{frame}. If @var{frame} is not provided, this defaults to the
5049 newest frame. The optional @var{internal} argument allows the breakpoint to
5050 become invisible to the user. @xref{Breakpoints In Python}, for further
5051 details about this argument.
5054 @defun FinishBreakpoint.out_of_scope (self)
5055 In some circumstances (e.g.@: @code{longjmp}, C@t{++} exceptions, @value{GDBN}
5056 @code{return} command, @dots{}), a function may not properly terminate, and
5057 thus never hit the finish breakpoint. When @value{GDBN} notices such a
5058 situation, the @code{out_of_scope} callback will be triggered.
5060 You may want to sub-class @code{gdb.FinishBreakpoint} and override this
5064 class MyFinishBreakpoint (gdb.FinishBreakpoint)
5066 print "normal finish"
5069 def out_of_scope ():
5070 print "abnormal finish"
5074 @defvar FinishBreakpoint.return_value
5075 When @value{GDBN} is stopped at a finish breakpoint and the frame
5076 used to build the @code{gdb.FinishBreakpoint} object had debug symbols, this
5077 attribute will contain a @code{gdb.Value} object corresponding to the return
5078 value of the function. The value will be @code{None} if the function return
5079 type is @code{void} or if the return value was not computable. This attribute
5083 @node Lazy Strings In Python
5084 @subsubsection Python representation of lazy strings.
5086 @cindex lazy strings in python
5087 @tindex gdb.LazyString
5089 A @dfn{lazy string} is a string whose contents is not retrieved or
5090 encoded until it is needed.
5092 A @code{gdb.LazyString} is represented in @value{GDBN} as an
5093 @code{address} that points to a region of memory, an @code{encoding}
5094 that will be used to encode that region of memory, and a @code{length}
5095 to delimit the region of memory that represents the string. The
5096 difference between a @code{gdb.LazyString} and a string wrapped within
5097 a @code{gdb.Value} is that a @code{gdb.LazyString} will be treated
5098 differently by @value{GDBN} when printing. A @code{gdb.LazyString} is
5099 retrieved and encoded during printing, while a @code{gdb.Value}
5100 wrapping a string is immediately retrieved and encoded on creation.
5102 A @code{gdb.LazyString} object has the following functions:
5104 @defun LazyString.value ()
5105 Convert the @code{gdb.LazyString} to a @code{gdb.Value}. This value
5106 will point to the string in memory, but will lose all the delayed
5107 retrieval, encoding and handling that @value{GDBN} applies to a
5108 @code{gdb.LazyString}.
5111 @defvar LazyString.address
5112 This attribute holds the address of the string. This attribute is not
5116 @defvar LazyString.length
5117 This attribute holds the length of the string in characters. If the
5118 length is -1, then the string will be fetched and encoded up to the
5119 first null of appropriate width. This attribute is not writable.
5122 @defvar LazyString.encoding
5123 This attribute holds the encoding that will be applied to the string
5124 when the string is printed by @value{GDBN}. If the encoding is not
5125 set, or contains an empty string, then @value{GDBN} will select the
5126 most appropriate encoding when the string is printed. This attribute
5130 @defvar LazyString.type
5131 This attribute holds the type that is represented by the lazy string's
5132 type. For a lazy string this will always be a pointer type. To
5133 resolve this to the lazy string's character type, use the type's
5134 @code{target} method. @xref{Types In Python}. This attribute is not
5138 @node Architectures In Python
5139 @subsubsection Python representation of architectures
5140 @cindex Python architectures
5142 @value{GDBN} uses architecture specific parameters and artifacts in a
5143 number of its various computations. An architecture is represented
5144 by an instance of the @code{gdb.Architecture} class.
5146 A @code{gdb.Architecture} class has the following methods:
5148 @defun Architecture.name ()
5149 Return the name (string value) of the architecture.
5152 @defun Architecture.disassemble (@var{start_pc} @r{[}, @var{end_pc} @r{[}, @var{count}@r{]]})
5153 Return a list of disassembled instructions starting from the memory
5154 address @var{start_pc}. The optional arguments @var{end_pc} and
5155 @var{count} determine the number of instructions in the returned list.
5156 If both the optional arguments @var{end_pc} and @var{count} are
5157 specified, then a list of at most @var{count} disassembled instructions
5158 whose start address falls in the closed memory address interval from
5159 @var{start_pc} to @var{end_pc} are returned. If @var{end_pc} is not
5160 specified, but @var{count} is specified, then @var{count} number of
5161 instructions starting from the address @var{start_pc} are returned. If
5162 @var{count} is not specified but @var{end_pc} is specified, then all
5163 instructions whose start address falls in the closed memory address
5164 interval from @var{start_pc} to @var{end_pc} are returned. If neither
5165 @var{end_pc} nor @var{count} are specified, then a single instruction at
5166 @var{start_pc} is returned. For all of these cases, each element of the
5167 returned list is a Python @code{dict} with the following string keys:
5172 The value corresponding to this key is a Python long integer capturing
5173 the memory address of the instruction.
5176 The value corresponding to this key is a string value which represents
5177 the instruction with assembly language mnemonics. The assembly
5178 language flavor used is the same as that specified by the current CLI
5179 variable @code{disassembly-flavor}. @xref{Machine Code}.
5182 The value corresponding to this key is the length (integer value) of the
5183 instruction in bytes.
5188 @node Python Auto-loading
5189 @subsection Python Auto-loading
5190 @cindex Python auto-loading
5192 When a new object file is read (for example, due to the @code{file}
5193 command, or because the inferior has loaded a shared library),
5194 @value{GDBN} will look for Python support scripts in several ways:
5195 @file{@var{objfile}-gdb.py} and @code{.debug_gdb_scripts} section.
5196 @xref{Auto-loading extensions}.
5198 The auto-loading feature is useful for supplying application-specific
5199 debugging commands and scripts.
5201 Auto-loading can be enabled or disabled,
5202 and the list of auto-loaded scripts can be printed.
5205 @anchor{set auto-load python-scripts}
5206 @kindex set auto-load python-scripts
5207 @item set auto-load python-scripts [on|off]
5208 Enable or disable the auto-loading of Python scripts.
5210 @anchor{show auto-load python-scripts}
5211 @kindex show auto-load python-scripts
5212 @item show auto-load python-scripts
5213 Show whether auto-loading of Python scripts is enabled or disabled.
5215 @anchor{info auto-load python-scripts}
5216 @kindex info auto-load python-scripts
5217 @cindex print list of auto-loaded Python scripts
5218 @item info auto-load python-scripts [@var{regexp}]
5219 Print the list of all Python scripts that @value{GDBN} auto-loaded.
5221 Also printed is the list of Python scripts that were mentioned in
5222 the @code{.debug_gdb_scripts} section and were either not found
5223 (@pxref{dotdebug_gdb_scripts section}) or were not auto-loaded due to
5224 @code{auto-load safe-path} rejection (@pxref{Auto-loading}).
5225 This is useful because their names are not printed when @value{GDBN}
5226 tries to load them and fails. There may be many of them, and printing
5227 an error message for each one is problematic.
5229 If @var{regexp} is supplied only Python scripts with matching names are printed.
5234 (gdb) info auto-load python-scripts
5236 Yes py-section-script.py
5237 full name: /tmp/py-section-script.py
5238 No my-foo-pretty-printers.py
5242 When reading an auto-loaded file or script, @value{GDBN} sets the
5243 @dfn{current objfile}. This is available via the @code{gdb.current_objfile}
5244 function (@pxref{Objfiles In Python}). This can be useful for
5245 registering objfile-specific pretty-printers and frame-filters.
5247 @node Python modules
5248 @subsection Python modules
5249 @cindex python modules
5251 @value{GDBN} comes with several modules to assist writing Python code.
5254 * gdb.printing:: Building and registering pretty-printers.
5255 * gdb.types:: Utilities for working with types.
5256 * gdb.prompt:: Utilities for prompt value substitution.
5260 @subsubsection gdb.printing
5261 @cindex gdb.printing
5263 This module provides a collection of utilities for working with
5267 @item PrettyPrinter (@var{name}, @var{subprinters}=None)
5268 This class specifies the API that makes @samp{info pretty-printer},
5269 @samp{enable pretty-printer} and @samp{disable pretty-printer} work.
5270 Pretty-printers should generally inherit from this class.
5272 @item SubPrettyPrinter (@var{name})
5273 For printers that handle multiple types, this class specifies the
5274 corresponding API for the subprinters.
5276 @item RegexpCollectionPrettyPrinter (@var{name})
5277 Utility class for handling multiple printers, all recognized via
5278 regular expressions.
5279 @xref{Writing a Pretty-Printer}, for an example.
5281 @item FlagEnumerationPrinter (@var{name})
5282 A pretty-printer which handles printing of @code{enum} values. Unlike
5283 @value{GDBN}'s built-in @code{enum} printing, this printer attempts to
5284 work properly when there is some overlap between the enumeration
5285 constants. The argument @var{name} is the name of the printer and
5286 also the name of the @code{enum} type to look up.
5288 @item register_pretty_printer (@var{obj}, @var{printer}, @var{replace}=False)
5289 Register @var{printer} with the pretty-printer list of @var{obj}.
5290 If @var{replace} is @code{True} then any existing copy of the printer
5291 is replaced. Otherwise a @code{RuntimeError} exception is raised
5292 if a printer with the same name already exists.
5296 @subsubsection gdb.types
5299 This module provides a collection of utilities for working with
5300 @code{gdb.Type} objects.
5303 @item get_basic_type (@var{type})
5304 Return @var{type} with const and volatile qualifiers stripped,
5305 and with typedefs and C@t{++} references converted to the underlying type.
5310 typedef const int const_int;
5312 const_int& foo_ref (foo);
5313 int main () @{ return 0; @}
5320 (gdb) python import gdb.types
5321 (gdb) python foo_ref = gdb.parse_and_eval("foo_ref")
5322 (gdb) python print gdb.types.get_basic_type(foo_ref.type)
5326 @item has_field (@var{type}, @var{field})
5327 Return @code{True} if @var{type}, assumed to be a type with fields
5328 (e.g., a structure or union), has field @var{field}.
5330 @item make_enum_dict (@var{enum_type})
5331 Return a Python @code{dictionary} type produced from @var{enum_type}.
5333 @item deep_items (@var{type})
5334 Returns a Python iterator similar to the standard
5335 @code{gdb.Type.iteritems} method, except that the iterator returned
5336 by @code{deep_items} will recursively traverse anonymous struct or
5337 union fields. For example:
5351 Then in @value{GDBN}:
5353 (@value{GDBP}) python import gdb.types
5354 (@value{GDBP}) python struct_a = gdb.lookup_type("struct A")
5355 (@value{GDBP}) python print struct_a.keys ()
5357 (@value{GDBP}) python print [k for k,v in gdb.types.deep_items(struct_a)]
5358 @{['a', 'b0', 'b1']@}
5361 @item get_type_recognizers ()
5362 Return a list of the enabled type recognizers for the current context.
5363 This is called by @value{GDBN} during the type-printing process
5364 (@pxref{Type Printing API}).
5366 @item apply_type_recognizers (recognizers, type_obj)
5367 Apply the type recognizers, @var{recognizers}, to the type object
5368 @var{type_obj}. If any recognizer returns a string, return that
5369 string. Otherwise, return @code{None}. This is called by
5370 @value{GDBN} during the type-printing process (@pxref{Type Printing
5373 @item register_type_printer (locus, printer)
5374 This is a convenience function to register a type printer
5375 @var{printer}. The printer must implement the type printer protocol.
5376 The @var{locus} argument is either a @code{gdb.Objfile}, in which case
5377 the printer is registered with that objfile; a @code{gdb.Progspace},
5378 in which case the printer is registered with that progspace; or
5379 @code{None}, in which case the printer is registered globally.
5382 This is a base class that implements the type printer protocol. Type
5383 printers are encouraged, but not required, to derive from this class.
5384 It defines a constructor:
5386 @defmethod TypePrinter __init__ (self, name)
5387 Initialize the type printer with the given name. The new printer
5388 starts in the enabled state.
5394 @subsubsection gdb.prompt
5397 This module provides a method for prompt value-substitution.
5400 @item substitute_prompt (@var{string})
5401 Return @var{string} with escape sequences substituted by values. Some
5402 escape sequences take arguments. You can specify arguments inside
5403 ``@{@}'' immediately following the escape sequence.
5405 The escape sequences you can pass to this function are:
5409 Substitute a backslash.
5411 Substitute an ESC character.
5413 Substitute the selected frame; an argument names a frame parameter.
5415 Substitute a newline.
5417 Substitute a parameter's value; the argument names the parameter.
5419 Substitute a carriage return.
5421 Substitute the selected thread; an argument names a thread parameter.
5423 Substitute the version of GDB.
5425 Substitute the current working directory.
5427 Begin a sequence of non-printing characters. These sequences are
5428 typically used with the ESC character, and are not counted in the string
5429 length. Example: ``\[\e[0;34m\](gdb)\[\e[0m\]'' will return a
5430 blue-colored ``(gdb)'' prompt where the length is five.
5432 End a sequence of non-printing characters.
5438 substitute_prompt (``frame: \f,
5439 print arguments: \p@{print frame-arguments@}'')
5442 @exdent will return the string:
5445 "frame: main, print arguments: scalars"