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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 * Commands In Python:: Implementing new commands in Python.
155 * Parameters In Python:: Adding new @value{GDBN} parameters.
156 * Functions In Python:: Writing new convenience functions.
157 * Progspaces In Python:: Program spaces.
158 * Objfiles In Python:: Object files.
159 * Frames In Python:: Accessing inferior stack frames from Python.
160 * Blocks In Python:: Accessing blocks from Python.
161 * Symbols In Python:: Python representation of symbols.
162 * Symbol Tables In Python:: Python representation of symbol tables.
163 * Line Tables In Python:: Python representation of line tables.
164 * Breakpoints In Python:: Manipulating breakpoints using Python.
165 * Finish Breakpoints in Python:: Setting Breakpoints on function return
167 * Lazy Strings In Python:: Python representation of lazy strings.
168 * Architectures In Python:: Python representation of architectures.
172 @subsubsection Basic Python
174 @cindex python stdout
175 @cindex python pagination
176 At startup, @value{GDBN} overrides Python's @code{sys.stdout} and
177 @code{sys.stderr} to print using @value{GDBN}'s output-paging streams.
178 A Python program which outputs to one of these streams may have its
179 output interrupted by the user (@pxref{Screen Size}). In this
180 situation, a Python @code{KeyboardInterrupt} exception is thrown.
182 Some care must be taken when writing Python code to run in
183 @value{GDBN}. Two things worth noting in particular:
187 @value{GDBN} install handlers for @code{SIGCHLD} and @code{SIGINT}.
188 Python code must not override these, or even change the options using
189 @code{sigaction}. If your program changes the handling of these
190 signals, @value{GDBN} will most likely stop working correctly. Note
191 that it is unfortunately common for GUI toolkits to install a
192 @code{SIGCHLD} handler.
195 @value{GDBN} takes care to mark its internal file descriptors as
196 close-on-exec. However, this cannot be done in a thread-safe way on
197 all platforms. Your Python programs should be aware of this and
198 should both create new file descriptors with the close-on-exec flag
199 set and arrange to close unneeded file descriptors before starting a
203 @cindex python functions
204 @cindex python module
206 @value{GDBN} introduces a new Python module, named @code{gdb}. All
207 methods and classes added by @value{GDBN} are placed in this module.
208 @value{GDBN} automatically @code{import}s the @code{gdb} module for
209 use in all scripts evaluated by the @code{python} command.
211 @findex gdb.PYTHONDIR
212 @defvar gdb.PYTHONDIR
213 A string containing the python directory (@pxref{Python}).
217 @defun gdb.execute (command @r{[}, from_tty @r{[}, to_string@r{]]})
218 Evaluate @var{command}, a string, as a @value{GDBN} CLI command.
219 If a GDB exception happens while @var{command} runs, it is
220 translated as described in @ref{Exception Handling,,Exception Handling}.
222 The @var{from_tty} flag specifies whether @value{GDBN} ought to consider this
223 command as having originated from the user invoking it interactively.
224 It must be a boolean value. If omitted, it defaults to @code{False}.
226 By default, any output produced by @var{command} is sent to
227 @value{GDBN}'s standard output (and to the log output if logging is
228 turned on). If the @var{to_string} parameter is
229 @code{True}, then output will be collected by @code{gdb.execute} and
230 returned as a string. The default is @code{False}, in which case the
231 return value is @code{None}. If @var{to_string} is @code{True}, the
232 @value{GDBN} virtual terminal will be temporarily set to unlimited width
233 and height, and its pagination will be disabled; @pxref{Screen Size}.
236 @findex gdb.breakpoints
237 @defun gdb.breakpoints ()
238 Return a sequence holding all of @value{GDBN}'s breakpoints.
239 @xref{Breakpoints In Python}, for more information.
242 @findex gdb.parameter
243 @defun gdb.parameter (parameter)
244 Return the value of a @value{GDBN} @var{parameter} given by its name,
245 a string; the parameter name string may contain spaces if the parameter has a
246 multi-part name. For example, @samp{print object} is a valid
249 If the named parameter does not exist, this function throws a
250 @code{gdb.error} (@pxref{Exception Handling}). Otherwise, the
251 parameter's value is converted to a Python value of the appropriate
256 @defun gdb.history (number)
257 Return a value from @value{GDBN}'s value history (@pxref{Value
258 History}). The @var{number} argument indicates which history element to return.
259 If @var{number} is negative, then @value{GDBN} will take its absolute value
260 and count backward from the last element (i.e., the most recent element) to
261 find the value to return. If @var{number} is zero, then @value{GDBN} will
262 return the most recent element. If the element specified by @var{number}
263 doesn't exist in the value history, a @code{gdb.error} exception will be
266 If no exception is raised, the return value is always an instance of
267 @code{gdb.Value} (@pxref{Values From Inferior}).
270 @findex gdb.parse_and_eval
271 @defun gdb.parse_and_eval (expression)
272 Parse @var{expression}, which must be a string, as an expression in
273 the current language, evaluate it, and return the result as a
276 This function can be useful when implementing a new command
277 (@pxref{Commands In Python}), as it provides a way to parse the
278 command's argument as an expression. It is also useful simply to
279 compute values, for example, it is the only way to get the value of a
280 convenience variable (@pxref{Convenience Vars}) as a @code{gdb.Value}.
283 @findex gdb.find_pc_line
284 @defun gdb.find_pc_line (pc)
285 Return the @code{gdb.Symtab_and_line} object corresponding to the
286 @var{pc} value. @xref{Symbol Tables In Python}. If an invalid
287 value of @var{pc} is passed as an argument, then the @code{symtab} and
288 @code{line} attributes of the returned @code{gdb.Symtab_and_line} object
289 will be @code{None} and 0 respectively.
292 @findex gdb.post_event
293 @defun gdb.post_event (event)
294 Put @var{event}, a callable object taking no arguments, into
295 @value{GDBN}'s internal event queue. This callable will be invoked at
296 some later point, during @value{GDBN}'s event processing. Events
297 posted using @code{post_event} will be run in the order in which they
298 were posted; however, there is no way to know when they will be
299 processed relative to other events inside @value{GDBN}.
301 @value{GDBN} is not thread-safe. If your Python program uses multiple
302 threads, you must be careful to only call @value{GDBN}-specific
303 functions in the @value{GDBN} thread. @code{post_event} ensures
307 (@value{GDBP}) python
311 > def __init__(self, message):
312 > self.message = message;
313 > def __call__(self):
314 > gdb.write(self.message)
316 >class MyThread1 (threading.Thread):
318 > gdb.post_event(Writer("Hello "))
320 >class MyThread2 (threading.Thread):
322 > gdb.post_event(Writer("World\n"))
327 (@value{GDBP}) Hello World
332 @defun gdb.write (string @r{[}, stream{]})
333 Print a string to @value{GDBN}'s paginated output stream. The
334 optional @var{stream} determines the stream to print to. The default
335 stream is @value{GDBN}'s standard output stream. Possible stream
342 @value{GDBN}'s standard output stream.
347 @value{GDBN}'s standard error stream.
352 @value{GDBN}'s log stream (@pxref{Logging Output}).
355 Writing to @code{sys.stdout} or @code{sys.stderr} will automatically
356 call this function and will automatically direct the output to the
362 Flush the buffer of a @value{GDBN} paginated stream so that the
363 contents are displayed immediately. @value{GDBN} will flush the
364 contents of a stream automatically when it encounters a newline in the
365 buffer. The optional @var{stream} determines the stream to flush. The
366 default stream is @value{GDBN}'s standard output stream. Possible
373 @value{GDBN}'s standard output stream.
378 @value{GDBN}'s standard error stream.
383 @value{GDBN}'s log stream (@pxref{Logging Output}).
387 Flushing @code{sys.stdout} or @code{sys.stderr} will automatically
388 call this function for the relevant stream.
391 @findex gdb.target_charset
392 @defun gdb.target_charset ()
393 Return the name of the current target character set (@pxref{Character
394 Sets}). This differs from @code{gdb.parameter('target-charset')} in
395 that @samp{auto} is never returned.
398 @findex gdb.target_wide_charset
399 @defun gdb.target_wide_charset ()
400 Return the name of the current target wide character set
401 (@pxref{Character Sets}). This differs from
402 @code{gdb.parameter('target-wide-charset')} in that @samp{auto} is
406 @findex gdb.solib_name
407 @defun gdb.solib_name (address)
408 Return the name of the shared library holding the given @var{address}
409 as a string, or @code{None}.
412 @findex gdb.decode_line
413 @defun gdb.decode_line @r{[}expression@r{]}
414 Return locations of the line specified by @var{expression}, or of the
415 current line if no argument was given. This function returns a Python
416 tuple containing two elements. The first element contains a string
417 holding any unparsed section of @var{expression} (or @code{None} if
418 the expression has been fully parsed). The second element contains
419 either @code{None} or another tuple that contains all the locations
420 that match the expression represented as @code{gdb.Symtab_and_line}
421 objects (@pxref{Symbol Tables In Python}). If @var{expression} is
422 provided, it is decoded the way that @value{GDBN}'s inbuilt
423 @code{break} or @code{edit} commands do (@pxref{Specify Location}).
426 @defun gdb.prompt_hook (current_prompt)
429 If @var{prompt_hook} is callable, @value{GDBN} will call the method
430 assigned to this operation before a prompt is displayed by
433 The parameter @code{current_prompt} contains the current @value{GDBN}
434 prompt. This method must return a Python string, or @code{None}. If
435 a string is returned, the @value{GDBN} prompt will be set to that
436 string. If @code{None} is returned, @value{GDBN} will continue to use
439 Some prompts cannot be substituted in @value{GDBN}. Secondary prompts
440 such as those used by readline for command input, and annotation
441 related prompts are prohibited from being changed.
444 @node Exception Handling
445 @subsubsection Exception Handling
446 @cindex python exceptions
447 @cindex exceptions, python
449 When executing the @code{python} command, Python exceptions
450 uncaught within the Python code are translated to calls to
451 @value{GDBN} error-reporting mechanism. If the command that called
452 @code{python} does not handle the error, @value{GDBN} will
453 terminate it and print an error message containing the Python
454 exception name, the associated value, and the Python call stack
455 backtrace at the point where the exception was raised. Example:
458 (@value{GDBP}) python print foo
459 Traceback (most recent call last):
460 File "<string>", line 1, in <module>
461 NameError: name 'foo' is not defined
464 @value{GDBN} errors that happen in @value{GDBN} commands invoked by
465 Python code are converted to Python exceptions. The type of the
466 Python exception depends on the error.
470 This is the base class for most exceptions generated by @value{GDBN}.
471 It is derived from @code{RuntimeError}, for compatibility with earlier
472 versions of @value{GDBN}.
474 If an error occurring in @value{GDBN} does not fit into some more
475 specific category, then the generated exception will have this type.
477 @item gdb.MemoryError
478 This is a subclass of @code{gdb.error} which is thrown when an
479 operation tried to access invalid memory in the inferior.
481 @item KeyboardInterrupt
482 User interrupt (via @kbd{C-c} or by typing @kbd{q} at a pagination
483 prompt) is translated to a Python @code{KeyboardInterrupt} exception.
486 In all cases, your exception handler will see the @value{GDBN} error
487 message as its value and the Python call stack backtrace at the Python
488 statement closest to where the @value{GDBN} error occured as the
492 When implementing @value{GDBN} commands in Python via @code{gdb.Command},
493 it is useful to be able to throw an exception that doesn't cause a
494 traceback to be printed. For example, the user may have invoked the
495 command incorrectly. Use the @code{gdb.GdbError} exception
496 to handle this case. Example:
500 >class HelloWorld (gdb.Command):
501 > """Greet the whole world."""
502 > def __init__ (self):
503 > super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)
504 > def invoke (self, args, from_tty):
505 > argv = gdb.string_to_argv (args)
506 > if len (argv) != 0:
507 > raise gdb.GdbError ("hello-world takes no arguments")
508 > print "Hello, World!"
512 hello-world takes no arguments
515 @node Values From Inferior
516 @subsubsection Values From Inferior
517 @cindex values from inferior, with Python
518 @cindex python, working with values from inferior
520 @cindex @code{gdb.Value}
521 @value{GDBN} provides values it obtains from the inferior program in
522 an object of type @code{gdb.Value}. @value{GDBN} uses this object
523 for its internal bookkeeping of the inferior's values, and for
524 fetching values when necessary.
526 Inferior values that are simple scalars can be used directly in
527 Python expressions that are valid for the value's data type. Here's
528 an example for an integer or floating-point value @code{some_val}:
535 As result of this, @code{bar} will also be a @code{gdb.Value} object
536 whose values are of the same type as those of @code{some_val}. Valid
537 Python operations can also be performed on @code{gdb.Value} objects
538 representing a @code{struct} or @code{class} object. For such cases,
539 the overloaded operator (if present), is used to perform the operation.
540 For example, if @code{val1} and @code{val2} are @code{gdb.Value} objects
541 representing instances of a @code{class} which overloads the @code{+}
542 operator, then one can use the @code{+} operator in their Python script
550 The result of the operation @code{val3} is also a @code{gdb.Value}
551 object corresponding to the value returned by the overloaded @code{+}
552 operator. In general, overloaded operators are invoked for the
553 following operations: @code{+} (binary addition), @code{-} (binary
554 subtraction), @code{*} (multiplication), @code{/}, @code{%}, @code{<<},
555 @code{>>}, @code{|}, @code{&}, @code{^}.
557 Inferior values that are structures or instances of some class can
558 be accessed using the Python @dfn{dictionary syntax}. For example, if
559 @code{some_val} is a @code{gdb.Value} instance holding a structure, you
560 can access its @code{foo} element with:
563 bar = some_val['foo']
566 @cindex getting structure elements using gdb.Field objects as subscripts
567 Again, @code{bar} will also be a @code{gdb.Value} object. Structure
568 elements can also be accessed by using @code{gdb.Field} objects as
569 subscripts (@pxref{Types In Python}, for more information on
570 @code{gdb.Field} objects). For example, if @code{foo_field} is a
571 @code{gdb.Field} object corresponding to element @code{foo} of the above
572 structure, then @code{bar} can also be accessed as follows:
575 bar = some_val[foo_field]
578 A @code{gdb.Value} that represents a function can be executed via
579 inferior function call. Any arguments provided to the call must match
580 the function's prototype, and must be provided in the order specified
583 For example, @code{some_val} is a @code{gdb.Value} instance
584 representing a function that takes two integers as arguments. To
585 execute this function, call it like so:
588 result = some_val (10,20)
591 Any values returned from a function call will be stored as a
594 The following attributes are provided:
596 @defvar Value.address
597 If this object is addressable, this read-only attribute holds a
598 @code{gdb.Value} object representing the address. Otherwise,
599 this attribute holds @code{None}.
602 @cindex optimized out value in Python
603 @defvar Value.is_optimized_out
604 This read-only boolean attribute is true if the compiler optimized out
605 this value, thus it is not available for fetching from the inferior.
609 The type of this @code{gdb.Value}. The value of this attribute is a
610 @code{gdb.Type} object (@pxref{Types In Python}).
613 @defvar Value.dynamic_type
614 The dynamic type of this @code{gdb.Value}. This uses C@t{++} run-time
615 type information (@acronym{RTTI}) to determine the dynamic type of the
616 value. If this value is of class type, it will return the class in
617 which the value is embedded, if any. If this value is of pointer or
618 reference to a class type, it will compute the dynamic type of the
619 referenced object, and return a pointer or reference to that type,
620 respectively. In all other cases, it will return the value's static
623 Note that this feature will only work when debugging a C@t{++} program
624 that includes @acronym{RTTI} for the object in question. Otherwise,
625 it will just return the static type of the value as in @kbd{ptype foo}
626 (@pxref{Symbols, ptype}).
629 @defvar Value.is_lazy
630 The value of this read-only boolean attribute is @code{True} if this
631 @code{gdb.Value} has not yet been fetched from the inferior.
632 @value{GDBN} does not fetch values until necessary, for efficiency.
636 myval = gdb.parse_and_eval ('somevar')
639 The value of @code{somevar} is not fetched at this time. It will be
640 fetched when the value is needed, or when the @code{fetch_lazy}
644 The following methods are provided:
646 @defun Value.__init__ (@var{val})
647 Many Python values can be converted directly to a @code{gdb.Value} via
648 this object initializer. Specifically:
652 A Python boolean is converted to the boolean type from the current
656 A Python integer is converted to the C @code{long} type for the
657 current architecture.
660 A Python long is converted to the C @code{long long} type for the
661 current architecture.
664 A Python float is converted to the C @code{double} type for the
665 current architecture.
668 A Python string is converted to a target string in the current target
669 language using the current target encoding.
670 If a character cannot be represented in the current target encoding,
671 then an exception is thrown.
673 @item @code{gdb.Value}
674 If @code{val} is a @code{gdb.Value}, then a copy of the value is made.
676 @item @code{gdb.LazyString}
677 If @code{val} is a @code{gdb.LazyString} (@pxref{Lazy Strings In
678 Python}), then the lazy string's @code{value} method is called, and
683 @defun Value.cast (type)
684 Return a new instance of @code{gdb.Value} that is the result of
685 casting this instance to the type described by @var{type}, which must
686 be a @code{gdb.Type} object. If the cast cannot be performed for some
687 reason, this method throws an exception.
690 @defun Value.dereference ()
691 For pointer data types, this method returns a new @code{gdb.Value} object
692 whose contents is the object pointed to by the pointer. For example, if
693 @code{foo} is a C pointer to an @code{int}, declared in your C program as
700 then you can use the corresponding @code{gdb.Value} to access what
701 @code{foo} points to like this:
704 bar = foo.dereference ()
707 The result @code{bar} will be a @code{gdb.Value} object holding the
708 value pointed to by @code{foo}.
710 A similar function @code{Value.referenced_value} exists which also
711 returns @code{gdb.Value} objects corresonding to the values pointed to
712 by pointer values (and additionally, values referenced by reference
713 values). However, the behavior of @code{Value.dereference}
714 differs from @code{Value.referenced_value} by the fact that the
715 behavior of @code{Value.dereference} is identical to applying the C
716 unary operator @code{*} on a given value. For example, consider a
717 reference to a pointer @code{ptrref}, declared in your C@t{++} program
725 intptr &ptrref = ptr;
728 Though @code{ptrref} is a reference value, one can apply the method
729 @code{Value.dereference} to the @code{gdb.Value} object corresponding
730 to it and obtain a @code{gdb.Value} which is identical to that
731 corresponding to @code{val}. However, if you apply the method
732 @code{Value.referenced_value}, the result would be a @code{gdb.Value}
733 object identical to that corresponding to @code{ptr}.
736 py_ptrref = gdb.parse_and_eval ("ptrref")
737 py_val = py_ptrref.dereference ()
738 py_ptr = py_ptrref.referenced_value ()
741 The @code{gdb.Value} object @code{py_val} is identical to that
742 corresponding to @code{val}, and @code{py_ptr} is identical to that
743 corresponding to @code{ptr}. In general, @code{Value.dereference} can
744 be applied whenever the C unary operator @code{*} can be applied
745 to the corresponding C value. For those cases where applying both
746 @code{Value.dereference} and @code{Value.referenced_value} is allowed,
747 the results obtained need not be identical (as we have seen in the above
748 example). The results are however identical when applied on
749 @code{gdb.Value} objects corresponding to pointers (@code{gdb.Value}
750 objects with type code @code{TYPE_CODE_PTR}) in a C/C@t{++} program.
753 @defun Value.referenced_value ()
754 For pointer or reference data types, this method returns a new
755 @code{gdb.Value} object corresponding to the value referenced by the
756 pointer/reference value. For pointer data types,
757 @code{Value.dereference} and @code{Value.referenced_value} produce
758 identical results. The difference between these methods is that
759 @code{Value.dereference} cannot get the values referenced by reference
760 values. For example, consider a reference to an @code{int}, declared
761 in your C@t{++} program as
769 then applying @code{Value.dereference} to the @code{gdb.Value} object
770 corresponding to @code{ref} will result in an error, while applying
771 @code{Value.referenced_value} will result in a @code{gdb.Value} object
772 identical to that corresponding to @code{val}.
775 py_ref = gdb.parse_and_eval ("ref")
776 er_ref = py_ref.dereference () # Results in error
777 py_val = py_ref.referenced_value () # Returns the referenced value
780 The @code{gdb.Value} object @code{py_val} is identical to that
781 corresponding to @code{val}.
784 @defun Value.dynamic_cast (type)
785 Like @code{Value.cast}, but works as if the C@t{++} @code{dynamic_cast}
786 operator were used. Consult a C@t{++} reference for details.
789 @defun Value.reinterpret_cast (type)
790 Like @code{Value.cast}, but works as if the C@t{++} @code{reinterpret_cast}
791 operator were used. Consult a C@t{++} reference for details.
794 @defun Value.string (@r{[}encoding@r{[}, errors@r{[}, length@r{]]]})
795 If this @code{gdb.Value} represents a string, then this method
796 converts the contents to a Python string. Otherwise, this method will
799 Values are interpreted as strings according to the rules of the
800 current language. If the optional length argument is given, the
801 string will be converted to that length, and will include any embedded
802 zeroes that the string may contain. Otherwise, for languages
803 where the string is zero-terminated, the entire string will be
806 For example, in C-like languages, a value is a string if it is a pointer
807 to or an array of characters or ints of type @code{wchar_t}, @code{char16_t},
810 If the optional @var{encoding} argument is given, it must be a string
811 naming the encoding of the string in the @code{gdb.Value}, such as
812 @code{"ascii"}, @code{"iso-8859-6"} or @code{"utf-8"}. It accepts
813 the same encodings as the corresponding argument to Python's
814 @code{string.decode} method, and the Python codec machinery will be used
815 to convert the string. If @var{encoding} is not given, or if
816 @var{encoding} is the empty string, then either the @code{target-charset}
817 (@pxref{Character Sets}) will be used, or a language-specific encoding
818 will be used, if the current language is able to supply one.
820 The optional @var{errors} argument is the same as the corresponding
821 argument to Python's @code{string.decode} method.
823 If the optional @var{length} argument is given, the string will be
824 fetched and converted to the given length.
827 @defun Value.lazy_string (@r{[}encoding @r{[}, length@r{]]})
828 If this @code{gdb.Value} represents a string, then this method
829 converts the contents to a @code{gdb.LazyString} (@pxref{Lazy Strings
830 In Python}). Otherwise, this method will throw an exception.
832 If the optional @var{encoding} argument is given, it must be a string
833 naming the encoding of the @code{gdb.LazyString}. Some examples are:
834 @samp{ascii}, @samp{iso-8859-6} or @samp{utf-8}. If the
835 @var{encoding} argument is an encoding that @value{GDBN} does
836 recognize, @value{GDBN} will raise an error.
838 When a lazy string is printed, the @value{GDBN} encoding machinery is
839 used to convert the string during printing. If the optional
840 @var{encoding} argument is not provided, or is an empty string,
841 @value{GDBN} will automatically select the encoding most suitable for
842 the string type. For further information on encoding in @value{GDBN}
843 please see @ref{Character Sets}.
845 If the optional @var{length} argument is given, the string will be
846 fetched and encoded to the length of characters specified. If
847 the @var{length} argument is not provided, the string will be fetched
848 and encoded until a null of appropriate width is found.
851 @defun Value.fetch_lazy ()
852 If the @code{gdb.Value} object is currently a lazy value
853 (@code{gdb.Value.is_lazy} is @code{True}), then the value is
854 fetched from the inferior. Any errors that occur in the process
855 will produce a Python exception.
857 If the @code{gdb.Value} object is not a lazy value, this method
860 This method does not return a value.
864 @node Types In Python
865 @subsubsection Types In Python
866 @cindex types in Python
867 @cindex Python, working with types
870 @value{GDBN} represents types from the inferior using the class
873 The following type-related functions are available in the @code{gdb}
876 @findex gdb.lookup_type
877 @defun gdb.lookup_type (name @r{[}, block@r{]})
878 This function looks up a type by its @var{name}, which must be a string.
880 If @var{block} is given, then @var{name} is looked up in that scope.
881 Otherwise, it is searched for globally.
883 Ordinarily, this function will return an instance of @code{gdb.Type}.
884 If the named type cannot be found, it will throw an exception.
887 If the type is a structure or class type, or an enum type, the fields
888 of that type can be accessed using the Python @dfn{dictionary syntax}.
889 For example, if @code{some_type} is a @code{gdb.Type} instance holding
890 a structure type, you can access its @code{foo} field with:
893 bar = some_type['foo']
896 @code{bar} will be a @code{gdb.Field} object; see below under the
897 description of the @code{Type.fields} method for a description of the
898 @code{gdb.Field} class.
900 An instance of @code{Type} has the following attributes:
903 The type code for this type. The type code will be one of the
904 @code{TYPE_CODE_} constants defined below.
908 The name of this type. If this type has no name, then @code{None}
913 The size of this type, in target @code{char} units. Usually, a
914 target's @code{char} type will be an 8-bit byte. However, on some
915 unusual platforms, this type may have a different size.
919 The tag name for this type. The tag name is the name after
920 @code{struct}, @code{union}, or @code{enum} in C and C@t{++}; not all
921 languages have this concept. If this type has no tag name, then
922 @code{None} is returned.
925 The following methods are provided:
927 @defun Type.fields ()
928 For structure and union types, this method returns the fields. Range
929 types have two fields, the minimum and maximum values. Enum types
930 have one field per enum constant. Function and method types have one
931 field per parameter. The base types of C@t{++} classes are also
932 represented as fields. If the type has no fields, or does not fit
933 into one of these categories, an empty sequence will be returned.
935 Each field is a @code{gdb.Field} object, with some pre-defined attributes:
938 This attribute is not available for @code{enum} or @code{static}
939 (as in C@t{++} or Java) fields. The value is the position, counting
940 in bits, from the start of the containing type.
943 This attribute is only available for @code{enum} fields, and its value
944 is the enumeration member's integer representation.
947 The name of the field, or @code{None} for anonymous fields.
950 This is @code{True} if the field is artificial, usually meaning that
951 it was provided by the compiler and not the user. This attribute is
952 always provided, and is @code{False} if the field is not artificial.
955 This is @code{True} if the field represents a base class of a C@t{++}
956 structure. This attribute is always provided, and is @code{False}
957 if the field is not a base class of the type that is the argument of
958 @code{fields}, or if that type was not a C@t{++} class.
961 If the field is packed, or is a bitfield, then this will have a
962 non-zero value, which is the size of the field in bits. Otherwise,
963 this will be zero; in this case the field's size is given by its type.
966 The type of the field. This is usually an instance of @code{Type},
967 but it can be @code{None} in some situations.
970 The type which contains this field. This is an instance of
975 @defun Type.array (@var{n1} @r{[}, @var{n2}@r{]})
976 Return a new @code{gdb.Type} object which represents an array of this
977 type. If one argument is given, it is the inclusive upper bound of
978 the array; in this case the lower bound is zero. If two arguments are
979 given, the first argument is the lower bound of the array, and the
980 second argument is the upper bound of the array. An array's length
981 must not be negative, but the bounds can be.
984 @defun Type.vector (@var{n1} @r{[}, @var{n2}@r{]})
985 Return a new @code{gdb.Type} object which represents a vector of this
986 type. If one argument is given, it is the inclusive upper bound of
987 the vector; in this case the lower bound is zero. If two arguments are
988 given, the first argument is the lower bound of the vector, and the
989 second argument is the upper bound of the vector. A vector's length
990 must not be negative, but the bounds can be.
992 The difference between an @code{array} and a @code{vector} is that
993 arrays behave like in C: when used in expressions they decay to a pointer
994 to the first element whereas vectors are treated as first class values.
998 Return a new @code{gdb.Type} object which represents a
999 @code{const}-qualified variant of this type.
1002 @defun Type.volatile ()
1003 Return a new @code{gdb.Type} object which represents a
1004 @code{volatile}-qualified variant of this type.
1007 @defun Type.unqualified ()
1008 Return a new @code{gdb.Type} object which represents an unqualified
1009 variant of this type. That is, the result is neither @code{const} nor
1013 @defun Type.range ()
1014 Return a Python @code{Tuple} object that contains two elements: the
1015 low bound of the argument type and the high bound of that type. If
1016 the type does not have a range, @value{GDBN} will raise a
1017 @code{gdb.error} exception (@pxref{Exception Handling}).
1020 @defun Type.reference ()
1021 Return a new @code{gdb.Type} object which represents a reference to this
1025 @defun Type.pointer ()
1026 Return a new @code{gdb.Type} object which represents a pointer to this
1030 @defun Type.strip_typedefs ()
1031 Return a new @code{gdb.Type} that represents the real type,
1032 after removing all layers of typedefs.
1035 @defun Type.target ()
1036 Return a new @code{gdb.Type} object which represents the target type
1039 For a pointer type, the target type is the type of the pointed-to
1040 object. For an array type (meaning C-like arrays), the target type is
1041 the type of the elements of the array. For a function or method type,
1042 the target type is the type of the return value. For a complex type,
1043 the target type is the type of the elements. For a typedef, the
1044 target type is the aliased type.
1046 If the type does not have a target, this method will throw an
1050 @defun Type.template_argument (n @r{[}, block@r{]})
1051 If this @code{gdb.Type} is an instantiation of a template, this will
1052 return a new @code{gdb.Value} or @code{gdb.Type} which represents the
1053 value of the @var{n}th template argument (indexed starting at 0).
1055 If this @code{gdb.Type} is not a template type, or if the type has fewer
1056 than @var{n} template arguments, this will throw an exception.
1057 Ordinarily, only C@t{++} code will have template types.
1059 If @var{block} is given, then @var{name} is looked up in that scope.
1060 Otherwise, it is searched for globally.
1064 Each type has a code, which indicates what category this type falls
1065 into. The available type categories are represented by constants
1066 defined in the @code{gdb} module:
1069 @vindex TYPE_CODE_PTR
1070 @item gdb.TYPE_CODE_PTR
1071 The type is a pointer.
1073 @vindex TYPE_CODE_ARRAY
1074 @item gdb.TYPE_CODE_ARRAY
1075 The type is an array.
1077 @vindex TYPE_CODE_STRUCT
1078 @item gdb.TYPE_CODE_STRUCT
1079 The type is a structure.
1081 @vindex TYPE_CODE_UNION
1082 @item gdb.TYPE_CODE_UNION
1083 The type is a union.
1085 @vindex TYPE_CODE_ENUM
1086 @item gdb.TYPE_CODE_ENUM
1087 The type is an enum.
1089 @vindex TYPE_CODE_FLAGS
1090 @item gdb.TYPE_CODE_FLAGS
1091 A bit flags type, used for things such as status registers.
1093 @vindex TYPE_CODE_FUNC
1094 @item gdb.TYPE_CODE_FUNC
1095 The type is a function.
1097 @vindex TYPE_CODE_INT
1098 @item gdb.TYPE_CODE_INT
1099 The type is an integer type.
1101 @vindex TYPE_CODE_FLT
1102 @item gdb.TYPE_CODE_FLT
1103 A floating point type.
1105 @vindex TYPE_CODE_VOID
1106 @item gdb.TYPE_CODE_VOID
1107 The special type @code{void}.
1109 @vindex TYPE_CODE_SET
1110 @item gdb.TYPE_CODE_SET
1113 @vindex TYPE_CODE_RANGE
1114 @item gdb.TYPE_CODE_RANGE
1115 A range type, that is, an integer type with bounds.
1117 @vindex TYPE_CODE_STRING
1118 @item gdb.TYPE_CODE_STRING
1119 A string type. Note that this is only used for certain languages with
1120 language-defined string types; C strings are not represented this way.
1122 @vindex TYPE_CODE_BITSTRING
1123 @item gdb.TYPE_CODE_BITSTRING
1124 A string of bits. It is deprecated.
1126 @vindex TYPE_CODE_ERROR
1127 @item gdb.TYPE_CODE_ERROR
1128 An unknown or erroneous type.
1130 @vindex TYPE_CODE_METHOD
1131 @item gdb.TYPE_CODE_METHOD
1132 A method type, as found in C@t{++} or Java.
1134 @vindex TYPE_CODE_METHODPTR
1135 @item gdb.TYPE_CODE_METHODPTR
1136 A pointer-to-member-function.
1138 @vindex TYPE_CODE_MEMBERPTR
1139 @item gdb.TYPE_CODE_MEMBERPTR
1140 A pointer-to-member.
1142 @vindex TYPE_CODE_REF
1143 @item gdb.TYPE_CODE_REF
1146 @vindex TYPE_CODE_CHAR
1147 @item gdb.TYPE_CODE_CHAR
1150 @vindex TYPE_CODE_BOOL
1151 @item gdb.TYPE_CODE_BOOL
1154 @vindex TYPE_CODE_COMPLEX
1155 @item gdb.TYPE_CODE_COMPLEX
1156 A complex float type.
1158 @vindex TYPE_CODE_TYPEDEF
1159 @item gdb.TYPE_CODE_TYPEDEF
1160 A typedef to some other type.
1162 @vindex TYPE_CODE_NAMESPACE
1163 @item gdb.TYPE_CODE_NAMESPACE
1164 A C@t{++} namespace.
1166 @vindex TYPE_CODE_DECFLOAT
1167 @item gdb.TYPE_CODE_DECFLOAT
1168 A decimal floating point type.
1170 @vindex TYPE_CODE_INTERNAL_FUNCTION
1171 @item gdb.TYPE_CODE_INTERNAL_FUNCTION
1172 A function internal to @value{GDBN}. This is the type used to represent
1173 convenience functions.
1176 Further support for types is provided in the @code{gdb.types}
1177 Python module (@pxref{gdb.types}).
1179 @node Pretty Printing API
1180 @subsubsection Pretty Printing API
1181 @cindex python pretty printing api
1183 An example output is provided (@pxref{Pretty Printing}).
1185 A pretty-printer is just an object that holds a value and implements a
1186 specific interface, defined here.
1188 @defun pretty_printer.children (self)
1189 @value{GDBN} will call this method on a pretty-printer to compute the
1190 children of the pretty-printer's value.
1192 This method must return an object conforming to the Python iterator
1193 protocol. Each item returned by the iterator must be a tuple holding
1194 two elements. The first element is the ``name'' of the child; the
1195 second element is the child's value. The value can be any Python
1196 object which is convertible to a @value{GDBN} value.
1198 This method is optional. If it does not exist, @value{GDBN} will act
1199 as though the value has no children.
1202 @defun pretty_printer.display_hint (self)
1203 The CLI may call this method and use its result to change the
1204 formatting of a value. The result will also be supplied to an MI
1205 consumer as a @samp{displayhint} attribute of the variable being
1208 This method is optional. If it does exist, this method must return a
1211 Some display hints are predefined by @value{GDBN}:
1215 Indicate that the object being printed is ``array-like''. The CLI
1216 uses this to respect parameters such as @code{set print elements} and
1217 @code{set print array}.
1220 Indicate that the object being printed is ``map-like'', and that the
1221 children of this value can be assumed to alternate between keys and
1225 Indicate that the object being printed is ``string-like''. If the
1226 printer's @code{to_string} method returns a Python string of some
1227 kind, then @value{GDBN} will call its internal language-specific
1228 string-printing function to format the string. For the CLI this means
1229 adding quotation marks, possibly escaping some characters, respecting
1230 @code{set print elements}, and the like.
1234 @defun pretty_printer.to_string (self)
1235 @value{GDBN} will call this method to display the string
1236 representation of the value passed to the object's constructor.
1238 When printing from the CLI, if the @code{to_string} method exists,
1239 then @value{GDBN} will prepend its result to the values returned by
1240 @code{children}. Exactly how this formatting is done is dependent on
1241 the display hint, and may change as more hints are added. Also,
1242 depending on the print settings (@pxref{Print Settings}), the CLI may
1243 print just the result of @code{to_string} in a stack trace, omitting
1244 the result of @code{children}.
1246 If this method returns a string, it is printed verbatim.
1248 Otherwise, if this method returns an instance of @code{gdb.Value},
1249 then @value{GDBN} prints this value. This may result in a call to
1250 another pretty-printer.
1252 If instead the method returns a Python value which is convertible to a
1253 @code{gdb.Value}, then @value{GDBN} performs the conversion and prints
1254 the resulting value. Again, this may result in a call to another
1255 pretty-printer. Python scalars (integers, floats, and booleans) and
1256 strings are convertible to @code{gdb.Value}; other types are not.
1258 Finally, if this method returns @code{None} then no further operations
1259 are peformed in this method and nothing is printed.
1261 If the result is not one of these types, an exception is raised.
1264 @value{GDBN} provides a function which can be used to look up the
1265 default pretty-printer for a @code{gdb.Value}:
1267 @findex gdb.default_visualizer
1268 @defun gdb.default_visualizer (value)
1269 This function takes a @code{gdb.Value} object as an argument. If a
1270 pretty-printer for this value exists, then it is returned. If no such
1271 printer exists, then this returns @code{None}.
1274 @node Selecting Pretty-Printers
1275 @subsubsection Selecting Pretty-Printers
1276 @cindex selecting python pretty-printers
1278 The Python list @code{gdb.pretty_printers} contains an array of
1279 functions or callable objects that have been registered via addition
1280 as a pretty-printer. Printers in this list are called @code{global}
1281 printers, they're available when debugging all inferiors.
1282 Each @code{gdb.Progspace} contains a @code{pretty_printers} attribute.
1283 Each @code{gdb.Objfile} also contains a @code{pretty_printers}
1286 Each function on these lists is passed a single @code{gdb.Value}
1287 argument and should return a pretty-printer object conforming to the
1288 interface definition above (@pxref{Pretty Printing API}). If a function
1289 cannot create a pretty-printer for the value, it should return
1292 @value{GDBN} first checks the @code{pretty_printers} attribute of each
1293 @code{gdb.Objfile} in the current program space and iteratively calls
1294 each enabled lookup routine in the list for that @code{gdb.Objfile}
1295 until it receives a pretty-printer object.
1296 If no pretty-printer is found in the objfile lists, @value{GDBN} then
1297 searches the pretty-printer list of the current program space,
1298 calling each enabled function until an object is returned.
1299 After these lists have been exhausted, it tries the global
1300 @code{gdb.pretty_printers} list, again calling each enabled function until an
1303 The order in which the objfiles are searched is not specified. For a
1304 given list, functions are always invoked from the head of the list,
1305 and iterated over sequentially until the end of the list, or a printer
1308 For various reasons a pretty-printer may not work.
1309 For example, the underlying data structure may have changed and
1310 the pretty-printer is out of date.
1312 The consequences of a broken pretty-printer are severe enough that
1313 @value{GDBN} provides support for enabling and disabling individual
1314 printers. For example, if @code{print frame-arguments} is on,
1315 a backtrace can become highly illegible if any argument is printed
1316 with a broken printer.
1318 Pretty-printers are enabled and disabled by attaching an @code{enabled}
1319 attribute to the registered function or callable object. If this attribute
1320 is present and its value is @code{False}, the printer is disabled, otherwise
1321 the printer is enabled.
1323 @node Writing a Pretty-Printer
1324 @subsubsection Writing a Pretty-Printer
1325 @cindex writing a pretty-printer
1327 A pretty-printer consists of two parts: a lookup function to detect
1328 if the type is supported, and the printer itself.
1330 Here is an example showing how a @code{std::string} printer might be
1331 written. @xref{Pretty Printing API}, for details on the API this class
1335 class StdStringPrinter(object):
1336 "Print a std::string"
1338 def __init__(self, val):
1341 def to_string(self):
1342 return self.val['_M_dataplus']['_M_p']
1344 def display_hint(self):
1348 And here is an example showing how a lookup function for the printer
1349 example above might be written.
1352 def str_lookup_function(val):
1353 lookup_tag = val.type.tag
1354 if lookup_tag == None:
1356 regex = re.compile("^std::basic_string<char,.*>$")
1357 if regex.match(lookup_tag):
1358 return StdStringPrinter(val)
1362 The example lookup function extracts the value's type, and attempts to
1363 match it to a type that it can pretty-print. If it is a type the
1364 printer can pretty-print, it will return a printer object. If not, it
1365 returns @code{None}.
1367 We recommend that you put your core pretty-printers into a Python
1368 package. If your pretty-printers are for use with a library, we
1369 further recommend embedding a version number into the package name.
1370 This practice will enable @value{GDBN} to load multiple versions of
1371 your pretty-printers at the same time, because they will have
1374 You should write auto-loaded code (@pxref{Python Auto-loading}) such that it
1375 can be evaluated multiple times without changing its meaning. An
1376 ideal auto-load file will consist solely of @code{import}s of your
1377 printer modules, followed by a call to a register pretty-printers with
1378 the current objfile.
1380 Taken as a whole, this approach will scale nicely to multiple
1381 inferiors, each potentially using a different library version.
1382 Embedding a version number in the Python package name will ensure that
1383 @value{GDBN} is able to load both sets of printers simultaneously.
1384 Then, because the search for pretty-printers is done by objfile, and
1385 because your auto-loaded code took care to register your library's
1386 printers with a specific objfile, @value{GDBN} will find the correct
1387 printers for the specific version of the library used by each
1390 To continue the @code{std::string} example (@pxref{Pretty Printing API}),
1391 this code might appear in @code{gdb.libstdcxx.v6}:
1394 def register_printers(objfile):
1395 objfile.pretty_printers.append(str_lookup_function)
1399 And then the corresponding contents of the auto-load file would be:
1402 import gdb.libstdcxx.v6
1403 gdb.libstdcxx.v6.register_printers(gdb.current_objfile())
1406 The previous example illustrates a basic pretty-printer.
1407 There are a few things that can be improved on.
1408 The printer doesn't have a name, making it hard to identify in a
1409 list of installed printers. The lookup function has a name, but
1410 lookup functions can have arbitrary, even identical, names.
1412 Second, the printer only handles one type, whereas a library typically has
1413 several types. One could install a lookup function for each desired type
1414 in the library, but one could also have a single lookup function recognize
1415 several types. The latter is the conventional way this is handled.
1416 If a pretty-printer can handle multiple data types, then its
1417 @dfn{subprinters} are the printers for the individual data types.
1419 The @code{gdb.printing} module provides a formal way of solving these
1420 problems (@pxref{gdb.printing}).
1421 Here is another example that handles multiple types.
1423 These are the types we are going to pretty-print:
1426 struct foo @{ int a, b; @};
1427 struct bar @{ struct foo x, y; @};
1430 Here are the printers:
1434 """Print a foo object."""
1436 def __init__(self, val):
1439 def to_string(self):
1440 return ("a=<" + str(self.val["a"]) +
1441 "> b=<" + str(self.val["b"]) + ">")
1444 """Print a bar object."""
1446 def __init__(self, val):
1449 def to_string(self):
1450 return ("x=<" + str(self.val["x"]) +
1451 "> y=<" + str(self.val["y"]) + ">")
1454 This example doesn't need a lookup function, that is handled by the
1455 @code{gdb.printing} module. Instead a function is provided to build up
1456 the object that handles the lookup.
1461 def build_pretty_printer():
1462 pp = gdb.printing.RegexpCollectionPrettyPrinter(
1464 pp.add_printer('foo', '^foo$', fooPrinter)
1465 pp.add_printer('bar', '^bar$', barPrinter)
1469 And here is the autoload support:
1474 gdb.printing.register_pretty_printer(
1475 gdb.current_objfile(),
1476 my_library.build_pretty_printer())
1479 Finally, when this printer is loaded into @value{GDBN}, here is the
1480 corresponding output of @samp{info pretty-printer}:
1483 (gdb) info pretty-printer
1490 @node Type Printing API
1491 @subsubsection Type Printing API
1492 @cindex type printing API for Python
1494 @value{GDBN} provides a way for Python code to customize type display.
1495 This is mainly useful for substituting canonical typedef names for
1498 @cindex type printer
1499 A @dfn{type printer} is just a Python object conforming to a certain
1500 protocol. A simple base class implementing the protocol is provided;
1501 see @ref{gdb.types}. A type printer must supply at least:
1503 @defivar type_printer enabled
1504 A boolean which is True if the printer is enabled, and False
1505 otherwise. This is manipulated by the @code{enable type-printer}
1506 and @code{disable type-printer} commands.
1509 @defivar type_printer name
1510 The name of the type printer. This must be a string. This is used by
1511 the @code{enable type-printer} and @code{disable type-printer}
1515 @defmethod type_printer instantiate (self)
1516 This is called by @value{GDBN} at the start of type-printing. It is
1517 only called if the type printer is enabled. This method must return a
1518 new object that supplies a @code{recognize} method, as described below.
1522 When displaying a type, say via the @code{ptype} command, @value{GDBN}
1523 will compute a list of type recognizers. This is done by iterating
1524 first over the per-objfile type printers (@pxref{Objfiles In Python}),
1525 followed by the per-progspace type printers (@pxref{Progspaces In
1526 Python}), and finally the global type printers.
1528 @value{GDBN} will call the @code{instantiate} method of each enabled
1529 type printer. If this method returns @code{None}, then the result is
1530 ignored; otherwise, it is appended to the list of recognizers.
1532 Then, when @value{GDBN} is going to display a type name, it iterates
1533 over the list of recognizers. For each one, it calls the recognition
1534 function, stopping if the function returns a non-@code{None} value.
1535 The recognition function is defined as:
1537 @defmethod type_recognizer recognize (self, type)
1538 If @var{type} is not recognized, return @code{None}. Otherwise,
1539 return a string which is to be printed as the name of @var{type}.
1540 The @var{type} argument will be an instance of @code{gdb.Type}
1541 (@pxref{Types In Python}).
1544 @value{GDBN} uses this two-pass approach so that type printers can
1545 efficiently cache information without holding on to it too long. For
1546 example, it can be convenient to look up type information in a type
1547 printer and hold it for a recognizer's lifetime; if a single pass were
1548 done then type printers would have to make use of the event system in
1549 order to avoid holding information that could become stale as the
1552 @node Frame Filter API
1553 @subsubsection Filtering Frames.
1554 @cindex frame filters api
1556 Frame filters are Python objects that manipulate the visibility of a
1557 frame or frames when a backtrace (@pxref{Backtrace}) is printed by
1560 Only commands that print a backtrace, or, in the case of @sc{gdb/mi}
1561 commands (@pxref{GDB/MI}), those that return a collection of frames
1562 are affected. The commands that work with frame filters are:
1564 @code{backtrace} (@pxref{backtrace-command,, The backtrace command}),
1565 @code{-stack-list-frames}
1566 (@pxref{-stack-list-frames,, The -stack-list-frames command}),
1567 @code{-stack-list-variables} (@pxref{-stack-list-variables,, The
1568 -stack-list-variables command}), @code{-stack-list-arguments}
1569 @pxref{-stack-list-arguments,, The -stack-list-arguments command}) and
1570 @code{-stack-list-locals} (@pxref{-stack-list-locals,, The
1571 -stack-list-locals command}).
1573 A frame filter works by taking an iterator as an argument, applying
1574 actions to the contents of that iterator, and returning another
1575 iterator (or, possibly, the same iterator it was provided in the case
1576 where the filter does not perform any operations). Typically, frame
1577 filters utilize tools such as the Python's @code{itertools} module to
1578 work with and create new iterators from the source iterator.
1579 Regardless of how a filter chooses to apply actions, it must not alter
1580 the underlying @value{GDBN} frame or frames, or attempt to alter the
1581 call-stack within @value{GDBN}. This preserves data integrity within
1582 @value{GDBN}. Frame filters are executed on a priority basis and care
1583 should be taken that some frame filters may have been executed before,
1584 and that some frame filters will be executed after.
1586 An important consideration when designing frame filters, and well
1587 worth reflecting upon, is that frame filters should avoid unwinding
1588 the call stack if possible. Some stacks can run very deep, into the
1589 tens of thousands in some cases. To search every frame when a frame
1590 filter executes may be too expensive at that step. The frame filter
1591 cannot know how many frames it has to iterate over, and it may have to
1592 iterate through them all. This ends up duplicating effort as
1593 @value{GDBN} performs this iteration when it prints the frames. If
1594 the filter can defer unwinding frames until frame decorators are
1595 executed, after the last filter has executed, it should. @xref{Frame
1596 Decorator API}, for more information on decorators. Also, there are
1597 examples for both frame decorators and filters in later chapters.
1598 @xref{Writing a Frame Filter}, for more information.
1600 The Python dictionary @code{gdb.frame_filters} contains key/object
1601 pairings that comprise a frame filter. Frame filters in this
1602 dictionary are called @code{global} frame filters, and they are
1603 available when debugging all inferiors. These frame filters must
1604 register with the dictionary directly. In addition to the
1605 @code{global} dictionary, there are other dictionaries that are loaded
1606 with different inferiors via auto-loading (@pxref{Python
1607 Auto-loading}). The two other areas where frame filter dictionaries
1608 can be found are: @code{gdb.Progspace} which contains a
1609 @code{frame_filters} dictionary attribute, and each @code{gdb.Objfile}
1610 object which also contains a @code{frame_filters} dictionary
1613 When a command is executed from @value{GDBN} that is compatible with
1614 frame filters, @value{GDBN} combines the @code{global},
1615 @code{gdb.Progspace} and all @code{gdb.Objfile} dictionaries currently
1616 loaded. All of the @code{gdb.Objfile} dictionaries are combined, as
1617 several frames, and thus several object files, might be in use.
1618 @value{GDBN} then prunes any frame filter whose @code{enabled}
1619 attribute is @code{False}. This pruned list is then sorted according
1620 to the @code{priority} attribute in each filter.
1622 Once the dictionaries are combined, pruned and sorted, @value{GDBN}
1623 creates an iterator which wraps each frame in the call stack in a
1624 @code{FrameDecorator} object, and calls each filter in order. The
1625 output from the previous filter will always be the input to the next
1628 Frame filters have a mandatory interface which each frame filter must
1629 implement, defined here:
1631 @defun FrameFilter.filter (iterator)
1632 @value{GDBN} will call this method on a frame filter when it has
1633 reached the order in the priority list for that filter.
1635 For example, if there are four frame filters:
1646 The order that the frame filters will be called is:
1649 Filter3 -> Filter2 -> Filter1 -> Filter4
1652 Note that the output from @code{Filter3} is passed to the input of
1653 @code{Filter2}, and so on.
1655 This @code{filter} method is passed a Python iterator. This iterator
1656 contains a sequence of frame decorators that wrap each
1657 @code{gdb.Frame}, or a frame decorator that wraps another frame
1658 decorator. The first filter that is executed in the sequence of frame
1659 filters will receive an iterator entirely comprised of default
1660 @code{FrameDecorator} objects. However, after each frame filter is
1661 executed, the previous frame filter may have wrapped some or all of
1662 the frame decorators with their own frame decorator. As frame
1663 decorators must also conform to a mandatory interface, these
1664 decorators can be assumed to act in a uniform manner (@pxref{Frame
1667 This method must return an object conforming to the Python iterator
1668 protocol. Each item in the iterator must be an object conforming to
1669 the frame decorator interface. If a frame filter does not wish to
1670 perform any operations on this iterator, it should return that
1673 This method is not optional. If it does not exist, @value{GDBN} will
1674 raise and print an error.
1677 @defvar FrameFilter.name
1678 The @code{name} attribute must be Python string which contains the
1679 name of the filter displayed by @value{GDBN} (@pxref{Frame Filter
1680 Management}). This attribute may contain any combination of letters
1681 or numbers. Care should be taken to ensure that it is unique. This
1682 attribute is mandatory.
1685 @defvar FrameFilter.enabled
1686 The @code{enabled} attribute must be Python boolean. This attribute
1687 indicates to @value{GDBN} whether the frame filter is enabled, and
1688 should be considered when frame filters are executed. If
1689 @code{enabled} is @code{True}, then the frame filter will be executed
1690 when any of the backtrace commands detailed earlier in this chapter
1691 are executed. If @code{enabled} is @code{False}, then the frame
1692 filter will not be executed. This attribute is mandatory.
1695 @defvar FrameFilter.priority
1696 The @code{priority} attribute must be Python integer. This attribute
1697 controls the order of execution in relation to other frame filters.
1698 There are no imposed limits on the range of @code{priority} other than
1699 it must be a valid integer. The higher the @code{priority} attribute,
1700 the sooner the frame filter will be executed in relation to other
1701 frame filters. Although @code{priority} can be negative, it is
1702 recommended practice to assume zero is the lowest priority that a
1703 frame filter can be assigned. Frame filters that have the same
1704 priority are executed in unsorted order in that priority slot. This
1705 attribute is mandatory.
1708 @node Frame Decorator API
1709 @subsubsection Decorating Frames.
1710 @cindex frame decorator api
1712 Frame decorators are sister objects to frame filters (@pxref{Frame
1713 Filter API}). Frame decorators are applied by a frame filter and can
1714 only be used in conjunction with frame filters.
1716 The purpose of a frame decorator is to customize the printed content
1717 of each @code{gdb.Frame} in commands where frame filters are executed.
1718 This concept is called decorating a frame. Frame decorators decorate
1719 a @code{gdb.Frame} with Python code contained within each API call.
1720 This separates the actual data contained in a @code{gdb.Frame} from
1721 the decorated data produced by a frame decorator. This abstraction is
1722 necessary to maintain integrity of the data contained in each
1725 Frame decorators have a mandatory interface, defined below.
1727 @value{GDBN} already contains a frame decorator called
1728 @code{FrameDecorator}. This contains substantial amounts of
1729 boilerplate code to decorate the content of a @code{gdb.Frame}. It is
1730 recommended that other frame decorators inherit and extend this
1731 object, and only to override the methods needed.
1733 @defun FrameDecorator.elided (self)
1735 The @code{elided} method groups frames together in a hierarchical
1736 system. An example would be an interpreter, where multiple low-level
1737 frames make up a single call in the interpreted language. In this
1738 example, the frame filter would elide the low-level frames and present
1739 a single high-level frame, representing the call in the interpreted
1740 language, to the user.
1742 The @code{elided} function must return an iterable and this iterable
1743 must contain the frames that are being elided wrapped in a suitable
1744 frame decorator. If no frames are being elided this function may
1745 return an empty iterable, or @code{None}. Elided frames are indented
1746 from normal frames in a @code{CLI} backtrace, or in the case of
1747 @code{GDB/MI}, are placed in the @code{children} field of the eliding
1750 It is the frame filter's task to also filter out the elided frames from
1751 the source iterator. This will avoid printing the frame twice.
1754 @defun FrameDecorator.function (self)
1756 This method returns the name of the function in the frame that is to
1759 This method must return a Python string describing the function, or
1762 If this function returns @code{None}, @value{GDBN} will not print any
1763 data for this field.
1766 @defun FrameDecorator.address (self)
1768 This method returns the address of the frame that is to be printed.
1770 This method must return a Python numeric integer type of sufficient
1771 size to describe the address of the frame, or @code{None}.
1773 If this function returns a @code{None}, @value{GDBN} will not print
1774 any data for this field.
1777 @defun FrameDecorator.filename (self)
1779 This method returns the filename and path associated with this frame.
1781 This method must return a Python string containing the filename and
1782 the path to the object file backing the frame, or @code{None}.
1784 If this function returns a @code{None}, @value{GDBN} will not print
1785 any data for this field.
1788 @defun FrameDecorator.line (self):
1790 This method returns the line number associated with the current
1791 position within the function addressed by this frame.
1793 This method must return a Python integer type, or @code{None}.
1795 If this function returns a @code{None}, @value{GDBN} will not print
1796 any data for this field.
1799 @defun FrameDecorator.frame_args (self)
1802 This method must return an iterable, or @code{None}. Returning an
1803 empty iterable, or @code{None} means frame arguments will not be
1804 printed for this frame. This iterable must contain objects that
1805 implement two methods, described here.
1807 This object must implement a @code{argument} method which takes a
1808 single @code{self} parameter and must return a @code{gdb.Symbol}
1809 (@pxref{Symbols In Python}), or a Python string. The object must also
1810 implement a @code{value} method which takes a single @code{self}
1811 parameter and must return a @code{gdb.Value} (@pxref{Values From
1812 Inferior}), a Python value, or @code{None}. If the @code{value}
1813 method returns @code{None}, and the @code{argument} method returns a
1814 @code{gdb.Symbol}, @value{GDBN} will look-up and print the value of
1815 the @code{gdb.Symbol} automatically.
1820 class SymValueWrapper():
1822 def __init__(self, symbol, value):
1832 class SomeFrameDecorator()
1835 def frame_args(self):
1838 block = self.inferior_frame.block()
1842 # Iterate over all symbols in a block. Only add
1843 # symbols that are arguments.
1845 if not sym.is_argument:
1847 args.append(SymValueWrapper(sym,None))
1849 # Add example synthetic argument.
1850 args.append(SymValueWrapper(``foo'', 42))
1856 @defun FrameDecorator.frame_locals (self)
1858 This method must return an iterable or @code{None}. Returning an
1859 empty iterable, or @code{None} means frame local arguments will not be
1860 printed for this frame.
1862 The object interface, the description of the various strategies for
1863 reading frame locals, and the example are largely similar to those
1864 described in the @code{frame_args} function, (@pxref{frame_args,,The
1865 frame filter frame_args function}). Below is a modified example:
1868 class SomeFrameDecorator()
1871 def frame_locals(self):
1874 block = self.inferior_frame.block()
1878 # Iterate over all symbols in a block. Add all
1879 # symbols, except arguments.
1883 vars.append(SymValueWrapper(sym,None))
1885 # Add an example of a synthetic local variable.
1886 vars.append(SymValueWrapper(``bar'', 99))
1892 @defun FrameDecorator.inferior_frame (self):
1894 This method must return the underlying @code{gdb.Frame} that this
1895 frame decorator is decorating. @value{GDBN} requires the underlying
1896 frame for internal frame information to determine how to print certain
1897 values when printing a frame.
1900 @node Writing a Frame Filter
1901 @subsubsection Writing a Frame Filter
1902 @cindex writing a frame filter
1904 There are three basic elements that a frame filter must implement: it
1905 must correctly implement the documented interface (@pxref{Frame Filter
1906 API}), it must register itself with @value{GDBN}, and finally, it must
1907 decide if it is to work on the data provided by @value{GDBN}. In all
1908 cases, whether it works on the iterator or not, each frame filter must
1909 return an iterator. A bare-bones frame filter follows the pattern in
1910 the following example.
1915 class FrameFilter():
1918 # Frame filter attribute creation.
1920 # 'name' is the name of the filter that GDB will display.
1922 # 'priority' is the priority of the filter relative to other
1925 # 'enabled' is a boolean that indicates whether this filter is
1926 # enabled and should be executed.
1932 # Register this frame filter with the global frame_filters
1934 gdb.frame_filters[self.name] = self
1936 def filter(self, frame_iter):
1937 # Just return the iterator.
1941 The frame filter in the example above implements the three
1942 requirements for all frame filters. It implements the API, self
1943 registers, and makes a decision on the iterator (in this case, it just
1944 returns the iterator untouched).
1946 The first step is attribute creation and assignment, and as shown in
1947 the comments the filter assigns the following attributes: @code{name},
1948 @code{priority} and whether the filter should be enabled with the
1949 @code{enabled} attribute.
1951 The second step is registering the frame filter with the dictionary or
1952 dictionaries that the frame filter has interest in. As shown in the
1953 comments, this filter just registers itself with the global dictionary
1954 @code{gdb.frame_filters}. As noted earlier, @code{gdb.frame_filters}
1955 is a dictionary that is initialized in the @code{gdb} module when
1956 @value{GDBN} starts. What dictionary a filter registers with is an
1957 important consideration. Generally, if a filter is specific to a set
1958 of code, it should be registered either in the @code{objfile} or
1959 @code{progspace} dictionaries as they are specific to the program
1960 currently loaded in @value{GDBN}. The global dictionary is always
1961 present in @value{GDBN} and is never unloaded. Any filters registered
1962 with the global dictionary will exist until @value{GDBN} exits. To
1963 avoid filters that may conflict, it is generally better to register
1964 frame filters against the dictionaries that more closely align with
1965 the usage of the filter currently in question. @xref{Python
1966 Auto-loading}, for further information on auto-loading Python scripts.
1968 @value{GDBN} takes a hands-off approach to frame filter registration,
1969 therefore it is the frame filter's responsibility to ensure
1970 registration has occurred, and that any exceptions are handled
1971 appropriately. In particular, you may wish to handle exceptions
1972 relating to Python dictionary key uniqueness. It is mandatory that
1973 the dictionary key is the same as frame filter's @code{name}
1974 attribute. When a user manages frame filters (@pxref{Frame Filter
1975 Management}), the names @value{GDBN} will display are those contained
1976 in the @code{name} attribute.
1978 The final step of this example is the implementation of the
1979 @code{filter} method. As shown in the example comments, we define the
1980 @code{filter} method and note that the method must take an iterator,
1981 and also must return an iterator. In this bare-bones example, the
1982 frame filter is not very useful as it just returns the iterator
1983 untouched. However this is a valid operation for frame filters that
1984 have the @code{enabled} attribute set, but decide not to operate on
1987 In the next example, the frame filter operates on all frames and
1988 utilizes a frame decorator to perform some work on the frames.
1989 @xref{Frame Decorator API}, for further information on the frame
1990 decorator interface.
1992 This example works on inlined frames. It highlights frames which are
1993 inlined by tagging them with an ``[inlined]'' tag. By applying a
1994 frame decorator to all frames with the Python @code{itertools imap}
1995 method, the example defers actions to the frame decorator. Frame
1996 decorators are only processed when @value{GDBN} prints the backtrace.
1998 This introduces a new decision making topic: whether to perform
1999 decision making operations at the filtering step, or at the printing
2000 step. In this example's approach, it does not perform any filtering
2001 decisions at the filtering step beyond mapping a frame decorator to
2002 each frame. This allows the actual decision making to be performed
2003 when each frame is printed. This is an important consideration, and
2004 well worth reflecting upon when designing a frame filter. An issue
2005 that frame filters should avoid is unwinding the stack if possible.
2006 Some stacks can run very deep, into the tens of thousands in some
2007 cases. To search every frame to determine if it is inlined ahead of
2008 time may be too expensive at the filtering step. The frame filter
2009 cannot know how many frames it has to iterate over, and it would have
2010 to iterate through them all. This ends up duplicating effort as
2011 @value{GDBN} performs this iteration when it prints the frames.
2013 In this example decision making can be deferred to the printing step.
2014 As each frame is printed, the frame decorator can examine each frame
2015 in turn when @value{GDBN} iterates. From a performance viewpoint,
2016 this is the most appropriate decision to make as it avoids duplicating
2017 the effort that the printing step would undertake anyway. Also, if
2018 there are many frame filters unwinding the stack during filtering, it
2019 can substantially delay the printing of the backtrace which will
2020 result in large memory usage, and a poor user experience.
2023 class InlineFilter():
2026 self.name = "InlinedFrameFilter"
2029 gdb.frame_filters[self.name] = self
2031 def filter(self, frame_iter):
2032 frame_iter = itertools.imap(InlinedFrameDecorator,
2037 This frame filter is somewhat similar to the earlier example, except
2038 that the @code{filter} method applies a frame decorator object called
2039 @code{InlinedFrameDecorator} to each element in the iterator. The
2040 @code{imap} Python method is light-weight. It does not proactively
2041 iterate over the iterator, but rather creates a new iterator which
2042 wraps the existing one.
2044 Below is the frame decorator for this example.
2047 class InlinedFrameDecorator(FrameDecorator):
2049 def __init__(self, fobj):
2050 super(InlinedFrameDecorator, self).__init__(fobj)
2053 frame = fobj.inferior_frame()
2054 name = str(frame.name())
2056 if frame.type() == gdb.INLINE_FRAME:
2057 name = name + " [inlined]"
2062 This frame decorator only defines and overrides the @code{function}
2063 method. It lets the supplied @code{FrameDecorator}, which is shipped
2064 with @value{GDBN}, perform the other work associated with printing
2067 The combination of these two objects create this output from a
2071 #0 0x004004e0 in bar () at inline.c:11
2072 #1 0x00400566 in max [inlined] (b=6, a=12) at inline.c:21
2073 #2 0x00400566 in main () at inline.c:31
2076 So in the case of this example, a frame decorator is applied to all
2077 frames, regardless of whether they may be inlined or not. As
2078 @value{GDBN} iterates over the iterator produced by the frame filters,
2079 @value{GDBN} executes each frame decorator which then makes a decision
2080 on what to print in the @code{function} callback. Using a strategy
2081 like this is a way to defer decisions on the frame content to printing
2084 @subheading Eliding Frames
2086 It might be that the above example is not desirable for representing
2087 inlined frames, and a hierarchical approach may be preferred. If we
2088 want to hierarchically represent frames, the @code{elided} frame
2089 decorator interface might be preferable.
2091 This example approaches the issue with the @code{elided} method. This
2092 example is quite long, but very simplistic. It is out-of-scope for
2093 this section to write a complete example that comprehensively covers
2094 all approaches of finding and printing inlined frames. However, this
2095 example illustrates the approach an author might use.
2097 This example comprises of three sections.
2100 class InlineFrameFilter():
2103 self.name = "InlinedFrameFilter"
2106 gdb.frame_filters[self.name] = self
2108 def filter(self, frame_iter):
2109 return ElidingInlineIterator(frame_iter)
2112 This frame filter is very similar to the other examples. The only
2113 difference is this frame filter is wrapping the iterator provided to
2114 it (@code{frame_iter}) with a custom iterator called
2115 @code{ElidingInlineIterator}. This again defers actions to when
2116 @value{GDBN} prints the backtrace, as the iterator is not traversed
2119 The iterator for this example is as follows. It is in this section of
2120 the example where decisions are made on the content of the backtrace.
2123 class ElidingInlineIterator:
2124 def __init__(self, ii):
2125 self.input_iterator = ii
2131 frame = next(self.input_iterator)
2133 if frame.inferior_frame().type() != gdb.INLINE_FRAME:
2137 eliding_frame = next(self.input_iterator)
2138 except StopIteration:
2140 return ElidingFrameDecorator(eliding_frame, [frame])
2143 This iterator implements the Python iterator protocol. When the
2144 @code{next} function is called (when @value{GDBN} prints each frame),
2145 the iterator checks if this frame decorator, @code{frame}, is wrapping
2146 an inlined frame. If it is not, it returns the existing frame decorator
2147 untouched. If it is wrapping an inlined frame, it assumes that the
2148 inlined frame was contained within the next oldest frame,
2149 @code{eliding_frame}, which it fetches. It then creates and returns a
2150 frame decorator, @code{ElidingFrameDecorator}, which contains both the
2151 elided frame, and the eliding frame.
2154 class ElidingInlineDecorator(FrameDecorator):
2156 def __init__(self, frame, elided_frames):
2157 super(ElidingInlineDecorator, self).__init__(frame)
2159 self.elided_frames = elided_frames
2162 return iter(self.elided_frames)
2165 This frame decorator overrides one function and returns the inlined
2166 frame in the @code{elided} method. As before it lets
2167 @code{FrameDecorator} do the rest of the work involved in printing
2168 this frame. This produces the following output.
2171 #0 0x004004e0 in bar () at inline.c:11
2172 #2 0x00400529 in main () at inline.c:25
2173 #1 0x00400529 in max (b=6, a=12) at inline.c:15
2176 In that output, @code{max} which has been inlined into @code{main} is
2177 printed hierarchically. Another approach would be to combine the
2178 @code{function} method, and the @code{elided} method to both print a
2179 marker in the inlined frame, and also show the hierarchical
2182 @node Unwinding Frames in Python
2183 @subsubsection Unwinding Frames in Python
2184 @cindex unwinding frames in Python
2186 In @value{GDBN} terminology ``unwinding'' is the process of finding
2187 the previous frame (that is, caller's) from the current one. An
2188 unwinder has three methods. The first one checks if it can handle
2189 given frame (``sniff'' it). For the frames it can sniff an unwinder
2190 provides two additional methods: it can return frame's ID, and it can
2191 fetch registers from the previous frame. A running @value{GDBN}
2192 mantains a list of the unwinders and calls each unwinder's sniffer in
2193 turn until it finds the one that recognizes the current frame. There
2194 is an API to register an unwinder.
2196 The unwinders that come with @value{GDBN} handle standard frames.
2197 However, mixed language applications (for example, an application
2198 running Java Virtual Machine) sometimes use frame layouts that cannot
2199 be handled by the @value{GDBN} unwinders. You can write Python code
2200 that can handle such custom frames.
2202 You implement a frame unwinder in Python as a class with which has two
2203 attributes, @code{name} and @code{enabled}, with obvious meanings, and
2204 a single method @code{__call__}, which examines a given frame and
2205 returns an object (an instance of @code{gdb.UnwindInfo class)}
2206 describing it. If an unwinder does not recognize a frame, it should
2207 return @code{None}. The code in @value{GDBN} that enables writing
2208 unwinders in Python uses this object to return frame's ID and previous
2209 frame registers when @value{GDBN} core asks for them.
2211 @subheading Unwinder Input
2213 An object passed to an unwinder (a @code{gdb.PendingFrame} instance)
2214 provides a method to read frame's registers:
2216 @defun PendingFrame.read_register (reg)
2217 This method returns the contents of the register @var{regn} in the
2218 frame as a @code{gdb.Value} object. @var{reg} can be either a
2219 register number or a register name; the values are platform-specific.
2220 They are usually found in the corresponding
2221 @file{@var{platform}-tdep.h} file in the @value{GDBN} source tree.
2224 It also provides a factory method to create a @code{gdb.UnwindInfo}
2225 instance to be returned to @value{GDBN}:
2227 @defun PendingFrame.create_unwind_info (frame_id)
2228 Returns a new @code{gdb.UnwindInfo} instance identified by given
2229 @var{frame_id}. The argument is used to build @value{GDBN}'s frame ID
2230 using one of functions provided by @value{GDBN}. @var{frame_id}'s attributes
2231 determine which function will be used, as follows:
2234 @item sp, pc, special
2235 @code{frame_id_build_special (@var{frame_id}.sp, @var{frame_id}.pc, @var{frame_id}.special)}
2238 @code{frame_id_build (@var{frame_id}.sp, @var{frame_id}.pc)}
2240 This is the most common case.
2243 @code{frame_id_build_wild (@var{frame_id}.sp)}
2245 The attribute values should be @code{gdb.Value}
2249 @subheading Unwinder Output: UnwindInfo
2251 Use @code{PendingFrame.create_unwind_info} method described above to
2252 create a @code{gdb.UnwindInfo} instance. Use the following method to
2253 specify caller registers that have been saved in this frame:
2255 @defun gdb.UnwindInfo.add_saved_register (reg, value)
2256 @var{reg} identifies the register. It can be a number or a name, just
2257 as for the @code{PendingFrame.read_register} method above.
2258 @var{value} is a register value (a @code{gdb.Value} object).
2261 @subheading Unwinder Skeleton Code
2263 @value{GDBN} comes with the module containing the base @code{Unwinder}
2264 class. Derive your unwinder class from it and structure the code as
2268 from gdb.unwinders import Unwinder
2270 class FrameId(object):
2271 def __init__(self, sp, pc):
2276 class MyUnwinder(Unwinder):
2278 supe(MyUnwinder, self).__init___(<expects unwinder name argument>)
2280 def __call__(pending_frame):
2281 if not <we recognize frame>:
2283 # Create UnwindInfo. Usually the frame is identified by the stack
2284 # pointer and the program counter.
2285 sp = pending_frame.read_register(<SP number>)
2286 pc = pending_frame.read_register(<PC number>)
2287 unwind_info = pending_frame.create_unwind_info(FrameId(sp, pc))
2289 # Find the values of the registers in the caller's frame and
2290 # save them in the result:
2291 unwind_info.add_saved_register(<register>, <value>)
2294 # Return the result:
2299 @subheading Registering a Unwinder
2301 An object file, a program space, and the @value{GDBN} proper can have
2302 unwinders registered with it.
2304 The @code{gdb.unwinders} module provides the function to register a
2307 @defun gdb.unwinder.register_unwinder (locus, unwinder, replace=False)
2308 @var{locus} is specifies an object file or a program space to which
2309 @var{unwinder} is added. Passing @code{None} or @code{gdb} adds
2310 @var{unwinder} to the @value{GDBN}'s global unwinder list. The newly
2311 added @var{unwinder} will be called before any other unwinder from the
2312 same locus. Two unwinders in the same locus cannot have the same
2313 name. An attempt to add a unwinder with already existing name raises
2314 an exception unless @var{replace} is @code{True}, in which case the
2315 old unwinder is deleted.
2318 @subheading Unwinder Precedence
2320 @value{GDBN} first calls the unwinders from all the object files in no
2321 particular order, then the unwinders from the current program space,
2322 and finally the unwinders from @value{GDBN}.
2324 @node Xmethods In Python
2325 @subsubsection Xmethods In Python
2326 @cindex xmethods in Python
2328 @dfn{Xmethods} are additional methods or replacements for existing
2329 methods of a C@t{++} class. This feature is useful for those cases
2330 where a method defined in C@t{++} source code could be inlined or
2331 optimized out by the compiler, making it unavailable to @value{GDBN}.
2332 For such cases, one can define an xmethod to serve as a replacement
2333 for the method defined in the C@t{++} source code. @value{GDBN} will
2334 then invoke the xmethod, instead of the C@t{++} method, to
2335 evaluate expressions. One can also use xmethods when debugging
2336 with core files. Moreover, when debugging live programs, invoking an
2337 xmethod need not involve running the inferior (which can potentially
2338 perturb its state). Hence, even if the C@t{++} method is available, it
2339 is better to use its replacement xmethod if one is defined.
2341 The xmethods feature in Python is available via the concepts of an
2342 @dfn{xmethod matcher} and an @dfn{xmethod worker}. To
2343 implement an xmethod, one has to implement a matcher and a
2344 corresponding worker for it (more than one worker can be
2345 implemented, each catering to a different overloaded instance of the
2346 method). Internally, @value{GDBN} invokes the @code{match} method of a
2347 matcher to match the class type and method name. On a match, the
2348 @code{match} method returns a list of matching @emph{worker} objects.
2349 Each worker object typically corresponds to an overloaded instance of
2350 the xmethod. They implement a @code{get_arg_types} method which
2351 returns a sequence of types corresponding to the arguments the xmethod
2352 requires. @value{GDBN} uses this sequence of types to perform
2353 overload resolution and picks a winning xmethod worker. A winner
2354 is also selected from among the methods @value{GDBN} finds in the
2355 C@t{++} source code. Next, the winning xmethod worker and the
2356 winning C@t{++} method are compared to select an overall winner. In
2357 case of a tie between a xmethod worker and a C@t{++} method, the
2358 xmethod worker is selected as the winner. That is, if a winning
2359 xmethod worker is found to be equivalent to the winning C@t{++}
2360 method, then the xmethod worker is treated as a replacement for
2361 the C@t{++} method. @value{GDBN} uses the overall winner to invoke the
2362 method. If the winning xmethod worker is the overall winner, then
2363 the corresponding xmethod is invoked via the @code{__call__} method
2364 of the worker object.
2366 If one wants to implement an xmethod as a replacement for an
2367 existing C@t{++} method, then they have to implement an equivalent
2368 xmethod which has exactly the same name and takes arguments of
2369 exactly the same type as the C@t{++} method. If the user wants to
2370 invoke the C@t{++} method even though a replacement xmethod is
2371 available for that method, then they can disable the xmethod.
2373 @xref{Xmethod API}, for API to implement xmethods in Python.
2374 @xref{Writing an Xmethod}, for implementing xmethods in Python.
2377 @subsubsection Xmethod API
2380 The @value{GDBN} Python API provides classes, interfaces and functions
2381 to implement, register and manipulate xmethods.
2382 @xref{Xmethods In Python}.
2384 An xmethod matcher should be an instance of a class derived from
2385 @code{XMethodMatcher} defined in the module @code{gdb.xmethod}, or an
2386 object with similar interface and attributes. An instance of
2387 @code{XMethodMatcher} has the following attributes:
2390 The name of the matcher.
2394 A boolean value indicating whether the matcher is enabled or disabled.
2398 A list of named methods managed by the matcher. Each object in the list
2399 is an instance of the class @code{XMethod} defined in the module
2400 @code{gdb.xmethod}, or any object with the following attributes:
2405 Name of the xmethod which should be unique for each xmethod
2406 managed by the matcher.
2409 A boolean value indicating whether the xmethod is enabled or
2414 The class @code{XMethod} is a convenience class with same
2415 attributes as above along with the following constructor:
2417 @defun XMethod.__init__ (self, name)
2418 Constructs an enabled xmethod with name @var{name}.
2423 The @code{XMethodMatcher} class has the following methods:
2425 @defun XMethodMatcher.__init__ (self, name)
2426 Constructs an enabled xmethod matcher with name @var{name}. The
2427 @code{methods} attribute is initialized to @code{None}.
2430 @defun XMethodMatcher.match (self, class_type, method_name)
2431 Derived classes should override this method. It should return a
2432 xmethod worker object (or a sequence of xmethod worker
2433 objects) matching the @var{class_type} and @var{method_name}.
2434 @var{class_type} is a @code{gdb.Type} object, and @var{method_name}
2435 is a string value. If the matcher manages named methods as listed in
2436 its @code{methods} attribute, then only those worker objects whose
2437 corresponding entries in the @code{methods} list are enabled should be
2441 An xmethod worker should be an instance of a class derived from
2442 @code{XMethodWorker} defined in the module @code{gdb.xmethod},
2443 or support the following interface:
2445 @defun XMethodWorker.get_arg_types (self)
2446 This method returns a sequence of @code{gdb.Type} objects corresponding
2447 to the arguments that the xmethod takes. It can return an empty
2448 sequence or @code{None} if the xmethod does not take any arguments.
2449 If the xmethod takes a single argument, then a single
2450 @code{gdb.Type} object corresponding to it can be returned.
2453 @defun XMethodWorker.__call__ (self, *args)
2454 This is the method which does the @emph{work} of the xmethod. The
2455 @var{args} arguments is the tuple of arguments to the xmethod. Each
2456 element in this tuple is a gdb.Value object. The first element is
2457 always the @code{this} pointer value.
2460 For @value{GDBN} to lookup xmethods, the xmethod matchers
2461 should be registered using the following function defined in the module
2464 @defun register_xmethod_matcher (locus, matcher, replace=False)
2465 The @code{matcher} is registered with @code{locus}, replacing an
2466 existing matcher with the same name as @code{matcher} if
2467 @code{replace} is @code{True}. @code{locus} can be a
2468 @code{gdb.Objfile} object (@pxref{Objfiles In Python}), or a
2469 @code{gdb.Progspace} object (@pxref{Progspaces In Python}), or
2470 @code{None}. If it is @code{None}, then @code{matcher} is registered
2474 @node Writing an Xmethod
2475 @subsubsection Writing an Xmethod
2476 @cindex writing xmethods in Python
2478 Implementing xmethods in Python will require implementing xmethod
2479 matchers and xmethod workers (@pxref{Xmethods In Python}). Consider
2480 the following C@t{++} class:
2486 MyClass (int a) : a_(a) @{ @}
2488 int geta (void) @{ return a_; @}
2489 int operator+ (int b);
2496 MyClass::operator+ (int b)
2503 Let us define two xmethods for the class @code{MyClass}, one
2504 replacing the method @code{geta}, and another adding an overloaded
2505 flavor of @code{operator+} which takes a @code{MyClass} argument (the
2506 C@t{++} code above already has an overloaded @code{operator+}
2507 which takes an @code{int} argument). The xmethod matcher can be
2511 class MyClass_geta(gdb.xmethod.XMethod):
2513 gdb.xmethod.XMethod.__init__(self, 'geta')
2515 def get_worker(self, method_name):
2516 if method_name == 'geta':
2517 return MyClassWorker_geta()
2520 class MyClass_sum(gdb.xmethod.XMethod):
2522 gdb.xmethod.XMethod.__init__(self, 'sum')
2524 def get_worker(self, method_name):
2525 if method_name == 'operator+':
2526 return MyClassWorker_plus()
2529 class MyClassMatcher(gdb.xmethod.XMethodMatcher):
2531 gdb.xmethod.XMethodMatcher.__init__(self, 'MyClassMatcher')
2532 # List of methods 'managed' by this matcher
2533 self.methods = [MyClass_geta(), MyClass_sum()]
2535 def match(self, class_type, method_name):
2536 if class_type.tag != 'MyClass':
2539 for method in self.methods:
2541 worker = method.get_worker(method_name)
2543 workers.append(worker)
2549 Notice that the @code{match} method of @code{MyClassMatcher} returns
2550 a worker object of type @code{MyClassWorker_geta} for the @code{geta}
2551 method, and a worker object of type @code{MyClassWorker_plus} for the
2552 @code{operator+} method. This is done indirectly via helper classes
2553 derived from @code{gdb.xmethod.XMethod}. One does not need to use the
2554 @code{methods} attribute in a matcher as it is optional. However, if a
2555 matcher manages more than one xmethod, it is a good practice to list the
2556 xmethods in the @code{methods} attribute of the matcher. This will then
2557 facilitate enabling and disabling individual xmethods via the
2558 @code{enable/disable} commands. Notice also that a worker object is
2559 returned only if the corresponding entry in the @code{methods} attribute
2560 of the matcher is enabled.
2562 The implementation of the worker classes returned by the matcher setup
2563 above is as follows:
2566 class MyClassWorker_geta(gdb.xmethod.XMethodWorker):
2567 def get_arg_types(self):
2570 def __call__(self, obj):
2574 class MyClassWorker_plus(gdb.xmethod.XMethodWorker):
2575 def get_arg_types(self):
2576 return gdb.lookup_type('MyClass')
2578 def __call__(self, obj, other):
2579 return obj['a_'] + other['a_']
2582 For @value{GDBN} to actually lookup a xmethod, it has to be
2583 registered with it. The matcher defined above is registered with
2584 @value{GDBN} globally as follows:
2587 gdb.xmethod.register_xmethod_matcher(None, MyClassMatcher())
2590 If an object @code{obj} of type @code{MyClass} is initialized in C@t{++}
2598 then, after loading the Python script defining the xmethod matchers
2599 and workers into @code{GDBN}, invoking the method @code{geta} or using
2600 the operator @code{+} on @code{obj} will invoke the xmethods
2611 Consider another example with a C++ template class:
2618 MyTemplate () : dsize_(10), data_ (new T [10]) @{ @}
2619 ~MyTemplate () @{ delete [] data_; @}
2621 int footprint (void)
2623 return sizeof (T) * dsize_ + sizeof (MyTemplate<T>);
2632 Let us implement an xmethod for the above class which serves as a
2633 replacement for the @code{footprint} method. The full code listing
2634 of the xmethod workers and xmethod matchers is as follows:
2637 class MyTemplateWorker_footprint(gdb.xmethod.XMethodWorker):
2638 def __init__(self, class_type):
2639 self.class_type = class_type
2641 def get_arg_types(self):
2644 def __call__(self, obj):
2645 return (self.class_type.sizeof +
2647 self.class_type.template_argument(0).sizeof)
2650 class MyTemplateMatcher_footprint(gdb.xmethod.XMethodMatcher):
2652 gdb.xmethod.XMethodMatcher.__init__(self, 'MyTemplateMatcher')
2654 def match(self, class_type, method_name):
2655 if (re.match('MyTemplate<[ \t\n]*[_a-zA-Z][ _a-zA-Z0-9]*>',
2657 method_name == 'footprint'):
2658 return MyTemplateWorker_footprint(class_type)
2661 Notice that, in this example, we have not used the @code{methods}
2662 attribute of the matcher as the matcher manages only one xmethod. The
2663 user can enable/disable this xmethod by enabling/disabling the matcher
2666 @node Inferiors In Python
2667 @subsubsection Inferiors In Python
2668 @cindex inferiors in Python
2670 @findex gdb.Inferior
2671 Programs which are being run under @value{GDBN} are called inferiors
2672 (@pxref{Inferiors and Programs}). Python scripts can access
2673 information about and manipulate inferiors controlled by @value{GDBN}
2674 via objects of the @code{gdb.Inferior} class.
2676 The following inferior-related functions are available in the @code{gdb}
2679 @defun gdb.inferiors ()
2680 Return a tuple containing all inferior objects.
2683 @defun gdb.selected_inferior ()
2684 Return an object representing the current inferior.
2687 A @code{gdb.Inferior} object has the following attributes:
2689 @defvar Inferior.num
2690 ID of inferior, as assigned by GDB.
2693 @defvar Inferior.pid
2694 Process ID of the inferior, as assigned by the underlying operating
2698 @defvar Inferior.was_attached
2699 Boolean signaling whether the inferior was created using `attach', or
2700 started by @value{GDBN} itself.
2703 A @code{gdb.Inferior} object has the following methods:
2705 @defun Inferior.is_valid ()
2706 Returns @code{True} if the @code{gdb.Inferior} object is valid,
2707 @code{False} if not. A @code{gdb.Inferior} object will become invalid
2708 if the inferior no longer exists within @value{GDBN}. All other
2709 @code{gdb.Inferior} methods will throw an exception if it is invalid
2710 at the time the method is called.
2713 @defun Inferior.threads ()
2714 This method returns a tuple holding all the threads which are valid
2715 when it is called. If there are no valid threads, the method will
2716 return an empty tuple.
2719 @findex Inferior.read_memory
2720 @defun Inferior.read_memory (address, length)
2721 Read @var{length} bytes of memory from the inferior, starting at
2722 @var{address}. Returns a buffer object, which behaves much like an array
2723 or a string. It can be modified and given to the
2724 @code{Inferior.write_memory} function. In @code{Python} 3, the return
2725 value is a @code{memoryview} object.
2728 @findex Inferior.write_memory
2729 @defun Inferior.write_memory (address, buffer @r{[}, length@r{]})
2730 Write the contents of @var{buffer} to the inferior, starting at
2731 @var{address}. The @var{buffer} parameter must be a Python object
2732 which supports the buffer protocol, i.e., a string, an array or the
2733 object returned from @code{Inferior.read_memory}. If given, @var{length}
2734 determines the number of bytes from @var{buffer} to be written.
2737 @findex gdb.search_memory
2738 @defun Inferior.search_memory (address, length, pattern)
2739 Search a region of the inferior memory starting at @var{address} with
2740 the given @var{length} using the search pattern supplied in
2741 @var{pattern}. The @var{pattern} parameter must be a Python object
2742 which supports the buffer protocol, i.e., a string, an array or the
2743 object returned from @code{gdb.read_memory}. Returns a Python @code{Long}
2744 containing the address where the pattern was found, or @code{None} if
2745 the pattern could not be found.
2748 @node Events In Python
2749 @subsubsection Events In Python
2750 @cindex inferior events in Python
2752 @value{GDBN} provides a general event facility so that Python code can be
2753 notified of various state changes, particularly changes that occur in
2756 An @dfn{event} is just an object that describes some state change. The
2757 type of the object and its attributes will vary depending on the details
2758 of the change. All the existing events are described below.
2760 In order to be notified of an event, you must register an event handler
2761 with an @dfn{event registry}. An event registry is an object in the
2762 @code{gdb.events} module which dispatches particular events. A registry
2763 provides methods to register and unregister event handlers:
2765 @defun EventRegistry.connect (object)
2766 Add the given callable @var{object} to the registry. This object will be
2767 called when an event corresponding to this registry occurs.
2770 @defun EventRegistry.disconnect (object)
2771 Remove the given @var{object} from the registry. Once removed, the object
2772 will no longer receive notifications of events.
2778 def exit_handler (event):
2779 print "event type: exit"
2780 print "exit code: %d" % (event.exit_code)
2782 gdb.events.exited.connect (exit_handler)
2785 In the above example we connect our handler @code{exit_handler} to the
2786 registry @code{events.exited}. Once connected, @code{exit_handler} gets
2787 called when the inferior exits. The argument @dfn{event} in this example is
2788 of type @code{gdb.ExitedEvent}. As you can see in the example the
2789 @code{ExitedEvent} object has an attribute which indicates the exit code of
2792 The following is a listing of the event registries that are available and
2793 details of the events they emit:
2798 Emits @code{gdb.ThreadEvent}.
2800 Some events can be thread specific when @value{GDBN} is running in non-stop
2801 mode. When represented in Python, these events all extend
2802 @code{gdb.ThreadEvent}. Note, this event is not emitted directly; instead,
2803 events which are emitted by this or other modules might extend this event.
2804 Examples of these events are @code{gdb.BreakpointEvent} and
2805 @code{gdb.ContinueEvent}.
2807 @defvar ThreadEvent.inferior_thread
2808 In non-stop mode this attribute will be set to the specific thread which was
2809 involved in the emitted event. Otherwise, it will be set to @code{None}.
2812 Emits @code{gdb.ContinueEvent} which extends @code{gdb.ThreadEvent}.
2814 This event indicates that the inferior has been continued after a stop. For
2815 inherited attribute refer to @code{gdb.ThreadEvent} above.
2818 Emits @code{events.ExitedEvent} which indicates that the inferior has exited.
2819 @code{events.ExitedEvent} has two attributes:
2820 @defvar ExitedEvent.exit_code
2821 An integer representing the exit code, if available, which the inferior
2822 has returned. (The exit code could be unavailable if, for example,
2823 @value{GDBN} detaches from the inferior.) If the exit code is unavailable,
2824 the attribute does not exist.
2826 @defvar ExitedEvent inferior
2827 A reference to the inferior which triggered the @code{exited} event.
2831 Emits @code{gdb.StopEvent} which extends @code{gdb.ThreadEvent}.
2833 Indicates that the inferior has stopped. All events emitted by this registry
2834 extend StopEvent. As a child of @code{gdb.ThreadEvent}, @code{gdb.StopEvent}
2835 will indicate the stopped thread when @value{GDBN} is running in non-stop
2836 mode. Refer to @code{gdb.ThreadEvent} above for more details.
2838 Emits @code{gdb.SignalEvent} which extends @code{gdb.StopEvent}.
2840 This event indicates that the inferior or one of its threads has received as
2841 signal. @code{gdb.SignalEvent} has the following attributes:
2843 @defvar SignalEvent.stop_signal
2844 A string representing the signal received by the inferior. A list of possible
2845 signal values can be obtained by running the command @code{info signals} in
2846 the @value{GDBN} command prompt.
2849 Also emits @code{gdb.BreakpointEvent} which extends @code{gdb.StopEvent}.
2851 @code{gdb.BreakpointEvent} event indicates that one or more breakpoints have
2852 been hit, and has the following attributes:
2854 @defvar BreakpointEvent.breakpoints
2855 A sequence containing references to all the breakpoints (type
2856 @code{gdb.Breakpoint}) that were hit.
2857 @xref{Breakpoints In Python}, for details of the @code{gdb.Breakpoint} object.
2859 @defvar BreakpointEvent.breakpoint
2860 A reference to the first breakpoint that was hit.
2861 This function is maintained for backward compatibility and is now deprecated
2862 in favor of the @code{gdb.BreakpointEvent.breakpoints} attribute.
2865 @item events.new_objfile
2866 Emits @code{gdb.NewObjFileEvent} which indicates that a new object file has
2867 been loaded by @value{GDBN}. @code{gdb.NewObjFileEvent} has one attribute:
2869 @defvar NewObjFileEvent.new_objfile
2870 A reference to the object file (@code{gdb.Objfile}) which has been loaded.
2871 @xref{Objfiles In Python}, for details of the @code{gdb.Objfile} object.
2874 @item events.clear_objfiles
2875 Emits @code{gdb.ClearObjFilesEvent} which indicates that the list of object
2876 files for a program space has been reset.
2877 @code{gdb.ClearObjFilesEvent} has one attribute:
2879 @defvar ClearObjFilesEvent.progspace
2880 A reference to the program space (@code{gdb.Progspace}) whose objfile list has
2881 been cleared. @xref{Progspaces In Python}.
2884 @item events.inferior_call_pre
2885 Emits @code{gdb.InferiorCallPreEvent} which indicates that a function in
2886 the inferior is about to be called.
2888 @defvar InferiorCallPreEvent.ptid
2889 The thread in which the call will be run.
2892 @defvar InferiorCallPreEvent.address
2893 The location of the function to be called.
2896 @item events.inferior_call_post
2897 Emits @code{gdb.InferiorCallPostEvent} which indicates that a function in
2898 the inferior has returned.
2900 @defvar InferiorCallPostEvent.ptid
2901 The thread in which the call was run.
2904 @defvar InferiorCallPostEvent.address
2905 The location of the function that was called.
2908 @item events.memory_changed
2909 Emits @code{gdb.MemoryChangedEvent} which indicates that the memory of the
2910 inferior has been modified by the @value{GDBN} user, for instance via a
2911 command like @w{@code{set *addr = value}}. The event has the following
2914 @defvar MemoryChangedEvent.address
2915 The start address of the changed region.
2918 @defvar MemoryChangedEvent.length
2919 Length in bytes of the changed region.
2922 @item events.register_changed
2923 Emits @code{gdb.RegisterChangedEvent} which indicates that a register in the
2924 inferior has been modified by the @value{GDBN} user.
2926 @defvar RegisterChangedEvent.frame
2927 A gdb.Frame object representing the frame in which the register was modified.
2929 @defvar RegisterChangedEvent.regnum
2930 Denotes which register was modified.
2935 @node Threads In Python
2936 @subsubsection Threads In Python
2937 @cindex threads in python
2939 @findex gdb.InferiorThread
2940 Python scripts can access information about, and manipulate inferior threads
2941 controlled by @value{GDBN}, via objects of the @code{gdb.InferiorThread} class.
2943 The following thread-related functions are available in the @code{gdb}
2946 @findex gdb.selected_thread
2947 @defun gdb.selected_thread ()
2948 This function returns the thread object for the selected thread. If there
2949 is no selected thread, this will return @code{None}.
2952 A @code{gdb.InferiorThread} object has the following attributes:
2954 @defvar InferiorThread.name
2955 The name of the thread. If the user specified a name using
2956 @code{thread name}, then this returns that name. Otherwise, if an
2957 OS-supplied name is available, then it is returned. Otherwise, this
2958 returns @code{None}.
2960 This attribute can be assigned to. The new value must be a string
2961 object, which sets the new name, or @code{None}, which removes any
2962 user-specified thread name.
2965 @defvar InferiorThread.num
2966 ID of the thread, as assigned by GDB.
2969 @defvar InferiorThread.ptid
2970 ID of the thread, as assigned by the operating system. This attribute is a
2971 tuple containing three integers. The first is the Process ID (PID); the second
2972 is the Lightweight Process ID (LWPID), and the third is the Thread ID (TID).
2973 Either the LWPID or TID may be 0, which indicates that the operating system
2974 does not use that identifier.
2977 A @code{gdb.InferiorThread} object has the following methods:
2979 @defun InferiorThread.is_valid ()
2980 Returns @code{True} if the @code{gdb.InferiorThread} object is valid,
2981 @code{False} if not. A @code{gdb.InferiorThread} object will become
2982 invalid if the thread exits, or the inferior that the thread belongs
2983 is deleted. All other @code{gdb.InferiorThread} methods will throw an
2984 exception if it is invalid at the time the method is called.
2987 @defun InferiorThread.switch ()
2988 This changes @value{GDBN}'s currently selected thread to the one represented
2992 @defun InferiorThread.is_stopped ()
2993 Return a Boolean indicating whether the thread is stopped.
2996 @defun InferiorThread.is_running ()
2997 Return a Boolean indicating whether the thread is running.
3000 @defun InferiorThread.is_exited ()
3001 Return a Boolean indicating whether the thread is exited.
3004 @node Commands In Python
3005 @subsubsection Commands In Python
3007 @cindex commands in python
3008 @cindex python commands
3009 You can implement new @value{GDBN} CLI commands in Python. A CLI
3010 command is implemented using an instance of the @code{gdb.Command}
3011 class, most commonly using a subclass.
3013 @defun Command.__init__ (name, @var{command_class} @r{[}, @var{completer_class} @r{[}, @var{prefix}@r{]]})
3014 The object initializer for @code{Command} registers the new command
3015 with @value{GDBN}. This initializer is normally invoked from the
3016 subclass' own @code{__init__} method.
3018 @var{name} is the name of the command. If @var{name} consists of
3019 multiple words, then the initial words are looked for as prefix
3020 commands. In this case, if one of the prefix commands does not exist,
3021 an exception is raised.
3023 There is no support for multi-line commands.
3025 @var{command_class} should be one of the @samp{COMMAND_} constants
3026 defined below. This argument tells @value{GDBN} how to categorize the
3027 new command in the help system.
3029 @var{completer_class} is an optional argument. If given, it should be
3030 one of the @samp{COMPLETE_} constants defined below. This argument
3031 tells @value{GDBN} how to perform completion for this command. If not
3032 given, @value{GDBN} will attempt to complete using the object's
3033 @code{complete} method (see below); if no such method is found, an
3034 error will occur when completion is attempted.
3036 @var{prefix} is an optional argument. If @code{True}, then the new
3037 command is a prefix command; sub-commands of this command may be
3040 The help text for the new command is taken from the Python
3041 documentation string for the command's class, if there is one. If no
3042 documentation string is provided, the default value ``This command is
3043 not documented.'' is used.
3046 @cindex don't repeat Python command
3047 @defun Command.dont_repeat ()
3048 By default, a @value{GDBN} command is repeated when the user enters a
3049 blank line at the command prompt. A command can suppress this
3050 behavior by invoking the @code{dont_repeat} method. This is similar
3051 to the user command @code{dont-repeat}, see @ref{Define, dont-repeat}.
3054 @defun Command.invoke (argument, from_tty)
3055 This method is called by @value{GDBN} when this command is invoked.
3057 @var{argument} is a string. It is the argument to the command, after
3058 leading and trailing whitespace has been stripped.
3060 @var{from_tty} is a boolean argument. When true, this means that the
3061 command was entered by the user at the terminal; when false it means
3062 that the command came from elsewhere.
3064 If this method throws an exception, it is turned into a @value{GDBN}
3065 @code{error} call. Otherwise, the return value is ignored.
3067 @findex gdb.string_to_argv
3068 To break @var{argument} up into an argv-like string use
3069 @code{gdb.string_to_argv}. This function behaves identically to
3070 @value{GDBN}'s internal argument lexer @code{buildargv}.
3071 It is recommended to use this for consistency.
3072 Arguments are separated by spaces and may be quoted.
3076 print gdb.string_to_argv ("1 2\ \\\"3 '4 \"5' \"6 '7\"")
3077 ['1', '2 "3', '4 "5', "6 '7"]
3082 @cindex completion of Python commands
3083 @defun Command.complete (text, word)
3084 This method is called by @value{GDBN} when the user attempts
3085 completion on this command. All forms of completion are handled by
3086 this method, that is, the @key{TAB} and @key{M-?} key bindings
3087 (@pxref{Completion}), and the @code{complete} command (@pxref{Help,
3090 The arguments @var{text} and @var{word} are both strings; @var{text}
3091 holds the complete command line up to the cursor's location, while
3092 @var{word} holds the last word of the command line; this is computed
3093 using a word-breaking heuristic.
3095 The @code{complete} method can return several values:
3098 If the return value is a sequence, the contents of the sequence are
3099 used as the completions. It is up to @code{complete} to ensure that the
3100 contents actually do complete the word. A zero-length sequence is
3101 allowed, it means that there were no completions available. Only
3102 string elements of the sequence are used; other elements in the
3103 sequence are ignored.
3106 If the return value is one of the @samp{COMPLETE_} constants defined
3107 below, then the corresponding @value{GDBN}-internal completion
3108 function is invoked, and its result is used.
3111 All other results are treated as though there were no available
3116 When a new command is registered, it must be declared as a member of
3117 some general class of commands. This is used to classify top-level
3118 commands in the on-line help system; note that prefix commands are not
3119 listed under their own category but rather that of their top-level
3120 command. The available classifications are represented by constants
3121 defined in the @code{gdb} module:
3124 @findex COMMAND_NONE
3125 @findex gdb.COMMAND_NONE
3126 @item gdb.COMMAND_NONE
3127 The command does not belong to any particular class. A command in
3128 this category will not be displayed in any of the help categories.
3130 @findex COMMAND_RUNNING
3131 @findex gdb.COMMAND_RUNNING
3132 @item gdb.COMMAND_RUNNING
3133 The command is related to running the inferior. For example,
3134 @code{start}, @code{step}, and @code{continue} are in this category.
3135 Type @kbd{help running} at the @value{GDBN} prompt to see a list of
3136 commands in this category.
3138 @findex COMMAND_DATA
3139 @findex gdb.COMMAND_DATA
3140 @item gdb.COMMAND_DATA
3141 The command is related to data or variables. For example,
3142 @code{call}, @code{find}, and @code{print} are in this category. Type
3143 @kbd{help data} at the @value{GDBN} prompt to see a list of commands
3146 @findex COMMAND_STACK
3147 @findex gdb.COMMAND_STACK
3148 @item gdb.COMMAND_STACK
3149 The command has to do with manipulation of the stack. For example,
3150 @code{backtrace}, @code{frame}, and @code{return} are in this
3151 category. Type @kbd{help stack} at the @value{GDBN} prompt to see a
3152 list of commands in this category.
3154 @findex COMMAND_FILES
3155 @findex gdb.COMMAND_FILES
3156 @item gdb.COMMAND_FILES
3157 This class is used for file-related commands. For example,
3158 @code{file}, @code{list} and @code{section} are in this category.
3159 Type @kbd{help files} at the @value{GDBN} prompt to see a list of
3160 commands in this category.
3162 @findex COMMAND_SUPPORT
3163 @findex gdb.COMMAND_SUPPORT
3164 @item gdb.COMMAND_SUPPORT
3165 This should be used for ``support facilities'', generally meaning
3166 things that are useful to the user when interacting with @value{GDBN},
3167 but not related to the state of the inferior. For example,
3168 @code{help}, @code{make}, and @code{shell} are in this category. Type
3169 @kbd{help support} at the @value{GDBN} prompt to see a list of
3170 commands in this category.
3172 @findex COMMAND_STATUS
3173 @findex gdb.COMMAND_STATUS
3174 @item gdb.COMMAND_STATUS
3175 The command is an @samp{info}-related command, that is, related to the
3176 state of @value{GDBN} itself. For example, @code{info}, @code{macro},
3177 and @code{show} are in this category. Type @kbd{help status} at the
3178 @value{GDBN} prompt to see a list of commands in this category.
3180 @findex COMMAND_BREAKPOINTS
3181 @findex gdb.COMMAND_BREAKPOINTS
3182 @item gdb.COMMAND_BREAKPOINTS
3183 The command has to do with breakpoints. For example, @code{break},
3184 @code{clear}, and @code{delete} are in this category. Type @kbd{help
3185 breakpoints} at the @value{GDBN} prompt to see a list of commands in
3188 @findex COMMAND_TRACEPOINTS
3189 @findex gdb.COMMAND_TRACEPOINTS
3190 @item gdb.COMMAND_TRACEPOINTS
3191 The command has to do with tracepoints. For example, @code{trace},
3192 @code{actions}, and @code{tfind} are in this category. Type
3193 @kbd{help tracepoints} at the @value{GDBN} prompt to see a list of
3194 commands in this category.
3196 @findex COMMAND_USER
3197 @findex gdb.COMMAND_USER
3198 @item gdb.COMMAND_USER
3199 The command is a general purpose command for the user, and typically
3200 does not fit in one of the other categories.
3201 Type @kbd{help user-defined} at the @value{GDBN} prompt to see
3202 a list of commands in this category, as well as the list of gdb macros
3203 (@pxref{Sequences}).
3205 @findex COMMAND_OBSCURE
3206 @findex gdb.COMMAND_OBSCURE
3207 @item gdb.COMMAND_OBSCURE
3208 The command is only used in unusual circumstances, or is not of
3209 general interest to users. For example, @code{checkpoint},
3210 @code{fork}, and @code{stop} are in this category. Type @kbd{help
3211 obscure} at the @value{GDBN} prompt to see a list of commands in this
3214 @findex COMMAND_MAINTENANCE
3215 @findex gdb.COMMAND_MAINTENANCE
3216 @item gdb.COMMAND_MAINTENANCE
3217 The command is only useful to @value{GDBN} maintainers. The
3218 @code{maintenance} and @code{flushregs} commands are in this category.
3219 Type @kbd{help internals} at the @value{GDBN} prompt to see a list of
3220 commands in this category.
3223 A new command can use a predefined completion function, either by
3224 specifying it via an argument at initialization, or by returning it
3225 from the @code{complete} method. These predefined completion
3226 constants are all defined in the @code{gdb} module:
3229 @vindex COMPLETE_NONE
3230 @item gdb.COMPLETE_NONE
3231 This constant means that no completion should be done.
3233 @vindex COMPLETE_FILENAME
3234 @item gdb.COMPLETE_FILENAME
3235 This constant means that filename completion should be performed.
3237 @vindex COMPLETE_LOCATION
3238 @item gdb.COMPLETE_LOCATION
3239 This constant means that location completion should be done.
3240 @xref{Specify Location}.
3242 @vindex COMPLETE_COMMAND
3243 @item gdb.COMPLETE_COMMAND
3244 This constant means that completion should examine @value{GDBN}
3247 @vindex COMPLETE_SYMBOL
3248 @item gdb.COMPLETE_SYMBOL
3249 This constant means that completion should be done using symbol names
3252 @vindex COMPLETE_EXPRESSION
3253 @item gdb.COMPLETE_EXPRESSION
3254 This constant means that completion should be done on expressions.
3255 Often this means completing on symbol names, but some language
3256 parsers also have support for completing on field names.
3259 The following code snippet shows how a trivial CLI command can be
3260 implemented in Python:
3263 class HelloWorld (gdb.Command):
3264 """Greet the whole world."""
3266 def __init__ (self):
3267 super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)
3269 def invoke (self, arg, from_tty):
3270 print "Hello, World!"
3275 The last line instantiates the class, and is necessary to trigger the
3276 registration of the command with @value{GDBN}. Depending on how the
3277 Python code is read into @value{GDBN}, you may need to import the
3278 @code{gdb} module explicitly.
3280 @node Parameters In Python
3281 @subsubsection Parameters In Python
3283 @cindex parameters in python
3284 @cindex python parameters
3285 @tindex gdb.Parameter
3287 You can implement new @value{GDBN} parameters using Python. A new
3288 parameter is implemented as an instance of the @code{gdb.Parameter}
3291 Parameters are exposed to the user via the @code{set} and
3292 @code{show} commands. @xref{Help}.
3294 There are many parameters that already exist and can be set in
3295 @value{GDBN}. Two examples are: @code{set follow fork} and
3296 @code{set charset}. Setting these parameters influences certain
3297 behavior in @value{GDBN}. Similarly, you can define parameters that
3298 can be used to influence behavior in custom Python scripts and commands.
3300 @defun Parameter.__init__ (name, @var{command-class}, @var{parameter-class} @r{[}, @var{enum-sequence}@r{]})
3301 The object initializer for @code{Parameter} registers the new
3302 parameter with @value{GDBN}. This initializer is normally invoked
3303 from the subclass' own @code{__init__} method.
3305 @var{name} is the name of the new parameter. If @var{name} consists
3306 of multiple words, then the initial words are looked for as prefix
3307 parameters. An example of this can be illustrated with the
3308 @code{set print} set of parameters. If @var{name} is
3309 @code{print foo}, then @code{print} will be searched as the prefix
3310 parameter. In this case the parameter can subsequently be accessed in
3311 @value{GDBN} as @code{set print foo}.
3313 If @var{name} consists of multiple words, and no prefix parameter group
3314 can be found, an exception is raised.
3316 @var{command-class} should be one of the @samp{COMMAND_} constants
3317 (@pxref{Commands In Python}). This argument tells @value{GDBN} how to
3318 categorize the new parameter in the help system.
3320 @var{parameter-class} should be one of the @samp{PARAM_} constants
3321 defined below. This argument tells @value{GDBN} the type of the new
3322 parameter; this information is used for input validation and
3325 If @var{parameter-class} is @code{PARAM_ENUM}, then
3326 @var{enum-sequence} must be a sequence of strings. These strings
3327 represent the possible values for the parameter.
3329 If @var{parameter-class} is not @code{PARAM_ENUM}, then the presence
3330 of a fourth argument will cause an exception to be thrown.
3332 The help text for the new parameter is taken from the Python
3333 documentation string for the parameter's class, if there is one. If
3334 there is no documentation string, a default value is used.
3337 @defvar Parameter.set_doc
3338 If this attribute exists, and is a string, then its value is used as
3339 the help text for this parameter's @code{set} command. The value is
3340 examined when @code{Parameter.__init__} is invoked; subsequent changes
3344 @defvar Parameter.show_doc
3345 If this attribute exists, and is a string, then its value is used as
3346 the help text for this parameter's @code{show} command. The value is
3347 examined when @code{Parameter.__init__} is invoked; subsequent changes
3351 @defvar Parameter.value
3352 The @code{value} attribute holds the underlying value of the
3353 parameter. It can be read and assigned to just as any other
3354 attribute. @value{GDBN} does validation when assignments are made.
3357 There are two methods that should be implemented in any
3358 @code{Parameter} class. These are:
3360 @defun Parameter.get_set_string (self)
3361 @value{GDBN} will call this method when a @var{parameter}'s value has
3362 been changed via the @code{set} API (for example, @kbd{set foo off}).
3363 The @code{value} attribute has already been populated with the new
3364 value and may be used in output. This method must return a string.
3367 @defun Parameter.get_show_string (self, svalue)
3368 @value{GDBN} will call this method when a @var{parameter}'s
3369 @code{show} API has been invoked (for example, @kbd{show foo}). The
3370 argument @code{svalue} receives the string representation of the
3371 current value. This method must return a string.
3374 When a new parameter is defined, its type must be specified. The
3375 available types are represented by constants defined in the @code{gdb}
3379 @findex PARAM_BOOLEAN
3380 @findex gdb.PARAM_BOOLEAN
3381 @item gdb.PARAM_BOOLEAN
3382 The value is a plain boolean. The Python boolean values, @code{True}
3383 and @code{False} are the only valid values.
3385 @findex PARAM_AUTO_BOOLEAN
3386 @findex gdb.PARAM_AUTO_BOOLEAN
3387 @item gdb.PARAM_AUTO_BOOLEAN
3388 The value has three possible states: true, false, and @samp{auto}. In
3389 Python, true and false are represented using boolean constants, and
3390 @samp{auto} is represented using @code{None}.
3392 @findex PARAM_UINTEGER
3393 @findex gdb.PARAM_UINTEGER
3394 @item gdb.PARAM_UINTEGER
3395 The value is an unsigned integer. The value of 0 should be
3396 interpreted to mean ``unlimited''.
3398 @findex PARAM_INTEGER
3399 @findex gdb.PARAM_INTEGER
3400 @item gdb.PARAM_INTEGER
3401 The value is a signed integer. The value of 0 should be interpreted
3402 to mean ``unlimited''.
3404 @findex PARAM_STRING
3405 @findex gdb.PARAM_STRING
3406 @item gdb.PARAM_STRING
3407 The value is a string. When the user modifies the string, any escape
3408 sequences, such as @samp{\t}, @samp{\f}, and octal escapes, are
3409 translated into corresponding characters and encoded into the current
3412 @findex PARAM_STRING_NOESCAPE
3413 @findex gdb.PARAM_STRING_NOESCAPE
3414 @item gdb.PARAM_STRING_NOESCAPE
3415 The value is a string. When the user modifies the string, escapes are
3416 passed through untranslated.
3418 @findex PARAM_OPTIONAL_FILENAME
3419 @findex gdb.PARAM_OPTIONAL_FILENAME
3420 @item gdb.PARAM_OPTIONAL_FILENAME
3421 The value is a either a filename (a string), or @code{None}.
3423 @findex PARAM_FILENAME
3424 @findex gdb.PARAM_FILENAME
3425 @item gdb.PARAM_FILENAME
3426 The value is a filename. This is just like
3427 @code{PARAM_STRING_NOESCAPE}, but uses file names for completion.
3429 @findex PARAM_ZINTEGER
3430 @findex gdb.PARAM_ZINTEGER
3431 @item gdb.PARAM_ZINTEGER
3432 The value is an integer. This is like @code{PARAM_INTEGER}, except 0
3433 is interpreted as itself.
3436 @findex gdb.PARAM_ENUM
3437 @item gdb.PARAM_ENUM
3438 The value is a string, which must be one of a collection string
3439 constants provided when the parameter is created.
3442 @node Functions In Python
3443 @subsubsection Writing new convenience functions
3445 @cindex writing convenience functions
3446 @cindex convenience functions in python
3447 @cindex python convenience functions
3448 @tindex gdb.Function
3450 You can implement new convenience functions (@pxref{Convenience Vars})
3451 in Python. A convenience function is an instance of a subclass of the
3452 class @code{gdb.Function}.
3454 @defun Function.__init__ (name)
3455 The initializer for @code{Function} registers the new function with
3456 @value{GDBN}. The argument @var{name} is the name of the function,
3457 a string. The function will be visible to the user as a convenience
3458 variable of type @code{internal function}, whose name is the same as
3459 the given @var{name}.
3461 The documentation for the new function is taken from the documentation
3462 string for the new class.
3465 @defun Function.invoke (@var{*args})
3466 When a convenience function is evaluated, its arguments are converted
3467 to instances of @code{gdb.Value}, and then the function's
3468 @code{invoke} method is called. Note that @value{GDBN} does not
3469 predetermine the arity of convenience functions. Instead, all
3470 available arguments are passed to @code{invoke}, following the
3471 standard Python calling convention. In particular, a convenience
3472 function can have default values for parameters without ill effect.
3474 The return value of this method is used as its value in the enclosing
3475 expression. If an ordinary Python value is returned, it is converted
3476 to a @code{gdb.Value} following the usual rules.
3479 The following code snippet shows how a trivial convenience function can
3480 be implemented in Python:
3483 class Greet (gdb.Function):
3484 """Return string to greet someone.
3485 Takes a name as argument."""
3487 def __init__ (self):
3488 super (Greet, self).__init__ ("greet")
3490 def invoke (self, name):
3491 return "Hello, %s!" % name.string ()
3496 The last line instantiates the class, and is necessary to trigger the
3497 registration of the function with @value{GDBN}. Depending on how the
3498 Python code is read into @value{GDBN}, you may need to import the
3499 @code{gdb} module explicitly.
3501 Now you can use the function in an expression:
3504 (gdb) print $greet("Bob")
3508 @node Progspaces In Python
3509 @subsubsection Program Spaces In Python
3511 @cindex progspaces in python
3512 @tindex gdb.Progspace
3514 A program space, or @dfn{progspace}, represents a symbolic view
3515 of an address space.
3516 It consists of all of the objfiles of the program.
3517 @xref{Objfiles In Python}.
3518 @xref{Inferiors and Programs, program spaces}, for more details
3519 about program spaces.
3521 The following progspace-related functions are available in the
3524 @findex gdb.current_progspace
3525 @defun gdb.current_progspace ()
3526 This function returns the program space of the currently selected inferior.
3527 @xref{Inferiors and Programs}.
3530 @findex gdb.progspaces
3531 @defun gdb.progspaces ()
3532 Return a sequence of all the progspaces currently known to @value{GDBN}.
3535 Each progspace is represented by an instance of the @code{gdb.Progspace}
3538 @defvar Progspace.filename
3539 The file name of the progspace as a string.
3542 @defvar Progspace.pretty_printers
3543 The @code{pretty_printers} attribute is a list of functions. It is
3544 used to look up pretty-printers. A @code{Value} is passed to each
3545 function in order; if the function returns @code{None}, then the
3546 search continues. Otherwise, the return value should be an object
3547 which is used to format the value. @xref{Pretty Printing API}, for more
3551 @defvar Progspace.type_printers
3552 The @code{type_printers} attribute is a list of type printer objects.
3553 @xref{Type Printing API}, for more information.
3556 @defvar Progspace.frame_filters
3557 The @code{frame_filters} attribute is a dictionary of frame filter
3558 objects. @xref{Frame Filter API}, for more information.
3561 One may add arbitrary attributes to @code{gdb.Progspace} objects
3562 in the usual Python way.
3563 This is useful if, for example, one needs to do some extra record keeping
3564 associated with the program space.
3566 In this contrived example, we want to perform some processing when
3567 an objfile with a certain symbol is loaded, but we only want to do
3568 this once because it is expensive. To achieve this we record the results
3569 with the program space because we can't predict when the desired objfile
3574 def clear_objfiles_handler(event):
3575 event.progspace.expensive_computation = None
3576 def expensive(symbol):
3577 """A mock routine to perform an "expensive" computation on symbol."""
3578 print "Computing the answer to the ultimate question ..."
3580 def new_objfile_handler(event):
3581 objfile = event.new_objfile
3582 progspace = objfile.progspace
3583 if not hasattr(progspace, 'expensive_computation') or \
3584 progspace.expensive_computation is None:
3585 # We use 'main' for the symbol to keep the example simple.
3586 # Note: There's no current way to constrain the lookup
3588 symbol = gdb.lookup_global_symbol('main')
3589 if symbol is not None:
3590 progspace.expensive_computation = expensive(symbol)
3591 gdb.events.clear_objfiles.connect(clear_objfiles_handler)
3592 gdb.events.new_objfile.connect(new_objfile_handler)
3594 (gdb) file /tmp/hello
3595 Reading symbols from /tmp/hello...done.
3596 Computing the answer to the ultimate question ...
3597 (gdb) python print gdb.current_progspace().expensive_computation
3600 Starting program: /tmp/hello
3602 [Inferior 1 (process 4242) exited normally]
3605 @node Objfiles In Python
3606 @subsubsection Objfiles In Python
3608 @cindex objfiles in python
3611 @value{GDBN} loads symbols for an inferior from various
3612 symbol-containing files (@pxref{Files}). These include the primary
3613 executable file, any shared libraries used by the inferior, and any
3614 separate debug info files (@pxref{Separate Debug Files}).
3615 @value{GDBN} calls these symbol-containing files @dfn{objfiles}.
3617 The following objfile-related functions are available in the
3620 @findex gdb.current_objfile
3621 @defun gdb.current_objfile ()
3622 When auto-loading a Python script (@pxref{Python Auto-loading}), @value{GDBN}
3623 sets the ``current objfile'' to the corresponding objfile. This
3624 function returns the current objfile. If there is no current objfile,
3625 this function returns @code{None}.
3628 @findex gdb.objfiles
3629 @defun gdb.objfiles ()
3630 Return a sequence of all the objfiles current known to @value{GDBN}.
3631 @xref{Objfiles In Python}.
3634 @findex gdb.lookup_objfile
3635 @defun gdb.lookup_objfile (name @r{[}, by_build_id{]})
3636 Look up @var{name}, a file name or build ID, in the list of objfiles
3637 for the current program space (@pxref{Progspaces In Python}).
3638 If the objfile is not found throw the Python @code{ValueError} exception.
3640 If @var{name} is a relative file name, then it will match any
3641 source file name with the same trailing components. For example, if
3642 @var{name} is @samp{gcc/expr.c}, then it will match source file
3643 name of @file{/build/trunk/gcc/expr.c}, but not
3644 @file{/build/trunk/libcpp/expr.c} or @file{/build/trunk/gcc/x-expr.c}.
3646 If @var{by_build_id} is provided and is @code{True} then @var{name}
3647 is the build ID of the objfile. Otherwise, @var{name} is a file name.
3648 This is supported only on some operating systems, notably those which use
3649 the ELF format for binary files and the @sc{gnu} Binutils. For more details
3650 about this feature, see the description of the @option{--build-id}
3651 command-line option in @ref{Options, , Command Line Options, ld.info,
3655 Each objfile is represented by an instance of the @code{gdb.Objfile}
3658 @defvar Objfile.filename
3659 The file name of the objfile as a string, with symbolic links resolved.
3661 The value is @code{None} if the objfile is no longer valid.
3662 See the @code{gdb.Objfile.is_valid} method, described below.
3665 @defvar Objfile.username
3666 The file name of the objfile as specified by the user as a string.
3668 The value is @code{None} if the objfile is no longer valid.
3669 See the @code{gdb.Objfile.is_valid} method, described below.
3672 @defvar Objfile.owner
3673 For separate debug info objfiles this is the corresponding @code{gdb.Objfile}
3674 object that debug info is being provided for.
3675 Otherwise this is @code{None}.
3676 Separate debug info objfiles are added with the
3677 @code{gdb.Objfile.add_separate_debug_file} method, described below.
3680 @defvar Objfile.build_id
3681 The build ID of the objfile as a string.
3682 If the objfile does not have a build ID then the value is @code{None}.
3684 This is supported only on some operating systems, notably those which use
3685 the ELF format for binary files and the @sc{gnu} Binutils. For more details
3686 about this feature, see the description of the @option{--build-id}
3687 command-line option in @ref{Options, , Command Line Options, ld.info,
3691 @defvar Objfile.progspace
3692 The containing program space of the objfile as a @code{gdb.Progspace}
3693 object. @xref{Progspaces In Python}.
3696 @defvar Objfile.pretty_printers
3697 The @code{pretty_printers} attribute is a list of functions. It is
3698 used to look up pretty-printers. A @code{Value} is passed to each
3699 function in order; if the function returns @code{None}, then the
3700 search continues. Otherwise, the return value should be an object
3701 which is used to format the value. @xref{Pretty Printing API}, for more
3705 @defvar Objfile.type_printers
3706 The @code{type_printers} attribute is a list of type printer objects.
3707 @xref{Type Printing API}, for more information.
3710 @defvar Objfile.frame_filters
3711 The @code{frame_filters} attribute is a dictionary of frame filter
3712 objects. @xref{Frame Filter API}, for more information.
3715 One may add arbitrary attributes to @code{gdb.Objfile} objects
3716 in the usual Python way.
3717 This is useful if, for example, one needs to do some extra record keeping
3718 associated with the objfile.
3720 In this contrived example we record the time when @value{GDBN}
3726 def new_objfile_handler(event):
3727 # Set the time_loaded attribute of the new objfile.
3728 event.new_objfile.time_loaded = datetime.datetime.today()
3729 gdb.events.new_objfile.connect(new_objfile_handler)
3732 Reading symbols from ./hello...done.
3733 (gdb) python print gdb.objfiles()[0].time_loaded
3734 2014-10-09 11:41:36.770345
3737 A @code{gdb.Objfile} object has the following methods:
3739 @defun Objfile.is_valid ()
3740 Returns @code{True} if the @code{gdb.Objfile} object is valid,
3741 @code{False} if not. A @code{gdb.Objfile} object can become invalid
3742 if the object file it refers to is not loaded in @value{GDBN} any
3743 longer. All other @code{gdb.Objfile} methods will throw an exception
3744 if it is invalid at the time the method is called.
3747 @defun Objfile.add_separate_debug_file (file)
3748 Add @var{file} to the list of files that @value{GDBN} will search for
3749 debug information for the objfile.
3750 This is useful when the debug info has been removed from the program
3751 and stored in a separate file. @value{GDBN} has built-in support for
3752 finding separate debug info files (@pxref{Separate Debug Files}), but if
3753 the file doesn't live in one of the standard places that @value{GDBN}
3754 searches then this function can be used to add a debug info file
3755 from a different place.
3758 @node Frames In Python
3759 @subsubsection Accessing inferior stack frames from Python.
3761 @cindex frames in python
3762 When the debugged program stops, @value{GDBN} is able to analyze its call
3763 stack (@pxref{Frames,,Stack frames}). The @code{gdb.Frame} class
3764 represents a frame in the stack. A @code{gdb.Frame} object is only valid
3765 while its corresponding frame exists in the inferior's stack. If you try
3766 to use an invalid frame object, @value{GDBN} will throw a @code{gdb.error}
3767 exception (@pxref{Exception Handling}).
3769 Two @code{gdb.Frame} objects can be compared for equality with the @code{==}
3773 (@value{GDBP}) python print gdb.newest_frame() == gdb.selected_frame ()
3777 The following frame-related functions are available in the @code{gdb} module:
3779 @findex gdb.selected_frame
3780 @defun gdb.selected_frame ()
3781 Return the selected frame object. (@pxref{Selection,,Selecting a Frame}).
3784 @findex gdb.newest_frame
3785 @defun gdb.newest_frame ()
3786 Return the newest frame object for the selected thread.
3789 @defun gdb.frame_stop_reason_string (reason)
3790 Return a string explaining the reason why @value{GDBN} stopped unwinding
3791 frames, as expressed by the given @var{reason} code (an integer, see the
3792 @code{unwind_stop_reason} method further down in this section).
3795 A @code{gdb.Frame} object has the following methods:
3797 @defun Frame.is_valid ()
3798 Returns true if the @code{gdb.Frame} object is valid, false if not.
3799 A frame object can become invalid if the frame it refers to doesn't
3800 exist anymore in the inferior. All @code{gdb.Frame} methods will throw
3801 an exception if it is invalid at the time the method is called.
3804 @defun Frame.name ()
3805 Returns the function name of the frame, or @code{None} if it can't be
3809 @defun Frame.architecture ()
3810 Returns the @code{gdb.Architecture} object corresponding to the frame's
3811 architecture. @xref{Architectures In Python}.
3814 @defun Frame.type ()
3815 Returns the type of the frame. The value can be one of:
3817 @item gdb.NORMAL_FRAME
3818 An ordinary stack frame.
3820 @item gdb.DUMMY_FRAME
3821 A fake stack frame that was created by @value{GDBN} when performing an
3822 inferior function call.
3824 @item gdb.INLINE_FRAME
3825 A frame representing an inlined function. The function was inlined
3826 into a @code{gdb.NORMAL_FRAME} that is older than this one.
3828 @item gdb.TAILCALL_FRAME
3829 A frame representing a tail call. @xref{Tail Call Frames}.
3831 @item gdb.SIGTRAMP_FRAME
3832 A signal trampoline frame. This is the frame created by the OS when
3833 it calls into a signal handler.
3835 @item gdb.ARCH_FRAME
3836 A fake stack frame representing a cross-architecture call.
3838 @item gdb.SENTINEL_FRAME
3839 This is like @code{gdb.NORMAL_FRAME}, but it is only used for the
3844 @defun Frame.unwind_stop_reason ()
3845 Return an integer representing the reason why it's not possible to find
3846 more frames toward the outermost frame. Use
3847 @code{gdb.frame_stop_reason_string} to convert the value returned by this
3848 function to a string. The value can be one of:
3851 @item gdb.FRAME_UNWIND_NO_REASON
3852 No particular reason (older frames should be available).
3854 @item gdb.FRAME_UNWIND_NULL_ID
3855 The previous frame's analyzer returns an invalid result. This is no
3856 longer used by @value{GDBN}, and is kept only for backward
3859 @item gdb.FRAME_UNWIND_OUTERMOST
3860 This frame is the outermost.
3862 @item gdb.FRAME_UNWIND_UNAVAILABLE
3863 Cannot unwind further, because that would require knowing the
3864 values of registers or memory that have not been collected.
3866 @item gdb.FRAME_UNWIND_INNER_ID
3867 This frame ID looks like it ought to belong to a NEXT frame,
3868 but we got it for a PREV frame. Normally, this is a sign of
3869 unwinder failure. It could also indicate stack corruption.
3871 @item gdb.FRAME_UNWIND_SAME_ID
3872 This frame has the same ID as the previous one. That means
3873 that unwinding further would almost certainly give us another
3874 frame with exactly the same ID, so break the chain. Normally,
3875 this is a sign of unwinder failure. It could also indicate
3878 @item gdb.FRAME_UNWIND_NO_SAVED_PC
3879 The frame unwinder did not find any saved PC, but we needed
3880 one to unwind further.
3882 @item gdb.FRAME_UNWIND_MEMORY_ERROR
3883 The frame unwinder caused an error while trying to access memory.
3885 @item gdb.FRAME_UNWIND_FIRST_ERROR
3886 Any stop reason greater or equal to this value indicates some kind
3887 of error. This special value facilitates writing code that tests
3888 for errors in unwinding in a way that will work correctly even if
3889 the list of the other values is modified in future @value{GDBN}
3890 versions. Using it, you could write:
3892 reason = gdb.selected_frame().unwind_stop_reason ()
3893 reason_str = gdb.frame_stop_reason_string (reason)
3894 if reason >= gdb.FRAME_UNWIND_FIRST_ERROR:
3895 print "An error occured: %s" % reason_str
3902 Returns the frame's resume address.
3905 @defun Frame.block ()
3906 Return the frame's code block. @xref{Blocks In Python}.
3909 @defun Frame.function ()
3910 Return the symbol for the function corresponding to this frame.
3911 @xref{Symbols In Python}.
3914 @defun Frame.older ()
3915 Return the frame that called this frame.
3918 @defun Frame.newer ()
3919 Return the frame called by this frame.
3922 @defun Frame.find_sal ()
3923 Return the frame's symtab and line object.
3924 @xref{Symbol Tables In Python}.
3927 @defun Frame.read_register (register)
3928 Return the value of @var{register} in this frame. The @var{register}
3929 argument must be a string (e.g., @code{'sp'} or @code{'rax'}).
3930 Returns a @code{Gdb.Value} object. Throws an exception if @var{register}
3934 @defun Frame.read_var (variable @r{[}, block@r{]})
3935 Return the value of @var{variable} in this frame. If the optional
3936 argument @var{block} is provided, search for the variable from that
3937 block; otherwise start at the frame's current block (which is
3938 determined by the frame's current program counter). The @var{variable}
3939 argument must be a string or a @code{gdb.Symbol} object; @var{block} must be a
3940 @code{gdb.Block} object.
3943 @defun Frame.select ()
3944 Set this frame to be the selected frame. @xref{Stack, ,Examining the
3948 @node Blocks In Python
3949 @subsubsection Accessing blocks from Python.
3951 @cindex blocks in python
3954 In @value{GDBN}, symbols are stored in blocks. A block corresponds
3955 roughly to a scope in the source code. Blocks are organized
3956 hierarchically, and are represented individually in Python as a
3957 @code{gdb.Block}. Blocks rely on debugging information being
3960 A frame has a block. Please see @ref{Frames In Python}, for a more
3961 in-depth discussion of frames.
3963 The outermost block is known as the @dfn{global block}. The global
3964 block typically holds public global variables and functions.
3966 The block nested just inside the global block is the @dfn{static
3967 block}. The static block typically holds file-scoped variables and
3970 @value{GDBN} provides a method to get a block's superblock, but there
3971 is currently no way to examine the sub-blocks of a block, or to
3972 iterate over all the blocks in a symbol table (@pxref{Symbol Tables In
3975 Here is a short example that should help explain blocks:
3978 /* This is in the global block. */
3981 /* This is in the static block. */
3982 static int file_scope;
3984 /* 'function' is in the global block, and 'argument' is
3985 in a block nested inside of 'function'. */
3986 int function (int argument)
3988 /* 'local' is in a block inside 'function'. It may or may
3989 not be in the same block as 'argument'. */
3993 /* 'inner' is in a block whose superblock is the one holding
3997 /* If this call is expanded by the compiler, you may see
3998 a nested block here whose function is 'inline_function'
3999 and whose superblock is the one holding 'inner'. */
4005 A @code{gdb.Block} is iterable. The iterator returns the symbols
4006 (@pxref{Symbols In Python}) local to the block. Python programs
4007 should not assume that a specific block object will always contain a
4008 given symbol, since changes in @value{GDBN} features and
4009 infrastructure may cause symbols move across blocks in a symbol
4012 The following block-related functions are available in the @code{gdb}
4015 @findex gdb.block_for_pc
4016 @defun gdb.block_for_pc (pc)
4017 Return the innermost @code{gdb.Block} containing the given @var{pc}
4018 value. If the block cannot be found for the @var{pc} value specified,
4019 the function will return @code{None}.
4022 A @code{gdb.Block} object has the following methods:
4024 @defun Block.is_valid ()
4025 Returns @code{True} if the @code{gdb.Block} object is valid,
4026 @code{False} if not. A block object can become invalid if the block it
4027 refers to doesn't exist anymore in the inferior. All other
4028 @code{gdb.Block} methods will throw an exception if it is invalid at
4029 the time the method is called. The block's validity is also checked
4030 during iteration over symbols of the block.
4033 A @code{gdb.Block} object has the following attributes:
4036 The start address of the block. This attribute is not writable.
4040 The end address of the block. This attribute is not writable.
4043 @defvar Block.function
4044 The name of the block represented as a @code{gdb.Symbol}. If the
4045 block is not named, then this attribute holds @code{None}. This
4046 attribute is not writable.
4048 For ordinary function blocks, the superblock is the static block.
4049 However, you should note that it is possible for a function block to
4050 have a superblock that is not the static block -- for instance this
4051 happens for an inlined function.
4054 @defvar Block.superblock
4055 The block containing this block. If this parent block does not exist,
4056 this attribute holds @code{None}. This attribute is not writable.
4059 @defvar Block.global_block
4060 The global block associated with this block. This attribute is not
4064 @defvar Block.static_block
4065 The static block associated with this block. This attribute is not
4069 @defvar Block.is_global
4070 @code{True} if the @code{gdb.Block} object is a global block,
4071 @code{False} if not. This attribute is not
4075 @defvar Block.is_static
4076 @code{True} if the @code{gdb.Block} object is a static block,
4077 @code{False} if not. This attribute is not writable.
4080 @node Symbols In Python
4081 @subsubsection Python representation of Symbols.
4083 @cindex symbols in python
4086 @value{GDBN} represents every variable, function and type as an
4087 entry in a symbol table. @xref{Symbols, ,Examining the Symbol Table}.
4088 Similarly, Python represents these symbols in @value{GDBN} with the
4089 @code{gdb.Symbol} object.
4091 The following symbol-related functions are available in the @code{gdb}
4094 @findex gdb.lookup_symbol
4095 @defun gdb.lookup_symbol (name @r{[}, block @r{[}, domain@r{]]})
4096 This function searches for a symbol by name. The search scope can be
4097 restricted to the parameters defined in the optional domain and block
4100 @var{name} is the name of the symbol. It must be a string. The
4101 optional @var{block} argument restricts the search to symbols visible
4102 in that @var{block}. The @var{block} argument must be a
4103 @code{gdb.Block} object. If omitted, the block for the current frame
4104 is used. The optional @var{domain} argument restricts
4105 the search to the domain type. The @var{domain} argument must be a
4106 domain constant defined in the @code{gdb} module and described later
4109 The result is a tuple of two elements.
4110 The first element is a @code{gdb.Symbol} object or @code{None} if the symbol
4112 If the symbol is found, the second element is @code{True} if the symbol
4113 is a field of a method's object (e.g., @code{this} in C@t{++}),
4114 otherwise it is @code{False}.
4115 If the symbol is not found, the second element is @code{False}.
4118 @findex gdb.lookup_global_symbol
4119 @defun gdb.lookup_global_symbol (name @r{[}, domain@r{]})
4120 This function searches for a global symbol by name.
4121 The search scope can be restricted to by the domain argument.
4123 @var{name} is the name of the symbol. It must be a string.
4124 The optional @var{domain} argument restricts the search to the domain type.
4125 The @var{domain} argument must be a domain constant defined in the @code{gdb}
4126 module and described later in this chapter.
4128 The result is a @code{gdb.Symbol} object or @code{None} if the symbol
4132 A @code{gdb.Symbol} object has the following attributes:
4135 The type of the symbol or @code{None} if no type is recorded.
4136 This attribute is represented as a @code{gdb.Type} object.
4137 @xref{Types In Python}. This attribute is not writable.
4140 @defvar Symbol.symtab
4141 The symbol table in which the symbol appears. This attribute is
4142 represented as a @code{gdb.Symtab} object. @xref{Symbol Tables In
4143 Python}. This attribute is not writable.
4147 The line number in the source code at which the symbol was defined.
4152 The name of the symbol as a string. This attribute is not writable.
4155 @defvar Symbol.linkage_name
4156 The name of the symbol, as used by the linker (i.e., may be mangled).
4157 This attribute is not writable.
4160 @defvar Symbol.print_name
4161 The name of the symbol in a form suitable for output. This is either
4162 @code{name} or @code{linkage_name}, depending on whether the user
4163 asked @value{GDBN} to display demangled or mangled names.
4166 @defvar Symbol.addr_class
4167 The address class of the symbol. This classifies how to find the value
4168 of a symbol. Each address class is a constant defined in the
4169 @code{gdb} module and described later in this chapter.
4172 @defvar Symbol.needs_frame
4173 This is @code{True} if evaluating this symbol's value requires a frame
4174 (@pxref{Frames In Python}) and @code{False} otherwise. Typically,
4175 local variables will require a frame, but other symbols will not.
4178 @defvar Symbol.is_argument
4179 @code{True} if the symbol is an argument of a function.
4182 @defvar Symbol.is_constant
4183 @code{True} if the symbol is a constant.
4186 @defvar Symbol.is_function
4187 @code{True} if the symbol is a function or a method.
4190 @defvar Symbol.is_variable
4191 @code{True} if the symbol is a variable.
4194 A @code{gdb.Symbol} object has the following methods:
4196 @defun Symbol.is_valid ()
4197 Returns @code{True} if the @code{gdb.Symbol} object is valid,
4198 @code{False} if not. A @code{gdb.Symbol} object can become invalid if
4199 the symbol it refers to does not exist in @value{GDBN} any longer.
4200 All other @code{gdb.Symbol} methods will throw an exception if it is
4201 invalid at the time the method is called.
4204 @defun Symbol.value (@r{[}frame@r{]})
4205 Compute the value of the symbol, as a @code{gdb.Value}. For
4206 functions, this computes the address of the function, cast to the
4207 appropriate type. If the symbol requires a frame in order to compute
4208 its value, then @var{frame} must be given. If @var{frame} is not
4209 given, or if @var{frame} is invalid, then this method will throw an
4213 The available domain categories in @code{gdb.Symbol} are represented
4214 as constants in the @code{gdb} module:
4217 @vindex SYMBOL_UNDEF_DOMAIN
4218 @item gdb.SYMBOL_UNDEF_DOMAIN
4219 This is used when a domain has not been discovered or none of the
4220 following domains apply. This usually indicates an error either
4221 in the symbol information or in @value{GDBN}'s handling of symbols.
4223 @vindex SYMBOL_VAR_DOMAIN
4224 @item gdb.SYMBOL_VAR_DOMAIN
4225 This domain contains variables, function names, typedef names and enum
4228 @vindex SYMBOL_STRUCT_DOMAIN
4229 @item gdb.SYMBOL_STRUCT_DOMAIN
4230 This domain holds struct, union and enum type names.
4232 @vindex SYMBOL_LABEL_DOMAIN
4233 @item gdb.SYMBOL_LABEL_DOMAIN
4234 This domain contains names of labels (for gotos).
4236 @vindex SYMBOL_VARIABLES_DOMAIN
4237 @item gdb.SYMBOL_VARIABLES_DOMAIN
4238 This domain holds a subset of the @code{SYMBOLS_VAR_DOMAIN}; it
4239 contains everything minus functions and types.
4241 @vindex SYMBOL_FUNCTIONS_DOMAIN
4242 @item gdb.SYMBOL_FUNCTION_DOMAIN
4243 This domain contains all functions.
4245 @vindex SYMBOL_TYPES_DOMAIN
4246 @item gdb.SYMBOL_TYPES_DOMAIN
4247 This domain contains all types.
4250 The available address class categories in @code{gdb.Symbol} are represented
4251 as constants in the @code{gdb} module:
4254 @vindex SYMBOL_LOC_UNDEF
4255 @item gdb.SYMBOL_LOC_UNDEF
4256 If this is returned by address class, it indicates an error either in
4257 the symbol information or in @value{GDBN}'s handling of symbols.
4259 @vindex SYMBOL_LOC_CONST
4260 @item gdb.SYMBOL_LOC_CONST
4261 Value is constant int.
4263 @vindex SYMBOL_LOC_STATIC
4264 @item gdb.SYMBOL_LOC_STATIC
4265 Value is at a fixed address.
4267 @vindex SYMBOL_LOC_REGISTER
4268 @item gdb.SYMBOL_LOC_REGISTER
4269 Value is in a register.
4271 @vindex SYMBOL_LOC_ARG
4272 @item gdb.SYMBOL_LOC_ARG
4273 Value is an argument. This value is at the offset stored within the
4274 symbol inside the frame's argument list.
4276 @vindex SYMBOL_LOC_REF_ARG
4277 @item gdb.SYMBOL_LOC_REF_ARG
4278 Value address is stored in the frame's argument list. Just like
4279 @code{LOC_ARG} except that the value's address is stored at the
4280 offset, not the value itself.
4282 @vindex SYMBOL_LOC_REGPARM_ADDR
4283 @item gdb.SYMBOL_LOC_REGPARM_ADDR
4284 Value is a specified register. Just like @code{LOC_REGISTER} except
4285 the register holds the address of the argument instead of the argument
4288 @vindex SYMBOL_LOC_LOCAL
4289 @item gdb.SYMBOL_LOC_LOCAL
4290 Value is a local variable.
4292 @vindex SYMBOL_LOC_TYPEDEF
4293 @item gdb.SYMBOL_LOC_TYPEDEF
4294 Value not used. Symbols in the domain @code{SYMBOL_STRUCT_DOMAIN} all
4297 @vindex SYMBOL_LOC_BLOCK
4298 @item gdb.SYMBOL_LOC_BLOCK
4301 @vindex SYMBOL_LOC_CONST_BYTES
4302 @item gdb.SYMBOL_LOC_CONST_BYTES
4303 Value is a byte-sequence.
4305 @vindex SYMBOL_LOC_UNRESOLVED
4306 @item gdb.SYMBOL_LOC_UNRESOLVED
4307 Value is at a fixed address, but the address of the variable has to be
4308 determined from the minimal symbol table whenever the variable is
4311 @vindex SYMBOL_LOC_OPTIMIZED_OUT
4312 @item gdb.SYMBOL_LOC_OPTIMIZED_OUT
4313 The value does not actually exist in the program.
4315 @vindex SYMBOL_LOC_COMPUTED
4316 @item gdb.SYMBOL_LOC_COMPUTED
4317 The value's address is a computed location.
4320 @node Symbol Tables In Python
4321 @subsubsection Symbol table representation in Python.
4323 @cindex symbol tables in python
4325 @tindex gdb.Symtab_and_line
4327 Access to symbol table data maintained by @value{GDBN} on the inferior
4328 is exposed to Python via two objects: @code{gdb.Symtab_and_line} and
4329 @code{gdb.Symtab}. Symbol table and line data for a frame is returned
4330 from the @code{find_sal} method in @code{gdb.Frame} object.
4331 @xref{Frames In Python}.
4333 For more information on @value{GDBN}'s symbol table management, see
4334 @ref{Symbols, ,Examining the Symbol Table}, for more information.
4336 A @code{gdb.Symtab_and_line} object has the following attributes:
4338 @defvar Symtab_and_line.symtab
4339 The symbol table object (@code{gdb.Symtab}) for this frame.
4340 This attribute is not writable.
4343 @defvar Symtab_and_line.pc
4344 Indicates the start of the address range occupied by code for the
4345 current source line. This attribute is not writable.
4348 @defvar Symtab_and_line.last
4349 Indicates the end of the address range occupied by code for the current
4350 source line. This attribute is not writable.
4353 @defvar Symtab_and_line.line
4354 Indicates the current line number for this object. This
4355 attribute is not writable.
4358 A @code{gdb.Symtab_and_line} object has the following methods:
4360 @defun Symtab_and_line.is_valid ()
4361 Returns @code{True} if the @code{gdb.Symtab_and_line} object is valid,
4362 @code{False} if not. A @code{gdb.Symtab_and_line} object can become
4363 invalid if the Symbol table and line object it refers to does not
4364 exist in @value{GDBN} any longer. All other
4365 @code{gdb.Symtab_and_line} methods will throw an exception if it is
4366 invalid at the time the method is called.
4369 A @code{gdb.Symtab} object has the following attributes:
4371 @defvar Symtab.filename
4372 The symbol table's source filename. This attribute is not writable.
4375 @defvar Symtab.objfile
4376 The symbol table's backing object file. @xref{Objfiles In Python}.
4377 This attribute is not writable.
4380 @defvar Symtab.producer
4381 The name and possibly version number of the program that
4382 compiled the code in the symbol table.
4383 The contents of this string is up to the compiler.
4384 If no producer information is available then @code{None} is returned.
4385 This attribute is not writable.
4388 A @code{gdb.Symtab} object has the following methods:
4390 @defun Symtab.is_valid ()
4391 Returns @code{True} if the @code{gdb.Symtab} object is valid,
4392 @code{False} if not. A @code{gdb.Symtab} object can become invalid if
4393 the symbol table it refers to does not exist in @value{GDBN} any
4394 longer. All other @code{gdb.Symtab} methods will throw an exception
4395 if it is invalid at the time the method is called.
4398 @defun Symtab.fullname ()
4399 Return the symbol table's source absolute file name.
4402 @defun Symtab.global_block ()
4403 Return the global block of the underlying symbol table.
4404 @xref{Blocks In Python}.
4407 @defun Symtab.static_block ()
4408 Return the static block of the underlying symbol table.
4409 @xref{Blocks In Python}.
4412 @defun Symtab.linetable ()
4413 Return the line table associated with the symbol table.
4414 @xref{Line Tables In Python}.
4417 @node Line Tables In Python
4418 @subsubsection Manipulating line tables using Python
4420 @cindex line tables in python
4421 @tindex gdb.LineTable
4423 Python code can request and inspect line table information from a
4424 symbol table that is loaded in @value{GDBN}. A line table is a
4425 mapping of source lines to their executable locations in memory. To
4426 acquire the line table information for a particular symbol table, use
4427 the @code{linetable} function (@pxref{Symbol Tables In Python}).
4429 A @code{gdb.LineTable} is iterable. The iterator returns
4430 @code{LineTableEntry} objects that correspond to the source line and
4431 address for each line table entry. @code{LineTableEntry} objects have
4432 the following attributes:
4434 @defvar LineTableEntry.line
4435 The source line number for this line table entry. This number
4436 corresponds to the actual line of source. This attribute is not
4440 @defvar LineTableEntry.pc
4441 The address that is associated with the line table entry where the
4442 executable code for that source line resides in memory. This
4443 attribute is not writable.
4446 As there can be multiple addresses for a single source line, you may
4447 receive multiple @code{LineTableEntry} objects with matching
4448 @code{line} attributes, but with different @code{pc} attributes. The
4449 iterator is sorted in ascending @code{pc} order. Here is a small
4450 example illustrating iterating over a line table.
4453 symtab = gdb.selected_frame().find_sal().symtab
4454 linetable = symtab.linetable()
4455 for line in linetable:
4456 print "Line: "+str(line.line)+" Address: "+hex(line.pc)
4459 This will have the following output:
4462 Line: 33 Address: 0x4005c8L
4463 Line: 37 Address: 0x4005caL
4464 Line: 39 Address: 0x4005d2L
4465 Line: 40 Address: 0x4005f8L
4466 Line: 42 Address: 0x4005ffL
4467 Line: 44 Address: 0x400608L
4468 Line: 42 Address: 0x40060cL
4469 Line: 45 Address: 0x400615L
4472 In addition to being able to iterate over a @code{LineTable}, it also
4473 has the following direct access methods:
4475 @defun LineTable.line (line)
4476 Return a Python @code{Tuple} of @code{LineTableEntry} objects for any
4477 entries in the line table for the given @var{line}, which specifies
4478 the source code line. If there are no entries for that source code
4479 @var{line}, the Python @code{None} is returned.
4482 @defun LineTable.has_line (line)
4483 Return a Python @code{Boolean} indicating whether there is an entry in
4484 the line table for this source line. Return @code{True} if an entry
4485 is found, or @code{False} if not.
4488 @defun LineTable.source_lines ()
4489 Return a Python @code{List} of the source line numbers in the symbol
4490 table. Only lines with executable code locations are returned. The
4491 contents of the @code{List} will just be the source line entries
4492 represented as Python @code{Long} values.
4495 @node Breakpoints In Python
4496 @subsubsection Manipulating breakpoints using Python
4498 @cindex breakpoints in python
4499 @tindex gdb.Breakpoint
4501 Python code can manipulate breakpoints via the @code{gdb.Breakpoint}
4504 @defun Breakpoint.__init__ (spec @r{[}, type @r{[}, wp_class @r{[},internal @r{[},temporary@r{]]]]})
4505 Create a new breakpoint according to @var{spec}, which is a string
4506 naming the location of the breakpoint, or an expression that defines a
4507 watchpoint. The contents can be any location recognized by the
4508 @code{break} command, or in the case of a watchpoint, by the
4509 @code{watch} command. The optional @var{type} denotes the breakpoint
4510 to create from the types defined later in this chapter. This argument
4511 can be either @code{gdb.BP_BREAKPOINT} or @code{gdb.BP_WATCHPOINT}; it
4512 defaults to @code{gdb.BP_BREAKPOINT}. The optional @var{internal}
4513 argument allows the breakpoint to become invisible to the user. The
4514 breakpoint will neither be reported when created, nor will it be
4515 listed in the output from @code{info breakpoints} (but will be listed
4516 with the @code{maint info breakpoints} command). The optional
4517 @var{temporary} argument makes the breakpoint a temporary breakpoint.
4518 Temporary breakpoints are deleted after they have been hit. Any
4519 further access to the Python breakpoint after it has been hit will
4520 result in a runtime error (as that breakpoint has now been
4521 automatically deleted). The optional @var{wp_class} argument defines
4522 the class of watchpoint to create, if @var{type} is
4523 @code{gdb.BP_WATCHPOINT}. If a watchpoint class is not provided, it
4524 is assumed to be a @code{gdb.WP_WRITE} class.
4527 @defun Breakpoint.stop (self)
4528 The @code{gdb.Breakpoint} class can be sub-classed and, in
4529 particular, you may choose to implement the @code{stop} method.
4530 If this method is defined in a sub-class of @code{gdb.Breakpoint},
4531 it will be called when the inferior reaches any location of a
4532 breakpoint which instantiates that sub-class. If the method returns
4533 @code{True}, the inferior will be stopped at the location of the
4534 breakpoint, otherwise the inferior will continue.
4536 If there are multiple breakpoints at the same location with a
4537 @code{stop} method, each one will be called regardless of the
4538 return status of the previous. This ensures that all @code{stop}
4539 methods have a chance to execute at that location. In this scenario
4540 if one of the methods returns @code{True} but the others return
4541 @code{False}, the inferior will still be stopped.
4543 You should not alter the execution state of the inferior (i.e.@:, step,
4544 next, etc.), alter the current frame context (i.e.@:, change the current
4545 active frame), or alter, add or delete any breakpoint. As a general
4546 rule, you should not alter any data within @value{GDBN} or the inferior
4549 Example @code{stop} implementation:
4552 class MyBreakpoint (gdb.Breakpoint):
4554 inf_val = gdb.parse_and_eval("foo")
4561 The available watchpoint types represented by constants are defined in the
4567 Read only watchpoint.
4571 Write only watchpoint.
4575 Read/Write watchpoint.
4578 @defun Breakpoint.is_valid ()
4579 Return @code{True} if this @code{Breakpoint} object is valid,
4580 @code{False} otherwise. A @code{Breakpoint} object can become invalid
4581 if the user deletes the breakpoint. In this case, the object still
4582 exists, but the underlying breakpoint does not. In the cases of
4583 watchpoint scope, the watchpoint remains valid even if execution of the
4584 inferior leaves the scope of that watchpoint.
4587 @defun Breakpoint.delete ()
4588 Permanently deletes the @value{GDBN} breakpoint. This also
4589 invalidates the Python @code{Breakpoint} object. Any further access
4590 to this object's attributes or methods will raise an error.
4593 @defvar Breakpoint.enabled
4594 This attribute is @code{True} if the breakpoint is enabled, and
4595 @code{False} otherwise. This attribute is writable. You can use it to enable
4596 or disable the breakpoint.
4599 @defvar Breakpoint.silent
4600 This attribute is @code{True} if the breakpoint is silent, and
4601 @code{False} otherwise. This attribute is writable.
4603 Note that a breakpoint can also be silent if it has commands and the
4604 first command is @code{silent}. This is not reported by the
4605 @code{silent} attribute.
4608 @defvar Breakpoint.thread
4609 If the breakpoint is thread-specific, this attribute holds the thread
4610 id. If the breakpoint is not thread-specific, this attribute is
4611 @code{None}. This attribute is writable.
4614 @defvar Breakpoint.task
4615 If the breakpoint is Ada task-specific, this attribute holds the Ada task
4616 id. If the breakpoint is not task-specific (or the underlying
4617 language is not Ada), this attribute is @code{None}. This attribute
4621 @defvar Breakpoint.ignore_count
4622 This attribute holds the ignore count for the breakpoint, an integer.
4623 This attribute is writable.
4626 @defvar Breakpoint.number
4627 This attribute holds the breakpoint's number --- the identifier used by
4628 the user to manipulate the breakpoint. This attribute is not writable.
4631 @defvar Breakpoint.type
4632 This attribute holds the breakpoint's type --- the identifier used to
4633 determine the actual breakpoint type or use-case. This attribute is not
4637 @defvar Breakpoint.visible
4638 This attribute tells whether the breakpoint is visible to the user
4639 when set, or when the @samp{info breakpoints} command is run. This
4640 attribute is not writable.
4643 @defvar Breakpoint.temporary
4644 This attribute indicates whether the breakpoint was created as a
4645 temporary breakpoint. Temporary breakpoints are automatically deleted
4646 after that breakpoint has been hit. Access to this attribute, and all
4647 other attributes and functions other than the @code{is_valid}
4648 function, will result in an error after the breakpoint has been hit
4649 (as it has been automatically deleted). This attribute is not
4653 The available types are represented by constants defined in the @code{gdb}
4657 @vindex BP_BREAKPOINT
4658 @item gdb.BP_BREAKPOINT
4659 Normal code breakpoint.
4661 @vindex BP_WATCHPOINT
4662 @item gdb.BP_WATCHPOINT
4663 Watchpoint breakpoint.
4665 @vindex BP_HARDWARE_WATCHPOINT
4666 @item gdb.BP_HARDWARE_WATCHPOINT
4667 Hardware assisted watchpoint.
4669 @vindex BP_READ_WATCHPOINT
4670 @item gdb.BP_READ_WATCHPOINT
4671 Hardware assisted read watchpoint.
4673 @vindex BP_ACCESS_WATCHPOINT
4674 @item gdb.BP_ACCESS_WATCHPOINT
4675 Hardware assisted access watchpoint.
4678 @defvar Breakpoint.hit_count
4679 This attribute holds the hit count for the breakpoint, an integer.
4680 This attribute is writable, but currently it can only be set to zero.
4683 @defvar Breakpoint.location
4684 This attribute holds the location of the breakpoint, as specified by
4685 the user. It is a string. If the breakpoint does not have a location
4686 (that is, it is a watchpoint) the attribute's value is @code{None}. This
4687 attribute is not writable.
4690 @defvar Breakpoint.expression
4691 This attribute holds a breakpoint expression, as specified by
4692 the user. It is a string. If the breakpoint does not have an
4693 expression (the breakpoint is not a watchpoint) the attribute's value
4694 is @code{None}. This attribute is not writable.
4697 @defvar Breakpoint.condition
4698 This attribute holds the condition of the breakpoint, as specified by
4699 the user. It is a string. If there is no condition, this attribute's
4700 value is @code{None}. This attribute is writable.
4703 @defvar Breakpoint.commands
4704 This attribute holds the commands attached to the breakpoint. If
4705 there are commands, this attribute's value is a string holding all the
4706 commands, separated by newlines. If there are no commands, this
4707 attribute is @code{None}. This attribute is not writable.
4710 @node Finish Breakpoints in Python
4711 @subsubsection Finish Breakpoints
4713 @cindex python finish breakpoints
4714 @tindex gdb.FinishBreakpoint
4716 A finish breakpoint is a temporary breakpoint set at the return address of
4717 a frame, based on the @code{finish} command. @code{gdb.FinishBreakpoint}
4718 extends @code{gdb.Breakpoint}. The underlying breakpoint will be disabled
4719 and deleted when the execution will run out of the breakpoint scope (i.e.@:
4720 @code{Breakpoint.stop} or @code{FinishBreakpoint.out_of_scope} triggered).
4721 Finish breakpoints are thread specific and must be create with the right
4724 @defun FinishBreakpoint.__init__ (@r{[}frame@r{]} @r{[}, internal@r{]})
4725 Create a finish breakpoint at the return address of the @code{gdb.Frame}
4726 object @var{frame}. If @var{frame} is not provided, this defaults to the
4727 newest frame. The optional @var{internal} argument allows the breakpoint to
4728 become invisible to the user. @xref{Breakpoints In Python}, for further
4729 details about this argument.
4732 @defun FinishBreakpoint.out_of_scope (self)
4733 In some circumstances (e.g.@: @code{longjmp}, C@t{++} exceptions, @value{GDBN}
4734 @code{return} command, @dots{}), a function may not properly terminate, and
4735 thus never hit the finish breakpoint. When @value{GDBN} notices such a
4736 situation, the @code{out_of_scope} callback will be triggered.
4738 You may want to sub-class @code{gdb.FinishBreakpoint} and override this
4742 class MyFinishBreakpoint (gdb.FinishBreakpoint)
4744 print "normal finish"
4747 def out_of_scope ():
4748 print "abnormal finish"
4752 @defvar FinishBreakpoint.return_value
4753 When @value{GDBN} is stopped at a finish breakpoint and the frame
4754 used to build the @code{gdb.FinishBreakpoint} object had debug symbols, this
4755 attribute will contain a @code{gdb.Value} object corresponding to the return
4756 value of the function. The value will be @code{None} if the function return
4757 type is @code{void} or if the return value was not computable. This attribute
4761 @node Lazy Strings In Python
4762 @subsubsection Python representation of lazy strings.
4764 @cindex lazy strings in python
4765 @tindex gdb.LazyString
4767 A @dfn{lazy string} is a string whose contents is not retrieved or
4768 encoded until it is needed.
4770 A @code{gdb.LazyString} is represented in @value{GDBN} as an
4771 @code{address} that points to a region of memory, an @code{encoding}
4772 that will be used to encode that region of memory, and a @code{length}
4773 to delimit the region of memory that represents the string. The
4774 difference between a @code{gdb.LazyString} and a string wrapped within
4775 a @code{gdb.Value} is that a @code{gdb.LazyString} will be treated
4776 differently by @value{GDBN} when printing. A @code{gdb.LazyString} is
4777 retrieved and encoded during printing, while a @code{gdb.Value}
4778 wrapping a string is immediately retrieved and encoded on creation.
4780 A @code{gdb.LazyString} object has the following functions:
4782 @defun LazyString.value ()
4783 Convert the @code{gdb.LazyString} to a @code{gdb.Value}. This value
4784 will point to the string in memory, but will lose all the delayed
4785 retrieval, encoding and handling that @value{GDBN} applies to a
4786 @code{gdb.LazyString}.
4789 @defvar LazyString.address
4790 This attribute holds the address of the string. This attribute is not
4794 @defvar LazyString.length
4795 This attribute holds the length of the string in characters. If the
4796 length is -1, then the string will be fetched and encoded up to the
4797 first null of appropriate width. This attribute is not writable.
4800 @defvar LazyString.encoding
4801 This attribute holds the encoding that will be applied to the string
4802 when the string is printed by @value{GDBN}. If the encoding is not
4803 set, or contains an empty string, then @value{GDBN} will select the
4804 most appropriate encoding when the string is printed. This attribute
4808 @defvar LazyString.type
4809 This attribute holds the type that is represented by the lazy string's
4810 type. For a lazy string this will always be a pointer type. To
4811 resolve this to the lazy string's character type, use the type's
4812 @code{target} method. @xref{Types In Python}. This attribute is not
4816 @node Architectures In Python
4817 @subsubsection Python representation of architectures
4818 @cindex Python architectures
4820 @value{GDBN} uses architecture specific parameters and artifacts in a
4821 number of its various computations. An architecture is represented
4822 by an instance of the @code{gdb.Architecture} class.
4824 A @code{gdb.Architecture} class has the following methods:
4826 @defun Architecture.name ()
4827 Return the name (string value) of the architecture.
4830 @defun Architecture.disassemble (@var{start_pc} @r{[}, @var{end_pc} @r{[}, @var{count}@r{]]})
4831 Return a list of disassembled instructions starting from the memory
4832 address @var{start_pc}. The optional arguments @var{end_pc} and
4833 @var{count} determine the number of instructions in the returned list.
4834 If both the optional arguments @var{end_pc} and @var{count} are
4835 specified, then a list of at most @var{count} disassembled instructions
4836 whose start address falls in the closed memory address interval from
4837 @var{start_pc} to @var{end_pc} are returned. If @var{end_pc} is not
4838 specified, but @var{count} is specified, then @var{count} number of
4839 instructions starting from the address @var{start_pc} are returned. If
4840 @var{count} is not specified but @var{end_pc} is specified, then all
4841 instructions whose start address falls in the closed memory address
4842 interval from @var{start_pc} to @var{end_pc} are returned. If neither
4843 @var{end_pc} nor @var{count} are specified, then a single instruction at
4844 @var{start_pc} is returned. For all of these cases, each element of the
4845 returned list is a Python @code{dict} with the following string keys:
4850 The value corresponding to this key is a Python long integer capturing
4851 the memory address of the instruction.
4854 The value corresponding to this key is a string value which represents
4855 the instruction with assembly language mnemonics. The assembly
4856 language flavor used is the same as that specified by the current CLI
4857 variable @code{disassembly-flavor}. @xref{Machine Code}.
4860 The value corresponding to this key is the length (integer value) of the
4861 instruction in bytes.
4866 @node Python Auto-loading
4867 @subsection Python Auto-loading
4868 @cindex Python auto-loading
4870 When a new object file is read (for example, due to the @code{file}
4871 command, or because the inferior has loaded a shared library),
4872 @value{GDBN} will look for Python support scripts in several ways:
4873 @file{@var{objfile}-gdb.py} and @code{.debug_gdb_scripts} section.
4874 @xref{Auto-loading extensions}.
4876 The auto-loading feature is useful for supplying application-specific
4877 debugging commands and scripts.
4879 Auto-loading can be enabled or disabled,
4880 and the list of auto-loaded scripts can be printed.
4883 @anchor{set auto-load python-scripts}
4884 @kindex set auto-load python-scripts
4885 @item set auto-load python-scripts [on|off]
4886 Enable or disable the auto-loading of Python scripts.
4888 @anchor{show auto-load python-scripts}
4889 @kindex show auto-load python-scripts
4890 @item show auto-load python-scripts
4891 Show whether auto-loading of Python scripts is enabled or disabled.
4893 @anchor{info auto-load python-scripts}
4894 @kindex info auto-load python-scripts
4895 @cindex print list of auto-loaded Python scripts
4896 @item info auto-load python-scripts [@var{regexp}]
4897 Print the list of all Python scripts that @value{GDBN} auto-loaded.
4899 Also printed is the list of Python scripts that were mentioned in
4900 the @code{.debug_gdb_scripts} section and were either not found
4901 (@pxref{dotdebug_gdb_scripts section}) or were not auto-loaded due to
4902 @code{auto-load safe-path} rejection (@pxref{Auto-loading}).
4903 This is useful because their names are not printed when @value{GDBN}
4904 tries to load them and fails. There may be many of them, and printing
4905 an error message for each one is problematic.
4907 If @var{regexp} is supplied only Python scripts with matching names are printed.
4912 (gdb) info auto-load python-scripts
4914 Yes py-section-script.py
4915 full name: /tmp/py-section-script.py
4916 No my-foo-pretty-printers.py
4920 When reading an auto-loaded file or script, @value{GDBN} sets the
4921 @dfn{current objfile}. This is available via the @code{gdb.current_objfile}
4922 function (@pxref{Objfiles In Python}). This can be useful for
4923 registering objfile-specific pretty-printers and frame-filters.
4925 @node Python modules
4926 @subsection Python modules
4927 @cindex python modules
4929 @value{GDBN} comes with several modules to assist writing Python code.
4932 * gdb.printing:: Building and registering pretty-printers.
4933 * gdb.types:: Utilities for working with types.
4934 * gdb.prompt:: Utilities for prompt value substitution.
4938 @subsubsection gdb.printing
4939 @cindex gdb.printing
4941 This module provides a collection of utilities for working with
4945 @item PrettyPrinter (@var{name}, @var{subprinters}=None)
4946 This class specifies the API that makes @samp{info pretty-printer},
4947 @samp{enable pretty-printer} and @samp{disable pretty-printer} work.
4948 Pretty-printers should generally inherit from this class.
4950 @item SubPrettyPrinter (@var{name})
4951 For printers that handle multiple types, this class specifies the
4952 corresponding API for the subprinters.
4954 @item RegexpCollectionPrettyPrinter (@var{name})
4955 Utility class for handling multiple printers, all recognized via
4956 regular expressions.
4957 @xref{Writing a Pretty-Printer}, for an example.
4959 @item FlagEnumerationPrinter (@var{name})
4960 A pretty-printer which handles printing of @code{enum} values. Unlike
4961 @value{GDBN}'s built-in @code{enum} printing, this printer attempts to
4962 work properly when there is some overlap between the enumeration
4963 constants. The argument @var{name} is the name of the printer and
4964 also the name of the @code{enum} type to look up.
4966 @item register_pretty_printer (@var{obj}, @var{printer}, @var{replace}=False)
4967 Register @var{printer} with the pretty-printer list of @var{obj}.
4968 If @var{replace} is @code{True} then any existing copy of the printer
4969 is replaced. Otherwise a @code{RuntimeError} exception is raised
4970 if a printer with the same name already exists.
4974 @subsubsection gdb.types
4977 This module provides a collection of utilities for working with
4978 @code{gdb.Type} objects.
4981 @item get_basic_type (@var{type})
4982 Return @var{type} with const and volatile qualifiers stripped,
4983 and with typedefs and C@t{++} references converted to the underlying type.
4988 typedef const int const_int;
4990 const_int& foo_ref (foo);
4991 int main () @{ return 0; @}
4998 (gdb) python import gdb.types
4999 (gdb) python foo_ref = gdb.parse_and_eval("foo_ref")
5000 (gdb) python print gdb.types.get_basic_type(foo_ref.type)
5004 @item has_field (@var{type}, @var{field})
5005 Return @code{True} if @var{type}, assumed to be a type with fields
5006 (e.g., a structure or union), has field @var{field}.
5008 @item make_enum_dict (@var{enum_type})
5009 Return a Python @code{dictionary} type produced from @var{enum_type}.
5011 @item deep_items (@var{type})
5012 Returns a Python iterator similar to the standard
5013 @code{gdb.Type.iteritems} method, except that the iterator returned
5014 by @code{deep_items} will recursively traverse anonymous struct or
5015 union fields. For example:
5029 Then in @value{GDBN}:
5031 (@value{GDBP}) python import gdb.types
5032 (@value{GDBP}) python struct_a = gdb.lookup_type("struct A")
5033 (@value{GDBP}) python print struct_a.keys ()
5035 (@value{GDBP}) python print [k for k,v in gdb.types.deep_items(struct_a)]
5036 @{['a', 'b0', 'b1']@}
5039 @item get_type_recognizers ()
5040 Return a list of the enabled type recognizers for the current context.
5041 This is called by @value{GDBN} during the type-printing process
5042 (@pxref{Type Printing API}).
5044 @item apply_type_recognizers (recognizers, type_obj)
5045 Apply the type recognizers, @var{recognizers}, to the type object
5046 @var{type_obj}. If any recognizer returns a string, return that
5047 string. Otherwise, return @code{None}. This is called by
5048 @value{GDBN} during the type-printing process (@pxref{Type Printing
5051 @item register_type_printer (locus, printer)
5052 This is a convenience function to register a type printer
5053 @var{printer}. The printer must implement the type printer protocol.
5054 The @var{locus} argument is either a @code{gdb.Objfile}, in which case
5055 the printer is registered with that objfile; a @code{gdb.Progspace},
5056 in which case the printer is registered with that progspace; or
5057 @code{None}, in which case the printer is registered globally.
5060 This is a base class that implements the type printer protocol. Type
5061 printers are encouraged, but not required, to derive from this class.
5062 It defines a constructor:
5064 @defmethod TypePrinter __init__ (self, name)
5065 Initialize the type printer with the given name. The new printer
5066 starts in the enabled state.
5072 @subsubsection gdb.prompt
5075 This module provides a method for prompt value-substitution.
5078 @item substitute_prompt (@var{string})
5079 Return @var{string} with escape sequences substituted by values. Some
5080 escape sequences take arguments. You can specify arguments inside
5081 ``@{@}'' immediately following the escape sequence.
5083 The escape sequences you can pass to this function are:
5087 Substitute a backslash.
5089 Substitute an ESC character.
5091 Substitute the selected frame; an argument names a frame parameter.
5093 Substitute a newline.
5095 Substitute a parameter's value; the argument names the parameter.
5097 Substitute a carriage return.
5099 Substitute the selected thread; an argument names a thread parameter.
5101 Substitute the version of GDB.
5103 Substitute the current working directory.
5105 Begin a sequence of non-printing characters. These sequences are
5106 typically used with the ESC character, and are not counted in the string
5107 length. Example: ``\[\e[0;34m\](gdb)\[\e[0m\]'' will return a
5108 blue-colored ``(gdb)'' prompt where the length is five.
5110 End a sequence of non-printing characters.
5116 substitute_prompt (``frame: \f,
5117 print arguments: \p@{print frame-arguments@}'')
5120 @exdent will return the string:
5123 "frame: main, print arguments: scalars"