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7 @c and with the Back-Cover Texts as in (a) below.
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14 @section Extending @value{GDBN} using Python
15 @cindex python scripting
16 @cindex scripting with python
18 You can extend @value{GDBN} using the @uref{http://www.python.org/,
19 Python programming language}. This feature is available only if
20 @value{GDBN} was configured using @option{--with-python}.
22 @cindex python directory
23 Python scripts used by @value{GDBN} should be installed in
24 @file{@var{data-directory}/python}, where @var{data-directory} is
25 the data directory as determined at @value{GDBN} startup (@pxref{Data Files}).
26 This directory, known as the @dfn{python directory},
27 is automatically added to the Python Search Path in order to allow
28 the Python interpreter to locate all scripts installed at this location.
30 Additionally, @value{GDBN} commands and convenience functions which
31 are written in Python and are located in the
32 @file{@var{data-directory}/python/gdb/command} or
33 @file{@var{data-directory}/python/gdb/function} directories are
34 automatically imported when @value{GDBN} starts.
37 * Python Commands:: Accessing Python from @value{GDBN}.
38 * Python API:: Accessing @value{GDBN} from Python.
39 * Python Auto-loading:: Automatically loading Python code.
40 * Python modules:: Python modules provided by @value{GDBN}.
44 @subsection Python Commands
45 @cindex python commands
46 @cindex commands to access python
48 @value{GDBN} provides two commands for accessing the Python interpreter,
49 and one related setting:
52 @kindex python-interactive
54 @item python-interactive @r{[}@var{command}@r{]}
55 @itemx pi @r{[}@var{command}@r{]}
56 Without an argument, the @code{python-interactive} command can be used
57 to start an interactive Python prompt. To return to @value{GDBN},
58 type the @code{EOF} character (e.g., @kbd{Ctrl-D} on an empty prompt).
60 Alternatively, a single-line Python command can be given as an
61 argument and evaluated. If the command is an expression, the result
62 will be printed; otherwise, nothing will be printed. For example:
65 (@value{GDBP}) python-interactive 2 + 3
71 @item python @r{[}@var{command}@r{]}
72 @itemx py @r{[}@var{command}@r{]}
73 The @code{python} command can be used to evaluate Python code.
75 If given an argument, the @code{python} command will evaluate the
76 argument as a Python command. For example:
79 (@value{GDBP}) python print 23
83 If you do not provide an argument to @code{python}, it will act as a
84 multi-line command, like @code{define}. In this case, the Python
85 script is made up of subsequent command lines, given after the
86 @code{python} command. This command list is terminated using a line
87 containing @code{end}. For example:
92 End with a line saying just "end".
98 @kindex set python print-stack
99 @item set python print-stack
100 By default, @value{GDBN} will print only the message component of a
101 Python exception when an error occurs in a Python script. This can be
102 controlled using @code{set python print-stack}: if @code{full}, then
103 full Python stack printing is enabled; if @code{none}, then Python stack
104 and message printing is disabled; if @code{message}, the default, only
105 the message component of the error is printed.
108 It is also possible to execute a Python script from the @value{GDBN}
112 @item source @file{script-name}
113 The script name must end with @samp{.py} and @value{GDBN} must be configured
114 to recognize the script language based on filename extension using
115 the @code{script-extension} setting. @xref{Extending GDB, ,Extending GDB}.
117 @item python execfile ("script-name")
118 This method is based on the @code{execfile} Python built-in function,
119 and thus is always available.
123 @subsection Python API
125 @cindex programming in python
127 You can get quick online help for @value{GDBN}'s Python API by issuing
128 the command @w{@kbd{python help (gdb)}}.
130 Functions and methods which have two or more optional arguments allow
131 them to be specified using keyword syntax. This allows passing some
132 optional arguments while skipping others. Example:
133 @w{@code{gdb.some_function ('foo', bar = 1, baz = 2)}}.
136 * Basic Python:: Basic Python Functions.
137 * Exception Handling:: How Python exceptions are translated.
138 * Values From Inferior:: Python representation of values.
139 * Types In Python:: Python representation of types.
140 * Pretty Printing API:: Pretty-printing values.
141 * Selecting Pretty-Printers:: How GDB chooses a pretty-printer.
142 * Writing a Pretty-Printer:: Writing a Pretty-Printer.
143 * Type Printing API:: Pretty-printing types.
144 * Frame Filter API:: Filtering Frames.
145 * Frame Decorator API:: Decorating Frames.
146 * Writing a Frame Filter:: Writing a Frame Filter.
147 * Unwinding Frames in Python:: Writing frame unwinder.
148 * Xmethods In Python:: Adding and replacing methods of C++ classes.
149 * Xmethod API:: Xmethod types.
150 * Writing an Xmethod:: Writing an xmethod.
151 * Inferiors In Python:: Python representation of inferiors (processes)
152 * Events In Python:: Listening for events from @value{GDBN}.
153 * Threads In Python:: Accessing inferior threads from Python.
154 * Recordings In Python:: Accessing recordings from Python.
155 * Commands In Python:: Implementing new commands in Python.
156 * Parameters In Python:: Adding new @value{GDBN} parameters.
157 * Functions In Python:: Writing new convenience functions.
158 * Progspaces In Python:: Program spaces.
159 * Objfiles In Python:: Object files.
160 * Frames In Python:: Accessing inferior stack frames from Python.
161 * Blocks In Python:: Accessing blocks from Python.
162 * Symbols In Python:: Python representation of symbols.
163 * Symbol Tables In Python:: Python representation of symbol tables.
164 * Line Tables In Python:: Python representation of line tables.
165 * Breakpoints In Python:: Manipulating breakpoints using Python.
166 * Finish Breakpoints in Python:: Setting Breakpoints on function return
168 * Lazy Strings In Python:: Python representation of lazy strings.
169 * Architectures In Python:: Python representation of architectures.
173 @subsubsection Basic Python
175 @cindex python stdout
176 @cindex python pagination
177 At startup, @value{GDBN} overrides Python's @code{sys.stdout} and
178 @code{sys.stderr} to print using @value{GDBN}'s output-paging streams.
179 A Python program which outputs to one of these streams may have its
180 output interrupted by the user (@pxref{Screen Size}). In this
181 situation, a Python @code{KeyboardInterrupt} exception is thrown.
183 Some care must be taken when writing Python code to run in
184 @value{GDBN}. Two things worth noting in particular:
188 @value{GDBN} install handlers for @code{SIGCHLD} and @code{SIGINT}.
189 Python code must not override these, or even change the options using
190 @code{sigaction}. If your program changes the handling of these
191 signals, @value{GDBN} will most likely stop working correctly. Note
192 that it is unfortunately common for GUI toolkits to install a
193 @code{SIGCHLD} handler.
196 @value{GDBN} takes care to mark its internal file descriptors as
197 close-on-exec. However, this cannot be done in a thread-safe way on
198 all platforms. Your Python programs should be aware of this and
199 should both create new file descriptors with the close-on-exec flag
200 set and arrange to close unneeded file descriptors before starting a
204 @cindex python functions
205 @cindex python module
207 @value{GDBN} introduces a new Python module, named @code{gdb}. All
208 methods and classes added by @value{GDBN} are placed in this module.
209 @value{GDBN} automatically @code{import}s the @code{gdb} module for
210 use in all scripts evaluated by the @code{python} command.
212 @findex gdb.PYTHONDIR
213 @defvar gdb.PYTHONDIR
214 A string containing the python directory (@pxref{Python}).
218 @defun gdb.execute (command @r{[}, from_tty @r{[}, to_string@r{]]})
219 Evaluate @var{command}, a string, as a @value{GDBN} CLI command.
220 If a GDB exception happens while @var{command} runs, it is
221 translated as described in @ref{Exception Handling,,Exception Handling}.
223 The @var{from_tty} flag specifies whether @value{GDBN} ought to consider this
224 command as having originated from the user invoking it interactively.
225 It must be a boolean value. If omitted, it defaults to @code{False}.
227 By default, any output produced by @var{command} is sent to
228 @value{GDBN}'s standard output (and to the log output if logging is
229 turned on). If the @var{to_string} parameter is
230 @code{True}, then output will be collected by @code{gdb.execute} and
231 returned as a string. The default is @code{False}, in which case the
232 return value is @code{None}. If @var{to_string} is @code{True}, the
233 @value{GDBN} virtual terminal will be temporarily set to unlimited width
234 and height, and its pagination will be disabled; @pxref{Screen Size}.
237 @findex gdb.breakpoints
238 @defun gdb.breakpoints ()
239 Return a sequence holding all of @value{GDBN}'s breakpoints.
240 @xref{Breakpoints In Python}, for more information. In @value{GDBN}
241 version 7.11 and earlier, this function returned @code{None} if there
242 were no breakpoints. This peculiarity was subsequently fixed, and now
243 @code{gdb.breakpoints} returns an empty sequence in this case.
246 @defun gdb.rbreak (regex @r{[}, minsyms @r{[}, throttle, @r{[}, symtabs @r{]]]})
247 Return a Python list holding a collection of newly set
248 @code{gdb.Breakpoint} objects matching function names defined by the
249 @var{regex} pattern. If the @var{minsyms} keyword is @code{True}, all
250 system functions (those not explicitly defined in the inferior) will
251 also be included in the match. The @var{throttle} keyword takes an
252 integer that defines the maximum number of pattern matches for
253 functions matched by the @var{regex} pattern. If the number of
254 matches exceeds the integer value of @var{throttle}, a
255 @code{RuntimeError} will be raised and no breakpoints will be created.
256 If @var{throttle} is not defined then there is no imposed limit on the
257 maximum number of matches and breakpoints to be created. The
258 @var{symtabs} keyword takes a Python iterable that yields a collection
259 of @code{gdb.Symtab} objects and will restrict the search to those
260 functions only contained within the @code{gdb.Symtab} objects.
263 @findex gdb.parameter
264 @defun gdb.parameter (parameter)
265 Return the value of a @value{GDBN} @var{parameter} given by its name,
266 a string; the parameter name string may contain spaces if the parameter has a
267 multi-part name. For example, @samp{print object} is a valid
270 If the named parameter does not exist, this function throws a
271 @code{gdb.error} (@pxref{Exception Handling}). Otherwise, the
272 parameter's value is converted to a Python value of the appropriate
277 @defun gdb.history (number)
278 Return a value from @value{GDBN}'s value history (@pxref{Value
279 History}). The @var{number} argument indicates which history element to return.
280 If @var{number} is negative, then @value{GDBN} will take its absolute value
281 and count backward from the last element (i.e., the most recent element) to
282 find the value to return. If @var{number} is zero, then @value{GDBN} will
283 return the most recent element. If the element specified by @var{number}
284 doesn't exist in the value history, a @code{gdb.error} exception will be
287 If no exception is raised, the return value is always an instance of
288 @code{gdb.Value} (@pxref{Values From Inferior}).
291 @findex gdb.convenience_variable
292 @defun gdb.convenience_variable (name)
293 Return the value of the convenience variable (@pxref{Convenience
294 Vars}) named @var{name}. @var{name} must be a string. The name
295 should not include the @samp{$} that is used to mark a convenience
296 variable in an expression. If the convenience variable does not
297 exist, then @code{None} is returned.
300 @findex gdb.set_convenience_variable
301 @defun gdb.set_convenience_variable (name, value)
302 Set the value of the convenience variable (@pxref{Convenience Vars})
303 named @var{name}. @var{name} must be a string. The name should not
304 include the @samp{$} that is used to mark a convenience variable in an
305 expression. If @var{value} is @code{None}, then the convenience
306 variable is removed. Otherwise, if @var{value} is not a
307 @code{gdb.Value} (@pxref{Values From Inferior}), it is is converted
308 using the @code{gdb.Value} constructor.
311 @findex gdb.parse_and_eval
312 @defun gdb.parse_and_eval (expression)
313 Parse @var{expression}, which must be a string, as an expression in
314 the current language, evaluate it, and return the result as a
317 This function can be useful when implementing a new command
318 (@pxref{Commands In Python}), as it provides a way to parse the
319 command's argument as an expression. It is also useful simply to
323 @findex gdb.find_pc_line
324 @defun gdb.find_pc_line (pc)
325 Return the @code{gdb.Symtab_and_line} object corresponding to the
326 @var{pc} value. @xref{Symbol Tables In Python}. If an invalid
327 value of @var{pc} is passed as an argument, then the @code{symtab} and
328 @code{line} attributes of the returned @code{gdb.Symtab_and_line} object
329 will be @code{None} and 0 respectively.
332 @findex gdb.post_event
333 @defun gdb.post_event (event)
334 Put @var{event}, a callable object taking no arguments, into
335 @value{GDBN}'s internal event queue. This callable will be invoked at
336 some later point, during @value{GDBN}'s event processing. Events
337 posted using @code{post_event} will be run in the order in which they
338 were posted; however, there is no way to know when they will be
339 processed relative to other events inside @value{GDBN}.
341 @value{GDBN} is not thread-safe. If your Python program uses multiple
342 threads, you must be careful to only call @value{GDBN}-specific
343 functions in the @value{GDBN} thread. @code{post_event} ensures
347 (@value{GDBP}) python
351 > def __init__(self, message):
352 > self.message = message;
353 > def __call__(self):
354 > gdb.write(self.message)
356 >class MyThread1 (threading.Thread):
358 > gdb.post_event(Writer("Hello "))
360 >class MyThread2 (threading.Thread):
362 > gdb.post_event(Writer("World\n"))
367 (@value{GDBP}) Hello World
372 @defun gdb.write (string @r{[}, stream{]})
373 Print a string to @value{GDBN}'s paginated output stream. The
374 optional @var{stream} determines the stream to print to. The default
375 stream is @value{GDBN}'s standard output stream. Possible stream
382 @value{GDBN}'s standard output stream.
387 @value{GDBN}'s standard error stream.
392 @value{GDBN}'s log stream (@pxref{Logging Output}).
395 Writing to @code{sys.stdout} or @code{sys.stderr} will automatically
396 call this function and will automatically direct the output to the
402 Flush the buffer of a @value{GDBN} paginated stream so that the
403 contents are displayed immediately. @value{GDBN} will flush the
404 contents of a stream automatically when it encounters a newline in the
405 buffer. The optional @var{stream} determines the stream to flush. The
406 default stream is @value{GDBN}'s standard output stream. Possible
413 @value{GDBN}'s standard output stream.
418 @value{GDBN}'s standard error stream.
423 @value{GDBN}'s log stream (@pxref{Logging Output}).
427 Flushing @code{sys.stdout} or @code{sys.stderr} will automatically
428 call this function for the relevant stream.
431 @findex gdb.target_charset
432 @defun gdb.target_charset ()
433 Return the name of the current target character set (@pxref{Character
434 Sets}). This differs from @code{gdb.parameter('target-charset')} in
435 that @samp{auto} is never returned.
438 @findex gdb.target_wide_charset
439 @defun gdb.target_wide_charset ()
440 Return the name of the current target wide character set
441 (@pxref{Character Sets}). This differs from
442 @code{gdb.parameter('target-wide-charset')} in that @samp{auto} is
446 @findex gdb.solib_name
447 @defun gdb.solib_name (address)
448 Return the name of the shared library holding the given @var{address}
449 as a string, or @code{None}.
452 @findex gdb.decode_line
453 @defun gdb.decode_line @r{[}expression@r{]}
454 Return locations of the line specified by @var{expression}, or of the
455 current line if no argument was given. This function returns a Python
456 tuple containing two elements. The first element contains a string
457 holding any unparsed section of @var{expression} (or @code{None} if
458 the expression has been fully parsed). The second element contains
459 either @code{None} or another tuple that contains all the locations
460 that match the expression represented as @code{gdb.Symtab_and_line}
461 objects (@pxref{Symbol Tables In Python}). If @var{expression} is
462 provided, it is decoded the way that @value{GDBN}'s inbuilt
463 @code{break} or @code{edit} commands do (@pxref{Specify Location}).
466 @defun gdb.prompt_hook (current_prompt)
469 If @var{prompt_hook} is callable, @value{GDBN} will call the method
470 assigned to this operation before a prompt is displayed by
473 The parameter @code{current_prompt} contains the current @value{GDBN}
474 prompt. This method must return a Python string, or @code{None}. If
475 a string is returned, the @value{GDBN} prompt will be set to that
476 string. If @code{None} is returned, @value{GDBN} will continue to use
479 Some prompts cannot be substituted in @value{GDBN}. Secondary prompts
480 such as those used by readline for command input, and annotation
481 related prompts are prohibited from being changed.
484 @node Exception Handling
485 @subsubsection Exception Handling
486 @cindex python exceptions
487 @cindex exceptions, python
489 When executing the @code{python} command, Python exceptions
490 uncaught within the Python code are translated to calls to
491 @value{GDBN} error-reporting mechanism. If the command that called
492 @code{python} does not handle the error, @value{GDBN} will
493 terminate it and print an error message containing the Python
494 exception name, the associated value, and the Python call stack
495 backtrace at the point where the exception was raised. Example:
498 (@value{GDBP}) python print foo
499 Traceback (most recent call last):
500 File "<string>", line 1, in <module>
501 NameError: name 'foo' is not defined
504 @value{GDBN} errors that happen in @value{GDBN} commands invoked by
505 Python code are converted to Python exceptions. The type of the
506 Python exception depends on the error.
510 This is the base class for most exceptions generated by @value{GDBN}.
511 It is derived from @code{RuntimeError}, for compatibility with earlier
512 versions of @value{GDBN}.
514 If an error occurring in @value{GDBN} does not fit into some more
515 specific category, then the generated exception will have this type.
517 @item gdb.MemoryError
518 This is a subclass of @code{gdb.error} which is thrown when an
519 operation tried to access invalid memory in the inferior.
521 @item KeyboardInterrupt
522 User interrupt (via @kbd{C-c} or by typing @kbd{q} at a pagination
523 prompt) is translated to a Python @code{KeyboardInterrupt} exception.
526 In all cases, your exception handler will see the @value{GDBN} error
527 message as its value and the Python call stack backtrace at the Python
528 statement closest to where the @value{GDBN} error occured as the
532 When implementing @value{GDBN} commands in Python via @code{gdb.Command},
533 it is useful to be able to throw an exception that doesn't cause a
534 traceback to be printed. For example, the user may have invoked the
535 command incorrectly. Use the @code{gdb.GdbError} exception
536 to handle this case. Example:
540 >class HelloWorld (gdb.Command):
541 > """Greet the whole world."""
542 > def __init__ (self):
543 > super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)
544 > def invoke (self, args, from_tty):
545 > argv = gdb.string_to_argv (args)
546 > if len (argv) != 0:
547 > raise gdb.GdbError ("hello-world takes no arguments")
548 > print "Hello, World!"
552 hello-world takes no arguments
555 @node Values From Inferior
556 @subsubsection Values From Inferior
557 @cindex values from inferior, with Python
558 @cindex python, working with values from inferior
560 @cindex @code{gdb.Value}
561 @value{GDBN} provides values it obtains from the inferior program in
562 an object of type @code{gdb.Value}. @value{GDBN} uses this object
563 for its internal bookkeeping of the inferior's values, and for
564 fetching values when necessary.
566 Inferior values that are simple scalars can be used directly in
567 Python expressions that are valid for the value's data type. Here's
568 an example for an integer or floating-point value @code{some_val}:
575 As result of this, @code{bar} will also be a @code{gdb.Value} object
576 whose values are of the same type as those of @code{some_val}. Valid
577 Python operations can also be performed on @code{gdb.Value} objects
578 representing a @code{struct} or @code{class} object. For such cases,
579 the overloaded operator (if present), is used to perform the operation.
580 For example, if @code{val1} and @code{val2} are @code{gdb.Value} objects
581 representing instances of a @code{class} which overloads the @code{+}
582 operator, then one can use the @code{+} operator in their Python script
590 The result of the operation @code{val3} is also a @code{gdb.Value}
591 object corresponding to the value returned by the overloaded @code{+}
592 operator. In general, overloaded operators are invoked for the
593 following operations: @code{+} (binary addition), @code{-} (binary
594 subtraction), @code{*} (multiplication), @code{/}, @code{%}, @code{<<},
595 @code{>>}, @code{|}, @code{&}, @code{^}.
597 Inferior values that are structures or instances of some class can
598 be accessed using the Python @dfn{dictionary syntax}. For example, if
599 @code{some_val} is a @code{gdb.Value} instance holding a structure, you
600 can access its @code{foo} element with:
603 bar = some_val['foo']
606 @cindex getting structure elements using gdb.Field objects as subscripts
607 Again, @code{bar} will also be a @code{gdb.Value} object. Structure
608 elements can also be accessed by using @code{gdb.Field} objects as
609 subscripts (@pxref{Types In Python}, for more information on
610 @code{gdb.Field} objects). For example, if @code{foo_field} is a
611 @code{gdb.Field} object corresponding to element @code{foo} of the above
612 structure, then @code{bar} can also be accessed as follows:
615 bar = some_val[foo_field]
618 A @code{gdb.Value} that represents a function can be executed via
619 inferior function call. Any arguments provided to the call must match
620 the function's prototype, and must be provided in the order specified
623 For example, @code{some_val} is a @code{gdb.Value} instance
624 representing a function that takes two integers as arguments. To
625 execute this function, call it like so:
628 result = some_val (10,20)
631 Any values returned from a function call will be stored as a
634 The following attributes are provided:
636 @defvar Value.address
637 If this object is addressable, this read-only attribute holds a
638 @code{gdb.Value} object representing the address. Otherwise,
639 this attribute holds @code{None}.
642 @cindex optimized out value in Python
643 @defvar Value.is_optimized_out
644 This read-only boolean attribute is true if the compiler optimized out
645 this value, thus it is not available for fetching from the inferior.
649 The type of this @code{gdb.Value}. The value of this attribute is a
650 @code{gdb.Type} object (@pxref{Types In Python}).
653 @defvar Value.dynamic_type
654 The dynamic type of this @code{gdb.Value}. This uses C@t{++} run-time
655 type information (@acronym{RTTI}) to determine the dynamic type of the
656 value. If this value is of class type, it will return the class in
657 which the value is embedded, if any. If this value is of pointer or
658 reference to a class type, it will compute the dynamic type of the
659 referenced object, and return a pointer or reference to that type,
660 respectively. In all other cases, it will return the value's static
663 Note that this feature will only work when debugging a C@t{++} program
664 that includes @acronym{RTTI} for the object in question. Otherwise,
665 it will just return the static type of the value as in @kbd{ptype foo}
666 (@pxref{Symbols, ptype}).
669 @defvar Value.is_lazy
670 The value of this read-only boolean attribute is @code{True} if this
671 @code{gdb.Value} has not yet been fetched from the inferior.
672 @value{GDBN} does not fetch values until necessary, for efficiency.
676 myval = gdb.parse_and_eval ('somevar')
679 The value of @code{somevar} is not fetched at this time. It will be
680 fetched when the value is needed, or when the @code{fetch_lazy}
684 The following methods are provided:
686 @defun Value.__init__ (@var{val})
687 Many Python values can be converted directly to a @code{gdb.Value} via
688 this object initializer. Specifically:
692 A Python boolean is converted to the boolean type from the current
696 A Python integer is converted to the C @code{long} type for the
697 current architecture.
700 A Python long is converted to the C @code{long long} type for the
701 current architecture.
704 A Python float is converted to the C @code{double} type for the
705 current architecture.
708 A Python string is converted to a target string in the current target
709 language using the current target encoding.
710 If a character cannot be represented in the current target encoding,
711 then an exception is thrown.
713 @item @code{gdb.Value}
714 If @code{val} is a @code{gdb.Value}, then a copy of the value is made.
716 @item @code{gdb.LazyString}
717 If @code{val} is a @code{gdb.LazyString} (@pxref{Lazy Strings In
718 Python}), then the lazy string's @code{value} method is called, and
723 @defun Value.cast (type)
724 Return a new instance of @code{gdb.Value} that is the result of
725 casting this instance to the type described by @var{type}, which must
726 be a @code{gdb.Type} object. If the cast cannot be performed for some
727 reason, this method throws an exception.
730 @defun Value.dereference ()
731 For pointer data types, this method returns a new @code{gdb.Value} object
732 whose contents is the object pointed to by the pointer. For example, if
733 @code{foo} is a C pointer to an @code{int}, declared in your C program as
740 then you can use the corresponding @code{gdb.Value} to access what
741 @code{foo} points to like this:
744 bar = foo.dereference ()
747 The result @code{bar} will be a @code{gdb.Value} object holding the
748 value pointed to by @code{foo}.
750 A similar function @code{Value.referenced_value} exists which also
751 returns @code{gdb.Value} objects corresonding to the values pointed to
752 by pointer values (and additionally, values referenced by reference
753 values). However, the behavior of @code{Value.dereference}
754 differs from @code{Value.referenced_value} by the fact that the
755 behavior of @code{Value.dereference} is identical to applying the C
756 unary operator @code{*} on a given value. For example, consider a
757 reference to a pointer @code{ptrref}, declared in your C@t{++} program
765 intptr &ptrref = ptr;
768 Though @code{ptrref} is a reference value, one can apply the method
769 @code{Value.dereference} to the @code{gdb.Value} object corresponding
770 to it and obtain a @code{gdb.Value} which is identical to that
771 corresponding to @code{val}. However, if you apply the method
772 @code{Value.referenced_value}, the result would be a @code{gdb.Value}
773 object identical to that corresponding to @code{ptr}.
776 py_ptrref = gdb.parse_and_eval ("ptrref")
777 py_val = py_ptrref.dereference ()
778 py_ptr = py_ptrref.referenced_value ()
781 The @code{gdb.Value} object @code{py_val} is identical to that
782 corresponding to @code{val}, and @code{py_ptr} is identical to that
783 corresponding to @code{ptr}. In general, @code{Value.dereference} can
784 be applied whenever the C unary operator @code{*} can be applied
785 to the corresponding C value. For those cases where applying both
786 @code{Value.dereference} and @code{Value.referenced_value} is allowed,
787 the results obtained need not be identical (as we have seen in the above
788 example). The results are however identical when applied on
789 @code{gdb.Value} objects corresponding to pointers (@code{gdb.Value}
790 objects with type code @code{TYPE_CODE_PTR}) in a C/C@t{++} program.
793 @defun Value.referenced_value ()
794 For pointer or reference data types, this method returns a new
795 @code{gdb.Value} object corresponding to the value referenced by the
796 pointer/reference value. For pointer data types,
797 @code{Value.dereference} and @code{Value.referenced_value} produce
798 identical results. The difference between these methods is that
799 @code{Value.dereference} cannot get the values referenced by reference
800 values. For example, consider a reference to an @code{int}, declared
801 in your C@t{++} program as
809 then applying @code{Value.dereference} to the @code{gdb.Value} object
810 corresponding to @code{ref} will result in an error, while applying
811 @code{Value.referenced_value} will result in a @code{gdb.Value} object
812 identical to that corresponding to @code{val}.
815 py_ref = gdb.parse_and_eval ("ref")
816 er_ref = py_ref.dereference () # Results in error
817 py_val = py_ref.referenced_value () # Returns the referenced value
820 The @code{gdb.Value} object @code{py_val} is identical to that
821 corresponding to @code{val}.
824 @defun Value.reference_value ()
825 Return a @code{gdb.Value} object which is a reference to the value
826 encapsulated by this instance.
829 @defun Value.const_value ()
830 Return a @code{gdb.Value} object which is a @code{const} version of the
831 value encapsulated by this instance.
834 @defun Value.dynamic_cast (type)
835 Like @code{Value.cast}, but works as if the C@t{++} @code{dynamic_cast}
836 operator were used. Consult a C@t{++} reference for details.
839 @defun Value.reinterpret_cast (type)
840 Like @code{Value.cast}, but works as if the C@t{++} @code{reinterpret_cast}
841 operator were used. Consult a C@t{++} reference for details.
844 @defun Value.string (@r{[}encoding@r{[}, errors@r{[}, length@r{]]]})
845 If this @code{gdb.Value} represents a string, then this method
846 converts the contents to a Python string. Otherwise, this method will
849 Values are interpreted as strings according to the rules of the
850 current language. If the optional length argument is given, the
851 string will be converted to that length, and will include any embedded
852 zeroes that the string may contain. Otherwise, for languages
853 where the string is zero-terminated, the entire string will be
856 For example, in C-like languages, a value is a string if it is a pointer
857 to or an array of characters or ints of type @code{wchar_t}, @code{char16_t},
860 If the optional @var{encoding} argument is given, it must be a string
861 naming the encoding of the string in the @code{gdb.Value}, such as
862 @code{"ascii"}, @code{"iso-8859-6"} or @code{"utf-8"}. It accepts
863 the same encodings as the corresponding argument to Python's
864 @code{string.decode} method, and the Python codec machinery will be used
865 to convert the string. If @var{encoding} is not given, or if
866 @var{encoding} is the empty string, then either the @code{target-charset}
867 (@pxref{Character Sets}) will be used, or a language-specific encoding
868 will be used, if the current language is able to supply one.
870 The optional @var{errors} argument is the same as the corresponding
871 argument to Python's @code{string.decode} method.
873 If the optional @var{length} argument is given, the string will be
874 fetched and converted to the given length.
877 @defun Value.lazy_string (@r{[}encoding @r{[}, length@r{]]})
878 If this @code{gdb.Value} represents a string, then this method
879 converts the contents to a @code{gdb.LazyString} (@pxref{Lazy Strings
880 In Python}). Otherwise, this method will throw an exception.
882 If the optional @var{encoding} argument is given, it must be a string
883 naming the encoding of the @code{gdb.LazyString}. Some examples are:
884 @samp{ascii}, @samp{iso-8859-6} or @samp{utf-8}. If the
885 @var{encoding} argument is an encoding that @value{GDBN} does
886 recognize, @value{GDBN} will raise an error.
888 When a lazy string is printed, the @value{GDBN} encoding machinery is
889 used to convert the string during printing. If the optional
890 @var{encoding} argument is not provided, or is an empty string,
891 @value{GDBN} will automatically select the encoding most suitable for
892 the string type. For further information on encoding in @value{GDBN}
893 please see @ref{Character Sets}.
895 If the optional @var{length} argument is given, the string will be
896 fetched and encoded to the length of characters specified. If
897 the @var{length} argument is not provided, the string will be fetched
898 and encoded until a null of appropriate width is found.
901 @defun Value.fetch_lazy ()
902 If the @code{gdb.Value} object is currently a lazy value
903 (@code{gdb.Value.is_lazy} is @code{True}), then the value is
904 fetched from the inferior. Any errors that occur in the process
905 will produce a Python exception.
907 If the @code{gdb.Value} object is not a lazy value, this method
910 This method does not return a value.
914 @node Types In Python
915 @subsubsection Types In Python
916 @cindex types in Python
917 @cindex Python, working with types
920 @value{GDBN} represents types from the inferior using the class
923 The following type-related functions are available in the @code{gdb}
926 @findex gdb.lookup_type
927 @defun gdb.lookup_type (name @r{[}, block@r{]})
928 This function looks up a type by its @var{name}, which must be a string.
930 If @var{block} is given, then @var{name} is looked up in that scope.
931 Otherwise, it is searched for globally.
933 Ordinarily, this function will return an instance of @code{gdb.Type}.
934 If the named type cannot be found, it will throw an exception.
937 If the type is a structure or class type, or an enum type, the fields
938 of that type can be accessed using the Python @dfn{dictionary syntax}.
939 For example, if @code{some_type} is a @code{gdb.Type} instance holding
940 a structure type, you can access its @code{foo} field with:
943 bar = some_type['foo']
946 @code{bar} will be a @code{gdb.Field} object; see below under the
947 description of the @code{Type.fields} method for a description of the
948 @code{gdb.Field} class.
950 An instance of @code{Type} has the following attributes:
953 The alignment of this type, in bytes. Type alignment comes from the
954 debugging information; if it was not specified, then @value{GDBN} will
955 use the relevant ABI to try to determine the alignment. In some
956 cases, even this is not possible, and zero will be returned.
960 The type code for this type. The type code will be one of the
961 @code{TYPE_CODE_} constants defined below.
965 The name of this type. If this type has no name, then @code{None}
970 The size of this type, in target @code{char} units. Usually, a
971 target's @code{char} type will be an 8-bit byte. However, on some
972 unusual platforms, this type may have a different size.
976 The tag name for this type. The tag name is the name after
977 @code{struct}, @code{union}, or @code{enum} in C and C@t{++}; not all
978 languages have this concept. If this type has no tag name, then
979 @code{None} is returned.
982 The following methods are provided:
984 @defun Type.fields ()
985 For structure and union types, this method returns the fields. Range
986 types have two fields, the minimum and maximum values. Enum types
987 have one field per enum constant. Function and method types have one
988 field per parameter. The base types of C@t{++} classes are also
989 represented as fields. If the type has no fields, or does not fit
990 into one of these categories, an empty sequence will be returned.
992 Each field is a @code{gdb.Field} object, with some pre-defined attributes:
995 This attribute is not available for @code{enum} or @code{static}
996 (as in C@t{++}) fields. The value is the position, counting
997 in bits, from the start of the containing type.
1000 This attribute is only available for @code{enum} fields, and its value
1001 is the enumeration member's integer representation.
1004 The name of the field, or @code{None} for anonymous fields.
1007 This is @code{True} if the field is artificial, usually meaning that
1008 it was provided by the compiler and not the user. This attribute is
1009 always provided, and is @code{False} if the field is not artificial.
1012 This is @code{True} if the field represents a base class of a C@t{++}
1013 structure. This attribute is always provided, and is @code{False}
1014 if the field is not a base class of the type that is the argument of
1015 @code{fields}, or if that type was not a C@t{++} class.
1018 If the field is packed, or is a bitfield, then this will have a
1019 non-zero value, which is the size of the field in bits. Otherwise,
1020 this will be zero; in this case the field's size is given by its type.
1023 The type of the field. This is usually an instance of @code{Type},
1024 but it can be @code{None} in some situations.
1027 The type which contains this field. This is an instance of
1032 @defun Type.array (@var{n1} @r{[}, @var{n2}@r{]})
1033 Return a new @code{gdb.Type} object which represents an array of this
1034 type. If one argument is given, it is the inclusive upper bound of
1035 the array; in this case the lower bound is zero. If two arguments are
1036 given, the first argument is the lower bound of the array, and the
1037 second argument is the upper bound of the array. An array's length
1038 must not be negative, but the bounds can be.
1041 @defun Type.vector (@var{n1} @r{[}, @var{n2}@r{]})
1042 Return a new @code{gdb.Type} object which represents a vector of this
1043 type. If one argument is given, it is the inclusive upper bound of
1044 the vector; in this case the lower bound is zero. If two arguments are
1045 given, the first argument is the lower bound of the vector, and the
1046 second argument is the upper bound of the vector. A vector's length
1047 must not be negative, but the bounds can be.
1049 The difference between an @code{array} and a @code{vector} is that
1050 arrays behave like in C: when used in expressions they decay to a pointer
1051 to the first element whereas vectors are treated as first class values.
1054 @defun Type.const ()
1055 Return a new @code{gdb.Type} object which represents a
1056 @code{const}-qualified variant of this type.
1059 @defun Type.volatile ()
1060 Return a new @code{gdb.Type} object which represents a
1061 @code{volatile}-qualified variant of this type.
1064 @defun Type.unqualified ()
1065 Return a new @code{gdb.Type} object which represents an unqualified
1066 variant of this type. That is, the result is neither @code{const} nor
1070 @defun Type.range ()
1071 Return a Python @code{Tuple} object that contains two elements: the
1072 low bound of the argument type and the high bound of that type. If
1073 the type does not have a range, @value{GDBN} will raise a
1074 @code{gdb.error} exception (@pxref{Exception Handling}).
1077 @defun Type.reference ()
1078 Return a new @code{gdb.Type} object which represents a reference to this
1082 @defun Type.pointer ()
1083 Return a new @code{gdb.Type} object which represents a pointer to this
1087 @defun Type.strip_typedefs ()
1088 Return a new @code{gdb.Type} that represents the real type,
1089 after removing all layers of typedefs.
1092 @defun Type.target ()
1093 Return a new @code{gdb.Type} object which represents the target type
1096 For a pointer type, the target type is the type of the pointed-to
1097 object. For an array type (meaning C-like arrays), the target type is
1098 the type of the elements of the array. For a function or method type,
1099 the target type is the type of the return value. For a complex type,
1100 the target type is the type of the elements. For a typedef, the
1101 target type is the aliased type.
1103 If the type does not have a target, this method will throw an
1107 @defun Type.template_argument (n @r{[}, block@r{]})
1108 If this @code{gdb.Type} is an instantiation of a template, this will
1109 return a new @code{gdb.Value} or @code{gdb.Type} which represents the
1110 value of the @var{n}th template argument (indexed starting at 0).
1112 If this @code{gdb.Type} is not a template type, or if the type has fewer
1113 than @var{n} template arguments, this will throw an exception.
1114 Ordinarily, only C@t{++} code will have template types.
1116 If @var{block} is given, then @var{name} is looked up in that scope.
1117 Otherwise, it is searched for globally.
1120 @defun Type.optimized_out ()
1121 Return @code{gdb.Value} instance of this type whose value is optimized
1122 out. This allows a frame decorator to indicate that the value of an
1123 argument or a local variable is not known.
1126 Each type has a code, which indicates what category this type falls
1127 into. The available type categories are represented by constants
1128 defined in the @code{gdb} module:
1131 @vindex TYPE_CODE_PTR
1132 @item gdb.TYPE_CODE_PTR
1133 The type is a pointer.
1135 @vindex TYPE_CODE_ARRAY
1136 @item gdb.TYPE_CODE_ARRAY
1137 The type is an array.
1139 @vindex TYPE_CODE_STRUCT
1140 @item gdb.TYPE_CODE_STRUCT
1141 The type is a structure.
1143 @vindex TYPE_CODE_UNION
1144 @item gdb.TYPE_CODE_UNION
1145 The type is a union.
1147 @vindex TYPE_CODE_ENUM
1148 @item gdb.TYPE_CODE_ENUM
1149 The type is an enum.
1151 @vindex TYPE_CODE_FLAGS
1152 @item gdb.TYPE_CODE_FLAGS
1153 A bit flags type, used for things such as status registers.
1155 @vindex TYPE_CODE_FUNC
1156 @item gdb.TYPE_CODE_FUNC
1157 The type is a function.
1159 @vindex TYPE_CODE_INT
1160 @item gdb.TYPE_CODE_INT
1161 The type is an integer type.
1163 @vindex TYPE_CODE_FLT
1164 @item gdb.TYPE_CODE_FLT
1165 A floating point type.
1167 @vindex TYPE_CODE_VOID
1168 @item gdb.TYPE_CODE_VOID
1169 The special type @code{void}.
1171 @vindex TYPE_CODE_SET
1172 @item gdb.TYPE_CODE_SET
1175 @vindex TYPE_CODE_RANGE
1176 @item gdb.TYPE_CODE_RANGE
1177 A range type, that is, an integer type with bounds.
1179 @vindex TYPE_CODE_STRING
1180 @item gdb.TYPE_CODE_STRING
1181 A string type. Note that this is only used for certain languages with
1182 language-defined string types; C strings are not represented this way.
1184 @vindex TYPE_CODE_BITSTRING
1185 @item gdb.TYPE_CODE_BITSTRING
1186 A string of bits. It is deprecated.
1188 @vindex TYPE_CODE_ERROR
1189 @item gdb.TYPE_CODE_ERROR
1190 An unknown or erroneous type.
1192 @vindex TYPE_CODE_METHOD
1193 @item gdb.TYPE_CODE_METHOD
1194 A method type, as found in C@t{++}.
1196 @vindex TYPE_CODE_METHODPTR
1197 @item gdb.TYPE_CODE_METHODPTR
1198 A pointer-to-member-function.
1200 @vindex TYPE_CODE_MEMBERPTR
1201 @item gdb.TYPE_CODE_MEMBERPTR
1202 A pointer-to-member.
1204 @vindex TYPE_CODE_REF
1205 @item gdb.TYPE_CODE_REF
1208 @vindex TYPE_CODE_RVALUE_REF
1209 @item gdb.TYPE_CODE_RVALUE_REF
1210 A C@t{++}11 rvalue reference type.
1212 @vindex TYPE_CODE_CHAR
1213 @item gdb.TYPE_CODE_CHAR
1216 @vindex TYPE_CODE_BOOL
1217 @item gdb.TYPE_CODE_BOOL
1220 @vindex TYPE_CODE_COMPLEX
1221 @item gdb.TYPE_CODE_COMPLEX
1222 A complex float type.
1224 @vindex TYPE_CODE_TYPEDEF
1225 @item gdb.TYPE_CODE_TYPEDEF
1226 A typedef to some other type.
1228 @vindex TYPE_CODE_NAMESPACE
1229 @item gdb.TYPE_CODE_NAMESPACE
1230 A C@t{++} namespace.
1232 @vindex TYPE_CODE_DECFLOAT
1233 @item gdb.TYPE_CODE_DECFLOAT
1234 A decimal floating point type.
1236 @vindex TYPE_CODE_INTERNAL_FUNCTION
1237 @item gdb.TYPE_CODE_INTERNAL_FUNCTION
1238 A function internal to @value{GDBN}. This is the type used to represent
1239 convenience functions.
1242 Further support for types is provided in the @code{gdb.types}
1243 Python module (@pxref{gdb.types}).
1245 @node Pretty Printing API
1246 @subsubsection Pretty Printing API
1247 @cindex python pretty printing api
1249 An example output is provided (@pxref{Pretty Printing}).
1251 A pretty-printer is just an object that holds a value and implements a
1252 specific interface, defined here.
1254 @defun pretty_printer.children (self)
1255 @value{GDBN} will call this method on a pretty-printer to compute the
1256 children of the pretty-printer's value.
1258 This method must return an object conforming to the Python iterator
1259 protocol. Each item returned by the iterator must be a tuple holding
1260 two elements. The first element is the ``name'' of the child; the
1261 second element is the child's value. The value can be any Python
1262 object which is convertible to a @value{GDBN} value.
1264 This method is optional. If it does not exist, @value{GDBN} will act
1265 as though the value has no children.
1268 @defun pretty_printer.display_hint (self)
1269 The CLI may call this method and use its result to change the
1270 formatting of a value. The result will also be supplied to an MI
1271 consumer as a @samp{displayhint} attribute of the variable being
1274 This method is optional. If it does exist, this method must return a
1277 Some display hints are predefined by @value{GDBN}:
1281 Indicate that the object being printed is ``array-like''. The CLI
1282 uses this to respect parameters such as @code{set print elements} and
1283 @code{set print array}.
1286 Indicate that the object being printed is ``map-like'', and that the
1287 children of this value can be assumed to alternate between keys and
1291 Indicate that the object being printed is ``string-like''. If the
1292 printer's @code{to_string} method returns a Python string of some
1293 kind, then @value{GDBN} will call its internal language-specific
1294 string-printing function to format the string. For the CLI this means
1295 adding quotation marks, possibly escaping some characters, respecting
1296 @code{set print elements}, and the like.
1300 @defun pretty_printer.to_string (self)
1301 @value{GDBN} will call this method to display the string
1302 representation of the value passed to the object's constructor.
1304 When printing from the CLI, if the @code{to_string} method exists,
1305 then @value{GDBN} will prepend its result to the values returned by
1306 @code{children}. Exactly how this formatting is done is dependent on
1307 the display hint, and may change as more hints are added. Also,
1308 depending on the print settings (@pxref{Print Settings}), the CLI may
1309 print just the result of @code{to_string} in a stack trace, omitting
1310 the result of @code{children}.
1312 If this method returns a string, it is printed verbatim.
1314 Otherwise, if this method returns an instance of @code{gdb.Value},
1315 then @value{GDBN} prints this value. This may result in a call to
1316 another pretty-printer.
1318 If instead the method returns a Python value which is convertible to a
1319 @code{gdb.Value}, then @value{GDBN} performs the conversion and prints
1320 the resulting value. Again, this may result in a call to another
1321 pretty-printer. Python scalars (integers, floats, and booleans) and
1322 strings are convertible to @code{gdb.Value}; other types are not.
1324 Finally, if this method returns @code{None} then no further operations
1325 are peformed in this method and nothing is printed.
1327 If the result is not one of these types, an exception is raised.
1330 @value{GDBN} provides a function which can be used to look up the
1331 default pretty-printer for a @code{gdb.Value}:
1333 @findex gdb.default_visualizer
1334 @defun gdb.default_visualizer (value)
1335 This function takes a @code{gdb.Value} object as an argument. If a
1336 pretty-printer for this value exists, then it is returned. If no such
1337 printer exists, then this returns @code{None}.
1340 @node Selecting Pretty-Printers
1341 @subsubsection Selecting Pretty-Printers
1342 @cindex selecting python pretty-printers
1344 The Python list @code{gdb.pretty_printers} contains an array of
1345 functions or callable objects that have been registered via addition
1346 as a pretty-printer. Printers in this list are called @code{global}
1347 printers, they're available when debugging all inferiors.
1348 Each @code{gdb.Progspace} contains a @code{pretty_printers} attribute.
1349 Each @code{gdb.Objfile} also contains a @code{pretty_printers}
1352 Each function on these lists is passed a single @code{gdb.Value}
1353 argument and should return a pretty-printer object conforming to the
1354 interface definition above (@pxref{Pretty Printing API}). If a function
1355 cannot create a pretty-printer for the value, it should return
1358 @value{GDBN} first checks the @code{pretty_printers} attribute of each
1359 @code{gdb.Objfile} in the current program space and iteratively calls
1360 each enabled lookup routine in the list for that @code{gdb.Objfile}
1361 until it receives a pretty-printer object.
1362 If no pretty-printer is found in the objfile lists, @value{GDBN} then
1363 searches the pretty-printer list of the current program space,
1364 calling each enabled function until an object is returned.
1365 After these lists have been exhausted, it tries the global
1366 @code{gdb.pretty_printers} list, again calling each enabled function until an
1369 The order in which the objfiles are searched is not specified. For a
1370 given list, functions are always invoked from the head of the list,
1371 and iterated over sequentially until the end of the list, or a printer
1374 For various reasons a pretty-printer may not work.
1375 For example, the underlying data structure may have changed and
1376 the pretty-printer is out of date.
1378 The consequences of a broken pretty-printer are severe enough that
1379 @value{GDBN} provides support for enabling and disabling individual
1380 printers. For example, if @code{print frame-arguments} is on,
1381 a backtrace can become highly illegible if any argument is printed
1382 with a broken printer.
1384 Pretty-printers are enabled and disabled by attaching an @code{enabled}
1385 attribute to the registered function or callable object. If this attribute
1386 is present and its value is @code{False}, the printer is disabled, otherwise
1387 the printer is enabled.
1389 @node Writing a Pretty-Printer
1390 @subsubsection Writing a Pretty-Printer
1391 @cindex writing a pretty-printer
1393 A pretty-printer consists of two parts: a lookup function to detect
1394 if the type is supported, and the printer itself.
1396 Here is an example showing how a @code{std::string} printer might be
1397 written. @xref{Pretty Printing API}, for details on the API this class
1401 class StdStringPrinter(object):
1402 "Print a std::string"
1404 def __init__(self, val):
1407 def to_string(self):
1408 return self.val['_M_dataplus']['_M_p']
1410 def display_hint(self):
1414 And here is an example showing how a lookup function for the printer
1415 example above might be written.
1418 def str_lookup_function(val):
1419 lookup_tag = val.type.tag
1420 if lookup_tag == None:
1422 regex = re.compile("^std::basic_string<char,.*>$")
1423 if regex.match(lookup_tag):
1424 return StdStringPrinter(val)
1428 The example lookup function extracts the value's type, and attempts to
1429 match it to a type that it can pretty-print. If it is a type the
1430 printer can pretty-print, it will return a printer object. If not, it
1431 returns @code{None}.
1433 We recommend that you put your core pretty-printers into a Python
1434 package. If your pretty-printers are for use with a library, we
1435 further recommend embedding a version number into the package name.
1436 This practice will enable @value{GDBN} to load multiple versions of
1437 your pretty-printers at the same time, because they will have
1440 You should write auto-loaded code (@pxref{Python Auto-loading}) such that it
1441 can be evaluated multiple times without changing its meaning. An
1442 ideal auto-load file will consist solely of @code{import}s of your
1443 printer modules, followed by a call to a register pretty-printers with
1444 the current objfile.
1446 Taken as a whole, this approach will scale nicely to multiple
1447 inferiors, each potentially using a different library version.
1448 Embedding a version number in the Python package name will ensure that
1449 @value{GDBN} is able to load both sets of printers simultaneously.
1450 Then, because the search for pretty-printers is done by objfile, and
1451 because your auto-loaded code took care to register your library's
1452 printers with a specific objfile, @value{GDBN} will find the correct
1453 printers for the specific version of the library used by each
1456 To continue the @code{std::string} example (@pxref{Pretty Printing API}),
1457 this code might appear in @code{gdb.libstdcxx.v6}:
1460 def register_printers(objfile):
1461 objfile.pretty_printers.append(str_lookup_function)
1465 And then the corresponding contents of the auto-load file would be:
1468 import gdb.libstdcxx.v6
1469 gdb.libstdcxx.v6.register_printers(gdb.current_objfile())
1472 The previous example illustrates a basic pretty-printer.
1473 There are a few things that can be improved on.
1474 The printer doesn't have a name, making it hard to identify in a
1475 list of installed printers. The lookup function has a name, but
1476 lookup functions can have arbitrary, even identical, names.
1478 Second, the printer only handles one type, whereas a library typically has
1479 several types. One could install a lookup function for each desired type
1480 in the library, but one could also have a single lookup function recognize
1481 several types. The latter is the conventional way this is handled.
1482 If a pretty-printer can handle multiple data types, then its
1483 @dfn{subprinters} are the printers for the individual data types.
1485 The @code{gdb.printing} module provides a formal way of solving these
1486 problems (@pxref{gdb.printing}).
1487 Here is another example that handles multiple types.
1489 These are the types we are going to pretty-print:
1492 struct foo @{ int a, b; @};
1493 struct bar @{ struct foo x, y; @};
1496 Here are the printers:
1500 """Print a foo object."""
1502 def __init__(self, val):
1505 def to_string(self):
1506 return ("a=<" + str(self.val["a"]) +
1507 "> b=<" + str(self.val["b"]) + ">")
1510 """Print a bar object."""
1512 def __init__(self, val):
1515 def to_string(self):
1516 return ("x=<" + str(self.val["x"]) +
1517 "> y=<" + str(self.val["y"]) + ">")
1520 This example doesn't need a lookup function, that is handled by the
1521 @code{gdb.printing} module. Instead a function is provided to build up
1522 the object that handles the lookup.
1527 def build_pretty_printer():
1528 pp = gdb.printing.RegexpCollectionPrettyPrinter(
1530 pp.add_printer('foo', '^foo$', fooPrinter)
1531 pp.add_printer('bar', '^bar$', barPrinter)
1535 And here is the autoload support:
1540 gdb.printing.register_pretty_printer(
1541 gdb.current_objfile(),
1542 my_library.build_pretty_printer())
1545 Finally, when this printer is loaded into @value{GDBN}, here is the
1546 corresponding output of @samp{info pretty-printer}:
1549 (gdb) info pretty-printer
1556 @node Type Printing API
1557 @subsubsection Type Printing API
1558 @cindex type printing API for Python
1560 @value{GDBN} provides a way for Python code to customize type display.
1561 This is mainly useful for substituting canonical typedef names for
1564 @cindex type printer
1565 A @dfn{type printer} is just a Python object conforming to a certain
1566 protocol. A simple base class implementing the protocol is provided;
1567 see @ref{gdb.types}. A type printer must supply at least:
1569 @defivar type_printer enabled
1570 A boolean which is True if the printer is enabled, and False
1571 otherwise. This is manipulated by the @code{enable type-printer}
1572 and @code{disable type-printer} commands.
1575 @defivar type_printer name
1576 The name of the type printer. This must be a string. This is used by
1577 the @code{enable type-printer} and @code{disable type-printer}
1581 @defmethod type_printer instantiate (self)
1582 This is called by @value{GDBN} at the start of type-printing. It is
1583 only called if the type printer is enabled. This method must return a
1584 new object that supplies a @code{recognize} method, as described below.
1588 When displaying a type, say via the @code{ptype} command, @value{GDBN}
1589 will compute a list of type recognizers. This is done by iterating
1590 first over the per-objfile type printers (@pxref{Objfiles In Python}),
1591 followed by the per-progspace type printers (@pxref{Progspaces In
1592 Python}), and finally the global type printers.
1594 @value{GDBN} will call the @code{instantiate} method of each enabled
1595 type printer. If this method returns @code{None}, then the result is
1596 ignored; otherwise, it is appended to the list of recognizers.
1598 Then, when @value{GDBN} is going to display a type name, it iterates
1599 over the list of recognizers. For each one, it calls the recognition
1600 function, stopping if the function returns a non-@code{None} value.
1601 The recognition function is defined as:
1603 @defmethod type_recognizer recognize (self, type)
1604 If @var{type} is not recognized, return @code{None}. Otherwise,
1605 return a string which is to be printed as the name of @var{type}.
1606 The @var{type} argument will be an instance of @code{gdb.Type}
1607 (@pxref{Types In Python}).
1610 @value{GDBN} uses this two-pass approach so that type printers can
1611 efficiently cache information without holding on to it too long. For
1612 example, it can be convenient to look up type information in a type
1613 printer and hold it for a recognizer's lifetime; if a single pass were
1614 done then type printers would have to make use of the event system in
1615 order to avoid holding information that could become stale as the
1618 @node Frame Filter API
1619 @subsubsection Filtering Frames.
1620 @cindex frame filters api
1622 Frame filters are Python objects that manipulate the visibility of a
1623 frame or frames when a backtrace (@pxref{Backtrace}) is printed by
1626 Only commands that print a backtrace, or, in the case of @sc{gdb/mi}
1627 commands (@pxref{GDB/MI}), those that return a collection of frames
1628 are affected. The commands that work with frame filters are:
1630 @code{backtrace} (@pxref{backtrace-command,, The backtrace command}),
1631 @code{-stack-list-frames}
1632 (@pxref{-stack-list-frames,, The -stack-list-frames command}),
1633 @code{-stack-list-variables} (@pxref{-stack-list-variables,, The
1634 -stack-list-variables command}), @code{-stack-list-arguments}
1635 @pxref{-stack-list-arguments,, The -stack-list-arguments command}) and
1636 @code{-stack-list-locals} (@pxref{-stack-list-locals,, The
1637 -stack-list-locals command}).
1639 A frame filter works by taking an iterator as an argument, applying
1640 actions to the contents of that iterator, and returning another
1641 iterator (or, possibly, the same iterator it was provided in the case
1642 where the filter does not perform any operations). Typically, frame
1643 filters utilize tools such as the Python's @code{itertools} module to
1644 work with and create new iterators from the source iterator.
1645 Regardless of how a filter chooses to apply actions, it must not alter
1646 the underlying @value{GDBN} frame or frames, or attempt to alter the
1647 call-stack within @value{GDBN}. This preserves data integrity within
1648 @value{GDBN}. Frame filters are executed on a priority basis and care
1649 should be taken that some frame filters may have been executed before,
1650 and that some frame filters will be executed after.
1652 An important consideration when designing frame filters, and well
1653 worth reflecting upon, is that frame filters should avoid unwinding
1654 the call stack if possible. Some stacks can run very deep, into the
1655 tens of thousands in some cases. To search every frame when a frame
1656 filter executes may be too expensive at that step. The frame filter
1657 cannot know how many frames it has to iterate over, and it may have to
1658 iterate through them all. This ends up duplicating effort as
1659 @value{GDBN} performs this iteration when it prints the frames. If
1660 the filter can defer unwinding frames until frame decorators are
1661 executed, after the last filter has executed, it should. @xref{Frame
1662 Decorator API}, for more information on decorators. Also, there are
1663 examples for both frame decorators and filters in later chapters.
1664 @xref{Writing a Frame Filter}, for more information.
1666 The Python dictionary @code{gdb.frame_filters} contains key/object
1667 pairings that comprise a frame filter. Frame filters in this
1668 dictionary are called @code{global} frame filters, and they are
1669 available when debugging all inferiors. These frame filters must
1670 register with the dictionary directly. In addition to the
1671 @code{global} dictionary, there are other dictionaries that are loaded
1672 with different inferiors via auto-loading (@pxref{Python
1673 Auto-loading}). The two other areas where frame filter dictionaries
1674 can be found are: @code{gdb.Progspace} which contains a
1675 @code{frame_filters} dictionary attribute, and each @code{gdb.Objfile}
1676 object which also contains a @code{frame_filters} dictionary
1679 When a command is executed from @value{GDBN} that is compatible with
1680 frame filters, @value{GDBN} combines the @code{global},
1681 @code{gdb.Progspace} and all @code{gdb.Objfile} dictionaries currently
1682 loaded. All of the @code{gdb.Objfile} dictionaries are combined, as
1683 several frames, and thus several object files, might be in use.
1684 @value{GDBN} then prunes any frame filter whose @code{enabled}
1685 attribute is @code{False}. This pruned list is then sorted according
1686 to the @code{priority} attribute in each filter.
1688 Once the dictionaries are combined, pruned and sorted, @value{GDBN}
1689 creates an iterator which wraps each frame in the call stack in a
1690 @code{FrameDecorator} object, and calls each filter in order. The
1691 output from the previous filter will always be the input to the next
1694 Frame filters have a mandatory interface which each frame filter must
1695 implement, defined here:
1697 @defun FrameFilter.filter (iterator)
1698 @value{GDBN} will call this method on a frame filter when it has
1699 reached the order in the priority list for that filter.
1701 For example, if there are four frame filters:
1712 The order that the frame filters will be called is:
1715 Filter3 -> Filter2 -> Filter1 -> Filter4
1718 Note that the output from @code{Filter3} is passed to the input of
1719 @code{Filter2}, and so on.
1721 This @code{filter} method is passed a Python iterator. This iterator
1722 contains a sequence of frame decorators that wrap each
1723 @code{gdb.Frame}, or a frame decorator that wraps another frame
1724 decorator. The first filter that is executed in the sequence of frame
1725 filters will receive an iterator entirely comprised of default
1726 @code{FrameDecorator} objects. However, after each frame filter is
1727 executed, the previous frame filter may have wrapped some or all of
1728 the frame decorators with their own frame decorator. As frame
1729 decorators must also conform to a mandatory interface, these
1730 decorators can be assumed to act in a uniform manner (@pxref{Frame
1733 This method must return an object conforming to the Python iterator
1734 protocol. Each item in the iterator must be an object conforming to
1735 the frame decorator interface. If a frame filter does not wish to
1736 perform any operations on this iterator, it should return that
1739 This method is not optional. If it does not exist, @value{GDBN} will
1740 raise and print an error.
1743 @defvar FrameFilter.name
1744 The @code{name} attribute must be Python string which contains the
1745 name of the filter displayed by @value{GDBN} (@pxref{Frame Filter
1746 Management}). This attribute may contain any combination of letters
1747 or numbers. Care should be taken to ensure that it is unique. This
1748 attribute is mandatory.
1751 @defvar FrameFilter.enabled
1752 The @code{enabled} attribute must be Python boolean. This attribute
1753 indicates to @value{GDBN} whether the frame filter is enabled, and
1754 should be considered when frame filters are executed. If
1755 @code{enabled} is @code{True}, then the frame filter will be executed
1756 when any of the backtrace commands detailed earlier in this chapter
1757 are executed. If @code{enabled} is @code{False}, then the frame
1758 filter will not be executed. This attribute is mandatory.
1761 @defvar FrameFilter.priority
1762 The @code{priority} attribute must be Python integer. This attribute
1763 controls the order of execution in relation to other frame filters.
1764 There are no imposed limits on the range of @code{priority} other than
1765 it must be a valid integer. The higher the @code{priority} attribute,
1766 the sooner the frame filter will be executed in relation to other
1767 frame filters. Although @code{priority} can be negative, it is
1768 recommended practice to assume zero is the lowest priority that a
1769 frame filter can be assigned. Frame filters that have the same
1770 priority are executed in unsorted order in that priority slot. This
1771 attribute is mandatory.
1774 @node Frame Decorator API
1775 @subsubsection Decorating Frames.
1776 @cindex frame decorator api
1778 Frame decorators are sister objects to frame filters (@pxref{Frame
1779 Filter API}). Frame decorators are applied by a frame filter and can
1780 only be used in conjunction with frame filters.
1782 The purpose of a frame decorator is to customize the printed content
1783 of each @code{gdb.Frame} in commands where frame filters are executed.
1784 This concept is called decorating a frame. Frame decorators decorate
1785 a @code{gdb.Frame} with Python code contained within each API call.
1786 This separates the actual data contained in a @code{gdb.Frame} from
1787 the decorated data produced by a frame decorator. This abstraction is
1788 necessary to maintain integrity of the data contained in each
1791 Frame decorators have a mandatory interface, defined below.
1793 @value{GDBN} already contains a frame decorator called
1794 @code{FrameDecorator}. This contains substantial amounts of
1795 boilerplate code to decorate the content of a @code{gdb.Frame}. It is
1796 recommended that other frame decorators inherit and extend this
1797 object, and only to override the methods needed.
1799 @defun FrameDecorator.elided (self)
1801 The @code{elided} method groups frames together in a hierarchical
1802 system. An example would be an interpreter, where multiple low-level
1803 frames make up a single call in the interpreted language. In this
1804 example, the frame filter would elide the low-level frames and present
1805 a single high-level frame, representing the call in the interpreted
1806 language, to the user.
1808 The @code{elided} function must return an iterable and this iterable
1809 must contain the frames that are being elided wrapped in a suitable
1810 frame decorator. If no frames are being elided this function may
1811 return an empty iterable, or @code{None}. Elided frames are indented
1812 from normal frames in a @code{CLI} backtrace, or in the case of
1813 @code{GDB/MI}, are placed in the @code{children} field of the eliding
1816 It is the frame filter's task to also filter out the elided frames from
1817 the source iterator. This will avoid printing the frame twice.
1820 @defun FrameDecorator.function (self)
1822 This method returns the name of the function in the frame that is to
1825 This method must return a Python string describing the function, or
1828 If this function returns @code{None}, @value{GDBN} will not print any
1829 data for this field.
1832 @defun FrameDecorator.address (self)
1834 This method returns the address of the frame that is to be printed.
1836 This method must return a Python numeric integer type of sufficient
1837 size to describe the address of the frame, or @code{None}.
1839 If this function returns a @code{None}, @value{GDBN} will not print
1840 any data for this field.
1843 @defun FrameDecorator.filename (self)
1845 This method returns the filename and path associated with this frame.
1847 This method must return a Python string containing the filename and
1848 the path to the object file backing the frame, or @code{None}.
1850 If this function returns a @code{None}, @value{GDBN} will not print
1851 any data for this field.
1854 @defun FrameDecorator.line (self):
1856 This method returns the line number associated with the current
1857 position within the function addressed by this frame.
1859 This method must return a Python integer type, or @code{None}.
1861 If this function returns a @code{None}, @value{GDBN} will not print
1862 any data for this field.
1865 @defun FrameDecorator.frame_args (self)
1868 This method must return an iterable, or @code{None}. Returning an
1869 empty iterable, or @code{None} means frame arguments will not be
1870 printed for this frame. This iterable must contain objects that
1871 implement two methods, described here.
1873 This object must implement a @code{argument} method which takes a
1874 single @code{self} parameter and must return a @code{gdb.Symbol}
1875 (@pxref{Symbols In Python}), or a Python string. The object must also
1876 implement a @code{value} method which takes a single @code{self}
1877 parameter and must return a @code{gdb.Value} (@pxref{Values From
1878 Inferior}), a Python value, or @code{None}. If the @code{value}
1879 method returns @code{None}, and the @code{argument} method returns a
1880 @code{gdb.Symbol}, @value{GDBN} will look-up and print the value of
1881 the @code{gdb.Symbol} automatically.
1886 class SymValueWrapper():
1888 def __init__(self, symbol, value):
1898 class SomeFrameDecorator()
1901 def frame_args(self):
1904 block = self.inferior_frame.block()
1908 # Iterate over all symbols in a block. Only add
1909 # symbols that are arguments.
1911 if not sym.is_argument:
1913 args.append(SymValueWrapper(sym,None))
1915 # Add example synthetic argument.
1916 args.append(SymValueWrapper(``foo'', 42))
1922 @defun FrameDecorator.frame_locals (self)
1924 This method must return an iterable or @code{None}. Returning an
1925 empty iterable, or @code{None} means frame local arguments will not be
1926 printed for this frame.
1928 The object interface, the description of the various strategies for
1929 reading frame locals, and the example are largely similar to those
1930 described in the @code{frame_args} function, (@pxref{frame_args,,The
1931 frame filter frame_args function}). Below is a modified example:
1934 class SomeFrameDecorator()
1937 def frame_locals(self):
1940 block = self.inferior_frame.block()
1944 # Iterate over all symbols in a block. Add all
1945 # symbols, except arguments.
1949 vars.append(SymValueWrapper(sym,None))
1951 # Add an example of a synthetic local variable.
1952 vars.append(SymValueWrapper(``bar'', 99))
1958 @defun FrameDecorator.inferior_frame (self):
1960 This method must return the underlying @code{gdb.Frame} that this
1961 frame decorator is decorating. @value{GDBN} requires the underlying
1962 frame for internal frame information to determine how to print certain
1963 values when printing a frame.
1966 @node Writing a Frame Filter
1967 @subsubsection Writing a Frame Filter
1968 @cindex writing a frame filter
1970 There are three basic elements that a frame filter must implement: it
1971 must correctly implement the documented interface (@pxref{Frame Filter
1972 API}), it must register itself with @value{GDBN}, and finally, it must
1973 decide if it is to work on the data provided by @value{GDBN}. In all
1974 cases, whether it works on the iterator or not, each frame filter must
1975 return an iterator. A bare-bones frame filter follows the pattern in
1976 the following example.
1981 class FrameFilter():
1984 # Frame filter attribute creation.
1986 # 'name' is the name of the filter that GDB will display.
1988 # 'priority' is the priority of the filter relative to other
1991 # 'enabled' is a boolean that indicates whether this filter is
1992 # enabled and should be executed.
1998 # Register this frame filter with the global frame_filters
2000 gdb.frame_filters[self.name] = self
2002 def filter(self, frame_iter):
2003 # Just return the iterator.
2007 The frame filter in the example above implements the three
2008 requirements for all frame filters. It implements the API, self
2009 registers, and makes a decision on the iterator (in this case, it just
2010 returns the iterator untouched).
2012 The first step is attribute creation and assignment, and as shown in
2013 the comments the filter assigns the following attributes: @code{name},
2014 @code{priority} and whether the filter should be enabled with the
2015 @code{enabled} attribute.
2017 The second step is registering the frame filter with the dictionary or
2018 dictionaries that the frame filter has interest in. As shown in the
2019 comments, this filter just registers itself with the global dictionary
2020 @code{gdb.frame_filters}. As noted earlier, @code{gdb.frame_filters}
2021 is a dictionary that is initialized in the @code{gdb} module when
2022 @value{GDBN} starts. What dictionary a filter registers with is an
2023 important consideration. Generally, if a filter is specific to a set
2024 of code, it should be registered either in the @code{objfile} or
2025 @code{progspace} dictionaries as they are specific to the program
2026 currently loaded in @value{GDBN}. The global dictionary is always
2027 present in @value{GDBN} and is never unloaded. Any filters registered
2028 with the global dictionary will exist until @value{GDBN} exits. To
2029 avoid filters that may conflict, it is generally better to register
2030 frame filters against the dictionaries that more closely align with
2031 the usage of the filter currently in question. @xref{Python
2032 Auto-loading}, for further information on auto-loading Python scripts.
2034 @value{GDBN} takes a hands-off approach to frame filter registration,
2035 therefore it is the frame filter's responsibility to ensure
2036 registration has occurred, and that any exceptions are handled
2037 appropriately. In particular, you may wish to handle exceptions
2038 relating to Python dictionary key uniqueness. It is mandatory that
2039 the dictionary key is the same as frame filter's @code{name}
2040 attribute. When a user manages frame filters (@pxref{Frame Filter
2041 Management}), the names @value{GDBN} will display are those contained
2042 in the @code{name} attribute.
2044 The final step of this example is the implementation of the
2045 @code{filter} method. As shown in the example comments, we define the
2046 @code{filter} method and note that the method must take an iterator,
2047 and also must return an iterator. In this bare-bones example, the
2048 frame filter is not very useful as it just returns the iterator
2049 untouched. However this is a valid operation for frame filters that
2050 have the @code{enabled} attribute set, but decide not to operate on
2053 In the next example, the frame filter operates on all frames and
2054 utilizes a frame decorator to perform some work on the frames.
2055 @xref{Frame Decorator API}, for further information on the frame
2056 decorator interface.
2058 This example works on inlined frames. It highlights frames which are
2059 inlined by tagging them with an ``[inlined]'' tag. By applying a
2060 frame decorator to all frames with the Python @code{itertools imap}
2061 method, the example defers actions to the frame decorator. Frame
2062 decorators are only processed when @value{GDBN} prints the backtrace.
2064 This introduces a new decision making topic: whether to perform
2065 decision making operations at the filtering step, or at the printing
2066 step. In this example's approach, it does not perform any filtering
2067 decisions at the filtering step beyond mapping a frame decorator to
2068 each frame. This allows the actual decision making to be performed
2069 when each frame is printed. This is an important consideration, and
2070 well worth reflecting upon when designing a frame filter. An issue
2071 that frame filters should avoid is unwinding the stack if possible.
2072 Some stacks can run very deep, into the tens of thousands in some
2073 cases. To search every frame to determine if it is inlined ahead of
2074 time may be too expensive at the filtering step. The frame filter
2075 cannot know how many frames it has to iterate over, and it would have
2076 to iterate through them all. This ends up duplicating effort as
2077 @value{GDBN} performs this iteration when it prints the frames.
2079 In this example decision making can be deferred to the printing step.
2080 As each frame is printed, the frame decorator can examine each frame
2081 in turn when @value{GDBN} iterates. From a performance viewpoint,
2082 this is the most appropriate decision to make as it avoids duplicating
2083 the effort that the printing step would undertake anyway. Also, if
2084 there are many frame filters unwinding the stack during filtering, it
2085 can substantially delay the printing of the backtrace which will
2086 result in large memory usage, and a poor user experience.
2089 class InlineFilter():
2092 self.name = "InlinedFrameFilter"
2095 gdb.frame_filters[self.name] = self
2097 def filter(self, frame_iter):
2098 frame_iter = itertools.imap(InlinedFrameDecorator,
2103 This frame filter is somewhat similar to the earlier example, except
2104 that the @code{filter} method applies a frame decorator object called
2105 @code{InlinedFrameDecorator} to each element in the iterator. The
2106 @code{imap} Python method is light-weight. It does not proactively
2107 iterate over the iterator, but rather creates a new iterator which
2108 wraps the existing one.
2110 Below is the frame decorator for this example.
2113 class InlinedFrameDecorator(FrameDecorator):
2115 def __init__(self, fobj):
2116 super(InlinedFrameDecorator, self).__init__(fobj)
2119 frame = fobj.inferior_frame()
2120 name = str(frame.name())
2122 if frame.type() == gdb.INLINE_FRAME:
2123 name = name + " [inlined]"
2128 This frame decorator only defines and overrides the @code{function}
2129 method. It lets the supplied @code{FrameDecorator}, which is shipped
2130 with @value{GDBN}, perform the other work associated with printing
2133 The combination of these two objects create this output from a
2137 #0 0x004004e0 in bar () at inline.c:11
2138 #1 0x00400566 in max [inlined] (b=6, a=12) at inline.c:21
2139 #2 0x00400566 in main () at inline.c:31
2142 So in the case of this example, a frame decorator is applied to all
2143 frames, regardless of whether they may be inlined or not. As
2144 @value{GDBN} iterates over the iterator produced by the frame filters,
2145 @value{GDBN} executes each frame decorator which then makes a decision
2146 on what to print in the @code{function} callback. Using a strategy
2147 like this is a way to defer decisions on the frame content to printing
2150 @subheading Eliding Frames
2152 It might be that the above example is not desirable for representing
2153 inlined frames, and a hierarchical approach may be preferred. If we
2154 want to hierarchically represent frames, the @code{elided} frame
2155 decorator interface might be preferable.
2157 This example approaches the issue with the @code{elided} method. This
2158 example is quite long, but very simplistic. It is out-of-scope for
2159 this section to write a complete example that comprehensively covers
2160 all approaches of finding and printing inlined frames. However, this
2161 example illustrates the approach an author might use.
2163 This example comprises of three sections.
2166 class InlineFrameFilter():
2169 self.name = "InlinedFrameFilter"
2172 gdb.frame_filters[self.name] = self
2174 def filter(self, frame_iter):
2175 return ElidingInlineIterator(frame_iter)
2178 This frame filter is very similar to the other examples. The only
2179 difference is this frame filter is wrapping the iterator provided to
2180 it (@code{frame_iter}) with a custom iterator called
2181 @code{ElidingInlineIterator}. This again defers actions to when
2182 @value{GDBN} prints the backtrace, as the iterator is not traversed
2185 The iterator for this example is as follows. It is in this section of
2186 the example where decisions are made on the content of the backtrace.
2189 class ElidingInlineIterator:
2190 def __init__(self, ii):
2191 self.input_iterator = ii
2197 frame = next(self.input_iterator)
2199 if frame.inferior_frame().type() != gdb.INLINE_FRAME:
2203 eliding_frame = next(self.input_iterator)
2204 except StopIteration:
2206 return ElidingFrameDecorator(eliding_frame, [frame])
2209 This iterator implements the Python iterator protocol. When the
2210 @code{next} function is called (when @value{GDBN} prints each frame),
2211 the iterator checks if this frame decorator, @code{frame}, is wrapping
2212 an inlined frame. If it is not, it returns the existing frame decorator
2213 untouched. If it is wrapping an inlined frame, it assumes that the
2214 inlined frame was contained within the next oldest frame,
2215 @code{eliding_frame}, which it fetches. It then creates and returns a
2216 frame decorator, @code{ElidingFrameDecorator}, which contains both the
2217 elided frame, and the eliding frame.
2220 class ElidingInlineDecorator(FrameDecorator):
2222 def __init__(self, frame, elided_frames):
2223 super(ElidingInlineDecorator, self).__init__(frame)
2225 self.elided_frames = elided_frames
2228 return iter(self.elided_frames)
2231 This frame decorator overrides one function and returns the inlined
2232 frame in the @code{elided} method. As before it lets
2233 @code{FrameDecorator} do the rest of the work involved in printing
2234 this frame. This produces the following output.
2237 #0 0x004004e0 in bar () at inline.c:11
2238 #2 0x00400529 in main () at inline.c:25
2239 #1 0x00400529 in max (b=6, a=12) at inline.c:15
2242 In that output, @code{max} which has been inlined into @code{main} is
2243 printed hierarchically. Another approach would be to combine the
2244 @code{function} method, and the @code{elided} method to both print a
2245 marker in the inlined frame, and also show the hierarchical
2248 @node Unwinding Frames in Python
2249 @subsubsection Unwinding Frames in Python
2250 @cindex unwinding frames in Python
2252 In @value{GDBN} terminology ``unwinding'' is the process of finding
2253 the previous frame (that is, caller's) from the current one. An
2254 unwinder has three methods. The first one checks if it can handle
2255 given frame (``sniff'' it). For the frames it can sniff an unwinder
2256 provides two additional methods: it can return frame's ID, and it can
2257 fetch registers from the previous frame. A running @value{GDBN}
2258 mantains a list of the unwinders and calls each unwinder's sniffer in
2259 turn until it finds the one that recognizes the current frame. There
2260 is an API to register an unwinder.
2262 The unwinders that come with @value{GDBN} handle standard frames.
2263 However, mixed language applications (for example, an application
2264 running Java Virtual Machine) sometimes use frame layouts that cannot
2265 be handled by the @value{GDBN} unwinders. You can write Python code
2266 that can handle such custom frames.
2268 You implement a frame unwinder in Python as a class with which has two
2269 attributes, @code{name} and @code{enabled}, with obvious meanings, and
2270 a single method @code{__call__}, which examines a given frame and
2271 returns an object (an instance of @code{gdb.UnwindInfo class)}
2272 describing it. If an unwinder does not recognize a frame, it should
2273 return @code{None}. The code in @value{GDBN} that enables writing
2274 unwinders in Python uses this object to return frame's ID and previous
2275 frame registers when @value{GDBN} core asks for them.
2277 @subheading Unwinder Input
2279 An object passed to an unwinder (a @code{gdb.PendingFrame} instance)
2280 provides a method to read frame's registers:
2282 @defun PendingFrame.read_register (reg)
2283 This method returns the contents of the register @var{regn} in the
2284 frame as a @code{gdb.Value} object. @var{reg} can be either a
2285 register number or a register name; the values are platform-specific.
2286 They are usually found in the corresponding
2287 @file{@var{platform}-tdep.h} file in the @value{GDBN} source tree.
2290 It also provides a factory method to create a @code{gdb.UnwindInfo}
2291 instance to be returned to @value{GDBN}:
2293 @defun PendingFrame.create_unwind_info (frame_id)
2294 Returns a new @code{gdb.UnwindInfo} instance identified by given
2295 @var{frame_id}. The argument is used to build @value{GDBN}'s frame ID
2296 using one of functions provided by @value{GDBN}. @var{frame_id}'s attributes
2297 determine which function will be used, as follows:
2300 @item sp, pc, special
2301 @code{frame_id_build_special (@var{frame_id}.sp, @var{frame_id}.pc, @var{frame_id}.special)}
2304 @code{frame_id_build (@var{frame_id}.sp, @var{frame_id}.pc)}
2306 This is the most common case.
2309 @code{frame_id_build_wild (@var{frame_id}.sp)}
2311 The attribute values should be @code{gdb.Value}
2315 @subheading Unwinder Output: UnwindInfo
2317 Use @code{PendingFrame.create_unwind_info} method described above to
2318 create a @code{gdb.UnwindInfo} instance. Use the following method to
2319 specify caller registers that have been saved in this frame:
2321 @defun gdb.UnwindInfo.add_saved_register (reg, value)
2322 @var{reg} identifies the register. It can be a number or a name, just
2323 as for the @code{PendingFrame.read_register} method above.
2324 @var{value} is a register value (a @code{gdb.Value} object).
2327 @subheading Unwinder Skeleton Code
2329 @value{GDBN} comes with the module containing the base @code{Unwinder}
2330 class. Derive your unwinder class from it and structure the code as
2334 from gdb.unwinders import Unwinder
2336 class FrameId(object):
2337 def __init__(self, sp, pc):
2342 class MyUnwinder(Unwinder):
2344 supe(MyUnwinder, self).__init___(<expects unwinder name argument>)
2346 def __call__(pending_frame):
2347 if not <we recognize frame>:
2349 # Create UnwindInfo. Usually the frame is identified by the stack
2350 # pointer and the program counter.
2351 sp = pending_frame.read_register(<SP number>)
2352 pc = pending_frame.read_register(<PC number>)
2353 unwind_info = pending_frame.create_unwind_info(FrameId(sp, pc))
2355 # Find the values of the registers in the caller's frame and
2356 # save them in the result:
2357 unwind_info.add_saved_register(<register>, <value>)
2360 # Return the result:
2365 @subheading Registering a Unwinder
2367 An object file, a program space, and the @value{GDBN} proper can have
2368 unwinders registered with it.
2370 The @code{gdb.unwinders} module provides the function to register a
2373 @defun gdb.unwinder.register_unwinder (locus, unwinder, replace=False)
2374 @var{locus} is specifies an object file or a program space to which
2375 @var{unwinder} is added. Passing @code{None} or @code{gdb} adds
2376 @var{unwinder} to the @value{GDBN}'s global unwinder list. The newly
2377 added @var{unwinder} will be called before any other unwinder from the
2378 same locus. Two unwinders in the same locus cannot have the same
2379 name. An attempt to add a unwinder with already existing name raises
2380 an exception unless @var{replace} is @code{True}, in which case the
2381 old unwinder is deleted.
2384 @subheading Unwinder Precedence
2386 @value{GDBN} first calls the unwinders from all the object files in no
2387 particular order, then the unwinders from the current program space,
2388 and finally the unwinders from @value{GDBN}.
2390 @node Xmethods In Python
2391 @subsubsection Xmethods In Python
2392 @cindex xmethods in Python
2394 @dfn{Xmethods} are additional methods or replacements for existing
2395 methods of a C@t{++} class. This feature is useful for those cases
2396 where a method defined in C@t{++} source code could be inlined or
2397 optimized out by the compiler, making it unavailable to @value{GDBN}.
2398 For such cases, one can define an xmethod to serve as a replacement
2399 for the method defined in the C@t{++} source code. @value{GDBN} will
2400 then invoke the xmethod, instead of the C@t{++} method, to
2401 evaluate expressions. One can also use xmethods when debugging
2402 with core files. Moreover, when debugging live programs, invoking an
2403 xmethod need not involve running the inferior (which can potentially
2404 perturb its state). Hence, even if the C@t{++} method is available, it
2405 is better to use its replacement xmethod if one is defined.
2407 The xmethods feature in Python is available via the concepts of an
2408 @dfn{xmethod matcher} and an @dfn{xmethod worker}. To
2409 implement an xmethod, one has to implement a matcher and a
2410 corresponding worker for it (more than one worker can be
2411 implemented, each catering to a different overloaded instance of the
2412 method). Internally, @value{GDBN} invokes the @code{match} method of a
2413 matcher to match the class type and method name. On a match, the
2414 @code{match} method returns a list of matching @emph{worker} objects.
2415 Each worker object typically corresponds to an overloaded instance of
2416 the xmethod. They implement a @code{get_arg_types} method which
2417 returns a sequence of types corresponding to the arguments the xmethod
2418 requires. @value{GDBN} uses this sequence of types to perform
2419 overload resolution and picks a winning xmethod worker. A winner
2420 is also selected from among the methods @value{GDBN} finds in the
2421 C@t{++} source code. Next, the winning xmethod worker and the
2422 winning C@t{++} method are compared to select an overall winner. In
2423 case of a tie between a xmethod worker and a C@t{++} method, the
2424 xmethod worker is selected as the winner. That is, if a winning
2425 xmethod worker is found to be equivalent to the winning C@t{++}
2426 method, then the xmethod worker is treated as a replacement for
2427 the C@t{++} method. @value{GDBN} uses the overall winner to invoke the
2428 method. If the winning xmethod worker is the overall winner, then
2429 the corresponding xmethod is invoked via the @code{__call__} method
2430 of the worker object.
2432 If one wants to implement an xmethod as a replacement for an
2433 existing C@t{++} method, then they have to implement an equivalent
2434 xmethod which has exactly the same name and takes arguments of
2435 exactly the same type as the C@t{++} method. If the user wants to
2436 invoke the C@t{++} method even though a replacement xmethod is
2437 available for that method, then they can disable the xmethod.
2439 @xref{Xmethod API}, for API to implement xmethods in Python.
2440 @xref{Writing an Xmethod}, for implementing xmethods in Python.
2443 @subsubsection Xmethod API
2446 The @value{GDBN} Python API provides classes, interfaces and functions
2447 to implement, register and manipulate xmethods.
2448 @xref{Xmethods In Python}.
2450 An xmethod matcher should be an instance of a class derived from
2451 @code{XMethodMatcher} defined in the module @code{gdb.xmethod}, or an
2452 object with similar interface and attributes. An instance of
2453 @code{XMethodMatcher} has the following attributes:
2456 The name of the matcher.
2460 A boolean value indicating whether the matcher is enabled or disabled.
2464 A list of named methods managed by the matcher. Each object in the list
2465 is an instance of the class @code{XMethod} defined in the module
2466 @code{gdb.xmethod}, or any object with the following attributes:
2471 Name of the xmethod which should be unique for each xmethod
2472 managed by the matcher.
2475 A boolean value indicating whether the xmethod is enabled or
2480 The class @code{XMethod} is a convenience class with same
2481 attributes as above along with the following constructor:
2483 @defun XMethod.__init__ (self, name)
2484 Constructs an enabled xmethod with name @var{name}.
2489 The @code{XMethodMatcher} class has the following methods:
2491 @defun XMethodMatcher.__init__ (self, name)
2492 Constructs an enabled xmethod matcher with name @var{name}. The
2493 @code{methods} attribute is initialized to @code{None}.
2496 @defun XMethodMatcher.match (self, class_type, method_name)
2497 Derived classes should override this method. It should return a
2498 xmethod worker object (or a sequence of xmethod worker
2499 objects) matching the @var{class_type} and @var{method_name}.
2500 @var{class_type} is a @code{gdb.Type} object, and @var{method_name}
2501 is a string value. If the matcher manages named methods as listed in
2502 its @code{methods} attribute, then only those worker objects whose
2503 corresponding entries in the @code{methods} list are enabled should be
2507 An xmethod worker should be an instance of a class derived from
2508 @code{XMethodWorker} defined in the module @code{gdb.xmethod},
2509 or support the following interface:
2511 @defun XMethodWorker.get_arg_types (self)
2512 This method returns a sequence of @code{gdb.Type} objects corresponding
2513 to the arguments that the xmethod takes. It can return an empty
2514 sequence or @code{None} if the xmethod does not take any arguments.
2515 If the xmethod takes a single argument, then a single
2516 @code{gdb.Type} object corresponding to it can be returned.
2519 @defun XMethodWorker.get_result_type (self, *args)
2520 This method returns a @code{gdb.Type} object representing the type
2521 of the result of invoking this xmethod.
2522 The @var{args} argument is the same tuple of arguments that would be
2523 passed to the @code{__call__} method of this worker.
2526 @defun XMethodWorker.__call__ (self, *args)
2527 This is the method which does the @emph{work} of the xmethod. The
2528 @var{args} arguments is the tuple of arguments to the xmethod. Each
2529 element in this tuple is a gdb.Value object. The first element is
2530 always the @code{this} pointer value.
2533 For @value{GDBN} to lookup xmethods, the xmethod matchers
2534 should be registered using the following function defined in the module
2537 @defun register_xmethod_matcher (locus, matcher, replace=False)
2538 The @code{matcher} is registered with @code{locus}, replacing an
2539 existing matcher with the same name as @code{matcher} if
2540 @code{replace} is @code{True}. @code{locus} can be a
2541 @code{gdb.Objfile} object (@pxref{Objfiles In Python}), or a
2542 @code{gdb.Progspace} object (@pxref{Progspaces In Python}), or
2543 @code{None}. If it is @code{None}, then @code{matcher} is registered
2547 @node Writing an Xmethod
2548 @subsubsection Writing an Xmethod
2549 @cindex writing xmethods in Python
2551 Implementing xmethods in Python will require implementing xmethod
2552 matchers and xmethod workers (@pxref{Xmethods In Python}). Consider
2553 the following C@t{++} class:
2559 MyClass (int a) : a_(a) @{ @}
2561 int geta (void) @{ return a_; @}
2562 int operator+ (int b);
2569 MyClass::operator+ (int b)
2576 Let us define two xmethods for the class @code{MyClass}, one
2577 replacing the method @code{geta}, and another adding an overloaded
2578 flavor of @code{operator+} which takes a @code{MyClass} argument (the
2579 C@t{++} code above already has an overloaded @code{operator+}
2580 which takes an @code{int} argument). The xmethod matcher can be
2584 class MyClass_geta(gdb.xmethod.XMethod):
2586 gdb.xmethod.XMethod.__init__(self, 'geta')
2588 def get_worker(self, method_name):
2589 if method_name == 'geta':
2590 return MyClassWorker_geta()
2593 class MyClass_sum(gdb.xmethod.XMethod):
2595 gdb.xmethod.XMethod.__init__(self, 'sum')
2597 def get_worker(self, method_name):
2598 if method_name == 'operator+':
2599 return MyClassWorker_plus()
2602 class MyClassMatcher(gdb.xmethod.XMethodMatcher):
2604 gdb.xmethod.XMethodMatcher.__init__(self, 'MyClassMatcher')
2605 # List of methods 'managed' by this matcher
2606 self.methods = [MyClass_geta(), MyClass_sum()]
2608 def match(self, class_type, method_name):
2609 if class_type.tag != 'MyClass':
2612 for method in self.methods:
2614 worker = method.get_worker(method_name)
2616 workers.append(worker)
2622 Notice that the @code{match} method of @code{MyClassMatcher} returns
2623 a worker object of type @code{MyClassWorker_geta} for the @code{geta}
2624 method, and a worker object of type @code{MyClassWorker_plus} for the
2625 @code{operator+} method. This is done indirectly via helper classes
2626 derived from @code{gdb.xmethod.XMethod}. One does not need to use the
2627 @code{methods} attribute in a matcher as it is optional. However, if a
2628 matcher manages more than one xmethod, it is a good practice to list the
2629 xmethods in the @code{methods} attribute of the matcher. This will then
2630 facilitate enabling and disabling individual xmethods via the
2631 @code{enable/disable} commands. Notice also that a worker object is
2632 returned only if the corresponding entry in the @code{methods} attribute
2633 of the matcher is enabled.
2635 The implementation of the worker classes returned by the matcher setup
2636 above is as follows:
2639 class MyClassWorker_geta(gdb.xmethod.XMethodWorker):
2640 def get_arg_types(self):
2643 def get_result_type(self, obj):
2644 return gdb.lookup_type('int')
2646 def __call__(self, obj):
2650 class MyClassWorker_plus(gdb.xmethod.XMethodWorker):
2651 def get_arg_types(self):
2652 return gdb.lookup_type('MyClass')
2654 def get_result_type(self, obj):
2655 return gdb.lookup_type('int')
2657 def __call__(self, obj, other):
2658 return obj['a_'] + other['a_']
2661 For @value{GDBN} to actually lookup a xmethod, it has to be
2662 registered with it. The matcher defined above is registered with
2663 @value{GDBN} globally as follows:
2666 gdb.xmethod.register_xmethod_matcher(None, MyClassMatcher())
2669 If an object @code{obj} of type @code{MyClass} is initialized in C@t{++}
2677 then, after loading the Python script defining the xmethod matchers
2678 and workers into @code{GDBN}, invoking the method @code{geta} or using
2679 the operator @code{+} on @code{obj} will invoke the xmethods
2690 Consider another example with a C++ template class:
2697 MyTemplate () : dsize_(10), data_ (new T [10]) @{ @}
2698 ~MyTemplate () @{ delete [] data_; @}
2700 int footprint (void)
2702 return sizeof (T) * dsize_ + sizeof (MyTemplate<T>);
2711 Let us implement an xmethod for the above class which serves as a
2712 replacement for the @code{footprint} method. The full code listing
2713 of the xmethod workers and xmethod matchers is as follows:
2716 class MyTemplateWorker_footprint(gdb.xmethod.XMethodWorker):
2717 def __init__(self, class_type):
2718 self.class_type = class_type
2720 def get_arg_types(self):
2723 def get_result_type(self):
2724 return gdb.lookup_type('int')
2726 def __call__(self, obj):
2727 return (self.class_type.sizeof +
2729 self.class_type.template_argument(0).sizeof)
2732 class MyTemplateMatcher_footprint(gdb.xmethod.XMethodMatcher):
2734 gdb.xmethod.XMethodMatcher.__init__(self, 'MyTemplateMatcher')
2736 def match(self, class_type, method_name):
2737 if (re.match('MyTemplate<[ \t\n]*[_a-zA-Z][ _a-zA-Z0-9]*>',
2739 method_name == 'footprint'):
2740 return MyTemplateWorker_footprint(class_type)
2743 Notice that, in this example, we have not used the @code{methods}
2744 attribute of the matcher as the matcher manages only one xmethod. The
2745 user can enable/disable this xmethod by enabling/disabling the matcher
2748 @node Inferiors In Python
2749 @subsubsection Inferiors In Python
2750 @cindex inferiors in Python
2752 @findex gdb.Inferior
2753 Programs which are being run under @value{GDBN} are called inferiors
2754 (@pxref{Inferiors and Programs}). Python scripts can access
2755 information about and manipulate inferiors controlled by @value{GDBN}
2756 via objects of the @code{gdb.Inferior} class.
2758 The following inferior-related functions are available in the @code{gdb}
2761 @defun gdb.inferiors ()
2762 Return a tuple containing all inferior objects.
2765 @defun gdb.selected_inferior ()
2766 Return an object representing the current inferior.
2769 A @code{gdb.Inferior} object has the following attributes:
2771 @defvar Inferior.num
2772 ID of inferior, as assigned by GDB.
2775 @defvar Inferior.pid
2776 Process ID of the inferior, as assigned by the underlying operating
2780 @defvar Inferior.was_attached
2781 Boolean signaling whether the inferior was created using `attach', or
2782 started by @value{GDBN} itself.
2785 A @code{gdb.Inferior} object has the following methods:
2787 @defun Inferior.is_valid ()
2788 Returns @code{True} if the @code{gdb.Inferior} object is valid,
2789 @code{False} if not. A @code{gdb.Inferior} object will become invalid
2790 if the inferior no longer exists within @value{GDBN}. All other
2791 @code{gdb.Inferior} methods will throw an exception if it is invalid
2792 at the time the method is called.
2795 @defun Inferior.threads ()
2796 This method returns a tuple holding all the threads which are valid
2797 when it is called. If there are no valid threads, the method will
2798 return an empty tuple.
2801 @findex Inferior.read_memory
2802 @defun Inferior.read_memory (address, length)
2803 Read @var{length} addressable memory units from the inferior, starting at
2804 @var{address}. Returns a buffer object, which behaves much like an array
2805 or a string. It can be modified and given to the
2806 @code{Inferior.write_memory} function. In Python 3, the return
2807 value is a @code{memoryview} object.
2810 @findex Inferior.write_memory
2811 @defun Inferior.write_memory (address, buffer @r{[}, length@r{]})
2812 Write the contents of @var{buffer} to the inferior, starting at
2813 @var{address}. The @var{buffer} parameter must be a Python object
2814 which supports the buffer protocol, i.e., a string, an array or the
2815 object returned from @code{Inferior.read_memory}. If given, @var{length}
2816 determines the number of addressable memory units from @var{buffer} to be
2820 @findex gdb.search_memory
2821 @defun Inferior.search_memory (address, length, pattern)
2822 Search a region of the inferior memory starting at @var{address} with
2823 the given @var{length} using the search pattern supplied in
2824 @var{pattern}. The @var{pattern} parameter must be a Python object
2825 which supports the buffer protocol, i.e., a string, an array or the
2826 object returned from @code{gdb.read_memory}. Returns a Python @code{Long}
2827 containing the address where the pattern was found, or @code{None} if
2828 the pattern could not be found.
2831 @findex Inferior.thread_from_thread_handle
2832 @defun Inferior.thread_from_thread_handle (thread_handle)
2833 Return the thread object corresponding to @var{thread_handle}, a thread
2834 library specific data structure such as @code{pthread_t} for pthreads
2835 library implementations.
2838 @node Events In Python
2839 @subsubsection Events In Python
2840 @cindex inferior events in Python
2842 @value{GDBN} provides a general event facility so that Python code can be
2843 notified of various state changes, particularly changes that occur in
2846 An @dfn{event} is just an object that describes some state change. The
2847 type of the object and its attributes will vary depending on the details
2848 of the change. All the existing events are described below.
2850 In order to be notified of an event, you must register an event handler
2851 with an @dfn{event registry}. An event registry is an object in the
2852 @code{gdb.events} module which dispatches particular events. A registry
2853 provides methods to register and unregister event handlers:
2855 @defun EventRegistry.connect (object)
2856 Add the given callable @var{object} to the registry. This object will be
2857 called when an event corresponding to this registry occurs.
2860 @defun EventRegistry.disconnect (object)
2861 Remove the given @var{object} from the registry. Once removed, the object
2862 will no longer receive notifications of events.
2868 def exit_handler (event):
2869 print "event type: exit"
2870 print "exit code: %d" % (event.exit_code)
2872 gdb.events.exited.connect (exit_handler)
2875 In the above example we connect our handler @code{exit_handler} to the
2876 registry @code{events.exited}. Once connected, @code{exit_handler} gets
2877 called when the inferior exits. The argument @dfn{event} in this example is
2878 of type @code{gdb.ExitedEvent}. As you can see in the example the
2879 @code{ExitedEvent} object has an attribute which indicates the exit code of
2882 The following is a listing of the event registries that are available and
2883 details of the events they emit:
2888 Emits @code{gdb.ThreadEvent}.
2890 Some events can be thread specific when @value{GDBN} is running in non-stop
2891 mode. When represented in Python, these events all extend
2892 @code{gdb.ThreadEvent}. Note, this event is not emitted directly; instead,
2893 events which are emitted by this or other modules might extend this event.
2894 Examples of these events are @code{gdb.BreakpointEvent} and
2895 @code{gdb.ContinueEvent}.
2897 @defvar ThreadEvent.inferior_thread
2898 In non-stop mode this attribute will be set to the specific thread which was
2899 involved in the emitted event. Otherwise, it will be set to @code{None}.
2902 Emits @code{gdb.ContinueEvent} which extends @code{gdb.ThreadEvent}.
2904 This event indicates that the inferior has been continued after a stop. For
2905 inherited attribute refer to @code{gdb.ThreadEvent} above.
2908 Emits @code{events.ExitedEvent} which indicates that the inferior has exited.
2909 @code{events.ExitedEvent} has two attributes:
2910 @defvar ExitedEvent.exit_code
2911 An integer representing the exit code, if available, which the inferior
2912 has returned. (The exit code could be unavailable if, for example,
2913 @value{GDBN} detaches from the inferior.) If the exit code is unavailable,
2914 the attribute does not exist.
2916 @defvar ExitedEvent.inferior
2917 A reference to the inferior which triggered the @code{exited} event.
2921 Emits @code{gdb.StopEvent} which extends @code{gdb.ThreadEvent}.
2923 Indicates that the inferior has stopped. All events emitted by this registry
2924 extend StopEvent. As a child of @code{gdb.ThreadEvent}, @code{gdb.StopEvent}
2925 will indicate the stopped thread when @value{GDBN} is running in non-stop
2926 mode. Refer to @code{gdb.ThreadEvent} above for more details.
2928 Emits @code{gdb.SignalEvent} which extends @code{gdb.StopEvent}.
2930 This event indicates that the inferior or one of its threads has received as
2931 signal. @code{gdb.SignalEvent} has the following attributes:
2933 @defvar SignalEvent.stop_signal
2934 A string representing the signal received by the inferior. A list of possible
2935 signal values can be obtained by running the command @code{info signals} in
2936 the @value{GDBN} command prompt.
2939 Also emits @code{gdb.BreakpointEvent} which extends @code{gdb.StopEvent}.
2941 @code{gdb.BreakpointEvent} event indicates that one or more breakpoints have
2942 been hit, and has the following attributes:
2944 @defvar BreakpointEvent.breakpoints
2945 A sequence containing references to all the breakpoints (type
2946 @code{gdb.Breakpoint}) that were hit.
2947 @xref{Breakpoints In Python}, for details of the @code{gdb.Breakpoint} object.
2949 @defvar BreakpointEvent.breakpoint
2950 A reference to the first breakpoint that was hit.
2951 This function is maintained for backward compatibility and is now deprecated
2952 in favor of the @code{gdb.BreakpointEvent.breakpoints} attribute.
2955 @item events.new_objfile
2956 Emits @code{gdb.NewObjFileEvent} which indicates that a new object file has
2957 been loaded by @value{GDBN}. @code{gdb.NewObjFileEvent} has one attribute:
2959 @defvar NewObjFileEvent.new_objfile
2960 A reference to the object file (@code{gdb.Objfile}) which has been loaded.
2961 @xref{Objfiles In Python}, for details of the @code{gdb.Objfile} object.
2964 @item events.clear_objfiles
2965 Emits @code{gdb.ClearObjFilesEvent} which indicates that the list of object
2966 files for a program space has been reset.
2967 @code{gdb.ClearObjFilesEvent} has one attribute:
2969 @defvar ClearObjFilesEvent.progspace
2970 A reference to the program space (@code{gdb.Progspace}) whose objfile list has
2971 been cleared. @xref{Progspaces In Python}.
2974 @item events.inferior_call_pre
2975 Emits @code{gdb.InferiorCallPreEvent} which indicates that a function in
2976 the inferior is about to be called.
2978 @defvar InferiorCallPreEvent.ptid
2979 The thread in which the call will be run.
2982 @defvar InferiorCallPreEvent.address
2983 The location of the function to be called.
2986 @item events.inferior_call_post
2987 Emits @code{gdb.InferiorCallPostEvent} which indicates that a function in
2988 the inferior has returned.
2990 @defvar InferiorCallPostEvent.ptid
2991 The thread in which the call was run.
2994 @defvar InferiorCallPostEvent.address
2995 The location of the function that was called.
2998 @item events.memory_changed
2999 Emits @code{gdb.MemoryChangedEvent} which indicates that the memory of the
3000 inferior has been modified by the @value{GDBN} user, for instance via a
3001 command like @w{@code{set *addr = value}}. The event has the following
3004 @defvar MemoryChangedEvent.address
3005 The start address of the changed region.
3008 @defvar MemoryChangedEvent.length
3009 Length in bytes of the changed region.
3012 @item events.register_changed
3013 Emits @code{gdb.RegisterChangedEvent} which indicates that a register in the
3014 inferior has been modified by the @value{GDBN} user.
3016 @defvar RegisterChangedEvent.frame
3017 A gdb.Frame object representing the frame in which the register was modified.
3019 @defvar RegisterChangedEvent.regnum
3020 Denotes which register was modified.
3023 @item events.breakpoint_created
3024 This is emitted when a new breakpoint has been created. The argument
3025 that is passed is the new @code{gdb.Breakpoint} object.
3027 @item events.breakpoint_modified
3028 This is emitted when a breakpoint has been modified in some way. The
3029 argument that is passed is the new @code{gdb.Breakpoint} object.
3031 @item events.breakpoint_deleted
3032 This is emitted when a breakpoint has been deleted. The argument that
3033 is passed is the @code{gdb.Breakpoint} object. When this event is
3034 emitted, the @code{gdb.Breakpoint} object will already be in its
3035 invalid state; that is, the @code{is_valid} method will return
3038 @item events.before_prompt
3039 This event carries no payload. It is emitted each time @value{GDBN}
3040 presents a prompt to the user.
3042 @item events.new_inferior
3043 This is emitted when a new inferior is created. Note that the
3044 inferior is not necessarily running; in fact, it may not even have an
3045 associated executable.
3047 The event is of type @code{gdb.NewInferiorEvent}. This has a single
3050 @defvar NewInferiorEvent.inferior
3051 The new inferior, a @code{gdb.Inferior} object.
3054 @item events.inferior_deleted
3055 This is emitted when an inferior has been deleted. Note that this is
3056 not the same as process exit; it is notified when the inferior itself
3057 is removed, say via @code{remove-inferiors}.
3059 The event is of type @code{gdb.InferiorDeletedEvent}. This has a single
3062 @defvar NewInferiorEvent.inferior
3063 The inferior that is being removed, a @code{gdb.Inferior} object.
3066 @item events.new_thread
3067 This is emitted when @value{GDBN} notices a new thread. The event is of
3068 type @code{gdb.NewThreadEvent}, which extends @code{gdb.ThreadEvent}.
3069 This has a single attribute:
3071 @defvar NewThreadEvent.inferior_thread
3077 @node Threads In Python
3078 @subsubsection Threads In Python
3079 @cindex threads in python
3081 @findex gdb.InferiorThread
3082 Python scripts can access information about, and manipulate inferior threads
3083 controlled by @value{GDBN}, via objects of the @code{gdb.InferiorThread} class.
3085 The following thread-related functions are available in the @code{gdb}
3088 @findex gdb.selected_thread
3089 @defun gdb.selected_thread ()
3090 This function returns the thread object for the selected thread. If there
3091 is no selected thread, this will return @code{None}.
3094 A @code{gdb.InferiorThread} object has the following attributes:
3096 @defvar InferiorThread.name
3097 The name of the thread. If the user specified a name using
3098 @code{thread name}, then this returns that name. Otherwise, if an
3099 OS-supplied name is available, then it is returned. Otherwise, this
3100 returns @code{None}.
3102 This attribute can be assigned to. The new value must be a string
3103 object, which sets the new name, or @code{None}, which removes any
3104 user-specified thread name.
3107 @defvar InferiorThread.num
3108 The per-inferior number of the thread, as assigned by GDB.
3111 @defvar InferiorThread.global_num
3112 The global ID of the thread, as assigned by GDB. You can use this to
3113 make Python breakpoints thread-specific, for example
3114 (@pxref{python_breakpoint_thread,,The Breakpoint.thread attribute}).
3117 @defvar InferiorThread.ptid
3118 ID of the thread, as assigned by the operating system. This attribute is a
3119 tuple containing three integers. The first is the Process ID (PID); the second
3120 is the Lightweight Process ID (LWPID), and the third is the Thread ID (TID).
3121 Either the LWPID or TID may be 0, which indicates that the operating system
3122 does not use that identifier.
3125 @defvar InferiorThread.inferior
3126 The inferior this thread belongs to. This attribute is represented as
3127 a @code{gdb.Inferior} object. This attribute is not writable.
3130 A @code{gdb.InferiorThread} object has the following methods:
3132 @defun InferiorThread.is_valid ()
3133 Returns @code{True} if the @code{gdb.InferiorThread} object is valid,
3134 @code{False} if not. A @code{gdb.InferiorThread} object will become
3135 invalid if the thread exits, or the inferior that the thread belongs
3136 is deleted. All other @code{gdb.InferiorThread} methods will throw an
3137 exception if it is invalid at the time the method is called.
3140 @defun InferiorThread.switch ()
3141 This changes @value{GDBN}'s currently selected thread to the one represented
3145 @defun InferiorThread.is_stopped ()
3146 Return a Boolean indicating whether the thread is stopped.
3149 @defun InferiorThread.is_running ()
3150 Return a Boolean indicating whether the thread is running.
3153 @defun InferiorThread.is_exited ()
3154 Return a Boolean indicating whether the thread is exited.
3157 @node Recordings In Python
3158 @subsubsection Recordings In Python
3159 @cindex recordings in python
3161 The following recordings-related functions
3162 (@pxref{Process Record and Replay}) are available in the @code{gdb}
3165 @defun gdb.start_recording (@r{[}method@r{]}, @r{[}format@r{]})
3166 Start a recording using the given @var{method} and @var{format}. If
3167 no @var{format} is given, the default format for the recording method
3168 is used. If no @var{method} is given, the default method will be used.
3169 Returns a @code{gdb.Record} object on success. Throw an exception on
3172 The following strings can be passed as @var{method}:
3178 @code{"btrace"}: Possible values for @var{format}: @code{"pt"},
3179 @code{"bts"} or leave out for default format.
3183 @defun gdb.current_recording ()
3184 Access a currently running recording. Return a @code{gdb.Record}
3185 object on success. Return @code{None} if no recording is currently
3189 @defun gdb.stop_recording ()
3190 Stop the current recording. Throw an exception if no recording is
3191 currently active. All record objects become invalid after this call.
3194 A @code{gdb.Record} object has the following attributes:
3196 @defvar Record.method
3197 A string with the current recording method, e.g.@: @code{full} or
3201 @defvar Record.format
3202 A string with the current recording format, e.g.@: @code{bt}, @code{pts} or
3206 @defvar Record.begin
3207 A method specific instruction object representing the first instruction
3212 A method specific instruction object representing the current
3213 instruction, that is not actually part of the recording.
3216 @defvar Record.replay_position
3217 The instruction representing the current replay position. If there is
3218 no replay active, this will be @code{None}.
3221 @defvar Record.instruction_history
3222 A list with all recorded instructions.
3225 @defvar Record.function_call_history
3226 A list with all recorded function call segments.
3229 A @code{gdb.Record} object has the following methods:
3231 @defun Record.goto (instruction)
3232 Move the replay position to the given @var{instruction}.
3235 The common @code{gdb.Instruction} class that recording method specific
3236 instruction objects inherit from, has the following attributes:
3238 @defvar Instruction.pc
3239 An integer representing this instruction's address.
3242 @defvar Instruction.data
3243 A buffer with the raw instruction data. In Python 3, the return value is a
3244 @code{memoryview} object.
3247 @defvar Instruction.decoded
3248 A human readable string with the disassembled instruction.
3251 @defvar Instruction.size
3252 The size of the instruction in bytes.
3255 Additionally @code{gdb.RecordInstruction} has the following attributes:
3257 @defvar RecordInstruction.number
3258 An integer identifying this instruction. @code{number} corresponds to
3259 the numbers seen in @code{record instruction-history}
3260 (@pxref{Process Record and Replay}).
3263 @defvar RecordInstruction.sal
3264 A @code{gdb.Symtab_and_line} object representing the associated symtab
3265 and line of this instruction. May be @code{None} if no debug information is
3269 @defvar RecordInstruction.is_speculative
3270 A boolean indicating whether the instruction was executed speculatively.
3273 If an error occured during recording or decoding a recording, this error is
3274 represented by a @code{gdb.RecordGap} object in the instruction list. It has
3275 the following attributes:
3277 @defvar RecordGap.number
3278 An integer identifying this gap. @code{number} corresponds to the numbers seen
3279 in @code{record instruction-history} (@pxref{Process Record and Replay}).
3282 @defvar RecordGap.error_code
3283 A numerical representation of the reason for the gap. The value is specific to
3284 the current recording method.
3287 @defvar RecordGap.error_string
3288 A human readable string with the reason for the gap.
3291 A @code{gdb.RecordFunctionSegment} object has the following attributes:
3293 @defvar RecordFunctionSegment.number
3294 An integer identifying this function segment. @code{number} corresponds to
3295 the numbers seen in @code{record function-call-history}
3296 (@pxref{Process Record and Replay}).
3299 @defvar RecordFunctionSegment.symbol
3300 A @code{gdb.Symbol} object representing the associated symbol. May be
3301 @code{None} if no debug information is available.
3304 @defvar RecordFunctionSegment.level
3305 An integer representing the function call's stack level. May be
3306 @code{None} if the function call is a gap.
3309 @defvar RecordFunctionSegment.instructions
3310 A list of @code{gdb.RecordInstruction} or @code{gdb.RecordGap} objects
3311 associated with this function call.
3314 @defvar RecordFunctionSegment.up
3315 A @code{gdb.RecordFunctionSegment} object representing the caller's
3316 function segment. If the call has not been recorded, this will be the
3317 function segment to which control returns. If neither the call nor the
3318 return have been recorded, this will be @code{None}.
3321 @defvar RecordFunctionSegment.prev
3322 A @code{gdb.RecordFunctionSegment} object representing the previous
3323 segment of this function call. May be @code{None}.
3326 @defvar RecordFunctionSegment.next
3327 A @code{gdb.RecordFunctionSegment} object representing the next segment of
3328 this function call. May be @code{None}.
3331 The following example demonstrates the usage of these objects and
3332 functions to create a function that will rewind a record to the last
3333 time a function in a different file was executed. This would typically
3334 be used to track the execution of user provided callback functions in a
3335 library which typically are not visible in a back trace.
3339 rec = gdb.current_recording ()
3343 insn = rec.instruction_history
3348 position = insn.index (rec.replay_position)
3352 filename = insn[position].sal.symtab.fullname ()
3356 for i in reversed (insn[:position]):
3358 current = i.sal.symtab.fullname ()
3362 if filename == current:
3369 Another possible application is to write a function that counts the
3370 number of code executions in a given line range. This line range can
3371 contain parts of functions or span across several functions and is not
3372 limited to be contiguous.
3375 def countrange (filename, linerange):
3378 def filter_only (file_name):
3379 for call in gdb.current_recording ().function_call_history:
3381 if file_name in call.symbol.symtab.fullname ():
3386 for c in filter_only (filename):
3387 for i in c.instructions:
3389 if i.sal.line in linerange:
3398 @node Commands In Python
3399 @subsubsection Commands In Python
3401 @cindex commands in python
3402 @cindex python commands
3403 You can implement new @value{GDBN} CLI commands in Python. A CLI
3404 command is implemented using an instance of the @code{gdb.Command}
3405 class, most commonly using a subclass.
3407 @defun Command.__init__ (name, @var{command_class} @r{[}, @var{completer_class} @r{[}, @var{prefix}@r{]]})
3408 The object initializer for @code{Command} registers the new command
3409 with @value{GDBN}. This initializer is normally invoked from the
3410 subclass' own @code{__init__} method.
3412 @var{name} is the name of the command. If @var{name} consists of
3413 multiple words, then the initial words are looked for as prefix
3414 commands. In this case, if one of the prefix commands does not exist,
3415 an exception is raised.
3417 There is no support for multi-line commands.
3419 @var{command_class} should be one of the @samp{COMMAND_} constants
3420 defined below. This argument tells @value{GDBN} how to categorize the
3421 new command in the help system.
3423 @var{completer_class} is an optional argument. If given, it should be
3424 one of the @samp{COMPLETE_} constants defined below. This argument
3425 tells @value{GDBN} how to perform completion for this command. If not
3426 given, @value{GDBN} will attempt to complete using the object's
3427 @code{complete} method (see below); if no such method is found, an
3428 error will occur when completion is attempted.
3430 @var{prefix} is an optional argument. If @code{True}, then the new
3431 command is a prefix command; sub-commands of this command may be
3434 The help text for the new command is taken from the Python
3435 documentation string for the command's class, if there is one. If no
3436 documentation string is provided, the default value ``This command is
3437 not documented.'' is used.
3440 @cindex don't repeat Python command
3441 @defun Command.dont_repeat ()
3442 By default, a @value{GDBN} command is repeated when the user enters a
3443 blank line at the command prompt. A command can suppress this
3444 behavior by invoking the @code{dont_repeat} method. This is similar
3445 to the user command @code{dont-repeat}, see @ref{Define, dont-repeat}.
3448 @defun Command.invoke (argument, from_tty)
3449 This method is called by @value{GDBN} when this command is invoked.
3451 @var{argument} is a string. It is the argument to the command, after
3452 leading and trailing whitespace has been stripped.
3454 @var{from_tty} is a boolean argument. When true, this means that the
3455 command was entered by the user at the terminal; when false it means
3456 that the command came from elsewhere.
3458 If this method throws an exception, it is turned into a @value{GDBN}
3459 @code{error} call. Otherwise, the return value is ignored.
3461 @findex gdb.string_to_argv
3462 To break @var{argument} up into an argv-like string use
3463 @code{gdb.string_to_argv}. This function behaves identically to
3464 @value{GDBN}'s internal argument lexer @code{buildargv}.
3465 It is recommended to use this for consistency.
3466 Arguments are separated by spaces and may be quoted.
3470 print gdb.string_to_argv ("1 2\ \\\"3 '4 \"5' \"6 '7\"")
3471 ['1', '2 "3', '4 "5', "6 '7"]
3476 @cindex completion of Python commands
3477 @defun Command.complete (text, word)
3478 This method is called by @value{GDBN} when the user attempts
3479 completion on this command. All forms of completion are handled by
3480 this method, that is, the @key{TAB} and @key{M-?} key bindings
3481 (@pxref{Completion}), and the @code{complete} command (@pxref{Help,
3484 The arguments @var{text} and @var{word} are both strings; @var{text}
3485 holds the complete command line up to the cursor's location, while
3486 @var{word} holds the last word of the command line; this is computed
3487 using a word-breaking heuristic.
3489 The @code{complete} method can return several values:
3492 If the return value is a sequence, the contents of the sequence are
3493 used as the completions. It is up to @code{complete} to ensure that the
3494 contents actually do complete the word. A zero-length sequence is
3495 allowed, it means that there were no completions available. Only
3496 string elements of the sequence are used; other elements in the
3497 sequence are ignored.
3500 If the return value is one of the @samp{COMPLETE_} constants defined
3501 below, then the corresponding @value{GDBN}-internal completion
3502 function is invoked, and its result is used.
3505 All other results are treated as though there were no available
3510 When a new command is registered, it must be declared as a member of
3511 some general class of commands. This is used to classify top-level
3512 commands in the on-line help system; note that prefix commands are not
3513 listed under their own category but rather that of their top-level
3514 command. The available classifications are represented by constants
3515 defined in the @code{gdb} module:
3518 @findex COMMAND_NONE
3519 @findex gdb.COMMAND_NONE
3520 @item gdb.COMMAND_NONE
3521 The command does not belong to any particular class. A command in
3522 this category will not be displayed in any of the help categories.
3524 @findex COMMAND_RUNNING
3525 @findex gdb.COMMAND_RUNNING
3526 @item gdb.COMMAND_RUNNING
3527 The command is related to running the inferior. For example,
3528 @code{start}, @code{step}, and @code{continue} are in this category.
3529 Type @kbd{help running} at the @value{GDBN} prompt to see a list of
3530 commands in this category.
3532 @findex COMMAND_DATA
3533 @findex gdb.COMMAND_DATA
3534 @item gdb.COMMAND_DATA
3535 The command is related to data or variables. For example,
3536 @code{call}, @code{find}, and @code{print} are in this category. Type
3537 @kbd{help data} at the @value{GDBN} prompt to see a list of commands
3540 @findex COMMAND_STACK
3541 @findex gdb.COMMAND_STACK
3542 @item gdb.COMMAND_STACK
3543 The command has to do with manipulation of the stack. For example,
3544 @code{backtrace}, @code{frame}, and @code{return} are in this
3545 category. Type @kbd{help stack} at the @value{GDBN} prompt to see a
3546 list of commands in this category.
3548 @findex COMMAND_FILES
3549 @findex gdb.COMMAND_FILES
3550 @item gdb.COMMAND_FILES
3551 This class is used for file-related commands. For example,
3552 @code{file}, @code{list} and @code{section} are in this category.
3553 Type @kbd{help files} at the @value{GDBN} prompt to see a list of
3554 commands in this category.
3556 @findex COMMAND_SUPPORT
3557 @findex gdb.COMMAND_SUPPORT
3558 @item gdb.COMMAND_SUPPORT
3559 This should be used for ``support facilities'', generally meaning
3560 things that are useful to the user when interacting with @value{GDBN},
3561 but not related to the state of the inferior. For example,
3562 @code{help}, @code{make}, and @code{shell} are in this category. Type
3563 @kbd{help support} at the @value{GDBN} prompt to see a list of
3564 commands in this category.
3566 @findex COMMAND_STATUS
3567 @findex gdb.COMMAND_STATUS
3568 @item gdb.COMMAND_STATUS
3569 The command is an @samp{info}-related command, that is, related to the
3570 state of @value{GDBN} itself. For example, @code{info}, @code{macro},
3571 and @code{show} are in this category. Type @kbd{help status} at the
3572 @value{GDBN} prompt to see a list of commands in this category.
3574 @findex COMMAND_BREAKPOINTS
3575 @findex gdb.COMMAND_BREAKPOINTS
3576 @item gdb.COMMAND_BREAKPOINTS
3577 The command has to do with breakpoints. For example, @code{break},
3578 @code{clear}, and @code{delete} are in this category. Type @kbd{help
3579 breakpoints} at the @value{GDBN} prompt to see a list of commands in
3582 @findex COMMAND_TRACEPOINTS
3583 @findex gdb.COMMAND_TRACEPOINTS
3584 @item gdb.COMMAND_TRACEPOINTS
3585 The command has to do with tracepoints. For example, @code{trace},
3586 @code{actions}, and @code{tfind} are in this category. Type
3587 @kbd{help tracepoints} at the @value{GDBN} prompt to see a list of
3588 commands in this category.
3590 @findex COMMAND_USER
3591 @findex gdb.COMMAND_USER
3592 @item gdb.COMMAND_USER
3593 The command is a general purpose command for the user, and typically
3594 does not fit in one of the other categories.
3595 Type @kbd{help user-defined} at the @value{GDBN} prompt to see
3596 a list of commands in this category, as well as the list of gdb macros
3597 (@pxref{Sequences}).
3599 @findex COMMAND_OBSCURE
3600 @findex gdb.COMMAND_OBSCURE
3601 @item gdb.COMMAND_OBSCURE
3602 The command is only used in unusual circumstances, or is not of
3603 general interest to users. For example, @code{checkpoint},
3604 @code{fork}, and @code{stop} are in this category. Type @kbd{help
3605 obscure} at the @value{GDBN} prompt to see a list of commands in this
3608 @findex COMMAND_MAINTENANCE
3609 @findex gdb.COMMAND_MAINTENANCE
3610 @item gdb.COMMAND_MAINTENANCE
3611 The command is only useful to @value{GDBN} maintainers. The
3612 @code{maintenance} and @code{flushregs} commands are in this category.
3613 Type @kbd{help internals} at the @value{GDBN} prompt to see a list of
3614 commands in this category.
3617 A new command can use a predefined completion function, either by
3618 specifying it via an argument at initialization, or by returning it
3619 from the @code{complete} method. These predefined completion
3620 constants are all defined in the @code{gdb} module:
3623 @vindex COMPLETE_NONE
3624 @item gdb.COMPLETE_NONE
3625 This constant means that no completion should be done.
3627 @vindex COMPLETE_FILENAME
3628 @item gdb.COMPLETE_FILENAME
3629 This constant means that filename completion should be performed.
3631 @vindex COMPLETE_LOCATION
3632 @item gdb.COMPLETE_LOCATION
3633 This constant means that location completion should be done.
3634 @xref{Specify Location}.
3636 @vindex COMPLETE_COMMAND
3637 @item gdb.COMPLETE_COMMAND
3638 This constant means that completion should examine @value{GDBN}
3641 @vindex COMPLETE_SYMBOL
3642 @item gdb.COMPLETE_SYMBOL
3643 This constant means that completion should be done using symbol names
3646 @vindex COMPLETE_EXPRESSION
3647 @item gdb.COMPLETE_EXPRESSION
3648 This constant means that completion should be done on expressions.
3649 Often this means completing on symbol names, but some language
3650 parsers also have support for completing on field names.
3653 The following code snippet shows how a trivial CLI command can be
3654 implemented in Python:
3657 class HelloWorld (gdb.Command):
3658 """Greet the whole world."""
3660 def __init__ (self):
3661 super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)
3663 def invoke (self, arg, from_tty):
3664 print "Hello, World!"
3669 The last line instantiates the class, and is necessary to trigger the
3670 registration of the command with @value{GDBN}. Depending on how the
3671 Python code is read into @value{GDBN}, you may need to import the
3672 @code{gdb} module explicitly.
3674 @node Parameters In Python
3675 @subsubsection Parameters In Python
3677 @cindex parameters in python
3678 @cindex python parameters
3679 @tindex gdb.Parameter
3681 You can implement new @value{GDBN} parameters using Python. A new
3682 parameter is implemented as an instance of the @code{gdb.Parameter}
3685 Parameters are exposed to the user via the @code{set} and
3686 @code{show} commands. @xref{Help}.
3688 There are many parameters that already exist and can be set in
3689 @value{GDBN}. Two examples are: @code{set follow fork} and
3690 @code{set charset}. Setting these parameters influences certain
3691 behavior in @value{GDBN}. Similarly, you can define parameters that
3692 can be used to influence behavior in custom Python scripts and commands.
3694 @defun Parameter.__init__ (name, @var{command-class}, @var{parameter-class} @r{[}, @var{enum-sequence}@r{]})
3695 The object initializer for @code{Parameter} registers the new
3696 parameter with @value{GDBN}. This initializer is normally invoked
3697 from the subclass' own @code{__init__} method.
3699 @var{name} is the name of the new parameter. If @var{name} consists
3700 of multiple words, then the initial words are looked for as prefix
3701 parameters. An example of this can be illustrated with the
3702 @code{set print} set of parameters. If @var{name} is
3703 @code{print foo}, then @code{print} will be searched as the prefix
3704 parameter. In this case the parameter can subsequently be accessed in
3705 @value{GDBN} as @code{set print foo}.
3707 If @var{name} consists of multiple words, and no prefix parameter group
3708 can be found, an exception is raised.
3710 @var{command-class} should be one of the @samp{COMMAND_} constants
3711 (@pxref{Commands In Python}). This argument tells @value{GDBN} how to
3712 categorize the new parameter in the help system.
3714 @var{parameter-class} should be one of the @samp{PARAM_} constants
3715 defined below. This argument tells @value{GDBN} the type of the new
3716 parameter; this information is used for input validation and
3719 If @var{parameter-class} is @code{PARAM_ENUM}, then
3720 @var{enum-sequence} must be a sequence of strings. These strings
3721 represent the possible values for the parameter.
3723 If @var{parameter-class} is not @code{PARAM_ENUM}, then the presence
3724 of a fourth argument will cause an exception to be thrown.
3726 The help text for the new parameter is taken from the Python
3727 documentation string for the parameter's class, if there is one. If
3728 there is no documentation string, a default value is used.
3731 @defvar Parameter.set_doc
3732 If this attribute exists, and is a string, then its value is used as
3733 the help text for this parameter's @code{set} command. The value is
3734 examined when @code{Parameter.__init__} is invoked; subsequent changes
3738 @defvar Parameter.show_doc
3739 If this attribute exists, and is a string, then its value is used as
3740 the help text for this parameter's @code{show} command. The value is
3741 examined when @code{Parameter.__init__} is invoked; subsequent changes
3745 @defvar Parameter.value
3746 The @code{value} attribute holds the underlying value of the
3747 parameter. It can be read and assigned to just as any other
3748 attribute. @value{GDBN} does validation when assignments are made.
3751 There are two methods that should be implemented in any
3752 @code{Parameter} class. These are:
3754 @defun Parameter.get_set_string (self)
3755 @value{GDBN} will call this method when a @var{parameter}'s value has
3756 been changed via the @code{set} API (for example, @kbd{set foo off}).
3757 The @code{value} attribute has already been populated with the new
3758 value and may be used in output. This method must return a string.
3761 @defun Parameter.get_show_string (self, svalue)
3762 @value{GDBN} will call this method when a @var{parameter}'s
3763 @code{show} API has been invoked (for example, @kbd{show foo}). The
3764 argument @code{svalue} receives the string representation of the
3765 current value. This method must return a string.
3768 When a new parameter is defined, its type must be specified. The
3769 available types are represented by constants defined in the @code{gdb}
3773 @findex PARAM_BOOLEAN
3774 @findex gdb.PARAM_BOOLEAN
3775 @item gdb.PARAM_BOOLEAN
3776 The value is a plain boolean. The Python boolean values, @code{True}
3777 and @code{False} are the only valid values.
3779 @findex PARAM_AUTO_BOOLEAN
3780 @findex gdb.PARAM_AUTO_BOOLEAN
3781 @item gdb.PARAM_AUTO_BOOLEAN
3782 The value has three possible states: true, false, and @samp{auto}. In
3783 Python, true and false are represented using boolean constants, and
3784 @samp{auto} is represented using @code{None}.
3786 @findex PARAM_UINTEGER
3787 @findex gdb.PARAM_UINTEGER
3788 @item gdb.PARAM_UINTEGER
3789 The value is an unsigned integer. The value of 0 should be
3790 interpreted to mean ``unlimited''.
3792 @findex PARAM_INTEGER
3793 @findex gdb.PARAM_INTEGER
3794 @item gdb.PARAM_INTEGER
3795 The value is a signed integer. The value of 0 should be interpreted
3796 to mean ``unlimited''.
3798 @findex PARAM_STRING
3799 @findex gdb.PARAM_STRING
3800 @item gdb.PARAM_STRING
3801 The value is a string. When the user modifies the string, any escape
3802 sequences, such as @samp{\t}, @samp{\f}, and octal escapes, are
3803 translated into corresponding characters and encoded into the current
3806 @findex PARAM_STRING_NOESCAPE
3807 @findex gdb.PARAM_STRING_NOESCAPE
3808 @item gdb.PARAM_STRING_NOESCAPE
3809 The value is a string. When the user modifies the string, escapes are
3810 passed through untranslated.
3812 @findex PARAM_OPTIONAL_FILENAME
3813 @findex gdb.PARAM_OPTIONAL_FILENAME
3814 @item gdb.PARAM_OPTIONAL_FILENAME
3815 The value is a either a filename (a string), or @code{None}.
3817 @findex PARAM_FILENAME
3818 @findex gdb.PARAM_FILENAME
3819 @item gdb.PARAM_FILENAME
3820 The value is a filename. This is just like
3821 @code{PARAM_STRING_NOESCAPE}, but uses file names for completion.
3823 @findex PARAM_ZINTEGER
3824 @findex gdb.PARAM_ZINTEGER
3825 @item gdb.PARAM_ZINTEGER
3826 The value is an integer. This is like @code{PARAM_INTEGER}, except 0
3827 is interpreted as itself.
3829 @findex PARAM_ZUINTEGER
3830 @findex gdb.PARAM_ZUINTEGER
3831 @item gdb.PARAM_ZUINTEGER
3832 The value is an unsigned integer. This is like @code{PARAM_INTEGER},
3833 except 0 is interpreted as itself, and the value cannot be negative.
3835 @findex PARAM_ZUINTEGER_UNLIMITED
3836 @findex gdb.PARAM_ZUINTEGER_UNLIMITED
3837 @item gdb.PARAM_ZUINTEGER_UNLIMITED
3838 The value is a signed integer. This is like @code{PARAM_ZUINTEGER},
3839 except the special value -1 should be interpreted to mean
3840 ``unlimited''. Other negative values are not allowed.
3843 @findex gdb.PARAM_ENUM
3844 @item gdb.PARAM_ENUM
3845 The value is a string, which must be one of a collection string
3846 constants provided when the parameter is created.
3849 @node Functions In Python
3850 @subsubsection Writing new convenience functions
3852 @cindex writing convenience functions
3853 @cindex convenience functions in python
3854 @cindex python convenience functions
3855 @tindex gdb.Function
3857 You can implement new convenience functions (@pxref{Convenience Vars})
3858 in Python. A convenience function is an instance of a subclass of the
3859 class @code{gdb.Function}.
3861 @defun Function.__init__ (name)
3862 The initializer for @code{Function} registers the new function with
3863 @value{GDBN}. The argument @var{name} is the name of the function,
3864 a string. The function will be visible to the user as a convenience
3865 variable of type @code{internal function}, whose name is the same as
3866 the given @var{name}.
3868 The documentation for the new function is taken from the documentation
3869 string for the new class.
3872 @defun Function.invoke (@var{*args})
3873 When a convenience function is evaluated, its arguments are converted
3874 to instances of @code{gdb.Value}, and then the function's
3875 @code{invoke} method is called. Note that @value{GDBN} does not
3876 predetermine the arity of convenience functions. Instead, all
3877 available arguments are passed to @code{invoke}, following the
3878 standard Python calling convention. In particular, a convenience
3879 function can have default values for parameters without ill effect.
3881 The return value of this method is used as its value in the enclosing
3882 expression. If an ordinary Python value is returned, it is converted
3883 to a @code{gdb.Value} following the usual rules.
3886 The following code snippet shows how a trivial convenience function can
3887 be implemented in Python:
3890 class Greet (gdb.Function):
3891 """Return string to greet someone.
3892 Takes a name as argument."""
3894 def __init__ (self):
3895 super (Greet, self).__init__ ("greet")
3897 def invoke (self, name):
3898 return "Hello, %s!" % name.string ()
3903 The last line instantiates the class, and is necessary to trigger the
3904 registration of the function with @value{GDBN}. Depending on how the
3905 Python code is read into @value{GDBN}, you may need to import the
3906 @code{gdb} module explicitly.
3908 Now you can use the function in an expression:
3911 (gdb) print $greet("Bob")
3915 @node Progspaces In Python
3916 @subsubsection Program Spaces In Python
3918 @cindex progspaces in python
3919 @tindex gdb.Progspace
3921 A program space, or @dfn{progspace}, represents a symbolic view
3922 of an address space.
3923 It consists of all of the objfiles of the program.
3924 @xref{Objfiles In Python}.
3925 @xref{Inferiors and Programs, program spaces}, for more details
3926 about program spaces.
3928 The following progspace-related functions are available in the
3931 @findex gdb.current_progspace
3932 @defun gdb.current_progspace ()
3933 This function returns the program space of the currently selected inferior.
3934 @xref{Inferiors and Programs}.
3937 @findex gdb.progspaces
3938 @defun gdb.progspaces ()
3939 Return a sequence of all the progspaces currently known to @value{GDBN}.
3942 Each progspace is represented by an instance of the @code{gdb.Progspace}
3945 @defvar Progspace.filename
3946 The file name of the progspace as a string.
3949 @defvar Progspace.pretty_printers
3950 The @code{pretty_printers} attribute is a list of functions. It is
3951 used to look up pretty-printers. A @code{Value} is passed to each
3952 function in order; if the function returns @code{None}, then the
3953 search continues. Otherwise, the return value should be an object
3954 which is used to format the value. @xref{Pretty Printing API}, for more
3958 @defvar Progspace.type_printers
3959 The @code{type_printers} attribute is a list of type printer objects.
3960 @xref{Type Printing API}, for more information.
3963 @defvar Progspace.frame_filters
3964 The @code{frame_filters} attribute is a dictionary of frame filter
3965 objects. @xref{Frame Filter API}, for more information.
3968 One may add arbitrary attributes to @code{gdb.Progspace} objects
3969 in the usual Python way.
3970 This is useful if, for example, one needs to do some extra record keeping
3971 associated with the program space.
3973 In this contrived example, we want to perform some processing when
3974 an objfile with a certain symbol is loaded, but we only want to do
3975 this once because it is expensive. To achieve this we record the results
3976 with the program space because we can't predict when the desired objfile
3981 def clear_objfiles_handler(event):
3982 event.progspace.expensive_computation = None
3983 def expensive(symbol):
3984 """A mock routine to perform an "expensive" computation on symbol."""
3985 print "Computing the answer to the ultimate question ..."
3987 def new_objfile_handler(event):
3988 objfile = event.new_objfile
3989 progspace = objfile.progspace
3990 if not hasattr(progspace, 'expensive_computation') or \
3991 progspace.expensive_computation is None:
3992 # We use 'main' for the symbol to keep the example simple.
3993 # Note: There's no current way to constrain the lookup
3995 symbol = gdb.lookup_global_symbol('main')
3996 if symbol is not None:
3997 progspace.expensive_computation = expensive(symbol)
3998 gdb.events.clear_objfiles.connect(clear_objfiles_handler)
3999 gdb.events.new_objfile.connect(new_objfile_handler)
4001 (gdb) file /tmp/hello
4002 Reading symbols from /tmp/hello...done.
4003 Computing the answer to the ultimate question ...
4004 (gdb) python print gdb.current_progspace().expensive_computation
4007 Starting program: /tmp/hello
4009 [Inferior 1 (process 4242) exited normally]
4012 @node Objfiles In Python
4013 @subsubsection Objfiles In Python
4015 @cindex objfiles in python
4018 @value{GDBN} loads symbols for an inferior from various
4019 symbol-containing files (@pxref{Files}). These include the primary
4020 executable file, any shared libraries used by the inferior, and any
4021 separate debug info files (@pxref{Separate Debug Files}).
4022 @value{GDBN} calls these symbol-containing files @dfn{objfiles}.
4024 The following objfile-related functions are available in the
4027 @findex gdb.current_objfile
4028 @defun gdb.current_objfile ()
4029 When auto-loading a Python script (@pxref{Python Auto-loading}), @value{GDBN}
4030 sets the ``current objfile'' to the corresponding objfile. This
4031 function returns the current objfile. If there is no current objfile,
4032 this function returns @code{None}.
4035 @findex gdb.objfiles
4036 @defun gdb.objfiles ()
4037 Return a sequence of all the objfiles current known to @value{GDBN}.
4038 @xref{Objfiles In Python}.
4041 @findex gdb.lookup_objfile
4042 @defun gdb.lookup_objfile (name @r{[}, by_build_id{]})
4043 Look up @var{name}, a file name or build ID, in the list of objfiles
4044 for the current program space (@pxref{Progspaces In Python}).
4045 If the objfile is not found throw the Python @code{ValueError} exception.
4047 If @var{name} is a relative file name, then it will match any
4048 source file name with the same trailing components. For example, if
4049 @var{name} is @samp{gcc/expr.c}, then it will match source file
4050 name of @file{/build/trunk/gcc/expr.c}, but not
4051 @file{/build/trunk/libcpp/expr.c} or @file{/build/trunk/gcc/x-expr.c}.
4053 If @var{by_build_id} is provided and is @code{True} then @var{name}
4054 is the build ID of the objfile. Otherwise, @var{name} is a file name.
4055 This is supported only on some operating systems, notably those which use
4056 the ELF format for binary files and the @sc{gnu} Binutils. For more details
4057 about this feature, see the description of the @option{--build-id}
4058 command-line option in @ref{Options, , Command Line Options, ld.info,
4062 Each objfile is represented by an instance of the @code{gdb.Objfile}
4065 @defvar Objfile.filename
4066 The file name of the objfile as a string, with symbolic links resolved.
4068 The value is @code{None} if the objfile is no longer valid.
4069 See the @code{gdb.Objfile.is_valid} method, described below.
4072 @defvar Objfile.username
4073 The file name of the objfile as specified by the user as a string.
4075 The value is @code{None} if the objfile is no longer valid.
4076 See the @code{gdb.Objfile.is_valid} method, described below.
4079 @defvar Objfile.owner
4080 For separate debug info objfiles this is the corresponding @code{gdb.Objfile}
4081 object that debug info is being provided for.
4082 Otherwise this is @code{None}.
4083 Separate debug info objfiles are added with the
4084 @code{gdb.Objfile.add_separate_debug_file} method, described below.
4087 @defvar Objfile.build_id
4088 The build ID of the objfile as a string.
4089 If the objfile does not have a build ID then the value is @code{None}.
4091 This is supported only on some operating systems, notably those which use
4092 the ELF format for binary files and the @sc{gnu} Binutils. For more details
4093 about this feature, see the description of the @option{--build-id}
4094 command-line option in @ref{Options, , Command Line Options, ld.info,
4098 @defvar Objfile.progspace
4099 The containing program space of the objfile as a @code{gdb.Progspace}
4100 object. @xref{Progspaces In Python}.
4103 @defvar Objfile.pretty_printers
4104 The @code{pretty_printers} attribute is a list of functions. It is
4105 used to look up pretty-printers. A @code{Value} is passed to each
4106 function in order; if the function returns @code{None}, then the
4107 search continues. Otherwise, the return value should be an object
4108 which is used to format the value. @xref{Pretty Printing API}, for more
4112 @defvar Objfile.type_printers
4113 The @code{type_printers} attribute is a list of type printer objects.
4114 @xref{Type Printing API}, for more information.
4117 @defvar Objfile.frame_filters
4118 The @code{frame_filters} attribute is a dictionary of frame filter
4119 objects. @xref{Frame Filter API}, for more information.
4122 One may add arbitrary attributes to @code{gdb.Objfile} objects
4123 in the usual Python way.
4124 This is useful if, for example, one needs to do some extra record keeping
4125 associated with the objfile.
4127 In this contrived example we record the time when @value{GDBN}
4133 def new_objfile_handler(event):
4134 # Set the time_loaded attribute of the new objfile.
4135 event.new_objfile.time_loaded = datetime.datetime.today()
4136 gdb.events.new_objfile.connect(new_objfile_handler)
4139 Reading symbols from ./hello...done.
4140 (gdb) python print gdb.objfiles()[0].time_loaded
4141 2014-10-09 11:41:36.770345
4144 A @code{gdb.Objfile} object has the following methods:
4146 @defun Objfile.is_valid ()
4147 Returns @code{True} if the @code{gdb.Objfile} object is valid,
4148 @code{False} if not. A @code{gdb.Objfile} object can become invalid
4149 if the object file it refers to is not loaded in @value{GDBN} any
4150 longer. All other @code{gdb.Objfile} methods will throw an exception
4151 if it is invalid at the time the method is called.
4154 @defun Objfile.add_separate_debug_file (file)
4155 Add @var{file} to the list of files that @value{GDBN} will search for
4156 debug information for the objfile.
4157 This is useful when the debug info has been removed from the program
4158 and stored in a separate file. @value{GDBN} has built-in support for
4159 finding separate debug info files (@pxref{Separate Debug Files}), but if
4160 the file doesn't live in one of the standard places that @value{GDBN}
4161 searches then this function can be used to add a debug info file
4162 from a different place.
4165 @node Frames In Python
4166 @subsubsection Accessing inferior stack frames from Python.
4168 @cindex frames in python
4169 When the debugged program stops, @value{GDBN} is able to analyze its call
4170 stack (@pxref{Frames,,Stack frames}). The @code{gdb.Frame} class
4171 represents a frame in the stack. A @code{gdb.Frame} object is only valid
4172 while its corresponding frame exists in the inferior's stack. If you try
4173 to use an invalid frame object, @value{GDBN} will throw a @code{gdb.error}
4174 exception (@pxref{Exception Handling}).
4176 Two @code{gdb.Frame} objects can be compared for equality with the @code{==}
4180 (@value{GDBP}) python print gdb.newest_frame() == gdb.selected_frame ()
4184 The following frame-related functions are available in the @code{gdb} module:
4186 @findex gdb.selected_frame
4187 @defun gdb.selected_frame ()
4188 Return the selected frame object. (@pxref{Selection,,Selecting a Frame}).
4191 @findex gdb.newest_frame
4192 @defun gdb.newest_frame ()
4193 Return the newest frame object for the selected thread.
4196 @defun gdb.frame_stop_reason_string (reason)
4197 Return a string explaining the reason why @value{GDBN} stopped unwinding
4198 frames, as expressed by the given @var{reason} code (an integer, see the
4199 @code{unwind_stop_reason} method further down in this section).
4202 @findex gdb.invalidate_cached_frames
4203 @defun gdb.invalidate_cached_frames
4204 @value{GDBN} internally keeps a cache of the frames that have been
4205 unwound. This function invalidates this cache.
4207 This function should not generally be called by ordinary Python code.
4208 It is documented for the sake of completeness.
4211 A @code{gdb.Frame} object has the following methods:
4213 @defun Frame.is_valid ()
4214 Returns true if the @code{gdb.Frame} object is valid, false if not.
4215 A frame object can become invalid if the frame it refers to doesn't
4216 exist anymore in the inferior. All @code{gdb.Frame} methods will throw
4217 an exception if it is invalid at the time the method is called.
4220 @defun Frame.name ()
4221 Returns the function name of the frame, or @code{None} if it can't be
4225 @defun Frame.architecture ()
4226 Returns the @code{gdb.Architecture} object corresponding to the frame's
4227 architecture. @xref{Architectures In Python}.
4230 @defun Frame.type ()
4231 Returns the type of the frame. The value can be one of:
4233 @item gdb.NORMAL_FRAME
4234 An ordinary stack frame.
4236 @item gdb.DUMMY_FRAME
4237 A fake stack frame that was created by @value{GDBN} when performing an
4238 inferior function call.
4240 @item gdb.INLINE_FRAME
4241 A frame representing an inlined function. The function was inlined
4242 into a @code{gdb.NORMAL_FRAME} that is older than this one.
4244 @item gdb.TAILCALL_FRAME
4245 A frame representing a tail call. @xref{Tail Call Frames}.
4247 @item gdb.SIGTRAMP_FRAME
4248 A signal trampoline frame. This is the frame created by the OS when
4249 it calls into a signal handler.
4251 @item gdb.ARCH_FRAME
4252 A fake stack frame representing a cross-architecture call.
4254 @item gdb.SENTINEL_FRAME
4255 This is like @code{gdb.NORMAL_FRAME}, but it is only used for the
4260 @defun Frame.unwind_stop_reason ()
4261 Return an integer representing the reason why it's not possible to find
4262 more frames toward the outermost frame. Use
4263 @code{gdb.frame_stop_reason_string} to convert the value returned by this
4264 function to a string. The value can be one of:
4267 @item gdb.FRAME_UNWIND_NO_REASON
4268 No particular reason (older frames should be available).
4270 @item gdb.FRAME_UNWIND_NULL_ID
4271 The previous frame's analyzer returns an invalid result. This is no
4272 longer used by @value{GDBN}, and is kept only for backward
4275 @item gdb.FRAME_UNWIND_OUTERMOST
4276 This frame is the outermost.
4278 @item gdb.FRAME_UNWIND_UNAVAILABLE
4279 Cannot unwind further, because that would require knowing the
4280 values of registers or memory that have not been collected.
4282 @item gdb.FRAME_UNWIND_INNER_ID
4283 This frame ID looks like it ought to belong to a NEXT frame,
4284 but we got it for a PREV frame. Normally, this is a sign of
4285 unwinder failure. It could also indicate stack corruption.
4287 @item gdb.FRAME_UNWIND_SAME_ID
4288 This frame has the same ID as the previous one. That means
4289 that unwinding further would almost certainly give us another
4290 frame with exactly the same ID, so break the chain. Normally,
4291 this is a sign of unwinder failure. It could also indicate
4294 @item gdb.FRAME_UNWIND_NO_SAVED_PC
4295 The frame unwinder did not find any saved PC, but we needed
4296 one to unwind further.
4298 @item gdb.FRAME_UNWIND_MEMORY_ERROR
4299 The frame unwinder caused an error while trying to access memory.
4301 @item gdb.FRAME_UNWIND_FIRST_ERROR
4302 Any stop reason greater or equal to this value indicates some kind
4303 of error. This special value facilitates writing code that tests
4304 for errors in unwinding in a way that will work correctly even if
4305 the list of the other values is modified in future @value{GDBN}
4306 versions. Using it, you could write:
4308 reason = gdb.selected_frame().unwind_stop_reason ()
4309 reason_str = gdb.frame_stop_reason_string (reason)
4310 if reason >= gdb.FRAME_UNWIND_FIRST_ERROR:
4311 print "An error occured: %s" % reason_str
4318 Returns the frame's resume address.
4321 @defun Frame.block ()
4322 Return the frame's code block. @xref{Blocks In Python}.
4325 @defun Frame.function ()
4326 Return the symbol for the function corresponding to this frame.
4327 @xref{Symbols In Python}.
4330 @defun Frame.older ()
4331 Return the frame that called this frame.
4334 @defun Frame.newer ()
4335 Return the frame called by this frame.
4338 @defun Frame.find_sal ()
4339 Return the frame's symtab and line object.
4340 @xref{Symbol Tables In Python}.
4343 @defun Frame.read_register (register)
4344 Return the value of @var{register} in this frame. The @var{register}
4345 argument must be a string (e.g., @code{'sp'} or @code{'rax'}).
4346 Returns a @code{Gdb.Value} object. Throws an exception if @var{register}
4350 @defun Frame.read_var (variable @r{[}, block@r{]})
4351 Return the value of @var{variable} in this frame. If the optional
4352 argument @var{block} is provided, search for the variable from that
4353 block; otherwise start at the frame's current block (which is
4354 determined by the frame's current program counter). The @var{variable}
4355 argument must be a string or a @code{gdb.Symbol} object; @var{block} must be a
4356 @code{gdb.Block} object.
4359 @defun Frame.select ()
4360 Set this frame to be the selected frame. @xref{Stack, ,Examining the
4364 @node Blocks In Python
4365 @subsubsection Accessing blocks from Python.
4367 @cindex blocks in python
4370 In @value{GDBN}, symbols are stored in blocks. A block corresponds
4371 roughly to a scope in the source code. Blocks are organized
4372 hierarchically, and are represented individually in Python as a
4373 @code{gdb.Block}. Blocks rely on debugging information being
4376 A frame has a block. Please see @ref{Frames In Python}, for a more
4377 in-depth discussion of frames.
4379 The outermost block is known as the @dfn{global block}. The global
4380 block typically holds public global variables and functions.
4382 The block nested just inside the global block is the @dfn{static
4383 block}. The static block typically holds file-scoped variables and
4386 @value{GDBN} provides a method to get a block's superblock, but there
4387 is currently no way to examine the sub-blocks of a block, or to
4388 iterate over all the blocks in a symbol table (@pxref{Symbol Tables In
4391 Here is a short example that should help explain blocks:
4394 /* This is in the global block. */
4397 /* This is in the static block. */
4398 static int file_scope;
4400 /* 'function' is in the global block, and 'argument' is
4401 in a block nested inside of 'function'. */
4402 int function (int argument)
4404 /* 'local' is in a block inside 'function'. It may or may
4405 not be in the same block as 'argument'. */
4409 /* 'inner' is in a block whose superblock is the one holding
4413 /* If this call is expanded by the compiler, you may see
4414 a nested block here whose function is 'inline_function'
4415 and whose superblock is the one holding 'inner'. */
4421 A @code{gdb.Block} is iterable. The iterator returns the symbols
4422 (@pxref{Symbols In Python}) local to the block. Python programs
4423 should not assume that a specific block object will always contain a
4424 given symbol, since changes in @value{GDBN} features and
4425 infrastructure may cause symbols move across blocks in a symbol
4428 The following block-related functions are available in the @code{gdb}
4431 @findex gdb.block_for_pc
4432 @defun gdb.block_for_pc (pc)
4433 Return the innermost @code{gdb.Block} containing the given @var{pc}
4434 value. If the block cannot be found for the @var{pc} value specified,
4435 the function will return @code{None}.
4438 A @code{gdb.Block} object has the following methods:
4440 @defun Block.is_valid ()
4441 Returns @code{True} if the @code{gdb.Block} object is valid,
4442 @code{False} if not. A block object can become invalid if the block it
4443 refers to doesn't exist anymore in the inferior. All other
4444 @code{gdb.Block} methods will throw an exception if it is invalid at
4445 the time the method is called. The block's validity is also checked
4446 during iteration over symbols of the block.
4449 A @code{gdb.Block} object has the following attributes:
4452 The start address of the block. This attribute is not writable.
4456 The end address of the block. This attribute is not writable.
4459 @defvar Block.function
4460 The name of the block represented as a @code{gdb.Symbol}. If the
4461 block is not named, then this attribute holds @code{None}. This
4462 attribute is not writable.
4464 For ordinary function blocks, the superblock is the static block.
4465 However, you should note that it is possible for a function block to
4466 have a superblock that is not the static block -- for instance this
4467 happens for an inlined function.
4470 @defvar Block.superblock
4471 The block containing this block. If this parent block does not exist,
4472 this attribute holds @code{None}. This attribute is not writable.
4475 @defvar Block.global_block
4476 The global block associated with this block. This attribute is not
4480 @defvar Block.static_block
4481 The static block associated with this block. This attribute is not
4485 @defvar Block.is_global
4486 @code{True} if the @code{gdb.Block} object is a global block,
4487 @code{False} if not. This attribute is not
4491 @defvar Block.is_static
4492 @code{True} if the @code{gdb.Block} object is a static block,
4493 @code{False} if not. This attribute is not writable.
4496 @node Symbols In Python
4497 @subsubsection Python representation of Symbols.
4499 @cindex symbols in python
4502 @value{GDBN} represents every variable, function and type as an
4503 entry in a symbol table. @xref{Symbols, ,Examining the Symbol Table}.
4504 Similarly, Python represents these symbols in @value{GDBN} with the
4505 @code{gdb.Symbol} object.
4507 The following symbol-related functions are available in the @code{gdb}
4510 @findex gdb.lookup_symbol
4511 @defun gdb.lookup_symbol (name @r{[}, block @r{[}, domain@r{]]})
4512 This function searches for a symbol by name. The search scope can be
4513 restricted to the parameters defined in the optional domain and block
4516 @var{name} is the name of the symbol. It must be a string. The
4517 optional @var{block} argument restricts the search to symbols visible
4518 in that @var{block}. The @var{block} argument must be a
4519 @code{gdb.Block} object. If omitted, the block for the current frame
4520 is used. The optional @var{domain} argument restricts
4521 the search to the domain type. The @var{domain} argument must be a
4522 domain constant defined in the @code{gdb} module and described later
4525 The result is a tuple of two elements.
4526 The first element is a @code{gdb.Symbol} object or @code{None} if the symbol
4528 If the symbol is found, the second element is @code{True} if the symbol
4529 is a field of a method's object (e.g., @code{this} in C@t{++}),
4530 otherwise it is @code{False}.
4531 If the symbol is not found, the second element is @code{False}.
4534 @findex gdb.lookup_global_symbol
4535 @defun gdb.lookup_global_symbol (name @r{[}, domain@r{]})
4536 This function searches for a global symbol by name.
4537 The search scope can be restricted to by the domain argument.
4539 @var{name} is the name of the symbol. It must be a string.
4540 The optional @var{domain} argument restricts the search to the domain type.
4541 The @var{domain} argument must be a domain constant defined in the @code{gdb}
4542 module and described later in this chapter.
4544 The result is a @code{gdb.Symbol} object or @code{None} if the symbol
4548 A @code{gdb.Symbol} object has the following attributes:
4551 The type of the symbol or @code{None} if no type is recorded.
4552 This attribute is represented as a @code{gdb.Type} object.
4553 @xref{Types In Python}. This attribute is not writable.
4556 @defvar Symbol.symtab
4557 The symbol table in which the symbol appears. This attribute is
4558 represented as a @code{gdb.Symtab} object. @xref{Symbol Tables In
4559 Python}. This attribute is not writable.
4563 The line number in the source code at which the symbol was defined.
4568 The name of the symbol as a string. This attribute is not writable.
4571 @defvar Symbol.linkage_name
4572 The name of the symbol, as used by the linker (i.e., may be mangled).
4573 This attribute is not writable.
4576 @defvar Symbol.print_name
4577 The name of the symbol in a form suitable for output. This is either
4578 @code{name} or @code{linkage_name}, depending on whether the user
4579 asked @value{GDBN} to display demangled or mangled names.
4582 @defvar Symbol.addr_class
4583 The address class of the symbol. This classifies how to find the value
4584 of a symbol. Each address class is a constant defined in the
4585 @code{gdb} module and described later in this chapter.
4588 @defvar Symbol.needs_frame
4589 This is @code{True} if evaluating this symbol's value requires a frame
4590 (@pxref{Frames In Python}) and @code{False} otherwise. Typically,
4591 local variables will require a frame, but other symbols will not.
4594 @defvar Symbol.is_argument
4595 @code{True} if the symbol is an argument of a function.
4598 @defvar Symbol.is_constant
4599 @code{True} if the symbol is a constant.
4602 @defvar Symbol.is_function
4603 @code{True} if the symbol is a function or a method.
4606 @defvar Symbol.is_variable
4607 @code{True} if the symbol is a variable.
4610 A @code{gdb.Symbol} object has the following methods:
4612 @defun Symbol.is_valid ()
4613 Returns @code{True} if the @code{gdb.Symbol} object is valid,
4614 @code{False} if not. A @code{gdb.Symbol} object can become invalid if
4615 the symbol it refers to does not exist in @value{GDBN} any longer.
4616 All other @code{gdb.Symbol} methods will throw an exception if it is
4617 invalid at the time the method is called.
4620 @defun Symbol.value (@r{[}frame@r{]})
4621 Compute the value of the symbol, as a @code{gdb.Value}. For
4622 functions, this computes the address of the function, cast to the
4623 appropriate type. If the symbol requires a frame in order to compute
4624 its value, then @var{frame} must be given. If @var{frame} is not
4625 given, or if @var{frame} is invalid, then this method will throw an
4629 The available domain categories in @code{gdb.Symbol} are represented
4630 as constants in the @code{gdb} module:
4633 @vindex SYMBOL_UNDEF_DOMAIN
4634 @item gdb.SYMBOL_UNDEF_DOMAIN
4635 This is used when a domain has not been discovered or none of the
4636 following domains apply. This usually indicates an error either
4637 in the symbol information or in @value{GDBN}'s handling of symbols.
4639 @vindex SYMBOL_VAR_DOMAIN
4640 @item gdb.SYMBOL_VAR_DOMAIN
4641 This domain contains variables, function names, typedef names and enum
4644 @vindex SYMBOL_STRUCT_DOMAIN
4645 @item gdb.SYMBOL_STRUCT_DOMAIN
4646 This domain holds struct, union and enum type names.
4648 @vindex SYMBOL_LABEL_DOMAIN
4649 @item gdb.SYMBOL_LABEL_DOMAIN
4650 This domain contains names of labels (for gotos).
4652 @vindex SYMBOL_VARIABLES_DOMAIN
4653 @item gdb.SYMBOL_VARIABLES_DOMAIN
4654 This domain holds a subset of the @code{SYMBOLS_VAR_DOMAIN}; it
4655 contains everything minus functions and types.
4657 @vindex SYMBOL_FUNCTIONS_DOMAIN
4658 @item gdb.SYMBOL_FUNCTIONS_DOMAIN
4659 This domain contains all functions.
4661 @vindex SYMBOL_TYPES_DOMAIN
4662 @item gdb.SYMBOL_TYPES_DOMAIN
4663 This domain contains all types.
4666 The available address class categories in @code{gdb.Symbol} are represented
4667 as constants in the @code{gdb} module:
4670 @vindex SYMBOL_LOC_UNDEF
4671 @item gdb.SYMBOL_LOC_UNDEF
4672 If this is returned by address class, it indicates an error either in
4673 the symbol information or in @value{GDBN}'s handling of symbols.
4675 @vindex SYMBOL_LOC_CONST
4676 @item gdb.SYMBOL_LOC_CONST
4677 Value is constant int.
4679 @vindex SYMBOL_LOC_STATIC
4680 @item gdb.SYMBOL_LOC_STATIC
4681 Value is at a fixed address.
4683 @vindex SYMBOL_LOC_REGISTER
4684 @item gdb.SYMBOL_LOC_REGISTER
4685 Value is in a register.
4687 @vindex SYMBOL_LOC_ARG
4688 @item gdb.SYMBOL_LOC_ARG
4689 Value is an argument. This value is at the offset stored within the
4690 symbol inside the frame's argument list.
4692 @vindex SYMBOL_LOC_REF_ARG
4693 @item gdb.SYMBOL_LOC_REF_ARG
4694 Value address is stored in the frame's argument list. Just like
4695 @code{LOC_ARG} except that the value's address is stored at the
4696 offset, not the value itself.
4698 @vindex SYMBOL_LOC_REGPARM_ADDR
4699 @item gdb.SYMBOL_LOC_REGPARM_ADDR
4700 Value is a specified register. Just like @code{LOC_REGISTER} except
4701 the register holds the address of the argument instead of the argument
4704 @vindex SYMBOL_LOC_LOCAL
4705 @item gdb.SYMBOL_LOC_LOCAL
4706 Value is a local variable.
4708 @vindex SYMBOL_LOC_TYPEDEF
4709 @item gdb.SYMBOL_LOC_TYPEDEF
4710 Value not used. Symbols in the domain @code{SYMBOL_STRUCT_DOMAIN} all
4713 @vindex SYMBOL_LOC_BLOCK
4714 @item gdb.SYMBOL_LOC_BLOCK
4717 @vindex SYMBOL_LOC_CONST_BYTES
4718 @item gdb.SYMBOL_LOC_CONST_BYTES
4719 Value is a byte-sequence.
4721 @vindex SYMBOL_LOC_UNRESOLVED
4722 @item gdb.SYMBOL_LOC_UNRESOLVED
4723 Value is at a fixed address, but the address of the variable has to be
4724 determined from the minimal symbol table whenever the variable is
4727 @vindex SYMBOL_LOC_OPTIMIZED_OUT
4728 @item gdb.SYMBOL_LOC_OPTIMIZED_OUT
4729 The value does not actually exist in the program.
4731 @vindex SYMBOL_LOC_COMPUTED
4732 @item gdb.SYMBOL_LOC_COMPUTED
4733 The value's address is a computed location.
4736 @node Symbol Tables In Python
4737 @subsubsection Symbol table representation in Python.
4739 @cindex symbol tables in python
4741 @tindex gdb.Symtab_and_line
4743 Access to symbol table data maintained by @value{GDBN} on the inferior
4744 is exposed to Python via two objects: @code{gdb.Symtab_and_line} and
4745 @code{gdb.Symtab}. Symbol table and line data for a frame is returned
4746 from the @code{find_sal} method in @code{gdb.Frame} object.
4747 @xref{Frames In Python}.
4749 For more information on @value{GDBN}'s symbol table management, see
4750 @ref{Symbols, ,Examining the Symbol Table}, for more information.
4752 A @code{gdb.Symtab_and_line} object has the following attributes:
4754 @defvar Symtab_and_line.symtab
4755 The symbol table object (@code{gdb.Symtab}) for this frame.
4756 This attribute is not writable.
4759 @defvar Symtab_and_line.pc
4760 Indicates the start of the address range occupied by code for the
4761 current source line. This attribute is not writable.
4764 @defvar Symtab_and_line.last
4765 Indicates the end of the address range occupied by code for the current
4766 source line. This attribute is not writable.
4769 @defvar Symtab_and_line.line
4770 Indicates the current line number for this object. This
4771 attribute is not writable.
4774 A @code{gdb.Symtab_and_line} object has the following methods:
4776 @defun Symtab_and_line.is_valid ()
4777 Returns @code{True} if the @code{gdb.Symtab_and_line} object is valid,
4778 @code{False} if not. A @code{gdb.Symtab_and_line} object can become
4779 invalid if the Symbol table and line object it refers to does not
4780 exist in @value{GDBN} any longer. All other
4781 @code{gdb.Symtab_and_line} methods will throw an exception if it is
4782 invalid at the time the method is called.
4785 A @code{gdb.Symtab} object has the following attributes:
4787 @defvar Symtab.filename
4788 The symbol table's source filename. This attribute is not writable.
4791 @defvar Symtab.objfile
4792 The symbol table's backing object file. @xref{Objfiles In Python}.
4793 This attribute is not writable.
4796 @defvar Symtab.producer
4797 The name and possibly version number of the program that
4798 compiled the code in the symbol table.
4799 The contents of this string is up to the compiler.
4800 If no producer information is available then @code{None} is returned.
4801 This attribute is not writable.
4804 A @code{gdb.Symtab} object has the following methods:
4806 @defun Symtab.is_valid ()
4807 Returns @code{True} if the @code{gdb.Symtab} object is valid,
4808 @code{False} if not. A @code{gdb.Symtab} object can become invalid if
4809 the symbol table it refers to does not exist in @value{GDBN} any
4810 longer. All other @code{gdb.Symtab} methods will throw an exception
4811 if it is invalid at the time the method is called.
4814 @defun Symtab.fullname ()
4815 Return the symbol table's source absolute file name.
4818 @defun Symtab.global_block ()
4819 Return the global block of the underlying symbol table.
4820 @xref{Blocks In Python}.
4823 @defun Symtab.static_block ()
4824 Return the static block of the underlying symbol table.
4825 @xref{Blocks In Python}.
4828 @defun Symtab.linetable ()
4829 Return the line table associated with the symbol table.
4830 @xref{Line Tables In Python}.
4833 @node Line Tables In Python
4834 @subsubsection Manipulating line tables using Python
4836 @cindex line tables in python
4837 @tindex gdb.LineTable
4839 Python code can request and inspect line table information from a
4840 symbol table that is loaded in @value{GDBN}. A line table is a
4841 mapping of source lines to their executable locations in memory. To
4842 acquire the line table information for a particular symbol table, use
4843 the @code{linetable} function (@pxref{Symbol Tables In Python}).
4845 A @code{gdb.LineTable} is iterable. The iterator returns
4846 @code{LineTableEntry} objects that correspond to the source line and
4847 address for each line table entry. @code{LineTableEntry} objects have
4848 the following attributes:
4850 @defvar LineTableEntry.line
4851 The source line number for this line table entry. This number
4852 corresponds to the actual line of source. This attribute is not
4856 @defvar LineTableEntry.pc
4857 The address that is associated with the line table entry where the
4858 executable code for that source line resides in memory. This
4859 attribute is not writable.
4862 As there can be multiple addresses for a single source line, you may
4863 receive multiple @code{LineTableEntry} objects with matching
4864 @code{line} attributes, but with different @code{pc} attributes. The
4865 iterator is sorted in ascending @code{pc} order. Here is a small
4866 example illustrating iterating over a line table.
4869 symtab = gdb.selected_frame().find_sal().symtab
4870 linetable = symtab.linetable()
4871 for line in linetable:
4872 print "Line: "+str(line.line)+" Address: "+hex(line.pc)
4875 This will have the following output:
4878 Line: 33 Address: 0x4005c8L
4879 Line: 37 Address: 0x4005caL
4880 Line: 39 Address: 0x4005d2L
4881 Line: 40 Address: 0x4005f8L
4882 Line: 42 Address: 0x4005ffL
4883 Line: 44 Address: 0x400608L
4884 Line: 42 Address: 0x40060cL
4885 Line: 45 Address: 0x400615L
4888 In addition to being able to iterate over a @code{LineTable}, it also
4889 has the following direct access methods:
4891 @defun LineTable.line (line)
4892 Return a Python @code{Tuple} of @code{LineTableEntry} objects for any
4893 entries in the line table for the given @var{line}, which specifies
4894 the source code line. If there are no entries for that source code
4895 @var{line}, the Python @code{None} is returned.
4898 @defun LineTable.has_line (line)
4899 Return a Python @code{Boolean} indicating whether there is an entry in
4900 the line table for this source line. Return @code{True} if an entry
4901 is found, or @code{False} if not.
4904 @defun LineTable.source_lines ()
4905 Return a Python @code{List} of the source line numbers in the symbol
4906 table. Only lines with executable code locations are returned. The
4907 contents of the @code{List} will just be the source line entries
4908 represented as Python @code{Long} values.
4911 @node Breakpoints In Python
4912 @subsubsection Manipulating breakpoints using Python
4914 @cindex breakpoints in python
4915 @tindex gdb.Breakpoint
4917 Python code can manipulate breakpoints via the @code{gdb.Breakpoint}
4920 A breakpoint can be created using one of the two forms of the
4921 @code{gdb.Breakpoint} constructor. The first one accepts a string
4922 like one would pass to the @code{break}
4923 (@pxref{Set Breaks,,Setting Breakpoints}) and @code{watch}
4924 (@pxref{Set Watchpoints, , Setting Watchpoints}) commands, and can be used to
4925 create both breakpoints and watchpoints. The second accepts separate Python
4926 arguments similar to @ref{Explicit Locations}, and can only be used to create
4929 @defun Breakpoint.__init__ (spec @r{[}, type @r{][}, wp_class @r{][}, internal @r{][}, temporary @r{][}, qualified @r{]})
4930 Create a new breakpoint according to @var{spec}, which is a string naming the
4931 location of a breakpoint, or an expression that defines a watchpoint. The
4932 string should describe a location in a format recognized by the @code{break}
4933 command (@pxref{Set Breaks,,Setting Breakpoints}) or, in the case of a
4934 watchpoint, by the @code{watch} command
4935 (@pxref{Set Watchpoints, , Setting Watchpoints}).
4937 The optional @var{type} argument specifies the type of the breakpoint to create,
4940 The optional @var{wp_class} argument defines the class of watchpoint to create,
4941 if @var{type} is @code{gdb.BP_WATCHPOINT}. If @var{wp_class} is omitted, it
4942 defaults to @code{gdb.WP_WRITE}.
4944 The optional @var{internal} argument allows the breakpoint to become invisible
4945 to the user. The breakpoint will neither be reported when created, nor will it
4946 be listed in the output from @code{info breakpoints} (but will be listed with
4947 the @code{maint info breakpoints} command).
4949 The optional @var{temporary} argument makes the breakpoint a temporary
4950 breakpoint. Temporary breakpoints are deleted after they have been hit. Any
4951 further access to the Python breakpoint after it has been hit will result in a
4952 runtime error (as that breakpoint has now been automatically deleted).
4954 The optional @var{qualified} argument is a boolean that allows interpreting
4955 the function passed in @code{spec} as a fully-qualified name. It is equivalent
4956 to @code{break}'s @code{-qualified} flag (@pxref{Linespec Locations} and
4957 @ref{Explicit Locations}).
4961 @defun Breakpoint.__init__ (@r{[} source @r{][}, function @r{][}, label @r{][}, line @r{]}, @r{][} internal @r{][}, temporary @r{][}, qualified @r{]})
4962 This second form of creating a new breakpoint specifies the explicit
4963 location (@pxref{Explicit Locations}) using keywords. The new breakpoint will
4964 be created in the specified source file @var{source}, at the specified
4965 @var{function}, @var{label} and @var{line}.
4967 @var{internal}, @var{temporary} and @var{qualified} have the same usage as
4968 explained previously.
4971 The available types are represented by constants defined in the @code{gdb}
4975 @vindex BP_BREAKPOINT
4976 @item gdb.BP_BREAKPOINT
4977 Normal code breakpoint.
4979 @vindex BP_WATCHPOINT
4980 @item gdb.BP_WATCHPOINT
4981 Watchpoint breakpoint.
4983 @vindex BP_HARDWARE_WATCHPOINT
4984 @item gdb.BP_HARDWARE_WATCHPOINT
4985 Hardware assisted watchpoint.
4987 @vindex BP_READ_WATCHPOINT
4988 @item gdb.BP_READ_WATCHPOINT
4989 Hardware assisted read watchpoint.
4991 @vindex BP_ACCESS_WATCHPOINT
4992 @item gdb.BP_ACCESS_WATCHPOINT
4993 Hardware assisted access watchpoint.
4996 The available watchpoint types represented by constants are defined in the
5002 Read only watchpoint.
5006 Write only watchpoint.
5010 Read/Write watchpoint.
5013 @defun Breakpoint.stop (self)
5014 The @code{gdb.Breakpoint} class can be sub-classed and, in
5015 particular, you may choose to implement the @code{stop} method.
5016 If this method is defined in a sub-class of @code{gdb.Breakpoint},
5017 it will be called when the inferior reaches any location of a
5018 breakpoint which instantiates that sub-class. If the method returns
5019 @code{True}, the inferior will be stopped at the location of the
5020 breakpoint, otherwise the inferior will continue.
5022 If there are multiple breakpoints at the same location with a
5023 @code{stop} method, each one will be called regardless of the
5024 return status of the previous. This ensures that all @code{stop}
5025 methods have a chance to execute at that location. In this scenario
5026 if one of the methods returns @code{True} but the others return
5027 @code{False}, the inferior will still be stopped.
5029 You should not alter the execution state of the inferior (i.e.@:, step,
5030 next, etc.), alter the current frame context (i.e.@:, change the current
5031 active frame), or alter, add or delete any breakpoint. As a general
5032 rule, you should not alter any data within @value{GDBN} or the inferior
5035 Example @code{stop} implementation:
5038 class MyBreakpoint (gdb.Breakpoint):
5040 inf_val = gdb.parse_and_eval("foo")
5047 @defun Breakpoint.is_valid ()
5048 Return @code{True} if this @code{Breakpoint} object is valid,
5049 @code{False} otherwise. A @code{Breakpoint} object can become invalid
5050 if the user deletes the breakpoint. In this case, the object still
5051 exists, but the underlying breakpoint does not. In the cases of
5052 watchpoint scope, the watchpoint remains valid even if execution of the
5053 inferior leaves the scope of that watchpoint.
5056 @defun Breakpoint.delete ()
5057 Permanently deletes the @value{GDBN} breakpoint. This also
5058 invalidates the Python @code{Breakpoint} object. Any further access
5059 to this object's attributes or methods will raise an error.
5062 @defvar Breakpoint.enabled
5063 This attribute is @code{True} if the breakpoint is enabled, and
5064 @code{False} otherwise. This attribute is writable. You can use it to enable
5065 or disable the breakpoint.
5068 @defvar Breakpoint.silent
5069 This attribute is @code{True} if the breakpoint is silent, and
5070 @code{False} otherwise. This attribute is writable.
5072 Note that a breakpoint can also be silent if it has commands and the
5073 first command is @code{silent}. This is not reported by the
5074 @code{silent} attribute.
5077 @defvar Breakpoint.pending
5078 This attribute is @code{True} if the breakpoint is pending, and
5079 @code{False} otherwise. @xref{Set Breaks}. This attribute is
5083 @anchor{python_breakpoint_thread}
5084 @defvar Breakpoint.thread
5085 If the breakpoint is thread-specific, this attribute holds the
5086 thread's global id. If the breakpoint is not thread-specific, this
5087 attribute is @code{None}. This attribute is writable.
5090 @defvar Breakpoint.task
5091 If the breakpoint is Ada task-specific, this attribute holds the Ada task
5092 id. If the breakpoint is not task-specific (or the underlying
5093 language is not Ada), this attribute is @code{None}. This attribute
5097 @defvar Breakpoint.ignore_count
5098 This attribute holds the ignore count for the breakpoint, an integer.
5099 This attribute is writable.
5102 @defvar Breakpoint.number
5103 This attribute holds the breakpoint's number --- the identifier used by
5104 the user to manipulate the breakpoint. This attribute is not writable.
5107 @defvar Breakpoint.type
5108 This attribute holds the breakpoint's type --- the identifier used to
5109 determine the actual breakpoint type or use-case. This attribute is not
5113 @defvar Breakpoint.visible
5114 This attribute tells whether the breakpoint is visible to the user
5115 when set, or when the @samp{info breakpoints} command is run. This
5116 attribute is not writable.
5119 @defvar Breakpoint.temporary
5120 This attribute indicates whether the breakpoint was created as a
5121 temporary breakpoint. Temporary breakpoints are automatically deleted
5122 after that breakpoint has been hit. Access to this attribute, and all
5123 other attributes and functions other than the @code{is_valid}
5124 function, will result in an error after the breakpoint has been hit
5125 (as it has been automatically deleted). This attribute is not
5129 @defvar Breakpoint.hit_count
5130 This attribute holds the hit count for the breakpoint, an integer.
5131 This attribute is writable, but currently it can only be set to zero.
5134 @defvar Breakpoint.location
5135 This attribute holds the location of the breakpoint, as specified by
5136 the user. It is a string. If the breakpoint does not have a location
5137 (that is, it is a watchpoint) the attribute's value is @code{None}. This
5138 attribute is not writable.
5141 @defvar Breakpoint.expression
5142 This attribute holds a breakpoint expression, as specified by
5143 the user. It is a string. If the breakpoint does not have an
5144 expression (the breakpoint is not a watchpoint) the attribute's value
5145 is @code{None}. This attribute is not writable.
5148 @defvar Breakpoint.condition
5149 This attribute holds the condition of the breakpoint, as specified by
5150 the user. It is a string. If there is no condition, this attribute's
5151 value is @code{None}. This attribute is writable.
5154 @defvar Breakpoint.commands
5155 This attribute holds the commands attached to the breakpoint. If
5156 there are commands, this attribute's value is a string holding all the
5157 commands, separated by newlines. If there are no commands, this
5158 attribute is @code{None}. This attribute is writable.
5161 @node Finish Breakpoints in Python
5162 @subsubsection Finish Breakpoints
5164 @cindex python finish breakpoints
5165 @tindex gdb.FinishBreakpoint
5167 A finish breakpoint is a temporary breakpoint set at the return address of
5168 a frame, based on the @code{finish} command. @code{gdb.FinishBreakpoint}
5169 extends @code{gdb.Breakpoint}. The underlying breakpoint will be disabled
5170 and deleted when the execution will run out of the breakpoint scope (i.e.@:
5171 @code{Breakpoint.stop} or @code{FinishBreakpoint.out_of_scope} triggered).
5172 Finish breakpoints are thread specific and must be create with the right
5175 @defun FinishBreakpoint.__init__ (@r{[}frame@r{]} @r{[}, internal@r{]})
5176 Create a finish breakpoint at the return address of the @code{gdb.Frame}
5177 object @var{frame}. If @var{frame} is not provided, this defaults to the
5178 newest frame. The optional @var{internal} argument allows the breakpoint to
5179 become invisible to the user. @xref{Breakpoints In Python}, for further
5180 details about this argument.
5183 @defun FinishBreakpoint.out_of_scope (self)
5184 In some circumstances (e.g.@: @code{longjmp}, C@t{++} exceptions, @value{GDBN}
5185 @code{return} command, @dots{}), a function may not properly terminate, and
5186 thus never hit the finish breakpoint. When @value{GDBN} notices such a
5187 situation, the @code{out_of_scope} callback will be triggered.
5189 You may want to sub-class @code{gdb.FinishBreakpoint} and override this
5193 class MyFinishBreakpoint (gdb.FinishBreakpoint)
5195 print "normal finish"
5198 def out_of_scope ():
5199 print "abnormal finish"
5203 @defvar FinishBreakpoint.return_value
5204 When @value{GDBN} is stopped at a finish breakpoint and the frame
5205 used to build the @code{gdb.FinishBreakpoint} object had debug symbols, this
5206 attribute will contain a @code{gdb.Value} object corresponding to the return
5207 value of the function. The value will be @code{None} if the function return
5208 type is @code{void} or if the return value was not computable. This attribute
5212 @node Lazy Strings In Python
5213 @subsubsection Python representation of lazy strings.
5215 @cindex lazy strings in python
5216 @tindex gdb.LazyString
5218 A @dfn{lazy string} is a string whose contents is not retrieved or
5219 encoded until it is needed.
5221 A @code{gdb.LazyString} is represented in @value{GDBN} as an
5222 @code{address} that points to a region of memory, an @code{encoding}
5223 that will be used to encode that region of memory, and a @code{length}
5224 to delimit the region of memory that represents the string. The
5225 difference between a @code{gdb.LazyString} and a string wrapped within
5226 a @code{gdb.Value} is that a @code{gdb.LazyString} will be treated
5227 differently by @value{GDBN} when printing. A @code{gdb.LazyString} is
5228 retrieved and encoded during printing, while a @code{gdb.Value}
5229 wrapping a string is immediately retrieved and encoded on creation.
5231 A @code{gdb.LazyString} object has the following functions:
5233 @defun LazyString.value ()
5234 Convert the @code{gdb.LazyString} to a @code{gdb.Value}. This value
5235 will point to the string in memory, but will lose all the delayed
5236 retrieval, encoding and handling that @value{GDBN} applies to a
5237 @code{gdb.LazyString}.
5240 @defvar LazyString.address
5241 This attribute holds the address of the string. This attribute is not
5245 @defvar LazyString.length
5246 This attribute holds the length of the string in characters. If the
5247 length is -1, then the string will be fetched and encoded up to the
5248 first null of appropriate width. This attribute is not writable.
5251 @defvar LazyString.encoding
5252 This attribute holds the encoding that will be applied to the string
5253 when the string is printed by @value{GDBN}. If the encoding is not
5254 set, or contains an empty string, then @value{GDBN} will select the
5255 most appropriate encoding when the string is printed. This attribute
5259 @defvar LazyString.type
5260 This attribute holds the type that is represented by the lazy string's
5261 type. For a lazy string this is a pointer or array type. To
5262 resolve this to the lazy string's character type, use the type's
5263 @code{target} method. @xref{Types In Python}. This attribute is not
5267 @node Architectures In Python
5268 @subsubsection Python representation of architectures
5269 @cindex Python architectures
5271 @value{GDBN} uses architecture specific parameters and artifacts in a
5272 number of its various computations. An architecture is represented
5273 by an instance of the @code{gdb.Architecture} class.
5275 A @code{gdb.Architecture} class has the following methods:
5277 @defun Architecture.name ()
5278 Return the name (string value) of the architecture.
5281 @defun Architecture.disassemble (@var{start_pc} @r{[}, @var{end_pc} @r{[}, @var{count}@r{]]})
5282 Return a list of disassembled instructions starting from the memory
5283 address @var{start_pc}. The optional arguments @var{end_pc} and
5284 @var{count} determine the number of instructions in the returned list.
5285 If both the optional arguments @var{end_pc} and @var{count} are
5286 specified, then a list of at most @var{count} disassembled instructions
5287 whose start address falls in the closed memory address interval from
5288 @var{start_pc} to @var{end_pc} are returned. If @var{end_pc} is not
5289 specified, but @var{count} is specified, then @var{count} number of
5290 instructions starting from the address @var{start_pc} are returned. If
5291 @var{count} is not specified but @var{end_pc} is specified, then all
5292 instructions whose start address falls in the closed memory address
5293 interval from @var{start_pc} to @var{end_pc} are returned. If neither
5294 @var{end_pc} nor @var{count} are specified, then a single instruction at
5295 @var{start_pc} is returned. For all of these cases, each element of the
5296 returned list is a Python @code{dict} with the following string keys:
5301 The value corresponding to this key is a Python long integer capturing
5302 the memory address of the instruction.
5305 The value corresponding to this key is a string value which represents
5306 the instruction with assembly language mnemonics. The assembly
5307 language flavor used is the same as that specified by the current CLI
5308 variable @code{disassembly-flavor}. @xref{Machine Code}.
5311 The value corresponding to this key is the length (integer value) of the
5312 instruction in bytes.
5317 @node Python Auto-loading
5318 @subsection Python Auto-loading
5319 @cindex Python auto-loading
5321 When a new object file is read (for example, due to the @code{file}
5322 command, or because the inferior has loaded a shared library),
5323 @value{GDBN} will look for Python support scripts in several ways:
5324 @file{@var{objfile}-gdb.py} and @code{.debug_gdb_scripts} section.
5325 @xref{Auto-loading extensions}.
5327 The auto-loading feature is useful for supplying application-specific
5328 debugging commands and scripts.
5330 Auto-loading can be enabled or disabled,
5331 and the list of auto-loaded scripts can be printed.
5334 @anchor{set auto-load python-scripts}
5335 @kindex set auto-load python-scripts
5336 @item set auto-load python-scripts [on|off]
5337 Enable or disable the auto-loading of Python scripts.
5339 @anchor{show auto-load python-scripts}
5340 @kindex show auto-load python-scripts
5341 @item show auto-load python-scripts
5342 Show whether auto-loading of Python scripts is enabled or disabled.
5344 @anchor{info auto-load python-scripts}
5345 @kindex info auto-load python-scripts
5346 @cindex print list of auto-loaded Python scripts
5347 @item info auto-load python-scripts [@var{regexp}]
5348 Print the list of all Python scripts that @value{GDBN} auto-loaded.
5350 Also printed is the list of Python scripts that were mentioned in
5351 the @code{.debug_gdb_scripts} section and were either not found
5352 (@pxref{dotdebug_gdb_scripts section}) or were not auto-loaded due to
5353 @code{auto-load safe-path} rejection (@pxref{Auto-loading}).
5354 This is useful because their names are not printed when @value{GDBN}
5355 tries to load them and fails. There may be many of them, and printing
5356 an error message for each one is problematic.
5358 If @var{regexp} is supplied only Python scripts with matching names are printed.
5363 (gdb) info auto-load python-scripts
5365 Yes py-section-script.py
5366 full name: /tmp/py-section-script.py
5367 No my-foo-pretty-printers.py
5371 When reading an auto-loaded file or script, @value{GDBN} sets the
5372 @dfn{current objfile}. This is available via the @code{gdb.current_objfile}
5373 function (@pxref{Objfiles In Python}). This can be useful for
5374 registering objfile-specific pretty-printers and frame-filters.
5376 @node Python modules
5377 @subsection Python modules
5378 @cindex python modules
5380 @value{GDBN} comes with several modules to assist writing Python code.
5383 * gdb.printing:: Building and registering pretty-printers.
5384 * gdb.types:: Utilities for working with types.
5385 * gdb.prompt:: Utilities for prompt value substitution.
5389 @subsubsection gdb.printing
5390 @cindex gdb.printing
5392 This module provides a collection of utilities for working with
5396 @item PrettyPrinter (@var{name}, @var{subprinters}=None)
5397 This class specifies the API that makes @samp{info pretty-printer},
5398 @samp{enable pretty-printer} and @samp{disable pretty-printer} work.
5399 Pretty-printers should generally inherit from this class.
5401 @item SubPrettyPrinter (@var{name})
5402 For printers that handle multiple types, this class specifies the
5403 corresponding API for the subprinters.
5405 @item RegexpCollectionPrettyPrinter (@var{name})
5406 Utility class for handling multiple printers, all recognized via
5407 regular expressions.
5408 @xref{Writing a Pretty-Printer}, for an example.
5410 @item FlagEnumerationPrinter (@var{name})
5411 A pretty-printer which handles printing of @code{enum} values. Unlike
5412 @value{GDBN}'s built-in @code{enum} printing, this printer attempts to
5413 work properly when there is some overlap between the enumeration
5414 constants. The argument @var{name} is the name of the printer and
5415 also the name of the @code{enum} type to look up.
5417 @item register_pretty_printer (@var{obj}, @var{printer}, @var{replace}=False)
5418 Register @var{printer} with the pretty-printer list of @var{obj}.
5419 If @var{replace} is @code{True} then any existing copy of the printer
5420 is replaced. Otherwise a @code{RuntimeError} exception is raised
5421 if a printer with the same name already exists.
5425 @subsubsection gdb.types
5428 This module provides a collection of utilities for working with
5429 @code{gdb.Type} objects.
5432 @item get_basic_type (@var{type})
5433 Return @var{type} with const and volatile qualifiers stripped,
5434 and with typedefs and C@t{++} references converted to the underlying type.
5439 typedef const int const_int;
5441 const_int& foo_ref (foo);
5442 int main () @{ return 0; @}
5449 (gdb) python import gdb.types
5450 (gdb) python foo_ref = gdb.parse_and_eval("foo_ref")
5451 (gdb) python print gdb.types.get_basic_type(foo_ref.type)
5455 @item has_field (@var{type}, @var{field})
5456 Return @code{True} if @var{type}, assumed to be a type with fields
5457 (e.g., a structure or union), has field @var{field}.
5459 @item make_enum_dict (@var{enum_type})
5460 Return a Python @code{dictionary} type produced from @var{enum_type}.
5462 @item deep_items (@var{type})
5463 Returns a Python iterator similar to the standard
5464 @code{gdb.Type.iteritems} method, except that the iterator returned
5465 by @code{deep_items} will recursively traverse anonymous struct or
5466 union fields. For example:
5480 Then in @value{GDBN}:
5482 (@value{GDBP}) python import gdb.types
5483 (@value{GDBP}) python struct_a = gdb.lookup_type("struct A")
5484 (@value{GDBP}) python print struct_a.keys ()
5486 (@value{GDBP}) python print [k for k,v in gdb.types.deep_items(struct_a)]
5487 @{['a', 'b0', 'b1']@}
5490 @item get_type_recognizers ()
5491 Return a list of the enabled type recognizers for the current context.
5492 This is called by @value{GDBN} during the type-printing process
5493 (@pxref{Type Printing API}).
5495 @item apply_type_recognizers (recognizers, type_obj)
5496 Apply the type recognizers, @var{recognizers}, to the type object
5497 @var{type_obj}. If any recognizer returns a string, return that
5498 string. Otherwise, return @code{None}. This is called by
5499 @value{GDBN} during the type-printing process (@pxref{Type Printing
5502 @item register_type_printer (locus, printer)
5503 This is a convenience function to register a type printer
5504 @var{printer}. The printer must implement the type printer protocol.
5505 The @var{locus} argument is either a @code{gdb.Objfile}, in which case
5506 the printer is registered with that objfile; a @code{gdb.Progspace},
5507 in which case the printer is registered with that progspace; or
5508 @code{None}, in which case the printer is registered globally.
5511 This is a base class that implements the type printer protocol. Type
5512 printers are encouraged, but not required, to derive from this class.
5513 It defines a constructor:
5515 @defmethod TypePrinter __init__ (self, name)
5516 Initialize the type printer with the given name. The new printer
5517 starts in the enabled state.
5523 @subsubsection gdb.prompt
5526 This module provides a method for prompt value-substitution.
5529 @item substitute_prompt (@var{string})
5530 Return @var{string} with escape sequences substituted by values. Some
5531 escape sequences take arguments. You can specify arguments inside
5532 ``@{@}'' immediately following the escape sequence.
5534 The escape sequences you can pass to this function are:
5538 Substitute a backslash.
5540 Substitute an ESC character.
5542 Substitute the selected frame; an argument names a frame parameter.
5544 Substitute a newline.
5546 Substitute a parameter's value; the argument names the parameter.
5548 Substitute a carriage return.
5550 Substitute the selected thread; an argument names a thread parameter.
5552 Substitute the version of GDB.
5554 Substitute the current working directory.
5556 Begin a sequence of non-printing characters. These sequences are
5557 typically used with the ESC character, and are not counted in the string
5558 length. Example: ``\[\e[0;34m\](gdb)\[\e[0m\]'' will return a
5559 blue-colored ``(gdb)'' prompt where the length is five.
5561 End a sequence of non-printing characters.
5567 substitute_prompt (``frame: \f,
5568 print arguments: \p@{print frame-arguments@}'')
5571 @exdent will return the string:
5574 "frame: main, print arguments: scalars"