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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
533 @code{gdb.Command}, or functions via @code{gdb.Function}, it is useful
534 to be able to throw an exception that doesn't cause a traceback to be
535 printed. For example, the user may have invoked the command
536 incorrectly. @value{GDBN} provides a special exception class that can
537 be used for this purpose.
541 When thrown from a command or function, this exception will cause the
542 command or function to fail, but the Python stack will not be
543 displayed. @value{GDBN} does not throw this exception itself, but
544 rather recognizes it when thrown from user Python code. Example:
548 >class HelloWorld (gdb.Command):
549 > """Greet the whole world."""
550 > def __init__ (self):
551 > super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)
552 > def invoke (self, args, from_tty):
553 > argv = gdb.string_to_argv (args)
554 > if len (argv) != 0:
555 > raise gdb.GdbError ("hello-world takes no arguments")
556 > print "Hello, World!"
560 hello-world takes no arguments
564 @node Values From Inferior
565 @subsubsection Values From Inferior
566 @cindex values from inferior, with Python
567 @cindex python, working with values from inferior
569 @cindex @code{gdb.Value}
570 @value{GDBN} provides values it obtains from the inferior program in
571 an object of type @code{gdb.Value}. @value{GDBN} uses this object
572 for its internal bookkeeping of the inferior's values, and for
573 fetching values when necessary.
575 Inferior values that are simple scalars can be used directly in
576 Python expressions that are valid for the value's data type. Here's
577 an example for an integer or floating-point value @code{some_val}:
584 As result of this, @code{bar} will also be a @code{gdb.Value} object
585 whose values are of the same type as those of @code{some_val}. Valid
586 Python operations can also be performed on @code{gdb.Value} objects
587 representing a @code{struct} or @code{class} object. For such cases,
588 the overloaded operator (if present), is used to perform the operation.
589 For example, if @code{val1} and @code{val2} are @code{gdb.Value} objects
590 representing instances of a @code{class} which overloads the @code{+}
591 operator, then one can use the @code{+} operator in their Python script
599 The result of the operation @code{val3} is also a @code{gdb.Value}
600 object corresponding to the value returned by the overloaded @code{+}
601 operator. In general, overloaded operators are invoked for the
602 following operations: @code{+} (binary addition), @code{-} (binary
603 subtraction), @code{*} (multiplication), @code{/}, @code{%}, @code{<<},
604 @code{>>}, @code{|}, @code{&}, @code{^}.
606 Inferior values that are structures or instances of some class can
607 be accessed using the Python @dfn{dictionary syntax}. For example, if
608 @code{some_val} is a @code{gdb.Value} instance holding a structure, you
609 can access its @code{foo} element with:
612 bar = some_val['foo']
615 @cindex getting structure elements using gdb.Field objects as subscripts
616 Again, @code{bar} will also be a @code{gdb.Value} object. Structure
617 elements can also be accessed by using @code{gdb.Field} objects as
618 subscripts (@pxref{Types In Python}, for more information on
619 @code{gdb.Field} objects). For example, if @code{foo_field} is a
620 @code{gdb.Field} object corresponding to element @code{foo} of the above
621 structure, then @code{bar} can also be accessed as follows:
624 bar = some_val[foo_field]
627 A @code{gdb.Value} that represents a function can be executed via
628 inferior function call. Any arguments provided to the call must match
629 the function's prototype, and must be provided in the order specified
632 For example, @code{some_val} is a @code{gdb.Value} instance
633 representing a function that takes two integers as arguments. To
634 execute this function, call it like so:
637 result = some_val (10,20)
640 Any values returned from a function call will be stored as a
643 The following attributes are provided:
645 @defvar Value.address
646 If this object is addressable, this read-only attribute holds a
647 @code{gdb.Value} object representing the address. Otherwise,
648 this attribute holds @code{None}.
651 @cindex optimized out value in Python
652 @defvar Value.is_optimized_out
653 This read-only boolean attribute is true if the compiler optimized out
654 this value, thus it is not available for fetching from the inferior.
658 The type of this @code{gdb.Value}. The value of this attribute is a
659 @code{gdb.Type} object (@pxref{Types In Python}).
662 @defvar Value.dynamic_type
663 The dynamic type of this @code{gdb.Value}. This uses C@t{++} run-time
664 type information (@acronym{RTTI}) to determine the dynamic type of the
665 value. If this value is of class type, it will return the class in
666 which the value is embedded, if any. If this value is of pointer or
667 reference to a class type, it will compute the dynamic type of the
668 referenced object, and return a pointer or reference to that type,
669 respectively. In all other cases, it will return the value's static
672 Note that this feature will only work when debugging a C@t{++} program
673 that includes @acronym{RTTI} for the object in question. Otherwise,
674 it will just return the static type of the value as in @kbd{ptype foo}
675 (@pxref{Symbols, ptype}).
678 @defvar Value.is_lazy
679 The value of this read-only boolean attribute is @code{True} if this
680 @code{gdb.Value} has not yet been fetched from the inferior.
681 @value{GDBN} does not fetch values until necessary, for efficiency.
685 myval = gdb.parse_and_eval ('somevar')
688 The value of @code{somevar} is not fetched at this time. It will be
689 fetched when the value is needed, or when the @code{fetch_lazy}
693 The following methods are provided:
695 @defun Value.__init__ (@var{val})
696 Many Python values can be converted directly to a @code{gdb.Value} via
697 this object initializer. Specifically:
701 A Python boolean is converted to the boolean type from the current
705 A Python integer is converted to the C @code{long} type for the
706 current architecture.
709 A Python long is converted to the C @code{long long} type for the
710 current architecture.
713 A Python float is converted to the C @code{double} type for the
714 current architecture.
717 A Python string is converted to a target string in the current target
718 language using the current target encoding.
719 If a character cannot be represented in the current target encoding,
720 then an exception is thrown.
722 @item @code{gdb.Value}
723 If @code{val} is a @code{gdb.Value}, then a copy of the value is made.
725 @item @code{gdb.LazyString}
726 If @code{val} is a @code{gdb.LazyString} (@pxref{Lazy Strings In
727 Python}), then the lazy string's @code{value} method is called, and
732 @defun Value.cast (type)
733 Return a new instance of @code{gdb.Value} that is the result of
734 casting this instance to the type described by @var{type}, which must
735 be a @code{gdb.Type} object. If the cast cannot be performed for some
736 reason, this method throws an exception.
739 @defun Value.dereference ()
740 For pointer data types, this method returns a new @code{gdb.Value} object
741 whose contents is the object pointed to by the pointer. For example, if
742 @code{foo} is a C pointer to an @code{int}, declared in your C program as
749 then you can use the corresponding @code{gdb.Value} to access what
750 @code{foo} points to like this:
753 bar = foo.dereference ()
756 The result @code{bar} will be a @code{gdb.Value} object holding the
757 value pointed to by @code{foo}.
759 A similar function @code{Value.referenced_value} exists which also
760 returns @code{gdb.Value} objects corresonding to the values pointed to
761 by pointer values (and additionally, values referenced by reference
762 values). However, the behavior of @code{Value.dereference}
763 differs from @code{Value.referenced_value} by the fact that the
764 behavior of @code{Value.dereference} is identical to applying the C
765 unary operator @code{*} on a given value. For example, consider a
766 reference to a pointer @code{ptrref}, declared in your C@t{++} program
774 intptr &ptrref = ptr;
777 Though @code{ptrref} is a reference value, one can apply the method
778 @code{Value.dereference} to the @code{gdb.Value} object corresponding
779 to it and obtain a @code{gdb.Value} which is identical to that
780 corresponding to @code{val}. However, if you apply the method
781 @code{Value.referenced_value}, the result would be a @code{gdb.Value}
782 object identical to that corresponding to @code{ptr}.
785 py_ptrref = gdb.parse_and_eval ("ptrref")
786 py_val = py_ptrref.dereference ()
787 py_ptr = py_ptrref.referenced_value ()
790 The @code{gdb.Value} object @code{py_val} is identical to that
791 corresponding to @code{val}, and @code{py_ptr} is identical to that
792 corresponding to @code{ptr}. In general, @code{Value.dereference} can
793 be applied whenever the C unary operator @code{*} can be applied
794 to the corresponding C value. For those cases where applying both
795 @code{Value.dereference} and @code{Value.referenced_value} is allowed,
796 the results obtained need not be identical (as we have seen in the above
797 example). The results are however identical when applied on
798 @code{gdb.Value} objects corresponding to pointers (@code{gdb.Value}
799 objects with type code @code{TYPE_CODE_PTR}) in a C/C@t{++} program.
802 @defun Value.referenced_value ()
803 For pointer or reference data types, this method returns a new
804 @code{gdb.Value} object corresponding to the value referenced by the
805 pointer/reference value. For pointer data types,
806 @code{Value.dereference} and @code{Value.referenced_value} produce
807 identical results. The difference between these methods is that
808 @code{Value.dereference} cannot get the values referenced by reference
809 values. For example, consider a reference to an @code{int}, declared
810 in your C@t{++} program as
818 then applying @code{Value.dereference} to the @code{gdb.Value} object
819 corresponding to @code{ref} will result in an error, while applying
820 @code{Value.referenced_value} will result in a @code{gdb.Value} object
821 identical to that corresponding to @code{val}.
824 py_ref = gdb.parse_and_eval ("ref")
825 er_ref = py_ref.dereference () # Results in error
826 py_val = py_ref.referenced_value () # Returns the referenced value
829 The @code{gdb.Value} object @code{py_val} is identical to that
830 corresponding to @code{val}.
833 @defun Value.reference_value ()
834 Return a @code{gdb.Value} object which is a reference to the value
835 encapsulated by this instance.
838 @defun Value.const_value ()
839 Return a @code{gdb.Value} object which is a @code{const} version of the
840 value encapsulated by this instance.
843 @defun Value.dynamic_cast (type)
844 Like @code{Value.cast}, but works as if the C@t{++} @code{dynamic_cast}
845 operator were used. Consult a C@t{++} reference for details.
848 @defun Value.reinterpret_cast (type)
849 Like @code{Value.cast}, but works as if the C@t{++} @code{reinterpret_cast}
850 operator were used. Consult a C@t{++} reference for details.
853 @defun Value.string (@r{[}encoding@r{[}, errors@r{[}, length@r{]]]})
854 If this @code{gdb.Value} represents a string, then this method
855 converts the contents to a Python string. Otherwise, this method will
858 Values are interpreted as strings according to the rules of the
859 current language. If the optional length argument is given, the
860 string will be converted to that length, and will include any embedded
861 zeroes that the string may contain. Otherwise, for languages
862 where the string is zero-terminated, the entire string will be
865 For example, in C-like languages, a value is a string if it is a pointer
866 to or an array of characters or ints of type @code{wchar_t}, @code{char16_t},
869 If the optional @var{encoding} argument is given, it must be a string
870 naming the encoding of the string in the @code{gdb.Value}, such as
871 @code{"ascii"}, @code{"iso-8859-6"} or @code{"utf-8"}. It accepts
872 the same encodings as the corresponding argument to Python's
873 @code{string.decode} method, and the Python codec machinery will be used
874 to convert the string. If @var{encoding} is not given, or if
875 @var{encoding} is the empty string, then either the @code{target-charset}
876 (@pxref{Character Sets}) will be used, or a language-specific encoding
877 will be used, if the current language is able to supply one.
879 The optional @var{errors} argument is the same as the corresponding
880 argument to Python's @code{string.decode} method.
882 If the optional @var{length} argument is given, the string will be
883 fetched and converted to the given length.
886 @defun Value.lazy_string (@r{[}encoding @r{[}, length@r{]]})
887 If this @code{gdb.Value} represents a string, then this method
888 converts the contents to a @code{gdb.LazyString} (@pxref{Lazy Strings
889 In Python}). Otherwise, this method will throw an exception.
891 If the optional @var{encoding} argument is given, it must be a string
892 naming the encoding of the @code{gdb.LazyString}. Some examples are:
893 @samp{ascii}, @samp{iso-8859-6} or @samp{utf-8}. If the
894 @var{encoding} argument is an encoding that @value{GDBN} does
895 recognize, @value{GDBN} will raise an error.
897 When a lazy string is printed, the @value{GDBN} encoding machinery is
898 used to convert the string during printing. If the optional
899 @var{encoding} argument is not provided, or is an empty string,
900 @value{GDBN} will automatically select the encoding most suitable for
901 the string type. For further information on encoding in @value{GDBN}
902 please see @ref{Character Sets}.
904 If the optional @var{length} argument is given, the string will be
905 fetched and encoded to the length of characters specified. If
906 the @var{length} argument is not provided, the string will be fetched
907 and encoded until a null of appropriate width is found.
910 @defun Value.fetch_lazy ()
911 If the @code{gdb.Value} object is currently a lazy value
912 (@code{gdb.Value.is_lazy} is @code{True}), then the value is
913 fetched from the inferior. Any errors that occur in the process
914 will produce a Python exception.
916 If the @code{gdb.Value} object is not a lazy value, this method
919 This method does not return a value.
923 @node Types In Python
924 @subsubsection Types In Python
925 @cindex types in Python
926 @cindex Python, working with types
929 @value{GDBN} represents types from the inferior using the class
932 The following type-related functions are available in the @code{gdb}
935 @findex gdb.lookup_type
936 @defun gdb.lookup_type (name @r{[}, block@r{]})
937 This function looks up a type by its @var{name}, which must be a string.
939 If @var{block} is given, then @var{name} is looked up in that scope.
940 Otherwise, it is searched for globally.
942 Ordinarily, this function will return an instance of @code{gdb.Type}.
943 If the named type cannot be found, it will throw an exception.
946 If the type is a structure or class type, or an enum type, the fields
947 of that type can be accessed using the Python @dfn{dictionary syntax}.
948 For example, if @code{some_type} is a @code{gdb.Type} instance holding
949 a structure type, you can access its @code{foo} field with:
952 bar = some_type['foo']
955 @code{bar} will be a @code{gdb.Field} object; see below under the
956 description of the @code{Type.fields} method for a description of the
957 @code{gdb.Field} class.
959 An instance of @code{Type} has the following attributes:
962 The alignment of this type, in bytes. Type alignment comes from the
963 debugging information; if it was not specified, then @value{GDBN} will
964 use the relevant ABI to try to determine the alignment. In some
965 cases, even this is not possible, and zero will be returned.
969 The type code for this type. The type code will be one of the
970 @code{TYPE_CODE_} constants defined below.
974 The name of this type. If this type has no name, then @code{None}
979 The size of this type, in target @code{char} units. Usually, a
980 target's @code{char} type will be an 8-bit byte. However, on some
981 unusual platforms, this type may have a different size.
985 The tag name for this type. The tag name is the name after
986 @code{struct}, @code{union}, or @code{enum} in C and C@t{++}; not all
987 languages have this concept. If this type has no tag name, then
988 @code{None} is returned.
991 The following methods are provided:
993 @defun Type.fields ()
994 For structure and union types, this method returns the fields. Range
995 types have two fields, the minimum and maximum values. Enum types
996 have one field per enum constant. Function and method types have one
997 field per parameter. The base types of C@t{++} classes are also
998 represented as fields. If the type has no fields, or does not fit
999 into one of these categories, an empty sequence will be returned.
1001 Each field is a @code{gdb.Field} object, with some pre-defined attributes:
1004 This attribute is not available for @code{enum} or @code{static}
1005 (as in C@t{++}) fields. The value is the position, counting
1006 in bits, from the start of the containing type.
1009 This attribute is only available for @code{enum} fields, and its value
1010 is the enumeration member's integer representation.
1013 The name of the field, or @code{None} for anonymous fields.
1016 This is @code{True} if the field is artificial, usually meaning that
1017 it was provided by the compiler and not the user. This attribute is
1018 always provided, and is @code{False} if the field is not artificial.
1021 This is @code{True} if the field represents a base class of a C@t{++}
1022 structure. This attribute is always provided, and is @code{False}
1023 if the field is not a base class of the type that is the argument of
1024 @code{fields}, or if that type was not a C@t{++} class.
1027 If the field is packed, or is a bitfield, then this will have a
1028 non-zero value, which is the size of the field in bits. Otherwise,
1029 this will be zero; in this case the field's size is given by its type.
1032 The type of the field. This is usually an instance of @code{Type},
1033 but it can be @code{None} in some situations.
1036 The type which contains this field. This is an instance of
1041 @defun Type.array (@var{n1} @r{[}, @var{n2}@r{]})
1042 Return a new @code{gdb.Type} object which represents an array of this
1043 type. If one argument is given, it is the inclusive upper bound of
1044 the array; in this case the lower bound is zero. If two arguments are
1045 given, the first argument is the lower bound of the array, and the
1046 second argument is the upper bound of the array. An array's length
1047 must not be negative, but the bounds can be.
1050 @defun Type.vector (@var{n1} @r{[}, @var{n2}@r{]})
1051 Return a new @code{gdb.Type} object which represents a vector of this
1052 type. If one argument is given, it is the inclusive upper bound of
1053 the vector; in this case the lower bound is zero. If two arguments are
1054 given, the first argument is the lower bound of the vector, and the
1055 second argument is the upper bound of the vector. A vector's length
1056 must not be negative, but the bounds can be.
1058 The difference between an @code{array} and a @code{vector} is that
1059 arrays behave like in C: when used in expressions they decay to a pointer
1060 to the first element whereas vectors are treated as first class values.
1063 @defun Type.const ()
1064 Return a new @code{gdb.Type} object which represents a
1065 @code{const}-qualified variant of this type.
1068 @defun Type.volatile ()
1069 Return a new @code{gdb.Type} object which represents a
1070 @code{volatile}-qualified variant of this type.
1073 @defun Type.unqualified ()
1074 Return a new @code{gdb.Type} object which represents an unqualified
1075 variant of this type. That is, the result is neither @code{const} nor
1079 @defun Type.range ()
1080 Return a Python @code{Tuple} object that contains two elements: the
1081 low bound of the argument type and the high bound of that type. If
1082 the type does not have a range, @value{GDBN} will raise a
1083 @code{gdb.error} exception (@pxref{Exception Handling}).
1086 @defun Type.reference ()
1087 Return a new @code{gdb.Type} object which represents a reference to this
1091 @defun Type.pointer ()
1092 Return a new @code{gdb.Type} object which represents a pointer to this
1096 @defun Type.strip_typedefs ()
1097 Return a new @code{gdb.Type} that represents the real type,
1098 after removing all layers of typedefs.
1101 @defun Type.target ()
1102 Return a new @code{gdb.Type} object which represents the target type
1105 For a pointer type, the target type is the type of the pointed-to
1106 object. For an array type (meaning C-like arrays), the target type is
1107 the type of the elements of the array. For a function or method type,
1108 the target type is the type of the return value. For a complex type,
1109 the target type is the type of the elements. For a typedef, the
1110 target type is the aliased type.
1112 If the type does not have a target, this method will throw an
1116 @defun Type.template_argument (n @r{[}, block@r{]})
1117 If this @code{gdb.Type} is an instantiation of a template, this will
1118 return a new @code{gdb.Value} or @code{gdb.Type} which represents the
1119 value of the @var{n}th template argument (indexed starting at 0).
1121 If this @code{gdb.Type} is not a template type, or if the type has fewer
1122 than @var{n} template arguments, this will throw an exception.
1123 Ordinarily, only C@t{++} code will have template types.
1125 If @var{block} is given, then @var{name} is looked up in that scope.
1126 Otherwise, it is searched for globally.
1129 @defun Type.optimized_out ()
1130 Return @code{gdb.Value} instance of this type whose value is optimized
1131 out. This allows a frame decorator to indicate that the value of an
1132 argument or a local variable is not known.
1135 Each type has a code, which indicates what category this type falls
1136 into. The available type categories are represented by constants
1137 defined in the @code{gdb} module:
1140 @vindex TYPE_CODE_PTR
1141 @item gdb.TYPE_CODE_PTR
1142 The type is a pointer.
1144 @vindex TYPE_CODE_ARRAY
1145 @item gdb.TYPE_CODE_ARRAY
1146 The type is an array.
1148 @vindex TYPE_CODE_STRUCT
1149 @item gdb.TYPE_CODE_STRUCT
1150 The type is a structure.
1152 @vindex TYPE_CODE_UNION
1153 @item gdb.TYPE_CODE_UNION
1154 The type is a union.
1156 @vindex TYPE_CODE_ENUM
1157 @item gdb.TYPE_CODE_ENUM
1158 The type is an enum.
1160 @vindex TYPE_CODE_FLAGS
1161 @item gdb.TYPE_CODE_FLAGS
1162 A bit flags type, used for things such as status registers.
1164 @vindex TYPE_CODE_FUNC
1165 @item gdb.TYPE_CODE_FUNC
1166 The type is a function.
1168 @vindex TYPE_CODE_INT
1169 @item gdb.TYPE_CODE_INT
1170 The type is an integer type.
1172 @vindex TYPE_CODE_FLT
1173 @item gdb.TYPE_CODE_FLT
1174 A floating point type.
1176 @vindex TYPE_CODE_VOID
1177 @item gdb.TYPE_CODE_VOID
1178 The special type @code{void}.
1180 @vindex TYPE_CODE_SET
1181 @item gdb.TYPE_CODE_SET
1184 @vindex TYPE_CODE_RANGE
1185 @item gdb.TYPE_CODE_RANGE
1186 A range type, that is, an integer type with bounds.
1188 @vindex TYPE_CODE_STRING
1189 @item gdb.TYPE_CODE_STRING
1190 A string type. Note that this is only used for certain languages with
1191 language-defined string types; C strings are not represented this way.
1193 @vindex TYPE_CODE_BITSTRING
1194 @item gdb.TYPE_CODE_BITSTRING
1195 A string of bits. It is deprecated.
1197 @vindex TYPE_CODE_ERROR
1198 @item gdb.TYPE_CODE_ERROR
1199 An unknown or erroneous type.
1201 @vindex TYPE_CODE_METHOD
1202 @item gdb.TYPE_CODE_METHOD
1203 A method type, as found in C@t{++}.
1205 @vindex TYPE_CODE_METHODPTR
1206 @item gdb.TYPE_CODE_METHODPTR
1207 A pointer-to-member-function.
1209 @vindex TYPE_CODE_MEMBERPTR
1210 @item gdb.TYPE_CODE_MEMBERPTR
1211 A pointer-to-member.
1213 @vindex TYPE_CODE_REF
1214 @item gdb.TYPE_CODE_REF
1217 @vindex TYPE_CODE_RVALUE_REF
1218 @item gdb.TYPE_CODE_RVALUE_REF
1219 A C@t{++}11 rvalue reference type.
1221 @vindex TYPE_CODE_CHAR
1222 @item gdb.TYPE_CODE_CHAR
1225 @vindex TYPE_CODE_BOOL
1226 @item gdb.TYPE_CODE_BOOL
1229 @vindex TYPE_CODE_COMPLEX
1230 @item gdb.TYPE_CODE_COMPLEX
1231 A complex float type.
1233 @vindex TYPE_CODE_TYPEDEF
1234 @item gdb.TYPE_CODE_TYPEDEF
1235 A typedef to some other type.
1237 @vindex TYPE_CODE_NAMESPACE
1238 @item gdb.TYPE_CODE_NAMESPACE
1239 A C@t{++} namespace.
1241 @vindex TYPE_CODE_DECFLOAT
1242 @item gdb.TYPE_CODE_DECFLOAT
1243 A decimal floating point type.
1245 @vindex TYPE_CODE_INTERNAL_FUNCTION
1246 @item gdb.TYPE_CODE_INTERNAL_FUNCTION
1247 A function internal to @value{GDBN}. This is the type used to represent
1248 convenience functions.
1251 Further support for types is provided in the @code{gdb.types}
1252 Python module (@pxref{gdb.types}).
1254 @node Pretty Printing API
1255 @subsubsection Pretty Printing API
1256 @cindex python pretty printing api
1258 An example output is provided (@pxref{Pretty Printing}).
1260 A pretty-printer is just an object that holds a value and implements a
1261 specific interface, defined here.
1263 @defun pretty_printer.children (self)
1264 @value{GDBN} will call this method on a pretty-printer to compute the
1265 children of the pretty-printer's value.
1267 This method must return an object conforming to the Python iterator
1268 protocol. Each item returned by the iterator must be a tuple holding
1269 two elements. The first element is the ``name'' of the child; the
1270 second element is the child's value. The value can be any Python
1271 object which is convertible to a @value{GDBN} value.
1273 This method is optional. If it does not exist, @value{GDBN} will act
1274 as though the value has no children.
1277 @defun pretty_printer.display_hint (self)
1278 The CLI may call this method and use its result to change the
1279 formatting of a value. The result will also be supplied to an MI
1280 consumer as a @samp{displayhint} attribute of the variable being
1283 This method is optional. If it does exist, this method must return a
1286 Some display hints are predefined by @value{GDBN}:
1290 Indicate that the object being printed is ``array-like''. The CLI
1291 uses this to respect parameters such as @code{set print elements} and
1292 @code{set print array}.
1295 Indicate that the object being printed is ``map-like'', and that the
1296 children of this value can be assumed to alternate between keys and
1300 Indicate that the object being printed is ``string-like''. If the
1301 printer's @code{to_string} method returns a Python string of some
1302 kind, then @value{GDBN} will call its internal language-specific
1303 string-printing function to format the string. For the CLI this means
1304 adding quotation marks, possibly escaping some characters, respecting
1305 @code{set print elements}, and the like.
1309 @defun pretty_printer.to_string (self)
1310 @value{GDBN} will call this method to display the string
1311 representation of the value passed to the object's constructor.
1313 When printing from the CLI, if the @code{to_string} method exists,
1314 then @value{GDBN} will prepend its result to the values returned by
1315 @code{children}. Exactly how this formatting is done is dependent on
1316 the display hint, and may change as more hints are added. Also,
1317 depending on the print settings (@pxref{Print Settings}), the CLI may
1318 print just the result of @code{to_string} in a stack trace, omitting
1319 the result of @code{children}.
1321 If this method returns a string, it is printed verbatim.
1323 Otherwise, if this method returns an instance of @code{gdb.Value},
1324 then @value{GDBN} prints this value. This may result in a call to
1325 another pretty-printer.
1327 If instead the method returns a Python value which is convertible to a
1328 @code{gdb.Value}, then @value{GDBN} performs the conversion and prints
1329 the resulting value. Again, this may result in a call to another
1330 pretty-printer. Python scalars (integers, floats, and booleans) and
1331 strings are convertible to @code{gdb.Value}; other types are not.
1333 Finally, if this method returns @code{None} then no further operations
1334 are peformed in this method and nothing is printed.
1336 If the result is not one of these types, an exception is raised.
1339 @value{GDBN} provides a function which can be used to look up the
1340 default pretty-printer for a @code{gdb.Value}:
1342 @findex gdb.default_visualizer
1343 @defun gdb.default_visualizer (value)
1344 This function takes a @code{gdb.Value} object as an argument. If a
1345 pretty-printer for this value exists, then it is returned. If no such
1346 printer exists, then this returns @code{None}.
1349 @node Selecting Pretty-Printers
1350 @subsubsection Selecting Pretty-Printers
1351 @cindex selecting python pretty-printers
1353 The Python list @code{gdb.pretty_printers} contains an array of
1354 functions or callable objects that have been registered via addition
1355 as a pretty-printer. Printers in this list are called @code{global}
1356 printers, they're available when debugging all inferiors.
1357 Each @code{gdb.Progspace} contains a @code{pretty_printers} attribute.
1358 Each @code{gdb.Objfile} also contains a @code{pretty_printers}
1361 Each function on these lists is passed a single @code{gdb.Value}
1362 argument and should return a pretty-printer object conforming to the
1363 interface definition above (@pxref{Pretty Printing API}). If a function
1364 cannot create a pretty-printer for the value, it should return
1367 @value{GDBN} first checks the @code{pretty_printers} attribute of each
1368 @code{gdb.Objfile} in the current program space and iteratively calls
1369 each enabled lookup routine in the list for that @code{gdb.Objfile}
1370 until it receives a pretty-printer object.
1371 If no pretty-printer is found in the objfile lists, @value{GDBN} then
1372 searches the pretty-printer list of the current program space,
1373 calling each enabled function until an object is returned.
1374 After these lists have been exhausted, it tries the global
1375 @code{gdb.pretty_printers} list, again calling each enabled function until an
1378 The order in which the objfiles are searched is not specified. For a
1379 given list, functions are always invoked from the head of the list,
1380 and iterated over sequentially until the end of the list, or a printer
1383 For various reasons a pretty-printer may not work.
1384 For example, the underlying data structure may have changed and
1385 the pretty-printer is out of date.
1387 The consequences of a broken pretty-printer are severe enough that
1388 @value{GDBN} provides support for enabling and disabling individual
1389 printers. For example, if @code{print frame-arguments} is on,
1390 a backtrace can become highly illegible if any argument is printed
1391 with a broken printer.
1393 Pretty-printers are enabled and disabled by attaching an @code{enabled}
1394 attribute to the registered function or callable object. If this attribute
1395 is present and its value is @code{False}, the printer is disabled, otherwise
1396 the printer is enabled.
1398 @node Writing a Pretty-Printer
1399 @subsubsection Writing a Pretty-Printer
1400 @cindex writing a pretty-printer
1402 A pretty-printer consists of two parts: a lookup function to detect
1403 if the type is supported, and the printer itself.
1405 Here is an example showing how a @code{std::string} printer might be
1406 written. @xref{Pretty Printing API}, for details on the API this class
1410 class StdStringPrinter(object):
1411 "Print a std::string"
1413 def __init__(self, val):
1416 def to_string(self):
1417 return self.val['_M_dataplus']['_M_p']
1419 def display_hint(self):
1423 And here is an example showing how a lookup function for the printer
1424 example above might be written.
1427 def str_lookup_function(val):
1428 lookup_tag = val.type.tag
1429 if lookup_tag == None:
1431 regex = re.compile("^std::basic_string<char,.*>$")
1432 if regex.match(lookup_tag):
1433 return StdStringPrinter(val)
1437 The example lookup function extracts the value's type, and attempts to
1438 match it to a type that it can pretty-print. If it is a type the
1439 printer can pretty-print, it will return a printer object. If not, it
1440 returns @code{None}.
1442 We recommend that you put your core pretty-printers into a Python
1443 package. If your pretty-printers are for use with a library, we
1444 further recommend embedding a version number into the package name.
1445 This practice will enable @value{GDBN} to load multiple versions of
1446 your pretty-printers at the same time, because they will have
1449 You should write auto-loaded code (@pxref{Python Auto-loading}) such that it
1450 can be evaluated multiple times without changing its meaning. An
1451 ideal auto-load file will consist solely of @code{import}s of your
1452 printer modules, followed by a call to a register pretty-printers with
1453 the current objfile.
1455 Taken as a whole, this approach will scale nicely to multiple
1456 inferiors, each potentially using a different library version.
1457 Embedding a version number in the Python package name will ensure that
1458 @value{GDBN} is able to load both sets of printers simultaneously.
1459 Then, because the search for pretty-printers is done by objfile, and
1460 because your auto-loaded code took care to register your library's
1461 printers with a specific objfile, @value{GDBN} will find the correct
1462 printers for the specific version of the library used by each
1465 To continue the @code{std::string} example (@pxref{Pretty Printing API}),
1466 this code might appear in @code{gdb.libstdcxx.v6}:
1469 def register_printers(objfile):
1470 objfile.pretty_printers.append(str_lookup_function)
1474 And then the corresponding contents of the auto-load file would be:
1477 import gdb.libstdcxx.v6
1478 gdb.libstdcxx.v6.register_printers(gdb.current_objfile())
1481 The previous example illustrates a basic pretty-printer.
1482 There are a few things that can be improved on.
1483 The printer doesn't have a name, making it hard to identify in a
1484 list of installed printers. The lookup function has a name, but
1485 lookup functions can have arbitrary, even identical, names.
1487 Second, the printer only handles one type, whereas a library typically has
1488 several types. One could install a lookup function for each desired type
1489 in the library, but one could also have a single lookup function recognize
1490 several types. The latter is the conventional way this is handled.
1491 If a pretty-printer can handle multiple data types, then its
1492 @dfn{subprinters} are the printers for the individual data types.
1494 The @code{gdb.printing} module provides a formal way of solving these
1495 problems (@pxref{gdb.printing}).
1496 Here is another example that handles multiple types.
1498 These are the types we are going to pretty-print:
1501 struct foo @{ int a, b; @};
1502 struct bar @{ struct foo x, y; @};
1505 Here are the printers:
1509 """Print a foo object."""
1511 def __init__(self, val):
1514 def to_string(self):
1515 return ("a=<" + str(self.val["a"]) +
1516 "> b=<" + str(self.val["b"]) + ">")
1519 """Print a bar object."""
1521 def __init__(self, val):
1524 def to_string(self):
1525 return ("x=<" + str(self.val["x"]) +
1526 "> y=<" + str(self.val["y"]) + ">")
1529 This example doesn't need a lookup function, that is handled by the
1530 @code{gdb.printing} module. Instead a function is provided to build up
1531 the object that handles the lookup.
1536 def build_pretty_printer():
1537 pp = gdb.printing.RegexpCollectionPrettyPrinter(
1539 pp.add_printer('foo', '^foo$', fooPrinter)
1540 pp.add_printer('bar', '^bar$', barPrinter)
1544 And here is the autoload support:
1549 gdb.printing.register_pretty_printer(
1550 gdb.current_objfile(),
1551 my_library.build_pretty_printer())
1554 Finally, when this printer is loaded into @value{GDBN}, here is the
1555 corresponding output of @samp{info pretty-printer}:
1558 (gdb) info pretty-printer
1565 @node Type Printing API
1566 @subsubsection Type Printing API
1567 @cindex type printing API for Python
1569 @value{GDBN} provides a way for Python code to customize type display.
1570 This is mainly useful for substituting canonical typedef names for
1573 @cindex type printer
1574 A @dfn{type printer} is just a Python object conforming to a certain
1575 protocol. A simple base class implementing the protocol is provided;
1576 see @ref{gdb.types}. A type printer must supply at least:
1578 @defivar type_printer enabled
1579 A boolean which is True if the printer is enabled, and False
1580 otherwise. This is manipulated by the @code{enable type-printer}
1581 and @code{disable type-printer} commands.
1584 @defivar type_printer name
1585 The name of the type printer. This must be a string. This is used by
1586 the @code{enable type-printer} and @code{disable type-printer}
1590 @defmethod type_printer instantiate (self)
1591 This is called by @value{GDBN} at the start of type-printing. It is
1592 only called if the type printer is enabled. This method must return a
1593 new object that supplies a @code{recognize} method, as described below.
1597 When displaying a type, say via the @code{ptype} command, @value{GDBN}
1598 will compute a list of type recognizers. This is done by iterating
1599 first over the per-objfile type printers (@pxref{Objfiles In Python}),
1600 followed by the per-progspace type printers (@pxref{Progspaces In
1601 Python}), and finally the global type printers.
1603 @value{GDBN} will call the @code{instantiate} method of each enabled
1604 type printer. If this method returns @code{None}, then the result is
1605 ignored; otherwise, it is appended to the list of recognizers.
1607 Then, when @value{GDBN} is going to display a type name, it iterates
1608 over the list of recognizers. For each one, it calls the recognition
1609 function, stopping if the function returns a non-@code{None} value.
1610 The recognition function is defined as:
1612 @defmethod type_recognizer recognize (self, type)
1613 If @var{type} is not recognized, return @code{None}. Otherwise,
1614 return a string which is to be printed as the name of @var{type}.
1615 The @var{type} argument will be an instance of @code{gdb.Type}
1616 (@pxref{Types In Python}).
1619 @value{GDBN} uses this two-pass approach so that type printers can
1620 efficiently cache information without holding on to it too long. For
1621 example, it can be convenient to look up type information in a type
1622 printer and hold it for a recognizer's lifetime; if a single pass were
1623 done then type printers would have to make use of the event system in
1624 order to avoid holding information that could become stale as the
1627 @node Frame Filter API
1628 @subsubsection Filtering Frames.
1629 @cindex frame filters api
1631 Frame filters are Python objects that manipulate the visibility of a
1632 frame or frames when a backtrace (@pxref{Backtrace}) is printed by
1635 Only commands that print a backtrace, or, in the case of @sc{gdb/mi}
1636 commands (@pxref{GDB/MI}), those that return a collection of frames
1637 are affected. The commands that work with frame filters are:
1639 @code{backtrace} (@pxref{backtrace-command,, The backtrace command}),
1640 @code{-stack-list-frames}
1641 (@pxref{-stack-list-frames,, The -stack-list-frames command}),
1642 @code{-stack-list-variables} (@pxref{-stack-list-variables,, The
1643 -stack-list-variables command}), @code{-stack-list-arguments}
1644 @pxref{-stack-list-arguments,, The -stack-list-arguments command}) and
1645 @code{-stack-list-locals} (@pxref{-stack-list-locals,, The
1646 -stack-list-locals command}).
1648 A frame filter works by taking an iterator as an argument, applying
1649 actions to the contents of that iterator, and returning another
1650 iterator (or, possibly, the same iterator it was provided in the case
1651 where the filter does not perform any operations). Typically, frame
1652 filters utilize tools such as the Python's @code{itertools} module to
1653 work with and create new iterators from the source iterator.
1654 Regardless of how a filter chooses to apply actions, it must not alter
1655 the underlying @value{GDBN} frame or frames, or attempt to alter the
1656 call-stack within @value{GDBN}. This preserves data integrity within
1657 @value{GDBN}. Frame filters are executed on a priority basis and care
1658 should be taken that some frame filters may have been executed before,
1659 and that some frame filters will be executed after.
1661 An important consideration when designing frame filters, and well
1662 worth reflecting upon, is that frame filters should avoid unwinding
1663 the call stack if possible. Some stacks can run very deep, into the
1664 tens of thousands in some cases. To search every frame when a frame
1665 filter executes may be too expensive at that step. The frame filter
1666 cannot know how many frames it has to iterate over, and it may have to
1667 iterate through them all. This ends up duplicating effort as
1668 @value{GDBN} performs this iteration when it prints the frames. If
1669 the filter can defer unwinding frames until frame decorators are
1670 executed, after the last filter has executed, it should. @xref{Frame
1671 Decorator API}, for more information on decorators. Also, there are
1672 examples for both frame decorators and filters in later chapters.
1673 @xref{Writing a Frame Filter}, for more information.
1675 The Python dictionary @code{gdb.frame_filters} contains key/object
1676 pairings that comprise a frame filter. Frame filters in this
1677 dictionary are called @code{global} frame filters, and they are
1678 available when debugging all inferiors. These frame filters must
1679 register with the dictionary directly. In addition to the
1680 @code{global} dictionary, there are other dictionaries that are loaded
1681 with different inferiors via auto-loading (@pxref{Python
1682 Auto-loading}). The two other areas where frame filter dictionaries
1683 can be found are: @code{gdb.Progspace} which contains a
1684 @code{frame_filters} dictionary attribute, and each @code{gdb.Objfile}
1685 object which also contains a @code{frame_filters} dictionary
1688 When a command is executed from @value{GDBN} that is compatible with
1689 frame filters, @value{GDBN} combines the @code{global},
1690 @code{gdb.Progspace} and all @code{gdb.Objfile} dictionaries currently
1691 loaded. All of the @code{gdb.Objfile} dictionaries are combined, as
1692 several frames, and thus several object files, might be in use.
1693 @value{GDBN} then prunes any frame filter whose @code{enabled}
1694 attribute is @code{False}. This pruned list is then sorted according
1695 to the @code{priority} attribute in each filter.
1697 Once the dictionaries are combined, pruned and sorted, @value{GDBN}
1698 creates an iterator which wraps each frame in the call stack in a
1699 @code{FrameDecorator} object, and calls each filter in order. The
1700 output from the previous filter will always be the input to the next
1703 Frame filters have a mandatory interface which each frame filter must
1704 implement, defined here:
1706 @defun FrameFilter.filter (iterator)
1707 @value{GDBN} will call this method on a frame filter when it has
1708 reached the order in the priority list for that filter.
1710 For example, if there are four frame filters:
1721 The order that the frame filters will be called is:
1724 Filter3 -> Filter2 -> Filter1 -> Filter4
1727 Note that the output from @code{Filter3} is passed to the input of
1728 @code{Filter2}, and so on.
1730 This @code{filter} method is passed a Python iterator. This iterator
1731 contains a sequence of frame decorators that wrap each
1732 @code{gdb.Frame}, or a frame decorator that wraps another frame
1733 decorator. The first filter that is executed in the sequence of frame
1734 filters will receive an iterator entirely comprised of default
1735 @code{FrameDecorator} objects. However, after each frame filter is
1736 executed, the previous frame filter may have wrapped some or all of
1737 the frame decorators with their own frame decorator. As frame
1738 decorators must also conform to a mandatory interface, these
1739 decorators can be assumed to act in a uniform manner (@pxref{Frame
1742 This method must return an object conforming to the Python iterator
1743 protocol. Each item in the iterator must be an object conforming to
1744 the frame decorator interface. If a frame filter does not wish to
1745 perform any operations on this iterator, it should return that
1748 This method is not optional. If it does not exist, @value{GDBN} will
1749 raise and print an error.
1752 @defvar FrameFilter.name
1753 The @code{name} attribute must be Python string which contains the
1754 name of the filter displayed by @value{GDBN} (@pxref{Frame Filter
1755 Management}). This attribute may contain any combination of letters
1756 or numbers. Care should be taken to ensure that it is unique. This
1757 attribute is mandatory.
1760 @defvar FrameFilter.enabled
1761 The @code{enabled} attribute must be Python boolean. This attribute
1762 indicates to @value{GDBN} whether the frame filter is enabled, and
1763 should be considered when frame filters are executed. If
1764 @code{enabled} is @code{True}, then the frame filter will be executed
1765 when any of the backtrace commands detailed earlier in this chapter
1766 are executed. If @code{enabled} is @code{False}, then the frame
1767 filter will not be executed. This attribute is mandatory.
1770 @defvar FrameFilter.priority
1771 The @code{priority} attribute must be Python integer. This attribute
1772 controls the order of execution in relation to other frame filters.
1773 There are no imposed limits on the range of @code{priority} other than
1774 it must be a valid integer. The higher the @code{priority} attribute,
1775 the sooner the frame filter will be executed in relation to other
1776 frame filters. Although @code{priority} can be negative, it is
1777 recommended practice to assume zero is the lowest priority that a
1778 frame filter can be assigned. Frame filters that have the same
1779 priority are executed in unsorted order in that priority slot. This
1780 attribute is mandatory.
1783 @node Frame Decorator API
1784 @subsubsection Decorating Frames.
1785 @cindex frame decorator api
1787 Frame decorators are sister objects to frame filters (@pxref{Frame
1788 Filter API}). Frame decorators are applied by a frame filter and can
1789 only be used in conjunction with frame filters.
1791 The purpose of a frame decorator is to customize the printed content
1792 of each @code{gdb.Frame} in commands where frame filters are executed.
1793 This concept is called decorating a frame. Frame decorators decorate
1794 a @code{gdb.Frame} with Python code contained within each API call.
1795 This separates the actual data contained in a @code{gdb.Frame} from
1796 the decorated data produced by a frame decorator. This abstraction is
1797 necessary to maintain integrity of the data contained in each
1800 Frame decorators have a mandatory interface, defined below.
1802 @value{GDBN} already contains a frame decorator called
1803 @code{FrameDecorator}. This contains substantial amounts of
1804 boilerplate code to decorate the content of a @code{gdb.Frame}. It is
1805 recommended that other frame decorators inherit and extend this
1806 object, and only to override the methods needed.
1808 @defun FrameDecorator.elided (self)
1810 The @code{elided} method groups frames together in a hierarchical
1811 system. An example would be an interpreter, where multiple low-level
1812 frames make up a single call in the interpreted language. In this
1813 example, the frame filter would elide the low-level frames and present
1814 a single high-level frame, representing the call in the interpreted
1815 language, to the user.
1817 The @code{elided} function must return an iterable and this iterable
1818 must contain the frames that are being elided wrapped in a suitable
1819 frame decorator. If no frames are being elided this function may
1820 return an empty iterable, or @code{None}. Elided frames are indented
1821 from normal frames in a @code{CLI} backtrace, or in the case of
1822 @code{GDB/MI}, are placed in the @code{children} field of the eliding
1825 It is the frame filter's task to also filter out the elided frames from
1826 the source iterator. This will avoid printing the frame twice.
1829 @defun FrameDecorator.function (self)
1831 This method returns the name of the function in the frame that is to
1834 This method must return a Python string describing the function, or
1837 If this function returns @code{None}, @value{GDBN} will not print any
1838 data for this field.
1841 @defun FrameDecorator.address (self)
1843 This method returns the address of the frame that is to be printed.
1845 This method must return a Python numeric integer type of sufficient
1846 size to describe the address of the frame, or @code{None}.
1848 If this function returns a @code{None}, @value{GDBN} will not print
1849 any data for this field.
1852 @defun FrameDecorator.filename (self)
1854 This method returns the filename and path associated with this frame.
1856 This method must return a Python string containing the filename and
1857 the path to the object file backing the frame, or @code{None}.
1859 If this function returns a @code{None}, @value{GDBN} will not print
1860 any data for this field.
1863 @defun FrameDecorator.line (self):
1865 This method returns the line number associated with the current
1866 position within the function addressed by this frame.
1868 This method must return a Python integer type, or @code{None}.
1870 If this function returns a @code{None}, @value{GDBN} will not print
1871 any data for this field.
1874 @defun FrameDecorator.frame_args (self)
1877 This method must return an iterable, or @code{None}. Returning an
1878 empty iterable, or @code{None} means frame arguments will not be
1879 printed for this frame. This iterable must contain objects that
1880 implement two methods, described here.
1882 This object must implement a @code{argument} method which takes a
1883 single @code{self} parameter and must return a @code{gdb.Symbol}
1884 (@pxref{Symbols In Python}), or a Python string. The object must also
1885 implement a @code{value} method which takes a single @code{self}
1886 parameter and must return a @code{gdb.Value} (@pxref{Values From
1887 Inferior}), a Python value, or @code{None}. If the @code{value}
1888 method returns @code{None}, and the @code{argument} method returns a
1889 @code{gdb.Symbol}, @value{GDBN} will look-up and print the value of
1890 the @code{gdb.Symbol} automatically.
1895 class SymValueWrapper():
1897 def __init__(self, symbol, value):
1907 class SomeFrameDecorator()
1910 def frame_args(self):
1913 block = self.inferior_frame.block()
1917 # Iterate over all symbols in a block. Only add
1918 # symbols that are arguments.
1920 if not sym.is_argument:
1922 args.append(SymValueWrapper(sym,None))
1924 # Add example synthetic argument.
1925 args.append(SymValueWrapper(``foo'', 42))
1931 @defun FrameDecorator.frame_locals (self)
1933 This method must return an iterable or @code{None}. Returning an
1934 empty iterable, or @code{None} means frame local arguments will not be
1935 printed for this frame.
1937 The object interface, the description of the various strategies for
1938 reading frame locals, and the example are largely similar to those
1939 described in the @code{frame_args} function, (@pxref{frame_args,,The
1940 frame filter frame_args function}). Below is a modified example:
1943 class SomeFrameDecorator()
1946 def frame_locals(self):
1949 block = self.inferior_frame.block()
1953 # Iterate over all symbols in a block. Add all
1954 # symbols, except arguments.
1958 vars.append(SymValueWrapper(sym,None))
1960 # Add an example of a synthetic local variable.
1961 vars.append(SymValueWrapper(``bar'', 99))
1967 @defun FrameDecorator.inferior_frame (self):
1969 This method must return the underlying @code{gdb.Frame} that this
1970 frame decorator is decorating. @value{GDBN} requires the underlying
1971 frame for internal frame information to determine how to print certain
1972 values when printing a frame.
1975 @node Writing a Frame Filter
1976 @subsubsection Writing a Frame Filter
1977 @cindex writing a frame filter
1979 There are three basic elements that a frame filter must implement: it
1980 must correctly implement the documented interface (@pxref{Frame Filter
1981 API}), it must register itself with @value{GDBN}, and finally, it must
1982 decide if it is to work on the data provided by @value{GDBN}. In all
1983 cases, whether it works on the iterator or not, each frame filter must
1984 return an iterator. A bare-bones frame filter follows the pattern in
1985 the following example.
1990 class FrameFilter():
1993 # Frame filter attribute creation.
1995 # 'name' is the name of the filter that GDB will display.
1997 # 'priority' is the priority of the filter relative to other
2000 # 'enabled' is a boolean that indicates whether this filter is
2001 # enabled and should be executed.
2007 # Register this frame filter with the global frame_filters
2009 gdb.frame_filters[self.name] = self
2011 def filter(self, frame_iter):
2012 # Just return the iterator.
2016 The frame filter in the example above implements the three
2017 requirements for all frame filters. It implements the API, self
2018 registers, and makes a decision on the iterator (in this case, it just
2019 returns the iterator untouched).
2021 The first step is attribute creation and assignment, and as shown in
2022 the comments the filter assigns the following attributes: @code{name},
2023 @code{priority} and whether the filter should be enabled with the
2024 @code{enabled} attribute.
2026 The second step is registering the frame filter with the dictionary or
2027 dictionaries that the frame filter has interest in. As shown in the
2028 comments, this filter just registers itself with the global dictionary
2029 @code{gdb.frame_filters}. As noted earlier, @code{gdb.frame_filters}
2030 is a dictionary that is initialized in the @code{gdb} module when
2031 @value{GDBN} starts. What dictionary a filter registers with is an
2032 important consideration. Generally, if a filter is specific to a set
2033 of code, it should be registered either in the @code{objfile} or
2034 @code{progspace} dictionaries as they are specific to the program
2035 currently loaded in @value{GDBN}. The global dictionary is always
2036 present in @value{GDBN} and is never unloaded. Any filters registered
2037 with the global dictionary will exist until @value{GDBN} exits. To
2038 avoid filters that may conflict, it is generally better to register
2039 frame filters against the dictionaries that more closely align with
2040 the usage of the filter currently in question. @xref{Python
2041 Auto-loading}, for further information on auto-loading Python scripts.
2043 @value{GDBN} takes a hands-off approach to frame filter registration,
2044 therefore it is the frame filter's responsibility to ensure
2045 registration has occurred, and that any exceptions are handled
2046 appropriately. In particular, you may wish to handle exceptions
2047 relating to Python dictionary key uniqueness. It is mandatory that
2048 the dictionary key is the same as frame filter's @code{name}
2049 attribute. When a user manages frame filters (@pxref{Frame Filter
2050 Management}), the names @value{GDBN} will display are those contained
2051 in the @code{name} attribute.
2053 The final step of this example is the implementation of the
2054 @code{filter} method. As shown in the example comments, we define the
2055 @code{filter} method and note that the method must take an iterator,
2056 and also must return an iterator. In this bare-bones example, the
2057 frame filter is not very useful as it just returns the iterator
2058 untouched. However this is a valid operation for frame filters that
2059 have the @code{enabled} attribute set, but decide not to operate on
2062 In the next example, the frame filter operates on all frames and
2063 utilizes a frame decorator to perform some work on the frames.
2064 @xref{Frame Decorator API}, for further information on the frame
2065 decorator interface.
2067 This example works on inlined frames. It highlights frames which are
2068 inlined by tagging them with an ``[inlined]'' tag. By applying a
2069 frame decorator to all frames with the Python @code{itertools imap}
2070 method, the example defers actions to the frame decorator. Frame
2071 decorators are only processed when @value{GDBN} prints the backtrace.
2073 This introduces a new decision making topic: whether to perform
2074 decision making operations at the filtering step, or at the printing
2075 step. In this example's approach, it does not perform any filtering
2076 decisions at the filtering step beyond mapping a frame decorator to
2077 each frame. This allows the actual decision making to be performed
2078 when each frame is printed. This is an important consideration, and
2079 well worth reflecting upon when designing a frame filter. An issue
2080 that frame filters should avoid is unwinding the stack if possible.
2081 Some stacks can run very deep, into the tens of thousands in some
2082 cases. To search every frame to determine if it is inlined ahead of
2083 time may be too expensive at the filtering step. The frame filter
2084 cannot know how many frames it has to iterate over, and it would have
2085 to iterate through them all. This ends up duplicating effort as
2086 @value{GDBN} performs this iteration when it prints the frames.
2088 In this example decision making can be deferred to the printing step.
2089 As each frame is printed, the frame decorator can examine each frame
2090 in turn when @value{GDBN} iterates. From a performance viewpoint,
2091 this is the most appropriate decision to make as it avoids duplicating
2092 the effort that the printing step would undertake anyway. Also, if
2093 there are many frame filters unwinding the stack during filtering, it
2094 can substantially delay the printing of the backtrace which will
2095 result in large memory usage, and a poor user experience.
2098 class InlineFilter():
2101 self.name = "InlinedFrameFilter"
2104 gdb.frame_filters[self.name] = self
2106 def filter(self, frame_iter):
2107 frame_iter = itertools.imap(InlinedFrameDecorator,
2112 This frame filter is somewhat similar to the earlier example, except
2113 that the @code{filter} method applies a frame decorator object called
2114 @code{InlinedFrameDecorator} to each element in the iterator. The
2115 @code{imap} Python method is light-weight. It does not proactively
2116 iterate over the iterator, but rather creates a new iterator which
2117 wraps the existing one.
2119 Below is the frame decorator for this example.
2122 class InlinedFrameDecorator(FrameDecorator):
2124 def __init__(self, fobj):
2125 super(InlinedFrameDecorator, self).__init__(fobj)
2128 frame = fobj.inferior_frame()
2129 name = str(frame.name())
2131 if frame.type() == gdb.INLINE_FRAME:
2132 name = name + " [inlined]"
2137 This frame decorator only defines and overrides the @code{function}
2138 method. It lets the supplied @code{FrameDecorator}, which is shipped
2139 with @value{GDBN}, perform the other work associated with printing
2142 The combination of these two objects create this output from a
2146 #0 0x004004e0 in bar () at inline.c:11
2147 #1 0x00400566 in max [inlined] (b=6, a=12) at inline.c:21
2148 #2 0x00400566 in main () at inline.c:31
2151 So in the case of this example, a frame decorator is applied to all
2152 frames, regardless of whether they may be inlined or not. As
2153 @value{GDBN} iterates over the iterator produced by the frame filters,
2154 @value{GDBN} executes each frame decorator which then makes a decision
2155 on what to print in the @code{function} callback. Using a strategy
2156 like this is a way to defer decisions on the frame content to printing
2159 @subheading Eliding Frames
2161 It might be that the above example is not desirable for representing
2162 inlined frames, and a hierarchical approach may be preferred. If we
2163 want to hierarchically represent frames, the @code{elided} frame
2164 decorator interface might be preferable.
2166 This example approaches the issue with the @code{elided} method. This
2167 example is quite long, but very simplistic. It is out-of-scope for
2168 this section to write a complete example that comprehensively covers
2169 all approaches of finding and printing inlined frames. However, this
2170 example illustrates the approach an author might use.
2172 This example comprises of three sections.
2175 class InlineFrameFilter():
2178 self.name = "InlinedFrameFilter"
2181 gdb.frame_filters[self.name] = self
2183 def filter(self, frame_iter):
2184 return ElidingInlineIterator(frame_iter)
2187 This frame filter is very similar to the other examples. The only
2188 difference is this frame filter is wrapping the iterator provided to
2189 it (@code{frame_iter}) with a custom iterator called
2190 @code{ElidingInlineIterator}. This again defers actions to when
2191 @value{GDBN} prints the backtrace, as the iterator is not traversed
2194 The iterator for this example is as follows. It is in this section of
2195 the example where decisions are made on the content of the backtrace.
2198 class ElidingInlineIterator:
2199 def __init__(self, ii):
2200 self.input_iterator = ii
2206 frame = next(self.input_iterator)
2208 if frame.inferior_frame().type() != gdb.INLINE_FRAME:
2212 eliding_frame = next(self.input_iterator)
2213 except StopIteration:
2215 return ElidingFrameDecorator(eliding_frame, [frame])
2218 This iterator implements the Python iterator protocol. When the
2219 @code{next} function is called (when @value{GDBN} prints each frame),
2220 the iterator checks if this frame decorator, @code{frame}, is wrapping
2221 an inlined frame. If it is not, it returns the existing frame decorator
2222 untouched. If it is wrapping an inlined frame, it assumes that the
2223 inlined frame was contained within the next oldest frame,
2224 @code{eliding_frame}, which it fetches. It then creates and returns a
2225 frame decorator, @code{ElidingFrameDecorator}, which contains both the
2226 elided frame, and the eliding frame.
2229 class ElidingInlineDecorator(FrameDecorator):
2231 def __init__(self, frame, elided_frames):
2232 super(ElidingInlineDecorator, self).__init__(frame)
2234 self.elided_frames = elided_frames
2237 return iter(self.elided_frames)
2240 This frame decorator overrides one function and returns the inlined
2241 frame in the @code{elided} method. As before it lets
2242 @code{FrameDecorator} do the rest of the work involved in printing
2243 this frame. This produces the following output.
2246 #0 0x004004e0 in bar () at inline.c:11
2247 #2 0x00400529 in main () at inline.c:25
2248 #1 0x00400529 in max (b=6, a=12) at inline.c:15
2251 In that output, @code{max} which has been inlined into @code{main} is
2252 printed hierarchically. Another approach would be to combine the
2253 @code{function} method, and the @code{elided} method to both print a
2254 marker in the inlined frame, and also show the hierarchical
2257 @node Unwinding Frames in Python
2258 @subsubsection Unwinding Frames in Python
2259 @cindex unwinding frames in Python
2261 In @value{GDBN} terminology ``unwinding'' is the process of finding
2262 the previous frame (that is, caller's) from the current one. An
2263 unwinder has three methods. The first one checks if it can handle
2264 given frame (``sniff'' it). For the frames it can sniff an unwinder
2265 provides two additional methods: it can return frame's ID, and it can
2266 fetch registers from the previous frame. A running @value{GDBN}
2267 mantains a list of the unwinders and calls each unwinder's sniffer in
2268 turn until it finds the one that recognizes the current frame. There
2269 is an API to register an unwinder.
2271 The unwinders that come with @value{GDBN} handle standard frames.
2272 However, mixed language applications (for example, an application
2273 running Java Virtual Machine) sometimes use frame layouts that cannot
2274 be handled by the @value{GDBN} unwinders. You can write Python code
2275 that can handle such custom frames.
2277 You implement a frame unwinder in Python as a class with which has two
2278 attributes, @code{name} and @code{enabled}, with obvious meanings, and
2279 a single method @code{__call__}, which examines a given frame and
2280 returns an object (an instance of @code{gdb.UnwindInfo class)}
2281 describing it. If an unwinder does not recognize a frame, it should
2282 return @code{None}. The code in @value{GDBN} that enables writing
2283 unwinders in Python uses this object to return frame's ID and previous
2284 frame registers when @value{GDBN} core asks for them.
2286 @subheading Unwinder Input
2288 An object passed to an unwinder (a @code{gdb.PendingFrame} instance)
2289 provides a method to read frame's registers:
2291 @defun PendingFrame.read_register (reg)
2292 This method returns the contents of the register @var{regn} in the
2293 frame as a @code{gdb.Value} object. @var{reg} can be either a
2294 register number or a register name; the values are platform-specific.
2295 They are usually found in the corresponding
2296 @file{@var{platform}-tdep.h} file in the @value{GDBN} source tree.
2299 It also provides a factory method to create a @code{gdb.UnwindInfo}
2300 instance to be returned to @value{GDBN}:
2302 @defun PendingFrame.create_unwind_info (frame_id)
2303 Returns a new @code{gdb.UnwindInfo} instance identified by given
2304 @var{frame_id}. The argument is used to build @value{GDBN}'s frame ID
2305 using one of functions provided by @value{GDBN}. @var{frame_id}'s attributes
2306 determine which function will be used, as follows:
2309 @item sp, pc, special
2310 @code{frame_id_build_special (@var{frame_id}.sp, @var{frame_id}.pc, @var{frame_id}.special)}
2313 @code{frame_id_build (@var{frame_id}.sp, @var{frame_id}.pc)}
2315 This is the most common case.
2318 @code{frame_id_build_wild (@var{frame_id}.sp)}
2320 The attribute values should be @code{gdb.Value}
2324 @subheading Unwinder Output: UnwindInfo
2326 Use @code{PendingFrame.create_unwind_info} method described above to
2327 create a @code{gdb.UnwindInfo} instance. Use the following method to
2328 specify caller registers that have been saved in this frame:
2330 @defun gdb.UnwindInfo.add_saved_register (reg, value)
2331 @var{reg} identifies the register. It can be a number or a name, just
2332 as for the @code{PendingFrame.read_register} method above.
2333 @var{value} is a register value (a @code{gdb.Value} object).
2336 @subheading Unwinder Skeleton Code
2338 @value{GDBN} comes with the module containing the base @code{Unwinder}
2339 class. Derive your unwinder class from it and structure the code as
2343 from gdb.unwinders import Unwinder
2345 class FrameId(object):
2346 def __init__(self, sp, pc):
2351 class MyUnwinder(Unwinder):
2353 supe(MyUnwinder, self).__init___(<expects unwinder name argument>)
2355 def __call__(pending_frame):
2356 if not <we recognize frame>:
2358 # Create UnwindInfo. Usually the frame is identified by the stack
2359 # pointer and the program counter.
2360 sp = pending_frame.read_register(<SP number>)
2361 pc = pending_frame.read_register(<PC number>)
2362 unwind_info = pending_frame.create_unwind_info(FrameId(sp, pc))
2364 # Find the values of the registers in the caller's frame and
2365 # save them in the result:
2366 unwind_info.add_saved_register(<register>, <value>)
2369 # Return the result:
2374 @subheading Registering a Unwinder
2376 An object file, a program space, and the @value{GDBN} proper can have
2377 unwinders registered with it.
2379 The @code{gdb.unwinders} module provides the function to register a
2382 @defun gdb.unwinder.register_unwinder (locus, unwinder, replace=False)
2383 @var{locus} is specifies an object file or a program space to which
2384 @var{unwinder} is added. Passing @code{None} or @code{gdb} adds
2385 @var{unwinder} to the @value{GDBN}'s global unwinder list. The newly
2386 added @var{unwinder} will be called before any other unwinder from the
2387 same locus. Two unwinders in the same locus cannot have the same
2388 name. An attempt to add a unwinder with already existing name raises
2389 an exception unless @var{replace} is @code{True}, in which case the
2390 old unwinder is deleted.
2393 @subheading Unwinder Precedence
2395 @value{GDBN} first calls the unwinders from all the object files in no
2396 particular order, then the unwinders from the current program space,
2397 and finally the unwinders from @value{GDBN}.
2399 @node Xmethods In Python
2400 @subsubsection Xmethods In Python
2401 @cindex xmethods in Python
2403 @dfn{Xmethods} are additional methods or replacements for existing
2404 methods of a C@t{++} class. This feature is useful for those cases
2405 where a method defined in C@t{++} source code could be inlined or
2406 optimized out by the compiler, making it unavailable to @value{GDBN}.
2407 For such cases, one can define an xmethod to serve as a replacement
2408 for the method defined in the C@t{++} source code. @value{GDBN} will
2409 then invoke the xmethod, instead of the C@t{++} method, to
2410 evaluate expressions. One can also use xmethods when debugging
2411 with core files. Moreover, when debugging live programs, invoking an
2412 xmethod need not involve running the inferior (which can potentially
2413 perturb its state). Hence, even if the C@t{++} method is available, it
2414 is better to use its replacement xmethod if one is defined.
2416 The xmethods feature in Python is available via the concepts of an
2417 @dfn{xmethod matcher} and an @dfn{xmethod worker}. To
2418 implement an xmethod, one has to implement a matcher and a
2419 corresponding worker for it (more than one worker can be
2420 implemented, each catering to a different overloaded instance of the
2421 method). Internally, @value{GDBN} invokes the @code{match} method of a
2422 matcher to match the class type and method name. On a match, the
2423 @code{match} method returns a list of matching @emph{worker} objects.
2424 Each worker object typically corresponds to an overloaded instance of
2425 the xmethod. They implement a @code{get_arg_types} method which
2426 returns a sequence of types corresponding to the arguments the xmethod
2427 requires. @value{GDBN} uses this sequence of types to perform
2428 overload resolution and picks a winning xmethod worker. A winner
2429 is also selected from among the methods @value{GDBN} finds in the
2430 C@t{++} source code. Next, the winning xmethod worker and the
2431 winning C@t{++} method are compared to select an overall winner. In
2432 case of a tie between a xmethod worker and a C@t{++} method, the
2433 xmethod worker is selected as the winner. That is, if a winning
2434 xmethod worker is found to be equivalent to the winning C@t{++}
2435 method, then the xmethod worker is treated as a replacement for
2436 the C@t{++} method. @value{GDBN} uses the overall winner to invoke the
2437 method. If the winning xmethod worker is the overall winner, then
2438 the corresponding xmethod is invoked via the @code{__call__} method
2439 of the worker object.
2441 If one wants to implement an xmethod as a replacement for an
2442 existing C@t{++} method, then they have to implement an equivalent
2443 xmethod which has exactly the same name and takes arguments of
2444 exactly the same type as the C@t{++} method. If the user wants to
2445 invoke the C@t{++} method even though a replacement xmethod is
2446 available for that method, then they can disable the xmethod.
2448 @xref{Xmethod API}, for API to implement xmethods in Python.
2449 @xref{Writing an Xmethod}, for implementing xmethods in Python.
2452 @subsubsection Xmethod API
2455 The @value{GDBN} Python API provides classes, interfaces and functions
2456 to implement, register and manipulate xmethods.
2457 @xref{Xmethods In Python}.
2459 An xmethod matcher should be an instance of a class derived from
2460 @code{XMethodMatcher} defined in the module @code{gdb.xmethod}, or an
2461 object with similar interface and attributes. An instance of
2462 @code{XMethodMatcher} has the following attributes:
2465 The name of the matcher.
2469 A boolean value indicating whether the matcher is enabled or disabled.
2473 A list of named methods managed by the matcher. Each object in the list
2474 is an instance of the class @code{XMethod} defined in the module
2475 @code{gdb.xmethod}, or any object with the following attributes:
2480 Name of the xmethod which should be unique for each xmethod
2481 managed by the matcher.
2484 A boolean value indicating whether the xmethod is enabled or
2489 The class @code{XMethod} is a convenience class with same
2490 attributes as above along with the following constructor:
2492 @defun XMethod.__init__ (self, name)
2493 Constructs an enabled xmethod with name @var{name}.
2498 The @code{XMethodMatcher} class has the following methods:
2500 @defun XMethodMatcher.__init__ (self, name)
2501 Constructs an enabled xmethod matcher with name @var{name}. The
2502 @code{methods} attribute is initialized to @code{None}.
2505 @defun XMethodMatcher.match (self, class_type, method_name)
2506 Derived classes should override this method. It should return a
2507 xmethod worker object (or a sequence of xmethod worker
2508 objects) matching the @var{class_type} and @var{method_name}.
2509 @var{class_type} is a @code{gdb.Type} object, and @var{method_name}
2510 is a string value. If the matcher manages named methods as listed in
2511 its @code{methods} attribute, then only those worker objects whose
2512 corresponding entries in the @code{methods} list are enabled should be
2516 An xmethod worker should be an instance of a class derived from
2517 @code{XMethodWorker} defined in the module @code{gdb.xmethod},
2518 or support the following interface:
2520 @defun XMethodWorker.get_arg_types (self)
2521 This method returns a sequence of @code{gdb.Type} objects corresponding
2522 to the arguments that the xmethod takes. It can return an empty
2523 sequence or @code{None} if the xmethod does not take any arguments.
2524 If the xmethod takes a single argument, then a single
2525 @code{gdb.Type} object corresponding to it can be returned.
2528 @defun XMethodWorker.get_result_type (self, *args)
2529 This method returns a @code{gdb.Type} object representing the type
2530 of the result of invoking this xmethod.
2531 The @var{args} argument is the same tuple of arguments that would be
2532 passed to the @code{__call__} method of this worker.
2535 @defun XMethodWorker.__call__ (self, *args)
2536 This is the method which does the @emph{work} of the xmethod. The
2537 @var{args} arguments is the tuple of arguments to the xmethod. Each
2538 element in this tuple is a gdb.Value object. The first element is
2539 always the @code{this} pointer value.
2542 For @value{GDBN} to lookup xmethods, the xmethod matchers
2543 should be registered using the following function defined in the module
2546 @defun register_xmethod_matcher (locus, matcher, replace=False)
2547 The @code{matcher} is registered with @code{locus}, replacing an
2548 existing matcher with the same name as @code{matcher} if
2549 @code{replace} is @code{True}. @code{locus} can be a
2550 @code{gdb.Objfile} object (@pxref{Objfiles In Python}), or a
2551 @code{gdb.Progspace} object (@pxref{Progspaces In Python}), or
2552 @code{None}. If it is @code{None}, then @code{matcher} is registered
2556 @node Writing an Xmethod
2557 @subsubsection Writing an Xmethod
2558 @cindex writing xmethods in Python
2560 Implementing xmethods in Python will require implementing xmethod
2561 matchers and xmethod workers (@pxref{Xmethods In Python}). Consider
2562 the following C@t{++} class:
2568 MyClass (int a) : a_(a) @{ @}
2570 int geta (void) @{ return a_; @}
2571 int operator+ (int b);
2578 MyClass::operator+ (int b)
2585 Let us define two xmethods for the class @code{MyClass}, one
2586 replacing the method @code{geta}, and another adding an overloaded
2587 flavor of @code{operator+} which takes a @code{MyClass} argument (the
2588 C@t{++} code above already has an overloaded @code{operator+}
2589 which takes an @code{int} argument). The xmethod matcher can be
2593 class MyClass_geta(gdb.xmethod.XMethod):
2595 gdb.xmethod.XMethod.__init__(self, 'geta')
2597 def get_worker(self, method_name):
2598 if method_name == 'geta':
2599 return MyClassWorker_geta()
2602 class MyClass_sum(gdb.xmethod.XMethod):
2604 gdb.xmethod.XMethod.__init__(self, 'sum')
2606 def get_worker(self, method_name):
2607 if method_name == 'operator+':
2608 return MyClassWorker_plus()
2611 class MyClassMatcher(gdb.xmethod.XMethodMatcher):
2613 gdb.xmethod.XMethodMatcher.__init__(self, 'MyClassMatcher')
2614 # List of methods 'managed' by this matcher
2615 self.methods = [MyClass_geta(), MyClass_sum()]
2617 def match(self, class_type, method_name):
2618 if class_type.tag != 'MyClass':
2621 for method in self.methods:
2623 worker = method.get_worker(method_name)
2625 workers.append(worker)
2631 Notice that the @code{match} method of @code{MyClassMatcher} returns
2632 a worker object of type @code{MyClassWorker_geta} for the @code{geta}
2633 method, and a worker object of type @code{MyClassWorker_plus} for the
2634 @code{operator+} method. This is done indirectly via helper classes
2635 derived from @code{gdb.xmethod.XMethod}. One does not need to use the
2636 @code{methods} attribute in a matcher as it is optional. However, if a
2637 matcher manages more than one xmethod, it is a good practice to list the
2638 xmethods in the @code{methods} attribute of the matcher. This will then
2639 facilitate enabling and disabling individual xmethods via the
2640 @code{enable/disable} commands. Notice also that a worker object is
2641 returned only if the corresponding entry in the @code{methods} attribute
2642 of the matcher is enabled.
2644 The implementation of the worker classes returned by the matcher setup
2645 above is as follows:
2648 class MyClassWorker_geta(gdb.xmethod.XMethodWorker):
2649 def get_arg_types(self):
2652 def get_result_type(self, obj):
2653 return gdb.lookup_type('int')
2655 def __call__(self, obj):
2659 class MyClassWorker_plus(gdb.xmethod.XMethodWorker):
2660 def get_arg_types(self):
2661 return gdb.lookup_type('MyClass')
2663 def get_result_type(self, obj):
2664 return gdb.lookup_type('int')
2666 def __call__(self, obj, other):
2667 return obj['a_'] + other['a_']
2670 For @value{GDBN} to actually lookup a xmethod, it has to be
2671 registered with it. The matcher defined above is registered with
2672 @value{GDBN} globally as follows:
2675 gdb.xmethod.register_xmethod_matcher(None, MyClassMatcher())
2678 If an object @code{obj} of type @code{MyClass} is initialized in C@t{++}
2686 then, after loading the Python script defining the xmethod matchers
2687 and workers into @code{GDBN}, invoking the method @code{geta} or using
2688 the operator @code{+} on @code{obj} will invoke the xmethods
2699 Consider another example with a C++ template class:
2706 MyTemplate () : dsize_(10), data_ (new T [10]) @{ @}
2707 ~MyTemplate () @{ delete [] data_; @}
2709 int footprint (void)
2711 return sizeof (T) * dsize_ + sizeof (MyTemplate<T>);
2720 Let us implement an xmethod for the above class which serves as a
2721 replacement for the @code{footprint} method. The full code listing
2722 of the xmethod workers and xmethod matchers is as follows:
2725 class MyTemplateWorker_footprint(gdb.xmethod.XMethodWorker):
2726 def __init__(self, class_type):
2727 self.class_type = class_type
2729 def get_arg_types(self):
2732 def get_result_type(self):
2733 return gdb.lookup_type('int')
2735 def __call__(self, obj):
2736 return (self.class_type.sizeof +
2738 self.class_type.template_argument(0).sizeof)
2741 class MyTemplateMatcher_footprint(gdb.xmethod.XMethodMatcher):
2743 gdb.xmethod.XMethodMatcher.__init__(self, 'MyTemplateMatcher')
2745 def match(self, class_type, method_name):
2746 if (re.match('MyTemplate<[ \t\n]*[_a-zA-Z][ _a-zA-Z0-9]*>',
2748 method_name == 'footprint'):
2749 return MyTemplateWorker_footprint(class_type)
2752 Notice that, in this example, we have not used the @code{methods}
2753 attribute of the matcher as the matcher manages only one xmethod. The
2754 user can enable/disable this xmethod by enabling/disabling the matcher
2757 @node Inferiors In Python
2758 @subsubsection Inferiors In Python
2759 @cindex inferiors in Python
2761 @findex gdb.Inferior
2762 Programs which are being run under @value{GDBN} are called inferiors
2763 (@pxref{Inferiors and Programs}). Python scripts can access
2764 information about and manipulate inferiors controlled by @value{GDBN}
2765 via objects of the @code{gdb.Inferior} class.
2767 The following inferior-related functions are available in the @code{gdb}
2770 @defun gdb.inferiors ()
2771 Return a tuple containing all inferior objects.
2774 @defun gdb.selected_inferior ()
2775 Return an object representing the current inferior.
2778 A @code{gdb.Inferior} object has the following attributes:
2780 @defvar Inferior.num
2781 ID of inferior, as assigned by GDB.
2784 @defvar Inferior.pid
2785 Process ID of the inferior, as assigned by the underlying operating
2789 @defvar Inferior.was_attached
2790 Boolean signaling whether the inferior was created using `attach', or
2791 started by @value{GDBN} itself.
2794 A @code{gdb.Inferior} object has the following methods:
2796 @defun Inferior.is_valid ()
2797 Returns @code{True} if the @code{gdb.Inferior} object is valid,
2798 @code{False} if not. A @code{gdb.Inferior} object will become invalid
2799 if the inferior no longer exists within @value{GDBN}. All other
2800 @code{gdb.Inferior} methods will throw an exception if it is invalid
2801 at the time the method is called.
2804 @defun Inferior.threads ()
2805 This method returns a tuple holding all the threads which are valid
2806 when it is called. If there are no valid threads, the method will
2807 return an empty tuple.
2810 @findex Inferior.read_memory
2811 @defun Inferior.read_memory (address, length)
2812 Read @var{length} addressable memory units from the inferior, starting at
2813 @var{address}. Returns a buffer object, which behaves much like an array
2814 or a string. It can be modified and given to the
2815 @code{Inferior.write_memory} function. In Python 3, the return
2816 value is a @code{memoryview} object.
2819 @findex Inferior.write_memory
2820 @defun Inferior.write_memory (address, buffer @r{[}, length@r{]})
2821 Write the contents of @var{buffer} to the inferior, starting at
2822 @var{address}. The @var{buffer} parameter must be a Python object
2823 which supports the buffer protocol, i.e., a string, an array or the
2824 object returned from @code{Inferior.read_memory}. If given, @var{length}
2825 determines the number of addressable memory units from @var{buffer} to be
2829 @findex gdb.search_memory
2830 @defun Inferior.search_memory (address, length, pattern)
2831 Search a region of the inferior memory starting at @var{address} with
2832 the given @var{length} using the search pattern supplied in
2833 @var{pattern}. The @var{pattern} parameter must be a Python object
2834 which supports the buffer protocol, i.e., a string, an array or the
2835 object returned from @code{gdb.read_memory}. Returns a Python @code{Long}
2836 containing the address where the pattern was found, or @code{None} if
2837 the pattern could not be found.
2840 @findex Inferior.thread_from_thread_handle
2841 @defun Inferior.thread_from_thread_handle (thread_handle)
2842 Return the thread object corresponding to @var{thread_handle}, a thread
2843 library specific data structure such as @code{pthread_t} for pthreads
2844 library implementations.
2847 @node Events In Python
2848 @subsubsection Events In Python
2849 @cindex inferior events in Python
2851 @value{GDBN} provides a general event facility so that Python code can be
2852 notified of various state changes, particularly changes that occur in
2855 An @dfn{event} is just an object that describes some state change. The
2856 type of the object and its attributes will vary depending on the details
2857 of the change. All the existing events are described below.
2859 In order to be notified of an event, you must register an event handler
2860 with an @dfn{event registry}. An event registry is an object in the
2861 @code{gdb.events} module which dispatches particular events. A registry
2862 provides methods to register and unregister event handlers:
2864 @defun EventRegistry.connect (object)
2865 Add the given callable @var{object} to the registry. This object will be
2866 called when an event corresponding to this registry occurs.
2869 @defun EventRegistry.disconnect (object)
2870 Remove the given @var{object} from the registry. Once removed, the object
2871 will no longer receive notifications of events.
2877 def exit_handler (event):
2878 print "event type: exit"
2879 print "exit code: %d" % (event.exit_code)
2881 gdb.events.exited.connect (exit_handler)
2884 In the above example we connect our handler @code{exit_handler} to the
2885 registry @code{events.exited}. Once connected, @code{exit_handler} gets
2886 called when the inferior exits. The argument @dfn{event} in this example is
2887 of type @code{gdb.ExitedEvent}. As you can see in the example the
2888 @code{ExitedEvent} object has an attribute which indicates the exit code of
2891 The following is a listing of the event registries that are available and
2892 details of the events they emit:
2897 Emits @code{gdb.ThreadEvent}.
2899 Some events can be thread specific when @value{GDBN} is running in non-stop
2900 mode. When represented in Python, these events all extend
2901 @code{gdb.ThreadEvent}. Note, this event is not emitted directly; instead,
2902 events which are emitted by this or other modules might extend this event.
2903 Examples of these events are @code{gdb.BreakpointEvent} and
2904 @code{gdb.ContinueEvent}.
2906 @defvar ThreadEvent.inferior_thread
2907 In non-stop mode this attribute will be set to the specific thread which was
2908 involved in the emitted event. Otherwise, it will be set to @code{None}.
2911 Emits @code{gdb.ContinueEvent} which extends @code{gdb.ThreadEvent}.
2913 This event indicates that the inferior has been continued after a stop. For
2914 inherited attribute refer to @code{gdb.ThreadEvent} above.
2917 Emits @code{events.ExitedEvent} which indicates that the inferior has exited.
2918 @code{events.ExitedEvent} has two attributes:
2919 @defvar ExitedEvent.exit_code
2920 An integer representing the exit code, if available, which the inferior
2921 has returned. (The exit code could be unavailable if, for example,
2922 @value{GDBN} detaches from the inferior.) If the exit code is unavailable,
2923 the attribute does not exist.
2925 @defvar ExitedEvent.inferior
2926 A reference to the inferior which triggered the @code{exited} event.
2930 Emits @code{gdb.StopEvent} which extends @code{gdb.ThreadEvent}.
2932 Indicates that the inferior has stopped. All events emitted by this registry
2933 extend StopEvent. As a child of @code{gdb.ThreadEvent}, @code{gdb.StopEvent}
2934 will indicate the stopped thread when @value{GDBN} is running in non-stop
2935 mode. Refer to @code{gdb.ThreadEvent} above for more details.
2937 Emits @code{gdb.SignalEvent} which extends @code{gdb.StopEvent}.
2939 This event indicates that the inferior or one of its threads has received as
2940 signal. @code{gdb.SignalEvent} has the following attributes:
2942 @defvar SignalEvent.stop_signal
2943 A string representing the signal received by the inferior. A list of possible
2944 signal values can be obtained by running the command @code{info signals} in
2945 the @value{GDBN} command prompt.
2948 Also emits @code{gdb.BreakpointEvent} which extends @code{gdb.StopEvent}.
2950 @code{gdb.BreakpointEvent} event indicates that one or more breakpoints have
2951 been hit, and has the following attributes:
2953 @defvar BreakpointEvent.breakpoints
2954 A sequence containing references to all the breakpoints (type
2955 @code{gdb.Breakpoint}) that were hit.
2956 @xref{Breakpoints In Python}, for details of the @code{gdb.Breakpoint} object.
2958 @defvar BreakpointEvent.breakpoint
2959 A reference to the first breakpoint that was hit.
2960 This function is maintained for backward compatibility and is now deprecated
2961 in favor of the @code{gdb.BreakpointEvent.breakpoints} attribute.
2964 @item events.new_objfile
2965 Emits @code{gdb.NewObjFileEvent} which indicates that a new object file has
2966 been loaded by @value{GDBN}. @code{gdb.NewObjFileEvent} has one attribute:
2968 @defvar NewObjFileEvent.new_objfile
2969 A reference to the object file (@code{gdb.Objfile}) which has been loaded.
2970 @xref{Objfiles In Python}, for details of the @code{gdb.Objfile} object.
2973 @item events.clear_objfiles
2974 Emits @code{gdb.ClearObjFilesEvent} which indicates that the list of object
2975 files for a program space has been reset.
2976 @code{gdb.ClearObjFilesEvent} has one attribute:
2978 @defvar ClearObjFilesEvent.progspace
2979 A reference to the program space (@code{gdb.Progspace}) whose objfile list has
2980 been cleared. @xref{Progspaces In Python}.
2983 @item events.inferior_call_pre
2984 Emits @code{gdb.InferiorCallPreEvent} which indicates that a function in
2985 the inferior is about to be called.
2987 @defvar InferiorCallPreEvent.ptid
2988 The thread in which the call will be run.
2991 @defvar InferiorCallPreEvent.address
2992 The location of the function to be called.
2995 @item events.inferior_call_post
2996 Emits @code{gdb.InferiorCallPostEvent} which indicates that a function in
2997 the inferior has returned.
2999 @defvar InferiorCallPostEvent.ptid
3000 The thread in which the call was run.
3003 @defvar InferiorCallPostEvent.address
3004 The location of the function that was called.
3007 @item events.memory_changed
3008 Emits @code{gdb.MemoryChangedEvent} which indicates that the memory of the
3009 inferior has been modified by the @value{GDBN} user, for instance via a
3010 command like @w{@code{set *addr = value}}. The event has the following
3013 @defvar MemoryChangedEvent.address
3014 The start address of the changed region.
3017 @defvar MemoryChangedEvent.length
3018 Length in bytes of the changed region.
3021 @item events.register_changed
3022 Emits @code{gdb.RegisterChangedEvent} which indicates that a register in the
3023 inferior has been modified by the @value{GDBN} user.
3025 @defvar RegisterChangedEvent.frame
3026 A gdb.Frame object representing the frame in which the register was modified.
3028 @defvar RegisterChangedEvent.regnum
3029 Denotes which register was modified.
3032 @item events.breakpoint_created
3033 This is emitted when a new breakpoint has been created. The argument
3034 that is passed is the new @code{gdb.Breakpoint} object.
3036 @item events.breakpoint_modified
3037 This is emitted when a breakpoint has been modified in some way. The
3038 argument that is passed is the new @code{gdb.Breakpoint} object.
3040 @item events.breakpoint_deleted
3041 This is emitted when a breakpoint has been deleted. The argument that
3042 is passed is the @code{gdb.Breakpoint} object. When this event is
3043 emitted, the @code{gdb.Breakpoint} object will already be in its
3044 invalid state; that is, the @code{is_valid} method will return
3047 @item events.before_prompt
3048 This event carries no payload. It is emitted each time @value{GDBN}
3049 presents a prompt to the user.
3051 @item events.new_inferior
3052 This is emitted when a new inferior is created. Note that the
3053 inferior is not necessarily running; in fact, it may not even have an
3054 associated executable.
3056 The event is of type @code{gdb.NewInferiorEvent}. This has a single
3059 @defvar NewInferiorEvent.inferior
3060 The new inferior, a @code{gdb.Inferior} object.
3063 @item events.inferior_deleted
3064 This is emitted when an inferior has been deleted. Note that this is
3065 not the same as process exit; it is notified when the inferior itself
3066 is removed, say via @code{remove-inferiors}.
3068 The event is of type @code{gdb.InferiorDeletedEvent}. This has a single
3071 @defvar NewInferiorEvent.inferior
3072 The inferior that is being removed, a @code{gdb.Inferior} object.
3075 @item events.new_thread
3076 This is emitted when @value{GDBN} notices a new thread. The event is of
3077 type @code{gdb.NewThreadEvent}, which extends @code{gdb.ThreadEvent}.
3078 This has a single attribute:
3080 @defvar NewThreadEvent.inferior_thread
3086 @node Threads In Python
3087 @subsubsection Threads In Python
3088 @cindex threads in python
3090 @findex gdb.InferiorThread
3091 Python scripts can access information about, and manipulate inferior threads
3092 controlled by @value{GDBN}, via objects of the @code{gdb.InferiorThread} class.
3094 The following thread-related functions are available in the @code{gdb}
3097 @findex gdb.selected_thread
3098 @defun gdb.selected_thread ()
3099 This function returns the thread object for the selected thread. If there
3100 is no selected thread, this will return @code{None}.
3103 A @code{gdb.InferiorThread} object has the following attributes:
3105 @defvar InferiorThread.name
3106 The name of the thread. If the user specified a name using
3107 @code{thread name}, then this returns that name. Otherwise, if an
3108 OS-supplied name is available, then it is returned. Otherwise, this
3109 returns @code{None}.
3111 This attribute can be assigned to. The new value must be a string
3112 object, which sets the new name, or @code{None}, which removes any
3113 user-specified thread name.
3116 @defvar InferiorThread.num
3117 The per-inferior number of the thread, as assigned by GDB.
3120 @defvar InferiorThread.global_num
3121 The global ID of the thread, as assigned by GDB. You can use this to
3122 make Python breakpoints thread-specific, for example
3123 (@pxref{python_breakpoint_thread,,The Breakpoint.thread attribute}).
3126 @defvar InferiorThread.ptid
3127 ID of the thread, as assigned by the operating system. This attribute is a
3128 tuple containing three integers. The first is the Process ID (PID); the second
3129 is the Lightweight Process ID (LWPID), and the third is the Thread ID (TID).
3130 Either the LWPID or TID may be 0, which indicates that the operating system
3131 does not use that identifier.
3134 @defvar InferiorThread.inferior
3135 The inferior this thread belongs to. This attribute is represented as
3136 a @code{gdb.Inferior} object. This attribute is not writable.
3139 A @code{gdb.InferiorThread} object has the following methods:
3141 @defun InferiorThread.is_valid ()
3142 Returns @code{True} if the @code{gdb.InferiorThread} object is valid,
3143 @code{False} if not. A @code{gdb.InferiorThread} object will become
3144 invalid if the thread exits, or the inferior that the thread belongs
3145 is deleted. All other @code{gdb.InferiorThread} methods will throw an
3146 exception if it is invalid at the time the method is called.
3149 @defun InferiorThread.switch ()
3150 This changes @value{GDBN}'s currently selected thread to the one represented
3154 @defun InferiorThread.is_stopped ()
3155 Return a Boolean indicating whether the thread is stopped.
3158 @defun InferiorThread.is_running ()
3159 Return a Boolean indicating whether the thread is running.
3162 @defun InferiorThread.is_exited ()
3163 Return a Boolean indicating whether the thread is exited.
3166 @node Recordings In Python
3167 @subsubsection Recordings In Python
3168 @cindex recordings in python
3170 The following recordings-related functions
3171 (@pxref{Process Record and Replay}) are available in the @code{gdb}
3174 @defun gdb.start_recording (@r{[}method@r{]}, @r{[}format@r{]})
3175 Start a recording using the given @var{method} and @var{format}. If
3176 no @var{format} is given, the default format for the recording method
3177 is used. If no @var{method} is given, the default method will be used.
3178 Returns a @code{gdb.Record} object on success. Throw an exception on
3181 The following strings can be passed as @var{method}:
3187 @code{"btrace"}: Possible values for @var{format}: @code{"pt"},
3188 @code{"bts"} or leave out for default format.
3192 @defun gdb.current_recording ()
3193 Access a currently running recording. Return a @code{gdb.Record}
3194 object on success. Return @code{None} if no recording is currently
3198 @defun gdb.stop_recording ()
3199 Stop the current recording. Throw an exception if no recording is
3200 currently active. All record objects become invalid after this call.
3203 A @code{gdb.Record} object has the following attributes:
3205 @defvar Record.method
3206 A string with the current recording method, e.g.@: @code{full} or
3210 @defvar Record.format
3211 A string with the current recording format, e.g.@: @code{bt}, @code{pts} or
3215 @defvar Record.begin
3216 A method specific instruction object representing the first instruction
3221 A method specific instruction object representing the current
3222 instruction, that is not actually part of the recording.
3225 @defvar Record.replay_position
3226 The instruction representing the current replay position. If there is
3227 no replay active, this will be @code{None}.
3230 @defvar Record.instruction_history
3231 A list with all recorded instructions.
3234 @defvar Record.function_call_history
3235 A list with all recorded function call segments.
3238 A @code{gdb.Record} object has the following methods:
3240 @defun Record.goto (instruction)
3241 Move the replay position to the given @var{instruction}.
3244 The common @code{gdb.Instruction} class that recording method specific
3245 instruction objects inherit from, has the following attributes:
3247 @defvar Instruction.pc
3248 An integer representing this instruction's address.
3251 @defvar Instruction.data
3252 A buffer with the raw instruction data. In Python 3, the return value is a
3253 @code{memoryview} object.
3256 @defvar Instruction.decoded
3257 A human readable string with the disassembled instruction.
3260 @defvar Instruction.size
3261 The size of the instruction in bytes.
3264 Additionally @code{gdb.RecordInstruction} has the following attributes:
3266 @defvar RecordInstruction.number
3267 An integer identifying this instruction. @code{number} corresponds to
3268 the numbers seen in @code{record instruction-history}
3269 (@pxref{Process Record and Replay}).
3272 @defvar RecordInstruction.sal
3273 A @code{gdb.Symtab_and_line} object representing the associated symtab
3274 and line of this instruction. May be @code{None} if no debug information is
3278 @defvar RecordInstruction.is_speculative
3279 A boolean indicating whether the instruction was executed speculatively.
3282 If an error occured during recording or decoding a recording, this error is
3283 represented by a @code{gdb.RecordGap} object in the instruction list. It has
3284 the following attributes:
3286 @defvar RecordGap.number
3287 An integer identifying this gap. @code{number} corresponds to the numbers seen
3288 in @code{record instruction-history} (@pxref{Process Record and Replay}).
3291 @defvar RecordGap.error_code
3292 A numerical representation of the reason for the gap. The value is specific to
3293 the current recording method.
3296 @defvar RecordGap.error_string
3297 A human readable string with the reason for the gap.
3300 A @code{gdb.RecordFunctionSegment} object has the following attributes:
3302 @defvar RecordFunctionSegment.number
3303 An integer identifying this function segment. @code{number} corresponds to
3304 the numbers seen in @code{record function-call-history}
3305 (@pxref{Process Record and Replay}).
3308 @defvar RecordFunctionSegment.symbol
3309 A @code{gdb.Symbol} object representing the associated symbol. May be
3310 @code{None} if no debug information is available.
3313 @defvar RecordFunctionSegment.level
3314 An integer representing the function call's stack level. May be
3315 @code{None} if the function call is a gap.
3318 @defvar RecordFunctionSegment.instructions
3319 A list of @code{gdb.RecordInstruction} or @code{gdb.RecordGap} objects
3320 associated with this function call.
3323 @defvar RecordFunctionSegment.up
3324 A @code{gdb.RecordFunctionSegment} object representing the caller's
3325 function segment. If the call has not been recorded, this will be the
3326 function segment to which control returns. If neither the call nor the
3327 return have been recorded, this will be @code{None}.
3330 @defvar RecordFunctionSegment.prev
3331 A @code{gdb.RecordFunctionSegment} object representing the previous
3332 segment of this function call. May be @code{None}.
3335 @defvar RecordFunctionSegment.next
3336 A @code{gdb.RecordFunctionSegment} object representing the next segment of
3337 this function call. May be @code{None}.
3340 The following example demonstrates the usage of these objects and
3341 functions to create a function that will rewind a record to the last
3342 time a function in a different file was executed. This would typically
3343 be used to track the execution of user provided callback functions in a
3344 library which typically are not visible in a back trace.
3348 rec = gdb.current_recording ()
3352 insn = rec.instruction_history
3357 position = insn.index (rec.replay_position)
3361 filename = insn[position].sal.symtab.fullname ()
3365 for i in reversed (insn[:position]):
3367 current = i.sal.symtab.fullname ()
3371 if filename == current:
3378 Another possible application is to write a function that counts the
3379 number of code executions in a given line range. This line range can
3380 contain parts of functions or span across several functions and is not
3381 limited to be contiguous.
3384 def countrange (filename, linerange):
3387 def filter_only (file_name):
3388 for call in gdb.current_recording ().function_call_history:
3390 if file_name in call.symbol.symtab.fullname ():
3395 for c in filter_only (filename):
3396 for i in c.instructions:
3398 if i.sal.line in linerange:
3407 @node Commands In Python
3408 @subsubsection Commands In Python
3410 @cindex commands in python
3411 @cindex python commands
3412 You can implement new @value{GDBN} CLI commands in Python. A CLI
3413 command is implemented using an instance of the @code{gdb.Command}
3414 class, most commonly using a subclass.
3416 @defun Command.__init__ (name, @var{command_class} @r{[}, @var{completer_class} @r{[}, @var{prefix}@r{]]})
3417 The object initializer for @code{Command} registers the new command
3418 with @value{GDBN}. This initializer is normally invoked from the
3419 subclass' own @code{__init__} method.
3421 @var{name} is the name of the command. If @var{name} consists of
3422 multiple words, then the initial words are looked for as prefix
3423 commands. In this case, if one of the prefix commands does not exist,
3424 an exception is raised.
3426 There is no support for multi-line commands.
3428 @var{command_class} should be one of the @samp{COMMAND_} constants
3429 defined below. This argument tells @value{GDBN} how to categorize the
3430 new command in the help system.
3432 @var{completer_class} is an optional argument. If given, it should be
3433 one of the @samp{COMPLETE_} constants defined below. This argument
3434 tells @value{GDBN} how to perform completion for this command. If not
3435 given, @value{GDBN} will attempt to complete using the object's
3436 @code{complete} method (see below); if no such method is found, an
3437 error will occur when completion is attempted.
3439 @var{prefix} is an optional argument. If @code{True}, then the new
3440 command is a prefix command; sub-commands of this command may be
3443 The help text for the new command is taken from the Python
3444 documentation string for the command's class, if there is one. If no
3445 documentation string is provided, the default value ``This command is
3446 not documented.'' is used.
3449 @cindex don't repeat Python command
3450 @defun Command.dont_repeat ()
3451 By default, a @value{GDBN} command is repeated when the user enters a
3452 blank line at the command prompt. A command can suppress this
3453 behavior by invoking the @code{dont_repeat} method. This is similar
3454 to the user command @code{dont-repeat}, see @ref{Define, dont-repeat}.
3457 @defun Command.invoke (argument, from_tty)
3458 This method is called by @value{GDBN} when this command is invoked.
3460 @var{argument} is a string. It is the argument to the command, after
3461 leading and trailing whitespace has been stripped.
3463 @var{from_tty} is a boolean argument. When true, this means that the
3464 command was entered by the user at the terminal; when false it means
3465 that the command came from elsewhere.
3467 If this method throws an exception, it is turned into a @value{GDBN}
3468 @code{error} call. Otherwise, the return value is ignored.
3470 @findex gdb.string_to_argv
3471 To break @var{argument} up into an argv-like string use
3472 @code{gdb.string_to_argv}. This function behaves identically to
3473 @value{GDBN}'s internal argument lexer @code{buildargv}.
3474 It is recommended to use this for consistency.
3475 Arguments are separated by spaces and may be quoted.
3479 print gdb.string_to_argv ("1 2\ \\\"3 '4 \"5' \"6 '7\"")
3480 ['1', '2 "3', '4 "5', "6 '7"]
3485 @cindex completion of Python commands
3486 @defun Command.complete (text, word)
3487 This method is called by @value{GDBN} when the user attempts
3488 completion on this command. All forms of completion are handled by
3489 this method, that is, the @key{TAB} and @key{M-?} key bindings
3490 (@pxref{Completion}), and the @code{complete} command (@pxref{Help,
3493 The arguments @var{text} and @var{word} are both strings; @var{text}
3494 holds the complete command line up to the cursor's location, while
3495 @var{word} holds the last word of the command line; this is computed
3496 using a word-breaking heuristic.
3498 The @code{complete} method can return several values:
3501 If the return value is a sequence, the contents of the sequence are
3502 used as the completions. It is up to @code{complete} to ensure that the
3503 contents actually do complete the word. A zero-length sequence is
3504 allowed, it means that there were no completions available. Only
3505 string elements of the sequence are used; other elements in the
3506 sequence are ignored.
3509 If the return value is one of the @samp{COMPLETE_} constants defined
3510 below, then the corresponding @value{GDBN}-internal completion
3511 function is invoked, and its result is used.
3514 All other results are treated as though there were no available
3519 When a new command is registered, it must be declared as a member of
3520 some general class of commands. This is used to classify top-level
3521 commands in the on-line help system; note that prefix commands are not
3522 listed under their own category but rather that of their top-level
3523 command. The available classifications are represented by constants
3524 defined in the @code{gdb} module:
3527 @findex COMMAND_NONE
3528 @findex gdb.COMMAND_NONE
3529 @item gdb.COMMAND_NONE
3530 The command does not belong to any particular class. A command in
3531 this category will not be displayed in any of the help categories.
3533 @findex COMMAND_RUNNING
3534 @findex gdb.COMMAND_RUNNING
3535 @item gdb.COMMAND_RUNNING
3536 The command is related to running the inferior. For example,
3537 @code{start}, @code{step}, and @code{continue} are in this category.
3538 Type @kbd{help running} at the @value{GDBN} prompt to see a list of
3539 commands in this category.
3541 @findex COMMAND_DATA
3542 @findex gdb.COMMAND_DATA
3543 @item gdb.COMMAND_DATA
3544 The command is related to data or variables. For example,
3545 @code{call}, @code{find}, and @code{print} are in this category. Type
3546 @kbd{help data} at the @value{GDBN} prompt to see a list of commands
3549 @findex COMMAND_STACK
3550 @findex gdb.COMMAND_STACK
3551 @item gdb.COMMAND_STACK
3552 The command has to do with manipulation of the stack. For example,
3553 @code{backtrace}, @code{frame}, and @code{return} are in this
3554 category. Type @kbd{help stack} at the @value{GDBN} prompt to see a
3555 list of commands in this category.
3557 @findex COMMAND_FILES
3558 @findex gdb.COMMAND_FILES
3559 @item gdb.COMMAND_FILES
3560 This class is used for file-related commands. For example,
3561 @code{file}, @code{list} and @code{section} are in this category.
3562 Type @kbd{help files} at the @value{GDBN} prompt to see a list of
3563 commands in this category.
3565 @findex COMMAND_SUPPORT
3566 @findex gdb.COMMAND_SUPPORT
3567 @item gdb.COMMAND_SUPPORT
3568 This should be used for ``support facilities'', generally meaning
3569 things that are useful to the user when interacting with @value{GDBN},
3570 but not related to the state of the inferior. For example,
3571 @code{help}, @code{make}, and @code{shell} are in this category. Type
3572 @kbd{help support} at the @value{GDBN} prompt to see a list of
3573 commands in this category.
3575 @findex COMMAND_STATUS
3576 @findex gdb.COMMAND_STATUS
3577 @item gdb.COMMAND_STATUS
3578 The command is an @samp{info}-related command, that is, related to the
3579 state of @value{GDBN} itself. For example, @code{info}, @code{macro},
3580 and @code{show} are in this category. Type @kbd{help status} at the
3581 @value{GDBN} prompt to see a list of commands in this category.
3583 @findex COMMAND_BREAKPOINTS
3584 @findex gdb.COMMAND_BREAKPOINTS
3585 @item gdb.COMMAND_BREAKPOINTS
3586 The command has to do with breakpoints. For example, @code{break},
3587 @code{clear}, and @code{delete} are in this category. Type @kbd{help
3588 breakpoints} at the @value{GDBN} prompt to see a list of commands in
3591 @findex COMMAND_TRACEPOINTS
3592 @findex gdb.COMMAND_TRACEPOINTS
3593 @item gdb.COMMAND_TRACEPOINTS
3594 The command has to do with tracepoints. For example, @code{trace},
3595 @code{actions}, and @code{tfind} are in this category. Type
3596 @kbd{help tracepoints} at the @value{GDBN} prompt to see a list of
3597 commands in this category.
3599 @findex COMMAND_USER
3600 @findex gdb.COMMAND_USER
3601 @item gdb.COMMAND_USER
3602 The command is a general purpose command for the user, and typically
3603 does not fit in one of the other categories.
3604 Type @kbd{help user-defined} at the @value{GDBN} prompt to see
3605 a list of commands in this category, as well as the list of gdb macros
3606 (@pxref{Sequences}).
3608 @findex COMMAND_OBSCURE
3609 @findex gdb.COMMAND_OBSCURE
3610 @item gdb.COMMAND_OBSCURE
3611 The command is only used in unusual circumstances, or is not of
3612 general interest to users. For example, @code{checkpoint},
3613 @code{fork}, and @code{stop} are in this category. Type @kbd{help
3614 obscure} at the @value{GDBN} prompt to see a list of commands in this
3617 @findex COMMAND_MAINTENANCE
3618 @findex gdb.COMMAND_MAINTENANCE
3619 @item gdb.COMMAND_MAINTENANCE
3620 The command is only useful to @value{GDBN} maintainers. The
3621 @code{maintenance} and @code{flushregs} commands are in this category.
3622 Type @kbd{help internals} at the @value{GDBN} prompt to see a list of
3623 commands in this category.
3626 A new command can use a predefined completion function, either by
3627 specifying it via an argument at initialization, or by returning it
3628 from the @code{complete} method. These predefined completion
3629 constants are all defined in the @code{gdb} module:
3632 @vindex COMPLETE_NONE
3633 @item gdb.COMPLETE_NONE
3634 This constant means that no completion should be done.
3636 @vindex COMPLETE_FILENAME
3637 @item gdb.COMPLETE_FILENAME
3638 This constant means that filename completion should be performed.
3640 @vindex COMPLETE_LOCATION
3641 @item gdb.COMPLETE_LOCATION
3642 This constant means that location completion should be done.
3643 @xref{Specify Location}.
3645 @vindex COMPLETE_COMMAND
3646 @item gdb.COMPLETE_COMMAND
3647 This constant means that completion should examine @value{GDBN}
3650 @vindex COMPLETE_SYMBOL
3651 @item gdb.COMPLETE_SYMBOL
3652 This constant means that completion should be done using symbol names
3655 @vindex COMPLETE_EXPRESSION
3656 @item gdb.COMPLETE_EXPRESSION
3657 This constant means that completion should be done on expressions.
3658 Often this means completing on symbol names, but some language
3659 parsers also have support for completing on field names.
3662 The following code snippet shows how a trivial CLI command can be
3663 implemented in Python:
3666 class HelloWorld (gdb.Command):
3667 """Greet the whole world."""
3669 def __init__ (self):
3670 super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)
3672 def invoke (self, arg, from_tty):
3673 print "Hello, World!"
3678 The last line instantiates the class, and is necessary to trigger the
3679 registration of the command with @value{GDBN}. Depending on how the
3680 Python code is read into @value{GDBN}, you may need to import the
3681 @code{gdb} module explicitly.
3683 @node Parameters In Python
3684 @subsubsection Parameters In Python
3686 @cindex parameters in python
3687 @cindex python parameters
3688 @tindex gdb.Parameter
3690 You can implement new @value{GDBN} parameters using Python. A new
3691 parameter is implemented as an instance of the @code{gdb.Parameter}
3694 Parameters are exposed to the user via the @code{set} and
3695 @code{show} commands. @xref{Help}.
3697 There are many parameters that already exist and can be set in
3698 @value{GDBN}. Two examples are: @code{set follow fork} and
3699 @code{set charset}. Setting these parameters influences certain
3700 behavior in @value{GDBN}. Similarly, you can define parameters that
3701 can be used to influence behavior in custom Python scripts and commands.
3703 @defun Parameter.__init__ (name, @var{command-class}, @var{parameter-class} @r{[}, @var{enum-sequence}@r{]})
3704 The object initializer for @code{Parameter} registers the new
3705 parameter with @value{GDBN}. This initializer is normally invoked
3706 from the subclass' own @code{__init__} method.
3708 @var{name} is the name of the new parameter. If @var{name} consists
3709 of multiple words, then the initial words are looked for as prefix
3710 parameters. An example of this can be illustrated with the
3711 @code{set print} set of parameters. If @var{name} is
3712 @code{print foo}, then @code{print} will be searched as the prefix
3713 parameter. In this case the parameter can subsequently be accessed in
3714 @value{GDBN} as @code{set print foo}.
3716 If @var{name} consists of multiple words, and no prefix parameter group
3717 can be found, an exception is raised.
3719 @var{command-class} should be one of the @samp{COMMAND_} constants
3720 (@pxref{Commands In Python}). This argument tells @value{GDBN} how to
3721 categorize the new parameter in the help system.
3723 @var{parameter-class} should be one of the @samp{PARAM_} constants
3724 defined below. This argument tells @value{GDBN} the type of the new
3725 parameter; this information is used for input validation and
3728 If @var{parameter-class} is @code{PARAM_ENUM}, then
3729 @var{enum-sequence} must be a sequence of strings. These strings
3730 represent the possible values for the parameter.
3732 If @var{parameter-class} is not @code{PARAM_ENUM}, then the presence
3733 of a fourth argument will cause an exception to be thrown.
3735 The help text for the new parameter is taken from the Python
3736 documentation string for the parameter's class, if there is one. If
3737 there is no documentation string, a default value is used.
3740 @defvar Parameter.set_doc
3741 If this attribute exists, and is a string, then its value is used as
3742 the help text for this parameter's @code{set} command. The value is
3743 examined when @code{Parameter.__init__} is invoked; subsequent changes
3747 @defvar Parameter.show_doc
3748 If this attribute exists, and is a string, then its value is used as
3749 the help text for this parameter's @code{show} command. The value is
3750 examined when @code{Parameter.__init__} is invoked; subsequent changes
3754 @defvar Parameter.value
3755 The @code{value} attribute holds the underlying value of the
3756 parameter. It can be read and assigned to just as any other
3757 attribute. @value{GDBN} does validation when assignments are made.
3760 There are two methods that may be implemented in any @code{Parameter}
3763 @defun Parameter.get_set_string (self)
3764 If this method exists, @value{GDBN} will call it when a
3765 @var{parameter}'s value has been changed via the @code{set} API (for
3766 example, @kbd{set foo off}). The @code{value} attribute has already
3767 been populated with the new value and may be used in output. This
3768 method must return a string. If the returned string is not empty,
3769 @value{GDBN} will present it to the user.
3772 @defun Parameter.get_show_string (self, svalue)
3773 @value{GDBN} will call this method when a @var{parameter}'s
3774 @code{show} API has been invoked (for example, @kbd{show foo}). The
3775 argument @code{svalue} receives the string representation of the
3776 current value. This method must return a string.
3779 When a new parameter is defined, its type must be specified. The
3780 available types are represented by constants defined in the @code{gdb}
3784 @findex PARAM_BOOLEAN
3785 @findex gdb.PARAM_BOOLEAN
3786 @item gdb.PARAM_BOOLEAN
3787 The value is a plain boolean. The Python boolean values, @code{True}
3788 and @code{False} are the only valid values.
3790 @findex PARAM_AUTO_BOOLEAN
3791 @findex gdb.PARAM_AUTO_BOOLEAN
3792 @item gdb.PARAM_AUTO_BOOLEAN
3793 The value has three possible states: true, false, and @samp{auto}. In
3794 Python, true and false are represented using boolean constants, and
3795 @samp{auto} is represented using @code{None}.
3797 @findex PARAM_UINTEGER
3798 @findex gdb.PARAM_UINTEGER
3799 @item gdb.PARAM_UINTEGER
3800 The value is an unsigned integer. The value of 0 should be
3801 interpreted to mean ``unlimited''.
3803 @findex PARAM_INTEGER
3804 @findex gdb.PARAM_INTEGER
3805 @item gdb.PARAM_INTEGER
3806 The value is a signed integer. The value of 0 should be interpreted
3807 to mean ``unlimited''.
3809 @findex PARAM_STRING
3810 @findex gdb.PARAM_STRING
3811 @item gdb.PARAM_STRING
3812 The value is a string. When the user modifies the string, any escape
3813 sequences, such as @samp{\t}, @samp{\f}, and octal escapes, are
3814 translated into corresponding characters and encoded into the current
3817 @findex PARAM_STRING_NOESCAPE
3818 @findex gdb.PARAM_STRING_NOESCAPE
3819 @item gdb.PARAM_STRING_NOESCAPE
3820 The value is a string. When the user modifies the string, escapes are
3821 passed through untranslated.
3823 @findex PARAM_OPTIONAL_FILENAME
3824 @findex gdb.PARAM_OPTIONAL_FILENAME
3825 @item gdb.PARAM_OPTIONAL_FILENAME
3826 The value is a either a filename (a string), or @code{None}.
3828 @findex PARAM_FILENAME
3829 @findex gdb.PARAM_FILENAME
3830 @item gdb.PARAM_FILENAME
3831 The value is a filename. This is just like
3832 @code{PARAM_STRING_NOESCAPE}, but uses file names for completion.
3834 @findex PARAM_ZINTEGER
3835 @findex gdb.PARAM_ZINTEGER
3836 @item gdb.PARAM_ZINTEGER
3837 The value is an integer. This is like @code{PARAM_INTEGER}, except 0
3838 is interpreted as itself.
3840 @findex PARAM_ZUINTEGER
3841 @findex gdb.PARAM_ZUINTEGER
3842 @item gdb.PARAM_ZUINTEGER
3843 The value is an unsigned integer. This is like @code{PARAM_INTEGER},
3844 except 0 is interpreted as itself, and the value cannot be negative.
3846 @findex PARAM_ZUINTEGER_UNLIMITED
3847 @findex gdb.PARAM_ZUINTEGER_UNLIMITED
3848 @item gdb.PARAM_ZUINTEGER_UNLIMITED
3849 The value is a signed integer. This is like @code{PARAM_ZUINTEGER},
3850 except the special value -1 should be interpreted to mean
3851 ``unlimited''. Other negative values are not allowed.
3854 @findex gdb.PARAM_ENUM
3855 @item gdb.PARAM_ENUM
3856 The value is a string, which must be one of a collection string
3857 constants provided when the parameter is created.
3860 @node Functions In Python
3861 @subsubsection Writing new convenience functions
3863 @cindex writing convenience functions
3864 @cindex convenience functions in python
3865 @cindex python convenience functions
3866 @tindex gdb.Function
3868 You can implement new convenience functions (@pxref{Convenience Vars})
3869 in Python. A convenience function is an instance of a subclass of the
3870 class @code{gdb.Function}.
3872 @defun Function.__init__ (name)
3873 The initializer for @code{Function} registers the new function with
3874 @value{GDBN}. The argument @var{name} is the name of the function,
3875 a string. The function will be visible to the user as a convenience
3876 variable of type @code{internal function}, whose name is the same as
3877 the given @var{name}.
3879 The documentation for the new function is taken from the documentation
3880 string for the new class.
3883 @defun Function.invoke (@var{*args})
3884 When a convenience function is evaluated, its arguments are converted
3885 to instances of @code{gdb.Value}, and then the function's
3886 @code{invoke} method is called. Note that @value{GDBN} does not
3887 predetermine the arity of convenience functions. Instead, all
3888 available arguments are passed to @code{invoke}, following the
3889 standard Python calling convention. In particular, a convenience
3890 function can have default values for parameters without ill effect.
3892 The return value of this method is used as its value in the enclosing
3893 expression. If an ordinary Python value is returned, it is converted
3894 to a @code{gdb.Value} following the usual rules.
3897 The following code snippet shows how a trivial convenience function can
3898 be implemented in Python:
3901 class Greet (gdb.Function):
3902 """Return string to greet someone.
3903 Takes a name as argument."""
3905 def __init__ (self):
3906 super (Greet, self).__init__ ("greet")
3908 def invoke (self, name):
3909 return "Hello, %s!" % name.string ()
3914 The last line instantiates the class, and is necessary to trigger the
3915 registration of the function with @value{GDBN}. Depending on how the
3916 Python code is read into @value{GDBN}, you may need to import the
3917 @code{gdb} module explicitly.
3919 Now you can use the function in an expression:
3922 (gdb) print $greet("Bob")
3926 @node Progspaces In Python
3927 @subsubsection Program Spaces In Python
3929 @cindex progspaces in python
3930 @tindex gdb.Progspace
3932 A program space, or @dfn{progspace}, represents a symbolic view
3933 of an address space.
3934 It consists of all of the objfiles of the program.
3935 @xref{Objfiles In Python}.
3936 @xref{Inferiors and Programs, program spaces}, for more details
3937 about program spaces.
3939 The following progspace-related functions are available in the
3942 @findex gdb.current_progspace
3943 @defun gdb.current_progspace ()
3944 This function returns the program space of the currently selected inferior.
3945 @xref{Inferiors and Programs}.
3948 @findex gdb.progspaces
3949 @defun gdb.progspaces ()
3950 Return a sequence of all the progspaces currently known to @value{GDBN}.
3953 Each progspace is represented by an instance of the @code{gdb.Progspace}
3956 @defvar Progspace.filename
3957 The file name of the progspace as a string.
3960 @defvar Progspace.pretty_printers
3961 The @code{pretty_printers} attribute is a list of functions. It is
3962 used to look up pretty-printers. A @code{Value} is passed to each
3963 function in order; if the function returns @code{None}, then the
3964 search continues. Otherwise, the return value should be an object
3965 which is used to format the value. @xref{Pretty Printing API}, for more
3969 @defvar Progspace.type_printers
3970 The @code{type_printers} attribute is a list of type printer objects.
3971 @xref{Type Printing API}, for more information.
3974 @defvar Progspace.frame_filters
3975 The @code{frame_filters} attribute is a dictionary of frame filter
3976 objects. @xref{Frame Filter API}, for more information.
3979 One may add arbitrary attributes to @code{gdb.Progspace} objects
3980 in the usual Python way.
3981 This is useful if, for example, one needs to do some extra record keeping
3982 associated with the program space.
3984 In this contrived example, we want to perform some processing when
3985 an objfile with a certain symbol is loaded, but we only want to do
3986 this once because it is expensive. To achieve this we record the results
3987 with the program space because we can't predict when the desired objfile
3992 def clear_objfiles_handler(event):
3993 event.progspace.expensive_computation = None
3994 def expensive(symbol):
3995 """A mock routine to perform an "expensive" computation on symbol."""
3996 print "Computing the answer to the ultimate question ..."
3998 def new_objfile_handler(event):
3999 objfile = event.new_objfile
4000 progspace = objfile.progspace
4001 if not hasattr(progspace, 'expensive_computation') or \
4002 progspace.expensive_computation is None:
4003 # We use 'main' for the symbol to keep the example simple.
4004 # Note: There's no current way to constrain the lookup
4006 symbol = gdb.lookup_global_symbol('main')
4007 if symbol is not None:
4008 progspace.expensive_computation = expensive(symbol)
4009 gdb.events.clear_objfiles.connect(clear_objfiles_handler)
4010 gdb.events.new_objfile.connect(new_objfile_handler)
4012 (gdb) file /tmp/hello
4013 Reading symbols from /tmp/hello...done.
4014 Computing the answer to the ultimate question ...
4015 (gdb) python print gdb.current_progspace().expensive_computation
4018 Starting program: /tmp/hello
4020 [Inferior 1 (process 4242) exited normally]
4023 @node Objfiles In Python
4024 @subsubsection Objfiles In Python
4026 @cindex objfiles in python
4029 @value{GDBN} loads symbols for an inferior from various
4030 symbol-containing files (@pxref{Files}). These include the primary
4031 executable file, any shared libraries used by the inferior, and any
4032 separate debug info files (@pxref{Separate Debug Files}).
4033 @value{GDBN} calls these symbol-containing files @dfn{objfiles}.
4035 The following objfile-related functions are available in the
4038 @findex gdb.current_objfile
4039 @defun gdb.current_objfile ()
4040 When auto-loading a Python script (@pxref{Python Auto-loading}), @value{GDBN}
4041 sets the ``current objfile'' to the corresponding objfile. This
4042 function returns the current objfile. If there is no current objfile,
4043 this function returns @code{None}.
4046 @findex gdb.objfiles
4047 @defun gdb.objfiles ()
4048 Return a sequence of all the objfiles current known to @value{GDBN}.
4049 @xref{Objfiles In Python}.
4052 @findex gdb.lookup_objfile
4053 @defun gdb.lookup_objfile (name @r{[}, by_build_id{]})
4054 Look up @var{name}, a file name or build ID, in the list of objfiles
4055 for the current program space (@pxref{Progspaces In Python}).
4056 If the objfile is not found throw the Python @code{ValueError} exception.
4058 If @var{name} is a relative file name, then it will match any
4059 source file name with the same trailing components. For example, if
4060 @var{name} is @samp{gcc/expr.c}, then it will match source file
4061 name of @file{/build/trunk/gcc/expr.c}, but not
4062 @file{/build/trunk/libcpp/expr.c} or @file{/build/trunk/gcc/x-expr.c}.
4064 If @var{by_build_id} is provided and is @code{True} then @var{name}
4065 is the build ID of the objfile. Otherwise, @var{name} is a file name.
4066 This is supported only on some operating systems, notably those which use
4067 the ELF format for binary files and the @sc{gnu} Binutils. For more details
4068 about this feature, see the description of the @option{--build-id}
4069 command-line option in @ref{Options, , Command Line Options, ld,
4073 Each objfile is represented by an instance of the @code{gdb.Objfile}
4076 @defvar Objfile.filename
4077 The file name of the objfile as a string, with symbolic links resolved.
4079 The value is @code{None} if the objfile is no longer valid.
4080 See the @code{gdb.Objfile.is_valid} method, described below.
4083 @defvar Objfile.username
4084 The file name of the objfile as specified by the user as a string.
4086 The value is @code{None} if the objfile is no longer valid.
4087 See the @code{gdb.Objfile.is_valid} method, described below.
4090 @defvar Objfile.owner
4091 For separate debug info objfiles this is the corresponding @code{gdb.Objfile}
4092 object that debug info is being provided for.
4093 Otherwise this is @code{None}.
4094 Separate debug info objfiles are added with the
4095 @code{gdb.Objfile.add_separate_debug_file} method, described below.
4098 @defvar Objfile.build_id
4099 The build ID of the objfile as a string.
4100 If the objfile does not have a build ID then the value is @code{None}.
4102 This is supported only on some operating systems, notably those which use
4103 the ELF format for binary files and the @sc{gnu} Binutils. For more details
4104 about this feature, see the description of the @option{--build-id}
4105 command-line option in @ref{Options, , Command Line Options, ld,
4109 @defvar Objfile.progspace
4110 The containing program space of the objfile as a @code{gdb.Progspace}
4111 object. @xref{Progspaces In Python}.
4114 @defvar Objfile.pretty_printers
4115 The @code{pretty_printers} attribute is a list of functions. It is
4116 used to look up pretty-printers. A @code{Value} is passed to each
4117 function in order; if the function returns @code{None}, then the
4118 search continues. Otherwise, the return value should be an object
4119 which is used to format the value. @xref{Pretty Printing API}, for more
4123 @defvar Objfile.type_printers
4124 The @code{type_printers} attribute is a list of type printer objects.
4125 @xref{Type Printing API}, for more information.
4128 @defvar Objfile.frame_filters
4129 The @code{frame_filters} attribute is a dictionary of frame filter
4130 objects. @xref{Frame Filter API}, for more information.
4133 One may add arbitrary attributes to @code{gdb.Objfile} objects
4134 in the usual Python way.
4135 This is useful if, for example, one needs to do some extra record keeping
4136 associated with the objfile.
4138 In this contrived example we record the time when @value{GDBN}
4144 def new_objfile_handler(event):
4145 # Set the time_loaded attribute of the new objfile.
4146 event.new_objfile.time_loaded = datetime.datetime.today()
4147 gdb.events.new_objfile.connect(new_objfile_handler)
4150 Reading symbols from ./hello...done.
4151 (gdb) python print gdb.objfiles()[0].time_loaded
4152 2014-10-09 11:41:36.770345
4155 A @code{gdb.Objfile} object has the following methods:
4157 @defun Objfile.is_valid ()
4158 Returns @code{True} if the @code{gdb.Objfile} object is valid,
4159 @code{False} if not. A @code{gdb.Objfile} object can become invalid
4160 if the object file it refers to is not loaded in @value{GDBN} any
4161 longer. All other @code{gdb.Objfile} methods will throw an exception
4162 if it is invalid at the time the method is called.
4165 @defun Objfile.add_separate_debug_file (file)
4166 Add @var{file} to the list of files that @value{GDBN} will search for
4167 debug information for the objfile.
4168 This is useful when the debug info has been removed from the program
4169 and stored in a separate file. @value{GDBN} has built-in support for
4170 finding separate debug info files (@pxref{Separate Debug Files}), but if
4171 the file doesn't live in one of the standard places that @value{GDBN}
4172 searches then this function can be used to add a debug info file
4173 from a different place.
4176 @node Frames In Python
4177 @subsubsection Accessing inferior stack frames from Python.
4179 @cindex frames in python
4180 When the debugged program stops, @value{GDBN} is able to analyze its call
4181 stack (@pxref{Frames,,Stack frames}). The @code{gdb.Frame} class
4182 represents a frame in the stack. A @code{gdb.Frame} object is only valid
4183 while its corresponding frame exists in the inferior's stack. If you try
4184 to use an invalid frame object, @value{GDBN} will throw a @code{gdb.error}
4185 exception (@pxref{Exception Handling}).
4187 Two @code{gdb.Frame} objects can be compared for equality with the @code{==}
4191 (@value{GDBP}) python print gdb.newest_frame() == gdb.selected_frame ()
4195 The following frame-related functions are available in the @code{gdb} module:
4197 @findex gdb.selected_frame
4198 @defun gdb.selected_frame ()
4199 Return the selected frame object. (@pxref{Selection,,Selecting a Frame}).
4202 @findex gdb.newest_frame
4203 @defun gdb.newest_frame ()
4204 Return the newest frame object for the selected thread.
4207 @defun gdb.frame_stop_reason_string (reason)
4208 Return a string explaining the reason why @value{GDBN} stopped unwinding
4209 frames, as expressed by the given @var{reason} code (an integer, see the
4210 @code{unwind_stop_reason} method further down in this section).
4213 @findex gdb.invalidate_cached_frames
4214 @defun gdb.invalidate_cached_frames
4215 @value{GDBN} internally keeps a cache of the frames that have been
4216 unwound. This function invalidates this cache.
4218 This function should not generally be called by ordinary Python code.
4219 It is documented for the sake of completeness.
4222 A @code{gdb.Frame} object has the following methods:
4224 @defun Frame.is_valid ()
4225 Returns true if the @code{gdb.Frame} object is valid, false if not.
4226 A frame object can become invalid if the frame it refers to doesn't
4227 exist anymore in the inferior. All @code{gdb.Frame} methods will throw
4228 an exception if it is invalid at the time the method is called.
4231 @defun Frame.name ()
4232 Returns the function name of the frame, or @code{None} if it can't be
4236 @defun Frame.architecture ()
4237 Returns the @code{gdb.Architecture} object corresponding to the frame's
4238 architecture. @xref{Architectures In Python}.
4241 @defun Frame.type ()
4242 Returns the type of the frame. The value can be one of:
4244 @item gdb.NORMAL_FRAME
4245 An ordinary stack frame.
4247 @item gdb.DUMMY_FRAME
4248 A fake stack frame that was created by @value{GDBN} when performing an
4249 inferior function call.
4251 @item gdb.INLINE_FRAME
4252 A frame representing an inlined function. The function was inlined
4253 into a @code{gdb.NORMAL_FRAME} that is older than this one.
4255 @item gdb.TAILCALL_FRAME
4256 A frame representing a tail call. @xref{Tail Call Frames}.
4258 @item gdb.SIGTRAMP_FRAME
4259 A signal trampoline frame. This is the frame created by the OS when
4260 it calls into a signal handler.
4262 @item gdb.ARCH_FRAME
4263 A fake stack frame representing a cross-architecture call.
4265 @item gdb.SENTINEL_FRAME
4266 This is like @code{gdb.NORMAL_FRAME}, but it is only used for the
4271 @defun Frame.unwind_stop_reason ()
4272 Return an integer representing the reason why it's not possible to find
4273 more frames toward the outermost frame. Use
4274 @code{gdb.frame_stop_reason_string} to convert the value returned by this
4275 function to a string. The value can be one of:
4278 @item gdb.FRAME_UNWIND_NO_REASON
4279 No particular reason (older frames should be available).
4281 @item gdb.FRAME_UNWIND_NULL_ID
4282 The previous frame's analyzer returns an invalid result. This is no
4283 longer used by @value{GDBN}, and is kept only for backward
4286 @item gdb.FRAME_UNWIND_OUTERMOST
4287 This frame is the outermost.
4289 @item gdb.FRAME_UNWIND_UNAVAILABLE
4290 Cannot unwind further, because that would require knowing the
4291 values of registers or memory that have not been collected.
4293 @item gdb.FRAME_UNWIND_INNER_ID
4294 This frame ID looks like it ought to belong to a NEXT frame,
4295 but we got it for a PREV frame. Normally, this is a sign of
4296 unwinder failure. It could also indicate stack corruption.
4298 @item gdb.FRAME_UNWIND_SAME_ID
4299 This frame has the same ID as the previous one. That means
4300 that unwinding further would almost certainly give us another
4301 frame with exactly the same ID, so break the chain. Normally,
4302 this is a sign of unwinder failure. It could also indicate
4305 @item gdb.FRAME_UNWIND_NO_SAVED_PC
4306 The frame unwinder did not find any saved PC, but we needed
4307 one to unwind further.
4309 @item gdb.FRAME_UNWIND_MEMORY_ERROR
4310 The frame unwinder caused an error while trying to access memory.
4312 @item gdb.FRAME_UNWIND_FIRST_ERROR
4313 Any stop reason greater or equal to this value indicates some kind
4314 of error. This special value facilitates writing code that tests
4315 for errors in unwinding in a way that will work correctly even if
4316 the list of the other values is modified in future @value{GDBN}
4317 versions. Using it, you could write:
4319 reason = gdb.selected_frame().unwind_stop_reason ()
4320 reason_str = gdb.frame_stop_reason_string (reason)
4321 if reason >= gdb.FRAME_UNWIND_FIRST_ERROR:
4322 print "An error occured: %s" % reason_str
4329 Returns the frame's resume address.
4332 @defun Frame.block ()
4333 Return the frame's code block. @xref{Blocks In Python}. If the frame
4334 does not have a block -- for example, if there is no debugging
4335 information for the code in question -- then this will throw an
4339 @defun Frame.function ()
4340 Return the symbol for the function corresponding to this frame.
4341 @xref{Symbols In Python}.
4344 @defun Frame.older ()
4345 Return the frame that called this frame.
4348 @defun Frame.newer ()
4349 Return the frame called by this frame.
4352 @defun Frame.find_sal ()
4353 Return the frame's symtab and line object.
4354 @xref{Symbol Tables In Python}.
4357 @defun Frame.read_register (register)
4358 Return the value of @var{register} in this frame. The @var{register}
4359 argument must be a string (e.g., @code{'sp'} or @code{'rax'}).
4360 Returns a @code{Gdb.Value} object. Throws an exception if @var{register}
4364 @defun Frame.read_var (variable @r{[}, block@r{]})
4365 Return the value of @var{variable} in this frame. If the optional
4366 argument @var{block} is provided, search for the variable from that
4367 block; otherwise start at the frame's current block (which is
4368 determined by the frame's current program counter). The @var{variable}
4369 argument must be a string or a @code{gdb.Symbol} object; @var{block} must be a
4370 @code{gdb.Block} object.
4373 @defun Frame.select ()
4374 Set this frame to be the selected frame. @xref{Stack, ,Examining the
4378 @node Blocks In Python
4379 @subsubsection Accessing blocks from Python.
4381 @cindex blocks in python
4384 In @value{GDBN}, symbols are stored in blocks. A block corresponds
4385 roughly to a scope in the source code. Blocks are organized
4386 hierarchically, and are represented individually in Python as a
4387 @code{gdb.Block}. Blocks rely on debugging information being
4390 A frame has a block. Please see @ref{Frames In Python}, for a more
4391 in-depth discussion of frames.
4393 The outermost block is known as the @dfn{global block}. The global
4394 block typically holds public global variables and functions.
4396 The block nested just inside the global block is the @dfn{static
4397 block}. The static block typically holds file-scoped variables and
4400 @value{GDBN} provides a method to get a block's superblock, but there
4401 is currently no way to examine the sub-blocks of a block, or to
4402 iterate over all the blocks in a symbol table (@pxref{Symbol Tables In
4405 Here is a short example that should help explain blocks:
4408 /* This is in the global block. */
4411 /* This is in the static block. */
4412 static int file_scope;
4414 /* 'function' is in the global block, and 'argument' is
4415 in a block nested inside of 'function'. */
4416 int function (int argument)
4418 /* 'local' is in a block inside 'function'. It may or may
4419 not be in the same block as 'argument'. */
4423 /* 'inner' is in a block whose superblock is the one holding
4427 /* If this call is expanded by the compiler, you may see
4428 a nested block here whose function is 'inline_function'
4429 and whose superblock is the one holding 'inner'. */
4435 A @code{gdb.Block} is iterable. The iterator returns the symbols
4436 (@pxref{Symbols In Python}) local to the block. Python programs
4437 should not assume that a specific block object will always contain a
4438 given symbol, since changes in @value{GDBN} features and
4439 infrastructure may cause symbols move across blocks in a symbol
4442 The following block-related functions are available in the @code{gdb}
4445 @findex gdb.block_for_pc
4446 @defun gdb.block_for_pc (pc)
4447 Return the innermost @code{gdb.Block} containing the given @var{pc}
4448 value. If the block cannot be found for the @var{pc} value specified,
4449 the function will return @code{None}.
4452 A @code{gdb.Block} object has the following methods:
4454 @defun Block.is_valid ()
4455 Returns @code{True} if the @code{gdb.Block} object is valid,
4456 @code{False} if not. A block object can become invalid if the block it
4457 refers to doesn't exist anymore in the inferior. All other
4458 @code{gdb.Block} methods will throw an exception if it is invalid at
4459 the time the method is called. The block's validity is also checked
4460 during iteration over symbols of the block.
4463 A @code{gdb.Block} object has the following attributes:
4466 The start address of the block. This attribute is not writable.
4470 One past the last address that appears in the block. This attribute
4474 @defvar Block.function
4475 The name of the block represented as a @code{gdb.Symbol}. If the
4476 block is not named, then this attribute holds @code{None}. This
4477 attribute is not writable.
4479 For ordinary function blocks, the superblock is the static block.
4480 However, you should note that it is possible for a function block to
4481 have a superblock that is not the static block -- for instance this
4482 happens for an inlined function.
4485 @defvar Block.superblock
4486 The block containing this block. If this parent block does not exist,
4487 this attribute holds @code{None}. This attribute is not writable.
4490 @defvar Block.global_block
4491 The global block associated with this block. This attribute is not
4495 @defvar Block.static_block
4496 The static block associated with this block. This attribute is not
4500 @defvar Block.is_global
4501 @code{True} if the @code{gdb.Block} object is a global block,
4502 @code{False} if not. This attribute is not
4506 @defvar Block.is_static
4507 @code{True} if the @code{gdb.Block} object is a static block,
4508 @code{False} if not. This attribute is not writable.
4511 @node Symbols In Python
4512 @subsubsection Python representation of Symbols.
4514 @cindex symbols in python
4517 @value{GDBN} represents every variable, function and type as an
4518 entry in a symbol table. @xref{Symbols, ,Examining the Symbol Table}.
4519 Similarly, Python represents these symbols in @value{GDBN} with the
4520 @code{gdb.Symbol} object.
4522 The following symbol-related functions are available in the @code{gdb}
4525 @findex gdb.lookup_symbol
4526 @defun gdb.lookup_symbol (name @r{[}, block @r{[}, domain@r{]]})
4527 This function searches for a symbol by name. The search scope can be
4528 restricted to the parameters defined in the optional domain and block
4531 @var{name} is the name of the symbol. It must be a string. The
4532 optional @var{block} argument restricts the search to symbols visible
4533 in that @var{block}. The @var{block} argument must be a
4534 @code{gdb.Block} object. If omitted, the block for the current frame
4535 is used. The optional @var{domain} argument restricts
4536 the search to the domain type. The @var{domain} argument must be a
4537 domain constant defined in the @code{gdb} module and described later
4540 The result is a tuple of two elements.
4541 The first element is a @code{gdb.Symbol} object or @code{None} if the symbol
4543 If the symbol is found, the second element is @code{True} if the symbol
4544 is a field of a method's object (e.g., @code{this} in C@t{++}),
4545 otherwise it is @code{False}.
4546 If the symbol is not found, the second element is @code{False}.
4549 @findex gdb.lookup_global_symbol
4550 @defun gdb.lookup_global_symbol (name @r{[}, domain@r{]})
4551 This function searches for a global symbol by name.
4552 The search scope can be restricted to by the domain argument.
4554 @var{name} is the name of the symbol. It must be a string.
4555 The optional @var{domain} argument restricts the search to the domain type.
4556 The @var{domain} argument must be a domain constant defined in the @code{gdb}
4557 module and described later in this chapter.
4559 The result is a @code{gdb.Symbol} object or @code{None} if the symbol
4563 A @code{gdb.Symbol} object has the following attributes:
4566 The type of the symbol or @code{None} if no type is recorded.
4567 This attribute is represented as a @code{gdb.Type} object.
4568 @xref{Types In Python}. This attribute is not writable.
4571 @defvar Symbol.symtab
4572 The symbol table in which the symbol appears. This attribute is
4573 represented as a @code{gdb.Symtab} object. @xref{Symbol Tables In
4574 Python}. This attribute is not writable.
4578 The line number in the source code at which the symbol was defined.
4583 The name of the symbol as a string. This attribute is not writable.
4586 @defvar Symbol.linkage_name
4587 The name of the symbol, as used by the linker (i.e., may be mangled).
4588 This attribute is not writable.
4591 @defvar Symbol.print_name
4592 The name of the symbol in a form suitable for output. This is either
4593 @code{name} or @code{linkage_name}, depending on whether the user
4594 asked @value{GDBN} to display demangled or mangled names.
4597 @defvar Symbol.addr_class
4598 The address class of the symbol. This classifies how to find the value
4599 of a symbol. Each address class is a constant defined in the
4600 @code{gdb} module and described later in this chapter.
4603 @defvar Symbol.needs_frame
4604 This is @code{True} if evaluating this symbol's value requires a frame
4605 (@pxref{Frames In Python}) and @code{False} otherwise. Typically,
4606 local variables will require a frame, but other symbols will not.
4609 @defvar Symbol.is_argument
4610 @code{True} if the symbol is an argument of a function.
4613 @defvar Symbol.is_constant
4614 @code{True} if the symbol is a constant.
4617 @defvar Symbol.is_function
4618 @code{True} if the symbol is a function or a method.
4621 @defvar Symbol.is_variable
4622 @code{True} if the symbol is a variable.
4625 A @code{gdb.Symbol} object has the following methods:
4627 @defun Symbol.is_valid ()
4628 Returns @code{True} if the @code{gdb.Symbol} object is valid,
4629 @code{False} if not. A @code{gdb.Symbol} object can become invalid if
4630 the symbol it refers to does not exist in @value{GDBN} any longer.
4631 All other @code{gdb.Symbol} methods will throw an exception if it is
4632 invalid at the time the method is called.
4635 @defun Symbol.value (@r{[}frame@r{]})
4636 Compute the value of the symbol, as a @code{gdb.Value}. For
4637 functions, this computes the address of the function, cast to the
4638 appropriate type. If the symbol requires a frame in order to compute
4639 its value, then @var{frame} must be given. If @var{frame} is not
4640 given, or if @var{frame} is invalid, then this method will throw an
4644 The available domain categories in @code{gdb.Symbol} are represented
4645 as constants in the @code{gdb} module:
4648 @vindex SYMBOL_UNDEF_DOMAIN
4649 @item gdb.SYMBOL_UNDEF_DOMAIN
4650 This is used when a domain has not been discovered or none of the
4651 following domains apply. This usually indicates an error either
4652 in the symbol information or in @value{GDBN}'s handling of symbols.
4654 @vindex SYMBOL_VAR_DOMAIN
4655 @item gdb.SYMBOL_VAR_DOMAIN
4656 This domain contains variables, function names, typedef names and enum
4659 @vindex SYMBOL_STRUCT_DOMAIN
4660 @item gdb.SYMBOL_STRUCT_DOMAIN
4661 This domain holds struct, union and enum type names.
4663 @vindex SYMBOL_LABEL_DOMAIN
4664 @item gdb.SYMBOL_LABEL_DOMAIN
4665 This domain contains names of labels (for gotos).
4667 @vindex SYMBOL_VARIABLES_DOMAIN
4668 @item gdb.SYMBOL_VARIABLES_DOMAIN
4669 This domain holds a subset of the @code{SYMBOLS_VAR_DOMAIN}; it
4670 contains everything minus functions and types.
4672 @vindex SYMBOL_FUNCTIONS_DOMAIN
4673 @item gdb.SYMBOL_FUNCTIONS_DOMAIN
4674 This domain contains all functions.
4676 @vindex SYMBOL_TYPES_DOMAIN
4677 @item gdb.SYMBOL_TYPES_DOMAIN
4678 This domain contains all types.
4681 The available address class categories in @code{gdb.Symbol} are represented
4682 as constants in the @code{gdb} module:
4685 @vindex SYMBOL_LOC_UNDEF
4686 @item gdb.SYMBOL_LOC_UNDEF
4687 If this is returned by address class, it indicates an error either in
4688 the symbol information or in @value{GDBN}'s handling of symbols.
4690 @vindex SYMBOL_LOC_CONST
4691 @item gdb.SYMBOL_LOC_CONST
4692 Value is constant int.
4694 @vindex SYMBOL_LOC_STATIC
4695 @item gdb.SYMBOL_LOC_STATIC
4696 Value is at a fixed address.
4698 @vindex SYMBOL_LOC_REGISTER
4699 @item gdb.SYMBOL_LOC_REGISTER
4700 Value is in a register.
4702 @vindex SYMBOL_LOC_ARG
4703 @item gdb.SYMBOL_LOC_ARG
4704 Value is an argument. This value is at the offset stored within the
4705 symbol inside the frame's argument list.
4707 @vindex SYMBOL_LOC_REF_ARG
4708 @item gdb.SYMBOL_LOC_REF_ARG
4709 Value address is stored in the frame's argument list. Just like
4710 @code{LOC_ARG} except that the value's address is stored at the
4711 offset, not the value itself.
4713 @vindex SYMBOL_LOC_REGPARM_ADDR
4714 @item gdb.SYMBOL_LOC_REGPARM_ADDR
4715 Value is a specified register. Just like @code{LOC_REGISTER} except
4716 the register holds the address of the argument instead of the argument
4719 @vindex SYMBOL_LOC_LOCAL
4720 @item gdb.SYMBOL_LOC_LOCAL
4721 Value is a local variable.
4723 @vindex SYMBOL_LOC_TYPEDEF
4724 @item gdb.SYMBOL_LOC_TYPEDEF
4725 Value not used. Symbols in the domain @code{SYMBOL_STRUCT_DOMAIN} all
4728 @vindex SYMBOL_LOC_BLOCK
4729 @item gdb.SYMBOL_LOC_BLOCK
4732 @vindex SYMBOL_LOC_CONST_BYTES
4733 @item gdb.SYMBOL_LOC_CONST_BYTES
4734 Value is a byte-sequence.
4736 @vindex SYMBOL_LOC_UNRESOLVED
4737 @item gdb.SYMBOL_LOC_UNRESOLVED
4738 Value is at a fixed address, but the address of the variable has to be
4739 determined from the minimal symbol table whenever the variable is
4742 @vindex SYMBOL_LOC_OPTIMIZED_OUT
4743 @item gdb.SYMBOL_LOC_OPTIMIZED_OUT
4744 The value does not actually exist in the program.
4746 @vindex SYMBOL_LOC_COMPUTED
4747 @item gdb.SYMBOL_LOC_COMPUTED
4748 The value's address is a computed location.
4751 @node Symbol Tables In Python
4752 @subsubsection Symbol table representation in Python.
4754 @cindex symbol tables in python
4756 @tindex gdb.Symtab_and_line
4758 Access to symbol table data maintained by @value{GDBN} on the inferior
4759 is exposed to Python via two objects: @code{gdb.Symtab_and_line} and
4760 @code{gdb.Symtab}. Symbol table and line data for a frame is returned
4761 from the @code{find_sal} method in @code{gdb.Frame} object.
4762 @xref{Frames In Python}.
4764 For more information on @value{GDBN}'s symbol table management, see
4765 @ref{Symbols, ,Examining the Symbol Table}, for more information.
4767 A @code{gdb.Symtab_and_line} object has the following attributes:
4769 @defvar Symtab_and_line.symtab
4770 The symbol table object (@code{gdb.Symtab}) for this frame.
4771 This attribute is not writable.
4774 @defvar Symtab_and_line.pc
4775 Indicates the start of the address range occupied by code for the
4776 current source line. This attribute is not writable.
4779 @defvar Symtab_and_line.last
4780 Indicates the end of the address range occupied by code for the current
4781 source line. This attribute is not writable.
4784 @defvar Symtab_and_line.line
4785 Indicates the current line number for this object. This
4786 attribute is not writable.
4789 A @code{gdb.Symtab_and_line} object has the following methods:
4791 @defun Symtab_and_line.is_valid ()
4792 Returns @code{True} if the @code{gdb.Symtab_and_line} object is valid,
4793 @code{False} if not. A @code{gdb.Symtab_and_line} object can become
4794 invalid if the Symbol table and line object it refers to does not
4795 exist in @value{GDBN} any longer. All other
4796 @code{gdb.Symtab_and_line} methods will throw an exception if it is
4797 invalid at the time the method is called.
4800 A @code{gdb.Symtab} object has the following attributes:
4802 @defvar Symtab.filename
4803 The symbol table's source filename. This attribute is not writable.
4806 @defvar Symtab.objfile
4807 The symbol table's backing object file. @xref{Objfiles In Python}.
4808 This attribute is not writable.
4811 @defvar Symtab.producer
4812 The name and possibly version number of the program that
4813 compiled the code in the symbol table.
4814 The contents of this string is up to the compiler.
4815 If no producer information is available then @code{None} is returned.
4816 This attribute is not writable.
4819 A @code{gdb.Symtab} object has the following methods:
4821 @defun Symtab.is_valid ()
4822 Returns @code{True} if the @code{gdb.Symtab} object is valid,
4823 @code{False} if not. A @code{gdb.Symtab} object can become invalid if
4824 the symbol table it refers to does not exist in @value{GDBN} any
4825 longer. All other @code{gdb.Symtab} methods will throw an exception
4826 if it is invalid at the time the method is called.
4829 @defun Symtab.fullname ()
4830 Return the symbol table's source absolute file name.
4833 @defun Symtab.global_block ()
4834 Return the global block of the underlying symbol table.
4835 @xref{Blocks In Python}.
4838 @defun Symtab.static_block ()
4839 Return the static block of the underlying symbol table.
4840 @xref{Blocks In Python}.
4843 @defun Symtab.linetable ()
4844 Return the line table associated with the symbol table.
4845 @xref{Line Tables In Python}.
4848 @node Line Tables In Python
4849 @subsubsection Manipulating line tables using Python
4851 @cindex line tables in python
4852 @tindex gdb.LineTable
4854 Python code can request and inspect line table information from a
4855 symbol table that is loaded in @value{GDBN}. A line table is a
4856 mapping of source lines to their executable locations in memory. To
4857 acquire the line table information for a particular symbol table, use
4858 the @code{linetable} function (@pxref{Symbol Tables In Python}).
4860 A @code{gdb.LineTable} is iterable. The iterator returns
4861 @code{LineTableEntry} objects that correspond to the source line and
4862 address for each line table entry. @code{LineTableEntry} objects have
4863 the following attributes:
4865 @defvar LineTableEntry.line
4866 The source line number for this line table entry. This number
4867 corresponds to the actual line of source. This attribute is not
4871 @defvar LineTableEntry.pc
4872 The address that is associated with the line table entry where the
4873 executable code for that source line resides in memory. This
4874 attribute is not writable.
4877 As there can be multiple addresses for a single source line, you may
4878 receive multiple @code{LineTableEntry} objects with matching
4879 @code{line} attributes, but with different @code{pc} attributes. The
4880 iterator is sorted in ascending @code{pc} order. Here is a small
4881 example illustrating iterating over a line table.
4884 symtab = gdb.selected_frame().find_sal().symtab
4885 linetable = symtab.linetable()
4886 for line in linetable:
4887 print "Line: "+str(line.line)+" Address: "+hex(line.pc)
4890 This will have the following output:
4893 Line: 33 Address: 0x4005c8L
4894 Line: 37 Address: 0x4005caL
4895 Line: 39 Address: 0x4005d2L
4896 Line: 40 Address: 0x4005f8L
4897 Line: 42 Address: 0x4005ffL
4898 Line: 44 Address: 0x400608L
4899 Line: 42 Address: 0x40060cL
4900 Line: 45 Address: 0x400615L
4903 In addition to being able to iterate over a @code{LineTable}, it also
4904 has the following direct access methods:
4906 @defun LineTable.line (line)
4907 Return a Python @code{Tuple} of @code{LineTableEntry} objects for any
4908 entries in the line table for the given @var{line}, which specifies
4909 the source code line. If there are no entries for that source code
4910 @var{line}, the Python @code{None} is returned.
4913 @defun LineTable.has_line (line)
4914 Return a Python @code{Boolean} indicating whether there is an entry in
4915 the line table for this source line. Return @code{True} if an entry
4916 is found, or @code{False} if not.
4919 @defun LineTable.source_lines ()
4920 Return a Python @code{List} of the source line numbers in the symbol
4921 table. Only lines with executable code locations are returned. The
4922 contents of the @code{List} will just be the source line entries
4923 represented as Python @code{Long} values.
4926 @node Breakpoints In Python
4927 @subsubsection Manipulating breakpoints using Python
4929 @cindex breakpoints in python
4930 @tindex gdb.Breakpoint
4932 Python code can manipulate breakpoints via the @code{gdb.Breakpoint}
4935 A breakpoint can be created using one of the two forms of the
4936 @code{gdb.Breakpoint} constructor. The first one accepts a string
4937 like one would pass to the @code{break}
4938 (@pxref{Set Breaks,,Setting Breakpoints}) and @code{watch}
4939 (@pxref{Set Watchpoints, , Setting Watchpoints}) commands, and can be used to
4940 create both breakpoints and watchpoints. The second accepts separate Python
4941 arguments similar to @ref{Explicit Locations}, and can only be used to create
4944 @defun Breakpoint.__init__ (spec @r{[}, type @r{][}, wp_class @r{][}, internal @r{][}, temporary @r{][}, qualified @r{]})
4945 Create a new breakpoint according to @var{spec}, which is a string naming the
4946 location of a breakpoint, or an expression that defines a watchpoint. The
4947 string should describe a location in a format recognized by the @code{break}
4948 command (@pxref{Set Breaks,,Setting Breakpoints}) or, in the case of a
4949 watchpoint, by the @code{watch} command
4950 (@pxref{Set Watchpoints, , Setting Watchpoints}).
4952 The optional @var{type} argument specifies the type of the breakpoint to create,
4955 The optional @var{wp_class} argument defines the class of watchpoint to create,
4956 if @var{type} is @code{gdb.BP_WATCHPOINT}. If @var{wp_class} is omitted, it
4957 defaults to @code{gdb.WP_WRITE}.
4959 The optional @var{internal} argument allows the breakpoint to become invisible
4960 to the user. The breakpoint will neither be reported when created, nor will it
4961 be listed in the output from @code{info breakpoints} (but will be listed with
4962 the @code{maint info breakpoints} command).
4964 The optional @var{temporary} argument makes the breakpoint a temporary
4965 breakpoint. Temporary breakpoints are deleted after they have been hit. Any
4966 further access to the Python breakpoint after it has been hit will result in a
4967 runtime error (as that breakpoint has now been automatically deleted).
4969 The optional @var{qualified} argument is a boolean that allows interpreting
4970 the function passed in @code{spec} as a fully-qualified name. It is equivalent
4971 to @code{break}'s @code{-qualified} flag (@pxref{Linespec Locations} and
4972 @ref{Explicit Locations}).
4976 @defun Breakpoint.__init__ (@r{[} source @r{][}, function @r{][}, label @r{][}, line @r{]}, @r{][} internal @r{][}, temporary @r{][}, qualified @r{]})
4977 This second form of creating a new breakpoint specifies the explicit
4978 location (@pxref{Explicit Locations}) using keywords. The new breakpoint will
4979 be created in the specified source file @var{source}, at the specified
4980 @var{function}, @var{label} and @var{line}.
4982 @var{internal}, @var{temporary} and @var{qualified} have the same usage as
4983 explained previously.
4986 The available types are represented by constants defined in the @code{gdb}
4990 @vindex BP_BREAKPOINT
4991 @item gdb.BP_BREAKPOINT
4992 Normal code breakpoint.
4994 @vindex BP_WATCHPOINT
4995 @item gdb.BP_WATCHPOINT
4996 Watchpoint breakpoint.
4998 @vindex BP_HARDWARE_WATCHPOINT
4999 @item gdb.BP_HARDWARE_WATCHPOINT
5000 Hardware assisted watchpoint.
5002 @vindex BP_READ_WATCHPOINT
5003 @item gdb.BP_READ_WATCHPOINT
5004 Hardware assisted read watchpoint.
5006 @vindex BP_ACCESS_WATCHPOINT
5007 @item gdb.BP_ACCESS_WATCHPOINT
5008 Hardware assisted access watchpoint.
5011 The available watchpoint types represented by constants are defined in the
5017 Read only watchpoint.
5021 Write only watchpoint.
5025 Read/Write watchpoint.
5028 @defun Breakpoint.stop (self)
5029 The @code{gdb.Breakpoint} class can be sub-classed and, in
5030 particular, you may choose to implement the @code{stop} method.
5031 If this method is defined in a sub-class of @code{gdb.Breakpoint},
5032 it will be called when the inferior reaches any location of a
5033 breakpoint which instantiates that sub-class. If the method returns
5034 @code{True}, the inferior will be stopped at the location of the
5035 breakpoint, otherwise the inferior will continue.
5037 If there are multiple breakpoints at the same location with a
5038 @code{stop} method, each one will be called regardless of the
5039 return status of the previous. This ensures that all @code{stop}
5040 methods have a chance to execute at that location. In this scenario
5041 if one of the methods returns @code{True} but the others return
5042 @code{False}, the inferior will still be stopped.
5044 You should not alter the execution state of the inferior (i.e.@:, step,
5045 next, etc.), alter the current frame context (i.e.@:, change the current
5046 active frame), or alter, add or delete any breakpoint. As a general
5047 rule, you should not alter any data within @value{GDBN} or the inferior
5050 Example @code{stop} implementation:
5053 class MyBreakpoint (gdb.Breakpoint):
5055 inf_val = gdb.parse_and_eval("foo")
5062 @defun Breakpoint.is_valid ()
5063 Return @code{True} if this @code{Breakpoint} object is valid,
5064 @code{False} otherwise. A @code{Breakpoint} object can become invalid
5065 if the user deletes the breakpoint. In this case, the object still
5066 exists, but the underlying breakpoint does not. In the cases of
5067 watchpoint scope, the watchpoint remains valid even if execution of the
5068 inferior leaves the scope of that watchpoint.
5071 @defun Breakpoint.delete ()
5072 Permanently deletes the @value{GDBN} breakpoint. This also
5073 invalidates the Python @code{Breakpoint} object. Any further access
5074 to this object's attributes or methods will raise an error.
5077 @defvar Breakpoint.enabled
5078 This attribute is @code{True} if the breakpoint is enabled, and
5079 @code{False} otherwise. This attribute is writable. You can use it to enable
5080 or disable the breakpoint.
5083 @defvar Breakpoint.silent
5084 This attribute is @code{True} if the breakpoint is silent, and
5085 @code{False} otherwise. This attribute is writable.
5087 Note that a breakpoint can also be silent if it has commands and the
5088 first command is @code{silent}. This is not reported by the
5089 @code{silent} attribute.
5092 @defvar Breakpoint.pending
5093 This attribute is @code{True} if the breakpoint is pending, and
5094 @code{False} otherwise. @xref{Set Breaks}. This attribute is
5098 @anchor{python_breakpoint_thread}
5099 @defvar Breakpoint.thread
5100 If the breakpoint is thread-specific, this attribute holds the
5101 thread's global id. If the breakpoint is not thread-specific, this
5102 attribute is @code{None}. This attribute is writable.
5105 @defvar Breakpoint.task
5106 If the breakpoint is Ada task-specific, this attribute holds the Ada task
5107 id. If the breakpoint is not task-specific (or the underlying
5108 language is not Ada), this attribute is @code{None}. This attribute
5112 @defvar Breakpoint.ignore_count
5113 This attribute holds the ignore count for the breakpoint, an integer.
5114 This attribute is writable.
5117 @defvar Breakpoint.number
5118 This attribute holds the breakpoint's number --- the identifier used by
5119 the user to manipulate the breakpoint. This attribute is not writable.
5122 @defvar Breakpoint.type
5123 This attribute holds the breakpoint's type --- the identifier used to
5124 determine the actual breakpoint type or use-case. This attribute is not
5128 @defvar Breakpoint.visible
5129 This attribute tells whether the breakpoint is visible to the user
5130 when set, or when the @samp{info breakpoints} command is run. This
5131 attribute is not writable.
5134 @defvar Breakpoint.temporary
5135 This attribute indicates whether the breakpoint was created as a
5136 temporary breakpoint. Temporary breakpoints are automatically deleted
5137 after that breakpoint has been hit. Access to this attribute, and all
5138 other attributes and functions other than the @code{is_valid}
5139 function, will result in an error after the breakpoint has been hit
5140 (as it has been automatically deleted). This attribute is not
5144 @defvar Breakpoint.hit_count
5145 This attribute holds the hit count for the breakpoint, an integer.
5146 This attribute is writable, but currently it can only be set to zero.
5149 @defvar Breakpoint.location
5150 This attribute holds the location of the breakpoint, as specified by
5151 the user. It is a string. If the breakpoint does not have a location
5152 (that is, it is a watchpoint) the attribute's value is @code{None}. This
5153 attribute is not writable.
5156 @defvar Breakpoint.expression
5157 This attribute holds a breakpoint expression, as specified by
5158 the user. It is a string. If the breakpoint does not have an
5159 expression (the breakpoint is not a watchpoint) the attribute's value
5160 is @code{None}. This attribute is not writable.
5163 @defvar Breakpoint.condition
5164 This attribute holds the condition of the breakpoint, as specified by
5165 the user. It is a string. If there is no condition, this attribute's
5166 value is @code{None}. This attribute is writable.
5169 @defvar Breakpoint.commands
5170 This attribute holds the commands attached to the breakpoint. If
5171 there are commands, this attribute's value is a string holding all the
5172 commands, separated by newlines. If there are no commands, this
5173 attribute is @code{None}. This attribute is writable.
5176 @node Finish Breakpoints in Python
5177 @subsubsection Finish Breakpoints
5179 @cindex python finish breakpoints
5180 @tindex gdb.FinishBreakpoint
5182 A finish breakpoint is a temporary breakpoint set at the return address of
5183 a frame, based on the @code{finish} command. @code{gdb.FinishBreakpoint}
5184 extends @code{gdb.Breakpoint}. The underlying breakpoint will be disabled
5185 and deleted when the execution will run out of the breakpoint scope (i.e.@:
5186 @code{Breakpoint.stop} or @code{FinishBreakpoint.out_of_scope} triggered).
5187 Finish breakpoints are thread specific and must be create with the right
5190 @defun FinishBreakpoint.__init__ (@r{[}frame@r{]} @r{[}, internal@r{]})
5191 Create a finish breakpoint at the return address of the @code{gdb.Frame}
5192 object @var{frame}. If @var{frame} is not provided, this defaults to the
5193 newest frame. The optional @var{internal} argument allows the breakpoint to
5194 become invisible to the user. @xref{Breakpoints In Python}, for further
5195 details about this argument.
5198 @defun FinishBreakpoint.out_of_scope (self)
5199 In some circumstances (e.g.@: @code{longjmp}, C@t{++} exceptions, @value{GDBN}
5200 @code{return} command, @dots{}), a function may not properly terminate, and
5201 thus never hit the finish breakpoint. When @value{GDBN} notices such a
5202 situation, the @code{out_of_scope} callback will be triggered.
5204 You may want to sub-class @code{gdb.FinishBreakpoint} and override this
5208 class MyFinishBreakpoint (gdb.FinishBreakpoint)
5210 print "normal finish"
5213 def out_of_scope ():
5214 print "abnormal finish"
5218 @defvar FinishBreakpoint.return_value
5219 When @value{GDBN} is stopped at a finish breakpoint and the frame
5220 used to build the @code{gdb.FinishBreakpoint} object had debug symbols, this
5221 attribute will contain a @code{gdb.Value} object corresponding to the return
5222 value of the function. The value will be @code{None} if the function return
5223 type is @code{void} or if the return value was not computable. This attribute
5227 @node Lazy Strings In Python
5228 @subsubsection Python representation of lazy strings.
5230 @cindex lazy strings in python
5231 @tindex gdb.LazyString
5233 A @dfn{lazy string} is a string whose contents is not retrieved or
5234 encoded until it is needed.
5236 A @code{gdb.LazyString} is represented in @value{GDBN} as an
5237 @code{address} that points to a region of memory, an @code{encoding}
5238 that will be used to encode that region of memory, and a @code{length}
5239 to delimit the region of memory that represents the string. The
5240 difference between a @code{gdb.LazyString} and a string wrapped within
5241 a @code{gdb.Value} is that a @code{gdb.LazyString} will be treated
5242 differently by @value{GDBN} when printing. A @code{gdb.LazyString} is
5243 retrieved and encoded during printing, while a @code{gdb.Value}
5244 wrapping a string is immediately retrieved and encoded on creation.
5246 A @code{gdb.LazyString} object has the following functions:
5248 @defun LazyString.value ()
5249 Convert the @code{gdb.LazyString} to a @code{gdb.Value}. This value
5250 will point to the string in memory, but will lose all the delayed
5251 retrieval, encoding and handling that @value{GDBN} applies to a
5252 @code{gdb.LazyString}.
5255 @defvar LazyString.address
5256 This attribute holds the address of the string. This attribute is not
5260 @defvar LazyString.length
5261 This attribute holds the length of the string in characters. If the
5262 length is -1, then the string will be fetched and encoded up to the
5263 first null of appropriate width. This attribute is not writable.
5266 @defvar LazyString.encoding
5267 This attribute holds the encoding that will be applied to the string
5268 when the string is printed by @value{GDBN}. If the encoding is not
5269 set, or contains an empty string, then @value{GDBN} will select the
5270 most appropriate encoding when the string is printed. This attribute
5274 @defvar LazyString.type
5275 This attribute holds the type that is represented by the lazy string's
5276 type. For a lazy string this is a pointer or array type. To
5277 resolve this to the lazy string's character type, use the type's
5278 @code{target} method. @xref{Types In Python}. This attribute is not
5282 @node Architectures In Python
5283 @subsubsection Python representation of architectures
5284 @cindex Python architectures
5286 @value{GDBN} uses architecture specific parameters and artifacts in a
5287 number of its various computations. An architecture is represented
5288 by an instance of the @code{gdb.Architecture} class.
5290 A @code{gdb.Architecture} class has the following methods:
5292 @defun Architecture.name ()
5293 Return the name (string value) of the architecture.
5296 @defun Architecture.disassemble (@var{start_pc} @r{[}, @var{end_pc} @r{[}, @var{count}@r{]]})
5297 Return a list of disassembled instructions starting from the memory
5298 address @var{start_pc}. The optional arguments @var{end_pc} and
5299 @var{count} determine the number of instructions in the returned list.
5300 If both the optional arguments @var{end_pc} and @var{count} are
5301 specified, then a list of at most @var{count} disassembled instructions
5302 whose start address falls in the closed memory address interval from
5303 @var{start_pc} to @var{end_pc} are returned. If @var{end_pc} is not
5304 specified, but @var{count} is specified, then @var{count} number of
5305 instructions starting from the address @var{start_pc} are returned. If
5306 @var{count} is not specified but @var{end_pc} is specified, then all
5307 instructions whose start address falls in the closed memory address
5308 interval from @var{start_pc} to @var{end_pc} are returned. If neither
5309 @var{end_pc} nor @var{count} are specified, then a single instruction at
5310 @var{start_pc} is returned. For all of these cases, each element of the
5311 returned list is a Python @code{dict} with the following string keys:
5316 The value corresponding to this key is a Python long integer capturing
5317 the memory address of the instruction.
5320 The value corresponding to this key is a string value which represents
5321 the instruction with assembly language mnemonics. The assembly
5322 language flavor used is the same as that specified by the current CLI
5323 variable @code{disassembly-flavor}. @xref{Machine Code}.
5326 The value corresponding to this key is the length (integer value) of the
5327 instruction in bytes.
5332 @node Python Auto-loading
5333 @subsection Python Auto-loading
5334 @cindex Python auto-loading
5336 When a new object file is read (for example, due to the @code{file}
5337 command, or because the inferior has loaded a shared library),
5338 @value{GDBN} will look for Python support scripts in several ways:
5339 @file{@var{objfile}-gdb.py} and @code{.debug_gdb_scripts} section.
5340 @xref{Auto-loading extensions}.
5342 The auto-loading feature is useful for supplying application-specific
5343 debugging commands and scripts.
5345 Auto-loading can be enabled or disabled,
5346 and the list of auto-loaded scripts can be printed.
5349 @anchor{set auto-load python-scripts}
5350 @kindex set auto-load python-scripts
5351 @item set auto-load python-scripts [on|off]
5352 Enable or disable the auto-loading of Python scripts.
5354 @anchor{show auto-load python-scripts}
5355 @kindex show auto-load python-scripts
5356 @item show auto-load python-scripts
5357 Show whether auto-loading of Python scripts is enabled or disabled.
5359 @anchor{info auto-load python-scripts}
5360 @kindex info auto-load python-scripts
5361 @cindex print list of auto-loaded Python scripts
5362 @item info auto-load python-scripts [@var{regexp}]
5363 Print the list of all Python scripts that @value{GDBN} auto-loaded.
5365 Also printed is the list of Python scripts that were mentioned in
5366 the @code{.debug_gdb_scripts} section and were either not found
5367 (@pxref{dotdebug_gdb_scripts section}) or were not auto-loaded due to
5368 @code{auto-load safe-path} rejection (@pxref{Auto-loading}).
5369 This is useful because their names are not printed when @value{GDBN}
5370 tries to load them and fails. There may be many of them, and printing
5371 an error message for each one is problematic.
5373 If @var{regexp} is supplied only Python scripts with matching names are printed.
5378 (gdb) info auto-load python-scripts
5380 Yes py-section-script.py
5381 full name: /tmp/py-section-script.py
5382 No my-foo-pretty-printers.py
5386 When reading an auto-loaded file or script, @value{GDBN} sets the
5387 @dfn{current objfile}. This is available via the @code{gdb.current_objfile}
5388 function (@pxref{Objfiles In Python}). This can be useful for
5389 registering objfile-specific pretty-printers and frame-filters.
5391 @node Python modules
5392 @subsection Python modules
5393 @cindex python modules
5395 @value{GDBN} comes with several modules to assist writing Python code.
5398 * gdb.printing:: Building and registering pretty-printers.
5399 * gdb.types:: Utilities for working with types.
5400 * gdb.prompt:: Utilities for prompt value substitution.
5404 @subsubsection gdb.printing
5405 @cindex gdb.printing
5407 This module provides a collection of utilities for working with
5411 @item PrettyPrinter (@var{name}, @var{subprinters}=None)
5412 This class specifies the API that makes @samp{info pretty-printer},
5413 @samp{enable pretty-printer} and @samp{disable pretty-printer} work.
5414 Pretty-printers should generally inherit from this class.
5416 @item SubPrettyPrinter (@var{name})
5417 For printers that handle multiple types, this class specifies the
5418 corresponding API for the subprinters.
5420 @item RegexpCollectionPrettyPrinter (@var{name})
5421 Utility class for handling multiple printers, all recognized via
5422 regular expressions.
5423 @xref{Writing a Pretty-Printer}, for an example.
5425 @item FlagEnumerationPrinter (@var{name})
5426 A pretty-printer which handles printing of @code{enum} values. Unlike
5427 @value{GDBN}'s built-in @code{enum} printing, this printer attempts to
5428 work properly when there is some overlap between the enumeration
5429 constants. The argument @var{name} is the name of the printer and
5430 also the name of the @code{enum} type to look up.
5432 @item register_pretty_printer (@var{obj}, @var{printer}, @var{replace}=False)
5433 Register @var{printer} with the pretty-printer list of @var{obj}.
5434 If @var{replace} is @code{True} then any existing copy of the printer
5435 is replaced. Otherwise a @code{RuntimeError} exception is raised
5436 if a printer with the same name already exists.
5440 @subsubsection gdb.types
5443 This module provides a collection of utilities for working with
5444 @code{gdb.Type} objects.
5447 @item get_basic_type (@var{type})
5448 Return @var{type} with const and volatile qualifiers stripped,
5449 and with typedefs and C@t{++} references converted to the underlying type.
5454 typedef const int const_int;
5456 const_int& foo_ref (foo);
5457 int main () @{ return 0; @}
5464 (gdb) python import gdb.types
5465 (gdb) python foo_ref = gdb.parse_and_eval("foo_ref")
5466 (gdb) python print gdb.types.get_basic_type(foo_ref.type)
5470 @item has_field (@var{type}, @var{field})
5471 Return @code{True} if @var{type}, assumed to be a type with fields
5472 (e.g., a structure or union), has field @var{field}.
5474 @item make_enum_dict (@var{enum_type})
5475 Return a Python @code{dictionary} type produced from @var{enum_type}.
5477 @item deep_items (@var{type})
5478 Returns a Python iterator similar to the standard
5479 @code{gdb.Type.iteritems} method, except that the iterator returned
5480 by @code{deep_items} will recursively traverse anonymous struct or
5481 union fields. For example:
5495 Then in @value{GDBN}:
5497 (@value{GDBP}) python import gdb.types
5498 (@value{GDBP}) python struct_a = gdb.lookup_type("struct A")
5499 (@value{GDBP}) python print struct_a.keys ()
5501 (@value{GDBP}) python print [k for k,v in gdb.types.deep_items(struct_a)]
5502 @{['a', 'b0', 'b1']@}
5505 @item get_type_recognizers ()
5506 Return a list of the enabled type recognizers for the current context.
5507 This is called by @value{GDBN} during the type-printing process
5508 (@pxref{Type Printing API}).
5510 @item apply_type_recognizers (recognizers, type_obj)
5511 Apply the type recognizers, @var{recognizers}, to the type object
5512 @var{type_obj}. If any recognizer returns a string, return that
5513 string. Otherwise, return @code{None}. This is called by
5514 @value{GDBN} during the type-printing process (@pxref{Type Printing
5517 @item register_type_printer (locus, printer)
5518 This is a convenience function to register a type printer
5519 @var{printer}. The printer must implement the type printer protocol.
5520 The @var{locus} argument is either a @code{gdb.Objfile}, in which case
5521 the printer is registered with that objfile; a @code{gdb.Progspace},
5522 in which case the printer is registered with that progspace; or
5523 @code{None}, in which case the printer is registered globally.
5526 This is a base class that implements the type printer protocol. Type
5527 printers are encouraged, but not required, to derive from this class.
5528 It defines a constructor:
5530 @defmethod TypePrinter __init__ (self, name)
5531 Initialize the type printer with the given name. The new printer
5532 starts in the enabled state.
5538 @subsubsection gdb.prompt
5541 This module provides a method for prompt value-substitution.
5544 @item substitute_prompt (@var{string})
5545 Return @var{string} with escape sequences substituted by values. Some
5546 escape sequences take arguments. You can specify arguments inside
5547 ``@{@}'' immediately following the escape sequence.
5549 The escape sequences you can pass to this function are:
5553 Substitute a backslash.
5555 Substitute an ESC character.
5557 Substitute the selected frame; an argument names a frame parameter.
5559 Substitute a newline.
5561 Substitute a parameter's value; the argument names the parameter.
5563 Substitute a carriage return.
5565 Substitute the selected thread; an argument names a thread parameter.
5567 Substitute the version of GDB.
5569 Substitute the current working directory.
5571 Begin a sequence of non-printing characters. These sequences are
5572 typically used with the ESC character, and are not counted in the string
5573 length. Example: ``\[\e[0;34m\](gdb)\[\e[0m\]'' will return a
5574 blue-colored ``(gdb)'' prompt where the length is five.
5576 End a sequence of non-printing characters.
5582 substitute_prompt (``frame: \f,
5583 print arguments: \p@{print frame-arguments@}'')
5586 @exdent will return the string:
5589 "frame: main, print arguments: scalars"