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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. 100 is a good default priority.
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 @tindex gdb.FrameDecorator
1809 @code{FrameDecorator} is defined in the Python module
1810 @code{gdb.FrameDecorator}, so your code can import it like:
1812 from gdb.FrameDecorator import FrameDecorator
1815 @defun FrameDecorator.elided (self)
1817 The @code{elided} method groups frames together in a hierarchical
1818 system. An example would be an interpreter, where multiple low-level
1819 frames make up a single call in the interpreted language. In this
1820 example, the frame filter would elide the low-level frames and present
1821 a single high-level frame, representing the call in the interpreted
1822 language, to the user.
1824 The @code{elided} function must return an iterable and this iterable
1825 must contain the frames that are being elided wrapped in a suitable
1826 frame decorator. If no frames are being elided this function may
1827 return an empty iterable, or @code{None}. Elided frames are indented
1828 from normal frames in a @code{CLI} backtrace, or in the case of
1829 @code{GDB/MI}, are placed in the @code{children} field of the eliding
1832 It is the frame filter's task to also filter out the elided frames from
1833 the source iterator. This will avoid printing the frame twice.
1836 @defun FrameDecorator.function (self)
1838 This method returns the name of the function in the frame that is to
1841 This method must return a Python string describing the function, or
1844 If this function returns @code{None}, @value{GDBN} will not print any
1845 data for this field.
1848 @defun FrameDecorator.address (self)
1850 This method returns the address of the frame that is to be printed.
1852 This method must return a Python numeric integer type of sufficient
1853 size to describe the address of the frame, or @code{None}.
1855 If this function returns a @code{None}, @value{GDBN} will not print
1856 any data for this field.
1859 @defun FrameDecorator.filename (self)
1861 This method returns the filename and path associated with this frame.
1863 This method must return a Python string containing the filename and
1864 the path to the object file backing the frame, or @code{None}.
1866 If this function returns a @code{None}, @value{GDBN} will not print
1867 any data for this field.
1870 @defun FrameDecorator.line (self):
1872 This method returns the line number associated with the current
1873 position within the function addressed by this frame.
1875 This method must return a Python integer type, or @code{None}.
1877 If this function returns a @code{None}, @value{GDBN} will not print
1878 any data for this field.
1881 @defun FrameDecorator.frame_args (self)
1884 This method must return an iterable, or @code{None}. Returning an
1885 empty iterable, or @code{None} means frame arguments will not be
1886 printed for this frame. This iterable must contain objects that
1887 implement two methods, described here.
1889 This object must implement a @code{argument} method which takes a
1890 single @code{self} parameter and must return a @code{gdb.Symbol}
1891 (@pxref{Symbols In Python}), or a Python string. The object must also
1892 implement a @code{value} method which takes a single @code{self}
1893 parameter and must return a @code{gdb.Value} (@pxref{Values From
1894 Inferior}), a Python value, or @code{None}. If the @code{value}
1895 method returns @code{None}, and the @code{argument} method returns a
1896 @code{gdb.Symbol}, @value{GDBN} will look-up and print the value of
1897 the @code{gdb.Symbol} automatically.
1902 class SymValueWrapper():
1904 def __init__(self, symbol, value):
1914 class SomeFrameDecorator()
1917 def frame_args(self):
1920 block = self.inferior_frame.block()
1924 # Iterate over all symbols in a block. Only add
1925 # symbols that are arguments.
1927 if not sym.is_argument:
1929 args.append(SymValueWrapper(sym,None))
1931 # Add example synthetic argument.
1932 args.append(SymValueWrapper(``foo'', 42))
1938 @defun FrameDecorator.frame_locals (self)
1940 This method must return an iterable or @code{None}. Returning an
1941 empty iterable, or @code{None} means frame local arguments will not be
1942 printed for this frame.
1944 The object interface, the description of the various strategies for
1945 reading frame locals, and the example are largely similar to those
1946 described in the @code{frame_args} function, (@pxref{frame_args,,The
1947 frame filter frame_args function}). Below is a modified example:
1950 class SomeFrameDecorator()
1953 def frame_locals(self):
1956 block = self.inferior_frame.block()
1960 # Iterate over all symbols in a block. Add all
1961 # symbols, except arguments.
1965 vars.append(SymValueWrapper(sym,None))
1967 # Add an example of a synthetic local variable.
1968 vars.append(SymValueWrapper(``bar'', 99))
1974 @defun FrameDecorator.inferior_frame (self):
1976 This method must return the underlying @code{gdb.Frame} that this
1977 frame decorator is decorating. @value{GDBN} requires the underlying
1978 frame for internal frame information to determine how to print certain
1979 values when printing a frame.
1982 @node Writing a Frame Filter
1983 @subsubsection Writing a Frame Filter
1984 @cindex writing a frame filter
1986 There are three basic elements that a frame filter must implement: it
1987 must correctly implement the documented interface (@pxref{Frame Filter
1988 API}), it must register itself with @value{GDBN}, and finally, it must
1989 decide if it is to work on the data provided by @value{GDBN}. In all
1990 cases, whether it works on the iterator or not, each frame filter must
1991 return an iterator. A bare-bones frame filter follows the pattern in
1992 the following example.
1997 class FrameFilter():
2000 # Frame filter attribute creation.
2002 # 'name' is the name of the filter that GDB will display.
2004 # 'priority' is the priority of the filter relative to other
2007 # 'enabled' is a boolean that indicates whether this filter is
2008 # enabled and should be executed.
2014 # Register this frame filter with the global frame_filters
2016 gdb.frame_filters[self.name] = self
2018 def filter(self, frame_iter):
2019 # Just return the iterator.
2023 The frame filter in the example above implements the three
2024 requirements for all frame filters. It implements the API, self
2025 registers, and makes a decision on the iterator (in this case, it just
2026 returns the iterator untouched).
2028 The first step is attribute creation and assignment, and as shown in
2029 the comments the filter assigns the following attributes: @code{name},
2030 @code{priority} and whether the filter should be enabled with the
2031 @code{enabled} attribute.
2033 The second step is registering the frame filter with the dictionary or
2034 dictionaries that the frame filter has interest in. As shown in the
2035 comments, this filter just registers itself with the global dictionary
2036 @code{gdb.frame_filters}. As noted earlier, @code{gdb.frame_filters}
2037 is a dictionary that is initialized in the @code{gdb} module when
2038 @value{GDBN} starts. What dictionary a filter registers with is an
2039 important consideration. Generally, if a filter is specific to a set
2040 of code, it should be registered either in the @code{objfile} or
2041 @code{progspace} dictionaries as they are specific to the program
2042 currently loaded in @value{GDBN}. The global dictionary is always
2043 present in @value{GDBN} and is never unloaded. Any filters registered
2044 with the global dictionary will exist until @value{GDBN} exits. To
2045 avoid filters that may conflict, it is generally better to register
2046 frame filters against the dictionaries that more closely align with
2047 the usage of the filter currently in question. @xref{Python
2048 Auto-loading}, for further information on auto-loading Python scripts.
2050 @value{GDBN} takes a hands-off approach to frame filter registration,
2051 therefore it is the frame filter's responsibility to ensure
2052 registration has occurred, and that any exceptions are handled
2053 appropriately. In particular, you may wish to handle exceptions
2054 relating to Python dictionary key uniqueness. It is mandatory that
2055 the dictionary key is the same as frame filter's @code{name}
2056 attribute. When a user manages frame filters (@pxref{Frame Filter
2057 Management}), the names @value{GDBN} will display are those contained
2058 in the @code{name} attribute.
2060 The final step of this example is the implementation of the
2061 @code{filter} method. As shown in the example comments, we define the
2062 @code{filter} method and note that the method must take an iterator,
2063 and also must return an iterator. In this bare-bones example, the
2064 frame filter is not very useful as it just returns the iterator
2065 untouched. However this is a valid operation for frame filters that
2066 have the @code{enabled} attribute set, but decide not to operate on
2069 In the next example, the frame filter operates on all frames and
2070 utilizes a frame decorator to perform some work on the frames.
2071 @xref{Frame Decorator API}, for further information on the frame
2072 decorator interface.
2074 This example works on inlined frames. It highlights frames which are
2075 inlined by tagging them with an ``[inlined]'' tag. By applying a
2076 frame decorator to all frames with the Python @code{itertools imap}
2077 method, the example defers actions to the frame decorator. Frame
2078 decorators are only processed when @value{GDBN} prints the backtrace.
2080 This introduces a new decision making topic: whether to perform
2081 decision making operations at the filtering step, or at the printing
2082 step. In this example's approach, it does not perform any filtering
2083 decisions at the filtering step beyond mapping a frame decorator to
2084 each frame. This allows the actual decision making to be performed
2085 when each frame is printed. This is an important consideration, and
2086 well worth reflecting upon when designing a frame filter. An issue
2087 that frame filters should avoid is unwinding the stack if possible.
2088 Some stacks can run very deep, into the tens of thousands in some
2089 cases. To search every frame to determine if it is inlined ahead of
2090 time may be too expensive at the filtering step. The frame filter
2091 cannot know how many frames it has to iterate over, and it would have
2092 to iterate through them all. This ends up duplicating effort as
2093 @value{GDBN} performs this iteration when it prints the frames.
2095 In this example decision making can be deferred to the printing step.
2096 As each frame is printed, the frame decorator can examine each frame
2097 in turn when @value{GDBN} iterates. From a performance viewpoint,
2098 this is the most appropriate decision to make as it avoids duplicating
2099 the effort that the printing step would undertake anyway. Also, if
2100 there are many frame filters unwinding the stack during filtering, it
2101 can substantially delay the printing of the backtrace which will
2102 result in large memory usage, and a poor user experience.
2105 class InlineFilter():
2108 self.name = "InlinedFrameFilter"
2111 gdb.frame_filters[self.name] = self
2113 def filter(self, frame_iter):
2114 frame_iter = itertools.imap(InlinedFrameDecorator,
2119 This frame filter is somewhat similar to the earlier example, except
2120 that the @code{filter} method applies a frame decorator object called
2121 @code{InlinedFrameDecorator} to each element in the iterator. The
2122 @code{imap} Python method is light-weight. It does not proactively
2123 iterate over the iterator, but rather creates a new iterator which
2124 wraps the existing one.
2126 Below is the frame decorator for this example.
2129 class InlinedFrameDecorator(FrameDecorator):
2131 def __init__(self, fobj):
2132 super(InlinedFrameDecorator, self).__init__(fobj)
2135 frame = fobj.inferior_frame()
2136 name = str(frame.name())
2138 if frame.type() == gdb.INLINE_FRAME:
2139 name = name + " [inlined]"
2144 This frame decorator only defines and overrides the @code{function}
2145 method. It lets the supplied @code{FrameDecorator}, which is shipped
2146 with @value{GDBN}, perform the other work associated with printing
2149 The combination of these two objects create this output from a
2153 #0 0x004004e0 in bar () at inline.c:11
2154 #1 0x00400566 in max [inlined] (b=6, a=12) at inline.c:21
2155 #2 0x00400566 in main () at inline.c:31
2158 So in the case of this example, a frame decorator is applied to all
2159 frames, regardless of whether they may be inlined or not. As
2160 @value{GDBN} iterates over the iterator produced by the frame filters,
2161 @value{GDBN} executes each frame decorator which then makes a decision
2162 on what to print in the @code{function} callback. Using a strategy
2163 like this is a way to defer decisions on the frame content to printing
2166 @subheading Eliding Frames
2168 It might be that the above example is not desirable for representing
2169 inlined frames, and a hierarchical approach may be preferred. If we
2170 want to hierarchically represent frames, the @code{elided} frame
2171 decorator interface might be preferable.
2173 This example approaches the issue with the @code{elided} method. This
2174 example is quite long, but very simplistic. It is out-of-scope for
2175 this section to write a complete example that comprehensively covers
2176 all approaches of finding and printing inlined frames. However, this
2177 example illustrates the approach an author might use.
2179 This example comprises of three sections.
2182 class InlineFrameFilter():
2185 self.name = "InlinedFrameFilter"
2188 gdb.frame_filters[self.name] = self
2190 def filter(self, frame_iter):
2191 return ElidingInlineIterator(frame_iter)
2194 This frame filter is very similar to the other examples. The only
2195 difference is this frame filter is wrapping the iterator provided to
2196 it (@code{frame_iter}) with a custom iterator called
2197 @code{ElidingInlineIterator}. This again defers actions to when
2198 @value{GDBN} prints the backtrace, as the iterator is not traversed
2201 The iterator for this example is as follows. It is in this section of
2202 the example where decisions are made on the content of the backtrace.
2205 class ElidingInlineIterator:
2206 def __init__(self, ii):
2207 self.input_iterator = ii
2213 frame = next(self.input_iterator)
2215 if frame.inferior_frame().type() != gdb.INLINE_FRAME:
2219 eliding_frame = next(self.input_iterator)
2220 except StopIteration:
2222 return ElidingFrameDecorator(eliding_frame, [frame])
2225 This iterator implements the Python iterator protocol. When the
2226 @code{next} function is called (when @value{GDBN} prints each frame),
2227 the iterator checks if this frame decorator, @code{frame}, is wrapping
2228 an inlined frame. If it is not, it returns the existing frame decorator
2229 untouched. If it is wrapping an inlined frame, it assumes that the
2230 inlined frame was contained within the next oldest frame,
2231 @code{eliding_frame}, which it fetches. It then creates and returns a
2232 frame decorator, @code{ElidingFrameDecorator}, which contains both the
2233 elided frame, and the eliding frame.
2236 class ElidingInlineDecorator(FrameDecorator):
2238 def __init__(self, frame, elided_frames):
2239 super(ElidingInlineDecorator, self).__init__(frame)
2241 self.elided_frames = elided_frames
2244 return iter(self.elided_frames)
2247 This frame decorator overrides one function and returns the inlined
2248 frame in the @code{elided} method. As before it lets
2249 @code{FrameDecorator} do the rest of the work involved in printing
2250 this frame. This produces the following output.
2253 #0 0x004004e0 in bar () at inline.c:11
2254 #2 0x00400529 in main () at inline.c:25
2255 #1 0x00400529 in max (b=6, a=12) at inline.c:15
2258 In that output, @code{max} which has been inlined into @code{main} is
2259 printed hierarchically. Another approach would be to combine the
2260 @code{function} method, and the @code{elided} method to both print a
2261 marker in the inlined frame, and also show the hierarchical
2264 @node Unwinding Frames in Python
2265 @subsubsection Unwinding Frames in Python
2266 @cindex unwinding frames in Python
2268 In @value{GDBN} terminology ``unwinding'' is the process of finding
2269 the previous frame (that is, caller's) from the current one. An
2270 unwinder has three methods. The first one checks if it can handle
2271 given frame (``sniff'' it). For the frames it can sniff an unwinder
2272 provides two additional methods: it can return frame's ID, and it can
2273 fetch registers from the previous frame. A running @value{GDBN}
2274 mantains a list of the unwinders and calls each unwinder's sniffer in
2275 turn until it finds the one that recognizes the current frame. There
2276 is an API to register an unwinder.
2278 The unwinders that come with @value{GDBN} handle standard frames.
2279 However, mixed language applications (for example, an application
2280 running Java Virtual Machine) sometimes use frame layouts that cannot
2281 be handled by the @value{GDBN} unwinders. You can write Python code
2282 that can handle such custom frames.
2284 You implement a frame unwinder in Python as a class with which has two
2285 attributes, @code{name} and @code{enabled}, with obvious meanings, and
2286 a single method @code{__call__}, which examines a given frame and
2287 returns an object (an instance of @code{gdb.UnwindInfo class)}
2288 describing it. If an unwinder does not recognize a frame, it should
2289 return @code{None}. The code in @value{GDBN} that enables writing
2290 unwinders in Python uses this object to return frame's ID and previous
2291 frame registers when @value{GDBN} core asks for them.
2293 @subheading Unwinder Input
2295 An object passed to an unwinder (a @code{gdb.PendingFrame} instance)
2296 provides a method to read frame's registers:
2298 @defun PendingFrame.read_register (reg)
2299 This method returns the contents of the register @var{regn} in the
2300 frame as a @code{gdb.Value} object. @var{reg} can be either a
2301 register number or a register name; the values are platform-specific.
2302 They are usually found in the corresponding
2303 @file{@var{platform}-tdep.h} file in the @value{GDBN} source tree.
2306 It also provides a factory method to create a @code{gdb.UnwindInfo}
2307 instance to be returned to @value{GDBN}:
2309 @defun PendingFrame.create_unwind_info (frame_id)
2310 Returns a new @code{gdb.UnwindInfo} instance identified by given
2311 @var{frame_id}. The argument is used to build @value{GDBN}'s frame ID
2312 using one of functions provided by @value{GDBN}. @var{frame_id}'s attributes
2313 determine which function will be used, as follows:
2316 @item sp, pc, special
2317 @code{frame_id_build_special (@var{frame_id}.sp, @var{frame_id}.pc, @var{frame_id}.special)}
2320 @code{frame_id_build (@var{frame_id}.sp, @var{frame_id}.pc)}
2322 This is the most common case.
2325 @code{frame_id_build_wild (@var{frame_id}.sp)}
2327 The attribute values should be @code{gdb.Value}
2331 @subheading Unwinder Output: UnwindInfo
2333 Use @code{PendingFrame.create_unwind_info} method described above to
2334 create a @code{gdb.UnwindInfo} instance. Use the following method to
2335 specify caller registers that have been saved in this frame:
2337 @defun gdb.UnwindInfo.add_saved_register (reg, value)
2338 @var{reg} identifies the register. It can be a number or a name, just
2339 as for the @code{PendingFrame.read_register} method above.
2340 @var{value} is a register value (a @code{gdb.Value} object).
2343 @subheading Unwinder Skeleton Code
2345 @value{GDBN} comes with the module containing the base @code{Unwinder}
2346 class. Derive your unwinder class from it and structure the code as
2350 from gdb.unwinders import Unwinder
2352 class FrameId(object):
2353 def __init__(self, sp, pc):
2358 class MyUnwinder(Unwinder):
2360 supe(MyUnwinder, self).__init___(<expects unwinder name argument>)
2362 def __call__(pending_frame):
2363 if not <we recognize frame>:
2365 # Create UnwindInfo. Usually the frame is identified by the stack
2366 # pointer and the program counter.
2367 sp = pending_frame.read_register(<SP number>)
2368 pc = pending_frame.read_register(<PC number>)
2369 unwind_info = pending_frame.create_unwind_info(FrameId(sp, pc))
2371 # Find the values of the registers in the caller's frame and
2372 # save them in the result:
2373 unwind_info.add_saved_register(<register>, <value>)
2376 # Return the result:
2381 @subheading Registering a Unwinder
2383 An object file, a program space, and the @value{GDBN} proper can have
2384 unwinders registered with it.
2386 The @code{gdb.unwinders} module provides the function to register a
2389 @defun gdb.unwinder.register_unwinder (locus, unwinder, replace=False)
2390 @var{locus} is specifies an object file or a program space to which
2391 @var{unwinder} is added. Passing @code{None} or @code{gdb} adds
2392 @var{unwinder} to the @value{GDBN}'s global unwinder list. The newly
2393 added @var{unwinder} will be called before any other unwinder from the
2394 same locus. Two unwinders in the same locus cannot have the same
2395 name. An attempt to add a unwinder with already existing name raises
2396 an exception unless @var{replace} is @code{True}, in which case the
2397 old unwinder is deleted.
2400 @subheading Unwinder Precedence
2402 @value{GDBN} first calls the unwinders from all the object files in no
2403 particular order, then the unwinders from the current program space,
2404 and finally the unwinders from @value{GDBN}.
2406 @node Xmethods In Python
2407 @subsubsection Xmethods In Python
2408 @cindex xmethods in Python
2410 @dfn{Xmethods} are additional methods or replacements for existing
2411 methods of a C@t{++} class. This feature is useful for those cases
2412 where a method defined in C@t{++} source code could be inlined or
2413 optimized out by the compiler, making it unavailable to @value{GDBN}.
2414 For such cases, one can define an xmethod to serve as a replacement
2415 for the method defined in the C@t{++} source code. @value{GDBN} will
2416 then invoke the xmethod, instead of the C@t{++} method, to
2417 evaluate expressions. One can also use xmethods when debugging
2418 with core files. Moreover, when debugging live programs, invoking an
2419 xmethod need not involve running the inferior (which can potentially
2420 perturb its state). Hence, even if the C@t{++} method is available, it
2421 is better to use its replacement xmethod if one is defined.
2423 The xmethods feature in Python is available via the concepts of an
2424 @dfn{xmethod matcher} and an @dfn{xmethod worker}. To
2425 implement an xmethod, one has to implement a matcher and a
2426 corresponding worker for it (more than one worker can be
2427 implemented, each catering to a different overloaded instance of the
2428 method). Internally, @value{GDBN} invokes the @code{match} method of a
2429 matcher to match the class type and method name. On a match, the
2430 @code{match} method returns a list of matching @emph{worker} objects.
2431 Each worker object typically corresponds to an overloaded instance of
2432 the xmethod. They implement a @code{get_arg_types} method which
2433 returns a sequence of types corresponding to the arguments the xmethod
2434 requires. @value{GDBN} uses this sequence of types to perform
2435 overload resolution and picks a winning xmethod worker. A winner
2436 is also selected from among the methods @value{GDBN} finds in the
2437 C@t{++} source code. Next, the winning xmethod worker and the
2438 winning C@t{++} method are compared to select an overall winner. In
2439 case of a tie between a xmethod worker and a C@t{++} method, the
2440 xmethod worker is selected as the winner. That is, if a winning
2441 xmethod worker is found to be equivalent to the winning C@t{++}
2442 method, then the xmethod worker is treated as a replacement for
2443 the C@t{++} method. @value{GDBN} uses the overall winner to invoke the
2444 method. If the winning xmethod worker is the overall winner, then
2445 the corresponding xmethod is invoked via the @code{__call__} method
2446 of the worker object.
2448 If one wants to implement an xmethod as a replacement for an
2449 existing C@t{++} method, then they have to implement an equivalent
2450 xmethod which has exactly the same name and takes arguments of
2451 exactly the same type as the C@t{++} method. If the user wants to
2452 invoke the C@t{++} method even though a replacement xmethod is
2453 available for that method, then they can disable the xmethod.
2455 @xref{Xmethod API}, for API to implement xmethods in Python.
2456 @xref{Writing an Xmethod}, for implementing xmethods in Python.
2459 @subsubsection Xmethod API
2462 The @value{GDBN} Python API provides classes, interfaces and functions
2463 to implement, register and manipulate xmethods.
2464 @xref{Xmethods In Python}.
2466 An xmethod matcher should be an instance of a class derived from
2467 @code{XMethodMatcher} defined in the module @code{gdb.xmethod}, or an
2468 object with similar interface and attributes. An instance of
2469 @code{XMethodMatcher} has the following attributes:
2472 The name of the matcher.
2476 A boolean value indicating whether the matcher is enabled or disabled.
2480 A list of named methods managed by the matcher. Each object in the list
2481 is an instance of the class @code{XMethod} defined in the module
2482 @code{gdb.xmethod}, or any object with the following attributes:
2487 Name of the xmethod which should be unique for each xmethod
2488 managed by the matcher.
2491 A boolean value indicating whether the xmethod is enabled or
2496 The class @code{XMethod} is a convenience class with same
2497 attributes as above along with the following constructor:
2499 @defun XMethod.__init__ (self, name)
2500 Constructs an enabled xmethod with name @var{name}.
2505 The @code{XMethodMatcher} class has the following methods:
2507 @defun XMethodMatcher.__init__ (self, name)
2508 Constructs an enabled xmethod matcher with name @var{name}. The
2509 @code{methods} attribute is initialized to @code{None}.
2512 @defun XMethodMatcher.match (self, class_type, method_name)
2513 Derived classes should override this method. It should return a
2514 xmethod worker object (or a sequence of xmethod worker
2515 objects) matching the @var{class_type} and @var{method_name}.
2516 @var{class_type} is a @code{gdb.Type} object, and @var{method_name}
2517 is a string value. If the matcher manages named methods as listed in
2518 its @code{methods} attribute, then only those worker objects whose
2519 corresponding entries in the @code{methods} list are enabled should be
2523 An xmethod worker should be an instance of a class derived from
2524 @code{XMethodWorker} defined in the module @code{gdb.xmethod},
2525 or support the following interface:
2527 @defun XMethodWorker.get_arg_types (self)
2528 This method returns a sequence of @code{gdb.Type} objects corresponding
2529 to the arguments that the xmethod takes. It can return an empty
2530 sequence or @code{None} if the xmethod does not take any arguments.
2531 If the xmethod takes a single argument, then a single
2532 @code{gdb.Type} object corresponding to it can be returned.
2535 @defun XMethodWorker.get_result_type (self, *args)
2536 This method returns a @code{gdb.Type} object representing the type
2537 of the result of invoking this xmethod.
2538 The @var{args} argument is the same tuple of arguments that would be
2539 passed to the @code{__call__} method of this worker.
2542 @defun XMethodWorker.__call__ (self, *args)
2543 This is the method which does the @emph{work} of the xmethod. The
2544 @var{args} arguments is the tuple of arguments to the xmethod. Each
2545 element in this tuple is a gdb.Value object. The first element is
2546 always the @code{this} pointer value.
2549 For @value{GDBN} to lookup xmethods, the xmethod matchers
2550 should be registered using the following function defined in the module
2553 @defun register_xmethod_matcher (locus, matcher, replace=False)
2554 The @code{matcher} is registered with @code{locus}, replacing an
2555 existing matcher with the same name as @code{matcher} if
2556 @code{replace} is @code{True}. @code{locus} can be a
2557 @code{gdb.Objfile} object (@pxref{Objfiles In Python}), or a
2558 @code{gdb.Progspace} object (@pxref{Progspaces In Python}), or
2559 @code{None}. If it is @code{None}, then @code{matcher} is registered
2563 @node Writing an Xmethod
2564 @subsubsection Writing an Xmethod
2565 @cindex writing xmethods in Python
2567 Implementing xmethods in Python will require implementing xmethod
2568 matchers and xmethod workers (@pxref{Xmethods In Python}). Consider
2569 the following C@t{++} class:
2575 MyClass (int a) : a_(a) @{ @}
2577 int geta (void) @{ return a_; @}
2578 int operator+ (int b);
2585 MyClass::operator+ (int b)
2592 Let us define two xmethods for the class @code{MyClass}, one
2593 replacing the method @code{geta}, and another adding an overloaded
2594 flavor of @code{operator+} which takes a @code{MyClass} argument (the
2595 C@t{++} code above already has an overloaded @code{operator+}
2596 which takes an @code{int} argument). The xmethod matcher can be
2600 class MyClass_geta(gdb.xmethod.XMethod):
2602 gdb.xmethod.XMethod.__init__(self, 'geta')
2604 def get_worker(self, method_name):
2605 if method_name == 'geta':
2606 return MyClassWorker_geta()
2609 class MyClass_sum(gdb.xmethod.XMethod):
2611 gdb.xmethod.XMethod.__init__(self, 'sum')
2613 def get_worker(self, method_name):
2614 if method_name == 'operator+':
2615 return MyClassWorker_plus()
2618 class MyClassMatcher(gdb.xmethod.XMethodMatcher):
2620 gdb.xmethod.XMethodMatcher.__init__(self, 'MyClassMatcher')
2621 # List of methods 'managed' by this matcher
2622 self.methods = [MyClass_geta(), MyClass_sum()]
2624 def match(self, class_type, method_name):
2625 if class_type.tag != 'MyClass':
2628 for method in self.methods:
2630 worker = method.get_worker(method_name)
2632 workers.append(worker)
2638 Notice that the @code{match} method of @code{MyClassMatcher} returns
2639 a worker object of type @code{MyClassWorker_geta} for the @code{geta}
2640 method, and a worker object of type @code{MyClassWorker_plus} for the
2641 @code{operator+} method. This is done indirectly via helper classes
2642 derived from @code{gdb.xmethod.XMethod}. One does not need to use the
2643 @code{methods} attribute in a matcher as it is optional. However, if a
2644 matcher manages more than one xmethod, it is a good practice to list the
2645 xmethods in the @code{methods} attribute of the matcher. This will then
2646 facilitate enabling and disabling individual xmethods via the
2647 @code{enable/disable} commands. Notice also that a worker object is
2648 returned only if the corresponding entry in the @code{methods} attribute
2649 of the matcher is enabled.
2651 The implementation of the worker classes returned by the matcher setup
2652 above is as follows:
2655 class MyClassWorker_geta(gdb.xmethod.XMethodWorker):
2656 def get_arg_types(self):
2659 def get_result_type(self, obj):
2660 return gdb.lookup_type('int')
2662 def __call__(self, obj):
2666 class MyClassWorker_plus(gdb.xmethod.XMethodWorker):
2667 def get_arg_types(self):
2668 return gdb.lookup_type('MyClass')
2670 def get_result_type(self, obj):
2671 return gdb.lookup_type('int')
2673 def __call__(self, obj, other):
2674 return obj['a_'] + other['a_']
2677 For @value{GDBN} to actually lookup a xmethod, it has to be
2678 registered with it. The matcher defined above is registered with
2679 @value{GDBN} globally as follows:
2682 gdb.xmethod.register_xmethod_matcher(None, MyClassMatcher())
2685 If an object @code{obj} of type @code{MyClass} is initialized in C@t{++}
2693 then, after loading the Python script defining the xmethod matchers
2694 and workers into @code{GDBN}, invoking the method @code{geta} or using
2695 the operator @code{+} on @code{obj} will invoke the xmethods
2706 Consider another example with a C++ template class:
2713 MyTemplate () : dsize_(10), data_ (new T [10]) @{ @}
2714 ~MyTemplate () @{ delete [] data_; @}
2716 int footprint (void)
2718 return sizeof (T) * dsize_ + sizeof (MyTemplate<T>);
2727 Let us implement an xmethod for the above class which serves as a
2728 replacement for the @code{footprint} method. The full code listing
2729 of the xmethod workers and xmethod matchers is as follows:
2732 class MyTemplateWorker_footprint(gdb.xmethod.XMethodWorker):
2733 def __init__(self, class_type):
2734 self.class_type = class_type
2736 def get_arg_types(self):
2739 def get_result_type(self):
2740 return gdb.lookup_type('int')
2742 def __call__(self, obj):
2743 return (self.class_type.sizeof +
2745 self.class_type.template_argument(0).sizeof)
2748 class MyTemplateMatcher_footprint(gdb.xmethod.XMethodMatcher):
2750 gdb.xmethod.XMethodMatcher.__init__(self, 'MyTemplateMatcher')
2752 def match(self, class_type, method_name):
2753 if (re.match('MyTemplate<[ \t\n]*[_a-zA-Z][ _a-zA-Z0-9]*>',
2755 method_name == 'footprint'):
2756 return MyTemplateWorker_footprint(class_type)
2759 Notice that, in this example, we have not used the @code{methods}
2760 attribute of the matcher as the matcher manages only one xmethod. The
2761 user can enable/disable this xmethod by enabling/disabling the matcher
2764 @node Inferiors In Python
2765 @subsubsection Inferiors In Python
2766 @cindex inferiors in Python
2768 @findex gdb.Inferior
2769 Programs which are being run under @value{GDBN} are called inferiors
2770 (@pxref{Inferiors and Programs}). Python scripts can access
2771 information about and manipulate inferiors controlled by @value{GDBN}
2772 via objects of the @code{gdb.Inferior} class.
2774 The following inferior-related functions are available in the @code{gdb}
2777 @defun gdb.inferiors ()
2778 Return a tuple containing all inferior objects.
2781 @defun gdb.selected_inferior ()
2782 Return an object representing the current inferior.
2785 A @code{gdb.Inferior} object has the following attributes:
2787 @defvar Inferior.num
2788 ID of inferior, as assigned by GDB.
2791 @defvar Inferior.pid
2792 Process ID of the inferior, as assigned by the underlying operating
2796 @defvar Inferior.was_attached
2797 Boolean signaling whether the inferior was created using `attach', or
2798 started by @value{GDBN} itself.
2801 A @code{gdb.Inferior} object has the following methods:
2803 @defun Inferior.is_valid ()
2804 Returns @code{True} if the @code{gdb.Inferior} object is valid,
2805 @code{False} if not. A @code{gdb.Inferior} object will become invalid
2806 if the inferior no longer exists within @value{GDBN}. All other
2807 @code{gdb.Inferior} methods will throw an exception if it is invalid
2808 at the time the method is called.
2811 @defun Inferior.threads ()
2812 This method returns a tuple holding all the threads which are valid
2813 when it is called. If there are no valid threads, the method will
2814 return an empty tuple.
2817 @findex Inferior.read_memory
2818 @defun Inferior.read_memory (address, length)
2819 Read @var{length} addressable memory units from the inferior, starting at
2820 @var{address}. Returns a buffer object, which behaves much like an array
2821 or a string. It can be modified and given to the
2822 @code{Inferior.write_memory} function. In Python 3, the return
2823 value is a @code{memoryview} object.
2826 @findex Inferior.write_memory
2827 @defun Inferior.write_memory (address, buffer @r{[}, length@r{]})
2828 Write the contents of @var{buffer} to the inferior, starting at
2829 @var{address}. The @var{buffer} parameter must be a Python object
2830 which supports the buffer protocol, i.e., a string, an array or the
2831 object returned from @code{Inferior.read_memory}. If given, @var{length}
2832 determines the number of addressable memory units from @var{buffer} to be
2836 @findex gdb.search_memory
2837 @defun Inferior.search_memory (address, length, pattern)
2838 Search a region of the inferior memory starting at @var{address} with
2839 the given @var{length} using the search pattern supplied in
2840 @var{pattern}. The @var{pattern} parameter must be a Python object
2841 which supports the buffer protocol, i.e., a string, an array or the
2842 object returned from @code{gdb.read_memory}. Returns a Python @code{Long}
2843 containing the address where the pattern was found, or @code{None} if
2844 the pattern could not be found.
2847 @findex Inferior.thread_from_thread_handle
2848 @defun Inferior.thread_from_thread_handle (thread_handle)
2849 Return the thread object corresponding to @var{thread_handle}, a thread
2850 library specific data structure such as @code{pthread_t} for pthreads
2851 library implementations.
2854 @node Events In Python
2855 @subsubsection Events In Python
2856 @cindex inferior events in Python
2858 @value{GDBN} provides a general event facility so that Python code can be
2859 notified of various state changes, particularly changes that occur in
2862 An @dfn{event} is just an object that describes some state change. The
2863 type of the object and its attributes will vary depending on the details
2864 of the change. All the existing events are described below.
2866 In order to be notified of an event, you must register an event handler
2867 with an @dfn{event registry}. An event registry is an object in the
2868 @code{gdb.events} module which dispatches particular events. A registry
2869 provides methods to register and unregister event handlers:
2871 @defun EventRegistry.connect (object)
2872 Add the given callable @var{object} to the registry. This object will be
2873 called when an event corresponding to this registry occurs.
2876 @defun EventRegistry.disconnect (object)
2877 Remove the given @var{object} from the registry. Once removed, the object
2878 will no longer receive notifications of events.
2884 def exit_handler (event):
2885 print "event type: exit"
2886 print "exit code: %d" % (event.exit_code)
2888 gdb.events.exited.connect (exit_handler)
2891 In the above example we connect our handler @code{exit_handler} to the
2892 registry @code{events.exited}. Once connected, @code{exit_handler} gets
2893 called when the inferior exits. The argument @dfn{event} in this example is
2894 of type @code{gdb.ExitedEvent}. As you can see in the example the
2895 @code{ExitedEvent} object has an attribute which indicates the exit code of
2898 The following is a listing of the event registries that are available and
2899 details of the events they emit:
2904 Emits @code{gdb.ThreadEvent}.
2906 Some events can be thread specific when @value{GDBN} is running in non-stop
2907 mode. When represented in Python, these events all extend
2908 @code{gdb.ThreadEvent}. Note, this event is not emitted directly; instead,
2909 events which are emitted by this or other modules might extend this event.
2910 Examples of these events are @code{gdb.BreakpointEvent} and
2911 @code{gdb.ContinueEvent}.
2913 @defvar ThreadEvent.inferior_thread
2914 In non-stop mode this attribute will be set to the specific thread which was
2915 involved in the emitted event. Otherwise, it will be set to @code{None}.
2918 Emits @code{gdb.ContinueEvent} which extends @code{gdb.ThreadEvent}.
2920 This event indicates that the inferior has been continued after a stop. For
2921 inherited attribute refer to @code{gdb.ThreadEvent} above.
2924 Emits @code{events.ExitedEvent} which indicates that the inferior has exited.
2925 @code{events.ExitedEvent} has two attributes:
2926 @defvar ExitedEvent.exit_code
2927 An integer representing the exit code, if available, which the inferior
2928 has returned. (The exit code could be unavailable if, for example,
2929 @value{GDBN} detaches from the inferior.) If the exit code is unavailable,
2930 the attribute does not exist.
2932 @defvar ExitedEvent.inferior
2933 A reference to the inferior which triggered the @code{exited} event.
2937 Emits @code{gdb.StopEvent} which extends @code{gdb.ThreadEvent}.
2939 Indicates that the inferior has stopped. All events emitted by this registry
2940 extend StopEvent. As a child of @code{gdb.ThreadEvent}, @code{gdb.StopEvent}
2941 will indicate the stopped thread when @value{GDBN} is running in non-stop
2942 mode. Refer to @code{gdb.ThreadEvent} above for more details.
2944 Emits @code{gdb.SignalEvent} which extends @code{gdb.StopEvent}.
2946 This event indicates that the inferior or one of its threads has received as
2947 signal. @code{gdb.SignalEvent} has the following attributes:
2949 @defvar SignalEvent.stop_signal
2950 A string representing the signal received by the inferior. A list of possible
2951 signal values can be obtained by running the command @code{info signals} in
2952 the @value{GDBN} command prompt.
2955 Also emits @code{gdb.BreakpointEvent} which extends @code{gdb.StopEvent}.
2957 @code{gdb.BreakpointEvent} event indicates that one or more breakpoints have
2958 been hit, and has the following attributes:
2960 @defvar BreakpointEvent.breakpoints
2961 A sequence containing references to all the breakpoints (type
2962 @code{gdb.Breakpoint}) that were hit.
2963 @xref{Breakpoints In Python}, for details of the @code{gdb.Breakpoint} object.
2965 @defvar BreakpointEvent.breakpoint
2966 A reference to the first breakpoint that was hit.
2967 This function is maintained for backward compatibility and is now deprecated
2968 in favor of the @code{gdb.BreakpointEvent.breakpoints} attribute.
2971 @item events.new_objfile
2972 Emits @code{gdb.NewObjFileEvent} which indicates that a new object file has
2973 been loaded by @value{GDBN}. @code{gdb.NewObjFileEvent} has one attribute:
2975 @defvar NewObjFileEvent.new_objfile
2976 A reference to the object file (@code{gdb.Objfile}) which has been loaded.
2977 @xref{Objfiles In Python}, for details of the @code{gdb.Objfile} object.
2980 @item events.clear_objfiles
2981 Emits @code{gdb.ClearObjFilesEvent} which indicates that the list of object
2982 files for a program space has been reset.
2983 @code{gdb.ClearObjFilesEvent} has one attribute:
2985 @defvar ClearObjFilesEvent.progspace
2986 A reference to the program space (@code{gdb.Progspace}) whose objfile list has
2987 been cleared. @xref{Progspaces In Python}.
2990 @item events.inferior_call
2991 Emits events just before and after a function in the inferior is
2992 called by @value{GDBN}. Before an inferior call, this emits an event
2993 of type @code{gdb.InferiorCallPreEvent}, and after an inferior call,
2994 this emits an event of type @code{gdb.InferiorCallPostEvent}.
2997 @tindex gdb.InferiorCallPreEvent
2998 @item @code{gdb.InferiorCallPreEvent}
2999 Indicates that a function in the inferior is about to be called.
3001 @defvar InferiorCallPreEvent.ptid
3002 The thread in which the call will be run.
3005 @defvar InferiorCallPreEvent.address
3006 The location of the function to be called.
3009 @tindex gdb.InferiorCallPostEvent
3010 @item @code{gdb.InferiorCallPostEvent}
3011 Indicates that a function in the inferior has just been called.
3013 @defvar InferiorCallPostEvent.ptid
3014 The thread in which the call was run.
3017 @defvar InferiorCallPostEvent.address
3018 The location of the function that was called.
3022 @item events.memory_changed
3023 Emits @code{gdb.MemoryChangedEvent} which indicates that the memory of the
3024 inferior has been modified by the @value{GDBN} user, for instance via a
3025 command like @w{@code{set *addr = value}}. The event has the following
3028 @defvar MemoryChangedEvent.address
3029 The start address of the changed region.
3032 @defvar MemoryChangedEvent.length
3033 Length in bytes of the changed region.
3036 @item events.register_changed
3037 Emits @code{gdb.RegisterChangedEvent} which indicates that a register in the
3038 inferior has been modified by the @value{GDBN} user.
3040 @defvar RegisterChangedEvent.frame
3041 A gdb.Frame object representing the frame in which the register was modified.
3043 @defvar RegisterChangedEvent.regnum
3044 Denotes which register was modified.
3047 @item events.breakpoint_created
3048 This is emitted when a new breakpoint has been created. The argument
3049 that is passed is the new @code{gdb.Breakpoint} object.
3051 @item events.breakpoint_modified
3052 This is emitted when a breakpoint has been modified in some way. The
3053 argument that is passed is the new @code{gdb.Breakpoint} object.
3055 @item events.breakpoint_deleted
3056 This is emitted when a breakpoint has been deleted. The argument that
3057 is passed is the @code{gdb.Breakpoint} object. When this event is
3058 emitted, the @code{gdb.Breakpoint} object will already be in its
3059 invalid state; that is, the @code{is_valid} method will return
3062 @item events.before_prompt
3063 This event carries no payload. It is emitted each time @value{GDBN}
3064 presents a prompt to the user.
3066 @item events.new_inferior
3067 This is emitted when a new inferior is created. Note that the
3068 inferior is not necessarily running; in fact, it may not even have an
3069 associated executable.
3071 The event is of type @code{gdb.NewInferiorEvent}. This has a single
3074 @defvar NewInferiorEvent.inferior
3075 The new inferior, a @code{gdb.Inferior} object.
3078 @item events.inferior_deleted
3079 This is emitted when an inferior has been deleted. Note that this is
3080 not the same as process exit; it is notified when the inferior itself
3081 is removed, say via @code{remove-inferiors}.
3083 The event is of type @code{gdb.InferiorDeletedEvent}. This has a single
3086 @defvar NewInferiorEvent.inferior
3087 The inferior that is being removed, a @code{gdb.Inferior} object.
3090 @item events.new_thread
3091 This is emitted when @value{GDBN} notices a new thread. The event is of
3092 type @code{gdb.NewThreadEvent}, which extends @code{gdb.ThreadEvent}.
3093 This has a single attribute:
3095 @defvar NewThreadEvent.inferior_thread
3101 @node Threads In Python
3102 @subsubsection Threads In Python
3103 @cindex threads in python
3105 @findex gdb.InferiorThread
3106 Python scripts can access information about, and manipulate inferior threads
3107 controlled by @value{GDBN}, via objects of the @code{gdb.InferiorThread} class.
3109 The following thread-related functions are available in the @code{gdb}
3112 @findex gdb.selected_thread
3113 @defun gdb.selected_thread ()
3114 This function returns the thread object for the selected thread. If there
3115 is no selected thread, this will return @code{None}.
3118 A @code{gdb.InferiorThread} object has the following attributes:
3120 @defvar InferiorThread.name
3121 The name of the thread. If the user specified a name using
3122 @code{thread name}, then this returns that name. Otherwise, if an
3123 OS-supplied name is available, then it is returned. Otherwise, this
3124 returns @code{None}.
3126 This attribute can be assigned to. The new value must be a string
3127 object, which sets the new name, or @code{None}, which removes any
3128 user-specified thread name.
3131 @defvar InferiorThread.num
3132 The per-inferior number of the thread, as assigned by GDB.
3135 @defvar InferiorThread.global_num
3136 The global ID of the thread, as assigned by GDB. You can use this to
3137 make Python breakpoints thread-specific, for example
3138 (@pxref{python_breakpoint_thread,,The Breakpoint.thread attribute}).
3141 @defvar InferiorThread.ptid
3142 ID of the thread, as assigned by the operating system. This attribute is a
3143 tuple containing three integers. The first is the Process ID (PID); the second
3144 is the Lightweight Process ID (LWPID), and the third is the Thread ID (TID).
3145 Either the LWPID or TID may be 0, which indicates that the operating system
3146 does not use that identifier.
3149 @defvar InferiorThread.inferior
3150 The inferior this thread belongs to. This attribute is represented as
3151 a @code{gdb.Inferior} object. This attribute is not writable.
3154 A @code{gdb.InferiorThread} object has the following methods:
3156 @defun InferiorThread.is_valid ()
3157 Returns @code{True} if the @code{gdb.InferiorThread} object is valid,
3158 @code{False} if not. A @code{gdb.InferiorThread} object will become
3159 invalid if the thread exits, or the inferior that the thread belongs
3160 is deleted. All other @code{gdb.InferiorThread} methods will throw an
3161 exception if it is invalid at the time the method is called.
3164 @defun InferiorThread.switch ()
3165 This changes @value{GDBN}'s currently selected thread to the one represented
3169 @defun InferiorThread.is_stopped ()
3170 Return a Boolean indicating whether the thread is stopped.
3173 @defun InferiorThread.is_running ()
3174 Return a Boolean indicating whether the thread is running.
3177 @defun InferiorThread.is_exited ()
3178 Return a Boolean indicating whether the thread is exited.
3181 @node Recordings In Python
3182 @subsubsection Recordings In Python
3183 @cindex recordings in python
3185 The following recordings-related functions
3186 (@pxref{Process Record and Replay}) are available in the @code{gdb}
3189 @defun gdb.start_recording (@r{[}method@r{]}, @r{[}format@r{]})
3190 Start a recording using the given @var{method} and @var{format}. If
3191 no @var{format} is given, the default format for the recording method
3192 is used. If no @var{method} is given, the default method will be used.
3193 Returns a @code{gdb.Record} object on success. Throw an exception on
3196 The following strings can be passed as @var{method}:
3202 @code{"btrace"}: Possible values for @var{format}: @code{"pt"},
3203 @code{"bts"} or leave out for default format.
3207 @defun gdb.current_recording ()
3208 Access a currently running recording. Return a @code{gdb.Record}
3209 object on success. Return @code{None} if no recording is currently
3213 @defun gdb.stop_recording ()
3214 Stop the current recording. Throw an exception if no recording is
3215 currently active. All record objects become invalid after this call.
3218 A @code{gdb.Record} object has the following attributes:
3220 @defvar Record.method
3221 A string with the current recording method, e.g.@: @code{full} or
3225 @defvar Record.format
3226 A string with the current recording format, e.g.@: @code{bt}, @code{pts} or
3230 @defvar Record.begin
3231 A method specific instruction object representing the first instruction
3236 A method specific instruction object representing the current
3237 instruction, that is not actually part of the recording.
3240 @defvar Record.replay_position
3241 The instruction representing the current replay position. If there is
3242 no replay active, this will be @code{None}.
3245 @defvar Record.instruction_history
3246 A list with all recorded instructions.
3249 @defvar Record.function_call_history
3250 A list with all recorded function call segments.
3253 A @code{gdb.Record} object has the following methods:
3255 @defun Record.goto (instruction)
3256 Move the replay position to the given @var{instruction}.
3259 The common @code{gdb.Instruction} class that recording method specific
3260 instruction objects inherit from, has the following attributes:
3262 @defvar Instruction.pc
3263 An integer representing this instruction's address.
3266 @defvar Instruction.data
3267 A buffer with the raw instruction data. In Python 3, the return value is a
3268 @code{memoryview} object.
3271 @defvar Instruction.decoded
3272 A human readable string with the disassembled instruction.
3275 @defvar Instruction.size
3276 The size of the instruction in bytes.
3279 Additionally @code{gdb.RecordInstruction} has the following attributes:
3281 @defvar RecordInstruction.number
3282 An integer identifying this instruction. @code{number} corresponds to
3283 the numbers seen in @code{record instruction-history}
3284 (@pxref{Process Record and Replay}).
3287 @defvar RecordInstruction.sal
3288 A @code{gdb.Symtab_and_line} object representing the associated symtab
3289 and line of this instruction. May be @code{None} if no debug information is
3293 @defvar RecordInstruction.is_speculative
3294 A boolean indicating whether the instruction was executed speculatively.
3297 If an error occured during recording or decoding a recording, this error is
3298 represented by a @code{gdb.RecordGap} object in the instruction list. It has
3299 the following attributes:
3301 @defvar RecordGap.number
3302 An integer identifying this gap. @code{number} corresponds to the numbers seen
3303 in @code{record instruction-history} (@pxref{Process Record and Replay}).
3306 @defvar RecordGap.error_code
3307 A numerical representation of the reason for the gap. The value is specific to
3308 the current recording method.
3311 @defvar RecordGap.error_string
3312 A human readable string with the reason for the gap.
3315 A @code{gdb.RecordFunctionSegment} object has the following attributes:
3317 @defvar RecordFunctionSegment.number
3318 An integer identifying this function segment. @code{number} corresponds to
3319 the numbers seen in @code{record function-call-history}
3320 (@pxref{Process Record and Replay}).
3323 @defvar RecordFunctionSegment.symbol
3324 A @code{gdb.Symbol} object representing the associated symbol. May be
3325 @code{None} if no debug information is available.
3328 @defvar RecordFunctionSegment.level
3329 An integer representing the function call's stack level. May be
3330 @code{None} if the function call is a gap.
3333 @defvar RecordFunctionSegment.instructions
3334 A list of @code{gdb.RecordInstruction} or @code{gdb.RecordGap} objects
3335 associated with this function call.
3338 @defvar RecordFunctionSegment.up
3339 A @code{gdb.RecordFunctionSegment} object representing the caller's
3340 function segment. If the call has not been recorded, this will be the
3341 function segment to which control returns. If neither the call nor the
3342 return have been recorded, this will be @code{None}.
3345 @defvar RecordFunctionSegment.prev
3346 A @code{gdb.RecordFunctionSegment} object representing the previous
3347 segment of this function call. May be @code{None}.
3350 @defvar RecordFunctionSegment.next
3351 A @code{gdb.RecordFunctionSegment} object representing the next segment of
3352 this function call. May be @code{None}.
3355 The following example demonstrates the usage of these objects and
3356 functions to create a function that will rewind a record to the last
3357 time a function in a different file was executed. This would typically
3358 be used to track the execution of user provided callback functions in a
3359 library which typically are not visible in a back trace.
3363 rec = gdb.current_recording ()
3367 insn = rec.instruction_history
3372 position = insn.index (rec.replay_position)
3376 filename = insn[position].sal.symtab.fullname ()
3380 for i in reversed (insn[:position]):
3382 current = i.sal.symtab.fullname ()
3386 if filename == current:
3393 Another possible application is to write a function that counts the
3394 number of code executions in a given line range. This line range can
3395 contain parts of functions or span across several functions and is not
3396 limited to be contiguous.
3399 def countrange (filename, linerange):
3402 def filter_only (file_name):
3403 for call in gdb.current_recording ().function_call_history:
3405 if file_name in call.symbol.symtab.fullname ():
3410 for c in filter_only (filename):
3411 for i in c.instructions:
3413 if i.sal.line in linerange:
3422 @node Commands In Python
3423 @subsubsection Commands In Python
3425 @cindex commands in python
3426 @cindex python commands
3427 You can implement new @value{GDBN} CLI commands in Python. A CLI
3428 command is implemented using an instance of the @code{gdb.Command}
3429 class, most commonly using a subclass.
3431 @defun Command.__init__ (name, @var{command_class} @r{[}, @var{completer_class} @r{[}, @var{prefix}@r{]]})
3432 The object initializer for @code{Command} registers the new command
3433 with @value{GDBN}. This initializer is normally invoked from the
3434 subclass' own @code{__init__} method.
3436 @var{name} is the name of the command. If @var{name} consists of
3437 multiple words, then the initial words are looked for as prefix
3438 commands. In this case, if one of the prefix commands does not exist,
3439 an exception is raised.
3441 There is no support for multi-line commands.
3443 @var{command_class} should be one of the @samp{COMMAND_} constants
3444 defined below. This argument tells @value{GDBN} how to categorize the
3445 new command in the help system.
3447 @var{completer_class} is an optional argument. If given, it should be
3448 one of the @samp{COMPLETE_} constants defined below. This argument
3449 tells @value{GDBN} how to perform completion for this command. If not
3450 given, @value{GDBN} will attempt to complete using the object's
3451 @code{complete} method (see below); if no such method is found, an
3452 error will occur when completion is attempted.
3454 @var{prefix} is an optional argument. If @code{True}, then the new
3455 command is a prefix command; sub-commands of this command may be
3458 The help text for the new command is taken from the Python
3459 documentation string for the command's class, if there is one. If no
3460 documentation string is provided, the default value ``This command is
3461 not documented.'' is used.
3464 @cindex don't repeat Python command
3465 @defun Command.dont_repeat ()
3466 By default, a @value{GDBN} command is repeated when the user enters a
3467 blank line at the command prompt. A command can suppress this
3468 behavior by invoking the @code{dont_repeat} method. This is similar
3469 to the user command @code{dont-repeat}, see @ref{Define, dont-repeat}.
3472 @defun Command.invoke (argument, from_tty)
3473 This method is called by @value{GDBN} when this command is invoked.
3475 @var{argument} is a string. It is the argument to the command, after
3476 leading and trailing whitespace has been stripped.
3478 @var{from_tty} is a boolean argument. When true, this means that the
3479 command was entered by the user at the terminal; when false it means
3480 that the command came from elsewhere.
3482 If this method throws an exception, it is turned into a @value{GDBN}
3483 @code{error} call. Otherwise, the return value is ignored.
3485 @findex gdb.string_to_argv
3486 To break @var{argument} up into an argv-like string use
3487 @code{gdb.string_to_argv}. This function behaves identically to
3488 @value{GDBN}'s internal argument lexer @code{buildargv}.
3489 It is recommended to use this for consistency.
3490 Arguments are separated by spaces and may be quoted.
3494 print gdb.string_to_argv ("1 2\ \\\"3 '4 \"5' \"6 '7\"")
3495 ['1', '2 "3', '4 "5', "6 '7"]
3500 @cindex completion of Python commands
3501 @defun Command.complete (text, word)
3502 This method is called by @value{GDBN} when the user attempts
3503 completion on this command. All forms of completion are handled by
3504 this method, that is, the @key{TAB} and @key{M-?} key bindings
3505 (@pxref{Completion}), and the @code{complete} command (@pxref{Help,
3508 The arguments @var{text} and @var{word} are both strings; @var{text}
3509 holds the complete command line up to the cursor's location, while
3510 @var{word} holds the last word of the command line; this is computed
3511 using a word-breaking heuristic.
3513 The @code{complete} method can return several values:
3516 If the return value is a sequence, the contents of the sequence are
3517 used as the completions. It is up to @code{complete} to ensure that the
3518 contents actually do complete the word. A zero-length sequence is
3519 allowed, it means that there were no completions available. Only
3520 string elements of the sequence are used; other elements in the
3521 sequence are ignored.
3524 If the return value is one of the @samp{COMPLETE_} constants defined
3525 below, then the corresponding @value{GDBN}-internal completion
3526 function is invoked, and its result is used.
3529 All other results are treated as though there were no available
3534 When a new command is registered, it must be declared as a member of
3535 some general class of commands. This is used to classify top-level
3536 commands in the on-line help system; note that prefix commands are not
3537 listed under their own category but rather that of their top-level
3538 command. The available classifications are represented by constants
3539 defined in the @code{gdb} module:
3542 @findex COMMAND_NONE
3543 @findex gdb.COMMAND_NONE
3544 @item gdb.COMMAND_NONE
3545 The command does not belong to any particular class. A command in
3546 this category will not be displayed in any of the help categories.
3548 @findex COMMAND_RUNNING
3549 @findex gdb.COMMAND_RUNNING
3550 @item gdb.COMMAND_RUNNING
3551 The command is related to running the inferior. For example,
3552 @code{start}, @code{step}, and @code{continue} are in this category.
3553 Type @kbd{help running} at the @value{GDBN} prompt to see a list of
3554 commands in this category.
3556 @findex COMMAND_DATA
3557 @findex gdb.COMMAND_DATA
3558 @item gdb.COMMAND_DATA
3559 The command is related to data or variables. For example,
3560 @code{call}, @code{find}, and @code{print} are in this category. Type
3561 @kbd{help data} at the @value{GDBN} prompt to see a list of commands
3564 @findex COMMAND_STACK
3565 @findex gdb.COMMAND_STACK
3566 @item gdb.COMMAND_STACK
3567 The command has to do with manipulation of the stack. For example,
3568 @code{backtrace}, @code{frame}, and @code{return} are in this
3569 category. Type @kbd{help stack} at the @value{GDBN} prompt to see a
3570 list of commands in this category.
3572 @findex COMMAND_FILES
3573 @findex gdb.COMMAND_FILES
3574 @item gdb.COMMAND_FILES
3575 This class is used for file-related commands. For example,
3576 @code{file}, @code{list} and @code{section} are in this category.
3577 Type @kbd{help files} at the @value{GDBN} prompt to see a list of
3578 commands in this category.
3580 @findex COMMAND_SUPPORT
3581 @findex gdb.COMMAND_SUPPORT
3582 @item gdb.COMMAND_SUPPORT
3583 This should be used for ``support facilities'', generally meaning
3584 things that are useful to the user when interacting with @value{GDBN},
3585 but not related to the state of the inferior. For example,
3586 @code{help}, @code{make}, and @code{shell} are in this category. Type
3587 @kbd{help support} at the @value{GDBN} prompt to see a list of
3588 commands in this category.
3590 @findex COMMAND_STATUS
3591 @findex gdb.COMMAND_STATUS
3592 @item gdb.COMMAND_STATUS
3593 The command is an @samp{info}-related command, that is, related to the
3594 state of @value{GDBN} itself. For example, @code{info}, @code{macro},
3595 and @code{show} are in this category. Type @kbd{help status} at the
3596 @value{GDBN} prompt to see a list of commands in this category.
3598 @findex COMMAND_BREAKPOINTS
3599 @findex gdb.COMMAND_BREAKPOINTS
3600 @item gdb.COMMAND_BREAKPOINTS
3601 The command has to do with breakpoints. For example, @code{break},
3602 @code{clear}, and @code{delete} are in this category. Type @kbd{help
3603 breakpoints} at the @value{GDBN} prompt to see a list of commands in
3606 @findex COMMAND_TRACEPOINTS
3607 @findex gdb.COMMAND_TRACEPOINTS
3608 @item gdb.COMMAND_TRACEPOINTS
3609 The command has to do with tracepoints. For example, @code{trace},
3610 @code{actions}, and @code{tfind} are in this category. Type
3611 @kbd{help tracepoints} at the @value{GDBN} prompt to see a list of
3612 commands in this category.
3614 @findex COMMAND_USER
3615 @findex gdb.COMMAND_USER
3616 @item gdb.COMMAND_USER
3617 The command is a general purpose command for the user, and typically
3618 does not fit in one of the other categories.
3619 Type @kbd{help user-defined} at the @value{GDBN} prompt to see
3620 a list of commands in this category, as well as the list of gdb macros
3621 (@pxref{Sequences}).
3623 @findex COMMAND_OBSCURE
3624 @findex gdb.COMMAND_OBSCURE
3625 @item gdb.COMMAND_OBSCURE
3626 The command is only used in unusual circumstances, or is not of
3627 general interest to users. For example, @code{checkpoint},
3628 @code{fork}, and @code{stop} are in this category. Type @kbd{help
3629 obscure} at the @value{GDBN} prompt to see a list of commands in this
3632 @findex COMMAND_MAINTENANCE
3633 @findex gdb.COMMAND_MAINTENANCE
3634 @item gdb.COMMAND_MAINTENANCE
3635 The command is only useful to @value{GDBN} maintainers. The
3636 @code{maintenance} and @code{flushregs} commands are in this category.
3637 Type @kbd{help internals} at the @value{GDBN} prompt to see a list of
3638 commands in this category.
3641 A new command can use a predefined completion function, either by
3642 specifying it via an argument at initialization, or by returning it
3643 from the @code{complete} method. These predefined completion
3644 constants are all defined in the @code{gdb} module:
3647 @vindex COMPLETE_NONE
3648 @item gdb.COMPLETE_NONE
3649 This constant means that no completion should be done.
3651 @vindex COMPLETE_FILENAME
3652 @item gdb.COMPLETE_FILENAME
3653 This constant means that filename completion should be performed.
3655 @vindex COMPLETE_LOCATION
3656 @item gdb.COMPLETE_LOCATION
3657 This constant means that location completion should be done.
3658 @xref{Specify Location}.
3660 @vindex COMPLETE_COMMAND
3661 @item gdb.COMPLETE_COMMAND
3662 This constant means that completion should examine @value{GDBN}
3665 @vindex COMPLETE_SYMBOL
3666 @item gdb.COMPLETE_SYMBOL
3667 This constant means that completion should be done using symbol names
3670 @vindex COMPLETE_EXPRESSION
3671 @item gdb.COMPLETE_EXPRESSION
3672 This constant means that completion should be done on expressions.
3673 Often this means completing on symbol names, but some language
3674 parsers also have support for completing on field names.
3677 The following code snippet shows how a trivial CLI command can be
3678 implemented in Python:
3681 class HelloWorld (gdb.Command):
3682 """Greet the whole world."""
3684 def __init__ (self):
3685 super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)
3687 def invoke (self, arg, from_tty):
3688 print "Hello, World!"
3693 The last line instantiates the class, and is necessary to trigger the
3694 registration of the command with @value{GDBN}. Depending on how the
3695 Python code is read into @value{GDBN}, you may need to import the
3696 @code{gdb} module explicitly.
3698 @node Parameters In Python
3699 @subsubsection Parameters In Python
3701 @cindex parameters in python
3702 @cindex python parameters
3703 @tindex gdb.Parameter
3705 You can implement new @value{GDBN} parameters using Python. A new
3706 parameter is implemented as an instance of the @code{gdb.Parameter}
3709 Parameters are exposed to the user via the @code{set} and
3710 @code{show} commands. @xref{Help}.
3712 There are many parameters that already exist and can be set in
3713 @value{GDBN}. Two examples are: @code{set follow fork} and
3714 @code{set charset}. Setting these parameters influences certain
3715 behavior in @value{GDBN}. Similarly, you can define parameters that
3716 can be used to influence behavior in custom Python scripts and commands.
3718 @defun Parameter.__init__ (name, @var{command-class}, @var{parameter-class} @r{[}, @var{enum-sequence}@r{]})
3719 The object initializer for @code{Parameter} registers the new
3720 parameter with @value{GDBN}. This initializer is normally invoked
3721 from the subclass' own @code{__init__} method.
3723 @var{name} is the name of the new parameter. If @var{name} consists
3724 of multiple words, then the initial words are looked for as prefix
3725 parameters. An example of this can be illustrated with the
3726 @code{set print} set of parameters. If @var{name} is
3727 @code{print foo}, then @code{print} will be searched as the prefix
3728 parameter. In this case the parameter can subsequently be accessed in
3729 @value{GDBN} as @code{set print foo}.
3731 If @var{name} consists of multiple words, and no prefix parameter group
3732 can be found, an exception is raised.
3734 @var{command-class} should be one of the @samp{COMMAND_} constants
3735 (@pxref{Commands In Python}). This argument tells @value{GDBN} how to
3736 categorize the new parameter in the help system.
3738 @var{parameter-class} should be one of the @samp{PARAM_} constants
3739 defined below. This argument tells @value{GDBN} the type of the new
3740 parameter; this information is used for input validation and
3743 If @var{parameter-class} is @code{PARAM_ENUM}, then
3744 @var{enum-sequence} must be a sequence of strings. These strings
3745 represent the possible values for the parameter.
3747 If @var{parameter-class} is not @code{PARAM_ENUM}, then the presence
3748 of a fourth argument will cause an exception to be thrown.
3750 The help text for the new parameter is taken from the Python
3751 documentation string for the parameter's class, if there is one. If
3752 there is no documentation string, a default value is used.
3755 @defvar Parameter.set_doc
3756 If this attribute exists, and is a string, then its value is used as
3757 the help text for this parameter's @code{set} command. The value is
3758 examined when @code{Parameter.__init__} is invoked; subsequent changes
3762 @defvar Parameter.show_doc
3763 If this attribute exists, and is a string, then its value is used as
3764 the help text for this parameter's @code{show} command. The value is
3765 examined when @code{Parameter.__init__} is invoked; subsequent changes
3769 @defvar Parameter.value
3770 The @code{value} attribute holds the underlying value of the
3771 parameter. It can be read and assigned to just as any other
3772 attribute. @value{GDBN} does validation when assignments are made.
3775 There are two methods that may be implemented in any @code{Parameter}
3778 @defun Parameter.get_set_string (self)
3779 If this method exists, @value{GDBN} will call it when a
3780 @var{parameter}'s value has been changed via the @code{set} API (for
3781 example, @kbd{set foo off}). The @code{value} attribute has already
3782 been populated with the new value and may be used in output. This
3783 method must return a string. If the returned string is not empty,
3784 @value{GDBN} will present it to the user.
3787 @defun Parameter.get_show_string (self, svalue)
3788 @value{GDBN} will call this method when a @var{parameter}'s
3789 @code{show} API has been invoked (for example, @kbd{show foo}). The
3790 argument @code{svalue} receives the string representation of the
3791 current value. This method must return a string.
3794 When a new parameter is defined, its type must be specified. The
3795 available types are represented by constants defined in the @code{gdb}
3799 @findex PARAM_BOOLEAN
3800 @findex gdb.PARAM_BOOLEAN
3801 @item gdb.PARAM_BOOLEAN
3802 The value is a plain boolean. The Python boolean values, @code{True}
3803 and @code{False} are the only valid values.
3805 @findex PARAM_AUTO_BOOLEAN
3806 @findex gdb.PARAM_AUTO_BOOLEAN
3807 @item gdb.PARAM_AUTO_BOOLEAN
3808 The value has three possible states: true, false, and @samp{auto}. In
3809 Python, true and false are represented using boolean constants, and
3810 @samp{auto} is represented using @code{None}.
3812 @findex PARAM_UINTEGER
3813 @findex gdb.PARAM_UINTEGER
3814 @item gdb.PARAM_UINTEGER
3815 The value is an unsigned integer. The value of 0 should be
3816 interpreted to mean ``unlimited''.
3818 @findex PARAM_INTEGER
3819 @findex gdb.PARAM_INTEGER
3820 @item gdb.PARAM_INTEGER
3821 The value is a signed integer. The value of 0 should be interpreted
3822 to mean ``unlimited''.
3824 @findex PARAM_STRING
3825 @findex gdb.PARAM_STRING
3826 @item gdb.PARAM_STRING
3827 The value is a string. When the user modifies the string, any escape
3828 sequences, such as @samp{\t}, @samp{\f}, and octal escapes, are
3829 translated into corresponding characters and encoded into the current
3832 @findex PARAM_STRING_NOESCAPE
3833 @findex gdb.PARAM_STRING_NOESCAPE
3834 @item gdb.PARAM_STRING_NOESCAPE
3835 The value is a string. When the user modifies the string, escapes are
3836 passed through untranslated.
3838 @findex PARAM_OPTIONAL_FILENAME
3839 @findex gdb.PARAM_OPTIONAL_FILENAME
3840 @item gdb.PARAM_OPTIONAL_FILENAME
3841 The value is a either a filename (a string), or @code{None}.
3843 @findex PARAM_FILENAME
3844 @findex gdb.PARAM_FILENAME
3845 @item gdb.PARAM_FILENAME
3846 The value is a filename. This is just like
3847 @code{PARAM_STRING_NOESCAPE}, but uses file names for completion.
3849 @findex PARAM_ZINTEGER
3850 @findex gdb.PARAM_ZINTEGER
3851 @item gdb.PARAM_ZINTEGER
3852 The value is an integer. This is like @code{PARAM_INTEGER}, except 0
3853 is interpreted as itself.
3855 @findex PARAM_ZUINTEGER
3856 @findex gdb.PARAM_ZUINTEGER
3857 @item gdb.PARAM_ZUINTEGER
3858 The value is an unsigned integer. This is like @code{PARAM_INTEGER},
3859 except 0 is interpreted as itself, and the value cannot be negative.
3861 @findex PARAM_ZUINTEGER_UNLIMITED
3862 @findex gdb.PARAM_ZUINTEGER_UNLIMITED
3863 @item gdb.PARAM_ZUINTEGER_UNLIMITED
3864 The value is a signed integer. This is like @code{PARAM_ZUINTEGER},
3865 except the special value -1 should be interpreted to mean
3866 ``unlimited''. Other negative values are not allowed.
3869 @findex gdb.PARAM_ENUM
3870 @item gdb.PARAM_ENUM
3871 The value is a string, which must be one of a collection string
3872 constants provided when the parameter is created.
3875 @node Functions In Python
3876 @subsubsection Writing new convenience functions
3878 @cindex writing convenience functions
3879 @cindex convenience functions in python
3880 @cindex python convenience functions
3881 @tindex gdb.Function
3883 You can implement new convenience functions (@pxref{Convenience Vars})
3884 in Python. A convenience function is an instance of a subclass of the
3885 class @code{gdb.Function}.
3887 @defun Function.__init__ (name)
3888 The initializer for @code{Function} registers the new function with
3889 @value{GDBN}. The argument @var{name} is the name of the function,
3890 a string. The function will be visible to the user as a convenience
3891 variable of type @code{internal function}, whose name is the same as
3892 the given @var{name}.
3894 The documentation for the new function is taken from the documentation
3895 string for the new class.
3898 @defun Function.invoke (@var{*args})
3899 When a convenience function is evaluated, its arguments are converted
3900 to instances of @code{gdb.Value}, and then the function's
3901 @code{invoke} method is called. Note that @value{GDBN} does not
3902 predetermine the arity of convenience functions. Instead, all
3903 available arguments are passed to @code{invoke}, following the
3904 standard Python calling convention. In particular, a convenience
3905 function can have default values for parameters without ill effect.
3907 The return value of this method is used as its value in the enclosing
3908 expression. If an ordinary Python value is returned, it is converted
3909 to a @code{gdb.Value} following the usual rules.
3912 The following code snippet shows how a trivial convenience function can
3913 be implemented in Python:
3916 class Greet (gdb.Function):
3917 """Return string to greet someone.
3918 Takes a name as argument."""
3920 def __init__ (self):
3921 super (Greet, self).__init__ ("greet")
3923 def invoke (self, name):
3924 return "Hello, %s!" % name.string ()
3929 The last line instantiates the class, and is necessary to trigger the
3930 registration of the function with @value{GDBN}. Depending on how the
3931 Python code is read into @value{GDBN}, you may need to import the
3932 @code{gdb} module explicitly.
3934 Now you can use the function in an expression:
3937 (gdb) print $greet("Bob")
3941 @node Progspaces In Python
3942 @subsubsection Program Spaces In Python
3944 @cindex progspaces in python
3945 @tindex gdb.Progspace
3947 A program space, or @dfn{progspace}, represents a symbolic view
3948 of an address space.
3949 It consists of all of the objfiles of the program.
3950 @xref{Objfiles In Python}.
3951 @xref{Inferiors and Programs, program spaces}, for more details
3952 about program spaces.
3954 The following progspace-related functions are available in the
3957 @findex gdb.current_progspace
3958 @defun gdb.current_progspace ()
3959 This function returns the program space of the currently selected inferior.
3960 @xref{Inferiors and Programs}.
3963 @findex gdb.progspaces
3964 @defun gdb.progspaces ()
3965 Return a sequence of all the progspaces currently known to @value{GDBN}.
3968 Each progspace is represented by an instance of the @code{gdb.Progspace}
3971 @defvar Progspace.filename
3972 The file name of the progspace as a string.
3975 @defvar Progspace.pretty_printers
3976 The @code{pretty_printers} attribute is a list of functions. It is
3977 used to look up pretty-printers. A @code{Value} is passed to each
3978 function in order; if the function returns @code{None}, then the
3979 search continues. Otherwise, the return value should be an object
3980 which is used to format the value. @xref{Pretty Printing API}, for more
3984 @defvar Progspace.type_printers
3985 The @code{type_printers} attribute is a list of type printer objects.
3986 @xref{Type Printing API}, for more information.
3989 @defvar Progspace.frame_filters
3990 The @code{frame_filters} attribute is a dictionary of frame filter
3991 objects. @xref{Frame Filter API}, for more information.
3994 One may add arbitrary attributes to @code{gdb.Progspace} objects
3995 in the usual Python way.
3996 This is useful if, for example, one needs to do some extra record keeping
3997 associated with the program space.
3999 In this contrived example, we want to perform some processing when
4000 an objfile with a certain symbol is loaded, but we only want to do
4001 this once because it is expensive. To achieve this we record the results
4002 with the program space because we can't predict when the desired objfile
4007 def clear_objfiles_handler(event):
4008 event.progspace.expensive_computation = None
4009 def expensive(symbol):
4010 """A mock routine to perform an "expensive" computation on symbol."""
4011 print "Computing the answer to the ultimate question ..."
4013 def new_objfile_handler(event):
4014 objfile = event.new_objfile
4015 progspace = objfile.progspace
4016 if not hasattr(progspace, 'expensive_computation') or \
4017 progspace.expensive_computation is None:
4018 # We use 'main' for the symbol to keep the example simple.
4019 # Note: There's no current way to constrain the lookup
4021 symbol = gdb.lookup_global_symbol('main')
4022 if symbol is not None:
4023 progspace.expensive_computation = expensive(symbol)
4024 gdb.events.clear_objfiles.connect(clear_objfiles_handler)
4025 gdb.events.new_objfile.connect(new_objfile_handler)
4027 (gdb) file /tmp/hello
4028 Reading symbols from /tmp/hello...done.
4029 Computing the answer to the ultimate question ...
4030 (gdb) python print gdb.current_progspace().expensive_computation
4033 Starting program: /tmp/hello
4035 [Inferior 1 (process 4242) exited normally]
4038 @node Objfiles In Python
4039 @subsubsection Objfiles In Python
4041 @cindex objfiles in python
4044 @value{GDBN} loads symbols for an inferior from various
4045 symbol-containing files (@pxref{Files}). These include the primary
4046 executable file, any shared libraries used by the inferior, and any
4047 separate debug info files (@pxref{Separate Debug Files}).
4048 @value{GDBN} calls these symbol-containing files @dfn{objfiles}.
4050 The following objfile-related functions are available in the
4053 @findex gdb.current_objfile
4054 @defun gdb.current_objfile ()
4055 When auto-loading a Python script (@pxref{Python Auto-loading}), @value{GDBN}
4056 sets the ``current objfile'' to the corresponding objfile. This
4057 function returns the current objfile. If there is no current objfile,
4058 this function returns @code{None}.
4061 @findex gdb.objfiles
4062 @defun gdb.objfiles ()
4063 Return a sequence of all the objfiles current known to @value{GDBN}.
4064 @xref{Objfiles In Python}.
4067 @findex gdb.lookup_objfile
4068 @defun gdb.lookup_objfile (name @r{[}, by_build_id{]})
4069 Look up @var{name}, a file name or build ID, in the list of objfiles
4070 for the current program space (@pxref{Progspaces In Python}).
4071 If the objfile is not found throw the Python @code{ValueError} exception.
4073 If @var{name} is a relative file name, then it will match any
4074 source file name with the same trailing components. For example, if
4075 @var{name} is @samp{gcc/expr.c}, then it will match source file
4076 name of @file{/build/trunk/gcc/expr.c}, but not
4077 @file{/build/trunk/libcpp/expr.c} or @file{/build/trunk/gcc/x-expr.c}.
4079 If @var{by_build_id} is provided and is @code{True} then @var{name}
4080 is the build ID of the objfile. Otherwise, @var{name} is a file name.
4081 This is supported only on some operating systems, notably those which use
4082 the ELF format for binary files and the @sc{gnu} Binutils. For more details
4083 about this feature, see the description of the @option{--build-id}
4084 command-line option in @ref{Options, , Command Line Options, ld,
4088 Each objfile is represented by an instance of the @code{gdb.Objfile}
4091 @defvar Objfile.filename
4092 The file name of the objfile as a string, with symbolic links resolved.
4094 The value is @code{None} if the objfile is no longer valid.
4095 See the @code{gdb.Objfile.is_valid} method, described below.
4098 @defvar Objfile.username
4099 The file name of the objfile as specified by the user as a string.
4101 The value is @code{None} if the objfile is no longer valid.
4102 See the @code{gdb.Objfile.is_valid} method, described below.
4105 @defvar Objfile.owner
4106 For separate debug info objfiles this is the corresponding @code{gdb.Objfile}
4107 object that debug info is being provided for.
4108 Otherwise this is @code{None}.
4109 Separate debug info objfiles are added with the
4110 @code{gdb.Objfile.add_separate_debug_file} method, described below.
4113 @defvar Objfile.build_id
4114 The build ID of the objfile as a string.
4115 If the objfile does not have a build ID then the value is @code{None}.
4117 This is supported only on some operating systems, notably those which use
4118 the ELF format for binary files and the @sc{gnu} Binutils. For more details
4119 about this feature, see the description of the @option{--build-id}
4120 command-line option in @ref{Options, , Command Line Options, ld,
4124 @defvar Objfile.progspace
4125 The containing program space of the objfile as a @code{gdb.Progspace}
4126 object. @xref{Progspaces In Python}.
4129 @defvar Objfile.pretty_printers
4130 The @code{pretty_printers} attribute is a list of functions. It is
4131 used to look up pretty-printers. A @code{Value} is passed to each
4132 function in order; if the function returns @code{None}, then the
4133 search continues. Otherwise, the return value should be an object
4134 which is used to format the value. @xref{Pretty Printing API}, for more
4138 @defvar Objfile.type_printers
4139 The @code{type_printers} attribute is a list of type printer objects.
4140 @xref{Type Printing API}, for more information.
4143 @defvar Objfile.frame_filters
4144 The @code{frame_filters} attribute is a dictionary of frame filter
4145 objects. @xref{Frame Filter API}, for more information.
4148 One may add arbitrary attributes to @code{gdb.Objfile} objects
4149 in the usual Python way.
4150 This is useful if, for example, one needs to do some extra record keeping
4151 associated with the objfile.
4153 In this contrived example we record the time when @value{GDBN}
4159 def new_objfile_handler(event):
4160 # Set the time_loaded attribute of the new objfile.
4161 event.new_objfile.time_loaded = datetime.datetime.today()
4162 gdb.events.new_objfile.connect(new_objfile_handler)
4165 Reading symbols from ./hello...done.
4166 (gdb) python print gdb.objfiles()[0].time_loaded
4167 2014-10-09 11:41:36.770345
4170 A @code{gdb.Objfile} object has the following methods:
4172 @defun Objfile.is_valid ()
4173 Returns @code{True} if the @code{gdb.Objfile} object is valid,
4174 @code{False} if not. A @code{gdb.Objfile} object can become invalid
4175 if the object file it refers to is not loaded in @value{GDBN} any
4176 longer. All other @code{gdb.Objfile} methods will throw an exception
4177 if it is invalid at the time the method is called.
4180 @defun Objfile.add_separate_debug_file (file)
4181 Add @var{file} to the list of files that @value{GDBN} will search for
4182 debug information for the objfile.
4183 This is useful when the debug info has been removed from the program
4184 and stored in a separate file. @value{GDBN} has built-in support for
4185 finding separate debug info files (@pxref{Separate Debug Files}), but if
4186 the file doesn't live in one of the standard places that @value{GDBN}
4187 searches then this function can be used to add a debug info file
4188 from a different place.
4191 @node Frames In Python
4192 @subsubsection Accessing inferior stack frames from Python.
4194 @cindex frames in python
4195 When the debugged program stops, @value{GDBN} is able to analyze its call
4196 stack (@pxref{Frames,,Stack frames}). The @code{gdb.Frame} class
4197 represents a frame in the stack. A @code{gdb.Frame} object is only valid
4198 while its corresponding frame exists in the inferior's stack. If you try
4199 to use an invalid frame object, @value{GDBN} will throw a @code{gdb.error}
4200 exception (@pxref{Exception Handling}).
4202 Two @code{gdb.Frame} objects can be compared for equality with the @code{==}
4206 (@value{GDBP}) python print gdb.newest_frame() == gdb.selected_frame ()
4210 The following frame-related functions are available in the @code{gdb} module:
4212 @findex gdb.selected_frame
4213 @defun gdb.selected_frame ()
4214 Return the selected frame object. (@pxref{Selection,,Selecting a Frame}).
4217 @findex gdb.newest_frame
4218 @defun gdb.newest_frame ()
4219 Return the newest frame object for the selected thread.
4222 @defun gdb.frame_stop_reason_string (reason)
4223 Return a string explaining the reason why @value{GDBN} stopped unwinding
4224 frames, as expressed by the given @var{reason} code (an integer, see the
4225 @code{unwind_stop_reason} method further down in this section).
4228 @findex gdb.invalidate_cached_frames
4229 @defun gdb.invalidate_cached_frames
4230 @value{GDBN} internally keeps a cache of the frames that have been
4231 unwound. This function invalidates this cache.
4233 This function should not generally be called by ordinary Python code.
4234 It is documented for the sake of completeness.
4237 A @code{gdb.Frame} object has the following methods:
4239 @defun Frame.is_valid ()
4240 Returns true if the @code{gdb.Frame} object is valid, false if not.
4241 A frame object can become invalid if the frame it refers to doesn't
4242 exist anymore in the inferior. All @code{gdb.Frame} methods will throw
4243 an exception if it is invalid at the time the method is called.
4246 @defun Frame.name ()
4247 Returns the function name of the frame, or @code{None} if it can't be
4251 @defun Frame.architecture ()
4252 Returns the @code{gdb.Architecture} object corresponding to the frame's
4253 architecture. @xref{Architectures In Python}.
4256 @defun Frame.type ()
4257 Returns the type of the frame. The value can be one of:
4259 @item gdb.NORMAL_FRAME
4260 An ordinary stack frame.
4262 @item gdb.DUMMY_FRAME
4263 A fake stack frame that was created by @value{GDBN} when performing an
4264 inferior function call.
4266 @item gdb.INLINE_FRAME
4267 A frame representing an inlined function. The function was inlined
4268 into a @code{gdb.NORMAL_FRAME} that is older than this one.
4270 @item gdb.TAILCALL_FRAME
4271 A frame representing a tail call. @xref{Tail Call Frames}.
4273 @item gdb.SIGTRAMP_FRAME
4274 A signal trampoline frame. This is the frame created by the OS when
4275 it calls into a signal handler.
4277 @item gdb.ARCH_FRAME
4278 A fake stack frame representing a cross-architecture call.
4280 @item gdb.SENTINEL_FRAME
4281 This is like @code{gdb.NORMAL_FRAME}, but it is only used for the
4286 @defun Frame.unwind_stop_reason ()
4287 Return an integer representing the reason why it's not possible to find
4288 more frames toward the outermost frame. Use
4289 @code{gdb.frame_stop_reason_string} to convert the value returned by this
4290 function to a string. The value can be one of:
4293 @item gdb.FRAME_UNWIND_NO_REASON
4294 No particular reason (older frames should be available).
4296 @item gdb.FRAME_UNWIND_NULL_ID
4297 The previous frame's analyzer returns an invalid result. This is no
4298 longer used by @value{GDBN}, and is kept only for backward
4301 @item gdb.FRAME_UNWIND_OUTERMOST
4302 This frame is the outermost.
4304 @item gdb.FRAME_UNWIND_UNAVAILABLE
4305 Cannot unwind further, because that would require knowing the
4306 values of registers or memory that have not been collected.
4308 @item gdb.FRAME_UNWIND_INNER_ID
4309 This frame ID looks like it ought to belong to a NEXT frame,
4310 but we got it for a PREV frame. Normally, this is a sign of
4311 unwinder failure. It could also indicate stack corruption.
4313 @item gdb.FRAME_UNWIND_SAME_ID
4314 This frame has the same ID as the previous one. That means
4315 that unwinding further would almost certainly give us another
4316 frame with exactly the same ID, so break the chain. Normally,
4317 this is a sign of unwinder failure. It could also indicate
4320 @item gdb.FRAME_UNWIND_NO_SAVED_PC
4321 The frame unwinder did not find any saved PC, but we needed
4322 one to unwind further.
4324 @item gdb.FRAME_UNWIND_MEMORY_ERROR
4325 The frame unwinder caused an error while trying to access memory.
4327 @item gdb.FRAME_UNWIND_FIRST_ERROR
4328 Any stop reason greater or equal to this value indicates some kind
4329 of error. This special value facilitates writing code that tests
4330 for errors in unwinding in a way that will work correctly even if
4331 the list of the other values is modified in future @value{GDBN}
4332 versions. Using it, you could write:
4334 reason = gdb.selected_frame().unwind_stop_reason ()
4335 reason_str = gdb.frame_stop_reason_string (reason)
4336 if reason >= gdb.FRAME_UNWIND_FIRST_ERROR:
4337 print "An error occured: %s" % reason_str
4344 Returns the frame's resume address.
4347 @defun Frame.block ()
4348 Return the frame's code block. @xref{Blocks In Python}. If the frame
4349 does not have a block -- for example, if there is no debugging
4350 information for the code in question -- then this will throw an
4354 @defun Frame.function ()
4355 Return the symbol for the function corresponding to this frame.
4356 @xref{Symbols In Python}.
4359 @defun Frame.older ()
4360 Return the frame that called this frame.
4363 @defun Frame.newer ()
4364 Return the frame called by this frame.
4367 @defun Frame.find_sal ()
4368 Return the frame's symtab and line object.
4369 @xref{Symbol Tables In Python}.
4372 @defun Frame.read_register (register)
4373 Return the value of @var{register} in this frame. The @var{register}
4374 argument must be a string (e.g., @code{'sp'} or @code{'rax'}).
4375 Returns a @code{Gdb.Value} object. Throws an exception if @var{register}
4379 @defun Frame.read_var (variable @r{[}, block@r{]})
4380 Return the value of @var{variable} in this frame. If the optional
4381 argument @var{block} is provided, search for the variable from that
4382 block; otherwise start at the frame's current block (which is
4383 determined by the frame's current program counter). The @var{variable}
4384 argument must be a string or a @code{gdb.Symbol} object; @var{block} must be a
4385 @code{gdb.Block} object.
4388 @defun Frame.select ()
4389 Set this frame to be the selected frame. @xref{Stack, ,Examining the
4393 @node Blocks In Python
4394 @subsubsection Accessing blocks from Python.
4396 @cindex blocks in python
4399 In @value{GDBN}, symbols are stored in blocks. A block corresponds
4400 roughly to a scope in the source code. Blocks are organized
4401 hierarchically, and are represented individually in Python as a
4402 @code{gdb.Block}. Blocks rely on debugging information being
4405 A frame has a block. Please see @ref{Frames In Python}, for a more
4406 in-depth discussion of frames.
4408 The outermost block is known as the @dfn{global block}. The global
4409 block typically holds public global variables and functions.
4411 The block nested just inside the global block is the @dfn{static
4412 block}. The static block typically holds file-scoped variables and
4415 @value{GDBN} provides a method to get a block's superblock, but there
4416 is currently no way to examine the sub-blocks of a block, or to
4417 iterate over all the blocks in a symbol table (@pxref{Symbol Tables In
4420 Here is a short example that should help explain blocks:
4423 /* This is in the global block. */
4426 /* This is in the static block. */
4427 static int file_scope;
4429 /* 'function' is in the global block, and 'argument' is
4430 in a block nested inside of 'function'. */
4431 int function (int argument)
4433 /* 'local' is in a block inside 'function'. It may or may
4434 not be in the same block as 'argument'. */
4438 /* 'inner' is in a block whose superblock is the one holding
4442 /* If this call is expanded by the compiler, you may see
4443 a nested block here whose function is 'inline_function'
4444 and whose superblock is the one holding 'inner'. */
4450 A @code{gdb.Block} is iterable. The iterator returns the symbols
4451 (@pxref{Symbols In Python}) local to the block. Python programs
4452 should not assume that a specific block object will always contain a
4453 given symbol, since changes in @value{GDBN} features and
4454 infrastructure may cause symbols move across blocks in a symbol
4457 The following block-related functions are available in the @code{gdb}
4460 @findex gdb.block_for_pc
4461 @defun gdb.block_for_pc (pc)
4462 Return the innermost @code{gdb.Block} containing the given @var{pc}
4463 value. If the block cannot be found for the @var{pc} value specified,
4464 the function will return @code{None}.
4467 A @code{gdb.Block} object has the following methods:
4469 @defun Block.is_valid ()
4470 Returns @code{True} if the @code{gdb.Block} object is valid,
4471 @code{False} if not. A block object can become invalid if the block it
4472 refers to doesn't exist anymore in the inferior. All other
4473 @code{gdb.Block} methods will throw an exception if it is invalid at
4474 the time the method is called. The block's validity is also checked
4475 during iteration over symbols of the block.
4478 A @code{gdb.Block} object has the following attributes:
4481 The start address of the block. This attribute is not writable.
4485 One past the last address that appears in the block. This attribute
4489 @defvar Block.function
4490 The name of the block represented as a @code{gdb.Symbol}. If the
4491 block is not named, then this attribute holds @code{None}. This
4492 attribute is not writable.
4494 For ordinary function blocks, the superblock is the static block.
4495 However, you should note that it is possible for a function block to
4496 have a superblock that is not the static block -- for instance this
4497 happens for an inlined function.
4500 @defvar Block.superblock
4501 The block containing this block. If this parent block does not exist,
4502 this attribute holds @code{None}. This attribute is not writable.
4505 @defvar Block.global_block
4506 The global block associated with this block. This attribute is not
4510 @defvar Block.static_block
4511 The static block associated with this block. This attribute is not
4515 @defvar Block.is_global
4516 @code{True} if the @code{gdb.Block} object is a global block,
4517 @code{False} if not. This attribute is not
4521 @defvar Block.is_static
4522 @code{True} if the @code{gdb.Block} object is a static block,
4523 @code{False} if not. This attribute is not writable.
4526 @node Symbols In Python
4527 @subsubsection Python representation of Symbols.
4529 @cindex symbols in python
4532 @value{GDBN} represents every variable, function and type as an
4533 entry in a symbol table. @xref{Symbols, ,Examining the Symbol Table}.
4534 Similarly, Python represents these symbols in @value{GDBN} with the
4535 @code{gdb.Symbol} object.
4537 The following symbol-related functions are available in the @code{gdb}
4540 @findex gdb.lookup_symbol
4541 @defun gdb.lookup_symbol (name @r{[}, block @r{[}, domain@r{]]})
4542 This function searches for a symbol by name. The search scope can be
4543 restricted to the parameters defined in the optional domain and block
4546 @var{name} is the name of the symbol. It must be a string. The
4547 optional @var{block} argument restricts the search to symbols visible
4548 in that @var{block}. The @var{block} argument must be a
4549 @code{gdb.Block} object. If omitted, the block for the current frame
4550 is used. The optional @var{domain} argument restricts
4551 the search to the domain type. The @var{domain} argument must be a
4552 domain constant defined in the @code{gdb} module and described later
4555 The result is a tuple of two elements.
4556 The first element is a @code{gdb.Symbol} object or @code{None} if the symbol
4558 If the symbol is found, the second element is @code{True} if the symbol
4559 is a field of a method's object (e.g., @code{this} in C@t{++}),
4560 otherwise it is @code{False}.
4561 If the symbol is not found, the second element is @code{False}.
4564 @findex gdb.lookup_global_symbol
4565 @defun gdb.lookup_global_symbol (name @r{[}, domain@r{]})
4566 This function searches for a global symbol by name.
4567 The search scope can be restricted to by the domain argument.
4569 @var{name} is the name of the symbol. It must be a string.
4570 The optional @var{domain} argument restricts the search to the domain type.
4571 The @var{domain} argument must be a domain constant defined in the @code{gdb}
4572 module and described later in this chapter.
4574 The result is a @code{gdb.Symbol} object or @code{None} if the symbol
4578 A @code{gdb.Symbol} object has the following attributes:
4581 The type of the symbol or @code{None} if no type is recorded.
4582 This attribute is represented as a @code{gdb.Type} object.
4583 @xref{Types In Python}. This attribute is not writable.
4586 @defvar Symbol.symtab
4587 The symbol table in which the symbol appears. This attribute is
4588 represented as a @code{gdb.Symtab} object. @xref{Symbol Tables In
4589 Python}. This attribute is not writable.
4593 The line number in the source code at which the symbol was defined.
4598 The name of the symbol as a string. This attribute is not writable.
4601 @defvar Symbol.linkage_name
4602 The name of the symbol, as used by the linker (i.e., may be mangled).
4603 This attribute is not writable.
4606 @defvar Symbol.print_name
4607 The name of the symbol in a form suitable for output. This is either
4608 @code{name} or @code{linkage_name}, depending on whether the user
4609 asked @value{GDBN} to display demangled or mangled names.
4612 @defvar Symbol.addr_class
4613 The address class of the symbol. This classifies how to find the value
4614 of a symbol. Each address class is a constant defined in the
4615 @code{gdb} module and described later in this chapter.
4618 @defvar Symbol.needs_frame
4619 This is @code{True} if evaluating this symbol's value requires a frame
4620 (@pxref{Frames In Python}) and @code{False} otherwise. Typically,
4621 local variables will require a frame, but other symbols will not.
4624 @defvar Symbol.is_argument
4625 @code{True} if the symbol is an argument of a function.
4628 @defvar Symbol.is_constant
4629 @code{True} if the symbol is a constant.
4632 @defvar Symbol.is_function
4633 @code{True} if the symbol is a function or a method.
4636 @defvar Symbol.is_variable
4637 @code{True} if the symbol is a variable.
4640 A @code{gdb.Symbol} object has the following methods:
4642 @defun Symbol.is_valid ()
4643 Returns @code{True} if the @code{gdb.Symbol} object is valid,
4644 @code{False} if not. A @code{gdb.Symbol} object can become invalid if
4645 the symbol it refers to does not exist in @value{GDBN} any longer.
4646 All other @code{gdb.Symbol} methods will throw an exception if it is
4647 invalid at the time the method is called.
4650 @defun Symbol.value (@r{[}frame@r{]})
4651 Compute the value of the symbol, as a @code{gdb.Value}. For
4652 functions, this computes the address of the function, cast to the
4653 appropriate type. If the symbol requires a frame in order to compute
4654 its value, then @var{frame} must be given. If @var{frame} is not
4655 given, or if @var{frame} is invalid, then this method will throw an
4659 The available domain categories in @code{gdb.Symbol} are represented
4660 as constants in the @code{gdb} module:
4663 @vindex SYMBOL_UNDEF_DOMAIN
4664 @item gdb.SYMBOL_UNDEF_DOMAIN
4665 This is used when a domain has not been discovered or none of the
4666 following domains apply. This usually indicates an error either
4667 in the symbol information or in @value{GDBN}'s handling of symbols.
4669 @vindex SYMBOL_VAR_DOMAIN
4670 @item gdb.SYMBOL_VAR_DOMAIN
4671 This domain contains variables, function names, typedef names and enum
4674 @vindex SYMBOL_STRUCT_DOMAIN
4675 @item gdb.SYMBOL_STRUCT_DOMAIN
4676 This domain holds struct, union and enum type names.
4678 @vindex SYMBOL_LABEL_DOMAIN
4679 @item gdb.SYMBOL_LABEL_DOMAIN
4680 This domain contains names of labels (for gotos).
4682 @vindex SYMBOL_VARIABLES_DOMAIN
4683 @item gdb.SYMBOL_VARIABLES_DOMAIN
4684 This domain holds a subset of the @code{SYMBOLS_VAR_DOMAIN}; it
4685 contains everything minus functions and types.
4687 @vindex SYMBOL_FUNCTIONS_DOMAIN
4688 @item gdb.SYMBOL_FUNCTIONS_DOMAIN
4689 This domain contains all functions.
4691 @vindex SYMBOL_TYPES_DOMAIN
4692 @item gdb.SYMBOL_TYPES_DOMAIN
4693 This domain contains all types.
4696 The available address class categories in @code{gdb.Symbol} are represented
4697 as constants in the @code{gdb} module:
4700 @vindex SYMBOL_LOC_UNDEF
4701 @item gdb.SYMBOL_LOC_UNDEF
4702 If this is returned by address class, it indicates an error either in
4703 the symbol information or in @value{GDBN}'s handling of symbols.
4705 @vindex SYMBOL_LOC_CONST
4706 @item gdb.SYMBOL_LOC_CONST
4707 Value is constant int.
4709 @vindex SYMBOL_LOC_STATIC
4710 @item gdb.SYMBOL_LOC_STATIC
4711 Value is at a fixed address.
4713 @vindex SYMBOL_LOC_REGISTER
4714 @item gdb.SYMBOL_LOC_REGISTER
4715 Value is in a register.
4717 @vindex SYMBOL_LOC_ARG
4718 @item gdb.SYMBOL_LOC_ARG
4719 Value is an argument. This value is at the offset stored within the
4720 symbol inside the frame's argument list.
4722 @vindex SYMBOL_LOC_REF_ARG
4723 @item gdb.SYMBOL_LOC_REF_ARG
4724 Value address is stored in the frame's argument list. Just like
4725 @code{LOC_ARG} except that the value's address is stored at the
4726 offset, not the value itself.
4728 @vindex SYMBOL_LOC_REGPARM_ADDR
4729 @item gdb.SYMBOL_LOC_REGPARM_ADDR
4730 Value is a specified register. Just like @code{LOC_REGISTER} except
4731 the register holds the address of the argument instead of the argument
4734 @vindex SYMBOL_LOC_LOCAL
4735 @item gdb.SYMBOL_LOC_LOCAL
4736 Value is a local variable.
4738 @vindex SYMBOL_LOC_TYPEDEF
4739 @item gdb.SYMBOL_LOC_TYPEDEF
4740 Value not used. Symbols in the domain @code{SYMBOL_STRUCT_DOMAIN} all
4743 @vindex SYMBOL_LOC_BLOCK
4744 @item gdb.SYMBOL_LOC_BLOCK
4747 @vindex SYMBOL_LOC_CONST_BYTES
4748 @item gdb.SYMBOL_LOC_CONST_BYTES
4749 Value is a byte-sequence.
4751 @vindex SYMBOL_LOC_UNRESOLVED
4752 @item gdb.SYMBOL_LOC_UNRESOLVED
4753 Value is at a fixed address, but the address of the variable has to be
4754 determined from the minimal symbol table whenever the variable is
4757 @vindex SYMBOL_LOC_OPTIMIZED_OUT
4758 @item gdb.SYMBOL_LOC_OPTIMIZED_OUT
4759 The value does not actually exist in the program.
4761 @vindex SYMBOL_LOC_COMPUTED
4762 @item gdb.SYMBOL_LOC_COMPUTED
4763 The value's address is a computed location.
4766 @node Symbol Tables In Python
4767 @subsubsection Symbol table representation in Python.
4769 @cindex symbol tables in python
4771 @tindex gdb.Symtab_and_line
4773 Access to symbol table data maintained by @value{GDBN} on the inferior
4774 is exposed to Python via two objects: @code{gdb.Symtab_and_line} and
4775 @code{gdb.Symtab}. Symbol table and line data for a frame is returned
4776 from the @code{find_sal} method in @code{gdb.Frame} object.
4777 @xref{Frames In Python}.
4779 For more information on @value{GDBN}'s symbol table management, see
4780 @ref{Symbols, ,Examining the Symbol Table}, for more information.
4782 A @code{gdb.Symtab_and_line} object has the following attributes:
4784 @defvar Symtab_and_line.symtab
4785 The symbol table object (@code{gdb.Symtab}) for this frame.
4786 This attribute is not writable.
4789 @defvar Symtab_and_line.pc
4790 Indicates the start of the address range occupied by code for the
4791 current source line. This attribute is not writable.
4794 @defvar Symtab_and_line.last
4795 Indicates the end of the address range occupied by code for the current
4796 source line. This attribute is not writable.
4799 @defvar Symtab_and_line.line
4800 Indicates the current line number for this object. This
4801 attribute is not writable.
4804 A @code{gdb.Symtab_and_line} object has the following methods:
4806 @defun Symtab_and_line.is_valid ()
4807 Returns @code{True} if the @code{gdb.Symtab_and_line} object is valid,
4808 @code{False} if not. A @code{gdb.Symtab_and_line} object can become
4809 invalid if the Symbol table and line object it refers to does not
4810 exist in @value{GDBN} any longer. All other
4811 @code{gdb.Symtab_and_line} methods will throw an exception if it is
4812 invalid at the time the method is called.
4815 A @code{gdb.Symtab} object has the following attributes:
4817 @defvar Symtab.filename
4818 The symbol table's source filename. This attribute is not writable.
4821 @defvar Symtab.objfile
4822 The symbol table's backing object file. @xref{Objfiles In Python}.
4823 This attribute is not writable.
4826 @defvar Symtab.producer
4827 The name and possibly version number of the program that
4828 compiled the code in the symbol table.
4829 The contents of this string is up to the compiler.
4830 If no producer information is available then @code{None} is returned.
4831 This attribute is not writable.
4834 A @code{gdb.Symtab} object has the following methods:
4836 @defun Symtab.is_valid ()
4837 Returns @code{True} if the @code{gdb.Symtab} object is valid,
4838 @code{False} if not. A @code{gdb.Symtab} object can become invalid if
4839 the symbol table it refers to does not exist in @value{GDBN} any
4840 longer. All other @code{gdb.Symtab} methods will throw an exception
4841 if it is invalid at the time the method is called.
4844 @defun Symtab.fullname ()
4845 Return the symbol table's source absolute file name.
4848 @defun Symtab.global_block ()
4849 Return the global block of the underlying symbol table.
4850 @xref{Blocks In Python}.
4853 @defun Symtab.static_block ()
4854 Return the static block of the underlying symbol table.
4855 @xref{Blocks In Python}.
4858 @defun Symtab.linetable ()
4859 Return the line table associated with the symbol table.
4860 @xref{Line Tables In Python}.
4863 @node Line Tables In Python
4864 @subsubsection Manipulating line tables using Python
4866 @cindex line tables in python
4867 @tindex gdb.LineTable
4869 Python code can request and inspect line table information from a
4870 symbol table that is loaded in @value{GDBN}. A line table is a
4871 mapping of source lines to their executable locations in memory. To
4872 acquire the line table information for a particular symbol table, use
4873 the @code{linetable} function (@pxref{Symbol Tables In Python}).
4875 A @code{gdb.LineTable} is iterable. The iterator returns
4876 @code{LineTableEntry} objects that correspond to the source line and
4877 address for each line table entry. @code{LineTableEntry} objects have
4878 the following attributes:
4880 @defvar LineTableEntry.line
4881 The source line number for this line table entry. This number
4882 corresponds to the actual line of source. This attribute is not
4886 @defvar LineTableEntry.pc
4887 The address that is associated with the line table entry where the
4888 executable code for that source line resides in memory. This
4889 attribute is not writable.
4892 As there can be multiple addresses for a single source line, you may
4893 receive multiple @code{LineTableEntry} objects with matching
4894 @code{line} attributes, but with different @code{pc} attributes. The
4895 iterator is sorted in ascending @code{pc} order. Here is a small
4896 example illustrating iterating over a line table.
4899 symtab = gdb.selected_frame().find_sal().symtab
4900 linetable = symtab.linetable()
4901 for line in linetable:
4902 print "Line: "+str(line.line)+" Address: "+hex(line.pc)
4905 This will have the following output:
4908 Line: 33 Address: 0x4005c8L
4909 Line: 37 Address: 0x4005caL
4910 Line: 39 Address: 0x4005d2L
4911 Line: 40 Address: 0x4005f8L
4912 Line: 42 Address: 0x4005ffL
4913 Line: 44 Address: 0x400608L
4914 Line: 42 Address: 0x40060cL
4915 Line: 45 Address: 0x400615L
4918 In addition to being able to iterate over a @code{LineTable}, it also
4919 has the following direct access methods:
4921 @defun LineTable.line (line)
4922 Return a Python @code{Tuple} of @code{LineTableEntry} objects for any
4923 entries in the line table for the given @var{line}, which specifies
4924 the source code line. If there are no entries for that source code
4925 @var{line}, the Python @code{None} is returned.
4928 @defun LineTable.has_line (line)
4929 Return a Python @code{Boolean} indicating whether there is an entry in
4930 the line table for this source line. Return @code{True} if an entry
4931 is found, or @code{False} if not.
4934 @defun LineTable.source_lines ()
4935 Return a Python @code{List} of the source line numbers in the symbol
4936 table. Only lines with executable code locations are returned. The
4937 contents of the @code{List} will just be the source line entries
4938 represented as Python @code{Long} values.
4941 @node Breakpoints In Python
4942 @subsubsection Manipulating breakpoints using Python
4944 @cindex breakpoints in python
4945 @tindex gdb.Breakpoint
4947 Python code can manipulate breakpoints via the @code{gdb.Breakpoint}
4950 A breakpoint can be created using one of the two forms of the
4951 @code{gdb.Breakpoint} constructor. The first one accepts a string
4952 like one would pass to the @code{break}
4953 (@pxref{Set Breaks,,Setting Breakpoints}) and @code{watch}
4954 (@pxref{Set Watchpoints, , Setting Watchpoints}) commands, and can be used to
4955 create both breakpoints and watchpoints. The second accepts separate Python
4956 arguments similar to @ref{Explicit Locations}, and can only be used to create
4959 @defun Breakpoint.__init__ (spec @r{[}, type @r{][}, wp_class @r{][}, internal @r{][}, temporary @r{][}, qualified @r{]})
4960 Create a new breakpoint according to @var{spec}, which is a string naming the
4961 location of a breakpoint, or an expression that defines a watchpoint. The
4962 string should describe a location in a format recognized by the @code{break}
4963 command (@pxref{Set Breaks,,Setting Breakpoints}) or, in the case of a
4964 watchpoint, by the @code{watch} command
4965 (@pxref{Set Watchpoints, , Setting Watchpoints}).
4967 The optional @var{type} argument specifies the type of the breakpoint to create,
4970 The optional @var{wp_class} argument defines the class of watchpoint to create,
4971 if @var{type} is @code{gdb.BP_WATCHPOINT}. If @var{wp_class} is omitted, it
4972 defaults to @code{gdb.WP_WRITE}.
4974 The optional @var{internal} argument allows the breakpoint to become invisible
4975 to the user. The breakpoint will neither be reported when created, nor will it
4976 be listed in the output from @code{info breakpoints} (but will be listed with
4977 the @code{maint info breakpoints} command).
4979 The optional @var{temporary} argument makes the breakpoint a temporary
4980 breakpoint. Temporary breakpoints are deleted after they have been hit. Any
4981 further access to the Python breakpoint after it has been hit will result in a
4982 runtime error (as that breakpoint has now been automatically deleted).
4984 The optional @var{qualified} argument is a boolean that allows interpreting
4985 the function passed in @code{spec} as a fully-qualified name. It is equivalent
4986 to @code{break}'s @code{-qualified} flag (@pxref{Linespec Locations} and
4987 @ref{Explicit Locations}).
4991 @defun Breakpoint.__init__ (@r{[} source @r{][}, function @r{][}, label @r{][}, line @r{]}, @r{][} internal @r{][}, temporary @r{][}, qualified @r{]})
4992 This second form of creating a new breakpoint specifies the explicit
4993 location (@pxref{Explicit Locations}) using keywords. The new breakpoint will
4994 be created in the specified source file @var{source}, at the specified
4995 @var{function}, @var{label} and @var{line}.
4997 @var{internal}, @var{temporary} and @var{qualified} have the same usage as
4998 explained previously.
5001 The available types are represented by constants defined in the @code{gdb}
5005 @vindex BP_BREAKPOINT
5006 @item gdb.BP_BREAKPOINT
5007 Normal code breakpoint.
5009 @vindex BP_WATCHPOINT
5010 @item gdb.BP_WATCHPOINT
5011 Watchpoint breakpoint.
5013 @vindex BP_HARDWARE_WATCHPOINT
5014 @item gdb.BP_HARDWARE_WATCHPOINT
5015 Hardware assisted watchpoint.
5017 @vindex BP_READ_WATCHPOINT
5018 @item gdb.BP_READ_WATCHPOINT
5019 Hardware assisted read watchpoint.
5021 @vindex BP_ACCESS_WATCHPOINT
5022 @item gdb.BP_ACCESS_WATCHPOINT
5023 Hardware assisted access watchpoint.
5026 The available watchpoint types represented by constants are defined in the
5032 Read only watchpoint.
5036 Write only watchpoint.
5040 Read/Write watchpoint.
5043 @defun Breakpoint.stop (self)
5044 The @code{gdb.Breakpoint} class can be sub-classed and, in
5045 particular, you may choose to implement the @code{stop} method.
5046 If this method is defined in a sub-class of @code{gdb.Breakpoint},
5047 it will be called when the inferior reaches any location of a
5048 breakpoint which instantiates that sub-class. If the method returns
5049 @code{True}, the inferior will be stopped at the location of the
5050 breakpoint, otherwise the inferior will continue.
5052 If there are multiple breakpoints at the same location with a
5053 @code{stop} method, each one will be called regardless of the
5054 return status of the previous. This ensures that all @code{stop}
5055 methods have a chance to execute at that location. In this scenario
5056 if one of the methods returns @code{True} but the others return
5057 @code{False}, the inferior will still be stopped.
5059 You should not alter the execution state of the inferior (i.e.@:, step,
5060 next, etc.), alter the current frame context (i.e.@:, change the current
5061 active frame), or alter, add or delete any breakpoint. As a general
5062 rule, you should not alter any data within @value{GDBN} or the inferior
5065 Example @code{stop} implementation:
5068 class MyBreakpoint (gdb.Breakpoint):
5070 inf_val = gdb.parse_and_eval("foo")
5077 @defun Breakpoint.is_valid ()
5078 Return @code{True} if this @code{Breakpoint} object is valid,
5079 @code{False} otherwise. A @code{Breakpoint} object can become invalid
5080 if the user deletes the breakpoint. In this case, the object still
5081 exists, but the underlying breakpoint does not. In the cases of
5082 watchpoint scope, the watchpoint remains valid even if execution of the
5083 inferior leaves the scope of that watchpoint.
5086 @defun Breakpoint.delete ()
5087 Permanently deletes the @value{GDBN} breakpoint. This also
5088 invalidates the Python @code{Breakpoint} object. Any further access
5089 to this object's attributes or methods will raise an error.
5092 @defvar Breakpoint.enabled
5093 This attribute is @code{True} if the breakpoint is enabled, and
5094 @code{False} otherwise. This attribute is writable. You can use it to enable
5095 or disable the breakpoint.
5098 @defvar Breakpoint.silent
5099 This attribute is @code{True} if the breakpoint is silent, and
5100 @code{False} otherwise. This attribute is writable.
5102 Note that a breakpoint can also be silent if it has commands and the
5103 first command is @code{silent}. This is not reported by the
5104 @code{silent} attribute.
5107 @defvar Breakpoint.pending
5108 This attribute is @code{True} if the breakpoint is pending, and
5109 @code{False} otherwise. @xref{Set Breaks}. This attribute is
5113 @anchor{python_breakpoint_thread}
5114 @defvar Breakpoint.thread
5115 If the breakpoint is thread-specific, this attribute holds the
5116 thread's global id. If the breakpoint is not thread-specific, this
5117 attribute is @code{None}. This attribute is writable.
5120 @defvar Breakpoint.task
5121 If the breakpoint is Ada task-specific, this attribute holds the Ada task
5122 id. If the breakpoint is not task-specific (or the underlying
5123 language is not Ada), this attribute is @code{None}. This attribute
5127 @defvar Breakpoint.ignore_count
5128 This attribute holds the ignore count for the breakpoint, an integer.
5129 This attribute is writable.
5132 @defvar Breakpoint.number
5133 This attribute holds the breakpoint's number --- the identifier used by
5134 the user to manipulate the breakpoint. This attribute is not writable.
5137 @defvar Breakpoint.type
5138 This attribute holds the breakpoint's type --- the identifier used to
5139 determine the actual breakpoint type or use-case. This attribute is not
5143 @defvar Breakpoint.visible
5144 This attribute tells whether the breakpoint is visible to the user
5145 when set, or when the @samp{info breakpoints} command is run. This
5146 attribute is not writable.
5149 @defvar Breakpoint.temporary
5150 This attribute indicates whether the breakpoint was created as a
5151 temporary breakpoint. Temporary breakpoints are automatically deleted
5152 after that breakpoint has been hit. Access to this attribute, and all
5153 other attributes and functions other than the @code{is_valid}
5154 function, will result in an error after the breakpoint has been hit
5155 (as it has been automatically deleted). This attribute is not
5159 @defvar Breakpoint.hit_count
5160 This attribute holds the hit count for the breakpoint, an integer.
5161 This attribute is writable, but currently it can only be set to zero.
5164 @defvar Breakpoint.location
5165 This attribute holds the location of the breakpoint, as specified by
5166 the user. It is a string. If the breakpoint does not have a location
5167 (that is, it is a watchpoint) the attribute's value is @code{None}. This
5168 attribute is not writable.
5171 @defvar Breakpoint.expression
5172 This attribute holds a breakpoint expression, as specified by
5173 the user. It is a string. If the breakpoint does not have an
5174 expression (the breakpoint is not a watchpoint) the attribute's value
5175 is @code{None}. This attribute is not writable.
5178 @defvar Breakpoint.condition
5179 This attribute holds the condition of the breakpoint, as specified by
5180 the user. It is a string. If there is no condition, this attribute's
5181 value is @code{None}. This attribute is writable.
5184 @defvar Breakpoint.commands
5185 This attribute holds the commands attached to the breakpoint. If
5186 there are commands, this attribute's value is a string holding all the
5187 commands, separated by newlines. If there are no commands, this
5188 attribute is @code{None}. This attribute is writable.
5191 @node Finish Breakpoints in Python
5192 @subsubsection Finish Breakpoints
5194 @cindex python finish breakpoints
5195 @tindex gdb.FinishBreakpoint
5197 A finish breakpoint is a temporary breakpoint set at the return address of
5198 a frame, based on the @code{finish} command. @code{gdb.FinishBreakpoint}
5199 extends @code{gdb.Breakpoint}. The underlying breakpoint will be disabled
5200 and deleted when the execution will run out of the breakpoint scope (i.e.@:
5201 @code{Breakpoint.stop} or @code{FinishBreakpoint.out_of_scope} triggered).
5202 Finish breakpoints are thread specific and must be create with the right
5205 @defun FinishBreakpoint.__init__ (@r{[}frame@r{]} @r{[}, internal@r{]})
5206 Create a finish breakpoint at the return address of the @code{gdb.Frame}
5207 object @var{frame}. If @var{frame} is not provided, this defaults to the
5208 newest frame. The optional @var{internal} argument allows the breakpoint to
5209 become invisible to the user. @xref{Breakpoints In Python}, for further
5210 details about this argument.
5213 @defun FinishBreakpoint.out_of_scope (self)
5214 In some circumstances (e.g.@: @code{longjmp}, C@t{++} exceptions, @value{GDBN}
5215 @code{return} command, @dots{}), a function may not properly terminate, and
5216 thus never hit the finish breakpoint. When @value{GDBN} notices such a
5217 situation, the @code{out_of_scope} callback will be triggered.
5219 You may want to sub-class @code{gdb.FinishBreakpoint} and override this
5223 class MyFinishBreakpoint (gdb.FinishBreakpoint)
5225 print "normal finish"
5228 def out_of_scope ():
5229 print "abnormal finish"
5233 @defvar FinishBreakpoint.return_value
5234 When @value{GDBN} is stopped at a finish breakpoint and the frame
5235 used to build the @code{gdb.FinishBreakpoint} object had debug symbols, this
5236 attribute will contain a @code{gdb.Value} object corresponding to the return
5237 value of the function. The value will be @code{None} if the function return
5238 type is @code{void} or if the return value was not computable. This attribute
5242 @node Lazy Strings In Python
5243 @subsubsection Python representation of lazy strings.
5245 @cindex lazy strings in python
5246 @tindex gdb.LazyString
5248 A @dfn{lazy string} is a string whose contents is not retrieved or
5249 encoded until it is needed.
5251 A @code{gdb.LazyString} is represented in @value{GDBN} as an
5252 @code{address} that points to a region of memory, an @code{encoding}
5253 that will be used to encode that region of memory, and a @code{length}
5254 to delimit the region of memory that represents the string. The
5255 difference between a @code{gdb.LazyString} and a string wrapped within
5256 a @code{gdb.Value} is that a @code{gdb.LazyString} will be treated
5257 differently by @value{GDBN} when printing. A @code{gdb.LazyString} is
5258 retrieved and encoded during printing, while a @code{gdb.Value}
5259 wrapping a string is immediately retrieved and encoded on creation.
5261 A @code{gdb.LazyString} object has the following functions:
5263 @defun LazyString.value ()
5264 Convert the @code{gdb.LazyString} to a @code{gdb.Value}. This value
5265 will point to the string in memory, but will lose all the delayed
5266 retrieval, encoding and handling that @value{GDBN} applies to a
5267 @code{gdb.LazyString}.
5270 @defvar LazyString.address
5271 This attribute holds the address of the string. This attribute is not
5275 @defvar LazyString.length
5276 This attribute holds the length of the string in characters. If the
5277 length is -1, then the string will be fetched and encoded up to the
5278 first null of appropriate width. This attribute is not writable.
5281 @defvar LazyString.encoding
5282 This attribute holds the encoding that will be applied to the string
5283 when the string is printed by @value{GDBN}. If the encoding is not
5284 set, or contains an empty string, then @value{GDBN} will select the
5285 most appropriate encoding when the string is printed. This attribute
5289 @defvar LazyString.type
5290 This attribute holds the type that is represented by the lazy string's
5291 type. For a lazy string this is a pointer or array type. To
5292 resolve this to the lazy string's character type, use the type's
5293 @code{target} method. @xref{Types In Python}. This attribute is not
5297 @node Architectures In Python
5298 @subsubsection Python representation of architectures
5299 @cindex Python architectures
5301 @value{GDBN} uses architecture specific parameters and artifacts in a
5302 number of its various computations. An architecture is represented
5303 by an instance of the @code{gdb.Architecture} class.
5305 A @code{gdb.Architecture} class has the following methods:
5307 @defun Architecture.name ()
5308 Return the name (string value) of the architecture.
5311 @defun Architecture.disassemble (@var{start_pc} @r{[}, @var{end_pc} @r{[}, @var{count}@r{]]})
5312 Return a list of disassembled instructions starting from the memory
5313 address @var{start_pc}. The optional arguments @var{end_pc} and
5314 @var{count} determine the number of instructions in the returned list.
5315 If both the optional arguments @var{end_pc} and @var{count} are
5316 specified, then a list of at most @var{count} disassembled instructions
5317 whose start address falls in the closed memory address interval from
5318 @var{start_pc} to @var{end_pc} are returned. If @var{end_pc} is not
5319 specified, but @var{count} is specified, then @var{count} number of
5320 instructions starting from the address @var{start_pc} are returned. If
5321 @var{count} is not specified but @var{end_pc} is specified, then all
5322 instructions whose start address falls in the closed memory address
5323 interval from @var{start_pc} to @var{end_pc} are returned. If neither
5324 @var{end_pc} nor @var{count} are specified, then a single instruction at
5325 @var{start_pc} is returned. For all of these cases, each element of the
5326 returned list is a Python @code{dict} with the following string keys:
5331 The value corresponding to this key is a Python long integer capturing
5332 the memory address of the instruction.
5335 The value corresponding to this key is a string value which represents
5336 the instruction with assembly language mnemonics. The assembly
5337 language flavor used is the same as that specified by the current CLI
5338 variable @code{disassembly-flavor}. @xref{Machine Code}.
5341 The value corresponding to this key is the length (integer value) of the
5342 instruction in bytes.
5347 @node Python Auto-loading
5348 @subsection Python Auto-loading
5349 @cindex Python auto-loading
5351 When a new object file is read (for example, due to the @code{file}
5352 command, or because the inferior has loaded a shared library),
5353 @value{GDBN} will look for Python support scripts in several ways:
5354 @file{@var{objfile}-gdb.py} and @code{.debug_gdb_scripts} section.
5355 @xref{Auto-loading extensions}.
5357 The auto-loading feature is useful for supplying application-specific
5358 debugging commands and scripts.
5360 Auto-loading can be enabled or disabled,
5361 and the list of auto-loaded scripts can be printed.
5364 @anchor{set auto-load python-scripts}
5365 @kindex set auto-load python-scripts
5366 @item set auto-load python-scripts [on|off]
5367 Enable or disable the auto-loading of Python scripts.
5369 @anchor{show auto-load python-scripts}
5370 @kindex show auto-load python-scripts
5371 @item show auto-load python-scripts
5372 Show whether auto-loading of Python scripts is enabled or disabled.
5374 @anchor{info auto-load python-scripts}
5375 @kindex info auto-load python-scripts
5376 @cindex print list of auto-loaded Python scripts
5377 @item info auto-load python-scripts [@var{regexp}]
5378 Print the list of all Python scripts that @value{GDBN} auto-loaded.
5380 Also printed is the list of Python scripts that were mentioned in
5381 the @code{.debug_gdb_scripts} section and were either not found
5382 (@pxref{dotdebug_gdb_scripts section}) or were not auto-loaded due to
5383 @code{auto-load safe-path} rejection (@pxref{Auto-loading}).
5384 This is useful because their names are not printed when @value{GDBN}
5385 tries to load them and fails. There may be many of them, and printing
5386 an error message for each one is problematic.
5388 If @var{regexp} is supplied only Python scripts with matching names are printed.
5393 (gdb) info auto-load python-scripts
5395 Yes py-section-script.py
5396 full name: /tmp/py-section-script.py
5397 No my-foo-pretty-printers.py
5401 When reading an auto-loaded file or script, @value{GDBN} sets the
5402 @dfn{current objfile}. This is available via the @code{gdb.current_objfile}
5403 function (@pxref{Objfiles In Python}). This can be useful for
5404 registering objfile-specific pretty-printers and frame-filters.
5406 @node Python modules
5407 @subsection Python modules
5408 @cindex python modules
5410 @value{GDBN} comes with several modules to assist writing Python code.
5413 * gdb.printing:: Building and registering pretty-printers.
5414 * gdb.types:: Utilities for working with types.
5415 * gdb.prompt:: Utilities for prompt value substitution.
5419 @subsubsection gdb.printing
5420 @cindex gdb.printing
5422 This module provides a collection of utilities for working with
5426 @item PrettyPrinter (@var{name}, @var{subprinters}=None)
5427 This class specifies the API that makes @samp{info pretty-printer},
5428 @samp{enable pretty-printer} and @samp{disable pretty-printer} work.
5429 Pretty-printers should generally inherit from this class.
5431 @item SubPrettyPrinter (@var{name})
5432 For printers that handle multiple types, this class specifies the
5433 corresponding API for the subprinters.
5435 @item RegexpCollectionPrettyPrinter (@var{name})
5436 Utility class for handling multiple printers, all recognized via
5437 regular expressions.
5438 @xref{Writing a Pretty-Printer}, for an example.
5440 @item FlagEnumerationPrinter (@var{name})
5441 A pretty-printer which handles printing of @code{enum} values. Unlike
5442 @value{GDBN}'s built-in @code{enum} printing, this printer attempts to
5443 work properly when there is some overlap between the enumeration
5444 constants. The argument @var{name} is the name of the printer and
5445 also the name of the @code{enum} type to look up.
5447 @item register_pretty_printer (@var{obj}, @var{printer}, @var{replace}=False)
5448 Register @var{printer} with the pretty-printer list of @var{obj}.
5449 If @var{replace} is @code{True} then any existing copy of the printer
5450 is replaced. Otherwise a @code{RuntimeError} exception is raised
5451 if a printer with the same name already exists.
5455 @subsubsection gdb.types
5458 This module provides a collection of utilities for working with
5459 @code{gdb.Type} objects.
5462 @item get_basic_type (@var{type})
5463 Return @var{type} with const and volatile qualifiers stripped,
5464 and with typedefs and C@t{++} references converted to the underlying type.
5469 typedef const int const_int;
5471 const_int& foo_ref (foo);
5472 int main () @{ return 0; @}
5479 (gdb) python import gdb.types
5480 (gdb) python foo_ref = gdb.parse_and_eval("foo_ref")
5481 (gdb) python print gdb.types.get_basic_type(foo_ref.type)
5485 @item has_field (@var{type}, @var{field})
5486 Return @code{True} if @var{type}, assumed to be a type with fields
5487 (e.g., a structure or union), has field @var{field}.
5489 @item make_enum_dict (@var{enum_type})
5490 Return a Python @code{dictionary} type produced from @var{enum_type}.
5492 @item deep_items (@var{type})
5493 Returns a Python iterator similar to the standard
5494 @code{gdb.Type.iteritems} method, except that the iterator returned
5495 by @code{deep_items} will recursively traverse anonymous struct or
5496 union fields. For example:
5510 Then in @value{GDBN}:
5512 (@value{GDBP}) python import gdb.types
5513 (@value{GDBP}) python struct_a = gdb.lookup_type("struct A")
5514 (@value{GDBP}) python print struct_a.keys ()
5516 (@value{GDBP}) python print [k for k,v in gdb.types.deep_items(struct_a)]
5517 @{['a', 'b0', 'b1']@}
5520 @item get_type_recognizers ()
5521 Return a list of the enabled type recognizers for the current context.
5522 This is called by @value{GDBN} during the type-printing process
5523 (@pxref{Type Printing API}).
5525 @item apply_type_recognizers (recognizers, type_obj)
5526 Apply the type recognizers, @var{recognizers}, to the type object
5527 @var{type_obj}. If any recognizer returns a string, return that
5528 string. Otherwise, return @code{None}. This is called by
5529 @value{GDBN} during the type-printing process (@pxref{Type Printing
5532 @item register_type_printer (locus, printer)
5533 This is a convenience function to register a type printer
5534 @var{printer}. The printer must implement the type printer protocol.
5535 The @var{locus} argument is either a @code{gdb.Objfile}, in which case
5536 the printer is registered with that objfile; a @code{gdb.Progspace},
5537 in which case the printer is registered with that progspace; or
5538 @code{None}, in which case the printer is registered globally.
5541 This is a base class that implements the type printer protocol. Type
5542 printers are encouraged, but not required, to derive from this class.
5543 It defines a constructor:
5545 @defmethod TypePrinter __init__ (self, name)
5546 Initialize the type printer with the given name. The new printer
5547 starts in the enabled state.
5553 @subsubsection gdb.prompt
5556 This module provides a method for prompt value-substitution.
5559 @item substitute_prompt (@var{string})
5560 Return @var{string} with escape sequences substituted by values. Some
5561 escape sequences take arguments. You can specify arguments inside
5562 ``@{@}'' immediately following the escape sequence.
5564 The escape sequences you can pass to this function are:
5568 Substitute a backslash.
5570 Substitute an ESC character.
5572 Substitute the selected frame; an argument names a frame parameter.
5574 Substitute a newline.
5576 Substitute a parameter's value; the argument names the parameter.
5578 Substitute a carriage return.
5580 Substitute the selected thread; an argument names a thread parameter.
5582 Substitute the version of GDB.
5584 Substitute the current working directory.
5586 Begin a sequence of non-printing characters. These sequences are
5587 typically used with the ESC character, and are not counted in the string
5588 length. Example: ``\[\e[0;34m\](gdb)\[\e[0m\]'' will return a
5589 blue-colored ``(gdb)'' prompt where the length is five.
5591 End a sequence of non-printing characters.
5597 substitute_prompt (``frame: \f,
5598 print arguments: \p@{print frame-arguments@}'')
5601 @exdent will return the string:
5604 "frame: main, print arguments: scalars"