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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.parse_and_eval
292 @defun gdb.parse_and_eval (expression)
293 Parse @var{expression}, which must be a string, as an expression in
294 the current language, evaluate it, and return the result as a
297 This function can be useful when implementing a new command
298 (@pxref{Commands In Python}), as it provides a way to parse the
299 command's argument as an expression. It is also useful simply to
300 compute values, for example, it is the only way to get the value of a
301 convenience variable (@pxref{Convenience Vars}) as a @code{gdb.Value}.
304 @findex gdb.find_pc_line
305 @defun gdb.find_pc_line (pc)
306 Return the @code{gdb.Symtab_and_line} object corresponding to the
307 @var{pc} value. @xref{Symbol Tables In Python}. If an invalid
308 value of @var{pc} is passed as an argument, then the @code{symtab} and
309 @code{line} attributes of the returned @code{gdb.Symtab_and_line} object
310 will be @code{None} and 0 respectively.
313 @findex gdb.post_event
314 @defun gdb.post_event (event)
315 Put @var{event}, a callable object taking no arguments, into
316 @value{GDBN}'s internal event queue. This callable will be invoked at
317 some later point, during @value{GDBN}'s event processing. Events
318 posted using @code{post_event} will be run in the order in which they
319 were posted; however, there is no way to know when they will be
320 processed relative to other events inside @value{GDBN}.
322 @value{GDBN} is not thread-safe. If your Python program uses multiple
323 threads, you must be careful to only call @value{GDBN}-specific
324 functions in the @value{GDBN} thread. @code{post_event} ensures
328 (@value{GDBP}) python
332 > def __init__(self, message):
333 > self.message = message;
334 > def __call__(self):
335 > gdb.write(self.message)
337 >class MyThread1 (threading.Thread):
339 > gdb.post_event(Writer("Hello "))
341 >class MyThread2 (threading.Thread):
343 > gdb.post_event(Writer("World\n"))
348 (@value{GDBP}) Hello World
353 @defun gdb.write (string @r{[}, stream{]})
354 Print a string to @value{GDBN}'s paginated output stream. The
355 optional @var{stream} determines the stream to print to. The default
356 stream is @value{GDBN}'s standard output stream. Possible stream
363 @value{GDBN}'s standard output stream.
368 @value{GDBN}'s standard error stream.
373 @value{GDBN}'s log stream (@pxref{Logging Output}).
376 Writing to @code{sys.stdout} or @code{sys.stderr} will automatically
377 call this function and will automatically direct the output to the
383 Flush the buffer of a @value{GDBN} paginated stream so that the
384 contents are displayed immediately. @value{GDBN} will flush the
385 contents of a stream automatically when it encounters a newline in the
386 buffer. The optional @var{stream} determines the stream to flush. The
387 default stream is @value{GDBN}'s standard output stream. Possible
394 @value{GDBN}'s standard output stream.
399 @value{GDBN}'s standard error stream.
404 @value{GDBN}'s log stream (@pxref{Logging Output}).
408 Flushing @code{sys.stdout} or @code{sys.stderr} will automatically
409 call this function for the relevant stream.
412 @findex gdb.target_charset
413 @defun gdb.target_charset ()
414 Return the name of the current target character set (@pxref{Character
415 Sets}). This differs from @code{gdb.parameter('target-charset')} in
416 that @samp{auto} is never returned.
419 @findex gdb.target_wide_charset
420 @defun gdb.target_wide_charset ()
421 Return the name of the current target wide character set
422 (@pxref{Character Sets}). This differs from
423 @code{gdb.parameter('target-wide-charset')} in that @samp{auto} is
427 @findex gdb.solib_name
428 @defun gdb.solib_name (address)
429 Return the name of the shared library holding the given @var{address}
430 as a string, or @code{None}.
433 @findex gdb.decode_line
434 @defun gdb.decode_line @r{[}expression@r{]}
435 Return locations of the line specified by @var{expression}, or of the
436 current line if no argument was given. This function returns a Python
437 tuple containing two elements. The first element contains a string
438 holding any unparsed section of @var{expression} (or @code{None} if
439 the expression has been fully parsed). The second element contains
440 either @code{None} or another tuple that contains all the locations
441 that match the expression represented as @code{gdb.Symtab_and_line}
442 objects (@pxref{Symbol Tables In Python}). If @var{expression} is
443 provided, it is decoded the way that @value{GDBN}'s inbuilt
444 @code{break} or @code{edit} commands do (@pxref{Specify Location}).
447 @defun gdb.prompt_hook (current_prompt)
450 If @var{prompt_hook} is callable, @value{GDBN} will call the method
451 assigned to this operation before a prompt is displayed by
454 The parameter @code{current_prompt} contains the current @value{GDBN}
455 prompt. This method must return a Python string, or @code{None}. If
456 a string is returned, the @value{GDBN} prompt will be set to that
457 string. If @code{None} is returned, @value{GDBN} will continue to use
460 Some prompts cannot be substituted in @value{GDBN}. Secondary prompts
461 such as those used by readline for command input, and annotation
462 related prompts are prohibited from being changed.
465 @node Exception Handling
466 @subsubsection Exception Handling
467 @cindex python exceptions
468 @cindex exceptions, python
470 When executing the @code{python} command, Python exceptions
471 uncaught within the Python code are translated to calls to
472 @value{GDBN} error-reporting mechanism. If the command that called
473 @code{python} does not handle the error, @value{GDBN} will
474 terminate it and print an error message containing the Python
475 exception name, the associated value, and the Python call stack
476 backtrace at the point where the exception was raised. Example:
479 (@value{GDBP}) python print foo
480 Traceback (most recent call last):
481 File "<string>", line 1, in <module>
482 NameError: name 'foo' is not defined
485 @value{GDBN} errors that happen in @value{GDBN} commands invoked by
486 Python code are converted to Python exceptions. The type of the
487 Python exception depends on the error.
491 This is the base class for most exceptions generated by @value{GDBN}.
492 It is derived from @code{RuntimeError}, for compatibility with earlier
493 versions of @value{GDBN}.
495 If an error occurring in @value{GDBN} does not fit into some more
496 specific category, then the generated exception will have this type.
498 @item gdb.MemoryError
499 This is a subclass of @code{gdb.error} which is thrown when an
500 operation tried to access invalid memory in the inferior.
502 @item KeyboardInterrupt
503 User interrupt (via @kbd{C-c} or by typing @kbd{q} at a pagination
504 prompt) is translated to a Python @code{KeyboardInterrupt} exception.
507 In all cases, your exception handler will see the @value{GDBN} error
508 message as its value and the Python call stack backtrace at the Python
509 statement closest to where the @value{GDBN} error occured as the
513 When implementing @value{GDBN} commands in Python via @code{gdb.Command},
514 it is useful to be able to throw an exception that doesn't cause a
515 traceback to be printed. For example, the user may have invoked the
516 command incorrectly. Use the @code{gdb.GdbError} exception
517 to handle this case. Example:
521 >class HelloWorld (gdb.Command):
522 > """Greet the whole world."""
523 > def __init__ (self):
524 > super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)
525 > def invoke (self, args, from_tty):
526 > argv = gdb.string_to_argv (args)
527 > if len (argv) != 0:
528 > raise gdb.GdbError ("hello-world takes no arguments")
529 > print "Hello, World!"
533 hello-world takes no arguments
536 @node Values From Inferior
537 @subsubsection Values From Inferior
538 @cindex values from inferior, with Python
539 @cindex python, working with values from inferior
541 @cindex @code{gdb.Value}
542 @value{GDBN} provides values it obtains from the inferior program in
543 an object of type @code{gdb.Value}. @value{GDBN} uses this object
544 for its internal bookkeeping of the inferior's values, and for
545 fetching values when necessary.
547 Inferior values that are simple scalars can be used directly in
548 Python expressions that are valid for the value's data type. Here's
549 an example for an integer or floating-point value @code{some_val}:
556 As result of this, @code{bar} will also be a @code{gdb.Value} object
557 whose values are of the same type as those of @code{some_val}. Valid
558 Python operations can also be performed on @code{gdb.Value} objects
559 representing a @code{struct} or @code{class} object. For such cases,
560 the overloaded operator (if present), is used to perform the operation.
561 For example, if @code{val1} and @code{val2} are @code{gdb.Value} objects
562 representing instances of a @code{class} which overloads the @code{+}
563 operator, then one can use the @code{+} operator in their Python script
571 The result of the operation @code{val3} is also a @code{gdb.Value}
572 object corresponding to the value returned by the overloaded @code{+}
573 operator. In general, overloaded operators are invoked for the
574 following operations: @code{+} (binary addition), @code{-} (binary
575 subtraction), @code{*} (multiplication), @code{/}, @code{%}, @code{<<},
576 @code{>>}, @code{|}, @code{&}, @code{^}.
578 Inferior values that are structures or instances of some class can
579 be accessed using the Python @dfn{dictionary syntax}. For example, if
580 @code{some_val} is a @code{gdb.Value} instance holding a structure, you
581 can access its @code{foo} element with:
584 bar = some_val['foo']
587 @cindex getting structure elements using gdb.Field objects as subscripts
588 Again, @code{bar} will also be a @code{gdb.Value} object. Structure
589 elements can also be accessed by using @code{gdb.Field} objects as
590 subscripts (@pxref{Types In Python}, for more information on
591 @code{gdb.Field} objects). For example, if @code{foo_field} is a
592 @code{gdb.Field} object corresponding to element @code{foo} of the above
593 structure, then @code{bar} can also be accessed as follows:
596 bar = some_val[foo_field]
599 A @code{gdb.Value} that represents a function can be executed via
600 inferior function call. Any arguments provided to the call must match
601 the function's prototype, and must be provided in the order specified
604 For example, @code{some_val} is a @code{gdb.Value} instance
605 representing a function that takes two integers as arguments. To
606 execute this function, call it like so:
609 result = some_val (10,20)
612 Any values returned from a function call will be stored as a
615 The following attributes are provided:
617 @defvar Value.address
618 If this object is addressable, this read-only attribute holds a
619 @code{gdb.Value} object representing the address. Otherwise,
620 this attribute holds @code{None}.
623 @cindex optimized out value in Python
624 @defvar Value.is_optimized_out
625 This read-only boolean attribute is true if the compiler optimized out
626 this value, thus it is not available for fetching from the inferior.
630 The type of this @code{gdb.Value}. The value of this attribute is a
631 @code{gdb.Type} object (@pxref{Types In Python}).
634 @defvar Value.dynamic_type
635 The dynamic type of this @code{gdb.Value}. This uses C@t{++} run-time
636 type information (@acronym{RTTI}) to determine the dynamic type of the
637 value. If this value is of class type, it will return the class in
638 which the value is embedded, if any. If this value is of pointer or
639 reference to a class type, it will compute the dynamic type of the
640 referenced object, and return a pointer or reference to that type,
641 respectively. In all other cases, it will return the value's static
644 Note that this feature will only work when debugging a C@t{++} program
645 that includes @acronym{RTTI} for the object in question. Otherwise,
646 it will just return the static type of the value as in @kbd{ptype foo}
647 (@pxref{Symbols, ptype}).
650 @defvar Value.is_lazy
651 The value of this read-only boolean attribute is @code{True} if this
652 @code{gdb.Value} has not yet been fetched from the inferior.
653 @value{GDBN} does not fetch values until necessary, for efficiency.
657 myval = gdb.parse_and_eval ('somevar')
660 The value of @code{somevar} is not fetched at this time. It will be
661 fetched when the value is needed, or when the @code{fetch_lazy}
665 The following methods are provided:
667 @defun Value.__init__ (@var{val})
668 Many Python values can be converted directly to a @code{gdb.Value} via
669 this object initializer. Specifically:
673 A Python boolean is converted to the boolean type from the current
677 A Python integer is converted to the C @code{long} type for the
678 current architecture.
681 A Python long is converted to the C @code{long long} type for the
682 current architecture.
685 A Python float is converted to the C @code{double} type for the
686 current architecture.
689 A Python string is converted to a target string in the current target
690 language using the current target encoding.
691 If a character cannot be represented in the current target encoding,
692 then an exception is thrown.
694 @item @code{gdb.Value}
695 If @code{val} is a @code{gdb.Value}, then a copy of the value is made.
697 @item @code{gdb.LazyString}
698 If @code{val} is a @code{gdb.LazyString} (@pxref{Lazy Strings In
699 Python}), then the lazy string's @code{value} method is called, and
704 @defun Value.cast (type)
705 Return a new instance of @code{gdb.Value} that is the result of
706 casting this instance to the type described by @var{type}, which must
707 be a @code{gdb.Type} object. If the cast cannot be performed for some
708 reason, this method throws an exception.
711 @defun Value.dereference ()
712 For pointer data types, this method returns a new @code{gdb.Value} object
713 whose contents is the object pointed to by the pointer. For example, if
714 @code{foo} is a C pointer to an @code{int}, declared in your C program as
721 then you can use the corresponding @code{gdb.Value} to access what
722 @code{foo} points to like this:
725 bar = foo.dereference ()
728 The result @code{bar} will be a @code{gdb.Value} object holding the
729 value pointed to by @code{foo}.
731 A similar function @code{Value.referenced_value} exists which also
732 returns @code{gdb.Value} objects corresonding to the values pointed to
733 by pointer values (and additionally, values referenced by reference
734 values). However, the behavior of @code{Value.dereference}
735 differs from @code{Value.referenced_value} by the fact that the
736 behavior of @code{Value.dereference} is identical to applying the C
737 unary operator @code{*} on a given value. For example, consider a
738 reference to a pointer @code{ptrref}, declared in your C@t{++} program
746 intptr &ptrref = ptr;
749 Though @code{ptrref} is a reference value, one can apply the method
750 @code{Value.dereference} to the @code{gdb.Value} object corresponding
751 to it and obtain a @code{gdb.Value} which is identical to that
752 corresponding to @code{val}. However, if you apply the method
753 @code{Value.referenced_value}, the result would be a @code{gdb.Value}
754 object identical to that corresponding to @code{ptr}.
757 py_ptrref = gdb.parse_and_eval ("ptrref")
758 py_val = py_ptrref.dereference ()
759 py_ptr = py_ptrref.referenced_value ()
762 The @code{gdb.Value} object @code{py_val} is identical to that
763 corresponding to @code{val}, and @code{py_ptr} is identical to that
764 corresponding to @code{ptr}. In general, @code{Value.dereference} can
765 be applied whenever the C unary operator @code{*} can be applied
766 to the corresponding C value. For those cases where applying both
767 @code{Value.dereference} and @code{Value.referenced_value} is allowed,
768 the results obtained need not be identical (as we have seen in the above
769 example). The results are however identical when applied on
770 @code{gdb.Value} objects corresponding to pointers (@code{gdb.Value}
771 objects with type code @code{TYPE_CODE_PTR}) in a C/C@t{++} program.
774 @defun Value.referenced_value ()
775 For pointer or reference data types, this method returns a new
776 @code{gdb.Value} object corresponding to the value referenced by the
777 pointer/reference value. For pointer data types,
778 @code{Value.dereference} and @code{Value.referenced_value} produce
779 identical results. The difference between these methods is that
780 @code{Value.dereference} cannot get the values referenced by reference
781 values. For example, consider a reference to an @code{int}, declared
782 in your C@t{++} program as
790 then applying @code{Value.dereference} to the @code{gdb.Value} object
791 corresponding to @code{ref} will result in an error, while applying
792 @code{Value.referenced_value} will result in a @code{gdb.Value} object
793 identical to that corresponding to @code{val}.
796 py_ref = gdb.parse_and_eval ("ref")
797 er_ref = py_ref.dereference () # Results in error
798 py_val = py_ref.referenced_value () # Returns the referenced value
801 The @code{gdb.Value} object @code{py_val} is identical to that
802 corresponding to @code{val}.
805 @defun Value.reference_value ()
806 Return a @code{gdb.Value} object which is a reference to the value
807 encapsulated by this instance.
810 @defun Value.const_value ()
811 Return a @code{gdb.Value} object which is a @code{const} version of the
812 value encapsulated by this instance.
815 @defun Value.dynamic_cast (type)
816 Like @code{Value.cast}, but works as if the C@t{++} @code{dynamic_cast}
817 operator were used. Consult a C@t{++} reference for details.
820 @defun Value.reinterpret_cast (type)
821 Like @code{Value.cast}, but works as if the C@t{++} @code{reinterpret_cast}
822 operator were used. Consult a C@t{++} reference for details.
825 @defun Value.string (@r{[}encoding@r{[}, errors@r{[}, length@r{]]]})
826 If this @code{gdb.Value} represents a string, then this method
827 converts the contents to a Python string. Otherwise, this method will
830 Values are interpreted as strings according to the rules of the
831 current language. If the optional length argument is given, the
832 string will be converted to that length, and will include any embedded
833 zeroes that the string may contain. Otherwise, for languages
834 where the string is zero-terminated, the entire string will be
837 For example, in C-like languages, a value is a string if it is a pointer
838 to or an array of characters or ints of type @code{wchar_t}, @code{char16_t},
841 If the optional @var{encoding} argument is given, it must be a string
842 naming the encoding of the string in the @code{gdb.Value}, such as
843 @code{"ascii"}, @code{"iso-8859-6"} or @code{"utf-8"}. It accepts
844 the same encodings as the corresponding argument to Python's
845 @code{string.decode} method, and the Python codec machinery will be used
846 to convert the string. If @var{encoding} is not given, or if
847 @var{encoding} is the empty string, then either the @code{target-charset}
848 (@pxref{Character Sets}) will be used, or a language-specific encoding
849 will be used, if the current language is able to supply one.
851 The optional @var{errors} argument is the same as the corresponding
852 argument to Python's @code{string.decode} method.
854 If the optional @var{length} argument is given, the string will be
855 fetched and converted to the given length.
858 @defun Value.lazy_string (@r{[}encoding @r{[}, length@r{]]})
859 If this @code{gdb.Value} represents a string, then this method
860 converts the contents to a @code{gdb.LazyString} (@pxref{Lazy Strings
861 In Python}). Otherwise, this method will throw an exception.
863 If the optional @var{encoding} argument is given, it must be a string
864 naming the encoding of the @code{gdb.LazyString}. Some examples are:
865 @samp{ascii}, @samp{iso-8859-6} or @samp{utf-8}. If the
866 @var{encoding} argument is an encoding that @value{GDBN} does
867 recognize, @value{GDBN} will raise an error.
869 When a lazy string is printed, the @value{GDBN} encoding machinery is
870 used to convert the string during printing. If the optional
871 @var{encoding} argument is not provided, or is an empty string,
872 @value{GDBN} will automatically select the encoding most suitable for
873 the string type. For further information on encoding in @value{GDBN}
874 please see @ref{Character Sets}.
876 If the optional @var{length} argument is given, the string will be
877 fetched and encoded to the length of characters specified. If
878 the @var{length} argument is not provided, the string will be fetched
879 and encoded until a null of appropriate width is found.
882 @defun Value.fetch_lazy ()
883 If the @code{gdb.Value} object is currently a lazy value
884 (@code{gdb.Value.is_lazy} is @code{True}), then the value is
885 fetched from the inferior. Any errors that occur in the process
886 will produce a Python exception.
888 If the @code{gdb.Value} object is not a lazy value, this method
891 This method does not return a value.
895 @node Types In Python
896 @subsubsection Types In Python
897 @cindex types in Python
898 @cindex Python, working with types
901 @value{GDBN} represents types from the inferior using the class
904 The following type-related functions are available in the @code{gdb}
907 @findex gdb.lookup_type
908 @defun gdb.lookup_type (name @r{[}, block@r{]})
909 This function looks up a type by its @var{name}, which must be a string.
911 If @var{block} is given, then @var{name} is looked up in that scope.
912 Otherwise, it is searched for globally.
914 Ordinarily, this function will return an instance of @code{gdb.Type}.
915 If the named type cannot be found, it will throw an exception.
918 If the type is a structure or class type, or an enum type, the fields
919 of that type can be accessed using the Python @dfn{dictionary syntax}.
920 For example, if @code{some_type} is a @code{gdb.Type} instance holding
921 a structure type, you can access its @code{foo} field with:
924 bar = some_type['foo']
927 @code{bar} will be a @code{gdb.Field} object; see below under the
928 description of the @code{Type.fields} method for a description of the
929 @code{gdb.Field} class.
931 An instance of @code{Type} has the following attributes:
934 The alignment of this type, in bytes. Type alignment comes from the
935 debugging information; if it was not specified, then @value{GDBN} will
936 use the relevant ABI to try to determine the alignment. In some
937 cases, even this is not possible, and zero will be returned.
941 The type code for this type. The type code will be one of the
942 @code{TYPE_CODE_} constants defined below.
946 The name of this type. If this type has no name, then @code{None}
951 The size of this type, in target @code{char} units. Usually, a
952 target's @code{char} type will be an 8-bit byte. However, on some
953 unusual platforms, this type may have a different size.
957 The tag name for this type. The tag name is the name after
958 @code{struct}, @code{union}, or @code{enum} in C and C@t{++}; not all
959 languages have this concept. If this type has no tag name, then
960 @code{None} is returned.
963 The following methods are provided:
965 @defun Type.fields ()
966 For structure and union types, this method returns the fields. Range
967 types have two fields, the minimum and maximum values. Enum types
968 have one field per enum constant. Function and method types have one
969 field per parameter. The base types of C@t{++} classes are also
970 represented as fields. If the type has no fields, or does not fit
971 into one of these categories, an empty sequence will be returned.
973 Each field is a @code{gdb.Field} object, with some pre-defined attributes:
976 This attribute is not available for @code{enum} or @code{static}
977 (as in C@t{++}) fields. The value is the position, counting
978 in bits, from the start of the containing type.
981 This attribute is only available for @code{enum} fields, and its value
982 is the enumeration member's integer representation.
985 The name of the field, or @code{None} for anonymous fields.
988 This is @code{True} if the field is artificial, usually meaning that
989 it was provided by the compiler and not the user. This attribute is
990 always provided, and is @code{False} if the field is not artificial.
993 This is @code{True} if the field represents a base class of a C@t{++}
994 structure. This attribute is always provided, and is @code{False}
995 if the field is not a base class of the type that is the argument of
996 @code{fields}, or if that type was not a C@t{++} class.
999 If the field is packed, or is a bitfield, then this will have a
1000 non-zero value, which is the size of the field in bits. Otherwise,
1001 this will be zero; in this case the field's size is given by its type.
1004 The type of the field. This is usually an instance of @code{Type},
1005 but it can be @code{None} in some situations.
1008 The type which contains this field. This is an instance of
1013 @defun Type.array (@var{n1} @r{[}, @var{n2}@r{]})
1014 Return a new @code{gdb.Type} object which represents an array of this
1015 type. If one argument is given, it is the inclusive upper bound of
1016 the array; in this case the lower bound is zero. If two arguments are
1017 given, the first argument is the lower bound of the array, and the
1018 second argument is the upper bound of the array. An array's length
1019 must not be negative, but the bounds can be.
1022 @defun Type.vector (@var{n1} @r{[}, @var{n2}@r{]})
1023 Return a new @code{gdb.Type} object which represents a vector of this
1024 type. If one argument is given, it is the inclusive upper bound of
1025 the vector; in this case the lower bound is zero. If two arguments are
1026 given, the first argument is the lower bound of the vector, and the
1027 second argument is the upper bound of the vector. A vector's length
1028 must not be negative, but the bounds can be.
1030 The difference between an @code{array} and a @code{vector} is that
1031 arrays behave like in C: when used in expressions they decay to a pointer
1032 to the first element whereas vectors are treated as first class values.
1035 @defun Type.const ()
1036 Return a new @code{gdb.Type} object which represents a
1037 @code{const}-qualified variant of this type.
1040 @defun Type.volatile ()
1041 Return a new @code{gdb.Type} object which represents a
1042 @code{volatile}-qualified variant of this type.
1045 @defun Type.unqualified ()
1046 Return a new @code{gdb.Type} object which represents an unqualified
1047 variant of this type. That is, the result is neither @code{const} nor
1051 @defun Type.range ()
1052 Return a Python @code{Tuple} object that contains two elements: the
1053 low bound of the argument type and the high bound of that type. If
1054 the type does not have a range, @value{GDBN} will raise a
1055 @code{gdb.error} exception (@pxref{Exception Handling}).
1058 @defun Type.reference ()
1059 Return a new @code{gdb.Type} object which represents a reference to this
1063 @defun Type.pointer ()
1064 Return a new @code{gdb.Type} object which represents a pointer to this
1068 @defun Type.strip_typedefs ()
1069 Return a new @code{gdb.Type} that represents the real type,
1070 after removing all layers of typedefs.
1073 @defun Type.target ()
1074 Return a new @code{gdb.Type} object which represents the target type
1077 For a pointer type, the target type is the type of the pointed-to
1078 object. For an array type (meaning C-like arrays), the target type is
1079 the type of the elements of the array. For a function or method type,
1080 the target type is the type of the return value. For a complex type,
1081 the target type is the type of the elements. For a typedef, the
1082 target type is the aliased type.
1084 If the type does not have a target, this method will throw an
1088 @defun Type.template_argument (n @r{[}, block@r{]})
1089 If this @code{gdb.Type} is an instantiation of a template, this will
1090 return a new @code{gdb.Value} or @code{gdb.Type} which represents the
1091 value of the @var{n}th template argument (indexed starting at 0).
1093 If this @code{gdb.Type} is not a template type, or if the type has fewer
1094 than @var{n} template arguments, this will throw an exception.
1095 Ordinarily, only C@t{++} code will have template types.
1097 If @var{block} is given, then @var{name} is looked up in that scope.
1098 Otherwise, it is searched for globally.
1101 @defun Type.optimized_out ()
1102 Return @code{gdb.Value} instance of this type whose value is optimized
1103 out. This allows a frame decorator to indicate that the value of an
1104 argument or a local variable is not known.
1107 Each type has a code, which indicates what category this type falls
1108 into. The available type categories are represented by constants
1109 defined in the @code{gdb} module:
1112 @vindex TYPE_CODE_PTR
1113 @item gdb.TYPE_CODE_PTR
1114 The type is a pointer.
1116 @vindex TYPE_CODE_ARRAY
1117 @item gdb.TYPE_CODE_ARRAY
1118 The type is an array.
1120 @vindex TYPE_CODE_STRUCT
1121 @item gdb.TYPE_CODE_STRUCT
1122 The type is a structure.
1124 @vindex TYPE_CODE_UNION
1125 @item gdb.TYPE_CODE_UNION
1126 The type is a union.
1128 @vindex TYPE_CODE_ENUM
1129 @item gdb.TYPE_CODE_ENUM
1130 The type is an enum.
1132 @vindex TYPE_CODE_FLAGS
1133 @item gdb.TYPE_CODE_FLAGS
1134 A bit flags type, used for things such as status registers.
1136 @vindex TYPE_CODE_FUNC
1137 @item gdb.TYPE_CODE_FUNC
1138 The type is a function.
1140 @vindex TYPE_CODE_INT
1141 @item gdb.TYPE_CODE_INT
1142 The type is an integer type.
1144 @vindex TYPE_CODE_FLT
1145 @item gdb.TYPE_CODE_FLT
1146 A floating point type.
1148 @vindex TYPE_CODE_VOID
1149 @item gdb.TYPE_CODE_VOID
1150 The special type @code{void}.
1152 @vindex TYPE_CODE_SET
1153 @item gdb.TYPE_CODE_SET
1156 @vindex TYPE_CODE_RANGE
1157 @item gdb.TYPE_CODE_RANGE
1158 A range type, that is, an integer type with bounds.
1160 @vindex TYPE_CODE_STRING
1161 @item gdb.TYPE_CODE_STRING
1162 A string type. Note that this is only used for certain languages with
1163 language-defined string types; C strings are not represented this way.
1165 @vindex TYPE_CODE_BITSTRING
1166 @item gdb.TYPE_CODE_BITSTRING
1167 A string of bits. It is deprecated.
1169 @vindex TYPE_CODE_ERROR
1170 @item gdb.TYPE_CODE_ERROR
1171 An unknown or erroneous type.
1173 @vindex TYPE_CODE_METHOD
1174 @item gdb.TYPE_CODE_METHOD
1175 A method type, as found in C@t{++}.
1177 @vindex TYPE_CODE_METHODPTR
1178 @item gdb.TYPE_CODE_METHODPTR
1179 A pointer-to-member-function.
1181 @vindex TYPE_CODE_MEMBERPTR
1182 @item gdb.TYPE_CODE_MEMBERPTR
1183 A pointer-to-member.
1185 @vindex TYPE_CODE_REF
1186 @item gdb.TYPE_CODE_REF
1189 @vindex TYPE_CODE_RVALUE_REF
1190 @item gdb.TYPE_CODE_RVALUE_REF
1191 A C@t{++}11 rvalue reference type.
1193 @vindex TYPE_CODE_CHAR
1194 @item gdb.TYPE_CODE_CHAR
1197 @vindex TYPE_CODE_BOOL
1198 @item gdb.TYPE_CODE_BOOL
1201 @vindex TYPE_CODE_COMPLEX
1202 @item gdb.TYPE_CODE_COMPLEX
1203 A complex float type.
1205 @vindex TYPE_CODE_TYPEDEF
1206 @item gdb.TYPE_CODE_TYPEDEF
1207 A typedef to some other type.
1209 @vindex TYPE_CODE_NAMESPACE
1210 @item gdb.TYPE_CODE_NAMESPACE
1211 A C@t{++} namespace.
1213 @vindex TYPE_CODE_DECFLOAT
1214 @item gdb.TYPE_CODE_DECFLOAT
1215 A decimal floating point type.
1217 @vindex TYPE_CODE_INTERNAL_FUNCTION
1218 @item gdb.TYPE_CODE_INTERNAL_FUNCTION
1219 A function internal to @value{GDBN}. This is the type used to represent
1220 convenience functions.
1223 Further support for types is provided in the @code{gdb.types}
1224 Python module (@pxref{gdb.types}).
1226 @node Pretty Printing API
1227 @subsubsection Pretty Printing API
1228 @cindex python pretty printing api
1230 An example output is provided (@pxref{Pretty Printing}).
1232 A pretty-printer is just an object that holds a value and implements a
1233 specific interface, defined here.
1235 @defun pretty_printer.children (self)
1236 @value{GDBN} will call this method on a pretty-printer to compute the
1237 children of the pretty-printer's value.
1239 This method must return an object conforming to the Python iterator
1240 protocol. Each item returned by the iterator must be a tuple holding
1241 two elements. The first element is the ``name'' of the child; the
1242 second element is the child's value. The value can be any Python
1243 object which is convertible to a @value{GDBN} value.
1245 This method is optional. If it does not exist, @value{GDBN} will act
1246 as though the value has no children.
1249 @defun pretty_printer.display_hint (self)
1250 The CLI may call this method and use its result to change the
1251 formatting of a value. The result will also be supplied to an MI
1252 consumer as a @samp{displayhint} attribute of the variable being
1255 This method is optional. If it does exist, this method must return a
1258 Some display hints are predefined by @value{GDBN}:
1262 Indicate that the object being printed is ``array-like''. The CLI
1263 uses this to respect parameters such as @code{set print elements} and
1264 @code{set print array}.
1267 Indicate that the object being printed is ``map-like'', and that the
1268 children of this value can be assumed to alternate between keys and
1272 Indicate that the object being printed is ``string-like''. If the
1273 printer's @code{to_string} method returns a Python string of some
1274 kind, then @value{GDBN} will call its internal language-specific
1275 string-printing function to format the string. For the CLI this means
1276 adding quotation marks, possibly escaping some characters, respecting
1277 @code{set print elements}, and the like.
1281 @defun pretty_printer.to_string (self)
1282 @value{GDBN} will call this method to display the string
1283 representation of the value passed to the object's constructor.
1285 When printing from the CLI, if the @code{to_string} method exists,
1286 then @value{GDBN} will prepend its result to the values returned by
1287 @code{children}. Exactly how this formatting is done is dependent on
1288 the display hint, and may change as more hints are added. Also,
1289 depending on the print settings (@pxref{Print Settings}), the CLI may
1290 print just the result of @code{to_string} in a stack trace, omitting
1291 the result of @code{children}.
1293 If this method returns a string, it is printed verbatim.
1295 Otherwise, if this method returns an instance of @code{gdb.Value},
1296 then @value{GDBN} prints this value. This may result in a call to
1297 another pretty-printer.
1299 If instead the method returns a Python value which is convertible to a
1300 @code{gdb.Value}, then @value{GDBN} performs the conversion and prints
1301 the resulting value. Again, this may result in a call to another
1302 pretty-printer. Python scalars (integers, floats, and booleans) and
1303 strings are convertible to @code{gdb.Value}; other types are not.
1305 Finally, if this method returns @code{None} then no further operations
1306 are peformed in this method and nothing is printed.
1308 If the result is not one of these types, an exception is raised.
1311 @value{GDBN} provides a function which can be used to look up the
1312 default pretty-printer for a @code{gdb.Value}:
1314 @findex gdb.default_visualizer
1315 @defun gdb.default_visualizer (value)
1316 This function takes a @code{gdb.Value} object as an argument. If a
1317 pretty-printer for this value exists, then it is returned. If no such
1318 printer exists, then this returns @code{None}.
1321 @node Selecting Pretty-Printers
1322 @subsubsection Selecting Pretty-Printers
1323 @cindex selecting python pretty-printers
1325 The Python list @code{gdb.pretty_printers} contains an array of
1326 functions or callable objects that have been registered via addition
1327 as a pretty-printer. Printers in this list are called @code{global}
1328 printers, they're available when debugging all inferiors.
1329 Each @code{gdb.Progspace} contains a @code{pretty_printers} attribute.
1330 Each @code{gdb.Objfile} also contains a @code{pretty_printers}
1333 Each function on these lists is passed a single @code{gdb.Value}
1334 argument and should return a pretty-printer object conforming to the
1335 interface definition above (@pxref{Pretty Printing API}). If a function
1336 cannot create a pretty-printer for the value, it should return
1339 @value{GDBN} first checks the @code{pretty_printers} attribute of each
1340 @code{gdb.Objfile} in the current program space and iteratively calls
1341 each enabled lookup routine in the list for that @code{gdb.Objfile}
1342 until it receives a pretty-printer object.
1343 If no pretty-printer is found in the objfile lists, @value{GDBN} then
1344 searches the pretty-printer list of the current program space,
1345 calling each enabled function until an object is returned.
1346 After these lists have been exhausted, it tries the global
1347 @code{gdb.pretty_printers} list, again calling each enabled function until an
1350 The order in which the objfiles are searched is not specified. For a
1351 given list, functions are always invoked from the head of the list,
1352 and iterated over sequentially until the end of the list, or a printer
1355 For various reasons a pretty-printer may not work.
1356 For example, the underlying data structure may have changed and
1357 the pretty-printer is out of date.
1359 The consequences of a broken pretty-printer are severe enough that
1360 @value{GDBN} provides support for enabling and disabling individual
1361 printers. For example, if @code{print frame-arguments} is on,
1362 a backtrace can become highly illegible if any argument is printed
1363 with a broken printer.
1365 Pretty-printers are enabled and disabled by attaching an @code{enabled}
1366 attribute to the registered function or callable object. If this attribute
1367 is present and its value is @code{False}, the printer is disabled, otherwise
1368 the printer is enabled.
1370 @node Writing a Pretty-Printer
1371 @subsubsection Writing a Pretty-Printer
1372 @cindex writing a pretty-printer
1374 A pretty-printer consists of two parts: a lookup function to detect
1375 if the type is supported, and the printer itself.
1377 Here is an example showing how a @code{std::string} printer might be
1378 written. @xref{Pretty Printing API}, for details on the API this class
1382 class StdStringPrinter(object):
1383 "Print a std::string"
1385 def __init__(self, val):
1388 def to_string(self):
1389 return self.val['_M_dataplus']['_M_p']
1391 def display_hint(self):
1395 And here is an example showing how a lookup function for the printer
1396 example above might be written.
1399 def str_lookup_function(val):
1400 lookup_tag = val.type.tag
1401 if lookup_tag == None:
1403 regex = re.compile("^std::basic_string<char,.*>$")
1404 if regex.match(lookup_tag):
1405 return StdStringPrinter(val)
1409 The example lookup function extracts the value's type, and attempts to
1410 match it to a type that it can pretty-print. If it is a type the
1411 printer can pretty-print, it will return a printer object. If not, it
1412 returns @code{None}.
1414 We recommend that you put your core pretty-printers into a Python
1415 package. If your pretty-printers are for use with a library, we
1416 further recommend embedding a version number into the package name.
1417 This practice will enable @value{GDBN} to load multiple versions of
1418 your pretty-printers at the same time, because they will have
1421 You should write auto-loaded code (@pxref{Python Auto-loading}) such that it
1422 can be evaluated multiple times without changing its meaning. An
1423 ideal auto-load file will consist solely of @code{import}s of your
1424 printer modules, followed by a call to a register pretty-printers with
1425 the current objfile.
1427 Taken as a whole, this approach will scale nicely to multiple
1428 inferiors, each potentially using a different library version.
1429 Embedding a version number in the Python package name will ensure that
1430 @value{GDBN} is able to load both sets of printers simultaneously.
1431 Then, because the search for pretty-printers is done by objfile, and
1432 because your auto-loaded code took care to register your library's
1433 printers with a specific objfile, @value{GDBN} will find the correct
1434 printers for the specific version of the library used by each
1437 To continue the @code{std::string} example (@pxref{Pretty Printing API}),
1438 this code might appear in @code{gdb.libstdcxx.v6}:
1441 def register_printers(objfile):
1442 objfile.pretty_printers.append(str_lookup_function)
1446 And then the corresponding contents of the auto-load file would be:
1449 import gdb.libstdcxx.v6
1450 gdb.libstdcxx.v6.register_printers(gdb.current_objfile())
1453 The previous example illustrates a basic pretty-printer.
1454 There are a few things that can be improved on.
1455 The printer doesn't have a name, making it hard to identify in a
1456 list of installed printers. The lookup function has a name, but
1457 lookup functions can have arbitrary, even identical, names.
1459 Second, the printer only handles one type, whereas a library typically has
1460 several types. One could install a lookup function for each desired type
1461 in the library, but one could also have a single lookup function recognize
1462 several types. The latter is the conventional way this is handled.
1463 If a pretty-printer can handle multiple data types, then its
1464 @dfn{subprinters} are the printers for the individual data types.
1466 The @code{gdb.printing} module provides a formal way of solving these
1467 problems (@pxref{gdb.printing}).
1468 Here is another example that handles multiple types.
1470 These are the types we are going to pretty-print:
1473 struct foo @{ int a, b; @};
1474 struct bar @{ struct foo x, y; @};
1477 Here are the printers:
1481 """Print a foo object."""
1483 def __init__(self, val):
1486 def to_string(self):
1487 return ("a=<" + str(self.val["a"]) +
1488 "> b=<" + str(self.val["b"]) + ">")
1491 """Print a bar object."""
1493 def __init__(self, val):
1496 def to_string(self):
1497 return ("x=<" + str(self.val["x"]) +
1498 "> y=<" + str(self.val["y"]) + ">")
1501 This example doesn't need a lookup function, that is handled by the
1502 @code{gdb.printing} module. Instead a function is provided to build up
1503 the object that handles the lookup.
1508 def build_pretty_printer():
1509 pp = gdb.printing.RegexpCollectionPrettyPrinter(
1511 pp.add_printer('foo', '^foo$', fooPrinter)
1512 pp.add_printer('bar', '^bar$', barPrinter)
1516 And here is the autoload support:
1521 gdb.printing.register_pretty_printer(
1522 gdb.current_objfile(),
1523 my_library.build_pretty_printer())
1526 Finally, when this printer is loaded into @value{GDBN}, here is the
1527 corresponding output of @samp{info pretty-printer}:
1530 (gdb) info pretty-printer
1537 @node Type Printing API
1538 @subsubsection Type Printing API
1539 @cindex type printing API for Python
1541 @value{GDBN} provides a way for Python code to customize type display.
1542 This is mainly useful for substituting canonical typedef names for
1545 @cindex type printer
1546 A @dfn{type printer} is just a Python object conforming to a certain
1547 protocol. A simple base class implementing the protocol is provided;
1548 see @ref{gdb.types}. A type printer must supply at least:
1550 @defivar type_printer enabled
1551 A boolean which is True if the printer is enabled, and False
1552 otherwise. This is manipulated by the @code{enable type-printer}
1553 and @code{disable type-printer} commands.
1556 @defivar type_printer name
1557 The name of the type printer. This must be a string. This is used by
1558 the @code{enable type-printer} and @code{disable type-printer}
1562 @defmethod type_printer instantiate (self)
1563 This is called by @value{GDBN} at the start of type-printing. It is
1564 only called if the type printer is enabled. This method must return a
1565 new object that supplies a @code{recognize} method, as described below.
1569 When displaying a type, say via the @code{ptype} command, @value{GDBN}
1570 will compute a list of type recognizers. This is done by iterating
1571 first over the per-objfile type printers (@pxref{Objfiles In Python}),
1572 followed by the per-progspace type printers (@pxref{Progspaces In
1573 Python}), and finally the global type printers.
1575 @value{GDBN} will call the @code{instantiate} method of each enabled
1576 type printer. If this method returns @code{None}, then the result is
1577 ignored; otherwise, it is appended to the list of recognizers.
1579 Then, when @value{GDBN} is going to display a type name, it iterates
1580 over the list of recognizers. For each one, it calls the recognition
1581 function, stopping if the function returns a non-@code{None} value.
1582 The recognition function is defined as:
1584 @defmethod type_recognizer recognize (self, type)
1585 If @var{type} is not recognized, return @code{None}. Otherwise,
1586 return a string which is to be printed as the name of @var{type}.
1587 The @var{type} argument will be an instance of @code{gdb.Type}
1588 (@pxref{Types In Python}).
1591 @value{GDBN} uses this two-pass approach so that type printers can
1592 efficiently cache information without holding on to it too long. For
1593 example, it can be convenient to look up type information in a type
1594 printer and hold it for a recognizer's lifetime; if a single pass were
1595 done then type printers would have to make use of the event system in
1596 order to avoid holding information that could become stale as the
1599 @node Frame Filter API
1600 @subsubsection Filtering Frames.
1601 @cindex frame filters api
1603 Frame filters are Python objects that manipulate the visibility of a
1604 frame or frames when a backtrace (@pxref{Backtrace}) is printed by
1607 Only commands that print a backtrace, or, in the case of @sc{gdb/mi}
1608 commands (@pxref{GDB/MI}), those that return a collection of frames
1609 are affected. The commands that work with frame filters are:
1611 @code{backtrace} (@pxref{backtrace-command,, The backtrace command}),
1612 @code{-stack-list-frames}
1613 (@pxref{-stack-list-frames,, The -stack-list-frames command}),
1614 @code{-stack-list-variables} (@pxref{-stack-list-variables,, The
1615 -stack-list-variables command}), @code{-stack-list-arguments}
1616 @pxref{-stack-list-arguments,, The -stack-list-arguments command}) and
1617 @code{-stack-list-locals} (@pxref{-stack-list-locals,, The
1618 -stack-list-locals command}).
1620 A frame filter works by taking an iterator as an argument, applying
1621 actions to the contents of that iterator, and returning another
1622 iterator (or, possibly, the same iterator it was provided in the case
1623 where the filter does not perform any operations). Typically, frame
1624 filters utilize tools such as the Python's @code{itertools} module to
1625 work with and create new iterators from the source iterator.
1626 Regardless of how a filter chooses to apply actions, it must not alter
1627 the underlying @value{GDBN} frame or frames, or attempt to alter the
1628 call-stack within @value{GDBN}. This preserves data integrity within
1629 @value{GDBN}. Frame filters are executed on a priority basis and care
1630 should be taken that some frame filters may have been executed before,
1631 and that some frame filters will be executed after.
1633 An important consideration when designing frame filters, and well
1634 worth reflecting upon, is that frame filters should avoid unwinding
1635 the call stack if possible. Some stacks can run very deep, into the
1636 tens of thousands in some cases. To search every frame when a frame
1637 filter executes may be too expensive at that step. The frame filter
1638 cannot know how many frames it has to iterate over, and it may have to
1639 iterate through them all. This ends up duplicating effort as
1640 @value{GDBN} performs this iteration when it prints the frames. If
1641 the filter can defer unwinding frames until frame decorators are
1642 executed, after the last filter has executed, it should. @xref{Frame
1643 Decorator API}, for more information on decorators. Also, there are
1644 examples for both frame decorators and filters in later chapters.
1645 @xref{Writing a Frame Filter}, for more information.
1647 The Python dictionary @code{gdb.frame_filters} contains key/object
1648 pairings that comprise a frame filter. Frame filters in this
1649 dictionary are called @code{global} frame filters, and they are
1650 available when debugging all inferiors. These frame filters must
1651 register with the dictionary directly. In addition to the
1652 @code{global} dictionary, there are other dictionaries that are loaded
1653 with different inferiors via auto-loading (@pxref{Python
1654 Auto-loading}). The two other areas where frame filter dictionaries
1655 can be found are: @code{gdb.Progspace} which contains a
1656 @code{frame_filters} dictionary attribute, and each @code{gdb.Objfile}
1657 object which also contains a @code{frame_filters} dictionary
1660 When a command is executed from @value{GDBN} that is compatible with
1661 frame filters, @value{GDBN} combines the @code{global},
1662 @code{gdb.Progspace} and all @code{gdb.Objfile} dictionaries currently
1663 loaded. All of the @code{gdb.Objfile} dictionaries are combined, as
1664 several frames, and thus several object files, might be in use.
1665 @value{GDBN} then prunes any frame filter whose @code{enabled}
1666 attribute is @code{False}. This pruned list is then sorted according
1667 to the @code{priority} attribute in each filter.
1669 Once the dictionaries are combined, pruned and sorted, @value{GDBN}
1670 creates an iterator which wraps each frame in the call stack in a
1671 @code{FrameDecorator} object, and calls each filter in order. The
1672 output from the previous filter will always be the input to the next
1675 Frame filters have a mandatory interface which each frame filter must
1676 implement, defined here:
1678 @defun FrameFilter.filter (iterator)
1679 @value{GDBN} will call this method on a frame filter when it has
1680 reached the order in the priority list for that filter.
1682 For example, if there are four frame filters:
1693 The order that the frame filters will be called is:
1696 Filter3 -> Filter2 -> Filter1 -> Filter4
1699 Note that the output from @code{Filter3} is passed to the input of
1700 @code{Filter2}, and so on.
1702 This @code{filter} method is passed a Python iterator. This iterator
1703 contains a sequence of frame decorators that wrap each
1704 @code{gdb.Frame}, or a frame decorator that wraps another frame
1705 decorator. The first filter that is executed in the sequence of frame
1706 filters will receive an iterator entirely comprised of default
1707 @code{FrameDecorator} objects. However, after each frame filter is
1708 executed, the previous frame filter may have wrapped some or all of
1709 the frame decorators with their own frame decorator. As frame
1710 decorators must also conform to a mandatory interface, these
1711 decorators can be assumed to act in a uniform manner (@pxref{Frame
1714 This method must return an object conforming to the Python iterator
1715 protocol. Each item in the iterator must be an object conforming to
1716 the frame decorator interface. If a frame filter does not wish to
1717 perform any operations on this iterator, it should return that
1720 This method is not optional. If it does not exist, @value{GDBN} will
1721 raise and print an error.
1724 @defvar FrameFilter.name
1725 The @code{name} attribute must be Python string which contains the
1726 name of the filter displayed by @value{GDBN} (@pxref{Frame Filter
1727 Management}). This attribute may contain any combination of letters
1728 or numbers. Care should be taken to ensure that it is unique. This
1729 attribute is mandatory.
1732 @defvar FrameFilter.enabled
1733 The @code{enabled} attribute must be Python boolean. This attribute
1734 indicates to @value{GDBN} whether the frame filter is enabled, and
1735 should be considered when frame filters are executed. If
1736 @code{enabled} is @code{True}, then the frame filter will be executed
1737 when any of the backtrace commands detailed earlier in this chapter
1738 are executed. If @code{enabled} is @code{False}, then the frame
1739 filter will not be executed. This attribute is mandatory.
1742 @defvar FrameFilter.priority
1743 The @code{priority} attribute must be Python integer. This attribute
1744 controls the order of execution in relation to other frame filters.
1745 There are no imposed limits on the range of @code{priority} other than
1746 it must be a valid integer. The higher the @code{priority} attribute,
1747 the sooner the frame filter will be executed in relation to other
1748 frame filters. Although @code{priority} can be negative, it is
1749 recommended practice to assume zero is the lowest priority that a
1750 frame filter can be assigned. Frame filters that have the same
1751 priority are executed in unsorted order in that priority slot. This
1752 attribute is mandatory.
1755 @node Frame Decorator API
1756 @subsubsection Decorating Frames.
1757 @cindex frame decorator api
1759 Frame decorators are sister objects to frame filters (@pxref{Frame
1760 Filter API}). Frame decorators are applied by a frame filter and can
1761 only be used in conjunction with frame filters.
1763 The purpose of a frame decorator is to customize the printed content
1764 of each @code{gdb.Frame} in commands where frame filters are executed.
1765 This concept is called decorating a frame. Frame decorators decorate
1766 a @code{gdb.Frame} with Python code contained within each API call.
1767 This separates the actual data contained in a @code{gdb.Frame} from
1768 the decorated data produced by a frame decorator. This abstraction is
1769 necessary to maintain integrity of the data contained in each
1772 Frame decorators have a mandatory interface, defined below.
1774 @value{GDBN} already contains a frame decorator called
1775 @code{FrameDecorator}. This contains substantial amounts of
1776 boilerplate code to decorate the content of a @code{gdb.Frame}. It is
1777 recommended that other frame decorators inherit and extend this
1778 object, and only to override the methods needed.
1780 @defun FrameDecorator.elided (self)
1782 The @code{elided} method groups frames together in a hierarchical
1783 system. An example would be an interpreter, where multiple low-level
1784 frames make up a single call in the interpreted language. In this
1785 example, the frame filter would elide the low-level frames and present
1786 a single high-level frame, representing the call in the interpreted
1787 language, to the user.
1789 The @code{elided} function must return an iterable and this iterable
1790 must contain the frames that are being elided wrapped in a suitable
1791 frame decorator. If no frames are being elided this function may
1792 return an empty iterable, or @code{None}. Elided frames are indented
1793 from normal frames in a @code{CLI} backtrace, or in the case of
1794 @code{GDB/MI}, are placed in the @code{children} field of the eliding
1797 It is the frame filter's task to also filter out the elided frames from
1798 the source iterator. This will avoid printing the frame twice.
1801 @defun FrameDecorator.function (self)
1803 This method returns the name of the function in the frame that is to
1806 This method must return a Python string describing the function, or
1809 If this function returns @code{None}, @value{GDBN} will not print any
1810 data for this field.
1813 @defun FrameDecorator.address (self)
1815 This method returns the address of the frame that is to be printed.
1817 This method must return a Python numeric integer type of sufficient
1818 size to describe the address of the frame, or @code{None}.
1820 If this function returns a @code{None}, @value{GDBN} will not print
1821 any data for this field.
1824 @defun FrameDecorator.filename (self)
1826 This method returns the filename and path associated with this frame.
1828 This method must return a Python string containing the filename and
1829 the path to the object file backing the frame, or @code{None}.
1831 If this function returns a @code{None}, @value{GDBN} will not print
1832 any data for this field.
1835 @defun FrameDecorator.line (self):
1837 This method returns the line number associated with the current
1838 position within the function addressed by this frame.
1840 This method must return a Python integer type, or @code{None}.
1842 If this function returns a @code{None}, @value{GDBN} will not print
1843 any data for this field.
1846 @defun FrameDecorator.frame_args (self)
1849 This method must return an iterable, or @code{None}. Returning an
1850 empty iterable, or @code{None} means frame arguments will not be
1851 printed for this frame. This iterable must contain objects that
1852 implement two methods, described here.
1854 This object must implement a @code{argument} method which takes a
1855 single @code{self} parameter and must return a @code{gdb.Symbol}
1856 (@pxref{Symbols In Python}), or a Python string. The object must also
1857 implement a @code{value} method which takes a single @code{self}
1858 parameter and must return a @code{gdb.Value} (@pxref{Values From
1859 Inferior}), a Python value, or @code{None}. If the @code{value}
1860 method returns @code{None}, and the @code{argument} method returns a
1861 @code{gdb.Symbol}, @value{GDBN} will look-up and print the value of
1862 the @code{gdb.Symbol} automatically.
1867 class SymValueWrapper():
1869 def __init__(self, symbol, value):
1879 class SomeFrameDecorator()
1882 def frame_args(self):
1885 block = self.inferior_frame.block()
1889 # Iterate over all symbols in a block. Only add
1890 # symbols that are arguments.
1892 if not sym.is_argument:
1894 args.append(SymValueWrapper(sym,None))
1896 # Add example synthetic argument.
1897 args.append(SymValueWrapper(``foo'', 42))
1903 @defun FrameDecorator.frame_locals (self)
1905 This method must return an iterable or @code{None}. Returning an
1906 empty iterable, or @code{None} means frame local arguments will not be
1907 printed for this frame.
1909 The object interface, the description of the various strategies for
1910 reading frame locals, and the example are largely similar to those
1911 described in the @code{frame_args} function, (@pxref{frame_args,,The
1912 frame filter frame_args function}). Below is a modified example:
1915 class SomeFrameDecorator()
1918 def frame_locals(self):
1921 block = self.inferior_frame.block()
1925 # Iterate over all symbols in a block. Add all
1926 # symbols, except arguments.
1930 vars.append(SymValueWrapper(sym,None))
1932 # Add an example of a synthetic local variable.
1933 vars.append(SymValueWrapper(``bar'', 99))
1939 @defun FrameDecorator.inferior_frame (self):
1941 This method must return the underlying @code{gdb.Frame} that this
1942 frame decorator is decorating. @value{GDBN} requires the underlying
1943 frame for internal frame information to determine how to print certain
1944 values when printing a frame.
1947 @node Writing a Frame Filter
1948 @subsubsection Writing a Frame Filter
1949 @cindex writing a frame filter
1951 There are three basic elements that a frame filter must implement: it
1952 must correctly implement the documented interface (@pxref{Frame Filter
1953 API}), it must register itself with @value{GDBN}, and finally, it must
1954 decide if it is to work on the data provided by @value{GDBN}. In all
1955 cases, whether it works on the iterator or not, each frame filter must
1956 return an iterator. A bare-bones frame filter follows the pattern in
1957 the following example.
1962 class FrameFilter():
1965 # Frame filter attribute creation.
1967 # 'name' is the name of the filter that GDB will display.
1969 # 'priority' is the priority of the filter relative to other
1972 # 'enabled' is a boolean that indicates whether this filter is
1973 # enabled and should be executed.
1979 # Register this frame filter with the global frame_filters
1981 gdb.frame_filters[self.name] = self
1983 def filter(self, frame_iter):
1984 # Just return the iterator.
1988 The frame filter in the example above implements the three
1989 requirements for all frame filters. It implements the API, self
1990 registers, and makes a decision on the iterator (in this case, it just
1991 returns the iterator untouched).
1993 The first step is attribute creation and assignment, and as shown in
1994 the comments the filter assigns the following attributes: @code{name},
1995 @code{priority} and whether the filter should be enabled with the
1996 @code{enabled} attribute.
1998 The second step is registering the frame filter with the dictionary or
1999 dictionaries that the frame filter has interest in. As shown in the
2000 comments, this filter just registers itself with the global dictionary
2001 @code{gdb.frame_filters}. As noted earlier, @code{gdb.frame_filters}
2002 is a dictionary that is initialized in the @code{gdb} module when
2003 @value{GDBN} starts. What dictionary a filter registers with is an
2004 important consideration. Generally, if a filter is specific to a set
2005 of code, it should be registered either in the @code{objfile} or
2006 @code{progspace} dictionaries as they are specific to the program
2007 currently loaded in @value{GDBN}. The global dictionary is always
2008 present in @value{GDBN} and is never unloaded. Any filters registered
2009 with the global dictionary will exist until @value{GDBN} exits. To
2010 avoid filters that may conflict, it is generally better to register
2011 frame filters against the dictionaries that more closely align with
2012 the usage of the filter currently in question. @xref{Python
2013 Auto-loading}, for further information on auto-loading Python scripts.
2015 @value{GDBN} takes a hands-off approach to frame filter registration,
2016 therefore it is the frame filter's responsibility to ensure
2017 registration has occurred, and that any exceptions are handled
2018 appropriately. In particular, you may wish to handle exceptions
2019 relating to Python dictionary key uniqueness. It is mandatory that
2020 the dictionary key is the same as frame filter's @code{name}
2021 attribute. When a user manages frame filters (@pxref{Frame Filter
2022 Management}), the names @value{GDBN} will display are those contained
2023 in the @code{name} attribute.
2025 The final step of this example is the implementation of the
2026 @code{filter} method. As shown in the example comments, we define the
2027 @code{filter} method and note that the method must take an iterator,
2028 and also must return an iterator. In this bare-bones example, the
2029 frame filter is not very useful as it just returns the iterator
2030 untouched. However this is a valid operation for frame filters that
2031 have the @code{enabled} attribute set, but decide not to operate on
2034 In the next example, the frame filter operates on all frames and
2035 utilizes a frame decorator to perform some work on the frames.
2036 @xref{Frame Decorator API}, for further information on the frame
2037 decorator interface.
2039 This example works on inlined frames. It highlights frames which are
2040 inlined by tagging them with an ``[inlined]'' tag. By applying a
2041 frame decorator to all frames with the Python @code{itertools imap}
2042 method, the example defers actions to the frame decorator. Frame
2043 decorators are only processed when @value{GDBN} prints the backtrace.
2045 This introduces a new decision making topic: whether to perform
2046 decision making operations at the filtering step, or at the printing
2047 step. In this example's approach, it does not perform any filtering
2048 decisions at the filtering step beyond mapping a frame decorator to
2049 each frame. This allows the actual decision making to be performed
2050 when each frame is printed. This is an important consideration, and
2051 well worth reflecting upon when designing a frame filter. An issue
2052 that frame filters should avoid is unwinding the stack if possible.
2053 Some stacks can run very deep, into the tens of thousands in some
2054 cases. To search every frame to determine if it is inlined ahead of
2055 time may be too expensive at the filtering step. The frame filter
2056 cannot know how many frames it has to iterate over, and it would have
2057 to iterate through them all. This ends up duplicating effort as
2058 @value{GDBN} performs this iteration when it prints the frames.
2060 In this example decision making can be deferred to the printing step.
2061 As each frame is printed, the frame decorator can examine each frame
2062 in turn when @value{GDBN} iterates. From a performance viewpoint,
2063 this is the most appropriate decision to make as it avoids duplicating
2064 the effort that the printing step would undertake anyway. Also, if
2065 there are many frame filters unwinding the stack during filtering, it
2066 can substantially delay the printing of the backtrace which will
2067 result in large memory usage, and a poor user experience.
2070 class InlineFilter():
2073 self.name = "InlinedFrameFilter"
2076 gdb.frame_filters[self.name] = self
2078 def filter(self, frame_iter):
2079 frame_iter = itertools.imap(InlinedFrameDecorator,
2084 This frame filter is somewhat similar to the earlier example, except
2085 that the @code{filter} method applies a frame decorator object called
2086 @code{InlinedFrameDecorator} to each element in the iterator. The
2087 @code{imap} Python method is light-weight. It does not proactively
2088 iterate over the iterator, but rather creates a new iterator which
2089 wraps the existing one.
2091 Below is the frame decorator for this example.
2094 class InlinedFrameDecorator(FrameDecorator):
2096 def __init__(self, fobj):
2097 super(InlinedFrameDecorator, self).__init__(fobj)
2100 frame = fobj.inferior_frame()
2101 name = str(frame.name())
2103 if frame.type() == gdb.INLINE_FRAME:
2104 name = name + " [inlined]"
2109 This frame decorator only defines and overrides the @code{function}
2110 method. It lets the supplied @code{FrameDecorator}, which is shipped
2111 with @value{GDBN}, perform the other work associated with printing
2114 The combination of these two objects create this output from a
2118 #0 0x004004e0 in bar () at inline.c:11
2119 #1 0x00400566 in max [inlined] (b=6, a=12) at inline.c:21
2120 #2 0x00400566 in main () at inline.c:31
2123 So in the case of this example, a frame decorator is applied to all
2124 frames, regardless of whether they may be inlined or not. As
2125 @value{GDBN} iterates over the iterator produced by the frame filters,
2126 @value{GDBN} executes each frame decorator which then makes a decision
2127 on what to print in the @code{function} callback. Using a strategy
2128 like this is a way to defer decisions on the frame content to printing
2131 @subheading Eliding Frames
2133 It might be that the above example is not desirable for representing
2134 inlined frames, and a hierarchical approach may be preferred. If we
2135 want to hierarchically represent frames, the @code{elided} frame
2136 decorator interface might be preferable.
2138 This example approaches the issue with the @code{elided} method. This
2139 example is quite long, but very simplistic. It is out-of-scope for
2140 this section to write a complete example that comprehensively covers
2141 all approaches of finding and printing inlined frames. However, this
2142 example illustrates the approach an author might use.
2144 This example comprises of three sections.
2147 class InlineFrameFilter():
2150 self.name = "InlinedFrameFilter"
2153 gdb.frame_filters[self.name] = self
2155 def filter(self, frame_iter):
2156 return ElidingInlineIterator(frame_iter)
2159 This frame filter is very similar to the other examples. The only
2160 difference is this frame filter is wrapping the iterator provided to
2161 it (@code{frame_iter}) with a custom iterator called
2162 @code{ElidingInlineIterator}. This again defers actions to when
2163 @value{GDBN} prints the backtrace, as the iterator is not traversed
2166 The iterator for this example is as follows. It is in this section of
2167 the example where decisions are made on the content of the backtrace.
2170 class ElidingInlineIterator:
2171 def __init__(self, ii):
2172 self.input_iterator = ii
2178 frame = next(self.input_iterator)
2180 if frame.inferior_frame().type() != gdb.INLINE_FRAME:
2184 eliding_frame = next(self.input_iterator)
2185 except StopIteration:
2187 return ElidingFrameDecorator(eliding_frame, [frame])
2190 This iterator implements the Python iterator protocol. When the
2191 @code{next} function is called (when @value{GDBN} prints each frame),
2192 the iterator checks if this frame decorator, @code{frame}, is wrapping
2193 an inlined frame. If it is not, it returns the existing frame decorator
2194 untouched. If it is wrapping an inlined frame, it assumes that the
2195 inlined frame was contained within the next oldest frame,
2196 @code{eliding_frame}, which it fetches. It then creates and returns a
2197 frame decorator, @code{ElidingFrameDecorator}, which contains both the
2198 elided frame, and the eliding frame.
2201 class ElidingInlineDecorator(FrameDecorator):
2203 def __init__(self, frame, elided_frames):
2204 super(ElidingInlineDecorator, self).__init__(frame)
2206 self.elided_frames = elided_frames
2209 return iter(self.elided_frames)
2212 This frame decorator overrides one function and returns the inlined
2213 frame in the @code{elided} method. As before it lets
2214 @code{FrameDecorator} do the rest of the work involved in printing
2215 this frame. This produces the following output.
2218 #0 0x004004e0 in bar () at inline.c:11
2219 #2 0x00400529 in main () at inline.c:25
2220 #1 0x00400529 in max (b=6, a=12) at inline.c:15
2223 In that output, @code{max} which has been inlined into @code{main} is
2224 printed hierarchically. Another approach would be to combine the
2225 @code{function} method, and the @code{elided} method to both print a
2226 marker in the inlined frame, and also show the hierarchical
2229 @node Unwinding Frames in Python
2230 @subsubsection Unwinding Frames in Python
2231 @cindex unwinding frames in Python
2233 In @value{GDBN} terminology ``unwinding'' is the process of finding
2234 the previous frame (that is, caller's) from the current one. An
2235 unwinder has three methods. The first one checks if it can handle
2236 given frame (``sniff'' it). For the frames it can sniff an unwinder
2237 provides two additional methods: it can return frame's ID, and it can
2238 fetch registers from the previous frame. A running @value{GDBN}
2239 mantains a list of the unwinders and calls each unwinder's sniffer in
2240 turn until it finds the one that recognizes the current frame. There
2241 is an API to register an unwinder.
2243 The unwinders that come with @value{GDBN} handle standard frames.
2244 However, mixed language applications (for example, an application
2245 running Java Virtual Machine) sometimes use frame layouts that cannot
2246 be handled by the @value{GDBN} unwinders. You can write Python code
2247 that can handle such custom frames.
2249 You implement a frame unwinder in Python as a class with which has two
2250 attributes, @code{name} and @code{enabled}, with obvious meanings, and
2251 a single method @code{__call__}, which examines a given frame and
2252 returns an object (an instance of @code{gdb.UnwindInfo class)}
2253 describing it. If an unwinder does not recognize a frame, it should
2254 return @code{None}. The code in @value{GDBN} that enables writing
2255 unwinders in Python uses this object to return frame's ID and previous
2256 frame registers when @value{GDBN} core asks for them.
2258 @subheading Unwinder Input
2260 An object passed to an unwinder (a @code{gdb.PendingFrame} instance)
2261 provides a method to read frame's registers:
2263 @defun PendingFrame.read_register (reg)
2264 This method returns the contents of the register @var{regn} in the
2265 frame as a @code{gdb.Value} object. @var{reg} can be either a
2266 register number or a register name; the values are platform-specific.
2267 They are usually found in the corresponding
2268 @file{@var{platform}-tdep.h} file in the @value{GDBN} source tree.
2271 It also provides a factory method to create a @code{gdb.UnwindInfo}
2272 instance to be returned to @value{GDBN}:
2274 @defun PendingFrame.create_unwind_info (frame_id)
2275 Returns a new @code{gdb.UnwindInfo} instance identified by given
2276 @var{frame_id}. The argument is used to build @value{GDBN}'s frame ID
2277 using one of functions provided by @value{GDBN}. @var{frame_id}'s attributes
2278 determine which function will be used, as follows:
2281 @item sp, pc, special
2282 @code{frame_id_build_special (@var{frame_id}.sp, @var{frame_id}.pc, @var{frame_id}.special)}
2285 @code{frame_id_build (@var{frame_id}.sp, @var{frame_id}.pc)}
2287 This is the most common case.
2290 @code{frame_id_build_wild (@var{frame_id}.sp)}
2292 The attribute values should be @code{gdb.Value}
2296 @subheading Unwinder Output: UnwindInfo
2298 Use @code{PendingFrame.create_unwind_info} method described above to
2299 create a @code{gdb.UnwindInfo} instance. Use the following method to
2300 specify caller registers that have been saved in this frame:
2302 @defun gdb.UnwindInfo.add_saved_register (reg, value)
2303 @var{reg} identifies the register. It can be a number or a name, just
2304 as for the @code{PendingFrame.read_register} method above.
2305 @var{value} is a register value (a @code{gdb.Value} object).
2308 @subheading Unwinder Skeleton Code
2310 @value{GDBN} comes with the module containing the base @code{Unwinder}
2311 class. Derive your unwinder class from it and structure the code as
2315 from gdb.unwinders import Unwinder
2317 class FrameId(object):
2318 def __init__(self, sp, pc):
2323 class MyUnwinder(Unwinder):
2325 supe(MyUnwinder, self).__init___(<expects unwinder name argument>)
2327 def __call__(pending_frame):
2328 if not <we recognize frame>:
2330 # Create UnwindInfo. Usually the frame is identified by the stack
2331 # pointer and the program counter.
2332 sp = pending_frame.read_register(<SP number>)
2333 pc = pending_frame.read_register(<PC number>)
2334 unwind_info = pending_frame.create_unwind_info(FrameId(sp, pc))
2336 # Find the values of the registers in the caller's frame and
2337 # save them in the result:
2338 unwind_info.add_saved_register(<register>, <value>)
2341 # Return the result:
2346 @subheading Registering a Unwinder
2348 An object file, a program space, and the @value{GDBN} proper can have
2349 unwinders registered with it.
2351 The @code{gdb.unwinders} module provides the function to register a
2354 @defun gdb.unwinder.register_unwinder (locus, unwinder, replace=False)
2355 @var{locus} is specifies an object file or a program space to which
2356 @var{unwinder} is added. Passing @code{None} or @code{gdb} adds
2357 @var{unwinder} to the @value{GDBN}'s global unwinder list. The newly
2358 added @var{unwinder} will be called before any other unwinder from the
2359 same locus. Two unwinders in the same locus cannot have the same
2360 name. An attempt to add a unwinder with already existing name raises
2361 an exception unless @var{replace} is @code{True}, in which case the
2362 old unwinder is deleted.
2365 @subheading Unwinder Precedence
2367 @value{GDBN} first calls the unwinders from all the object files in no
2368 particular order, then the unwinders from the current program space,
2369 and finally the unwinders from @value{GDBN}.
2371 @node Xmethods In Python
2372 @subsubsection Xmethods In Python
2373 @cindex xmethods in Python
2375 @dfn{Xmethods} are additional methods or replacements for existing
2376 methods of a C@t{++} class. This feature is useful for those cases
2377 where a method defined in C@t{++} source code could be inlined or
2378 optimized out by the compiler, making it unavailable to @value{GDBN}.
2379 For such cases, one can define an xmethod to serve as a replacement
2380 for the method defined in the C@t{++} source code. @value{GDBN} will
2381 then invoke the xmethod, instead of the C@t{++} method, to
2382 evaluate expressions. One can also use xmethods when debugging
2383 with core files. Moreover, when debugging live programs, invoking an
2384 xmethod need not involve running the inferior (which can potentially
2385 perturb its state). Hence, even if the C@t{++} method is available, it
2386 is better to use its replacement xmethod if one is defined.
2388 The xmethods feature in Python is available via the concepts of an
2389 @dfn{xmethod matcher} and an @dfn{xmethod worker}. To
2390 implement an xmethod, one has to implement a matcher and a
2391 corresponding worker for it (more than one worker can be
2392 implemented, each catering to a different overloaded instance of the
2393 method). Internally, @value{GDBN} invokes the @code{match} method of a
2394 matcher to match the class type and method name. On a match, the
2395 @code{match} method returns a list of matching @emph{worker} objects.
2396 Each worker object typically corresponds to an overloaded instance of
2397 the xmethod. They implement a @code{get_arg_types} method which
2398 returns a sequence of types corresponding to the arguments the xmethod
2399 requires. @value{GDBN} uses this sequence of types to perform
2400 overload resolution and picks a winning xmethod worker. A winner
2401 is also selected from among the methods @value{GDBN} finds in the
2402 C@t{++} source code. Next, the winning xmethod worker and the
2403 winning C@t{++} method are compared to select an overall winner. In
2404 case of a tie between a xmethod worker and a C@t{++} method, the
2405 xmethod worker is selected as the winner. That is, if a winning
2406 xmethod worker is found to be equivalent to the winning C@t{++}
2407 method, then the xmethod worker is treated as a replacement for
2408 the C@t{++} method. @value{GDBN} uses the overall winner to invoke the
2409 method. If the winning xmethod worker is the overall winner, then
2410 the corresponding xmethod is invoked via the @code{__call__} method
2411 of the worker object.
2413 If one wants to implement an xmethod as a replacement for an
2414 existing C@t{++} method, then they have to implement an equivalent
2415 xmethod which has exactly the same name and takes arguments of
2416 exactly the same type as the C@t{++} method. If the user wants to
2417 invoke the C@t{++} method even though a replacement xmethod is
2418 available for that method, then they can disable the xmethod.
2420 @xref{Xmethod API}, for API to implement xmethods in Python.
2421 @xref{Writing an Xmethod}, for implementing xmethods in Python.
2424 @subsubsection Xmethod API
2427 The @value{GDBN} Python API provides classes, interfaces and functions
2428 to implement, register and manipulate xmethods.
2429 @xref{Xmethods In Python}.
2431 An xmethod matcher should be an instance of a class derived from
2432 @code{XMethodMatcher} defined in the module @code{gdb.xmethod}, or an
2433 object with similar interface and attributes. An instance of
2434 @code{XMethodMatcher} has the following attributes:
2437 The name of the matcher.
2441 A boolean value indicating whether the matcher is enabled or disabled.
2445 A list of named methods managed by the matcher. Each object in the list
2446 is an instance of the class @code{XMethod} defined in the module
2447 @code{gdb.xmethod}, or any object with the following attributes:
2452 Name of the xmethod which should be unique for each xmethod
2453 managed by the matcher.
2456 A boolean value indicating whether the xmethod is enabled or
2461 The class @code{XMethod} is a convenience class with same
2462 attributes as above along with the following constructor:
2464 @defun XMethod.__init__ (self, name)
2465 Constructs an enabled xmethod with name @var{name}.
2470 The @code{XMethodMatcher} class has the following methods:
2472 @defun XMethodMatcher.__init__ (self, name)
2473 Constructs an enabled xmethod matcher with name @var{name}. The
2474 @code{methods} attribute is initialized to @code{None}.
2477 @defun XMethodMatcher.match (self, class_type, method_name)
2478 Derived classes should override this method. It should return a
2479 xmethod worker object (or a sequence of xmethod worker
2480 objects) matching the @var{class_type} and @var{method_name}.
2481 @var{class_type} is a @code{gdb.Type} object, and @var{method_name}
2482 is a string value. If the matcher manages named methods as listed in
2483 its @code{methods} attribute, then only those worker objects whose
2484 corresponding entries in the @code{methods} list are enabled should be
2488 An xmethod worker should be an instance of a class derived from
2489 @code{XMethodWorker} defined in the module @code{gdb.xmethod},
2490 or support the following interface:
2492 @defun XMethodWorker.get_arg_types (self)
2493 This method returns a sequence of @code{gdb.Type} objects corresponding
2494 to the arguments that the xmethod takes. It can return an empty
2495 sequence or @code{None} if the xmethod does not take any arguments.
2496 If the xmethod takes a single argument, then a single
2497 @code{gdb.Type} object corresponding to it can be returned.
2500 @defun XMethodWorker.get_result_type (self, *args)
2501 This method returns a @code{gdb.Type} object representing the type
2502 of the result of invoking this xmethod.
2503 The @var{args} argument is the same tuple of arguments that would be
2504 passed to the @code{__call__} method of this worker.
2507 @defun XMethodWorker.__call__ (self, *args)
2508 This is the method which does the @emph{work} of the xmethod. The
2509 @var{args} arguments is the tuple of arguments to the xmethod. Each
2510 element in this tuple is a gdb.Value object. The first element is
2511 always the @code{this} pointer value.
2514 For @value{GDBN} to lookup xmethods, the xmethod matchers
2515 should be registered using the following function defined in the module
2518 @defun register_xmethod_matcher (locus, matcher, replace=False)
2519 The @code{matcher} is registered with @code{locus}, replacing an
2520 existing matcher with the same name as @code{matcher} if
2521 @code{replace} is @code{True}. @code{locus} can be a
2522 @code{gdb.Objfile} object (@pxref{Objfiles In Python}), or a
2523 @code{gdb.Progspace} object (@pxref{Progspaces In Python}), or
2524 @code{None}. If it is @code{None}, then @code{matcher} is registered
2528 @node Writing an Xmethod
2529 @subsubsection Writing an Xmethod
2530 @cindex writing xmethods in Python
2532 Implementing xmethods in Python will require implementing xmethod
2533 matchers and xmethod workers (@pxref{Xmethods In Python}). Consider
2534 the following C@t{++} class:
2540 MyClass (int a) : a_(a) @{ @}
2542 int geta (void) @{ return a_; @}
2543 int operator+ (int b);
2550 MyClass::operator+ (int b)
2557 Let us define two xmethods for the class @code{MyClass}, one
2558 replacing the method @code{geta}, and another adding an overloaded
2559 flavor of @code{operator+} which takes a @code{MyClass} argument (the
2560 C@t{++} code above already has an overloaded @code{operator+}
2561 which takes an @code{int} argument). The xmethod matcher can be
2565 class MyClass_geta(gdb.xmethod.XMethod):
2567 gdb.xmethod.XMethod.__init__(self, 'geta')
2569 def get_worker(self, method_name):
2570 if method_name == 'geta':
2571 return MyClassWorker_geta()
2574 class MyClass_sum(gdb.xmethod.XMethod):
2576 gdb.xmethod.XMethod.__init__(self, 'sum')
2578 def get_worker(self, method_name):
2579 if method_name == 'operator+':
2580 return MyClassWorker_plus()
2583 class MyClassMatcher(gdb.xmethod.XMethodMatcher):
2585 gdb.xmethod.XMethodMatcher.__init__(self, 'MyClassMatcher')
2586 # List of methods 'managed' by this matcher
2587 self.methods = [MyClass_geta(), MyClass_sum()]
2589 def match(self, class_type, method_name):
2590 if class_type.tag != 'MyClass':
2593 for method in self.methods:
2595 worker = method.get_worker(method_name)
2597 workers.append(worker)
2603 Notice that the @code{match} method of @code{MyClassMatcher} returns
2604 a worker object of type @code{MyClassWorker_geta} for the @code{geta}
2605 method, and a worker object of type @code{MyClassWorker_plus} for the
2606 @code{operator+} method. This is done indirectly via helper classes
2607 derived from @code{gdb.xmethod.XMethod}. One does not need to use the
2608 @code{methods} attribute in a matcher as it is optional. However, if a
2609 matcher manages more than one xmethod, it is a good practice to list the
2610 xmethods in the @code{methods} attribute of the matcher. This will then
2611 facilitate enabling and disabling individual xmethods via the
2612 @code{enable/disable} commands. Notice also that a worker object is
2613 returned only if the corresponding entry in the @code{methods} attribute
2614 of the matcher is enabled.
2616 The implementation of the worker classes returned by the matcher setup
2617 above is as follows:
2620 class MyClassWorker_geta(gdb.xmethod.XMethodWorker):
2621 def get_arg_types(self):
2624 def get_result_type(self, obj):
2625 return gdb.lookup_type('int')
2627 def __call__(self, obj):
2631 class MyClassWorker_plus(gdb.xmethod.XMethodWorker):
2632 def get_arg_types(self):
2633 return gdb.lookup_type('MyClass')
2635 def get_result_type(self, obj):
2636 return gdb.lookup_type('int')
2638 def __call__(self, obj, other):
2639 return obj['a_'] + other['a_']
2642 For @value{GDBN} to actually lookup a xmethod, it has to be
2643 registered with it. The matcher defined above is registered with
2644 @value{GDBN} globally as follows:
2647 gdb.xmethod.register_xmethod_matcher(None, MyClassMatcher())
2650 If an object @code{obj} of type @code{MyClass} is initialized in C@t{++}
2658 then, after loading the Python script defining the xmethod matchers
2659 and workers into @code{GDBN}, invoking the method @code{geta} or using
2660 the operator @code{+} on @code{obj} will invoke the xmethods
2671 Consider another example with a C++ template class:
2678 MyTemplate () : dsize_(10), data_ (new T [10]) @{ @}
2679 ~MyTemplate () @{ delete [] data_; @}
2681 int footprint (void)
2683 return sizeof (T) * dsize_ + sizeof (MyTemplate<T>);
2692 Let us implement an xmethod for the above class which serves as a
2693 replacement for the @code{footprint} method. The full code listing
2694 of the xmethod workers and xmethod matchers is as follows:
2697 class MyTemplateWorker_footprint(gdb.xmethod.XMethodWorker):
2698 def __init__(self, class_type):
2699 self.class_type = class_type
2701 def get_arg_types(self):
2704 def get_result_type(self):
2705 return gdb.lookup_type('int')
2707 def __call__(self, obj):
2708 return (self.class_type.sizeof +
2710 self.class_type.template_argument(0).sizeof)
2713 class MyTemplateMatcher_footprint(gdb.xmethod.XMethodMatcher):
2715 gdb.xmethod.XMethodMatcher.__init__(self, 'MyTemplateMatcher')
2717 def match(self, class_type, method_name):
2718 if (re.match('MyTemplate<[ \t\n]*[_a-zA-Z][ _a-zA-Z0-9]*>',
2720 method_name == 'footprint'):
2721 return MyTemplateWorker_footprint(class_type)
2724 Notice that, in this example, we have not used the @code{methods}
2725 attribute of the matcher as the matcher manages only one xmethod. The
2726 user can enable/disable this xmethod by enabling/disabling the matcher
2729 @node Inferiors In Python
2730 @subsubsection Inferiors In Python
2731 @cindex inferiors in Python
2733 @findex gdb.Inferior
2734 Programs which are being run under @value{GDBN} are called inferiors
2735 (@pxref{Inferiors and Programs}). Python scripts can access
2736 information about and manipulate inferiors controlled by @value{GDBN}
2737 via objects of the @code{gdb.Inferior} class.
2739 The following inferior-related functions are available in the @code{gdb}
2742 @defun gdb.inferiors ()
2743 Return a tuple containing all inferior objects.
2746 @defun gdb.selected_inferior ()
2747 Return an object representing the current inferior.
2750 A @code{gdb.Inferior} object has the following attributes:
2752 @defvar Inferior.num
2753 ID of inferior, as assigned by GDB.
2756 @defvar Inferior.pid
2757 Process ID of the inferior, as assigned by the underlying operating
2761 @defvar Inferior.was_attached
2762 Boolean signaling whether the inferior was created using `attach', or
2763 started by @value{GDBN} itself.
2766 A @code{gdb.Inferior} object has the following methods:
2768 @defun Inferior.is_valid ()
2769 Returns @code{True} if the @code{gdb.Inferior} object is valid,
2770 @code{False} if not. A @code{gdb.Inferior} object will become invalid
2771 if the inferior no longer exists within @value{GDBN}. All other
2772 @code{gdb.Inferior} methods will throw an exception if it is invalid
2773 at the time the method is called.
2776 @defun Inferior.threads ()
2777 This method returns a tuple holding all the threads which are valid
2778 when it is called. If there are no valid threads, the method will
2779 return an empty tuple.
2782 @findex Inferior.read_memory
2783 @defun Inferior.read_memory (address, length)
2784 Read @var{length} addressable memory units from the inferior, starting at
2785 @var{address}. Returns a buffer object, which behaves much like an array
2786 or a string. It can be modified and given to the
2787 @code{Inferior.write_memory} function. In Python 3, the return
2788 value is a @code{memoryview} object.
2791 @findex Inferior.write_memory
2792 @defun Inferior.write_memory (address, buffer @r{[}, length@r{]})
2793 Write the contents of @var{buffer} to the inferior, starting at
2794 @var{address}. The @var{buffer} parameter must be a Python object
2795 which supports the buffer protocol, i.e., a string, an array or the
2796 object returned from @code{Inferior.read_memory}. If given, @var{length}
2797 determines the number of addressable memory units from @var{buffer} to be
2801 @findex gdb.search_memory
2802 @defun Inferior.search_memory (address, length, pattern)
2803 Search a region of the inferior memory starting at @var{address} with
2804 the given @var{length} using the search pattern supplied in
2805 @var{pattern}. The @var{pattern} parameter must be a Python object
2806 which supports the buffer protocol, i.e., a string, an array or the
2807 object returned from @code{gdb.read_memory}. Returns a Python @code{Long}
2808 containing the address where the pattern was found, or @code{None} if
2809 the pattern could not be found.
2812 @findex Inferior.thread_from_thread_handle
2813 @defun Inferior.thread_from_thread_handle (thread_handle)
2814 Return the thread object corresponding to @var{thread_handle}, a thread
2815 library specific data structure such as @code{pthread_t} for pthreads
2816 library implementations.
2819 @node Events In Python
2820 @subsubsection Events In Python
2821 @cindex inferior events in Python
2823 @value{GDBN} provides a general event facility so that Python code can be
2824 notified of various state changes, particularly changes that occur in
2827 An @dfn{event} is just an object that describes some state change. The
2828 type of the object and its attributes will vary depending on the details
2829 of the change. All the existing events are described below.
2831 In order to be notified of an event, you must register an event handler
2832 with an @dfn{event registry}. An event registry is an object in the
2833 @code{gdb.events} module which dispatches particular events. A registry
2834 provides methods to register and unregister event handlers:
2836 @defun EventRegistry.connect (object)
2837 Add the given callable @var{object} to the registry. This object will be
2838 called when an event corresponding to this registry occurs.
2841 @defun EventRegistry.disconnect (object)
2842 Remove the given @var{object} from the registry. Once removed, the object
2843 will no longer receive notifications of events.
2849 def exit_handler (event):
2850 print "event type: exit"
2851 print "exit code: %d" % (event.exit_code)
2853 gdb.events.exited.connect (exit_handler)
2856 In the above example we connect our handler @code{exit_handler} to the
2857 registry @code{events.exited}. Once connected, @code{exit_handler} gets
2858 called when the inferior exits. The argument @dfn{event} in this example is
2859 of type @code{gdb.ExitedEvent}. As you can see in the example the
2860 @code{ExitedEvent} object has an attribute which indicates the exit code of
2863 The following is a listing of the event registries that are available and
2864 details of the events they emit:
2869 Emits @code{gdb.ThreadEvent}.
2871 Some events can be thread specific when @value{GDBN} is running in non-stop
2872 mode. When represented in Python, these events all extend
2873 @code{gdb.ThreadEvent}. Note, this event is not emitted directly; instead,
2874 events which are emitted by this or other modules might extend this event.
2875 Examples of these events are @code{gdb.BreakpointEvent} and
2876 @code{gdb.ContinueEvent}.
2878 @defvar ThreadEvent.inferior_thread
2879 In non-stop mode this attribute will be set to the specific thread which was
2880 involved in the emitted event. Otherwise, it will be set to @code{None}.
2883 Emits @code{gdb.ContinueEvent} which extends @code{gdb.ThreadEvent}.
2885 This event indicates that the inferior has been continued after a stop. For
2886 inherited attribute refer to @code{gdb.ThreadEvent} above.
2889 Emits @code{events.ExitedEvent} which indicates that the inferior has exited.
2890 @code{events.ExitedEvent} has two attributes:
2891 @defvar ExitedEvent.exit_code
2892 An integer representing the exit code, if available, which the inferior
2893 has returned. (The exit code could be unavailable if, for example,
2894 @value{GDBN} detaches from the inferior.) If the exit code is unavailable,
2895 the attribute does not exist.
2897 @defvar ExitedEvent.inferior
2898 A reference to the inferior which triggered the @code{exited} event.
2902 Emits @code{gdb.StopEvent} which extends @code{gdb.ThreadEvent}.
2904 Indicates that the inferior has stopped. All events emitted by this registry
2905 extend StopEvent. As a child of @code{gdb.ThreadEvent}, @code{gdb.StopEvent}
2906 will indicate the stopped thread when @value{GDBN} is running in non-stop
2907 mode. Refer to @code{gdb.ThreadEvent} above for more details.
2909 Emits @code{gdb.SignalEvent} which extends @code{gdb.StopEvent}.
2911 This event indicates that the inferior or one of its threads has received as
2912 signal. @code{gdb.SignalEvent} has the following attributes:
2914 @defvar SignalEvent.stop_signal
2915 A string representing the signal received by the inferior. A list of possible
2916 signal values can be obtained by running the command @code{info signals} in
2917 the @value{GDBN} command prompt.
2920 Also emits @code{gdb.BreakpointEvent} which extends @code{gdb.StopEvent}.
2922 @code{gdb.BreakpointEvent} event indicates that one or more breakpoints have
2923 been hit, and has the following attributes:
2925 @defvar BreakpointEvent.breakpoints
2926 A sequence containing references to all the breakpoints (type
2927 @code{gdb.Breakpoint}) that were hit.
2928 @xref{Breakpoints In Python}, for details of the @code{gdb.Breakpoint} object.
2930 @defvar BreakpointEvent.breakpoint
2931 A reference to the first breakpoint that was hit.
2932 This function is maintained for backward compatibility and is now deprecated
2933 in favor of the @code{gdb.BreakpointEvent.breakpoints} attribute.
2936 @item events.new_objfile
2937 Emits @code{gdb.NewObjFileEvent} which indicates that a new object file has
2938 been loaded by @value{GDBN}. @code{gdb.NewObjFileEvent} has one attribute:
2940 @defvar NewObjFileEvent.new_objfile
2941 A reference to the object file (@code{gdb.Objfile}) which has been loaded.
2942 @xref{Objfiles In Python}, for details of the @code{gdb.Objfile} object.
2945 @item events.clear_objfiles
2946 Emits @code{gdb.ClearObjFilesEvent} which indicates that the list of object
2947 files for a program space has been reset.
2948 @code{gdb.ClearObjFilesEvent} has one attribute:
2950 @defvar ClearObjFilesEvent.progspace
2951 A reference to the program space (@code{gdb.Progspace}) whose objfile list has
2952 been cleared. @xref{Progspaces In Python}.
2955 @item events.inferior_call_pre
2956 Emits @code{gdb.InferiorCallPreEvent} which indicates that a function in
2957 the inferior is about to be called.
2959 @defvar InferiorCallPreEvent.ptid
2960 The thread in which the call will be run.
2963 @defvar InferiorCallPreEvent.address
2964 The location of the function to be called.
2967 @item events.inferior_call_post
2968 Emits @code{gdb.InferiorCallPostEvent} which indicates that a function in
2969 the inferior has returned.
2971 @defvar InferiorCallPostEvent.ptid
2972 The thread in which the call was run.
2975 @defvar InferiorCallPostEvent.address
2976 The location of the function that was called.
2979 @item events.memory_changed
2980 Emits @code{gdb.MemoryChangedEvent} which indicates that the memory of the
2981 inferior has been modified by the @value{GDBN} user, for instance via a
2982 command like @w{@code{set *addr = value}}. The event has the following
2985 @defvar MemoryChangedEvent.address
2986 The start address of the changed region.
2989 @defvar MemoryChangedEvent.length
2990 Length in bytes of the changed region.
2993 @item events.register_changed
2994 Emits @code{gdb.RegisterChangedEvent} which indicates that a register in the
2995 inferior has been modified by the @value{GDBN} user.
2997 @defvar RegisterChangedEvent.frame
2998 A gdb.Frame object representing the frame in which the register was modified.
3000 @defvar RegisterChangedEvent.regnum
3001 Denotes which register was modified.
3004 @item events.breakpoint_created
3005 This is emitted when a new breakpoint has been created. The argument
3006 that is passed is the new @code{gdb.Breakpoint} object.
3008 @item events.breakpoint_modified
3009 This is emitted when a breakpoint has been modified in some way. The
3010 argument that is passed is the new @code{gdb.Breakpoint} object.
3012 @item events.breakpoint_deleted
3013 This is emitted when a breakpoint has been deleted. The argument that
3014 is passed is the @code{gdb.Breakpoint} object. When this event is
3015 emitted, the @code{gdb.Breakpoint} object will already be in its
3016 invalid state; that is, the @code{is_valid} method will return
3019 @item events.before_prompt
3020 This event carries no payload. It is emitted each time @value{GDBN}
3021 presents a prompt to the user.
3023 @item events.new_inferior
3024 This is emitted when a new inferior is created. Note that the
3025 inferior is not necessarily running; in fact, it may not even have an
3026 associated executable.
3028 The event is of type @code{gdb.NewInferiorEvent}. This has a single
3031 @defvar NewInferiorEvent.inferior
3032 The new inferior, a @code{gdb.Inferior} object.
3035 @item events.inferior_deleted
3036 This is emitted when an inferior has been deleted. Note that this is
3037 not the same as process exit; it is notified when the inferior itself
3038 is removed, say via @code{remove-inferiors}.
3040 The event is of type @code{gdb.InferiorDeletedEvent}. This has a single
3043 @defvar NewInferiorEvent.inferior
3044 The inferior that is being removed, a @code{gdb.Inferior} object.
3047 @item events.new_thread
3048 This is emitted when @value{GDBN} notices a new thread. The event is of
3049 type @code{gdb.NewThreadEvent}, which extends @code{gdb.ThreadEvent}.
3050 This has a single attribute:
3052 @defvar NewThreadEvent.inferior_thread
3058 @node Threads In Python
3059 @subsubsection Threads In Python
3060 @cindex threads in python
3062 @findex gdb.InferiorThread
3063 Python scripts can access information about, and manipulate inferior threads
3064 controlled by @value{GDBN}, via objects of the @code{gdb.InferiorThread} class.
3066 The following thread-related functions are available in the @code{gdb}
3069 @findex gdb.selected_thread
3070 @defun gdb.selected_thread ()
3071 This function returns the thread object for the selected thread. If there
3072 is no selected thread, this will return @code{None}.
3075 A @code{gdb.InferiorThread} object has the following attributes:
3077 @defvar InferiorThread.name
3078 The name of the thread. If the user specified a name using
3079 @code{thread name}, then this returns that name. Otherwise, if an
3080 OS-supplied name is available, then it is returned. Otherwise, this
3081 returns @code{None}.
3083 This attribute can be assigned to. The new value must be a string
3084 object, which sets the new name, or @code{None}, which removes any
3085 user-specified thread name.
3088 @defvar InferiorThread.num
3089 The per-inferior number of the thread, as assigned by GDB.
3092 @defvar InferiorThread.global_num
3093 The global ID of the thread, as assigned by GDB. You can use this to
3094 make Python breakpoints thread-specific, for example
3095 (@pxref{python_breakpoint_thread,,The Breakpoint.thread attribute}).
3098 @defvar InferiorThread.ptid
3099 ID of the thread, as assigned by the operating system. This attribute is a
3100 tuple containing three integers. The first is the Process ID (PID); the second
3101 is the Lightweight Process ID (LWPID), and the third is the Thread ID (TID).
3102 Either the LWPID or TID may be 0, which indicates that the operating system
3103 does not use that identifier.
3106 @defvar InferiorThread.inferior
3107 The inferior this thread belongs to. This attribute is represented as
3108 a @code{gdb.Inferior} object. This attribute is not writable.
3111 A @code{gdb.InferiorThread} object has the following methods:
3113 @defun InferiorThread.is_valid ()
3114 Returns @code{True} if the @code{gdb.InferiorThread} object is valid,
3115 @code{False} if not. A @code{gdb.InferiorThread} object will become
3116 invalid if the thread exits, or the inferior that the thread belongs
3117 is deleted. All other @code{gdb.InferiorThread} methods will throw an
3118 exception if it is invalid at the time the method is called.
3121 @defun InferiorThread.switch ()
3122 This changes @value{GDBN}'s currently selected thread to the one represented
3126 @defun InferiorThread.is_stopped ()
3127 Return a Boolean indicating whether the thread is stopped.
3130 @defun InferiorThread.is_running ()
3131 Return a Boolean indicating whether the thread is running.
3134 @defun InferiorThread.is_exited ()
3135 Return a Boolean indicating whether the thread is exited.
3138 @node Recordings In Python
3139 @subsubsection Recordings In Python
3140 @cindex recordings in python
3142 The following recordings-related functions
3143 (@pxref{Process Record and Replay}) are available in the @code{gdb}
3146 @defun gdb.start_recording (@r{[}method@r{]}, @r{[}format@r{]})
3147 Start a recording using the given @var{method} and @var{format}. If
3148 no @var{format} is given, the default format for the recording method
3149 is used. If no @var{method} is given, the default method will be used.
3150 Returns a @code{gdb.Record} object on success. Throw an exception on
3153 The following strings can be passed as @var{method}:
3159 @code{"btrace"}: Possible values for @var{format}: @code{"pt"},
3160 @code{"bts"} or leave out for default format.
3164 @defun gdb.current_recording ()
3165 Access a currently running recording. Return a @code{gdb.Record}
3166 object on success. Return @code{None} if no recording is currently
3170 @defun gdb.stop_recording ()
3171 Stop the current recording. Throw an exception if no recording is
3172 currently active. All record objects become invalid after this call.
3175 A @code{gdb.Record} object has the following attributes:
3177 @defvar Record.method
3178 A string with the current recording method, e.g.@: @code{full} or
3182 @defvar Record.format
3183 A string with the current recording format, e.g.@: @code{bt}, @code{pts} or
3187 @defvar Record.begin
3188 A method specific instruction object representing the first instruction
3193 A method specific instruction object representing the current
3194 instruction, that is not actually part of the recording.
3197 @defvar Record.replay_position
3198 The instruction representing the current replay position. If there is
3199 no replay active, this will be @code{None}.
3202 @defvar Record.instruction_history
3203 A list with all recorded instructions.
3206 @defvar Record.function_call_history
3207 A list with all recorded function call segments.
3210 A @code{gdb.Record} object has the following methods:
3212 @defun Record.goto (instruction)
3213 Move the replay position to the given @var{instruction}.
3216 The common @code{gdb.Instruction} class that recording method specific
3217 instruction objects inherit from, has the following attributes:
3219 @defvar Instruction.pc
3220 An integer representing this instruction's address.
3223 @defvar Instruction.data
3224 A buffer with the raw instruction data. In Python 3, the return value is a
3225 @code{memoryview} object.
3228 @defvar Instruction.decoded
3229 A human readable string with the disassembled instruction.
3232 @defvar Instruction.size
3233 The size of the instruction in bytes.
3236 Additionally @code{gdb.RecordInstruction} has the following attributes:
3238 @defvar RecordInstruction.number
3239 An integer identifying this instruction. @code{number} corresponds to
3240 the numbers seen in @code{record instruction-history}
3241 (@pxref{Process Record and Replay}).
3244 @defvar RecordInstruction.sal
3245 A @code{gdb.Symtab_and_line} object representing the associated symtab
3246 and line of this instruction. May be @code{None} if no debug information is
3250 @defvar RecordInstruction.is_speculative
3251 A boolean indicating whether the instruction was executed speculatively.
3254 If an error occured during recording or decoding a recording, this error is
3255 represented by a @code{gdb.RecordGap} object in the instruction list. It has
3256 the following attributes:
3258 @defvar RecordGap.number
3259 An integer identifying this gap. @code{number} corresponds to the numbers seen
3260 in @code{record instruction-history} (@pxref{Process Record and Replay}).
3263 @defvar RecordGap.error_code
3264 A numerical representation of the reason for the gap. The value is specific to
3265 the current recording method.
3268 @defvar RecordGap.error_string
3269 A human readable string with the reason for the gap.
3272 A @code{gdb.RecordFunctionSegment} object has the following attributes:
3274 @defvar RecordFunctionSegment.number
3275 An integer identifying this function segment. @code{number} corresponds to
3276 the numbers seen in @code{record function-call-history}
3277 (@pxref{Process Record and Replay}).
3280 @defvar RecordFunctionSegment.symbol
3281 A @code{gdb.Symbol} object representing the associated symbol. May be
3282 @code{None} if no debug information is available.
3285 @defvar RecordFunctionSegment.level
3286 An integer representing the function call's stack level. May be
3287 @code{None} if the function call is a gap.
3290 @defvar RecordFunctionSegment.instructions
3291 A list of @code{gdb.RecordInstruction} or @code{gdb.RecordGap} objects
3292 associated with this function call.
3295 @defvar RecordFunctionSegment.up
3296 A @code{gdb.RecordFunctionSegment} object representing the caller's
3297 function segment. If the call has not been recorded, this will be the
3298 function segment to which control returns. If neither the call nor the
3299 return have been recorded, this will be @code{None}.
3302 @defvar RecordFunctionSegment.prev
3303 A @code{gdb.RecordFunctionSegment} object representing the previous
3304 segment of this function call. May be @code{None}.
3307 @defvar RecordFunctionSegment.next
3308 A @code{gdb.RecordFunctionSegment} object representing the next segment of
3309 this function call. May be @code{None}.
3312 The following example demonstrates the usage of these objects and
3313 functions to create a function that will rewind a record to the last
3314 time a function in a different file was executed. This would typically
3315 be used to track the execution of user provided callback functions in a
3316 library which typically are not visible in a back trace.
3320 rec = gdb.current_recording ()
3324 insn = rec.instruction_history
3329 position = insn.index (rec.replay_position)
3333 filename = insn[position].sal.symtab.fullname ()
3337 for i in reversed (insn[:position]):
3339 current = i.sal.symtab.fullname ()
3343 if filename == current:
3350 Another possible application is to write a function that counts the
3351 number of code executions in a given line range. This line range can
3352 contain parts of functions or span across several functions and is not
3353 limited to be contiguous.
3356 def countrange (filename, linerange):
3359 def filter_only (file_name):
3360 for call in gdb.current_recording ().function_call_history:
3362 if file_name in call.symbol.symtab.fullname ():
3367 for c in filter_only (filename):
3368 for i in c.instructions:
3370 if i.sal.line in linerange:
3379 @node Commands In Python
3380 @subsubsection Commands In Python
3382 @cindex commands in python
3383 @cindex python commands
3384 You can implement new @value{GDBN} CLI commands in Python. A CLI
3385 command is implemented using an instance of the @code{gdb.Command}
3386 class, most commonly using a subclass.
3388 @defun Command.__init__ (name, @var{command_class} @r{[}, @var{completer_class} @r{[}, @var{prefix}@r{]]})
3389 The object initializer for @code{Command} registers the new command
3390 with @value{GDBN}. This initializer is normally invoked from the
3391 subclass' own @code{__init__} method.
3393 @var{name} is the name of the command. If @var{name} consists of
3394 multiple words, then the initial words are looked for as prefix
3395 commands. In this case, if one of the prefix commands does not exist,
3396 an exception is raised.
3398 There is no support for multi-line commands.
3400 @var{command_class} should be one of the @samp{COMMAND_} constants
3401 defined below. This argument tells @value{GDBN} how to categorize the
3402 new command in the help system.
3404 @var{completer_class} is an optional argument. If given, it should be
3405 one of the @samp{COMPLETE_} constants defined below. This argument
3406 tells @value{GDBN} how to perform completion for this command. If not
3407 given, @value{GDBN} will attempt to complete using the object's
3408 @code{complete} method (see below); if no such method is found, an
3409 error will occur when completion is attempted.
3411 @var{prefix} is an optional argument. If @code{True}, then the new
3412 command is a prefix command; sub-commands of this command may be
3415 The help text for the new command is taken from the Python
3416 documentation string for the command's class, if there is one. If no
3417 documentation string is provided, the default value ``This command is
3418 not documented.'' is used.
3421 @cindex don't repeat Python command
3422 @defun Command.dont_repeat ()
3423 By default, a @value{GDBN} command is repeated when the user enters a
3424 blank line at the command prompt. A command can suppress this
3425 behavior by invoking the @code{dont_repeat} method. This is similar
3426 to the user command @code{dont-repeat}, see @ref{Define, dont-repeat}.
3429 @defun Command.invoke (argument, from_tty)
3430 This method is called by @value{GDBN} when this command is invoked.
3432 @var{argument} is a string. It is the argument to the command, after
3433 leading and trailing whitespace has been stripped.
3435 @var{from_tty} is a boolean argument. When true, this means that the
3436 command was entered by the user at the terminal; when false it means
3437 that the command came from elsewhere.
3439 If this method throws an exception, it is turned into a @value{GDBN}
3440 @code{error} call. Otherwise, the return value is ignored.
3442 @findex gdb.string_to_argv
3443 To break @var{argument} up into an argv-like string use
3444 @code{gdb.string_to_argv}. This function behaves identically to
3445 @value{GDBN}'s internal argument lexer @code{buildargv}.
3446 It is recommended to use this for consistency.
3447 Arguments are separated by spaces and may be quoted.
3451 print gdb.string_to_argv ("1 2\ \\\"3 '4 \"5' \"6 '7\"")
3452 ['1', '2 "3', '4 "5', "6 '7"]
3457 @cindex completion of Python commands
3458 @defun Command.complete (text, word)
3459 This method is called by @value{GDBN} when the user attempts
3460 completion on this command. All forms of completion are handled by
3461 this method, that is, the @key{TAB} and @key{M-?} key bindings
3462 (@pxref{Completion}), and the @code{complete} command (@pxref{Help,
3465 The arguments @var{text} and @var{word} are both strings; @var{text}
3466 holds the complete command line up to the cursor's location, while
3467 @var{word} holds the last word of the command line; this is computed
3468 using a word-breaking heuristic.
3470 The @code{complete} method can return several values:
3473 If the return value is a sequence, the contents of the sequence are
3474 used as the completions. It is up to @code{complete} to ensure that the
3475 contents actually do complete the word. A zero-length sequence is
3476 allowed, it means that there were no completions available. Only
3477 string elements of the sequence are used; other elements in the
3478 sequence are ignored.
3481 If the return value is one of the @samp{COMPLETE_} constants defined
3482 below, then the corresponding @value{GDBN}-internal completion
3483 function is invoked, and its result is used.
3486 All other results are treated as though there were no available
3491 When a new command is registered, it must be declared as a member of
3492 some general class of commands. This is used to classify top-level
3493 commands in the on-line help system; note that prefix commands are not
3494 listed under their own category but rather that of their top-level
3495 command. The available classifications are represented by constants
3496 defined in the @code{gdb} module:
3499 @findex COMMAND_NONE
3500 @findex gdb.COMMAND_NONE
3501 @item gdb.COMMAND_NONE
3502 The command does not belong to any particular class. A command in
3503 this category will not be displayed in any of the help categories.
3505 @findex COMMAND_RUNNING
3506 @findex gdb.COMMAND_RUNNING
3507 @item gdb.COMMAND_RUNNING
3508 The command is related to running the inferior. For example,
3509 @code{start}, @code{step}, and @code{continue} are in this category.
3510 Type @kbd{help running} at the @value{GDBN} prompt to see a list of
3511 commands in this category.
3513 @findex COMMAND_DATA
3514 @findex gdb.COMMAND_DATA
3515 @item gdb.COMMAND_DATA
3516 The command is related to data or variables. For example,
3517 @code{call}, @code{find}, and @code{print} are in this category. Type
3518 @kbd{help data} at the @value{GDBN} prompt to see a list of commands
3521 @findex COMMAND_STACK
3522 @findex gdb.COMMAND_STACK
3523 @item gdb.COMMAND_STACK
3524 The command has to do with manipulation of the stack. For example,
3525 @code{backtrace}, @code{frame}, and @code{return} are in this
3526 category. Type @kbd{help stack} at the @value{GDBN} prompt to see a
3527 list of commands in this category.
3529 @findex COMMAND_FILES
3530 @findex gdb.COMMAND_FILES
3531 @item gdb.COMMAND_FILES
3532 This class is used for file-related commands. For example,
3533 @code{file}, @code{list} and @code{section} are in this category.
3534 Type @kbd{help files} at the @value{GDBN} prompt to see a list of
3535 commands in this category.
3537 @findex COMMAND_SUPPORT
3538 @findex gdb.COMMAND_SUPPORT
3539 @item gdb.COMMAND_SUPPORT
3540 This should be used for ``support facilities'', generally meaning
3541 things that are useful to the user when interacting with @value{GDBN},
3542 but not related to the state of the inferior. For example,
3543 @code{help}, @code{make}, and @code{shell} are in this category. Type
3544 @kbd{help support} at the @value{GDBN} prompt to see a list of
3545 commands in this category.
3547 @findex COMMAND_STATUS
3548 @findex gdb.COMMAND_STATUS
3549 @item gdb.COMMAND_STATUS
3550 The command is an @samp{info}-related command, that is, related to the
3551 state of @value{GDBN} itself. For example, @code{info}, @code{macro},
3552 and @code{show} are in this category. Type @kbd{help status} at the
3553 @value{GDBN} prompt to see a list of commands in this category.
3555 @findex COMMAND_BREAKPOINTS
3556 @findex gdb.COMMAND_BREAKPOINTS
3557 @item gdb.COMMAND_BREAKPOINTS
3558 The command has to do with breakpoints. For example, @code{break},
3559 @code{clear}, and @code{delete} are in this category. Type @kbd{help
3560 breakpoints} at the @value{GDBN} prompt to see a list of commands in
3563 @findex COMMAND_TRACEPOINTS
3564 @findex gdb.COMMAND_TRACEPOINTS
3565 @item gdb.COMMAND_TRACEPOINTS
3566 The command has to do with tracepoints. For example, @code{trace},
3567 @code{actions}, and @code{tfind} are in this category. Type
3568 @kbd{help tracepoints} at the @value{GDBN} prompt to see a list of
3569 commands in this category.
3571 @findex COMMAND_USER
3572 @findex gdb.COMMAND_USER
3573 @item gdb.COMMAND_USER
3574 The command is a general purpose command for the user, and typically
3575 does not fit in one of the other categories.
3576 Type @kbd{help user-defined} at the @value{GDBN} prompt to see
3577 a list of commands in this category, as well as the list of gdb macros
3578 (@pxref{Sequences}).
3580 @findex COMMAND_OBSCURE
3581 @findex gdb.COMMAND_OBSCURE
3582 @item gdb.COMMAND_OBSCURE
3583 The command is only used in unusual circumstances, or is not of
3584 general interest to users. For example, @code{checkpoint},
3585 @code{fork}, and @code{stop} are in this category. Type @kbd{help
3586 obscure} at the @value{GDBN} prompt to see a list of commands in this
3589 @findex COMMAND_MAINTENANCE
3590 @findex gdb.COMMAND_MAINTENANCE
3591 @item gdb.COMMAND_MAINTENANCE
3592 The command is only useful to @value{GDBN} maintainers. The
3593 @code{maintenance} and @code{flushregs} commands are in this category.
3594 Type @kbd{help internals} at the @value{GDBN} prompt to see a list of
3595 commands in this category.
3598 A new command can use a predefined completion function, either by
3599 specifying it via an argument at initialization, or by returning it
3600 from the @code{complete} method. These predefined completion
3601 constants are all defined in the @code{gdb} module:
3604 @vindex COMPLETE_NONE
3605 @item gdb.COMPLETE_NONE
3606 This constant means that no completion should be done.
3608 @vindex COMPLETE_FILENAME
3609 @item gdb.COMPLETE_FILENAME
3610 This constant means that filename completion should be performed.
3612 @vindex COMPLETE_LOCATION
3613 @item gdb.COMPLETE_LOCATION
3614 This constant means that location completion should be done.
3615 @xref{Specify Location}.
3617 @vindex COMPLETE_COMMAND
3618 @item gdb.COMPLETE_COMMAND
3619 This constant means that completion should examine @value{GDBN}
3622 @vindex COMPLETE_SYMBOL
3623 @item gdb.COMPLETE_SYMBOL
3624 This constant means that completion should be done using symbol names
3627 @vindex COMPLETE_EXPRESSION
3628 @item gdb.COMPLETE_EXPRESSION
3629 This constant means that completion should be done on expressions.
3630 Often this means completing on symbol names, but some language
3631 parsers also have support for completing on field names.
3634 The following code snippet shows how a trivial CLI command can be
3635 implemented in Python:
3638 class HelloWorld (gdb.Command):
3639 """Greet the whole world."""
3641 def __init__ (self):
3642 super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)
3644 def invoke (self, arg, from_tty):
3645 print "Hello, World!"
3650 The last line instantiates the class, and is necessary to trigger the
3651 registration of the command with @value{GDBN}. Depending on how the
3652 Python code is read into @value{GDBN}, you may need to import the
3653 @code{gdb} module explicitly.
3655 @node Parameters In Python
3656 @subsubsection Parameters In Python
3658 @cindex parameters in python
3659 @cindex python parameters
3660 @tindex gdb.Parameter
3662 You can implement new @value{GDBN} parameters using Python. A new
3663 parameter is implemented as an instance of the @code{gdb.Parameter}
3666 Parameters are exposed to the user via the @code{set} and
3667 @code{show} commands. @xref{Help}.
3669 There are many parameters that already exist and can be set in
3670 @value{GDBN}. Two examples are: @code{set follow fork} and
3671 @code{set charset}. Setting these parameters influences certain
3672 behavior in @value{GDBN}. Similarly, you can define parameters that
3673 can be used to influence behavior in custom Python scripts and commands.
3675 @defun Parameter.__init__ (name, @var{command-class}, @var{parameter-class} @r{[}, @var{enum-sequence}@r{]})
3676 The object initializer for @code{Parameter} registers the new
3677 parameter with @value{GDBN}. This initializer is normally invoked
3678 from the subclass' own @code{__init__} method.
3680 @var{name} is the name of the new parameter. If @var{name} consists
3681 of multiple words, then the initial words are looked for as prefix
3682 parameters. An example of this can be illustrated with the
3683 @code{set print} set of parameters. If @var{name} is
3684 @code{print foo}, then @code{print} will be searched as the prefix
3685 parameter. In this case the parameter can subsequently be accessed in
3686 @value{GDBN} as @code{set print foo}.
3688 If @var{name} consists of multiple words, and no prefix parameter group
3689 can be found, an exception is raised.
3691 @var{command-class} should be one of the @samp{COMMAND_} constants
3692 (@pxref{Commands In Python}). This argument tells @value{GDBN} how to
3693 categorize the new parameter in the help system.
3695 @var{parameter-class} should be one of the @samp{PARAM_} constants
3696 defined below. This argument tells @value{GDBN} the type of the new
3697 parameter; this information is used for input validation and
3700 If @var{parameter-class} is @code{PARAM_ENUM}, then
3701 @var{enum-sequence} must be a sequence of strings. These strings
3702 represent the possible values for the parameter.
3704 If @var{parameter-class} is not @code{PARAM_ENUM}, then the presence
3705 of a fourth argument will cause an exception to be thrown.
3707 The help text for the new parameter is taken from the Python
3708 documentation string for the parameter's class, if there is one. If
3709 there is no documentation string, a default value is used.
3712 @defvar Parameter.set_doc
3713 If this attribute exists, and is a string, then its value is used as
3714 the help text for this parameter's @code{set} command. The value is
3715 examined when @code{Parameter.__init__} is invoked; subsequent changes
3719 @defvar Parameter.show_doc
3720 If this attribute exists, and is a string, then its value is used as
3721 the help text for this parameter's @code{show} command. The value is
3722 examined when @code{Parameter.__init__} is invoked; subsequent changes
3726 @defvar Parameter.value
3727 The @code{value} attribute holds the underlying value of the
3728 parameter. It can be read and assigned to just as any other
3729 attribute. @value{GDBN} does validation when assignments are made.
3732 There are two methods that should be implemented in any
3733 @code{Parameter} class. These are:
3735 @defun Parameter.get_set_string (self)
3736 @value{GDBN} will call this method when a @var{parameter}'s value has
3737 been changed via the @code{set} API (for example, @kbd{set foo off}).
3738 The @code{value} attribute has already been populated with the new
3739 value and may be used in output. This method must return a string.
3742 @defun Parameter.get_show_string (self, svalue)
3743 @value{GDBN} will call this method when a @var{parameter}'s
3744 @code{show} API has been invoked (for example, @kbd{show foo}). The
3745 argument @code{svalue} receives the string representation of the
3746 current value. This method must return a string.
3749 When a new parameter is defined, its type must be specified. The
3750 available types are represented by constants defined in the @code{gdb}
3754 @findex PARAM_BOOLEAN
3755 @findex gdb.PARAM_BOOLEAN
3756 @item gdb.PARAM_BOOLEAN
3757 The value is a plain boolean. The Python boolean values, @code{True}
3758 and @code{False} are the only valid values.
3760 @findex PARAM_AUTO_BOOLEAN
3761 @findex gdb.PARAM_AUTO_BOOLEAN
3762 @item gdb.PARAM_AUTO_BOOLEAN
3763 The value has three possible states: true, false, and @samp{auto}. In
3764 Python, true and false are represented using boolean constants, and
3765 @samp{auto} is represented using @code{None}.
3767 @findex PARAM_UINTEGER
3768 @findex gdb.PARAM_UINTEGER
3769 @item gdb.PARAM_UINTEGER
3770 The value is an unsigned integer. The value of 0 should be
3771 interpreted to mean ``unlimited''.
3773 @findex PARAM_INTEGER
3774 @findex gdb.PARAM_INTEGER
3775 @item gdb.PARAM_INTEGER
3776 The value is a signed integer. The value of 0 should be interpreted
3777 to mean ``unlimited''.
3779 @findex PARAM_STRING
3780 @findex gdb.PARAM_STRING
3781 @item gdb.PARAM_STRING
3782 The value is a string. When the user modifies the string, any escape
3783 sequences, such as @samp{\t}, @samp{\f}, and octal escapes, are
3784 translated into corresponding characters and encoded into the current
3787 @findex PARAM_STRING_NOESCAPE
3788 @findex gdb.PARAM_STRING_NOESCAPE
3789 @item gdb.PARAM_STRING_NOESCAPE
3790 The value is a string. When the user modifies the string, escapes are
3791 passed through untranslated.
3793 @findex PARAM_OPTIONAL_FILENAME
3794 @findex gdb.PARAM_OPTIONAL_FILENAME
3795 @item gdb.PARAM_OPTIONAL_FILENAME
3796 The value is a either a filename (a string), or @code{None}.
3798 @findex PARAM_FILENAME
3799 @findex gdb.PARAM_FILENAME
3800 @item gdb.PARAM_FILENAME
3801 The value is a filename. This is just like
3802 @code{PARAM_STRING_NOESCAPE}, but uses file names for completion.
3804 @findex PARAM_ZINTEGER
3805 @findex gdb.PARAM_ZINTEGER
3806 @item gdb.PARAM_ZINTEGER
3807 The value is an integer. This is like @code{PARAM_INTEGER}, except 0
3808 is interpreted as itself.
3810 @findex PARAM_ZUINTEGER
3811 @findex gdb.PARAM_ZUINTEGER
3812 @item gdb.PARAM_ZUINTEGER
3813 The value is an unsigned integer. This is like @code{PARAM_INTEGER},
3814 except 0 is interpreted as itself, and the value cannot be negative.
3816 @findex PARAM_ZUINTEGER_UNLIMITED
3817 @findex gdb.PARAM_ZUINTEGER_UNLIMITED
3818 @item gdb.PARAM_ZUINTEGER_UNLIMITED
3819 The value is a signed integer. This is like @code{PARAM_ZUINTEGER},
3820 except the special value -1 should be interpreted to mean
3821 ``unlimited''. Other negative values are not allowed.
3824 @findex gdb.PARAM_ENUM
3825 @item gdb.PARAM_ENUM
3826 The value is a string, which must be one of a collection string
3827 constants provided when the parameter is created.
3830 @node Functions In Python
3831 @subsubsection Writing new convenience functions
3833 @cindex writing convenience functions
3834 @cindex convenience functions in python
3835 @cindex python convenience functions
3836 @tindex gdb.Function
3838 You can implement new convenience functions (@pxref{Convenience Vars})
3839 in Python. A convenience function is an instance of a subclass of the
3840 class @code{gdb.Function}.
3842 @defun Function.__init__ (name)
3843 The initializer for @code{Function} registers the new function with
3844 @value{GDBN}. The argument @var{name} is the name of the function,
3845 a string. The function will be visible to the user as a convenience
3846 variable of type @code{internal function}, whose name is the same as
3847 the given @var{name}.
3849 The documentation for the new function is taken from the documentation
3850 string for the new class.
3853 @defun Function.invoke (@var{*args})
3854 When a convenience function is evaluated, its arguments are converted
3855 to instances of @code{gdb.Value}, and then the function's
3856 @code{invoke} method is called. Note that @value{GDBN} does not
3857 predetermine the arity of convenience functions. Instead, all
3858 available arguments are passed to @code{invoke}, following the
3859 standard Python calling convention. In particular, a convenience
3860 function can have default values for parameters without ill effect.
3862 The return value of this method is used as its value in the enclosing
3863 expression. If an ordinary Python value is returned, it is converted
3864 to a @code{gdb.Value} following the usual rules.
3867 The following code snippet shows how a trivial convenience function can
3868 be implemented in Python:
3871 class Greet (gdb.Function):
3872 """Return string to greet someone.
3873 Takes a name as argument."""
3875 def __init__ (self):
3876 super (Greet, self).__init__ ("greet")
3878 def invoke (self, name):
3879 return "Hello, %s!" % name.string ()
3884 The last line instantiates the class, and is necessary to trigger the
3885 registration of the function with @value{GDBN}. Depending on how the
3886 Python code is read into @value{GDBN}, you may need to import the
3887 @code{gdb} module explicitly.
3889 Now you can use the function in an expression:
3892 (gdb) print $greet("Bob")
3896 @node Progspaces In Python
3897 @subsubsection Program Spaces In Python
3899 @cindex progspaces in python
3900 @tindex gdb.Progspace
3902 A program space, or @dfn{progspace}, represents a symbolic view
3903 of an address space.
3904 It consists of all of the objfiles of the program.
3905 @xref{Objfiles In Python}.
3906 @xref{Inferiors and Programs, program spaces}, for more details
3907 about program spaces.
3909 The following progspace-related functions are available in the
3912 @findex gdb.current_progspace
3913 @defun gdb.current_progspace ()
3914 This function returns the program space of the currently selected inferior.
3915 @xref{Inferiors and Programs}.
3918 @findex gdb.progspaces
3919 @defun gdb.progspaces ()
3920 Return a sequence of all the progspaces currently known to @value{GDBN}.
3923 Each progspace is represented by an instance of the @code{gdb.Progspace}
3926 @defvar Progspace.filename
3927 The file name of the progspace as a string.
3930 @defvar Progspace.pretty_printers
3931 The @code{pretty_printers} attribute is a list of functions. It is
3932 used to look up pretty-printers. A @code{Value} is passed to each
3933 function in order; if the function returns @code{None}, then the
3934 search continues. Otherwise, the return value should be an object
3935 which is used to format the value. @xref{Pretty Printing API}, for more
3939 @defvar Progspace.type_printers
3940 The @code{type_printers} attribute is a list of type printer objects.
3941 @xref{Type Printing API}, for more information.
3944 @defvar Progspace.frame_filters
3945 The @code{frame_filters} attribute is a dictionary of frame filter
3946 objects. @xref{Frame Filter API}, for more information.
3949 One may add arbitrary attributes to @code{gdb.Progspace} objects
3950 in the usual Python way.
3951 This is useful if, for example, one needs to do some extra record keeping
3952 associated with the program space.
3954 In this contrived example, we want to perform some processing when
3955 an objfile with a certain symbol is loaded, but we only want to do
3956 this once because it is expensive. To achieve this we record the results
3957 with the program space because we can't predict when the desired objfile
3962 def clear_objfiles_handler(event):
3963 event.progspace.expensive_computation = None
3964 def expensive(symbol):
3965 """A mock routine to perform an "expensive" computation on symbol."""
3966 print "Computing the answer to the ultimate question ..."
3968 def new_objfile_handler(event):
3969 objfile = event.new_objfile
3970 progspace = objfile.progspace
3971 if not hasattr(progspace, 'expensive_computation') or \
3972 progspace.expensive_computation is None:
3973 # We use 'main' for the symbol to keep the example simple.
3974 # Note: There's no current way to constrain the lookup
3976 symbol = gdb.lookup_global_symbol('main')
3977 if symbol is not None:
3978 progspace.expensive_computation = expensive(symbol)
3979 gdb.events.clear_objfiles.connect(clear_objfiles_handler)
3980 gdb.events.new_objfile.connect(new_objfile_handler)
3982 (gdb) file /tmp/hello
3983 Reading symbols from /tmp/hello...done.
3984 Computing the answer to the ultimate question ...
3985 (gdb) python print gdb.current_progspace().expensive_computation
3988 Starting program: /tmp/hello
3990 [Inferior 1 (process 4242) exited normally]
3993 @node Objfiles In Python
3994 @subsubsection Objfiles In Python
3996 @cindex objfiles in python
3999 @value{GDBN} loads symbols for an inferior from various
4000 symbol-containing files (@pxref{Files}). These include the primary
4001 executable file, any shared libraries used by the inferior, and any
4002 separate debug info files (@pxref{Separate Debug Files}).
4003 @value{GDBN} calls these symbol-containing files @dfn{objfiles}.
4005 The following objfile-related functions are available in the
4008 @findex gdb.current_objfile
4009 @defun gdb.current_objfile ()
4010 When auto-loading a Python script (@pxref{Python Auto-loading}), @value{GDBN}
4011 sets the ``current objfile'' to the corresponding objfile. This
4012 function returns the current objfile. If there is no current objfile,
4013 this function returns @code{None}.
4016 @findex gdb.objfiles
4017 @defun gdb.objfiles ()
4018 Return a sequence of all the objfiles current known to @value{GDBN}.
4019 @xref{Objfiles In Python}.
4022 @findex gdb.lookup_objfile
4023 @defun gdb.lookup_objfile (name @r{[}, by_build_id{]})
4024 Look up @var{name}, a file name or build ID, in the list of objfiles
4025 for the current program space (@pxref{Progspaces In Python}).
4026 If the objfile is not found throw the Python @code{ValueError} exception.
4028 If @var{name} is a relative file name, then it will match any
4029 source file name with the same trailing components. For example, if
4030 @var{name} is @samp{gcc/expr.c}, then it will match source file
4031 name of @file{/build/trunk/gcc/expr.c}, but not
4032 @file{/build/trunk/libcpp/expr.c} or @file{/build/trunk/gcc/x-expr.c}.
4034 If @var{by_build_id} is provided and is @code{True} then @var{name}
4035 is the build ID of the objfile. Otherwise, @var{name} is a file name.
4036 This is supported only on some operating systems, notably those which use
4037 the ELF format for binary files and the @sc{gnu} Binutils. For more details
4038 about this feature, see the description of the @option{--build-id}
4039 command-line option in @ref{Options, , Command Line Options, ld.info,
4043 Each objfile is represented by an instance of the @code{gdb.Objfile}
4046 @defvar Objfile.filename
4047 The file name of the objfile as a string, with symbolic links resolved.
4049 The value is @code{None} if the objfile is no longer valid.
4050 See the @code{gdb.Objfile.is_valid} method, described below.
4053 @defvar Objfile.username
4054 The file name of the objfile as specified by the user as a string.
4056 The value is @code{None} if the objfile is no longer valid.
4057 See the @code{gdb.Objfile.is_valid} method, described below.
4060 @defvar Objfile.owner
4061 For separate debug info objfiles this is the corresponding @code{gdb.Objfile}
4062 object that debug info is being provided for.
4063 Otherwise this is @code{None}.
4064 Separate debug info objfiles are added with the
4065 @code{gdb.Objfile.add_separate_debug_file} method, described below.
4068 @defvar Objfile.build_id
4069 The build ID of the objfile as a string.
4070 If the objfile does not have a build ID then the value is @code{None}.
4072 This is supported only on some operating systems, notably those which use
4073 the ELF format for binary files and the @sc{gnu} Binutils. For more details
4074 about this feature, see the description of the @option{--build-id}
4075 command-line option in @ref{Options, , Command Line Options, ld.info,
4079 @defvar Objfile.progspace
4080 The containing program space of the objfile as a @code{gdb.Progspace}
4081 object. @xref{Progspaces In Python}.
4084 @defvar Objfile.pretty_printers
4085 The @code{pretty_printers} attribute is a list of functions. It is
4086 used to look up pretty-printers. A @code{Value} is passed to each
4087 function in order; if the function returns @code{None}, then the
4088 search continues. Otherwise, the return value should be an object
4089 which is used to format the value. @xref{Pretty Printing API}, for more
4093 @defvar Objfile.type_printers
4094 The @code{type_printers} attribute is a list of type printer objects.
4095 @xref{Type Printing API}, for more information.
4098 @defvar Objfile.frame_filters
4099 The @code{frame_filters} attribute is a dictionary of frame filter
4100 objects. @xref{Frame Filter API}, for more information.
4103 One may add arbitrary attributes to @code{gdb.Objfile} objects
4104 in the usual Python way.
4105 This is useful if, for example, one needs to do some extra record keeping
4106 associated with the objfile.
4108 In this contrived example we record the time when @value{GDBN}
4114 def new_objfile_handler(event):
4115 # Set the time_loaded attribute of the new objfile.
4116 event.new_objfile.time_loaded = datetime.datetime.today()
4117 gdb.events.new_objfile.connect(new_objfile_handler)
4120 Reading symbols from ./hello...done.
4121 (gdb) python print gdb.objfiles()[0].time_loaded
4122 2014-10-09 11:41:36.770345
4125 A @code{gdb.Objfile} object has the following methods:
4127 @defun Objfile.is_valid ()
4128 Returns @code{True} if the @code{gdb.Objfile} object is valid,
4129 @code{False} if not. A @code{gdb.Objfile} object can become invalid
4130 if the object file it refers to is not loaded in @value{GDBN} any
4131 longer. All other @code{gdb.Objfile} methods will throw an exception
4132 if it is invalid at the time the method is called.
4135 @defun Objfile.add_separate_debug_file (file)
4136 Add @var{file} to the list of files that @value{GDBN} will search for
4137 debug information for the objfile.
4138 This is useful when the debug info has been removed from the program
4139 and stored in a separate file. @value{GDBN} has built-in support for
4140 finding separate debug info files (@pxref{Separate Debug Files}), but if
4141 the file doesn't live in one of the standard places that @value{GDBN}
4142 searches then this function can be used to add a debug info file
4143 from a different place.
4146 @node Frames In Python
4147 @subsubsection Accessing inferior stack frames from Python.
4149 @cindex frames in python
4150 When the debugged program stops, @value{GDBN} is able to analyze its call
4151 stack (@pxref{Frames,,Stack frames}). The @code{gdb.Frame} class
4152 represents a frame in the stack. A @code{gdb.Frame} object is only valid
4153 while its corresponding frame exists in the inferior's stack. If you try
4154 to use an invalid frame object, @value{GDBN} will throw a @code{gdb.error}
4155 exception (@pxref{Exception Handling}).
4157 Two @code{gdb.Frame} objects can be compared for equality with the @code{==}
4161 (@value{GDBP}) python print gdb.newest_frame() == gdb.selected_frame ()
4165 The following frame-related functions are available in the @code{gdb} module:
4167 @findex gdb.selected_frame
4168 @defun gdb.selected_frame ()
4169 Return the selected frame object. (@pxref{Selection,,Selecting a Frame}).
4172 @findex gdb.newest_frame
4173 @defun gdb.newest_frame ()
4174 Return the newest frame object for the selected thread.
4177 @defun gdb.frame_stop_reason_string (reason)
4178 Return a string explaining the reason why @value{GDBN} stopped unwinding
4179 frames, as expressed by the given @var{reason} code (an integer, see the
4180 @code{unwind_stop_reason} method further down in this section).
4183 @findex gdb.invalidate_cached_frames
4184 @defun gdb.invalidate_cached_frames
4185 @value{GDBN} internally keeps a cache of the frames that have been
4186 unwound. This function invalidates this cache.
4188 This function should not generally be called by ordinary Python code.
4189 It is documented for the sake of completeness.
4192 A @code{gdb.Frame} object has the following methods:
4194 @defun Frame.is_valid ()
4195 Returns true if the @code{gdb.Frame} object is valid, false if not.
4196 A frame object can become invalid if the frame it refers to doesn't
4197 exist anymore in the inferior. All @code{gdb.Frame} methods will throw
4198 an exception if it is invalid at the time the method is called.
4201 @defun Frame.name ()
4202 Returns the function name of the frame, or @code{None} if it can't be
4206 @defun Frame.architecture ()
4207 Returns the @code{gdb.Architecture} object corresponding to the frame's
4208 architecture. @xref{Architectures In Python}.
4211 @defun Frame.type ()
4212 Returns the type of the frame. The value can be one of:
4214 @item gdb.NORMAL_FRAME
4215 An ordinary stack frame.
4217 @item gdb.DUMMY_FRAME
4218 A fake stack frame that was created by @value{GDBN} when performing an
4219 inferior function call.
4221 @item gdb.INLINE_FRAME
4222 A frame representing an inlined function. The function was inlined
4223 into a @code{gdb.NORMAL_FRAME} that is older than this one.
4225 @item gdb.TAILCALL_FRAME
4226 A frame representing a tail call. @xref{Tail Call Frames}.
4228 @item gdb.SIGTRAMP_FRAME
4229 A signal trampoline frame. This is the frame created by the OS when
4230 it calls into a signal handler.
4232 @item gdb.ARCH_FRAME
4233 A fake stack frame representing a cross-architecture call.
4235 @item gdb.SENTINEL_FRAME
4236 This is like @code{gdb.NORMAL_FRAME}, but it is only used for the
4241 @defun Frame.unwind_stop_reason ()
4242 Return an integer representing the reason why it's not possible to find
4243 more frames toward the outermost frame. Use
4244 @code{gdb.frame_stop_reason_string} to convert the value returned by this
4245 function to a string. The value can be one of:
4248 @item gdb.FRAME_UNWIND_NO_REASON
4249 No particular reason (older frames should be available).
4251 @item gdb.FRAME_UNWIND_NULL_ID
4252 The previous frame's analyzer returns an invalid result. This is no
4253 longer used by @value{GDBN}, and is kept only for backward
4256 @item gdb.FRAME_UNWIND_OUTERMOST
4257 This frame is the outermost.
4259 @item gdb.FRAME_UNWIND_UNAVAILABLE
4260 Cannot unwind further, because that would require knowing the
4261 values of registers or memory that have not been collected.
4263 @item gdb.FRAME_UNWIND_INNER_ID
4264 This frame ID looks like it ought to belong to a NEXT frame,
4265 but we got it for a PREV frame. Normally, this is a sign of
4266 unwinder failure. It could also indicate stack corruption.
4268 @item gdb.FRAME_UNWIND_SAME_ID
4269 This frame has the same ID as the previous one. That means
4270 that unwinding further would almost certainly give us another
4271 frame with exactly the same ID, so break the chain. Normally,
4272 this is a sign of unwinder failure. It could also indicate
4275 @item gdb.FRAME_UNWIND_NO_SAVED_PC
4276 The frame unwinder did not find any saved PC, but we needed
4277 one to unwind further.
4279 @item gdb.FRAME_UNWIND_MEMORY_ERROR
4280 The frame unwinder caused an error while trying to access memory.
4282 @item gdb.FRAME_UNWIND_FIRST_ERROR
4283 Any stop reason greater or equal to this value indicates some kind
4284 of error. This special value facilitates writing code that tests
4285 for errors in unwinding in a way that will work correctly even if
4286 the list of the other values is modified in future @value{GDBN}
4287 versions. Using it, you could write:
4289 reason = gdb.selected_frame().unwind_stop_reason ()
4290 reason_str = gdb.frame_stop_reason_string (reason)
4291 if reason >= gdb.FRAME_UNWIND_FIRST_ERROR:
4292 print "An error occured: %s" % reason_str
4299 Returns the frame's resume address.
4302 @defun Frame.block ()
4303 Return the frame's code block. @xref{Blocks In Python}.
4306 @defun Frame.function ()
4307 Return the symbol for the function corresponding to this frame.
4308 @xref{Symbols In Python}.
4311 @defun Frame.older ()
4312 Return the frame that called this frame.
4315 @defun Frame.newer ()
4316 Return the frame called by this frame.
4319 @defun Frame.find_sal ()
4320 Return the frame's symtab and line object.
4321 @xref{Symbol Tables In Python}.
4324 @defun Frame.read_register (register)
4325 Return the value of @var{register} in this frame. The @var{register}
4326 argument must be a string (e.g., @code{'sp'} or @code{'rax'}).
4327 Returns a @code{Gdb.Value} object. Throws an exception if @var{register}
4331 @defun Frame.read_var (variable @r{[}, block@r{]})
4332 Return the value of @var{variable} in this frame. If the optional
4333 argument @var{block} is provided, search for the variable from that
4334 block; otherwise start at the frame's current block (which is
4335 determined by the frame's current program counter). The @var{variable}
4336 argument must be a string or a @code{gdb.Symbol} object; @var{block} must be a
4337 @code{gdb.Block} object.
4340 @defun Frame.select ()
4341 Set this frame to be the selected frame. @xref{Stack, ,Examining the
4345 @node Blocks In Python
4346 @subsubsection Accessing blocks from Python.
4348 @cindex blocks in python
4351 In @value{GDBN}, symbols are stored in blocks. A block corresponds
4352 roughly to a scope in the source code. Blocks are organized
4353 hierarchically, and are represented individually in Python as a
4354 @code{gdb.Block}. Blocks rely on debugging information being
4357 A frame has a block. Please see @ref{Frames In Python}, for a more
4358 in-depth discussion of frames.
4360 The outermost block is known as the @dfn{global block}. The global
4361 block typically holds public global variables and functions.
4363 The block nested just inside the global block is the @dfn{static
4364 block}. The static block typically holds file-scoped variables and
4367 @value{GDBN} provides a method to get a block's superblock, but there
4368 is currently no way to examine the sub-blocks of a block, or to
4369 iterate over all the blocks in a symbol table (@pxref{Symbol Tables In
4372 Here is a short example that should help explain blocks:
4375 /* This is in the global block. */
4378 /* This is in the static block. */
4379 static int file_scope;
4381 /* 'function' is in the global block, and 'argument' is
4382 in a block nested inside of 'function'. */
4383 int function (int argument)
4385 /* 'local' is in a block inside 'function'. It may or may
4386 not be in the same block as 'argument'. */
4390 /* 'inner' is in a block whose superblock is the one holding
4394 /* If this call is expanded by the compiler, you may see
4395 a nested block here whose function is 'inline_function'
4396 and whose superblock is the one holding 'inner'. */
4402 A @code{gdb.Block} is iterable. The iterator returns the symbols
4403 (@pxref{Symbols In Python}) local to the block. Python programs
4404 should not assume that a specific block object will always contain a
4405 given symbol, since changes in @value{GDBN} features and
4406 infrastructure may cause symbols move across blocks in a symbol
4409 The following block-related functions are available in the @code{gdb}
4412 @findex gdb.block_for_pc
4413 @defun gdb.block_for_pc (pc)
4414 Return the innermost @code{gdb.Block} containing the given @var{pc}
4415 value. If the block cannot be found for the @var{pc} value specified,
4416 the function will return @code{None}.
4419 A @code{gdb.Block} object has the following methods:
4421 @defun Block.is_valid ()
4422 Returns @code{True} if the @code{gdb.Block} object is valid,
4423 @code{False} if not. A block object can become invalid if the block it
4424 refers to doesn't exist anymore in the inferior. All other
4425 @code{gdb.Block} methods will throw an exception if it is invalid at
4426 the time the method is called. The block's validity is also checked
4427 during iteration over symbols of the block.
4430 A @code{gdb.Block} object has the following attributes:
4433 The start address of the block. This attribute is not writable.
4437 The end address of the block. This attribute is not writable.
4440 @defvar Block.function
4441 The name of the block represented as a @code{gdb.Symbol}. If the
4442 block is not named, then this attribute holds @code{None}. This
4443 attribute is not writable.
4445 For ordinary function blocks, the superblock is the static block.
4446 However, you should note that it is possible for a function block to
4447 have a superblock that is not the static block -- for instance this
4448 happens for an inlined function.
4451 @defvar Block.superblock
4452 The block containing this block. If this parent block does not exist,
4453 this attribute holds @code{None}. This attribute is not writable.
4456 @defvar Block.global_block
4457 The global block associated with this block. This attribute is not
4461 @defvar Block.static_block
4462 The static block associated with this block. This attribute is not
4466 @defvar Block.is_global
4467 @code{True} if the @code{gdb.Block} object is a global block,
4468 @code{False} if not. This attribute is not
4472 @defvar Block.is_static
4473 @code{True} if the @code{gdb.Block} object is a static block,
4474 @code{False} if not. This attribute is not writable.
4477 @node Symbols In Python
4478 @subsubsection Python representation of Symbols.
4480 @cindex symbols in python
4483 @value{GDBN} represents every variable, function and type as an
4484 entry in a symbol table. @xref{Symbols, ,Examining the Symbol Table}.
4485 Similarly, Python represents these symbols in @value{GDBN} with the
4486 @code{gdb.Symbol} object.
4488 The following symbol-related functions are available in the @code{gdb}
4491 @findex gdb.lookup_symbol
4492 @defun gdb.lookup_symbol (name @r{[}, block @r{[}, domain@r{]]})
4493 This function searches for a symbol by name. The search scope can be
4494 restricted to the parameters defined in the optional domain and block
4497 @var{name} is the name of the symbol. It must be a string. The
4498 optional @var{block} argument restricts the search to symbols visible
4499 in that @var{block}. The @var{block} argument must be a
4500 @code{gdb.Block} object. If omitted, the block for the current frame
4501 is used. The optional @var{domain} argument restricts
4502 the search to the domain type. The @var{domain} argument must be a
4503 domain constant defined in the @code{gdb} module and described later
4506 The result is a tuple of two elements.
4507 The first element is a @code{gdb.Symbol} object or @code{None} if the symbol
4509 If the symbol is found, the second element is @code{True} if the symbol
4510 is a field of a method's object (e.g., @code{this} in C@t{++}),
4511 otherwise it is @code{False}.
4512 If the symbol is not found, the second element is @code{False}.
4515 @findex gdb.lookup_global_symbol
4516 @defun gdb.lookup_global_symbol (name @r{[}, domain@r{]})
4517 This function searches for a global symbol by name.
4518 The search scope can be restricted to by the domain argument.
4520 @var{name} is the name of the symbol. It must be a string.
4521 The optional @var{domain} argument restricts the search to the domain type.
4522 The @var{domain} argument must be a domain constant defined in the @code{gdb}
4523 module and described later in this chapter.
4525 The result is a @code{gdb.Symbol} object or @code{None} if the symbol
4529 A @code{gdb.Symbol} object has the following attributes:
4532 The type of the symbol or @code{None} if no type is recorded.
4533 This attribute is represented as a @code{gdb.Type} object.
4534 @xref{Types In Python}. This attribute is not writable.
4537 @defvar Symbol.symtab
4538 The symbol table in which the symbol appears. This attribute is
4539 represented as a @code{gdb.Symtab} object. @xref{Symbol Tables In
4540 Python}. This attribute is not writable.
4544 The line number in the source code at which the symbol was defined.
4549 The name of the symbol as a string. This attribute is not writable.
4552 @defvar Symbol.linkage_name
4553 The name of the symbol, as used by the linker (i.e., may be mangled).
4554 This attribute is not writable.
4557 @defvar Symbol.print_name
4558 The name of the symbol in a form suitable for output. This is either
4559 @code{name} or @code{linkage_name}, depending on whether the user
4560 asked @value{GDBN} to display demangled or mangled names.
4563 @defvar Symbol.addr_class
4564 The address class of the symbol. This classifies how to find the value
4565 of a symbol. Each address class is a constant defined in the
4566 @code{gdb} module and described later in this chapter.
4569 @defvar Symbol.needs_frame
4570 This is @code{True} if evaluating this symbol's value requires a frame
4571 (@pxref{Frames In Python}) and @code{False} otherwise. Typically,
4572 local variables will require a frame, but other symbols will not.
4575 @defvar Symbol.is_argument
4576 @code{True} if the symbol is an argument of a function.
4579 @defvar Symbol.is_constant
4580 @code{True} if the symbol is a constant.
4583 @defvar Symbol.is_function
4584 @code{True} if the symbol is a function or a method.
4587 @defvar Symbol.is_variable
4588 @code{True} if the symbol is a variable.
4591 A @code{gdb.Symbol} object has the following methods:
4593 @defun Symbol.is_valid ()
4594 Returns @code{True} if the @code{gdb.Symbol} object is valid,
4595 @code{False} if not. A @code{gdb.Symbol} object can become invalid if
4596 the symbol it refers to does not exist in @value{GDBN} any longer.
4597 All other @code{gdb.Symbol} methods will throw an exception if it is
4598 invalid at the time the method is called.
4601 @defun Symbol.value (@r{[}frame@r{]})
4602 Compute the value of the symbol, as a @code{gdb.Value}. For
4603 functions, this computes the address of the function, cast to the
4604 appropriate type. If the symbol requires a frame in order to compute
4605 its value, then @var{frame} must be given. If @var{frame} is not
4606 given, or if @var{frame} is invalid, then this method will throw an
4610 The available domain categories in @code{gdb.Symbol} are represented
4611 as constants in the @code{gdb} module:
4614 @vindex SYMBOL_UNDEF_DOMAIN
4615 @item gdb.SYMBOL_UNDEF_DOMAIN
4616 This is used when a domain has not been discovered or none of the
4617 following domains apply. This usually indicates an error either
4618 in the symbol information or in @value{GDBN}'s handling of symbols.
4620 @vindex SYMBOL_VAR_DOMAIN
4621 @item gdb.SYMBOL_VAR_DOMAIN
4622 This domain contains variables, function names, typedef names and enum
4625 @vindex SYMBOL_STRUCT_DOMAIN
4626 @item gdb.SYMBOL_STRUCT_DOMAIN
4627 This domain holds struct, union and enum type names.
4629 @vindex SYMBOL_LABEL_DOMAIN
4630 @item gdb.SYMBOL_LABEL_DOMAIN
4631 This domain contains names of labels (for gotos).
4633 @vindex SYMBOL_VARIABLES_DOMAIN
4634 @item gdb.SYMBOL_VARIABLES_DOMAIN
4635 This domain holds a subset of the @code{SYMBOLS_VAR_DOMAIN}; it
4636 contains everything minus functions and types.
4638 @vindex SYMBOL_FUNCTIONS_DOMAIN
4639 @item gdb.SYMBOL_FUNCTIONS_DOMAIN
4640 This domain contains all functions.
4642 @vindex SYMBOL_TYPES_DOMAIN
4643 @item gdb.SYMBOL_TYPES_DOMAIN
4644 This domain contains all types.
4647 The available address class categories in @code{gdb.Symbol} are represented
4648 as constants in the @code{gdb} module:
4651 @vindex SYMBOL_LOC_UNDEF
4652 @item gdb.SYMBOL_LOC_UNDEF
4653 If this is returned by address class, it indicates an error either in
4654 the symbol information or in @value{GDBN}'s handling of symbols.
4656 @vindex SYMBOL_LOC_CONST
4657 @item gdb.SYMBOL_LOC_CONST
4658 Value is constant int.
4660 @vindex SYMBOL_LOC_STATIC
4661 @item gdb.SYMBOL_LOC_STATIC
4662 Value is at a fixed address.
4664 @vindex SYMBOL_LOC_REGISTER
4665 @item gdb.SYMBOL_LOC_REGISTER
4666 Value is in a register.
4668 @vindex SYMBOL_LOC_ARG
4669 @item gdb.SYMBOL_LOC_ARG
4670 Value is an argument. This value is at the offset stored within the
4671 symbol inside the frame's argument list.
4673 @vindex SYMBOL_LOC_REF_ARG
4674 @item gdb.SYMBOL_LOC_REF_ARG
4675 Value address is stored in the frame's argument list. Just like
4676 @code{LOC_ARG} except that the value's address is stored at the
4677 offset, not the value itself.
4679 @vindex SYMBOL_LOC_REGPARM_ADDR
4680 @item gdb.SYMBOL_LOC_REGPARM_ADDR
4681 Value is a specified register. Just like @code{LOC_REGISTER} except
4682 the register holds the address of the argument instead of the argument
4685 @vindex SYMBOL_LOC_LOCAL
4686 @item gdb.SYMBOL_LOC_LOCAL
4687 Value is a local variable.
4689 @vindex SYMBOL_LOC_TYPEDEF
4690 @item gdb.SYMBOL_LOC_TYPEDEF
4691 Value not used. Symbols in the domain @code{SYMBOL_STRUCT_DOMAIN} all
4694 @vindex SYMBOL_LOC_BLOCK
4695 @item gdb.SYMBOL_LOC_BLOCK
4698 @vindex SYMBOL_LOC_CONST_BYTES
4699 @item gdb.SYMBOL_LOC_CONST_BYTES
4700 Value is a byte-sequence.
4702 @vindex SYMBOL_LOC_UNRESOLVED
4703 @item gdb.SYMBOL_LOC_UNRESOLVED
4704 Value is at a fixed address, but the address of the variable has to be
4705 determined from the minimal symbol table whenever the variable is
4708 @vindex SYMBOL_LOC_OPTIMIZED_OUT
4709 @item gdb.SYMBOL_LOC_OPTIMIZED_OUT
4710 The value does not actually exist in the program.
4712 @vindex SYMBOL_LOC_COMPUTED
4713 @item gdb.SYMBOL_LOC_COMPUTED
4714 The value's address is a computed location.
4717 @node Symbol Tables In Python
4718 @subsubsection Symbol table representation in Python.
4720 @cindex symbol tables in python
4722 @tindex gdb.Symtab_and_line
4724 Access to symbol table data maintained by @value{GDBN} on the inferior
4725 is exposed to Python via two objects: @code{gdb.Symtab_and_line} and
4726 @code{gdb.Symtab}. Symbol table and line data for a frame is returned
4727 from the @code{find_sal} method in @code{gdb.Frame} object.
4728 @xref{Frames In Python}.
4730 For more information on @value{GDBN}'s symbol table management, see
4731 @ref{Symbols, ,Examining the Symbol Table}, for more information.
4733 A @code{gdb.Symtab_and_line} object has the following attributes:
4735 @defvar Symtab_and_line.symtab
4736 The symbol table object (@code{gdb.Symtab}) for this frame.
4737 This attribute is not writable.
4740 @defvar Symtab_and_line.pc
4741 Indicates the start of the address range occupied by code for the
4742 current source line. This attribute is not writable.
4745 @defvar Symtab_and_line.last
4746 Indicates the end of the address range occupied by code for the current
4747 source line. This attribute is not writable.
4750 @defvar Symtab_and_line.line
4751 Indicates the current line number for this object. This
4752 attribute is not writable.
4755 A @code{gdb.Symtab_and_line} object has the following methods:
4757 @defun Symtab_and_line.is_valid ()
4758 Returns @code{True} if the @code{gdb.Symtab_and_line} object is valid,
4759 @code{False} if not. A @code{gdb.Symtab_and_line} object can become
4760 invalid if the Symbol table and line object it refers to does not
4761 exist in @value{GDBN} any longer. All other
4762 @code{gdb.Symtab_and_line} methods will throw an exception if it is
4763 invalid at the time the method is called.
4766 A @code{gdb.Symtab} object has the following attributes:
4768 @defvar Symtab.filename
4769 The symbol table's source filename. This attribute is not writable.
4772 @defvar Symtab.objfile
4773 The symbol table's backing object file. @xref{Objfiles In Python}.
4774 This attribute is not writable.
4777 @defvar Symtab.producer
4778 The name and possibly version number of the program that
4779 compiled the code in the symbol table.
4780 The contents of this string is up to the compiler.
4781 If no producer information is available then @code{None} is returned.
4782 This attribute is not writable.
4785 A @code{gdb.Symtab} object has the following methods:
4787 @defun Symtab.is_valid ()
4788 Returns @code{True} if the @code{gdb.Symtab} object is valid,
4789 @code{False} if not. A @code{gdb.Symtab} object can become invalid if
4790 the symbol table it refers to does not exist in @value{GDBN} any
4791 longer. All other @code{gdb.Symtab} methods will throw an exception
4792 if it is invalid at the time the method is called.
4795 @defun Symtab.fullname ()
4796 Return the symbol table's source absolute file name.
4799 @defun Symtab.global_block ()
4800 Return the global block of the underlying symbol table.
4801 @xref{Blocks In Python}.
4804 @defun Symtab.static_block ()
4805 Return the static block of the underlying symbol table.
4806 @xref{Blocks In Python}.
4809 @defun Symtab.linetable ()
4810 Return the line table associated with the symbol table.
4811 @xref{Line Tables In Python}.
4814 @node Line Tables In Python
4815 @subsubsection Manipulating line tables using Python
4817 @cindex line tables in python
4818 @tindex gdb.LineTable
4820 Python code can request and inspect line table information from a
4821 symbol table that is loaded in @value{GDBN}. A line table is a
4822 mapping of source lines to their executable locations in memory. To
4823 acquire the line table information for a particular symbol table, use
4824 the @code{linetable} function (@pxref{Symbol Tables In Python}).
4826 A @code{gdb.LineTable} is iterable. The iterator returns
4827 @code{LineTableEntry} objects that correspond to the source line and
4828 address for each line table entry. @code{LineTableEntry} objects have
4829 the following attributes:
4831 @defvar LineTableEntry.line
4832 The source line number for this line table entry. This number
4833 corresponds to the actual line of source. This attribute is not
4837 @defvar LineTableEntry.pc
4838 The address that is associated with the line table entry where the
4839 executable code for that source line resides in memory. This
4840 attribute is not writable.
4843 As there can be multiple addresses for a single source line, you may
4844 receive multiple @code{LineTableEntry} objects with matching
4845 @code{line} attributes, but with different @code{pc} attributes. The
4846 iterator is sorted in ascending @code{pc} order. Here is a small
4847 example illustrating iterating over a line table.
4850 symtab = gdb.selected_frame().find_sal().symtab
4851 linetable = symtab.linetable()
4852 for line in linetable:
4853 print "Line: "+str(line.line)+" Address: "+hex(line.pc)
4856 This will have the following output:
4859 Line: 33 Address: 0x4005c8L
4860 Line: 37 Address: 0x4005caL
4861 Line: 39 Address: 0x4005d2L
4862 Line: 40 Address: 0x4005f8L
4863 Line: 42 Address: 0x4005ffL
4864 Line: 44 Address: 0x400608L
4865 Line: 42 Address: 0x40060cL
4866 Line: 45 Address: 0x400615L
4869 In addition to being able to iterate over a @code{LineTable}, it also
4870 has the following direct access methods:
4872 @defun LineTable.line (line)
4873 Return a Python @code{Tuple} of @code{LineTableEntry} objects for any
4874 entries in the line table for the given @var{line}, which specifies
4875 the source code line. If there are no entries for that source code
4876 @var{line}, the Python @code{None} is returned.
4879 @defun LineTable.has_line (line)
4880 Return a Python @code{Boolean} indicating whether there is an entry in
4881 the line table for this source line. Return @code{True} if an entry
4882 is found, or @code{False} if not.
4885 @defun LineTable.source_lines ()
4886 Return a Python @code{List} of the source line numbers in the symbol
4887 table. Only lines with executable code locations are returned. The
4888 contents of the @code{List} will just be the source line entries
4889 represented as Python @code{Long} values.
4892 @node Breakpoints In Python
4893 @subsubsection Manipulating breakpoints using Python
4895 @cindex breakpoints in python
4896 @tindex gdb.Breakpoint
4898 Python code can manipulate breakpoints via the @code{gdb.Breakpoint}
4901 A breakpoint can be created using one of the two forms of the
4902 @code{gdb.Breakpoint} constructor. The first one accepts a string
4903 like one would pass to the @code{break}
4904 (@pxref{Set Breaks,,Setting Breakpoints}) and @code{watch}
4905 (@pxref{Set Watchpoints, , Setting Watchpoints}) commands, and can be used to
4906 create both breakpoints and watchpoints. The second accepts separate Python
4907 arguments similar to @ref{Explicit Locations}, and can only be used to create
4910 @defun Breakpoint.__init__ (spec @r{[}, type @r{][}, wp_class @r{][}, internal @r{][}, temporary @r{][}, qualified @r{]})
4911 Create a new breakpoint according to @var{spec}, which is a string naming the
4912 location of a breakpoint, or an expression that defines a watchpoint. The
4913 string should describe a location in a format recognized by the @code{break}
4914 command (@pxref{Set Breaks,,Setting Breakpoints}) or, in the case of a
4915 watchpoint, by the @code{watch} command
4916 (@pxref{Set Watchpoints, , Setting Watchpoints}).
4918 The optional @var{type} argument specifies the type of the breakpoint to create,
4921 The optional @var{wp_class} argument defines the class of watchpoint to create,
4922 if @var{type} is @code{gdb.BP_WATCHPOINT}. If @var{wp_class} is omitted, it
4923 defaults to @code{gdb.WP_WRITE}.
4925 The optional @var{internal} argument allows the breakpoint to become invisible
4926 to the user. The breakpoint will neither be reported when created, nor will it
4927 be listed in the output from @code{info breakpoints} (but will be listed with
4928 the @code{maint info breakpoints} command).
4930 The optional @var{temporary} argument makes the breakpoint a temporary
4931 breakpoint. Temporary breakpoints are deleted after they have been hit. Any
4932 further access to the Python breakpoint after it has been hit will result in a
4933 runtime error (as that breakpoint has now been automatically deleted).
4935 The optional @var{qualified} argument is a boolean that allows interpreting
4936 the function passed in @code{spec} as a fully-qualified name. It is equivalent
4937 to @code{break}'s @code{-qualified} flag (@pxref{Linespec Locations} and
4938 @ref{Explicit Locations}).
4942 @defun Breakpoint.__init__ (@r{[} source @r{][}, function @r{][}, label @r{][}, line @r{]}, @r{][} internal @r{][}, temporary @r{][}, qualified @r{]})
4943 This second form of creating a new breakpoint specifies the explicit
4944 location (@pxref{Explicit Locations}) using keywords. The new breakpoint will
4945 be created in the specified source file @var{source}, at the specified
4946 @var{function}, @var{label} and @var{line}.
4948 @var{internal}, @var{temporary} and @var{qualified} have the same usage as
4949 explained previously.
4952 The available types are represented by constants defined in the @code{gdb}
4956 @vindex BP_BREAKPOINT
4957 @item gdb.BP_BREAKPOINT
4958 Normal code breakpoint.
4960 @vindex BP_WATCHPOINT
4961 @item gdb.BP_WATCHPOINT
4962 Watchpoint breakpoint.
4964 @vindex BP_HARDWARE_WATCHPOINT
4965 @item gdb.BP_HARDWARE_WATCHPOINT
4966 Hardware assisted watchpoint.
4968 @vindex BP_READ_WATCHPOINT
4969 @item gdb.BP_READ_WATCHPOINT
4970 Hardware assisted read watchpoint.
4972 @vindex BP_ACCESS_WATCHPOINT
4973 @item gdb.BP_ACCESS_WATCHPOINT
4974 Hardware assisted access watchpoint.
4977 The available watchpoint types represented by constants are defined in the
4983 Read only watchpoint.
4987 Write only watchpoint.
4991 Read/Write watchpoint.
4994 @defun Breakpoint.stop (self)
4995 The @code{gdb.Breakpoint} class can be sub-classed and, in
4996 particular, you may choose to implement the @code{stop} method.
4997 If this method is defined in a sub-class of @code{gdb.Breakpoint},
4998 it will be called when the inferior reaches any location of a
4999 breakpoint which instantiates that sub-class. If the method returns
5000 @code{True}, the inferior will be stopped at the location of the
5001 breakpoint, otherwise the inferior will continue.
5003 If there are multiple breakpoints at the same location with a
5004 @code{stop} method, each one will be called regardless of the
5005 return status of the previous. This ensures that all @code{stop}
5006 methods have a chance to execute at that location. In this scenario
5007 if one of the methods returns @code{True} but the others return
5008 @code{False}, the inferior will still be stopped.
5010 You should not alter the execution state of the inferior (i.e.@:, step,
5011 next, etc.), alter the current frame context (i.e.@:, change the current
5012 active frame), or alter, add or delete any breakpoint. As a general
5013 rule, you should not alter any data within @value{GDBN} or the inferior
5016 Example @code{stop} implementation:
5019 class MyBreakpoint (gdb.Breakpoint):
5021 inf_val = gdb.parse_and_eval("foo")
5028 @defun Breakpoint.is_valid ()
5029 Return @code{True} if this @code{Breakpoint} object is valid,
5030 @code{False} otherwise. A @code{Breakpoint} object can become invalid
5031 if the user deletes the breakpoint. In this case, the object still
5032 exists, but the underlying breakpoint does not. In the cases of
5033 watchpoint scope, the watchpoint remains valid even if execution of the
5034 inferior leaves the scope of that watchpoint.
5037 @defun Breakpoint.delete ()
5038 Permanently deletes the @value{GDBN} breakpoint. This also
5039 invalidates the Python @code{Breakpoint} object. Any further access
5040 to this object's attributes or methods will raise an error.
5043 @defvar Breakpoint.enabled
5044 This attribute is @code{True} if the breakpoint is enabled, and
5045 @code{False} otherwise. This attribute is writable. You can use it to enable
5046 or disable the breakpoint.
5049 @defvar Breakpoint.silent
5050 This attribute is @code{True} if the breakpoint is silent, and
5051 @code{False} otherwise. This attribute is writable.
5053 Note that a breakpoint can also be silent if it has commands and the
5054 first command is @code{silent}. This is not reported by the
5055 @code{silent} attribute.
5058 @defvar Breakpoint.pending
5059 This attribute is @code{True} if the breakpoint is pending, and
5060 @code{False} otherwise. @xref{Set Breaks}. This attribute is
5064 @anchor{python_breakpoint_thread}
5065 @defvar Breakpoint.thread
5066 If the breakpoint is thread-specific, this attribute holds the
5067 thread's global id. If the breakpoint is not thread-specific, this
5068 attribute is @code{None}. This attribute is writable.
5071 @defvar Breakpoint.task
5072 If the breakpoint is Ada task-specific, this attribute holds the Ada task
5073 id. If the breakpoint is not task-specific (or the underlying
5074 language is not Ada), this attribute is @code{None}. This attribute
5078 @defvar Breakpoint.ignore_count
5079 This attribute holds the ignore count for the breakpoint, an integer.
5080 This attribute is writable.
5083 @defvar Breakpoint.number
5084 This attribute holds the breakpoint's number --- the identifier used by
5085 the user to manipulate the breakpoint. This attribute is not writable.
5088 @defvar Breakpoint.type
5089 This attribute holds the breakpoint's type --- the identifier used to
5090 determine the actual breakpoint type or use-case. This attribute is not
5094 @defvar Breakpoint.visible
5095 This attribute tells whether the breakpoint is visible to the user
5096 when set, or when the @samp{info breakpoints} command is run. This
5097 attribute is not writable.
5100 @defvar Breakpoint.temporary
5101 This attribute indicates whether the breakpoint was created as a
5102 temporary breakpoint. Temporary breakpoints are automatically deleted
5103 after that breakpoint has been hit. Access to this attribute, and all
5104 other attributes and functions other than the @code{is_valid}
5105 function, will result in an error after the breakpoint has been hit
5106 (as it has been automatically deleted). This attribute is not
5110 @defvar Breakpoint.hit_count
5111 This attribute holds the hit count for the breakpoint, an integer.
5112 This attribute is writable, but currently it can only be set to zero.
5115 @defvar Breakpoint.location
5116 This attribute holds the location of the breakpoint, as specified by
5117 the user. It is a string. If the breakpoint does not have a location
5118 (that is, it is a watchpoint) the attribute's value is @code{None}. This
5119 attribute is not writable.
5122 @defvar Breakpoint.expression
5123 This attribute holds a breakpoint expression, as specified by
5124 the user. It is a string. If the breakpoint does not have an
5125 expression (the breakpoint is not a watchpoint) the attribute's value
5126 is @code{None}. This attribute is not writable.
5129 @defvar Breakpoint.condition
5130 This attribute holds the condition of the breakpoint, as specified by
5131 the user. It is a string. If there is no condition, this attribute's
5132 value is @code{None}. This attribute is writable.
5135 @defvar Breakpoint.commands
5136 This attribute holds the commands attached to the breakpoint. If
5137 there are commands, this attribute's value is a string holding all the
5138 commands, separated by newlines. If there are no commands, this
5139 attribute is @code{None}. This attribute is writable.
5142 @node Finish Breakpoints in Python
5143 @subsubsection Finish Breakpoints
5145 @cindex python finish breakpoints
5146 @tindex gdb.FinishBreakpoint
5148 A finish breakpoint is a temporary breakpoint set at the return address of
5149 a frame, based on the @code{finish} command. @code{gdb.FinishBreakpoint}
5150 extends @code{gdb.Breakpoint}. The underlying breakpoint will be disabled
5151 and deleted when the execution will run out of the breakpoint scope (i.e.@:
5152 @code{Breakpoint.stop} or @code{FinishBreakpoint.out_of_scope} triggered).
5153 Finish breakpoints are thread specific and must be create with the right
5156 @defun FinishBreakpoint.__init__ (@r{[}frame@r{]} @r{[}, internal@r{]})
5157 Create a finish breakpoint at the return address of the @code{gdb.Frame}
5158 object @var{frame}. If @var{frame} is not provided, this defaults to the
5159 newest frame. The optional @var{internal} argument allows the breakpoint to
5160 become invisible to the user. @xref{Breakpoints In Python}, for further
5161 details about this argument.
5164 @defun FinishBreakpoint.out_of_scope (self)
5165 In some circumstances (e.g.@: @code{longjmp}, C@t{++} exceptions, @value{GDBN}
5166 @code{return} command, @dots{}), a function may not properly terminate, and
5167 thus never hit the finish breakpoint. When @value{GDBN} notices such a
5168 situation, the @code{out_of_scope} callback will be triggered.
5170 You may want to sub-class @code{gdb.FinishBreakpoint} and override this
5174 class MyFinishBreakpoint (gdb.FinishBreakpoint)
5176 print "normal finish"
5179 def out_of_scope ():
5180 print "abnormal finish"
5184 @defvar FinishBreakpoint.return_value
5185 When @value{GDBN} is stopped at a finish breakpoint and the frame
5186 used to build the @code{gdb.FinishBreakpoint} object had debug symbols, this
5187 attribute will contain a @code{gdb.Value} object corresponding to the return
5188 value of the function. The value will be @code{None} if the function return
5189 type is @code{void} or if the return value was not computable. This attribute
5193 @node Lazy Strings In Python
5194 @subsubsection Python representation of lazy strings.
5196 @cindex lazy strings in python
5197 @tindex gdb.LazyString
5199 A @dfn{lazy string} is a string whose contents is not retrieved or
5200 encoded until it is needed.
5202 A @code{gdb.LazyString} is represented in @value{GDBN} as an
5203 @code{address} that points to a region of memory, an @code{encoding}
5204 that will be used to encode that region of memory, and a @code{length}
5205 to delimit the region of memory that represents the string. The
5206 difference between a @code{gdb.LazyString} and a string wrapped within
5207 a @code{gdb.Value} is that a @code{gdb.LazyString} will be treated
5208 differently by @value{GDBN} when printing. A @code{gdb.LazyString} is
5209 retrieved and encoded during printing, while a @code{gdb.Value}
5210 wrapping a string is immediately retrieved and encoded on creation.
5212 A @code{gdb.LazyString} object has the following functions:
5214 @defun LazyString.value ()
5215 Convert the @code{gdb.LazyString} to a @code{gdb.Value}. This value
5216 will point to the string in memory, but will lose all the delayed
5217 retrieval, encoding and handling that @value{GDBN} applies to a
5218 @code{gdb.LazyString}.
5221 @defvar LazyString.address
5222 This attribute holds the address of the string. This attribute is not
5226 @defvar LazyString.length
5227 This attribute holds the length of the string in characters. If the
5228 length is -1, then the string will be fetched and encoded up to the
5229 first null of appropriate width. This attribute is not writable.
5232 @defvar LazyString.encoding
5233 This attribute holds the encoding that will be applied to the string
5234 when the string is printed by @value{GDBN}. If the encoding is not
5235 set, or contains an empty string, then @value{GDBN} will select the
5236 most appropriate encoding when the string is printed. This attribute
5240 @defvar LazyString.type
5241 This attribute holds the type that is represented by the lazy string's
5242 type. For a lazy string this is a pointer or array type. To
5243 resolve this to the lazy string's character type, use the type's
5244 @code{target} method. @xref{Types In Python}. This attribute is not
5248 @node Architectures In Python
5249 @subsubsection Python representation of architectures
5250 @cindex Python architectures
5252 @value{GDBN} uses architecture specific parameters and artifacts in a
5253 number of its various computations. An architecture is represented
5254 by an instance of the @code{gdb.Architecture} class.
5256 A @code{gdb.Architecture} class has the following methods:
5258 @defun Architecture.name ()
5259 Return the name (string value) of the architecture.
5262 @defun Architecture.disassemble (@var{start_pc} @r{[}, @var{end_pc} @r{[}, @var{count}@r{]]})
5263 Return a list of disassembled instructions starting from the memory
5264 address @var{start_pc}. The optional arguments @var{end_pc} and
5265 @var{count} determine the number of instructions in the returned list.
5266 If both the optional arguments @var{end_pc} and @var{count} are
5267 specified, then a list of at most @var{count} disassembled instructions
5268 whose start address falls in the closed memory address interval from
5269 @var{start_pc} to @var{end_pc} are returned. If @var{end_pc} is not
5270 specified, but @var{count} is specified, then @var{count} number of
5271 instructions starting from the address @var{start_pc} are returned. If
5272 @var{count} is not specified but @var{end_pc} is specified, then all
5273 instructions whose start address falls in the closed memory address
5274 interval from @var{start_pc} to @var{end_pc} are returned. If neither
5275 @var{end_pc} nor @var{count} are specified, then a single instruction at
5276 @var{start_pc} is returned. For all of these cases, each element of the
5277 returned list is a Python @code{dict} with the following string keys:
5282 The value corresponding to this key is a Python long integer capturing
5283 the memory address of the instruction.
5286 The value corresponding to this key is a string value which represents
5287 the instruction with assembly language mnemonics. The assembly
5288 language flavor used is the same as that specified by the current CLI
5289 variable @code{disassembly-flavor}. @xref{Machine Code}.
5292 The value corresponding to this key is the length (integer value) of the
5293 instruction in bytes.
5298 @node Python Auto-loading
5299 @subsection Python Auto-loading
5300 @cindex Python auto-loading
5302 When a new object file is read (for example, due to the @code{file}
5303 command, or because the inferior has loaded a shared library),
5304 @value{GDBN} will look for Python support scripts in several ways:
5305 @file{@var{objfile}-gdb.py} and @code{.debug_gdb_scripts} section.
5306 @xref{Auto-loading extensions}.
5308 The auto-loading feature is useful for supplying application-specific
5309 debugging commands and scripts.
5311 Auto-loading can be enabled or disabled,
5312 and the list of auto-loaded scripts can be printed.
5315 @anchor{set auto-load python-scripts}
5316 @kindex set auto-load python-scripts
5317 @item set auto-load python-scripts [on|off]
5318 Enable or disable the auto-loading of Python scripts.
5320 @anchor{show auto-load python-scripts}
5321 @kindex show auto-load python-scripts
5322 @item show auto-load python-scripts
5323 Show whether auto-loading of Python scripts is enabled or disabled.
5325 @anchor{info auto-load python-scripts}
5326 @kindex info auto-load python-scripts
5327 @cindex print list of auto-loaded Python scripts
5328 @item info auto-load python-scripts [@var{regexp}]
5329 Print the list of all Python scripts that @value{GDBN} auto-loaded.
5331 Also printed is the list of Python scripts that were mentioned in
5332 the @code{.debug_gdb_scripts} section and were either not found
5333 (@pxref{dotdebug_gdb_scripts section}) or were not auto-loaded due to
5334 @code{auto-load safe-path} rejection (@pxref{Auto-loading}).
5335 This is useful because their names are not printed when @value{GDBN}
5336 tries to load them and fails. There may be many of them, and printing
5337 an error message for each one is problematic.
5339 If @var{regexp} is supplied only Python scripts with matching names are printed.
5344 (gdb) info auto-load python-scripts
5346 Yes py-section-script.py
5347 full name: /tmp/py-section-script.py
5348 No my-foo-pretty-printers.py
5352 When reading an auto-loaded file or script, @value{GDBN} sets the
5353 @dfn{current objfile}. This is available via the @code{gdb.current_objfile}
5354 function (@pxref{Objfiles In Python}). This can be useful for
5355 registering objfile-specific pretty-printers and frame-filters.
5357 @node Python modules
5358 @subsection Python modules
5359 @cindex python modules
5361 @value{GDBN} comes with several modules to assist writing Python code.
5364 * gdb.printing:: Building and registering pretty-printers.
5365 * gdb.types:: Utilities for working with types.
5366 * gdb.prompt:: Utilities for prompt value substitution.
5370 @subsubsection gdb.printing
5371 @cindex gdb.printing
5373 This module provides a collection of utilities for working with
5377 @item PrettyPrinter (@var{name}, @var{subprinters}=None)
5378 This class specifies the API that makes @samp{info pretty-printer},
5379 @samp{enable pretty-printer} and @samp{disable pretty-printer} work.
5380 Pretty-printers should generally inherit from this class.
5382 @item SubPrettyPrinter (@var{name})
5383 For printers that handle multiple types, this class specifies the
5384 corresponding API for the subprinters.
5386 @item RegexpCollectionPrettyPrinter (@var{name})
5387 Utility class for handling multiple printers, all recognized via
5388 regular expressions.
5389 @xref{Writing a Pretty-Printer}, for an example.
5391 @item FlagEnumerationPrinter (@var{name})
5392 A pretty-printer which handles printing of @code{enum} values. Unlike
5393 @value{GDBN}'s built-in @code{enum} printing, this printer attempts to
5394 work properly when there is some overlap between the enumeration
5395 constants. The argument @var{name} is the name of the printer and
5396 also the name of the @code{enum} type to look up.
5398 @item register_pretty_printer (@var{obj}, @var{printer}, @var{replace}=False)
5399 Register @var{printer} with the pretty-printer list of @var{obj}.
5400 If @var{replace} is @code{True} then any existing copy of the printer
5401 is replaced. Otherwise a @code{RuntimeError} exception is raised
5402 if a printer with the same name already exists.
5406 @subsubsection gdb.types
5409 This module provides a collection of utilities for working with
5410 @code{gdb.Type} objects.
5413 @item get_basic_type (@var{type})
5414 Return @var{type} with const and volatile qualifiers stripped,
5415 and with typedefs and C@t{++} references converted to the underlying type.
5420 typedef const int const_int;
5422 const_int& foo_ref (foo);
5423 int main () @{ return 0; @}
5430 (gdb) python import gdb.types
5431 (gdb) python foo_ref = gdb.parse_and_eval("foo_ref")
5432 (gdb) python print gdb.types.get_basic_type(foo_ref.type)
5436 @item has_field (@var{type}, @var{field})
5437 Return @code{True} if @var{type}, assumed to be a type with fields
5438 (e.g., a structure or union), has field @var{field}.
5440 @item make_enum_dict (@var{enum_type})
5441 Return a Python @code{dictionary} type produced from @var{enum_type}.
5443 @item deep_items (@var{type})
5444 Returns a Python iterator similar to the standard
5445 @code{gdb.Type.iteritems} method, except that the iterator returned
5446 by @code{deep_items} will recursively traverse anonymous struct or
5447 union fields. For example:
5461 Then in @value{GDBN}:
5463 (@value{GDBP}) python import gdb.types
5464 (@value{GDBP}) python struct_a = gdb.lookup_type("struct A")
5465 (@value{GDBP}) python print struct_a.keys ()
5467 (@value{GDBP}) python print [k for k,v in gdb.types.deep_items(struct_a)]
5468 @{['a', 'b0', 'b1']@}
5471 @item get_type_recognizers ()
5472 Return a list of the enabled type recognizers for the current context.
5473 This is called by @value{GDBN} during the type-printing process
5474 (@pxref{Type Printing API}).
5476 @item apply_type_recognizers (recognizers, type_obj)
5477 Apply the type recognizers, @var{recognizers}, to the type object
5478 @var{type_obj}. If any recognizer returns a string, return that
5479 string. Otherwise, return @code{None}. This is called by
5480 @value{GDBN} during the type-printing process (@pxref{Type Printing
5483 @item register_type_printer (locus, printer)
5484 This is a convenience function to register a type printer
5485 @var{printer}. The printer must implement the type printer protocol.
5486 The @var{locus} argument is either a @code{gdb.Objfile}, in which case
5487 the printer is registered with that objfile; a @code{gdb.Progspace},
5488 in which case the printer is registered with that progspace; or
5489 @code{None}, in which case the printer is registered globally.
5492 This is a base class that implements the type printer protocol. Type
5493 printers are encouraged, but not required, to derive from this class.
5494 It defines a constructor:
5496 @defmethod TypePrinter __init__ (self, name)
5497 Initialize the type printer with the given name. The new printer
5498 starts in the enabled state.
5504 @subsubsection gdb.prompt
5507 This module provides a method for prompt value-substitution.
5510 @item substitute_prompt (@var{string})
5511 Return @var{string} with escape sequences substituted by values. Some
5512 escape sequences take arguments. You can specify arguments inside
5513 ``@{@}'' immediately following the escape sequence.
5515 The escape sequences you can pass to this function are:
5519 Substitute a backslash.
5521 Substitute an ESC character.
5523 Substitute the selected frame; an argument names a frame parameter.
5525 Substitute a newline.
5527 Substitute a parameter's value; the argument names the parameter.
5529 Substitute a carriage return.
5531 Substitute the selected thread; an argument names a thread parameter.
5533 Substitute the version of GDB.
5535 Substitute the current working directory.
5537 Begin a sequence of non-printing characters. These sequences are
5538 typically used with the ESC character, and are not counted in the string
5539 length. Example: ``\[\e[0;34m\](gdb)\[\e[0m\]'' will return a
5540 blue-colored ``(gdb)'' prompt where the length is five.
5542 End a sequence of non-printing characters.
5548 substitute_prompt (``frame: \f,
5549 print arguments: \p@{print frame-arguments@}'')
5552 @exdent will return the string:
5555 "frame: main, print arguments: scalars"