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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}.
21 @value{GDBN} can be built against either Python 2 or Python 3; which
22 one you have depends on this configure-time option.
24 @cindex python directory
25 Python scripts used by @value{GDBN} should be installed in
26 @file{@var{data-directory}/python}, where @var{data-directory} is
27 the data directory as determined at @value{GDBN} startup (@pxref{Data Files}).
28 This directory, known as the @dfn{python directory},
29 is automatically added to the Python Search Path in order to allow
30 the Python interpreter to locate all scripts installed at this location.
32 Additionally, @value{GDBN} commands and convenience functions which
33 are written in Python and are located in the
34 @file{@var{data-directory}/python/gdb/command} or
35 @file{@var{data-directory}/python/gdb/function} directories are
36 automatically imported when @value{GDBN} starts.
39 * Python Commands:: Accessing Python from @value{GDBN}.
40 * Python API:: Accessing @value{GDBN} from Python.
41 * Python Auto-loading:: Automatically loading Python code.
42 * Python modules:: Python modules provided by @value{GDBN}.
46 @subsection Python Commands
47 @cindex python commands
48 @cindex commands to access python
50 @value{GDBN} provides two commands for accessing the Python interpreter,
51 and one related setting:
54 @kindex python-interactive
56 @item python-interactive @r{[}@var{command}@r{]}
57 @itemx pi @r{[}@var{command}@r{]}
58 Without an argument, the @code{python-interactive} command can be used
59 to start an interactive Python prompt. To return to @value{GDBN},
60 type the @code{EOF} character (e.g., @kbd{Ctrl-D} on an empty prompt).
62 Alternatively, a single-line Python command can be given as an
63 argument and evaluated. If the command is an expression, the result
64 will be printed; otherwise, nothing will be printed. For example:
67 (@value{GDBP}) python-interactive 2 + 3
73 @item python @r{[}@var{command}@r{]}
74 @itemx py @r{[}@var{command}@r{]}
75 The @code{python} command can be used to evaluate Python code.
77 If given an argument, the @code{python} command will evaluate the
78 argument as a Python command. For example:
81 (@value{GDBP}) python print 23
85 If you do not provide an argument to @code{python}, it will act as a
86 multi-line command, like @code{define}. In this case, the Python
87 script is made up of subsequent command lines, given after the
88 @code{python} command. This command list is terminated using a line
89 containing @code{end}. For example:
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.
107 @kindex set python ignore-environment
108 @item set python ignore-environment @r{[}on@r{|}off@r{]}
109 By default this option is @samp{off}, and, when @value{GDBN}
110 initializes its internal Python interpreter, the Python interpreter
111 will check the environment for variables that will effect how it
112 behaves, for example @env{PYTHONHOME}, and
113 @env{PYTHONPATH}@footnote{See the ENVIRONMENT VARIABLES section of
114 @command{man 1 python} for a comprehensive list.}.
116 If this option is set to @samp{on} before Python is initialized then
117 Python will ignore all such environment variables. As Python is
118 initialized early during @value{GDBN}'s startup process, then this
119 option must be placed into the early initialization file
120 (@pxref{Initialization Files}) to have the desired effect.
122 This option is equivalent to passing @option{-E} to the real
123 @command{python} executable.
125 @kindex set python dont-write-bytecode
126 @item set python dont-write-bytecode @r{[}auto@r{|}on@r{|}off@r{]}
127 When this option is @samp{off}, then, once @value{GDBN} has
128 initialized the Python interpreter, the interpreter will byte-compile
129 any Python modules that it imports and write the byte code to disk in
132 If this option is set to @samp{on} before Python is initialized then
133 Python will no longer write the byte code to disk. As Python is
134 initialized early during @value{GDBN}'s startup process, then this
135 option must be placed into the early initialization file
136 (@pxref{Initialization Files}) to have the desired effect.
138 By default this option is set to @samp{auto}, in this mode Python will
139 check the environment variable @env{PYTHONDONTWRITEBYTECODE} to see
140 if it should write out byte-code or not.
142 This option is equivalent to passing @option{-B} to the real
143 @command{python} executable.
146 It is also possible to execute a Python script from the @value{GDBN}
150 @item source @file{script-name}
151 The script name must end with @samp{.py} and @value{GDBN} must be configured
152 to recognize the script language based on filename extension using
153 the @code{script-extension} setting. @xref{Extending GDB, ,Extending GDB}.
156 The following commands are intended to help debug @value{GDBN} itself:
159 @kindex set debug py-breakpoint
160 @kindex show debug py-breakpoint
161 @item set debug py-breakpoint on@r{|}off
162 @itemx show debug py-breakpoint
163 When @samp{on}, @value{GDBN} prints debug messages related to the
164 Python breakpoint API. This is @samp{off} by default.
166 @kindex set debug py-unwind
167 @kindex show debug py-unwind
168 @item set debug py-unwind on@r{|}off
169 @itemx show debug py-unwind
170 When @samp{on}, @value{GDBN} prints debug messages related to the
171 Python unwinder API. This is @samp{off} by default.
175 @subsection Python API
177 @cindex programming in python
179 You can get quick online help for @value{GDBN}'s Python API by issuing
180 the command @w{@kbd{python help (gdb)}}.
182 Functions and methods which have two or more optional arguments allow
183 them to be specified using keyword syntax. This allows passing some
184 optional arguments while skipping others. Example:
185 @w{@code{gdb.some_function ('foo', bar = 1, baz = 2)}}.
188 * Basic Python:: Basic Python Functions.
189 * Exception Handling:: How Python exceptions are translated.
190 * Values From Inferior:: Python representation of values.
191 * Types In Python:: Python representation of types.
192 * Pretty Printing API:: Pretty-printing values.
193 * Selecting Pretty-Printers:: How GDB chooses a pretty-printer.
194 * Writing a Pretty-Printer:: Writing a Pretty-Printer.
195 * Type Printing API:: Pretty-printing types.
196 * Frame Filter API:: Filtering Frames.
197 * Frame Decorator API:: Decorating Frames.
198 * Writing a Frame Filter:: Writing a Frame Filter.
199 * Unwinding Frames in Python:: Writing frame unwinder.
200 * Xmethods In Python:: Adding and replacing methods of C++ classes.
201 * Xmethod API:: Xmethod types.
202 * Writing an Xmethod:: Writing an xmethod.
203 * Inferiors In Python:: Python representation of inferiors (processes)
204 * Events In Python:: Listening for events from @value{GDBN}.
205 * Threads In Python:: Accessing inferior threads from Python.
206 * Recordings In Python:: Accessing recordings from Python.
207 * Commands In Python:: Implementing new commands in Python.
208 * Parameters In Python:: Adding new @value{GDBN} parameters.
209 * Functions In Python:: Writing new convenience functions.
210 * Progspaces In Python:: Program spaces.
211 * Objfiles In Python:: Object files.
212 * Frames In Python:: Accessing inferior stack frames from Python.
213 * Blocks In Python:: Accessing blocks from Python.
214 * Symbols In Python:: Python representation of symbols.
215 * Symbol Tables In Python:: Python representation of symbol tables.
216 * Line Tables In Python:: Python representation of line tables.
217 * Breakpoints In Python:: Manipulating breakpoints using Python.
218 * Finish Breakpoints in Python:: Setting Breakpoints on function return
220 * Lazy Strings In Python:: Python representation of lazy strings.
221 * Architectures In Python:: Python representation of architectures.
222 * Registers In Python:: Python representation of registers.
223 * TUI Windows In Python:: Implementing new TUI windows.
227 @subsubsection Basic Python
229 @cindex python stdout
230 @cindex python pagination
231 At startup, @value{GDBN} overrides Python's @code{sys.stdout} and
232 @code{sys.stderr} to print using @value{GDBN}'s output-paging streams.
233 A Python program which outputs to one of these streams may have its
234 output interrupted by the user (@pxref{Screen Size}). In this
235 situation, a Python @code{KeyboardInterrupt} exception is thrown.
237 Some care must be taken when writing Python code to run in
238 @value{GDBN}. Two things worth noting in particular:
242 @value{GDBN} install handlers for @code{SIGCHLD} and @code{SIGINT}.
243 Python code must not override these, or even change the options using
244 @code{sigaction}. If your program changes the handling of these
245 signals, @value{GDBN} will most likely stop working correctly. Note
246 that it is unfortunately common for GUI toolkits to install a
247 @code{SIGCHLD} handler.
250 @value{GDBN} takes care to mark its internal file descriptors as
251 close-on-exec. However, this cannot be done in a thread-safe way on
252 all platforms. Your Python programs should be aware of this and
253 should both create new file descriptors with the close-on-exec flag
254 set and arrange to close unneeded file descriptors before starting a
258 @cindex python functions
259 @cindex python module
261 @value{GDBN} introduces a new Python module, named @code{gdb}. All
262 methods and classes added by @value{GDBN} are placed in this module.
263 @value{GDBN} automatically @code{import}s the @code{gdb} module for
264 use in all scripts evaluated by the @code{python} command.
266 Some types of the @code{gdb} module come with a textual representation
267 (accessible through the @code{repr} or @code{str} functions). These are
268 offered for debugging purposes only, expect them to change over time.
270 @findex gdb.PYTHONDIR
271 @defvar gdb.PYTHONDIR
272 A string containing the python directory (@pxref{Python}).
276 @defun gdb.execute (command @r{[}, from_tty @r{[}, to_string@r{]]})
277 Evaluate @var{command}, a string, as a @value{GDBN} CLI command.
278 If a GDB exception happens while @var{command} runs, it is
279 translated as described in @ref{Exception Handling,,Exception Handling}.
281 The @var{from_tty} flag specifies whether @value{GDBN} ought to consider this
282 command as having originated from the user invoking it interactively.
283 It must be a boolean value. If omitted, it defaults to @code{False}.
285 By default, any output produced by @var{command} is sent to
286 @value{GDBN}'s standard output (and to the log output if logging is
287 turned on). If the @var{to_string} parameter is
288 @code{True}, then output will be collected by @code{gdb.execute} and
289 returned as a string. The default is @code{False}, in which case the
290 return value is @code{None}. If @var{to_string} is @code{True}, the
291 @value{GDBN} virtual terminal will be temporarily set to unlimited width
292 and height, and its pagination will be disabled; @pxref{Screen Size}.
295 @findex gdb.breakpoints
296 @defun gdb.breakpoints ()
297 Return a sequence holding all of @value{GDBN}'s breakpoints.
298 @xref{Breakpoints In Python}, for more information. In @value{GDBN}
299 version 7.11 and earlier, this function returned @code{None} if there
300 were no breakpoints. This peculiarity was subsequently fixed, and now
301 @code{gdb.breakpoints} returns an empty sequence in this case.
304 @defun gdb.rbreak (regex @r{[}, minsyms @r{[}, throttle, @r{[}, symtabs @r{]]]})
305 Return a Python list holding a collection of newly set
306 @code{gdb.Breakpoint} objects matching function names defined by the
307 @var{regex} pattern. If the @var{minsyms} keyword is @code{True}, all
308 system functions (those not explicitly defined in the inferior) will
309 also be included in the match. The @var{throttle} keyword takes an
310 integer that defines the maximum number of pattern matches for
311 functions matched by the @var{regex} pattern. If the number of
312 matches exceeds the integer value of @var{throttle}, a
313 @code{RuntimeError} will be raised and no breakpoints will be created.
314 If @var{throttle} is not defined then there is no imposed limit on the
315 maximum number of matches and breakpoints to be created. The
316 @var{symtabs} keyword takes a Python iterable that yields a collection
317 of @code{gdb.Symtab} objects and will restrict the search to those
318 functions only contained within the @code{gdb.Symtab} objects.
321 @findex gdb.parameter
322 @defun gdb.parameter (parameter)
323 Return the value of a @value{GDBN} @var{parameter} given by its name,
324 a string; the parameter name string may contain spaces if the parameter has a
325 multi-part name. For example, @samp{print object} is a valid
328 If the named parameter does not exist, this function throws a
329 @code{gdb.error} (@pxref{Exception Handling}). Otherwise, the
330 parameter's value is converted to a Python value of the appropriate
335 @defun gdb.history (number)
336 Return a value from @value{GDBN}'s value history (@pxref{Value
337 History}). The @var{number} argument indicates which history element to return.
338 If @var{number} is negative, then @value{GDBN} will take its absolute value
339 and count backward from the last element (i.e., the most recent element) to
340 find the value to return. If @var{number} is zero, then @value{GDBN} will
341 return the most recent element. If the element specified by @var{number}
342 doesn't exist in the value history, a @code{gdb.error} exception will be
345 If no exception is raised, the return value is always an instance of
346 @code{gdb.Value} (@pxref{Values From Inferior}).
349 @findex gdb.convenience_variable
350 @defun gdb.convenience_variable (name)
351 Return the value of the convenience variable (@pxref{Convenience
352 Vars}) named @var{name}. @var{name} must be a string. The name
353 should not include the @samp{$} that is used to mark a convenience
354 variable in an expression. If the convenience variable does not
355 exist, then @code{None} is returned.
358 @findex gdb.set_convenience_variable
359 @defun gdb.set_convenience_variable (name, value)
360 Set the value of the convenience variable (@pxref{Convenience Vars})
361 named @var{name}. @var{name} must be a string. The name should not
362 include the @samp{$} that is used to mark a convenience variable in an
363 expression. If @var{value} is @code{None}, then the convenience
364 variable is removed. Otherwise, if @var{value} is not a
365 @code{gdb.Value} (@pxref{Values From Inferior}), it is is converted
366 using the @code{gdb.Value} constructor.
369 @findex gdb.parse_and_eval
370 @defun gdb.parse_and_eval (expression)
371 Parse @var{expression}, which must be a string, as an expression in
372 the current language, evaluate it, and return the result as a
375 This function can be useful when implementing a new command
376 (@pxref{Commands In Python}), as it provides a way to parse the
377 command's argument as an expression. It is also useful simply to
381 @findex gdb.find_pc_line
382 @defun gdb.find_pc_line (pc)
383 Return the @code{gdb.Symtab_and_line} object corresponding to the
384 @var{pc} value. @xref{Symbol Tables In Python}. If an invalid
385 value of @var{pc} is passed as an argument, then the @code{symtab} and
386 @code{line} attributes of the returned @code{gdb.Symtab_and_line} object
387 will be @code{None} and 0 respectively. This is identical to
388 @code{gdb.current_progspace().find_pc_line(pc)} and is included for
389 historical compatibility.
392 @findex gdb.post_event
393 @defun gdb.post_event (event)
394 Put @var{event}, a callable object taking no arguments, into
395 @value{GDBN}'s internal event queue. This callable will be invoked at
396 some later point, during @value{GDBN}'s event processing. Events
397 posted using @code{post_event} will be run in the order in which they
398 were posted; however, there is no way to know when they will be
399 processed relative to other events inside @value{GDBN}.
401 @value{GDBN} is not thread-safe. If your Python program uses multiple
402 threads, you must be careful to only call @value{GDBN}-specific
403 functions in the @value{GDBN} thread. @code{post_event} ensures
407 (@value{GDBP}) python
411 > def __init__(self, message):
412 > self.message = message;
413 > def __call__(self):
414 > gdb.write(self.message)
416 >class MyThread1 (threading.Thread):
418 > gdb.post_event(Writer("Hello "))
420 >class MyThread2 (threading.Thread):
422 > gdb.post_event(Writer("World\n"))
427 (@value{GDBP}) Hello World
432 @defun gdb.write (string @r{[}, stream{]})
433 Print a string to @value{GDBN}'s paginated output stream. The
434 optional @var{stream} determines the stream to print to. The default
435 stream is @value{GDBN}'s standard output stream. Possible stream
442 @value{GDBN}'s standard output stream.
447 @value{GDBN}'s standard error stream.
452 @value{GDBN}'s log stream (@pxref{Logging Output}).
455 Writing to @code{sys.stdout} or @code{sys.stderr} will automatically
456 call this function and will automatically direct the output to the
462 Flush the buffer of a @value{GDBN} paginated stream so that the
463 contents are displayed immediately. @value{GDBN} will flush the
464 contents of a stream automatically when it encounters a newline in the
465 buffer. The optional @var{stream} determines the stream to flush. The
466 default stream is @value{GDBN}'s standard output stream. Possible
473 @value{GDBN}'s standard output stream.
478 @value{GDBN}'s standard error stream.
483 @value{GDBN}'s log stream (@pxref{Logging Output}).
487 Flushing @code{sys.stdout} or @code{sys.stderr} will automatically
488 call this function for the relevant stream.
491 @findex gdb.target_charset
492 @defun gdb.target_charset ()
493 Return the name of the current target character set (@pxref{Character
494 Sets}). This differs from @code{gdb.parameter('target-charset')} in
495 that @samp{auto} is never returned.
498 @findex gdb.target_wide_charset
499 @defun gdb.target_wide_charset ()
500 Return the name of the current target wide character set
501 (@pxref{Character Sets}). This differs from
502 @code{gdb.parameter('target-wide-charset')} in that @samp{auto} is
506 @findex gdb.solib_name
507 @defun gdb.solib_name (address)
508 Return the name of the shared library holding the given @var{address}
509 as a string, or @code{None}. This is identical to
510 @code{gdb.current_progspace().solib_name(address)} and is included for
511 historical compatibility.
514 @findex gdb.decode_line
515 @defun gdb.decode_line (@r{[}expression@r{]})
516 Return locations of the line specified by @var{expression}, or of the
517 current line if no argument was given. This function returns a Python
518 tuple containing two elements. The first element contains a string
519 holding any unparsed section of @var{expression} (or @code{None} if
520 the expression has been fully parsed). The second element contains
521 either @code{None} or another tuple that contains all the locations
522 that match the expression represented as @code{gdb.Symtab_and_line}
523 objects (@pxref{Symbol Tables In Python}). If @var{expression} is
524 provided, it is decoded the way that @value{GDBN}'s inbuilt
525 @code{break} or @code{edit} commands do (@pxref{Specify Location}).
528 @defun gdb.prompt_hook (current_prompt)
531 If @var{prompt_hook} is callable, @value{GDBN} will call the method
532 assigned to this operation before a prompt is displayed by
535 The parameter @code{current_prompt} contains the current @value{GDBN}
536 prompt. This method must return a Python string, or @code{None}. If
537 a string is returned, the @value{GDBN} prompt will be set to that
538 string. If @code{None} is returned, @value{GDBN} will continue to use
541 Some prompts cannot be substituted in @value{GDBN}. Secondary prompts
542 such as those used by readline for command input, and annotation
543 related prompts are prohibited from being changed.
546 @node Exception Handling
547 @subsubsection Exception Handling
548 @cindex python exceptions
549 @cindex exceptions, python
551 When executing the @code{python} command, Python exceptions
552 uncaught within the Python code are translated to calls to
553 @value{GDBN} error-reporting mechanism. If the command that called
554 @code{python} does not handle the error, @value{GDBN} will
555 terminate it and print an error message containing the Python
556 exception name, the associated value, and the Python call stack
557 backtrace at the point where the exception was raised. Example:
560 (@value{GDBP}) python print foo
561 Traceback (most recent call last):
562 File "<string>", line 1, in <module>
563 NameError: name 'foo' is not defined
566 @value{GDBN} errors that happen in @value{GDBN} commands invoked by
567 Python code are converted to Python exceptions. The type of the
568 Python exception depends on the error.
572 This is the base class for most exceptions generated by @value{GDBN}.
573 It is derived from @code{RuntimeError}, for compatibility with earlier
574 versions of @value{GDBN}.
576 If an error occurring in @value{GDBN} does not fit into some more
577 specific category, then the generated exception will have this type.
579 @item gdb.MemoryError
580 This is a subclass of @code{gdb.error} which is thrown when an
581 operation tried to access invalid memory in the inferior.
583 @item KeyboardInterrupt
584 User interrupt (via @kbd{C-c} or by typing @kbd{q} at a pagination
585 prompt) is translated to a Python @code{KeyboardInterrupt} exception.
588 In all cases, your exception handler will see the @value{GDBN} error
589 message as its value and the Python call stack backtrace at the Python
590 statement closest to where the @value{GDBN} error occured as the
594 When implementing @value{GDBN} commands in Python via
595 @code{gdb.Command}, or functions via @code{gdb.Function}, it is useful
596 to be able to throw an exception that doesn't cause a traceback to be
597 printed. For example, the user may have invoked the command
598 incorrectly. @value{GDBN} provides a special exception class that can
599 be used for this purpose.
603 When thrown from a command or function, this exception will cause the
604 command or function to fail, but the Python stack will not be
605 displayed. @value{GDBN} does not throw this exception itself, but
606 rather recognizes it when thrown from user Python code. Example:
610 >class HelloWorld (gdb.Command):
611 > """Greet the whole world."""
612 > def __init__ (self):
613 > super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)
614 > def invoke (self, args, from_tty):
615 > argv = gdb.string_to_argv (args)
616 > if len (argv) != 0:
617 > raise gdb.GdbError ("hello-world takes no arguments")
618 > print ("Hello, World!")
622 hello-world takes no arguments
626 @node Values From Inferior
627 @subsubsection Values From Inferior
628 @cindex values from inferior, with Python
629 @cindex python, working with values from inferior
631 @cindex @code{gdb.Value}
632 @value{GDBN} provides values it obtains from the inferior program in
633 an object of type @code{gdb.Value}. @value{GDBN} uses this object
634 for its internal bookkeeping of the inferior's values, and for
635 fetching values when necessary.
637 Inferior values that are simple scalars can be used directly in
638 Python expressions that are valid for the value's data type. Here's
639 an example for an integer or floating-point value @code{some_val}:
646 As result of this, @code{bar} will also be a @code{gdb.Value} object
647 whose values are of the same type as those of @code{some_val}. Valid
648 Python operations can also be performed on @code{gdb.Value} objects
649 representing a @code{struct} or @code{class} object. For such cases,
650 the overloaded operator (if present), is used to perform the operation.
651 For example, if @code{val1} and @code{val2} are @code{gdb.Value} objects
652 representing instances of a @code{class} which overloads the @code{+}
653 operator, then one can use the @code{+} operator in their Python script
661 The result of the operation @code{val3} is also a @code{gdb.Value}
662 object corresponding to the value returned by the overloaded @code{+}
663 operator. In general, overloaded operators are invoked for the
664 following operations: @code{+} (binary addition), @code{-} (binary
665 subtraction), @code{*} (multiplication), @code{/}, @code{%}, @code{<<},
666 @code{>>}, @code{|}, @code{&}, @code{^}.
668 Inferior values that are structures or instances of some class can
669 be accessed using the Python @dfn{dictionary syntax}. For example, if
670 @code{some_val} is a @code{gdb.Value} instance holding a structure, you
671 can access its @code{foo} element with:
674 bar = some_val['foo']
677 @cindex getting structure elements using gdb.Field objects as subscripts
678 Again, @code{bar} will also be a @code{gdb.Value} object. Structure
679 elements can also be accessed by using @code{gdb.Field} objects as
680 subscripts (@pxref{Types In Python}, for more information on
681 @code{gdb.Field} objects). For example, if @code{foo_field} is a
682 @code{gdb.Field} object corresponding to element @code{foo} of the above
683 structure, then @code{bar} can also be accessed as follows:
686 bar = some_val[foo_field]
689 A @code{gdb.Value} that represents a function can be executed via
690 inferior function call. Any arguments provided to the call must match
691 the function's prototype, and must be provided in the order specified
694 For example, @code{some_val} is a @code{gdb.Value} instance
695 representing a function that takes two integers as arguments. To
696 execute this function, call it like so:
699 result = some_val (10,20)
702 Any values returned from a function call will be stored as a
705 The following attributes are provided:
707 @defvar Value.address
708 If this object is addressable, this read-only attribute holds a
709 @code{gdb.Value} object representing the address. Otherwise,
710 this attribute holds @code{None}.
713 @cindex optimized out value in Python
714 @defvar Value.is_optimized_out
715 This read-only boolean attribute is true if the compiler optimized out
716 this value, thus it is not available for fetching from the inferior.
720 The type of this @code{gdb.Value}. The value of this attribute is a
721 @code{gdb.Type} object (@pxref{Types In Python}).
724 @defvar Value.dynamic_type
725 The dynamic type of this @code{gdb.Value}. This uses the object's
726 virtual table and the C@t{++} run-time type information
727 (@acronym{RTTI}) to determine the dynamic type of the value. If this
728 value is of class type, it will return the class in which the value is
729 embedded, if any. If this value is of pointer or reference to a class
730 type, it will compute the dynamic type of the referenced object, and
731 return a pointer or reference to that type, respectively. In all
732 other cases, it will return the value's static type.
734 Note that this feature will only work when debugging a C@t{++} program
735 that includes @acronym{RTTI} for the object in question. Otherwise,
736 it will just return the static type of the value as in @kbd{ptype foo}
737 (@pxref{Symbols, ptype}).
740 @defvar Value.is_lazy
741 The value of this read-only boolean attribute is @code{True} if this
742 @code{gdb.Value} has not yet been fetched from the inferior.
743 @value{GDBN} does not fetch values until necessary, for efficiency.
747 myval = gdb.parse_and_eval ('somevar')
750 The value of @code{somevar} is not fetched at this time. It will be
751 fetched when the value is needed, or when the @code{fetch_lazy}
755 The following methods are provided:
757 @defun Value.__init__ (@var{val})
758 Many Python values can be converted directly to a @code{gdb.Value} via
759 this object initializer. Specifically:
763 A Python boolean is converted to the boolean type from the current
767 A Python integer is converted to the C @code{long} type for the
768 current architecture.
771 A Python long is converted to the C @code{long long} type for the
772 current architecture.
775 A Python float is converted to the C @code{double} type for the
776 current architecture.
779 A Python string is converted to a target string in the current target
780 language using the current target encoding.
781 If a character cannot be represented in the current target encoding,
782 then an exception is thrown.
784 @item @code{gdb.Value}
785 If @code{val} is a @code{gdb.Value}, then a copy of the value is made.
787 @item @code{gdb.LazyString}
788 If @code{val} is a @code{gdb.LazyString} (@pxref{Lazy Strings In
789 Python}), then the lazy string's @code{value} method is called, and
794 @defun Value.__init__ (@var{val}, @var{type})
795 This second form of the @code{gdb.Value} constructor returns a
796 @code{gdb.Value} of type @var{type} where the value contents are taken
797 from the Python buffer object specified by @var{val}. The number of
798 bytes in the Python buffer object must be greater than or equal to the
802 @defun Value.cast (type)
803 Return a new instance of @code{gdb.Value} that is the result of
804 casting this instance to the type described by @var{type}, which must
805 be a @code{gdb.Type} object. If the cast cannot be performed for some
806 reason, this method throws an exception.
809 @defun Value.dereference ()
810 For pointer data types, this method returns a new @code{gdb.Value} object
811 whose contents is the object pointed to by the pointer. For example, if
812 @code{foo} is a C pointer to an @code{int}, declared in your C program as
819 then you can use the corresponding @code{gdb.Value} to access what
820 @code{foo} points to like this:
823 bar = foo.dereference ()
826 The result @code{bar} will be a @code{gdb.Value} object holding the
827 value pointed to by @code{foo}.
829 A similar function @code{Value.referenced_value} exists which also
830 returns @code{gdb.Value} objects corresponding to the values pointed to
831 by pointer values (and additionally, values referenced by reference
832 values). However, the behavior of @code{Value.dereference}
833 differs from @code{Value.referenced_value} by the fact that the
834 behavior of @code{Value.dereference} is identical to applying the C
835 unary operator @code{*} on a given value. For example, consider a
836 reference to a pointer @code{ptrref}, declared in your C@t{++} program
844 intptr &ptrref = ptr;
847 Though @code{ptrref} is a reference value, one can apply the method
848 @code{Value.dereference} to the @code{gdb.Value} object corresponding
849 to it and obtain a @code{gdb.Value} which is identical to that
850 corresponding to @code{val}. However, if you apply the method
851 @code{Value.referenced_value}, the result would be a @code{gdb.Value}
852 object identical to that corresponding to @code{ptr}.
855 py_ptrref = gdb.parse_and_eval ("ptrref")
856 py_val = py_ptrref.dereference ()
857 py_ptr = py_ptrref.referenced_value ()
860 The @code{gdb.Value} object @code{py_val} is identical to that
861 corresponding to @code{val}, and @code{py_ptr} is identical to that
862 corresponding to @code{ptr}. In general, @code{Value.dereference} can
863 be applied whenever the C unary operator @code{*} can be applied
864 to the corresponding C value. For those cases where applying both
865 @code{Value.dereference} and @code{Value.referenced_value} is allowed,
866 the results obtained need not be identical (as we have seen in the above
867 example). The results are however identical when applied on
868 @code{gdb.Value} objects corresponding to pointers (@code{gdb.Value}
869 objects with type code @code{TYPE_CODE_PTR}) in a C/C@t{++} program.
872 @defun Value.referenced_value ()
873 For pointer or reference data types, this method returns a new
874 @code{gdb.Value} object corresponding to the value referenced by the
875 pointer/reference value. For pointer data types,
876 @code{Value.dereference} and @code{Value.referenced_value} produce
877 identical results. The difference between these methods is that
878 @code{Value.dereference} cannot get the values referenced by reference
879 values. For example, consider a reference to an @code{int}, declared
880 in your C@t{++} program as
888 then applying @code{Value.dereference} to the @code{gdb.Value} object
889 corresponding to @code{ref} will result in an error, while applying
890 @code{Value.referenced_value} will result in a @code{gdb.Value} object
891 identical to that corresponding to @code{val}.
894 py_ref = gdb.parse_and_eval ("ref")
895 er_ref = py_ref.dereference () # Results in error
896 py_val = py_ref.referenced_value () # Returns the referenced value
899 The @code{gdb.Value} object @code{py_val} is identical to that
900 corresponding to @code{val}.
903 @defun Value.reference_value ()
904 Return a @code{gdb.Value} object which is a reference to the value
905 encapsulated by this instance.
908 @defun Value.const_value ()
909 Return a @code{gdb.Value} object which is a @code{const} version of the
910 value encapsulated by this instance.
913 @defun Value.dynamic_cast (type)
914 Like @code{Value.cast}, but works as if the C@t{++} @code{dynamic_cast}
915 operator were used. Consult a C@t{++} reference for details.
918 @defun Value.reinterpret_cast (type)
919 Like @code{Value.cast}, but works as if the C@t{++} @code{reinterpret_cast}
920 operator were used. Consult a C@t{++} reference for details.
923 @defun Value.format_string (...)
924 Convert a @code{gdb.Value} to a string, similarly to what the @code{print}
925 command does. Invoked with no arguments, this is equivalent to calling
926 the @code{str} function on the @code{gdb.Value}. The representation of
927 the same value may change across different versions of @value{GDBN}, so
928 you shouldn't, for instance, parse the strings returned by this method.
930 All the arguments are keyword only. If an argument is not specified, the
931 current global default setting is used.
935 @code{True} if pretty-printers (@pxref{Pretty Printing}) should not be
936 used to format the value. @code{False} if enabled pretty-printers
937 matching the type represented by the @code{gdb.Value} should be used to
941 @code{True} if arrays should be pretty printed to be more convenient to
942 read, @code{False} if they shouldn't (see @code{set print array} in
943 @ref{Print Settings}).
946 @code{True} if structs should be pretty printed to be more convenient to
947 read, @code{False} if they shouldn't (see @code{set print pretty} in
948 @ref{Print Settings}).
951 @code{True} if array indexes should be included in the string
952 representation of arrays, @code{False} if they shouldn't (see @code{set
953 print array-indexes} in @ref{Print Settings}).
956 @code{True} if the string representation of a pointer should include the
957 corresponding symbol name (if one exists), @code{False} if it shouldn't
958 (see @code{set print symbol} in @ref{Print Settings}).
961 @code{True} if unions which are contained in other structures or unions
962 should be expanded, @code{False} if they shouldn't (see @code{set print
963 union} in @ref{Print Settings}).
966 @code{True} if the string representation of a pointer should include the
967 address, @code{False} if it shouldn't (see @code{set print address} in
968 @ref{Print Settings}).
971 @code{True} if C@t{++} references should be resolved to the value they
972 refer to, @code{False} (the default) if they shouldn't. Note that, unlike
973 for the @code{print} command, references are not automatically expanded
974 when using the @code{format_string} method or the @code{str}
975 function. There is no global @code{print} setting to change the default
979 @code{True} if the representation of a pointer to an object should
980 identify the @emph{actual} (derived) type of the object rather than the
981 @emph{declared} type, using the virtual function table. @code{False} if
982 the @emph{declared} type should be used. (See @code{set print object} in
983 @ref{Print Settings}).
986 @code{True} if static members should be included in the string
987 representation of a C@t{++} object, @code{False} if they shouldn't (see
988 @code{set print static-members} in @ref{Print Settings}).
991 Number of array elements to print, or @code{0} to print an unlimited
992 number of elements (see @code{set print elements} in @ref{Print
996 The maximum depth to print for nested structs and unions, or @code{-1}
997 to print an unlimited number of elements (see @code{set print
998 max-depth} in @ref{Print Settings}).
1000 @item repeat_threshold
1001 Set the threshold for suppressing display of repeated array elements, or
1002 @code{0} to represent all elements, even if repeated. (See @code{set
1003 print repeats} in @ref{Print Settings}).
1006 A string containing a single character representing the format to use for
1007 the returned string. For instance, @code{'x'} is equivalent to using the
1008 @value{GDBN} command @code{print} with the @code{/x} option and formats
1009 the value as a hexadecimal number.
1013 @defun Value.string (@r{[}encoding@r{[}, errors@r{[}, length@r{]]]})
1014 If this @code{gdb.Value} represents a string, then this method
1015 converts the contents to a Python string. Otherwise, this method will
1018 Values are interpreted as strings according to the rules of the
1019 current language. If the optional length argument is given, the
1020 string will be converted to that length, and will include any embedded
1021 zeroes that the string may contain. Otherwise, for languages
1022 where the string is zero-terminated, the entire string will be
1025 For example, in C-like languages, a value is a string if it is a pointer
1026 to or an array of characters or ints of type @code{wchar_t}, @code{char16_t},
1029 If the optional @var{encoding} argument is given, it must be a string
1030 naming the encoding of the string in the @code{gdb.Value}, such as
1031 @code{"ascii"}, @code{"iso-8859-6"} or @code{"utf-8"}. It accepts
1032 the same encodings as the corresponding argument to Python's
1033 @code{string.decode} method, and the Python codec machinery will be used
1034 to convert the string. If @var{encoding} is not given, or if
1035 @var{encoding} is the empty string, then either the @code{target-charset}
1036 (@pxref{Character Sets}) will be used, or a language-specific encoding
1037 will be used, if the current language is able to supply one.
1039 The optional @var{errors} argument is the same as the corresponding
1040 argument to Python's @code{string.decode} method.
1042 If the optional @var{length} argument is given, the string will be
1043 fetched and converted to the given length.
1046 @defun Value.lazy_string (@r{[}encoding @r{[}, length@r{]]})
1047 If this @code{gdb.Value} represents a string, then this method
1048 converts the contents to a @code{gdb.LazyString} (@pxref{Lazy Strings
1049 In Python}). Otherwise, this method will throw an exception.
1051 If the optional @var{encoding} argument is given, it must be a string
1052 naming the encoding of the @code{gdb.LazyString}. Some examples are:
1053 @samp{ascii}, @samp{iso-8859-6} or @samp{utf-8}. If the
1054 @var{encoding} argument is an encoding that @value{GDBN} does
1055 recognize, @value{GDBN} will raise an error.
1057 When a lazy string is printed, the @value{GDBN} encoding machinery is
1058 used to convert the string during printing. If the optional
1059 @var{encoding} argument is not provided, or is an empty string,
1060 @value{GDBN} will automatically select the encoding most suitable for
1061 the string type. For further information on encoding in @value{GDBN}
1062 please see @ref{Character Sets}.
1064 If the optional @var{length} argument is given, the string will be
1065 fetched and encoded to the length of characters specified. If
1066 the @var{length} argument is not provided, the string will be fetched
1067 and encoded until a null of appropriate width is found.
1070 @defun Value.fetch_lazy ()
1071 If the @code{gdb.Value} object is currently a lazy value
1072 (@code{gdb.Value.is_lazy} is @code{True}), then the value is
1073 fetched from the inferior. Any errors that occur in the process
1074 will produce a Python exception.
1076 If the @code{gdb.Value} object is not a lazy value, this method
1079 This method does not return a value.
1083 @node Types In Python
1084 @subsubsection Types In Python
1085 @cindex types in Python
1086 @cindex Python, working with types
1089 @value{GDBN} represents types from the inferior using the class
1092 The following type-related functions are available in the @code{gdb}
1095 @findex gdb.lookup_type
1096 @defun gdb.lookup_type (name @r{[}, block@r{]})
1097 This function looks up a type by its @var{name}, which must be a string.
1099 If @var{block} is given, then @var{name} is looked up in that scope.
1100 Otherwise, it is searched for globally.
1102 Ordinarily, this function will return an instance of @code{gdb.Type}.
1103 If the named type cannot be found, it will throw an exception.
1106 If the type is a structure or class type, or an enum type, the fields
1107 of that type can be accessed using the Python @dfn{dictionary syntax}.
1108 For example, if @code{some_type} is a @code{gdb.Type} instance holding
1109 a structure type, you can access its @code{foo} field with:
1112 bar = some_type['foo']
1115 @code{bar} will be a @code{gdb.Field} object; see below under the
1116 description of the @code{Type.fields} method for a description of the
1117 @code{gdb.Field} class.
1119 An instance of @code{Type} has the following attributes:
1121 @defvar Type.alignof
1122 The alignment of this type, in bytes. Type alignment comes from the
1123 debugging information; if it was not specified, then @value{GDBN} will
1124 use the relevant ABI to try to determine the alignment. In some
1125 cases, even this is not possible, and zero will be returned.
1129 The type code for this type. The type code will be one of the
1130 @code{TYPE_CODE_} constants defined below.
1133 @defvar Type.dynamic
1134 A boolean indicating whether this type is dynamic. In some
1135 situations, such as Rust @code{enum} types or Ada variant records, the
1136 concrete type of a value may vary depending on its contents. That is,
1137 the declared type of a variable, or the type returned by
1138 @code{gdb.lookup_type} may be dynamic; while the type of the
1139 variable's value will be a concrete instance of that dynamic type.
1141 For example, consider this code:
1147 Here, at least conceptually (whether your compiler actually does this
1148 is a separate issue), examining @w{@code{gdb.lookup_symbol("array", ...).type}}
1149 could yield a @code{gdb.Type} which reports a size of @code{None}.
1150 This is the dynamic type.
1152 However, examining @code{gdb.parse_and_eval("array").type} would yield
1153 a concrete type, whose length would be known.
1157 The name of this type. If this type has no name, then @code{None}
1162 The size of this type, in target @code{char} units. Usually, a
1163 target's @code{char} type will be an 8-bit byte. However, on some
1164 unusual platforms, this type may have a different size. A dynamic
1165 type may not have a fixed size; in this case, this attribute's value
1166 will be @code{None}.
1170 The tag name for this type. The tag name is the name after
1171 @code{struct}, @code{union}, or @code{enum} in C and C@t{++}; not all
1172 languages have this concept. If this type has no tag name, then
1173 @code{None} is returned.
1176 @defvar Type.objfile
1177 The @code{gdb.Objfile} that this type was defined in, or @code{None} if
1178 there is no associated objfile.
1181 The following methods are provided:
1183 @defun Type.fields ()
1185 Return the fields of this type. The behavior depends on the type code:
1190 For structure and union types, this method returns the fields.
1193 Range types have two fields, the minimum and maximum values.
1196 Enum types have one field per enum constant.
1199 Function and method types have one field per parameter. The base types of
1200 C@t{++} classes are also represented as fields.
1203 Array types have one field representing the array's range.
1206 If the type does not fit into one of these categories, a @code{TypeError}
1211 Each field is a @code{gdb.Field} object, with some pre-defined attributes:
1214 This attribute is not available for @code{enum} or @code{static}
1215 (as in C@t{++}) fields. The value is the position, counting
1216 in bits, from the start of the containing type. Note that, in a
1217 dynamic type, the position of a field may not be constant. In this
1218 case, the value will be @code{None}. Also, a dynamic type may have
1219 fields that do not appear in a corresponding concrete type.
1222 This attribute is only available for @code{enum} fields, and its value
1223 is the enumeration member's integer representation.
1226 The name of the field, or @code{None} for anonymous fields.
1229 This is @code{True} if the field is artificial, usually meaning that
1230 it was provided by the compiler and not the user. This attribute is
1231 always provided, and is @code{False} if the field is not artificial.
1234 This is @code{True} if the field represents a base class of a C@t{++}
1235 structure. This attribute is always provided, and is @code{False}
1236 if the field is not a base class of the type that is the argument of
1237 @code{fields}, or if that type was not a C@t{++} class.
1240 If the field is packed, or is a bitfield, then this will have a
1241 non-zero value, which is the size of the field in bits. Otherwise,
1242 this will be zero; in this case the field's size is given by its type.
1245 The type of the field. This is usually an instance of @code{Type},
1246 but it can be @code{None} in some situations.
1249 The type which contains this field. This is an instance of
1254 @defun Type.array (@var{n1} @r{[}, @var{n2}@r{]})
1255 Return a new @code{gdb.Type} object which represents an array of this
1256 type. If one argument is given, it is the inclusive upper bound of
1257 the array; in this case the lower bound is zero. If two arguments are
1258 given, the first argument is the lower bound of the array, and the
1259 second argument is the upper bound of the array. An array's length
1260 must not be negative, but the bounds can be.
1263 @defun Type.vector (@var{n1} @r{[}, @var{n2}@r{]})
1264 Return a new @code{gdb.Type} object which represents a vector of this
1265 type. If one argument is given, it is the inclusive upper bound of
1266 the vector; in this case the lower bound is zero. If two arguments are
1267 given, the first argument is the lower bound of the vector, and the
1268 second argument is the upper bound of the vector. A vector's length
1269 must not be negative, but the bounds can be.
1271 The difference between an @code{array} and a @code{vector} is that
1272 arrays behave like in C: when used in expressions they decay to a pointer
1273 to the first element whereas vectors are treated as first class values.
1276 @defun Type.const ()
1277 Return a new @code{gdb.Type} object which represents a
1278 @code{const}-qualified variant of this type.
1281 @defun Type.volatile ()
1282 Return a new @code{gdb.Type} object which represents a
1283 @code{volatile}-qualified variant of this type.
1286 @defun Type.unqualified ()
1287 Return a new @code{gdb.Type} object which represents an unqualified
1288 variant of this type. That is, the result is neither @code{const} nor
1292 @defun Type.range ()
1293 Return a Python @code{Tuple} object that contains two elements: the
1294 low bound of the argument type and the high bound of that type. If
1295 the type does not have a range, @value{GDBN} will raise a
1296 @code{gdb.error} exception (@pxref{Exception Handling}).
1299 @defun Type.reference ()
1300 Return a new @code{gdb.Type} object which represents a reference to this
1304 @defun Type.pointer ()
1305 Return a new @code{gdb.Type} object which represents a pointer to this
1309 @defun Type.strip_typedefs ()
1310 Return a new @code{gdb.Type} that represents the real type,
1311 after removing all layers of typedefs.
1314 @defun Type.target ()
1315 Return a new @code{gdb.Type} object which represents the target type
1318 For a pointer type, the target type is the type of the pointed-to
1319 object. For an array type (meaning C-like arrays), the target type is
1320 the type of the elements of the array. For a function or method type,
1321 the target type is the type of the return value. For a complex type,
1322 the target type is the type of the elements. For a typedef, the
1323 target type is the aliased type.
1325 If the type does not have a target, this method will throw an
1329 @defun Type.template_argument (n @r{[}, block@r{]})
1330 If this @code{gdb.Type} is an instantiation of a template, this will
1331 return a new @code{gdb.Value} or @code{gdb.Type} which represents the
1332 value of the @var{n}th template argument (indexed starting at 0).
1334 If this @code{gdb.Type} is not a template type, or if the type has fewer
1335 than @var{n} template arguments, this will throw an exception.
1336 Ordinarily, only C@t{++} code will have template types.
1338 If @var{block} is given, then @var{name} is looked up in that scope.
1339 Otherwise, it is searched for globally.
1342 @defun Type.optimized_out ()
1343 Return @code{gdb.Value} instance of this type whose value is optimized
1344 out. This allows a frame decorator to indicate that the value of an
1345 argument or a local variable is not known.
1348 Each type has a code, which indicates what category this type falls
1349 into. The available type categories are represented by constants
1350 defined in the @code{gdb} module:
1353 @vindex TYPE_CODE_PTR
1354 @item gdb.TYPE_CODE_PTR
1355 The type is a pointer.
1357 @vindex TYPE_CODE_ARRAY
1358 @item gdb.TYPE_CODE_ARRAY
1359 The type is an array.
1361 @vindex TYPE_CODE_STRUCT
1362 @item gdb.TYPE_CODE_STRUCT
1363 The type is a structure.
1365 @vindex TYPE_CODE_UNION
1366 @item gdb.TYPE_CODE_UNION
1367 The type is a union.
1369 @vindex TYPE_CODE_ENUM
1370 @item gdb.TYPE_CODE_ENUM
1371 The type is an enum.
1373 @vindex TYPE_CODE_FLAGS
1374 @item gdb.TYPE_CODE_FLAGS
1375 A bit flags type, used for things such as status registers.
1377 @vindex TYPE_CODE_FUNC
1378 @item gdb.TYPE_CODE_FUNC
1379 The type is a function.
1381 @vindex TYPE_CODE_INT
1382 @item gdb.TYPE_CODE_INT
1383 The type is an integer type.
1385 @vindex TYPE_CODE_FLT
1386 @item gdb.TYPE_CODE_FLT
1387 A floating point type.
1389 @vindex TYPE_CODE_VOID
1390 @item gdb.TYPE_CODE_VOID
1391 The special type @code{void}.
1393 @vindex TYPE_CODE_SET
1394 @item gdb.TYPE_CODE_SET
1397 @vindex TYPE_CODE_RANGE
1398 @item gdb.TYPE_CODE_RANGE
1399 A range type, that is, an integer type with bounds.
1401 @vindex TYPE_CODE_STRING
1402 @item gdb.TYPE_CODE_STRING
1403 A string type. Note that this is only used for certain languages with
1404 language-defined string types; C strings are not represented this way.
1406 @vindex TYPE_CODE_BITSTRING
1407 @item gdb.TYPE_CODE_BITSTRING
1408 A string of bits. It is deprecated.
1410 @vindex TYPE_CODE_ERROR
1411 @item gdb.TYPE_CODE_ERROR
1412 An unknown or erroneous type.
1414 @vindex TYPE_CODE_METHOD
1415 @item gdb.TYPE_CODE_METHOD
1416 A method type, as found in C@t{++}.
1418 @vindex TYPE_CODE_METHODPTR
1419 @item gdb.TYPE_CODE_METHODPTR
1420 A pointer-to-member-function.
1422 @vindex TYPE_CODE_MEMBERPTR
1423 @item gdb.TYPE_CODE_MEMBERPTR
1424 A pointer-to-member.
1426 @vindex TYPE_CODE_REF
1427 @item gdb.TYPE_CODE_REF
1430 @vindex TYPE_CODE_RVALUE_REF
1431 @item gdb.TYPE_CODE_RVALUE_REF
1432 A C@t{++}11 rvalue reference type.
1434 @vindex TYPE_CODE_CHAR
1435 @item gdb.TYPE_CODE_CHAR
1438 @vindex TYPE_CODE_BOOL
1439 @item gdb.TYPE_CODE_BOOL
1442 @vindex TYPE_CODE_COMPLEX
1443 @item gdb.TYPE_CODE_COMPLEX
1444 A complex float type.
1446 @vindex TYPE_CODE_TYPEDEF
1447 @item gdb.TYPE_CODE_TYPEDEF
1448 A typedef to some other type.
1450 @vindex TYPE_CODE_NAMESPACE
1451 @item gdb.TYPE_CODE_NAMESPACE
1452 A C@t{++} namespace.
1454 @vindex TYPE_CODE_DECFLOAT
1455 @item gdb.TYPE_CODE_DECFLOAT
1456 A decimal floating point type.
1458 @vindex TYPE_CODE_INTERNAL_FUNCTION
1459 @item gdb.TYPE_CODE_INTERNAL_FUNCTION
1460 A function internal to @value{GDBN}. This is the type used to represent
1461 convenience functions.
1464 Further support for types is provided in the @code{gdb.types}
1465 Python module (@pxref{gdb.types}).
1467 @node Pretty Printing API
1468 @subsubsection Pretty Printing API
1469 @cindex python pretty printing api
1471 A pretty-printer is just an object that holds a value and implements a
1472 specific interface, defined here. An example output is provided
1473 (@pxref{Pretty Printing}).
1475 @defun pretty_printer.children (self)
1476 @value{GDBN} will call this method on a pretty-printer to compute the
1477 children of the pretty-printer's value.
1479 This method must return an object conforming to the Python iterator
1480 protocol. Each item returned by the iterator must be a tuple holding
1481 two elements. The first element is the ``name'' of the child; the
1482 second element is the child's value. The value can be any Python
1483 object which is convertible to a @value{GDBN} value.
1485 This method is optional. If it does not exist, @value{GDBN} will act
1486 as though the value has no children.
1488 For efficiency, the @code{children} method should lazily compute its
1489 results. This will let @value{GDBN} read as few elements as
1490 necessary, for example when various print settings (@pxref{Print
1491 Settings}) or @code{-var-list-children} (@pxref{GDB/MI Variable
1492 Objects}) limit the number of elements to be displayed.
1494 Children may be hidden from display based on the value of @samp{set
1495 print max-depth} (@pxref{Print Settings}).
1498 @defun pretty_printer.display_hint (self)
1499 The CLI may call this method and use its result to change the
1500 formatting of a value. The result will also be supplied to an MI
1501 consumer as a @samp{displayhint} attribute of the variable being
1504 This method is optional. If it does exist, this method must return a
1505 string or the special value @code{None}.
1507 Some display hints are predefined by @value{GDBN}:
1511 Indicate that the object being printed is ``array-like''. The CLI
1512 uses this to respect parameters such as @code{set print elements} and
1513 @code{set print array}.
1516 Indicate that the object being printed is ``map-like'', and that the
1517 children of this value can be assumed to alternate between keys and
1521 Indicate that the object being printed is ``string-like''. If the
1522 printer's @code{to_string} method returns a Python string of some
1523 kind, then @value{GDBN} will call its internal language-specific
1524 string-printing function to format the string. For the CLI this means
1525 adding quotation marks, possibly escaping some characters, respecting
1526 @code{set print elements}, and the like.
1529 The special value @code{None} causes @value{GDBN} to apply the default
1533 @defun pretty_printer.to_string (self)
1534 @value{GDBN} will call this method to display the string
1535 representation of the value passed to the object's constructor.
1537 When printing from the CLI, if the @code{to_string} method exists,
1538 then @value{GDBN} will prepend its result to the values returned by
1539 @code{children}. Exactly how this formatting is done is dependent on
1540 the display hint, and may change as more hints are added. Also,
1541 depending on the print settings (@pxref{Print Settings}), the CLI may
1542 print just the result of @code{to_string} in a stack trace, omitting
1543 the result of @code{children}.
1545 If this method returns a string, it is printed verbatim.
1547 Otherwise, if this method returns an instance of @code{gdb.Value},
1548 then @value{GDBN} prints this value. This may result in a call to
1549 another pretty-printer.
1551 If instead the method returns a Python value which is convertible to a
1552 @code{gdb.Value}, then @value{GDBN} performs the conversion and prints
1553 the resulting value. Again, this may result in a call to another
1554 pretty-printer. Python scalars (integers, floats, and booleans) and
1555 strings are convertible to @code{gdb.Value}; other types are not.
1557 Finally, if this method returns @code{None} then no further operations
1558 are peformed in this method and nothing is printed.
1560 If the result is not one of these types, an exception is raised.
1563 @value{GDBN} provides a function which can be used to look up the
1564 default pretty-printer for a @code{gdb.Value}:
1566 @findex gdb.default_visualizer
1567 @defun gdb.default_visualizer (value)
1568 This function takes a @code{gdb.Value} object as an argument. If a
1569 pretty-printer for this value exists, then it is returned. If no such
1570 printer exists, then this returns @code{None}.
1573 @node Selecting Pretty-Printers
1574 @subsubsection Selecting Pretty-Printers
1575 @cindex selecting python pretty-printers
1577 @value{GDBN} provides several ways to register a pretty-printer:
1578 globally, per program space, and per objfile. When choosing how to
1579 register your pretty-printer, a good rule is to register it with the
1580 smallest scope possible: that is prefer a specific objfile first, then
1581 a program space, and only register a printer globally as a last
1584 @findex gdb.pretty_printers
1585 @defvar gdb.pretty_printers
1586 The Python list @code{gdb.pretty_printers} contains an array of
1587 functions or callable objects that have been registered via addition
1588 as a pretty-printer. Printers in this list are called @code{global}
1589 printers, they're available when debugging all inferiors.
1592 Each @code{gdb.Progspace} contains a @code{pretty_printers} attribute.
1593 Each @code{gdb.Objfile} also contains a @code{pretty_printers}
1596 Each function on these lists is passed a single @code{gdb.Value}
1597 argument and should return a pretty-printer object conforming to the
1598 interface definition above (@pxref{Pretty Printing API}). If a function
1599 cannot create a pretty-printer for the value, it should return
1602 @value{GDBN} first checks the @code{pretty_printers} attribute of each
1603 @code{gdb.Objfile} in the current program space and iteratively calls
1604 each enabled lookup routine in the list for that @code{gdb.Objfile}
1605 until it receives a pretty-printer object.
1606 If no pretty-printer is found in the objfile lists, @value{GDBN} then
1607 searches the pretty-printer list of the current program space,
1608 calling each enabled function until an object is returned.
1609 After these lists have been exhausted, it tries the global
1610 @code{gdb.pretty_printers} list, again calling each enabled function until an
1613 The order in which the objfiles are searched is not specified. For a
1614 given list, functions are always invoked from the head of the list,
1615 and iterated over sequentially until the end of the list, or a printer
1618 For various reasons a pretty-printer may not work.
1619 For example, the underlying data structure may have changed and
1620 the pretty-printer is out of date.
1622 The consequences of a broken pretty-printer are severe enough that
1623 @value{GDBN} provides support for enabling and disabling individual
1624 printers. For example, if @code{print frame-arguments} is on,
1625 a backtrace can become highly illegible if any argument is printed
1626 with a broken printer.
1628 Pretty-printers are enabled and disabled by attaching an @code{enabled}
1629 attribute to the registered function or callable object. If this attribute
1630 is present and its value is @code{False}, the printer is disabled, otherwise
1631 the printer is enabled.
1633 @node Writing a Pretty-Printer
1634 @subsubsection Writing a Pretty-Printer
1635 @cindex writing a pretty-printer
1637 A pretty-printer consists of two parts: a lookup function to detect
1638 if the type is supported, and the printer itself.
1640 Here is an example showing how a @code{std::string} printer might be
1641 written. @xref{Pretty Printing API}, for details on the API this class
1645 class StdStringPrinter(object):
1646 "Print a std::string"
1648 def __init__(self, val):
1651 def to_string(self):
1652 return self.val['_M_dataplus']['_M_p']
1654 def display_hint(self):
1658 And here is an example showing how a lookup function for the printer
1659 example above might be written.
1662 def str_lookup_function(val):
1663 lookup_tag = val.type.tag
1664 if lookup_tag is None:
1666 regex = re.compile("^std::basic_string<char,.*>$")
1667 if regex.match(lookup_tag):
1668 return StdStringPrinter(val)
1672 The example lookup function extracts the value's type, and attempts to
1673 match it to a type that it can pretty-print. If it is a type the
1674 printer can pretty-print, it will return a printer object. If not, it
1675 returns @code{None}.
1677 We recommend that you put your core pretty-printers into a Python
1678 package. If your pretty-printers are for use with a library, we
1679 further recommend embedding a version number into the package name.
1680 This practice will enable @value{GDBN} to load multiple versions of
1681 your pretty-printers at the same time, because they will have
1684 You should write auto-loaded code (@pxref{Python Auto-loading}) such that it
1685 can be evaluated multiple times without changing its meaning. An
1686 ideal auto-load file will consist solely of @code{import}s of your
1687 printer modules, followed by a call to a register pretty-printers with
1688 the current objfile.
1690 Taken as a whole, this approach will scale nicely to multiple
1691 inferiors, each potentially using a different library version.
1692 Embedding a version number in the Python package name will ensure that
1693 @value{GDBN} is able to load both sets of printers simultaneously.
1694 Then, because the search for pretty-printers is done by objfile, and
1695 because your auto-loaded code took care to register your library's
1696 printers with a specific objfile, @value{GDBN} will find the correct
1697 printers for the specific version of the library used by each
1700 To continue the @code{std::string} example (@pxref{Pretty Printing API}),
1701 this code might appear in @code{gdb.libstdcxx.v6}:
1704 def register_printers(objfile):
1705 objfile.pretty_printers.append(str_lookup_function)
1709 And then the corresponding contents of the auto-load file would be:
1712 import gdb.libstdcxx.v6
1713 gdb.libstdcxx.v6.register_printers(gdb.current_objfile())
1716 The previous example illustrates a basic pretty-printer.
1717 There are a few things that can be improved on.
1718 The printer doesn't have a name, making it hard to identify in a
1719 list of installed printers. The lookup function has a name, but
1720 lookup functions can have arbitrary, even identical, names.
1722 Second, the printer only handles one type, whereas a library typically has
1723 several types. One could install a lookup function for each desired type
1724 in the library, but one could also have a single lookup function recognize
1725 several types. The latter is the conventional way this is handled.
1726 If a pretty-printer can handle multiple data types, then its
1727 @dfn{subprinters} are the printers for the individual data types.
1729 The @code{gdb.printing} module provides a formal way of solving these
1730 problems (@pxref{gdb.printing}).
1731 Here is another example that handles multiple types.
1733 These are the types we are going to pretty-print:
1736 struct foo @{ int a, b; @};
1737 struct bar @{ struct foo x, y; @};
1740 Here are the printers:
1744 """Print a foo object."""
1746 def __init__(self, val):
1749 def to_string(self):
1750 return ("a=<" + str(self.val["a"]) +
1751 "> b=<" + str(self.val["b"]) + ">")
1754 """Print a bar object."""
1756 def __init__(self, val):
1759 def to_string(self):
1760 return ("x=<" + str(self.val["x"]) +
1761 "> y=<" + str(self.val["y"]) + ">")
1764 This example doesn't need a lookup function, that is handled by the
1765 @code{gdb.printing} module. Instead a function is provided to build up
1766 the object that handles the lookup.
1771 def build_pretty_printer():
1772 pp = gdb.printing.RegexpCollectionPrettyPrinter(
1774 pp.add_printer('foo', '^foo$', fooPrinter)
1775 pp.add_printer('bar', '^bar$', barPrinter)
1779 And here is the autoload support:
1784 gdb.printing.register_pretty_printer(
1785 gdb.current_objfile(),
1786 my_library.build_pretty_printer())
1789 Finally, when this printer is loaded into @value{GDBN}, here is the
1790 corresponding output of @samp{info pretty-printer}:
1793 (gdb) info pretty-printer
1800 @node Type Printing API
1801 @subsubsection Type Printing API
1802 @cindex type printing API for Python
1804 @value{GDBN} provides a way for Python code to customize type display.
1805 This is mainly useful for substituting canonical typedef names for
1808 @cindex type printer
1809 A @dfn{type printer} is just a Python object conforming to a certain
1810 protocol. A simple base class implementing the protocol is provided;
1811 see @ref{gdb.types}. A type printer must supply at least:
1813 @defivar type_printer enabled
1814 A boolean which is True if the printer is enabled, and False
1815 otherwise. This is manipulated by the @code{enable type-printer}
1816 and @code{disable type-printer} commands.
1819 @defivar type_printer name
1820 The name of the type printer. This must be a string. This is used by
1821 the @code{enable type-printer} and @code{disable type-printer}
1825 @defmethod type_printer instantiate (self)
1826 This is called by @value{GDBN} at the start of type-printing. It is
1827 only called if the type printer is enabled. This method must return a
1828 new object that supplies a @code{recognize} method, as described below.
1832 When displaying a type, say via the @code{ptype} command, @value{GDBN}
1833 will compute a list of type recognizers. This is done by iterating
1834 first over the per-objfile type printers (@pxref{Objfiles In Python}),
1835 followed by the per-progspace type printers (@pxref{Progspaces In
1836 Python}), and finally the global type printers.
1838 @value{GDBN} will call the @code{instantiate} method of each enabled
1839 type printer. If this method returns @code{None}, then the result is
1840 ignored; otherwise, it is appended to the list of recognizers.
1842 Then, when @value{GDBN} is going to display a type name, it iterates
1843 over the list of recognizers. For each one, it calls the recognition
1844 function, stopping if the function returns a non-@code{None} value.
1845 The recognition function is defined as:
1847 @defmethod type_recognizer recognize (self, type)
1848 If @var{type} is not recognized, return @code{None}. Otherwise,
1849 return a string which is to be printed as the name of @var{type}.
1850 The @var{type} argument will be an instance of @code{gdb.Type}
1851 (@pxref{Types In Python}).
1854 @value{GDBN} uses this two-pass approach so that type printers can
1855 efficiently cache information without holding on to it too long. For
1856 example, it can be convenient to look up type information in a type
1857 printer and hold it for a recognizer's lifetime; if a single pass were
1858 done then type printers would have to make use of the event system in
1859 order to avoid holding information that could become stale as the
1862 @node Frame Filter API
1863 @subsubsection Filtering Frames
1864 @cindex frame filters api
1866 Frame filters are Python objects that manipulate the visibility of a
1867 frame or frames when a backtrace (@pxref{Backtrace}) is printed by
1870 Only commands that print a backtrace, or, in the case of @sc{gdb/mi}
1871 commands (@pxref{GDB/MI}), those that return a collection of frames
1872 are affected. The commands that work with frame filters are:
1874 @code{backtrace} (@pxref{backtrace-command,, The backtrace command}),
1875 @code{-stack-list-frames}
1876 (@pxref{-stack-list-frames,, The -stack-list-frames command}),
1877 @code{-stack-list-variables} (@pxref{-stack-list-variables,, The
1878 -stack-list-variables command}), @code{-stack-list-arguments}
1879 @pxref{-stack-list-arguments,, The -stack-list-arguments command}) and
1880 @code{-stack-list-locals} (@pxref{-stack-list-locals,, The
1881 -stack-list-locals command}).
1883 A frame filter works by taking an iterator as an argument, applying
1884 actions to the contents of that iterator, and returning another
1885 iterator (or, possibly, the same iterator it was provided in the case
1886 where the filter does not perform any operations). Typically, frame
1887 filters utilize tools such as the Python's @code{itertools} module to
1888 work with and create new iterators from the source iterator.
1889 Regardless of how a filter chooses to apply actions, it must not alter
1890 the underlying @value{GDBN} frame or frames, or attempt to alter the
1891 call-stack within @value{GDBN}. This preserves data integrity within
1892 @value{GDBN}. Frame filters are executed on a priority basis and care
1893 should be taken that some frame filters may have been executed before,
1894 and that some frame filters will be executed after.
1896 An important consideration when designing frame filters, and well
1897 worth reflecting upon, is that frame filters should avoid unwinding
1898 the call stack if possible. Some stacks can run very deep, into the
1899 tens of thousands in some cases. To search every frame when a frame
1900 filter executes may be too expensive at that step. The frame filter
1901 cannot know how many frames it has to iterate over, and it may have to
1902 iterate through them all. This ends up duplicating effort as
1903 @value{GDBN} performs this iteration when it prints the frames. If
1904 the filter can defer unwinding frames until frame decorators are
1905 executed, after the last filter has executed, it should. @xref{Frame
1906 Decorator API}, for more information on decorators. Also, there are
1907 examples for both frame decorators and filters in later chapters.
1908 @xref{Writing a Frame Filter}, for more information.
1910 The Python dictionary @code{gdb.frame_filters} contains key/object
1911 pairings that comprise a frame filter. Frame filters in this
1912 dictionary are called @code{global} frame filters, and they are
1913 available when debugging all inferiors. These frame filters must
1914 register with the dictionary directly. In addition to the
1915 @code{global} dictionary, there are other dictionaries that are loaded
1916 with different inferiors via auto-loading (@pxref{Python
1917 Auto-loading}). The two other areas where frame filter dictionaries
1918 can be found are: @code{gdb.Progspace} which contains a
1919 @code{frame_filters} dictionary attribute, and each @code{gdb.Objfile}
1920 object which also contains a @code{frame_filters} dictionary
1923 When a command is executed from @value{GDBN} that is compatible with
1924 frame filters, @value{GDBN} combines the @code{global},
1925 @code{gdb.Progspace} and all @code{gdb.Objfile} dictionaries currently
1926 loaded. All of the @code{gdb.Objfile} dictionaries are combined, as
1927 several frames, and thus several object files, might be in use.
1928 @value{GDBN} then prunes any frame filter whose @code{enabled}
1929 attribute is @code{False}. This pruned list is then sorted according
1930 to the @code{priority} attribute in each filter.
1932 Once the dictionaries are combined, pruned and sorted, @value{GDBN}
1933 creates an iterator which wraps each frame in the call stack in a
1934 @code{FrameDecorator} object, and calls each filter in order. The
1935 output from the previous filter will always be the input to the next
1938 Frame filters have a mandatory interface which each frame filter must
1939 implement, defined here:
1941 @defun FrameFilter.filter (iterator)
1942 @value{GDBN} will call this method on a frame filter when it has
1943 reached the order in the priority list for that filter.
1945 For example, if there are four frame filters:
1956 The order that the frame filters will be called is:
1959 Filter3 -> Filter2 -> Filter1 -> Filter4
1962 Note that the output from @code{Filter3} is passed to the input of
1963 @code{Filter2}, and so on.
1965 This @code{filter} method is passed a Python iterator. This iterator
1966 contains a sequence of frame decorators that wrap each
1967 @code{gdb.Frame}, or a frame decorator that wraps another frame
1968 decorator. The first filter that is executed in the sequence of frame
1969 filters will receive an iterator entirely comprised of default
1970 @code{FrameDecorator} objects. However, after each frame filter is
1971 executed, the previous frame filter may have wrapped some or all of
1972 the frame decorators with their own frame decorator. As frame
1973 decorators must also conform to a mandatory interface, these
1974 decorators can be assumed to act in a uniform manner (@pxref{Frame
1977 This method must return an object conforming to the Python iterator
1978 protocol. Each item in the iterator must be an object conforming to
1979 the frame decorator interface. If a frame filter does not wish to
1980 perform any operations on this iterator, it should return that
1983 This method is not optional. If it does not exist, @value{GDBN} will
1984 raise and print an error.
1987 @defvar FrameFilter.name
1988 The @code{name} attribute must be Python string which contains the
1989 name of the filter displayed by @value{GDBN} (@pxref{Frame Filter
1990 Management}). This attribute may contain any combination of letters
1991 or numbers. Care should be taken to ensure that it is unique. This
1992 attribute is mandatory.
1995 @defvar FrameFilter.enabled
1996 The @code{enabled} attribute must be Python boolean. This attribute
1997 indicates to @value{GDBN} whether the frame filter is enabled, and
1998 should be considered when frame filters are executed. If
1999 @code{enabled} is @code{True}, then the frame filter will be executed
2000 when any of the backtrace commands detailed earlier in this chapter
2001 are executed. If @code{enabled} is @code{False}, then the frame
2002 filter will not be executed. This attribute is mandatory.
2005 @defvar FrameFilter.priority
2006 The @code{priority} attribute must be Python integer. This attribute
2007 controls the order of execution in relation to other frame filters.
2008 There are no imposed limits on the range of @code{priority} other than
2009 it must be a valid integer. The higher the @code{priority} attribute,
2010 the sooner the frame filter will be executed in relation to other
2011 frame filters. Although @code{priority} can be negative, it is
2012 recommended practice to assume zero is the lowest priority that a
2013 frame filter can be assigned. Frame filters that have the same
2014 priority are executed in unsorted order in that priority slot. This
2015 attribute is mandatory. 100 is a good default priority.
2018 @node Frame Decorator API
2019 @subsubsection Decorating Frames
2020 @cindex frame decorator api
2022 Frame decorators are sister objects to frame filters (@pxref{Frame
2023 Filter API}). Frame decorators are applied by a frame filter and can
2024 only be used in conjunction with frame filters.
2026 The purpose of a frame decorator is to customize the printed content
2027 of each @code{gdb.Frame} in commands where frame filters are executed.
2028 This concept is called decorating a frame. Frame decorators decorate
2029 a @code{gdb.Frame} with Python code contained within each API call.
2030 This separates the actual data contained in a @code{gdb.Frame} from
2031 the decorated data produced by a frame decorator. This abstraction is
2032 necessary to maintain integrity of the data contained in each
2035 Frame decorators have a mandatory interface, defined below.
2037 @value{GDBN} already contains a frame decorator called
2038 @code{FrameDecorator}. This contains substantial amounts of
2039 boilerplate code to decorate the content of a @code{gdb.Frame}. It is
2040 recommended that other frame decorators inherit and extend this
2041 object, and only to override the methods needed.
2043 @tindex gdb.FrameDecorator
2044 @code{FrameDecorator} is defined in the Python module
2045 @code{gdb.FrameDecorator}, so your code can import it like:
2047 from gdb.FrameDecorator import FrameDecorator
2050 @defun FrameDecorator.elided (self)
2052 The @code{elided} method groups frames together in a hierarchical
2053 system. An example would be an interpreter, where multiple low-level
2054 frames make up a single call in the interpreted language. In this
2055 example, the frame filter would elide the low-level frames and present
2056 a single high-level frame, representing the call in the interpreted
2057 language, to the user.
2059 The @code{elided} function must return an iterable and this iterable
2060 must contain the frames that are being elided wrapped in a suitable
2061 frame decorator. If no frames are being elided this function may
2062 return an empty iterable, or @code{None}. Elided frames are indented
2063 from normal frames in a @code{CLI} backtrace, or in the case of
2064 @code{GDB/MI}, are placed in the @code{children} field of the eliding
2067 It is the frame filter's task to also filter out the elided frames from
2068 the source iterator. This will avoid printing the frame twice.
2071 @defun FrameDecorator.function (self)
2073 This method returns the name of the function in the frame that is to
2076 This method must return a Python string describing the function, or
2079 If this function returns @code{None}, @value{GDBN} will not print any
2080 data for this field.
2083 @defun FrameDecorator.address (self)
2085 This method returns the address of the frame that is to be printed.
2087 This method must return a Python numeric integer type of sufficient
2088 size to describe the address of the frame, or @code{None}.
2090 If this function returns a @code{None}, @value{GDBN} will not print
2091 any data for this field.
2094 @defun FrameDecorator.filename (self)
2096 This method returns the filename and path associated with this frame.
2098 This method must return a Python string containing the filename and
2099 the path to the object file backing the frame, or @code{None}.
2101 If this function returns a @code{None}, @value{GDBN} will not print
2102 any data for this field.
2105 @defun FrameDecorator.line (self):
2107 This method returns the line number associated with the current
2108 position within the function addressed by this frame.
2110 This method must return a Python integer type, or @code{None}.
2112 If this function returns a @code{None}, @value{GDBN} will not print
2113 any data for this field.
2116 @defun FrameDecorator.frame_args (self)
2119 This method must return an iterable, or @code{None}. Returning an
2120 empty iterable, or @code{None} means frame arguments will not be
2121 printed for this frame. This iterable must contain objects that
2122 implement two methods, described here.
2124 This object must implement a @code{symbol} method which takes a
2125 single @code{self} parameter and must return a @code{gdb.Symbol}
2126 (@pxref{Symbols In Python}), or a Python string. The object must also
2127 implement a @code{value} method which takes a single @code{self}
2128 parameter and must return a @code{gdb.Value} (@pxref{Values From
2129 Inferior}), a Python value, or @code{None}. If the @code{value}
2130 method returns @code{None}, and the @code{argument} method returns a
2131 @code{gdb.Symbol}, @value{GDBN} will look-up and print the value of
2132 the @code{gdb.Symbol} automatically.
2137 class SymValueWrapper():
2139 def __init__(self, symbol, value):
2149 class SomeFrameDecorator()
2152 def frame_args(self):
2155 block = self.inferior_frame.block()
2159 # Iterate over all symbols in a block. Only add
2160 # symbols that are arguments.
2162 if not sym.is_argument:
2164 args.append(SymValueWrapper(sym,None))
2166 # Add example synthetic argument.
2167 args.append(SymValueWrapper(``foo'', 42))
2173 @defun FrameDecorator.frame_locals (self)
2175 This method must return an iterable or @code{None}. Returning an
2176 empty iterable, or @code{None} means frame local arguments will not be
2177 printed for this frame.
2179 The object interface, the description of the various strategies for
2180 reading frame locals, and the example are largely similar to those
2181 described in the @code{frame_args} function, (@pxref{frame_args,,The
2182 frame filter frame_args function}). Below is a modified example:
2185 class SomeFrameDecorator()
2188 def frame_locals(self):
2191 block = self.inferior_frame.block()
2195 # Iterate over all symbols in a block. Add all
2196 # symbols, except arguments.
2200 vars.append(SymValueWrapper(sym,None))
2202 # Add an example of a synthetic local variable.
2203 vars.append(SymValueWrapper(``bar'', 99))
2209 @defun FrameDecorator.inferior_frame (self):
2211 This method must return the underlying @code{gdb.Frame} that this
2212 frame decorator is decorating. @value{GDBN} requires the underlying
2213 frame for internal frame information to determine how to print certain
2214 values when printing a frame.
2217 @node Writing a Frame Filter
2218 @subsubsection Writing a Frame Filter
2219 @cindex writing a frame filter
2221 There are three basic elements that a frame filter must implement: it
2222 must correctly implement the documented interface (@pxref{Frame Filter
2223 API}), it must register itself with @value{GDBN}, and finally, it must
2224 decide if it is to work on the data provided by @value{GDBN}. In all
2225 cases, whether it works on the iterator or not, each frame filter must
2226 return an iterator. A bare-bones frame filter follows the pattern in
2227 the following example.
2232 class FrameFilter():
2235 # Frame filter attribute creation.
2237 # 'name' is the name of the filter that GDB will display.
2239 # 'priority' is the priority of the filter relative to other
2242 # 'enabled' is a boolean that indicates whether this filter is
2243 # enabled and should be executed.
2249 # Register this frame filter with the global frame_filters
2251 gdb.frame_filters[self.name] = self
2253 def filter(self, frame_iter):
2254 # Just return the iterator.
2258 The frame filter in the example above implements the three
2259 requirements for all frame filters. It implements the API, self
2260 registers, and makes a decision on the iterator (in this case, it just
2261 returns the iterator untouched).
2263 The first step is attribute creation and assignment, and as shown in
2264 the comments the filter assigns the following attributes: @code{name},
2265 @code{priority} and whether the filter should be enabled with the
2266 @code{enabled} attribute.
2268 The second step is registering the frame filter with the dictionary or
2269 dictionaries that the frame filter has interest in. As shown in the
2270 comments, this filter just registers itself with the global dictionary
2271 @code{gdb.frame_filters}. As noted earlier, @code{gdb.frame_filters}
2272 is a dictionary that is initialized in the @code{gdb} module when
2273 @value{GDBN} starts. What dictionary a filter registers with is an
2274 important consideration. Generally, if a filter is specific to a set
2275 of code, it should be registered either in the @code{objfile} or
2276 @code{progspace} dictionaries as they are specific to the program
2277 currently loaded in @value{GDBN}. The global dictionary is always
2278 present in @value{GDBN} and is never unloaded. Any filters registered
2279 with the global dictionary will exist until @value{GDBN} exits. To
2280 avoid filters that may conflict, it is generally better to register
2281 frame filters against the dictionaries that more closely align with
2282 the usage of the filter currently in question. @xref{Python
2283 Auto-loading}, for further information on auto-loading Python scripts.
2285 @value{GDBN} takes a hands-off approach to frame filter registration,
2286 therefore it is the frame filter's responsibility to ensure
2287 registration has occurred, and that any exceptions are handled
2288 appropriately. In particular, you may wish to handle exceptions
2289 relating to Python dictionary key uniqueness. It is mandatory that
2290 the dictionary key is the same as frame filter's @code{name}
2291 attribute. When a user manages frame filters (@pxref{Frame Filter
2292 Management}), the names @value{GDBN} will display are those contained
2293 in the @code{name} attribute.
2295 The final step of this example is the implementation of the
2296 @code{filter} method. As shown in the example comments, we define the
2297 @code{filter} method and note that the method must take an iterator,
2298 and also must return an iterator. In this bare-bones example, the
2299 frame filter is not very useful as it just returns the iterator
2300 untouched. However this is a valid operation for frame filters that
2301 have the @code{enabled} attribute set, but decide not to operate on
2304 In the next example, the frame filter operates on all frames and
2305 utilizes a frame decorator to perform some work on the frames.
2306 @xref{Frame Decorator API}, for further information on the frame
2307 decorator interface.
2309 This example works on inlined frames. It highlights frames which are
2310 inlined by tagging them with an ``[inlined]'' tag. By applying a
2311 frame decorator to all frames with the Python @code{itertools imap}
2312 method, the example defers actions to the frame decorator. Frame
2313 decorators are only processed when @value{GDBN} prints the backtrace.
2315 This introduces a new decision making topic: whether to perform
2316 decision making operations at the filtering step, or at the printing
2317 step. In this example's approach, it does not perform any filtering
2318 decisions at the filtering step beyond mapping a frame decorator to
2319 each frame. This allows the actual decision making to be performed
2320 when each frame is printed. This is an important consideration, and
2321 well worth reflecting upon when designing a frame filter. An issue
2322 that frame filters should avoid is unwinding the stack if possible.
2323 Some stacks can run very deep, into the tens of thousands in some
2324 cases. To search every frame to determine if it is inlined ahead of
2325 time may be too expensive at the filtering step. The frame filter
2326 cannot know how many frames it has to iterate over, and it would have
2327 to iterate through them all. This ends up duplicating effort as
2328 @value{GDBN} performs this iteration when it prints the frames.
2330 In this example decision making can be deferred to the printing step.
2331 As each frame is printed, the frame decorator can examine each frame
2332 in turn when @value{GDBN} iterates. From a performance viewpoint,
2333 this is the most appropriate decision to make as it avoids duplicating
2334 the effort that the printing step would undertake anyway. Also, if
2335 there are many frame filters unwinding the stack during filtering, it
2336 can substantially delay the printing of the backtrace which will
2337 result in large memory usage, and a poor user experience.
2340 class InlineFilter():
2343 self.name = "InlinedFrameFilter"
2346 gdb.frame_filters[self.name] = self
2348 def filter(self, frame_iter):
2349 frame_iter = itertools.imap(InlinedFrameDecorator,
2354 This frame filter is somewhat similar to the earlier example, except
2355 that the @code{filter} method applies a frame decorator object called
2356 @code{InlinedFrameDecorator} to each element in the iterator. The
2357 @code{imap} Python method is light-weight. It does not proactively
2358 iterate over the iterator, but rather creates a new iterator which
2359 wraps the existing one.
2361 Below is the frame decorator for this example.
2364 class InlinedFrameDecorator(FrameDecorator):
2366 def __init__(self, fobj):
2367 super(InlinedFrameDecorator, self).__init__(fobj)
2370 frame = self.inferior_frame()
2371 name = str(frame.name())
2373 if frame.type() == gdb.INLINE_FRAME:
2374 name = name + " [inlined]"
2379 This frame decorator only defines and overrides the @code{function}
2380 method. It lets the supplied @code{FrameDecorator}, which is shipped
2381 with @value{GDBN}, perform the other work associated with printing
2384 The combination of these two objects create this output from a
2388 #0 0x004004e0 in bar () at inline.c:11
2389 #1 0x00400566 in max [inlined] (b=6, a=12) at inline.c:21
2390 #2 0x00400566 in main () at inline.c:31
2393 So in the case of this example, a frame decorator is applied to all
2394 frames, regardless of whether they may be inlined or not. As
2395 @value{GDBN} iterates over the iterator produced by the frame filters,
2396 @value{GDBN} executes each frame decorator which then makes a decision
2397 on what to print in the @code{function} callback. Using a strategy
2398 like this is a way to defer decisions on the frame content to printing
2401 @subheading Eliding Frames
2403 It might be that the above example is not desirable for representing
2404 inlined frames, and a hierarchical approach may be preferred. If we
2405 want to hierarchically represent frames, the @code{elided} frame
2406 decorator interface might be preferable.
2408 This example approaches the issue with the @code{elided} method. This
2409 example is quite long, but very simplistic. It is out-of-scope for
2410 this section to write a complete example that comprehensively covers
2411 all approaches of finding and printing inlined frames. However, this
2412 example illustrates the approach an author might use.
2414 This example comprises of three sections.
2417 class InlineFrameFilter():
2420 self.name = "InlinedFrameFilter"
2423 gdb.frame_filters[self.name] = self
2425 def filter(self, frame_iter):
2426 return ElidingInlineIterator(frame_iter)
2429 This frame filter is very similar to the other examples. The only
2430 difference is this frame filter is wrapping the iterator provided to
2431 it (@code{frame_iter}) with a custom iterator called
2432 @code{ElidingInlineIterator}. This again defers actions to when
2433 @value{GDBN} prints the backtrace, as the iterator is not traversed
2436 The iterator for this example is as follows. It is in this section of
2437 the example where decisions are made on the content of the backtrace.
2440 class ElidingInlineIterator:
2441 def __init__(self, ii):
2442 self.input_iterator = ii
2448 frame = next(self.input_iterator)
2450 if frame.inferior_frame().type() != gdb.INLINE_FRAME:
2454 eliding_frame = next(self.input_iterator)
2455 except StopIteration:
2457 return ElidingFrameDecorator(eliding_frame, [frame])
2460 This iterator implements the Python iterator protocol. When the
2461 @code{next} function is called (when @value{GDBN} prints each frame),
2462 the iterator checks if this frame decorator, @code{frame}, is wrapping
2463 an inlined frame. If it is not, it returns the existing frame decorator
2464 untouched. If it is wrapping an inlined frame, it assumes that the
2465 inlined frame was contained within the next oldest frame,
2466 @code{eliding_frame}, which it fetches. It then creates and returns a
2467 frame decorator, @code{ElidingFrameDecorator}, which contains both the
2468 elided frame, and the eliding frame.
2471 class ElidingInlineDecorator(FrameDecorator):
2473 def __init__(self, frame, elided_frames):
2474 super(ElidingInlineDecorator, self).__init__(frame)
2476 self.elided_frames = elided_frames
2479 return iter(self.elided_frames)
2482 This frame decorator overrides one function and returns the inlined
2483 frame in the @code{elided} method. As before it lets
2484 @code{FrameDecorator} do the rest of the work involved in printing
2485 this frame. This produces the following output.
2488 #0 0x004004e0 in bar () at inline.c:11
2489 #2 0x00400529 in main () at inline.c:25
2490 #1 0x00400529 in max (b=6, a=12) at inline.c:15
2493 In that output, @code{max} which has been inlined into @code{main} is
2494 printed hierarchically. Another approach would be to combine the
2495 @code{function} method, and the @code{elided} method to both print a
2496 marker in the inlined frame, and also show the hierarchical
2499 @node Unwinding Frames in Python
2500 @subsubsection Unwinding Frames in Python
2501 @cindex unwinding frames in Python
2503 In @value{GDBN} terminology ``unwinding'' is the process of finding
2504 the previous frame (that is, caller's) from the current one. An
2505 unwinder has three methods. The first one checks if it can handle
2506 given frame (``sniff'' it). For the frames it can sniff an unwinder
2507 provides two additional methods: it can return frame's ID, and it can
2508 fetch registers from the previous frame. A running @value{GDBN}
2509 mantains a list of the unwinders and calls each unwinder's sniffer in
2510 turn until it finds the one that recognizes the current frame. There
2511 is an API to register an unwinder.
2513 The unwinders that come with @value{GDBN} handle standard frames.
2514 However, mixed language applications (for example, an application
2515 running Java Virtual Machine) sometimes use frame layouts that cannot
2516 be handled by the @value{GDBN} unwinders. You can write Python code
2517 that can handle such custom frames.
2519 You implement a frame unwinder in Python as a class with which has two
2520 attributes, @code{name} and @code{enabled}, with obvious meanings, and
2521 a single method @code{__call__}, which examines a given frame and
2522 returns an object (an instance of @code{gdb.UnwindInfo class)}
2523 describing it. If an unwinder does not recognize a frame, it should
2524 return @code{None}. The code in @value{GDBN} that enables writing
2525 unwinders in Python uses this object to return frame's ID and previous
2526 frame registers when @value{GDBN} core asks for them.
2528 An unwinder should do as little work as possible. Some otherwise
2529 innocuous operations can cause problems (even crashes, as this code is
2530 not not well-hardened yet). For example, making an inferior call from
2531 an unwinder is unadvisable, as an inferior call will reset
2532 @value{GDBN}'s stack unwinding process, potentially causing re-entrant
2535 @subheading Unwinder Input
2537 An object passed to an unwinder (a @code{gdb.PendingFrame} instance)
2538 provides a method to read frame's registers:
2540 @defun PendingFrame.read_register (reg)
2541 This method returns the contents of the register @var{reg} in the
2542 frame as a @code{gdb.Value} object. For a description of the
2543 acceptable values of @var{reg} see
2544 @ref{gdbpy_frame_read_register,,Frame.read_register}. If @var{reg}
2545 does not name a register for the current architecture, this method
2546 will throw an exception.
2548 Note that this method will always return a @code{gdb.Value} for a
2549 valid register name. This does not mean that the value will be valid.
2550 For example, you may request a register that an earlier unwinder could
2551 not unwind---the value will be unavailable. Instead, the
2552 @code{gdb.Value} returned from this method will be lazy; that is, its
2553 underlying bits will not be fetched until it is first used. So,
2554 attempting to use such a value will cause an exception at the point of
2557 The type of the returned @code{gdb.Value} depends on the register and
2558 the architecture. It is common for registers to have a scalar type,
2559 like @code{long long}; but many other types are possible, such as
2560 pointer, pointer-to-function, floating point or vector types.
2563 It also provides a factory method to create a @code{gdb.UnwindInfo}
2564 instance to be returned to @value{GDBN}:
2566 @defun PendingFrame.create_unwind_info (frame_id)
2567 Returns a new @code{gdb.UnwindInfo} instance identified by given
2568 @var{frame_id}. The argument is used to build @value{GDBN}'s frame ID
2569 using one of functions provided by @value{GDBN}. @var{frame_id}'s attributes
2570 determine which function will be used, as follows:
2574 The frame is identified by the given stack address and PC. The stack
2575 address must be chosen so that it is constant throughout the lifetime
2576 of the frame, so a typical choice is the value of the stack pointer at
2577 the start of the function---in the DWARF standard, this would be the
2578 ``Call Frame Address''.
2580 This is the most common case by far. The other cases are documented
2581 for completeness but are only useful in specialized situations.
2583 @item sp, pc, special
2584 The frame is identified by the stack address, the PC, and a
2585 ``special'' address. The special address is used on architectures
2586 that can have frames that do not change the stack, but which are still
2587 distinct, for example the IA-64, which has a second stack for
2588 registers. Both @var{sp} and @var{special} must be constant
2589 throughout the lifetime of the frame.
2592 The frame is identified by the stack address only. Any other stack
2593 frame with a matching @var{sp} will be considered to match this frame.
2594 Inside gdb, this is called a ``wild frame''. You will never need
2598 Each attribute value should be an instance of @code{gdb.Value}.
2602 @defun PendingFrame.architecture ()
2603 Return the @code{gdb.Architecture} (@pxref{Architectures In Python})
2604 for this @code{gdb.PendingFrame}. This represents the architecture of
2605 the particular frame being unwound.
2608 @subheading Unwinder Output: UnwindInfo
2610 Use @code{PendingFrame.create_unwind_info} method described above to
2611 create a @code{gdb.UnwindInfo} instance. Use the following method to
2612 specify caller registers that have been saved in this frame:
2614 @defun gdb.UnwindInfo.add_saved_register (reg, value)
2615 @var{reg} identifies the register, for a description of the acceptable
2616 values see @ref{gdbpy_frame_read_register,,Frame.read_register}.
2617 @var{value} is a register value (a @code{gdb.Value} object).
2620 @subheading Unwinder Skeleton Code
2622 @value{GDBN} comes with the module containing the base @code{Unwinder}
2623 class. Derive your unwinder class from it and structure the code as
2627 from gdb.unwinders import Unwinder
2629 class FrameId(object):
2630 def __init__(self, sp, pc):
2635 class MyUnwinder(Unwinder):
2637 super(MyUnwinder, self).__init___(<expects unwinder name argument>)
2639 def __call__(pending_frame):
2640 if not <we recognize frame>:
2642 # Create UnwindInfo. Usually the frame is identified by the stack
2643 # pointer and the program counter.
2644 sp = pending_frame.read_register(<SP number>)
2645 pc = pending_frame.read_register(<PC number>)
2646 unwind_info = pending_frame.create_unwind_info(FrameId(sp, pc))
2648 # Find the values of the registers in the caller's frame and
2649 # save them in the result:
2650 unwind_info.add_saved_register(<register>, <value>)
2653 # Return the result:
2658 @subheading Registering a Unwinder
2660 An object file, a program space, and the @value{GDBN} proper can have
2661 unwinders registered with it.
2663 The @code{gdb.unwinders} module provides the function to register a
2666 @defun gdb.unwinder.register_unwinder (locus, unwinder, replace=False)
2667 @var{locus} is specifies an object file or a program space to which
2668 @var{unwinder} is added. Passing @code{None} or @code{gdb} adds
2669 @var{unwinder} to the @value{GDBN}'s global unwinder list. The newly
2670 added @var{unwinder} will be called before any other unwinder from the
2671 same locus. Two unwinders in the same locus cannot have the same
2672 name. An attempt to add a unwinder with already existing name raises
2673 an exception unless @var{replace} is @code{True}, in which case the
2674 old unwinder is deleted.
2677 @subheading Unwinder Precedence
2679 @value{GDBN} first calls the unwinders from all the object files in no
2680 particular order, then the unwinders from the current program space,
2681 and finally the unwinders from @value{GDBN}.
2683 @node Xmethods In Python
2684 @subsubsection Xmethods In Python
2685 @cindex xmethods in Python
2687 @dfn{Xmethods} are additional methods or replacements for existing
2688 methods of a C@t{++} class. This feature is useful for those cases
2689 where a method defined in C@t{++} source code could be inlined or
2690 optimized out by the compiler, making it unavailable to @value{GDBN}.
2691 For such cases, one can define an xmethod to serve as a replacement
2692 for the method defined in the C@t{++} source code. @value{GDBN} will
2693 then invoke the xmethod, instead of the C@t{++} method, to
2694 evaluate expressions. One can also use xmethods when debugging
2695 with core files. Moreover, when debugging live programs, invoking an
2696 xmethod need not involve running the inferior (which can potentially
2697 perturb its state). Hence, even if the C@t{++} method is available, it
2698 is better to use its replacement xmethod if one is defined.
2700 The xmethods feature in Python is available via the concepts of an
2701 @dfn{xmethod matcher} and an @dfn{xmethod worker}. To
2702 implement an xmethod, one has to implement a matcher and a
2703 corresponding worker for it (more than one worker can be
2704 implemented, each catering to a different overloaded instance of the
2705 method). Internally, @value{GDBN} invokes the @code{match} method of a
2706 matcher to match the class type and method name. On a match, the
2707 @code{match} method returns a list of matching @emph{worker} objects.
2708 Each worker object typically corresponds to an overloaded instance of
2709 the xmethod. They implement a @code{get_arg_types} method which
2710 returns a sequence of types corresponding to the arguments the xmethod
2711 requires. @value{GDBN} uses this sequence of types to perform
2712 overload resolution and picks a winning xmethod worker. A winner
2713 is also selected from among the methods @value{GDBN} finds in the
2714 C@t{++} source code. Next, the winning xmethod worker and the
2715 winning C@t{++} method are compared to select an overall winner. In
2716 case of a tie between a xmethod worker and a C@t{++} method, the
2717 xmethod worker is selected as the winner. That is, if a winning
2718 xmethod worker is found to be equivalent to the winning C@t{++}
2719 method, then the xmethod worker is treated as a replacement for
2720 the C@t{++} method. @value{GDBN} uses the overall winner to invoke the
2721 method. If the winning xmethod worker is the overall winner, then
2722 the corresponding xmethod is invoked via the @code{__call__} method
2723 of the worker object.
2725 If one wants to implement an xmethod as a replacement for an
2726 existing C@t{++} method, then they have to implement an equivalent
2727 xmethod which has exactly the same name and takes arguments of
2728 exactly the same type as the C@t{++} method. If the user wants to
2729 invoke the C@t{++} method even though a replacement xmethod is
2730 available for that method, then they can disable the xmethod.
2732 @xref{Xmethod API}, for API to implement xmethods in Python.
2733 @xref{Writing an Xmethod}, for implementing xmethods in Python.
2736 @subsubsection Xmethod API
2739 The @value{GDBN} Python API provides classes, interfaces and functions
2740 to implement, register and manipulate xmethods.
2741 @xref{Xmethods In Python}.
2743 An xmethod matcher should be an instance of a class derived from
2744 @code{XMethodMatcher} defined in the module @code{gdb.xmethod}, or an
2745 object with similar interface and attributes. An instance of
2746 @code{XMethodMatcher} has the following attributes:
2749 The name of the matcher.
2753 A boolean value indicating whether the matcher is enabled or disabled.
2757 A list of named methods managed by the matcher. Each object in the list
2758 is an instance of the class @code{XMethod} defined in the module
2759 @code{gdb.xmethod}, or any object with the following attributes:
2764 Name of the xmethod which should be unique for each xmethod
2765 managed by the matcher.
2768 A boolean value indicating whether the xmethod is enabled or
2773 The class @code{XMethod} is a convenience class with same
2774 attributes as above along with the following constructor:
2776 @defun XMethod.__init__ (self, name)
2777 Constructs an enabled xmethod with name @var{name}.
2782 The @code{XMethodMatcher} class has the following methods:
2784 @defun XMethodMatcher.__init__ (self, name)
2785 Constructs an enabled xmethod matcher with name @var{name}. The
2786 @code{methods} attribute is initialized to @code{None}.
2789 @defun XMethodMatcher.match (self, class_type, method_name)
2790 Derived classes should override this method. It should return a
2791 xmethod worker object (or a sequence of xmethod worker
2792 objects) matching the @var{class_type} and @var{method_name}.
2793 @var{class_type} is a @code{gdb.Type} object, and @var{method_name}
2794 is a string value. If the matcher manages named methods as listed in
2795 its @code{methods} attribute, then only those worker objects whose
2796 corresponding entries in the @code{methods} list are enabled should be
2800 An xmethod worker should be an instance of a class derived from
2801 @code{XMethodWorker} defined in the module @code{gdb.xmethod},
2802 or support the following interface:
2804 @defun XMethodWorker.get_arg_types (self)
2805 This method returns a sequence of @code{gdb.Type} objects corresponding
2806 to the arguments that the xmethod takes. It can return an empty
2807 sequence or @code{None} if the xmethod does not take any arguments.
2808 If the xmethod takes a single argument, then a single
2809 @code{gdb.Type} object corresponding to it can be returned.
2812 @defun XMethodWorker.get_result_type (self, *args)
2813 This method returns a @code{gdb.Type} object representing the type
2814 of the result of invoking this xmethod.
2815 The @var{args} argument is the same tuple of arguments that would be
2816 passed to the @code{__call__} method of this worker.
2819 @defun XMethodWorker.__call__ (self, *args)
2820 This is the method which does the @emph{work} of the xmethod. The
2821 @var{args} arguments is the tuple of arguments to the xmethod. Each
2822 element in this tuple is a gdb.Value object. The first element is
2823 always the @code{this} pointer value.
2826 For @value{GDBN} to lookup xmethods, the xmethod matchers
2827 should be registered using the following function defined in the module
2830 @defun register_xmethod_matcher (locus, matcher, replace=False)
2831 The @code{matcher} is registered with @code{locus}, replacing an
2832 existing matcher with the same name as @code{matcher} if
2833 @code{replace} is @code{True}. @code{locus} can be a
2834 @code{gdb.Objfile} object (@pxref{Objfiles In Python}), or a
2835 @code{gdb.Progspace} object (@pxref{Progspaces In Python}), or
2836 @code{None}. If it is @code{None}, then @code{matcher} is registered
2840 @node Writing an Xmethod
2841 @subsubsection Writing an Xmethod
2842 @cindex writing xmethods in Python
2844 Implementing xmethods in Python will require implementing xmethod
2845 matchers and xmethod workers (@pxref{Xmethods In Python}). Consider
2846 the following C@t{++} class:
2852 MyClass (int a) : a_(a) @{ @}
2854 int geta (void) @{ return a_; @}
2855 int operator+ (int b);
2862 MyClass::operator+ (int b)
2869 Let us define two xmethods for the class @code{MyClass}, one
2870 replacing the method @code{geta}, and another adding an overloaded
2871 flavor of @code{operator+} which takes a @code{MyClass} argument (the
2872 C@t{++} code above already has an overloaded @code{operator+}
2873 which takes an @code{int} argument). The xmethod matcher can be
2877 class MyClass_geta(gdb.xmethod.XMethod):
2879 gdb.xmethod.XMethod.__init__(self, 'geta')
2881 def get_worker(self, method_name):
2882 if method_name == 'geta':
2883 return MyClassWorker_geta()
2886 class MyClass_sum(gdb.xmethod.XMethod):
2888 gdb.xmethod.XMethod.__init__(self, 'sum')
2890 def get_worker(self, method_name):
2891 if method_name == 'operator+':
2892 return MyClassWorker_plus()
2895 class MyClassMatcher(gdb.xmethod.XMethodMatcher):
2897 gdb.xmethod.XMethodMatcher.__init__(self, 'MyClassMatcher')
2898 # List of methods 'managed' by this matcher
2899 self.methods = [MyClass_geta(), MyClass_sum()]
2901 def match(self, class_type, method_name):
2902 if class_type.tag != 'MyClass':
2905 for method in self.methods:
2907 worker = method.get_worker(method_name)
2909 workers.append(worker)
2915 Notice that the @code{match} method of @code{MyClassMatcher} returns
2916 a worker object of type @code{MyClassWorker_geta} for the @code{geta}
2917 method, and a worker object of type @code{MyClassWorker_plus} for the
2918 @code{operator+} method. This is done indirectly via helper classes
2919 derived from @code{gdb.xmethod.XMethod}. One does not need to use the
2920 @code{methods} attribute in a matcher as it is optional. However, if a
2921 matcher manages more than one xmethod, it is a good practice to list the
2922 xmethods in the @code{methods} attribute of the matcher. This will then
2923 facilitate enabling and disabling individual xmethods via the
2924 @code{enable/disable} commands. Notice also that a worker object is
2925 returned only if the corresponding entry in the @code{methods} attribute
2926 of the matcher is enabled.
2928 The implementation of the worker classes returned by the matcher setup
2929 above is as follows:
2932 class MyClassWorker_geta(gdb.xmethod.XMethodWorker):
2933 def get_arg_types(self):
2936 def get_result_type(self, obj):
2937 return gdb.lookup_type('int')
2939 def __call__(self, obj):
2943 class MyClassWorker_plus(gdb.xmethod.XMethodWorker):
2944 def get_arg_types(self):
2945 return gdb.lookup_type('MyClass')
2947 def get_result_type(self, obj):
2948 return gdb.lookup_type('int')
2950 def __call__(self, obj, other):
2951 return obj['a_'] + other['a_']
2954 For @value{GDBN} to actually lookup a xmethod, it has to be
2955 registered with it. The matcher defined above is registered with
2956 @value{GDBN} globally as follows:
2959 gdb.xmethod.register_xmethod_matcher(None, MyClassMatcher())
2962 If an object @code{obj} of type @code{MyClass} is initialized in C@t{++}
2970 then, after loading the Python script defining the xmethod matchers
2971 and workers into @code{GDBN}, invoking the method @code{geta} or using
2972 the operator @code{+} on @code{obj} will invoke the xmethods
2983 Consider another example with a C++ template class:
2990 MyTemplate () : dsize_(10), data_ (new T [10]) @{ @}
2991 ~MyTemplate () @{ delete [] data_; @}
2993 int footprint (void)
2995 return sizeof (T) * dsize_ + sizeof (MyTemplate<T>);
3004 Let us implement an xmethod for the above class which serves as a
3005 replacement for the @code{footprint} method. The full code listing
3006 of the xmethod workers and xmethod matchers is as follows:
3009 class MyTemplateWorker_footprint(gdb.xmethod.XMethodWorker):
3010 def __init__(self, class_type):
3011 self.class_type = class_type
3013 def get_arg_types(self):
3016 def get_result_type(self):
3017 return gdb.lookup_type('int')
3019 def __call__(self, obj):
3020 return (self.class_type.sizeof +
3022 self.class_type.template_argument(0).sizeof)
3025 class MyTemplateMatcher_footprint(gdb.xmethod.XMethodMatcher):
3027 gdb.xmethod.XMethodMatcher.__init__(self, 'MyTemplateMatcher')
3029 def match(self, class_type, method_name):
3030 if (re.match('MyTemplate<[ \t\n]*[_a-zA-Z][ _a-zA-Z0-9]*>',
3032 method_name == 'footprint'):
3033 return MyTemplateWorker_footprint(class_type)
3036 Notice that, in this example, we have not used the @code{methods}
3037 attribute of the matcher as the matcher manages only one xmethod. The
3038 user can enable/disable this xmethod by enabling/disabling the matcher
3041 @node Inferiors In Python
3042 @subsubsection Inferiors In Python
3043 @cindex inferiors in Python
3045 @findex gdb.Inferior
3046 Programs which are being run under @value{GDBN} are called inferiors
3047 (@pxref{Inferiors Connections and Programs}). Python scripts can access
3048 information about and manipulate inferiors controlled by @value{GDBN}
3049 via objects of the @code{gdb.Inferior} class.
3051 The following inferior-related functions are available in the @code{gdb}
3054 @defun gdb.inferiors ()
3055 Return a tuple containing all inferior objects.
3058 @defun gdb.selected_inferior ()
3059 Return an object representing the current inferior.
3062 A @code{gdb.Inferior} object has the following attributes:
3064 @defvar Inferior.num
3065 ID of inferior, as assigned by GDB.
3068 @defvar Inferior.connection_num
3069 ID of inferior's connection as assigned by @value{GDBN}, or None if
3070 the inferior is not connected to a target.
3071 @xref{Inferiors Connections and Programs}.
3074 @defvar Inferior.pid
3075 Process ID of the inferior, as assigned by the underlying operating
3079 @defvar Inferior.was_attached
3080 Boolean signaling whether the inferior was created using `attach', or
3081 started by @value{GDBN} itself.
3084 @defvar Inferior.progspace
3085 The inferior's program space. @xref{Progspaces In Python}.
3088 A @code{gdb.Inferior} object has the following methods:
3090 @defun Inferior.is_valid ()
3091 Returns @code{True} if the @code{gdb.Inferior} object is valid,
3092 @code{False} if not. A @code{gdb.Inferior} object will become invalid
3093 if the inferior no longer exists within @value{GDBN}. All other
3094 @code{gdb.Inferior} methods will throw an exception if it is invalid
3095 at the time the method is called.
3098 @defun Inferior.threads ()
3099 This method returns a tuple holding all the threads which are valid
3100 when it is called. If there are no valid threads, the method will
3101 return an empty tuple.
3104 @defun Inferior.architecture ()
3105 Return the @code{gdb.Architecture} (@pxref{Architectures In Python})
3106 for this inferior. This represents the architecture of the inferior
3107 as a whole. Some platforms can have multiple architectures in a
3108 single address space, so this may not match the architecture of a
3109 particular frame (@pxref{Frames In Python}).
3112 @findex Inferior.read_memory
3113 @defun Inferior.read_memory (address, length)
3114 Read @var{length} addressable memory units from the inferior, starting at
3115 @var{address}. Returns a buffer object, which behaves much like an array
3116 or a string. It can be modified and given to the
3117 @code{Inferior.write_memory} function. In Python 3, the return
3118 value is a @code{memoryview} object.
3121 @findex Inferior.write_memory
3122 @defun Inferior.write_memory (address, buffer @r{[}, length@r{]})
3123 Write the contents of @var{buffer} to the inferior, starting at
3124 @var{address}. The @var{buffer} parameter must be a Python object
3125 which supports the buffer protocol, i.e., a string, an array or the
3126 object returned from @code{Inferior.read_memory}. If given, @var{length}
3127 determines the number of addressable memory units from @var{buffer} to be
3131 @findex gdb.search_memory
3132 @defun Inferior.search_memory (address, length, pattern)
3133 Search a region of the inferior memory starting at @var{address} with
3134 the given @var{length} using the search pattern supplied in
3135 @var{pattern}. The @var{pattern} parameter must be a Python object
3136 which supports the buffer protocol, i.e., a string, an array or the
3137 object returned from @code{gdb.read_memory}. Returns a Python @code{Long}
3138 containing the address where the pattern was found, or @code{None} if
3139 the pattern could not be found.
3142 @findex Inferior.thread_from_handle
3143 @findex Inferior.thread_from_thread_handle
3144 @defun Inferior.thread_from_handle (handle)
3145 Return the thread object corresponding to @var{handle}, a thread
3146 library specific data structure such as @code{pthread_t} for pthreads
3147 library implementations.
3149 The function @code{Inferior.thread_from_thread_handle} provides
3150 the same functionality, but use of @code{Inferior.thread_from_thread_handle}
3154 @node Events In Python
3155 @subsubsection Events In Python
3156 @cindex inferior events in Python
3158 @value{GDBN} provides a general event facility so that Python code can be
3159 notified of various state changes, particularly changes that occur in
3162 An @dfn{event} is just an object that describes some state change. The
3163 type of the object and its attributes will vary depending on the details
3164 of the change. All the existing events are described below.
3166 In order to be notified of an event, you must register an event handler
3167 with an @dfn{event registry}. An event registry is an object in the
3168 @code{gdb.events} module which dispatches particular events. A registry
3169 provides methods to register and unregister event handlers:
3171 @defun EventRegistry.connect (object)
3172 Add the given callable @var{object} to the registry. This object will be
3173 called when an event corresponding to this registry occurs.
3176 @defun EventRegistry.disconnect (object)
3177 Remove the given @var{object} from the registry. Once removed, the object
3178 will no longer receive notifications of events.
3184 def exit_handler (event):
3185 print ("event type: exit")
3186 print ("exit code: %d" % (event.exit_code))
3188 gdb.events.exited.connect (exit_handler)
3191 In the above example we connect our handler @code{exit_handler} to the
3192 registry @code{events.exited}. Once connected, @code{exit_handler} gets
3193 called when the inferior exits. The argument @dfn{event} in this example is
3194 of type @code{gdb.ExitedEvent}. As you can see in the example the
3195 @code{ExitedEvent} object has an attribute which indicates the exit code of
3198 The following is a listing of the event registries that are available and
3199 details of the events they emit:
3204 Emits @code{gdb.ThreadEvent}.
3206 Some events can be thread specific when @value{GDBN} is running in non-stop
3207 mode. When represented in Python, these events all extend
3208 @code{gdb.ThreadEvent}. Note, this event is not emitted directly; instead,
3209 events which are emitted by this or other modules might extend this event.
3210 Examples of these events are @code{gdb.BreakpointEvent} and
3211 @code{gdb.ContinueEvent}.
3213 @defvar ThreadEvent.inferior_thread
3214 In non-stop mode this attribute will be set to the specific thread which was
3215 involved in the emitted event. Otherwise, it will be set to @code{None}.
3218 Emits @code{gdb.ContinueEvent} which extends @code{gdb.ThreadEvent}.
3220 This event indicates that the inferior has been continued after a stop. For
3221 inherited attribute refer to @code{gdb.ThreadEvent} above.
3224 Emits @code{events.ExitedEvent} which indicates that the inferior has exited.
3225 @code{events.ExitedEvent} has two attributes:
3226 @defvar ExitedEvent.exit_code
3227 An integer representing the exit code, if available, which the inferior
3228 has returned. (The exit code could be unavailable if, for example,
3229 @value{GDBN} detaches from the inferior.) If the exit code is unavailable,
3230 the attribute does not exist.
3232 @defvar ExitedEvent.inferior
3233 A reference to the inferior which triggered the @code{exited} event.
3237 Emits @code{gdb.StopEvent} which extends @code{gdb.ThreadEvent}.
3239 Indicates that the inferior has stopped. All events emitted by this registry
3240 extend StopEvent. As a child of @code{gdb.ThreadEvent}, @code{gdb.StopEvent}
3241 will indicate the stopped thread when @value{GDBN} is running in non-stop
3242 mode. Refer to @code{gdb.ThreadEvent} above for more details.
3244 Emits @code{gdb.SignalEvent} which extends @code{gdb.StopEvent}.
3246 This event indicates that the inferior or one of its threads has received as
3247 signal. @code{gdb.SignalEvent} has the following attributes:
3249 @defvar SignalEvent.stop_signal
3250 A string representing the signal received by the inferior. A list of possible
3251 signal values can be obtained by running the command @code{info signals} in
3252 the @value{GDBN} command prompt.
3255 Also emits @code{gdb.BreakpointEvent} which extends @code{gdb.StopEvent}.
3257 @code{gdb.BreakpointEvent} event indicates that one or more breakpoints have
3258 been hit, and has the following attributes:
3260 @defvar BreakpointEvent.breakpoints
3261 A sequence containing references to all the breakpoints (type
3262 @code{gdb.Breakpoint}) that were hit.
3263 @xref{Breakpoints In Python}, for details of the @code{gdb.Breakpoint} object.
3265 @defvar BreakpointEvent.breakpoint
3266 A reference to the first breakpoint that was hit.
3267 This function is maintained for backward compatibility and is now deprecated
3268 in favor of the @code{gdb.BreakpointEvent.breakpoints} attribute.
3271 @item events.new_objfile
3272 Emits @code{gdb.NewObjFileEvent} which indicates that a new object file has
3273 been loaded by @value{GDBN}. @code{gdb.NewObjFileEvent} has one attribute:
3275 @defvar NewObjFileEvent.new_objfile
3276 A reference to the object file (@code{gdb.Objfile}) which has been loaded.
3277 @xref{Objfiles In Python}, for details of the @code{gdb.Objfile} object.
3280 @item events.clear_objfiles
3281 Emits @code{gdb.ClearObjFilesEvent} which indicates that the list of object
3282 files for a program space has been reset.
3283 @code{gdb.ClearObjFilesEvent} has one attribute:
3285 @defvar ClearObjFilesEvent.progspace
3286 A reference to the program space (@code{gdb.Progspace}) whose objfile list has
3287 been cleared. @xref{Progspaces In Python}.
3290 @item events.inferior_call
3291 Emits events just before and after a function in the inferior is
3292 called by @value{GDBN}. Before an inferior call, this emits an event
3293 of type @code{gdb.InferiorCallPreEvent}, and after an inferior call,
3294 this emits an event of type @code{gdb.InferiorCallPostEvent}.
3297 @tindex gdb.InferiorCallPreEvent
3298 @item @code{gdb.InferiorCallPreEvent}
3299 Indicates that a function in the inferior is about to be called.
3301 @defvar InferiorCallPreEvent.ptid
3302 The thread in which the call will be run.
3305 @defvar InferiorCallPreEvent.address
3306 The location of the function to be called.
3309 @tindex gdb.InferiorCallPostEvent
3310 @item @code{gdb.InferiorCallPostEvent}
3311 Indicates that a function in the inferior has just been called.
3313 @defvar InferiorCallPostEvent.ptid
3314 The thread in which the call was run.
3317 @defvar InferiorCallPostEvent.address
3318 The location of the function that was called.
3322 @item events.memory_changed
3323 Emits @code{gdb.MemoryChangedEvent} which indicates that the memory of the
3324 inferior has been modified by the @value{GDBN} user, for instance via a
3325 command like @w{@code{set *addr = value}}. The event has the following
3328 @defvar MemoryChangedEvent.address
3329 The start address of the changed region.
3332 @defvar MemoryChangedEvent.length
3333 Length in bytes of the changed region.
3336 @item events.register_changed
3337 Emits @code{gdb.RegisterChangedEvent} which indicates that a register in the
3338 inferior has been modified by the @value{GDBN} user.
3340 @defvar RegisterChangedEvent.frame
3341 A gdb.Frame object representing the frame in which the register was modified.
3343 @defvar RegisterChangedEvent.regnum
3344 Denotes which register was modified.
3347 @item events.breakpoint_created
3348 This is emitted when a new breakpoint has been created. The argument
3349 that is passed is the new @code{gdb.Breakpoint} object.
3351 @item events.breakpoint_modified
3352 This is emitted when a breakpoint has been modified in some way. The
3353 argument that is passed is the new @code{gdb.Breakpoint} object.
3355 @item events.breakpoint_deleted
3356 This is emitted when a breakpoint has been deleted. The argument that
3357 is passed is the @code{gdb.Breakpoint} object. When this event is
3358 emitted, the @code{gdb.Breakpoint} object will already be in its
3359 invalid state; that is, the @code{is_valid} method will return
3362 @item events.before_prompt
3363 This event carries no payload. It is emitted each time @value{GDBN}
3364 presents a prompt to the user.
3366 @item events.new_inferior
3367 This is emitted when a new inferior is created. Note that the
3368 inferior is not necessarily running; in fact, it may not even have an
3369 associated executable.
3371 The event is of type @code{gdb.NewInferiorEvent}. This has a single
3374 @defvar NewInferiorEvent.inferior
3375 The new inferior, a @code{gdb.Inferior} object.
3378 @item events.inferior_deleted
3379 This is emitted when an inferior has been deleted. Note that this is
3380 not the same as process exit; it is notified when the inferior itself
3381 is removed, say via @code{remove-inferiors}.
3383 The event is of type @code{gdb.InferiorDeletedEvent}. This has a single
3386 @defvar NewInferiorEvent.inferior
3387 The inferior that is being removed, a @code{gdb.Inferior} object.
3390 @item events.new_thread
3391 This is emitted when @value{GDBN} notices a new thread. The event is of
3392 type @code{gdb.NewThreadEvent}, which extends @code{gdb.ThreadEvent}.
3393 This has a single attribute:
3395 @defvar NewThreadEvent.inferior_thread
3401 @node Threads In Python
3402 @subsubsection Threads In Python
3403 @cindex threads in python
3405 @findex gdb.InferiorThread
3406 Python scripts can access information about, and manipulate inferior threads
3407 controlled by @value{GDBN}, via objects of the @code{gdb.InferiorThread} class.
3409 The following thread-related functions are available in the @code{gdb}
3412 @findex gdb.selected_thread
3413 @defun gdb.selected_thread ()
3414 This function returns the thread object for the selected thread. If there
3415 is no selected thread, this will return @code{None}.
3418 To get the list of threads for an inferior, use the @code{Inferior.threads()}
3419 method. @xref{Inferiors In Python}.
3421 A @code{gdb.InferiorThread} object has the following attributes:
3423 @defvar InferiorThread.name
3424 The name of the thread. If the user specified a name using
3425 @code{thread name}, then this returns that name. Otherwise, if an
3426 OS-supplied name is available, then it is returned. Otherwise, this
3427 returns @code{None}.
3429 This attribute can be assigned to. The new value must be a string
3430 object, which sets the new name, or @code{None}, which removes any
3431 user-specified thread name.
3434 @defvar InferiorThread.num
3435 The per-inferior number of the thread, as assigned by GDB.
3438 @defvar InferiorThread.global_num
3439 The global ID of the thread, as assigned by GDB. You can use this to
3440 make Python breakpoints thread-specific, for example
3441 (@pxref{python_breakpoint_thread,,The Breakpoint.thread attribute}).
3444 @defvar InferiorThread.ptid
3445 ID of the thread, as assigned by the operating system. This attribute is a
3446 tuple containing three integers. The first is the Process ID (PID); the second
3447 is the Lightweight Process ID (LWPID), and the third is the Thread ID (TID).
3448 Either the LWPID or TID may be 0, which indicates that the operating system
3449 does not use that identifier.
3452 @defvar InferiorThread.inferior
3453 The inferior this thread belongs to. This attribute is represented as
3454 a @code{gdb.Inferior} object. This attribute is not writable.
3457 A @code{gdb.InferiorThread} object has the following methods:
3459 @defun InferiorThread.is_valid ()
3460 Returns @code{True} if the @code{gdb.InferiorThread} object is valid,
3461 @code{False} if not. A @code{gdb.InferiorThread} object will become
3462 invalid if the thread exits, or the inferior that the thread belongs
3463 is deleted. All other @code{gdb.InferiorThread} methods will throw an
3464 exception if it is invalid at the time the method is called.
3467 @defun InferiorThread.switch ()
3468 This changes @value{GDBN}'s currently selected thread to the one represented
3472 @defun InferiorThread.is_stopped ()
3473 Return a Boolean indicating whether the thread is stopped.
3476 @defun InferiorThread.is_running ()
3477 Return a Boolean indicating whether the thread is running.
3480 @defun InferiorThread.is_exited ()
3481 Return a Boolean indicating whether the thread is exited.
3484 @defun InferiorThread.handle ()
3485 Return the thread object's handle, represented as a Python @code{bytes}
3486 object. A @code{gdb.Value} representation of the handle may be
3487 constructed via @code{gdb.Value(bufobj, type)} where @var{bufobj} is
3488 the Python @code{bytes} representation of the handle and @var{type} is
3489 a @code{gdb.Type} for the handle type.
3492 @node Recordings In Python
3493 @subsubsection Recordings In Python
3494 @cindex recordings in python
3496 The following recordings-related functions
3497 (@pxref{Process Record and Replay}) are available in the @code{gdb}
3500 @defun gdb.start_recording (@r{[}method@r{]}, @r{[}format@r{]})
3501 Start a recording using the given @var{method} and @var{format}. If
3502 no @var{format} is given, the default format for the recording method
3503 is used. If no @var{method} is given, the default method will be used.
3504 Returns a @code{gdb.Record} object on success. Throw an exception on
3507 The following strings can be passed as @var{method}:
3513 @code{"btrace"}: Possible values for @var{format}: @code{"pt"},
3514 @code{"bts"} or leave out for default format.
3518 @defun gdb.current_recording ()
3519 Access a currently running recording. Return a @code{gdb.Record}
3520 object on success. Return @code{None} if no recording is currently
3524 @defun gdb.stop_recording ()
3525 Stop the current recording. Throw an exception if no recording is
3526 currently active. All record objects become invalid after this call.
3529 A @code{gdb.Record} object has the following attributes:
3531 @defvar Record.method
3532 A string with the current recording method, e.g.@: @code{full} or
3536 @defvar Record.format
3537 A string with the current recording format, e.g.@: @code{bt}, @code{pts} or
3541 @defvar Record.begin
3542 A method specific instruction object representing the first instruction
3547 A method specific instruction object representing the current
3548 instruction, that is not actually part of the recording.
3551 @defvar Record.replay_position
3552 The instruction representing the current replay position. If there is
3553 no replay active, this will be @code{None}.
3556 @defvar Record.instruction_history
3557 A list with all recorded instructions.
3560 @defvar Record.function_call_history
3561 A list with all recorded function call segments.
3564 A @code{gdb.Record} object has the following methods:
3566 @defun Record.goto (instruction)
3567 Move the replay position to the given @var{instruction}.
3570 The common @code{gdb.Instruction} class that recording method specific
3571 instruction objects inherit from, has the following attributes:
3573 @defvar Instruction.pc
3574 An integer representing this instruction's address.
3577 @defvar Instruction.data
3578 A buffer with the raw instruction data. In Python 3, the return value is a
3579 @code{memoryview} object.
3582 @defvar Instruction.decoded
3583 A human readable string with the disassembled instruction.
3586 @defvar Instruction.size
3587 The size of the instruction in bytes.
3590 Additionally @code{gdb.RecordInstruction} has the following attributes:
3592 @defvar RecordInstruction.number
3593 An integer identifying this instruction. @code{number} corresponds to
3594 the numbers seen in @code{record instruction-history}
3595 (@pxref{Process Record and Replay}).
3598 @defvar RecordInstruction.sal
3599 A @code{gdb.Symtab_and_line} object representing the associated symtab
3600 and line of this instruction. May be @code{None} if no debug information is
3604 @defvar RecordInstruction.is_speculative
3605 A boolean indicating whether the instruction was executed speculatively.
3608 If an error occured during recording or decoding a recording, this error is
3609 represented by a @code{gdb.RecordGap} object in the instruction list. It has
3610 the following attributes:
3612 @defvar RecordGap.number
3613 An integer identifying this gap. @code{number} corresponds to the numbers seen
3614 in @code{record instruction-history} (@pxref{Process Record and Replay}).
3617 @defvar RecordGap.error_code
3618 A numerical representation of the reason for the gap. The value is specific to
3619 the current recording method.
3622 @defvar RecordGap.error_string
3623 A human readable string with the reason for the gap.
3626 A @code{gdb.RecordFunctionSegment} object has the following attributes:
3628 @defvar RecordFunctionSegment.number
3629 An integer identifying this function segment. @code{number} corresponds to
3630 the numbers seen in @code{record function-call-history}
3631 (@pxref{Process Record and Replay}).
3634 @defvar RecordFunctionSegment.symbol
3635 A @code{gdb.Symbol} object representing the associated symbol. May be
3636 @code{None} if no debug information is available.
3639 @defvar RecordFunctionSegment.level
3640 An integer representing the function call's stack level. May be
3641 @code{None} if the function call is a gap.
3644 @defvar RecordFunctionSegment.instructions
3645 A list of @code{gdb.RecordInstruction} or @code{gdb.RecordGap} objects
3646 associated with this function call.
3649 @defvar RecordFunctionSegment.up
3650 A @code{gdb.RecordFunctionSegment} object representing the caller's
3651 function segment. If the call has not been recorded, this will be the
3652 function segment to which control returns. If neither the call nor the
3653 return have been recorded, this will be @code{None}.
3656 @defvar RecordFunctionSegment.prev
3657 A @code{gdb.RecordFunctionSegment} object representing the previous
3658 segment of this function call. May be @code{None}.
3661 @defvar RecordFunctionSegment.next
3662 A @code{gdb.RecordFunctionSegment} object representing the next segment of
3663 this function call. May be @code{None}.
3666 The following example demonstrates the usage of these objects and
3667 functions to create a function that will rewind a record to the last
3668 time a function in a different file was executed. This would typically
3669 be used to track the execution of user provided callback functions in a
3670 library which typically are not visible in a back trace.
3674 rec = gdb.current_recording ()
3678 insn = rec.instruction_history
3683 position = insn.index (rec.replay_position)
3687 filename = insn[position].sal.symtab.fullname ()
3691 for i in reversed (insn[:position]):
3693 current = i.sal.symtab.fullname ()
3697 if filename == current:
3704 Another possible application is to write a function that counts the
3705 number of code executions in a given line range. This line range can
3706 contain parts of functions or span across several functions and is not
3707 limited to be contiguous.
3710 def countrange (filename, linerange):
3713 def filter_only (file_name):
3714 for call in gdb.current_recording ().function_call_history:
3716 if file_name in call.symbol.symtab.fullname ():
3721 for c in filter_only (filename):
3722 for i in c.instructions:
3724 if i.sal.line in linerange:
3733 @node Commands In Python
3734 @subsubsection Commands In Python
3736 @cindex commands in python
3737 @cindex python commands
3738 You can implement new @value{GDBN} CLI commands in Python. A CLI
3739 command is implemented using an instance of the @code{gdb.Command}
3740 class, most commonly using a subclass.
3742 @defun Command.__init__ (name, @var{command_class} @r{[}, @var{completer_class} @r{[}, @var{prefix}@r{]]})
3743 The object initializer for @code{Command} registers the new command
3744 with @value{GDBN}. This initializer is normally invoked from the
3745 subclass' own @code{__init__} method.
3747 @var{name} is the name of the command. If @var{name} consists of
3748 multiple words, then the initial words are looked for as prefix
3749 commands. In this case, if one of the prefix commands does not exist,
3750 an exception is raised.
3752 There is no support for multi-line commands.
3754 @var{command_class} should be one of the @samp{COMMAND_} constants
3755 defined below. This argument tells @value{GDBN} how to categorize the
3756 new command in the help system.
3758 @var{completer_class} is an optional argument. If given, it should be
3759 one of the @samp{COMPLETE_} constants defined below. This argument
3760 tells @value{GDBN} how to perform completion for this command. If not
3761 given, @value{GDBN} will attempt to complete using the object's
3762 @code{complete} method (see below); if no such method is found, an
3763 error will occur when completion is attempted.
3765 @var{prefix} is an optional argument. If @code{True}, then the new
3766 command is a prefix command; sub-commands of this command may be
3769 The help text for the new command is taken from the Python
3770 documentation string for the command's class, if there is one. If no
3771 documentation string is provided, the default value ``This command is
3772 not documented.'' is used.
3775 @cindex don't repeat Python command
3776 @defun Command.dont_repeat ()
3777 By default, a @value{GDBN} command is repeated when the user enters a
3778 blank line at the command prompt. A command can suppress this
3779 behavior by invoking the @code{dont_repeat} method. This is similar
3780 to the user command @code{dont-repeat}, see @ref{Define, dont-repeat}.
3783 @defun Command.invoke (argument, from_tty)
3784 This method is called by @value{GDBN} when this command is invoked.
3786 @var{argument} is a string. It is the argument to the command, after
3787 leading and trailing whitespace has been stripped.
3789 @var{from_tty} is a boolean argument. When true, this means that the
3790 command was entered by the user at the terminal; when false it means
3791 that the command came from elsewhere.
3793 If this method throws an exception, it is turned into a @value{GDBN}
3794 @code{error} call. Otherwise, the return value is ignored.
3796 @findex gdb.string_to_argv
3797 To break @var{argument} up into an argv-like string use
3798 @code{gdb.string_to_argv}. This function behaves identically to
3799 @value{GDBN}'s internal argument lexer @code{buildargv}.
3800 It is recommended to use this for consistency.
3801 Arguments are separated by spaces and may be quoted.
3805 print gdb.string_to_argv ("1 2\ \\\"3 '4 \"5' \"6 '7\"")
3806 ['1', '2 "3', '4 "5', "6 '7"]
3811 @cindex completion of Python commands
3812 @defun Command.complete (text, word)
3813 This method is called by @value{GDBN} when the user attempts
3814 completion on this command. All forms of completion are handled by
3815 this method, that is, the @key{TAB} and @key{M-?} key bindings
3816 (@pxref{Completion}), and the @code{complete} command (@pxref{Help,
3819 The arguments @var{text} and @var{word} are both strings; @var{text}
3820 holds the complete command line up to the cursor's location, while
3821 @var{word} holds the last word of the command line; this is computed
3822 using a word-breaking heuristic.
3824 The @code{complete} method can return several values:
3827 If the return value is a sequence, the contents of the sequence are
3828 used as the completions. It is up to @code{complete} to ensure that the
3829 contents actually do complete the word. A zero-length sequence is
3830 allowed, it means that there were no completions available. Only
3831 string elements of the sequence are used; other elements in the
3832 sequence are ignored.
3835 If the return value is one of the @samp{COMPLETE_} constants defined
3836 below, then the corresponding @value{GDBN}-internal completion
3837 function is invoked, and its result is used.
3840 All other results are treated as though there were no available
3845 When a new command is registered, it must be declared as a member of
3846 some general class of commands. This is used to classify top-level
3847 commands in the on-line help system; note that prefix commands are not
3848 listed under their own category but rather that of their top-level
3849 command. The available classifications are represented by constants
3850 defined in the @code{gdb} module:
3853 @findex COMMAND_NONE
3854 @findex gdb.COMMAND_NONE
3855 @item gdb.COMMAND_NONE
3856 The command does not belong to any particular class. A command in
3857 this category will not be displayed in any of the help categories.
3859 @findex COMMAND_RUNNING
3860 @findex gdb.COMMAND_RUNNING
3861 @item gdb.COMMAND_RUNNING
3862 The command is related to running the inferior. For example,
3863 @code{start}, @code{step}, and @code{continue} are in this category.
3864 Type @kbd{help running} at the @value{GDBN} prompt to see a list of
3865 commands in this category.
3867 @findex COMMAND_DATA
3868 @findex gdb.COMMAND_DATA
3869 @item gdb.COMMAND_DATA
3870 The command is related to data or variables. For example,
3871 @code{call}, @code{find}, and @code{print} are in this category. Type
3872 @kbd{help data} at the @value{GDBN} prompt to see a list of commands
3875 @findex COMMAND_STACK
3876 @findex gdb.COMMAND_STACK
3877 @item gdb.COMMAND_STACK
3878 The command has to do with manipulation of the stack. For example,
3879 @code{backtrace}, @code{frame}, and @code{return} are in this
3880 category. Type @kbd{help stack} at the @value{GDBN} prompt to see a
3881 list of commands in this category.
3883 @findex COMMAND_FILES
3884 @findex gdb.COMMAND_FILES
3885 @item gdb.COMMAND_FILES
3886 This class is used for file-related commands. For example,
3887 @code{file}, @code{list} and @code{section} are in this category.
3888 Type @kbd{help files} at the @value{GDBN} prompt to see a list of
3889 commands in this category.
3891 @findex COMMAND_SUPPORT
3892 @findex gdb.COMMAND_SUPPORT
3893 @item gdb.COMMAND_SUPPORT
3894 This should be used for ``support facilities'', generally meaning
3895 things that are useful to the user when interacting with @value{GDBN},
3896 but not related to the state of the inferior. For example,
3897 @code{help}, @code{make}, and @code{shell} are in this category. Type
3898 @kbd{help support} at the @value{GDBN} prompt to see a list of
3899 commands in this category.
3901 @findex COMMAND_STATUS
3902 @findex gdb.COMMAND_STATUS
3903 @item gdb.COMMAND_STATUS
3904 The command is an @samp{info}-related command, that is, related to the
3905 state of @value{GDBN} itself. For example, @code{info}, @code{macro},
3906 and @code{show} are in this category. Type @kbd{help status} at the
3907 @value{GDBN} prompt to see a list of commands in this category.
3909 @findex COMMAND_BREAKPOINTS
3910 @findex gdb.COMMAND_BREAKPOINTS
3911 @item gdb.COMMAND_BREAKPOINTS
3912 The command has to do with breakpoints. For example, @code{break},
3913 @code{clear}, and @code{delete} are in this category. Type @kbd{help
3914 breakpoints} at the @value{GDBN} prompt to see a list of commands in
3917 @findex COMMAND_TRACEPOINTS
3918 @findex gdb.COMMAND_TRACEPOINTS
3919 @item gdb.COMMAND_TRACEPOINTS
3920 The command has to do with tracepoints. For example, @code{trace},
3921 @code{actions}, and @code{tfind} are in this category. Type
3922 @kbd{help tracepoints} at the @value{GDBN} prompt to see a list of
3923 commands in this category.
3926 @findex gdb.COMMAND_TUI
3927 @item gdb.COMMAND_TUI
3928 The command has to do with the text user interface (@pxref{TUI}).
3929 Type @kbd{help tui} at the @value{GDBN} prompt to see a list of
3930 commands in this category.
3932 @findex COMMAND_USER
3933 @findex gdb.COMMAND_USER
3934 @item gdb.COMMAND_USER
3935 The command is a general purpose command for the user, and typically
3936 does not fit in one of the other categories.
3937 Type @kbd{help user-defined} at the @value{GDBN} prompt to see
3938 a list of commands in this category, as well as the list of gdb macros
3939 (@pxref{Sequences}).
3941 @findex COMMAND_OBSCURE
3942 @findex gdb.COMMAND_OBSCURE
3943 @item gdb.COMMAND_OBSCURE
3944 The command is only used in unusual circumstances, or is not of
3945 general interest to users. For example, @code{checkpoint},
3946 @code{fork}, and @code{stop} are in this category. Type @kbd{help
3947 obscure} at the @value{GDBN} prompt to see a list of commands in this
3950 @findex COMMAND_MAINTENANCE
3951 @findex gdb.COMMAND_MAINTENANCE
3952 @item gdb.COMMAND_MAINTENANCE
3953 The command is only useful to @value{GDBN} maintainers. The
3954 @code{maintenance} and @code{flushregs} commands are in this category.
3955 Type @kbd{help internals} at the @value{GDBN} prompt to see a list of
3956 commands in this category.
3959 A new command can use a predefined completion function, either by
3960 specifying it via an argument at initialization, or by returning it
3961 from the @code{complete} method. These predefined completion
3962 constants are all defined in the @code{gdb} module:
3965 @vindex COMPLETE_NONE
3966 @item gdb.COMPLETE_NONE
3967 This constant means that no completion should be done.
3969 @vindex COMPLETE_FILENAME
3970 @item gdb.COMPLETE_FILENAME
3971 This constant means that filename completion should be performed.
3973 @vindex COMPLETE_LOCATION
3974 @item gdb.COMPLETE_LOCATION
3975 This constant means that location completion should be done.
3976 @xref{Specify Location}.
3978 @vindex COMPLETE_COMMAND
3979 @item gdb.COMPLETE_COMMAND
3980 This constant means that completion should examine @value{GDBN}
3983 @vindex COMPLETE_SYMBOL
3984 @item gdb.COMPLETE_SYMBOL
3985 This constant means that completion should be done using symbol names
3988 @vindex COMPLETE_EXPRESSION
3989 @item gdb.COMPLETE_EXPRESSION
3990 This constant means that completion should be done on expressions.
3991 Often this means completing on symbol names, but some language
3992 parsers also have support for completing on field names.
3995 The following code snippet shows how a trivial CLI command can be
3996 implemented in Python:
3999 class HelloWorld (gdb.Command):
4000 """Greet the whole world."""
4002 def __init__ (self):
4003 super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)
4005 def invoke (self, arg, from_tty):
4006 print ("Hello, World!")
4011 The last line instantiates the class, and is necessary to trigger the
4012 registration of the command with @value{GDBN}. Depending on how the
4013 Python code is read into @value{GDBN}, you may need to import the
4014 @code{gdb} module explicitly.
4016 @node Parameters In Python
4017 @subsubsection Parameters In Python
4019 @cindex parameters in python
4020 @cindex python parameters
4021 @tindex gdb.Parameter
4023 You can implement new @value{GDBN} parameters using Python. A new
4024 parameter is implemented as an instance of the @code{gdb.Parameter}
4027 Parameters are exposed to the user via the @code{set} and
4028 @code{show} commands. @xref{Help}.
4030 There are many parameters that already exist and can be set in
4031 @value{GDBN}. Two examples are: @code{set follow fork} and
4032 @code{set charset}. Setting these parameters influences certain
4033 behavior in @value{GDBN}. Similarly, you can define parameters that
4034 can be used to influence behavior in custom Python scripts and commands.
4036 @defun Parameter.__init__ (name, @var{command-class}, @var{parameter-class} @r{[}, @var{enum-sequence}@r{]})
4037 The object initializer for @code{Parameter} registers the new
4038 parameter with @value{GDBN}. This initializer is normally invoked
4039 from the subclass' own @code{__init__} method.
4041 @var{name} is the name of the new parameter. If @var{name} consists
4042 of multiple words, then the initial words are looked for as prefix
4043 parameters. An example of this can be illustrated with the
4044 @code{set print} set of parameters. If @var{name} is
4045 @code{print foo}, then @code{print} will be searched as the prefix
4046 parameter. In this case the parameter can subsequently be accessed in
4047 @value{GDBN} as @code{set print foo}.
4049 If @var{name} consists of multiple words, and no prefix parameter group
4050 can be found, an exception is raised.
4052 @var{command-class} should be one of the @samp{COMMAND_} constants
4053 (@pxref{Commands In Python}). This argument tells @value{GDBN} how to
4054 categorize the new parameter in the help system.
4056 @var{parameter-class} should be one of the @samp{PARAM_} constants
4057 defined below. This argument tells @value{GDBN} the type of the new
4058 parameter; this information is used for input validation and
4061 If @var{parameter-class} is @code{PARAM_ENUM}, then
4062 @var{enum-sequence} must be a sequence of strings. These strings
4063 represent the possible values for the parameter.
4065 If @var{parameter-class} is not @code{PARAM_ENUM}, then the presence
4066 of a fourth argument will cause an exception to be thrown.
4068 The help text for the new parameter is taken from the Python
4069 documentation string for the parameter's class, if there is one. If
4070 there is no documentation string, a default value is used.
4073 @defvar Parameter.set_doc
4074 If this attribute exists, and is a string, then its value is used as
4075 the help text for this parameter's @code{set} command. The value is
4076 examined when @code{Parameter.__init__} is invoked; subsequent changes
4080 @defvar Parameter.show_doc
4081 If this attribute exists, and is a string, then its value is used as
4082 the help text for this parameter's @code{show} command. The value is
4083 examined when @code{Parameter.__init__} is invoked; subsequent changes
4087 @defvar Parameter.value
4088 The @code{value} attribute holds the underlying value of the
4089 parameter. It can be read and assigned to just as any other
4090 attribute. @value{GDBN} does validation when assignments are made.
4093 There are two methods that may be implemented in any @code{Parameter}
4096 @defun Parameter.get_set_string (self)
4097 If this method exists, @value{GDBN} will call it when a
4098 @var{parameter}'s value has been changed via the @code{set} API (for
4099 example, @kbd{set foo off}). The @code{value} attribute has already
4100 been populated with the new value and may be used in output. This
4101 method must return a string. If the returned string is not empty,
4102 @value{GDBN} will present it to the user.
4104 If this method raises the @code{gdb.GdbError} exception
4105 (@pxref{Exception Handling}), then @value{GDBN} will print the
4106 exception's string and the @code{set} command will fail. Note,
4107 however, that the @code{value} attribute will not be reset in this
4108 case. So, if your parameter must validate values, it should store the
4109 old value internally and reset the exposed value, like so:
4112 class ExampleParam (gdb.Parameter):
4113 def __init__ (self, name):
4114 super (ExampleParam, self).__init__ (name,
4118 self.saved_value = True
4121 def get_set_string (self):
4122 if not self.validate():
4123 self.value = self.saved_value
4124 raise gdb.GdbError('Failed to validate')
4125 self.saved_value = self.value
4130 @defun Parameter.get_show_string (self, svalue)
4131 @value{GDBN} will call this method when a @var{parameter}'s
4132 @code{show} API has been invoked (for example, @kbd{show foo}). The
4133 argument @code{svalue} receives the string representation of the
4134 current value. This method must return a string.
4137 When a new parameter is defined, its type must be specified. The
4138 available types are represented by constants defined in the @code{gdb}
4142 @findex PARAM_BOOLEAN
4143 @findex gdb.PARAM_BOOLEAN
4144 @item gdb.PARAM_BOOLEAN
4145 The value is a plain boolean. The Python boolean values, @code{True}
4146 and @code{False} are the only valid values.
4148 @findex PARAM_AUTO_BOOLEAN
4149 @findex gdb.PARAM_AUTO_BOOLEAN
4150 @item gdb.PARAM_AUTO_BOOLEAN
4151 The value has three possible states: true, false, and @samp{auto}. In
4152 Python, true and false are represented using boolean constants, and
4153 @samp{auto} is represented using @code{None}.
4155 @findex PARAM_UINTEGER
4156 @findex gdb.PARAM_UINTEGER
4157 @item gdb.PARAM_UINTEGER
4158 The value is an unsigned integer. The value of 0 should be
4159 interpreted to mean ``unlimited''.
4161 @findex PARAM_INTEGER
4162 @findex gdb.PARAM_INTEGER
4163 @item gdb.PARAM_INTEGER
4164 The value is a signed integer. The value of 0 should be interpreted
4165 to mean ``unlimited''.
4167 @findex PARAM_STRING
4168 @findex gdb.PARAM_STRING
4169 @item gdb.PARAM_STRING
4170 The value is a string. When the user modifies the string, any escape
4171 sequences, such as @samp{\t}, @samp{\f}, and octal escapes, are
4172 translated into corresponding characters and encoded into the current
4175 @findex PARAM_STRING_NOESCAPE
4176 @findex gdb.PARAM_STRING_NOESCAPE
4177 @item gdb.PARAM_STRING_NOESCAPE
4178 The value is a string. When the user modifies the string, escapes are
4179 passed through untranslated.
4181 @findex PARAM_OPTIONAL_FILENAME
4182 @findex gdb.PARAM_OPTIONAL_FILENAME
4183 @item gdb.PARAM_OPTIONAL_FILENAME
4184 The value is a either a filename (a string), or @code{None}.
4186 @findex PARAM_FILENAME
4187 @findex gdb.PARAM_FILENAME
4188 @item gdb.PARAM_FILENAME
4189 The value is a filename. This is just like
4190 @code{PARAM_STRING_NOESCAPE}, but uses file names for completion.
4192 @findex PARAM_ZINTEGER
4193 @findex gdb.PARAM_ZINTEGER
4194 @item gdb.PARAM_ZINTEGER
4195 The value is an integer. This is like @code{PARAM_INTEGER}, except 0
4196 is interpreted as itself.
4198 @findex PARAM_ZUINTEGER
4199 @findex gdb.PARAM_ZUINTEGER
4200 @item gdb.PARAM_ZUINTEGER
4201 The value is an unsigned integer. This is like @code{PARAM_INTEGER},
4202 except 0 is interpreted as itself, and the value cannot be negative.
4204 @findex PARAM_ZUINTEGER_UNLIMITED
4205 @findex gdb.PARAM_ZUINTEGER_UNLIMITED
4206 @item gdb.PARAM_ZUINTEGER_UNLIMITED
4207 The value is a signed integer. This is like @code{PARAM_ZUINTEGER},
4208 except the special value -1 should be interpreted to mean
4209 ``unlimited''. Other negative values are not allowed.
4212 @findex gdb.PARAM_ENUM
4213 @item gdb.PARAM_ENUM
4214 The value is a string, which must be one of a collection string
4215 constants provided when the parameter is created.
4218 @node Functions In Python
4219 @subsubsection Writing new convenience functions
4221 @cindex writing convenience functions
4222 @cindex convenience functions in python
4223 @cindex python convenience functions
4224 @tindex gdb.Function
4226 You can implement new convenience functions (@pxref{Convenience Vars})
4227 in Python. A convenience function is an instance of a subclass of the
4228 class @code{gdb.Function}.
4230 @defun Function.__init__ (name)
4231 The initializer for @code{Function} registers the new function with
4232 @value{GDBN}. The argument @var{name} is the name of the function,
4233 a string. The function will be visible to the user as a convenience
4234 variable of type @code{internal function}, whose name is the same as
4235 the given @var{name}.
4237 The documentation for the new function is taken from the documentation
4238 string for the new class.
4241 @defun Function.invoke (@var{*args})
4242 When a convenience function is evaluated, its arguments are converted
4243 to instances of @code{gdb.Value}, and then the function's
4244 @code{invoke} method is called. Note that @value{GDBN} does not
4245 predetermine the arity of convenience functions. Instead, all
4246 available arguments are passed to @code{invoke}, following the
4247 standard Python calling convention. In particular, a convenience
4248 function can have default values for parameters without ill effect.
4250 The return value of this method is used as its value in the enclosing
4251 expression. If an ordinary Python value is returned, it is converted
4252 to a @code{gdb.Value} following the usual rules.
4255 The following code snippet shows how a trivial convenience function can
4256 be implemented in Python:
4259 class Greet (gdb.Function):
4260 """Return string to greet someone.
4261 Takes a name as argument."""
4263 def __init__ (self):
4264 super (Greet, self).__init__ ("greet")
4266 def invoke (self, name):
4267 return "Hello, %s!" % name.string ()
4272 The last line instantiates the class, and is necessary to trigger the
4273 registration of the function with @value{GDBN}. Depending on how the
4274 Python code is read into @value{GDBN}, you may need to import the
4275 @code{gdb} module explicitly.
4277 Now you can use the function in an expression:
4280 (gdb) print $greet("Bob")
4284 @node Progspaces In Python
4285 @subsubsection Program Spaces In Python
4287 @cindex progspaces in python
4288 @tindex gdb.Progspace
4290 A program space, or @dfn{progspace}, represents a symbolic view
4291 of an address space.
4292 It consists of all of the objfiles of the program.
4293 @xref{Objfiles In Python}.
4294 @xref{Inferiors Connections and Programs, program spaces}, for more details
4295 about program spaces.
4297 The following progspace-related functions are available in the
4300 @findex gdb.current_progspace
4301 @defun gdb.current_progspace ()
4302 This function returns the program space of the currently selected inferior.
4303 @xref{Inferiors Connections and Programs}. This is identical to
4304 @code{gdb.selected_inferior().progspace} (@pxref{Inferiors In Python}) and is
4305 included for historical compatibility.
4308 @findex gdb.progspaces
4309 @defun gdb.progspaces ()
4310 Return a sequence of all the progspaces currently known to @value{GDBN}.
4313 Each progspace is represented by an instance of the @code{gdb.Progspace}
4316 @defvar Progspace.filename
4317 The file name of the progspace as a string.
4320 @defvar Progspace.pretty_printers
4321 The @code{pretty_printers} attribute is a list of functions. It is
4322 used to look up pretty-printers. A @code{Value} is passed to each
4323 function in order; if the function returns @code{None}, then the
4324 search continues. Otherwise, the return value should be an object
4325 which is used to format the value. @xref{Pretty Printing API}, for more
4329 @defvar Progspace.type_printers
4330 The @code{type_printers} attribute is a list of type printer objects.
4331 @xref{Type Printing API}, for more information.
4334 @defvar Progspace.frame_filters
4335 The @code{frame_filters} attribute is a dictionary of frame filter
4336 objects. @xref{Frame Filter API}, for more information.
4339 A program space has the following methods:
4341 @findex Progspace.block_for_pc
4342 @defun Progspace.block_for_pc (pc)
4343 Return the innermost @code{gdb.Block} containing the given @var{pc}
4344 value. If the block cannot be found for the @var{pc} value specified,
4345 the function will return @code{None}.
4348 @findex Progspace.find_pc_line
4349 @defun Progspace.find_pc_line (pc)
4350 Return the @code{gdb.Symtab_and_line} object corresponding to the
4351 @var{pc} value. @xref{Symbol Tables In Python}. If an invalid value
4352 of @var{pc} is passed as an argument, then the @code{symtab} and
4353 @code{line} attributes of the returned @code{gdb.Symtab_and_line}
4354 object will be @code{None} and 0 respectively.
4357 @findex Progspace.is_valid
4358 @defun Progspace.is_valid ()
4359 Returns @code{True} if the @code{gdb.Progspace} object is valid,
4360 @code{False} if not. A @code{gdb.Progspace} object can become invalid
4361 if the program space file it refers to is not referenced by any
4362 inferior. All other @code{gdb.Progspace} methods will throw an
4363 exception if it is invalid at the time the method is called.
4366 @findex Progspace.objfiles
4367 @defun Progspace.objfiles ()
4368 Return a sequence of all the objfiles referenced by this program
4369 space. @xref{Objfiles In Python}.
4372 @findex Progspace.solib_name
4373 @defun Progspace.solib_name (address)
4374 Return the name of the shared library holding the given @var{address}
4375 as a string, or @code{None}.
4378 One may add arbitrary attributes to @code{gdb.Progspace} objects
4379 in the usual Python way.
4380 This is useful if, for example, one needs to do some extra record keeping
4381 associated with the program space.
4383 In this contrived example, we want to perform some processing when
4384 an objfile with a certain symbol is loaded, but we only want to do
4385 this once because it is expensive. To achieve this we record the results
4386 with the program space because we can't predict when the desired objfile
4391 def clear_objfiles_handler(event):
4392 event.progspace.expensive_computation = None
4393 def expensive(symbol):
4394 """A mock routine to perform an "expensive" computation on symbol."""
4395 print ("Computing the answer to the ultimate question ...")
4397 def new_objfile_handler(event):
4398 objfile = event.new_objfile
4399 progspace = objfile.progspace
4400 if not hasattr(progspace, 'expensive_computation') or \
4401 progspace.expensive_computation is None:
4402 # We use 'main' for the symbol to keep the example simple.
4403 # Note: There's no current way to constrain the lookup
4405 symbol = gdb.lookup_global_symbol('main')
4406 if symbol is not None:
4407 progspace.expensive_computation = expensive(symbol)
4408 gdb.events.clear_objfiles.connect(clear_objfiles_handler)
4409 gdb.events.new_objfile.connect(new_objfile_handler)
4411 (gdb) file /tmp/hello
4412 Reading symbols from /tmp/hello...
4413 Computing the answer to the ultimate question ...
4414 (gdb) python print gdb.current_progspace().expensive_computation
4417 Starting program: /tmp/hello
4419 [Inferior 1 (process 4242) exited normally]
4422 @node Objfiles In Python
4423 @subsubsection Objfiles In Python
4425 @cindex objfiles in python
4428 @value{GDBN} loads symbols for an inferior from various
4429 symbol-containing files (@pxref{Files}). These include the primary
4430 executable file, any shared libraries used by the inferior, and any
4431 separate debug info files (@pxref{Separate Debug Files}).
4432 @value{GDBN} calls these symbol-containing files @dfn{objfiles}.
4434 The following objfile-related functions are available in the
4437 @findex gdb.current_objfile
4438 @defun gdb.current_objfile ()
4439 When auto-loading a Python script (@pxref{Python Auto-loading}), @value{GDBN}
4440 sets the ``current objfile'' to the corresponding objfile. This
4441 function returns the current objfile. If there is no current objfile,
4442 this function returns @code{None}.
4445 @findex gdb.objfiles
4446 @defun gdb.objfiles ()
4447 Return a sequence of objfiles referenced by the current program space.
4448 @xref{Objfiles In Python}, and @ref{Progspaces In Python}. This is identical
4449 to @code{gdb.selected_inferior().progspace.objfiles()} and is included for
4450 historical compatibility.
4453 @findex gdb.lookup_objfile
4454 @defun gdb.lookup_objfile (name @r{[}, by_build_id{]})
4455 Look up @var{name}, a file name or build ID, in the list of objfiles
4456 for the current program space (@pxref{Progspaces In Python}).
4457 If the objfile is not found throw the Python @code{ValueError} exception.
4459 If @var{name} is a relative file name, then it will match any
4460 source file name with the same trailing components. For example, if
4461 @var{name} is @samp{gcc/expr.c}, then it will match source file
4462 name of @file{/build/trunk/gcc/expr.c}, but not
4463 @file{/build/trunk/libcpp/expr.c} or @file{/build/trunk/gcc/x-expr.c}.
4465 If @var{by_build_id} is provided and is @code{True} then @var{name}
4466 is the build ID of the objfile. Otherwise, @var{name} is a file name.
4467 This is supported only on some operating systems, notably those which use
4468 the ELF format for binary files and the @sc{gnu} Binutils. For more details
4469 about this feature, see the description of the @option{--build-id}
4470 command-line option in @ref{Options, , Command Line Options, ld,
4474 Each objfile is represented by an instance of the @code{gdb.Objfile}
4477 @defvar Objfile.filename
4478 The file name of the objfile as a string, with symbolic links resolved.
4480 The value is @code{None} if the objfile is no longer valid.
4481 See the @code{gdb.Objfile.is_valid} method, described below.
4484 @defvar Objfile.username
4485 The file name of the objfile as specified by the user as a string.
4487 The value is @code{None} if the objfile is no longer valid.
4488 See the @code{gdb.Objfile.is_valid} method, described below.
4491 @defvar Objfile.owner
4492 For separate debug info objfiles this is the corresponding @code{gdb.Objfile}
4493 object that debug info is being provided for.
4494 Otherwise this is @code{None}.
4495 Separate debug info objfiles are added with the
4496 @code{gdb.Objfile.add_separate_debug_file} method, described below.
4499 @defvar Objfile.build_id
4500 The build ID of the objfile as a string.
4501 If the objfile does not have a build ID then the value is @code{None}.
4503 This is supported only on some operating systems, notably those which use
4504 the ELF format for binary files and the @sc{gnu} Binutils. For more details
4505 about this feature, see the description of the @option{--build-id}
4506 command-line option in @ref{Options, , Command Line Options, ld,
4510 @defvar Objfile.progspace
4511 The containing program space of the objfile as a @code{gdb.Progspace}
4512 object. @xref{Progspaces In Python}.
4515 @defvar Objfile.pretty_printers
4516 The @code{pretty_printers} attribute is a list of functions. It is
4517 used to look up pretty-printers. A @code{Value} is passed to each
4518 function in order; if the function returns @code{None}, then the
4519 search continues. Otherwise, the return value should be an object
4520 which is used to format the value. @xref{Pretty Printing API}, for more
4524 @defvar Objfile.type_printers
4525 The @code{type_printers} attribute is a list of type printer objects.
4526 @xref{Type Printing API}, for more information.
4529 @defvar Objfile.frame_filters
4530 The @code{frame_filters} attribute is a dictionary of frame filter
4531 objects. @xref{Frame Filter API}, for more information.
4534 One may add arbitrary attributes to @code{gdb.Objfile} objects
4535 in the usual Python way.
4536 This is useful if, for example, one needs to do some extra record keeping
4537 associated with the objfile.
4539 In this contrived example we record the time when @value{GDBN}
4545 def new_objfile_handler(event):
4546 # Set the time_loaded attribute of the new objfile.
4547 event.new_objfile.time_loaded = datetime.datetime.today()
4548 gdb.events.new_objfile.connect(new_objfile_handler)
4551 Reading symbols from ./hello...
4552 (gdb) python print gdb.objfiles()[0].time_loaded
4553 2014-10-09 11:41:36.770345
4556 A @code{gdb.Objfile} object has the following methods:
4558 @defun Objfile.is_valid ()
4559 Returns @code{True} if the @code{gdb.Objfile} object is valid,
4560 @code{False} if not. A @code{gdb.Objfile} object can become invalid
4561 if the object file it refers to is not loaded in @value{GDBN} any
4562 longer. All other @code{gdb.Objfile} methods will throw an exception
4563 if it is invalid at the time the method is called.
4566 @defun Objfile.add_separate_debug_file (file)
4567 Add @var{file} to the list of files that @value{GDBN} will search for
4568 debug information for the objfile.
4569 This is useful when the debug info has been removed from the program
4570 and stored in a separate file. @value{GDBN} has built-in support for
4571 finding separate debug info files (@pxref{Separate Debug Files}), but if
4572 the file doesn't live in one of the standard places that @value{GDBN}
4573 searches then this function can be used to add a debug info file
4574 from a different place.
4577 @defun Objfile.lookup_global_symbol (name @r{[}, domain@r{]})
4578 Search for a global symbol named @var{name} in this objfile. Optionally, the
4579 search scope can be restricted with the @var{domain} argument.
4580 The @var{domain} argument must be a domain constant defined in the @code{gdb}
4581 module and described in @ref{Symbols In Python}. This function is similar to
4582 @code{gdb.lookup_global_symbol}, except that the search is limited to this
4585 The result is a @code{gdb.Symbol} object or @code{None} if the symbol
4589 @defun Objfile.lookup_static_symbol (name @r{[}, domain@r{]})
4590 Like @code{Objfile.lookup_global_symbol}, but searches for a global
4591 symbol with static linkage named @var{name} in this objfile.
4594 @node Frames In Python
4595 @subsubsection Accessing inferior stack frames from Python
4597 @cindex frames in python
4598 When the debugged program stops, @value{GDBN} is able to analyze its call
4599 stack (@pxref{Frames,,Stack frames}). The @code{gdb.Frame} class
4600 represents a frame in the stack. A @code{gdb.Frame} object is only valid
4601 while its corresponding frame exists in the inferior's stack. If you try
4602 to use an invalid frame object, @value{GDBN} will throw a @code{gdb.error}
4603 exception (@pxref{Exception Handling}).
4605 Two @code{gdb.Frame} objects can be compared for equality with the @code{==}
4609 (@value{GDBP}) python print gdb.newest_frame() == gdb.selected_frame ()
4613 The following frame-related functions are available in the @code{gdb} module:
4615 @findex gdb.selected_frame
4616 @defun gdb.selected_frame ()
4617 Return the selected frame object. (@pxref{Selection,,Selecting a Frame}).
4620 @findex gdb.newest_frame
4621 @defun gdb.newest_frame ()
4622 Return the newest frame object for the selected thread.
4625 @defun gdb.frame_stop_reason_string (reason)
4626 Return a string explaining the reason why @value{GDBN} stopped unwinding
4627 frames, as expressed by the given @var{reason} code (an integer, see the
4628 @code{unwind_stop_reason} method further down in this section).
4631 @findex gdb.invalidate_cached_frames
4632 @defun gdb.invalidate_cached_frames
4633 @value{GDBN} internally keeps a cache of the frames that have been
4634 unwound. This function invalidates this cache.
4636 This function should not generally be called by ordinary Python code.
4637 It is documented for the sake of completeness.
4640 A @code{gdb.Frame} object has the following methods:
4642 @defun Frame.is_valid ()
4643 Returns true if the @code{gdb.Frame} object is valid, false if not.
4644 A frame object can become invalid if the frame it refers to doesn't
4645 exist anymore in the inferior. All @code{gdb.Frame} methods will throw
4646 an exception if it is invalid at the time the method is called.
4649 @defun Frame.name ()
4650 Returns the function name of the frame, or @code{None} if it can't be
4654 @defun Frame.architecture ()
4655 Returns the @code{gdb.Architecture} object corresponding to the frame's
4656 architecture. @xref{Architectures In Python}.
4659 @defun Frame.type ()
4660 Returns the type of the frame. The value can be one of:
4662 @item gdb.NORMAL_FRAME
4663 An ordinary stack frame.
4665 @item gdb.DUMMY_FRAME
4666 A fake stack frame that was created by @value{GDBN} when performing an
4667 inferior function call.
4669 @item gdb.INLINE_FRAME
4670 A frame representing an inlined function. The function was inlined
4671 into a @code{gdb.NORMAL_FRAME} that is older than this one.
4673 @item gdb.TAILCALL_FRAME
4674 A frame representing a tail call. @xref{Tail Call Frames}.
4676 @item gdb.SIGTRAMP_FRAME
4677 A signal trampoline frame. This is the frame created by the OS when
4678 it calls into a signal handler.
4680 @item gdb.ARCH_FRAME
4681 A fake stack frame representing a cross-architecture call.
4683 @item gdb.SENTINEL_FRAME
4684 This is like @code{gdb.NORMAL_FRAME}, but it is only used for the
4689 @defun Frame.unwind_stop_reason ()
4690 Return an integer representing the reason why it's not possible to find
4691 more frames toward the outermost frame. Use
4692 @code{gdb.frame_stop_reason_string} to convert the value returned by this
4693 function to a string. The value can be one of:
4696 @item gdb.FRAME_UNWIND_NO_REASON
4697 No particular reason (older frames should be available).
4699 @item gdb.FRAME_UNWIND_NULL_ID
4700 The previous frame's analyzer returns an invalid result. This is no
4701 longer used by @value{GDBN}, and is kept only for backward
4704 @item gdb.FRAME_UNWIND_OUTERMOST
4705 This frame is the outermost.
4707 @item gdb.FRAME_UNWIND_UNAVAILABLE
4708 Cannot unwind further, because that would require knowing the
4709 values of registers or memory that have not been collected.
4711 @item gdb.FRAME_UNWIND_INNER_ID
4712 This frame ID looks like it ought to belong to a NEXT frame,
4713 but we got it for a PREV frame. Normally, this is a sign of
4714 unwinder failure. It could also indicate stack corruption.
4716 @item gdb.FRAME_UNWIND_SAME_ID
4717 This frame has the same ID as the previous one. That means
4718 that unwinding further would almost certainly give us another
4719 frame with exactly the same ID, so break the chain. Normally,
4720 this is a sign of unwinder failure. It could also indicate
4723 @item gdb.FRAME_UNWIND_NO_SAVED_PC
4724 The frame unwinder did not find any saved PC, but we needed
4725 one to unwind further.
4727 @item gdb.FRAME_UNWIND_MEMORY_ERROR
4728 The frame unwinder caused an error while trying to access memory.
4730 @item gdb.FRAME_UNWIND_FIRST_ERROR
4731 Any stop reason greater or equal to this value indicates some kind
4732 of error. This special value facilitates writing code that tests
4733 for errors in unwinding in a way that will work correctly even if
4734 the list of the other values is modified in future @value{GDBN}
4735 versions. Using it, you could write:
4737 reason = gdb.selected_frame().unwind_stop_reason ()
4738 reason_str = gdb.frame_stop_reason_string (reason)
4739 if reason >= gdb.FRAME_UNWIND_FIRST_ERROR:
4740 print ("An error occured: %s" % reason_str)
4747 Returns the frame's resume address.
4750 @defun Frame.block ()
4751 Return the frame's code block. @xref{Blocks In Python}. If the frame
4752 does not have a block -- for example, if there is no debugging
4753 information for the code in question -- then this will throw an
4757 @defun Frame.function ()
4758 Return the symbol for the function corresponding to this frame.
4759 @xref{Symbols In Python}.
4762 @defun Frame.older ()
4763 Return the frame that called this frame.
4766 @defun Frame.newer ()
4767 Return the frame called by this frame.
4770 @defun Frame.find_sal ()
4771 Return the frame's symtab and line object.
4772 @xref{Symbol Tables In Python}.
4775 @anchor{gdbpy_frame_read_register}
4776 @defun Frame.read_register (register)
4777 Return the value of @var{register} in this frame. Returns a
4778 @code{Gdb.Value} object. Throws an exception if @var{register} does
4779 not exist. The @var{register} argument must be one of the following:
4782 A string that is the name of a valid register (e.g., @code{'sp'} or
4785 A @code{gdb.RegisterDescriptor} object (@pxref{Registers In Python}).
4787 A @value{GDBN} internal, platform specific number. Using these
4788 numbers is supported for historic reasons, but is not recommended as
4789 future changes to @value{GDBN} could change the mapping between
4790 numbers and the registers they represent, breaking any Python code
4791 that uses the platform-specific numbers. The numbers are usually
4792 found in the corresponding @file{@var{platform}-tdep.h} file in the
4793 @value{GDBN} source tree.
4795 Using a string to access registers will be slightly slower than the
4796 other two methods as @value{GDBN} must look up the mapping between
4797 name and internal register number. If performance is critical
4798 consider looking up and caching a @code{gdb.RegisterDescriptor}
4802 @defun Frame.read_var (variable @r{[}, block@r{]})
4803 Return the value of @var{variable} in this frame. If the optional
4804 argument @var{block} is provided, search for the variable from that
4805 block; otherwise start at the frame's current block (which is
4806 determined by the frame's current program counter). The @var{variable}
4807 argument must be a string or a @code{gdb.Symbol} object; @var{block} must be a
4808 @code{gdb.Block} object.
4811 @defun Frame.select ()
4812 Set this frame to be the selected frame. @xref{Stack, ,Examining the
4816 @node Blocks In Python
4817 @subsubsection Accessing blocks from Python
4819 @cindex blocks in python
4822 In @value{GDBN}, symbols are stored in blocks. A block corresponds
4823 roughly to a scope in the source code. Blocks are organized
4824 hierarchically, and are represented individually in Python as a
4825 @code{gdb.Block}. Blocks rely on debugging information being
4828 A frame has a block. Please see @ref{Frames In Python}, for a more
4829 in-depth discussion of frames.
4831 The outermost block is known as the @dfn{global block}. The global
4832 block typically holds public global variables and functions.
4834 The block nested just inside the global block is the @dfn{static
4835 block}. The static block typically holds file-scoped variables and
4838 @value{GDBN} provides a method to get a block's superblock, but there
4839 is currently no way to examine the sub-blocks of a block, or to
4840 iterate over all the blocks in a symbol table (@pxref{Symbol Tables In
4843 Here is a short example that should help explain blocks:
4846 /* This is in the global block. */
4849 /* This is in the static block. */
4850 static int file_scope;
4852 /* 'function' is in the global block, and 'argument' is
4853 in a block nested inside of 'function'. */
4854 int function (int argument)
4856 /* 'local' is in a block inside 'function'. It may or may
4857 not be in the same block as 'argument'. */
4861 /* 'inner' is in a block whose superblock is the one holding
4865 /* If this call is expanded by the compiler, you may see
4866 a nested block here whose function is 'inline_function'
4867 and whose superblock is the one holding 'inner'. */
4873 A @code{gdb.Block} is iterable. The iterator returns the symbols
4874 (@pxref{Symbols In Python}) local to the block. Python programs
4875 should not assume that a specific block object will always contain a
4876 given symbol, since changes in @value{GDBN} features and
4877 infrastructure may cause symbols move across blocks in a symbol
4878 table. You can also use Python's @dfn{dictionary syntax} to access
4879 variables in this block, e.g.:
4882 symbol = some_block['variable'] # symbol is of type gdb.Symbol
4885 The following block-related functions are available in the @code{gdb}
4888 @findex gdb.block_for_pc
4889 @defun gdb.block_for_pc (pc)
4890 Return the innermost @code{gdb.Block} containing the given @var{pc}
4891 value. If the block cannot be found for the @var{pc} value specified,
4892 the function will return @code{None}. This is identical to
4893 @code{gdb.current_progspace().block_for_pc(pc)} and is included for
4894 historical compatibility.
4897 A @code{gdb.Block} object has the following methods:
4899 @defun Block.is_valid ()
4900 Returns @code{True} if the @code{gdb.Block} object is valid,
4901 @code{False} if not. A block object can become invalid if the block it
4902 refers to doesn't exist anymore in the inferior. All other
4903 @code{gdb.Block} methods will throw an exception if it is invalid at
4904 the time the method is called. The block's validity is also checked
4905 during iteration over symbols of the block.
4908 A @code{gdb.Block} object has the following attributes:
4911 The start address of the block. This attribute is not writable.
4915 One past the last address that appears in the block. This attribute
4919 @defvar Block.function
4920 The name of the block represented as a @code{gdb.Symbol}. If the
4921 block is not named, then this attribute holds @code{None}. This
4922 attribute is not writable.
4924 For ordinary function blocks, the superblock is the static block.
4925 However, you should note that it is possible for a function block to
4926 have a superblock that is not the static block -- for instance this
4927 happens for an inlined function.
4930 @defvar Block.superblock
4931 The block containing this block. If this parent block does not exist,
4932 this attribute holds @code{None}. This attribute is not writable.
4935 @defvar Block.global_block
4936 The global block associated with this block. This attribute is not
4940 @defvar Block.static_block
4941 The static block associated with this block. This attribute is not
4945 @defvar Block.is_global
4946 @code{True} if the @code{gdb.Block} object is a global block,
4947 @code{False} if not. This attribute is not
4951 @defvar Block.is_static
4952 @code{True} if the @code{gdb.Block} object is a static block,
4953 @code{False} if not. This attribute is not writable.
4956 @node Symbols In Python
4957 @subsubsection Python representation of Symbols
4959 @cindex symbols in python
4962 @value{GDBN} represents every variable, function and type as an
4963 entry in a symbol table. @xref{Symbols, ,Examining the Symbol Table}.
4964 Similarly, Python represents these symbols in @value{GDBN} with the
4965 @code{gdb.Symbol} object.
4967 The following symbol-related functions are available in the @code{gdb}
4970 @findex gdb.lookup_symbol
4971 @defun gdb.lookup_symbol (name @r{[}, block @r{[}, domain@r{]]})
4972 This function searches for a symbol by name. The search scope can be
4973 restricted to the parameters defined in the optional domain and block
4976 @var{name} is the name of the symbol. It must be a string. The
4977 optional @var{block} argument restricts the search to symbols visible
4978 in that @var{block}. The @var{block} argument must be a
4979 @code{gdb.Block} object. If omitted, the block for the current frame
4980 is used. The optional @var{domain} argument restricts
4981 the search to the domain type. The @var{domain} argument must be a
4982 domain constant defined in the @code{gdb} module and described later
4985 The result is a tuple of two elements.
4986 The first element is a @code{gdb.Symbol} object or @code{None} if the symbol
4988 If the symbol is found, the second element is @code{True} if the symbol
4989 is a field of a method's object (e.g., @code{this} in C@t{++}),
4990 otherwise it is @code{False}.
4991 If the symbol is not found, the second element is @code{False}.
4994 @findex gdb.lookup_global_symbol
4995 @defun gdb.lookup_global_symbol (name @r{[}, domain@r{]})
4996 This function searches for a global symbol by name.
4997 The search scope can be restricted to by the domain argument.
4999 @var{name} is the name of the symbol. It must be a string.
5000 The optional @var{domain} argument restricts the search to the domain type.
5001 The @var{domain} argument must be a domain constant defined in the @code{gdb}
5002 module and described later in this chapter.
5004 The result is a @code{gdb.Symbol} object or @code{None} if the symbol
5008 @findex gdb.lookup_static_symbol
5009 @defun gdb.lookup_static_symbol (name @r{[}, domain@r{]})
5010 This function searches for a global symbol with static linkage by name.
5011 The search scope can be restricted to by the domain argument.
5013 @var{name} is the name of the symbol. It must be a string.
5014 The optional @var{domain} argument restricts the search to the domain type.
5015 The @var{domain} argument must be a domain constant defined in the @code{gdb}
5016 module and described later in this chapter.
5018 The result is a @code{gdb.Symbol} object or @code{None} if the symbol
5021 Note that this function will not find function-scoped static variables. To look
5022 up such variables, iterate over the variables of the function's
5023 @code{gdb.Block} and check that @code{block.addr_class} is
5024 @code{gdb.SYMBOL_LOC_STATIC}.
5026 There can be multiple global symbols with static linkage with the same
5027 name. This function will only return the first matching symbol that
5028 it finds. Which symbol is found depends on where @value{GDBN} is
5029 currently stopped, as @value{GDBN} will first search for matching
5030 symbols in the current object file, and then search all other object
5031 files. If the application is not yet running then @value{GDBN} will
5032 search all object files in the order they appear in the debug
5036 @findex gdb.lookup_static_symbols
5037 @defun gdb.lookup_static_symbols (name @r{[}, domain@r{]})
5038 Similar to @code{gdb.lookup_static_symbol}, this function searches for
5039 global symbols with static linkage by name, and optionally restricted
5040 by the domain argument. However, this function returns a list of all
5041 matching symbols found, not just the first one.
5043 @var{name} is the name of the symbol. It must be a string.
5044 The optional @var{domain} argument restricts the search to the domain type.
5045 The @var{domain} argument must be a domain constant defined in the @code{gdb}
5046 module and described later in this chapter.
5048 The result is a list of @code{gdb.Symbol} objects which could be empty
5049 if no matching symbols were found.
5051 Note that this function will not find function-scoped static variables. To look
5052 up such variables, iterate over the variables of the function's
5053 @code{gdb.Block} and check that @code{block.addr_class} is
5054 @code{gdb.SYMBOL_LOC_STATIC}.
5057 A @code{gdb.Symbol} object has the following attributes:
5060 The type of the symbol or @code{None} if no type is recorded.
5061 This attribute is represented as a @code{gdb.Type} object.
5062 @xref{Types In Python}. This attribute is not writable.
5065 @defvar Symbol.symtab
5066 The symbol table in which the symbol appears. This attribute is
5067 represented as a @code{gdb.Symtab} object. @xref{Symbol Tables In
5068 Python}. This attribute is not writable.
5072 The line number in the source code at which the symbol was defined.
5077 The name of the symbol as a string. This attribute is not writable.
5080 @defvar Symbol.linkage_name
5081 The name of the symbol, as used by the linker (i.e., may be mangled).
5082 This attribute is not writable.
5085 @defvar Symbol.print_name
5086 The name of the symbol in a form suitable for output. This is either
5087 @code{name} or @code{linkage_name}, depending on whether the user
5088 asked @value{GDBN} to display demangled or mangled names.
5091 @defvar Symbol.addr_class
5092 The address class of the symbol. This classifies how to find the value
5093 of a symbol. Each address class is a constant defined in the
5094 @code{gdb} module and described later in this chapter.
5097 @defvar Symbol.needs_frame
5098 This is @code{True} if evaluating this symbol's value requires a frame
5099 (@pxref{Frames In Python}) and @code{False} otherwise. Typically,
5100 local variables will require a frame, but other symbols will not.
5103 @defvar Symbol.is_argument
5104 @code{True} if the symbol is an argument of a function.
5107 @defvar Symbol.is_constant
5108 @code{True} if the symbol is a constant.
5111 @defvar Symbol.is_function
5112 @code{True} if the symbol is a function or a method.
5115 @defvar Symbol.is_variable
5116 @code{True} if the symbol is a variable.
5119 A @code{gdb.Symbol} object has the following methods:
5121 @defun Symbol.is_valid ()
5122 Returns @code{True} if the @code{gdb.Symbol} object is valid,
5123 @code{False} if not. A @code{gdb.Symbol} object can become invalid if
5124 the symbol it refers to does not exist in @value{GDBN} any longer.
5125 All other @code{gdb.Symbol} methods will throw an exception if it is
5126 invalid at the time the method is called.
5129 @defun Symbol.value (@r{[}frame@r{]})
5130 Compute the value of the symbol, as a @code{gdb.Value}. For
5131 functions, this computes the address of the function, cast to the
5132 appropriate type. If the symbol requires a frame in order to compute
5133 its value, then @var{frame} must be given. If @var{frame} is not
5134 given, or if @var{frame} is invalid, then this method will throw an
5138 The available domain categories in @code{gdb.Symbol} are represented
5139 as constants in the @code{gdb} module:
5142 @vindex SYMBOL_UNDEF_DOMAIN
5143 @item gdb.SYMBOL_UNDEF_DOMAIN
5144 This is used when a domain has not been discovered or none of the
5145 following domains apply. This usually indicates an error either
5146 in the symbol information or in @value{GDBN}'s handling of symbols.
5148 @vindex SYMBOL_VAR_DOMAIN
5149 @item gdb.SYMBOL_VAR_DOMAIN
5150 This domain contains variables, function names, typedef names and enum
5153 @vindex SYMBOL_STRUCT_DOMAIN
5154 @item gdb.SYMBOL_STRUCT_DOMAIN
5155 This domain holds struct, union and enum type names.
5157 @vindex SYMBOL_LABEL_DOMAIN
5158 @item gdb.SYMBOL_LABEL_DOMAIN
5159 This domain contains names of labels (for gotos).
5161 @vindex SYMBOL_MODULE_DOMAIN
5162 @item gdb.SYMBOL_MODULE_DOMAIN
5163 This domain contains names of Fortran module types.
5165 @vindex SYMBOL_COMMON_BLOCK_DOMAIN
5166 @item gdb.SYMBOL_COMMON_BLOCK_DOMAIN
5167 This domain contains names of Fortran common blocks.
5170 The available address class categories in @code{gdb.Symbol} are represented
5171 as constants in the @code{gdb} module:
5174 @vindex SYMBOL_LOC_UNDEF
5175 @item gdb.SYMBOL_LOC_UNDEF
5176 If this is returned by address class, it indicates an error either in
5177 the symbol information or in @value{GDBN}'s handling of symbols.
5179 @vindex SYMBOL_LOC_CONST
5180 @item gdb.SYMBOL_LOC_CONST
5181 Value is constant int.
5183 @vindex SYMBOL_LOC_STATIC
5184 @item gdb.SYMBOL_LOC_STATIC
5185 Value is at a fixed address.
5187 @vindex SYMBOL_LOC_REGISTER
5188 @item gdb.SYMBOL_LOC_REGISTER
5189 Value is in a register.
5191 @vindex SYMBOL_LOC_ARG
5192 @item gdb.SYMBOL_LOC_ARG
5193 Value is an argument. This value is at the offset stored within the
5194 symbol inside the frame's argument list.
5196 @vindex SYMBOL_LOC_REF_ARG
5197 @item gdb.SYMBOL_LOC_REF_ARG
5198 Value address is stored in the frame's argument list. Just like
5199 @code{LOC_ARG} except that the value's address is stored at the
5200 offset, not the value itself.
5202 @vindex SYMBOL_LOC_REGPARM_ADDR
5203 @item gdb.SYMBOL_LOC_REGPARM_ADDR
5204 Value is a specified register. Just like @code{LOC_REGISTER} except
5205 the register holds the address of the argument instead of the argument
5208 @vindex SYMBOL_LOC_LOCAL
5209 @item gdb.SYMBOL_LOC_LOCAL
5210 Value is a local variable.
5212 @vindex SYMBOL_LOC_TYPEDEF
5213 @item gdb.SYMBOL_LOC_TYPEDEF
5214 Value not used. Symbols in the domain @code{SYMBOL_STRUCT_DOMAIN} all
5217 @vindex SYMBOL_LOC_LABEL
5218 @item gdb.SYMBOL_LOC_LABEL
5221 @vindex SYMBOL_LOC_BLOCK
5222 @item gdb.SYMBOL_LOC_BLOCK
5225 @vindex SYMBOL_LOC_CONST_BYTES
5226 @item gdb.SYMBOL_LOC_CONST_BYTES
5227 Value is a byte-sequence.
5229 @vindex SYMBOL_LOC_UNRESOLVED
5230 @item gdb.SYMBOL_LOC_UNRESOLVED
5231 Value is at a fixed address, but the address of the variable has to be
5232 determined from the minimal symbol table whenever the variable is
5235 @vindex SYMBOL_LOC_OPTIMIZED_OUT
5236 @item gdb.SYMBOL_LOC_OPTIMIZED_OUT
5237 The value does not actually exist in the program.
5239 @vindex SYMBOL_LOC_COMPUTED
5240 @item gdb.SYMBOL_LOC_COMPUTED
5241 The value's address is a computed location.
5243 @vindex SYMBOL_LOC_COMMON_BLOCK
5244 @item gdb.SYMBOL_LOC_COMMON_BLOCK
5245 The value's address is a symbol. This is only used for Fortran common
5249 @node Symbol Tables In Python
5250 @subsubsection Symbol table representation in Python
5252 @cindex symbol tables in python
5254 @tindex gdb.Symtab_and_line
5256 Access to symbol table data maintained by @value{GDBN} on the inferior
5257 is exposed to Python via two objects: @code{gdb.Symtab_and_line} and
5258 @code{gdb.Symtab}. Symbol table and line data for a frame is returned
5259 from the @code{find_sal} method in @code{gdb.Frame} object.
5260 @xref{Frames In Python}.
5262 For more information on @value{GDBN}'s symbol table management, see
5263 @ref{Symbols, ,Examining the Symbol Table}, for more information.
5265 A @code{gdb.Symtab_and_line} object has the following attributes:
5267 @defvar Symtab_and_line.symtab
5268 The symbol table object (@code{gdb.Symtab}) for this frame.
5269 This attribute is not writable.
5272 @defvar Symtab_and_line.pc
5273 Indicates the start of the address range occupied by code for the
5274 current source line. This attribute is not writable.
5277 @defvar Symtab_and_line.last
5278 Indicates the end of the address range occupied by code for the current
5279 source line. This attribute is not writable.
5282 @defvar Symtab_and_line.line
5283 Indicates the current line number for this object. This
5284 attribute is not writable.
5287 A @code{gdb.Symtab_and_line} object has the following methods:
5289 @defun Symtab_and_line.is_valid ()
5290 Returns @code{True} if the @code{gdb.Symtab_and_line} object is valid,
5291 @code{False} if not. A @code{gdb.Symtab_and_line} object can become
5292 invalid if the Symbol table and line object it refers to does not
5293 exist in @value{GDBN} any longer. All other
5294 @code{gdb.Symtab_and_line} methods will throw an exception if it is
5295 invalid at the time the method is called.
5298 A @code{gdb.Symtab} object has the following attributes:
5300 @defvar Symtab.filename
5301 The symbol table's source filename. This attribute is not writable.
5304 @defvar Symtab.objfile
5305 The symbol table's backing object file. @xref{Objfiles In Python}.
5306 This attribute is not writable.
5309 @defvar Symtab.producer
5310 The name and possibly version number of the program that
5311 compiled the code in the symbol table.
5312 The contents of this string is up to the compiler.
5313 If no producer information is available then @code{None} is returned.
5314 This attribute is not writable.
5317 A @code{gdb.Symtab} object has the following methods:
5319 @defun Symtab.is_valid ()
5320 Returns @code{True} if the @code{gdb.Symtab} object is valid,
5321 @code{False} if not. A @code{gdb.Symtab} object can become invalid if
5322 the symbol table it refers to does not exist in @value{GDBN} any
5323 longer. All other @code{gdb.Symtab} methods will throw an exception
5324 if it is invalid at the time the method is called.
5327 @defun Symtab.fullname ()
5328 Return the symbol table's source absolute file name.
5331 @defun Symtab.global_block ()
5332 Return the global block of the underlying symbol table.
5333 @xref{Blocks In Python}.
5336 @defun Symtab.static_block ()
5337 Return the static block of the underlying symbol table.
5338 @xref{Blocks In Python}.
5341 @defun Symtab.linetable ()
5342 Return the line table associated with the symbol table.
5343 @xref{Line Tables In Python}.
5346 @node Line Tables In Python
5347 @subsubsection Manipulating line tables using Python
5349 @cindex line tables in python
5350 @tindex gdb.LineTable
5352 Python code can request and inspect line table information from a
5353 symbol table that is loaded in @value{GDBN}. A line table is a
5354 mapping of source lines to their executable locations in memory. To
5355 acquire the line table information for a particular symbol table, use
5356 the @code{linetable} function (@pxref{Symbol Tables In Python}).
5358 A @code{gdb.LineTable} is iterable. The iterator returns
5359 @code{LineTableEntry} objects that correspond to the source line and
5360 address for each line table entry. @code{LineTableEntry} objects have
5361 the following attributes:
5363 @defvar LineTableEntry.line
5364 The source line number for this line table entry. This number
5365 corresponds to the actual line of source. This attribute is not
5369 @defvar LineTableEntry.pc
5370 The address that is associated with the line table entry where the
5371 executable code for that source line resides in memory. This
5372 attribute is not writable.
5375 As there can be multiple addresses for a single source line, you may
5376 receive multiple @code{LineTableEntry} objects with matching
5377 @code{line} attributes, but with different @code{pc} attributes. The
5378 iterator is sorted in ascending @code{pc} order. Here is a small
5379 example illustrating iterating over a line table.
5382 symtab = gdb.selected_frame().find_sal().symtab
5383 linetable = symtab.linetable()
5384 for line in linetable:
5385 print ("Line: "+str(line.line)+" Address: "+hex(line.pc))
5388 This will have the following output:
5391 Line: 33 Address: 0x4005c8L
5392 Line: 37 Address: 0x4005caL
5393 Line: 39 Address: 0x4005d2L
5394 Line: 40 Address: 0x4005f8L
5395 Line: 42 Address: 0x4005ffL
5396 Line: 44 Address: 0x400608L
5397 Line: 42 Address: 0x40060cL
5398 Line: 45 Address: 0x400615L
5401 In addition to being able to iterate over a @code{LineTable}, it also
5402 has the following direct access methods:
5404 @defun LineTable.line (line)
5405 Return a Python @code{Tuple} of @code{LineTableEntry} objects for any
5406 entries in the line table for the given @var{line}, which specifies
5407 the source code line. If there are no entries for that source code
5408 @var{line}, the Python @code{None} is returned.
5411 @defun LineTable.has_line (line)
5412 Return a Python @code{Boolean} indicating whether there is an entry in
5413 the line table for this source line. Return @code{True} if an entry
5414 is found, or @code{False} if not.
5417 @defun LineTable.source_lines ()
5418 Return a Python @code{List} of the source line numbers in the symbol
5419 table. Only lines with executable code locations are returned. The
5420 contents of the @code{List} will just be the source line entries
5421 represented as Python @code{Long} values.
5424 @node Breakpoints In Python
5425 @subsubsection Manipulating breakpoints using Python
5427 @cindex breakpoints in python
5428 @tindex gdb.Breakpoint
5430 Python code can manipulate breakpoints via the @code{gdb.Breakpoint}
5433 A breakpoint can be created using one of the two forms of the
5434 @code{gdb.Breakpoint} constructor. The first one accepts a string
5435 like one would pass to the @code{break}
5436 (@pxref{Set Breaks,,Setting Breakpoints}) and @code{watch}
5437 (@pxref{Set Watchpoints, , Setting Watchpoints}) commands, and can be used to
5438 create both breakpoints and watchpoints. The second accepts separate Python
5439 arguments similar to @ref{Explicit Locations}, and can only be used to create
5442 @defun Breakpoint.__init__ (spec @r{[}, type @r{][}, wp_class @r{][}, internal @r{][}, temporary @r{][}, qualified @r{]})
5443 Create a new breakpoint according to @var{spec}, which is a string naming the
5444 location of a breakpoint, or an expression that defines a watchpoint. The
5445 string should describe a location in a format recognized by the @code{break}
5446 command (@pxref{Set Breaks,,Setting Breakpoints}) or, in the case of a
5447 watchpoint, by the @code{watch} command
5448 (@pxref{Set Watchpoints, , Setting Watchpoints}).
5450 The optional @var{type} argument specifies the type of the breakpoint to create,
5453 The optional @var{wp_class} argument defines the class of watchpoint to create,
5454 if @var{type} is @code{gdb.BP_WATCHPOINT}. If @var{wp_class} is omitted, it
5455 defaults to @code{gdb.WP_WRITE}.
5457 The optional @var{internal} argument allows the breakpoint to become invisible
5458 to the user. The breakpoint will neither be reported when created, nor will it
5459 be listed in the output from @code{info breakpoints} (but will be listed with
5460 the @code{maint info breakpoints} command).
5462 The optional @var{temporary} argument makes the breakpoint a temporary
5463 breakpoint. Temporary breakpoints are deleted after they have been hit. Any
5464 further access to the Python breakpoint after it has been hit will result in a
5465 runtime error (as that breakpoint has now been automatically deleted).
5467 The optional @var{qualified} argument is a boolean that allows interpreting
5468 the function passed in @code{spec} as a fully-qualified name. It is equivalent
5469 to @code{break}'s @code{-qualified} flag (@pxref{Linespec Locations} and
5470 @ref{Explicit Locations}).
5474 @defun Breakpoint.__init__ (@r{[} source @r{][}, function @r{][}, label @r{][}, line @r{]}, @r{][} internal @r{][}, temporary @r{][}, qualified @r{]})
5475 This second form of creating a new breakpoint specifies the explicit
5476 location (@pxref{Explicit Locations}) using keywords. The new breakpoint will
5477 be created in the specified source file @var{source}, at the specified
5478 @var{function}, @var{label} and @var{line}.
5480 @var{internal}, @var{temporary} and @var{qualified} have the same usage as
5481 explained previously.
5484 The available types are represented by constants defined in the @code{gdb}
5488 @vindex BP_BREAKPOINT
5489 @item gdb.BP_BREAKPOINT
5490 Normal code breakpoint.
5492 @vindex BP_HARDWARE_BREAKPOINT
5493 @item gdb.BP_HARDWARE_BREAKPOINT
5494 Hardware assisted code breakpoint.
5496 @vindex BP_WATCHPOINT
5497 @item gdb.BP_WATCHPOINT
5498 Watchpoint breakpoint.
5500 @vindex BP_HARDWARE_WATCHPOINT
5501 @item gdb.BP_HARDWARE_WATCHPOINT
5502 Hardware assisted watchpoint.
5504 @vindex BP_READ_WATCHPOINT
5505 @item gdb.BP_READ_WATCHPOINT
5506 Hardware assisted read watchpoint.
5508 @vindex BP_ACCESS_WATCHPOINT
5509 @item gdb.BP_ACCESS_WATCHPOINT
5510 Hardware assisted access watchpoint.
5513 The available watchpoint types are represented by constants defined in the
5519 Read only watchpoint.
5523 Write only watchpoint.
5527 Read/Write watchpoint.
5530 @defun Breakpoint.stop (self)
5531 The @code{gdb.Breakpoint} class can be sub-classed and, in
5532 particular, you may choose to implement the @code{stop} method.
5533 If this method is defined in a sub-class of @code{gdb.Breakpoint},
5534 it will be called when the inferior reaches any location of a
5535 breakpoint which instantiates that sub-class. If the method returns
5536 @code{True}, the inferior will be stopped at the location of the
5537 breakpoint, otherwise the inferior will continue.
5539 If there are multiple breakpoints at the same location with a
5540 @code{stop} method, each one will be called regardless of the
5541 return status of the previous. This ensures that all @code{stop}
5542 methods have a chance to execute at that location. In this scenario
5543 if one of the methods returns @code{True} but the others return
5544 @code{False}, the inferior will still be stopped.
5546 You should not alter the execution state of the inferior (i.e.@:, step,
5547 next, etc.), alter the current frame context (i.e.@:, change the current
5548 active frame), or alter, add or delete any breakpoint. As a general
5549 rule, you should not alter any data within @value{GDBN} or the inferior
5552 Example @code{stop} implementation:
5555 class MyBreakpoint (gdb.Breakpoint):
5557 inf_val = gdb.parse_and_eval("foo")
5564 @defun Breakpoint.is_valid ()
5565 Return @code{True} if this @code{Breakpoint} object is valid,
5566 @code{False} otherwise. A @code{Breakpoint} object can become invalid
5567 if the user deletes the breakpoint. In this case, the object still
5568 exists, but the underlying breakpoint does not. In the cases of
5569 watchpoint scope, the watchpoint remains valid even if execution of the
5570 inferior leaves the scope of that watchpoint.
5573 @defun Breakpoint.delete ()
5574 Permanently deletes the @value{GDBN} breakpoint. This also
5575 invalidates the Python @code{Breakpoint} object. Any further access
5576 to this object's attributes or methods will raise an error.
5579 @defvar Breakpoint.enabled
5580 This attribute is @code{True} if the breakpoint is enabled, and
5581 @code{False} otherwise. This attribute is writable. You can use it to enable
5582 or disable the breakpoint.
5585 @defvar Breakpoint.silent
5586 This attribute is @code{True} if the breakpoint is silent, and
5587 @code{False} otherwise. This attribute is writable.
5589 Note that a breakpoint can also be silent if it has commands and the
5590 first command is @code{silent}. This is not reported by the
5591 @code{silent} attribute.
5594 @defvar Breakpoint.pending
5595 This attribute is @code{True} if the breakpoint is pending, and
5596 @code{False} otherwise. @xref{Set Breaks}. This attribute is
5600 @anchor{python_breakpoint_thread}
5601 @defvar Breakpoint.thread
5602 If the breakpoint is thread-specific, this attribute holds the
5603 thread's global id. If the breakpoint is not thread-specific, this
5604 attribute is @code{None}. This attribute is writable.
5607 @defvar Breakpoint.task
5608 If the breakpoint is Ada task-specific, this attribute holds the Ada task
5609 id. If the breakpoint is not task-specific (or the underlying
5610 language is not Ada), this attribute is @code{None}. This attribute
5614 @defvar Breakpoint.ignore_count
5615 This attribute holds the ignore count for the breakpoint, an integer.
5616 This attribute is writable.
5619 @defvar Breakpoint.number
5620 This attribute holds the breakpoint's number --- the identifier used by
5621 the user to manipulate the breakpoint. This attribute is not writable.
5624 @defvar Breakpoint.type
5625 This attribute holds the breakpoint's type --- the identifier used to
5626 determine the actual breakpoint type or use-case. This attribute is not
5630 @defvar Breakpoint.visible
5631 This attribute tells whether the breakpoint is visible to the user
5632 when set, or when the @samp{info breakpoints} command is run. This
5633 attribute is not writable.
5636 @defvar Breakpoint.temporary
5637 This attribute indicates whether the breakpoint was created as a
5638 temporary breakpoint. Temporary breakpoints are automatically deleted
5639 after that breakpoint has been hit. Access to this attribute, and all
5640 other attributes and functions other than the @code{is_valid}
5641 function, will result in an error after the breakpoint has been hit
5642 (as it has been automatically deleted). This attribute is not
5646 @defvar Breakpoint.hit_count
5647 This attribute holds the hit count for the breakpoint, an integer.
5648 This attribute is writable, but currently it can only be set to zero.
5651 @defvar Breakpoint.location
5652 This attribute holds the location of the breakpoint, as specified by
5653 the user. It is a string. If the breakpoint does not have a location
5654 (that is, it is a watchpoint) the attribute's value is @code{None}. This
5655 attribute is not writable.
5658 @defvar Breakpoint.expression
5659 This attribute holds a breakpoint expression, as specified by
5660 the user. It is a string. If the breakpoint does not have an
5661 expression (the breakpoint is not a watchpoint) the attribute's value
5662 is @code{None}. This attribute is not writable.
5665 @defvar Breakpoint.condition
5666 This attribute holds the condition of the breakpoint, as specified by
5667 the user. It is a string. If there is no condition, this attribute's
5668 value is @code{None}. This attribute is writable.
5671 @defvar Breakpoint.commands
5672 This attribute holds the commands attached to the breakpoint. If
5673 there are commands, this attribute's value is a string holding all the
5674 commands, separated by newlines. If there are no commands, this
5675 attribute is @code{None}. This attribute is writable.
5678 @node Finish Breakpoints in Python
5679 @subsubsection Finish Breakpoints
5681 @cindex python finish breakpoints
5682 @tindex gdb.FinishBreakpoint
5684 A finish breakpoint is a temporary breakpoint set at the return address of
5685 a frame, based on the @code{finish} command. @code{gdb.FinishBreakpoint}
5686 extends @code{gdb.Breakpoint}. The underlying breakpoint will be disabled
5687 and deleted when the execution will run out of the breakpoint scope (i.e.@:
5688 @code{Breakpoint.stop} or @code{FinishBreakpoint.out_of_scope} triggered).
5689 Finish breakpoints are thread specific and must be create with the right
5692 @defun FinishBreakpoint.__init__ (@r{[}frame@r{]} @r{[}, internal@r{]})
5693 Create a finish breakpoint at the return address of the @code{gdb.Frame}
5694 object @var{frame}. If @var{frame} is not provided, this defaults to the
5695 newest frame. The optional @var{internal} argument allows the breakpoint to
5696 become invisible to the user. @xref{Breakpoints In Python}, for further
5697 details about this argument.
5700 @defun FinishBreakpoint.out_of_scope (self)
5701 In some circumstances (e.g.@: @code{longjmp}, C@t{++} exceptions, @value{GDBN}
5702 @code{return} command, @dots{}), a function may not properly terminate, and
5703 thus never hit the finish breakpoint. When @value{GDBN} notices such a
5704 situation, the @code{out_of_scope} callback will be triggered.
5706 You may want to sub-class @code{gdb.FinishBreakpoint} and override this
5710 class MyFinishBreakpoint (gdb.FinishBreakpoint)
5712 print ("normal finish")
5715 def out_of_scope ():
5716 print ("abnormal finish")
5720 @defvar FinishBreakpoint.return_value
5721 When @value{GDBN} is stopped at a finish breakpoint and the frame
5722 used to build the @code{gdb.FinishBreakpoint} object had debug symbols, this
5723 attribute will contain a @code{gdb.Value} object corresponding to the return
5724 value of the function. The value will be @code{None} if the function return
5725 type is @code{void} or if the return value was not computable. This attribute
5729 @node Lazy Strings In Python
5730 @subsubsection Python representation of lazy strings
5732 @cindex lazy strings in python
5733 @tindex gdb.LazyString
5735 A @dfn{lazy string} is a string whose contents is not retrieved or
5736 encoded until it is needed.
5738 A @code{gdb.LazyString} is represented in @value{GDBN} as an
5739 @code{address} that points to a region of memory, an @code{encoding}
5740 that will be used to encode that region of memory, and a @code{length}
5741 to delimit the region of memory that represents the string. The
5742 difference between a @code{gdb.LazyString} and a string wrapped within
5743 a @code{gdb.Value} is that a @code{gdb.LazyString} will be treated
5744 differently by @value{GDBN} when printing. A @code{gdb.LazyString} is
5745 retrieved and encoded during printing, while a @code{gdb.Value}
5746 wrapping a string is immediately retrieved and encoded on creation.
5748 A @code{gdb.LazyString} object has the following functions:
5750 @defun LazyString.value ()
5751 Convert the @code{gdb.LazyString} to a @code{gdb.Value}. This value
5752 will point to the string in memory, but will lose all the delayed
5753 retrieval, encoding and handling that @value{GDBN} applies to a
5754 @code{gdb.LazyString}.
5757 @defvar LazyString.address
5758 This attribute holds the address of the string. This attribute is not
5762 @defvar LazyString.length
5763 This attribute holds the length of the string in characters. If the
5764 length is -1, then the string will be fetched and encoded up to the
5765 first null of appropriate width. This attribute is not writable.
5768 @defvar LazyString.encoding
5769 This attribute holds the encoding that will be applied to the string
5770 when the string is printed by @value{GDBN}. If the encoding is not
5771 set, or contains an empty string, then @value{GDBN} will select the
5772 most appropriate encoding when the string is printed. This attribute
5776 @defvar LazyString.type
5777 This attribute holds the type that is represented by the lazy string's
5778 type. For a lazy string this is a pointer or array type. To
5779 resolve this to the lazy string's character type, use the type's
5780 @code{target} method. @xref{Types In Python}. This attribute is not
5784 @node Architectures In Python
5785 @subsubsection Python representation of architectures
5786 @cindex Python architectures
5788 @value{GDBN} uses architecture specific parameters and artifacts in a
5789 number of its various computations. An architecture is represented
5790 by an instance of the @code{gdb.Architecture} class.
5792 A @code{gdb.Architecture} class has the following methods:
5794 @defun Architecture.name ()
5795 Return the name (string value) of the architecture.
5798 @defun Architecture.disassemble (@var{start_pc} @r{[}, @var{end_pc} @r{[}, @var{count}@r{]]})
5799 Return a list of disassembled instructions starting from the memory
5800 address @var{start_pc}. The optional arguments @var{end_pc} and
5801 @var{count} determine the number of instructions in the returned list.
5802 If both the optional arguments @var{end_pc} and @var{count} are
5803 specified, then a list of at most @var{count} disassembled instructions
5804 whose start address falls in the closed memory address interval from
5805 @var{start_pc} to @var{end_pc} are returned. If @var{end_pc} is not
5806 specified, but @var{count} is specified, then @var{count} number of
5807 instructions starting from the address @var{start_pc} are returned. If
5808 @var{count} is not specified but @var{end_pc} is specified, then all
5809 instructions whose start address falls in the closed memory address
5810 interval from @var{start_pc} to @var{end_pc} are returned. If neither
5811 @var{end_pc} nor @var{count} are specified, then a single instruction at
5812 @var{start_pc} is returned. For all of these cases, each element of the
5813 returned list is a Python @code{dict} with the following string keys:
5818 The value corresponding to this key is a Python long integer capturing
5819 the memory address of the instruction.
5822 The value corresponding to this key is a string value which represents
5823 the instruction with assembly language mnemonics. The assembly
5824 language flavor used is the same as that specified by the current CLI
5825 variable @code{disassembly-flavor}. @xref{Machine Code}.
5828 The value corresponding to this key is the length (integer value) of the
5829 instruction in bytes.
5834 @anchor{gdbpy_architecture_registers}
5835 @defun Architecture.registers (@r{[} @var{reggroup} @r{]})
5836 Return a @code{gdb.RegisterDescriptorIterator} (@pxref{Registers In
5837 Python}) for all of the registers in @var{reggroup}, a string that is
5838 the name of a register group. If @var{reggroup} is omitted, or is the
5839 empty string, then the register group @samp{all} is assumed.
5842 @anchor{gdbpy_architecture_reggroups}
5843 @defun Architecture.register_groups ()
5844 Return a @code{gdb.RegisterGroupsIterator} (@pxref{Registers In
5845 Python}) for all of the register groups available for the
5846 @code{gdb.Architecture}.
5849 @node Registers In Python
5850 @subsubsection Registers In Python
5851 @cindex Registers In Python
5853 Python code can request from a @code{gdb.Architecture} information
5854 about the set of registers available
5855 (@pxref{gdbpy_architecture_registers,,@code{Architecture.registers}}).
5856 The register information is returned as a
5857 @code{gdb.RegisterDescriptorIterator}, which is an iterator that in
5858 turn returns @code{gdb.RegisterDescriptor} objects.
5860 A @code{gdb.RegisterDescriptor} does not provide the value of a
5861 register (@pxref{gdbpy_frame_read_register,,@code{Frame.read_register}}
5862 for reading a register's value), instead the @code{RegisterDescriptor}
5863 is a way to discover which registers are available for a particular
5866 A @code{gdb.RegisterDescriptor} has the following read-only properties:
5868 @defvar RegisterDescriptor.name
5869 The name of this register.
5872 It is also possible to lookup a register descriptor based on its name
5873 using the following @code{gdb.RegisterDescriptorIterator} function:
5875 @defun RegisterDescriptorIterator.find (@var{name})
5876 Takes @var{name} as an argument, which must be a string, and returns a
5877 @code{gdb.RegisterDescriptor} for the register with that name, or
5878 @code{None} if there is no register with that name.
5881 Python code can also request from a @code{gdb.Architecture}
5882 information about the set of register groups available on a given
5884 (@pxref{gdbpy_architecture_reggroups,,@code{Architecture.register_groups}}).
5886 Every register can be a member of zero or more register groups. Some
5887 register groups are used internally within @value{GDBN} to control
5888 things like which registers must be saved when calling into the
5889 program being debugged (@pxref{Calling,,Calling Program Functions}).
5890 Other register groups exist to allow users to easily see related sets
5891 of registers in commands like @code{info registers}
5892 (@pxref{info_registers_reggroup,,@code{info registers
5895 The register groups information is returned as a
5896 @code{gdb.RegisterGroupsIterator}, which is an iterator that in turn
5897 returns @code{gdb.RegisterGroup} objects.
5899 A @code{gdb.RegisterGroup} object has the following read-only
5902 @defvar RegisterGroup.name
5903 A string that is the name of this register group.
5906 @node TUI Windows In Python
5907 @subsubsection Implementing new TUI windows
5908 @cindex Python TUI Windows
5910 New TUI (@pxref{TUI}) windows can be implemented in Python.
5912 @findex gdb.register_window_type
5913 @defun gdb.register_window_type (@var{name}, @var{factory})
5914 Because TUI windows are created and destroyed depending on the layout
5915 the user chooses, new window types are implemented by registering a
5916 factory function with @value{GDBN}.
5918 @var{name} is the name of the new window. It's an error to try to
5919 replace one of the built-in windows, but other window types can be
5922 @var{function} is a factory function that is called to create the TUI
5923 window. This is called with a single argument of type
5924 @code{gdb.TuiWindow}, described below. It should return an object
5925 that implements the TUI window protocol, also described below.
5928 As mentioned above, when a factory function is called, it is passed
5929 an object of type @code{gdb.TuiWindow}. This object has these
5930 methods and attributes:
5932 @defun TuiWindow.is_valid ()
5933 This method returns @code{True} when this window is valid. When the
5934 user changes the TUI layout, windows no longer visible in the new
5935 layout will be destroyed. At this point, the @code{gdb.TuiWindow}
5936 will no longer be valid, and methods (and attributes) other than
5937 @code{is_valid} will throw an exception.
5939 When the TUI is disabled using @code{tui disable} (@pxref{TUI
5940 Commands,,tui disable}) the window is hidden rather than destroyed,
5941 but @code{is_valid} will still return @code{False} and other methods
5942 (and attributes) will still throw an exception.
5945 @defvar TuiWindow.width
5946 This attribute holds the width of the window. It is not writable.
5949 @defvar TuiWindow.height
5950 This attribute holds the height of the window. It is not writable.
5953 @defvar TuiWindow.title
5954 This attribute holds the window's title, a string. This is normally
5955 displayed above the window. This attribute can be modified.
5958 @defun TuiWindow.erase ()
5959 Remove all the contents of the window.
5962 @defun TuiWindow.write (@var{string} @r{[}, @var{full_window}@r{]})
5963 Write @var{string} to the window. @var{string} can contain ANSI
5964 terminal escape styling sequences; @value{GDBN} will translate these
5965 as appropriate for the terminal.
5967 If the @var{full_window} parameter is @code{True}, then @var{string}
5968 contains the full contents of the window. This is similar to calling
5969 @code{erase} before @code{write}, but avoids the flickering.
5972 The factory function that you supply should return an object
5973 conforming to the TUI window protocol. These are the method that can
5974 be called on this object, which is referred to below as the ``window
5975 object''. The methods documented below are optional; if the object
5976 does not implement one of these methods, @value{GDBN} will not attempt
5977 to call it. Additional new methods may be added to the window
5978 protocol in the future. @value{GDBN} guarantees that they will begin
5979 with a lower-case letter, so you can start implementation methods with
5980 upper-case letters or underscore to avoid any future conflicts.
5982 @defun Window.close ()
5983 When the TUI window is closed, the @code{gdb.TuiWindow} object will be
5984 put into an invalid state. At this time, @value{GDBN} will call
5985 @code{close} method on the window object.
5987 After this method is called, @value{GDBN} will discard any references
5988 it holds on this window object, and will no longer call methods on
5992 @defun Window.render ()
5993 In some situations, a TUI window can change size. For example, this
5994 can happen if the user resizes the terminal, or changes the layout.
5995 When this happens, @value{GDBN} will call the @code{render} method on
5998 If your window is intended to update in response to changes in the
5999 inferior, you will probably also want to register event listeners and
6000 send output to the @code{gdb.TuiWindow}.
6003 @defun Window.hscroll (@var{num})
6004 This is a request to scroll the window horizontally. @var{num} is the
6005 amount by which to scroll, with negative numbers meaning to scroll
6006 right. In the TUI model, it is the viewport that moves, not the
6007 contents. A positive argument should cause the viewport to move
6008 right, and so the content should appear to move to the left.
6011 @defun Window.vscroll (@var{num})
6012 This is a request to scroll the window vertically. @var{num} is the
6013 amount by which to scroll, with negative numbers meaning to scroll
6014 backward. In the TUI model, it is the viewport that moves, not the
6015 contents. A positive argument should cause the viewport to move down,
6016 and so the content should appear to move up.
6019 @defun Window.click (@var{x}, @var{y}, @var{button})
6020 This is called on a mouse click in this window. @var{x} and @var{y} are
6021 the mouse coordinates inside the window (0-based), and @var{button}
6022 specifies which mouse button was used, whose values can be 1 (left),
6023 2 (middle), or 3 (right).
6026 @node Python Auto-loading
6027 @subsection Python Auto-loading
6028 @cindex Python auto-loading
6030 When a new object file is read (for example, due to the @code{file}
6031 command, or because the inferior has loaded a shared library),
6032 @value{GDBN} will look for Python support scripts in several ways:
6033 @file{@var{objfile}-gdb.py} and @code{.debug_gdb_scripts} section.
6034 @xref{Auto-loading extensions}.
6036 The auto-loading feature is useful for supplying application-specific
6037 debugging commands and scripts.
6039 Auto-loading can be enabled or disabled,
6040 and the list of auto-loaded scripts can be printed.
6043 @anchor{set auto-load python-scripts}
6044 @kindex set auto-load python-scripts
6045 @item set auto-load python-scripts [on|off]
6046 Enable or disable the auto-loading of Python scripts.
6048 @anchor{show auto-load python-scripts}
6049 @kindex show auto-load python-scripts
6050 @item show auto-load python-scripts
6051 Show whether auto-loading of Python scripts is enabled or disabled.
6053 @anchor{info auto-load python-scripts}
6054 @kindex info auto-load python-scripts
6055 @cindex print list of auto-loaded Python scripts
6056 @item info auto-load python-scripts [@var{regexp}]
6057 Print the list of all Python scripts that @value{GDBN} auto-loaded.
6059 Also printed is the list of Python scripts that were mentioned in
6060 the @code{.debug_gdb_scripts} section and were either not found
6061 (@pxref{dotdebug_gdb_scripts section}) or were not auto-loaded due to
6062 @code{auto-load safe-path} rejection (@pxref{Auto-loading}).
6063 This is useful because their names are not printed when @value{GDBN}
6064 tries to load them and fails. There may be many of them, and printing
6065 an error message for each one is problematic.
6067 If @var{regexp} is supplied only Python scripts with matching names are printed.
6072 (gdb) info auto-load python-scripts
6074 Yes py-section-script.py
6075 full name: /tmp/py-section-script.py
6076 No my-foo-pretty-printers.py
6080 When reading an auto-loaded file or script, @value{GDBN} sets the
6081 @dfn{current objfile}. This is available via the @code{gdb.current_objfile}
6082 function (@pxref{Objfiles In Python}). This can be useful for
6083 registering objfile-specific pretty-printers and frame-filters.
6085 @node Python modules
6086 @subsection Python modules
6087 @cindex python modules
6089 @value{GDBN} comes with several modules to assist writing Python code.
6092 * gdb.printing:: Building and registering pretty-printers.
6093 * gdb.types:: Utilities for working with types.
6094 * gdb.prompt:: Utilities for prompt value substitution.
6098 @subsubsection gdb.printing
6099 @cindex gdb.printing
6101 This module provides a collection of utilities for working with
6105 @item PrettyPrinter (@var{name}, @var{subprinters}=None)
6106 This class specifies the API that makes @samp{info pretty-printer},
6107 @samp{enable pretty-printer} and @samp{disable pretty-printer} work.
6108 Pretty-printers should generally inherit from this class.
6110 @item SubPrettyPrinter (@var{name})
6111 For printers that handle multiple types, this class specifies the
6112 corresponding API for the subprinters.
6114 @item RegexpCollectionPrettyPrinter (@var{name})
6115 Utility class for handling multiple printers, all recognized via
6116 regular expressions.
6117 @xref{Writing a Pretty-Printer}, for an example.
6119 @item FlagEnumerationPrinter (@var{name})
6120 A pretty-printer which handles printing of @code{enum} values. Unlike
6121 @value{GDBN}'s built-in @code{enum} printing, this printer attempts to
6122 work properly when there is some overlap between the enumeration
6123 constants. The argument @var{name} is the name of the printer and
6124 also the name of the @code{enum} type to look up.
6126 @item register_pretty_printer (@var{obj}, @var{printer}, @var{replace}=False)
6127 Register @var{printer} with the pretty-printer list of @var{obj}.
6128 If @var{replace} is @code{True} then any existing copy of the printer
6129 is replaced. Otherwise a @code{RuntimeError} exception is raised
6130 if a printer with the same name already exists.
6134 @subsubsection gdb.types
6137 This module provides a collection of utilities for working with
6138 @code{gdb.Type} objects.
6141 @item get_basic_type (@var{type})
6142 Return @var{type} with const and volatile qualifiers stripped,
6143 and with typedefs and C@t{++} references converted to the underlying type.
6148 typedef const int const_int;
6150 const_int& foo_ref (foo);
6151 int main () @{ return 0; @}
6158 (gdb) python import gdb.types
6159 (gdb) python foo_ref = gdb.parse_and_eval("foo_ref")
6160 (gdb) python print gdb.types.get_basic_type(foo_ref.type)
6164 @item has_field (@var{type}, @var{field})
6165 Return @code{True} if @var{type}, assumed to be a type with fields
6166 (e.g., a structure or union), has field @var{field}.
6168 @item make_enum_dict (@var{enum_type})
6169 Return a Python @code{dictionary} type produced from @var{enum_type}.
6171 @item deep_items (@var{type})
6172 Returns a Python iterator similar to the standard
6173 @code{gdb.Type.iteritems} method, except that the iterator returned
6174 by @code{deep_items} will recursively traverse anonymous struct or
6175 union fields. For example:
6189 Then in @value{GDBN}:
6191 (@value{GDBP}) python import gdb.types
6192 (@value{GDBP}) python struct_a = gdb.lookup_type("struct A")
6193 (@value{GDBP}) python print struct_a.keys ()
6195 (@value{GDBP}) python print [k for k,v in gdb.types.deep_items(struct_a)]
6196 @{['a', 'b0', 'b1']@}
6199 @item get_type_recognizers ()
6200 Return a list of the enabled type recognizers for the current context.
6201 This is called by @value{GDBN} during the type-printing process
6202 (@pxref{Type Printing API}).
6204 @item apply_type_recognizers (recognizers, type_obj)
6205 Apply the type recognizers, @var{recognizers}, to the type object
6206 @var{type_obj}. If any recognizer returns a string, return that
6207 string. Otherwise, return @code{None}. This is called by
6208 @value{GDBN} during the type-printing process (@pxref{Type Printing
6211 @item register_type_printer (locus, printer)
6212 This is a convenience function to register a type printer
6213 @var{printer}. The printer must implement the type printer protocol.
6214 The @var{locus} argument is either a @code{gdb.Objfile}, in which case
6215 the printer is registered with that objfile; a @code{gdb.Progspace},
6216 in which case the printer is registered with that progspace; or
6217 @code{None}, in which case the printer is registered globally.
6220 This is a base class that implements the type printer protocol. Type
6221 printers are encouraged, but not required, to derive from this class.
6222 It defines a constructor:
6224 @defmethod TypePrinter __init__ (self, name)
6225 Initialize the type printer with the given name. The new printer
6226 starts in the enabled state.
6232 @subsubsection gdb.prompt
6235 This module provides a method for prompt value-substitution.
6238 @item substitute_prompt (@var{string})
6239 Return @var{string} with escape sequences substituted by values. Some
6240 escape sequences take arguments. You can specify arguments inside
6241 ``@{@}'' immediately following the escape sequence.
6243 The escape sequences you can pass to this function are:
6247 Substitute a backslash.
6249 Substitute an ESC character.
6251 Substitute the selected frame; an argument names a frame parameter.
6253 Substitute a newline.
6255 Substitute a parameter's value; the argument names the parameter.
6257 Substitute a carriage return.
6259 Substitute the selected thread; an argument names a thread parameter.
6261 Substitute the version of GDB.
6263 Substitute the current working directory.
6265 Begin a sequence of non-printing characters. These sequences are
6266 typically used with the ESC character, and are not counted in the string
6267 length. Example: ``\[\e[0;34m\](gdb)\[\e[0m\]'' will return a
6268 blue-colored ``(gdb)'' prompt where the length is five.
6270 End a sequence of non-printing characters.
6276 substitute_prompt ("frame: \f, args: \p@{print frame-arguments@}")
6279 @exdent will return the string:
6282 "frame: main, args: scalars"