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3 @c under the terms of the GNU Free Documentation License, Version 1.3 or
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7 @c and with the Back-Cover Texts as in (a) below.
9 @c (a) The FSF's Back-Cover Text is: ``You are free to copy and modify
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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:
94 End with a line saying just "end".
100 @kindex set python print-stack
101 @item set python print-stack
102 By default, @value{GDBN} will print only the message component of a
103 Python exception when an error occurs in a Python script. This can be
104 controlled using @code{set python print-stack}: if @code{full}, then
105 full Python stack printing is enabled; if @code{none}, then Python stack
106 and message printing is disabled; if @code{message}, the default, only
107 the message component of the error is printed.
110 It is also possible to execute a Python script from the @value{GDBN}
114 @item source @file{script-name}
115 The script name must end with @samp{.py} and @value{GDBN} must be configured
116 to recognize the script language based on filename extension using
117 the @code{script-extension} setting. @xref{Extending GDB, ,Extending GDB}.
121 @subsection Python API
123 @cindex programming in python
125 You can get quick online help for @value{GDBN}'s Python API by issuing
126 the command @w{@kbd{python help (gdb)}}.
128 Functions and methods which have two or more optional arguments allow
129 them to be specified using keyword syntax. This allows passing some
130 optional arguments while skipping others. Example:
131 @w{@code{gdb.some_function ('foo', bar = 1, baz = 2)}}.
134 * Basic Python:: Basic Python Functions.
135 * Exception Handling:: How Python exceptions are translated.
136 * Values From Inferior:: Python representation of values.
137 * Types In Python:: Python representation of types.
138 * Pretty Printing API:: Pretty-printing values.
139 * Selecting Pretty-Printers:: How GDB chooses a pretty-printer.
140 * Writing a Pretty-Printer:: Writing a Pretty-Printer.
141 * Type Printing API:: Pretty-printing types.
142 * Frame Filter API:: Filtering Frames.
143 * Frame Decorator API:: Decorating Frames.
144 * Writing a Frame Filter:: Writing a Frame Filter.
145 * Unwinding Frames in Python:: Writing frame unwinder.
146 * Xmethods In Python:: Adding and replacing methods of C++ classes.
147 * Xmethod API:: Xmethod types.
148 * Writing an Xmethod:: Writing an xmethod.
149 * Inferiors In Python:: Python representation of inferiors (processes)
150 * Events In Python:: Listening for events from @value{GDBN}.
151 * Threads In Python:: Accessing inferior threads from Python.
152 * Recordings In Python:: Accessing recordings from Python.
153 * Commands In Python:: Implementing new commands in Python.
154 * Parameters In Python:: Adding new @value{GDBN} parameters.
155 * Functions In Python:: Writing new convenience functions.
156 * Progspaces In Python:: Program spaces.
157 * Objfiles In Python:: Object files.
158 * Frames In Python:: Accessing inferior stack frames from Python.
159 * Blocks In Python:: Accessing blocks from Python.
160 * Symbols In Python:: Python representation of symbols.
161 * Symbol Tables In Python:: Python representation of symbol tables.
162 * Line Tables In Python:: Python representation of line tables.
163 * Breakpoints In Python:: Manipulating breakpoints using Python.
164 * Finish Breakpoints in Python:: Setting Breakpoints on function return
166 * Lazy Strings In Python:: Python representation of lazy strings.
167 * Architectures In Python:: Python representation of architectures.
171 @subsubsection Basic Python
173 @cindex python stdout
174 @cindex python pagination
175 At startup, @value{GDBN} overrides Python's @code{sys.stdout} and
176 @code{sys.stderr} to print using @value{GDBN}'s output-paging streams.
177 A Python program which outputs to one of these streams may have its
178 output interrupted by the user (@pxref{Screen Size}). In this
179 situation, a Python @code{KeyboardInterrupt} exception is thrown.
181 Some care must be taken when writing Python code to run in
182 @value{GDBN}. Two things worth noting in particular:
186 @value{GDBN} install handlers for @code{SIGCHLD} and @code{SIGINT}.
187 Python code must not override these, or even change the options using
188 @code{sigaction}. If your program changes the handling of these
189 signals, @value{GDBN} will most likely stop working correctly. Note
190 that it is unfortunately common for GUI toolkits to install a
191 @code{SIGCHLD} handler.
194 @value{GDBN} takes care to mark its internal file descriptors as
195 close-on-exec. However, this cannot be done in a thread-safe way on
196 all platforms. Your Python programs should be aware of this and
197 should both create new file descriptors with the close-on-exec flag
198 set and arrange to close unneeded file descriptors before starting a
202 @cindex python functions
203 @cindex python module
205 @value{GDBN} introduces a new Python module, named @code{gdb}. All
206 methods and classes added by @value{GDBN} are placed in this module.
207 @value{GDBN} automatically @code{import}s the @code{gdb} module for
208 use in all scripts evaluated by the @code{python} command.
210 Some types of the @code{gdb} module come with a textual representation
211 (accessible through the @code{repr} or @code{str} functions). These are
212 offered for debugging purposes only, expect them to change over time.
214 @findex gdb.PYTHONDIR
215 @defvar gdb.PYTHONDIR
216 A string containing the python directory (@pxref{Python}).
220 @defun gdb.execute (command @r{[}, from_tty @r{[}, to_string@r{]]})
221 Evaluate @var{command}, a string, as a @value{GDBN} CLI command.
222 If a GDB exception happens while @var{command} runs, it is
223 translated as described in @ref{Exception Handling,,Exception Handling}.
225 The @var{from_tty} flag specifies whether @value{GDBN} ought to consider this
226 command as having originated from the user invoking it interactively.
227 It must be a boolean value. If omitted, it defaults to @code{False}.
229 By default, any output produced by @var{command} is sent to
230 @value{GDBN}'s standard output (and to the log output if logging is
231 turned on). If the @var{to_string} parameter is
232 @code{True}, then output will be collected by @code{gdb.execute} and
233 returned as a string. The default is @code{False}, in which case the
234 return value is @code{None}. If @var{to_string} is @code{True}, the
235 @value{GDBN} virtual terminal will be temporarily set to unlimited width
236 and height, and its pagination will be disabled; @pxref{Screen Size}.
239 @findex gdb.breakpoints
240 @defun gdb.breakpoints ()
241 Return a sequence holding all of @value{GDBN}'s breakpoints.
242 @xref{Breakpoints In Python}, for more information. In @value{GDBN}
243 version 7.11 and earlier, this function returned @code{None} if there
244 were no breakpoints. This peculiarity was subsequently fixed, and now
245 @code{gdb.breakpoints} returns an empty sequence in this case.
248 @defun gdb.rbreak (regex @r{[}, minsyms @r{[}, throttle, @r{[}, symtabs @r{]]]})
249 Return a Python list holding a collection of newly set
250 @code{gdb.Breakpoint} objects matching function names defined by the
251 @var{regex} pattern. If the @var{minsyms} keyword is @code{True}, all
252 system functions (those not explicitly defined in the inferior) will
253 also be included in the match. The @var{throttle} keyword takes an
254 integer that defines the maximum number of pattern matches for
255 functions matched by the @var{regex} pattern. If the number of
256 matches exceeds the integer value of @var{throttle}, a
257 @code{RuntimeError} will be raised and no breakpoints will be created.
258 If @var{throttle} is not defined then there is no imposed limit on the
259 maximum number of matches and breakpoints to be created. The
260 @var{symtabs} keyword takes a Python iterable that yields a collection
261 of @code{gdb.Symtab} objects and will restrict the search to those
262 functions only contained within the @code{gdb.Symtab} objects.
265 @findex gdb.parameter
266 @defun gdb.parameter (parameter)
267 Return the value of a @value{GDBN} @var{parameter} given by its name,
268 a string; the parameter name string may contain spaces if the parameter has a
269 multi-part name. For example, @samp{print object} is a valid
272 If the named parameter does not exist, this function throws a
273 @code{gdb.error} (@pxref{Exception Handling}). Otherwise, the
274 parameter's value is converted to a Python value of the appropriate
279 @defun gdb.history (number)
280 Return a value from @value{GDBN}'s value history (@pxref{Value
281 History}). The @var{number} argument indicates which history element to return.
282 If @var{number} is negative, then @value{GDBN} will take its absolute value
283 and count backward from the last element (i.e., the most recent element) to
284 find the value to return. If @var{number} is zero, then @value{GDBN} will
285 return the most recent element. If the element specified by @var{number}
286 doesn't exist in the value history, a @code{gdb.error} exception will be
289 If no exception is raised, the return value is always an instance of
290 @code{gdb.Value} (@pxref{Values From Inferior}).
293 @findex gdb.convenience_variable
294 @defun gdb.convenience_variable (name)
295 Return the value of the convenience variable (@pxref{Convenience
296 Vars}) named @var{name}. @var{name} must be a string. The name
297 should not include the @samp{$} that is used to mark a convenience
298 variable in an expression. If the convenience variable does not
299 exist, then @code{None} is returned.
302 @findex gdb.set_convenience_variable
303 @defun gdb.set_convenience_variable (name, value)
304 Set the value of the convenience variable (@pxref{Convenience Vars})
305 named @var{name}. @var{name} must be a string. The name should not
306 include the @samp{$} that is used to mark a convenience variable in an
307 expression. If @var{value} is @code{None}, then the convenience
308 variable is removed. Otherwise, if @var{value} is not a
309 @code{gdb.Value} (@pxref{Values From Inferior}), it is is converted
310 using the @code{gdb.Value} constructor.
313 @findex gdb.parse_and_eval
314 @defun gdb.parse_and_eval (expression)
315 Parse @var{expression}, which must be a string, as an expression in
316 the current language, evaluate it, and return the result as a
319 This function can be useful when implementing a new command
320 (@pxref{Commands In Python}), as it provides a way to parse the
321 command's argument as an expression. It is also useful simply to
325 @findex gdb.find_pc_line
326 @defun gdb.find_pc_line (pc)
327 Return the @code{gdb.Symtab_and_line} object corresponding to the
328 @var{pc} value. @xref{Symbol Tables In Python}. If an invalid
329 value of @var{pc} is passed as an argument, then the @code{symtab} and
330 @code{line} attributes of the returned @code{gdb.Symtab_and_line} object
331 will be @code{None} and 0 respectively. This is identical to
332 @code{gdb.current_progspace().find_pc_line(pc)} and is included for
333 historical compatibility.
336 @findex gdb.post_event
337 @defun gdb.post_event (event)
338 Put @var{event}, a callable object taking no arguments, into
339 @value{GDBN}'s internal event queue. This callable will be invoked at
340 some later point, during @value{GDBN}'s event processing. Events
341 posted using @code{post_event} will be run in the order in which they
342 were posted; however, there is no way to know when they will be
343 processed relative to other events inside @value{GDBN}.
345 @value{GDBN} is not thread-safe. If your Python program uses multiple
346 threads, you must be careful to only call @value{GDBN}-specific
347 functions in the @value{GDBN} thread. @code{post_event} ensures
351 (@value{GDBP}) python
355 > def __init__(self, message):
356 > self.message = message;
357 > def __call__(self):
358 > gdb.write(self.message)
360 >class MyThread1 (threading.Thread):
362 > gdb.post_event(Writer("Hello "))
364 >class MyThread2 (threading.Thread):
366 > gdb.post_event(Writer("World\n"))
371 (@value{GDBP}) Hello World
376 @defun gdb.write (string @r{[}, stream{]})
377 Print a string to @value{GDBN}'s paginated output stream. The
378 optional @var{stream} determines the stream to print to. The default
379 stream is @value{GDBN}'s standard output stream. Possible stream
386 @value{GDBN}'s standard output stream.
391 @value{GDBN}'s standard error stream.
396 @value{GDBN}'s log stream (@pxref{Logging Output}).
399 Writing to @code{sys.stdout} or @code{sys.stderr} will automatically
400 call this function and will automatically direct the output to the
406 Flush the buffer of a @value{GDBN} paginated stream so that the
407 contents are displayed immediately. @value{GDBN} will flush the
408 contents of a stream automatically when it encounters a newline in the
409 buffer. The optional @var{stream} determines the stream to flush. The
410 default stream is @value{GDBN}'s standard output stream. Possible
417 @value{GDBN}'s standard output stream.
422 @value{GDBN}'s standard error stream.
427 @value{GDBN}'s log stream (@pxref{Logging Output}).
431 Flushing @code{sys.stdout} or @code{sys.stderr} will automatically
432 call this function for the relevant stream.
435 @findex gdb.target_charset
436 @defun gdb.target_charset ()
437 Return the name of the current target character set (@pxref{Character
438 Sets}). This differs from @code{gdb.parameter('target-charset')} in
439 that @samp{auto} is never returned.
442 @findex gdb.target_wide_charset
443 @defun gdb.target_wide_charset ()
444 Return the name of the current target wide character set
445 (@pxref{Character Sets}). This differs from
446 @code{gdb.parameter('target-wide-charset')} in that @samp{auto} is
450 @findex gdb.solib_name
451 @defun gdb.solib_name (address)
452 Return the name of the shared library holding the given @var{address}
453 as a string, or @code{None}. This is identical to
454 @code{gdb.current_progspace().solib_name(address)} and is included for
455 historical compatibility.
458 @findex gdb.decode_line
459 @defun gdb.decode_line (@r{[}expression@r{]})
460 Return locations of the line specified by @var{expression}, or of the
461 current line if no argument was given. This function returns a Python
462 tuple containing two elements. The first element contains a string
463 holding any unparsed section of @var{expression} (or @code{None} if
464 the expression has been fully parsed). The second element contains
465 either @code{None} or another tuple that contains all the locations
466 that match the expression represented as @code{gdb.Symtab_and_line}
467 objects (@pxref{Symbol Tables In Python}). If @var{expression} is
468 provided, it is decoded the way that @value{GDBN}'s inbuilt
469 @code{break} or @code{edit} commands do (@pxref{Specify Location}).
472 @defun gdb.prompt_hook (current_prompt)
475 If @var{prompt_hook} is callable, @value{GDBN} will call the method
476 assigned to this operation before a prompt is displayed by
479 The parameter @code{current_prompt} contains the current @value{GDBN}
480 prompt. This method must return a Python string, or @code{None}. If
481 a string is returned, the @value{GDBN} prompt will be set to that
482 string. If @code{None} is returned, @value{GDBN} will continue to use
485 Some prompts cannot be substituted in @value{GDBN}. Secondary prompts
486 such as those used by readline for command input, and annotation
487 related prompts are prohibited from being changed.
490 @node Exception Handling
491 @subsubsection Exception Handling
492 @cindex python exceptions
493 @cindex exceptions, python
495 When executing the @code{python} command, Python exceptions
496 uncaught within the Python code are translated to calls to
497 @value{GDBN} error-reporting mechanism. If the command that called
498 @code{python} does not handle the error, @value{GDBN} will
499 terminate it and print an error message containing the Python
500 exception name, the associated value, and the Python call stack
501 backtrace at the point where the exception was raised. Example:
504 (@value{GDBP}) python print foo
505 Traceback (most recent call last):
506 File "<string>", line 1, in <module>
507 NameError: name 'foo' is not defined
510 @value{GDBN} errors that happen in @value{GDBN} commands invoked by
511 Python code are converted to Python exceptions. The type of the
512 Python exception depends on the error.
516 This is the base class for most exceptions generated by @value{GDBN}.
517 It is derived from @code{RuntimeError}, for compatibility with earlier
518 versions of @value{GDBN}.
520 If an error occurring in @value{GDBN} does not fit into some more
521 specific category, then the generated exception will have this type.
523 @item gdb.MemoryError
524 This is a subclass of @code{gdb.error} which is thrown when an
525 operation tried to access invalid memory in the inferior.
527 @item KeyboardInterrupt
528 User interrupt (via @kbd{C-c} or by typing @kbd{q} at a pagination
529 prompt) is translated to a Python @code{KeyboardInterrupt} exception.
532 In all cases, your exception handler will see the @value{GDBN} error
533 message as its value and the Python call stack backtrace at the Python
534 statement closest to where the @value{GDBN} error occured as the
538 When implementing @value{GDBN} commands in Python via
539 @code{gdb.Command}, or functions via @code{gdb.Function}, it is useful
540 to be able to throw an exception that doesn't cause a traceback to be
541 printed. For example, the user may have invoked the command
542 incorrectly. @value{GDBN} provides a special exception class that can
543 be used for this purpose.
547 When thrown from a command or function, this exception will cause the
548 command or function to fail, but the Python stack will not be
549 displayed. @value{GDBN} does not throw this exception itself, but
550 rather recognizes it when thrown from user Python code. Example:
554 >class HelloWorld (gdb.Command):
555 > """Greet the whole world."""
556 > def __init__ (self):
557 > super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)
558 > def invoke (self, args, from_tty):
559 > argv = gdb.string_to_argv (args)
560 > if len (argv) != 0:
561 > raise gdb.GdbError ("hello-world takes no arguments")
562 > print "Hello, World!"
566 hello-world takes no arguments
570 @node Values From Inferior
571 @subsubsection Values From Inferior
572 @cindex values from inferior, with Python
573 @cindex python, working with values from inferior
575 @cindex @code{gdb.Value}
576 @value{GDBN} provides values it obtains from the inferior program in
577 an object of type @code{gdb.Value}. @value{GDBN} uses this object
578 for its internal bookkeeping of the inferior's values, and for
579 fetching values when necessary.
581 Inferior values that are simple scalars can be used directly in
582 Python expressions that are valid for the value's data type. Here's
583 an example for an integer or floating-point value @code{some_val}:
590 As result of this, @code{bar} will also be a @code{gdb.Value} object
591 whose values are of the same type as those of @code{some_val}. Valid
592 Python operations can also be performed on @code{gdb.Value} objects
593 representing a @code{struct} or @code{class} object. For such cases,
594 the overloaded operator (if present), is used to perform the operation.
595 For example, if @code{val1} and @code{val2} are @code{gdb.Value} objects
596 representing instances of a @code{class} which overloads the @code{+}
597 operator, then one can use the @code{+} operator in their Python script
605 The result of the operation @code{val3} is also a @code{gdb.Value}
606 object corresponding to the value returned by the overloaded @code{+}
607 operator. In general, overloaded operators are invoked for the
608 following operations: @code{+} (binary addition), @code{-} (binary
609 subtraction), @code{*} (multiplication), @code{/}, @code{%}, @code{<<},
610 @code{>>}, @code{|}, @code{&}, @code{^}.
612 Inferior values that are structures or instances of some class can
613 be accessed using the Python @dfn{dictionary syntax}. For example, if
614 @code{some_val} is a @code{gdb.Value} instance holding a structure, you
615 can access its @code{foo} element with:
618 bar = some_val['foo']
621 @cindex getting structure elements using gdb.Field objects as subscripts
622 Again, @code{bar} will also be a @code{gdb.Value} object. Structure
623 elements can also be accessed by using @code{gdb.Field} objects as
624 subscripts (@pxref{Types In Python}, for more information on
625 @code{gdb.Field} objects). For example, if @code{foo_field} is a
626 @code{gdb.Field} object corresponding to element @code{foo} of the above
627 structure, then @code{bar} can also be accessed as follows:
630 bar = some_val[foo_field]
633 A @code{gdb.Value} that represents a function can be executed via
634 inferior function call. Any arguments provided to the call must match
635 the function's prototype, and must be provided in the order specified
638 For example, @code{some_val} is a @code{gdb.Value} instance
639 representing a function that takes two integers as arguments. To
640 execute this function, call it like so:
643 result = some_val (10,20)
646 Any values returned from a function call will be stored as a
649 The following attributes are provided:
651 @defvar Value.address
652 If this object is addressable, this read-only attribute holds a
653 @code{gdb.Value} object representing the address. Otherwise,
654 this attribute holds @code{None}.
657 @cindex optimized out value in Python
658 @defvar Value.is_optimized_out
659 This read-only boolean attribute is true if the compiler optimized out
660 this value, thus it is not available for fetching from the inferior.
664 The type of this @code{gdb.Value}. The value of this attribute is a
665 @code{gdb.Type} object (@pxref{Types In Python}).
668 @defvar Value.dynamic_type
669 The dynamic type of this @code{gdb.Value}. This uses the object's
670 virtual table and the C@t{++} run-time type information
671 (@acronym{RTTI}) to determine the dynamic type of the value. If this
672 value is of class type, it will return the class in which the value is
673 embedded, if any. If this value is of pointer or reference to a class
674 type, it will compute the dynamic type of the referenced object, and
675 return a pointer or reference to that type, respectively. In all
676 other cases, it will return the value's static type.
678 Note that this feature will only work when debugging a C@t{++} program
679 that includes @acronym{RTTI} for the object in question. Otherwise,
680 it will just return the static type of the value as in @kbd{ptype foo}
681 (@pxref{Symbols, ptype}).
684 @defvar Value.is_lazy
685 The value of this read-only boolean attribute is @code{True} if this
686 @code{gdb.Value} has not yet been fetched from the inferior.
687 @value{GDBN} does not fetch values until necessary, for efficiency.
691 myval = gdb.parse_and_eval ('somevar')
694 The value of @code{somevar} is not fetched at this time. It will be
695 fetched when the value is needed, or when the @code{fetch_lazy}
699 The following methods are provided:
701 @defun Value.__init__ (@var{val})
702 Many Python values can be converted directly to a @code{gdb.Value} via
703 this object initializer. Specifically:
707 A Python boolean is converted to the boolean type from the current
711 A Python integer is converted to the C @code{long} type for the
712 current architecture.
715 A Python long is converted to the C @code{long long} type for the
716 current architecture.
719 A Python float is converted to the C @code{double} type for the
720 current architecture.
723 A Python string is converted to a target string in the current target
724 language using the current target encoding.
725 If a character cannot be represented in the current target encoding,
726 then an exception is thrown.
728 @item @code{gdb.Value}
729 If @code{val} is a @code{gdb.Value}, then a copy of the value is made.
731 @item @code{gdb.LazyString}
732 If @code{val} is a @code{gdb.LazyString} (@pxref{Lazy Strings In
733 Python}), then the lazy string's @code{value} method is called, and
738 @defun Value.__init__ (@var{val}, @var{type})
739 This second form of the @code{gdb.Value} constructor returns a
740 @code{gdb.Value} of type @var{type} where the value contents are taken
741 from the Python buffer object specified by @var{val}. The number of
742 bytes in the Python buffer object must be greater than or equal to the
746 @defun Value.cast (type)
747 Return a new instance of @code{gdb.Value} that is the result of
748 casting this instance to the type described by @var{type}, which must
749 be a @code{gdb.Type} object. If the cast cannot be performed for some
750 reason, this method throws an exception.
753 @defun Value.dereference ()
754 For pointer data types, this method returns a new @code{gdb.Value} object
755 whose contents is the object pointed to by the pointer. For example, if
756 @code{foo} is a C pointer to an @code{int}, declared in your C program as
763 then you can use the corresponding @code{gdb.Value} to access what
764 @code{foo} points to like this:
767 bar = foo.dereference ()
770 The result @code{bar} will be a @code{gdb.Value} object holding the
771 value pointed to by @code{foo}.
773 A similar function @code{Value.referenced_value} exists which also
774 returns @code{gdb.Value} objects corresonding to the values pointed to
775 by pointer values (and additionally, values referenced by reference
776 values). However, the behavior of @code{Value.dereference}
777 differs from @code{Value.referenced_value} by the fact that the
778 behavior of @code{Value.dereference} is identical to applying the C
779 unary operator @code{*} on a given value. For example, consider a
780 reference to a pointer @code{ptrref}, declared in your C@t{++} program
788 intptr &ptrref = ptr;
791 Though @code{ptrref} is a reference value, one can apply the method
792 @code{Value.dereference} to the @code{gdb.Value} object corresponding
793 to it and obtain a @code{gdb.Value} which is identical to that
794 corresponding to @code{val}. However, if you apply the method
795 @code{Value.referenced_value}, the result would be a @code{gdb.Value}
796 object identical to that corresponding to @code{ptr}.
799 py_ptrref = gdb.parse_and_eval ("ptrref")
800 py_val = py_ptrref.dereference ()
801 py_ptr = py_ptrref.referenced_value ()
804 The @code{gdb.Value} object @code{py_val} is identical to that
805 corresponding to @code{val}, and @code{py_ptr} is identical to that
806 corresponding to @code{ptr}. In general, @code{Value.dereference} can
807 be applied whenever the C unary operator @code{*} can be applied
808 to the corresponding C value. For those cases where applying both
809 @code{Value.dereference} and @code{Value.referenced_value} is allowed,
810 the results obtained need not be identical (as we have seen in the above
811 example). The results are however identical when applied on
812 @code{gdb.Value} objects corresponding to pointers (@code{gdb.Value}
813 objects with type code @code{TYPE_CODE_PTR}) in a C/C@t{++} program.
816 @defun Value.referenced_value ()
817 For pointer or reference data types, this method returns a new
818 @code{gdb.Value} object corresponding to the value referenced by the
819 pointer/reference value. For pointer data types,
820 @code{Value.dereference} and @code{Value.referenced_value} produce
821 identical results. The difference between these methods is that
822 @code{Value.dereference} cannot get the values referenced by reference
823 values. For example, consider a reference to an @code{int}, declared
824 in your C@t{++} program as
832 then applying @code{Value.dereference} to the @code{gdb.Value} object
833 corresponding to @code{ref} will result in an error, while applying
834 @code{Value.referenced_value} will result in a @code{gdb.Value} object
835 identical to that corresponding to @code{val}.
838 py_ref = gdb.parse_and_eval ("ref")
839 er_ref = py_ref.dereference () # Results in error
840 py_val = py_ref.referenced_value () # Returns the referenced value
843 The @code{gdb.Value} object @code{py_val} is identical to that
844 corresponding to @code{val}.
847 @defun Value.reference_value ()
848 Return a @code{gdb.Value} object which is a reference to the value
849 encapsulated by this instance.
852 @defun Value.const_value ()
853 Return a @code{gdb.Value} object which is a @code{const} version of the
854 value encapsulated by this instance.
857 @defun Value.dynamic_cast (type)
858 Like @code{Value.cast}, but works as if the C@t{++} @code{dynamic_cast}
859 operator were used. Consult a C@t{++} reference for details.
862 @defun Value.reinterpret_cast (type)
863 Like @code{Value.cast}, but works as if the C@t{++} @code{reinterpret_cast}
864 operator were used. Consult a C@t{++} reference for details.
867 @defun Value.format_string (...)
868 Convert a @code{gdb.Value} to a string, similarly to what the @code{print}
869 command does. Invoked with no arguments, this is equivalent to calling
870 the @code{str} function on the @code{gdb.Value}. The representation of
871 the same value may change across different versions of @value{GDBN}, so
872 you shouldn't, for instance, parse the strings returned by this method.
874 All the arguments are keyword only. If an argument is not specified, the
875 current global default setting is used.
879 @code{True} if pretty-printers (@pxref{Pretty Printing}) should not be
880 used to format the value. @code{False} if enabled pretty-printers
881 matching the type represented by the @code{gdb.Value} should be used to
885 @code{True} if arrays should be pretty printed to be more convenient to
886 read, @code{False} if they shouldn't (see @code{set print array} in
887 @ref{Print Settings}).
890 @code{True} if structs should be pretty printed to be more convenient to
891 read, @code{False} if they shouldn't (see @code{set print pretty} in
892 @ref{Print Settings}).
895 @code{True} if array indexes should be included in the string
896 representation of arrays, @code{False} if they shouldn't (see @code{set
897 print array-indexes} in @ref{Print Settings}).
900 @code{True} if the string representation of a pointer should include the
901 corresponding symbol name (if one exists), @code{False} if it shouldn't
902 (see @code{set print symbol} in @ref{Print Settings}).
905 @code{True} if unions which are contained in other structures or unions
906 should be expanded, @code{False} if they shouldn't (see @code{set print
907 union} in @ref{Print Settings}).
910 @code{True} if C@t{++} references should be resolved to the value they
911 refer to, @code{False} (the default) if they shouldn't. Note that, unlike
912 for the @code{print} command, references are not automatically expanded
913 when using the @code{format_string} method or the @code{str}
914 function. There is no global @code{print} setting to change the default
918 @code{True} if the representation of a pointer to an object should
919 identify the @emph{actual} (derived) type of the object rather than the
920 @emph{declared} type, using the virtual function table. @code{False} if
921 the @emph{declared} type should be used. (See @code{set print object} in
922 @ref{Print Settings}).
925 @code{True} if static members should be included in the string
926 representation of a C@t{++} object, @code{False} if they shouldn't (see
927 @code{set print static-members} in @ref{Print Settings}).
930 Number of array elements to print, or @code{0} to print an unlimited
931 number of elements (see @code{set print elements} in @ref{Print
934 @item repeat_threshold
935 Set the threshold for suppressing display of repeated array elements, or
936 @code{0} to represent all elements, even if repeated. (See @code{set
937 print repeats} in @ref{Print Settings}).
940 A string containing a single character representing the format to use for
941 the returned string. For instance, @code{'x'} is equivalent to using the
942 @value{GDBN} command @code{print} with the @code{/x} option and formats
943 the value as a hexadecimal number.
947 @defun Value.string (@r{[}encoding@r{[}, errors@r{[}, length@r{]]]})
948 If this @code{gdb.Value} represents a string, then this method
949 converts the contents to a Python string. Otherwise, this method will
952 Values are interpreted as strings according to the rules of the
953 current language. If the optional length argument is given, the
954 string will be converted to that length, and will include any embedded
955 zeroes that the string may contain. Otherwise, for languages
956 where the string is zero-terminated, the entire string will be
959 For example, in C-like languages, a value is a string if it is a pointer
960 to or an array of characters or ints of type @code{wchar_t}, @code{char16_t},
963 If the optional @var{encoding} argument is given, it must be a string
964 naming the encoding of the string in the @code{gdb.Value}, such as
965 @code{"ascii"}, @code{"iso-8859-6"} or @code{"utf-8"}. It accepts
966 the same encodings as the corresponding argument to Python's
967 @code{string.decode} method, and the Python codec machinery will be used
968 to convert the string. If @var{encoding} is not given, or if
969 @var{encoding} is the empty string, then either the @code{target-charset}
970 (@pxref{Character Sets}) will be used, or a language-specific encoding
971 will be used, if the current language is able to supply one.
973 The optional @var{errors} argument is the same as the corresponding
974 argument to Python's @code{string.decode} method.
976 If the optional @var{length} argument is given, the string will be
977 fetched and converted to the given length.
980 @defun Value.lazy_string (@r{[}encoding @r{[}, length@r{]]})
981 If this @code{gdb.Value} represents a string, then this method
982 converts the contents to a @code{gdb.LazyString} (@pxref{Lazy Strings
983 In Python}). Otherwise, this method will throw an exception.
985 If the optional @var{encoding} argument is given, it must be a string
986 naming the encoding of the @code{gdb.LazyString}. Some examples are:
987 @samp{ascii}, @samp{iso-8859-6} or @samp{utf-8}. If the
988 @var{encoding} argument is an encoding that @value{GDBN} does
989 recognize, @value{GDBN} will raise an error.
991 When a lazy string is printed, the @value{GDBN} encoding machinery is
992 used to convert the string during printing. If the optional
993 @var{encoding} argument is not provided, or is an empty string,
994 @value{GDBN} will automatically select the encoding most suitable for
995 the string type. For further information on encoding in @value{GDBN}
996 please see @ref{Character Sets}.
998 If the optional @var{length} argument is given, the string will be
999 fetched and encoded to the length of characters specified. If
1000 the @var{length} argument is not provided, the string will be fetched
1001 and encoded until a null of appropriate width is found.
1004 @defun Value.fetch_lazy ()
1005 If the @code{gdb.Value} object is currently a lazy value
1006 (@code{gdb.Value.is_lazy} is @code{True}), then the value is
1007 fetched from the inferior. Any errors that occur in the process
1008 will produce a Python exception.
1010 If the @code{gdb.Value} object is not a lazy value, this method
1013 This method does not return a value.
1017 @node Types In Python
1018 @subsubsection Types In Python
1019 @cindex types in Python
1020 @cindex Python, working with types
1023 @value{GDBN} represents types from the inferior using the class
1026 The following type-related functions are available in the @code{gdb}
1029 @findex gdb.lookup_type
1030 @defun gdb.lookup_type (name @r{[}, block@r{]})
1031 This function looks up a type by its @var{name}, which must be a string.
1033 If @var{block} is given, then @var{name} is looked up in that scope.
1034 Otherwise, it is searched for globally.
1036 Ordinarily, this function will return an instance of @code{gdb.Type}.
1037 If the named type cannot be found, it will throw an exception.
1040 If the type is a structure or class type, or an enum type, the fields
1041 of that type can be accessed using the Python @dfn{dictionary syntax}.
1042 For example, if @code{some_type} is a @code{gdb.Type} instance holding
1043 a structure type, you can access its @code{foo} field with:
1046 bar = some_type['foo']
1049 @code{bar} will be a @code{gdb.Field} object; see below under the
1050 description of the @code{Type.fields} method for a description of the
1051 @code{gdb.Field} class.
1053 An instance of @code{Type} has the following attributes:
1055 @defvar Type.alignof
1056 The alignment of this type, in bytes. Type alignment comes from the
1057 debugging information; if it was not specified, then @value{GDBN} will
1058 use the relevant ABI to try to determine the alignment. In some
1059 cases, even this is not possible, and zero will be returned.
1063 The type code for this type. The type code will be one of the
1064 @code{TYPE_CODE_} constants defined below.
1068 The name of this type. If this type has no name, then @code{None}
1073 The size of this type, in target @code{char} units. Usually, a
1074 target's @code{char} type will be an 8-bit byte. However, on some
1075 unusual platforms, this type may have a different size.
1079 The tag name for this type. The tag name is the name after
1080 @code{struct}, @code{union}, or @code{enum} in C and C@t{++}; not all
1081 languages have this concept. If this type has no tag name, then
1082 @code{None} is returned.
1085 The following methods are provided:
1087 @defun Type.fields ()
1088 For structure and union types, this method returns the fields. Range
1089 types have two fields, the minimum and maximum values. Enum types
1090 have one field per enum constant. Function and method types have one
1091 field per parameter. The base types of C@t{++} classes are also
1092 represented as fields. If the type has no fields, or does not fit
1093 into one of these categories, an empty sequence will be returned.
1095 Each field is a @code{gdb.Field} object, with some pre-defined attributes:
1098 This attribute is not available for @code{enum} or @code{static}
1099 (as in C@t{++}) fields. The value is the position, counting
1100 in bits, from the start of the containing type.
1103 This attribute is only available for @code{enum} fields, and its value
1104 is the enumeration member's integer representation.
1107 The name of the field, or @code{None} for anonymous fields.
1110 This is @code{True} if the field is artificial, usually meaning that
1111 it was provided by the compiler and not the user. This attribute is
1112 always provided, and is @code{False} if the field is not artificial.
1115 This is @code{True} if the field represents a base class of a C@t{++}
1116 structure. This attribute is always provided, and is @code{False}
1117 if the field is not a base class of the type that is the argument of
1118 @code{fields}, or if that type was not a C@t{++} class.
1121 If the field is packed, or is a bitfield, then this will have a
1122 non-zero value, which is the size of the field in bits. Otherwise,
1123 this will be zero; in this case the field's size is given by its type.
1126 The type of the field. This is usually an instance of @code{Type},
1127 but it can be @code{None} in some situations.
1130 The type which contains this field. This is an instance of
1135 @defun Type.array (@var{n1} @r{[}, @var{n2}@r{]})
1136 Return a new @code{gdb.Type} object which represents an array of this
1137 type. If one argument is given, it is the inclusive upper bound of
1138 the array; in this case the lower bound is zero. If two arguments are
1139 given, the first argument is the lower bound of the array, and the
1140 second argument is the upper bound of the array. An array's length
1141 must not be negative, but the bounds can be.
1144 @defun Type.vector (@var{n1} @r{[}, @var{n2}@r{]})
1145 Return a new @code{gdb.Type} object which represents a vector of this
1146 type. If one argument is given, it is the inclusive upper bound of
1147 the vector; in this case the lower bound is zero. If two arguments are
1148 given, the first argument is the lower bound of the vector, and the
1149 second argument is the upper bound of the vector. A vector's length
1150 must not be negative, but the bounds can be.
1152 The difference between an @code{array} and a @code{vector} is that
1153 arrays behave like in C: when used in expressions they decay to a pointer
1154 to the first element whereas vectors are treated as first class values.
1157 @defun Type.const ()
1158 Return a new @code{gdb.Type} object which represents a
1159 @code{const}-qualified variant of this type.
1162 @defun Type.volatile ()
1163 Return a new @code{gdb.Type} object which represents a
1164 @code{volatile}-qualified variant of this type.
1167 @defun Type.unqualified ()
1168 Return a new @code{gdb.Type} object which represents an unqualified
1169 variant of this type. That is, the result is neither @code{const} nor
1173 @defun Type.range ()
1174 Return a Python @code{Tuple} object that contains two elements: the
1175 low bound of the argument type and the high bound of that type. If
1176 the type does not have a range, @value{GDBN} will raise a
1177 @code{gdb.error} exception (@pxref{Exception Handling}).
1180 @defun Type.reference ()
1181 Return a new @code{gdb.Type} object which represents a reference to this
1185 @defun Type.pointer ()
1186 Return a new @code{gdb.Type} object which represents a pointer to this
1190 @defun Type.strip_typedefs ()
1191 Return a new @code{gdb.Type} that represents the real type,
1192 after removing all layers of typedefs.
1195 @defun Type.target ()
1196 Return a new @code{gdb.Type} object which represents the target type
1199 For a pointer type, the target type is the type of the pointed-to
1200 object. For an array type (meaning C-like arrays), the target type is
1201 the type of the elements of the array. For a function or method type,
1202 the target type is the type of the return value. For a complex type,
1203 the target type is the type of the elements. For a typedef, the
1204 target type is the aliased type.
1206 If the type does not have a target, this method will throw an
1210 @defun Type.template_argument (n @r{[}, block@r{]})
1211 If this @code{gdb.Type} is an instantiation of a template, this will
1212 return a new @code{gdb.Value} or @code{gdb.Type} which represents the
1213 value of the @var{n}th template argument (indexed starting at 0).
1215 If this @code{gdb.Type} is not a template type, or if the type has fewer
1216 than @var{n} template arguments, this will throw an exception.
1217 Ordinarily, only C@t{++} code will have template types.
1219 If @var{block} is given, then @var{name} is looked up in that scope.
1220 Otherwise, it is searched for globally.
1223 @defun Type.optimized_out ()
1224 Return @code{gdb.Value} instance of this type whose value is optimized
1225 out. This allows a frame decorator to indicate that the value of an
1226 argument or a local variable is not known.
1229 Each type has a code, which indicates what category this type falls
1230 into. The available type categories are represented by constants
1231 defined in the @code{gdb} module:
1234 @vindex TYPE_CODE_PTR
1235 @item gdb.TYPE_CODE_PTR
1236 The type is a pointer.
1238 @vindex TYPE_CODE_ARRAY
1239 @item gdb.TYPE_CODE_ARRAY
1240 The type is an array.
1242 @vindex TYPE_CODE_STRUCT
1243 @item gdb.TYPE_CODE_STRUCT
1244 The type is a structure.
1246 @vindex TYPE_CODE_UNION
1247 @item gdb.TYPE_CODE_UNION
1248 The type is a union.
1250 @vindex TYPE_CODE_ENUM
1251 @item gdb.TYPE_CODE_ENUM
1252 The type is an enum.
1254 @vindex TYPE_CODE_FLAGS
1255 @item gdb.TYPE_CODE_FLAGS
1256 A bit flags type, used for things such as status registers.
1258 @vindex TYPE_CODE_FUNC
1259 @item gdb.TYPE_CODE_FUNC
1260 The type is a function.
1262 @vindex TYPE_CODE_INT
1263 @item gdb.TYPE_CODE_INT
1264 The type is an integer type.
1266 @vindex TYPE_CODE_FLT
1267 @item gdb.TYPE_CODE_FLT
1268 A floating point type.
1270 @vindex TYPE_CODE_VOID
1271 @item gdb.TYPE_CODE_VOID
1272 The special type @code{void}.
1274 @vindex TYPE_CODE_SET
1275 @item gdb.TYPE_CODE_SET
1278 @vindex TYPE_CODE_RANGE
1279 @item gdb.TYPE_CODE_RANGE
1280 A range type, that is, an integer type with bounds.
1282 @vindex TYPE_CODE_STRING
1283 @item gdb.TYPE_CODE_STRING
1284 A string type. Note that this is only used for certain languages with
1285 language-defined string types; C strings are not represented this way.
1287 @vindex TYPE_CODE_BITSTRING
1288 @item gdb.TYPE_CODE_BITSTRING
1289 A string of bits. It is deprecated.
1291 @vindex TYPE_CODE_ERROR
1292 @item gdb.TYPE_CODE_ERROR
1293 An unknown or erroneous type.
1295 @vindex TYPE_CODE_METHOD
1296 @item gdb.TYPE_CODE_METHOD
1297 A method type, as found in C@t{++}.
1299 @vindex TYPE_CODE_METHODPTR
1300 @item gdb.TYPE_CODE_METHODPTR
1301 A pointer-to-member-function.
1303 @vindex TYPE_CODE_MEMBERPTR
1304 @item gdb.TYPE_CODE_MEMBERPTR
1305 A pointer-to-member.
1307 @vindex TYPE_CODE_REF
1308 @item gdb.TYPE_CODE_REF
1311 @vindex TYPE_CODE_RVALUE_REF
1312 @item gdb.TYPE_CODE_RVALUE_REF
1313 A C@t{++}11 rvalue reference type.
1315 @vindex TYPE_CODE_CHAR
1316 @item gdb.TYPE_CODE_CHAR
1319 @vindex TYPE_CODE_BOOL
1320 @item gdb.TYPE_CODE_BOOL
1323 @vindex TYPE_CODE_COMPLEX
1324 @item gdb.TYPE_CODE_COMPLEX
1325 A complex float type.
1327 @vindex TYPE_CODE_TYPEDEF
1328 @item gdb.TYPE_CODE_TYPEDEF
1329 A typedef to some other type.
1331 @vindex TYPE_CODE_NAMESPACE
1332 @item gdb.TYPE_CODE_NAMESPACE
1333 A C@t{++} namespace.
1335 @vindex TYPE_CODE_DECFLOAT
1336 @item gdb.TYPE_CODE_DECFLOAT
1337 A decimal floating point type.
1339 @vindex TYPE_CODE_INTERNAL_FUNCTION
1340 @item gdb.TYPE_CODE_INTERNAL_FUNCTION
1341 A function internal to @value{GDBN}. This is the type used to represent
1342 convenience functions.
1345 Further support for types is provided in the @code{gdb.types}
1346 Python module (@pxref{gdb.types}).
1348 @node Pretty Printing API
1349 @subsubsection Pretty Printing API
1350 @cindex python pretty printing api
1352 A pretty-printer is just an object that holds a value and implements a
1353 specific interface, defined here. An example output is provided
1354 (@pxref{Pretty Printing}).
1356 @defun pretty_printer.children (self)
1357 @value{GDBN} will call this method on a pretty-printer to compute the
1358 children of the pretty-printer's value.
1360 This method must return an object conforming to the Python iterator
1361 protocol. Each item returned by the iterator must be a tuple holding
1362 two elements. The first element is the ``name'' of the child; the
1363 second element is the child's value. The value can be any Python
1364 object which is convertible to a @value{GDBN} value.
1366 This method is optional. If it does not exist, @value{GDBN} will act
1367 as though the value has no children.
1370 @defun pretty_printer.display_hint (self)
1371 The CLI may call this method and use its result to change the
1372 formatting of a value. The result will also be supplied to an MI
1373 consumer as a @samp{displayhint} attribute of the variable being
1376 This method is optional. If it does exist, this method must return a
1377 string or the special value @code{None}.
1379 Some display hints are predefined by @value{GDBN}:
1383 Indicate that the object being printed is ``array-like''. The CLI
1384 uses this to respect parameters such as @code{set print elements} and
1385 @code{set print array}.
1388 Indicate that the object being printed is ``map-like'', and that the
1389 children of this value can be assumed to alternate between keys and
1393 Indicate that the object being printed is ``string-like''. If the
1394 printer's @code{to_string} method returns a Python string of some
1395 kind, then @value{GDBN} will call its internal language-specific
1396 string-printing function to format the string. For the CLI this means
1397 adding quotation marks, possibly escaping some characters, respecting
1398 @code{set print elements}, and the like.
1401 The special value @code{None} causes @value{GDBN} to apply the default
1405 @defun pretty_printer.to_string (self)
1406 @value{GDBN} will call this method to display the string
1407 representation of the value passed to the object's constructor.
1409 When printing from the CLI, if the @code{to_string} method exists,
1410 then @value{GDBN} will prepend its result to the values returned by
1411 @code{children}. Exactly how this formatting is done is dependent on
1412 the display hint, and may change as more hints are added. Also,
1413 depending on the print settings (@pxref{Print Settings}), the CLI may
1414 print just the result of @code{to_string} in a stack trace, omitting
1415 the result of @code{children}.
1417 If this method returns a string, it is printed verbatim.
1419 Otherwise, if this method returns an instance of @code{gdb.Value},
1420 then @value{GDBN} prints this value. This may result in a call to
1421 another pretty-printer.
1423 If instead the method returns a Python value which is convertible to a
1424 @code{gdb.Value}, then @value{GDBN} performs the conversion and prints
1425 the resulting value. Again, this may result in a call to another
1426 pretty-printer. Python scalars (integers, floats, and booleans) and
1427 strings are convertible to @code{gdb.Value}; other types are not.
1429 Finally, if this method returns @code{None} then no further operations
1430 are peformed in this method and nothing is printed.
1432 If the result is not one of these types, an exception is raised.
1435 @value{GDBN} provides a function which can be used to look up the
1436 default pretty-printer for a @code{gdb.Value}:
1438 @findex gdb.default_visualizer
1439 @defun gdb.default_visualizer (value)
1440 This function takes a @code{gdb.Value} object as an argument. If a
1441 pretty-printer for this value exists, then it is returned. If no such
1442 printer exists, then this returns @code{None}.
1445 @node Selecting Pretty-Printers
1446 @subsubsection Selecting Pretty-Printers
1447 @cindex selecting python pretty-printers
1449 @value{GDBN} provides several ways to register a pretty-printer:
1450 globally, per program space, and per objfile. When choosing how to
1451 register your pretty-printer, a good rule is to register it with the
1452 smallest scope possible: that is prefer a specific objfile first, then
1453 a program space, and only register a printer globally as a last
1456 @findex gdb.pretty_printers
1457 @defvar gdb.pretty_printers
1458 The Python list @code{gdb.pretty_printers} contains an array of
1459 functions or callable objects that have been registered via addition
1460 as a pretty-printer. Printers in this list are called @code{global}
1461 printers, they're available when debugging all inferiors.
1464 Each @code{gdb.Progspace} contains a @code{pretty_printers} attribute.
1465 Each @code{gdb.Objfile} also contains a @code{pretty_printers}
1468 Each function on these lists is passed a single @code{gdb.Value}
1469 argument and should return a pretty-printer object conforming to the
1470 interface definition above (@pxref{Pretty Printing API}). If a function
1471 cannot create a pretty-printer for the value, it should return
1474 @value{GDBN} first checks the @code{pretty_printers} attribute of each
1475 @code{gdb.Objfile} in the current program space and iteratively calls
1476 each enabled lookup routine in the list for that @code{gdb.Objfile}
1477 until it receives a pretty-printer object.
1478 If no pretty-printer is found in the objfile lists, @value{GDBN} then
1479 searches the pretty-printer list of the current program space,
1480 calling each enabled function until an object is returned.
1481 After these lists have been exhausted, it tries the global
1482 @code{gdb.pretty_printers} list, again calling each enabled function until an
1485 The order in which the objfiles are searched is not specified. For a
1486 given list, functions are always invoked from the head of the list,
1487 and iterated over sequentially until the end of the list, or a printer
1490 For various reasons a pretty-printer may not work.
1491 For example, the underlying data structure may have changed and
1492 the pretty-printer is out of date.
1494 The consequences of a broken pretty-printer are severe enough that
1495 @value{GDBN} provides support for enabling and disabling individual
1496 printers. For example, if @code{print frame-arguments} is on,
1497 a backtrace can become highly illegible if any argument is printed
1498 with a broken printer.
1500 Pretty-printers are enabled and disabled by attaching an @code{enabled}
1501 attribute to the registered function or callable object. If this attribute
1502 is present and its value is @code{False}, the printer is disabled, otherwise
1503 the printer is enabled.
1505 @node Writing a Pretty-Printer
1506 @subsubsection Writing a Pretty-Printer
1507 @cindex writing a pretty-printer
1509 A pretty-printer consists of two parts: a lookup function to detect
1510 if the type is supported, and the printer itself.
1512 Here is an example showing how a @code{std::string} printer might be
1513 written. @xref{Pretty Printing API}, for details on the API this class
1517 class StdStringPrinter(object):
1518 "Print a std::string"
1520 def __init__(self, val):
1523 def to_string(self):
1524 return self.val['_M_dataplus']['_M_p']
1526 def display_hint(self):
1530 And here is an example showing how a lookup function for the printer
1531 example above might be written.
1534 def str_lookup_function(val):
1535 lookup_tag = val.type.tag
1536 if lookup_tag == None:
1538 regex = re.compile("^std::basic_string<char,.*>$")
1539 if regex.match(lookup_tag):
1540 return StdStringPrinter(val)
1544 The example lookup function extracts the value's type, and attempts to
1545 match it to a type that it can pretty-print. If it is a type the
1546 printer can pretty-print, it will return a printer object. If not, it
1547 returns @code{None}.
1549 We recommend that you put your core pretty-printers into a Python
1550 package. If your pretty-printers are for use with a library, we
1551 further recommend embedding a version number into the package name.
1552 This practice will enable @value{GDBN} to load multiple versions of
1553 your pretty-printers at the same time, because they will have
1556 You should write auto-loaded code (@pxref{Python Auto-loading}) such that it
1557 can be evaluated multiple times without changing its meaning. An
1558 ideal auto-load file will consist solely of @code{import}s of your
1559 printer modules, followed by a call to a register pretty-printers with
1560 the current objfile.
1562 Taken as a whole, this approach will scale nicely to multiple
1563 inferiors, each potentially using a different library version.
1564 Embedding a version number in the Python package name will ensure that
1565 @value{GDBN} is able to load both sets of printers simultaneously.
1566 Then, because the search for pretty-printers is done by objfile, and
1567 because your auto-loaded code took care to register your library's
1568 printers with a specific objfile, @value{GDBN} will find the correct
1569 printers for the specific version of the library used by each
1572 To continue the @code{std::string} example (@pxref{Pretty Printing API}),
1573 this code might appear in @code{gdb.libstdcxx.v6}:
1576 def register_printers(objfile):
1577 objfile.pretty_printers.append(str_lookup_function)
1581 And then the corresponding contents of the auto-load file would be:
1584 import gdb.libstdcxx.v6
1585 gdb.libstdcxx.v6.register_printers(gdb.current_objfile())
1588 The previous example illustrates a basic pretty-printer.
1589 There are a few things that can be improved on.
1590 The printer doesn't have a name, making it hard to identify in a
1591 list of installed printers. The lookup function has a name, but
1592 lookup functions can have arbitrary, even identical, names.
1594 Second, the printer only handles one type, whereas a library typically has
1595 several types. One could install a lookup function for each desired type
1596 in the library, but one could also have a single lookup function recognize
1597 several types. The latter is the conventional way this is handled.
1598 If a pretty-printer can handle multiple data types, then its
1599 @dfn{subprinters} are the printers for the individual data types.
1601 The @code{gdb.printing} module provides a formal way of solving these
1602 problems (@pxref{gdb.printing}).
1603 Here is another example that handles multiple types.
1605 These are the types we are going to pretty-print:
1608 struct foo @{ int a, b; @};
1609 struct bar @{ struct foo x, y; @};
1612 Here are the printers:
1616 """Print a foo object."""
1618 def __init__(self, val):
1621 def to_string(self):
1622 return ("a=<" + str(self.val["a"]) +
1623 "> b=<" + str(self.val["b"]) + ">")
1626 """Print a bar object."""
1628 def __init__(self, val):
1631 def to_string(self):
1632 return ("x=<" + str(self.val["x"]) +
1633 "> y=<" + str(self.val["y"]) + ">")
1636 This example doesn't need a lookup function, that is handled by the
1637 @code{gdb.printing} module. Instead a function is provided to build up
1638 the object that handles the lookup.
1643 def build_pretty_printer():
1644 pp = gdb.printing.RegexpCollectionPrettyPrinter(
1646 pp.add_printer('foo', '^foo$', fooPrinter)
1647 pp.add_printer('bar', '^bar$', barPrinter)
1651 And here is the autoload support:
1656 gdb.printing.register_pretty_printer(
1657 gdb.current_objfile(),
1658 my_library.build_pretty_printer())
1661 Finally, when this printer is loaded into @value{GDBN}, here is the
1662 corresponding output of @samp{info pretty-printer}:
1665 (gdb) info pretty-printer
1672 @node Type Printing API
1673 @subsubsection Type Printing API
1674 @cindex type printing API for Python
1676 @value{GDBN} provides a way for Python code to customize type display.
1677 This is mainly useful for substituting canonical typedef names for
1680 @cindex type printer
1681 A @dfn{type printer} is just a Python object conforming to a certain
1682 protocol. A simple base class implementing the protocol is provided;
1683 see @ref{gdb.types}. A type printer must supply at least:
1685 @defivar type_printer enabled
1686 A boolean which is True if the printer is enabled, and False
1687 otherwise. This is manipulated by the @code{enable type-printer}
1688 and @code{disable type-printer} commands.
1691 @defivar type_printer name
1692 The name of the type printer. This must be a string. This is used by
1693 the @code{enable type-printer} and @code{disable type-printer}
1697 @defmethod type_printer instantiate (self)
1698 This is called by @value{GDBN} at the start of type-printing. It is
1699 only called if the type printer is enabled. This method must return a
1700 new object that supplies a @code{recognize} method, as described below.
1704 When displaying a type, say via the @code{ptype} command, @value{GDBN}
1705 will compute a list of type recognizers. This is done by iterating
1706 first over the per-objfile type printers (@pxref{Objfiles In Python}),
1707 followed by the per-progspace type printers (@pxref{Progspaces In
1708 Python}), and finally the global type printers.
1710 @value{GDBN} will call the @code{instantiate} method of each enabled
1711 type printer. If this method returns @code{None}, then the result is
1712 ignored; otherwise, it is appended to the list of recognizers.
1714 Then, when @value{GDBN} is going to display a type name, it iterates
1715 over the list of recognizers. For each one, it calls the recognition
1716 function, stopping if the function returns a non-@code{None} value.
1717 The recognition function is defined as:
1719 @defmethod type_recognizer recognize (self, type)
1720 If @var{type} is not recognized, return @code{None}. Otherwise,
1721 return a string which is to be printed as the name of @var{type}.
1722 The @var{type} argument will be an instance of @code{gdb.Type}
1723 (@pxref{Types In Python}).
1726 @value{GDBN} uses this two-pass approach so that type printers can
1727 efficiently cache information without holding on to it too long. For
1728 example, it can be convenient to look up type information in a type
1729 printer and hold it for a recognizer's lifetime; if a single pass were
1730 done then type printers would have to make use of the event system in
1731 order to avoid holding information that could become stale as the
1734 @node Frame Filter API
1735 @subsubsection Filtering Frames
1736 @cindex frame filters api
1738 Frame filters are Python objects that manipulate the visibility of a
1739 frame or frames when a backtrace (@pxref{Backtrace}) is printed by
1742 Only commands that print a backtrace, or, in the case of @sc{gdb/mi}
1743 commands (@pxref{GDB/MI}), those that return a collection of frames
1744 are affected. The commands that work with frame filters are:
1746 @code{backtrace} (@pxref{backtrace-command,, The backtrace command}),
1747 @code{-stack-list-frames}
1748 (@pxref{-stack-list-frames,, The -stack-list-frames command}),
1749 @code{-stack-list-variables} (@pxref{-stack-list-variables,, The
1750 -stack-list-variables command}), @code{-stack-list-arguments}
1751 @pxref{-stack-list-arguments,, The -stack-list-arguments command}) and
1752 @code{-stack-list-locals} (@pxref{-stack-list-locals,, The
1753 -stack-list-locals command}).
1755 A frame filter works by taking an iterator as an argument, applying
1756 actions to the contents of that iterator, and returning another
1757 iterator (or, possibly, the same iterator it was provided in the case
1758 where the filter does not perform any operations). Typically, frame
1759 filters utilize tools such as the Python's @code{itertools} module to
1760 work with and create new iterators from the source iterator.
1761 Regardless of how a filter chooses to apply actions, it must not alter
1762 the underlying @value{GDBN} frame or frames, or attempt to alter the
1763 call-stack within @value{GDBN}. This preserves data integrity within
1764 @value{GDBN}. Frame filters are executed on a priority basis and care
1765 should be taken that some frame filters may have been executed before,
1766 and that some frame filters will be executed after.
1768 An important consideration when designing frame filters, and well
1769 worth reflecting upon, is that frame filters should avoid unwinding
1770 the call stack if possible. Some stacks can run very deep, into the
1771 tens of thousands in some cases. To search every frame when a frame
1772 filter executes may be too expensive at that step. The frame filter
1773 cannot know how many frames it has to iterate over, and it may have to
1774 iterate through them all. This ends up duplicating effort as
1775 @value{GDBN} performs this iteration when it prints the frames. If
1776 the filter can defer unwinding frames until frame decorators are
1777 executed, after the last filter has executed, it should. @xref{Frame
1778 Decorator API}, for more information on decorators. Also, there are
1779 examples for both frame decorators and filters in later chapters.
1780 @xref{Writing a Frame Filter}, for more information.
1782 The Python dictionary @code{gdb.frame_filters} contains key/object
1783 pairings that comprise a frame filter. Frame filters in this
1784 dictionary are called @code{global} frame filters, and they are
1785 available when debugging all inferiors. These frame filters must
1786 register with the dictionary directly. In addition to the
1787 @code{global} dictionary, there are other dictionaries that are loaded
1788 with different inferiors via auto-loading (@pxref{Python
1789 Auto-loading}). The two other areas where frame filter dictionaries
1790 can be found are: @code{gdb.Progspace} which contains a
1791 @code{frame_filters} dictionary attribute, and each @code{gdb.Objfile}
1792 object which also contains a @code{frame_filters} dictionary
1795 When a command is executed from @value{GDBN} that is compatible with
1796 frame filters, @value{GDBN} combines the @code{global},
1797 @code{gdb.Progspace} and all @code{gdb.Objfile} dictionaries currently
1798 loaded. All of the @code{gdb.Objfile} dictionaries are combined, as
1799 several frames, and thus several object files, might be in use.
1800 @value{GDBN} then prunes any frame filter whose @code{enabled}
1801 attribute is @code{False}. This pruned list is then sorted according
1802 to the @code{priority} attribute in each filter.
1804 Once the dictionaries are combined, pruned and sorted, @value{GDBN}
1805 creates an iterator which wraps each frame in the call stack in a
1806 @code{FrameDecorator} object, and calls each filter in order. The
1807 output from the previous filter will always be the input to the next
1810 Frame filters have a mandatory interface which each frame filter must
1811 implement, defined here:
1813 @defun FrameFilter.filter (iterator)
1814 @value{GDBN} will call this method on a frame filter when it has
1815 reached the order in the priority list for that filter.
1817 For example, if there are four frame filters:
1828 The order that the frame filters will be called is:
1831 Filter3 -> Filter2 -> Filter1 -> Filter4
1834 Note that the output from @code{Filter3} is passed to the input of
1835 @code{Filter2}, and so on.
1837 This @code{filter} method is passed a Python iterator. This iterator
1838 contains a sequence of frame decorators that wrap each
1839 @code{gdb.Frame}, or a frame decorator that wraps another frame
1840 decorator. The first filter that is executed in the sequence of frame
1841 filters will receive an iterator entirely comprised of default
1842 @code{FrameDecorator} objects. However, after each frame filter is
1843 executed, the previous frame filter may have wrapped some or all of
1844 the frame decorators with their own frame decorator. As frame
1845 decorators must also conform to a mandatory interface, these
1846 decorators can be assumed to act in a uniform manner (@pxref{Frame
1849 This method must return an object conforming to the Python iterator
1850 protocol. Each item in the iterator must be an object conforming to
1851 the frame decorator interface. If a frame filter does not wish to
1852 perform any operations on this iterator, it should return that
1855 This method is not optional. If it does not exist, @value{GDBN} will
1856 raise and print an error.
1859 @defvar FrameFilter.name
1860 The @code{name} attribute must be Python string which contains the
1861 name of the filter displayed by @value{GDBN} (@pxref{Frame Filter
1862 Management}). This attribute may contain any combination of letters
1863 or numbers. Care should be taken to ensure that it is unique. This
1864 attribute is mandatory.
1867 @defvar FrameFilter.enabled
1868 The @code{enabled} attribute must be Python boolean. This attribute
1869 indicates to @value{GDBN} whether the frame filter is enabled, and
1870 should be considered when frame filters are executed. If
1871 @code{enabled} is @code{True}, then the frame filter will be executed
1872 when any of the backtrace commands detailed earlier in this chapter
1873 are executed. If @code{enabled} is @code{False}, then the frame
1874 filter will not be executed. This attribute is mandatory.
1877 @defvar FrameFilter.priority
1878 The @code{priority} attribute must be Python integer. This attribute
1879 controls the order of execution in relation to other frame filters.
1880 There are no imposed limits on the range of @code{priority} other than
1881 it must be a valid integer. The higher the @code{priority} attribute,
1882 the sooner the frame filter will be executed in relation to other
1883 frame filters. Although @code{priority} can be negative, it is
1884 recommended practice to assume zero is the lowest priority that a
1885 frame filter can be assigned. Frame filters that have the same
1886 priority are executed in unsorted order in that priority slot. This
1887 attribute is mandatory. 100 is a good default priority.
1890 @node Frame Decorator API
1891 @subsubsection Decorating Frames
1892 @cindex frame decorator api
1894 Frame decorators are sister objects to frame filters (@pxref{Frame
1895 Filter API}). Frame decorators are applied by a frame filter and can
1896 only be used in conjunction with frame filters.
1898 The purpose of a frame decorator is to customize the printed content
1899 of each @code{gdb.Frame} in commands where frame filters are executed.
1900 This concept is called decorating a frame. Frame decorators decorate
1901 a @code{gdb.Frame} with Python code contained within each API call.
1902 This separates the actual data contained in a @code{gdb.Frame} from
1903 the decorated data produced by a frame decorator. This abstraction is
1904 necessary to maintain integrity of the data contained in each
1907 Frame decorators have a mandatory interface, defined below.
1909 @value{GDBN} already contains a frame decorator called
1910 @code{FrameDecorator}. This contains substantial amounts of
1911 boilerplate code to decorate the content of a @code{gdb.Frame}. It is
1912 recommended that other frame decorators inherit and extend this
1913 object, and only to override the methods needed.
1915 @tindex gdb.FrameDecorator
1916 @code{FrameDecorator} is defined in the Python module
1917 @code{gdb.FrameDecorator}, so your code can import it like:
1919 from gdb.FrameDecorator import FrameDecorator
1922 @defun FrameDecorator.elided (self)
1924 The @code{elided} method groups frames together in a hierarchical
1925 system. An example would be an interpreter, where multiple low-level
1926 frames make up a single call in the interpreted language. In this
1927 example, the frame filter would elide the low-level frames and present
1928 a single high-level frame, representing the call in the interpreted
1929 language, to the user.
1931 The @code{elided} function must return an iterable and this iterable
1932 must contain the frames that are being elided wrapped in a suitable
1933 frame decorator. If no frames are being elided this function may
1934 return an empty iterable, or @code{None}. Elided frames are indented
1935 from normal frames in a @code{CLI} backtrace, or in the case of
1936 @code{GDB/MI}, are placed in the @code{children} field of the eliding
1939 It is the frame filter's task to also filter out the elided frames from
1940 the source iterator. This will avoid printing the frame twice.
1943 @defun FrameDecorator.function (self)
1945 This method returns the name of the function in the frame that is to
1948 This method must return a Python string describing the function, or
1951 If this function returns @code{None}, @value{GDBN} will not print any
1952 data for this field.
1955 @defun FrameDecorator.address (self)
1957 This method returns the address of the frame that is to be printed.
1959 This method must return a Python numeric integer type of sufficient
1960 size to describe the address of the frame, or @code{None}.
1962 If this function returns a @code{None}, @value{GDBN} will not print
1963 any data for this field.
1966 @defun FrameDecorator.filename (self)
1968 This method returns the filename and path associated with this frame.
1970 This method must return a Python string containing the filename and
1971 the path to the object file backing the frame, or @code{None}.
1973 If this function returns a @code{None}, @value{GDBN} will not print
1974 any data for this field.
1977 @defun FrameDecorator.line (self):
1979 This method returns the line number associated with the current
1980 position within the function addressed by this frame.
1982 This method must return a Python integer type, or @code{None}.
1984 If this function returns a @code{None}, @value{GDBN} will not print
1985 any data for this field.
1988 @defun FrameDecorator.frame_args (self)
1991 This method must return an iterable, or @code{None}. Returning an
1992 empty iterable, or @code{None} means frame arguments will not be
1993 printed for this frame. This iterable must contain objects that
1994 implement two methods, described here.
1996 This object must implement a @code{argument} method which takes a
1997 single @code{self} parameter and must return a @code{gdb.Symbol}
1998 (@pxref{Symbols In Python}), or a Python string. The object must also
1999 implement a @code{value} method which takes a single @code{self}
2000 parameter and must return a @code{gdb.Value} (@pxref{Values From
2001 Inferior}), a Python value, or @code{None}. If the @code{value}
2002 method returns @code{None}, and the @code{argument} method returns a
2003 @code{gdb.Symbol}, @value{GDBN} will look-up and print the value of
2004 the @code{gdb.Symbol} automatically.
2009 class SymValueWrapper():
2011 def __init__(self, symbol, value):
2021 class SomeFrameDecorator()
2024 def frame_args(self):
2027 block = self.inferior_frame.block()
2031 # Iterate over all symbols in a block. Only add
2032 # symbols that are arguments.
2034 if not sym.is_argument:
2036 args.append(SymValueWrapper(sym,None))
2038 # Add example synthetic argument.
2039 args.append(SymValueWrapper(``foo'', 42))
2045 @defun FrameDecorator.frame_locals (self)
2047 This method must return an iterable or @code{None}. Returning an
2048 empty iterable, or @code{None} means frame local arguments will not be
2049 printed for this frame.
2051 The object interface, the description of the various strategies for
2052 reading frame locals, and the example are largely similar to those
2053 described in the @code{frame_args} function, (@pxref{frame_args,,The
2054 frame filter frame_args function}). Below is a modified example:
2057 class SomeFrameDecorator()
2060 def frame_locals(self):
2063 block = self.inferior_frame.block()
2067 # Iterate over all symbols in a block. Add all
2068 # symbols, except arguments.
2072 vars.append(SymValueWrapper(sym,None))
2074 # Add an example of a synthetic local variable.
2075 vars.append(SymValueWrapper(``bar'', 99))
2081 @defun FrameDecorator.inferior_frame (self):
2083 This method must return the underlying @code{gdb.Frame} that this
2084 frame decorator is decorating. @value{GDBN} requires the underlying
2085 frame for internal frame information to determine how to print certain
2086 values when printing a frame.
2089 @node Writing a Frame Filter
2090 @subsubsection Writing a Frame Filter
2091 @cindex writing a frame filter
2093 There are three basic elements that a frame filter must implement: it
2094 must correctly implement the documented interface (@pxref{Frame Filter
2095 API}), it must register itself with @value{GDBN}, and finally, it must
2096 decide if it is to work on the data provided by @value{GDBN}. In all
2097 cases, whether it works on the iterator or not, each frame filter must
2098 return an iterator. A bare-bones frame filter follows the pattern in
2099 the following example.
2104 class FrameFilter():
2107 # Frame filter attribute creation.
2109 # 'name' is the name of the filter that GDB will display.
2111 # 'priority' is the priority of the filter relative to other
2114 # 'enabled' is a boolean that indicates whether this filter is
2115 # enabled and should be executed.
2121 # Register this frame filter with the global frame_filters
2123 gdb.frame_filters[self.name] = self
2125 def filter(self, frame_iter):
2126 # Just return the iterator.
2130 The frame filter in the example above implements the three
2131 requirements for all frame filters. It implements the API, self
2132 registers, and makes a decision on the iterator (in this case, it just
2133 returns the iterator untouched).
2135 The first step is attribute creation and assignment, and as shown in
2136 the comments the filter assigns the following attributes: @code{name},
2137 @code{priority} and whether the filter should be enabled with the
2138 @code{enabled} attribute.
2140 The second step is registering the frame filter with the dictionary or
2141 dictionaries that the frame filter has interest in. As shown in the
2142 comments, this filter just registers itself with the global dictionary
2143 @code{gdb.frame_filters}. As noted earlier, @code{gdb.frame_filters}
2144 is a dictionary that is initialized in the @code{gdb} module when
2145 @value{GDBN} starts. What dictionary a filter registers with is an
2146 important consideration. Generally, if a filter is specific to a set
2147 of code, it should be registered either in the @code{objfile} or
2148 @code{progspace} dictionaries as they are specific to the program
2149 currently loaded in @value{GDBN}. The global dictionary is always
2150 present in @value{GDBN} and is never unloaded. Any filters registered
2151 with the global dictionary will exist until @value{GDBN} exits. To
2152 avoid filters that may conflict, it is generally better to register
2153 frame filters against the dictionaries that more closely align with
2154 the usage of the filter currently in question. @xref{Python
2155 Auto-loading}, for further information on auto-loading Python scripts.
2157 @value{GDBN} takes a hands-off approach to frame filter registration,
2158 therefore it is the frame filter's responsibility to ensure
2159 registration has occurred, and that any exceptions are handled
2160 appropriately. In particular, you may wish to handle exceptions
2161 relating to Python dictionary key uniqueness. It is mandatory that
2162 the dictionary key is the same as frame filter's @code{name}
2163 attribute. When a user manages frame filters (@pxref{Frame Filter
2164 Management}), the names @value{GDBN} will display are those contained
2165 in the @code{name} attribute.
2167 The final step of this example is the implementation of the
2168 @code{filter} method. As shown in the example comments, we define the
2169 @code{filter} method and note that the method must take an iterator,
2170 and also must return an iterator. In this bare-bones example, the
2171 frame filter is not very useful as it just returns the iterator
2172 untouched. However this is a valid operation for frame filters that
2173 have the @code{enabled} attribute set, but decide not to operate on
2176 In the next example, the frame filter operates on all frames and
2177 utilizes a frame decorator to perform some work on the frames.
2178 @xref{Frame Decorator API}, for further information on the frame
2179 decorator interface.
2181 This example works on inlined frames. It highlights frames which are
2182 inlined by tagging them with an ``[inlined]'' tag. By applying a
2183 frame decorator to all frames with the Python @code{itertools imap}
2184 method, the example defers actions to the frame decorator. Frame
2185 decorators are only processed when @value{GDBN} prints the backtrace.
2187 This introduces a new decision making topic: whether to perform
2188 decision making operations at the filtering step, or at the printing
2189 step. In this example's approach, it does not perform any filtering
2190 decisions at the filtering step beyond mapping a frame decorator to
2191 each frame. This allows the actual decision making to be performed
2192 when each frame is printed. This is an important consideration, and
2193 well worth reflecting upon when designing a frame filter. An issue
2194 that frame filters should avoid is unwinding the stack if possible.
2195 Some stacks can run very deep, into the tens of thousands in some
2196 cases. To search every frame to determine if it is inlined ahead of
2197 time may be too expensive at the filtering step. The frame filter
2198 cannot know how many frames it has to iterate over, and it would have
2199 to iterate through them all. This ends up duplicating effort as
2200 @value{GDBN} performs this iteration when it prints the frames.
2202 In this example decision making can be deferred to the printing step.
2203 As each frame is printed, the frame decorator can examine each frame
2204 in turn when @value{GDBN} iterates. From a performance viewpoint,
2205 this is the most appropriate decision to make as it avoids duplicating
2206 the effort that the printing step would undertake anyway. Also, if
2207 there are many frame filters unwinding the stack during filtering, it
2208 can substantially delay the printing of the backtrace which will
2209 result in large memory usage, and a poor user experience.
2212 class InlineFilter():
2215 self.name = "InlinedFrameFilter"
2218 gdb.frame_filters[self.name] = self
2220 def filter(self, frame_iter):
2221 frame_iter = itertools.imap(InlinedFrameDecorator,
2226 This frame filter is somewhat similar to the earlier example, except
2227 that the @code{filter} method applies a frame decorator object called
2228 @code{InlinedFrameDecorator} to each element in the iterator. The
2229 @code{imap} Python method is light-weight. It does not proactively
2230 iterate over the iterator, but rather creates a new iterator which
2231 wraps the existing one.
2233 Below is the frame decorator for this example.
2236 class InlinedFrameDecorator(FrameDecorator):
2238 def __init__(self, fobj):
2239 super(InlinedFrameDecorator, self).__init__(fobj)
2242 frame = fobj.inferior_frame()
2243 name = str(frame.name())
2245 if frame.type() == gdb.INLINE_FRAME:
2246 name = name + " [inlined]"
2251 This frame decorator only defines and overrides the @code{function}
2252 method. It lets the supplied @code{FrameDecorator}, which is shipped
2253 with @value{GDBN}, perform the other work associated with printing
2256 The combination of these two objects create this output from a
2260 #0 0x004004e0 in bar () at inline.c:11
2261 #1 0x00400566 in max [inlined] (b=6, a=12) at inline.c:21
2262 #2 0x00400566 in main () at inline.c:31
2265 So in the case of this example, a frame decorator is applied to all
2266 frames, regardless of whether they may be inlined or not. As
2267 @value{GDBN} iterates over the iterator produced by the frame filters,
2268 @value{GDBN} executes each frame decorator which then makes a decision
2269 on what to print in the @code{function} callback. Using a strategy
2270 like this is a way to defer decisions on the frame content to printing
2273 @subheading Eliding Frames
2275 It might be that the above example is not desirable for representing
2276 inlined frames, and a hierarchical approach may be preferred. If we
2277 want to hierarchically represent frames, the @code{elided} frame
2278 decorator interface might be preferable.
2280 This example approaches the issue with the @code{elided} method. This
2281 example is quite long, but very simplistic. It is out-of-scope for
2282 this section to write a complete example that comprehensively covers
2283 all approaches of finding and printing inlined frames. However, this
2284 example illustrates the approach an author might use.
2286 This example comprises of three sections.
2289 class InlineFrameFilter():
2292 self.name = "InlinedFrameFilter"
2295 gdb.frame_filters[self.name] = self
2297 def filter(self, frame_iter):
2298 return ElidingInlineIterator(frame_iter)
2301 This frame filter is very similar to the other examples. The only
2302 difference is this frame filter is wrapping the iterator provided to
2303 it (@code{frame_iter}) with a custom iterator called
2304 @code{ElidingInlineIterator}. This again defers actions to when
2305 @value{GDBN} prints the backtrace, as the iterator is not traversed
2308 The iterator for this example is as follows. It is in this section of
2309 the example where decisions are made on the content of the backtrace.
2312 class ElidingInlineIterator:
2313 def __init__(self, ii):
2314 self.input_iterator = ii
2320 frame = next(self.input_iterator)
2322 if frame.inferior_frame().type() != gdb.INLINE_FRAME:
2326 eliding_frame = next(self.input_iterator)
2327 except StopIteration:
2329 return ElidingFrameDecorator(eliding_frame, [frame])
2332 This iterator implements the Python iterator protocol. When the
2333 @code{next} function is called (when @value{GDBN} prints each frame),
2334 the iterator checks if this frame decorator, @code{frame}, is wrapping
2335 an inlined frame. If it is not, it returns the existing frame decorator
2336 untouched. If it is wrapping an inlined frame, it assumes that the
2337 inlined frame was contained within the next oldest frame,
2338 @code{eliding_frame}, which it fetches. It then creates and returns a
2339 frame decorator, @code{ElidingFrameDecorator}, which contains both the
2340 elided frame, and the eliding frame.
2343 class ElidingInlineDecorator(FrameDecorator):
2345 def __init__(self, frame, elided_frames):
2346 super(ElidingInlineDecorator, self).__init__(frame)
2348 self.elided_frames = elided_frames
2351 return iter(self.elided_frames)
2354 This frame decorator overrides one function and returns the inlined
2355 frame in the @code{elided} method. As before it lets
2356 @code{FrameDecorator} do the rest of the work involved in printing
2357 this frame. This produces the following output.
2360 #0 0x004004e0 in bar () at inline.c:11
2361 #2 0x00400529 in main () at inline.c:25
2362 #1 0x00400529 in max (b=6, a=12) at inline.c:15
2365 In that output, @code{max} which has been inlined into @code{main} is
2366 printed hierarchically. Another approach would be to combine the
2367 @code{function} method, and the @code{elided} method to both print a
2368 marker in the inlined frame, and also show the hierarchical
2371 @node Unwinding Frames in Python
2372 @subsubsection Unwinding Frames in Python
2373 @cindex unwinding frames in Python
2375 In @value{GDBN} terminology ``unwinding'' is the process of finding
2376 the previous frame (that is, caller's) from the current one. An
2377 unwinder has three methods. The first one checks if it can handle
2378 given frame (``sniff'' it). For the frames it can sniff an unwinder
2379 provides two additional methods: it can return frame's ID, and it can
2380 fetch registers from the previous frame. A running @value{GDBN}
2381 mantains a list of the unwinders and calls each unwinder's sniffer in
2382 turn until it finds the one that recognizes the current frame. There
2383 is an API to register an unwinder.
2385 The unwinders that come with @value{GDBN} handle standard frames.
2386 However, mixed language applications (for example, an application
2387 running Java Virtual Machine) sometimes use frame layouts that cannot
2388 be handled by the @value{GDBN} unwinders. You can write Python code
2389 that can handle such custom frames.
2391 You implement a frame unwinder in Python as a class with which has two
2392 attributes, @code{name} and @code{enabled}, with obvious meanings, and
2393 a single method @code{__call__}, which examines a given frame and
2394 returns an object (an instance of @code{gdb.UnwindInfo class)}
2395 describing it. If an unwinder does not recognize a frame, it should
2396 return @code{None}. The code in @value{GDBN} that enables writing
2397 unwinders in Python uses this object to return frame's ID and previous
2398 frame registers when @value{GDBN} core asks for them.
2400 An unwinder should do as little work as possible. Some otherwise
2401 innocuous operations can cause problems (even crashes, as this code is
2402 not not well-hardened yet). For example, making an inferior call from
2403 an unwinder is unadvisable, as an inferior call will reset
2404 @value{GDBN}'s stack unwinding process, potentially causing re-entrant
2407 @subheading Unwinder Input
2409 An object passed to an unwinder (a @code{gdb.PendingFrame} instance)
2410 provides a method to read frame's registers:
2412 @defun PendingFrame.read_register (reg)
2413 This method returns the contents of the register @var{reg} in the
2414 frame as a @code{gdb.Value} object. @var{reg} can be either a
2415 register number or a register name; the values are platform-specific.
2416 They are usually found in the corresponding
2417 @file{@var{platform}-tdep.h} file in the @value{GDBN} source tree. If
2418 @var{reg} does not name a register for the current architecture, this
2419 method will throw an exception.
2421 Note that this method will always return a @code{gdb.Value} for a
2422 valid register name. This does not mean that the value will be valid.
2423 For example, you may request a register that an earlier unwinder could
2424 not unwind---the value will be unavailable. Instead, the
2425 @code{gdb.Value} returned from this method will be lazy; that is, its
2426 underlying bits will not be fetched until it is first used. So,
2427 attempting to use such a value will cause an exception at the point of
2430 The type of the returned @code{gdb.Value} depends on the register and
2431 the architecture. It is common for registers to have a scalar type,
2432 like @code{long long}; but many other types are possible, such as
2433 pointer, pointer-to-function, floating point or vector types.
2436 It also provides a factory method to create a @code{gdb.UnwindInfo}
2437 instance to be returned to @value{GDBN}:
2439 @defun PendingFrame.create_unwind_info (frame_id)
2440 Returns a new @code{gdb.UnwindInfo} instance identified by given
2441 @var{frame_id}. The argument is used to build @value{GDBN}'s frame ID
2442 using one of functions provided by @value{GDBN}. @var{frame_id}'s attributes
2443 determine which function will be used, as follows:
2447 The frame is identified by the given stack address and PC. The stack
2448 address must be chosen so that it is constant throughout the lifetime
2449 of the frame, so a typical choice is the value of the stack pointer at
2450 the start of the function---in the DWARF standard, this would be the
2451 ``Call Frame Address''.
2453 This is the most common case by far. The other cases are documented
2454 for completeness but are only useful in specialized situations.
2456 @item sp, pc, special
2457 The frame is identified by the stack address, the PC, and a
2458 ``special'' address. The special address is used on architectures
2459 that can have frames that do not change the stack, but which are still
2460 distinct, for example the IA-64, which has a second stack for
2461 registers. Both @var{sp} and @var{special} must be constant
2462 throughout the lifetime of the frame.
2465 The frame is identified by the stack address only. Any other stack
2466 frame with a matching @var{sp} will be considered to match this frame.
2467 Inside gdb, this is called a ``wild frame''. You will never need
2471 Each attribute value should be an instance of @code{gdb.Value}.
2475 @subheading Unwinder Output: UnwindInfo
2477 Use @code{PendingFrame.create_unwind_info} method described above to
2478 create a @code{gdb.UnwindInfo} instance. Use the following method to
2479 specify caller registers that have been saved in this frame:
2481 @defun gdb.UnwindInfo.add_saved_register (reg, value)
2482 @var{reg} identifies the register. It can be a number or a name, just
2483 as for the @code{PendingFrame.read_register} method above.
2484 @var{value} is a register value (a @code{gdb.Value} object).
2487 @subheading Unwinder Skeleton Code
2489 @value{GDBN} comes with the module containing the base @code{Unwinder}
2490 class. Derive your unwinder class from it and structure the code as
2494 from gdb.unwinders import Unwinder
2496 class FrameId(object):
2497 def __init__(self, sp, pc):
2502 class MyUnwinder(Unwinder):
2504 supe(MyUnwinder, self).__init___(<expects unwinder name argument>)
2506 def __call__(pending_frame):
2507 if not <we recognize frame>:
2509 # Create UnwindInfo. Usually the frame is identified by the stack
2510 # pointer and the program counter.
2511 sp = pending_frame.read_register(<SP number>)
2512 pc = pending_frame.read_register(<PC number>)
2513 unwind_info = pending_frame.create_unwind_info(FrameId(sp, pc))
2515 # Find the values of the registers in the caller's frame and
2516 # save them in the result:
2517 unwind_info.add_saved_register(<register>, <value>)
2520 # Return the result:
2525 @subheading Registering a Unwinder
2527 An object file, a program space, and the @value{GDBN} proper can have
2528 unwinders registered with it.
2530 The @code{gdb.unwinders} module provides the function to register a
2533 @defun gdb.unwinder.register_unwinder (locus, unwinder, replace=False)
2534 @var{locus} is specifies an object file or a program space to which
2535 @var{unwinder} is added. Passing @code{None} or @code{gdb} adds
2536 @var{unwinder} to the @value{GDBN}'s global unwinder list. The newly
2537 added @var{unwinder} will be called before any other unwinder from the
2538 same locus. Two unwinders in the same locus cannot have the same
2539 name. An attempt to add a unwinder with already existing name raises
2540 an exception unless @var{replace} is @code{True}, in which case the
2541 old unwinder is deleted.
2544 @subheading Unwinder Precedence
2546 @value{GDBN} first calls the unwinders from all the object files in no
2547 particular order, then the unwinders from the current program space,
2548 and finally the unwinders from @value{GDBN}.
2550 @node Xmethods In Python
2551 @subsubsection Xmethods In Python
2552 @cindex xmethods in Python
2554 @dfn{Xmethods} are additional methods or replacements for existing
2555 methods of a C@t{++} class. This feature is useful for those cases
2556 where a method defined in C@t{++} source code could be inlined or
2557 optimized out by the compiler, making it unavailable to @value{GDBN}.
2558 For such cases, one can define an xmethod to serve as a replacement
2559 for the method defined in the C@t{++} source code. @value{GDBN} will
2560 then invoke the xmethod, instead of the C@t{++} method, to
2561 evaluate expressions. One can also use xmethods when debugging
2562 with core files. Moreover, when debugging live programs, invoking an
2563 xmethod need not involve running the inferior (which can potentially
2564 perturb its state). Hence, even if the C@t{++} method is available, it
2565 is better to use its replacement xmethod if one is defined.
2567 The xmethods feature in Python is available via the concepts of an
2568 @dfn{xmethod matcher} and an @dfn{xmethod worker}. To
2569 implement an xmethod, one has to implement a matcher and a
2570 corresponding worker for it (more than one worker can be
2571 implemented, each catering to a different overloaded instance of the
2572 method). Internally, @value{GDBN} invokes the @code{match} method of a
2573 matcher to match the class type and method name. On a match, the
2574 @code{match} method returns a list of matching @emph{worker} objects.
2575 Each worker object typically corresponds to an overloaded instance of
2576 the xmethod. They implement a @code{get_arg_types} method which
2577 returns a sequence of types corresponding to the arguments the xmethod
2578 requires. @value{GDBN} uses this sequence of types to perform
2579 overload resolution and picks a winning xmethod worker. A winner
2580 is also selected from among the methods @value{GDBN} finds in the
2581 C@t{++} source code. Next, the winning xmethod worker and the
2582 winning C@t{++} method are compared to select an overall winner. In
2583 case of a tie between a xmethod worker and a C@t{++} method, the
2584 xmethod worker is selected as the winner. That is, if a winning
2585 xmethod worker is found to be equivalent to the winning C@t{++}
2586 method, then the xmethod worker is treated as a replacement for
2587 the C@t{++} method. @value{GDBN} uses the overall winner to invoke the
2588 method. If the winning xmethod worker is the overall winner, then
2589 the corresponding xmethod is invoked via the @code{__call__} method
2590 of the worker object.
2592 If one wants to implement an xmethod as a replacement for an
2593 existing C@t{++} method, then they have to implement an equivalent
2594 xmethod which has exactly the same name and takes arguments of
2595 exactly the same type as the C@t{++} method. If the user wants to
2596 invoke the C@t{++} method even though a replacement xmethod is
2597 available for that method, then they can disable the xmethod.
2599 @xref{Xmethod API}, for API to implement xmethods in Python.
2600 @xref{Writing an Xmethod}, for implementing xmethods in Python.
2603 @subsubsection Xmethod API
2606 The @value{GDBN} Python API provides classes, interfaces and functions
2607 to implement, register and manipulate xmethods.
2608 @xref{Xmethods In Python}.
2610 An xmethod matcher should be an instance of a class derived from
2611 @code{XMethodMatcher} defined in the module @code{gdb.xmethod}, or an
2612 object with similar interface and attributes. An instance of
2613 @code{XMethodMatcher} has the following attributes:
2616 The name of the matcher.
2620 A boolean value indicating whether the matcher is enabled or disabled.
2624 A list of named methods managed by the matcher. Each object in the list
2625 is an instance of the class @code{XMethod} defined in the module
2626 @code{gdb.xmethod}, or any object with the following attributes:
2631 Name of the xmethod which should be unique for each xmethod
2632 managed by the matcher.
2635 A boolean value indicating whether the xmethod is enabled or
2640 The class @code{XMethod} is a convenience class with same
2641 attributes as above along with the following constructor:
2643 @defun XMethod.__init__ (self, name)
2644 Constructs an enabled xmethod with name @var{name}.
2649 The @code{XMethodMatcher} class has the following methods:
2651 @defun XMethodMatcher.__init__ (self, name)
2652 Constructs an enabled xmethod matcher with name @var{name}. The
2653 @code{methods} attribute is initialized to @code{None}.
2656 @defun XMethodMatcher.match (self, class_type, method_name)
2657 Derived classes should override this method. It should return a
2658 xmethod worker object (or a sequence of xmethod worker
2659 objects) matching the @var{class_type} and @var{method_name}.
2660 @var{class_type} is a @code{gdb.Type} object, and @var{method_name}
2661 is a string value. If the matcher manages named methods as listed in
2662 its @code{methods} attribute, then only those worker objects whose
2663 corresponding entries in the @code{methods} list are enabled should be
2667 An xmethod worker should be an instance of a class derived from
2668 @code{XMethodWorker} defined in the module @code{gdb.xmethod},
2669 or support the following interface:
2671 @defun XMethodWorker.get_arg_types (self)
2672 This method returns a sequence of @code{gdb.Type} objects corresponding
2673 to the arguments that the xmethod takes. It can return an empty
2674 sequence or @code{None} if the xmethod does not take any arguments.
2675 If the xmethod takes a single argument, then a single
2676 @code{gdb.Type} object corresponding to it can be returned.
2679 @defun XMethodWorker.get_result_type (self, *args)
2680 This method returns a @code{gdb.Type} object representing the type
2681 of the result of invoking this xmethod.
2682 The @var{args} argument is the same tuple of arguments that would be
2683 passed to the @code{__call__} method of this worker.
2686 @defun XMethodWorker.__call__ (self, *args)
2687 This is the method which does the @emph{work} of the xmethod. The
2688 @var{args} arguments is the tuple of arguments to the xmethod. Each
2689 element in this tuple is a gdb.Value object. The first element is
2690 always the @code{this} pointer value.
2693 For @value{GDBN} to lookup xmethods, the xmethod matchers
2694 should be registered using the following function defined in the module
2697 @defun register_xmethod_matcher (locus, matcher, replace=False)
2698 The @code{matcher} is registered with @code{locus}, replacing an
2699 existing matcher with the same name as @code{matcher} if
2700 @code{replace} is @code{True}. @code{locus} can be a
2701 @code{gdb.Objfile} object (@pxref{Objfiles In Python}), or a
2702 @code{gdb.Progspace} object (@pxref{Progspaces In Python}), or
2703 @code{None}. If it is @code{None}, then @code{matcher} is registered
2707 @node Writing an Xmethod
2708 @subsubsection Writing an Xmethod
2709 @cindex writing xmethods in Python
2711 Implementing xmethods in Python will require implementing xmethod
2712 matchers and xmethod workers (@pxref{Xmethods In Python}). Consider
2713 the following C@t{++} class:
2719 MyClass (int a) : a_(a) @{ @}
2721 int geta (void) @{ return a_; @}
2722 int operator+ (int b);
2729 MyClass::operator+ (int b)
2736 Let us define two xmethods for the class @code{MyClass}, one
2737 replacing the method @code{geta}, and another adding an overloaded
2738 flavor of @code{operator+} which takes a @code{MyClass} argument (the
2739 C@t{++} code above already has an overloaded @code{operator+}
2740 which takes an @code{int} argument). The xmethod matcher can be
2744 class MyClass_geta(gdb.xmethod.XMethod):
2746 gdb.xmethod.XMethod.__init__(self, 'geta')
2748 def get_worker(self, method_name):
2749 if method_name == 'geta':
2750 return MyClassWorker_geta()
2753 class MyClass_sum(gdb.xmethod.XMethod):
2755 gdb.xmethod.XMethod.__init__(self, 'sum')
2757 def get_worker(self, method_name):
2758 if method_name == 'operator+':
2759 return MyClassWorker_plus()
2762 class MyClassMatcher(gdb.xmethod.XMethodMatcher):
2764 gdb.xmethod.XMethodMatcher.__init__(self, 'MyClassMatcher')
2765 # List of methods 'managed' by this matcher
2766 self.methods = [MyClass_geta(), MyClass_sum()]
2768 def match(self, class_type, method_name):
2769 if class_type.tag != 'MyClass':
2772 for method in self.methods:
2774 worker = method.get_worker(method_name)
2776 workers.append(worker)
2782 Notice that the @code{match} method of @code{MyClassMatcher} returns
2783 a worker object of type @code{MyClassWorker_geta} for the @code{geta}
2784 method, and a worker object of type @code{MyClassWorker_plus} for the
2785 @code{operator+} method. This is done indirectly via helper classes
2786 derived from @code{gdb.xmethod.XMethod}. One does not need to use the
2787 @code{methods} attribute in a matcher as it is optional. However, if a
2788 matcher manages more than one xmethod, it is a good practice to list the
2789 xmethods in the @code{methods} attribute of the matcher. This will then
2790 facilitate enabling and disabling individual xmethods via the
2791 @code{enable/disable} commands. Notice also that a worker object is
2792 returned only if the corresponding entry in the @code{methods} attribute
2793 of the matcher is enabled.
2795 The implementation of the worker classes returned by the matcher setup
2796 above is as follows:
2799 class MyClassWorker_geta(gdb.xmethod.XMethodWorker):
2800 def get_arg_types(self):
2803 def get_result_type(self, obj):
2804 return gdb.lookup_type('int')
2806 def __call__(self, obj):
2810 class MyClassWorker_plus(gdb.xmethod.XMethodWorker):
2811 def get_arg_types(self):
2812 return gdb.lookup_type('MyClass')
2814 def get_result_type(self, obj):
2815 return gdb.lookup_type('int')
2817 def __call__(self, obj, other):
2818 return obj['a_'] + other['a_']
2821 For @value{GDBN} to actually lookup a xmethod, it has to be
2822 registered with it. The matcher defined above is registered with
2823 @value{GDBN} globally as follows:
2826 gdb.xmethod.register_xmethod_matcher(None, MyClassMatcher())
2829 If an object @code{obj} of type @code{MyClass} is initialized in C@t{++}
2837 then, after loading the Python script defining the xmethod matchers
2838 and workers into @code{GDBN}, invoking the method @code{geta} or using
2839 the operator @code{+} on @code{obj} will invoke the xmethods
2850 Consider another example with a C++ template class:
2857 MyTemplate () : dsize_(10), data_ (new T [10]) @{ @}
2858 ~MyTemplate () @{ delete [] data_; @}
2860 int footprint (void)
2862 return sizeof (T) * dsize_ + sizeof (MyTemplate<T>);
2871 Let us implement an xmethod for the above class which serves as a
2872 replacement for the @code{footprint} method. The full code listing
2873 of the xmethod workers and xmethod matchers is as follows:
2876 class MyTemplateWorker_footprint(gdb.xmethod.XMethodWorker):
2877 def __init__(self, class_type):
2878 self.class_type = class_type
2880 def get_arg_types(self):
2883 def get_result_type(self):
2884 return gdb.lookup_type('int')
2886 def __call__(self, obj):
2887 return (self.class_type.sizeof +
2889 self.class_type.template_argument(0).sizeof)
2892 class MyTemplateMatcher_footprint(gdb.xmethod.XMethodMatcher):
2894 gdb.xmethod.XMethodMatcher.__init__(self, 'MyTemplateMatcher')
2896 def match(self, class_type, method_name):
2897 if (re.match('MyTemplate<[ \t\n]*[_a-zA-Z][ _a-zA-Z0-9]*>',
2899 method_name == 'footprint'):
2900 return MyTemplateWorker_footprint(class_type)
2903 Notice that, in this example, we have not used the @code{methods}
2904 attribute of the matcher as the matcher manages only one xmethod. The
2905 user can enable/disable this xmethod by enabling/disabling the matcher
2908 @node Inferiors In Python
2909 @subsubsection Inferiors In Python
2910 @cindex inferiors in Python
2912 @findex gdb.Inferior
2913 Programs which are being run under @value{GDBN} are called inferiors
2914 (@pxref{Inferiors and Programs}). Python scripts can access
2915 information about and manipulate inferiors controlled by @value{GDBN}
2916 via objects of the @code{gdb.Inferior} class.
2918 The following inferior-related functions are available in the @code{gdb}
2921 @defun gdb.inferiors ()
2922 Return a tuple containing all inferior objects.
2925 @defun gdb.selected_inferior ()
2926 Return an object representing the current inferior.
2929 A @code{gdb.Inferior} object has the following attributes:
2931 @defvar Inferior.num
2932 ID of inferior, as assigned by GDB.
2935 @defvar Inferior.pid
2936 Process ID of the inferior, as assigned by the underlying operating
2940 @defvar Inferior.was_attached
2941 Boolean signaling whether the inferior was created using `attach', or
2942 started by @value{GDBN} itself.
2945 @defvar Inferior.progspace
2946 The inferior's program space. @xref{Progspaces In Python}.
2949 A @code{gdb.Inferior} object has the following methods:
2951 @defun Inferior.is_valid ()
2952 Returns @code{True} if the @code{gdb.Inferior} object is valid,
2953 @code{False} if not. A @code{gdb.Inferior} object will become invalid
2954 if the inferior no longer exists within @value{GDBN}. All other
2955 @code{gdb.Inferior} methods will throw an exception if it is invalid
2956 at the time the method is called.
2959 @defun Inferior.threads ()
2960 This method returns a tuple holding all the threads which are valid
2961 when it is called. If there are no valid threads, the method will
2962 return an empty tuple.
2965 @defun Inferior.architecture ()
2966 Return the @code{gdb.Architecture} (@pxref{Architectures In Python})
2967 for this inferior. This represents the architecture of the inferior
2968 as a whole. Some platforms can have multiple architectures in a
2969 single address space, so this may not match the architecture of a
2970 particular frame (@pxref{Frames In Python}).
2973 @findex Inferior.read_memory
2974 @defun Inferior.read_memory (address, length)
2975 Read @var{length} addressable memory units from the inferior, starting at
2976 @var{address}. Returns a buffer object, which behaves much like an array
2977 or a string. It can be modified and given to the
2978 @code{Inferior.write_memory} function. In Python 3, the return
2979 value is a @code{memoryview} object.
2982 @findex Inferior.write_memory
2983 @defun Inferior.write_memory (address, buffer @r{[}, length@r{]})
2984 Write the contents of @var{buffer} to the inferior, starting at
2985 @var{address}. The @var{buffer} parameter must be a Python object
2986 which supports the buffer protocol, i.e., a string, an array or the
2987 object returned from @code{Inferior.read_memory}. If given, @var{length}
2988 determines the number of addressable memory units from @var{buffer} to be
2992 @findex gdb.search_memory
2993 @defun Inferior.search_memory (address, length, pattern)
2994 Search a region of the inferior memory starting at @var{address} with
2995 the given @var{length} using the search pattern supplied in
2996 @var{pattern}. The @var{pattern} parameter must be a Python object
2997 which supports the buffer protocol, i.e., a string, an array or the
2998 object returned from @code{gdb.read_memory}. Returns a Python @code{Long}
2999 containing the address where the pattern was found, or @code{None} if
3000 the pattern could not be found.
3003 @findex Inferior.thread_from_thread_handle
3004 @defun Inferior.thread_from_thread_handle (thread_handle)
3005 Return the thread object corresponding to @var{thread_handle}, a thread
3006 library specific data structure such as @code{pthread_t} for pthreads
3007 library implementations.
3010 @node Events In Python
3011 @subsubsection Events In Python
3012 @cindex inferior events in Python
3014 @value{GDBN} provides a general event facility so that Python code can be
3015 notified of various state changes, particularly changes that occur in
3018 An @dfn{event} is just an object that describes some state change. The
3019 type of the object and its attributes will vary depending on the details
3020 of the change. All the existing events are described below.
3022 In order to be notified of an event, you must register an event handler
3023 with an @dfn{event registry}. An event registry is an object in the
3024 @code{gdb.events} module which dispatches particular events. A registry
3025 provides methods to register and unregister event handlers:
3027 @defun EventRegistry.connect (object)
3028 Add the given callable @var{object} to the registry. This object will be
3029 called when an event corresponding to this registry occurs.
3032 @defun EventRegistry.disconnect (object)
3033 Remove the given @var{object} from the registry. Once removed, the object
3034 will no longer receive notifications of events.
3040 def exit_handler (event):
3041 print "event type: exit"
3042 print "exit code: %d" % (event.exit_code)
3044 gdb.events.exited.connect (exit_handler)
3047 In the above example we connect our handler @code{exit_handler} to the
3048 registry @code{events.exited}. Once connected, @code{exit_handler} gets
3049 called when the inferior exits. The argument @dfn{event} in this example is
3050 of type @code{gdb.ExitedEvent}. As you can see in the example the
3051 @code{ExitedEvent} object has an attribute which indicates the exit code of
3054 The following is a listing of the event registries that are available and
3055 details of the events they emit:
3060 Emits @code{gdb.ThreadEvent}.
3062 Some events can be thread specific when @value{GDBN} is running in non-stop
3063 mode. When represented in Python, these events all extend
3064 @code{gdb.ThreadEvent}. Note, this event is not emitted directly; instead,
3065 events which are emitted by this or other modules might extend this event.
3066 Examples of these events are @code{gdb.BreakpointEvent} and
3067 @code{gdb.ContinueEvent}.
3069 @defvar ThreadEvent.inferior_thread
3070 In non-stop mode this attribute will be set to the specific thread which was
3071 involved in the emitted event. Otherwise, it will be set to @code{None}.
3074 Emits @code{gdb.ContinueEvent} which extends @code{gdb.ThreadEvent}.
3076 This event indicates that the inferior has been continued after a stop. For
3077 inherited attribute refer to @code{gdb.ThreadEvent} above.
3080 Emits @code{events.ExitedEvent} which indicates that the inferior has exited.
3081 @code{events.ExitedEvent} has two attributes:
3082 @defvar ExitedEvent.exit_code
3083 An integer representing the exit code, if available, which the inferior
3084 has returned. (The exit code could be unavailable if, for example,
3085 @value{GDBN} detaches from the inferior.) If the exit code is unavailable,
3086 the attribute does not exist.
3088 @defvar ExitedEvent.inferior
3089 A reference to the inferior which triggered the @code{exited} event.
3093 Emits @code{gdb.StopEvent} which extends @code{gdb.ThreadEvent}.
3095 Indicates that the inferior has stopped. All events emitted by this registry
3096 extend StopEvent. As a child of @code{gdb.ThreadEvent}, @code{gdb.StopEvent}
3097 will indicate the stopped thread when @value{GDBN} is running in non-stop
3098 mode. Refer to @code{gdb.ThreadEvent} above for more details.
3100 Emits @code{gdb.SignalEvent} which extends @code{gdb.StopEvent}.
3102 This event indicates that the inferior or one of its threads has received as
3103 signal. @code{gdb.SignalEvent} has the following attributes:
3105 @defvar SignalEvent.stop_signal
3106 A string representing the signal received by the inferior. A list of possible
3107 signal values can be obtained by running the command @code{info signals} in
3108 the @value{GDBN} command prompt.
3111 Also emits @code{gdb.BreakpointEvent} which extends @code{gdb.StopEvent}.
3113 @code{gdb.BreakpointEvent} event indicates that one or more breakpoints have
3114 been hit, and has the following attributes:
3116 @defvar BreakpointEvent.breakpoints
3117 A sequence containing references to all the breakpoints (type
3118 @code{gdb.Breakpoint}) that were hit.
3119 @xref{Breakpoints In Python}, for details of the @code{gdb.Breakpoint} object.
3121 @defvar BreakpointEvent.breakpoint
3122 A reference to the first breakpoint that was hit.
3123 This function is maintained for backward compatibility and is now deprecated
3124 in favor of the @code{gdb.BreakpointEvent.breakpoints} attribute.
3127 @item events.new_objfile
3128 Emits @code{gdb.NewObjFileEvent} which indicates that a new object file has
3129 been loaded by @value{GDBN}. @code{gdb.NewObjFileEvent} has one attribute:
3131 @defvar NewObjFileEvent.new_objfile
3132 A reference to the object file (@code{gdb.Objfile}) which has been loaded.
3133 @xref{Objfiles In Python}, for details of the @code{gdb.Objfile} object.
3136 @item events.clear_objfiles
3137 Emits @code{gdb.ClearObjFilesEvent} which indicates that the list of object
3138 files for a program space has been reset.
3139 @code{gdb.ClearObjFilesEvent} has one attribute:
3141 @defvar ClearObjFilesEvent.progspace
3142 A reference to the program space (@code{gdb.Progspace}) whose objfile list has
3143 been cleared. @xref{Progspaces In Python}.
3146 @item events.inferior_call
3147 Emits events just before and after a function in the inferior is
3148 called by @value{GDBN}. Before an inferior call, this emits an event
3149 of type @code{gdb.InferiorCallPreEvent}, and after an inferior call,
3150 this emits an event of type @code{gdb.InferiorCallPostEvent}.
3153 @tindex gdb.InferiorCallPreEvent
3154 @item @code{gdb.InferiorCallPreEvent}
3155 Indicates that a function in the inferior is about to be called.
3157 @defvar InferiorCallPreEvent.ptid
3158 The thread in which the call will be run.
3161 @defvar InferiorCallPreEvent.address
3162 The location of the function to be called.
3165 @tindex gdb.InferiorCallPostEvent
3166 @item @code{gdb.InferiorCallPostEvent}
3167 Indicates that a function in the inferior has just been called.
3169 @defvar InferiorCallPostEvent.ptid
3170 The thread in which the call was run.
3173 @defvar InferiorCallPostEvent.address
3174 The location of the function that was called.
3178 @item events.memory_changed
3179 Emits @code{gdb.MemoryChangedEvent} which indicates that the memory of the
3180 inferior has been modified by the @value{GDBN} user, for instance via a
3181 command like @w{@code{set *addr = value}}. The event has the following
3184 @defvar MemoryChangedEvent.address
3185 The start address of the changed region.
3188 @defvar MemoryChangedEvent.length
3189 Length in bytes of the changed region.
3192 @item events.register_changed
3193 Emits @code{gdb.RegisterChangedEvent} which indicates that a register in the
3194 inferior has been modified by the @value{GDBN} user.
3196 @defvar RegisterChangedEvent.frame
3197 A gdb.Frame object representing the frame in which the register was modified.
3199 @defvar RegisterChangedEvent.regnum
3200 Denotes which register was modified.
3203 @item events.breakpoint_created
3204 This is emitted when a new breakpoint has been created. The argument
3205 that is passed is the new @code{gdb.Breakpoint} object.
3207 @item events.breakpoint_modified
3208 This is emitted when a breakpoint has been modified in some way. The
3209 argument that is passed is the new @code{gdb.Breakpoint} object.
3211 @item events.breakpoint_deleted
3212 This is emitted when a breakpoint has been deleted. The argument that
3213 is passed is the @code{gdb.Breakpoint} object. When this event is
3214 emitted, the @code{gdb.Breakpoint} object will already be in its
3215 invalid state; that is, the @code{is_valid} method will return
3218 @item events.before_prompt
3219 This event carries no payload. It is emitted each time @value{GDBN}
3220 presents a prompt to the user.
3222 @item events.new_inferior
3223 This is emitted when a new inferior is created. Note that the
3224 inferior is not necessarily running; in fact, it may not even have an
3225 associated executable.
3227 The event is of type @code{gdb.NewInferiorEvent}. This has a single
3230 @defvar NewInferiorEvent.inferior
3231 The new inferior, a @code{gdb.Inferior} object.
3234 @item events.inferior_deleted
3235 This is emitted when an inferior has been deleted. Note that this is
3236 not the same as process exit; it is notified when the inferior itself
3237 is removed, say via @code{remove-inferiors}.
3239 The event is of type @code{gdb.InferiorDeletedEvent}. This has a single
3242 @defvar NewInferiorEvent.inferior
3243 The inferior that is being removed, a @code{gdb.Inferior} object.
3246 @item events.new_thread
3247 This is emitted when @value{GDBN} notices a new thread. The event is of
3248 type @code{gdb.NewThreadEvent}, which extends @code{gdb.ThreadEvent}.
3249 This has a single attribute:
3251 @defvar NewThreadEvent.inferior_thread
3257 @node Threads In Python
3258 @subsubsection Threads In Python
3259 @cindex threads in python
3261 @findex gdb.InferiorThread
3262 Python scripts can access information about, and manipulate inferior threads
3263 controlled by @value{GDBN}, via objects of the @code{gdb.InferiorThread} class.
3265 The following thread-related functions are available in the @code{gdb}
3268 @findex gdb.selected_thread
3269 @defun gdb.selected_thread ()
3270 This function returns the thread object for the selected thread. If there
3271 is no selected thread, this will return @code{None}.
3274 A @code{gdb.InferiorThread} object has the following attributes:
3276 @defvar InferiorThread.name
3277 The name of the thread. If the user specified a name using
3278 @code{thread name}, then this returns that name. Otherwise, if an
3279 OS-supplied name is available, then it is returned. Otherwise, this
3280 returns @code{None}.
3282 This attribute can be assigned to. The new value must be a string
3283 object, which sets the new name, or @code{None}, which removes any
3284 user-specified thread name.
3287 @defvar InferiorThread.num
3288 The per-inferior number of the thread, as assigned by GDB.
3291 @defvar InferiorThread.global_num
3292 The global ID of the thread, as assigned by GDB. You can use this to
3293 make Python breakpoints thread-specific, for example
3294 (@pxref{python_breakpoint_thread,,The Breakpoint.thread attribute}).
3297 @defvar InferiorThread.ptid
3298 ID of the thread, as assigned by the operating system. This attribute is a
3299 tuple containing three integers. The first is the Process ID (PID); the second
3300 is the Lightweight Process ID (LWPID), and the third is the Thread ID (TID).
3301 Either the LWPID or TID may be 0, which indicates that the operating system
3302 does not use that identifier.
3305 @defvar InferiorThread.inferior
3306 The inferior this thread belongs to. This attribute is represented as
3307 a @code{gdb.Inferior} object. This attribute is not writable.
3310 A @code{gdb.InferiorThread} object has the following methods:
3312 @defun InferiorThread.is_valid ()
3313 Returns @code{True} if the @code{gdb.InferiorThread} object is valid,
3314 @code{False} if not. A @code{gdb.InferiorThread} object will become
3315 invalid if the thread exits, or the inferior that the thread belongs
3316 is deleted. All other @code{gdb.InferiorThread} methods will throw an
3317 exception if it is invalid at the time the method is called.
3320 @defun InferiorThread.switch ()
3321 This changes @value{GDBN}'s currently selected thread to the one represented
3325 @defun InferiorThread.is_stopped ()
3326 Return a Boolean indicating whether the thread is stopped.
3329 @defun InferiorThread.is_running ()
3330 Return a Boolean indicating whether the thread is running.
3333 @defun InferiorThread.is_exited ()
3334 Return a Boolean indicating whether the thread is exited.
3337 @defun InferiorThread.handle ()
3338 Return the thread object's handle, represented as a Python @code{bytes}
3339 object. A @code{gdb.Value} representation of the handle may be
3340 constructed via @code{gdb.Value(bufobj, type)} where @var{bufobj} is
3341 the Python @code{bytes} representation of the handle and @var{type} is
3342 a @code{gdb.Type} for the handle type.
3345 @node Recordings In Python
3346 @subsubsection Recordings In Python
3347 @cindex recordings in python
3349 The following recordings-related functions
3350 (@pxref{Process Record and Replay}) are available in the @code{gdb}
3353 @defun gdb.start_recording (@r{[}method@r{]}, @r{[}format@r{]})
3354 Start a recording using the given @var{method} and @var{format}. If
3355 no @var{format} is given, the default format for the recording method
3356 is used. If no @var{method} is given, the default method will be used.
3357 Returns a @code{gdb.Record} object on success. Throw an exception on
3360 The following strings can be passed as @var{method}:
3366 @code{"btrace"}: Possible values for @var{format}: @code{"pt"},
3367 @code{"bts"} or leave out for default format.
3371 @defun gdb.current_recording ()
3372 Access a currently running recording. Return a @code{gdb.Record}
3373 object on success. Return @code{None} if no recording is currently
3377 @defun gdb.stop_recording ()
3378 Stop the current recording. Throw an exception if no recording is
3379 currently active. All record objects become invalid after this call.
3382 A @code{gdb.Record} object has the following attributes:
3384 @defvar Record.method
3385 A string with the current recording method, e.g.@: @code{full} or
3389 @defvar Record.format
3390 A string with the current recording format, e.g.@: @code{bt}, @code{pts} or
3394 @defvar Record.begin
3395 A method specific instruction object representing the first instruction
3400 A method specific instruction object representing the current
3401 instruction, that is not actually part of the recording.
3404 @defvar Record.replay_position
3405 The instruction representing the current replay position. If there is
3406 no replay active, this will be @code{None}.
3409 @defvar Record.instruction_history
3410 A list with all recorded instructions.
3413 @defvar Record.function_call_history
3414 A list with all recorded function call segments.
3417 A @code{gdb.Record} object has the following methods:
3419 @defun Record.goto (instruction)
3420 Move the replay position to the given @var{instruction}.
3423 The common @code{gdb.Instruction} class that recording method specific
3424 instruction objects inherit from, has the following attributes:
3426 @defvar Instruction.pc
3427 An integer representing this instruction's address.
3430 @defvar Instruction.data
3431 A buffer with the raw instruction data. In Python 3, the return value is a
3432 @code{memoryview} object.
3435 @defvar Instruction.decoded
3436 A human readable string with the disassembled instruction.
3439 @defvar Instruction.size
3440 The size of the instruction in bytes.
3443 Additionally @code{gdb.RecordInstruction} has the following attributes:
3445 @defvar RecordInstruction.number
3446 An integer identifying this instruction. @code{number} corresponds to
3447 the numbers seen in @code{record instruction-history}
3448 (@pxref{Process Record and Replay}).
3451 @defvar RecordInstruction.sal
3452 A @code{gdb.Symtab_and_line} object representing the associated symtab
3453 and line of this instruction. May be @code{None} if no debug information is
3457 @defvar RecordInstruction.is_speculative
3458 A boolean indicating whether the instruction was executed speculatively.
3461 If an error occured during recording or decoding a recording, this error is
3462 represented by a @code{gdb.RecordGap} object in the instruction list. It has
3463 the following attributes:
3465 @defvar RecordGap.number
3466 An integer identifying this gap. @code{number} corresponds to the numbers seen
3467 in @code{record instruction-history} (@pxref{Process Record and Replay}).
3470 @defvar RecordGap.error_code
3471 A numerical representation of the reason for the gap. The value is specific to
3472 the current recording method.
3475 @defvar RecordGap.error_string
3476 A human readable string with the reason for the gap.
3479 A @code{gdb.RecordFunctionSegment} object has the following attributes:
3481 @defvar RecordFunctionSegment.number
3482 An integer identifying this function segment. @code{number} corresponds to
3483 the numbers seen in @code{record function-call-history}
3484 (@pxref{Process Record and Replay}).
3487 @defvar RecordFunctionSegment.symbol
3488 A @code{gdb.Symbol} object representing the associated symbol. May be
3489 @code{None} if no debug information is available.
3492 @defvar RecordFunctionSegment.level
3493 An integer representing the function call's stack level. May be
3494 @code{None} if the function call is a gap.
3497 @defvar RecordFunctionSegment.instructions
3498 A list of @code{gdb.RecordInstruction} or @code{gdb.RecordGap} objects
3499 associated with this function call.
3502 @defvar RecordFunctionSegment.up
3503 A @code{gdb.RecordFunctionSegment} object representing the caller's
3504 function segment. If the call has not been recorded, this will be the
3505 function segment to which control returns. If neither the call nor the
3506 return have been recorded, this will be @code{None}.
3509 @defvar RecordFunctionSegment.prev
3510 A @code{gdb.RecordFunctionSegment} object representing the previous
3511 segment of this function call. May be @code{None}.
3514 @defvar RecordFunctionSegment.next
3515 A @code{gdb.RecordFunctionSegment} object representing the next segment of
3516 this function call. May be @code{None}.
3519 The following example demonstrates the usage of these objects and
3520 functions to create a function that will rewind a record to the last
3521 time a function in a different file was executed. This would typically
3522 be used to track the execution of user provided callback functions in a
3523 library which typically are not visible in a back trace.
3527 rec = gdb.current_recording ()
3531 insn = rec.instruction_history
3536 position = insn.index (rec.replay_position)
3540 filename = insn[position].sal.symtab.fullname ()
3544 for i in reversed (insn[:position]):
3546 current = i.sal.symtab.fullname ()
3550 if filename == current:
3557 Another possible application is to write a function that counts the
3558 number of code executions in a given line range. This line range can
3559 contain parts of functions or span across several functions and is not
3560 limited to be contiguous.
3563 def countrange (filename, linerange):
3566 def filter_only (file_name):
3567 for call in gdb.current_recording ().function_call_history:
3569 if file_name in call.symbol.symtab.fullname ():
3574 for c in filter_only (filename):
3575 for i in c.instructions:
3577 if i.sal.line in linerange:
3586 @node Commands In Python
3587 @subsubsection Commands In Python
3589 @cindex commands in python
3590 @cindex python commands
3591 You can implement new @value{GDBN} CLI commands in Python. A CLI
3592 command is implemented using an instance of the @code{gdb.Command}
3593 class, most commonly using a subclass.
3595 @defun Command.__init__ (name, @var{command_class} @r{[}, @var{completer_class} @r{[}, @var{prefix}@r{]]})
3596 The object initializer for @code{Command} registers the new command
3597 with @value{GDBN}. This initializer is normally invoked from the
3598 subclass' own @code{__init__} method.
3600 @var{name} is the name of the command. If @var{name} consists of
3601 multiple words, then the initial words are looked for as prefix
3602 commands. In this case, if one of the prefix commands does not exist,
3603 an exception is raised.
3605 There is no support for multi-line commands.
3607 @var{command_class} should be one of the @samp{COMMAND_} constants
3608 defined below. This argument tells @value{GDBN} how to categorize the
3609 new command in the help system.
3611 @var{completer_class} is an optional argument. If given, it should be
3612 one of the @samp{COMPLETE_} constants defined below. This argument
3613 tells @value{GDBN} how to perform completion for this command. If not
3614 given, @value{GDBN} will attempt to complete using the object's
3615 @code{complete} method (see below); if no such method is found, an
3616 error will occur when completion is attempted.
3618 @var{prefix} is an optional argument. If @code{True}, then the new
3619 command is a prefix command; sub-commands of this command may be
3622 The help text for the new command is taken from the Python
3623 documentation string for the command's class, if there is one. If no
3624 documentation string is provided, the default value ``This command is
3625 not documented.'' is used.
3628 @cindex don't repeat Python command
3629 @defun Command.dont_repeat ()
3630 By default, a @value{GDBN} command is repeated when the user enters a
3631 blank line at the command prompt. A command can suppress this
3632 behavior by invoking the @code{dont_repeat} method. This is similar
3633 to the user command @code{dont-repeat}, see @ref{Define, dont-repeat}.
3636 @defun Command.invoke (argument, from_tty)
3637 This method is called by @value{GDBN} when this command is invoked.
3639 @var{argument} is a string. It is the argument to the command, after
3640 leading and trailing whitespace has been stripped.
3642 @var{from_tty} is a boolean argument. When true, this means that the
3643 command was entered by the user at the terminal; when false it means
3644 that the command came from elsewhere.
3646 If this method throws an exception, it is turned into a @value{GDBN}
3647 @code{error} call. Otherwise, the return value is ignored.
3649 @findex gdb.string_to_argv
3650 To break @var{argument} up into an argv-like string use
3651 @code{gdb.string_to_argv}. This function behaves identically to
3652 @value{GDBN}'s internal argument lexer @code{buildargv}.
3653 It is recommended to use this for consistency.
3654 Arguments are separated by spaces and may be quoted.
3658 print gdb.string_to_argv ("1 2\ \\\"3 '4 \"5' \"6 '7\"")
3659 ['1', '2 "3', '4 "5', "6 '7"]
3664 @cindex completion of Python commands
3665 @defun Command.complete (text, word)
3666 This method is called by @value{GDBN} when the user attempts
3667 completion on this command. All forms of completion are handled by
3668 this method, that is, the @key{TAB} and @key{M-?} key bindings
3669 (@pxref{Completion}), and the @code{complete} command (@pxref{Help,
3672 The arguments @var{text} and @var{word} are both strings; @var{text}
3673 holds the complete command line up to the cursor's location, while
3674 @var{word} holds the last word of the command line; this is computed
3675 using a word-breaking heuristic.
3677 The @code{complete} method can return several values:
3680 If the return value is a sequence, the contents of the sequence are
3681 used as the completions. It is up to @code{complete} to ensure that the
3682 contents actually do complete the word. A zero-length sequence is
3683 allowed, it means that there were no completions available. Only
3684 string elements of the sequence are used; other elements in the
3685 sequence are ignored.
3688 If the return value is one of the @samp{COMPLETE_} constants defined
3689 below, then the corresponding @value{GDBN}-internal completion
3690 function is invoked, and its result is used.
3693 All other results are treated as though there were no available
3698 When a new command is registered, it must be declared as a member of
3699 some general class of commands. This is used to classify top-level
3700 commands in the on-line help system; note that prefix commands are not
3701 listed under their own category but rather that of their top-level
3702 command. The available classifications are represented by constants
3703 defined in the @code{gdb} module:
3706 @findex COMMAND_NONE
3707 @findex gdb.COMMAND_NONE
3708 @item gdb.COMMAND_NONE
3709 The command does not belong to any particular class. A command in
3710 this category will not be displayed in any of the help categories.
3712 @findex COMMAND_RUNNING
3713 @findex gdb.COMMAND_RUNNING
3714 @item gdb.COMMAND_RUNNING
3715 The command is related to running the inferior. For example,
3716 @code{start}, @code{step}, and @code{continue} are in this category.
3717 Type @kbd{help running} at the @value{GDBN} prompt to see a list of
3718 commands in this category.
3720 @findex COMMAND_DATA
3721 @findex gdb.COMMAND_DATA
3722 @item gdb.COMMAND_DATA
3723 The command is related to data or variables. For example,
3724 @code{call}, @code{find}, and @code{print} are in this category. Type
3725 @kbd{help data} at the @value{GDBN} prompt to see a list of commands
3728 @findex COMMAND_STACK
3729 @findex gdb.COMMAND_STACK
3730 @item gdb.COMMAND_STACK
3731 The command has to do with manipulation of the stack. For example,
3732 @code{backtrace}, @code{frame}, and @code{return} are in this
3733 category. Type @kbd{help stack} at the @value{GDBN} prompt to see a
3734 list of commands in this category.
3736 @findex COMMAND_FILES
3737 @findex gdb.COMMAND_FILES
3738 @item gdb.COMMAND_FILES
3739 This class is used for file-related commands. For example,
3740 @code{file}, @code{list} and @code{section} are in this category.
3741 Type @kbd{help files} at the @value{GDBN} prompt to see a list of
3742 commands in this category.
3744 @findex COMMAND_SUPPORT
3745 @findex gdb.COMMAND_SUPPORT
3746 @item gdb.COMMAND_SUPPORT
3747 This should be used for ``support facilities'', generally meaning
3748 things that are useful to the user when interacting with @value{GDBN},
3749 but not related to the state of the inferior. For example,
3750 @code{help}, @code{make}, and @code{shell} are in this category. Type
3751 @kbd{help support} at the @value{GDBN} prompt to see a list of
3752 commands in this category.
3754 @findex COMMAND_STATUS
3755 @findex gdb.COMMAND_STATUS
3756 @item gdb.COMMAND_STATUS
3757 The command is an @samp{info}-related command, that is, related to the
3758 state of @value{GDBN} itself. For example, @code{info}, @code{macro},
3759 and @code{show} are in this category. Type @kbd{help status} at the
3760 @value{GDBN} prompt to see a list of commands in this category.
3762 @findex COMMAND_BREAKPOINTS
3763 @findex gdb.COMMAND_BREAKPOINTS
3764 @item gdb.COMMAND_BREAKPOINTS
3765 The command has to do with breakpoints. For example, @code{break},
3766 @code{clear}, and @code{delete} are in this category. Type @kbd{help
3767 breakpoints} at the @value{GDBN} prompt to see a list of commands in
3770 @findex COMMAND_TRACEPOINTS
3771 @findex gdb.COMMAND_TRACEPOINTS
3772 @item gdb.COMMAND_TRACEPOINTS
3773 The command has to do with tracepoints. For example, @code{trace},
3774 @code{actions}, and @code{tfind} are in this category. Type
3775 @kbd{help tracepoints} at the @value{GDBN} prompt to see a list of
3776 commands in this category.
3778 @findex COMMAND_USER
3779 @findex gdb.COMMAND_USER
3780 @item gdb.COMMAND_USER
3781 The command is a general purpose command for the user, and typically
3782 does not fit in one of the other categories.
3783 Type @kbd{help user-defined} at the @value{GDBN} prompt to see
3784 a list of commands in this category, as well as the list of gdb macros
3785 (@pxref{Sequences}).
3787 @findex COMMAND_OBSCURE
3788 @findex gdb.COMMAND_OBSCURE
3789 @item gdb.COMMAND_OBSCURE
3790 The command is only used in unusual circumstances, or is not of
3791 general interest to users. For example, @code{checkpoint},
3792 @code{fork}, and @code{stop} are in this category. Type @kbd{help
3793 obscure} at the @value{GDBN} prompt to see a list of commands in this
3796 @findex COMMAND_MAINTENANCE
3797 @findex gdb.COMMAND_MAINTENANCE
3798 @item gdb.COMMAND_MAINTENANCE
3799 The command is only useful to @value{GDBN} maintainers. The
3800 @code{maintenance} and @code{flushregs} commands are in this category.
3801 Type @kbd{help internals} at the @value{GDBN} prompt to see a list of
3802 commands in this category.
3805 A new command can use a predefined completion function, either by
3806 specifying it via an argument at initialization, or by returning it
3807 from the @code{complete} method. These predefined completion
3808 constants are all defined in the @code{gdb} module:
3811 @vindex COMPLETE_NONE
3812 @item gdb.COMPLETE_NONE
3813 This constant means that no completion should be done.
3815 @vindex COMPLETE_FILENAME
3816 @item gdb.COMPLETE_FILENAME
3817 This constant means that filename completion should be performed.
3819 @vindex COMPLETE_LOCATION
3820 @item gdb.COMPLETE_LOCATION
3821 This constant means that location completion should be done.
3822 @xref{Specify Location}.
3824 @vindex COMPLETE_COMMAND
3825 @item gdb.COMPLETE_COMMAND
3826 This constant means that completion should examine @value{GDBN}
3829 @vindex COMPLETE_SYMBOL
3830 @item gdb.COMPLETE_SYMBOL
3831 This constant means that completion should be done using symbol names
3834 @vindex COMPLETE_EXPRESSION
3835 @item gdb.COMPLETE_EXPRESSION
3836 This constant means that completion should be done on expressions.
3837 Often this means completing on symbol names, but some language
3838 parsers also have support for completing on field names.
3841 The following code snippet shows how a trivial CLI command can be
3842 implemented in Python:
3845 class HelloWorld (gdb.Command):
3846 """Greet the whole world."""
3848 def __init__ (self):
3849 super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)
3851 def invoke (self, arg, from_tty):
3852 print "Hello, World!"
3857 The last line instantiates the class, and is necessary to trigger the
3858 registration of the command with @value{GDBN}. Depending on how the
3859 Python code is read into @value{GDBN}, you may need to import the
3860 @code{gdb} module explicitly.
3862 @node Parameters In Python
3863 @subsubsection Parameters In Python
3865 @cindex parameters in python
3866 @cindex python parameters
3867 @tindex gdb.Parameter
3869 You can implement new @value{GDBN} parameters using Python. A new
3870 parameter is implemented as an instance of the @code{gdb.Parameter}
3873 Parameters are exposed to the user via the @code{set} and
3874 @code{show} commands. @xref{Help}.
3876 There are many parameters that already exist and can be set in
3877 @value{GDBN}. Two examples are: @code{set follow fork} and
3878 @code{set charset}. Setting these parameters influences certain
3879 behavior in @value{GDBN}. Similarly, you can define parameters that
3880 can be used to influence behavior in custom Python scripts and commands.
3882 @defun Parameter.__init__ (name, @var{command-class}, @var{parameter-class} @r{[}, @var{enum-sequence}@r{]})
3883 The object initializer for @code{Parameter} registers the new
3884 parameter with @value{GDBN}. This initializer is normally invoked
3885 from the subclass' own @code{__init__} method.
3887 @var{name} is the name of the new parameter. If @var{name} consists
3888 of multiple words, then the initial words are looked for as prefix
3889 parameters. An example of this can be illustrated with the
3890 @code{set print} set of parameters. If @var{name} is
3891 @code{print foo}, then @code{print} will be searched as the prefix
3892 parameter. In this case the parameter can subsequently be accessed in
3893 @value{GDBN} as @code{set print foo}.
3895 If @var{name} consists of multiple words, and no prefix parameter group
3896 can be found, an exception is raised.
3898 @var{command-class} should be one of the @samp{COMMAND_} constants
3899 (@pxref{Commands In Python}). This argument tells @value{GDBN} how to
3900 categorize the new parameter in the help system.
3902 @var{parameter-class} should be one of the @samp{PARAM_} constants
3903 defined below. This argument tells @value{GDBN} the type of the new
3904 parameter; this information is used for input validation and
3907 If @var{parameter-class} is @code{PARAM_ENUM}, then
3908 @var{enum-sequence} must be a sequence of strings. These strings
3909 represent the possible values for the parameter.
3911 If @var{parameter-class} is not @code{PARAM_ENUM}, then the presence
3912 of a fourth argument will cause an exception to be thrown.
3914 The help text for the new parameter is taken from the Python
3915 documentation string for the parameter's class, if there is one. If
3916 there is no documentation string, a default value is used.
3919 @defvar Parameter.set_doc
3920 If this attribute exists, and is a string, then its value is used as
3921 the help text for this parameter's @code{set} command. The value is
3922 examined when @code{Parameter.__init__} is invoked; subsequent changes
3926 @defvar Parameter.show_doc
3927 If this attribute exists, and is a string, then its value is used as
3928 the help text for this parameter's @code{show} command. The value is
3929 examined when @code{Parameter.__init__} is invoked; subsequent changes
3933 @defvar Parameter.value
3934 The @code{value} attribute holds the underlying value of the
3935 parameter. It can be read and assigned to just as any other
3936 attribute. @value{GDBN} does validation when assignments are made.
3939 There are two methods that may be implemented in any @code{Parameter}
3942 @defun Parameter.get_set_string (self)
3943 If this method exists, @value{GDBN} will call it when a
3944 @var{parameter}'s value has been changed via the @code{set} API (for
3945 example, @kbd{set foo off}). The @code{value} attribute has already
3946 been populated with the new value and may be used in output. This
3947 method must return a string. If the returned string is not empty,
3948 @value{GDBN} will present it to the user.
3950 If this method raises the @code{gdb.GdbError} exception
3951 (@pxref{Exception Handling}), then @value{GDBN} will print the
3952 exception's string and the @code{set} command will fail. Note,
3953 however, that the @code{value} attribute will not be reset in this
3954 case. So, if your parameter must validate values, it should store the
3955 old value internally and reset the exposed value, like so:
3958 class ExampleParam (gdb.Parameter):
3959 def __init__ (self, name):
3960 super (ExampleParam, self).__init__ (name,
3964 self.saved_value = True
3967 def get_set_string (self):
3968 if not self.validate():
3969 self.value = self.saved_value
3970 raise gdb.GdbError('Failed to validate')
3971 self.saved_value = self.value
3975 @defun Parameter.get_show_string (self, svalue)
3976 @value{GDBN} will call this method when a @var{parameter}'s
3977 @code{show} API has been invoked (for example, @kbd{show foo}). The
3978 argument @code{svalue} receives the string representation of the
3979 current value. This method must return a string.
3982 When a new parameter is defined, its type must be specified. The
3983 available types are represented by constants defined in the @code{gdb}
3987 @findex PARAM_BOOLEAN
3988 @findex gdb.PARAM_BOOLEAN
3989 @item gdb.PARAM_BOOLEAN
3990 The value is a plain boolean. The Python boolean values, @code{True}
3991 and @code{False} are the only valid values.
3993 @findex PARAM_AUTO_BOOLEAN
3994 @findex gdb.PARAM_AUTO_BOOLEAN
3995 @item gdb.PARAM_AUTO_BOOLEAN
3996 The value has three possible states: true, false, and @samp{auto}. In
3997 Python, true and false are represented using boolean constants, and
3998 @samp{auto} is represented using @code{None}.
4000 @findex PARAM_UINTEGER
4001 @findex gdb.PARAM_UINTEGER
4002 @item gdb.PARAM_UINTEGER
4003 The value is an unsigned integer. The value of 0 should be
4004 interpreted to mean ``unlimited''.
4006 @findex PARAM_INTEGER
4007 @findex gdb.PARAM_INTEGER
4008 @item gdb.PARAM_INTEGER
4009 The value is a signed integer. The value of 0 should be interpreted
4010 to mean ``unlimited''.
4012 @findex PARAM_STRING
4013 @findex gdb.PARAM_STRING
4014 @item gdb.PARAM_STRING
4015 The value is a string. When the user modifies the string, any escape
4016 sequences, such as @samp{\t}, @samp{\f}, and octal escapes, are
4017 translated into corresponding characters and encoded into the current
4020 @findex PARAM_STRING_NOESCAPE
4021 @findex gdb.PARAM_STRING_NOESCAPE
4022 @item gdb.PARAM_STRING_NOESCAPE
4023 The value is a string. When the user modifies the string, escapes are
4024 passed through untranslated.
4026 @findex PARAM_OPTIONAL_FILENAME
4027 @findex gdb.PARAM_OPTIONAL_FILENAME
4028 @item gdb.PARAM_OPTIONAL_FILENAME
4029 The value is a either a filename (a string), or @code{None}.
4031 @findex PARAM_FILENAME
4032 @findex gdb.PARAM_FILENAME
4033 @item gdb.PARAM_FILENAME
4034 The value is a filename. This is just like
4035 @code{PARAM_STRING_NOESCAPE}, but uses file names for completion.
4037 @findex PARAM_ZINTEGER
4038 @findex gdb.PARAM_ZINTEGER
4039 @item gdb.PARAM_ZINTEGER
4040 The value is an integer. This is like @code{PARAM_INTEGER}, except 0
4041 is interpreted as itself.
4043 @findex PARAM_ZUINTEGER
4044 @findex gdb.PARAM_ZUINTEGER
4045 @item gdb.PARAM_ZUINTEGER
4046 The value is an unsigned integer. This is like @code{PARAM_INTEGER},
4047 except 0 is interpreted as itself, and the value cannot be negative.
4049 @findex PARAM_ZUINTEGER_UNLIMITED
4050 @findex gdb.PARAM_ZUINTEGER_UNLIMITED
4051 @item gdb.PARAM_ZUINTEGER_UNLIMITED
4052 The value is a signed integer. This is like @code{PARAM_ZUINTEGER},
4053 except the special value -1 should be interpreted to mean
4054 ``unlimited''. Other negative values are not allowed.
4057 @findex gdb.PARAM_ENUM
4058 @item gdb.PARAM_ENUM
4059 The value is a string, which must be one of a collection string
4060 constants provided when the parameter is created.
4063 @node Functions In Python
4064 @subsubsection Writing new convenience functions
4066 @cindex writing convenience functions
4067 @cindex convenience functions in python
4068 @cindex python convenience functions
4069 @tindex gdb.Function
4071 You can implement new convenience functions (@pxref{Convenience Vars})
4072 in Python. A convenience function is an instance of a subclass of the
4073 class @code{gdb.Function}.
4075 @defun Function.__init__ (name)
4076 The initializer for @code{Function} registers the new function with
4077 @value{GDBN}. The argument @var{name} is the name of the function,
4078 a string. The function will be visible to the user as a convenience
4079 variable of type @code{internal function}, whose name is the same as
4080 the given @var{name}.
4082 The documentation for the new function is taken from the documentation
4083 string for the new class.
4086 @defun Function.invoke (@var{*args})
4087 When a convenience function is evaluated, its arguments are converted
4088 to instances of @code{gdb.Value}, and then the function's
4089 @code{invoke} method is called. Note that @value{GDBN} does not
4090 predetermine the arity of convenience functions. Instead, all
4091 available arguments are passed to @code{invoke}, following the
4092 standard Python calling convention. In particular, a convenience
4093 function can have default values for parameters without ill effect.
4095 The return value of this method is used as its value in the enclosing
4096 expression. If an ordinary Python value is returned, it is converted
4097 to a @code{gdb.Value} following the usual rules.
4100 The following code snippet shows how a trivial convenience function can
4101 be implemented in Python:
4104 class Greet (gdb.Function):
4105 """Return string to greet someone.
4106 Takes a name as argument."""
4108 def __init__ (self):
4109 super (Greet, self).__init__ ("greet")
4111 def invoke (self, name):
4112 return "Hello, %s!" % name.string ()
4117 The last line instantiates the class, and is necessary to trigger the
4118 registration of the function with @value{GDBN}. Depending on how the
4119 Python code is read into @value{GDBN}, you may need to import the
4120 @code{gdb} module explicitly.
4122 Now you can use the function in an expression:
4125 (gdb) print $greet("Bob")
4129 @node Progspaces In Python
4130 @subsubsection Program Spaces In Python
4132 @cindex progspaces in python
4133 @tindex gdb.Progspace
4135 A program space, or @dfn{progspace}, represents a symbolic view
4136 of an address space.
4137 It consists of all of the objfiles of the program.
4138 @xref{Objfiles In Python}.
4139 @xref{Inferiors and Programs, program spaces}, for more details
4140 about program spaces.
4142 The following progspace-related functions are available in the
4145 @findex gdb.current_progspace
4146 @defun gdb.current_progspace ()
4147 This function returns the program space of the currently selected inferior.
4148 @xref{Inferiors and Programs}. This is identical to
4149 @code{gdb.selected_inferior().progspace} (@pxref{Inferiors In Python}) and is
4150 included for historical compatibility.
4153 @findex gdb.progspaces
4154 @defun gdb.progspaces ()
4155 Return a sequence of all the progspaces currently known to @value{GDBN}.
4158 Each progspace is represented by an instance of the @code{gdb.Progspace}
4161 @defvar Progspace.filename
4162 The file name of the progspace as a string.
4165 @defvar Progspace.pretty_printers
4166 The @code{pretty_printers} attribute is a list of functions. It is
4167 used to look up pretty-printers. A @code{Value} is passed to each
4168 function in order; if the function returns @code{None}, then the
4169 search continues. Otherwise, the return value should be an object
4170 which is used to format the value. @xref{Pretty Printing API}, for more
4174 @defvar Progspace.type_printers
4175 The @code{type_printers} attribute is a list of type printer objects.
4176 @xref{Type Printing API}, for more information.
4179 @defvar Progspace.frame_filters
4180 The @code{frame_filters} attribute is a dictionary of frame filter
4181 objects. @xref{Frame Filter API}, for more information.
4184 A program space has the following methods:
4186 @findex Progspace.block_for_pc
4187 @defun Progspace.block_for_pc (pc)
4188 Return the innermost @code{gdb.Block} containing the given @var{pc}
4189 value. If the block cannot be found for the @var{pc} value specified,
4190 the function will return @code{None}.
4193 @findex Progspace.find_pc_line
4194 @defun Progspace.find_pc_line (pc)
4195 Return the @code{gdb.Symtab_and_line} object corresponding to the
4196 @var{pc} value. @xref{Symbol Tables In Python}. If an invalid value
4197 of @var{pc} is passed as an argument, then the @code{symtab} and
4198 @code{line} attributes of the returned @code{gdb.Symtab_and_line}
4199 object will be @code{None} and 0 respectively.
4202 @findex Progspace.is_valid
4203 @defun Progspace.is_valid ()
4204 Returns @code{True} if the @code{gdb.Progspace} object is valid,
4205 @code{False} if not. A @code{gdb.Progspace} object can become invalid
4206 if the program space file it refers to is not referenced by any
4207 inferior. All other @code{gdb.Progspace} methods will throw an
4208 exception if it is invalid at the time the method is called.
4211 @findex Progspace.objfiles
4212 @defun Progspace.objfiles ()
4213 Return a sequence of all the objfiles referenced by this program
4214 space. @xref{Objfiles In Python}.
4217 @findex Progspace.solib_name
4218 @defun Progspace.solib_name (address)
4219 Return the name of the shared library holding the given @var{address}
4220 as a string, or @code{None}.
4223 One may add arbitrary attributes to @code{gdb.Progspace} objects
4224 in the usual Python way.
4225 This is useful if, for example, one needs to do some extra record keeping
4226 associated with the program space.
4228 In this contrived example, we want to perform some processing when
4229 an objfile with a certain symbol is loaded, but we only want to do
4230 this once because it is expensive. To achieve this we record the results
4231 with the program space because we can't predict when the desired objfile
4236 def clear_objfiles_handler(event):
4237 event.progspace.expensive_computation = None
4238 def expensive(symbol):
4239 """A mock routine to perform an "expensive" computation on symbol."""
4240 print "Computing the answer to the ultimate question ..."
4242 def new_objfile_handler(event):
4243 objfile = event.new_objfile
4244 progspace = objfile.progspace
4245 if not hasattr(progspace, 'expensive_computation') or \
4246 progspace.expensive_computation is None:
4247 # We use 'main' for the symbol to keep the example simple.
4248 # Note: There's no current way to constrain the lookup
4250 symbol = gdb.lookup_global_symbol('main')
4251 if symbol is not None:
4252 progspace.expensive_computation = expensive(symbol)
4253 gdb.events.clear_objfiles.connect(clear_objfiles_handler)
4254 gdb.events.new_objfile.connect(new_objfile_handler)
4256 (gdb) file /tmp/hello
4257 Reading symbols from /tmp/hello...done.
4258 Computing the answer to the ultimate question ...
4259 (gdb) python print gdb.current_progspace().expensive_computation
4262 Starting program: /tmp/hello
4264 [Inferior 1 (process 4242) exited normally]
4267 @node Objfiles In Python
4268 @subsubsection Objfiles In Python
4270 @cindex objfiles in python
4273 @value{GDBN} loads symbols for an inferior from various
4274 symbol-containing files (@pxref{Files}). These include the primary
4275 executable file, any shared libraries used by the inferior, and any
4276 separate debug info files (@pxref{Separate Debug Files}).
4277 @value{GDBN} calls these symbol-containing files @dfn{objfiles}.
4279 The following objfile-related functions are available in the
4282 @findex gdb.current_objfile
4283 @defun gdb.current_objfile ()
4284 When auto-loading a Python script (@pxref{Python Auto-loading}), @value{GDBN}
4285 sets the ``current objfile'' to the corresponding objfile. This
4286 function returns the current objfile. If there is no current objfile,
4287 this function returns @code{None}.
4290 @findex gdb.objfiles
4291 @defun gdb.objfiles ()
4292 Return a sequence of objfiles referenced by the current program space.
4293 @xref{Objfiles In Python}, and @ref{Progspaces In Python}. This is identical
4294 to @code{gdb.selected_inferior().progspace.objfiles()} and is included for
4295 historical compatibility.
4298 @findex gdb.lookup_objfile
4299 @defun gdb.lookup_objfile (name @r{[}, by_build_id{]})
4300 Look up @var{name}, a file name or build ID, in the list of objfiles
4301 for the current program space (@pxref{Progspaces In Python}).
4302 If the objfile is not found throw the Python @code{ValueError} exception.
4304 If @var{name} is a relative file name, then it will match any
4305 source file name with the same trailing components. For example, if
4306 @var{name} is @samp{gcc/expr.c}, then it will match source file
4307 name of @file{/build/trunk/gcc/expr.c}, but not
4308 @file{/build/trunk/libcpp/expr.c} or @file{/build/trunk/gcc/x-expr.c}.
4310 If @var{by_build_id} is provided and is @code{True} then @var{name}
4311 is the build ID of the objfile. Otherwise, @var{name} is a file name.
4312 This is supported only on some operating systems, notably those which use
4313 the ELF format for binary files and the @sc{gnu} Binutils. For more details
4314 about this feature, see the description of the @option{--build-id}
4315 command-line option in @ref{Options, , Command Line Options, ld,
4319 Each objfile is represented by an instance of the @code{gdb.Objfile}
4322 @defvar Objfile.filename
4323 The file name of the objfile as a string, with symbolic links resolved.
4325 The value is @code{None} if the objfile is no longer valid.
4326 See the @code{gdb.Objfile.is_valid} method, described below.
4329 @defvar Objfile.username
4330 The file name of the objfile as specified by the user as a string.
4332 The value is @code{None} if the objfile is no longer valid.
4333 See the @code{gdb.Objfile.is_valid} method, described below.
4336 @defvar Objfile.owner
4337 For separate debug info objfiles this is the corresponding @code{gdb.Objfile}
4338 object that debug info is being provided for.
4339 Otherwise this is @code{None}.
4340 Separate debug info objfiles are added with the
4341 @code{gdb.Objfile.add_separate_debug_file} method, described below.
4344 @defvar Objfile.build_id
4345 The build ID of the objfile as a string.
4346 If the objfile does not have a build ID then the value is @code{None}.
4348 This is supported only on some operating systems, notably those which use
4349 the ELF format for binary files and the @sc{gnu} Binutils. For more details
4350 about this feature, see the description of the @option{--build-id}
4351 command-line option in @ref{Options, , Command Line Options, ld,
4355 @defvar Objfile.progspace
4356 The containing program space of the objfile as a @code{gdb.Progspace}
4357 object. @xref{Progspaces In Python}.
4360 @defvar Objfile.pretty_printers
4361 The @code{pretty_printers} attribute is a list of functions. It is
4362 used to look up pretty-printers. A @code{Value} is passed to each
4363 function in order; if the function returns @code{None}, then the
4364 search continues. Otherwise, the return value should be an object
4365 which is used to format the value. @xref{Pretty Printing API}, for more
4369 @defvar Objfile.type_printers
4370 The @code{type_printers} attribute is a list of type printer objects.
4371 @xref{Type Printing API}, for more information.
4374 @defvar Objfile.frame_filters
4375 The @code{frame_filters} attribute is a dictionary of frame filter
4376 objects. @xref{Frame Filter API}, for more information.
4379 One may add arbitrary attributes to @code{gdb.Objfile} objects
4380 in the usual Python way.
4381 This is useful if, for example, one needs to do some extra record keeping
4382 associated with the objfile.
4384 In this contrived example we record the time when @value{GDBN}
4390 def new_objfile_handler(event):
4391 # Set the time_loaded attribute of the new objfile.
4392 event.new_objfile.time_loaded = datetime.datetime.today()
4393 gdb.events.new_objfile.connect(new_objfile_handler)
4396 Reading symbols from ./hello...done.
4397 (gdb) python print gdb.objfiles()[0].time_loaded
4398 2014-10-09 11:41:36.770345
4401 A @code{gdb.Objfile} object has the following methods:
4403 @defun Objfile.is_valid ()
4404 Returns @code{True} if the @code{gdb.Objfile} object is valid,
4405 @code{False} if not. A @code{gdb.Objfile} object can become invalid
4406 if the object file it refers to is not loaded in @value{GDBN} any
4407 longer. All other @code{gdb.Objfile} methods will throw an exception
4408 if it is invalid at the time the method is called.
4411 @defun Objfile.add_separate_debug_file (file)
4412 Add @var{file} to the list of files that @value{GDBN} will search for
4413 debug information for the objfile.
4414 This is useful when the debug info has been removed from the program
4415 and stored in a separate file. @value{GDBN} has built-in support for
4416 finding separate debug info files (@pxref{Separate Debug Files}), but if
4417 the file doesn't live in one of the standard places that @value{GDBN}
4418 searches then this function can be used to add a debug info file
4419 from a different place.
4422 @node Frames In Python
4423 @subsubsection Accessing inferior stack frames from Python
4425 @cindex frames in python
4426 When the debugged program stops, @value{GDBN} is able to analyze its call
4427 stack (@pxref{Frames,,Stack frames}). The @code{gdb.Frame} class
4428 represents a frame in the stack. A @code{gdb.Frame} object is only valid
4429 while its corresponding frame exists in the inferior's stack. If you try
4430 to use an invalid frame object, @value{GDBN} will throw a @code{gdb.error}
4431 exception (@pxref{Exception Handling}).
4433 Two @code{gdb.Frame} objects can be compared for equality with the @code{==}
4437 (@value{GDBP}) python print gdb.newest_frame() == gdb.selected_frame ()
4441 The following frame-related functions are available in the @code{gdb} module:
4443 @findex gdb.selected_frame
4444 @defun gdb.selected_frame ()
4445 Return the selected frame object. (@pxref{Selection,,Selecting a Frame}).
4448 @findex gdb.newest_frame
4449 @defun gdb.newest_frame ()
4450 Return the newest frame object for the selected thread.
4453 @defun gdb.frame_stop_reason_string (reason)
4454 Return a string explaining the reason why @value{GDBN} stopped unwinding
4455 frames, as expressed by the given @var{reason} code (an integer, see the
4456 @code{unwind_stop_reason} method further down in this section).
4459 @findex gdb.invalidate_cached_frames
4460 @defun gdb.invalidate_cached_frames
4461 @value{GDBN} internally keeps a cache of the frames that have been
4462 unwound. This function invalidates this cache.
4464 This function should not generally be called by ordinary Python code.
4465 It is documented for the sake of completeness.
4468 A @code{gdb.Frame} object has the following methods:
4470 @defun Frame.is_valid ()
4471 Returns true if the @code{gdb.Frame} object is valid, false if not.
4472 A frame object can become invalid if the frame it refers to doesn't
4473 exist anymore in the inferior. All @code{gdb.Frame} methods will throw
4474 an exception if it is invalid at the time the method is called.
4477 @defun Frame.name ()
4478 Returns the function name of the frame, or @code{None} if it can't be
4482 @defun Frame.architecture ()
4483 Returns the @code{gdb.Architecture} object corresponding to the frame's
4484 architecture. @xref{Architectures In Python}.
4487 @defun Frame.type ()
4488 Returns the type of the frame. The value can be one of:
4490 @item gdb.NORMAL_FRAME
4491 An ordinary stack frame.
4493 @item gdb.DUMMY_FRAME
4494 A fake stack frame that was created by @value{GDBN} when performing an
4495 inferior function call.
4497 @item gdb.INLINE_FRAME
4498 A frame representing an inlined function. The function was inlined
4499 into a @code{gdb.NORMAL_FRAME} that is older than this one.
4501 @item gdb.TAILCALL_FRAME
4502 A frame representing a tail call. @xref{Tail Call Frames}.
4504 @item gdb.SIGTRAMP_FRAME
4505 A signal trampoline frame. This is the frame created by the OS when
4506 it calls into a signal handler.
4508 @item gdb.ARCH_FRAME
4509 A fake stack frame representing a cross-architecture call.
4511 @item gdb.SENTINEL_FRAME
4512 This is like @code{gdb.NORMAL_FRAME}, but it is only used for the
4517 @defun Frame.unwind_stop_reason ()
4518 Return an integer representing the reason why it's not possible to find
4519 more frames toward the outermost frame. Use
4520 @code{gdb.frame_stop_reason_string} to convert the value returned by this
4521 function to a string. The value can be one of:
4524 @item gdb.FRAME_UNWIND_NO_REASON
4525 No particular reason (older frames should be available).
4527 @item gdb.FRAME_UNWIND_NULL_ID
4528 The previous frame's analyzer returns an invalid result. This is no
4529 longer used by @value{GDBN}, and is kept only for backward
4532 @item gdb.FRAME_UNWIND_OUTERMOST
4533 This frame is the outermost.
4535 @item gdb.FRAME_UNWIND_UNAVAILABLE
4536 Cannot unwind further, because that would require knowing the
4537 values of registers or memory that have not been collected.
4539 @item gdb.FRAME_UNWIND_INNER_ID
4540 This frame ID looks like it ought to belong to a NEXT frame,
4541 but we got it for a PREV frame. Normally, this is a sign of
4542 unwinder failure. It could also indicate stack corruption.
4544 @item gdb.FRAME_UNWIND_SAME_ID
4545 This frame has the same ID as the previous one. That means
4546 that unwinding further would almost certainly give us another
4547 frame with exactly the same ID, so break the chain. Normally,
4548 this is a sign of unwinder failure. It could also indicate
4551 @item gdb.FRAME_UNWIND_NO_SAVED_PC
4552 The frame unwinder did not find any saved PC, but we needed
4553 one to unwind further.
4555 @item gdb.FRAME_UNWIND_MEMORY_ERROR
4556 The frame unwinder caused an error while trying to access memory.
4558 @item gdb.FRAME_UNWIND_FIRST_ERROR
4559 Any stop reason greater or equal to this value indicates some kind
4560 of error. This special value facilitates writing code that tests
4561 for errors in unwinding in a way that will work correctly even if
4562 the list of the other values is modified in future @value{GDBN}
4563 versions. Using it, you could write:
4565 reason = gdb.selected_frame().unwind_stop_reason ()
4566 reason_str = gdb.frame_stop_reason_string (reason)
4567 if reason >= gdb.FRAME_UNWIND_FIRST_ERROR:
4568 print "An error occured: %s" % reason_str
4575 Returns the frame's resume address.
4578 @defun Frame.block ()
4579 Return the frame's code block. @xref{Blocks In Python}. If the frame
4580 does not have a block -- for example, if there is no debugging
4581 information for the code in question -- then this will throw an
4585 @defun Frame.function ()
4586 Return the symbol for the function corresponding to this frame.
4587 @xref{Symbols In Python}.
4590 @defun Frame.older ()
4591 Return the frame that called this frame.
4594 @defun Frame.newer ()
4595 Return the frame called by this frame.
4598 @defun Frame.find_sal ()
4599 Return the frame's symtab and line object.
4600 @xref{Symbol Tables In Python}.
4603 @defun Frame.read_register (register)
4604 Return the value of @var{register} in this frame. The @var{register}
4605 argument must be a string (e.g., @code{'sp'} or @code{'rax'}).
4606 Returns a @code{Gdb.Value} object. Throws an exception if @var{register}
4610 @defun Frame.read_var (variable @r{[}, block@r{]})
4611 Return the value of @var{variable} in this frame. If the optional
4612 argument @var{block} is provided, search for the variable from that
4613 block; otherwise start at the frame's current block (which is
4614 determined by the frame's current program counter). The @var{variable}
4615 argument must be a string or a @code{gdb.Symbol} object; @var{block} must be a
4616 @code{gdb.Block} object.
4619 @defun Frame.select ()
4620 Set this frame to be the selected frame. @xref{Stack, ,Examining the
4624 @node Blocks In Python
4625 @subsubsection Accessing blocks from Python
4627 @cindex blocks in python
4630 In @value{GDBN}, symbols are stored in blocks. A block corresponds
4631 roughly to a scope in the source code. Blocks are organized
4632 hierarchically, and are represented individually in Python as a
4633 @code{gdb.Block}. Blocks rely on debugging information being
4636 A frame has a block. Please see @ref{Frames In Python}, for a more
4637 in-depth discussion of frames.
4639 The outermost block is known as the @dfn{global block}. The global
4640 block typically holds public global variables and functions.
4642 The block nested just inside the global block is the @dfn{static
4643 block}. The static block typically holds file-scoped variables and
4646 @value{GDBN} provides a method to get a block's superblock, but there
4647 is currently no way to examine the sub-blocks of a block, or to
4648 iterate over all the blocks in a symbol table (@pxref{Symbol Tables In
4651 Here is a short example that should help explain blocks:
4654 /* This is in the global block. */
4657 /* This is in the static block. */
4658 static int file_scope;
4660 /* 'function' is in the global block, and 'argument' is
4661 in a block nested inside of 'function'. */
4662 int function (int argument)
4664 /* 'local' is in a block inside 'function'. It may or may
4665 not be in the same block as 'argument'. */
4669 /* 'inner' is in a block whose superblock is the one holding
4673 /* If this call is expanded by the compiler, you may see
4674 a nested block here whose function is 'inline_function'
4675 and whose superblock is the one holding 'inner'. */
4681 A @code{gdb.Block} is iterable. The iterator returns the symbols
4682 (@pxref{Symbols In Python}) local to the block. Python programs
4683 should not assume that a specific block object will always contain a
4684 given symbol, since changes in @value{GDBN} features and
4685 infrastructure may cause symbols move across blocks in a symbol
4688 The following block-related functions are available in the @code{gdb}
4691 @findex gdb.block_for_pc
4692 @defun gdb.block_for_pc (pc)
4693 Return the innermost @code{gdb.Block} containing the given @var{pc}
4694 value. If the block cannot be found for the @var{pc} value specified,
4695 the function will return @code{None}. This is identical to
4696 @code{gdb.current_progspace().block_for_pc(pc)} and is included for
4697 historical compatibility.
4700 A @code{gdb.Block} object has the following methods:
4702 @defun Block.is_valid ()
4703 Returns @code{True} if the @code{gdb.Block} object is valid,
4704 @code{False} if not. A block object can become invalid if the block it
4705 refers to doesn't exist anymore in the inferior. All other
4706 @code{gdb.Block} methods will throw an exception if it is invalid at
4707 the time the method is called. The block's validity is also checked
4708 during iteration over symbols of the block.
4711 A @code{gdb.Block} object has the following attributes:
4714 The start address of the block. This attribute is not writable.
4718 One past the last address that appears in the block. This attribute
4722 @defvar Block.function
4723 The name of the block represented as a @code{gdb.Symbol}. If the
4724 block is not named, then this attribute holds @code{None}. This
4725 attribute is not writable.
4727 For ordinary function blocks, the superblock is the static block.
4728 However, you should note that it is possible for a function block to
4729 have a superblock that is not the static block -- for instance this
4730 happens for an inlined function.
4733 @defvar Block.superblock
4734 The block containing this block. If this parent block does not exist,
4735 this attribute holds @code{None}. This attribute is not writable.
4738 @defvar Block.global_block
4739 The global block associated with this block. This attribute is not
4743 @defvar Block.static_block
4744 The static block associated with this block. This attribute is not
4748 @defvar Block.is_global
4749 @code{True} if the @code{gdb.Block} object is a global block,
4750 @code{False} if not. This attribute is not
4754 @defvar Block.is_static
4755 @code{True} if the @code{gdb.Block} object is a static block,
4756 @code{False} if not. This attribute is not writable.
4759 @node Symbols In Python
4760 @subsubsection Python representation of Symbols
4762 @cindex symbols in python
4765 @value{GDBN} represents every variable, function and type as an
4766 entry in a symbol table. @xref{Symbols, ,Examining the Symbol Table}.
4767 Similarly, Python represents these symbols in @value{GDBN} with the
4768 @code{gdb.Symbol} object.
4770 The following symbol-related functions are available in the @code{gdb}
4773 @findex gdb.lookup_symbol
4774 @defun gdb.lookup_symbol (name @r{[}, block @r{[}, domain@r{]]})
4775 This function searches for a symbol by name. The search scope can be
4776 restricted to the parameters defined in the optional domain and block
4779 @var{name} is the name of the symbol. It must be a string. The
4780 optional @var{block} argument restricts the search to symbols visible
4781 in that @var{block}. The @var{block} argument must be a
4782 @code{gdb.Block} object. If omitted, the block for the current frame
4783 is used. The optional @var{domain} argument restricts
4784 the search to the domain type. The @var{domain} argument must be a
4785 domain constant defined in the @code{gdb} module and described later
4788 The result is a tuple of two elements.
4789 The first element is a @code{gdb.Symbol} object or @code{None} if the symbol
4791 If the symbol is found, the second element is @code{True} if the symbol
4792 is a field of a method's object (e.g., @code{this} in C@t{++}),
4793 otherwise it is @code{False}.
4794 If the symbol is not found, the second element is @code{False}.
4797 @findex gdb.lookup_global_symbol
4798 @defun gdb.lookup_global_symbol (name @r{[}, domain@r{]})
4799 This function searches for a global symbol by name.
4800 The search scope can be restricted to by the domain argument.
4802 @var{name} is the name of the symbol. It must be a string.
4803 The optional @var{domain} argument restricts the search to the domain type.
4804 The @var{domain} argument must be a domain constant defined in the @code{gdb}
4805 module and described later in this chapter.
4807 The result is a @code{gdb.Symbol} object or @code{None} if the symbol
4811 A @code{gdb.Symbol} object has the following attributes:
4814 The type of the symbol or @code{None} if no type is recorded.
4815 This attribute is represented as a @code{gdb.Type} object.
4816 @xref{Types In Python}. This attribute is not writable.
4819 @defvar Symbol.symtab
4820 The symbol table in which the symbol appears. This attribute is
4821 represented as a @code{gdb.Symtab} object. @xref{Symbol Tables In
4822 Python}. This attribute is not writable.
4826 The line number in the source code at which the symbol was defined.
4831 The name of the symbol as a string. This attribute is not writable.
4834 @defvar Symbol.linkage_name
4835 The name of the symbol, as used by the linker (i.e., may be mangled).
4836 This attribute is not writable.
4839 @defvar Symbol.print_name
4840 The name of the symbol in a form suitable for output. This is either
4841 @code{name} or @code{linkage_name}, depending on whether the user
4842 asked @value{GDBN} to display demangled or mangled names.
4845 @defvar Symbol.addr_class
4846 The address class of the symbol. This classifies how to find the value
4847 of a symbol. Each address class is a constant defined in the
4848 @code{gdb} module and described later in this chapter.
4851 @defvar Symbol.needs_frame
4852 This is @code{True} if evaluating this symbol's value requires a frame
4853 (@pxref{Frames In Python}) and @code{False} otherwise. Typically,
4854 local variables will require a frame, but other symbols will not.
4857 @defvar Symbol.is_argument
4858 @code{True} if the symbol is an argument of a function.
4861 @defvar Symbol.is_constant
4862 @code{True} if the symbol is a constant.
4865 @defvar Symbol.is_function
4866 @code{True} if the symbol is a function or a method.
4869 @defvar Symbol.is_variable
4870 @code{True} if the symbol is a variable.
4873 A @code{gdb.Symbol} object has the following methods:
4875 @defun Symbol.is_valid ()
4876 Returns @code{True} if the @code{gdb.Symbol} object is valid,
4877 @code{False} if not. A @code{gdb.Symbol} object can become invalid if
4878 the symbol it refers to does not exist in @value{GDBN} any longer.
4879 All other @code{gdb.Symbol} methods will throw an exception if it is
4880 invalid at the time the method is called.
4883 @defun Symbol.value (@r{[}frame@r{]})
4884 Compute the value of the symbol, as a @code{gdb.Value}. For
4885 functions, this computes the address of the function, cast to the
4886 appropriate type. If the symbol requires a frame in order to compute
4887 its value, then @var{frame} must be given. If @var{frame} is not
4888 given, or if @var{frame} is invalid, then this method will throw an
4892 The available domain categories in @code{gdb.Symbol} are represented
4893 as constants in the @code{gdb} module:
4896 @vindex SYMBOL_UNDEF_DOMAIN
4897 @item gdb.SYMBOL_UNDEF_DOMAIN
4898 This is used when a domain has not been discovered or none of the
4899 following domains apply. This usually indicates an error either
4900 in the symbol information or in @value{GDBN}'s handling of symbols.
4902 @vindex SYMBOL_VAR_DOMAIN
4903 @item gdb.SYMBOL_VAR_DOMAIN
4904 This domain contains variables, function names, typedef names and enum
4907 @vindex SYMBOL_STRUCT_DOMAIN
4908 @item gdb.SYMBOL_STRUCT_DOMAIN
4909 This domain holds struct, union and enum type names.
4911 @vindex SYMBOL_LABEL_DOMAIN
4912 @item gdb.SYMBOL_LABEL_DOMAIN
4913 This domain contains names of labels (for gotos).
4915 @vindex SYMBOL_MODULE_DOMAIN
4916 @item gdb.SYMBOL_MODULE_DOMAIN
4917 This domain contains names of Fortran module types.
4919 @vindex SYMBOL_COMMON_BLOCK_DOMAIN
4920 @item gdb.SYMBOL_COMMON_BLOCK_DOMAIN
4921 This domain contains names of Fortran common blocks.
4924 The available address class categories in @code{gdb.Symbol} are represented
4925 as constants in the @code{gdb} module:
4928 @vindex SYMBOL_LOC_UNDEF
4929 @item gdb.SYMBOL_LOC_UNDEF
4930 If this is returned by address class, it indicates an error either in
4931 the symbol information or in @value{GDBN}'s handling of symbols.
4933 @vindex SYMBOL_LOC_CONST
4934 @item gdb.SYMBOL_LOC_CONST
4935 Value is constant int.
4937 @vindex SYMBOL_LOC_STATIC
4938 @item gdb.SYMBOL_LOC_STATIC
4939 Value is at a fixed address.
4941 @vindex SYMBOL_LOC_REGISTER
4942 @item gdb.SYMBOL_LOC_REGISTER
4943 Value is in a register.
4945 @vindex SYMBOL_LOC_ARG
4946 @item gdb.SYMBOL_LOC_ARG
4947 Value is an argument. This value is at the offset stored within the
4948 symbol inside the frame's argument list.
4950 @vindex SYMBOL_LOC_REF_ARG
4951 @item gdb.SYMBOL_LOC_REF_ARG
4952 Value address is stored in the frame's argument list. Just like
4953 @code{LOC_ARG} except that the value's address is stored at the
4954 offset, not the value itself.
4956 @vindex SYMBOL_LOC_REGPARM_ADDR
4957 @item gdb.SYMBOL_LOC_REGPARM_ADDR
4958 Value is a specified register. Just like @code{LOC_REGISTER} except
4959 the register holds the address of the argument instead of the argument
4962 @vindex SYMBOL_LOC_LOCAL
4963 @item gdb.SYMBOL_LOC_LOCAL
4964 Value is a local variable.
4966 @vindex SYMBOL_LOC_TYPEDEF
4967 @item gdb.SYMBOL_LOC_TYPEDEF
4968 Value not used. Symbols in the domain @code{SYMBOL_STRUCT_DOMAIN} all
4971 @vindex SYMBOL_LOC_BLOCK
4972 @item gdb.SYMBOL_LOC_BLOCK
4975 @vindex SYMBOL_LOC_CONST_BYTES
4976 @item gdb.SYMBOL_LOC_CONST_BYTES
4977 Value is a byte-sequence.
4979 @vindex SYMBOL_LOC_UNRESOLVED
4980 @item gdb.SYMBOL_LOC_UNRESOLVED
4981 Value is at a fixed address, but the address of the variable has to be
4982 determined from the minimal symbol table whenever the variable is
4985 @vindex SYMBOL_LOC_OPTIMIZED_OUT
4986 @item gdb.SYMBOL_LOC_OPTIMIZED_OUT
4987 The value does not actually exist in the program.
4989 @vindex SYMBOL_LOC_COMPUTED
4990 @item gdb.SYMBOL_LOC_COMPUTED
4991 The value's address is a computed location.
4993 @vindex SYMBOL_LOC_COMPUTED
4994 @item gdb.SYMBOL_LOC_COMPUTED
4995 The value's address is a symbol. This is only used for Fortran common
4999 @node Symbol Tables In Python
5000 @subsubsection Symbol table representation in Python
5002 @cindex symbol tables in python
5004 @tindex gdb.Symtab_and_line
5006 Access to symbol table data maintained by @value{GDBN} on the inferior
5007 is exposed to Python via two objects: @code{gdb.Symtab_and_line} and
5008 @code{gdb.Symtab}. Symbol table and line data for a frame is returned
5009 from the @code{find_sal} method in @code{gdb.Frame} object.
5010 @xref{Frames In Python}.
5012 For more information on @value{GDBN}'s symbol table management, see
5013 @ref{Symbols, ,Examining the Symbol Table}, for more information.
5015 A @code{gdb.Symtab_and_line} object has the following attributes:
5017 @defvar Symtab_and_line.symtab
5018 The symbol table object (@code{gdb.Symtab}) for this frame.
5019 This attribute is not writable.
5022 @defvar Symtab_and_line.pc
5023 Indicates the start of the address range occupied by code for the
5024 current source line. This attribute is not writable.
5027 @defvar Symtab_and_line.last
5028 Indicates the end of the address range occupied by code for the current
5029 source line. This attribute is not writable.
5032 @defvar Symtab_and_line.line
5033 Indicates the current line number for this object. This
5034 attribute is not writable.
5037 A @code{gdb.Symtab_and_line} object has the following methods:
5039 @defun Symtab_and_line.is_valid ()
5040 Returns @code{True} if the @code{gdb.Symtab_and_line} object is valid,
5041 @code{False} if not. A @code{gdb.Symtab_and_line} object can become
5042 invalid if the Symbol table and line object it refers to does not
5043 exist in @value{GDBN} any longer. All other
5044 @code{gdb.Symtab_and_line} methods will throw an exception if it is
5045 invalid at the time the method is called.
5048 A @code{gdb.Symtab} object has the following attributes:
5050 @defvar Symtab.filename
5051 The symbol table's source filename. This attribute is not writable.
5054 @defvar Symtab.objfile
5055 The symbol table's backing object file. @xref{Objfiles In Python}.
5056 This attribute is not writable.
5059 @defvar Symtab.producer
5060 The name and possibly version number of the program that
5061 compiled the code in the symbol table.
5062 The contents of this string is up to the compiler.
5063 If no producer information is available then @code{None} is returned.
5064 This attribute is not writable.
5067 A @code{gdb.Symtab} object has the following methods:
5069 @defun Symtab.is_valid ()
5070 Returns @code{True} if the @code{gdb.Symtab} object is valid,
5071 @code{False} if not. A @code{gdb.Symtab} object can become invalid if
5072 the symbol table it refers to does not exist in @value{GDBN} any
5073 longer. All other @code{gdb.Symtab} methods will throw an exception
5074 if it is invalid at the time the method is called.
5077 @defun Symtab.fullname ()
5078 Return the symbol table's source absolute file name.
5081 @defun Symtab.global_block ()
5082 Return the global block of the underlying symbol table.
5083 @xref{Blocks In Python}.
5086 @defun Symtab.static_block ()
5087 Return the static block of the underlying symbol table.
5088 @xref{Blocks In Python}.
5091 @defun Symtab.linetable ()
5092 Return the line table associated with the symbol table.
5093 @xref{Line Tables In Python}.
5096 @node Line Tables In Python
5097 @subsubsection Manipulating line tables using Python
5099 @cindex line tables in python
5100 @tindex gdb.LineTable
5102 Python code can request and inspect line table information from a
5103 symbol table that is loaded in @value{GDBN}. A line table is a
5104 mapping of source lines to their executable locations in memory. To
5105 acquire the line table information for a particular symbol table, use
5106 the @code{linetable} function (@pxref{Symbol Tables In Python}).
5108 A @code{gdb.LineTable} is iterable. The iterator returns
5109 @code{LineTableEntry} objects that correspond to the source line and
5110 address for each line table entry. @code{LineTableEntry} objects have
5111 the following attributes:
5113 @defvar LineTableEntry.line
5114 The source line number for this line table entry. This number
5115 corresponds to the actual line of source. This attribute is not
5119 @defvar LineTableEntry.pc
5120 The address that is associated with the line table entry where the
5121 executable code for that source line resides in memory. This
5122 attribute is not writable.
5125 As there can be multiple addresses for a single source line, you may
5126 receive multiple @code{LineTableEntry} objects with matching
5127 @code{line} attributes, but with different @code{pc} attributes. The
5128 iterator is sorted in ascending @code{pc} order. Here is a small
5129 example illustrating iterating over a line table.
5132 symtab = gdb.selected_frame().find_sal().symtab
5133 linetable = symtab.linetable()
5134 for line in linetable:
5135 print "Line: "+str(line.line)+" Address: "+hex(line.pc)
5138 This will have the following output:
5141 Line: 33 Address: 0x4005c8L
5142 Line: 37 Address: 0x4005caL
5143 Line: 39 Address: 0x4005d2L
5144 Line: 40 Address: 0x4005f8L
5145 Line: 42 Address: 0x4005ffL
5146 Line: 44 Address: 0x400608L
5147 Line: 42 Address: 0x40060cL
5148 Line: 45 Address: 0x400615L
5151 In addition to being able to iterate over a @code{LineTable}, it also
5152 has the following direct access methods:
5154 @defun LineTable.line (line)
5155 Return a Python @code{Tuple} of @code{LineTableEntry} objects for any
5156 entries in the line table for the given @var{line}, which specifies
5157 the source code line. If there are no entries for that source code
5158 @var{line}, the Python @code{None} is returned.
5161 @defun LineTable.has_line (line)
5162 Return a Python @code{Boolean} indicating whether there is an entry in
5163 the line table for this source line. Return @code{True} if an entry
5164 is found, or @code{False} if not.
5167 @defun LineTable.source_lines ()
5168 Return a Python @code{List} of the source line numbers in the symbol
5169 table. Only lines with executable code locations are returned. The
5170 contents of the @code{List} will just be the source line entries
5171 represented as Python @code{Long} values.
5174 @node Breakpoints In Python
5175 @subsubsection Manipulating breakpoints using Python
5177 @cindex breakpoints in python
5178 @tindex gdb.Breakpoint
5180 Python code can manipulate breakpoints via the @code{gdb.Breakpoint}
5183 A breakpoint can be created using one of the two forms of the
5184 @code{gdb.Breakpoint} constructor. The first one accepts a string
5185 like one would pass to the @code{break}
5186 (@pxref{Set Breaks,,Setting Breakpoints}) and @code{watch}
5187 (@pxref{Set Watchpoints, , Setting Watchpoints}) commands, and can be used to
5188 create both breakpoints and watchpoints. The second accepts separate Python
5189 arguments similar to @ref{Explicit Locations}, and can only be used to create
5192 @defun Breakpoint.__init__ (spec @r{[}, type @r{][}, wp_class @r{][}, internal @r{][}, temporary @r{][}, qualified @r{]})
5193 Create a new breakpoint according to @var{spec}, which is a string naming the
5194 location of a breakpoint, or an expression that defines a watchpoint. The
5195 string should describe a location in a format recognized by the @code{break}
5196 command (@pxref{Set Breaks,,Setting Breakpoints}) or, in the case of a
5197 watchpoint, by the @code{watch} command
5198 (@pxref{Set Watchpoints, , Setting Watchpoints}).
5200 The optional @var{type} argument specifies the type of the breakpoint to create,
5203 The optional @var{wp_class} argument defines the class of watchpoint to create,
5204 if @var{type} is @code{gdb.BP_WATCHPOINT}. If @var{wp_class} is omitted, it
5205 defaults to @code{gdb.WP_WRITE}.
5207 The optional @var{internal} argument allows the breakpoint to become invisible
5208 to the user. The breakpoint will neither be reported when created, nor will it
5209 be listed in the output from @code{info breakpoints} (but will be listed with
5210 the @code{maint info breakpoints} command).
5212 The optional @var{temporary} argument makes the breakpoint a temporary
5213 breakpoint. Temporary breakpoints are deleted after they have been hit. Any
5214 further access to the Python breakpoint after it has been hit will result in a
5215 runtime error (as that breakpoint has now been automatically deleted).
5217 The optional @var{qualified} argument is a boolean that allows interpreting
5218 the function passed in @code{spec} as a fully-qualified name. It is equivalent
5219 to @code{break}'s @code{-qualified} flag (@pxref{Linespec Locations} and
5220 @ref{Explicit Locations}).
5224 @defun Breakpoint.__init__ (@r{[} source @r{][}, function @r{][}, label @r{][}, line @r{]}, @r{][} internal @r{][}, temporary @r{][}, qualified @r{]})
5225 This second form of creating a new breakpoint specifies the explicit
5226 location (@pxref{Explicit Locations}) using keywords. The new breakpoint will
5227 be created in the specified source file @var{source}, at the specified
5228 @var{function}, @var{label} and @var{line}.
5230 @var{internal}, @var{temporary} and @var{qualified} have the same usage as
5231 explained previously.
5234 The available types are represented by constants defined in the @code{gdb}
5238 @vindex BP_BREAKPOINT
5239 @item gdb.BP_BREAKPOINT
5240 Normal code breakpoint.
5242 @vindex BP_WATCHPOINT
5243 @item gdb.BP_WATCHPOINT
5244 Watchpoint breakpoint.
5246 @vindex BP_HARDWARE_WATCHPOINT
5247 @item gdb.BP_HARDWARE_WATCHPOINT
5248 Hardware assisted watchpoint.
5250 @vindex BP_READ_WATCHPOINT
5251 @item gdb.BP_READ_WATCHPOINT
5252 Hardware assisted read watchpoint.
5254 @vindex BP_ACCESS_WATCHPOINT
5255 @item gdb.BP_ACCESS_WATCHPOINT
5256 Hardware assisted access watchpoint.
5259 The available watchpoint types represented by constants are defined in the
5265 Read only watchpoint.
5269 Write only watchpoint.
5273 Read/Write watchpoint.
5276 @defun Breakpoint.stop (self)
5277 The @code{gdb.Breakpoint} class can be sub-classed and, in
5278 particular, you may choose to implement the @code{stop} method.
5279 If this method is defined in a sub-class of @code{gdb.Breakpoint},
5280 it will be called when the inferior reaches any location of a
5281 breakpoint which instantiates that sub-class. If the method returns
5282 @code{True}, the inferior will be stopped at the location of the
5283 breakpoint, otherwise the inferior will continue.
5285 If there are multiple breakpoints at the same location with a
5286 @code{stop} method, each one will be called regardless of the
5287 return status of the previous. This ensures that all @code{stop}
5288 methods have a chance to execute at that location. In this scenario
5289 if one of the methods returns @code{True} but the others return
5290 @code{False}, the inferior will still be stopped.
5292 You should not alter the execution state of the inferior (i.e.@:, step,
5293 next, etc.), alter the current frame context (i.e.@:, change the current
5294 active frame), or alter, add or delete any breakpoint. As a general
5295 rule, you should not alter any data within @value{GDBN} or the inferior
5298 Example @code{stop} implementation:
5301 class MyBreakpoint (gdb.Breakpoint):
5303 inf_val = gdb.parse_and_eval("foo")
5310 @defun Breakpoint.is_valid ()
5311 Return @code{True} if this @code{Breakpoint} object is valid,
5312 @code{False} otherwise. A @code{Breakpoint} object can become invalid
5313 if the user deletes the breakpoint. In this case, the object still
5314 exists, but the underlying breakpoint does not. In the cases of
5315 watchpoint scope, the watchpoint remains valid even if execution of the
5316 inferior leaves the scope of that watchpoint.
5319 @defun Breakpoint.delete ()
5320 Permanently deletes the @value{GDBN} breakpoint. This also
5321 invalidates the Python @code{Breakpoint} object. Any further access
5322 to this object's attributes or methods will raise an error.
5325 @defvar Breakpoint.enabled
5326 This attribute is @code{True} if the breakpoint is enabled, and
5327 @code{False} otherwise. This attribute is writable. You can use it to enable
5328 or disable the breakpoint.
5331 @defvar Breakpoint.silent
5332 This attribute is @code{True} if the breakpoint is silent, and
5333 @code{False} otherwise. This attribute is writable.
5335 Note that a breakpoint can also be silent if it has commands and the
5336 first command is @code{silent}. This is not reported by the
5337 @code{silent} attribute.
5340 @defvar Breakpoint.pending
5341 This attribute is @code{True} if the breakpoint is pending, and
5342 @code{False} otherwise. @xref{Set Breaks}. This attribute is
5346 @anchor{python_breakpoint_thread}
5347 @defvar Breakpoint.thread
5348 If the breakpoint is thread-specific, this attribute holds the
5349 thread's global id. If the breakpoint is not thread-specific, this
5350 attribute is @code{None}. This attribute is writable.
5353 @defvar Breakpoint.task
5354 If the breakpoint is Ada task-specific, this attribute holds the Ada task
5355 id. If the breakpoint is not task-specific (or the underlying
5356 language is not Ada), this attribute is @code{None}. This attribute
5360 @defvar Breakpoint.ignore_count
5361 This attribute holds the ignore count for the breakpoint, an integer.
5362 This attribute is writable.
5365 @defvar Breakpoint.number
5366 This attribute holds the breakpoint's number --- the identifier used by
5367 the user to manipulate the breakpoint. This attribute is not writable.
5370 @defvar Breakpoint.type
5371 This attribute holds the breakpoint's type --- the identifier used to
5372 determine the actual breakpoint type or use-case. This attribute is not
5376 @defvar Breakpoint.visible
5377 This attribute tells whether the breakpoint is visible to the user
5378 when set, or when the @samp{info breakpoints} command is run. This
5379 attribute is not writable.
5382 @defvar Breakpoint.temporary
5383 This attribute indicates whether the breakpoint was created as a
5384 temporary breakpoint. Temporary breakpoints are automatically deleted
5385 after that breakpoint has been hit. Access to this attribute, and all
5386 other attributes and functions other than the @code{is_valid}
5387 function, will result in an error after the breakpoint has been hit
5388 (as it has been automatically deleted). This attribute is not
5392 @defvar Breakpoint.hit_count
5393 This attribute holds the hit count for the breakpoint, an integer.
5394 This attribute is writable, but currently it can only be set to zero.
5397 @defvar Breakpoint.location
5398 This attribute holds the location of the breakpoint, as specified by
5399 the user. It is a string. If the breakpoint does not have a location
5400 (that is, it is a watchpoint) the attribute's value is @code{None}. This
5401 attribute is not writable.
5404 @defvar Breakpoint.expression
5405 This attribute holds a breakpoint expression, as specified by
5406 the user. It is a string. If the breakpoint does not have an
5407 expression (the breakpoint is not a watchpoint) the attribute's value
5408 is @code{None}. This attribute is not writable.
5411 @defvar Breakpoint.condition
5412 This attribute holds the condition of the breakpoint, as specified by
5413 the user. It is a string. If there is no condition, this attribute's
5414 value is @code{None}. This attribute is writable.
5417 @defvar Breakpoint.commands
5418 This attribute holds the commands attached to the breakpoint. If
5419 there are commands, this attribute's value is a string holding all the
5420 commands, separated by newlines. If there are no commands, this
5421 attribute is @code{None}. This attribute is writable.
5424 @node Finish Breakpoints in Python
5425 @subsubsection Finish Breakpoints
5427 @cindex python finish breakpoints
5428 @tindex gdb.FinishBreakpoint
5430 A finish breakpoint is a temporary breakpoint set at the return address of
5431 a frame, based on the @code{finish} command. @code{gdb.FinishBreakpoint}
5432 extends @code{gdb.Breakpoint}. The underlying breakpoint will be disabled
5433 and deleted when the execution will run out of the breakpoint scope (i.e.@:
5434 @code{Breakpoint.stop} or @code{FinishBreakpoint.out_of_scope} triggered).
5435 Finish breakpoints are thread specific and must be create with the right
5438 @defun FinishBreakpoint.__init__ (@r{[}frame@r{]} @r{[}, internal@r{]})
5439 Create a finish breakpoint at the return address of the @code{gdb.Frame}
5440 object @var{frame}. If @var{frame} is not provided, this defaults to the
5441 newest frame. The optional @var{internal} argument allows the breakpoint to
5442 become invisible to the user. @xref{Breakpoints In Python}, for further
5443 details about this argument.
5446 @defun FinishBreakpoint.out_of_scope (self)
5447 In some circumstances (e.g.@: @code{longjmp}, C@t{++} exceptions, @value{GDBN}
5448 @code{return} command, @dots{}), a function may not properly terminate, and
5449 thus never hit the finish breakpoint. When @value{GDBN} notices such a
5450 situation, the @code{out_of_scope} callback will be triggered.
5452 You may want to sub-class @code{gdb.FinishBreakpoint} and override this
5456 class MyFinishBreakpoint (gdb.FinishBreakpoint)
5458 print "normal finish"
5461 def out_of_scope ():
5462 print "abnormal finish"
5466 @defvar FinishBreakpoint.return_value
5467 When @value{GDBN} is stopped at a finish breakpoint and the frame
5468 used to build the @code{gdb.FinishBreakpoint} object had debug symbols, this
5469 attribute will contain a @code{gdb.Value} object corresponding to the return
5470 value of the function. The value will be @code{None} if the function return
5471 type is @code{void} or if the return value was not computable. This attribute
5475 @node Lazy Strings In Python
5476 @subsubsection Python representation of lazy strings
5478 @cindex lazy strings in python
5479 @tindex gdb.LazyString
5481 A @dfn{lazy string} is a string whose contents is not retrieved or
5482 encoded until it is needed.
5484 A @code{gdb.LazyString} is represented in @value{GDBN} as an
5485 @code{address} that points to a region of memory, an @code{encoding}
5486 that will be used to encode that region of memory, and a @code{length}
5487 to delimit the region of memory that represents the string. The
5488 difference between a @code{gdb.LazyString} and a string wrapped within
5489 a @code{gdb.Value} is that a @code{gdb.LazyString} will be treated
5490 differently by @value{GDBN} when printing. A @code{gdb.LazyString} is
5491 retrieved and encoded during printing, while a @code{gdb.Value}
5492 wrapping a string is immediately retrieved and encoded on creation.
5494 A @code{gdb.LazyString} object has the following functions:
5496 @defun LazyString.value ()
5497 Convert the @code{gdb.LazyString} to a @code{gdb.Value}. This value
5498 will point to the string in memory, but will lose all the delayed
5499 retrieval, encoding and handling that @value{GDBN} applies to a
5500 @code{gdb.LazyString}.
5503 @defvar LazyString.address
5504 This attribute holds the address of the string. This attribute is not
5508 @defvar LazyString.length
5509 This attribute holds the length of the string in characters. If the
5510 length is -1, then the string will be fetched and encoded up to the
5511 first null of appropriate width. This attribute is not writable.
5514 @defvar LazyString.encoding
5515 This attribute holds the encoding that will be applied to the string
5516 when the string is printed by @value{GDBN}. If the encoding is not
5517 set, or contains an empty string, then @value{GDBN} will select the
5518 most appropriate encoding when the string is printed. This attribute
5522 @defvar LazyString.type
5523 This attribute holds the type that is represented by the lazy string's
5524 type. For a lazy string this is a pointer or array type. To
5525 resolve this to the lazy string's character type, use the type's
5526 @code{target} method. @xref{Types In Python}. This attribute is not
5530 @node Architectures In Python
5531 @subsubsection Python representation of architectures
5532 @cindex Python architectures
5534 @value{GDBN} uses architecture specific parameters and artifacts in a
5535 number of its various computations. An architecture is represented
5536 by an instance of the @code{gdb.Architecture} class.
5538 A @code{gdb.Architecture} class has the following methods:
5540 @defun Architecture.name ()
5541 Return the name (string value) of the architecture.
5544 @defun Architecture.disassemble (@var{start_pc} @r{[}, @var{end_pc} @r{[}, @var{count}@r{]]})
5545 Return a list of disassembled instructions starting from the memory
5546 address @var{start_pc}. The optional arguments @var{end_pc} and
5547 @var{count} determine the number of instructions in the returned list.
5548 If both the optional arguments @var{end_pc} and @var{count} are
5549 specified, then a list of at most @var{count} disassembled instructions
5550 whose start address falls in the closed memory address interval from
5551 @var{start_pc} to @var{end_pc} are returned. If @var{end_pc} is not
5552 specified, but @var{count} is specified, then @var{count} number of
5553 instructions starting from the address @var{start_pc} are returned. If
5554 @var{count} is not specified but @var{end_pc} is specified, then all
5555 instructions whose start address falls in the closed memory address
5556 interval from @var{start_pc} to @var{end_pc} are returned. If neither
5557 @var{end_pc} nor @var{count} are specified, then a single instruction at
5558 @var{start_pc} is returned. For all of these cases, each element of the
5559 returned list is a Python @code{dict} with the following string keys:
5564 The value corresponding to this key is a Python long integer capturing
5565 the memory address of the instruction.
5568 The value corresponding to this key is a string value which represents
5569 the instruction with assembly language mnemonics. The assembly
5570 language flavor used is the same as that specified by the current CLI
5571 variable @code{disassembly-flavor}. @xref{Machine Code}.
5574 The value corresponding to this key is the length (integer value) of the
5575 instruction in bytes.
5580 @node Python Auto-loading
5581 @subsection Python Auto-loading
5582 @cindex Python auto-loading
5584 When a new object file is read (for example, due to the @code{file}
5585 command, or because the inferior has loaded a shared library),
5586 @value{GDBN} will look for Python support scripts in several ways:
5587 @file{@var{objfile}-gdb.py} and @code{.debug_gdb_scripts} section.
5588 @xref{Auto-loading extensions}.
5590 The auto-loading feature is useful for supplying application-specific
5591 debugging commands and scripts.
5593 Auto-loading can be enabled or disabled,
5594 and the list of auto-loaded scripts can be printed.
5597 @anchor{set auto-load python-scripts}
5598 @kindex set auto-load python-scripts
5599 @item set auto-load python-scripts [on|off]
5600 Enable or disable the auto-loading of Python scripts.
5602 @anchor{show auto-load python-scripts}
5603 @kindex show auto-load python-scripts
5604 @item show auto-load python-scripts
5605 Show whether auto-loading of Python scripts is enabled or disabled.
5607 @anchor{info auto-load python-scripts}
5608 @kindex info auto-load python-scripts
5609 @cindex print list of auto-loaded Python scripts
5610 @item info auto-load python-scripts [@var{regexp}]
5611 Print the list of all Python scripts that @value{GDBN} auto-loaded.
5613 Also printed is the list of Python scripts that were mentioned in
5614 the @code{.debug_gdb_scripts} section and were either not found
5615 (@pxref{dotdebug_gdb_scripts section}) or were not auto-loaded due to
5616 @code{auto-load safe-path} rejection (@pxref{Auto-loading}).
5617 This is useful because their names are not printed when @value{GDBN}
5618 tries to load them and fails. There may be many of them, and printing
5619 an error message for each one is problematic.
5621 If @var{regexp} is supplied only Python scripts with matching names are printed.
5626 (gdb) info auto-load python-scripts
5628 Yes py-section-script.py
5629 full name: /tmp/py-section-script.py
5630 No my-foo-pretty-printers.py
5634 When reading an auto-loaded file or script, @value{GDBN} sets the
5635 @dfn{current objfile}. This is available via the @code{gdb.current_objfile}
5636 function (@pxref{Objfiles In Python}). This can be useful for
5637 registering objfile-specific pretty-printers and frame-filters.
5639 @node Python modules
5640 @subsection Python modules
5641 @cindex python modules
5643 @value{GDBN} comes with several modules to assist writing Python code.
5646 * gdb.printing:: Building and registering pretty-printers.
5647 * gdb.types:: Utilities for working with types.
5648 * gdb.prompt:: Utilities for prompt value substitution.
5652 @subsubsection gdb.printing
5653 @cindex gdb.printing
5655 This module provides a collection of utilities for working with
5659 @item PrettyPrinter (@var{name}, @var{subprinters}=None)
5660 This class specifies the API that makes @samp{info pretty-printer},
5661 @samp{enable pretty-printer} and @samp{disable pretty-printer} work.
5662 Pretty-printers should generally inherit from this class.
5664 @item SubPrettyPrinter (@var{name})
5665 For printers that handle multiple types, this class specifies the
5666 corresponding API for the subprinters.
5668 @item RegexpCollectionPrettyPrinter (@var{name})
5669 Utility class for handling multiple printers, all recognized via
5670 regular expressions.
5671 @xref{Writing a Pretty-Printer}, for an example.
5673 @item FlagEnumerationPrinter (@var{name})
5674 A pretty-printer which handles printing of @code{enum} values. Unlike
5675 @value{GDBN}'s built-in @code{enum} printing, this printer attempts to
5676 work properly when there is some overlap between the enumeration
5677 constants. The argument @var{name} is the name of the printer and
5678 also the name of the @code{enum} type to look up.
5680 @item register_pretty_printer (@var{obj}, @var{printer}, @var{replace}=False)
5681 Register @var{printer} with the pretty-printer list of @var{obj}.
5682 If @var{replace} is @code{True} then any existing copy of the printer
5683 is replaced. Otherwise a @code{RuntimeError} exception is raised
5684 if a printer with the same name already exists.
5688 @subsubsection gdb.types
5691 This module provides a collection of utilities for working with
5692 @code{gdb.Type} objects.
5695 @item get_basic_type (@var{type})
5696 Return @var{type} with const and volatile qualifiers stripped,
5697 and with typedefs and C@t{++} references converted to the underlying type.
5702 typedef const int const_int;
5704 const_int& foo_ref (foo);
5705 int main () @{ return 0; @}
5712 (gdb) python import gdb.types
5713 (gdb) python foo_ref = gdb.parse_and_eval("foo_ref")
5714 (gdb) python print gdb.types.get_basic_type(foo_ref.type)
5718 @item has_field (@var{type}, @var{field})
5719 Return @code{True} if @var{type}, assumed to be a type with fields
5720 (e.g., a structure or union), has field @var{field}.
5722 @item make_enum_dict (@var{enum_type})
5723 Return a Python @code{dictionary} type produced from @var{enum_type}.
5725 @item deep_items (@var{type})
5726 Returns a Python iterator similar to the standard
5727 @code{gdb.Type.iteritems} method, except that the iterator returned
5728 by @code{deep_items} will recursively traverse anonymous struct or
5729 union fields. For example:
5743 Then in @value{GDBN}:
5745 (@value{GDBP}) python import gdb.types
5746 (@value{GDBP}) python struct_a = gdb.lookup_type("struct A")
5747 (@value{GDBP}) python print struct_a.keys ()
5749 (@value{GDBP}) python print [k for k,v in gdb.types.deep_items(struct_a)]
5750 @{['a', 'b0', 'b1']@}
5753 @item get_type_recognizers ()
5754 Return a list of the enabled type recognizers for the current context.
5755 This is called by @value{GDBN} during the type-printing process
5756 (@pxref{Type Printing API}).
5758 @item apply_type_recognizers (recognizers, type_obj)
5759 Apply the type recognizers, @var{recognizers}, to the type object
5760 @var{type_obj}. If any recognizer returns a string, return that
5761 string. Otherwise, return @code{None}. This is called by
5762 @value{GDBN} during the type-printing process (@pxref{Type Printing
5765 @item register_type_printer (locus, printer)
5766 This is a convenience function to register a type printer
5767 @var{printer}. The printer must implement the type printer protocol.
5768 The @var{locus} argument is either a @code{gdb.Objfile}, in which case
5769 the printer is registered with that objfile; a @code{gdb.Progspace},
5770 in which case the printer is registered with that progspace; or
5771 @code{None}, in which case the printer is registered globally.
5774 This is a base class that implements the type printer protocol. Type
5775 printers are encouraged, but not required, to derive from this class.
5776 It defines a constructor:
5778 @defmethod TypePrinter __init__ (self, name)
5779 Initialize the type printer with the given name. The new printer
5780 starts in the enabled state.
5786 @subsubsection gdb.prompt
5789 This module provides a method for prompt value-substitution.
5792 @item substitute_prompt (@var{string})
5793 Return @var{string} with escape sequences substituted by values. Some
5794 escape sequences take arguments. You can specify arguments inside
5795 ``@{@}'' immediately following the escape sequence.
5797 The escape sequences you can pass to this function are:
5801 Substitute a backslash.
5803 Substitute an ESC character.
5805 Substitute the selected frame; an argument names a frame parameter.
5807 Substitute a newline.
5809 Substitute a parameter's value; the argument names the parameter.
5811 Substitute a carriage return.
5813 Substitute the selected thread; an argument names a thread parameter.
5815 Substitute the version of GDB.
5817 Substitute the current working directory.
5819 Begin a sequence of non-printing characters. These sequences are
5820 typically used with the ESC character, and are not counted in the string
5821 length. Example: ``\[\e[0;34m\](gdb)\[\e[0m\]'' will return a
5822 blue-colored ``(gdb)'' prompt where the length is five.
5824 End a sequence of non-printing characters.
5830 substitute_prompt (``frame: \f,
5831 print arguments: \p@{print frame-arguments@}'')
5834 @exdent will return the string:
5837 "frame: main, print arguments: scalars"