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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
935 The maximum depth to print for nested structs and unions, or @code{-1}
936 to print an unlimited number of elements (see @code{set print
937 max-depth} in @ref{Print Settings}).
939 @item repeat_threshold
940 Set the threshold for suppressing display of repeated array elements, or
941 @code{0} to represent all elements, even if repeated. (See @code{set
942 print repeats} in @ref{Print Settings}).
945 A string containing a single character representing the format to use for
946 the returned string. For instance, @code{'x'} is equivalent to using the
947 @value{GDBN} command @code{print} with the @code{/x} option and formats
948 the value as a hexadecimal number.
952 @defun Value.string (@r{[}encoding@r{[}, errors@r{[}, length@r{]]]})
953 If this @code{gdb.Value} represents a string, then this method
954 converts the contents to a Python string. Otherwise, this method will
957 Values are interpreted as strings according to the rules of the
958 current language. If the optional length argument is given, the
959 string will be converted to that length, and will include any embedded
960 zeroes that the string may contain. Otherwise, for languages
961 where the string is zero-terminated, the entire string will be
964 For example, in C-like languages, a value is a string if it is a pointer
965 to or an array of characters or ints of type @code{wchar_t}, @code{char16_t},
968 If the optional @var{encoding} argument is given, it must be a string
969 naming the encoding of the string in the @code{gdb.Value}, such as
970 @code{"ascii"}, @code{"iso-8859-6"} or @code{"utf-8"}. It accepts
971 the same encodings as the corresponding argument to Python's
972 @code{string.decode} method, and the Python codec machinery will be used
973 to convert the string. If @var{encoding} is not given, or if
974 @var{encoding} is the empty string, then either the @code{target-charset}
975 (@pxref{Character Sets}) will be used, or a language-specific encoding
976 will be used, if the current language is able to supply one.
978 The optional @var{errors} argument is the same as the corresponding
979 argument to Python's @code{string.decode} method.
981 If the optional @var{length} argument is given, the string will be
982 fetched and converted to the given length.
985 @defun Value.lazy_string (@r{[}encoding @r{[}, length@r{]]})
986 If this @code{gdb.Value} represents a string, then this method
987 converts the contents to a @code{gdb.LazyString} (@pxref{Lazy Strings
988 In Python}). Otherwise, this method will throw an exception.
990 If the optional @var{encoding} argument is given, it must be a string
991 naming the encoding of the @code{gdb.LazyString}. Some examples are:
992 @samp{ascii}, @samp{iso-8859-6} or @samp{utf-8}. If the
993 @var{encoding} argument is an encoding that @value{GDBN} does
994 recognize, @value{GDBN} will raise an error.
996 When a lazy string is printed, the @value{GDBN} encoding machinery is
997 used to convert the string during printing. If the optional
998 @var{encoding} argument is not provided, or is an empty string,
999 @value{GDBN} will automatically select the encoding most suitable for
1000 the string type. For further information on encoding in @value{GDBN}
1001 please see @ref{Character Sets}.
1003 If the optional @var{length} argument is given, the string will be
1004 fetched and encoded to the length of characters specified. If
1005 the @var{length} argument is not provided, the string will be fetched
1006 and encoded until a null of appropriate width is found.
1009 @defun Value.fetch_lazy ()
1010 If the @code{gdb.Value} object is currently a lazy value
1011 (@code{gdb.Value.is_lazy} is @code{True}), then the value is
1012 fetched from the inferior. Any errors that occur in the process
1013 will produce a Python exception.
1015 If the @code{gdb.Value} object is not a lazy value, this method
1018 This method does not return a value.
1022 @node Types In Python
1023 @subsubsection Types In Python
1024 @cindex types in Python
1025 @cindex Python, working with types
1028 @value{GDBN} represents types from the inferior using the class
1031 The following type-related functions are available in the @code{gdb}
1034 @findex gdb.lookup_type
1035 @defun gdb.lookup_type (name @r{[}, block@r{]})
1036 This function looks up a type by its @var{name}, which must be a string.
1038 If @var{block} is given, then @var{name} is looked up in that scope.
1039 Otherwise, it is searched for globally.
1041 Ordinarily, this function will return an instance of @code{gdb.Type}.
1042 If the named type cannot be found, it will throw an exception.
1045 If the type is a structure or class type, or an enum type, the fields
1046 of that type can be accessed using the Python @dfn{dictionary syntax}.
1047 For example, if @code{some_type} is a @code{gdb.Type} instance holding
1048 a structure type, you can access its @code{foo} field with:
1051 bar = some_type['foo']
1054 @code{bar} will be a @code{gdb.Field} object; see below under the
1055 description of the @code{Type.fields} method for a description of the
1056 @code{gdb.Field} class.
1058 An instance of @code{Type} has the following attributes:
1060 @defvar Type.alignof
1061 The alignment of this type, in bytes. Type alignment comes from the
1062 debugging information; if it was not specified, then @value{GDBN} will
1063 use the relevant ABI to try to determine the alignment. In some
1064 cases, even this is not possible, and zero will be returned.
1068 The type code for this type. The type code will be one of the
1069 @code{TYPE_CODE_} constants defined below.
1073 The name of this type. If this type has no name, then @code{None}
1078 The size of this type, in target @code{char} units. Usually, a
1079 target's @code{char} type will be an 8-bit byte. However, on some
1080 unusual platforms, this type may have a different size.
1084 The tag name for this type. The tag name is the name after
1085 @code{struct}, @code{union}, or @code{enum} in C and C@t{++}; not all
1086 languages have this concept. If this type has no tag name, then
1087 @code{None} is returned.
1090 The following methods are provided:
1092 @defun Type.fields ()
1093 For structure and union types, this method returns the fields. Range
1094 types have two fields, the minimum and maximum values. Enum types
1095 have one field per enum constant. Function and method types have one
1096 field per parameter. The base types of C@t{++} classes are also
1097 represented as fields. If the type has no fields, or does not fit
1098 into one of these categories, an empty sequence will be returned.
1100 Each field is a @code{gdb.Field} object, with some pre-defined attributes:
1103 This attribute is not available for @code{enum} or @code{static}
1104 (as in C@t{++}) fields. The value is the position, counting
1105 in bits, from the start of the containing type.
1108 This attribute is only available for @code{enum} fields, and its value
1109 is the enumeration member's integer representation.
1112 The name of the field, or @code{None} for anonymous fields.
1115 This is @code{True} if the field is artificial, usually meaning that
1116 it was provided by the compiler and not the user. This attribute is
1117 always provided, and is @code{False} if the field is not artificial.
1120 This is @code{True} if the field represents a base class of a C@t{++}
1121 structure. This attribute is always provided, and is @code{False}
1122 if the field is not a base class of the type that is the argument of
1123 @code{fields}, or if that type was not a C@t{++} class.
1126 If the field is packed, or is a bitfield, then this will have a
1127 non-zero value, which is the size of the field in bits. Otherwise,
1128 this will be zero; in this case the field's size is given by its type.
1131 The type of the field. This is usually an instance of @code{Type},
1132 but it can be @code{None} in some situations.
1135 The type which contains this field. This is an instance of
1140 @defun Type.array (@var{n1} @r{[}, @var{n2}@r{]})
1141 Return a new @code{gdb.Type} object which represents an array of this
1142 type. If one argument is given, it is the inclusive upper bound of
1143 the array; in this case the lower bound is zero. If two arguments are
1144 given, the first argument is the lower bound of the array, and the
1145 second argument is the upper bound of the array. An array's length
1146 must not be negative, but the bounds can be.
1149 @defun Type.vector (@var{n1} @r{[}, @var{n2}@r{]})
1150 Return a new @code{gdb.Type} object which represents a vector of this
1151 type. If one argument is given, it is the inclusive upper bound of
1152 the vector; in this case the lower bound is zero. If two arguments are
1153 given, the first argument is the lower bound of the vector, and the
1154 second argument is the upper bound of the vector. A vector's length
1155 must not be negative, but the bounds can be.
1157 The difference between an @code{array} and a @code{vector} is that
1158 arrays behave like in C: when used in expressions they decay to a pointer
1159 to the first element whereas vectors are treated as first class values.
1162 @defun Type.const ()
1163 Return a new @code{gdb.Type} object which represents a
1164 @code{const}-qualified variant of this type.
1167 @defun Type.volatile ()
1168 Return a new @code{gdb.Type} object which represents a
1169 @code{volatile}-qualified variant of this type.
1172 @defun Type.unqualified ()
1173 Return a new @code{gdb.Type} object which represents an unqualified
1174 variant of this type. That is, the result is neither @code{const} nor
1178 @defun Type.range ()
1179 Return a Python @code{Tuple} object that contains two elements: the
1180 low bound of the argument type and the high bound of that type. If
1181 the type does not have a range, @value{GDBN} will raise a
1182 @code{gdb.error} exception (@pxref{Exception Handling}).
1185 @defun Type.reference ()
1186 Return a new @code{gdb.Type} object which represents a reference to this
1190 @defun Type.pointer ()
1191 Return a new @code{gdb.Type} object which represents a pointer to this
1195 @defun Type.strip_typedefs ()
1196 Return a new @code{gdb.Type} that represents the real type,
1197 after removing all layers of typedefs.
1200 @defun Type.target ()
1201 Return a new @code{gdb.Type} object which represents the target type
1204 For a pointer type, the target type is the type of the pointed-to
1205 object. For an array type (meaning C-like arrays), the target type is
1206 the type of the elements of the array. For a function or method type,
1207 the target type is the type of the return value. For a complex type,
1208 the target type is the type of the elements. For a typedef, the
1209 target type is the aliased type.
1211 If the type does not have a target, this method will throw an
1215 @defun Type.template_argument (n @r{[}, block@r{]})
1216 If this @code{gdb.Type} is an instantiation of a template, this will
1217 return a new @code{gdb.Value} or @code{gdb.Type} which represents the
1218 value of the @var{n}th template argument (indexed starting at 0).
1220 If this @code{gdb.Type} is not a template type, or if the type has fewer
1221 than @var{n} template arguments, this will throw an exception.
1222 Ordinarily, only C@t{++} code will have template types.
1224 If @var{block} is given, then @var{name} is looked up in that scope.
1225 Otherwise, it is searched for globally.
1228 @defun Type.optimized_out ()
1229 Return @code{gdb.Value} instance of this type whose value is optimized
1230 out. This allows a frame decorator to indicate that the value of an
1231 argument or a local variable is not known.
1234 Each type has a code, which indicates what category this type falls
1235 into. The available type categories are represented by constants
1236 defined in the @code{gdb} module:
1239 @vindex TYPE_CODE_PTR
1240 @item gdb.TYPE_CODE_PTR
1241 The type is a pointer.
1243 @vindex TYPE_CODE_ARRAY
1244 @item gdb.TYPE_CODE_ARRAY
1245 The type is an array.
1247 @vindex TYPE_CODE_STRUCT
1248 @item gdb.TYPE_CODE_STRUCT
1249 The type is a structure.
1251 @vindex TYPE_CODE_UNION
1252 @item gdb.TYPE_CODE_UNION
1253 The type is a union.
1255 @vindex TYPE_CODE_ENUM
1256 @item gdb.TYPE_CODE_ENUM
1257 The type is an enum.
1259 @vindex TYPE_CODE_FLAGS
1260 @item gdb.TYPE_CODE_FLAGS
1261 A bit flags type, used for things such as status registers.
1263 @vindex TYPE_CODE_FUNC
1264 @item gdb.TYPE_CODE_FUNC
1265 The type is a function.
1267 @vindex TYPE_CODE_INT
1268 @item gdb.TYPE_CODE_INT
1269 The type is an integer type.
1271 @vindex TYPE_CODE_FLT
1272 @item gdb.TYPE_CODE_FLT
1273 A floating point type.
1275 @vindex TYPE_CODE_VOID
1276 @item gdb.TYPE_CODE_VOID
1277 The special type @code{void}.
1279 @vindex TYPE_CODE_SET
1280 @item gdb.TYPE_CODE_SET
1283 @vindex TYPE_CODE_RANGE
1284 @item gdb.TYPE_CODE_RANGE
1285 A range type, that is, an integer type with bounds.
1287 @vindex TYPE_CODE_STRING
1288 @item gdb.TYPE_CODE_STRING
1289 A string type. Note that this is only used for certain languages with
1290 language-defined string types; C strings are not represented this way.
1292 @vindex TYPE_CODE_BITSTRING
1293 @item gdb.TYPE_CODE_BITSTRING
1294 A string of bits. It is deprecated.
1296 @vindex TYPE_CODE_ERROR
1297 @item gdb.TYPE_CODE_ERROR
1298 An unknown or erroneous type.
1300 @vindex TYPE_CODE_METHOD
1301 @item gdb.TYPE_CODE_METHOD
1302 A method type, as found in C@t{++}.
1304 @vindex TYPE_CODE_METHODPTR
1305 @item gdb.TYPE_CODE_METHODPTR
1306 A pointer-to-member-function.
1308 @vindex TYPE_CODE_MEMBERPTR
1309 @item gdb.TYPE_CODE_MEMBERPTR
1310 A pointer-to-member.
1312 @vindex TYPE_CODE_REF
1313 @item gdb.TYPE_CODE_REF
1316 @vindex TYPE_CODE_RVALUE_REF
1317 @item gdb.TYPE_CODE_RVALUE_REF
1318 A C@t{++}11 rvalue reference type.
1320 @vindex TYPE_CODE_CHAR
1321 @item gdb.TYPE_CODE_CHAR
1324 @vindex TYPE_CODE_BOOL
1325 @item gdb.TYPE_CODE_BOOL
1328 @vindex TYPE_CODE_COMPLEX
1329 @item gdb.TYPE_CODE_COMPLEX
1330 A complex float type.
1332 @vindex TYPE_CODE_TYPEDEF
1333 @item gdb.TYPE_CODE_TYPEDEF
1334 A typedef to some other type.
1336 @vindex TYPE_CODE_NAMESPACE
1337 @item gdb.TYPE_CODE_NAMESPACE
1338 A C@t{++} namespace.
1340 @vindex TYPE_CODE_DECFLOAT
1341 @item gdb.TYPE_CODE_DECFLOAT
1342 A decimal floating point type.
1344 @vindex TYPE_CODE_INTERNAL_FUNCTION
1345 @item gdb.TYPE_CODE_INTERNAL_FUNCTION
1346 A function internal to @value{GDBN}. This is the type used to represent
1347 convenience functions.
1350 Further support for types is provided in the @code{gdb.types}
1351 Python module (@pxref{gdb.types}).
1353 @node Pretty Printing API
1354 @subsubsection Pretty Printing API
1355 @cindex python pretty printing api
1357 A pretty-printer is just an object that holds a value and implements a
1358 specific interface, defined here. An example output is provided
1359 (@pxref{Pretty Printing}).
1361 @defun pretty_printer.children (self)
1362 @value{GDBN} will call this method on a pretty-printer to compute the
1363 children of the pretty-printer's value.
1365 This method must return an object conforming to the Python iterator
1366 protocol. Each item returned by the iterator must be a tuple holding
1367 two elements. The first element is the ``name'' of the child; the
1368 second element is the child's value. The value can be any Python
1369 object which is convertible to a @value{GDBN} value.
1371 This method is optional. If it does not exist, @value{GDBN} will act
1372 as though the value has no children.
1374 For efficiency, the @code{children} method should lazily compute its
1375 results. This will let @value{GDBN} read as few elements as
1376 necessary, for example when various print settings (@pxref{Print
1377 Settings}) or @code{-var-list-children} (@pxref{GDB/MI Variable
1378 Objects}) limit the number of elements to be displayed.
1380 Children may be hidden from display based on the value of @samp{set
1381 print max-depth} (@pxref{Print Settings}).
1384 @defun pretty_printer.display_hint (self)
1385 The CLI may call this method and use its result to change the
1386 formatting of a value. The result will also be supplied to an MI
1387 consumer as a @samp{displayhint} attribute of the variable being
1390 This method is optional. If it does exist, this method must return a
1391 string or the special value @code{None}.
1393 Some display hints are predefined by @value{GDBN}:
1397 Indicate that the object being printed is ``array-like''. The CLI
1398 uses this to respect parameters such as @code{set print elements} and
1399 @code{set print array}.
1402 Indicate that the object being printed is ``map-like'', and that the
1403 children of this value can be assumed to alternate between keys and
1407 Indicate that the object being printed is ``string-like''. If the
1408 printer's @code{to_string} method returns a Python string of some
1409 kind, then @value{GDBN} will call its internal language-specific
1410 string-printing function to format the string. For the CLI this means
1411 adding quotation marks, possibly escaping some characters, respecting
1412 @code{set print elements}, and the like.
1415 The special value @code{None} causes @value{GDBN} to apply the default
1419 @defun pretty_printer.to_string (self)
1420 @value{GDBN} will call this method to display the string
1421 representation of the value passed to the object's constructor.
1423 When printing from the CLI, if the @code{to_string} method exists,
1424 then @value{GDBN} will prepend its result to the values returned by
1425 @code{children}. Exactly how this formatting is done is dependent on
1426 the display hint, and may change as more hints are added. Also,
1427 depending on the print settings (@pxref{Print Settings}), the CLI may
1428 print just the result of @code{to_string} in a stack trace, omitting
1429 the result of @code{children}.
1431 If this method returns a string, it is printed verbatim.
1433 Otherwise, if this method returns an instance of @code{gdb.Value},
1434 then @value{GDBN} prints this value. This may result in a call to
1435 another pretty-printer.
1437 If instead the method returns a Python value which is convertible to a
1438 @code{gdb.Value}, then @value{GDBN} performs the conversion and prints
1439 the resulting value. Again, this may result in a call to another
1440 pretty-printer. Python scalars (integers, floats, and booleans) and
1441 strings are convertible to @code{gdb.Value}; other types are not.
1443 Finally, if this method returns @code{None} then no further operations
1444 are peformed in this method and nothing is printed.
1446 If the result is not one of these types, an exception is raised.
1449 @value{GDBN} provides a function which can be used to look up the
1450 default pretty-printer for a @code{gdb.Value}:
1452 @findex gdb.default_visualizer
1453 @defun gdb.default_visualizer (value)
1454 This function takes a @code{gdb.Value} object as an argument. If a
1455 pretty-printer for this value exists, then it is returned. If no such
1456 printer exists, then this returns @code{None}.
1459 @node Selecting Pretty-Printers
1460 @subsubsection Selecting Pretty-Printers
1461 @cindex selecting python pretty-printers
1463 @value{GDBN} provides several ways to register a pretty-printer:
1464 globally, per program space, and per objfile. When choosing how to
1465 register your pretty-printer, a good rule is to register it with the
1466 smallest scope possible: that is prefer a specific objfile first, then
1467 a program space, and only register a printer globally as a last
1470 @findex gdb.pretty_printers
1471 @defvar gdb.pretty_printers
1472 The Python list @code{gdb.pretty_printers} contains an array of
1473 functions or callable objects that have been registered via addition
1474 as a pretty-printer. Printers in this list are called @code{global}
1475 printers, they're available when debugging all inferiors.
1478 Each @code{gdb.Progspace} contains a @code{pretty_printers} attribute.
1479 Each @code{gdb.Objfile} also contains a @code{pretty_printers}
1482 Each function on these lists is passed a single @code{gdb.Value}
1483 argument and should return a pretty-printer object conforming to the
1484 interface definition above (@pxref{Pretty Printing API}). If a function
1485 cannot create a pretty-printer for the value, it should return
1488 @value{GDBN} first checks the @code{pretty_printers} attribute of each
1489 @code{gdb.Objfile} in the current program space and iteratively calls
1490 each enabled lookup routine in the list for that @code{gdb.Objfile}
1491 until it receives a pretty-printer object.
1492 If no pretty-printer is found in the objfile lists, @value{GDBN} then
1493 searches the pretty-printer list of the current program space,
1494 calling each enabled function until an object is returned.
1495 After these lists have been exhausted, it tries the global
1496 @code{gdb.pretty_printers} list, again calling each enabled function until an
1499 The order in which the objfiles are searched is not specified. For a
1500 given list, functions are always invoked from the head of the list,
1501 and iterated over sequentially until the end of the list, or a printer
1504 For various reasons a pretty-printer may not work.
1505 For example, the underlying data structure may have changed and
1506 the pretty-printer is out of date.
1508 The consequences of a broken pretty-printer are severe enough that
1509 @value{GDBN} provides support for enabling and disabling individual
1510 printers. For example, if @code{print frame-arguments} is on,
1511 a backtrace can become highly illegible if any argument is printed
1512 with a broken printer.
1514 Pretty-printers are enabled and disabled by attaching an @code{enabled}
1515 attribute to the registered function or callable object. If this attribute
1516 is present and its value is @code{False}, the printer is disabled, otherwise
1517 the printer is enabled.
1519 @node Writing a Pretty-Printer
1520 @subsubsection Writing a Pretty-Printer
1521 @cindex writing a pretty-printer
1523 A pretty-printer consists of two parts: a lookup function to detect
1524 if the type is supported, and the printer itself.
1526 Here is an example showing how a @code{std::string} printer might be
1527 written. @xref{Pretty Printing API}, for details on the API this class
1531 class StdStringPrinter(object):
1532 "Print a std::string"
1534 def __init__(self, val):
1537 def to_string(self):
1538 return self.val['_M_dataplus']['_M_p']
1540 def display_hint(self):
1544 And here is an example showing how a lookup function for the printer
1545 example above might be written.
1548 def str_lookup_function(val):
1549 lookup_tag = val.type.tag
1550 if lookup_tag == None:
1552 regex = re.compile("^std::basic_string<char,.*>$")
1553 if regex.match(lookup_tag):
1554 return StdStringPrinter(val)
1558 The example lookup function extracts the value's type, and attempts to
1559 match it to a type that it can pretty-print. If it is a type the
1560 printer can pretty-print, it will return a printer object. If not, it
1561 returns @code{None}.
1563 We recommend that you put your core pretty-printers into a Python
1564 package. If your pretty-printers are for use with a library, we
1565 further recommend embedding a version number into the package name.
1566 This practice will enable @value{GDBN} to load multiple versions of
1567 your pretty-printers at the same time, because they will have
1570 You should write auto-loaded code (@pxref{Python Auto-loading}) such that it
1571 can be evaluated multiple times without changing its meaning. An
1572 ideal auto-load file will consist solely of @code{import}s of your
1573 printer modules, followed by a call to a register pretty-printers with
1574 the current objfile.
1576 Taken as a whole, this approach will scale nicely to multiple
1577 inferiors, each potentially using a different library version.
1578 Embedding a version number in the Python package name will ensure that
1579 @value{GDBN} is able to load both sets of printers simultaneously.
1580 Then, because the search for pretty-printers is done by objfile, and
1581 because your auto-loaded code took care to register your library's
1582 printers with a specific objfile, @value{GDBN} will find the correct
1583 printers for the specific version of the library used by each
1586 To continue the @code{std::string} example (@pxref{Pretty Printing API}),
1587 this code might appear in @code{gdb.libstdcxx.v6}:
1590 def register_printers(objfile):
1591 objfile.pretty_printers.append(str_lookup_function)
1595 And then the corresponding contents of the auto-load file would be:
1598 import gdb.libstdcxx.v6
1599 gdb.libstdcxx.v6.register_printers(gdb.current_objfile())
1602 The previous example illustrates a basic pretty-printer.
1603 There are a few things that can be improved on.
1604 The printer doesn't have a name, making it hard to identify in a
1605 list of installed printers. The lookup function has a name, but
1606 lookup functions can have arbitrary, even identical, names.
1608 Second, the printer only handles one type, whereas a library typically has
1609 several types. One could install a lookup function for each desired type
1610 in the library, but one could also have a single lookup function recognize
1611 several types. The latter is the conventional way this is handled.
1612 If a pretty-printer can handle multiple data types, then its
1613 @dfn{subprinters} are the printers for the individual data types.
1615 The @code{gdb.printing} module provides a formal way of solving these
1616 problems (@pxref{gdb.printing}).
1617 Here is another example that handles multiple types.
1619 These are the types we are going to pretty-print:
1622 struct foo @{ int a, b; @};
1623 struct bar @{ struct foo x, y; @};
1626 Here are the printers:
1630 """Print a foo object."""
1632 def __init__(self, val):
1635 def to_string(self):
1636 return ("a=<" + str(self.val["a"]) +
1637 "> b=<" + str(self.val["b"]) + ">")
1640 """Print a bar object."""
1642 def __init__(self, val):
1645 def to_string(self):
1646 return ("x=<" + str(self.val["x"]) +
1647 "> y=<" + str(self.val["y"]) + ">")
1650 This example doesn't need a lookup function, that is handled by the
1651 @code{gdb.printing} module. Instead a function is provided to build up
1652 the object that handles the lookup.
1657 def build_pretty_printer():
1658 pp = gdb.printing.RegexpCollectionPrettyPrinter(
1660 pp.add_printer('foo', '^foo$', fooPrinter)
1661 pp.add_printer('bar', '^bar$', barPrinter)
1665 And here is the autoload support:
1670 gdb.printing.register_pretty_printer(
1671 gdb.current_objfile(),
1672 my_library.build_pretty_printer())
1675 Finally, when this printer is loaded into @value{GDBN}, here is the
1676 corresponding output of @samp{info pretty-printer}:
1679 (gdb) info pretty-printer
1686 @node Type Printing API
1687 @subsubsection Type Printing API
1688 @cindex type printing API for Python
1690 @value{GDBN} provides a way for Python code to customize type display.
1691 This is mainly useful for substituting canonical typedef names for
1694 @cindex type printer
1695 A @dfn{type printer} is just a Python object conforming to a certain
1696 protocol. A simple base class implementing the protocol is provided;
1697 see @ref{gdb.types}. A type printer must supply at least:
1699 @defivar type_printer enabled
1700 A boolean which is True if the printer is enabled, and False
1701 otherwise. This is manipulated by the @code{enable type-printer}
1702 and @code{disable type-printer} commands.
1705 @defivar type_printer name
1706 The name of the type printer. This must be a string. This is used by
1707 the @code{enable type-printer} and @code{disable type-printer}
1711 @defmethod type_printer instantiate (self)
1712 This is called by @value{GDBN} at the start of type-printing. It is
1713 only called if the type printer is enabled. This method must return a
1714 new object that supplies a @code{recognize} method, as described below.
1718 When displaying a type, say via the @code{ptype} command, @value{GDBN}
1719 will compute a list of type recognizers. This is done by iterating
1720 first over the per-objfile type printers (@pxref{Objfiles In Python}),
1721 followed by the per-progspace type printers (@pxref{Progspaces In
1722 Python}), and finally the global type printers.
1724 @value{GDBN} will call the @code{instantiate} method of each enabled
1725 type printer. If this method returns @code{None}, then the result is
1726 ignored; otherwise, it is appended to the list of recognizers.
1728 Then, when @value{GDBN} is going to display a type name, it iterates
1729 over the list of recognizers. For each one, it calls the recognition
1730 function, stopping if the function returns a non-@code{None} value.
1731 The recognition function is defined as:
1733 @defmethod type_recognizer recognize (self, type)
1734 If @var{type} is not recognized, return @code{None}. Otherwise,
1735 return a string which is to be printed as the name of @var{type}.
1736 The @var{type} argument will be an instance of @code{gdb.Type}
1737 (@pxref{Types In Python}).
1740 @value{GDBN} uses this two-pass approach so that type printers can
1741 efficiently cache information without holding on to it too long. For
1742 example, it can be convenient to look up type information in a type
1743 printer and hold it for a recognizer's lifetime; if a single pass were
1744 done then type printers would have to make use of the event system in
1745 order to avoid holding information that could become stale as the
1748 @node Frame Filter API
1749 @subsubsection Filtering Frames
1750 @cindex frame filters api
1752 Frame filters are Python objects that manipulate the visibility of a
1753 frame or frames when a backtrace (@pxref{Backtrace}) is printed by
1756 Only commands that print a backtrace, or, in the case of @sc{gdb/mi}
1757 commands (@pxref{GDB/MI}), those that return a collection of frames
1758 are affected. The commands that work with frame filters are:
1760 @code{backtrace} (@pxref{backtrace-command,, The backtrace command}),
1761 @code{-stack-list-frames}
1762 (@pxref{-stack-list-frames,, The -stack-list-frames command}),
1763 @code{-stack-list-variables} (@pxref{-stack-list-variables,, The
1764 -stack-list-variables command}), @code{-stack-list-arguments}
1765 @pxref{-stack-list-arguments,, The -stack-list-arguments command}) and
1766 @code{-stack-list-locals} (@pxref{-stack-list-locals,, The
1767 -stack-list-locals command}).
1769 A frame filter works by taking an iterator as an argument, applying
1770 actions to the contents of that iterator, and returning another
1771 iterator (or, possibly, the same iterator it was provided in the case
1772 where the filter does not perform any operations). Typically, frame
1773 filters utilize tools such as the Python's @code{itertools} module to
1774 work with and create new iterators from the source iterator.
1775 Regardless of how a filter chooses to apply actions, it must not alter
1776 the underlying @value{GDBN} frame or frames, or attempt to alter the
1777 call-stack within @value{GDBN}. This preserves data integrity within
1778 @value{GDBN}. Frame filters are executed on a priority basis and care
1779 should be taken that some frame filters may have been executed before,
1780 and that some frame filters will be executed after.
1782 An important consideration when designing frame filters, and well
1783 worth reflecting upon, is that frame filters should avoid unwinding
1784 the call stack if possible. Some stacks can run very deep, into the
1785 tens of thousands in some cases. To search every frame when a frame
1786 filter executes may be too expensive at that step. The frame filter
1787 cannot know how many frames it has to iterate over, and it may have to
1788 iterate through them all. This ends up duplicating effort as
1789 @value{GDBN} performs this iteration when it prints the frames. If
1790 the filter can defer unwinding frames until frame decorators are
1791 executed, after the last filter has executed, it should. @xref{Frame
1792 Decorator API}, for more information on decorators. Also, there are
1793 examples for both frame decorators and filters in later chapters.
1794 @xref{Writing a Frame Filter}, for more information.
1796 The Python dictionary @code{gdb.frame_filters} contains key/object
1797 pairings that comprise a frame filter. Frame filters in this
1798 dictionary are called @code{global} frame filters, and they are
1799 available when debugging all inferiors. These frame filters must
1800 register with the dictionary directly. In addition to the
1801 @code{global} dictionary, there are other dictionaries that are loaded
1802 with different inferiors via auto-loading (@pxref{Python
1803 Auto-loading}). The two other areas where frame filter dictionaries
1804 can be found are: @code{gdb.Progspace} which contains a
1805 @code{frame_filters} dictionary attribute, and each @code{gdb.Objfile}
1806 object which also contains a @code{frame_filters} dictionary
1809 When a command is executed from @value{GDBN} that is compatible with
1810 frame filters, @value{GDBN} combines the @code{global},
1811 @code{gdb.Progspace} and all @code{gdb.Objfile} dictionaries currently
1812 loaded. All of the @code{gdb.Objfile} dictionaries are combined, as
1813 several frames, and thus several object files, might be in use.
1814 @value{GDBN} then prunes any frame filter whose @code{enabled}
1815 attribute is @code{False}. This pruned list is then sorted according
1816 to the @code{priority} attribute in each filter.
1818 Once the dictionaries are combined, pruned and sorted, @value{GDBN}
1819 creates an iterator which wraps each frame in the call stack in a
1820 @code{FrameDecorator} object, and calls each filter in order. The
1821 output from the previous filter will always be the input to the next
1824 Frame filters have a mandatory interface which each frame filter must
1825 implement, defined here:
1827 @defun FrameFilter.filter (iterator)
1828 @value{GDBN} will call this method on a frame filter when it has
1829 reached the order in the priority list for that filter.
1831 For example, if there are four frame filters:
1842 The order that the frame filters will be called is:
1845 Filter3 -> Filter2 -> Filter1 -> Filter4
1848 Note that the output from @code{Filter3} is passed to the input of
1849 @code{Filter2}, and so on.
1851 This @code{filter} method is passed a Python iterator. This iterator
1852 contains a sequence of frame decorators that wrap each
1853 @code{gdb.Frame}, or a frame decorator that wraps another frame
1854 decorator. The first filter that is executed in the sequence of frame
1855 filters will receive an iterator entirely comprised of default
1856 @code{FrameDecorator} objects. However, after each frame filter is
1857 executed, the previous frame filter may have wrapped some or all of
1858 the frame decorators with their own frame decorator. As frame
1859 decorators must also conform to a mandatory interface, these
1860 decorators can be assumed to act in a uniform manner (@pxref{Frame
1863 This method must return an object conforming to the Python iterator
1864 protocol. Each item in the iterator must be an object conforming to
1865 the frame decorator interface. If a frame filter does not wish to
1866 perform any operations on this iterator, it should return that
1869 This method is not optional. If it does not exist, @value{GDBN} will
1870 raise and print an error.
1873 @defvar FrameFilter.name
1874 The @code{name} attribute must be Python string which contains the
1875 name of the filter displayed by @value{GDBN} (@pxref{Frame Filter
1876 Management}). This attribute may contain any combination of letters
1877 or numbers. Care should be taken to ensure that it is unique. This
1878 attribute is mandatory.
1881 @defvar FrameFilter.enabled
1882 The @code{enabled} attribute must be Python boolean. This attribute
1883 indicates to @value{GDBN} whether the frame filter is enabled, and
1884 should be considered when frame filters are executed. If
1885 @code{enabled} is @code{True}, then the frame filter will be executed
1886 when any of the backtrace commands detailed earlier in this chapter
1887 are executed. If @code{enabled} is @code{False}, then the frame
1888 filter will not be executed. This attribute is mandatory.
1891 @defvar FrameFilter.priority
1892 The @code{priority} attribute must be Python integer. This attribute
1893 controls the order of execution in relation to other frame filters.
1894 There are no imposed limits on the range of @code{priority} other than
1895 it must be a valid integer. The higher the @code{priority} attribute,
1896 the sooner the frame filter will be executed in relation to other
1897 frame filters. Although @code{priority} can be negative, it is
1898 recommended practice to assume zero is the lowest priority that a
1899 frame filter can be assigned. Frame filters that have the same
1900 priority are executed in unsorted order in that priority slot. This
1901 attribute is mandatory. 100 is a good default priority.
1904 @node Frame Decorator API
1905 @subsubsection Decorating Frames
1906 @cindex frame decorator api
1908 Frame decorators are sister objects to frame filters (@pxref{Frame
1909 Filter API}). Frame decorators are applied by a frame filter and can
1910 only be used in conjunction with frame filters.
1912 The purpose of a frame decorator is to customize the printed content
1913 of each @code{gdb.Frame} in commands where frame filters are executed.
1914 This concept is called decorating a frame. Frame decorators decorate
1915 a @code{gdb.Frame} with Python code contained within each API call.
1916 This separates the actual data contained in a @code{gdb.Frame} from
1917 the decorated data produced by a frame decorator. This abstraction is
1918 necessary to maintain integrity of the data contained in each
1921 Frame decorators have a mandatory interface, defined below.
1923 @value{GDBN} already contains a frame decorator called
1924 @code{FrameDecorator}. This contains substantial amounts of
1925 boilerplate code to decorate the content of a @code{gdb.Frame}. It is
1926 recommended that other frame decorators inherit and extend this
1927 object, and only to override the methods needed.
1929 @tindex gdb.FrameDecorator
1930 @code{FrameDecorator} is defined in the Python module
1931 @code{gdb.FrameDecorator}, so your code can import it like:
1933 from gdb.FrameDecorator import FrameDecorator
1936 @defun FrameDecorator.elided (self)
1938 The @code{elided} method groups frames together in a hierarchical
1939 system. An example would be an interpreter, where multiple low-level
1940 frames make up a single call in the interpreted language. In this
1941 example, the frame filter would elide the low-level frames and present
1942 a single high-level frame, representing the call in the interpreted
1943 language, to the user.
1945 The @code{elided} function must return an iterable and this iterable
1946 must contain the frames that are being elided wrapped in a suitable
1947 frame decorator. If no frames are being elided this function may
1948 return an empty iterable, or @code{None}. Elided frames are indented
1949 from normal frames in a @code{CLI} backtrace, or in the case of
1950 @code{GDB/MI}, are placed in the @code{children} field of the eliding
1953 It is the frame filter's task to also filter out the elided frames from
1954 the source iterator. This will avoid printing the frame twice.
1957 @defun FrameDecorator.function (self)
1959 This method returns the name of the function in the frame that is to
1962 This method must return a Python string describing the function, or
1965 If this function returns @code{None}, @value{GDBN} will not print any
1966 data for this field.
1969 @defun FrameDecorator.address (self)
1971 This method returns the address of the frame that is to be printed.
1973 This method must return a Python numeric integer type of sufficient
1974 size to describe the address of the frame, or @code{None}.
1976 If this function returns a @code{None}, @value{GDBN} will not print
1977 any data for this field.
1980 @defun FrameDecorator.filename (self)
1982 This method returns the filename and path associated with this frame.
1984 This method must return a Python string containing the filename and
1985 the path to the object file backing the frame, or @code{None}.
1987 If this function returns a @code{None}, @value{GDBN} will not print
1988 any data for this field.
1991 @defun FrameDecorator.line (self):
1993 This method returns the line number associated with the current
1994 position within the function addressed by this frame.
1996 This method must return a Python integer type, or @code{None}.
1998 If this function returns a @code{None}, @value{GDBN} will not print
1999 any data for this field.
2002 @defun FrameDecorator.frame_args (self)
2005 This method must return an iterable, or @code{None}. Returning an
2006 empty iterable, or @code{None} means frame arguments will not be
2007 printed for this frame. This iterable must contain objects that
2008 implement two methods, described here.
2010 This object must implement a @code{argument} method which takes a
2011 single @code{self} parameter and must return a @code{gdb.Symbol}
2012 (@pxref{Symbols In Python}), or a Python string. The object must also
2013 implement a @code{value} method which takes a single @code{self}
2014 parameter and must return a @code{gdb.Value} (@pxref{Values From
2015 Inferior}), a Python value, or @code{None}. If the @code{value}
2016 method returns @code{None}, and the @code{argument} method returns a
2017 @code{gdb.Symbol}, @value{GDBN} will look-up and print the value of
2018 the @code{gdb.Symbol} automatically.
2023 class SymValueWrapper():
2025 def __init__(self, symbol, value):
2035 class SomeFrameDecorator()
2038 def frame_args(self):
2041 block = self.inferior_frame.block()
2045 # Iterate over all symbols in a block. Only add
2046 # symbols that are arguments.
2048 if not sym.is_argument:
2050 args.append(SymValueWrapper(sym,None))
2052 # Add example synthetic argument.
2053 args.append(SymValueWrapper(``foo'', 42))
2059 @defun FrameDecorator.frame_locals (self)
2061 This method must return an iterable or @code{None}. Returning an
2062 empty iterable, or @code{None} means frame local arguments will not be
2063 printed for this frame.
2065 The object interface, the description of the various strategies for
2066 reading frame locals, and the example are largely similar to those
2067 described in the @code{frame_args} function, (@pxref{frame_args,,The
2068 frame filter frame_args function}). Below is a modified example:
2071 class SomeFrameDecorator()
2074 def frame_locals(self):
2077 block = self.inferior_frame.block()
2081 # Iterate over all symbols in a block. Add all
2082 # symbols, except arguments.
2086 vars.append(SymValueWrapper(sym,None))
2088 # Add an example of a synthetic local variable.
2089 vars.append(SymValueWrapper(``bar'', 99))
2095 @defun FrameDecorator.inferior_frame (self):
2097 This method must return the underlying @code{gdb.Frame} that this
2098 frame decorator is decorating. @value{GDBN} requires the underlying
2099 frame for internal frame information to determine how to print certain
2100 values when printing a frame.
2103 @node Writing a Frame Filter
2104 @subsubsection Writing a Frame Filter
2105 @cindex writing a frame filter
2107 There are three basic elements that a frame filter must implement: it
2108 must correctly implement the documented interface (@pxref{Frame Filter
2109 API}), it must register itself with @value{GDBN}, and finally, it must
2110 decide if it is to work on the data provided by @value{GDBN}. In all
2111 cases, whether it works on the iterator or not, each frame filter must
2112 return an iterator. A bare-bones frame filter follows the pattern in
2113 the following example.
2118 class FrameFilter():
2121 # Frame filter attribute creation.
2123 # 'name' is the name of the filter that GDB will display.
2125 # 'priority' is the priority of the filter relative to other
2128 # 'enabled' is a boolean that indicates whether this filter is
2129 # enabled and should be executed.
2135 # Register this frame filter with the global frame_filters
2137 gdb.frame_filters[self.name] = self
2139 def filter(self, frame_iter):
2140 # Just return the iterator.
2144 The frame filter in the example above implements the three
2145 requirements for all frame filters. It implements the API, self
2146 registers, and makes a decision on the iterator (in this case, it just
2147 returns the iterator untouched).
2149 The first step is attribute creation and assignment, and as shown in
2150 the comments the filter assigns the following attributes: @code{name},
2151 @code{priority} and whether the filter should be enabled with the
2152 @code{enabled} attribute.
2154 The second step is registering the frame filter with the dictionary or
2155 dictionaries that the frame filter has interest in. As shown in the
2156 comments, this filter just registers itself with the global dictionary
2157 @code{gdb.frame_filters}. As noted earlier, @code{gdb.frame_filters}
2158 is a dictionary that is initialized in the @code{gdb} module when
2159 @value{GDBN} starts. What dictionary a filter registers with is an
2160 important consideration. Generally, if a filter is specific to a set
2161 of code, it should be registered either in the @code{objfile} or
2162 @code{progspace} dictionaries as they are specific to the program
2163 currently loaded in @value{GDBN}. The global dictionary is always
2164 present in @value{GDBN} and is never unloaded. Any filters registered
2165 with the global dictionary will exist until @value{GDBN} exits. To
2166 avoid filters that may conflict, it is generally better to register
2167 frame filters against the dictionaries that more closely align with
2168 the usage of the filter currently in question. @xref{Python
2169 Auto-loading}, for further information on auto-loading Python scripts.
2171 @value{GDBN} takes a hands-off approach to frame filter registration,
2172 therefore it is the frame filter's responsibility to ensure
2173 registration has occurred, and that any exceptions are handled
2174 appropriately. In particular, you may wish to handle exceptions
2175 relating to Python dictionary key uniqueness. It is mandatory that
2176 the dictionary key is the same as frame filter's @code{name}
2177 attribute. When a user manages frame filters (@pxref{Frame Filter
2178 Management}), the names @value{GDBN} will display are those contained
2179 in the @code{name} attribute.
2181 The final step of this example is the implementation of the
2182 @code{filter} method. As shown in the example comments, we define the
2183 @code{filter} method and note that the method must take an iterator,
2184 and also must return an iterator. In this bare-bones example, the
2185 frame filter is not very useful as it just returns the iterator
2186 untouched. However this is a valid operation for frame filters that
2187 have the @code{enabled} attribute set, but decide not to operate on
2190 In the next example, the frame filter operates on all frames and
2191 utilizes a frame decorator to perform some work on the frames.
2192 @xref{Frame Decorator API}, for further information on the frame
2193 decorator interface.
2195 This example works on inlined frames. It highlights frames which are
2196 inlined by tagging them with an ``[inlined]'' tag. By applying a
2197 frame decorator to all frames with the Python @code{itertools imap}
2198 method, the example defers actions to the frame decorator. Frame
2199 decorators are only processed when @value{GDBN} prints the backtrace.
2201 This introduces a new decision making topic: whether to perform
2202 decision making operations at the filtering step, or at the printing
2203 step. In this example's approach, it does not perform any filtering
2204 decisions at the filtering step beyond mapping a frame decorator to
2205 each frame. This allows the actual decision making to be performed
2206 when each frame is printed. This is an important consideration, and
2207 well worth reflecting upon when designing a frame filter. An issue
2208 that frame filters should avoid is unwinding the stack if possible.
2209 Some stacks can run very deep, into the tens of thousands in some
2210 cases. To search every frame to determine if it is inlined ahead of
2211 time may be too expensive at the filtering step. The frame filter
2212 cannot know how many frames it has to iterate over, and it would have
2213 to iterate through them all. This ends up duplicating effort as
2214 @value{GDBN} performs this iteration when it prints the frames.
2216 In this example decision making can be deferred to the printing step.
2217 As each frame is printed, the frame decorator can examine each frame
2218 in turn when @value{GDBN} iterates. From a performance viewpoint,
2219 this is the most appropriate decision to make as it avoids duplicating
2220 the effort that the printing step would undertake anyway. Also, if
2221 there are many frame filters unwinding the stack during filtering, it
2222 can substantially delay the printing of the backtrace which will
2223 result in large memory usage, and a poor user experience.
2226 class InlineFilter():
2229 self.name = "InlinedFrameFilter"
2232 gdb.frame_filters[self.name] = self
2234 def filter(self, frame_iter):
2235 frame_iter = itertools.imap(InlinedFrameDecorator,
2240 This frame filter is somewhat similar to the earlier example, except
2241 that the @code{filter} method applies a frame decorator object called
2242 @code{InlinedFrameDecorator} to each element in the iterator. The
2243 @code{imap} Python method is light-weight. It does not proactively
2244 iterate over the iterator, but rather creates a new iterator which
2245 wraps the existing one.
2247 Below is the frame decorator for this example.
2250 class InlinedFrameDecorator(FrameDecorator):
2252 def __init__(self, fobj):
2253 super(InlinedFrameDecorator, self).__init__(fobj)
2256 frame = fobj.inferior_frame()
2257 name = str(frame.name())
2259 if frame.type() == gdb.INLINE_FRAME:
2260 name = name + " [inlined]"
2265 This frame decorator only defines and overrides the @code{function}
2266 method. It lets the supplied @code{FrameDecorator}, which is shipped
2267 with @value{GDBN}, perform the other work associated with printing
2270 The combination of these two objects create this output from a
2274 #0 0x004004e0 in bar () at inline.c:11
2275 #1 0x00400566 in max [inlined] (b=6, a=12) at inline.c:21
2276 #2 0x00400566 in main () at inline.c:31
2279 So in the case of this example, a frame decorator is applied to all
2280 frames, regardless of whether they may be inlined or not. As
2281 @value{GDBN} iterates over the iterator produced by the frame filters,
2282 @value{GDBN} executes each frame decorator which then makes a decision
2283 on what to print in the @code{function} callback. Using a strategy
2284 like this is a way to defer decisions on the frame content to printing
2287 @subheading Eliding Frames
2289 It might be that the above example is not desirable for representing
2290 inlined frames, and a hierarchical approach may be preferred. If we
2291 want to hierarchically represent frames, the @code{elided} frame
2292 decorator interface might be preferable.
2294 This example approaches the issue with the @code{elided} method. This
2295 example is quite long, but very simplistic. It is out-of-scope for
2296 this section to write a complete example that comprehensively covers
2297 all approaches of finding and printing inlined frames. However, this
2298 example illustrates the approach an author might use.
2300 This example comprises of three sections.
2303 class InlineFrameFilter():
2306 self.name = "InlinedFrameFilter"
2309 gdb.frame_filters[self.name] = self
2311 def filter(self, frame_iter):
2312 return ElidingInlineIterator(frame_iter)
2315 This frame filter is very similar to the other examples. The only
2316 difference is this frame filter is wrapping the iterator provided to
2317 it (@code{frame_iter}) with a custom iterator called
2318 @code{ElidingInlineIterator}. This again defers actions to when
2319 @value{GDBN} prints the backtrace, as the iterator is not traversed
2322 The iterator for this example is as follows. It is in this section of
2323 the example where decisions are made on the content of the backtrace.
2326 class ElidingInlineIterator:
2327 def __init__(self, ii):
2328 self.input_iterator = ii
2334 frame = next(self.input_iterator)
2336 if frame.inferior_frame().type() != gdb.INLINE_FRAME:
2340 eliding_frame = next(self.input_iterator)
2341 except StopIteration:
2343 return ElidingFrameDecorator(eliding_frame, [frame])
2346 This iterator implements the Python iterator protocol. When the
2347 @code{next} function is called (when @value{GDBN} prints each frame),
2348 the iterator checks if this frame decorator, @code{frame}, is wrapping
2349 an inlined frame. If it is not, it returns the existing frame decorator
2350 untouched. If it is wrapping an inlined frame, it assumes that the
2351 inlined frame was contained within the next oldest frame,
2352 @code{eliding_frame}, which it fetches. It then creates and returns a
2353 frame decorator, @code{ElidingFrameDecorator}, which contains both the
2354 elided frame, and the eliding frame.
2357 class ElidingInlineDecorator(FrameDecorator):
2359 def __init__(self, frame, elided_frames):
2360 super(ElidingInlineDecorator, self).__init__(frame)
2362 self.elided_frames = elided_frames
2365 return iter(self.elided_frames)
2368 This frame decorator overrides one function and returns the inlined
2369 frame in the @code{elided} method. As before it lets
2370 @code{FrameDecorator} do the rest of the work involved in printing
2371 this frame. This produces the following output.
2374 #0 0x004004e0 in bar () at inline.c:11
2375 #2 0x00400529 in main () at inline.c:25
2376 #1 0x00400529 in max (b=6, a=12) at inline.c:15
2379 In that output, @code{max} which has been inlined into @code{main} is
2380 printed hierarchically. Another approach would be to combine the
2381 @code{function} method, and the @code{elided} method to both print a
2382 marker in the inlined frame, and also show the hierarchical
2385 @node Unwinding Frames in Python
2386 @subsubsection Unwinding Frames in Python
2387 @cindex unwinding frames in Python
2389 In @value{GDBN} terminology ``unwinding'' is the process of finding
2390 the previous frame (that is, caller's) from the current one. An
2391 unwinder has three methods. The first one checks if it can handle
2392 given frame (``sniff'' it). For the frames it can sniff an unwinder
2393 provides two additional methods: it can return frame's ID, and it can
2394 fetch registers from the previous frame. A running @value{GDBN}
2395 mantains a list of the unwinders and calls each unwinder's sniffer in
2396 turn until it finds the one that recognizes the current frame. There
2397 is an API to register an unwinder.
2399 The unwinders that come with @value{GDBN} handle standard frames.
2400 However, mixed language applications (for example, an application
2401 running Java Virtual Machine) sometimes use frame layouts that cannot
2402 be handled by the @value{GDBN} unwinders. You can write Python code
2403 that can handle such custom frames.
2405 You implement a frame unwinder in Python as a class with which has two
2406 attributes, @code{name} and @code{enabled}, with obvious meanings, and
2407 a single method @code{__call__}, which examines a given frame and
2408 returns an object (an instance of @code{gdb.UnwindInfo class)}
2409 describing it. If an unwinder does not recognize a frame, it should
2410 return @code{None}. The code in @value{GDBN} that enables writing
2411 unwinders in Python uses this object to return frame's ID and previous
2412 frame registers when @value{GDBN} core asks for them.
2414 An unwinder should do as little work as possible. Some otherwise
2415 innocuous operations can cause problems (even crashes, as this code is
2416 not not well-hardened yet). For example, making an inferior call from
2417 an unwinder is unadvisable, as an inferior call will reset
2418 @value{GDBN}'s stack unwinding process, potentially causing re-entrant
2421 @subheading Unwinder Input
2423 An object passed to an unwinder (a @code{gdb.PendingFrame} instance)
2424 provides a method to read frame's registers:
2426 @defun PendingFrame.read_register (reg)
2427 This method returns the contents of the register @var{reg} in the
2428 frame as a @code{gdb.Value} object. @var{reg} can be either a
2429 register number or a register name; the values are platform-specific.
2430 They are usually found in the corresponding
2431 @file{@var{platform}-tdep.h} file in the @value{GDBN} source tree. If
2432 @var{reg} does not name a register for the current architecture, this
2433 method will throw an exception.
2435 Note that this method will always return a @code{gdb.Value} for a
2436 valid register name. This does not mean that the value will be valid.
2437 For example, you may request a register that an earlier unwinder could
2438 not unwind---the value will be unavailable. Instead, the
2439 @code{gdb.Value} returned from this method will be lazy; that is, its
2440 underlying bits will not be fetched until it is first used. So,
2441 attempting to use such a value will cause an exception at the point of
2444 The type of the returned @code{gdb.Value} depends on the register and
2445 the architecture. It is common for registers to have a scalar type,
2446 like @code{long long}; but many other types are possible, such as
2447 pointer, pointer-to-function, floating point or vector types.
2450 It also provides a factory method to create a @code{gdb.UnwindInfo}
2451 instance to be returned to @value{GDBN}:
2453 @defun PendingFrame.create_unwind_info (frame_id)
2454 Returns a new @code{gdb.UnwindInfo} instance identified by given
2455 @var{frame_id}. The argument is used to build @value{GDBN}'s frame ID
2456 using one of functions provided by @value{GDBN}. @var{frame_id}'s attributes
2457 determine which function will be used, as follows:
2461 The frame is identified by the given stack address and PC. The stack
2462 address must be chosen so that it is constant throughout the lifetime
2463 of the frame, so a typical choice is the value of the stack pointer at
2464 the start of the function---in the DWARF standard, this would be the
2465 ``Call Frame Address''.
2467 This is the most common case by far. The other cases are documented
2468 for completeness but are only useful in specialized situations.
2470 @item sp, pc, special
2471 The frame is identified by the stack address, the PC, and a
2472 ``special'' address. The special address is used on architectures
2473 that can have frames that do not change the stack, but which are still
2474 distinct, for example the IA-64, which has a second stack for
2475 registers. Both @var{sp} and @var{special} must be constant
2476 throughout the lifetime of the frame.
2479 The frame is identified by the stack address only. Any other stack
2480 frame with a matching @var{sp} will be considered to match this frame.
2481 Inside gdb, this is called a ``wild frame''. You will never need
2485 Each attribute value should be an instance of @code{gdb.Value}.
2489 @subheading Unwinder Output: UnwindInfo
2491 Use @code{PendingFrame.create_unwind_info} method described above to
2492 create a @code{gdb.UnwindInfo} instance. Use the following method to
2493 specify caller registers that have been saved in this frame:
2495 @defun gdb.UnwindInfo.add_saved_register (reg, value)
2496 @var{reg} identifies the register. It can be a number or a name, just
2497 as for the @code{PendingFrame.read_register} method above.
2498 @var{value} is a register value (a @code{gdb.Value} object).
2501 @subheading Unwinder Skeleton Code
2503 @value{GDBN} comes with the module containing the base @code{Unwinder}
2504 class. Derive your unwinder class from it and structure the code as
2508 from gdb.unwinders import Unwinder
2510 class FrameId(object):
2511 def __init__(self, sp, pc):
2516 class MyUnwinder(Unwinder):
2518 supe(MyUnwinder, self).__init___(<expects unwinder name argument>)
2520 def __call__(pending_frame):
2521 if not <we recognize frame>:
2523 # Create UnwindInfo. Usually the frame is identified by the stack
2524 # pointer and the program counter.
2525 sp = pending_frame.read_register(<SP number>)
2526 pc = pending_frame.read_register(<PC number>)
2527 unwind_info = pending_frame.create_unwind_info(FrameId(sp, pc))
2529 # Find the values of the registers in the caller's frame and
2530 # save them in the result:
2531 unwind_info.add_saved_register(<register>, <value>)
2534 # Return the result:
2539 @subheading Registering a Unwinder
2541 An object file, a program space, and the @value{GDBN} proper can have
2542 unwinders registered with it.
2544 The @code{gdb.unwinders} module provides the function to register a
2547 @defun gdb.unwinder.register_unwinder (locus, unwinder, replace=False)
2548 @var{locus} is specifies an object file or a program space to which
2549 @var{unwinder} is added. Passing @code{None} or @code{gdb} adds
2550 @var{unwinder} to the @value{GDBN}'s global unwinder list. The newly
2551 added @var{unwinder} will be called before any other unwinder from the
2552 same locus. Two unwinders in the same locus cannot have the same
2553 name. An attempt to add a unwinder with already existing name raises
2554 an exception unless @var{replace} is @code{True}, in which case the
2555 old unwinder is deleted.
2558 @subheading Unwinder Precedence
2560 @value{GDBN} first calls the unwinders from all the object files in no
2561 particular order, then the unwinders from the current program space,
2562 and finally the unwinders from @value{GDBN}.
2564 @node Xmethods In Python
2565 @subsubsection Xmethods In Python
2566 @cindex xmethods in Python
2568 @dfn{Xmethods} are additional methods or replacements for existing
2569 methods of a C@t{++} class. This feature is useful for those cases
2570 where a method defined in C@t{++} source code could be inlined or
2571 optimized out by the compiler, making it unavailable to @value{GDBN}.
2572 For such cases, one can define an xmethod to serve as a replacement
2573 for the method defined in the C@t{++} source code. @value{GDBN} will
2574 then invoke the xmethod, instead of the C@t{++} method, to
2575 evaluate expressions. One can also use xmethods when debugging
2576 with core files. Moreover, when debugging live programs, invoking an
2577 xmethod need not involve running the inferior (which can potentially
2578 perturb its state). Hence, even if the C@t{++} method is available, it
2579 is better to use its replacement xmethod if one is defined.
2581 The xmethods feature in Python is available via the concepts of an
2582 @dfn{xmethod matcher} and an @dfn{xmethod worker}. To
2583 implement an xmethod, one has to implement a matcher and a
2584 corresponding worker for it (more than one worker can be
2585 implemented, each catering to a different overloaded instance of the
2586 method). Internally, @value{GDBN} invokes the @code{match} method of a
2587 matcher to match the class type and method name. On a match, the
2588 @code{match} method returns a list of matching @emph{worker} objects.
2589 Each worker object typically corresponds to an overloaded instance of
2590 the xmethod. They implement a @code{get_arg_types} method which
2591 returns a sequence of types corresponding to the arguments the xmethod
2592 requires. @value{GDBN} uses this sequence of types to perform
2593 overload resolution and picks a winning xmethod worker. A winner
2594 is also selected from among the methods @value{GDBN} finds in the
2595 C@t{++} source code. Next, the winning xmethod worker and the
2596 winning C@t{++} method are compared to select an overall winner. In
2597 case of a tie between a xmethod worker and a C@t{++} method, the
2598 xmethod worker is selected as the winner. That is, if a winning
2599 xmethod worker is found to be equivalent to the winning C@t{++}
2600 method, then the xmethod worker is treated as a replacement for
2601 the C@t{++} method. @value{GDBN} uses the overall winner to invoke the
2602 method. If the winning xmethod worker is the overall winner, then
2603 the corresponding xmethod is invoked via the @code{__call__} method
2604 of the worker object.
2606 If one wants to implement an xmethod as a replacement for an
2607 existing C@t{++} method, then they have to implement an equivalent
2608 xmethod which has exactly the same name and takes arguments of
2609 exactly the same type as the C@t{++} method. If the user wants to
2610 invoke the C@t{++} method even though a replacement xmethod is
2611 available for that method, then they can disable the xmethod.
2613 @xref{Xmethod API}, for API to implement xmethods in Python.
2614 @xref{Writing an Xmethod}, for implementing xmethods in Python.
2617 @subsubsection Xmethod API
2620 The @value{GDBN} Python API provides classes, interfaces and functions
2621 to implement, register and manipulate xmethods.
2622 @xref{Xmethods In Python}.
2624 An xmethod matcher should be an instance of a class derived from
2625 @code{XMethodMatcher} defined in the module @code{gdb.xmethod}, or an
2626 object with similar interface and attributes. An instance of
2627 @code{XMethodMatcher} has the following attributes:
2630 The name of the matcher.
2634 A boolean value indicating whether the matcher is enabled or disabled.
2638 A list of named methods managed by the matcher. Each object in the list
2639 is an instance of the class @code{XMethod} defined in the module
2640 @code{gdb.xmethod}, or any object with the following attributes:
2645 Name of the xmethod which should be unique for each xmethod
2646 managed by the matcher.
2649 A boolean value indicating whether the xmethod is enabled or
2654 The class @code{XMethod} is a convenience class with same
2655 attributes as above along with the following constructor:
2657 @defun XMethod.__init__ (self, name)
2658 Constructs an enabled xmethod with name @var{name}.
2663 The @code{XMethodMatcher} class has the following methods:
2665 @defun XMethodMatcher.__init__ (self, name)
2666 Constructs an enabled xmethod matcher with name @var{name}. The
2667 @code{methods} attribute is initialized to @code{None}.
2670 @defun XMethodMatcher.match (self, class_type, method_name)
2671 Derived classes should override this method. It should return a
2672 xmethod worker object (or a sequence of xmethod worker
2673 objects) matching the @var{class_type} and @var{method_name}.
2674 @var{class_type} is a @code{gdb.Type} object, and @var{method_name}
2675 is a string value. If the matcher manages named methods as listed in
2676 its @code{methods} attribute, then only those worker objects whose
2677 corresponding entries in the @code{methods} list are enabled should be
2681 An xmethod worker should be an instance of a class derived from
2682 @code{XMethodWorker} defined in the module @code{gdb.xmethod},
2683 or support the following interface:
2685 @defun XMethodWorker.get_arg_types (self)
2686 This method returns a sequence of @code{gdb.Type} objects corresponding
2687 to the arguments that the xmethod takes. It can return an empty
2688 sequence or @code{None} if the xmethod does not take any arguments.
2689 If the xmethod takes a single argument, then a single
2690 @code{gdb.Type} object corresponding to it can be returned.
2693 @defun XMethodWorker.get_result_type (self, *args)
2694 This method returns a @code{gdb.Type} object representing the type
2695 of the result of invoking this xmethod.
2696 The @var{args} argument is the same tuple of arguments that would be
2697 passed to the @code{__call__} method of this worker.
2700 @defun XMethodWorker.__call__ (self, *args)
2701 This is the method which does the @emph{work} of the xmethod. The
2702 @var{args} arguments is the tuple of arguments to the xmethod. Each
2703 element in this tuple is a gdb.Value object. The first element is
2704 always the @code{this} pointer value.
2707 For @value{GDBN} to lookup xmethods, the xmethod matchers
2708 should be registered using the following function defined in the module
2711 @defun register_xmethod_matcher (locus, matcher, replace=False)
2712 The @code{matcher} is registered with @code{locus}, replacing an
2713 existing matcher with the same name as @code{matcher} if
2714 @code{replace} is @code{True}. @code{locus} can be a
2715 @code{gdb.Objfile} object (@pxref{Objfiles In Python}), or a
2716 @code{gdb.Progspace} object (@pxref{Progspaces In Python}), or
2717 @code{None}. If it is @code{None}, then @code{matcher} is registered
2721 @node Writing an Xmethod
2722 @subsubsection Writing an Xmethod
2723 @cindex writing xmethods in Python
2725 Implementing xmethods in Python will require implementing xmethod
2726 matchers and xmethod workers (@pxref{Xmethods In Python}). Consider
2727 the following C@t{++} class:
2733 MyClass (int a) : a_(a) @{ @}
2735 int geta (void) @{ return a_; @}
2736 int operator+ (int b);
2743 MyClass::operator+ (int b)
2750 Let us define two xmethods for the class @code{MyClass}, one
2751 replacing the method @code{geta}, and another adding an overloaded
2752 flavor of @code{operator+} which takes a @code{MyClass} argument (the
2753 C@t{++} code above already has an overloaded @code{operator+}
2754 which takes an @code{int} argument). The xmethod matcher can be
2758 class MyClass_geta(gdb.xmethod.XMethod):
2760 gdb.xmethod.XMethod.__init__(self, 'geta')
2762 def get_worker(self, method_name):
2763 if method_name == 'geta':
2764 return MyClassWorker_geta()
2767 class MyClass_sum(gdb.xmethod.XMethod):
2769 gdb.xmethod.XMethod.__init__(self, 'sum')
2771 def get_worker(self, method_name):
2772 if method_name == 'operator+':
2773 return MyClassWorker_plus()
2776 class MyClassMatcher(gdb.xmethod.XMethodMatcher):
2778 gdb.xmethod.XMethodMatcher.__init__(self, 'MyClassMatcher')
2779 # List of methods 'managed' by this matcher
2780 self.methods = [MyClass_geta(), MyClass_sum()]
2782 def match(self, class_type, method_name):
2783 if class_type.tag != 'MyClass':
2786 for method in self.methods:
2788 worker = method.get_worker(method_name)
2790 workers.append(worker)
2796 Notice that the @code{match} method of @code{MyClassMatcher} returns
2797 a worker object of type @code{MyClassWorker_geta} for the @code{geta}
2798 method, and a worker object of type @code{MyClassWorker_plus} for the
2799 @code{operator+} method. This is done indirectly via helper classes
2800 derived from @code{gdb.xmethod.XMethod}. One does not need to use the
2801 @code{methods} attribute in a matcher as it is optional. However, if a
2802 matcher manages more than one xmethod, it is a good practice to list the
2803 xmethods in the @code{methods} attribute of the matcher. This will then
2804 facilitate enabling and disabling individual xmethods via the
2805 @code{enable/disable} commands. Notice also that a worker object is
2806 returned only if the corresponding entry in the @code{methods} attribute
2807 of the matcher is enabled.
2809 The implementation of the worker classes returned by the matcher setup
2810 above is as follows:
2813 class MyClassWorker_geta(gdb.xmethod.XMethodWorker):
2814 def get_arg_types(self):
2817 def get_result_type(self, obj):
2818 return gdb.lookup_type('int')
2820 def __call__(self, obj):
2824 class MyClassWorker_plus(gdb.xmethod.XMethodWorker):
2825 def get_arg_types(self):
2826 return gdb.lookup_type('MyClass')
2828 def get_result_type(self, obj):
2829 return gdb.lookup_type('int')
2831 def __call__(self, obj, other):
2832 return obj['a_'] + other['a_']
2835 For @value{GDBN} to actually lookup a xmethod, it has to be
2836 registered with it. The matcher defined above is registered with
2837 @value{GDBN} globally as follows:
2840 gdb.xmethod.register_xmethod_matcher(None, MyClassMatcher())
2843 If an object @code{obj} of type @code{MyClass} is initialized in C@t{++}
2851 then, after loading the Python script defining the xmethod matchers
2852 and workers into @code{GDBN}, invoking the method @code{geta} or using
2853 the operator @code{+} on @code{obj} will invoke the xmethods
2864 Consider another example with a C++ template class:
2871 MyTemplate () : dsize_(10), data_ (new T [10]) @{ @}
2872 ~MyTemplate () @{ delete [] data_; @}
2874 int footprint (void)
2876 return sizeof (T) * dsize_ + sizeof (MyTemplate<T>);
2885 Let us implement an xmethod for the above class which serves as a
2886 replacement for the @code{footprint} method. The full code listing
2887 of the xmethod workers and xmethod matchers is as follows:
2890 class MyTemplateWorker_footprint(gdb.xmethod.XMethodWorker):
2891 def __init__(self, class_type):
2892 self.class_type = class_type
2894 def get_arg_types(self):
2897 def get_result_type(self):
2898 return gdb.lookup_type('int')
2900 def __call__(self, obj):
2901 return (self.class_type.sizeof +
2903 self.class_type.template_argument(0).sizeof)
2906 class MyTemplateMatcher_footprint(gdb.xmethod.XMethodMatcher):
2908 gdb.xmethod.XMethodMatcher.__init__(self, 'MyTemplateMatcher')
2910 def match(self, class_type, method_name):
2911 if (re.match('MyTemplate<[ \t\n]*[_a-zA-Z][ _a-zA-Z0-9]*>',
2913 method_name == 'footprint'):
2914 return MyTemplateWorker_footprint(class_type)
2917 Notice that, in this example, we have not used the @code{methods}
2918 attribute of the matcher as the matcher manages only one xmethod. The
2919 user can enable/disable this xmethod by enabling/disabling the matcher
2922 @node Inferiors In Python
2923 @subsubsection Inferiors In Python
2924 @cindex inferiors in Python
2926 @findex gdb.Inferior
2927 Programs which are being run under @value{GDBN} are called inferiors
2928 (@pxref{Inferiors and Programs}). Python scripts can access
2929 information about and manipulate inferiors controlled by @value{GDBN}
2930 via objects of the @code{gdb.Inferior} class.
2932 The following inferior-related functions are available in the @code{gdb}
2935 @defun gdb.inferiors ()
2936 Return a tuple containing all inferior objects.
2939 @defun gdb.selected_inferior ()
2940 Return an object representing the current inferior.
2943 A @code{gdb.Inferior} object has the following attributes:
2945 @defvar Inferior.num
2946 ID of inferior, as assigned by GDB.
2949 @defvar Inferior.pid
2950 Process ID of the inferior, as assigned by the underlying operating
2954 @defvar Inferior.was_attached
2955 Boolean signaling whether the inferior was created using `attach', or
2956 started by @value{GDBN} itself.
2959 @defvar Inferior.progspace
2960 The inferior's program space. @xref{Progspaces In Python}.
2963 A @code{gdb.Inferior} object has the following methods:
2965 @defun Inferior.is_valid ()
2966 Returns @code{True} if the @code{gdb.Inferior} object is valid,
2967 @code{False} if not. A @code{gdb.Inferior} object will become invalid
2968 if the inferior no longer exists within @value{GDBN}. All other
2969 @code{gdb.Inferior} methods will throw an exception if it is invalid
2970 at the time the method is called.
2973 @defun Inferior.threads ()
2974 This method returns a tuple holding all the threads which are valid
2975 when it is called. If there are no valid threads, the method will
2976 return an empty tuple.
2979 @defun Inferior.architecture ()
2980 Return the @code{gdb.Architecture} (@pxref{Architectures In Python})
2981 for this inferior. This represents the architecture of the inferior
2982 as a whole. Some platforms can have multiple architectures in a
2983 single address space, so this may not match the architecture of a
2984 particular frame (@pxref{Frames In Python}).
2987 @findex Inferior.read_memory
2988 @defun Inferior.read_memory (address, length)
2989 Read @var{length} addressable memory units from the inferior, starting at
2990 @var{address}. Returns a buffer object, which behaves much like an array
2991 or a string. It can be modified and given to the
2992 @code{Inferior.write_memory} function. In Python 3, the return
2993 value is a @code{memoryview} object.
2996 @findex Inferior.write_memory
2997 @defun Inferior.write_memory (address, buffer @r{[}, length@r{]})
2998 Write the contents of @var{buffer} to the inferior, starting at
2999 @var{address}. The @var{buffer} parameter must be a Python object
3000 which supports the buffer protocol, i.e., a string, an array or the
3001 object returned from @code{Inferior.read_memory}. If given, @var{length}
3002 determines the number of addressable memory units from @var{buffer} to be
3006 @findex gdb.search_memory
3007 @defun Inferior.search_memory (address, length, pattern)
3008 Search a region of the inferior memory starting at @var{address} with
3009 the given @var{length} using the search pattern supplied in
3010 @var{pattern}. The @var{pattern} parameter must be a Python object
3011 which supports the buffer protocol, i.e., a string, an array or the
3012 object returned from @code{gdb.read_memory}. Returns a Python @code{Long}
3013 containing the address where the pattern was found, or @code{None} if
3014 the pattern could not be found.
3017 @findex Inferior.thread_from_handle
3018 @findex Inferior.thread_from_thread_handle
3019 @defun Inferior.thread_from_handle (handle)
3020 Return the thread object corresponding to @var{handle}, a thread
3021 library specific data structure such as @code{pthread_t} for pthreads
3022 library implementations.
3024 The function @code{Inferior.thread_from_thread_handle} provides
3025 the same functionality, but use of @code{Inferior.thread_from_thread_handle}
3029 @node Events In Python
3030 @subsubsection Events In Python
3031 @cindex inferior events in Python
3033 @value{GDBN} provides a general event facility so that Python code can be
3034 notified of various state changes, particularly changes that occur in
3037 An @dfn{event} is just an object that describes some state change. The
3038 type of the object and its attributes will vary depending on the details
3039 of the change. All the existing events are described below.
3041 In order to be notified of an event, you must register an event handler
3042 with an @dfn{event registry}. An event registry is an object in the
3043 @code{gdb.events} module which dispatches particular events. A registry
3044 provides methods to register and unregister event handlers:
3046 @defun EventRegistry.connect (object)
3047 Add the given callable @var{object} to the registry. This object will be
3048 called when an event corresponding to this registry occurs.
3051 @defun EventRegistry.disconnect (object)
3052 Remove the given @var{object} from the registry. Once removed, the object
3053 will no longer receive notifications of events.
3059 def exit_handler (event):
3060 print "event type: exit"
3061 print "exit code: %d" % (event.exit_code)
3063 gdb.events.exited.connect (exit_handler)
3066 In the above example we connect our handler @code{exit_handler} to the
3067 registry @code{events.exited}. Once connected, @code{exit_handler} gets
3068 called when the inferior exits. The argument @dfn{event} in this example is
3069 of type @code{gdb.ExitedEvent}. As you can see in the example the
3070 @code{ExitedEvent} object has an attribute which indicates the exit code of
3073 The following is a listing of the event registries that are available and
3074 details of the events they emit:
3079 Emits @code{gdb.ThreadEvent}.
3081 Some events can be thread specific when @value{GDBN} is running in non-stop
3082 mode. When represented in Python, these events all extend
3083 @code{gdb.ThreadEvent}. Note, this event is not emitted directly; instead,
3084 events which are emitted by this or other modules might extend this event.
3085 Examples of these events are @code{gdb.BreakpointEvent} and
3086 @code{gdb.ContinueEvent}.
3088 @defvar ThreadEvent.inferior_thread
3089 In non-stop mode this attribute will be set to the specific thread which was
3090 involved in the emitted event. Otherwise, it will be set to @code{None}.
3093 Emits @code{gdb.ContinueEvent} which extends @code{gdb.ThreadEvent}.
3095 This event indicates that the inferior has been continued after a stop. For
3096 inherited attribute refer to @code{gdb.ThreadEvent} above.
3099 Emits @code{events.ExitedEvent} which indicates that the inferior has exited.
3100 @code{events.ExitedEvent} has two attributes:
3101 @defvar ExitedEvent.exit_code
3102 An integer representing the exit code, if available, which the inferior
3103 has returned. (The exit code could be unavailable if, for example,
3104 @value{GDBN} detaches from the inferior.) If the exit code is unavailable,
3105 the attribute does not exist.
3107 @defvar ExitedEvent.inferior
3108 A reference to the inferior which triggered the @code{exited} event.
3112 Emits @code{gdb.StopEvent} which extends @code{gdb.ThreadEvent}.
3114 Indicates that the inferior has stopped. All events emitted by this registry
3115 extend StopEvent. As a child of @code{gdb.ThreadEvent}, @code{gdb.StopEvent}
3116 will indicate the stopped thread when @value{GDBN} is running in non-stop
3117 mode. Refer to @code{gdb.ThreadEvent} above for more details.
3119 Emits @code{gdb.SignalEvent} which extends @code{gdb.StopEvent}.
3121 This event indicates that the inferior or one of its threads has received as
3122 signal. @code{gdb.SignalEvent} has the following attributes:
3124 @defvar SignalEvent.stop_signal
3125 A string representing the signal received by the inferior. A list of possible
3126 signal values can be obtained by running the command @code{info signals} in
3127 the @value{GDBN} command prompt.
3130 Also emits @code{gdb.BreakpointEvent} which extends @code{gdb.StopEvent}.
3132 @code{gdb.BreakpointEvent} event indicates that one or more breakpoints have
3133 been hit, and has the following attributes:
3135 @defvar BreakpointEvent.breakpoints
3136 A sequence containing references to all the breakpoints (type
3137 @code{gdb.Breakpoint}) that were hit.
3138 @xref{Breakpoints In Python}, for details of the @code{gdb.Breakpoint} object.
3140 @defvar BreakpointEvent.breakpoint
3141 A reference to the first breakpoint that was hit.
3142 This function is maintained for backward compatibility and is now deprecated
3143 in favor of the @code{gdb.BreakpointEvent.breakpoints} attribute.
3146 @item events.new_objfile
3147 Emits @code{gdb.NewObjFileEvent} which indicates that a new object file has
3148 been loaded by @value{GDBN}. @code{gdb.NewObjFileEvent} has one attribute:
3150 @defvar NewObjFileEvent.new_objfile
3151 A reference to the object file (@code{gdb.Objfile}) which has been loaded.
3152 @xref{Objfiles In Python}, for details of the @code{gdb.Objfile} object.
3155 @item events.clear_objfiles
3156 Emits @code{gdb.ClearObjFilesEvent} which indicates that the list of object
3157 files for a program space has been reset.
3158 @code{gdb.ClearObjFilesEvent} has one attribute:
3160 @defvar ClearObjFilesEvent.progspace
3161 A reference to the program space (@code{gdb.Progspace}) whose objfile list has
3162 been cleared. @xref{Progspaces In Python}.
3165 @item events.inferior_call
3166 Emits events just before and after a function in the inferior is
3167 called by @value{GDBN}. Before an inferior call, this emits an event
3168 of type @code{gdb.InferiorCallPreEvent}, and after an inferior call,
3169 this emits an event of type @code{gdb.InferiorCallPostEvent}.
3172 @tindex gdb.InferiorCallPreEvent
3173 @item @code{gdb.InferiorCallPreEvent}
3174 Indicates that a function in the inferior is about to be called.
3176 @defvar InferiorCallPreEvent.ptid
3177 The thread in which the call will be run.
3180 @defvar InferiorCallPreEvent.address
3181 The location of the function to be called.
3184 @tindex gdb.InferiorCallPostEvent
3185 @item @code{gdb.InferiorCallPostEvent}
3186 Indicates that a function in the inferior has just been called.
3188 @defvar InferiorCallPostEvent.ptid
3189 The thread in which the call was run.
3192 @defvar InferiorCallPostEvent.address
3193 The location of the function that was called.
3197 @item events.memory_changed
3198 Emits @code{gdb.MemoryChangedEvent} which indicates that the memory of the
3199 inferior has been modified by the @value{GDBN} user, for instance via a
3200 command like @w{@code{set *addr = value}}. The event has the following
3203 @defvar MemoryChangedEvent.address
3204 The start address of the changed region.
3207 @defvar MemoryChangedEvent.length
3208 Length in bytes of the changed region.
3211 @item events.register_changed
3212 Emits @code{gdb.RegisterChangedEvent} which indicates that a register in the
3213 inferior has been modified by the @value{GDBN} user.
3215 @defvar RegisterChangedEvent.frame
3216 A gdb.Frame object representing the frame in which the register was modified.
3218 @defvar RegisterChangedEvent.regnum
3219 Denotes which register was modified.
3222 @item events.breakpoint_created
3223 This is emitted when a new breakpoint has been created. The argument
3224 that is passed is the new @code{gdb.Breakpoint} object.
3226 @item events.breakpoint_modified
3227 This is emitted when a breakpoint has been modified in some way. The
3228 argument that is passed is the new @code{gdb.Breakpoint} object.
3230 @item events.breakpoint_deleted
3231 This is emitted when a breakpoint has been deleted. The argument that
3232 is passed is the @code{gdb.Breakpoint} object. When this event is
3233 emitted, the @code{gdb.Breakpoint} object will already be in its
3234 invalid state; that is, the @code{is_valid} method will return
3237 @item events.before_prompt
3238 This event carries no payload. It is emitted each time @value{GDBN}
3239 presents a prompt to the user.
3241 @item events.new_inferior
3242 This is emitted when a new inferior is created. Note that the
3243 inferior is not necessarily running; in fact, it may not even have an
3244 associated executable.
3246 The event is of type @code{gdb.NewInferiorEvent}. This has a single
3249 @defvar NewInferiorEvent.inferior
3250 The new inferior, a @code{gdb.Inferior} object.
3253 @item events.inferior_deleted
3254 This is emitted when an inferior has been deleted. Note that this is
3255 not the same as process exit; it is notified when the inferior itself
3256 is removed, say via @code{remove-inferiors}.
3258 The event is of type @code{gdb.InferiorDeletedEvent}. This has a single
3261 @defvar NewInferiorEvent.inferior
3262 The inferior that is being removed, a @code{gdb.Inferior} object.
3265 @item events.new_thread
3266 This is emitted when @value{GDBN} notices a new thread. The event is of
3267 type @code{gdb.NewThreadEvent}, which extends @code{gdb.ThreadEvent}.
3268 This has a single attribute:
3270 @defvar NewThreadEvent.inferior_thread
3276 @node Threads In Python
3277 @subsubsection Threads In Python
3278 @cindex threads in python
3280 @findex gdb.InferiorThread
3281 Python scripts can access information about, and manipulate inferior threads
3282 controlled by @value{GDBN}, via objects of the @code{gdb.InferiorThread} class.
3284 The following thread-related functions are available in the @code{gdb}
3287 @findex gdb.selected_thread
3288 @defun gdb.selected_thread ()
3289 This function returns the thread object for the selected thread. If there
3290 is no selected thread, this will return @code{None}.
3293 A @code{gdb.InferiorThread} object has the following attributes:
3295 @defvar InferiorThread.name
3296 The name of the thread. If the user specified a name using
3297 @code{thread name}, then this returns that name. Otherwise, if an
3298 OS-supplied name is available, then it is returned. Otherwise, this
3299 returns @code{None}.
3301 This attribute can be assigned to. The new value must be a string
3302 object, which sets the new name, or @code{None}, which removes any
3303 user-specified thread name.
3306 @defvar InferiorThread.num
3307 The per-inferior number of the thread, as assigned by GDB.
3310 @defvar InferiorThread.global_num
3311 The global ID of the thread, as assigned by GDB. You can use this to
3312 make Python breakpoints thread-specific, for example
3313 (@pxref{python_breakpoint_thread,,The Breakpoint.thread attribute}).
3316 @defvar InferiorThread.ptid
3317 ID of the thread, as assigned by the operating system. This attribute is a
3318 tuple containing three integers. The first is the Process ID (PID); the second
3319 is the Lightweight Process ID (LWPID), and the third is the Thread ID (TID).
3320 Either the LWPID or TID may be 0, which indicates that the operating system
3321 does not use that identifier.
3324 @defvar InferiorThread.inferior
3325 The inferior this thread belongs to. This attribute is represented as
3326 a @code{gdb.Inferior} object. This attribute is not writable.
3329 A @code{gdb.InferiorThread} object has the following methods:
3331 @defun InferiorThread.is_valid ()
3332 Returns @code{True} if the @code{gdb.InferiorThread} object is valid,
3333 @code{False} if not. A @code{gdb.InferiorThread} object will become
3334 invalid if the thread exits, or the inferior that the thread belongs
3335 is deleted. All other @code{gdb.InferiorThread} methods will throw an
3336 exception if it is invalid at the time the method is called.
3339 @defun InferiorThread.switch ()
3340 This changes @value{GDBN}'s currently selected thread to the one represented
3344 @defun InferiorThread.is_stopped ()
3345 Return a Boolean indicating whether the thread is stopped.
3348 @defun InferiorThread.is_running ()
3349 Return a Boolean indicating whether the thread is running.
3352 @defun InferiorThread.is_exited ()
3353 Return a Boolean indicating whether the thread is exited.
3356 @defun InferiorThread.handle ()
3357 Return the thread object's handle, represented as a Python @code{bytes}
3358 object. A @code{gdb.Value} representation of the handle may be
3359 constructed via @code{gdb.Value(bufobj, type)} where @var{bufobj} is
3360 the Python @code{bytes} representation of the handle and @var{type} is
3361 a @code{gdb.Type} for the handle type.
3364 @node Recordings In Python
3365 @subsubsection Recordings In Python
3366 @cindex recordings in python
3368 The following recordings-related functions
3369 (@pxref{Process Record and Replay}) are available in the @code{gdb}
3372 @defun gdb.start_recording (@r{[}method@r{]}, @r{[}format@r{]})
3373 Start a recording using the given @var{method} and @var{format}. If
3374 no @var{format} is given, the default format for the recording method
3375 is used. If no @var{method} is given, the default method will be used.
3376 Returns a @code{gdb.Record} object on success. Throw an exception on
3379 The following strings can be passed as @var{method}:
3385 @code{"btrace"}: Possible values for @var{format}: @code{"pt"},
3386 @code{"bts"} or leave out for default format.
3390 @defun gdb.current_recording ()
3391 Access a currently running recording. Return a @code{gdb.Record}
3392 object on success. Return @code{None} if no recording is currently
3396 @defun gdb.stop_recording ()
3397 Stop the current recording. Throw an exception if no recording is
3398 currently active. All record objects become invalid after this call.
3401 A @code{gdb.Record} object has the following attributes:
3403 @defvar Record.method
3404 A string with the current recording method, e.g.@: @code{full} or
3408 @defvar Record.format
3409 A string with the current recording format, e.g.@: @code{bt}, @code{pts} or
3413 @defvar Record.begin
3414 A method specific instruction object representing the first instruction
3419 A method specific instruction object representing the current
3420 instruction, that is not actually part of the recording.
3423 @defvar Record.replay_position
3424 The instruction representing the current replay position. If there is
3425 no replay active, this will be @code{None}.
3428 @defvar Record.instruction_history
3429 A list with all recorded instructions.
3432 @defvar Record.function_call_history
3433 A list with all recorded function call segments.
3436 A @code{gdb.Record} object has the following methods:
3438 @defun Record.goto (instruction)
3439 Move the replay position to the given @var{instruction}.
3442 The common @code{gdb.Instruction} class that recording method specific
3443 instruction objects inherit from, has the following attributes:
3445 @defvar Instruction.pc
3446 An integer representing this instruction's address.
3449 @defvar Instruction.data
3450 A buffer with the raw instruction data. In Python 3, the return value is a
3451 @code{memoryview} object.
3454 @defvar Instruction.decoded
3455 A human readable string with the disassembled instruction.
3458 @defvar Instruction.size
3459 The size of the instruction in bytes.
3462 Additionally @code{gdb.RecordInstruction} has the following attributes:
3464 @defvar RecordInstruction.number
3465 An integer identifying this instruction. @code{number} corresponds to
3466 the numbers seen in @code{record instruction-history}
3467 (@pxref{Process Record and Replay}).
3470 @defvar RecordInstruction.sal
3471 A @code{gdb.Symtab_and_line} object representing the associated symtab
3472 and line of this instruction. May be @code{None} if no debug information is
3476 @defvar RecordInstruction.is_speculative
3477 A boolean indicating whether the instruction was executed speculatively.
3480 If an error occured during recording or decoding a recording, this error is
3481 represented by a @code{gdb.RecordGap} object in the instruction list. It has
3482 the following attributes:
3484 @defvar RecordGap.number
3485 An integer identifying this gap. @code{number} corresponds to the numbers seen
3486 in @code{record instruction-history} (@pxref{Process Record and Replay}).
3489 @defvar RecordGap.error_code
3490 A numerical representation of the reason for the gap. The value is specific to
3491 the current recording method.
3494 @defvar RecordGap.error_string
3495 A human readable string with the reason for the gap.
3498 A @code{gdb.RecordFunctionSegment} object has the following attributes:
3500 @defvar RecordFunctionSegment.number
3501 An integer identifying this function segment. @code{number} corresponds to
3502 the numbers seen in @code{record function-call-history}
3503 (@pxref{Process Record and Replay}).
3506 @defvar RecordFunctionSegment.symbol
3507 A @code{gdb.Symbol} object representing the associated symbol. May be
3508 @code{None} if no debug information is available.
3511 @defvar RecordFunctionSegment.level
3512 An integer representing the function call's stack level. May be
3513 @code{None} if the function call is a gap.
3516 @defvar RecordFunctionSegment.instructions
3517 A list of @code{gdb.RecordInstruction} or @code{gdb.RecordGap} objects
3518 associated with this function call.
3521 @defvar RecordFunctionSegment.up
3522 A @code{gdb.RecordFunctionSegment} object representing the caller's
3523 function segment. If the call has not been recorded, this will be the
3524 function segment to which control returns. If neither the call nor the
3525 return have been recorded, this will be @code{None}.
3528 @defvar RecordFunctionSegment.prev
3529 A @code{gdb.RecordFunctionSegment} object representing the previous
3530 segment of this function call. May be @code{None}.
3533 @defvar RecordFunctionSegment.next
3534 A @code{gdb.RecordFunctionSegment} object representing the next segment of
3535 this function call. May be @code{None}.
3538 The following example demonstrates the usage of these objects and
3539 functions to create a function that will rewind a record to the last
3540 time a function in a different file was executed. This would typically
3541 be used to track the execution of user provided callback functions in a
3542 library which typically are not visible in a back trace.
3546 rec = gdb.current_recording ()
3550 insn = rec.instruction_history
3555 position = insn.index (rec.replay_position)
3559 filename = insn[position].sal.symtab.fullname ()
3563 for i in reversed (insn[:position]):
3565 current = i.sal.symtab.fullname ()
3569 if filename == current:
3576 Another possible application is to write a function that counts the
3577 number of code executions in a given line range. This line range can
3578 contain parts of functions or span across several functions and is not
3579 limited to be contiguous.
3582 def countrange (filename, linerange):
3585 def filter_only (file_name):
3586 for call in gdb.current_recording ().function_call_history:
3588 if file_name in call.symbol.symtab.fullname ():
3593 for c in filter_only (filename):
3594 for i in c.instructions:
3596 if i.sal.line in linerange:
3605 @node Commands In Python
3606 @subsubsection Commands In Python
3608 @cindex commands in python
3609 @cindex python commands
3610 You can implement new @value{GDBN} CLI commands in Python. A CLI
3611 command is implemented using an instance of the @code{gdb.Command}
3612 class, most commonly using a subclass.
3614 @defun Command.__init__ (name, @var{command_class} @r{[}, @var{completer_class} @r{[}, @var{prefix}@r{]]})
3615 The object initializer for @code{Command} registers the new command
3616 with @value{GDBN}. This initializer is normally invoked from the
3617 subclass' own @code{__init__} method.
3619 @var{name} is the name of the command. If @var{name} consists of
3620 multiple words, then the initial words are looked for as prefix
3621 commands. In this case, if one of the prefix commands does not exist,
3622 an exception is raised.
3624 There is no support for multi-line commands.
3626 @var{command_class} should be one of the @samp{COMMAND_} constants
3627 defined below. This argument tells @value{GDBN} how to categorize the
3628 new command in the help system.
3630 @var{completer_class} is an optional argument. If given, it should be
3631 one of the @samp{COMPLETE_} constants defined below. This argument
3632 tells @value{GDBN} how to perform completion for this command. If not
3633 given, @value{GDBN} will attempt to complete using the object's
3634 @code{complete} method (see below); if no such method is found, an
3635 error will occur when completion is attempted.
3637 @var{prefix} is an optional argument. If @code{True}, then the new
3638 command is a prefix command; sub-commands of this command may be
3641 The help text for the new command is taken from the Python
3642 documentation string for the command's class, if there is one. If no
3643 documentation string is provided, the default value ``This command is
3644 not documented.'' is used.
3647 @cindex don't repeat Python command
3648 @defun Command.dont_repeat ()
3649 By default, a @value{GDBN} command is repeated when the user enters a
3650 blank line at the command prompt. A command can suppress this
3651 behavior by invoking the @code{dont_repeat} method. This is similar
3652 to the user command @code{dont-repeat}, see @ref{Define, dont-repeat}.
3655 @defun Command.invoke (argument, from_tty)
3656 This method is called by @value{GDBN} when this command is invoked.
3658 @var{argument} is a string. It is the argument to the command, after
3659 leading and trailing whitespace has been stripped.
3661 @var{from_tty} is a boolean argument. When true, this means that the
3662 command was entered by the user at the terminal; when false it means
3663 that the command came from elsewhere.
3665 If this method throws an exception, it is turned into a @value{GDBN}
3666 @code{error} call. Otherwise, the return value is ignored.
3668 @findex gdb.string_to_argv
3669 To break @var{argument} up into an argv-like string use
3670 @code{gdb.string_to_argv}. This function behaves identically to
3671 @value{GDBN}'s internal argument lexer @code{buildargv}.
3672 It is recommended to use this for consistency.
3673 Arguments are separated by spaces and may be quoted.
3677 print gdb.string_to_argv ("1 2\ \\\"3 '4 \"5' \"6 '7\"")
3678 ['1', '2 "3', '4 "5', "6 '7"]
3683 @cindex completion of Python commands
3684 @defun Command.complete (text, word)
3685 This method is called by @value{GDBN} when the user attempts
3686 completion on this command. All forms of completion are handled by
3687 this method, that is, the @key{TAB} and @key{M-?} key bindings
3688 (@pxref{Completion}), and the @code{complete} command (@pxref{Help,
3691 The arguments @var{text} and @var{word} are both strings; @var{text}
3692 holds the complete command line up to the cursor's location, while
3693 @var{word} holds the last word of the command line; this is computed
3694 using a word-breaking heuristic.
3696 The @code{complete} method can return several values:
3699 If the return value is a sequence, the contents of the sequence are
3700 used as the completions. It is up to @code{complete} to ensure that the
3701 contents actually do complete the word. A zero-length sequence is
3702 allowed, it means that there were no completions available. Only
3703 string elements of the sequence are used; other elements in the
3704 sequence are ignored.
3707 If the return value is one of the @samp{COMPLETE_} constants defined
3708 below, then the corresponding @value{GDBN}-internal completion
3709 function is invoked, and its result is used.
3712 All other results are treated as though there were no available
3717 When a new command is registered, it must be declared as a member of
3718 some general class of commands. This is used to classify top-level
3719 commands in the on-line help system; note that prefix commands are not
3720 listed under their own category but rather that of their top-level
3721 command. The available classifications are represented by constants
3722 defined in the @code{gdb} module:
3725 @findex COMMAND_NONE
3726 @findex gdb.COMMAND_NONE
3727 @item gdb.COMMAND_NONE
3728 The command does not belong to any particular class. A command in
3729 this category will not be displayed in any of the help categories.
3731 @findex COMMAND_RUNNING
3732 @findex gdb.COMMAND_RUNNING
3733 @item gdb.COMMAND_RUNNING
3734 The command is related to running the inferior. For example,
3735 @code{start}, @code{step}, and @code{continue} are in this category.
3736 Type @kbd{help running} at the @value{GDBN} prompt to see a list of
3737 commands in this category.
3739 @findex COMMAND_DATA
3740 @findex gdb.COMMAND_DATA
3741 @item gdb.COMMAND_DATA
3742 The command is related to data or variables. For example,
3743 @code{call}, @code{find}, and @code{print} are in this category. Type
3744 @kbd{help data} at the @value{GDBN} prompt to see a list of commands
3747 @findex COMMAND_STACK
3748 @findex gdb.COMMAND_STACK
3749 @item gdb.COMMAND_STACK
3750 The command has to do with manipulation of the stack. For example,
3751 @code{backtrace}, @code{frame}, and @code{return} are in this
3752 category. Type @kbd{help stack} at the @value{GDBN} prompt to see a
3753 list of commands in this category.
3755 @findex COMMAND_FILES
3756 @findex gdb.COMMAND_FILES
3757 @item gdb.COMMAND_FILES
3758 This class is used for file-related commands. For example,
3759 @code{file}, @code{list} and @code{section} are in this category.
3760 Type @kbd{help files} at the @value{GDBN} prompt to see a list of
3761 commands in this category.
3763 @findex COMMAND_SUPPORT
3764 @findex gdb.COMMAND_SUPPORT
3765 @item gdb.COMMAND_SUPPORT
3766 This should be used for ``support facilities'', generally meaning
3767 things that are useful to the user when interacting with @value{GDBN},
3768 but not related to the state of the inferior. For example,
3769 @code{help}, @code{make}, and @code{shell} are in this category. Type
3770 @kbd{help support} at the @value{GDBN} prompt to see a list of
3771 commands in this category.
3773 @findex COMMAND_STATUS
3774 @findex gdb.COMMAND_STATUS
3775 @item gdb.COMMAND_STATUS
3776 The command is an @samp{info}-related command, that is, related to the
3777 state of @value{GDBN} itself. For example, @code{info}, @code{macro},
3778 and @code{show} are in this category. Type @kbd{help status} at the
3779 @value{GDBN} prompt to see a list of commands in this category.
3781 @findex COMMAND_BREAKPOINTS
3782 @findex gdb.COMMAND_BREAKPOINTS
3783 @item gdb.COMMAND_BREAKPOINTS
3784 The command has to do with breakpoints. For example, @code{break},
3785 @code{clear}, and @code{delete} are in this category. Type @kbd{help
3786 breakpoints} at the @value{GDBN} prompt to see a list of commands in
3789 @findex COMMAND_TRACEPOINTS
3790 @findex gdb.COMMAND_TRACEPOINTS
3791 @item gdb.COMMAND_TRACEPOINTS
3792 The command has to do with tracepoints. For example, @code{trace},
3793 @code{actions}, and @code{tfind} are in this category. Type
3794 @kbd{help tracepoints} at the @value{GDBN} prompt to see a list of
3795 commands in this category.
3797 @findex COMMAND_USER
3798 @findex gdb.COMMAND_USER
3799 @item gdb.COMMAND_USER
3800 The command is a general purpose command for the user, and typically
3801 does not fit in one of the other categories.
3802 Type @kbd{help user-defined} at the @value{GDBN} prompt to see
3803 a list of commands in this category, as well as the list of gdb macros
3804 (@pxref{Sequences}).
3806 @findex COMMAND_OBSCURE
3807 @findex gdb.COMMAND_OBSCURE
3808 @item gdb.COMMAND_OBSCURE
3809 The command is only used in unusual circumstances, or is not of
3810 general interest to users. For example, @code{checkpoint},
3811 @code{fork}, and @code{stop} are in this category. Type @kbd{help
3812 obscure} at the @value{GDBN} prompt to see a list of commands in this
3815 @findex COMMAND_MAINTENANCE
3816 @findex gdb.COMMAND_MAINTENANCE
3817 @item gdb.COMMAND_MAINTENANCE
3818 The command is only useful to @value{GDBN} maintainers. The
3819 @code{maintenance} and @code{flushregs} commands are in this category.
3820 Type @kbd{help internals} at the @value{GDBN} prompt to see a list of
3821 commands in this category.
3824 A new command can use a predefined completion function, either by
3825 specifying it via an argument at initialization, or by returning it
3826 from the @code{complete} method. These predefined completion
3827 constants are all defined in the @code{gdb} module:
3830 @vindex COMPLETE_NONE
3831 @item gdb.COMPLETE_NONE
3832 This constant means that no completion should be done.
3834 @vindex COMPLETE_FILENAME
3835 @item gdb.COMPLETE_FILENAME
3836 This constant means that filename completion should be performed.
3838 @vindex COMPLETE_LOCATION
3839 @item gdb.COMPLETE_LOCATION
3840 This constant means that location completion should be done.
3841 @xref{Specify Location}.
3843 @vindex COMPLETE_COMMAND
3844 @item gdb.COMPLETE_COMMAND
3845 This constant means that completion should examine @value{GDBN}
3848 @vindex COMPLETE_SYMBOL
3849 @item gdb.COMPLETE_SYMBOL
3850 This constant means that completion should be done using symbol names
3853 @vindex COMPLETE_EXPRESSION
3854 @item gdb.COMPLETE_EXPRESSION
3855 This constant means that completion should be done on expressions.
3856 Often this means completing on symbol names, but some language
3857 parsers also have support for completing on field names.
3860 The following code snippet shows how a trivial CLI command can be
3861 implemented in Python:
3864 class HelloWorld (gdb.Command):
3865 """Greet the whole world."""
3867 def __init__ (self):
3868 super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)
3870 def invoke (self, arg, from_tty):
3871 print "Hello, World!"
3876 The last line instantiates the class, and is necessary to trigger the
3877 registration of the command with @value{GDBN}. Depending on how the
3878 Python code is read into @value{GDBN}, you may need to import the
3879 @code{gdb} module explicitly.
3881 @node Parameters In Python
3882 @subsubsection Parameters In Python
3884 @cindex parameters in python
3885 @cindex python parameters
3886 @tindex gdb.Parameter
3888 You can implement new @value{GDBN} parameters using Python. A new
3889 parameter is implemented as an instance of the @code{gdb.Parameter}
3892 Parameters are exposed to the user via the @code{set} and
3893 @code{show} commands. @xref{Help}.
3895 There are many parameters that already exist and can be set in
3896 @value{GDBN}. Two examples are: @code{set follow fork} and
3897 @code{set charset}. Setting these parameters influences certain
3898 behavior in @value{GDBN}. Similarly, you can define parameters that
3899 can be used to influence behavior in custom Python scripts and commands.
3901 @defun Parameter.__init__ (name, @var{command-class}, @var{parameter-class} @r{[}, @var{enum-sequence}@r{]})
3902 The object initializer for @code{Parameter} registers the new
3903 parameter with @value{GDBN}. This initializer is normally invoked
3904 from the subclass' own @code{__init__} method.
3906 @var{name} is the name of the new parameter. If @var{name} consists
3907 of multiple words, then the initial words are looked for as prefix
3908 parameters. An example of this can be illustrated with the
3909 @code{set print} set of parameters. If @var{name} is
3910 @code{print foo}, then @code{print} will be searched as the prefix
3911 parameter. In this case the parameter can subsequently be accessed in
3912 @value{GDBN} as @code{set print foo}.
3914 If @var{name} consists of multiple words, and no prefix parameter group
3915 can be found, an exception is raised.
3917 @var{command-class} should be one of the @samp{COMMAND_} constants
3918 (@pxref{Commands In Python}). This argument tells @value{GDBN} how to
3919 categorize the new parameter in the help system.
3921 @var{parameter-class} should be one of the @samp{PARAM_} constants
3922 defined below. This argument tells @value{GDBN} the type of the new
3923 parameter; this information is used for input validation and
3926 If @var{parameter-class} is @code{PARAM_ENUM}, then
3927 @var{enum-sequence} must be a sequence of strings. These strings
3928 represent the possible values for the parameter.
3930 If @var{parameter-class} is not @code{PARAM_ENUM}, then the presence
3931 of a fourth argument will cause an exception to be thrown.
3933 The help text for the new parameter is taken from the Python
3934 documentation string for the parameter's class, if there is one. If
3935 there is no documentation string, a default value is used.
3938 @defvar Parameter.set_doc
3939 If this attribute exists, and is a string, then its value is used as
3940 the help text for this parameter's @code{set} command. The value is
3941 examined when @code{Parameter.__init__} is invoked; subsequent changes
3945 @defvar Parameter.show_doc
3946 If this attribute exists, and is a string, then its value is used as
3947 the help text for this parameter's @code{show} command. The value is
3948 examined when @code{Parameter.__init__} is invoked; subsequent changes
3952 @defvar Parameter.value
3953 The @code{value} attribute holds the underlying value of the
3954 parameter. It can be read and assigned to just as any other
3955 attribute. @value{GDBN} does validation when assignments are made.
3958 There are two methods that may be implemented in any @code{Parameter}
3961 @defun Parameter.get_set_string (self)
3962 If this method exists, @value{GDBN} will call it when a
3963 @var{parameter}'s value has been changed via the @code{set} API (for
3964 example, @kbd{set foo off}). The @code{value} attribute has already
3965 been populated with the new value and may be used in output. This
3966 method must return a string. If the returned string is not empty,
3967 @value{GDBN} will present it to the user.
3969 If this method raises the @code{gdb.GdbError} exception
3970 (@pxref{Exception Handling}), then @value{GDBN} will print the
3971 exception's string and the @code{set} command will fail. Note,
3972 however, that the @code{value} attribute will not be reset in this
3973 case. So, if your parameter must validate values, it should store the
3974 old value internally and reset the exposed value, like so:
3977 class ExampleParam (gdb.Parameter):
3978 def __init__ (self, name):
3979 super (ExampleParam, self).__init__ (name,
3983 self.saved_value = True
3986 def get_set_string (self):
3987 if not self.validate():
3988 self.value = self.saved_value
3989 raise gdb.GdbError('Failed to validate')
3990 self.saved_value = self.value
3994 @defun Parameter.get_show_string (self, svalue)
3995 @value{GDBN} will call this method when a @var{parameter}'s
3996 @code{show} API has been invoked (for example, @kbd{show foo}). The
3997 argument @code{svalue} receives the string representation of the
3998 current value. This method must return a string.
4001 When a new parameter is defined, its type must be specified. The
4002 available types are represented by constants defined in the @code{gdb}
4006 @findex PARAM_BOOLEAN
4007 @findex gdb.PARAM_BOOLEAN
4008 @item gdb.PARAM_BOOLEAN
4009 The value is a plain boolean. The Python boolean values, @code{True}
4010 and @code{False} are the only valid values.
4012 @findex PARAM_AUTO_BOOLEAN
4013 @findex gdb.PARAM_AUTO_BOOLEAN
4014 @item gdb.PARAM_AUTO_BOOLEAN
4015 The value has three possible states: true, false, and @samp{auto}. In
4016 Python, true and false are represented using boolean constants, and
4017 @samp{auto} is represented using @code{None}.
4019 @findex PARAM_UINTEGER
4020 @findex gdb.PARAM_UINTEGER
4021 @item gdb.PARAM_UINTEGER
4022 The value is an unsigned integer. The value of 0 should be
4023 interpreted to mean ``unlimited''.
4025 @findex PARAM_INTEGER
4026 @findex gdb.PARAM_INTEGER
4027 @item gdb.PARAM_INTEGER
4028 The value is a signed integer. The value of 0 should be interpreted
4029 to mean ``unlimited''.
4031 @findex PARAM_STRING
4032 @findex gdb.PARAM_STRING
4033 @item gdb.PARAM_STRING
4034 The value is a string. When the user modifies the string, any escape
4035 sequences, such as @samp{\t}, @samp{\f}, and octal escapes, are
4036 translated into corresponding characters and encoded into the current
4039 @findex PARAM_STRING_NOESCAPE
4040 @findex gdb.PARAM_STRING_NOESCAPE
4041 @item gdb.PARAM_STRING_NOESCAPE
4042 The value is a string. When the user modifies the string, escapes are
4043 passed through untranslated.
4045 @findex PARAM_OPTIONAL_FILENAME
4046 @findex gdb.PARAM_OPTIONAL_FILENAME
4047 @item gdb.PARAM_OPTIONAL_FILENAME
4048 The value is a either a filename (a string), or @code{None}.
4050 @findex PARAM_FILENAME
4051 @findex gdb.PARAM_FILENAME
4052 @item gdb.PARAM_FILENAME
4053 The value is a filename. This is just like
4054 @code{PARAM_STRING_NOESCAPE}, but uses file names for completion.
4056 @findex PARAM_ZINTEGER
4057 @findex gdb.PARAM_ZINTEGER
4058 @item gdb.PARAM_ZINTEGER
4059 The value is an integer. This is like @code{PARAM_INTEGER}, except 0
4060 is interpreted as itself.
4062 @findex PARAM_ZUINTEGER
4063 @findex gdb.PARAM_ZUINTEGER
4064 @item gdb.PARAM_ZUINTEGER
4065 The value is an unsigned integer. This is like @code{PARAM_INTEGER},
4066 except 0 is interpreted as itself, and the value cannot be negative.
4068 @findex PARAM_ZUINTEGER_UNLIMITED
4069 @findex gdb.PARAM_ZUINTEGER_UNLIMITED
4070 @item gdb.PARAM_ZUINTEGER_UNLIMITED
4071 The value is a signed integer. This is like @code{PARAM_ZUINTEGER},
4072 except the special value -1 should be interpreted to mean
4073 ``unlimited''. Other negative values are not allowed.
4076 @findex gdb.PARAM_ENUM
4077 @item gdb.PARAM_ENUM
4078 The value is a string, which must be one of a collection string
4079 constants provided when the parameter is created.
4082 @node Functions In Python
4083 @subsubsection Writing new convenience functions
4085 @cindex writing convenience functions
4086 @cindex convenience functions in python
4087 @cindex python convenience functions
4088 @tindex gdb.Function
4090 You can implement new convenience functions (@pxref{Convenience Vars})
4091 in Python. A convenience function is an instance of a subclass of the
4092 class @code{gdb.Function}.
4094 @defun Function.__init__ (name)
4095 The initializer for @code{Function} registers the new function with
4096 @value{GDBN}. The argument @var{name} is the name of the function,
4097 a string. The function will be visible to the user as a convenience
4098 variable of type @code{internal function}, whose name is the same as
4099 the given @var{name}.
4101 The documentation for the new function is taken from the documentation
4102 string for the new class.
4105 @defun Function.invoke (@var{*args})
4106 When a convenience function is evaluated, its arguments are converted
4107 to instances of @code{gdb.Value}, and then the function's
4108 @code{invoke} method is called. Note that @value{GDBN} does not
4109 predetermine the arity of convenience functions. Instead, all
4110 available arguments are passed to @code{invoke}, following the
4111 standard Python calling convention. In particular, a convenience
4112 function can have default values for parameters without ill effect.
4114 The return value of this method is used as its value in the enclosing
4115 expression. If an ordinary Python value is returned, it is converted
4116 to a @code{gdb.Value} following the usual rules.
4119 The following code snippet shows how a trivial convenience function can
4120 be implemented in Python:
4123 class Greet (gdb.Function):
4124 """Return string to greet someone.
4125 Takes a name as argument."""
4127 def __init__ (self):
4128 super (Greet, self).__init__ ("greet")
4130 def invoke (self, name):
4131 return "Hello, %s!" % name.string ()
4136 The last line instantiates the class, and is necessary to trigger the
4137 registration of the function with @value{GDBN}. Depending on how the
4138 Python code is read into @value{GDBN}, you may need to import the
4139 @code{gdb} module explicitly.
4141 Now you can use the function in an expression:
4144 (gdb) print $greet("Bob")
4148 @node Progspaces In Python
4149 @subsubsection Program Spaces In Python
4151 @cindex progspaces in python
4152 @tindex gdb.Progspace
4154 A program space, or @dfn{progspace}, represents a symbolic view
4155 of an address space.
4156 It consists of all of the objfiles of the program.
4157 @xref{Objfiles In Python}.
4158 @xref{Inferiors and Programs, program spaces}, for more details
4159 about program spaces.
4161 The following progspace-related functions are available in the
4164 @findex gdb.current_progspace
4165 @defun gdb.current_progspace ()
4166 This function returns the program space of the currently selected inferior.
4167 @xref{Inferiors and Programs}. This is identical to
4168 @code{gdb.selected_inferior().progspace} (@pxref{Inferiors In Python}) and is
4169 included for historical compatibility.
4172 @findex gdb.progspaces
4173 @defun gdb.progspaces ()
4174 Return a sequence of all the progspaces currently known to @value{GDBN}.
4177 Each progspace is represented by an instance of the @code{gdb.Progspace}
4180 @defvar Progspace.filename
4181 The file name of the progspace as a string.
4184 @defvar Progspace.pretty_printers
4185 The @code{pretty_printers} attribute is a list of functions. It is
4186 used to look up pretty-printers. A @code{Value} is passed to each
4187 function in order; if the function returns @code{None}, then the
4188 search continues. Otherwise, the return value should be an object
4189 which is used to format the value. @xref{Pretty Printing API}, for more
4193 @defvar Progspace.type_printers
4194 The @code{type_printers} attribute is a list of type printer objects.
4195 @xref{Type Printing API}, for more information.
4198 @defvar Progspace.frame_filters
4199 The @code{frame_filters} attribute is a dictionary of frame filter
4200 objects. @xref{Frame Filter API}, for more information.
4203 A program space has the following methods:
4205 @findex Progspace.block_for_pc
4206 @defun Progspace.block_for_pc (pc)
4207 Return the innermost @code{gdb.Block} containing the given @var{pc}
4208 value. If the block cannot be found for the @var{pc} value specified,
4209 the function will return @code{None}.
4212 @findex Progspace.find_pc_line
4213 @defun Progspace.find_pc_line (pc)
4214 Return the @code{gdb.Symtab_and_line} object corresponding to the
4215 @var{pc} value. @xref{Symbol Tables In Python}. If an invalid value
4216 of @var{pc} is passed as an argument, then the @code{symtab} and
4217 @code{line} attributes of the returned @code{gdb.Symtab_and_line}
4218 object will be @code{None} and 0 respectively.
4221 @findex Progspace.is_valid
4222 @defun Progspace.is_valid ()
4223 Returns @code{True} if the @code{gdb.Progspace} object is valid,
4224 @code{False} if not. A @code{gdb.Progspace} object can become invalid
4225 if the program space file it refers to is not referenced by any
4226 inferior. All other @code{gdb.Progspace} methods will throw an
4227 exception if it is invalid at the time the method is called.
4230 @findex Progspace.objfiles
4231 @defun Progspace.objfiles ()
4232 Return a sequence of all the objfiles referenced by this program
4233 space. @xref{Objfiles In Python}.
4236 @findex Progspace.solib_name
4237 @defun Progspace.solib_name (address)
4238 Return the name of the shared library holding the given @var{address}
4239 as a string, or @code{None}.
4242 One may add arbitrary attributes to @code{gdb.Progspace} objects
4243 in the usual Python way.
4244 This is useful if, for example, one needs to do some extra record keeping
4245 associated with the program space.
4247 In this contrived example, we want to perform some processing when
4248 an objfile with a certain symbol is loaded, but we only want to do
4249 this once because it is expensive. To achieve this we record the results
4250 with the program space because we can't predict when the desired objfile
4255 def clear_objfiles_handler(event):
4256 event.progspace.expensive_computation = None
4257 def expensive(symbol):
4258 """A mock routine to perform an "expensive" computation on symbol."""
4259 print "Computing the answer to the ultimate question ..."
4261 def new_objfile_handler(event):
4262 objfile = event.new_objfile
4263 progspace = objfile.progspace
4264 if not hasattr(progspace, 'expensive_computation') or \
4265 progspace.expensive_computation is None:
4266 # We use 'main' for the symbol to keep the example simple.
4267 # Note: There's no current way to constrain the lookup
4269 symbol = gdb.lookup_global_symbol('main')
4270 if symbol is not None:
4271 progspace.expensive_computation = expensive(symbol)
4272 gdb.events.clear_objfiles.connect(clear_objfiles_handler)
4273 gdb.events.new_objfile.connect(new_objfile_handler)
4275 (gdb) file /tmp/hello
4276 Reading symbols from /tmp/hello...done.
4277 Computing the answer to the ultimate question ...
4278 (gdb) python print gdb.current_progspace().expensive_computation
4281 Starting program: /tmp/hello
4283 [Inferior 1 (process 4242) exited normally]
4286 @node Objfiles In Python
4287 @subsubsection Objfiles In Python
4289 @cindex objfiles in python
4292 @value{GDBN} loads symbols for an inferior from various
4293 symbol-containing files (@pxref{Files}). These include the primary
4294 executable file, any shared libraries used by the inferior, and any
4295 separate debug info files (@pxref{Separate Debug Files}).
4296 @value{GDBN} calls these symbol-containing files @dfn{objfiles}.
4298 The following objfile-related functions are available in the
4301 @findex gdb.current_objfile
4302 @defun gdb.current_objfile ()
4303 When auto-loading a Python script (@pxref{Python Auto-loading}), @value{GDBN}
4304 sets the ``current objfile'' to the corresponding objfile. This
4305 function returns the current objfile. If there is no current objfile,
4306 this function returns @code{None}.
4309 @findex gdb.objfiles
4310 @defun gdb.objfiles ()
4311 Return a sequence of objfiles referenced by the current program space.
4312 @xref{Objfiles In Python}, and @ref{Progspaces In Python}. This is identical
4313 to @code{gdb.selected_inferior().progspace.objfiles()} and is included for
4314 historical compatibility.
4317 @findex gdb.lookup_objfile
4318 @defun gdb.lookup_objfile (name @r{[}, by_build_id{]})
4319 Look up @var{name}, a file name or build ID, in the list of objfiles
4320 for the current program space (@pxref{Progspaces In Python}).
4321 If the objfile is not found throw the Python @code{ValueError} exception.
4323 If @var{name} is a relative file name, then it will match any
4324 source file name with the same trailing components. For example, if
4325 @var{name} is @samp{gcc/expr.c}, then it will match source file
4326 name of @file{/build/trunk/gcc/expr.c}, but not
4327 @file{/build/trunk/libcpp/expr.c} or @file{/build/trunk/gcc/x-expr.c}.
4329 If @var{by_build_id} is provided and is @code{True} then @var{name}
4330 is the build ID of the objfile. Otherwise, @var{name} is a file name.
4331 This is supported only on some operating systems, notably those which use
4332 the ELF format for binary files and the @sc{gnu} Binutils. For more details
4333 about this feature, see the description of the @option{--build-id}
4334 command-line option in @ref{Options, , Command Line Options, ld,
4338 Each objfile is represented by an instance of the @code{gdb.Objfile}
4341 @defvar Objfile.filename
4342 The file name of the objfile as a string, with symbolic links resolved.
4344 The value is @code{None} if the objfile is no longer valid.
4345 See the @code{gdb.Objfile.is_valid} method, described below.
4348 @defvar Objfile.username
4349 The file name of the objfile as specified by the user as a string.
4351 The value is @code{None} if the objfile is no longer valid.
4352 See the @code{gdb.Objfile.is_valid} method, described below.
4355 @defvar Objfile.owner
4356 For separate debug info objfiles this is the corresponding @code{gdb.Objfile}
4357 object that debug info is being provided for.
4358 Otherwise this is @code{None}.
4359 Separate debug info objfiles are added with the
4360 @code{gdb.Objfile.add_separate_debug_file} method, described below.
4363 @defvar Objfile.build_id
4364 The build ID of the objfile as a string.
4365 If the objfile does not have a build ID then the value is @code{None}.
4367 This is supported only on some operating systems, notably those which use
4368 the ELF format for binary files and the @sc{gnu} Binutils. For more details
4369 about this feature, see the description of the @option{--build-id}
4370 command-line option in @ref{Options, , Command Line Options, ld,
4374 @defvar Objfile.progspace
4375 The containing program space of the objfile as a @code{gdb.Progspace}
4376 object. @xref{Progspaces In Python}.
4379 @defvar Objfile.pretty_printers
4380 The @code{pretty_printers} attribute is a list of functions. It is
4381 used to look up pretty-printers. A @code{Value} is passed to each
4382 function in order; if the function returns @code{None}, then the
4383 search continues. Otherwise, the return value should be an object
4384 which is used to format the value. @xref{Pretty Printing API}, for more
4388 @defvar Objfile.type_printers
4389 The @code{type_printers} attribute is a list of type printer objects.
4390 @xref{Type Printing API}, for more information.
4393 @defvar Objfile.frame_filters
4394 The @code{frame_filters} attribute is a dictionary of frame filter
4395 objects. @xref{Frame Filter API}, for more information.
4398 One may add arbitrary attributes to @code{gdb.Objfile} objects
4399 in the usual Python way.
4400 This is useful if, for example, one needs to do some extra record keeping
4401 associated with the objfile.
4403 In this contrived example we record the time when @value{GDBN}
4409 def new_objfile_handler(event):
4410 # Set the time_loaded attribute of the new objfile.
4411 event.new_objfile.time_loaded = datetime.datetime.today()
4412 gdb.events.new_objfile.connect(new_objfile_handler)
4415 Reading symbols from ./hello...done.
4416 (gdb) python print gdb.objfiles()[0].time_loaded
4417 2014-10-09 11:41:36.770345
4420 A @code{gdb.Objfile} object has the following methods:
4422 @defun Objfile.is_valid ()
4423 Returns @code{True} if the @code{gdb.Objfile} object is valid,
4424 @code{False} if not. A @code{gdb.Objfile} object can become invalid
4425 if the object file it refers to is not loaded in @value{GDBN} any
4426 longer. All other @code{gdb.Objfile} methods will throw an exception
4427 if it is invalid at the time the method is called.
4430 @defun Objfile.add_separate_debug_file (file)
4431 Add @var{file} to the list of files that @value{GDBN} will search for
4432 debug information for the objfile.
4433 This is useful when the debug info has been removed from the program
4434 and stored in a separate file. @value{GDBN} has built-in support for
4435 finding separate debug info files (@pxref{Separate Debug Files}), but if
4436 the file doesn't live in one of the standard places that @value{GDBN}
4437 searches then this function can be used to add a debug info file
4438 from a different place.
4441 @node Frames In Python
4442 @subsubsection Accessing inferior stack frames from Python
4444 @cindex frames in python
4445 When the debugged program stops, @value{GDBN} is able to analyze its call
4446 stack (@pxref{Frames,,Stack frames}). The @code{gdb.Frame} class
4447 represents a frame in the stack. A @code{gdb.Frame} object is only valid
4448 while its corresponding frame exists in the inferior's stack. If you try
4449 to use an invalid frame object, @value{GDBN} will throw a @code{gdb.error}
4450 exception (@pxref{Exception Handling}).
4452 Two @code{gdb.Frame} objects can be compared for equality with the @code{==}
4456 (@value{GDBP}) python print gdb.newest_frame() == gdb.selected_frame ()
4460 The following frame-related functions are available in the @code{gdb} module:
4462 @findex gdb.selected_frame
4463 @defun gdb.selected_frame ()
4464 Return the selected frame object. (@pxref{Selection,,Selecting a Frame}).
4467 @findex gdb.newest_frame
4468 @defun gdb.newest_frame ()
4469 Return the newest frame object for the selected thread.
4472 @defun gdb.frame_stop_reason_string (reason)
4473 Return a string explaining the reason why @value{GDBN} stopped unwinding
4474 frames, as expressed by the given @var{reason} code (an integer, see the
4475 @code{unwind_stop_reason} method further down in this section).
4478 @findex gdb.invalidate_cached_frames
4479 @defun gdb.invalidate_cached_frames
4480 @value{GDBN} internally keeps a cache of the frames that have been
4481 unwound. This function invalidates this cache.
4483 This function should not generally be called by ordinary Python code.
4484 It is documented for the sake of completeness.
4487 A @code{gdb.Frame} object has the following methods:
4489 @defun Frame.is_valid ()
4490 Returns true if the @code{gdb.Frame} object is valid, false if not.
4491 A frame object can become invalid if the frame it refers to doesn't
4492 exist anymore in the inferior. All @code{gdb.Frame} methods will throw
4493 an exception if it is invalid at the time the method is called.
4496 @defun Frame.name ()
4497 Returns the function name of the frame, or @code{None} if it can't be
4501 @defun Frame.architecture ()
4502 Returns the @code{gdb.Architecture} object corresponding to the frame's
4503 architecture. @xref{Architectures In Python}.
4506 @defun Frame.type ()
4507 Returns the type of the frame. The value can be one of:
4509 @item gdb.NORMAL_FRAME
4510 An ordinary stack frame.
4512 @item gdb.DUMMY_FRAME
4513 A fake stack frame that was created by @value{GDBN} when performing an
4514 inferior function call.
4516 @item gdb.INLINE_FRAME
4517 A frame representing an inlined function. The function was inlined
4518 into a @code{gdb.NORMAL_FRAME} that is older than this one.
4520 @item gdb.TAILCALL_FRAME
4521 A frame representing a tail call. @xref{Tail Call Frames}.
4523 @item gdb.SIGTRAMP_FRAME
4524 A signal trampoline frame. This is the frame created by the OS when
4525 it calls into a signal handler.
4527 @item gdb.ARCH_FRAME
4528 A fake stack frame representing a cross-architecture call.
4530 @item gdb.SENTINEL_FRAME
4531 This is like @code{gdb.NORMAL_FRAME}, but it is only used for the
4536 @defun Frame.unwind_stop_reason ()
4537 Return an integer representing the reason why it's not possible to find
4538 more frames toward the outermost frame. Use
4539 @code{gdb.frame_stop_reason_string} to convert the value returned by this
4540 function to a string. The value can be one of:
4543 @item gdb.FRAME_UNWIND_NO_REASON
4544 No particular reason (older frames should be available).
4546 @item gdb.FRAME_UNWIND_NULL_ID
4547 The previous frame's analyzer returns an invalid result. This is no
4548 longer used by @value{GDBN}, and is kept only for backward
4551 @item gdb.FRAME_UNWIND_OUTERMOST
4552 This frame is the outermost.
4554 @item gdb.FRAME_UNWIND_UNAVAILABLE
4555 Cannot unwind further, because that would require knowing the
4556 values of registers or memory that have not been collected.
4558 @item gdb.FRAME_UNWIND_INNER_ID
4559 This frame ID looks like it ought to belong to a NEXT frame,
4560 but we got it for a PREV frame. Normally, this is a sign of
4561 unwinder failure. It could also indicate stack corruption.
4563 @item gdb.FRAME_UNWIND_SAME_ID
4564 This frame has the same ID as the previous one. That means
4565 that unwinding further would almost certainly give us another
4566 frame with exactly the same ID, so break the chain. Normally,
4567 this is a sign of unwinder failure. It could also indicate
4570 @item gdb.FRAME_UNWIND_NO_SAVED_PC
4571 The frame unwinder did not find any saved PC, but we needed
4572 one to unwind further.
4574 @item gdb.FRAME_UNWIND_MEMORY_ERROR
4575 The frame unwinder caused an error while trying to access memory.
4577 @item gdb.FRAME_UNWIND_FIRST_ERROR
4578 Any stop reason greater or equal to this value indicates some kind
4579 of error. This special value facilitates writing code that tests
4580 for errors in unwinding in a way that will work correctly even if
4581 the list of the other values is modified in future @value{GDBN}
4582 versions. Using it, you could write:
4584 reason = gdb.selected_frame().unwind_stop_reason ()
4585 reason_str = gdb.frame_stop_reason_string (reason)
4586 if reason >= gdb.FRAME_UNWIND_FIRST_ERROR:
4587 print "An error occured: %s" % reason_str
4594 Returns the frame's resume address.
4597 @defun Frame.block ()
4598 Return the frame's code block. @xref{Blocks In Python}. If the frame
4599 does not have a block -- for example, if there is no debugging
4600 information for the code in question -- then this will throw an
4604 @defun Frame.function ()
4605 Return the symbol for the function corresponding to this frame.
4606 @xref{Symbols In Python}.
4609 @defun Frame.older ()
4610 Return the frame that called this frame.
4613 @defun Frame.newer ()
4614 Return the frame called by this frame.
4617 @defun Frame.find_sal ()
4618 Return the frame's symtab and line object.
4619 @xref{Symbol Tables In Python}.
4622 @defun Frame.read_register (register)
4623 Return the value of @var{register} in this frame. The @var{register}
4624 argument must be a string (e.g., @code{'sp'} or @code{'rax'}).
4625 Returns a @code{Gdb.Value} object. Throws an exception if @var{register}
4629 @defun Frame.read_var (variable @r{[}, block@r{]})
4630 Return the value of @var{variable} in this frame. If the optional
4631 argument @var{block} is provided, search for the variable from that
4632 block; otherwise start at the frame's current block (which is
4633 determined by the frame's current program counter). The @var{variable}
4634 argument must be a string or a @code{gdb.Symbol} object; @var{block} must be a
4635 @code{gdb.Block} object.
4638 @defun Frame.select ()
4639 Set this frame to be the selected frame. @xref{Stack, ,Examining the
4643 @node Blocks In Python
4644 @subsubsection Accessing blocks from Python
4646 @cindex blocks in python
4649 In @value{GDBN}, symbols are stored in blocks. A block corresponds
4650 roughly to a scope in the source code. Blocks are organized
4651 hierarchically, and are represented individually in Python as a
4652 @code{gdb.Block}. Blocks rely on debugging information being
4655 A frame has a block. Please see @ref{Frames In Python}, for a more
4656 in-depth discussion of frames.
4658 The outermost block is known as the @dfn{global block}. The global
4659 block typically holds public global variables and functions.
4661 The block nested just inside the global block is the @dfn{static
4662 block}. The static block typically holds file-scoped variables and
4665 @value{GDBN} provides a method to get a block's superblock, but there
4666 is currently no way to examine the sub-blocks of a block, or to
4667 iterate over all the blocks in a symbol table (@pxref{Symbol Tables In
4670 Here is a short example that should help explain blocks:
4673 /* This is in the global block. */
4676 /* This is in the static block. */
4677 static int file_scope;
4679 /* 'function' is in the global block, and 'argument' is
4680 in a block nested inside of 'function'. */
4681 int function (int argument)
4683 /* 'local' is in a block inside 'function'. It may or may
4684 not be in the same block as 'argument'. */
4688 /* 'inner' is in a block whose superblock is the one holding
4692 /* If this call is expanded by the compiler, you may see
4693 a nested block here whose function is 'inline_function'
4694 and whose superblock is the one holding 'inner'. */
4700 A @code{gdb.Block} is iterable. The iterator returns the symbols
4701 (@pxref{Symbols In Python}) local to the block. Python programs
4702 should not assume that a specific block object will always contain a
4703 given symbol, since changes in @value{GDBN} features and
4704 infrastructure may cause symbols move across blocks in a symbol
4707 The following block-related functions are available in the @code{gdb}
4710 @findex gdb.block_for_pc
4711 @defun gdb.block_for_pc (pc)
4712 Return the innermost @code{gdb.Block} containing the given @var{pc}
4713 value. If the block cannot be found for the @var{pc} value specified,
4714 the function will return @code{None}. This is identical to
4715 @code{gdb.current_progspace().block_for_pc(pc)} and is included for
4716 historical compatibility.
4719 A @code{gdb.Block} object has the following methods:
4721 @defun Block.is_valid ()
4722 Returns @code{True} if the @code{gdb.Block} object is valid,
4723 @code{False} if not. A block object can become invalid if the block it
4724 refers to doesn't exist anymore in the inferior. All other
4725 @code{gdb.Block} methods will throw an exception if it is invalid at
4726 the time the method is called. The block's validity is also checked
4727 during iteration over symbols of the block.
4730 A @code{gdb.Block} object has the following attributes:
4733 The start address of the block. This attribute is not writable.
4737 One past the last address that appears in the block. This attribute
4741 @defvar Block.function
4742 The name of the block represented as a @code{gdb.Symbol}. If the
4743 block is not named, then this attribute holds @code{None}. This
4744 attribute is not writable.
4746 For ordinary function blocks, the superblock is the static block.
4747 However, you should note that it is possible for a function block to
4748 have a superblock that is not the static block -- for instance this
4749 happens for an inlined function.
4752 @defvar Block.superblock
4753 The block containing this block. If this parent block does not exist,
4754 this attribute holds @code{None}. This attribute is not writable.
4757 @defvar Block.global_block
4758 The global block associated with this block. This attribute is not
4762 @defvar Block.static_block
4763 The static block associated with this block. This attribute is not
4767 @defvar Block.is_global
4768 @code{True} if the @code{gdb.Block} object is a global block,
4769 @code{False} if not. This attribute is not
4773 @defvar Block.is_static
4774 @code{True} if the @code{gdb.Block} object is a static block,
4775 @code{False} if not. This attribute is not writable.
4778 @node Symbols In Python
4779 @subsubsection Python representation of Symbols
4781 @cindex symbols in python
4784 @value{GDBN} represents every variable, function and type as an
4785 entry in a symbol table. @xref{Symbols, ,Examining the Symbol Table}.
4786 Similarly, Python represents these symbols in @value{GDBN} with the
4787 @code{gdb.Symbol} object.
4789 The following symbol-related functions are available in the @code{gdb}
4792 @findex gdb.lookup_symbol
4793 @defun gdb.lookup_symbol (name @r{[}, block @r{[}, domain@r{]]})
4794 This function searches for a symbol by name. The search scope can be
4795 restricted to the parameters defined in the optional domain and block
4798 @var{name} is the name of the symbol. It must be a string. The
4799 optional @var{block} argument restricts the search to symbols visible
4800 in that @var{block}. The @var{block} argument must be a
4801 @code{gdb.Block} object. If omitted, the block for the current frame
4802 is used. The optional @var{domain} argument restricts
4803 the search to the domain type. The @var{domain} argument must be a
4804 domain constant defined in the @code{gdb} module and described later
4807 The result is a tuple of two elements.
4808 The first element is a @code{gdb.Symbol} object or @code{None} if the symbol
4810 If the symbol is found, the second element is @code{True} if the symbol
4811 is a field of a method's object (e.g., @code{this} in C@t{++}),
4812 otherwise it is @code{False}.
4813 If the symbol is not found, the second element is @code{False}.
4816 @findex gdb.lookup_global_symbol
4817 @defun gdb.lookup_global_symbol (name @r{[}, domain@r{]})
4818 This function searches for a global symbol by name.
4819 The search scope can be restricted to by the domain argument.
4821 @var{name} is the name of the symbol. It must be a string.
4822 The optional @var{domain} argument restricts the search to the domain type.
4823 The @var{domain} argument must be a domain constant defined in the @code{gdb}
4824 module and described later in this chapter.
4826 The result is a @code{gdb.Symbol} object or @code{None} if the symbol
4830 A @code{gdb.Symbol} object has the following attributes:
4833 The type of the symbol or @code{None} if no type is recorded.
4834 This attribute is represented as a @code{gdb.Type} object.
4835 @xref{Types In Python}. This attribute is not writable.
4838 @defvar Symbol.symtab
4839 The symbol table in which the symbol appears. This attribute is
4840 represented as a @code{gdb.Symtab} object. @xref{Symbol Tables In
4841 Python}. This attribute is not writable.
4845 The line number in the source code at which the symbol was defined.
4850 The name of the symbol as a string. This attribute is not writable.
4853 @defvar Symbol.linkage_name
4854 The name of the symbol, as used by the linker (i.e., may be mangled).
4855 This attribute is not writable.
4858 @defvar Symbol.print_name
4859 The name of the symbol in a form suitable for output. This is either
4860 @code{name} or @code{linkage_name}, depending on whether the user
4861 asked @value{GDBN} to display demangled or mangled names.
4864 @defvar Symbol.addr_class
4865 The address class of the symbol. This classifies how to find the value
4866 of a symbol. Each address class is a constant defined in the
4867 @code{gdb} module and described later in this chapter.
4870 @defvar Symbol.needs_frame
4871 This is @code{True} if evaluating this symbol's value requires a frame
4872 (@pxref{Frames In Python}) and @code{False} otherwise. Typically,
4873 local variables will require a frame, but other symbols will not.
4876 @defvar Symbol.is_argument
4877 @code{True} if the symbol is an argument of a function.
4880 @defvar Symbol.is_constant
4881 @code{True} if the symbol is a constant.
4884 @defvar Symbol.is_function
4885 @code{True} if the symbol is a function or a method.
4888 @defvar Symbol.is_variable
4889 @code{True} if the symbol is a variable.
4892 A @code{gdb.Symbol} object has the following methods:
4894 @defun Symbol.is_valid ()
4895 Returns @code{True} if the @code{gdb.Symbol} object is valid,
4896 @code{False} if not. A @code{gdb.Symbol} object can become invalid if
4897 the symbol it refers to does not exist in @value{GDBN} any longer.
4898 All other @code{gdb.Symbol} methods will throw an exception if it is
4899 invalid at the time the method is called.
4902 @defun Symbol.value (@r{[}frame@r{]})
4903 Compute the value of the symbol, as a @code{gdb.Value}. For
4904 functions, this computes the address of the function, cast to the
4905 appropriate type. If the symbol requires a frame in order to compute
4906 its value, then @var{frame} must be given. If @var{frame} is not
4907 given, or if @var{frame} is invalid, then this method will throw an
4911 The available domain categories in @code{gdb.Symbol} are represented
4912 as constants in the @code{gdb} module:
4915 @vindex SYMBOL_UNDEF_DOMAIN
4916 @item gdb.SYMBOL_UNDEF_DOMAIN
4917 This is used when a domain has not been discovered or none of the
4918 following domains apply. This usually indicates an error either
4919 in the symbol information or in @value{GDBN}'s handling of symbols.
4921 @vindex SYMBOL_VAR_DOMAIN
4922 @item gdb.SYMBOL_VAR_DOMAIN
4923 This domain contains variables, function names, typedef names and enum
4926 @vindex SYMBOL_STRUCT_DOMAIN
4927 @item gdb.SYMBOL_STRUCT_DOMAIN
4928 This domain holds struct, union and enum type names.
4930 @vindex SYMBOL_LABEL_DOMAIN
4931 @item gdb.SYMBOL_LABEL_DOMAIN
4932 This domain contains names of labels (for gotos).
4934 @vindex SYMBOL_MODULE_DOMAIN
4935 @item gdb.SYMBOL_MODULE_DOMAIN
4936 This domain contains names of Fortran module types.
4938 @vindex SYMBOL_COMMON_BLOCK_DOMAIN
4939 @item gdb.SYMBOL_COMMON_BLOCK_DOMAIN
4940 This domain contains names of Fortran common blocks.
4943 The available address class categories in @code{gdb.Symbol} are represented
4944 as constants in the @code{gdb} module:
4947 @vindex SYMBOL_LOC_UNDEF
4948 @item gdb.SYMBOL_LOC_UNDEF
4949 If this is returned by address class, it indicates an error either in
4950 the symbol information or in @value{GDBN}'s handling of symbols.
4952 @vindex SYMBOL_LOC_CONST
4953 @item gdb.SYMBOL_LOC_CONST
4954 Value is constant int.
4956 @vindex SYMBOL_LOC_STATIC
4957 @item gdb.SYMBOL_LOC_STATIC
4958 Value is at a fixed address.
4960 @vindex SYMBOL_LOC_REGISTER
4961 @item gdb.SYMBOL_LOC_REGISTER
4962 Value is in a register.
4964 @vindex SYMBOL_LOC_ARG
4965 @item gdb.SYMBOL_LOC_ARG
4966 Value is an argument. This value is at the offset stored within the
4967 symbol inside the frame's argument list.
4969 @vindex SYMBOL_LOC_REF_ARG
4970 @item gdb.SYMBOL_LOC_REF_ARG
4971 Value address is stored in the frame's argument list. Just like
4972 @code{LOC_ARG} except that the value's address is stored at the
4973 offset, not the value itself.
4975 @vindex SYMBOL_LOC_REGPARM_ADDR
4976 @item gdb.SYMBOL_LOC_REGPARM_ADDR
4977 Value is a specified register. Just like @code{LOC_REGISTER} except
4978 the register holds the address of the argument instead of the argument
4981 @vindex SYMBOL_LOC_LOCAL
4982 @item gdb.SYMBOL_LOC_LOCAL
4983 Value is a local variable.
4985 @vindex SYMBOL_LOC_TYPEDEF
4986 @item gdb.SYMBOL_LOC_TYPEDEF
4987 Value not used. Symbols in the domain @code{SYMBOL_STRUCT_DOMAIN} all
4990 @vindex SYMBOL_LOC_BLOCK
4991 @item gdb.SYMBOL_LOC_BLOCK
4994 @vindex SYMBOL_LOC_CONST_BYTES
4995 @item gdb.SYMBOL_LOC_CONST_BYTES
4996 Value is a byte-sequence.
4998 @vindex SYMBOL_LOC_UNRESOLVED
4999 @item gdb.SYMBOL_LOC_UNRESOLVED
5000 Value is at a fixed address, but the address of the variable has to be
5001 determined from the minimal symbol table whenever the variable is
5004 @vindex SYMBOL_LOC_OPTIMIZED_OUT
5005 @item gdb.SYMBOL_LOC_OPTIMIZED_OUT
5006 The value does not actually exist in the program.
5008 @vindex SYMBOL_LOC_COMPUTED
5009 @item gdb.SYMBOL_LOC_COMPUTED
5010 The value's address is a computed location.
5012 @vindex SYMBOL_LOC_COMPUTED
5013 @item gdb.SYMBOL_LOC_COMPUTED
5014 The value's address is a symbol. This is only used for Fortran common
5018 @node Symbol Tables In Python
5019 @subsubsection Symbol table representation in Python
5021 @cindex symbol tables in python
5023 @tindex gdb.Symtab_and_line
5025 Access to symbol table data maintained by @value{GDBN} on the inferior
5026 is exposed to Python via two objects: @code{gdb.Symtab_and_line} and
5027 @code{gdb.Symtab}. Symbol table and line data for a frame is returned
5028 from the @code{find_sal} method in @code{gdb.Frame} object.
5029 @xref{Frames In Python}.
5031 For more information on @value{GDBN}'s symbol table management, see
5032 @ref{Symbols, ,Examining the Symbol Table}, for more information.
5034 A @code{gdb.Symtab_and_line} object has the following attributes:
5036 @defvar Symtab_and_line.symtab
5037 The symbol table object (@code{gdb.Symtab}) for this frame.
5038 This attribute is not writable.
5041 @defvar Symtab_and_line.pc
5042 Indicates the start of the address range occupied by code for the
5043 current source line. This attribute is not writable.
5046 @defvar Symtab_and_line.last
5047 Indicates the end of the address range occupied by code for the current
5048 source line. This attribute is not writable.
5051 @defvar Symtab_and_line.line
5052 Indicates the current line number for this object. This
5053 attribute is not writable.
5056 A @code{gdb.Symtab_and_line} object has the following methods:
5058 @defun Symtab_and_line.is_valid ()
5059 Returns @code{True} if the @code{gdb.Symtab_and_line} object is valid,
5060 @code{False} if not. A @code{gdb.Symtab_and_line} object can become
5061 invalid if the Symbol table and line object it refers to does not
5062 exist in @value{GDBN} any longer. All other
5063 @code{gdb.Symtab_and_line} methods will throw an exception if it is
5064 invalid at the time the method is called.
5067 A @code{gdb.Symtab} object has the following attributes:
5069 @defvar Symtab.filename
5070 The symbol table's source filename. This attribute is not writable.
5073 @defvar Symtab.objfile
5074 The symbol table's backing object file. @xref{Objfiles In Python}.
5075 This attribute is not writable.
5078 @defvar Symtab.producer
5079 The name and possibly version number of the program that
5080 compiled the code in the symbol table.
5081 The contents of this string is up to the compiler.
5082 If no producer information is available then @code{None} is returned.
5083 This attribute is not writable.
5086 A @code{gdb.Symtab} object has the following methods:
5088 @defun Symtab.is_valid ()
5089 Returns @code{True} if the @code{gdb.Symtab} object is valid,
5090 @code{False} if not. A @code{gdb.Symtab} object can become invalid if
5091 the symbol table it refers to does not exist in @value{GDBN} any
5092 longer. All other @code{gdb.Symtab} methods will throw an exception
5093 if it is invalid at the time the method is called.
5096 @defun Symtab.fullname ()
5097 Return the symbol table's source absolute file name.
5100 @defun Symtab.global_block ()
5101 Return the global block of the underlying symbol table.
5102 @xref{Blocks In Python}.
5105 @defun Symtab.static_block ()
5106 Return the static block of the underlying symbol table.
5107 @xref{Blocks In Python}.
5110 @defun Symtab.linetable ()
5111 Return the line table associated with the symbol table.
5112 @xref{Line Tables In Python}.
5115 @node Line Tables In Python
5116 @subsubsection Manipulating line tables using Python
5118 @cindex line tables in python
5119 @tindex gdb.LineTable
5121 Python code can request and inspect line table information from a
5122 symbol table that is loaded in @value{GDBN}. A line table is a
5123 mapping of source lines to their executable locations in memory. To
5124 acquire the line table information for a particular symbol table, use
5125 the @code{linetable} function (@pxref{Symbol Tables In Python}).
5127 A @code{gdb.LineTable} is iterable. The iterator returns
5128 @code{LineTableEntry} objects that correspond to the source line and
5129 address for each line table entry. @code{LineTableEntry} objects have
5130 the following attributes:
5132 @defvar LineTableEntry.line
5133 The source line number for this line table entry. This number
5134 corresponds to the actual line of source. This attribute is not
5138 @defvar LineTableEntry.pc
5139 The address that is associated with the line table entry where the
5140 executable code for that source line resides in memory. This
5141 attribute is not writable.
5144 As there can be multiple addresses for a single source line, you may
5145 receive multiple @code{LineTableEntry} objects with matching
5146 @code{line} attributes, but with different @code{pc} attributes. The
5147 iterator is sorted in ascending @code{pc} order. Here is a small
5148 example illustrating iterating over a line table.
5151 symtab = gdb.selected_frame().find_sal().symtab
5152 linetable = symtab.linetable()
5153 for line in linetable:
5154 print "Line: "+str(line.line)+" Address: "+hex(line.pc)
5157 This will have the following output:
5160 Line: 33 Address: 0x4005c8L
5161 Line: 37 Address: 0x4005caL
5162 Line: 39 Address: 0x4005d2L
5163 Line: 40 Address: 0x4005f8L
5164 Line: 42 Address: 0x4005ffL
5165 Line: 44 Address: 0x400608L
5166 Line: 42 Address: 0x40060cL
5167 Line: 45 Address: 0x400615L
5170 In addition to being able to iterate over a @code{LineTable}, it also
5171 has the following direct access methods:
5173 @defun LineTable.line (line)
5174 Return a Python @code{Tuple} of @code{LineTableEntry} objects for any
5175 entries in the line table for the given @var{line}, which specifies
5176 the source code line. If there are no entries for that source code
5177 @var{line}, the Python @code{None} is returned.
5180 @defun LineTable.has_line (line)
5181 Return a Python @code{Boolean} indicating whether there is an entry in
5182 the line table for this source line. Return @code{True} if an entry
5183 is found, or @code{False} if not.
5186 @defun LineTable.source_lines ()
5187 Return a Python @code{List} of the source line numbers in the symbol
5188 table. Only lines with executable code locations are returned. The
5189 contents of the @code{List} will just be the source line entries
5190 represented as Python @code{Long} values.
5193 @node Breakpoints In Python
5194 @subsubsection Manipulating breakpoints using Python
5196 @cindex breakpoints in python
5197 @tindex gdb.Breakpoint
5199 Python code can manipulate breakpoints via the @code{gdb.Breakpoint}
5202 A breakpoint can be created using one of the two forms of the
5203 @code{gdb.Breakpoint} constructor. The first one accepts a string
5204 like one would pass to the @code{break}
5205 (@pxref{Set Breaks,,Setting Breakpoints}) and @code{watch}
5206 (@pxref{Set Watchpoints, , Setting Watchpoints}) commands, and can be used to
5207 create both breakpoints and watchpoints. The second accepts separate Python
5208 arguments similar to @ref{Explicit Locations}, and can only be used to create
5211 @defun Breakpoint.__init__ (spec @r{[}, type @r{][}, wp_class @r{][}, internal @r{][}, temporary @r{][}, qualified @r{]})
5212 Create a new breakpoint according to @var{spec}, which is a string naming the
5213 location of a breakpoint, or an expression that defines a watchpoint. The
5214 string should describe a location in a format recognized by the @code{break}
5215 command (@pxref{Set Breaks,,Setting Breakpoints}) or, in the case of a
5216 watchpoint, by the @code{watch} command
5217 (@pxref{Set Watchpoints, , Setting Watchpoints}).
5219 The optional @var{type} argument specifies the type of the breakpoint to create,
5222 The optional @var{wp_class} argument defines the class of watchpoint to create,
5223 if @var{type} is @code{gdb.BP_WATCHPOINT}. If @var{wp_class} is omitted, it
5224 defaults to @code{gdb.WP_WRITE}.
5226 The optional @var{internal} argument allows the breakpoint to become invisible
5227 to the user. The breakpoint will neither be reported when created, nor will it
5228 be listed in the output from @code{info breakpoints} (but will be listed with
5229 the @code{maint info breakpoints} command).
5231 The optional @var{temporary} argument makes the breakpoint a temporary
5232 breakpoint. Temporary breakpoints are deleted after they have been hit. Any
5233 further access to the Python breakpoint after it has been hit will result in a
5234 runtime error (as that breakpoint has now been automatically deleted).
5236 The optional @var{qualified} argument is a boolean that allows interpreting
5237 the function passed in @code{spec} as a fully-qualified name. It is equivalent
5238 to @code{break}'s @code{-qualified} flag (@pxref{Linespec Locations} and
5239 @ref{Explicit Locations}).
5243 @defun Breakpoint.__init__ (@r{[} source @r{][}, function @r{][}, label @r{][}, line @r{]}, @r{][} internal @r{][}, temporary @r{][}, qualified @r{]})
5244 This second form of creating a new breakpoint specifies the explicit
5245 location (@pxref{Explicit Locations}) using keywords. The new breakpoint will
5246 be created in the specified source file @var{source}, at the specified
5247 @var{function}, @var{label} and @var{line}.
5249 @var{internal}, @var{temporary} and @var{qualified} have the same usage as
5250 explained previously.
5253 The available types are represented by constants defined in the @code{gdb}
5257 @vindex BP_BREAKPOINT
5258 @item gdb.BP_BREAKPOINT
5259 Normal code breakpoint.
5261 @vindex BP_WATCHPOINT
5262 @item gdb.BP_WATCHPOINT
5263 Watchpoint breakpoint.
5265 @vindex BP_HARDWARE_WATCHPOINT
5266 @item gdb.BP_HARDWARE_WATCHPOINT
5267 Hardware assisted watchpoint.
5269 @vindex BP_READ_WATCHPOINT
5270 @item gdb.BP_READ_WATCHPOINT
5271 Hardware assisted read watchpoint.
5273 @vindex BP_ACCESS_WATCHPOINT
5274 @item gdb.BP_ACCESS_WATCHPOINT
5275 Hardware assisted access watchpoint.
5278 The available watchpoint types represented by constants are defined in the
5284 Read only watchpoint.
5288 Write only watchpoint.
5292 Read/Write watchpoint.
5295 @defun Breakpoint.stop (self)
5296 The @code{gdb.Breakpoint} class can be sub-classed and, in
5297 particular, you may choose to implement the @code{stop} method.
5298 If this method is defined in a sub-class of @code{gdb.Breakpoint},
5299 it will be called when the inferior reaches any location of a
5300 breakpoint which instantiates that sub-class. If the method returns
5301 @code{True}, the inferior will be stopped at the location of the
5302 breakpoint, otherwise the inferior will continue.
5304 If there are multiple breakpoints at the same location with a
5305 @code{stop} method, each one will be called regardless of the
5306 return status of the previous. This ensures that all @code{stop}
5307 methods have a chance to execute at that location. In this scenario
5308 if one of the methods returns @code{True} but the others return
5309 @code{False}, the inferior will still be stopped.
5311 You should not alter the execution state of the inferior (i.e.@:, step,
5312 next, etc.), alter the current frame context (i.e.@:, change the current
5313 active frame), or alter, add or delete any breakpoint. As a general
5314 rule, you should not alter any data within @value{GDBN} or the inferior
5317 Example @code{stop} implementation:
5320 class MyBreakpoint (gdb.Breakpoint):
5322 inf_val = gdb.parse_and_eval("foo")
5329 @defun Breakpoint.is_valid ()
5330 Return @code{True} if this @code{Breakpoint} object is valid,
5331 @code{False} otherwise. A @code{Breakpoint} object can become invalid
5332 if the user deletes the breakpoint. In this case, the object still
5333 exists, but the underlying breakpoint does not. In the cases of
5334 watchpoint scope, the watchpoint remains valid even if execution of the
5335 inferior leaves the scope of that watchpoint.
5338 @defun Breakpoint.delete ()
5339 Permanently deletes the @value{GDBN} breakpoint. This also
5340 invalidates the Python @code{Breakpoint} object. Any further access
5341 to this object's attributes or methods will raise an error.
5344 @defvar Breakpoint.enabled
5345 This attribute is @code{True} if the breakpoint is enabled, and
5346 @code{False} otherwise. This attribute is writable. You can use it to enable
5347 or disable the breakpoint.
5350 @defvar Breakpoint.silent
5351 This attribute is @code{True} if the breakpoint is silent, and
5352 @code{False} otherwise. This attribute is writable.
5354 Note that a breakpoint can also be silent if it has commands and the
5355 first command is @code{silent}. This is not reported by the
5356 @code{silent} attribute.
5359 @defvar Breakpoint.pending
5360 This attribute is @code{True} if the breakpoint is pending, and
5361 @code{False} otherwise. @xref{Set Breaks}. This attribute is
5365 @anchor{python_breakpoint_thread}
5366 @defvar Breakpoint.thread
5367 If the breakpoint is thread-specific, this attribute holds the
5368 thread's global id. If the breakpoint is not thread-specific, this
5369 attribute is @code{None}. This attribute is writable.
5372 @defvar Breakpoint.task
5373 If the breakpoint is Ada task-specific, this attribute holds the Ada task
5374 id. If the breakpoint is not task-specific (or the underlying
5375 language is not Ada), this attribute is @code{None}. This attribute
5379 @defvar Breakpoint.ignore_count
5380 This attribute holds the ignore count for the breakpoint, an integer.
5381 This attribute is writable.
5384 @defvar Breakpoint.number
5385 This attribute holds the breakpoint's number --- the identifier used by
5386 the user to manipulate the breakpoint. This attribute is not writable.
5389 @defvar Breakpoint.type
5390 This attribute holds the breakpoint's type --- the identifier used to
5391 determine the actual breakpoint type or use-case. This attribute is not
5395 @defvar Breakpoint.visible
5396 This attribute tells whether the breakpoint is visible to the user
5397 when set, or when the @samp{info breakpoints} command is run. This
5398 attribute is not writable.
5401 @defvar Breakpoint.temporary
5402 This attribute indicates whether the breakpoint was created as a
5403 temporary breakpoint. Temporary breakpoints are automatically deleted
5404 after that breakpoint has been hit. Access to this attribute, and all
5405 other attributes and functions other than the @code{is_valid}
5406 function, will result in an error after the breakpoint has been hit
5407 (as it has been automatically deleted). This attribute is not
5411 @defvar Breakpoint.hit_count
5412 This attribute holds the hit count for the breakpoint, an integer.
5413 This attribute is writable, but currently it can only be set to zero.
5416 @defvar Breakpoint.location
5417 This attribute holds the location of the breakpoint, as specified by
5418 the user. It is a string. If the breakpoint does not have a location
5419 (that is, it is a watchpoint) the attribute's value is @code{None}. This
5420 attribute is not writable.
5423 @defvar Breakpoint.expression
5424 This attribute holds a breakpoint expression, as specified by
5425 the user. It is a string. If the breakpoint does not have an
5426 expression (the breakpoint is not a watchpoint) the attribute's value
5427 is @code{None}. This attribute is not writable.
5430 @defvar Breakpoint.condition
5431 This attribute holds the condition of the breakpoint, as specified by
5432 the user. It is a string. If there is no condition, this attribute's
5433 value is @code{None}. This attribute is writable.
5436 @defvar Breakpoint.commands
5437 This attribute holds the commands attached to the breakpoint. If
5438 there are commands, this attribute's value is a string holding all the
5439 commands, separated by newlines. If there are no commands, this
5440 attribute is @code{None}. This attribute is writable.
5443 @node Finish Breakpoints in Python
5444 @subsubsection Finish Breakpoints
5446 @cindex python finish breakpoints
5447 @tindex gdb.FinishBreakpoint
5449 A finish breakpoint is a temporary breakpoint set at the return address of
5450 a frame, based on the @code{finish} command. @code{gdb.FinishBreakpoint}
5451 extends @code{gdb.Breakpoint}. The underlying breakpoint will be disabled
5452 and deleted when the execution will run out of the breakpoint scope (i.e.@:
5453 @code{Breakpoint.stop} or @code{FinishBreakpoint.out_of_scope} triggered).
5454 Finish breakpoints are thread specific and must be create with the right
5457 @defun FinishBreakpoint.__init__ (@r{[}frame@r{]} @r{[}, internal@r{]})
5458 Create a finish breakpoint at the return address of the @code{gdb.Frame}
5459 object @var{frame}. If @var{frame} is not provided, this defaults to the
5460 newest frame. The optional @var{internal} argument allows the breakpoint to
5461 become invisible to the user. @xref{Breakpoints In Python}, for further
5462 details about this argument.
5465 @defun FinishBreakpoint.out_of_scope (self)
5466 In some circumstances (e.g.@: @code{longjmp}, C@t{++} exceptions, @value{GDBN}
5467 @code{return} command, @dots{}), a function may not properly terminate, and
5468 thus never hit the finish breakpoint. When @value{GDBN} notices such a
5469 situation, the @code{out_of_scope} callback will be triggered.
5471 You may want to sub-class @code{gdb.FinishBreakpoint} and override this
5475 class MyFinishBreakpoint (gdb.FinishBreakpoint)
5477 print "normal finish"
5480 def out_of_scope ():
5481 print "abnormal finish"
5485 @defvar FinishBreakpoint.return_value
5486 When @value{GDBN} is stopped at a finish breakpoint and the frame
5487 used to build the @code{gdb.FinishBreakpoint} object had debug symbols, this
5488 attribute will contain a @code{gdb.Value} object corresponding to the return
5489 value of the function. The value will be @code{None} if the function return
5490 type is @code{void} or if the return value was not computable. This attribute
5494 @node Lazy Strings In Python
5495 @subsubsection Python representation of lazy strings
5497 @cindex lazy strings in python
5498 @tindex gdb.LazyString
5500 A @dfn{lazy string} is a string whose contents is not retrieved or
5501 encoded until it is needed.
5503 A @code{gdb.LazyString} is represented in @value{GDBN} as an
5504 @code{address} that points to a region of memory, an @code{encoding}
5505 that will be used to encode that region of memory, and a @code{length}
5506 to delimit the region of memory that represents the string. The
5507 difference between a @code{gdb.LazyString} and a string wrapped within
5508 a @code{gdb.Value} is that a @code{gdb.LazyString} will be treated
5509 differently by @value{GDBN} when printing. A @code{gdb.LazyString} is
5510 retrieved and encoded during printing, while a @code{gdb.Value}
5511 wrapping a string is immediately retrieved and encoded on creation.
5513 A @code{gdb.LazyString} object has the following functions:
5515 @defun LazyString.value ()
5516 Convert the @code{gdb.LazyString} to a @code{gdb.Value}. This value
5517 will point to the string in memory, but will lose all the delayed
5518 retrieval, encoding and handling that @value{GDBN} applies to a
5519 @code{gdb.LazyString}.
5522 @defvar LazyString.address
5523 This attribute holds the address of the string. This attribute is not
5527 @defvar LazyString.length
5528 This attribute holds the length of the string in characters. If the
5529 length is -1, then the string will be fetched and encoded up to the
5530 first null of appropriate width. This attribute is not writable.
5533 @defvar LazyString.encoding
5534 This attribute holds the encoding that will be applied to the string
5535 when the string is printed by @value{GDBN}. If the encoding is not
5536 set, or contains an empty string, then @value{GDBN} will select the
5537 most appropriate encoding when the string is printed. This attribute
5541 @defvar LazyString.type
5542 This attribute holds the type that is represented by the lazy string's
5543 type. For a lazy string this is a pointer or array type. To
5544 resolve this to the lazy string's character type, use the type's
5545 @code{target} method. @xref{Types In Python}. This attribute is not
5549 @node Architectures In Python
5550 @subsubsection Python representation of architectures
5551 @cindex Python architectures
5553 @value{GDBN} uses architecture specific parameters and artifacts in a
5554 number of its various computations. An architecture is represented
5555 by an instance of the @code{gdb.Architecture} class.
5557 A @code{gdb.Architecture} class has the following methods:
5559 @defun Architecture.name ()
5560 Return the name (string value) of the architecture.
5563 @defun Architecture.disassemble (@var{start_pc} @r{[}, @var{end_pc} @r{[}, @var{count}@r{]]})
5564 Return a list of disassembled instructions starting from the memory
5565 address @var{start_pc}. The optional arguments @var{end_pc} and
5566 @var{count} determine the number of instructions in the returned list.
5567 If both the optional arguments @var{end_pc} and @var{count} are
5568 specified, then a list of at most @var{count} disassembled instructions
5569 whose start address falls in the closed memory address interval from
5570 @var{start_pc} to @var{end_pc} are returned. If @var{end_pc} is not
5571 specified, but @var{count} is specified, then @var{count} number of
5572 instructions starting from the address @var{start_pc} are returned. If
5573 @var{count} is not specified but @var{end_pc} is specified, then all
5574 instructions whose start address falls in the closed memory address
5575 interval from @var{start_pc} to @var{end_pc} are returned. If neither
5576 @var{end_pc} nor @var{count} are specified, then a single instruction at
5577 @var{start_pc} is returned. For all of these cases, each element of the
5578 returned list is a Python @code{dict} with the following string keys:
5583 The value corresponding to this key is a Python long integer capturing
5584 the memory address of the instruction.
5587 The value corresponding to this key is a string value which represents
5588 the instruction with assembly language mnemonics. The assembly
5589 language flavor used is the same as that specified by the current CLI
5590 variable @code{disassembly-flavor}. @xref{Machine Code}.
5593 The value corresponding to this key is the length (integer value) of the
5594 instruction in bytes.
5599 @node Python Auto-loading
5600 @subsection Python Auto-loading
5601 @cindex Python auto-loading
5603 When a new object file is read (for example, due to the @code{file}
5604 command, or because the inferior has loaded a shared library),
5605 @value{GDBN} will look for Python support scripts in several ways:
5606 @file{@var{objfile}-gdb.py} and @code{.debug_gdb_scripts} section.
5607 @xref{Auto-loading extensions}.
5609 The auto-loading feature is useful for supplying application-specific
5610 debugging commands and scripts.
5612 Auto-loading can be enabled or disabled,
5613 and the list of auto-loaded scripts can be printed.
5616 @anchor{set auto-load python-scripts}
5617 @kindex set auto-load python-scripts
5618 @item set auto-load python-scripts [on|off]
5619 Enable or disable the auto-loading of Python scripts.
5621 @anchor{show auto-load python-scripts}
5622 @kindex show auto-load python-scripts
5623 @item show auto-load python-scripts
5624 Show whether auto-loading of Python scripts is enabled or disabled.
5626 @anchor{info auto-load python-scripts}
5627 @kindex info auto-load python-scripts
5628 @cindex print list of auto-loaded Python scripts
5629 @item info auto-load python-scripts [@var{regexp}]
5630 Print the list of all Python scripts that @value{GDBN} auto-loaded.
5632 Also printed is the list of Python scripts that were mentioned in
5633 the @code{.debug_gdb_scripts} section and were either not found
5634 (@pxref{dotdebug_gdb_scripts section}) or were not auto-loaded due to
5635 @code{auto-load safe-path} rejection (@pxref{Auto-loading}).
5636 This is useful because their names are not printed when @value{GDBN}
5637 tries to load them and fails. There may be many of them, and printing
5638 an error message for each one is problematic.
5640 If @var{regexp} is supplied only Python scripts with matching names are printed.
5645 (gdb) info auto-load python-scripts
5647 Yes py-section-script.py
5648 full name: /tmp/py-section-script.py
5649 No my-foo-pretty-printers.py
5653 When reading an auto-loaded file or script, @value{GDBN} sets the
5654 @dfn{current objfile}. This is available via the @code{gdb.current_objfile}
5655 function (@pxref{Objfiles In Python}). This can be useful for
5656 registering objfile-specific pretty-printers and frame-filters.
5658 @node Python modules
5659 @subsection Python modules
5660 @cindex python modules
5662 @value{GDBN} comes with several modules to assist writing Python code.
5665 * gdb.printing:: Building and registering pretty-printers.
5666 * gdb.types:: Utilities for working with types.
5667 * gdb.prompt:: Utilities for prompt value substitution.
5671 @subsubsection gdb.printing
5672 @cindex gdb.printing
5674 This module provides a collection of utilities for working with
5678 @item PrettyPrinter (@var{name}, @var{subprinters}=None)
5679 This class specifies the API that makes @samp{info pretty-printer},
5680 @samp{enable pretty-printer} and @samp{disable pretty-printer} work.
5681 Pretty-printers should generally inherit from this class.
5683 @item SubPrettyPrinter (@var{name})
5684 For printers that handle multiple types, this class specifies the
5685 corresponding API for the subprinters.
5687 @item RegexpCollectionPrettyPrinter (@var{name})
5688 Utility class for handling multiple printers, all recognized via
5689 regular expressions.
5690 @xref{Writing a Pretty-Printer}, for an example.
5692 @item FlagEnumerationPrinter (@var{name})
5693 A pretty-printer which handles printing of @code{enum} values. Unlike
5694 @value{GDBN}'s built-in @code{enum} printing, this printer attempts to
5695 work properly when there is some overlap between the enumeration
5696 constants. The argument @var{name} is the name of the printer and
5697 also the name of the @code{enum} type to look up.
5699 @item register_pretty_printer (@var{obj}, @var{printer}, @var{replace}=False)
5700 Register @var{printer} with the pretty-printer list of @var{obj}.
5701 If @var{replace} is @code{True} then any existing copy of the printer
5702 is replaced. Otherwise a @code{RuntimeError} exception is raised
5703 if a printer with the same name already exists.
5707 @subsubsection gdb.types
5710 This module provides a collection of utilities for working with
5711 @code{gdb.Type} objects.
5714 @item get_basic_type (@var{type})
5715 Return @var{type} with const and volatile qualifiers stripped,
5716 and with typedefs and C@t{++} references converted to the underlying type.
5721 typedef const int const_int;
5723 const_int& foo_ref (foo);
5724 int main () @{ return 0; @}
5731 (gdb) python import gdb.types
5732 (gdb) python foo_ref = gdb.parse_and_eval("foo_ref")
5733 (gdb) python print gdb.types.get_basic_type(foo_ref.type)
5737 @item has_field (@var{type}, @var{field})
5738 Return @code{True} if @var{type}, assumed to be a type with fields
5739 (e.g., a structure or union), has field @var{field}.
5741 @item make_enum_dict (@var{enum_type})
5742 Return a Python @code{dictionary} type produced from @var{enum_type}.
5744 @item deep_items (@var{type})
5745 Returns a Python iterator similar to the standard
5746 @code{gdb.Type.iteritems} method, except that the iterator returned
5747 by @code{deep_items} will recursively traverse anonymous struct or
5748 union fields. For example:
5762 Then in @value{GDBN}:
5764 (@value{GDBP}) python import gdb.types
5765 (@value{GDBP}) python struct_a = gdb.lookup_type("struct A")
5766 (@value{GDBP}) python print struct_a.keys ()
5768 (@value{GDBP}) python print [k for k,v in gdb.types.deep_items(struct_a)]
5769 @{['a', 'b0', 'b1']@}
5772 @item get_type_recognizers ()
5773 Return a list of the enabled type recognizers for the current context.
5774 This is called by @value{GDBN} during the type-printing process
5775 (@pxref{Type Printing API}).
5777 @item apply_type_recognizers (recognizers, type_obj)
5778 Apply the type recognizers, @var{recognizers}, to the type object
5779 @var{type_obj}. If any recognizer returns a string, return that
5780 string. Otherwise, return @code{None}. This is called by
5781 @value{GDBN} during the type-printing process (@pxref{Type Printing
5784 @item register_type_printer (locus, printer)
5785 This is a convenience function to register a type printer
5786 @var{printer}. The printer must implement the type printer protocol.
5787 The @var{locus} argument is either a @code{gdb.Objfile}, in which case
5788 the printer is registered with that objfile; a @code{gdb.Progspace},
5789 in which case the printer is registered with that progspace; or
5790 @code{None}, in which case the printer is registered globally.
5793 This is a base class that implements the type printer protocol. Type
5794 printers are encouraged, but not required, to derive from this class.
5795 It defines a constructor:
5797 @defmethod TypePrinter __init__ (self, name)
5798 Initialize the type printer with the given name. The new printer
5799 starts in the enabled state.
5805 @subsubsection gdb.prompt
5808 This module provides a method for prompt value-substitution.
5811 @item substitute_prompt (@var{string})
5812 Return @var{string} with escape sequences substituted by values. Some
5813 escape sequences take arguments. You can specify arguments inside
5814 ``@{@}'' immediately following the escape sequence.
5816 The escape sequences you can pass to this function are:
5820 Substitute a backslash.
5822 Substitute an ESC character.
5824 Substitute the selected frame; an argument names a frame parameter.
5826 Substitute a newline.
5828 Substitute a parameter's value; the argument names the parameter.
5830 Substitute a carriage return.
5832 Substitute the selected thread; an argument names a thread parameter.
5834 Substitute the version of GDB.
5836 Substitute the current working directory.
5838 Begin a sequence of non-printing characters. These sequences are
5839 typically used with the ESC character, and are not counted in the string
5840 length. Example: ``\[\e[0;34m\](gdb)\[\e[0m\]'' will return a
5841 blue-colored ``(gdb)'' prompt where the length is five.
5843 End a sequence of non-printing characters.
5849 substitute_prompt (``frame: \f,
5850 print arguments: \p@{print frame-arguments@}'')
5853 @exdent will return the string:
5856 "frame: main, print arguments: scalars"