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2 @c Permission is granted to copy, distribute and/or modify this document
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7 @c and with the Back-Cover Texts as in (a) below.
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14 @section Extending @value{GDBN} using Python
15 @cindex python scripting
16 @cindex scripting with python
18 You can extend @value{GDBN} using the @uref{http://www.python.org/,
19 Python programming language}. This feature is available only if
20 @value{GDBN} was configured using @option{--with-python}.
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 @findex gdb.PYTHONDIR
211 @defvar gdb.PYTHONDIR
212 A string containing the python directory (@pxref{Python}).
216 @defun gdb.execute (command @r{[}, from_tty @r{[}, to_string@r{]]})
217 Evaluate @var{command}, a string, as a @value{GDBN} CLI command.
218 If a GDB exception happens while @var{command} runs, it is
219 translated as described in @ref{Exception Handling,,Exception Handling}.
221 The @var{from_tty} flag specifies whether @value{GDBN} ought to consider this
222 command as having originated from the user invoking it interactively.
223 It must be a boolean value. If omitted, it defaults to @code{False}.
225 By default, any output produced by @var{command} is sent to
226 @value{GDBN}'s standard output (and to the log output if logging is
227 turned on). If the @var{to_string} parameter is
228 @code{True}, then output will be collected by @code{gdb.execute} and
229 returned as a string. The default is @code{False}, in which case the
230 return value is @code{None}. If @var{to_string} is @code{True}, the
231 @value{GDBN} virtual terminal will be temporarily set to unlimited width
232 and height, and its pagination will be disabled; @pxref{Screen Size}.
235 @findex gdb.breakpoints
236 @defun gdb.breakpoints ()
237 Return a sequence holding all of @value{GDBN}'s breakpoints.
238 @xref{Breakpoints In Python}, for more information. In @value{GDBN}
239 version 7.11 and earlier, this function returned @code{None} if there
240 were no breakpoints. This peculiarity was subsequently fixed, and now
241 @code{gdb.breakpoints} returns an empty sequence in this case.
244 @defun gdb.rbreak (regex @r{[}, minsyms @r{[}, throttle, @r{[}, symtabs @r{]]]})
245 Return a Python list holding a collection of newly set
246 @code{gdb.Breakpoint} objects matching function names defined by the
247 @var{regex} pattern. If the @var{minsyms} keyword is @code{True}, all
248 system functions (those not explicitly defined in the inferior) will
249 also be included in the match. The @var{throttle} keyword takes an
250 integer that defines the maximum number of pattern matches for
251 functions matched by the @var{regex} pattern. If the number of
252 matches exceeds the integer value of @var{throttle}, a
253 @code{RuntimeError} will be raised and no breakpoints will be created.
254 If @var{throttle} is not defined then there is no imposed limit on the
255 maximum number of matches and breakpoints to be created. The
256 @var{symtabs} keyword takes a Python iterable that yields a collection
257 of @code{gdb.Symtab} objects and will restrict the search to those
258 functions only contained within the @code{gdb.Symtab} objects.
261 @findex gdb.parameter
262 @defun gdb.parameter (parameter)
263 Return the value of a @value{GDBN} @var{parameter} given by its name,
264 a string; the parameter name string may contain spaces if the parameter has a
265 multi-part name. For example, @samp{print object} is a valid
268 If the named parameter does not exist, this function throws a
269 @code{gdb.error} (@pxref{Exception Handling}). Otherwise, the
270 parameter's value is converted to a Python value of the appropriate
275 @defun gdb.history (number)
276 Return a value from @value{GDBN}'s value history (@pxref{Value
277 History}). The @var{number} argument indicates which history element to return.
278 If @var{number} is negative, then @value{GDBN} will take its absolute value
279 and count backward from the last element (i.e., the most recent element) to
280 find the value to return. If @var{number} is zero, then @value{GDBN} will
281 return the most recent element. If the element specified by @var{number}
282 doesn't exist in the value history, a @code{gdb.error} exception will be
285 If no exception is raised, the return value is always an instance of
286 @code{gdb.Value} (@pxref{Values From Inferior}).
289 @findex gdb.convenience_variable
290 @defun gdb.convenience_variable (name)
291 Return the value of the convenience variable (@pxref{Convenience
292 Vars}) named @var{name}. @var{name} must be a string. The name
293 should not include the @samp{$} that is used to mark a convenience
294 variable in an expression. If the convenience variable does not
295 exist, then @code{None} is returned.
298 @findex gdb.set_convenience_variable
299 @defun gdb.set_convenience_variable (name, value)
300 Set the value of the convenience variable (@pxref{Convenience Vars})
301 named @var{name}. @var{name} must be a string. The name should not
302 include the @samp{$} that is used to mark a convenience variable in an
303 expression. If @var{value} is @code{None}, then the convenience
304 variable is removed. Otherwise, if @var{value} is not a
305 @code{gdb.Value} (@pxref{Values From Inferior}), it is is converted
306 using the @code{gdb.Value} constructor.
309 @findex gdb.parse_and_eval
310 @defun gdb.parse_and_eval (expression)
311 Parse @var{expression}, which must be a string, as an expression in
312 the current language, evaluate it, and return the result as a
315 This function can be useful when implementing a new command
316 (@pxref{Commands In Python}), as it provides a way to parse the
317 command's argument as an expression. It is also useful simply to
321 @findex gdb.find_pc_line
322 @defun gdb.find_pc_line (pc)
323 Return the @code{gdb.Symtab_and_line} object corresponding to the
324 @var{pc} value. @xref{Symbol Tables In Python}. If an invalid
325 value of @var{pc} is passed as an argument, then the @code{symtab} and
326 @code{line} attributes of the returned @code{gdb.Symtab_and_line} object
327 will be @code{None} and 0 respectively.
330 @findex gdb.post_event
331 @defun gdb.post_event (event)
332 Put @var{event}, a callable object taking no arguments, into
333 @value{GDBN}'s internal event queue. This callable will be invoked at
334 some later point, during @value{GDBN}'s event processing. Events
335 posted using @code{post_event} will be run in the order in which they
336 were posted; however, there is no way to know when they will be
337 processed relative to other events inside @value{GDBN}.
339 @value{GDBN} is not thread-safe. If your Python program uses multiple
340 threads, you must be careful to only call @value{GDBN}-specific
341 functions in the @value{GDBN} thread. @code{post_event} ensures
345 (@value{GDBP}) python
349 > def __init__(self, message):
350 > self.message = message;
351 > def __call__(self):
352 > gdb.write(self.message)
354 >class MyThread1 (threading.Thread):
356 > gdb.post_event(Writer("Hello "))
358 >class MyThread2 (threading.Thread):
360 > gdb.post_event(Writer("World\n"))
365 (@value{GDBP}) Hello World
370 @defun gdb.write (string @r{[}, stream{]})
371 Print a string to @value{GDBN}'s paginated output stream. The
372 optional @var{stream} determines the stream to print to. The default
373 stream is @value{GDBN}'s standard output stream. Possible stream
380 @value{GDBN}'s standard output stream.
385 @value{GDBN}'s standard error stream.
390 @value{GDBN}'s log stream (@pxref{Logging Output}).
393 Writing to @code{sys.stdout} or @code{sys.stderr} will automatically
394 call this function and will automatically direct the output to the
400 Flush the buffer of a @value{GDBN} paginated stream so that the
401 contents are displayed immediately. @value{GDBN} will flush the
402 contents of a stream automatically when it encounters a newline in the
403 buffer. The optional @var{stream} determines the stream to flush. The
404 default stream is @value{GDBN}'s standard output stream. Possible
411 @value{GDBN}'s standard output stream.
416 @value{GDBN}'s standard error stream.
421 @value{GDBN}'s log stream (@pxref{Logging Output}).
425 Flushing @code{sys.stdout} or @code{sys.stderr} will automatically
426 call this function for the relevant stream.
429 @findex gdb.target_charset
430 @defun gdb.target_charset ()
431 Return the name of the current target character set (@pxref{Character
432 Sets}). This differs from @code{gdb.parameter('target-charset')} in
433 that @samp{auto} is never returned.
436 @findex gdb.target_wide_charset
437 @defun gdb.target_wide_charset ()
438 Return the name of the current target wide character set
439 (@pxref{Character Sets}). This differs from
440 @code{gdb.parameter('target-wide-charset')} in that @samp{auto} is
444 @findex gdb.solib_name
445 @defun gdb.solib_name (address)
446 Return the name of the shared library holding the given @var{address}
447 as a string, or @code{None}.
450 @findex gdb.decode_line
451 @defun gdb.decode_line @r{[}expression@r{]}
452 Return locations of the line specified by @var{expression}, or of the
453 current line if no argument was given. This function returns a Python
454 tuple containing two elements. The first element contains a string
455 holding any unparsed section of @var{expression} (or @code{None} if
456 the expression has been fully parsed). The second element contains
457 either @code{None} or another tuple that contains all the locations
458 that match the expression represented as @code{gdb.Symtab_and_line}
459 objects (@pxref{Symbol Tables In Python}). If @var{expression} is
460 provided, it is decoded the way that @value{GDBN}'s inbuilt
461 @code{break} or @code{edit} commands do (@pxref{Specify Location}).
464 @defun gdb.prompt_hook (current_prompt)
467 If @var{prompt_hook} is callable, @value{GDBN} will call the method
468 assigned to this operation before a prompt is displayed by
471 The parameter @code{current_prompt} contains the current @value{GDBN}
472 prompt. This method must return a Python string, or @code{None}. If
473 a string is returned, the @value{GDBN} prompt will be set to that
474 string. If @code{None} is returned, @value{GDBN} will continue to use
477 Some prompts cannot be substituted in @value{GDBN}. Secondary prompts
478 such as those used by readline for command input, and annotation
479 related prompts are prohibited from being changed.
482 @node Exception Handling
483 @subsubsection Exception Handling
484 @cindex python exceptions
485 @cindex exceptions, python
487 When executing the @code{python} command, Python exceptions
488 uncaught within the Python code are translated to calls to
489 @value{GDBN} error-reporting mechanism. If the command that called
490 @code{python} does not handle the error, @value{GDBN} will
491 terminate it and print an error message containing the Python
492 exception name, the associated value, and the Python call stack
493 backtrace at the point where the exception was raised. Example:
496 (@value{GDBP}) python print foo
497 Traceback (most recent call last):
498 File "<string>", line 1, in <module>
499 NameError: name 'foo' is not defined
502 @value{GDBN} errors that happen in @value{GDBN} commands invoked by
503 Python code are converted to Python exceptions. The type of the
504 Python exception depends on the error.
508 This is the base class for most exceptions generated by @value{GDBN}.
509 It is derived from @code{RuntimeError}, for compatibility with earlier
510 versions of @value{GDBN}.
512 If an error occurring in @value{GDBN} does not fit into some more
513 specific category, then the generated exception will have this type.
515 @item gdb.MemoryError
516 This is a subclass of @code{gdb.error} which is thrown when an
517 operation tried to access invalid memory in the inferior.
519 @item KeyboardInterrupt
520 User interrupt (via @kbd{C-c} or by typing @kbd{q} at a pagination
521 prompt) is translated to a Python @code{KeyboardInterrupt} exception.
524 In all cases, your exception handler will see the @value{GDBN} error
525 message as its value and the Python call stack backtrace at the Python
526 statement closest to where the @value{GDBN} error occured as the
530 When implementing @value{GDBN} commands in Python via
531 @code{gdb.Command}, or functions via @code{gdb.Function}, it is useful
532 to be able to throw an exception that doesn't cause a traceback to be
533 printed. For example, the user may have invoked the command
534 incorrectly. @value{GDBN} provides a special exception class that can
535 be used for this purpose.
539 When thrown from a command or function, this exception will cause the
540 command or function to fail, but the Python stack will not be
541 displayed. @value{GDBN} does not throw this exception itself, but
542 rather recognizes it when thrown from user Python code. Example:
546 >class HelloWorld (gdb.Command):
547 > """Greet the whole world."""
548 > def __init__ (self):
549 > super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)
550 > def invoke (self, args, from_tty):
551 > argv = gdb.string_to_argv (args)
552 > if len (argv) != 0:
553 > raise gdb.GdbError ("hello-world takes no arguments")
554 > print "Hello, World!"
558 hello-world takes no arguments
562 @node Values From Inferior
563 @subsubsection Values From Inferior
564 @cindex values from inferior, with Python
565 @cindex python, working with values from inferior
567 @cindex @code{gdb.Value}
568 @value{GDBN} provides values it obtains from the inferior program in
569 an object of type @code{gdb.Value}. @value{GDBN} uses this object
570 for its internal bookkeeping of the inferior's values, and for
571 fetching values when necessary.
573 Inferior values that are simple scalars can be used directly in
574 Python expressions that are valid for the value's data type. Here's
575 an example for an integer or floating-point value @code{some_val}:
582 As result of this, @code{bar} will also be a @code{gdb.Value} object
583 whose values are of the same type as those of @code{some_val}. Valid
584 Python operations can also be performed on @code{gdb.Value} objects
585 representing a @code{struct} or @code{class} object. For such cases,
586 the overloaded operator (if present), is used to perform the operation.
587 For example, if @code{val1} and @code{val2} are @code{gdb.Value} objects
588 representing instances of a @code{class} which overloads the @code{+}
589 operator, then one can use the @code{+} operator in their Python script
597 The result of the operation @code{val3} is also a @code{gdb.Value}
598 object corresponding to the value returned by the overloaded @code{+}
599 operator. In general, overloaded operators are invoked for the
600 following operations: @code{+} (binary addition), @code{-} (binary
601 subtraction), @code{*} (multiplication), @code{/}, @code{%}, @code{<<},
602 @code{>>}, @code{|}, @code{&}, @code{^}.
604 Inferior values that are structures or instances of some class can
605 be accessed using the Python @dfn{dictionary syntax}. For example, if
606 @code{some_val} is a @code{gdb.Value} instance holding a structure, you
607 can access its @code{foo} element with:
610 bar = some_val['foo']
613 @cindex getting structure elements using gdb.Field objects as subscripts
614 Again, @code{bar} will also be a @code{gdb.Value} object. Structure
615 elements can also be accessed by using @code{gdb.Field} objects as
616 subscripts (@pxref{Types In Python}, for more information on
617 @code{gdb.Field} objects). For example, if @code{foo_field} is a
618 @code{gdb.Field} object corresponding to element @code{foo} of the above
619 structure, then @code{bar} can also be accessed as follows:
622 bar = some_val[foo_field]
625 A @code{gdb.Value} that represents a function can be executed via
626 inferior function call. Any arguments provided to the call must match
627 the function's prototype, and must be provided in the order specified
630 For example, @code{some_val} is a @code{gdb.Value} instance
631 representing a function that takes two integers as arguments. To
632 execute this function, call it like so:
635 result = some_val (10,20)
638 Any values returned from a function call will be stored as a
641 The following attributes are provided:
643 @defvar Value.address
644 If this object is addressable, this read-only attribute holds a
645 @code{gdb.Value} object representing the address. Otherwise,
646 this attribute holds @code{None}.
649 @cindex optimized out value in Python
650 @defvar Value.is_optimized_out
651 This read-only boolean attribute is true if the compiler optimized out
652 this value, thus it is not available for fetching from the inferior.
656 The type of this @code{gdb.Value}. The value of this attribute is a
657 @code{gdb.Type} object (@pxref{Types In Python}).
660 @defvar Value.dynamic_type
661 The dynamic type of this @code{gdb.Value}. This uses C@t{++} run-time
662 type information (@acronym{RTTI}) to determine the dynamic type of the
663 value. If this value is of class type, it will return the class in
664 which the value is embedded, if any. If this value is of pointer or
665 reference to a class type, it will compute the dynamic type of the
666 referenced object, and return a pointer or reference to that type,
667 respectively. In all other cases, it will return the value's static
670 Note that this feature will only work when debugging a C@t{++} program
671 that includes @acronym{RTTI} for the object in question. Otherwise,
672 it will just return the static type of the value as in @kbd{ptype foo}
673 (@pxref{Symbols, ptype}).
676 @defvar Value.is_lazy
677 The value of this read-only boolean attribute is @code{True} if this
678 @code{gdb.Value} has not yet been fetched from the inferior.
679 @value{GDBN} does not fetch values until necessary, for efficiency.
683 myval = gdb.parse_and_eval ('somevar')
686 The value of @code{somevar} is not fetched at this time. It will be
687 fetched when the value is needed, or when the @code{fetch_lazy}
691 The following methods are provided:
693 @defun Value.__init__ (@var{val})
694 Many Python values can be converted directly to a @code{gdb.Value} via
695 this object initializer. Specifically:
699 A Python boolean is converted to the boolean type from the current
703 A Python integer is converted to the C @code{long} type for the
704 current architecture.
707 A Python long is converted to the C @code{long long} type for the
708 current architecture.
711 A Python float is converted to the C @code{double} type for the
712 current architecture.
715 A Python string is converted to a target string in the current target
716 language using the current target encoding.
717 If a character cannot be represented in the current target encoding,
718 then an exception is thrown.
720 @item @code{gdb.Value}
721 If @code{val} is a @code{gdb.Value}, then a copy of the value is made.
723 @item @code{gdb.LazyString}
724 If @code{val} is a @code{gdb.LazyString} (@pxref{Lazy Strings In
725 Python}), then the lazy string's @code{value} method is called, and
730 @defun Value.cast (type)
731 Return a new instance of @code{gdb.Value} that is the result of
732 casting this instance to the type described by @var{type}, which must
733 be a @code{gdb.Type} object. If the cast cannot be performed for some
734 reason, this method throws an exception.
737 @defun Value.dereference ()
738 For pointer data types, this method returns a new @code{gdb.Value} object
739 whose contents is the object pointed to by the pointer. For example, if
740 @code{foo} is a C pointer to an @code{int}, declared in your C program as
747 then you can use the corresponding @code{gdb.Value} to access what
748 @code{foo} points to like this:
751 bar = foo.dereference ()
754 The result @code{bar} will be a @code{gdb.Value} object holding the
755 value pointed to by @code{foo}.
757 A similar function @code{Value.referenced_value} exists which also
758 returns @code{gdb.Value} objects corresonding to the values pointed to
759 by pointer values (and additionally, values referenced by reference
760 values). However, the behavior of @code{Value.dereference}
761 differs from @code{Value.referenced_value} by the fact that the
762 behavior of @code{Value.dereference} is identical to applying the C
763 unary operator @code{*} on a given value. For example, consider a
764 reference to a pointer @code{ptrref}, declared in your C@t{++} program
772 intptr &ptrref = ptr;
775 Though @code{ptrref} is a reference value, one can apply the method
776 @code{Value.dereference} to the @code{gdb.Value} object corresponding
777 to it and obtain a @code{gdb.Value} which is identical to that
778 corresponding to @code{val}. However, if you apply the method
779 @code{Value.referenced_value}, the result would be a @code{gdb.Value}
780 object identical to that corresponding to @code{ptr}.
783 py_ptrref = gdb.parse_and_eval ("ptrref")
784 py_val = py_ptrref.dereference ()
785 py_ptr = py_ptrref.referenced_value ()
788 The @code{gdb.Value} object @code{py_val} is identical to that
789 corresponding to @code{val}, and @code{py_ptr} is identical to that
790 corresponding to @code{ptr}. In general, @code{Value.dereference} can
791 be applied whenever the C unary operator @code{*} can be applied
792 to the corresponding C value. For those cases where applying both
793 @code{Value.dereference} and @code{Value.referenced_value} is allowed,
794 the results obtained need not be identical (as we have seen in the above
795 example). The results are however identical when applied on
796 @code{gdb.Value} objects corresponding to pointers (@code{gdb.Value}
797 objects with type code @code{TYPE_CODE_PTR}) in a C/C@t{++} program.
800 @defun Value.referenced_value ()
801 For pointer or reference data types, this method returns a new
802 @code{gdb.Value} object corresponding to the value referenced by the
803 pointer/reference value. For pointer data types,
804 @code{Value.dereference} and @code{Value.referenced_value} produce
805 identical results. The difference between these methods is that
806 @code{Value.dereference} cannot get the values referenced by reference
807 values. For example, consider a reference to an @code{int}, declared
808 in your C@t{++} program as
816 then applying @code{Value.dereference} to the @code{gdb.Value} object
817 corresponding to @code{ref} will result in an error, while applying
818 @code{Value.referenced_value} will result in a @code{gdb.Value} object
819 identical to that corresponding to @code{val}.
822 py_ref = gdb.parse_and_eval ("ref")
823 er_ref = py_ref.dereference () # Results in error
824 py_val = py_ref.referenced_value () # Returns the referenced value
827 The @code{gdb.Value} object @code{py_val} is identical to that
828 corresponding to @code{val}.
831 @defun Value.reference_value ()
832 Return a @code{gdb.Value} object which is a reference to the value
833 encapsulated by this instance.
836 @defun Value.const_value ()
837 Return a @code{gdb.Value} object which is a @code{const} version of the
838 value encapsulated by this instance.
841 @defun Value.dynamic_cast (type)
842 Like @code{Value.cast}, but works as if the C@t{++} @code{dynamic_cast}
843 operator were used. Consult a C@t{++} reference for details.
846 @defun Value.reinterpret_cast (type)
847 Like @code{Value.cast}, but works as if the C@t{++} @code{reinterpret_cast}
848 operator were used. Consult a C@t{++} reference for details.
851 @defun Value.string (@r{[}encoding@r{[}, errors@r{[}, length@r{]]]})
852 If this @code{gdb.Value} represents a string, then this method
853 converts the contents to a Python string. Otherwise, this method will
856 Values are interpreted as strings according to the rules of the
857 current language. If the optional length argument is given, the
858 string will be converted to that length, and will include any embedded
859 zeroes that the string may contain. Otherwise, for languages
860 where the string is zero-terminated, the entire string will be
863 For example, in C-like languages, a value is a string if it is a pointer
864 to or an array of characters or ints of type @code{wchar_t}, @code{char16_t},
867 If the optional @var{encoding} argument is given, it must be a string
868 naming the encoding of the string in the @code{gdb.Value}, such as
869 @code{"ascii"}, @code{"iso-8859-6"} or @code{"utf-8"}. It accepts
870 the same encodings as the corresponding argument to Python's
871 @code{string.decode} method, and the Python codec machinery will be used
872 to convert the string. If @var{encoding} is not given, or if
873 @var{encoding} is the empty string, then either the @code{target-charset}
874 (@pxref{Character Sets}) will be used, or a language-specific encoding
875 will be used, if the current language is able to supply one.
877 The optional @var{errors} argument is the same as the corresponding
878 argument to Python's @code{string.decode} method.
880 If the optional @var{length} argument is given, the string will be
881 fetched and converted to the given length.
884 @defun Value.lazy_string (@r{[}encoding @r{[}, length@r{]]})
885 If this @code{gdb.Value} represents a string, then this method
886 converts the contents to a @code{gdb.LazyString} (@pxref{Lazy Strings
887 In Python}). Otherwise, this method will throw an exception.
889 If the optional @var{encoding} argument is given, it must be a string
890 naming the encoding of the @code{gdb.LazyString}. Some examples are:
891 @samp{ascii}, @samp{iso-8859-6} or @samp{utf-8}. If the
892 @var{encoding} argument is an encoding that @value{GDBN} does
893 recognize, @value{GDBN} will raise an error.
895 When a lazy string is printed, the @value{GDBN} encoding machinery is
896 used to convert the string during printing. If the optional
897 @var{encoding} argument is not provided, or is an empty string,
898 @value{GDBN} will automatically select the encoding most suitable for
899 the string type. For further information on encoding in @value{GDBN}
900 please see @ref{Character Sets}.
902 If the optional @var{length} argument is given, the string will be
903 fetched and encoded to the length of characters specified. If
904 the @var{length} argument is not provided, the string will be fetched
905 and encoded until a null of appropriate width is found.
908 @defun Value.fetch_lazy ()
909 If the @code{gdb.Value} object is currently a lazy value
910 (@code{gdb.Value.is_lazy} is @code{True}), then the value is
911 fetched from the inferior. Any errors that occur in the process
912 will produce a Python exception.
914 If the @code{gdb.Value} object is not a lazy value, this method
917 This method does not return a value.
921 @node Types In Python
922 @subsubsection Types In Python
923 @cindex types in Python
924 @cindex Python, working with types
927 @value{GDBN} represents types from the inferior using the class
930 The following type-related functions are available in the @code{gdb}
933 @findex gdb.lookup_type
934 @defun gdb.lookup_type (name @r{[}, block@r{]})
935 This function looks up a type by its @var{name}, which must be a string.
937 If @var{block} is given, then @var{name} is looked up in that scope.
938 Otherwise, it is searched for globally.
940 Ordinarily, this function will return an instance of @code{gdb.Type}.
941 If the named type cannot be found, it will throw an exception.
944 If the type is a structure or class type, or an enum type, the fields
945 of that type can be accessed using the Python @dfn{dictionary syntax}.
946 For example, if @code{some_type} is a @code{gdb.Type} instance holding
947 a structure type, you can access its @code{foo} field with:
950 bar = some_type['foo']
953 @code{bar} will be a @code{gdb.Field} object; see below under the
954 description of the @code{Type.fields} method for a description of the
955 @code{gdb.Field} class.
957 An instance of @code{Type} has the following attributes:
960 The alignment of this type, in bytes. Type alignment comes from the
961 debugging information; if it was not specified, then @value{GDBN} will
962 use the relevant ABI to try to determine the alignment. In some
963 cases, even this is not possible, and zero will be returned.
967 The type code for this type. The type code will be one of the
968 @code{TYPE_CODE_} constants defined below.
972 The name of this type. If this type has no name, then @code{None}
977 The size of this type, in target @code{char} units. Usually, a
978 target's @code{char} type will be an 8-bit byte. However, on some
979 unusual platforms, this type may have a different size.
983 The tag name for this type. The tag name is the name after
984 @code{struct}, @code{union}, or @code{enum} in C and C@t{++}; not all
985 languages have this concept. If this type has no tag name, then
986 @code{None} is returned.
989 The following methods are provided:
991 @defun Type.fields ()
992 For structure and union types, this method returns the fields. Range
993 types have two fields, the minimum and maximum values. Enum types
994 have one field per enum constant. Function and method types have one
995 field per parameter. The base types of C@t{++} classes are also
996 represented as fields. If the type has no fields, or does not fit
997 into one of these categories, an empty sequence will be returned.
999 Each field is a @code{gdb.Field} object, with some pre-defined attributes:
1002 This attribute is not available for @code{enum} or @code{static}
1003 (as in C@t{++}) fields. The value is the position, counting
1004 in bits, from the start of the containing type.
1007 This attribute is only available for @code{enum} fields, and its value
1008 is the enumeration member's integer representation.
1011 The name of the field, or @code{None} for anonymous fields.
1014 This is @code{True} if the field is artificial, usually meaning that
1015 it was provided by the compiler and not the user. This attribute is
1016 always provided, and is @code{False} if the field is not artificial.
1019 This is @code{True} if the field represents a base class of a C@t{++}
1020 structure. This attribute is always provided, and is @code{False}
1021 if the field is not a base class of the type that is the argument of
1022 @code{fields}, or if that type was not a C@t{++} class.
1025 If the field is packed, or is a bitfield, then this will have a
1026 non-zero value, which is the size of the field in bits. Otherwise,
1027 this will be zero; in this case the field's size is given by its type.
1030 The type of the field. This is usually an instance of @code{Type},
1031 but it can be @code{None} in some situations.
1034 The type which contains this field. This is an instance of
1039 @defun Type.array (@var{n1} @r{[}, @var{n2}@r{]})
1040 Return a new @code{gdb.Type} object which represents an array of this
1041 type. If one argument is given, it is the inclusive upper bound of
1042 the array; in this case the lower bound is zero. If two arguments are
1043 given, the first argument is the lower bound of the array, and the
1044 second argument is the upper bound of the array. An array's length
1045 must not be negative, but the bounds can be.
1048 @defun Type.vector (@var{n1} @r{[}, @var{n2}@r{]})
1049 Return a new @code{gdb.Type} object which represents a vector of this
1050 type. If one argument is given, it is the inclusive upper bound of
1051 the vector; in this case the lower bound is zero. If two arguments are
1052 given, the first argument is the lower bound of the vector, and the
1053 second argument is the upper bound of the vector. A vector's length
1054 must not be negative, but the bounds can be.
1056 The difference between an @code{array} and a @code{vector} is that
1057 arrays behave like in C: when used in expressions they decay to a pointer
1058 to the first element whereas vectors are treated as first class values.
1061 @defun Type.const ()
1062 Return a new @code{gdb.Type} object which represents a
1063 @code{const}-qualified variant of this type.
1066 @defun Type.volatile ()
1067 Return a new @code{gdb.Type} object which represents a
1068 @code{volatile}-qualified variant of this type.
1071 @defun Type.unqualified ()
1072 Return a new @code{gdb.Type} object which represents an unqualified
1073 variant of this type. That is, the result is neither @code{const} nor
1077 @defun Type.range ()
1078 Return a Python @code{Tuple} object that contains two elements: the
1079 low bound of the argument type and the high bound of that type. If
1080 the type does not have a range, @value{GDBN} will raise a
1081 @code{gdb.error} exception (@pxref{Exception Handling}).
1084 @defun Type.reference ()
1085 Return a new @code{gdb.Type} object which represents a reference to this
1089 @defun Type.pointer ()
1090 Return a new @code{gdb.Type} object which represents a pointer to this
1094 @defun Type.strip_typedefs ()
1095 Return a new @code{gdb.Type} that represents the real type,
1096 after removing all layers of typedefs.
1099 @defun Type.target ()
1100 Return a new @code{gdb.Type} object which represents the target type
1103 For a pointer type, the target type is the type of the pointed-to
1104 object. For an array type (meaning C-like arrays), the target type is
1105 the type of the elements of the array. For a function or method type,
1106 the target type is the type of the return value. For a complex type,
1107 the target type is the type of the elements. For a typedef, the
1108 target type is the aliased type.
1110 If the type does not have a target, this method will throw an
1114 @defun Type.template_argument (n @r{[}, block@r{]})
1115 If this @code{gdb.Type} is an instantiation of a template, this will
1116 return a new @code{gdb.Value} or @code{gdb.Type} which represents the
1117 value of the @var{n}th template argument (indexed starting at 0).
1119 If this @code{gdb.Type} is not a template type, or if the type has fewer
1120 than @var{n} template arguments, this will throw an exception.
1121 Ordinarily, only C@t{++} code will have template types.
1123 If @var{block} is given, then @var{name} is looked up in that scope.
1124 Otherwise, it is searched for globally.
1127 @defun Type.optimized_out ()
1128 Return @code{gdb.Value} instance of this type whose value is optimized
1129 out. This allows a frame decorator to indicate that the value of an
1130 argument or a local variable is not known.
1133 Each type has a code, which indicates what category this type falls
1134 into. The available type categories are represented by constants
1135 defined in the @code{gdb} module:
1138 @vindex TYPE_CODE_PTR
1139 @item gdb.TYPE_CODE_PTR
1140 The type is a pointer.
1142 @vindex TYPE_CODE_ARRAY
1143 @item gdb.TYPE_CODE_ARRAY
1144 The type is an array.
1146 @vindex TYPE_CODE_STRUCT
1147 @item gdb.TYPE_CODE_STRUCT
1148 The type is a structure.
1150 @vindex TYPE_CODE_UNION
1151 @item gdb.TYPE_CODE_UNION
1152 The type is a union.
1154 @vindex TYPE_CODE_ENUM
1155 @item gdb.TYPE_CODE_ENUM
1156 The type is an enum.
1158 @vindex TYPE_CODE_FLAGS
1159 @item gdb.TYPE_CODE_FLAGS
1160 A bit flags type, used for things such as status registers.
1162 @vindex TYPE_CODE_FUNC
1163 @item gdb.TYPE_CODE_FUNC
1164 The type is a function.
1166 @vindex TYPE_CODE_INT
1167 @item gdb.TYPE_CODE_INT
1168 The type is an integer type.
1170 @vindex TYPE_CODE_FLT
1171 @item gdb.TYPE_CODE_FLT
1172 A floating point type.
1174 @vindex TYPE_CODE_VOID
1175 @item gdb.TYPE_CODE_VOID
1176 The special type @code{void}.
1178 @vindex TYPE_CODE_SET
1179 @item gdb.TYPE_CODE_SET
1182 @vindex TYPE_CODE_RANGE
1183 @item gdb.TYPE_CODE_RANGE
1184 A range type, that is, an integer type with bounds.
1186 @vindex TYPE_CODE_STRING
1187 @item gdb.TYPE_CODE_STRING
1188 A string type. Note that this is only used for certain languages with
1189 language-defined string types; C strings are not represented this way.
1191 @vindex TYPE_CODE_BITSTRING
1192 @item gdb.TYPE_CODE_BITSTRING
1193 A string of bits. It is deprecated.
1195 @vindex TYPE_CODE_ERROR
1196 @item gdb.TYPE_CODE_ERROR
1197 An unknown or erroneous type.
1199 @vindex TYPE_CODE_METHOD
1200 @item gdb.TYPE_CODE_METHOD
1201 A method type, as found in C@t{++}.
1203 @vindex TYPE_CODE_METHODPTR
1204 @item gdb.TYPE_CODE_METHODPTR
1205 A pointer-to-member-function.
1207 @vindex TYPE_CODE_MEMBERPTR
1208 @item gdb.TYPE_CODE_MEMBERPTR
1209 A pointer-to-member.
1211 @vindex TYPE_CODE_REF
1212 @item gdb.TYPE_CODE_REF
1215 @vindex TYPE_CODE_RVALUE_REF
1216 @item gdb.TYPE_CODE_RVALUE_REF
1217 A C@t{++}11 rvalue reference type.
1219 @vindex TYPE_CODE_CHAR
1220 @item gdb.TYPE_CODE_CHAR
1223 @vindex TYPE_CODE_BOOL
1224 @item gdb.TYPE_CODE_BOOL
1227 @vindex TYPE_CODE_COMPLEX
1228 @item gdb.TYPE_CODE_COMPLEX
1229 A complex float type.
1231 @vindex TYPE_CODE_TYPEDEF
1232 @item gdb.TYPE_CODE_TYPEDEF
1233 A typedef to some other type.
1235 @vindex TYPE_CODE_NAMESPACE
1236 @item gdb.TYPE_CODE_NAMESPACE
1237 A C@t{++} namespace.
1239 @vindex TYPE_CODE_DECFLOAT
1240 @item gdb.TYPE_CODE_DECFLOAT
1241 A decimal floating point type.
1243 @vindex TYPE_CODE_INTERNAL_FUNCTION
1244 @item gdb.TYPE_CODE_INTERNAL_FUNCTION
1245 A function internal to @value{GDBN}. This is the type used to represent
1246 convenience functions.
1249 Further support for types is provided in the @code{gdb.types}
1250 Python module (@pxref{gdb.types}).
1252 @node Pretty Printing API
1253 @subsubsection Pretty Printing API
1254 @cindex python pretty printing api
1256 An example output is provided (@pxref{Pretty Printing}).
1258 A pretty-printer is just an object that holds a value and implements a
1259 specific interface, defined here.
1261 @defun pretty_printer.children (self)
1262 @value{GDBN} will call this method on a pretty-printer to compute the
1263 children of the pretty-printer's value.
1265 This method must return an object conforming to the Python iterator
1266 protocol. Each item returned by the iterator must be a tuple holding
1267 two elements. The first element is the ``name'' of the child; the
1268 second element is the child's value. The value can be any Python
1269 object which is convertible to a @value{GDBN} value.
1271 This method is optional. If it does not exist, @value{GDBN} will act
1272 as though the value has no children.
1275 @defun pretty_printer.display_hint (self)
1276 The CLI may call this method and use its result to change the
1277 formatting of a value. The result will also be supplied to an MI
1278 consumer as a @samp{displayhint} attribute of the variable being
1281 This method is optional. If it does exist, this method must return a
1284 Some display hints are predefined by @value{GDBN}:
1288 Indicate that the object being printed is ``array-like''. The CLI
1289 uses this to respect parameters such as @code{set print elements} and
1290 @code{set print array}.
1293 Indicate that the object being printed is ``map-like'', and that the
1294 children of this value can be assumed to alternate between keys and
1298 Indicate that the object being printed is ``string-like''. If the
1299 printer's @code{to_string} method returns a Python string of some
1300 kind, then @value{GDBN} will call its internal language-specific
1301 string-printing function to format the string. For the CLI this means
1302 adding quotation marks, possibly escaping some characters, respecting
1303 @code{set print elements}, and the like.
1307 @defun pretty_printer.to_string (self)
1308 @value{GDBN} will call this method to display the string
1309 representation of the value passed to the object's constructor.
1311 When printing from the CLI, if the @code{to_string} method exists,
1312 then @value{GDBN} will prepend its result to the values returned by
1313 @code{children}. Exactly how this formatting is done is dependent on
1314 the display hint, and may change as more hints are added. Also,
1315 depending on the print settings (@pxref{Print Settings}), the CLI may
1316 print just the result of @code{to_string} in a stack trace, omitting
1317 the result of @code{children}.
1319 If this method returns a string, it is printed verbatim.
1321 Otherwise, if this method returns an instance of @code{gdb.Value},
1322 then @value{GDBN} prints this value. This may result in a call to
1323 another pretty-printer.
1325 If instead the method returns a Python value which is convertible to a
1326 @code{gdb.Value}, then @value{GDBN} performs the conversion and prints
1327 the resulting value. Again, this may result in a call to another
1328 pretty-printer. Python scalars (integers, floats, and booleans) and
1329 strings are convertible to @code{gdb.Value}; other types are not.
1331 Finally, if this method returns @code{None} then no further operations
1332 are peformed in this method and nothing is printed.
1334 If the result is not one of these types, an exception is raised.
1337 @value{GDBN} provides a function which can be used to look up the
1338 default pretty-printer for a @code{gdb.Value}:
1340 @findex gdb.default_visualizer
1341 @defun gdb.default_visualizer (value)
1342 This function takes a @code{gdb.Value} object as an argument. If a
1343 pretty-printer for this value exists, then it is returned. If no such
1344 printer exists, then this returns @code{None}.
1347 @node Selecting Pretty-Printers
1348 @subsubsection Selecting Pretty-Printers
1349 @cindex selecting python pretty-printers
1351 The Python list @code{gdb.pretty_printers} contains an array of
1352 functions or callable objects that have been registered via addition
1353 as a pretty-printer. Printers in this list are called @code{global}
1354 printers, they're available when debugging all inferiors.
1355 Each @code{gdb.Progspace} contains a @code{pretty_printers} attribute.
1356 Each @code{gdb.Objfile} also contains a @code{pretty_printers}
1359 Each function on these lists is passed a single @code{gdb.Value}
1360 argument and should return a pretty-printer object conforming to the
1361 interface definition above (@pxref{Pretty Printing API}). If a function
1362 cannot create a pretty-printer for the value, it should return
1365 @value{GDBN} first checks the @code{pretty_printers} attribute of each
1366 @code{gdb.Objfile} in the current program space and iteratively calls
1367 each enabled lookup routine in the list for that @code{gdb.Objfile}
1368 until it receives a pretty-printer object.
1369 If no pretty-printer is found in the objfile lists, @value{GDBN} then
1370 searches the pretty-printer list of the current program space,
1371 calling each enabled function until an object is returned.
1372 After these lists have been exhausted, it tries the global
1373 @code{gdb.pretty_printers} list, again calling each enabled function until an
1376 The order in which the objfiles are searched is not specified. For a
1377 given list, functions are always invoked from the head of the list,
1378 and iterated over sequentially until the end of the list, or a printer
1381 For various reasons a pretty-printer may not work.
1382 For example, the underlying data structure may have changed and
1383 the pretty-printer is out of date.
1385 The consequences of a broken pretty-printer are severe enough that
1386 @value{GDBN} provides support for enabling and disabling individual
1387 printers. For example, if @code{print frame-arguments} is on,
1388 a backtrace can become highly illegible if any argument is printed
1389 with a broken printer.
1391 Pretty-printers are enabled and disabled by attaching an @code{enabled}
1392 attribute to the registered function or callable object. If this attribute
1393 is present and its value is @code{False}, the printer is disabled, otherwise
1394 the printer is enabled.
1396 @node Writing a Pretty-Printer
1397 @subsubsection Writing a Pretty-Printer
1398 @cindex writing a pretty-printer
1400 A pretty-printer consists of two parts: a lookup function to detect
1401 if the type is supported, and the printer itself.
1403 Here is an example showing how a @code{std::string} printer might be
1404 written. @xref{Pretty Printing API}, for details on the API this class
1408 class StdStringPrinter(object):
1409 "Print a std::string"
1411 def __init__(self, val):
1414 def to_string(self):
1415 return self.val['_M_dataplus']['_M_p']
1417 def display_hint(self):
1421 And here is an example showing how a lookup function for the printer
1422 example above might be written.
1425 def str_lookup_function(val):
1426 lookup_tag = val.type.tag
1427 if lookup_tag == None:
1429 regex = re.compile("^std::basic_string<char,.*>$")
1430 if regex.match(lookup_tag):
1431 return StdStringPrinter(val)
1435 The example lookup function extracts the value's type, and attempts to
1436 match it to a type that it can pretty-print. If it is a type the
1437 printer can pretty-print, it will return a printer object. If not, it
1438 returns @code{None}.
1440 We recommend that you put your core pretty-printers into a Python
1441 package. If your pretty-printers are for use with a library, we
1442 further recommend embedding a version number into the package name.
1443 This practice will enable @value{GDBN} to load multiple versions of
1444 your pretty-printers at the same time, because they will have
1447 You should write auto-loaded code (@pxref{Python Auto-loading}) such that it
1448 can be evaluated multiple times without changing its meaning. An
1449 ideal auto-load file will consist solely of @code{import}s of your
1450 printer modules, followed by a call to a register pretty-printers with
1451 the current objfile.
1453 Taken as a whole, this approach will scale nicely to multiple
1454 inferiors, each potentially using a different library version.
1455 Embedding a version number in the Python package name will ensure that
1456 @value{GDBN} is able to load both sets of printers simultaneously.
1457 Then, because the search for pretty-printers is done by objfile, and
1458 because your auto-loaded code took care to register your library's
1459 printers with a specific objfile, @value{GDBN} will find the correct
1460 printers for the specific version of the library used by each
1463 To continue the @code{std::string} example (@pxref{Pretty Printing API}),
1464 this code might appear in @code{gdb.libstdcxx.v6}:
1467 def register_printers(objfile):
1468 objfile.pretty_printers.append(str_lookup_function)
1472 And then the corresponding contents of the auto-load file would be:
1475 import gdb.libstdcxx.v6
1476 gdb.libstdcxx.v6.register_printers(gdb.current_objfile())
1479 The previous example illustrates a basic pretty-printer.
1480 There are a few things that can be improved on.
1481 The printer doesn't have a name, making it hard to identify in a
1482 list of installed printers. The lookup function has a name, but
1483 lookup functions can have arbitrary, even identical, names.
1485 Second, the printer only handles one type, whereas a library typically has
1486 several types. One could install a lookup function for each desired type
1487 in the library, but one could also have a single lookup function recognize
1488 several types. The latter is the conventional way this is handled.
1489 If a pretty-printer can handle multiple data types, then its
1490 @dfn{subprinters} are the printers for the individual data types.
1492 The @code{gdb.printing} module provides a formal way of solving these
1493 problems (@pxref{gdb.printing}).
1494 Here is another example that handles multiple types.
1496 These are the types we are going to pretty-print:
1499 struct foo @{ int a, b; @};
1500 struct bar @{ struct foo x, y; @};
1503 Here are the printers:
1507 """Print a foo object."""
1509 def __init__(self, val):
1512 def to_string(self):
1513 return ("a=<" + str(self.val["a"]) +
1514 "> b=<" + str(self.val["b"]) + ">")
1517 """Print a bar object."""
1519 def __init__(self, val):
1522 def to_string(self):
1523 return ("x=<" + str(self.val["x"]) +
1524 "> y=<" + str(self.val["y"]) + ">")
1527 This example doesn't need a lookup function, that is handled by the
1528 @code{gdb.printing} module. Instead a function is provided to build up
1529 the object that handles the lookup.
1534 def build_pretty_printer():
1535 pp = gdb.printing.RegexpCollectionPrettyPrinter(
1537 pp.add_printer('foo', '^foo$', fooPrinter)
1538 pp.add_printer('bar', '^bar$', barPrinter)
1542 And here is the autoload support:
1547 gdb.printing.register_pretty_printer(
1548 gdb.current_objfile(),
1549 my_library.build_pretty_printer())
1552 Finally, when this printer is loaded into @value{GDBN}, here is the
1553 corresponding output of @samp{info pretty-printer}:
1556 (gdb) info pretty-printer
1563 @node Type Printing API
1564 @subsubsection Type Printing API
1565 @cindex type printing API for Python
1567 @value{GDBN} provides a way for Python code to customize type display.
1568 This is mainly useful for substituting canonical typedef names for
1571 @cindex type printer
1572 A @dfn{type printer} is just a Python object conforming to a certain
1573 protocol. A simple base class implementing the protocol is provided;
1574 see @ref{gdb.types}. A type printer must supply at least:
1576 @defivar type_printer enabled
1577 A boolean which is True if the printer is enabled, and False
1578 otherwise. This is manipulated by the @code{enable type-printer}
1579 and @code{disable type-printer} commands.
1582 @defivar type_printer name
1583 The name of the type printer. This must be a string. This is used by
1584 the @code{enable type-printer} and @code{disable type-printer}
1588 @defmethod type_printer instantiate (self)
1589 This is called by @value{GDBN} at the start of type-printing. It is
1590 only called if the type printer is enabled. This method must return a
1591 new object that supplies a @code{recognize} method, as described below.
1595 When displaying a type, say via the @code{ptype} command, @value{GDBN}
1596 will compute a list of type recognizers. This is done by iterating
1597 first over the per-objfile type printers (@pxref{Objfiles In Python}),
1598 followed by the per-progspace type printers (@pxref{Progspaces In
1599 Python}), and finally the global type printers.
1601 @value{GDBN} will call the @code{instantiate} method of each enabled
1602 type printer. If this method returns @code{None}, then the result is
1603 ignored; otherwise, it is appended to the list of recognizers.
1605 Then, when @value{GDBN} is going to display a type name, it iterates
1606 over the list of recognizers. For each one, it calls the recognition
1607 function, stopping if the function returns a non-@code{None} value.
1608 The recognition function is defined as:
1610 @defmethod type_recognizer recognize (self, type)
1611 If @var{type} is not recognized, return @code{None}. Otherwise,
1612 return a string which is to be printed as the name of @var{type}.
1613 The @var{type} argument will be an instance of @code{gdb.Type}
1614 (@pxref{Types In Python}).
1617 @value{GDBN} uses this two-pass approach so that type printers can
1618 efficiently cache information without holding on to it too long. For
1619 example, it can be convenient to look up type information in a type
1620 printer and hold it for a recognizer's lifetime; if a single pass were
1621 done then type printers would have to make use of the event system in
1622 order to avoid holding information that could become stale as the
1625 @node Frame Filter API
1626 @subsubsection Filtering Frames
1627 @cindex frame filters api
1629 Frame filters are Python objects that manipulate the visibility of a
1630 frame or frames when a backtrace (@pxref{Backtrace}) is printed by
1633 Only commands that print a backtrace, or, in the case of @sc{gdb/mi}
1634 commands (@pxref{GDB/MI}), those that return a collection of frames
1635 are affected. The commands that work with frame filters are:
1637 @code{backtrace} (@pxref{backtrace-command,, The backtrace command}),
1638 @code{-stack-list-frames}
1639 (@pxref{-stack-list-frames,, The -stack-list-frames command}),
1640 @code{-stack-list-variables} (@pxref{-stack-list-variables,, The
1641 -stack-list-variables command}), @code{-stack-list-arguments}
1642 @pxref{-stack-list-arguments,, The -stack-list-arguments command}) and
1643 @code{-stack-list-locals} (@pxref{-stack-list-locals,, The
1644 -stack-list-locals command}).
1646 A frame filter works by taking an iterator as an argument, applying
1647 actions to the contents of that iterator, and returning another
1648 iterator (or, possibly, the same iterator it was provided in the case
1649 where the filter does not perform any operations). Typically, frame
1650 filters utilize tools such as the Python's @code{itertools} module to
1651 work with and create new iterators from the source iterator.
1652 Regardless of how a filter chooses to apply actions, it must not alter
1653 the underlying @value{GDBN} frame or frames, or attempt to alter the
1654 call-stack within @value{GDBN}. This preserves data integrity within
1655 @value{GDBN}. Frame filters are executed on a priority basis and care
1656 should be taken that some frame filters may have been executed before,
1657 and that some frame filters will be executed after.
1659 An important consideration when designing frame filters, and well
1660 worth reflecting upon, is that frame filters should avoid unwinding
1661 the call stack if possible. Some stacks can run very deep, into the
1662 tens of thousands in some cases. To search every frame when a frame
1663 filter executes may be too expensive at that step. The frame filter
1664 cannot know how many frames it has to iterate over, and it may have to
1665 iterate through them all. This ends up duplicating effort as
1666 @value{GDBN} performs this iteration when it prints the frames. If
1667 the filter can defer unwinding frames until frame decorators are
1668 executed, after the last filter has executed, it should. @xref{Frame
1669 Decorator API}, for more information on decorators. Also, there are
1670 examples for both frame decorators and filters in later chapters.
1671 @xref{Writing a Frame Filter}, for more information.
1673 The Python dictionary @code{gdb.frame_filters} contains key/object
1674 pairings that comprise a frame filter. Frame filters in this
1675 dictionary are called @code{global} frame filters, and they are
1676 available when debugging all inferiors. These frame filters must
1677 register with the dictionary directly. In addition to the
1678 @code{global} dictionary, there are other dictionaries that are loaded
1679 with different inferiors via auto-loading (@pxref{Python
1680 Auto-loading}). The two other areas where frame filter dictionaries
1681 can be found are: @code{gdb.Progspace} which contains a
1682 @code{frame_filters} dictionary attribute, and each @code{gdb.Objfile}
1683 object which also contains a @code{frame_filters} dictionary
1686 When a command is executed from @value{GDBN} that is compatible with
1687 frame filters, @value{GDBN} combines the @code{global},
1688 @code{gdb.Progspace} and all @code{gdb.Objfile} dictionaries currently
1689 loaded. All of the @code{gdb.Objfile} dictionaries are combined, as
1690 several frames, and thus several object files, might be in use.
1691 @value{GDBN} then prunes any frame filter whose @code{enabled}
1692 attribute is @code{False}. This pruned list is then sorted according
1693 to the @code{priority} attribute in each filter.
1695 Once the dictionaries are combined, pruned and sorted, @value{GDBN}
1696 creates an iterator which wraps each frame in the call stack in a
1697 @code{FrameDecorator} object, and calls each filter in order. The
1698 output from the previous filter will always be the input to the next
1701 Frame filters have a mandatory interface which each frame filter must
1702 implement, defined here:
1704 @defun FrameFilter.filter (iterator)
1705 @value{GDBN} will call this method on a frame filter when it has
1706 reached the order in the priority list for that filter.
1708 For example, if there are four frame filters:
1719 The order that the frame filters will be called is:
1722 Filter3 -> Filter2 -> Filter1 -> Filter4
1725 Note that the output from @code{Filter3} is passed to the input of
1726 @code{Filter2}, and so on.
1728 This @code{filter} method is passed a Python iterator. This iterator
1729 contains a sequence of frame decorators that wrap each
1730 @code{gdb.Frame}, or a frame decorator that wraps another frame
1731 decorator. The first filter that is executed in the sequence of frame
1732 filters will receive an iterator entirely comprised of default
1733 @code{FrameDecorator} objects. However, after each frame filter is
1734 executed, the previous frame filter may have wrapped some or all of
1735 the frame decorators with their own frame decorator. As frame
1736 decorators must also conform to a mandatory interface, these
1737 decorators can be assumed to act in a uniform manner (@pxref{Frame
1740 This method must return an object conforming to the Python iterator
1741 protocol. Each item in the iterator must be an object conforming to
1742 the frame decorator interface. If a frame filter does not wish to
1743 perform any operations on this iterator, it should return that
1746 This method is not optional. If it does not exist, @value{GDBN} will
1747 raise and print an error.
1750 @defvar FrameFilter.name
1751 The @code{name} attribute must be Python string which contains the
1752 name of the filter displayed by @value{GDBN} (@pxref{Frame Filter
1753 Management}). This attribute may contain any combination of letters
1754 or numbers. Care should be taken to ensure that it is unique. This
1755 attribute is mandatory.
1758 @defvar FrameFilter.enabled
1759 The @code{enabled} attribute must be Python boolean. This attribute
1760 indicates to @value{GDBN} whether the frame filter is enabled, and
1761 should be considered when frame filters are executed. If
1762 @code{enabled} is @code{True}, then the frame filter will be executed
1763 when any of the backtrace commands detailed earlier in this chapter
1764 are executed. If @code{enabled} is @code{False}, then the frame
1765 filter will not be executed. This attribute is mandatory.
1768 @defvar FrameFilter.priority
1769 The @code{priority} attribute must be Python integer. This attribute
1770 controls the order of execution in relation to other frame filters.
1771 There are no imposed limits on the range of @code{priority} other than
1772 it must be a valid integer. The higher the @code{priority} attribute,
1773 the sooner the frame filter will be executed in relation to other
1774 frame filters. Although @code{priority} can be negative, it is
1775 recommended practice to assume zero is the lowest priority that a
1776 frame filter can be assigned. Frame filters that have the same
1777 priority are executed in unsorted order in that priority slot. This
1778 attribute is mandatory. 100 is a good default priority.
1781 @node Frame Decorator API
1782 @subsubsection Decorating Frames
1783 @cindex frame decorator api
1785 Frame decorators are sister objects to frame filters (@pxref{Frame
1786 Filter API}). Frame decorators are applied by a frame filter and can
1787 only be used in conjunction with frame filters.
1789 The purpose of a frame decorator is to customize the printed content
1790 of each @code{gdb.Frame} in commands where frame filters are executed.
1791 This concept is called decorating a frame. Frame decorators decorate
1792 a @code{gdb.Frame} with Python code contained within each API call.
1793 This separates the actual data contained in a @code{gdb.Frame} from
1794 the decorated data produced by a frame decorator. This abstraction is
1795 necessary to maintain integrity of the data contained in each
1798 Frame decorators have a mandatory interface, defined below.
1800 @value{GDBN} already contains a frame decorator called
1801 @code{FrameDecorator}. This contains substantial amounts of
1802 boilerplate code to decorate the content of a @code{gdb.Frame}. It is
1803 recommended that other frame decorators inherit and extend this
1804 object, and only to override the methods needed.
1806 @tindex gdb.FrameDecorator
1807 @code{FrameDecorator} is defined in the Python module
1808 @code{gdb.FrameDecorator}, so your code can import it like:
1810 from gdb.FrameDecorator import FrameDecorator
1813 @defun FrameDecorator.elided (self)
1815 The @code{elided} method groups frames together in a hierarchical
1816 system. An example would be an interpreter, where multiple low-level
1817 frames make up a single call in the interpreted language. In this
1818 example, the frame filter would elide the low-level frames and present
1819 a single high-level frame, representing the call in the interpreted
1820 language, to the user.
1822 The @code{elided} function must return an iterable and this iterable
1823 must contain the frames that are being elided wrapped in a suitable
1824 frame decorator. If no frames are being elided this function may
1825 return an empty iterable, or @code{None}. Elided frames are indented
1826 from normal frames in a @code{CLI} backtrace, or in the case of
1827 @code{GDB/MI}, are placed in the @code{children} field of the eliding
1830 It is the frame filter's task to also filter out the elided frames from
1831 the source iterator. This will avoid printing the frame twice.
1834 @defun FrameDecorator.function (self)
1836 This method returns the name of the function in the frame that is to
1839 This method must return a Python string describing the function, or
1842 If this function returns @code{None}, @value{GDBN} will not print any
1843 data for this field.
1846 @defun FrameDecorator.address (self)
1848 This method returns the address of the frame that is to be printed.
1850 This method must return a Python numeric integer type of sufficient
1851 size to describe the address of the frame, or @code{None}.
1853 If this function returns a @code{None}, @value{GDBN} will not print
1854 any data for this field.
1857 @defun FrameDecorator.filename (self)
1859 This method returns the filename and path associated with this frame.
1861 This method must return a Python string containing the filename and
1862 the path to the object file backing the frame, or @code{None}.
1864 If this function returns a @code{None}, @value{GDBN} will not print
1865 any data for this field.
1868 @defun FrameDecorator.line (self):
1870 This method returns the line number associated with the current
1871 position within the function addressed by this frame.
1873 This method must return a Python integer type, or @code{None}.
1875 If this function returns a @code{None}, @value{GDBN} will not print
1876 any data for this field.
1879 @defun FrameDecorator.frame_args (self)
1882 This method must return an iterable, or @code{None}. Returning an
1883 empty iterable, or @code{None} means frame arguments will not be
1884 printed for this frame. This iterable must contain objects that
1885 implement two methods, described here.
1887 This object must implement a @code{argument} method which takes a
1888 single @code{self} parameter and must return a @code{gdb.Symbol}
1889 (@pxref{Symbols In Python}), or a Python string. The object must also
1890 implement a @code{value} method which takes a single @code{self}
1891 parameter and must return a @code{gdb.Value} (@pxref{Values From
1892 Inferior}), a Python value, or @code{None}. If the @code{value}
1893 method returns @code{None}, and the @code{argument} method returns a
1894 @code{gdb.Symbol}, @value{GDBN} will look-up and print the value of
1895 the @code{gdb.Symbol} automatically.
1900 class SymValueWrapper():
1902 def __init__(self, symbol, value):
1912 class SomeFrameDecorator()
1915 def frame_args(self):
1918 block = self.inferior_frame.block()
1922 # Iterate over all symbols in a block. Only add
1923 # symbols that are arguments.
1925 if not sym.is_argument:
1927 args.append(SymValueWrapper(sym,None))
1929 # Add example synthetic argument.
1930 args.append(SymValueWrapper(``foo'', 42))
1936 @defun FrameDecorator.frame_locals (self)
1938 This method must return an iterable or @code{None}. Returning an
1939 empty iterable, or @code{None} means frame local arguments will not be
1940 printed for this frame.
1942 The object interface, the description of the various strategies for
1943 reading frame locals, and the example are largely similar to those
1944 described in the @code{frame_args} function, (@pxref{frame_args,,The
1945 frame filter frame_args function}). Below is a modified example:
1948 class SomeFrameDecorator()
1951 def frame_locals(self):
1954 block = self.inferior_frame.block()
1958 # Iterate over all symbols in a block. Add all
1959 # symbols, except arguments.
1963 vars.append(SymValueWrapper(sym,None))
1965 # Add an example of a synthetic local variable.
1966 vars.append(SymValueWrapper(``bar'', 99))
1972 @defun FrameDecorator.inferior_frame (self):
1974 This method must return the underlying @code{gdb.Frame} that this
1975 frame decorator is decorating. @value{GDBN} requires the underlying
1976 frame for internal frame information to determine how to print certain
1977 values when printing a frame.
1980 @node Writing a Frame Filter
1981 @subsubsection Writing a Frame Filter
1982 @cindex writing a frame filter
1984 There are three basic elements that a frame filter must implement: it
1985 must correctly implement the documented interface (@pxref{Frame Filter
1986 API}), it must register itself with @value{GDBN}, and finally, it must
1987 decide if it is to work on the data provided by @value{GDBN}. In all
1988 cases, whether it works on the iterator or not, each frame filter must
1989 return an iterator. A bare-bones frame filter follows the pattern in
1990 the following example.
1995 class FrameFilter():
1998 # Frame filter attribute creation.
2000 # 'name' is the name of the filter that GDB will display.
2002 # 'priority' is the priority of the filter relative to other
2005 # 'enabled' is a boolean that indicates whether this filter is
2006 # enabled and should be executed.
2012 # Register this frame filter with the global frame_filters
2014 gdb.frame_filters[self.name] = self
2016 def filter(self, frame_iter):
2017 # Just return the iterator.
2021 The frame filter in the example above implements the three
2022 requirements for all frame filters. It implements the API, self
2023 registers, and makes a decision on the iterator (in this case, it just
2024 returns the iterator untouched).
2026 The first step is attribute creation and assignment, and as shown in
2027 the comments the filter assigns the following attributes: @code{name},
2028 @code{priority} and whether the filter should be enabled with the
2029 @code{enabled} attribute.
2031 The second step is registering the frame filter with the dictionary or
2032 dictionaries that the frame filter has interest in. As shown in the
2033 comments, this filter just registers itself with the global dictionary
2034 @code{gdb.frame_filters}. As noted earlier, @code{gdb.frame_filters}
2035 is a dictionary that is initialized in the @code{gdb} module when
2036 @value{GDBN} starts. What dictionary a filter registers with is an
2037 important consideration. Generally, if a filter is specific to a set
2038 of code, it should be registered either in the @code{objfile} or
2039 @code{progspace} dictionaries as they are specific to the program
2040 currently loaded in @value{GDBN}. The global dictionary is always
2041 present in @value{GDBN} and is never unloaded. Any filters registered
2042 with the global dictionary will exist until @value{GDBN} exits. To
2043 avoid filters that may conflict, it is generally better to register
2044 frame filters against the dictionaries that more closely align with
2045 the usage of the filter currently in question. @xref{Python
2046 Auto-loading}, for further information on auto-loading Python scripts.
2048 @value{GDBN} takes a hands-off approach to frame filter registration,
2049 therefore it is the frame filter's responsibility to ensure
2050 registration has occurred, and that any exceptions are handled
2051 appropriately. In particular, you may wish to handle exceptions
2052 relating to Python dictionary key uniqueness. It is mandatory that
2053 the dictionary key is the same as frame filter's @code{name}
2054 attribute. When a user manages frame filters (@pxref{Frame Filter
2055 Management}), the names @value{GDBN} will display are those contained
2056 in the @code{name} attribute.
2058 The final step of this example is the implementation of the
2059 @code{filter} method. As shown in the example comments, we define the
2060 @code{filter} method and note that the method must take an iterator,
2061 and also must return an iterator. In this bare-bones example, the
2062 frame filter is not very useful as it just returns the iterator
2063 untouched. However this is a valid operation for frame filters that
2064 have the @code{enabled} attribute set, but decide not to operate on
2067 In the next example, the frame filter operates on all frames and
2068 utilizes a frame decorator to perform some work on the frames.
2069 @xref{Frame Decorator API}, for further information on the frame
2070 decorator interface.
2072 This example works on inlined frames. It highlights frames which are
2073 inlined by tagging them with an ``[inlined]'' tag. By applying a
2074 frame decorator to all frames with the Python @code{itertools imap}
2075 method, the example defers actions to the frame decorator. Frame
2076 decorators are only processed when @value{GDBN} prints the backtrace.
2078 This introduces a new decision making topic: whether to perform
2079 decision making operations at the filtering step, or at the printing
2080 step. In this example's approach, it does not perform any filtering
2081 decisions at the filtering step beyond mapping a frame decorator to
2082 each frame. This allows the actual decision making to be performed
2083 when each frame is printed. This is an important consideration, and
2084 well worth reflecting upon when designing a frame filter. An issue
2085 that frame filters should avoid is unwinding the stack if possible.
2086 Some stacks can run very deep, into the tens of thousands in some
2087 cases. To search every frame to determine if it is inlined ahead of
2088 time may be too expensive at the filtering step. The frame filter
2089 cannot know how many frames it has to iterate over, and it would have
2090 to iterate through them all. This ends up duplicating effort as
2091 @value{GDBN} performs this iteration when it prints the frames.
2093 In this example decision making can be deferred to the printing step.
2094 As each frame is printed, the frame decorator can examine each frame
2095 in turn when @value{GDBN} iterates. From a performance viewpoint,
2096 this is the most appropriate decision to make as it avoids duplicating
2097 the effort that the printing step would undertake anyway. Also, if
2098 there are many frame filters unwinding the stack during filtering, it
2099 can substantially delay the printing of the backtrace which will
2100 result in large memory usage, and a poor user experience.
2103 class InlineFilter():
2106 self.name = "InlinedFrameFilter"
2109 gdb.frame_filters[self.name] = self
2111 def filter(self, frame_iter):
2112 frame_iter = itertools.imap(InlinedFrameDecorator,
2117 This frame filter is somewhat similar to the earlier example, except
2118 that the @code{filter} method applies a frame decorator object called
2119 @code{InlinedFrameDecorator} to each element in the iterator. The
2120 @code{imap} Python method is light-weight. It does not proactively
2121 iterate over the iterator, but rather creates a new iterator which
2122 wraps the existing one.
2124 Below is the frame decorator for this example.
2127 class InlinedFrameDecorator(FrameDecorator):
2129 def __init__(self, fobj):
2130 super(InlinedFrameDecorator, self).__init__(fobj)
2133 frame = fobj.inferior_frame()
2134 name = str(frame.name())
2136 if frame.type() == gdb.INLINE_FRAME:
2137 name = name + " [inlined]"
2142 This frame decorator only defines and overrides the @code{function}
2143 method. It lets the supplied @code{FrameDecorator}, which is shipped
2144 with @value{GDBN}, perform the other work associated with printing
2147 The combination of these two objects create this output from a
2151 #0 0x004004e0 in bar () at inline.c:11
2152 #1 0x00400566 in max [inlined] (b=6, a=12) at inline.c:21
2153 #2 0x00400566 in main () at inline.c:31
2156 So in the case of this example, a frame decorator is applied to all
2157 frames, regardless of whether they may be inlined or not. As
2158 @value{GDBN} iterates over the iterator produced by the frame filters,
2159 @value{GDBN} executes each frame decorator which then makes a decision
2160 on what to print in the @code{function} callback. Using a strategy
2161 like this is a way to defer decisions on the frame content to printing
2164 @subheading Eliding Frames
2166 It might be that the above example is not desirable for representing
2167 inlined frames, and a hierarchical approach may be preferred. If we
2168 want to hierarchically represent frames, the @code{elided} frame
2169 decorator interface might be preferable.
2171 This example approaches the issue with the @code{elided} method. This
2172 example is quite long, but very simplistic. It is out-of-scope for
2173 this section to write a complete example that comprehensively covers
2174 all approaches of finding and printing inlined frames. However, this
2175 example illustrates the approach an author might use.
2177 This example comprises of three sections.
2180 class InlineFrameFilter():
2183 self.name = "InlinedFrameFilter"
2186 gdb.frame_filters[self.name] = self
2188 def filter(self, frame_iter):
2189 return ElidingInlineIterator(frame_iter)
2192 This frame filter is very similar to the other examples. The only
2193 difference is this frame filter is wrapping the iterator provided to
2194 it (@code{frame_iter}) with a custom iterator called
2195 @code{ElidingInlineIterator}. This again defers actions to when
2196 @value{GDBN} prints the backtrace, as the iterator is not traversed
2199 The iterator for this example is as follows. It is in this section of
2200 the example where decisions are made on the content of the backtrace.
2203 class ElidingInlineIterator:
2204 def __init__(self, ii):
2205 self.input_iterator = ii
2211 frame = next(self.input_iterator)
2213 if frame.inferior_frame().type() != gdb.INLINE_FRAME:
2217 eliding_frame = next(self.input_iterator)
2218 except StopIteration:
2220 return ElidingFrameDecorator(eliding_frame, [frame])
2223 This iterator implements the Python iterator protocol. When the
2224 @code{next} function is called (when @value{GDBN} prints each frame),
2225 the iterator checks if this frame decorator, @code{frame}, is wrapping
2226 an inlined frame. If it is not, it returns the existing frame decorator
2227 untouched. If it is wrapping an inlined frame, it assumes that the
2228 inlined frame was contained within the next oldest frame,
2229 @code{eliding_frame}, which it fetches. It then creates and returns a
2230 frame decorator, @code{ElidingFrameDecorator}, which contains both the
2231 elided frame, and the eliding frame.
2234 class ElidingInlineDecorator(FrameDecorator):
2236 def __init__(self, frame, elided_frames):
2237 super(ElidingInlineDecorator, self).__init__(frame)
2239 self.elided_frames = elided_frames
2242 return iter(self.elided_frames)
2245 This frame decorator overrides one function and returns the inlined
2246 frame in the @code{elided} method. As before it lets
2247 @code{FrameDecorator} do the rest of the work involved in printing
2248 this frame. This produces the following output.
2251 #0 0x004004e0 in bar () at inline.c:11
2252 #2 0x00400529 in main () at inline.c:25
2253 #1 0x00400529 in max (b=6, a=12) at inline.c:15
2256 In that output, @code{max} which has been inlined into @code{main} is
2257 printed hierarchically. Another approach would be to combine the
2258 @code{function} method, and the @code{elided} method to both print a
2259 marker in the inlined frame, and also show the hierarchical
2262 @node Unwinding Frames in Python
2263 @subsubsection Unwinding Frames in Python
2264 @cindex unwinding frames in Python
2266 In @value{GDBN} terminology ``unwinding'' is the process of finding
2267 the previous frame (that is, caller's) from the current one. An
2268 unwinder has three methods. The first one checks if it can handle
2269 given frame (``sniff'' it). For the frames it can sniff an unwinder
2270 provides two additional methods: it can return frame's ID, and it can
2271 fetch registers from the previous frame. A running @value{GDBN}
2272 mantains a list of the unwinders and calls each unwinder's sniffer in
2273 turn until it finds the one that recognizes the current frame. There
2274 is an API to register an unwinder.
2276 The unwinders that come with @value{GDBN} handle standard frames.
2277 However, mixed language applications (for example, an application
2278 running Java Virtual Machine) sometimes use frame layouts that cannot
2279 be handled by the @value{GDBN} unwinders. You can write Python code
2280 that can handle such custom frames.
2282 You implement a frame unwinder in Python as a class with which has two
2283 attributes, @code{name} and @code{enabled}, with obvious meanings, and
2284 a single method @code{__call__}, which examines a given frame and
2285 returns an object (an instance of @code{gdb.UnwindInfo class)}
2286 describing it. If an unwinder does not recognize a frame, it should
2287 return @code{None}. The code in @value{GDBN} that enables writing
2288 unwinders in Python uses this object to return frame's ID and previous
2289 frame registers when @value{GDBN} core asks for them.
2291 An unwinder should do as little work as possible. Some otherwise
2292 innocuous operations can cause problems (even crashes, as this code is
2293 not not well-hardened yet). For example, making an inferior call from
2294 an unwinder is unadvisable, as an inferior call will reset
2295 @value{GDBN}'s stack unwinding process, potentially causing re-entrant
2298 @subheading Unwinder Input
2300 An object passed to an unwinder (a @code{gdb.PendingFrame} instance)
2301 provides a method to read frame's registers:
2303 @defun PendingFrame.read_register (reg)
2304 This method returns the contents of the register @var{reg} in the
2305 frame as a @code{gdb.Value} object. @var{reg} can be either a
2306 register number or a register name; the values are platform-specific.
2307 They are usually found in the corresponding
2308 @file{@var{platform}-tdep.h} file in the @value{GDBN} source tree. If
2309 @var{reg} does not name a register for the current architecture, this
2310 method will throw an exception.
2312 Note that this method will always return a @code{gdb.Value} for a
2313 valid register name. This does not mean that the value will be valid.
2314 For example, you may request a register that an earlier unwinder could
2315 not unwind---the value will be unavailable. Instead, the
2316 @code{gdb.Value} returned from this method will be lazy; that is, its
2317 underlying bits will not be fetched until it is first used. So,
2318 attempting to use such a value will cause an exception at the point of
2321 The type of the returned @code{gdb.Value} depends on the register and
2322 the architecture. It is common for registers to have a scalar type,
2323 like @code{long long}; but many other types are possible, such as
2324 pointer, pointer-to-function, floating point or vector types.
2327 It also provides a factory method to create a @code{gdb.UnwindInfo}
2328 instance to be returned to @value{GDBN}:
2330 @defun PendingFrame.create_unwind_info (frame_id)
2331 Returns a new @code{gdb.UnwindInfo} instance identified by given
2332 @var{frame_id}. The argument is used to build @value{GDBN}'s frame ID
2333 using one of functions provided by @value{GDBN}. @var{frame_id}'s attributes
2334 determine which function will be used, as follows:
2338 The frame is identified by the given stack address and PC. The stack
2339 address must be chosen so that it is constant throughout the lifetime
2340 of the frame, so a typical choice is the value of the stack pointer at
2341 the start of the function---in the DWARF standard, this would be the
2342 ``Call Frame Address''.
2344 This is the most common case by far. The other cases are documented
2345 for completeness but are only useful in specialized situations.
2347 @item sp, pc, special
2348 The frame is identified by the stack address, the PC, and a
2349 ``special'' address. The special address is used on architectures
2350 that can have frames that do not change the stack, but which are still
2351 distinct, for example the IA-64, which has a second stack for
2352 registers. Both @var{sp} and @var{special} must be constant
2353 throughout the lifetime of the frame.
2356 The frame is identified by the stack address only. Any other stack
2357 frame with a matching @var{sp} will be considered to match this frame.
2358 Inside gdb, this is called a ``wild frame''. You will never need
2362 Each attribute value should be an instance of @code{gdb.Value}.
2366 @subheading Unwinder Output: UnwindInfo
2368 Use @code{PendingFrame.create_unwind_info} method described above to
2369 create a @code{gdb.UnwindInfo} instance. Use the following method to
2370 specify caller registers that have been saved in this frame:
2372 @defun gdb.UnwindInfo.add_saved_register (reg, value)
2373 @var{reg} identifies the register. It can be a number or a name, just
2374 as for the @code{PendingFrame.read_register} method above.
2375 @var{value} is a register value (a @code{gdb.Value} object).
2378 @subheading Unwinder Skeleton Code
2380 @value{GDBN} comes with the module containing the base @code{Unwinder}
2381 class. Derive your unwinder class from it and structure the code as
2385 from gdb.unwinders import Unwinder
2387 class FrameId(object):
2388 def __init__(self, sp, pc):
2393 class MyUnwinder(Unwinder):
2395 supe(MyUnwinder, self).__init___(<expects unwinder name argument>)
2397 def __call__(pending_frame):
2398 if not <we recognize frame>:
2400 # Create UnwindInfo. Usually the frame is identified by the stack
2401 # pointer and the program counter.
2402 sp = pending_frame.read_register(<SP number>)
2403 pc = pending_frame.read_register(<PC number>)
2404 unwind_info = pending_frame.create_unwind_info(FrameId(sp, pc))
2406 # Find the values of the registers in the caller's frame and
2407 # save them in the result:
2408 unwind_info.add_saved_register(<register>, <value>)
2411 # Return the result:
2416 @subheading Registering a Unwinder
2418 An object file, a program space, and the @value{GDBN} proper can have
2419 unwinders registered with it.
2421 The @code{gdb.unwinders} module provides the function to register a
2424 @defun gdb.unwinder.register_unwinder (locus, unwinder, replace=False)
2425 @var{locus} is specifies an object file or a program space to which
2426 @var{unwinder} is added. Passing @code{None} or @code{gdb} adds
2427 @var{unwinder} to the @value{GDBN}'s global unwinder list. The newly
2428 added @var{unwinder} will be called before any other unwinder from the
2429 same locus. Two unwinders in the same locus cannot have the same
2430 name. An attempt to add a unwinder with already existing name raises
2431 an exception unless @var{replace} is @code{True}, in which case the
2432 old unwinder is deleted.
2435 @subheading Unwinder Precedence
2437 @value{GDBN} first calls the unwinders from all the object files in no
2438 particular order, then the unwinders from the current program space,
2439 and finally the unwinders from @value{GDBN}.
2441 @node Xmethods In Python
2442 @subsubsection Xmethods In Python
2443 @cindex xmethods in Python
2445 @dfn{Xmethods} are additional methods or replacements for existing
2446 methods of a C@t{++} class. This feature is useful for those cases
2447 where a method defined in C@t{++} source code could be inlined or
2448 optimized out by the compiler, making it unavailable to @value{GDBN}.
2449 For such cases, one can define an xmethod to serve as a replacement
2450 for the method defined in the C@t{++} source code. @value{GDBN} will
2451 then invoke the xmethod, instead of the C@t{++} method, to
2452 evaluate expressions. One can also use xmethods when debugging
2453 with core files. Moreover, when debugging live programs, invoking an
2454 xmethod need not involve running the inferior (which can potentially
2455 perturb its state). Hence, even if the C@t{++} method is available, it
2456 is better to use its replacement xmethod if one is defined.
2458 The xmethods feature in Python is available via the concepts of an
2459 @dfn{xmethod matcher} and an @dfn{xmethod worker}. To
2460 implement an xmethod, one has to implement a matcher and a
2461 corresponding worker for it (more than one worker can be
2462 implemented, each catering to a different overloaded instance of the
2463 method). Internally, @value{GDBN} invokes the @code{match} method of a
2464 matcher to match the class type and method name. On a match, the
2465 @code{match} method returns a list of matching @emph{worker} objects.
2466 Each worker object typically corresponds to an overloaded instance of
2467 the xmethod. They implement a @code{get_arg_types} method which
2468 returns a sequence of types corresponding to the arguments the xmethod
2469 requires. @value{GDBN} uses this sequence of types to perform
2470 overload resolution and picks a winning xmethod worker. A winner
2471 is also selected from among the methods @value{GDBN} finds in the
2472 C@t{++} source code. Next, the winning xmethod worker and the
2473 winning C@t{++} method are compared to select an overall winner. In
2474 case of a tie between a xmethod worker and a C@t{++} method, the
2475 xmethod worker is selected as the winner. That is, if a winning
2476 xmethod worker is found to be equivalent to the winning C@t{++}
2477 method, then the xmethod worker is treated as a replacement for
2478 the C@t{++} method. @value{GDBN} uses the overall winner to invoke the
2479 method. If the winning xmethod worker is the overall winner, then
2480 the corresponding xmethod is invoked via the @code{__call__} method
2481 of the worker object.
2483 If one wants to implement an xmethod as a replacement for an
2484 existing C@t{++} method, then they have to implement an equivalent
2485 xmethod which has exactly the same name and takes arguments of
2486 exactly the same type as the C@t{++} method. If the user wants to
2487 invoke the C@t{++} method even though a replacement xmethod is
2488 available for that method, then they can disable the xmethod.
2490 @xref{Xmethod API}, for API to implement xmethods in Python.
2491 @xref{Writing an Xmethod}, for implementing xmethods in Python.
2494 @subsubsection Xmethod API
2497 The @value{GDBN} Python API provides classes, interfaces and functions
2498 to implement, register and manipulate xmethods.
2499 @xref{Xmethods In Python}.
2501 An xmethod matcher should be an instance of a class derived from
2502 @code{XMethodMatcher} defined in the module @code{gdb.xmethod}, or an
2503 object with similar interface and attributes. An instance of
2504 @code{XMethodMatcher} has the following attributes:
2507 The name of the matcher.
2511 A boolean value indicating whether the matcher is enabled or disabled.
2515 A list of named methods managed by the matcher. Each object in the list
2516 is an instance of the class @code{XMethod} defined in the module
2517 @code{gdb.xmethod}, or any object with the following attributes:
2522 Name of the xmethod which should be unique for each xmethod
2523 managed by the matcher.
2526 A boolean value indicating whether the xmethod is enabled or
2531 The class @code{XMethod} is a convenience class with same
2532 attributes as above along with the following constructor:
2534 @defun XMethod.__init__ (self, name)
2535 Constructs an enabled xmethod with name @var{name}.
2540 The @code{XMethodMatcher} class has the following methods:
2542 @defun XMethodMatcher.__init__ (self, name)
2543 Constructs an enabled xmethod matcher with name @var{name}. The
2544 @code{methods} attribute is initialized to @code{None}.
2547 @defun XMethodMatcher.match (self, class_type, method_name)
2548 Derived classes should override this method. It should return a
2549 xmethod worker object (or a sequence of xmethod worker
2550 objects) matching the @var{class_type} and @var{method_name}.
2551 @var{class_type} is a @code{gdb.Type} object, and @var{method_name}
2552 is a string value. If the matcher manages named methods as listed in
2553 its @code{methods} attribute, then only those worker objects whose
2554 corresponding entries in the @code{methods} list are enabled should be
2558 An xmethod worker should be an instance of a class derived from
2559 @code{XMethodWorker} defined in the module @code{gdb.xmethod},
2560 or support the following interface:
2562 @defun XMethodWorker.get_arg_types (self)
2563 This method returns a sequence of @code{gdb.Type} objects corresponding
2564 to the arguments that the xmethod takes. It can return an empty
2565 sequence or @code{None} if the xmethod does not take any arguments.
2566 If the xmethod takes a single argument, then a single
2567 @code{gdb.Type} object corresponding to it can be returned.
2570 @defun XMethodWorker.get_result_type (self, *args)
2571 This method returns a @code{gdb.Type} object representing the type
2572 of the result of invoking this xmethod.
2573 The @var{args} argument is the same tuple of arguments that would be
2574 passed to the @code{__call__} method of this worker.
2577 @defun XMethodWorker.__call__ (self, *args)
2578 This is the method which does the @emph{work} of the xmethod. The
2579 @var{args} arguments is the tuple of arguments to the xmethod. Each
2580 element in this tuple is a gdb.Value object. The first element is
2581 always the @code{this} pointer value.
2584 For @value{GDBN} to lookup xmethods, the xmethod matchers
2585 should be registered using the following function defined in the module
2588 @defun register_xmethod_matcher (locus, matcher, replace=False)
2589 The @code{matcher} is registered with @code{locus}, replacing an
2590 existing matcher with the same name as @code{matcher} if
2591 @code{replace} is @code{True}. @code{locus} can be a
2592 @code{gdb.Objfile} object (@pxref{Objfiles In Python}), or a
2593 @code{gdb.Progspace} object (@pxref{Progspaces In Python}), or
2594 @code{None}. If it is @code{None}, then @code{matcher} is registered
2598 @node Writing an Xmethod
2599 @subsubsection Writing an Xmethod
2600 @cindex writing xmethods in Python
2602 Implementing xmethods in Python will require implementing xmethod
2603 matchers and xmethod workers (@pxref{Xmethods In Python}). Consider
2604 the following C@t{++} class:
2610 MyClass (int a) : a_(a) @{ @}
2612 int geta (void) @{ return a_; @}
2613 int operator+ (int b);
2620 MyClass::operator+ (int b)
2627 Let us define two xmethods for the class @code{MyClass}, one
2628 replacing the method @code{geta}, and another adding an overloaded
2629 flavor of @code{operator+} which takes a @code{MyClass} argument (the
2630 C@t{++} code above already has an overloaded @code{operator+}
2631 which takes an @code{int} argument). The xmethod matcher can be
2635 class MyClass_geta(gdb.xmethod.XMethod):
2637 gdb.xmethod.XMethod.__init__(self, 'geta')
2639 def get_worker(self, method_name):
2640 if method_name == 'geta':
2641 return MyClassWorker_geta()
2644 class MyClass_sum(gdb.xmethod.XMethod):
2646 gdb.xmethod.XMethod.__init__(self, 'sum')
2648 def get_worker(self, method_name):
2649 if method_name == 'operator+':
2650 return MyClassWorker_plus()
2653 class MyClassMatcher(gdb.xmethod.XMethodMatcher):
2655 gdb.xmethod.XMethodMatcher.__init__(self, 'MyClassMatcher')
2656 # List of methods 'managed' by this matcher
2657 self.methods = [MyClass_geta(), MyClass_sum()]
2659 def match(self, class_type, method_name):
2660 if class_type.tag != 'MyClass':
2663 for method in self.methods:
2665 worker = method.get_worker(method_name)
2667 workers.append(worker)
2673 Notice that the @code{match} method of @code{MyClassMatcher} returns
2674 a worker object of type @code{MyClassWorker_geta} for the @code{geta}
2675 method, and a worker object of type @code{MyClassWorker_plus} for the
2676 @code{operator+} method. This is done indirectly via helper classes
2677 derived from @code{gdb.xmethod.XMethod}. One does not need to use the
2678 @code{methods} attribute in a matcher as it is optional. However, if a
2679 matcher manages more than one xmethod, it is a good practice to list the
2680 xmethods in the @code{methods} attribute of the matcher. This will then
2681 facilitate enabling and disabling individual xmethods via the
2682 @code{enable/disable} commands. Notice also that a worker object is
2683 returned only if the corresponding entry in the @code{methods} attribute
2684 of the matcher is enabled.
2686 The implementation of the worker classes returned by the matcher setup
2687 above is as follows:
2690 class MyClassWorker_geta(gdb.xmethod.XMethodWorker):
2691 def get_arg_types(self):
2694 def get_result_type(self, obj):
2695 return gdb.lookup_type('int')
2697 def __call__(self, obj):
2701 class MyClassWorker_plus(gdb.xmethod.XMethodWorker):
2702 def get_arg_types(self):
2703 return gdb.lookup_type('MyClass')
2705 def get_result_type(self, obj):
2706 return gdb.lookup_type('int')
2708 def __call__(self, obj, other):
2709 return obj['a_'] + other['a_']
2712 For @value{GDBN} to actually lookup a xmethod, it has to be
2713 registered with it. The matcher defined above is registered with
2714 @value{GDBN} globally as follows:
2717 gdb.xmethod.register_xmethod_matcher(None, MyClassMatcher())
2720 If an object @code{obj} of type @code{MyClass} is initialized in C@t{++}
2728 then, after loading the Python script defining the xmethod matchers
2729 and workers into @code{GDBN}, invoking the method @code{geta} or using
2730 the operator @code{+} on @code{obj} will invoke the xmethods
2741 Consider another example with a C++ template class:
2748 MyTemplate () : dsize_(10), data_ (new T [10]) @{ @}
2749 ~MyTemplate () @{ delete [] data_; @}
2751 int footprint (void)
2753 return sizeof (T) * dsize_ + sizeof (MyTemplate<T>);
2762 Let us implement an xmethod for the above class which serves as a
2763 replacement for the @code{footprint} method. The full code listing
2764 of the xmethod workers and xmethod matchers is as follows:
2767 class MyTemplateWorker_footprint(gdb.xmethod.XMethodWorker):
2768 def __init__(self, class_type):
2769 self.class_type = class_type
2771 def get_arg_types(self):
2774 def get_result_type(self):
2775 return gdb.lookup_type('int')
2777 def __call__(self, obj):
2778 return (self.class_type.sizeof +
2780 self.class_type.template_argument(0).sizeof)
2783 class MyTemplateMatcher_footprint(gdb.xmethod.XMethodMatcher):
2785 gdb.xmethod.XMethodMatcher.__init__(self, 'MyTemplateMatcher')
2787 def match(self, class_type, method_name):
2788 if (re.match('MyTemplate<[ \t\n]*[_a-zA-Z][ _a-zA-Z0-9]*>',
2790 method_name == 'footprint'):
2791 return MyTemplateWorker_footprint(class_type)
2794 Notice that, in this example, we have not used the @code{methods}
2795 attribute of the matcher as the matcher manages only one xmethod. The
2796 user can enable/disable this xmethod by enabling/disabling the matcher
2799 @node Inferiors In Python
2800 @subsubsection Inferiors In Python
2801 @cindex inferiors in Python
2803 @findex gdb.Inferior
2804 Programs which are being run under @value{GDBN} are called inferiors
2805 (@pxref{Inferiors and Programs}). Python scripts can access
2806 information about and manipulate inferiors controlled by @value{GDBN}
2807 via objects of the @code{gdb.Inferior} class.
2809 The following inferior-related functions are available in the @code{gdb}
2812 @defun gdb.inferiors ()
2813 Return a tuple containing all inferior objects.
2816 @defun gdb.selected_inferior ()
2817 Return an object representing the current inferior.
2820 A @code{gdb.Inferior} object has the following attributes:
2822 @defvar Inferior.num
2823 ID of inferior, as assigned by GDB.
2826 @defvar Inferior.pid
2827 Process ID of the inferior, as assigned by the underlying operating
2831 @defvar Inferior.was_attached
2832 Boolean signaling whether the inferior was created using `attach', or
2833 started by @value{GDBN} itself.
2836 A @code{gdb.Inferior} object has the following methods:
2838 @defun Inferior.is_valid ()
2839 Returns @code{True} if the @code{gdb.Inferior} object is valid,
2840 @code{False} if not. A @code{gdb.Inferior} object will become invalid
2841 if the inferior no longer exists within @value{GDBN}. All other
2842 @code{gdb.Inferior} methods will throw an exception if it is invalid
2843 at the time the method is called.
2846 @defun Inferior.threads ()
2847 This method returns a tuple holding all the threads which are valid
2848 when it is called. If there are no valid threads, the method will
2849 return an empty tuple.
2852 @findex Inferior.read_memory
2853 @defun Inferior.read_memory (address, length)
2854 Read @var{length} addressable memory units from the inferior, starting at
2855 @var{address}. Returns a buffer object, which behaves much like an array
2856 or a string. It can be modified and given to the
2857 @code{Inferior.write_memory} function. In Python 3, the return
2858 value is a @code{memoryview} object.
2861 @findex Inferior.write_memory
2862 @defun Inferior.write_memory (address, buffer @r{[}, length@r{]})
2863 Write the contents of @var{buffer} to the inferior, starting at
2864 @var{address}. The @var{buffer} parameter must be a Python object
2865 which supports the buffer protocol, i.e., a string, an array or the
2866 object returned from @code{Inferior.read_memory}. If given, @var{length}
2867 determines the number of addressable memory units from @var{buffer} to be
2871 @findex gdb.search_memory
2872 @defun Inferior.search_memory (address, length, pattern)
2873 Search a region of the inferior memory starting at @var{address} with
2874 the given @var{length} using the search pattern supplied in
2875 @var{pattern}. The @var{pattern} parameter must be a Python object
2876 which supports the buffer protocol, i.e., a string, an array or the
2877 object returned from @code{gdb.read_memory}. Returns a Python @code{Long}
2878 containing the address where the pattern was found, or @code{None} if
2879 the pattern could not be found.
2882 @findex Inferior.thread_from_thread_handle
2883 @defun Inferior.thread_from_thread_handle (thread_handle)
2884 Return the thread object corresponding to @var{thread_handle}, a thread
2885 library specific data structure such as @code{pthread_t} for pthreads
2886 library implementations.
2889 @node Events In Python
2890 @subsubsection Events In Python
2891 @cindex inferior events in Python
2893 @value{GDBN} provides a general event facility so that Python code can be
2894 notified of various state changes, particularly changes that occur in
2897 An @dfn{event} is just an object that describes some state change. The
2898 type of the object and its attributes will vary depending on the details
2899 of the change. All the existing events are described below.
2901 In order to be notified of an event, you must register an event handler
2902 with an @dfn{event registry}. An event registry is an object in the
2903 @code{gdb.events} module which dispatches particular events. A registry
2904 provides methods to register and unregister event handlers:
2906 @defun EventRegistry.connect (object)
2907 Add the given callable @var{object} to the registry. This object will be
2908 called when an event corresponding to this registry occurs.
2911 @defun EventRegistry.disconnect (object)
2912 Remove the given @var{object} from the registry. Once removed, the object
2913 will no longer receive notifications of events.
2919 def exit_handler (event):
2920 print "event type: exit"
2921 print "exit code: %d" % (event.exit_code)
2923 gdb.events.exited.connect (exit_handler)
2926 In the above example we connect our handler @code{exit_handler} to the
2927 registry @code{events.exited}. Once connected, @code{exit_handler} gets
2928 called when the inferior exits. The argument @dfn{event} in this example is
2929 of type @code{gdb.ExitedEvent}. As you can see in the example the
2930 @code{ExitedEvent} object has an attribute which indicates the exit code of
2933 The following is a listing of the event registries that are available and
2934 details of the events they emit:
2939 Emits @code{gdb.ThreadEvent}.
2941 Some events can be thread specific when @value{GDBN} is running in non-stop
2942 mode. When represented in Python, these events all extend
2943 @code{gdb.ThreadEvent}. Note, this event is not emitted directly; instead,
2944 events which are emitted by this or other modules might extend this event.
2945 Examples of these events are @code{gdb.BreakpointEvent} and
2946 @code{gdb.ContinueEvent}.
2948 @defvar ThreadEvent.inferior_thread
2949 In non-stop mode this attribute will be set to the specific thread which was
2950 involved in the emitted event. Otherwise, it will be set to @code{None}.
2953 Emits @code{gdb.ContinueEvent} which extends @code{gdb.ThreadEvent}.
2955 This event indicates that the inferior has been continued after a stop. For
2956 inherited attribute refer to @code{gdb.ThreadEvent} above.
2959 Emits @code{events.ExitedEvent} which indicates that the inferior has exited.
2960 @code{events.ExitedEvent} has two attributes:
2961 @defvar ExitedEvent.exit_code
2962 An integer representing the exit code, if available, which the inferior
2963 has returned. (The exit code could be unavailable if, for example,
2964 @value{GDBN} detaches from the inferior.) If the exit code is unavailable,
2965 the attribute does not exist.
2967 @defvar ExitedEvent.inferior
2968 A reference to the inferior which triggered the @code{exited} event.
2972 Emits @code{gdb.StopEvent} which extends @code{gdb.ThreadEvent}.
2974 Indicates that the inferior has stopped. All events emitted by this registry
2975 extend StopEvent. As a child of @code{gdb.ThreadEvent}, @code{gdb.StopEvent}
2976 will indicate the stopped thread when @value{GDBN} is running in non-stop
2977 mode. Refer to @code{gdb.ThreadEvent} above for more details.
2979 Emits @code{gdb.SignalEvent} which extends @code{gdb.StopEvent}.
2981 This event indicates that the inferior or one of its threads has received as
2982 signal. @code{gdb.SignalEvent} has the following attributes:
2984 @defvar SignalEvent.stop_signal
2985 A string representing the signal received by the inferior. A list of possible
2986 signal values can be obtained by running the command @code{info signals} in
2987 the @value{GDBN} command prompt.
2990 Also emits @code{gdb.BreakpointEvent} which extends @code{gdb.StopEvent}.
2992 @code{gdb.BreakpointEvent} event indicates that one or more breakpoints have
2993 been hit, and has the following attributes:
2995 @defvar BreakpointEvent.breakpoints
2996 A sequence containing references to all the breakpoints (type
2997 @code{gdb.Breakpoint}) that were hit.
2998 @xref{Breakpoints In Python}, for details of the @code{gdb.Breakpoint} object.
3000 @defvar BreakpointEvent.breakpoint
3001 A reference to the first breakpoint that was hit.
3002 This function is maintained for backward compatibility and is now deprecated
3003 in favor of the @code{gdb.BreakpointEvent.breakpoints} attribute.
3006 @item events.new_objfile
3007 Emits @code{gdb.NewObjFileEvent} which indicates that a new object file has
3008 been loaded by @value{GDBN}. @code{gdb.NewObjFileEvent} has one attribute:
3010 @defvar NewObjFileEvent.new_objfile
3011 A reference to the object file (@code{gdb.Objfile}) which has been loaded.
3012 @xref{Objfiles In Python}, for details of the @code{gdb.Objfile} object.
3015 @item events.clear_objfiles
3016 Emits @code{gdb.ClearObjFilesEvent} which indicates that the list of object
3017 files for a program space has been reset.
3018 @code{gdb.ClearObjFilesEvent} has one attribute:
3020 @defvar ClearObjFilesEvent.progspace
3021 A reference to the program space (@code{gdb.Progspace}) whose objfile list has
3022 been cleared. @xref{Progspaces In Python}.
3025 @item events.inferior_call
3026 Emits events just before and after a function in the inferior is
3027 called by @value{GDBN}. Before an inferior call, this emits an event
3028 of type @code{gdb.InferiorCallPreEvent}, and after an inferior call,
3029 this emits an event of type @code{gdb.InferiorCallPostEvent}.
3032 @tindex gdb.InferiorCallPreEvent
3033 @item @code{gdb.InferiorCallPreEvent}
3034 Indicates that a function in the inferior is about to be called.
3036 @defvar InferiorCallPreEvent.ptid
3037 The thread in which the call will be run.
3040 @defvar InferiorCallPreEvent.address
3041 The location of the function to be called.
3044 @tindex gdb.InferiorCallPostEvent
3045 @item @code{gdb.InferiorCallPostEvent}
3046 Indicates that a function in the inferior has just been called.
3048 @defvar InferiorCallPostEvent.ptid
3049 The thread in which the call was run.
3052 @defvar InferiorCallPostEvent.address
3053 The location of the function that was called.
3057 @item events.memory_changed
3058 Emits @code{gdb.MemoryChangedEvent} which indicates that the memory of the
3059 inferior has been modified by the @value{GDBN} user, for instance via a
3060 command like @w{@code{set *addr = value}}. The event has the following
3063 @defvar MemoryChangedEvent.address
3064 The start address of the changed region.
3067 @defvar MemoryChangedEvent.length
3068 Length in bytes of the changed region.
3071 @item events.register_changed
3072 Emits @code{gdb.RegisterChangedEvent} which indicates that a register in the
3073 inferior has been modified by the @value{GDBN} user.
3075 @defvar RegisterChangedEvent.frame
3076 A gdb.Frame object representing the frame in which the register was modified.
3078 @defvar RegisterChangedEvent.regnum
3079 Denotes which register was modified.
3082 @item events.breakpoint_created
3083 This is emitted when a new breakpoint has been created. The argument
3084 that is passed is the new @code{gdb.Breakpoint} object.
3086 @item events.breakpoint_modified
3087 This is emitted when a breakpoint has been modified in some way. The
3088 argument that is passed is the new @code{gdb.Breakpoint} object.
3090 @item events.breakpoint_deleted
3091 This is emitted when a breakpoint has been deleted. The argument that
3092 is passed is the @code{gdb.Breakpoint} object. When this event is
3093 emitted, the @code{gdb.Breakpoint} object will already be in its
3094 invalid state; that is, the @code{is_valid} method will return
3097 @item events.before_prompt
3098 This event carries no payload. It is emitted each time @value{GDBN}
3099 presents a prompt to the user.
3101 @item events.new_inferior
3102 This is emitted when a new inferior is created. Note that the
3103 inferior is not necessarily running; in fact, it may not even have an
3104 associated executable.
3106 The event is of type @code{gdb.NewInferiorEvent}. This has a single
3109 @defvar NewInferiorEvent.inferior
3110 The new inferior, a @code{gdb.Inferior} object.
3113 @item events.inferior_deleted
3114 This is emitted when an inferior has been deleted. Note that this is
3115 not the same as process exit; it is notified when the inferior itself
3116 is removed, say via @code{remove-inferiors}.
3118 The event is of type @code{gdb.InferiorDeletedEvent}. This has a single
3121 @defvar NewInferiorEvent.inferior
3122 The inferior that is being removed, a @code{gdb.Inferior} object.
3125 @item events.new_thread
3126 This is emitted when @value{GDBN} notices a new thread. The event is of
3127 type @code{gdb.NewThreadEvent}, which extends @code{gdb.ThreadEvent}.
3128 This has a single attribute:
3130 @defvar NewThreadEvent.inferior_thread
3136 @node Threads In Python
3137 @subsubsection Threads In Python
3138 @cindex threads in python
3140 @findex gdb.InferiorThread
3141 Python scripts can access information about, and manipulate inferior threads
3142 controlled by @value{GDBN}, via objects of the @code{gdb.InferiorThread} class.
3144 The following thread-related functions are available in the @code{gdb}
3147 @findex gdb.selected_thread
3148 @defun gdb.selected_thread ()
3149 This function returns the thread object for the selected thread. If there
3150 is no selected thread, this will return @code{None}.
3153 A @code{gdb.InferiorThread} object has the following attributes:
3155 @defvar InferiorThread.name
3156 The name of the thread. If the user specified a name using
3157 @code{thread name}, then this returns that name. Otherwise, if an
3158 OS-supplied name is available, then it is returned. Otherwise, this
3159 returns @code{None}.
3161 This attribute can be assigned to. The new value must be a string
3162 object, which sets the new name, or @code{None}, which removes any
3163 user-specified thread name.
3166 @defvar InferiorThread.num
3167 The per-inferior number of the thread, as assigned by GDB.
3170 @defvar InferiorThread.global_num
3171 The global ID of the thread, as assigned by GDB. You can use this to
3172 make Python breakpoints thread-specific, for example
3173 (@pxref{python_breakpoint_thread,,The Breakpoint.thread attribute}).
3176 @defvar InferiorThread.ptid
3177 ID of the thread, as assigned by the operating system. This attribute is a
3178 tuple containing three integers. The first is the Process ID (PID); the second
3179 is the Lightweight Process ID (LWPID), and the third is the Thread ID (TID).
3180 Either the LWPID or TID may be 0, which indicates that the operating system
3181 does not use that identifier.
3184 @defvar InferiorThread.inferior
3185 The inferior this thread belongs to. This attribute is represented as
3186 a @code{gdb.Inferior} object. This attribute is not writable.
3189 A @code{gdb.InferiorThread} object has the following methods:
3191 @defun InferiorThread.is_valid ()
3192 Returns @code{True} if the @code{gdb.InferiorThread} object is valid,
3193 @code{False} if not. A @code{gdb.InferiorThread} object will become
3194 invalid if the thread exits, or the inferior that the thread belongs
3195 is deleted. All other @code{gdb.InferiorThread} methods will throw an
3196 exception if it is invalid at the time the method is called.
3199 @defun InferiorThread.switch ()
3200 This changes @value{GDBN}'s currently selected thread to the one represented
3204 @defun InferiorThread.is_stopped ()
3205 Return a Boolean indicating whether the thread is stopped.
3208 @defun InferiorThread.is_running ()
3209 Return a Boolean indicating whether the thread is running.
3212 @defun InferiorThread.is_exited ()
3213 Return a Boolean indicating whether the thread is exited.
3216 @node Recordings In Python
3217 @subsubsection Recordings In Python
3218 @cindex recordings in python
3220 The following recordings-related functions
3221 (@pxref{Process Record and Replay}) are available in the @code{gdb}
3224 @defun gdb.start_recording (@r{[}method@r{]}, @r{[}format@r{]})
3225 Start a recording using the given @var{method} and @var{format}. If
3226 no @var{format} is given, the default format for the recording method
3227 is used. If no @var{method} is given, the default method will be used.
3228 Returns a @code{gdb.Record} object on success. Throw an exception on
3231 The following strings can be passed as @var{method}:
3237 @code{"btrace"}: Possible values for @var{format}: @code{"pt"},
3238 @code{"bts"} or leave out for default format.
3242 @defun gdb.current_recording ()
3243 Access a currently running recording. Return a @code{gdb.Record}
3244 object on success. Return @code{None} if no recording is currently
3248 @defun gdb.stop_recording ()
3249 Stop the current recording. Throw an exception if no recording is
3250 currently active. All record objects become invalid after this call.
3253 A @code{gdb.Record} object has the following attributes:
3255 @defvar Record.method
3256 A string with the current recording method, e.g.@: @code{full} or
3260 @defvar Record.format
3261 A string with the current recording format, e.g.@: @code{bt}, @code{pts} or
3265 @defvar Record.begin
3266 A method specific instruction object representing the first instruction
3271 A method specific instruction object representing the current
3272 instruction, that is not actually part of the recording.
3275 @defvar Record.replay_position
3276 The instruction representing the current replay position. If there is
3277 no replay active, this will be @code{None}.
3280 @defvar Record.instruction_history
3281 A list with all recorded instructions.
3284 @defvar Record.function_call_history
3285 A list with all recorded function call segments.
3288 A @code{gdb.Record} object has the following methods:
3290 @defun Record.goto (instruction)
3291 Move the replay position to the given @var{instruction}.
3294 The common @code{gdb.Instruction} class that recording method specific
3295 instruction objects inherit from, has the following attributes:
3297 @defvar Instruction.pc
3298 An integer representing this instruction's address.
3301 @defvar Instruction.data
3302 A buffer with the raw instruction data. In Python 3, the return value is a
3303 @code{memoryview} object.
3306 @defvar Instruction.decoded
3307 A human readable string with the disassembled instruction.
3310 @defvar Instruction.size
3311 The size of the instruction in bytes.
3314 Additionally @code{gdb.RecordInstruction} has the following attributes:
3316 @defvar RecordInstruction.number
3317 An integer identifying this instruction. @code{number} corresponds to
3318 the numbers seen in @code{record instruction-history}
3319 (@pxref{Process Record and Replay}).
3322 @defvar RecordInstruction.sal
3323 A @code{gdb.Symtab_and_line} object representing the associated symtab
3324 and line of this instruction. May be @code{None} if no debug information is
3328 @defvar RecordInstruction.is_speculative
3329 A boolean indicating whether the instruction was executed speculatively.
3332 If an error occured during recording or decoding a recording, this error is
3333 represented by a @code{gdb.RecordGap} object in the instruction list. It has
3334 the following attributes:
3336 @defvar RecordGap.number
3337 An integer identifying this gap. @code{number} corresponds to the numbers seen
3338 in @code{record instruction-history} (@pxref{Process Record and Replay}).
3341 @defvar RecordGap.error_code
3342 A numerical representation of the reason for the gap. The value is specific to
3343 the current recording method.
3346 @defvar RecordGap.error_string
3347 A human readable string with the reason for the gap.
3350 A @code{gdb.RecordFunctionSegment} object has the following attributes:
3352 @defvar RecordFunctionSegment.number
3353 An integer identifying this function segment. @code{number} corresponds to
3354 the numbers seen in @code{record function-call-history}
3355 (@pxref{Process Record and Replay}).
3358 @defvar RecordFunctionSegment.symbol
3359 A @code{gdb.Symbol} object representing the associated symbol. May be
3360 @code{None} if no debug information is available.
3363 @defvar RecordFunctionSegment.level
3364 An integer representing the function call's stack level. May be
3365 @code{None} if the function call is a gap.
3368 @defvar RecordFunctionSegment.instructions
3369 A list of @code{gdb.RecordInstruction} or @code{gdb.RecordGap} objects
3370 associated with this function call.
3373 @defvar RecordFunctionSegment.up
3374 A @code{gdb.RecordFunctionSegment} object representing the caller's
3375 function segment. If the call has not been recorded, this will be the
3376 function segment to which control returns. If neither the call nor the
3377 return have been recorded, this will be @code{None}.
3380 @defvar RecordFunctionSegment.prev
3381 A @code{gdb.RecordFunctionSegment} object representing the previous
3382 segment of this function call. May be @code{None}.
3385 @defvar RecordFunctionSegment.next
3386 A @code{gdb.RecordFunctionSegment} object representing the next segment of
3387 this function call. May be @code{None}.
3390 The following example demonstrates the usage of these objects and
3391 functions to create a function that will rewind a record to the last
3392 time a function in a different file was executed. This would typically
3393 be used to track the execution of user provided callback functions in a
3394 library which typically are not visible in a back trace.
3398 rec = gdb.current_recording ()
3402 insn = rec.instruction_history
3407 position = insn.index (rec.replay_position)
3411 filename = insn[position].sal.symtab.fullname ()
3415 for i in reversed (insn[:position]):
3417 current = i.sal.symtab.fullname ()
3421 if filename == current:
3428 Another possible application is to write a function that counts the
3429 number of code executions in a given line range. This line range can
3430 contain parts of functions or span across several functions and is not
3431 limited to be contiguous.
3434 def countrange (filename, linerange):
3437 def filter_only (file_name):
3438 for call in gdb.current_recording ().function_call_history:
3440 if file_name in call.symbol.symtab.fullname ():
3445 for c in filter_only (filename):
3446 for i in c.instructions:
3448 if i.sal.line in linerange:
3457 @node Commands In Python
3458 @subsubsection Commands In Python
3460 @cindex commands in python
3461 @cindex python commands
3462 You can implement new @value{GDBN} CLI commands in Python. A CLI
3463 command is implemented using an instance of the @code{gdb.Command}
3464 class, most commonly using a subclass.
3466 @defun Command.__init__ (name, @var{command_class} @r{[}, @var{completer_class} @r{[}, @var{prefix}@r{]]})
3467 The object initializer for @code{Command} registers the new command
3468 with @value{GDBN}. This initializer is normally invoked from the
3469 subclass' own @code{__init__} method.
3471 @var{name} is the name of the command. If @var{name} consists of
3472 multiple words, then the initial words are looked for as prefix
3473 commands. In this case, if one of the prefix commands does not exist,
3474 an exception is raised.
3476 There is no support for multi-line commands.
3478 @var{command_class} should be one of the @samp{COMMAND_} constants
3479 defined below. This argument tells @value{GDBN} how to categorize the
3480 new command in the help system.
3482 @var{completer_class} is an optional argument. If given, it should be
3483 one of the @samp{COMPLETE_} constants defined below. This argument
3484 tells @value{GDBN} how to perform completion for this command. If not
3485 given, @value{GDBN} will attempt to complete using the object's
3486 @code{complete} method (see below); if no such method is found, an
3487 error will occur when completion is attempted.
3489 @var{prefix} is an optional argument. If @code{True}, then the new
3490 command is a prefix command; sub-commands of this command may be
3493 The help text for the new command is taken from the Python
3494 documentation string for the command's class, if there is one. If no
3495 documentation string is provided, the default value ``This command is
3496 not documented.'' is used.
3499 @cindex don't repeat Python command
3500 @defun Command.dont_repeat ()
3501 By default, a @value{GDBN} command is repeated when the user enters a
3502 blank line at the command prompt. A command can suppress this
3503 behavior by invoking the @code{dont_repeat} method. This is similar
3504 to the user command @code{dont-repeat}, see @ref{Define, dont-repeat}.
3507 @defun Command.invoke (argument, from_tty)
3508 This method is called by @value{GDBN} when this command is invoked.
3510 @var{argument} is a string. It is the argument to the command, after
3511 leading and trailing whitespace has been stripped.
3513 @var{from_tty} is a boolean argument. When true, this means that the
3514 command was entered by the user at the terminal; when false it means
3515 that the command came from elsewhere.
3517 If this method throws an exception, it is turned into a @value{GDBN}
3518 @code{error} call. Otherwise, the return value is ignored.
3520 @findex gdb.string_to_argv
3521 To break @var{argument} up into an argv-like string use
3522 @code{gdb.string_to_argv}. This function behaves identically to
3523 @value{GDBN}'s internal argument lexer @code{buildargv}.
3524 It is recommended to use this for consistency.
3525 Arguments are separated by spaces and may be quoted.
3529 print gdb.string_to_argv ("1 2\ \\\"3 '4 \"5' \"6 '7\"")
3530 ['1', '2 "3', '4 "5', "6 '7"]
3535 @cindex completion of Python commands
3536 @defun Command.complete (text, word)
3537 This method is called by @value{GDBN} when the user attempts
3538 completion on this command. All forms of completion are handled by
3539 this method, that is, the @key{TAB} and @key{M-?} key bindings
3540 (@pxref{Completion}), and the @code{complete} command (@pxref{Help,
3543 The arguments @var{text} and @var{word} are both strings; @var{text}
3544 holds the complete command line up to the cursor's location, while
3545 @var{word} holds the last word of the command line; this is computed
3546 using a word-breaking heuristic.
3548 The @code{complete} method can return several values:
3551 If the return value is a sequence, the contents of the sequence are
3552 used as the completions. It is up to @code{complete} to ensure that the
3553 contents actually do complete the word. A zero-length sequence is
3554 allowed, it means that there were no completions available. Only
3555 string elements of the sequence are used; other elements in the
3556 sequence are ignored.
3559 If the return value is one of the @samp{COMPLETE_} constants defined
3560 below, then the corresponding @value{GDBN}-internal completion
3561 function is invoked, and its result is used.
3564 All other results are treated as though there were no available
3569 When a new command is registered, it must be declared as a member of
3570 some general class of commands. This is used to classify top-level
3571 commands in the on-line help system; note that prefix commands are not
3572 listed under their own category but rather that of their top-level
3573 command. The available classifications are represented by constants
3574 defined in the @code{gdb} module:
3577 @findex COMMAND_NONE
3578 @findex gdb.COMMAND_NONE
3579 @item gdb.COMMAND_NONE
3580 The command does not belong to any particular class. A command in
3581 this category will not be displayed in any of the help categories.
3583 @findex COMMAND_RUNNING
3584 @findex gdb.COMMAND_RUNNING
3585 @item gdb.COMMAND_RUNNING
3586 The command is related to running the inferior. For example,
3587 @code{start}, @code{step}, and @code{continue} are in this category.
3588 Type @kbd{help running} at the @value{GDBN} prompt to see a list of
3589 commands in this category.
3591 @findex COMMAND_DATA
3592 @findex gdb.COMMAND_DATA
3593 @item gdb.COMMAND_DATA
3594 The command is related to data or variables. For example,
3595 @code{call}, @code{find}, and @code{print} are in this category. Type
3596 @kbd{help data} at the @value{GDBN} prompt to see a list of commands
3599 @findex COMMAND_STACK
3600 @findex gdb.COMMAND_STACK
3601 @item gdb.COMMAND_STACK
3602 The command has to do with manipulation of the stack. For example,
3603 @code{backtrace}, @code{frame}, and @code{return} are in this
3604 category. Type @kbd{help stack} at the @value{GDBN} prompt to see a
3605 list of commands in this category.
3607 @findex COMMAND_FILES
3608 @findex gdb.COMMAND_FILES
3609 @item gdb.COMMAND_FILES
3610 This class is used for file-related commands. For example,
3611 @code{file}, @code{list} and @code{section} are in this category.
3612 Type @kbd{help files} at the @value{GDBN} prompt to see a list of
3613 commands in this category.
3615 @findex COMMAND_SUPPORT
3616 @findex gdb.COMMAND_SUPPORT
3617 @item gdb.COMMAND_SUPPORT
3618 This should be used for ``support facilities'', generally meaning
3619 things that are useful to the user when interacting with @value{GDBN},
3620 but not related to the state of the inferior. For example,
3621 @code{help}, @code{make}, and @code{shell} are in this category. Type
3622 @kbd{help support} at the @value{GDBN} prompt to see a list of
3623 commands in this category.
3625 @findex COMMAND_STATUS
3626 @findex gdb.COMMAND_STATUS
3627 @item gdb.COMMAND_STATUS
3628 The command is an @samp{info}-related command, that is, related to the
3629 state of @value{GDBN} itself. For example, @code{info}, @code{macro},
3630 and @code{show} are in this category. Type @kbd{help status} at the
3631 @value{GDBN} prompt to see a list of commands in this category.
3633 @findex COMMAND_BREAKPOINTS
3634 @findex gdb.COMMAND_BREAKPOINTS
3635 @item gdb.COMMAND_BREAKPOINTS
3636 The command has to do with breakpoints. For example, @code{break},
3637 @code{clear}, and @code{delete} are in this category. Type @kbd{help
3638 breakpoints} at the @value{GDBN} prompt to see a list of commands in
3641 @findex COMMAND_TRACEPOINTS
3642 @findex gdb.COMMAND_TRACEPOINTS
3643 @item gdb.COMMAND_TRACEPOINTS
3644 The command has to do with tracepoints. For example, @code{trace},
3645 @code{actions}, and @code{tfind} are in this category. Type
3646 @kbd{help tracepoints} at the @value{GDBN} prompt to see a list of
3647 commands in this category.
3649 @findex COMMAND_USER
3650 @findex gdb.COMMAND_USER
3651 @item gdb.COMMAND_USER
3652 The command is a general purpose command for the user, and typically
3653 does not fit in one of the other categories.
3654 Type @kbd{help user-defined} at the @value{GDBN} prompt to see
3655 a list of commands in this category, as well as the list of gdb macros
3656 (@pxref{Sequences}).
3658 @findex COMMAND_OBSCURE
3659 @findex gdb.COMMAND_OBSCURE
3660 @item gdb.COMMAND_OBSCURE
3661 The command is only used in unusual circumstances, or is not of
3662 general interest to users. For example, @code{checkpoint},
3663 @code{fork}, and @code{stop} are in this category. Type @kbd{help
3664 obscure} at the @value{GDBN} prompt to see a list of commands in this
3667 @findex COMMAND_MAINTENANCE
3668 @findex gdb.COMMAND_MAINTENANCE
3669 @item gdb.COMMAND_MAINTENANCE
3670 The command is only useful to @value{GDBN} maintainers. The
3671 @code{maintenance} and @code{flushregs} commands are in this category.
3672 Type @kbd{help internals} at the @value{GDBN} prompt to see a list of
3673 commands in this category.
3676 A new command can use a predefined completion function, either by
3677 specifying it via an argument at initialization, or by returning it
3678 from the @code{complete} method. These predefined completion
3679 constants are all defined in the @code{gdb} module:
3682 @vindex COMPLETE_NONE
3683 @item gdb.COMPLETE_NONE
3684 This constant means that no completion should be done.
3686 @vindex COMPLETE_FILENAME
3687 @item gdb.COMPLETE_FILENAME
3688 This constant means that filename completion should be performed.
3690 @vindex COMPLETE_LOCATION
3691 @item gdb.COMPLETE_LOCATION
3692 This constant means that location completion should be done.
3693 @xref{Specify Location}.
3695 @vindex COMPLETE_COMMAND
3696 @item gdb.COMPLETE_COMMAND
3697 This constant means that completion should examine @value{GDBN}
3700 @vindex COMPLETE_SYMBOL
3701 @item gdb.COMPLETE_SYMBOL
3702 This constant means that completion should be done using symbol names
3705 @vindex COMPLETE_EXPRESSION
3706 @item gdb.COMPLETE_EXPRESSION
3707 This constant means that completion should be done on expressions.
3708 Often this means completing on symbol names, but some language
3709 parsers also have support for completing on field names.
3712 The following code snippet shows how a trivial CLI command can be
3713 implemented in Python:
3716 class HelloWorld (gdb.Command):
3717 """Greet the whole world."""
3719 def __init__ (self):
3720 super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)
3722 def invoke (self, arg, from_tty):
3723 print "Hello, World!"
3728 The last line instantiates the class, and is necessary to trigger the
3729 registration of the command with @value{GDBN}. Depending on how the
3730 Python code is read into @value{GDBN}, you may need to import the
3731 @code{gdb} module explicitly.
3733 @node Parameters In Python
3734 @subsubsection Parameters In Python
3736 @cindex parameters in python
3737 @cindex python parameters
3738 @tindex gdb.Parameter
3740 You can implement new @value{GDBN} parameters using Python. A new
3741 parameter is implemented as an instance of the @code{gdb.Parameter}
3744 Parameters are exposed to the user via the @code{set} and
3745 @code{show} commands. @xref{Help}.
3747 There are many parameters that already exist and can be set in
3748 @value{GDBN}. Two examples are: @code{set follow fork} and
3749 @code{set charset}. Setting these parameters influences certain
3750 behavior in @value{GDBN}. Similarly, you can define parameters that
3751 can be used to influence behavior in custom Python scripts and commands.
3753 @defun Parameter.__init__ (name, @var{command-class}, @var{parameter-class} @r{[}, @var{enum-sequence}@r{]})
3754 The object initializer for @code{Parameter} registers the new
3755 parameter with @value{GDBN}. This initializer is normally invoked
3756 from the subclass' own @code{__init__} method.
3758 @var{name} is the name of the new parameter. If @var{name} consists
3759 of multiple words, then the initial words are looked for as prefix
3760 parameters. An example of this can be illustrated with the
3761 @code{set print} set of parameters. If @var{name} is
3762 @code{print foo}, then @code{print} will be searched as the prefix
3763 parameter. In this case the parameter can subsequently be accessed in
3764 @value{GDBN} as @code{set print foo}.
3766 If @var{name} consists of multiple words, and no prefix parameter group
3767 can be found, an exception is raised.
3769 @var{command-class} should be one of the @samp{COMMAND_} constants
3770 (@pxref{Commands In Python}). This argument tells @value{GDBN} how to
3771 categorize the new parameter in the help system.
3773 @var{parameter-class} should be one of the @samp{PARAM_} constants
3774 defined below. This argument tells @value{GDBN} the type of the new
3775 parameter; this information is used for input validation and
3778 If @var{parameter-class} is @code{PARAM_ENUM}, then
3779 @var{enum-sequence} must be a sequence of strings. These strings
3780 represent the possible values for the parameter.
3782 If @var{parameter-class} is not @code{PARAM_ENUM}, then the presence
3783 of a fourth argument will cause an exception to be thrown.
3785 The help text for the new parameter is taken from the Python
3786 documentation string for the parameter's class, if there is one. If
3787 there is no documentation string, a default value is used.
3790 @defvar Parameter.set_doc
3791 If this attribute exists, and is a string, then its value is used as
3792 the help text for this parameter's @code{set} command. The value is
3793 examined when @code{Parameter.__init__} is invoked; subsequent changes
3797 @defvar Parameter.show_doc
3798 If this attribute exists, and is a string, then its value is used as
3799 the help text for this parameter's @code{show} command. The value is
3800 examined when @code{Parameter.__init__} is invoked; subsequent changes
3804 @defvar Parameter.value
3805 The @code{value} attribute holds the underlying value of the
3806 parameter. It can be read and assigned to just as any other
3807 attribute. @value{GDBN} does validation when assignments are made.
3810 There are two methods that may be implemented in any @code{Parameter}
3813 @defun Parameter.get_set_string (self)
3814 If this method exists, @value{GDBN} will call it when a
3815 @var{parameter}'s value has been changed via the @code{set} API (for
3816 example, @kbd{set foo off}). The @code{value} attribute has already
3817 been populated with the new value and may be used in output. This
3818 method must return a string. If the returned string is not empty,
3819 @value{GDBN} will present it to the user.
3822 @defun Parameter.get_show_string (self, svalue)
3823 @value{GDBN} will call this method when a @var{parameter}'s
3824 @code{show} API has been invoked (for example, @kbd{show foo}). The
3825 argument @code{svalue} receives the string representation of the
3826 current value. This method must return a string.
3829 When a new parameter is defined, its type must be specified. The
3830 available types are represented by constants defined in the @code{gdb}
3834 @findex PARAM_BOOLEAN
3835 @findex gdb.PARAM_BOOLEAN
3836 @item gdb.PARAM_BOOLEAN
3837 The value is a plain boolean. The Python boolean values, @code{True}
3838 and @code{False} are the only valid values.
3840 @findex PARAM_AUTO_BOOLEAN
3841 @findex gdb.PARAM_AUTO_BOOLEAN
3842 @item gdb.PARAM_AUTO_BOOLEAN
3843 The value has three possible states: true, false, and @samp{auto}. In
3844 Python, true and false are represented using boolean constants, and
3845 @samp{auto} is represented using @code{None}.
3847 @findex PARAM_UINTEGER
3848 @findex gdb.PARAM_UINTEGER
3849 @item gdb.PARAM_UINTEGER
3850 The value is an unsigned integer. The value of 0 should be
3851 interpreted to mean ``unlimited''.
3853 @findex PARAM_INTEGER
3854 @findex gdb.PARAM_INTEGER
3855 @item gdb.PARAM_INTEGER
3856 The value is a signed integer. The value of 0 should be interpreted
3857 to mean ``unlimited''.
3859 @findex PARAM_STRING
3860 @findex gdb.PARAM_STRING
3861 @item gdb.PARAM_STRING
3862 The value is a string. When the user modifies the string, any escape
3863 sequences, such as @samp{\t}, @samp{\f}, and octal escapes, are
3864 translated into corresponding characters and encoded into the current
3867 @findex PARAM_STRING_NOESCAPE
3868 @findex gdb.PARAM_STRING_NOESCAPE
3869 @item gdb.PARAM_STRING_NOESCAPE
3870 The value is a string. When the user modifies the string, escapes are
3871 passed through untranslated.
3873 @findex PARAM_OPTIONAL_FILENAME
3874 @findex gdb.PARAM_OPTIONAL_FILENAME
3875 @item gdb.PARAM_OPTIONAL_FILENAME
3876 The value is a either a filename (a string), or @code{None}.
3878 @findex PARAM_FILENAME
3879 @findex gdb.PARAM_FILENAME
3880 @item gdb.PARAM_FILENAME
3881 The value is a filename. This is just like
3882 @code{PARAM_STRING_NOESCAPE}, but uses file names for completion.
3884 @findex PARAM_ZINTEGER
3885 @findex gdb.PARAM_ZINTEGER
3886 @item gdb.PARAM_ZINTEGER
3887 The value is an integer. This is like @code{PARAM_INTEGER}, except 0
3888 is interpreted as itself.
3890 @findex PARAM_ZUINTEGER
3891 @findex gdb.PARAM_ZUINTEGER
3892 @item gdb.PARAM_ZUINTEGER
3893 The value is an unsigned integer. This is like @code{PARAM_INTEGER},
3894 except 0 is interpreted as itself, and the value cannot be negative.
3896 @findex PARAM_ZUINTEGER_UNLIMITED
3897 @findex gdb.PARAM_ZUINTEGER_UNLIMITED
3898 @item gdb.PARAM_ZUINTEGER_UNLIMITED
3899 The value is a signed integer. This is like @code{PARAM_ZUINTEGER},
3900 except the special value -1 should be interpreted to mean
3901 ``unlimited''. Other negative values are not allowed.
3904 @findex gdb.PARAM_ENUM
3905 @item gdb.PARAM_ENUM
3906 The value is a string, which must be one of a collection string
3907 constants provided when the parameter is created.
3910 @node Functions In Python
3911 @subsubsection Writing new convenience functions
3913 @cindex writing convenience functions
3914 @cindex convenience functions in python
3915 @cindex python convenience functions
3916 @tindex gdb.Function
3918 You can implement new convenience functions (@pxref{Convenience Vars})
3919 in Python. A convenience function is an instance of a subclass of the
3920 class @code{gdb.Function}.
3922 @defun Function.__init__ (name)
3923 The initializer for @code{Function} registers the new function with
3924 @value{GDBN}. The argument @var{name} is the name of the function,
3925 a string. The function will be visible to the user as a convenience
3926 variable of type @code{internal function}, whose name is the same as
3927 the given @var{name}.
3929 The documentation for the new function is taken from the documentation
3930 string for the new class.
3933 @defun Function.invoke (@var{*args})
3934 When a convenience function is evaluated, its arguments are converted
3935 to instances of @code{gdb.Value}, and then the function's
3936 @code{invoke} method is called. Note that @value{GDBN} does not
3937 predetermine the arity of convenience functions. Instead, all
3938 available arguments are passed to @code{invoke}, following the
3939 standard Python calling convention. In particular, a convenience
3940 function can have default values for parameters without ill effect.
3942 The return value of this method is used as its value in the enclosing
3943 expression. If an ordinary Python value is returned, it is converted
3944 to a @code{gdb.Value} following the usual rules.
3947 The following code snippet shows how a trivial convenience function can
3948 be implemented in Python:
3951 class Greet (gdb.Function):
3952 """Return string to greet someone.
3953 Takes a name as argument."""
3955 def __init__ (self):
3956 super (Greet, self).__init__ ("greet")
3958 def invoke (self, name):
3959 return "Hello, %s!" % name.string ()
3964 The last line instantiates the class, and is necessary to trigger the
3965 registration of the function with @value{GDBN}. Depending on how the
3966 Python code is read into @value{GDBN}, you may need to import the
3967 @code{gdb} module explicitly.
3969 Now you can use the function in an expression:
3972 (gdb) print $greet("Bob")
3976 @node Progspaces In Python
3977 @subsubsection Program Spaces In Python
3979 @cindex progspaces in python
3980 @tindex gdb.Progspace
3982 A program space, or @dfn{progspace}, represents a symbolic view
3983 of an address space.
3984 It consists of all of the objfiles of the program.
3985 @xref{Objfiles In Python}.
3986 @xref{Inferiors and Programs, program spaces}, for more details
3987 about program spaces.
3989 The following progspace-related functions are available in the
3992 @findex gdb.current_progspace
3993 @defun gdb.current_progspace ()
3994 This function returns the program space of the currently selected inferior.
3995 @xref{Inferiors and Programs}.
3998 @findex gdb.progspaces
3999 @defun gdb.progspaces ()
4000 Return a sequence of all the progspaces currently known to @value{GDBN}.
4003 Each progspace is represented by an instance of the @code{gdb.Progspace}
4006 @defvar Progspace.filename
4007 The file name of the progspace as a string.
4010 @defvar Progspace.pretty_printers
4011 The @code{pretty_printers} attribute is a list of functions. It is
4012 used to look up pretty-printers. A @code{Value} is passed to each
4013 function in order; if the function returns @code{None}, then the
4014 search continues. Otherwise, the return value should be an object
4015 which is used to format the value. @xref{Pretty Printing API}, for more
4019 @defvar Progspace.type_printers
4020 The @code{type_printers} attribute is a list of type printer objects.
4021 @xref{Type Printing API}, for more information.
4024 @defvar Progspace.frame_filters
4025 The @code{frame_filters} attribute is a dictionary of frame filter
4026 objects. @xref{Frame Filter API}, for more information.
4029 One may add arbitrary attributes to @code{gdb.Progspace} objects
4030 in the usual Python way.
4031 This is useful if, for example, one needs to do some extra record keeping
4032 associated with the program space.
4034 In this contrived example, we want to perform some processing when
4035 an objfile with a certain symbol is loaded, but we only want to do
4036 this once because it is expensive. To achieve this we record the results
4037 with the program space because we can't predict when the desired objfile
4042 def clear_objfiles_handler(event):
4043 event.progspace.expensive_computation = None
4044 def expensive(symbol):
4045 """A mock routine to perform an "expensive" computation on symbol."""
4046 print "Computing the answer to the ultimate question ..."
4048 def new_objfile_handler(event):
4049 objfile = event.new_objfile
4050 progspace = objfile.progspace
4051 if not hasattr(progspace, 'expensive_computation') or \
4052 progspace.expensive_computation is None:
4053 # We use 'main' for the symbol to keep the example simple.
4054 # Note: There's no current way to constrain the lookup
4056 symbol = gdb.lookup_global_symbol('main')
4057 if symbol is not None:
4058 progspace.expensive_computation = expensive(symbol)
4059 gdb.events.clear_objfiles.connect(clear_objfiles_handler)
4060 gdb.events.new_objfile.connect(new_objfile_handler)
4062 (gdb) file /tmp/hello
4063 Reading symbols from /tmp/hello...done.
4064 Computing the answer to the ultimate question ...
4065 (gdb) python print gdb.current_progspace().expensive_computation
4068 Starting program: /tmp/hello
4070 [Inferior 1 (process 4242) exited normally]
4073 @node Objfiles In Python
4074 @subsubsection Objfiles In Python
4076 @cindex objfiles in python
4079 @value{GDBN} loads symbols for an inferior from various
4080 symbol-containing files (@pxref{Files}). These include the primary
4081 executable file, any shared libraries used by the inferior, and any
4082 separate debug info files (@pxref{Separate Debug Files}).
4083 @value{GDBN} calls these symbol-containing files @dfn{objfiles}.
4085 The following objfile-related functions are available in the
4088 @findex gdb.current_objfile
4089 @defun gdb.current_objfile ()
4090 When auto-loading a Python script (@pxref{Python Auto-loading}), @value{GDBN}
4091 sets the ``current objfile'' to the corresponding objfile. This
4092 function returns the current objfile. If there is no current objfile,
4093 this function returns @code{None}.
4096 @findex gdb.objfiles
4097 @defun gdb.objfiles ()
4098 Return a sequence of all the objfiles current known to @value{GDBN}.
4099 @xref{Objfiles In Python}.
4102 @findex gdb.lookup_objfile
4103 @defun gdb.lookup_objfile (name @r{[}, by_build_id{]})
4104 Look up @var{name}, a file name or build ID, in the list of objfiles
4105 for the current program space (@pxref{Progspaces In Python}).
4106 If the objfile is not found throw the Python @code{ValueError} exception.
4108 If @var{name} is a relative file name, then it will match any
4109 source file name with the same trailing components. For example, if
4110 @var{name} is @samp{gcc/expr.c}, then it will match source file
4111 name of @file{/build/trunk/gcc/expr.c}, but not
4112 @file{/build/trunk/libcpp/expr.c} or @file{/build/trunk/gcc/x-expr.c}.
4114 If @var{by_build_id} is provided and is @code{True} then @var{name}
4115 is the build ID of the objfile. Otherwise, @var{name} is a file name.
4116 This is supported only on some operating systems, notably those which use
4117 the ELF format for binary files and the @sc{gnu} Binutils. For more details
4118 about this feature, see the description of the @option{--build-id}
4119 command-line option in @ref{Options, , Command Line Options, ld,
4123 Each objfile is represented by an instance of the @code{gdb.Objfile}
4126 @defvar Objfile.filename
4127 The file name of the objfile as a string, with symbolic links resolved.
4129 The value is @code{None} if the objfile is no longer valid.
4130 See the @code{gdb.Objfile.is_valid} method, described below.
4133 @defvar Objfile.username
4134 The file name of the objfile as specified by the user as a string.
4136 The value is @code{None} if the objfile is no longer valid.
4137 See the @code{gdb.Objfile.is_valid} method, described below.
4140 @defvar Objfile.owner
4141 For separate debug info objfiles this is the corresponding @code{gdb.Objfile}
4142 object that debug info is being provided for.
4143 Otherwise this is @code{None}.
4144 Separate debug info objfiles are added with the
4145 @code{gdb.Objfile.add_separate_debug_file} method, described below.
4148 @defvar Objfile.build_id
4149 The build ID of the objfile as a string.
4150 If the objfile does not have a build ID then the value is @code{None}.
4152 This is supported only on some operating systems, notably those which use
4153 the ELF format for binary files and the @sc{gnu} Binutils. For more details
4154 about this feature, see the description of the @option{--build-id}
4155 command-line option in @ref{Options, , Command Line Options, ld,
4159 @defvar Objfile.progspace
4160 The containing program space of the objfile as a @code{gdb.Progspace}
4161 object. @xref{Progspaces In Python}.
4164 @defvar Objfile.pretty_printers
4165 The @code{pretty_printers} attribute is a list of functions. It is
4166 used to look up pretty-printers. A @code{Value} is passed to each
4167 function in order; if the function returns @code{None}, then the
4168 search continues. Otherwise, the return value should be an object
4169 which is used to format the value. @xref{Pretty Printing API}, for more
4173 @defvar Objfile.type_printers
4174 The @code{type_printers} attribute is a list of type printer objects.
4175 @xref{Type Printing API}, for more information.
4178 @defvar Objfile.frame_filters
4179 The @code{frame_filters} attribute is a dictionary of frame filter
4180 objects. @xref{Frame Filter API}, for more information.
4183 One may add arbitrary attributes to @code{gdb.Objfile} objects
4184 in the usual Python way.
4185 This is useful if, for example, one needs to do some extra record keeping
4186 associated with the objfile.
4188 In this contrived example we record the time when @value{GDBN}
4194 def new_objfile_handler(event):
4195 # Set the time_loaded attribute of the new objfile.
4196 event.new_objfile.time_loaded = datetime.datetime.today()
4197 gdb.events.new_objfile.connect(new_objfile_handler)
4200 Reading symbols from ./hello...done.
4201 (gdb) python print gdb.objfiles()[0].time_loaded
4202 2014-10-09 11:41:36.770345
4205 A @code{gdb.Objfile} object has the following methods:
4207 @defun Objfile.is_valid ()
4208 Returns @code{True} if the @code{gdb.Objfile} object is valid,
4209 @code{False} if not. A @code{gdb.Objfile} object can become invalid
4210 if the object file it refers to is not loaded in @value{GDBN} any
4211 longer. All other @code{gdb.Objfile} methods will throw an exception
4212 if it is invalid at the time the method is called.
4215 @defun Objfile.add_separate_debug_file (file)
4216 Add @var{file} to the list of files that @value{GDBN} will search for
4217 debug information for the objfile.
4218 This is useful when the debug info has been removed from the program
4219 and stored in a separate file. @value{GDBN} has built-in support for
4220 finding separate debug info files (@pxref{Separate Debug Files}), but if
4221 the file doesn't live in one of the standard places that @value{GDBN}
4222 searches then this function can be used to add a debug info file
4223 from a different place.
4226 @node Frames In Python
4227 @subsubsection Accessing inferior stack frames from Python.
4229 @cindex frames in python
4230 When the debugged program stops, @value{GDBN} is able to analyze its call
4231 stack (@pxref{Frames,,Stack frames}). The @code{gdb.Frame} class
4232 represents a frame in the stack. A @code{gdb.Frame} object is only valid
4233 while its corresponding frame exists in the inferior's stack. If you try
4234 to use an invalid frame object, @value{GDBN} will throw a @code{gdb.error}
4235 exception (@pxref{Exception Handling}).
4237 Two @code{gdb.Frame} objects can be compared for equality with the @code{==}
4241 (@value{GDBP}) python print gdb.newest_frame() == gdb.selected_frame ()
4245 The following frame-related functions are available in the @code{gdb} module:
4247 @findex gdb.selected_frame
4248 @defun gdb.selected_frame ()
4249 Return the selected frame object. (@pxref{Selection,,Selecting a Frame}).
4252 @findex gdb.newest_frame
4253 @defun gdb.newest_frame ()
4254 Return the newest frame object for the selected thread.
4257 @defun gdb.frame_stop_reason_string (reason)
4258 Return a string explaining the reason why @value{GDBN} stopped unwinding
4259 frames, as expressed by the given @var{reason} code (an integer, see the
4260 @code{unwind_stop_reason} method further down in this section).
4263 @findex gdb.invalidate_cached_frames
4264 @defun gdb.invalidate_cached_frames
4265 @value{GDBN} internally keeps a cache of the frames that have been
4266 unwound. This function invalidates this cache.
4268 This function should not generally be called by ordinary Python code.
4269 It is documented for the sake of completeness.
4272 A @code{gdb.Frame} object has the following methods:
4274 @defun Frame.is_valid ()
4275 Returns true if the @code{gdb.Frame} object is valid, false if not.
4276 A frame object can become invalid if the frame it refers to doesn't
4277 exist anymore in the inferior. All @code{gdb.Frame} methods will throw
4278 an exception if it is invalid at the time the method is called.
4281 @defun Frame.name ()
4282 Returns the function name of the frame, or @code{None} if it can't be
4286 @defun Frame.architecture ()
4287 Returns the @code{gdb.Architecture} object corresponding to the frame's
4288 architecture. @xref{Architectures In Python}.
4291 @defun Frame.type ()
4292 Returns the type of the frame. The value can be one of:
4294 @item gdb.NORMAL_FRAME
4295 An ordinary stack frame.
4297 @item gdb.DUMMY_FRAME
4298 A fake stack frame that was created by @value{GDBN} when performing an
4299 inferior function call.
4301 @item gdb.INLINE_FRAME
4302 A frame representing an inlined function. The function was inlined
4303 into a @code{gdb.NORMAL_FRAME} that is older than this one.
4305 @item gdb.TAILCALL_FRAME
4306 A frame representing a tail call. @xref{Tail Call Frames}.
4308 @item gdb.SIGTRAMP_FRAME
4309 A signal trampoline frame. This is the frame created by the OS when
4310 it calls into a signal handler.
4312 @item gdb.ARCH_FRAME
4313 A fake stack frame representing a cross-architecture call.
4315 @item gdb.SENTINEL_FRAME
4316 This is like @code{gdb.NORMAL_FRAME}, but it is only used for the
4321 @defun Frame.unwind_stop_reason ()
4322 Return an integer representing the reason why it's not possible to find
4323 more frames toward the outermost frame. Use
4324 @code{gdb.frame_stop_reason_string} to convert the value returned by this
4325 function to a string. The value can be one of:
4328 @item gdb.FRAME_UNWIND_NO_REASON
4329 No particular reason (older frames should be available).
4331 @item gdb.FRAME_UNWIND_NULL_ID
4332 The previous frame's analyzer returns an invalid result. This is no
4333 longer used by @value{GDBN}, and is kept only for backward
4336 @item gdb.FRAME_UNWIND_OUTERMOST
4337 This frame is the outermost.
4339 @item gdb.FRAME_UNWIND_UNAVAILABLE
4340 Cannot unwind further, because that would require knowing the
4341 values of registers or memory that have not been collected.
4343 @item gdb.FRAME_UNWIND_INNER_ID
4344 This frame ID looks like it ought to belong to a NEXT frame,
4345 but we got it for a PREV frame. Normally, this is a sign of
4346 unwinder failure. It could also indicate stack corruption.
4348 @item gdb.FRAME_UNWIND_SAME_ID
4349 This frame has the same ID as the previous one. That means
4350 that unwinding further would almost certainly give us another
4351 frame with exactly the same ID, so break the chain. Normally,
4352 this is a sign of unwinder failure. It could also indicate
4355 @item gdb.FRAME_UNWIND_NO_SAVED_PC
4356 The frame unwinder did not find any saved PC, but we needed
4357 one to unwind further.
4359 @item gdb.FRAME_UNWIND_MEMORY_ERROR
4360 The frame unwinder caused an error while trying to access memory.
4362 @item gdb.FRAME_UNWIND_FIRST_ERROR
4363 Any stop reason greater or equal to this value indicates some kind
4364 of error. This special value facilitates writing code that tests
4365 for errors in unwinding in a way that will work correctly even if
4366 the list of the other values is modified in future @value{GDBN}
4367 versions. Using it, you could write:
4369 reason = gdb.selected_frame().unwind_stop_reason ()
4370 reason_str = gdb.frame_stop_reason_string (reason)
4371 if reason >= gdb.FRAME_UNWIND_FIRST_ERROR:
4372 print "An error occured: %s" % reason_str
4379 Returns the frame's resume address.
4382 @defun Frame.block ()
4383 Return the frame's code block. @xref{Blocks In Python}. If the frame
4384 does not have a block -- for example, if there is no debugging
4385 information for the code in question -- then this will throw an
4389 @defun Frame.function ()
4390 Return the symbol for the function corresponding to this frame.
4391 @xref{Symbols In Python}.
4394 @defun Frame.older ()
4395 Return the frame that called this frame.
4398 @defun Frame.newer ()
4399 Return the frame called by this frame.
4402 @defun Frame.find_sal ()
4403 Return the frame's symtab and line object.
4404 @xref{Symbol Tables In Python}.
4407 @defun Frame.read_register (register)
4408 Return the value of @var{register} in this frame. The @var{register}
4409 argument must be a string (e.g., @code{'sp'} or @code{'rax'}).
4410 Returns a @code{Gdb.Value} object. Throws an exception if @var{register}
4414 @defun Frame.read_var (variable @r{[}, block@r{]})
4415 Return the value of @var{variable} in this frame. If the optional
4416 argument @var{block} is provided, search for the variable from that
4417 block; otherwise start at the frame's current block (which is
4418 determined by the frame's current program counter). The @var{variable}
4419 argument must be a string or a @code{gdb.Symbol} object; @var{block} must be a
4420 @code{gdb.Block} object.
4423 @defun Frame.select ()
4424 Set this frame to be the selected frame. @xref{Stack, ,Examining the
4428 @node Blocks In Python
4429 @subsubsection Accessing blocks from Python.
4431 @cindex blocks in python
4434 In @value{GDBN}, symbols are stored in blocks. A block corresponds
4435 roughly to a scope in the source code. Blocks are organized
4436 hierarchically, and are represented individually in Python as a
4437 @code{gdb.Block}. Blocks rely on debugging information being
4440 A frame has a block. Please see @ref{Frames In Python}, for a more
4441 in-depth discussion of frames.
4443 The outermost block is known as the @dfn{global block}. The global
4444 block typically holds public global variables and functions.
4446 The block nested just inside the global block is the @dfn{static
4447 block}. The static block typically holds file-scoped variables and
4450 @value{GDBN} provides a method to get a block's superblock, but there
4451 is currently no way to examine the sub-blocks of a block, or to
4452 iterate over all the blocks in a symbol table (@pxref{Symbol Tables In
4455 Here is a short example that should help explain blocks:
4458 /* This is in the global block. */
4461 /* This is in the static block. */
4462 static int file_scope;
4464 /* 'function' is in the global block, and 'argument' is
4465 in a block nested inside of 'function'. */
4466 int function (int argument)
4468 /* 'local' is in a block inside 'function'. It may or may
4469 not be in the same block as 'argument'. */
4473 /* 'inner' is in a block whose superblock is the one holding
4477 /* If this call is expanded by the compiler, you may see
4478 a nested block here whose function is 'inline_function'
4479 and whose superblock is the one holding 'inner'. */
4485 A @code{gdb.Block} is iterable. The iterator returns the symbols
4486 (@pxref{Symbols In Python}) local to the block. Python programs
4487 should not assume that a specific block object will always contain a
4488 given symbol, since changes in @value{GDBN} features and
4489 infrastructure may cause symbols move across blocks in a symbol
4492 The following block-related functions are available in the @code{gdb}
4495 @findex gdb.block_for_pc
4496 @defun gdb.block_for_pc (pc)
4497 Return the innermost @code{gdb.Block} containing the given @var{pc}
4498 value. If the block cannot be found for the @var{pc} value specified,
4499 the function will return @code{None}.
4502 A @code{gdb.Block} object has the following methods:
4504 @defun Block.is_valid ()
4505 Returns @code{True} if the @code{gdb.Block} object is valid,
4506 @code{False} if not. A block object can become invalid if the block it
4507 refers to doesn't exist anymore in the inferior. All other
4508 @code{gdb.Block} methods will throw an exception if it is invalid at
4509 the time the method is called. The block's validity is also checked
4510 during iteration over symbols of the block.
4513 A @code{gdb.Block} object has the following attributes:
4516 The start address of the block. This attribute is not writable.
4520 One past the last address that appears in the block. This attribute
4524 @defvar Block.function
4525 The name of the block represented as a @code{gdb.Symbol}. If the
4526 block is not named, then this attribute holds @code{None}. This
4527 attribute is not writable.
4529 For ordinary function blocks, the superblock is the static block.
4530 However, you should note that it is possible for a function block to
4531 have a superblock that is not the static block -- for instance this
4532 happens for an inlined function.
4535 @defvar Block.superblock
4536 The block containing this block. If this parent block does not exist,
4537 this attribute holds @code{None}. This attribute is not writable.
4540 @defvar Block.global_block
4541 The global block associated with this block. This attribute is not
4545 @defvar Block.static_block
4546 The static block associated with this block. This attribute is not
4550 @defvar Block.is_global
4551 @code{True} if the @code{gdb.Block} object is a global block,
4552 @code{False} if not. This attribute is not
4556 @defvar Block.is_static
4557 @code{True} if the @code{gdb.Block} object is a static block,
4558 @code{False} if not. This attribute is not writable.
4561 @node Symbols In Python
4562 @subsubsection Python representation of Symbols.
4564 @cindex symbols in python
4567 @value{GDBN} represents every variable, function and type as an
4568 entry in a symbol table. @xref{Symbols, ,Examining the Symbol Table}.
4569 Similarly, Python represents these symbols in @value{GDBN} with the
4570 @code{gdb.Symbol} object.
4572 The following symbol-related functions are available in the @code{gdb}
4575 @findex gdb.lookup_symbol
4576 @defun gdb.lookup_symbol (name @r{[}, block @r{[}, domain@r{]]})
4577 This function searches for a symbol by name. The search scope can be
4578 restricted to the parameters defined in the optional domain and block
4581 @var{name} is the name of the symbol. It must be a string. The
4582 optional @var{block} argument restricts the search to symbols visible
4583 in that @var{block}. The @var{block} argument must be a
4584 @code{gdb.Block} object. If omitted, the block for the current frame
4585 is used. The optional @var{domain} argument restricts
4586 the search to the domain type. The @var{domain} argument must be a
4587 domain constant defined in the @code{gdb} module and described later
4590 The result is a tuple of two elements.
4591 The first element is a @code{gdb.Symbol} object or @code{None} if the symbol
4593 If the symbol is found, the second element is @code{True} if the symbol
4594 is a field of a method's object (e.g., @code{this} in C@t{++}),
4595 otherwise it is @code{False}.
4596 If the symbol is not found, the second element is @code{False}.
4599 @findex gdb.lookup_global_symbol
4600 @defun gdb.lookup_global_symbol (name @r{[}, domain@r{]})
4601 This function searches for a global symbol by name.
4602 The search scope can be restricted to by the domain argument.
4604 @var{name} is the name of the symbol. It must be a string.
4605 The optional @var{domain} argument restricts the search to the domain type.
4606 The @var{domain} argument must be a domain constant defined in the @code{gdb}
4607 module and described later in this chapter.
4609 The result is a @code{gdb.Symbol} object or @code{None} if the symbol
4613 A @code{gdb.Symbol} object has the following attributes:
4616 The type of the symbol or @code{None} if no type is recorded.
4617 This attribute is represented as a @code{gdb.Type} object.
4618 @xref{Types In Python}. This attribute is not writable.
4621 @defvar Symbol.symtab
4622 The symbol table in which the symbol appears. This attribute is
4623 represented as a @code{gdb.Symtab} object. @xref{Symbol Tables In
4624 Python}. This attribute is not writable.
4628 The line number in the source code at which the symbol was defined.
4633 The name of the symbol as a string. This attribute is not writable.
4636 @defvar Symbol.linkage_name
4637 The name of the symbol, as used by the linker (i.e., may be mangled).
4638 This attribute is not writable.
4641 @defvar Symbol.print_name
4642 The name of the symbol in a form suitable for output. This is either
4643 @code{name} or @code{linkage_name}, depending on whether the user
4644 asked @value{GDBN} to display demangled or mangled names.
4647 @defvar Symbol.addr_class
4648 The address class of the symbol. This classifies how to find the value
4649 of a symbol. Each address class is a constant defined in the
4650 @code{gdb} module and described later in this chapter.
4653 @defvar Symbol.needs_frame
4654 This is @code{True} if evaluating this symbol's value requires a frame
4655 (@pxref{Frames In Python}) and @code{False} otherwise. Typically,
4656 local variables will require a frame, but other symbols will not.
4659 @defvar Symbol.is_argument
4660 @code{True} if the symbol is an argument of a function.
4663 @defvar Symbol.is_constant
4664 @code{True} if the symbol is a constant.
4667 @defvar Symbol.is_function
4668 @code{True} if the symbol is a function or a method.
4671 @defvar Symbol.is_variable
4672 @code{True} if the symbol is a variable.
4675 A @code{gdb.Symbol} object has the following methods:
4677 @defun Symbol.is_valid ()
4678 Returns @code{True} if the @code{gdb.Symbol} object is valid,
4679 @code{False} if not. A @code{gdb.Symbol} object can become invalid if
4680 the symbol it refers to does not exist in @value{GDBN} any longer.
4681 All other @code{gdb.Symbol} methods will throw an exception if it is
4682 invalid at the time the method is called.
4685 @defun Symbol.value (@r{[}frame@r{]})
4686 Compute the value of the symbol, as a @code{gdb.Value}. For
4687 functions, this computes the address of the function, cast to the
4688 appropriate type. If the symbol requires a frame in order to compute
4689 its value, then @var{frame} must be given. If @var{frame} is not
4690 given, or if @var{frame} is invalid, then this method will throw an
4694 The available domain categories in @code{gdb.Symbol} are represented
4695 as constants in the @code{gdb} module:
4698 @vindex SYMBOL_UNDEF_DOMAIN
4699 @item gdb.SYMBOL_UNDEF_DOMAIN
4700 This is used when a domain has not been discovered or none of the
4701 following domains apply. This usually indicates an error either
4702 in the symbol information or in @value{GDBN}'s handling of symbols.
4704 @vindex SYMBOL_VAR_DOMAIN
4705 @item gdb.SYMBOL_VAR_DOMAIN
4706 This domain contains variables, function names, typedef names and enum
4709 @vindex SYMBOL_STRUCT_DOMAIN
4710 @item gdb.SYMBOL_STRUCT_DOMAIN
4711 This domain holds struct, union and enum type names.
4713 @vindex SYMBOL_LABEL_DOMAIN
4714 @item gdb.SYMBOL_LABEL_DOMAIN
4715 This domain contains names of labels (for gotos).
4717 @vindex SYMBOL_VARIABLES_DOMAIN
4718 @item gdb.SYMBOL_VARIABLES_DOMAIN
4719 This domain holds a subset of the @code{SYMBOLS_VAR_DOMAIN}; it
4720 contains everything minus functions and types.
4722 @vindex SYMBOL_FUNCTIONS_DOMAIN
4723 @item gdb.SYMBOL_FUNCTIONS_DOMAIN
4724 This domain contains all functions.
4726 @vindex SYMBOL_TYPES_DOMAIN
4727 @item gdb.SYMBOL_TYPES_DOMAIN
4728 This domain contains all types.
4731 The available address class categories in @code{gdb.Symbol} are represented
4732 as constants in the @code{gdb} module:
4735 @vindex SYMBOL_LOC_UNDEF
4736 @item gdb.SYMBOL_LOC_UNDEF
4737 If this is returned by address class, it indicates an error either in
4738 the symbol information or in @value{GDBN}'s handling of symbols.
4740 @vindex SYMBOL_LOC_CONST
4741 @item gdb.SYMBOL_LOC_CONST
4742 Value is constant int.
4744 @vindex SYMBOL_LOC_STATIC
4745 @item gdb.SYMBOL_LOC_STATIC
4746 Value is at a fixed address.
4748 @vindex SYMBOL_LOC_REGISTER
4749 @item gdb.SYMBOL_LOC_REGISTER
4750 Value is in a register.
4752 @vindex SYMBOL_LOC_ARG
4753 @item gdb.SYMBOL_LOC_ARG
4754 Value is an argument. This value is at the offset stored within the
4755 symbol inside the frame's argument list.
4757 @vindex SYMBOL_LOC_REF_ARG
4758 @item gdb.SYMBOL_LOC_REF_ARG
4759 Value address is stored in the frame's argument list. Just like
4760 @code{LOC_ARG} except that the value's address is stored at the
4761 offset, not the value itself.
4763 @vindex SYMBOL_LOC_REGPARM_ADDR
4764 @item gdb.SYMBOL_LOC_REGPARM_ADDR
4765 Value is a specified register. Just like @code{LOC_REGISTER} except
4766 the register holds the address of the argument instead of the argument
4769 @vindex SYMBOL_LOC_LOCAL
4770 @item gdb.SYMBOL_LOC_LOCAL
4771 Value is a local variable.
4773 @vindex SYMBOL_LOC_TYPEDEF
4774 @item gdb.SYMBOL_LOC_TYPEDEF
4775 Value not used. Symbols in the domain @code{SYMBOL_STRUCT_DOMAIN} all
4778 @vindex SYMBOL_LOC_BLOCK
4779 @item gdb.SYMBOL_LOC_BLOCK
4782 @vindex SYMBOL_LOC_CONST_BYTES
4783 @item gdb.SYMBOL_LOC_CONST_BYTES
4784 Value is a byte-sequence.
4786 @vindex SYMBOL_LOC_UNRESOLVED
4787 @item gdb.SYMBOL_LOC_UNRESOLVED
4788 Value is at a fixed address, but the address of the variable has to be
4789 determined from the minimal symbol table whenever the variable is
4792 @vindex SYMBOL_LOC_OPTIMIZED_OUT
4793 @item gdb.SYMBOL_LOC_OPTIMIZED_OUT
4794 The value does not actually exist in the program.
4796 @vindex SYMBOL_LOC_COMPUTED
4797 @item gdb.SYMBOL_LOC_COMPUTED
4798 The value's address is a computed location.
4801 @node Symbol Tables In Python
4802 @subsubsection Symbol table representation in Python.
4804 @cindex symbol tables in python
4806 @tindex gdb.Symtab_and_line
4808 Access to symbol table data maintained by @value{GDBN} on the inferior
4809 is exposed to Python via two objects: @code{gdb.Symtab_and_line} and
4810 @code{gdb.Symtab}. Symbol table and line data for a frame is returned
4811 from the @code{find_sal} method in @code{gdb.Frame} object.
4812 @xref{Frames In Python}.
4814 For more information on @value{GDBN}'s symbol table management, see
4815 @ref{Symbols, ,Examining the Symbol Table}, for more information.
4817 A @code{gdb.Symtab_and_line} object has the following attributes:
4819 @defvar Symtab_and_line.symtab
4820 The symbol table object (@code{gdb.Symtab}) for this frame.
4821 This attribute is not writable.
4824 @defvar Symtab_and_line.pc
4825 Indicates the start of the address range occupied by code for the
4826 current source line. This attribute is not writable.
4829 @defvar Symtab_and_line.last
4830 Indicates the end of the address range occupied by code for the current
4831 source line. This attribute is not writable.
4834 @defvar Symtab_and_line.line
4835 Indicates the current line number for this object. This
4836 attribute is not writable.
4839 A @code{gdb.Symtab_and_line} object has the following methods:
4841 @defun Symtab_and_line.is_valid ()
4842 Returns @code{True} if the @code{gdb.Symtab_and_line} object is valid,
4843 @code{False} if not. A @code{gdb.Symtab_and_line} object can become
4844 invalid if the Symbol table and line object it refers to does not
4845 exist in @value{GDBN} any longer. All other
4846 @code{gdb.Symtab_and_line} methods will throw an exception if it is
4847 invalid at the time the method is called.
4850 A @code{gdb.Symtab} object has the following attributes:
4852 @defvar Symtab.filename
4853 The symbol table's source filename. This attribute is not writable.
4856 @defvar Symtab.objfile
4857 The symbol table's backing object file. @xref{Objfiles In Python}.
4858 This attribute is not writable.
4861 @defvar Symtab.producer
4862 The name and possibly version number of the program that
4863 compiled the code in the symbol table.
4864 The contents of this string is up to the compiler.
4865 If no producer information is available then @code{None} is returned.
4866 This attribute is not writable.
4869 A @code{gdb.Symtab} object has the following methods:
4871 @defun Symtab.is_valid ()
4872 Returns @code{True} if the @code{gdb.Symtab} object is valid,
4873 @code{False} if not. A @code{gdb.Symtab} object can become invalid if
4874 the symbol table it refers to does not exist in @value{GDBN} any
4875 longer. All other @code{gdb.Symtab} methods will throw an exception
4876 if it is invalid at the time the method is called.
4879 @defun Symtab.fullname ()
4880 Return the symbol table's source absolute file name.
4883 @defun Symtab.global_block ()
4884 Return the global block of the underlying symbol table.
4885 @xref{Blocks In Python}.
4888 @defun Symtab.static_block ()
4889 Return the static block of the underlying symbol table.
4890 @xref{Blocks In Python}.
4893 @defun Symtab.linetable ()
4894 Return the line table associated with the symbol table.
4895 @xref{Line Tables In Python}.
4898 @node Line Tables In Python
4899 @subsubsection Manipulating line tables using Python
4901 @cindex line tables in python
4902 @tindex gdb.LineTable
4904 Python code can request and inspect line table information from a
4905 symbol table that is loaded in @value{GDBN}. A line table is a
4906 mapping of source lines to their executable locations in memory. To
4907 acquire the line table information for a particular symbol table, use
4908 the @code{linetable} function (@pxref{Symbol Tables In Python}).
4910 A @code{gdb.LineTable} is iterable. The iterator returns
4911 @code{LineTableEntry} objects that correspond to the source line and
4912 address for each line table entry. @code{LineTableEntry} objects have
4913 the following attributes:
4915 @defvar LineTableEntry.line
4916 The source line number for this line table entry. This number
4917 corresponds to the actual line of source. This attribute is not
4921 @defvar LineTableEntry.pc
4922 The address that is associated with the line table entry where the
4923 executable code for that source line resides in memory. This
4924 attribute is not writable.
4927 As there can be multiple addresses for a single source line, you may
4928 receive multiple @code{LineTableEntry} objects with matching
4929 @code{line} attributes, but with different @code{pc} attributes. The
4930 iterator is sorted in ascending @code{pc} order. Here is a small
4931 example illustrating iterating over a line table.
4934 symtab = gdb.selected_frame().find_sal().symtab
4935 linetable = symtab.linetable()
4936 for line in linetable:
4937 print "Line: "+str(line.line)+" Address: "+hex(line.pc)
4940 This will have the following output:
4943 Line: 33 Address: 0x4005c8L
4944 Line: 37 Address: 0x4005caL
4945 Line: 39 Address: 0x4005d2L
4946 Line: 40 Address: 0x4005f8L
4947 Line: 42 Address: 0x4005ffL
4948 Line: 44 Address: 0x400608L
4949 Line: 42 Address: 0x40060cL
4950 Line: 45 Address: 0x400615L
4953 In addition to being able to iterate over a @code{LineTable}, it also
4954 has the following direct access methods:
4956 @defun LineTable.line (line)
4957 Return a Python @code{Tuple} of @code{LineTableEntry} objects for any
4958 entries in the line table for the given @var{line}, which specifies
4959 the source code line. If there are no entries for that source code
4960 @var{line}, the Python @code{None} is returned.
4963 @defun LineTable.has_line (line)
4964 Return a Python @code{Boolean} indicating whether there is an entry in
4965 the line table for this source line. Return @code{True} if an entry
4966 is found, or @code{False} if not.
4969 @defun LineTable.source_lines ()
4970 Return a Python @code{List} of the source line numbers in the symbol
4971 table. Only lines with executable code locations are returned. The
4972 contents of the @code{List} will just be the source line entries
4973 represented as Python @code{Long} values.
4976 @node Breakpoints In Python
4977 @subsubsection Manipulating breakpoints using Python
4979 @cindex breakpoints in python
4980 @tindex gdb.Breakpoint
4982 Python code can manipulate breakpoints via the @code{gdb.Breakpoint}
4985 A breakpoint can be created using one of the two forms of the
4986 @code{gdb.Breakpoint} constructor. The first one accepts a string
4987 like one would pass to the @code{break}
4988 (@pxref{Set Breaks,,Setting Breakpoints}) and @code{watch}
4989 (@pxref{Set Watchpoints, , Setting Watchpoints}) commands, and can be used to
4990 create both breakpoints and watchpoints. The second accepts separate Python
4991 arguments similar to @ref{Explicit Locations}, and can only be used to create
4994 @defun Breakpoint.__init__ (spec @r{[}, type @r{][}, wp_class @r{][}, internal @r{][}, temporary @r{][}, qualified @r{]})
4995 Create a new breakpoint according to @var{spec}, which is a string naming the
4996 location of a breakpoint, or an expression that defines a watchpoint. The
4997 string should describe a location in a format recognized by the @code{break}
4998 command (@pxref{Set Breaks,,Setting Breakpoints}) or, in the case of a
4999 watchpoint, by the @code{watch} command
5000 (@pxref{Set Watchpoints, , Setting Watchpoints}).
5002 The optional @var{type} argument specifies the type of the breakpoint to create,
5005 The optional @var{wp_class} argument defines the class of watchpoint to create,
5006 if @var{type} is @code{gdb.BP_WATCHPOINT}. If @var{wp_class} is omitted, it
5007 defaults to @code{gdb.WP_WRITE}.
5009 The optional @var{internal} argument allows the breakpoint to become invisible
5010 to the user. The breakpoint will neither be reported when created, nor will it
5011 be listed in the output from @code{info breakpoints} (but will be listed with
5012 the @code{maint info breakpoints} command).
5014 The optional @var{temporary} argument makes the breakpoint a temporary
5015 breakpoint. Temporary breakpoints are deleted after they have been hit. Any
5016 further access to the Python breakpoint after it has been hit will result in a
5017 runtime error (as that breakpoint has now been automatically deleted).
5019 The optional @var{qualified} argument is a boolean that allows interpreting
5020 the function passed in @code{spec} as a fully-qualified name. It is equivalent
5021 to @code{break}'s @code{-qualified} flag (@pxref{Linespec Locations} and
5022 @ref{Explicit Locations}).
5026 @defun Breakpoint.__init__ (@r{[} source @r{][}, function @r{][}, label @r{][}, line @r{]}, @r{][} internal @r{][}, temporary @r{][}, qualified @r{]})
5027 This second form of creating a new breakpoint specifies the explicit
5028 location (@pxref{Explicit Locations}) using keywords. The new breakpoint will
5029 be created in the specified source file @var{source}, at the specified
5030 @var{function}, @var{label} and @var{line}.
5032 @var{internal}, @var{temporary} and @var{qualified} have the same usage as
5033 explained previously.
5036 The available types are represented by constants defined in the @code{gdb}
5040 @vindex BP_BREAKPOINT
5041 @item gdb.BP_BREAKPOINT
5042 Normal code breakpoint.
5044 @vindex BP_WATCHPOINT
5045 @item gdb.BP_WATCHPOINT
5046 Watchpoint breakpoint.
5048 @vindex BP_HARDWARE_WATCHPOINT
5049 @item gdb.BP_HARDWARE_WATCHPOINT
5050 Hardware assisted watchpoint.
5052 @vindex BP_READ_WATCHPOINT
5053 @item gdb.BP_READ_WATCHPOINT
5054 Hardware assisted read watchpoint.
5056 @vindex BP_ACCESS_WATCHPOINT
5057 @item gdb.BP_ACCESS_WATCHPOINT
5058 Hardware assisted access watchpoint.
5061 The available watchpoint types represented by constants are defined in the
5067 Read only watchpoint.
5071 Write only watchpoint.
5075 Read/Write watchpoint.
5078 @defun Breakpoint.stop (self)
5079 The @code{gdb.Breakpoint} class can be sub-classed and, in
5080 particular, you may choose to implement the @code{stop} method.
5081 If this method is defined in a sub-class of @code{gdb.Breakpoint},
5082 it will be called when the inferior reaches any location of a
5083 breakpoint which instantiates that sub-class. If the method returns
5084 @code{True}, the inferior will be stopped at the location of the
5085 breakpoint, otherwise the inferior will continue.
5087 If there are multiple breakpoints at the same location with a
5088 @code{stop} method, each one will be called regardless of the
5089 return status of the previous. This ensures that all @code{stop}
5090 methods have a chance to execute at that location. In this scenario
5091 if one of the methods returns @code{True} but the others return
5092 @code{False}, the inferior will still be stopped.
5094 You should not alter the execution state of the inferior (i.e.@:, step,
5095 next, etc.), alter the current frame context (i.e.@:, change the current
5096 active frame), or alter, add or delete any breakpoint. As a general
5097 rule, you should not alter any data within @value{GDBN} or the inferior
5100 Example @code{stop} implementation:
5103 class MyBreakpoint (gdb.Breakpoint):
5105 inf_val = gdb.parse_and_eval("foo")
5112 @defun Breakpoint.is_valid ()
5113 Return @code{True} if this @code{Breakpoint} object is valid,
5114 @code{False} otherwise. A @code{Breakpoint} object can become invalid
5115 if the user deletes the breakpoint. In this case, the object still
5116 exists, but the underlying breakpoint does not. In the cases of
5117 watchpoint scope, the watchpoint remains valid even if execution of the
5118 inferior leaves the scope of that watchpoint.
5121 @defun Breakpoint.delete ()
5122 Permanently deletes the @value{GDBN} breakpoint. This also
5123 invalidates the Python @code{Breakpoint} object. Any further access
5124 to this object's attributes or methods will raise an error.
5127 @defvar Breakpoint.enabled
5128 This attribute is @code{True} if the breakpoint is enabled, and
5129 @code{False} otherwise. This attribute is writable. You can use it to enable
5130 or disable the breakpoint.
5133 @defvar Breakpoint.silent
5134 This attribute is @code{True} if the breakpoint is silent, and
5135 @code{False} otherwise. This attribute is writable.
5137 Note that a breakpoint can also be silent if it has commands and the
5138 first command is @code{silent}. This is not reported by the
5139 @code{silent} attribute.
5142 @defvar Breakpoint.pending
5143 This attribute is @code{True} if the breakpoint is pending, and
5144 @code{False} otherwise. @xref{Set Breaks}. This attribute is
5148 @anchor{python_breakpoint_thread}
5149 @defvar Breakpoint.thread
5150 If the breakpoint is thread-specific, this attribute holds the
5151 thread's global id. If the breakpoint is not thread-specific, this
5152 attribute is @code{None}. This attribute is writable.
5155 @defvar Breakpoint.task
5156 If the breakpoint is Ada task-specific, this attribute holds the Ada task
5157 id. If the breakpoint is not task-specific (or the underlying
5158 language is not Ada), this attribute is @code{None}. This attribute
5162 @defvar Breakpoint.ignore_count
5163 This attribute holds the ignore count for the breakpoint, an integer.
5164 This attribute is writable.
5167 @defvar Breakpoint.number
5168 This attribute holds the breakpoint's number --- the identifier used by
5169 the user to manipulate the breakpoint. This attribute is not writable.
5172 @defvar Breakpoint.type
5173 This attribute holds the breakpoint's type --- the identifier used to
5174 determine the actual breakpoint type or use-case. This attribute is not
5178 @defvar Breakpoint.visible
5179 This attribute tells whether the breakpoint is visible to the user
5180 when set, or when the @samp{info breakpoints} command is run. This
5181 attribute is not writable.
5184 @defvar Breakpoint.temporary
5185 This attribute indicates whether the breakpoint was created as a
5186 temporary breakpoint. Temporary breakpoints are automatically deleted
5187 after that breakpoint has been hit. Access to this attribute, and all
5188 other attributes and functions other than the @code{is_valid}
5189 function, will result in an error after the breakpoint has been hit
5190 (as it has been automatically deleted). This attribute is not
5194 @defvar Breakpoint.hit_count
5195 This attribute holds the hit count for the breakpoint, an integer.
5196 This attribute is writable, but currently it can only be set to zero.
5199 @defvar Breakpoint.location
5200 This attribute holds the location of the breakpoint, as specified by
5201 the user. It is a string. If the breakpoint does not have a location
5202 (that is, it is a watchpoint) the attribute's value is @code{None}. This
5203 attribute is not writable.
5206 @defvar Breakpoint.expression
5207 This attribute holds a breakpoint expression, as specified by
5208 the user. It is a string. If the breakpoint does not have an
5209 expression (the breakpoint is not a watchpoint) the attribute's value
5210 is @code{None}. This attribute is not writable.
5213 @defvar Breakpoint.condition
5214 This attribute holds the condition of the breakpoint, as specified by
5215 the user. It is a string. If there is no condition, this attribute's
5216 value is @code{None}. This attribute is writable.
5219 @defvar Breakpoint.commands
5220 This attribute holds the commands attached to the breakpoint. If
5221 there are commands, this attribute's value is a string holding all the
5222 commands, separated by newlines. If there are no commands, this
5223 attribute is @code{None}. This attribute is writable.
5226 @node Finish Breakpoints in Python
5227 @subsubsection Finish Breakpoints
5229 @cindex python finish breakpoints
5230 @tindex gdb.FinishBreakpoint
5232 A finish breakpoint is a temporary breakpoint set at the return address of
5233 a frame, based on the @code{finish} command. @code{gdb.FinishBreakpoint}
5234 extends @code{gdb.Breakpoint}. The underlying breakpoint will be disabled
5235 and deleted when the execution will run out of the breakpoint scope (i.e.@:
5236 @code{Breakpoint.stop} or @code{FinishBreakpoint.out_of_scope} triggered).
5237 Finish breakpoints are thread specific and must be create with the right
5240 @defun FinishBreakpoint.__init__ (@r{[}frame@r{]} @r{[}, internal@r{]})
5241 Create a finish breakpoint at the return address of the @code{gdb.Frame}
5242 object @var{frame}. If @var{frame} is not provided, this defaults to the
5243 newest frame. The optional @var{internal} argument allows the breakpoint to
5244 become invisible to the user. @xref{Breakpoints In Python}, for further
5245 details about this argument.
5248 @defun FinishBreakpoint.out_of_scope (self)
5249 In some circumstances (e.g.@: @code{longjmp}, C@t{++} exceptions, @value{GDBN}
5250 @code{return} command, @dots{}), a function may not properly terminate, and
5251 thus never hit the finish breakpoint. When @value{GDBN} notices such a
5252 situation, the @code{out_of_scope} callback will be triggered.
5254 You may want to sub-class @code{gdb.FinishBreakpoint} and override this
5258 class MyFinishBreakpoint (gdb.FinishBreakpoint)
5260 print "normal finish"
5263 def out_of_scope ():
5264 print "abnormal finish"
5268 @defvar FinishBreakpoint.return_value
5269 When @value{GDBN} is stopped at a finish breakpoint and the frame
5270 used to build the @code{gdb.FinishBreakpoint} object had debug symbols, this
5271 attribute will contain a @code{gdb.Value} object corresponding to the return
5272 value of the function. The value will be @code{None} if the function return
5273 type is @code{void} or if the return value was not computable. This attribute
5277 @node Lazy Strings In Python
5278 @subsubsection Python representation of lazy strings.
5280 @cindex lazy strings in python
5281 @tindex gdb.LazyString
5283 A @dfn{lazy string} is a string whose contents is not retrieved or
5284 encoded until it is needed.
5286 A @code{gdb.LazyString} is represented in @value{GDBN} as an
5287 @code{address} that points to a region of memory, an @code{encoding}
5288 that will be used to encode that region of memory, and a @code{length}
5289 to delimit the region of memory that represents the string. The
5290 difference between a @code{gdb.LazyString} and a string wrapped within
5291 a @code{gdb.Value} is that a @code{gdb.LazyString} will be treated
5292 differently by @value{GDBN} when printing. A @code{gdb.LazyString} is
5293 retrieved and encoded during printing, while a @code{gdb.Value}
5294 wrapping a string is immediately retrieved and encoded on creation.
5296 A @code{gdb.LazyString} object has the following functions:
5298 @defun LazyString.value ()
5299 Convert the @code{gdb.LazyString} to a @code{gdb.Value}. This value
5300 will point to the string in memory, but will lose all the delayed
5301 retrieval, encoding and handling that @value{GDBN} applies to a
5302 @code{gdb.LazyString}.
5305 @defvar LazyString.address
5306 This attribute holds the address of the string. This attribute is not
5310 @defvar LazyString.length
5311 This attribute holds the length of the string in characters. If the
5312 length is -1, then the string will be fetched and encoded up to the
5313 first null of appropriate width. This attribute is not writable.
5316 @defvar LazyString.encoding
5317 This attribute holds the encoding that will be applied to the string
5318 when the string is printed by @value{GDBN}. If the encoding is not
5319 set, or contains an empty string, then @value{GDBN} will select the
5320 most appropriate encoding when the string is printed. This attribute
5324 @defvar LazyString.type
5325 This attribute holds the type that is represented by the lazy string's
5326 type. For a lazy string this is a pointer or array type. To
5327 resolve this to the lazy string's character type, use the type's
5328 @code{target} method. @xref{Types In Python}. This attribute is not
5332 @node Architectures In Python
5333 @subsubsection Python representation of architectures
5334 @cindex Python architectures
5336 @value{GDBN} uses architecture specific parameters and artifacts in a
5337 number of its various computations. An architecture is represented
5338 by an instance of the @code{gdb.Architecture} class.
5340 A @code{gdb.Architecture} class has the following methods:
5342 @defun Architecture.name ()
5343 Return the name (string value) of the architecture.
5346 @defun Architecture.disassemble (@var{start_pc} @r{[}, @var{end_pc} @r{[}, @var{count}@r{]]})
5347 Return a list of disassembled instructions starting from the memory
5348 address @var{start_pc}. The optional arguments @var{end_pc} and
5349 @var{count} determine the number of instructions in the returned list.
5350 If both the optional arguments @var{end_pc} and @var{count} are
5351 specified, then a list of at most @var{count} disassembled instructions
5352 whose start address falls in the closed memory address interval from
5353 @var{start_pc} to @var{end_pc} are returned. If @var{end_pc} is not
5354 specified, but @var{count} is specified, then @var{count} number of
5355 instructions starting from the address @var{start_pc} are returned. If
5356 @var{count} is not specified but @var{end_pc} is specified, then all
5357 instructions whose start address falls in the closed memory address
5358 interval from @var{start_pc} to @var{end_pc} are returned. If neither
5359 @var{end_pc} nor @var{count} are specified, then a single instruction at
5360 @var{start_pc} is returned. For all of these cases, each element of the
5361 returned list is a Python @code{dict} with the following string keys:
5366 The value corresponding to this key is a Python long integer capturing
5367 the memory address of the instruction.
5370 The value corresponding to this key is a string value which represents
5371 the instruction with assembly language mnemonics. The assembly
5372 language flavor used is the same as that specified by the current CLI
5373 variable @code{disassembly-flavor}. @xref{Machine Code}.
5376 The value corresponding to this key is the length (integer value) of the
5377 instruction in bytes.
5382 @node Python Auto-loading
5383 @subsection Python Auto-loading
5384 @cindex Python auto-loading
5386 When a new object file is read (for example, due to the @code{file}
5387 command, or because the inferior has loaded a shared library),
5388 @value{GDBN} will look for Python support scripts in several ways:
5389 @file{@var{objfile}-gdb.py} and @code{.debug_gdb_scripts} section.
5390 @xref{Auto-loading extensions}.
5392 The auto-loading feature is useful for supplying application-specific
5393 debugging commands and scripts.
5395 Auto-loading can be enabled or disabled,
5396 and the list of auto-loaded scripts can be printed.
5399 @anchor{set auto-load python-scripts}
5400 @kindex set auto-load python-scripts
5401 @item set auto-load python-scripts [on|off]
5402 Enable or disable the auto-loading of Python scripts.
5404 @anchor{show auto-load python-scripts}
5405 @kindex show auto-load python-scripts
5406 @item show auto-load python-scripts
5407 Show whether auto-loading of Python scripts is enabled or disabled.
5409 @anchor{info auto-load python-scripts}
5410 @kindex info auto-load python-scripts
5411 @cindex print list of auto-loaded Python scripts
5412 @item info auto-load python-scripts [@var{regexp}]
5413 Print the list of all Python scripts that @value{GDBN} auto-loaded.
5415 Also printed is the list of Python scripts that were mentioned in
5416 the @code{.debug_gdb_scripts} section and were either not found
5417 (@pxref{dotdebug_gdb_scripts section}) or were not auto-loaded due to
5418 @code{auto-load safe-path} rejection (@pxref{Auto-loading}).
5419 This is useful because their names are not printed when @value{GDBN}
5420 tries to load them and fails. There may be many of them, and printing
5421 an error message for each one is problematic.
5423 If @var{regexp} is supplied only Python scripts with matching names are printed.
5428 (gdb) info auto-load python-scripts
5430 Yes py-section-script.py
5431 full name: /tmp/py-section-script.py
5432 No my-foo-pretty-printers.py
5436 When reading an auto-loaded file or script, @value{GDBN} sets the
5437 @dfn{current objfile}. This is available via the @code{gdb.current_objfile}
5438 function (@pxref{Objfiles In Python}). This can be useful for
5439 registering objfile-specific pretty-printers and frame-filters.
5441 @node Python modules
5442 @subsection Python modules
5443 @cindex python modules
5445 @value{GDBN} comes with several modules to assist writing Python code.
5448 * gdb.printing:: Building and registering pretty-printers.
5449 * gdb.types:: Utilities for working with types.
5450 * gdb.prompt:: Utilities for prompt value substitution.
5454 @subsubsection gdb.printing
5455 @cindex gdb.printing
5457 This module provides a collection of utilities for working with
5461 @item PrettyPrinter (@var{name}, @var{subprinters}=None)
5462 This class specifies the API that makes @samp{info pretty-printer},
5463 @samp{enable pretty-printer} and @samp{disable pretty-printer} work.
5464 Pretty-printers should generally inherit from this class.
5466 @item SubPrettyPrinter (@var{name})
5467 For printers that handle multiple types, this class specifies the
5468 corresponding API for the subprinters.
5470 @item RegexpCollectionPrettyPrinter (@var{name})
5471 Utility class for handling multiple printers, all recognized via
5472 regular expressions.
5473 @xref{Writing a Pretty-Printer}, for an example.
5475 @item FlagEnumerationPrinter (@var{name})
5476 A pretty-printer which handles printing of @code{enum} values. Unlike
5477 @value{GDBN}'s built-in @code{enum} printing, this printer attempts to
5478 work properly when there is some overlap between the enumeration
5479 constants. The argument @var{name} is the name of the printer and
5480 also the name of the @code{enum} type to look up.
5482 @item register_pretty_printer (@var{obj}, @var{printer}, @var{replace}=False)
5483 Register @var{printer} with the pretty-printer list of @var{obj}.
5484 If @var{replace} is @code{True} then any existing copy of the printer
5485 is replaced. Otherwise a @code{RuntimeError} exception is raised
5486 if a printer with the same name already exists.
5490 @subsubsection gdb.types
5493 This module provides a collection of utilities for working with
5494 @code{gdb.Type} objects.
5497 @item get_basic_type (@var{type})
5498 Return @var{type} with const and volatile qualifiers stripped,
5499 and with typedefs and C@t{++} references converted to the underlying type.
5504 typedef const int const_int;
5506 const_int& foo_ref (foo);
5507 int main () @{ return 0; @}
5514 (gdb) python import gdb.types
5515 (gdb) python foo_ref = gdb.parse_and_eval("foo_ref")
5516 (gdb) python print gdb.types.get_basic_type(foo_ref.type)
5520 @item has_field (@var{type}, @var{field})
5521 Return @code{True} if @var{type}, assumed to be a type with fields
5522 (e.g., a structure or union), has field @var{field}.
5524 @item make_enum_dict (@var{enum_type})
5525 Return a Python @code{dictionary} type produced from @var{enum_type}.
5527 @item deep_items (@var{type})
5528 Returns a Python iterator similar to the standard
5529 @code{gdb.Type.iteritems} method, except that the iterator returned
5530 by @code{deep_items} will recursively traverse anonymous struct or
5531 union fields. For example:
5545 Then in @value{GDBN}:
5547 (@value{GDBP}) python import gdb.types
5548 (@value{GDBP}) python struct_a = gdb.lookup_type("struct A")
5549 (@value{GDBP}) python print struct_a.keys ()
5551 (@value{GDBP}) python print [k for k,v in gdb.types.deep_items(struct_a)]
5552 @{['a', 'b0', 'b1']@}
5555 @item get_type_recognizers ()
5556 Return a list of the enabled type recognizers for the current context.
5557 This is called by @value{GDBN} during the type-printing process
5558 (@pxref{Type Printing API}).
5560 @item apply_type_recognizers (recognizers, type_obj)
5561 Apply the type recognizers, @var{recognizers}, to the type object
5562 @var{type_obj}. If any recognizer returns a string, return that
5563 string. Otherwise, return @code{None}. This is called by
5564 @value{GDBN} during the type-printing process (@pxref{Type Printing
5567 @item register_type_printer (locus, printer)
5568 This is a convenience function to register a type printer
5569 @var{printer}. The printer must implement the type printer protocol.
5570 The @var{locus} argument is either a @code{gdb.Objfile}, in which case
5571 the printer is registered with that objfile; a @code{gdb.Progspace},
5572 in which case the printer is registered with that progspace; or
5573 @code{None}, in which case the printer is registered globally.
5576 This is a base class that implements the type printer protocol. Type
5577 printers are encouraged, but not required, to derive from this class.
5578 It defines a constructor:
5580 @defmethod TypePrinter __init__ (self, name)
5581 Initialize the type printer with the given name. The new printer
5582 starts in the enabled state.
5588 @subsubsection gdb.prompt
5591 This module provides a method for prompt value-substitution.
5594 @item substitute_prompt (@var{string})
5595 Return @var{string} with escape sequences substituted by values. Some
5596 escape sequences take arguments. You can specify arguments inside
5597 ``@{@}'' immediately following the escape sequence.
5599 The escape sequences you can pass to this function are:
5603 Substitute a backslash.
5605 Substitute an ESC character.
5607 Substitute the selected frame; an argument names a frame parameter.
5609 Substitute a newline.
5611 Substitute a parameter's value; the argument names the parameter.
5613 Substitute a carriage return.
5615 Substitute the selected thread; an argument names a thread parameter.
5617 Substitute the version of GDB.
5619 Substitute the current working directory.
5621 Begin a sequence of non-printing characters. These sequences are
5622 typically used with the ESC character, and are not counted in the string
5623 length. Example: ``\[\e[0;34m\](gdb)\[\e[0m\]'' will return a
5624 blue-colored ``(gdb)'' prompt where the length is five.
5626 End a sequence of non-printing characters.
5632 substitute_prompt (``frame: \f,
5633 print arguments: \p@{print frame-arguments@}'')
5636 @exdent will return the string:
5639 "frame: main, print arguments: scalars"