1 @c Copyright (C) 2008-2018 Free Software Foundation, Inc.
2 @c Permission is granted to copy, distribute and/or modify this document
3 @c under the terms of the GNU Free Documentation License, Version 1.3 or
4 @c any later version published by the Free Software Foundation; with the
5 @c Invariant Sections being ``Free Software'' and ``Free Software Needs
6 @c Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,''
7 @c and with the Back-Cover Texts as in (a) below.
9 @c (a) The FSF's Back-Cover Text is: ``You are free to copy and modify
10 @c this GNU Manual. Buying copies from GNU Press supports the FSF in
11 @c developing GNU and promoting software freedom.''
14 @section Extending @value{GDBN} using Python
15 @cindex python scripting
16 @cindex scripting with python
18 You can extend @value{GDBN} using the @uref{http://www.python.org/,
19 Python programming language}. This feature is available only if
20 @value{GDBN} was configured using @option{--with-python}.
21 @value{GDBN} can be built against either Python 2 or Python 3; which
22 one you have depends on this configure-time option.
24 @cindex python directory
25 Python scripts used by @value{GDBN} should be installed in
26 @file{@var{data-directory}/python}, where @var{data-directory} is
27 the data directory as determined at @value{GDBN} startup (@pxref{Data Files}).
28 This directory, known as the @dfn{python directory},
29 is automatically added to the Python Search Path in order to allow
30 the Python interpreter to locate all scripts installed at this location.
32 Additionally, @value{GDBN} commands and convenience functions which
33 are written in Python and are located in the
34 @file{@var{data-directory}/python/gdb/command} or
35 @file{@var{data-directory}/python/gdb/function} directories are
36 automatically imported when @value{GDBN} starts.
39 * Python Commands:: Accessing Python from @value{GDBN}.
40 * Python API:: Accessing @value{GDBN} from Python.
41 * Python Auto-loading:: Automatically loading Python code.
42 * Python modules:: Python modules provided by @value{GDBN}.
46 @subsection Python Commands
47 @cindex python commands
48 @cindex commands to access python
50 @value{GDBN} provides two commands for accessing the Python interpreter,
51 and one related setting:
54 @kindex python-interactive
56 @item python-interactive @r{[}@var{command}@r{]}
57 @itemx pi @r{[}@var{command}@r{]}
58 Without an argument, the @code{python-interactive} command can be used
59 to start an interactive Python prompt. To return to @value{GDBN},
60 type the @code{EOF} character (e.g., @kbd{Ctrl-D} on an empty prompt).
62 Alternatively, a single-line Python command can be given as an
63 argument and evaluated. If the command is an expression, the result
64 will be printed; otherwise, nothing will be printed. For example:
67 (@value{GDBP}) python-interactive 2 + 3
73 @item python @r{[}@var{command}@r{]}
74 @itemx py @r{[}@var{command}@r{]}
75 The @code{python} command can be used to evaluate Python code.
77 If given an argument, the @code{python} command will evaluate the
78 argument as a Python command. For example:
81 (@value{GDBP}) python print 23
85 If you do not provide an argument to @code{python}, it will act as a
86 multi-line command, like @code{define}. In this case, the Python
87 script is made up of subsequent command lines, given after the
88 @code{python} command. This command list is terminated using a line
89 containing @code{end}. For example:
94 End with a line saying just "end".
100 @kindex set python print-stack
101 @item set python print-stack
102 By default, @value{GDBN} will print only the message component of a
103 Python exception when an error occurs in a Python script. This can be
104 controlled using @code{set python print-stack}: if @code{full}, then
105 full Python stack printing is enabled; if @code{none}, then Python stack
106 and message printing is disabled; if @code{message}, the default, only
107 the message component of the error is printed.
110 It is also possible to execute a Python script from the @value{GDBN}
114 @item source @file{script-name}
115 The script name must end with @samp{.py} and @value{GDBN} must be configured
116 to recognize the script language based on filename extension using
117 the @code{script-extension} setting. @xref{Extending GDB, ,Extending GDB}.
121 @subsection Python API
123 @cindex programming in python
125 You can get quick online help for @value{GDBN}'s Python API by issuing
126 the command @w{@kbd{python help (gdb)}}.
128 Functions and methods which have two or more optional arguments allow
129 them to be specified using keyword syntax. This allows passing some
130 optional arguments while skipping others. Example:
131 @w{@code{gdb.some_function ('foo', bar = 1, baz = 2)}}.
134 * Basic Python:: Basic Python Functions.
135 * Exception Handling:: How Python exceptions are translated.
136 * Values From Inferior:: Python representation of values.
137 * Types In Python:: Python representation of types.
138 * Pretty Printing API:: Pretty-printing values.
139 * Selecting Pretty-Printers:: How GDB chooses a pretty-printer.
140 * Writing a Pretty-Printer:: Writing a Pretty-Printer.
141 * Type Printing API:: Pretty-printing types.
142 * Frame Filter API:: Filtering Frames.
143 * Frame Decorator API:: Decorating Frames.
144 * Writing a Frame Filter:: Writing a Frame Filter.
145 * Unwinding Frames in Python:: Writing frame unwinder.
146 * Xmethods In Python:: Adding and replacing methods of C++ classes.
147 * Xmethod API:: Xmethod types.
148 * Writing an Xmethod:: Writing an xmethod.
149 * Inferiors In Python:: Python representation of inferiors (processes)
150 * Events In Python:: Listening for events from @value{GDBN}.
151 * Threads In Python:: Accessing inferior threads from Python.
152 * Recordings In Python:: Accessing recordings from Python.
153 * Commands In Python:: Implementing new commands in Python.
154 * Parameters In Python:: Adding new @value{GDBN} parameters.
155 * Functions In Python:: Writing new convenience functions.
156 * Progspaces In Python:: Program spaces.
157 * Objfiles In Python:: Object files.
158 * Frames In Python:: Accessing inferior stack frames from Python.
159 * Blocks In Python:: Accessing blocks from Python.
160 * Symbols In Python:: Python representation of symbols.
161 * Symbol Tables In Python:: Python representation of symbol tables.
162 * Line Tables In Python:: Python representation of line tables.
163 * Breakpoints In Python:: Manipulating breakpoints using Python.
164 * Finish Breakpoints in Python:: Setting Breakpoints on function return
166 * Lazy Strings In Python:: Python representation of lazy strings.
167 * Architectures In Python:: Python representation of architectures.
171 @subsubsection Basic Python
173 @cindex python stdout
174 @cindex python pagination
175 At startup, @value{GDBN} overrides Python's @code{sys.stdout} and
176 @code{sys.stderr} to print using @value{GDBN}'s output-paging streams.
177 A Python program which outputs to one of these streams may have its
178 output interrupted by the user (@pxref{Screen Size}). In this
179 situation, a Python @code{KeyboardInterrupt} exception is thrown.
181 Some care must be taken when writing Python code to run in
182 @value{GDBN}. Two things worth noting in particular:
186 @value{GDBN} install handlers for @code{SIGCHLD} and @code{SIGINT}.
187 Python code must not override these, or even change the options using
188 @code{sigaction}. If your program changes the handling of these
189 signals, @value{GDBN} will most likely stop working correctly. Note
190 that it is unfortunately common for GUI toolkits to install a
191 @code{SIGCHLD} handler.
194 @value{GDBN} takes care to mark its internal file descriptors as
195 close-on-exec. However, this cannot be done in a thread-safe way on
196 all platforms. Your Python programs should be aware of this and
197 should both create new file descriptors with the close-on-exec flag
198 set and arrange to close unneeded file descriptors before starting a
202 @cindex python functions
203 @cindex python module
205 @value{GDBN} introduces a new Python module, named @code{gdb}. All
206 methods and classes added by @value{GDBN} are placed in this module.
207 @value{GDBN} automatically @code{import}s the @code{gdb} module for
208 use in all scripts evaluated by the @code{python} command.
210 Some types of the @code{gdb} module come with a textual representation
211 (accessible through the @code{repr} or @code{str} functions). These are
212 offered for debugging purposes only, expect them to change over time.
214 @findex gdb.PYTHONDIR
215 @defvar gdb.PYTHONDIR
216 A string containing the python directory (@pxref{Python}).
220 @defun gdb.execute (command @r{[}, from_tty @r{[}, to_string@r{]]})
221 Evaluate @var{command}, a string, as a @value{GDBN} CLI command.
222 If a GDB exception happens while @var{command} runs, it is
223 translated as described in @ref{Exception Handling,,Exception Handling}.
225 The @var{from_tty} flag specifies whether @value{GDBN} ought to consider this
226 command as having originated from the user invoking it interactively.
227 It must be a boolean value. If omitted, it defaults to @code{False}.
229 By default, any output produced by @var{command} is sent to
230 @value{GDBN}'s standard output (and to the log output if logging is
231 turned on). If the @var{to_string} parameter is
232 @code{True}, then output will be collected by @code{gdb.execute} and
233 returned as a string. The default is @code{False}, in which case the
234 return value is @code{None}. If @var{to_string} is @code{True}, the
235 @value{GDBN} virtual terminal will be temporarily set to unlimited width
236 and height, and its pagination will be disabled; @pxref{Screen Size}.
239 @findex gdb.breakpoints
240 @defun gdb.breakpoints ()
241 Return a sequence holding all of @value{GDBN}'s breakpoints.
242 @xref{Breakpoints In Python}, for more information. In @value{GDBN}
243 version 7.11 and earlier, this function returned @code{None} if there
244 were no breakpoints. This peculiarity was subsequently fixed, and now
245 @code{gdb.breakpoints} returns an empty sequence in this case.
248 @defun gdb.rbreak (regex @r{[}, minsyms @r{[}, throttle, @r{[}, symtabs @r{]]]})
249 Return a Python list holding a collection of newly set
250 @code{gdb.Breakpoint} objects matching function names defined by the
251 @var{regex} pattern. If the @var{minsyms} keyword is @code{True}, all
252 system functions (those not explicitly defined in the inferior) will
253 also be included in the match. The @var{throttle} keyword takes an
254 integer that defines the maximum number of pattern matches for
255 functions matched by the @var{regex} pattern. If the number of
256 matches exceeds the integer value of @var{throttle}, a
257 @code{RuntimeError} will be raised and no breakpoints will be created.
258 If @var{throttle} is not defined then there is no imposed limit on the
259 maximum number of matches and breakpoints to be created. The
260 @var{symtabs} keyword takes a Python iterable that yields a collection
261 of @code{gdb.Symtab} objects and will restrict the search to those
262 functions only contained within the @code{gdb.Symtab} objects.
265 @findex gdb.parameter
266 @defun gdb.parameter (parameter)
267 Return the value of a @value{GDBN} @var{parameter} given by its name,
268 a string; the parameter name string may contain spaces if the parameter has a
269 multi-part name. For example, @samp{print object} is a valid
272 If the named parameter does not exist, this function throws a
273 @code{gdb.error} (@pxref{Exception Handling}). Otherwise, the
274 parameter's value is converted to a Python value of the appropriate
279 @defun gdb.history (number)
280 Return a value from @value{GDBN}'s value history (@pxref{Value
281 History}). The @var{number} argument indicates which history element to return.
282 If @var{number} is negative, then @value{GDBN} will take its absolute value
283 and count backward from the last element (i.e., the most recent element) to
284 find the value to return. If @var{number} is zero, then @value{GDBN} will
285 return the most recent element. If the element specified by @var{number}
286 doesn't exist in the value history, a @code{gdb.error} exception will be
289 If no exception is raised, the return value is always an instance of
290 @code{gdb.Value} (@pxref{Values From Inferior}).
293 @findex gdb.convenience_variable
294 @defun gdb.convenience_variable (name)
295 Return the value of the convenience variable (@pxref{Convenience
296 Vars}) named @var{name}. @var{name} must be a string. The name
297 should not include the @samp{$} that is used to mark a convenience
298 variable in an expression. If the convenience variable does not
299 exist, then @code{None} is returned.
302 @findex gdb.set_convenience_variable
303 @defun gdb.set_convenience_variable (name, value)
304 Set the value of the convenience variable (@pxref{Convenience Vars})
305 named @var{name}. @var{name} must be a string. The name should not
306 include the @samp{$} that is used to mark a convenience variable in an
307 expression. If @var{value} is @code{None}, then the convenience
308 variable is removed. Otherwise, if @var{value} is not a
309 @code{gdb.Value} (@pxref{Values From Inferior}), it is is converted
310 using the @code{gdb.Value} constructor.
313 @findex gdb.parse_and_eval
314 @defun gdb.parse_and_eval (expression)
315 Parse @var{expression}, which must be a string, as an expression in
316 the current language, evaluate it, and return the result as a
319 This function can be useful when implementing a new command
320 (@pxref{Commands In Python}), as it provides a way to parse the
321 command's argument as an expression. It is also useful simply to
325 @findex gdb.find_pc_line
326 @defun gdb.find_pc_line (pc)
327 Return the @code{gdb.Symtab_and_line} object corresponding to the
328 @var{pc} value. @xref{Symbol Tables In Python}. If an invalid
329 value of @var{pc} is passed as an argument, then the @code{symtab} and
330 @code{line} attributes of the returned @code{gdb.Symtab_and_line} object
331 will be @code{None} and 0 respectively. This is identical to
332 @code{gdb.current_progspace().find_pc_line(pc)} and is included for
333 historical compatibility.
336 @findex gdb.post_event
337 @defun gdb.post_event (event)
338 Put @var{event}, a callable object taking no arguments, into
339 @value{GDBN}'s internal event queue. This callable will be invoked at
340 some later point, during @value{GDBN}'s event processing. Events
341 posted using @code{post_event} will be run in the order in which they
342 were posted; however, there is no way to know when they will be
343 processed relative to other events inside @value{GDBN}.
345 @value{GDBN} is not thread-safe. If your Python program uses multiple
346 threads, you must be careful to only call @value{GDBN}-specific
347 functions in the @value{GDBN} thread. @code{post_event} ensures
351 (@value{GDBP}) python
355 > def __init__(self, message):
356 > self.message = message;
357 > def __call__(self):
358 > gdb.write(self.message)
360 >class MyThread1 (threading.Thread):
362 > gdb.post_event(Writer("Hello "))
364 >class MyThread2 (threading.Thread):
366 > gdb.post_event(Writer("World\n"))
371 (@value{GDBP}) Hello World
376 @defun gdb.write (string @r{[}, stream{]})
377 Print a string to @value{GDBN}'s paginated output stream. The
378 optional @var{stream} determines the stream to print to. The default
379 stream is @value{GDBN}'s standard output stream. Possible stream
386 @value{GDBN}'s standard output stream.
391 @value{GDBN}'s standard error stream.
396 @value{GDBN}'s log stream (@pxref{Logging Output}).
399 Writing to @code{sys.stdout} or @code{sys.stderr} will automatically
400 call this function and will automatically direct the output to the
406 Flush the buffer of a @value{GDBN} paginated stream so that the
407 contents are displayed immediately. @value{GDBN} will flush the
408 contents of a stream automatically when it encounters a newline in the
409 buffer. The optional @var{stream} determines the stream to flush. The
410 default stream is @value{GDBN}'s standard output stream. Possible
417 @value{GDBN}'s standard output stream.
422 @value{GDBN}'s standard error stream.
427 @value{GDBN}'s log stream (@pxref{Logging Output}).
431 Flushing @code{sys.stdout} or @code{sys.stderr} will automatically
432 call this function for the relevant stream.
435 @findex gdb.target_charset
436 @defun gdb.target_charset ()
437 Return the name of the current target character set (@pxref{Character
438 Sets}). This differs from @code{gdb.parameter('target-charset')} in
439 that @samp{auto} is never returned.
442 @findex gdb.target_wide_charset
443 @defun gdb.target_wide_charset ()
444 Return the name of the current target wide character set
445 (@pxref{Character Sets}). This differs from
446 @code{gdb.parameter('target-wide-charset')} in that @samp{auto} is
450 @findex gdb.solib_name
451 @defun gdb.solib_name (address)
452 Return the name of the shared library holding the given @var{address}
453 as a string, or @code{None}. This is identical to
454 @code{gdb.current_progspace().solib_name(address)} and is included for
455 historical compatibility.
458 @findex gdb.decode_line
459 @defun gdb.decode_line (@r{[}expression@r{]})
460 Return locations of the line specified by @var{expression}, or of the
461 current line if no argument was given. This function returns a Python
462 tuple containing two elements. The first element contains a string
463 holding any unparsed section of @var{expression} (or @code{None} if
464 the expression has been fully parsed). The second element contains
465 either @code{None} or another tuple that contains all the locations
466 that match the expression represented as @code{gdb.Symtab_and_line}
467 objects (@pxref{Symbol Tables In Python}). If @var{expression} is
468 provided, it is decoded the way that @value{GDBN}'s inbuilt
469 @code{break} or @code{edit} commands do (@pxref{Specify Location}).
472 @defun gdb.prompt_hook (current_prompt)
475 If @var{prompt_hook} is callable, @value{GDBN} will call the method
476 assigned to this operation before a prompt is displayed by
479 The parameter @code{current_prompt} contains the current @value{GDBN}
480 prompt. This method must return a Python string, or @code{None}. If
481 a string is returned, the @value{GDBN} prompt will be set to that
482 string. If @code{None} is returned, @value{GDBN} will continue to use
485 Some prompts cannot be substituted in @value{GDBN}. Secondary prompts
486 such as those used by readline for command input, and annotation
487 related prompts are prohibited from being changed.
490 @node Exception Handling
491 @subsubsection Exception Handling
492 @cindex python exceptions
493 @cindex exceptions, python
495 When executing the @code{python} command, Python exceptions
496 uncaught within the Python code are translated to calls to
497 @value{GDBN} error-reporting mechanism. If the command that called
498 @code{python} does not handle the error, @value{GDBN} will
499 terminate it and print an error message containing the Python
500 exception name, the associated value, and the Python call stack
501 backtrace at the point where the exception was raised. Example:
504 (@value{GDBP}) python print foo
505 Traceback (most recent call last):
506 File "<string>", line 1, in <module>
507 NameError: name 'foo' is not defined
510 @value{GDBN} errors that happen in @value{GDBN} commands invoked by
511 Python code are converted to Python exceptions. The type of the
512 Python exception depends on the error.
516 This is the base class for most exceptions generated by @value{GDBN}.
517 It is derived from @code{RuntimeError}, for compatibility with earlier
518 versions of @value{GDBN}.
520 If an error occurring in @value{GDBN} does not fit into some more
521 specific category, then the generated exception will have this type.
523 @item gdb.MemoryError
524 This is a subclass of @code{gdb.error} which is thrown when an
525 operation tried to access invalid memory in the inferior.
527 @item KeyboardInterrupt
528 User interrupt (via @kbd{C-c} or by typing @kbd{q} at a pagination
529 prompt) is translated to a Python @code{KeyboardInterrupt} exception.
532 In all cases, your exception handler will see the @value{GDBN} error
533 message as its value and the Python call stack backtrace at the Python
534 statement closest to where the @value{GDBN} error occured as the
538 When implementing @value{GDBN} commands in Python via
539 @code{gdb.Command}, or functions via @code{gdb.Function}, it is useful
540 to be able to throw an exception that doesn't cause a traceback to be
541 printed. For example, the user may have invoked the command
542 incorrectly. @value{GDBN} provides a special exception class that can
543 be used for this purpose.
547 When thrown from a command or function, this exception will cause the
548 command or function to fail, but the Python stack will not be
549 displayed. @value{GDBN} does not throw this exception itself, but
550 rather recognizes it when thrown from user Python code. Example:
554 >class HelloWorld (gdb.Command):
555 > """Greet the whole world."""
556 > def __init__ (self):
557 > super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)
558 > def invoke (self, args, from_tty):
559 > argv = gdb.string_to_argv (args)
560 > if len (argv) != 0:
561 > raise gdb.GdbError ("hello-world takes no arguments")
562 > print "Hello, World!"
566 hello-world takes no arguments
570 @node Values From Inferior
571 @subsubsection Values From Inferior
572 @cindex values from inferior, with Python
573 @cindex python, working with values from inferior
575 @cindex @code{gdb.Value}
576 @value{GDBN} provides values it obtains from the inferior program in
577 an object of type @code{gdb.Value}. @value{GDBN} uses this object
578 for its internal bookkeeping of the inferior's values, and for
579 fetching values when necessary.
581 Inferior values that are simple scalars can be used directly in
582 Python expressions that are valid for the value's data type. Here's
583 an example for an integer or floating-point value @code{some_val}:
590 As result of this, @code{bar} will also be a @code{gdb.Value} object
591 whose values are of the same type as those of @code{some_val}. Valid
592 Python operations can also be performed on @code{gdb.Value} objects
593 representing a @code{struct} or @code{class} object. For such cases,
594 the overloaded operator (if present), is used to perform the operation.
595 For example, if @code{val1} and @code{val2} are @code{gdb.Value} objects
596 representing instances of a @code{class} which overloads the @code{+}
597 operator, then one can use the @code{+} operator in their Python script
605 The result of the operation @code{val3} is also a @code{gdb.Value}
606 object corresponding to the value returned by the overloaded @code{+}
607 operator. In general, overloaded operators are invoked for the
608 following operations: @code{+} (binary addition), @code{-} (binary
609 subtraction), @code{*} (multiplication), @code{/}, @code{%}, @code{<<},
610 @code{>>}, @code{|}, @code{&}, @code{^}.
612 Inferior values that are structures or instances of some class can
613 be accessed using the Python @dfn{dictionary syntax}. For example, if
614 @code{some_val} is a @code{gdb.Value} instance holding a structure, you
615 can access its @code{foo} element with:
618 bar = some_val['foo']
621 @cindex getting structure elements using gdb.Field objects as subscripts
622 Again, @code{bar} will also be a @code{gdb.Value} object. Structure
623 elements can also be accessed by using @code{gdb.Field} objects as
624 subscripts (@pxref{Types In Python}, for more information on
625 @code{gdb.Field} objects). For example, if @code{foo_field} is a
626 @code{gdb.Field} object corresponding to element @code{foo} of the above
627 structure, then @code{bar} can also be accessed as follows:
630 bar = some_val[foo_field]
633 A @code{gdb.Value} that represents a function can be executed via
634 inferior function call. Any arguments provided to the call must match
635 the function's prototype, and must be provided in the order specified
638 For example, @code{some_val} is a @code{gdb.Value} instance
639 representing a function that takes two integers as arguments. To
640 execute this function, call it like so:
643 result = some_val (10,20)
646 Any values returned from a function call will be stored as a
649 The following attributes are provided:
651 @defvar Value.address
652 If this object is addressable, this read-only attribute holds a
653 @code{gdb.Value} object representing the address. Otherwise,
654 this attribute holds @code{None}.
657 @cindex optimized out value in Python
658 @defvar Value.is_optimized_out
659 This read-only boolean attribute is true if the compiler optimized out
660 this value, thus it is not available for fetching from the inferior.
664 The type of this @code{gdb.Value}. The value of this attribute is a
665 @code{gdb.Type} object (@pxref{Types In Python}).
668 @defvar Value.dynamic_type
669 The dynamic type of this @code{gdb.Value}. This uses the object's
670 virtual table and the C@t{++} run-time type information
671 (@acronym{RTTI}) to determine the dynamic type of the value. If this
672 value is of class type, it will return the class in which the value is
673 embedded, if any. If this value is of pointer or reference to a class
674 type, it will compute the dynamic type of the referenced object, and
675 return a pointer or reference to that type, respectively. In all
676 other cases, it will return the value's static type.
678 Note that this feature will only work when debugging a C@t{++} program
679 that includes @acronym{RTTI} for the object in question. Otherwise,
680 it will just return the static type of the value as in @kbd{ptype foo}
681 (@pxref{Symbols, ptype}).
684 @defvar Value.is_lazy
685 The value of this read-only boolean attribute is @code{True} if this
686 @code{gdb.Value} has not yet been fetched from the inferior.
687 @value{GDBN} does not fetch values until necessary, for efficiency.
691 myval = gdb.parse_and_eval ('somevar')
694 The value of @code{somevar} is not fetched at this time. It will be
695 fetched when the value is needed, or when the @code{fetch_lazy}
699 The following methods are provided:
701 @defun Value.__init__ (@var{val})
702 Many Python values can be converted directly to a @code{gdb.Value} via
703 this object initializer. Specifically:
707 A Python boolean is converted to the boolean type from the current
711 A Python integer is converted to the C @code{long} type for the
712 current architecture.
715 A Python long is converted to the C @code{long long} type for the
716 current architecture.
719 A Python float is converted to the C @code{double} type for the
720 current architecture.
723 A Python string is converted to a target string in the current target
724 language using the current target encoding.
725 If a character cannot be represented in the current target encoding,
726 then an exception is thrown.
728 @item @code{gdb.Value}
729 If @code{val} is a @code{gdb.Value}, then a copy of the value is made.
731 @item @code{gdb.LazyString}
732 If @code{val} is a @code{gdb.LazyString} (@pxref{Lazy Strings In
733 Python}), then the lazy string's @code{value} method is called, and
738 @defun Value.cast (type)
739 Return a new instance of @code{gdb.Value} that is the result of
740 casting this instance to the type described by @var{type}, which must
741 be a @code{gdb.Type} object. If the cast cannot be performed for some
742 reason, this method throws an exception.
745 @defun Value.dereference ()
746 For pointer data types, this method returns a new @code{gdb.Value} object
747 whose contents is the object pointed to by the pointer. For example, if
748 @code{foo} is a C pointer to an @code{int}, declared in your C program as
755 then you can use the corresponding @code{gdb.Value} to access what
756 @code{foo} points to like this:
759 bar = foo.dereference ()
762 The result @code{bar} will be a @code{gdb.Value} object holding the
763 value pointed to by @code{foo}.
765 A similar function @code{Value.referenced_value} exists which also
766 returns @code{gdb.Value} objects corresonding to the values pointed to
767 by pointer values (and additionally, values referenced by reference
768 values). However, the behavior of @code{Value.dereference}
769 differs from @code{Value.referenced_value} by the fact that the
770 behavior of @code{Value.dereference} is identical to applying the C
771 unary operator @code{*} on a given value. For example, consider a
772 reference to a pointer @code{ptrref}, declared in your C@t{++} program
780 intptr &ptrref = ptr;
783 Though @code{ptrref} is a reference value, one can apply the method
784 @code{Value.dereference} to the @code{gdb.Value} object corresponding
785 to it and obtain a @code{gdb.Value} which is identical to that
786 corresponding to @code{val}. However, if you apply the method
787 @code{Value.referenced_value}, the result would be a @code{gdb.Value}
788 object identical to that corresponding to @code{ptr}.
791 py_ptrref = gdb.parse_and_eval ("ptrref")
792 py_val = py_ptrref.dereference ()
793 py_ptr = py_ptrref.referenced_value ()
796 The @code{gdb.Value} object @code{py_val} is identical to that
797 corresponding to @code{val}, and @code{py_ptr} is identical to that
798 corresponding to @code{ptr}. In general, @code{Value.dereference} can
799 be applied whenever the C unary operator @code{*} can be applied
800 to the corresponding C value. For those cases where applying both
801 @code{Value.dereference} and @code{Value.referenced_value} is allowed,
802 the results obtained need not be identical (as we have seen in the above
803 example). The results are however identical when applied on
804 @code{gdb.Value} objects corresponding to pointers (@code{gdb.Value}
805 objects with type code @code{TYPE_CODE_PTR}) in a C/C@t{++} program.
808 @defun Value.referenced_value ()
809 For pointer or reference data types, this method returns a new
810 @code{gdb.Value} object corresponding to the value referenced by the
811 pointer/reference value. For pointer data types,
812 @code{Value.dereference} and @code{Value.referenced_value} produce
813 identical results. The difference between these methods is that
814 @code{Value.dereference} cannot get the values referenced by reference
815 values. For example, consider a reference to an @code{int}, declared
816 in your C@t{++} program as
824 then applying @code{Value.dereference} to the @code{gdb.Value} object
825 corresponding to @code{ref} will result in an error, while applying
826 @code{Value.referenced_value} will result in a @code{gdb.Value} object
827 identical to that corresponding to @code{val}.
830 py_ref = gdb.parse_and_eval ("ref")
831 er_ref = py_ref.dereference () # Results in error
832 py_val = py_ref.referenced_value () # Returns the referenced value
835 The @code{gdb.Value} object @code{py_val} is identical to that
836 corresponding to @code{val}.
839 @defun Value.reference_value ()
840 Return a @code{gdb.Value} object which is a reference to the value
841 encapsulated by this instance.
844 @defun Value.const_value ()
845 Return a @code{gdb.Value} object which is a @code{const} version of the
846 value encapsulated by this instance.
849 @defun Value.dynamic_cast (type)
850 Like @code{Value.cast}, but works as if the C@t{++} @code{dynamic_cast}
851 operator were used. Consult a C@t{++} reference for details.
854 @defun Value.reinterpret_cast (type)
855 Like @code{Value.cast}, but works as if the C@t{++} @code{reinterpret_cast}
856 operator were used. Consult a C@t{++} reference for details.
859 @defun Value.string (@r{[}encoding@r{[}, errors@r{[}, length@r{]]]})
860 If this @code{gdb.Value} represents a string, then this method
861 converts the contents to a Python string. Otherwise, this method will
864 Values are interpreted as strings according to the rules of the
865 current language. If the optional length argument is given, the
866 string will be converted to that length, and will include any embedded
867 zeroes that the string may contain. Otherwise, for languages
868 where the string is zero-terminated, the entire string will be
871 For example, in C-like languages, a value is a string if it is a pointer
872 to or an array of characters or ints of type @code{wchar_t}, @code{char16_t},
875 If the optional @var{encoding} argument is given, it must be a string
876 naming the encoding of the string in the @code{gdb.Value}, such as
877 @code{"ascii"}, @code{"iso-8859-6"} or @code{"utf-8"}. It accepts
878 the same encodings as the corresponding argument to Python's
879 @code{string.decode} method, and the Python codec machinery will be used
880 to convert the string. If @var{encoding} is not given, or if
881 @var{encoding} is the empty string, then either the @code{target-charset}
882 (@pxref{Character Sets}) will be used, or a language-specific encoding
883 will be used, if the current language is able to supply one.
885 The optional @var{errors} argument is the same as the corresponding
886 argument to Python's @code{string.decode} method.
888 If the optional @var{length} argument is given, the string will be
889 fetched and converted to the given length.
892 @defun Value.lazy_string (@r{[}encoding @r{[}, length@r{]]})
893 If this @code{gdb.Value} represents a string, then this method
894 converts the contents to a @code{gdb.LazyString} (@pxref{Lazy Strings
895 In Python}). Otherwise, this method will throw an exception.
897 If the optional @var{encoding} argument is given, it must be a string
898 naming the encoding of the @code{gdb.LazyString}. Some examples are:
899 @samp{ascii}, @samp{iso-8859-6} or @samp{utf-8}. If the
900 @var{encoding} argument is an encoding that @value{GDBN} does
901 recognize, @value{GDBN} will raise an error.
903 When a lazy string is printed, the @value{GDBN} encoding machinery is
904 used to convert the string during printing. If the optional
905 @var{encoding} argument is not provided, or is an empty string,
906 @value{GDBN} will automatically select the encoding most suitable for
907 the string type. For further information on encoding in @value{GDBN}
908 please see @ref{Character Sets}.
910 If the optional @var{length} argument is given, the string will be
911 fetched and encoded to the length of characters specified. If
912 the @var{length} argument is not provided, the string will be fetched
913 and encoded until a null of appropriate width is found.
916 @defun Value.fetch_lazy ()
917 If the @code{gdb.Value} object is currently a lazy value
918 (@code{gdb.Value.is_lazy} is @code{True}), then the value is
919 fetched from the inferior. Any errors that occur in the process
920 will produce a Python exception.
922 If the @code{gdb.Value} object is not a lazy value, this method
925 This method does not return a value.
929 @node Types In Python
930 @subsubsection Types In Python
931 @cindex types in Python
932 @cindex Python, working with types
935 @value{GDBN} represents types from the inferior using the class
938 The following type-related functions are available in the @code{gdb}
941 @findex gdb.lookup_type
942 @defun gdb.lookup_type (name @r{[}, block@r{]})
943 This function looks up a type by its @var{name}, which must be a string.
945 If @var{block} is given, then @var{name} is looked up in that scope.
946 Otherwise, it is searched for globally.
948 Ordinarily, this function will return an instance of @code{gdb.Type}.
949 If the named type cannot be found, it will throw an exception.
952 If the type is a structure or class type, or an enum type, the fields
953 of that type can be accessed using the Python @dfn{dictionary syntax}.
954 For example, if @code{some_type} is a @code{gdb.Type} instance holding
955 a structure type, you can access its @code{foo} field with:
958 bar = some_type['foo']
961 @code{bar} will be a @code{gdb.Field} object; see below under the
962 description of the @code{Type.fields} method for a description of the
963 @code{gdb.Field} class.
965 An instance of @code{Type} has the following attributes:
968 The alignment of this type, in bytes. Type alignment comes from the
969 debugging information; if it was not specified, then @value{GDBN} will
970 use the relevant ABI to try to determine the alignment. In some
971 cases, even this is not possible, and zero will be returned.
975 The type code for this type. The type code will be one of the
976 @code{TYPE_CODE_} constants defined below.
980 The name of this type. If this type has no name, then @code{None}
985 The size of this type, in target @code{char} units. Usually, a
986 target's @code{char} type will be an 8-bit byte. However, on some
987 unusual platforms, this type may have a different size.
991 The tag name for this type. The tag name is the name after
992 @code{struct}, @code{union}, or @code{enum} in C and C@t{++}; not all
993 languages have this concept. If this type has no tag name, then
994 @code{None} is returned.
997 The following methods are provided:
999 @defun Type.fields ()
1000 For structure and union types, this method returns the fields. Range
1001 types have two fields, the minimum and maximum values. Enum types
1002 have one field per enum constant. Function and method types have one
1003 field per parameter. The base types of C@t{++} classes are also
1004 represented as fields. If the type has no fields, or does not fit
1005 into one of these categories, an empty sequence will be returned.
1007 Each field is a @code{gdb.Field} object, with some pre-defined attributes:
1010 This attribute is not available for @code{enum} or @code{static}
1011 (as in C@t{++}) fields. The value is the position, counting
1012 in bits, from the start of the containing type.
1015 This attribute is only available for @code{enum} fields, and its value
1016 is the enumeration member's integer representation.
1019 The name of the field, or @code{None} for anonymous fields.
1022 This is @code{True} if the field is artificial, usually meaning that
1023 it was provided by the compiler and not the user. This attribute is
1024 always provided, and is @code{False} if the field is not artificial.
1027 This is @code{True} if the field represents a base class of a C@t{++}
1028 structure. This attribute is always provided, and is @code{False}
1029 if the field is not a base class of the type that is the argument of
1030 @code{fields}, or if that type was not a C@t{++} class.
1033 If the field is packed, or is a bitfield, then this will have a
1034 non-zero value, which is the size of the field in bits. Otherwise,
1035 this will be zero; in this case the field's size is given by its type.
1038 The type of the field. This is usually an instance of @code{Type},
1039 but it can be @code{None} in some situations.
1042 The type which contains this field. This is an instance of
1047 @defun Type.array (@var{n1} @r{[}, @var{n2}@r{]})
1048 Return a new @code{gdb.Type} object which represents an array of this
1049 type. If one argument is given, it is the inclusive upper bound of
1050 the array; in this case the lower bound is zero. If two arguments are
1051 given, the first argument is the lower bound of the array, and the
1052 second argument is the upper bound of the array. An array's length
1053 must not be negative, but the bounds can be.
1056 @defun Type.vector (@var{n1} @r{[}, @var{n2}@r{]})
1057 Return a new @code{gdb.Type} object which represents a vector of this
1058 type. If one argument is given, it is the inclusive upper bound of
1059 the vector; in this case the lower bound is zero. If two arguments are
1060 given, the first argument is the lower bound of the vector, and the
1061 second argument is the upper bound of the vector. A vector's length
1062 must not be negative, but the bounds can be.
1064 The difference between an @code{array} and a @code{vector} is that
1065 arrays behave like in C: when used in expressions they decay to a pointer
1066 to the first element whereas vectors are treated as first class values.
1069 @defun Type.const ()
1070 Return a new @code{gdb.Type} object which represents a
1071 @code{const}-qualified variant of this type.
1074 @defun Type.volatile ()
1075 Return a new @code{gdb.Type} object which represents a
1076 @code{volatile}-qualified variant of this type.
1079 @defun Type.unqualified ()
1080 Return a new @code{gdb.Type} object which represents an unqualified
1081 variant of this type. That is, the result is neither @code{const} nor
1085 @defun Type.range ()
1086 Return a Python @code{Tuple} object that contains two elements: the
1087 low bound of the argument type and the high bound of that type. If
1088 the type does not have a range, @value{GDBN} will raise a
1089 @code{gdb.error} exception (@pxref{Exception Handling}).
1092 @defun Type.reference ()
1093 Return a new @code{gdb.Type} object which represents a reference to this
1097 @defun Type.pointer ()
1098 Return a new @code{gdb.Type} object which represents a pointer to this
1102 @defun Type.strip_typedefs ()
1103 Return a new @code{gdb.Type} that represents the real type,
1104 after removing all layers of typedefs.
1107 @defun Type.target ()
1108 Return a new @code{gdb.Type} object which represents the target type
1111 For a pointer type, the target type is the type of the pointed-to
1112 object. For an array type (meaning C-like arrays), the target type is
1113 the type of the elements of the array. For a function or method type,
1114 the target type is the type of the return value. For a complex type,
1115 the target type is the type of the elements. For a typedef, the
1116 target type is the aliased type.
1118 If the type does not have a target, this method will throw an
1122 @defun Type.template_argument (n @r{[}, block@r{]})
1123 If this @code{gdb.Type} is an instantiation of a template, this will
1124 return a new @code{gdb.Value} or @code{gdb.Type} which represents the
1125 value of the @var{n}th template argument (indexed starting at 0).
1127 If this @code{gdb.Type} is not a template type, or if the type has fewer
1128 than @var{n} template arguments, this will throw an exception.
1129 Ordinarily, only C@t{++} code will have template types.
1131 If @var{block} is given, then @var{name} is looked up in that scope.
1132 Otherwise, it is searched for globally.
1135 @defun Type.optimized_out ()
1136 Return @code{gdb.Value} instance of this type whose value is optimized
1137 out. This allows a frame decorator to indicate that the value of an
1138 argument or a local variable is not known.
1141 Each type has a code, which indicates what category this type falls
1142 into. The available type categories are represented by constants
1143 defined in the @code{gdb} module:
1146 @vindex TYPE_CODE_PTR
1147 @item gdb.TYPE_CODE_PTR
1148 The type is a pointer.
1150 @vindex TYPE_CODE_ARRAY
1151 @item gdb.TYPE_CODE_ARRAY
1152 The type is an array.
1154 @vindex TYPE_CODE_STRUCT
1155 @item gdb.TYPE_CODE_STRUCT
1156 The type is a structure.
1158 @vindex TYPE_CODE_UNION
1159 @item gdb.TYPE_CODE_UNION
1160 The type is a union.
1162 @vindex TYPE_CODE_ENUM
1163 @item gdb.TYPE_CODE_ENUM
1164 The type is an enum.
1166 @vindex TYPE_CODE_FLAGS
1167 @item gdb.TYPE_CODE_FLAGS
1168 A bit flags type, used for things such as status registers.
1170 @vindex TYPE_CODE_FUNC
1171 @item gdb.TYPE_CODE_FUNC
1172 The type is a function.
1174 @vindex TYPE_CODE_INT
1175 @item gdb.TYPE_CODE_INT
1176 The type is an integer type.
1178 @vindex TYPE_CODE_FLT
1179 @item gdb.TYPE_CODE_FLT
1180 A floating point type.
1182 @vindex TYPE_CODE_VOID
1183 @item gdb.TYPE_CODE_VOID
1184 The special type @code{void}.
1186 @vindex TYPE_CODE_SET
1187 @item gdb.TYPE_CODE_SET
1190 @vindex TYPE_CODE_RANGE
1191 @item gdb.TYPE_CODE_RANGE
1192 A range type, that is, an integer type with bounds.
1194 @vindex TYPE_CODE_STRING
1195 @item gdb.TYPE_CODE_STRING
1196 A string type. Note that this is only used for certain languages with
1197 language-defined string types; C strings are not represented this way.
1199 @vindex TYPE_CODE_BITSTRING
1200 @item gdb.TYPE_CODE_BITSTRING
1201 A string of bits. It is deprecated.
1203 @vindex TYPE_CODE_ERROR
1204 @item gdb.TYPE_CODE_ERROR
1205 An unknown or erroneous type.
1207 @vindex TYPE_CODE_METHOD
1208 @item gdb.TYPE_CODE_METHOD
1209 A method type, as found in C@t{++}.
1211 @vindex TYPE_CODE_METHODPTR
1212 @item gdb.TYPE_CODE_METHODPTR
1213 A pointer-to-member-function.
1215 @vindex TYPE_CODE_MEMBERPTR
1216 @item gdb.TYPE_CODE_MEMBERPTR
1217 A pointer-to-member.
1219 @vindex TYPE_CODE_REF
1220 @item gdb.TYPE_CODE_REF
1223 @vindex TYPE_CODE_RVALUE_REF
1224 @item gdb.TYPE_CODE_RVALUE_REF
1225 A C@t{++}11 rvalue reference type.
1227 @vindex TYPE_CODE_CHAR
1228 @item gdb.TYPE_CODE_CHAR
1231 @vindex TYPE_CODE_BOOL
1232 @item gdb.TYPE_CODE_BOOL
1235 @vindex TYPE_CODE_COMPLEX
1236 @item gdb.TYPE_CODE_COMPLEX
1237 A complex float type.
1239 @vindex TYPE_CODE_TYPEDEF
1240 @item gdb.TYPE_CODE_TYPEDEF
1241 A typedef to some other type.
1243 @vindex TYPE_CODE_NAMESPACE
1244 @item gdb.TYPE_CODE_NAMESPACE
1245 A C@t{++} namespace.
1247 @vindex TYPE_CODE_DECFLOAT
1248 @item gdb.TYPE_CODE_DECFLOAT
1249 A decimal floating point type.
1251 @vindex TYPE_CODE_INTERNAL_FUNCTION
1252 @item gdb.TYPE_CODE_INTERNAL_FUNCTION
1253 A function internal to @value{GDBN}. This is the type used to represent
1254 convenience functions.
1257 Further support for types is provided in the @code{gdb.types}
1258 Python module (@pxref{gdb.types}).
1260 @node Pretty Printing API
1261 @subsubsection Pretty Printing API
1262 @cindex python pretty printing api
1264 A pretty-printer is just an object that holds a value and implements a
1265 specific interface, defined here. An example output is provided
1266 (@pxref{Pretty Printing}).
1268 @defun pretty_printer.children (self)
1269 @value{GDBN} will call this method on a pretty-printer to compute the
1270 children of the pretty-printer's value.
1272 This method must return an object conforming to the Python iterator
1273 protocol. Each item returned by the iterator must be a tuple holding
1274 two elements. The first element is the ``name'' of the child; the
1275 second element is the child's value. The value can be any Python
1276 object which is convertible to a @value{GDBN} value.
1278 This method is optional. If it does not exist, @value{GDBN} will act
1279 as though the value has no children.
1282 @defun pretty_printer.display_hint (self)
1283 The CLI may call this method and use its result to change the
1284 formatting of a value. The result will also be supplied to an MI
1285 consumer as a @samp{displayhint} attribute of the variable being
1288 This method is optional. If it does exist, this method must return a
1291 Some display hints are predefined by @value{GDBN}:
1295 Indicate that the object being printed is ``array-like''. The CLI
1296 uses this to respect parameters such as @code{set print elements} and
1297 @code{set print array}.
1300 Indicate that the object being printed is ``map-like'', and that the
1301 children of this value can be assumed to alternate between keys and
1305 Indicate that the object being printed is ``string-like''. If the
1306 printer's @code{to_string} method returns a Python string of some
1307 kind, then @value{GDBN} will call its internal language-specific
1308 string-printing function to format the string. For the CLI this means
1309 adding quotation marks, possibly escaping some characters, respecting
1310 @code{set print elements}, and the like.
1314 @defun pretty_printer.to_string (self)
1315 @value{GDBN} will call this method to display the string
1316 representation of the value passed to the object's constructor.
1318 When printing from the CLI, if the @code{to_string} method exists,
1319 then @value{GDBN} will prepend its result to the values returned by
1320 @code{children}. Exactly how this formatting is done is dependent on
1321 the display hint, and may change as more hints are added. Also,
1322 depending on the print settings (@pxref{Print Settings}), the CLI may
1323 print just the result of @code{to_string} in a stack trace, omitting
1324 the result of @code{children}.
1326 If this method returns a string, it is printed verbatim.
1328 Otherwise, if this method returns an instance of @code{gdb.Value},
1329 then @value{GDBN} prints this value. This may result in a call to
1330 another pretty-printer.
1332 If instead the method returns a Python value which is convertible to a
1333 @code{gdb.Value}, then @value{GDBN} performs the conversion and prints
1334 the resulting value. Again, this may result in a call to another
1335 pretty-printer. Python scalars (integers, floats, and booleans) and
1336 strings are convertible to @code{gdb.Value}; other types are not.
1338 Finally, if this method returns @code{None} then no further operations
1339 are peformed in this method and nothing is printed.
1341 If the result is not one of these types, an exception is raised.
1344 @value{GDBN} provides a function which can be used to look up the
1345 default pretty-printer for a @code{gdb.Value}:
1347 @findex gdb.default_visualizer
1348 @defun gdb.default_visualizer (value)
1349 This function takes a @code{gdb.Value} object as an argument. If a
1350 pretty-printer for this value exists, then it is returned. If no such
1351 printer exists, then this returns @code{None}.
1354 @node Selecting Pretty-Printers
1355 @subsubsection Selecting Pretty-Printers
1356 @cindex selecting python pretty-printers
1358 The Python list @code{gdb.pretty_printers} contains an array of
1359 functions or callable objects that have been registered via addition
1360 as a pretty-printer. Printers in this list are called @code{global}
1361 printers, they're available when debugging all inferiors.
1362 Each @code{gdb.Progspace} contains a @code{pretty_printers} attribute.
1363 Each @code{gdb.Objfile} also contains a @code{pretty_printers}
1366 Each function on these lists is passed a single @code{gdb.Value}
1367 argument and should return a pretty-printer object conforming to the
1368 interface definition above (@pxref{Pretty Printing API}). If a function
1369 cannot create a pretty-printer for the value, it should return
1372 @value{GDBN} first checks the @code{pretty_printers} attribute of each
1373 @code{gdb.Objfile} in the current program space and iteratively calls
1374 each enabled lookup routine in the list for that @code{gdb.Objfile}
1375 until it receives a pretty-printer object.
1376 If no pretty-printer is found in the objfile lists, @value{GDBN} then
1377 searches the pretty-printer list of the current program space,
1378 calling each enabled function until an object is returned.
1379 After these lists have been exhausted, it tries the global
1380 @code{gdb.pretty_printers} list, again calling each enabled function until an
1383 The order in which the objfiles are searched is not specified. For a
1384 given list, functions are always invoked from the head of the list,
1385 and iterated over sequentially until the end of the list, or a printer
1388 For various reasons a pretty-printer may not work.
1389 For example, the underlying data structure may have changed and
1390 the pretty-printer is out of date.
1392 The consequences of a broken pretty-printer are severe enough that
1393 @value{GDBN} provides support for enabling and disabling individual
1394 printers. For example, if @code{print frame-arguments} is on,
1395 a backtrace can become highly illegible if any argument is printed
1396 with a broken printer.
1398 Pretty-printers are enabled and disabled by attaching an @code{enabled}
1399 attribute to the registered function or callable object. If this attribute
1400 is present and its value is @code{False}, the printer is disabled, otherwise
1401 the printer is enabled.
1403 @node Writing a Pretty-Printer
1404 @subsubsection Writing a Pretty-Printer
1405 @cindex writing a pretty-printer
1407 A pretty-printer consists of two parts: a lookup function to detect
1408 if the type is supported, and the printer itself.
1410 Here is an example showing how a @code{std::string} printer might be
1411 written. @xref{Pretty Printing API}, for details on the API this class
1415 class StdStringPrinter(object):
1416 "Print a std::string"
1418 def __init__(self, val):
1421 def to_string(self):
1422 return self.val['_M_dataplus']['_M_p']
1424 def display_hint(self):
1428 And here is an example showing how a lookup function for the printer
1429 example above might be written.
1432 def str_lookup_function(val):
1433 lookup_tag = val.type.tag
1434 if lookup_tag == None:
1436 regex = re.compile("^std::basic_string<char,.*>$")
1437 if regex.match(lookup_tag):
1438 return StdStringPrinter(val)
1442 The example lookup function extracts the value's type, and attempts to
1443 match it to a type that it can pretty-print. If it is a type the
1444 printer can pretty-print, it will return a printer object. If not, it
1445 returns @code{None}.
1447 We recommend that you put your core pretty-printers into a Python
1448 package. If your pretty-printers are for use with a library, we
1449 further recommend embedding a version number into the package name.
1450 This practice will enable @value{GDBN} to load multiple versions of
1451 your pretty-printers at the same time, because they will have
1454 You should write auto-loaded code (@pxref{Python Auto-loading}) such that it
1455 can be evaluated multiple times without changing its meaning. An
1456 ideal auto-load file will consist solely of @code{import}s of your
1457 printer modules, followed by a call to a register pretty-printers with
1458 the current objfile.
1460 Taken as a whole, this approach will scale nicely to multiple
1461 inferiors, each potentially using a different library version.
1462 Embedding a version number in the Python package name will ensure that
1463 @value{GDBN} is able to load both sets of printers simultaneously.
1464 Then, because the search for pretty-printers is done by objfile, and
1465 because your auto-loaded code took care to register your library's
1466 printers with a specific objfile, @value{GDBN} will find the correct
1467 printers for the specific version of the library used by each
1470 To continue the @code{std::string} example (@pxref{Pretty Printing API}),
1471 this code might appear in @code{gdb.libstdcxx.v6}:
1474 def register_printers(objfile):
1475 objfile.pretty_printers.append(str_lookup_function)
1479 And then the corresponding contents of the auto-load file would be:
1482 import gdb.libstdcxx.v6
1483 gdb.libstdcxx.v6.register_printers(gdb.current_objfile())
1486 The previous example illustrates a basic pretty-printer.
1487 There are a few things that can be improved on.
1488 The printer doesn't have a name, making it hard to identify in a
1489 list of installed printers. The lookup function has a name, but
1490 lookup functions can have arbitrary, even identical, names.
1492 Second, the printer only handles one type, whereas a library typically has
1493 several types. One could install a lookup function for each desired type
1494 in the library, but one could also have a single lookup function recognize
1495 several types. The latter is the conventional way this is handled.
1496 If a pretty-printer can handle multiple data types, then its
1497 @dfn{subprinters} are the printers for the individual data types.
1499 The @code{gdb.printing} module provides a formal way of solving these
1500 problems (@pxref{gdb.printing}).
1501 Here is another example that handles multiple types.
1503 These are the types we are going to pretty-print:
1506 struct foo @{ int a, b; @};
1507 struct bar @{ struct foo x, y; @};
1510 Here are the printers:
1514 """Print a foo object."""
1516 def __init__(self, val):
1519 def to_string(self):
1520 return ("a=<" + str(self.val["a"]) +
1521 "> b=<" + str(self.val["b"]) + ">")
1524 """Print a bar object."""
1526 def __init__(self, val):
1529 def to_string(self):
1530 return ("x=<" + str(self.val["x"]) +
1531 "> y=<" + str(self.val["y"]) + ">")
1534 This example doesn't need a lookup function, that is handled by the
1535 @code{gdb.printing} module. Instead a function is provided to build up
1536 the object that handles the lookup.
1541 def build_pretty_printer():
1542 pp = gdb.printing.RegexpCollectionPrettyPrinter(
1544 pp.add_printer('foo', '^foo$', fooPrinter)
1545 pp.add_printer('bar', '^bar$', barPrinter)
1549 And here is the autoload support:
1554 gdb.printing.register_pretty_printer(
1555 gdb.current_objfile(),
1556 my_library.build_pretty_printer())
1559 Finally, when this printer is loaded into @value{GDBN}, here is the
1560 corresponding output of @samp{info pretty-printer}:
1563 (gdb) info pretty-printer
1570 @node Type Printing API
1571 @subsubsection Type Printing API
1572 @cindex type printing API for Python
1574 @value{GDBN} provides a way for Python code to customize type display.
1575 This is mainly useful for substituting canonical typedef names for
1578 @cindex type printer
1579 A @dfn{type printer} is just a Python object conforming to a certain
1580 protocol. A simple base class implementing the protocol is provided;
1581 see @ref{gdb.types}. A type printer must supply at least:
1583 @defivar type_printer enabled
1584 A boolean which is True if the printer is enabled, and False
1585 otherwise. This is manipulated by the @code{enable type-printer}
1586 and @code{disable type-printer} commands.
1589 @defivar type_printer name
1590 The name of the type printer. This must be a string. This is used by
1591 the @code{enable type-printer} and @code{disable type-printer}
1595 @defmethod type_printer instantiate (self)
1596 This is called by @value{GDBN} at the start of type-printing. It is
1597 only called if the type printer is enabled. This method must return a
1598 new object that supplies a @code{recognize} method, as described below.
1602 When displaying a type, say via the @code{ptype} command, @value{GDBN}
1603 will compute a list of type recognizers. This is done by iterating
1604 first over the per-objfile type printers (@pxref{Objfiles In Python}),
1605 followed by the per-progspace type printers (@pxref{Progspaces In
1606 Python}), and finally the global type printers.
1608 @value{GDBN} will call the @code{instantiate} method of each enabled
1609 type printer. If this method returns @code{None}, then the result is
1610 ignored; otherwise, it is appended to the list of recognizers.
1612 Then, when @value{GDBN} is going to display a type name, it iterates
1613 over the list of recognizers. For each one, it calls the recognition
1614 function, stopping if the function returns a non-@code{None} value.
1615 The recognition function is defined as:
1617 @defmethod type_recognizer recognize (self, type)
1618 If @var{type} is not recognized, return @code{None}. Otherwise,
1619 return a string which is to be printed as the name of @var{type}.
1620 The @var{type} argument will be an instance of @code{gdb.Type}
1621 (@pxref{Types In Python}).
1624 @value{GDBN} uses this two-pass approach so that type printers can
1625 efficiently cache information without holding on to it too long. For
1626 example, it can be convenient to look up type information in a type
1627 printer and hold it for a recognizer's lifetime; if a single pass were
1628 done then type printers would have to make use of the event system in
1629 order to avoid holding information that could become stale as the
1632 @node Frame Filter API
1633 @subsubsection Filtering Frames
1634 @cindex frame filters api
1636 Frame filters are Python objects that manipulate the visibility of a
1637 frame or frames when a backtrace (@pxref{Backtrace}) is printed by
1640 Only commands that print a backtrace, or, in the case of @sc{gdb/mi}
1641 commands (@pxref{GDB/MI}), those that return a collection of frames
1642 are affected. The commands that work with frame filters are:
1644 @code{backtrace} (@pxref{backtrace-command,, The backtrace command}),
1645 @code{-stack-list-frames}
1646 (@pxref{-stack-list-frames,, The -stack-list-frames command}),
1647 @code{-stack-list-variables} (@pxref{-stack-list-variables,, The
1648 -stack-list-variables command}), @code{-stack-list-arguments}
1649 @pxref{-stack-list-arguments,, The -stack-list-arguments command}) and
1650 @code{-stack-list-locals} (@pxref{-stack-list-locals,, The
1651 -stack-list-locals command}).
1653 A frame filter works by taking an iterator as an argument, applying
1654 actions to the contents of that iterator, and returning another
1655 iterator (or, possibly, the same iterator it was provided in the case
1656 where the filter does not perform any operations). Typically, frame
1657 filters utilize tools such as the Python's @code{itertools} module to
1658 work with and create new iterators from the source iterator.
1659 Regardless of how a filter chooses to apply actions, it must not alter
1660 the underlying @value{GDBN} frame or frames, or attempt to alter the
1661 call-stack within @value{GDBN}. This preserves data integrity within
1662 @value{GDBN}. Frame filters are executed on a priority basis and care
1663 should be taken that some frame filters may have been executed before,
1664 and that some frame filters will be executed after.
1666 An important consideration when designing frame filters, and well
1667 worth reflecting upon, is that frame filters should avoid unwinding
1668 the call stack if possible. Some stacks can run very deep, into the
1669 tens of thousands in some cases. To search every frame when a frame
1670 filter executes may be too expensive at that step. The frame filter
1671 cannot know how many frames it has to iterate over, and it may have to
1672 iterate through them all. This ends up duplicating effort as
1673 @value{GDBN} performs this iteration when it prints the frames. If
1674 the filter can defer unwinding frames until frame decorators are
1675 executed, after the last filter has executed, it should. @xref{Frame
1676 Decorator API}, for more information on decorators. Also, there are
1677 examples for both frame decorators and filters in later chapters.
1678 @xref{Writing a Frame Filter}, for more information.
1680 The Python dictionary @code{gdb.frame_filters} contains key/object
1681 pairings that comprise a frame filter. Frame filters in this
1682 dictionary are called @code{global} frame filters, and they are
1683 available when debugging all inferiors. These frame filters must
1684 register with the dictionary directly. In addition to the
1685 @code{global} dictionary, there are other dictionaries that are loaded
1686 with different inferiors via auto-loading (@pxref{Python
1687 Auto-loading}). The two other areas where frame filter dictionaries
1688 can be found are: @code{gdb.Progspace} which contains a
1689 @code{frame_filters} dictionary attribute, and each @code{gdb.Objfile}
1690 object which also contains a @code{frame_filters} dictionary
1693 When a command is executed from @value{GDBN} that is compatible with
1694 frame filters, @value{GDBN} combines the @code{global},
1695 @code{gdb.Progspace} and all @code{gdb.Objfile} dictionaries currently
1696 loaded. All of the @code{gdb.Objfile} dictionaries are combined, as
1697 several frames, and thus several object files, might be in use.
1698 @value{GDBN} then prunes any frame filter whose @code{enabled}
1699 attribute is @code{False}. This pruned list is then sorted according
1700 to the @code{priority} attribute in each filter.
1702 Once the dictionaries are combined, pruned and sorted, @value{GDBN}
1703 creates an iterator which wraps each frame in the call stack in a
1704 @code{FrameDecorator} object, and calls each filter in order. The
1705 output from the previous filter will always be the input to the next
1708 Frame filters have a mandatory interface which each frame filter must
1709 implement, defined here:
1711 @defun FrameFilter.filter (iterator)
1712 @value{GDBN} will call this method on a frame filter when it has
1713 reached the order in the priority list for that filter.
1715 For example, if there are four frame filters:
1726 The order that the frame filters will be called is:
1729 Filter3 -> Filter2 -> Filter1 -> Filter4
1732 Note that the output from @code{Filter3} is passed to the input of
1733 @code{Filter2}, and so on.
1735 This @code{filter} method is passed a Python iterator. This iterator
1736 contains a sequence of frame decorators that wrap each
1737 @code{gdb.Frame}, or a frame decorator that wraps another frame
1738 decorator. The first filter that is executed in the sequence of frame
1739 filters will receive an iterator entirely comprised of default
1740 @code{FrameDecorator} objects. However, after each frame filter is
1741 executed, the previous frame filter may have wrapped some or all of
1742 the frame decorators with their own frame decorator. As frame
1743 decorators must also conform to a mandatory interface, these
1744 decorators can be assumed to act in a uniform manner (@pxref{Frame
1747 This method must return an object conforming to the Python iterator
1748 protocol. Each item in the iterator must be an object conforming to
1749 the frame decorator interface. If a frame filter does not wish to
1750 perform any operations on this iterator, it should return that
1753 This method is not optional. If it does not exist, @value{GDBN} will
1754 raise and print an error.
1757 @defvar FrameFilter.name
1758 The @code{name} attribute must be Python string which contains the
1759 name of the filter displayed by @value{GDBN} (@pxref{Frame Filter
1760 Management}). This attribute may contain any combination of letters
1761 or numbers. Care should be taken to ensure that it is unique. This
1762 attribute is mandatory.
1765 @defvar FrameFilter.enabled
1766 The @code{enabled} attribute must be Python boolean. This attribute
1767 indicates to @value{GDBN} whether the frame filter is enabled, and
1768 should be considered when frame filters are executed. If
1769 @code{enabled} is @code{True}, then the frame filter will be executed
1770 when any of the backtrace commands detailed earlier in this chapter
1771 are executed. If @code{enabled} is @code{False}, then the frame
1772 filter will not be executed. This attribute is mandatory.
1775 @defvar FrameFilter.priority
1776 The @code{priority} attribute must be Python integer. This attribute
1777 controls the order of execution in relation to other frame filters.
1778 There are no imposed limits on the range of @code{priority} other than
1779 it must be a valid integer. The higher the @code{priority} attribute,
1780 the sooner the frame filter will be executed in relation to other
1781 frame filters. Although @code{priority} can be negative, it is
1782 recommended practice to assume zero is the lowest priority that a
1783 frame filter can be assigned. Frame filters that have the same
1784 priority are executed in unsorted order in that priority slot. This
1785 attribute is mandatory. 100 is a good default priority.
1788 @node Frame Decorator API
1789 @subsubsection Decorating Frames
1790 @cindex frame decorator api
1792 Frame decorators are sister objects to frame filters (@pxref{Frame
1793 Filter API}). Frame decorators are applied by a frame filter and can
1794 only be used in conjunction with frame filters.
1796 The purpose of a frame decorator is to customize the printed content
1797 of each @code{gdb.Frame} in commands where frame filters are executed.
1798 This concept is called decorating a frame. Frame decorators decorate
1799 a @code{gdb.Frame} with Python code contained within each API call.
1800 This separates the actual data contained in a @code{gdb.Frame} from
1801 the decorated data produced by a frame decorator. This abstraction is
1802 necessary to maintain integrity of the data contained in each
1805 Frame decorators have a mandatory interface, defined below.
1807 @value{GDBN} already contains a frame decorator called
1808 @code{FrameDecorator}. This contains substantial amounts of
1809 boilerplate code to decorate the content of a @code{gdb.Frame}. It is
1810 recommended that other frame decorators inherit and extend this
1811 object, and only to override the methods needed.
1813 @tindex gdb.FrameDecorator
1814 @code{FrameDecorator} is defined in the Python module
1815 @code{gdb.FrameDecorator}, so your code can import it like:
1817 from gdb.FrameDecorator import FrameDecorator
1820 @defun FrameDecorator.elided (self)
1822 The @code{elided} method groups frames together in a hierarchical
1823 system. An example would be an interpreter, where multiple low-level
1824 frames make up a single call in the interpreted language. In this
1825 example, the frame filter would elide the low-level frames and present
1826 a single high-level frame, representing the call in the interpreted
1827 language, to the user.
1829 The @code{elided} function must return an iterable and this iterable
1830 must contain the frames that are being elided wrapped in a suitable
1831 frame decorator. If no frames are being elided this function may
1832 return an empty iterable, or @code{None}. Elided frames are indented
1833 from normal frames in a @code{CLI} backtrace, or in the case of
1834 @code{GDB/MI}, are placed in the @code{children} field of the eliding
1837 It is the frame filter's task to also filter out the elided frames from
1838 the source iterator. This will avoid printing the frame twice.
1841 @defun FrameDecorator.function (self)
1843 This method returns the name of the function in the frame that is to
1846 This method must return a Python string describing the function, or
1849 If this function returns @code{None}, @value{GDBN} will not print any
1850 data for this field.
1853 @defun FrameDecorator.address (self)
1855 This method returns the address of the frame that is to be printed.
1857 This method must return a Python numeric integer type of sufficient
1858 size to describe the address of the frame, or @code{None}.
1860 If this function returns a @code{None}, @value{GDBN} will not print
1861 any data for this field.
1864 @defun FrameDecorator.filename (self)
1866 This method returns the filename and path associated with this frame.
1868 This method must return a Python string containing the filename and
1869 the path to the object file backing the frame, or @code{None}.
1871 If this function returns a @code{None}, @value{GDBN} will not print
1872 any data for this field.
1875 @defun FrameDecorator.line (self):
1877 This method returns the line number associated with the current
1878 position within the function addressed by this frame.
1880 This method must return a Python integer type, or @code{None}.
1882 If this function returns a @code{None}, @value{GDBN} will not print
1883 any data for this field.
1886 @defun FrameDecorator.frame_args (self)
1889 This method must return an iterable, or @code{None}. Returning an
1890 empty iterable, or @code{None} means frame arguments will not be
1891 printed for this frame. This iterable must contain objects that
1892 implement two methods, described here.
1894 This object must implement a @code{argument} method which takes a
1895 single @code{self} parameter and must return a @code{gdb.Symbol}
1896 (@pxref{Symbols In Python}), or a Python string. The object must also
1897 implement a @code{value} method which takes a single @code{self}
1898 parameter and must return a @code{gdb.Value} (@pxref{Values From
1899 Inferior}), a Python value, or @code{None}. If the @code{value}
1900 method returns @code{None}, and the @code{argument} method returns a
1901 @code{gdb.Symbol}, @value{GDBN} will look-up and print the value of
1902 the @code{gdb.Symbol} automatically.
1907 class SymValueWrapper():
1909 def __init__(self, symbol, value):
1919 class SomeFrameDecorator()
1922 def frame_args(self):
1925 block = self.inferior_frame.block()
1929 # Iterate over all symbols in a block. Only add
1930 # symbols that are arguments.
1932 if not sym.is_argument:
1934 args.append(SymValueWrapper(sym,None))
1936 # Add example synthetic argument.
1937 args.append(SymValueWrapper(``foo'', 42))
1943 @defun FrameDecorator.frame_locals (self)
1945 This method must return an iterable or @code{None}. Returning an
1946 empty iterable, or @code{None} means frame local arguments will not be
1947 printed for this frame.
1949 The object interface, the description of the various strategies for
1950 reading frame locals, and the example are largely similar to those
1951 described in the @code{frame_args} function, (@pxref{frame_args,,The
1952 frame filter frame_args function}). Below is a modified example:
1955 class SomeFrameDecorator()
1958 def frame_locals(self):
1961 block = self.inferior_frame.block()
1965 # Iterate over all symbols in a block. Add all
1966 # symbols, except arguments.
1970 vars.append(SymValueWrapper(sym,None))
1972 # Add an example of a synthetic local variable.
1973 vars.append(SymValueWrapper(``bar'', 99))
1979 @defun FrameDecorator.inferior_frame (self):
1981 This method must return the underlying @code{gdb.Frame} that this
1982 frame decorator is decorating. @value{GDBN} requires the underlying
1983 frame for internal frame information to determine how to print certain
1984 values when printing a frame.
1987 @node Writing a Frame Filter
1988 @subsubsection Writing a Frame Filter
1989 @cindex writing a frame filter
1991 There are three basic elements that a frame filter must implement: it
1992 must correctly implement the documented interface (@pxref{Frame Filter
1993 API}), it must register itself with @value{GDBN}, and finally, it must
1994 decide if it is to work on the data provided by @value{GDBN}. In all
1995 cases, whether it works on the iterator or not, each frame filter must
1996 return an iterator. A bare-bones frame filter follows the pattern in
1997 the following example.
2002 class FrameFilter():
2005 # Frame filter attribute creation.
2007 # 'name' is the name of the filter that GDB will display.
2009 # 'priority' is the priority of the filter relative to other
2012 # 'enabled' is a boolean that indicates whether this filter is
2013 # enabled and should be executed.
2019 # Register this frame filter with the global frame_filters
2021 gdb.frame_filters[self.name] = self
2023 def filter(self, frame_iter):
2024 # Just return the iterator.
2028 The frame filter in the example above implements the three
2029 requirements for all frame filters. It implements the API, self
2030 registers, and makes a decision on the iterator (in this case, it just
2031 returns the iterator untouched).
2033 The first step is attribute creation and assignment, and as shown in
2034 the comments the filter assigns the following attributes: @code{name},
2035 @code{priority} and whether the filter should be enabled with the
2036 @code{enabled} attribute.
2038 The second step is registering the frame filter with the dictionary or
2039 dictionaries that the frame filter has interest in. As shown in the
2040 comments, this filter just registers itself with the global dictionary
2041 @code{gdb.frame_filters}. As noted earlier, @code{gdb.frame_filters}
2042 is a dictionary that is initialized in the @code{gdb} module when
2043 @value{GDBN} starts. What dictionary a filter registers with is an
2044 important consideration. Generally, if a filter is specific to a set
2045 of code, it should be registered either in the @code{objfile} or
2046 @code{progspace} dictionaries as they are specific to the program
2047 currently loaded in @value{GDBN}. The global dictionary is always
2048 present in @value{GDBN} and is never unloaded. Any filters registered
2049 with the global dictionary will exist until @value{GDBN} exits. To
2050 avoid filters that may conflict, it is generally better to register
2051 frame filters against the dictionaries that more closely align with
2052 the usage of the filter currently in question. @xref{Python
2053 Auto-loading}, for further information on auto-loading Python scripts.
2055 @value{GDBN} takes a hands-off approach to frame filter registration,
2056 therefore it is the frame filter's responsibility to ensure
2057 registration has occurred, and that any exceptions are handled
2058 appropriately. In particular, you may wish to handle exceptions
2059 relating to Python dictionary key uniqueness. It is mandatory that
2060 the dictionary key is the same as frame filter's @code{name}
2061 attribute. When a user manages frame filters (@pxref{Frame Filter
2062 Management}), the names @value{GDBN} will display are those contained
2063 in the @code{name} attribute.
2065 The final step of this example is the implementation of the
2066 @code{filter} method. As shown in the example comments, we define the
2067 @code{filter} method and note that the method must take an iterator,
2068 and also must return an iterator. In this bare-bones example, the
2069 frame filter is not very useful as it just returns the iterator
2070 untouched. However this is a valid operation for frame filters that
2071 have the @code{enabled} attribute set, but decide not to operate on
2074 In the next example, the frame filter operates on all frames and
2075 utilizes a frame decorator to perform some work on the frames.
2076 @xref{Frame Decorator API}, for further information on the frame
2077 decorator interface.
2079 This example works on inlined frames. It highlights frames which are
2080 inlined by tagging them with an ``[inlined]'' tag. By applying a
2081 frame decorator to all frames with the Python @code{itertools imap}
2082 method, the example defers actions to the frame decorator. Frame
2083 decorators are only processed when @value{GDBN} prints the backtrace.
2085 This introduces a new decision making topic: whether to perform
2086 decision making operations at the filtering step, or at the printing
2087 step. In this example's approach, it does not perform any filtering
2088 decisions at the filtering step beyond mapping a frame decorator to
2089 each frame. This allows the actual decision making to be performed
2090 when each frame is printed. This is an important consideration, and
2091 well worth reflecting upon when designing a frame filter. An issue
2092 that frame filters should avoid is unwinding the stack if possible.
2093 Some stacks can run very deep, into the tens of thousands in some
2094 cases. To search every frame to determine if it is inlined ahead of
2095 time may be too expensive at the filtering step. The frame filter
2096 cannot know how many frames it has to iterate over, and it would have
2097 to iterate through them all. This ends up duplicating effort as
2098 @value{GDBN} performs this iteration when it prints the frames.
2100 In this example decision making can be deferred to the printing step.
2101 As each frame is printed, the frame decorator can examine each frame
2102 in turn when @value{GDBN} iterates. From a performance viewpoint,
2103 this is the most appropriate decision to make as it avoids duplicating
2104 the effort that the printing step would undertake anyway. Also, if
2105 there are many frame filters unwinding the stack during filtering, it
2106 can substantially delay the printing of the backtrace which will
2107 result in large memory usage, and a poor user experience.
2110 class InlineFilter():
2113 self.name = "InlinedFrameFilter"
2116 gdb.frame_filters[self.name] = self
2118 def filter(self, frame_iter):
2119 frame_iter = itertools.imap(InlinedFrameDecorator,
2124 This frame filter is somewhat similar to the earlier example, except
2125 that the @code{filter} method applies a frame decorator object called
2126 @code{InlinedFrameDecorator} to each element in the iterator. The
2127 @code{imap} Python method is light-weight. It does not proactively
2128 iterate over the iterator, but rather creates a new iterator which
2129 wraps the existing one.
2131 Below is the frame decorator for this example.
2134 class InlinedFrameDecorator(FrameDecorator):
2136 def __init__(self, fobj):
2137 super(InlinedFrameDecorator, self).__init__(fobj)
2140 frame = fobj.inferior_frame()
2141 name = str(frame.name())
2143 if frame.type() == gdb.INLINE_FRAME:
2144 name = name + " [inlined]"
2149 This frame decorator only defines and overrides the @code{function}
2150 method. It lets the supplied @code{FrameDecorator}, which is shipped
2151 with @value{GDBN}, perform the other work associated with printing
2154 The combination of these two objects create this output from a
2158 #0 0x004004e0 in bar () at inline.c:11
2159 #1 0x00400566 in max [inlined] (b=6, a=12) at inline.c:21
2160 #2 0x00400566 in main () at inline.c:31
2163 So in the case of this example, a frame decorator is applied to all
2164 frames, regardless of whether they may be inlined or not. As
2165 @value{GDBN} iterates over the iterator produced by the frame filters,
2166 @value{GDBN} executes each frame decorator which then makes a decision
2167 on what to print in the @code{function} callback. Using a strategy
2168 like this is a way to defer decisions on the frame content to printing
2171 @subheading Eliding Frames
2173 It might be that the above example is not desirable for representing
2174 inlined frames, and a hierarchical approach may be preferred. If we
2175 want to hierarchically represent frames, the @code{elided} frame
2176 decorator interface might be preferable.
2178 This example approaches the issue with the @code{elided} method. This
2179 example is quite long, but very simplistic. It is out-of-scope for
2180 this section to write a complete example that comprehensively covers
2181 all approaches of finding and printing inlined frames. However, this
2182 example illustrates the approach an author might use.
2184 This example comprises of three sections.
2187 class InlineFrameFilter():
2190 self.name = "InlinedFrameFilter"
2193 gdb.frame_filters[self.name] = self
2195 def filter(self, frame_iter):
2196 return ElidingInlineIterator(frame_iter)
2199 This frame filter is very similar to the other examples. The only
2200 difference is this frame filter is wrapping the iterator provided to
2201 it (@code{frame_iter}) with a custom iterator called
2202 @code{ElidingInlineIterator}. This again defers actions to when
2203 @value{GDBN} prints the backtrace, as the iterator is not traversed
2206 The iterator for this example is as follows. It is in this section of
2207 the example where decisions are made on the content of the backtrace.
2210 class ElidingInlineIterator:
2211 def __init__(self, ii):
2212 self.input_iterator = ii
2218 frame = next(self.input_iterator)
2220 if frame.inferior_frame().type() != gdb.INLINE_FRAME:
2224 eliding_frame = next(self.input_iterator)
2225 except StopIteration:
2227 return ElidingFrameDecorator(eliding_frame, [frame])
2230 This iterator implements the Python iterator protocol. When the
2231 @code{next} function is called (when @value{GDBN} prints each frame),
2232 the iterator checks if this frame decorator, @code{frame}, is wrapping
2233 an inlined frame. If it is not, it returns the existing frame decorator
2234 untouched. If it is wrapping an inlined frame, it assumes that the
2235 inlined frame was contained within the next oldest frame,
2236 @code{eliding_frame}, which it fetches. It then creates and returns a
2237 frame decorator, @code{ElidingFrameDecorator}, which contains both the
2238 elided frame, and the eliding frame.
2241 class ElidingInlineDecorator(FrameDecorator):
2243 def __init__(self, frame, elided_frames):
2244 super(ElidingInlineDecorator, self).__init__(frame)
2246 self.elided_frames = elided_frames
2249 return iter(self.elided_frames)
2252 This frame decorator overrides one function and returns the inlined
2253 frame in the @code{elided} method. As before it lets
2254 @code{FrameDecorator} do the rest of the work involved in printing
2255 this frame. This produces the following output.
2258 #0 0x004004e0 in bar () at inline.c:11
2259 #2 0x00400529 in main () at inline.c:25
2260 #1 0x00400529 in max (b=6, a=12) at inline.c:15
2263 In that output, @code{max} which has been inlined into @code{main} is
2264 printed hierarchically. Another approach would be to combine the
2265 @code{function} method, and the @code{elided} method to both print a
2266 marker in the inlined frame, and also show the hierarchical
2269 @node Unwinding Frames in Python
2270 @subsubsection Unwinding Frames in Python
2271 @cindex unwinding frames in Python
2273 In @value{GDBN} terminology ``unwinding'' is the process of finding
2274 the previous frame (that is, caller's) from the current one. An
2275 unwinder has three methods. The first one checks if it can handle
2276 given frame (``sniff'' it). For the frames it can sniff an unwinder
2277 provides two additional methods: it can return frame's ID, and it can
2278 fetch registers from the previous frame. A running @value{GDBN}
2279 mantains a list of the unwinders and calls each unwinder's sniffer in
2280 turn until it finds the one that recognizes the current frame. There
2281 is an API to register an unwinder.
2283 The unwinders that come with @value{GDBN} handle standard frames.
2284 However, mixed language applications (for example, an application
2285 running Java Virtual Machine) sometimes use frame layouts that cannot
2286 be handled by the @value{GDBN} unwinders. You can write Python code
2287 that can handle such custom frames.
2289 You implement a frame unwinder in Python as a class with which has two
2290 attributes, @code{name} and @code{enabled}, with obvious meanings, and
2291 a single method @code{__call__}, which examines a given frame and
2292 returns an object (an instance of @code{gdb.UnwindInfo class)}
2293 describing it. If an unwinder does not recognize a frame, it should
2294 return @code{None}. The code in @value{GDBN} that enables writing
2295 unwinders in Python uses this object to return frame's ID and previous
2296 frame registers when @value{GDBN} core asks for them.
2298 An unwinder should do as little work as possible. Some otherwise
2299 innocuous operations can cause problems (even crashes, as this code is
2300 not not well-hardened yet). For example, making an inferior call from
2301 an unwinder is unadvisable, as an inferior call will reset
2302 @value{GDBN}'s stack unwinding process, potentially causing re-entrant
2305 @subheading Unwinder Input
2307 An object passed to an unwinder (a @code{gdb.PendingFrame} instance)
2308 provides a method to read frame's registers:
2310 @defun PendingFrame.read_register (reg)
2311 This method returns the contents of the register @var{reg} in the
2312 frame as a @code{gdb.Value} object. @var{reg} can be either a
2313 register number or a register name; the values are platform-specific.
2314 They are usually found in the corresponding
2315 @file{@var{platform}-tdep.h} file in the @value{GDBN} source tree. If
2316 @var{reg} does not name a register for the current architecture, this
2317 method will throw an exception.
2319 Note that this method will always return a @code{gdb.Value} for a
2320 valid register name. This does not mean that the value will be valid.
2321 For example, you may request a register that an earlier unwinder could
2322 not unwind---the value will be unavailable. Instead, the
2323 @code{gdb.Value} returned from this method will be lazy; that is, its
2324 underlying bits will not be fetched until it is first used. So,
2325 attempting to use such a value will cause an exception at the point of
2328 The type of the returned @code{gdb.Value} depends on the register and
2329 the architecture. It is common for registers to have a scalar type,
2330 like @code{long long}; but many other types are possible, such as
2331 pointer, pointer-to-function, floating point or vector types.
2334 It also provides a factory method to create a @code{gdb.UnwindInfo}
2335 instance to be returned to @value{GDBN}:
2337 @defun PendingFrame.create_unwind_info (frame_id)
2338 Returns a new @code{gdb.UnwindInfo} instance identified by given
2339 @var{frame_id}. The argument is used to build @value{GDBN}'s frame ID
2340 using one of functions provided by @value{GDBN}. @var{frame_id}'s attributes
2341 determine which function will be used, as follows:
2345 The frame is identified by the given stack address and PC. The stack
2346 address must be chosen so that it is constant throughout the lifetime
2347 of the frame, so a typical choice is the value of the stack pointer at
2348 the start of the function---in the DWARF standard, this would be the
2349 ``Call Frame Address''.
2351 This is the most common case by far. The other cases are documented
2352 for completeness but are only useful in specialized situations.
2354 @item sp, pc, special
2355 The frame is identified by the stack address, the PC, and a
2356 ``special'' address. The special address is used on architectures
2357 that can have frames that do not change the stack, but which are still
2358 distinct, for example the IA-64, which has a second stack for
2359 registers. Both @var{sp} and @var{special} must be constant
2360 throughout the lifetime of the frame.
2363 The frame is identified by the stack address only. Any other stack
2364 frame with a matching @var{sp} will be considered to match this frame.
2365 Inside gdb, this is called a ``wild frame''. You will never need
2369 Each attribute value should be an instance of @code{gdb.Value}.
2373 @subheading Unwinder Output: UnwindInfo
2375 Use @code{PendingFrame.create_unwind_info} method described above to
2376 create a @code{gdb.UnwindInfo} instance. Use the following method to
2377 specify caller registers that have been saved in this frame:
2379 @defun gdb.UnwindInfo.add_saved_register (reg, value)
2380 @var{reg} identifies the register. It can be a number or a name, just
2381 as for the @code{PendingFrame.read_register} method above.
2382 @var{value} is a register value (a @code{gdb.Value} object).
2385 @subheading Unwinder Skeleton Code
2387 @value{GDBN} comes with the module containing the base @code{Unwinder}
2388 class. Derive your unwinder class from it and structure the code as
2392 from gdb.unwinders import Unwinder
2394 class FrameId(object):
2395 def __init__(self, sp, pc):
2400 class MyUnwinder(Unwinder):
2402 supe(MyUnwinder, self).__init___(<expects unwinder name argument>)
2404 def __call__(pending_frame):
2405 if not <we recognize frame>:
2407 # Create UnwindInfo. Usually the frame is identified by the stack
2408 # pointer and the program counter.
2409 sp = pending_frame.read_register(<SP number>)
2410 pc = pending_frame.read_register(<PC number>)
2411 unwind_info = pending_frame.create_unwind_info(FrameId(sp, pc))
2413 # Find the values of the registers in the caller's frame and
2414 # save them in the result:
2415 unwind_info.add_saved_register(<register>, <value>)
2418 # Return the result:
2423 @subheading Registering a Unwinder
2425 An object file, a program space, and the @value{GDBN} proper can have
2426 unwinders registered with it.
2428 The @code{gdb.unwinders} module provides the function to register a
2431 @defun gdb.unwinder.register_unwinder (locus, unwinder, replace=False)
2432 @var{locus} is specifies an object file or a program space to which
2433 @var{unwinder} is added. Passing @code{None} or @code{gdb} adds
2434 @var{unwinder} to the @value{GDBN}'s global unwinder list. The newly
2435 added @var{unwinder} will be called before any other unwinder from the
2436 same locus. Two unwinders in the same locus cannot have the same
2437 name. An attempt to add a unwinder with already existing name raises
2438 an exception unless @var{replace} is @code{True}, in which case the
2439 old unwinder is deleted.
2442 @subheading Unwinder Precedence
2444 @value{GDBN} first calls the unwinders from all the object files in no
2445 particular order, then the unwinders from the current program space,
2446 and finally the unwinders from @value{GDBN}.
2448 @node Xmethods In Python
2449 @subsubsection Xmethods In Python
2450 @cindex xmethods in Python
2452 @dfn{Xmethods} are additional methods or replacements for existing
2453 methods of a C@t{++} class. This feature is useful for those cases
2454 where a method defined in C@t{++} source code could be inlined or
2455 optimized out by the compiler, making it unavailable to @value{GDBN}.
2456 For such cases, one can define an xmethod to serve as a replacement
2457 for the method defined in the C@t{++} source code. @value{GDBN} will
2458 then invoke the xmethod, instead of the C@t{++} method, to
2459 evaluate expressions. One can also use xmethods when debugging
2460 with core files. Moreover, when debugging live programs, invoking an
2461 xmethod need not involve running the inferior (which can potentially
2462 perturb its state). Hence, even if the C@t{++} method is available, it
2463 is better to use its replacement xmethod if one is defined.
2465 The xmethods feature in Python is available via the concepts of an
2466 @dfn{xmethod matcher} and an @dfn{xmethod worker}. To
2467 implement an xmethod, one has to implement a matcher and a
2468 corresponding worker for it (more than one worker can be
2469 implemented, each catering to a different overloaded instance of the
2470 method). Internally, @value{GDBN} invokes the @code{match} method of a
2471 matcher to match the class type and method name. On a match, the
2472 @code{match} method returns a list of matching @emph{worker} objects.
2473 Each worker object typically corresponds to an overloaded instance of
2474 the xmethod. They implement a @code{get_arg_types} method which
2475 returns a sequence of types corresponding to the arguments the xmethod
2476 requires. @value{GDBN} uses this sequence of types to perform
2477 overload resolution and picks a winning xmethod worker. A winner
2478 is also selected from among the methods @value{GDBN} finds in the
2479 C@t{++} source code. Next, the winning xmethod worker and the
2480 winning C@t{++} method are compared to select an overall winner. In
2481 case of a tie between a xmethod worker and a C@t{++} method, the
2482 xmethod worker is selected as the winner. That is, if a winning
2483 xmethod worker is found to be equivalent to the winning C@t{++}
2484 method, then the xmethod worker is treated as a replacement for
2485 the C@t{++} method. @value{GDBN} uses the overall winner to invoke the
2486 method. If the winning xmethod worker is the overall winner, then
2487 the corresponding xmethod is invoked via the @code{__call__} method
2488 of the worker object.
2490 If one wants to implement an xmethod as a replacement for an
2491 existing C@t{++} method, then they have to implement an equivalent
2492 xmethod which has exactly the same name and takes arguments of
2493 exactly the same type as the C@t{++} method. If the user wants to
2494 invoke the C@t{++} method even though a replacement xmethod is
2495 available for that method, then they can disable the xmethod.
2497 @xref{Xmethod API}, for API to implement xmethods in Python.
2498 @xref{Writing an Xmethod}, for implementing xmethods in Python.
2501 @subsubsection Xmethod API
2504 The @value{GDBN} Python API provides classes, interfaces and functions
2505 to implement, register and manipulate xmethods.
2506 @xref{Xmethods In Python}.
2508 An xmethod matcher should be an instance of a class derived from
2509 @code{XMethodMatcher} defined in the module @code{gdb.xmethod}, or an
2510 object with similar interface and attributes. An instance of
2511 @code{XMethodMatcher} has the following attributes:
2514 The name of the matcher.
2518 A boolean value indicating whether the matcher is enabled or disabled.
2522 A list of named methods managed by the matcher. Each object in the list
2523 is an instance of the class @code{XMethod} defined in the module
2524 @code{gdb.xmethod}, or any object with the following attributes:
2529 Name of the xmethod which should be unique for each xmethod
2530 managed by the matcher.
2533 A boolean value indicating whether the xmethod is enabled or
2538 The class @code{XMethod} is a convenience class with same
2539 attributes as above along with the following constructor:
2541 @defun XMethod.__init__ (self, name)
2542 Constructs an enabled xmethod with name @var{name}.
2547 The @code{XMethodMatcher} class has the following methods:
2549 @defun XMethodMatcher.__init__ (self, name)
2550 Constructs an enabled xmethod matcher with name @var{name}. The
2551 @code{methods} attribute is initialized to @code{None}.
2554 @defun XMethodMatcher.match (self, class_type, method_name)
2555 Derived classes should override this method. It should return a
2556 xmethod worker object (or a sequence of xmethod worker
2557 objects) matching the @var{class_type} and @var{method_name}.
2558 @var{class_type} is a @code{gdb.Type} object, and @var{method_name}
2559 is a string value. If the matcher manages named methods as listed in
2560 its @code{methods} attribute, then only those worker objects whose
2561 corresponding entries in the @code{methods} list are enabled should be
2565 An xmethod worker should be an instance of a class derived from
2566 @code{XMethodWorker} defined in the module @code{gdb.xmethod},
2567 or support the following interface:
2569 @defun XMethodWorker.get_arg_types (self)
2570 This method returns a sequence of @code{gdb.Type} objects corresponding
2571 to the arguments that the xmethod takes. It can return an empty
2572 sequence or @code{None} if the xmethod does not take any arguments.
2573 If the xmethod takes a single argument, then a single
2574 @code{gdb.Type} object corresponding to it can be returned.
2577 @defun XMethodWorker.get_result_type (self, *args)
2578 This method returns a @code{gdb.Type} object representing the type
2579 of the result of invoking this xmethod.
2580 The @var{args} argument is the same tuple of arguments that would be
2581 passed to the @code{__call__} method of this worker.
2584 @defun XMethodWorker.__call__ (self, *args)
2585 This is the method which does the @emph{work} of the xmethod. The
2586 @var{args} arguments is the tuple of arguments to the xmethod. Each
2587 element in this tuple is a gdb.Value object. The first element is
2588 always the @code{this} pointer value.
2591 For @value{GDBN} to lookup xmethods, the xmethod matchers
2592 should be registered using the following function defined in the module
2595 @defun register_xmethod_matcher (locus, matcher, replace=False)
2596 The @code{matcher} is registered with @code{locus}, replacing an
2597 existing matcher with the same name as @code{matcher} if
2598 @code{replace} is @code{True}. @code{locus} can be a
2599 @code{gdb.Objfile} object (@pxref{Objfiles In Python}), or a
2600 @code{gdb.Progspace} object (@pxref{Progspaces In Python}), or
2601 @code{None}. If it is @code{None}, then @code{matcher} is registered
2605 @node Writing an Xmethod
2606 @subsubsection Writing an Xmethod
2607 @cindex writing xmethods in Python
2609 Implementing xmethods in Python will require implementing xmethod
2610 matchers and xmethod workers (@pxref{Xmethods In Python}). Consider
2611 the following C@t{++} class:
2617 MyClass (int a) : a_(a) @{ @}
2619 int geta (void) @{ return a_; @}
2620 int operator+ (int b);
2627 MyClass::operator+ (int b)
2634 Let us define two xmethods for the class @code{MyClass}, one
2635 replacing the method @code{geta}, and another adding an overloaded
2636 flavor of @code{operator+} which takes a @code{MyClass} argument (the
2637 C@t{++} code above already has an overloaded @code{operator+}
2638 which takes an @code{int} argument). The xmethod matcher can be
2642 class MyClass_geta(gdb.xmethod.XMethod):
2644 gdb.xmethod.XMethod.__init__(self, 'geta')
2646 def get_worker(self, method_name):
2647 if method_name == 'geta':
2648 return MyClassWorker_geta()
2651 class MyClass_sum(gdb.xmethod.XMethod):
2653 gdb.xmethod.XMethod.__init__(self, 'sum')
2655 def get_worker(self, method_name):
2656 if method_name == 'operator+':
2657 return MyClassWorker_plus()
2660 class MyClassMatcher(gdb.xmethod.XMethodMatcher):
2662 gdb.xmethod.XMethodMatcher.__init__(self, 'MyClassMatcher')
2663 # List of methods 'managed' by this matcher
2664 self.methods = [MyClass_geta(), MyClass_sum()]
2666 def match(self, class_type, method_name):
2667 if class_type.tag != 'MyClass':
2670 for method in self.methods:
2672 worker = method.get_worker(method_name)
2674 workers.append(worker)
2680 Notice that the @code{match} method of @code{MyClassMatcher} returns
2681 a worker object of type @code{MyClassWorker_geta} for the @code{geta}
2682 method, and a worker object of type @code{MyClassWorker_plus} for the
2683 @code{operator+} method. This is done indirectly via helper classes
2684 derived from @code{gdb.xmethod.XMethod}. One does not need to use the
2685 @code{methods} attribute in a matcher as it is optional. However, if a
2686 matcher manages more than one xmethod, it is a good practice to list the
2687 xmethods in the @code{methods} attribute of the matcher. This will then
2688 facilitate enabling and disabling individual xmethods via the
2689 @code{enable/disable} commands. Notice also that a worker object is
2690 returned only if the corresponding entry in the @code{methods} attribute
2691 of the matcher is enabled.
2693 The implementation of the worker classes returned by the matcher setup
2694 above is as follows:
2697 class MyClassWorker_geta(gdb.xmethod.XMethodWorker):
2698 def get_arg_types(self):
2701 def get_result_type(self, obj):
2702 return gdb.lookup_type('int')
2704 def __call__(self, obj):
2708 class MyClassWorker_plus(gdb.xmethod.XMethodWorker):
2709 def get_arg_types(self):
2710 return gdb.lookup_type('MyClass')
2712 def get_result_type(self, obj):
2713 return gdb.lookup_type('int')
2715 def __call__(self, obj, other):
2716 return obj['a_'] + other['a_']
2719 For @value{GDBN} to actually lookup a xmethod, it has to be
2720 registered with it. The matcher defined above is registered with
2721 @value{GDBN} globally as follows:
2724 gdb.xmethod.register_xmethod_matcher(None, MyClassMatcher())
2727 If an object @code{obj} of type @code{MyClass} is initialized in C@t{++}
2735 then, after loading the Python script defining the xmethod matchers
2736 and workers into @code{GDBN}, invoking the method @code{geta} or using
2737 the operator @code{+} on @code{obj} will invoke the xmethods
2748 Consider another example with a C++ template class:
2755 MyTemplate () : dsize_(10), data_ (new T [10]) @{ @}
2756 ~MyTemplate () @{ delete [] data_; @}
2758 int footprint (void)
2760 return sizeof (T) * dsize_ + sizeof (MyTemplate<T>);
2769 Let us implement an xmethod for the above class which serves as a
2770 replacement for the @code{footprint} method. The full code listing
2771 of the xmethod workers and xmethod matchers is as follows:
2774 class MyTemplateWorker_footprint(gdb.xmethod.XMethodWorker):
2775 def __init__(self, class_type):
2776 self.class_type = class_type
2778 def get_arg_types(self):
2781 def get_result_type(self):
2782 return gdb.lookup_type('int')
2784 def __call__(self, obj):
2785 return (self.class_type.sizeof +
2787 self.class_type.template_argument(0).sizeof)
2790 class MyTemplateMatcher_footprint(gdb.xmethod.XMethodMatcher):
2792 gdb.xmethod.XMethodMatcher.__init__(self, 'MyTemplateMatcher')
2794 def match(self, class_type, method_name):
2795 if (re.match('MyTemplate<[ \t\n]*[_a-zA-Z][ _a-zA-Z0-9]*>',
2797 method_name == 'footprint'):
2798 return MyTemplateWorker_footprint(class_type)
2801 Notice that, in this example, we have not used the @code{methods}
2802 attribute of the matcher as the matcher manages only one xmethod. The
2803 user can enable/disable this xmethod by enabling/disabling the matcher
2806 @node Inferiors In Python
2807 @subsubsection Inferiors In Python
2808 @cindex inferiors in Python
2810 @findex gdb.Inferior
2811 Programs which are being run under @value{GDBN} are called inferiors
2812 (@pxref{Inferiors and Programs}). Python scripts can access
2813 information about and manipulate inferiors controlled by @value{GDBN}
2814 via objects of the @code{gdb.Inferior} class.
2816 The following inferior-related functions are available in the @code{gdb}
2819 @defun gdb.inferiors ()
2820 Return a tuple containing all inferior objects.
2823 @defun gdb.selected_inferior ()
2824 Return an object representing the current inferior.
2827 A @code{gdb.Inferior} object has the following attributes:
2829 @defvar Inferior.num
2830 ID of inferior, as assigned by GDB.
2833 @defvar Inferior.pid
2834 Process ID of the inferior, as assigned by the underlying operating
2838 @defvar Inferior.was_attached
2839 Boolean signaling whether the inferior was created using `attach', or
2840 started by @value{GDBN} itself.
2843 @defvar Inferior.progspace
2844 The inferior's program space. @xref{Progspaces In Python}.
2847 A @code{gdb.Inferior} object has the following methods:
2849 @defun Inferior.is_valid ()
2850 Returns @code{True} if the @code{gdb.Inferior} object is valid,
2851 @code{False} if not. A @code{gdb.Inferior} object will become invalid
2852 if the inferior no longer exists within @value{GDBN}. All other
2853 @code{gdb.Inferior} methods will throw an exception if it is invalid
2854 at the time the method is called.
2857 @defun Inferior.threads ()
2858 This method returns a tuple holding all the threads which are valid
2859 when it is called. If there are no valid threads, the method will
2860 return an empty tuple.
2863 @findex Inferior.read_memory
2864 @defun Inferior.read_memory (address, length)
2865 Read @var{length} addressable memory units from the inferior, starting at
2866 @var{address}. Returns a buffer object, which behaves much like an array
2867 or a string. It can be modified and given to the
2868 @code{Inferior.write_memory} function. In Python 3, the return
2869 value is a @code{memoryview} object.
2872 @findex Inferior.write_memory
2873 @defun Inferior.write_memory (address, buffer @r{[}, length@r{]})
2874 Write the contents of @var{buffer} to the inferior, starting at
2875 @var{address}. The @var{buffer} 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{Inferior.read_memory}. If given, @var{length}
2878 determines the number of addressable memory units from @var{buffer} to be
2882 @findex gdb.search_memory
2883 @defun Inferior.search_memory (address, length, pattern)
2884 Search a region of the inferior memory starting at @var{address} with
2885 the given @var{length} using the search pattern supplied in
2886 @var{pattern}. The @var{pattern} parameter must be a Python object
2887 which supports the buffer protocol, i.e., a string, an array or the
2888 object returned from @code{gdb.read_memory}. Returns a Python @code{Long}
2889 containing the address where the pattern was found, or @code{None} if
2890 the pattern could not be found.
2893 @findex Inferior.thread_from_thread_handle
2894 @defun Inferior.thread_from_thread_handle (thread_handle)
2895 Return the thread object corresponding to @var{thread_handle}, a thread
2896 library specific data structure such as @code{pthread_t} for pthreads
2897 library implementations.
2900 @node Events In Python
2901 @subsubsection Events In Python
2902 @cindex inferior events in Python
2904 @value{GDBN} provides a general event facility so that Python code can be
2905 notified of various state changes, particularly changes that occur in
2908 An @dfn{event} is just an object that describes some state change. The
2909 type of the object and its attributes will vary depending on the details
2910 of the change. All the existing events are described below.
2912 In order to be notified of an event, you must register an event handler
2913 with an @dfn{event registry}. An event registry is an object in the
2914 @code{gdb.events} module which dispatches particular events. A registry
2915 provides methods to register and unregister event handlers:
2917 @defun EventRegistry.connect (object)
2918 Add the given callable @var{object} to the registry. This object will be
2919 called when an event corresponding to this registry occurs.
2922 @defun EventRegistry.disconnect (object)
2923 Remove the given @var{object} from the registry. Once removed, the object
2924 will no longer receive notifications of events.
2930 def exit_handler (event):
2931 print "event type: exit"
2932 print "exit code: %d" % (event.exit_code)
2934 gdb.events.exited.connect (exit_handler)
2937 In the above example we connect our handler @code{exit_handler} to the
2938 registry @code{events.exited}. Once connected, @code{exit_handler} gets
2939 called when the inferior exits. The argument @dfn{event} in this example is
2940 of type @code{gdb.ExitedEvent}. As you can see in the example the
2941 @code{ExitedEvent} object has an attribute which indicates the exit code of
2944 The following is a listing of the event registries that are available and
2945 details of the events they emit:
2950 Emits @code{gdb.ThreadEvent}.
2952 Some events can be thread specific when @value{GDBN} is running in non-stop
2953 mode. When represented in Python, these events all extend
2954 @code{gdb.ThreadEvent}. Note, this event is not emitted directly; instead,
2955 events which are emitted by this or other modules might extend this event.
2956 Examples of these events are @code{gdb.BreakpointEvent} and
2957 @code{gdb.ContinueEvent}.
2959 @defvar ThreadEvent.inferior_thread
2960 In non-stop mode this attribute will be set to the specific thread which was
2961 involved in the emitted event. Otherwise, it will be set to @code{None}.
2964 Emits @code{gdb.ContinueEvent} which extends @code{gdb.ThreadEvent}.
2966 This event indicates that the inferior has been continued after a stop. For
2967 inherited attribute refer to @code{gdb.ThreadEvent} above.
2970 Emits @code{events.ExitedEvent} which indicates that the inferior has exited.
2971 @code{events.ExitedEvent} has two attributes:
2972 @defvar ExitedEvent.exit_code
2973 An integer representing the exit code, if available, which the inferior
2974 has returned. (The exit code could be unavailable if, for example,
2975 @value{GDBN} detaches from the inferior.) If the exit code is unavailable,
2976 the attribute does not exist.
2978 @defvar ExitedEvent.inferior
2979 A reference to the inferior which triggered the @code{exited} event.
2983 Emits @code{gdb.StopEvent} which extends @code{gdb.ThreadEvent}.
2985 Indicates that the inferior has stopped. All events emitted by this registry
2986 extend StopEvent. As a child of @code{gdb.ThreadEvent}, @code{gdb.StopEvent}
2987 will indicate the stopped thread when @value{GDBN} is running in non-stop
2988 mode. Refer to @code{gdb.ThreadEvent} above for more details.
2990 Emits @code{gdb.SignalEvent} which extends @code{gdb.StopEvent}.
2992 This event indicates that the inferior or one of its threads has received as
2993 signal. @code{gdb.SignalEvent} has the following attributes:
2995 @defvar SignalEvent.stop_signal
2996 A string representing the signal received by the inferior. A list of possible
2997 signal values can be obtained by running the command @code{info signals} in
2998 the @value{GDBN} command prompt.
3001 Also emits @code{gdb.BreakpointEvent} which extends @code{gdb.StopEvent}.
3003 @code{gdb.BreakpointEvent} event indicates that one or more breakpoints have
3004 been hit, and has the following attributes:
3006 @defvar BreakpointEvent.breakpoints
3007 A sequence containing references to all the breakpoints (type
3008 @code{gdb.Breakpoint}) that were hit.
3009 @xref{Breakpoints In Python}, for details of the @code{gdb.Breakpoint} object.
3011 @defvar BreakpointEvent.breakpoint
3012 A reference to the first breakpoint that was hit.
3013 This function is maintained for backward compatibility and is now deprecated
3014 in favor of the @code{gdb.BreakpointEvent.breakpoints} attribute.
3017 @item events.new_objfile
3018 Emits @code{gdb.NewObjFileEvent} which indicates that a new object file has
3019 been loaded by @value{GDBN}. @code{gdb.NewObjFileEvent} has one attribute:
3021 @defvar NewObjFileEvent.new_objfile
3022 A reference to the object file (@code{gdb.Objfile}) which has been loaded.
3023 @xref{Objfiles In Python}, for details of the @code{gdb.Objfile} object.
3026 @item events.clear_objfiles
3027 Emits @code{gdb.ClearObjFilesEvent} which indicates that the list of object
3028 files for a program space has been reset.
3029 @code{gdb.ClearObjFilesEvent} has one attribute:
3031 @defvar ClearObjFilesEvent.progspace
3032 A reference to the program space (@code{gdb.Progspace}) whose objfile list has
3033 been cleared. @xref{Progspaces In Python}.
3036 @item events.inferior_call
3037 Emits events just before and after a function in the inferior is
3038 called by @value{GDBN}. Before an inferior call, this emits an event
3039 of type @code{gdb.InferiorCallPreEvent}, and after an inferior call,
3040 this emits an event of type @code{gdb.InferiorCallPostEvent}.
3043 @tindex gdb.InferiorCallPreEvent
3044 @item @code{gdb.InferiorCallPreEvent}
3045 Indicates that a function in the inferior is about to be called.
3047 @defvar InferiorCallPreEvent.ptid
3048 The thread in which the call will be run.
3051 @defvar InferiorCallPreEvent.address
3052 The location of the function to be called.
3055 @tindex gdb.InferiorCallPostEvent
3056 @item @code{gdb.InferiorCallPostEvent}
3057 Indicates that a function in the inferior has just been called.
3059 @defvar InferiorCallPostEvent.ptid
3060 The thread in which the call was run.
3063 @defvar InferiorCallPostEvent.address
3064 The location of the function that was called.
3068 @item events.memory_changed
3069 Emits @code{gdb.MemoryChangedEvent} which indicates that the memory of the
3070 inferior has been modified by the @value{GDBN} user, for instance via a
3071 command like @w{@code{set *addr = value}}. The event has the following
3074 @defvar MemoryChangedEvent.address
3075 The start address of the changed region.
3078 @defvar MemoryChangedEvent.length
3079 Length in bytes of the changed region.
3082 @item events.register_changed
3083 Emits @code{gdb.RegisterChangedEvent} which indicates that a register in the
3084 inferior has been modified by the @value{GDBN} user.
3086 @defvar RegisterChangedEvent.frame
3087 A gdb.Frame object representing the frame in which the register was modified.
3089 @defvar RegisterChangedEvent.regnum
3090 Denotes which register was modified.
3093 @item events.breakpoint_created
3094 This is emitted when a new breakpoint has been created. The argument
3095 that is passed is the new @code{gdb.Breakpoint} object.
3097 @item events.breakpoint_modified
3098 This is emitted when a breakpoint has been modified in some way. The
3099 argument that is passed is the new @code{gdb.Breakpoint} object.
3101 @item events.breakpoint_deleted
3102 This is emitted when a breakpoint has been deleted. The argument that
3103 is passed is the @code{gdb.Breakpoint} object. When this event is
3104 emitted, the @code{gdb.Breakpoint} object will already be in its
3105 invalid state; that is, the @code{is_valid} method will return
3108 @item events.before_prompt
3109 This event carries no payload. It is emitted each time @value{GDBN}
3110 presents a prompt to the user.
3112 @item events.new_inferior
3113 This is emitted when a new inferior is created. Note that the
3114 inferior is not necessarily running; in fact, it may not even have an
3115 associated executable.
3117 The event is of type @code{gdb.NewInferiorEvent}. This has a single
3120 @defvar NewInferiorEvent.inferior
3121 The new inferior, a @code{gdb.Inferior} object.
3124 @item events.inferior_deleted
3125 This is emitted when an inferior has been deleted. Note that this is
3126 not the same as process exit; it is notified when the inferior itself
3127 is removed, say via @code{remove-inferiors}.
3129 The event is of type @code{gdb.InferiorDeletedEvent}. This has a single
3132 @defvar NewInferiorEvent.inferior
3133 The inferior that is being removed, a @code{gdb.Inferior} object.
3136 @item events.new_thread
3137 This is emitted when @value{GDBN} notices a new thread. The event is of
3138 type @code{gdb.NewThreadEvent}, which extends @code{gdb.ThreadEvent}.
3139 This has a single attribute:
3141 @defvar NewThreadEvent.inferior_thread
3147 @node Threads In Python
3148 @subsubsection Threads In Python
3149 @cindex threads in python
3151 @findex gdb.InferiorThread
3152 Python scripts can access information about, and manipulate inferior threads
3153 controlled by @value{GDBN}, via objects of the @code{gdb.InferiorThread} class.
3155 The following thread-related functions are available in the @code{gdb}
3158 @findex gdb.selected_thread
3159 @defun gdb.selected_thread ()
3160 This function returns the thread object for the selected thread. If there
3161 is no selected thread, this will return @code{None}.
3164 A @code{gdb.InferiorThread} object has the following attributes:
3166 @defvar InferiorThread.name
3167 The name of the thread. If the user specified a name using
3168 @code{thread name}, then this returns that name. Otherwise, if an
3169 OS-supplied name is available, then it is returned. Otherwise, this
3170 returns @code{None}.
3172 This attribute can be assigned to. The new value must be a string
3173 object, which sets the new name, or @code{None}, which removes any
3174 user-specified thread name.
3177 @defvar InferiorThread.num
3178 The per-inferior number of the thread, as assigned by GDB.
3181 @defvar InferiorThread.global_num
3182 The global ID of the thread, as assigned by GDB. You can use this to
3183 make Python breakpoints thread-specific, for example
3184 (@pxref{python_breakpoint_thread,,The Breakpoint.thread attribute}).
3187 @defvar InferiorThread.ptid
3188 ID of the thread, as assigned by the operating system. This attribute is a
3189 tuple containing three integers. The first is the Process ID (PID); the second
3190 is the Lightweight Process ID (LWPID), and the third is the Thread ID (TID).
3191 Either the LWPID or TID may be 0, which indicates that the operating system
3192 does not use that identifier.
3195 @defvar InferiorThread.inferior
3196 The inferior this thread belongs to. This attribute is represented as
3197 a @code{gdb.Inferior} object. This attribute is not writable.
3200 A @code{gdb.InferiorThread} object has the following methods:
3202 @defun InferiorThread.is_valid ()
3203 Returns @code{True} if the @code{gdb.InferiorThread} object is valid,
3204 @code{False} if not. A @code{gdb.InferiorThread} object will become
3205 invalid if the thread exits, or the inferior that the thread belongs
3206 is deleted. All other @code{gdb.InferiorThread} methods will throw an
3207 exception if it is invalid at the time the method is called.
3210 @defun InferiorThread.switch ()
3211 This changes @value{GDBN}'s currently selected thread to the one represented
3215 @defun InferiorThread.is_stopped ()
3216 Return a Boolean indicating whether the thread is stopped.
3219 @defun InferiorThread.is_running ()
3220 Return a Boolean indicating whether the thread is running.
3223 @defun InferiorThread.is_exited ()
3224 Return a Boolean indicating whether the thread is exited.
3227 @node Recordings In Python
3228 @subsubsection Recordings In Python
3229 @cindex recordings in python
3231 The following recordings-related functions
3232 (@pxref{Process Record and Replay}) are available in the @code{gdb}
3235 @defun gdb.start_recording (@r{[}method@r{]}, @r{[}format@r{]})
3236 Start a recording using the given @var{method} and @var{format}. If
3237 no @var{format} is given, the default format for the recording method
3238 is used. If no @var{method} is given, the default method will be used.
3239 Returns a @code{gdb.Record} object on success. Throw an exception on
3242 The following strings can be passed as @var{method}:
3248 @code{"btrace"}: Possible values for @var{format}: @code{"pt"},
3249 @code{"bts"} or leave out for default format.
3253 @defun gdb.current_recording ()
3254 Access a currently running recording. Return a @code{gdb.Record}
3255 object on success. Return @code{None} if no recording is currently
3259 @defun gdb.stop_recording ()
3260 Stop the current recording. Throw an exception if no recording is
3261 currently active. All record objects become invalid after this call.
3264 A @code{gdb.Record} object has the following attributes:
3266 @defvar Record.method
3267 A string with the current recording method, e.g.@: @code{full} or
3271 @defvar Record.format
3272 A string with the current recording format, e.g.@: @code{bt}, @code{pts} or
3276 @defvar Record.begin
3277 A method specific instruction object representing the first instruction
3282 A method specific instruction object representing the current
3283 instruction, that is not actually part of the recording.
3286 @defvar Record.replay_position
3287 The instruction representing the current replay position. If there is
3288 no replay active, this will be @code{None}.
3291 @defvar Record.instruction_history
3292 A list with all recorded instructions.
3295 @defvar Record.function_call_history
3296 A list with all recorded function call segments.
3299 A @code{gdb.Record} object has the following methods:
3301 @defun Record.goto (instruction)
3302 Move the replay position to the given @var{instruction}.
3305 The common @code{gdb.Instruction} class that recording method specific
3306 instruction objects inherit from, has the following attributes:
3308 @defvar Instruction.pc
3309 An integer representing this instruction's address.
3312 @defvar Instruction.data
3313 A buffer with the raw instruction data. In Python 3, the return value is a
3314 @code{memoryview} object.
3317 @defvar Instruction.decoded
3318 A human readable string with the disassembled instruction.
3321 @defvar Instruction.size
3322 The size of the instruction in bytes.
3325 Additionally @code{gdb.RecordInstruction} has the following attributes:
3327 @defvar RecordInstruction.number
3328 An integer identifying this instruction. @code{number} corresponds to
3329 the numbers seen in @code{record instruction-history}
3330 (@pxref{Process Record and Replay}).
3333 @defvar RecordInstruction.sal
3334 A @code{gdb.Symtab_and_line} object representing the associated symtab
3335 and line of this instruction. May be @code{None} if no debug information is
3339 @defvar RecordInstruction.is_speculative
3340 A boolean indicating whether the instruction was executed speculatively.
3343 If an error occured during recording or decoding a recording, this error is
3344 represented by a @code{gdb.RecordGap} object in the instruction list. It has
3345 the following attributes:
3347 @defvar RecordGap.number
3348 An integer identifying this gap. @code{number} corresponds to the numbers seen
3349 in @code{record instruction-history} (@pxref{Process Record and Replay}).
3352 @defvar RecordGap.error_code
3353 A numerical representation of the reason for the gap. The value is specific to
3354 the current recording method.
3357 @defvar RecordGap.error_string
3358 A human readable string with the reason for the gap.
3361 A @code{gdb.RecordFunctionSegment} object has the following attributes:
3363 @defvar RecordFunctionSegment.number
3364 An integer identifying this function segment. @code{number} corresponds to
3365 the numbers seen in @code{record function-call-history}
3366 (@pxref{Process Record and Replay}).
3369 @defvar RecordFunctionSegment.symbol
3370 A @code{gdb.Symbol} object representing the associated symbol. May be
3371 @code{None} if no debug information is available.
3374 @defvar RecordFunctionSegment.level
3375 An integer representing the function call's stack level. May be
3376 @code{None} if the function call is a gap.
3379 @defvar RecordFunctionSegment.instructions
3380 A list of @code{gdb.RecordInstruction} or @code{gdb.RecordGap} objects
3381 associated with this function call.
3384 @defvar RecordFunctionSegment.up
3385 A @code{gdb.RecordFunctionSegment} object representing the caller's
3386 function segment. If the call has not been recorded, this will be the
3387 function segment to which control returns. If neither the call nor the
3388 return have been recorded, this will be @code{None}.
3391 @defvar RecordFunctionSegment.prev
3392 A @code{gdb.RecordFunctionSegment} object representing the previous
3393 segment of this function call. May be @code{None}.
3396 @defvar RecordFunctionSegment.next
3397 A @code{gdb.RecordFunctionSegment} object representing the next segment of
3398 this function call. May be @code{None}.
3401 The following example demonstrates the usage of these objects and
3402 functions to create a function that will rewind a record to the last
3403 time a function in a different file was executed. This would typically
3404 be used to track the execution of user provided callback functions in a
3405 library which typically are not visible in a back trace.
3409 rec = gdb.current_recording ()
3413 insn = rec.instruction_history
3418 position = insn.index (rec.replay_position)
3422 filename = insn[position].sal.symtab.fullname ()
3426 for i in reversed (insn[:position]):
3428 current = i.sal.symtab.fullname ()
3432 if filename == current:
3439 Another possible application is to write a function that counts the
3440 number of code executions in a given line range. This line range can
3441 contain parts of functions or span across several functions and is not
3442 limited to be contiguous.
3445 def countrange (filename, linerange):
3448 def filter_only (file_name):
3449 for call in gdb.current_recording ().function_call_history:
3451 if file_name in call.symbol.symtab.fullname ():
3456 for c in filter_only (filename):
3457 for i in c.instructions:
3459 if i.sal.line in linerange:
3468 @node Commands In Python
3469 @subsubsection Commands In Python
3471 @cindex commands in python
3472 @cindex python commands
3473 You can implement new @value{GDBN} CLI commands in Python. A CLI
3474 command is implemented using an instance of the @code{gdb.Command}
3475 class, most commonly using a subclass.
3477 @defun Command.__init__ (name, @var{command_class} @r{[}, @var{completer_class} @r{[}, @var{prefix}@r{]]})
3478 The object initializer for @code{Command} registers the new command
3479 with @value{GDBN}. This initializer is normally invoked from the
3480 subclass' own @code{__init__} method.
3482 @var{name} is the name of the command. If @var{name} consists of
3483 multiple words, then the initial words are looked for as prefix
3484 commands. In this case, if one of the prefix commands does not exist,
3485 an exception is raised.
3487 There is no support for multi-line commands.
3489 @var{command_class} should be one of the @samp{COMMAND_} constants
3490 defined below. This argument tells @value{GDBN} how to categorize the
3491 new command in the help system.
3493 @var{completer_class} is an optional argument. If given, it should be
3494 one of the @samp{COMPLETE_} constants defined below. This argument
3495 tells @value{GDBN} how to perform completion for this command. If not
3496 given, @value{GDBN} will attempt to complete using the object's
3497 @code{complete} method (see below); if no such method is found, an
3498 error will occur when completion is attempted.
3500 @var{prefix} is an optional argument. If @code{True}, then the new
3501 command is a prefix command; sub-commands of this command may be
3504 The help text for the new command is taken from the Python
3505 documentation string for the command's class, if there is one. If no
3506 documentation string is provided, the default value ``This command is
3507 not documented.'' is used.
3510 @cindex don't repeat Python command
3511 @defun Command.dont_repeat ()
3512 By default, a @value{GDBN} command is repeated when the user enters a
3513 blank line at the command prompt. A command can suppress this
3514 behavior by invoking the @code{dont_repeat} method. This is similar
3515 to the user command @code{dont-repeat}, see @ref{Define, dont-repeat}.
3518 @defun Command.invoke (argument, from_tty)
3519 This method is called by @value{GDBN} when this command is invoked.
3521 @var{argument} is a string. It is the argument to the command, after
3522 leading and trailing whitespace has been stripped.
3524 @var{from_tty} is a boolean argument. When true, this means that the
3525 command was entered by the user at the terminal; when false it means
3526 that the command came from elsewhere.
3528 If this method throws an exception, it is turned into a @value{GDBN}
3529 @code{error} call. Otherwise, the return value is ignored.
3531 @findex gdb.string_to_argv
3532 To break @var{argument} up into an argv-like string use
3533 @code{gdb.string_to_argv}. This function behaves identically to
3534 @value{GDBN}'s internal argument lexer @code{buildargv}.
3535 It is recommended to use this for consistency.
3536 Arguments are separated by spaces and may be quoted.
3540 print gdb.string_to_argv ("1 2\ \\\"3 '4 \"5' \"6 '7\"")
3541 ['1', '2 "3', '4 "5', "6 '7"]
3546 @cindex completion of Python commands
3547 @defun Command.complete (text, word)
3548 This method is called by @value{GDBN} when the user attempts
3549 completion on this command. All forms of completion are handled by
3550 this method, that is, the @key{TAB} and @key{M-?} key bindings
3551 (@pxref{Completion}), and the @code{complete} command (@pxref{Help,
3554 The arguments @var{text} and @var{word} are both strings; @var{text}
3555 holds the complete command line up to the cursor's location, while
3556 @var{word} holds the last word of the command line; this is computed
3557 using a word-breaking heuristic.
3559 The @code{complete} method can return several values:
3562 If the return value is a sequence, the contents of the sequence are
3563 used as the completions. It is up to @code{complete} to ensure that the
3564 contents actually do complete the word. A zero-length sequence is
3565 allowed, it means that there were no completions available. Only
3566 string elements of the sequence are used; other elements in the
3567 sequence are ignored.
3570 If the return value is one of the @samp{COMPLETE_} constants defined
3571 below, then the corresponding @value{GDBN}-internal completion
3572 function is invoked, and its result is used.
3575 All other results are treated as though there were no available
3580 When a new command is registered, it must be declared as a member of
3581 some general class of commands. This is used to classify top-level
3582 commands in the on-line help system; note that prefix commands are not
3583 listed under their own category but rather that of their top-level
3584 command. The available classifications are represented by constants
3585 defined in the @code{gdb} module:
3588 @findex COMMAND_NONE
3589 @findex gdb.COMMAND_NONE
3590 @item gdb.COMMAND_NONE
3591 The command does not belong to any particular class. A command in
3592 this category will not be displayed in any of the help categories.
3594 @findex COMMAND_RUNNING
3595 @findex gdb.COMMAND_RUNNING
3596 @item gdb.COMMAND_RUNNING
3597 The command is related to running the inferior. For example,
3598 @code{start}, @code{step}, and @code{continue} are in this category.
3599 Type @kbd{help running} at the @value{GDBN} prompt to see a list of
3600 commands in this category.
3602 @findex COMMAND_DATA
3603 @findex gdb.COMMAND_DATA
3604 @item gdb.COMMAND_DATA
3605 The command is related to data or variables. For example,
3606 @code{call}, @code{find}, and @code{print} are in this category. Type
3607 @kbd{help data} at the @value{GDBN} prompt to see a list of commands
3610 @findex COMMAND_STACK
3611 @findex gdb.COMMAND_STACK
3612 @item gdb.COMMAND_STACK
3613 The command has to do with manipulation of the stack. For example,
3614 @code{backtrace}, @code{frame}, and @code{return} are in this
3615 category. Type @kbd{help stack} at the @value{GDBN} prompt to see a
3616 list of commands in this category.
3618 @findex COMMAND_FILES
3619 @findex gdb.COMMAND_FILES
3620 @item gdb.COMMAND_FILES
3621 This class is used for file-related commands. For example,
3622 @code{file}, @code{list} and @code{section} are in this category.
3623 Type @kbd{help files} at the @value{GDBN} prompt to see a list of
3624 commands in this category.
3626 @findex COMMAND_SUPPORT
3627 @findex gdb.COMMAND_SUPPORT
3628 @item gdb.COMMAND_SUPPORT
3629 This should be used for ``support facilities'', generally meaning
3630 things that are useful to the user when interacting with @value{GDBN},
3631 but not related to the state of the inferior. For example,
3632 @code{help}, @code{make}, and @code{shell} are in this category. Type
3633 @kbd{help support} at the @value{GDBN} prompt to see a list of
3634 commands in this category.
3636 @findex COMMAND_STATUS
3637 @findex gdb.COMMAND_STATUS
3638 @item gdb.COMMAND_STATUS
3639 The command is an @samp{info}-related command, that is, related to the
3640 state of @value{GDBN} itself. For example, @code{info}, @code{macro},
3641 and @code{show} are in this category. Type @kbd{help status} at the
3642 @value{GDBN} prompt to see a list of commands in this category.
3644 @findex COMMAND_BREAKPOINTS
3645 @findex gdb.COMMAND_BREAKPOINTS
3646 @item gdb.COMMAND_BREAKPOINTS
3647 The command has to do with breakpoints. For example, @code{break},
3648 @code{clear}, and @code{delete} are in this category. Type @kbd{help
3649 breakpoints} at the @value{GDBN} prompt to see a list of commands in
3652 @findex COMMAND_TRACEPOINTS
3653 @findex gdb.COMMAND_TRACEPOINTS
3654 @item gdb.COMMAND_TRACEPOINTS
3655 The command has to do with tracepoints. For example, @code{trace},
3656 @code{actions}, and @code{tfind} are in this category. Type
3657 @kbd{help tracepoints} at the @value{GDBN} prompt to see a list of
3658 commands in this category.
3660 @findex COMMAND_USER
3661 @findex gdb.COMMAND_USER
3662 @item gdb.COMMAND_USER
3663 The command is a general purpose command for the user, and typically
3664 does not fit in one of the other categories.
3665 Type @kbd{help user-defined} at the @value{GDBN} prompt to see
3666 a list of commands in this category, as well as the list of gdb macros
3667 (@pxref{Sequences}).
3669 @findex COMMAND_OBSCURE
3670 @findex gdb.COMMAND_OBSCURE
3671 @item gdb.COMMAND_OBSCURE
3672 The command is only used in unusual circumstances, or is not of
3673 general interest to users. For example, @code{checkpoint},
3674 @code{fork}, and @code{stop} are in this category. Type @kbd{help
3675 obscure} at the @value{GDBN} prompt to see a list of commands in this
3678 @findex COMMAND_MAINTENANCE
3679 @findex gdb.COMMAND_MAINTENANCE
3680 @item gdb.COMMAND_MAINTENANCE
3681 The command is only useful to @value{GDBN} maintainers. The
3682 @code{maintenance} and @code{flushregs} commands are in this category.
3683 Type @kbd{help internals} at the @value{GDBN} prompt to see a list of
3684 commands in this category.
3687 A new command can use a predefined completion function, either by
3688 specifying it via an argument at initialization, or by returning it
3689 from the @code{complete} method. These predefined completion
3690 constants are all defined in the @code{gdb} module:
3693 @vindex COMPLETE_NONE
3694 @item gdb.COMPLETE_NONE
3695 This constant means that no completion should be done.
3697 @vindex COMPLETE_FILENAME
3698 @item gdb.COMPLETE_FILENAME
3699 This constant means that filename completion should be performed.
3701 @vindex COMPLETE_LOCATION
3702 @item gdb.COMPLETE_LOCATION
3703 This constant means that location completion should be done.
3704 @xref{Specify Location}.
3706 @vindex COMPLETE_COMMAND
3707 @item gdb.COMPLETE_COMMAND
3708 This constant means that completion should examine @value{GDBN}
3711 @vindex COMPLETE_SYMBOL
3712 @item gdb.COMPLETE_SYMBOL
3713 This constant means that completion should be done using symbol names
3716 @vindex COMPLETE_EXPRESSION
3717 @item gdb.COMPLETE_EXPRESSION
3718 This constant means that completion should be done on expressions.
3719 Often this means completing on symbol names, but some language
3720 parsers also have support for completing on field names.
3723 The following code snippet shows how a trivial CLI command can be
3724 implemented in Python:
3727 class HelloWorld (gdb.Command):
3728 """Greet the whole world."""
3730 def __init__ (self):
3731 super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)
3733 def invoke (self, arg, from_tty):
3734 print "Hello, World!"
3739 The last line instantiates the class, and is necessary to trigger the
3740 registration of the command with @value{GDBN}. Depending on how the
3741 Python code is read into @value{GDBN}, you may need to import the
3742 @code{gdb} module explicitly.
3744 @node Parameters In Python
3745 @subsubsection Parameters In Python
3747 @cindex parameters in python
3748 @cindex python parameters
3749 @tindex gdb.Parameter
3751 You can implement new @value{GDBN} parameters using Python. A new
3752 parameter is implemented as an instance of the @code{gdb.Parameter}
3755 Parameters are exposed to the user via the @code{set} and
3756 @code{show} commands. @xref{Help}.
3758 There are many parameters that already exist and can be set in
3759 @value{GDBN}. Two examples are: @code{set follow fork} and
3760 @code{set charset}. Setting these parameters influences certain
3761 behavior in @value{GDBN}. Similarly, you can define parameters that
3762 can be used to influence behavior in custom Python scripts and commands.
3764 @defun Parameter.__init__ (name, @var{command-class}, @var{parameter-class} @r{[}, @var{enum-sequence}@r{]})
3765 The object initializer for @code{Parameter} registers the new
3766 parameter with @value{GDBN}. This initializer is normally invoked
3767 from the subclass' own @code{__init__} method.
3769 @var{name} is the name of the new parameter. If @var{name} consists
3770 of multiple words, then the initial words are looked for as prefix
3771 parameters. An example of this can be illustrated with the
3772 @code{set print} set of parameters. If @var{name} is
3773 @code{print foo}, then @code{print} will be searched as the prefix
3774 parameter. In this case the parameter can subsequently be accessed in
3775 @value{GDBN} as @code{set print foo}.
3777 If @var{name} consists of multiple words, and no prefix parameter group
3778 can be found, an exception is raised.
3780 @var{command-class} should be one of the @samp{COMMAND_} constants
3781 (@pxref{Commands In Python}). This argument tells @value{GDBN} how to
3782 categorize the new parameter in the help system.
3784 @var{parameter-class} should be one of the @samp{PARAM_} constants
3785 defined below. This argument tells @value{GDBN} the type of the new
3786 parameter; this information is used for input validation and
3789 If @var{parameter-class} is @code{PARAM_ENUM}, then
3790 @var{enum-sequence} must be a sequence of strings. These strings
3791 represent the possible values for the parameter.
3793 If @var{parameter-class} is not @code{PARAM_ENUM}, then the presence
3794 of a fourth argument will cause an exception to be thrown.
3796 The help text for the new parameter is taken from the Python
3797 documentation string for the parameter's class, if there is one. If
3798 there is no documentation string, a default value is used.
3801 @defvar Parameter.set_doc
3802 If this attribute exists, and is a string, then its value is used as
3803 the help text for this parameter's @code{set} command. The value is
3804 examined when @code{Parameter.__init__} is invoked; subsequent changes
3808 @defvar Parameter.show_doc
3809 If this attribute exists, and is a string, then its value is used as
3810 the help text for this parameter's @code{show} command. The value is
3811 examined when @code{Parameter.__init__} is invoked; subsequent changes
3815 @defvar Parameter.value
3816 The @code{value} attribute holds the underlying value of the
3817 parameter. It can be read and assigned to just as any other
3818 attribute. @value{GDBN} does validation when assignments are made.
3821 There are two methods that may be implemented in any @code{Parameter}
3824 @defun Parameter.get_set_string (self)
3825 If this method exists, @value{GDBN} will call it when a
3826 @var{parameter}'s value has been changed via the @code{set} API (for
3827 example, @kbd{set foo off}). The @code{value} attribute has already
3828 been populated with the new value and may be used in output. This
3829 method must return a string. If the returned string is not empty,
3830 @value{GDBN} will present it to the user.
3832 If this method raises the @code{gdb.GdbError} exception
3833 (@pxref{Exception Handling}), then @value{GDBN} will print the
3834 exception's string and the @code{set} command will fail. Note,
3835 however, that the @code{value} attribute will not be reset in this
3836 case. So, if your parameter must validate values, it should store the
3837 old value internally and reset the exposed value, like so:
3840 class ExampleParam (gdb.Parameter):
3841 def __init__ (self, name):
3842 super (ExampleParam, self).__init__ (name,
3846 self.saved_value = True
3849 def get_set_string (self):
3850 if not self.validate():
3851 self.value = self.saved_value
3852 raise gdb.GdbError('Failed to validate')
3853 self.saved_value = self.value
3857 @defun Parameter.get_show_string (self, svalue)
3858 @value{GDBN} will call this method when a @var{parameter}'s
3859 @code{show} API has been invoked (for example, @kbd{show foo}). The
3860 argument @code{svalue} receives the string representation of the
3861 current value. This method must return a string.
3864 When a new parameter is defined, its type must be specified. The
3865 available types are represented by constants defined in the @code{gdb}
3869 @findex PARAM_BOOLEAN
3870 @findex gdb.PARAM_BOOLEAN
3871 @item gdb.PARAM_BOOLEAN
3872 The value is a plain boolean. The Python boolean values, @code{True}
3873 and @code{False} are the only valid values.
3875 @findex PARAM_AUTO_BOOLEAN
3876 @findex gdb.PARAM_AUTO_BOOLEAN
3877 @item gdb.PARAM_AUTO_BOOLEAN
3878 The value has three possible states: true, false, and @samp{auto}. In
3879 Python, true and false are represented using boolean constants, and
3880 @samp{auto} is represented using @code{None}.
3882 @findex PARAM_UINTEGER
3883 @findex gdb.PARAM_UINTEGER
3884 @item gdb.PARAM_UINTEGER
3885 The value is an unsigned integer. The value of 0 should be
3886 interpreted to mean ``unlimited''.
3888 @findex PARAM_INTEGER
3889 @findex gdb.PARAM_INTEGER
3890 @item gdb.PARAM_INTEGER
3891 The value is a signed integer. The value of 0 should be interpreted
3892 to mean ``unlimited''.
3894 @findex PARAM_STRING
3895 @findex gdb.PARAM_STRING
3896 @item gdb.PARAM_STRING
3897 The value is a string. When the user modifies the string, any escape
3898 sequences, such as @samp{\t}, @samp{\f}, and octal escapes, are
3899 translated into corresponding characters and encoded into the current
3902 @findex PARAM_STRING_NOESCAPE
3903 @findex gdb.PARAM_STRING_NOESCAPE
3904 @item gdb.PARAM_STRING_NOESCAPE
3905 The value is a string. When the user modifies the string, escapes are
3906 passed through untranslated.
3908 @findex PARAM_OPTIONAL_FILENAME
3909 @findex gdb.PARAM_OPTIONAL_FILENAME
3910 @item gdb.PARAM_OPTIONAL_FILENAME
3911 The value is a either a filename (a string), or @code{None}.
3913 @findex PARAM_FILENAME
3914 @findex gdb.PARAM_FILENAME
3915 @item gdb.PARAM_FILENAME
3916 The value is a filename. This is just like
3917 @code{PARAM_STRING_NOESCAPE}, but uses file names for completion.
3919 @findex PARAM_ZINTEGER
3920 @findex gdb.PARAM_ZINTEGER
3921 @item gdb.PARAM_ZINTEGER
3922 The value is an integer. This is like @code{PARAM_INTEGER}, except 0
3923 is interpreted as itself.
3925 @findex PARAM_ZUINTEGER
3926 @findex gdb.PARAM_ZUINTEGER
3927 @item gdb.PARAM_ZUINTEGER
3928 The value is an unsigned integer. This is like @code{PARAM_INTEGER},
3929 except 0 is interpreted as itself, and the value cannot be negative.
3931 @findex PARAM_ZUINTEGER_UNLIMITED
3932 @findex gdb.PARAM_ZUINTEGER_UNLIMITED
3933 @item gdb.PARAM_ZUINTEGER_UNLIMITED
3934 The value is a signed integer. This is like @code{PARAM_ZUINTEGER},
3935 except the special value -1 should be interpreted to mean
3936 ``unlimited''. Other negative values are not allowed.
3939 @findex gdb.PARAM_ENUM
3940 @item gdb.PARAM_ENUM
3941 The value is a string, which must be one of a collection string
3942 constants provided when the parameter is created.
3945 @node Functions In Python
3946 @subsubsection Writing new convenience functions
3948 @cindex writing convenience functions
3949 @cindex convenience functions in python
3950 @cindex python convenience functions
3951 @tindex gdb.Function
3953 You can implement new convenience functions (@pxref{Convenience Vars})
3954 in Python. A convenience function is an instance of a subclass of the
3955 class @code{gdb.Function}.
3957 @defun Function.__init__ (name)
3958 The initializer for @code{Function} registers the new function with
3959 @value{GDBN}. The argument @var{name} is the name of the function,
3960 a string. The function will be visible to the user as a convenience
3961 variable of type @code{internal function}, whose name is the same as
3962 the given @var{name}.
3964 The documentation for the new function is taken from the documentation
3965 string for the new class.
3968 @defun Function.invoke (@var{*args})
3969 When a convenience function is evaluated, its arguments are converted
3970 to instances of @code{gdb.Value}, and then the function's
3971 @code{invoke} method is called. Note that @value{GDBN} does not
3972 predetermine the arity of convenience functions. Instead, all
3973 available arguments are passed to @code{invoke}, following the
3974 standard Python calling convention. In particular, a convenience
3975 function can have default values for parameters without ill effect.
3977 The return value of this method is used as its value in the enclosing
3978 expression. If an ordinary Python value is returned, it is converted
3979 to a @code{gdb.Value} following the usual rules.
3982 The following code snippet shows how a trivial convenience function can
3983 be implemented in Python:
3986 class Greet (gdb.Function):
3987 """Return string to greet someone.
3988 Takes a name as argument."""
3990 def __init__ (self):
3991 super (Greet, self).__init__ ("greet")
3993 def invoke (self, name):
3994 return "Hello, %s!" % name.string ()
3999 The last line instantiates the class, and is necessary to trigger the
4000 registration of the function with @value{GDBN}. Depending on how the
4001 Python code is read into @value{GDBN}, you may need to import the
4002 @code{gdb} module explicitly.
4004 Now you can use the function in an expression:
4007 (gdb) print $greet("Bob")
4011 @node Progspaces In Python
4012 @subsubsection Program Spaces In Python
4014 @cindex progspaces in python
4015 @tindex gdb.Progspace
4017 A program space, or @dfn{progspace}, represents a symbolic view
4018 of an address space.
4019 It consists of all of the objfiles of the program.
4020 @xref{Objfiles In Python}.
4021 @xref{Inferiors and Programs, program spaces}, for more details
4022 about program spaces.
4024 The following progspace-related functions are available in the
4027 @findex gdb.current_progspace
4028 @defun gdb.current_progspace ()
4029 This function returns the program space of the currently selected inferior.
4030 @xref{Inferiors and Programs}. This is identical to
4031 @code{gdb.selected_inferior().progspace} (@pxref{Inferiors In Python}) and is
4032 included for historical compatibility.
4035 @findex gdb.progspaces
4036 @defun gdb.progspaces ()
4037 Return a sequence of all the progspaces currently known to @value{GDBN}.
4040 Each progspace is represented by an instance of the @code{gdb.Progspace}
4043 @defvar Progspace.filename
4044 The file name of the progspace as a string.
4047 @defvar Progspace.pretty_printers
4048 The @code{pretty_printers} attribute is a list of functions. It is
4049 used to look up pretty-printers. A @code{Value} is passed to each
4050 function in order; if the function returns @code{None}, then the
4051 search continues. Otherwise, the return value should be an object
4052 which is used to format the value. @xref{Pretty Printing API}, for more
4056 @defvar Progspace.type_printers
4057 The @code{type_printers} attribute is a list of type printer objects.
4058 @xref{Type Printing API}, for more information.
4061 @defvar Progspace.frame_filters
4062 The @code{frame_filters} attribute is a dictionary of frame filter
4063 objects. @xref{Frame Filter API}, for more information.
4066 A program space has the following methods:
4068 @findex Progspace.block_for_pc
4069 @defun Progspace.block_for_pc (pc)
4070 Return the innermost @code{gdb.Block} containing the given @var{pc}
4071 value. If the block cannot be found for the @var{pc} value specified,
4072 the function will return @code{None}.
4075 @findex Progspace.find_pc_line
4076 @defun Progspace.find_pc_line (pc)
4077 Return the @code{gdb.Symtab_and_line} object corresponding to the
4078 @var{pc} value. @xref{Symbol Tables In Python}. If an invalid value
4079 of @var{pc} is passed as an argument, then the @code{symtab} and
4080 @code{line} attributes of the returned @code{gdb.Symtab_and_line}
4081 object will be @code{None} and 0 respectively.
4084 @findex Progspace.is_valid
4085 @defun Progspace.is_valid ()
4086 Returns @code{True} if the @code{gdb.Progspace} object is valid,
4087 @code{False} if not. A @code{gdb.Progspace} object can become invalid
4088 if the program space file it refers to is not referenced by any
4089 inferior. All other @code{gdb.Progspace} methods will throw an
4090 exception if it is invalid at the time the method is called.
4093 @findex Progspace.objfiles
4094 @defun Progspace.objfiles ()
4095 Return a sequence of all the objfiles referenced by this program
4096 space. @xref{Objfiles In Python}.
4099 @findex Progspace.solib_name
4100 @defun Progspace.solib_name (address)
4101 Return the name of the shared library holding the given @var{address}
4102 as a string, or @code{None}.
4105 One may add arbitrary attributes to @code{gdb.Progspace} objects
4106 in the usual Python way.
4107 This is useful if, for example, one needs to do some extra record keeping
4108 associated with the program space.
4110 In this contrived example, we want to perform some processing when
4111 an objfile with a certain symbol is loaded, but we only want to do
4112 this once because it is expensive. To achieve this we record the results
4113 with the program space because we can't predict when the desired objfile
4118 def clear_objfiles_handler(event):
4119 event.progspace.expensive_computation = None
4120 def expensive(symbol):
4121 """A mock routine to perform an "expensive" computation on symbol."""
4122 print "Computing the answer to the ultimate question ..."
4124 def new_objfile_handler(event):
4125 objfile = event.new_objfile
4126 progspace = objfile.progspace
4127 if not hasattr(progspace, 'expensive_computation') or \
4128 progspace.expensive_computation is None:
4129 # We use 'main' for the symbol to keep the example simple.
4130 # Note: There's no current way to constrain the lookup
4132 symbol = gdb.lookup_global_symbol('main')
4133 if symbol is not None:
4134 progspace.expensive_computation = expensive(symbol)
4135 gdb.events.clear_objfiles.connect(clear_objfiles_handler)
4136 gdb.events.new_objfile.connect(new_objfile_handler)
4138 (gdb) file /tmp/hello
4139 Reading symbols from /tmp/hello...done.
4140 Computing the answer to the ultimate question ...
4141 (gdb) python print gdb.current_progspace().expensive_computation
4144 Starting program: /tmp/hello
4146 [Inferior 1 (process 4242) exited normally]
4149 @node Objfiles In Python
4150 @subsubsection Objfiles In Python
4152 @cindex objfiles in python
4155 @value{GDBN} loads symbols for an inferior from various
4156 symbol-containing files (@pxref{Files}). These include the primary
4157 executable file, any shared libraries used by the inferior, and any
4158 separate debug info files (@pxref{Separate Debug Files}).
4159 @value{GDBN} calls these symbol-containing files @dfn{objfiles}.
4161 The following objfile-related functions are available in the
4164 @findex gdb.current_objfile
4165 @defun gdb.current_objfile ()
4166 When auto-loading a Python script (@pxref{Python Auto-loading}), @value{GDBN}
4167 sets the ``current objfile'' to the corresponding objfile. This
4168 function returns the current objfile. If there is no current objfile,
4169 this function returns @code{None}.
4172 @findex gdb.objfiles
4173 @defun gdb.objfiles ()
4174 Return a sequence of objfiles referenced by the current program space.
4175 @xref{Objfiles In Python}, and @ref{Progspaces In Python}. This is identical
4176 to @code{gdb.selected_inferior().progspace.objfiles()} and is included for
4177 historical compatibility.
4180 @findex gdb.lookup_objfile
4181 @defun gdb.lookup_objfile (name @r{[}, by_build_id{]})
4182 Look up @var{name}, a file name or build ID, in the list of objfiles
4183 for the current program space (@pxref{Progspaces In Python}).
4184 If the objfile is not found throw the Python @code{ValueError} exception.
4186 If @var{name} is a relative file name, then it will match any
4187 source file name with the same trailing components. For example, if
4188 @var{name} is @samp{gcc/expr.c}, then it will match source file
4189 name of @file{/build/trunk/gcc/expr.c}, but not
4190 @file{/build/trunk/libcpp/expr.c} or @file{/build/trunk/gcc/x-expr.c}.
4192 If @var{by_build_id} is provided and is @code{True} then @var{name}
4193 is the build ID of the objfile. Otherwise, @var{name} is a file name.
4194 This is supported only on some operating systems, notably those which use
4195 the ELF format for binary files and the @sc{gnu} Binutils. For more details
4196 about this feature, see the description of the @option{--build-id}
4197 command-line option in @ref{Options, , Command Line Options, ld,
4201 Each objfile is represented by an instance of the @code{gdb.Objfile}
4204 @defvar Objfile.filename
4205 The file name of the objfile as a string, with symbolic links resolved.
4207 The value is @code{None} if the objfile is no longer valid.
4208 See the @code{gdb.Objfile.is_valid} method, described below.
4211 @defvar Objfile.username
4212 The file name of the objfile as specified by the user as a string.
4214 The value is @code{None} if the objfile is no longer valid.
4215 See the @code{gdb.Objfile.is_valid} method, described below.
4218 @defvar Objfile.owner
4219 For separate debug info objfiles this is the corresponding @code{gdb.Objfile}
4220 object that debug info is being provided for.
4221 Otherwise this is @code{None}.
4222 Separate debug info objfiles are added with the
4223 @code{gdb.Objfile.add_separate_debug_file} method, described below.
4226 @defvar Objfile.build_id
4227 The build ID of the objfile as a string.
4228 If the objfile does not have a build ID then the value is @code{None}.
4230 This is supported only on some operating systems, notably those which use
4231 the ELF format for binary files and the @sc{gnu} Binutils. For more details
4232 about this feature, see the description of the @option{--build-id}
4233 command-line option in @ref{Options, , Command Line Options, ld,
4237 @defvar Objfile.progspace
4238 The containing program space of the objfile as a @code{gdb.Progspace}
4239 object. @xref{Progspaces In Python}.
4242 @defvar Objfile.pretty_printers
4243 The @code{pretty_printers} attribute is a list of functions. It is
4244 used to look up pretty-printers. A @code{Value} is passed to each
4245 function in order; if the function returns @code{None}, then the
4246 search continues. Otherwise, the return value should be an object
4247 which is used to format the value. @xref{Pretty Printing API}, for more
4251 @defvar Objfile.type_printers
4252 The @code{type_printers} attribute is a list of type printer objects.
4253 @xref{Type Printing API}, for more information.
4256 @defvar Objfile.frame_filters
4257 The @code{frame_filters} attribute is a dictionary of frame filter
4258 objects. @xref{Frame Filter API}, for more information.
4261 One may add arbitrary attributes to @code{gdb.Objfile} objects
4262 in the usual Python way.
4263 This is useful if, for example, one needs to do some extra record keeping
4264 associated with the objfile.
4266 In this contrived example we record the time when @value{GDBN}
4272 def new_objfile_handler(event):
4273 # Set the time_loaded attribute of the new objfile.
4274 event.new_objfile.time_loaded = datetime.datetime.today()
4275 gdb.events.new_objfile.connect(new_objfile_handler)
4278 Reading symbols from ./hello...done.
4279 (gdb) python print gdb.objfiles()[0].time_loaded
4280 2014-10-09 11:41:36.770345
4283 A @code{gdb.Objfile} object has the following methods:
4285 @defun Objfile.is_valid ()
4286 Returns @code{True} if the @code{gdb.Objfile} object is valid,
4287 @code{False} if not. A @code{gdb.Objfile} object can become invalid
4288 if the object file it refers to is not loaded in @value{GDBN} any
4289 longer. All other @code{gdb.Objfile} methods will throw an exception
4290 if it is invalid at the time the method is called.
4293 @defun Objfile.add_separate_debug_file (file)
4294 Add @var{file} to the list of files that @value{GDBN} will search for
4295 debug information for the objfile.
4296 This is useful when the debug info has been removed from the program
4297 and stored in a separate file. @value{GDBN} has built-in support for
4298 finding separate debug info files (@pxref{Separate Debug Files}), but if
4299 the file doesn't live in one of the standard places that @value{GDBN}
4300 searches then this function can be used to add a debug info file
4301 from a different place.
4304 @node Frames In Python
4305 @subsubsection Accessing inferior stack frames from Python
4307 @cindex frames in python
4308 When the debugged program stops, @value{GDBN} is able to analyze its call
4309 stack (@pxref{Frames,,Stack frames}). The @code{gdb.Frame} class
4310 represents a frame in the stack. A @code{gdb.Frame} object is only valid
4311 while its corresponding frame exists in the inferior's stack. If you try
4312 to use an invalid frame object, @value{GDBN} will throw a @code{gdb.error}
4313 exception (@pxref{Exception Handling}).
4315 Two @code{gdb.Frame} objects can be compared for equality with the @code{==}
4319 (@value{GDBP}) python print gdb.newest_frame() == gdb.selected_frame ()
4323 The following frame-related functions are available in the @code{gdb} module:
4325 @findex gdb.selected_frame
4326 @defun gdb.selected_frame ()
4327 Return the selected frame object. (@pxref{Selection,,Selecting a Frame}).
4330 @findex gdb.newest_frame
4331 @defun gdb.newest_frame ()
4332 Return the newest frame object for the selected thread.
4335 @defun gdb.frame_stop_reason_string (reason)
4336 Return a string explaining the reason why @value{GDBN} stopped unwinding
4337 frames, as expressed by the given @var{reason} code (an integer, see the
4338 @code{unwind_stop_reason} method further down in this section).
4341 @findex gdb.invalidate_cached_frames
4342 @defun gdb.invalidate_cached_frames
4343 @value{GDBN} internally keeps a cache of the frames that have been
4344 unwound. This function invalidates this cache.
4346 This function should not generally be called by ordinary Python code.
4347 It is documented for the sake of completeness.
4350 A @code{gdb.Frame} object has the following methods:
4352 @defun Frame.is_valid ()
4353 Returns true if the @code{gdb.Frame} object is valid, false if not.
4354 A frame object can become invalid if the frame it refers to doesn't
4355 exist anymore in the inferior. All @code{gdb.Frame} methods will throw
4356 an exception if it is invalid at the time the method is called.
4359 @defun Frame.name ()
4360 Returns the function name of the frame, or @code{None} if it can't be
4364 @defun Frame.architecture ()
4365 Returns the @code{gdb.Architecture} object corresponding to the frame's
4366 architecture. @xref{Architectures In Python}.
4369 @defun Frame.type ()
4370 Returns the type of the frame. The value can be one of:
4372 @item gdb.NORMAL_FRAME
4373 An ordinary stack frame.
4375 @item gdb.DUMMY_FRAME
4376 A fake stack frame that was created by @value{GDBN} when performing an
4377 inferior function call.
4379 @item gdb.INLINE_FRAME
4380 A frame representing an inlined function. The function was inlined
4381 into a @code{gdb.NORMAL_FRAME} that is older than this one.
4383 @item gdb.TAILCALL_FRAME
4384 A frame representing a tail call. @xref{Tail Call Frames}.
4386 @item gdb.SIGTRAMP_FRAME
4387 A signal trampoline frame. This is the frame created by the OS when
4388 it calls into a signal handler.
4390 @item gdb.ARCH_FRAME
4391 A fake stack frame representing a cross-architecture call.
4393 @item gdb.SENTINEL_FRAME
4394 This is like @code{gdb.NORMAL_FRAME}, but it is only used for the
4399 @defun Frame.unwind_stop_reason ()
4400 Return an integer representing the reason why it's not possible to find
4401 more frames toward the outermost frame. Use
4402 @code{gdb.frame_stop_reason_string} to convert the value returned by this
4403 function to a string. The value can be one of:
4406 @item gdb.FRAME_UNWIND_NO_REASON
4407 No particular reason (older frames should be available).
4409 @item gdb.FRAME_UNWIND_NULL_ID
4410 The previous frame's analyzer returns an invalid result. This is no
4411 longer used by @value{GDBN}, and is kept only for backward
4414 @item gdb.FRAME_UNWIND_OUTERMOST
4415 This frame is the outermost.
4417 @item gdb.FRAME_UNWIND_UNAVAILABLE
4418 Cannot unwind further, because that would require knowing the
4419 values of registers or memory that have not been collected.
4421 @item gdb.FRAME_UNWIND_INNER_ID
4422 This frame ID looks like it ought to belong to a NEXT frame,
4423 but we got it for a PREV frame. Normally, this is a sign of
4424 unwinder failure. It could also indicate stack corruption.
4426 @item gdb.FRAME_UNWIND_SAME_ID
4427 This frame has the same ID as the previous one. That means
4428 that unwinding further would almost certainly give us another
4429 frame with exactly the same ID, so break the chain. Normally,
4430 this is a sign of unwinder failure. It could also indicate
4433 @item gdb.FRAME_UNWIND_NO_SAVED_PC
4434 The frame unwinder did not find any saved PC, but we needed
4435 one to unwind further.
4437 @item gdb.FRAME_UNWIND_MEMORY_ERROR
4438 The frame unwinder caused an error while trying to access memory.
4440 @item gdb.FRAME_UNWIND_FIRST_ERROR
4441 Any stop reason greater or equal to this value indicates some kind
4442 of error. This special value facilitates writing code that tests
4443 for errors in unwinding in a way that will work correctly even if
4444 the list of the other values is modified in future @value{GDBN}
4445 versions. Using it, you could write:
4447 reason = gdb.selected_frame().unwind_stop_reason ()
4448 reason_str = gdb.frame_stop_reason_string (reason)
4449 if reason >= gdb.FRAME_UNWIND_FIRST_ERROR:
4450 print "An error occured: %s" % reason_str
4457 Returns the frame's resume address.
4460 @defun Frame.block ()
4461 Return the frame's code block. @xref{Blocks In Python}. If the frame
4462 does not have a block -- for example, if there is no debugging
4463 information for the code in question -- then this will throw an
4467 @defun Frame.function ()
4468 Return the symbol for the function corresponding to this frame.
4469 @xref{Symbols In Python}.
4472 @defun Frame.older ()
4473 Return the frame that called this frame.
4476 @defun Frame.newer ()
4477 Return the frame called by this frame.
4480 @defun Frame.find_sal ()
4481 Return the frame's symtab and line object.
4482 @xref{Symbol Tables In Python}.
4485 @defun Frame.read_register (register)
4486 Return the value of @var{register} in this frame. The @var{register}
4487 argument must be a string (e.g., @code{'sp'} or @code{'rax'}).
4488 Returns a @code{Gdb.Value} object. Throws an exception if @var{register}
4492 @defun Frame.read_var (variable @r{[}, block@r{]})
4493 Return the value of @var{variable} in this frame. If the optional
4494 argument @var{block} is provided, search for the variable from that
4495 block; otherwise start at the frame's current block (which is
4496 determined by the frame's current program counter). The @var{variable}
4497 argument must be a string or a @code{gdb.Symbol} object; @var{block} must be a
4498 @code{gdb.Block} object.
4501 @defun Frame.select ()
4502 Set this frame to be the selected frame. @xref{Stack, ,Examining the
4506 @node Blocks In Python
4507 @subsubsection Accessing blocks from Python
4509 @cindex blocks in python
4512 In @value{GDBN}, symbols are stored in blocks. A block corresponds
4513 roughly to a scope in the source code. Blocks are organized
4514 hierarchically, and are represented individually in Python as a
4515 @code{gdb.Block}. Blocks rely on debugging information being
4518 A frame has a block. Please see @ref{Frames In Python}, for a more
4519 in-depth discussion of frames.
4521 The outermost block is known as the @dfn{global block}. The global
4522 block typically holds public global variables and functions.
4524 The block nested just inside the global block is the @dfn{static
4525 block}. The static block typically holds file-scoped variables and
4528 @value{GDBN} provides a method to get a block's superblock, but there
4529 is currently no way to examine the sub-blocks of a block, or to
4530 iterate over all the blocks in a symbol table (@pxref{Symbol Tables In
4533 Here is a short example that should help explain blocks:
4536 /* This is in the global block. */
4539 /* This is in the static block. */
4540 static int file_scope;
4542 /* 'function' is in the global block, and 'argument' is
4543 in a block nested inside of 'function'. */
4544 int function (int argument)
4546 /* 'local' is in a block inside 'function'. It may or may
4547 not be in the same block as 'argument'. */
4551 /* 'inner' is in a block whose superblock is the one holding
4555 /* If this call is expanded by the compiler, you may see
4556 a nested block here whose function is 'inline_function'
4557 and whose superblock is the one holding 'inner'. */
4563 A @code{gdb.Block} is iterable. The iterator returns the symbols
4564 (@pxref{Symbols In Python}) local to the block. Python programs
4565 should not assume that a specific block object will always contain a
4566 given symbol, since changes in @value{GDBN} features and
4567 infrastructure may cause symbols move across blocks in a symbol
4570 The following block-related functions are available in the @code{gdb}
4573 @findex gdb.block_for_pc
4574 @defun gdb.block_for_pc (pc)
4575 Return the innermost @code{gdb.Block} containing the given @var{pc}
4576 value. If the block cannot be found for the @var{pc} value specified,
4577 the function will return @code{None}. This is identical to
4578 @code{gdb.current_progspace().block_for_pc(pc)} and is included for
4579 historical compatibility.
4582 A @code{gdb.Block} object has the following methods:
4584 @defun Block.is_valid ()
4585 Returns @code{True} if the @code{gdb.Block} object is valid,
4586 @code{False} if not. A block object can become invalid if the block it
4587 refers to doesn't exist anymore in the inferior. All other
4588 @code{gdb.Block} methods will throw an exception if it is invalid at
4589 the time the method is called. The block's validity is also checked
4590 during iteration over symbols of the block.
4593 A @code{gdb.Block} object has the following attributes:
4596 The start address of the block. This attribute is not writable.
4600 One past the last address that appears in the block. This attribute
4604 @defvar Block.function
4605 The name of the block represented as a @code{gdb.Symbol}. If the
4606 block is not named, then this attribute holds @code{None}. This
4607 attribute is not writable.
4609 For ordinary function blocks, the superblock is the static block.
4610 However, you should note that it is possible for a function block to
4611 have a superblock that is not the static block -- for instance this
4612 happens for an inlined function.
4615 @defvar Block.superblock
4616 The block containing this block. If this parent block does not exist,
4617 this attribute holds @code{None}. This attribute is not writable.
4620 @defvar Block.global_block
4621 The global block associated with this block. This attribute is not
4625 @defvar Block.static_block
4626 The static block associated with this block. This attribute is not
4630 @defvar Block.is_global
4631 @code{True} if the @code{gdb.Block} object is a global block,
4632 @code{False} if not. This attribute is not
4636 @defvar Block.is_static
4637 @code{True} if the @code{gdb.Block} object is a static block,
4638 @code{False} if not. This attribute is not writable.
4641 @node Symbols In Python
4642 @subsubsection Python representation of Symbols
4644 @cindex symbols in python
4647 @value{GDBN} represents every variable, function and type as an
4648 entry in a symbol table. @xref{Symbols, ,Examining the Symbol Table}.
4649 Similarly, Python represents these symbols in @value{GDBN} with the
4650 @code{gdb.Symbol} object.
4652 The following symbol-related functions are available in the @code{gdb}
4655 @findex gdb.lookup_symbol
4656 @defun gdb.lookup_symbol (name @r{[}, block @r{[}, domain@r{]]})
4657 This function searches for a symbol by name. The search scope can be
4658 restricted to the parameters defined in the optional domain and block
4661 @var{name} is the name of the symbol. It must be a string. The
4662 optional @var{block} argument restricts the search to symbols visible
4663 in that @var{block}. The @var{block} argument must be a
4664 @code{gdb.Block} object. If omitted, the block for the current frame
4665 is used. The optional @var{domain} argument restricts
4666 the search to the domain type. The @var{domain} argument must be a
4667 domain constant defined in the @code{gdb} module and described later
4670 The result is a tuple of two elements.
4671 The first element is a @code{gdb.Symbol} object or @code{None} if the symbol
4673 If the symbol is found, the second element is @code{True} if the symbol
4674 is a field of a method's object (e.g., @code{this} in C@t{++}),
4675 otherwise it is @code{False}.
4676 If the symbol is not found, the second element is @code{False}.
4679 @findex gdb.lookup_global_symbol
4680 @defun gdb.lookup_global_symbol (name @r{[}, domain@r{]})
4681 This function searches for a global symbol by name.
4682 The search scope can be restricted to by the domain argument.
4684 @var{name} is the name of the symbol. It must be a string.
4685 The optional @var{domain} argument restricts the search to the domain type.
4686 The @var{domain} argument must be a domain constant defined in the @code{gdb}
4687 module and described later in this chapter.
4689 The result is a @code{gdb.Symbol} object or @code{None} if the symbol
4693 A @code{gdb.Symbol} object has the following attributes:
4696 The type of the symbol or @code{None} if no type is recorded.
4697 This attribute is represented as a @code{gdb.Type} object.
4698 @xref{Types In Python}. This attribute is not writable.
4701 @defvar Symbol.symtab
4702 The symbol table in which the symbol appears. This attribute is
4703 represented as a @code{gdb.Symtab} object. @xref{Symbol Tables In
4704 Python}. This attribute is not writable.
4708 The line number in the source code at which the symbol was defined.
4713 The name of the symbol as a string. This attribute is not writable.
4716 @defvar Symbol.linkage_name
4717 The name of the symbol, as used by the linker (i.e., may be mangled).
4718 This attribute is not writable.
4721 @defvar Symbol.print_name
4722 The name of the symbol in a form suitable for output. This is either
4723 @code{name} or @code{linkage_name}, depending on whether the user
4724 asked @value{GDBN} to display demangled or mangled names.
4727 @defvar Symbol.addr_class
4728 The address class of the symbol. This classifies how to find the value
4729 of a symbol. Each address class is a constant defined in the
4730 @code{gdb} module and described later in this chapter.
4733 @defvar Symbol.needs_frame
4734 This is @code{True} if evaluating this symbol's value requires a frame
4735 (@pxref{Frames In Python}) and @code{False} otherwise. Typically,
4736 local variables will require a frame, but other symbols will not.
4739 @defvar Symbol.is_argument
4740 @code{True} if the symbol is an argument of a function.
4743 @defvar Symbol.is_constant
4744 @code{True} if the symbol is a constant.
4747 @defvar Symbol.is_function
4748 @code{True} if the symbol is a function or a method.
4751 @defvar Symbol.is_variable
4752 @code{True} if the symbol is a variable.
4755 A @code{gdb.Symbol} object has the following methods:
4757 @defun Symbol.is_valid ()
4758 Returns @code{True} if the @code{gdb.Symbol} object is valid,
4759 @code{False} if not. A @code{gdb.Symbol} object can become invalid if
4760 the symbol it refers to does not exist in @value{GDBN} any longer.
4761 All other @code{gdb.Symbol} methods will throw an exception if it is
4762 invalid at the time the method is called.
4765 @defun Symbol.value (@r{[}frame@r{]})
4766 Compute the value of the symbol, as a @code{gdb.Value}. For
4767 functions, this computes the address of the function, cast to the
4768 appropriate type. If the symbol requires a frame in order to compute
4769 its value, then @var{frame} must be given. If @var{frame} is not
4770 given, or if @var{frame} is invalid, then this method will throw an
4774 The available domain categories in @code{gdb.Symbol} are represented
4775 as constants in the @code{gdb} module:
4778 @vindex SYMBOL_UNDEF_DOMAIN
4779 @item gdb.SYMBOL_UNDEF_DOMAIN
4780 This is used when a domain has not been discovered or none of the
4781 following domains apply. This usually indicates an error either
4782 in the symbol information or in @value{GDBN}'s handling of symbols.
4784 @vindex SYMBOL_VAR_DOMAIN
4785 @item gdb.SYMBOL_VAR_DOMAIN
4786 This domain contains variables, function names, typedef names and enum
4789 @vindex SYMBOL_STRUCT_DOMAIN
4790 @item gdb.SYMBOL_STRUCT_DOMAIN
4791 This domain holds struct, union and enum type names.
4793 @vindex SYMBOL_LABEL_DOMAIN
4794 @item gdb.SYMBOL_LABEL_DOMAIN
4795 This domain contains names of labels (for gotos).
4797 @vindex SYMBOL_MODULE_DOMAIN
4798 @item gdb.SYMBOL_MODULE_DOMAIN
4799 This domain contains names of Fortran module types.
4801 @vindex SYMBOL_COMMON_BLOCK_DOMAIN
4802 @item gdb.SYMBOL_COMMON_BLOCK_DOMAIN
4803 This domain contains names of Fortran common blocks.
4806 The available address class categories in @code{gdb.Symbol} are represented
4807 as constants in the @code{gdb} module:
4810 @vindex SYMBOL_LOC_UNDEF
4811 @item gdb.SYMBOL_LOC_UNDEF
4812 If this is returned by address class, it indicates an error either in
4813 the symbol information or in @value{GDBN}'s handling of symbols.
4815 @vindex SYMBOL_LOC_CONST
4816 @item gdb.SYMBOL_LOC_CONST
4817 Value is constant int.
4819 @vindex SYMBOL_LOC_STATIC
4820 @item gdb.SYMBOL_LOC_STATIC
4821 Value is at a fixed address.
4823 @vindex SYMBOL_LOC_REGISTER
4824 @item gdb.SYMBOL_LOC_REGISTER
4825 Value is in a register.
4827 @vindex SYMBOL_LOC_ARG
4828 @item gdb.SYMBOL_LOC_ARG
4829 Value is an argument. This value is at the offset stored within the
4830 symbol inside the frame's argument list.
4832 @vindex SYMBOL_LOC_REF_ARG
4833 @item gdb.SYMBOL_LOC_REF_ARG
4834 Value address is stored in the frame's argument list. Just like
4835 @code{LOC_ARG} except that the value's address is stored at the
4836 offset, not the value itself.
4838 @vindex SYMBOL_LOC_REGPARM_ADDR
4839 @item gdb.SYMBOL_LOC_REGPARM_ADDR
4840 Value is a specified register. Just like @code{LOC_REGISTER} except
4841 the register holds the address of the argument instead of the argument
4844 @vindex SYMBOL_LOC_LOCAL
4845 @item gdb.SYMBOL_LOC_LOCAL
4846 Value is a local variable.
4848 @vindex SYMBOL_LOC_TYPEDEF
4849 @item gdb.SYMBOL_LOC_TYPEDEF
4850 Value not used. Symbols in the domain @code{SYMBOL_STRUCT_DOMAIN} all
4853 @vindex SYMBOL_LOC_BLOCK
4854 @item gdb.SYMBOL_LOC_BLOCK
4857 @vindex SYMBOL_LOC_CONST_BYTES
4858 @item gdb.SYMBOL_LOC_CONST_BYTES
4859 Value is a byte-sequence.
4861 @vindex SYMBOL_LOC_UNRESOLVED
4862 @item gdb.SYMBOL_LOC_UNRESOLVED
4863 Value is at a fixed address, but the address of the variable has to be
4864 determined from the minimal symbol table whenever the variable is
4867 @vindex SYMBOL_LOC_OPTIMIZED_OUT
4868 @item gdb.SYMBOL_LOC_OPTIMIZED_OUT
4869 The value does not actually exist in the program.
4871 @vindex SYMBOL_LOC_COMPUTED
4872 @item gdb.SYMBOL_LOC_COMPUTED
4873 The value's address is a computed location.
4875 @vindex SYMBOL_LOC_COMPUTED
4876 @item gdb.SYMBOL_LOC_COMPUTED
4877 The value's address is a symbol. This is only used for Fortran common
4881 @node Symbol Tables In Python
4882 @subsubsection Symbol table representation in Python
4884 @cindex symbol tables in python
4886 @tindex gdb.Symtab_and_line
4888 Access to symbol table data maintained by @value{GDBN} on the inferior
4889 is exposed to Python via two objects: @code{gdb.Symtab_and_line} and
4890 @code{gdb.Symtab}. Symbol table and line data for a frame is returned
4891 from the @code{find_sal} method in @code{gdb.Frame} object.
4892 @xref{Frames In Python}.
4894 For more information on @value{GDBN}'s symbol table management, see
4895 @ref{Symbols, ,Examining the Symbol Table}, for more information.
4897 A @code{gdb.Symtab_and_line} object has the following attributes:
4899 @defvar Symtab_and_line.symtab
4900 The symbol table object (@code{gdb.Symtab}) for this frame.
4901 This attribute is not writable.
4904 @defvar Symtab_and_line.pc
4905 Indicates the start of the address range occupied by code for the
4906 current source line. This attribute is not writable.
4909 @defvar Symtab_and_line.last
4910 Indicates the end of the address range occupied by code for the current
4911 source line. This attribute is not writable.
4914 @defvar Symtab_and_line.line
4915 Indicates the current line number for this object. This
4916 attribute is not writable.
4919 A @code{gdb.Symtab_and_line} object has the following methods:
4921 @defun Symtab_and_line.is_valid ()
4922 Returns @code{True} if the @code{gdb.Symtab_and_line} object is valid,
4923 @code{False} if not. A @code{gdb.Symtab_and_line} object can become
4924 invalid if the Symbol table and line object it refers to does not
4925 exist in @value{GDBN} any longer. All other
4926 @code{gdb.Symtab_and_line} methods will throw an exception if it is
4927 invalid at the time the method is called.
4930 A @code{gdb.Symtab} object has the following attributes:
4932 @defvar Symtab.filename
4933 The symbol table's source filename. This attribute is not writable.
4936 @defvar Symtab.objfile
4937 The symbol table's backing object file. @xref{Objfiles In Python}.
4938 This attribute is not writable.
4941 @defvar Symtab.producer
4942 The name and possibly version number of the program that
4943 compiled the code in the symbol table.
4944 The contents of this string is up to the compiler.
4945 If no producer information is available then @code{None} is returned.
4946 This attribute is not writable.
4949 A @code{gdb.Symtab} object has the following methods:
4951 @defun Symtab.is_valid ()
4952 Returns @code{True} if the @code{gdb.Symtab} object is valid,
4953 @code{False} if not. A @code{gdb.Symtab} object can become invalid if
4954 the symbol table it refers to does not exist in @value{GDBN} any
4955 longer. All other @code{gdb.Symtab} methods will throw an exception
4956 if it is invalid at the time the method is called.
4959 @defun Symtab.fullname ()
4960 Return the symbol table's source absolute file name.
4963 @defun Symtab.global_block ()
4964 Return the global block of the underlying symbol table.
4965 @xref{Blocks In Python}.
4968 @defun Symtab.static_block ()
4969 Return the static block of the underlying symbol table.
4970 @xref{Blocks In Python}.
4973 @defun Symtab.linetable ()
4974 Return the line table associated with the symbol table.
4975 @xref{Line Tables In Python}.
4978 @node Line Tables In Python
4979 @subsubsection Manipulating line tables using Python
4981 @cindex line tables in python
4982 @tindex gdb.LineTable
4984 Python code can request and inspect line table information from a
4985 symbol table that is loaded in @value{GDBN}. A line table is a
4986 mapping of source lines to their executable locations in memory. To
4987 acquire the line table information for a particular symbol table, use
4988 the @code{linetable} function (@pxref{Symbol Tables In Python}).
4990 A @code{gdb.LineTable} is iterable. The iterator returns
4991 @code{LineTableEntry} objects that correspond to the source line and
4992 address for each line table entry. @code{LineTableEntry} objects have
4993 the following attributes:
4995 @defvar LineTableEntry.line
4996 The source line number for this line table entry. This number
4997 corresponds to the actual line of source. This attribute is not
5001 @defvar LineTableEntry.pc
5002 The address that is associated with the line table entry where the
5003 executable code for that source line resides in memory. This
5004 attribute is not writable.
5007 As there can be multiple addresses for a single source line, you may
5008 receive multiple @code{LineTableEntry} objects with matching
5009 @code{line} attributes, but with different @code{pc} attributes. The
5010 iterator is sorted in ascending @code{pc} order. Here is a small
5011 example illustrating iterating over a line table.
5014 symtab = gdb.selected_frame().find_sal().symtab
5015 linetable = symtab.linetable()
5016 for line in linetable:
5017 print "Line: "+str(line.line)+" Address: "+hex(line.pc)
5020 This will have the following output:
5023 Line: 33 Address: 0x4005c8L
5024 Line: 37 Address: 0x4005caL
5025 Line: 39 Address: 0x4005d2L
5026 Line: 40 Address: 0x4005f8L
5027 Line: 42 Address: 0x4005ffL
5028 Line: 44 Address: 0x400608L
5029 Line: 42 Address: 0x40060cL
5030 Line: 45 Address: 0x400615L
5033 In addition to being able to iterate over a @code{LineTable}, it also
5034 has the following direct access methods:
5036 @defun LineTable.line (line)
5037 Return a Python @code{Tuple} of @code{LineTableEntry} objects for any
5038 entries in the line table for the given @var{line}, which specifies
5039 the source code line. If there are no entries for that source code
5040 @var{line}, the Python @code{None} is returned.
5043 @defun LineTable.has_line (line)
5044 Return a Python @code{Boolean} indicating whether there is an entry in
5045 the line table for this source line. Return @code{True} if an entry
5046 is found, or @code{False} if not.
5049 @defun LineTable.source_lines ()
5050 Return a Python @code{List} of the source line numbers in the symbol
5051 table. Only lines with executable code locations are returned. The
5052 contents of the @code{List} will just be the source line entries
5053 represented as Python @code{Long} values.
5056 @node Breakpoints In Python
5057 @subsubsection Manipulating breakpoints using Python
5059 @cindex breakpoints in python
5060 @tindex gdb.Breakpoint
5062 Python code can manipulate breakpoints via the @code{gdb.Breakpoint}
5065 A breakpoint can be created using one of the two forms of the
5066 @code{gdb.Breakpoint} constructor. The first one accepts a string
5067 like one would pass to the @code{break}
5068 (@pxref{Set Breaks,,Setting Breakpoints}) and @code{watch}
5069 (@pxref{Set Watchpoints, , Setting Watchpoints}) commands, and can be used to
5070 create both breakpoints and watchpoints. The second accepts separate Python
5071 arguments similar to @ref{Explicit Locations}, and can only be used to create
5074 @defun Breakpoint.__init__ (spec @r{[}, type @r{][}, wp_class @r{][}, internal @r{][}, temporary @r{][}, qualified @r{]})
5075 Create a new breakpoint according to @var{spec}, which is a string naming the
5076 location of a breakpoint, or an expression that defines a watchpoint. The
5077 string should describe a location in a format recognized by the @code{break}
5078 command (@pxref{Set Breaks,,Setting Breakpoints}) or, in the case of a
5079 watchpoint, by the @code{watch} command
5080 (@pxref{Set Watchpoints, , Setting Watchpoints}).
5082 The optional @var{type} argument specifies the type of the breakpoint to create,
5085 The optional @var{wp_class} argument defines the class of watchpoint to create,
5086 if @var{type} is @code{gdb.BP_WATCHPOINT}. If @var{wp_class} is omitted, it
5087 defaults to @code{gdb.WP_WRITE}.
5089 The optional @var{internal} argument allows the breakpoint to become invisible
5090 to the user. The breakpoint will neither be reported when created, nor will it
5091 be listed in the output from @code{info breakpoints} (but will be listed with
5092 the @code{maint info breakpoints} command).
5094 The optional @var{temporary} argument makes the breakpoint a temporary
5095 breakpoint. Temporary breakpoints are deleted after they have been hit. Any
5096 further access to the Python breakpoint after it has been hit will result in a
5097 runtime error (as that breakpoint has now been automatically deleted).
5099 The optional @var{qualified} argument is a boolean that allows interpreting
5100 the function passed in @code{spec} as a fully-qualified name. It is equivalent
5101 to @code{break}'s @code{-qualified} flag (@pxref{Linespec Locations} and
5102 @ref{Explicit Locations}).
5106 @defun Breakpoint.__init__ (@r{[} source @r{][}, function @r{][}, label @r{][}, line @r{]}, @r{][} internal @r{][}, temporary @r{][}, qualified @r{]})
5107 This second form of creating a new breakpoint specifies the explicit
5108 location (@pxref{Explicit Locations}) using keywords. The new breakpoint will
5109 be created in the specified source file @var{source}, at the specified
5110 @var{function}, @var{label} and @var{line}.
5112 @var{internal}, @var{temporary} and @var{qualified} have the same usage as
5113 explained previously.
5116 The available types are represented by constants defined in the @code{gdb}
5120 @vindex BP_BREAKPOINT
5121 @item gdb.BP_BREAKPOINT
5122 Normal code breakpoint.
5124 @vindex BP_WATCHPOINT
5125 @item gdb.BP_WATCHPOINT
5126 Watchpoint breakpoint.
5128 @vindex BP_HARDWARE_WATCHPOINT
5129 @item gdb.BP_HARDWARE_WATCHPOINT
5130 Hardware assisted watchpoint.
5132 @vindex BP_READ_WATCHPOINT
5133 @item gdb.BP_READ_WATCHPOINT
5134 Hardware assisted read watchpoint.
5136 @vindex BP_ACCESS_WATCHPOINT
5137 @item gdb.BP_ACCESS_WATCHPOINT
5138 Hardware assisted access watchpoint.
5141 The available watchpoint types represented by constants are defined in the
5147 Read only watchpoint.
5151 Write only watchpoint.
5155 Read/Write watchpoint.
5158 @defun Breakpoint.stop (self)
5159 The @code{gdb.Breakpoint} class can be sub-classed and, in
5160 particular, you may choose to implement the @code{stop} method.
5161 If this method is defined in a sub-class of @code{gdb.Breakpoint},
5162 it will be called when the inferior reaches any location of a
5163 breakpoint which instantiates that sub-class. If the method returns
5164 @code{True}, the inferior will be stopped at the location of the
5165 breakpoint, otherwise the inferior will continue.
5167 If there are multiple breakpoints at the same location with a
5168 @code{stop} method, each one will be called regardless of the
5169 return status of the previous. This ensures that all @code{stop}
5170 methods have a chance to execute at that location. In this scenario
5171 if one of the methods returns @code{True} but the others return
5172 @code{False}, the inferior will still be stopped.
5174 You should not alter the execution state of the inferior (i.e.@:, step,
5175 next, etc.), alter the current frame context (i.e.@:, change the current
5176 active frame), or alter, add or delete any breakpoint. As a general
5177 rule, you should not alter any data within @value{GDBN} or the inferior
5180 Example @code{stop} implementation:
5183 class MyBreakpoint (gdb.Breakpoint):
5185 inf_val = gdb.parse_and_eval("foo")
5192 @defun Breakpoint.is_valid ()
5193 Return @code{True} if this @code{Breakpoint} object is valid,
5194 @code{False} otherwise. A @code{Breakpoint} object can become invalid
5195 if the user deletes the breakpoint. In this case, the object still
5196 exists, but the underlying breakpoint does not. In the cases of
5197 watchpoint scope, the watchpoint remains valid even if execution of the
5198 inferior leaves the scope of that watchpoint.
5201 @defun Breakpoint.delete ()
5202 Permanently deletes the @value{GDBN} breakpoint. This also
5203 invalidates the Python @code{Breakpoint} object. Any further access
5204 to this object's attributes or methods will raise an error.
5207 @defvar Breakpoint.enabled
5208 This attribute is @code{True} if the breakpoint is enabled, and
5209 @code{False} otherwise. This attribute is writable. You can use it to enable
5210 or disable the breakpoint.
5213 @defvar Breakpoint.silent
5214 This attribute is @code{True} if the breakpoint is silent, and
5215 @code{False} otherwise. This attribute is writable.
5217 Note that a breakpoint can also be silent if it has commands and the
5218 first command is @code{silent}. This is not reported by the
5219 @code{silent} attribute.
5222 @defvar Breakpoint.pending
5223 This attribute is @code{True} if the breakpoint is pending, and
5224 @code{False} otherwise. @xref{Set Breaks}. This attribute is
5228 @anchor{python_breakpoint_thread}
5229 @defvar Breakpoint.thread
5230 If the breakpoint is thread-specific, this attribute holds the
5231 thread's global id. If the breakpoint is not thread-specific, this
5232 attribute is @code{None}. This attribute is writable.
5235 @defvar Breakpoint.task
5236 If the breakpoint is Ada task-specific, this attribute holds the Ada task
5237 id. If the breakpoint is not task-specific (or the underlying
5238 language is not Ada), this attribute is @code{None}. This attribute
5242 @defvar Breakpoint.ignore_count
5243 This attribute holds the ignore count for the breakpoint, an integer.
5244 This attribute is writable.
5247 @defvar Breakpoint.number
5248 This attribute holds the breakpoint's number --- the identifier used by
5249 the user to manipulate the breakpoint. This attribute is not writable.
5252 @defvar Breakpoint.type
5253 This attribute holds the breakpoint's type --- the identifier used to
5254 determine the actual breakpoint type or use-case. This attribute is not
5258 @defvar Breakpoint.visible
5259 This attribute tells whether the breakpoint is visible to the user
5260 when set, or when the @samp{info breakpoints} command is run. This
5261 attribute is not writable.
5264 @defvar Breakpoint.temporary
5265 This attribute indicates whether the breakpoint was created as a
5266 temporary breakpoint. Temporary breakpoints are automatically deleted
5267 after that breakpoint has been hit. Access to this attribute, and all
5268 other attributes and functions other than the @code{is_valid}
5269 function, will result in an error after the breakpoint has been hit
5270 (as it has been automatically deleted). This attribute is not
5274 @defvar Breakpoint.hit_count
5275 This attribute holds the hit count for the breakpoint, an integer.
5276 This attribute is writable, but currently it can only be set to zero.
5279 @defvar Breakpoint.location
5280 This attribute holds the location of the breakpoint, as specified by
5281 the user. It is a string. If the breakpoint does not have a location
5282 (that is, it is a watchpoint) the attribute's value is @code{None}. This
5283 attribute is not writable.
5286 @defvar Breakpoint.expression
5287 This attribute holds a breakpoint expression, as specified by
5288 the user. It is a string. If the breakpoint does not have an
5289 expression (the breakpoint is not a watchpoint) the attribute's value
5290 is @code{None}. This attribute is not writable.
5293 @defvar Breakpoint.condition
5294 This attribute holds the condition of the breakpoint, as specified by
5295 the user. It is a string. If there is no condition, this attribute's
5296 value is @code{None}. This attribute is writable.
5299 @defvar Breakpoint.commands
5300 This attribute holds the commands attached to the breakpoint. If
5301 there are commands, this attribute's value is a string holding all the
5302 commands, separated by newlines. If there are no commands, this
5303 attribute is @code{None}. This attribute is writable.
5306 @node Finish Breakpoints in Python
5307 @subsubsection Finish Breakpoints
5309 @cindex python finish breakpoints
5310 @tindex gdb.FinishBreakpoint
5312 A finish breakpoint is a temporary breakpoint set at the return address of
5313 a frame, based on the @code{finish} command. @code{gdb.FinishBreakpoint}
5314 extends @code{gdb.Breakpoint}. The underlying breakpoint will be disabled
5315 and deleted when the execution will run out of the breakpoint scope (i.e.@:
5316 @code{Breakpoint.stop} or @code{FinishBreakpoint.out_of_scope} triggered).
5317 Finish breakpoints are thread specific and must be create with the right
5320 @defun FinishBreakpoint.__init__ (@r{[}frame@r{]} @r{[}, internal@r{]})
5321 Create a finish breakpoint at the return address of the @code{gdb.Frame}
5322 object @var{frame}. If @var{frame} is not provided, this defaults to the
5323 newest frame. The optional @var{internal} argument allows the breakpoint to
5324 become invisible to the user. @xref{Breakpoints In Python}, for further
5325 details about this argument.
5328 @defun FinishBreakpoint.out_of_scope (self)
5329 In some circumstances (e.g.@: @code{longjmp}, C@t{++} exceptions, @value{GDBN}
5330 @code{return} command, @dots{}), a function may not properly terminate, and
5331 thus never hit the finish breakpoint. When @value{GDBN} notices such a
5332 situation, the @code{out_of_scope} callback will be triggered.
5334 You may want to sub-class @code{gdb.FinishBreakpoint} and override this
5338 class MyFinishBreakpoint (gdb.FinishBreakpoint)
5340 print "normal finish"
5343 def out_of_scope ():
5344 print "abnormal finish"
5348 @defvar FinishBreakpoint.return_value
5349 When @value{GDBN} is stopped at a finish breakpoint and the frame
5350 used to build the @code{gdb.FinishBreakpoint} object had debug symbols, this
5351 attribute will contain a @code{gdb.Value} object corresponding to the return
5352 value of the function. The value will be @code{None} if the function return
5353 type is @code{void} or if the return value was not computable. This attribute
5357 @node Lazy Strings In Python
5358 @subsubsection Python representation of lazy strings
5360 @cindex lazy strings in python
5361 @tindex gdb.LazyString
5363 A @dfn{lazy string} is a string whose contents is not retrieved or
5364 encoded until it is needed.
5366 A @code{gdb.LazyString} is represented in @value{GDBN} as an
5367 @code{address} that points to a region of memory, an @code{encoding}
5368 that will be used to encode that region of memory, and a @code{length}
5369 to delimit the region of memory that represents the string. The
5370 difference between a @code{gdb.LazyString} and a string wrapped within
5371 a @code{gdb.Value} is that a @code{gdb.LazyString} will be treated
5372 differently by @value{GDBN} when printing. A @code{gdb.LazyString} is
5373 retrieved and encoded during printing, while a @code{gdb.Value}
5374 wrapping a string is immediately retrieved and encoded on creation.
5376 A @code{gdb.LazyString} object has the following functions:
5378 @defun LazyString.value ()
5379 Convert the @code{gdb.LazyString} to a @code{gdb.Value}. This value
5380 will point to the string in memory, but will lose all the delayed
5381 retrieval, encoding and handling that @value{GDBN} applies to a
5382 @code{gdb.LazyString}.
5385 @defvar LazyString.address
5386 This attribute holds the address of the string. This attribute is not
5390 @defvar LazyString.length
5391 This attribute holds the length of the string in characters. If the
5392 length is -1, then the string will be fetched and encoded up to the
5393 first null of appropriate width. This attribute is not writable.
5396 @defvar LazyString.encoding
5397 This attribute holds the encoding that will be applied to the string
5398 when the string is printed by @value{GDBN}. If the encoding is not
5399 set, or contains an empty string, then @value{GDBN} will select the
5400 most appropriate encoding when the string is printed. This attribute
5404 @defvar LazyString.type
5405 This attribute holds the type that is represented by the lazy string's
5406 type. For a lazy string this is a pointer or array type. To
5407 resolve this to the lazy string's character type, use the type's
5408 @code{target} method. @xref{Types In Python}. This attribute is not
5412 @node Architectures In Python
5413 @subsubsection Python representation of architectures
5414 @cindex Python architectures
5416 @value{GDBN} uses architecture specific parameters and artifacts in a
5417 number of its various computations. An architecture is represented
5418 by an instance of the @code{gdb.Architecture} class.
5420 A @code{gdb.Architecture} class has the following methods:
5422 @defun Architecture.name ()
5423 Return the name (string value) of the architecture.
5426 @defun Architecture.disassemble (@var{start_pc} @r{[}, @var{end_pc} @r{[}, @var{count}@r{]]})
5427 Return a list of disassembled instructions starting from the memory
5428 address @var{start_pc}. The optional arguments @var{end_pc} and
5429 @var{count} determine the number of instructions in the returned list.
5430 If both the optional arguments @var{end_pc} and @var{count} are
5431 specified, then a list of at most @var{count} disassembled instructions
5432 whose start address falls in the closed memory address interval from
5433 @var{start_pc} to @var{end_pc} are returned. If @var{end_pc} is not
5434 specified, but @var{count} is specified, then @var{count} number of
5435 instructions starting from the address @var{start_pc} are returned. If
5436 @var{count} is not specified but @var{end_pc} is specified, then all
5437 instructions whose start address falls in the closed memory address
5438 interval from @var{start_pc} to @var{end_pc} are returned. If neither
5439 @var{end_pc} nor @var{count} are specified, then a single instruction at
5440 @var{start_pc} is returned. For all of these cases, each element of the
5441 returned list is a Python @code{dict} with the following string keys:
5446 The value corresponding to this key is a Python long integer capturing
5447 the memory address of the instruction.
5450 The value corresponding to this key is a string value which represents
5451 the instruction with assembly language mnemonics. The assembly
5452 language flavor used is the same as that specified by the current CLI
5453 variable @code{disassembly-flavor}. @xref{Machine Code}.
5456 The value corresponding to this key is the length (integer value) of the
5457 instruction in bytes.
5462 @node Python Auto-loading
5463 @subsection Python Auto-loading
5464 @cindex Python auto-loading
5466 When a new object file is read (for example, due to the @code{file}
5467 command, or because the inferior has loaded a shared library),
5468 @value{GDBN} will look for Python support scripts in several ways:
5469 @file{@var{objfile}-gdb.py} and @code{.debug_gdb_scripts} section.
5470 @xref{Auto-loading extensions}.
5472 The auto-loading feature is useful for supplying application-specific
5473 debugging commands and scripts.
5475 Auto-loading can be enabled or disabled,
5476 and the list of auto-loaded scripts can be printed.
5479 @anchor{set auto-load python-scripts}
5480 @kindex set auto-load python-scripts
5481 @item set auto-load python-scripts [on|off]
5482 Enable or disable the auto-loading of Python scripts.
5484 @anchor{show auto-load python-scripts}
5485 @kindex show auto-load python-scripts
5486 @item show auto-load python-scripts
5487 Show whether auto-loading of Python scripts is enabled or disabled.
5489 @anchor{info auto-load python-scripts}
5490 @kindex info auto-load python-scripts
5491 @cindex print list of auto-loaded Python scripts
5492 @item info auto-load python-scripts [@var{regexp}]
5493 Print the list of all Python scripts that @value{GDBN} auto-loaded.
5495 Also printed is the list of Python scripts that were mentioned in
5496 the @code{.debug_gdb_scripts} section and were either not found
5497 (@pxref{dotdebug_gdb_scripts section}) or were not auto-loaded due to
5498 @code{auto-load safe-path} rejection (@pxref{Auto-loading}).
5499 This is useful because their names are not printed when @value{GDBN}
5500 tries to load them and fails. There may be many of them, and printing
5501 an error message for each one is problematic.
5503 If @var{regexp} is supplied only Python scripts with matching names are printed.
5508 (gdb) info auto-load python-scripts
5510 Yes py-section-script.py
5511 full name: /tmp/py-section-script.py
5512 No my-foo-pretty-printers.py
5516 When reading an auto-loaded file or script, @value{GDBN} sets the
5517 @dfn{current objfile}. This is available via the @code{gdb.current_objfile}
5518 function (@pxref{Objfiles In Python}). This can be useful for
5519 registering objfile-specific pretty-printers and frame-filters.
5521 @node Python modules
5522 @subsection Python modules
5523 @cindex python modules
5525 @value{GDBN} comes with several modules to assist writing Python code.
5528 * gdb.printing:: Building and registering pretty-printers.
5529 * gdb.types:: Utilities for working with types.
5530 * gdb.prompt:: Utilities for prompt value substitution.
5534 @subsubsection gdb.printing
5535 @cindex gdb.printing
5537 This module provides a collection of utilities for working with
5541 @item PrettyPrinter (@var{name}, @var{subprinters}=None)
5542 This class specifies the API that makes @samp{info pretty-printer},
5543 @samp{enable pretty-printer} and @samp{disable pretty-printer} work.
5544 Pretty-printers should generally inherit from this class.
5546 @item SubPrettyPrinter (@var{name})
5547 For printers that handle multiple types, this class specifies the
5548 corresponding API for the subprinters.
5550 @item RegexpCollectionPrettyPrinter (@var{name})
5551 Utility class for handling multiple printers, all recognized via
5552 regular expressions.
5553 @xref{Writing a Pretty-Printer}, for an example.
5555 @item FlagEnumerationPrinter (@var{name})
5556 A pretty-printer which handles printing of @code{enum} values. Unlike
5557 @value{GDBN}'s built-in @code{enum} printing, this printer attempts to
5558 work properly when there is some overlap between the enumeration
5559 constants. The argument @var{name} is the name of the printer and
5560 also the name of the @code{enum} type to look up.
5562 @item register_pretty_printer (@var{obj}, @var{printer}, @var{replace}=False)
5563 Register @var{printer} with the pretty-printer list of @var{obj}.
5564 If @var{replace} is @code{True} then any existing copy of the printer
5565 is replaced. Otherwise a @code{RuntimeError} exception is raised
5566 if a printer with the same name already exists.
5570 @subsubsection gdb.types
5573 This module provides a collection of utilities for working with
5574 @code{gdb.Type} objects.
5577 @item get_basic_type (@var{type})
5578 Return @var{type} with const and volatile qualifiers stripped,
5579 and with typedefs and C@t{++} references converted to the underlying type.
5584 typedef const int const_int;
5586 const_int& foo_ref (foo);
5587 int main () @{ return 0; @}
5594 (gdb) python import gdb.types
5595 (gdb) python foo_ref = gdb.parse_and_eval("foo_ref")
5596 (gdb) python print gdb.types.get_basic_type(foo_ref.type)
5600 @item has_field (@var{type}, @var{field})
5601 Return @code{True} if @var{type}, assumed to be a type with fields
5602 (e.g., a structure or union), has field @var{field}.
5604 @item make_enum_dict (@var{enum_type})
5605 Return a Python @code{dictionary} type produced from @var{enum_type}.
5607 @item deep_items (@var{type})
5608 Returns a Python iterator similar to the standard
5609 @code{gdb.Type.iteritems} method, except that the iterator returned
5610 by @code{deep_items} will recursively traverse anonymous struct or
5611 union fields. For example:
5625 Then in @value{GDBN}:
5627 (@value{GDBP}) python import gdb.types
5628 (@value{GDBP}) python struct_a = gdb.lookup_type("struct A")
5629 (@value{GDBP}) python print struct_a.keys ()
5631 (@value{GDBP}) python print [k for k,v in gdb.types.deep_items(struct_a)]
5632 @{['a', 'b0', 'b1']@}
5635 @item get_type_recognizers ()
5636 Return a list of the enabled type recognizers for the current context.
5637 This is called by @value{GDBN} during the type-printing process
5638 (@pxref{Type Printing API}).
5640 @item apply_type_recognizers (recognizers, type_obj)
5641 Apply the type recognizers, @var{recognizers}, to the type object
5642 @var{type_obj}. If any recognizer returns a string, return that
5643 string. Otherwise, return @code{None}. This is called by
5644 @value{GDBN} during the type-printing process (@pxref{Type Printing
5647 @item register_type_printer (locus, printer)
5648 This is a convenience function to register a type printer
5649 @var{printer}. The printer must implement the type printer protocol.
5650 The @var{locus} argument is either a @code{gdb.Objfile}, in which case
5651 the printer is registered with that objfile; a @code{gdb.Progspace},
5652 in which case the printer is registered with that progspace; or
5653 @code{None}, in which case the printer is registered globally.
5656 This is a base class that implements the type printer protocol. Type
5657 printers are encouraged, but not required, to derive from this class.
5658 It defines a constructor:
5660 @defmethod TypePrinter __init__ (self, name)
5661 Initialize the type printer with the given name. The new printer
5662 starts in the enabled state.
5668 @subsubsection gdb.prompt
5671 This module provides a method for prompt value-substitution.
5674 @item substitute_prompt (@var{string})
5675 Return @var{string} with escape sequences substituted by values. Some
5676 escape sequences take arguments. You can specify arguments inside
5677 ``@{@}'' immediately following the escape sequence.
5679 The escape sequences you can pass to this function are:
5683 Substitute a backslash.
5685 Substitute an ESC character.
5687 Substitute the selected frame; an argument names a frame parameter.
5689 Substitute a newline.
5691 Substitute a parameter's value; the argument names the parameter.
5693 Substitute a carriage return.
5695 Substitute the selected thread; an argument names a thread parameter.
5697 Substitute the version of GDB.
5699 Substitute the current working directory.
5701 Begin a sequence of non-printing characters. These sequences are
5702 typically used with the ESC character, and are not counted in the string
5703 length. Example: ``\[\e[0;34m\](gdb)\[\e[0m\]'' will return a
5704 blue-colored ``(gdb)'' prompt where the length is five.
5706 End a sequence of non-printing characters.
5712 substitute_prompt (``frame: \f,
5713 print arguments: \p@{print frame-arguments@}'')
5716 @exdent will return the string:
5719 "frame: main, print arguments: scalars"