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This is gdb.info, produced by makeinfo version 5.2 from gdb.texinfo.
Copyright (C) 1988-2015 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "Free Software" and "Free Software Needs Free
Documentation", with the Front-Cover Texts being "A GNU Manual," and
with the Back-Cover Texts as in (a) below.
(a) The FSF's Back-Cover Text is: "You are free to copy and modify
this GNU Manual. Buying copies from GNU Press supports the FSF in
developing GNU and promoting software freedom."
INFO-DIR-SECTION Software development
START-INFO-DIR-ENTRY
* Gdb: (gdb). The GNU debugger.
* gdbserver: (gdb) Server. The GNU debugging server.
END-INFO-DIR-ENTRY
This file documents the GNU debugger GDB.
This is the Tenth Edition, of 'Debugging with GDB: the GNU
Source-Level Debugger' for GDB (GDB) Version 7.10.
Copyright (C) 1988-2015 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "Free Software" and "Free Software Needs Free
Documentation", with the Front-Cover Texts being "A GNU Manual," and
with the Back-Cover Texts as in (a) below.
(a) The FSF's Back-Cover Text is: "You are free to copy and modify
this GNU Manual. Buying copies from GNU Press supports the FSF in
developing GNU and promoting software freedom."

File: gdb.info, Node: Selecting Pretty-Printers, Next: Writing a Pretty-Printer, Prev: Pretty Printing API, Up: Python API
23.2.2.6 Selecting Pretty-Printers
..................................
The Python list 'gdb.pretty_printers' contains an array of functions or
callable objects that have been registered via addition as a
pretty-printer. Printers in this list are called 'global' printers,
they're available when debugging all inferiors. Each 'gdb.Progspace'
contains a 'pretty_printers' attribute. Each 'gdb.Objfile' also
contains a 'pretty_printers' attribute.
Each function on these lists is passed a single 'gdb.Value' argument
and should return a pretty-printer object conforming to the interface
definition above (*note Pretty Printing API::). If a function cannot
create a pretty-printer for the value, it should return 'None'.
GDB first checks the 'pretty_printers' attribute of each
'gdb.Objfile' in the current program space and iteratively calls each
enabled lookup routine in the list for that 'gdb.Objfile' until it
receives a pretty-printer object. If no pretty-printer is found in the
objfile lists, GDB then searches the pretty-printer list of the current
program space, calling each enabled function until an object is
returned. After these lists have been exhausted, it tries the global
'gdb.pretty_printers' list, again calling each enabled function until an
object is returned.
The order in which the objfiles are searched is not specified. For a
given list, functions are always invoked from the head of the list, and
iterated over sequentially until the end of the list, or a printer
object is returned.
For various reasons a pretty-printer may not work. For example, the
underlying data structure may have changed and the pretty-printer is out
of date.
The consequences of a broken pretty-printer are severe enough that
GDB provides support for enabling and disabling individual printers.
For example, if 'print frame-arguments' is on, a backtrace can become
highly illegible if any argument is printed with a broken printer.
Pretty-printers are enabled and disabled by attaching an 'enabled'
attribute to the registered function or callable object. If this
attribute is present and its value is 'False', the printer is disabled,
otherwise the printer is enabled.

File: gdb.info, Node: Writing a Pretty-Printer, Next: Type Printing API, Prev: Selecting Pretty-Printers, Up: Python API
23.2.2.7 Writing a Pretty-Printer
.................................
A pretty-printer consists of two parts: a lookup function to detect if
the type is supported, and the printer itself.
Here is an example showing how a 'std::string' printer might be
written. *Note Pretty Printing API::, for details on the API this class
must provide.
class StdStringPrinter(object):
"Print a std::string"
def __init__(self, val):
self.val = val
def to_string(self):
return self.val['_M_dataplus']['_M_p']
def display_hint(self):
return 'string'
And here is an example showing how a lookup function for the printer
example above might be written.
def str_lookup_function(val):
lookup_tag = val.type.tag
if lookup_tag == None:
return None
regex = re.compile("^std::basic_string<char,.*>$")
if regex.match(lookup_tag):
return StdStringPrinter(val)
return None
The example lookup function extracts the value's type, and attempts
to match it to a type that it can pretty-print. If it is a type the
printer can pretty-print, it will return a printer object. If not, it
returns 'None'.
We recommend that you put your core pretty-printers into a Python
package. If your pretty-printers are for use with a library, we further
recommend embedding a version number into the package name. This
practice will enable GDB to load multiple versions of your
pretty-printers at the same time, because they will have different
names.
You should write auto-loaded code (*note Python Auto-loading::) such
that it can be evaluated multiple times without changing its meaning.
An ideal auto-load file will consist solely of 'import's of your printer
modules, followed by a call to a register pretty-printers with the
current objfile.
Taken as a whole, this approach will scale nicely to multiple
inferiors, each potentially using a different library version.
Embedding a version number in the Python package name will ensure that
GDB is able to load both sets of printers simultaneously. Then, because
the search for pretty-printers is done by objfile, and because your
auto-loaded code took care to register your library's printers with a
specific objfile, GDB will find the correct printers for the specific
version of the library used by each inferior.
To continue the 'std::string' example (*note Pretty Printing API::),
this code might appear in 'gdb.libstdcxx.v6':
def register_printers(objfile):
objfile.pretty_printers.append(str_lookup_function)
And then the corresponding contents of the auto-load file would be:
import gdb.libstdcxx.v6
gdb.libstdcxx.v6.register_printers(gdb.current_objfile())
The previous example illustrates a basic pretty-printer. There are a
few things that can be improved on. The printer doesn't have a name,
making it hard to identify in a list of installed printers. The lookup
function has a name, but lookup functions can have arbitrary, even
identical, names.
Second, the printer only handles one type, whereas a library
typically has several types. One could install a lookup function for
each desired type in the library, but one could also have a single
lookup function recognize several types. The latter is the conventional
way this is handled. If a pretty-printer can handle multiple data
types, then its "subprinters" are the printers for the individual data
types.
The 'gdb.printing' module provides a formal way of solving these
problems (*note gdb.printing::). Here is another example that handles
multiple types.
These are the types we are going to pretty-print:
struct foo { int a, b; };
struct bar { struct foo x, y; };
Here are the printers:
class fooPrinter:
"""Print a foo object."""
def __init__(self, val):
self.val = val
def to_string(self):
return ("a=<" + str(self.val["a"]) +
"> b=<" + str(self.val["b"]) + ">")
class barPrinter:
"""Print a bar object."""
def __init__(self, val):
self.val = val
def to_string(self):
return ("x=<" + str(self.val["x"]) +
"> y=<" + str(self.val["y"]) + ">")
This example doesn't need a lookup function, that is handled by the
'gdb.printing' module. Instead a function is provided to build up the
object that handles the lookup.
import gdb.printing
def build_pretty_printer():
pp = gdb.printing.RegexpCollectionPrettyPrinter(
"my_library")
pp.add_printer('foo', '^foo$', fooPrinter)
pp.add_printer('bar', '^bar$', barPrinter)
return pp
And here is the autoload support:
import gdb.printing
import my_library
gdb.printing.register_pretty_printer(
gdb.current_objfile(),
my_library.build_pretty_printer())
Finally, when this printer is loaded into GDB, here is the
corresponding output of 'info pretty-printer':
(gdb) info pretty-printer
my_library.so:
my_library
foo
bar

File: gdb.info, Node: Type Printing API, Next: Frame Filter API, Prev: Writing a Pretty-Printer, Up: Python API
23.2.2.8 Type Printing API
..........................
GDB provides a way for Python code to customize type display. This is
mainly useful for substituting canonical typedef names for types.
A "type printer" is just a Python object conforming to a certain
protocol. A simple base class implementing the protocol is provided;
see *note gdb.types::. A type printer must supply at least:
-- Instance Variable of type_printer: enabled
A boolean which is True if the printer is enabled, and False
otherwise. This is manipulated by the 'enable type-printer' and
'disable type-printer' commands.
-- Instance Variable of type_printer: name
The name of the type printer. This must be a string. This is used
by the 'enable type-printer' and 'disable type-printer' commands.
-- Method on type_printer: instantiate (self)
This is called by GDB at the start of type-printing. It is only
called if the type printer is enabled. This method must return a
new object that supplies a 'recognize' method, as described below.
When displaying a type, say via the 'ptype' command, GDB will compute
a list of type recognizers. This is done by iterating first over the
per-objfile type printers (*note Objfiles In Python::), followed by the
per-progspace type printers (*note Progspaces In Python::), and finally
the global type printers.
GDB will call the 'instantiate' method of each enabled type printer.
If this method returns 'None', then the result is ignored; otherwise, it
is appended to the list of recognizers.
Then, when GDB is going to display a type name, it iterates over the
list of recognizers. For each one, it calls the recognition function,
stopping if the function returns a non-'None' value. The recognition
function is defined as:
-- Method on type_recognizer: recognize (self, type)
If TYPE is not recognized, return 'None'. Otherwise, return a
string which is to be printed as the name of TYPE. The TYPE
argument will be an instance of 'gdb.Type' (*note Types In
Python::).
GDB uses this two-pass approach so that type printers can efficiently
cache information without holding on to it too long. For example, it
can be convenient to look up type information in a type printer and hold
it for a recognizer's lifetime; if a single pass were done then type
printers would have to make use of the event system in order to avoid
holding information that could become stale as the inferior changed.

File: gdb.info, Node: Frame Filter API, Next: Frame Decorator API, Prev: Type Printing API, Up: Python API
23.2.2.9 Filtering Frames.
..........................
Frame filters are Python objects that manipulate the visibility of a
frame or frames when a backtrace (*note Backtrace::) is printed by GDB.
Only commands that print a backtrace, or, in the case of GDB/MI
commands (*note GDB/MI::), those that return a collection of frames are
affected. The commands that work with frame filters are:
'backtrace' (*note The backtrace command: backtrace-command.),
'-stack-list-frames' (*note The -stack-list-frames command:
-stack-list-frames.), '-stack-list-variables' (*note The
-stack-list-variables command: -stack-list-variables.),
'-stack-list-arguments' *note The -stack-list-arguments command:
-stack-list-arguments.) and '-stack-list-locals' (*note The
-stack-list-locals command: -stack-list-locals.).
A frame filter works by taking an iterator as an argument, applying
actions to the contents of that iterator, and returning another iterator
(or, possibly, the same iterator it was provided in the case where the
filter does not perform any operations). Typically, frame filters
utilize tools such as the Python's 'itertools' module to work with and
create new iterators from the source iterator. Regardless of how a
filter chooses to apply actions, it must not alter the underlying GDB
frame or frames, or attempt to alter the call-stack within GDB. This
preserves data integrity within GDB. Frame filters are executed on a
priority basis and care should be taken that some frame filters may have
been executed before, and that some frame filters will be executed
after.
An important consideration when designing frame filters, and well
worth reflecting upon, is that frame filters should avoid unwinding the
call stack if possible. Some stacks can run very deep, into the tens of
thousands in some cases. To search every frame when a frame filter
executes may be too expensive at that step. The frame filter cannot
know how many frames it has to iterate over, and it may have to iterate
through them all. This ends up duplicating effort as GDB performs this
iteration when it prints the frames. If the filter can defer unwinding
frames until frame decorators are executed, after the last filter has
executed, it should. *Note Frame Decorator API::, for more information
on decorators. Also, there are examples for both frame decorators and
filters in later chapters. *Note Writing a Frame Filter::, for more
information.
The Python dictionary 'gdb.frame_filters' contains key/object
pairings that comprise a frame filter. Frame filters in this dictionary
are called 'global' frame filters, and they are available when debugging
all inferiors. These frame filters must register with the dictionary
directly. In addition to the 'global' dictionary, there are other
dictionaries that are loaded with different inferiors via auto-loading
(*note Python Auto-loading::). The two other areas where frame filter
dictionaries can be found are: 'gdb.Progspace' which contains a
'frame_filters' dictionary attribute, and each 'gdb.Objfile' object
which also contains a 'frame_filters' dictionary attribute.
When a command is executed from GDB that is compatible with frame
filters, GDB combines the 'global', 'gdb.Progspace' and all
'gdb.Objfile' dictionaries currently loaded. All of the 'gdb.Objfile'
dictionaries are combined, as several frames, and thus several object
files, might be in use. GDB then prunes any frame filter whose
'enabled' attribute is 'False'. This pruned list is then sorted
according to the 'priority' attribute in each filter.
Once the dictionaries are combined, pruned and sorted, GDB creates an
iterator which wraps each frame in the call stack in a 'FrameDecorator'
object, and calls each filter in order. The output from the previous
filter will always be the input to the next filter, and so on.
Frame filters have a mandatory interface which each frame filter must
implement, defined here:
-- Function: FrameFilter.filter (iterator)
GDB will call this method on a frame filter when it has reached the
order in the priority list for that filter.
For example, if there are four frame filters:
Name Priority
Filter1 5
Filter2 10
Filter3 100
Filter4 1
The order that the frame filters will be called is:
Filter3 -> Filter2 -> Filter1 -> Filter4
Note that the output from 'Filter3' is passed to the input of
'Filter2', and so on.
This 'filter' method is passed a Python iterator. This iterator
contains a sequence of frame decorators that wrap each 'gdb.Frame',
or a frame decorator that wraps another frame decorator. The first
filter that is executed in the sequence of frame filters will
receive an iterator entirely comprised of default 'FrameDecorator'
objects. However, after each frame filter is executed, the
previous frame filter may have wrapped some or all of the frame
decorators with their own frame decorator. As frame decorators
must also conform to a mandatory interface, these decorators can be
assumed to act in a uniform manner (*note Frame Decorator API::).
This method must return an object conforming to the Python iterator
protocol. Each item in the iterator must be an object conforming
to the frame decorator interface. If a frame filter does not wish
to perform any operations on this iterator, it should return that
iterator untouched.
This method is not optional. If it does not exist, GDB will raise
and print an error.
-- Variable: FrameFilter.name
The 'name' attribute must be Python string which contains the name
of the filter displayed by GDB (*note Frame Filter Management::).
This attribute may contain any combination of letters or numbers.
Care should be taken to ensure that it is unique. This attribute
is mandatory.
-- Variable: FrameFilter.enabled
The 'enabled' attribute must be Python boolean. This attribute
indicates to GDB whether the frame filter is enabled, and should be
considered when frame filters are executed. If 'enabled' is
'True', then the frame filter will be executed when any of the
backtrace commands detailed earlier in this chapter are executed.
If 'enabled' is 'False', then the frame filter will not be
executed. This attribute is mandatory.
-- Variable: FrameFilter.priority
The 'priority' attribute must be Python integer. This attribute
controls the order of execution in relation to other frame filters.
There are no imposed limits on the range of 'priority' other than
it must be a valid integer. The higher the 'priority' attribute,
the sooner the frame filter will be executed in relation to other
frame filters. Although 'priority' can be negative, it is
recommended practice to assume zero is the lowest priority that a
frame filter can be assigned. Frame filters that have the same
priority are executed in unsorted order in that priority slot.
This attribute is mandatory.

File: gdb.info, Node: Frame Decorator API, Next: Writing a Frame Filter, Prev: Frame Filter API, Up: Python API
23.2.2.10 Decorating Frames.
............................
Frame decorators are sister objects to frame filters (*note Frame Filter
API::). Frame decorators are applied by a frame filter and can only be
used in conjunction with frame filters.
The purpose of a frame decorator is to customize the printed content
of each 'gdb.Frame' in commands where frame filters are executed. This
concept is called decorating a frame. Frame decorators decorate a
'gdb.Frame' with Python code contained within each API call. This
separates the actual data contained in a 'gdb.Frame' from the decorated
data produced by a frame decorator. This abstraction is necessary to
maintain integrity of the data contained in each 'gdb.Frame'.
Frame decorators have a mandatory interface, defined below.
GDB already contains a frame decorator called 'FrameDecorator'. This
contains substantial amounts of boilerplate code to decorate the content
of a 'gdb.Frame'. It is recommended that other frame decorators inherit
and extend this object, and only to override the methods needed.
-- Function: FrameDecorator.elided (self)
The 'elided' method groups frames together in a hierarchical
system. An example would be an interpreter, where multiple
low-level frames make up a single call in the interpreted language.
In this example, the frame filter would elide the low-level frames
and present a single high-level frame, representing the call in the
interpreted language, to the user.
The 'elided' function must return an iterable and this iterable
must contain the frames that are being elided wrapped in a suitable
frame decorator. If no frames are being elided this function may
return an empty iterable, or 'None'. Elided frames are indented
from normal frames in a 'CLI' backtrace, or in the case of
'GDB/MI', are placed in the 'children' field of the eliding frame.
It is the frame filter's task to also filter out the elided frames
from the source iterator. This will avoid printing the frame
twice.
-- Function: FrameDecorator.function (self)
This method returns the name of the function in the frame that is
to be printed.
This method must return a Python string describing the function, or
'None'.
If this function returns 'None', GDB will not print any data for
this field.
-- Function: FrameDecorator.address (self)
This method returns the address of the frame that is to be printed.
This method must return a Python numeric integer type of sufficient
size to describe the address of the frame, or 'None'.
If this function returns a 'None', GDB will not print any data for
this field.
-- Function: FrameDecorator.filename (self)
This method returns the filename and path associated with this
frame.
This method must return a Python string containing the filename and
the path to the object file backing the frame, or 'None'.
If this function returns a 'None', GDB will not print any data for
this field.
-- Function: FrameDecorator.line (self):
This method returns the line number associated with the current
position within the function addressed by this frame.
This method must return a Python integer type, or 'None'.
If this function returns a 'None', GDB will not print any data for
this field.
-- Function: FrameDecorator.frame_args (self)
This method must return an iterable, or 'None'. Returning an empty
iterable, or 'None' means frame arguments will not be printed for
this frame. This iterable must contain objects that implement two
methods, described here.
This object must implement a 'argument' method which takes a single
'self' parameter and must return a 'gdb.Symbol' (*note Symbols In
Python::), or a Python string. The object must also implement a
'value' method which takes a single 'self' parameter and must
return a 'gdb.Value' (*note Values From Inferior::), a Python
value, or 'None'. If the 'value' method returns 'None', and the
'argument' method returns a 'gdb.Symbol', GDB will look-up and
print the value of the 'gdb.Symbol' automatically.
A brief example:
class SymValueWrapper():
def __init__(self, symbol, value):
self.sym = symbol
self.val = value
def value(self):
return self.val
def symbol(self):
return self.sym
class SomeFrameDecorator()
...
...
def frame_args(self):
args = []
try:
block = self.inferior_frame.block()
except:
return None
# Iterate over all symbols in a block. Only add
# symbols that are arguments.
for sym in block:
if not sym.is_argument:
continue
args.append(SymValueWrapper(sym,None))
# Add example synthetic argument.
args.append(SymValueWrapper(``foo'', 42))
return args
-- Function: FrameDecorator.frame_locals (self)
This method must return an iterable or 'None'. Returning an empty
iterable, or 'None' means frame local arguments will not be printed
for this frame.
The object interface, the description of the various strategies for
reading frame locals, and the example are largely similar to those
described in the 'frame_args' function, (*note The frame filter
frame_args function: frame_args.). Below is a modified example:
class SomeFrameDecorator()
...
...
def frame_locals(self):
vars = []
try:
block = self.inferior_frame.block()
except:
return None
# Iterate over all symbols in a block. Add all
# symbols, except arguments.
for sym in block:
if sym.is_argument:
continue
vars.append(SymValueWrapper(sym,None))
# Add an example of a synthetic local variable.
vars.append(SymValueWrapper(``bar'', 99))
return vars
-- Function: FrameDecorator.inferior_frame (self):
This method must return the underlying 'gdb.Frame' that this frame
decorator is decorating. GDB requires the underlying frame for
internal frame information to determine how to print certain values
when printing a frame.

File: gdb.info, Node: Writing a Frame Filter, Next: Unwinding Frames in Python, Prev: Frame Decorator API, Up: Python API
23.2.2.11 Writing a Frame Filter
................................
There are three basic elements that a frame filter must implement: it
must correctly implement the documented interface (*note Frame Filter
API::), it must register itself with GDB, and finally, it must decide if
it is to work on the data provided by GDB. In all cases, whether it
works on the iterator or not, each frame filter must return an iterator.
A bare-bones frame filter follows the pattern in the following example.
import gdb
class FrameFilter():
def __init__(self):
# Frame filter attribute creation.
#
# 'name' is the name of the filter that GDB will display.
#
# 'priority' is the priority of the filter relative to other
# filters.
#
# 'enabled' is a boolean that indicates whether this filter is
# enabled and should be executed.
self.name = "Foo"
self.priority = 100
self.enabled = True
# Register this frame filter with the global frame_filters
# dictionary.
gdb.frame_filters[self.name] = self
def filter(self, frame_iter):
# Just return the iterator.
return frame_iter
The frame filter in the example above implements the three
requirements for all frame filters. It implements the API, self
registers, and makes a decision on the iterator (in this case, it just
returns the iterator untouched).
The first step is attribute creation and assignment, and as shown in
the comments the filter assigns the following attributes: 'name',
'priority' and whether the filter should be enabled with the 'enabled'
attribute.
The second step is registering the frame filter with the dictionary
or dictionaries that the frame filter has interest in. As shown in the
comments, this filter just registers itself with the global dictionary
'gdb.frame_filters'. As noted earlier, 'gdb.frame_filters' is a
dictionary that is initialized in the 'gdb' module when GDB starts.
What dictionary a filter registers with is an important consideration.
Generally, if a filter is specific to a set of code, it should be
registered either in the 'objfile' or 'progspace' dictionaries as they
are specific to the program currently loaded in GDB. The global
dictionary is always present in GDB and is never unloaded. Any filters
registered with the global dictionary will exist until GDB exits. To
avoid filters that may conflict, it is generally better to register
frame filters against the dictionaries that more closely align with the
usage of the filter currently in question. *Note Python Auto-loading::,
for further information on auto-loading Python scripts.
GDB takes a hands-off approach to frame filter registration,
therefore it is the frame filter's responsibility to ensure registration
has occurred, and that any exceptions are handled appropriately. In
particular, you may wish to handle exceptions relating to Python
dictionary key uniqueness. It is mandatory that the dictionary key is
the same as frame filter's 'name' attribute. When a user manages frame
filters (*note Frame Filter Management::), the names GDB will display
are those contained in the 'name' attribute.
The final step of this example is the implementation of the 'filter'
method. As shown in the example comments, we define the 'filter' method
and note that the method must take an iterator, and also must return an
iterator. In this bare-bones example, the frame filter is not very
useful as it just returns the iterator untouched. However this is a
valid operation for frame filters that have the 'enabled' attribute set,
but decide not to operate on any frames.
In the next example, the frame filter operates on all frames and
utilizes a frame decorator to perform some work on the frames. *Note
Frame Decorator API::, for further information on the frame decorator
interface.
This example works on inlined frames. It highlights frames which are
inlined by tagging them with an "[inlined]" tag. By applying a frame
decorator to all frames with the Python 'itertools imap' method, the
example defers actions to the frame decorator. Frame decorators are
only processed when GDB prints the backtrace.
This introduces a new decision making topic: whether to perform
decision making operations at the filtering step, or at the printing
step. In this example's approach, it does not perform any filtering
decisions at the filtering step beyond mapping a frame decorator to each
frame. This allows the actual decision making to be performed when each
frame is printed. This is an important consideration, and well worth
reflecting upon when designing a frame filter. An issue that frame
filters should avoid is unwinding the stack if possible. Some stacks
can run very deep, into the tens of thousands in some cases. To search
every frame to determine if it is inlined ahead of time may be too
expensive at the filtering step. The frame filter cannot know how many
frames it has to iterate over, and it would have to iterate through them
all. This ends up duplicating effort as GDB performs this iteration
when it prints the frames.
In this example decision making can be deferred to the printing step.
As each frame is printed, the frame decorator can examine each frame in
turn when GDB iterates. From a performance viewpoint, this is the most
appropriate decision to make as it avoids duplicating the effort that
the printing step would undertake anyway. Also, if there are many frame
filters unwinding the stack during filtering, it can substantially delay
the printing of the backtrace which will result in large memory usage,
and a poor user experience.
class InlineFilter():
def __init__(self):
self.name = "InlinedFrameFilter"
self.priority = 100
self.enabled = True
gdb.frame_filters[self.name] = self
def filter(self, frame_iter):
frame_iter = itertools.imap(InlinedFrameDecorator,
frame_iter)
return frame_iter
This frame filter is somewhat similar to the earlier example, except
that the 'filter' method applies a frame decorator object called
'InlinedFrameDecorator' to each element in the iterator. The 'imap'
Python method is light-weight. It does not proactively iterate over the
iterator, but rather creates a new iterator which wraps the existing
one.
Below is the frame decorator for this example.
class InlinedFrameDecorator(FrameDecorator):
def __init__(self, fobj):
super(InlinedFrameDecorator, self).__init__(fobj)
def function(self):
frame = fobj.inferior_frame()
name = str(frame.name())
if frame.type() == gdb.INLINE_FRAME:
name = name + " [inlined]"
return name
This frame decorator only defines and overrides the 'function'
method. It lets the supplied 'FrameDecorator', which is shipped with
GDB, perform the other work associated with printing this frame.
The combination of these two objects create this output from a
backtrace:
#0 0x004004e0 in bar () at inline.c:11
#1 0x00400566 in max [inlined] (b=6, a=12) at inline.c:21
#2 0x00400566 in main () at inline.c:31
So in the case of this example, a frame decorator is applied to all
frames, regardless of whether they may be inlined or not. As GDB
iterates over the iterator produced by the frame filters, GDB executes
each frame decorator which then makes a decision on what to print in the
'function' callback. Using a strategy like this is a way to defer
decisions on the frame content to printing time.
Eliding Frames
--------------
It might be that the above example is not desirable for representing
inlined frames, and a hierarchical approach may be preferred. If we
want to hierarchically represent frames, the 'elided' frame decorator
interface might be preferable.
This example approaches the issue with the 'elided' method. This
example is quite long, but very simplistic. It is out-of-scope for this
section to write a complete example that comprehensively covers all
approaches of finding and printing inlined frames. However, this
example illustrates the approach an author might use.
This example comprises of three sections.
class InlineFrameFilter():
def __init__(self):
self.name = "InlinedFrameFilter"
self.priority = 100
self.enabled = True
gdb.frame_filters[self.name] = self
def filter(self, frame_iter):
return ElidingInlineIterator(frame_iter)
This frame filter is very similar to the other examples. The only
difference is this frame filter is wrapping the iterator provided to it
('frame_iter') with a custom iterator called 'ElidingInlineIterator'.
This again defers actions to when GDB prints the backtrace, as the
iterator is not traversed until printing.
The iterator for this example is as follows. It is in this section
of the example where decisions are made on the content of the backtrace.
class ElidingInlineIterator:
def __init__(self, ii):
self.input_iterator = ii
def __iter__(self):
return self
def next(self):
frame = next(self.input_iterator)
if frame.inferior_frame().type() != gdb.INLINE_FRAME:
return frame
try:
eliding_frame = next(self.input_iterator)
except StopIteration:
return frame
return ElidingFrameDecorator(eliding_frame, [frame])
This iterator implements the Python iterator protocol. When the
'next' function is called (when GDB prints each frame), the iterator
checks if this frame decorator, 'frame', is wrapping an inlined frame.
If it is not, it returns the existing frame decorator untouched. If it
is wrapping an inlined frame, it assumes that the inlined frame was
contained within the next oldest frame, 'eliding_frame', which it
fetches. It then creates and returns a frame decorator,
'ElidingFrameDecorator', which contains both the elided frame, and the
eliding frame.
class ElidingInlineDecorator(FrameDecorator):
def __init__(self, frame, elided_frames):
super(ElidingInlineDecorator, self).__init__(frame)
self.frame = frame
self.elided_frames = elided_frames
def elided(self):
return iter(self.elided_frames)
This frame decorator overrides one function and returns the inlined
frame in the 'elided' method. As before it lets 'FrameDecorator' do the
rest of the work involved in printing this frame. This produces the
following output.
#0 0x004004e0 in bar () at inline.c:11
#2 0x00400529 in main () at inline.c:25
#1 0x00400529 in max (b=6, a=12) at inline.c:15
In that output, 'max' which has been inlined into 'main' is printed
hierarchically. Another approach would be to combine the 'function'
method, and the 'elided' method to both print a marker in the inlined
frame, and also show the hierarchical relationship.

File: gdb.info, Node: Unwinding Frames in Python, Next: Xmethods In Python, Prev: Writing a Frame Filter, Up: Python API
23.2.2.12 Unwinding Frames in Python
....................................
In GDB terminology "unwinding" is the process of finding the previous
frame (that is, caller's) from the current one. An unwinder has three
methods. The first one checks if it can handle given frame ("sniff"
it). For the frames it can sniff an unwinder provides two additional
methods: it can return frame's ID, and it can fetch registers from the
previous frame. A running GDB mantains a list of the unwinders and
calls each unwinder's sniffer in turn until it finds the one that
recognizes the current frame. There is an API to register an unwinder.
The unwinders that come with GDB handle standard frames. However,
mixed language applications (for example, an application running Java
Virtual Machine) sometimes use frame layouts that cannot be handled by
the GDB unwinders. You can write Python code that can handle such
custom frames.
You implement a frame unwinder in Python as a class with which has
two attributes, 'name' and 'enabled', with obvious meanings, and a
single method '__call__', which examines a given frame and returns an
object (an instance of 'gdb.UnwindInfo class)' describing it. If an
unwinder does not recognize a frame, it should return 'None'. The code
in GDB that enables writing unwinders in Python uses this object to
return frame's ID and previous frame registers when GDB core asks for
them.
Unwinder Input
--------------
An object passed to an unwinder (a 'gdb.PendingFrame' instance) provides
a method to read frame's registers:
-- Function: PendingFrame.read_register (reg)
This method returns the contents of the register REGN in the frame
as a 'gdb.Value' object. REG can be either a register number or a
register name; the values are platform-specific. They are usually
found in the corresponding 'PLATFORM-tdep.h' file in the GDB source
tree.
It also provides a factory method to create a 'gdb.UnwindInfo'
instance to be returned to GDB:
-- Function: PendingFrame.create_unwind_info (frame_id)
Returns a new 'gdb.UnwindInfo' instance identified by given
FRAME_ID. The argument is used to build GDB's frame ID using one
of functions provided by GDB. FRAME_ID's attributes determine
which function will be used, as follows:
'sp, pc, special'
'frame_id_build_special (FRAME_ID.sp, FRAME_ID.pc,
FRAME_ID.special)'
'sp, pc'
'frame_id_build (FRAME_ID.sp, FRAME_ID.pc)'
This is the most common case.
'sp'
'frame_id_build_wild (FRAME_ID.sp)'
The attribute values should be 'gdb.Value'
Unwinder Output: UnwindInfo
---------------------------
Use 'PendingFrame.create_unwind_info' method described above to create a
'gdb.UnwindInfo' instance. Use the following method to specify caller
registers that have been saved in this frame:
-- Function: gdb.UnwindInfo.add_saved_register (reg, value)
REG identifies the register. It can be a number or a name, just as
for the 'PendingFrame.read_register' method above. VALUE is a
register value (a 'gdb.Value' object).
Unwinder Skeleton Code
----------------------
GDB comes with the module containing the base 'Unwinder' class. Derive
your unwinder class from it and structure the code as follows:
from gdb.unwinders import Unwinder
class FrameId(object):
def __init__(self, sp, pc):
self.sp = sp
self.pc = pc
class MyUnwinder(Unwinder):
def __init__(....):
supe(MyUnwinder, self).__init___(<expects unwinder name argument>)
def __call__(pending_frame):
if not <we recognize frame>:
return None
# Create UnwindInfo. Usually the frame is identified by the stack
# pointer and the program counter.
sp = pending_frame.read_register(<SP number>)
pc = pending_frame.read_register(<PC number>)
unwind_info = pending_frame.create_unwind_info(FrameId(sp, pc))
# Find the values of the registers in the caller's frame and
# save them in the result:
unwind_info.add_saved_register(<register>, <value>)
....
# Return the result:
return unwind_info
Registering a Unwinder
----------------------
An object file, a program space, and the GDB proper can have unwinders
registered with it.
The 'gdb.unwinders' module provides the function to register a
unwinder:
-- Function: gdb.unwinder.register_unwinder (locus, unwinder,
replace=False)
LOCUS is specifies an object file or a program space to which
UNWINDER is added. Passing 'None' or 'gdb' adds UNWINDER to the
GDB's global unwinder list. The newly added UNWINDER will be
called before any other unwinder from the same locus. Two
unwinders in the same locus cannot have the same name. An attempt
to add a unwinder with already existing name raises an exception
unless REPLACE is 'True', in which case the old unwinder is
deleted.
Unwinder Precedence
-------------------
GDB first calls the unwinders from all the object files in no particular
order, then the unwinders from the current program space, and finally
the unwinders from GDB.

File: gdb.info, Node: Xmethods In Python, Next: Xmethod API, Prev: Unwinding Frames in Python, Up: Python API
23.2.2.13 Xmethods In Python
............................
"Xmethods" are additional methods or replacements for existing methods
of a C++ class. This feature is useful for those cases where a method
defined in C++ source code could be inlined or optimized out by the
compiler, making it unavailable to GDB. For such cases, one can define
an xmethod to serve as a replacement for the method defined in the C++
source code. GDB will then invoke the xmethod, instead of the C++
method, to evaluate expressions. One can also use xmethods when
debugging with core files. Moreover, when debugging live programs,
invoking an xmethod need not involve running the inferior (which can
potentially perturb its state). Hence, even if the C++ method is
available, it is better to use its replacement xmethod if one is
defined.
The xmethods feature in Python is available via the concepts of an
"xmethod matcher" and an "xmethod worker". To implement an xmethod, one
has to implement a matcher and a corresponding worker for it (more than
one worker can be implemented, each catering to a different overloaded
instance of the method). Internally, GDB invokes the 'match' method of
a matcher to match the class type and method name. On a match, the
'match' method returns a list of matching _worker_ objects. Each worker
object typically corresponds to an overloaded instance of the xmethod.
They implement a 'get_arg_types' method which returns a sequence of
types corresponding to the arguments the xmethod requires. GDB uses
this sequence of types to perform overload resolution and picks a
winning xmethod worker. A winner is also selected from among the
methods GDB finds in the C++ source code. Next, the winning xmethod
worker and the winning C++ method are compared to select an overall
winner. In case of a tie between a xmethod worker and a C++ method, the
xmethod worker is selected as the winner. That is, if a winning xmethod
worker is found to be equivalent to the winning C++ method, then the
xmethod worker is treated as a replacement for the C++ method. GDB uses
the overall winner to invoke the method. If the winning xmethod worker
is the overall winner, then the corresponding xmethod is invoked via the
'__call__' method of the worker object.
If one wants to implement an xmethod as a replacement for an existing
C++ method, then they have to implement an equivalent xmethod which has
exactly the same name and takes arguments of exactly the same type as
the C++ method. If the user wants to invoke the C++ method even though
a replacement xmethod is available for that method, then they can
disable the xmethod.
*Note Xmethod API::, for API to implement xmethods in Python. *Note
Writing an Xmethod::, for implementing xmethods in Python.

File: gdb.info, Node: Xmethod API, Next: Writing an Xmethod, Prev: Xmethods In Python, Up: Python API
23.2.2.14 Xmethod API
.....................
The GDB Python API provides classes, interfaces and functions to
implement, register and manipulate xmethods. *Note Xmethods In
Python::.
An xmethod matcher should be an instance of a class derived from
'XMethodMatcher' defined in the module 'gdb.xmethod', or an object with
similar interface and attributes. An instance of 'XMethodMatcher' has
the following attributes:
-- Variable: name
The name of the matcher.
-- Variable: enabled
A boolean value indicating whether the matcher is enabled or
disabled.
-- Variable: methods
A list of named methods managed by the matcher. Each object in the
list is an instance of the class 'XMethod' defined in the module
'gdb.xmethod', or any object with the following attributes:
'name'
Name of the xmethod which should be unique for each xmethod
managed by the matcher.
'enabled'
A boolean value indicating whether the xmethod is enabled or
disabled.
The class 'XMethod' is a convenience class with same attributes as
above along with the following constructor:
-- Function: XMethod.__init__ (self, name)
Constructs an enabled xmethod with name NAME.
The 'XMethodMatcher' class has the following methods:
-- Function: XMethodMatcher.__init__ (self, name)
Constructs an enabled xmethod matcher with name NAME. The
'methods' attribute is initialized to 'None'.
-- Function: XMethodMatcher.match (self, class_type, method_name)
Derived classes should override this method. It should return a
xmethod worker object (or a sequence of xmethod worker objects)
matching the CLASS_TYPE and METHOD_NAME. CLASS_TYPE is a
'gdb.Type' object, and METHOD_NAME is a string value. If the
matcher manages named methods as listed in its 'methods' attribute,
then only those worker objects whose corresponding entries in the
'methods' list are enabled should be returned.
An xmethod worker should be an instance of a class derived from
'XMethodWorker' defined in the module 'gdb.xmethod', or support the
following interface:
-- Function: XMethodWorker.get_arg_types (self)
This method returns a sequence of 'gdb.Type' objects corresponding
to the arguments that the xmethod takes. It can return an empty
sequence or 'None' if the xmethod does not take any arguments. If
the xmethod takes a single argument, then a single 'gdb.Type'
object corresponding to it can be returned.
-- Function: XMethodWorker.get_result_type (self, *args)
This method returns a 'gdb.Type' object representing the type of
the result of invoking this xmethod. The ARGS argument is the same
tuple of arguments that would be passed to the '__call__' method of
this worker.
-- Function: XMethodWorker.__call__ (self, *args)
This is the method which does the _work_ of the xmethod. The ARGS
arguments is the tuple of arguments to the xmethod. Each element
in this tuple is a gdb.Value object. The first element is always
the 'this' pointer value.
For GDB to lookup xmethods, the xmethod matchers should be registered
using the following function defined in the module 'gdb.xmethod':
-- Function: register_xmethod_matcher (locus, matcher, replace=False)
The 'matcher' is registered with 'locus', replacing an existing
matcher with the same name as 'matcher' if 'replace' is 'True'.
'locus' can be a 'gdb.Objfile' object (*note Objfiles In Python::),
or a 'gdb.Progspace' object (*note Progspaces In Python::), or
'None'. If it is 'None', then 'matcher' is registered globally.

File: gdb.info, Node: Writing an Xmethod, Next: Inferiors In Python, Prev: Xmethod API, Up: Python API
23.2.2.15 Writing an Xmethod
............................
Implementing xmethods in Python will require implementing xmethod
matchers and xmethod workers (*note Xmethods In Python::). Consider the
following C++ class:
class MyClass
{
public:
MyClass (int a) : a_(a) { }
int geta (void) { return a_; }
int operator+ (int b);
private:
int a_;
};
int
MyClass::operator+ (int b)
{
return a_ + b;
}
Let us define two xmethods for the class 'MyClass', one replacing the
method 'geta', and another adding an overloaded flavor of 'operator+'
which takes a 'MyClass' argument (the C++ code above already has an
overloaded 'operator+' which takes an 'int' argument). The xmethod
matcher can be defined as follows:
class MyClass_geta(gdb.xmethod.XMethod):
def __init__(self):
gdb.xmethod.XMethod.__init__(self, 'geta')
def get_worker(self, method_name):
if method_name == 'geta':
return MyClassWorker_geta()
class MyClass_sum(gdb.xmethod.XMethod):
def __init__(self):
gdb.xmethod.XMethod.__init__(self, 'sum')
def get_worker(self, method_name):
if method_name == 'operator+':
return MyClassWorker_plus()
class MyClassMatcher(gdb.xmethod.XMethodMatcher):
def __init__(self):
gdb.xmethod.XMethodMatcher.__init__(self, 'MyClassMatcher')
# List of methods 'managed' by this matcher
self.methods = [MyClass_geta(), MyClass_sum()]
def match(self, class_type, method_name):
if class_type.tag != 'MyClass':
return None
workers = []
for method in self.methods:
if method.enabled:
worker = method.get_worker(method_name)
if worker:
workers.append(worker)
return workers
Notice that the 'match' method of 'MyClassMatcher' returns a worker
object of type 'MyClassWorker_geta' for the 'geta' method, and a worker
object of type 'MyClassWorker_plus' for the 'operator+' method. This is
done indirectly via helper classes derived from 'gdb.xmethod.XMethod'.
One does not need to use the 'methods' attribute in a matcher as it is
optional. However, if a matcher manages more than one xmethod, it is a
good practice to list the xmethods in the 'methods' attribute of the
matcher. This will then facilitate enabling and disabling individual
xmethods via the 'enable/disable' commands. Notice also that a worker
object is returned only if the corresponding entry in the 'methods'
attribute of the matcher is enabled.
The implementation of the worker classes returned by the matcher
setup above is as follows:
class MyClassWorker_geta(gdb.xmethod.XMethodWorker):
def get_arg_types(self):
return None
def get_result_type(self, obj):
return gdb.lookup_type('int')
def __call__(self, obj):
return obj['a_']
class MyClassWorker_plus(gdb.xmethod.XMethodWorker):
def get_arg_types(self):
return gdb.lookup_type('MyClass')
def get_result_type(self, obj):
return gdb.lookup_type('int')
def __call__(self, obj, other):
return obj['a_'] + other['a_']
For GDB to actually lookup a xmethod, it has to be registered with
it. The matcher defined above is registered with GDB globally as
follows:
gdb.xmethod.register_xmethod_matcher(None, MyClassMatcher())
If an object 'obj' of type 'MyClass' is initialized in C++ code as
follows:
MyClass obj(5);
then, after loading the Python script defining the xmethod matchers and
workers into 'GDBN', invoking the method 'geta' or using the operator
'+' on 'obj' will invoke the xmethods defined above:
(gdb) p obj.geta()
$1 = 5
(gdb) p obj + obj
$2 = 10
Consider another example with a C++ template class:
template <class T>
class MyTemplate
{
public:
MyTemplate () : dsize_(10), data_ (new T [10]) { }
~MyTemplate () { delete [] data_; }
int footprint (void)
{
return sizeof (T) * dsize_ + sizeof (MyTemplate<T>);
}
private:
int dsize_;
T *data_;
};
Let us implement an xmethod for the above class which serves as a
replacement for the 'footprint' method. The full code listing of the
xmethod workers and xmethod matchers is as follows:
class MyTemplateWorker_footprint(gdb.xmethod.XMethodWorker):
def __init__(self, class_type):
self.class_type = class_type
def get_arg_types(self):
return None
def get_result_type(self):
return gdb.lookup_type('int')
def __call__(self, obj):
return (self.class_type.sizeof +
obj['dsize_'] *
self.class_type.template_argument(0).sizeof)
class MyTemplateMatcher_footprint(gdb.xmethod.XMethodMatcher):
def __init__(self):
gdb.xmethod.XMethodMatcher.__init__(self, 'MyTemplateMatcher')
def match(self, class_type, method_name):
if (re.match('MyTemplate<[ \t\n]*[_a-zA-Z][ _a-zA-Z0-9]*>',
class_type.tag) and
method_name == 'footprint'):
return MyTemplateWorker_footprint(class_type)
Notice that, in this example, we have not used the 'methods'
attribute of the matcher as the matcher manages only one xmethod. The
user can enable/disable this xmethod by enabling/disabling the matcher
itself.

File: gdb.info, Node: Inferiors In Python, Next: Events In Python, Prev: Writing an Xmethod, Up: Python API
23.2.2.16 Inferiors In Python
.............................
Programs which are being run under GDB are called inferiors (*note
Inferiors and Programs::). Python scripts can access information about
and manipulate inferiors controlled by GDB via objects of the
'gdb.Inferior' class.
The following inferior-related functions are available in the 'gdb'
module:
-- Function: gdb.inferiors ()
Return a tuple containing all inferior objects.
-- Function: gdb.selected_inferior ()
Return an object representing the current inferior.
A 'gdb.Inferior' object has the following attributes:
-- Variable: Inferior.num
ID of inferior, as assigned by GDB.
-- Variable: Inferior.pid
Process ID of the inferior, as assigned by the underlying operating
system.
-- Variable: Inferior.was_attached
Boolean signaling whether the inferior was created using 'attach',
or started by GDB itself.
A 'gdb.Inferior' object has the following methods:
-- Function: Inferior.is_valid ()
Returns 'True' if the 'gdb.Inferior' object is valid, 'False' if
not. A 'gdb.Inferior' object will become invalid if the inferior
no longer exists within GDB. All other 'gdb.Inferior' methods will
throw an exception if it is invalid at the time the method is
called.
-- Function: Inferior.threads ()
This method returns a tuple holding all the threads which are valid
when it is called. If there are no valid threads, the method will
return an empty tuple.
-- Function: Inferior.read_memory (address, length)
Read LENGTH addressable memory units from the inferior, starting at
ADDRESS. Returns a buffer object, which behaves much like an array
or a string. It can be modified and given to the
'Inferior.write_memory' function. In 'Python' 3, the return value
is a 'memoryview' object.
-- Function: Inferior.write_memory (address, buffer [, length])
Write the contents of BUFFER to the inferior, starting at ADDRESS.
The BUFFER parameter must be a Python object which supports the
buffer protocol, i.e., a string, an array or the object returned
from 'Inferior.read_memory'. If given, LENGTH determines the
number of addressable memory units from BUFFER to be written.
-- Function: Inferior.search_memory (address, length, pattern)
Search a region of the inferior memory starting at ADDRESS with the
given LENGTH using the search pattern supplied in PATTERN. The
PATTERN parameter must be a Python object which supports the buffer
protocol, i.e., a string, an array or the object returned from
'gdb.read_memory'. Returns a Python 'Long' containing the address
where the pattern was found, or 'None' if the pattern could not be
found.

File: gdb.info, Node: Events In Python, Next: Threads In Python, Prev: Inferiors In Python, Up: Python API
23.2.2.17 Events In Python
..........................
GDB provides a general event facility so that Python code can be
notified of various state changes, particularly changes that occur in
the inferior.
An "event" is just an object that describes some state change. The
type of the object and its attributes will vary depending on the details
of the change. All the existing events are described below.
In order to be notified of an event, you must register an event
handler with an "event registry". An event registry is an object in the
'gdb.events' module which dispatches particular events. A registry
provides methods to register and unregister event handlers:
-- Function: EventRegistry.connect (object)
Add the given callable OBJECT to the registry. This object will be
called when an event corresponding to this registry occurs.
-- Function: EventRegistry.disconnect (object)
Remove the given OBJECT from the registry. Once removed, the
object will no longer receive notifications of events.
Here is an example:
def exit_handler (event):
print "event type: exit"
print "exit code: %d" % (event.exit_code)
gdb.events.exited.connect (exit_handler)
In the above example we connect our handler 'exit_handler' to the
registry 'events.exited'. Once connected, 'exit_handler' gets called
when the inferior exits. The argument "event" in this example is of
type 'gdb.ExitedEvent'. As you can see in the example the 'ExitedEvent'
object has an attribute which indicates the exit code of the inferior.
The following is a listing of the event registries that are available
and details of the events they emit:
'events.cont'
Emits 'gdb.ThreadEvent'.
Some events can be thread specific when GDB is running in non-stop
mode. When represented in Python, these events all extend
'gdb.ThreadEvent'. Note, this event is not emitted directly;
instead, events which are emitted by this or other modules might
extend this event. Examples of these events are
'gdb.BreakpointEvent' and 'gdb.ContinueEvent'.
-- Variable: ThreadEvent.inferior_thread
In non-stop mode this attribute will be set to the specific
thread which was involved in the emitted event. Otherwise, it
will be set to 'None'.
Emits 'gdb.ContinueEvent' which extends 'gdb.ThreadEvent'.
This event indicates that the inferior has been continued after a
stop. For inherited attribute refer to 'gdb.ThreadEvent' above.
'events.exited'
Emits 'events.ExitedEvent' which indicates that the inferior has
exited. 'events.ExitedEvent' has two attributes:
-- Variable: ExitedEvent.exit_code
An integer representing the exit code, if available, which the
inferior has returned. (The exit code could be unavailable
if, for example, GDB detaches from the inferior.) If the exit
code is unavailable, the attribute does not exist.
-- Variable: ExitedEvent inferior
A reference to the inferior which triggered the 'exited'
event.
'events.stop'
Emits 'gdb.StopEvent' which extends 'gdb.ThreadEvent'.
Indicates that the inferior has stopped. All events emitted by
this registry extend StopEvent. As a child of 'gdb.ThreadEvent',
'gdb.StopEvent' will indicate the stopped thread when GDB is
running in non-stop mode. Refer to 'gdb.ThreadEvent' above for
more details.
Emits 'gdb.SignalEvent' which extends 'gdb.StopEvent'.
This event indicates that the inferior or one of its threads has
received as signal. 'gdb.SignalEvent' has the following
attributes:
-- Variable: SignalEvent.stop_signal
A string representing the signal received by the inferior. A
list of possible signal values can be obtained by running the
command 'info signals' in the GDB command prompt.
Also emits 'gdb.BreakpointEvent' which extends 'gdb.StopEvent'.
'gdb.BreakpointEvent' event indicates that one or more breakpoints
have been hit, and has the following attributes:
-- Variable: BreakpointEvent.breakpoints
A sequence containing references to all the breakpoints (type
'gdb.Breakpoint') that were hit. *Note Breakpoints In
Python::, for details of the 'gdb.Breakpoint' object.
-- Variable: BreakpointEvent.breakpoint
A reference to the first breakpoint that was hit. This
function is maintained for backward compatibility and is now
deprecated in favor of the 'gdb.BreakpointEvent.breakpoints'
attribute.
'events.new_objfile'
Emits 'gdb.NewObjFileEvent' which indicates that a new object file
has been loaded by GDB. 'gdb.NewObjFileEvent' has one attribute:
-- Variable: NewObjFileEvent.new_objfile
A reference to the object file ('gdb.Objfile') which has been
loaded. *Note Objfiles In Python::, for details of the
'gdb.Objfile' object.
'events.clear_objfiles'
Emits 'gdb.ClearObjFilesEvent' which indicates that the list of
object files for a program space has been reset.
'gdb.ClearObjFilesEvent' has one attribute:
-- Variable: ClearObjFilesEvent.progspace
A reference to the program space ('gdb.Progspace') whose
objfile list has been cleared. *Note Progspaces In Python::.
'events.inferior_call_pre'
Emits 'gdb.InferiorCallPreEvent' which indicates that a function in
the inferior is about to be called.
-- Variable: InferiorCallPreEvent.ptid
The thread in which the call will be run.
-- Variable: InferiorCallPreEvent.address
The location of the function to be called.
'events.inferior_call_post'
Emits 'gdb.InferiorCallPostEvent' which indicates that a function
in the inferior has returned.
-- Variable: InferiorCallPostEvent.ptid
The thread in which the call was run.
-- Variable: InferiorCallPostEvent.address
The location of the function that was called.
'events.memory_changed'
Emits 'gdb.MemoryChangedEvent' which indicates that the memory of
the inferior has been modified by the GDB user, for instance via a
command like 'set *addr = value'. The event has the following
attributes:
-- Variable: MemoryChangedEvent.address
The start address of the changed region.
-- Variable: MemoryChangedEvent.length
Length in bytes of the changed region.
'events.register_changed'
Emits 'gdb.RegisterChangedEvent' which indicates that a register in
the inferior has been modified by the GDB user.
-- Variable: RegisterChangedEvent.frame
A gdb.Frame object representing the frame in which the
register was modified.
-- Variable: RegisterChangedEvent.regnum
Denotes which register was modified.

File: gdb.info, Node: Threads In Python, Next: Commands In Python, Prev: Events In Python, Up: Python API
23.2.2.18 Threads In Python
...........................
Python scripts can access information about, and manipulate inferior
threads controlled by GDB, via objects of the 'gdb.InferiorThread'
class.
The following thread-related functions are available in the 'gdb'
module:
-- Function: gdb.selected_thread ()
This function returns the thread object for the selected thread.
If there is no selected thread, this will return 'None'.
A 'gdb.InferiorThread' object has the following attributes:
-- Variable: InferiorThread.name
The name of the thread. If the user specified a name using 'thread
name', then this returns that name. Otherwise, if an OS-supplied
name is available, then it is returned. Otherwise, this returns
'None'.
This attribute can be assigned to. The new value must be a string
object, which sets the new name, or 'None', which removes any
user-specified thread name.
-- Variable: InferiorThread.num
ID of the thread, as assigned by GDB.
-- Variable: InferiorThread.ptid
ID of the thread, as assigned by the operating system. This
attribute is a tuple containing three integers. The first is the
Process ID (PID); the second is the Lightweight Process ID (LWPID),
and the third is the Thread ID (TID). Either the LWPID or TID may
be 0, which indicates that the operating system does not use that
identifier.
A 'gdb.InferiorThread' object has the following methods:
-- Function: InferiorThread.is_valid ()
Returns 'True' if the 'gdb.InferiorThread' object is valid, 'False'
if not. A 'gdb.InferiorThread' object will become invalid if the
thread exits, or the inferior that the thread belongs is deleted.
All other 'gdb.InferiorThread' methods will throw an exception if
it is invalid at the time the method is called.
-- Function: InferiorThread.switch ()
This changes GDB's currently selected thread to the one represented
by this object.
-- Function: InferiorThread.is_stopped ()
Return a Boolean indicating whether the thread is stopped.
-- Function: InferiorThread.is_running ()
Return a Boolean indicating whether the thread is running.
-- Function: InferiorThread.is_exited ()
Return a Boolean indicating whether the thread is exited.

File: gdb.info, Node: Commands In Python, Next: Parameters In Python, Prev: Threads In Python, Up: Python API
23.2.2.19 Commands In Python
............................
You can implement new GDB CLI commands in Python. A CLI command is
implemented using an instance of the 'gdb.Command' class, most commonly
using a subclass.
-- Function: Command.__init__ (name, COMMAND_CLASS [, COMPLETER_CLASS
[, PREFIX]])
The object initializer for 'Command' registers the new command with
GDB. This initializer is normally invoked from the subclass' own
'__init__' method.
NAME is the name of the command. If NAME consists of multiple
words, then the initial words are looked for as prefix commands.
In this case, if one of the prefix commands does not exist, an
exception is raised.
There is no support for multi-line commands.
COMMAND_CLASS should be one of the 'COMMAND_' constants defined
below. This argument tells GDB how to categorize the new command
in the help system.
COMPLETER_CLASS is an optional argument. If given, it should be
one of the 'COMPLETE_' constants defined below. This argument
tells GDB how to perform completion for this command. If not
given, GDB will attempt to complete using the object's 'complete'
method (see below); if no such method is found, an error will occur
when completion is attempted.
PREFIX is an optional argument. If 'True', then the new command is
a prefix command; sub-commands of this command may be registered.
The help text for the new command is taken from the Python
documentation string for the command's class, if there is one. If
no documentation string is provided, the default value "This
command is not documented." is used.
-- Function: Command.dont_repeat ()
By default, a GDB command is repeated when the user enters a blank
line at the command prompt. A command can suppress this behavior
by invoking the 'dont_repeat' method. This is similar to the user
command 'dont-repeat', see *note dont-repeat: Define.
-- Function: Command.invoke (argument, from_tty)
This method is called by GDB when this command is invoked.
ARGUMENT is a string. It is the argument to the command, after
leading and trailing whitespace has been stripped.
FROM_TTY is a boolean argument. When true, this means that the
command was entered by the user at the terminal; when false it
means that the command came from elsewhere.
If this method throws an exception, it is turned into a GDB 'error'
call. Otherwise, the return value is ignored.
To break ARGUMENT up into an argv-like string use
'gdb.string_to_argv'. This function behaves identically to GDB's
internal argument lexer 'buildargv'. It is recommended to use this
for consistency. Arguments are separated by spaces and may be
quoted. Example:
print gdb.string_to_argv ("1 2\ \\\"3 '4 \"5' \"6 '7\"")
['1', '2 "3', '4 "5', "6 '7"]
-- Function: Command.complete (text, word)
This method is called by GDB when the user attempts completion on
this command. All forms of completion are handled by this method,
that is, the <TAB> and <M-?> key bindings (*note Completion::), and
the 'complete' command (*note complete: Help.).
The arguments TEXT and WORD are both strings; TEXT holds the
complete command line up to the cursor's location, while WORD holds
the last word of the command line; this is computed using a
word-breaking heuristic.
The 'complete' method can return several values:
* If the return value is a sequence, the contents of the
sequence are used as the completions. It is up to 'complete'
to ensure that the contents actually do complete the word. A
zero-length sequence is allowed, it means that there were no
completions available. Only string elements of the sequence
are used; other elements in the sequence are ignored.
* If the return value is one of the 'COMPLETE_' constants
defined below, then the corresponding GDB-internal completion
function is invoked, and its result is used.
* All other results are treated as though there were no
available completions.
When a new command is registered, it must be declared as a member of
some general class of commands. This is used to classify top-level
commands in the on-line help system; note that prefix commands are not
listed under their own category but rather that of their top-level
command. The available classifications are represented by constants
defined in the 'gdb' module:
'gdb.COMMAND_NONE'
The command does not belong to any particular class. A command in
this category will not be displayed in any of the help categories.
'gdb.COMMAND_RUNNING'
The command is related to running the inferior. For example,
'start', 'step', and 'continue' are in this category. Type 'help
running' at the GDB prompt to see a list of commands in this
category.
'gdb.COMMAND_DATA'
The command is related to data or variables. For example, 'call',
'find', and 'print' are in this category. Type 'help data' at the
GDB prompt to see a list of commands in this category.
'gdb.COMMAND_STACK'
The command has to do with manipulation of the stack. For example,
'backtrace', 'frame', and 'return' are in this category. Type
'help stack' at the GDB prompt to see a list of commands in this
category.
'gdb.COMMAND_FILES'
This class is used for file-related commands. For example, 'file',
'list' and 'section' are in this category. Type 'help files' at
the GDB prompt to see a list of commands in this category.
'gdb.COMMAND_SUPPORT'
This should be used for "support facilities", generally meaning
things that are useful to the user when interacting with GDB, but
not related to the state of the inferior. For example, 'help',
'make', and 'shell' are in this category. Type 'help support' at
the GDB prompt to see a list of commands in this category.
'gdb.COMMAND_STATUS'
The command is an 'info'-related command, that is, related to the
state of GDB itself. For example, 'info', 'macro', and 'show' are
in this category. Type 'help status' at the GDB prompt to see a
list of commands in this category.
'gdb.COMMAND_BREAKPOINTS'
The command has to do with breakpoints. For example, 'break',
'clear', and 'delete' are in this category. Type 'help
breakpoints' at the GDB prompt to see a list of commands in this
category.
'gdb.COMMAND_TRACEPOINTS'
The command has to do with tracepoints. For example, 'trace',
'actions', and 'tfind' are in this category. Type 'help
tracepoints' at the GDB prompt to see a list of commands in this
category.
'gdb.COMMAND_USER'
The command is a general purpose command for the user, and
typically does not fit in one of the other categories. Type 'help
user-defined' at the GDB prompt to see a list of commands in this
category, as well as the list of gdb macros (*note Sequences::).
'gdb.COMMAND_OBSCURE'
The command is only used in unusual circumstances, or is not of
general interest to users. For example, 'checkpoint', 'fork', and
'stop' are in this category. Type 'help obscure' at the GDB prompt
to see a list of commands in this category.
'gdb.COMMAND_MAINTENANCE'
The command is only useful to GDB maintainers. The 'maintenance'
and 'flushregs' commands are in this category. Type 'help
internals' at the GDB prompt to see a list of commands in this
category.
A new command can use a predefined completion function, either by
specifying it via an argument at initialization, or by returning it from
the 'complete' method. These predefined completion constants are all
defined in the 'gdb' module:
'gdb.COMPLETE_NONE'
This constant means that no completion should be done.
'gdb.COMPLETE_FILENAME'
This constant means that filename completion should be performed.
'gdb.COMPLETE_LOCATION'
This constant means that location completion should be done. *Note
Specify Location::.
'gdb.COMPLETE_COMMAND'
This constant means that completion should examine GDB command
names.
'gdb.COMPLETE_SYMBOL'
This constant means that completion should be done using symbol
names as the source.
'gdb.COMPLETE_EXPRESSION'
This constant means that completion should be done on expressions.
Often this means completing on symbol names, but some language
parsers also have support for completing on field names.
The following code snippet shows how a trivial CLI command can be
implemented in Python:
class HelloWorld (gdb.Command):
"""Greet the whole world."""
def __init__ (self):
super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)
def invoke (self, arg, from_tty):
print "Hello, World!"
HelloWorld ()
The last line instantiates the class, and is necessary to trigger the
registration of the command with GDB. Depending on how the Python code
is read into GDB, you may need to import the 'gdb' module explicitly.

File: gdb.info, Node: Parameters In Python, Next: Functions In Python, Prev: Commands In Python, Up: Python API
23.2.2.20 Parameters In Python
..............................
You can implement new GDB parameters using Python. A new parameter is
implemented as an instance of the 'gdb.Parameter' class.
Parameters are exposed to the user via the 'set' and 'show' commands.
*Note Help::.
There are many parameters that already exist and can be set in GDB.
Two examples are: 'set follow fork' and 'set charset'. Setting these
parameters influences certain behavior in GDB. Similarly, you can
define parameters that can be used to influence behavior in custom
Python scripts and commands.
-- Function: Parameter.__init__ (name, COMMAND-CLASS, PARAMETER-CLASS
[, ENUM-SEQUENCE])
The object initializer for 'Parameter' registers the new parameter
with GDB. This initializer is normally invoked from the subclass'
own '__init__' method.
NAME is the name of the new parameter. If NAME consists of
multiple words, then the initial words are looked for as prefix
parameters. An example of this can be illustrated with the 'set
print' set of parameters. If NAME is 'print foo', then 'print'
will be searched as the prefix parameter. In this case the
parameter can subsequently be accessed in GDB as 'set print foo'.
If NAME consists of multiple words, and no prefix parameter group
can be found, an exception is raised.
COMMAND-CLASS should be one of the 'COMMAND_' constants (*note
Commands In Python::). This argument tells GDB how to categorize
the new parameter in the help system.
PARAMETER-CLASS should be one of the 'PARAM_' constants defined
below. This argument tells GDB the type of the new parameter; this
information is used for input validation and completion.
If PARAMETER-CLASS is 'PARAM_ENUM', then ENUM-SEQUENCE must be a
sequence of strings. These strings represent the possible values
for the parameter.
If PARAMETER-CLASS is not 'PARAM_ENUM', then the presence of a
fourth argument will cause an exception to be thrown.
The help text for the new parameter is taken from the Python
documentation string for the parameter's class, if there is one.
If there is no documentation string, a default value is used.
-- Variable: Parameter.set_doc
If this attribute exists, and is a string, then its value is used
as the help text for this parameter's 'set' command. The value is
examined when 'Parameter.__init__' is invoked; subsequent changes
have no effect.
-- Variable: Parameter.show_doc
If this attribute exists, and is a string, then its value is used
as the help text for this parameter's 'show' command. The value is
examined when 'Parameter.__init__' is invoked; subsequent changes
have no effect.
-- Variable: Parameter.value
The 'value' attribute holds the underlying value of the parameter.
It can be read and assigned to just as any other attribute. GDB
does validation when assignments are made.
There are two methods that should be implemented in any 'Parameter'
class. These are:
-- Function: Parameter.get_set_string (self)
GDB will call this method when a PARAMETER's value has been changed
via the 'set' API (for example, 'set foo off'). The 'value'
attribute has already been populated with the new value and may be
used in output. This method must return a string.
-- Function: Parameter.get_show_string (self, svalue)
GDB will call this method when a PARAMETER's 'show' API has been
invoked (for example, 'show foo'). The argument 'svalue' receives
the string representation of the current value. This method must
return a string.
When a new parameter is defined, its type must be specified. The
available types are represented by constants defined in the 'gdb'
module:
'gdb.PARAM_BOOLEAN'
The value is a plain boolean. The Python boolean values, 'True'
and 'False' are the only valid values.
'gdb.PARAM_AUTO_BOOLEAN'
The value has three possible states: true, false, and 'auto'. In
Python, true and false are represented using boolean constants, and
'auto' is represented using 'None'.
'gdb.PARAM_UINTEGER'
The value is an unsigned integer. The value of 0 should be
interpreted to mean "unlimited".
'gdb.PARAM_INTEGER'
The value is a signed integer. The value of 0 should be
interpreted to mean "unlimited".
'gdb.PARAM_STRING'
The value is a string. When the user modifies the string, any
escape sequences, such as '\t', '\f', and octal escapes, are
translated into corresponding characters and encoded into the
current host charset.
'gdb.PARAM_STRING_NOESCAPE'
The value is a string. When the user modifies the string, escapes
are passed through untranslated.
'gdb.PARAM_OPTIONAL_FILENAME'
The value is a either a filename (a string), or 'None'.
'gdb.PARAM_FILENAME'
The value is a filename. This is just like
'PARAM_STRING_NOESCAPE', but uses file names for completion.
'gdb.PARAM_ZINTEGER'
The value is an integer. This is like 'PARAM_INTEGER', except 0 is
interpreted as itself.
'gdb.PARAM_ENUM'
The value is a string, which must be one of a collection string
constants provided when the parameter is created.

File: gdb.info, Node: Functions In Python, Next: Progspaces In Python, Prev: Parameters In Python, Up: Python API
23.2.2.21 Writing new convenience functions
...........................................
You can implement new convenience functions (*note Convenience Vars::)
in Python. A convenience function is an instance of a subclass of the
class 'gdb.Function'.
-- Function: Function.__init__ (name)
The initializer for 'Function' registers the new function with GDB.
The argument NAME is the name of the function, a string. The
function will be visible to the user as a convenience variable of
type 'internal function', whose name is the same as the given NAME.
The documentation for the new function is taken from the
documentation string for the new class.
-- Function: Function.invoke (*ARGS)
When a convenience function is evaluated, its arguments are
converted to instances of 'gdb.Value', and then the function's
'invoke' method is called. Note that GDB does not predetermine the
arity of convenience functions. Instead, all available arguments
are passed to 'invoke', following the standard Python calling
convention. In particular, a convenience function can have default
values for parameters without ill effect.
The return value of this method is used as its value in the
enclosing expression. If an ordinary Python value is returned, it
is converted to a 'gdb.Value' following the usual rules.
The following code snippet shows how a trivial convenience function
can be implemented in Python:
class Greet (gdb.Function):
"""Return string to greet someone.
Takes a name as argument."""
def __init__ (self):
super (Greet, self).__init__ ("greet")
def invoke (self, name):
return "Hello, %s!" % name.string ()
Greet ()
The last line instantiates the class, and is necessary to trigger the
registration of the function with GDB. Depending on how the Python code
is read into GDB, you may need to import the 'gdb' module explicitly.
Now you can use the function in an expression:
(gdb) print $greet("Bob")
$1 = "Hello, Bob!"

File: gdb.info, Node: Progspaces In Python, Next: Objfiles In Python, Prev: Functions In Python, Up: Python API
23.2.2.22 Program Spaces In Python
..................................
A program space, or "progspace", represents a symbolic view of an
address space. It consists of all of the objfiles of the program.
*Note Objfiles In Python::. *Note program spaces: Inferiors and
Programs, for more details about program spaces.
The following progspace-related functions are available in the 'gdb'
module:
-- Function: gdb.current_progspace ()
This function returns the program space of the currently selected
inferior. *Note Inferiors and Programs::.
-- Function: gdb.progspaces ()
Return a sequence of all the progspaces currently known to GDB.
Each progspace is represented by an instance of the 'gdb.Progspace'
class.
-- Variable: Progspace.filename
The file name of the progspace as a string.
-- Variable: Progspace.pretty_printers
The 'pretty_printers' attribute is a list of functions. It is used
to look up pretty-printers. A 'Value' is passed to each function
in order; if the function returns 'None', then the search
continues. Otherwise, the return value should be an object which
is used to format the value. *Note Pretty Printing API::, for more
information.
-- Variable: Progspace.type_printers
The 'type_printers' attribute is a list of type printer objects.
*Note Type Printing API::, for more information.
-- Variable: Progspace.frame_filters
The 'frame_filters' attribute is a dictionary of frame filter
objects. *Note Frame Filter API::, for more information.
One may add arbitrary attributes to 'gdb.Progspace' objects in the
usual Python way. This is useful if, for example, one needs to do some
extra record keeping associated with the program space.
In this contrived example, we want to perform some processing when an
objfile with a certain symbol is loaded, but we only want to do this
once because it is expensive. To achieve this we record the results
with the program space because we can't predict when the desired objfile
will be loaded.
(gdb) python
def clear_objfiles_handler(event):
event.progspace.expensive_computation = None
def expensive(symbol):
"""A mock routine to perform an "expensive" computation on symbol."""
print "Computing the answer to the ultimate question ..."
return 42
def new_objfile_handler(event):
objfile = event.new_objfile
progspace = objfile.progspace
if not hasattr(progspace, 'expensive_computation') or \
progspace.expensive_computation is None:
# We use 'main' for the symbol to keep the example simple.
# Note: There's no current way to constrain the lookup
# to one objfile.
symbol = gdb.lookup_global_symbol('main')
if symbol is not None:
progspace.expensive_computation = expensive(symbol)
gdb.events.clear_objfiles.connect(clear_objfiles_handler)
gdb.events.new_objfile.connect(new_objfile_handler)
end
(gdb) file /tmp/hello
Reading symbols from /tmp/hello...done.
Computing the answer to the ultimate question ...
(gdb) python print gdb.current_progspace().expensive_computation
42
(gdb) run
Starting program: /tmp/hello
Hello.
[Inferior 1 (process 4242) exited normally]

File: gdb.info, Node: Objfiles In Python, Next: Frames In Python, Prev: Progspaces In Python, Up: Python API
23.2.2.23 Objfiles In Python
............................
GDB loads symbols for an inferior from various symbol-containing files
(*note Files::). These include the primary executable file, any shared
libraries used by the inferior, and any separate debug info files (*note
Separate Debug Files::). GDB calls these symbol-containing files
"objfiles".
The following objfile-related functions are available in the 'gdb'
module:
-- Function: gdb.current_objfile ()
When auto-loading a Python script (*note Python Auto-loading::),
GDB sets the "current objfile" to the corresponding objfile. This
function returns the current objfile. If there is no current
objfile, this function returns 'None'.
-- Function: gdb.objfiles ()
Return a sequence of all the objfiles current known to GDB. *Note
Objfiles In Python::.
-- Function: gdb.lookup_objfile (name [, by_build_id])
Look up NAME, a file name or build ID, in the list of objfiles for
the current program space (*note Progspaces In Python::). If the
objfile is not found throw the Python 'ValueError' exception.
If NAME is a relative file name, then it will match any source file
name with the same trailing components. For example, if NAME is
'gcc/expr.c', then it will match source file name of
'/build/trunk/gcc/expr.c', but not '/build/trunk/libcpp/expr.c' or
'/build/trunk/gcc/x-expr.c'.
If BY_BUILD_ID is provided and is 'True' then NAME is the build ID
of the objfile. Otherwise, NAME is a file name. This is supported
only on some operating systems, notably those which use the ELF
format for binary files and the GNU Binutils. For more details
about this feature, see the description of the '--build-id'
command-line option in *note Command Line Options:
(ld.info)Options.
Each objfile is represented by an instance of the 'gdb.Objfile'
class.
-- Variable: Objfile.filename
The file name of the objfile as a string, with symbolic links
resolved.
The value is 'None' if the objfile is no longer valid. See the
'gdb.Objfile.is_valid' method, described below.
-- Variable: Objfile.username
The file name of the objfile as specified by the user as a string.
The value is 'None' if the objfile is no longer valid. See the
'gdb.Objfile.is_valid' method, described below.
-- Variable: Objfile.owner
For separate debug info objfiles this is the corresponding
'gdb.Objfile' object that debug info is being provided for.
Otherwise this is 'None'. Separate debug info objfiles are added
with the 'gdb.Objfile.add_separate_debug_file' method, described
below.
-- Variable: Objfile.build_id
The build ID of the objfile as a string. If the objfile does not
have a build ID then the value is 'None'.
This is supported only on some operating systems, notably those
which use the ELF format for binary files and the GNU Binutils.
For more details about this feature, see the description of the
'--build-id' command-line option in *note Command Line Options:
(ld.info)Options.
-- Variable: Objfile.progspace
The containing program space of the objfile as a 'gdb.Progspace'
object. *Note Progspaces In Python::.
-- Variable: Objfile.pretty_printers
The 'pretty_printers' attribute is a list of functions. It is used
to look up pretty-printers. A 'Value' is passed to each function
in order; if the function returns 'None', then the search
continues. Otherwise, the return value should be an object which
is used to format the value. *Note Pretty Printing API::, for more
information.
-- Variable: Objfile.type_printers
The 'type_printers' attribute is a list of type printer objects.
*Note Type Printing API::, for more information.
-- Variable: Objfile.frame_filters
The 'frame_filters' attribute is a dictionary of frame filter
objects. *Note Frame Filter API::, for more information.
One may add arbitrary attributes to 'gdb.Objfile' objects in the
usual Python way. This is useful if, for example, one needs to do some
extra record keeping associated with the objfile.
In this contrived example we record the time when GDB loaded the
objfile.
(gdb) python
import datetime
def new_objfile_handler(event):
# Set the time_loaded attribute of the new objfile.
event.new_objfile.time_loaded = datetime.datetime.today()
gdb.events.new_objfile.connect(new_objfile_handler)
end
(gdb) file ./hello
Reading symbols from ./hello...done.
(gdb) python print gdb.objfiles()[0].time_loaded
2014-10-09 11:41:36.770345
A 'gdb.Objfile' object has the following methods:
-- Function: Objfile.is_valid ()
Returns 'True' if the 'gdb.Objfile' object is valid, 'False' if
not. A 'gdb.Objfile' object can become invalid if the object file
it refers to is not loaded in GDB any longer. All other
'gdb.Objfile' methods will throw an exception if it is invalid at
the time the method is called.
-- Function: Objfile.add_separate_debug_file (file)
Add FILE to the list of files that GDB will search for debug
information for the objfile. This is useful when the debug info
has been removed from the program and stored in a separate file.
GDB has built-in support for finding separate debug info files
(*note Separate Debug Files::), but if the file doesn't live in one
of the standard places that GDB searches then this function can be
used to add a debug info file from a different place.

File: gdb.info, Node: Frames In Python, Next: Blocks In Python, Prev: Objfiles In Python, Up: Python API
23.2.2.24 Accessing inferior stack frames from Python.
......................................................
When the debugged program stops, GDB is able to analyze its call stack
(*note Stack frames: Frames.). The 'gdb.Frame' class represents a frame
in the stack. A 'gdb.Frame' object is only valid while its
corresponding frame exists in the inferior's stack. If you try to use
an invalid frame object, GDB will throw a 'gdb.error' exception (*note
Exception Handling::).
Two 'gdb.Frame' objects can be compared for equality with the '=='
operator, like:
(gdb) python print gdb.newest_frame() == gdb.selected_frame ()
True
The following frame-related functions are available in the 'gdb'
module:
-- Function: gdb.selected_frame ()
Return the selected frame object. (*note Selecting a Frame:
Selection.).
-- Function: gdb.newest_frame ()
Return the newest frame object for the selected thread.
-- Function: gdb.frame_stop_reason_string (reason)
Return a string explaining the reason why GDB stopped unwinding
frames, as expressed by the given REASON code (an integer, see the
'unwind_stop_reason' method further down in this section).
A 'gdb.Frame' object has the following methods:
-- Function: Frame.is_valid ()
Returns true if the 'gdb.Frame' object is valid, false if not. A
frame object can become invalid if the frame it refers to doesn't
exist anymore in the inferior. All 'gdb.Frame' methods will throw
an exception if it is invalid at the time the method is called.
-- Function: Frame.name ()
Returns the function name of the frame, or 'None' if it can't be
obtained.
-- Function: Frame.architecture ()
Returns the 'gdb.Architecture' object corresponding to the frame's
architecture. *Note Architectures In Python::.
-- Function: Frame.type ()
Returns the type of the frame. The value can be one of:
'gdb.NORMAL_FRAME'
An ordinary stack frame.
'gdb.DUMMY_FRAME'
A fake stack frame that was created by GDB when performing an
inferior function call.
'gdb.INLINE_FRAME'
A frame representing an inlined function. The function was
inlined into a 'gdb.NORMAL_FRAME' that is older than this one.
'gdb.TAILCALL_FRAME'
A frame representing a tail call. *Note Tail Call Frames::.
'gdb.SIGTRAMP_FRAME'
A signal trampoline frame. This is the frame created by the
OS when it calls into a signal handler.
'gdb.ARCH_FRAME'
A fake stack frame representing a cross-architecture call.
'gdb.SENTINEL_FRAME'
This is like 'gdb.NORMAL_FRAME', but it is only used for the
newest frame.
-- Function: Frame.unwind_stop_reason ()
Return an integer representing the reason why it's not possible to
find more frames toward the outermost frame. Use
'gdb.frame_stop_reason_string' to convert the value returned by
this function to a string. The value can be one of:
'gdb.FRAME_UNWIND_NO_REASON'
No particular reason (older frames should be available).
'gdb.FRAME_UNWIND_NULL_ID'
The previous frame's analyzer returns an invalid result. This
is no longer used by GDB, and is kept only for backward
compatibility.
'gdb.FRAME_UNWIND_OUTERMOST'
This frame is the outermost.
'gdb.FRAME_UNWIND_UNAVAILABLE'
Cannot unwind further, because that would require knowing the
values of registers or memory that have not been collected.
'gdb.FRAME_UNWIND_INNER_ID'
This frame ID looks like it ought to belong to a NEXT frame,
but we got it for a PREV frame. Normally, this is a sign of
unwinder failure. It could also indicate stack corruption.
'gdb.FRAME_UNWIND_SAME_ID'
This frame has the same ID as the previous one. That means
that unwinding further would almost certainly give us another
frame with exactly the same ID, so break the chain. Normally,
this is a sign of unwinder failure. It could also indicate
stack corruption.
'gdb.FRAME_UNWIND_NO_SAVED_PC'
The frame unwinder did not find any saved PC, but we needed
one to unwind further.
'gdb.FRAME_UNWIND_MEMORY_ERROR'
The frame unwinder caused an error while trying to access
memory.
'gdb.FRAME_UNWIND_FIRST_ERROR'
Any stop reason greater or equal to this value indicates some
kind of error. This special value facilitates writing code
that tests for errors in unwinding in a way that will work
correctly even if the list of the other values is modified in
future GDB versions. Using it, you could write:
reason = gdb.selected_frame().unwind_stop_reason ()
reason_str = gdb.frame_stop_reason_string (reason)
if reason >= gdb.FRAME_UNWIND_FIRST_ERROR:
print "An error occured: %s" % reason_str
-- Function: Frame.pc ()
Returns the frame's resume address.
-- Function: Frame.block ()
Return the frame's code block. *Note Blocks In Python::.
-- Function: Frame.function ()
Return the symbol for the function corresponding to this frame.
*Note Symbols In Python::.
-- Function: Frame.older ()
Return the frame that called this frame.
-- Function: Frame.newer ()
Return the frame called by this frame.
-- Function: Frame.find_sal ()
Return the frame's symtab and line object. *Note Symbol Tables In
Python::.
-- Function: Frame.read_register (register)
Return the value of REGISTER in this frame. The REGISTER argument
must be a string (e.g., ''sp'' or ''rax''). Returns a 'Gdb.Value'
object. Throws an exception if REGISTER does not exist.
-- Function: Frame.read_var (variable [, block])
Return the value of VARIABLE in this frame. If the optional
argument BLOCK is provided, search for the variable from that
block; otherwise start at the frame's current block (which is
determined by the frame's current program counter). The VARIABLE
argument must be a string or a 'gdb.Symbol' object; BLOCK must be a
'gdb.Block' object.
-- Function: Frame.select ()
Set this frame to be the selected frame. *Note Examining the
Stack: Stack.

File: gdb.info, Node: Blocks In Python, Next: Symbols In Python, Prev: Frames In Python, Up: Python API
23.2.2.25 Accessing blocks from Python.
.......................................
In GDB, symbols are stored in blocks. A block corresponds roughly to a
scope in the source code. Blocks are organized hierarchically, and are
represented individually in Python as a 'gdb.Block'. Blocks rely on
debugging information being available.
A frame has a block. Please see *note Frames In Python::, for a more
in-depth discussion of frames.
The outermost block is known as the "global block". The global block
typically holds public global variables and functions.
The block nested just inside the global block is the "static block".
The static block typically holds file-scoped variables and functions.
GDB provides a method to get a block's superblock, but there is
currently no way to examine the sub-blocks of a block, or to iterate
over all the blocks in a symbol table (*note Symbol Tables In Python::).
Here is a short example that should help explain blocks:
/* This is in the global block. */
int global;
/* This is in the static block. */
static int file_scope;
/* 'function' is in the global block, and 'argument' is
in a block nested inside of 'function'. */
int function (int argument)
{
/* 'local' is in a block inside 'function'. It may or may
not be in the same block as 'argument'. */
int local;
{
/* 'inner' is in a block whose superblock is the one holding
'local'. */
int inner;
/* If this call is expanded by the compiler, you may see
a nested block here whose function is 'inline_function'
and whose superblock is the one holding 'inner'. */
inline_function ();
}
}
A 'gdb.Block' is iterable. The iterator returns the symbols (*note
Symbols In Python::) local to the block. Python programs should not
assume that a specific block object will always contain a given symbol,
since changes in GDB features and infrastructure may cause symbols move
across blocks in a symbol table.
The following block-related functions are available in the 'gdb'
module:
-- Function: gdb.block_for_pc (pc)
Return the innermost 'gdb.Block' containing the given PC value. If
the block cannot be found for the PC value specified, the function
will return 'None'.
A 'gdb.Block' object has the following methods:
-- Function: Block.is_valid ()
Returns 'True' if the 'gdb.Block' object is valid, 'False' if not.
A block object can become invalid if the block it refers to doesn't
exist anymore in the inferior. All other 'gdb.Block' methods will
throw an exception if it is invalid at the time the method is
called. The block's validity is also checked during iteration over
symbols of the block.
A 'gdb.Block' object has the following attributes:
-- Variable: Block.start
The start address of the block. This attribute is not writable.
-- Variable: Block.end
The end address of the block. This attribute is not writable.
-- Variable: Block.function
The name of the block represented as a 'gdb.Symbol'. If the block
is not named, then this attribute holds 'None'. This attribute is
not writable.
For ordinary function blocks, the superblock is the static block.
However, you should note that it is possible for a function block
to have a superblock that is not the static block - for instance
this happens for an inlined function.
-- Variable: Block.superblock
The block containing this block. If this parent block does not
exist, this attribute holds 'None'. This attribute is not
writable.
-- Variable: Block.global_block
The global block associated with this block. This attribute is not
writable.
-- Variable: Block.static_block
The static block associated with this block. This attribute is not
writable.
-- Variable: Block.is_global
'True' if the 'gdb.Block' object is a global block, 'False' if not.
This attribute is not writable.
-- Variable: Block.is_static
'True' if the 'gdb.Block' object is a static block, 'False' if not.
This attribute is not writable.

File: gdb.info, Node: Symbols In Python, Next: Symbol Tables In Python, Prev: Blocks In Python, Up: Python API
23.2.2.26 Python representation of Symbols.
...........................................
GDB represents every variable, function and type as an entry in a symbol
table. *Note Examining the Symbol Table: Symbols. Similarly, Python
represents these symbols in GDB with the 'gdb.Symbol' object.
The following symbol-related functions are available in the 'gdb'
module:
-- Function: gdb.lookup_symbol (name [, block [, domain]])
This function searches for a symbol by name. The search scope can
be restricted to the parameters defined in the optional domain and
block arguments.
NAME is the name of the symbol. It must be a string. The optional
BLOCK argument restricts the search to symbols visible in that
BLOCK. The BLOCK argument must be a 'gdb.Block' object. If
omitted, the block for the current frame is used. The optional
DOMAIN argument restricts the search to the domain type. The
DOMAIN argument must be a domain constant defined in the 'gdb'
module and described later in this chapter.
The result is a tuple of two elements. The first element is a
'gdb.Symbol' object or 'None' if the symbol is not found. If the
symbol is found, the second element is 'True' if the symbol is a
field of a method's object (e.g., 'this' in C++), otherwise it is
'False'. If the symbol is not found, the second element is
'False'.
-- Function: gdb.lookup_global_symbol (name [, domain])
This function searches for a global symbol by name. The search
scope can be restricted to by the domain argument.
NAME is the name of the symbol. It must be a string. The optional
DOMAIN argument restricts the search to the domain type. The
DOMAIN argument must be a domain constant defined in the 'gdb'
module and described later in this chapter.
The result is a 'gdb.Symbol' object or 'None' if the symbol is not
found.
A 'gdb.Symbol' object has the following attributes:
-- Variable: Symbol.type
The type of the symbol or 'None' if no type is recorded. This
attribute is represented as a 'gdb.Type' object. *Note Types In
Python::. This attribute is not writable.
-- Variable: Symbol.symtab
The symbol table in which the symbol appears. This attribute is
represented as a 'gdb.Symtab' object. *Note Symbol Tables In
Python::. This attribute is not writable.
-- Variable: Symbol.line
The line number in the source code at which the symbol was defined.
This is an integer.
-- Variable: Symbol.name
The name of the symbol as a string. This attribute is not
writable.
-- Variable: Symbol.linkage_name
The name of the symbol, as used by the linker (i.e., may be
mangled). This attribute is not writable.
-- Variable: Symbol.print_name
The name of the symbol in a form suitable for output. This is
either 'name' or 'linkage_name', depending on whether the user
asked GDB to display demangled or mangled names.
-- Variable: Symbol.addr_class
The address class of the symbol. This classifies how to find the
value of a symbol. Each address class is a constant defined in the
'gdb' module and described later in this chapter.
-- Variable: Symbol.needs_frame
This is 'True' if evaluating this symbol's value requires a frame
(*note Frames In Python::) and 'False' otherwise. Typically, local
variables will require a frame, but other symbols will not.
-- Variable: Symbol.is_argument
'True' if the symbol is an argument of a function.
-- Variable: Symbol.is_constant
'True' if the symbol is a constant.
-- Variable: Symbol.is_function
'True' if the symbol is a function or a method.
-- Variable: Symbol.is_variable
'True' if the symbol is a variable.
A 'gdb.Symbol' object has the following methods:
-- Function: Symbol.is_valid ()
Returns 'True' if the 'gdb.Symbol' object is valid, 'False' if not.
A 'gdb.Symbol' object can become invalid if the symbol it refers to
does not exist in GDB any longer. All other 'gdb.Symbol' methods
will throw an exception if it is invalid at the time the method is
called.
-- Function: Symbol.value ([frame])
Compute the value of the symbol, as a 'gdb.Value'. For functions,
this computes the address of the function, cast to the appropriate
type. If the symbol requires a frame in order to compute its
value, then FRAME must be given. If FRAME is not given, or if
FRAME is invalid, then this method will throw an exception.
The available domain categories in 'gdb.Symbol' are represented as
constants in the 'gdb' module:
'gdb.SYMBOL_UNDEF_DOMAIN'
This is used when a domain has not been discovered or none of the
following domains apply. This usually indicates an error either in
the symbol information or in GDB's handling of symbols.
'gdb.SYMBOL_VAR_DOMAIN'
This domain contains variables, function names, typedef names and
enum type values.
'gdb.SYMBOL_STRUCT_DOMAIN'
This domain holds struct, union and enum type names.
'gdb.SYMBOL_LABEL_DOMAIN'
This domain contains names of labels (for gotos).
'gdb.SYMBOL_VARIABLES_DOMAIN'
This domain holds a subset of the 'SYMBOLS_VAR_DOMAIN'; it contains
everything minus functions and types.
'gdb.SYMBOL_FUNCTION_DOMAIN'
This domain contains all functions.
'gdb.SYMBOL_TYPES_DOMAIN'
This domain contains all types.
The available address class categories in 'gdb.Symbol' are
represented as constants in the 'gdb' module:
'gdb.SYMBOL_LOC_UNDEF'
If this is returned by address class, it indicates an error either
in the symbol information or in GDB's handling of symbols.
'gdb.SYMBOL_LOC_CONST'
Value is constant int.
'gdb.SYMBOL_LOC_STATIC'
Value is at a fixed address.
'gdb.SYMBOL_LOC_REGISTER'
Value is in a register.
'gdb.SYMBOL_LOC_ARG'
Value is an argument. This value is at the offset stored within
the symbol inside the frame's argument list.
'gdb.SYMBOL_LOC_REF_ARG'
Value address is stored in the frame's argument list. Just like
'LOC_ARG' except that the value's address is stored at the offset,
not the value itself.
'gdb.SYMBOL_LOC_REGPARM_ADDR'
Value is a specified register. Just like 'LOC_REGISTER' except the
register holds the address of the argument instead of the argument
itself.
'gdb.SYMBOL_LOC_LOCAL'
Value is a local variable.
'gdb.SYMBOL_LOC_TYPEDEF'
Value not used. Symbols in the domain 'SYMBOL_STRUCT_DOMAIN' all
have this class.
'gdb.SYMBOL_LOC_BLOCK'
Value is a block.
'gdb.SYMBOL_LOC_CONST_BYTES'
Value is a byte-sequence.
'gdb.SYMBOL_LOC_UNRESOLVED'
Value is at a fixed address, but the address of the variable has to
be determined from the minimal symbol table whenever the variable
is referenced.
'gdb.SYMBOL_LOC_OPTIMIZED_OUT'
The value does not actually exist in the program.
'gdb.SYMBOL_LOC_COMPUTED'
The value's address is a computed location.

File: gdb.info, Node: Symbol Tables In Python, Next: Line Tables In Python, Prev: Symbols In Python, Up: Python API
23.2.2.27 Symbol table representation in Python.
................................................
Access to symbol table data maintained by GDB on the inferior is exposed
to Python via two objects: 'gdb.Symtab_and_line' and 'gdb.Symtab'.
Symbol table and line data for a frame is returned from the 'find_sal'
method in 'gdb.Frame' object. *Note Frames In Python::.
For more information on GDB's symbol table management, see *note
Examining the Symbol Table: Symbols, for more information.
A 'gdb.Symtab_and_line' object has the following attributes:
-- Variable: Symtab_and_line.symtab
The symbol table object ('gdb.Symtab') for this frame. This
attribute is not writable.
-- Variable: Symtab_and_line.pc
Indicates the start of the address range occupied by code for the
current source line. This attribute is not writable.
-- Variable: Symtab_and_line.last
Indicates the end of the address range occupied by code for the
current source line. This attribute is not writable.
-- Variable: Symtab_and_line.line
Indicates the current line number for this object. This attribute
is not writable.
A 'gdb.Symtab_and_line' object has the following methods:
-- Function: Symtab_and_line.is_valid ()
Returns 'True' if the 'gdb.Symtab_and_line' object is valid,
'False' if not. A 'gdb.Symtab_and_line' object can become invalid
if the Symbol table and line object it refers to does not exist in
GDB any longer. All other 'gdb.Symtab_and_line' methods will throw
an exception if it is invalid at the time the method is called.
A 'gdb.Symtab' object has the following attributes:
-- Variable: Symtab.filename
The symbol table's source filename. This attribute is not
writable.
-- Variable: Symtab.objfile
The symbol table's backing object file. *Note Objfiles In
Python::. This attribute is not writable.
-- Variable: Symtab.producer
The name and possibly version number of the program that compiled
the code in the symbol table. The contents of this string is up to
the compiler. If no producer information is available then 'None'
is returned. This attribute is not writable.
A 'gdb.Symtab' object has the following methods:
-- Function: Symtab.is_valid ()
Returns 'True' if the 'gdb.Symtab' object is valid, 'False' if not.
A 'gdb.Symtab' object can become invalid if the symbol table it
refers to does not exist in GDB any longer. All other 'gdb.Symtab'
methods will throw an exception if it is invalid at the time the
method is called.
-- Function: Symtab.fullname ()
Return the symbol table's source absolute file name.
-- Function: Symtab.global_block ()
Return the global block of the underlying symbol table. *Note
Blocks In Python::.
-- Function: Symtab.static_block ()
Return the static block of the underlying symbol table. *Note
Blocks In Python::.
-- Function: Symtab.linetable ()
Return the line table associated with the symbol table. *Note Line
Tables In Python::.

File: gdb.info, Node: Line Tables In Python, Next: Breakpoints In Python, Prev: Symbol Tables In Python, Up: Python API
23.2.2.28 Manipulating line tables using Python
...............................................
Python code can request and inspect line table information from a symbol
table that is loaded in GDB. A line table is a mapping of source lines
to their executable locations in memory. To acquire the line table
information for a particular symbol table, use the 'linetable' function
(*note Symbol Tables In Python::).
A 'gdb.LineTable' is iterable. The iterator returns 'LineTableEntry'
objects that correspond to the source line and address for each line
table entry. 'LineTableEntry' objects have the following attributes:
-- Variable: LineTableEntry.line
The source line number for this line table entry. This number
corresponds to the actual line of source. This attribute is not
writable.
-- Variable: LineTableEntry.pc
The address that is associated with the line table entry where the
executable code for that source line resides in memory. This
attribute is not writable.
As there can be multiple addresses for a single source line, you may
receive multiple 'LineTableEntry' objects with matching 'line'
attributes, but with different 'pc' attributes. The iterator is sorted
in ascending 'pc' order. Here is a small example illustrating iterating
over a line table.
symtab = gdb.selected_frame().find_sal().symtab
linetable = symtab.linetable()
for line in linetable:
print "Line: "+str(line.line)+" Address: "+hex(line.pc)
This will have the following output:
Line: 33 Address: 0x4005c8L
Line: 37 Address: 0x4005caL
Line: 39 Address: 0x4005d2L
Line: 40 Address: 0x4005f8L
Line: 42 Address: 0x4005ffL
Line: 44 Address: 0x400608L
Line: 42 Address: 0x40060cL
Line: 45 Address: 0x400615L
In addition to being able to iterate over a 'LineTable', it also has
the following direct access methods:
-- Function: LineTable.line (line)
Return a Python 'Tuple' of 'LineTableEntry' objects for any entries
in the line table for the given LINE, which specifies the source
code line. If there are no entries for that source code LINE, the
Python 'None' is returned.
-- Function: LineTable.has_line (line)
Return a Python 'Boolean' indicating whether there is an entry in
the line table for this source line. Return 'True' if an entry is
found, or 'False' if not.
-- Function: LineTable.source_lines ()
Return a Python 'List' of the source line numbers in the symbol
table. Only lines with executable code locations are returned.
The contents of the 'List' will just be the source line entries
represented as Python 'Long' values.

File: gdb.info, Node: Breakpoints In Python, Next: Finish Breakpoints in Python, Prev: Line Tables In Python, Up: Python API
23.2.2.29 Manipulating breakpoints using Python
...............................................
Python code can manipulate breakpoints via the 'gdb.Breakpoint' class.
-- Function: Breakpoint.__init__ (spec [, type [, wp_class [,internal
[,temporary]]]])
Create a new breakpoint according to SPEC, which is a string naming
the location of the breakpoint, or an expression that defines a
watchpoint. The contents can be any location recognized by the
'break' command, or in the case of a watchpoint, by the 'watch'
command. The optional TYPE denotes the breakpoint to create from
the types defined later in this chapter. This argument can be
either 'gdb.BP_BREAKPOINT' or 'gdb.BP_WATCHPOINT'; it defaults to
'gdb.BP_BREAKPOINT'. The optional INTERNAL argument allows the
breakpoint to become invisible to the user. The breakpoint will
neither be reported when created, nor will it be listed in the
output from 'info breakpoints' (but will be listed with the 'maint
info breakpoints' command). The optional TEMPORARY argument makes
the breakpoint a temporary breakpoint. Temporary breakpoints are
deleted after they have been hit. Any further access to the Python
breakpoint after it has been hit will result in a runtime error (as
that breakpoint has now been automatically deleted). The optional
WP_CLASS argument defines the class of watchpoint to create, if
TYPE is 'gdb.BP_WATCHPOINT'. If a watchpoint class is not
provided, it is assumed to be a 'gdb.WP_WRITE' class.
-- Function: Breakpoint.stop (self)
The 'gdb.Breakpoint' class can be sub-classed and, in particular,
you may choose to implement the 'stop' method. If this method is
defined in a sub-class of 'gdb.Breakpoint', it will be called when
the inferior reaches any location of a breakpoint which
instantiates that sub-class. If the method returns 'True', the
inferior will be stopped at the location of the breakpoint,
otherwise the inferior will continue.
If there are multiple breakpoints at the same location with a
'stop' method, each one will be called regardless of the return
status of the previous. This ensures that all 'stop' methods have
a chance to execute at that location. In this scenario if one of
the methods returns 'True' but the others return 'False', the
inferior will still be stopped.
You should not alter the execution state of the inferior (i.e.,
step, next, etc.), alter the current frame context (i.e., change
the current active frame), or alter, add or delete any breakpoint.
As a general rule, you should not alter any data within GDB or the
inferior at this time.
Example 'stop' implementation:
class MyBreakpoint (gdb.Breakpoint):
def stop (self):
inf_val = gdb.parse_and_eval("foo")
if inf_val == 3:
return True
return False
The available watchpoint types represented by constants are defined
in the 'gdb' module:
'gdb.WP_READ'
Read only watchpoint.
'gdb.WP_WRITE'
Write only watchpoint.
'gdb.WP_ACCESS'
Read/Write watchpoint.
-- Function: Breakpoint.is_valid ()
Return 'True' if this 'Breakpoint' object is valid, 'False'
otherwise. A 'Breakpoint' object can become invalid if the user
deletes the breakpoint. In this case, the object still exists, but
the underlying breakpoint does not. In the cases of watchpoint
scope, the watchpoint remains valid even if execution of the
inferior leaves the scope of that watchpoint.
-- Function: Breakpoint.delete ()
Permanently deletes the GDB breakpoint. This also invalidates the
Python 'Breakpoint' object. Any further access to this object's
attributes or methods will raise an error.
-- Variable: Breakpoint.enabled
This attribute is 'True' if the breakpoint is enabled, and 'False'
otherwise. This attribute is writable. You can use it to enable
or disable the breakpoint.
-- Variable: Breakpoint.silent
This attribute is 'True' if the breakpoint is silent, and 'False'
otherwise. This attribute is writable.
Note that a breakpoint can also be silent if it has commands and
the first command is 'silent'. This is not reported by the
'silent' attribute.
-- Variable: Breakpoint.thread
If the breakpoint is thread-specific, this attribute holds the
thread id. If the breakpoint is not thread-specific, this
attribute is 'None'. This attribute is writable.
-- Variable: Breakpoint.task
If the breakpoint is Ada task-specific, this attribute holds the
Ada task id. If the breakpoint is not task-specific (or the
underlying language is not Ada), this attribute is 'None'. This
attribute is writable.
-- Variable: Breakpoint.ignore_count
This attribute holds the ignore count for the breakpoint, an
integer. This attribute is writable.
-- Variable: Breakpoint.number
This attribute holds the breakpoint's number -- the identifier used
by the user to manipulate the breakpoint. This attribute is not
writable.
-- Variable: Breakpoint.type
This attribute holds the breakpoint's type -- the identifier used
to determine the actual breakpoint type or use-case. This
attribute is not writable.
-- Variable: Breakpoint.visible
This attribute tells whether the breakpoint is visible to the user
when set, or when the 'info breakpoints' command is run. This
attribute is not writable.
-- Variable: Breakpoint.temporary
This attribute indicates whether the breakpoint was created as a
temporary breakpoint. Temporary breakpoints are automatically
deleted after that breakpoint has been hit. Access to this
attribute, and all other attributes and functions other than the
'is_valid' function, will result in an error after the breakpoint
has been hit (as it has been automatically deleted). This
attribute is not writable.
The available types are represented by constants defined in the 'gdb'
module:
'gdb.BP_BREAKPOINT'
Normal code breakpoint.
'gdb.BP_WATCHPOINT'
Watchpoint breakpoint.
'gdb.BP_HARDWARE_WATCHPOINT'
Hardware assisted watchpoint.
'gdb.BP_READ_WATCHPOINT'
Hardware assisted read watchpoint.
'gdb.BP_ACCESS_WATCHPOINT'
Hardware assisted access watchpoint.
-- Variable: Breakpoint.hit_count
This attribute holds the hit count for the breakpoint, an integer.
This attribute is writable, but currently it can only be set to
zero.
-- Variable: Breakpoint.location
This attribute holds the location of the breakpoint, as specified
by the user. It is a string. If the breakpoint does not have a
location (that is, it is a watchpoint) the attribute's value is
'None'. This attribute is not writable.
-- Variable: Breakpoint.expression
This attribute holds a breakpoint expression, as specified by the
user. It is a string. If the breakpoint does not have an
expression (the breakpoint is not a watchpoint) the attribute's
value is 'None'. This attribute is not writable.
-- Variable: Breakpoint.condition
This attribute holds the condition of the breakpoint, as specified
by the user. It is a string. If there is no condition, this
attribute's value is 'None'. This attribute is writable.
-- Variable: Breakpoint.commands
This attribute holds the commands attached to the breakpoint. If
there are commands, this attribute's value is a string holding all
the commands, separated by newlines. If there are no commands,
this attribute is 'None'. This attribute is not writable.

File: gdb.info, Node: Finish Breakpoints in Python, Next: Lazy Strings In Python, Prev: Breakpoints In Python, Up: Python API
23.2.2.30 Finish Breakpoints
............................
A finish breakpoint is a temporary breakpoint set at the return address
of a frame, based on the 'finish' command. 'gdb.FinishBreakpoint'
extends 'gdb.Breakpoint'. The underlying breakpoint will be disabled
and deleted when the execution will run out of the breakpoint scope
(i.e. 'Breakpoint.stop' or 'FinishBreakpoint.out_of_scope' triggered).
Finish breakpoints are thread specific and must be create with the right
thread selected.
-- Function: FinishBreakpoint.__init__ ([frame] [, internal])
Create a finish breakpoint at the return address of the 'gdb.Frame'
object FRAME. If FRAME is not provided, this defaults to the
newest frame. The optional INTERNAL argument allows the breakpoint
to become invisible to the user. *Note Breakpoints In Python::,
for further details about this argument.
-- Function: FinishBreakpoint.out_of_scope (self)
In some circumstances (e.g. 'longjmp', C++ exceptions, GDB 'return'
command, ...), a function may not properly terminate, and thus
never hit the finish breakpoint. When GDB notices such a
situation, the 'out_of_scope' callback will be triggered.
You may want to sub-class 'gdb.FinishBreakpoint' and override this
method:
class MyFinishBreakpoint (gdb.FinishBreakpoint)
def stop (self):
print "normal finish"
return True
def out_of_scope ():
print "abnormal finish"
-- Variable: FinishBreakpoint.return_value
When GDB is stopped at a finish breakpoint and the frame used to
build the 'gdb.FinishBreakpoint' object had debug symbols, this
attribute will contain a 'gdb.Value' object corresponding to the
return value of the function. The value will be 'None' if the
function return type is 'void' or if the return value was not
computable. This attribute is not writable.

File: gdb.info, Node: Lazy Strings In Python, Next: Architectures In Python, Prev: Finish Breakpoints in Python, Up: Python API
23.2.2.31 Python representation of lazy strings.
................................................
A "lazy string" is a string whose contents is not retrieved or encoded
until it is needed.
A 'gdb.LazyString' is represented in GDB as an 'address' that points
to a region of memory, an 'encoding' that will be used to encode that
region of memory, and a 'length' to delimit the region of memory that
represents the string. The difference between a 'gdb.LazyString' and a
string wrapped within a 'gdb.Value' is that a 'gdb.LazyString' will be
treated differently by GDB when printing. A 'gdb.LazyString' is
retrieved and encoded during printing, while a 'gdb.Value' wrapping a
string is immediately retrieved and encoded on creation.
A 'gdb.LazyString' object has the following functions:
-- Function: LazyString.value ()
Convert the 'gdb.LazyString' to a 'gdb.Value'. This value will
point to the string in memory, but will lose all the delayed
retrieval, encoding and handling that GDB applies to a
'gdb.LazyString'.
-- Variable: LazyString.address
This attribute holds the address of the string. This attribute is
not writable.
-- Variable: LazyString.length
This attribute holds the length of the string in characters. If
the length is -1, then the string will be fetched and encoded up to
the first null of appropriate width. This attribute is not
writable.
-- Variable: LazyString.encoding
This attribute holds the encoding that will be applied to the
string when the string is printed by GDB. If the encoding is not
set, or contains an empty string, then GDB will select the most
appropriate encoding when the string is printed. This attribute is
not writable.
-- Variable: LazyString.type
This attribute holds the type that is represented by the lazy
string's type. For a lazy string this will always be a pointer
type. To resolve this to the lazy string's character type, use the
type's 'target' method. *Note Types In Python::. This attribute
is not writable.

File: gdb.info, Node: Architectures In Python, Prev: Lazy Strings In Python, Up: Python API
23.2.2.32 Python representation of architectures
................................................
GDB uses architecture specific parameters and artifacts in a number of
its various computations. An architecture is represented by an instance
of the 'gdb.Architecture' class.
A 'gdb.Architecture' class has the following methods:
-- Function: Architecture.name ()
Return the name (string value) of the architecture.
-- Function: Architecture.disassemble (START_PC [, END_PC [, COUNT]])
Return a list of disassembled instructions starting from the memory
address START_PC. The optional arguments END_PC and COUNT
determine the number of instructions in the returned list. If both
the optional arguments END_PC and COUNT are specified, then a list
of at most COUNT disassembled instructions whose start address
falls in the closed memory address interval from START_PC to END_PC
are returned. If END_PC is not specified, but COUNT is specified,
then COUNT number of instructions starting from the address
START_PC are returned. If COUNT is not specified but END_PC is
specified, then all instructions whose start address falls in the
closed memory address interval from START_PC to END_PC are
returned. If neither END_PC nor COUNT are specified, then a single
instruction at START_PC is returned. For all of these cases, each
element of the returned list is a Python 'dict' with the following
string keys:
'addr'
The value corresponding to this key is a Python long integer
capturing the memory address of the instruction.
'asm'
The value corresponding to this key is a string value which
represents the instruction with assembly language mnemonics.
The assembly language flavor used is the same as that
specified by the current CLI variable 'disassembly-flavor'.
*Note Machine Code::.
'length'
The value corresponding to this key is the length (integer
value) of the instruction in bytes.

File: gdb.info, Node: Python Auto-loading, Next: Python modules, Prev: Python API, Up: Python
23.2.3 Python Auto-loading
--------------------------
When a new object file is read (for example, due to the 'file' command,
or because the inferior has loaded a shared library), GDB will look for
Python support scripts in several ways: 'OBJFILE-gdb.py' and
'.debug_gdb_scripts' section. *Note Auto-loading extensions::.
The auto-loading feature is useful for supplying application-specific
debugging commands and scripts.
Auto-loading can be enabled or disabled, and the list of auto-loaded
scripts can be printed.
'set auto-load python-scripts [on|off]'
Enable or disable the auto-loading of Python scripts.
'show auto-load python-scripts'
Show whether auto-loading of Python scripts is enabled or disabled.
'info auto-load python-scripts [REGEXP]'
Print the list of all Python scripts that GDB auto-loaded.
Also printed is the list of Python scripts that were mentioned in
the '.debug_gdb_scripts' section and were either not found (*note
dotdebug_gdb_scripts section::) or were not auto-loaded due to
'auto-load safe-path' rejection (*note Auto-loading::). This is
useful because their names are not printed when GDB tries to load
them and fails. There may be many of them, and printing an error
message for each one is problematic.
If REGEXP is supplied only Python scripts with matching names are
printed.
Example:
(gdb) info auto-load python-scripts
Loaded Script
Yes py-section-script.py
full name: /tmp/py-section-script.py
No my-foo-pretty-printers.py
When reading an auto-loaded file or script, GDB sets the "current
objfile". This is available via the 'gdb.current_objfile' function
(*note Objfiles In Python::). This can be useful for registering
objfile-specific pretty-printers and frame-filters.

File: gdb.info, Node: Python modules, Prev: Python Auto-loading, Up: Python
23.2.4 Python modules
---------------------
GDB comes with several modules to assist writing Python code.
* Menu:
* gdb.printing:: Building and registering pretty-printers.
* gdb.types:: Utilities for working with types.
* gdb.prompt:: Utilities for prompt value substitution.

File: gdb.info, Node: gdb.printing, Next: gdb.types, Up: Python modules
23.2.4.1 gdb.printing
.....................
This module provides a collection of utilities for working with
pretty-printers.
'PrettyPrinter (NAME, SUBPRINTERS=None)'
This class specifies the API that makes 'info pretty-printer',
'enable pretty-printer' and 'disable pretty-printer' work.
Pretty-printers should generally inherit from this class.
'SubPrettyPrinter (NAME)'
For printers that handle multiple types, this class specifies the
corresponding API for the subprinters.
'RegexpCollectionPrettyPrinter (NAME)'
Utility class for handling multiple printers, all recognized via
regular expressions. *Note Writing a Pretty-Printer::, for an
example.
'FlagEnumerationPrinter (NAME)'
A pretty-printer which handles printing of 'enum' values. Unlike
GDB's built-in 'enum' printing, this printer attempts to work
properly when there is some overlap between the enumeration
constants. The argument NAME is the name of the printer and also
the name of the 'enum' type to look up.
'register_pretty_printer (OBJ, PRINTER, REPLACE=False)'
Register PRINTER with the pretty-printer list of OBJ. If REPLACE
is 'True' then any existing copy of the printer is replaced.
Otherwise a 'RuntimeError' exception is raised if a printer with
the same name already exists.

File: gdb.info, Node: gdb.types, Next: gdb.prompt, Prev: gdb.printing, Up: Python modules
23.2.4.2 gdb.types
..................
This module provides a collection of utilities for working with
'gdb.Type' objects.
'get_basic_type (TYPE)'
Return TYPE with const and volatile qualifiers stripped, and with
typedefs and C++ references converted to the underlying type.
C++ example:
typedef const int const_int;
const_int foo (3);
const_int& foo_ref (foo);
int main () { return 0; }
Then in gdb:
(gdb) start
(gdb) python import gdb.types
(gdb) python foo_ref = gdb.parse_and_eval("foo_ref")
(gdb) python print gdb.types.get_basic_type(foo_ref.type)
int
'has_field (TYPE, FIELD)'
Return 'True' if TYPE, assumed to be a type with fields (e.g., a
structure or union), has field FIELD.
'make_enum_dict (ENUM_TYPE)'
Return a Python 'dictionary' type produced from ENUM_TYPE.
'deep_items (TYPE)'
Returns a Python iterator similar to the standard
'gdb.Type.iteritems' method, except that the iterator returned by
'deep_items' will recursively traverse anonymous struct or union
fields. For example:
struct A
{
int a;
union {
int b0;
int b1;
};
};
Then in GDB:
(gdb) python import gdb.types
(gdb) python struct_a = gdb.lookup_type("struct A")
(gdb) python print struct_a.keys ()
{['a', '']}
(gdb) python print [k for k,v in gdb.types.deep_items(struct_a)]
{['a', 'b0', 'b1']}
'get_type_recognizers ()'
Return a list of the enabled type recognizers for the current
context. This is called by GDB during the type-printing process
(*note Type Printing API::).
'apply_type_recognizers (recognizers, type_obj)'
Apply the type recognizers, RECOGNIZERS, to the type object
TYPE_OBJ. If any recognizer returns a string, return that string.
Otherwise, return 'None'. This is called by GDB during the
type-printing process (*note Type Printing API::).
'register_type_printer (locus, printer)'
This is a convenience function to register a type printer PRINTER.
The printer must implement the type printer protocol. The LOCUS
argument is either a 'gdb.Objfile', in which case the printer is
registered with that objfile; a 'gdb.Progspace', in which case the
printer is registered with that progspace; or 'None', in which case
the printer is registered globally.
'TypePrinter'
This is a base class that implements the type printer protocol.
Type printers are encouraged, but not required, to derive from this
class. It defines a constructor:
-- Method on TypePrinter: __init__ (self, name)
Initialize the type printer with the given name. The new
printer starts in the enabled state.

File: gdb.info, Node: gdb.prompt, Prev: gdb.types, Up: Python modules
23.2.4.3 gdb.prompt
...................
This module provides a method for prompt value-substitution.
'substitute_prompt (STRING)'
Return STRING with escape sequences substituted by values. Some
escape sequences take arguments. You can specify arguments inside
"{}" immediately following the escape sequence.
The escape sequences you can pass to this function are:
'\\'
Substitute a backslash.
'\e'
Substitute an ESC character.
'\f'
Substitute the selected frame; an argument names a frame
parameter.
'\n'
Substitute a newline.
'\p'
Substitute a parameter's value; the argument names the
parameter.
'\r'
Substitute a carriage return.
'\t'
Substitute the selected thread; an argument names a thread
parameter.
'\v'
Substitute the version of GDB.
'\w'
Substitute the current working directory.
'\['
Begin a sequence of non-printing characters. These sequences
are typically used with the ESC character, and are not counted
in the string length. Example: "\[\e[0;34m\](gdb)\[\e[0m\]"
will return a blue-colored "(gdb)" prompt where the length is
five.
'\]'
End a sequence of non-printing characters.
For example:
substitute_prompt (``frame: \f,
print arguments: \p{print frame-arguments}'')
will return the string:
"frame: main, print arguments: scalars"

File: gdb.info, Node: Guile, Next: Auto-loading extensions, Prev: Python, Up: Extending GDB
23.3 Extending GDB using Guile
==============================
You can extend GDB using the Guile implementation of the Scheme
programming language (http://www.gnu.org/software/guile/). This feature
is available only if GDB was configured using '--with-guile'.
* Menu:
* Guile Introduction:: Introduction to Guile scripting in GDB
* Guile Commands:: Accessing Guile from GDB
* Guile API:: Accessing GDB from Guile
* Guile Auto-loading:: Automatically loading Guile code
* Guile Modules:: Guile modules provided by GDB

File: gdb.info, Node: Guile Introduction, Next: Guile Commands, Up: Guile
23.3.1 Guile Introduction
-------------------------
Guile is an implementation of the Scheme programming language and is the
GNU project's official extension language.
Guile support in GDB follows the Python support in GDB reasonably
closely, so concepts there should carry over. However, some things are
done differently where it makes sense.
GDB requires Guile version 2.0 or greater. Older versions are not
supported.
Guile scripts used by GDB should be installed in
'DATA-DIRECTORY/guile', where DATA-DIRECTORY is the data directory as
determined at GDB startup (*note Data Files::). This directory, known
as the "guile directory", is automatically added to the Guile Search
Path in order to allow the Guile interpreter to locate all scripts
installed at this location.

File: gdb.info, Node: Guile Commands, Next: Guile API, Prev: Guile Introduction, Up: Guile
23.3.2 Guile Commands
---------------------
GDB provides two commands for accessing the Guile interpreter:
'guile-repl'
'gr'
The 'guile-repl' command can be used to start an interactive Guile
prompt or "repl". To return to GDB, type ',q' or the 'EOF'
character (e.g., 'Ctrl-D' on an empty prompt). These commands do
not take any arguments.
'guile [SCHEME-EXPRESSION]'
'gu [SCHEME-EXPRESSION]'
The 'guile' command can be used to evaluate a Scheme expression.
If given an argument, GDB will pass the argument to the Guile
interpreter for evaluation.
(gdb) guile (display (+ 20 3)) (newline)
23
The result of the Scheme expression is displayed using normal Guile
rules.
(gdb) guile (+ 20 3)
23
If you do not provide an argument to 'guile', it will act as a
multi-line command, like 'define'. In this case, the Guile script
is made up of subsequent command lines, given after the 'guile'
command. This command list is terminated using a line containing
'end'. For example:
(gdb) guile
>(display 23)
>(newline)
>end
23
It is also possible to execute a Guile script from the GDB
interpreter:
'source script-name'
The script name must end with '.scm' and GDB must be configured to
recognize the script language based on filename extension using the
'script-extension' setting. *Note Extending GDB: Extending GDB.
'guile (load "script-name")'
This method uses the 'load' Guile function. It takes a string
argument that is the name of the script to load. See the Guile
documentation for a description of this function. (*note
(guile)Loading::).

File: gdb.info, Node: Guile API, Next: Guile Auto-loading, Prev: Guile Commands, Up: Guile
23.3.3 Guile API
----------------
You can get quick online help for GDB's Guile API by issuing the command
'help guile', or by issuing the command ',help' from an interactive
Guile session. Furthermore, most Guile procedures provided by GDB have
doc strings which can be obtained with ',describe PROCEDURE-NAME' or ',d
PROCEDURE-NAME' from the Guile interactive prompt.
* Menu:
* Basic Guile:: Basic Guile Functions
* Guile Configuration:: Guile configuration variables
* GDB Scheme Data Types:: Scheme representations of GDB objects
* Guile Exception Handling:: How Guile exceptions are translated
* Values From Inferior In Guile:: Guile representation of values
* Arithmetic In Guile:: Arithmetic in Guile
* Types In Guile:: Guile representation of types
* Guile Pretty Printing API:: Pretty-printing values with Guile
* Selecting Guile Pretty-Printers:: How GDB chooses a pretty-printer
* Writing a Guile Pretty-Printer:: Writing a pretty-printer
* Commands In Guile:: Implementing new commands in Guile
* Parameters In Guile:: Adding new GDB parameters
* Progspaces In Guile:: Program spaces
* Objfiles In Guile:: Object files in Guile
* Frames In Guile:: Accessing inferior stack frames from Guile
* Blocks In Guile:: Accessing blocks from Guile
* Symbols In Guile:: Guile representation of symbols
* Symbol Tables In Guile:: Guile representation of symbol tables
* Breakpoints In Guile:: Manipulating breakpoints using Guile
* Lazy Strings In Guile:: Guile representation of lazy strings
* Architectures In Guile:: Guile representation of architectures
* Disassembly In Guile:: Disassembling instructions from Guile
* I/O Ports in Guile:: GDB I/O ports
* Memory Ports in Guile:: Accessing memory through ports and bytevectors
* Iterators In Guile:: Basic iterator support

File: gdb.info, Node: Basic Guile, Next: Guile Configuration, Up: Guile API
23.3.3.1 Basic Guile
....................
At startup, GDB overrides Guile's 'current-output-port' and
'current-error-port' to print using GDB's output-paging streams. A
Guile program which outputs to one of these streams may have its output
interrupted by the user (*note Screen Size::). In this situation, a
Guile 'signal' exception is thrown with value 'SIGINT'.
Guile's history mechanism uses the same naming as GDB's, namely the
user of dollar-variables (e.g., $1, $2, etc.). The results of
evaluations in Guile and in GDB are counted separately, '$1' in Guile is
not the same value as '$1' in GDB.
GDB is not thread-safe. If your Guile program uses multiple threads,
you must be careful to only call GDB-specific functions in the GDB
thread.
Some care must be taken when writing Guile code to run in GDB. Two
things are worth noting in particular:
* GDB installs handlers for 'SIGCHLD' and 'SIGINT'. Guile code must
not override these, or even change the options using 'sigaction'.
If your program changes the handling of these signals, GDB will
most likely stop working correctly. Note that it is unfortunately
common for GUI toolkits to install a 'SIGCHLD' handler.
* GDB takes care to mark its internal file descriptors as
close-on-exec. However, this cannot be done in a thread-safe way
on all platforms. Your Guile programs should be aware of this and
should both create new file descriptors with the close-on-exec flag
set and arrange to close unneeded file descriptors before starting
a child process.
GDB introduces a new Guile module, named 'gdb'. All methods and
classes added by GDB are placed in this module. GDB does not
automatically 'import' the 'gdb' module, scripts must do this
themselves. There are various options for how to import a module, so
GDB leaves the choice of how the 'gdb' module is imported to the user.
To simplify interactive use, it is recommended to add one of the
following to your ~/.gdbinit.
guile (use-modules (gdb))
guile (use-modules ((gdb) #:renamer (symbol-prefix-proc 'gdb:)))
Which one to choose depends on your preference. The second one adds
'gdb:' as a prefix to all module functions and variables.
The rest of this manual assumes the 'gdb' module has been imported
without any prefix. See the Guile documentation for 'use-modules' for
more information (*note (guile)Using Guile Modules::).
Example:
(gdb) guile (value-type (make-value 1))
ERROR: Unbound variable: value-type
Error while executing Scheme code.
(gdb) guile (use-modules (gdb))
(gdb) guile (value-type (make-value 1))
int
(gdb)
The '(gdb)' module provides these basic Guile functions.
-- Scheme Procedure: execute command [#:from-tty boolean] [#:to-string
boolean]
Evaluate COMMAND, a string, as a GDB CLI command. If a GDB
exception happens while COMMAND runs, it is translated as described
in *note Guile Exception Handling: Guile Exception Handling.
FROM-TTY specifies whether GDB ought to consider this command as
having originated from the user invoking it interactively. It must
be a boolean value. If omitted, it defaults to '#f'.
By default, any output produced by COMMAND is sent to GDB's
standard output (and to the log output if logging is turned on).
If the TO-STRING parameter is '#t', then output will be collected
by 'execute' and returned as a string. The default is '#f', in
which case the return value is unspecified. If TO-STRING is '#t',
the GDB virtual terminal will be temporarily set to unlimited width
and height, and its pagination will be disabled; *note Screen
Size::.
-- Scheme Procedure: history-ref number
Return a value from GDB's value history (*note Value History::).
The NUMBER argument indicates which history element to return. If
NUMBER is negative, then GDB will take its absolute value and count
backward from the last element (i.e., the most recent element) to
find the value to return. If NUMBER is zero, then GDB will return
the most recent element. If the element specified by NUMBER
doesn't exist in the value history, a 'gdb:error' exception will be
raised.
If no exception is raised, the return value is always an instance
of '<gdb:value>' (*note Values From Inferior In Guile::).
_Note:_ GDB's value history is independent of Guile's. '$1' in
GDB's value history contains the result of evaluating an expression
from GDB's command line and '$1' from Guile's history contains the
result of evaluating an expression from Guile's command line.
-- Scheme Procedure: history-append! value
Append VALUE, an instance of '<gdb:value>', to GDB's value history.
Return its index in the history.
Putting into history values returned by Guile extensions will allow
the user convenient access to those values via CLI history
facilities.
-- Scheme Procedure: parse-and-eval expression
Parse EXPRESSION as an expression in the current language, evaluate
it, and return the result as a '<gdb:value>'. The EXPRESSION must
be a string.
This function can be useful when implementing a new command (*note
Commands In Guile::), as it provides a way to parse the command's
arguments as an expression. It is also is useful when computing
values. For example, it is the only way to get the value of a
convenience variable (*note Convenience Vars::) as a '<gdb:value>'.

File: gdb.info, Node: Guile Configuration, Next: GDB Scheme Data Types, Prev: Basic Guile, Up: Guile API
23.3.3.2 Guile Configuration
............................
GDB provides these Scheme functions to access various configuration
parameters.
-- Scheme Procedure: data-directory
Return a string containing GDB's data directory. This directory
contains GDB's ancillary files.
-- Scheme Procedure: guile-data-directory
Return a string containing GDB's Guile data directory. This
directory contains the Guile modules provided by GDB.
-- Scheme Procedure: gdb-version
Return a string containing the GDB version.
-- Scheme Procedure: host-config
Return a string containing the host configuration. This is the
string passed to '--host' when GDB was configured.
-- Scheme Procedure: target-config
Return a string containing the target configuration. This is the
string passed to '--target' when GDB was configured.

File: gdb.info, Node: GDB Scheme Data Types, Next: Guile Exception Handling, Prev: Guile Configuration, Up: Guile API
23.3.3.3 GDB Scheme Data Types
..............................
The values exposed by GDB to Guile are known as "GDB objects". There
are several kinds of GDB object, and each is disjoint from all other
types known to Guile.
-- Scheme Procedure: gdb-object-kind object
Return the kind of the GDB object, e.g., '<gdb:breakpoint>', as a
symbol.
GDB defines the following object types:
'<gdb:arch>'
*Note Architectures In Guile::.
'<gdb:block>'
*Note Blocks In Guile::.
'<gdb:block-symbols-iterator>'
*Note Blocks In Guile::.
'<gdb:breakpoint>'
*Note Breakpoints In Guile::.
'<gdb:command>'
*Note Commands In Guile::.
'<gdb:exception>'
*Note Guile Exception Handling::.
'<gdb:frame>'
*Note Frames In Guile::.
'<gdb:iterator>'
*Note Iterators In Guile::.
'<gdb:lazy-string>'
*Note Lazy Strings In Guile::.
'<gdb:objfile>'
*Note Objfiles In Guile::.
'<gdb:parameter>'
*Note Parameters In Guile::.
'<gdb:pretty-printer>'
*Note Guile Pretty Printing API::.
'<gdb:pretty-printer-worker>'
*Note Guile Pretty Printing API::.
'<gdb:progspace>'
*Note Progspaces In Guile::.
'<gdb:symbol>'
*Note Symbols In Guile::.
'<gdb:symtab>'
*Note Symbol Tables In Guile::.
'<gdb:sal>'
*Note Symbol Tables In Guile::.
'<gdb:type>'
*Note Types In Guile::.
'<gdb:field>'
*Note Types In Guile::.
'<gdb:value>'
*Note Values From Inferior In Guile::.
The following GDB objects are managed internally so that the Scheme
function 'eq?' may be applied to them.
'<gdb:arch>'
'<gdb:block>'
'<gdb:breakpoint>'
'<gdb:frame>'
'<gdb:objfile>'
'<gdb:progspace>'
'<gdb:symbol>'
'<gdb:symtab>'
'<gdb:type>'

File: gdb.info, Node: Guile Exception Handling, Next: Values From Inferior In Guile, Prev: GDB Scheme Data Types, Up: Guile API
23.3.3.4 Guile Exception Handling
.................................
When executing the 'guile' command, Guile exceptions uncaught within the
Guile code are translated to calls to the GDB error-reporting mechanism.
If the command that called 'guile' does not handle the error, GDB will
terminate it and report the error according to the setting of the 'guile
print-stack' parameter.
The 'guile print-stack' parameter has three settings:
'none'
Nothing is printed.
'message'
An error message is printed containing the Guile exception name,
the associated value, and the Guile call stack backtrace at the
point where the exception was raised. Example:
(gdb) guile (display foo)
ERROR: In procedure memoize-variable-access!:
ERROR: Unbound variable: foo
Error while executing Scheme code.
'full'
In addition to an error message a full backtrace is printed.
(gdb) set guile print-stack full
(gdb) guile (display foo)
Guile Backtrace:
In ice-9/boot-9.scm:
157: 10 [catch #t #<catch-closure 2c76e20> ...]
In unknown file:
?: 9 [apply-smob/1 #<catch-closure 2c76e20>]
In ice-9/boot-9.scm:
157: 8 [catch #t #<catch-closure 2c76d20> ...]
In unknown file:
?: 7 [apply-smob/1 #<catch-closure 2c76d20>]
?: 6 [call-with-input-string "(display foo)" ...]
In ice-9/boot-9.scm:
2320: 5 [save-module-excursion #<procedure 2c2dc30 ... ()>]
In ice-9/eval-string.scm:
44: 4 [read-and-eval #<input: string 27cb410> #:lang ...]
37: 3 [lp (display foo)]
In ice-9/eval.scm:
387: 2 [eval # ()]
393: 1 [eval #<memoized foo> ()]
In unknown file:
?: 0 [memoize-variable-access! #<memoized foo> ...]
ERROR: In procedure memoize-variable-access!:
ERROR: Unbound variable: foo
Error while executing Scheme code.
GDB errors that happen in GDB commands invoked by Guile code are
converted to Guile exceptions. The type of the Guile exception depends
on the error.
Guile procedures provided by GDB can throw the standard Guile
exceptions like 'wrong-type-arg' and 'out-of-range'.
User interrupt (via 'C-c' or by typing 'q' at a pagination prompt) is
translated to a Guile 'signal' exception with value 'SIGINT'.
GDB Guile procedures can also throw these exceptions:
'gdb:error'
This exception is a catch-all for errors generated from within GDB.
'gdb:invalid-object'
This exception is thrown when accessing Guile objects that wrap
underlying GDB objects have become invalid. For example, a
'<gdb:breakpoint>' object becomes invalid if the user deletes it
from the command line. The object still exists in Guile, but the
object it represents is gone. Further operations on this
breakpoint will throw this exception.
'gdb:memory-error'
This exception is thrown when an operation tried to access invalid
memory in the inferior.
'gdb:pp-type-error'
This exception is thrown when a Guile pretty-printer passes a bad
object to GDB.
The following exception-related procedures are provided by the
'(gdb)' module.
-- Scheme Procedure: make-exception key args
Return a '<gdb:exception>' object given by its KEY and ARGS, which
are the standard Guile parameters of an exception. See the Guile
documentation for more information (*note (guile)Exceptions::).
-- Scheme Procedure: exception? object
Return '#t' if OBJECT is a '<gdb:exception>' object. Otherwise
return '#f'.
-- Scheme Procedure: exception-key exception
Return the ARGS field of a '<gdb:exception>' object.
-- Scheme Procedure: exception-args exception
Return the ARGS field of a '<gdb:exception>' object.

File: gdb.info, Node: Values From Inferior In Guile, Next: Arithmetic In Guile, Prev: Guile Exception Handling, Up: Guile API
23.3.3.5 Values From Inferior In Guile
......................................
GDB provides values it obtains from the inferior program in an object of
type '<gdb:value>'. GDB uses this object for its internal bookkeeping
of the inferior's values, and for fetching values when necessary.
GDB does not memoize '<gdb:value>' objects. 'make-value' always
returns a fresh object.
(gdb) guile (eq? (make-value 1) (make-value 1))
$1 = #f
(gdb) guile (equal? (make-value 1) (make-value 1))
$1 = #t
A '<gdb:value>' that represents a function can be executed via
inferior function call with 'value-call'. Any arguments provided to the
call must match the function's prototype, and must be provided in the
order specified by that prototype.
For example, 'some-val' is a '<gdb:value>' instance representing a
function that takes two integers as arguments. To execute this
function, call it like so:
(define result (value-call some-val 10 20))
Any values returned from a function call are '<gdb:value>' objects.
Note: Unlike Python scripting in GDB, inferior values that are simple
scalars cannot be used directly in Scheme expressions that are valid for
the value's data type. For example, '(+ (parse-and-eval "int_variable")
2)' does not work. And inferior values that are structures or instances
of some class cannot be accessed using any special syntax, instead
'value-field' must be used.
The following value-related procedures are provided by the '(gdb)'
module.
-- Scheme Procedure: value? object
Return '#t' if OBJECT is a '<gdb:value>' object. Otherwise return
'#f'.
-- Scheme Procedure: make-value value [#:type type]
Many Scheme values can be converted directly to a '<gdb:value>'
with this procedure. If TYPE is specified, the result is a value
of this type, and if VALUE can't be represented with this type an
exception is thrown. Otherwise the type of the result is
determined from VALUE as described below.
*Note Architectures In Guile::, for a list of the builtin types for
an architecture.
Here's how Scheme values are converted when TYPE argument to
'make-value' is not specified:
Scheme boolean
A Scheme boolean is converted the boolean type for the current
language.
Scheme integer
A Scheme integer is converted to the first of a C 'int',
'unsigned int', 'long', 'unsigned long', 'long long' or
'unsigned long long' type for the current architecture that
can represent the value.
If the Scheme integer cannot be represented as a target
integer an 'out-of-range' exception is thrown.
Scheme real
A Scheme real is converted to the C 'double' type for the
current architecture.
Scheme string
A Scheme string is converted to a string in the current target
language using the current target encoding. Characters that
cannot be represented in the current target encoding are
replaced with the corresponding escape sequence. This is
Guile's 'SCM_FAILED_CONVERSION_ESCAPE_SEQUENCE' conversion
strategy (*note (guile)Strings::).
Passing TYPE is not supported in this case, if it is provided
a 'wrong-type-arg' exception is thrown.
'<gdb:lazy-string>'
If VALUE is a '<gdb:lazy-string>' object (*note Lazy Strings
In Guile::), then the 'lazy-string->value' procedure is
called, and its result is used.
Passing TYPE is not supported in this case, if it is provided
a 'wrong-type-arg' exception is thrown.
Scheme bytevector
If VALUE is a Scheme bytevector and TYPE is provided, VALUE
must be the same size, in bytes, of values of type TYPE, and
the result is essentially created by using 'memcpy'.
If VALUE is a Scheme bytevector and TYPE is not provided, the
result is an array of type 'uint8' of the same length.
-- Scheme Procedure: value-optimized-out? value
Return '#t' if the compiler optimized out VALUE, thus it is not
available for fetching from the inferior. Otherwise return '#f'.
-- Scheme Procedure: value-address value
If VALUE is addressable, returns a '<gdb:value>' object
representing the address. Otherwise, '#f' is returned.
-- Scheme Procedure: value-type value
Return the type of VALUE as a '<gdb:type>' object (*note Types In
Guile::).
-- Scheme Procedure: value-dynamic-type value
Return the dynamic type of VALUE. This uses C++ run-time type
information (RTTI) to determine the dynamic type of the value. If
the value is of class type, it will return the class in which the
value is embedded, if any. If the value is of pointer or reference
to a class type, it will compute the dynamic type of the referenced
object, and return a pointer or reference to that type,
respectively. In all other cases, it will return the value's
static type.
Note that this feature will only work when debugging a C++ program
that includes RTTI for the object in question. Otherwise, it will
just return the static type of the value as in 'ptype foo'. *Note
ptype: Symbols.
-- Scheme Procedure: value-cast value type
Return a new instance of '<gdb:value>' that is the result of
casting VALUE to the type described by TYPE, which must be a
'<gdb:type>' object. If the cast cannot be performed for some
reason, this method throws an exception.
-- Scheme Procedure: value-dynamic-cast value type
Like 'value-cast', but works as if the C++ 'dynamic_cast' operator
were used. Consult a C++ reference for details.
-- Scheme Procedure: value-reinterpret-cast value type
Like 'value-cast', but works as if the C++ 'reinterpret_cast'
operator were used. Consult a C++ reference for details.
-- Scheme Procedure: value-dereference value
For pointer data types, this method returns a new '<gdb:value>'
object whose contents is the object pointed to by VALUE. For
example, if 'foo' is a C pointer to an 'int', declared in your C
program as
int *foo;
then you can use the corresponding '<gdb:value>' to access what
'foo' points to like this:
(define bar (value-dereference foo))
The result 'bar' will be a '<gdb:value>' object holding the value
pointed to by 'foo'.
A similar function 'value-referenced-value' exists which also
returns '<gdb:value>' objects corresonding to the values pointed to
by pointer values (and additionally, values referenced by reference
values). However, the behavior of 'value-dereference' differs from
'value-referenced-value' by the fact that the behavior of
'value-dereference' is identical to applying the C unary operator
'*' on a given value. For example, consider a reference to a
pointer 'ptrref', declared in your C++ program as
typedef int *intptr;
...
int val = 10;
intptr ptr = &val;
intptr &ptrref = ptr;
Though 'ptrref' is a reference value, one can apply the method
'value-dereference' to the '<gdb:value>' object corresponding to it
and obtain a '<gdb:value>' which is identical to that corresponding
to 'val'. However, if you apply the method
'value-referenced-value', the result would be a '<gdb:value>'
object identical to that corresponding to 'ptr'.
(define scm-ptrref (parse-and-eval "ptrref"))
(define scm-val (value-dereference scm-ptrref))
(define scm-ptr (value-referenced-value scm-ptrref))
The '<gdb:value>' object 'scm-val' is identical to that
corresponding to 'val', and 'scm-ptr' is identical to that
corresponding to 'ptr'. In general, 'value-dereference' can be
applied whenever the C unary operator '*' can be applied to the
corresponding C value. For those cases where applying both
'value-dereference' and 'value-referenced-value' is allowed, the
results obtained need not be identical (as we have seen in the
above example). The results are however identical when applied on
'<gdb:value>' objects corresponding to pointers ('<gdb:value>'
objects with type code 'TYPE_CODE_PTR') in a C/C++ program.
-- Scheme Procedure: value-referenced-value value
For pointer or reference data types, this method returns a new
'<gdb:value>' object corresponding to the value referenced by the
pointer/reference value. For pointer data types,
'value-dereference' and 'value-referenced-value' produce identical
results. The difference between these methods is that
'value-dereference' cannot get the values referenced by reference
values. For example, consider a reference to an 'int', declared in
your C++ program as
int val = 10;
int &ref = val;
then applying 'value-dereference' to the '<gdb:value>' object
corresponding to 'ref' will result in an error, while applying
'value-referenced-value' will result in a '<gdb:value>' object
identical to that corresponding to 'val'.
(define scm-ref (parse-and-eval "ref"))
(define err-ref (value-dereference scm-ref)) ;; error
(define scm-val (value-referenced-value scm-ref)) ;; ok
The '<gdb:value>' object 'scm-val' is identical to that
corresponding to 'val'.
-- Scheme Procedure: value-field value field-name
Return field FIELD-NAME from '<gdb:value>' object VALUE.
-- Scheme Procedure: value-subscript value index
Return the value of array VALUE at index INDEX. The VALUE argument
must be a subscriptable '<gdb:value>' object.
-- Scheme Procedure: value-call value arg-list
Perform an inferior function call, taking VALUE as a pointer to the
function to call. Each element of list ARG-LIST must be a
<gdb:value> object or an object that can be converted to a value.
The result is the value returned by the function.
-- Scheme Procedure: value->bool value
Return the Scheme boolean representing '<gdb:value>' VALUE. The
value must be "integer like". Pointers are ok.
-- Scheme Procedure: value->integer
Return the Scheme integer representing '<gdb:value>' VALUE. The
value must be "integer like". Pointers are ok.
-- Scheme Procedure: value->real
Return the Scheme real number representing '<gdb:value>' VALUE.
The value must be a number.
-- Scheme Procedure: value->bytevector
Return a Scheme bytevector with the raw contents of '<gdb:value>'
VALUE. No transformation, endian or otherwise, is performed.
-- Scheme Procedure: value->string value [#:encoding encoding]
[#:errors errors] [#:length length]
If VALUE> represents a string, then this method converts the
contents to a Guile string. Otherwise, this method will throw an
exception.
Values are interpreted as strings according to the rules of the
current language. If the optional length argument is given, the
string will be converted to that length, and will include any
embedded zeroes that the string may contain. Otherwise, for
languages where the string is zero-terminated, the entire string
will be converted.
For example, in C-like languages, a value is a string if it is a
pointer to or an array of characters or ints of type 'wchar_t',
'char16_t', or 'char32_t'.
If the optional ENCODING argument is given, it must be a string
naming the encoding of the string in the '<gdb:value>', such as
'"ascii"', '"iso-8859-6"' or '"utf-8"'. It accepts the same
encodings as the corresponding argument to Guile's
'scm_from_stringn' function, and the Guile codec machinery will be
used to convert the string. If ENCODING is not given, or if
ENCODING is the empty string, then either the 'target-charset'
(*note Character Sets::) will be used, or a language-specific
encoding will be used, if the current language is able to supply
one.
The optional ERRORS argument is one of '#f', 'error' or
'substitute'. 'error' and 'substitute' must be symbols. If ERRORS
is not specified, or if its value is '#f', then the default
conversion strategy is used, which is set with the Scheme function
'set-port-conversion-strategy!'. If the value is ''error' then an
exception is thrown if there is any conversion error. If the value
is ''substitute' then any conversion error is replaced with
question marks. *Note (guile)Strings::.
If the optional LENGTH argument is given, the string will be
fetched and converted to the given length. The length must be a
Scheme integer and not a '<gdb:value>' integer.
-- Scheme Procedure: value->lazy-string value [#:encoding encoding]
[#:length length]
If this '<gdb:value>' represents a string, then this method
converts VALUE to a '<gdb:lazy-string' (*note Lazy Strings In
Guile::). Otherwise, this method will throw an exception.
If the optional ENCODING argument is given, it must be a string
naming the encoding of the '<gdb:lazy-string'. Some examples are:
'"ascii"', '"iso-8859-6"' or '"utf-8"'. If the ENCODING argument
is an encoding that GDB does not recognize, GDB will raise an
error.
When a lazy string is printed, the GDB encoding machinery is used
to convert the string during printing. If the optional ENCODING
argument is not provided, or is an empty string, GDB will
automatically select the encoding most suitable for the string
type. For further information on encoding in GDB please see *note
Character Sets::.
If the optional LENGTH argument is given, the string will be
fetched and encoded to the length of characters specified. If the
LENGTH argument is not provided, the string will be fetched and
encoded until a null of appropriate width is found. The length
must be a Scheme integer and not a '<gdb:value>' integer.
-- Scheme Procedure: value-lazy? value
Return '#t' if VALUE has not yet been fetched from the inferior.
Otherwise return '#f'. GDB does not fetch values until necessary,
for efficiency. For example:
(define myval (parse-and-eval "somevar"))
The value of 'somevar' is not fetched at this time. It will be
fetched when the value is needed, or when the 'fetch-lazy'
procedure is invoked.
-- Scheme Procedure: make-lazy-value type address
Return a '<gdb:value>' that will be lazily fetched from the target.
The object of type '<gdb:type>' whose value to fetch is specified
by its TYPE and its target memory ADDRESS, which is a Scheme
integer.
-- Scheme Procedure: value-fetch-lazy! value
If VALUE is a lazy value ('(value-lazy? value)' is '#t'), then the
value is fetched from the inferior. Any errors that occur in the
process will produce a Guile exception.
If VALUE is not a lazy value, this method has no effect.
The result of this function is unspecified.
-- Scheme Procedure: value-print value
Return the string representation (print form) of '<gdb:value>'
VALUE.

File: gdb.info, Node: Arithmetic In Guile, Next: Types In Guile, Prev: Values From Inferior In Guile, Up: Guile API
23.3.3.6 Arithmetic In Guile
............................
The '(gdb)' module provides several functions for performing arithmetic
on '<gdb:value>' objects. The arithmetic is performed as if it were
done by the target, and therefore has target semantics which are not
necessarily those of Scheme. For example operations work with a fixed
precision, not the arbitrary precision of Scheme.
Wherever a function takes an integer or pointer as an operand, GDB
will convert appropriate Scheme values to perform the operation.
-- Scheme Procedure: value-add a b
-- Scheme Procedure: value-sub a b
-- Scheme Procedure: value-mul a b
-- Scheme Procedure: value-div a b
-- Scheme Procedure: value-rem a b
-- Scheme Procedure: value-mod a b
-- Scheme Procedure: value-pow a b
-- Scheme Procedure: value-not a
-- Scheme Procedure: value-neg a
-- Scheme Procedure: value-pos a
-- Scheme Procedure: value-abs a
-- Scheme Procedure: value-lsh a b
-- Scheme Procedure: value-rsh a b
-- Scheme Procedure: value-min a b
-- Scheme Procedure: value-max a b
-- Scheme Procedure: value-lognot a
-- Scheme Procedure: value-logand a b
-- Scheme Procedure: value-logior a b
-- Scheme Procedure: value-logxor a b
-- Scheme Procedure: value=? a b
-- Scheme Procedure: value<? a b
-- Scheme Procedure: value<=? a b
-- Scheme Procedure: value>? a b
-- Scheme Procedure: value>=? a b
Scheme does not provide a 'not-equal' function, and thus Guile
support in GDB does not either.

File: gdb.info, Node: Types In Guile, Next: Guile Pretty Printing API, Prev: Arithmetic In Guile, Up: Guile API
23.3.3.7 Types In Guile
.......................
GDB represents types from the inferior in objects of type '<gdb:type>'.
The following type-related procedures are provided by the '(gdb)'
module.
-- Scheme Procedure: type? object
Return '#t' if OBJECT is an object of type '<gdb:type>'. Otherwise
return '#f'.
-- Scheme Procedure: lookup-type name [#:block block]
This function looks up a type by its NAME, which must be a string.
If BLOCK is given, it is an object of type '<gdb:block>', and NAME
is looked up in that scope. Otherwise, it is searched for
globally.
Ordinarily, this function will return an instance of '<gdb:type>'.
If the named type cannot be found, it will throw an exception.
-- Scheme Procedure: type-code type
Return the type code of TYPE. The type code will be one of the
'TYPE_CODE_' constants defined below.
-- Scheme Procedure: type-tag type
Return the tag name of TYPE. The tag name is the name after
'struct', 'union', or 'enum' in C and C++; not all languages have
this concept. If this type has no tag name, then '#f' is returned.
-- Scheme Procedure: type-name type
Return the name of TYPE. If this type has no name, then '#f' is
returned.
-- Scheme Procedure: type-print-name type
Return the print name of TYPE. This returns something even for
anonymous types. For example, for an anonymous C struct '"struct
{...}"' is returned.
-- Scheme Procedure: type-sizeof type
Return the size of this type, in target 'char' units. Usually, a
target's 'char' type will be an 8-bit byte. However, on some
unusual platforms, this type may have a different size.
-- Scheme Procedure: type-strip-typedefs type
Return a new '<gdb:type>' that represents the real type of TYPE,
after removing all layers of typedefs.
-- Scheme Procedure: type-array type n1 [n2]
Return a new '<gdb:type>' object which represents an array of this
type. If one argument is given, it is the inclusive upper bound of
the array; in this case the lower bound is zero. If two arguments
are given, the first argument is the lower bound of the array, and
the second argument is the upper bound of the array. An array's
length must not be negative, but the bounds can be.
-- Scheme Procedure: type-vector type n1 [n2]
Return a new '<gdb:type>' object which represents a vector of this
type. If one argument is given, it is the inclusive upper bound of
the vector; in this case the lower bound is zero. If two arguments
are given, the first argument is the lower bound of the vector, and
the second argument is the upper bound of the vector. A vector's
length must not be negative, but the bounds can be.
The difference between an 'array' and a 'vector' is that arrays
behave like in C: when used in expressions they decay to a pointer
to the first element whereas vectors are treated as first class
values.
-- Scheme Procedure: type-pointer type
Return a new '<gdb:type>' object which represents a pointer to
TYPE.
-- Scheme Procedure: type-range type
Return a list of two elements: the low bound and high bound of
TYPE. If TYPE does not have a range, an exception is thrown.
-- Scheme Procedure: type-reference type
Return a new '<gdb:type>' object which represents a reference to
TYPE.
-- Scheme Procedure: type-target type
Return a new '<gdb:type>' object which represents the target type
of TYPE.
For a pointer type, the target type is the type of the pointed-to
object. For an array type (meaning C-like arrays), the target type
is the type of the elements of the array. For a function or method
type, the target type is the type of the return value. For a
complex type, the target type is the type of the elements. For a
typedef, the target type is the aliased type.
If the type does not have a target, this method will throw an
exception.
-- Scheme Procedure: type-const type
Return a new '<gdb:type>' object which represents a
'const'-qualified variant of TYPE.
-- Scheme Procedure: type-volatile type
Return a new '<gdb:type>' object which represents a
'volatile'-qualified variant of TYPE.
-- Scheme Procedure: type-unqualified type
Return a new '<gdb:type>' object which represents an unqualified
variant of TYPE. That is, the result is neither 'const' nor
'volatile'.
-- Scheme Procedure: type-num-fields
Return the number of fields of '<gdb:type>' TYPE.
-- Scheme Procedure: type-fields type
Return the fields of TYPE as a list. For structure and union
types, 'fields' has the usual meaning. Range types have two
fields, the minimum and maximum values. Enum types have one field
per enum constant. Function and method types have one field per
parameter. The base types of C++ classes are also represented as
fields. If the type has no fields, or does not fit into one of
these categories, an empty list will be returned. *Note Fields of
a type in Guile::.
-- Scheme Procedure: make-field-iterator type
Return the fields of TYPE as a <gdb:iterator> object. *Note
Iterators In Guile::.
-- Scheme Procedure: type-field type field-name
Return field named FIELD-NAME in TYPE. The result is an object of
type '<gdb:field>'. *Note Fields of a type in Guile::. If the
type does not have fields, or FIELD-NAME is not a field of TYPE, an
exception is thrown.
For example, if 'some-type' is a '<gdb:type>' instance holding a
structure type, you can access its 'foo' field with:
(define bar (type-field some-type "foo"))
'bar' will be a '<gdb:field>' object.
-- Scheme Procedure: type-has-field? type name
Return '#t' if '<gdb:type>' TYPE has field named NAME. Otherwise
return '#f'.
Each type has a code, which indicates what category this type falls
into. The available type categories are represented by constants
defined in the '(gdb)' module:
'TYPE_CODE_PTR'
The type is a pointer.
'TYPE_CODE_ARRAY'
The type is an array.
'TYPE_CODE_STRUCT'
The type is a structure.
'TYPE_CODE_UNION'
The type is a union.
'TYPE_CODE_ENUM'
The type is an enum.
'TYPE_CODE_FLAGS'
A bit flags type, used for things such as status registers.
'TYPE_CODE_FUNC'
The type is a function.
'TYPE_CODE_INT'
The type is an integer type.
'TYPE_CODE_FLT'
A floating point type.
'TYPE_CODE_VOID'
The special type 'void'.
'TYPE_CODE_SET'
A Pascal set type.
'TYPE_CODE_RANGE'
A range type, that is, an integer type with bounds.
'TYPE_CODE_STRING'
A string type. Note that this is only used for certain languages
with language-defined string types; C strings are not represented
this way.
'TYPE_CODE_BITSTRING'
A string of bits. It is deprecated.
'TYPE_CODE_ERROR'
An unknown or erroneous type.
'TYPE_CODE_METHOD'
A method type, as found in C++ or Java.
'TYPE_CODE_METHODPTR'
A pointer-to-member-function.
'TYPE_CODE_MEMBERPTR'
A pointer-to-member.
'TYPE_CODE_REF'
A reference type.
'TYPE_CODE_CHAR'
A character type.
'TYPE_CODE_BOOL'
A boolean type.
'TYPE_CODE_COMPLEX'
A complex float type.
'TYPE_CODE_TYPEDEF'
A typedef to some other type.
'TYPE_CODE_NAMESPACE'
A C++ namespace.
'TYPE_CODE_DECFLOAT'
A decimal floating point type.
'TYPE_CODE_INTERNAL_FUNCTION'
A function internal to GDB. This is the type used to represent
convenience functions (*note Convenience Funs::).
Further support for types is provided in the '(gdb types)' Guile
module (*note Guile Types Module::).
Each field is represented as an object of type '<gdb:field>'.
The following field-related procedures are provided by the '(gdb)'
module:
-- Scheme Procedure: field? object
Return '#t' if OBJECT is an object of type '<gdb:field>'.
Otherwise return '#f'.
-- Scheme Procedure: field-name field
Return the name of the field, or '#f' for anonymous fields.
-- Scheme Procedure: field-type field
Return the type of the field. This is usually an instance of
'<gdb:type>', but it can be '#f' in some situations.
-- Scheme Procedure: field-enumval field
Return the enum value represented by '<gdb:field>' FIELD.
-- Scheme Procedure: field-bitpos field
Return the bit position of '<gdb:field>' FIELD. This attribute is
not available for 'static' fields (as in C++ or Java).
-- Scheme Procedure: field-bitsize field
If the field is packed, or is a bitfield, return the size of
'<gdb:field>' FIELD in bits. Otherwise, zero is returned; in which
case the field's size is given by its type.
-- Scheme Procedure: field-artificial? field
Return '#t' if the field is artificial, usually meaning that it was
provided by the compiler and not the user. Otherwise return '#f'.
-- Scheme Procedure: field-base-class? field
Return '#t' if the field represents a base class of a C++
structure. Otherwise return '#f'.

File: gdb.info, Node: Guile Pretty Printing API, Next: Selecting Guile Pretty-Printers, Prev: Types In Guile, Up: Guile API
23.3.3.8 Guile Pretty Printing API
..................................
An example output is provided (*note Pretty Printing::).
A pretty-printer is represented by an object of type
<gdb:pretty-printer>. Pretty-printer objects are created with
'make-pretty-printer'.
The following pretty-printer-related procedures are provided by the
'(gdb)' module:
-- Scheme Procedure: make-pretty-printer name lookup-function
Return a '<gdb:pretty-printer>' object named NAME.
LOOKUP-FUNCTION is a function of one parameter: the value to be
printed. If the value is handled by this pretty-printer, then
LOOKUP-FUNCTION returns an object of type
<gdb:pretty-printer-worker> to perform the actual pretty-printing.
Otherwise LOOKUP-FUNCTION returns '#f'.
-- Scheme Procedure: pretty-printer? object
Return '#t' if OBJECT is a '<gdb:pretty-printer>' object.
Otherwise return '#f'.
-- Scheme Procedure: pretty-printer-enabled? pretty-printer
Return '#t' if PRETTY-PRINTER is enabled. Otherwise return '#f'.
-- Scheme Procedure: set-pretty-printer-enabled! pretty-printer flag
Set the enabled flag of PRETTY-PRINTER to FLAG. The value returned
is unspecified.
-- Scheme Procedure: pretty-printers
Return the list of global pretty-printers.
-- Scheme Procedure: set-pretty-printers! pretty-printers
Set the list of global pretty-printers to PRETTY-PRINTERS. The
value returned is unspecified.
-- Scheme Procedure: make-pretty-printer-worker display-hint to-string
children
Return an object of type '<gdb:pretty-printer-worker>'.
This function takes three parameters:
'display-hint'
DISPLAY-HINT provides a hint to GDB or GDB front end via MI to
change the formatting of the value being printed. The value
must be a string or '#f' (meaning there is no hint). Several
values for DISPLAY-HINT are predefined by GDB:
'array'
Indicate that the object being printed is "array-like".
The CLI uses this to respect parameters such as 'set
print elements' and 'set print array'.
'map'
Indicate that the object being printed is "map-like", and
that the children of this value can be assumed to
alternate between keys and values.
'string'
Indicate that the object being printed is "string-like".
If the printer's 'to-string' function returns a Guile
string of some kind, then GDB will call its internal
language-specific string-printing function to format the
string. For the CLI this means adding quotation marks,
possibly escaping some characters, respecting 'set print
elements', and the like.
'to-string'
TO-STRING is either a function of one parameter, the
'<gdb:pretty-printer-worker>' object, or '#f'.
When printing from the CLI, if the 'to-string' method exists,
then GDB will prepend its result to the values returned by
'children'. Exactly how this formatting is done is dependent
on the display hint, and may change as more hints are added.
Also, depending on the print settings (*note Print
Settings::), the CLI may print just the result of 'to-string'
in a stack trace, omitting the result of 'children'.
If this method returns a string, it is printed verbatim.
Otherwise, if this method returns an instance of
'<gdb:value>', then GDB prints this value. This may result in
a call to another pretty-printer.
If instead the method returns a Guile value which is
convertible to a '<gdb:value>', then GDB performs the
conversion and prints the resulting value. Again, this may
result in a call to another pretty-printer. Guile scalars
(integers, floats, and booleans) and strings are convertible
to '<gdb:value>'; other types are not.
Finally, if this method returns '#f' then no further
operations are peformed in this method and nothing is printed.
If the result is not one of these types, an exception is
raised.
TO-STRING may also be '#f' in which case it is left to
CHILDREN to print the value.
'children'
CHILDREN is either a function of one parameter, the
'<gdb:pretty-printer-worker>' object, or '#f'.
GDB will call this function on a pretty-printer to compute the
children of the pretty-printer's value.
This function must return a <gdb:iterator> object. Each item
returned by the iterator must be a tuple holding two elements.
The first element is the "name" of the child; the second
element is the child's value. The value can be any Guile
object which is convertible to a GDB value.
If CHILDREN is '#f', GDB will act as though the value has no
children.
GDB provides a function which can be used to look up the default
pretty-printer for a '<gdb:value>':
-- Scheme Procedure: default-visualizer value
This function takes a '<gdb:value>' object as an argument. If a
pretty-printer for this value exists, then it is returned. If no
such printer exists, then this returns '#f'.

File: gdb.info, Node: Selecting Guile Pretty-Printers, Next: Writing a Guile Pretty-Printer, Prev: Guile Pretty Printing API, Up: Guile API
23.3.3.9 Selecting Guile Pretty-Printers
........................................
There are three sets of pretty-printers that GDB searches:
* Per-objfile list of pretty-printers (*note Objfiles In Guile::).
* Per-progspace list of pretty-printers (*note Progspaces In
Guile::).
* The global list of pretty-printers (*note Guile Pretty Printing
API::). These printers are available when debugging any inferior.
Pretty-printer lookup is done by passing the value to be printed to
the lookup function of each enabled object in turn. Lookup stops when a
lookup function returns a non-'#f' value or when the list is exhausted.
Lookup functions must return either a '<gdb:pretty-printer-worker>'
object or '#f'. Otherwise an exception is thrown.
GDB first checks the result of 'objfile-pretty-printers' of each
'<gdb:objfile>' in the current program space and iteratively calls each
enabled lookup function in the list for that '<gdb:objfile>' until a
non-'#f' object is returned. If no pretty-printer is found in the
objfile lists, GDB then searches the result of
'progspace-pretty-printers' of the current program space, calling each
enabled function until a non-'#f' object is returned. After these lists
have been exhausted, it tries the global pretty-printers list, obtained
with 'pretty-printers', again calling each enabled function until a
non-'#f' object is returned.
The order in which the objfiles are searched is not specified. For a
given list, functions are always invoked from the head of the list, and
iterated over sequentially until the end of the list, or a
'<gdb:pretty-printer-worker>' object is returned.
For various reasons a pretty-printer may not work. For example, the
underlying data structure may have changed and the pretty-printer is out
of date.
The consequences of a broken pretty-printer are severe enough that
GDB provides support for enabling and disabling individual printers.
For example, if 'print frame-arguments' is on, a backtrace can become
highly illegible if any argument is printed with a broken printer.
Pretty-printers are enabled and disabled from Scheme by calling
'set-pretty-printer-enabled!'. *Note Guile Pretty Printing API::.

File: gdb.info, Node: Writing a Guile Pretty-Printer, Next: Commands In Guile, Prev: Selecting Guile Pretty-Printers, Up: Guile API
23.3.3.10 Writing a Guile Pretty-Printer
........................................
A pretty-printer consists of two basic parts: a lookup function to
determine if the type is supported, and the printer itself.
Here is an example showing how a 'std::string' printer might be
written. *Note Guile Pretty Printing API::, for details.
(define (make-my-string-printer value)
"Print a my::string string"
(make-pretty-printer-worker
"string"
(lambda (printer)
(value-field value "_data"))
#f))
And here is an example showing how a lookup function for the printer
example above might be written.
(define (str-lookup-function pretty-printer value)
(let ((tag (type-tag (value-type value))))
(and tag
(string-prefix? "std::string<" tag)
(make-my-string-printer value))))
Then to register this printer in the global printer list:
(append-pretty-printer!
(make-pretty-printer "my-string" str-lookup-function))
The example lookup function extracts the value's type, and attempts
to match it to a type that it can pretty-print. If it is a type the
printer can pretty-print, it will return a <gdb:pretty-printer-worker>
object. If not, it returns '#f'.
We recommend that you put your core pretty-printers into a Guile
package. If your pretty-printers are for use with a library, we further
recommend embedding a version number into the package name. This
practice will enable GDB to load multiple versions of your
pretty-printers at the same time, because they will have different
names.
You should write auto-loaded code (*note Guile Auto-loading::) such
that it can be evaluated multiple times without changing its meaning.
An ideal auto-load file will consist solely of 'import's of your printer
modules, followed by a call to a register pretty-printers with the
current objfile.
Taken as a whole, this approach will scale nicely to multiple
inferiors, each potentially using a different library version.
Embedding a version number in the Guile package name will ensure that
GDB is able to load both sets of printers simultaneously. Then, because
the search for pretty-printers is done by objfile, and because your
auto-loaded code took care to register your library's printers with a
specific objfile, GDB will find the correct printers for the specific
version of the library used by each inferior.
To continue the 'my::string' example, this code might appear in
'(my-project my-library v1)':
(use-modules (gdb))
(define (register-printers objfile)
(append-objfile-pretty-printer!
(make-pretty-printer "my-string" str-lookup-function)))
And then the corresponding contents of the auto-load file would be:
(use-modules (gdb) (my-project my-library v1))
(register-printers (current-objfile))
The previous example illustrates a basic pretty-printer. There are a
few things that can be improved on. The printer only handles one type,
whereas a library typically has several types. One could install a
lookup function for each desired type in the library, but one could also
have a single lookup function recognize several types. The latter is
the conventional way this is handled. If a pretty-printer can handle
multiple data types, then its "subprinters" are the printers for the
individual data types.
The '(gdb printing)' module provides a formal way of solving this
problem (*note Guile Printing Module::). Here is another example that
handles multiple types.
These are the types we are going to pretty-print:
struct foo { int a, b; };
struct bar { struct foo x, y; };
Here are the printers:
(define (make-foo-printer value)
"Print a foo object"
(make-pretty-printer-worker
"foo"
(lambda (printer)
(format #f "a=<~a> b=<~a>"
(value-field value "a") (value-field value "a")))
#f))
(define (make-bar-printer value)
"Print a bar object"
(make-pretty-printer-worker
"foo"
(lambda (printer)
(format #f "x=<~a> y=<~a>"
(value-field value "x") (value-field value "y")))
#f))
This example doesn't need a lookup function, that is handled by the
'(gdb printing)' module. Instead a function is provided to build up the
object that handles the lookup.
(use-modules (gdb printing))
(define (build-pretty-printer)
(let ((pp (make-pretty-printer-collection "my-library")))
(pp-collection-add-tag-printer "foo" make-foo-printer)
(pp-collection-add-tag-printer "bar" make-bar-printer)
pp))
And here is the autoload support:
(use-modules (gdb) (my-library))
(append-objfile-pretty-printer! (current-objfile) (build-pretty-printer))
Finally, when this printer is loaded into GDB, here is the
corresponding output of 'info pretty-printer':
(gdb) info pretty-printer
my_library.so:
my-library
foo
bar

File: gdb.info, Node: Commands In Guile, Next: Parameters In Guile, Prev: Writing a Guile Pretty-Printer, Up: Guile API
23.3.3.11 Commands In Guile
...........................
You can implement new GDB CLI commands in Guile. A CLI command object
is created with the 'make-command' Guile function, and added to GDB with
the 'register-command!' Guile function. This two-step approach is taken
to separate out the side-effect of adding the command to GDB from
'make-command'.
There is no support for multi-line commands, that is commands that
consist of multiple lines and are terminated with 'end'.
-- Scheme Procedure: (make-command name [#:invoke invoke]
[#:command-class command-class] [#:completer-class completer]
[#:prefix? prefix] [#:doc doc-string])
The argument NAME is the name of the command. If NAME consists of
multiple words, then the initial words are looked for as prefix
commands. In this case, if one of the prefix commands does not
exist, an exception is raised.
The result is the '<gdb:command>' object representing the command.
The command is not usable until it has been registered with GDB
with 'register-command!'.
The rest of the arguments are optional.
The argument INVOKE is a procedure of three arguments: SELF, ARGS
and FROM-TTY. The argument SELF is the '<gdb:command>' object
representing the command. The argument ARGS is a string
representing the arguments passed to the command, after leading and
trailing whitespace has been stripped. The argument FROM-TTY is a
boolean flag and specifies whether the command should consider
itself to have been originated from the user invoking it
interactively. If this function throws an exception, it is turned
into a GDB 'error' call. Otherwise, the return value is ignored.
The argument COMMAND-CLASS is one of the 'COMMAND_' constants
defined below. This argument tells GDB how to categorize the new
command in the help system. The default is 'COMMAND_NONE'.
The argument COMPLETER is either '#f', one of the 'COMPLETE_'
constants defined below, or a procedure, also defined below. This
argument tells GDB how to perform completion for this command. If
not provided or if the value is '#f', then no completion is
performed on the command.
The argument PREFIX is a boolean flag indicating whether the new
command is a prefix command; sub-commands of this command may be
registered.
The argument DOC-STRING is help text for the new command. If no
documentation string is provided, the default value "This command
is not documented." is used.
-- Scheme Procedure: register-command! command
Add COMMAND, a '<gdb:command>' object, to GDB's list of commands.
It is an error to register a command more than once. The result is
unspecified.
-- Scheme Procedure: command? object
Return '#t' if OBJECT is a '<gdb:command>' object. Otherwise
return '#f'.
-- Scheme Procedure: dont-repeat
By default, a GDB command is repeated when the user enters a blank
line at the command prompt. A command can suppress this behavior
by invoking the 'dont-repeat' function. This is similar to the
user command 'dont-repeat', see *note dont-repeat: Define.
-- Scheme Procedure: string->argv string
Convert a string to a list of strings split up according to GDB's
argv parsing rules. It is recommended to use this for consistency.
Arguments are separated by spaces and may be quoted. Example:
scheme@(guile-user)> (string->argv "1 2\\ \\\"3 '4 \"5' \"6 '7\"")
$1 = ("1" "2 \"3" "4 \"5" "6 '7")
-- Scheme Procedure: throw-user-error message . args
Throw a 'gdb:user-error' exception. The argument MESSAGE is the
error message as a format string, like the FMT argument to the
'format' Scheme function. *Note (guile)Formatted Output::. The
argument ARGS is a list of the optional arguments of MESSAGE.
This is used when the command detects a user error of some kind,
say a bad command argument.
(gdb) guile (use-modules (gdb))
(gdb) guile
(register-command! (make-command "test-user-error"
#:command-class COMMAND_OBSCURE
#:invoke (lambda (self arg from-tty)
(throw-user-error "Bad argument ~a" arg))))
end
(gdb) test-user-error ugh
ERROR: Bad argument ugh
-- completer: self text word
If the COMPLETER option to 'make-command' is a procedure, it takes
three arguments: SELF which is the '<gdb:command>' object, and TEXT
and WORD which are both strings. The argument TEXT holds the
complete command line up to the cursor's location. The argument
WORD holds the last word of the command line; this is computed
using a word-breaking heuristic.
All forms of completion are handled by this function, that is, the
<TAB> and <M-?> key bindings (*note Completion::), and the
'complete' command (*note complete: Help.).
This procedure can return several kinds of values:
* If the return value is a list, the contents of the list are
used as the completions. It is up to COMPLETER to ensure that
the contents actually do complete the word. An empty list is
allowed, it means that there were no completions available.
Only string elements of the list are used; other elements in
the list are ignored.
* If the return value is a '<gdb:iterator>' object, it is
iterated over to obtain the completions. It is up to
'completer-procedure' to ensure that the results actually do
complete the word. Only string elements of the result are
used; other elements in the sequence are ignored.
* All other results are treated as though there were no
available completions.
When a new command is registered, it will have been declared as a
member of some general class of commands. This is used to classify
top-level commands in the on-line help system; note that prefix commands
are not listed under their own category but rather that of their
top-level command. The available classifications are represented by
constants defined in the 'gdb' module:
'COMMAND_NONE'
The command does not belong to any particular class. A command in
this category will not be displayed in any of the help categories.
This is the default.
'COMMAND_RUNNING'
The command is related to running the inferior. For example,
'start', 'step', and 'continue' are in this category. Type 'help
running' at the GDB prompt to see a list of commands in this
category.
'COMMAND_DATA'
The command is related to data or variables. For example, 'call',
'find', and 'print' are in this category. Type 'help data' at the
GDB prompt to see a list of commands in this category.
'COMMAND_STACK'
The command has to do with manipulation of the stack. For example,
'backtrace', 'frame', and 'return' are in this category. Type
'help stack' at the GDB prompt to see a list of commands in this
category.
'COMMAND_FILES'
This class is used for file-related commands. For example, 'file',
'list' and 'section' are in this category. Type 'help files' at
the GDB prompt to see a list of commands in this category.
'COMMAND_SUPPORT'
This should be used for "support facilities", generally meaning
things that are useful to the user when interacting with GDB, but
not related to the state of the inferior. For example, 'help',
'make', and 'shell' are in this category. Type 'help support' at
the GDB prompt to see a list of commands in this category.
'COMMAND_STATUS'
The command is an 'info'-related command, that is, related to the
state of GDB itself. For example, 'info', 'macro', and 'show' are
in this category. Type 'help status' at the GDB prompt to see a
list of commands in this category.
'COMMAND_BREAKPOINTS'
The command has to do with breakpoints. For example, 'break',
'clear', and 'delete' are in this category. Type 'help
breakpoints' at the GDB prompt to see a list of commands in this
category.
'COMMAND_TRACEPOINTS'
The command has to do with tracepoints. For example, 'trace',
'actions', and 'tfind' are in this category. Type 'help
tracepoints' at the GDB prompt to see a list of commands in this
category.
'COMMAND_USER'
The command is a general purpose command for the user, and
typically does not fit in one of the other categories. Type 'help
user-defined' at the GDB prompt to see a list of commands in this
category, as well as the list of gdb macros (*note Sequences::).
'COMMAND_OBSCURE'
The command is only used in unusual circumstances, or is not of
general interest to users. For example, 'checkpoint', 'fork', and
'stop' are in this category. Type 'help obscure' at the GDB prompt
to see a list of commands in this category.
'COMMAND_MAINTENANCE'
The command is only useful to GDB maintainers. The 'maintenance'
and 'flushregs' commands are in this category. Type 'help
internals' at the GDB prompt to see a list of commands in this
category.
A new command can use a predefined completion function, either by
specifying it via an argument at initialization, or by returning it from
the 'completer' procedure. These predefined completion constants are
all defined in the 'gdb' module:
'COMPLETE_NONE'
This constant means that no completion should be done.
'COMPLETE_FILENAME'
This constant means that filename completion should be performed.
'COMPLETE_LOCATION'
This constant means that location completion should be done. *Note
Specify Location::.
'COMPLETE_COMMAND'
This constant means that completion should examine GDB command
names.
'COMPLETE_SYMBOL'
This constant means that completion should be done using symbol
names as the source.
'COMPLETE_EXPRESSION'
This constant means that completion should be done on expressions.
Often this means completing on symbol names, but some language
parsers also have support for completing on field names.
The following code snippet shows how a trivial CLI command can be
implemented in Guile:
(gdb) guile
(register-command! (make-command "hello-world"
#:command-class COMMAND_USER
#:doc "Greet the whole world."
#:invoke (lambda (self args from-tty) (display "Hello, World!\n"))))
end
(gdb) hello-world
Hello, World!

File: gdb.info, Node: Parameters In Guile, Next: Progspaces In Guile, Prev: Commands In Guile, Up: Guile API
23.3.3.12 Parameters In Guile
.............................
You can implement new GDB "parameters" using Guile (1).
There are many parameters that already exist and can be set in GDB.
Two examples are: 'set follow-fork' and 'set charset'. Setting these
parameters influences certain behavior in GDB. Similarly, you can
define parameters that can be used to influence behavior in custom Guile
scripts and commands.
A new parameter is defined with the 'make-parameter' Guile function,
and added to GDB with the 'register-parameter!' Guile function. This
two-step approach is taken to separate out the side-effect of adding the
parameter to GDB from 'make-parameter'.
Parameters are exposed to the user via the 'set' and 'show' commands.
*Note Help::.
-- Scheme Procedure: (make-parameter name [#:command-class
command-class] [#:parameter-type parameter-type] [#:enum-list
enum-list] [#:set-func set-func] [#:show-func show-func]
[#:doc doc] [#:set-doc set-doc] [#:show-doc show-doc]
[#:initial-value initial-value])
The argument NAME is the name of the new parameter. If NAME
consists of multiple words, then the initial words are looked for
as prefix parameters. An example of this can be illustrated with
the 'set print' set of parameters. If NAME is 'print foo', then
'print' will be searched as the prefix parameter. In this case the
parameter can subsequently be accessed in GDB as 'set print foo'.
If NAME consists of multiple words, and no prefix parameter group
can be found, an exception is raised.
The result is the '<gdb:parameter>' object representing the
parameter. The parameter is not usable until it has been
registered with GDB with 'register-parameter!'.
The rest of the arguments are optional.
The argument COMMAND-CLASS should be one of the 'COMMAND_'
constants (*note Commands In Guile::). This argument tells GDB how
to categorize the new parameter in the help system. The default is
'COMMAND_NONE'.
The argument PARAMETER-TYPE should be one of the 'PARAM_' constants
defined below. This argument tells GDB the type of the new
parameter; this information is used for input validation and
completion. The default is 'PARAM_BOOLEAN'.
If PARAMETER-TYPE is 'PARAM_ENUM', then ENUM-LIST must be a list of
strings. These strings represent the possible values for the
parameter.
If PARAMETER-TYPE is not 'PARAM_ENUM', then the presence of
ENUM-LIST will cause an exception to be thrown.
The argument SET-FUNC is a function of one argument: SELF which is
the '<gdb:parameter>' object representing the parameter. GDB will
call this function when a PARAMETER's value has been changed via
the 'set' API (for example, 'set foo off'). The value of the
parameter has already been set to the new value. This function
must return a string to be displayed to the user. GDB will add a
trailing newline if the string is non-empty. GDB generally doesn't
print anything when a parameter is set, thus typically this
function should return '""'. A non-empty string result should
typically be used for displaying warnings and errors.
The argument SHOW-FUNC is a function of two arguments: SELF which
is the '<gdb:parameter>' object representing the parameter, and
SVALUE which is the string representation of the current value.
GDB will call this function when a PARAMETER's 'show' API has been
invoked (for example, 'show foo'). This function must return a
string, and will be displayed to the user. GDB will add a trailing
newline.
The argument DOC is the help text for the new parameter. If there
is no documentation string, a default value is used.
The argument SET-DOC is the help text for this parameter's 'set'
command.
The argument SHOW-DOC is the help text for this parameter's 'show'
command.
The argument INITIAL-VALUE specifies the initial value of the
parameter. If it is a function, it takes one parameter, the
'<gdb:parameter>' object and its result is used as the initial
value of the parameter. The initial value must be valid for the
parameter type, otherwise an exception is thrown.
-- Scheme Procedure: register-parameter! parameter
Add PARAMETER, a '<gdb:parameter>' object, to GDB's list of
parameters. It is an error to register a parameter more than once.
The result is unspecified.
-- Scheme Procedure: parameter? object
Return '#t' if OBJECT is a '<gdb:parameter>' object. Otherwise
return '#f'.
-- Scheme Procedure: parameter-value parameter
Return the value of PARAMETER which may either be a
'<gdb:parameter>' object or a string naming the parameter.
-- Scheme Procedure: set-parameter-value! parameter new-value
Assign PARAMETER the value of NEW-VALUE. The argument PARAMETER
must be an object of type '<gdb:parameter>'. GDB does validation
when assignments are made.
When a new parameter is defined, its type must be specified. The
available types are represented by constants defined in the 'gdb'
module:
'PARAM_BOOLEAN'
The value is a plain boolean. The Guile boolean values, '#t' and
'#f' are the only valid values.
'PARAM_AUTO_BOOLEAN'
The value has three possible states: true, false, and 'auto'. In
Guile, true and false are represented using boolean constants, and
'auto' is represented using '#:auto'.
'PARAM_UINTEGER'
The value is an unsigned integer. The value of 0 should be
interpreted to mean "unlimited".
'PARAM_ZINTEGER'
The value is an integer.
'PARAM_ZUINTEGER'
The value is an unsigned integer.
'PARAM_ZUINTEGER_UNLIMITED'
The value is an integer in the range '[0, INT_MAX]'. A value of
'-1' means "unlimited", and other negative numbers are not allowed.
'PARAM_STRING'
The value is a string. When the user modifies the string, any
escape sequences, such as '\t', '\f', and octal escapes, are
translated into corresponding characters and encoded into the
current host charset.
'PARAM_STRING_NOESCAPE'
The value is a string. When the user modifies the string, escapes
are passed through untranslated.
'PARAM_OPTIONAL_FILENAME'
The value is a either a filename (a string), or '#f'.
'PARAM_FILENAME'
The value is a filename. This is just like
'PARAM_STRING_NOESCAPE', but uses file names for completion.
'PARAM_ENUM'
The value is a string, which must be one of a collection of string
constants provided when the parameter is created.
---------- Footnotes ----------
(1) Note that GDB parameters must not be confused with Guile’s
parameter objects (*note (guile)Parameters::).

File: gdb.info, Node: Progspaces In Guile, Next: Objfiles In Guile, Prev: Parameters In Guile, Up: Guile API
23.3.3.13 Program Spaces In Guile
.................................
A program space, or "progspace", represents a symbolic view of an
address space. It consists of all of the objfiles of the program.
*Note Objfiles In Guile::. *Note program spaces: Inferiors and
Programs, for more details about program spaces.
Each progspace is represented by an instance of the '<gdb:progspace>'
smob. *Note GDB Scheme Data Types::.
The following progspace-related functions are available in the
'(gdb)' module:
-- Scheme Procedure: progspace? object
Return '#t' if OBJECT is a '<gdb:progspace>' object. Otherwise
return '#f'.
-- Scheme Procedure: progspace-valid? progspace
Return '#t' if PROGSPACE is valid, '#f' if not. A
'<gdb:progspace>' object can become invalid if the program it
refers to is not loaded in GDB any longer.
-- Scheme Procedure: current-progspace
This function returns the program space of the currently selected
inferior. There is always a current progspace, this never returns
'#f'. *Note Inferiors and Programs::.
-- Scheme Procedure: progspaces
Return a list of all the progspaces currently known to GDB.
-- Scheme Procedure: progspace-filename progspace
Return the absolute file name of PROGSPACE as a string. This is
the name of the file passed as the argument to the 'file' or
'symbol-file' commands. If the program space does not have an
associated file name, then '#f' is returned. This occurs, for
example, when GDB is started without a program to debug.
A 'gdb:invalid-object-error' exception is thrown if PROGSPACE is
invalid.
-- Scheme Procedure: progspace-objfiles progspace
Return the list of objfiles of PROGSPACE. The order of objfiles in
the result is arbitrary. Each element is an object of type
'<gdb:objfile>'. *Note Objfiles In Guile::.
A 'gdb:invalid-object-error' exception is thrown if PROGSPACE is
invalid.
-- Scheme Procedure: progspace-pretty-printers progspace
Return the list of pretty-printers of PROGSPACE. Each element is
an object of type '<gdb:pretty-printer>'. *Note Guile Pretty
Printing API::, for more information.
-- Scheme Procedure: set-progspace-pretty-printers! progspace
printer-list
Set the list of registered '<gdb:pretty-printer>' objects for
PROGSPACE to PRINTER-LIST. *Note Guile Pretty Printing API::, for
more information.

File: gdb.info, Node: Objfiles In Guile, Next: Frames In Guile, Prev: Progspaces In Guile, Up: Guile API
23.3.3.14 Objfiles In Guile
...........................
GDB loads symbols for an inferior from various symbol-containing files
(*note Files::). These include the primary executable file, any shared
libraries used by the inferior, and any separate debug info files (*note
Separate Debug Files::). GDB calls these symbol-containing files
"objfiles".
Each objfile is represented as an object of type '<gdb:objfile>'.
The following objfile-related procedures are provided by the '(gdb)'
module:
-- Scheme Procedure: objfile? object
Return '#t' if OBJECT is a '<gdb:objfile>' object. Otherwise
return '#f'.
-- Scheme Procedure: objfile-valid? objfile
Return '#t' if OBJFILE is valid, '#f' if not. A '<gdb:objfile>'
object can become invalid if the object file it refers to is not
loaded in GDB any longer. All other '<gdb:objfile>' procedures
will throw an exception if it is invalid at the time the procedure
is called.
-- Scheme Procedure: objfile-filename objfile
Return the file name of OBJFILE as a string, with symbolic links
resolved.
-- Scheme Procedure: objfile-progspace objfile
Return the '<gdb:progspace>' that this object file lives in. *Note
Progspaces In Guile::, for more on progspaces.
-- Scheme Procedure: objfile-pretty-printers objfile
Return the list of registered '<gdb:pretty-printer>' objects for
OBJFILE. *Note Guile Pretty Printing API::, for more information.
-- Scheme Procedure: set-objfile-pretty-printers! objfile printer-list
Set the list of registered '<gdb:pretty-printer>' objects for
OBJFILE to PRINTER-LIST. The PRINTER-LIST must be a list of
'<gdb:pretty-printer>' objects. *Note Guile Pretty Printing API::,
for more information.
-- Scheme Procedure: current-objfile
When auto-loading a Guile script (*note Guile Auto-loading::), GDB
sets the "current objfile" to the corresponding objfile. This
function returns the current objfile. If there is no current
objfile, this function returns '#f'.
-- Scheme Procedure: objfiles
Return a list of all the objfiles in the current program space.

File: gdb.info, Node: Frames In Guile, Next: Blocks In Guile, Prev: Objfiles In Guile, Up: Guile API
23.3.3.15 Accessing inferior stack frames from Guile.
.....................................................
When the debugged program stops, GDB is able to analyze its call stack
(*note Stack frames: Frames.). The '<gdb:frame>' class represents a
frame in the stack. A '<gdb:frame>' object is only valid while its
corresponding frame exists in the inferior's stack. If you try to use
an invalid frame object, GDB will throw a 'gdb:invalid-object' exception
(*note Guile Exception Handling::).
Two '<gdb:frame>' objects can be compared for equality with the
'equal?' function, like:
(gdb) guile (equal? (newest-frame) (selected-frame))
#t
The following frame-related procedures are provided by the '(gdb)'
module:
-- Scheme Procedure: frame? object
Return '#t' if OBJECT is a '<gdb:frame>' object. Otherwise return
'#f'.
-- Scheme Procedure: frame-valid? frame
Returns '#t' if FRAME is valid, '#f' if not. A frame object can
become invalid if the frame it refers to doesn't exist anymore in
the inferior. All '<gdb:frame>' procedures will throw an exception
if the frame is invalid at the time the procedure is called.
-- Scheme Procedure: frame-name frame
Return the function name of FRAME, or '#f' if it can't be obtained.
-- Scheme Procedure: frame-arch frame
Return the '<gdb:architecture>' object corresponding to FRAME's
architecture. *Note Architectures In Guile::.
-- Scheme Procedure: frame-type frame
Return the type of FRAME. The value can be one of:
'NORMAL_FRAME'
An ordinary stack frame.
'DUMMY_FRAME'
A fake stack frame that was created by GDB when performing an
inferior function call.
'INLINE_FRAME'
A frame representing an inlined function. The function was
inlined into a 'NORMAL_FRAME' that is older than this one.
'TAILCALL_FRAME'
A frame representing a tail call. *Note Tail Call Frames::.
'SIGTRAMP_FRAME'
A signal trampoline frame. This is the frame created by the
OS when it calls into a signal handler.
'ARCH_FRAME'
A fake stack frame representing a cross-architecture call.
'SENTINEL_FRAME'
This is like 'NORMAL_FRAME', but it is only used for the
newest frame.
-- Scheme Procedure: frame-unwind-stop-reason frame
Return an integer representing the reason why it's not possible to
find more frames toward the outermost frame. Use
'unwind-stop-reason-string' to convert the value returned by this
function to a string. The value can be one of:
'FRAME_UNWIND_NO_REASON'
No particular reason (older frames should be available).
'FRAME_UNWIND_NULL_ID'
The previous frame's analyzer returns an invalid result.
'FRAME_UNWIND_OUTERMOST'
This frame is the outermost.
'FRAME_UNWIND_UNAVAILABLE'
Cannot unwind further, because that would require knowing the
values of registers or memory that have not been collected.
'FRAME_UNWIND_INNER_ID'
This frame ID looks like it ought to belong to a NEXT frame,
but we got it for a PREV frame. Normally, this is a sign of
unwinder failure. It could also indicate stack corruption.
'FRAME_UNWIND_SAME_ID'
This frame has the same ID as the previous one. That means
that unwinding further would almost certainly give us another
frame with exactly the same ID, so break the chain. Normally,
this is a sign of unwinder failure. It could also indicate
stack corruption.
'FRAME_UNWIND_NO_SAVED_PC'
The frame unwinder did not find any saved PC, but we needed
one to unwind further.
'FRAME_UNWIND_MEMORY_ERROR'
The frame unwinder caused an error while trying to access
memory.
'FRAME_UNWIND_FIRST_ERROR'
Any stop reason greater or equal to this value indicates some
kind of error. This special value facilitates writing code
that tests for errors in unwinding in a way that will work
correctly even if the list of the other values is modified in
future GDB versions. Using it, you could write:
(define reason (frame-unwind-stop-readon (selected-frame)))
(define reason-str (unwind-stop-reason-string reason))
(if (>= reason FRAME_UNWIND_FIRST_ERROR)
(format #t "An error occured: ~s\n" reason-str))
-- Scheme Procedure: frame-pc frame
Return the frame's resume address.
-- Scheme Procedure: frame-block frame
Return the frame's code block as a '<gdb:block>' object. *Note
Blocks In Guile::.
-- Scheme Procedure: frame-function frame
Return the symbol for the function corresponding to this frame as a
'<gdb:symbol>' object, or '#f' if there isn't one. *Note Symbols
In Guile::.
-- Scheme Procedure: frame-older frame
Return the frame that called FRAME.
-- Scheme Procedure: frame-newer frame
Return the frame called by FRAME.
-- Scheme Procedure: frame-sal frame
Return the frame's '<gdb:sal>' (symtab and line) object. *Note
Symbol Tables In Guile::.
-- Scheme Procedure: frame-read-register frame register
Return the value of REGISTER in FRAME. REGISTER should be a
string, like 'pc'.
-- Scheme Procedure: frame-read-var frame variable [#:block block]
Return the value of VARIABLE in FRAME. If the optional argument
BLOCK is provided, search for the variable from that block;
otherwise start at the frame's current block (which is determined
by the frame's current program counter). The VARIABLE must be
given as a string or a '<gdb:symbol>' object, and BLOCK must be a
'<gdb:block>' object.
-- Scheme Procedure: frame-select frame
Set FRAME to be the selected frame. *Note Examining the Stack:
Stack.
-- Scheme Procedure: selected-frame
Return the selected frame object. *Note Selecting a Frame:
Selection.
-- Scheme Procedure: newest-frame
Return the newest frame object for the selected thread.
-- Scheme Procedure: unwind-stop-reason-string reason
Return a string explaining the reason why GDB stopped unwinding
frames, as expressed by the given REASON code (an integer, see the
'frame-unwind-stop-reason' procedure above in this section).

File: gdb.info, Node: Blocks In Guile, Next: Symbols In Guile, Prev: Frames In Guile, Up: Guile API
23.3.3.16 Accessing blocks from Guile.
......................................
In GDB, symbols are stored in blocks. A block corresponds roughly to a
scope in the source code. Blocks are organized hierarchically, and are
represented individually in Guile as an object of type '<gdb:block>'.
Blocks rely on debugging information being available.
A frame has a block. Please see *note Frames In Guile::, for a more
in-depth discussion of frames.
The outermost block is known as the "global block". The global block
typically holds public global variables and functions.
The block nested just inside the global block is the "static block".
The static block typically holds file-scoped variables and functions.
GDB provides a method to get a block's superblock, but there is
currently no way to examine the sub-blocks of a block, or to iterate
over all the blocks in a symbol table (*note Symbol Tables In Guile::).
Here is a short example that should help explain blocks:
/* This is in the global block. */
int global;
/* This is in the static block. */
static int file_scope;
/* 'function' is in the global block, and 'argument' is
in a block nested inside of 'function'. */
int function (int argument)
{
/* 'local' is in a block inside 'function'. It may or may
not be in the same block as 'argument'. */
int local;
{
/* 'inner' is in a block whose superblock is the one holding
'local'. */
int inner;
/* If this call is expanded by the compiler, you may see
a nested block here whose function is 'inline_function'
and whose superblock is the one holding 'inner'. */
inline_function ();
}
}
The following block-related procedures are provided by the '(gdb)'
module:
-- Scheme Procedure: block? object
Return '#t' if OBJECT is a '<gdb:block>' object. Otherwise return
'#f'.
-- Scheme Procedure: block-valid? block
Returns '#t' if '<gdb:block>' BLOCK is valid, '#f' if not. A block
object can become invalid if the block it refers to doesn't exist
anymore in the inferior. All other '<gdb:block>' methods will
throw an exception if it is invalid at the time the procedure is
called. The block's validity is also checked during iteration over
symbols of the block.
-- Scheme Procedure: block-start block
Return the start address of '<gdb:block>' BLOCK.
-- Scheme Procedure: block-end block
Return the end address of '<gdb:block>' BLOCK.
-- Scheme Procedure: block-function block
Return the name of '<gdb:block>' BLOCK represented as a
'<gdb:symbol>' object. If the block is not named, then '#f' is
returned.
For ordinary function blocks, the superblock is the static block.
However, you should note that it is possible for a function block
to have a superblock that is not the static block - for instance
this happens for an inlined function.
-- Scheme Procedure: block-superblock block
Return the block containing '<gdb:block>' BLOCK. If the parent
block does not exist, then '#f' is returned.
-- Scheme Procedure: block-global-block block
Return the global block associated with '<gdb:block>' BLOCK.
-- Scheme Procedure: block-static-block block
Return the static block associated with '<gdb:block>' BLOCK.
-- Scheme Procedure: block-global? block
Return '#t' if '<gdb:block>' BLOCK is a global block. Otherwise
return '#f'.
-- Scheme Procedure: block-static? block
Return '#t' if '<gdb:block>' BLOCK is a static block. Otherwise
return '#f'.
-- Scheme Procedure: block-symbols
Return a list of all symbols (as <gdb:symbol> objects) in
'<gdb:block>' BLOCK.
-- Scheme Procedure: make-block-symbols-iterator block
Return an object of type '<gdb:iterator>' that will iterate over
all symbols of the block. Guile programs should not assume that a
specific block object will always contain a given symbol, since
changes in GDB features and infrastructure may cause symbols move
across blocks in a symbol table. *Note Iterators In Guile::.
-- Scheme Procedure: block-symbols-progress?
Return #t if the object is a <gdb:block-symbols-progress> object.
This object would be obtained from the 'progress' element of the
'<gdb:iterator>' object returned by 'make-block-symbols-iterator'.
-- Scheme Procedure: lookup-block pc
Return the innermost '<gdb:block>' containing the given PC value.
If the block cannot be found for the PC value specified, the
function will return '#f'.

File: gdb.info, Node: Symbols In Guile, Next: Symbol Tables In Guile, Prev: Blocks In Guile, Up: Guile API
23.3.3.17 Guile representation of Symbols.
..........................................
GDB represents every variable, function and type as an entry in a symbol
table. *Note Examining the Symbol Table: Symbols. Guile represents
these symbols in GDB with the '<gdb:symbol>' object.
The following symbol-related procedures are provided by the '(gdb)'
module:
-- Scheme Procedure: symbol? object
Return '#t' if OBJECT is an object of type '<gdb:symbol>'.
Otherwise return '#f'.
-- Scheme Procedure: symbol-valid? symbol
Return '#t' if the '<gdb:symbol>' object is valid, '#f' if not. A
'<gdb:symbol>' object can become invalid if the symbol it refers to
does not exist in GDB any longer. All other '<gdb:symbol>'
procedures will throw an exception if it is invalid at the time the
procedure is called.
-- Scheme Procedure: symbol-type symbol
Return the type of SYMBOL or '#f' if no type is recorded. The
result is an object of type '<gdb:type>'. *Note Types In Guile::.
-- Scheme Procedure: symbol-symtab symbol
Return the symbol table in which SYMBOL appears. The result is an
object of type '<gdb:symtab>'. *Note Symbol Tables In Guile::.
-- Scheme Procedure: symbol-line symbol
Return the line number in the source code at which SYMBOL was
defined. This is an integer.
-- Scheme Procedure: symbol-name symbol
Return the name of SYMBOL as a string.
-- Scheme Procedure: symbol-linkage-name symbol
Return the name of SYMBOL, as used by the linker (i.e., may be
mangled).
-- Scheme Procedure: symbol-print-name symbol
Return the name of SYMBOL in a form suitable for output. This is
either 'name' or 'linkage_name', depending on whether the user
asked GDB to display demangled or mangled names.
-- Scheme Procedure: symbol-addr-class symbol
Return the address class of the symbol. This classifies how to
find the value of a symbol. Each address class is a constant
defined in the '(gdb)' module and described later in this chapter.
-- Scheme Procedure: symbol-needs-frame? symbol
Return '#t' if evaluating SYMBOL's value requires a frame (*note
Frames In Guile::) and '#f' otherwise. Typically, local variables
will require a frame, but other symbols will not.
-- Scheme Procedure: symbol-argument? symbol
Return '#t' if SYMBOL is an argument of a function. Otherwise
return '#f'.
-- Scheme Procedure: symbol-constant? symbol
Return '#t' if SYMBOL is a constant. Otherwise return '#f'.
-- Scheme Procedure: symbol-function? symbol
Return '#t' if SYMBOL is a function or a method. Otherwise return
'#f'.
-- Scheme Procedure: symbol-variable? symbol
Return '#t' if SYMBOL is a variable. Otherwise return '#f'.
-- Scheme Procedure: symbol-value symbol [#:frame frame]
Compute the value of SYMBOL, as a '<gdb:value>'. For functions,
this computes the address of the function, cast to the appropriate
type. If the symbol requires a frame in order to compute its
value, then FRAME must be given. If FRAME is not given, or if
FRAME is invalid, then an exception is thrown.
-- Scheme Procedure: lookup-symbol name [#:block block] [#:domain
domain]
This function searches for a symbol by name. The search scope can
be restricted to the parameters defined in the optional domain and
block arguments.
NAME is the name of the symbol. It must be a string. The optional
BLOCK argument restricts the search to symbols visible in that
BLOCK. The BLOCK argument must be a '<gdb:block>' object. If
omitted, the block for the current frame is used. The optional
DOMAIN argument restricts the search to the domain type. The
DOMAIN argument must be a domain constant defined in the '(gdb)'
module and described later in this chapter.
The result is a list of two elements. The first element is a
'<gdb:symbol>' object or '#f' if the symbol is not found. If the
symbol is found, the second element is '#t' if the symbol is a
field of a method's object (e.g., 'this' in C++), otherwise it is
'#f'. If the symbol is not found, the second element is '#f'.
-- Scheme Procedure: lookup-global-symbol name [#:domain domain]
This function searches for a global symbol by name. The search
scope can be restricted by the domain argument.
NAME is the name of the symbol. It must be a string. The optional
DOMAIN argument restricts the search to the domain type. The
DOMAIN argument must be a domain constant defined in the '(gdb)'
module and described later in this chapter.
The result is a '<gdb:symbol>' object or '#f' if the symbol is not
found.
The available domain categories in '<gdb:symbol>' are represented as
constants in the '(gdb)' module:
'SYMBOL_UNDEF_DOMAIN'
This is used when a domain has not been discovered or none of the
following domains apply. This usually indicates an error either in
the symbol information or in GDB's handling of symbols.
'SYMBOL_VAR_DOMAIN'
This domain contains variables, function names, typedef names and
enum type values.
'SYMBOL_STRUCT_DOMAIN'
This domain holds struct, union and enum type names.
'SYMBOL_LABEL_DOMAIN'
This domain contains names of labels (for gotos).
'SYMBOL_VARIABLES_DOMAIN'
This domain holds a subset of the 'SYMBOLS_VAR_DOMAIN'; it contains
everything minus functions and types.
'SYMBOL_FUNCTION_DOMAIN'
This domain contains all functions.
'SYMBOL_TYPES_DOMAIN'
This domain contains all types.
The available address class categories in '<gdb:symbol>' are
represented as constants in the 'gdb' module:
'SYMBOL_LOC_UNDEF'
If this is returned by address class, it indicates an error either
in the symbol information or in GDB's handling of symbols.
'SYMBOL_LOC_CONST'
Value is constant int.
'SYMBOL_LOC_STATIC'
Value is at a fixed address.
'SYMBOL_LOC_REGISTER'
Value is in a register.
'SYMBOL_LOC_ARG'
Value is an argument. This value is at the offset stored within
the symbol inside the frame's argument list.
'SYMBOL_LOC_REF_ARG'
Value address is stored in the frame's argument list. Just like
'LOC_ARG' except that the value's address is stored at the offset,
not the value itself.
'SYMBOL_LOC_REGPARM_ADDR'
Value is a specified register. Just like 'LOC_REGISTER' except the
register holds the address of the argument instead of the argument
itself.
'SYMBOL_LOC_LOCAL'
Value is a local variable.
'SYMBOL_LOC_TYPEDEF'
Value not used. Symbols in the domain 'SYMBOL_STRUCT_DOMAIN' all
have this class.
'SYMBOL_LOC_BLOCK'
Value is a block.
'SYMBOL_LOC_CONST_BYTES'
Value is a byte-sequence.
'SYMBOL_LOC_UNRESOLVED'
Value is at a fixed address, but the address of the variable has to
be determined from the minimal symbol table whenever the variable
is referenced.
'SYMBOL_LOC_OPTIMIZED_OUT'
The value does not actually exist in the program.
'SYMBOL_LOC_COMPUTED'
The value's address is a computed location.

File: gdb.info, Node: Symbol Tables In Guile, Next: Breakpoints In Guile, Prev: Symbols In Guile, Up: Guile API
23.3.3.18 Symbol table representation in Guile.
...............................................
Access to symbol table data maintained by GDB on the inferior is exposed
to Guile via two objects: '<gdb:sal>' (symtab-and-line) and
'<gdb:symtab>'. Symbol table and line data for a frame is returned from
the 'frame-find-sal' '<gdb:frame>' procedure. *Note Frames In Guile::.
For more information on GDB's symbol table management, see *note
Examining the Symbol Table: Symbols.
The following symtab-related procedures are provided by the '(gdb)'
module:
-- Scheme Procedure: symtab? object
Return '#t' if OBJECT is an object of type '<gdb:symtab>'.
Otherwise return '#f'.
-- Scheme Procedure: symtab-valid? symtab
Return '#t' if the '<gdb:symtab>' object is valid, '#f' if not. A
'<gdb:symtab>' object becomes invalid when the symbol table it
refers to no longer exists in GDB. All other '<gdb:symtab>'
procedures will throw an exception if it is invalid at the time the
procedure is called.
-- Scheme Procedure: symtab-filename symtab
Return the symbol table's source filename.
-- Scheme Procedure: symtab-fullname symtab
Return the symbol table's source absolute file name.
-- Scheme Procedure: symtab-objfile symtab
Return the symbol table's backing object file. *Note Objfiles In
Guile::.
-- Scheme Procedure: symtab-global-block symtab
Return the global block of the underlying symbol table. *Note
Blocks In Guile::.
-- Scheme Procedure: symtab-static-block symtab
Return the static block of the underlying symbol table. *Note
Blocks In Guile::.
The following symtab-and-line-related procedures are provided by the
'(gdb)' module:
-- Scheme Procedure: sal? object
Return '#t' if OBJECT is an object of type '<gdb:sal>'. Otherwise
return '#f'.
-- Scheme Procedure: sal-valid? sal
Return '#t' if SAL is valid, '#f' if not. A '<gdb:sal>' object
becomes invalid when the Symbol table object it refers to no longer
exists in GDB. All other '<gdb:sal>' procedures will throw an
exception if it is invalid at the time the procedure is called.
-- Scheme Procedure: sal-symtab sal
Return the symbol table object ('<gdb:symtab>') for SAL.
-- Scheme Procedure: sal-line sal
Return the line number for SAL.
-- Scheme Procedure: sal-pc sal
Return the start of the address range occupied by code for SAL.
-- Scheme Procedure: sal-last sal
Return the end of the address range occupied by code for SAL.
-- Scheme Procedure: find-pc-line pc
Return the '<gdb:sal>' object corresponding to the PC value. If an
invalid value of PC is passed as an argument, then the 'symtab' and
'line' attributes of the returned '<gdb:sal>' object will be '#f'
and 0 respectively.

File: gdb.info, Node: Breakpoints In Guile, Next: Lazy Strings In Guile, Prev: Symbol Tables In Guile, Up: Guile API
23.3.3.19 Manipulating breakpoints using Guile
..............................................
Breakpoints in Guile are represented by objects of type
'<gdb:breakpoint>'. New breakpoints can be created with the
'make-breakpoint' Guile function, and then added to GDB with the
'register-breakpoint!' Guile function. This two-step approach is taken
to separate out the side-effect of adding the breakpoint to GDB from
'make-breakpoint'.
Support is also provided to view and manipulate breakpoints created
outside of Guile.
The following breakpoint-related procedures are provided by the
'(gdb)' module:
-- Scheme Procedure: make-breakpoint location [#:type type] [#:wp-class
wp-class] [#:internal internal]
Create a new breakpoint at LOCATION, a string naming the location
of the breakpoint, or an expression that defines a watchpoint. The
contents can be any location recognized by the 'break' command, or
in the case of a watchpoint, by the 'watch' command.
The breakpoint is initially marked as 'invalid'. The breakpoint is
not usable until it has been registered with GDB with
'register-breakpoint!', at which point it becomes 'valid'. The
result is the '<gdb:breakpoint>' object representing the
breakpoint.
The optional TYPE denotes the breakpoint to create. This argument
can be either 'BP_BREAKPOINT' or 'BP_WATCHPOINT', and defaults to
'BP_BREAKPOINT'.
The optional WP-CLASS argument defines the class of watchpoint to
create, if TYPE is 'BP_WATCHPOINT'. If a watchpoint class is not
provided, it is assumed to be a 'WP_WRITE' class.
The optional INTERNAL argument allows the breakpoint to become
invisible to the user. The breakpoint will neither be reported
when registered, nor will it be listed in the output from 'info
breakpoints' (but will be listed with the 'maint info breakpoints'
command). If an internal flag is not provided, the breakpoint is
visible (non-internal).
When a watchpoint is created, GDB will try to create a hardware
assisted watchpoint. If successful, the type of the watchpoint is
changed from 'BP_WATCHPOINT' to 'BP_HARDWARE_WATCHPOINT' for
'WP_WRITE', 'BP_READ_WATCHPOINT' for 'WP_READ', and
'BP_ACCESS_WATCHPOINT' for 'WP_ACCESS'. If not successful, the
type of the watchpoint is left as 'WP_WATCHPOINT'.
The available types are represented by constants defined in the
'gdb' module:
'BP_BREAKPOINT'
Normal code breakpoint.
'BP_WATCHPOINT'
Watchpoint breakpoint.
'BP_HARDWARE_WATCHPOINT'
Hardware assisted watchpoint. This value cannot be specified
when creating the breakpoint.
'BP_READ_WATCHPOINT'
Hardware assisted read watchpoint. This value cannot be
specified when creating the breakpoint.
'BP_ACCESS_WATCHPOINT'
Hardware assisted access watchpoint. This value cannot be
specified when creating the breakpoint.
The available watchpoint types represented by constants are defined
in the '(gdb)' module:
'WP_READ'
Read only watchpoint.
'WP_WRITE'
Write only watchpoint.
'WP_ACCESS'
Read/Write watchpoint.
-- Scheme Procedure: register-breakpoint! breakpoint
Add BREAKPOINT, a '<gdb:breakpoint>' object, to GDB's list of
breakpoints. The breakpoint must have been created with
'make-breakpoint'. One cannot register breakpoints that have been
created outside of Guile. Once a breakpoint is registered it
becomes 'valid'. It is an error to register an already registered
breakpoint. The result is unspecified.
-- Scheme Procedure: delete-breakpoint! breakpoint
Remove BREAKPOINT from GDB's list of breakpoints. This also
invalidates the Guile BREAKPOINT object. Any further attempt to
access the object will throw an exception.
If BREAKPOINT was created from Guile with 'make-breakpoint' it may
be re-registered with GDB, in which case the breakpoint becomes
valid again.
-- Scheme Procedure: breakpoints
Return a list of all breakpoints. Each element of the list is a
'<gdb:breakpoint>' object.
-- Scheme Procedure: breakpoint? object
Return '#t' if OBJECT is a '<gdb:breakpoint>' object, and '#f'
otherwise.
-- Scheme Procedure: breakpoint-valid? breakpoint
Return '#t' if BREAKPOINT is valid, '#f' otherwise. Breakpoints
created with 'make-breakpoint' are marked as invalid until they are
registered with GDB with 'register-breakpoint!'. A
'<gdb:breakpoint>' object can become invalid if the user deletes
the breakpoint. In this case, the object still exists, but the
underlying breakpoint does not. In the cases of watchpoint scope,
the watchpoint remains valid even if execution of the inferior
leaves the scope of that watchpoint.
-- Scheme Procedure: breakpoint-number breakpoint
Return the breakpoint's number -- the identifier used by the user
to manipulate the breakpoint.
-- Scheme Procedure: breakpoint-type breakpoint
Return the breakpoint's type -- the identifier used to determine
the actual breakpoint type or use-case.
-- Scheme Procedure: breakpoint-visible? breakpoint
Return '#t' if the breakpoint is visible to the user when hit, or
when the 'info breakpoints' command is run. Otherwise return '#f'.
-- Scheme Procedure: breakpoint-location breakpoint
Return the location of the breakpoint, as specified by the user.
It is a string. If the breakpoint does not have a location (that
is, it is a watchpoint) return '#f'.
-- Scheme Procedure: breakpoint-expression breakpoint
Return the breakpoint expression, as specified by the user. It is
a string. If the breakpoint does not have an expression (the
breakpoint is not a watchpoint) return '#f'.
-- Scheme Procedure: breakpoint-enabled? breakpoint
Return '#t' if the breakpoint is enabled, and '#f' otherwise.
-- Scheme Procedure: set-breakpoint-enabled! breakpoint flag
Set the enabled state of BREAKPOINT to FLAG. If flag is '#f' it is
disabled, otherwise it is enabled.
-- Scheme Procedure: breakpoint-silent? breakpoint
Return '#t' if the breakpoint is silent, and '#f' otherwise.
Note that a breakpoint can also be silent if it has commands and
the first command is 'silent'. This is not reported by the
'silent' attribute.
-- Scheme Procedure: set-breakpoint-silent! breakpoint flag
Set the silent state of BREAKPOINT to FLAG. If flag is '#f' the
breakpoint is made silent, otherwise it is made non-silent (or
noisy).
-- Scheme Procedure: breakpoint-ignore-count breakpoint
Return the ignore count for BREAKPOINT.
-- Scheme Procedure: set-breakpoint-ignore-count! breakpoint count
Set the ignore count for BREAKPOINT to COUNT.
-- Scheme Procedure: breakpoint-hit-count breakpoint
Return hit count of BREAKPOINT.
-- Scheme Procedure: set-breakpoint-hit-count! breakpoint count
Set the hit count of BREAKPOINT to COUNT. At present, COUNT must
be zero.
-- Scheme Procedure: breakpoint-thread breakpoint
Return the thread-id for thread-specific breakpoint BREAKPOINT.
Return #f if BREAKPOINT is not thread-specific.
-- Scheme Procedure: set-breakpoint-thread! breakpoint thread-id|#f
Set the thread-id for BREAKPOINT to THREAD-ID. If set to '#f', the
breakpoint is no longer thread-specific.
-- Scheme Procedure: breakpoint-task breakpoint
If the breakpoint is Ada task-specific, return the Ada task id. If
the breakpoint is not task-specific (or the underlying language is
not Ada), return '#f'.
-- Scheme Procedure: set-breakpoint-task! breakpoint task
Set the Ada task of BREAKPOINT to TASK. If set to '#f', the
breakpoint is no longer task-specific.
-- Scheme Procedure: breakpoint-condition breakpoint
Return the condition of BREAKPOINT, as specified by the user. It
is a string. If there is no condition, return '#f'.
-- Scheme Procedure: set-breakpoint-condition! breakpoint condition
Set the condition of BREAKPOINT to CONDITION, which must be a
string. If set to '#f' then the breakpoint becomes unconditional.
-- Scheme Procedure: breakpoint-stop breakpoint
Return the stop predicate of BREAKPOINT. See
'set-breakpoint-stop!' below in this section.
-- Scheme Procedure: set-breakpoint-stop! breakpoint procedure|#f
Set the stop predicate of BREAKPOINT. The predicate PROCEDURE
takes one argument: the <gdb:breakpoint> object. If this predicate
is set to a procedure then it is invoked whenever the inferior
reaches this breakpoint. If it returns '#t', or any non-'#f'
value, then the inferior is stopped, otherwise the inferior will
continue.
If there are multiple breakpoints at the same location with a
'stop' predicate, each one will be called regardless of the return
status of the previous. This ensures that all 'stop' predicates
have a chance to execute at that location. In this scenario if one
of the methods returns '#t' but the others return '#f', the
inferior will still be stopped.
You should not alter the execution state of the inferior (i.e.,
step, next, etc.), alter the current frame context (i.e., change
the current active frame), or alter, add or delete any breakpoint.
As a general rule, you should not alter any data within GDB or the
inferior at this time.
Example 'stop' implementation:
(define (my-stop? bkpt)
(let ((int-val (parse-and-eval "foo")))
(value=? int-val 3)))
(define bkpt (make-breakpoint "main.c:42"))
(register-breakpoint! bkpt)
(set-breakpoint-stop! bkpt my-stop?)
-- Scheme Procedure: breakpoint-commands breakpoint
Return the commands attached to BREAKPOINT as a string, or '#f' if
there are none.

File: gdb.info, Node: Lazy Strings In Guile, Next: Architectures In Guile, Prev: Breakpoints In Guile, Up: Guile API
23.3.3.20 Guile representation of lazy strings.
...............................................
A "lazy string" is a string whose contents is not retrieved or encoded
until it is needed.
A '<gdb:lazy-string>' is represented in GDB as an 'address' that
points to a region of memory, an 'encoding' that will be used to encode
that region of memory, and a 'length' to delimit the region of memory
that represents the string. The difference between a
'<gdb:lazy-string>' and a string wrapped within a '<gdb:value>' is that
a '<gdb:lazy-string>' will be treated differently by GDB when printing.
A '<gdb:lazy-string>' is retrieved and encoded during printing, while a
'<gdb:value>' wrapping a string is immediately retrieved and encoded on
creation.
The following lazy-string-related procedures are provided by the
'(gdb)' module:
-- Scheme Procedure: lazy-string? object
Return '#t' if OBJECT is an object of type '<gdb:lazy-string>'.
Otherwise return '#f'.
-- Scheme Procedure: lazy-string-address lazy-sring
Return the address of LAZY-STRING.
-- Scheme Procedure: lazy-string-length lazy-string
Return the length of LAZY-STRING in characters. If the length is
-1, then the string will be fetched and encoded up to the first
null of appropriate width.
-- Scheme Procedure: lazy-string-encoding lazy-string
Return the encoding that will be applied to LAZY-STRING when the
string is printed by GDB. If the encoding is not set, or contains
an empty string, then GDB will select the most appropriate encoding
when the string is printed.
-- Scheme Procedure: lazy-string-type lazy-string
Return the type that is represented by LAZY-STRING's type. For a
lazy string this will always be a pointer type. To resolve this to
the lazy string's character type, use 'type-target-type'. *Note
Types In Guile::.
-- Scheme Procedure: lazy-string->value lazy-string
Convert the '<gdb:lazy-string>' to a '<gdb:value>'. This value
will point to the string in memory, but will lose all the delayed
retrieval, encoding and handling that GDB applies to a
'<gdb:lazy-string>'.

File: gdb.info, Node: Architectures In Guile, Next: Disassembly In Guile, Prev: Lazy Strings In Guile, Up: Guile API
23.3.3.21 Guile representation of architectures
...............................................
GDB uses architecture specific parameters and artifacts in a number of
its various computations. An architecture is represented by an instance
of the '<gdb:arch>' class.
The following architecture-related procedures are provided by the
'(gdb)' module:
-- Scheme Procedure: arch? object
Return '#t' if OBJECT is an object of type '<gdb:arch>'. Otherwise
return '#f'.
-- Scheme Procedure: current-arch
Return the current architecture as a '<gdb:arch>' object.
-- Scheme Procedure: arch-name arch
Return the name (string value) of '<gdb:arch>' ARCH.
-- Scheme Procedure: arch-charset arch
Return name of target character set of '<gdb:arch>' ARCH.
-- Scheme Procedure: arch-wide-charset
Return name of target wide character set of '<gdb:arch>' ARCH.
Each architecture provides a set of predefined types, obtained by the
following functions.
-- Scheme Procedure: arch-void-type arch
Return the '<gdb:type>' object for a 'void' type of architecture
ARCH.
-- Scheme Procedure: arch-char-type arch
Return the '<gdb:type>' object for a 'char' type of architecture
ARCH.
-- Scheme Procedure: arch-short-type arch
Return the '<gdb:type>' object for a 'short' type of architecture
ARCH.
-- Scheme Procedure: arch-int-type arch
Return the '<gdb:type>' object for an 'int' type of architecture
ARCH.
-- Scheme Procedure: arch-long-type arch
Return the '<gdb:type>' object for a 'long' type of architecture
ARCH.
-- Scheme Procedure: arch-schar-type arch
Return the '<gdb:type>' object for a 'signed char' type of
architecture ARCH.
-- Scheme Procedure: arch-uchar-type arch
Return the '<gdb:type>' object for an 'unsigned char' type of
architecture ARCH.
-- Scheme Procedure: arch-ushort-type arch
Return the '<gdb:type>' object for an 'unsigned short' type of
architecture ARCH.
-- Scheme Procedure: arch-uint-type arch
Return the '<gdb:type>' object for an 'unsigned int' type of
architecture ARCH.
-- Scheme Procedure: arch-ulong-type arch
Return the '<gdb:type>' object for an 'unsigned long' type of
architecture ARCH.
-- Scheme Procedure: arch-float-type arch
Return the '<gdb:type>' object for a 'float' type of architecture
ARCH.
-- Scheme Procedure: arch-double-type arch
Return the '<gdb:type>' object for a 'double' type of architecture
ARCH.
-- Scheme Procedure: arch-longdouble-type arch
Return the '<gdb:type>' object for a 'long double' type of
architecture ARCH.
-- Scheme Procedure: arch-bool-type arch
Return the '<gdb:type>' object for a 'bool' type of architecture
ARCH.
-- Scheme Procedure: arch-longlong-type arch
Return the '<gdb:type>' object for a 'long long' type of
architecture ARCH.
-- Scheme Procedure: arch-ulonglong-type arch
Return the '<gdb:type>' object for an 'unsigned long long' type of
architecture ARCH.
-- Scheme Procedure: arch-int8-type arch
Return the '<gdb:type>' object for an 'int8' type of architecture
ARCH.
-- Scheme Procedure: arch-uint8-type arch
Return the '<gdb:type>' object for a 'uint8' type of architecture
ARCH.
-- Scheme Procedure: arch-int16-type arch
Return the '<gdb:type>' object for an 'int16' type of architecture
ARCH.
-- Scheme Procedure: arch-uint16-type arch
Return the '<gdb:type>' object for a 'uint16' type of architecture
ARCH.
-- Scheme Procedure: arch-int32-type arch
Return the '<gdb:type>' object for an 'int32' type of architecture
ARCH.
-- Scheme Procedure: arch-uint32-type arch
Return the '<gdb:type>' object for a 'uint32' type of architecture
ARCH.
-- Scheme Procedure: arch-int64-type arch
Return the '<gdb:type>' object for an 'int64' type of architecture
ARCH.
-- Scheme Procedure: arch-uint64-type arch
Return the '<gdb:type>' object for a 'uint64' type of architecture
ARCH.
Example:
(gdb) guile (type-name (arch-uchar-type (current-arch)))
"unsigned char"

File: gdb.info, Node: Disassembly In Guile, Next: I/O Ports in Guile, Prev: Architectures In Guile, Up: Guile API
23.3.3.22 Disassembly In Guile
..............................
The disassembler can be invoked from Scheme code. Furthermore, the
disassembler can take a Guile port as input, allowing one to disassemble
from any source, and not just target memory.
-- Scheme Procedure: arch-disassemble arch start-pc [#:port port]
[#:offset offset] [#:size size] [#:count count]
Return a list of disassembled instructions starting from the memory
address START-PC.
The optional argument PORT specifies the input port to read bytes
from. If PORT is '#f' then bytes are read from target memory.
The optional argument OFFSET specifies the address offset of the
first byte in PORT. This is useful, for example, when PORT
specifies a 'bytevector' and you want the bytevector to be
disassembled as if it came from that address. The START-PC passed
to the reader for PORT is offset by the same amount.
Example:
(gdb) guile (use-modules (rnrs io ports))
(gdb) guile (define pc (value->integer (parse-and-eval "$pc")))
(gdb) guile (define mem (open-memory #:start pc))
(gdb) guile (define bv (get-bytevector-n mem 10))
(gdb) guile (define bv-port (open-bytevector-input-port bv))
(gdb) guile (define arch (current-arch))
(gdb) guile (arch-disassemble arch pc #:port bv-port #:offset pc)
(((address . 4195516) (asm . "mov $0x4005c8,%edi") (length . 5)))
The optional arguments SIZE and COUNT determine the number of
instructions in the returned list. If either SIZE or COUNT is
specified as zero, then no instructions are disassembled and an
empty list is returned. If both the optional arguments SIZE and
COUNT are specified, then a list of at most COUNT disassembled
instructions whose start address falls in the closed memory address
interval from START-PC to (START-PC + SIZE - 1) are returned. If
SIZE is not specified, but COUNT is specified, then COUNT number of
instructions starting from the address START-PC are returned. If
COUNT is not specified but SIZE is specified, then all instructions
whose start address falls in the closed memory address interval
from START-PC to (START-PC + SIZE - 1) are returned. If neither
SIZE nor COUNT are specified, then a single instruction at START-PC
is returned.
Each element of the returned list is an alist (associative list)
with the following keys:
'address'
The value corresponding to this key is a Guile integer of the
memory address of the instruction.
'asm'
The value corresponding to this key is a string value which
represents the instruction with assembly language mnemonics.
The assembly language flavor used is the same as that
specified by the current CLI variable 'disassembly-flavor'.
*Note Machine Code::.
'length'
The value corresponding to this key is the length of the
instruction in bytes.

File: gdb.info, Node: I/O Ports in Guile, Next: Memory Ports in Guile, Prev: Disassembly In Guile, Up: Guile API
23.3.3.23 I/O Ports in Guile
............................
-- Scheme Procedure: input-port
Return GDB's input port as a Guile port object.
-- Scheme Procedure: output-port
Return GDB's output port as a Guile port object.
-- Scheme Procedure: error-port
Return GDB's error port as a Guile port object.
-- Scheme Procedure: stdio-port? object
Return '#t' if OBJECT is a GDB stdio port. Otherwise return '#f'.

File: gdb.info, Node: Memory Ports in Guile, Next: Iterators In Guile, Prev: I/O Ports in Guile, Up: Guile API
23.3.3.24 Memory Ports in Guile
...............................
GDB provides a 'port' interface to target memory. This allows Guile
code to read/write target memory using Guile's port and bytevector
functionality. The main routine is 'open-memory' which returns a port
object. One can then read/write memory using that object.
-- Scheme Procedure: open-memory [#:mode mode] [#:start address]
[#:size size]
Return a port object that can be used for reading and writing
memory. The port will be open according to MODE, which is the
standard mode argument to Guile port open routines, except that the
'"a"' and '"l"' modes are not supported. *Note (guile)File
Ports::. The '"b"' (binary) character may be present, but is
ignored: memory ports are binary only. If '"0"' is appended then
the port is marked as unbuffered. The default is '"r"', read-only
and buffered.
The chunk of memory that can be accessed can be bounded. If both
START and SIZE are unspecified, all of memory can be accessed. If
only START is specified, all of memory from that point on can be
accessed. If only SIZE if specified, all memory in the range
[0,SIZE) can be accessed. If both are specified, all memory in the
rane [START,START+SIZE) can be accessed.
-- Scheme Procedure: memory-port?
Return '#t' if OBJECT is an object of type '<gdb:memory-port>'.
Otherwise return '#f'.
-- Scheme Procedure: memory-port-range memory-port
Return the range of '<gdb:memory-port>' MEMORY-PORT as a list of
two elements: '(start end)'. The range is START to END inclusive.
-- Scheme Procedure: memory-port-read-buffer-size memory-port
Return the size of the read buffer of '<gdb:memory-port>'
MEMORY-PORT.
-- Scheme Procedure: set-memory-port-read-buffer-size! memory-port size
Set the size of the read buffer of '<gdb:memory-port>' MEMORY-PORT
to SIZE. The result is unspecified.
-- Scheme Procedure: memory-port-write-buffer-size memory-port
Return the size of the write buffer of '<gdb:memory-port>'
MEMORY-PORT.
-- Scheme Procedure: set-memory-port-write-buffer-size! memory-port
size
Set the size of the write buffer of '<gdb:memory-port>' MEMORY-PORT
to SIZE. The result is unspecified.
A memory port is closed like any other port, with 'close-port'.
Combined with Guile's 'bytevectors', memory ports provide a lot of
utility. For example, to fill a buffer of 10 integers in memory, one
can do something like the following.
;; In the program: int buffer[10];
(use-modules (rnrs bytevectors))
(use-modules (rnrs io ports))
(define addr (parse-and-eval "buffer"))
(define n 10)
(define byte-size (* n 4))
(define mem-port (open-memory #:mode "r+" #:start
(value->integer addr) #:size byte-size))
(define byte-vec (make-bytevector byte-size))
(do ((i 0 (+ i 1)))
((>= i n))
(bytevector-s32-native-set! byte-vec (* i 4) (* i 42)))
(put-bytevector mem-port byte-vec)
(close-port mem-port)

File: gdb.info, Node: Iterators In Guile, Prev: Memory Ports in Guile, Up: Guile API
23.3.3.25 Iterators In Guile
............................
A simple iterator facility is provided to allow, for example, iterating
over the set of program symbols without having to first construct a list
of all of them. A useful contribution would be to add support for SRFI
41 and SRFI 45.
-- Scheme Procedure: make-iterator object progress next!
A '<gdb:iterator>' object is constructed with the 'make-iterator'
procedure. It takes three arguments: the object to be iterated
over, an object to record the progress of the iteration, and a
procedure to return the next element in the iteration, or an
implementation chosen value to denote the end of iteration.
By convention, end of iteration is marked with
'(end-of-iteration)', and may be tested with the
'end-of-iteration?' predicate. The result of '(end-of-iteration)'
is chosen so that it is not otherwise used by the '(gdb)' module.
If you are using '<gdb:iterator>' in your own code it is your
responsibility to maintain this invariant.
A trivial example for illustration's sake:
(use-modules (gdb iterator))
(define my-list (list 1 2 3))
(define iter
(make-iterator my-list my-list
(lambda (iter)
(let ((l (iterator-progress iter)))
(if (eq? l '())
(end-of-iteration)
(begin
(set-iterator-progress! iter (cdr l))
(car l)))))))
Here is a slightly more realistic example, which computes a list of
all the functions in 'my-global-block'.
(use-modules (gdb iterator))
(define this-sal (find-pc-line (frame-pc (selected-frame))))
(define this-symtab (sal-symtab this-sal))
(define this-global-block (symtab-global-block this-symtab))
(define syms-iter (make-block-symbols-iterator this-global-block))
(define functions (iterator-filter symbol-function? syms-iter))
-- Scheme Procedure: iterator? object
Return '#t' if OBJECT is a '<gdb:iterator>' object. Otherwise
return '#f'.
-- Scheme Procedure: iterator-object iterator
Return the first argument that was passed to 'make-iterator'. This
is the object being iterated over.
-- Scheme Procedure: iterator-progress iterator
Return the object tracking iteration progress.
-- Scheme Procedure: set-iterator-progress! iterator new-value
Set the object tracking iteration progress.
-- Scheme Procedure: iterator-next! iterator
Invoke the procedure that was the third argument to
'make-iterator', passing it one argument, the '<gdb:iterator>'
object. The result is either the next element in the iteration, or
an end marker as implemented by the 'next!' procedure. By
convention the end marker is the result of '(end-of-iteration)'.
-- Scheme Procedure: end-of-iteration
Return the Scheme object that denotes end of iteration.
-- Scheme Procedure: end-of-iteration? object
Return '#t' if OBJECT is the end of iteration marker. Otherwise
return '#f'.
These functions are provided by the '(gdb iterator)' module to assist
in using iterators.
-- Scheme Procedure: make-list-iterator list
Return a '<gdb:iterator>' object that will iterate over LIST.
-- Scheme Procedure: iterator->list iterator
Return the elements pointed to by ITERATOR as a list.
-- Scheme Procedure: iterator-map proc iterator
Return the list of objects obtained by applying PROC to the object
pointed to by ITERATOR and to each subsequent object.
-- Scheme Procedure: iterator-for-each proc iterator
Apply PROC to each element pointed to by ITERATOR. The result is
unspecified.
-- Scheme Procedure: iterator-filter pred iterator
Return the list of elements pointed to by ITERATOR that satisfy
PRED.
-- Scheme Procedure: iterator-until pred iterator
Run ITERATOR until the result of '(pred element)' is true and
return that as the result. Otherwise return '#f'.

File: gdb.info, Node: Guile Auto-loading, Next: Guile Modules, Prev: Guile API, Up: Guile
23.3.4 Guile Auto-loading
-------------------------
When a new object file is read (for example, due to the 'file' command,
or because the inferior has loaded a shared library), GDB will look for
Guile support scripts in two ways: 'OBJFILE-gdb.scm' and the
'.debug_gdb_scripts' section. *Note Auto-loading extensions::.
The auto-loading feature is useful for supplying application-specific
debugging commands and scripts.
Auto-loading can be enabled or disabled, and the list of auto-loaded
scripts can be printed.
'set auto-load guile-scripts [on|off]'
Enable or disable the auto-loading of Guile scripts.
'show auto-load guile-scripts'
Show whether auto-loading of Guile scripts is enabled or disabled.
'info auto-load guile-scripts [REGEXP]'
Print the list of all Guile scripts that GDB auto-loaded.
Also printed is the list of Guile scripts that were mentioned in
the '.debug_gdb_scripts' section and were not found. This is
useful because their names are not printed when GDB tries to load
them and fails. There may be many of them, and printing an error
message for each one is problematic.
If REGEXP is supplied only Guile scripts with matching names are
printed.
Example:
(gdb) info auto-load guile-scripts
Loaded Script
Yes scm-section-script.scm
full name: /tmp/scm-section-script.scm
No my-foo-pretty-printers.scm
When reading an auto-loaded file, GDB sets the "current objfile".
This is available via the 'current-objfile' procedure (*note Objfiles In
Guile::). This can be useful for registering objfile-specific
pretty-printers.

File: gdb.info, Node: Guile Modules, Prev: Guile Auto-loading, Up: Guile
23.3.5 Guile Modules
--------------------
GDB comes with several modules to assist writing Guile code.
* Menu:
* Guile Printing Module:: Building and registering pretty-printers
* Guile Types Module:: Utilities for working with types

File: gdb.info, Node: Guile Printing Module, Next: Guile Types Module, Up: Guile Modules
23.3.5.1 Guile Printing Module
..............................
This module provides a collection of utilities for working with
pretty-printers.
Usage:
(use-modules (gdb printing))
-- Scheme Procedure: prepend-pretty-printer! object printer
Add PRINTER to the front of the list of pretty-printers for OBJECT.
The OBJECT must either be a '<gdb:objfile>' object, or '#f' in
which case PRINTER is added to the global list of printers.
-- Scheme Procecure: append-pretty-printer! object printer
Add PRINTER to the end of the list of pretty-printers for OBJECT.
The OBJECT must either be a '<gdb:objfile>' object, or '#f' in
which case PRINTER is added to the global list of printers.

File: gdb.info, Node: Guile Types Module, Prev: Guile Printing Module, Up: Guile Modules
23.3.5.2 Guile Types Module
...........................
This module provides a collection of utilities for working with
'<gdb:type>' objects.
Usage:
(use-modules (gdb types))
-- Scheme Procedure: get-basic-type type
Return TYPE with const and volatile qualifiers stripped, and with
typedefs and C++ references converted to the underlying type.
C++ example:
typedef const int const_int;
const_int foo (3);
const_int& foo_ref (foo);
int main () { return 0; }
Then in gdb:
(gdb) start
(gdb) guile (use-modules (gdb) (gdb types))
(gdb) guile (define foo-ref (parse-and-eval "foo_ref"))
(gdb) guile (get-basic-type (value-type foo-ref))
int
-- Scheme Procedure: type-has-field-deep? type field
Return '#t' if TYPE, assumed to be a type with fields (e.g., a
structure or union), has field FIELD. Otherwise return '#f'. This
searches baseclasses, whereas 'type-has-field?' does not.
-- Scheme Procedure: make-enum-hashtable enum-type
Return a Guile hash table produced from ENUM-TYPE. Elements in the
hash table are referenced with 'hashq-ref'.

File: gdb.info, Node: Auto-loading extensions, Next: Multiple Extension Languages, Prev: Guile, Up: Extending GDB
23.4 Auto-loading extensions
============================
GDB provides two mechanisms for automatically loading extensions when a
new object file is read (for example, due to the 'file' command, or
because the inferior has loaded a shared library): 'OBJFILE-gdb.EXT' and
the '.debug_gdb_scripts' section of modern file formats like ELF.
* Menu:
* objfile-gdb.ext file: objfile-gdbdotext file. The 'OBJFILE-gdb.EXT' file
* .debug_gdb_scripts section: dotdebug_gdb_scripts section. The '.debug_gdb_scripts' section
* Which flavor to choose?::
The auto-loading feature is useful for supplying application-specific
debugging commands and features.
Auto-loading can be enabled or disabled, and the list of auto-loaded
scripts can be printed. See the 'auto-loading' section of each
extension language for more information. For GDB command files see
*note Auto-loading sequences::. For Python files see *note Python
Auto-loading::.
Note that loading of this script file also requires accordingly
configured 'auto-load safe-path' (*note Auto-loading safe path::).

File: gdb.info, Node: objfile-gdbdotext file, Next: dotdebug_gdb_scripts section, Up: Auto-loading extensions
23.4.1 The 'OBJFILE-gdb.EXT' file
---------------------------------
When a new object file is read, GDB looks for a file named
'OBJFILE-gdb.EXT' (we call it SCRIPT-NAME below), where OBJFILE is the
object file's name and where EXT is the file extension for the extension
language:
'OBJFILE-gdb.gdb'
GDB's own command language
'OBJFILE-gdb.py'
Python
'OBJFILE-gdb.scm'
Guile
SCRIPT-NAME is formed by ensuring that the file name of OBJFILE is
absolute, following all symlinks, and resolving '.' and '..' components,
and appending the '-gdb.EXT' suffix. If this file exists and is
readable, GDB will evaluate it as a script in the specified extension
language.
If this file does not exist, then GDB will look for SCRIPT-NAME file
in all of the directories as specified below.
Note that loading of these files requires an accordingly configured
'auto-load safe-path' (*note Auto-loading safe path::).
For object files using '.exe' suffix GDB tries to load first the
scripts normally according to its '.exe' filename. But if no scripts
are found GDB also tries script filenames matching the object file
without its '.exe' suffix. This '.exe' stripping is case insensitive
and it is attempted on any platform. This makes the script filenames
compatible between Unix and MS-Windows hosts.
'set auto-load scripts-directory [DIRECTORIES]'
Control GDB auto-loaded scripts location. Multiple directory
entries may be delimited by the host platform path separator in use
(':' on Unix, ';' on MS-Windows and MS-DOS).
Each entry here needs to be covered also by the security setting
'set auto-load safe-path' (*note set auto-load safe-path::).
This variable defaults to '$debugdir:$datadir/auto-load'. The
default 'set auto-load safe-path' value can be also overriden by
GDB configuration option '--with-auto-load-dir'.
Any reference to '$debugdir' will get replaced by
DEBUG-FILE-DIRECTORY value (*note Separate Debug Files::) and any
reference to '$datadir' will get replaced by DATA-DIRECTORY which
is determined at GDB startup (*note Data Files::). '$debugdir' and
'$datadir' must be placed as a directory component -- either alone
or delimited by '/' or '\' directory separators, depending on the
host platform.
The list of directories uses path separator (':' on GNU and Unix
systems, ';' on MS-Windows and MS-DOS) to separate directories,
similarly to the 'PATH' environment variable.
'show auto-load scripts-directory'
Show GDB auto-loaded scripts location.
'add-auto-load-scripts-directory [DIRECTORIES...]'
Add an entry (or list of entries) to the list of auto-loaded
scripts locations. Multiple entries may be delimited by the host
platform path separator in use.
GDB does not track which files it has already auto-loaded this way.
GDB will load the associated script every time the corresponding OBJFILE
is opened. So your '-gdb.EXT' file should be careful to avoid errors if
it is evaluated more than once.

File: gdb.info, Node: dotdebug_gdb_scripts section, Next: Which flavor to choose?, Prev: objfile-gdbdotext file, Up: Auto-loading extensions
23.4.2 The '.debug_gdb_scripts' section
---------------------------------------
For systems using file formats like ELF and COFF, when GDB loads a new
object file it will look for a special section named
'.debug_gdb_scripts'. If this section exists, its contents is a list of
null-terminated entries specifying scripts to load. Each entry begins
with a non-null prefix byte that specifies the kind of entry, typically
the extension language and whether the script is in a file or inlined in
'.debug_gdb_scripts'.
The following entries are supported:
'SECTION_SCRIPT_ID_PYTHON_FILE = 1'
'SECTION_SCRIPT_ID_SCHEME_FILE = 3'
'SECTION_SCRIPT_ID_PYTHON_TEXT = 4'
'SECTION_SCRIPT_ID_SCHEME_TEXT = 6'
23.4.2.1 Script File Entries
............................
If the entry specifies a file, GDB will look for the file first in the
current directory and then along the source search path (*note
Specifying Source Directories: Source Path.), except that '$cdir' is not
searched, since the compilation directory is not relevant to scripts.
File entries can be placed in section '.debug_gdb_scripts' with, for
example, this GCC macro for Python scripts.
/* Note: The "MS" section flags are to remove duplicates. */
#define DEFINE_GDB_PY_SCRIPT(script_name) \
asm("\
.pushsection \".debug_gdb_scripts\", \"MS\",@progbits,1\n\
.byte 1 /* Python */\n\
.asciz \"" script_name "\"\n\
.popsection \n\
");
For Guile scripts, replace '.byte 1' with '.byte 3'. Then one can
reference the macro in a header or source file like this:
DEFINE_GDB_PY_SCRIPT ("my-app-scripts.py")
The script name may include directories if desired.
Note that loading of this script file also requires accordingly
configured 'auto-load safe-path' (*note Auto-loading safe path::).
If the macro invocation is put in a header, any application or
library using this header will get a reference to the specified script,
and with the use of '"MS"' attributes on the section, the linker will
remove duplicates.
23.4.2.2 Script Text Entries
............................
Script text entries allow to put the executable script in the entry
itself instead of loading it from a file. The first line of the entry,
everything after the prefix byte and up to the first newline ('0xa')
character, is the script name, and must not contain any kind of space
character, e.g., spaces or tabs. The rest of the entry, up to the
trailing null byte, is the script to execute in the specified language.
The name needs to be unique among all script names, as GDB executes each
script only once based on its name.
Here is an example from file 'py-section-script.c' in the GDB
testsuite.
#include "symcat.h"
#include "gdb/section-scripts.h"
asm(
".pushsection \".debug_gdb_scripts\", \"MS\",@progbits,1\n"
".byte " XSTRING (SECTION_SCRIPT_ID_PYTHON_TEXT) "\n"
".ascii \"gdb.inlined-script\\n\"\n"
".ascii \"class test_cmd (gdb.Command):\\n\"\n"
".ascii \" def __init__ (self):\\n\"\n"
".ascii \" super (test_cmd, self).__init__ ("
"\\\"test-cmd\\\", gdb.COMMAND_OBSCURE)\\n\"\n"
".ascii \" def invoke (self, arg, from_tty):\\n\"\n"
".ascii \" print (\\\"test-cmd output, arg = %s\\\" % arg)\\n\"\n"
".ascii \"test_cmd ()\\n\"\n"
".byte 0\n"
".popsection\n"
);
Loading of inlined scripts requires a properly configured 'auto-load
safe-path' (*note Auto-loading safe path::). The path to specify in
'auto-load safe-path' is the path of the file containing the
'.debug_gdb_scripts' section.

File: gdb.info, Node: Which flavor to choose?, Prev: dotdebug_gdb_scripts section, Up: Auto-loading extensions
23.4.3 Which flavor to choose?
------------------------------
Given the multiple ways of auto-loading extensions, it might not always
be clear which one to choose. This section provides some guidance.
Benefits of the '-gdb.EXT' way:
* Can be used with file formats that don't support multiple sections.
* Ease of finding scripts for public libraries.
Scripts specified in the '.debug_gdb_scripts' section are searched
for in the source search path. For publicly installed libraries,
e.g., 'libstdc++', there typically isn't a source directory in
which to find the script.
* Doesn't require source code additions.
Benefits of the '.debug_gdb_scripts' way:
* Works with static linking.
Scripts for libraries done the '-gdb.EXT' way require an objfile to
trigger their loading. When an application is statically linked
the only objfile available is the executable, and it is cumbersome
to attach all the scripts from all the input libraries to the
executable's '-gdb.EXT' script.
* Works with classes that are entirely inlined.
Some classes can be entirely inlined, and thus there may not be an
associated shared library to attach a '-gdb.EXT' script to.
* Scripts needn't be copied out of the source tree.
In some circumstances, apps can be built out of large collections
of internal libraries, and the build infrastructure necessary to
install the '-gdb.EXT' scripts in a place where GDB can find them
is cumbersome. It may be easier to specify the scripts in the
'.debug_gdb_scripts' section as relative paths, and add a path to
the top of the source tree to the source search path.

File: gdb.info, Node: Multiple Extension Languages, Next: Aliases, Prev: Auto-loading extensions, Up: Extending GDB
23.5 Multiple Extension Languages
=================================
The Guile and Python extension languages do not share any state, and
generally do not interfere with each other. There are some things to be
aware of, however.
23.5.1 Python comes first
-------------------------
Python was GDB's first extension language, and to avoid breaking
existing behaviour Python comes first. This is generally solved by the
"first one wins" principle. GDB maintains a list of enabled extension
languages, and when it makes a call to an extension language, (say to
pretty-print a value), it tries each in turn until an extension language
indicates it has performed the request (e.g., has returned the
pretty-printed form of a value). This extends to errors while
performing such requests: If an error happens while, for example, trying
to pretty-print an object then the error is reported and any following
extension languages are not tried.

File: gdb.info, Node: Aliases, Prev: Multiple Extension Languages, Up: Extending GDB
23.6 Creating new spellings of existing commands
================================================
It is often useful to define alternate spellings of existing commands.
For example, if a new GDB command defined in Python has a long name to
type, it is handy to have an abbreviated version of it that involves
less typing.
GDB itself uses aliases. For example 's' is an alias of the 'step'
command even though it is otherwise an ambiguous abbreviation of other
commands like 'set' and 'show'.
Aliases are also used to provide shortened or more common versions of
multi-word commands. For example, GDB provides the 'tty' alias of the
'set inferior-tty' command.
You can define a new alias with the 'alias' command.
'alias [-a] [--] ALIAS = COMMAND'
ALIAS specifies the name of the new alias. Each word of ALIAS must
consist of letters, numbers, dashes and underscores.
COMMAND specifies the name of an existing command that is being
aliased.
The '-a' option specifies that the new alias is an abbreviation of
the command. Abbreviations are not shown in command lists displayed by
the 'help' command.
The '--' option specifies the end of options, and is useful when
ALIAS begins with a dash.
Here is a simple example showing how to make an abbreviation of a
command so that there is less to type. Suppose you were tired of typing
'disas', the current shortest unambiguous abbreviation of the
'disassemble' command and you wanted an even shorter version named 'di'.
The following will accomplish this.
(gdb) alias -a di = disas
Note that aliases are different from user-defined commands. With a
user-defined command, you also need to write documentation for it with
the 'document' command. An alias automatically picks up the
documentation of the existing command.
Here is an example where we make 'elms' an abbreviation of 'elements'
in the 'set print elements' command. This is to show that you can make
an abbreviation of any part of a command.
(gdb) alias -a set print elms = set print elements
(gdb) alias -a show print elms = show print elements
(gdb) set p elms 20
(gdb) show p elms
Limit on string chars or array elements to print is 200.
Note that if you are defining an alias of a 'set' command, and you
want to have an alias for the corresponding 'show' command, then you
need to define the latter separately.
Unambiguously abbreviated commands are allowed in COMMAND and ALIAS,
just as they are normally.
(gdb) alias -a set pr elms = set p ele
Finally, here is an example showing the creation of a one word alias
for a more complex command. This creates alias 'spe' of the command
'set print elements'.
(gdb) alias spe = set print elements
(gdb) spe 20

File: gdb.info, Node: Interpreters, Next: TUI, Prev: Extending GDB, Up: Top
24 Command Interpreters
***********************
GDB supports multiple command interpreters, and some command
infrastructure to allow users or user interface writers to switch
between interpreters or run commands in other interpreters.
GDB currently supports two command interpreters, the console
interpreter (sometimes called the command-line interpreter or CLI) and
the machine interface interpreter (or GDB/MI). This manual describes
both of these interfaces in great detail.
By default, GDB will start with the console interpreter. However,
the user may choose to start GDB with another interpreter by specifying
the '-i' or '--interpreter' startup options. Defined interpreters
include:
'console'
The traditional console or command-line interpreter. This is the
most often used interpreter with GDB. With no interpreter
specified at runtime, GDB will use this interpreter.
'mi'
The newest GDB/MI interface (currently 'mi2'). Used primarily by
programs wishing to use GDB as a backend for a debugger GUI or an
IDE. For more information, see *note The GDB/MI Interface: GDB/MI.
'mi2'
The current GDB/MI interface.
'mi1'
The GDB/MI interface included in GDB 5.1, 5.2, and 5.3.
The interpreter being used by GDB may not be dynamically switched at
runtime. Although possible, this could lead to a very precarious
situation. Consider an IDE using GDB/MI. If a user enters the command
"interpreter-set console" in a console view, GDB would switch to using
the console interpreter, rendering the IDE inoperable!
Although you may only choose a single interpreter at startup, you may
execute commands in any interpreter from the current interpreter using
the appropriate command. If you are running the console interpreter,
simply use the 'interpreter-exec' command:
interpreter-exec mi "-data-list-register-names"
GDB/MI has a similar command, although it is only available in
versions of GDB which support GDB/MI version 2 (or greater).

File: gdb.info, Node: TUI, Next: Emacs, Prev: Interpreters, Up: Top
25 GDB Text User Interface
**************************
* Menu:
* TUI Overview:: TUI overview
* TUI Keys:: TUI key bindings
* TUI Single Key Mode:: TUI single key mode
* TUI Commands:: TUI-specific commands
* TUI Configuration:: TUI configuration variables
The GDB Text User Interface (TUI) is a terminal interface which uses the
'curses' library to show the source file, the assembly output, the
program registers and GDB commands in separate text windows. The TUI
mode is supported only on platforms where a suitable version of the
'curses' library is available.
The TUI mode is enabled by default when you invoke GDB as 'gdb -tui'.
You can also switch in and out of TUI mode while GDB runs by using
various TUI commands and key bindings, such as 'tui enable' or 'C-x
C-a'. *Note TUI Commands: TUI Commands, and *note TUI Key Bindings: TUI
Keys.

File: gdb.info, Node: TUI Overview, Next: TUI Keys, Up: TUI
25.1 TUI Overview
=================
In TUI mode, GDB can display several text windows:
_command_
This window is the GDB command window with the GDB prompt and the
GDB output. The GDB input is still managed using readline.
_source_
The source window shows the source file of the program. The
current line and active breakpoints are displayed in this window.
_assembly_
The assembly window shows the disassembly output of the program.
_register_
This window shows the processor registers. Registers are
highlighted when their values change.
The source and assembly windows show the current program position by
highlighting the current line and marking it with a '>' marker.
Breakpoints are indicated with two markers. The first marker indicates
the breakpoint type:
'B'
Breakpoint which was hit at least once.
'b'
Breakpoint which was never hit.
'H'
Hardware breakpoint which was hit at least once.
'h'
Hardware breakpoint which was never hit.
The second marker indicates whether the breakpoint is enabled or not:
'+'
Breakpoint is enabled.
'-'
Breakpoint is disabled.
The source, assembly and register windows are updated when the
current thread changes, when the frame changes, or when the program
counter changes.
These windows are not all visible at the same time. The command
window is always visible. The others can be arranged in several
layouts:
* source only,
* assembly only,
* source and assembly,
* source and registers, or
* assembly and registers.
A status line above the command window shows the following
information:
_target_
Indicates the current GDB target. (*note Specifying a Debugging
Target: Targets.).
_process_
Gives the current process or thread number. When no process is
being debugged, this field is set to 'No process'.
_function_
Gives the current function name for the selected frame. The name
is demangled if demangling is turned on (*note Print Settings::).
When there is no symbol corresponding to the current program
counter, the string '??' is displayed.
_line_
Indicates the current line number for the selected frame. When the
current line number is not known, the string '??' is displayed.
_pc_
Indicates the current program counter address.

File: gdb.info, Node: TUI Keys, Next: TUI Single Key Mode, Prev: TUI Overview, Up: TUI
25.2 TUI Key Bindings
=====================
The TUI installs several key bindings in the readline keymaps (*note
Command Line Editing::). The following key bindings are installed for
both TUI mode and the GDB standard mode.
'C-x C-a'
'C-x a'
'C-x A'
Enter or leave the TUI mode. When leaving the TUI mode, the curses
window management stops and GDB operates using its standard mode,
writing on the terminal directly. When reentering the TUI mode,
control is given back to the curses windows. The screen is then
refreshed.
'C-x 1'
Use a TUI layout with only one window. The layout will either be
'source' or 'assembly'. When the TUI mode is not active, it will
switch to the TUI mode.
Think of this key binding as the Emacs 'C-x 1' binding.
'C-x 2'
Use a TUI layout with at least two windows. When the current
layout already has two windows, the next layout with two windows is
used. When a new layout is chosen, one window will always be
common to the previous layout and the new one.
Think of it as the Emacs 'C-x 2' binding.
'C-x o'
Change the active window. The TUI associates several key bindings
(like scrolling and arrow keys) with the active window. This
command gives the focus to the next TUI window.
Think of it as the Emacs 'C-x o' binding.
'C-x s'
Switch in and out of the TUI SingleKey mode that binds single keys
to GDB commands (*note TUI Single Key Mode::).
The following key bindings only work in the TUI mode:
<PgUp>
Scroll the active window one page up.
<PgDn>
Scroll the active window one page down.
<Up>
Scroll the active window one line up.
<Down>
Scroll the active window one line down.
<Left>
Scroll the active window one column left.
<Right>
Scroll the active window one column right.
'C-L'
Refresh the screen.
Because the arrow keys scroll the active window in the TUI mode, they
are not available for their normal use by readline unless the command
window has the focus. When another window is active, you must use other
readline key bindings such as 'C-p', 'C-n', 'C-b' and 'C-f' to control
the command window.

File: gdb.info, Node: TUI Single Key Mode, Next: TUI Commands, Prev: TUI Keys, Up: TUI
25.3 TUI Single Key Mode
========================
The TUI also provides a "SingleKey" mode, which binds several frequently
used GDB commands to single keys. Type 'C-x s' to switch into this
mode, where the following key bindings are used:
'c'
continue
'd'
down
'f'
finish
'n'
next
'q'
exit the SingleKey mode.
'r'
run
's'
step
'u'
up
'v'
info locals
'w'
where
Other keys temporarily switch to the GDB command prompt. The key
that was pressed is inserted in the editing buffer so that it is
possible to type most GDB commands without interaction with the TUI
SingleKey mode. Once the command is entered the TUI SingleKey mode is
restored. The only way to permanently leave this mode is by typing 'q'
or 'C-x s'.