This is gdb.info, produced by makeinfo version 6.3 from gdb.texinfo. Copyright (C) 1988-2017 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 8.0.1. Copyright (C) 1988-2017 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: Types In Python, Next: Pretty Printing API, Prev: Values From Inferior, Up: Python API 23.2.2.4 Types In Python ........................ GDB represents types from the inferior using the class 'gdb.Type'. The following type-related functions are available in the 'gdb' module: -- Function: gdb.lookup_type (name [, block]) This function looks up a type by its NAME, which must be a string. If BLOCK is given, then 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. If the type is a structure or class type, or an enum type, the fields of that type can be accessed using the Python "dictionary syntax". For example, if 'some_type' is a 'gdb.Type' instance holding a structure type, you can access its 'foo' field with: bar = some_type['foo'] 'bar' will be a 'gdb.Field' object; see below under the description of the 'Type.fields' method for a description of the 'gdb.Field' class. An instance of 'Type' has the following attributes: -- Variable: Type.code The type code for this type. The type code will be one of the 'TYPE_CODE_' constants defined below. -- Variable: Type.name The name of this type. If this type has no name, then 'None' is returned. -- Variable: Type.sizeof 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. -- Variable: Type.tag The tag name for this 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 'None' is returned. The following methods are provided: -- Function: Type.fields () For structure and union types, this method returns the fields. 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 sequence will be returned. Each field is a 'gdb.Field' object, with some pre-defined attributes: 'bitpos' This attribute is not available for 'enum' or 'static' (as in C++) fields. The value is the position, counting in bits, from the start of the containing type. 'enumval' This attribute is only available for 'enum' fields, and its value is the enumeration member's integer representation. 'name' The name of the field, or 'None' for anonymous fields. 'artificial' This is 'True' if the field is artificial, usually meaning that it was provided by the compiler and not the user. This attribute is always provided, and is 'False' if the field is not artificial. 'is_base_class' This is 'True' if the field represents a base class of a C++ structure. This attribute is always provided, and is 'False' if the field is not a base class of the type that is the argument of 'fields', or if that type was not a C++ class. 'bitsize' If the field is packed, or is a bitfield, then this will have a non-zero value, which is the size of the field in bits. Otherwise, this will be zero; in this case the field's size is given by its type. 'type' The type of the field. This is usually an instance of 'Type', but it can be 'None' in some situations. 'parent_type' The type which contains this field. This is an instance of 'gdb.Type'. -- Function: Type.array (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. -- Function: Type.vector (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. -- Function: Type.const () Return a new 'gdb.Type' object which represents a 'const'-qualified variant of this type. -- Function: Type.volatile () Return a new 'gdb.Type' object which represents a 'volatile'-qualified variant of this type. -- Function: Type.unqualified () Return a new 'gdb.Type' object which represents an unqualified variant of this type. That is, the result is neither 'const' nor 'volatile'. -- Function: Type.range () Return a Python 'Tuple' object that contains two elements: the low bound of the argument type and the high bound of that type. If the type does not have a range, GDB will raise a 'gdb.error' exception (*note Exception Handling::). -- Function: Type.reference () Return a new 'gdb.Type' object which represents a reference to this type. -- Function: Type.pointer () Return a new 'gdb.Type' object which represents a pointer to this type. -- Function: Type.strip_typedefs () Return a new 'gdb.Type' that represents the real type, after removing all layers of typedefs. -- Function: Type.target () Return a new 'gdb.Type' object which represents the target type of this 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. -- Function: Type.template_argument (n [, block]) If this 'gdb.Type' is an instantiation of a template, this will return a new 'gdb.Value' or 'gdb.Type' which represents the value of the Nth template argument (indexed starting at 0). If this 'gdb.Type' is not a template type, or if the type has fewer than N template arguments, this will throw an exception. Ordinarily, only C++ code will have template types. If BLOCK is given, then NAME is looked up in that scope. Otherwise, it is searched for globally. -- Function: Type.optimized_out () Return 'gdb.Value' instance of this type whose value is optimized out. This allows a frame decorator to indicate that the value of an argument or a local variable is not known. 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: 'gdb.TYPE_CODE_PTR' The type is a pointer. 'gdb.TYPE_CODE_ARRAY' The type is an array. 'gdb.TYPE_CODE_STRUCT' The type is a structure. 'gdb.TYPE_CODE_UNION' The type is a union. 'gdb.TYPE_CODE_ENUM' The type is an enum. 'gdb.TYPE_CODE_FLAGS' A bit flags type, used for things such as status registers. 'gdb.TYPE_CODE_FUNC' The type is a function. 'gdb.TYPE_CODE_INT' The type is an integer type. 'gdb.TYPE_CODE_FLT' A floating point type. 'gdb.TYPE_CODE_VOID' The special type 'void'. 'gdb.TYPE_CODE_SET' A Pascal set type. 'gdb.TYPE_CODE_RANGE' A range type, that is, an integer type with bounds. 'gdb.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. 'gdb.TYPE_CODE_BITSTRING' A string of bits. It is deprecated. 'gdb.TYPE_CODE_ERROR' An unknown or erroneous type. 'gdb.TYPE_CODE_METHOD' A method type, as found in C++. 'gdb.TYPE_CODE_METHODPTR' A pointer-to-member-function. 'gdb.TYPE_CODE_MEMBERPTR' A pointer-to-member. 'gdb.TYPE_CODE_REF' A reference type. 'gdb.TYPE_CODE_RVALUE_REF' A C++11 rvalue reference type. 'gdb.TYPE_CODE_CHAR' A character type. 'gdb.TYPE_CODE_BOOL' A boolean type. 'gdb.TYPE_CODE_COMPLEX' A complex float type. 'gdb.TYPE_CODE_TYPEDEF' A typedef to some other type. 'gdb.TYPE_CODE_NAMESPACE' A C++ namespace. 'gdb.TYPE_CODE_DECFLOAT' A decimal floating point type. 'gdb.TYPE_CODE_INTERNAL_FUNCTION' A function internal to GDB. This is the type used to represent convenience functions. Further support for types is provided in the 'gdb.types' Python module (*note gdb.types::).  File: gdb.info, Node: Pretty Printing API, Next: Selecting Pretty-Printers, Prev: Types In Python, Up: Python API 23.2.2.5 Pretty Printing API ............................ An example output is provided (*note Pretty Printing::). A pretty-printer is just an object that holds a value and implements a specific interface, defined here. -- Function: pretty_printer.children (self) GDB will call this method on a pretty-printer to compute the children of the pretty-printer's value. This method must return an object conforming to the Python iterator protocol. 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 Python object which is convertible to a GDB value. This method is optional. If it does not exist, GDB will act as though the value has no children. -- Function: pretty_printer.display_hint (self) The CLI may call this method and use its result to change the formatting of a value. The result will also be supplied to an MI consumer as a 'displayhint' attribute of the variable being printed. This method is optional. If it does exist, this method must return a string. Some display hints 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' method returns a Python 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. -- Function: pretty_printer.to_string (self) GDB will call this method to display the string representation of the value passed to the object's constructor. 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 Python 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. Python scalars (integers, floats, and booleans) and strings are convertible to 'gdb.Value'; other types are not. Finally, if this method returns 'None' 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. GDB provides a function which can be used to look up the default pretty-printer for a 'gdb.Value': -- Function: gdb.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 'None'.  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$") 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___() def __call__(pending_frame): if not : return None # Create UnwindInfo. Usually the frame is identified by the stack # pointer and the program counter. sp = pending_frame.read_register() pc = pending_frame.read_register() 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(, ) .... # 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 MyTemplate { public: MyTemplate () : dsize_(10), data_ (new T [10]) { } ~MyTemplate () { delete [] data_; } int footprint (void) { return sizeof (T) * dsize_ + sizeof (MyTemplate); } 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. 'events.breakpoint_created' This is emitted when a new breakpoint has been created. The argument that is passed is the new 'gdb.Breakpoint' object. 'events.breakpoint_modified' This is emitted when a breakpoint has been modified in some way. The argument that is passed is the new 'gdb.Breakpoint' object. 'events.breakpoint_deleted' This is emitted when a breakpoint has been deleted. The argument that is passed is the 'gdb.Breakpoint' object. When this event is emitted, the 'gdb.Breakpoint' object will already be in its invalid state; that is, the 'is_valid' method will return 'False'. 'events.before_prompt' This event carries no payload. It is emitted each time GDB presents a prompt to the user.  File: gdb.info, Node: Threads In Python, Next: Recordings 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 The per-inferior number of the thread, as assigned by GDB. -- Variable: InferiorThread.global_num The global ID of the thread, as assigned by GDB. You can use this to make Python breakpoints thread-specific, for example (*note The Breakpoint.thread attribute: python_breakpoint_thread.). -- 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. -- Variable: InferiorThread.inferior The inferior this thread belongs to. This attribute is represented as a 'gdb.Inferior' object. This attribute is not writable. 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: Recordings In Python, Next: Commands In Python, Prev: Threads In Python, Up: Python API 23.2.2.19 Recordings In Python .............................. The following recordings-related functions (*note Process Record and Replay::) are available in the 'gdb' module: -- Function: gdb.start_recording ([method], [format]) Start a recording using the given METHOD and FORMAT. If no FORMAT is given, the default format for the recording method is used. If no METHOD is given, the default method will be used. Returns a 'gdb.Record' object on success. Throw an exception on failure. The following strings can be passed as METHOD: * '"full"' * '"btrace"': Possible values for FORMAT: '"pt"', '"bts"' or leave out for default format. -- Function: gdb.current_recording () Access a currently running recording. Return a 'gdb.Record' object on success. Return 'None' if no recording is currently active. -- Function: gdb.stop_recording () Stop the current recording. Throw an exception if no recording is currently active. All record objects become invalid after this call. A 'gdb.Record' object has the following attributes: -- Variable: Record.method A string with the current recording method, e.g. 'full' or 'btrace'. -- Variable: Record.format A string with the current recording format, e.g. 'bt', 'pts' or 'None'. -- Variable: Record.begin A method specific instruction object representing the first instruction in this recording. -- Variable: Record.end A method specific instruction object representing the current instruction, that is not actually part of the recording. -- Variable: Record.replay_position The instruction representing the current replay position. If there is no replay active, this will be 'None'. -- Variable: Record.instruction_history A list with all recorded instructions. -- Variable: Record.function_call_history A list with all recorded function call segments. A 'gdb.Record' object has the following methods: -- Function: Record.goto (instruction) Move the replay position to the given INSTRUCTION. The common 'gdb.Instruction' class that recording method specific instruction objects inherit from, has the following attributes: -- Variable: Instruction.pc An integer representing this instruction's address. -- Variable: Instruction.data A buffer with the raw instruction data. In Python 3, the return value is a 'memoryview' object. -- Variable: Instruction.decoded A human readable string with the disassembled instruction. -- Variable: Instruction.size The size of the instruction in bytes. Additionally 'gdb.RecordInstruction' has the following attributes: -- Variable: RecordInstruction.number An integer identifying this instruction. 'number' corresponds to the numbers seen in 'record instruction-history' (*note Process Record and Replay::). -- Variable: RecordInstruction.sal A 'gdb.Symtab_and_line' object representing the associated symtab and line of this instruction. May be 'None' if no debug information is available. -- Variable: RecordInstruction.is_speculative A boolean indicating whether the instruction was executed speculatively. If an error occured during recording or decoding a recording, this error is represented by a 'gdb.RecordGap' object in the instruction list. It has the following attributes: -- Variable: RecordGap.number An integer identifying this gap. 'number' corresponds to the numbers seen in 'record instruction-history' (*note Process Record and Replay::). -- Variable: RecordGap.error_code A numerical representation of the reason for the gap. The value is specific to the current recording method. -- Variable: RecordGap.error_string A human readable string with the reason for the gap. A 'gdb.RecordFunctionSegment' object has the following attributes: -- Variable: RecordFunctionSegment.number An integer identifying this function segment. 'number' corresponds to the numbers seen in 'record function-call-history' (*note Process Record and Replay::). -- Variable: RecordFunctionSegment.symbol A 'gdb.Symbol' object representing the associated symbol. May be 'None' if no debug information is available. -- Variable: RecordFunctionSegment.level An integer representing the function call's stack level. May be 'None' if the function call is a gap. -- Variable: RecordFunctionSegment.instructions A list of 'gdb.RecordInstruction' or 'gdb.RecordGap' objects associated with this function call. -- Variable: RecordFunctionSegment.up A 'gdb.RecordFunctionSegment' object representing the caller's function segment. If the call has not been recorded, this will be the function segment to which control returns. If neither the call nor the return have been recorded, this will be 'None'. -- Variable: RecordFunctionSegment.prev A 'gdb.RecordFunctionSegment' object representing the previous segment of this function call. May be 'None'. -- Variable: RecordFunctionSegment.next A 'gdb.RecordFunctionSegment' object representing the next segment of this function call. May be 'None'. The following example demonstrates the usage of these objects and functions to create a function that will rewind a record to the last time a function in a different file was executed. This would typically be used to track the execution of user provided callback functions in a library which typically are not visible in a back trace. def bringback (): rec = gdb.current_recording () if not rec: return insn = rec.instruction_history if len (insn) == 0: return try: position = insn.index (rec.replay_position) except: position = -1 try: filename = insn[position].sal.symtab.fullname () except: filename = None for i in reversed (insn[:position]): try: current = i.sal.symtab.fullname () except: current = None if filename == current: continue rec.goto (i) return Another possible application is to write a function that counts the number of code executions in a given line range. This line range can contain parts of functions or span across several functions and is not limited to be contiguous. def countrange (filename, linerange): count = 0 def filter_only (file_name): for call in gdb.current_recording ().function_call_history: try: if file_name in call.symbol.symtab.fullname (): yield call except: pass for c in filter_only (filename): for i in c.instructions: try: if i.sal.line in linerange: count += 1 break; except: pass return count  File: gdb.info, Node: Commands In Python, Next: Parameters In Python, Prev: Recordings In Python, Up: Python API 23.2.2.20 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 and 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 23.2.2.21 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 23.2.2.22 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 23.2.2.23 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 23.2.2.24 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 23.2.2.25 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). -- Function: gdb.invalidate_cached_frames GDB internally keeps a cache of the frames that have been unwound. This function invalidates this cache. This function should not generally be called by ordinary Python code. It is documented for the sake of completeness. 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 23.2.2.26 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 23.2.2.27 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 23.2.2.28 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 23.2.2.29 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 23.2.2.30 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. 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. 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.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 -- 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.pending This attribute is 'True' if the breakpoint is pending, and 'False' otherwise. *Note Set Breaks::. This attribute is read-only. -- Variable: Breakpoint.thread If the breakpoint is thread-specific, this attribute holds the thread's global 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. -- 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 23.2.2.31 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 23.2.2.32 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 is a pointer or array 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 23.2.2.33 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 '' (*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 '', 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 ''. 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 ''.  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., '', as a symbol. GDB defines the following object types: '' *Note Architectures In Guile::. '' *Note Blocks In Guile::. '' *Note Blocks In Guile::. '' *Note Breakpoints In Guile::. '' *Note Commands In Guile::. '' *Note Guile Exception Handling::. '' *Note Frames In Guile::. '' *Note Iterators In Guile::. '' *Note Lazy Strings In Guile::. '' *Note Objfiles In Guile::. '' *Note Parameters In Guile::. '' *Note Guile Pretty Printing API::. '' *Note Guile Pretty Printing API::. '' *Note Progspaces In Guile::. '' *Note Symbols In Guile::. '' *Note Symbol Tables In Guile::. '' *Note Symbol Tables In Guile::. '' *Note Types In Guile::. '' *Note Types In Guile::. '' *Note Values From Inferior In Guile::. The following GDB objects are managed internally so that the Scheme function 'eq?' may be applied to them. '' '' '' '' '' '' '' '' ''  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 # ...] In unknown file: ?: 9 [apply-smob/1 #] In ice-9/boot-9.scm: 157: 8 [catch #t # ...] In unknown file: ?: 7 [apply-smob/1 #] ?: 6 [call-with-input-string "(display foo)" ...] In ice-9/boot-9.scm: 2320: 5 [save-module-excursion #] In ice-9/eval-string.scm: 44: 4 [read-and-eval # #:lang ...] 37: 3 [lp (display foo)] In ice-9/eval.scm: 387: 2 [eval # ()] 393: 1 [eval # ()] In unknown file: ?: 0 [memoize-variable-access! # ...] 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 '' 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 '' 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 '' object. Otherwise return '#f'. -- Scheme Procedure: exception-key exception Return the ARGS field of a '' object. -- Scheme Procedure: exception-args exception Return the ARGS field of a '' 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 uses this object for its internal bookkeeping of the inferior's values, and for fetching values when necessary. GDB does not memoize '' 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 '' 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 '' 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 '' 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 '' object. Otherwise return '#f'. -- Scheme Procedure: make-value value [#:type type] Many Scheme values can be converted directly to a '' 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. '' If VALUE is a '' 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 '' object representing the address. Otherwise, '#f' is returned. -- Scheme Procedure: value-type value Return the type of VALUE as a '' 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 '' that is the result of casting VALUE to the type described by TYPE, which must be a '' 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 '' 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 '' to access what 'foo' points to like this: (define bar (value-dereference foo)) The result 'bar' will be a '' object holding the value pointed to by 'foo'. A similar function 'value-referenced-value' exists which also returns '' 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 '' object corresponding to it and obtain a '' which is identical to that corresponding to 'val'. However, if you apply the method 'value-referenced-value', the result would be a '' 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 '' 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 '' objects corresponding to pointers ('' 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 '' 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 '' object corresponding to 'ref' will result in an error, while applying 'value-referenced-value' will result in a '' 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 '' object 'scm-val' is identical to that corresponding to 'val'. -- Scheme Procedure: value-field value field-name Return field FIELD-NAME from '' object VALUE. -- Scheme Procedure: value-subscript value index Return the value of array VALUE at index INDEX. The VALUE argument must be a subscriptable '' 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 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 '' VALUE. The value must be "integer like". Pointers are ok. -- Scheme Procedure: value->integer Return the Scheme integer representing '' VALUE. The value must be "integer like". Pointers are ok. -- Scheme Procedure: value->real Return the Scheme real number representing '' VALUE. The value must be a number. -- Scheme Procedure: value->bytevector Return a Scheme bytevector with the raw contents of '' 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 '', 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 '' integer. -- Scheme Procedure: value->lazy-string value [#:encoding encoding] [#:length length] If this '' represents a string, then this method converts VALUE to a '' 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 '' that will be lazily fetched from the target. The object of 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 '' 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 '' 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 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 ''. The following type-related procedures are provided by the '(gdb)' module. -- Scheme Procedure: type? object Return '#t' if OBJECT is an object of 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 '', and NAME is looked up in that scope. Otherwise, it is searched for globally. Ordinarily, this function will return an instance of ''. 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 '' that represents the real type of TYPE, after removing all layers of typedefs. -- Scheme Procedure: type-array type n1 [n2] Return a new '' 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 '' 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 '' 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 '' object which represents a reference to TYPE. -- Scheme Procedure: type-target type Return a new '' 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 '' object which represents a 'const'-qualified variant of TYPE. -- Scheme Procedure: type-volatile type Return a new '' object which represents a 'volatile'-qualified variant of TYPE. -- Scheme Procedure: type-unqualified type Return a new '' 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 '' 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 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 ''. *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 '' instance holding a structure type, you can access its 'foo' field with: (define bar (type-field some-type "foo")) 'bar' will be a '' object. -- Scheme Procedure: type-has-field? type name Return '#t' if '' 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++. '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 ''. The following field-related procedures are provided by the '(gdb)' module: -- Scheme Procedure: field? object Return '#t' if OBJECT is an object of type ''. 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 '', but it can be '#f' in some situations. -- Scheme Procedure: field-enumval field Return the enum value represented by '' FIELD. -- Scheme Procedure: field-bitpos field Return the bit position of '' FIELD. This attribute is not available for 'static' fields (as in C++). -- Scheme Procedure: field-bitsize field If the field is packed, or is a bitfield, return the size of '' 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 . 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 '' 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 to perform the actual pretty-printing. Otherwise LOOKUP-FUNCTION returns '#f'. -- Scheme Procedure: pretty-printer? object Return '#t' if OBJECT is a '' 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 ''. 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 '' 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 '', 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 '', 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 ''; 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 '' 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 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 '': -- Scheme Procedure: default-visualizer value This function takes a '' 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 '' object or '#f'. Otherwise an exception is thrown. GDB first checks the result of 'objfile-pretty-printers' of each '' in the current program space and iteratively calls each enabled lookup function in the list for that '' 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 '' 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 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 '' 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 '' 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 '' 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 '' 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 '' 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 and 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 '' 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 '' 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 '' 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 '' 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 '' 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 '' 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 '' object. Otherwise return '#f'. -- Scheme Procedure: parameter-value parameter Return the value of PARAMETER which may either be a '' 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 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 '' 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 '' object. Otherwise return '#f'. -- Scheme Procedure: progspace-valid? progspace Return '#t' if PROGSPACE is valid, '#f' if not. A '' 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 ''. *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 ''. *Note Guile Pretty Printing API::, for more information. -- Scheme Procedure: set-progspace-pretty-printers! progspace printer-list Set the list of registered '' 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 ''. The following objfile-related procedures are provided by the '(gdb)' module: -- Scheme Procedure: objfile? object Return '#t' if OBJECT is a '' object. Otherwise return '#f'. -- Scheme Procedure: objfile-valid? objfile Return '#t' if OBJFILE is valid, '#f' if not. A '' object can become invalid if the object file it refers to is not loaded in GDB any longer. All other '' 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 '' 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 '' 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 '' objects for OBJFILE to PRINTER-LIST. The PRINTER-LIST must be a list of '' 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 '' class represents a frame in the stack. A '' 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 '' 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 '' 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 '' 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 '' 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 '' object. *Note Blocks In Guile::. -- Scheme Procedure: frame-function frame Return the symbol for the function corresponding to this frame as a '' 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 '' (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 '' object, and BLOCK must be a '' 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 ''. 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 '' object. Otherwise return '#f'. -- Scheme Procedure: block-valid? block Returns '#t' if '' 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 '' 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 '' BLOCK. -- Scheme Procedure: block-end block Return the end address of '' BLOCK. -- Scheme Procedure: block-function block Return the name of '' BLOCK represented as a '' 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 '' BLOCK. If the parent block does not exist, then '#f' is returned. -- Scheme Procedure: block-global-block block Return the global block associated with '' BLOCK. -- Scheme Procedure: block-static-block block Return the static block associated with '' BLOCK. -- Scheme Procedure: block-global? block Return '#t' if '' BLOCK is a global block. Otherwise return '#f'. -- Scheme Procedure: block-static? block Return '#t' if '' BLOCK is a static block. Otherwise return '#f'. -- Scheme Procedure: block-symbols Return a list of all symbols (as objects) in '' BLOCK. -- Scheme Procedure: make-block-symbols-iterator block Return an object of type '' 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 object. This object would be obtained from the 'progress' element of the '' object returned by 'make-block-symbols-iterator'. -- Scheme Procedure: lookup-block pc Return the innermost '' 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 '' 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 ''. Otherwise return '#f'. -- Scheme Procedure: symbol-valid? symbol Return '#t' if the '' object is valid, '#f' if not. A '' object can become invalid if the symbol it refers to does not exist in GDB any longer. All other '' 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 ''. *Note Types In Guile::. -- Scheme Procedure: symbol-symtab symbol Return the symbol table in which SYMBOL appears. The result is an object of type ''. *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 ''. 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 '' 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 '' 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 '' object or '#f' if the symbol is not found. The available domain categories in '' 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 '' 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: '' (symtab-and-line) and ''. Symbol table and line data for a frame is returned from the 'frame-find-sal' '' 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 ''. Otherwise return '#f'. -- Scheme Procedure: symtab-valid? symtab Return '#t' if the '' object is valid, '#f' if not. A '' object becomes invalid when the symbol table it refers to no longer exists in GDB. All other '' 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 ''. Otherwise return '#f'. -- Scheme Procedure: sal-valid? sal Return '#t' if SAL is valid, '#f' if not. A '' object becomes invalid when the Symbol table object it refers to no longer exists in GDB. All other '' 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 ('') 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 '' 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 '' 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 ''. 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 '' 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 '' 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 '' object. -- Scheme Procedure: breakpoint? object Return '#t' if OBJECT is a '' 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 '' 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 global-thread-id for thread-specific breakpoint BREAKPOINT. Return #f if BREAKPOINT is not thread-specific. -- Scheme Procedure: set-breakpoint-thread! breakpoint global-thread-id|#f Set the thread-id for BREAKPOINT to GLOBAL-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 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 '' 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 '' and a string wrapped within a '' is that a '' will be treated differently by GDB when printing. A '' is retrieved and encoded during printing, while a '' 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 ''. 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 is a pointer or array 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 '' to a ''. This value will point to the string in memory, but will lose all the delayed retrieval, encoding and handling that GDB applies to a ''.  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 '' 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 ''. Otherwise return '#f'. -- Scheme Procedure: current-arch Return the current architecture as a '' object. -- Scheme Procedure: arch-name arch Return the name (string value) of '' ARCH. -- Scheme Procedure: arch-charset arch Return name of target character set of '' ARCH. -- Scheme Procedure: arch-wide-charset Return name of target wide character set of '' ARCH. Each architecture provides a set of predefined types, obtained by the following functions. -- Scheme Procedure: arch-void-type arch Return the '' object for a 'void' type of architecture ARCH. -- Scheme Procedure: arch-char-type arch Return the '' object for a 'char' type of architecture ARCH. -- Scheme Procedure: arch-short-type arch Return the '' object for a 'short' type of architecture ARCH. -- Scheme Procedure: arch-int-type arch Return the '' object for an 'int' type of architecture ARCH. -- Scheme Procedure: arch-long-type arch Return the '' object for a 'long' type of architecture ARCH. -- Scheme Procedure: arch-schar-type arch Return the '' object for a 'signed char' type of architecture ARCH. -- Scheme Procedure: arch-uchar-type arch Return the '' object for an 'unsigned char' type of architecture ARCH. -- Scheme Procedure: arch-ushort-type arch Return the '' object for an 'unsigned short' type of architecture ARCH. -- Scheme Procedure: arch-uint-type arch Return the '' object for an 'unsigned int' type of architecture ARCH. -- Scheme Procedure: arch-ulong-type arch Return the '' object for an 'unsigned long' type of architecture ARCH. -- Scheme Procedure: arch-float-type arch Return the '' object for a 'float' type of architecture ARCH. -- Scheme Procedure: arch-double-type arch Return the '' object for a 'double' type of architecture ARCH. -- Scheme Procedure: arch-longdouble-type arch Return the '' object for a 'long double' type of architecture ARCH. -- Scheme Procedure: arch-bool-type arch Return the '' object for a 'bool' type of architecture ARCH. -- Scheme Procedure: arch-longlong-type arch Return the '' object for a 'long long' type of architecture ARCH. -- Scheme Procedure: arch-ulonglong-type arch Return the '' object for an 'unsigned long long' type of architecture ARCH. -- Scheme Procedure: arch-int8-type arch Return the '' object for an 'int8' type of architecture ARCH. -- Scheme Procedure: arch-uint8-type arch Return the '' object for a 'uint8' type of architecture ARCH. -- Scheme Procedure: arch-int16-type arch Return the '' object for an 'int16' type of architecture ARCH. -- Scheme Procedure: arch-uint16-type arch Return the '' object for a 'uint16' type of architecture ARCH. -- Scheme Procedure: arch-int32-type arch Return the '' object for an 'int32' type of architecture ARCH. -- Scheme Procedure: arch-uint32-type arch Return the '' object for a 'uint32' type of architecture ARCH. -- Scheme Procedure: arch-int64-type arch Return the '' object for an 'int64' type of architecture ARCH. -- Scheme Procedure: arch-uint64-type arch Return the '' 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 ''. Otherwise return '#f'. -- Scheme Procedure: memory-port-range memory-port Return the range of '' 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 '' MEMORY-PORT. -- Scheme Procedure: set-memory-port-read-buffer-size! memory-port size Set the size of the read buffer of '' 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 '' MEMORY-PORT. -- Scheme Procedure: set-memory-port-write-buffer-size! memory-port size Set the size of the write buffer of '' 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 '' 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 '' 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 '' 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 '' 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 '' 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'.