* Gdb-Internals: (gdbint). The GNU debugger's internals.
@end direntry
-@ifinfo
-This file documents the internals of the GNU debugger @value{GDBN}.
-Copyright (C) 1990, 1991, 1992, 1993, 1994, 1996, 1998, 1999, 2000, 2001,
- 2002, 2003, 2004, 2005, 2006, 2008
- Free Software Foundation, Inc.
+@copying
+Copyright @copyright{} 1990, 1991, 1992, 1993, 1994, 1996, 1998, 1999,
+2000, 2001, 2002, 2003, 2004, 2005, 2006, 2008, 2009
+Free Software Foundation, Inc.
Contributed by Cygnus Solutions. Written by John Gilmore.
Second Edition by Stan Shebs.
Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
Texts. A copy of the license is included in the section entitled ``GNU
Free Documentation License''.
-@end ifinfo
+@end copying
+
+@ifnottex
+This file documents the internals of the GNU debugger @value{GDBN}.
+
+@insertcopying
+@end ifnottex
@setchapternewpage off
@settitle @value{GDBN} Internals
@end tex
@vskip 0pt plus 1filll
-Copyright @copyright{} 1990,1991,1992,1993,1994,1996,1998,1999,2000,2001,
- 2002, 2003, 2004, 2005, 2006 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 1.1 or
-any later version published by the Free Software Foundation; with no
-Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
-Texts. A copy of the license is included in the section entitled ``GNU
-Free Documentation License''.
+@insertcopying
@end titlepage
@contents
* Algorithms::
* User Interface::
* libgdb::
+* Values::
* Stack Frames::
* Symbol Handling::
* Language Support::
builder. The result of the query is constructed using that builder
before the query function returns.
+@node Values
+@chapter Values
+@section Values
+
+@cindex values
+@cindex @code{value} structure
+@value{GDBN} uses @code{struct value}, or @dfn{values}, as an internal
+abstraction for the representation of a variety of inferior objects
+and @value{GDBN} convenience objects.
+
+Values have an associated @code{struct type}, that describes a virtual
+view of the raw data or object stored in or accessed through the
+value.
+
+A value is in addition discriminated by its lvalue-ness, given its
+@code{enum lval_type} enumeration type:
+
+@cindex @code{lval_type} enumeration, for values.
+@table @code
+@item @code{not_lval}
+This value is not an lval. It can't be assigned to.
+
+@item @code{lval_memory}
+This value represents an object in memory.
+
+@item @code{lval_register}
+This value represents an object that lives in a register.
+
+@item @code{lval_internalvar}
+Represents the value of an internal variable.
+
+@item @code{lval_internalvar_component}
+Represents part of a @value{GDBN} internal variable. E.g., a
+structure field.
+
+@cindex computed values
+@item @code{lval_computed}
+These are ``computed'' values. They allow creating specialized value
+objects for specific purposes, all abstracted away from the core value
+support code. The creator of such a value writes specialized
+functions to handle the reading and writing to/from the value's
+backend data, and optionally, a ``copy operator'' and a
+``destructor''.
+
+Pointers to these functions are stored in a @code{struct lval_funcs}
+instance (declared in @file{value.h}), and passed to the
+@code{allocate_computed_value} function, as in the example below.
+
+@smallexample
+static void
+nil_value_read (struct value *v)
+@{
+ /* This callback reads data from some backend, and stores it in V.
+ In this case, we always read null data. You'll want to fill in
+ something more interesting. */
+
+ memset (value_contents_all_raw (v),
+ value_offset (v),
+ TYPE_LENGTH (value_type (v)));
+@}
+
+static void
+nil_value_write (struct value *v, struct value *fromval)
+@{
+ /* Takes the data from FROMVAL and stores it in the backend of V. */
+
+ to_oblivion (value_contents_all_raw (fromval),
+ value_offset (v),
+ TYPE_LENGTH (value_type (fromval)));
+@}
+
+static struct lval_funcs nil_value_funcs =
+ @{
+ nil_value_read,
+ nil_value_write
+ @};
+
+struct value *
+make_nil_value (void)
+@{
+ struct type *type;
+ struct value *v;
+
+ type = make_nils_type ();
+ v = allocate_computed_value (type, &nil_value_funcs, NULL);
+
+ return v;
+@}
+@end smallexample
+
+See the implementation of the @code{$_siginfo} convenience variable in
+@file{infrun.c} as a real example use of lval_computed.
+
+@end table
+
@node Stack Frames
@chapter Stack Frames
projects / deliverable / binutils-gdb.git / blobdiff