<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
<html>
|
<!-- Copyright (C) 1988-2021 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." -->
|
<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ -->
|
<head>
|
<title>Debugging with GDB: Writing an Xmethod</title>
|
|
<meta name="description" content="Debugging with GDB: Writing an Xmethod">
|
<meta name="keywords" content="Debugging with GDB: Writing an Xmethod">
|
<meta name="resource-type" content="document">
|
<meta name="distribution" content="global">
|
<meta name="Generator" content="makeinfo">
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
<link href="index.html#Top" rel="start" title="Top">
|
<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
|
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
<link href="Python-API.html#Python-API" rel="up" title="Python API">
|
<link href="Inferiors-In-Python.html#Inferiors-In-Python" rel="next" title="Inferiors In Python">
|
<link href="Xmethod-API.html#Xmethod-API" rel="previous" title="Xmethod API">
|
<style type="text/css">
|
<!--
|
a.summary-letter {text-decoration: none}
|
blockquote.smallquotation {font-size: smaller}
|
div.display {margin-left: 3.2em}
|
div.example {margin-left: 3.2em}
|
div.indentedblock {margin-left: 3.2em}
|
div.lisp {margin-left: 3.2em}
|
div.smalldisplay {margin-left: 3.2em}
|
div.smallexample {margin-left: 3.2em}
|
div.smallindentedblock {margin-left: 3.2em; font-size: smaller}
|
div.smalllisp {margin-left: 3.2em}
|
kbd {font-style:oblique}
|
pre.display {font-family: inherit}
|
pre.format {font-family: inherit}
|
pre.menu-comment {font-family: serif}
|
pre.menu-preformatted {font-family: serif}
|
pre.smalldisplay {font-family: inherit; font-size: smaller}
|
pre.smallexample {font-size: smaller}
|
pre.smallformat {font-family: inherit; font-size: smaller}
|
pre.smalllisp {font-size: smaller}
|
span.nocodebreak {white-space:nowrap}
|
span.nolinebreak {white-space:nowrap}
|
span.roman {font-family:serif; font-weight:normal}
|
span.sansserif {font-family:sans-serif; font-weight:normal}
|
ul.no-bullet {list-style: none}
|
-->
|
</style>
|
|
|
</head>
|
|
<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
|
<a name="Writing-an-Xmethod"></a>
|
<div class="header">
|
<p>
|
Next: <a href="Inferiors-In-Python.html#Inferiors-In-Python" accesskey="n" rel="next">Inferiors In Python</a>, Previous: <a href="Xmethod-API.html#Xmethod-API" accesskey="p" rel="previous">Xmethod API</a>, Up: <a href="Python-API.html#Python-API" accesskey="u" rel="up">Python API</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
|
</div>
|
<hr>
|
<a name="Writing-an-Xmethod-1"></a>
|
<h4 class="subsubsection">23.2.2.15 Writing an Xmethod</h4>
|
<a name="index-writing-xmethods-in-Python"></a>
|
|
<p>Implementing xmethods in Python will require implementing xmethod
|
matchers and xmethod workers (see <a href="Xmethods-In-Python.html#Xmethods-In-Python">Xmethods In Python</a>). Consider
|
the following C<tt>++</tt> class:
|
</p>
|
<div class="smallexample">
|
<pre class="smallexample">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;
|
}
|
</pre></div>
|
|
<p>Let us define two xmethods for the class <code>MyClass</code>, one
|
replacing the method <code>geta</code>, and another adding an overloaded
|
flavor of <code>operator+</code> which takes a <code>MyClass</code> argument (the
|
C<tt>++</tt> code above already has an overloaded <code>operator+</code>
|
which takes an <code>int</code> argument). The xmethod matcher can be
|
defined as follows:
|
</p>
|
<div class="smallexample">
|
<pre class="smallexample">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
|
</pre></div>
|
|
<p>Notice that the <code>match</code> method of <code>MyClassMatcher</code> returns
|
a worker object of type <code>MyClassWorker_geta</code> for the <code>geta</code>
|
method, and a worker object of type <code>MyClassWorker_plus</code> for the
|
<code>operator+</code> method. This is done indirectly via helper classes
|
derived from <code>gdb.xmethod.XMethod</code>. One does not need to use the
|
<code>methods</code> 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 <code>methods</code> attribute of the matcher. This will then
|
facilitate enabling and disabling individual xmethods via the
|
<code>enable/disable</code> commands. Notice also that a worker object is
|
returned only if the corresponding entry in the <code>methods</code> attribute
|
of the matcher is enabled.
|
</p>
|
<p>The implementation of the worker classes returned by the matcher setup
|
above is as follows:
|
</p>
|
<div class="smallexample">
|
<pre class="smallexample">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_']
|
</pre></div>
|
|
<p>For <small>GDB</small> to actually lookup a xmethod, it has to be
|
registered with it. The matcher defined above is registered with
|
<small>GDB</small> globally as follows:
|
</p>
|
<div class="smallexample">
|
<pre class="smallexample">gdb.xmethod.register_xmethod_matcher(None, MyClassMatcher())
|
</pre></div>
|
|
<p>If an object <code>obj</code> of type <code>MyClass</code> is initialized in C<tt>++</tt>
|
code as follows:
|
</p>
|
<div class="smallexample">
|
<pre class="smallexample">MyClass obj(5);
|
</pre></div>
|
|
<p>then, after loading the Python script defining the xmethod matchers
|
and workers into <code>GDBN</code>, invoking the method <code>geta</code> or using
|
the operator <code>+</code> on <code>obj</code> will invoke the xmethods
|
defined above:
|
</p>
|
<div class="smallexample">
|
<pre class="smallexample">(gdb) p obj.geta()
|
$1 = 5
|
|
(gdb) p obj + obj
|
$2 = 10
|
</pre></div>
|
|
<p>Consider another example with a C++ template class:
|
</p>
|
<div class="smallexample">
|
<pre class="smallexample">template <class T>
|
class MyTemplate
|
{
|
public:
|
MyTemplate () : dsize_(10), data_ (new T [10]) { }
|
~MyTemplate () { delete [] data_; }
|
|
int footprint (void)
|
{
|
return sizeof (T) * dsize_ + sizeof (MyTemplate<T>);
|
}
|
|
private:
|
int dsize_;
|
T *data_;
|
};
|
</pre></div>
|
|
<p>Let us implement an xmethod for the above class which serves as a
|
replacement for the <code>footprint</code> method. The full code listing
|
of the xmethod workers and xmethod matchers is as follows:
|
</p>
|
<div class="smallexample">
|
<pre class="smallexample">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)
|
</pre></div>
|
|
<p>Notice that, in this example, we have not used the <code>methods</code>
|
attribute of the matcher as the matcher manages only one xmethod. The
|
user can enable/disable this xmethod by enabling/disabling the matcher
|
itself.
|
</p>
|
<hr>
|
<div class="header">
|
<p>
|
Next: <a href="Inferiors-In-Python.html#Inferiors-In-Python" accesskey="n" rel="next">Inferiors In Python</a>, Previous: <a href="Xmethod-API.html#Xmethod-API" accesskey="p" rel="previous">Xmethod API</a>, Up: <a href="Python-API.html#Python-API" accesskey="u" rel="up">Python API</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
|
</div>
|
|
|
|
</body>
|
</html>
|
