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<title>Debugging with GDB: Xmethod API</title>
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<a name="Xmethod-API"></a>
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<div class="header">
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<p>
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Next: <a href="Writing-an-Xmethod.html#Writing-an-Xmethod" accesskey="n" rel="next">Writing an Xmethod</a>, Previous: <a href="Xmethods-In-Python.html#Xmethods-In-Python" accesskey="p" rel="previous">Xmethods In Python</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>
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</div>
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<hr>
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<a name="Xmethod-API-1"></a>
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<h4 class="subsubsection">23.2.2.14 Xmethod API</h4>
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<a name="index-xmethod-API"></a>
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<p>The <small>GDB</small> Python API provides classes, interfaces and functions
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to implement, register and manipulate xmethods.
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See <a href="Xmethods-In-Python.html#Xmethods-In-Python">Xmethods In Python</a>.
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</p>
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<p>An xmethod matcher should be an instance of a class derived from
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<code>XMethodMatcher</code> defined in the module <code>gdb.xmethod</code>, or an
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object with similar interface and attributes. An instance of
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<code>XMethodMatcher</code> has the following attributes:
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</p>
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<dl>
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<dt><a name="index-name"></a>Variable: <strong>name</strong></dt>
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<dd><p>The name of the matcher.
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</p></dd></dl>
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<dl>
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<dt><a name="index-enabled"></a>Variable: <strong>enabled</strong></dt>
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<dd><p>A boolean value indicating whether the matcher is enabled or disabled.
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</p></dd></dl>
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<dl>
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<dt><a name="index-methods"></a>Variable: <strong>methods</strong></dt>
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<dd><p>A list of named methods managed by the matcher. Each object in the list
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is an instance of the class <code>XMethod</code> defined in the module
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<code>gdb.xmethod</code>, or any object with the following attributes:
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</p>
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<dl compact="compact">
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<dt><code>name</code></dt>
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<dd><p>Name of the xmethod which should be unique for each xmethod
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managed by the matcher.
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</p>
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</dd>
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<dt><code>enabled</code></dt>
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<dd><p>A boolean value indicating whether the xmethod is enabled or
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disabled.
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</p>
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</dd>
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</dl>
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<p>The class <code>XMethod</code> is a convenience class with same
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attributes as above along with the following constructor:
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</p>
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<dl>
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<dt><a name="index-XMethod_002e_005f_005finit_005f_005f"></a>Function: <strong>XMethod.__init__</strong> <em>(self, name)</em></dt>
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<dd><p>Constructs an enabled xmethod with name <var>name</var>.
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</p></dd></dl>
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</dd></dl>
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<p>The <code>XMethodMatcher</code> class has the following methods:
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</p>
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<dl>
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<dt><a name="index-XMethodMatcher_002e_005f_005finit_005f_005f"></a>Function: <strong>XMethodMatcher.__init__</strong> <em>(self, name)</em></dt>
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<dd><p>Constructs an enabled xmethod matcher with name <var>name</var>. The
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<code>methods</code> attribute is initialized to <code>None</code>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-XMethodMatcher_002ematch"></a>Function: <strong>XMethodMatcher.match</strong> <em>(self, class_type, method_name)</em></dt>
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<dd><p>Derived classes should override this method. It should return a
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xmethod worker object (or a sequence of xmethod worker
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objects) matching the <var>class_type</var> and <var>method_name</var>.
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<var>class_type</var> is a <code>gdb.Type</code> object, and <var>method_name</var>
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is a string value. If the matcher manages named methods as listed in
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its <code>methods</code> attribute, then only those worker objects whose
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corresponding entries in the <code>methods</code> list are enabled should be
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returned.
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</p></dd></dl>
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<p>An xmethod worker should be an instance of a class derived from
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<code>XMethodWorker</code> defined in the module <code>gdb.xmethod</code>,
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or support the following interface:
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</p>
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<dl>
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<dt><a name="index-XMethodWorker_002eget_005farg_005ftypes"></a>Function: <strong>XMethodWorker.get_arg_types</strong> <em>(self)</em></dt>
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<dd><p>This method returns a sequence of <code>gdb.Type</code> objects corresponding
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to the arguments that the xmethod takes. It can return an empty
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sequence or <code>None</code> if the xmethod does not take any arguments.
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If the xmethod takes a single argument, then a single
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<code>gdb.Type</code> object corresponding to it can be returned.
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</p></dd></dl>
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<dl>
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<dt><a name="index-XMethodWorker_002eget_005fresult_005ftype"></a>Function: <strong>XMethodWorker.get_result_type</strong> <em>(self, *args)</em></dt>
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<dd><p>This method returns a <code>gdb.Type</code> object representing the type
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of the result of invoking this xmethod.
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The <var>args</var> argument is the same tuple of arguments that would be
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passed to the <code>__call__</code> method of this worker.
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</p></dd></dl>
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<dl>
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<dt><a name="index-XMethodWorker_002e_005f_005fcall_005f_005f"></a>Function: <strong>XMethodWorker.__call__</strong> <em>(self, *args)</em></dt>
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<dd><p>This is the method which does the <em>work</em> of the xmethod. The
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<var>args</var> arguments is the tuple of arguments to the xmethod. Each
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element in this tuple is a gdb.Value object. The first element is
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always the <code>this</code> pointer value.
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</p></dd></dl>
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<p>For <small>GDB</small> to lookup xmethods, the xmethod matchers
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should be registered using the following function defined in the module
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<code>gdb.xmethod</code>:
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</p>
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<dl>
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<dt><a name="index-register_005fxmethod_005fmatcher"></a>Function: <strong>register_xmethod_matcher</strong> <em>(locus, matcher, replace=False)</em></dt>
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<dd><p>The <code>matcher</code> is registered with <code>locus</code>, replacing an
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existing matcher with the same name as <code>matcher</code> if
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<code>replace</code> is <code>True</code>. <code>locus</code> can be a
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<code>gdb.Objfile</code> object (see <a href="Objfiles-In-Python.html#Objfiles-In-Python">Objfiles In Python</a>), or a
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<code>gdb.Progspace</code> object (see <a href="Progspaces-In-Python.html#Progspaces-In-Python">Progspaces In Python</a>), or
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<code>None</code>. If it is <code>None</code>, then <code>matcher</code> is registered
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globally.
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</p></dd></dl>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Writing-an-Xmethod.html#Writing-an-Xmethod" accesskey="n" rel="next">Writing an Xmethod</a>, Previous: <a href="Xmethods-In-Python.html#Xmethods-In-Python" accesskey="p" rel="previous">Xmethods In Python</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>
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