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<h3 class="section">22.4 Marking Roots for the Garbage Collector</h3>
<p><a name="index-roots_002c-marking-5095"></a><a name="index-marking-roots-5096"></a>
In addition to keeping track of types, the type machinery also locates
the global variables (<dfn>roots</dfn>) that the garbage collector starts
at. Roots must be declared using one of the following syntaxes:
<ul>
<li><code>extern GTY(([</code><var>options</var><code>])) </code><var>type</var> <var>name</var><code>;</code>
<li><code>static GTY(([</code><var>options</var><code>])) </code><var>type</var> <var>name</var><code>;</code>
</ul>
The syntax
<ul>
<li><code>GTY(([</code><var>options</var><code>])) </code><var>type</var> <var>name</var><code>;</code>
</ul>
is <em>not</em> accepted. There should be an <code>extern</code> declaration
of such a variable in a header somewhere—mark that, not the
definition. Or, if the variable is only used in one file, make it
<code>static</code>.
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