<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <!-- Copyright (C) 1988-2018 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 "Funding Free Software", the Front-Cover Texts being (a) (see below), and with the Back-Cover Texts being (b) (see below). A copy of the license is included in the section entitled "GNU Free Documentation License". (a) The FSF's Front-Cover Text is: A GNU Manual (b) The FSF's Back-Cover Text is: You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development. --> <!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ --> <head> <title>GGC Roots (GNU Compiler Collection (GCC) Internals)</title> <meta name="description" content="GGC Roots (GNU Compiler Collection (GCC) Internals)"> <meta name="keywords" content="GGC Roots (GNU Compiler Collection (GCC) Internals)"> <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="Option-Index.html#Option-Index" rel="index" title="Option Index"> <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> <link href="Type-Information.html#Type-Information" rel="up" title="Type Information"> <link href="Files.html#Files" rel="next" title="Files"> <link href="User-GC.html#User-GC" rel="prev" title="User GC"> <style type="text/css"> <!-- a.summary-letter {text-decoration: none} blockquote.indentedblock {margin-right: 0em} blockquote.smallindentedblock {margin-right: 0em; font-size: smaller} blockquote.smallquotation {font-size: smaller} div.display {margin-left: 3.2em} div.example {margin-left: 3.2em} div.lisp {margin-left: 3.2em} div.smalldisplay {margin-left: 3.2em} div.smallexample {margin-left: 3.2em} 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.nolinebreak {white-space: nowrap} span.roman {font-family: initial; font-weight: normal} span.sansserif {font-family: sans-serif; font-weight: normal} ul.no-bullet {list-style: none} --> </style> </head> <body lang="en"> <a name="GGC-Roots"></a> <div class="header"> <p> Next: <a href="Files.html#Files" accesskey="n" rel="next">Files</a>, Previous: <a href="User-GC.html#User-GC" accesskey="p" rel="prev">User GC</a>, Up: <a href="Type-Information.html#Type-Information" accesskey="u" rel="up">Type Information</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p> </div> <hr> <a name="Marking-Roots-for-the-Garbage-Collector"></a> <h3 class="section">23.4 Marking Roots for the Garbage Collector</h3> <a name="index-roots_002c-marking"></a> <a name="index-marking-roots"></a> <p>In addition to keeping track of types, the type machinery also locates the global variables (<em>roots</em>) that the garbage collector starts at. Roots must be declared using one of the following syntaxes: </p> <ul> <li> <code>extern GTY(([<var>options</var>])) <var>type</var> <var>name</var>;</code> </li><li> <code>static GTY(([<var>options</var>])) <var>type</var> <var>name</var>;</code> </li></ul> <p>The syntax </p><ul> <li> <code>GTY(([<var>options</var>])) <var>type</var> <var>name</var>;</code> </li></ul> <p>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>. </p> </body> </html>