144 lines
6.5 KiB
HTML
144 lines
6.5 KiB
HTML
|
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
||
|
|
<html>
|
||
|
|
<!-- Copyright (C) 1988-2016 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 5.2, http://www.gnu.org/software/texinfo/ -->
|
||
|
|
<head>
|
||
|
|
<title>Using the GNU Compiler Collection (GCC): Label Attributes</title>
|
||
|
|
|
||
|
|
<meta name="description" content="Using the GNU Compiler Collection (GCC): Label Attributes">
|
||
|
|
<meta name="keywords" content="Using the GNU Compiler Collection (GCC): Label Attributes">
|
||
|
|
<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="C-Extensions.html#C-Extensions" rel="up" title="C Extensions">
|
||
|
|
<link href="Enumerator-Attributes.html#Enumerator-Attributes" rel="next" title="Enumerator Attributes">
|
||
|
|
<link href="x86-Type-Attributes.html#x86-Type-Attributes" rel="prev" title="x86 Type Attributes">
|
||
|
|
<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="Label-Attributes"></a>
|
||
|
|
<div class="header">
|
||
|
|
<p>
|
||
|
|
Next: <a href="Enumerator-Attributes.html#Enumerator-Attributes" accesskey="n" rel="next">Enumerator Attributes</a>, Previous: <a href="Type-Attributes.html#Type-Attributes" accesskey="p" rel="prev">Type Attributes</a>, Up: <a href="C-Extensions.html#C-Extensions" accesskey="u" rel="up">C Extensions</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="Label-Attributes-1"></a>
|
||
|
|
<h3 class="section">6.34 Label Attributes</h3>
|
||
|
|
<a name="index-Label-Attributes"></a>
|
||
|
|
|
||
|
|
<p>GCC allows attributes to be set on C labels. See <a href="Attribute-Syntax.html#Attribute-Syntax">Attribute Syntax</a>, for
|
||
|
|
details of the exact syntax for using attributes. Other attributes are
|
||
|
|
available for functions (see <a href="Function-Attributes.html#Function-Attributes">Function Attributes</a>), variables
|
||
|
|
(see <a href="Variable-Attributes.html#Variable-Attributes">Variable Attributes</a>), enumerators (see <a href="Enumerator-Attributes.html#Enumerator-Attributes">Enumerator Attributes</a>),
|
||
|
|
and for types (see <a href="Type-Attributes.html#Type-Attributes">Type Attributes</a>).
|
||
|
|
</p>
|
||
|
|
<p>This example uses the <code>cold</code> label attribute to indicate the
|
||
|
|
<code>ErrorHandling</code> branch is unlikely to be taken and that the
|
||
|
|
<code>ErrorHandling</code> label is unused:
|
||
|
|
</p>
|
||
|
|
<div class="smallexample">
|
||
|
|
<pre class="smallexample">
|
||
|
|
asm goto ("some asm" : : : : NoError);
|
||
|
|
|
||
|
|
/* This branch (the fall-through from the asm) is less commonly used */
|
||
|
|
ErrorHandling:
|
||
|
|
__attribute__((cold, unused)); /* Semi-colon is required here */
|
||
|
|
printf("error\n");
|
||
|
|
return 0;
|
||
|
|
|
||
|
|
NoError:
|
||
|
|
printf("no error\n");
|
||
|
|
return 1;
|
||
|
|
</pre></div>
|
||
|
|
|
||
|
|
<dl compact="compact">
|
||
|
|
<dt><code>unused</code></dt>
|
||
|
|
<dd><a name="index-unused-label-attribute"></a>
|
||
|
|
<p>This feature is intended for program-generated code that may contain
|
||
|
|
unused labels, but which is compiled with <samp>-Wall</samp>. It is
|
||
|
|
not normally appropriate to use in it human-written code, though it
|
||
|
|
could be useful in cases where the code that jumps to the label is
|
||
|
|
contained within an <code>#ifdef</code> conditional.
|
||
|
|
</p>
|
||
|
|
</dd>
|
||
|
|
<dt><code>hot</code></dt>
|
||
|
|
<dd><a name="index-hot-label-attribute"></a>
|
||
|
|
<p>The <code>hot</code> attribute on a label is used to inform the compiler that
|
||
|
|
the path following the label is more likely than paths that are not so
|
||
|
|
annotated. This attribute is used in cases where <code>__builtin_expect</code>
|
||
|
|
cannot be used, for instance with computed goto or <code>asm goto</code>.
|
||
|
|
</p>
|
||
|
|
</dd>
|
||
|
|
<dt><code>cold</code></dt>
|
||
|
|
<dd><a name="index-cold-label-attribute"></a>
|
||
|
|
<p>The <code>cold</code> attribute on labels is used to inform the compiler that
|
||
|
|
the path following the label is unlikely to be executed. This attribute
|
||
|
|
is used in cases where <code>__builtin_expect</code> cannot be used, for instance
|
||
|
|
with computed goto or <code>asm goto</code>.
|
||
|
|
</p>
|
||
|
|
</dd>
|
||
|
|
</dl>
|
||
|
|
|
||
|
|
<hr>
|
||
|
|
<div class="header">
|
||
|
|
<p>
|
||
|
|
Next: <a href="Enumerator-Attributes.html#Enumerator-Attributes" accesskey="n" rel="next">Enumerator Attributes</a>, Previous: <a href="Type-Attributes.html#Type-Attributes" accesskey="p" rel="prev">Type Attributes</a>, Up: <a href="C-Extensions.html#C-Extensions" accesskey="u" rel="up">C Extensions</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>
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
</body>
|
||
|
|
</html>
|