You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
144 lines
6.9 KiB
HTML
144 lines
6.9 KiB
HTML
<!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>Per-Function Data (GNU Compiler Collection (GCC) Internals)</title>
|
|
|
|
<meta name="description" content="Per-Function Data (GNU Compiler Collection (GCC) Internals)">
|
|
<meta name="keywords" content="Per-Function Data (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="Target-Macros.html#Target-Macros" rel="up" title="Target Macros">
|
|
<link href="Storage-Layout.html#Storage-Layout" rel="next" title="Storage Layout">
|
|
<link href="Run_002dtime-Target.html#Run_002dtime-Target" rel="prev" title="Run-time Target">
|
|
<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="Per_002dFunction-Data"></a>
|
|
<div class="header">
|
|
<p>
|
|
Next: <a href="Storage-Layout.html#Storage-Layout" accesskey="n" rel="next">Storage Layout</a>, Previous: <a href="Run_002dtime-Target.html#Run_002dtime-Target" accesskey="p" rel="prev">Run-time Target</a>, Up: <a href="Target-Macros.html#Target-Macros" accesskey="u" rel="up">Target Macros</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="Defining-data-structures-for-per_002dfunction-information_002e"></a>
|
|
<h3 class="section">18.4 Defining data structures for per-function information.</h3>
|
|
<a name="index-per_002dfunction-data"></a>
|
|
<a name="index-data-structures"></a>
|
|
|
|
<p>If the target needs to store information on a per-function basis, GCC
|
|
provides a macro and a couple of variables to allow this. Note, just
|
|
using statics to store the information is a bad idea, since GCC supports
|
|
nested functions, so you can be halfway through encoding one function
|
|
when another one comes along.
|
|
</p>
|
|
<p>GCC defines a data structure called <code>struct function</code> which
|
|
contains all of the data specific to an individual function. This
|
|
structure contains a field called <code>machine</code> whose type is
|
|
<code>struct machine_function *</code>, which can be used by targets to point
|
|
to their own specific data.
|
|
</p>
|
|
<p>If a target needs per-function specific data it should define the type
|
|
<code>struct machine_function</code> and also the macro <code>INIT_EXPANDERS</code>.
|
|
This macro should be used to initialize the function pointer
|
|
<code>init_machine_status</code>. This pointer is explained below.
|
|
</p>
|
|
<p>One typical use of per-function, target specific data is to create an
|
|
RTX to hold the register containing the function’s return address. This
|
|
RTX can then be used to implement the <code>__builtin_return_address</code>
|
|
function, for level 0.
|
|
</p>
|
|
<p>Note—earlier implementations of GCC used a single data area to hold
|
|
all of the per-function information. Thus when processing of a nested
|
|
function began the old per-function data had to be pushed onto a
|
|
stack, and when the processing was finished, it had to be popped off the
|
|
stack. GCC used to provide function pointers called
|
|
<code>save_machine_status</code> and <code>restore_machine_status</code> to handle
|
|
the saving and restoring of the target specific information. Since the
|
|
single data area approach is no longer used, these pointers are no
|
|
longer supported.
|
|
</p>
|
|
<dl>
|
|
<dt><a name="index-INIT_005fEXPANDERS"></a>Macro: <strong>INIT_EXPANDERS</strong></dt>
|
|
<dd><p>Macro called to initialize any target specific information. This macro
|
|
is called once per function, before generation of any RTL has begun.
|
|
The intention of this macro is to allow the initialization of the
|
|
function pointer <code>init_machine_status</code>.
|
|
</p></dd></dl>
|
|
|
|
<dl>
|
|
<dt><a name="index-init_005fmachine_005fstatus"></a>Variable: <em>void (*)(struct function *)</em> <strong>init_machine_status</strong></dt>
|
|
<dd><p>If this function pointer is non-<code>NULL</code> it will be called once per
|
|
function, before function compilation starts, in order to allow the
|
|
target to perform any target specific initialization of the
|
|
<code>struct function</code> structure. It is intended that this would be
|
|
used to initialize the <code>machine</code> of that structure.
|
|
</p>
|
|
<p><code>struct machine_function</code> structures are expected to be freed by GC.
|
|
Generally, any memory that they reference must be allocated by using
|
|
GC allocation, including the structure itself.
|
|
</p></dd></dl>
|
|
|
|
<hr>
|
|
<div class="header">
|
|
<p>
|
|
Next: <a href="Storage-Layout.html#Storage-Layout" accesskey="n" rel="next">Storage Layout</a>, Previous: <a href="Run_002dtime-Target.html#Run_002dtime-Target" accesskey="p" rel="prev">Run-time Target</a>, Up: <a href="Target-Macros.html#Target-Macros" accesskey="u" rel="up">Target Macros</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>
|