154 lines
6.3 KiB
HTML
154 lines
6.3 KiB
HTML
|
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
||
|
|
<html>
|
||
|
|
<!-- This file documents the GNU Assembler "as".
|
||
|
|
|
||
|
|
Copyright (C) 1991-2016 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 no Invariant Sections, with no Front-Cover Texts, and with no
|
||
|
|
Back-Cover Texts. A copy of the license is included in the
|
||
|
|
section entitled "GNU Free Documentation License".
|
||
|
|
-->
|
||
|
|
<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
|
||
|
|
<head>
|
||
|
|
<title>Using as: Ld Sections</title>
|
||
|
|
|
||
|
|
<meta name="description" content="Using as: Ld Sections">
|
||
|
|
<meta name="keywords" content="Using as: Ld Sections">
|
||
|
|
<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="AS-Index.html#AS-Index" rel="index" title="AS Index">
|
||
|
|
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
||
|
|
<link href="Sections.html#Sections" rel="up" title="Sections">
|
||
|
|
<link href="As-Sections.html#As-Sections" rel="next" title="As Sections">
|
||
|
|
<link href="Secs-Background.html#Secs-Background" rel="prev" title="Secs Background">
|
||
|
|
<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="Ld-Sections"></a>
|
||
|
|
<div class="header">
|
||
|
|
<p>
|
||
|
|
Next: <a href="As-Sections.html#As-Sections" accesskey="n" rel="next">As Sections</a>, Previous: <a href="Secs-Background.html#Secs-Background" accesskey="p" rel="prev">Secs Background</a>, Up: <a href="Sections.html#Sections" accesskey="u" rel="up">Sections</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p>
|
||
|
|
</div>
|
||
|
|
<hr>
|
||
|
|
<a name="Linker-Sections"></a>
|
||
|
|
<h3 class="section">4.2 Linker Sections</h3>
|
||
|
|
<p><code>ld</code> deals with just four kinds of sections, summarized below.
|
||
|
|
</p>
|
||
|
|
<dl compact="compact">
|
||
|
|
<dd>
|
||
|
|
<a name="index-named-sections"></a>
|
||
|
|
<a name="index-sections_002c-named"></a>
|
||
|
|
</dd>
|
||
|
|
<dt><strong>named sections</strong></dt>
|
||
|
|
<dd><a name="index-text-section"></a>
|
||
|
|
<a name="index-data-section"></a>
|
||
|
|
</dd>
|
||
|
|
<dt><strong>text section</strong></dt>
|
||
|
|
<dt><strong>data section</strong></dt>
|
||
|
|
<dd><p>These sections hold your program. <code>as</code> and <code>ld</code> treat them as
|
||
|
|
separate but equal sections. Anything you can say of one section is
|
||
|
|
true of another.
|
||
|
|
When the program is running, however, it is
|
||
|
|
customary for the text section to be unalterable. The
|
||
|
|
text section is often shared among processes: it contains
|
||
|
|
instructions, constants and the like. The data section of a running
|
||
|
|
program is usually alterable: for example, C variables would be stored
|
||
|
|
in the data section.
|
||
|
|
</p>
|
||
|
|
<a name="index-bss-section"></a>
|
||
|
|
</dd>
|
||
|
|
<dt><strong>bss section</strong></dt>
|
||
|
|
<dd><p>This section contains zeroed bytes when your program begins running. It
|
||
|
|
is used to hold uninitialized variables or common storage. The length of
|
||
|
|
each partial program’s bss section is important, but because it starts
|
||
|
|
out containing zeroed bytes there is no need to store explicit zero
|
||
|
|
bytes in the object file. The bss section was invented to eliminate
|
||
|
|
those explicit zeros from object files.
|
||
|
|
</p>
|
||
|
|
<a name="index-absolute-section"></a>
|
||
|
|
</dd>
|
||
|
|
<dt><strong>absolute section</strong></dt>
|
||
|
|
<dd><p>Address 0 of this section is always “relocated” to runtime address 0.
|
||
|
|
This is useful if you want to refer to an address that <code>ld</code> must
|
||
|
|
not change when relocating. In this sense we speak of absolute
|
||
|
|
addresses being “unrelocatable”: they do not change during relocation.
|
||
|
|
</p>
|
||
|
|
<a name="index-undefined-section"></a>
|
||
|
|
</dd>
|
||
|
|
<dt><strong>undefined section</strong></dt>
|
||
|
|
<dd><p>This “section” is a catch-all for address references to objects not in
|
||
|
|
the preceding sections.
|
||
|
|
</p></dd>
|
||
|
|
</dl>
|
||
|
|
|
||
|
|
<a name="index-relocation-example"></a>
|
||
|
|
<p>An idealized example of three relocatable sections follows.
|
||
|
|
The example uses the traditional section names ‘<samp>.text</samp>’ and ‘<samp>.data</samp>’.
|
||
|
|
Memory addresses are on the horizontal axis.
|
||
|
|
</p>
|
||
|
|
<div class="smallexample">
|
||
|
|
<pre class="smallexample"> +-----+----+--+
|
||
|
|
partial program # 1: |ttttt|dddd|00|
|
||
|
|
+-----+----+--+
|
||
|
|
|
||
|
|
text data bss
|
||
|
|
seg. seg. seg.
|
||
|
|
|
||
|
|
+---+---+---+
|
||
|
|
partial program # 2: |TTT|DDD|000|
|
||
|
|
+---+---+---+
|
||
|
|
|
||
|
|
+--+---+-----+--+----+---+-----+~~
|
||
|
|
linked program: | |TTT|ttttt| |dddd|DDD|00000|
|
||
|
|
+--+---+-----+--+----+---+-----+~~
|
||
|
|
|
||
|
|
addresses: 0 …
|
||
|
|
</pre></div>
|
||
|
|
|
||
|
|
<hr>
|
||
|
|
<div class="header">
|
||
|
|
<p>
|
||
|
|
Next: <a href="As-Sections.html#As-Sections" accesskey="n" rel="next">As Sections</a>, Previous: <a href="Secs-Background.html#Secs-Background" accesskey="p" rel="prev">Secs Background</a>, Up: <a href="Sections.html#Sections" accesskey="u" rel="up">Sections</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
</body>
|
||
|
|
</html>
|