96 lines
4.6 KiB
HTML
96 lines
4.6 KiB
HTML
<html lang="en">
|
|
<head>
|
|
<title>Basic Script Concepts - Untitled</title>
|
|
<meta http-equiv="Content-Type" content="text/html">
|
|
<meta name="description" content="Untitled">
|
|
<meta name="generator" content="makeinfo 4.7">
|
|
<link title="Top" rel="start" href="index.html#Top">
|
|
<link rel="up" href="Scripts.html#Scripts" title="Scripts">
|
|
<link rel="next" href="Script-Format.html#Script-Format" title="Script Format">
|
|
<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
|
|
<!--
|
|
This file documents the GNU linker LD
|
|
(GNU Binutils)
|
|
version 2.19.
|
|
|
|
Copyright (C) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000,
|
|
2001, 2002, 2003, 2004, 2005, 2006, 2007 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 1.1
|
|
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''.-->
|
|
<meta http-equiv="Content-Style-Type" content="text/css">
|
|
<style type="text/css"><!--
|
|
pre.display { font-family:inherit }
|
|
pre.format { font-family:inherit }
|
|
pre.smalldisplay { font-family:inherit; font-size:smaller }
|
|
pre.smallformat { font-family:inherit; font-size:smaller }
|
|
pre.smallexample { font-size:smaller }
|
|
pre.smalllisp { font-size:smaller }
|
|
span.sc { font-variant:small-caps }
|
|
span.roman { font-family: serif; font-weight: normal; }
|
|
--></style>
|
|
</head>
|
|
<body>
|
|
<div class="node">
|
|
<p>
|
|
<a name="Basic-Script-Concepts"></a>Next: <a rel="next" accesskey="n" href="Script-Format.html#Script-Format">Script Format</a>,
|
|
Up: <a rel="up" accesskey="u" href="Scripts.html#Scripts">Scripts</a>
|
|
<hr><br>
|
|
</div>
|
|
|
|
<h3 class="section">3.1 Basic Linker Script Concepts</h3>
|
|
|
|
<p><a name="index-linker-script-concepts-310"></a>We need to define some basic concepts and vocabulary in order to
|
|
describe the linker script language.
|
|
|
|
<p>The linker combines input files into a single output file. The output
|
|
file and each input file are in a special data format known as an
|
|
<dfn>object file format</dfn>. Each file is called an <dfn>object file</dfn>.
|
|
The output file is often called an <dfn>executable</dfn>, but for our
|
|
purposes we will also call it an object file. Each object file has,
|
|
among other things, a list of <dfn>sections</dfn>. We sometimes refer to a
|
|
section in an input file as an <dfn>input section</dfn>; similarly, a section
|
|
in the output file is an <dfn>output section</dfn>.
|
|
|
|
<p>Each section in an object file has a name and a size. Most sections
|
|
also have an associated block of data, known as the <dfn>section
|
|
contents</dfn>. A section may be marked as <dfn>loadable</dfn>, which mean that
|
|
the contents should be loaded into memory when the output file is run.
|
|
A section with no contents may be <dfn>allocatable</dfn>, which means that an
|
|
area in memory should be set aside, but nothing in particular should be
|
|
loaded there (in some cases this memory must be zeroed out). A section
|
|
which is neither loadable nor allocatable typically contains some sort
|
|
of debugging information.
|
|
|
|
<p>Every loadable or allocatable output section has two addresses. The
|
|
first is the <dfn>VMA</dfn>, or virtual memory address. This is the address
|
|
the section will have when the output file is run. The second is the
|
|
<dfn>LMA</dfn>, or load memory address. This is the address at which the
|
|
section will be loaded. In most cases the two addresses will be the
|
|
same. An example of when they might be different is when a data section
|
|
is loaded into ROM, and then copied into RAM when the program starts up
|
|
(this technique is often used to initialize global variables in a ROM
|
|
based system). In this case the ROM address would be the LMA, and the
|
|
RAM address would be the VMA.
|
|
|
|
<p>You can see the sections in an object file by using the <code>objdump</code>
|
|
program with the <span class="samp">-h</span> option.
|
|
|
|
<p>Every object file also has a list of <dfn>symbols</dfn>, known as the
|
|
<dfn>symbol table</dfn>. A symbol may be defined or undefined. Each symbol
|
|
has a name, and each defined symbol has an address, among other
|
|
information. If you compile a C or C++ program into an object file, you
|
|
will get a defined symbol for every defined function and global or
|
|
static variable. Every undefined function or global variable which is
|
|
referenced in the input file will become an undefined symbol.
|
|
|
|
<p>You can see the symbols in an object file by using the <code>nm</code>
|
|
program, or by using the <code>objdump</code> program with the <span class="samp">-t</span>
|
|
option.
|
|
|
|
</body></html>
|
|
|