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
7.3 KiB
HTML
144 lines
7.3 KiB
HTML
<html lang="en">
|
|
<head>
|
|
<title>MEMORY - 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="prev" href="SECTIONS.html#SECTIONS" title="SECTIONS">
|
|
<link rel="next" href="PHDRS.html#PHDRS" title="PHDRS">
|
|
<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="MEMORY"></a>Next: <a rel="next" accesskey="n" href="PHDRS.html#PHDRS">PHDRS</a>,
|
|
Previous: <a rel="previous" accesskey="p" href="SECTIONS.html#SECTIONS">SECTIONS</a>,
|
|
Up: <a rel="up" accesskey="u" href="Scripts.html#Scripts">Scripts</a>
|
|
<hr><br>
|
|
</div>
|
|
|
|
<h3 class="section">3.7 MEMORY Command</h3>
|
|
|
|
<p><a name="index-MEMORY-431"></a><a name="index-memory-regions-432"></a><a name="index-regions-of-memory-433"></a><a name="index-allocating-memory-434"></a><a name="index-discontinuous-memory-435"></a>The linker's default configuration permits allocation of all available
|
|
memory. You can override this by using the <code>MEMORY</code> command.
|
|
|
|
<p>The <code>MEMORY</code> command describes the location and size of blocks of
|
|
memory in the target. You can use it to describe which memory regions
|
|
may be used by the linker, and which memory regions it must avoid. You
|
|
can then assign sections to particular memory regions. The linker will
|
|
set section addresses based on the memory regions, and will warn about
|
|
regions that become too full. The linker will not shuffle sections
|
|
around to fit into the available regions.
|
|
|
|
<p>A linker script may contain at most one use of the <code>MEMORY</code>
|
|
command. However, you can define as many blocks of memory within it as
|
|
you wish. The syntax is:
|
|
<pre class="smallexample"> MEMORY
|
|
{
|
|
<var>name</var> [(<var>attr</var>)] : ORIGIN = <var>origin</var>, LENGTH = <var>len</var>
|
|
...
|
|
}
|
|
</pre>
|
|
<p>The <var>name</var> is a name used in the linker script to refer to the
|
|
region. The region name has no meaning outside of the linker script.
|
|
Region names are stored in a separate name space, and will not conflict
|
|
with symbol names, file names, or section names. Each memory region
|
|
must have a distinct name.
|
|
|
|
<p><a name="index-memory-region-attributes-436"></a>The <var>attr</var> string is an optional list of attributes that specify
|
|
whether to use a particular memory region for an input section which is
|
|
not explicitly mapped in the linker script. As described in
|
|
<a href="SECTIONS.html#SECTIONS">SECTIONS</a>, if you do not specify an output section for some input
|
|
section, the linker will create an output section with the same name as
|
|
the input section. If you define region attributes, the linker will use
|
|
them to select the memory region for the output section that it creates.
|
|
|
|
<p>The <var>attr</var> string must consist only of the following characters:
|
|
<dl>
|
|
<dt><span class="samp">R</span><dd>Read-only section
|
|
<br><dt><span class="samp">W</span><dd>Read/write section
|
|
<br><dt><span class="samp">X</span><dd>Executable section
|
|
<br><dt><span class="samp">A</span><dd>Allocatable section
|
|
<br><dt><span class="samp">I</span><dd>Initialized section
|
|
<br><dt><span class="samp">L</span><dd>Same as <span class="samp">I</span>
|
|
<br><dt><span class="samp">!</span><dd>Invert the sense of any of the preceding attributes
|
|
</dl>
|
|
|
|
<p>If a unmapped section matches any of the listed attributes other than
|
|
<span class="samp">!</span>, it will be placed in the memory region. The <span class="samp">!</span>
|
|
attribute reverses this test, so that an unmapped section will be placed
|
|
in the memory region only if it does not match any of the listed
|
|
attributes.
|
|
|
|
<p><a name="index-ORIGIN-_003d-437"></a><a name="index-o-_003d-438"></a><a name="index-org-_003d-439"></a>The <var>origin</var> is an numerical expression for the start address of
|
|
the memory region. The expression must evaluate to a constant and it
|
|
cannot involve any symbols. The keyword <code>ORIGIN</code> may be
|
|
abbreviated to <code>org</code> or <code>o</code> (but not, for example,
|
|
<code>ORG</code>).
|
|
|
|
<p><a name="index-LENGTH-_003d-440"></a><a name="index-len-_003d-441"></a><a name="index-l-_003d-442"></a>The <var>len</var> is an expression for the size in bytes of the memory
|
|
region. As with the <var>origin</var> expression, the expression must
|
|
be numerical only and must evaluate to a constant. The keyword
|
|
<code>LENGTH</code> may be abbreviated to <code>len</code> or <code>l</code>.
|
|
|
|
<p>In the following example, we specify that there are two memory regions
|
|
available for allocation: one starting at <span class="samp">0</span> for 256 kilobytes,
|
|
and the other starting at <span class="samp">0x40000000</span> for four megabytes. The
|
|
linker will place into the <span class="samp">rom</span> memory region every section which
|
|
is not explicitly mapped into a memory region, and is either read-only
|
|
or executable. The linker will place other sections which are not
|
|
explicitly mapped into a memory region into the <span class="samp">ram</span> memory
|
|
region.
|
|
|
|
<pre class="smallexample"> MEMORY
|
|
{
|
|
rom (rx) : ORIGIN = 0, LENGTH = 256K
|
|
ram (!rx) : org = 0x40000000, l = 4M
|
|
}
|
|
</pre>
|
|
<p>Once you define a memory region, you can direct the linker to place
|
|
specific output sections into that memory region by using the
|
|
<span class="samp">></span><var>region</var> output section attribute. For example, if you have
|
|
a memory region named <span class="samp">mem</span>, you would use <span class="samp">>mem</span> in the
|
|
output section definition. See <a href="Output-Section-Region.html#Output-Section-Region">Output Section Region</a>. If no address
|
|
was specified for the output section, the linker will set the address to
|
|
the next available address within the memory region. If the combined
|
|
output sections directed to a memory region are too large for the
|
|
region, the linker will issue an error message.
|
|
|
|
<p>It is possible to access the origin and length of a memory in an
|
|
expression via the <code>ORIGIN(</code><var>memory</var><code>)</code> and
|
|
<code>LENGTH(</code><var>memory</var><code>)</code> functions:
|
|
|
|
<pre class="smallexample"> _fstack = ORIGIN(ram) + LENGTH(ram) - 4;
|
|
</pre>
|
|
</body></html>
|
|
|