112 lines
4.8 KiB
HTML
112 lines
4.8 KiB
HTML
|
<html lang="en">
|
||
|
|
<head>
|
||
|
|
<title>Section Output - 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="Sections.html#Sections" title="Sections">
|
||
|
|
<link rel="prev" href="Section-Input.html#Section-Input" title="Section Input">
|
||
|
|
<link rel="next" href="typedef-asection.html#typedef-asection" title="typedef asection">
|
||
|
|
<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
|
||
|
|
<!--
|
||
|
|
This file documents the BFD library.
|
||
|
|
|
||
|
|
Copyright (C) 1991, 2000, 2001, 2003, 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 the
|
||
|
|
Invariant Sections being ``GNU General Public License'' and ``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.-->
|
||
|
|
<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="Section-Output"></a>Next: <a rel="next" accesskey="n" href="typedef-asection.html#typedef-asection">typedef asection</a>,
|
||
|
|
Previous: <a rel="previous" accesskey="p" href="Section-Input.html#Section-Input">Section Input</a>,
|
||
|
|
Up: <a rel="up" accesskey="u" href="Sections.html#Sections">Sections</a>
|
||
|
|
<hr><br>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<h4 class="subsection">2.6.2 Section output</h4>
|
||
|
|
|
||
|
|
<p>To write a new object style BFD, the various sections to be
|
||
|
|
written have to be created. They are attached to the BFD in
|
||
|
|
the same way as input sections; data is written to the
|
||
|
|
sections using <code>bfd_set_section_contents</code>.
|
||
|
|
|
||
|
|
<p>Any program that creates or combines sections (e.g., the assembler
|
||
|
|
and linker) must use the <code>asection</code> fields <code>output_section</code> and
|
||
|
|
<code>output_offset</code> to indicate the file sections to which each
|
||
|
|
section must be written. (If the section is being created from
|
||
|
|
scratch, <code>output_section</code> should probably point to the section
|
||
|
|
itself and <code>output_offset</code> should probably be zero.)
|
||
|
|
|
||
|
|
<p>The data to be written comes from input sections attached
|
||
|
|
(via <code>output_section</code> pointers) to
|
||
|
|
the output sections. The output section structure can be
|
||
|
|
considered a filter for the input section: the output section
|
||
|
|
determines the vma of the output data and the name, but the
|
||
|
|
input section determines the offset into the output section of
|
||
|
|
the data to be written.
|
||
|
|
|
||
|
|
<p>E.g., to create a section "O", starting at 0x100, 0x123 long,
|
||
|
|
containing two subsections, "A" at offset 0x0 (i.e., at vma
|
||
|
|
0x100) and "B" at offset 0x20 (i.e., at vma 0x120) the <code>asection</code>
|
||
|
|
structures would look like:
|
||
|
|
|
||
|
|
<pre class="example"> section name "A"
|
||
|
|
output_offset 0x00
|
||
|
|
size 0x20
|
||
|
|
output_section -----------> section name "O"
|
||
|
|
| vma 0x100
|
||
|
|
section name "B" | size 0x123
|
||
|
|
output_offset 0x20 |
|
||
|
|
size 0x103 |
|
||
|
|
output_section --------|
|
||
|
|
</pre>
|
||
|
|
<h4 class="subsection">2.6.3 Link orders</h4>
|
||
|
|
|
||
|
|
<p>The data within a section is stored in a <dfn>link_order</dfn>.
|
||
|
|
These are much like the fixups in <code>gas</code>. The link_order
|
||
|
|
abstraction allows a section to grow and shrink within itself.
|
||
|
|
|
||
|
|
<p>A link_order knows how big it is, and which is the next
|
||
|
|
link_order and where the raw data for it is; it also points to
|
||
|
|
a list of relocations which apply to it.
|
||
|
|
|
||
|
|
<p>The link_order is used by the linker to perform relaxing on
|
||
|
|
final code. The compiler creates code which is as big as
|
||
|
|
necessary to make it work without relaxing, and the user can
|
||
|
|
select whether to relax. Sometimes relaxing takes a lot of
|
||
|
|
time. The linker runs around the relocations to see if any
|
||
|
|
are attached to data which can be shrunk, if so it does it on
|
||
|
|
a link_order by link_order basis.
|
||
|
|
|
||
|
|
</body></html>
|
||
|
|
|