| <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> |
| <html> |
| <!-- This file documents the BFD library. |
| |
| Copyright (C) 1991 - 2013 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 "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. --> |
| <!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ --> |
| <head> |
| <title>Untitled Document: Section Output</title> |
| |
| <meta name="description" content="Untitled Document: Section Output"> |
| <meta name="keywords" content="Untitled Document: Section Output"> |
| <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="BFD-Index.html#BFD-Index" rel="index" title="BFD Index"> |
| <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> |
| <link href="Sections.html#Sections" rel="up" title="Sections"> |
| <link href="typedef-asection.html#typedef-asection" rel="next" title="typedef asection"> |
| <link href="Section-Input.html#Section-Input" rel="prev" title="Section Input"> |
| <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="Section-Output"></a> |
| <div class="header"> |
| <p> |
| Next: <a href="typedef-asection.html#typedef-asection" accesskey="n" rel="next">typedef asection</a>, Previous: <a href="Section-Input.html#Section-Input" accesskey="p" rel="prev">Section Input</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="BFD-Index.html#BFD-Index" title="Index" rel="index">Index</a>]</p> |
| </div> |
| <hr> |
| <a name="Section-output"></a> |
| <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> |
| <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> |
| <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> |
| <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: |
| </p> |
| <div class="example"> |
| <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></div> |
| |
| <a name="Link-orders"></a> |
| <h4 class="subsection">2.6.3 Link orders</h4> |
| <p>The data within a section is stored in a <em>link_order</em>. |
| These are much like the fixups in <code>gas</code>. The link_order |
| abstraction allows a section to grow and shrink within itself. |
| </p> |
| <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> |
| <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. |
| </p> |
| |
| <hr> |
| <div class="header"> |
| <p> |
| Next: <a href="typedef-asection.html#typedef-asection" accesskey="n" rel="next">typedef asection</a>, Previous: <a href="Section-Input.html#Section-Input" accesskey="p" rel="prev">Section Input</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="BFD-Index.html#BFD-Index" title="Index" rel="index">Index</a>]</p> |
| </div> |
| |
| |
| |
| </body> |
| </html> |
