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117 lines
5.4 KiB
HTML
117 lines
5.4 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- This file documents the BFD library.
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Copyright (C) 1991-2019 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being "GNU General Public License" and "Funding
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Free Software", the Front-Cover texts being (a) (see below), and with
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the Back-Cover Texts being (b) (see below). A copy of the license is
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included in the section entitled "GNU Free Documentation License".
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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software. Copies published by the Free Software Foundation raise
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funds for GNU development. -->
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Differing file formats (Untitled Document)</title>
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<meta name="description" content="Differing file formats (Untitled Document)">
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<meta name="keywords" content="Differing file formats (Untitled Document)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="BFD-Index.html#BFD-Index" rel="index" title="BFD Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Adding-Symbols-to-the-Hash-Table.html#Adding-Symbols-to-the-Hash-Table" rel="up" title="Adding Symbols to the Hash Table">
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<link href="Adding-symbols-from-an-object-file.html#Adding-symbols-from-an-object-file" rel="next" title="Adding symbols from an object file">
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<link href="Adding-Symbols-to-the-Hash-Table.html#Adding-Symbols-to-the-Hash-Table" rel="prev" title="Adding Symbols to the Hash Table">
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<style type="text/css">
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<!--
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a.summary-letter {text-decoration: none}
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div.example {margin-left: 3.2em}
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kbd {font-style: oblique}
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span.nolinebreak {white-space: nowrap}
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span.roman {font-family: initial; font-weight: normal}
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span.sansserif {font-family: sans-serif; font-weight: normal}
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ul.no-bullet {list-style: none}
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-->
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</style>
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</head>
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<body lang="en">
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<a name="Differing-file-formats"></a>
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<div class="header">
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<p>
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Next: <a href="Adding-symbols-from-an-object-file.html#Adding-symbols-from-an-object-file" accesskey="n" rel="next">Adding symbols from an object file</a>, Previous: <a href="Adding-Symbols-to-the-Hash-Table.html#Adding-Symbols-to-the-Hash-Table" accesskey="p" rel="prev">Adding Symbols to the Hash Table</a>, Up: <a href="Adding-Symbols-to-the-Hash-Table.html#Adding-Symbols-to-the-Hash-Table" accesskey="u" rel="up">Adding Symbols to the Hash Table</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>
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</div>
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<hr>
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<a name="Differing-file-formats-1"></a>
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<h4 class="subsubsection">2.17.2.1 Differing file formats</h4>
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<p>Normally all the files involved in a link will be of the same
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format, but it is also possible to link together different
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format object files, and the back end must support that. The
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<code>_bfd_link_add_symbols</code> entry point is called via the target
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vector of the file to be added. This has an important
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consequence: the function may not assume that the hash table
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is the type created by the corresponding
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<code>_bfd_link_hash_table_create</code> vector. All the
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<code>_bfd_link_add_symbols</code> function can assume about the hash
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table is that it is derived from <code>struct
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bfd_link_hash_table</code>.
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</p>
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<p>Sometimes the <code>_bfd_link_add_symbols</code> function must store
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some information in the hash table entry to be used by the
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<code>_bfd_final_link</code> function. In such a case the output bfd
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xvec must be checked to make sure that the hash table was
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created by an object file of the same format.
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</p>
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<p>The <code>_bfd_final_link</code> routine must be prepared to handle a
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hash entry without any extra information added by the
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<code>_bfd_link_add_symbols</code> function. A hash entry without
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extra information will also occur when the linker script
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directs the linker to create a symbol. Note that, regardless
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of how a hash table entry is added, all the fields will be
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initialized to some sort of null value by the hash table entry
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initialization function.
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</p>
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<p>See <code>ecoff_link_add_externals</code> for an example of how to
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check the output bfd before saving information (in this
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case, the ECOFF external symbol debugging information) in a
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hash table entry.
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</p>
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</body>
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</html>
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