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<p>
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Next: <a href="Architectures.html#Architectures" accesskey="n" rel="next">Architectures</a>, Previous: <a href="Core-Files.html#Core-Files" accesskey="p" rel="prev">Core Files</a>, Up: <a href="BFD-front-end.html#BFD-front-end" accesskey="u" rel="up">BFD front end</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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<a name="Targets-1"></a>
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<h3 class="section">2.12 Targets</h3>
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<p><strong>Description</strong><br>
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Each port of BFD to a different machine requires the creation
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of a target back end. All the back end provides to the root
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part of BFD is a structure containing pointers to functions
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which perform certain low level operations on files. BFD
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translates the applications’s requests through a pointer into
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calls to the back end routines.
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</p>
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<p>When a file is opened with <code>bfd_openr</code>, its format and
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target are unknown. BFD uses various mechanisms to determine
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how to interpret the file. The operations performed are:
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</p>
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<ul>
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<li> Create a BFD by calling the internal routine
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<code>_bfd_new_bfd</code>, then call <code>bfd_find_target</code> with the
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target string supplied to <code>bfd_openr</code> and the new BFD pointer.
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</li><li> If a null target string was provided to <code>bfd_find_target</code>,
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look up the environment variable <code>GNUTARGET</code> and use
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that as the target string.
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</li><li> If the target string is still <code>NULL</code>, or the target string is
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<code>default</code>, then use the first item in the target vector
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as the target type, and set <code>target_defaulted</code> in the BFD to
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cause <code>bfd_check_format</code> to loop through all the targets.
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See <a href="bfd_005ftarget.html#bfd_005ftarget">bfd_target</a>. See <a href="Formats.html#Formats">Formats</a>.
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</li><li> Otherwise, inspect the elements in the target vector
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one by one, until a match on target name is found. When found,
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use it.
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</li><li> Otherwise return the error <code>bfd_error_invalid_target</code> to
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<code>bfd_openr</code>.
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</li><li> <code>bfd_openr</code> attempts to open the file using
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<code>bfd_open_file</code>, and returns the BFD.
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</li></ul>
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<p>Once the BFD has been opened and the target selected, the file
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format may be determined. This is done by calling
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<code>bfd_check_format</code> on the BFD with a suggested format.
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If <code>target_defaulted</code> has been set, each possible target
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type is tried to see if it recognizes the specified format.
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<code>bfd_check_format</code> returns <code>TRUE</code> when the caller guesses right.
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</p><table class="menu" border="0" cellspacing="0">
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<tr><td align="left" valign="top">• <a href="bfd_005ftarget.html#bfd_005ftarget" accesskey="1">bfd_target</a>:</td><td> </td><td align="left" valign="top">
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