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<H1><A NAME="SECTION007600000000000000000"></A><A NAME="link-reqs"></A>
<BR>
5.6 Linking Requirements
         
</H1>

<P>
While the <b class="program">configure</b> script shipped with the Python sources
will correctly build Python to export the symbols needed by
dynamically linked extensions, this is not automatically inherited by
applications which embed the Python library statically, at least on
<span class="Unix">Unix</span>.  This is an issue when the application is linked to the static
runtime library (<span class="file">libpython.a</span>) and needs to load dynamic
extensions (implemented as <span class="file">.so</span> files).

<P>
The problem is that some entry points are defined by the Python
runtime solely for extension modules to use.  If the embedding
application does not use any of these entry points, some linkers will
not include those entries in the symbol table of the finished
executable.  Some additional options are needed to inform the linker
not to remove these symbols.

<P>
Determining the right options to use for any given platform can be
quite difficult, but fortunately the Python configuration already has
those values.  To retrieve them from an installed Python interpreter,
start an interactive interpreter and have a short session like this:

<P>
<div class="verbatim"><pre>
&gt;&gt;&gt; import distutils.sysconfig
&gt;&gt;&gt; distutils.sysconfig.get_config_var('LINKFORSHARED')
'-Xlinker -export-dynamic'
</pre></div>
<a id='l2h-15' xml:id='l2h-15'></a>

<P>
The contents of the string presented will be the options that should
be used.  If the string is empty, there's no need to add any
additional options.  The <tt class="constant">LINKFORSHARED</tt> definition
corresponds to the variable of the same name in Python's top-level
<span class="file">Makefile</span>.

<P>

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	52	<H1><A NAME="SECTION007600000000000000000"></A><A NAME="link-reqs"></A>
	53	<BR>
	54	5.6 Linking Requirements
	55
	56	</H1>
	57
	58	<P>
	59	While the <b class="program">configure</b> script shipped with the Python sources
	60	will correctly build Python to export the symbols needed by
	61	dynamically linked extensions, this is not automatically inherited by
	62	applications which embed the Python library statically, at least on
	63	<span class="Unix">Unix</span>. This is an issue when the application is linked to the static
	64	runtime library (<span class="file">libpython.a</span>) and needs to load dynamic
65	extensions (implemented as <span class="file">.so</span> files).
66
67	<P>
68	The problem is that some entry points are defined by the Python
69	runtime solely for extension modules to use. If the embedding
70	application does not use any of these entry points, some linkers will
71	not include those entries in the symbol table of the finished
72	executable. Some additional options are needed to inform the linker
73	not to remove these symbols.
74
75	<P>
76	Determining the right options to use for any given platform can be
77	quite difficult, but fortunately the Python configuration already has
78	those values. To retrieve them from an installed Python interpreter,
79	start an interactive interpreter and have a short session like this:
80
81	<P>
82	<div class="verbatim"><pre>
83	>>> import distutils.sysconfig
84	>>> distutils.sysconfig.get_config_var('LINKFORSHARED')
85	'-Xlinker -export-dynamic'
86	</pre></div>
87	<a id='l2h-15' xml:id='l2h-15'></a>
88
89	<P>
90	The contents of the string presented will be the options that should
91	be used. If the string is empty, there's no need to add any
92	additional options. The <tt class="constant">LINKFORSHARED</tt> definition
93	corresponds to the variable of the same name in Python's top-level
94	<span class="file">Makefile</span>.
95
96	<P>
97
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