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| 51 | |
| 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 | |
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| 131 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> |
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