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| = How to Package an Unversioned Library =
| | See [[TipsAndTricks/Packaging_Prebuilt_Libraries#Non-versioned_Libraries]] |
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| First some background: libraries in Linux systems are generally versioned so that it is possible to have multiple versions of the same library installed, to ease upgrades or support older software. For example in versioned libraries the actual library is called <tt>libfoo.so.1.2</tt>, and then there will be a <tt>libfoo.so.1</tt> symbolic link to <tt>libfoo.so.1.2</tt>, and finally a <tt>libfoo.so</tt> symbolic link to <tt>libfoo.so.1.2</tt>. When linking a binary against a library you typically tell it the unversioned file name (<tt>-lfoo</tt> to the linker) but the linker will follow the symbolic link and actually link against the versioned filename. The unversioned symbolic link is only used at development time, so is packaged along with the headers in the development package <tt>${PN}-dev</tt>, with the actual library and versioned symbolic links in <tt>${PN}</tt>. As versioned libraries are far more common than unversioned libraries, the default packaging rules assume versioned libraries.
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| However this means that packaging an unversioned library means a bit of work in the recipe, as by default libfoo.so will get packaged into <tt>${PN}-dev</tt> (triggerring a QA warning that a non-symlink library is in a <tt>-dev</tt> package), and binaries in the same recipe will link to the library in <tt>${PN}-dev</tt> (triggering more QA warnings). To solve this the unversioned library needs to be packaged into <tt>${PN}</tt> where it belongs. These are the (abridged) default <tt>FILES</tt> variables in <tt>bitbake.conf</tt>:
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| SOLIBS = ".so.*"
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| SOLIBSDEV = ".so"
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| FILES_${PN} = "... ${libdir}/lib*${SOLIBS} ..."
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| FILES_SOLIBSDEV ?= "... ${libdir}/lib*${SOLIBSDEV} ..."
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| FILES_${PN}-dev = "... ${FILES_SOLIBSDEV} ..."
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| <tt>SOLIBS</tt> defines a pattern that matches real shared object libraries, and <tt>SOLIBSDEV</tt> matches the development form (unversioned symlink). These are then used in <tt>FILES_${PN}</tt> and <tt>FILES_${PN}-dev</tt> which puts the real libraries into <tt>${PN}</tt> and the unversioned symbolic link into <tt>PN-dev</tt>. To package unversioned libraries, this needs to be modified as follows in the recipe:
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| SOLIBS = ".so"
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| FILES_SOLIBSDEV = ""
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| This says that <tt>.so</tt> is the real library, and unsets <tt>FILES_SOLIBSDEV</tt> so that no libraries get packaged into <tt>PN-dev</tt>. This is required because unless <tt>PACKAGES</tt> is changed <tt>PN-dev</tt> collects files before <tt>PN</tt>, so <tt>PN-dev</tt> must not collect any of the files we want in <tt>PN</tt>.
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| Finally loadable modules, essentially unversioned libraries that are linked at runtime using <tt>dlopen()</tt> instead of at build time, should generally be installed in a private directory. However if they are installed in <tt>${libdir}</tt> then they can be treated as unversioned libraries.
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