Versioned Shared Libraries and loadable modules

The following env variables can affect the command line and created files for these

• SHLIBVERSION
• SONAME
• SOVERSION
• APPLELINK_NO_CURRENT_VERSION (applelink only)
• APPLELINK_CURRENT_VERSION (applelink only)
• APPLELINK_COMPATIBILITY_VERSION (applelink only)

In most cases the linker will create a file named as

${SHLIBPREFIX}lib_name${SHLIBSUFFIX}.${SHLIBVERSION}

Which will have a soname baked into it as one of the

• ${SONAME}
• ${SHLIBPREFIX}lib_name${SHLIBSUFFIX}.${SOVERSION}
• (for applelink only)
  • ${SHLIBPREFIX}lib_name${major version only from SHLIBVERSION}${SHLIBSUFFIX}
  • -Wl,-compatibility_version,%s
  • -Wl,-current_version,%s

For applelink the version has to follow these rules to verify that the version # is valid.

• For version # = X[.Y[.Z]]
• where X 0-65535
• where Y either not specified or 0-255
• where Z either not specified or 0-255

For most platforms this will lead to a series of symlinks eventually pointing to the actual shared library (or loadable module file).

(This info it stored in a list of tuples stored in target[0].attributes.shliblinks this is currently done in the emitter)

1. ${SHLIBPREFIX}lib_name${SHLIBSUFFIX} -> ${SHLIBPREFIX}lib_name${SHLIBSUFFIX}.${SHLIBVERSION}
2. ${SHLIBPREFIX}lib_name${SHLIBSUFFIX}.${SOVERSION} -> ${SHLIBPREFIX}lib_name${SHLIBSUFFIX}.${SHLIBVERSION}

For openbsd the following rules for symlinks apply

• OpenBSD uses x.y shared library versioning numbering convention and doesn't use symlinks to backwards-compatible libraries

The current code provides the following hooks a compiler can use to customize:

        'VersionedShLibSuffix': _versioned_lib_suffix,
        'VersionedLdModSuffix': _versioned_lib_suffix,
        'VersionedShLibSymlinks': _versioned_shlib_symlinks,
        'VersionedLdModSymlinks': _versioned_ldmod_symlinks,
        'VersionedShLibName': _versioned_shlib_name,
        'VersionedLdModName': _versioned_ldmod_name,
        'VersionedShLibSoname': _versioned_shlib_soname,
        'VersionedLdModSoname': _versioned_ldmod_soname,

Thoughts on new implementation

so if I define

env['SONAME']='$GenSONAME'

And then if the user sets SONAME directly that works. GenSONAME is a function which uses any values of SHLIBVERSION, SOVERSION, (or if user implemented any values it wants) fairly straightforward t generated shared library name from variables as well. and get rid of all the levels of indirection.