See the current Perl documentation for ExtUtils::Mksymlists.
Here is our local, out-dated (pre-5.6) version:

ExtUtils::Mksymlists - write linker options files for dynamic extension

use ExtUtils::Mksymlists;
Mksymlists({ NAME => $name ,
DL_VARS => [ $var1, $var2, $var3 ],
DL_FUNCS => { $pkg1 => [ $func1, $func2 ],
$

ExtUtils::Mksymlists produces files used by the linker under some OSs during the creation of
shared libraries for dynamic extensions. It is normally called from a
MakeMaker-generated Makefile when the extension is built. The linker option
file is generated by calling the function
Mksymlists, which is exported by default from ExtUtils::Mksymlists. It takes one argument, a list of key-value pairs, in which the following
keys are recognized:
DL_FUNCS => { Homer::Iliad => [ qw(trojans greeks) ],
Homer::Odyssey => [ qw(travellers family suitors) ] }. The function names should be identical to those in the
XSUB code;
Mksymlists will alter the names written to the linker option file to match the changes
made by xsubpp. In addition, if none of the functions in a list begin with the string boot_,
Mksymlists will add a bootstrap function for that package, just as xsubpp does. (If a boot_<pkg> function is present in the list, it is passed through unchanged.) If
DL_FUNCS is not specified, it defaults to the bootstrap function for the extension specified in
NAME.
When calling Mksymlists, one should always specify the
NAME attribute. In most cases, this is all that's
necessary. In the case of unusual extensions, however, the other attributes
can be used to provide additional information to the linker.
Charles Bailey <bailey@genetics.upenn.edu>
Last revised 14-Feb-1996, for Perl 5.002.