Any suggestions?

You can use http://perldoc.perl.org/perlapi.html#Callback-Functions like call_pv to call the perl version of a function

It helps if you skip the script concept and create modules (namespace other than main ) -- see Inline#Writing Modules with Inline

Otherwise I think you'll have to create commonlib and link both a.c and b.c against it

IIRC it is possible to manually manipulate modname.def so that you can link with -lmodname and call the c versions, but not without modifying Inline::C -- this might help (never used it) Module::CAPIMaker - Provide a C API for your XS modules

Also curious Re: How to use C Libraries in Perl Script?, ExtUtils::Depends - Easily build XS extensions that depend on XS extensions, InlineX::XS - Auto-convert Inline::C based modules to XS, InlineX::C2XS