[foobarqux]

You cannot certify libraries.[1] The best you can do is to provide a certification kit which consists of tests to be run in the target environment and appropriate documentation/traceability.

However, as the GP notes the libraries must merely be "certifiable": You can do all the certification work yourself as long as it is possible with the libraries in question. Having access to the source code and the lack of non-determinism are two big requirements that come to mind.

[1] In fact you cannot even certify software only entire systems.

[pmr_]

Referring to [1]: So, if I would try to sell libraries targeted at avionics there is no way for me to get certification for that specific library? Is there a way to guarantee "certifiability"?

Sorry for the late reply.