This document describes the way to add custom modifications to OpenSSL sources.
If you are adding new public functions to the custom library build, you need to either add a prototype in one of the existing OpenSSL header files; or provide a new header file and edit Configurations/unix-Makefile.tmpl to pick up that file.
After that perform the following steps:
./Configure -Werror --strict-warnings [your-options] make update make make test
make update ensures that your functions declarations are added to util/libcrypto.num or util/libssl.num. If you plan to submit the changes you made to OpenSSL (see CONTRIBUTING.md), it's worth running:
make doc-nits
after running make update to ensure that documentation has correct format.
make update also generates files related to OIDs (in the crypto/objects/ folder) and errors. If a merge error occurs in one of these generated files then the generated files need to be removed and regenerated using make update. To aid in this process the generated files can be committed separately so they can be removed easily.