Most people has confusion about DPDK EAL parameters. The EAL parameters are documented here https://doc.dpdk.org/guides/linux_gsg/linux_eal_parameters.html. These EAL parameters are initialized by rte_eal_init().

Other parameters documented in testpmd and other applications are not handled by rte_eal_init(). They are custom parameters and the programmers has to parse and handle them all in the application. You will see getopt_long() api with struct option in testpmd and example applications to parse the custom command line arguments.