I don't think NuttX supports booting directly to an init or other ENTRYPOINT in SD card. I will be surprised and happy to discover it is possible.
Yes it is possible it is included in the design. Controlled by and CONFIG_INIT_FILE and CONFIG_INIT_FILEPATH ; the relevant start-up code is: https://github.com/apache/incubator-nuttx/blob/master/sched/init/nx_bringup.c#L295
That is the normal way NSH (or any init process) is started in the KERNEL build mode.
Nimish's problem has to do with symbol tables, not missing functionality.
